Activation of beta2-adrenergic receptors hastens relaxation and mediates phosphorylation of phospholamban, troponin I, and C-protein in ventricular myocardium from patients with terminal heart failure

Triiodo-L-thyronine (T3) downregulates Npr1 gene (coding for natriuretic peptide receptor-A) transcription in H9c2 cells: involvement of β-AR-ROS signaling

INTRODUCTION

Natriuretic peptide receptor-A (NPR-A) signaling system is considered as an intrinsic productive mechanism of the heart that opposes abnormal cardiac remodeling and hypertrophic growth. NPR-A is coded by Npr1 gene, and its expression is downregulated in the hypertrophied heart.

AIM

We sought to examine the levels of Npr1 gene transcription in triiodo-L-thyronine (T3) treated hypertrophied cardiomyocyte (H9c2) cells, in vitro, and also the involvement of β-adrenergic receptor (β-AR) - Reactive oxygen species (ROS) signaling system in the down-regulation of Npr1 transcription also studied.

MAIN METHODS

Anti-hypertrophic Npr1 gene transcription was monitored in control and T3-treated (dose and time dependent) H9c2 cells, using a real time PCR method. Further, cell size, intracellular cGMP, ROS, hypertrophy markers (ANP, BNP, α-sk, α-MHC and β-MHC), β-AR, and protein kinase cGMP-dependent 1 (PKG-I) genes expression were also determined. The intracellular cGMP and ROS levels were determined by ELISA and DCF dye method, respectively. In addition, to neutralize T3 mediated ROS generation, H9c2 cells were treated with T3 in the presence and absence of antioxidants [curcumin (CU) or N-acetyl-L-cysteine (NAC)].

RESULTS

A dose dependent (10 pM, 100 pM, 1 nM and 10 nM) and time dependent (12 h, 24 h and 48 h) down-regulation of Npr1 gene transcription (20, 39, 60, and 74% respectively; 18, 55, and 85%, respectively) were observed in T3-treated H9c2 cells as compared with control cells. Immunofluorescence analysis also revealed that a marked down regulation of NPR- A protein in T3-treated cells as compared with control cells. Further, a parallel downregulation of cGMP and PKG-I (2.4 fold) were noticed in the T3-treated cells. In contrast, a time dependent increased expression of β-AR (60, 72, and 80% respectively) and ROS (26, 48, and 74%, respectively) levels were noticed in T3-treated H9c2 cells as compared with control cells. Interestingly, antioxidants, CU or NAC co-treated T3 cells displayed a significant reduction in ROS (69 and 81%, respectively) generation and to increased Npr1 gene transcription (81 and 88%, respectively) as compared with T3 alone treated cells.

CONCLUSION

Our result suggest that down regulation of Npr1 gene transcription is critically involved in T3- induced hypertrophic growth in H9c2 cells, and identifies the cross-talk between T3-β-AR-ROS and NPR-A signaling.

Therapeutic strategies targeting mechanisms of macrophages in diabetic heart disease

Diabetic heart disease (DHD) is a serious complication in patients with diabetes. Despite numerous studies on the pathogenic mechanisms and therapeutic targets of DHD, effective means of prevention and treatment are still lacking. The pathogenic mechanisms of DHD include cardiac inflammation, insulin resistance, myocardial fibrosis, and oxidative stress. Macrophages, the primary cells of the human innate immune system, contribute significantly to these pathological processes, playing an important role in human disease and health. Therefore, drugs targeting macrophages hold great promise for the treatment of DHD. In this review, we examine how macrophages contribute to the development of DHD and which drugs could potentially be used to target macrophages in the treatment of DHD.

Roles of β-adrenoceptor Subtypes and Therapeutics in Human Cardiovascular Disease: Heart Failure, Tachyarrhythmias and Other Cardiovascular Disorders

β-Adrenoceptors (β-ARs) provide an important therapeutic target for the treatment of cardiovascular disease. Three β-ARs, β1-AR, β2-AR, β3-AR are localized to the human heart. Activation of β1-AR and β2-ARs increases heart rate, force of contraction (inotropy) and consequently cardiac output to meet physiological demand. However, in disease, chronic over-activation of β1-AR is responsible for the progression of disease (e.g. heart failure) mediated by pathological hypertrophy, adverse remodelling and premature cell death. Furthermore, activation of β1-AR is critical in the pathogenesis of cardiac arrhythmias while activation of β2-AR directly influences blood pressure haemostasis. There is an increasing awareness of the contribution of β2-AR in cardiovascular disease, particularly arrhythmia generation. All β-blockers used therapeutically to treat cardiovascular disease block β1-AR with variable blockade of β2-AR depending on relative affinity for β1-AR vs β2-AR. Since the introduction of β-blockers into clinical practice in 1965, β-blockers with different properties have been trialled, used and evaluated, leading to better understanding of their therapeutic effects and tolerability in various cardiovascular conditions. β-Blockers with the property of intrinsic sympathomimetic activity (ISA), i.e. β-blockers that also activate the receptor, were used in the past for post-treatment of myocardial infarction and had limited use in heart failure. The β-blocker carvedilol continues to intrigue due to numerous properties that differentiate it from other β-blockers and is used successfully in the treatment of heart failure. The discovery of β3-AR in human heart created interest in the role of β3-AR in heart failure but has not resulted in therapeutics at this stage.

Cardiac contraction and relaxation are regulated by distinct subcellular cAMP pools

Cells interpret a variety of signals through G-protein-coupled receptors (GPCRs) and stimulate the generation of second messengers such as cyclic adenosine monophosphate (cAMP). A long-standing puzzle is deciphering how GPCRs elicit different physiological responses despite generating similar levels of cAMP. We previously showed that some GPCRs generate cAMP from both the plasma membrane and the Golgi apparatus. Here we demonstrate that cardiomyocytes distinguish between subcellular cAMP inputs to elicit different physiological outputs. We show that generating cAMP from the Golgi leads to the regulation of a specific protein kinase A (PKA) target that increases the rate of cardiomyocyte relaxation. In contrast, cAMP generation from the plasma membrane activates a different PKA target that increases contractile force. We further validated the physiological consequences of these observations in intact zebrafish and mice. Thus, we demonstrate that the same GPCR acting through the same second messenger regulates cardiac contraction and relaxation dependent on its subcellular location.

Managing Diastolic Dysfunction Perioperatively

Preoperative cardiac evaluation is a cornerstone of the practice of anesthesiology. This consists of a thorough history and physical attempting to elucidate signs and symptoms of heart failure, angina or anginal equivalents, and valvular heart disease. Current guidelines rarely recommend preoperative echocardiography in the setting of an adequate functional capacity. Many patients may have poor functional capacity and/or have medical history such that echocardiographic data is available for review. Much focus is often placed on evaluating major valvular abnormalities and systolic function as measured by ejection fraction, but a key impactful component is often overlooked-diastolic function. A diagnosis of diastolic heart failure is an independent predictor of mortality and is not uncommon in patients with normal systolic function. This narrative review addresses the clinical relevance and management of diastolic dysfunction in the perioperative setting.

Pathological changes in GPCR signal organisation: Opportunities for targeted therapies for triple negative breast cancer

Triple negative breast cancer (TNBC) has the poorest prognosis compared to other breast cancer subtypes, due to a historical lack of targeted therapies and high rates of relapse. Greater insight into the components of signalling pathways in TNBC tumour cells has led to the clinical evaluation, and in some cases approval, of targeted therapies. In the last decade, G protein-coupled receptors, such as the β₂-adrenoceptor, have emerged as potential new therapeutic targets. Here, we describe how the β₂-adrenoceptor accelerates TNBC progression in response to stress, and the unique signalling pathway activated by the β₂-adrenoceptor to drive the invasion of an aggressive TNBC tumour cell. We highlight evidence that supports an altered organisation of GPCRs in tumour cells, and suggests that activation of the same GPCR in a different cellular location can control unique cell responses. Finally, we speculate how the relocation of GPCRs to the "wrong" place in tumour cells presents opportunities to develop targeted anti-cancer GPCR drugs with greater efficacy and minimal adverse effects.

Probing spatiotemporal PKA activity at the ryanodine receptor and SERCA2a nanodomains in cardomyocytes

Spatiotemporal regulation of subcellular protein kinase A (PKA) activity for precise substrate phosphorylation is essential for cellular responses to hormonal stimulation. Ryanodine receptor 2 (RyR2) and (sarco)endoplasmic reticulum calcium ATPase 2a (SERCA2a) represent two critical targets of β adrenoceptor (βAR) signaling on the sarcoplasmic reticulum membrane for cardiac excitation and contraction coupling. Using novel biosensors, we show that cardiac β1AR signals to both RyR2 and SERCA2a nanodomains in cardiomyocytes from mice, rats, and rabbits, whereas the β2AR signaling is restricted from these nanodomains. Phosphodiesterase 4 (PDE4) and PDE3 control the baseline PKA activity and prevent β2AR signaling from reaching the RyR2 and SERCA2a nanodomains. Moreover, blocking inhibitory G protein allows β2AR signaling to the RyR2 but not the SERCA2a nanodomains. This study provides evidence for the differential roles of inhibitory G protein and PDEs in controlling the adrenergic subtype signaling at the RyR2 and SERCA2a nanodomains in cardiomyocytes.

