Pruritic dermatitis in asthmatic basenji-greyhound dogs: a model for human atopic dermatitis

IL-31-induced pruritus in dogs: a novel experimental model to evaluate anti-pruritic effects of canine therapeutics

BACKGROUND

Pruritus is a characteristic clinical sign of allergic skin conditions including atopic dermatitis (AD) in the dog. IL-31 is a cytokine found in the serum of some dogs with AD and can induce pruritic behaviours in laboratory beagle dogs.

HYPOTHESIS/OBJECTIVES

The objectives were to characterize an IL-31-induced pruritus model by evaluating the efficacy of prednisolone, dexamethasone and oclacitinib, and to compare the speed of anti-pruritic effects of oclacitinib against those of prednisolone and dexamethasone.

ANIMALS

Purpose-bred beagle dogs were used in all studies.

METHODS

Randomized, blinded, placebo-controlled studies were designed to evaluate and compare the anti-pruritic properties of prednisolone, dexamethasone and oclacitinib following a single intravenous injection of recombinant canine IL-31. Video surveillance was used to monitor and score pruritic behaviours in study animals.

RESULTS

Prednisolone [0.5 mg/kg, per os (p.o.)] reduced IL-31-induced pruritus when given 10 h prior to observation. When the time interval between drug treatment and observation was shortened to 1 h, dexamethasone (0.2 mg/kg, intramuscular) but not prednisolone (0.25 or 0.5 mg/kg, p.o.) reduced IL-31-induced pruritus. Oclacitinib (0.4 mg/kg, p.o.) reduced pruritus when given 1, 6, 11 and 16 h prior to the observation period, and the anti-pruritic activity of oclacitinib was greater when compared to prednisolone and dexamethasone at all time points assessed.

CONCLUSION AND CLINICAL IMPORTANCE

The efficacy of prednisolone, dexamethasone and oclacitinib in the IL-31-induced pruritus model gives confidence that this may be a relevant model for acute pruritus associated with allergic dermatitis including AD and can be used to evaluate novel compounds or formulations.

The role of mast cells in atopy: what can we learn from canine models? A thorough review of the biology of mast cells in canine and human systems

Mast cell research has largely focused on the role of these cells in the early phase of allergic reactions. However, their involvement may well extend beyond this stage, and even reach across nonallergic conditions. Mast cells from different sources have helped advance our knowledge of their biology. Although in vitro and in vivo research in this area has mainly focused on humans, such studies are limited by the extent to which cells from certain human tissues and/or human patients can be collected or studied. While rodents also provide valuable models with which to further our understanding of the behaviour of mast cells and their contribution to allergy, reported differences between human and murine mast cells, and, in some instances, the limitations of in vivo rodent models of mast cell-mediated allergic conditions, preclude their use. In this review, we introduce a relatively unknown mast cell population, that of the dog. Canine mast cells display many phenotypic and functional similarities with their human counterparts, and dogs develop spontaneous and induced allergic diseases that share clinical and pathophysiological features with the human condition. Therefore, the use of canine cells can shed light on the general role of mast cells, particularly in relation to allergic diseases given the potential of in vivo dog models within this field. Here we provide a detailed review of the data reported from in vitro and in vivo studies of canine mast cells, and compare them with results obtained in human systems. We also highlight direct evidence of the mast cell contribution to canine atopy. We conclude that the dog offers useful in vitro and in vivo models in which to investigate mast cell behaviour, and that its use should be considered when undertaking studies aimed either at elucidating the role of mast cells in health and disease, or at prescreening novel therapies prior to entry into man.

Pilot investigation of a model for canine atopic dermatitis: environmental house dust mite challenge of high-IgE-producing beagles, mite hypersensitive dogs with atopic dermatitis and normal dogs

Although canine atopic dermatitis (cAD) is common, few models are available. The aim of this study was to evaluate high-IgE beagles epicutaneously sensitized to house dust mite (HDM) as a possible model for cAD. Six high-IgE beagles were environmentally challenged with HDM using various doses and protocols. Similar challenge protocols were used in positive and negative control dogs: three dogs with naturally occurring cAD and positive intradermal skin test (IDT) to HDM and three normal dogs without history of skin disease and negative IDT to HDM. All high-IgE beagles and all atopic dogs developed severe cutaneous lesions and pruritus after challenge. Lesions were erythematous papules and macules in contact areas such as face, ears, ventral abdomen, groin, axillae and feet. They were first visible after 6 h and increased in severity over time. No normal dog developed pruritus or lesions. Biopsies of representative lesions in the high-IgE beagles were taken for histopathology and immunohistochemistry. There was superficial perivascular dermatitis with mononuclear infiltrates and spongiosis. Lymphocytes and eosinophils accumulated in small epidermal micro-abscesses with hyperplasia of epidermal IgE-bearing dendritic cells. These findings suggest that this colony of high-IgE beagles develops a dermatitis that clinically, histopathologically and immunologically resembles the naturally occurring canine disease. It is also concluded that this modality of challenge is not irritating to normal dogs but induces flare-ups in hypersensitive atopic dogs.

