Pruritus-associated response mediated by cutaneous histamine H3 receptors

BACKGROUND: Histamine is one of the most common chemical mediators causing pruritus, and H1 receptor antagonists have been used as a first choice in its treatment. On the other hand, although the presence of H3 receptors has been identified in the skin, few studies have investigated the involvement of H3 receptors on pruritus. OBJECTIVE: The purpose of this study was to examine whether H3 receptor agonist or antagonist influences the incidence of scratching behaviour in ICR or mast cell-deficient WBB6F1-W/WV mice. METHODS: The mice were given an intradermal injection of H3 receptor agonist or antagonist into the rostral part of the back, and the occurrence of scratching behaviour at the injected site by the hind paws was counted over 60 min. RESULTS: H3 receptor antagonists, thioperamide and AQ0145 significantly increased the incidence of scratching behaviour in ICR mice. H3 receptor agonist, (R)-alpha-methylhistamine, had no effect. On the other hand, (R)-alpha-methylhistamine significantly inhibited thioperamide or AQ0145-induced scratching behaviour. In addition, both thioperamide and AQ0145 elicited scratching behaviour in mast cell-deficient WBB6F1-W/WV mice. CONCLUSION: From these results, it may be concluded that H3 receptors are involved in the modulation of pruritus in the skin, and mast cells are not essential in this response. In addition, H3 receptor agonists can be useful as a novel therapeutic approach against pruritus.     

Increased expression of histamine H1 receptor mRNA in allergic rhinitis

Background Histamine plays an important role in producing nasal symptoms via histamine H₁ receptor (H₁R) in allergic rhinitis. It is reported that the minimum histamine concentration that induces sneezing is lower in allergic patients than in normal control subjects. Previous studies by binding assay on H₁R gave divided results on whether the number of H₁Rs is increased in allergic rhinitis or not. Objective The objective of this study was to examine if H₁R mRNA expression is increased in patients with allergic rhinitis compared with normal healthy volunteers. Methods We extracted RNA from scrapings of inferior turbinate mucosa of 10 patients suft'ering from allergic rhinitis and 10 control subjects. As the H₁R gene lacks introns. we treated RNA pellets by DNase to distinguish RNA from contaminating genomic DNA. Since amplification of H₁R and β-actin mRNA remained in an exponential phase at 35 cycles. H₁R and β-actin mRNAs were amplified for 35 cycles by reverse transcHption-polymerase chain reaction (RT-PCR). The PCR products were hybridized with internal probes and band intensities were quantitated by a densitometer. Results The mean ± sd of H₁R/β-actin ratio was 0.88 ± 0.62 for the patients with allergic rhinitis and 0.29 ± 0.17 for the normal subjects; the difference was statistically significant (P<0.01). Conclusions These data suggest that expression of H₁R mRNA is increased in the nasal mucosa of the patients with allergic rhinitis.     

Modulation of histamine H3 receptor function by monovalent ions

Monovalent ions differently affect ligand binding to G protein-coupled receptors (GPCRs) by as yet poorly defined mechanisms. In particular, NaCl often decreases the affinity of agonists but increases it for antagonists. We examined the effect of various monovalent ions on human histamine H₃ receptor (hH₃R), co-expressed with mammalian G proteins (Gα_i1, Gα_i2, Gα_i3 or Gα_o1, and β₁γ₂ dimers, respectively) in Sf9 insect cell membranes, with respect to agonist binding and G protein activation. NaCl (100 mM) had no effect on affinity of the agonist [³H]N^α-methylhistamine ([³H]NAMH). In steady-state GTPase assays, the endogenous agonist histamine had a lower potency and the inverse agonist thioperamide had a higher potency, when NaCl (100 mM) was present. Monovalent ions reduced H₃R-regulated signalling in the order of efficacy Li⁺ ∼ Na⁺ ∼ K⁺ < Cl⁻ < Br⁻ < I⁻. NaCl had a stronger effect on basal hH3R-signalling when Gα_i3 was co-expressed. Asp80^2.50, a putative interaction site for Na⁺, was mutated to Asn80^2.50 (D2.50N-hH₃R). Strikingly, the mutation was unable to activate Gα_i3 at all. The effects can be explained by a model, where (i) monovalent ions as well as a charge-neutralizing mutation of Asp80^2.50 generally reduce the interaction of hH₃R with G proteins, (ii) monovalent anions increase the affinity of G proteins for GDP and thus, indirectly affect their interaction with hH₃R and, (iii) Asp80^2.50 is a key residue for hH₃R/Gα_i3-protein activation. The latter result suggests that hH₃R/G protein-coupling interfaces may differ even between closely related subunits.     

