Serotonin 5-HT(2B) receptor blockade prevents reactive oxygen species-induced cardiac hypertrophy in mice

2-(Piperidin-3-yl)phthalimides reduce classical markers of cellular inflammation in LPS-challenged RAW 264.7 cells and also demonstrate potentially relevant sigma and serotonin receptor affinity in membrane preparations

Herein, we report the synthesis of new 4-amino-2-(piperidin-3-yl)isoindoline-1,3-diones and their biological evaluation in a series of in vitro experiments. The synthetic production of these materials was initiated upon the condensation of appropriate nitrophthalic acid derivatives with various 3-aminopiperidines; subsequent reduction provided the final products in moderate to good yields. Readily available chiral pool reagents facilitated entry into optically enriched samples, while the piperidine scaffold furnished a variety of amide and alkylated entries. In total, 16 candidates were produced, and their ensuing treatment in LPS-challenged RAW cells effected slight reductions in secreted TNF-α but provided more robust and dose-dependent declines in nitrite and IL-6 levels relative to basal amounts, all concurrent with maintenance of cellular viability across the concentration ranges screened. The secondary amine cohort including rac-6, (R)-7, and (S)-8 rendered the most pronounced dose-dependent reductions in nitrite and IL-6. When dosed at 30 μM, (R)-7 demonstrated the most compelling effects, with decreases of 32 % and 40 % for nitrite and IL-6, respectively. Notable reductions in the inflammatory markers were also observed for 19 which effected declines in TNF-α (14 %), nitrite (19 %), and IL-6 (11 %) when treated at 30 μM. Additionally, four representative compounds were further evaluated against numerous CNS receptors, channels, and transporters, with 6, 9, and 19 demonstrating varying degrees of nanomolar-to-low-micromolar binding to the σ-1 and σ-2 receptors and also to serotonin receptors 5HT2A, 5HT2B and 5HT3. In this regard, 6 displayed perhaps the most noteworthy affinities, with binding at σ-2 (Ki = 2.2uM), 5HT2B (Ki = 561 nM) and 5HT3 (Ki = 536 nM). Furthermore, no pronounced or dose-dependent Cereblon/DDB1 binding was observed for the screened representative compounds 6, 9, 18 and 19.

Role of Vasoactive Hormone-Induced Signal Transduction in Cardiac Hypertrophy and Heart Failure

Heart failure is the common concluding pathway for a majority of cardiovascular diseases and is associated with cardiac dysfunction. Since heart failure is invariably preceded by adaptive or maladaptive cardiac hypertrophy, several biochemical mechanisms have been proposed to explain the development of cardiac hypertrophy and progression to heart failure. One of these includes the activation of different neuroendocrine systems for elevating the circulating levels of different vasoactive hormones such as catecholamines, angiotensin II, vasopressin, serotonin and endothelins. All these hormones are released in the circulation and stimulate different signal transduction systems by acting on their respective receptors on the cell membrane to promote protein synthesis in cardiomyocytes and induce cardiac hypertrophy. The elevated levels of these vasoactive hormones induce hemodynamic overload, increase ventricular wall tension, increase protein synthesis and the occurrence of cardiac remodeling. In addition, there occurs an increase in proinflammatory cytokines and collagen synthesis for the induction of myocardial fibrosis and the transition of adaptive to maladaptive hypertrophy. The prolonged exposure of the hypertrophied heart to these vasoactive hormones has been reported to result in the oxidation of catecholamines and serotonin via monoamine oxidase as well as the activation of NADPH oxidase via angiotensin II and endothelins to promote oxidative stress. The development of oxidative stress produces subcellular defects, Ca2+-handling abnormalities, mitochondrial Ca2+-overload and cardiac dysfunction by activating different proteases and depressing cardiac gene expression, in addition to destabilizing the extracellular matrix upon activating some metalloproteinases. These observations support the view that elevated levels of various vasoactive hormones, by producing hemodynamic overload and activating their respective receptor-mediated signal transduction mechanisms, induce cardiac hypertrophy. Furthermore, the occurrence of oxidative stress due to the prolonged exposure of the hypertrophied heart to these hormones plays a critical role in the progression of heart failure.

