B7-H1 agonists suppress the PI3K/AKT/mtor pathway by degrading p110γ and independently induce cell death

The biological role of B7-H1 intrinsic signal is reportedly diverse and controversial, its signal pathway remains unclear. Although B7-H1 blocking antibodies were found to have agonist capacity, their binding features and agonist mechanisms need further investigation. Here, by constructing cell strains with full-length or truncated B7-H1, we found that B7-H1 functioned as a receptor to transmit cell death signal from PD-1 protein or anti-B7-H1s through its cytoplasmic domain. Specific binding to the IgV-like domain of B7-H1 was required for the downstream signal. Upon agonists interaction, B7-H1 regulated the degradation of phosphoinositide 3-kinases (PI3Ks) subunit p110γ, subsequently inhibited the PI3K/AKT/mTOR pathway, and significantly increased autophagy. Moreover, B7-H1 agonists also suppressed ubiquitylation in B7-H1+cells by reducing ubiquitin-activating enzyme (E1), eventually leading to cell death. Finally, we validated the receptor role of B7-H1 in multiple tumor cells and demonstrated that B7-H1 agonists could suppress tumor progression independent of T cells in vivo. Our findings revealed that B7-H1 agonists functions as a PI3K inhibitor and may offer new strategies for PI3K targeting therapy.

Olanzapine-activated AMPK signaling in the dorsal vagal complex is attenuated by histamine H1 receptor agonist in female rats

Weight gain and its related metabolic disorders are major side effects associated with second generation antipsychotic drug treatment. The dorsal vagal complex (DVC) and AMP-activated protein kinase (AMPK) are implicated in the regulation of food intake and body weight. Blocking the histamine H1 receptor contributes to antipsychotic-induced weight gain. The present study investigated the time-dependent effect of olanzapine treatment (8, 16, and 36 d) on DVC AMPK signaling in olanzapine-induced weight gain and whether these changes are associated with olanzapine-induced H1 receptor antagonism. During the 8-day olanzapine treatment, the rats were hyperphagic and rapidly gained weight. The phosphorylation of AMPK (pAMPK) (activated AMPK) as well as its directly downstream phospho-acetyl-coenzyme A carboxylase was significantly increased. The pAMPK/AMPK ratio, an indicator of AMPK activity, was significantly positively correlated with feeding efficiency and weight gain. As treatment was prolonged (16 and 36 d of olanzapine treatment), the rats were no longer hyperphagic, and there were no longer any changes in DVC AMPK signaling. Although the DVC H1 receptor protein expression was not significantly altered by olanzapine, the pAMPK expression was significantly positively correlated with the H1 receptor level after the 8-, 16-, and 36-day olanzapine treatments. Moreover, we showed that an H1 receptor agonist, 2-(3-trifluoromethylphenyl) histamine, significantly inhibited the olanzapine-induced hyperphagia and DVC AMPK activation in a dose-dependent manner. These results suggest a time-dependent role of DVC AMPK in olanzapine-induced obesity. Thus, olanzapine-induced DVC AMPK activation may be at least partially related to olanzapine's antagonistic effect on the H1 receptor.

Anticonvulsant properties of histamine H3 receptor ligands belonging to N-substituted carbamates of imidazopropanol

