The role of 5-HT2B receptors in mitral valvulopathy: bone marrow mobilization of endothelial progenitors

Use of methylphenidate and reporting of valvular heart disease: Global pharmacovigilance analysis in children and adults

INTRODUCTION

Methylphenidate (MPH) is a common treatment of attention-deficit/hyperactivity disorder (ADHD). Concern has been raised regarding its cardiovascular safety, partly in relation with its micromolar affinity for the 5-HT2B receptor, whose activation may result in valvular heart disease (VHD).

METHODS

To explore the association between the use of MPH and VHD reporting, we performed a disproportionality analysis within the WHO global safety database (VigiBase) using data, since inception until March 6th 2024, from: (i) the full database and (ii) different age groups (children/adolescents 6-17 years; adults 18-64 years). To avoid competition bias, safety reports with amphetamine-like appetite suppressants were excluded. Disproportionality was expressed using reporting odds-ratio (ROR) and its 95% confidence interval (CI).

RESULTS

Of 29 129 spontaneous reports with MPH, 23 VHD cases (7.9 per 10 000 reports) were identified, including 13 adults and 10 children. Most cases concerned injury on the mitral valve. A disproportionate reporting was observed overall (ROR 1.6, 95% CI 1.1-2.4). Analysis according to age group found that disproportionality in VHD reporting was found in adults only (ROR 2.7, 95% CI 1.6-4.7) but not in children/adolescents (ROR 1.7, 95% CI 0.9-3.2). Furthermore, amongst MPH users only, VHD reporting was higher in adults compared to children (ROR 2.7, 95% CI 1.2-6.3).

CONCLUSION

VHD reporting appears rare with MPH compared to other adverse events and is increased in adults only. Our findings support a potential safety signal of VHD in adults exposed to MPH. A risk in that population cannot be excluded and requires further assessment.

5-HTP inhibits eosinophilia via intracellular endothelial 5-HTRs; SNPs in 5-HTRs associate with asthmatic lung function

Background

Previous research showed that 5-hydroxytryptophan (5HTP), a metabolic precursor of serotonin, reduces allergic lung inflammation by inhibiting eosinophil migration across endothelial monolayers.

Objective

It is unknown if serotonin receptors are involved in mediating this 5HTP function or if serotonin receptor (HTR) single nucleotide polymorphisms (SNPs) associate with lung function in humans.

Methods

Serotonin receptor subtypes were assessed by qPCR, western blot, confocal microscopy, pharmacological inhibitors and siRNA knockdown. HTR SNPs were assessed in two cohorts.

Results

Pharmacological inhibition or siRNA knockdown of the serotonin receptors HTR1A or HTR1B in endothelial cells abrogated the inhibitory effects of 5HTP on eosinophil transendothelial migration. In contrast, eosinophil transendothelial migration was not inhibited by siRNA knockdown of HTR1A or HTR1B in eosinophils. Surprisingly, these HTRs were intracellular in endothelial cells and an extracellular supplementation with serotonin did not inhibit eosinophil transendothelial migration. This is consistent with the inability of serotonin to cross membranes, the lack of selective serotonin reuptake receptors on endothelial cells, and the studies showing minimal impact of selective serotonin reuptake inhibitors on asthma. To extend our HTR studies to humans with asthma, we examined the CHIRAH and GALA cohorts for HTR SNPs that affect HTR function or are associated with behavior disorders. A polygenic index of SNPs in HTRs was associated with lower lung function in asthmatics.

Conclusions

Serotonin receptors mediate 5HTP inhibition of transendothelial migration and HTR SNPs associate with lower lung function. These results may serve to aid in design of novel interventions for allergic inflammation.

Microdosing psychedelics and the risk of cardiac fibrosis and valvulopathy: Comparison to known cardiotoxins

Though microdosing psychedelics has become increasingly popular, its long-term effects on cardiac health remain unknown. Microdosing most commonly involves ingesting sub-threshold doses of lysergic acid diethylamide (LSD), psilocybin, or other psychedelic drugs 2-4 times a week for at least several weeks, but potentially months or years. Concerningly, both LSD and psilocybin share structural similarities with medications which raise the risk of cardiac fibrosis and valvulopathy when taken regularly, including methysergide, pergolide, and fenfluramine. 3,4-Methylenedioxymethamphetamine, which is also reportedly used for microdosing, is likewise associated with heart valve damage when taken chronically. In this review, we evaluate the evidence that microdosing LSD, psilocybin, and other psychedelics for several months or more could raise the risk of cardiac fibrosis. We discuss the relationship between drug-induced cardiac fibrosis and the 5-HT2B receptor, and we make recommendations for evaluating the safety of microdosing psychedelics in future studies.