Plasma Serotonin and Cardiovascular Outcomes in Chronic Kidney Disease

Background Platelet-poor plasma serotonin levels are associated with adverse cardiovascular outcomes. Although plasma serotonin levels increase in chronic kidney disease, the cardiovascular implications remain unknown. Methods and Results In 1114 participants from the prospective CRIC (Chronic Renal Insufficiency Cohort) Study, we evaluated the association between plasma serotonin, categorized as undetectable, intermediate, and high (≥20 ng/mL) levels, and cross-sectional findings on echocardiography, including left ventricular hypertrophy, left ventricular ejection fraction, and pulmonary hypertension. We also analyzed whether serotonin was associated with time-to-event cardiovascular outcomes, including heart failure hospitalization and atherosclerotic cardiovascular disease (ASCVD) events, in addition to mortality. Because selective serotonin reuptake inhibitors decrease plasma serotonin levels, we specifically evaluated the influence of selective serotonin reuptake inhibitor use in the relationship between serotonin and outcomes. Plasma serotonin level inversely correlated with estimated glomerular filtration rate and directly correlated with blood pressure. High plasma serotonin was associated with left ventricular hypertrophy (adjusted odds ratio, 2.74 [95% CI, 1.11-7.41]). In contrast, undetectable plasma serotonin level was associated with the highest risk of heart failure (adjusted hazard ratio [HR], 2.26 [95% CI, 1.40-3.66]) and ASCVD events (adjusted HR, 1.96 [95% CI, 1.15-3.32]). Conclusions In a large chronic kidney disease cohort, plasma serotonin levels correlated with blood pressure, and elevated serotonin levels were associated with left ventricular hypertrophy. In contrast, undetectable plasma serotonin was associated with the highest risk of heart failure and ASCVD events.

Cardiac Roles of Serotonin (5-HT) and 5-HT-Receptors in Health and Disease

Serotonin acts solely via 5-HT4-receptors to control human cardiac contractile function. The effects of serotonin via 5-HT4-receptors lead to positive inotropic and chronotropic effects, as well as arrhythmias, in the human heart. In addition, 5-HT4-receptors may play a role in sepsis, ischaemia, and reperfusion. These presumptive effects of 5-HT4-receptors are the focus of the present review. We also discuss the formation and inactivation of serotonin in the body, namely, in the heart. We identify cardiovascular diseases where serotonin might play a causative or additional role. We address the mechanisms which 5-HT4-receptors can use for cardiac signal transduction and their possible roles in cardiac diseases. We define areas where further research in this regard should be directed in the future, and identify animal models that might be generated to this end. Finally, we discuss in what regard 5-HT4-receptor agonists or antagonists might be useful drugs that could enter clinical practice. Serotonin has been the target of many studies for decades; thus, we found it timely to summarise our current knowledge here.

Development of Pharmacophore Models for the Important Off-Target 5-HT2B Receptor

Toxicity is a major cause of attrition in the development of pharmaceuticals, and the off-target effects are a frequent contributor. The 5-HT_2B receptor agonism is known to be responsible for a variety of safety concerns including valvular heart disease which was the cause for the withdrawal of several compounds from the market. An early detection of potential binding to this receptor is thus desirable. Herein, we present the identification of key amino acid residues in the active site of 5-HT_2B by molecular dynamics simulations, the development of pharmacophore models and their performance on in-house data, and a structurally highly diverse subset of Enamine REAL labeled for 5-HT_2B activity by a machine learning model. These models may be used as filters employed on screening compound sets for the early filtration of compounds with potential 5-HT_2B off-target liabilities.

Integrative identification of immune-related key genes in atrial fibrillation using weighted gene coexpression network analysis and machine learning

Background

The immune system significantly participates in the pathologic process of atrial fibrillation (AF). However, the molecular mechanisms underlying this participation are not completely explained. The current research aimed to identify critical genes and immune cells that participate in the pathologic process of AF.

Methods

CIBERSORT was utilized to reveal the immune cell infiltration pattern in AF patients. Meanwhile, weighted gene coexpression network analysis (WGCNA) was utilized to identify meaningful modules that were significantly correlated with AF. The characteristic genes correlated with AF were identified by the least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine recursive feature elimination (SVM-RFE) algorithm.

Results

In comparison to sinus rhythm (SR) individuals, we observed that fewer activated mast cells and regulatory T cells (Tregs), as well as more gamma delta T cells, resting mast cells, and M2 macrophages, were infiltrated in AF patients. Three significant modules (pink, red, and magenta) were identified to be significantly associated with AF. Gene enrichment analysis showed that all 717 genes were associated with immunity- or inflammation-related pathways and biological processes. Four hub genes (GALNT16, HTR2B, BEX2, and RAB8A) were revealed to be significantly correlated with AF by the SVM-RFE algorithm and LASSO logistic regression. qRT–PCR results suggested that compared to the SR subjects, AF patients exhibited significantly reduced BEX2 and GALNT16 expression, as well as dramatically elevated HTR2B expression. The AUC measurement showed that the diagnostic efficiency of BEX2, HTR2B, and GALNT16 in the training set was 0.836, 0.883, and 0.893, respectively, and 0.858, 0.861, and 0.915, respectively, in the validation set.

