Effect of Mucosal TRPV1 Inhibition in Allergic Rhinitis

Transient receptor potential vanilloid-1 (TRPV1) has been implicated as a mediator of itch in allergic rhinitis. To address this possibility, we synthesized a TRPV1 blocker (SB-705498) for nasal administration in patients with seasonal allergic rhinitis. The pharmacological activity of SB-705498 was confirmed on human TRPV1-expressing HEK293 cells, using fluorometric calcium imaging, and in patients with allergic rhinitis subjected to nasal capsaicin challenges. The effect of SB-705498 was studied in patients with seasonal allergic rhinitis subjected to daily allergen challenges for seven days, using a double-blind, placebo-controlled, randomized and cross-over design. SB-705498 was delivered by nasal lavage 10 min. before each allergen challenge. Primary end-point was total nasal symptom score on days 5 to 7. Nasal peak inspiratory flow and eosinophil cationic protein content in nasal lavages were also monitored. Daily topical applications of SB-705498 at a concentration that inhibited capsaicin-induced nasal symptoms had no effect on total symptom score, nasal peak inspiratory flow and eosinophil cationic protein levels in allergen-challenged patients with seasonal allergic rhinitis. The individual symptom nasal itch or sneezes was also not affected. These findings may indicate that TRPV1 is not a key mediator of the symptoms in allergic rhinitis. However, additional studies, using drug formulations with a prolonged duration of action, should be conducted before TRPV1 is ruled out as a drug target in allergic rhinitis. (Less)