Regulation of histamine release from human basophil leucocytes: role of H1, H2 and H3 receptors

A novel class of histamine receptors (H3), controlling histamine synthesis and release, was described in rat and human brain and peripheral nerve endings. The present study was undertaken to evaluate whether H3 receptors contribute to the regulation of histamine release from human basophils. Basophil leucocytes were incubated with a H3 antagonist (thioperamide; concentrations ranging from 1 nM to 10 microM) or with a H3 ((R)alpha methyl-histamine; concentrations ranging from 1 to 100 mM), and subsequently were stimulated with optimal doses of anti-IgE and formyl-methionyl-leucyl-phenyl-alanine (f-met peptide). No significant modifications of histamine release were observed after incubation either with the H3 agonist or with the H3 antagonist. By contrast, a H2 antagonist (cimetidine; concentrations ranging from 1 to 100 microM) exerted a dose-dependent enhancing effect on anti-IgE- and, to a lesser extent, on f-met peptide-induced histamine release. A H1 antihistamine (chlorpheniramine; concentrations ranging from 100 nM to 1 microM), at the highest concentration employed, displayed an inhibitory activity on IgE-dependent and IgE-independent histamine release. Exogenous histamine was shown to exert a dose-dependent inhibitory effect on two-staged anti-IgE-induced histamine release. Taken as a whole, these results suggest that H3 receptors are not involved in the regulation of histamine release from human basophils; by contrast, H2 receptors participate in controlling histamine release from human basophils, as previously demonstrated by other authors.     

Molecular properties and signalling pathways of the histamine H1 receptor

With cloning of the gene encoding the histamine H₁ receptor, a new area of histamine research has become reality. Finally, it seems feasible to study the target of the thera-peutically important clans of antihistamine. Expression of the genes in mammalian cells allows detailed investigations of the various signal transduction routes of the histamine H₁ receptor. Moreover, using molecular biological techniques, it is now possible to investigate ligand receptor interaction at the molecular level. Studies with mutant H₁ receptors have shown that H₁ antagonists bind to a specific amino acid residues in TM3 and 5. It is expected that these new developments will provide much fundamental knowledge on the ligand interaction with the H₁ receptor.     

Novel function of histamine signaling in hyperlipidemia‐induced atherosclerosis: Histamine H1 receptors protect and H2 receptors accelerate atherosclerosis

Histamine is not only essential for acute inflammatory reactions, but it also participates in a chronic inflammatory disorder. We generated apolipoprotein E (apoE) and histamine receptors (HHRs), including the major H1 and H2 receptors (HH1R, HH2R) double knockout mice (DKO) to clarify the role of HHRs in hyperlipidemia‐induced atherosclerosis, in which apoE‐KO and DKO mice were fed a high cholesterol diet. We found that pronounced hyperlipidemia‐induced atherosclerotic progression occurred in HH1R/apoE‐DKO mice, but in HH2R/apoE‐DKO mice less atherosclerosis, despite pro‐atherogenic serum cholesterol levels compared with apoE‐KO mice. Furthermore, the increased expressions of scavenger receptors (SRs), such as SR‐A, CD36 and lectin‐like oxidized low‐density lipoprotein receptor 1 (LOX‐1), nuclear factor‐kappa B (NFκB), monocyte chemoattractant protein (MCP‐1), matrix metalloproteinases (MMPs) or liver X receptor (LXR)‐related inflammatory signaling factors, were consistent with the pro‐atherogenic phenotype of HH2R/apoE‐DKO mice. We hypothesize that histamine/HH1R and HH2R signaling has conflicting innate functions, inflammatory/atherogenic and anti‐inflammatory/anti‐atherogenic actions, and that there are innate links between histamine signaling and hyperlipidemia‐induced atherosclerosis, independently of serum cholesterol metabolism. Specific histamine signaling blockers, in particular, HH2R blockers, are a possible novel therapeutic target for hyperlipidemia‐induced atherosclerosis.     