Influence of β1 Adrenergic Receptor Genotype on Longitudinal Measures of Left Ventricular Ejection Fraction and Responsiveness to ß-Blocker Therapy in Patients With Duchenne Muscular Dystrophy

The purpose of this study was to determine whether the longitudinal progression of decline in left ventricular ejection fraction (LVEF) in Duchenne muscular dystrophy (DMD) patients is moderated by ADRB1 genotype and whether the efficacy of ß-blocker therapy is influenced by genotype status. About 147 DMD patients (6-34 years.) were analyzed with a focus on β1 adrenergic receptor (ADRB1) genotype variants. Patients were grouped by ADRB1 genotype resulting in Gly389 patients and Arg389 patients. A generalized additive mixed effects model was used to examine differences in the nonlinear trend of LVEF across patient ages between genotype groups and for ß-blocker use. Both genotype groups displayed a progressive decline in LVEF starting around the mean age of ambulation loss (~12 years). However, there was no difference between genotype groups in the progression of decline in LVEF. There was a significant effect of ß-blocker use on longitudinal LVEF, wherein patients on ß-blockers had systematically lower LVEF when compared to patients not on ß-blockers. However, the effect of ß-blocker therapy on LVEF was not affected by ADRB1 genotype. The current study did not demonstrate an influence of patient ADRB1 genotype on longitudinal LVEF in our cohort. Despite previous literature suggesting a positive influence of ß-blocker use on cardiac function in DMD patients and of an ADRB1 genotypic difference in responsiveness to ß-blocker use, we did not observe this in our cohort. Interestingly, our cohort did not demonstrate a positive influence of ß-blocker use on LVEF measures.

Lipids: a Potential Molecular Pathway Towards Diastolic Dysfunction in Youth-Onset Type 2 Diabetes

PURPOSE OF THE REVIEW

Obesity and type 2 diabetes (T2D) with onset in youth are emerging public health concerns. Youth with obesity and T2D are at risk for the development of heart failure with preserved ejection fraction (HFpEF) due to diabetes-related cardiomyopathy with evidence of precursor stages, namely diastolic dysfunction, present in youth. We review the literature regarding diastolic dysfunction in youth with obesity and T2D; discuss the potential mechanisms including the role of lipids, contractile proteins and their post-translational modifications, and conclude with studies to guide future treatments.

RECENT FINDINGS

The diabetes milieu namely hyperglycemia, hyperinsulinemia, and lipotoxicity favor development of diastolic dysfunction and HFpEF. Recent studies show HFpEF is associated with slow left ventricular relaxation and sarcomere stiffness induced by reduced calcium (Ca2+) and β-adrenergic responses. There are currently no effective therapies available for treating HFpEF. Targeting the sarcomere is an area of ongoing research.

Sympatho-adrenergic mechanisms in heart failure: new insights into pathophysiology

The sympathetic nervous system is activated in the setting of heart failure (HF) to compensate for hemodynamic instability. However, acute sympathetic surge or sustained high neuronal firing rates activates β-adrenergic receptor (βAR) signaling contributing to myocardial remodeling, dysfunction and electrical instability. Thus, sympatho-βAR activation is regarded as a hallmark of HF and forms pathophysiological basis for β-blocking therapy. Building upon earlier research findings, studies conducted in the recent decades have significantly advanced our understanding on the sympatho-adrenergic mechanism in HF, which forms the focus of this article. This review notes recent research progress regarding the roles of cardiac β2AR or α1AR in the failing heart, significance of β1AR-autoantibodies, and βAR signaling through G-protein independent signaling pathways. Sympatho-βAR regulation of immune cells or fibroblasts is specifically discussed. On the neuronal aspects, knowledge is assembled on the remodeling of sympathetic nerves of the failing heart, regulation by presynaptic α2AR of NE release, and findings on device-based neuromodulation of the sympathetic nervous system. The review ends with highlighting areas where significant knowledge gaps exist but hold promise for new breakthroughs.

Selective activation of adrenoceptors potentiates IKs current in pulmonary vein cardiomyocytes through the protein kinase A and C signaling pathways

Delayed rectifier K⁺ current (I_Ks) is a key contributor to repolarization of action potentials. This study investigated the mechanisms underlying the adrenoceptor-induced potentiation of I_Ks in pulmonary vein cardiomyocytes (PVC). PVC were isolated from guinea pig pulmonary vein. The action potentials and I_Ks current were recorded using perforated and conventional whole-cell patch-clamp techniques. The expression of I_Ks was examined using immunocytochemistry and Western blotting. KCNQ1, a I_Ks pore-forming protein was detected as a signal band approximately 100 kDa in size, and its immunofluorescence signal was found to be mainly localized on the cell membrane. The I_Ks current in PVC was markedly enhanced by both β₁- and β₂-adrenoceptor stimulation with a negative voltage shift in the current activation, although the potentiation was more effectively induced by β₂-adrenoceptor stimulation than β₁-adrenoceptor stimulation. Both β-adrenoceptor-mediated increases in I_Ks were attenuated by treatment with the adenylyl cyclase (AC) inhibitor or protein kinase A (PKA) inhibitor. Furthermore, the I_Ks current was increased by α₁-adrenoceptor agonist but attenuated by the protein kinase C (PKC) inhibitor. PVC exhibited action potentials in normal Tyrode solution which was slightly reduced by HMR-1556 a selective I_Ks blocker. However, HMR-1556 markedly reduced the β-adrenoceptor-potentiated firing rate. The stimulatory effects of β- and α₁-adrenoceptor on I_Ks in PVC are mediated via the PKA and PKC signal pathways. HMR-1556 effectively reduced the firing rate under β-adrenoceptor activation, suggesting that the functional role of I_Ks might increase during sympathetic excitation under in vivo conditions.

Adiponectin up-regulates the decrease of myocardial autophagic flux induced by β1 -adrenergic receptor autoantibody partly dependent on AMPK

Cardiomyocytes autophagy is essential for maintaining cardiac function. Our previous studies have found that β₁‐adrenergic receptor autoantibody (β₁‐AA) induced the decreased myocardial autophagic flux, which resulted in cardiomyocyte death and cardiac dysfunction. And other studies demonstrated that β₁‐AA induced the decrease of AMPK phosphorylation, the key hub of autophagy pathway, while adiponectin up‐regulated autophagic flux mediated by AMPK. However, it is not clear whether adiponectin improves the inhibition of myocardial autophagic flux induced by β₁‐AA by up‐regulating the level of AMPK phosphorylation. In this study, it has been confirmed that β₁‐AA induced the decrease of AMPK phosphorylation level in both vivo and vitro. Moreover, pretreatment of cardiomyocytes with AMPK inhibitor Compound C could further reduce the autophagic flux induced by β₁‐AA. Adiponectin deficiency could aggravate the decrease of myocardial AMPK phosphorylation level, autophagic flux and cardiac function induced by β₁‐AA. Further, exogenous adiponectin could reverse the decline of AMPK phosphorylation level and autophagic flux induced by β₁‐AA and even reduce cardiomyocyte death. While pretreated with the Compound C, the adiponectin treatment did not improve the decreased autophagosome formation, but still improved the decreased autophagosome clearance induced by β₁‐AA in cardiomyocytes. This study is the first time to confirm that β₁‐AA could inhibit myocardial autophagic flux by down‐regulating AMPK phosphorylation level. Adiponectin could improve the inhibition of myocardial autophagic flux induced by β₁‐AA partly dependent on AMPK, so as to provide an experimental basis for the treatment of patients with β₁‐AA‐positive cardiac dysfunction.

Effects of omecamtiv mecarbil on failing human ventricular trabeculae and interaction with (-)-noradrenaline

Omecamtiv mecarbil (OM) is a novel medicine for systolic heart failure, targeting myosin to enhance cardiomyocyte performance. To assist translation to clinical practice we investigated OMs effect on explanted human failing hearts, specifically; contractile dynamics, interaction with the β₁–adrenoceptor (AR) agonist (−)‐noradrenaline and spontaneous contractions. Left and right ventricular trabeculae from 13 explanted failing hearts, and trabeculae from 58 right atrial appendages of non‐failing hearts, were incubated with or without a single concentration of OM for 120 min. Time to peak force (TPF) and 50% relaxation (t_50%) were recorded. In other experiments, trabeculae were observed for spontaneous contractions and cumulative concentration‐effect curves were established to (−)‐noradrenaline at β₁‐ARs in the absence or presence of OM. OM prolonged TPF and t_50% in ventricular trabeculae (600 nM, 2 µM, p < .001). OM had no significant inotropic effect but reduced time dependent deterioration in contractile strength compared to control (p < .001). OM did not affect the generation of spontaneous contractions. The potency of (−)‐noradrenaline (pEC₅₀ 6.05 ± 0.10), for inotropic effect, was unchanged in the presence of OM 600 nM or 2 µM. Co‐incubation with (−)‐noradrenaline reduced TPF and t_50%, reversing the negative diastolic effects of OM. OM, at both 600 nM and 2 µM, preserved contractile force in left ventricular trabeculae, but imparted negative diastolic effects in trabeculae from human failing heart. (−)‐Noradrenaline reversed the negative diastolic effects, co‐administration may limit the titration of inotropes by reducing the threshold for ischemic side effects.

Compromised right ventricular contractility in an ovine model of heart transplantation following 24 h donor brain stem death

BACKGROUND

Heart failure is an inexorably progressive disease with a high mortality, for which heart transplantation (HTx) remains the gold standard treatment. Currently, donor hearts are primarily derived from patients following brain stem death (BSD). BSD causes activation of the sympathetic nervous system, increases endothelin levels, and triggers significant inflammation that together with potential myocardial injury associated with the transplant procedure, may affect contractility of the donor heart. We examined peri-transplant myocardial catecholamine sensitivity and cardiac contractility post-BSD and transplantation in a clinically relevant ovine model.

METHODS

Donor sheep underwent BSD (BSD, n = 5) or sham (no BSD) procedures (SHAM, n = 4) and were monitored for 24h prior to heart procurement. Orthotopic HTx was performed on a separate group of donor animals following 24h of BSD (BSD-Tx, n = 6) or SHAM injury (SH-Tx, n = 5). The healthy recipient heart was used as a control (HC, n = 11). A cumulative concentration-effect curve to (-)-noradrenaline (NA) was established using left (LV) and right ventricular (RV) trabeculae to determine β₁-adrenoceptor mediated potency (-logEC₅₀ [(-)-noradrenaline] M) and maximal contractility (Emax).

