Therapeutic efficacy of a combination of a beta1-adrenoreceptor (AR) blocker and beta2-AR agonist in a rat model of postmyocardial infarction dilated heart failure exceeds that of a beta1-AR blocker plus angiotensin-converting enzyme inhibitor

Early donepezil monotherapy or combination with metoprolol significantly prevents subsequent chronic heart failure in rats with reperfused myocardial infarction

Despite the presence of clinical guidelines recommending that β-blocker treatment be initiated early after reperfused myocardial infarction (RMI), acute myocardial infarction remains a leading cause of chronic heart failure (CHF). In this study, we compared the effects of donepezil, metoprolol, and their combination on the progression of cardiac remodeling in rats with RMI. The animals were randomly assigned to untreated (UT), donepezil-treated (DT), metoprolol-treated (MT), and a combination of donepezil and metoprolol (DMT) groups. On day 8 after surgery, compared to the UT, the DT and DMT significantly improved myocardial salvage, owing to the suppression of macrophage infiltration and apoptosis. After the 10-week treatment, the DT and DMT exhibited decreased heart rate, reduced myocardial infarct size, attenuated cardiac dysfunction, and decreased plasma levels of brain natriuretic peptide and catecholamine, thereby preventing subsequent CHF. These results suggest that donepezil monotherapy or combined therapy with β-blocker may be an alternative pharmacotherapy post-RMI.

Role of β-Adrenergic Receptors and Estrogen in Cardiac Repair after Myocardial Infarction: An Overview

Acute myocardial infarction (MI) is associated with an intense inflammatory response that is critical for cardiac repair but is also involved in the pathogenesis of adverse cardiac remodeling, i.e., the set of size, geometry, and structure changes that represent the structural substrate for the development of post-MI heart failure. Deciphering the pathophysiological mechanisms underlying cardiac repair after MI is, therefore, critical to favorably regulate cardiac wound repair and to prevent development of heart failure. Catecholamines and estrogen play an active role in regulating the inflammatory response in the infarcted area. For example, stress-induced catecholamines alter recruitment and trafficking of leukocytes to the heart. Additionally, estrogen affects rate of cardiac rupture during the acute phase of MI, as well as infarct size and survival in animal models of MI. In this review, we will summarize the role of β-adrenergic receptors and estrogen in cardiac repair after infarction in preclinical studies.

Recent Advances in β2-Agonists for Treatment of Chronic Respiratory Diseases and Heart Failure

β₂-Adrenoceptor (β₂-AR) agonists are widely used as bronchodilators. The emerge of ultralong acting β₂-agonists is an important breakthrough in pulmonary medicine. In this review, we will provide mechanistic insights into the application of β₂-agonists in asthma, chronic obstructive pulmonary disease (COPD), and heart failure (HF). Recent studies in β-AR signal transduction have revealed opposing functions of the β₁-AR and the β₂-AR on cardiomyocyte survival. Thus, β₂-agonists and β-blockers in combination may represent a novel strategy for HF management. Allosteric modulation and biased agonism at the β₂-AR also provide a theoretical basis for developing drugs with novel mechanisms of action and pharmacological profiles. Overlap of COPD and HF presents a substantial clinical challenge but also a unique opportunity for evaluation of the cardiovascular safety of β₂-agonists. Further basic and clinical research along these lines can help us develop better drugs and innovative strategies for the management of these difficult-to-treat diseases.

Impact of Peripheral α7-Nicotinic Acetylcholine Receptors on Cardioprotective Effects of Donepezil in Chronic Heart Failure Rats

PURPOSE

Pharmacological modulation of parasympathetic activity with donepezil, an acetylcholinesterase inhibitor, improves the long-term survival of rats with chronic heart failure (CHF) after myocardial infarction (MI). However, its mechanism is not well understood. The α7-nicotinic acetylcholine receptor (α7-nAChR) reportedly plays an important role in the cholinergic anti-inflammatory pathway. The purpose of this study was to examine whether blockade of α7-nAChR, either centrally or peripherally, affects cardioprotection by donepezil during CHF.

