thioperamide and 4-methylhistamine

It is a well-known fact that histamine is involved in eosinophil-dependent inflammatory responses including cellular chemotaxis and migration. Nevertheless, the relative role of histamine receptors in the mechanisms of eosinophils adhesion to endothelial cells is not known. Therefore the aim of presented study was to examine the effect of selective histamine receptors ligands on eosinophils adhesion to endothelium. For that purpose the highly purified human eosinophils have been isolated from the peripheral blood. The viability and functional integrity of isolated eosinophils have been validated in several tests. Histamine as well as 4-methylhistamine (selective H4 agonist) in concentration-dependent manner significantly increased number of eosinophils that adhere to endothelium. Among the selective histamine receptors antagonist or H1 inverse agonist only JNJ7777120 (histamine H4 antagonist) and thioperamide (dual histamine H3/H4 antagonist) had direct effect on eosinophils adhesion to endothelial cells. Antagonists of H1 (diphenhydramine, mepyramine) H2 (ranitidine and famotidine) and H3 (pitolisant) histamine receptors were ineffective. To the best of our knowledge, this is the first study to demonstrate that histamine receptor H4 plays a dominant role in histamine-induced eosinophils adhesion to endothelium.

Topics: Cell Adhesion; Cell Communication; Cell Line; Cell Separation; Cell Survival; Drug Inverse Agonism; Endothelium; Eosinophils; Histamine; Histamine Agonists; Histamine H1 Antagonists; Humans; Indoles; Ligands; Methylhistamines; N-Formylmethionine Leucyl-Phenylalanine; Piperazines; Piperidines; Receptors, Histamine

Clozapine is an effective antipsychotic for treatment-resistant schizophrenia, but can cause fatal hematopoietic toxicity as agranulocytosis. To elucidate the mechanism of hematopoietic toxicity induced by clozapine, we developed an in vitro assay system using HL-60 cells, and investigated the effect on hematopoiesis. HL-60 cells were differentiated by all-trans retinoic acid (ATRA) into three states according to the following hematopoietic process: undifferentiated HL-60 cells, those undergoing granulocytic ATRA-differentiation, and ATRA-differentiated granulocytic cells. Hematopoietic toxicity was evaluated by analyzing cell survival, cell proliferation, granulocytic differentiation, apoptosis, and necrosis. In undifferentiated HL-60 cells and ATRA-differentiated granulocytic cells, both clozapine (50 and 100μM) and doxorubicin (0.2µM) decreased the cell survival rate, but olanzapine (1-100µM) did not. Under granulocytic differentiation for 5days, clozapine, even at a concentration of 25μM, decreased survival without affecting granulocytic differentiation, increased caspase activity, and caused apoptosis rather than necrosis. Histamine H4 receptor mRNA was expressed in HL-60 cells, whereas the expression decreased under granulocytic ATRA-differentiation little by little. Both thioperamide, a histamine H4 receptor antagonist, and DEVD-FMK, a caspase-3 inhibitor, exerted protection against clozapine-induced survival rate reduction, but not of live cell counts. 4-Methylhistamine, a histamine H4 receptor agonist, decreased the survival rate and live cell counts, as did clozapine. HL-60 cells under granulocytic differentiation are vulnerable under in vitro assay conditions to hematopoietic toxicity induced by clozapine. Histamine H4 receptor is involved in the development of clozapine-induced hematopoietic toxicity through apoptosis, and may be a potential target for preventing its occurrence through granulocytic differentiation.

Topics: Antipsychotic Agents; Apoptosis; Cell Differentiation; Clozapine; Granulocytes; Histamine Antagonists; HL-60 Cells; Humans; Methylhistamines; Piperidines; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H4; Tretinoin

