Histamine H3 Receptor Antagonist Thioperamide Research Articles

Anxiolytic- and antidepressive-like effects of harmaline in mice are mediated via histamine H3 receptor blockade

Many neuropsychiatric disorders can be caused by neurotransmitter dysfunction. Experimental studies have demonstrated that histamine and the harmaline affect physiological processes through interaction with other neurotransmitter systems. The objective of these experiments was to investigate the involvement of the histaminergic system in the effects of harmaline on anxiety- and depressive-related effects in male NMRI mice. Behavioral tests were employed to evaluate anxiety-related symptoms (elevated plus maze; EPM), depressive-like symptoms (forced swim test; FST), and cognitive decline (step-down test). The histamine H3 receptor (H3R) agonist α-methylhistamine dihydrobromide (α-MH; 5 mg/kg, i.p.) had anxiolytic- and depressive-like effects, while the H3R antagonist thioperamide (10 mg/kg, i.p.) showed an antidepressive-like property. The subthreshold dose of α-MH resulted in an increase in the tendency of mice treated with the harmaline (2.5 mg/kg) to remain in the EPM open-arms. A subthreshold dose of thioperamide (5 mg/kg) increased the time spent in the open-arms in mice treated with harmaline (2.5 and 5 mg/kg) while a high dose of harmaline decreased the immobility time. Furthermore, two higher doses of harmaline resulted in a reduction in the number of open-arm entries. Similarly, mice administered with thioperamide and a low dose of harmaline decreased locomotor activity in the EPM. Ultimately, the combined thioperamide and harmaline did not impair memory retrieval of mice. These experiments demonstrate that the histaminergic system is implicated in the anxiety- and depressive-related effects of harmaline. The combination of thioperamide and harmaline is effective in treating anxiety and depression without having an adverse effect on memory formation.

Histamine H3R antagonist counteracts the impaired hippocampal neurogenesis in Lipopolysaccharide-induced neuroinflammation

Adult neurogenesis in hippocampus dentate gyrus (DG) is associated with numerous neurodegenerative diseases such as aging and Alzheimer's disease (AD). Overactivation of microglia induced neuroinflammation is well acknowledged to contribute to the impaired neurogenesis in pathologies of these diseases and then leading to cognitive dysfunction. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Recently, studies show that H3R are highly expressed not only in neurons but also in microglia to modulate inflammatory response. However, whether inhibition of H3R is responsible for the neurogenesis and cognition in chronic neuroinflammation induced injury and the mechanism remains unclear. In this study, we found that inhibition of H3R by thioperamide reduced the microglia activity and promoted a phenotypical switch from pro-inflammatory M1 to anti-inflammatory M2 in microglia, and ultimately attenuated lipopolysaccharide (LPS) induced neuroinflammation in mice. Additionally, thioperamide rescued the neuroinflammation induced impairments of neurogenesis and cognitive function. Mechanically, the neuroprotection of thioperamide was involved in histamine dependent H2 receptor (H2R) activation, because cimetidine, an H2R antagonist but not pyrilamine, an H1R antagonist reversed the above effects of thioperamide. Moreover, thioperamide activated the H2R downstream phosphorylated protein kinase A (PKA)/cyclic AMP response element-binding protein (CREB) pathway but inhibited nuclear factor kappa-B (NF-κB) signaling. Activation of CREB by thioperamide promoted interaction of CREB-CREB Binding Protein (CBP) to increase anti-inflammatory cytokines (Interleukin-4 and Interleukin-10) and brain-derived neurotrophic factor (BDNF) release but inhibited NF-κB-CBP interaction to decrease pro-inflammatory cytokines (Interleukin-1β, Interleukin-6 and Tumor necrosis factor α) release. H89, an inhibitor of PKA/CREB signaling, abolished effects of thioperamide on neuroinflammation and neurogenesis. Taken together, these results suggested under LPS induced neuroinflammation, the H3R antagonist thioperamide inhibited microglia activity and inflammatory response, and ameliorated impairment of neurogenesis and cognitive dysfunction via enhancing histamine release. Histamine activated H2R and reinforced CREB-CBP interaction but weakened NF-κB-CBP interaction to exert anti-inflammatory effects. This study uncovered a novel histamine dependent mechanism behind the therapeutic effect of thioperamide on neuroinflammation.

