Patent Publication Number: US-2022226283-A1

Title: Combination product containing limonoid compound and dpp-4 inhibitor

Description:
TECHNICAL FIELD 
     The present invention belongs to the technical field of medicine, and specifically relates to a combination product comprising a limonoid compound (and a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and a DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof). The present invention also relates to a use of the combination product in the treatment and/or prevention of a disease associated with diabetes and metabolic syndrome. 
     BACKGROUND ART 
     According to IDF statistics, there were about 425 million people with diabetes worldwide in 2017, i.e., 1 out of every 11 people has diabetes. The number of diabetic patients in China is about 110 million, ranking first in the world. It is predicted that by 2040, 642 million people worldwide will have diabetes, and the diabetic patients in China will reach 151 million. Diabetes requires life-long monitoring and treatment, and if not being well controlled, it will lead to secondary cardiovascular diseases, blindness, stroke, diabetic nephropathy, diabetic gangrene and other complications in patients, which will seriously endanger human health and life. 
     More than 90% of diabetes is type II diabetes, and oral hypoglycemic agents are the main treatment method. At present, the main oral hypoglycemic drugs include: sulfonylureas, biguanides, α-glucosidase inhibitors, thiazolidinediones, DPP-4 inhibitors, etc., but the oral hypoglycemic drugs are prone to severe side effects such as drug resistance, low blood glucose, and toxicity to liver and kidney. 
     DPP-4 inhibitor, i.e., dipeptidyl peptidase 4 inhibitor, is a class of drugs for the treatment of type II diabetes, and these drugs can inhibit the inactivation of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), thereby increasing the level of endogenous GLP-1 and GIP, promoting the release of insulin from islet β cells, inhibiting the secretion of glucagon from islet α-cells, increasing insulin levels and lowering blood glucose. Wherein, the features of GLP-1 include that: {circle around ( 1 )} it is generated after meal, and promotes the secretion of insulin by pancreatic β-cells in a glucose-dependent manner, thereby reducing blood glucose, and it is not easy to induce hypoglycemia; {circle around ( 2 )} it inhibits the secretion of glucagon from pancreatic α-cells; it delays gastric emptying to conducive to the control of postprandial blood glucose; {circle around ( 4 )} it reduces appetite and reduces food intake; {circle around ( 5 )} it inhibits intestinal secretion of lipoproteins and may reduce postprandial hyperlipidemia, which is a risk factor for cardiovascular disease, thereby having a cardioprotective effect; {circle around ( 6 )} it can regulate the regeneration, proliferation and survival of islet β cells in vitro. DPP-4 is a serine protease on the cell surface. DPP-4 is most highly expressed in intestine, and is also expressed in liver, pancreas, placenta and thymus. DPP-4 can inactivate a variety of biologically active peptides, including GLP-1 and GIP. DPP-4 inhibitor can inactivate DPP-4, so as not to decompose GLP-1, thereby increasing the level of GLP-1; thus, it can play a role in controlling blood glucose, and is currently one of the main directions for the treatment of diabetes. 
     The main side effects of DPP-4 inhibitors are: hypersensitivity reactions, including allergic reaction, angioedema, rash, urticaria, skin vasculitis, and exfoliative skin damage, elevated liver enzyme, upper respiratory tract infection, nasopharyngitis, pancreatitis, congestive heart failure, renal impairment, bullous pemphigoid, severe joint pain. 
     The limonoid compounds are mainly present in fruits of rutaceous plants, such as immature bitter orange, navel orange,  citrus reticulata , fragrant citrus, pomelo and the like. Their contents are higher in the cores (seeds), and lower in the peel (about 1/10,000 to 5/100,000). About 50 kinds of limonoid compounds have been isolated and identified from citrus plants. The limonoid compounds have various biological activities such as antitumor, insect antifeedant, antiviral, analgesic, anti-inflammatory and hypnotic, and can be used in functional food additives, anti-cancer foods, pesticides, feed additives, etc. 
     Considering the hypoglycemic effect and side effects of DPP-4 inhibitor, it is urgent to find a pharmaceutical composition product that is simple to take, good in effect, and low in side effects. 
     CONTENTS OF THE INVENTION 
     The present invention provides a combination product comprising a limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and a DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof), and a use of this composition for preventing or/and treating a disease associated with diabetes and metabolic syndrome. Compared with DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) or limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) as monotherapy at the same dose, the combination product containing a limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and a DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) as mentioned in the present invention can significantly enhance therapeutic effects such as hypoglycemic effect, and show synergistic effect. At the same time, the amount of DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) is reduced, thereby reducing its side effects. 
     In a first aspect of the present invention, there is provided a combination product comprising a limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof), and a DPP-4 inhibitor (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof), or a combination product comprising only a limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof), and a DPP-4 inhibitor as active ingredients. 
     The limonoid compound as mentioned in the present invention is a general term for a class of highly oxidized compounds with a 4,4,8-trimethyl-17-furanosteroid skeleton or derivatives thereof (or can be expressed as compounds consisting of variants of furanolactone polycyclic core structure, and having four fused 6-membered rings and one furan ring). Specifically, the examples of the limonoid compound include, but are not limited to: limonin, isolimonic acid, 7α-limonol, obacunone, ichangin, ichangensin, nomilin, deacetylnomilin, nomilin acid, deacetylnomilin acid, citrusin, isoobacunoic acid, etc., and any glycoside derivatives thereof. The structural formula of an exemplary limonoid compound, i.e., limonin, is shown below. 
     
       
         
         
             
             
         
       
     