The histamine H(4) receptor (H(4)R) is involved in the chemotaxis of leukocytes and mast cells to sites of inflammation and is suggested to be a potential drug target for asthma and allergy. So far, selective H(4)R agonists have not been identified. In the present study, we therefore evaluated the human H(4)R (hH(4)R) for its interaction with various known histaminergic ligands. Almost all of the tested H(1)R and H(2)R antagonists, including several important therapeutics, displaced less than 30% of specific [(3)H]histamine binding to the hH(4)R at concentrations up to 10 microM. Most of the tested H(2)R agonists and imidazole-based H(3)R ligands show micromolar-to-nanomolar range hH(4)R affinity, and these ligands exert different intrinsic hH(4)R activities, ranging from full agonists to inverse agonists. Interestingly, we identified 4-methylhistamine as a high-affinity H(4)R ligand (K(i) = 50 nM) that has a >100-fold selectivity for the hH(4)R over the other histamine receptor subtypes. Moreover, 4-methylhistamine potently activated the hH(4)R (pEC(50) = 7.4 +/- 0.1; alpha = 1), and this response was competitively antagonized by the selective H(4)R antagonist JNJ 7777120 [1-[(5-chloro-1H-indol-2-yl)-carbonyl]-4-methylpiperazine] (pA(2) = 7.8). The identification of 4-methylhistamine as a potent H(4)R agonist is of major importance for future studies to unravel the physiological roles of the H(4)R.

Topics: Cell Line; Histamine Agonists; Humans; Imidazoles; Indoles; Isothiuronium; Ligands; Methylhistamines; Piperazines; Radioligand Assay; Receptors, G-Protein-Coupled; Receptors, Histamine; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Histamine H3; Receptors, Histamine H4

Effects of histamine and related compounds on the bovine iris dilator were investigated. Histamine caused a concentration-related contraction of the bovine iris dilator and IC50 was 1.57 x 10(-7) M. The potency of histamine on the bovine iris dilator was almost the same as that observed in guinea pig ileum. Histamine-induced contraction of the bovine iris dilator was antagonized by the H1 antagonists pyrilamine, diphenhydramine and chlorpheniramine, whereas pretreatment with the H2 antagonists cimetidine and ranitidine was most effective. In addition, histamine and the H1 agonist 2-methylhistamine caused a contraction of bovine iris dilator, but the H2 agonist 4-methylhistamine was not effective. An H3 antagonist, thioperamide, also had no contractive effects on the bovine iris dilator. The bovine iris dilator contained a considerable amount of histamine, which was not released by compound 48/80, substance P or by increasing K+ concentration in the medium. In conclusion, histamine caused a potent contraction of the bovine iris dilator via H1 receptor, and this muscle showed a high sensitivity to histamine similar to guinea pig ileum.

Topics: Analysis of Variance; Animals; Cattle; Chlorpheniramine; Cimetidine; Diphenhydramine; Dose-Response Relationship, Drug; Female; Guinea Pigs; Histamine; Histamine Antagonists; Histamine H1 Antagonists; Histamine H2 Antagonists; Ileum; Iris; Lethal Dose 50; Male; Methylhistamines; Muscle Contraction; Muscle, Smooth; p-Methoxy-N-methylphenethylamine; Piperidines; Potassium; Pyrilamine; Ranitidine; Receptors, Histamine H1; Substance P

The recent availability of potent and selective ligands, namely R-(alpha)-methylhistamine and thioperamide, led to conclusive progresses as regards histamine H3-receptor knowledge. The aim of this work is to investigate by in vitro tests the pharmacological properties of new amino and methyl derivatives of the H3-antagonist thioperamide. Such original compounds, developed by the modulation of the thioperamide imidazolyl moiety, were assayed at guinea-pig ileal contractile H1-, atrial chronotropic H2- and enteric neuronal H3-receptors. None of the drugs exhibited interaction with H1 or H2 sites. On electrically stimulated ileum, two of the thioperamide methyl derivatives competitively antagonized the inhibitory effect of the H3-agonist R-(alpha)-methylhistamine. On the basis of the Schild analysis, the more active isomer (compound IV) displayed an affinity at H3-receptors only five times lower than thioperamide. These results could contribute to elucidate further the structural features required to develop potent and selective H3-antagonists. On the other hand, to prove the hypothesized apparent heterogeneity between peripheral and central H3-sites, as emerged by pharmacological and binding studies, autoradiographic investigations are in progress.

Topics: Animals; Electric Stimulation; Female; Guinea Pigs; Heart Atria; Heart Rate; Histamine; Ileum; In Vitro Techniques; Male; Methylhistamines; Muscle Contraction; Muscle, Smooth; Piperidines; Receptors, Histamine H1; Receptors, Histamine H2; Receptors, Histamine H3