Inverse agonistic activity of antihistamines and suppression of histamine H1 receptor gene expression

Establishment of a human nasal epithelium model of histamine-induced inflammation to assess the activity of fexofenadine as an inverse agonist and its link to clinical benefit

Background

Fexofenadine (FEX) is an antihistamine that acts as an inverse agonist against histamine (HIS) receptor 1 (H1R), which mediates the allergic reaction. Inverse agonists may be more potent than neutral antagonists, as they bind the same receptor as the agonist (HIS) but stabilize the inactive form and induce an opposite pharmacological response, suppressing the basal activity of H1R and preventing HIS from binding. This study aims to establish and validate a model of HIS-induced inflammation based on fully reconstituted human nasal epithelial tissue to assess the activity of FEX as an inverse agonist in this model and explore its link to clinical benefit.

Methods

The model was developed using nasal MucilAir™ (Epithelix) in vitro epithelium challenged by HIS. Two conditions were assessed in a side-by-side comparison: tissue was exposed to HIS + FEX with or without FEX pre-treatment (one-hour prior to HIS challenge). Tissue functionality, cytotoxicity, H1R gene expression, and inflammatory cytokines were assessed.

Results

HIS at 100 µM induced significant 3.1-fold and 2.2-fold increases for inflammatory biomarkers interleukin (IL)-8 and IL-6, respectively (p < 0.0001), as well as rapid upregulation of H1R mRNA. Inflammatory biomarkers were inhibited by FEX and H1R expression was significantly reduced (p < 0.0001). FEX alone decreased H1R expression at all doses tested. With one-hour FEX pre-treatment, there was significantly higher downregulation of IL-8 (p < 0.05) and further downregulation of H1R expression and IL-6 versus without FEX pre-treatment; the effects of FEX were improved from 22% to 40%.

Conclusion

A model of HIS-induced airway inflammation was established based on IL-8, IL-6 and H1R gene expression and was validated with FEX. FEX works as an inverse agonist, with a higher effect when used before+during versus only during the HIS challenge. Taking FEX before+during allergen exposure, or when symptoms first occur, may reduce basal activity and H1R gene expression, providing stronger protection against the worsening of symptoms upon allergen exposure.

The role of histamine H1 receptor in the anterior cingulate cortex on nociception level following acute restraint stress in male rats

Considering the importance of pain and stress, we decided to investigate the intra-anterior cingulate cortex (ACC) microinjection of histamine and mepyramine alone and concurrently on acute pain induced by hot plate following restraint stress in male rats. 24-gauge, 10 mm stainless steel guide cannula was implanted over the ACC in the incised scalp of 4 groups. Restraint stress in healthy rats produced a significant increase (p < .05) in the pain threshold. The simultaneous microinjection of 4 μg/side histamine and 8 μg/side mepyramine as a histaminergic system inverse agonist in healthy nonrestraint animals did not affect the pain threshold. Although Histamine decreased the threshold of pain meaningfully, mepyramine elevated it in a significant manner (p < .05). In the restrained animals, intra-ACC microinjection of histamine produced no significant impact on the pain threshold. However, intra-ACC microinjection of mepyramine before histamine, significantly (p < .01) altered the result and enhanced the threshold of pain. The results of our study demonstrated that histaminergic neurons have an important role in the processing of pain in the ACC following restraint stress.