Effects of topical treatment with H1 and H2 antagonists on clinical symptoms and nasal vascular reactions in patients with allergic rhinitis

Fifteen asymptomatic subjects with allergic rhinitis participated in a double-blind, randomized, crossover, placebo-controlled study. The subjects were pretreated intranasally with a single dose of a selective H1 receptor antagonist, levocabastine, and/or selective H2 receptor antagonist, ranitidine, prior to a nasal allergen challenge. The nasal symptoms obtained at the challenge were assessed using a scoring technique 15 min after the allergen exposure. The nasal airway resistance was determined twice prior to and once after the allergen challenge using anterior rhinomanometry. The nasal mucosal blood flow was determined before and 15 min after allergen challenge using the 133Xe wash-out technique. After pretreatment with the H1 antagonist there was a statistically significant reduction in the number of sneezes and rhinorrhea compared to pretreatment with placebo. Pretreatment with the H2 receptor significantly decreased the rhinorrhea but not the sneeze. The nasal blockage was unaffected by both the H1 and the H2 antagonists. Pretreatment with the H1 and/or the H2 antagonists inhibited the reduction in the nasal mucosal blood flow induced by the allergen challenge to a significant degree. The present findings suggest that topical treatment with the highly selective histamine antagonist, levocabastine, inhibits allergen-induced reflex-mediated symptoms. H1 and H2 receptors do not appear to be involved in the regulation of the tone of the capacitance vessels. This indicates that a more complex mechanism participates in the induction of nasal blockage than the direct effect of histamine on H1 and H2 receptors on the capacitance vessels of the nasal mucosa alone. Both H1 and H2 receptors are of importance for the regulation of nasal mucosal blood flow during the allergic reaction.     

Effect of the H1 Antihistamine Chlorpheniramine Maleate on Histamine-Induced Symptoms in the Human Conjunctiva

Earlier studies have shown that intranasal chlorpheniramine (0.77%) can inhibit histamine-induced tickling, sneezing, and hypersecretion by a local effect on nerve fibres. The aim of the present study was to examine whether this solution had local anaesthetic of parasympatholytic properties. If neither of these properties are present it suggests that the anti-pruritic effects of the solution are caused by inhibition of H1 receptors, which in turn is indirect evidence for the presence of H1 receptors on nerve fibers. In a double-blind design 15 normal subjects were provoked with histamine in the eye after pretreatment with chlorpheniramine or with a local anaesthetic, oxybuprocain. Both drugs inhibited itching, but the H1 antihistamine was significantly more effective than the local anaesthetic (P less than 0.01). Corneal sensitivity was measured by an esthesiometer, and pupil difference was used as a measure for atropine activity. Chlorpheniramine had neither a local anaesthetic nor a parasympatholytic effect. This study has therefore strengthened the hypothesis that there are nervous H1 receptors in the mucous membranes of the eye and airways and has extended its application in animals to also include man.     