Thioperamide attenuates neuroinflammation and cognitive impairments in Alzheimer's disease via inhibiting gliosis

Alzheimer's disease (AD) is an age-related neurodegenerative disease, which characterized by deposition of amyloid-β (Aβ) plaques, neurofibrillary tangles, neuronal loss, and accompanied by neuroinflammation. Neuroinflammatory processes are well acknowledged to contribute to the progression of AD pathology. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Recently, studies show that H3R are highly expressed not only in neurons but also in microglia and astrocytes. H3R antagonist has been reported to have anti-inflammatory efficacy. However, whether inhibition of H3R is responsible for the anti-neuroinflammation in glial cells and neuroprotection on APPswe, PSEN1dE9 (APP/PS1 Tg) mice remain unclear. In this study, we found that inhibition of H3R by thioperamide reduced the gliosis and induced a phenotypical switch from A1 to A2 in astrocytes, and ultimately attenuated neuroinflammation in APP/PS1 Tg mice. Additionally, thioperamide rescued the decrease of cyclic AMP response element-binding protein (CREB) phosphorylation and suppressed the phosphorylated P65 nuclear factor kappa B (p-P65 NF-κB) in APP/PS1 Tg mice. H89, an inhibitor of CREB signaling, abolished these effects of thioperamide to suppress gliosis and proinflammatory cytokine release. Lastly, thioperamide alleviated the deposition of amyloid-β (Aβ) and cognitive dysfunction in APP/PS1 mice, which were both reversed by administration of H89. Taken together, these results suggested the H3R antagonist thioperamide improved cognitive impairment in APP/PS1 Tg mice via modulation of the CREB-mediated gliosis and inflammation inhibiting, which contributed to Aβ clearance. This study uncovered a novel mechanism involving inflammatory regulating behind the therapeutic effect of thioperamide in AD.

Activation of CREB-mediated autophagy by thioperamide ameliorates β-amyloid pathology and cognition in Alzheimer's disease.

Alzheimer's disease (AD) is an age‐related neurodegenerative disease, and the imbalance between production and clearance of β‐amyloid (Aβ) is involved in its pathogenesis. Autophagy is an intracellular degradation pathway whereby leads to removal of aggregated proteins, up‐regulation of which may be a plausible therapeutic strategy for the treatment of AD. Histamine H3 receptor (H3R) is a presynaptic autoreceptor regulating histamine release via negative feedback way. Our previous study showed that thioperamide, as an antagonist of H3R, enhances autophagy and protects against ischemic injury. However, the effect of thioperamide on autophagic function and Aβ pathology in AD remains unknown. In this study, we found that thioperamide promoted cognitive function, ameliorated neuronal loss, and Aβ pathology in APP/PS1 transgenic (Tg) mice. Interestingly, thioperamide up‐regulated autophagic level and lysosomal function both in APP/PS1 Tg mice and in primary neurons under Aβ‐induced injury. The neuroprotection by thioperamide against AD was reversed by 3‐MA, inhibitor of autophagy, and siRNA of Atg7, key autophagic‐related gene. Furthermore, inhibition of activity of CREB, H3R downstream signaling, by H89 reversed the effect of thioperamide on promoted cell viability, activated autophagic flux, and increased autophagic‐lysosomal proteins expression, including Atg7, TFEB, and LAMP1, suggesting a CREB‐dependent autophagic activation by thioperamide in AD. Taken together, these results suggested that H3R antagonist thioperamide improved cognitive impairment in APP/PS1 Tg mice via modulation of the CREB‐mediated autophagy and lysosomal pathway, which contributed to Aβ clearance. This study uncovered a novel mechanism involving autophagic regulating behind the therapeutic effect of thioperamide in AD.

