Abstract:
The purpose of the present invention is to establish a novel therapy method for hyperbilirubinemia and therefore, to provide a bilirubin excretion enhancer. The present invention provides a bilirubin excretion enhancer comprising, as an active ingredient, a serum albumin domain II-like protein comprising a serum albumin subdomain IIA. In one embodiment, the serum albumin subdomain IIA has an amino acid sequence of SEQ ID NO: 1. in one embodiment, the serum albumin domain II-like protein is a serum albumin domain II. In one embodiment, the serum albumin domain II comprises the amino acid sequence of SEQ ID NO: 4.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/237,694, filed Aug. 9, 2012, which is the United States national phase of International Application No. PCT/JP2012/070310 filed Aug. 9, 2012, and claims priority to Japanese Patent Application No. 2011-175403 filed Aug. 10, 2011, the disclosures of which are hereby incorporated in their entirety by reference. 
    
    
     The Sequence Listing associated with this application is filed in electronic format via EFS-Web and is hereby incorporated by reference into the specification in its entirety. The name of the text file containing the Sequence Listing is SequenceListing.txt. The size of the text file is 17,419 bytes and the text file was created on Jan. 28, 2014. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a bilirubin excretion enhancer. More specifically, the present invention relates to a bilirubin excretion enhancer with a serum albumin domain II-like protein, containing the subdomain IIA of serum albumin, as an active ingredient. 
     Description of Related Art 
     Bilirubin is a final product of the degradation of a heme which is a component of a red blood cell. Within various isomers thereof, the isomer that exists most abundantly in the body is 4Z, 15Z-bilirubin-IXα (hereinafter, referred to as 4Z, 15Z-BR). A newborn is susceptible to hyperbilirubinemia and jaundice because of the immaturity of liver, which is a 4Z, 15Z-BR metabolizing tissue. If the level of bilirubin becomes high, bilirubin may deposit on cranial nerves, thereby causing encephalopathy. Nowadays, the first-line therapy for jaundice of the newborn is phototherapy. Phototherapy is a therapy in which the skin of a newborn is irradiated with light to convert 4Z, 15Z-BR having a low water solubility to an isomer having a high water solubility such as 4Z, 15E-bilirubin-IXα (4Z, 15E-BR) or Z-lumirubin, and promote the excretion of bilirubin into urine and bile. The mechanism for bilirubin phototherapy is shown in  FIG. 1 . However, although phototherapy is effective for bilirubin deposited on the skin, it is not effective for bilirubin in blood because light does not reach bilirubin in blood. Moreover, since the skin of an adult hardly transmits light, phototherapy is performed only on a newborn. 
     Therefore, at this time, plasma exchange in which plasma in blood is exchanged to lower the bilirubin concentration or adsorption removal of bilirubin using a column for bilirubin adsorption is performed. However, the adsorption removal method involves an increased risk of infectious diseases, and removes proteins and vitamins useful for a living body. 
     Human serum albumin (hereinafter, referred to as HSA) is the main protein present in adult serum, is produced in the liver, and functions as a carrier transporting various serum molecules. Moreover, bilirubin binds to HSA and is carried to the liver, and then binds to glucuronic acid in the liver to become a conjugated bilirubin that dissolves in water more easily. This conjugated bilirubin is secreted from the liver as bile. 
     HSA is a single-stranded protein (SEQ ID NO: 10) of 585 amino acids, and the basic structure is composed of three domains (domain I, II and III) having a high homology, each of which is segmented into subdomains (A and B). The domain I ranges amino acid positions 1 to 197, the domain II ranges amino acid positions 187 to 385, and the domain III ranges amino acid positions 381 to 585. 
     It is reported that the site I (domain II) is a high affinity binding site for bilirubin. The inventors have obtained an albumin variant having a high binding activity with respect to bilirubin, and found that the amino acids at positions 195 and 199 contribute to bilirubin binding (Patent Document 1). Moreover, the inventors have produced a protein including the domain I of HSA by genetic recombination (Patent Document 2). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-172277 
     Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-245268 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     It is an object of the present invention to provide a bilirubin excretion enhancer in order to establish a novel therapeutic method for hyperbilirubinemia. 