METHODS

One-week post-MI, the surviving rats were implanted with an electrocardiogram or blood pressure transmitter to monitor hemodynamics continuously. Seven days after implantation, the MI rats (n = 74) were administered donepezil in drinking water or were untreated (UT). Donepezil-treated MI rats were randomly assigned to the following four groups: peripheral infusion of saline (SPDT) or an α7-nAChR antagonist methyllycaconitine (α7PDT), and brain infusion of saline (SBDT) or the α7-nAChR antagonist (α7BDT).

RESULTS

After the 4-week treatment, the role of α7-nAChR was evaluated using hemodynamic parameters, neurohumoral states, and histological and morphological assessment. Between the peripheral infusion groups, α7PDT (vs. SPDT) showed significantly increased heart weight and cardiac fibrosis, deteriorated hemodynamics, increased plasma neurohumoral and cytokine levels, and significantly decreased microvessel density (as assessed by anti-von Willebrand factor-positive cells). In contrast, between the brain infusion groups, α7BDT (vs. SBDT) showed no changes in either cardiac remodeling or hemodynamics.

CONCLUSION

Peripheral blockade of α7-nAChR significantly attenuated the cardioprotective effects of donepezil in CHF rats, whereas central blockade did not. This suggests that peripheral activation of α7-nAChR plays an important role in cholinergic pharmacotherapy for CHF.

Discovery of β-arrestin-biased β2-adrenoceptor agonists from 2-amino-2-phenylethanol derivatives

β-Arrestins are a small family of proteins important for signal transduction at G protein-coupled receptors (GPCRs). β-Arrestins are involved in the desensitization of GPCRs. Recently, biased ligands possessing different efficacies in activating the G protein- versus the β-arrestin-dependent signals downstream of a single GPCR have emerged, which can be used to selectively modulate GPCR signal transduction in such a way that desirable signals are enhanced to produce therapeutic effects while undesirable signals of the same GPCR are suppressed to avoid side effects. In the present study, we evaluated agonist bias for compounds developed along a drug discovery project of β₂-adrenoceptor agonists. About 150 compounds, including derivatives of fenoterol, 2-amino-1-phenylethanol and 2-amino-2-phenylethanol, were obtained or synthesized, and initially screened for their β-adrenoceptor-mediated activities in the guinea pig tracheal smooth muscle relaxation assay or the cardiomyocyte contractility assay. Nineteen bioactive compounds were further assessed using both the HTRF cAMP assay and the PathHunter β-arrestin assay. Their concentration-response data in stimulating cAMP synthesis and β-arrestin recruitment were applied to the Black-Leff operational model for ligand bias quantitation. As a result, three compounds (L-2, L-4, and L-12) with the core structure of 5-(1-amino-2-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one were identified as a new series of β-arrestin-biased β₂-adrenoceptor agonists, whereas salmeterol was found to be G_s-biased. These findings would facilitate the development of novel drugs for the treatment of both heart failure and asthma.

Mitochondrial function remains impaired in the hypertrophied right ventricle of pulmonary hypertensive rats following short duration metoprolol treatment

Pulmonary hypertension (PH) increases the work of the right ventricle (RV) and causes right-sided heart failure. This study examined RV mitochondrial function and ADP transfer in PH animals advancing to right heart failure, and investigated a potential therapy with the specific β1-adrenergic-blocker metoprolol. Adult Wistar rats (317 ± 4 g) were injected either with monocrotaline (MCT, 60 mg kg-1) to induce PH, or with an equivalent volume of saline for controls (CON). At three weeks post-injection the MCT rats began oral metoprolol (10 mg kg-1 day-1-) or placebo treatment until heart failure was observed in the MCT group. Mitochondrial function was then measured using high-resolution respirometry from permeabilised RV fibres. Relative to controls, MCT animals had impaired mitochondrial function but maintained coupling between myofibrillar ATPases and mitochondria, despite an increase in ADP diffusion distances. Cardiomyocytes from the RV of MCT rats were enlarged, primarily due to an increase in myofibrillar protein. The ratio of mitochondria per myofilament area was decreased in both MCT groups (p ≤ 0.05) in comparison to control (CON: 1.03 ± 0.04; MCT: 0.74 ± 0.04; MCT + BB: 0.74 ± 0.03). This not only implicates impaired energy production in PH, but also increases the diffusion distance for metabolites within the MCT cardiomyocytes, adding an additional hindrance to energy supply. Together, these changes may limit energy supply in MCT rat hearts, particularly at high cardiac workloads. Metoprolol treatment did not delay the onset of heart failure symptoms, improve mitochondrial function, or regress RV hypertrophy.