The histamine H3 receptor antagonist thioperamide rescues circadian rhythm and memory function in experimental parkinsonism

Parkinson’s disease (PD) is a common neurodegenerative disorder, characterized by motor impairment and a wide range of non-motor symptoms, including sleep disorders and cognitive and affective deficits. In this study, we used a mouse model of PD based on 6-hydroxydopamine (6-OHDA) to examine the effect of thioperamide, a histamine H3 receptor antagonist, on circadian activity, recognition memory and anxiety. A partial, bilateral 6-OHDA lesion of the striatum reduces motor activity during the active phase of the 24 h cycle. In addition, the lesion disrupts the endogenous circadian rhythm observed when mice are maintained in constant darkness. Administration of thioperamide to 6-OHDA-lesion mice rescues the normal rest/activity cycle. Moreover, thioperamide counteracts the deficit of novel object recognition produced by 6-OHDA. Our experiments show that this memory impairment is accompanied by disrupted gamma oscillations in the hippocampus, which are also rescued by thioperamide. In contrast, we do not observe any modification of the anxiogenic effect of 6-OHDA in response to administration of thioperamide. Our results indicate that thioperamide may act as a multifunctional drug, able to counteract disruptions of circadian rhythm and cognitive deficits associated with PD.

Histaminergic Receptors Modulate Spinal Cord Injury-Induced Neuronal Nitric Oxide Synthase Upregulation and Cord Pathology: New Roles of Nanowired Drug Delivery for Neuroprotection.

The possibility that histamine influences the spinal cord pathophysiology following trauma through specific receptor-mediated upregulation of neuronal nitric oxide synthase (nNOS) was examined in a rat model. A focal spinal cord injury (SCI) was inflicted by a longitudinal incision into the right dorsal horn of the T10-11 segments. The animals were allowed to survive 5h. The SCI significantly induced breakdown of the blood-spinal cord barrier to protein tracers, reduced the spinal cord blood flow at 5h, and increased the edema formation and massive upregulation of nNOS expression. Pretreatment with histamine H1 receptor antagonist mepyramine (1mg, 5mg, and 10mg/kg, i.p., 30min before injury) failed to attenuate nNOS expression and spinal cord pathology following SCI. On the other hand, blockade of histamine H2 receptors with cimetidine or ranitidine (1mg, 5mg, or 10mg/kg) significantly reduced these early pathophysiological events and attenuated nNOS expression in a dose-dependent manner. Interestingly, TiO2-naowire delivery of cimetidine or ranitidine (5mg doses) exerted superior neuroprotective effects on SCI-induced nNOS expression and cord pathology. It appears that effects of ranitidine were far superior than cimetidine at identical doses in SCI. On the other hand, pretreatment with histamine H3 receptor agonist α-methylhistamine (1mg, 2mg, or 5mg/kg, i.p.) that inhibits histamine synthesis and release in the central nervous system thwarted the spinal cord pathophysiology and nNOS expression when used in lower doses. Interestingly, histamine H3 receptor antagonist thioperamide (1mg, 2mg, or 5mg/kg, i.p.) exacerbated nNOS expression and cord pathology after SCI. These novel observations suggest that blockade of histamine H2 receptors or stimulation of histamine H3 receptors attenuates nNOS expression and induces neuroprotection in SCI. Taken together, our results are the first to demonstrate that histamine-induced pathophysiology of SCI is mediated via nNOS expression involving specific histamine receptors.

Histamine H3 Receptor Agonist Imetit Attenuated Isoproterenol Induced Renin Angiotensin System and Sympathetic Nervous System Overactivity in Myocardial Infarction of Rats.

Myocardial infarction is an alarming health issue, needs great attention. The present study investigated the role of histamine-H3 receptor (H3R) agonist imetit in relationship to sympathetic and renin angiotensin system in Wistar rats. Subcutaneous injection of isoproterenol (85 mg/kg) on last 2 consecutive days in per se group and 7 days treatment of different groups at 24 h interval induced myocardial infarction in Wistar rats. H3R agonist imetit (10 mg/kg), H3R antagonist thioperamide (5 mg/kg), losartan (10 mg/kg) were administered orally to evaluate imetit's cardioprotective potential effect by measuring plasma cardiac antioxidant markers, angiotensin II, norepinephrine levels and histopathological analysis. Isoproterenol significantly elevated the angiotensin II and norepinephrine levels in rat plasma. This study revealed that pre-treatment with imetit similar to losartan attenuated norepinephrine and angiotensin II levels whereas thioperamide showed its antagonistic effect by diminishing imetit's effects. Furthermore, its protective effect was confirmed by restoration of cardiac antioxidant markers and histopathological improvement of myocardium integrity. This study confirm imetit's cardioprotective potential and also reveals renin angiotensin system, sympathetic system and H3R correlation in isoproterenol induced toxicity in rats. However, molecular studies must be warranted to prove the role of H3R in myocardial infarction.