Ligands targeting central histamine H3 receptors (H3Rs) for epilepsy might be a promising therapeutic approach. Therefore, the previously described and structurally strongly related imidazole-based derivatives belonging to carbamate class with high H3R in vitro affinity, in-vivo antagonist potency, and H3R selectivity profile were investigated on their anticonvulsant activity in maximal electroshock (MES)-induced and pentylenetetrazole (PTZ)-kindled seizure models in Wistar rats. The effects of systemic injection of H3R ligands 1-13 on MES-induced and PTZ-kindled seizures were screened and evaluated against the reference antiepileptic drug (AED) Phenytoin (PHT) and the standard histamine H3R inverse agonist/antagonist Thioperamide (THP) to determine their potential as new antiepileptic drugs. Following administration of the H3R ligands 1-13 (5, 10 and 15 mg/kg, ip) there was a significant dose dependent reduction in MES-induced seizure duration. The protective action observed for the pentenyl carbamate derivative 4, the most protective H3R ligand among 1-13, was significantly higher (P <0.05) than that of standard H3R antagonist THP, and was reversed when rats were pretreated with the selective H3R agonist R-(α)-methyl-histamine (RAMH) (10mg/kg), or with the CNS penetrant H1R antagonist Pyrilamine (PYR) (10mg/kg). In addition, subeffective dose of H3R ligand 4 (5mg/kg, ip) significantly potentiated the protective action in rats pretreated with PHT (5mg/kg, ip), a dose without appreciable protective effect when given alone. In contrast, pretreatment with H3R ligand 4 (10mg/kg ip) failed to modify PTZ-kindled convulsion, whereas the reference drug PHT was found to fully protect PTZ-induced seizure. These results indicate that some of the investigated imidazole-based H3R ligands 1-13 may be of future therapeutic value in epilepsy.

Comparison of perceived itch induced by skin prick-tests with histamine and codeine

The role of personal factors makes it difficult to correlate subjective data, such as those obtained with the use of a visual analogue scale, and objective data, such as a quantity of injected histamine. In this study, prick tests with histamine and codeine on the forearms allowed a coherent variation in itch scores to be obtained over time, with highly significant differences from controls and with a peak at 4 minutes. These tests are therefore valuable for screening anti-pruritic agents. A significant difference between initial scores and scores for new prick tests after 7 days suggest that tachyphylaxis persists.

[Changes in external respiration function in response to berotek and histamine in diabetic patients]

AIM

To study airways reactivity in patients with diabetes mellitus (DM).

MATERIAL AND METHODS

Berotek and histamine tests were performed in 29 DM patients (type 1 DM - 20, type 2 DM - 9 patients) and 39 DM patients (12 and 27 patients, respectively). The age of the patients varied from 16 to 66 years.

RESULTS

Positive berotek test was in 6 (20.7%) patients (delta FEV1 > 200). Of them 5 had type 1 DM. Positive histamine test was registered in 9 patients with type 2 DM (23.1%). This indicates bronchial hyperreactivity (BH). A qualitative analysis with Fisher's criterion detected correlation between BH and type of DM, BH and intake of sugar reducing tablets. Correlations between BH, body mass index, diabetes duration and late complications were not found.

CONCLUSION

DM patients have predisposition to bronchial spasm. Positive bronchodilation test was mainly in type 1 DM, BH in response to histamine was obtained in type 2 DM. Different mechanisms of a bronchospasm in type 1 and 2 DM are demonstrated. Predisposition to bronchospasm may play an unfavourable role in the course of nonspecific pulmonary diseases in DM patients.

Cerebral processing of histamine-induced itch using short-term alternating temperature modulation--an FMRI study

Human neuroimaging studies on the physiology of itch have been hampered by the lack of reproducible "on-off" stimuli. Using a previously established biphasic temperature stimulus model, we investigated the cerebral activation pattern of itch processing in 12 healthy volunteers with functional magnetic resonance imaging. Itch was provoked on the right forearm with skin prick application of 1% histamine-dihydrochloride. Local temperature modulation allowed reproducible itch provocation above scratch threshold (defined as 33/100 on a visual analogue scale) during 25 degrees C, whereas itch declined below scratch threshold during the 32 degrees C stimulation period. No itch sensation was reported using 0.9% saline with temperature modulation. Itch sensation above scratch threshold was associated with increased activation of the thalamus, presupplementary motor area, anterior insular, inferior parietal, and dorsolateral prefrontal cortex, and decreased activation of the orbitofrontal, medial frontal, mid-cingulate, and primary motor cortex in comparison to saline. The biphasic temperature model allows rapid modulation of histamine-induced itch. The evoked itch sensation above scratch threshold is processed by a network of brain regions contributing to the encoding of sensory, emotional, attention-dependent, cognitive-evaluative and motivational aspects of itch.

