Estelle Ayme-Dietrich

New therapeutic opportunities for 5-HT2 receptor ligands.

ABSTRACT Serotonergic dysfunction is mainly associated with neuropsychiatric and cardiovascular disorders but has also been linked with many other pathological conditions. Serotonin (5‐hydroxytryptamine, 5‐HT) mediates numerous physiological functions in the brain and the periphery by activating a variety of receptors. 5‐HT receptors are divided into four classes, three of which belong to the G protein‐coupled receptor family. This review provides an overview of the recent pharmacological developments involving the Gq‐coupled 5‐HT2 receptor subfamily as well as the pathological implications of this receptor subfamily with regard to fibrosis, the central nervous system, cardiovascular disorders, and cancer. The final section highlights new therapeutic opportunities and emerging research revealing unexplored medical opportunities for this class of 5‐HT receptors. The development of biased 5‐HT2 receptor ligands appears to be an interesting topic in various areas. In light of recent discoveries, the need for the development of new and safer drugs should take into account the risk of cardiovascular side effects such as pulmonary hypertension and heart valve disease.

Cardiovascular remodeling and the peripheral serotonergic system

Plasma 5-hydroxytryptamine (5-HT; serotonin), released from blood platelets, plays a major role in the human cardiovascular system. Besides the effect of endogenous serotonin, many drugs targeting serotonergic receptors are widely used in the general population (antiobesity agents, antidepressants, antipsychotics, antimigraine agents), and may enhance the cardiovascular risk. Depending on the type of serotonin receptor activated and its location, the use of these compounds triggers acute and chronic effects. The acute cardiovascular response to 5-HT, named the Bezold-Jarish reflex, leads to intense bradycardia associated with atrioventricular block, and involves 5-HT3, 5-HT1B/1D, 5-HT7 and 5-HT2A/2B receptors. The chronic contribution of 5-HT and its receptors (5-HT4 and 5-HT2A/2B) in cardiovascular tissue remodeling, with a particular emphasis on cardiac hypertrophy, fibrosis and valve degeneration, will be explored in this review. Finally, through the analysis of the effects of sarpogrelate, some new aspects of 5-HT2A receptor pharmacology in vasomotor tone regulation and the interaction between endothelial and smooth muscle cells will also be discussed. The aim of this review is to emphasize the cardiac side effects caused by serotonin receptor activation, and to highlight their possible prevention by the development of new drugs targeting this system.

Old spontaneously hypertensive rats gather together typical features of human chronic left-ventricular dysfunction with preserved ejection fraction

Objective: Heart failure with preserved left-ventricular ejection fraction (HF-PEF) is an entity leading to pulmonary congestion because of impaired diastolic filling. This syndrome usually strikes those who have experienced a long history of hypertension or metabolic risk factors. Pathophysiological mechanisms are not fully understood, and standard therapy is not established. Relevant preclinical models are still lacking. The aim of this work was to evaluate aging spontaneously hypertensive rats (SHRs) as a model of HF-PEF. Methods: Serial echocardiographic and blood pressure (BP) measurements were performed in 28, 36, 43, 47 and 51-week-old SHRs and their normotensive controls (Wistar–Kyoto rats). In 52–53-week-old animals, final investigations included ECG, invasive left-ventricular (LV) and aortic catheterization, brain natriuretic peptide (BNP) plasma concentrations, ventricular reverse transcription-qPCR evaluations (&bgr;-myosin heavy chain, atrial natriuretic peptide, BNP, sarco/endoplasmic reticulum calcium ATPase 2a and collagens 1a, 3a and 2a) and cardiac histology. Results: SHRs develop a progressive alteration of the early diastole, some of the echocardiographic parameters being not sensitive to BP reduction by the calcium blocker, nicardipine. The systolic function evaluated by echocardiography and invasive catheterization was preserved. When the observation period was over, an increase in collagen synthesis and deposits were identified in subendocardial layers. This attested a probable myocardial ischemia that was confirmed by ECG changes of the ST segment. BNP increased in the blood and at the mRNA level in the myocardium. Conclusion: When aging, SHRs progressively develop HF-PEF showed by impaired LV relaxation and hypertrophy, BNP increase but preserved contractility and fibrosis. This model seems pertinent for further pharmacological preclinical studies in the field.