     Further, the glucoside derivatives of the limonoid compound as mentioned in the present invention include, but are not limited to: limonin 17-β-glucopyranoiside, ichangin 17-β-D-glucopyranoiside, isolimonic acid 17-β-D-glucopyranoside, deactylnomilin 17-β-D-glucopyranoside, nomilin 17-β-D-glucopyranoside, obacunone 17-β-D-glucopynoside, nomilinic acid 17-β-D-glucopyranosid, deacetylnomilinic acid 17-β-D-glucopyranosid, etc. 
     In some embodiments, the limonoid compound as mentioned in the present invention is in the form of a monomer or an extract. The monomer is extracted or artificially synthesized, and its sources may be commercially available, or they can be easily prepared and obtained by the prior art in the art. 
     The DPP-4 inhibitor mentioned in the present invention includes but is not limited to sitagliptin, saxagliptin, vildagliptin, linagliptin, alogliptin, trelagliptin and omarigliptin. Further, DPP-4 inhibitor includes but is not limited to sitagliptin, saxagliptin, vildagliptin, linagliptin, and alogliptin. The DPP-4 inhibitor can exist in the form of original compound or in the form of pharmaceutically acceptable derivative thereof. 
     In some embodiments, the combination product is in the form of a pharmaceutical composition, and the pharmaceutical composition is in a unit dosage form. 
     In some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt, or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt, or prodrug thereof) are each in the form of a separate preparation. Further, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt, or prodrug thereof) are each in the form of a separate unit dose. Further, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) can be administered simultaneously or sequentially. 
     In some embodiments, the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) has an amount of 10 mg, 20 mg, 40 mg, 50 mg, 75 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 375 mg, 500 mg, 750 mg, 1500 mg, 1875 mg, or 2000 mg, and the ranges between these amounts, wherein the ranges include but are not limited to: 10 mg to 20 mg, 10 mg to 40 mg, 10 mg to 50 mg, 10 mg to 75 mg, 10 mg to 100 mg, 10 mg to 150 mg, 10 mg to 200 mg, 10 mg to 250 mg, 10 mg to 300 mg, 10 mg to 375 mg, 10 mg to 500 mg, 10 mg to 750 mg, 10 mg to 1500 mg, 10 mg to 1875 mg, 10 mg to 2000 mg, 20 mg to 40 mg, 20 mg to 50 mg, 20 mg to 75 mg, 20 mg to 100 mg, 20 mg to 150 mg, 20 mg to 200 mg, 20 mg to 250 mg, 20 mg to 300 mg, 20 mg to 375 mg, 20 mg to 500 mg, 20 mg to 750 mg, 20 mg to 1500 mg, 20 mg to 1875 mg, 20 mg to 2000 mg, 40 mg to 50 mg, 40 mg to 75 mg, 40 mg to 100 mg, 40 mg to 150 mg, 40 mg to 200 mg, 40 mg to 250 mg, 40 mg to 300 mg, 40 mg to 375 mg, 40 mg to 500 mg, 40 mg to 750 mg, 40 mg to 1500 mg, 40 mg to 1875 mg, 40 mg to 2000 mg, 50 mg to 75 mg, 50 mg to 100 mg, 50 mg to 150 mg, 50 mg to 200 mg, 50 mg to 250 mg, 50 mg to 300 mg, 50 mg to 375 mg, 50 mg to 500 mg, 50 mg to 750 mg, 50 mg to 1500 mg, 50 mg to 1875 mg, 50 mg to 2000 mg, 75 mg to 100 mg, 75 mg to 150 mg, 75 mg to 200 mg, 75 mg to 250 mg, 75 mg to 300 mg, 75 mg to 375 mg, 75 mg to 500 mg, 75 mg to 750 mg, 75 mg to 1500 mg, 75 mg to 1875 mg, 75 mg to 2000 mg, 100 mg to 150 mg, 100 mg to 200 mg, 100 mg to 250 mg, 100 mg to 300 mg, 100 mg to 375 mg, 100 mg to 500 mg, 100 mg to 750 mg, 100 mg to 1500 mg, 100 mg to 1875 mg, 100 mg to 2000 mg, 150 mg to 200 mg, 150 mg to 250 mg, 150 mg to 300 mg, 150 mg to 375 mg, 150 mg to 500 mg, 150 mg to 750 mg, 150 mg to 1500 mg, 150 mg to 1875 mg, 150 mg to 2000 mg, 200 mg to 250 mg, 200 mg to 300 mg, 200 mg to 375 mg, 200 mg to 500 mg, 200 mg to 750 mg, 200 mg to 1500 mg, 200 mg to 1875 mg, 200 mg to 2000 mg, 250 mg to 300 mg, 250 mg to 375 mg, 250 mg to 500 mg, 250 mg to 750 mg, 250 mg to 1500 mg, 250 mg to 1875 mg, 250 mg to 2000 mg, 300 mg to 375 mg, 300 mg to 500 mg, 300 mg to 750 mg, 300 mg to 1500 mg, 300 mg to 1875 mg, 300 mg to 2000 mg, 375 mg to 500 mg, 375 mg to 750 mg, 375 mg to 1500 mg, 375 mg to 1875 mg, 375 mg to 2000 mg, 500 mg to 750 mg, 500 mg to 1500 mg, 500 mg to 1875 mg, 500 mg to 2000 mg, 750 mg to 1500 mg, 750 mg to 1875 mg, 750 mg to 2000 mg, and 1875 mg to 2000 mg. 
     In some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) has an amount of 10 mg, 20 mg, 40 mg, 50 mg, 75 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 375 mg, 500 mg, 750 mg, 1500 mg, 1875 mg, or 2000 mg, and the ranges between these amounts, wherein the ranges include but are not limited to: 10 mg to 20 mg, 10 mg to 40 mg, 10 mg to 50 mg, 10 mg to 75 mg, 10 mg to 100 mg, 10 mg to 150 mg, 10 mg to 200 mg, 10 mg to 250 mg, 10 mg to 300 mg, 10 mg to 375 mg, 10 mg to 500 mg, 10 mg to 750 mg, 10 mg to 1500 mg, 10 mg to 1875 mg, 10 mg to 2000 mg, 20 mg to 40 mg, 20 mg to 50 mg, 20 mg to 75 mg, 20 mg to 100 mg, 20 mg to 150 mg, 20 mg to 200 mg, 20 mg to 250 mg, 20 mg to 300 mg, 20 mg to 375 mg, 20 mg to 500 mg, 20 mg to 750 mg, 20 mg to 1500 mg, 20 mg to 1875 mg, 20 mg to 2000 mg, 40 mg to 50 mg, 40 mg to 75 mg, 40 mg to 100 mg, 40 mg to 150 mg, 40 mg to 200 mg, 40 mg to 250 mg, 40 mg to 300 mg, 40 mg to 375 mg, 40 mg to 500 mg, 40 mg to 750 mg, 40 mg to 1500 mg, 40 mg to 1875 mg, 40 mg to 2000 mg, 50 mg to 75 mg, 50 mg to 100 mg, 50 mg to 150 mg, 50 mg to 200 mg, 50 mg to 250 mg, 50 mg to 300 mg, 50 mg to 375 mg, 50 mg to 500 mg, 50 mg to 750 mg, 50 mg to 1500 mg, 50 mg to 1875 mg, 50 mg to 2000 mg, 75 mg to 100 mg, 75 mg to 150 mg, 75 mg to 200 mg, 75 mg to 250 mg, 75 mg to 300 mg, 75 mg to 375 mg, 75 mg to 500 mg, 75 mg to 750 mg, 75 mg to 1500 mg, 75 mg to 1875 mg, 75 mg to 2000 mg, 100 mg to 150 mg, 100 mg to 200 mg, 100 mg to 250 mg, 100 mg to 300 mg, 100 mg to 375 mg, 100 mg to 500 mg, 100 mg to 750 mg, 100 mg to 1500 mg, 100 mg to 1875 mg, 100 mg to 2000 mg, 150 mg to 200 mg, 150 mg to 250 mg, 150 mg to 300 mg, 150 mg to 375 mg, 150 mg to 500 mg, 150 mg to 750 mg, 150 mg to 1500 mg, 150 mg to 1875 mg, 150 mg to 2000 mg, 200 mg to 250 mg, 200 mg to 300 mg, 200 mg to 375 mg, 200 mg to 500 mg, 200 mg to 750 mg, 200 mg to 1500 mg, 200 mg to 1875 mg, 200 mg to 2000 mg, 250 mg to 300 mg, 250 mg to 375 mg, 250 mg to 500 mg, 250 mg to 750 mg, 250 mg to 1500 mg, 250 mg to 1875 mg, 250 mg to 2000 mg, 300 mg to 375 mg, 300 mg to 500 mg, 300 mg to 750 mg, 300 mg to 1500 mg, 300 mg to 1875 mg, 300 mg to 2000 mg, 375 mg to 500 mg, 375 mg to 750 mg, 375 mg to 1500 mg, 375 mg to 1875 mg, 375 mg to 2000 mg, 500 mg to 750 mg, 500 mg to 1500 mg, 500 mg to 1875 mg, 500 mg to 2000 mg, 750 mg to 1500 mg, 750 mg to 1875 mg, 750 mg to 2000 mg, and 1875 mg to 2000 mg. 
     In some embodiments, the DPP-4 inhibitor is selected from sitagliptin, saxagliptin, vildagliptin, linagliptin, alogliptin, trelagliptin and omarigliptin, and the limonoid compound is one or more selected from: limonin, isolimonic acid, 7α-limonol, obacunone, ichangin, ichangensin, nomilin, deacetylnomilin, nomilin acid, deacetylnomilin acid, citrusin, isoobacunoic acid, etc., and any glycoside derivatives thereof. 
     In some embodiments, the combination product further comprises a pharmaceutically acceptable carrier, diluent, or excipient. 
     In some embodiments, the combination product is in the form of tablet, capsule, granule, syrup, powder, lozenge, sachet, cachet, elixir, suspension, emulsion, solution, syrup, aerosol, ointment, cream and injection. 
     In a second aspect of the present invention, there is provided a use of the combination product in manufacture of a medicament for the prevention and/or treatment of a disease associated with diabetes and metabolic syndrome. In some embodiments, the diabetes is type I diabetes. In some embodiments, the diabetes is type II diabetes. 
     In a third aspect of the present invention, there is provided a method of administering the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) in combination to prevent and/or treat a disease. In some embodiments, there is provided a method of administering the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) in combination to prevent and/or treat a disease associated with diabetes and metabolic syndrome. In some embodiments, there is provided a method of administering the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) in combination to lower a blood glucose. In some embodiments, there is provided a method of administering the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) in combination to improve an insulin sensitivity. In some embodiments, there is provided a method of administering the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) in combination to improve a leptin sensitivity. 
     In some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) can be mixed into a preparation and administered in the form of a pharmaceutical composition (preferably, a dosage unit form); in some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) are each in separate preparation form (preferably, each in separate dosage unit form) and separately administered; in some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) are administered simultaneously; in some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) are administered one after another; in some embodiments, the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) are administered one after another at a time interval of about 30 minutes, or about 1 hour, or about 2 hours, or about 4 hours, or about 8 hours, or about 12 hours. In some embodiments, as required, the combination product comprising the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) according to the present invention that is in the form of pharmaceutical composition (preferably, a dosage unit form) is administered for, including, but are not limited to: 1, 2, 3, 4, 5 or 6 times per day. In some embodiments, as required, the combination product comprising the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) according to the present invention that are each in separate preparation form (preferably, each in separate dosage unit form) is administered for, including, but are not limited to: 1, 2, 3, 4, 5 or 6 times per day. 