Cholinergic and glutamatergic activation reverses working memory failure by hippocampal histamine H1 receptor blockade in rats

Intrahippocampal administration of the histamine H1 receptor antagonist pyrilamine (3.2-32 ug/ side) but not the histamine H2 receptor antagonist cimetidine (1.0-10 microg/side) increased the number of errors in the working memory task with a three-panel runway setup. The increase in working memory errors induced by intrahippocampal 32 microg/side pyrilamine was significantly reduced by concurrent infusion of the histamine H1 receptor agonist 2-pyridylethylamine (3.2 and 10 microg/side). The cholinesterase inhibitor physostigmine ( 1.0 and 3.2 microg/side) and D-cycloserine (0.32 and 1.0 microg/side), the partial agonist at the glycine binding site on the NMDA receptor/channel complex, reduced the increase in working memory errors induced by intrahippocampal 32 microg/side pyrilamine. These results suggest that the hippocampal histaminergic activity via histamine H1 receptor is necessary for normal working memory processes and that the septohippocampal cholinergic activation and positive modulation of the NMDA receptor/channel through activation of the glycine site can alleviate dysfunction of hippocampal histamine H1 receptor-mediated neurotransmission involved in working memory function.

The intradermal effects of the H3 receptor agonist R alpha methylhistamine in human skin

We have investigated the possible existence of the H3 histamine receptor in human skin with the highly selective ligands R alpha methylhistamine (RAMHA) (H3 agonist) and thioperamide (H3 antagonist). We compared the intradermal effects of RAMHA with histamine, and studied their potential modulation by the H1 antagonist terfenadine, and H2 antagonist cimetidine. The effects of RAMHA and thioperamide on codeine phosphate-, substance P- and histamine-induced weal and flare responses were also studied. RAMHA produced dose-related weal and flare responses that were approximately 10- and fivefold less, respectively, than responses to histamine. Flare responses to RAMHA were significantly inhibited by oral terfenadine (P < 0.05). Weal and flare responses to histamine after oral cimetidine showed much intersubject variation, and cimetidine did not significantly alter either RAMHA- or histamine-induced weal and flare responses. Codeine phosphate-, substance P- and histamine-induced responses were not significantly affected by concurrent administration of RAMHA. Thioperamide was not found to influence codeine phosphate-, substance P-, RAMHA- or histamine-induced effects. RAMHA induces vascular (weal and flare) responses in human skin, and these responses are partially inhibited by terfenadine. There is a trend for RAMHA to have an additive effect to the weal induced by substance P and histamine, although our results largely do not reach statistical significance. Thioperamide does not affect the vascular responses to RAMHA, codeine phosphate, histamine or substance P. We cannot conclude that the effects of RAMHA are induced by H3 receptors on cutaneous endothelial or mast cells.

A novel pyrrolidine analog of histamine as a potent, highly selective histamine H3 receptor agonist

Employing classical conformational analysis on a known H3 agonist, (R)-alpha-methylhistamine (1), a series of conformationally constrained H3 agonists were proposed and synthesized. Pyrrolidine (+/-)-4a, a compound proposed to mimic the anti-conformation of (R)-alpha-methylhistamine (1), was found to be a potent and selective H3 agonist. The pyrrolidine (+/-)-4a was resolved, and its (+) enantiomer, immepyr [(+)-4a], showed a greater separation of H3 and H1 activities in vivo (H3/H1 ratio >> 550) than (R)-alpha-methylhistamine (1) (H3/H1 ratio = 17), the standard H3 agonist. In fact, no evidence of H1 activity was detected at doses of immepyr [(+)-4a] as high as 100 mg/kg i.v. This pyrrolidine, immepyr [(2R,3S)-(+)-4a], represents, to our knowledge, the first reported cyclic, conformationally restricted analog of histamine to possess selective in vivo H3 agonist activity.