Conclusions

Three novel genes, BEX2, HTR2B, and GALNT16, were identified by WGCNA combined with machine learning, which provides potential new therapeutic targets for the early diagnosis and prevention of AF.

Diversity among differentially expressed genes in atrial appendages of atrial fibrillation: The role and mechanism of SPP1 in atrial fibrosis

BACKGROUND

Structural remodeling plays an important role in the occurrence and maintenance of atrial fibrillation (AF), but the mechanism is currently unclear. This study was designed to investigate the transcriptomic mechanism of structural remodeling of AF through bioinformatic analysis and in vivo and vitro experiments.

METHODS

Transcriptomic datasets were retrieved from the Gene Expression Omnibus (GEO) database, and bioinformatics analysis was performed to screen mRNAs associated with AF. Cell and animal models were constructed to verify the bioinformatic findings using RT-qPCR and western blot analysis. Then, SPP1 was screened as the target gene, and the mechanism by which it promotes fibrosis was further studied in human cardiac fibroblasts (HCFs) using western blot analysis.

RESULTS

After retrieval, the GSE14975, GSE31821, GSE79768, GSE115574 and GSE128188 datasets were used in this study. In total, 147 differentially expressed genes (DEGs) were identified in left atrial appendix tissue and 85 in right atrial appendix tissue. According to the enrichment analysis results, the calcium signaling pathway was found to play an important role in AF, in which EGFR, AGTR1, HTR2B, CD38 and BDKRB1 might be the key genes. Moreover, SPP1 was identified as a key driver through PPI analysis and experimentally proved to reduce the expression of p27 by regulating the PI3K/Akt signaling pathway, sequentially promoting HCF fibrosis.

CONCLUSION

Bioinformatics analysis showed that the calcium signaling pathway might play an important role in AF, while SPP1 could promote myocardial fibrosis through the PI3K/Akt/p27 signaling axis.

Heterodimerization With 5-HT2BR Is Indispensable for β2AR-Mediated Cardioprotection

RATIONALE

The β2-adrenoceptor (β2-AR), a prototypical GPCR (G protein-coupled receptor), couples to both Gs and Gi proteins. Stimulation of the β2-AR is beneficial to humans and animals with heart failure presumably because it activates the downstream Gi-PI3K-Akt cell survival pathway. Cardiac β2-AR signaling can be regulated by crosstalk or heterodimerization with other GPCRs, but the physiological and pathophysiological significance of this type of regulation has not been sufficiently demonstrated.

OBJECTIVE

Here, we aim to investigate the potential cardioprotective effect of β2-adrenergic stimulation with a subtype-selective agonist, (R,R')-4-methoxy-1-naphthylfenoterol (MNF), and to decipher the underlying mechanism with a particular emphasis on the role of heterodimerization of β2-ARs with another GPCR, 5-hydroxytryptamine receptors 2B (5-HT2BRs).

METHODS AND RESULTS

Using pharmacological, genetic and biophysical protein-protein interaction approaches, we studied the cardioprotective effect of the β2-agonist, MNF, and explored the underlying mechanism in both in vivo in mice and cultured rodent cardiomyocytes insulted with doxorubicin, hydrogen peroxide (H2O2) or ischemia/reperfusion. In doxorubicin (Dox)-treated mice, MNF reduced mortality and body weight loss, while improving cardiac function and cardiomyocyte viability. MNF also alleviated myocardial ischemia/reperfusion injury. In cultured rodent cardiomyocytes, MNF inhibited DNA damage and cell death caused by Dox, H2O2 or hypoxia/reoxygenation. Mechanistically, we found that MNF or another β2-agonist zinterol markedly promoted heterodimerization of β2-ARs with 5-HT2BRs. Upregulation of the heterodimerized 5-HT2BRs and β2-ARs enhanced β2-AR-stimulated Gi-Akt signaling and cardioprotection while knockdown or pharmacological inhibition of the 5-HT2BR attenuated β2-AR-stimulated Gi signaling and cardioprotection.

CONCLUSIONS

These data demonstrate that the β2-AR-stimulated cardioprotective Gi signaling depends on the heterodimerization of β2-ARs and 5-HT2BRs.