Targeting myocardial reperfusion injuries with cyclosporine in the CIRCUS Trial - pharmacological reasons for failure.

The mitochondrial permeability transition (mPTP) is a key feature of cardiac cell death in ischaemia‐reperfusion injury (I/R). The mPTP blocker, cyclosporine A (CsA), has been shown to give protection against reperfusion‐induced myocardial necrosis and troubles generated by acute coronary artery repermeabilization. Nevertheless, the results of the CIRCUS trial (Does Cyclosporine Improve Clinical Outcome in ST‐Elevation Myocardial Infarction Patients) seem to go against this hypothesis. Pharmacological reasons linked to CsA pharmacokinetics and pharmacodynamics could be suggested. First, it could be explained by a limited diffusion of the drug in the area at risk, due to the only inclusion of patients with a TIMI 0 or 1 coronary blood flow in the anterior territory and the absence of collateral perfusion. Second, to explain a low tissue diffusion of the compound, blood cell capture and high metabolism could be suggested. Moreover, CsA is highly metabolized by cytochrome P450 3A4 (CYP3A4), a polymorphic enzyme leading to variations of Cmax and AUC between 10–20% in patients using CsA. Finally, CsA blocks calcineurin, a protein implied in I/R damage but calcineurin inhibition could contribute to protection towards I/R damage only when Rcan1, a calcineurin natural inhibitor, expression is low. The results of the CIRCUS trial are disappointing and could contribute to the withdrawal of the mPTP blockade pharmacological strategy as a way to protect the myocardium from I/R lesions. Nevertheless, many pharmacological insights could have contributed to an increased variability and, as a consequence, an important reduction of the pharmacological power of the study.

Contribution of serotonin to cardiac remodeling associated with hypertensive diastolic ventricular dysfunction in rats.

Objective: Left-ventricular hypertrophy and interstitial fibrosis are the main pathophysiological factors of heart failure with preserved ejection fraction. Blockade of the serotonin 5-HT2B receptor (5-HT2BR) has been shown to reduce cardiac hypertrophy, oxidative stress, and extracellular cell matrix activation. In this study, we evaluated the effects of the 5-HT2BR blockade, on hemodynamic and cardiac remodeling, in spontaneously hypertensive rats (SHRs) that display a diastolic dysfunction with preserved ejection fraction. Method: Thirty-seven-week-old SHRs were randomized in four groups receiving either saline, the selective 5-HT2BR antagonist RS-127445 (1 mg/kg per day), a calcium channel blocker nicardipine (6 mg/kg per day), or RS-127445 + nicardipine. During the 14 weeks of treatment period, cardiac function and blood pressure were monitored by echocardiography and tail-cuff. Finally, electrocardiograms and invasive hemodynamics were obtained before blood collection. Heart was analyzed for morphology and mRNA expression. A complementary study evaluated the cardiac and vascular effects of serotonin on wild-type and mice knockout for the 5-HT2BR (Htr2B−/−) and/or the 5-HT2AR (Htr2A−/−). Results: Despite the left ventricular 5-HT2BR overexpression, 5-HT2BR blockade by RS-127445 did not affect left ventricular hypertrophy and fibrosis in SHRs. This antagonist did not improve diastolic dysfunction, neither alone nor in combination with nicardipine, although it induced plasma brain natriuretic peptide decrease. Moreover, RS-127445 amplified subendocardial fibrosis and favored left ventricular dilatation. Finally, a subendocardial left ventricular fibrosis was induced by chronic serotonin in wild-type mice, which was increased in Htr2B−/− animals, but prevented in Htr2A−/− and Htr2A/2B−/− mice, and could be explained by a contribution of the endothelial 5-HT2BRs to coronary vasodilatation. Conclusion: This work is the first to identify a cardioprotective function of the 5-HT2BR in an integrated model of diastolic dysfunction with preserved ejection fraction.