Measurement of PC20 histamine with the use of two different nebulizers and measurement of FEV1 and PEF

Histamine challenge was performed in 19 patients using two nebulizers (PARI and Wright) and FEV1 and PEF were measured to determine PC20 histamine. FEV1 and PEF gave identical PC20 histamine values. The PARI nebulizer gave PC20 histamine values that were 2.5 doubling concentrations lower than the Wright nebulizer. The reproducibility of histamine challenge with the PARI nebulizer was studied in 15 patients and the results suggested that the challenge was reproducible within one doubling concentration of histamine.     

Leukotriene C4 and histamine in early allergic reaction in the nose

We have examined the measurements of LTC4 and histamine in nasal lavage fluids and blown secretions as a possible model of the early mediator events during nasal allergy. A nasal challenge with grass pollen extract was undertaken on two separate occasions in 20 patients with a history of seasonal rhinitis and a positive immediate skin test to grass pollen. A 2 ml nasal lavage was performed before allergen challenge, and blown secretion collected separately 15 min after the provocation, followed by a final 2 ml nasal lavage. The dilution of nasal secretion by the lavage fluid was determined using 99mTc-labelled albumin as an exogenous marker added to the fluid. The amounts of admixture in the nasal lavages did not correlate to the concentrations of LTC4 and histamine, indicating that the variable amounts of nasal secretion in nasal lavage do not constitute a confounding variable for measurements of LTC4 and histamine. In the pre-challenge lavages, the median concentrations, of LTC4 and histamine were 1.7 and 52 nmol/l respectively. Following allergen challenge neither LTC4 nor histamine measured in nasal lavage showed any significant change from pre-challenge baseline values. However, measurements of both mediators in the blown secretion showed a significantly higher concentration than in the pre- or post-challenge lavage samples, compatible with transitory release during the acute allergic reaction. However, it seems doubtful whether measurements of LTC4 or histamine can be compared between blown secretion and nasal lavage fluid, even if the dilution factor is disregarded.(ABSTRACT TRUNCATED AT 250 WORDS)     

Critical in vivo roles of histamine and histamine receptor signaling in animal models of metabolic syndrome

Histamine, a classic low‐molecular‐weight amine, is synthesized from L‐histidine by histidine decarboxylase (HDC), and histamine‐specific receptors (HRs) are essential for its actions. Our serial in vivo studies have uniquely reported that expression of histamine/HRs is variably identified in atherosclerotic lesions, and that HDC‐gene knockout mice without histamine/HRs signaling show a marked reduction of atherosclerotic progression. These data have convinced us that histamine plays a pivotal role in the pathogenesis of atherosclerosis. Among four subclasses of HRs, the expression profile of the main receptors (H1/2R) has been shown to be switched from H2R to H1R during monocyte to macrophage differentiation, and H1R is also predominant in smooth muscle and endothelial cells of atheromatous plaque. Using various animal models of H1/2R–gene knockout mice, H1R and H2R were found to reciprocally but critically regulate not only hypercholesterolemia‐induced atherosclerosis and injury‐induced arteriosclerosis, but also hyperlipidemia‐induced nonalcoholic fatty liver disease (NAFLD). Metabolic syndrome manifests obesity, dyslipidemia, insulin resistance, atherosclerosis, and/or NAFLD, i.e. the dysregulation of lipid/bile acid/glucose metabolism. Therefore, although its etiology is complicated and multifactorial, histamine/HRs signaling has a close relationship with the development of metabolic syndrome. We herein review diverse, key in vivo roles of histamine/HR signaling in the pathogenesis of metabolic syndrome.     

In vitro effects of H1-antihistamines on histamine and PGD2 release from mast cells of human lung, tonsil, and skin