     In some embodiments, the limonin compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof), and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative) or the combination product comprising them can be administered by the following administration modes, for example, oral administration, injection administration (e.g., subcutaneous and parenteral administration) and topical administration. 
     In some embodiments, the limonin compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt, or prodrug thereof), and the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) have a daily dosage as follows: as calculated according to adult body weight of 60 kg, the daily dosage of the DPP-4 inhibitor (or a pharmaceutically acceptable derivative thereof) is 10 mg, 20 mg, 40 mg, 50 mg, 75 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 375 mg, 500 mg, 750 mg, 1500 mg, 1875 mg or 2000 mg, and the ranges between these dosages, wherein the ranges include but are not limited to: 10 mg to 20 mg, 10 mg to 40 mg, 10 mg to 50 mg, 10 mg to 75 mg, 10 mg to 100 mg, 10 mg to 150 mg, 10 mg to 200 mg, 10 mg to 250 mg, 10 mg to 300 mg, 10 mg to 375 mg, 10 mg to 500 mg, 10 mg to 750 mg, 10 mg to 1500 mg, 10 mg to 1875 mg, 10 mg to 2000 mg, 20 mg to 40 mg, 20 mg to 50 mg, 20 mg to 75 mg, 20 mg to 100 mg, 20 mg to 150 mg, 20 mg to 200 mg, 20 mg to 250 mg, 20 mg to 300 mg, 20 mg to 375 mg, 20 mg to 500 mg, 20 mg to 750 mg, 20 mg to 1500 mg, 20 mg to 1875 mg, 20 mg to 2000 mg, 40 mg to 50 mg, 40 mg to 75 mg, 40 mg to 100 mg, 40 mg to 150 mg, 40 mg to 200 mg, 40 mg to 250 mg, 40 mg to 300 mg, 40 mg to 375 mg, 40 mg to 500 mg, 40 mg to 750 mg, 40 mg to 1500 mg, 40 mg to 1875 mg, 40 mg to 2000 mg, 50 mg to 75 mg, 50 mg to 100 mg, 50 mg to 150 mg, 50 mg to 200 mg, 50 mg to 250 mg, 50 mg to 300 mg, 50 mg to 375 mg, 50 mg to 500 mg, 50 mg to 750 mg, 50 mg to 1500 mg, 50 mg to 1875 mg, 50 mg to 2000 mg, 75 mg to 100 mg, 75 mg to 150 mg, 75 mg to 200 mg, 75 mg to 250 mg, 75 mg to 300 mg, 75 mg to 375 mg, 75 mg to 500 mg, 75 mg to 750 mg, 75 mg to 1500 mg, 75 mg to 1875 mg, 75 mg to 2000 mg, 100 mg to 150 mg, 100 mg to 200 mg, 100 mg to 250 mg, 100 mg to 300 mg, 100 mg to 375 mg, 100 mg to 500 mg, 100 mg to 750 mg, 100 mg to 1500 mg, 100 mg to 1875 mg, 100 mg to 2000 mg, 150 mg to 200 mg, 150 mg to 250 mg, 150 mg to 300 mg, 150 mg to 375 mg, 150 mg to 500 mg, 150 mg to 750 mg, 150 mg to 1500 mg, 150 mg to 1875 mg, 150 mg to 2000 mg, 200 mg to 250 mg, 200 mg to 300 mg, 200 mg to 375 mg, 200 mg to 500 mg, 200 mg to 750 mg, 200 mg to 1500 mg, 200 mg to 1875 mg, 200 mg to 2000 mg, 250 mg to 300 mg, 250 mg to 375 mg, 250 mg to 500 mg, 250 mg to 750 mg, 250 mg to 1500 mg, 250 mg to 1875 mg, 250 mg to 2000 mg, 300 mg to 375 mg, 300 mg to 500 mg, 300 mg to 750 mg, 300 mg to 1500 mg, 300 mg to 1875 mg, 300 mg to 2000 mg, 375 mg to 500 mg, 375 mg to 750 mg, 375 mg to 1500 mg, 375 mg to 1875 mg, 375 mg to 2000 mg, 500 mg to 750 mg, 500 mg to 1500 mg, 500 mg to 1875 mg, 500 mg to 2000 mg, 750 mg to 1500 mg, 750 mg to 1875 mg, 750 mg to 2000 mg and 1875 mg to 2000 mg. As calculated according to adult body weight of 60 kg, the daily dosage of the limonoid compound (or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof) is 10 mg, 20 mg, 40 mg, 50 mg, 75 mg, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, 375 mg, 500 mg, 750 mg, 1500 mg, 1875 mg or 2000 mg, and the ranges of between these dosages, wherein the ranges includes but are not limited to: 10 mg to 20 mg, 10 mg to 40 mg, 10 mg to 50 mg, 10 mg to 75 mg, 10 mg to 100 mg, 10 mg to 150 mg, 10 mg to 200 mg, 10 mg to 250 mg, 10 mg to 300 mg, 10 mg to 375 mg, 10 mg to 500 mg, 10 mg to 750 mg, 10 mg to 1500 mg, 10 mg to 1875 mg, 10 mg to 2000 mg, 20 mg to 40 mg, 20 mg to 50 mg, 20 mg to 75 mg, 20 mg to 100 mg, 20 mg to 150 mg, 20 mg to 200 mg, 20 mg to 250 mg, 20 mg to 300 mg, 20 mg to 375 mg, 20 mg to 500 mg, 20 mg to 750 mg, 20 mg to 1500 mg, 20 mg to 1875 mg, 20 mg to 2000 mg, 40 mg to 50 mg, 40 mg to 75 mg, 40 mg to 100 mg, 40 mg to 150 mg, 40 mg to 200 mg, 40 mg to 250 mg, 40 mg to 300 mg, 40 mg to 375 mg, 40 mg to 500 mg, 40 mg to 750 mg, 40 mg to 1500 mg, 40 mg to 1875 mg, 40 mg to 2000 mg, 50 mg to 75 mg, 50 mg to 100 mg, 50 mg to 150 mg, 50 mg to 200 mg, 50 mg to 250 mg, 50 mg to 300 mg, 50 mg to 375 mg, 50 mg to 500 mg, 50 mg to 750 mg, 50 mg to 1500 mg, 50 mg to 1875 mg, 50 mg to 2000 mg, 75 mg to 100 mg, 75 mg to 150 mg, 75 mg to 200 mg, 75 mg to 250 mg, 75 mg to 300 mg, 75 mg to 375 mg, 75 mg to 500 mg, 75 mg to 750 mg, 75 mg to 1500 mg, 75 mg to 1875 mg, 75 mg to 2000 mg, 100 mg to 150 mg, 100 mg to 200 mg, 100 mg to 250 mg, 100 mg to 300 mg, 100 mg to 375 mg, 100 mg to 500 mg, 100 mg to 750 mg, 100 mg to 1500 mg, 100 mg to 1875 mg, 100 mg to 2000 mg, 150 mg to 200 mg, 150 mg to 250 mg, 150 mg to 300 mg, 150 mg to 375 mg, 150 mg to 500 mg, 150 mg to 750 mg, 150 mg to 1500 mg, 150 mg to 1875 mg, 150 mg to 2000 mg, 200 mg to 250 mg, 200 mg to 300 mg, 200 mg to 375 mg, 200 mg to 500 mg, 200 mg to 750 mg, 200 mg to 1500 mg, 200 mg to 1875 mg, 200 mg to 2000 mg, 250 mg to 300 mg, 250 mg to 375 mg, 250 mg to 500 mg, 250 mg to 750 mg, 250 mg to 1500 mg, 250 mg to 1875 mg, 250 mg to 2000 mg, 300 mg to 375 mg, 300 mg to 500 mg, 300 mg to 750 mg, 300 mg to 1500 mg, 300 mg to 1875 mg, 300 mg to 2000 mg, 375 mg to 500 mg, 375 mg to 750 mg, 375 mg to 1500 mg, 375 mg to 1875 mg, 375 mg to 2000 mg, 500 mg to 750 mg, 500 mg to 1500 mg, 500 mg to 1875 mg, 500 mg to 2000 mg, 750 mg to 1500 mg, 750 mg to 1875 mg, 750 mg to 2000 mg and 1875 mg to 2000 mg. 
     In a fourth aspect of the present invention, there is provided a method for preparing a combination product in the form of a pharmaceutical composition. In order to improve its operability as a drug or its absorbability when used in a living body, the limonoid compound or a pharmaceutically acceptable derivative, ester, stereoisomer, salt or prodrug thereof and the DPP-4 inhibitor or a pharmaceutically acceptable derivative thereof are preferably combined with a pharmaceutical adjuvant such as a pharmaceutically acceptable carrier, excipient, diluent, etc., so as to form a preparation, thereby obtaining the form. 
     In a fifth aspect of the invention, there is provided a kit, the kit comprising the combination product described herein. 
     The term “pharmaceutically acceptable salt” as used throughout this description refers to a salt of a free acid or a free base, that is typically prepared by reacting the free base with a suitable organic or inorganic acid or by reacting the acid with a suitable organic or inorganic base. The term can be used for any compound, including limonoid compounds (having the function of free acid or free base) and the like. Representative salts include: acetate, benzenesulfonate, benzoate, bicarbonate, bisulfate, hydrogen tartrate, borate, bromide, calcium edetate, camphorsulfonate, carbonate, chloride, clavulanate, citrate, dihydrochloride, edetate, ethanedisulfonate, estolate, esylate, fumarate, glucoheptonate, gluconate, glutamate, glycol lylarsanilate, hexylresorcinate, hydrabamine, hydrobromide, hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate, lactobionate, laurate, malate, maleate, mandelate, methanesulfonate, methobromate), methonitrate, methosulfate, monopotassium maleate, mucate, naphthalenesulfonate, nitrate, N-methylglucosamine salt, oxalate, pamoate, palmitate, pantothenate, phosphate/bisphosphate, polygalacturonate, potassium salt, salicylate, sodium salt, stearate, subacetate, succinate, tannate, tartrate, teoclate, p-toluenesulfonate, triethiodide, trimethylamine salt, and valerate. When an acidic substituent is present, for example, —COOH, an ammonium salt, morpholine salt, sodium salt, potassium salt, barium salt, calcium salt, and the like can be formed for use in a dosage form. When a basic group, for example an amino group or a basic heteroaryl group such as pyridyl, is present, an acidic salt such as a hydrochloride, hydrobromide, phosphate, sulfate, trifluoroacetate, trichloroacetate, acetate, oxalate, maleate, pyruvate, malonate, succinate, citrate, tartrate, fumarate, mandelate, benzoate, cinnamate, mesylate, ethanesulfonate, picrate, etc. 
     The source of the DPP-4 inhibitor referred to in the present invention may include but is not limited to: sitagliptin single tablets, saxagliptin single tablets, vildagliptin single tablets, linagliptin single tablets, alogliptin single tablets, trelagliptin single tablets, omarigliptin single tablets, sitagliptin/metformin tablets, saxagliptin/metformin tablets, vildagliptin/metformin tablets, linagliptin/metformin tablets, alogliptin/metformin tablets, trelagliptin/metformin tablets, omarigliptin/metformin tablets and so on. 
    
