Silencing of H4R inhibits the production of IL-1ß through SAPK/JNK signaling in human mast cells.

CONTEXT: Mast cell (MC) activation through H4R releases various inflammatory mediators which are associated with allergic asthma. OBJECTIVES: To investigate the siRNA-mediated gene silencing effect of H4R on human mast cells (HMCs) functions and the activation of stress-activated protein kinases (SAPK)/jun amino-terminal kinases (JNK) signaling pathways for the release of ineterleukin-1ß (IL-1ß) in HMCs. MATERIALS AND METHODS: H4R expression was analyzed by RT-PCR and western blotting in human mast cell line-1 (HMC-1) cells and H4RsiRNA transfected cells. The effect of H4RsiRNA and H4R-antagonist on H4R mediated MC functions such as intracellular Ca2+ release, degranulation, IL-6 and IL-1ß release, and the activation SAPK/JNK signaling pathways were studied. HMC-1 cells were stimulated with 10 µM of histamine (His) and 4-methylhistamine (4-MH) and pretreated individually with H4R-antagonist JNJ7777120 (JNJ), histamine H1 receptor (H1R)-antagonist mepyramine, and signaling molecule inhibitors SP600125 (SP) and Bay117082. RESULTS: We found that the HMC-1 cells expressed H4R and H4RsiRNA treatment down regulated the H4R expression in HMC-1 cells. Both His and 4-MH induced the intracellular Ca2+ release and degranulation whereas; H4R siRNA and JNJ inhibited the effect. Furthermore, the activation of H4R caused the phosphorylation of SAPK/JNK pathways. H4R gene silencing and pretreatment with SP and JNJ decreased His and 4-MH induced phosphorylation of SAPK/JNK. We found that the activation of H4R caused the release of IL-1ß (124.22 pg/ml) and IL-6 (122.50 pg/ml) on HMC-1 cells. Whereas, SAPK/JNK inhibitor (68.36 pg/ml) inhibited the H4R mediated IL-1ß release. CONCLUSIONS: Taken together, the silencing of H4R inhibited the H4R mediated MC functions and SAPK/JNK phosphorylation. Furthermore, the H4R activation utilized SAPK/JNK signaling pathway for IL-1ß release in HMC-1 cells.

Stimulation of the histamine 4 receptor upregulates thymic stromal lymphopoietin (TSLP) in human and murine keratinocytes.

The cytokine thymic stromal lymphopoietin (TSLP) is involved in the development and the progression of allergic diseases. It is mainly released by epithelial cells at barriers such as skin and gut in response to danger signals. Overexpression of TSLP in keratinocytes (KC) can provoke the development of a type 2 inflammatory response. Additionally, TSLP directly acts on sensory neurons and thereby triggers itch. Since histamine is also increased in lesions of inflammatory skin diseases, the aim of this study was to investigate possible effects of histamine as well as different histamine receptor subtype agonists and antagonists on TSLP production in KC. We therefore stimulated human KC with histamine in the presence or absence of the known TSLP-inductor poly I:C and measured TSLP production at protein as well as mRNA level. Histamine alone did not induce TSLP production in human KC, but pre-incubation with histamine prior to challenge with poly I:C resulted in a significant increase of TSLP production compared to stimulation with poly I:C alone. Experiments with different histamine receptor agonists (H1R: 2-pyridylethylamine; H2R: amthamine; H2R/H4R: 4-methylhistamine (4MH)) revealed a dominant role for the H4R receptor, as 4-MH in combination with poly I:C displayed a significant increase of TSLP secretion, while the other agonists did not show any effect. The increase in TSLP production by 4MH was blocked with the H4R antagonist JNJ7777120. This effect was reproducible also in the murine KC cell line MSC. Taken together, our study indicates a new role for the H4 receptor in the regulation of TSLP in keratinocytes. Therefore, blocking of the H4R receptor in allergic diseases might be promising to alleviate inflammation and pruritus via TSLP.

