Human Histamine Receptor Research Articles

Activation of Brain Histaminergic Neurotransmission: A Mechanism for Cognitive Effects of Memantine in Alzheimer's Disease

We previously reported that some N-methyl-D-aspartate (NMDA)-receptor antagonists enhanced histamine neuron activity in rodents. Here, we have investigated the effects of memantine, an NMDA-receptor antagonist used for the treatment of Alzheimer's disease, on histaminergic neurotransmission. In vitro, memantine antagonized native NMDA receptors with a micromolar potency but had no effect at recombinant human histamine receptors. In vivo, a single administration of memantine increased histamine neuron activity, as shown by the 60% increase of tele-methylhistamine (t-MeHA) levels observed in the brain of mice. This increase occurred with an ED(50) of 0.3 ± 0.1 mg/kg, similar to that found on inhibition of ex vivo [(3)H]dizocilpine maleate (MK-801) binding (1.8 ± 1.3 mg/kg). Two days after pretreatment of mice with memantine at 5 mg/kg twice daily for 5 days, t-MeHA levels were enhanced by 50 ± 7% (p < 0.001), indicating a long-lasting activation of histamine neurons. Quantitative polymerase chain reaction analysis was used to explore genes involved in this persistent effect. H(3) receptor mRNAs were strongly increased, but the density of H(3) receptor binding sites was increased solely in hypothalamus (by 141 ± 24%). Up-regulations of brain-derived neurotrophic factor and NMDA-receptor 1 subunit mRNAs were also found but were restricted to hippocampus. mRNA expression of α7-nicotinic receptors remained unchanged in any region. Considering the well established cognitive effects of histamine neurons, the increase in brain t-MeHA levels after single or repeated administration of therapeutic doses of memantine suggests that the drug exerts its beneficial effects on cognitive deficits of Alzheimer's disease, at least partly, by activating histamine neurons.

Stable isotope labelling of human histamine receptor H1R: Prospects for structure-based drug design

Stable isotope labelling of human histamine receptor H1R: Prospects for structure-based drug design

An in Silico Development of Selective Inhibitor for Histamine Receptors

This study aimed to design a reliable homology model of human histamine H1 and H4 receptors (hH1R, hH4R), that would guide future biochemical and genetic efforts in its evaluation as a potential therapeutic target. Furthermore, these accurate models could aid in the structure-based inhibitor design for antagonists against the histamine H1 and H4 receptors. The homologous protein sequences of histamine receptors were retrieved from the NCBI REFSEQ which by using the sequence alignment program ClustalW alignment of the human histamine receptors sequence with Bovine Rhodopsin was conducted to locate the homology aligned regions. The present study found that Asp107 and Asn198 are in favorable positions for anchoring histamine. Identification of novel interaction sites for antagonist binding mutational data suggest a crucial role for Asp107, Trp158, Phe 432 and Phe 435 in antagonist binding. This study identified several novel amino acids at the binding site. Binding mode analysis of known H1 antagonists four known H1 antagonists (mepyramine, acrivastine, desloratadine, loratadine) were docked successfully to the binding site of the hH1R model by FlexiDock. The ligand used for optimizing the receptor model, the pharmacophore constraints and the different scoring functions applied in high throughput docking had all significant effect on the results. This research identified 16 compounds with 7 significant H4 activities representing an overall hit rate of 5.2%. To the best of our knowledge, this is one of the largest structure-based virtual screenings, where the virtual hits were confirmed by an in vitro assay. Moreover, this is the first structure-based drug design study reported on the hH4R. After the virtual screening, we identified several novel ligands with significant H4 affinity. These scaffolds can serve as starting points in the development of potent and selective H4 ligands in future.

Polymorphisms in human histamine receptor H4 gene are associated with atopic dermatitis

