Human Histamine Receptor Research Articles

Mucosal sugars delineate pyrazine vs pyrazinone autoinducer signaling in Klebsiella oxytoca

Virulent Klebsiella oxytoca strains are associated with gut and lung pathologies, yet our understanding of the molecular signals governing pathogenesis remains limited. Here, we characterized a family of K. oxytoca pyrazine and pyrazinone autoinducers and explored their roles in microbial and host signaling. We identified the human mucin capping sugar Neu5Ac as a selective elicitor of leupeptin, a protease inhibitor prevalent in clinical lung isolates of K. oxytoca, and leupeptin-derived pyrazinone biosynthesis. Additionally, we uncovered a separate pyrazine pathway, regulated by general carbohydrate metabolism, derived from a broadly conserved PLP-dependent enzyme. While both pyrazine and pyrazinone signaling induce iron acquisition responses, including enterobactin biosynthesis, pyrazinone signaling enhances yersiniabactin virulence factor production and selectively activates the proinflammatory human histamine receptor H4 (HRH4). Our findings suggest that the availability of specific carbohydrates delineates distinct autoinducer pathways in K. oxytoca that may have differential effects on bacterial virulence and host immune responses.

Structural basis for recognition of antihistamine drug by human histamine receptor

The histamine receptors belong to the G protein-coupled receptor (GPCR) superfamily, and play important roles in the regulation of histamine and other neurotransmitters in the central nervous system, as potential targets for the treatment of neurologic and psychiatric disorders. Here we report the crystal structure of human histamine receptor H3R bound to an antagonist PF-03654746 at 2.6 Å resolution. Combined with the computational and functional assays, our structure reveals binding modes of the antagonist and allosteric cholesterol. Molecular dynamic simulations and molecular docking of different antihistamines further elucidate the conserved ligand-binding modes. These findings are therefore expected to facilitate the structure-based design of novel antihistamines.

Unraveling the venom chemistry with evidence for histamine as key regulator in the envenomation by caterpillar Automeris zaruma.

Over the past decades, envenomation by caterpillars of Automeris spp. became an increasing health problem in Latin America. Accidental contact with the stinging spines of these caterpillars cause acute local pain, itching, inflammation and skin rashes that persists for days. Even when the cause is obvious, the exact molecular mechanisms responsible for the observed symptoms are yet to be elucidated. Here, we describe for the first time, an active compound in the venom and the study of the bioactivity of the venom extracted from the spines of the caterpillar Automeris zaruma. Electrophysiological screening of a library of membrane proteins important for pain and itch enabled us to investigate and reveal the mode of action of the venom of A. zaruma. Further mass spectrometric analysis (Q-TOF-MS) made it possible to establish a link between the bioactivity and the components found in the venom. We show that the spine extract of A. zaruma contains histamine that potently activates the four types of the human histamine receptors (H1R, H2R, H3R and H4R) with a selectivity preference towards H3R and H4R. Furthermore, a modulation of the target MRGPRX2 was found. Together, these findings are the first to explain the symptomology of A. zaruma envenomation, enabling us a better understanding of caterpillar envenomation and predict that the hurdle of the scarce efficacy of the currently used antihistaminic drugs can be overcome by including H3R and H4R blockers in the clinical used medication. Such an approach might be used for other caterpillar envenomation in the world and represent a significant improvement for the well-being of the patient.

VIRTUAL TARGET CONSTRUCTION FOR DISCOVERY OF HUMAN HISTAMINE H4 RECEPTOR LIGANDS EMPLOYING A STRUCTURE-BASED VIRTUAL SCREENING APPROACH

Objective: This study aimed to construct a virtual target to be used in structure-based virtual screening (SBVS) campaigns to discover ligands for human histamine receptor H4 (hHRH4). Methods: The virtual targets construction was initiated by hHRH4 homology modeling, followed by molecular docking of seliforant to the homolog model, and the virtual target candidate was constructed. The hHRH4 complexed to seliforant was subjected to molecular dynamics (MD) simulations in 100 ns. Finally, the pose with the least free energy of binding from the MD simulations was selected for further validation through re-docking simulations. All simulations were conducted by using the YASARA-Structure program package. Results: This study resulted in one validated target for SBVS protocols development. All RMSD values in the internal validation in snapshot 519 molecular dynamics simulation results were less than 2 Å, and this hHRH4 homology model is valid as a virtual target in an SBVS protocol. Moreover, using the clusterization module on MD simulations analysis, ten different virtual targets were available for further utilization. Conclusion: Virtual targets resulted from this study offer more possibilities to construct SBVS protocols to identify hHRH4 ligands. The validated virtual target and the ten different virtual targets resulted from clusterization can be accessed in the following GitHub repository: https://github.com/nugrahagerry/hHRH4.