Structure, Function, and Pharmaceutical Ligands of 5-Hydroxytryptamine 2B Receptor

Since the first characterization of the 5-hydroxytryptamine 2B receptor (5-HT2BR) in 1992, significant progress has been made in 5-HT2BR research. Herein, we summarize the biological function, structure, and small-molecule pharmaceutical ligands of the 5-HT2BR. Emerging evidence has suggested that the 5-HT2BR is implicated in the regulation of the cardiovascular system, fibrosis disorders, cancer, the gastrointestinal (GI) tract, and the nervous system. Eight crystal complex structures of the 5-HT2BR bound with different ligands provided great insights into ligand recognition, activation mechanism, and biased signaling. Numerous 5-HT2BR antagonists have been discovered and developed, and several of them have advanced to clinical trials. It is expected that the novel 5-HT2BR antagonists with high potency and selectivity will lead to the development of first-in-class drugs in various therapeutic areas.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Genetic ablation of serotonin receptor 2B improves aortic valve hemodynamics of Notch1 heterozygous mice in a high-cholesterol diet model

Calcific aortic valve disease (CAVD) is a deadly disease that is rising in prevalence due to population aging. While the disease is complex and poorly understood, one well-documented driver of valvulopathy is serotonin agonism. Both serotonin overexpression, as seen with carcinoid tumors and drug-related agonism, such as with Fenfluramine use, are linked with various diseases of the valves. Thus, the objective of this study was to determine if genetic ablation or pharmacological antagonism of the 5-HT_2B serotonin receptor (gene: Htr2b) could improve the hemodynamic and histological progression of calcific aortic valve disease. Htr2b mutant mice were crossed with Notch1^+/- mice, an established small animal model of CAVD, to determine if genetic ablation affects CAVD progression. To assess the effect of pharmacological inhibition on CAVD progression, Notch1^+/- mice were treated with the 5-HT_2B receptor antagonist SB204741. Mice were analyzed using echocardiography, histology, immunofluorescence, and real-time quantitative polymerase chain reaction. Htr2b mutant mice showed lower aortic valve peak velocity and mean pressure gradient–classical hemodynamic indicators of aortic valve stenosis–without concurrent left ventricle change. 5-HT_2B receptor antagonism, however, did not affect hemodynamic progression. Leaflet thickness, collagen density, and CAVD-associated transcriptional markers were not significantly different in any group. This study reveals that genetic ablation of Htr2b attenuates hemodynamic development of CAVD in the Notch1^+/- mice, but pharmacological antagonism may require high doses or long-term treatment to slow progression.

G-Protein-Coupled Receptors in Heart Disease

GPCRs (G-protein [guanine nucleotide-binding protein]-coupled receptors) play a central physiological role in the regulation of cardiac function in both health and disease and thus represent one of the largest class of surface receptors targeted by drugs. Several antagonists of GPCRs, such as βARs (β-adrenergic receptors) and Ang II (angiotensin II) receptors, are now considered standard of therapy for a wide range of cardiovascular disease, such as hypertension, coronary artery disease, and heart failure. Although the mechanism of action for GPCRs was thought to be largely worked out in the 80s and 90s, recent discoveries have brought to the fore new and previously unappreciated mechanisms for GPCR activation and subsequent downstream signaling. In this review, we focus on GPCRs most relevant to the cardiovascular system and discuss traditional components of GPCR signaling and highlight evolving concepts in the field, such as ligand bias, β-arrestin-mediated signaling, and conformational heterogeneity.

Serotonin and catecholamines in the development and progression of heart valve diseases

Heart valve diseases (HVDs) arise from a number of different processes that affect both the structure and function of the valve apparatus. Despite diverse aetiologies, treatments for HVDs are limited to percutaneous or surgical interventions. The search for medical therapies to prevent or slow the progression of HVDs has been hampered by our poor understanding of the progression from subclinical to symptomatic phases, and our limited knowledge of the molecular signals that control the susceptibility of valve interstitial cells to pathological remodeling. Clinical evidence has suggested a link between certain neurotransmitters and valvular diseases of the heart. The fenfluramine-phentermine appetite suppressants popular in the 1980s were linked to mitral valve dysfunction, and ergot-derived dopamine agonists for Parkinson's disease have been associated with an increased risk of mitral and aortic valve regurgitation. The effect does not appear to be limited to medications, as valvular pathologies have also been observed in patients with carcinoid tumours of serotonin-producing enterochromaffin cells. The role of neurotransmitter molecules in valve pathology has not been adequately characterized and may represent a target for future medical therapies. Here we present current evidence from both clinical and basic science suggesting a link between neurotransmitters and HVDs, opening the door to future research in this area.

