5-Hydroxytryptamine receptor 2B (5-HT2B) also known as serotonin receptor 2B is a protein that in humans is encoded by the HTR2B gene. [5] [6] 5-HT2B is a member of the 5-HT2 receptor family that binds the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Like all 5-HT2 receptors, the 5-HT2B receptor is Gq/G11-protein coupled, leading to downstream activation of phospholipase C.
First discovered in the stomach of rats, 5-HT2B was challenging to characterize initially because of its structural similarity to the other 5-HT2 receptors, particularly 5-HT2C. [7] The 5-HT2 receptors (of which the 5-HT2B receptor is a subtype) mediate many of the central and peripheral physiologic functions of serotonin. Cardiovascular effects include contraction of blood vessels and shape changes in platelets; central nervous system (CNS) effects include neuronal sensitization to tactile stimuli and mediation of some of the effects of hallucinogenic substituted amphetamines. The 5-HT2B receptor is expressed in several areas of the CNS, including the dorsal hypothalamus, frontal cortex, medial amygdala, and meninges. [8] However, its most important role is in the peripheral nervous system (PNS) where it maintains the viability and efficiency of the cardiac valve leaflets. [9]
The 5-HT2B receptor subtype is involved in:
5-HT2B receptors have been strongly implicated in causing drug-induced valvular heart disease. [21] [22] [23] The Fen-Phen scandal in the 80s and 90s revealed the cardiotoxic effects of 5-HT2B stimulation. [24] Today, 5-HT2B agonism is considered a toxicity signal precluding further clinical development of a compound. [25]
The structure of the 5-HT2B receptor was resolved in a complex with the valvulopathogenic drug ergotamine. [26] As of 2009, few highly selective 5-HT2B receptor ligands have been discovered, although numerous potent non-selective compounds are known, particularly agents with concomitant 5-HT2C binding. Research in this area has been limited due to the cardiotoxicity of 5-HT2B agonists, and the lack of clear therapeutic application for 5-HT2B antagonists, but there is still a need for selective ligands for scientific research. [27]
A number of notable drugs appear to be inactive or very weak as serotonin 5-HT2B receptor agonists, at least in vitro . [30] These include the stimulants and/or entactogens dextroamphetamine, dextromethamphetamine, 4-fluoroamphetamine, 4-fluoromethamphetamine, phentermine, methylone, mephedrone, MDAI, and MMAI, among others. [30] [47] [37] [71] [72] [73] Findings are somewhat conflicting for certain psychedelics, such as psilocin and LSD, but most studies find that these drugs are indeed potent serotonin 5-HT2B receptor agonists. [63] [30] [32]
BW-501C67 and xylamidine are known peripherally selective antagonists of the serotonin 5-HT2 receptors, including of the serotonin 5-HT2A and 5-HT2B receptors, but their serotonin 5-HT2B receptor interactions do not appear to have been described. [122] [123] [124]
5-HT2B antagonists have previously been proposed as treatment for migraine headaches, and RS-127,445 was trialled in humans up to Phase I for this indication, but development was not continued. [125] More recent research has focused on possible application of 5-HT2B antagonists as treatments for chronic heart disease. [126] [127] Research claims serotonin 5-HT2B receptors have effect on liver regeneration. [128] Antagonism of 5-HT2B may attenuate fibrogenesis and improve liver function in disease models in which fibrosis is pre-established and progressive.
{{cite journal}}
: CS1 maint: overridden setting (link)Bromocriptine was first described as a 5HT-2BR antagonist (22) but was subsequently found to have partial agonist properties (23,24). [...] Regarding bromocriptine, there was no increased incidence of valve regurgitation in PD patients on bromocriptine in the population-based study of Schade et al (33), despite the significant findings for cabergoline and pergolide. However, there is a case report implicating high doses of bromocriptine as the cause of triple valve disease in a PD patient (37), and 1 study reported a significant correlation between cumulative dose of bromocriptine and the risk of valve regurgitation in a PD cohort (38). Other publications have reported fibrotic events, including retroperitoneal, pericardial and pleural fibrosis, in PD patients on high-dose bromocriptine (39-43). [...] Although there seems to be a lower risk of valvulopathy with bromocriptine, as a partial 5HT-2BR agonist, there still appears to be some risk with high-dose bromocriptine in PD patients.
Various polycyclic agents such as butaclamol, mianserin, cyproheptadine, pizotyline bind at 5-HT2 receptors with high affinity. These agents are not selective and bind with comparable affinty either at other populations of 5-HT receptors or at other neurotransmitter receptors. Other, structurally unique agents have also been investigated including cinanserin and xylamidine. The latter compound has seen application as a peripheral 5-HT2 antagonist in that it does not readily penetrate the blood-brain barrier; however, xylamidine binds equally well at 5-HTIC and 5-HT2 receptors. See references 3 and 5 for additional information on these types of agents.
Systemic administration of the peripheral 5-HT2A/2C antagonist xylamidine [...] First, systemic injections of the peripherally acting 5-HT2A/2C receptor antagonist xylamidine were employed to study its effects on head bobs and body shakes produced by systemic injections of DOI.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.