Analysis of Missense Variants in the Human Histamine Receptor Family Reveals Increased Constitutive Activity of E4106.30×30K Variant in the Histamine H1 Receptor.

The Exome Aggregation Consortium has collected the protein-encoding DNA sequences of almost 61,000 unrelated humans. Analysis of this dataset for G protein-coupled receptor (GPCR) proteins (available at GPCRdb) revealed a total of 463 naturally occurring genetic missense variations in the histamine receptor family. In this research, we have analyzed the distribution of these missense variations in the four histamine receptor subtypes concerning structural segments and sites important for GPCR function. Four missense variants R1273.52×52H, R13934.57×57H, R4096.29×29H, and E4106.30×30K, were selected for the histamine H1 receptor (H1R) that were hypothesized to affect receptor activity by interfering with the interaction pattern of the highly conserved D(E)RY motif, the so-called ionic lock. The E4106.30×30K missense variant displays higher constitutive activity in G protein signaling as compared to wild-type H1R, whereas the opposite was observed for R1273.52×52H, R13934.57×57H, and R4096.29×29H. The E4106.30×30K missense variant displays a higher affinity for the endogenous agonist histamine than wild-type H1R, whereas antagonist affinity was not affected. These data support the hypothesis that the E4106.30×30K mutation shifts the equilibrium towards active conformations. The study of these selected missense variants gives additional insight into the structural basis of H1R activation and, moreover, highlights that missense variants can result in pharmacologically different behavior as compared to wild-type receptors and should consequently be considered in the drug discovery process.

Amitriptyline functionally antagonizes cardiac H2 histamine receptors in transgenic mice and human atria

We have previously shown that histamine (2-(1H-imidazol-4-yl)ethanamine) exerted concentration-dependent positive inotropic effects (PIE) or positive chronotropic effects (PCE) on isolated left and right atria, respectively, of transgenic (H2R-TG) mice that overexpress the human H2 histamine receptor (H2R) in the heart; however, the effects were not seen in their wild-type (WT) littermates. Amitriptyline, which is still a highly prescribed antidepressant drug, was reported to act as antagonist on H2Rs. Here, we wanted to determine whether the histamine effects in H2R-TG were antagonized by amitriptyline. Contractile studies were performed on isolated left and right atrial preparations, isolated perfused hearts from H2R-TG and WT mice and human atrial preparations. Amitriptyline shifted the concentration-dependent PIE of histamine (1 nM–10 μM) to higher concentrations (rightward shift) in left atrial preparations from H2R-TG. Similarly, in isolated perfused hearts from H2R-TG and WT mice, histamine increased the contractile parameters and the phosphorylation state of phospholamban (PLB) at serine 16 in the H2R-TG mice, but not in the WT mice. However, the increases in contractility and PLB phosphorylation were attenuated by the addition of amitriptyline in perfused hearts from H2R-TG. In isolated electrically stimulated human atria, the PIE of histamine that was applied in increasing concentrations from 1 nM to 10 μM was reduced by 10-μM amitriptyline. In summary, we present functional evidence that amitriptyline also acts as an antagonist of contractility at H2Rs in H2R-TG mouse hearts and in the human heart which might in part explain the side effects of amitriptyline.