Reintroducing Fenfluramine as a Treatment for Seizures: Current Knowledge, Recommendations and Gaps in Understanding

Despite the introduction of new anti-seizure medications in recent years, approximately one-third of the epileptic population continues to experience seizures. Recently, the anti-obesity medication fenfluramine (FFA) has been successfully repurposed, and it has received approval from various regulatory agencies for the treatment of seizures associated with Dravet syndrome and Lennox-Gastaut syndrome. The potential antiseizure effects of FFA were initially observed in patients with photosensitive epilepsy in the 1980s but it was not rigorously explored as a treatment option until 30 years later. This narrative review aims to provide an overview of the historical progression of FFA's use, starting from initial clinical observations to preclinical studies and, ultimately, successful clinical trials in the field of epilepsy.

Synergistic Interaction of 5-HT1B and 5-HT2B Receptors in Cytoplasmic Ca2+ Regulation in Human Umbilical Vein Endothelial Cells: Possible Involvement in Pathologies

The aim of this work was to explore the involvement of 5-HT1B and 5-HT2B receptors (5-HT1BR and 5-HT2BR) in the regulation of free cytoplasmic calcium concentration ([Ca2+]i) in human umbilical vein endothelial cells (HUVEC). We have shown by quantitative PCR analysis, that 5-HT1BR and 5-HT2BR mRNAs levels are almost equal in HUVEC. Immunofluorescent staining demonstrated, that 5-HT1BR and 5-HT2BR are expressed both in plasma membrane and inside the cells. Intracellular 5-HT1BR are localized mainly in the nuclear region, whereas 5-HT2BR receptors are almost evenly distributed in HUVEC. 5-HT, 5-HT1BR agonist CGS12066B, or 5-HT2BR agonist BW723C86 added to HUVEC caused a slight increase in [Ca2+]i, which was much lower than that of histamine, ATP, or SFLLRN, an agonist of protease-activated receptors (PAR1). However, activation of 5-HT1BR with CGS12066B followed by activation of 5-HT2BR with BW723C86 manifested a synergism of response, since several-fold higher rise in [Ca2+]i occurred. CGS12066B caused more than a 5-fold increase in [Ca2+]i rise in HUVEC in response to 5-HT. This 5-HT induced [Ca2+]i rise was abolished by 5-HT2BR antagonist RS127445, indicating that extracellular 5-HT acts through 5-HT2BR. Synergistic [Ca2+]i rise in response to activation of 5-HT1BR and 5-HT2BR persisted in a calcium-free medium. It was suppressed by the phospholipase C inhibitor U73122 and was not inhibited by the ryanodine and NAADP receptors antagonists dantrolene and NED-19. [Ca2+]i measurements in single cells demonstrated that activation of 5-HT2BR alone by BW723C86 caused single asynchronous [Ca2+]i oscillations in 19.8 ± 4.2% (n = 3) of HUVEC that occur with a long delay (66.1 ± 4.3 s, n = 71). On the contrary, histamine causes a simultaneous and almost immediate increase in [Ca2+]i in all the cells. Pre-activation of 5-HT1BR by CGS12066B led to a 3-4 fold increase in the number of HUVEC responding to BW723C86, to synchronization of their responses with a delay shortening, and to the bursts of [Ca2+]i oscillations in addition to single oscillations. In conclusion, to get a full rise of [Ca2+]i in HUVEC in response to 5-HT, simultaneous activation of 5-HT1BR and 5-HT2BR is required. 5-HT causes an increase in [Ca2+]i via 5-HT2BR while 5-HT1BR could be activated by the membrane-permeable agonist CGS12066B. We hypothesized that CGS12066B acts via intracellular 5-HT1BR inaccessible to extracellular 5-HT. Intracellular 5-HT1BR might be activated by 5-HT which could be accumulated in EC under certain pathological conditions.

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.

