Patent Publication Number: US-11642397-B2

Title: Method and drug for preventing or treating osteoarthritis

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Phase application under 35 U.S.C. § 371 of International Application No. PCT/CN2018/121535, filed Dec. 17, 2018, which claims priority to International Application No. PCT/CN2017/116636, filed Dec. 15, 2017, the contents of each of which are incorporated herein by reference in their entirety. 
     SUBMISSION OF SEQUENCE LISTING ON ASCII TEXT FILE 
     The content of the following submission on ASCII text file is incorporated herein by reference in its entirety: a computer readable form (CRF) of the Sequence Listing (file name 794922001800SEQLIST.txt, date recorded: Jun. 15, 2020, size: 46 KB). 
     FIELD OF THE INVENTION 
     The present invention relates to a method and a medicament for preventing or treating osteoarthritis by using plasminogen. 
     BACKGROUND OF THE INVENTION 
     Osteoarthritis is also known as osteo-arthritis, degenerative arthritis, degenerative joint disease, and osteoarthropathy. It is the most common form of arthritis, affecting about 237 million (3.3%) of the population, and is also one of the leading reasons for joint pain and even disability  [1] , among people over the age of 60, about 10% of men and 18% of women are affected by it  [2] . Osteoarthritis is a heterogeneous disease caused by multiple factors, and is characterized by the progressive breakdown of articular cartilage; these factors include trauma, abnormal mechanical load, inadequate nutrition supply, and genetic causes, as well as metabolic factors and subpatellar fat pad. Previous studies have focused on the impact of abnormal biomechanics on subchondral bone, articular cartilage integrity, and chondrocyte pathophysiology; but recent evidences indicate that the clinical symptoms of osteoarthritis affect not only articular cartilage, but also the integrity of multiple joint tissues, including synovium, bone, ligaments, supporting muscles and meniscus, etc.  [3]   
     The primary cause of osteoarthritis is not a bone lesion. Modern medical research has found that the primary cause of the disease is the loss of joint protection capabilities of the “joint protection systems” such as cartilage. Particularly, the occurrence of various types of osteoarticular diseases often starts from synovial lesions, damaged or degenerated cartilage: cartilage injury caused by taking certain anti-inflammatory and hormonal medicaments is also one of the main causes of many osteoarticular diseases. Due to the damage of joint synovium and cartilage, and the lack of articular synovia, the joint bones lack the necessary protection, so that when the human body is active, the bones at the joints directly suffer from severe hard friction for lacking the necessary “cartilage protection”, thereby leading to joint pain, swelling, deformation, bone spur hyperplasia and other symptoms in a patient  [4] . Therefore, the key points for treating osteoarticular diseases are to repair damaged articular cartilage and synovium, promoting the regeneration ability of cartilage and synovium, and stimulating articular synovia, thereby restoring the “cartilage protective layer” of joint organs. This study proves that plasminogen can improve the structural integrity of bone joints, enhance the activity of local osteoblasts in a joint, and/or reduce the activity of osteoclasts, promote cartilage regeneration and the bone remodeling of subchondral bone, and effectively relieve pain, etc.: thereby developing a new way for treating joint injury diseases including osteoarthritis. 
     CONTENTS OF THE INVENTION/SUMMARY OF THE INVENTION 
     The present invention relates to a method and a medicament for preventing or treating osteoarticular diseases by using plasminogen. The present invention proves that plasminogen can improve the structural integrity of bone joints, enhance the activity of local osteoblasts in a joint, and/or reduce the activity of osteoclasts, promote cartilage regeneration and the bone remodeling of subchondral bone, and effectively relieve pain and other symptoms; thereby developing a new way for treating joint injury diseases including osteoarthritis. 
     Particularly, the present invention relates to: 
     1. A method for treating osteoarthritis, which includes administering an effective amount of plasminogen to a subject. 
     2. The method according to item 1, the plasminogen increases the amount of articular cartilage, and/or promotes the repair of articular cartilage injury. 
     3. The method according to item 1 or 2, the plasminogen improves the inflammation condition of joint synovium. 
     4. The method according to any one of items 1-3, the plasminogen promotes the bone remodeling of subchondral bone for joints. 
     5. The method according to any one of items 1-4, wherein the plasminogen improves the inflammation condition and pain of joint, and/or improves joint function. 
     6. The method according to any one of items 1-5, wherein the plasminogen reduces joint swelling and pain. 
     7. A method for promoting the regeneration of articular cartilage in an osteoarthritis subject, which includes administering an effective amount of plasminogen to the subject. 
     8. A method for promoting the repair of joint injury in a subject, which includes administering an effective amount of plasminogen to the subject. 
     9. The method according to item 8, wherein the plasminogen promotes the regeneration of articular cartilage and/or the bone remodeling of subchondral bone. 
     10. The method according to item 8 or 9, wherein the subject is an osteoarthritis subject. 
     11. The method according to any one of items 8-10, wherein the plasminogen improves the inflammation condition of joint tissue, and/or reduces joint pain. 
     12. The method according to any one of items 1-11, wherein the plasminogen has at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% sequence identity with SEQ ID NO: 2, and still has plasminogen activity. 
     13. The method according to any one of items 1-11, wherein the plasminogen is a protein comprising a plasminogen active fragment and still having plasminogen activity. 
     14. The method according to any one of items 1-11, wherein the plasminogen is selected from Glu-plasminogen. Lys-plasminogen, small plasminogen, microplasminogen, delta-plasminogen, or their variants retaining plasminogen activity. 
     15. The method according to any one of items 1-11, wherein the plasminogen is natural or synthetic human plasminogen, or a variant or fragment thereof still retaining plasminogen activity. 
     16. The method according to any one of items 1-11, wherein the plasminogen is an ortholog of human plasminogen from a primate or rodent, or a variant or fragment thereof retaining plasminogen activity. 
     17. The method according to any one of items 1-11, wherein the amino acid sequence of the plasminogen is represented by SEQ ID NO: 2, 6, 8, 10, or 12. 
     18. The method according to any one of items 1-11, wherein the plasminogen is human native plasminogen. 
     19. The method according to any one of items 1-18, wherein the subject is a human. 
     20. The method according to any one of items 1-19, wherein the subject is deficient in or lacks plasminogen. 
     21. The method according to any one of items 1-20, wherein the plasminogen is used in combination with one or more medicaments or methods for treating joint injury, or one or more medicaments or methods for treating osteoarthritis. 
     22. A plasminogen for use in the method according to any of items 1-21. 
     23. A pharmaceutical composition, comprising a pharmaceutically acceptable carrier, and a plasminogen for use in the method according to any one of items 1-21. 
     24. A prophylactic or therapeutic kit, comprising: (i) a plasminogen for use in the method according to any of items 1-21, and (ii) component/means for delivering the plasminogen to the subject. 
     25. The kit according to item 24, wherein the component is a syringe or a vial. 
     26. The kit according to item 24 or 25, further comprising a label or an instruction manual indicating that the plasminogen is administered to the subject to perform the method according to any one of items 1-21. 
     27. A product comprising: a container with label; and comprising (i) a plasminogen for use in the method according to any one of items 
     1-21, or a pharmaceutical composition comprising the plasminogen, wherein the label indicates that the plasminogen or composition is administered to the subject to perform the method according to any one of items 1-21. 
     28. The kit according to any one of items 24-26 or the product according to item 27, further comprising one or more components or containers which contains one or more other medicaments or supplies for treating joint injury, or one or more other medicaments or supplies for treating osteoarthritis.
 
29. The kit according to any one of items 24-26 or the product according to item 27, further includes medicaments for treating other diseases concomitant with osteoarthritis.
 
30. An agent containing plasminogen for treating osteoarthritis.
 
31. An agent containing plasminogen for treating joint injury.
 
32. A pharmaceutical composition, kit, and product containing plasminogen for treating osteoarthritis.
 
33. A pharmaceutical composition, kit, and product containing plasminogen for treating joint injury.
 
34. Use of plasminogen in the preparation of a medicament, product, or kit for treating osteoarthritis.
 
35. The use according to item 34, the plasminogen increases the amount of articular cartilage, and/or promotes the repair of articular cartilage injury.
 
36. The use according to item 34 or 35, the plasminogen improves the inflammation condition of joint synovium.
 
37. The use according to any one of items 34-36, the plasminogen promotes the bone remodeling of subchondral bone for joints.
 
38. The use according to any one of items 34-37, wherein the plasminogen improves the inflammatory condition and pain of joints, and/or improves joint function.
 
39. The use according to any one of items 34-38, wherein the plasminogen reduces joint swelling and pain.
 
40. Use of plasminogen in the preparation of a medicament for promoting the regeneration of articular cartilage in an osteoarthritis subject.
 
41. Use of plasminogen in the preparation of a medicament for promoting the repair of joint injury in a subject.
 
42. The use according to item 41, the plasminogen promotes the regeneration of articular cartilage and/or the bone remodeling of subchondral bone.
 
43. The use according to item 41 or 42, wherein the subject is an osteoarthritis subject.
 
44. The use according to any one of items 41-43, wherein the plasminogen improves the inflammation condition of joint tissues, and/or reduces joint pain.
 
45. The method according to any one of items 34-44, wherein the plasminogen has at least 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% of sequence identity with SEQ ID NO: 2, 6, 8, 10, or 12, and still have plasminogen activity.
 
46. The use according to any one of items 34-44, wherein the plasminogen is a protein containing a plasminogen active fragment and still having plasminogen activity.
 
47. The use according to any one of items 34-44, the plasminogen is selected from Glu-plasminogen Lys-plasminogen, small plasminogen, microplasminogen, and delta-plasminogen, or their variants retaining plasminogen activity.
 
48. The use according to any one of items 34-44, wherein the plasminogen is natural or synthetic human plasminogen, or a variant or fragment thereof retaining plasminogen activity.
 
49. The use according to any one of items 34-44, wherein the plasminogen is an ortholog of human plasminogen from a primate or rodent, or a variant or fragment thereof retaining plasminogen activity.
 
50. The use according to any one of items 34-44, wherein the amino acid sequence of the plasminogen is represented by SEQ ID NO: 2, 6, 8, 10, or 12.
 
51. The use according to any one of items 34-44, wherein the plasminogen is human native plasminogen.
 
52. The use according to any one of items 34-51, wherein the subject is a human.
 
53. The use according to any one of items 34-52, wherein the plasminogen is used in combination with one or more medicaments or methods for treating joint injury, or one or more medicaments or methods for treating osteoarthritis.
 
