Finished thinking
Hutcheson JD, Setola V, Roth BL, Merryman WD.
Pharmacology & Therapeutics. 2011;132(2):146-57. doi:10.1016/j.pharmthera.2011.03.008.
Carcinoid heart disease was one of the first valvular pathologies studied in molecular detail, and early research identified serotonin produced by oncogenic enterochromaffin cells as the likely culprit in causing changes in heart valve tissue. Researchers and physicians in the mid-1960s noted a connection between the use of several ergot-derived medications with structures similar to serotonin and the development of heart valve pathologies similar to those observed in carcinoid patients. The exact serotonergic target that mediated valvular pathogenesis remained a mystery for many years until similar cases were reported in patients using the popular diet drug Fen-Phen in the late 1990s. The Fen-Phen episode sparked renewed interest in serotonin-mediated valve disease, and studies led to the identification of the 5-HT(2B) receptor as the likely molecular target leading to heart valve tissue fibrosis. Subsequent studies have identified numerous other activators of the 5-HT(2B) receptor, and consequently, the use of many of these molecules has been linked to heart valve disease. Herein, we: review the molecular properties of the 5-HT(2B) receptor including factors that differentiate the 5-HT(2B) receptor from other 5-HT receptor subtypes, discuss the studies that led to the identification of the 5-HT(2B) receptor as the mediator of heart valve disease, present current efforts to identify potential valvulopathogens by screening for 5-HT(2B) receptor activity, and speculate on potential therapeutic benefits of 5-HT(2B) receptor targeting.
Rothman RB, Baumann MH, Savage JE, et al.
Circulation. 2000;102(23):2836-41. doi:10.1161/01.cir.102.23.2836.
Background: Serotonergic medications with various mechanisms of action are used to treat psychiatric disorders and are being investigated as treatments for drug dependence. The occurrence of fenfluramine-associated valvular heart disease (VHD) has raised concerns that other serotonergic medications might also increase the risk of developing VHD. We hypothesized that fenfluramine or its metabolite norfenfluramine and other medications known to produce VHD have preferentially high affinities for a particular serotonin receptor subtype capable of stimulating mitogenesis.
Methods And Results: Medications known or suspected to cause VHD (positive controls) and medications not associated with VHD (negative controls) were screened for activity at 11 cloned serotonin receptor subtypes by use of ligand-binding methods and functional assays. The positive control drugs were (+/-)-fenfluramine; (+)-fenfluramine; (-)-fenfluramine; its metabolites (+/-)-norfenfluramine, (+)-norfenfluramine, and (-)-norfenfluramine; ergotamine; and methysergide and its metabolite methylergonovine. The negative control drugs were phentermine, fluoxetine, its metabolite norfluoxetine, and trazodone and its active metabolite m-chlorophenylpiperazine. (+/-)-, (+)-, and (-)-Norfenfluramine, ergotamine, and methylergonovine all had preferentially high affinities for the cloned human serotonin 5-HT(2B) receptor and were partial to full agonists at the 5-HT(2B) receptor.
Conclusions: Our data imply that activation of 5-HT(2B) receptors is necessary to produce VHD and that serotonergic medications that do not activate 5-HT(2B) receptors are unlikely to produce VHD. We suggest that all clinically available medications with serotonergic activity and their active metabolites be screened for agonist activity at 5-HT(2B) receptors and that clinicians should consider suspending their use of medications with significant activity at 5-HT(2B) receptors.
Huang XP, Setola V, Yadav PN, et al.
Molecular Pharmacology. 2009;76(4):710-22. doi:10.1124/mol.109.058057.
Drug-induced valvular heart disease (VHD) is a serious side effect of a few medications, including some that are on the market. Pharmacological studies of VHD-associated medications (e.g., fenfluramine, pergolide, methysergide, and cabergoline) have revealed that they and/or their metabolites are potent 5-hydroxytryptamine(2B) (5-HT(2B)) receptor agonists. We have shown that activation of 5-HT(2B) receptors on human heart valve interstitial cells in vitro induces a proliferative response reminiscent of the fibrosis that typifies VHD. To identify current or future drugs that might induce VHD, we screened approximately 2200 U.S. Food and Drug Administration (FDA)-approved or investigational medications to identify 5-HT(2B) receptor agonists, using calcium-based high-throughput screening. Of these 2200 compounds, 27 were 5-HT(2B) receptor agonists (hits); 14 of these had previously been identified as 5-HT(2B) receptor agonists, including seven bona fide valvulopathogens. Six of the hits (guanfacine, quinidine, xylometazoline, oxymetazoline, fenoldopam, and ropinirole) are approved medications. Twenty-three of the hits were then "functionally profiled" (i.e., assayed in parallel for 5-HT(2B) receptor agonism using multiple readouts to test for functional selectivity). In these assays, the known valvulopathogens were efficacious at concentrations as low as 30 nM, whereas the other compounds were less so. Hierarchical clustering analysis of the pEC(50) data revealed that ropinirole (which is not associated with valvulopathy) was clearly segregated from known valvulopathogens. Taken together, our data demonstrate that patterns of 5-HT(2B) receptor functional selectivity might be useful for identifying compounds likely to induce valvular heart disease.