     Means for Solving the Problems 
     The inventors have intensively studied a method for direct excretion of bilirubin, particularly 4Z,15Z-BR in order to solve the above problems, and found that a serum albumin domain II-like protein including the subdomain IIA of serum albumin binds to bilirubin and the bound bilirubin is excreted to urine. Thus the present invention was accomplished. 
     The present invention provides a bilirubin excretion enhancer comprising, as an active ingredient, a serum albumin domain II-like protein comprising a serum albumin subdomain IIA. 
     In one embodiment, the serum albumin subdomain IIA has an amino acid sequence of SEQ ID NO: 1. 
     In one embodiment, the serum albumin domain II-like protein is a serum albumin domain II. 
     In one embodiment, the serum albumin domain II has an amino acid sequence of SEQ ID NO: 4. 
     In one embodiment, the serum albumin domain II-like protein comprises a serum albumin subdomain IB. 
     In one embodiment, the bilirubin excretion enhancer is a urinary excretion enhancer. 
     In one embodiment, the bilirubin excretion enhancer is a 4Z, 15Z-bilirubin-IXα excretion enhancer. 
     Effects of Invention 
     A serum albumin domain II-like protein as the active ingredient of the bilirubin excretion enhancer of the present invention can bind to bilirubin to allow for rapidly excreting bilirubin into urine. Particularly, it can bind to 4Z, 15Z-BR that has poor water solubility and is not normally excreted into urine, thereby enhancing the renal excretion. Accordingly, it is effective as a bilirubin excretion enhancer and a therapeutic agent of hyperbilirubinemia. Moreover, it can be safely administered to a newborn as well as to an adult, since HSA is present in the body and has excellent safety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the mechanism for bilirubin phototherapy. 
         FIG. 2  is a graph showing the binding ability with respect to 4Z, 15Z-BR for serum albumin domain II-like proteins obtained in Example 1 and Example 2. 
         FIG. 3  is a graph showing the 4Z, 15Z-BR excretion enhancing effect of a human serum albumin domain II-like protein obtained in Example 1. 
         FIG. 4  is a graph showing the 4Z, 15Z-BR excretion enhancing effect of a human serum albumin domain II-like protein obtained in Example 1. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     A serum albumin subdomain IIA in the present invention refers to a region constituting the subdomain A of the domain II of serum albumin, and a serum albumin fragment of that region. 
     In the present invention, serum albumin is albumin contained in serum, and may be derived from, for example, humans or other warm-blooded animals (e.g., cattle, monkeys, pigs, horses, sheep, goats, dogs, cats, rabbits, mice, rats, hamsters, guinea pigs, chickens, and quails). In view of the application to pharmaceutical drugs, human serum albumin is preferable. 
     Wild type human serum albumin (hereinafter, referred to as HSA) has a molecular weight of 66.5 kDa, and the amino acid sequence from positions 1 to 585t of SEQ ID NO: 10 in Sequence Listing. Serum albumin of the present invention includes genetic polymorphisms of HSA and mutants thereof. Up to now, 60 or more types of genetic polymorphisms of HSA are reported. The variant here refers to HSA whose one or more amino acids are deleted, substituted or added. 
     The serum albumin subdomain IIA of the present invention includes the subdomain IIA of serum albumin, genetic polymorphisms thereof, and mutants thereof. Preferably, it is the subdomain IIA of HSA (hereinafter, referred to as HSA subdomain IIA). The serum albumin subdomain IIA contains a bilirubin binding site. 
     The HSA subdomain IIA has at least the amino acid sequence of SEQ ID NO: 1 (positions 187 to 248 of SEQ ID NO: 10). More preferably, it has the amino acid sequence of SEQ ID NO: 2 (positions 187 to 295 of SEQ ID NO: 10). Even more preferably, it has the amino acid sequence of SEQ ID NO: 3 (positions 187 to 298 of SEQ ID NO: 10). 