     DETAILED DESCRIPTION OF THE INVENTION 
     Definition of Terms, and Description of Technical Solutions 
     The “joint” is the connecting tissue between the bones. There is a cavity in the connecting tissue, which enables joint to do activities at different degrees. The main structures of a joint are joint capsule, articular cavity, articular cartilage, synovia, as well as ligaments, muscles and tendons around the joint, synovial folds, bursa mucosa, meniscus, subchondral bone, etc. The joint capsule is a connective tissue membrane sac that surrounds the two opposite bone ends of the joint. It consists of the inner and outer layers: the outer layer is a fibrous layer composed of dense connective tissue, and it is thick and tough, and mainly plays a role in maintaining the firmness and stability of the joint: the inner layer is a thin and soft synovial layer composed of loose connective tissue rich in blood vessels, and it covers the inner surface of the fiber layer to form a sac surrounding the synovial cavity. The articular cavity is a tissue cavity formed by the joint capsule and the joint surface. Under normal circumstances, there will be a little viscous liquid (i.e., synovia) in the articular cavity, which has the effect of lubricating and nourishing the joint. Articular cartilage refers to the thin layer of cartilage covering the surface of the joint, and it covers the joint surface and has good elasticity, thereby reducing friction, cushioning shock and impact. Synovia is synovial fluid, and is secreted by the synovial membrane. Normal synovia is clear and viscous. When the joint is inflamed, the amount of synovia increases significantly, and the pressure in the articular cavity increases, thereby resulting in local swelling and pain. 
     Some embodiments of the present invention relate to a method for treating joint injury by plasminogen and a method for promoting the repair of joint injury in a subject with joint injury, comprising: administering an effective amount of plasminogen to the subject. In some embodiments, the joint injury includes joint injury caused by inflammation condition, degenerative disease, metabolic disorder, or trauma. In some embodiments, the plasminogen treats joint injury or promotes the repair of joint injury by promoting the regeneration of articular cartilage and/or the bone remodeling of subchondral bone. In some embodiments, the plasminogen improves inflammation condition and/or reduces joint pain in joint tissue of a subject with joint injury. In some embodiments, the inflammation condition of the joint tissue includes inflammation condition of the joint synovium. In some embodiments, the plasminogen reduces joint swelling and pain in a joint injury subject. 
     In some embodiments, the present invention relates to a method for promoting the regeneration of articular cartilage, comprising: administering an effective amount of plasminogen to a subject. In some embodiments, the present invention relates to promoting the repair of joint injury and treating joint injury diseases via the enhancement of cartilage regeneration by plasminogen. 
     In some above-mentioned embodiments for treating joint injury and promoting the repair of joint injury by plasminogen, the joint injury is caused by osteoarthritis. 
     In some above-mentioned embodiments for treating joint injury and promoting the repair of joint injury by plasminogen, the plasminogen promotes the regeneration of articular cartilage and/or the bone remodeling of subchondral bone, so that the joint injury is repaired, thereby the process of development of joint injury into osteoarthritis is cut off. Therefore, the present invention also relates to a method for preventing osteoarthritis by plasminogen, which comprises administering an effective amount of plasminogen to a subject with joint injury. 
     In all the above methods for treating joint injury, promoting the repair of joint injury, promoting cartilage regeneration, and preventing joint injury from developing into osteoarthritis by plasminogen, the plasminogen may be administered alone or in combination with one or more other medicaments or methods. The co-administration includes administration of plasminogen before, at the same time of, or after the administration of one or more other medicaments or methods. 
     “Osteoarthritis (OA)” is a degenerative disease, which is caused by degeneration and injury of articular cartilage, and reactive hyperplasia of joint margins and subchondral cartilage due to many factors such as aging, obesity, strain, trauma, congenital abnormalities of joints, and joint deformities; and it is also known as osteoarthropathy, degenerative arthritis, senile arthritis, etc. The clinical manifestations are slowly developing joint pain, tenderness, stiffness, joint swelling, restricted mobility, and joint deformities, etc. 
     Osteoarthritis is a degenerative disease of bone joints, which occurs in weight-bearing joints and joints with a lot of activity, such as cervical vertebrae, lumbar vertebrae, knee joints, and hip joints. Excessive weight-bearing or overuse of these joints can promote the occurrence of degenerative changes. The clinical manifestations are slowly developing joint pain, tenderness, stiffness, joint swelling, restricted mobility, and joint deformities. Imaging changes include abnormal changes in articular cartilage and subchondral bone, joint space narrowing (this indicates that articular cartilage has begun to thin), calcification of bone, sharpening of the edge of joint, osteophyte formation, and/or the formation of subchondral bone cyst. The “osteoarthritis” according to the present invention covers osteoarthritis occurring in various parts of the body, including the osteoarthritis or related degenerative lesions in the cervical vertebrae, lumbar vertebrae, knee joints, and hip joints. 
     Some embodiments of the present invention relate to a method for treating osteoarthritis by plasminogen, which comprises administering an effective amount of plasminogen to a subject. In some embodiments, the plasminogen promotes the regeneration of articular cartilage and/or the bone remodeling of subchondral bone. In some embodiments, the plasminogen improves the inflammation condition of joint tissue, and/or reduces joint swelling and/or pain. In some embodiments, the plasminogen improves inflammation condition of the joint synovium, and/or reduces joint swelling and/or pain. In some embodiments, the osteoarthritis is osteoarthritis in the cervical vertebrae, lumbar vertebrae, knee joints and hip joints, or related degenerative diseases. 
     In the above embodiments for treating osteoarthritis by plasminogen, the “treatment” includes reducing, relieving, ameliorating or eliminating one or more of the following symptoms or signs: joint pain, tenderness, stiffness, joint swelling, joint function disorders or limitations, abnormal changes in articular cartilage or subchondral bone, stenosis of joint space, calcification of bone, sharpening of joint margins, osteophytes, subchondral bone cyst. In the embodiment for treating osteoarthritis by plasminogen, the osteoarthritis includes osteoarthritis of the cervical vertebrae, lumbar vertebrae, knee joints and hip joints, and related degenerative diseases. 
     “Bone remodeling” is also called “bone metabolism”, and refers to the removal of mature bone tissue from the bone (a process called bone resorption) and the formation of new bone tissue (a process called ossification or new bone formation). These processes also control the reshaping or replacement of bones after fractures and other injuries, as well as micro-damages that occur during normal activities. Remodeling also responds to the functional requirements of mechanical loads. The structure of the bone and the adequate supply of calcium, require close cooperation between the two types of cells, i.e., osteoblasts (secreting new bone) and osteoclasts (destroying the bone), and other cell groups (such as immune cells, etc.) present in the bone remodeling site, and rely on complex signal transduction pathway and control mechanism, so as to achieve an appropriate growth and differentiation rate. 
     In some embodiments, the present invention relates to promoting the regeneration of articular cartilage and/or the bone remodeling of subchondral bone by plasminogen. In some embodiments, the present invention relates to promoting (enhancing) the activity of osteoblasts and/or reducing the activity of osteoclasts at the site of osteoarthritis in an osteoarthritis subject by plasminogen. 
     In some embodiments, the present invention relates to a method for promoting the repair of joint injury in a subject by plasminogen, comprising: administering to the subject an effective amount of plasminogen. In some embodiments, the joint injury includes a joint injury caused by inflammation condition, degenerative disease, metabolic disorder, or trauma. In some embodiments, the plasminogen treats joint injury or promotes the repair of joint injury by promoting the regeneration of articular cartilage and/or the bone remodeling of subchondral bone. In some embodiments, the plasminogen promotes (enhances) the activity of osteoblasts and/or reduces the activity of osteoclasts at the joint injury site of the subject with joint injury. In some embodiments, the joint injury is a joint injury caused by osteoarthritis. In some embodiments, the joint injury is a joint injury caused by inflammation, metabolic disorders, or trauma. 
     “Improving” inflammation (condition) of joint synovium, “improving” inflammation (condition) of joint, “improving” inflammation (condition) of joint tissue, or “improving” inflammation of joint tissue, means inflammation or inflammatory condition is improved after the treatment of administering plasminogen, and the inflammatory response is eventually relieved and resolved. 
     In all the above embodiments for treating osteoarthritis by plasminogen, the plasminogen can be administered alone or in combination with one or more other medicaments or methods. The co-administration includes administration of plasminogen before, at the same time of, or after the administration of one or more other medicaments or methods. 
     Plasmin is a key component of the plasminogen activation system (PA system). It is a broad-spectrum protease capable of hydrolyzing several components of the extracellular matrix (ECM), including fibrin, gelatin, fibronectin, laminin, and proteoglycan  [5] . In addition, plasmin can activate some precursors of metalloproteinase (pro-MMPs) to form active metalloproteases (MMPs). Therefore, plasmin is considered to be an important upstream regulator of extracellular proteolysis  [6,7] . Plasmin is formed by proteolysis of plasminogen through two physiological PAs: tissue-type plasminogen activator (tPA) or urokinase-type plasminogen activator (uPA). Due to the relatively high levels of plasminogen in plasma and other body fluids, it is typically believed that the regulation of the PA system is mainly achieved through the synthesis and activity levels of PAs. The synthesis of the components of PA system is strictly regulated by different factors, such as hormones, growth factors and cytokines. In addition, there are specific physiological inhibitors of plasmin and PAs. The main inhibitor of plasmin is α2-antiplasmin (α2-antiplasmin). The activity of PAs is regulated by both the plasminogen activator inhibitor-1 (PAI-1) of uPA and tPA and the plasminogen activator inhibitor-2 (PAI-2) which mainly inhibits uPA. The surface of certain cells has uPA-specific cell surface receptors (uPAR) with direct hydrolytic activity  [8,9] . 
     Plasminogen is a single-chain glycoprotein consisting of 791 amino acids with a molecular weight of approximately 92 kDa  [10,11] . Plasminogen is mainly synthesized in the liver, and is abundant in extracellular fluid. Plasminogen content in plasma is about 2 μM. Therefore, plasminogen is a huge potential source of proteolytic activity in tissues and body fluids  [12,13] . There are two molecular forms of plasminogen: glutamate-plasminogen (Glu-plasminogen) and lysine-plasminogen (Lys-plasminogen). The naturally secreted and uncleaved form of plasminogen has an amino-terminal (N-terminal) glutamic acid, and is therefore called glutamate-plasminogen. However, in the presence of plasmin, glutamate-plasminogen is hydrolyzed to lysine-plasminogen at Lys76-Lys77. Compared with glutamate-plasminogen, lysine-plasminogen has a higher affinity for fibrin, and can be activated by PAs at a higher rate. The Arg560-Val561 peptide bond of these two forms of plasminogen can be cleaved by uPA or tPA, resulting in the formation of a disulfide-linked double-chain protease plasmin  [14] . The amino-terminal portion of plasminogen contains five homologous triple-loops, so-called kringles, and the carboxy-terminal portion contains a protease domain. Some kringles contain lysine binding sites that mediate the specific interaction of plasminogen with fibrin and its inhibitor α2-AP. The latest discovered plasminogen is a 38 kDa fragment including kringles 1-4, and it is an effective inhibitor of angiogenesis. This fragment is named angiostatin, and can be produced by the hydrolysis of plasminogen by several proteases. 
     The main substrate of plasmin is fibrin, and the dissolution of fibrin is the key to preventing pathological thrombosis  [15] . Plasmin also has substrate specificity for several components of ECM including laminin, fibronectin, proteoglycan, and gelatin, and this indicates that plasmin also plays an important role in ECM reconstruction  [11,16, 17] . Indirectly, plasmin can also degrade other components of ECM by converting certain protease precursors into active proteases, including MMP-1, MMP-2, MMP-3 and MMP-9. Therefore, it has been suggested that plasmin may be an important upstream regulator of extracellular proteolysis  [18] . In addition, plasmin has the ability to activate certain potential forms of growth factors  [19-21] . In vitro plasmin can also hydrolyze components of the complement system, and release chemotactic complement fragments. 
     “Plasmin” is a very important enzyme that exists in the blood and is capable of hydrolyzing fibrin clots into fibrin degradation products and D-dimers. 
     “Plasminogen” is the zymogen form of plasmin, and it is a glycoprotein composed of 810 amino acids calculated based on the amino acid sequence (SEQ ID NO: 4) of the native human plasminogen containing a signal peptide according to the sequence in the swiss prot, having a molecular weight of about 90 kD, being synthesized mainly in the liver and being capable of circulating in the blood; and the cDNA sequence encoding this amino acid sequence is as shown in SEQ ID NO: 3. Full-length plasminogen contains seven domains: a C-terminal serine protease domain, an N-terminal Pan Apple (PAp) domain and five Kringle domains (Kringles 1-5). Referring to the sequence in the swiss prot, the signal peptide comprises residues Met1-Gly19. PAp comprises residues Glu20-Val98, Kringle 1 comprises residues Cys103-Cys181, Kringle 2 comprises residues Glu184-Cys262, Kringle 3 comprises residues Cys275-Cys352, Kringle 4 comprises residues Cys377-Cys454, and Kringle 5 comprises residues Cys481-Cys560. According to the NCBI data, the serine protease domain comprises residues Val581-Arg804. 
     Glu-plasminogen is a native full-length plasminogen and is composed of 791 amino acids (without a signal peptide of 19 amino acids): the cDNA sequence encoding this sequence is as shown in SEQ ID NO: 1; and the amino acid sequence is as shown in SEQ ID NO: 2. In vivo, Lys-plasminogen, which is formed by hydrolysis of amino acids at positions 76-77 of Glu-plasminogen, is also present, as shown in SEQ ID No.6; and the cDNA sequence encoding this amino acid sequence is as shown in SEQ ID No.5. δ-plasminogen is a fragment of full-length plasminogen that lacks the structure of Kringle 2-Kringle 5 and contains only Kringle 1 and the serine protease domain  [22,23] . The amino acid sequence (SEQ ID No.8) of δ-plasminogen has been reported in the literature  [23] , and the cDNA sequence encoding this amino acid sequence is as shown in SEQ ID No.7. Mini-plasminogen is composed of Kringle 5 and the serine protease domain, and has been reported in the literature to comprise residues Val443-Asn791 (with the Glu residue of the Glu-plasminogen sequence that does not contain a signal peptide as the starting amino acid)  [24] ; the amino acid sequence is as shown in SEQ ID NO: 10: and the cDNA sequence encoding this amino acid sequence is as shown in SEQ ID NO: 9. In addition, micro-plasminogen comprises only the serine protease domain, the amino acid sequence of which has been reported in the literature to comprise residues Ala543-Asn791 (with the Glu residue of the Glu-plasminogen sequence that does not contain a signal peptide as the starting amino acid)  [25] , and the sequence of which has been also reported in patent literature CN102154253A to comprise residues Lys531-Asn791 (with the Glu residue of the Glu-plasminogen sequence that does not contain a signal peptide as the starting amino acid) (the sequence in this patent application refers to the patent literature CN102154253A); the amino acid sequence is as shown in SEQ ID NO: 12 and the cDNA sequence encoding this amino acid sequence is as shown in SEQ ID NO: 11. 
     In the present invention, “plasmin” is used interchangeably with “fibrinolysin” and “fibrinolytic enzyme”, and the terms have the same meaning; and “plasminogen” is used interchangeably with “profibrinolysin” and “fibrinolytic zymogen”, and the terms have the same meaning. 
     In the present application, the “deficiency” of plasminogen or its activity means that the content of plasminogen in a subject is lower than that of a normal person, i.e., being low enough to affect the normal physiological function of the subject; the “lack” of plasminogen or its activity means that the content of plasminogen in a subject is significantly lower than that of a normal person, and even the activity or expression is extremely low so that the normal physiological function can only be maintained by providing external source of plasminogen. 
     Those skilled in the art can understand that all the technical solutions of the plasminogen of the present invention are suitable for plasmin. Therefore, the technical solutions described in the present invention cover plasminogen and plasmin. 
     In the course of circulation, plasminogen is in a closed, inactive conformation, but when bound to thrombi or cell surfaces, it is converted into an active plasmin in an open conformation under the mediation of a plasminogen activator (PA). The active plasmin can further hydrolyze the fibrin clots to fibrin degradation products and D-dimers, thereby dissolving the thrombi. The PAp domain of plasminogen comprises an important determinant that maintains plasminogen in an inactive, closed conformation, and the KR domain is capable of binding to lysine residues present on receptors and substrates. A variety of enzymes that can serve as plasminogen activators are known, including: tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), kallikrein, coagulation factor XII (Hagmann factor), and the like. 
     “Plasminogen active fragment” refers to an active fragment in the plasminogen protein that is capable of binding to a target sequence in a substrate and exerting the proteolytic function. The technical solutions of the present invention involving plasminogen comprise such a technical solution in which plasminogen is replaced with a plasminogen active fragment. The plasminogen active fragment of the present invention is a protein comprising a serine protease domain of plasminogen. Preferably, the plasminogen active fragment of the present invention comprises SEQ ID No.14, or an amino acid sequence having an amino acid sequence identity of at least 80%, 90%, 95%, 96%, 97%, 98% or 99% with SEQ ID No.14. Therefore, plasminogen of the present invention comprises a protein containing the plasminogen active fragment and still having the plasminogen activity. 
     At present, methods for determining plasminogen and its activity in blood include: detection of tissue plasminogen activator activity (t-PAA), detection of tissue plasminogen activator antigen (t-PAAg) in plasma, detection of tissue plasminogen activity (pIgA) in plasma, detection of tissue plasminogen antigen (pIgAg) in plasma, detection of activity of the inhibitor of tissue plasminogen activators in plasma, detection of inhibitor antigens of tissue plasminogen activators in plasma and detection of plasmin-anti-plasmin (PAP) complex in plasma. The most commonly used detection method is the chromogenic substrate assay: streptokinase (SK) and a chromogenic substrate are added to a test plasma, the plasminogen in the test plasma is converted into plasmin by the action of SK, plasmin acts on the chromogenic substrate, and then it is determined that the increase in absorbance is directly proportional to plasminogen activity using a spectrophotometer. In addition, plasminogen activity in blood can also be determined by immunochemistry, gel electrophoresis, immunonephelometry, radioimmuno-diffusion and the like. 
     “Orthologues or orthologs” refer to homologs between different species, including both protein homologs and DNA homologs, and are also known as orthologs homologs and vertical homologs. The term specifically refers to proteins or genes that have evolved from the same ancestral gene in different species. The plasminogen of the present invention includes human native plasminogen, and also includes orthologues or orthologs of plasminogens derived from different species and having plasminogen activity. 
     “Conservative substitution variant” refers to one in which a given amino acid residue is changed without altering the overall conformation and function of the protein or enzyme, including, but not limited to, replacing an amino acid in the amino acid sequence of the parent protein by an amino acid with similar properties (such as acidity, alkalinity, hydrophobicity, etc.). Amino acids with similar properties are well known. For example, arginine, histidine and lysine are hydrophilic basic amino acids and are interchangeable. Similarly, isoleucine is a hydrophobic amino acid that can be replaced by leucine, methionine or valine. Therefore, the similarity of two proteins or amino acid sequences with similar functions may be different. For example, the similarity (identity) is 70%-99% based on the MEGALIGN algorithm. “Conservation substitution variant” also includes a polypeptide or enzyme having amino acid identity of 60% or more, preferably 75% or more, more preferably 85% or more, even more preferably 90% or more as determined by the BLAST or FASTA algorithm, and having the same or substantially similar properties or functions as the native or parent protein or enzyme. “Isolated” plasminogen refers to the plasminogen protein that is isolated and/or recovered from its natural environment. In some embodiments, the plasminogen will be purified (1) to a purity of greater than 90%, greater than 95% or greater than 98% (by weight), as determined by the Lowry method, such as more than 99% (by weight); (2) to a degree sufficiently to obtain at least 15 residues of the N-terminal or internal amino acid sequence using a spinning cup sequenator; or (3) to homogeneity, which is determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing or non-reducing conditions using Coomassie blue or silver staining. Isolated plasminogen also includes plasminogen prepared from recombinant cells by bioengineering techniques and separated by at least one purification step. 
     The terms “polypeptide”, “peptide” and “protein” are used interchangeably herein and refer to polymeric forms of amino acids of any length, which may include genetically encoded and non-genetically encoded amino acids, chemically or biochemically modified or derivative amino acids, and polypeptides having modified peptide backbones. The term includes fusion proteins, including, but not limited to, fusion proteins having heterologous amino acid sequences, fusions having heterologous and homologous leader sequences (with or without N-terminal methionine residues): and the like. 
     The “percent amino acid sequence identity (%)” with respect to the reference polypeptide sequence is defined as the percentage of amino acid residues in the candidate sequence identical to the amino acid residues in the reference polypeptide sequence when a gap is introduced as necessary to achieve maximal percent sequence identity and no conservative substitutions are considered as part of sequence identity. The comparison for purposes of determining percent amino acid sequence identity can be achieved in a variety of ways within the technical scope of the art, for example using publicly available computer softwares, such as BLAST, BLAST-2, ALIGN or Megalign (DNASTAR) software. Those skilled in the art can determine appropriate parameters for aligning sequences, including any algorithm needed to achieve the maximum comparison over the full length of the sequences being compared. However, for purposes of the present invention, the percent amino acid sequence identity value is generated using the sequence comparison computer program ALIGN-2. 
     In the case of comparing amino acid sequences using ALIGN-2, the % amino acid sequence identity of a given amino acid sequence A relative to a given amino acid sequence B (or may be expressed as a given amino acid sequence A having or containing a certain % amino acid sequence identity relative to, with or for a given amino acid sequence B) is calculated as follows:
 
