In vitro study of paraquat effects on malondialdehyde formation in thymus cells.

The present experiments have shown that paraquat enhanced both O2- production and oxidation of exogenous NADPH in thymus cells by NADPH-dependent enzyme system. The effects of paraquat on malondialdehyde formation were also NADPH-dependent and opposite in the absence and in the presence of ferrous ions: Paraquat inhibited the NADPH-dependent malondialdehyde formation in the absence of Fe2+; it activated this formation in the presence of Fe2+ and had no effect on the nonenzymic Fe2+- and Fe2+-ascorbate-stimulated lipid peroxidation. It is suggested that the activating effect of paraquat on the enzymic NADPH-dependent MDA formation in the presence of Fe2+ is due to the formation of a powerful oxidant product (FeO2)+ or to some Fe2+-paraquat radical complex, acting similarly to the ADP-chelated ferrous ions.