The Effect of Subchronic Dosing of Ciproxifan and Clobenpropit on Dopamine and Histamine Levels in Rats

Design, synthesis, and in vitro and in vivo characterization of 1-{4-[4-(substituted)piperazin-1-yl]butyl}guanidines and their piperidine analogues as histamine H3 receptor antagonists

Previously, we have shown that 1-substituted-[4-(7-phenoxyheptylpiperazin-1-yl)butyl]guanidine with electron withdrawing substituents at position 4 in the benzyl moiety exhibits high in vitro affinities toward the guinea pig jejunal histamine H₃ receptor with pA ₂ ranging from 8.49 to 8.43. Here, we present data on the impact of replacement of the piperazine scaffold by the piperidine ring (compounds 2a and 2b), moving benzyl- and 4-trifluoromethylbenzyl substituents from position 1 to 3 of the guanidine moiety (compounds 2c and 2d), which decreases the guanidine basicity (compound 2e), and the influence of individual synthons (compounds 2f-h), present in the lead compounds 1b and 1c, on the antagonistic activity against the histamine H₃ receptor. Additionally, the most active compounds 1a, 1c, and 1d were evaluated for their affinity to the rat histamine H₃ receptor and the human histamine H₃ and H₄ receptors. It was also shown that compounds 1a, 1c and 1d, given parenterally for five days, reduced the food intake of rats and did not influence the brain histamine or noradrenaline concentrations; however, significantly reduced serotonin and dopamine concentrations were found in rats administered with compounds 1a and 1c, respectively.

Histamine H3 receptors and its antagonism as a novel mechanism for antipsychotic effect: a current preclinical & clinical perspective

Histamine H3 receptors are present as autoreceptors on histaminergic neurons and as heteroreceptors on nonhistaminergic neurones. They control the release and synthesis of histamine and several other key neurotransmitters in the brain. H3 antagonism may be a novel approach to develop a new class of antipsychotic medications given the gathering evidence reporting therapeutic efficacy in several central nervous system disorders. Several medications such as cariprazine, lurasidone, LY214002, bexarotene, rasagiline, raloxifene, BL-1020 and ITI-070 are being developed to treat the negative symptoms and cognitive impairments of schizophrenia. These medications works through diverse mechanisms which include agonism at metabotropic glutamate receptor (mGluR2/3), partial agonism at dopamine D2, D3 and serotonin 5-HT1A receptors, antagonism at D2, 5-HT2A, 5-HT2B and 5-HT7 receptors, combined dopamine antagonism with GABA agonist activity, inhibition of monoamine oxidase-B, modulation of oestrogen receptor, and activation of nuclear retinoid X receptor. However, still specific safe therapy for psychosis remains at large. Schizophrenia is a severe neuropsychiatric disorder result both from hyper- and hypo-dopaminergic transmission causing positive and negative symptoms, respectively. Pharmacological stimulation of dopamine release in the prefrontal cortex has been a viable approach in treating negative symptoms and cognitive deficits of schizophrenia symptoms that are currently not well treated and continue to represent significant unmet medical challenges. Administration of H3 antagonists/inverse agonists increase extracellular dopamine concentrations in rat prefrontal cortex, but not in the striatum suggesting that antagonism via H3 receptor may be a potential target for treating negative symptoms and cognitive deficits associated with schizophrenia. Further, insights are emerging into the potential role of histamine H3 receptors as a target of antiobesity therapeutics which is one of the limiting adverse effects of second generation schizophrenia medications. The recent failures of two promising H3 compounds in clinical trial dampened the interest in seeking antipsychotic like activities of H3 receptor antagonists. However, due to the inconclusive nature of many of these studies, the development of H3 compounds via H3 antagonism/inverse agonism approach still hold lot of promises and may be developed as a novel class of drugs for schizophrenia and its related complications e.g. weight gain.