Hepatic bioactivation of skin-sensitizing drugs to immunogenic reactive metabolites

The clinical use of some drugs, such as carbamazepine, phenytoin, and allopurinol, is often associated with adverse cutaneous reactions. The bioactivation of drugs into immunologically reactive metabolites by the liver is postulated to be the first step in initiating a downstream cascade of pathological immune responses. Current mechanistic understanding and the ability to predict such adverse drug cutaneous responses have been partly limited by the lack of appropriate cutaneous drug bioactivation experimental models. Although in vitro human liver models have been extensively investigated for predicting hepatotoxicity and drug-drug interactions, their ability to model the generation of antigenic reactive drug metabolites that are capable of eliciting immunological reactions is not well understood. Here, we employed a human progenitor cell (HepaRG)-derived hepatocyte model and established highly sensitive liquid chromatography-mass spectrometry analytical assays to generate and quantify different reactive metabolite species of three paradigm skin sensitizers, namely, carbamazepine, phenytoin, and allopurinol. We found that the generation of reactive drug metabolites by the HepaRG-hepatocytes was sensitive to the medium composition. In addition, a functional assay based on the activation of U937 myeloid cells into the antigen-presenting cell (APC) phenotype was established to evaluate the immunogenicity potential of the reactive drug metabolites produced by HepaRG-derived hepatocytes. We showed that the reactive drug metabolites of known skin sensitizers could significantly upregulate IL8, IL1β, and CD86 expressions in U937 cells compared to the metabolites from a nonskin sensitizer (i.e., acetaminophen). Thus, the extent of APC activation by HepaRG-hepatocytes conditioned medium containing reactive drug metabolites can potentially be used to predict their skin sensitization potential.