The ACVD task force on canine atopic dermatitis (IX): the controversy surrounding the route of allergen challenge in canine atopic dermatitis

For decades, the dogma that environmental allergens trigger cutaneous inflammation led to the denomination of canine atopic dermatitis as "allergic inhalant dermatitis". Definitive proof for a respiratory route of allergen challenge is lacking, however. Recent observations suggest, in fact, that skin inflammation could occur because of epidermal allergenic contact. The aim of this paper is to review the evidence published in favor and against the two suspected routes of allergen provocation.

The ACVD task force on canine atopic dermatitis (III): the role of antibodies in canine atopic dermatitis

Although an important pathogenic role for IgE is established in the case of allergic asthma and rhinitis in man, its role in atopic dermatitis is less clear. There are many studies where allergists and immunologists have provided evidence in favour of such a role, whereas dermatologists are less than convinced. In dogs, however, there is an abundance of clinical evidence implying that atopic dermatitis is antigen driven, and recent studies suggest that there may be a role for IgE, not only in the effector pathway, but also in antigen capture. Although an IgG response often accompanies an IgE response in dogs with atopic dermatitis, there is little evidence in support of a pathogenic role in respect of the former isotype.

The ACVD task force on canine atopic dermatitis (XXII): nonsteroidal anti-inflammatory pharmacotherapy

The pharmacotherapy of canine atopic dermatitis has relied primarily on the use of glucocorticoids and anti-histamines. During the last decade, other anti-inflammatory drugs have been investigated in clinical trials. This paper will review the studies using misoprostol, cyclosporine, tacrolimus, phosphodiesterase inhibitors, capsaicin, leukotriene inhibitors and serotonin-reuptake inhibitors for treatment of dogs with atopic dermatitis. For each drug the mechanism of action, the rationale for use in atopic dermatitis, the clinical efficacy, reported adverse effects and strength of recommendation for treatment of canine atopic dermatitis are described. At the time of this writing, there is fair evidence to support the recommendation for using cyclosporine, misoprostol and pentoxifylline for treatment of canine atopic dermatitis. This recommendation can be strengthened by the performance of additional blinded randomized controlled trials with larger number of dogs. In contrast, there is insufficient evidence to recommend for or against treatment with tacrolimus, leukotriene inhibitors, serotonin-reuptake antagonists and capsaicin.

The ACVD task force on canine atopic dermatitis (VII): mediators of cutaneous inflammation

Controversy still exists on the role of various inflammatory mediators in the pathogenesis of canine atopic dermatitis. The objective of this article is to review the most recent information available on the inflammatory mediators that have been implicated in the pathogenesis of this disease. Studies on the role of histamine, serotonin, leukotrienes and various cytokines are presented in a comparative manner reviewing the experimental evidence for a role in the pathogenesis and the arguments against it.

Update on the role of leukotrienes in the pathogenesis of atopy: a comparative review

The pathogenesis of atopic disease (AD) is controversial in humans and dogs. In humans, leukotrienes (LT) are thought to play an important role in this disease and LT inhibitors are commonly used as treatment for AD. Leukotrienes are a heterogeneous group of biologically active compounds that mediate many aspects of inflammatory and allergic reactions. This paper will review the role of LT in atopic disease in a comparative manner. Leukotriene inhibitors and their therapeutic use in the management of atopic disease in humans and dogs are discussed.

Murine model of atopic dermatitis associated with food hypersensitivity

BACKGROUND

Atopic dermatitis (AD) is an eczematous skin eruption that generally begins in early infancy and affects up to 12% of the population. The cause of this disorder is not fully understood, although it is frequently the first sign of atopic disease and is characterized by an elevated serum IgE level, eosinophilia, and histologic tissue changes characterized early by spongiosis and a CD4(+) T(H)2 cellular infiltrate. Hypersensitivity to foods has been implicated as one causative factor in up to 40% of children with moderate-to-severe AD.

OBJECTIVE

The purpose of this study was to establish a murine model of food-induced AD.