Mast cells from different anatomic sites differ in cytochemistry and response to various secretory stimuli. We have investigated whether responsiveness to the second-generation H₁-receptor antagonists, which are important first-line drugs for the relief of symptoms in patients with chronic urticaria and allergic rhinoconjunctivitis, also differs according to the site of origin of mast cells. The effects of terfenadine, ketotifen, and cetirizine were therefore examined in relation to the IgE-dependent release of histamine and prostaglandin D₂ (PGD₂) from dispersed human lung, tonsil, and skin mast cells. Terfenadine had a biphasic effect on lung and skin mast cells: at low concentrations, a concentration-dependent inhibition of histamine release from lung and skin mast cells was observed, whereas at higher concentrations the drug stimulated mediator release. Even at a high concentration, terfenadine inhibited mediator release from tonsil mast cells. Ketotifen had low potency as an inhibitor of mediator release from lung and tonsil mast cells. In skin mast cells, no inhibition of mediator release was observed below 1.0 μM, and above that concentration it induced mediator release. Cetirizine, a much less lipophilic drug than the others tested, did not induce mediator release from mast cells even at concentrations up to 100 μM. This drug showed concentration-dependent inhibition of IgE-dependent mediator release from lung and tonsil mast cells only. Our results show that human mast cells are heterogeneous with respect to modulation of mediator release by these H₁-antihistamines. In particular, differences were observed between skin mast cells and those dispersed from lung and tonsils.     

Novel function of histamine signaling via histamine receptors in cholesterol and bile acid metabolism: Histamine H2 receptor protects against nonalcoholic fatty liver disease

We have reported that the function of histamine and its receptors (HRs) has a close relationship with the development of nonalcoholic fatty liver disease (NAFLD). However, much less is known regarding its pathogenic and molecular mechanism(s), including the early stage of hepatic and intestinal function for lipid and bile acid (BA) metabolism. We used H1R and H2R knockout mice (H1/2R‐KO) to clarify those pivotal roles in cholesterol/BA metabolism, in which H1/2R‐KO mice were separately fed a short‐term 1% cholesterol or cholic acid (CA) diet. [³H]Cholesterol absorption study revealed that significantly enhanced accumulation occurred in the jejunum, blood and liver, but not in the feces, of H2R‐KO mice, compared to wild‐type and H1R‐KO mice. Furthermore, four weeks after the high‐cholesterol diet, the H2R‐KO jejunum but not liver exhibited increased expressions of cholesterol transporters, consistent with higher plasma lipoprotein levels. Five days after CA diet, the H2R‐KO mice showed significantly higher expressions of ileal BA‐reabsorption and hepatic BA‐efflux factors, corresponding to higher serum but lower fecal BA levels. The following long‐term CA diets resulted in severe injury to the H2R‐KO liver. Histamine/H2R signaling might have a protective role in the initial phase during NAFLD progression, correlated with cholesterol and BA metabolism in the liver/intestine.     

Microvascular actions of histamine: synergism with leukotriene B4 and role in allergic leucocyte recruitment

Background Previous studies have shown that antihistamities provide little or no protection against the recruitment of leucocytes in allergic inflammation. Objective We wanted to examine if threshold doses of histamine can potentiate chemoattractant-induced leukocyte adhesion and if complete inhibition of histamine-induced microvascular effects is necessary to reduce allergic leucocyte recruitment. Methods The role of histamine in allergic leucocyte recruitment was examined by use of intravital microscopy of the hamster cheek pouch microcirculation. Results We found that topical administration of histamine caused a concentration-dependent increase in microvascular permeability in the cheek pouch; i.e. 0.3 μM histamine caused no detectable plasma leakage, while 1 μM and 10 μM histamine resulted in 29 ± 9.3 and 356 ± 47 leakage sites/cm² cheek pouch area, respectively. The percentage of postcapillary venules with more than five adherent leucocytes (an index of early leucocyte recruitment) was 1.1 ± 0.51% in the control situation, and did not increase significantly after stimulation with histamine alone (0.3–10μM) or with 1 nM ieukotriene B₄ (LTB₄). On the other hand, coapplication of 10μM histamine and 1 nM LTB₄ increased leucocyte adhesion 24-fold. In fact, the 10 times lower dose of histamine (1 μM) together with 1 nM LTB₄ increased leucocyte adhesion to a similar extent (20 fold). The increase in vascular permeabihty evoked by exogenous 10μM histamine (with or without LTB₄), or by histamine released from activated mast cells (antigen challenge), was completely reversed by local pretreatment with the H₁-receptor antagonist mepyramine. This mepyramine treatment also abohshed the enhanced leucocyte adhesion in response to coapplication of histamine and LTB₄. Moreover, mepyramine, which had no effect on leucocyte recruitment evoked by 3 nM LTB₄per se, reduced antigen-induced recruitment of leucocytes to the extravascular tissue by 79.5 ± 14.8%. Conclusion We conclude that threshold concentrations of histamine can strikingly potentiate chemoattractant-induced leucocyte responses, and that in order to reduce allergic leucocyte recruitment it may be necessary to use antihistamines in doses high enough to abolish the microvascular actions of histamine.     