5-HT2B receptor antagonists inhibit fibrosis and protect from RV heart failure

Objective. The serotonin (5-HT) pathway was shown to play a role in pulmonary hypertension (PH), but its functions in right ventricular failure (RVF) remain poorly understood. The aim of the current study was to investigate the effects of Terguride (5-HT2A and 2B receptor antagonist) or SB204741 (5-HT2B receptor antagonist) on right heart function and structure upon pulmonary artery banding (PAB) in mice. Methods. Seven days after PAB, mice were treated for 14 days with Terguride (0.2 mg/kg bid) or SB204741 (5 mg/kg day). Right heart function and remodeling were assessed by right heart catheterization, magnetic resonance imaging (MRI), and histomorphometric methods. Total secreted collagen content was determined in mouse cardiac fibroblasts isolated from RV tissues. Results. Chronic treatment with Terguride or SB204741 reduced right ventricular fibrosis and showed improved heart function in mice after PAB. Moreover, 5-HT2B receptor antagonists diminished TGF-beta1 induced collagen synthesis of RV cardiac fibroblasts in vitro. Conclusion. 5-HT2B receptor antagonists reduce collagen deposition, thereby inhibiting right ventricular fibrosis. Chronic treatment prevented the development and progression of pressure overload-induced RVF in mice. Thus, 5-HT2B receptor antagonists represent a valuable novel therapeutic approach for RVF.

Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties

Agomelatine behaves both as a potent agonist at melatonin MT1 and MT2 receptors and as a neutral antagonist at 5-HT2C receptors. Accumulating evidence in a broad range of experimental procedures supports the notion that the psychotropic effects of agomelatine are due to the synergy between its melatonergic and 5-hydroxytryptaminergic effects. The recent demonstration of the existence of heteromeric complexes of MT1 and MT2 with 5-HT2C receptors at the cellular level may explain how these two properties of agomelatine translate into a synergistic action that, for example, leads to increases in hippocampal proliferation, maturation and survival through modulation of multiple cellular pathways (increase in trophic factors, synaptic remodelling, glutamate signalling) and key targets (early genes, kinases). The present review focuses on the pharmacological properties of this novel antidepressant. Its mechanism of action, strikingly different from that of conventional classes of antidepressants, opens perspectives towards a better understanding of the physiopathological bases underlying depression.

Role of serotonin 5-HT2A receptors in the development of cardiac hypertrophy in response to aortic constriction in mice

Serotonin, in addition to its fundamental role as a neurotransmitter, plays a critical role in the cardiovascular system, where it is thought to be involved in the development of cardiac hypertrophy and failure. Indeed, we recently found that mice with deletion of monoamine oxidase A had enhanced levels of blood and cardiac 5-HT, which contributed to exacerbation of hypertrophy in a model of experimental pressure overload. 5-HT2A receptors are expressed in the heart and mediate a hypertrophic response to 5-HT in cardiac cells. However, their role in cardiac remodeling in vivo and the signaling pathways associated are not well understood. In the present study, we evaluated the effect of a selective 5-HT2A receptor antagonist, M100907, on the development of cardiac hypertrophy induced by transverse aortic constriction (TAC). Cardiac 5-HT2A receptor expression was transiently increased after TAC, and was recapitulated in cardiomyocytes, as observed with 5-HT2A in situ labeling by immunohistochemistry. Selective blockade of 5-HT2A receptors prevented the development of cardiac hypertrophy, as measured by echocardiography, cardiomyocyte area and heart weight-to-body weight ratio. Interestingly, activation of calmodulin kinase (CamKII), which is a core mechanism in cardiac hypertrophy, was reduced in cardiac samples from M100907-treated TAC mice compared to vehicle-treated mice. In addition, phosphorylation of histone deacetylase 4 (HDAC4), a downstream partner of CamKII was significantly diminished in M100907-treated TAC mice. Thus, our results show that selective blockade of 5-HT2A receptors has beneficial effect in the development of cardiac hypertrophy through inhibition of the CamKII/HDAC4 pathway.

Serotonin paracrine signaling in tissue fibrosis

The molecule serotonin (5-hydroxytryptamine or 5-HT) is involved in numerous biological processes both inside and outside of the central nervous system. 5-HT signals through 5-HT receptors and it is the diversity of these receptors and their subtypes that give rise to the varied physiological responses. It is clear that platelet derived serotonin is critical for normal wound healing in multiple organs including, liver, lung heart and skin. 5-HT stimulates both vasoconstriction and vasodilation, influences inflammatory responses and promotes formation of a temporary scar which acts as a scaffold for normal tissue to be restored. However, in situations of chronic injury or damage 5-HT signaling can have deleterious effects and promote aberrant wound healing resulting in tissue fibrosis and impaired organ regeneration. This review highlights the diverse actions of serotonin signaling in the pathogenesis of fibrotic disease and explores how modulating the activity of specific 5-HT receptors, in particular the 5-HT2 subclass could have the potential to limit fibrosis and restore tissue regeneration. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