Histamine in Macaca mulatto monkey cardiac sympathetic nerve system: a morphological and functional assessment.

Our previous study demonstrated the co-localization of histamine with norepinephrine (NE) within superior cervical ganglia (SCG), and the release of histamine from sympathetic nerve endings of guinea pig evoked by stimulations. We have now further investigated that whether the histamine can be synthesized, stored and released from the sympathetic nerve systems of Macaca mulatto monkey, and investigated the modulation of the sympathetic endogenous histamine release through histamine H(3) receptor in the monkey cardiac sympathetic nerve system. Double-labeled immunofluorescence technique was applied to investigate co-localization of histamine and NE in SCG of Macaca mulatto monkey. The cardiac sympathetic nerve terminals (synaptosomes) of Macaca mulatto monkey was prepared and depolarized with 50 mmol/L K(+). Histamine released from synaptosomes was detected by spectrofluorometer and regulations of histamine release through Ca(2+), Ca(2+)-channel blockers, H(3)-receptor agonist (R)-alpha-methylhistamine and histamine H(3)-receptor antagonist, thioperamide were observed. Co-localization of histamine and NE was identified within the same neuron of SCG. Release of histamine was Ca(2+)-dependent and inhibited by N-type Ca(2+)-channel blocker omega-conotoxin, but not affected by the L-type Ca(2+)-channel blocker lacidipine. Compound 48/80, a mast cell releaser, did not affect cardiac synaptosome histamine exocytosis. Cardiac synaptosome histamine release was augmented by the enhanced synthesis of histamine or the inhibition of histamine metabolism. Histamine H(3)-receptor activation by (R)-alpha-methylhistamine inhibited high K(+)-evoked histamine release and thioperamide blocked the effects of (R)-alpha-methylhistamine. These results firstly showed that histamine co-existed with NE within sympathetic neurons of monkey and the exocytosis of histamine from sympathetic terminals could be regulated by presynaptic histamine H(3) receptors. Sympathetic histamine may act as a neurotransmitter to modulate sympathetic neurotransmission.

Does the histaminergic system mediate bombesin/GRP-induced suppression of food intake?

Bombesin (BN) and its mammalian homologue, gastrin-releasing peptide (GRP), are potent satiety agents and have been implicated in the physiological regulation of food intake. The mechanism(s) of action of this effect remains unclear. There is a functional and anatomic overlap between histamine and BN in relationship to feeding, which led us to hypothesize that BN may mediate its satiety effects through activation of the histaminergic system. To assess this contention, we examined the effects of R-alpha-methylhistamine (alpha-MH) and Imetit, selective H3-receptor agonists that inhibit the release and synthesis of histamine, on BN- or cholecystokinin (CCK)-induced satiety. In this report we present the first evidence for the role of histamine H3 receptors in the mediation of BN-elicited satiety. During the first hour of the 4-h daily feeding session, BN reduced food intake by > 50% relative to the control condition; this suppression was blocked by prior treatment with the H3-receptor agonist, alpha-MH. This blockade of BN-induced satiety was dose related and selective to BN as alpha-MH failed to attenuate sulfated CCK-8-induced satiety. When alpha-MH was administered alone, it failed to significantly affect food intake. The specificity of this effect was further supported by the demonstration that another H3 agonist, Imetit, was also able to block the feeding-suppressant effects of BN. Furthermore, thioperamide, an H3-receptor antagonist, blocked these effects of Imetit.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible participation of histamine H3-receptors in the regulation of anaphylactic histamine release from isolated rat peritoneal mast cells.

