Changes in the composition of molecular species of covalently bound and free ceramides [EOS], and their correlation with disease severity in atopic dermatitis

Abstract Ceramides are major constituents of stratum corneum (SC) intercellular lipids involved in skin barrier function. The ratio of molecular species of ceramides and their correlation with disease severity was examined in patients with atopic dermatitis (AD). Thirty‐eight patients with AD and 32 healthy controls (HCs) were assessed for transepidermal water loss, SC collection and clinical assessment. The ceramide content of different molecular species in the samples was quantified using high‐performance liquid chromatography coupled with tandem mass spectrometry. Unsaturated acyl chains of both covalently bound and free ceramides [EOS] were higher in AD lesional skin than those in AD non‐lesional or normal HC skin. The proportion of unsaturated acyl chains (C30:1, C32:1 and C34:1) was higher than other ceramide molecular species among covalently bound and free ceramides [EOS] in patients with AD. The proportion of unsaturated acyl chains in covalently bound ceramides was positively correlated with transepidermal water loss ( r = 0.600) when considering the total number of non‐lesional and lesional skin. Additionally, thymus and activation‐regulated chemokine (TARC) showed a positive correlation with unsaturated acyl chains proportion in AD non‐lesional ( r = 0.676) and lesional ( r = 0.503) skin. Our study is the first to show the increase in unsaturated acyl chains of both covalently bound and free ceramides [EOS] in lesional and non‐lesional skin in AD for each molecular species. This increase is associated with dryness and impaired barrier function, which correlates with TARC levels, a marker for the degree of type 2 inflammation. We speculate that type 2 inflammation exacerbation leads to abnormal epidermal lipid metabolism in the skin of patients with AD.