Novel potent (dihydro)benzofuranyl piperazines as human histamine receptor ligands – Functional characterization and modeling studies on H3 and H4 receptors

Histamine acts through four different receptors (H1R-H4R), the H3R and H4R being the most explored in the last years as drug targets. The H3R is a potential target to treat narcolepsy, Parkinson’s disease, epilepsy, schizophrenia and several other CNS-related conditions, while H4R blockade leads to anti-inflammatory and immunomodulatory effects. Our group has been exploring the dihydrobenzofuranyl-piperazines (LINS01 series) as human H3R/H4R ligands as potential drug candidates. In the present study, a set of 12 compounds were synthesized from adequate (dihydro)benzofuran synthons through simple reactions with corresponding piperazines, giving moderate to high yields. Four compounds (1b, 1f, 1g and 1h) showed high hH3R affinity (pKi > 7), compound 1h being the most potent (pKi 8.4), and compound 1f showed the best efficiency (pKi 8.2, LE 0.53, LLE 5.85). BRET-based assays monitoring Gαi activity indicated that the compounds are potent antagonists. Only one compound (2c, pKi 7.1) presented high affinity for hH4R. In contrast to what was observed for hH3R, it showed partial agonist activity. Docking experiments indicated that bulky substituents occupy a hydrophobic pocket in hH3R, while the N-allyl group forms favorable interactions with hydrophobic residues in the TM2, 3 and 7, increasing the selectivity towards hH3R. Additionally, the importance of the indole NH in the interaction with Glu5.46 from hH4R was confirmed by the modeling results, explaining the affinity and agonistic activity of compound 2c. The data reported in this work represent important findings for the rational design of future compounds for hH3R and hH4R.

Pharmacological Characterization of Human Histamine Receptors and Histamine Receptor Mutants in the Sf9 Cell Expression System.

A large problem of histamine receptor research is data heterogeneity. Various experimental approaches, the complex signaling pathways of mammalian cells, and the use of different species orthologues render it difficult to compare and interpret the published results. Thus, the four human histamine receptor subtypes were analyzed side-by-side in the Sf9 insect cell expression system, using radioligand binding assays as well as functional readouts proximal to the receptor activation event (steady-state GTPase assays and [35S]GTPγS assays). The human H1R was co-expressed with the regulators of G protein signaling RGS4 or GAIP, which unmasked a productive interaction between hH1R and insect cell Gαq. By contrast, functional expression of the hH2R required the generation of an hH2R-Gsα fusion protein to ensure close proximity of G protein and receptor. Fusion of hH2R to the long (GsαL) or short (GsαS) splice variant of Gαs resulted in comparable constitutive hH2R activity, although both G protein variants show different GDP affinities. Medicinal chemistry studies revealed profound species differences between hH1R/hH2R and their guinea pig orthologues gpH1R/gpH2R. The causes for these differences were analyzed by molecular modeling in combination with mutational studies. Co-expression of the hH3R with Gαi1, Gαi2, Gαi3, and Gαi/o in Sf9 cells revealed high constitutive activity and comparable interaction efficiency with all G protein isoforms. A comparison of various cations (Li+, Na+, K+) and anions (Cl−, Br−, I−) revealed that anions with large radii most efficiently stabilize the inactive hH3R state. Potential sodium binding sites in the hH3R protein were analyzed by expressing specific hH3R mutants in Sf9 cells. In contrast to the hH3R, the hH4R preferentially couples to co-expressed Gαi2 in Sf9 cells. Its high constitutive activity is resistant to NaCl or GTPγS. The hH4R shows structural instability and adopts a G protein-independent high-affinity state. A detailed characterization of affinity and activity of a series of hH4R antagonists/inverse agonists allowed first conclusions about structure/activity relationships for inverse agonists at hH4R. In summary, the Sf9 cell system permitted a successful side-by-side comparison of all four human histamine receptor subtypes. This chapter summarizes the results of pharmacological as well as medicinal chemistry/molecular modeling approaches and demonstrates that these data are not only important for a deeper understanding of HxR pharmacology, but also have significant implications for the molecular pharmacology of GPCRs in general.

Human eosinophils - potential pharmacological model applied in human histamine H4 receptor research.

