Investigation of the cannabinoidergic system's role in allergic asthma and the associated TRP channel mechanisms

Asthma is a chronic respiratory system disease in which hypersensitivity, inflammation and physiological/structural changes are seen in the respiratory tract. The endocannabinoid system consists of cannabinoid CB1 and CB2 receptors, endocannabinoid ligands and their synthesis and degradation pathways. The aim of this study is to investigate the effects of the cannabinoidergic system on airway inflammation and airway hypersensitivity in allergic asthma and the role of TRP channel-related mechanisms in these effects. BALB/c mice were sensitized and provoked with ovalbumin in order to create a model of allergic asthma. CB1 selective agonist ACEA and CB2 selective agonist JWH133 were administered intraperitoneal to separate groups at doses of 0.5, 3, and 5 mg/kg. Receptor antagonism studies were performed with CB1 antagonist AM251, CB2 antagonist AM630 and TRPV1 antagonist capsazepine. Penh values were recorded in vivo by whole-body plethysmograph under methacholine challenge. Inflammatory cell count was performed in bronchoalveolar lavage fluid (BALF). Serum levels of pro-inflammatory cytokines were measured by ELISA. Inflammation in the lung tissue was scored histopathologically. Statistical significance was determined using One-way ANOVA or Kruskal-Wallis test and expressed as p<0.05. In sensitized animals, provocation with inhaled ovalbumin increased Penh values, serum IL-4, IL-5, IL-13 levels, eosinophil, neutrophil, lymphocyte, macrophage counts in BALF, inflammation in the lung tissue. JWH133 decreased Penh values, serum cytokine levels, inflammatory cell migration in BALF, and inflammation in the lung tissue in a dose-dependent manner. AM251 decreased Penh values, inflammatory cell migration in BALF, and inflammation in the lung tissue region compared to the disease group. Although Penh values, serum cytokine levels, inflammatory cell migration in BALF, and inflammation in the lung tissue ensued from co-administration of ACEA and JWH133 were lower than those in the disease group, they still higher than the values obtained when JWH133 was administered alone. Penh values and inflammatory cell migration in BALF were higher in the AM251 then those in ACEA administered group, in contrast to the group administered AM251 alone. When AM360 then JWH133 were administered, serum cytokine levels and inflammatory cell migration in BALF were lower in comparison to the group that was administered AM630 alone. Penh values, BAL fluid eosinophil and lymphocyte levels and lung tissue inflammation score were significantly lower in the KPZ+ACEA and KPZ+JWH133 groups compared to the disease group. In addition, serum IL-4 and IL-13 levels in the KPZ+ACEA group and serum IL-5 and IL-13 levels in the KPZ+JWH133 group were lower than those in the disease group. This study proves that there is a significant interference of the cannabinoidergic system in allergic asthma. CB2 agonism and CB1 antagonism reduce airway hyperresponsiveness and inflammation and display immunomodulatory effects. CB1/CB2 receptor-independent factors may also play a role in the observed antiasthmatic effect. Keywords: Allergic asthma, CB1 and CB2 receptors, JWH133, AM251