Increased transepidermal water loss and decreased ceramide content in lesional and non-lesional skin of dogs with atopic dermatitis

This study evaluated changes in transepidermal water loss (TEWL), skin hydration and intercorneal lipid content in dogs with atopic dermatitis (AD). TEWL and skin hydration were measured in the inguinal skin of 10 dogs with AD and 30 normal dogs. TEWL was significantly higher in both lesional skin (94.3 ± 38.8 g/m²/h) and non-lesional skin (28.8 ± 9.5) of dogs with AD than healthy controls (12.3 ± 2.3) (P < 0.05). Water content in the lesional skin of dogs with AD (15.8 ± 7.0 AU) was significantly lower than that of controls (24.2 ± 8.8) (P < 0.05), whereas no significant differences were recognized in water content between non-lesional skin of dogs with AD and controls. To compare the lipid content between lesional and non-lesional skin of dogs with AD and controls, intercorneal lipids, extracted from the stratum corneum, were quantified by thin-layer chromatography. The relative amounts of ceramides in the lesional skin (24.4 ± 5.6%) and non-lesional skin (25.6 ± 3.8%) of dogs with AD were significantly lower than those in controls (31.4 ± 6.9%) (P < 0.05). Conversely, no significant differences were recognized in the relative amounts of cholesterols and free fatty acids (FFA) between dogs with AD and controls. Moreover, there are statistical correlations between TEWL and the relative amounts of ceramides, but not those of cholesterols and FFA, in both lesional and non-lesional skin of dogs with AD. These results strongly suggest that decreased ceramide content accelerates TEWL in dogs with AD, similar to the situation seen in the corresponding human disease.