RESULTS

Our data showed reduced basal and maximal (-)-noradrenaline induced contractility of the RV (but not LV) following BSD as well as HTx, regardless of whether the donor heart was exposed to BSD or SHAM. The potency of (-)-noradrenaline was lower in left and right ventricles for BSD-Tx and SH-Tx compared to HC.

CONCLUSION

These studies show that the combination of BSD and transplantation are likely to impair contractility of the donor heart, particularly for the RV. For the donor heart, this contractile dysfunction appears to be independent of changes to β₁-adrenoceptor sensitivity. However, altered β₁-adrenoceptor signalling is likely to be involved in post-HTx contractile dysfunction.

Understanding How Phosphorylation and Redox Modifications Regulate Cardiac Ryanodine Receptor Type 2 Activity to Produce an Arrhythmogenic Phenotype in Advanced Heart Failure

Heart failure (HF) is a global pandemic with significant mortality and morbidity. Despite current medications, 50% of individuals die within 5 years of diagnosis. Of these deaths, 30-50% will be a result of sudden cardiac death from ventricular arrhythmias. This review discusses two stress-induced mechanisms, phosphorylation from chronic β-adrenoceptor (β-AR) stimulation and thiol modifications from oxidative stress, and how they modulate the cardiac ryanodine receptor type 2 (RyR2) and foster an arrhythmogenic phenotype. Calcium (Ca²⁺) is the ubiquitous secondary messenger of excitation-contraction coupling and provides a common pathway for contractile dysfunction and arrhythmia genesis. In a healthy heart, Ca²⁺ is released from the sarcoplasmic reticulum (SR) by RyR2. The open probability of RyR2 is under the dynamic influence of co-proteins, ions, and kinases that are in strict balance to ensure normal physiological functioning. In HF, chronic β-AR activity and production of reactive oxygen species and reactive nitrogen species provide two stress-induced mechanisms uncoupling RyR2 control, resulting in pathological diastolic SR Ca²⁺ leak. This increased cytosolic [Ca²⁺] promotes Ca²⁺ extrusion via the local Na⁺/Ca²⁺ exchanger, resulting in net sarcolemmal depolarization, delayed after depolarization and ventricular arrhythmia. Experimental models researching oxidative stress and phosphorylation have aimed to identify how post-translational modifications to the RyR2 macromolecular complex, and the associated Na⁺/Ca²⁺ cycling proteins, result in pathological Ca²⁺ handling and diastolic leak. However, the causative molecular changes remain controversial and undefined. Through understanding the molecular mechanisms that produce an arrhythmic phenotype, novel therapeutic targets to treat HF and prevent its malignant course can be identified.

Sarcoplasmic reticulum calcium mishandling: central tenet in heart failure?

Excitation-contraction coupling links excitation of the sarcolemmal surface membrane to mechanical contraction. In the heart this link is established via a Ca²⁺-induced Ca²⁺ release process, which, following sarcolemmal depolarisation, prompts Ca²⁺ release from the sarcoplasmic reticulum (SR) though the ryanodine receptor (RyR2). This substantially raises the cytoplasmic Ca²⁺ concentration to trigger systole. In diastole, Ca²⁺ is removed from the cytoplasm, primarily via the sarcoplasmic-endoplasmic reticulum Ca²⁺-dependent ATPase (SERCA) pump on the SR membrane, returning Ca²⁺ to the SR store. Ca²⁺ movement across the SR is thus fundamental to the systole/diastole cycle and plays an essential role in maintaining cardiac contractile function. Altered SR Ca²⁺ homeostasis (due to disrupted Ca²⁺ release, storage, and reuptake pathways) is a central tenet of heart failure and contributes to depressed contractility, impaired relaxation, and propensity to arrhythmia. This review will focus on the molecular mechanisms that underlie asynchronous Ca²⁺ cycling around the SR in the failing heart. Further, this review will illustrate that the combined effects of expression changes and disruptions to RyR2 and SERCA2a regulatory pathways are critical to the pathogenesis of heart failure.

Cardiac β-adrenergic receptor activation mediates distinct and cell type-dependent changes in the expression and distribution of connexin 43

Activation of the sympatho-β-adrenergic receptors (β-ARs) system is a hallmark of heart failure, leading to fibrosis and arrhythmias. Connexin 43 (Cx43) is the most abundant gap junctional protein in the myocardium. Current knowledge is limited regarding Cx43 remodelling in diverse cell types in the diseased myocardium and the underlying mechanism. We studied cell type-dependent changes in Cx43 remodelling due to β-AR overactivation and molecular mechanisms involved. Mouse models of isoproterenol stimulation or transgenic cardiomyocyte overexpression of β₂ -AR were used, which exhibited cardiac fibrosis and up-regulated total Cx43 abundance. In both models, whereas Cx43 expression in cardiomyocytes was reduced and more laterally distributed, fibroblasts exhibited elevated Cx43 expression and enhanced gap junction communication. Mechanistically, activation of β₂ -AR in fibroblasts in vitro elevated Cx43 expression, which was abolished by the β₂ -antagonist ICI-118551 or protein kinase A inhibitor H-89, but simulated by the adenylyl cyclase activator forskolin. Our in vitro and in vivo data showed that β-AR activation-induced production of IL-18 sequentially stimulated Cx43 expression in fibroblasts in a paracrine fashion. In summary, our findings demonstrate a pivotal role of β-AR in mediating distinct and cell type-dependent changes in the expression and distribution of Cx43, leading to pathological gap junction remodelling in the myocardium.

Multiparametric Mechanistic Profiling of Inotropic Drugs in Adult Human Primary Cardiomyocytes

Effects of non-cardiac drugs on cardiac contractility can lead to serious adverse events. Furthermore, programs aimed at treating heart failure have had limited success and this therapeutic area remains a major unmet medical need. The challenges in assessing drug effect on cardiac contractility point to the fundamental translational value of the current preclinical models. Therefore, we sought to develop an adult human primary cardiomyocyte contractility model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic effect (sarcomere shortening) and generating multi-parameter data to profile different mechanisms of action based on cluster analysis of a set of 12 contractility parameters. We report that 17 positive and 9 negative inotropes covering diverse mechanisms of action exerted concentration-dependent increases and decreases in sarcomere shortening, respectively. Interestingly, the multiparametric readout allowed for the differentiation of inotropes operating via distinct mechanisms. Hierarchical clustering of contractility transient parameters, coupled with principal component analysis, enabled the classification of subsets of both positive as well as negative inotropes, in a mechanism-related mode. Thus, human cardiomyocyte contractility model could accurately facilitate informed mechanistic-based decision making, risk management and discovery of molecules with the most desirable pharmacological profile for the correction of heart failure.

Phenytoin Reduces Activity of Cardiac Ryanodine Receptor 2; A Potential Mechanism for Its Cardioprotective Action

Phenytoin is a hydantoin derivative that is used clinically for the treatment of epilepsy and has been reported to have antiarrhythmic actions on the heart. In a failing heart, the elevated diastolic Ca2+ leak from the sarcoplasmic reticulum can be normalized by the cardiac ryanodine receptor 2 (RyR2) inhibitor, dantrolene, without inhibiting Ca2+ release during systole or affecting Ca2+ release in normal healthy hearts. Unfortunately, dantrolene is hepatotoxic and unsuitable for chronic long-term administration. Because phenytoin and dantrolene belong to the hydantoin class of compounds, we test the hypothesis that dantrolene and phenytoin have similar inhibitory effects on RyR2 using a single-channel recording of RyR2 activity in artificial lipid bilayers. Phenytoin produced a reversible inhibition of RyR2 channels from sheep and human failing hearts. It followed a hyperbolic dose response with maximal inhibition of ∼50%, Hill coefficient ∼1, and IC50 ranging from 10 to 20 µM. It caused inhibition at diastolic cytoplasmic [Ca2+] but not at Ca2+ levels in the dyadic cleft during systole. Notably, phenytoin inhibits RyR2 from failing human heart but not from healthy heart, indicating that phenytoin may selectively target defective RyR2 channels in humans. We conclude that phenytoin could effectively inhibit RyR2-mediated release of Ca2+ in a manner paralleling that of dantrolene. Moreover, the IC50 of phenytoin in RyR2 is at least threefold lower than for other ion channels and clinically used serum levels, pointing to phenytoin as a more human-safe alternative to dantrolene for therapies against heart failure and cardiac arrythmias. SIGNIFICANCE STATEMENT: We show that phenytoin, a Na channel blocker used clinically for treatment of epilepsy, is a diastolic inhibitor of cardiac calcium release channels [cardiac ryanodine receptor 2 (RyR2)] at doses threefold lower than its current therapeutic levels. Phenytoin inhibits RyR2 from failing human heart and not from healthy heart, indicating that phenytoin may selectively target defective RyR2 channels in humans and pointing to phenytoin as a more human-safe alternative to dantrolene for therapies against heart failure and cardiac arrhythmias.