Intravenous 1α, 25[OH]2 vitamin D3 (calcitriol) pulse therapy for bone lesions in a murine model of chronic cadmium toxicosis

The aim of the present study was to clarify the therapeutic effects of 1alpha, 25[OH]2 vitamin D3 (calcitriol) pulse injection on bone lesions induced in a rat model of chronic cadmium toxicosis. Ovariectomized (OVX) and control-operated (sham-OVX) rats were given repeated intravenous injections of 0.5 mg/kg/day CdCl2 for 70 weeks. The rats were then treated intravenously with 0.02 microg/kg/day calcitriol 3 days per week for 8 weeks. CdCl2 treatment induced increases in osteoid volumes of the femur cortex and trabecula. This change was accompanied by an increase in the volume of iron deposition at the mineralization front of the trabeculae and a reduction in mineral density. Abnormalities of bone metabolic parameters, which were increases in the blood calcium, inorganic phosphorous, bone-specific alkaline phosphatase, parathyroid hormone (PTH) and osteocalcin levels, and in the urine deoxypyridinoline (D-PYR) level, were also induced. Calcitriol treatment increased the blood calcium and inorganic phosphorous levels, and reduced the blood PTH level. Decreases in blood tartrate-resistant acid phosphatase and urine d-PYR levels were also induced indicating that bone resorption was suppressed. The findings indicated that the increased osteoid volume of the cortex and Fe-deposition volume of the trabecula were improved. These effects or improvements were observed in the sham-OVX rats but not in the OVX rats.     

Role of tachykinin NK1 and NK2 receptors in allergen-induced early and late asthmatic reactions, airway hyperresponsiveness, and airway inflammation in conscious, unrestrained guinea pigs

Using a guinea pig model of allergic asthma, we investigated the effects of the inhaled, highly selective nonpeptide tachykinin NK₁ and NK₂ receptor antagonists SR 140333 and SR 48968, respectively, on allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions, and infiltration of inflammatory cells in the airways. Both SR 140333 (100 nM, 3 min) and SR 48968 (100 nM, 3 min) had no effect on the severity of the EAR, while the NK₂ receptor antagonist SR 48968, but not the NK₁ receptor antagonist SR 140333, caused significant inhibition of the LAR. SR 140333 significantly reduced the allergen-induced AHR to histamine, both after the EAR and the LAR. By contrast, SR 48968 did not affect the AHR after the EAR, but significantly attenuated the AHR after the LAR. Bronchoalveolar lavage studies performed after the LAR indicated that SR 140333 caused significant inhibition of allergen-induced infiltration of eosinophils, neutrophils and lymphocytes, while SR 48968 attenuated the infiltration of neutrophils and lymphocytes, but not of eosinophils. Both NK receptor antagonists tended to reduce the accumulation of ciliated epithelial cells in the airways. These results indicate that NK₁ and NK₂ receptors are importantly, but differentially, involved in the development of allergen-induced airways obstruction, AHR and infiltration of inflammatory cells in the airways. Therefore, both NK₁ and NK₂ receptor antagonists, or dual NK₁ and NK₂ antagonists, could be useful in the treatment of allergic asthma.