    
     SPECIFIC MODELS FOR CARRYING OUT THE INVENTION 
     The present invention is further described below through specific examples and comparative examples. However, it should be understood that these examples and comparative examples are only used for more detailed and specific explanation, and should not be understood as limiting the present invention in any form. 
     In the examples of the present invention, the following diabetic mouse models (the models were well known to those skilled in the art or were easily available according to conventional textbooks, technical manuals, and scientific literature in the art) were used to simulate the pathological conditions of different stages of diabetes in humans. The limonoid compound mentioned in the examples was present in the form of a monomer or an extract. The monomer was extracted or artificially synthesized, and its sources were commercially available, or it could be easily prepared and obtained by the prior art in the art. 
     EXAMPLE 1 
     Effects of Limonoid Compound, Sitagliptin or Combination Thereof on Blood Glucose in Mouse Pancreatic Islet β-Cell Injury Model 
     In this example, a mouse pancreatic islet β-cell injury model was established by modeling ICR mice with streptozotocin (STZ) (Li Nan et al., Protective effect of pine pollen on kidney damage in diabetic nephropathy mice, Science and Technology Review, 2014, 32 (4/5): 95-99), and used to complete the evaluation of hypoglycemic effect in animals (this model could simulate pancreatic islet β-cell damage state of type I and type II diabetics). The limonoid compound was selected from the group consisting of limonin, isolimonic acid, limonin glycoside, and isolimonic acid glycoside, and sitagliptin single administration group, limonin single administration group, isolimonic acid single administration group, limonin glycoside singe administration group, isolimonic acid glycoside singe administration group, and respective combination thereof with sitagliptin administration groups were set. 
     Conditions of experimental feeding: ICR mice (20±2 g), aged 6 weeks, purchased from Zhejiang Academy of Medical Sciences, and subjected to experimental feeding after 7 days of preliminary feeding. It should be noted that the conditions for raising the mice were as follows: the temperature was 23±1° C., the humidity was 55±10%, the lights were turned on between 7 am and 7 pm (the lights were turned off at other time), and the mice were allowed to freely take in water and feed. The experimental feed was mouse growth-stable feed (GB M2118), and the daily feeding and management of the animals were under the responsibility of the animal security department, which provided the animals with sufficient diet and fresh drinking water daily. 
     Experimental grouping: 15 male mice were randomly selected as the normal control group. After fasting for 12 hours, the remaining mice were intraperitoneally injected once with STZ at a dose of 150 mg/kg, and 72 hours later, the mice with blood glucose value of 15 to 25 mmol/L were undifferentiatedly grouped and used in the experiment, 15 animals in each group, and subjected to blood sampling and detection of indicators after two weeks of administration. 
     Gavage doses: the gavage dose was 0.02 g/kg per day for the limonin group, the gavage dose was 0.02 g/kg per day for the isolimonic acid group, the gavage dose was 0.02 g/kg per day for the limonin glycoside group, the gavage dose was 0.02 g/kg per day for the isolimonic acid glycoside group, the gavage dose of sitagliptin was 0.02 g/kg per day for the sitagliptin group, limonin at a dose of 0.01 g/kg and sitagliptin at a dose of 0.01 g/kg were simultaneously gavaged per day for the limonin/sitagliptin combination group, isolimonic acid at a dose of 0.01 g/kg and sitagliptin at a dose of 0.01 g/kg were simultaneously gavaged per day for the isolimonic acid/sitagliptin combination group, limonin glycoside at a dose of 0.01 g/kg and sitagliptin at a dose of 0.01 g/kg were simultaneously gavaged per day for the limonin glycoside/sitagliptin combination group, isolimonic acid glycoside at a dose of 0.01 g/kg and sitagliptin at a dose of 0.01 g/kg were simultaneously gavaged per day for the isolimonic acid glycoside/sitagliptin combination group, the gavage volume was 10 mL/kg, and the normal group and the model group were administrated with 10 mL/kg of distilled water. Two weeks later, the blood glucose values were measured by tail trimming method (Johnson&#39;s blood glucose meter) 1 h after the last administration, and the average of each group was obtained. SPSS 16.0 software was used for statistical analysis. The data were expressed as mean and standard deviation. The data before and after were analyzed by t-test, and P&lt;0.05 was considered statistically significant. The test results were shown in Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Blood glucose values of STZ mice after 
               