First quantitative dosages: Strong correlations between non-5-HT2Rs serotonin receptors on normal human heart valves

Objectives

Although critical in animal and human development and pathology, a measurement of the quantitative expression of 5-HTR serotonin receptors on animal or human valvular tissues has never been performed.

Methods

Quantification of the most frequent 5-HTRs reported as being present in human peripheral tissue was performed using radiolabeled agonists/antagonists. A membrane protein extract from normal human valves (aortic/mitral/tricuspid and some pulmonary) and associated diseased left myocardium, all unusable in clinics, were obtained from the Homograft bank.

Results

We analyzed 5-HT1AR/5-HT1B/DR/5-HT2AR/5-HT2BR/5-HT 2CR/5-HT4R/5-HT7R from 28 hearts. We confirmed the presence of tissue and measured the quantitative content for respective proteins in femtomol/mg of protein extracts: for 5-HT2AR (35.9+/−0.7), 5-HT2BR (28.8+/−1.3) but also a newly observed and robust expression for 5-HT4R (38+/−4.2). We identified one, 5-HT1ARs (4.9+/−0.3), and the possible expression, but at a very low level, of previously reported 5-HT1B/DRs (1.3+/−0.5) as well as the new 5-HT7Rs (3.5+/0.1) and 5-HT2CRs (1.2+/−0.1). Interestingly, by using univariate analysis, we were able to observe many correlations between the different 5-HTR levels of expression especially between 5-HT1AR/5-HT1B/DR and also between 5-HT4R/5-HT7R, but none were observed between 5-HT2AR and 5-HT2BR. Using multivariate analyses for a specific 5-HTR level of expression, after adjustment for implantation sites and other 5-HTRs, we found that 5-HT1AR was correlated with 5-HT1B/DR;5-HT4R with 5-HT7R and 5-HT1AR;5-HT2BR with 5-HT2AR only. For 5-HT2C, no correlation was observed.

Conclusion

5-HT2AR/5-HT2BR and 5-HT4R were all observed to have a high and equal level of expression on human valves, but that of 5-HT1AR was more limited. Since these non-5-HT2Rs are coupled with different G-proteins, with specific signaling, theoretically they may control the main 5-HT2R signaling (i.e., PLC/DAG-PKC-ERK/Ras/Src signaling) involved in valvular fibrosis and degeneration.

The Role of Transforming Growth Factor-β Signaling in Myxomatous Mitral Valve Degeneration

Mitral valve prolapse (MVP) due to myxomatous degeneration is one of the most important chronic degenerative cardiovascular diseases in people and dogs. It is a common cause of heart failure leading to significant morbidity and mortality in both species. Human MVP is usually classified into primary or non-syndromic, including Barlow’s Disease (BD), fibro-elastic deficiency (FED) and Filamin-A mutation, and secondary or syndromic forms (typically familial), such as Marfan syndrome (MFS), Ehlers-Danlos syndrome, and Loeys–Dietz syndrome. Despite different etiologies the diseased valves share pathological features consistent with myxomatous degeneration. To reflect this common pathology the condition is often called myxomatous mitral valve degeneration (disease) (MMVD) and this term is universally used to describe the analogous condition in the dog. MMVD in both species is characterized by leaflet thickening and deformity, disorganized extracellular matrix, increased transformation of the quiescent valve interstitial cell (qVICs) to an activated state (aVICs), also known as activated myofibroblasts. Significant alterations in these cellular activities contribute to the initiation and progression of MMVD due to the increased expression of transforming growth factor-β (TGF-β) superfamily cytokines and the dysregulation of the TGF-β signaling pathways. Further understanding the molecular mechanisms of MMVD is needed to identify pharmacological manipulation strategies of the signaling pathway that might regulate VIC differentiation and so control the disease onset and development. This review briefly summarizes current understanding of the histopathology, cellular activities, molecular mechanisms and pathogenesis of MMVD in dogs and humans, and in more detail reviews the evidence for the role of TGF-β.

Lorcaserin for Dravet Syndrome: A Potential Advance Over Fenfluramine?