Structure-activity studies with histamine H3-receptor ligands

Starting from thioperamide, the first potent and selective H3-receptor histamine antagonist, analogues have been synthesised and tested in vitro on rat cerebral cortex to explore structure-activity relationships. The aim has been to design compounds which do not possess the thiourea group of thioperamide and which may have improved brain penetration. Some compounds derived from histamine and possessing an aromatic nitrogen-containing heterocycle on the side-chain amino group show strong H3-antagonist activity. These have served as leads to provide aryloxyethyl- and aryloxy-propylimidazoles which are potent H3 antagonists of histamine. Structure-activity studies of the very potent and selective agonist, imetit (S-[2-imidazol-4-yl)ethyl]isothiourea), have explored the the transition between agonist, partial agonist and antagonist. The isosteric isourea is also a potent agonist. N,N'-Dibutyl-[S-[3-(imidazol-4-yl)propyl]isothiourea is a very potent antagonist having Ki = 1.5 nM.

Homologs of histamine as histamine H3 receptor antagonists: a new potent and selective H3 antagonist, 4(5)-(5-aminopentyl)-1H-imidazole

The influence of alkyl chain length variation on the histamine H3 receptor activity of histamine homologs 1 was investigated. A series of 4(5)-(omega-aminoalkyl)-1H-imidazoles 1 was prepared with an alkyl chain length varying from one methylene group to 10 methylene groups. Besides the H3 activity, the affinities of these compounds for the H1 and H2 receptors were determined. The ethylene chain of histamine is optimal for agonistic activity on all three histamine receptor subtypes. For the H3 receptor, elongation of the alkyl chain from three methylene groups on leads to compounds with antagonistic properties. 4(5)-(5-Aminopentyl)-1H-imidazole (impentamine, 1e) is the most potent and selective H3 antagonist from this series of 4(5)-(omega-aminoalkyl)-1H-imidazoles 1, with a pA2 value of 8.4 (on guinea pig jejunum). A specific antagonistic binding site for this compound is proposed.

Intermediate affinity and potency of clozapine and low affinity of other neuroleptics and of antidepressants at H3 receptors

It was the aim of the present study to determine the affinities of four neuroleptics and five antidepressants for histamine H3 receptors. In rat brain cortex membranes, the specifically bound [3H]-N alpha-methylhistamine was monophasically displaced by clozapine (pKi 6.15). The other drugs did not completely displace the radioligand even at 100 microM; the pKi values were: haloperidol (4.91); sulpiride (4.73); amitriptyline (4.56); desipramine (4.15); levomepromazine (4.14); fluovoxamine (4.13); maprotiline (4.09); moclobemide (< 4.0). The effect of clozapine was further examined in a functional H3 receptor model, i.e., in superfused mouse brain cortex slices preincubated with [3H]-noradrenaline. The electrically evoked tritium overflow was not affected by clozapine 0.5-32 microM. However, clozapine shifted the concentration-response curve of histamine for its inhibitory effect on the evoked overflow to the right, but did not affect the maximum effect of histamine. The Schild plot yielded a pA2 value of 6.33. In conclusion, clozapine shows an intermediate affinity and potency (as a competitive antagonist) at H3 receptors. The Ki value of clozapine at H3 receptors resembles its Ki value at D2 receptors (the target of the classical neuroleptics), but is higher than its Ki values at D4, 5-HT2 or muscarinic acetylcholine receptors, which according to current hypotheses, might be involved in the atypical profile of clozapine.

Design of histamine H3-receptor agonists and antagonists

The development of highly potent and selective ligands for the characterization of histamine H3-receptors is reviewed. In the field of agonists stereoselectively methylated derivatives of the natural ligand are found to have the desired pharmacodynamic properties. Pharmacokinetic properties could be improved by forming bioreversible azomethine prodrugs of the primary amine with benzophenone derivatives. In the antagonist field a number of new leads belonging to different chemical classes are discovered. Potential compounds for drug development are identified. The radiolabelled probe [125I]iodoproxyfan shows high potency and selectivity in functional and binding studies. It is a useful compound for binding assays as well as for the detection and localization of histamine H3-receptors.