Function and Role of Histamine H1 Receptor in the Mammalian Heart

Histamine can change the force of cardiac contraction and alter the beating rate in mammals, including humans. However, striking species and regional differences have been observed. Depending on the species and the cardiac region (atrium versus ventricle) studied, the contractile, chronotropic, dromotropic, and bathmotropic effects of histamine vary. Histamine is present and is produced in the mammalian heart. Thus, histamine may exert autocrine or paracrine effects in the mammalian heart. Histamine uses at least four heptahelical receptors: H1, H2, H3 and H4. Depending on the species and region studied, cardiomyocytes express only histamine H1 or only histamine H2 receptors or both. These receptors are not necessarily functional concerning contractility. We have considerable knowledge of the cardiac expression and function of histamine H2 receptors. In contrast, we have a poor understanding of the cardiac role of the histamine H1 receptor. Therefore, we address the structure, signal transduction, and expressional regulation of the histamine H1 receptor with an eye on its cardiac role. We point out signal transduction and the role of the histamine H1 receptor in various animal species. This review aims to identify gaps in our knowledge of cardiac histamine H1 receptors. We highlight where the published research shows disagreements and requires a new approach. Moreover, we show that diseases alter the expression and functional effects of histamine H1 receptors in the heart. We found that antidepressive drugs and neuroleptic drugs might act as antagonists of cardiac histamine H1 receptors, and believe that histamine H1 receptors in the heart might be attractive targets for drug therapy. The authors believe that a better understanding of the role of histamine H1 receptors in the human heart might be clinically relevant for improving drug therapy.

Electrochemical Cross-Dehydrogenative Aromatization Protocol for the Synthesis of Aromatic Amines

The introduction of amines onto aromatics without metal catalysts and chemical oxidants is synthetically challenging. Herein, we report the first example of an electrochemical cross-dehydrogenative aromatization (ECDA) reaction of saturated cyclohexanones and amines to construct anilines without additional metal catalysts and chemical oxidants. This reaction exhibits a broad scope of cyclohexanones including heterocyclic ketones, affording a variety of aromatic amines with various functionalities, and shows great potential in the synthesis of biologically active compounds.

Japanese cedar and cypress pollinosis updated: New allergens, cross-reactivity, and treatment

Pollen from many tree species in the Cupressaceae family is a well-known cause of seasonal allergic diseases worldwide. Japanese cedar pollinosis and Japanese cypress pollinosis, which are caused by pollen from Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa), respectively, are the most prevalent seasonal allergic diseases in Japan. Recently, the novel major Japanese cypress allergen Cha o 3 and the homologous Japanese cedar allergen Cry j cellulase were identified, and it was shown, for the first time, that cellulase in plants is allergenic. Although the allergenic components of pollen from both species exhibit high amino acid sequence identity, their pollinosis responded differently to allergen-specific immunotherapy (ASIT) using a standardized extract of Japanese cedar pollen. Pharmacotherapy and ASIT for Japanese cedar and cypress pollinosis have advanced considerably in recent years. In particular, Japanese cedar ASIT has entered a new phase, primarily in response to the generation of updated efficacy data and the development of new formulations. In this review, we focus on both Japanese cypress and cedar pollinosis, and discuss the latest findings, newly identified causative allergens, and new treatments. To manage pollinosis symptoms during spring effectively, ASIT for both Japanese cedar and Japanese cypress pollen is considered necessary.

Elucidation of Inverse Agonist Activity of Bilastine

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.

Suppression of IFN-γ Production in Murine Splenocytes by Histamine Receptor Antagonists

Accumulating evidence suggests that histamine synthesis induced in several types of tumor tissues modulates tumor immunity. We found that a transient histamine synthesis was induced in CD11b⁺Gr-1⁺ splenocytes derived from BALB/c mice transplanted with a syngeneic colon carcinoma, CT-26, when they were co-cultured with CT-26 cells. Significant levels of IFN-γ were produced under this co-culture condition. We explored the modulatory roles of histamine on IFN-γ production and found that several histamine receptor antagonists, such as pyrilamine, diphenhydramine, JNJ7777120, and thioperamide, could significantly suppress IFN-γ production. However, suppression of IFN-γ production by these antagonists was also found when splenocytes were derived from the Hdc-/- BALB/c mice. Suppressive effects of these antagonists were found on IFN-γ production induced by concanavalin A or the combination of an anti-CD3 antibody and an anti-CD28 antibody in a histamine-independent manner. Murine splenocytes were found to express H₁ and H₂ receptors, but not H₃ and H₄ receptors. IFN-γ production in the Hh1r-/- splenocytes induced by the combination of an anti-CD3 antibody and an anti-CD28 antibody was significantly suppressed by these antagonists. These findings suggest that pyrilamine, diphenhydramine, JNJ7777120, and thioperamide can suppress IFN-γ production in activated splenocytes in a histamine-independent manner.

