Altered lipid properties of the stratum corneum in Canine Atopic Dermatitis

Updated insights into the molecular pathogenesis of canine atopic dermatitis

Atopic dermatitis (AD) is a common and chronic inflammatory skin disease with frequent relapses. The genomics revolution has greatly contributed and revolutionised our knowledge of human AD; understanding the molecular skin fingerprint of AD and associated pathogenic immune pathways has led to preclinical assessments of several novel treatments. Initial studies using microarray analysis to analyse transcriptome (gene expression) changes provided relevant insight on the inflammatory and structural changes occurring at the time of acute or chronic AD skin lesions, or after immunomodulating treatments with drugs ciclosporin and dupilumab, a monoclonal antibody anti-IL4 receptor. The studies revealed that human AD is characterised by the activation of multiple cytokine pathways (predominance of T helper cell [Th]2 with some activation of Th1, Th17 and Th22) as well as dysregulated expression of barrier components in the skin. There are several reports on the expression of different single molecular targets (e.g. interleukin [IL]-13, CCL17 and periostin) in spontaneous canine AD (cAD). However, significant studies of the transcriptome have been limited to a single microarray study analysing chronic AD skin lesions in dogs. While revealing a large number of genes differentially expressed in cAD skin, the small sample size (n = 13 dogs) and the lack of changes in key epidermal barrier and inflammatory cytokine genes in the microarrays have inhibited discussion towards specific immunological changes. This review summarises the current literature regarding the molecular mechanisms of spontaneous cAD, including the recent data regarding RNA sequencing, and compares some pathogenic aspects to the previously published data from human AD.

Epidermal barrier impairment predisposes for excessive growth of the allergy-associated yeast Malassezia on murine skin

BACKGROUND

The skin barrier is vital for protection against environmental threats including insults caused by skin-resident microbes. Dysregulation of this barrier is a hallmark of atopic dermatitis (AD) and ichthyosis, with variable consequences for host immune control of colonizing commensals and opportunistic pathogens. While Malassezia is the most abundant commensal fungus of the skin, little is known about the host control of this fungus in inflammatory skin diseases.

METHODS

In this experimental study, MC903-treated mice were colonized with Malassezia spp. to assess the host-fungal interactions in atopic dermatitis. Additional murine models of AD and ichthyosis, including tape stripping, K5-Nrf2 overexpression and flaky tail mice, were employed to confirm and expand the findings. Skin fungal counts were enumerated. High parameter flow cytometry was used to characterize the antifungal response in the AD-like skin. Structural and functional alterations in the skin barrier were determined by histology and transcriptomics of bulk skin. Finally, differential expression of metabolic genes in Malassezia in atopic and control skin was quantified.

RESULTS

Malassezia grows excessively in AD-like skin. Fungal overgrowth could, however, not be explained by the altered immune status of the atopic skin. Instead, we found that by upregulating key metabolic genes in the altered cutaneous niche, Malassezia acquired enhanced fitness to efficiently colonise the impaired skin barrier.

CONCLUSIONS

This study provides evidence that structural and metabolic changes in the dysfunctional epidermal barrier environment provide increased accessibility and an altered lipid profile, to which the lipid-dependent yeast adapts for enhanced nutrient assimilation. Our findings reveal fundamental insights into the implication of the mycobiota in the pathogenesis of common skin barrier disorders.

The epidermal lipid-microbiome loop and immunity: Important players in atopic dermatitis

BACKGROUND

The promotion of epidermal barrier dysfunction is attributed to abnormalities in the lipid-microbiome positive feedback loop which significantly influences the imbalance of the epithelial immune microenvironment (EIME) in atopic dermatitis (AD). This imbalance encompasses impaired lamellar membrane integrity, heightened exposure to epidermal pathogens, and the regulation of innate and adaptive immunity. The lipid-microbiome loop is substantially influenced by intense adaptive immunity which is triggered by abnormal loop activity and affects the loop's integrity through the induction of atypical lipid composition and responses to dysregulated epidermal microbes. Immune responses participate in lipid abnormalities within the EIME by downregulating barrier gene expression and are further cascade-amplified by microbial dysregulation which is instigated by barrier impairment.