METHODS

Female C3H/HeJ mice were sensitized orally to cow's milk or peanut with a cholera toxin adjuvant and then subjected to low-grade allergen exposure. Histologic examination of skin lesions, allergen-specific serum Ig levels, and allergen-induced T-cell proliferation and cytokine production were examined.

RESULTS

An eczematous eruption developed in approximately one third of mice after low-grade exposure to milk or peanut proteins. Peripheral blood eosinophilia and elevated serum IgE levels were noted. Histologic examination of the lesional skin revealed spongiosis and a cellular infiltrate consisting of CD4(+) lymphocytes, eosinophils, and mast cells. IL-5 and IL-13 mRNA expression was elevated only in the skin of mice with the eczematous eruption. Treatment of the eruption with topical corticosteroids led to decreased pruritus and resolution of the cutaneous eruption.

CONCLUSION

This eczematous eruption resembles AD in human subjects and should provide a useful model for studying immunopathogenic mechanisms of food hypersensitivity in AD.

Role of selectins on IgE-mediated skin reaction

Selectins play an important role on leukocytes infiltration into inflammatory tissues. To understand the role of selectins, we investigated the effects of selectin-IgG chimeras and anti selectin antibodies on the murine IgE-mediated skin inflammation model. Biphasic skin reactions were induced by intradermal challenge with ovalbumin (OA) to ears of actively sensitized mice. This reaction was characterized by immediate and late phase responses observed as which were induced via a rapid increase in capillary permeability and leukocyte infiltration, respectively. The expression of E-selectin mRNA was significantly increased to reach its highest level at 2 h after OA challenge. E-, P-, and L-selectin-IgG chimeras inhibited the late phase responses, i.e. ear swelling, neutrophil infiltration and eosinophil infiltration at 24 h after OA challenge in a dose-dependent manner at dose range of 0.1 - 10 mg kg(-1), i.v. Antiselectin antibodies did not inhibit the increase of ear swelling. But anti E- and P-selectin antibodies significantly inhibited neutrophil infiltration and eosinophil infiltration. These results indicate that selectins play an important role on the late phase response of the murine IgE-mediated skin inflammation model by mediating inflammatory cell adhesion to endothelium.

Clinical anti-inflammatory efficacy of arofylline, a new selective phosphodiesterase-4 inhibitor, in dogs with atopic dermatitis

Forty atopic dogs were studied for 28 days after the oral administration of four randomised treatments: (A) arofylline (1 mg/kg) twice daily for four weeks; (B) prednisone (0.5 mg/kg) twice daily for the first week, once a day during the second week and every 48 hours for the remaining two weeks; (C) prednisone following the same protocol but at a dose of 0.25 mg/kg; or (D) arofylline (1 mg/kg) twice daily for four weeks plus prednisone (0.25 mg/kg) following the same protocol as in (B) and (C). The degree of pruritus and skin lesions and the side effects were evaluated and graded from 0 to 3 before and weekly during the treatments. In all cases there was a progressive clinical improvement in the clinical signs, with no statistical differences among the four treatments. However, many of the dogs treated with arofylline vomited and had adverse gastrointestinal signs.

Bronchial and cutaneous responses in atopic dermatitis patients after allergen inhalation challenge

BACKGROUND

Atopic dermatitis (AD) is often associated with allergic asthma (AA). Inhalation of allergens influences the activity of AA but the effect on the skin in AD is unclear.

OBJECTIVES

We evaluated the degree of bronchial hyperresponsiveness to methacholine in eight AD patients with AA (AD+) and eight AD patients without AA (AD-) and studied bronchial and cutaneous responses after allergen inhalation challenge.

METHODS

All patients were treated in hospital for their eczema with tar ointment (pix liquida) and orally administered antihistamines (mean hospital stay 37 days). After clearing of the skin lesions allergen inhalation challenge was performed. Cutaneous responses were studied by measuring the 'Costa' score before and 24 h after allergen inhalation challenge.

RESULTS

The median value of the provocative concentration of methacholine causing a 20% fall (PC20 Mch) in forced expiratory volume in 1 second (FEV1) was significantly higher in the AD- group compared to the AD+ group with median values of 10.70 and 0.60 mg/mL, respectively. These values did not change significantly in both groups during hospital stay. After challenge all AD+ patients showed early and late asthmatic responses whereas only four AD patients showed early asthmatic responses (mean values of the maximal fall in FEV1 during the EAR 37%/16% and in PEF during the LAR 27%/4% for AD+ and AD-patients, respectively). The 'Costa' score increased in both groups (mean score before 19.1/24.4 and after challenge 26.8/26.9 for AD+ and AD- patients, respectively). The increase in the AD+ group was significantly higher compared with the AD- group (P=0.016).