Lorcaserin, a selective serotonin 5-HT_2C receptor agonist, was developed as an appetite suppressant with the rationale of minimizing the risk of cardiovascular toxicity associated with non-selective serotoninergic agents such as fenfluramine. Eight years after FDA approval, however, it was withdrawn from the market, when a large safety study suggested a potential cancer risk. Following in the fenfluramine footsteps and utilizing the repurposing approach coupled with the regulatory orphan drug designation, lorcaserin is currently in clinical development for the treatment of epilepsy. This potential novel indication builds on the evidence that 5-HT_2C receptor stimulation can protect against seizures, and accounts at least in part for fenfluramine's antiseizure effects in Dravet syndrome models. In animal models, lorcaserin shows a narrower range of antiseizure activity than fenfluramine. In particular, lorcaserin is inactive in classical acute seizure tests such as maximal electroshock and subcutaneous pentylenetetrazole in mice and rats, and the 6-Hz stimulation model in mice. However, it is active in the GAERS absence seizure model, and in mutant zebrafish models of Dravet syndrome. Preliminary uncontrolled studies in patients with Dravet syndrome have yielded promising results, and a phase III, double-blind, placebo-controlled, parallel group trial is currently ongoing to assess its efficacy and safety in children and adults with Dravet syndrome.

Evaluation of a 5-HT2B receptor agonist in a murine model of amyotrophic lateral sclerosis

Degeneration of brainstem serotonin neurons has been demonstrated in ALS patients and mouse models and was found responsible for the development of spasticity. Consistent with involvement of central serotonin pathways, 5-HT_2B receptor (5-HT_2BR) was upregulated in microglia of ALS mice. Its deletion worsened disease outcome in the Sod1^G86R mouse model and led to microglial degeneration. In ALS patients, a polymorphism in HTR2B gene leading to higher receptor expression in CNS, was associated with increased survival in patients as well as prevention of microglial degeneration. Thus, the aim of our study was to determine the effect of a 5-HT_2BR agonist : BW723C86 (BW), in the Sod1^G86R mouse model. Despite good pharmacokinetic and pharmacological profiles, BW did not ameliorate disease outcome or motor neuron degeneration in a fast progressing mouse model of ALS despite evidence of modulation of microglial gene expression.

A new class of serotonin 5-HT2A /5-HT2C receptor inverse agonists: Synthesis, molecular modeling, in vitro and in vivo pharmacology of novel 2-aminotetralins

BACKGROUND AND PURPOSE

The 5-HT receptor (5-HTR) subtypes 5-HT_2A and 5-HT_2C are important neurotherapeutic targets, though, obtaining selectivity over 5-HT_2B and closely related histamine H₁ Rs is challenging. Here, we delineated molecular determinants of selective binding to 5-HT_2A and 5-HT_2C Rs for novel 4-phenyl-2-dimethylaminotetralins (4-PATs).

EXPERIMENTAL APPROACH

We synthesized 42 novel 4-PATs with halogen or aryl moieties at the C(4)-phenyl meta position. Affinity, function, molecular modeling, and 5-HT_2A R mutagenesis studies were undertaken to understand structure-activity relationships at 5-HT₂ -type and H₁ Rs. Lead 4-PAT-type selective 5-HT_2A /5-HT_2C R inverse agonists were compared to pimavanserin, a selective 5-HT_2A /5-HT_2C R inverse agonist approved to treat psychoses, in the mouse head twitch response, and locomotor activity assays, as models relevant to antipsychotic drug development.

KEY RESULTS

Most 4-PAT diastereomers in the (2S,4R)-configuration bound non-selectively to 5-HT_2A , 5-HT_2C, and H₁ Rs, with >100-fold selectivity over 5-HT_2B Rs, whereas, diastereomers in the (2R,4R)-configuration bound preferentially to 5-HT_2A over 5-HT_2C Rs and had >100-fold selectivity over 5-HT_2B and H₁ Rs. Results suggest that G238^5.42 and V235^5.39 in 5-HT_2A Rs (conserved in 5-HT_2C Rs) are important for high affinity binding, whereas, interactions with T194^5.42 and W158^4.56 determine H₁ R affinity. The 4-PAT (2S,4R)-2k, a potent and selective 5-HT_2A /5-HT_2C R inverse agonist, had activity like pimavanserin in the mouse head-twitch response assay, but was distinct in not suppressing locomotor activity.

CONCLUSIONS AND IMPLICATIONS

We provide evidence that the novel 4-PAT chemotype can yield selective 5-HT_2A /5-HT_2C R inverse agonists for antipsychotic drug development by optimizing ligand-receptor interactions in transmembrane domain 5. We also show that chirality can be exploited to attain selectivity over H₁ Rs which may circumvent sedative effects.

