Bronchial angiogenesis in horses with severe asthma and its response to corticosteroids

Abstract

Background: Severe asthma in horses is characterized by structural changes that thicken the lower airway wall, a change that is only partially reversible by current treatments. Increased vascularization contributes to the thickening of the bronchial wall in humans with asthma and is considered a potential new therapeutic target. Objective: To determine the presence of angiogenesis in the bronchi of severely asthmatic horses, and if present, to evaluate its reversibility by treatment with corticosteroids. Animals: Study 1: Bronchial samples from asthmatic horses in exacerbation (7), in remission (7), and aged-matched healthy horses. Study 2: Endobronchial biopsy samples from asthmatic horses in exacerbation (6) and healthy horses (6) before and after treatment with dexamethasone. Methods: Blinded, randomized controlled study. Immunohistochemistry was performed using collagen IV as a marker for vascular basement membranes. Number of vessels, vascular area, and mean vessel size in the bronchial lamina propria were measured by histomorphometry. Reversibility of vascular changes in Study 2 was assessed after 2 weeks of treatment with dexamethasone. Results: The number of vessels and vascular area were increased in the airway walls of asthmatic horses in exacerbation (P =.01 and P =.02, respectively) and in remission (P =.02 and P =.04, respectively) when compared to controls. In Study 2, the differences observed between groups disappeared after 2 weeks of treatment with corticosteroids because of the increased number of vessels in healthy horses. Conclusions and Clinical Importance: Angiogenesis contributes to thickening of the airway wall in asthmatic horses and was not reversed by a 2-week treatment with corticosteroids.