CONCLUSION

We conclude that allergen inhalation challenge causes a flare up of the skin lesions in atopic dermatitis patients. This was more prominent in atopic dermatitis patients who already suffered from an IgE-mediated allergic inflammation in the lung.

Skin mast cell releasability in dogs with atopic dermatitis

Isolated dermal mast cells from atopic dogs are a valuable tool for the analysis of their functional properties in atopic dermatitis. We have characterized the histamine secretory pattern of mast cells enzymatically dispersed from the skin of dogs naturally suffering from this condition. The total histamine content found per isolated skin mast cell was higher in the allergic dogs than in nonatopic (control) animals (8.7 pg/mast cell versus 5.2 pg/mast cell). This phenomenon together with the well known higher concentration of skin mast cell number in atopic dermatitis lesions might account for the observed increase in local histamine concentration (15.0 micrograms/g versus 9.0 micrograms/g). Atopic dog-derived mast cells were highly reactive to both non-immunological (ionophore A23187) and an immunological-like (concanavalin A) stimulus. Furthermore, histamine net release induced by concanavalin A (1 mg/ml) stimulation was clearly enhanced in the atopic dogs (33.3% net release versus 15.4% in controls). These results have not been described in dermal mast cells dispersed from the skin of individuals with atopic dermatitis and clearly support the hypothesis that mast cells play a major role in causing and possibly modulating atopic dermatitis, through enhanced sensitivity or releasability. However, whether these two phenomena are primary abnormalities of atopic dermatitis, or only secondary changes, remains undetermined.

Canine cutaneous mast cells dispersion and histamine secretory characterization

In view of the high incidence of canine cutaneous atopic disease and the relevance of mast cells to its pathogenesis, it was considered important to isolate firstly cutaneous mast cells from normal dog skin and to assess the histamine secretory activity, as this can be further used as a tool for the study of canine skin mast cell pharmacology in cutaneous atopy. The procedure for canine dermal mast cell dispersion following a skin enzymatic digestion (as for previous human skin mast cell dispersion methods) is described in detail. The number of canine cutaneous mast cells yielded per gram of skin was 2.31 +/- 0.21 x 10(5) representing 1.00% of the total cutaneous cells. The total histamine content per mast cell is 4.93 +/- 0.39 pg. Net histamine release owing to stimulation by calcium ionophore A23187 (1 microM) and concanavalin A (1 mg ml-1) was respectively 32.17 +/- 3.56% and 20.39 +/- 2.41% of the total amount per cell. Viability and reactivity to both stimuli of dispersed cutaneous mast cells were similar to the results found in humans. The present study allows further research on the role of mast cells immunopharmacology in allergy by investigation of cells isolated from canine skin in naturally occurring or experimentally induced atopy in the dog to be undertaken.

Changes in cell-mediated immune responses after experimentally-induced anaphylaxis in dogs

Experimentally-induced type 1 hypersensitivities were induced in normal dogs to either ovalbumin or Ascaris antigen. In vitro and in vivo cell-mediated immune responses were measured before sensitization and again at 1 and 6 days after induction of anaphylaxis by intravenous challenge with antigen. Histamine-modulated lymphocyte functions, such as histamine-induced suppression, histamine co-mitogen induced blastogenesis and the in vivo cutaneous responses to intradermally injected mitogens decreased post anaphylaxis. Spontaneous suppression of the autologous mixed-lymphocyte reaction increased post anaphylaxis. Lymphocyte blastogenic response to Concanavalin A (Con A) decreased at 6 (but not at 1) days post anaphylaxis probably due to a mediator other than histamine. Blastogenesis of 24 h preincubated cells by suboptimal concentration of Con A, declined post anaphylaxis, but Con A-induced suppression was not significantly altered. Dogs with atopic dermatitis have some altered cell-mediated immune responses. Altered histamine-induced and spontaneous suppression, histamine suppression of mitogenesis and decreased contact sensitivity observed in this experimental type 1 hypersensitivity mimicked that of atopic dogs. Increased cutaneous response to mitogens observed in atopic dogs was not reproduced in the type 1 hypersensitive dogs. These findings suggest some of the altered cell-mediated immune functions observed in dogs with atopic dermatitis result from type 1 hypersensitivity. The other abnormalities may be intrinsic to the atopic state.