Mechanism of the histamine H3 receptor-mediated increase in exploratory locomotor activity and anxiety-like behaviours in mice

Histaminergic neurons are activated by histamine H3 receptor (H3R) antagonists, increasing histamine and other neurotransmitters in the brain. The prototype H3R antagonist thioperamide increases locomotor activity and anxiety-like behaviours; however, the mechanisms underlying these effects have not been fully elucidated. This study aimed to determine the mechanism underlying H3R-mediated behavioural changes using a specific H3R antagonist, JNJ-10181457 (JNJ).First, we examined the effect of JNJ injection to mice on the concentrations of brain monoamines and their metabolites. JNJ exclusively increased Nτ-methylhistamine, the metabolite of brain histamine used as an indicator of histamine release, suggesting that JNJ dominantly stimulates the release of histamine release but not of other monoamines.Next, we examined the mechanism underlying JNJ-induced behavioural changes using open-field tests and elevated zero maze tests. JNJ-induced increase in locomotor activity was inhibited by α-fluoromethyl histidine, an inhibitor of histamine synthesis, supporting that H3R exerted its effect through histamine neurotransmission. The JNJ-induced increase in locomotor activity in wild-type mice was preserved in H1R gene knockout mice but not in histamine H2 receptor (H2R) gene knockout mice. JNJ-induced anxiety-like behaviours were partially reduced by diphenhydramine, an H1R antagonist, and dominantly by zolantidine, an H2R antagonist. These results suggest that H3R blockade induces histamine release, activates H2R and elicits exploratory locomotor activity and anxiety-like behaviours.

Histamine infused into basolateral amygdala enhances memory consolidation of inhibitory avoidance

The role of the basolateral amygdala (BLA) in the consolidation of aversive memory is well established. Here we investigate the involvement of the histaminergic system in BLA on this variable. Rats were chronically implanted with bilateral cannulae in the BLA and after recovery were trained in a one-trial step-down inhibitory avoidance task. Immediately after training histaminergic compounds either alone or in combination were infused through the cannulae. Memory was assessed in test sessions carried out 24 h after the training session. Post-training histamine (1-10 nmol; 0.5 μl/side) enhanced consolidation and the histamine H₃ receptor antagonist thioperamide (50 nmol; 0.5 μl/side) impaired memory consolidation. The effect was shared by the histamine N-methyltransferase inhibitor SKF-91844 (50 nmol; 0.5 μl/side) as well as by the H₃ receptor agonist imetit (10 nmol; 0.5 μl/side). The promnesic action of histamine was unaffected by the H₁ receptor antagonist pyrilamine (50 nmol; 0.5 μl/side). The H1 receptor agonist pyridylethylamine (10 nmol; 0.5 μl/side), the H₂ agonist dimaprit (10 nmol; 0.5 μl/side) and the H₂ antagonist ranitidine (50 nmol; 0.5 μl/side) were ineffective. Histaminergic compounds infused into the BLA had no effect on open-field or elevated plus-maze behaviour. The data show that histamine induces a dose-dependent mnemonic effect in rats and indicate that this reflects a role of endogenous histamine in the BLA mediated by H₃ receptors.

Thioperamide, an H3 Receptor Antagonist Prevents [3H]Glucose Uptake in Brain of Adult Rats Lesioned as Neonates with 5,7-Dihydroxytryptamine

