Glucose Toxicity and Pancreatic Beta Cell Dysfunction in Type 2 Diabetes / 당뇨병

ABSTRACT

The adverse effects of prolonged exposure of pancreatic islets to supraphysiologic glucose concentrations (i.e. glucose toxicity) is mediated at least in part by glucose oxidation and the subsequent generation of reactive oxygen species (ROS) that can impair insulin gene expression and beta cell function. Multiple biochemical pathways and mechanisms of action for glucose toxicity have been suggested. These include glucose autoxidation, protein kinase C activation, methylglyoxal formation and glycation, hexosamine metabolism, sorbitol formation, and oxidative phosphorylation. There are many potential mechanisms whereby excess glucose metabolites traveling along these pathways might cause beta cell damage. However, all these pathways have in common the formation of reactive oxygen species that, in excess and over time, cause chronic oxidative stress, which in turn causes defective insulin gene expression and insulin secretion as well as increased apoptosis. The intracellular peroxide levels of the pancreatic islets (INS-1 cells, rat islets) by flow cytometry were increased in the high glucose media compared to 5.6 mM glucose media. The insulin, MafA, PDX-1 mRNA levels and glucose stimulated insulin secretion (GSIS) were decreased in high glucose media compared to 5.6 mM glucose media. The HO-1 seems to mediate the protective response of pancreatic islets against the oxidative stress that is due to high glucose conditions. Also, we observed decreased glutathione level, gamma-GCS expression and increased oxidized LDL, malondialdehyde level at leukocytes and mesothelial cells from patients with Korean Type 2 Diabetes (esp, poorly controlled patients). In conclusion, this pathophysiologic sequence sets the scene for considering antioxidant therapy as an adjunct in the management of diabetes, especially type 2 Diabetes.