Prolonged elevated levels of c-kit+ progenitor cells after a myocardial infarction by beta 2 adrenergic receptor priming

Endogenous progenitor cells may participate in cardiac repair after a myocardial infarction (MI). The beta 2 adrenergic receptor (ß2-AR) pathway induces proliferation of c-kit+ cardiac progenitor cells (CPC) in vitro. We investigated if ß2-AR pharmacological stimulation could ameliorate endogenous CPC-mediated regeneration after a MI. C-kit+ CPC ß1-AR and ß2-AR expression was evaluated in vivo and in vitro. A significant increase in the percentage of CPCs expressing ß1-AR and ß2-AR was measured 7 days post-MI. Accordingly, 24 hrs of low serum and hypoxia in vitro significantly increased CPC ß2-AR expression. Cell viability and differentiation assays validated a functional role of CPC ß2-AR. The effect of pharmacological activation of ß2-AR was studied in C57 mice using fenoterol administered in the drinking water 1 week before MI or sham surgery or at the time of the surgery. MI induced a significant increase in the percentage of c-kit+ progenitor cells at 7 days, whereas pretreatment with fenoterol prolonged this response resulting in a significant elevated number of CPC up to 21 days post-MI. This increased number of CPC correlated with a decrease in infarct size. The immunofluorescence analysis of the heart tissue for proliferation, apoptosis, macrophage infiltration, cardiomyocytes surface area, and vessel density showed significant changes on the basis of surgery but no benefit due to fenoterol treatment. Cardiac function was not ameliorated by fenoterol administration when evaluated by echocardiography. Our results suggest that ß2-AR stimulation may improve the cardiac repair process by supporting an endogenous progenitor cell response but is not sufficient to improve the cardiac function.

Inhaled therapies and cardiovascular risk in patients with chronic obstructive pulmonary disease

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) therapy includes a multi-dimensional approach, taking into account both symptoms of the patient and the number of acute exacerbations of COPD (AECOPDs). There are three main pharmaceutical classes currently available including long-acting muscarinic antagonists (LAMA), long-acting β₂-agonists (LABA) and inhaled corticosteroids (ICS). COPD is a major risk factor for most cardiovascular diseases, and cardiac comorbidities are very common in COPD patients. Both LAMA and LABA have a considerable impact on cardiac function by stimulating cardiac β2-adrenergic receptors or inhibiting the heart M₂ muscarinic receptors. ICS alone or in combination has never been associated with a real cardiovascular risk.

AREAS COVERED

This review explores the data published on the safety of COPD therapy and the implications for current pharmacotherapy.

EXPERT OPINION

Several studies have confirmed the good safety profile of bronchodilators available both in monotherapy and in association with other bronchodilators of different classes or with ICS despite the device used. Cardiovascular events in clinical trials are generally low and balanced between groups. The actual cardiovascular risk of fixed-dose combinations (FDCs) in an unselected COPD population will need to be investigated through post-marketing surveillance studies and observational studies.

Leukocyte-Expressed β2-Adrenergic Receptors Are Essential for Survival After Acute Myocardial Injury

BACKGROUND

Immune cell-mediated inflammation is an essential process for mounting a repair response after myocardial infarction (MI). The sympathetic nervous system is known to regulate immune system function through β-adrenergic receptors (βARs); however, their role in regulating immune cell responses to acute cardiac injury is unknown.

METHODS

Wild-type (WT) mice were irradiated followed by isoform-specific βAR knockout (βARKO) or WT bone-marrow transplantation (BMT) and after full reconstitution underwent MI surgery. Survival was monitored over time, and alterations in immune cell infiltration after MI were examined through immunohistochemistry. Alterations in splenic function were identified through the investigation of altered adhesion receptor expression.