AIM OF REVIEW

This review examines the relationship between abnormal lipid composition, microbiome disturbances, and immune responses in AD while progressively substantiating the crosstalk mechanism among these factors. Based on this analysis, the "lipid-microbiome" positive feedback loop, regulated by immune responses, is proposed.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review delves into the impact of adaptive immune responses that regulate the EIME, driving AD, and investigates potential mechanisms by which lipid supplementation and probiotics may alleviate AD through the up-regulation of the epidermal barrier and modulation of immune signaling. This exploration offers support for targeting the EIME to attenuate AD.

Update on the skin barrier, cutaneous microbiome and host defence peptides in canine atopic dermatitis

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.

Primary Prevention of Canine Atopic Dermatitis: Breaking the Cycle-A Narrative Review

Canine atopic dermatitis (cAD) is a common and distressing skin condition in dogs, affecting up to 30% of the canine population. It not only impacts their quality of life but also that of their owners. Like human atopic dermatitis (hAD), cAD has a complex pathogenesis, including genetic and environmental factors. Current treatments focus on managing clinical signs, but they can be costly and have limitations. This article emphasizes the importance of preventing cAD from developing in the first place. Understanding the role of the skin's protective barrier is crucial, as its dysfunction plays a vital role in both hAD and cAD. hAD prevention studies have shown promising results in enhancing the skin barrier, but more research is needed to support more robust conclusions. While hAD primary prevention is currently a focal point of intensive investigation in human medicine, research on cAD primary prevention remains under-researched and almost non-existent. Pioneering effective prevention strategies for cAD holds immense potential to enhance the quality of life for both dogs and their owners. Additionally, it bears the promise of a translational impact on human research. Hence, further exploration of this crucial topic is not only relevant but also timely and imperative, warranting support and encouragement.

The skin barrier: An extraordinary interface with an exceptional lipid organization

The barrier function of the skin is primarily located in the stratum corneum (SC), the outermost layer of the skin. The SC is composed of dead cells with highly organized lipid lamellae in the intercellular space. As the lipid matrix forms the only continuous pathway, the lipids play an important role in the permeation of compounds through the SC. The main lipid classes are ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs). Analysis of the SC lipid matrix is of crucial importance in understanding the skin barrier function, not only in healthy skin, but also in inflammatory skin diseases with an impaired skin barrier. In this review we provide i) a historical overview of the steps undertaken to obtain information on the lipid composition and organization in SC of healthy skin and inflammatory skin diseases, ii) information on the role CERs, CHOL and FFAs play in the lipid phase behavior of very complex lipid model systems and how this knowledge can be used to understand the deviation in lipid phase behavior in inflammatory skin diseases, iii) knowledge on the role of both, CER subclasses and chain length distribution, on lipid organization and lipid membrane permeability in complex and simple model systems with synthetic CERs, CHOL and FFAs, iv) similarity in lipid phase behavior in SC of different species and complex model systems, and vi) future directions in modulating lipid composition that is expected to improve the skin barrier in inflammatory skin diseases.

Topically applied lipid-containing emulsions based on PEGylated emulsifiers: Formulation, characterization, and evaluation of their impact on skin properties ex vivo and in vivo

PEGylated emulsifiers have been largely used in topical formulations for skin research. They have been a continuous study focus in our group as well. According to our previous studies, severe interruptions of the skin barrier were observed with certain types of emulsifiers. To restore the skin barrier function and counteract the effects of emulsifiers, we considered topically delivering lipids into the lipid matrix of the SC. Herein, PEG-20 cetyl ether (C20) -based oil-in-water (O/W) emulsions were developed owing to the stronger interactions of C20 with skin. The lipids containing ceramides (Cers), palmitic acids (PA), and cholesterol with different ratios and combinations were merged into the base emulsion. PEG-40 stearyl ether (S40)-based emulsion was used as a reference as S40 showed negligible impact on SC lipids. The evaluations were conducted ex vivo with confocal Raman spectroscopy (CRS) regarding the SC lipid, SC thickness, and skin penetration properties. In parallel, the in vivo irritation studies were also implemented including the transepidermal-water-loss (TEWL), skin hydration, and erythema index. The results indicated less SC lipid extraction of topically delivered lipids on ex vivo porcine skin with the addition and ratio of incorporated Cers influencing the extent of formulations counteracting the skin interruption by C20. The ex vivo penetration study showed a similar trend in drug penetration depths. In regards to the in vivo studies, TEWL was demonstrated to be suitable for differentiating the impact on skin barrier properties. The in vivo observations were generally correlated with the ex vivo results. The exact findings in this research can lead us to a better selection of applied lipid components and compositions. Future research will elucidate which type of Cer was predominantly extracted by C20, advancing future formulation development.

