Abstract Existing data on the expression of H4 histamine receptor in the CNS are conflicting and inconclusive. In this report, we present the results of experiments that were conducted in order to ...elucidate H4 receptor expression and localization in the brain, spinal cord, and dorsal root ganglia (DRG). Here we show that transcripts of H4 receptor are present in all analyzed regions of the human CNS, including spinal cord, hippocampus, cortex, thalamus and amygdala, with the highest levels of H4 mRNA detected in the spinal cord. In rat, H4 mRNA was detected in cortex, cerebellum, brainstem, amygdala, thalamus and striatum. Very low levels of H4 mRNA were detected in hypothalamus, and no H4 signal was detected in the rat hippocampus. Fairly low levels of H4 mRNA were detected in examined peripheral tissues including spleen and liver. Interestingly, strong expression of H4 mRNA was detected in the rat DRG and spinal cord. Immunohistochemical analysis revealed expression of H4 receptors on neurons in the rat lumbar DRG and in the lumbar spinal cord. Our observations provide evidence of the H4 presence in both human and rodent CNS and offer some insight into possible role of H4 in itch and pain.
Alzheimer disease (AD) is a progressive neurodegenerative disorder with associated memory loss, spatial disorientation, and other psychiatric problems. Cholinergic system dysfunction is an early and ...salient feature of AD, and enhancing cholinergic signaling with acetylcholinesterase inhibitors is currently the primary strategy for improving cognition. The beneficial effects of acetylcholinesterase inhibitors, however, are typically short-lived and accompanied by adverse effects. Recent evidence suggests that activating α7 nicotinic acetylcholine receptors (α7 nAChR) may facilitate the specific modulation of brain cholinergic signaling, leading to cognitive enhancement and possibly to amelioration of AD pathologic findings. In the present study, we determined the effect of long-term treatment with the selective α7 nAChR agonist A-582941 in aged 3xTg-AD mice with robust AD-like pathology, which is particularly significant not only because this is the only mouse model that co-develops amyloid plaques and neurofibrillary tangles but also because it enabled us to explore whether A-582941 is able to restore brain function after the severe damage associated with AD. Analysis of β-amyloid deposits, tau phosphorylation, and inflammatory cells revealed that, overall, pathologic findings were unchanged. Rather, α7 nAChR activation induced expression of c-Fos and brain-derived neurotrophic factor and phosphorylation of cyclic adenosine monophosphate response element binding and neurotrophic tyrosine receptor kinase type 2. More important, A-582941 completely restored cognition in aged 3xTg-AD mice to the level of that in age-matched nontransgenic mice. These novel findings indicate that activating α7 nAChR is a promising treatment for cognitive impairment in AD.
Acute pharmacological blockade of central histamine H3 receptors (H3Rs) enhances arousal/attention in rodents. However, there is little information available for other behavioral domains or for ...repeated administration using selective compounds. ABT-239 4-(2-{2-(2R)-2-methylpyrrolidinylethyl}-benzofuran-5-yl)benzonitrile exemplifies such a selective, nonimidazole H3R antagonist with high affinity for rat (pK(i) = 8.9) and human (pK(i) = 9.5) H3Rs. Acute functional blockade of central H3Rs was demonstrated by blocking the dipsogenia response to the selective H3R agonist (R)-alpha-methylhistamine in mice. In cognition studies, acquisition of a five-trial, inhibitory avoidance test in rat pups was improved with ABT-239 (0.1-1.0 mg/kg), a 10- to 150-fold gain in potency, with similar efficacy, over previous antagonists such as thioperamide, ciproxifan, A-304121 (4-(3-(4-((2R)-2-aminopropanoyl)-1-piperazinyl)propoxy)phenyl)(cyclopropyl) methanone, A-317920 N-((1R)-2-(4-(3-(4-(cyclopropylcarbonyl) phenoxy)propyl)-1-piperazinyl)-1-methyl-2-oxoethyl)-2-furamide, and A-349821 (4'-(3-((R,R)2,5-dimethyl-pyrrolidin-1-yl)-propoxy)-biphenyl-4-yl)-morpholin-4-yl-methanone. Efficacy in this model was maintained for 3 to 6 h and following repeated dosing with ABT-239. Social memory was also improved in adult (0.01-0.3 mg/kg) and aged (0.3-1.0 mg/kg) rats. In schizophrenia models, ABT-239 improved gating deficits in DBA/2 mice using prepulse inhibition of startle (1.0-3.0 mg/kg) and N40 (1.0-10.0 mg/kg). Furthermore, ABT-239 (1.0 mg/kg) attenuated methamphetamine-induced hyperactivity in mice. In freely moving rat microdialysis studies, ABT-239 enhanced acetylcholine release (0.1-3.0 mg/kg) in adult rat frontal cortex and hippocampus and enhanced dopamine release in frontal cortex (3.0 mg/kg), but not striatum. In summary, broad efficacy was observed with ABT-239 across animal models such that potential clinical efficacy may extend beyond disorders such as ADHD to include Alzheimer's disease and schizophrenia.
H3 receptor antagonists based on a 2-aminoethylbenzofuran skeleton have been discovered, which are potent in vitro at human and rat H3 receptors, with K i values of 0.1−5.8 nM. Analogues were ...discovered with potent (0.01−1 mg/kg) cognition and attention enhancing properties in animal models. One compound in particular, 4-(2-2-(2(R)-methylpyrrolidin-1-yl)ethylbenzofuran-5-yl)benzonitrile (ABT-239), combined potent and selective H3 receptor antagonism and excellent pharmacokinetic and metabolic properties across species, with full efficacy in two behavioral models: a five-trial inhibitory avoidance acquisition model in rat pups at 0.1 mg/kg and a social recognition memory model in adult rats at 0.01 mg/kg. Furthermore, this compound did not stimulate locomotor activity and showed high selectivity for the induction of behavioral efficacy versus central nervous system based side effects. The potency and selectivity of this compound and of analogues from this class support the potential of H3 receptor antagonists for the treatment of cognitive dysfunction.