RESULTS

β2ARKO BMT mice displayed 100% mortality resulting from cardiac rupture within 12 days after MI compared with ≈20% mortality in WT BMT mice. β2ARKO BMT mice displayed severely reduced post-MI cardiac infiltration of leukocytes with reciprocally enhanced splenic retention of the same immune cell populations. Splenic retention of the leukocytes was associated with an increase in vascular cell adhesion molecule-1 expression, which itself was regulated via β-arrestin-dependent β2AR signaling. Furthermore, vascular cell adhesion molecule-1 expression in both mouse and human macrophages was sensitive to β2AR activity, and spleens from human tissue donors treated with β-blocker showed enhanced vascular cell adhesion molecule-1 expression. The impairments in splenic retention and cardiac infiltration of leukocytes after MI were restored to WT levels via lentiviral-mediated re-expression of β2AR in β2ARKO bone marrow before transplantation, which also resulted in post-MI survival rates comparable to those in WT BMT mice.

CONCLUSIONS

Immune cell-expressed β2AR plays an essential role in regulating the early inflammatory repair response to acute myocardial injury by facilitating cardiac leukocyte infiltration.

Effects of chronic treatment with the new ultra-long-acting β2 -adrenoceptor agonist indacaterol alone or in combination with the β1 -adrenoceptor blocker metoprolol on cardiac remodelling

BACKGROUND AND PURPOSE

The ability of a chronic treatment with indacaterol, a new ultra-long-acting β2 -adrenoceptor agonist, to reverse cardiac remodelling and its effects in combination with metoprolol, a selective β1 -adrenoceptor antagonist, were investigated on myocardial infarction in a rat model of heart failure (HF).

EXPERIMENTAL APPROACH

We investigated the effects of indacaterol and metoprolol, administered alone or in combination, on myocardial histology, β-adrenoceptor-mediated pathways, markers of remodelling and haemodynamic parameters in a rat model of HF. Five groups of rats were assessed: sham-operated rats; HF rats; HF + indacaterol 0.3 mg·kg(-1) ·day(-1) ; HF + metoprolol 100 mg·kg(-1) ·day(-1) ; HF + metoprolol + indacaterol. All pharmacological treatments continued for 15 weeks.

KEY RESULTS

Treatment with either indacaterol or metoprolol significantly reduced the infarct size in HF rats. However, the combination of indacaterol and metoprolol reduced the infarct size even further, reduced both BP and heart rate, reversed the decrease in ejection fraction, normalized left ventricular systolic and diastolic internal diameters, normalized the decreased β1 adrenoceptor mRNA expression as well as cardiac cAMP levels and reduced cardiac GPCR kinase 2 expression, compared with the untreated HF group.

CONCLUSION AND IMPLICATIONS

The results of our study demonstrated an additive interaction between indacaterol and metoprolol in normalizing and reversing cardiac remodelling in our experimental model of HF. The translation of these findings to clinical practice might be of interest, as this combination of drugs could be safer and more effective in patients suffering from HF and COPD.

Advances in receptor conformation research: the quest for functionally selective conformations focusing on the β2-adrenoceptor

Seven-transmembrane receptors, also called GPCRs, represent the largest class of drug targets. Upon ligand binding, a GPCR undergoes conformational rearrangement and thereby changes its interaction with effector proteins including the cognate G-proteins and the multifunctional adaptor proteins, β-arrestins. These proteins, by initiating distinct signal transduction mechanisms, mediate one or several functional responses. Recently, the concept of ligand-directed GPCR signalling, also called functional selectivity or biased agonism, has been proposed to explain the phenomenon that chemically diverse ligands exhibit different efficacies towards the different signalling pathways of a single GPCR, and thereby act as functionally selective or 'biased' ligands. Current concepts support the notion that ligand-specific GPCR conformations are the basis of ligand-directed signalling. Multiple studies using fluorescence spectroscopy, X-ray crystallography, mass spectroscopy, nuclear magnetic resonance spectroscopy, single-molecule force spectroscopy and other techniques have provided the evidence to support this notion. It is anticipated that these techniques will ultimately help elucidate the structural basis of ligand-directed GPCR signalling at a precision meaningful for structure-based drug design and how a specific ligand molecular structure induces a unique receptor conformation leading to biased signalling. In this review, we will summarize recent advances in experimental techniques applied in the study of functionally selective GPCR conformations and breakthrough data obtained in these studies particularly those of the β2-adrenoceptor.