     The HSA subdomain IIA includes genetic polymorphisms of the HSA subdomain IIA and mutants thereof. The mutant here refers to an HSA subdomain IIA whose one or more amino acids are deleted, substituted or added, and is not limited as long as it has an affinity to bilirubin. Preferably 1 to 20 amino acids, more preferably 1 to 10 amino acids, and even more preferably 1 to 5 amino acids are deleted, substituted or added. Preferable examples of an HSA subdomain IIA mutant include F211R/R218L and F211/R218S/R222W. F211R/R218L is an HSA subdomain IIA mutant in which phenylalanine at the position 211 is substituted with arginine and arginine at the position 218 is substituted with leucine, and F211/R218S/R222W is an HSA subdomain IIA mutant in which phenylalanine at the position 211 is substituted with leucine, arginine at the position 218 is substituted with serine and arginine at the position 222 is substituted with tryptophan. 
     The HSA subdomain IIA includes proteins having an amino acid sequence different from but substantially identical to that of the subdomain IIA of HSA having the amino acid sequence of Sequence ID No: 1, 2 or 3, and having an affinity to bilirubin equivalent to or more than that of the subdomain IIA of HSA having the amino acid sequence of SEQ ID NO: 1, 2 or 3 so that it can bind to bilirubin to allow for facilitating renal excretion. 
     In the present invention, the amino acid sequence that is substantially identical to that of the subdomain IIA of HSA having the amino acid sequence of SEQ ID NO: 1, 2 or 3 refers to an amino acid sequence that has preferably approximately 80% or more, more preferably approximately 90% or more, and even more preferably approximately 95% or more homology to the subdomain IIA of HSA having the amino acid sequence of SEQ ID NO: 1, 2 or 3. 
     Here, “homology” means a ratio (%) of the same amino acid residues and similar amino acid residues to all the overlapping amino acid residues in an optimal alignment of two amino acid sequences determined by using a known mathematical algorithm in the art (preferably, the algorithm may be taken account of the introduction of gaps into one or both of the two sequences for the optimal alignment). “Similar amino acids” refers to amino acids that are similar in physicochemical properties, and examples thereof include amino acids classified into the same group such as aromatic amino acids (Phe, Trp, and Tyr), aliphatic amino acids (Ala, Leu, Ile, and Val), polar amino acids (Gln and Asn), basic amino acid (Lys, Arg, and His), acidic amino acids (Glu and Asp), amino acids having a hydroxyl group (Ser and Thr), or amino acids having a small side chain (Gly, Ala, Ser, Thr, and Met). It is predicted that the substitution with such a similar amino acid does not lead to any change in protein phenotype (i.e., conservative amino acid substitution). Specific examples of conservative amino acid substitution are well known in the art and described in various documents (see, for example, Bowie et al., Science, 247: 1306-1310 (1990)). 
     A serum albumin domain II-like protein of the present invention is a fragment of serum albumin that contains the serum albumin subdomain IIA, and has a half or less molecular weight of that of serum albumin. Preferably, the molecular weight is one-third or less. A human serum albumin domain II-like protein (hereinafter, referred to as HSA domain II-like protein) is an HSA fragment containing the HSA subdomain IIA, and has a half (33 kDa) or less molecular weight of that of HSA, preferably the molecular weight is one-third (22 kDa) or less. 
     A serum albumin domain II-like protein of the present invention is a fragment of serum albumin that contains the serum albumin subdomain IIA of the present invention. Preferable serum albumin domain II-like protein is HSA domain II-like protein. HSA domain II-like protein is an HSA fragment containing the HSA subdomain IIA of the present invention. Examples thereof include an HSA fragment composed of the subdomain IIA, an HSA fragment composed of the domain II, an HSA fragment composed of the subdomain IB and the subdomain IIA, an HSA fragment composed of the domain II and the subdomain IB, and an HSA fragment composed of the domain I and the subdomain IIA. Preferably, the serum albumin domain II-like protein of the present invention does not contain the domain III. 
