Toxicity of 1,2-dibromoethane in primary hepatocyte monolayer cultures: lack of dependence on oxygen concentration.

Hepatic 1,2-dibromoethane (DBE) metabolism proceeds via two pathways: oxidation by cytochrome P-450 and direct conjugation with the ubiquitous tripeptide glutathione (GSH) via the GSH S-transferases. The toxicity of DBE in monolayers of hepatocytes was assessed to establish whether the toxicity of this compound is increased under conditions of reductive metabolism at low oxygen concentrations. Our previous studies with t-butyl hydroperoxide and the calcium ionophore A23187 suggested that hypoxia would exacerbate toxicity that was mediated through lipid peroxidation or loss of calcium homeostasis. Monolayers of hepatocytes were exposed for 2 hr to 0, 14, 140, 1400, or 14,000 ppm of DBE in an atmosphere of either 1, 2, or 20% oxygen. Toxicity was measured by leakage of aspartate aminotransferase (AST) and trypan blue exclusion. The time course of the development of cytotoxicity was examined by assaying cell death both immediately following a 2-hr exposure and 24 hr later. The LC50 of DBE vapor was found to be approximately 14,000 ppm when assayed immediately after exposure but only 140 ppm when assayed 24 hr after exposure. The similarity of the percentages of DBE-induced cell death after incubations at 1, 2, and 20% oxygen demonstrates that the toxicity of DBE is oxygen-independent. We conclude that while DBE is highly toxic to rat hepatocytes, hypoxia does not appear to contribute to the toxicity of DBE, even under conditions of low oxygen concentrations. This result is in direct contrast to a previous report where we showed that the toxicity of halothane is potentiated under hypoxic conditions.