Effects of MP-AzeFlu enhanced by activation of bitter taste receptor TAS2R

MP-AzeFlu is relatively new a pharmaceutical drug used in the treatment of allergic rhinitis. It is comprised of azelastine hydrochloride (AZE), a potent histamine-H1-receptor antagonist and fluticasone propionate (FP), corticosteroid. It’s somewhat bitter taste (often considered a disadvantage) can be attributed to AZE. We here hypothesize that MP-AzeFlu may induce some of its beneficial effects through activation of bitter taste receptors (Tas2R), which have recently been described in human airways. In the nose Tas2Rs induce secretion of antimicrobial peptides and increase ciliary activity, while in the lung they cause airway smooth muscle relaxation. The mechanisms behind Tas2R-mediated effects are not yet fully known. In order to evaluate the role of Tas2R in the effects induced by MP-AzeFlu the dilatory response of pre-contracted isolated airways from Balb/c mice was investigated in tissue bath myographs in the presence or absence of various well-characterized pharmacological antagonists or their corresponding vehicles. MP-AzeFlu caused a potent dose-dependent relaxation of pre-contracted airways, an effect probably mediated by its AZE component. The dilatory effect of MP-AzeFlu and AZE both mimicked the response induced by the Tas2R agonist, chloroquine, but was independent of histamine receptor (H1-, H2- and H3-), prostaglandins, cAMP and cGMP involvement, all known to be common pathways for airway dilation. Other bitter-tasting antihistamines (i.e. olopatadine and desloratadine) also relaxed airway segments. These data support the notion that MP-AzeFlu has the ability to activate Tas2R in the same way as chloroquine. The effect appears to be mediated by AZE, but not via the histamine receptor. Activation of Tas2R by MP-AzeFlu may contribute to its superior efficacy over FP observed in controlled clinical trials in patients with moderate/severe allergic rhinitis.