Phytosphingosine ceramide mainly localizes in the central layer of the unique lamellar phase of skin lipid model systems

Understanding the lipid arrangement within the skin's outermost layer, the stratum corneum (SC), is important for advancing knowledge on the skin barrier function. The SC lipid matrix consists of ceramides (CERs), cholesterol, and free fatty acids, which form unique crystalline lamellar phases, referred to as the long periodicity phase (LPP) and short periodicity phases. As the SC lipid composition is complex, lipid model systems that mimic the properties of native SC are used to study the SC lipid organization and molecular arrangement. In previous studies, such lipid models were used to determine the molecular organization in the trilayer structure of the LPP unit cell. The aim of this study was to examine the location of CER N-(tetracosanoyl)-phytosphingosine (CER NP) in the unit cell of this lamellar phase and compare its position with CER N-(tetracosanoyl)-sphingosine (CER NS). We selected CER NP as it is the most prevalent CER subclass in the human SC, and its location in the LPP is not known. Our neutron diffraction results demonstrate that the acyl chain of CER NP was positioned in the central part of the trilayer structure, with a fraction also present in the outer layers, the same location as determined for the acyl chain of CER NS. In addition, our Fourier transformed infrared spectroscopy results are in agreement with this molecular arrangement, suggesting a linear arrangement for the CER NS and CER NP. These findings provide more detailed insight into the lipid organization in the SC lipid matrix.

Skin Barrier Reinforcement Effect Assessment of a Spot-on Based on Natural Ingredients in a Dog Model of Tape Stripping

Simple Summary

Canine atopic dermatitis is a disease of dogs in which the skin becomes permeable. Part of treating canine atopic dermatitis involves restoring the skin barrier function; however, few effective therapeutic options exist. The goal of this study was to evaluate the effect of a spot-on containing fatty acids, ceramides and essential oils on two parameters to evaluate the skin barrier function of dogs. We found that this spot-on had a protective effect on the skin barrier function for both parameters. This study suggests that the investigated product may be useful as an adjunctive treatment for canine atopic dermatitis.

Abstract

Skin barrier restoration is an important part of atopic dermatitis therapy. We investigated the effect of a spot-on containing plant-based essential fatty acids and essential oils on skin barrier parameters in a dog model of acute skin barrier disruption, using five healthy beagle dogs maintained in a laboratory setting. Four test sites on the dorsum and a control site on the abdomen were defined on each dog. Transepidermal water loss (TEWL) and skin surface hydration (SSH) were measured before and after tape stripping on the first day and then for three consecutive days, over four consecutive weeks. The spot-on was applied at the end of each of the first three weeks. The increase in TEWL after tape stripping was reduced after the spot-on application and reached control values in Weeks 3 and 4. SSH after tape stripping was reduced in Week 4 compared with the baseline. Thus, the ATOP 7^® spot-on significantly reduced acute skin barrier impairment in a dog model. The use of this product should be further evaluated as a potential treatment for skin barrier defects such as canine atopic dermatitis.

An explorative study comparing skin surface lipids in the West Highland white terrier dog with and without atopic dermatitis

Background

The skin barrier is important in the pathogenesis of atopic dermatitis and stratum corneum lipids have a critical role. Skin surface lipids have been largely overlooked but also contribute to barrier function. An untargeted approach was used to compare the skin surface lipids from atopic and non-atopic West Highland White terrier dogs (WHWT).

Objectives

The primary hypothesis was that a difference in the lipidome would exist. The secondary hypothesis was that affected and unaffected skin lipids would differ.

Animals and methods

This prospective, cross-sectional, case-controlled study included thirty-nine privately owned WHWTs. Dogs were assigned to one of four disease status groups based on strict criteria. Samples for lipid analysis were collected from the skin surface of unaffected and affected sites. Lipid analysis was by untargeted liquid chromatography/mass spectrometry and utilised lipid identification software packages. Principle component analysis (PCA) and partial least-squares discriminant analysis (sPLS-DA) statistical methods analysed the association between the relative lipid abundance and disease status and affected and unaffected skin.

