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.
5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in the central and peripheral nervous systems. They mediate both excitatory and inhibitory neurotransmission. The serotonin receptors are activated by the neurotransmitter serotonin, which acts as their natural ligand.
Methysergide, sold under the brand names Deseril and Sansert, is a monoaminergic medication of the ergoline and lysergamide groups which is used in the prophylaxis and treatment of migraine and cluster headaches. It has been withdrawn from the market in the United States and Canada due to safety concerns. It is taken by mouth.
The 5-HT2A receptor is a subtype of the 5-HT2 receptor that belongs to the serotonin receptor family and is a G protein-coupled receptor (GPCR). The 5-HT2A receptor is a cell surface receptor, but has several intracellular locations.
The 5-HT2 receptors are a subfamily of 5-HT receptors that bind the endogenous neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). The 5-HT2 subfamily consists of three G protein-coupled receptors (GPCRs) which are coupled to Gq/G11 and mediate excitatory neurotransmission, including 5-HT2A, 5-HT2B, and 5-HT2C. For more information, please see the respective main articles of the individual subtypes:
A serotonin receptor agonist is an agonist of one or more serotonin receptors. They activate serotonin receptors in a manner similar to that of serotonin, a neurotransmitter and hormone and the endogenous ligand of the serotonin receptors.
Sarpogrelate is a drug which acts as an antagonist at the serotonin 5-HT2A5-HT2B, and 5-HT2C receptors. However, its affinities for the human 5-HT2C and 5-HT2B receptors are about one and two orders of magnitude lower than for the human 5-HT2A receptor, respectively. The drug blocks serotonin-induced platelet aggregation, and has potential applications in the treatment of many diseases including diabetes mellitus, Buerger's disease, Raynaud's disease, coronary artery disease, angina pectoris, and atherosclerosis.
Xylamidine is a drug which acts as an antagonist of the serotonin 5-HT2A and 5-HT2C receptors, and to a lesser extent of the serotonin 5-HT1A receptor. The drug does not cross the blood–brain barrier and hence is peripherally selective, which makes it useful for blocking peripheral serotonergic responses like cardiovascular and gastrointestinal effects, without producing the central effects of 5-HT2A receptor blockade such as sedation, or interfering with the central actions of 5-HT2A receptor agonists.
RS-127445, also known as MT-500, is a drug which acts as a potent and selective antagonist at the serotonin 5-HT2B receptor, with around 1,000-fold selectivity over the closely related 5-HT2A and 5-HT2C receptors. The role of the 5-HT2B receptor in the body is still poorly understood, and RS-127445 has been a useful tool in unravelling the function of the various systems in which this receptor is expressed. The drug was under development for potential use as a pharmaceutical drug by Roche and reached phase 1 clinical trials but was discontinued for unknown reasons.
SB-204741 is a drug which acts as a potent and selective antagonist at the serotonin 5-HT2B receptor, with around 135x selectivity over the closely related 5-HT2C receptor, and even higher over the 5-HT2A receptor and other targets. It is used in scientific research for investigating the functions of the 5-HT2B receptor.
BW-723C86 is a tryptamine derivative drug which acts as a 5-HT2B receptor agonist. It has anxiolytic effects in animal studies, and is also used for investigating the function of the 5-HT2B receptor in a range of other tissues.
α-Methylserotonin (αMS), also known as α-methyl-5-hydroxytryptamine (α-methyl-5-HT) or 5-hydroxy-α-methyltryptamine (5-HO-αMT), is a tryptamine derivative closely related to the neurotransmitter serotonin (5-HT). It acts as a non-selective serotonin receptor agonist and has been used extensively in scientific research to study the function of the serotonin system.
SDZ SER-082 is a drug which acts as a mixed antagonist for the 5-HT2B and 5-HT2C serotonin receptors, with good selectivity over other serotonin receptor subtypes and slight preference for 5-HT2C over 5-HT2B. It has been used in animal studies into the behavioural effects of the different 5-HT2 subtypes, and how they influence the effects of other drugs such as cocaine.
SB-215505 is a drug which acts as a potent and selective antagonist at the serotonin 5-HT2B receptor, with good selectivity over the related 5-HT2A and 5-HT2C receptors. It is used in scientific research into the function of the 5-HT2 family of receptors, especially to study the role of 5-HT2B receptors in the heart, and to distinguish 5-HT2B-mediated responses from those produced by 5-HT2A or 5-HT2C.
Serotonin antagonist and reuptake inhibitors (SARIs) are a class of drugs used mainly as antidepressants, but also as anxiolytics and hypnotics. They act by antagonizing serotonin receptors such as 5-HT2A and inhibiting the reuptake of serotonin, norepinephrine, and/or dopamine. Additionally, most also antagonize α1-adrenergic receptors. The majority of the currently marketed SARIs belong to the phenylpiperazine class of compounds.
PRX-08066 is a drug discovered and developed by Predix Pharmaceuticals [Dale S. Dhanoa et al. Patent US 7,030,240 B2], which acts as a potent and selective antagonist at the serotonin 5-HT2B receptor, with a 5-HT2Bbinding affinity (Ki) of 3.4nM, and high selectivity over the closely related 5-HT2A and 5-HT2C receptors and other receptor targets. PRX-08066 and other selective 5-HT2B antagonists are being researched for the treatment of pulmonary arterial hypertension, following the discovery that the potent 5-HT2B agonist norfenfluramine produces pulmonary arterial hypertension and subsequent heart valve damage. In animal studies, PRX-08066 has been found to reduce several key indicators of pulmonary arterial hypertension and improved cardiac output, with similar efficacy to established drugs for this condition such as bosentan, sildenafil, beraprost and iloprost. It is also being researched for potential anti-cancer applications, due to its ability to inhibit fibroblast activation.
SB-206553 is a drug which acts as a mixed antagonist for the 5-HT2B and 5-HT2C serotonin receptors. It has anxiolytic properties in animal studies and interacts with a range of other drugs. It has also been shown to act as a positive allosteric modulator of α7 nicotinic acetylcholine receptors. Modified derivatives of SB-206553 have been used to probe the structure of the 5-HT2B receptor.
5-HT2C receptor agonists are a class of drugs that activate 5-HT2C receptors. They have been investigated for the treatment of a number of conditions including obesity, psychiatric disorders, sexual dysfunction and urinary incontinence.
25CN-NBOH is a compound indirectly derived from the phenethylamine series of hallucinogens, which was discovered in 2014 at the University of Copenhagen. This compound is notable as one of the most selective agonist ligands for the 5-HT2A receptor yet discovered, with a pKi of 8.88 at the human 5-HT2A receptor and with 100x selectivity for 5-HT2A over 5-HT2C, and 46x selectivity for 5-HT2A over 5-HT2B. A tritiated version of 25CN-NBOH has also been accessed and used for more detailed investigations of the binding to 5-HT2 receptors and autoradiography.
Peripherally selective drugs have their primary mechanism of action outside of the central nervous system (CNS), usually because they are excluded from the CNS by the blood–brain barrier. By being excluded from the CNS, drugs may act on the rest of the body without producing side-effects related to their effects on the brain or spinal cord. For example, most opioids cause sedation when given at a sufficiently high dose, but peripherally selective opioids can act on the rest of the body without entering the brain and are less likely to cause sedation. These peripherally selective opioids can be used as antidiarrheals, for instance loperamide (Imodium).
BW-501C67 is a peripherally selective serotonin 5-HT2A and 5-HT2C receptor antagonist which is used in scientific research. It shows selectivity for the serotonin 5-HT2 receptors over the α1-adrenergic receptor.
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: 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.