WITHDRAWN: Hsp70 overexpression coordinately regulates myocardial hypertrophy, fibrosis and contractile function in 5-HT(2B) blockade mediated anti-hypertrophic effect

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Cellular Interplay between Cardiomyocytes and Nonmyocytes in Cardiac Remodeling

Cardiac hypertrophy entails complex structural remodeling involving rearrangement of muscle fibers, interstitial fibrosis, accumulation of extracellular matrix, and angiogenesis. Many of the processes underlying cardiac remodeling have features in common with chronic inflammatory processes. During these processes, nonmyocytes, such as endothelial cells, fibroblasts, and immune cells, residing in or infiltrating into the myocardial interstitium play active roles. This paper mainly addresses the functional roles of nonmyocytes during cardiac remodeling. In particular, we focus on the communication between cardiomyocytes and nonmyocytes through direct cell-cell interactions and autocrine/paracrine-mediated pathways.

Serotonin receptors and heart valve disease--it was meant 2B

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.

Cardiovascular effects of chronic treatment with a β2-adrenoceptor agonist relieving neuropathic pain in mice

Neuropathic pain is often a chronic condition, disabling and difficult to treat. Using a murine model of neuropathic pain induced by placing a polyethylene cuff around the main branch of the sciatic nerve, we have shown that chronic treatment with β-AR agonists is effective against neuropathic allodynia. β-mimetics are widely used against asthma and chronic obstructive pulmonary disease and may offer an interesting option for neuropathic pain management. The most prominent adverse effects of chronic treatment with β-mimetics are cardiovascular. In this study, we compared the action of low doses of the selective β(2)-AR agonist terbutaline and of a high dose of the mixed β(1)/β(2)-AR agonist isoproterenol on cardiovascular parameters in a neuropathic pain context. Isoproterenol was used as a positive control for some heart-related changes. Cardiac functions were studied by echocardiography, hemodynamic measurements, histological analysis of fibrosis and cardiac hypertrophy, and by quantitative real time PCR analysis of atrial natriuretic peptide (Nppa), periostin (Postn), connective tissue growth factor (Ctgf) and β-myosin heavy chain (Myh7). Our data show that a chronic treatment with the β(2)-AR agonist terbutaline at low antiallodynic dose does not affect cardiovascular parameters, whereas the mixed β(1)/β(2)-AR agonist isoproterenol induces cardiac hypertrophy. These data suggest that low doses of β(2)-AR agonists may provide a suitable treatment with rare side effects in neuropathic pain management. This study conducted in an animal model requires clinical confirmation in humans.

Involvement of Depressive Catecholamines as Thrombosis Risk/Inflammatory Markers in Non-Smoker, Non-Obese Congestive Heart Failure, Linked to Increased Epidermal Growth Factor-Receptor (EGF-R) Production

The EGF-R, also known as HER-1 or erbB-1 (EGF-R/HER-1/erbB-1), is a member of the human epithelial receptor tyrosine kinase family. sEGF-R is considered to play a role in cardiac (patho)physiology. We aimed to investigate whether soluble EGF-R is increased in congestive heart failure (CHF) patients and if related to disease severity. Soluble EGF-R, vitamin D, parathyroid hormone (PTH) was studied, and being evaluated in relation to Ca(2+), lipids, hsCRP, fibrinogen, serotonin, norepinepherine (NE). The study compared non-smoker, non-obese male CHF patients (n = 50) with age and gender-matched essential hypertension (HTN) patients (n = 20). Moreover, comparison with healthy control volunteers (n = 20) were employed. EGF-R/HER-1/erbB-1 was higher (P = 0.013) in 50 CHF male patients mean 12 ± 0.7 fmol/ml, than in 20 HTN, 9.25 ± 0.6 fmol/ml or in 20 controls, 6.25 ± 1 fmol/ml. Serum EGF-R levels correlated positively with hsCRP and NE, and were highest among CVD patients (n = 70) as well as negatively with vitamin D and HDL-C. EGF-R/HER-1/erbB-1 levels are increased in HTN and more in CHF patients. This study confirms a strong association between catecholamines as well as EGF-R/HER-1/erbB-1 levels with PTH and low vitamin D levels, being related to hyperlipidemia and inflammation (hsCRP and fibrinogen) in CVD. Moreover, contributing to the complex process of the inflammatory component of atherosclerosis in hypertensive patients that leads eventually to CHF.