fraction  X/Y× 100
 
     wherein X is the number of identically matched amino acid residues scored by the sequence alignment program ALIGN-2 in the alignment of A and B using the program, and wherein Y is the total number of amino acid residues in B. It will be appreciated that where the length of amino acid sequence A is not equal to the length of amino acid sequence B, the % amino acid sequence identity of A relative to B will not be equal to the % amino acid sequence identity of B relative to A. Unless specifically stated otherwise, all the % amino acid sequence identity values used herein are obtained using the ALIGN-2 computer program as described in the previous paragraph. 
     As used herein, the terms “treatment” and “treating” refer to obtaining a desired pharmacological and/or physiologic effect. The effect may be complete or partial prevention of a disease or its symptoms and/or partial or complete cure of the disease and/or its symptoms, and includes: (a) prevention of the disease from developing in a subject that may have a predisposition to the disease but has not been diagnosed as having the disease; (b) suppression of the disease, i.e., blocking its formation; and (c) alleviation of the disease and/or its symptoms, i.e., eliminating the disease and/or its symptoms. 
     The terms “individual”, “subject” and “patient” are used interchangeably herein and refer to mammals, including, but not limited to, murine (rats and mice), non-human primates, humans, dogs, cats, hoofed animals (e.g., horses, cattle, sheep, pigs, goats) and so on. 
     “Therapeutically effective amount” or “effective amount” refers to an amount of plasminogen sufficient to achieve the prevention and/or treatment of a disease when administered to a mammal or another subject to treat the disease. The “therapeutically effective amount” will vary depending on the plasminogen used, the severity of the disease and/or its symptoms, as well as the age, body weight of the subject to be treated, and the like. 
     Preparation of the Plasminogen of the Present Invention 
     Plasminogen can be isolated and purified from nature for further therapeutic uses, and can also be synthesized by standard chemical peptide synthesis techniques. When chemically synthesized, a polypeptide can be subjected to liquid or solid phase synthesis. Solid phase polypeptide synthesis (SPPS) is a method suitable for chemical synthesis of plasminogen, in which the C-terminal amino acid of a sequence is attached to an insoluble support, followed by the sequential addition of the remaining amino acids in the sequence. Various forms of SPPS, such as Fmoc and Boc, can be used to synthesize plasminogen. Techniques for solid phase synthesis are described in Barany and Solid-Phase Peptide Synthesis: pp. 3-284 in The Peptides: Analysis, Synthesis, Biology. Vol. 2: Special Methods in Peptide Synthesis, Part A., Merrifield et al. J. Am. Chem. Soc., 85: 2149-2156 (1963): Stewart et al. Solid Phase Peptide Synthesis, 2nd ed. Pierce Chem. Co., Rockford, Ill. (1984): and Ganesan A. 2006 Mini Rev. Med Chem. 6:3-10 and Camarero J A et al. 2005 Protein Pept Lett. 12:723-8. Briefly, small insoluble porous beads are treated with a functional unit on which a peptide chain is constructed. After repeated cycles of coupling/deprotection, the attached solid phase free N-terminal amine is coupled to a single N-protected amino acid unit. This unit is then deprotected to expose a new N-terminal amine that can be attached to another amino acid. The peptide remains immobilized on the solid phase before it is cut off. 
     Standard recombinant methods can be used to produce the plasminogen of the present invention. For example, a nucleic acid encoding plasminogen is inserted into an expression vector, so that it is operably linked to a regulatory sequence in the expression vector. Expression regulatory sequence includes, but is not limited to, promoters (e.g., naturally associated or heterologous promoters), signal sequences, enhancer elements and transcription termination sequences. Expression regulation can be a eukaryotic promoter system in a vector that is capable of transforming or transfecting eukaryotic host cells (e.g., COS or CHO cells). Once the vector is incorporated into a suitable host, the host is maintained under conditions suitable for high-level expression of the nucleotide sequence and collection and purification of plasminogen. 
     A suitable expression vector is usually replicated in a host organism as an episome or as an integral part of the host chromosomal DNA. In general, an expression vector contains a selective marker (e.g., ampicillin resistance, hygromycin resistance, tetracycline resistance, kanamycin resistance or neomycin resistance) to facilitate detection of those exogenous cells transformed with a desired DNA sequence. 
       Escherichia coli  is an example of prokaryotic host cells that can be used to clone a polynucleotide encoding the subject antibody. Other microbial hosts suitable for use include  Bacillus , for example,  Bacillus subtilis  and other species of enterobacteriaceae (such as genus  Salmonella  and genus  Serratia ), and various genus  Pseudomonas . In these prokaryotic hosts, expression vectors can also be generated which will typically contain an expression control sequence (e.g., origin of replication) that is compatible with the host cell. In addition, there will be many well-known promoters, such as the lactose promoter system, the tryptophan (trp) promoter system, the beta-lactamase promoter system or the promoter system from phage A. Optionally in the case of manipulation of a gene sequence, a promoter will usually control expression, and has a ribosome binding site sequence and the like to initiate and complete transcription and translation. 
     Other microorganisms, such as yeast, can also be used for expression.  Saccharomyces  (e.g.,  S. cerevisiae ) and  Pichia  are examples of suitable yeast host cells, in which a suitable vector has an expression control sequence (e.g., promoter), an origin of replication, a termination sequence and the like, as required. A typical promoter comprises 3-phosphoglycerate kinase and other glycolytic enzymes. Inducible yeast is initiated by promoters specifically including those derived from alcohol dehydrogenase, isocytochrome C. and enzymes responsible for maltose and galactose utilization. 
     In addition to microorganisms, mammalian cells (e.g., mammalian cells cultured in cell culture material in vitro) may also be used to express and produce the anti-Tau antibody (e.g., a polynucleotide encoding the subject anti-Tau antibody) of the present invention. See Winnacker, From Genes to Clones, VCH Publishers, N.Y., N.Y. (1987). Suitable mammalian host cells include CHO cell lines, various Cos cell lines, HeLa cells, myeloma cell lines and transformed B cells or hybridomas. Expression vectors for these cells may comprise an expression control sequence, such as an origin of replication, promoter and enhancer (Queen et al. Immunol. Rev. 89:49 (1986)), as well as necessary information processing sites, such as a ribosome binding site, RNA splice site, polyadenylation site and transcription terminator sequence. Examples of suitable expression control sequences are promoters derived from immunoglobulin gene, SV40, adenovirus, bovine papilloma virus, cytomegalovirus and the like. See Co et al. J. Immunol. 148:1149 (1992). 
     Once synthesized (chemically or recombinantly), the plasminogen of the present invention can be purified according to standard procedures in the art, including ammonium sulfate precipitation, affinity column, column chromatography, high performance liquid chromatography (HPLC), gel electrophoresis and the like. The plasminogen is substantially pure, e.g., at least about 80% to 85% pure, at least about 85% to 90% pure, at least about 90% to 95% pure, or 98% to 99% pure or purer, for example free of contaminants such as cell debris, macromolecules other than the subject antibody and the like. 
     Pharmaceutical Formulations 
     A therapeutic formulation can be prepared by mixing plasminogen of a desired purity with an optional pharmaceutical carrier, excipient or stabilizer (Remington&#39;s Pharmaceutical Sciences, 16th edition. Osol, A. ed. (1980)) to form a lyophilized preparation or an aqueous solution. Acceptable carriers, excipients and stabilizers are non-toxic to the recipient at the dosages and concentrations employed, and include buffers, such as phosphates, citrates and other organic acids antioxidants, including ascorbic acid and methionine; preservatives (e.g., octadecyl dimethyl benzyl ammonium chloride hexane chloride diamine; benzalkonium chloride and benzethonium chloride: phenol, butanol or benzyl alcohol alkyl p-hydroxybenzoates, such as methyl or propyl p-hydroxybenzoate; catechol; resorcinol; cyclohexanol; 3-pentanol; and m-cresol); low molecular weight polypeptides (less than about 10 residues): proteins, such as serum albumin. gelatin or immunoglobulins; hydrophilic polymers, such as polyvinylpyrrolidone; amino acids, such as glycine, glutamine, asparagine, histidine, arginine or lysine; monosaccharides, disaccharides and other carbohydrates, including glucose, mannose or dextrins; chelating agents, such as EDTA; sugars, such as sucrose, mannitol, fucose or sorbitol; salt-forming counter ions, such as sodium metal complexes (e.g., zinc-protein complexes); and/or non-ionic surfactants, e.g., TWEEN™, PLURONICS™, or polyethylene glycol (PEG). Preferable formulation of lyophilized anti-VEGF antibody is described in WO 97/04801, which is incorporated herein by reference. 
     The formulations of the invention may also comprise one or more active compounds required for the particular disorder to be treated, preferably those that are complementary in activity and have no side effects with one another, for instance, drugs for treating hypertension, arrhythmia, and diabetes, etc. 
     The plasminogen of the present invention may be encapsulated in microcapsules prepared by techniques such as coacervation or interfacial polymerization, for example, it may be incorporated in a colloid drug delivery system (e.g., liposomes, albumin microspheres, microemulsions, nanoparticles and nanocapsules), or incorporated in hydroxymethyl cellulose or gel-microcapsules and poly-(methyl methacrylate) microcapsules in macroemulsions. These techniques are disclosed in Remington&#39;s Pharmaceutical Sciences, 16th edition, Osol, A. Ed. (1980). 
     The plasminogen of the present invention for in vivo administration must be sterile. This can be easily achieved by filtration through a sterile filtration membrane before or after lyophilization and reconstitution. 
     The plasminogen of the present invention can be prepared into a sustained-release preparation. Suitable examples of sustained-release preparations include solid hydrophobic polymer semi-permeable matrices having a shape and containing glycoproteins, such as films or microcapsules. Examples of sustained-release matrices include polyesters, hydrogels (e.g., poly(2-hydroxyethyl-methacrylate)) (Langer et al. J. Biomed. Mater. Res., 15: 167-277 (1981) and Langer, Chem. Tech., 12:98-105 (1982)), or poly(vinyl alcohol), polylactides (U.S. Pat. No. 3,773,919, and EP 58,481), copolymer of L-glutamic acid and y ethyl-L-glutamic acid (Sidman et al. Biopolymers 22:547(1983)), nondegradable ethylene-vinyl acetate (Langer et al. supra), or degradable lactic acid-glycolic acid copolymers such as Lupron Depot™ (injectable microspheres composed of lactic acid-glycolic acid copolymer and leuprolide acetate), and poly D-(−)-3-hydroxybutyric acid. Polymers, such as ethylene-vinyl acetate and lactic acid-glycolic acid, are able to persistently release molecules for 100 days or longer, while some hydrogels release proteins for a shorter period of time. A rational strategy for protein stabilization can be designed based on relevant mechanisms. For example, if the aggregation mechanism is discovered to be formation of an intermolecular S—S bond through thio-disulfide interchange, stability is achieved by modifying sulhydryl residues, lyophilizing from acidic solutions, controlling moisture content, using appropriate additives, and developing specific polymer matrix compositions. 
     Administration and Dosage 
     The pharmaceutical composition of the present invention can be administered in different ways, for example by intravenous, intraperitoneal, subcutaneous, intracranial, intrathecal, intraarterial (e.g., via carotid), intramuscular administration. 
     Preparations for parenteral administration include sterile aqueous or non-aqueous solutions, suspensions and emulsions. Examples of non-aqueous solvents are propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, and alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer&#39;s dextrose, dextrose and sodium chloride, or fixed oils. Intravenous vehicles include liquid and nutrient supplements, electrolyte supplements and the like. Preservatives and other additives may also be present, for example, such as antimicrobial agents, antioxidants, chelating agents and inert gases. 
     The medical staff will determine the dosage regimen based on various clinical factors. As is well known in the medical field, the dosage of any patient depends on a variety of factors, including the patient&#39;s size, body surface area, age, the specific compound to be administered, sex, frequency and route of administration, overall health and other drugs administered simultaneously. The dosage range of the pharmaceutical composition comprising plasminogen of the present invention may be, for example, such as about 0.0001 to 2000 mg/kg, or about 0.001 to 500 mg/kg (such as 0.02 mg/kg, 0.25 mg/kg, 0.5 mg/kg, 0.75 mg/kg, 10 mg/kg and 50 mg/kg) of the subject&#39;s body weight daily. For example, the dosage may be 1 mg/kg body weight or 50 mg/kg body weight, or in the range of 1 mg/kg-50 mg/kg, or at least 1 mg/kg. Dosages above or below this exemplary range are also contemplated, especially considering the above factors. The intermediate dosages in the above range are also included in the scope of the present invention. A subject may be administered with such dosages daily, every other day, weekly or based on any other schedule determined by empirical analysis. An exemplary dosage schedule includes 1-10 mg/kg for consecutive days. During administration of the drug of the present invention, the therapeutic effect and safety are required to be assessed real-timely. 
