Non-additive effects of changing the cytochrome P450 ensemble: incorporation of CYP2E1 into human liver microsomes and its impact on CYP1A2

Abstract

The aim of this study is to investigate the ability of ethanol-inducible CYP2E1 to interact with other cytochrome P450 species and affect the metabolism of their substrates. As a model system we used CYP2E1-enriched microsomes obtained by incorporation of purified CYP2E1 protein into HLM. Using the method based on homo-FRET in homo-oligomers of CYP2E1 labeled with BODIPY 577/618 maleimide we demonstrated that the interactions of CYP2E1 with microsomes result in dissociation of the protein homo-oligomers. The finding that this effect is much better pronounced in HLM as compared to the microsomes containing no P450 proteins indicates the formation of mixed oligomers of CYP2E1 with other P450 species that takes place in expense of dissociation of the homo-oligomers.\n\nIncorporation of CYP2E1 into HLM results in a multifold increase in the rate of metabolism of CYP2E1-specific substrates p-Nitrophenol (pNP) and Chlorzaxozone (CLZ). The rate of their oxidation remains proportional to the amount of incorporated CYP2E1 up to the content of 0.3-0.4 nmol/mg protein (or about 50% CYP2E1 in the P450 pool). These results demonstrate that the incorporated CYP2E1 becomes a fully-functional member of the P450 ensemble and do not exhibit any detectable functional differences with the endogenous CYP2E1 in HLM.\n\nEnrichment of HLM with CYP2E1 results in a pronounced alteration of the metabolism of 7-etoxy-4-cyanocoumarin (CEC), the substrate of CYP2C19 and CYP1A2, that suggests an important augmentation of the involvement of CYP1A2 in its metabolism. This effect goes together with a remarkable increase in the rate of dealkylation of CYP1A2-specific substrate 7-ethoxyresorufin by CYP2E1-enriched HLM. Furthermore, probing the interactions of CYP2E1 with model microsomes (Supersomes) containing individual P450 enzymes we found that CYP2E1 efficiently interacts with CYP1A2, but lacks any ability to form complexes with CYP2C19. This finding goes inline with CYP2E1-induced redirection of the main route of CEC metabolism from CYP2C19 to CYP1A2.