5-Hydroxytryptamine receptor 2B (5-HT2B) also known as serotonin receptor 2B is a protein that in humans is encoded by the HTR2Bgene.[5][6] 5-HT2B is a member of the 5-HT2 receptor family that binds the neurotransmitterserotonin (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.
Tissue distribution and function
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 hallucinogenicsubstituted 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:
CNS: inhibition of serotonin and dopamine uptake, behavioral effects[10]
Cardiac: The 5-HT2B receptor regulates cardiac structure and functions, as demonstrated by the abnormal cardiac development observed in 5-HT2B receptor null mice.[12] Excessive stimulation of this receptor causes pathological proliferation of cardiac valve fibroblasts,[13] with chronic overstimulation leading to valvulopathy.[14][15] These receptors are also overexpressed in human failing heart and antagonists of 5-HT2B receptors were discovered to prevent both angiotensin II or beta-adrenergic agonist-induced pathological cardiac hypertrophy in mouse.[16][17][18]
Serotonin transporter: 5-HT2B receptors regulate serotonin release via the serotonin transporter, and are important both to normal physiological regulation of serotonin levels in blood plasma,[19] and with the abnormal acute serotonin release produced by drugs such as MDMA.[10] Surprisingly, however, 5-HT2B receptor activation appears to be protective against the development of serotonin syndrome following elevated extracellular serotonin levels,[20] despite its role in modulating serotonin release.
Clinical significance
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]
Ligands
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]
Agonists
Selective
BW-723C86[28] – fair functional subtype selectivity; almost full agonist. Anxiolytic in vivo[29]
Ro60-0175[28] – functionally selective over 5-HT2A, potent agonist at both 5-HT2B/C
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.[47] More recent research has focused on possible application of 5-HT2B antagonists as treatments for chronic heart disease.[48][49] Research claims serotonin 5-HT2B receptors have effect on liver regeneration.[50] Antagonism of 5-HT2B may attenuate fibrogenesis and improve liver function in disease models in which fibrosis is pre-established and progressive.
"5-HT2B". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Archived from the original on 2017-02-02. Retrieved 2008-11-25.