Cowhage can induce itch in the atopic dog

Characterization of a chloroquine-induced canine model of pruritus and skin inflammation

BACKGROUND

Chloroquine (CQ) is a prototypical systemic and intradermal pruritogen for histamine-independent (nonhistaminergic) itch in mice and humans. The predictive validity of this model is poorly documented in dogs.

HYPOTHESIS/OBJECTIVE

To determine pruritogenic and inflammatory effects of systemic and i.d. CQ injections in healthy dogs.

ANIMALS

Ten healthy purpose-bred laboratory beagles.

METHODS AND MATERIALS

All dogs were randomized to receive i.d. (200 and 400 µg/site), intravenous (2 mg/kg) and subcutaneous (3 mg/kg) CQ injections. Dogs were video-recorded for 30 min after i.d. injections and for 300 min after i.v. and s.c. injections. Buffered saline injections served as controls for each route. Global wheal scores were evaluated at 30 min post-i.d. injection by a blinded investigator.

RESULTS

All dogs showed wheal and erythema at the CQ i.d. injection sites; global wheal scores of each CQ concentration were significantly increased compared to placebo (P ≤ 0.05). Blinded evaluation revealed no significant increase in generalized pruritic behaviour (pruritic seconds) after i.v. or s.c. administration of CQ. Intradermal injections induced mild localized acute pruritic behaviours at the site of injections at 200 µg (P = 0.06) and 400 µg (P = 0.27) CQ in dogs.

CONCLUSION AND CLINICAL SIGNIFICANCE

To the best of the authors' knowledge, this is the first report which shows that i.d. CQ injections may induce acute inflammation in healthy dogs. By contrast to the systemic CQ-induced pruritus reported previously in healthy mice and dogs, no significant pruritic behaviours were observed after CQ injection, regardless of the route of administration.

Atopic itch in dogs: pharmacology and modeling

Itch is the most common clinical problem seen in dogs with skin diseases. Although an etiological classification of canine pruritus does not yet exist, most causes would likely fall into the IFSI class I (dermatological) itch. One of the most common causes of canine itch is that associated with atopic dermatitis, and there is randomized controlled trial grade evidence of the efficacy of several antipruritic interventions. At this time, the mainstay of treatment of canine atopic itch relies principally on the use of topical and/or oral glucocorticoids and oral cyclosporine. Type 1 receptor antihistamines are notorious in their inconsistency in reducing pruritus in atopic dogs. A new Janus kinase (JAK)-1 inhibitor has recently been approved for treatment of allergic itch in dogs, and its onset of efficacy is remarkably fast. Modeling itch in dogs can be achieved by allergen sensitization (fleas, house dust mites), and challenges that elicit pruritic manifestation can be used for mechanistic studies as well as for testing of novel anti-itch modalities.