Amino acid composition, including key derivatives of eccrine sweat: potential biomarkers of certain atopic skin conditions

Synopsis The free amino acid (AA) composition of eccrine sweat is different from other biological fluids, for reasons which are not properly understood. We undertook the detailed analysis of the AA composition of freshly isolated pure human eccrine sweat, including some of the key derivatives of AA metabolism, to better understand the key biological mechanisms governing its composition. Eccrine sweat was collected from the axillae of 12 healthy subjects immediately upon formation. Free AA analysis was performed using an automatic AA analyser after ninhydrin derivatization. Pyrrolidine‐5‐carboxylic acid (PCA) and urocanic acid (UCA) levels were determined using GC/MS. The free AA composition of sweat was dominated by the presence of serine accounting for just over one‐fifth of the total free AA composition. Glycine was the next most abundant followed by PCA, alanine, citrulline and threonine, respectively. The data obtained indicate that the AA content of sweat bears a remarkable similarity to the AA composition of the epidermal protein profilaggrin. This protein is the key source of free AAs and their derivatives that form a major part of the natural moisturizing factor (NMF) within the stratum corneum (SC) and plays a major role in maintaining the barrier integrity of human skin. As perturbations in the production of NMF can lead to abnormal barrier function and can arise as a consequence of filaggrin genotype, we propose the quantification of AAs in sweat may serve as a non‐invasive diagnostic biomarker for certain atopic skin conditions, that is, atopic dermatitis (AD). Résumé La composition en acides aminés libres (AA) de la sueur eccrine est différente des autresfluides biologiques, pour des raisons qui ne sont pas bien comprises. Nous avons entrepris l'analyse détaillée de la composition des AA fraîchement isolés de la sueur eccrine humaine pure,y compris certains des dérivés clés du métabolisme des AA, afin de mieux comprendre les mécanismes biologiques qui régissent sa composition. La sueur eccrinea été recueillie auprès des aisselles de 12 sujets sains immédiatement après la formation. L'analyse des AA libres étaitréalisée à l'aide d'un analyseur automatique AA après dérivatisation à la ninhydrine.Le Pyrrolidine‐5‐carboxylique (PCA) et l'acide urocanique (UCA) ont été déterminéspar GC / MS. La composition en AA libres de la sueur a été dominée par la présence de la sérine, comptant pour un peu plus d'un cinquième de la composition totale en AA lib