               
                 two weeks of daily intragastric gavage. 
               
            
           
           
               
               
               
            
               
                   
                 Formulation and dosage 
                 Blood glucose 
               
               
                 Group 
                 of administration 
                 value (mmol/L) 
               
               
                   
               
               
                 Normal control group 
                 None 
                 7.5 ± 0.6  
               
               
                 Model group 
                 None 
                 29.5 ± 4.6  
               
               
                 Sitagliptin group 
                 Sitagliptin 0.02 g/kg 
                 21.7 ± 4.9** 
               
               
                 Limonin group 
                 Limonin 0.02 g/kg 
                 19.5 ± 1.8** 
               
               
                 Isolimonic acid group 
                 Isolimonic acid 0.02 g/kg 
                 18.2 ± 3.1** 
               
               
                 Limonin glycoside 
                 Limonin glycoside 0.02 
                 18.9 ± 2.2** 
               
               
                 group 
                 g/kg 
               
               
                 Isolimonic acid 
                 Isolimonic acid glycoside 
                 17.9 ± 2.8** 
               
               
                 glycoside group 
                 0.02 g/kg 
               
               
                 Limonin combination 
                 Limonin 0.01 g/kg + 
                  8.0 ± 1.1** 
               
               
                 group 
                 Sitagliptin 0.01 g/kg 
               
               
                 Isolimonic acid 
                 Isolimonic acid 0.01 g/kg + 
                  8.8 ± 1.9** 
               
               
                 combination group 
                 Sitagliptin 0.01 g/kg 
               
               
                 Limonin glycoside 
                 Limonin glycoside 0.01 g/kg + 
                  8.5 ± 1.4** 
               
               
                 combination 
                 Sitagliptin 0.01 g/kg 
               
               
                 Isolimonic acid 
                 Isolimonic acid glycoside 
                  8.9 ± 1.7** 
               
               
                 glycoside combination 
                 0.01 g/kg + Sitagliptin 
               
               
                 group 
                 0.01 g/kg 
               
               
                   
               
               
                 Note 
               
               
                 * After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.05) 
               
               
                 **After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.01) 
               
            
           
         
       
     
     Discussion of Experimental Results 
     From the above results, it could be seen that, compared with the model group, either in single administration or in combination administration with sitagliptin, limonin and its derivatives could significantly reduce the blood glucose values of the mice with STZ islet cell injury. The administration of limonin and its derivatives in combination with sitagliptin had significantly improved the effect as compared with their single administration, showing a synergistic effect. In addition, when limonin and its derivatives were administrated in combination with sitagliptin, as compared with their single administration, the doses of both could be effectively reduced while comparable glucose-lowering effects could still be achieved, which improved the safety of therapeutic regimen and reduced side effects. 
     EXAMPLE 2 
     Effects of Limonoid Compound, Saxagliptin or Combination Thereof on Blood Glucose and Leptin in Mouse Type II Diabetes Model 
     In the present example, db/db mice (line name BKS.Cg-Dock7 m+/+ Lepr db /Nju) were used to perform hypoglycemic efficacy evaluation test of animals (blood glucose level and leptin). The limonoid compound was selected from obacunone, isoobacunoic acid and obacunone glycoside, and saxagliptin single administration group, obacunone single administration group, isoobacunoic acid single administration group, obacunone glycoside single administered group, and respective combination thereof with saxagliptin administration groups were set. 
     Conditions for experimental feeding: as type II diabetes model mice, 6-week-old SPF-grade db/db mice were purchased from the Nanjing Model Biology Institute, and subjected to experimental feeding after 7 days of preliminary feeding. It should be noted that the conditions for raising the mice were as follows: the temperature was 23±1° C., the humidity was 55±10%, the lights were turned on between 7 am and 7 pm (the lights were turned off at other time), and the mice were allowed to freely take in water and feed. The experimental feed was mouse growth-stable feed (GB M2118), and the daily feeding and management of the animals were under the responsibility of the animal security department, which provided the animals with sufficient diet and fresh drinking water daily. 
     Experimental grouping: male db/db mice (20±2 g) were selected, and 18 male mice in each group were tested. The experimental groups included normal control group (db/m, n=18), model group (db/db, n=18), obacunone group (db/db, n=18), isoobacunoic acid group (db/db, n=18), obacunone glycoside group (db/db, n=18), saxagliptin group (db/db, n=18), obacunone/saxagliptin combination group (db/db, n=18), isoobacunoic acid/saxagliptin combination group (db/db, n=18), obacunone glycoside/saxagliptin combination group (db/db, n=18). 
     Gavage doses: obacunone at a dose of 0.04 g/kg was gavaged per day for the obacunone group, isoobacunoic acid at a dose of 0.04 g/kg was gavaged per day for the isoobacunoic acid group, obacunone glycoside at a dose of 0.04 g/kg was gavaged per day for the obacunone glycoside group, saxagliptin at a dose of 0.04 g/kg was gavaged per day for the saxagliptin group, obacunone at a dose of 0.02 g/kg and saxagliptin at a dose of 0.02 g/kg were simultaneously gavaged per day for the obacunone/saxagliptin combination group, isoobacunoic acid at a dose of 0.02 g/kg and saxagliptin at a dose of 0.02 g/kg were simultaneously gavaged per day for the isoobacunoic acid/saxagliptin combination group, obacunone glycoside at a dose of 0.02 g/kg and saxagliptin at a dose of 0.02 g/kg were simultaneously gavaged per day for the obacunone glycoside/saxagliptin combination group, the gavage volume was 10 mL/kg, and the normal group and the model group were administrated with 10 mL/kg of distilled water. Two weeks later, the blood glucose values were measured by tail trimming method (Johnson&#39;s blood glucose meter) 1 h after the last administration, and serum leptin levels were measured with blood collected from orbital cavity by enzyme-linked immunosorbent assay (Elisa), and the average of each group was obtained. SPSS 16.0 software was used for statistical analysis. The data were expressed as mean and standard deviation. The data before and after were analyzed by t-test, and P&lt;0.05 was considered statistically significant. The test results were shown in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Blood glucose values and leptin of db/db mice after two weeks of daily gavage. 
               
