LOWER INTRACELLULAR HYDROGEN-PEROXIDE LEVELS IN CELLS OVEREXPRESSING CUZN SUPEROXIDE-DISMUTASE

Transfection of V79 Chinese hamster cells produced clones in which CuZ n-superoxide dismutase (CuZn- SOD) activities were 2.2- to 3.5-fold hi gher than in the parental cells. An overall reduction of antioxidant e nzyme activities and both total and oxidized glutathione levels had be en found in these clones. Aconitase activities in these cells were det ermined to indirectly measure the O-2(-) steady state levels. As expec ted, in cells overexpressing CuZn-SOD, both total and cytosolic aconit ase activities have increased. Because these clones showed reduced oxi dized glutathione contents, it is unlikely that they present higher H2 O2 steady-state levels as a consequence of the higher SOD levels, This was confirmed by measuring H2O2 steady state levels in cells by flow cytometric analysis of 2',7'-dichlorofluorescein diacetate-treated cel ls. Despite the decreased antioxidant defenses, three of the clones ov erexpressing CuZn-SOD showed reduced H2O2 steady-state levels. These r educed H2O2 steady-state levels were found even when the cells were tr eated with the O-2(-) generator 2,3-dimethoxy-1,4-naphthoquinone. Thes e data provide in vivo support for the hypothesis proposed by Liochev and Fridovich [Liochev, S, I. & Fridovich, I. (1994) Free Radical Biol , Med, 16, 29-33] that O-2(-) dismutation prevents the formation of hi gher H2O2 levels by other reactions.