Biased β2-adrenoceptor signalling in heart failure: pathophysiology and drug discovery

The body is constantly faced with a dynamic requirement for blood flow. The heart is able to respond to these changing needs by adjusting cardiac output based on cues emitted by circulating catecholamine levels. Cardiac β-adrenoceptors transduce the signal produced by catecholamine stimulation via Gs proteins to their downstream effectors to increase heart contractility. During heart failure, cardiac output is insufficient to meet the needs of the body; catecholamine levels are high and β-adrenoceptors become hyperstimulated. The hyperstimulated β1-adrenoceptors induce a cardiotoxic effect, which could be counteracted by the cardioprotective effect of β2-adrenoceptor-mediated Gi signalling. However, β2-adrenoceptor-Gi signalling negates the stimulatory effect of the Gs signalling on cardiomyocyte contraction and further exacerbates cardiodepression. Here, further to the localization of β1- and β2-adrenoceptors and β2-adrenoceptor-mediated β-arrestin signalling in cardiomyocytes, we discuss features of the dysregulation of β-adrenoceptor subtype signalling in the failing heart, and conclude that Gi-biased β2-adrenoceptor signalling is a pathogenic pathway in heart failure that plays a crucial role in cardiac remodelling. In contrast, β2-adrenoceptor-Gs signalling increases cardiomyocyte contractility without causing cardiotoxicity. Finally, we discuss a novel therapeutic approach for heart failure using a Gs-biased β2-adrenoceptor agonist and a β1-adrenoceptor antagonist in combination. This combination treatment normalizes the β-adrenoceptor subtype signalling in the failing heart and produces therapeutic effects that outperform traditional heart failure therapies in animal models. The present review illustrates how the concept of biased signalling can be applied to increase our understanding of the pathophysiology of diseases and in the development of novel therapies.

Effects of β-adrenoceptor subtypes on cardiac function in myocardial infarction rats exposed to fine particulate matter (PM 2.5)

The pathophysiological mechanisms of heart failure (HF) stems were mainly from longstanding overactivation of the sympathetic nervous system and renin-angiotensin-aldosterone system. Recent studies highlighted the potential benefits of β1-adrenoceptor (β1-AR) blocker combined with β2-adrenergic receptor (β2-AR) agonist in patients with HF. Long-term exposure to fine particulate air pollution, such as particulate matter ≤ 2.5 μm in diameter (PM_2.5), has been found associated with acute myocardial infarction (AMI) which is the most common cause of congestive HF. In this study, we have investigated the effect of combined metoprolol and terbutaline on cardiac function in a rat model of AMI exposed to PM_2.5. Our results demonstrated that short-term exposure to PM_2.5 contributes to aggravate cardiac function in rats with myocardial infarction. The combined use of β1-AR blocker and β2-AR agonist is superior to β1-AR blocker alone for the treatment of AMI rats exposed to PM_2.5. The combination of β1-AR blocker and β2-AR agonist may decrease the mortality of patients with myocardial infarction who have been exposed to PM_2.5.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat

BACKGROUND

Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects.

METHODS

A total of 60 male Sprague-Dawley rats were subjected to 60 min of coronary artery occlusion and 120 min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (α/β myosin heavy chains, α-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase).

RESULTS

Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7 ± 0.1 vs. 0.9 ± 0.3 and 1.0 ± 0.3g/ml), better ejection fraction (62 ± 9 vs. 49 ± 7 and 35 ± 6%), and reduced expression of β-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable.

CONCLUSIONS

Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.

Increased beta2-adrenoceptors in doxorubicin-induced cardiomyopathy in rat

BACKGROUND

The toxicity of doxorubicin, leading to an irreversible heart failure, limits its use as chemotherapeutic agent. The beneficial effects of early administration of β-blocker were reported in patients with heart failure due to doxorubicin, suggesting an important role of β-adrenoceptors (β-ARs). This study aimed to identify a putative target (β-AR and/or its effectors) at the early phase of a chronic doxorubicin-induced cardiomyopathy (Dox-CM) in a rat model.

METHODOLOGY

Dox-CM was induced by six doxorubicin injections (cumulative dose: 15 mg x kg(-1)) and validated by echocardiography and left ventricle (LV) catheterization. The β-AR protein expressions in LV were evaluated by western-blot at days 35 (d35) and 70 (d70) after the first doxorubicin injection. Ex vivo cardiac contractility (dP/dtmax, dP/dtmin) was evaluated on isolated heart in response to specific β-AR stimulations at d35.