            
           
           
               
               
               
               
            
               
                   
                 Formulation and dosage 
                 Blood glucose 
                 Leptin 
               
               
                 Group 
                 of administration 
                 value (mmol/L) 
                 (pg/ml) 
               
               
                   
               
               
                 Normal control group 
                 None 
                 6.0 ± 0.7  
                 0.88 ± 0.18  
               
               
                 Model group 
                 None 
                 23.9 ± 4.2  
                 48.19 ± 8.12  
               
               
                 Obacunone group 
                 Obacunone 0.04 g/kg 
                 12.7 ± 2.8** 
                 25.99 ± 3.92** 
               
               
                 Isoobacunoic acid group 
                 Isoobacunoic acid 0.04 g/kg 
                 14.6 ± 3.1** 
                 27.68 ± 3.25** 
               
               
                 Obacunone glycosidegroup 
                 Obacunone glycoside 0.04 g/kg 
                 13.6 ± 2.9** 
                 28.55 ± 4.00** 
               
               
                 Saxagliptin group 
                 Saxagliptin 0.04 g/kg 
                 13.9 ± 3.5** 
                 32.52 ± 5.11** 
               
               
                 Obacunone combinationgroup 
                 Obacunone 0.02 g/kg + 
                  6.8 ± 0.9** 
                 15.71 ± 4.13** 
               
               
                   
                 Saxagliptin 0.02 g/kg 
               
               
                 Isoobacunoic acid combination 
                 Isoobacunoic acid 0.02 g/kg + 
                  7.3 ± 1.5** 
                 16.14 ± 3.85** 
               
               
                 group 
                 Saxagliptin 0.02 g/kg 
               
               
                 Obacunone glycoside combination 
                 Obacunone glycoside 0.02 g/kg + 
                  7 0 ± 1.6** 
                 15.25 ± 4.54** 
               
               
                   
                 Saxagliptin 0.02 g/kg 
               
               
                   
               
               
                 Note 
               
               
                 **after independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.01) 
               
               
                 * after independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.05) 
               
            
           
         
       
     
     Discussion of Experimental Results 
     From the above results, it could be seen that, compared with the model group, either in single administration or in combination administration with saxagliptin, obacunone and derivatives thereof could significantly reduce the blood glucose levels in the db/db diabetic mice. When obacunone and derivatives thereof were administrated in combination with saxagliptin, significantly improved effect was observed relative to the single administration thereof, showing a synergistic effect. In addition, when obacunone and derivatives thereof were administrated in combination with saxagliptin, as compared with their single administration, the doses of both could be effectively reduced while comparable glucose-lowering effects could still be achieved, which improved the safety of therapeutic regimen and reduced side effects. 
     Meanwhile, the limonoid compound represented by obacunone and its derivatives could significantly improve the sensitivity to leptin; and especially when administrated in combination with saxagliptin, it could significantly improve the utilization efficiency of leptin in the body, improve the glucose metabolism of the body, and improve the functions relevant to the glucose metabolism in diabetes mice. 
     EXAMPLE 3 
     Effects of Limonoid Compound, Vildagliptin or Combination Thereof on Blood Glucose in Mouse Pancreatic Islet β-Cell Injury Model 
     In this example, a mouse pancreatic islet β-cell injury model was established by modeling ICR mice with streptozotocin (STZ) (Li Nan et al., Protective effect of pine pollen on kidney damage in diabetic nephropathy mice, Science and Technology Review, 2014, 32 (4/5): 95-99), and used to complete the evaluation of hypoglycemic effect in animals (this model could simulate pancreatic islet β-cell damage state of type I and type II diabetics). The limonoid compound was selected from the group consisting of ichangin, ichangensin, and ichangin glycoside, and vildagliptin single administration group, ichangin single administration group, ichangensi single administration group, ichangin glycoside singe administration group, and respective combination thereof with vildagliptin administration groups were set. 
     Conditions of experimental feeding: ICR mice (20±2 g), aged 6 weeks, purchased from Zhejiang Academy of Medical Sciences, and subjected to experimental feeding after 7 days of preliminary feeding. It should be noted that the conditions for raising the mice were as follows: the temperature was 23±1° C., the humidity was 55±10%, the lights were turned on between 7 am and 7 pm (the lights were turned off at other time), and the mice were allowed to freely take in water and feed. The experimental feed was mouse growth-stable feed (GB M2118), and the daily feeding and management of the animals were under the responsibility of the animal security department, which provided the animals with sufficient diet and fresh drinking water daily. 
     Experimental grouping: 15 male mice were randomly selected as the normal control group. After fasting for 12 hours, the remaining mice were intraperitoneally injected once with STZ at a dose of 150 mg/kg, and 72 hours later, the mice with blood glucose value of 15 to 25 mmol/L were undifferentiatedly grouped and used in the experiment, 15 animals in each group, and subjected to blood sampling and detection of indicators after two weeks of administration. 
     Gavage doses: the gavage dose was 0.1 g/kg per day for the ichangin group, the gavage dose was 0.1 g/kg per day for the ichangensin group, the gavage dose was 0.1 g/kg per day for the ichangin glycoside group, the gavage dose of vildagliptin was 0.1 g/kg per day for the vildagliptin group, ichangin at a dose of 0.05 g/kg and vildagliptin at a dose of 0.05 g/kg were simultaneously gavaged per day for the ichangin/vildagliptin combination group, ichangensin at a dose of 0.05 g/kg and vildagliptin at a dose of 0.05 g/kg were simultaneously gavaged per day for the ichangensin/vildagliptin combination group, ichangin glycoside at a dose of 0.05 g/kg and vildagliptin at a dose of 0.05 g/kg were simultaneously gavaged per day for the ichangin glycoside/vildagliptin combination group, the gavage volume was 10 mL/kg, and the normal group and the model group were administrated with 10 mL/kg of distilled water. Two weeks later, the blood glucose values were measured by tail trimming method (Johnson&#39;s blood glucose meter) 1 h after the last administration, and the average of each group was obtained. SPSS 16.0 software was used for statistical analysis. The data were expressed as mean and standard deviation. The data before and after were analyzed by t-test, and P&lt;0.05 was considered statistically significant. The test results were shown in Table 3 below. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Blood glucose values of STZ mice after 
               
               
                 two weeks of daily intragastric gavage. 
               
            
           
           
               
               
               
            
               
                   
                 Formulation and dosage 
                 Blood glucose 
               
               
                 Group 
                 of administration 
                 value (mmol/L) 
               
               
                   
               
               
                 Normal control group 
                 None 
                 7.5 ± 0.6  
               
               
                 Model group 
                 None 
                 29.5 ± 4.6  
               
               
                 Vildagliptin group 
                 Vildagliptin 0.1 g/kg 
                 16.9 ± 2.6** 
               
               
                 Ichangin group 
                 Ichangin 0.1 g/kg 
                 14.8 ± 1.9** 
               
               
                 Ichangensin group 
                 Ichangensin 0.1 g/kg 
                 14.5 ± 3.5** 
               
               
                 Ichangin glycoside 
                 Ichangin glycoside 
                 14.9 ± 2.1** 
               
               
                 group 
                 0.1 g/kg 
               
               
                 Ichangin combination 
                 Ichangin 0.05 g/kg + 
                  8.1 ± 0.9** 
               
               
                 group 
                 Vildagliptin 0.05 g/kg 
               
               
                 Ichangensin combination 
                 Ichangensin 0.05 g/kg + 
                  8.2 ± 1.8** 
               
               
                 group 
                 Vildagliptin 0.05 g/kg 
               
               
                 Ichangin glycoside 
                 Ichangin glycoside 0.05 
                  7.9 ± 1.2** 
               
               
                 combination group 
                 g/kg + Vildagliptin 
               
               
                   
                 0.05 g/kg 
               
               
                   
               
               
                 Note 
               
               
                 **After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.01) 
               
               
                 * After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.05) 
               
            
           
         
       
