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Background: Canine atopic dermatitis (AD) is a complex inflammatory skin disease associated with cutaneous microbiome, immunological and skin barrier alterations. This review summarises the current evidence on skin barrier defects and on cutaneous microbiome dysfunction in canine AD. Objective: To this aim, online citation databases, abstracts and proceedings from international meetings on skin barrier and cutaneous microbiome published between 2015 and 2023 were reviewed. Results: Since the last update on the pathogenesis of canine AD, published by the International Committee on Allergic Diseases of Animals in 2015, 49 articles have been published on skin barrier function, cutaneous/aural innate immunity and the cutaneous/aural microbiome in atopic dogs. Skin barrier dysfunction and cutaneous microbial dysbiosis are essential players in the pathogenesis of canine AD. It is still unclear if such alterations are primary or secondary to cutaneous inflammation, although some evidence supports their primary involvement in the pathogenesis of canine AD. Conclusion and Clinical Relevance: Although many studies have been published since 2015, the understanding of the cutaneous host–microbe interaction is still unclear, as is the role that cutaneous dysbiosis plays in the development and/or worsening of canine AD. More studies are needed aiming to design new therapeutic approaches to restore the skin barrier, to increase and optimise the cutaneous natural defences, and to rebalance the cutaneous microbiome. [ABSTRACT FROM AUTHOR]

Atopic dermatitis (AD)/atopic eczema is a chronic relapsing inflammatory skin disease affecting nearly 14% of the adult population. An important pathogenetic pillar in AD is the disrupted skin barrier function (SBF). The atopic stratum corneum (SC) has been examined using several methods, including Raman microspectroscopy, yet so far, there is no depth-dependent analysis over the entire SC thickness. Therefore, we recruited 21 AD patients (9 female, 12 male) and compared the lesional (LAS) with non-lesional atopic skin (nLAS) in vivo with confocal Raman microspectroscopy. Our results demonstrated decreased total intercellular lipid and carotenoid concentrations, as well as a shift towards decreased orthorhombic lateral lipid organisation in LAS. Further, we observed a lower concentration of natural moisturising factor (NMF) and a trend towards increased strongly bound and decreased weakly bound water in LAS. Finally, LAS showed an altered secondary and tertiary keratin structure, demonstrating a more folded keratin state than nLAS. The obtained results are discussed in comparison with healthy skin and yield detailed insights into the atopic SC structure. LAS clearly shows molecular alterations at certain SC depths compared with nLAS which imply a reduced SBF. A thorough understanding of these alterations provides useful information on the aetiology of AD and for the development/control of targeted topical therapies. [ABSTRACT FROM AUTHOR]

Ceramides (CERs) are the backbone of the intercellular lipid lamellae of the stratum corneum (SC), the outer layer of the skin. Skin diseases such as atopic dermatitis, psoriasis, and aged skin are characterized by dysfunctional skin barrier and dryness which are associated with reduced levels of CERs. Replenishing the depleted epidermal CERs with exogenous CERs has been shown to have beneficial effects in improving the skin barrier and hydration. The exogenous CERs such as phyto-derived CERs (PhytoCERs) can be delivered deep into the SC using novel topical formulations. This, however, requires investigating the rate and extent of skin permeation of CERs. In this study, an LC/APCI-MS method to detect and quantify PhytoCERs in different layers of the skin has been developed and validated. The method was used to investigate the skin permeation of PhytoCERs using Franz diffusion cells after applying an amphiphilic cream containing PhytoCERs to the surface of ex vivo human skin. As plant-specific CERs are not commercially available, well-characterized CERs isolated from oat (Avena abyssinica) were used as reference standards for the development and validation of the method. The method was linear over the range of 30-1050 ng/mL and sensitive with limit of detection and quantification of 10 and 30 ng/mL, respectively. The method was also selective, accurate, and precise with minimal matrix effect (with mean matrix factor around 100%). Even if more than 85% of oat CERs in the cream remained in the cream after the incubation periods of 30, 100, and 300 min, it was possible to quantify the small quantities of oat CERs distributed across the SC, epidermis, and dermis of the skin indicating the method’s sensitivity. Therefore, the method can be used to investigate the skin permeation of oat CERs from the various pharmaceutical and cosmeceutical products without any interference from the skin constituents such as the epidermal lipids.ᅟ [ABSTRACT FROM AUTHOR]