[Paraoxonase activity and lipid peroxides concentration in serum of rats subchronically intoxicated with chlorpyrifos--organophosphate insecticide].

BACKGROUND Toxicity of organophosphate insecticides is mainly due to the inhibition of acetylcholinesterase (AChE). However, organophosphate insecticides in acute, as well as in chronic and subchronic intoxication may lead to oxidative stress causing the enhancement of lipid peroxidation and changing the activities of antioxidative enzymes. Paraoxonase PON1 is synthesized by the liver. This enzyme hydrolyzes organophosphate compounds, phospholipid hydroperoxides and cholesterol ester hydroperoxides. Its role as an antioxidant has also been suggested. For this reason the aim of the work was to estimate the activity of paraoxonase and the level of serum lipid peroxides in the rats subchronically intoxicated with chlorpyrifos. MATERIALS AND METHODS The animals received chlorpyrifos at a single daily dose of 0.2, 2 or 5 mg/kg b.w./day for 14 days. For biochemical determinations of paraoxonase activity in serum of rats, Aryloesterase/Paraoksonase Assay Kit (ZeptoMetrix Corporation Buffalo, USA) and for lipid peroxides level, LPO-586 (OXIS International, Foster City, Calif., USA) were used. RESULTS Chlorpyrifos administration resulted in a decreased activity of paraoxonase in serum. The highest decrease was observed after administration of chlorpyrifos in doses 2 and 5 mg/kg b.w./day. In the intoxication with the highest insecticide dose under study the decreased paraoxonase activity was accompanied by the increased level of lipid peroxides. CONCLUSIONS In view of the literature data, the finding that low doses of chlorpyrifos lead to statistically significant decrease in paraoxonase activity in serum of rats provides evidence that exposure to organophosphate insecticides induces oxidative stress. It also suggests the need to take into consideration a possible development of arteriosclerosis, hypercholesterolemia and diabetes mellitus in people exposed to these compounds.