Optimization of a Canine-Specific Ceramide Complex and Evaluation of Its Effects on In Vitro and In Vivo Canine Skin

Alterations in the ceramide (CER) profile have been associated with atopic dermatitis in dogs; however, the specific effects of CER subclasses on canine keratinocytes remain unclear. This study aimed to optimize a CER complex and evaluate its effects on cytokine expression, CER synthesis, and skin barrier formation using canine epidermal keratinocyte progenitor (CPEK) cells and a reconstructed canine epidermis (RCE) model. Among various CER combinations tested, only the mixture of CER [NS] and [EOP] significantly reduced proinflammatory cytokine mRNA levels in Staphylococcus pseudintermedius-stimulated CPEK cells. Further optimization revealed that a 4:1 ratio of CER [NS] to [EOP] (cCER complex) markedly decreased CCL17 and CCL22 mRNA expression while upregulating keratin 10, ceramide synthase 3 (CERS3), and ceramide synthase 4, as well as enzymes involved in both de novo and salvage CER biosynthesis pathways. In the RCE model, cCER administration improved stratum corneum organization and increased the expression of loricrin, CERS3, and CER. In vivo application of cCER in dogs accelerated skin barrier repair and improved hair condition. These findings suggest that a CER [NS]/[EOP] mixture represents a promising therapeutic option with anti-inflammatory and skin barrier-enhancing effects for canine atopic dermatitis.