Abstract

BACKGOUND: Chronic hyperglycemia is the proximate cause of many complications of diabetes. The beta cells in type 2 diabetes are also adversely affected by chronic hyperglycemia, with this relentless deterioration in cell function, due to constant exposure to supraphysiologic concentrations of glucose, is termed glucose toxicity; however, the mechanism of glucose toxicity is uncertain. The purpose of this study was to determine whether prolonged exposure of pancreatic islets to supraphysiologic glucose concentration disrupts the intracellular balance between reactive oxygen species(ROS) and antioxidant enzyme; thereby, causing defective insulin secretion. METHODS: HIT-T15 cells were treated with H2O2(20, 50 and 100micrometer) directly added to the culture media, and then intracellular peroxide and insulin mRNA were then measured. The effects of H2O2 on the total peroxide level and insulin secretion were also examined. Isolated pancreatic islet cells from Wistar and 2 beta cell lines (INS-1, HIT-T15) were cultured in either a glucose or ribose (5.6, 11.1, 22.2, 30 and 50mM) containing culture media for 72hours. The intracellular peroxide was measured using flow cytometry and glucose stimulated insulin secretion(GSIS). RESULTS: The intracellular peroxide levels due to H2O2 in HIT-T15 cells were higher with a high concentration of H2O2, and the insulin mRNA in HIT-T15 cells decreased when the cells are treated with a high concentration H2O2. The insulin mRNA of the HIT-T15 cells cultured in a high concentration of ribose was lower than of those cultured in a low concentration of glucose. INS-1, HIT-T15 and rat islet cells, cultured for 72 hours, had progressively greater peroxide levels with higher concentrations of both glucose and ribose. The GSIS in the cells cultured in high concentrations of both glucose and ribose were decreased. CONCLUSION: These results suggest only one potential central mechanism for glucose toxicity in beta cells, this being the formation of excess ROS.

• Keywords: Glucose toxicity;Oxidative stress;Reactive oxygen species;Type 2 diabetes