A mini review of inhaled beta 2 agonists in acute decompensated heart failure requiring respiratory support

Acute decompensated heart failure (HF) results in over one million hospital admissions per year, many requiring invasive or noninvasive mechanical ventilation for respiratory/cardiovascular support. Inhaled beta-2 adrenergic receptor agonists have been shown to be effective at clearance of extravascular lung water in HF patients. However, studies done in the late 1990s and early 2000s, prior to standardization and wide adoption of guideline directed medical therapy for HF, suggested that inhaled beta-2 agonist use increased admissions for HF exacerbations as well as in-hospital mortality. One study even attempted to utilize intravenous Beta-2 agonists in Acute Respiratory Distress Syndrome patients, however the study was stopped prematurely due to an 11% increased mortality in the treatment group. More recently however, studies examining patients who have concurrent diagnoses of chronic obstructive pulmonary disease (COPD) and HF showed that beta-2 agonist therapy resulted in similar or better outcomes compared to controls. Likewise, in-vitro studies, animal models, and studies utilizing chronic heart failure patients treated with nebulized beta-2 agonists with no concurrent respiratory diagnosis had a therapeutic effect of treatment over controls. These studies have the advantage of being performed with the standardization of guideline directed HF medical therapy. In conclusion, while we continue to recommend the use of Beta-2 agonist therapy in patients with concurrent COPD and HF requiring respiratory support, further studies, preferably single or double blinded prospective trials, will need to be performed to determine whether Beta-2 agonist therapy offers morbidity and mortality benefits in patients with strictly acute decompensated heart failure requiring respiratory support.

Physiologic, Pathologic, and Therapeutic Paracrine Modulation of Cardiac Excitation-Contraction Coupling

Cardiac excitation-contraction coupling (ECC) is the orchestrated process of initial myocyte electrical excitation, which leads to calcium entry, intracellular trafficking, and subsequent sarcomere shortening and myofibrillar contraction. Neurohumoral β-adrenergic signaling is a well-established mediator of ECC; other signaling mechanisms, such as paracrine signaling, have also demonstrated significant impact on ECC but are less well understood. For example, resident heart endothelial cells are well-known physiological paracrine modulators of cardiac myocyte ECC mainly via NO and endothelin-1. Moreover, recent studies have demonstrated other resident noncardiomyocyte heart cells (eg, physiological fibroblasts and pathological myofibroblasts), and even experimental cardiotherapeutic cells (eg, mesenchymal stem cells) are also capable of altering cardiomyocyte ECC through paracrine mechanisms. In this review, we first focus on the paracrine-mediated effects of resident and therapeutic noncardiomyocytes on cardiomyocyte hypertrophy, electrophysiology, and calcium handling, each of which can modulate ECC, and then discuss the current knowledge about key paracrine factors and their underlying mechanisms of action. Next, we provide a case example demonstrating the promise of tissue-engineering approaches to study paracrine effects on tissue-level contractility. More specifically, we present new functional and molecular data on the effects of human adult cardiac fibroblast conditioned media on human engineered cardiac tissue contractility and ion channel gene expression that generally agrees with previous murine studies but also suggests possible species-specific differences. By contrast, paracrine secretions by human dermal fibroblasts had no discernible effect on human engineered cardiac tissue contractile function and gene expression. Finally, we discuss systems biology approaches to help identify key stem cell paracrine mediators of ECC and their associated mechanistic pathways. Such integration of tissue-engineering and systems biology methods shows promise to reveal novel insights into paracrine mediators of ECC and their underlying mechanisms of action, ultimately leading to improved cell-based therapies for patients with heart disease.

Stimulation of β-adrenoceptors up-regulates cardiac expression of galectin-3 and BIM through the Hippo signalling pathway

Background and Purpose

Expression of the pro‐fibrotic galectin‐3 and the pro‐apoptotic BIM is elevated in diseased heart or after β‐adrenoceptor stimulation, but the underlying mechanisms are unclear. This question was addressed in the present study.

Experimental Approach

Wild‐type mice and mice with cardiac transgenic expression of β₂‐adrenoceptors, mammalian sterile‐20 like kinase 1 (Mst1) or dominant‐negative Mst1, and non‐specific galectin‐3 knockout mice were used. Effects of the β‐adrenoceptor agonist isoprenaline or β‐adrenoceptor antagonists were studied. Rat cardiomyoblasts (H9c2) were used for mechanistic exploration. Biochemical assays were performed.

Key Results

Isoprenaline treatment up‐regulated expression of galectin‐3 and BIM, and this was inhibited by non‐selective or selective β‐adrenoceptor antagonists (by 60–70%). Cardiac expression of galectin‐3 and BIM was increased in β₂‐adrenoceptor transgenic mice. Isoprenaline‐induced up‐regulation of galectin‐3 and BIM was attenuated by Mst1 inactivation, but isoprenaline‐induced galectin‐3 expression was exaggerated by transgenic Mst1 activation. Pharmacological or genetic activation of β‐adrenoceptors induced Mst1 expression and yes‐associated protein (YAP) phosphorylation. YAP hyper‐phosphorylation was also evident in Mst1 transgenic hearts with up‐regulated expression of galectin‐3 (40‐fold) and BIM as well as up‐regulation of many YAP‐target genes by RNA sequencing. In H9c2 cells, isoprenaline induced YAP phosphorylation and expression of galectin‐3 and BIM, effects simulated by forskolin but abolished by PKA inhibitors, and YAP knockdown induced expression of galectin‐3 and BIM.

Conclusions and Implications

Stimulation of cardiac β‐adrenoceptors activated the Mst1/Hippo pathway leading to YAP hyper‐phosphorylation with enhanced expression of galectin‐3 and BIM. This signalling pathway would have therapeutic potential.

Linked Articles

This article is part of a themed section on Adrenoceptors—New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc

Estrogen regulation of cardiac cAMP-L-type Ca2+ channel pathway modulates sex differences in basal contraction and responses to β2AR-mediated stress in left ventricular apical myocytes

Backgrounds/Aim

Male and female hearts have many structural and functional differences. Here, we investigated the role of estrogen (E2) in the mechanisms of sex differences in contraction through the cAMP-L-type Ca²⁺channel pathway in adult mice left ventricular (LV) apical myocytes at basal and stress state.

Methods

Isolated LV apical myocytes from male, female (Sham) and ovariectomised mice (OVX) were used to investigate contractility, Ca²⁺ transients and L-type Ca²⁺ channel (LTCC) function. The levels of β₂AR, intracellular cAMP, phosphodiesterase (PDE 3 and PDE 4), RyR2, PLB, SLN, and SERCA2a were compared among the experimental groups.

Results

We found that (1) intracellular cAMP, I_CaL density, contraction and Ca²⁺ transient amplitudes were larger in Sham and OVX + E2 myocytes compared to male and OVX. (2) The mRNA expression of PDE 3 and 4 were lower in Sham and OVX + E2 groups compared with male and OVX groups. Treatment of myocytes with IBMX (100 μM) increased contraction and Ca²⁺ transient amplitude in both sexes and canceled differences between them. (3) β₂AR-mediated stress decreased cAMP concentration and peak contraction and Ca²⁺ transient amplitude only in male and OVX groups but not in Sham or OVX + E2 groups suggesting a cardioprotective role of E2 in female mice. (4) Pretreatment of OVX myocytes with GPR30 antagonist G15 (100 nM) abolished the effects of E2, but ERα and ERβ antagonist ICI 182,780 (1 μM) did not. Moreover, activation of GPR30 with G1 (100 nM) replicated the effects of E2 on cAMP, contraction and Ca²⁺ transient amplitudes suggesting that the acute effects of E2 were mediated by GPR30 via non-genomic signaling. (5) mRNA expression of RyR2 was higher in myocytes from Sham than those of male while PLB and SLN were higher in male than Sham but no sex differences were observed in the mRNA of SERCA2a.

Conclusion

Collectively, these results demonstrate that E2 modulates the expression of genes related to the cAMP-LTCC pathway and contributes to sex differences in cardiac contraction and responses to stress. We also show that estrogen confers cardioprotection against cardiac stress by non-genomic acute signaling via GPR30.

Calmodulin inhibition of human RyR2 channels requires phosphorylation of RyR2-S2808 or RyR2-S2814

Calmodulin (CaM) is a Ca-binding protein that binds to, and can directly inhibit cardiac ryanodine receptor calcium release channels (RyR2). Animal studies have shown that RyR2 hyperphosphorylation reduces CaM binding to RyR2 in failing hearts, but data are lacking on how CaM regulates human RyR2 and how this regulation is affected by RyR2 phosphorylation. Physiological concentrations of CaM (100 nM) inhibited the diastolic activity of RyR2 isolated from failing human hearts by ~50% but had no effect on RyR2 from healthy human hearts. Using FRET between donor-FKBP12.6 and acceptor-CaM bound to RyR2, we determined that CaM binds to RyR2 from healthy human heart with a K_d = 121 ± 14 nM. Ex-vivo phosphorylation/dephosphorylation experiments suggested that the divergent CaM regulation of healthy and failing human RyR2 was caused by differences in RyR2 phosphorylation by protein kinase A and Ca-CaM-dependent kinase II. Ca²⁺-spark measurements in murine cardiomyocytes harbouring RyR2 phosphomimetic or phosphoablated mutants at S2814 and S2808 suggest that phosphorylation of residues corresponding to either human RyR2-S2808 or S2814 is both necessary and sufficient for RyR2 regulation by CaM. Our results challenge the current concept that CaM universally functions as a canonical inhibitor of RyR2 across species. Rather, CaM's biological action on human RyR2 appears to be more nuanced, with inhibitory activity only on phosphorylated RyR2 channels, which occurs during exercise or in patients with heart failure.

Influence of Beta-1 Adrenergic Receptor Genotype on Cardiovascular Response to Exercise in Healthy Subjects

Background

The beta-1 adrenergic receptor (ADRB1) has been shown to play a functional role in cardiomyocyte function and accounts for up to 80% of the cardiac tissue adrenergic receptors with ADRB1 stimulation increasing cardiac rate, contractility and work. Multiple polymorphisms of the ADRB1 have been identified such as the Gly49 polymorphism that includes at least one glycine (Gly) for serine (Ser) at amino acid 49 resulting in either homozygous for Gly (Gly49Gly) or heterozygous for Gly (Gly49Ser) polymorphisms. Heart failure patients with this polymorphism (Gly49) have been shown to have improved cardiac function and decreased mortality risk, but if there is an effect in healthy subjects is less clear. The purpose of this study was to determine the effects of the Gly/Ser polymorphism at position 49 of the ADRB1on the cardiovascular response to exercise in healthy subjects.