Characterization of the spontaneous degenerative mitral valve disease in FVB mice

BACKGROUND

The development of new non-surgical treatments dedicated to mitral valve degeneration is limited by the absence of relevant spontaneous and rapidly progressing animal experimental models.

ANIMALS

We characterized the spontaneous mitral valve degeneration in two inbred FVB mouse strains compared to C57BL/6J and investigated a contribution of the serotonergic system.

METHODS

Males and females FVB/NJ and FVB/NRj were compared to the putative C57BL/6J control at 12, 16, 20 and 24 weeks of age. Body weight, systolic blood pressure, heart rate, urinary 5-hydroxyindoleacetic acid (5-HIAA), whole blood and plasma serotonin, tail bleeding time, blood cell count, plasma TGF-β1 and plasma natriuretic peptide concentrations were measured. Myocardium and mitral valves were characterized by histology. mRNA mitral expression of 5-HT2A and 5-HT2B receptors was measured in the anterior leaflet. Cardiac anatomy and function were assessed by echocardiography.

RESULTS

Compared to C57BL/6J, FVB mice strains did not significantly differ regarding body weight increase, arterial blood pressure and heart rate. A progressive augmentation of plasma pro-ANP was observed in FVB mice. Nevertheless, no cardiac hypertrophy or left-ventricular fibrosis were observed. Accordingly, plasma TGF-β1 was not different among the three strains. Conversely, FVB mice demonstrated a high prevalence of fibromyxoid highly cellularized and enriched in glycosaminoglycans lesions, inducing major mitral leaflets thickening without increase in length. The increased thickness was correlated with urinary 5-HIAA and blood platelet count. Whole blood serotonin concentration was similar in the two strains but, in FVB, a reduction of plasma serotonin was observed together with an increase of the bleeding time. Finally, echocardiography identified left atrial and left ventricular remodeling associated with thickening of both mitral leaflets and mitral insufficient in 30% of FVB mice but no systolic protrusion of mitral leaflets towards the atrium.

CONCLUSION

The FVB mouse strain is highly prone to spontaneous mitral myxomatous degeneration. A contribution of the peripheral serotonergic system is suggested.

Fenfluramine repurposing from weight loss to epilepsy: What we do and do not know

In 2020, racemic-fenfluramine was approved in the U.S. and Europe for the treatment of seizures associated with Dravet syndrome, through a restricted/controlled access program aimed at minimizing safety risks. Fenfluramine had been used extensively in the past as an appetite suppressant, but it was withdrawn from the market in 1997 when it was found to cause cardiac valvulopathy. Available evidence indicates that appetite suppression and cardiac valvulopathy are mediated by different serotonergic mechanisms. In particular, appetite suppression can be ascribed mainly to the enantiomers d-fenfluramine and d-norfenfluramine, the primary metabolite of d-fenfluramine, whereas cardiac valvulopathy can be ascribed mainly to d-norfenfluramine. Because of early observations of markedly improved seizure control in some forms of epilepsy, fenfluramine remained available in Belgium through a Royal Decree after 1997 for use in a clinical trial in patients with Dravet syndrome at average dosages lower than those generally prescribed for appetite suppression. More recently, double-blind placebo-controlled trials established its efficacy in the treatment of convulsive seizures associated with Dravet syndrome and of drop seizures associated with Lennox-Gastaut syndrome, at doses up to 0.7 mg/kg/day (maximum 26 mg/day). Although no cardiovascular toxicity has been associated with the use of fenfluramine in epilepsy, the number of patients exposed to date has been limited and only few patients had duration of exposure longer than 3 years. This article analyzes available evidence on the mechanisms involved in fenfluramine-induced appetite suppression, antiseizure effects and cardiovascular toxicity. Despite evidence that stimulation of 5-HT_2B receptors (the main mechanism leading to cardiac valvulopathy) is not required for antiseizure activity, there are many critical gaps in understanding fenfluramine's properties which are relevant to its use in epilepsy. Particular emphasis is placed on the remarkable lack of publicly accessible information about the comparative activity of the individual enantiomers of fenfluramine and norfenfluramine in experimental models of seizures and epilepsy, and on receptors systems considered to be involved in antiseizure effects. Preliminary data suggest that l-fenfluramine retains prominent antiseizure effects in a genetic zebrafish model of Dravet syndrome. If these findings are confirmed and extended to other seizure/epilepsy models, there would be an incentive for a chiral switch from racemic-fenfluramine to l-fenfluramine, which could minimize the risk of cardiovascular toxicity and reduce the incidence of adverse effects such as loss of appetite and weight loss.

