O papel dos receptores B1 e B2 de cininas no modelo dermatite atópica induzida por oxazolona em camundongos

Abstract

Atopic dermatitis is a chronic inflammatory skin disorder featured by recurrent eczematous lesions and intense pruritus. It affects a great number of children and adults worldwide, greatly affecting the life quality of affected individuals. The participation of kinin receptors has been previously demonstrated in different mouse models of itching, justifying further investigations on the relevance of these receptors in models of chronic skin inflammatory diseases. This study evaluated the role of kinin B1 and B2 receptors in the pre-clinical mouse model of oxazolone-induced atopic dermatitis. Moreover, we have also investigated the implication of kinin receptors in the acute mouse model of pruritus induced by gastrinreleasing peptide (GRP), a selective mediator of spinal pruritus transmission. The B1 R715 or B2 HOE140 receptor antagonists were dosed at different schemes of treatment. After assessment of clinical lesion scores and pruritus, lesional skin samples were collected for histopathological analysis. The plasma extravasation and the expression of the metalloproteinase ADAMTS5 were also assessed. The immunopositivity for kinin receptors was evaluated in skin, dorsal root ganglion (DRG), thoracic spinal cord and brain cortex sections. A marked upregulation of B1 and B2 receptors was observed in the skin of oxazolone-treated mice. The induction of atopic dermatitis led to a downregulation of both receptors in the DRG, without any alteration in the spinal cord and cortex. The repeated administration of HOE140 (50nmol/kg; i.p.) partially inhibited the oxazolone-related pruritus, associated with a reduction of ADAMTS5 immunolabelling in the skin. Alternatively, R715 (438nmol/kg; i.p.) produced a mild inhibition of plasma extravasation in oxazolonechallenged mice. Noteworthy, the repeated i.d. injection of R715 (30nmol/site) or HOE140 (3nmol/site) significantly reduced the histiocyte numbers, according to the histopathological analysis. Either B1 or B2 kinin antagonists, irrespective of the protocol of treatment, did not alter any other evaluated clinical or histological parameters. In the mouse model of acute pruritus induced by the intrathecal (i.t.) injection of GRP, the systemic treatment with R715 (876nmol/kg) significantly reduced the scratching bouts. Alternatively, the treatment with R715 at a lower dose (438nmol/kg), or with HOE140 (25 e 50nmol/kg) did not affect GRPinduced pruritus. To analyze the possible site of action, the kinin antagonists were also coinjected with GRP by i.t. route. The co-treatment with HOE140 (30pmol/site) was able to prevent the itching behavior elicited by GRP, whereas R715 (25 e 50nmol/site) or a lower dose of HOE140 (10pmol/site) did not change this parameter. Evaluation of brain activation by positron emission tomography did not reveal any significant differences between vehicle- and GRP-treated mice. We also evaluated whether the pre-treatment with the selective GRP receptor antagonist PD176252 (5mg/kg; i.p.) might prevent the upregulation of B1 e B2 receptors in the skin of mice with atopic dermatitis. No alteration was observed in this experimental set. Altogether, the present data confirm and extend previous evidence on the relevance of kinin receptors in either acute or chronic pruritogenic transmission, indicating a role for the kinin system in atopic dermatitis. Additional studies are necessary to evaluate the effects of long-term protocols of treatment with kinin antagonists in the mouse model of atopic dermatitis evoked by oxazolone. It is also relevant to further investigating other mechanisms implicated in atopic dermatitis, including the assessment of cytokine levels, besides a detailed cell characterization by flow cytometry. Future studies should be also focused on the relationship between GRP and kinin receptors in atopic dermatitis.