Histamine H1 Receptor Gene Expression and Drug Action of Antihistamines

The upregulation mechanism of histamine H₁ receptor through the activation of protein kinase C-δ (PKCδ) and the receptor gene expression was discovered. Levels of histamine H₁ receptor mRNA and IL-4 mRNA in nasal mucosa were elevated by the provocation of nasal hypersensitivity model rats. Pretreatment with antihistamines suppressed the elevation of mRNA levels. Scores of nasal symptoms were correlatively alleviated to the suppression level of mRNAs above. A correlation between scores of nasal symptoms and levels of histamine H₁ receptor mRNA in the nasal mucosa was observed in patients with pollinosis. Both scores of nasal symptoms and the level of histamine H₁ receptor mRNA were improved by prophylactic treatment of antihistamines. Similar to the antihistamines, pretreatment with antiallergic natural medicines showed alleviation of nasal symptoms with correlative suppression of gene expression in nasal hypersensitivity model rats through the suppression of PKCδ. Similar effects of antihistamines and antiallergic natural medicines support that histamine H₁ receptor-mediated activation of histamine H₁ receptor gene expression is an important signaling pathway for the symptoms of allergic diseases. Antihistamines with inverse agonist activity showed the suppression of constitutive histamine H₁ receptor gene expression, suggesting the advantage of therapeutic effect.

Antihistamines suppress upregulation of histidine decarboxylase gene expression with potencies different from their binding affinities for histamine H1 receptor in toluene 2,4-diisocyanate-sensitized rats

Antihistamines inhibit histamine signaling by blocking histamine H1 receptor (H1R) or suppressing H1R signaling as inverse agonists. The H1R gene is upregulated in patients with pollinosis, and its expression level is correlated with the severity of nasal symptoms. Here, we show that antihistamine suppressed upregulation of histidine decarboxylase (HDC) mRNA expression in patients with pollinosis, and its expression level was correlated with that of H1R mRNA. Certain antihistamines, including mepyramine and diphenhydramine, suppress toluene-2,4-diisocyanate (TDI)-induced upregulation of HDC gene expression and increase HDC activity in TDI-sensitized rats. However, d-chlorpheniramine did not demonstrate any effect. The potencies of antihistamine suppressive effects on HDC mRNA elevation were different from their H1R receptor binding affinities. In TDI-sensitized rats, the potencies of antihistamine inhibitory effects on sneezing in the early phase were related to H1R binding. In contrast, the potencies of their inhibitory effects on sneezing in the late phase were correlated with those of suppressive effects on HDC mRNA elevation. Data suggest that in addition to the antihistaminic and inverse agonistic activities, certain antihistamines possess additional properties unrelated to receptor binding and alleviate nasal symptoms in the late phase by inhibiting synthesis and release of histamine by suppressing HDC gene transcription.

Effects of antihistamine on up-regulation of histamine H1 receptor mRNA in the nasal mucosa of patients with pollinosis induced by controlled cedar pollen challenge in an environmental exposure unit

In the present study, we examined the effects of antihistamine on the up-regulation of H1R mRNA in the nasal mucosa of patients with pollinosis induced by controlled exposure to pollen using an environmental exposure unit. Out of 20 patients, we designated 14 responders, whose levels of H1R mRNA in the nasal mucosa were increased after the first pollen exposure and excluded 6 non-responders. Accordingly, the first exposure to pollen without treatment significantly induced both nasal symptoms and the up-regulation of H1R mRNA in the nasal mucosa of the responders. Subsequently, prophylactic administration of antihistamine prior to the second pollen exposure significantly inhibited both of the above effects in the responders. Moreover, the nasal expression of H1R mRNA before the second pollen exposure in the responders pretreated with antihistamine was significantly decreased, as compared with that before the first pollen exposure without treatment. These findings suggest that antihistamines suppressed histamine-induced transcriptional activation of H1R gene in the nasal mucosa, in addition to their blocking effect against histamine on H1R, resulting in a decrease of nasal symptoms. These findings further suggest that by their inverse agonistic activity, antihistamines suppress the basal transcription of nasal H1R in the absence of histamine in responders.

