In Vitro Cytotoxicity of Mono-, Di-, and Trichioroacetate and Its Modulation by Hepatic Peroxisome Proliferation

Dichloroacetate (DCA) and trichloroacetate (TCA) are major by-productsof drinking water chlorination. Recent experiments have shownthat both of these compounds produce hepatic tumors in B6C3FImice. There was evidence that these effects may be associatedwith cytotoxic effects and/or peroxisomal proliferation. Therefore,in the present study the in vitro cytotoxicity of monochloroacetate(MCA), DCA, TCA and a metabolite, glycolate (GLY), was determinedin hepatocyte suspensions prepared from naive and clofibricacid-pretreated male Sprague-Dawley rats and B6C3F1 mice. Cytotoxicresponses, measured by release of lactic dehydrogenase and/ortrypan blue exclusion, were only observed with high concentrations(5.0 mM) of MCA and GLY in hepatocytes from naive animals (p=0.025and 0.008, respectively, Sprague-Dawley rat; p=0.033 and 0.001,respectively, B6C3F1 mouse). The cytotoxic responses to bothcompounds were observed much earlier and at much lower concentrationsin hepatocytes taken from mice and rats that had been pretreatedwith clofibric acid (p0.001, Sprague-Dawley rat and B6C3F1 mouse).DCA and TCA produced no evidence of cytotoxicity in hepatocytesfrom naive or clofibric acid-pretreated animals of either speciesat concentrations up to 5.0 mM. Increasing concentrations ofMCA and GLY resulted in dose-related depletion of intracellularreduced glutathione (GSH) that closely paralleled the cytotoxicresponses. Only GLY (0.25–5.0 mM) produced increased intracellularoxidized glutathione. Neither DCA nor TCA was found to altercellular GSH status in hepatocytes isolated from either Sprague-Dawleyrats or B6C3F1 mice. It was concluded from these in vitro observationsthat DCA and TCA are not highly cytotoxic to hepatocytes. Moreover,the rates of their conversion to MCA or GLY may be insufficientto induce cytotoxic effects in hepatocytes in vivo.