     The subdomain IIA in serum albumin domain II-like protein may not have the same conformation as that of the subdomain IIA in serum albumin, and may contain any structure in which the subdomain IIA hardly retains the conformation. Also, a region other than the subdomain IIA region of serum albumin domain II-like protein may or may not constitute a domain, and there is no limitation on the positions of the N-terminus and the C-terminus as long as the subdomain IIA region is contained therein. 
     In one embodiment of a serum albumin domain II-like protein of the present invention, the serum albumin domain IIA is a protein composed of the foregoing serum albumin domain IIA region. 
     In one embodiment of a serum albumin domain II-like protein of the present invention, the serum albumin domain II includes the domain II of serum albumin, genetic polymorphisms thereof and mutants thereof. Preferably, it is the domain II of HSA (hereinafter, referred to as HSA domain II). 
     Preferably, the HSA domain II has the amino acid sequence of SEQ ID NO: 4 (positions 187 to 341 of SEQ ID NO: 10). More preferably, it has the amino acid sequence of SEQ ID NO: 5 (positions 187 to 361 of SEQ ID NO: 10). Even more preferably, it has the amino acid sequence of SEQ ID NO: 6 (positions 187 to 385 of SEQ ID NO: 10). 
     The HSA domain II includes genetic polymorphisms of the HSA domain II and their mutants. The mutant here refers to a HSA domain II whose one or more amino acids are deleted, substituted or added, and is not limited as long as it has the affinity to bilirubin. Preferably 1 to 20 amino acids, more preferably 1 to 10 amino acids, and even more preferably 1 to 5 amino acids are deleted, substituted or added. 
     The HSA domain II includes a protein that has an amino acid sequence different from but substantially identical to that of the domain II of HSA having the amino acid sequence of SEQ ID NO: 4, 5 or 6, and that has an affinity to bilirubin equivalent to or more than that of the HSA domain II having the amino acid sequence of SEQ ID NO: 4, 5 or 6 so that it can bind to bilirubin to allow for renal excretion. 
     In the present invention, the amino acid sequence that is substantially identical to that of the domain II of HSA having the amino acid sequence of SEQ ID NO: 4, 5 or 6 refers to an amino acid sequence that has preferably approximately 80% or more, more preferably approximately 90% or more, and even more preferably approximately 95% or more homology to the domain II of HSA having the amino acid sequence of SEQ ID NO: 4, 5 or 6. Homology is as described above. 
     Serum albumin domain II-like protein of the present invention contains the subdomain IIA region, and may additionally contain the domain I, the subdomain IB or the subdomain IIB. These include genetic polymorphisms thereof and mutants thereof. 
     In one embodiment of a serum albumin domain II-like protein of the present invention, a protein containing the serum albumin subdomain IB contains the subdomain IB and the subdomain IIA. The protein includes genetic polymorphisms thereof and mutants thereof. Preferably, it is an HSA fragment composed of the HSA domain IB and the HSA subdomain IIA. 
     Preferably, the HSA fragment composed of the HSA domain IB and the HSA subdomain IIA has the amino acid sequence of SEQ ID NO: 7 (positions 187 to 298 of SEQ ID NO: 10). More preferably, it has the amino acid sequence of SEQ ID NO: 8 (positions 150 to 298 of SEQ ID NO: 10). Even more preferably, it has the amino acid sequence of SEQ ID NO: 9 (positions 124 to 298 of SEQ ID NO: 10). 
     The HSA fragment composed of the HSA domain IB and the HSA subdomain IIA includes genetic polymorphisms thereof and mutants thereof. The mutant here refers to an HSA fragment composed of the HSA domain IB and the HSA subdomain IIA, whose one or more amino acids are deleted, substituted or added, and is not limited as long as it has the affinity to bilirubin. Preferably 1 to 20 amino acids, more preferably 1 to 10 amino acids, and even more preferably 1 to 5 amino acids are deleted, substituted or added. 
     The HSA fragment composed of the HSA domain IB and the HSA subdomain IIA includes a protein that has an amino acid sequence different from but substantially identical to that of the HSA fragment having the amino acid sequence of SEQ ID NO: 7, 8 or 9, and that has an affinity to bilirubin equal to or more than that of the HSA fragment having the amino acid sequence of SEQ ID NO: 7, 8 or 9 so that it can bind to bilirubin to allow for renal excretion. 
