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Phase II metabolism in human skin: skin explants show full coverage for glucuronidation, sulfation, N-acetylation, catechol methylation, and glutathione conjugation. | LitMetric
Drug Metabolism and Pharmacokinetics (N.M., P.S., G.C., O.K., H.S., M.W., K.L.), Pre-clinical Safety (K.K.B., B.B., F.P., A.W.), and Clinical Sciences and Innovation Translational Medicine (J.A.-C.), Novartis Institutes for BioMedical Research, Novartis Pharma, Basel, Switzerland; and Department of Plastic, Reconstructive, Aesthetic and Hand Surgery (B.L., R.W., D.J.S.), and Department of Dermatology (P.I.), University Hospital Basel, Basel, Switzerland
Published: January 2015
AI Article Synopsis
Article Abstract
Although skin is the largest organ of the human body, cutaneous drug metabolism is often overlooked, and existing experimental models are insufficiently validated. This proof-of-concept study investigated phase II biotransformation of 11 test substrates in fresh full-thickness human skin explants, a model containing all skin cell types. Results show that skin explants have significant capacity for glucuronidation, sulfation, N-acetylation, catechol methylation, and glutathione conjugation. Novel skin metabolites were identified, including acyl glucuronides of indomethacin and diclofenac, glucuronides of 17β-estradiol, N-acetylprocainamide, and methoxy derivatives of 4-nitrocatechol and 2,3-dihydroxynaphthalene. Measured activities for 10 μM substrate incubations spanned a 1000-fold: from the highest 4.758 pmol·mg skin(-1)·h(-1) for p-toluidine N-acetylation to the lowest 0.006 pmol·mg skin(-1)·h(-1) for 17β-estradiol 17-glucuronidation. Interindividual variability was 1.4- to 13.0-fold, the highest being 4-methylumbelliferone and diclofenac glucuronidation. Reaction rates were generally linear up to 4 hours, although 24-hour incubations enabled detection of metabolites in trace amounts. All reactions were unaffected by the inclusion of cosubstrates, and freezing of the fresh skin led to loss of glucuronidation activity. The predicted whole-skin intrinsic metabolic clearances were significantly lower compared with corresponding whole-liver intrinsic clearances, suggesting a relatively limited contribution of the skin to the body's total systemic phase II enzyme-mediated metabolic clearance. Nevertheless, the fresh full-thickness skin explants represent a suitable model to study cutaneous phase II metabolism not only in drug elimination but also in toxicity, as formation of acyl glucuronides and sulfate conjugates could play a role in skin adverse reactions.