Serotonin 2A and 2B receptor-induced phrenic motor facilitation: differential requirement for spinal NADPH oxidase activity

Acute intermittent hypoxia (AIH) facilitates phrenic motor output by a mechanism that requires spinal serotonin (type 2) receptor activation, NADPH oxidase activity and formation of reactive oxygen species (ROS). Episodic spinal serotonin (5-HT) receptor activation alone, without changes in oxygenation, is sufficient to elicit NADPH oxidase-dependent phrenic motor facilitation (pMF). Here we investigated: (1) whether serotonin 2A and/or 2B (5-HT2A/B) receptors are expressed in identified phrenic motor neurons, and (2) which receptor subtype is capable of eliciting NADPH-oxidase-dependent pMF. In anesthetized, artificially ventilated adult rats, episodic C4 intrathecal injections (3×6 μl injections, 5 min intervals) of a 5-HT2A (DOI) or 5-HT2B (BW723C86) receptor agonist elicited progressive and sustained increases in integrated phrenic nerve burst amplitude (i.e. pMF), an effect lasting at least 90 min post-injection for both receptor subtypes. 5-HT2A and 5-HT2B receptor agonist-induced pMF were both blocked by selective antagonists (ketanserin and SB206553, respectively), but not by antagonists to the other receptor subtype. Single injections of either agonist failed to elicit pMF, demonstrating a need for episodic receptor activation. Phrenic motor neurons retrogradely labeled with cholera toxin B fragment expressed both 5-HT2A and 5-HT2B receptors. Pre-treatment with NADPH oxidase inhibitors (apocynin and diphenylenodium (DPI)) blocked 5-HT2B, but not 5-HT2A-induced pMF. Thus, multiple spinal type 2 serotonin receptors elicit pMF, but they act via distinct mechanisms that differ in their requirement for NADPH oxidase activity.

Vascular BDNF expression and oxidative stress during aging and the development of chronic hypertension

Brain-derived neurotrophic factor (BDNF) and TrK receptors play an important role in vascular development and response to injury. In this study, we investigated the participation of the BDNF/TrK pathway and oxidative stress during the development of hypertension in spontaneously hypertensive rats (SHR). In SHR and normotensive rats (WKY) at 6 and 13 weeks of age, we studied (i) plasma antioxidant capacity, (ii) production of superoxide and NAD(P)H oxidase activity in aorta (iii) plasma BDNF and vascular expression of BDNF, TrKB, NAD(P)H oxidase subunits, AT1 receptor, and MCP-1. In 6- and 13-week-old SHR aorta, superoxide level was twice than in WKY aorta. At 13 weeks, when blood pressure in SHR was 60 mmHg higher in SHR than in WKY, an enhancement of NAD(P)H oxidase activity in SHR was associated with an increase in p47phox, AT1, and BDNF expression in vessels. MCP-1 expression increased with blood pressure. Our study demonstrated that in SHR rats, an increase in levels of vascular oxidative stress and in aortic BDNF and TrKB expression occurs prior to the rise in blood pressure, while a reinforcement of vascular and circulating oxidative stress markers is brought about later by hypertension.

Contribution of gene-modified mice and rats to our understanding of the cardiovascular pharmacology of serotonin

This review focuses on new insights provided by gene-modified animals into the cardiovascular pharmacology of serotonin. During their development, mice mutant for tryptophan hydroxylase 1 and lacking peripheral serotonin, or mutant for 5-HT(2B) receptors, display cardiac defects and dilated cardiomyopathy. The 5-HT(4) receptor is important for the maturation of cardiac conduction. In fact, transgenic approaches have revealed that adult cardiac status is strongly influenced by maternal serotonin. Serotonin has long been known to be a vasoconstrictor in adult physiology. Analysis of animals knocked-out for the serotonin transporter suggested a role in blood pressure control and revealed an effect of 5-HT(2B) receptor antagonists in hypertension. In the lung vasculature, mice lacking the 5-HT(2B) receptor gene that are exposed to chronic hypoxia are resistant to pulmonary hypertension, while 5-HT(1B) receptor and serotonin transporter mutant animals show partial resistance. In platelets, mutant mice revealed that serotonin transporter regulates not only the mechanisms by which serotonin is packaged and secreted but also platelet aggregation. Studies looking at adult cardiac remodeling showed that mice lacking the 5-HT(2B) receptor gene were protected from cardiac hypertrophy. Their fibroblasts were unable to secrete cytokines. Crossing these animals with mice overexpressing the receptor in cardiomyocytes revealed the contribution of cardiac fibroblasts and 5-HT(2B) receptors to cardiac hypertrophy. In mice lacking the monoamine oxidase-A gene, the role of serotonin degradation in cardiac hypertrophy was confirmed. Works with gene-modified animals has contributed strongly to the re-evaluation of the influence of serotonin on cardiovascular regulation, though several unknowns remain to be investigated.