     A Product or a Kit 
     One embodiment of the present invention relates to a product or a kit comprising the plasminogen or plasmin for treat osteoarthritis according to the present invention. The product preferably comprises a container, label or package insert. Suitable containers include bottles, vials, syringes and the like. The container can be made of various materials, such as glass or plastic. The container contains a composition that is effective to treat the disease or disorder of the present invention and has a sterile access (for example, the container may be an intravenous solution bag or vial containing a plug that can be pierced by a hypodermic injection needle). At least one active agent in the composition is plasminogen/plasmin. The label on or attached to the container indicates that the composition is used for treating the osteoarthritis according to the present invention. The article of manufacture may further comprise a second container containing a pharmaceutically acceptable buffer, such as phosphate buffered saline, Ringer&#39;s solution and glucose solution. It may further comprise other substances required from a commercial and user perspective, including other buffers, diluents, filters, needles and syringes. In addition, the article of manufacture comprises a package insert with instructions for use, including, for example, instructions to a user of the composition to administer the plasminogen composition and other drugs to treat an accompanying disease to a patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 D  show the Safranin O staining results of knee joints in the aging model mice induced by 0.5 μg/kg vitamin D.  FIG.  1 A  is from the blank control group,  FIG.  1 B  is from the vehicle (PBS) control group,  FIG.  1 C  is from the plasminogen group, and  FIG.  1 D  is the quantitative analysis result. The results show that the knee cartilage (marked by arrow) in the plasminogen group is significantly more than that of the vehicle (PBS) control group, and the statistical difference is significant (* indicates P&lt;0.05); and compared with the vehicle (PBS) control group, in the plasminogen group the amount of knee cartilage is closer to that of the mice in the blank control group. It indicates that plasminogen can significantly reduce the loss of cartilage in the knee joints of the aging model mice induced by vitamin D. 
         FIGS.  2 A- 2 E : Scoring results of Safranin O staining of knee joints in osteoarthritis model mice induced by type II collagenase 14 days after the administration of plasminogen.  FIG.  2 A  and  FIG.  2 C  are from the vehicle (PBS) control group,  FIG.  2 B  and  FIG.  2 D  are from the plasminogen group, and E is the quantitative analysis result. The results show that the pathological score of the knee joints in the plasminogen group is significantly lower than that in the vehicle (PBS) control group, and the statistical difference is extremely significant (** indicates P&lt;0.01). It indicates that plasminogen can alleviate the knee joint injury of osteoarthritis model mice induced by type II collagenase. 
         FIGS.  3 A- 3 D : Representative Safranin O staining pictures of the knee joints in the osteoarthritis model PIg −/−  mice induced by type II collagenase 14 days after the administration of plasminogen.  FIG.  3 A  and  FIG.  3 C  are from the vehicle (PBS) control group, and  FIG.  3 B  and  FIG.  3 D  are from the plasminogen group. The results show that the structural arrangement of cartilage tissue (thin arrow marked) in the vehicle (PBS) control group is disordered, the number of cells is significantly reduced, the staining of Safranin O is significantly reduced, and the bone trabecula (thick arrow marked) became thinner and broken. Compared with the vehicle (PBS) control group, in the plasminogen group the cartilage tissue structure is relatively neat, the number of cells in the cartilage is relatively large, and the staining range of safranin O is relatively wide. It indicates that plasminogen can reduce the knee joint injury of osteoarthritis PIg −/−  mice induced by type II collagenase. 
         FIGS.  4 A- 4 B : Representative Safranin O staining pictures of the knee joints in the osteoarthritis model mice induced by ligament transection 14 days after the administration of plasminogen.  FIG.  4 A  is from the vehicle (PBS) control group, and  FIG.  4 B  is from the plasminogen group. The results show that in the vehicle (PBS) control group, the cartilage (triangle marked) is severely lost, and the bone trabecula (arrow marked) becomes thinner and broken, and there is a large area of the marrow cavity without bone trabecula; and compared with the vehicle (PBS) control group, in the plasminogen group the bone trabecula has good continuity, no severe fracture, no large area of the region without bone trabecula, and relatively more cartilage tissue. It indicates that plasminogen can improve the knee joint tissue structure of osteoarthritis model mice induced by ligament transection. 
         FIGS.  5 A- 5 E : Results of alkaline phosphatase staining of the knee joints in the osteoarthritis model mice induced by ligament transection 14 days after the administration of plasminogen.  FIG.  5 A  and  FIG.  5 C  are from the vehicle (PBS) control group,  FIG.  5 B  and  FIG.  5 D  are from the plasminogen group, and  FIG.  5 E  is from the quantitative analysis result. The results show that the alkaline phosphatase staining of the knee cartilage surface (thin arrow marked) and growth plate (thick arrow marked) of the plasminogen group mice is more than that of the vehicle (PBS) control group, and the statistical difference is significant (* indicates P&lt;0.05). It indicates that plasminogen can significantly promote the increase of alkaline phosphatase activity in the knee joints of osteoarthritis model mice induced by ligament transection, that is, plasminogen promotes the activity of knee cartilage osteoblast to increase significantly. 
         FIGS.  6 A- 6 D : Results of immunohistochemical staining of type II collagen in the knee joint of MIA osteoarthritis model mice 28 days after the administration of plasminogen.  FIG.  6 A  is from the sham operation group,  FIG.  6 B  is from the vehicle control group,  FIG.  6 C  is from the plasminogen group, and  FIG.  6 D  is the quantitative analysis result. The results show that there is a certain amount of type II collagen (arrow marked) in the knee joint of the sham operation group; the amount of type II collagen in the knee joint of the vehicle control group is not significantly different from that of the sham operation group, while the amount of type II collagen of the plasminogen group is significantly higher than that of the vehicle control group and the sham operation group, and the statistical difference of quantitative analysis of the average optical density is significant (* indicates P&lt;0.05). The results show that plasminogen can promote the regeneration of knee cartilage in osteoarthritis model mice. 
         FIGS.  7 A- 7 D : Representative Safranin O staining pictures of the knee joint of MIA osteoarthritis model mice 28 days after the administration of plasminogen.  FIG.  7 A  is from the sham operation group,  FIG.  7 B  is from the vehicle control group,  FIG.  7 C  is from the plasminogen group, and  FIG.  7 D  is the pathological scoring result. The results show that there is a certain amount of cartilage in the knee joint of the sham operation group (arrow marked) the amount of knee cartilage in the vehicle control group is significantly reduced and the pathological score is significantly increased, indicating that MIA successfully induces osteoarthritis; the amount of knee cartilage in the plasminogen group is significantly higher than that in the vehicle control group, and the pathological scores are also significantly lower than those in the vehicle control group, and the statistical difference is significant (* indicates P&lt;0.05). This result indicates that plasminogen can promote cartilage regeneration and improve osteoarthritis injury. 
         FIGS.  8 A- 8 D : Results of Safranin 0 staining on the femoral surface of the left knee joint of the osteoarthritis model mice 28 days after the administration of plasminogen.  FIG.  8 A  is from the sham operation group,  FIG.  8 B  is from the vehicle control group,  FIG.  8 C  is from the plasminogen group, and  FIG.  8 D  is the quantitative analysis result of average optical density. The results show that there is a small amount of cartilage (marked by arrows) on the femoral surface of the knee joints in the sham operation group; there is no significant difference between the amount of cartilage on the femoral surface in the vehicle control group and that in the sham operation group, while the amount of cartilage on the femoral surface in the plasminogen group is significantly higher than that in the vehicle control group and the sham operation group, and the statistical difference of quantitative analysis results of average optical density is significant (* indicates P&lt;0.05). The results show that plasminogen can promote the regeneration of cartilage on the femoral surface of osteoarthritis model mice. 
         FIG.  9   : Results of pain detection of MIA osteoarthritis model rats 7 days after the administration of plasminogen. The results show that the rats in the sham operation group have higher pain thresholds the pain thresholds of the left and right legs in the vehicle control group have significantly decreased, and are significantly lower than those in the sham operation group the pain thresholds of the left and right legs in the plasminogen group are significantly increased, compared with the vehicle control group, the statistical difference between the left legs is close to significance (P=0.08), and the statistical difference between the right legs is significant (* indicates P&lt;0.05). The results show that plasminogen can significantly reduce the pain of osteoarthritis. 
         FIG.  10   : Results of pain detection of osteoarthritis model mice 7 days after the administration of plasminogen. The results show that the pain thresholds of the mice in the sham operation group are relatively higher: the pain thresholds of the mice in the vehicle control group are significantly reduced, and are significantly lower than those in the sham operation group while the pain thresholds of the mice in the plasminogen group are significantly increased, and are significantly higher than those in the vehicle control group, and the statistical difference is close to significance (P=0.09). This result indicates that plasminogen can reduce osteoarthritis pain. 
         FIGS.  11 A- 11 F : Results of Safranin O staining on the left knee joints of osteoarthritis model mice 28 days after the administration of plasminogen. The results show that there is a certain amount of articular cartilage (arrow marked) on the femur and tibia surfaces of the left knee joints in the sham operation group, there is no significant difference between the amount of cartilage on the tibia and femoral surfaces in the vehicle control group and that in the sham operation group, while the amount of cartilage in the plasminogen group is significantly higher than that in the vehicle control group and the sham operation group. It indicates that plasminogen can promote the regeneration of articular cartilage in osteoarthritis model mice. 
         FIGS.  12 A- 12 D  show that plasminogen inhibits bone resorption in osteoarthritis model mice. The results show that there is a certain amount of acid phosphatase (arrow marked) in the knee joints of the sham operation group ( FIG.  12 A ); the acid phosphatase of the knee joints in the vehicle control group is increased ( FIG.  12 B ), and is significantly more than that of the sham operation group while the acid phosphatase of the knee joints in the plasminogen group ( FIG.  12 C ) is significantly less than that in the vehicle control group, and the statistical difference is significant (* indicates P&lt;0.05) ( FIG.  12 D ). This result indicates that plasminogen can reduce acid phosphatase of osteoarthritis knee joint, reduce osteoclast activity, and inhibit bone resorption. 
         FIGS.  13 A- 13 F  show that plasminogen promotes an increase in the number of Sox-9 positive stem cells at the tibial end of the knee joint of MIA osteoarthritis. The results show that there is a certain amount of Sox 9 positive stem cells (arrow marked) in the knee joint tibia in the sham operation group ( FIG.  13 A ,  FIG.  13 D ); the number of Sox 9 positive stem cells in the knee joint tibia in the vehicle control group ( FIG.  13 B ,  FIG.  13 E ) is significantly reduced, while in the plasminogen group ( FIG.  13 C ,  FIG.  13 F ) the number of Sox 9 positive stem cells in the knee joint tibia is significantly higher than that in the vehicle control group. This result indicates that plasminogen can promote the increase of the number of Sox-9 positive stem cells in the tibial end of osteoarthritis knee joint, and repair the knee joint injury caused by osteoarthritis. 
         FIGS.  14 A- 14 C  show that plasminogen improves knee joint synovial inflammation in MIA osteoarthritis model mice. The results show that there is no obvious inflammatory cell infiltration in the knee joint synovium in the sham operation group ( FIG.  14 A ); while in the vehicle control group ( FIG.  14 B ), there is obvious inflammation cell infiltration (arrow marked) in the knee joint synovium, and in the plasminogen group ( FIG.  14 C ) the infiltration of inflammatory cells in the synovium of the knee joints is significantly less than that in the vehicle control group. This result indicates that plasminogen can improve inflammation condition of the knee joint synovium in osteoarthritis. 
     