The histamine H(4) receptor (H(4)R) is expressed primarily on cells involved in inflammation and immune responses. To determine the potential role of H(4)R in pain transmission, the effects of ...JNJ7777120, a potent and selective H(4) antagonist, were characterized in preclinical pain models. Administration of JNJ7777120 fully blocked neutrophil influx observed in a mouse zymosan-induced peritonitis model (ED(50)=17 mg/kg s.c., 95% CI=8.5-26) in a mast cell-dependent manner. JNJ7777120 potently reversed thermal hyperalgesia observed following intraplantar carrageenan injection of acute inflammatory pain (ED(50)=22 mg/kg i.p., 95% CI=10-35) in rats and significantly decreased the myeloperoxide activity in the carrageenan-injected paw. In contrast, no effects were produced by either H(1)R antagonist diphenhydramine, H(2)R antagonists ranitidine, or H(3)R antagonist ABT-239. JNJ7777120 also exhibited robust anti-nociceptive activity in persistent inflammatory (CFA) pain with an ED(50) of 29 mg/kg i.p. (95% CI=19-40) and effectively reversed monoiodoacetate (MIA)-induced osteoarthritic joint pain. This compound also produced dose-dependent anti-allodynic effects in the spinal nerve ligation (ED(50)=60 mg/kg) and sciatic nerve constriction injury (ED(50)=88 mg/kg) models of chronic neuropathic pain, as well as in a skin-incision model of acute post-operative pain (ED(50)=68 mg/kg). In addition, the analgesic effects of JNJ7777120 were maintained following repeated administration and were evident at the doses that did not cause neurologic deficits in rotarod test. Our results demonstrate that selective blockade of H(4) receptors in vivo produces significant anti-nociception in animal models of inflammatory and neuropathic pain.
A series of 2-aminopyrimidines was synthesized as ligands of the histamine H4 receptor (H4R). Working in part from a pyrimidine hit that was identified in an HTS campaign, SAR studies were carried ...out to optimize the potency, which led to compound 3, 4-tert-butyl-6-(4-methylpiperazin-1-yl)pyrimidin-2-ylamine. We further studied this compound by systematically modifying the core pyrimidine moiety, the methylpiperazine at position 4, the NH2 at position 2, and positions 5 and 6 of the pyrimidine ring. The pyrimidine 6 position benefited the most from this optimization, especially in analogs in which the 6-tert-butyl was replaced with aromatic and secondary amine moieties. The highlight of the optimization campaign was compound 4, 4-2-amino-6-(4-methylpiperazin-1-yl)pyrimidin-4-ylbenzonitrile, which was potent in vitro and was active as an anti-inflammatory agent in an animal model and had antinociceptive activity in a pain model, which supports the potential of H4R antagonists in pain.
Blockade of the histamine H(3) receptor (H(3)R) enhances central neurotransmitter release, making it an attractive target for the treatment of cognitive disorders. Here, we present in vitro and in ...vivo pharmacological profiles for the H(3)R antagonist 2-4'-((3aR,6aR)-5-methyl-hexahydro-pyrrolo3,4-bpyrrol-1-yl)-biphenyl-4-yl-2H-pyridazin-3-one (ABT-288). ABT-288 is a competitive antagonist with high affinity and selectivity for human and rat H(3)Rs (K(i) = 1.9 and 8.2 nM, respectively) that enhances the release of acetylcholine and dopamine in rat prefrontal cortex. In rat behavioral tests, ABT-288 improved acquisition of a five-trial inhibitory avoidance test in rat pups (0.001-0.03 mg/kg), social recognition memory in adult rats (0.03-0.1 mg/kg), and spatial learning and reference memory in a rat water maze test (0.1-1.0 mg/kg). ABT-288 attenuated methamphetamine-induced hyperactivity in mice. In vivo rat brain H(3)R occupancy of ABT-288 was assessed in relation to rodent doses and exposure levels in behavioral tests. ABT-288 demonstrated a number of other favorable attributes, including good pharmacokinetics and oral bioavailability of 37 to 66%, with a wide central nervous system and cardiovascular safety margin. Thus, ABT-288 is a selective H(3)R antagonist with broad procognitive efficacy in rodents and excellent drug-like properties that support its advancement to the clinical area.
A new structural class of histamine H4 receptor antagonists (6−14) was designed based on rotationally restricted 2,4-diaminopyrimidines. Series compounds showed potent and selective in vitro H4 ...antagonism across multiple species, good CNS penetration, improved PK properties compared to reference H4 antagonists, functional H4 antagonism in cellular and in vivo pharmacological assays, and in vivo anti-inflammatory and antinociceptive efficacy. One compound, 10 (A-943931), combined the best features of the series in a single molecule and is an excellent tool compound to probe H4 pharmacology. It is a potent H4 antagonist in functional assays across species (FLIPR Ca2+ flux, K b < 5.7 nM), has high (>190×) selectivity for H4, and combines good PK in rats and mice (t 1/2 of 2.6 and 1.6 h, oral bioavailability of 37% and 90%) with anti-inflammatory activity (ED50 = 37 μmol/kg, mouse) and efficacy in pain models (thermal hyperalgesia, ED50 = 72 μmol/kg, rat).
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