As a first attempt at exploring an association between histaminergic and serotoninergic neuronal phenotypes in glucose regulation, the influence of the histamine H₃ receptor antagonist thioperamide on glucose uptake by brain was determined in rats in which the serotoninergic innervations of brain was largely destroyed perinatally. Male Wistar rats were initially treated on the 3rd day after birth with the serotoninergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) (75 μg icv) or saline vehicle (10 μl icv). At 8 weeks lesioned and control rats were terminated in order to validate the effectiveness of 5,7-DHT: reduction in 5-HT and 5-HIAA by 83-91% and 69-83% in striatum, frontal cortex, and hippocampus (HPLC/ED method). Other groups of rats were pretreated with thioperamide (5.0 mg/kg ip) or saline vehicle 60 min prior to 6-[³H]-D-glucose (500 μCi/kg ip). Fifteen-min later rats were decapitated and brains were excised and dissected to remove frontal cortex, striatum, hippocampus, thalamus/hypothalamus, pons, and cerebellum. Liquid scintillation spectroscopy was used to determine that [³H]glucose uptake, which was enhanced in 5,7-DHT lesioned rats in cortex (by 88%), hippocampus, thalamus/hypothalamus, pons and cerebellum (each by 47-56%), and in striatum (by 35%). In contrast, thioperamide prevented the enhancement in [³H]glucose uptake in all brain regions of 5,7-DHT neonatally lesioned rats; and [³H]glucose levels were significantly different in all brain regions (except thalamus/hypothalamus) in thioperamide-versus saline-treated rats. These findings indicate a functional association between histaminergic and serotoninergic systems in brain in relation to glucose regulation.

Oral l‐histidine exerts antihypertensive effects via central histamine H3 receptors and decreases nitric oxide content in the rostral ventrolateral medulla in spontaneously hypertensive rats

1. L-histidine is generally found in meat, poultry and fish. To investigate its effects on blood pressure, L-histidine was administered to 9-week-old spontaneously hypertensive rats (SHR). 2. Oral administration of L-histidine (100 mg / kg) increased histamine content in cerebrospinal fluid and reduced mean arterial pressure (MAP) in SHR. Intracerebroventricular injection of L-histidine (0.01 microg / 5 microL) also caused a decrease in MAP, which was reversed by cotreatment with the histamine H3 receptor antagonist thioperamide (20.4 microg / 5 microL, i.c.v.). There was a significant, time-dependent increase (over 6 h) in the NOx (NO2- + NO3-) content of the dialysate from the rostral ventrolateral medulla (RVLM), a major vasomotor centre, after oral administration of L-histidine. 3. In another experiment, SHR were treated with l-histidine (100 mg / kg) twice a day for 4 weeks. Chronic treatment with L-histidine inhibited the age-dependent increases in systolic blood pressure and urinary noradrenaline excretion seen in vehicle-treated SHR. Conversely, intracerebroventricular injection of thioperamide (20.4 microg / 5 microL, i.c.v.) reversed the decrease in MAP in response to L-histidine in SHR. 4. Reverse transcription-polymerase chain reaction analysis revealed that the aortic expression of angiotensin-converting enzyme mRNA was suppressed by chronic treatment with L-histidine. 5. These results suggest that L-histidine decreases blood pressure by attenuating sympathetic output via the central histamine H3 receptor in SHR. In addition, the antihypertensive effects of L-histidine appear to be associated with an increase in nitric oxide in the RVLM.

Evidence for histamine as a neurotransmitter in the cardiac sympathetic nervous system

The colocalization of histamine (HA) and norepinephrine (NE) immunoreactivities was identified within the superior cervical ganglia neurons of the guinea pig. HA and NE immunoreactivity levels were significantly attenuated after chemical sympathectomy with 6-hydroxydopamine (6-OHDA). Coexistence of NE and HA was also visualized in the cardiac sympathetic axon and varicosities labeled with anterograde tracer biotinylated dextran amine. Depolarization of cardiac sympathetic nerve endings (synaptosomes) with 50 mM potassium stimulated endogenous HA release, which was significantly attenuated by 6-OHDA or a vesicular monoamine transporter 2 (VMAT2) inhibitor reserpine pretreatments. Compound 48/80, a mast cell releaser, did not affect cardiac synaptosome HA exocytosis. Furthermore, K+ -evoked HA release was abolished by the N-type Ca2+ -channel blocker omega-conotoxin but was not affected by the L-type Ca2+ -channel blocker lacidipine. Cardiac synaptosome HA exocytosis was augmented by the enhanced synthesis of HA or the inhibition of HA metabolism. HA H3-receptor activation by (R)-alpha-methylhistamine inhibited high K+ -evoked histamine release. The HA H3 receptor antagonist thioperamide enhanced K+ -evoked HA release and blocked the (R)-alpha-methylhistamine effect. The K+ -evoked endogenous NE release was attenuated by preloading the cardiac synaptosomes with L-histidine or quinacrine. These inhibitory effects were reversed by thioperamide or antagonized by alpha-fluoromethylhistidine. Our findings indicate that high K+ -evoked corelease of NE and HA may be inhibited by endogenous HA via activation of presynaptic HA H3-receptors. The H3-receptor may function as an autoreceptor, rather than a heteroreceptor, in the regulation of sympathetic neurotransmission and HA may be a novel sympathetic neurotransmitter.