    
    
     EXAMPLES 
     Example 1: Plasminogen Reduces Cartilage Loss in Knee Joints of Vitamin D Induced Osteoporosis Mice 
     Fifteen 5-6 weeks aged male C57 mice are taken, and randomly divided into 3 groups after weighing, i.e., a blank control group, a plasminogen group, and a vehicle (PBS) control group; 5 mice in each group. The mice in the blank control group are injected intraperitoneally with 50 μl of corn oil every day: the mice in the plasminogen group and the vehicle (PBS) control group are injected intraperitoneally with vitamin D (Sigma Aldrich) at 0.5 μg/kg body weight every day to induce osteoporosis model  [6, 27] . At the same time, administration to the mice starts. The human plasminogen is injected into the tail vein of the plasminogen group mice at 1 mg/0.1 mL/mouse/day, and the same volume of PBS is injected into the tail vein of the vehicle (PBS) control group mice, the mice in the blank control group are not administered, and the administration is taken 28 consecutive days to generate the model. During the administration period, all mice are fed with low calcium feed. The first day of model generation and medicine administration is set as day 1, after being sacrificed on day 29, the knee joints are taken and fixed with 4% paraformaldehyde for 24 hours, then decalcifying in 10% EDTA for three weeks, and washing with gradient sucrose solution the above operations need to be operated at 4° C. condition. Then the samples are embedded in paraffin, cut into 8 μm sections and stained with safranin O. The sections are observed under a 100× optical microscope. 
     The staining principle of cartilage staining solution (safranin O method) lies in that: the basophilic cartilage is combined with the basic dye safranin O to show a red color safranin O is a cationic dye combined with multiple anions, and revealing of cartilage by safranin O is based on the fact that cationic dyes will combine with the anionic groups in polysaccharide (chondroitin sulfate or keratan sulfate). Safranin O color density is approximately proportional to the anion concentration, indirectly reflecting the content and distribution of proteoglycans in the matrix. 
     Safranin O staining, namely safranin staining, mainly shows the acidic proteoglycan component in cartilage tissue, and it can show the formation of cartilage  [28] . 
     The results show that the knee cartilage (marked by arrows) in the plasminogen group ( FIG.  1 C ) is significantly more than that in the vehicle (PBS) control group ( FIG.  1 B ), and the statistical difference is significant (* indicates P&lt;0.05) ( FIG.  1 D ); compared with the vehicle (PBS) control group, the knee cartilage in the plasminogen group is closer to that in the blank control mice ( FIG.  1 A ). This indicates that plasminogen can significantly reduce the cartilage loss in the knee joints of vitamin D induced osteoporosis model mice. 
     Example 2: Plasminogen Reduces Knee Joint Injury in Osteoarthritis Model Mice Induced by Type II Collagenase 
     Twelve 10-week-old C57 male mice are injected intraperitoneally with pentobarbital sodium at 50 mg/kg body weight, then anesthetizing the mice, and intramuscularly injecting Tolfedine (0.1 ml/kg). A gap is made in the right knee joint of a mouse, and the knee joint is bent 90 degrees, then the articular cavity of the mouse is injected with type II collagenase (C6885, sigma) at 5 μg/6 μl per mouse; the left knee joint is treated identically to the right knee joint, but only the same volume of normal saline is injected  [29,30] . Seven days after the injection, the mice are randomly divided into two groups according to their body weights, 6 mice in each group for the vehicle (PBS) control group and the plasminogen group; then the administration starts. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS is injected into the tail vein of the vehicle (PBS) control group mice for 14 consecutive days. The first day of administration is set as day 1, after being sacrificed on day 15, the knee joints are taken and fixed with 4% paraformaldehyde for 24 hours, then decalcifying in 10% EDTA for three weeks, and washing with gradient sucrose solution: the above operations need to be operated at 4° C. condition. Then the samples are embedded in paraffin, sectioned at 8 μm and stained with safranin O. The sections are observed under 40× (A, B) and 100× (C, D) optical microscopes, and the pathological scores of the knee joints are evaluated according to the following Table 1  [31] . 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Types 
                 Subtypes 
                 Scores 
               
               
                   
                   
               
             
            
               
                   
                 Structure of the 
                 Normal 
                 0 
               
               
                   
                 soft tissues 
                 unorganized, but the layer 
                 1 
               
               
                   
                   
                 are distinguishable. 
                   
