HR-MAS NMR spectroscopy of reconstructed human epidermis: potential for the in situ investigation of the chemical interactions between skin allergens and nucleophilic amino acids.

High-resolution magic angle spinning (HR-MAS) is a nuclear magnetic resonance (NMR) technique that enables the characterization of metabolic phenotypes/metabolite profiles of cells, tissues, and organs, under both normal and pathological conditions, without resorting to time-consuming extraction techniques. In this article, we explore a new domain of application of HR-MAS, namely, reconstructed human epidermis (RHE) and the in situ observation of chemical interactions between skin sensitizers and nucleophilic amino acids. First, the preparation, storage, and analysis of RHE were optimized, and this work demonstrated that HR-MAS NMR was well adapted for investigating RHE with spectra of good quality allowing qualitative as well as quantitative studies of metabolites. Second, in order to study the response of RHE to chemical sensitizers, the ((13)C)methyldodecanesulfonate was chosen as an NMR probe, and we compared adducts formed on human serum albumin (HSA) in solution and adducts formed in RHE. Thus, while the modification of proteins or peptides in solution takes several days to lead to a significant amount of modification, in RHE the modifications of nucleophilic amino acids were observable already at 24 h. The chemioselectivity also appeared to be different with major modifications taking place on histidine, methionine, and cysteine residues in RHE, while on HSA, significant modifications were observed on lysine residues with the formation of methylated and dimethylated amino groups. We thus demonstrated that RHE could be used to investigate in situ chemical interactions taking place between skin sensitizers and nucleophilic amino acids. This opens perspectives for the molecular understanding of the skin immune system activation by sensitizing chemicals.