Histamine and histamine receptors are well known for their immunomodulatory role in inflammation. In this review we describe the role of histamine and histamine H4 receptor on human eosinophils. In the first part of article we provide short summary of histamine and histamine receptors role in physiology and histamine related therapeutics used in clinics. We briefly describe the human histamine receptor H4 and its ligands, as well as human eosinophils. In the second part of the review we provide detailed description of known histamine effects on eosinophils including: intracellular calcium concentration flux, actin polymerization, cellular shape change, upregulation of adhesion proteins and cellular chemotaxis. We provide proofs that these effects are mainly connected with the activation of histamine H4 receptor. When examining experimental data we discuss the controversial results and limitations of the studies performed on isolated eosinophils. In conclusion we believe that studies on histamine H4 receptor on human eosinophils can provide interesting new biomarkers that can be used in clinical studies of histamine receptors, that in future might result in the development of new strategies in the treatment of chronic inflammatory conditions like asthma or allergy, in which eosinophils are involved.

Antihistamine response: a dynamically refined function at the host-tick interface.

BackgroundTicks counteract host inflammatory responses by secreting proteins from their saliva that compete for histamine binding. Among these tick salivary proteins are lipocalins, antiparallel beta-barrel proteins that sequester small molecules. A tick salivary lipocalin has been structurally resolved and experimentally shown to efficiently compete for histamine with its native receptor (e.g., H1 histamine receptor). To date, molecular dynamics simulations focus on protein-protein and protein-ligand interactions, but there are currently no studies for simultaneous ligand exploration between two competing proteins.MethodsAided by state-of-the-art, high-throughput computational methods, the current study simulated and analyzed the dynamics of competitive histamine binding at the tick-host interface using the available crystal structures of both the tick salivary lipocalin histamine-binding protein from Rhipicephalus appendiculatus and the human histamine receptor 1.ResultsThe attraction towards the tick salivary lipocalin seems to depend on the protonated (adding a hydrogen ion) state of histamine since the current study shows that as histamine becomes more protonated it increases its exploration for the tick salivary lipocalin. This implies that during tick feeding, histamine may need to be protonated for the tick salivary lipocalin to efficiently sequester it in order to counteract inflammation. Additionally, the beta-hairpin loops (at both ends of the tick salivary lipocalin barrel) were reported to have a functional role in sequestering histamine and the results in the current study concur and provide evidence for this hypothesis. These beta-hairpin loops of the tick salivary lipocalin possess more acidic residues than a structurally similar but functionally unrelated lipocalin from the butterfly, Pieris brassicae; comparative results indicate these acidic residues may be responsible for the ability of the tick lipocalin to out-compete the native (H1) receptor for histamine.ConclusionsThree explanatory types of data can be obtained from the current study: (i) the dynamics of multiple binding sites, (ii) competition between two proteins for a ligand, and (iii) the intrinsic molecular components involved in the competition. These data can provide further insight at the atomic level of the host-tick interface that cannot be experimentally determined. Additionally, the methods used in this study can be applied in rationally designing drugs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0491-9) contains supplementary material, which is available to authorized users.

Integrative genomic analyses of the histamine H1 receptor and its role in cancer prediction

The human histamine receptor H1 (HRH1) gene is located on chromosome 3p25 and encodes for a 487 amino acid G protein-coupled receptor (GPCR) with a long third intracellular loop (IL3). The HRH1 predominantly couples to Gαq/11 proteins, leading to the activation of phospholipase C (PLC) and subsequent release of the second messengers inositol trisphosphate (IP3) and diacylglycerol (DAG) followed by the activation of PKC and the release of [Ca2+]i. In the present study, we identified HRH1 genes from 14 vertebrate genomes and found that HRH1 exists in all types of vertebrates including fish, amphibians, birds and mammals. We identified 88 SNPs including 4 available alleles disrupting an existing exonic splicing enhancer and 84 SNPs causing missense mutation, which may impact the effect of histamine on the HRH1 protein. We found that the human HRH1 gene was expressed in many tissues or organs, and predominant expression of HRH1 was shown in the bone marrow, whole blood, lymph node, thymus, brain, cerebellum, retina, spinal cord, heart, smooth muscle, skeletal muscle, small intestine, colon, adipocytes, kidney, liver, lung, pancreas, thyroid salivary gland, skin, ovary, uterus, placenta, prostate and testis. When searched in the PrognoScan database, human HRH1 was also found to be expressed in bladder cancer, blood cancer, brain cancer, breast cancer, colorectal cancer, eye cancer, head and neck cancer, lung cancer, ovarian cancer, skin cancer and soft tissue cancer tissues. The relationship between the expression of HRH1 and prognosis was found to vary in different types of cancers, even in the same cancer from different databases. This implies that the function of HRH1 in these tumors may be multidimensional. GR, STAT5A and c-Myb regulatory transcription factor binding sites were identified in the HRH1 gene upstream (promoter) region, which may be involved in the effect of HRH1 in tumors.