Results

Samples for lipid analysis found 421 lipid soluble features of which ten lipids were positively identified. Statistical analysis could not distinguish between non-atopic and atopic dogs but did reveal a statistically significant difference in the lipid profiles from affected and non-affected skin irrespective of disease status.

Conclusions

A large array of unidentified lipids from the skin surface were found with a difference between affected and unaffected skin unrelated to disease status. Investigation into the lipidome of the skin surface is an emerging area of research with clinical and therapeutic applications.

Randomized, double-blind, placebo-controlled clinical trial measuring the effect of a dietetic food on dermatologic scoring and pruritus in dogs with atopic dermatitis

Background

Canine atopic dermatitis (AD) is a common condition that often requires multimodal therapy. Including a diet in the multimodal management of AD may reduce medication doses, saving pet owners money and reducing side effects. The objective of this randomized, double-blind, placebo-controlled clinical trial was to determine if a diet fortified in antioxidants, polyphenols, and omega-3 fatty acids can reduce the clinical signs of AD. Forty client-owned dogs with AD were enrolled in the study and assigned to either an enriched diet (diet B) or control diet (diet A) for 60-days. CADESI-4 index scores and owner-reported pruritus scores were measured periodically.

Results

Total CADESI-4 index scores for dogs eating diet B were lower on day 60 compared to baseline (P = 0.003). There was no statistical difference in scores for dogs eating diet A over a 60-day period. Diet B dogs had 25 and 49% reductions in CADESI-4 index scores on days 30 and 60, respectively (P = 0.0007) while diet A had no change over the study period. When comparing the percent change in owner-reported pruritus scores, diet B also performed better than diet A. By day 60, owners feeding diet B to their dogs reported a significant reduction (P < 0.0001) of 46.4% in itching, while those on diet A reported a 26.8% reduction, which was not statistically significant (P = 0.08).

Conclusions

These study results demonstrate feeding a diet enriched with ingredients to improve skin health and reduce inflammation improves the clinical signs of AD in dogs.

Ceramides in Skin Health and Disease: An Update

Ceramides are a class of sphingolipid that is the backbone structure for all sphingolipids, such as glycosphingolipids and phosphosphingolipids. While being a minor constituent of cellular membranes, ceramides are the major lipid component (along with cholesterol, free fatty acid, and other minor components) of the intercellular spaces of stratum corneum that forms the epidermal permeability barrier. These stratum corneum ceramides consist of unique heterogenous molecular species that have only been identified in terrestrial mammals. Alterations of ceramide molecular profiles are characterized in skin diseases associated with compromised permeability barrier functions, such as atopic dermatitis, psoriasis and xerosis. In addition, hereditary abnormalities of some ichthyoses are associated with an epidermal unique ceramide species, omega-O-acylceramide. Ceramides also serve as lipid modulators to regulate cellular functions, including cell cycle arrest, differentiation, and apoptosis, and it has been demonstrated that changes in ceramide metabolism also cause certain diseases. In addition, ceramide metabolites, sphingoid bases, sphingoid base-1-phosphate and ceramide-1-phosphate are also lipid mediators that regulate cellular functions. In this review article, we describe diverse physiological and pathological roles of ceramides and their metabolites in epidermal permeability barrier function, epidermal cell proliferation and differentiation, immunity, and cutaneous diseases. Finally, we summarize the utilization of ceramides as therapy to treat cutaneous disease.

Local and Systemic Changes in Lipid Profile as Potential Biomarkers for Canine Atopic Dermatitis

Lipids play a critical role in the skin as components of the epidermal barrier and as signaling and antimicrobial molecules. Atopic dermatitis in dogs is associated with changes in the lipid composition of the skin, but whether these precede or follow the onset of dermatitis is unclear. We applied rapid lipid-profiling mass spectrometry to skin and blood of 30 control and 30 atopic dogs. Marked differences in lipid profiles were observed between control, nonlesional, and lesional skin. The lipid composition of blood from control and atopic dogs was different, indicating systemic changes in lipid metabolism. Female and male dogs differed in the degree of changes in the skin and blood lipid profiles. Treatment with oclacitinib or lokivetmab ameliorated the skin condition and caused changes in skin and blood lipids. A set of lipid features of the skin was selected as a biomarker that classified samples as control or atopic dermatitis with 95% accuracy, whereas blood lipids discriminated between control and atopic dogs with 90% accuracy. These data suggest that canine atopic dermatitis is a systemic disease and support the use of rapid lipid profiling to identify novel biomarkers.