Anaphylactic histamine release from isolated rat peritoneal mast cells was concentration-dependently blocked by a 5-min treatment with exogenous histamine at 0.9 and 9 microM and enhanced by a 20- to 30-min treatment with thioperamide (H3-antagonist) at 3 microM with significance, but little affected by mepyramine (H1-antagonist) and cimetidine (H2-antagonist) at the cell concentration of 10(6) mast cells/ml. At a low concentration of mast cells (10(4) mast cells/ml), (R)-alpha-methylhistamine (alpha-MH), an H3-agonist, at 0.9-90 microM also inhibited the release in a concentration-dependent fashion. Thioperamide, but neither mepyramine nor cimetidine, significantly restored the decreased release by alpha-MH. However, the complete restoration by thioperamide could not be achieved because the drug itself slightly but concentration-dependently inhibited anaphylactic histamine release. On the other hand, not only betahistine and dimaprit but also alpha-MH did not suppress histamine release from the mast cells induced by compound 48/80. In rat plasma, considerable levels of histamine were detected. From these results, it is strongly suggested that histamine H3-like receptors are largely responsible for the negative feedback regulation of the anaphylactic histamine release from rat peritoneal mast cells.

Histamine H3 receptor-mediated inhibition of gastric acid secretion in conscious dogs.

The effect of (R)alpha-methylhistamine (MH) and thioperamide (selective agonist and antagonist respectively of histamine H3 receptors) was examined in conscious gastric fistula dogs to investigate the role of histamine H3 receptors in the control of basal and stimulated gastric acid secretion. Intravenous infusion of MH at 0.3 and 0.6 mumol/kg/h caused a significant reduction of the 2-deoxy-D-glucose (2-DG)-stimulated acid output, maximal inhibition being 60%. The inhibitory effect of MH was counteracted by thioperamide (0.1 mumol/kg/h), which, by itself, did not modify the 2-DG-induced acid secretion. The increase in plasma gastrin levels induced by 2-DG was not significantly affected either by MH or by thioperamide. Under basal conditions MH (0.3 mumol/kg/h) did not induce any significant change in acid secretion and in plasma gastrin levels; by contrast, thioperamide (0.1 mumol/kg/h) produced a significant increase both in acid output and in plasma gastrin. These results suggest that activation of H3 receptors can exert a negative control in stimulated acid secretion in conscious dogs, when cholinergic pathways to acid secretion are activated by 2-DG; moreover, the slight, but significant, stimulatory effect of thioperamide on basal acid output and basal plasma gastrin may be suggestive for a tonic inhibitory role of H3 receptors in the regulation of basal acid secretion, however, a nonspecific effect of this drug cannot be excluded.

Effects of the histamine H3-agonist (R)-alpha-methylhistamine and the antagonist thioperamide on histamine metabolism in the mouse and rat brain.

To study the feedback control by histamine (HA) H3-receptors on the synthesis and release of HA at nerve endings in the brain, the effects of a potent and selective H3-agonist, (R)-alpha-methylhistamine, and an H3-antagonist, thioperamide, on the pargyline-induced accumulation of tele-methylhistamine (t-MH) in the brain of mice and rats were examined in vivo. (R)-alpha-Methylhistamine dihydrochloride (6.3 mg free base/kg, i.p.) and thioperamide (2 mg/kg, i.p.), respectively, significantly decreased and increased the steady-state t-MH level in the mouse brain, whereas these compounds produced no significant changes in the HA level. When administered to mice immediately after pargyline (65 mg/kg, i.p.), (R)-alpha-methylhistamine (3.2 mg/kg, i.p.) inhibited the pargyline-induced increase in the t-MH level almost completely during the first 2 h after treatment. Thioperamide (2 mg/kg, i.p.) enhanced the pargyline-induced t-MH accumulation by approximately 70% 1 and 2 h after treatment. Lower doses of (R)-alpha-methylhistamine (1.3 mg/kg) and thioperamide (1 mg/kg) induced significant changes in the pargyline-induced t-MH accumulation in the mouse brain. In the rat, (R)-alpha-methylhistamine (3.2 mg/kg, i.p.) and thioperamide (2 mg/kg, i.p.) also affected the pargyline-induced t-MH accumulation in eight brain regions and the effects were especially marked in the cerebral cortex and amygdala. These results indicate that these compounds have potent effects on HA turnover in vivo in the brain.