RESULTS

At d35, Dox-CM hearts were characterized by mild LV systolic and diastolic dysfunctions, which were exacerbated at d70. In Dox-CM hearts, β3-AR expression was only decreased at d70 (-37±8%). At d35, β1-AR expression was decreased by 68±6%, but ex vivo β1-AR function was preserved due to, at least in part, an increased adenylyl cyclase response assessed by forskolin. β2-AR expression was increased both at d35 (+58±22%) and d70 (+174±35%), with an increase of ex vivo β2-AR response at d35. Inhibition of Gi protein with pertussis toxin did not affect β2-AR response in Dox-CM hearts, suggesting a decoupling of β2-AR to Gi protein.

CONCLUSION

This study highlights the β1/β2-AR imbalance in early Dox-CM and reveals the important role that β2-AR/Gi coupling could play in this pathology. Our results suggest that β2-AR could be an interesting target at early stage of Dox-CM.

Chronic administration of small nonerythropoietic peptide sequence of erythropoietin effectively ameliorates the progression of postmyocardial infarction-dilated cardiomyopathy

The cardioprotective properties of erythropoietin (EPO) in preclinical studies are well documented, but erythropoietic and prothrombotic properties of EPO preclude its use in chronic heart failure (CHF). We tested the effect of long-term treatment with a small peptide sequence within the EPO molecule, helix B surface peptide (HBSP), that possesses tissue-protective, but not erythropoietic properties of EPO, on mortality and cardiac remodeling in postmyocardial infarction-dilated cardiomyopathy in rats. Starting 2 weeks after permanent left coronary artery ligation, rats received i.p. injections of HBSP (60 µg/kg) or saline two times per week for 10 months. Treatment did not elicit an immune response, and did not affect the hematocrit. Compared with untreated rats, HBSP treatment reduced mortality by 50% (P < 0.05). Repeated echocardiography demonstrated remarkable attenuation of left ventricular dilatation (end-diastolic volume: 41 versus 86%; end-systolic volume: 44 versus 135%; P < 0.05), left ventricle functional deterioration (ejection fraction: -4 versus -63%; P < 0.05), and myocardial infarction (MI) expansion (3 versus 38%; P < 0.05). A hemodynamic assessment at study termination demonstrated normal preload independent stroke work (63 ± 5 versus 40 ± 4; P < 0.05) and arterioventricular coupling (1.2 ± 0.2 versus 2.7 ± 0.7; P < 0.05). Histologic analysis revealed reduced apoptosis (P < 0.05) and fibrosis (P < 0.05), increased cardiomyocyte density (P < 0.05), and increased number of cardiomyocytes in myocardium among HBSP-treated rats. The results indicate that HBSP effectively reduces mortality, ameliorates the MI expansion and CHF progression, and preserves systolic reserve in the rat post-MI model. There is also a possibility that HBSP promoted the increase of the myocytes number in the myocardial wall remote from the infarct. Thus, HBSP peptide merits consideration for clinical testing.

Functional evidence for an active role of B-type natriuretic peptide in cardiac remodelling and pro-arrhythmogenicity

AIMS

During heart failure (HF), the left ventricle (LV) releases B-type natriuretic peptide (BNP), possibly contributing to adverse cardiovascular events including ventricular arrhythmias (VAs) and LV remodelling. We investigated the cardiac effects of chronic BNP elevation in healthy mice and compared the results with a model of HF after myocardial infarction (PMI mice).

METHODS AND RESULTS

Healthy mice were exposed to circulating BNP levels (BNP-Sham) similar to those measured in PMI mice. Telemetric surface electrocardiograms showed that in contrast with fibrotic PMI mice, electrical conduction was not affected in BNP-Sham mice. VAs were observed in both BNP-Sham and PMI but not in Sham mice. Analysis of heart rate variability indicated that chronic BNP infusion increased cardiac sympathetic tone. At the cellular level, BNP reduced Ca(2+) transients and impaired Ca(2+) reuptake in the sarcoplasmic reticulum, in line with blunted SR Ca(2+) ATPase 2a and S100A1 expression. BNP increased Ca(2+) spark frequency, reflecting Ca(2+) leak through ryanodine receptors, elevated diastolic Ca(2+), and promoted spontaneous Ca(2+) waves. Similar effects were observed in PMI mice. Most of these effects were reduced in BNP-Sham and PMI mice by the selective β1-adrenergic blocker metoprolol.