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.

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.

Possible Link Between the ABO Blood Group of Bioprosthesis Recipients and Specific Types of Structural Degeneration

Background Pigs/bovines share common antigens with humans: α-Gal, present in all pigs/bovines close to the human B-antigen; and AH-histo-blood-group antigen, identical to human AH-antigen and present only in some animals. We investigate the possible impact of patients' ABO blood group on bioprosthesis structural valve degeneration (SVD) through calcification/pannus/tears/perforations for patients ≤60 years at implantation. Methods and Results This was a single-center study (Paris, France) that included all degenerative bioprostheses explanted between 1985 and 1998, mostly porcine bioprostheses (Carpentier-Edwards second/third porcine bioprostheses) and some bovine bioprostheses. For the period 1998 to 2014, only porcine bioprostheses with longevity ≥13 years were included (total follow-up ≥29 years). Except for blood groups, important predictive factors for SVD were prospectively collected (age at implantation/longevity/number/site/sex/SVD types) and analyzed using logistic regression. All variables were available for 500 explanted porcine bioprostheses. By multivariate analyses, the A group was associated with an increased risk of: tears (odds ratio[OR], 1.61; P=0.026); pannus (OR, 1.5; P=0.054), pannus with tears (OR, 1.73; P=0.037), and tendency for lower risk of: calcifications (OR, 0.63; P=0.087) or isolated calcification (OR, 0.67; P=0.17). A-antigen was associated with lower risk of perforations (OR 0.56; P=0.087). B-group patients had an increased risk of: perforations (OR, 1.73; P=0.043); having a pannus that was calcified (OR, 3.0, P=0.025). B-antigen was associated with a propensity for calcifications in general (OR, 1.34; P=0.25). Conclusions Patient's ABO blood group is associated with specific SVD types. We hypothesize that carbohydrate antigens, which may or may not be common to patient and animal bioprosthetic tissue, will determine a patient's specific immunoreactivity with respect to xenograft tissue and thus bioprosthesis outcome in terms of SVD.

Beneficial Effects of Mineralocorticoid Receptor Antagonism on Myocardial Fibrosis in an Experimental Model of the Myxomatous Degeneration of the Mitral Valve

Mitral valve prolapse (MVP) patients develop myocardial fibrosis that is not solely explained by volume overload, but the pathophysiology has not been defined. Mineralocorticoid receptor antagonists (MRAs) improve cardiac function by decreasing cardiac fibrosis in other heart diseases. We examined the role of MRA in myocardial fibrosis associated with myxomatous degeneration of the mitral valve. Myocardial fibrosis has been analyzed in a mouse model of mitral valve myxomatous degeneration generated by pharmacological treatment with Nordexfenfluramine (NDF) in the presence of the MRA spironolactone. In vitro, adult human cardiac fibroblasts were treated with NDF and spironolactone. In an experimental mouse, MRA treatment reduced interstitial/perivascular fibrosis and collagen type I deposition. MRA administration blunted NDF-induced cardiac expression of vimentin and the profibrotic molecules galectin-3/cardiotrophin-1. In parallel, MRA blocked the increase in cardiac non-fibrillar proteins such as fibronectin, aggrecan, decorin, lumican and syndecan-4. The following effects are blocked by MRA: in vitro, in adult human cardiac fibroblasts, NDF-treatment-induced myofibroblast activation, collagen type I and proteoglycans secretion. Our findings demonstrate, for the first time, the contribution of the mineralocorticoid receptor (MR) to the development of myocardial fibrosis associated with mitral valve myxomatous degeneration. MRA could be a therapeutic approach to reduce myocardial fibrosis associated with MVP.

