A study of human atopic dermatitis (AD) showed obvious reduction of protein-bound ceramides in AD skin compared with normal skin. The canine stratum corneum (SC) has a pattern of free and protein-bound ceramides like that in humans. The SC of atopic dogs shows decreased free lipids and a highly significant reduction of protein-bound fatty acids and ceramides compared to normal canine SC. Large amounts of glucosylceramides are present, although they are nearly absent in normal canine SC.

This study analyzed the changes that occurred in SC lipids of dogs after 3 weeks of topical treatment with an emulsion (skin lipid complex [SLC]) containing ceramides, free fatty acids (FFAs), and cholesterol. Nonlesional SC was collected from control and treated areas of both atopic and healthy dogs. Free and protein-bound lipids were purified, analyzed, and assayed. Levels of cholesterol and FFAs were lower in atopic dogs, although differences were not significant. Total ceramides were significantly reduced in untreated atopic SC, and high levels of glucosylceramides were found, in contrast to their near absence in normal SC. Free ceramide content of atopic SC was significantly increased after treatment, near that of normal canine SC; glucosylceramides were barely detectable. Topical treatment with SLC resulted in significant improvement of lipid biosynthesis of keratinocytes in atopic dogs, potentially enabling the formation of a tighter epidermal barrier.

Commentary
The clinical features of human and canine AD are similar and appear to result from an impaired skin barrier, resulting in increased transepidermal water loss. In this study, twice-weekly application of a sphingolipid-containing emulsion resulted in significant increases in free ceramides and normalization of glucosylceramides within the SC of atopic dogs. There were also increases in some protein-bound ceramides within treated SC, suggesting treatment with this emulsion may stimulate biosynthesis of some ceramides rather than simply replenishing deficient quantities. Further studies are needed to show whether repair of deficient skin barrier function in atopic dogs results in reduced clinical disease.—Lisa Akucewich, DVM, DACVD

Source
The lipid alterations in the stratum corneum of dogs with atopic dermatitis are alleviated by topical application of a sphingolipid-containing emulsion. Popa I, Remoue N, Osta B, et al. CLIN EXP DERMATOL doi: 10.1111/j.1365-2230.2011.04313.x.