Protective action of sodium ascorbate against the DNA-damaging effect of malaoxon

In our previous work we showed that malaoxon, the first and main metabolite of the commonly used organophosphorus insecticide malathion, unlike its parent compound, damaged DNA in human lymphocytes. To search for the mechanism(s) underlying the observed effect we investigated the action of malaoxon on DNA in lymphocytes pretreated with sodium ascorbate using the single-cell gel electrophoresis (comet assay). On 1-h incubation at 37 degrees C, sodium ascorbate at a concentration of 10 mu M reduced a dose-dependent DNA damaging effect of 1-h incubation of human peripheral blood lymphocytes at 37 degrees C with malaoxon at 25, 75, or 200 mu M, measured as the increase in the comet tail moment of the lymphocytes. Treated cells were able to recover within a 30-min incubation in malaoxon-free medium at 37 degrees C, except for the lymphocytes exposed to the chemical at 200 mu M, which did not show measurable DNA repair even on a 120-min incubation. The latter result suggests a considerable cytotoxic effect (cell death) of malaoxon at the highest concentration used. Sodium ascorbate at 10 mu M abolished this cytotoxic effect of malaoxon. Sodium ascorbate displayed an antioxidant potency in the concentrations up to 50 mu M, reducing DNA damage evoked by hydrogen peroxide. We showed that the ascorbate partly inactivated malaoxon and this inactivation may be. at least in part, responsible for the observed protective effect of the ascorbate. Lymphocytes treated with endonuclease III, which recognizes oxidized pyrimidines, displayed greater tail moment than those untreated with the enzyme, suggesting that the damages induced by malaoxon have, at least in part, an oxidative origin. In conclusions, sodium ascorbate exerted the protective effect against DNA damage induced by malaoxon by direct inactivation of it and probably by a mechanism which may involve antioxidative action. (C) 1999 Academic Press.