REGIONAL VARIATION IN CONTENT, COMPOSITION AND ORGANIZATION OF PORCINE EPITHELIAL BARRIER LIPIDS REVEALED BY THIN-LAYER CHROMATOGRAPHY AND TRANSMISSION ELECTRON-MICROSCOPY

Epidermis and oral epithelia provide permeability barriers that limit penetration of potentially harmful agents. Barrier function is determi ned by lipids in the superficial epithelial layers and varies regional ly by more than 10-fold. The purpose of this study was to determine wh ether differences in lipid content, composition or organization could account for this variation in barrier function. Stratum corneum from s kin, gingiva and palate and superficial layers from buccal regions and the floor of the mouth were isolated, and lipids were extracted and a nalysed by thin-layer chromatography. Tissue from each region was exam ined by electron microscopy. There was an inverse correlation between permeability and ceramide content and a direct correlation with trigly ceride content. Electron microscopy revealed that the intercellular sp ace in epidermal stratum corneum contained multiple lipid lamellae dis playing an alternating broad-narrow-broad spacing. In palatal and ging ival stratum corneum, uniformly spaced lamellae were present at the pe riphery of dilations of the intercellular space, but the interiors of the dilations contained disorganized lamellae and electron-dense mater ial. In the non-keratinized barriers, there was a single, broad lamell a at the cell periphery and occasional short stacks of lamellae traver sing the intercellular space. These intercellular lamellae may be deri ved from a population of membrane-coating granules that contain intern al lamellae. The results suggest that ceramides may be important barri er components, even in non-keratinizing epithelia where they are very minor components. Regional differences in the physical organization of barrier lipids may also contribute to differences in barrier function .