Fitzgerald LW, Burn TC, Brown BS, et al.
Molecular Pharmacology. 2000;57(1):75-81.
Dexfenfluramine was approved in the United States for long-term use as an appetite suppressant until it was reported to be associated with valvular heart disease. The valvular changes (myofibroblast proliferation) are histopathologically indistinguishable from those observed in carcinoid disease or after long-term exposure to 5-hydroxytryptamine (5-HT)(2)-preferring ergot drugs (ergotamine, methysergide). 5-HT(2) receptor stimulation is known to cause fibroblast mitogenesis, which could contribute to this lesion. To elucidate the mechanism of "fen-phen"-associated valvular lesions, we examined the interaction of fenfluramine and its metabolite norfenfluramine with 5-HT(2) receptor subtypes and examined the expression of these receptors in human and porcine heart valves. Fenfluramine binds weakly to 5-HT(2A), 5-HT(2B), and 5-HT(2C) receptors. In contrast, norfenfluramine exhibited high affinity for 5-HT(2B) and 5-HT(2C) receptors and more moderate affinity for 5-HT(2A) receptors. In cells expressing recombinant 5-HT(2B) receptors, norfenfluramine potently stimulated the hydrolysis of inositol phosphates, increased intracellular Ca(2+), and activated the mitogen-activated protein kinase cascade, the latter of which has been linked to mitogenic actions of the 5-HT(2B) receptor. The level of 5-HT(2B) and 5-HT(2A) receptor transcripts in heart valves was at least 300-fold higher than the levels of 5-HT(2C) receptor transcript, which were barely detectable. We propose that preferential stimulation of valvular 5-HT(2B) receptors by norfenfluramine, ergot drugs, or 5-HT released from carcinoid tumors (with or without accompanying 5-HT(2A) receptor activation) may contribute to valvular fibroplasia in humans.
Castillero E, Camillo C, Levine D, et al.
Cardiovascular Pathology : The Official Journal of the Society for Cardiovascular Pathology. 2025 Jan-Feb;74:107689. doi:10.1016/j.carpath.2024.107689.
Increased serotonin (5HT) concentration and signaling, can lead to pathological remodeling of the cardiac valves. We previously showed that a reduction of the 5HT transporter (SERT) expression in the mitral valve (MV) contributes to the progression of degenerative MV regurgitation (MR). We sought to investigate the myocardial and valvular phenotype of SERT-/- mice in order to identify remodeling mechanisms specific to the MV and left ventricular (LV) remodeling. Using 8- and 16-week-old WT and SERT-/- mice we show that male and female animals deficient of SERT have pathological remodeling of the cardiac valves, myocardial fibrosis, diminished ejection fraction and altered left ventricular dimensions. In the MV and intervalvular area of the aortic valve (AV)-MV, gene expression, including Col1a1 mRNA, was progressively altered with age up until 16 weeks of age. In contrast, in the AV and myocardium, most gene expression changes occurred earlier and plateaued by 8 weeks. To explore basal differences in susceptibility to remodeling stimuli among cardiac valves, valve interstitial cells (VIC) were isolated from AV, MV, tricuspid valve (TV), pulmonary valve (PV) and fibroblasts (Fb) from the myocardial apex from 16 weeks old wild type (WT) mice. After 24h stimulation with 10 µM of 5HT, the gene expression of Col1a1 and Acta2 were upregulated in MVIC to a higher degree than in VIC from other valves and Fb. Treatment with TGFβ1 similarly upregulated Cola1 and Acta2 in MVIC and AVIC, while the increase was milder in right heart VIC and Fb. Experiments were also carried out with human VIC. In comparison to mice, human left heart VIC were more sensitive to 5HT and TGFβ1, upregulating COL1A1 and ACTA2; TGFβ1 upregulated HTR2B expression in all VIC. Our results support the hypothesis that a deleterious cardiac effect of SERT downregulation may be mediated by increased susceptibility to HTR2B-dependent pro-fibrotic mechanisms, which are distinct among VIC populations and cardiac fibroblasts, regardless of SERT activity. Given that HTR2B mechanisms involved in VIC and myocardial remodeling response are due to both 5HT and also to downstream related TGFβ1 and TNFα activity, targeting HTR2B could be a therapeutic strategy for dual treatment of MR and LV remodeling.
Ayme-Dietrich E, Lawson R, Da-Silva S, Mazzucotelli JP, Monassier L.
Pharmacological Research. 2019;140:33-42. doi:10.1016/j.phrs.2018.09.009.
