FTIR spectroscopic analyses of the temperature and pH influences on stratum corneum lipid phase behaviors and interactions

New Advances on the Functions of Epidermal Growth Factor Receptor and Ceramides in Skin Cell Differentiation, Disorders and Cancers

“…Notably, the structural characteristics of the natural ceramides found in SC which are composed of long nonpolar acyl chains and a small polar headgroup permit these lipids to adopt a closely packed arrangement in SC lamellar bilayers that contributes to the effective functioning of the skin permeability barrier [54][55][56][57][58][59][60][61]. In addition to ceramides, the SC lipid lamellae contain a large amount of free fatty acids and cholesterol, which also assume a critical function in maintaining SC structural integrity and cohesion [4,6,9,[61][62][63][64][65]. The outermost layer of the epidermis consists of keratinized and dead cornified cells called corneocytes which are rich in proteins, such as keratins, but do not contain any lipids.…”

“…This function has been principally associated with SC structure and lipid composition [1][2][3][4][5][6][7][8][54][55][56][57][58][59][60][61]. In particular, the ceramides from SC, with the exception of ceramide 1, are lipids with saturated acyl chains which permit a very tightly packed stacking and the formation of a lamellar structure that is highly water impermeable and oxidation resistant.…”

“…All the types of ceramides contribute to the permeability barrier, but only ceramide 1 acts as a rivet between the lipid disks of the matrix and, thereby, permits the fusion and stabilization of the intercellular lipid lamellae [10,54]. In addition, fatty acids as well as cholesterol and cholesterol sulfate, whose sterols are responsible for the cohesion between the keratinocytes, are important for maintaining the SC structural architecture and permeability barrier [9,[61][62][63][64][65][66][67][68]. In fact, the ordered lamellar structure of the intercellular lipids of SC, including the formation of crystalline and liquid domains, is considered to be crucial for the skin barrier function [54,56,61,[63][64][65]69].…”

“…Notably, it has been proposed that the stability of SC could be due, in part, to the formation of strong hydrogen bonds and van der Waals interactions in interfacial and hydrophobic regions of the intercellular lamellar lipids [69]. Moreover, certain studies revealed that the mixtures prepared with isolated SC lipids mimic the SC lipid phase behavior very well suggesting that other SC constituents, including the proteins and corneocytes, do not significantly influence the SC lipid phase behavior [56,61,64,70,71]. In particular, investigations of the model membranes composed of ceramides, palmitic acid and sterols carried out by NMR spectroscopy and X-ray diffraction electron miscroscopy revealed that these lipid dispersions adopt a highly ordered bilayer structure at low temperatures, while hexagonal packing was observed at temperatures above 60°C [63,66,69].…”

“…In particular, investigations of the model membranes composed of ceramides, palmitic acid and sterols carried out by NMR spectroscopy and X-ray diffraction electron miscroscopy revealed that these lipid dispersions adopt a highly ordered bilayer structure at low temperatures, while hexagonal packing was observed at temperatures above 60°C [63,66,69]. In addition, it has been observed that the changes in the proportion of these three lipid species as well as the ceramide types used in the mixtures significantly alter the thermal phase behavior, which suggests that a specific content and class of lipids may be necessary for maintaining the permeability barrier function of SC [61,70,72].…”