Impact of sorbitan esters and topical formulation containing sorbitan monostearate on the skin barrier function

Abstract

Skin research offers a wide range of methods with many challenges. In the following thesis, the main focus was the effect of emulsifiers on porcine skin. The opportunities provided by TEWL (trans-epidermal water loss) measurements were investigated. A protocol was developed for measuring in-vitro in porcine skin. Some emulsifiers, like S20 (PEG-20 stearyl ether) and C20 (PEG-20 cetyl ether) showed adverse effects, while S40 (PEG-40 stearyl ether), S100 (PEG-100 stearyl ether), SE 60 (Sorbitan monostearate), SE 80 (Sorbitan monooleate), cholesterol and lecithin showed none. A multimodal approach was developed to analyze the impact of emulsifiers on the skin barrier function. TEWL, CRS (confocal Raman spectroscopy), and LC-MS (liquid chromatography-mass spectrometry) were combined to analyze sorbitan esters effects on porcine SC (stratum corneum). The determination of lipids with CRS and LC-MS offered the possibility to analyze the SC's ceramides individually and to obtain a specific ceramide profile for each sample. Sorbitan esters showed no adverse effects on the skin barrier function whereas SLS did. Formulations for basic therapy containing sorbitan monostearate and PEG— (polyethylene glycol) 100 stearyl ether were developed and tested on porcine skin in- vitro. Initially, the formulations were tested for its stability by rheology and polarized light microscopy. Afterward, the effects on porcine skin barrier function were analyzed by TEWL and pyranine staining to image the lipids uptake by fluorescent light microscopy. It was shown that the developed formulations delivered lipids to the SC that had been partially lipid extracted prior to the investigation. This underlines the importance of testing topical formulations with respect to their real effects on the skin. The effectiveness of these formulations for treatment of skin diseases is an important parameter for basic therapy.