CYP3A4 and CYP4A5 share specificity for a wide range of xenobiotics with the CYP3 subfamily collectively involved in the biotransformation of approximately 30% of all drugs. CYP3A4/5 mRNA transcripts have been reported in the skin, yet knowledge of their protein expression and function is lacking. In this study, we observed gene and protein expression of CYP3A4/5 in both human skin and tissue-engineered skin equivalents (TESEs), and enzyme activity was detected using the model substrate benzyl-Omethyl-cyanocoumarin. Mass spectrometric analysis of TESE lysates following testosterone application revealed a time-dependent increase in metabolite production, confirming the functional expression of these enzymes in skin.
K E Y W O R D Sepithelium, steroids, three-dimensional tissue models, toxicity, xenobiotic metabolism
| BACKGROUNDCytochrome P450 (CYP450) enzymes are a superfamily of haemoproteins that metabolize a multitude of endogenous and xenobiotic molecules and are essential to maintain homoeostasis. [1,2] As the most highly expressed xenobiotic enzymes in the liver, they are responsible for the majority of phase I reactions, metabolizing between 70%and 80% of all drugs. [3,4] The CYP3 subfamily of the CYP450 enzymes, comprising of CYP3A4, CYP3A5, CYP3A7 and CYP3A43, are collectively involved in the metabolism of over a third of these drugs.[4]CYP3A4, the most abundantly expressed isoform in the liver, [5] has a large active site that enables its interaction with a wide range of structurally diverse compounds and permits metabolism of such molecules and drugs as hormones (testosterone, oestrogen), anticancer drugs (paclitaxel, tamoxifen) and antifungal agents (ketoconazole) amongst others. [4,6] CYP3A5 shares 85% amino acid sequence homology with CYP3A4 and displays similar substrate specificity. [7] Gene expression of CYP3A4 and CYP3A5 has been detected in skin and tissue-engineered skin equivalents (TESEs) by genomic analysis in some studies [8,9,S1,S2] but not others, [S3] and to date, protein expression has not been detected. [S4,S5] Given the use of skin as a drug delivery route, it is extremely important to determine functional expression of CYP3A4/5. Moreover, the increasing use of TESE as an alternative to animal testing for drug irritation and sensitivity assays has led to their proposed use in drug-induced toxicity assays. However, data on functional xenobiotic enzyme activity in these models are lacking and urgently required.
| QUESTIONS ADDRESSEDThe relative gene and protein expression of CYP3A4 and CYP3A5 in human skin in comparison with liver remains unclear. It is also unknown whether the expression is localized to the dermis or epidermisThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
