Elucidation of Inverse Agonist Activity of Bilastine.

Hiroyuki Mizuguchi,Tomoharu Wakugawa,Hiroyuki Fukui,Mai Takemoto,Tomomi Nakagawa,Seiichiro Kamimura,Noriaki Takeda,Masami Yabumoto,Hisato Sadakata,Yoshiaki Kitamura

doi:10.3390/pharmaceutics12060525

Hiroyuki Mizuguchi, Tomoharu Wakugawa + Show 8 more

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https://doi.org/10.3390/pharmaceutics12060525

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Abstract

H1-antihistamines antagonize histamine and prevent it from binding to the histamine H1 receptor (H1R). Some of them also act as inverse agonists, which are more potent than pure antagonists because they suppress the constitutive H1R activity. Bilastine is a non-sedative antihistamine which is one of the most satisfy the requirements for oral antihistamines. However, there is no information to show the inverse agonist activity of bilastine including inositol phosphates accumulation, and its inverse agonist activity is yet to be elucidated. Here we evaluated whether bilastine has inverse agonist activity or not. 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. At rest, Ca2+ oscillation was observed, indicating that H1R has intrinsic activity. Bilastine attenuated this fluorescence oscillation. Bilastine suppressed the increase in IPs formation in a dose-dependent manner and it was about 80% of the control level at the dose of 3 μM. Bilastine also suppressed histamine-induced increase in IPs formation to the control level. Furthermore, bilastine suppressed basal H1R gene expression in a dose-dependent manner. Data suggest that bilastine is an inverse agonist. Preseasonal prophylactic administration with bilastine could down-regulate basal H1R gene expression in the nasal mucosa and ameliorate the nasal symptoms during the peak pollen period.

Highlights

Histamine is an important chemical mediator causing symptoms of pollinosis [1]
We showed that protein kinase Cδ (PKCδ) signaling was involved in H1 receptor (H1R) gene expression, and that suppression of the H1R gene up-regulation alleviated these nasal symptoms in TDI-sensitized rats [5,6,7], suggesting that keeping the H1R gene expression level low is effective for improving nasal symptoms
H1-antihistamines with inverse agonist activity are more potent than neutral antagonists, as they suppress this intrinsic signal in addition to the H1-antihistamine effect

Summary

Introduction

Histamine is an important chemical mediator causing symptoms of pollinosis [1]. Its action occurs mainly through the activation of histamine H1 receptor (H1R). We demonstrated that H1R gene expression is correlated with the severity of nasal symptoms in toluene-2,4-diisocyanate (TDI)-sensitized rats and patients with pollinosis [2,3,4]. H1R is in an equilibrium state between an active form and an inactive form, and a constant level of signal always operates even without histamine stimulation [8]. It is well-known that H1-antihistamines antagonize histamine and prevent it from binding to the H1R and are widely used as the first-line medicine for nasal symptoms of pollinosis, some H1-antihistamines act as inverse agonists that bind to and stabilize the inactive form of H1R, and down-regulate constitutive receptor activity. We have demonstrated that HeLa cells expressing H1R endogenously are useful to assess inverse activity of H1-antihistamines [9,10,11]

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