The Role Of Alteration Of Gut Microbiota And Metabolites Induced By Hypoglycemic Agent Sitagliptin In The Regulation Of Glucose Metabolism

Part 1 The alteration of gut microbiota and metabolites induced by sitagliptin improves glucose homeostasisBackgroundIncreasing evidence has indicated that gut microbiota contributes to the occurrence and development of metabolic diseases,including diabetes and obesity.Prebiotics,probiotics and antibiotics could regulate glucose metabolism through intervening the structure of gut microbiota,and reconstruction of the gut microbiota may be a new treatment for diabetes.Recent studies found that antidiabetic agents have beneficial effects on the composition of gut microbiota,such as metformin and acarbose,but little is known about the effects of commonly used antidiabetic agents,dipeptidyl peptidase–4 inhibitors(DPP-4i),on the gut microbiota.In this study,we investigated the roles of sitagliptin,one kind of DPP-4i,in modulating the gut microbiota.AimTo detect the changes of gut microbiota and metabolites in high-fat diet(HFD)mice after the treatment of sitagliptin,and to explore the mechanism of altered gut microbiota regulating the glucose metabolism.Methods1.HFD mice were treated by sitagliptin for 4 weeks.The effects of sitagliptin on the gut microbiota were analyzed by 16S-rDNA sequencing.Fecal metabolites were analyzed by both untargeted and targeted gas chromatography-mass spectrometry(GC–MS)systems.2.HFD mice were treated by sitagliptin with or without antibiotics(vancomycin 0.5g/L,bacitracin 1g/L)for 4 weeks.Fasting plasma glucose(FPG)and intraperitoneal glucose tolerance test(IPGTT)were assessed.3.Germ-free(GF)mice were administered with succinate for 6 weeks during fed a HFD.FPG and IPGTT were assessed.Results1.Sitagliptin altered the gut microbial composition.Specifically,the changes of 68.6% genera induced by HFD were rescued by sitagliptin,especially the abundance of phylum Bacteroidetes was significantly increased after Sit treatment.2.Compared to treatment with Sit alone,the combination of antibiotics attenuated the hypoglycemic effect of sitagliptin.The FPG was higher in HFD mice supplemented with antibiotics when compared with control group(P < 0.05).3.Sitagliptin promoted a functional shift in gut microbiome,especially increasing the production of succinate(P < 0.001).Besides,there is an increasing trend of short chain fatty acids(SCFAs).4.Compared with the control group,GF mice supplemented with succinate showed lower FPG and improved glucose tolerance(P < 0.05).ConclusionsIn this study,sitagliptin showed an important effect on the composition of gut microbiota,especially increasing the phylum Bacteroidetes.Furthermore,sitagliptin promoted a functional shift in the gut microbiome.Succinate,increased bacterial metabolite by sitagliptin,significantly improved the glucose homeostasis of GF mice.Thus,modulating the microbial composition and the level of metabolites might be a potential strategy for improving glucose homeostasis.Part 2 A high level of circulating valine is a biomarker for type 2 diabetes and associated with the hypoglycemic effect of sitagliptinBackground High concentration of branched-chain amino acids(BCAAs)and aromatic amino acids(AAAs)were associated with insulin resistance and the onset of type 2 diabetes(T2D).In the first part of study,we have found that most amino acids presented a decreasing trend in HFD mice treated with sitagliptin,suggesting a potential correlation between amino acids and glucose metabolism regulated by gut microbiota.Aim To analyze the levels of amino acids,especially valine,in HFD mice treated with sitagliptin.To assess circulating valine concentrations in healthy controls,subjects with T2 D and T2 D patients treated with sitagliptin,and analyze the association between valine concentrations and metabolic parameters in T2 D patients.Methods Amino acids concentrations in HFD mice were tested by untargeted GC–MS systems.Circulating valine concentrations were detected with a commercial kit in 53 subjects with normal glucose levels(n = 19),newly diagnosed T2D(n = 20),placebo-treated T2D(n = 7),and sitagliptin-treated T2D(n = 7).Biochemical parameters were also assessed in all participants.Insulin resistance index(HOMA-IR)and homeostasis model assessment for ? cell function index(HOMA-?)were measured.Results Sitagliptin treatment markedly changed the pattern of amino acid in HFD-fed mice,especially reducing the level of the BCAA valine(P < 0.001).Compared with healthy controls,the plasma valine concentrations were significantly higher in the T2 D patients(P < 0.05).Correlation analysis showed that the level of valine was positively correlated with fasting plasma glucose(r = 0.322,P = 0.046).Moreover,the concentrations of plasma valine were obviously reduced after sitagliptin treatment in T2 D patients(P < 0.05).Conclusions T2 D patients have significant higher levels of plasma valine compared with healthy controls.The levels of valine are attenuated by hypoglycemic agent sitagliptin both in T2 D patients and HFD mice.The results suggest that the circulating valine might be a potential biomarker for T2 D,and restoring the level of valine might be a potential strategy for diabetes therapy.