Effect of Thioperamide on Modified Forced Swimming Test‐Induced Oxidative Stress in Mice

This study was designed i) to investigate the role of histamine H3-receptor ligands on mouse modified forced swimming test, a method that distinguishes the catecholaminergic behaviour with that of serotonergic compounds and ii) to evaluate the role of free radicals in mediation of such effects. Swiss strain albino mice were treated with different doses of histamine H3-receptor antagonist thioperamide (3.75, 7.5 and 15 mg/kg intraperitoneally) and agonist (R)-alpha-methylhistamine (5 microg intracerebroventricularly). The climbing, swimming and immobility times were recorded for 6 min. Immediately after modified forced swimming test, the animals were sacrificed and parameters of oxidative stress were assessed in the brain by measuring the thiobarbituric acid reactive substance (TBARS), glutathione (GSH) and catalase levels. Thioperamide (7.5 and 15 mg/kg intraperitoneally) dose-dependently decreased immobility time and increased swimming time but not climbing time. The behaviour of mice treated with (R)-alpha-methylhistamine was similar to that of control mice. A significant reduction in GSH and an increase in catalase levels were observed in brains of mice exposed to modified forced swimming test. Thioperamide pretreatment dose-dependently reversed such an alteration in oxidative stress parameters. (R)-alpha-methylhistamine caused a reversal of altered catalase but not GSH levels. Thioperamide shows antidepressant effects in the modified forced swimming test and causes a reversal of the test-induced oxidative stress indicating its antioxidant potential. The antidepressant effect of thioperamide appears to be mediated via serotonergic and/or antioxidant mechanisms.

Neuroimmune interactions in guinea pig stomach and small intestine.

Enteric neuroimmune interactions in gastrointestinal hypersensitivity responses involve antigen detection by mast cells, mast cell degranulation, release of chemical mediators, and modulatory actions of the mediators on the enteric nervous system (ENS). Electrophysiological methods were used to investigate electrical and synaptic behavior of neurons in the stomach and small intestine during exposure to beta-lactoglobulin in guinea pigs sensitized to cow's milk. Application of beta-lactoglobulin to sensitized preparations depolarized the membrane potential and increased neuronal excitability in small intestinal neurons but not in gastric neurons. Effects on membrane potential and excitability in the small intestine were suppressed by the mast cell stabilizing drug ketotifen, the histamine H(2) receptor antagonist cimetidine, the cyclooxygenase inhibitor piroxicam, and the 5-lipoxygenase inhibitor caffeic acid. Unlike small intestinal ganglion cells, gastric myenteric neurons did not respond to histamine applied exogenously. Antigenic exposure suppressed noradrenergic inhibitory neurotransmission in the small intestinal submucosal plexus. The histamine H(3) receptor antagonist thioperamide and piroxicam, but not caffeic acid, prevented the allergic suppression of noradrenergic inhibitory neurotransmission. Antigenic stimulation of neuronal excitability and suppression of synaptic transmission occurred only in milk-sensitized animals. Results suggest that signaling between mast cells and the ENS underlies intestinal, but not gastric, anaphylactic responses associated with food allergies. Histamine, prostaglandins, and leukotrienes are paracrine signals in the communication pathway from mast cells to the small intestinal ENS.

Histamine H1 and H2 Receptor Antagonists Accelerate Skin Barrier Repair and Prevent Epidermal Hyperplasia Induced by Barrier Disruption in a Dry Environment

Keratinocytes have histamine H1 and H2 receptors, but their functions are poorly understood. To clarify the role of histamine receptors in the epidermis, we examined the effects of histamine receptor antagonists and agonists applied epicutaneously on the recovery of skin barrier function disrupted by tape stripping in hairless mice. Histamine H2 receptor antagonists famotidine and cimetidine accelerated the recovery of skin barrier function, but histamine and histamine H2 receptor agonist dimaprit delayed the barrier repair. Application of compound 48/80, a histamine releaser, also delayed the recovery. Imidazole, an analog of histamine, had no effect. The histamine H1 receptor antagonists diphenhydramine and tripelennamine accelerated the recovery. Histamine H3 receptor agonist Nalpha-methylhistamine and antagonist thioperamide had no effect. In addition, topical application of famotidine or diphenhydramine prevented epidermal hyperplasia in mice with skin barrier disrupted by acetone treatment in a dry environment (humidity < 10%) for 4 d. In conclusion, both the histamine H1 and H2 receptors in the epidermis are involved in skin barrier function and the cutaneous condition of epidermal hyperplasia.