Methods

We performed genotyping of the ADRB1 (amino acid 49) and high-intensity, steady-state exercise on 71 healthy subjects (Ser49Ser = 52, Gly49Ser = 19).

Results

There were no differences between genotype groups in age, height, weight, body mass index (BMI), or watts achieved (age = 28.9 ± 5.6 years (yrs.), 30.6 ± 6.4yrs., height = 173.6 ± 9.9 cm, 174 ± 7.5 cm, weight = 74.4 ± 13.3 kg, 71.9 ± 13.5 kg, BMI = 24.6 ± 3.5, 23.6 ± 3.3, and watts = 223.8 ± 76.8, 205 ± 49.4, for Ser49Ser and Gly49Ser respectively). Additionally, there were no differences for genotype groups for cardiac output (CO), systolic blood pressure (BP_sys), or diastolic blood pressure (BP_dias) at rest, maximal exercise, or in change from rest to maximal exercise. The genotype groups differed significantly in heart rate (HR_max) at maximal exercise and cardiac index at rest (CI) (HR_max = 184.2 ± 9.5 bpm, 190.7 ± 10.6 bpm, CI = 0.063 ± 0.014, 0.071 ± 0.013, for Ser49Ser and Gly49Ser respectively). There was a trend towards significance (P = 0.058) for the change in stroke volume from rest to peak exercise (ΔSV) (0.016 ± 0.018 L, 0.0076 ± 0.012 L, for Ser49Ser and Gly49Ser respectively).

Conclusions

These data suggest genetic variations of the ADRB1 may influence cardiovascular responses to exercise in healthy subjects.

Understanding Key Mechanisms of Exercise-Induced Cardiac Protection to Mitigate Disease: Current Knowledge and Emerging Concepts

The benefits of exercise on the heart are well recognized, and clinical studies have demonstrated that exercise is an intervention that can improve cardiac function in heart failure patients. This has led to significant research into understanding the key mechanisms responsible for exercise-induced cardiac protection. Here, we summarize molecular mechanisms that regulate exercise-induced cardiac myocyte growth and proliferation. We discuss in detail the effects of exercise on other cardiac cells, organelles, and systems that have received less or little attention and require further investigation. This includes cardiac excitation and contraction, mitochondrial adaptations, cellular stress responses to promote survival (heat shock response, ubiquitin-proteasome system, autophagy-lysosomal system, endoplasmic reticulum unfolded protein response, DNA damage response), extracellular matrix, inflammatory response, and organ-to-organ crosstalk. We summarize therapeutic strategies targeting known regulators of exercise-induced protection and the challenges translating findings from bench to bedside. We conclude that technological advancements that allow for in-depth profiling of the genome, transcriptome, proteome and metabolome, combined with animal and human studies, provide new opportunities for comprehensively defining the signaling and regulatory aspects of cell/organelle functions that underpin the protective properties of exercise. This is likely to lead to the identification of novel biomarkers and therapeutic targets for heart disease.

Cardioprotective and Anti-arrhythmic Effects of Magnesium Pretreatment Against Ischaemia/Reperfusion Injury in Isoprenaline-Induced Hypertrophic Rat Heart

The effects of magnesium (Mg²⁺) on ischaemic complications of pathological cardiac hypertrophy are unclear. In this study, we investigated effects of Mg²⁺ pretreatment on ischaemia/reperfusion (I/R) injury in isoprenaline (ISO)-induced hypertrophic hearts. Wistar rats were treated for 7 days with different combinations of ISO (1.25 mg/kg) subcutaneously, MgSO₄ (270 mg/kg) intraperitoneally, or vehicle (saline). On the eighth day, hearts were either subjected to regional I/R during Langendorff perfusion or histologically stained with haematoxylin and eosin and Masson's trichrome. Haemodynamic and electrocardiographic parameters were recorded using the PowerLab data-acquisition system. Infarcts were identified by triphenyltetrazolium chloride staining. Plasma Mg²⁺ was measured using photometric assays. Mg²⁺ pretreatment significantly decreased I/R-induced infarct size (p = 0.001) and the overall arrhythmia score (p < 0.001) of I/R-induced ventricular ectopics, ventricular tachycardia, and ventricular fibrillation in hypertrophic hearts, but not non-hypertrophied hearts. Mg²⁺ also improved post-I/R left ventricular developed pressure in hypertrophic hearts. However, Mg²⁺ did not reverse the ISO-induced myocyte thickening and interstitial fibrosis or increases in heart weight. Plasma Mg²⁺ was not different among treatment groups. These results suggest that Mg²⁺ pretreatment may protect against I/R-induced injury and malignant arrhythmias in hypertrophic hearts, possibly via mechanisms unrelated to long-lasting changes in plasma Mg²⁺ or prevention of structural changes such as fibrosis.

Evaluation of cardiac function in unrestrained dogs and monkeys using left ventricular dP/dt

INTRODUCTION

Preclinical assessment for alterations in cardiac ventricular function for drug candidates has not been a focus of ICH S7b guidelines for cardiovascular safety studies, but there is growing interest given that the cardiovascular risk is associated with positive and negative inotropes.

METHODS

From 2003 through 2013, 163 telemetry studies with left-ventricular function analyses were conducted in dogs and monkeys at Bristol Myers Squibb (BMS) in support for drug development programs. The ability of the telemetry system to detect changes in cardiac contractility was verified with positive control agents pimobendan and atenolol. Control data from a subset of studies were analyzed to determine dP/dt reference range values, and minimum detectable mean differences (control vs. treated) for statistical significance.

RESULTS

Median minimum detectable differences for dogs ranged from 14 to 21% for positive dP/dt and 11 to 21% for negative dP/dt. For monkeys, median minimum detectable differences were 25 and 14% for positive and negative dP/dt, respectively. For BMS programs, 15 drug candidates were identified that produced primary effects on contractility. Changes in contractility that were associated with, and potentially secondary to, drug-related effects on heart rate or systemic blood pressure were observed with an additional 29 drug candidates.

DISCUSSION

Changes in contractility have been observed in large animals during drug development studies at BMS over the past 10years. Model sensitivity has been demonstrated and a dP/dt beat-to-beat cloud analysis tool has been developed to help distinguish primary effects from those potentially secondary to systemic hemodynamic changes.

High throughput physiological screening of iPSC-derived cardiomyocytes for drug development

Cardiac drug discovery is hampered by the reliance on non-human animal and cellular models with inadequate throughput and physiological fidelity to accurately identify new targets and test novel therapeutic strategies. Similarly, adverse drug effects on the heart are challenging to model, contributing to costly failure of drugs during development and even after market launch. Human induced pluripotent stem cell derived cardiac tissue represents a potentially powerful means to model aspects of heart physiology relevant to disease and adverse drug effects, providing both the human context and throughput needed to improve the efficiency of drug development. Here we review emerging technologies for high throughput measurements of cardiomyocyte physiology, and comment on the promises and challenges of using iPSC-derived cardiomyocytes to model disease and introduce the human context into early stages of drug discovery. This article is part of a Special Issue entitled: Cardiomyocyte biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Time-dependent evolution of functional vs. remodeling signaling in induced pluripotent stem cell-derived cardiomyocytes and induced maturation with biomechanical stimulation

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a powerful platform for uncovering disease mechanisms and assessing drugs for efficacy/toxicity. However, the accuracy with which hiPSC-CMs recapitulate the contractile and remodeling signaling of adult cardiomyocytes is not fully known. We used β-adrenergic receptor (β-AR) signaling as a prototype to determine the evolution of signaling component expression and function during hiPSC-CM maturation. In "early" hiPSC-CMs (less than or equal to d 30), β2-ARs are a primary source of cAMP/PKA signaling. With longer culture, β1-AR signaling increases: from 0% of cAMP generation at d 30 to 56.8 ± 6.6% by d 60. PKA signaling shows a similar increase: 15.7 ± 5.2% (d 30), 49.8 ± 0.5% (d 60), and 71.0 ± 6.1% (d 90). cAMP generation increases 9-fold from d 30 to 60, with enhanced coupling to remodeling pathways (e.g., Akt and Ca(2+)/calmodulin-dependent protein kinase type II) and development of caveolin-mediated signaling compartmentalization. By contrast, cardiotoxicity induced by chronic β-AR stimulation, a major component of heart failure, develops much later: 5% cell death at d 30vs 55% at d 90. Moreover, β-AR maturation can be accelerated by biomechanical stimulation. The differential maturation of β-AR functionalvs remodeling signaling in hiPSC-CMs has important implications for their use in disease modeling and drug testing. We propose that assessment of signaling be added to the indices of phenotypic maturation of hiPSC-CMs.-Jung, G., Fajardo, G., Ribeiro, A. J. S., Kooiker, K. B., Coronado, M., Zhao, M., Hu, D.-Q., Reddy, S., Kodo, K., Sriram, K., Insel, P. A., Wu, J. C., Pruitt, B. L., Bernstein, D. Time-dependent evolution of functionalvs remodeling signaling in induced pluripotent stem cell-derived cardiomyocytes and induced maturation with biomechanical stimulation.