     
     Discussion of Experimental Results 
     From the above results, it could be seen that, compared with the model group, either in single administration or in combination administration with vildagliptin, the three limonoid compounds all could significantly lower the blood glucose levels in the mice of the STZ pancreatic islet cell injury model. When they were administrated in combination with vildagliptin, their effects were significantly increased as compared with their single administration, similar to the normal mice in blood glucose level, showing a synergistic effect. In addition, when the above three limonoid compounds were administrated in combination with vildagliptin, as compared with their single administration, the doses of both could be effectively reduced while comparable glucose-lowering effects could still be achieved, which improved the safety of therapeutic regimen and reduced side effects. 
     EXAMPLE 4 
     Effects of Limonoid Compound, Linagliptin or Combination Thereof on Blood Glucose and Insulin in Mouse Type II Diabetes Model 
     In the present embodiment, the limonoid compound was selected from nomilin, deacetylnomilin, nomilin acid, deacetylnomilin acid glycoside, and linagliptin single administration group, nomilin single administration group, deacetylnomilin single administration group, nomilin acid single administered group, deacetylnomilin acid glycoside single administration group, and respective combination thereof with linagliptin administration groups were set. 
     Conditions for experimental feeding: as type II diabetes model mice, 6-week-old SPF-grade db/db mice were purchased from the Nanjing Model Biology Institute, and subjected to experimental feeding after 7 days of preliminary feeding. It should be noted that the conditions for raising the mice were as follows: the temperature was 23±1° C., the humidity was 55±10%, the lights were turned on between 7 am and 7 pm (the lights were turned off at other time), and the mice were allowed to freely take in water and feed. The experimental feed was mouse growth-stable feed (GB M2118), and the daily feeding and management of the animals were under the responsibility of the animal security department, which provided the animals with sufficient diet and fresh drinking water daily. 
     Experimental grouping: male db/db mice (20±2 g) were selected, 18 male mice in each group were tested, and drinking bottles were sterilized weekly. The experimental groups included normal control group (db/m, n=18), model group (db/db, n=18), nomilin group (db/db, n=18), deacetylnomilin group (db/db, n=18), nomilin acid group (db/db, n=18), deacetylnomilin acid glycoside group (db/db, n=18), linagliptin group (db/db, n=18), nomilin combination group (db/db, n=18), deacetylnomilin combination group (db/db, n=18), nomilin acid combination group (db/db, n=18), deacetylnomilin acid glycoside combination group (db/db, n=18). 
     Gavage doses: nomilin at a dose of 0.2 g/kg was gavaged per day for the nomilin group, deacetylnomilin at a dose of 0.2 g/kg was gavaged per day for the deacetylnomilin group, nomilin acid at a dose of 0.2 g/kg was gavaged per day for the nomilin acid group, deacetylnomilin acid glycoside at a dose of 0.2 g/kg was gavaged per day for the deacetylnomilin acid glycoside group, linagliptin at a dose of 0.2 g/kg was gavaged per day for the linagliptin group, nomilin at a dose of 0.1 g/kg and linagliptin at a dose of 0.1 g/kg were simultaneously gavaged per day for the nomilin combination group, nomilin acid at a dose of 0.1 g/kg and linagliptin at a dose of 0.1 g/kg were simultaneously gavaged per day for the nomilin acid combination group, deacetylnomilin at a dose of 0.1 g/kg and linagliptin at a dose of 0.1 g/kg were simultaneously gavaged per day for the deacetylnomilin combination group, deacetylnomilin acid glycoside at a dose of 0.1 g/kg and linagliptin at a dose of 0.1 g/kg were simultaneously gavaged per day for the deacetylnomilin acid glycoside combination group, the gavage volume was 10 mL/kg, and the normal group and the model group were administrated with 10 mL/kg of distilled water. Two weeks later, the blood glucose values were measured by tail trimming method (Johnson&#39;s blood glucose meter) 1 h after the last administration, and serum insulin levels were measured with blood collected from orbital cavity by enzyme-linked immunosorbent assay (Elisa), and the average of each group was obtained. SPSS 16.0 software was used for statistical analysis. The data were expressed as mean and standard deviation. The data before and after were analyzed by t-test, and P&lt;0.05 was considered statistically significant. The test results were shown in Table 4 below. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Blood glucose values and insulin of db/db mice after two weeks of daily gavage. 
               
            
           
           
               
               
               
               
            
               
                   
                 Formulation and dosage 
                 Blood glucose 
                 Insulin 
               
               
                 Group 
                 of administration 
                 value (mmol/L) 
                 (pg/ml) 
               
               
                   
               
               
                 Normal control group 
                 None 
                 6.0 ± 0.7  
                 1.05 ± 0.39  
               
               
                 Model group 
                 None 
                 23.9 ± 4.2  
                 10.56 ± 3.00   
               
               
                 Linagliptin group 
                 Linagliptin 0.2 g/kg 
                 11.9 ± 2.1** 
                 8.00 ± 1.94** 
               
               
                 Nomilin group 
                 Nomilin acid 0.2 g/kg 
                 10.1 ± 3.9** 
                 8.82 ± 3.42** 
               
               
                 Nomilin acid group 
                 Nomilin acid 0.2 g/kg 
                 11.0 ± 4.1** 
                 8.08 ± 1.49** 
               
               
                 Deacetylnomilin group 
                 Deacetylnomilin 0.2 g/kg 
                 11.9 ± 2.9** 
                 8.59 ± 2.61** 
               
               
                 Deacetylnomilin acid glycoside 
                 Deacetylnomilin acid 
                 12.8 ± 5.5** 
                 8.40 ± 3.27** 
               
               
                 group 
                 glycoside 0.2 g/kg 
               
               
                 Nomilin combination group 
                 Nomilin 0.1 g/kg + 
                  6.8 ± 1.1** 
                 4.43 ± 1.13** 
               
               
                   
                 linagliptin 0.1 g/kg 
               
               
                 Nomilin acid combination 
                 Nomilin acid 0.1 g/kg + 
                  7.1 ± 2.0** 
                 4.12 ± 0.92** 
               
               
                 group 
                 linagliptin 0.1 g/kg 
               
               
                 Deacetylnomilin combination 
                 Deacetylnomilin 0.1 g/kg + 
                  6.9 ± 1.3** 
                 4.87 ± 0.81** 
               
               
                 group 
                 linagliptin 0.1 g/kg 
               
               
                 Deacetylnomilin acid glycoside 
                 Deacetylnomilin acid 
                  6.7 ± 1.8** 
                 4.56 ± 0.73** 
               
               
                 combination group 
                 glycoside 0.1 g/kg + 
               
               
                   
                 linagliptin 0.1 g/kg 
               
               
                   
               
               
                 Note 
               
               
                 **after independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.01) 
               
               
                 * after independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.05) 
               
            
           
         
       
