BackgroundNo study has directly compared the various treatment options for canine atopic dermatitis and their effects on skin barrier.Hypothesis/ObjectivesTo compare prednisone, oclacitinib, ciclosporin and lokivetmab treatment of atopic dermatitis.AnimalsNineteen atopic beagle dogs.Methods and materialsControlled, blinded study. Dogs were challenged with allergen twice weekly and randomized to oclacitinib, ciclosporin, lokivetmab, prednisone or no treatment for four weeks. Dermatitis and pruritus were assessed at baseline and after each challenge. Transepidermal water loss (TEWL) and hydration were measured at baseline, Day (D)14 and D28 (pinnae, axilla, groin). Area under the curve (AUC) was calculated for Canine Atopic Dermatitis Extent and Severity Index, 3rd iteration (CADESI‐03), pruritus, TEWL and hydration. For CADESI, the AUC of the first two weeks was compared to that of the last two weeks.ResultsFor CADESI, restricted maximum‐likelihood ANOVA showed effect of time (P = 0034) and group x time interaction (P = 0.0169). In the first two weeks, prednisone and oclacitinib were significantly lower than controls (P = 0.019 and P = 0.015, respectively). Lokivetmab prevented flares. Due to variability, no significance differences in pruritus were observed among groups. The TEWL increased with time in controls (P = 0.0237) and ciclosporin (P = 0.04, axilla, D28 versus D0) but not in the oclacitinib and lokivetmab groups. CADESI‐03 correlated with TEWL (P = 0.0043) and pruritus (P = 0.0283). Hydration did not correlate with any parameters. Hydration decreased in controls and prednisone group (axilla, D14 versus D0, P = 0.004 and P = 0.027, respectively). AUC for hydration, over time, was higher for lokivetmab and oclacitinib than controls (P = 0.014 and P = 0.04, respectively).Conclusions and clinical importanceLokivetmab prevented flares when given before challenge. Oclacitinib and lokivetmab have some positive effects on skin barrier parameters.

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Skin barrier dysfunction is important in atopic dermatitis and can be secondary to inflammation. Observation of keratinocytes in culture may show intrinsic differences. TransEpithelial Electrical Resistance (TEER) measures epithelial permeability. We cultured normal and atopic keratinocytes and found that TEER of atopic keratinocytes was significantly lower (p < 0.0001) than that of normals. Atopic keratinocytes grew upwards, first creating isolated dome-like structures and later horizontally into a monolayer. At time of confluence (D0), atopic keratinocytes were more differentiated, with higher filaggrin gene expression than normals. No differences existed between groups for TJ proteins (claudin, occludin, and Zonula Occludens-1) on D0 and D6. On D6, claudin and occludin were higher than D0, in normal (p = 0.0296 and p = 0.0011) and atopic keratinocytes (p = 0.0348 and 0.0491). Immunofluorescent staining showed nuclear location of filaggrin on D0 and cytoplasmic on D6. ANOVA showed increased cell size from D0 to D6 in both groups (effect of time, p = 0.0076) but no differences between groups. Significant subject effect (p = 0.0022) was found, indicating that cell size was subject-dependent but not disease-dependent. No difference for continuity for TJ protein existed between groups. These observations suggest that decreased TEER in atopics is not linked to TJ differences but is possibly linked to different growth behavior.

Canine progenitor epidermal keratinocytes (CPEK) are used as canine keratinocyte cell line. Their suitability for skin barrier studies is unknown. Measurement of transepithelial electric resistance (TEER) evaluates epithelial permeability. We compared TEER and tight junction (TJ) expression in CPEKs and normal keratinocytes (NK) harvested from biopsies of normal dogs. CPEKs and NK were grown until confluence (D0) and for 13 additional days. Slides were fixed on D0 and stained with ZO-1 and claudin-1 antibodies. Five images/antibody were taken, randomized and evaluated blindly by three investigators for intensity, staining location, granularity, and continuousness. Cell size and variability were evaluated. TEER increased overtime to 2000 Ohms/cm in NK, while remained around 100–150 Ohms/cm in CPEK. ANOVA showed significant effect of time (p < 0.0001), group (p < 0.0001) and group x time interaction (p < 0.0001) for TEER. Size of CPEKs was significantly (p < 0.0001) smaller and less variable (p = 0.0078) than NK. Intensity of claudin-1 staining was greater in CPEKs (p < 0.0001) while granularity was less in CPEKs (p = 0.0012). For ZO-1, cytoplasmic staining was greater in CPEK (p < 0.0001) while membrane continuousness of staining was greater in NK (p = 0.0002). We conclude that CPEKs grown in monolayer are not representative of NK for permeability studies.

This prospective, 4‐week, placebo‐controlled, cross‐over study aimed to investigate the efficacy of 1% topical κ‐opioid agonist, asimadoline, in a model of canine atopic dermatitis (AD). Fourteen beagles were challenged with house dust mites every 3–4 days for a total of 9 challenges. Severity of dermatitis was assessed, and pruritus was monitored using GoPro HERO cameras. Pruritus scoring was evaluated at 10 time periods; baseline, 4 h post allergen challenge and the last day of the study on Day 28. Scoring was done blindly by personnel using BORIS software. A global subjective score was also given using a visual analogue scale (VAS). A 4‐week washout period occurred and dogs were crossed‐over, the study was repeated, and the results were analysed using combined data. Gel was applied once daily on inguinal area (0.6 ml/dog). ANOVA showed significant effect of time (p < 0.0001) and group (p = 0.0001) on dermatitis scores. Overall, no statistically significant effect on pruritus was found due to a crossing of scores on Day 17. Overtime the placebo scores increased while the active ingredient showed decrease after first 3 weeks. It is concluded that this approach is promising in dogs with AD and longer studies with more frequent application may be beneficial.