Kinetic studies on the hydrogen peroxide elimination by cultured PC12 cells: rate limitation by glucose-6-phosphate dehydrogenase

Oxidative stress is implicated in the pathogenesis of neurodegenerative disorders and brain ischemia, and hydrogen peroxide (H2O2) plays a central role in the stress. In this study, we have examined the kinetics of H2O2 elimination by PC12 cells as a neuronal model in connection with the enzyme activities supporting the reaction. Similarly to other cell lines previously studied, H2O2 removal kinetics could be divided into two reactions: one apparently following the Michaelis-Menten kinetics (GSH-dependent reaction) and the other following the first-order kinetics (mainly catalyzed by catalase). Based on the enzyme activities in the cell homogenate, it was inferred that glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme in the GSH- and NADPH-dependent H2O2 elimination by PC12 cells. This is in contrast with fibroblasts and endothelial cells previously examined, in which glutathione reductase (GR) is rate-limiting in the reaction sequence. Treatment of PC12 cells with nerve growth factor increased G6PD activity in the cell homogenate and H2O2 removal activity of the whole cells, with a concomitant increase in the resistance against H2O2 toxicity. These results suggest the importance of G6PD in the antioxidant function of brain and pathogenesis of the oxidative stress-related diseases. (C) 2002 Elsevier Science B.V. All rights reserved.