Epigenetic Regulation of Phosphodiesterases 2A and 3A Underlies Compromised β-Adrenergic Signaling in an iPSC Model of Dilated Cardiomyopathy

β-adrenergic signaling pathways mediate key aspects of cardiac function. Its dysregulation is associated with a range of cardiac diseases, including dilated cardiomyopathy (DCM). Previously, we established an iPSC model of familial DCM from patients with a mutation in TNNT2, a sarcomeric protein. Here, we found that the β-adrenergic agonist isoproterenol induced mature β-adrenergic signaling in iPSC-derived cardiomyocytes (iPSC-CMs) but that this pathway was blunted in DCM iPSC-CMs. Although expression levels of several β-adrenergic signaling components were unaltered between control and DCM iPSC-CMs, we found that phosphodiesterases (PDEs) 2A and PDE3A were upregulated in DCM iPSC-CMs and that PDE2A was also upregulated in DCM patient tissue. We further discovered increased nuclear localization of mutant TNNT2 and epigenetic modifications of PDE genes in both DCM iPSC-CMs and patient tissue. Notably, pharmacologic inhibition of PDE2A and PDE3A restored cAMP levels and ameliorated the impaired β-adrenergic signaling of DCM iPSC-CMs, suggesting therapeutic potential.

G protein-coupled receptors in cardiac biology: old and new receptors

G protein-coupled receptors (GPCRs) are seven-transmembrane-spanning proteins that mediate cellular and physiological responses. They are critical for cardiovascular function and are targeted for the treatment of hypertension and heart failure. Nevertheless, current therapies only target a small fraction of the cardiac GPCR repertoire, indicating that there are many opportunities to investigate unappreciated aspects of heart biology. Here, we offer an update on the contemporary view of GPCRs and the complexities of their signalling, and review the roles of the 'classical' GPCRs in cardiovascular physiology and disease. We then provide insights into other GPCRs that have been less extensively studied in the heart, including orphan, odorant and taste receptors. We contend that these novel cardiac GPCRs contribute to heart function in health and disease and thereby offer exciting opportunities to therapeutically modulate heart function.

PDE3, but not PDE4, reduces β₁ - and β₂-adrenoceptor-mediated inotropic and lusitropic effects in failing ventricle from metoprolol-treated patients

BACKGROUND AND PURPOSE

PDE3 and/or PDE4 control ventricular effects of catecholamines in several species but their relative effects in failing human ventricle are unknown. We investigated whether the PDE3-selective inhibitor cilostamide (0.3-1 μM) or PDE4 inhibitor rolipram (1-10 μM) modified the positive inotropic and lusitropic effects of catecholamines in human failing myocardium.

EXPERIMENTAL APPROACH

Right and left ventricular trabeculae from freshly explanted hearts of 5 non-β-blocker-treated and 15 metoprolol-treated patients with terminal heart failure were paced to contract at 1 Hz. The effects of (-)-noradrenaline, mediated through β₁ adrenoceptors (β₂ adrenoceptors blocked with ICI118551), and (-)-adrenaline, mediated through β₂ adrenoceptors (β₁ adrenoceptors blocked with CGP20712A), were assessed in the absence and presence of PDE inhibitors. Catecholamine potencies were estimated from -logEC₅₀s.

KEY RESULTS

Cilostamide did not significantly potentiate the inotropic effects of the catecholamines in non-β-blocker-treated patients. Cilostamide caused greater potentiation (P = 0.037) of the positive inotropic effects of (-)-adrenaline (0.78 ± 0.12 log units) than (-)-noradrenaline (0.47 ± 0.12 log units) in metoprolol-treated patients. Lusitropic effects of the catecholamines were also potentiated by cilostamide. Rolipram did not affect the inotropic and lusitropic potencies of (-)-noradrenaline or (-)-adrenaline on right and left ventricular trabeculae from metoprolol-treated patients.

CONCLUSIONS AND IMPLICATIONS

Metoprolol induces a control by PDE3 of ventricular effects mediated through both β₁ and β₂ adrenoceptors, thereby further reducing sympathetic cardiostimulation in patients with terminal heart failure. Concurrent therapy with a PDE3 blocker and metoprolol could conceivably facilitate cardiostimulation evoked by adrenaline through β₂ adrenoceptors. PDE4 does not appear to reduce inotropic and lusitropic effects of catecholamines in failing human ventricle.

Carvedilol induces greater control of β2- than β 1-adrenoceptor-mediated inotropic and lusitropic effects by PDE3, while PDE4 has no effect in human failing myocardium

The β-blockers carvedilol and metoprolol provide important therapeutic strategies for heart failure treatment. Therapy with metoprolol facilitates the control by phosphodiesterase PDE3, but not PDE4, of inotropic effects of catecholamines in human failing ventricle. However, it is not known whether carvedilol has the same effect. We investigated whether the PDE3-selective inhibitor cilostamide (0.3 μM) or PDE4-selective inhibitor rolipram (1 μM) modified the positive inotropic and lusitropic effects of catecholamines in ventricular myocardium of heart failure patients treated with carvedilol. Right ventricular trabeculae from explanted hearts of nine carvedilol-treated patients with terminal heart failure were paced to contract at 1 Hz. The effects of (-)-noradrenaline, mediated through β1-adrenoceptors (β2-adrenoceptors blocked with ICI118551), and (-)-adrenaline, mediated through β2-adrenoceptors (β1-adrenoceptors blocked with CGP20712A), were assessed in the absence and presence of the PDE inhibitors. The inotropic potency, estimated from -logEC50s, was unchanged for (-)-noradrenaline but decreased 16-fold for (-)-adrenaline in carvedilol-treated compared to non-β-blocker-treated patients, consistent with the previously reported β2-adrenoceptor-selectivity of carvedilol. Cilostamide caused 2- to 3-fold and 10- to 35-fold potentiations of the inotropic and lusitropic effects of (-)-noradrenaline and (-)-adrenaline, respectively, in trabeculae from carvedilol-treated patients. Rolipram did not affect the inotropic and lusitropic potencies of (-)-noradrenaline or (-)-adrenaline. Treatment of heart failure patients with carvedilol induces PDE3 to selectively control the positive inotropic and lusitropic effects mediated through ventricular β2-adrenoceptors compared to β1-adrenoceptors. The β2-adrenoceptor-selectivity of carvedilol may provide protection against β2-adrenoceptor-mediated ventricular overstimulation in PDE3 inhibitor-treated patients. PDE4 does not control β1- and β2-adrenoceptor-mediated inotropic and lusitropic effects in carvedilol-treated patients.

Expression, regulation and putative nutrient-sensing function of taste GPCRs in the heart

G protein-coupled receptors (GPCRs) are critical for cardiovascular physiology. Cardiac cells express >100 nonchemosensory GPCRs, indicating that important physiological and potential therapeutic targets remain to be discovered. Moreover, there is a growing appreciation that members of the large, distinct taste and odorant GPCR families have specific functions in tissues beyond the oronasal cavity, including in the brain, gastrointestinal tract and respiratory system. To date, these chemosensory GPCRs have not been systematically studied in the heart. We performed RT-qPCR taste receptor screens in rodent and human heart tissues that revealed discrete subsets of type 2 taste receptors (TAS2/Tas2) as well as Tas1r1 and Tas1r3 (comprising the umami receptor) are expressed. These taste GPCRs are present in cultured cardiac myocytes and fibroblasts, and by in situ hybridization can be visualized across the myocardium in isolated cardiac cells. Tas1r1 gene-targeted mice (Tas1r1(Cre)/Rosa26(tdRFP)) strikingly recapitulated these data. In vivo taste receptor expression levels were developmentally regulated in the postnatal period. Intriguingly, several Tas2rs were upregulated in cultured rat myocytes and in mouse heart in vivo following starvation. The discovery of taste GPCRs in the heart opens an exciting new field of cardiac research. We predict that these taste receptors may function as nutrient sensors in the heart.

Subendocardial increase in reactive oxygen species production affects regional contractile function in ischemic heart failure

AIMS

Heart failure (HF) is characterized by regionalized contractile alterations resulting in loss of the transmural contractile gradient across the left ventricular free wall. We tested whether a regional alteration in mitochondrial oxidative metabolism during HF could affect myofilament function through protein kinase A (PKA) signaling.

RESULTS

Twelve weeks after permanent left coronary artery ligation that induced myocardial infarction (MI), subendocardial (Endo) cardiomyocytes had decreased activity of complex I and IV of the mitochondrial electron transport chain and produced twice more superoxide anions than sham Endo and subepicardial cells. This effect was associated with a reduced antioxidant activity of superoxide dismutase and Catalase only in MI Endo cells. The myofilament contractile properties (Ca(2+) sensitivity and maximal tension), evaluated in skinned cardiomyocytes, were also reduced only in MI Endo myocytes. Conversely, in MI rats treated with the antioxidant N-acetylcysteine (NAC) for 4 weeks, the generation of superoxide anions in Endo cardiomyocytes was normalized and the contractile properties of skinned cardiomyocytes restored. This effect was accompanied by improved in vivo contractility. The beneficial effects of NAC were mediated, at least, in part, through reduction of the PKA activity, which was higher in MI myofilaments, particularly, the PKA-mediated hyperphosphorylation of cardiac Troponin I.

INNOVATION

The Transmural gradient in the mitochondrial content/activity is lost during HF and mediates reactive oxygen species-dependent contractile dysfunction.

CONCLUSIONS

Regionalized alterations in redox signaling affect the contractile machinery of sub-Endo myocytes through a PKA-dependent pathway that contributes to the loss of the transmural contractile gradient and impairs global contractility.

Selective β2-adrenoreceptor stimulation attenuates myocardial cell death and preserves cardiac function after ischemia-reperfusion injury

OBJECTIVE

β(2)-adrenoreceptor activation has been shown to protect cardiac myocytes from cell death. We hypothesized that acute β(2)-adrenoreceptor stimulation, using arformoterol (ARF), would attenuate myocardial ischemia/reperfusion (R) injury via NO synthase activation and cause a subsequent increase in NO bioavailability.