Advances in our understanding of canine atopic dermatitis

Canine atopic dermatitis (cAD) is a genetically inherited clinical syndrome that encompasses a diversity of mechanisms and can have a variety of triggers. Development of clinical disease is the result of genetic factors and environmental conditions, which shape the resulting immunological response. Clinical disease becomes evident once a threshold of inflammatory response is achieved. Skin barrier impairment plays a role in promoting cutaneous dysbiosis and increased allergen penetration. Keratinocytes shape the response of dendritic cells and subsequent lymphocytic response. Thymic stromal lymphopoietin is one of the links between the damaged skin barrier and the modulation of a T-helper (Th)2 response. It is still unclear whether mutations in skin barrier genes exist in atopic dogs, as they do in humans, or whether the observed alterations are purely secondary to inflammation. A dysregulated immune response with increased Th2, Th17 and CD4+ CD25+ regulatory T cells has been reported. A variety of cytokines [interleukin(IL)-31, IL-34, Macrophage migration inhibitory factor] are proposed as potential biomarkers and treatment targets because they are increased in the serum of atopic dogs when compared to controls, although a correlation between serum levels of these factors and severity of disease is not always present. The main issue with many published studies is that atopic dogs are always only compared to normal controls. Thus, it is unclear whether the changes that we find are truly a signature of cAD or merely a manifestation of nonspecific broad inflammatory responses. Studies considering comparison with other inflammatory diseases different from cAD are urgently needed to correctly identify what is specific to this complicated syndrome.

A descriptive study of allergen-specific IgE serological tests for canine atopic dermatitis in Thailand

Background

This study describes the usefulness of allergen-specific Immunoglobulin E (IgE) serology (ASIS) for identifying allergens in dogs with atopic dermatitis. ASIS tests were conducted in 23 dogs diagnosed with atopic dermatitis for indoor allergens (yeast and mites), outdoor allergens (grass pollen, weed pollen, and tree pollen), and fleas. The relationship among positive ASIS tests were determined using Pearson’s correlation coefficient (r).

Results

Of the atopic dogs, 26.09%, 4.35%, and 47.83% had positive ASIS tests for only indoor allergens, only outdoor allergens, and both indoor and outdoor allergens, respectively. The prevalence of positive ASIS tests was highest for mites (69.57%) and did not differ between indoor and outdoor allergens by age, breed, or sex. The prevalence of positive ASIS tests for indoor allergens during the rainy season (84.21%) was significantly higher than during winter (25.00%, P-value = 0.030). The correlation coefficient of the ASIS results among the outdoor allergens indicated a strong correlation between grass and tree pollen (r = 0.840, P-value < 0.01), grass and weed pollen (r = 0.812, P-value < 0.01), and tree and weed pollen (r = 0.714, P-value < 0.01). The correlation coefficient of the ASIS results of D. farinae indicated a strong correlation with A. siro (r = 0.951, P-value < 0.01) and a moderate correlation with B. tropicalis (r = 0.656, P-value < 0.01) and T. putrescentie (r = 0.672, P-value < 0.01).

Conclusions

ASIS tests are useful in screening for multiple allergens in dogs with atopic dermatitis. Dust mites are an important source of indoor allergens and may be responsible for a higher titer of IgE antibodies against indoor allergens during the rainy season.

Comparing the results of intradermal skin tests for four dust mite allergens in dogs with atopic dermatitis in Thailand

Background and Aim

Hypersensitivity to house dust mites is a common cause of atopic dermatitis in dogs. The intradermal test (IDT) identifies allergens to be included in allergen-specific immunotherapy. Common mite allergens used for IDT include single source extracts obtained from Dermatophagoides farinae or Dermatophagoides pteronyssinus or multisource extracts from multimite species (mixed mites), as well as a combination of multimite species and proteins from feces and shed skin (house dust). The objectives of the present study were to evaluate the prevalence of mite sensitivity in dogs diagnosed with atopic dermatitis in different Thailand provinces and to determine if positive test results to mite allergens aligned.