Atopic dermatitis (AD) is a chronic skin disease affecting more than 15% of children and 2% of adults. A strong connection between genetic factors and AD has been described for a long time. Histamine receptor H4 (HRH4) has been shown to be related to different kinds of allergic and autoimmune disorders. However, an association between HRH4 and AD has not yet been reported. To examine a possible association between HRH4 and AD. Genomic DNA from 301 patients with AD and 313 healthy controls was extracted and three exons of HRH4 were sequenced. We found three new single nucleotide polymorphisms (SNPs) in HRH4 which were significantly associated with AD: ss142022671 [odds ratio (OR) 1.87, 95% confidence interval (CI) 1.24-2.81; P = 0.002], ss142022677 (OR 4.40, 95% CI 2.42-8.00; P = 1.5 x 10(-7)) and ss142022679 (OR 4.26, 95% CI 2.38-7.61; P = 1.3 x 10(-7)). The SNPs ss142022677 and ss142022679 were found to be in strong linkage disequilibrium (D' = 0.98; r(2) = 0.92). Two-SNP haplotype analysis (ss142022677 and ss142022679) showed that the major AA haplotype was protective against AD (OR 0.22, 95% CI 0.12-0.40; P = 3.1 x 10(-8)) and the minor TT haplotype was significantly associated with AD (OR 4.13, 95% CI 2.27-7.54; P = 6.6 x 10(-7)). In addition, in a three-SNP haplotype analysis (ss142022671, ss142022677 and ss142022679), the major TAA haplotype was protective against AD (OR 0.46, 95% CI 0.31-0.69; P = 0.0001), while the complementary ATT haplotype was found to be significantly associated with AD (OR 3.81, 95% CI 2.03-7.14; P = 8.3 x 10(-6)). Polymorphisms of ss142022671, ss142022677 and ss142022679 in HRH4 are associated with AD.

In vitro and in vivo pharmacological analysis of imidazole-free histamine H3 receptor antagonists: promising results for a brain-penetrating H3 blocker with weak anticholinesterase activity

The pharmacological profiling of potent histamine H(3)-ligands initiated in a previous study is completed here. In vitro functional and binding studies revealed that several derivatives were selective H(3)-antagonists with nanomolar potency at human and guinea-pig histamine receptors, able to inhibit rat brain cholinesterase at micromolar concentrations and devoid of any cytotoxicity on cultured cells. Ex vivo binding experiments in rats showed that the most potent H(3)-antagonist, compound 5, had a prompt and long-lasting presence in the central nervous system (CNS), inhibiting [(3)H](R)-alpha-methylhistamine cortical binding [ED(50) (dose that elicits a 50% response) = 0.63 mg/kg intraperitoneally (i.p.)]. In the passive-avoidance test, compound 5, at 1.25 mg/kg i.p., was as effective as the anti-Alzheimer drug donepezil in attenuating scopolamine-induced amnesia in rats. These results suggest that a good CNS penetration and multitarget activity could account for the antiamnesic effect of this weak cholinesterase inhibitor and potent H(3)-antagonist (compound 5). This result represents a potential benchmark for the development of non-imidazole H(3)-antagonists/cholinesterase inhibitors with therapeutic potential in cognitive disorders.

Histamine alters E-cadherin cell adhesion to increase human airway epithelial permeability.

During the immediate response to an inhaled allergen, there is an increase in the paracellular permeability of the airway epithelium.1 Histamine is an important agonist released during the immediate response to inhaled allergen. We hypothesized that histamine would increase human airway epithelial paracellular permeability and that it would do this by interrupting E-cadherin-based cell adhesion. Histamine, applied to the basolateral surface, increased the paracellular permeability of cultured human airway epithelia, and this effect of histamine was blocked by the histamine receptor antagonist promethazine. ECV304 cells express a histamine receptor, N-cadherin, and elements of the tight junction, including claudins, but they do not express E-cadherin. Histamine increased the paracellular permeability of ECV304 cells transfected with a vector and expressing E-cadherin but not ECV304 cells expressing lac-Z in the same vector. L cells do not express the histamine receptor, cadherins, or claudins. Histamine decreased adhesion of L cells expressing the human histamine receptor and E-cadherin to an E-cadherin-Fc fusion protein. Histamine did not alter the adhesion to the E-cadherin fusion protein of L cells expressing either the histamine receptor or E-cadherin alone. When applied to the apical surface, adenovirus poorly infects airway epithelial cells because its receptor, CAR, is restricted to the basolateral surface of the cells. When histamine was applied to the basolateral surface of airway epithelial cells, infection of the cells by adenovirus increased by approximately one log. This effect of histamine was also blocked by promethazine. Histamine increases airway paracellular permeability and increases susceptibility of airway epithelial cells to infection by adenovirus by interrupting E-cadherin adhesion.

