Lipid content and water permeability of skin and oral mucosa

It has been claimed that total lipid content may be the critical factor determining the water permeability of skin. The present study examined this relationship in various oral epithelia and epidermis. Epithelia was heat separated from specimens of porcine skin, gingiva, buccal mucosa, palate, and floor of mouth. Lipids were solvent extracted and separated by thin layer chromatography with appropriate standards. The plates were sprayed with sulfuric acid and charred, and the concentration of lipids was determined by densitometry as mg lipid/gm tissue dry weight. Permeability constants were determined for each tissue by using tritiated water in perfusion chambers. When these values were compared over all regions, total lipid did not appear to be related to the permeability of these tissues. However, in the keratinized regions (epidermis, gingiva, and palate) a lower water permeability was related to a greater content of total lipid, nonpolar lipid, ceramide, and glucosylceramide. In non-keratinized tissues, a lower permeability corresponded to increased amounts of an unidentified glycosylceramide. The role of lipid in the permeability barrier of these tissues was further demonstrated by extracting specimens of skin and oral mucosa with chloroform/methanol and then determining Kp values; in both tissue regions, there was a significant increase in water permeability. Thus, although lipid is a component of the water permeability barrier in both skin and oral mucosa, different lipid components subserve this function in keratinized and non-keratinized tissues.