Hiroyuki Mizuguchi, et al.
Pharmaceutics 2020, 12, 525; doi: 10.3390/pharmaceutics12060525.
Histamine is a chemical mediator that causes pollinosis symptoms such as a sneezing, rhinorrhoea, nasal obstruction, nasal itching, and itching of the eyes. H1-antihistamines antagonize histamine H1, preventing it from binding to the histamine H1 receptor (H1R). Bilastine is a non-sedative recently launched H1-antihistamine which has high affinity for H1R. It is one of the H1-antihistamines that most satisfies the requirements of allergic rhinitis and asthma guidelines. Inverse agonists are thought to be more potent than neutral antagonists because they supress the intrinsic histamine signalling in addition to the H1-antihistamine effect. Nevertheless, there is a lack of information regarding bilastine inverse agonist activity.
This study assessed if bilastine has inverse agonist activity or not. HeLa cells that express H1R endogenously here used, and three methods applied: time-lapse Ca2+ imaging, inositol phosphates (IPs) accumulation and H1R gene expression. Intracellular calcium concentration was measured using Fluo-8. Inositol phosphates accumulation was assayed using [3H]myo-inositol. The H1R mRNA level was measured using real-time RT-PCR.
H1R intrinsic activity was shown by Ca2+ oscillation. Also, bilastine suppressed IPs formation and basal H1R gene expression in a dose-dependent manner.
These results elucidate that bilastine has an inverse agonist activity. Taking bilastine before pollen season, the H1R gene expression level can be kept low, improving pollinosis symptoms.