Role of oxidant stress and antioxidant protection in acephate-induced renal tubular cytotoxicity

Acephate (AT) is an organophosphate (OP) insecticide. Due to their reputati on for low environmental persistence, OP pesticides are often used indiscri minately resulting in detrimental exposure to humans and other nontarget sp ecies. Although the toxicity of OP compounds is primarily through blockade of neural transmission via inhibition of acetylcholinesterase, studies have revealed histopathological alterations in the renal proximal tubules, sugg esting a role for additional mechanisms in renal toxicity. It is our hypoth esis that Reactive Oxygen Species (ROS) may play a role in OF-induced renal tubular injury for the following reasoning. Renal tubular cells concentrat e many nephrotoxic chemicals including OPs, and renal injury from many of t hese compounds has been shown to arise from excessive ROS production. Furth ermore, it has been established that many phosphorothiolates, which are sul fur-containing OPs and constitute the class of OP compounds to which AT bel ongs, are S-oxidized to highly reactive intermediates within cells and tiss ues. Because of these considerations, we examined whether ROS play a role i n OP-induced renal tubular epithelial cell (LLC-PK1) toxicity using AT as a prototype. AT produced a concentration- and time-dependent increase in cel l damage in LLC-PK1 cells, measured by lactate dehydrogenase (LDH, % of tot al) leakage. The cytotoxicity (LDH) induced by 2500 ppm of AT over 72 h was significantly suppressed by antioxidants 2-methylaminochroman (2-MAC) and desferrioxamine (DFO). H2O2 levels were significantly elevated following ex posure of LLC-PK1 cells to 2500 ppm of AT. Malondialdehyde (MDA) formation was also significantly increased in AT-exposed cells compared to the contro l cells, indicating the occurrence of enhanced lipid peroxidation. 2-MAC an d DFO, in addition to providing cytoprotection, inhibited AT-induced MDA ge neration in a significant and concentration-dependent manner. Results from this study, which is the first to explore the toxic effects of AT on renal tubular cells, demonstrate that toxic action of AT on kidney cells is partl y through an ROS-mediated mechanism. Based on these direct in vitro finding s, we further hypothesize that oxidant stress may play a role in the pathog enesis of AT-induced acute tubular necrosis and renal dysfunction observed in cases of AT overdoses. (C) 1998 Society of Toxicology.