Dermal mast cell releasability and end organ responsiveness in atopic and nonatopic dogs

The Basenji greyhound (BG) has been proposed as a model of atopic disease because of its chronic relapsing atopic dermatitis as well as airway hyperresponsiveness. We attempted to characterize this model further by comparing its skin wheal-and-flare responses to morphine sulfate and histamine with those of control, nonatopic mongrel dogs. We found that BG dogs had significantly smaller skin responses than did the control dogs to all but two concentrations of histamine used. In contrast, BG dogs demonstrated greater skin response to morphine at the three lowest concentrations used but had a significantly smaller skin response at the highest dose of morphine. Skin punch biopsy specimens revealed decreases in histamine content after morphine exposure but no difference in histamine content of the unexposed skin or of morphine-exposed skin for the two groups of dogs. When percent histamine release was compared, however, BG dogs were found to release a significantly greater proportion of histamine in response to morphine than control dogs. Although there was no significant difference in total mast cell counts for the two groups, the BG dogs had significantly fewer formalin-insensitive mast cells in unexposed skin than control dogs. We conclude that skin responses in BG dogs are characterized by decreased end organ responsiveness and greater releasability of mast cells in response to nonimmunologic stimulation.

Comparison of in vitro drug responses in airways of atopic dogs with and without in vivo airway hyperresponsiveness

For comparison with previous studies in greyhounds and in the Basenji-Greyhound dog model of asthma (BG), basenji dogs were studied under identical conditions with respect to airway responsiveness to inhaled methacholine, cutaneous responses to intradermal antigen injection, and the sensitivity of isolated trachealis muscle to methacholine and isoproterenol. The relaxant effect of isoproterenol was assessed in trachealis muscle precontracted with methacholine (ED50). The basenji dogs resembled the BG dogs in that they showed multiple positive skin tests. Further, trachealis muscle showed a markedly reduced sensitivity to methacholine (pD2 6.64 +/- 0.10) (+/- S.E.) in vitro. However, basenji dogs resembled the greyhounds in requiring high concentrations of methacholine aerosols to produce a 2-fold increase in pulmonary resistance (1.68 mg/ml +/- 1.21). Thus, there were no significant correlations between sensitivity to methacholine in vitro and airway responsiveness to methacholine in vivo; however, the reduced sensitivity to methacholine in vitro in both basenji and BG dogs may be related to the marked atopy characteristic of both groups. In vitro sensitivity to isoproterenol was correlated (r = 0.82) with the concentration of methacholine needed to elicit the test contraction, but isoproterenol sensitivity in BG dogs was significantly less (p = .0027) than that predicted by the common regression line. This deficit in beta adrenergic function in trachealis muscle unrelated to atopy may be important in the in vivo airway hyperresponsiveness of BG dogs.

Immunopharmacology of the atopic diseases

The atopic conditions, atopic dermatitis, asthma, and allergic rhinitis, may arise as a result of infiltrating bone marrow-derived cells into skin or respiratory mucosae. Release of inflammatory factors from these cells could account for cutaneous vascular instability and pruritus in atopic dermatitis. Erythema and itch have been induced by experimental stress interviews and by blind food challenges. In the latter, increased plasma histamine was detected and correlated with cutaneous reactions. Basophils from patients with atopic dermatitis have increased histamine release after exposure to immunologic or nonimmunologic lectin stimuli. This increased releasability may relate to inadequate cyclic AMP regulation of cell function. We have found that leukocytes of patients with atopic dermatitis have elevated phosphodiesterase activity and consequently reduced intracellular cyclic AMP. Exposure of the cells to a phosphodiesterase inhibitor caused considerable reduction in histamine release. Similarly, exposure of atopic B lymphocytes to a phosphodiesterase inhibitor greatly reduced the high spontaneous IgE synthesis in mononuclear leukocyte cultures. Elevated leukocyte phosphodiesterase activity may also serve as a marker for the atopic diathesis. We have found elevated enzyme activity in umbilical cord blood from newborns with atopic parents, suggesting that this defect may relate to a genetically determined defect. These studies have provided insight into basic abnormalities associated with atopic dermatitis and the atopic diathesis. Defects of regulatory mechanisms in immune and inflammatory cells may help explain the seemingly disparate disorders of physiologic, pharmacologic, and immunologic systems in atopy.

Airway constrictor effects of leukotriene D4 in dogs with hyperreactive airways

Leukotriene D4 (5 micrograms/ml) aerosol constricts airways of dogs with nonspecific airway hyperreactivity but not of mongrel dogs which lack nonspecific airway hyperreactivity. RL increased 200 +/- 25% and Cdyn decreased to 77 +/- 5% of the prechallenge value. LTD4 (10 micrograms/ml) produced no further increase. Atropine (0.2 mg/kg) prevented the increase in RL and decrease in Cdyn, suggesting that part of the effect of LTD4 on airways is neurally mediated.