Dexfenfluramine and Pergolide Cause Heart Valve Disease via Valve Metabolic Reprogramming and Ongoing Matrix Remodeling

Several clinical reports indicate that the use of amphetaminic anorectic drugs or ergot derivatives could cause valvular heart disease (VHD). We sought to investigate whether valvular lesions develop in response to long-term oral administration of these drugs and to identify drug-targeted biological processes that may lead to VHD. Treatment of New Zealand White rabbits with pergolide, dexfenfluramine, or high-dose serotonin for 16 weeks induced valvular alterations characterized by extracellular matrix remodeling. Transcriptome profiling of tricuspid valves using RNA sequencing revealed distinct patterns of differentially expressed genes (DEGs) that clustered according to the different treatments. Genes that were affected by the three treatments were functionally enriched for reduced cell metabolism processes. The two drugs yielded more changes in gene expression than serotonin and shared most of the DEGs. These DEGs were mostly enriched for decreased biosynthetic processes, increased cell-matrix interaction, and cell response to growth factors, including TGF-β, which was associated with p38 MAPK activation. Treatment with pergolide specifically affected genes involved in homeostasis, which was corroborated by the activation of the master regulator of cell energy homeostasis, AMPK-α, as well as decreased levels of metabolism-related miR-107. Thus, both pergolide and dexfenfluramine may cause VHD through valve metabolic reprogramming and matrix remodeling.

A New Role for the Aldosterone/Mineralocorticoid Receptor Pathway in the Development of Mitral Valve Prolapse

RATIONALE

Mitral valve prolapse (MVP) is one of the most common valvular disorders. However, the molecular and cellular mechanisms involved in fibromyxomatous changes in the mitral leaflet tissue have not been elucidated. Aldosterone (Aldo) promotes fibrosis in myocardium, and MR (mineralocorticoid receptor) antagonists (MRAs) improve cardiac function by decreasing cardiac fibrosis.

OBJECTIVE

We investigated the role of the Aldo/MR in the fibromyxomatous modifications associated with MVP.

METHODS AND RESULTS

Aldo enhanced valvular interstitial cell activation markers and induced endothelial-mesenchymal transition in valvular endothelial cells, resulting in increased proteoglycan secretion. MRA blocked all the above effects. Cytokine arrays showed CT-1 (cardiotrophin-1) to be a mediator of Aldo-induced valvular interstitial cell activation and proteoglycan secretion and CD (cluster of differentiation) 14 to be a mediator of Aldo-induced endothelial-mesenchymal transition and proteoglycan secretion in valvular endothelial cells. In an experimental mouse model of MVP generated by nordexfenfluramine administration, MRA treatment reduced mitral valve thickness and proteoglycan content. Endothelial-specific MR deletion prevented fibromyxomatous changes induced by nordexfenfluramine administration. Moreover, proteoglycan expression was slightly lower in the mitral valves of MVP patients treated with MRA.

CONCLUSIONS

These findings demonstrate, for the first time, that the Aldo/MR pathway regulates the phenotypic, molecular, and histological changes of valvular interstitial cells and valvular endothelial cells associated with MVP development. MRA treatment appears to be a promising option to reduce fibromyxomatous alterations in MVP.

Comparative pathology of human and canine myxomatous mitral valve degeneration: 5HT and TGF-β mechanisms

Myxomatous mitral valve degeneration (MMVD) is a leading cause of valve repair or replacement secondary to the production of mitral regurgitation, cardiac enlargement, systolic dysfunction, and heart failure. The pathophysiology of myxomatous mitral valve degeneration is complex and incompletely understood, but key features include activation and transformation of mitral valve (MV) valvular interstitial cells (VICs) into an active phenotype leading to remodeling of the extracellular matrix and compromise of the structural components of the mitral valve leaflets. Uncovering the mechanisms behind these events offers the potential for therapies to prevent, delay, or reverse myxomatous mitral valve degeneration. One such mechanism involves the neurotransmitter serotonin (5HT), which has been linked to development of valvulopathy in a variety of settings, including valvulopathy induced by serotonergic drugs, Serotonin-producing carcinoid tumors, and development of valvulopathy in laboratory animals exposed to high levels of serotonin. Similar to humans, the domestic dog also experiences naturally occurring myxomatous mitral valve degeneration, and in some breeds of dogs, the lifetime prevalence of myxomatous mitral valve degeneration reaches 100%. In dogs, myxomatous mitral valve degeneration has been associated with high serum serotonin, increased expression of serotonin-receptors, autocrine production of serotonin within the mitral valve leaflets, and downregulation of serotonin clearance mechanisms. One pathway closely associated with serotonin involves transforming growth factor beta (TGF-β) and the two pathways share a common ability to activate mitral valve valvular interstitial cells in both humans and dogs. Understanding the role of serotonin and transforming growth factor beta in myxomatous mitral valve degeneration gives rise to potential therapies, such as 5HT receptor (5HT-R) antagonists. The main purposes of this review are to highlight the commonalities between myxomatous mitral valve degeneration in humans and dogs, with specific regards to serotonin and transforming growth factor beta, and to champion the dog as a relevant and particularly valuable model of human disease that can accelerate development of novel therapies.