Thioperamide, the selective histamine H3 receptor antagonist, attenuates stimulant-induced locomotor activity in the mouse

The effects of the selective histamine H3 receptor agonist (R)-alpha-methylhistamine and antagonist thioperamide on stimulant-induced locomotor activity in the mouse were examined. Amphetamine (1 mg.kg-1 s.c.), apomorphine (2 mg.kg-1 s.c.) or cocaine (5 mg.kg-1 s.c.) increased locomotor activity. Neither thioperamide (10 mg.kg-1 i.p.) nor (R)-alpha-methylhistamine (20 mg.kg-1 i.p.) affected spontaneous locomotor activity in their own right. (R)-alpha-Methylhistamine (0.3, 3 or 20 mg.kg-1 i.p.) also had no effect on amphetamine (1 mg.kg-1 s.c.)-induced locomotor activity. In contrast, thioperamide (0.2-10 mg.kg-1 i.p. or 0.3-20 micrograms i.c.v.) inhibited, in a dose-dependent manner, the hyperactivity response induced by amphetamine (1 mg.kg-1 s.c.). (R)-alpha-Methylhistamine (20 mg.kg-1 i.p.) completely reversed the inhibitory response to thioperamide (2 mg.kg-1 i.p.). Thioperamide (2 or 10 mg.kg-1 i.p.) also inhibited apomorphine (2 mg.kg-1 s.c.)- and, to a lesser extent, cocaine (5 mg.kg-1 s.c.)-induced hyperactivity. We therefore conclude that antagonism of the central histamine H3 receptor inhibits, to a varying degree, the effects of locomotor stimulants.

Modulation of morphine-induced antinociception in mice by histamine H3-receptor ligands

The effects of compounds active at histamine H3-receptors on morphine-induced antinociception have been investigated in thermal and chemical tests in mice; tail-immersion (50 degrees C) and hot-plate (49 degrees and 55 degrees C) tests and acetic acid-induced writhing. Neither (R)alpha-methylhistamine, a specific agonist, (S)alpha-methylhistamine, a chemical control, nor thioperamide, an antagonist, had any antinociceptive action alone but thioperamide (3 mg kg-1) attenuated the effects of morphine in the tail-immersion test while (R)alpha-methylhistamine (1 mg kg-1), but not the (S) isomer, potentiated its effects in the hot-plate test at 55 degrees C. These results are consistent with the morphine potentiation seen with H1-antagonists and suggest that central histaminergic mechanisms can modulate opioid actions.

Modulation of the intracellular and H3-histamine receptors and chemically-induced seizures in mice

Central histaminergic modulation of H1 rather than H2-receptors has been shown to modify epileptic activity. Compounds acting on the HIC- and H3-receptors were tested against chemically-induced seizures in mice. Compounds antagonising the microsomal and nuclear intracellular receptors (HIC) only modified seizures at doses where toxicity was observed. Antagonists of the histamine H3-receptor (thioperamide and burimamide) only potentiated the severity of clonic convulsions induced by picrotoxin, while impromidine (i.c.v.), an antagonist with H2-agonist activity, inhibited leptazol-induced seizures. The H3-agonist, (R)alpha-methylhistamine, potentiated chemically-induced seizures, but at lower doses there was slight inhibition.

Receptor autoradiography with 11C and [3H]-labelled ligands visualized by imaging plates

The distribution of histamine H1, H3, dopamine D1 and D2 receptors in the brain was studied by receptor autoradiography using a high-sensitivity and high-resolution imaging plate system. [3H]Pyrilamine, [3H](R)alpha-methyl-histamine, [11C]SCH23390, and [11C]N-methylspiperone (or [11C]YM-09151-2) were used as ligands to identify H1, H3, D1 and D2 receptors, respectively. Two different receptors (dopamine D2 and histamine H3) could be also labelled simultaneously in a single cryostat-sliced section using [11C]N-methylspiperone and [3H](R)alpha-methylhistamine, respectively. The imaging plate system is useful for receptor autoradiography of positron emitter-labelled and tritium-labelled receptor-ligands because of its high sensitivity.