Cyproheptadine prevents pergolide-induced valvulopathy in rats: an echocardiographic and histopathological study

Serotonergic drugs, such as pergolide, have been associated with the development of cardiac valvular myxoid thickening and regurgitation in humans and more recently in rats. These effects are potentially mediated by the 5-hydroxytryptamine (5-HT)(2B) receptor (5-HT(2B)R). Therefore, we sought to determine whether cyproheptadine, a 5-HT(2B)R antagonist, might prevent toxic valvulopathy in an animal model of pergolide-induced valvular heart disease. For this purpose, 50 male Wistar rats received daily intraperitoneal injections of pergolide (0.5 mg/kg, n = 14), pergolide (0.5 mg/kg) combined with cyproheptadine (10 mg/kg, n = 12), cyproheptadine (10 mg/kg, n = 12), or no injections (control, n = 12) for 20 wk. Echocardiography was performed blindly at baseline and at 10 and 20 wk followed by pathology. At baseline, no differences between groups were found with echocardiography. At 20 wk, aortic regurgitation was present in all pergolide-treated animals, whereas it was less frequently observed in the other groups (P < 0.0001). For the other valves, this difference was less pronounced. On histopathology, not only aortic but also mitral valves were thicker, myxoid, and exhibited more 5-HT(2B)R-positive cells in pergolide-treated animals compared with the other groups. Moreover, regurgitant aortic and mitral valves were thicker than nonregurgitant aortic and mitral valves. In conclusion, we found that cyproheptadine prevented pergolide-induced valvulopathy in rats, which was associated with a reduced number of 5-HT(2B)R-positive valvular cells. This may have important clinical implications for the prevention of serotonergic drug-induced valvular heart disease.

A new class of 5-HT2B antagonists possesses favorable potency, selectivity, and rat pharmacokinetic properties

We have been exploring the potential of 5-HT(2B) antagonists as a therapy for chronic heart failure. To assess the potential of this therapeutic approach, we sought compounds possessing the following attributes: (a) potent and selective antagonism of the 5-HT(2B) receptor, (b) low impact of serum proteins on potency, and (c) desirable pharmacokinetic properties. This Letter describes our investigation of a biphenyl benzimidazole class of compounds that resulted in 5-HT(2B) antagonists possessing the above attributes. Improving potency in a human serum albumin shift assay proved to be the most significant SAR discovery.

Serotonin and angiotensin receptors in cardiac fibroblasts coregulate adrenergic-dependent cardiac hypertrophy

By mimicking sympathetic stimulation in vivo, we previously reported that mice globally lacking serotonin 5-HT(2B) receptors did not develop isoproterenol-induced left ventricular hypertrophy. However, the exact cardiac cell type(s) expressing 5-HT(2B) receptors (cardiomyocytes versus noncardiomyocytes) involved in pathological heart hypertrophy was never addressed in vivo. We report here that mice expressing the 5-HT(2B) receptor solely in cardiomyocytes, like global 5-HT(2B) receptor-null mice, are resistant to isoproterenol-induced cardiac hypertrophy and dysfunction, as well as to isoproterenol-induced increases in cytokine plasma-levels. These data reveal a key role of noncardiomyocytes in isoproterenol-induced hypertrophy in vivo. Interestingly, we show that primary cultures of angiotensinogen null adult cardiac fibroblasts are releasing cytokines on stimulation with either angiotensin II or serotonin, but not in response to isoproterenol stimulation, demonstrating a critical role of angiotensinogen in adrenergic-dependent cytokine production. We then show a functional interdependence between AT(1)Rs and 5-HT(2B) receptors in fibroblasts by revealing a transinhibition mechanism that may involve heterodimeric receptor complexes. Both serotonin- and angiotensin II-dependent cytokine production occur via a Src/heparin-binding epidermal growth factor-dependent transactivation of epidermal growth factor receptors in cardiac fibroblasts, supporting a common signaling pathway. Finally, we demonstrate that 5-HT(2B) receptors are overexpressed in hearts from patients with congestive heart failure, this overexpression being positively correlated with cytokine and norepinephrine plasma levels. Collectively, these results reveal for the first time that interactions between AT(1) and 5-HT(2B) receptors coexpressed by noncardiomyocytes are limiting key events in adrenergic agonist-induced, angiotensin-dependent cardiac hypertrophy. Accordingly, antagonists of 5-HT(2B) receptors might represent novel therapeutics for sympathetic overstimulation-dependent heart failure.