Differential Activation of Dual Signaling Responses by Human H1 and H2 Histamine Receptors

Stimulation of human H1 and H2‐histamine receptors (HRs) primarily activates signaling pathways to increase intracellular calcium [Ca2+]i and cyclic AMP (cAMP), respectively. Activation of H2‐HR in human embryonic kidney (HEK) cells by histamine and dimaprit increases both cAMP formation and [Ca2+]i, as determined by cAMP‐scintillation proximity assays and fluorescence imaging plate reader (FLIPR) assays. In HEK cells expressing relatively high levels of H2‐HR (Bmax = 26 pmol/mg protein), histamine and dimaprit are full agonists in eliciting cAMP responses with pEC50 values of 9.30 and 7.72 that are 1000‐fold more potent than their respective pEC50 values of 6.13 and 4.91 for increasing [Ca2+]i. The agonist potencies decrease for both responses at lower H2‐HR density (5 pmol/mg protein) and dimaprit exhibits partial agonist behavior for the [Ca2+]i response. The inverse agonists ranitidine and cimetidine more potently inhibit cAMP production in the higher expressing H2‐HR line. Histamine also activated both signaling pathways via human H1‐HRs highly expressed (Bmax = 17 pmol/mg protein) in HEK cells, with a 1000‐fold greater potency for [Ca2+]i vs. cAMP responses (pEC50 = 7.86 and 4.82, respectively). These studies demonstrate a markedly different potency for activation of multiple signaling pathways by H1‐ and H2‐HRs that may contribute to the selectivity of histamine responses in vivo.

Cloning, expression, and pharmacological characterization of a novel human histamine receptor.

Using a genomics-based reverse pharmacological approach for screening orphan G-protein coupled receptors, we have identified and cloned a novel high-affinity histamine receptor. This receptor, termed AXOR35, is most closely related to the H3 histamine receptor, sharing 37% protein sequence identity. A multiple responsive element/cyclic AMP-responsive element-luciferase reporter assay was used to identify histamine as a ligand for AXOR35. When transfected into human embryonic kidney 293 cells, the AXOR35 receptor showed a strong, dose-dependent calcium mobilization response to histamine and H3 receptor agonists including imetit and immepip. Radioligand binding confirmed that the AXOR35 receptor was a high-affinity histamine receptor. The pharmacology of the AXOR35 receptor was found to closely resemble that of the H3 receptor; the major difference was that (R)-alpha-methylhistamine was a low potency agonist of the AXOR35 receptor. Thioperamide is an antagonist at AXOR 35. Expression of AXOR35 mRNA in human tissues is highest in peripheral blood mononuclear cells and in tissues likely to contain high concentrations of blood cells, such as bone marrow and lung. In situ hybridization analysis of a wide survey of mouse tissues showed that mouse AXOR35 mRNA is selectively expressed in hippocampus. The identification and localization of this new histamine receptor will expand our understanding of the physiological and pathological roles of histamine and may provide additional opportunities for pharmacological modification of these actions.

Molecular Cloning and Characterization of a New Human Histamine Receptor, HH4R

A new histamine receptor, HH4R, was cloned from human leukocyte cDNA. The deduced amino acid sequence showed about 40% identity to that of the human histamine H3 receptor, HH3R. HH4R-expressing cells responded to histamine, inhibiting forskolin-induced cAMP accumulation. An H3 agonist, N-α-methylhistamine (NAMHA), bound specifically to HH4R, while another H3 agonist, R(−)-α-methylhistamine (RAMHA), and the H3 antagonist, thioperamide, competed with this binding. RAMHA, NAMHA, and imetit inhibited forskolin-induced cAMP accumulation in HH4R-expressing cells. However, the binding affinities and agonistic activities of H3 agonists to HH4R were weaker than those to HH3R. Low expression of HH4R was detected in a wide variety of peripheral tissues by RT-PCR; however, in contrast with HH3R, expression was not detected in the brain. These observations indicate that the clone is a distinct histamine receptor from HH3R, and thus is named HH4R.

Expression of the histamine receptor in Xenopus oocyte and its application to the histamine sensor

We developed a receptor-mediated biological sensor for real time detection of histamine derived from granules of mast cell and basophils. A human histamine receptor gene was cloned by polymerase chain reaction and its mRNA was injected into Xenopus oocyte. After incubation for 2–3 days, the histamine receptor was expressed in the cell membrane of the oocyte. When the oocyte was activated by histamine, a calcium-activated chloride channel was opened, and the chloride ions in the oocyte flowed to the outside. The chloride ion current intensity was correlated with the histamine concentration. The histamine sensitivity of the oocyte was sufficient to allow comparison with other methods histamine analyses, such as enzyme immunoassay or HPLC analysis. The oocyte sensor system described here is a new chemical sensor system using receptor-mediated biological reactions.