CONCLUSION

Elevated BNP levels, by inducing sympathetic overdrive and altering Ca(2+) handling, promote adverse cardiac remodelling and VAs, which could account in part for the progression of HF after MI. The early use of β-blockers to prevent the deleterious effects of chronic BNP exposure may be beneficial in HF.

Fenoterol enantiomers do not possess beneficial therapeutic properties of their racemic mixture in the rat model of post myocardial infarction dilated cardiomyopathy

PURPOSE

A salutary effect of β(2) adrenergic receptor (AR) agonist, fenoterol has been demonstrated in a rat model of post-myocardial infarction (MI) dilated cardiomyopathy (DCM). Recent reports on single cardiomyocyte experiments suggested that out of two enantiomers, RR and SS, that constitute a racemic mixture of fenoterol, only RR-enantiomer is an active component that might be a promising new drug for treatment of chronic heart failure. The objective of this study was to compare the efficacy of the RR enantiomer of fenoterol with efficacy of racemic fenoterol, and SS, an inactive enantiomer, in whole animal experimental models of DCM.

METHODS

Two weeks after induction of MI by permanent ligation of the anterior descending coronary artery early cardiac remodeling and MI size were assessed via echocardiography and rats were divided into treatment groups. Treatment (placebo, racemic fenoterol, RR- or SS-enantiomers of fenoterol) continued for 6 months while progression of DCM was followed by serial echocardiography.

RESULTS

Compared with untreated rats, rats treated with racemic fenoterol demonstrated previously described attenuation of LV remodeling, functional decline and the arrest of the MI expansion during the first 2 months of treatment. On the contrary, the treatment with either RR-, or with SS-enantiomers of fenoterol was completely ineffective.

CONCLUSION

The conclusion drawn on the basis of previous experiments with single cardiomyocytes that RR-enantiomer of fenoterol represents an active component of racemic fenoterol and can be further investigated as a new drug for treatment of chronic heart failure was not confirmed in the whole animal model of DCM.

The Effects of Prenatal Protein Restriction on β-Adrenergic Signalling of the Adult Rat Heart during Ischaemia Reperfusion

A maternal low-protein diet (MLP) fed during pregnancy leads to hypertension in adult rat offspring. Hypertension is a major risk factor for ischaemic heart disease. This study examined the capacity of hearts from MLP-exposed offspring to recover from myocardial ischaemia-reperfusion (IR) and related this to cardiac expression of β-adrenergic receptors (β-AR) and their associated G proteins. Pregnant rats were fed control (CON) or MLP diets (n = 12 each group) throughout pregnancy. When aged 6 months, hearts from offspring underwent Langendorff cannulation to assess contractile function during baseline perfusion, 30 min ischemia and 60 min reperfusion. CON male hearts demonstrated impaired recovery in left ventricular pressure (LVP) and dP/dt_max (P < 0.01) during reperfusion when compared to MLP male hearts. Maternal diet had no effect on female hearts to recover from IR. MLP males exhibited greater membrane expression of β₂-AR following reperfusion and urinary excretion of noradrenaline and dopamine was lower in MLP and CON female rats versus CON males. In conclusion, the improved cardiac recovery in MLP male offspring following IR was attributed to greater membrane expression of β₂-AR and reduced noradrenaline and dopamine levels. In contrast, females exhibiting both decreased membrane expression of β₂-AR and catecholamine levels were protected from IR injury.

β-Adrenergic receptor subtype signaling in heart: from bench to bedside

β-adrenergic receptor (βAR) stimulation by the sympathetic nervous system or circulating catecholamines is broadly involved in peripheral blood circulation, metabolic regulation, muscle contraction, and central neural activities. In the heart, acute βAR stimulation serves as the most powerful means to regulate cardiac output in response to a fight-or-flight situation, whereas chronic βAR stimulation plays an important role in physiological and pathological cardiac remodeling.There are three βAR subtypes, β(1)AR, β(2)AR and β(3)AR, in cardiac myocytes. Over the past two decades, we systematically investigated the molecular and cellular mechanisms underlying the different even opposite functional roles of β(1)AR and β(2)AR subtypes in regulating cardiac structure and function, with keen interest in the development of novel therapies based on our discoveries. We have made three major discoveries, including (1) dual coupling of β(2)AR to G(s) and G(i) proteins in cardiomyocytes, (2) cardioprotection by β(2)AR signaling in improving cardiac function and myocyte viability, and (3) PKA-independent, CaMKII-mediated β(1)AR apoptotic and maladaptive remodeling signaling in the heart. Based on these discoveries and salutary effects of β(1)AR blockade on patients with heart failure, we envision that activation of β(2)AR in combination with clinically used β(1)AR blockade should provide a safer and more effective therapy for the treatment of heart failure.

