The gene sequence for H3 receptors expresses only about 22% and 20% homology with both H1 and H2 receptors respectively.
There is much interest in the histamine H3 receptor as a potential therapeutic target because of its involvement in the neuronal mechanism behind many cognitive disorders and especially its location in the central nervous system.[6][7]
Like all histamine receptors, the H3 receptor is a G-protein coupled receptor. The H3 receptor is coupled to the GiG-protein, so it leads to inhibition of the formation of cAMP. Also, the β and γ subunits interact with N-type voltage gated calcium channels, to reduce action potential mediated influx of calcium and hence reduce neurotransmitter release.
H3 receptors function as presynaptic autoreceptors on histamine-containing neurons.[8]
The diverse expression of H3 receptors throughout the cortex and subcortex indicates its ability to modulate the release of a large number of neurotransmitters.
H3 receptors are thought to play a part in the control of satiety.[9]
Isoforms
There are at least six H3 receptor isoforms in the human, and more than 20 discovered so far.[10] In rats six H3receptor subtypes have been identified so far. Mice also have three reported isoforms.[11] These subtypes all have subtle difference in their pharmacology (and presumably distribution, based on studies in rats) but the exact physiological role of these isoforms is still unclear.
Pharmacology
Agonists
There are currently no therapeutic products acting as selective agonists for H3 receptors, although there are several compounds used as research tools which are reasonably selective agonists. Some examples are:
Cipralisant (initially assessed as H3 antagonist, later found to be an agonist, shows functional selectivity, activating some G-protein coupled pathways but not others)[12]
Proxyfan (complex functional selectivity; partial agonist effects on cAMP inhibition and MAPK activity, antagonist on histamine release, and inverse agonist on arachidonic acid release)
The H3-receptor is a promising potential therapeutical target for many (cognitive) disorders that are caused by a histaminergic H3R dysfunction, because it is linked to the central nervous system and its regulation of other neurotransmitters.[6][16][17] Examples of such disorders are: sleep disorders (including narcolepsy), Tourette syndrome, Parkinson, OCD, ADHD, ASS and drug addictions.[6][17]
This receptor has been proposed as a target for treating sleep disorders.[18] The receptor has also been proposed as a target for treating neuropathic pain.[19]
Because of its ability to modulate other neurotransmitters, H3 receptor ligands are being investigated for the treatment of numerous neurological conditions, including obesity (because of the histamine/orexinergic system interaction), movement disorders (because of H3 receptor-modulation of dopamine and GABA in the basal ganglia), schizophrenia and ADHD (again because of dopamine modulation) and research is underway to determine whether H3 receptor ligands could be useful in modulating wakefulness (because of effects on noradrenaline, glutamate and histamine).[20][7]
There is also evidence that the H3-receptor plays an important role in Tourette syndrome.[21] Mouse-models and other research demonstrated that reducing histamine concentration in the H3R causes tics, but adding histamine in the striatum decreases the symptoms.[22][23][24] The interaction between histamine (H3-receptor) and dopamine as well as other neurotransmitters is an important underlying mechanism behind the disorder.[25]
History
1983 The H3 receptor is pharmacologically identified.[26]
1988 H3 receptor found to mediate inhibition of serotonin release in rat brain cortex.[27]
^ abcRapanelli, Maximiliano. “The Magnificent Two: Histamine and the H3 Receptor as Key Modulators of Striatal Circuitry.” Progress in Neuro-Psychopharmacology and Biological Psychiatry 73 (February 2017): 36–40
^ abSadek, Bassem, Ali Saad, Adel Sadeq, Fakhreya Jalal, and Holger Stark. “Histamine H3 Receptor as a Potential Target for Cognitive Symptoms in Neuropsychiatric Diseases.” Behavioural Brain Research 312 (October 2016): 415–430
^Attoub S, Moizo L, Sobhani I, Laigneau JP, Lewin MJ, Bado A (Jun 2001). "The H3 receptor is involved in cholecystokinin inhibition of food intake in rats". Life Sciences. 69 (4): 469–78. doi:10.1016/S0024-3205(01)01138-9. PMID11459437.
^Krueger KM, Witte DG, Ireland-Denny L, et al. (July 2005). "G protein-dependent pharmacology of histamine H3 receptor ligands: evidence for heterogeneous active state receptor conformations". J. Pharmacol. Exp. Ther. 314 (1): 271–81. doi:10.1124/jpet.104.078865. PMID15821027. S2CID20470970.
^Pan JB, Yao BB, Miller TR, Kroeger PE, Bennani YL, Komater VA, et al. (August 2006). "Evidence for tolerance following repeated dosing in rats with ciproxifan, but not with A-304121". Life Sciences. 79 (14): 1366–1379. doi:10.1016/j.lfs.2006.04.002. PMID16730751.
^Esbenshade TA, Fox GB, Krueger KM, et al. (September 2004). "Pharmacological and behavioral properties of A-349821, a selective and potent human histamine H3 receptor antagonist". Biochem. Pharmacol. 68 (5): 933–45. doi:10.1016/j.bcp.2004.05.048. PMID15294456.
