The effects of mechanism-based suicide inhibitors of cytochrome P-450 on cell-mediated mutagenesis and cytotoxicity
Description
Several aryl acetylenes and aryl olefins have been examined as substrates and inhibitors of cytochrome P-450 dependent monooxygenases in liver microsomes from 5,6-benzoflavone or phenobarbital pretreated rats. Methyl 1-pyrenyl acetylene (MPA), 2-ethynylfluorene (EF), 9-ethynylphenanthrene (EPH), and 3-ethynylperylene (EPE) serve as mechanism-based irreversible inactivators (suicide inhibitors) of benzo (a) pyrene (BP) hydroxylase activity, while 3-vinylperylene (VPE) does not cause a detectable suicide inhibition of the BP hydroxylase. The mechanism-based loss of the BP hydroxylase activity caused by the aryl acetylenes is not accompanied by a corresponding loss of the P-450 content of the microsomes (suicide destruction) The results of the effects of these aryl derivatives in the mammalian cell-mediated cytotoxicity show that among all these polycyclic arylhydrocabon (PAH) derivatives only VPE and its potential metabolites produced in the incubation system with keratinocytes are cytotoxic to the Chinese hamster V79 fibroblast cells in the concentration range 10 to 50 nM. The results of the studies on the epidermal keratinocyte-mediated mutagenesis produced by 7,12-dimethylbenz (a) anthracene (DMBA) and by BP in the presence or absence of arachidonic acid (AA) show that the presence of AA may enhance the mutations produced by BP while it seems to decrease slightly the mutation produced by DMBA. It is found that EP (1-ethynylpyrene) and EPE both are effective at preventing the mutation produced by DMBA and by BP in the presence or absence of arachidonic acid and these inhibitions are comparable to those of a reference antimutagen, 7,8-benzoflavone. However, differences were seen when other PAH derivatives were tested as modifiers in these cell systems. Unlike effects shown in the DMBA system, all the PAH derivatives, except EF, show some inhibitory effects on the mutagenesis produced by BP in the absence of arachidonic acid. In the presence of arachidonic acid, EPH and EF may be more effective at preventing the mutations produced by BP whereas VPE and 2-EN seem to have no effect under this condition. The most significant variation in these systems is opposite effects shown by 2-EN; although 2-EN may prevent the mutation produced by BP, at least in the absence of AA, it enhances mutations produced by DMBA metabolism. (Abstract shortened with permission of author.)