Synthesis and Functional Characterization of Imbutamine Analogs as Histamine H3 and H4 Receptor Ligands

Imbutamine (4-(1H-imidazol-4-yl)butanamine) is a potent histamine H3 (H3R) and H4 receptor (H4R) agonist (EC50 values: 3 and 66 nM, respectively). Aiming at improved selectivity for the H4R, the imidazole ring in imbutamine was methyl-substituted or replaced by various differently substituted heterocycles (1,2,3-triazoles, 1,2,4-triazoles, pyridines, pyrimidines) as potential bioisosteres. Investigations in [(35)S]GTPγS binding assays using membranes of Sf9 insect cells expressing the respective human histamine receptor subtype revealed only very weak activity of most of the synthesized hetarylalkylamines at both receptors. By contrast, the introduction of substituents at the 4-imidazolyl ring was most effective regarding H4R selectivity. This holds for methyl substitution in position 2 and, especially, in position 5. 5-Methylimbutamine (H4R: EC50 = 59 nM, α = 0.8) was equipotent with imbutamine at the hH4R, but revealed about 16-fold selectivity for the hH4R compared to the hH3R (EC50 980 nM, α = 0.36), whereas imbutamine preferred the hH3R. The functional activities were in agreement with radioligand binding data. The results support the hypothesis that, by analogy with histamine, methyl substitution in histamine homologs offers a way to shift the selectivity in favor of the H4R.

Polymorphisms of human histamine receptor H4 gene are associated with breast cancer in Chinese Han population

Previous investigations indicated that histamine receptor H4 (HRH4) played important roles in many aspects of breast cancer pathogenesis, and that the polymorphisms of HRH4 gene may result in expression and functional changes of HRH4 proteins. However, the relationship between polymorphisms of HRH4 and breast cancer risk and malignant degree is unclear. In the present study, we conducted a case–control investigation among 185 Chinese Han breast cancer patients and 199 ethnicity-matched health controls. Four tag-SNPs (i.e. rs623590, rs16940762, rs11662595 and rs1421125) of HRH4 were genotyped and association analysis was performed. Odds ratios (ORs) with 95% confidence intervals (CI) were used to assess the association. We found that the T allele of rs623590 had a decreased risk of breast cancer (adjusted OR, 0.667; 95% CI, 0.486–0.913; P=0.012) while the A allele of rs1421125 had an increased risk (adjusted OR, 1.653; 95% CI, 1.139–2.397; P=0.008). Further haplotype analysis showed that the CAA haplotype of rs623590–rs11662595–rs1421125 was more frequent among patients with breast cancer (adjusted OR, 1.856; 95% CI, 1.236–2.787; P=0.003). Additionally, polymorphisms of rs623590 and rs11662595 were also correlated with clinical stages, lymph node involvement, and HER2 status. These findings indicated that the variants of rs623590, rs11662595 and rs1421125 genotypes of HRH4 gene were significantly associated with the risk and malignant degree of breast cancer in Chinese Han populations, which may provide us novel insight into the pathogenesis of breast cancer although further studies with larger participants worldwide are still needed for conclusion validation.

Synthesis and pharmacological characterization of new tetrahydrofuran based compounds as conformationally constrained histamine receptor ligands

A series of tetrahydrofuran based compounds with a bicyclic core that provides conformational restriction were synthesized and investigated by radioligand displacement studies and functional [(35)S]GTPγS binding assays at the human histamine receptor (hHR) subtypes. The amines and ((1S,3R,5S,6R)- and ((1S,3S,5S,6R)-3-(1H-imidazol-5-yl)-2-oxabicyclo[3.1.0]hexan-6-yl)methanamine), exhibited submicromolar Ki values at the hH3R with 10-fold higher affinities than their corresponding (6S)-epimers and 25- and >34-fold selectivity over the hH4R, respectively. Both compounds act as neutral antagonists at the hH3R with KB values of 181 and 32 nM, respectively. The cyanoguanidines of the imidazole series and the oxazole analogues turned out to be inactive at all hHR subtypes.

