Drug-Metabolizing Enzymes in Human Keratinocytes and In Vitro Detection of Cytochrome P450-Mediated Phenolic Lamotrigine Metabolite

Drug-induced hypersensitivity reactions can manifest as severe cutaneous adverse reactions, with lamotrigine (LTG) being a known elicitor in a subset of patients. While reactive metabolites are proposed to play a role, the contribution of skin metabolism is not well established. Here, we characterized drug-metabolizing enzymes and transporters in primary human keratinocytes and assessed the LTG metabolism in vitro. Using a combined transcriptomic and metabolomic approach, we demonstrated that primary human keratinocytes show a limited drug-metabolizing capacity. Although xenobiotic-metabolizing enzymes and drug transporters (phases I-III) were expressed at the transcript level, key hepatic cytochrome P450 enzymes (CYPs) were undetectable at both mRNA and protein levels. Following LTG incubation, low levels of LTG-N2-glucuronide were formed in keratinocytes as well as (reactive) metabolites, including a glutathione (GSH) adduct and a putative phenolic LTG derivative, in several in vitro assays. LTG-N2-sulfate formation could not be achieved under aqueous conditions. Transcriptome profiling of keratinocytes revealed no significant response to LTG, LTG-N2-oxide, or LTG+valproate, whereas interferon-γ triggered a pronounced proinflammatory gene expression signature. These findings provide new data of LTG metabolism, highlighting a novel CYP-derived phenolic pathway linked to GSH conjugation.