Abstract
The skin surface lipids (SSL) result from the blending of sebaceous and epidermal lipids, which derive from the sebaceous gland (SG) secretion and the permeability barrier of the stratum corneum (SC), respectively. In humans, the composition of the SSL is distinctive of the anatomical distribution of the SG. Thus, the abundance of sebum biomarkers is consistent with the density of the SG. Limited evidence on the influence that the SG exerts on the SC lipidome is available. We explored the differential amounts of sebaceous and epidermal lipids in areas at different SG density with lipidomics approaches. SC was sampled with adhesive patches from forearm, chest, and forehead of 10 healthy adults (8F, 2M) after mechanical removal of sebum with absorbing paper. Lipid extracts of SC were analysed by HPLC/(-)ESI-TOF-MS. In the untargeted approach, the naïve molecular features extraction algorithm was used to extract meaningful entities. Aligned and normalized data were evaluated by univariate and multivariate statistics. Quantitative analysis of free fatty acids (FFA) and cholesterol sulfate (CHS) was performed by targeted HPLC/(-)ESI-TOF-MS, whereas cholesterol and squalene were quantified by GC-MS. Untargeted approaches demonstrated that the relative abundance of numerous lipid species was distinctive of SC depending upon the different SG density. The discriminating species included FFA, CHS, and ceramides. Targeted analyses confirmed that sebaceous FFA and epidermal FFA were increased and decreased, respectively, in areas at high SG density. CHS and squalene, which are biomarkers of epidermal and sebaceous lipid matrices, respectively, were both significantly higher in areas at elevated SG density. Overall, results indicated that the SG secretion intervenes in shaping the lipid composition of the epidermal permeability barrier.
Highlights
Skin is a tissue exceptionally enriched in lipids
Twenty-four stratum corneum (SC) samples were collected from forearms (ARM), chests (CHEST), and foreheads (HEAD) of 8 females, whereas four SC samples were obtained from ARM and HEAD of 2 males
While the weight of the SC sampled at the CHEST was not significantly different from the one determined at the ARM site, the SC sampled at the HEAD site was significantly higher than both ARM and CHEST (p = 0.002, and p = 0.001, respectively)
Summary
Skin is a tissue exceptionally enriched in lipids. The involvement of skin lipids in the maintenance of skin and entire body homeostasis is well documented[1,2]. Squalene is specific to human sebum where it is present at exceptionally high concentrations compared to other body lipid compartments. The epidermal lipid compartment localized in the SC contains approximately 50% ceramides, 15% FFA, and 25% cholesterol and cholesterol sulfate (CHS)[6,13,14] The latter one is present at a fairly high concentration in the SC wherein it regulates cohesion and desquamation. Approaches to investigate the two major skin lipid sources have been designed for both sebum and epidermal lipids[12,18,26,27,28,29,30,31,32,33,34,35]. The present results open new perspectives in the investigation of the role of SG in the SC homeostasis and dysfunction
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