Evaluation of compound 48/80 as a model of immediate hypersensitivity in the skin of dogs

Effect of diphenhydramine and cetirizine on immediate and late-phase cutaneous allergic reactions in healthy dogs: a randomized, double-blinded crossover study

BACKGROUND

Currently, there is insufficient evidence to confirm oral diphenhydramine (DPH) efficacy to prevent mast cell degranulation and histamine release in dogs.

HYPOTHESIS/OBJECTIVE

To determine and compare the effects oral of DPH and cetirizine on the immediate- and late-phase cutaneous allergic reactions in healthy dogs.

ANIMALS

Twelve healthy laboratory beagle dogs.

METHODS AND MATERIALS

The study was designed as a randomized, double-blinded crossover study in which each dog served as its own control; twice-daily oral DPH (2.2 mg/kg) or cetirizine (2 mg/kg) were given for six days with a two week washout period. Intradermal injections of histamine, compound 48/80 (positive control) and saline (negative control) were performed on the right thorax 10 days before drug administration (baseline), during oral antihistamine administration on Day 6 and 10 days after last medication dosage. Global wheal scores (GWS) at 20 min and late-phase reactions (LPR) at 6 h post-injection were evaluated by an investigator blinded to the drug and the interventions.

RESULTS

Treatment with cetirizine significantly reduced histamine and compound 48/80 GWS and LPR compared to baseline; there was no significant difference for DPH. In all dogs, oral DPH and cetirizine reached plasma concentrations considered therapeutic in people. No adverse effect or behavioural changes were observed during the study.

CONCLUSION AND CLINICAL SIGNIFICANCE

In conclusion, oral cetirizine was effective in preventing cutaneous allergic reactions without any obvious adverse effects in dogs. Oral DPH failed to show an inhibitory effect despite attaining plasma drug concentrations that are considered effective in people.

Dose-dependent pruritogenic and inflammatory effects of intradermal injections of histamine, compound 48/80 and anti-canine IgE in healthy dogs

BACKGROUND

Scratching behaviours associated with intradermal (i.d.) injection of pruritogens such as histamine and compound 48/80 into the skin of mice and humans is the commonly used model to advance itch research and drug development. The predictive validity of this model is poorly documented in dogs.

OBJECTIVES

To evaluate the dose-dependent effects of pruritogenic substances, each with a different mechanism of action, in healthy dogs.

ANIMALS

Ten healthy laboratory beagles.

METHODS AND MATERIALS

All dogs were video-recorded for 30 min post-injection (mpi) of i.d. goat anti-canine IgE (4 and 25 μg/site), histamine and compound 48/80 (50, 100, 200, 400 μg/site); two buffered saline injections served as controls. Two blinded investigators reviewed the pruritic behaviours of all video recordings. Global wheal scores were evaluated at 30 min by a blinded investigator.

RESULTS

All dogs showed wheal and erythema at the pruritogen injection site; global wheal scores at 30 min of each substance significantly increased at all concentrations compared to control (P ≤ 0.05). A blinded evaluation revealed that all pruritogens induced mild acute pruritic behaviours at the site of injection. There was no injection site pain seen in any dog. Compared to controls, injections of pruritogens did not significantly affect the pruritic seconds or occurrence of pruritic episodes for any of the substances.

CONCLUSIONS AND CLINICAL SIGNIFICANCE

These preliminary results suggest that i.d. injections of the studied pruritogens can induce cutaneous wheal and flare response in healthy dogs; but inconsistencies occur in the induction of itch, even with the different concentrations of pruritogens.

Ultramicronized palmitoylethanolamide counteracts the effects of compound 48/80 in a canine skin organ culture model

BACKGROUND

Ultramicronized palmitoylethanolamide (PEA-um) has been reported to reduce pruritus and skin lesions in dogs with moderate atopic dermatitis and pruritus.

HYPOTHESIS/OBJECTIVES

A canine ex vivo skin model was used to investigate the ability of PEA-um to counteract changes induced by compound 48/80, a well-known secretagogue that causes mast cell degranulation.

ANIMALS

Normal skin was obtained from three donor dogs subjected to surgery for reasons unrelated to the study.

METHODS

Cultured skin biopsy samples in triplicate were treated with 10 and 100 μg/mL compound 48/80, without or with 30 μM PEA-um. Mast cell (MC) degranulation, histamine release into the culture medium, local microvascular dilatation, epidermal thickness, keratinocyte proliferation and epidermal differentiation markers were evaluated.

RESULTS

Exposure of the skin organ culture to PEA-um 24 h before and 72 h concomitantly to compound 48/80 resulted in a significant decrease of degranulating MCs. PEA-um also reduced the histamine content in the culture medium by half, although the effect did not reach statistical significance. PEA-um significantly counteracted vasodilation induced by 100 μg/mL compound 48/80. Finally, PEA-um alone did not induce changes in epidermal thickness, differentiation markers, keratinocyte proliferation, MC density and/or degranulation.

CONCLUSIONS AND CLINICAL IMPORTANCE

Collectively, these results support the protective action PEA-um on the skin of dogs undergoing allergic changes.