     In the present invention, the amino acid sequence that is substantially identical to that of the HSA fragment having the amino acid sequence of SEQ ID NO: 7, 8 or 9 refers to an amino acid sequence that has preferably approximately 80% or more, more preferably approximately 90% or more, and even more preferably approximately 95% or more homology to the HSA fragment having the amino acid sequence of SEQ ID NO: 7, 8 or 9. Homology is as described above. 
     HSA domain II-like protein as an active ingredient of the bilirubin excretion enhancer of the present invention can be obtained by cleaving HSA obtained from plasma with a reagent such as CNBr and purifying a fragment containing the subdomain IIA. Also, HSA domain II-like protein can be obtained by genetic recombination, for example, by inserting a DNA encoding the protein of interest into an expression vector, is transforming a suitable host with the vector, and culturing the host. For example, HSA domain II-like protein can be produced and purified according to the procedures as described in Japanese Laid-Open Patent Publication Nos. 2010-172277 and 2005-245268. 
     Bilirubin, of which excretion is enhanced according to the present invention, includes stereoisomers such as 4Z, 15Z-BR and 4Z, 15E-BR, and structural isomers such as Z-lumirubin. 
     Bilirubin excretion enhancement according to the present invention refers to enhancement of the excretion of bilirubin in the body out of the body to reduce the amount of bilirubin in the body, particularly in blood. Preferably, the excretion of bilirubin into urine is enhanced. More specifically, the conjugate of bilirubin with the HSA domain II-like protein of the present invention is filtered and excreted by the kidney to promote the excretion of bilirubin out of the body. 
     As the formulation of the bilirubin excretion enhancer of the present invention, tablets, pills, powders, suspensions, capsules, suppositories, injections, ointments, and patches are exemplified. Preferably, it is liquid formulation obtained from purified HSA domain II-like protein or lyophilized formulation obtained by lyophilizing HSA domain II-like protein. A kit formulation may be prepared with lyophilized formulation in combination with dissolving liquid. 
     A stabilizer such as sugar, sugar alcohol and amino acid, a pH regulator, and a vehicle can be added to the formulation. Also, if necessary, viral inactivating treatment or sterilizing treatment can be performed before or after drug formulation. 
     There is no limitation on the administration mute of the bilirubin excretion enhancer of the present invention. Examples thereof include transvenous, transarterial, oral, transcutaneous, and transmucosal. The dose and frequency of administration are adjusted while observing the condition of a patient considering the patient&#39;s condition, age, sex, body weight, meal, and so on. For example, in the case of injections, a dose of 10-50 mg/bodyweight can be administered once to three times a day. Also, the administration can be once a few days, or only as needed. 
     Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the examples. 
     EXAMPLES 
     Example 1 
     HSA donated by The Chemo-Sero-Therapeutic Research Institute was used. Ten milliliters of the solution of CNBr in 70% formic acid solution was added to 30 mg of HSA so that the molar concentration ratio of CNBr to methionine residues in HSA is 200:1, and the mixture was incubated for 24 hours at room temperature in the dark. After that, 40 ml of ion exchanged water was added to the mixture to quench the reaction, and the obtained solution was subjected to centrifugal concentration with Speed vac (registered trademark) plus (Savant Inc.). After buffer was exchange, the sample was purified with HiTrap Blue HP using AKTA Prime plus (GE Healthcare). The column was equilibrated with 20 mM sodium phosphate (pH 7.0), and eluted with gradient of 2 M potassium thiocyanate+20 mM sodium phosphate (pH 7.0). Fractions in which 20 kDa protein was eluted were confirmed by SDS-PAGE, and subjected to the following experiment. 
     The obtained protein of 20 kDa was confirmed to be HSA domain II-like protein (SEQ ID NO: 9 (Cys124-Met298 of SEQ ID NO: 10)) composed of the domains IB and IIA by non-reducing SDS-PAGE. The resultant HSA domain II-like protein was lyophilized in the usual manner to obtain a lyophilized formulation. 