METHODS AND RESULTS

Male C57BL/6J and endothelial NO synthase (eNOS) knockout mice were subjected to 45 minutes of myocardial ischemia and 24 hours of R. ARF or vehicle was administered 5 minutes before R. Serum troponin-I was measured, and infarct size per area-at-risk was evaluated at 24 hours of R. Echocardiography was performed at baseline and 2 weeks after R. Myocardial cAMP, protein kinase A, eNOS/Akt phosphorylation status, and NO metabolite levels were assayed. ARF (1 µg/kg) reduced infarct size per area-at-risk by 53.1% (P<0.001 versus vehicle) and significantly reduced troponin-I levels (P<0.001 versus vehicle). Ejection fraction was significantly preserved in ARF-treated hearts compared with vehicle hearts at 2 weeks of R. Serum cAMP and nuclear protein kinase A C-α increased 5 and 15 minutes after ARF injection, respectively (P<0.01). ARF increased Akt phosphorylation at Thr(308) (P<0.001) and Ser(473) (P<0.01), and eNOS phosphorylation at Ser(1177) (P<0.01). ARF treatment increased heart nitrosothiol levels (P<0.001) at 15 min after injection. ARF failed to reduce infarct size in eNOS(-/-) mice.

CONCLUSIONS

Our results indicate that β(2)-adrenoreceptor stimulation activates cAMP, protein kinase A, Akt, and eNOS and augments NO bioavailability. Activation of this prosurvival signaling pathway attenuates myocardial cell death and preserves cardiac function after ischemia/reperfusion.

Regulation of murine cardiac function by phosphodiesterases type 3 and 4

Cyclic nucleotide phosphodiesterases (PDEs) encompass a large group of enzymes that regulate intracellular levels of two-second messengers, cAMP and cGMP, by controlling the rates of their degradation. More than 60 isoforms, subdivided into 11 gene families (PDE1-11), exist in mammals with at least six families (PDE1-5 and PDE8) identified in mammalian hearts. The two predominant families implicated in regulating contraction strength of the heart are PDE3 and PDE4. Studies using transgenic models in combination with family-specific PDE inhibitors have demonstrated that PDE3A, PDE4B, and PDE4D isoforms regulate cardiac contractility by modulating cAMP levels in various subcellular compartments. These studies have further uncovered contributions of PDE4B and PDE4D in preventing ventricular arrhythmias.

Differential regulation of β2 -adrenoceptor-mediated inotropic and lusitropic response by PDE3 and PDE4 in failing and non-failing rat cardiac ventricle

BACKGROUND AND PURPOSE

β-Adrenoceptors play a major role in regulating myocardial function through cAMP-dependent pathways. Different phosphodiesterases (PDEs) regulate intracellular cAMP-pools and thereby contribute to the compartmentalization of cAMP-dependent effects. We explored the involvement of PDEs in limiting the β(2) adrenoceptor-mediated positive inotropic (PIR) and lusitropic (LR) responses in sham-operated (Sham) and failing rat hearts.

EXPERIMENTAL APPROACH

Extensive myocardial infarctions were induced by coronary artery ligation in Wistar rats. Rats developing heart failure were studied 6 weeks after surgery. Contractility was measured in left ventricular strips from failing and Sham hearts. cAMP was quantified by RIA.

KEY RESULTS

In ventricular strips, stimulation of β(2) -adrenoceptors with (-)-adrenaline (300 nM CGP20712A present) exerted a small PIR and LR. In Sham hearts, β(2) -adrenoceptor-mediated as well as β(1) -adrenoceptor-mediated PIR and LR were increased by selective inhibition of either PDE3 (1 µM cilostamide) or PDE4 (10 µM rolipram). In failing rat hearts, PDE3 inhibition enhanced PIR and LR to both β(1) - and β(2) -adrenoceptor stimulation while PDE4 inhibition had no effect on these responses despite a significant increase in cAMP levels. Combined PDE3/4 inhibition further enhanced the PIR and LR of β(2) - and β(1) -adrenoceptor activation both in Sham and failing hearts, compared with PDE3 inhibition alone. PDE4 enzyme activity was reduced in failing hearts.

CONCLUSIONS AND IMPLICATIONS

Both PDE3 and PDE4 attenuated β(2) - and β(1) -adrenoceptor-mediated contractile responses in Sham hearts. In failing hearts, these responses are attenuated solely by PDE3 and thus even selective PDE3 inhibitors may provide a profound enhancement of β-adrenoceptor-mediated responses in heart failure.

Beneficial effects of SR33805 in failing myocardium

AIMS

SR33805, a potent Ca(2+) channel blocker, increases cardiac myofilament Ca(2+) sensitivity in healthy rat cardiomyocytes. Therefore, the aim of the present study was to evaluate the effects of SR33805 on contractile properties in ischaemic failing hearts after myocardial infarction (MI) in vivo and in vitro at the cellular level.

METHODS AND RESULTS

The effect of SR33805 (10 µM) was tested on the excitation-contraction coupling of cardiomyocytes isolated from rat with end-stage heart failure. Cell shortening and Ca(2+) transients were measured in intact cardiomyocytes, while contractile properties were determined in Triton X-100 permeabilized myocytes. Acute treatment with SR33805 restored the MI-altered cell shortening without affecting the Ca(2+) transient amplitude, suggesting an increase of myofilament Ca(2+) sensitivity in MI myocytes. Indeed, a SR33805-induced sensitization of myofilament activation was found to be associated with a slight increase in myosin light chain-2 phosphorylation and a more significant decrease on troponin I (TnI) phosphorylation. Decreased TnI phosphorylation was related to inhibition of protein kinase A activity by SR33805. Finally, administration of a single intra-peritoneal bolus of SR33805 (20 mg/kg) improved end-systolic strain and fractional shortening of MI hearts.

CONCLUSION

The present study indicates that treatment with SR33805 improved contractility of ischaemic failing hearts after MI in the rat by selectively modulating the phosphorylation status of sarcomeric regulatory proteins, which then sensitized the myofilaments to Ca(2+). Our results gave a proof of concept that manipulation of the Ca(2+) sensitivity of sarcomeric regulatory proteins can be used to improve contractility of a failing heart.

Distinctive ERK and p38 signaling in remote and infarcted myocardium during post-MI remodeling in the mouse

Global activation of MAP kinases has been reported in both human and experimental heart failure. Chronic remodeling of the surviving ventricular wall after myocardial infarction (MI) involves both myocyte loss and fibrosis; we hypothesized that this cardiomyopathy involves differential shifts in pro- and anti-apoptotic MAP kinase signaling in cardiac myocyte (CM) and non-myocyte. Cardiomyopathy after coronary artery ligation in mice was characterized by echocardiography, ex vivo Langendorff preparation, histologic analysis and measurements of apoptosis. Phosphorylation (activation) of signaling molecules was analyzed by Western blot, ELISA and immunohistochemistry. Post-MI remodeling involved dramatic changes in the phosphorylation of both stress-activated MAP (SAP) kinase p38 as well as ERK, a known mediator of cell survival, but not of SAP kinase JNK or the anti-apoptotic mediator of PI3K, Akt. Phosphorylation of p38 rose early after MI in the infarct, whereas a more gradual rise in the remote myocardium accompanied a rise in apoptosis in that region. In both areas, ERK phosphorylation was lowest early after MI and rose steadily thereafter, though infarct phosphorylation was consistently higher. Immunostaining of p-ERK localized to fibrotic areas populated primarily by non-myocytes, whereas staining of p38 phosphorylation was stronger in areas of progressive CM apoptosis. Relative segregation of CMs and non-myocytes in different regions of the post-MI myocardium revealed signaling patterns that imply cell type-specific changes in pro- and anti-apoptotic MAP kinase signaling. Prevention of myocyte loss and of LV remodeling after MI may therefore require cell type-specific manipulation of p38 and ERK activation.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Beta2-adrenergic receptor redistribution in heart failure changes cAMP compartmentation

The beta1- and beta2-adrenergic receptors (betaARs) on the surface of cardiomyocytes mediate distinct effects on cardiac function and the development of heart failure by regulating production of the second messenger cyclic adenosine monophosphate (cAMP). The spatial localization in cardiomyocytes of these betaARs, which are coupled to heterotrimeric guanine nucleotide-binding proteins (G proteins), and the functional implications of their localization have been unclear. We combined nanoscale live-cell scanning ion conductance and fluorescence resonance energy transfer microscopy techniques and found that, in cardiomyocytes from healthy adult rats and mice, spatially confined beta2AR-induced cAMP signals are localized exclusively to the deep transverse tubules, whereas functional beta1ARs are distributed across the entire cell surface. In cardiomyocytes derived from a rat model of chronic heart failure, beta2ARs were redistributed from the transverse tubules to the cell crest, which led to diffuse receptor-mediated cAMP signaling. Thus, the redistribution of beta(2)ARs in heart failure changes compartmentation of cAMP and might contribute to the failing myocardial phenotype.

The rush to adrenaline: drugs in sport acting on the beta-adrenergic system

Athletes attempt to improve performance with drugs that act on the beta-adrenergic system directly or indirectly. Of three beta-adrenoceptor (AR) subtypes, the beta(2)-AR is the main target in sport; they have bronchodilator and anabolic actions and enhance anti-inflammatory actions of corticosteroids. Although demonstrable in animal experiments and humans, there is little evidence that these properties can significantly improve performance in trained athletes. Their actions may also be compromised by receptor desensitization and by common, naturally occurring receptor mutations (polymorphisms) that can influence receptor signalling and desensitization properties in individuals. Indirectly acting agents affect release and reuptake of noradrenaline and adrenaline, thereby influencing all AR subtypes including the three beta-ARs. These agents can have potent psychostimulant effects that provide an illusion of better performance that does not usually translate into improvement in practice. Amphetamines and cocaine also have considerable potential for cardiac damage. beta-AR antagonists (beta-blockers) are used in sports that require steadiness and accuracy, such as archery and shooting, where their ability to reduce heart rate and muscle tremor may improve performance. They have a deleterious effect in endurance sports because they reduce physical performance and maximum exercise load. Recent studies have identified that many beta-AR antagonists not only block the actions of agonists but also activate other (mitogen-activated PK) signalling pathways influencing cell growth and fate. The concept that many compounds previously regarded as 'blockers' may express their own spectrum of pharmacological properties has potentially far-reaching consequences for the use of drugs both therapeutically and illicitly.