     
     Discussion of Experimental Results 
     From the above results, it could be seen that, compared with the model group, either in single administration or in combination administration with linagliptin, nomilin and derivatives thereof could significantly reduce the blood glucose levels in the db/db diabetic mice. When nomilin and derivatives thereof were administrated in combination with linagliptin, significantly improved effect was observed relative to the single administration thereof, showing a synergistic effect. In addition, when nomilin and derivatives thereof were administrated in combination with linagliptin, as compared with their single administration, the doses of both could be effectively reduced while comparable glucose-lowering effects could still be achieved, which improved the safety of therapeutic regimen and reduced side effects. 
     Meanwhile, the limonoid compound represented by nomilin and derivatives thereof could significantly improve the sensitivity to insulin; and especially when administrated in combination with linagliptin, it could significantly improve the utilization efficiency of insulin in the body, improve the glucose metabolism of the body, and improve the functions relevant to the glucose metabolism in diabetes mice. 
     EXAMPLE 5 
     Effects of Limonoid Compound, Alogliptin or Combination Thereof on Blood Glucose in Mouse Type II Diabetes Model with Pancreatic Islet Damage and Obesity 
     In this example, a mouse model of type II diabetes with pancreatic islet damage and obesity was established by multiple modeling ICR mice with a small dose of streptozotocin (STZ), following with continuous high-fat diets (referring to literature: Zhang Jiyuan et al, Study on the effect of three plant extracts on improving glucose and lipid metabolism in type 2 diabetic mice, Food and Machinery, 2016, 32 (12): 142-147). The limonoid compound was selected from the group consisting of nomilin glycoside, deacetylnomilin glycoside, and nomilin acid glycoside, and alogliptin single administration group, nomilin glycoside single administration group, deacetylnomilin single administration group, nomilin acid glycoside single administration group, and respective combination thereof with alogliptin administration groups were set. 
     Conditions of experimental feeding: ICR mice (20±2 g), aged 6 weeks, purchased from Zhejiang Academy of Medical Sciences, and subjected to experimental feeding after 7 days of preliminary feeding. It should be noted that the conditions for raising the mice were as follows: the temperature was 23±1° C., the humidity was 55±10%, the lights were turned on between 7 am and 7 pm (the lights were turned off at other time), and the mice were allowed to freely take in water and feed. The experimental feed was mouse growth-stable feed (GB M2118), and the daily feeding and management of the animals were under the responsibility of the animal security department, which provided the animals with sufficient diet and fresh drinking water daily. 
     Experimental grouping: 15 male mice were randomly selected as the normal control group, and the remaining mice were subjected to a high-fat diet (high-fat diet formula: cholesterol 1%, egg yolk powder 10%, lard oil 10%, and basic feed 79%, for establishing an obesity mouse model) for consecutive 4 weeks and intraperitoneal injection of STZ at a dose of 35 mg/kg for three consecutive days. After one week, the mice were subject to 24 hours of fasting and water deprivation, their fasting blood glucose was measured, and the mice with a blood glucose level of 15 to 25 mmol/L were selected and undifferentiatedly grouped and used in the experiment, continuously subjected to the high-fat diet, 15 mice in each group, and subjected to blood sampling and detection of indicators after 2 weeks of administration. 
     Gavage doses: the gavage dose was 0.5 g/kg per day for the nomilin glycoside group, the gavage dose was 0.5 g/kg per day for the deacetylnomilin glycoside group, the gavage dose was 0.5 g/kg per day for the nomilin acid glycoside group, alogliptin at a dose of 0.5 g/kg was gavaged per day for the alogliptin group, nomilin glycoside at a dose of 0.25 g/kg and alogliptin at a dose of 0.25 g/kg were simultaneously gavaged per day for the nomilin glycoside/alogliptin combination group, deacetylnomilin glycoside at a dose of 0.25 g/kg and alogliptin at a dose of 0.25 g/kg were simultaneously gavaged per day for the deacetylnomilin glycoside/alogliptin combination group, nomilin acid glycoside at a dose of 0.25 g/kg and alogliptin at a dose of 0.25 g/kg were simultaneously gavaged per day for the nomilin acid glycoside/alogliptin combination group, the gavage volume was 10 mL/kg, and the normal group and the model group were administrated with 10 mL/kg of distilled water. Two weeks later, the blood glucose values were measured by tail trimming method (Johnson&#39;s blood glucose meter) 1 h after the last administration, and the average of each group was obtained. SPSS 16.0 software was used for statistical analysis. The data were expressed as mean and standard deviation. The data before and after were analyzed by t-test, and P&lt;0.05 was considered statistically significant. The test results were shown in Table 5 below. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Blood glucose values of STZ mice after 
               
               
                 two weeks of daily intragastric gavage. 
               
            
           
           
               
               
               
            
               
                   
                 Formulation and dosage 
                 Blood glucose 
               
               
                 Group 
                 of administration 
                 value (mmol/L) 
               
               
                   
               
               
                 Normal control group 
                 None 
                 5.9 ± 0.54 
               
               
                 Model group 
                 None 
                 29.6 ± 6.0  
               
               
                 Alogliptin group 
                 Alogliptin 0.5 g/kg 
                 14.5 ± 2.8** 
               
               
                 Nomilin glycoside 
                 Nomilin glycoside 0.5 g/kg 
                 12.8 ± 2.9** 
               
               
                 group 
               
               
                 Deacetylnomilin 
                 Deacetylnomilin glycoside 
                 12.7 ± 2.5** 
               
               
                 glycoside group 
                 0.5 g/kg 
               
               
                 Nomilin acid 
                 Nomilin acid glycoside 
                 13.5 ± 2.4** 
               
               
                 glycoside group 
                 0.5 g/kg 
               
               
                 Nomilin glycoside 
                 Nomilin glycoside 0.25 
                  6.4 ± 0.8** 
               
               
                 combination group 
                 g/kg + Alogliptin 
               
               
                   
                 0.25 g/kg 
               
               
                 Deacetylnomilin 
                 Deacetylnomilin glycoside 
                  6.5 ± 1.0** 
               
               
                 glycoside combination 
                 0.25 g/kg + Alogliptin 
               
               
                 group 
                 0.25 g/kg 
               
               
                 Nomilin acid glycoside 
                 Nomilin acid glycoside 
                  6.2 ± 1.1** 
               
               
                 combination group 
                 0.25 g/kg + Alogliptin 
               
               
                   
                 0.25 g/kg 
               
               
                   
               
               
                 Note 
               
               
                 **After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.01) 
               
               
                 * After independent t-test, compared with the model group, the difference was extremely significant (P &lt; 0.05) 
               
            
           
         
       
     
     Discussion of Experimental Results 
     From the above results, it could be seen that, compared with the model group, either in single administration or in combination administration with alogliptin, the three limonoid glycosides all could significantly lower the blood glucose levels in the mice of the STZ type II diabetes model. When they were administrated in combination with alogliptin, their effects were significantly increased as compared with their single administration, similar to the normal mice in blood glucose level, showing a synergistic effect. In addition, when the above three limonoid glycosides were administrated in combination with alogliptin, as compared with their single administration, the doses of both could be effectively reduced while comparable glucose-lowering effects could still be achieved, which improved the safety of therapeutic regimen and reduced side effects. 
     EXAMPLE 6 
     Method for Preparing a Tablet Containing Combination Product of Nomilin and Sitagliptin 
     In this example, a method for preparing a tablet of a combination product (nomilin and sitagliptin) of the present invention was exemplarily provided. A single tablet contained the following ingredients: 50 mg of nomilin, 400 mg of sitagliptin hydrochloride, 20 mg of hydroxypropylmethylcellulose, 30 mg of sodium carboxymethylcellulose, and 20 mg of microcrystalline cellulose, 5.2 mg of magnesium stearate, 20.8 mg of Opadry, and there were a total of 1000 tablets. 
     The preparation method comprised the following steps: 
     a) dissolving 50 g of nomilin in 5 L of 50% ethanol; 
     b) passing the raw and auxiliary materials through 100 mesh sieves, leaving them on standby; 
     c) weighing 400 g of sitagliptin hydrochloride, 20 g of hydroxypropylmethylcellulose, 30 g of sodium carboxymethylcellulose, and 20 g of microcrystalline cellulose, placing in a fluidized bed, and setting an inlet air volume of 500±50 m 3 /h, an inlet air temperature of 90±5° C., and a product temperature of 70±5° C., to perform hot melt granulation; 
     d) spraying a nomilin solution into the fluidized bed, setting an atomizing pressure of 1.0±0.2 bar, and a spraying speed of 30±10 Hz, to perform one-step granulation; 
     e) passing the resultant granules through a 1.0 mm round-hole screen to perform dry granulation; 
     f) adding 5.2 g of magnesium stearate and mixing for 5 min; 
     g) tabletting by using a 17×8.5 mm oval puncher at a pressure of 15 KN; 
     h) dissolving 20.8 g of Opadry 85F32004 in distilled water at a ratio of 1:4, setting parameters of a coating pan as: bed temperature of 40±2° C., outlet air temperature of 48±2° C., atomizing pressure of 0.6 Mpa, pan speed of 7 rpm, spray volume of 120 g/min, to complete film coating.