               
               
                   
                   
                 apparently unorganized,  
                 2 
               
               
                   
                   
                 and the layers are disordered. 
                   
               
               
                   
                   
                 Significantly disordered 
                 3 
               
               
                   
                 Number of the 
                 Normal 
                 0 
               
               
                   
                 cartilage cells 
                 Slight reduction 
                 1 
               
               
                   
                   
                 Moderate reduction 
                 2 
               
               
                   
                   
                 Severe reduction 
                 3 
               
               
                   
                 Safranin O staining 
                 Normal 
                 0 
               
               
                   
                   
                 Slight decrease 
                 1 
               
               
                   
                   
                 Moderate decrease 
                 2 
               
               
                   
                   
                 Severe decrease 
                 3 
               
               
                   
                   
                 Non-staining 
                 4 
               
               
                   
                 Tidemark 
                 Normal 
                 0 
               
               
                   
                   
                 Uncompleted 
                 1 
               
               
                   
                 Total score 
                   
                 0-11 
               
               
                   
                   
               
            
           
         
       
     
     The results show that the pathological scores of the knee joints in the plasminogen group ( FIGS.  2 B , D) are significantly lower than those in the vehicle (PBS) control group ( FIGS.  2 A , C), and the statistical difference is extremely significant (** indicates P&lt;0.01) ( FIG.  2 E ). It indicates that plasminogen can significantly reduce the knee joint injury of type II collagenase induced osteoarthritis, and reduce the loss of articular cartilage. 
     Example 3: Plasminogen Improves the Structure States of Knee Joint Tissues in Osteoarthritis Model PIg −/−  Mice Induced by Type II Collagenase 
     Ten 10-week-old PIg −/−  male mice are intraperitoneally injected with pentobarbital sodium at 50 mg/kg body weight, then anesthetizing the mice, and intramuscularly injecting Tolfedine (0.1 ml/kg). A gap is made in the right knee joint of a mouse, and the knee joint is bent 90 degrees, then the articular cavity of the mouse is injected with type II collagenase (C6885, sigma) at 5 μg/6 μl per mouse; the left knee joint is treated identically to the right knee joint, but only the same volume of normal saline is injected  [29,30] . Seven days after the injection, the mice are randomly divided into two groups according to their body weights, 5 mice in each group for the vehicle (PBS) control group and the plasminogen group; then the administration starts. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS is injected into the tail vein of the vehicle (PBS) control group mice for 14 consecutive days. The first day of administration is set as day 1, after being sacrificed on day 15, the knee joints are taken and fixed with 4% paraformaldehyde for 24 hours, then decalcifying in 10% EDTA for three weeks, and washing with gradient sucrose solution: the above operations need to be operated at 4° C. condition. Then the samples are embedded in paraffin, sectioned at 8 μm and stained with safranin O. The sections are observed under 40× (A, B) and 100× (C, D) optical microscopes. 
     The results show that in the vehicle (PBS) control group ( FIGS.  3 A , C), the structural arrangement of the cartilage tissue (thin arrow marked) is disordered, the number of cells is significantly reduced, safranin O staining is significantly reduced, and the bone trabecula (thick arrow marked) becomes thinner and broken compared with the vehicle (PBS) control group, the plasminogen group ( FIGS.  3 B , D) has relatively neat cartilage tissue structure, relatively large numbers of cells in the cartilage, and a relatively wide staining range for safranin O. It indicates that plasminogen can reduce the knee joint injury of osteoarthritis PIg −/−  mice induced by type II collagenase. 
     Example 4: Plasminogen Improves the Structural States of the Knee Joint Tissues in Osteoarthritis Model Mice Induced by Ligament Transection 
     Ten 9-10 weeks aged male C57 mice are injected intraperitoneally with pentobarbital sodium at 50 mg/kg body weight, then anesthetizing the mice. The hair around the knee joint is removed, and Tolfedine (0.1 ml/kg) analgesic is intramuscularly injected into a mouse immediately before surgery. The mouse is placed under a dissecting microscope, and a gap is made at the distal end of the right patella and tibial plateau to separate the patellar ligament and expose the articular cavity; bluntly separating the fat pad between the femoral condyles so that the anterior cruciate ligament can be observed; cutting the anterior cruciate ligament and inside collateral ligament with microblade, and sewing the joint capsule and skin to establish an osteoarthritis model  [33,33] . As for the left knee joint, only the articular cavity is exposed and the transection operation is not performed. Care should be taken to avoid damaging the articular cartilage during the operation, the limbs are not fixed after the operation, and mice can move freely in the cage. On the first day after the surgery, the mice are injected intramuscularly with Tolfedine (0.1 mg/kg) and potassium penicillin (40,000 units/kg) every 12 hours. Two weeks later, the mice are randomly divided into two groups according to their body weights, 5 mice in each group for the vehicle (PBS) control group and the plasminogen group then the administration to the mice starts. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS is injected into the tail vein of the vehicle (PBS) control group mice for 14 consecutive days. The first day of administration is set as day 1, after being sacrificed on day 15, the knee joints are taken and fixed with 4% paraformaldehyde for 24 hours, then decalcifying in 10% EDTA for three weeks, and washing with gradient sucrose solution the above operations need to be operated at 4° C. condition. Then the samples are embedded in paraffin, sectioned at 4 μm and stained with safranin O. The sections are observed under a 40× optical microscope. 
     The results show that in the vehicle (PBS) control group ( FIG.  4 A ), the cartilage (triangle marked) is severely lost, and the bone trabecula (arrow marked) becomes thinner and broken, and there is a large area of the marrow cavity without bone trabecula; and compared with the vehicle (PBS) control group, in the plasminogen group ( FIG.  4 B ) the bone trabecula has good continuity, no severe fracture, no large area of the region without bone trabecula, and relatively more cartilage tissue. It indicates that plasminogen can improve the knee joint tissue structure of osteoarthritis model mice induced by ligament transection. 
     Example 5: Plasminogen Increases Alkaline Phosphatase Activity in the Knee Joints of Osteoarthritis Model Mice Induced by Ligament Transection 
     Ten 9-10 weeks aged male C57 mice are injected intraperitoneally with pentobarbital sodium at 50 mg/kg body weight, then anesthetizing the mice. The hair around the knee joint is removed, and Tolfedine (0.1 ml/kg) analgesic is intramuscularly injected into a mouse immediately before surgery. The mouse is placed under a dissecting microscope, and a gap is made at the distal end of the right patella and tibial plateau n separate the patellar ligament and expose the articular cavity: bluntly separating the fat pad between the femoral condyles so that the anterior cruciate ligament can be observed cutting the anterior cruciate ligament with microblade, and sewing the joint capsule and skin to establish an osteoarthritis model  [32,33] . As for the left knee joint, only the articular cavity is exposed and the transection operation is not performed. Care should be taken to avoid damaging the articular cartilage during the operation, the limbs are not fixed after the operation, and mice can move freely in the cage. On the first day after the surgery, the mice are injected intramuscularly with Tolfedine (0.1 mg/kg) and potassium penicillin (40,000 units/kg) every 12 hours. Two weeks later, the mice are randomly divided into two groups according to their body weights, 5 mice in each group for the vehicle (PBS) control group and the plasminogen group; then the administration to the mice starts. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS is injected into the tail vein of the vehicle (PBS) control group mice for 14 consecutive days. The first day of administration is set as day 1, after being sacrificed on day 15, the knee joints are taken and fixed in fixative. The fixative formula: 2% paraformaldehyde, 0.075 mol/L lysine, 0.01 mol/L sodium periodate. After fixation, gradient washing is performed for each sample with PBS solution at 4° C. for 12 hours, and then placing in 4° C. decalcifying solution for 2 weeks, and the decalcifying solution is changed every 5 days. After decalcification is completed, gradient washing is performed for each sample with PBS solution at 4° C. for 12 hours, and then the knee joint is dehydrated with alcohol gradient, made transparent with xylene, and embedded in paraffin. 5 μm sections are cut, dewaxing and rehydrating, and incubating with magnesium chloride buffer at 4° C. overnight. Then the sections are incubated in alkaline phosphatase substrate solution for 1 hour at room temperature, counterstaining with hematoxylin for 2 min, rinsing in running water for 5 min, baking at 60° C. for 30 min, sealing with neutral gum, and then observing the sections under a 200× optical microscope. 
     Alkaline phosphatase (ALP) is a marker of early differentiation of osteoblasts  [32] . 
     The results show that the alkaline phosphatase staining (arrow marked) on the surface of the knee cartilage and the growth plate of the plasminogen group mice ( FIGS.  5 B , D) is more than that in the vehicle (PBS) control group mice ( FIGS.  5 A , C), and the statistical difference is significant (* indicates P&lt;0.05) ( FIG.  5 E ). It indicates that plasminogen can significantly promote the increase of alkaline phosphatase activity in the knee joints of osteoarthritis model mice induced by ligament transection, that is, plasminogen promotes the osteoblast activity of knee cartilage to increase significantly. 
     Example 6: Plasminogen Promotes the Regeneration of Knee Cartilage in MIA Osteoarthritis Model Mice 
     Twenty five 8-10 weeks aged C57 male mice are weighed and randomly divided into two groups according to body weights; 5 mice in the sham operation group, and 20 mice in the model group. All mice are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight. After anesthesia, for the mice in the model group, the hair of the left knee is removed, disinfecting with 70% alcohol and iodine tincture: and the left knee joint is bent 90 degrees, moving the needle of the syringe horizontally along the knee (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia, and MIA (monoiodoacetic acid) physiological saline solution is injected into the articular cavity at 0.1 mg/10 μl; in the sham operation group, 10 μl saline is injected into the left articular cavity, after the injection, massaging the knee to ensure even distribution  [34] . The right knee joint is not treated. Three days after the MIA injection in the articular cavity, the mice in the model group are subjected to a pain test. According to the test results, the mice are randomly divided into two groups: 10 mice in each group for the vehicle control group and the plasminogen group; then the drugs are administered to the mice, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle (PBS) control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The preparation of MIA solution: MIA powder (Sigma. 57858-5G) is dissolved in physiological saline at a concentration of 10 mg/ml, and then filtering with a 0.22 μm filter membrane, and using right after it is ready. The mice are sacrificed on day 29, and the left knee joints are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin. The thickness of the tissue section is 5 μm, and the sections are washed once after dewaxing and rehydrating. The tissues are circled with a PAP pen, then incubating with 3% hydrogen peroxide for 15 min, and washing twice with 0.01M PBS for 5 min each time. 5% normal sheep serum (Vector laboratories, Inc., USA) is used to block for 30 min after the time is expired, the sheep serum is discarded, then adding rabbit-derived anti-type II collagen antibody (Abcam, ab34712) dropwise, incubating overnight at 4° C., and washing twice with 0.01M PBS for 5 min each time. Goat anti-rabbit IgG (HRP) antibody (Abcam) (secondary antibody) is incubated for 1 hour at room temperature, then washing twice with 0.01M PBS for 5 min each time. Color development is performed according to the DAB kit (Vector laboratories, Inc., USA), after washing three times with water, counterstaining with hematoxylin for 30 seconds, and rinsing under running water for 5 min. Dehydration is performed with gradient alcohol, then making transparent with xylene and sealing with neutral gum: and the sections are observed and photographed under a 200× optical microscope, processing with Image-Pro software to collect data. 