Synthesis,in vitro pharmacology and radiosynthesis ofN-(cis-4-fluoromethylcycloyhexyl)-4-(1(H)-imidazol-4-yl)piperidine-11-thiocarbonamide (VUF 5000), a potential PET ligand for the histamine H3 receptor

The synthesis of N-(cis-4-fluoromethylcyclohexyl)-4-(1(H)-imidazol-4-yl)piperidine-1-thiocarbonamide (VUF 5000) 3, a fluorinated analogue of the potent (pA2 value of 8·9±0·1, Ki=4·3±0·9 nM) histamine H3 receptor antagonist thioperamide 2 is described. After the establishment of the H3 antagonistic activity of VUF 5000, pA2 value=9·0±0·2, Ki=2·3±0·5 nM, a four step synthesis for the radiolabelling of VUF 5000 with 18F (half life 110 min) was developed. Within 4 hours of the end of the bombartment, [18F]VUF 5000 was obtained with an average radiochemical yield of 23% (decay corrected) and a specific activity >96·2 TBq/μmol (2·6 Ci/μmol). Copyright © 1999 John Wiley & Sons, Ltd.

Effects of histamine H3 receptor ligands in experimental models of anxiety and depression.

Histamine H3 receptor ligands have been proposed to be of potential therapeutic interest for the treatment of different central nervous system disorders; however, the psychopharmacological properties of these drugs have not been studied extensively. In this work, we investigated the possible involvement of histamine H3 receptor function in experimental models of anxiety (elevated plus-maze) and depression (forced swimming test). Male Sprague-Dawley rats were treated i.p. with the histamine H3 receptor agonist R-alpha-methylhistamine (10 mg/kg) or the histamine H3 receptor antagonist thioperamide (0.2, 2 and 10 mg/kg) and 30 min afterwards the time spent in the open arms of an elevated plus-maze was registered for 5 min. The immobility time of male OF1 mice in the forced swimming test was recorded for 6 min, 1 h after the i.p. administration of R-alpha-methylhistamine (10 and 20 mg/kg), thioperamide (0.2, 2, 10 and 20 mg/kg) or another histamine H3 receptor antagonist, clobenpropit (5 mg/kg). The locomotor activity of mice was checked in parallel by means of an activity meter. Both saline controls and active drug controls were used in all the paradigms. Neither thioperamide nor R-alpha-methylhistamine significantly changed animal behaviour in the elevated plus-maze. R-alpha-methylhistamine and the higher dose of thioperamide assayed (20 mg/kg) were also inactive in the forced swimming test. By contrast, thioperamide (0.2-10 mg/kg) dose-dependently decreased immobility, the effect being significant at 10 mg/kg (33% reduction of immobility); clobenpropit produced an effect qualitatively similar (24% reduction of immobility). None of these histamine H3 receptor antagonists affected locomotor activity. These preliminary results suggest that the histamine H3 receptor blockade could be devoid of anxiolytic potential but have antidepressant effects. Besides, the stimulation of these receptors does not seem to be followed by changes in the behavioural parameters studied.

R-(-)-alpha-methyl-histamine has nitric oxide-mediated vasodilator activity in the mesenteric vascular bed of the cat.