Maackiain is a novel antiallergic compound that suppresses transcriptional upregulation of the histamine H1 receptor and interleukin-4 genes

Kujin contains antiallergic compounds that inhibit upregulation of histamine H1 receptor (H1R) and interleukin (IL)-4 gene expression. However, the underlying mechanism remains unknown. We sought to identify a Kujin-derived antiallergic compound and investigate its mechanism of action. The H1R and IL-4 mRNA levels were determined by real-time quantitative RT-PCR. To investigate the effects of maackiain in vivo, toluene-2,4-diisocyanate (TDI)-sensitized rats were used as a nasal hypersensitivity animal model. We identified (-)-maackiain as the responsible component. Synthetic maackiain showed stereoselectivity for the suppression of IL-4 gene expression but not for H1R gene expression, suggesting distinct target proteins for transcriptional signaling. (-)-Maackiain inhibited of PKCδ translocation to the Golgi and phosphorylation of Tyr(311) on PKCδ, which led to the suppression of H1R gene transcription. However, (-)-maackiain did not show any antioxidant activity or inhibition of PKCδ enzymatic activity per se. Pretreatment with maackiain alleviated nasal symptoms and suppressed TDI-induced upregulations of H1R and IL-4 gene expressions in TDI-sensitized rats. These data suggest that (-)-maackiain is a novel antiallergic compound that alleviates nasal symptoms in TDI-sensitized allergy model rats through the inhibition of H1R and IL-4 gene expression. The molecular mechanism underlying its suppressive effect for H1R gene expression is mediated by the inhibition of PKCδ activation.

The neglected role of histamine in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by beta-amyloid plaques accumulation and cognitive impairment. Both environmental factors and heritable predisposition have a role in AD. Histamine is a biogenic monoamine that plays a role in several physiological functions, including induction of inflammatory reactions, wound healing, and regeneration. The Histamine mediates its functions via its 4 G-protein-coupled Histamine H1 receptor (H1R) to histamine H1 receptor (H4R). The histaminergic system has a role in the treatment of brain disorders by the development of histamine receptor agonists, antagonists. The H1R and H4R are responsible for allergic inflammation. But recent studies show that histamine antagonists against H3R and regulation of H2R can be more efficient in AD therapy. In this review, we focus on the role of histamine and its receptors in the treatment of AD, and we hope that histamine could be an effective therapeutic factor in the treatment of AD.

Usefulness of HeLa cells to evaluate inverse agonistic activity of antihistamines

Antihistamines are thought to antagonize histamine and prevent it from binding to the histamine H1 receptor (H1R). However, recent studies indicate that antihistamines are classified into two groups, i.e., inverse agonists and neutral antagonists on the basis of their ability to down-regulate the constitutive activity of H1R. As H1R is an allergy-sensitive gene whose expression influences the severity of allergic symptoms, inverse agonists should more potently alleviate allergic symptoms than neutral antagonists by inhibiting H1R constitutive activity. Therefore, it is important to assess inverse agonistic activity of antihistamines. Here we report a novel assay method using HeLa cells expressing H1R endogenously for evaluation of inverse agonistic activity of antihistamines. Pretreatment with inverse agonists down-regulated H1R gene expression below to its basal level. On the other hand, basal H1R mRNA expression was unchanged by neutral antagonist pretreatment. Both inverse agonists and neutral antagonists suppressed histamine-induced H1R mRNA elevation. Classification of antihistamines on the basis of their suppressive activity of basal H1R gene expression was consistent with that of inositol phosphate accumulation in H1R-overexpressed cells. Our data suggest that the assay method using HeLa cells is more convenient and useful than the existing methods and may contribute to develop new antihistamines with inverse agonistic activity.