Materials and Methods

Eighty-two dogs (median age [range]: 5 years [11 months-11 years]; 51 males and 31 females) diagnosed with atopic dermatitis underwent IDTs with four different mite-related allergens (D. farinae, D. pteronyssinus, mixed mites, and house dust). The skin reactions were reported on a scale of 0-4 and the reactions 2+ were considered clinically relevant. The relationship between IDT results from different allergens was determined using Pearson's correlation coefficient (r). Fisher's exact test was used to compare IDT results for different mite allergens as well as for dogs residing in Bangkok versus other provinces in Thailand.

Results

The prevalence (95% confidence interval [CI]) of positive IDT results for D. farinae, D. pteronyssinus, mixed mites, and house dust in dogs with atopic dermatitis was 64.63% (52.30-74.88), 58.54% (47.12-69.32), 47.56% (36.41-58.89), and 35.37% (25.12-46.70), respectively. A moderate correlation was found in IDT results between D. pteronyssinus and house dust (r=0.514), between D. pteronyssinus and D. farinae (r=0.426), and between D. farinae and mixed mites (r=0.423). The prevalence of dogs with positive IDT results for mite allergens with mono-sensitization, bi-sensitization, tri-sensitization, and quadru-sensitization did not differ significantly between dogs residing in Bangkok (11.63%, 18.60%, 25.58%, and 16.28%) and dogs residing in other provinces (12.82%, 30.77%, 35.90%, and 10.26%). The overall sensitivity (95% CI) and specificity (95% CI) of the mixed mites test associated with atopic dermatitis in dogs were 60.32% (47.20-72.40%) and 94.70% (74.00-99.90%), respectively. The overall sensitivity (95% CI) and specificity (95% CI) of the house dust test associated with atopic dermatitis in dogs were 42.90% (30.50-56.00%) and 89.50% (66.90-98.70%), respectively.

Conclusion

House dust mites are an important source of allergens for dogs with atopic dermatitis. In the present study, no significant difference in the prevalence of atopic dermatitis was found in dogs living in the urban area compared with dogs living in the countryside. Application of multisource extracts from mites for IDT revealed a higher reaction to mixed mites than that of house dust.

Systematic Investigation of the Effect of Non-Ionic Emulsifiers on Skin by Confocal Raman Spectroscopy-A Comprehensive Lipid Analysis

Non-ionic emulsifiers are commonly found in existing pharmaceutical and cosmetic formulations and have been widely employed to enhance the penetration and permeation of active ingredients into the skin. With the potential of disrupting skin barrier function and increasing fluidity of stratum corneum (SC) lipids, we herein examined the effects of two kinds of non-ionic emulsifiers on intercellular lipids of skin, using confocal Raman spectroscopy (CRS) with lipid signals on skin CRS spectrum. Non-ionic emulsifiers of polyethylene glycol alkyl ethers and sorbitan fatty acid esters were studied to obtain a deep understanding of the mechanism between non-ionic emulsifiers and SC lipids. Emulsifier solutions and dispersions were prepared and applied onto excised porcine skin. Water and sodium laureth sulfate solution (SLS) served as controls. SC lipid signals were analysed by CRS regarding lipid content, conformation and lateral packing order. Polyethylene glycol (PEG) sorbitan esters revealed no alteration of intercellular lipid properties while PEG-20 ethers appeared to have the most significant effects on reducing lipid content and interrupting lipid organization. In general, the polyoxyethylene chain and alkyl chain of PEG derivative emulsifiers might indicate their ability of interaction with SC components. HLB values remained critical for complete explanation of emulsifier effects on skin lipids. With this study, it is possible to characterize the molecular effects of non-ionic emulsifiers on skin lipids and further deepen the understanding of enhancing substance penetration with reduced skin barrier properties and increased lipid fluidity.