Arrhythmogenic effects of beta2-adrenergic stimulation in the failing heart are attributable to enhanced sarcoplasmic reticulum Ca load

Ventricular tachycardia in heart failure (HF) can initiate by nonreentrant mechanisms such as delayed afterdepolarizations. In an arrhythmogenic rabbit model of HF, we have shown that isoproterenol induces ventricular tachycardia in vivo and aftercontractions and transient inward currents in HF myocytes. To determine whether beta(2)-adrenergic receptor (beta(2)-AR) stimulation contributes, we performed in vivo drug infusion, in vitro myocyte and biochemical studies. Intravenous zinterol (2.5 microg/kg) led to ventricular arrhythmias, including ventricular tachycardia up to 13 beats long in 4 of 6 HF rabbits (versus 0 of 5 controls, P<0.01), an effect blocked by beta(2)-AR antagonist ICI-118,551 (0.2 mg/kg). In field-stimulated myocytes (0.5 to 4 Hz, 37 degrees C), beta(2)-AR stimulation (1 micromol/L zinterol+300 nmol/L beta(1)-AR antagonist CGP-29712A) induced aftercontractions and Ca aftertransients in 88% of HF versus 0% of control myocytes (P<0.01). beta(2)-AR stimulation in HF (but not control) myocytes increased Ca transient amplitude (by 29%), sarcoplasmic reticulum (SR) Ca load (by 28%), the rate of [Ca](i) decline (by 28%; n=12, all P<0.05), and phospholamban phosphorylation at Ser16, but Ca current was unchanged. All of these effects in HF myocytes were blocked by ICI-118,551 (100 nmol/L). Although total beta-AR expression was reduced by 47% in HF rabbit left ventricle, beta(2)-AR number was unchanged, indicating more potent beta(2)-AR-dependent SR Ca uptake and arrhythmogenesis in HF. Human HF myocytes showed similar beta(2)-AR-induced aftercontractions, aftertransients, and enhanced Ca transient amplitude, SR Ca load and twitch [Ca](i) decline rate. Thus, beta(2)-AR stimulation is arrhythmogenic in HF, mediated by SR Ca overload-induced spontaneous SR Ca release and aftercontractions.

Chronic beta2-adrenoceptor stimulation impairs cardiac relaxation via reduced SR Ca2+-ATPase protein and activity

We determined the cardiovascular effects of chronic beta2-adrenoceptor (beta2-AR) stimulation in vivo and examined the mechanism for the previously observed prolonged diastolic relaxation. Rats (3 mo old; n = 6), instrumented with implantable radiotelemeters, received the selective beta2-AR agonist formoterol (25 microg.kg(-1).day(-1) ip) for 4 wk, with selected cardiovascular parameters measured daily throughout this period, and for a further 7 days after cessation of treatment. Chronic beta2-AR stimulation was associated with an increase in heart rate (HR) of 17% (days 1-14) and 5% (days 15-28); a 11% (days 1-14) and 6% (days 15-28) decrease in mean arterial blood pressure; and a 24% (days 1-14) increase in the rate of cardiac relaxation (-dP/dt) compared with initial values (P < 0.05). Cessation of beta2-AR stimulation resulted in an 8% decrease in HR and a 7% decrease in -dP/dt, compared with initial values (P < 0.05). The prolonged cardiac relaxation with chronic beta2-AR stimulation was associated with a 30% decrease in the maximal rate (Vmax) of sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) activity, likely attributed to a 50% decrease in SERCA2a protein (P < 0.05). glycogen synthase kinase-3beta (GSK-3beta) has been implicated as a negative regulator of SERCA2 gene transcription, and we observed a approximately 60% decrease (P < 0.05) in phosphorylated GSK-3beta protein after chronic beta2-AR stimulation. Finally, we found a 40% decrease (P < 0.05) in the mRNA expression of the novel A kinase anchoring protein AKAP18, also implicated in beta2-AR-mediated cardiac relaxation. These findings highlight some detrimental cardiovascular effects of chronic beta2-AR agonist administration and identify concerns for their current and future use for treating asthma or for conditions where muscle wasting and weakness are indicated.

HUMAN HEART ?-ADRENOCEPTORS: ?1-ADRENOCEPTOR DIVERSIFICATION THROUGH ?AFFINITY STATES? AND POLYMORPHISM

1. In atrium and ventricle from failing and non-failing human hearts, activation of beta(1)- or beta(2)-adrenoceptors causes increases in contractile force, hastening of relaxation, protein kinase A-catalysed phosphorylation of proteins implicated in the hastening of relaxation, phospholamban, troponin I and C-protein, consistent with coupling of both beta(1)- and beta(2)-adrenoceptors to stimulatory G(salpha)-protein but not inhibitory G(ialpha)-protein. 2. Two 'affinity states', namely beta(1H) and beta(1L), of the beta(1)-adrenoceptor exist. In human heart, noradrenaline elicits powerful increases in contractile force and hastening of relaxation. These effects are blocked with high affinity by beta-adenoceptor antagonists, including propranolol, (-)-pindolol, (-)-CGP 12177 and carvedilol. Some beta-blockers, typified by (-)-pindolol and (-)-CGP 12177, not only block the receptor, but also activate it, albeit at much higher concentrations (approximately 2 log units) than those required to antagonize the effects of catecholamines. In human heart, both (-)-CGP 12177 and (-)-pindolol increase contractile force and hasten relaxation. However, the involvement of the beta(1)-adrenoceptor was not immediately obvious because (-)-pindolol- and (-)-CGP 12177-evoked responses were relatively resistant to blockade by (-)-propranolol. Abrogation of cardiostimulant effects of (-)-CGP 12177 in beta(1)-/beta(2)-adrenoceptor double-knockout mice, but not beta(2)-adrenoceptor-knockout mice, revealed an obligatory role of the beta(1)-adrenoceptor. On the basis of these results, two 'affinity states' have been designated, the beta(1H)- and beta(1L)-adrenoceptor, where the beta(1H)-adrenoceptor is activated by noradrenaline and blocked with high affinity by beta-blockers and the beta(1L)-adrenoceptor is activated by drugs such as (-)-CGP 12177 and (-)-pindolol and blocked with low affinity by beta-blockers such as (-)-propranolol. The beta(1H)- and beta(1L)-adrenoceptor states are consistent with high- and low-affinity binding sites for (-)-[(3)H]-CGP 12177 radioligand binding found in cardiac muscle and recombinant beta(1)-adrenoceptors. 3. There are two common polymorphic locations of the beta(1)-adrenoceptor, at amino acids 49 (Ser/Gly) and 389 (Arg/Gly). Their existence has raised several questions, including their role in determining the effectiveness of heart failure treatment with beta-blockers. We have investigated the effect of long-term maximally tolerated carvedilol administration (> 1 year) on left ventricular ejection fraction (LVEF) in patients with non-ischaemic cardiomyopathy (mean left ventricular ejection fraction 23 +/- 7%; n = 135 patients). The administration of carvedilol improved LVEF to 37 +/- 13% (P < 0.005); however, the improvement was variable, with 32% of patients showing pound 5% improvement. Upon segregation of patients into Arg389Gly-beta(1)-adrenoceptors, it was found that carvedilol caused a greater increase in left ventricular ejection faction in patients carrying the Arg389 allele with Arg389Arg > Arg389Gly > Gly389Gly.

Arginine 16 Glycine β2-Adrenoceptor Polymorphism and Cardiovascular Structure and Function in Patients with Heart Failure

The beta2/beta1 adrenoceptor ratio increases in congestive heart failure (CHF), making the heart relatively more dependent on inotropic, lusitropic, and chronotropic stimulation by the beta2-adrenergic receptor (ADRB2). In healthy human beings, those who are homozygous for arginine (Arg) at amino acid 16 of the ADRB2 have reduced receptor function when compared with individuals homozygous for glycine (Gly) at this position. The cardiovascular effects of the Arg16Gly polymorphism of the ADRB2 in CHF are not well understood. The aim of this study was to examine the influence of common polymorphisms of the ADRB2 on cardiovascular structure and function in patients with CHF. Echocardiography, neurohormonal assays, and exercise tests were performed in 68 healthy individuals and 95 patients with CHF. All of the patients with CHF were stable, New York Heart Association class II to III, of ischemic or nonischemic cause, with an ejection fraction of 40% or less. Of the patients with CHF, 16 were Arg/Arg, 36 were Arg/Gly, and 43 were Gly/Gly at amino acid 16. In those without CHF, the Arg16Gly polymorphism of the ADRB2 had no effect on cardiovascular function. In contrast, in CHF, Arg/Arg homozygotes had higher plasma norepinephrine and atrial natriuretic peptide levels, greater left atrial diastolic dimension, higher peak velocity of early/late diastolic filling ratio, and shorter deceleration time compared with Gly16 homozygotes. Furthermore, Arg16 homozygotes had reduced exercise tolerance compared with Gly16 homozygotes (evidenced by shorter exercise duration and lower peak oxygen consumption per unit time), and a lesser chronotropic response to exercise. In patients with CHF, but not in demographically matched healthy persons, the Arg16Gly polymorphism of the ADRB2 exerts important effects on cardiovascular structure and function, neurohormonal activation, and exercise tolerance.