Quantitative IR Spectroscopy Studies of Changes in Lipid Dynamics and Organization in Isolated Stratum Corneum Exposed to Basic pH

Abstract

The outer layers of the epidermis, the stratum corneum (SC), provide the barrier function that is essential to life, primarily through the extracellular lamellar lipid matrix. Previous IR spectroscopy studies of isolated SC have shown the presence of ordered lipid bilayers, packed in orthorhombic and hexagonal domains. This lipid organization is essential to the barrier function of SC. In the current work we have investigated the effect of basic pH on lipid organization in SC. The outer surface of skin is routinely subjected to pH 10 solutions when exposed to soaps during cleansing. This exposure to basic pH has been shown to result in reduced barrier function and can lead to clinical irritation of the skin. Using IR spectroscopy methods previously developed in our laboratories to study isolated SC, we have examined the effect of pH 10 exposure on lipid organization in SC, monitoring both the intra- and inter-molecular lipid organization. The results of these studies show the Tm of SC lipids is significantly increased after pH 10 exposure. Furthermore, the change in bilayer Tm is not reversible. To explore changes in lipid packing underlying the pH-induced change in Tm, we are developing quantitative approaches evaluating changes in the amount of orthorhombic and hexagonal chain packing in normal and challenged SC. The results of these quantitative approaches to chain packing are being correlated to the changes in conformational order and increasing Tm after SC is exposed to pH 10. We will present our IR spectroscopic data showing irreversible increases in lipid Tm and the accompanying quantitative analysis of lipid packing changes.