Novel phenotype in beagle dogs characterized by skin response to compound 48/80 focusing on skin mast cell degranulation

Beagle dogs have long been employed in toxicology studies and as skin disease models. Compared with other experimental animal species, they are known to be susceptible to skin responses, such as rashes, from exposure to various chemical compounds. Here, a unique dog phenotype was identified that showed no skin response to compound 48/80, a mast cell degranulating agent. Although the skin responses to intradermal injection of polyoxyethylene castor oil derivative (HCO-60, a nonionic detergent), histamine dihydrochloride, concanavalin A (IgE receptor-mediated stimuli), or calcium ionophore A23187 were comparable in wild-type (WT) dogs and these nonresponder (NR) dogs, only the response to compound 48/80 was entirely absent from NR dogs. The skin mast cell density and histamine content per mast cell were histologically comparable between WT and NR dogs. By checking for skin responses to compound 48/80, NR dogs were found to exist at the proportion of 17-20% among four animal breeders. From retrospective analysis of in-house breeding histories, the NR phenotype appears to conform to the Mendelian pattern of recessive inheritance. The standard skin response in WT dogs developed at 2-4 months of age. In conclusion, this unique phenotype, typified by insensitivity in the compound 48/80-induced degranulation pathway in mast cells, has been widely retained by recessive inheritance in beagle dogs among general experimental animal breeders. The knowledge concerning this phenotype could lead to better utilization of dogs in studies and aid in model development.

Late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with house dust mite-induced atopic dermatitis

OBJECTIVE

To determine the prevalence of late-phase reactions to intradermal testing with Dermatophagoides farinae in healthy dogs and dogs with atopic dermatitis and an immediate reaction to D farinae.

ANIMALS

6 healthy dogs and 20 dogs with atopic dermatitis and immediate reactions to D farinae.

PROCEDURE

ntradermal tests were performed with D farinae at 1:1,000 wt/vol and 1:50,000 wt/vol concentrations, and skin reactivity was evaluated after 0.25, 6, and 24 hours. Serum D farinae-specific IgE antibodies were assayed. Extent of lesions (atopy index) and pruritus (visual analogue scale) were evaluated in dogs with atopic dermatitis.

RESULTS

Late-phase reactions were observed in healthy dogs at 6 hours (n = 2 dogs) and 24 hours (1) with the 1:1,000 wt/vol concentration, and at 6 hours (1) and 24 hours (1) with the 1:50,000 wt/vol concentration of allergen. Late-phase reactions in healthy dogs were only observed in dogs with an immediate reaction to D farinae. Late-phase reactions were observed in 11 of 20 dogs with atopic dermatitis at 6 and 24 hours with the 1:1,000 wt/vol concentration and in 10 of 20 at 6 and 24 hours with the 1:50,000 wt/vol concentration of allergen. There was no difference in mean atopy index, mean visual analogue scale of pruritus, or mean serum D farinae-specific IgE concentration of dogs with a late-phase reaction, compared to dogs without a late-phase reaction.

CONCLUSIONS AND CLINICAL RELEVANCE

Late-phase reactions may be observed after an immediate reaction to intradermal skin testing in healthy and allergic dogs but are more commonly observed in dogs with atopic dermatitis.

The ACVD task force on canine atopic dermatitis (XVII): intradermal testing

Intradermal testing has been practiced for decades in human and veterinary medicine. The primary utility of intradermal testing is in the demonstration of IgE-mediated allergen hypersensitivity. The presence of a positive reaction on an intradermal test is not always indicative of allergy, as it may sometimes be an indication of sub-clinical hypersensitivity. Despite its widespread use by veterinary dermatologists, the usefulness of the intradermal test would be greatly enhanced by the use of standardized allergen extracts and homogeneous criteria for the interpretation of results. Irrespective of these shortcomings, intradermal testing is regarded as a valuable tool in the demonstration of allergen-specific hypersensitivity when performed according to accepted guidelines.

The ACVD task force on canine atopic dermatitis (VI): IgE-induced immediate and late-phase reactions, two inflammatory sequences at sites of intradermal allergen injections

Intradermal testing is a common diagnostic procedure used in the evaluation of dogs with suspected atopic dermatitis (AD). To do this, most investigators assess the appearance of wheals that develop at the sites of intradermal allergen injections. However, wheals are rarely seen in dogs with naturally occurring AD. Furthermore, infiltration of inflammatory cells into the injection sites can occur 6-24h later, a phenomenon known as the late-phase reaction. The histological appearance of these late-phase reactions closely approximates that seen in the natural disease, suggesting that they might be more relevant than the immediate reactions. In this paper, we review the literature on immediate and late-phase reactions and re-assess the evidence for using current intradermal testing procedures as a diagnostic test in dogs.

The use of compound 48/80 and codeine phosphate as positive controls for intradermal skin testing in dogs

The mast cell secretagogues compound 48/80 and codeine phosphate were evaluated as potential positive controls for intradermal skin testing in dogs. Wheal responses to both agents were compared with responses to histamine and saline in 11 normal dogs, and were strong and not significantly different from histamine responses in nine dogs (P < 0.01), and significantly weaker than histamine in two dogs (P < 0.05). Wheal responses to compound 48/80 (1 mg mL-1) were evaluated in 82 suspected atopic dogs and were similar to histamine in 79 dogs and markedly weaker than histamine in three dogs. Of nine confirmed atopic dogs with weak responses to injected allergens, seven had strong responses to compound 48/80, and eight had strong responses to histamine. Compound 48/80 and codeine phosphate appear unreliable positive controls for skin testing in normal dogs. Compound 48/80 (1 mg mL-1) may be a reliable positive control in atopic dogs but is a poor indicator of skin reactivity to allergens.

The use of compound 48/80 as a positive control in equine intradermal allergy testing

The macroscopic and microscopic effects following the intradermal injection of the mast cell degranulator compound 48/80 were investigated in horses. It was found that a 1000 μg mL^-1 solution of compound 48/80 could be used as an alternative to histamine as a positive control in equine intradermal allergy tests. An inflammatory cell infiltration was noted on histological examination, following compound 48/80 injection. This inflammatory cell pattern was similar to that noted for Type-I hypersensitivity.