Stratum corneum lipid abnormalities in UVB-irradiated skin

Stratum corneum (SC) lipids are of particular importance in maintaining the permeability barrier function, Although many studies have demonstrated tha t UVB irradiation of mammalian skin reduces barrier function, the responsib le alterations in SC lipid profiles are not known. In this study, we invest igated both compositional and morphological alterations in SC lipids with t he development of barrier abnormalities caused by daily UVB irradiation in hairless rat skin. The UVB irradiation of suberythemal doses (0.5 minimal e rythema dose) significantly increased transepidermal water loss (TEWL) rela tive to nonirradiated control, indicating a diminished barrier function. Un der these conditions, the total amounts of major SC lipid species (ceramide s, cholesterol, free fatty acids) in UVB-irradiated SC did not differ from those in nonirradiated SC. However, electron microscopic observations revea led marked abnormalities in the intercellular domains of UVB-irradiated SC, where naturally occurring intercellular multilamellar structures were ofte n absent and leaving the area with the appearance of an empty space. Moreov er, in UVB-irradiated SC, individual corneocytes often showed small amounts of intercellular deposition product with abnormal lamellar structure, wher e lamellar body sphingomyelinase activity was present. These observations d emonstrated a partial failure of lamellar body secretion in UVB-irradiated SC and suggested that a defect in the secretion of lamellar body-derived li pids and enzymes to SC intercellular space is, at least in part, responsibl e for the observed abnormal intercellular structure and barrier disruption.