Responses to the histamine H3 receptor agonist R-(-)-alpha-methyl-histamine were investigated in the mesenteric vascular bed of the cat under constant-flow conditions. Injections of R-(-)-alpha-methyl-histamine and histamine caused dose-related decreases in mesenteric perfusion pressure with R-(-)-alpha-methyl-histamine being 1000-fold less potent than histamine when doses were compared on a nmol basis to take molecular weight into account. Responses to R-(-)-alpha-methyl-histamine were not altered by histamine H1 or H2 receptor antagonists at a time when responses to histamine were significantly reduced. The histamine H3 receptor antagonist thioperamide reduced responses to R-(-)-alpha-methyl-histamine but was without effect on responses to histamine [6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoro-methylphenyl)heptaneca rdoxamide dimaleate] (HTMT), or dimaprit. These data suggest the presence of histamine H1, H2 and H3 receptors mediating vasodilation in the mesenteric vascular bed. Responses to R-(-)-alpha-methyl-histamine and histamine were reduced by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) but were not altered by the cyclooxygenase inhibitor meclofenamate, the alpha-adrenoceptor blocker phentolamine, or adrenergic nerve terminal depleting agent reserpine. The present data suggest that histamine H3 receptors mediating vasodilation are present in the mesenteric vascular bed and that responses are mediated by the release of nitric oxide but not vasodilator prostaglandins or an effect on the adrenergic nervous system. These results indicate that vasodilator responses to histamine involve the activation of histamine H1 and H2 receptors and the release of nitric oxide in the mesenteric vascular bed of the cat.

Prejunctional histamine H3-receptors inhibit electrically evoked endogenous noradrenaline overflow in the portal vein of freely moving rats.

The effects of intra-arterial injection of different doses of the selective histamine H3-receptor agonist R-alpha-methylhistamine and the selective histamine H3-receptor antagonist thioperamide on basal and electrically evoked noradrenaline overflow in the portal vein as well as on mean arterial pressure (MAP) and heart rate (HR) were investigated in permanently instrumented freely moving rats. R-alpha-Methylhistamine (0.01, 0.1 and 1 mumol/kg) inhibited the evoked noradrenaline overflow up to 43%, the ED50 value being 0.013 mumol/kg. Thioperamide (0.1, 0.5 and 1.0 mumol/kg) antagonized the effect of 1.0 mumol/kg R-alpha-methylhistamine dose-dependently, evoked overflow returning to control values at 1.0 mumol/kg of the antagonist; thioperamide alone had no effect on electrically evoked noradrenaline overflow. Basal noradrenaline levels, blood pressure and heart rate were not at all influenced by R-alpha-methylhistamine and thioperamide, alone or in combination. The results clearly show the presence of prejunctional histamine H3-receptors inhibiting the electrically evoked noradrenaline overflow from vascular sympathetic nerve terminals in the portal vein of freely moving rats.

Purification of a histamine H3 receptor negatively coupled to phosphoinositide turnover in the human gastric cell line HGT1.

The histamine H3 receptor agonist (R)alpha-methylhistamine (MeHA) inhibited, in a nanomolar range, basal and carbachol-stimulated inositol phosphate formation in the human gastric tumoral cell line HGT1-clone 6. The inhibition was reversed by micromolar concentrations of the histamine H3 receptor antagonist thioperamide and was sensitive to cholera or pertussis toxin treatment. Using [3H]N alpha-MeHA as specific tracer, high affinity binding sites were demonstrated with a Bmax of 54 +/- 3 fmol/mg of protein and a KD of either 0.61 +/- 0.04 or 2.2 +/- 0.4 nM, in the absence or presence of 50 microM GTP[gamma]S, respectively. The binding sites were solubilized by Triton X-100 and prepurified by gel chromatography. They were separated from the histamine H2 receptor sites by filtration through Sepharose-famotidine and finally retained on Sepharose-thioperamide. The purified sites concentrated in one single silver-stained protein band of 70 kDa in SDS-polyacrylamide gel electrophoresis. They specifically bound [3H]N alpha-MeHA with a KD of 1.6 +/- 0.1 nM and a Bmax of 12,000 +/- 750 pmol/mg of protein. This corresponds to a 90,225-fold purification over cell lysate and a purity degree of 84%. Binding was competitively displaced by N alpha-MeHA (IC50 = 5.8 +/- 0.7 nM), (R) alpha-MeHA (IC50 = 9 +/- 1 nM), and thioperamide (IC50 = 85 +/- 10 nM), but not by famotidine (H2 antagonist) or by mepyramine (H1 antagonist). These findings provide the first evidence for solubilization, purification, and molecular mass characterization of the histamine H3 receptor protein and for the negative coupling of this receptor phosphatidylinositol turnover through a so far unidentified G protein.