Bioactivation and covalent binding of halothane to liver macromolecules

In this manuscript we report our attempts to determine if 14C-halothane or its metabolites interact with DNA. Three bioactivation systems were used: in vitro microsomal incubations, isolated hepatocytes, and in vivo administration. Even though we used optimal conditions for bioactivation, no significant covalent binding of 14C to DNA was observed. Slight 14C activity above background (6 dpm/0.1 mg DNA) was observed in the microsomal incubations but is considered insignificant because it was not reduced when NADPH was omitted from the incubations. We are able to demonstrate covalent binding to nuclear lipids and proteins when rats were pretreated with phenobarbital and maintained in a hypoxic environment (14% O2). Similarly, these conditions markedly increased covalent binding of 14C from 14C-halothane to microsomal proteins and lipids. Isolated rat hepatocytes proved to be a viable system for studying the bioactivation of halothane. In this system it was also possible to demonstrate increased binding under N2 and/or phenobarbital pretreatment.