The Effects And Mechanisms Of Long-term High-fat Diet On Dysfunction And Apoptosis In Beta Cell In Rats

PartⅠThe effect of long-term high-fat diet on insulin resistance and pancreatic beta cell function in ratsObjective To investigate the effects on insulin resistance in peripheral tissue and pancreatic beta cell function after long-term high-fat diet in rats.Methods Forty one male Sprague-Dawley(SD) rats were randomly divided into 2 groups:high-fat diet group(HF group) and normal diet group(NC group).After 28 weeks feeding,the following items were detected:(1) Body weight,visceral fat weight,subcutaneous fat weight.(2) Fasting blood glucose(FBG),fasting insulin(FINS),fasting serum free fatty acids(FFA) and triglyceride(TG).(3)The early phase insulin secretory function of beta cells was assessed by intravenous glucose tolerance test(IVGTT).(4)Insulin sensitivity(glucose infusion rate,GIR) was evaluated by euglycemic hyper-insulinemia clamp.Results(1)Body weight,visceral fat weight and subcutaneous fat weight were significantly increased in HF group.(2)Compared with NC group, the levels of FBG and FINS were higher in HF group.Serum concentration of FFA and TG was higher as well in HF group (P＜0.05).(3)The GIR during euglycemic hyperinsulinemia clamp in HF group was significantly lower than in NC group(3.60±1.2 mg·min^-1·kg^-1 vs.11.94±1.7mg·min^-1·kg^-1,P＜0.01).(4)Compared with NC group,insulin secretion response to glucose load significantly decreased in HF group (3.0fold vs.5.7fold,P＜0.05).The levels of blood glucose in HF group decreased slowly after 1min glucose load,but those at 3min,5min and 10min during IVGTT were significantly higher in HF group than in NC group(P＜0.05).Glucose decreased rate constant(K) was significantly lower in HF group than in NC group(8.9±1.29vs.13.3±1.4,P＜0.01).(5) Correlation analysis showed that visceral fat weight,subcutaneous fat weight and serum FFA concentration were negatively related to GIR, while serum FFA concentration was negatively related to glucose decreased rate constant(K).GIR was positively related to glucose decreased rate constant(K).Conclusion High-fat diet resulted in insulin resistance in peripheral tissue and impaired acute insulin response to intravenous glucose in rat pancreatic beta cells,which was associated with the elevation of serum FFA. PartⅡA study on the relationships of oxidative stress, endoplasmic reticulum stress and beta cell lipoapoptosis in ratsObjective To observe the impacts on beta cell lipoapoptosis after long term high-fat diet in rats,and to investigate the relationships oxidative stress,endoplasmic reticulum stress and beta cell lipoapoptosis.Methods Forty one SD male rats were randomly divided into 2 groups: high-fat diet group(HF group) and normal diet group(NC group).After 28 weeks feeding,the following items were detected:(1)The levels of malondialdehyde(MDA) and glutathione(GSH) in serum and pancreatic tissue.(2)Islet ultrastructure was studied by electron microscope.(3)The beta cell apoptosis was studied by TUNEL technology and the rate of beta cell apoptosis in pancreatic islet was calculated.(4)The uncoupling protein 2(UCP2) and caspase-12 gene expression of islets were detected by real-time PCR.Results:(1)The concentrations of MDA both in serum and pancreatic tissue were higher in HF group than in NC group(P＜0.05).In contrast, The levels of GSH both in serum and pancreatic tissues in HF group were lower than that in NC group(P＜0.01).(2) At the ultrastructural level,the marked fat droplets in cytoplasma,nuclear chromatin condensation and dilated lumen of endoplasmic reticulum were present in islet cells of HF group.The swelling of matrix and the disruption of cristae in mitochondria could be observed in islet cells of HF group.(3)The frequency of beta cell apoptosis was increased by 40.0%in HF group(P＜0.01).(4)The gene expressions of UCP2 in islet cells was significantly increased by 22.4%in HF group(P＜0.01),while caspase-12 gene expressions in islet cells was obviously increased by 40.8%in HF group(P＜0.01).Conclusion The frequency of beta cell apoptosis in high-fat diet rats was probably affected by oxidative stress and endoplasmic reticulum stress,which resulted in increased gene expression of UCP2 and caspase-12. PartⅢInflammatory path mediated by NF-κB induced functional disorder and apoptosis in beta cell after long-term high-fat diet in ratsObjective To investigate the relationship between inflammatory path mediated by nuclear factor-κB and functional disorder,apoptosis in beta cell after long-term high-fat diet in rats.Methods Forty one SD male rats were randomly divided into 2 groups: high-fat diet group(HF group) and normal diet group(NC group).After 28 weeks feeding,the following items were detected:(1)Fasting serum free fatty acids(FFA).(2) The early-phase insulin secretory function of beta cells was assessed by IVGTT.(3) Insulin sensitivity was evaluated by euglycemic hyper-insulinemia clamp.(4) The beta cell apoptosis was studied by TUNEL technology and the rate of beta cell apoptosis in pancreatic islet was calculated.(5)The protein expression levels of nuclear factor-κB(NF-κB),inhibitor of NF-κB(IκBα) and inducible nitric oxide synthase(iNOS) in beta cells by real-time PCR.(6)The gene expression of NF-κB,IκBαand iNOS in islet cells.Results(1)Serum FFA concentration in HF group was significantly higher than in NC group(P＜0.01).(2)Compared with NC group,insulin secretion response to glucose load decreased in HF group(3.0 fold vs.5.7 fold,P＜0.05).The levels of blood glucose in HF group decreased slowly after 1min glucose load,but those at 3min,5min and 10min during IVGTT were higher in HF group than in NC group(P＜0.05).(3)The GIR in HF group was significantly lower than in NC group(P＜0.01).(4)The frequency of beta cell apoptosis was significantly increased by 40.0%in HF group(P＜0.01).(5) The protein expression of NF-κB and iNOS in beta cell was significantly higher in HF group compared with NC group.In contrast,the protein expression of IκBαin HF group was significantly lower than in NC group.(6)The gene expression of NF-κB in islet cells was significantly increased by 37.2%in HF group compared with NC group(P＜0.01),the gene expression of iNOS in islet cells was increased by 19.6%in HF group compared with NC group(P＜0.05) and the expression of IκBαgene was decreased by 22.4%in HF group compared with NC group(P＜0.05).Conclusion High-fat diet resulted in impaired acute insulin response to intravenous glucose and elevated apoptosis frequency in rat pancreatic beta cells in HF group,which was associated with the activation of inflammatory path mediated by NF-κB.