     Example 2 
     According to the procedures described in Japanese Laid-Open Patent Publication No. 2010-172277, HSA domain II gene (SEQ ID NO: 11) was obtained and integrated into the genome of  Pichia  yeast to produce cells expressing HSA domain II. After that, the yeast was cultured, and HSA domain II was expressed and purified. The purified HSA domain II was confirmed by SDS-PAGE. The resultant HSA domain II-like protein was a protein composed of the domain II, having the amino acid sequence of SEQ ID NO: 6 (positions 187 to 385 of SEQ ID NO: 10), and having a molecular weight of 22 kDa. The resultant HSA domain II-like protein was lyophilized in the usual manner to obtain a lyophilized formulation. 
     Experimental Example 1 
     The HSA domain II-like protein obtained in Example 1 (hereinafter, referred to as 20 kDa fragment) and HSA domain II-like protein obtained in Example 2 (hereinafter, also referred to as domain II) were examined for binding ability with respect to 4Z, 15Z-BR. 
     The concentration of free BR (4Z, 15Z-BR) was measured with improvement of the method of Brodersen (Brodersen et al. J Clin Invest 1974; 54: 1353-64). Two hundred microliters of a mixed solution of 60 μM BR and 30 μM protein was added to a 96 well immunoplate, and was allowed to stand for 20 minutes at 37° C. Ten microliters of 1.75 mM H 2 O 2  was added thereto, and the mixture was allowed to stand for 3 minutes, and 10 μL of 1 μg/mL peroxidase (derived from horseradish) (Sigma) solution was then added to start the reaction. For 10 minutes after the addition, absorbance at 450 nm of each well was measured with an immunoplate reader. A calibration curve was created by plotting the initial oxidation rate and BR concentration, and the concentration of free BR was calculated. The results are shown in  FIG. 2 . The binding ability of 20 kDa fragment with respect to 4Z, 15Z-BR was equivalent to that of the domain II. 
     Experimental Example 2 
     The 20 kDa fragment was examined on 4Z, 15Z-BR renal excretion enhancing effect. Rats were divided into three groups, each of which consisted of three rats. 4Z,15Z-BR (560 μg/bodyweight) was administered to the rats of the first group (BR group), 4Z,15Z-BR (560 μg/bodyweight) and HSA (62,800 μg/bodyweight) were administered to the rats of the second group (BR-HSA group), and 4Z,15Z-BR (560 μg/bodyweight) and the 20 kDa fragment (18,900 μg/bodyweight) were administered to the rats of the third group (BR-20 kDa group). After 2 hours, blood samples and urine samples were collected, and the concentration of 4Z, 15Z-BR in serum and the concentration of 4Z, 15Z-BR in 0.75-2.25 ml of urine were measured. The concentrations of BR in serum and in urine were measured using QuantiChrom™ Bilirubin Assay Kit (BioAssay Systems). The concentrations of total BR and indirect BR were measured according to the procedure of the kit. The results are shown in  FIG. 3 . The concentration of total 4Z, 15Z-BR in serum in the combined administration with the 20 kDa fragment was significantly lowered compared with the combined administration with HSA. Particularly, the concentration of protein bound type 4Z, 15Z-BR was remarkably lowered. The amount of total 4Z, 15Z-BR in urine in the combined administration with the 20 kDa fragment was significantly increased compared with the combined administration with HSA. Moreover, the amount of protein in urine was measured. The results are shown in  FIG. 4 . Protein in urine in the combined administration with the 20 kDa fragment was significantly increased compared with the combined administration with HSA. This shows that the 20 kDa fragment was bound to 4Z, 15Z-BR and excreted into urine. 
     INDUSTRIAL APPLICABILITY 
     Since the bilirubin excretion enhancer of the present invention binds to bilirubin in the body and is excreted out of the body, it is effective for the excretion and removal of bilirubin in the body, the treatment of hyperbilirubinemia, and so on.