Recent Advances on Topical Application of Ceramides to Restore Barrier Function of Skin

Human skin is the largest organ of the body and is an effective physical barrier keeping it from environmental conditions. This barrier function of the skin is based on stratum corneum, located in the uppermost skin. Stratum corneum has corneocytes surrounded by multilamellar lipid membranes which are composed of cholesterol, free fatty acids and ceramides (CERs). Alterations in ceramide content of the stratum corneum are associated with numerous skin disorders. In recent years, CERs have been incorporated into conventional and novel carrier systems with the purpose of exogenously applying CERs to help the barrier function of the skin. This review provides an overview of the structure, function and importance of CERs to restore the barrier function of the skin following their topical application.

The bacterial and fungal microbiome of the skin of healthy dogs and dogs with atopic dermatitis and the impact of topical antimicrobial therapy, an exploratory study

Canine atopic dermatitis is a genetically predisposed inflammatory and pruritic allergic skin disease that is often complicated by (secondary) bacterial and fungal (yeast) infections. High-throughput DNA sequencing was used to characterize the composition of the microbiome (bacteria and fungi) inhabiting specific sites of skin in healthy dogs and dogs with atopic dermatitis (AD) before and after topical antimicrobial treatment. Skin microbiome samples were collected from six healthy control dogs and three dogs spontaneously affected by AD by swabbing at (non-) predilection sites before, during and after treatment. Bacteria and fungi were profiled by Illumina sequencing of the 16S ribosomal RNA gene of bacteria (16S) and the internally transcribed spacer of the ribosomal gene cassette in fungi (ITS). The total cohort of dogs showed a high diversity of microbes on skin with a strong individual variability of both 16S and ITS profiles. The genera of Staphylococcus and Porphyromonas were dominantly present both on atopic and healthy skin and across all skin sites studied. In addition, bacterial and fungal alpha diversity were similar at the different skin sites. The topical antimicrobial treatment increased the diversity of bacterial and fungal compositions in course of time on both AD and healthy skin.

A canine keratinocyte cell line expresses antimicrobial peptide and cytokine genes upon stimulation with bacteria, microbial ligands and recombinant cytokines

Keratinocytes (KC) are the main cellular components of the stratum corneum that constitutes a solid physical skin barrier representing the first line of defense against pathogens. Moreover, KC are potent producers of inflammatory mediators and antimicrobial peptides (AMP) when activated through their pattern recognition receptors. In atopic dermatitis (AD) the protective skin barrier may be compromised due to barrier disruption, secondary infection and accelerated secretion of inflammatory cytokines which may also affect AMP expression in the skin. In the present study, we addressed the responses of a canine KC cell line upon exposure to Staphylococcus pseudintermedius, typically found on canine atopic skin during secondary infections, and stimulation by individual AD-associated ligands and cytokines. All stimuli induced a significant increase in expression of the pro-inflammatory cytokine genes tumor necrosis factor (TNF)-α and interleukin (IL)-8, but with different kinetics. Limited effects were observed on AMP gene expression except for K9CATH which was significantly upregulated upon bacterial infection but with none of the individual AD-associated ligands. Interestingly, K9CATH possessed antimicrobial activity towards Staphylococcus pseudintermedius, indicating that K9CATH expression is a specific defense reaction towards bacterial infection and not part of a general pro-inflammatory profile of KC.

Atopic dermatitis in cats and dogs: a difficult disease for animals and owners

The purpose of this review article is to give an overview of atopic dermatitis in companion animals and of recent developments including knowledge on immunological background, novel treatment options and difficulties in disease management. The prevalence of hypersensitivities seems to be increasing. The pathogenetic mechanisms are not fully understood, yet multiple gene abnormalities and altered immunological processes are involved. In dogs and cats, the diagnosis of atopic dermatitis is based on history, clinical examination and exclusion of other differential diagnoses. Intradermal testing or testing for serum allergen-specific Immunoglobulin E is only used to identify allergens for inclusion in the extract for allergen immunotherapy. Symptomatic therapy includes glucocorticoids, ciclosporin, essential fatty acids and antihistamines. A selective janus kinase 1 inhibitor and a caninized monoclonal interleukin-31 antibody are the newest options for symptomatic treatment, although longterm effects still need to be assessed. The chronic and often severe nature of the disease, the costly diagnostic workup, frequent clinical flares and lifelong treatment are challenging for owners, pets and veterinarians. Patience and excellent communication skills are needed to achieve a good owner compliance and satisfactory clinical outcome for the animal.