^Bolam, J. Paul, and Tommas J. Ellender. “Histamine and the Striatum.” Neuropharmacology 106 (July 2016): 74–84
^ abSadek, Bassem, Ali Saad, Adel Sadeq, Fakhreya Jalal, and Holger Stark. “Histamine H3 Receptor as a Potential Target for Cognitive Symptoms in Neuropsychiatric Diseases.” Behavioural Brain Research 312 (October 2016): 415–430
^Passani MB, Lin JS, Hancock A, Crochet S, Blandina P (Dec 2004). "The histamine H3 receptor as a novel therapeutic target for cognitive and sleep disorders". Trends in Pharmacological Sciences. 25 (12): 618–25. doi:10.1016/j.tips.2004.10.003. PMID15530639.
^Medhurst SJ, Collins SD, Billinton A, Bingham S, Dalziel RG, Brass A, et al. (Aug 2008). "Novel histamine H3 receptor antagonists GSK189254 and GSK334429 are efficacious in surgically-induced and virally-induced rat models of neuropathic pain". Pain. 138 (1): 61–9. doi:10.1016/j.pain.2007.11.006. PMID18164820. S2CID43724064.
^Cox, Joanna H., Stefano Seri, and Andrea E. Cavanna. “Histaminergic Modulation in Tourette Syndrome.” Expert Opinion on Orphan Drugs 4, no. 2 (February 1, 2016): 205–213
^Bolam, J. Paul, and Tommas J. Ellender. “Histamine and the Striatum.” Neuropharmacology 106 (July 2016): 74–84
^Rapanelli, Maximiliano, Luciana Frick, Haruhiko Bito, and Christopher Pittenger. “Histamine Modulation of the Basal Ganglia Circuitry in the Development of Pathological Grooming.” Proceedings of the National Academy of Sciences (June 5, 2017): 6599–6604
^Rapanelli, Maximiliano, and Christopher Pittenger. “Histamine and Histamine Receptors in Tourette Syndrome and Other Neuropsychiatric Conditions.” Neuropharmacology 106 (July 2016): 85–90
^Baldan, Lissandra Castellan, Kyle A. Williams, Jean-Dominique Gallezot, Vladimir Pogorelov, Maximiliano Rapanelli, Michael Crowley, George M. Anderson, et al. “Histidine Decarboxylase Deficiency Causes Tourette Syndrome: Parallel Findings in Humans and Mice.” Neuron 81, no. 1 (January 8, 2014): 77–90
^Schlicker E, Betz R, Göthert M (May 1988). "Histamine H3 receptor-mediated inhibition of serotonin release in the rat brain cortex". Naunyn-Schmiedeberg's Archives of Pharmacology. 337 (5): 588–90. doi:10.1007/BF00182737. PMID3412497. S2CID24168192.
^Lovenberg TW, Roland BL, Wilson SJ, Jiang X, Pyati J, Huvar A, et al. (Jun 1999). "Cloning and functional expression of the human histamine H3 receptor". Molecular Pharmacology. 55 (6): 1101–7. doi:10.1124/mol.55.6.1101. PMID10347254. S2CID25542667.
Hill SJ, Ganellin CR, Timmerman H, Schwartz JC, Shankley NP, Young JM, et al. (Sep 1997). "International Union of Pharmacology. XIII. Classification of histamine receptors". Pharmacological Reviews. 49 (3): 253–78. PMID9311023.
Malinowska B, Godlewski G, Schlicker E (Jun 1998). "Histamine H3 receptors--general characterization and their function in the cardiovascular system". Journal of Physiology and Pharmacology. 49 (2): 191–211. PMID9670104.
Leurs R, Hoffmann M, Wieland K, Timmerman H (Jan 2000). "H3 receptor gene is cloned at last". Trends in Pharmacological Sciences. 21 (1): 11–2. doi:10.1016/S0165-6147(99)01411-X. PMID10637648.
Esbenshade TA, Fox GB, Cowart MD (Apr 2006). "Histamine H3 receptor antagonists: preclinical promise for treating obesity and cognitive disorders". Molecular Interventions. 6 (2): 77–88, 59. doi:10.1124/mi.6.2.5. PMID16565470.
Lovenberg TW, Roland BL, Wilson SJ, Jiang X, Pyati J, Huvar A, et al. (Jun 1999). "Cloning and functional expression of the human histamine H3 receptor". Molecular Pharmacology. 55 (6): 1101–7. doi:10.1124/mol.55.6.1101. PMID10347254. S2CID25542667.
Nakamura T, Itadani H, Hidaka Y, Ohta M, Tanaka K (Dec 2000). "Molecular cloning and characterization of a new human histamine receptor, HH4R". Biochemical and Biophysical Research Communications. 279 (2): 615–20. doi:10.1006/bbrc.2000.4008. PMID11118334.
Wiedemann P, Bönisch H, Oerters F, Brüss M (Apr 2002). "Structure of the human histamine H3 receptor gene (HRH3) and identification of naturally occurring variations". Journal of Neural Transmission. 109 (4): 443–53. doi:10.1007/s007020200036. PMID11956964. S2CID32434148.
Wellendorph P, Goodman MW, Burstein ES, Nash NR, Brann MR, Weiner DM (Jun 2002). "Molecular cloning and pharmacology of functionally distinct isoforms of the human histamine H(3) receptor". Neuropharmacology. 42 (7): 929–40. doi:10.1016/S0028-3908(02)00041-2. PMID12069903. S2CID54326678.
"Histamine Receptors: H3". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived from the original on 2013-12-25. Retrieved 2006-07-20.