Enhancement by Hydrogen Peroxide of Calcium Signals in Endothelial Cells Induced by 5-HT1B and 5-HT2B Receptor Agonists

Hydrogen peroxide, formed in the endothelium, acts as a factor contributing to the relaxation of blood vessels. The reason for this vasodilatory effect could be modulation by H₂O₂ of calcium metabolism, since mobilization of calcium ions in endothelial cells is a trigger of endothelium-dependent relaxation. The aim of this work was to investigate the influence of H₂O₂ on the effects of Ca²⁺-mobilizing agonists in human umbilical vein endothelial cells (HUVEC). We have found that H₂O₂ in concentration range 10-100 μM increases the rise of [Ca²⁺]_i induced by 5-hydroxytryptamine (5-HT) and carbachol and does not affect the calcium signals of ATP, agonist of type 1 protease-activated receptor SFLLRN, histamine and bradykinin. Using specific agonists of 5-HT1B and 5-HT2B receptors CGS12066B and BW723C86, we have demonstrated that H₂O₂ potentiates the effects mediated by these types of 5-HT receptors. Potentiation of the effect of BW723C86 can be produced by the induction of endogenous oxidative stress in HUVEC. We have shown that the activation of 5-HT2B receptor by BW723C86 causes production of reactive oxygen species (ROS). Inhibitor of NADPH oxidases VAS2870 suppressed formation of ROS and partially inhibited [Ca²⁺]_i rise induced by BW723C86. Thus, it can be assumed that vasorelaxation induced by endogenous H₂O₂ in endothelial cells partially occurs due to the potentiation of the agonist-induced calcium signaling.

The role of 5-HT2B receptors in mitral valvulopathy: bone marrow mobilization of endothelial progenitors

BACKGROUND AND PURPOSE

Valvular heart disease (VHD) is highly prevalent in industrialized countries. Chronic use of anorexigens, amphetamine or ergot derivatives targeting the 5-HT system is associated with VHD. Here, we investigated the contribution of 5-HT receptors in a model of valve degeneration induced by nordexfenfluramine, the main metabolite of the anorexigens, dexfenfluramine and benfluorex.

EXPERIMENTAL APPROACH

Nordexfenfluramine was infused chronically (28 days) in mice ((WT and transgenic Htr_2B   ^-/- , Htr_2A   ^-/- , and Htr_2B/2A   ^-/- ) to induce mitral valve lesions. Bone marrow transplantation was also carried out. Haemodynamics were measured with echocardiography; tissues and cells were analysed by histology, immunocytochemistry, flow cytometry and RT -qPCR. Samples of human prolapsed mitral valves were also analysed.

KEY RESULTS

Chronic treatment of mice with nordexfenfluramine activated 5-HT_2B receptors and increased valve thickness and cell density in a thick extracellular matrix, mimicking early steps of mitral valve remodelling. Lesions were prevented by 5-HT_2A or 5-HT_2B receptor antagonists and in transgenic Htr_2B   ^-/- or Htr_2A/2B   ^-/- mice. Surprisingly, valve lesions were mainly formed by numerous non-proliferative CD34⁺ endothelial progenitors. These progenitors originated from bone marrow (BM) as revealed by BM transplantation. The initial steps of mitral valve remodelling involved mobilization of BM-derived CD34⁺ CD31⁺ cells by 5-HT_2B receptor stimulation. Analysis of human prolapsed mitral valves showing spontaneous degenerative lesions, demonstrated the presence of non-proliferating CD34⁺ /CD309⁺ /NOS3⁺ endothelial progenitors expressing 5-HT_2B receptors.

CONCLUSIONS AND IMPLICATIONS

BM-derived endothelial progenitor cells make a crucial contribution to the remodelling of mitral valve tissue. Our data describe a new and important mechanism underlying human VHD.