LONG EXPOSURE TO HIGH GLUCOSE-CONCENTRATION IMPAIRS THE RESPONSIVE EXPRESSION OF GAMMA-GLUTAMYLCYSTEINE SYNTHETASE BY INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA IN MOUSE ENDOTHELIAL-CELLS

To elucidate the pathological metabolism of glutathione synthesis in d iabetic endothelial cells, we studied the expression of gamma-glutamyl cysteine synthetase (gamma-GCS) using a mouse vascular endothelial cel l line. Exposing normoglycemic endothelial cells to tumor necrosis fac tor-alpha (TNF-alpha) or interleukin-1 beta (IL-1 beta) increased the activity and the mRNA expression of gamma-GCS, The addition of inhibit ors for nuclear factor kappa B (NF-kappa B) to the cells caused a loss of the gamma-GCS mRNA expression in response to TNF-alpha. A shift of the concentration of glucose in the medium from 5.5 to 28 mM glucose and a following incubation for 7 days decreased the expression of gamm a-GCS mRNA. These cells showed no apparent responses of gamma-GCS mRNA or the activity of NF-kappa B to TNF-alpha or IL-beta. Increase in th e GSH concentration of the cells treated with 28 mM glucose restored t he expression of gamma-GCS mRNA and its response to TNF-alpha or IL-be ta, suggesting that redox regulation is involved in the expression of gamma-GCS. In summary, the expression of gamma-GCS is regulated by TNF -alpha or IL-1 beta in endothelial cells mediated by NF-kappa B stimul ation, and impairment of the regulation of gamma-GCS in hyperglycemic cells may be a cause of medical complications that develop in diabetes mellitus.