Ceramide Profiling of Porcine Skin and Systematic Investigation of the Impact of Sorbitan Esters (SEs) on the Barrier Function of the Skin

The stratum corneum (SC) lipids provide the main barrier of the skin against the environment. Ceramides make up about half of the lipids by weight and are thus of particular interest. Emulsifiers are used in a multitude of topical formulations, e.g., to stabilize emulsions against coalescence. Investigations showed that some emulsifiers have the potential to impair skin barrier function. Sorbitan esters (SEs) are frequently used emulsifiers in pharmaceutical and cosmetic dermal formulations. Further, cholesterol and lecithin were used as natural alternatives. However, information on their impact on ceramides is very scarce. Thus, we first analyzed the SEs by LC-MS with regard to their composition. Then we developed an LC-MS method to identify and quantify the ceramides in porcine skin and subsequently investigated the impact of emulsifiers on the ceramide profile. Besides the LC-MS measurements, the effect of emulsifiers on the skin barrier function was investigated by trans-epidermal water loss (TEWL) measurements and confocal Raman spectroscopy (CRS). Throughout the experiments, water was used as a negative control and sodium lauryl sulfate (SLS) as a positive control. It was found that SEs are mixtures of mono-, di-, and triesters, partially with a complex fatty acid distribution. LC-MS measurements of the total ceramide content of the SC samples revealed the SE 60 and cholesterol-treated samples to be those showing the least ceramide depletion, implying a high skin tolerability in general. The TEWL measurements showed that SEs 40, 60, 80, and 120 showed no significant changes in skin barrier function. The lipid content, measured by CRS, was mostly decreased except for SE 120. Conformation, chain order, and SC thickness, also measured by CRS, showed no significant differences. These detailed investigations lead to the view that SEs are skin-friendly substances and can be used for topical applications, e.g., those commonly used to treat skin diseases.