The Relationship Between Homocysteine And Islet Beta Cell Function, Apoptosis And The Possible Mechanism

Both the impaired islet beta cell function and insulin resistance are the most important pathogenesis in type 2 diabetes.When the impaired islet beta cell function can not overcome the insulin resistance,clinical hyperglycemia will develop.The impaired islet beta cell function is related to reduced beta cell mass.The apoptosis is the basic mechanism in reducing beta cell mass.The mechanism of beta cell apoptosis was focus on glucose toxicity and lipo-toxicity.Hyperglycemia could induce the apoptosis by oxidative stress or non -oxidative stress pathway.Then the insulin release was impaired.Hyperglycemia could induce the apoptosis of beta cell by imbalanced the Bcl gene family.In the islet beta cell,the levels of antioxidative enzyme were lower than other tissues.There were many studies that homocysteine impaired the vascular endothelial cell and nerve cell.But few study about homocysteine impaired the islet beta cell.In our study,we investigated the relationship between plasma homocysteine(Hcy)and insulin resistance(IR),islet beta cell function in different glucose tolerance individuals.And we studied the possible effect of homocysteine on insulin secretion,apoptosis and SOD activity in NIT-1 cell line,a pancreatic beta-cell line established from a transgenic NOD/Lt mouse.The Study of the relationship between plasma homocysteine and insulin resistance,islet beta cell function in different glucose tolerance individualsObjective To investigate the relationship between plasma homocysteine(Hcy) and insulin resistance(IR),islet beta cell function in different glucose tolerance individuals.Methods A total 83 subjects were recruited by oral glucose tolerance test(OGTT)in this study,including 32 normal glucose tolerance(NGT), 24 impaired glucose tolerance(IGT)and 27 newly diagnosed patient with type 2 diabetes mellitus(DM).The levels of BMI,blood pressure,liver and renal function,total cholesterol,triglycerides and HDL cholesterol were measured at fasting time.The levels of glucose and insulin were measured at fasting and 2 hours post-prandial.Plasma Hey levels were measured by Polarization Immunoassay(FPIA),serum C Reactive Proteine(CRP)concentrations were determined with Enzymatic Linked Immunity Sorb Assay(ELISA).Result The serum CRP levels were increased gradually with the worsening of glucose tolerance(P＜0.05).Body mass index(BMI)and waist circumference(WC)were higher significantly in IGT and DM compared with NGT group(P＜0.01,P＜0.05).The levels of systolic pressure were higher in IGT group and DM group compared with NGT group(P＜0.01,P＜0.01).The levels of diastolic pressure were higher in IGT group compared with NGT group and DM group(P＜0.01,P＜0.01).The levels of triglycerides were higher significantly in IGT group and DM group compared with NGT group(P＜0.01,P＜0.01).The levels of total cholesterol were higher in IGT group compared with NGT group and DM group (P＜0.01,P＜0.01).The levels of serum creatinine were much higher significantly in IGT group compared with NGT group and DM group.Fasting plasma Hcy concentrations in IGT and DM group were higher significantly compared with NGT group(P＜0.01).Fasting plasma Hey concentrations in IGT group were higher than DM group,but no significant difference(P＞0.05).The levels of fasting insulin were higher significantly in IGT group than NGT group and DM group(P＜0.01,P＜0.01).The levels of 2-hour insulin were higher in IGT and DM groups compared with NGT group(P＜0.01,P＜0.01).The HOMA-IR of NGT group were lower than IGT and DM group(P＜0.01).The insulin sensitive index of NGT group were higher than IGT and DM group(P＜0.01).HBCI,HBCI/IR,FBCI/IR,â–³I₁₂₀/â–³G₂₀andâ–³I₁₂₀/â–³G₁₂₀/IR of NGT group were significantly higher than IGT group and DM group(P＜0.01). HOMA-IR was positively correlated with plasma Hcy.ISI was negatively correlated with Hey.FIBCI/IR,FBCI/IR andâ–³I₁₂₀/â–³G₁₂₀/IR were negatively correlated with plasma Hey.Conclusion The concentration of Hey was higher in IGT and DM groups compared with NGT group.And the beta cell function was impaired more severe in IGT and DM group compared with NGT group. HOMA-IR,ISI,HBCI/IR,FBCI/IR andâ–³I₁₂₀/â–³G₁₂₀/IR were the major factors that affected the concentration of serum Hey.Hey might provide a plausible chemical mechanism in explaining Hey toxicity to the islet beta cell function. Detrimental effects of homocysteine on insulin release and apoptosis of beta cell lineObjective To study the possible effect of homocysteine on insulin secretion, apoptosis and SOD activity in NIT-1 cell line,a pancreatic beta-cell line established from a transgenic NOD/Lt mouse.Methods Colonal NIT-1 cells were cultured in culture medium,which containing different glucose concentrations.Homocysteine of different concentrations were added to the culture medium at different time.The insulin concentrations in the culture medium were determined by radioimmunoassay.The apoptosis of pancreatic beta-cell were determined with flow cytometry and agarose gel electrophoresis. The superoxide dismutase(SOD)activity in NIT-1 cells was also assayed by xanthine oxidase-WST combined method.Protein expression of apoptotic genes were determined by Western blot.Results Homocysteine inhibited basal and glucose-induced insulin secretion in a time- and dose-dependent manner. Incubating NIT-1 with 50μmol/L homocysteine for 24 hours and with 100μmol/L homocysteine for 12 hours showed obvious reduction of insulin release as compared with control group(P＜0.01,P＜0.01).Incubating NIT-1 with 100μmol/L homocysteine for 12 hours and 24 hours,the cells viability were 94.56 %and 87.93%(P＜0.05,P＜0.01).Incubating NIT-1 with 100μmol/L homocysteine for 24 hours,the apoptosis rate was 7.21%(P＜0.01).Incubating NIT-1 with 250μmol/L homocysteine for 12 hours,the apoptosis rate was 12.93% (P＜0.01).Both Annexin V/PI FACS and agarose gel electrophoresis analysis indicated that homocysteine induced cell apoptosis in a time and concentration dependent manner.In comparison with the control group,intra-cellular SOD activity was significantly declined as the concentrations of homocysteine was 100 umol/L(P＜0.01).The protein expression of bax was up-regulated by Hcy. Conclusion Homocysteine impaired insulin secretion and induced cell apoptosis of Colonal NIT-1 cells.The potential effect of homocysteine in possible beta cell demise merits further investigation.Conclusions1.The concentration of Hcy was higher in IGT and DM group compared with NGT group.And the beta cell function was impaired more severe in IGT and DM groups comparied with NGT group.HOMA-IR,ISI,HBCI/IR,FBCI/IR andâ–³I₁₂₀/â–³G₁₂₀/IR were the major factors that affecteed the concentration of serum Hcy.Hcy might provide a plausible chemical mechanism in explaining Hcy toxicity to the islet beta cell function.2.Homocysteine impaired insulin secretion and induced cell apoptosis of Colonal NIT-1 cells.The potential effect of homocysteine in possible beta cell demise merits further investigation.