     Monoiodoacetic acid (MIA) has the effect of destroying articular cartilage and the surrounding synovial ligaments the original steady state of the articular cavity may be changed by injecting MIA into the articular cavity, and an intra-articular inflammatory reaction may also be triggered, thereby changing the metabolism of the cartilage and the subchondral bone, destroying the stability of the environment in the joints, and causing chondrocyte apoptosis and cartilage wear. Studies have shown that monoiodoacetic acid can inhibit the metabolism of articular chondrocytes, causing the death of chondrocytes, which in turn leads to the degradation of cartilage matrix, inducing arthritis cartilage changes and osteoarthritis models. Type II collagen is one of the main components of cartilage matrix, and plays an important role in maintaining the mechanical properties of cartilage  [35] . 
     The results show that there is a certain amount of type II collagen (marked by arrow) in the knee joints of the sham operation group mice ( FIG.  6 A ); the amount of type II collagen in the knee joints of the vehicle control group mice ( FIG.  6 B ) is not significantly different from that of the sham operation group mice, while the amount of type II collagen in the knee joints of the plasminogen group mice ( FIG.  6 C ) is significantly higher than that of the vehicle control group and the sham operation group mice, and the statistical difference of the quantitative analysis result of the average optical density is significant (* indicates P&lt;0.05) ( FIG.  6 D ). The results show that plasminogen can promote the regeneration of knee cartilage in osteoarthritis model mice. 
     Example 7: Improvement Effect of Plasminogen on MIA-Induced Osteoarthritis 
     Twenty five 8-10 weeks aged C57 male mice are weighed and randomly divided into two groups according to body weights; 5 mice in the sham operation group, and 20 mice in the model group. All mice are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight. After anesthesia, for the mice in the model group, the hair of the left knee is removed, disinfecting with 70% alcohol and iodine tincture; and the left knee joint is bent 90 degrees, moving the needle of the syringe horizontally along the knee (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia, and MIA physiological saline solution is injected into the articular cavity at 0.1 mg/10 μl; in the sham operation group, 10 μl saline is injected into the left articular cavity, after the injection, massaging the knee to ensure even distribution  [34] . The right knee joint is not treated. Three days after the MIA injection in the articular cavity, the mice in the model group are subjected to a pain test. According to the test results, the mice are randomly divided into two groups: 10 mice in each group for the vehicle control group and the plasminogen group then the administration starts, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle (PBS) control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The preparation of MIA solution: MIA powder (Sigma, 57858-5G) is dissolved in physiological saline at a concentration of 10 mg/ml, and then filtering with a 0.22 μm filter membrane, and using right after it is ready. The mice are sacrificed on day 29, and the left knee joints are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin. The 5 μm sections are stained with safranin O. The sections are observed and photographed under a 40× optical microscope, and the pathological scores are evaluated according to Table 1. 
     The results show that there is a certain amount of cartilage in the knee joints of the sham operation group mice ( FIG.  7 A ) (marked by arrows): for the vehicle control group ( FIG.  7 B ), the amount of knee cartilage is significantly reduced, and the pathological scores are significantly increased, indicating that MIA successfully induces osteoarthritis: the amount of cartilage in the knee joints of the plasminogen group mice ( FIG.  7 C ) is significantly more than that in the vehicle control group, and the pathological scores are also significantly lower than those in the vehicle control group, and the statistical difference is significant (* indicates P&lt;0.05) ( FIG.  7 D ). This result indicates that plasminogen can promote cartilage regeneration and repair the articular injury caused by osteoarthritis. 
     Example 8: Plasminogen Promotes Regeneration of Knee Cartilage in Osteoarthritis Model Mice 
     Eighteen 11-15 weeks aged female db/db mice are weighed and randomly divided into two groups according to body weights, 3 mice in the sham operation group and 15 mice in the model group. The mice in the model group are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight the hair on both sides of the back is removed, disinfecting with 70% alcohol and iodine tincture: the skin, back muscles and peritoneum are cut open, and the white shiny fat tissue is gently pulled out through the incision by using small forceps so as to separate the fat tissue, and the ovaries can be seen. The fallopian tube at the lower end of ovary is ligated with silk thread, and then the ovary is removed. After anesthesia, for the mice in the sham operation group, only the skin, back muscles and peritoneum are cut open, and the ovaries are not removed. After suture and disinfection, all surgical mice are intramuscularly injected with antibiotics (5000U/mouse), and subcutaneously injected with analgesic (2 mg/kg). The injection is taken for 3 consecutive days. 65 days after the ovariectomy, all mice are intraperitoneally injected with pentobarbital sodium for anesthesia, removing the hair on the right knee, disinfecting with 70% alcohol and iodine tincture; the right knee is bent 90 degrees to find the precise injection site, moving the needle of the syringe along the knee horizontally (so as not to pierce the skin) until a gap under the patella is found; marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, though the patellar tendon perpendicular to the tibia and no resistance should be felt. As for the model group mice, 5 μg/6 μl Type II collagenase physiological saline solution is injected into the right articular cavity of the mice; as for the sham operation group mice, 6 μl of physiological saline is injected into the right articular cavity of the mice  [36,37] . After the injection, the knee is massaged to ensure even distribution. The left knee joint is not treated with injection. 7 days after the collagenase injection, all mice are weighed. The mice in the model group are randomly divided into two groups according to their body weights, 7 mice in the vehicle control group and 8 mice in the plasminogen group: then the administration starts, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The mice are sacrificed on day 29, and the left knee joints are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin. The 5 μm sections are stained with safranin O. The sections are observed and photographed under a 100× optical microscope, processing with Image-Pro software to collect data. 
     The results show that there is a small amount of cartilage (marked by arrows) on the femoral surface of the knee joints in the sham operation group mice ( FIG.  8 A ); there is no significant difference between the amount of cartilage on the femoral surface in the vehicle control group ( FIG.  8 B ) and that in the sham operation group, while the amount of cartilage on the femoral surface in the plasminogen group ( FIG.  8 C ) is significantly higher than that in the vehicle control group and the sham operation group, and the statistical difference of quantitative analysis of the average optical density is significant (* indicates P&lt;0.05) ( FIG.  8 D ). The results show that plasminogen can promote the regeneration of cartilage on the femoral surface of osteoarthritis model mice. 
     Example 9: Plasminogen Reduces Arthritis Pain in MIA Osteoarthritis Model Rats 
     Twenty-one SD rats are weighed (about 200-250 g of body weights), and randomly divided into two groups according to body weights, 5 rats in the sham operation group and 16 rats in the model group. All rats are anesthetized by intraperitoneal injection of 3% pentobarbital sodium (50 mg/kg); for the rats in the model group, the hair of the left and right knee joints is removed, disinfecting with 70% alcohol and iodine tincture and the left knee joint is bent 90 degrees to find the precise injection site, moving the needle of the syringe horizontally along the knee (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia: and no resistance should be felt. Then MIA physiological saline solution (2 mg/50 μl) is injected into each articular cavity at both sides of the knee joints; and 50 μl of saline is injected into each articular cavity at the left and right sides of the knee joints in the sham operation group. After the injection, the knee is massaged to ensure an even distribution  [38] . The preparation of MIA solution: MIA powder (Sigma, 57858-5G) is dissolved in physiological saline at a concentration of 40 mg/ml, and then filtering with a 0.22 μm filter membrane, and using right after it is ready. Three days after the MIA injection, the rats in the model group are subjected to a pain test. According to the test results, the rats are randomly divided into two groups: 8 rats in each group for the vehicle control group and the plasminogen group; then the administration starts, and the day of first administration is set as day 1. Each rat in the vehicle control group is injected with 0.7 ml of vehicle (10 mM sodium citrate buffer, 2% arginine hydrochloride, 3% mannitol, pH 7.4) in the tail vein every day, and the rats in the plasminogen group are administered with human plasminogen by tail vein injection at 7 mg/0.7 ml/rate/day. The administration is taken 7 consecutive days. Animal status is observed during the administration. On day 8, the pain tests are performed for the left and right legs 3. 
     The results show that the rats in the sham operation group have relatively higher pain thresholds: the pain thresholds of the left and right legs in the vehicle control group are significantly lower, and are significantly lower than those in the sham operation group the pain thresholds of the left and right legs in the plasminogen group are significantly increased, compared with the vehicle control group, the statistical difference between the left legs is close to significance (P=0.08), and the statistical difference between the right legs is significant (* indicates P&lt;0.05) ( FIG.  9   ). The results show that plasminogen can significantly reduce the pain of osteoarthritis. 
     Example 10: Plasminogen Reduces Arthritis Pain in Osteoarthritis Model Mice 
     Nineteen 7-week-old C57 female mice are weighed and randomly divided into two groups according to body weights, 3 mice in the sham operation group and 16 mice in the model group. The mice in the model group are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight the hair on both sides of the back is removed, disinfecting with 70% alcohol and iodine tincture the skin, back muscles and peritoneum are cut open, and the white shiny fat tissue is gently pulled out through the incision by using small forceps so as to separate the fat tissue, and the ovaries can be seen. The fallopian tube at the lower end of ovary is ligated with silk thread, and then the ovary is removed. After anesthesia, for the mice in the sham operation group, only the skin, back muscles and peritoneum are cut open, and the ovaries are not removed. After suture and disinfection, all surgical mice are intramuscularly injected with antibiotics (5000U/mouse), and subcutaneously injected with analgesic (2 mg/kg). The injection is taken for 3 consecutive days. 65 days after the ovariectomy, all mice are intraperitoneally injected with pentobarbital sodium for anesthesia, removing the hair on the right knee, disinfecting with 70% alcohol and iodine tincture the right knee is bent 90 degrees to find the precise injection site, moving the needle of the syringe along the knee horizontally (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia and no resistance should be felt. As for the model group mice, 5 μg/6 μl Type II collagenase physiological saline solution is injected into the right articular cavity of the mice: as for the sham operation group mice, 6 μl of physiological saline is injected into the right articular cavity of the mice [3].After the injection, the knee is massaged to ensure even distribution. The left knee joint is not treated with injection. 7 days after the collagenase injection, all mice are weighed. The mice in the model group are randomly divided into two groups according to their body weights, 8 mice in each of the vehicle control group and the plasminogen group; then the drugs are administered to the mice, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle control group mice for 28 consecutive days. The mice in the sham operation group are not t administered. The pain tests are performed for the right legs on day 29  [34] . 
     The results show that the pain thresholds of the mice in the sham operation group are relatively higher: the pain thresholds of the mice in the vehicle control group are significantly reduced, and are significantly lower than those in the sham operation group mice: while the pain thresholds of the mice in the plasminogen group are significantly increased, and are significantly higher than those in the vehicle control group mice, and the statistical difference is close to significance (P=0.09) ( FIG.  10   ). This result indicates that plasminogen can reduce osteoarthritis pain. 
     Example 11: Plasminogen Promotes Cartilage Regeneration in Osteoarthritis Model Mice 