Mitral bioprosthesis hypertrophic scaring and native aortic valve fibrosis during benfluorex therapy

The authors describe the case of a simultaneous mitral bioprosthesis hypertrophic scaring and native aortic valve fibrosis during benfluorex therapy in a 40‐year‐old woman. Four years before, she underwent a mitral valve replacement after the diagnosis of mitral regurgitation during benfluorex treatment (150 mg/day). This drug was reintroduced postoperatively. She presented with exercise and sometimes resting dyspnoea. The bioprosthesis and aortic valves exhibited similar histopathological lesions. Thickening and plaque deposits made by smooth muscle alpha actin‐ and vimentin‐positive cells in a glycosaminoglycan matrix were observed. The study discusses the putative contribution of circulating progenitor cells activated by 5‐HT2B receptor agonists in the development of drug‐induced heart disease.

How Does Circadian Rhythm Impact Salt Sensitivity of Blood Pressure in Mice? A Study in Two Close C57Bl/6 Substrains

Background Mouse transgenesis has provided the unique opportunity to investigate mechanisms underlying sodium kidney reabsorption as well as end organ damage. However, understanding mouse background and the experimental conditions effects on phenotypic readouts of engineered mouse lines such as blood pressure presents a challenge. Despite the ability to generate high sodium and chloride plasma levels during high-salt diet, observed changes in blood pressure are not consistent between wild-type background strains and studies. Methods The present work was designed in an attempt to determine guidelines in the field of salt-induced hypertension by recording continuously blood pressure by telemetry in mice submitted to different sodium and potassium loaded diets and changing experimental conditions in both C57BL/6N and C57BL/6J mice strain (Normal salt vs. Low salt vs. High-salt/normal potassium vs. High salt/low potassium, standard vs. modified light cycle, Non-invasive tail cuff blood pressure vs. telemetry). Results In this study, we have shown that, despite a strong blood pressure (BP) basal difference between C57BL/6N and C57BL/6J mice, High salt/normal potassium diet increases BP and heart rate during the active phase only (dark period) in the same extent in both strains. On the other hand, while potassium level has no effect on salt-induced hypertension in C57BL/6N mice, high-salt/low potassium diet amplifies the effect of the high-salt challenge only in C57BL/6J mice. Indeed, in this condition, salt-induced hypertension can also be detected during light period even though this BP increase is lower compared to the one occurring during the dark period. Finally, from a methodological perspective, light cycle inversion has no effect on this circadian BP phenotype and tail-cuff method is less sensitive than telemetry to detect BP phenotypes due to salt challenges. Conclusions Therefore, to carry investigations on salt-induced hypertension in mice, chronic telemetry and studies in the active phase are essential prerequisites.

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

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.

Imidazoline-like drugs improve insulin sensitivity through peripheral stimulation of adiponectin and AMPK pathways in a rat model of glucose intolerance

Altered adiponectin signaling and chronic sympathetic hyperactivity have both been proposed as key factors in the pathogenesis of metabolic syndrome. We recently reported that activation of I1 imidazoline receptors (I1R) improves several symptoms of the metabolic syndrome through sympathoinhibition and increases adiponectin plasma levels in a rat model of metabolic syndrome (Fellmann L, Regnault V, Greney H, et al. J Pharmacol Exp Ther 346: 370-380, 2013). The present study was designed to explore the peripheral component of the beneficial actions of I1R ligands (i.e., sympathoinhibitory independent effects). Aged rats displaying insulin resistance and glucose intolerance were treated with LNP509, a peripherally acting I1R agonist. Glucose tolerance, insulin sensitivity, and adiponectin signaling were assessed at the end of the treatment. Direct actions of the ligand on hepatocyte and adipocyte signaling were also studied. LNP509 reduced the area under the curve of the intravenous glucose tolerance test and enhanced insulin hypoglycemic action and intracellular signaling (Akt phosphorylation), indicating improved glucose tolerance and insulin sensitivity. LNP509 stimulated adiponectin secretion acting at I1R on adipocytes, resulting in increased plasma levels of adiponectin; it also enhanced AMPK phosphorylation in hepatic tissues. Additionally, I1R activation on hepatocytes directly enhanced AMPK phosphorylation. To conclude, I1R ligands can improve insulin sensitivity acting peripherally, independently of sympathoinhibition; stimulation of adiponectin and AMPK pathways at insulin target tissues may account for this effect. This may open a promising new way for the treatment of the metabolic syndrome.

Serotonin contribution to cardiac valve degeneration: new insights for novel therapies?

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-HT2B 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-HT2B 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.