Heart valve disease (HVD) is a complex entity made by different pathological processes that ultimately lead to the abnormal structure and disorganization of extracellular matrix proteins resulting to dysfunction of the leaflets. At its final evolutionary step, treatments are limited to the percutaneous or surgical valve replacement, whatever the original cause of the degeneration. Understanding early molecular mechanisms that regulate valve interstitial cells remodeling and disease progression is challenging and could pave the way for future drugs aiming to prevent and/or reverse the process. Some valve degenerative processes such as the carcinoid heart disease, drug-induced valvulopathy and degenerative mitral valve disease in small-breed dogs are clearly linked to serotonin. The carcinoid heart is typically characterized by a right-sided valve dysfunction, observed in patients with carcinoid tumors developed from serotonin-producing gut enterochromaffin cells. Fenfluramine or ergot derivatives were linked to mitral and aortic valve dysfunction and share in common the pharmacological property of being 5-HT receptor agonists. Finally, some small-breed dogs, such as the Cavalier King Charles Spaniel are highly prone to degenerative mitral valve disease with a prevalence of 40% at 4 years-old, 70% at 7 years-old and 100% in 10-year-old animals. This degeneration has been linked to high serum serotonin, 5-HT receptor overexpression and SERT downregulation. Through the comprehension of serotonergic mechanisms involved into these specific situations, new therapeutic approaches could be extended to HVD in general. More recently, a serotonin dependent/ receptor independent mechanism has been suggested in congenital mitral valve prolapse through the filamin-A serotonylation. This review summarizes clinical and molecular mechanisms linking the serotonergic system and heart valve disease, opening the way for future pharmacological research in the field.
Smith SA, Waggoner AD, de las Fuentes L, Davila-Roman VG.
Journal of the American Society of Echocardiography : Official Publication of the American Society of Echocardiography. 2009;22(8):883-9. doi:10.1016/j.echo.2009.05.002.
Serotonin plays a significant role in the development of carcinoid heart disease, which primarily leads to fibrosis and contraction of right-sided heart valves. Recently, strong evidence has emerged that the use of specific drug classes, such as ergot alkaloids (for migraine headaches), 5-hydroxytryptamine (5-HT or serotonin) uptake regulators or inhibitors (for weight reduction), and ergot-derived dopamine agonists (for Parkinson's disease), can result in left-sided heart valve damage that resembles carcinoid heart disease. Recent studies have suggested that both right-sided and left-sided drug-induced heart valve disease involves increased serotoninergic activity and in particular activation of the 5-HT receptors, including the 5-HT2B receptor subtype, which mediate many of the central and peripheral functions of serotonin. G-proteins that inhibit adenylate cyclase activity mediate the activity of the 5-HT2B receptor subunit, which is widely expressed in a variety of tissues, including liver, lung, heart, and coronary and pulmonary arteries; it has also been reported in embryonic mouse heart, particularly on mouse heart valve leaflets. In this review, the authors discuss the salient features of serotoninergic manifestations of both carcinoid heart disease and drug-induced cardiac valvulopathy, with an emphasis on echocardiographic diagnosis.
Fortier JH, Pizzarotti B, Shaw RE, et al.
Heart (British Cardiac Society). 2019;105(15):1140-1148. doi:10.1136/heartjnl-2018-314403.
Objective: Serotonergic appetite suppressants and ergot-derived dopamine agonists have been associated with drug-induced valvular heart disease. The purpose of this meta-analysis is to synthesise the current evidence of a link between several medications affecting sertonergic pathways and valvular heart disease.
Methods: PubMed was searched to identify studies evaluating an association between medications with serotonergic activity and cardiac valvular pathology. Case reports, uncontrolled studies and in vitro studies were excluded. Relevant studies were assessed for quality and potential bias; those of adequate quality were included in a quantitative synthesis. Sensitivity analyses were conducted, and potential publication bias was examined.
Results: There was a consistent, significant relationship between certain medications and heart valve disease, including serotonergic medications (OR 3.30, 95% CI 1.99 to 5.49) and dopaminergic medications (OR 2.56, 95% CI 1.68 to 3.91). Subanalyses, including analyses that limited exposure to a single medication or effects to a single heart valve were also consistently significant. Most studies were retrospective or observational in nature, with a higher risk of selection and presentation biases. There was significant heterogeneity and variability between studies, particularly when it came to dose and duration of exposure.
Conclusions: There was a consistent, significant association between many medications that affect serotonergic pathways and valvular heart disease. Although many of these medications have been withdrawn from the market, some small studies suggest that recreational drug 3,4-methylenedioxymethamphetamine and widely prescribed selective serotonin reuptake inhibitors may affect similar pathways.
Hajjo R, Grulke CM, Golbraikh A, et al.
Journal of Medicinal Chemistry. 2010;53(21):7573-86. doi:10.1021/jm100600y.
Some antipsychotic drugs are known to cause valvular heart disease by activating serotonin 5-HT(2B) receptors. We have developed and validated binary classification QSAR models capable of predicting potential 5-HT(2B) actives. The classification accuracies of the models built to discriminate 5-HT(2B) actives from the inactives were as high as 80% for the external test set. These models were used to screen in silico 59,000 compounds included in the World Drug Index, and 122 compounds were predicted as actives with high confidence. Ten of them were tested in radioligand binding assays and nine were found active, suggesting a success rate of 90%. All validated actives were then tested in functional assays, and one compound was identified as a true 5-HT(2B) agonist. We suggest that the QSAR models developed in this study could be used as reliable predictors to flag drug candidates that are likely to cause valvulopathy.