Covalent binding of procainamide in vitro and in vivo to hepatic protein in mice.

Procainamide (PA) formed reactive metabolites capable of covalently binding to protein both in vivo and in vitro. The in vitro covalent binding of PA to washed hepatic microsomal protein prepared from control male mice was dependent upon mixed-function oxidase activity. The binding was proportional with time and protein concentration. Glutathione and SKF 525-A inhibited the in vitro covalent binding by 88 and 51%, respectively. The addition of NaF to the incubation medium produced a concentration-dependent decrease in covalent binding. Covalent binding of N-acetylprocainamide in vitro was 90% less than that of procainamide and was not increased by NaF. The in vivo covalent binding of PA to hepatic protein in male mice was increased with phenobarbital and 3-methylcholanthrene pretreatment, resulting in increase in binding of 29 and 56%, respectively, compared to control mice. Pretreatment of mice with SKF 525-A inhibited binding by 39%. Depletion of hepatic glutathione with diethyl maleate pretreatment increased the amount of covalent binding in vivo. Bioactivation of PA by hepatic microsomal enzymes in the mouse produces a metabolite capable of covalent interactions with cellular macromolecules.