Modulation of Phagocytosis in Tetrahymena thermophila by Histamine and the Antihistamine Diphenhydramine

Histamine is a significant biological compound because of its role in mediating the human allergic and inflammatory pathways. Antihistamines are often administered to control the irritating symptoms of allergic reactions. We evaluated phagocytosis in the protist Tetrahymena thermophil a for use in screening for potential therapeutic compounds that mimic histamine and antihistamines. Tetrahymena has been frequently used as an experimental model to study compounds for biological effects or to study biological processes. Histamine and the antihistamine diphenhydramine were administered at concentrations ranging from 10–6 μM to 1000 μM, and the corresponding changes in phagocytosis were detected by flow cytometry. Treatment with histamine had no measurable effect on phagocytosis while diphenhydramine decreased phagocytic levels at concentrations above 50 μM. In a competition experiment between histamine and diphenhydramine, histamine did not reverse the dosage-dependent decrease in phagocytosis elicited by diphenhydramine. BLAST searches revealed no significant homologs of the human histamine receptors in T. thermophila . These results suggest that T. thermophila has a receptor for diphenhydramine that is linked to the phagocytic process, but not a histamine receptor. Further study is necessary to elucidate the nature of this previously uninvestigated receptor. The experimental protocol developed as a part of this study may serve as an inexpensive, high throughput, flow cytometric method to screen natural and synthetic compounds for pharmacologically significant properties.

A report on anti-oedemogenic activity of Byttneria herbacea roots – Possible involvement of histamine receptor (type I)

Ethnopharmacological relevanceThe traditional healers of the Kol tribes of West Bengal, Bihar and Jharkhand (India), widely use the woody rootstock of Byttneria herbacea to reduce the swelling of limbs, due to filariasis. Besides filariasis different part of this plant is used for the treatment of cholera, diarrhoea and asthma. Aim of this studyThis study is a preliminary attempt to evaluate the anti-oedemogenic activity of the roots of Byttneria herbacea. Materials and methodsThe anti-oedemogenic activity of the hydroalcoholic extract of the roots of Byttneria herbacea (HBH) was evaluated against carrageenan and histamine induced rat paw oedema, acetic acid induced writhing and histamine induced vascular permeability in mice. Further, the effect of HBH on the expression of human histamine receptor type I (H1R) was studied in HeLa cells. ResultsHBH exhibited significant dose-dependent inhibition (*p<0.05) against carrageenan and histamine induced rat paw oedema. Similar significant dose-dependent inhibition was observed against acetic acid induced writhing and histamine-induced vascular permeability in mice. Moreover, H1R specific mRNA expression was also significantly (*p<0.05) suppressed by HBH. ConclusionHBH was observed to possess anti-oedemogenic activity which is probably mediated through suppression of H1R.

QSAR study on the histamine (H3) receptor antagonists using the genetic algorithm: Multi parameter linear regression

A quantitative structure activity relationship (QSAR) model has been produced for predicting antagonist potency of biphenyl derivatives as human histamine (H3) receptors. The molecular structures of the compounds are numerically represented by various kinds of molecular descriptors. The whole data set was divided into training and test sets. Genetic algorithm based multiple linear regression is used to select most statistically effective descriptors. The final QSAR model (N =24, R2=0.916, F = 51.771, Q2 LOO = 0.872, Q2 LGO = 0.847, Q2 BOOT = 0.857) was fully validated employing leaveone- out (LOO) cross-validation approach, Fischer statistics (F), Yrandomisation test, and predictions based on the test data set. The test set presented an external prediction power of R2 test=0.855. In conclusion, the QSAR model generated can be used as a valuable tool for designing similar groups of new antagonists of histamine (H3) receptors.