β₂-Adrenoceptors, NADPH oxidase, ROS and p38 MAPK: another 'radical' road to heart failure?

Persistent activation of the cardiac β-adrenergic system may contribute to the pathogenesis of congestive heart failure. Both β₁- and β₂-adrenoceptors are known to mediate these noxious effects, yet the β₁-adrenoceptor-PKA axis has received greater attention with less information available on β₂-adrenoceptor driven pathways. In the present issue, Xu and colleagues provide new evidence, showing that β₂-adrenoceptor over-expression leads to increased reactive oxygen species (ROS) emission, mainly caused by up-regulation of reduced nicotinamide adenine dinucleotide phosphate oxidase (Nox) 2 and 4. Increase in ROS levels is accompanied by p38 mitogen-activated protein kinase activation, fibrosis, apoptosis and cardiac dysfunction. Both Nox inhibition and administration of the antioxidant N-acetyl cysteine prevent these adverse effects. Interestingly, antioxidant treatment also prevents the increase in Nox expression, suggesting that β₂-adrenoceptor stimulation triggers a vicious cycle eventually amplified by both Nox isoforms. The possible existence of a circuitry to enhance ROS signalling and detrimental consequences on myocardial remodelling are also discussed, in light of the recent description of intracellular localization of Nox4.

Left ventricular remodeling in the post-infarction heart: a review of cellular, molecular mechanisms, and therapeutic modalities

As more patients survive myocardial infarctions, the incidence of heart failure increases. After an infarction, the human heart undergoes a series of structural changes, which are governed by cellular and molecular mechanisms in a pathological metamorphosis termed "remodeling." This review will discuss the current developments in our understanding of these molecular and cellular events in remodeling and the various pharmacological, cellular and device therapies used to treat, and potentially retard, this condition. Specifically, this paper will examine the neurohormonal activity of the renin-angiotensin-aldosterone axis and its molecular effects on the heart. The emerging understanding of the extra-cellular matrix and the various active molecules within it, such as the matrix metalloproteinases, elicits new appreciation for their role in cardiac remodeling and as possible future therapeutic targets. Cell therapy with stem cells is another recent therapy with great potential in improving post-infarcted hearts. Lastly, the cellular and molecular effects of left ventricular assist devices on remodeling will be reviewed. Our increasing knowledge of the cellular and molecular mechanisms underlying cardiac remodeling enables us not only to better understand how our more successful therapies, like angiotensin-converting enzyme inhibitors, work, but also to explore new therapies of the future.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

β₂ AR agonists in treatment of chronic heart failure: long path to translation

The main clinical manifestations of advanced chronic heart failure (CHF), e.g. in dilated cardiomyopathy (DCM), are reduced systolic and diastolic functions, increased arterial elastance and arterio-ventricular uncoupling, accompanied and exacerbated by an excessive sympathetic activation and extensive abnormalities in the βAR signaling. Loss of cardiomyocytes due to apoptosis is one mechanism that undoubtedly contributes to cardiac remodeling and functional deterioration associated with dilated cardiomyopathy (DCM). Research during the last decade on the single cardiomyocyte level strongly suggested that selective stimulation of β(1) AR activates the proapoptotic signaling pathways, while selective stimulation of β(2) AR is antiapoptotic, but its precise mechanisms remain to be elucidated. Extensive research in the rat model of DCM following induction of myocardial infarction (MI) showed that prolonged treatment with of β(2) AR agonist, fenoterol, in combination with a β(1) AR blocker, metoprolol, is more effective than β(1) AR blocker alone and as effective as β(1) AR blocker with ACE inhibitor with respect to survival and cardiac remodeling. This combined regimen of β(2) AR agonists and a β(1) AR blocker might be considered for clinical testing as alternative or adjunct therapy to currently acceptable CHF arsenal. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."