Inhibition of hepatocyte gap junctional intercellular communication by endosulfan, chlordane and heptachlor

Abstract

The cyclodiene pesticides endosulfan, chlordane and heptachlor have been reported to be non-genotoxic rodent hepatocarcinogens. These three compounds and several metabolites of endosulfan (endosulfan sulfate, endosulfan ether and endosulfan lactone) were examined for their effects on gap junctional intercellular communication (GJIC) in primary cultured male F344 rat hepatocytes and B6C3F1 mouse hepatocytes. GJIC was evaluated by Lucifer Yellow CH dye-coupling. Endosulfan and endosulfan sulfate inhibited rat and mouse hepatocyte GJIC in a dose-responsive manner (50-200 microM) after 4 h treatment. Endosulfan ether inhibited rat hepatocyte GJIC only at 200 microM and had no effect on mouse hepatocytes. Endosulfan lactone did not affect rat or mouse hepatocyte GJIC. Chlordane and heptachlor inhibited both mouse and rat hepatocyte GJIC at concentrations of 50-200 microM. The inhibition of GJIC by the cyclodienes showed similar dose-response relationships and kinetics of onset of inhibition and reversibility for both mouse and rat hepatocytes. Concomitant treatment of the cells with inhibitors of cytochrome P450 monooxygenases (SKF-525A, piperonyl butoxide or carbon monoxide) did not alter the inhibition of GJIC by the cyclodienes, suggesting that cytochrome P450 metabolism was not involved in the inhibitory mechanism. Dibutyryl cyclic AMP (0.5 mM), however, decreased the inhibition of GJIC by the cyclodienes and may indicate that these compounds inhibit intercellular communication through a cAMP-dependent process. The inhibition of mouse and rat hepatocyte GJIC by the cyclodienes correlated with previous reports indicating that these compounds are non-genotoxic rodent liver carcinogens.