ABNORMAL GLUTATHIONE METABOLISM AND INCREASED CYTOTOXICITY CAUSED BY H2O2 IN HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS CULTURED IN HIGH GLUCOSE MEDIUM

To determine whether increased oxidative stress in diabetes mellitus i s due to an impaired free-radical scavenger function in endothelial ce lls, GSH-dependent H2O2 degradation in human umbilical vein endothelia l cells was studied. The GSH-dependent, NaN3-uninhibitable H2O2-degrad ation in endothelial cells was reduced by 48% (p < 0.001) when the cel ls were exposed to 33 mmol/l D-glucose vs 5.5 mmol/l D-glucose. This i mpairment was dependent not only on the D-glucose concentration in the medium but also on D-glucose specific metabolism, since neither 27.5 mmol/l L-glucose nor 27.5 mmol/l D-raffinose had any effect on the per oxide degradation activity. Activation of the glutathione redox cycle by H2O2 in cells exposed to high glucose concentrations was attenuated as compared with 5.5 mmol/l D-glucose because of: I)a 42% decrease (p < 0.001) in intracellular NADPH content, and 2) a 34% reduction (p < 0.01) in glutathione release into the media. This results in an accumu lation of GSSG in the cells following exposure to H2O2. Both H2O2-evok ed Cr-51-release and H2O2-induced endothelial cell damage were signifi cantly (p < 0.01) greater in the 33 mmol/l D-glucose group than in the 5.5 mmol/l D-glucose group. These results indicate that the abnormal glutathione redox cycle observed in endothelial cells is induced by hi gh glucose concentrations in the medium, resulting in an impairment of reduced GSH-dependent H2O2-degradation. These abnormalities may assoc iate with the increased cellular damage following an exogenous exposur e to H2O2