     Nineteen 7-week-old C57 female mice are weighed and randomly divided into two groups according to body weights, 3 mice in the sham operation group and 16 mice in the model group. The mice in the model group are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight the hair on both sides of the back is removed, disinfecting with 70% alcohol and iodine tincture the skin, back muscles and peritoneum are cut open, and the white shiny fat tissue is gently pulled out from the incision by using small forceps so as to separate the fat tissue, and the ovaries can be seen. The fallopian tube at the lower end of ovary is ligated with silk thread, and then the ovary is removed. After anesthesia, for the mice in the sham operation group, only the skin, back muscles and peritoneum are cut open, and the ovaries are not removed. After suture and disinfection, all surgical mice are intramuscularly injected with antibiotics (5000U/mouse), and subcutaneously injected with analgesic (2 mg/kg). The injection is taken for 3 consecutive days. 65 days after the ovariectomy, all mice are intraperitoneally injected with pentobarbital sodium for anesthesia, removing the hair on the right knee, disinfecting with 70% alcohol and iodine tincture the right knee is bent 90 degrees to find the precise injection site, moving the needle of the syringe along the knee horizontally (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia and no resistance should be felt. As for the model group mice, 5 μg/6 μl Type II collagenase physiological saline solution is injected into the right articular cavity of the mice; as for the sham operation group mice, 6 μl of physiological saline is injected into the right articular cavity of the mice [3].After the injection, the knee is massaged to ensure even distribution. The left knee joint is not treated with injection. 7 days after the collagenase injection, all mice are weighed. The mice in the model group are randomly divided into two groups according to their body weights, 8 mice in each of the vehicle control group and the plasminogen group then the drugs are administered to the mice, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The mice are sacrificed on day 29, and the knee joints of both sides are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin, then slicing into 5 μm sections and staining with safranin O. The sections are observed and photographed under a 100× optical microscope, processing with Image-Pro software to collect data. 
     The results show that there is a certain amount of articular cartilage (arrow marked) on the femur and tibia surfaces of the left knee joints in the sham operation group ( FIGS.  11 A , D), there is no significant difference between the amount of cartilage on the tibia and femur surfaces in the vehicle control group and that in the sham operation group, while the amount of cartilage in the plasminogen group ( FIGS.  11 C , F) is significantly higher than that in the vehicle control group and the sham operation group. It indicates that plasminogen can promote the regeneration of articular cartilage in osteoarthritis model mice. 
     Example 12: Plasminogen Inhibits Bone Resorption in Osteoarthritis Model Mice 
     Nineteen 7-week-old C57 female mice are weighed and randomly divided into two groups according to body weights, 3 mice in the sham operation group and 16 mice in the model group. The mice in the model group are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight the hair on both sides of the back is removed, disinfecting with 70% alcohol and iodine tincture the skin, back muscles and peritoneum are cut open, and the white shiny fat tissue is gently pulled out from the incision by using small forceps so as to separate the fat tissue, and the ovaries can be seen. The fallopian tube at the lower end of ovary is ligated with silk thread, and then the ovary is removed. After anesthesia, for the mice in the sham operation group, only the skin, back muscles and peritoneum are cut open, and the ovaries are not removed. After suture and disinfection, all surgical mice are intramuscularly injected with antibiotics (5000U/mouse), and subcutaneously injected with analgesic (2 mg/kg). The injection is taken for 3 consecutive days. 65 days after the ovariectomy, all mice are intraperitoneally injected with pentobarbital sodium for anesthesia, removing the hair on the right knee, disinfecting with 70% alcohol and iodine tincture the right knee is bent 90 degrees to find the precise injection site, moving the needle of the syringe along the knee horizontally (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia and no resistance should be felt. As for the model group mice, 5 μg/6 μl Type II collagenase physiological saline solution is injected into the right articular cavity of the mice as for the sham operation group mice, 6 μl of physiological saline is injected into the right articular cavity of the mice  [36,37] . After the injection, the knee is massaged to ensure even distribution. The left knee joint is not treated with injection. 7 days after the collagenase injection, all mice are weighed. The mice in the model group are randomly divided into two groups according to their body weights, 8 mice in each of the vehicle control group and the plasminogen group: then the administration starts, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The mice are sacrificed on day 29, and the knee joints of both sides are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, sectioning into 5 μm, dewaxing and rehydrating, then staining with acid phosphatase (TRAP). 
     Acid phosphatase (TRAP) is a specific marker enzyme for osteoclasts, and osteoclasts are the main functional cells for bone resorption. The results show that there is a certain amount of acid phosphatase (arrow marked) in the knee joints of the sham operation group ( FIG.  12 A ); the acid phosphatase of the knee joints in the vehicle control group is increased ( FIG.  12 B ), and is significantly more than that of the sham operation group; while the acid phosphatase of the knee joints in the plasminogen group ( FIG.  12 C ) is significantly less than that in the vehicle control group, and the statistical difference is significant (* indicates P&lt;0.05) ( FIG.  12 D ). This result indicates that plasminogen can reduce acid phosphatase of osteoarthritis knee joint, reduce osteoclast activity, and inhibit bone resorption. 
     Example 13: Plasminogen Promotes Increase of the Number of Sox 9 Positive Stem Cells in Tibial End of the Knee Joint in MIA Osteoarthritis 
     Twenty five 8-10 weeks aged C57 male mice are weighed and randomly divided into two groups according to body weights 5 mice in the sham operation group, and 20 mice in the model group. All mice are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight. After anesthesia, for the mice in the model group, the hair of the left knee is removed, disinfecting with 70% alcohol and iodine tincture: and the left knee joint is bent 90 degrees, moving the needle of the syringe horizontally along the knee (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia, and MIA physiological saline solution is injected into the articular cavity at 0.1 mg/10 μl; in the sham operation group, 10 μl saline is injected into the left articular cavity, after the injection, massaging the knee to ensure even distribution  [34] . The right knee joint is not treated. Three days after the MIA injection in the articular cavity, the mice in the model group are subjected to a pain test. According to the test results, the mice are randomly divided into two groups: 10 mice in each group for the vehicle control group and the plasminogen group then the drugs are administered to the mice, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle (PBS) control group mice for 28 consecutive days. The mice in the sham operation group are not treated with administration. The preparation of MIA solution: MIA powder (Sigma, 57858-5G) is dissolved in physiological saline at a concentration of 10 mg/ml, and then filtering with a 0.22 μm filter membrane, and using right after it is ready. The mice are sacrificed on day 29, and the left knee joints are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin. The thickness of the tissue section is 5 μm, and the sections are washed once after dewaxing and rehydrating. The tissues are circled with a PAP pen, then incubating with 3% hydrogen peroxide for 15 min, and washing twice with 0.01M PBS for 5 min each time. 5% normal sheep serum (Vector laboratories, Inc., USA) is used to block for 30 min after the time is expired, the sheep serum is discarded, then adding rabbit-derived anti-Sox 9 antibody (Abcam, ab185966) dropwise, incubating overnight at 4° C., and washing twice with 0.01M PBS for 5 min each time. Goat anti-rabbit IgG (HRP) antibody (Abcam) (secondary antibody) is incubated for 1 hour at room temperature, then washing twice with 0.01M PBS for 5 min each time. Color development is performed according to the DAB kit (Vector laboratories, Inc., USA), after washing three times with water, counterstaining with hematoxylin for 30 seconds, and rinsing under running water for 5 min. Dehydration is performed with gradient alcohol, then making transparent with xylene and sealing with neutral gum; and the sections are observed and photographed under 100× (A-C) and 400× (D-F) optical microscopes, processing with Image-Pro software to collect data. 
     Sox9 is a key transcription factor in the process of cartilage development and formation, and it determines the mesenchymal stem cells aggregation and differentiation into chondrocytes, playing an important role in regulating the process of cartilage development, maturation and repair  [39] . 
     The results show that there is a certain amount of Sox 9 positive stem cells (arrow marked) in the knee joint tibia in the sham operation group ( FIGS.  13 A , D); the number of Sox 9 positive stem cells in the knee joint tibia in the vehicle control group ( FIGS.  13 B , E) is significantly reduced, while in the plasminogen group ( FIGS.  13 C , F) the number of Sox 9 positive stem cells in the knee joint tibia is significantly higher than that in the vehicle control group. This result indicates that plasminogen can promote increase of the number of Sox-9 positive stem cells in the tibial end of osteoarthritis knee joint, and repair the knee joint injury caused by osteoarthritis. 
     Example 14: Plasminogen Improves Inflammation Condition of Knee Joint Synovium in MIA Osteoarthritis Model Mice 
     Twenty five 8-10 weeks aged C57 male mice are weighed and randomly divided into two groups according to body weights 5 mice in the sham operation group, and 20 mice in the model group. All mice are anesthetized by intraperitoneal injection of 3% pentobarbital sodium at 50 mg/kg body weight. After anesthesia, for the mice in the model group, the hair of the left knee is removed, disinfecting with 70% alcohol and iodine tincture: and the left knee joint is bent 90 degrees, moving the needle of the syringe horizontally along the knee (so as not to pierce the skin) until a gap under the patella is found marking the area with slight pressure, then lifting the needle and syringe vertically, inserting the needle into the marked area, through the patellar tendon perpendicular to the tibia, and MIA physiological saline solution is injected into the articular cavity at 0.1 mg/10 μl; in the sham operation group, 10 μl saline is injected into the left articular cavity, after the injection, massaging the knee to ensure even distribution  [34] . The right knee joint is not treated. Three days after the MIA injection in the articular cavity, the mice in the model group are subjected to a pain test. According to the test results, the mice are randomly divided into two groups: 10 mice in each group for the vehicle control group and the plasminogen group then the drugs are administered to the mice, and the day of first administration is set as day 1. The human plasminogen is administered to the plasminogen group mice by tail vein injection at 1 mg/0.1 ml/mouse/day, and the same volume of PBS buffer is injected into the tail vein of the vehicle (PBS) control group mice for 28 consecutive days. The mice in the sham operation group are not administered. The preparation of MIA solution: MIA powder (Sigma, 57858-5G) is dissolved in physiological saline at a concentration of 10 mg/ml, and then filtering with a 0.22 μm filter membrane, and using right after it is ready. The mice are sacrificed on day 29, and the left knee joints are taken and fixed in PLP fixative solution, then decalcifying in 10% EDTA for three weeks, washing with gradient sucrose solution, and embedding in paraffin (preserving muscles around the knee joint). The thickness of the tissue section is 5 μm, and the sections are dewaxed and rehydrated, then staining with hematoxylin and eosin (H &amp; E staining), differentiating with 1% hydrochloric acid-alcohol solution, blueing with aqueous ammonia, and then dehydrating with alcohol gradient, making transparent with xylene, sealing with neutral gum; and the sections are observed under 400× optical microscope. 
     The results show that there is no obvious inflammatory cell infiltration in the knee joint synovium in the sham operation group ( FIG.  14 A ); while in the vehicle control group ( FIG.  14 B ), there is obvious inflammation cell infiltration (arrow marked) in the knee joint synovium, and in the plasminogen group ( FIG.  14 C ) the infiltration of inflammatory cells in the synovium of the knee joints is significantly less than that in the vehicle control group. This result indicates that plasminogen can improve inflammation condition of the knee joint synovium in osteoarthritis. 
     The (human) plasminogen used in all of the above examples is derived from human donor plasma, and it is purified from human plasma based on the method described in the document  [40-42]  with process optimization. The purity of plasminogen monomer is higher than 95%. 
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