Abstract
The CYP4F subfamily of enzymes has been identified recently to be involved in the metabolism of endogenous compounds (arachidonic acid and leukotriene B4), nutrients (vitamins K1 and E), and xenobiotics (pafuramidine and fingolimod). CYP4F2 and CYP4F3B are reported to be expressed in the human liver. However, absolute concentrations of these enzymes in human liver microsomes (HLMs) and their inter-individual variability have yet to be determined due to the lack of specific antibodies. Here, an LC-MS/MS-based targeted quantitative proteomic approach was employed to determine the absolute protein concentrations of CYP4F2 and CYP4F3B, comparing to CYP3A, in two panels of HLMs (n = 31). As a result, the human hepatic P450 "pie" has been revised to include the contribution of CYP4F enzymes, which amounts to 15% of the total hepatic P450s. CYP4F3B displayed low inter-individual variability (3.3-fold) in the HLM panels, whereas CYP4F2 displayed large variability (21-fold). However, CYP4F2 variability decreased to 3.4-fold if the two donors with the lowest expression were excluded. In contrast, CYP3A exhibited 29-fold inter-individual variability in the same HLM panels. A proposed marker reaction for CYP4F enzymes, pafuramidine/DB289 M1 formation, did not correlate with CYP4F protein content, suggesting alternate metabolic pathways for DB289 M1 formation in HLMs. In conclusion, CYP4F enzymes are highly expressed in the human liver and their physiologic and pharmacologic roles warrant further investigation.
- The American Society for Pharmacology and Experimental Therapeutics