Human Memory Th17 Cells Express a Functional Histamine H4 Receptor

The histamine H4 receptor is functionally expressed on CD4(+) T cells and in particular on human CD4(+) Th2-polarized T cells. Interleukin (IL)-17-producing T cells (Th17 cells) represent a newly defined major CD4(+) T-cell subset, having been identified in psoriatic plaques and in acute skin lesions of atopic dermatitis where histamine is also present in high concentrations. To elucidate the role of the histamine H4 receptor (H4R) on these effector T cells, we polarized human memory T cells into Th17 cells. Further, we investigated H4R expression and assessed its function by real-time PCR, by a cytokine secretion assay of IL-17, and by electrophoretic mobility shift assay of activating protein-1 (AP-1). We show that Th17 cells polarized by IL-1β together with IL-23 express the H4R on mRNA and protein level. Additionally, we identified IL-17-positive cells in psoriatic skin lesions. The IL-17-positive lymphocytes were all positive also for functional H4R. Stimulation with histamine or a H4R agonist increased the production of IL-17 and induced activating protein-1 in Th17 cells. In inflammatory skin diseases with enhanced histamine release, such as psoriasis and atopic dermatitis, histamine might foster the immunomodulatory potency of skin-infiltrating Th17 cells.

Involvement of histamine receptors in the atypical antipsychotic profile of clozapine: a reassessment in vitro and in vivo

The basis of the unique clinical profile of the antipsychotic clozapine is not yet elucidated. Brain histamine receptors may play a role in schizophrenia and its treatment, but their involvement in the profile of clozapine remained unknown. We explored the properties of clozapine and its two metabolites, N-desmethylclozapine (NDMC) and clozapine N-oxide, at the four human histaminergic receptors. We compared their active concentrations with their blood concentrations in patients treated by clozapine. We investigated the changes in receptor densities induced in rat brain by repeated administration of a therapeutic dose of clozapine. Clozapine and NDMC behaved as very potent, and partial, H(1)-receptor inverse agonists, weak, and full, H(2)-receptor inverse agonists, moderate, and protean, H(3)-receptor agonists, and moderate, and partial, H(4)-receptor agonists. Taking into account their micromolar mean blood concentrations found in 75 treated patients, and assuming that they are enriched in human brain as they are in rat brain, a full occupation of H(1)-, H(3)-, and H(4)-receptors, and a partial occupation of H(2) receptors, is expected. In agreement, repeated administration of clozapine at a therapeutic dose (20 mg/kg/day for 20 days) induced an up-regulation of H(1)- and H(2)-receptors in rat brain. Clozapine and its active metabolite NDMC interact with the four human histamine receptors at clinically relevant concentrations. This interaction may substantiate, at least in part, the atypical antipsychotic profile of clozapine, as well as its central and peripheral side effects such as sedation and weight gain.

C-027 Inhibits IgE-mediated passive sensitization bronchoconstriction and acts as a histamine and serotonin antagonist in human airways

Atopic asthma is poorly controlled by current therapies. Newer therapies and novel antihistamines are, therefore, required to treat patients whose atopic asthma is not controlled. For the first time, C-027 is shown to antagonize histamine, IgE-mediated and serotonin-induced contraction in human airways and vessels. Human precision-cut lung slices (PCLS, 250 μm thick), containing an airway or blood vessel, were pretreated with either C-027 (2 hours) or with vehicle alone and were contracted with histamine or serotonin. Known antihistamine was used as a comparator in antihistamine studies. Also, human airways were contracted via IgE passive sensitization in the presence or absence of C-027 or fexofenadine. Affinity of C-027 toward human G-protein coupled receptors was also determined, as well as the drug's biodistribution in murine model. C-027 was shown to have the highest affinity toward human histamine and serotonin receptors. Subsequently, C-027 was shown to antagonize histamine- and serotonin-induced airway and vascular smooth muscle contraction, respectively, and histamine-released bronchocontraction mediated by IgE passive sensitization in human small airways. C-027 also inhibited histamine-mediated single-cell calcium ion release. Low levels of C-027 were found in murine brain tissue. Collectively, these data suggest that C-027 markedly inhibits IgE-induced bronchoconstriction and antagonizes histamine and serotonin-contraction with little biodistribution in the brain. The compound may offer a future therapy for allergen-induced airway hyperresponsiveness in patients with asthma.