Calcium cycling in congestive heart failure

Effect of acute peritonitis on rocuronium-induced intraperitoneal pressure reduction and the uptake function of the sarcoplasmic reticulum

Previous studies have reported the incomplete relaxation effect of neuromuscular blockers on skeletal muscles in acute peritonitis (AP) and other inflammatory processes; however, the underlying mechanisms responsible for this effect have not yet been satisfactorily identified. The impaired removal of cytosolic Ca²⁺ through sarcoendoplasmic Ca²⁺-ATPase (SERCA) and defects in sarcoplasmic reticulum (SR) Ca²⁺ uptake are the major contributing factors to diastolic dysfunction. Previous studies on the effects of neuromuscular blockers have primarily focused on neuromuscular transmission. Because of the reduced calcium uptake in the SR itself, even when neuromuscular transmission is fully blocked, the muscle is not able to relax effectively. In the present study, the impact of AP on rocuronium-induced intraperitoneal pressure reduction and rectus abdominal muscle relaxation, and SERCA uptake function was investigated. AP was induced via gastric perforation and changes in the intraperitoneal pressure before and after the administration of rocuronium were recorded. Muscle contractile properties, uptake and release functions and SERCA activity in the rectus abdominal muscles of AP model rats were measured. The half-relaxation time in the AP group was significantly prolonged compared with that in the control group (P<0.01). The peak rate of SR Ca²⁺ uptake for whole muscle homogenates was significantly reduced (P<0.05) in AP model rats without reduction of the rate of Ca²⁺ release evoked through AgNO₃. In conclusion, gastric perforation-induced AP attenuates the intraperitoneal pressure-reducing effect of rocuronium, and AP induces diastolic dysfunction of the rectus abdominal muscle. The SR Ca²⁺-ATPase uptake rate was also reduced by AP.

Small-Conductance Calcium-Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells

Background

Purkinje cells (PCs) are important in cardiac arrhythmogenesis. Whether small‐conductance calcium‐activated potassium (SK) channels are present in PCs remains unclear. We tested the hypotheses that subtype 2 SK (SK2) channel proteins and apamin‐sensitive SK currents are abundantly present in PCs.

Methods and Results

We studied 25 normal rabbit ventricles, including 13 patch‐clamp studies, 4 for Western blotting, and 8 for immunohistochemical staining. Transmembrane action potentials were recorded in current‐clamp mode using the perforated‐patch technique. For PCs, the apamin (100 nmol/L) significantly prolonged action potential duration measured to 80% repolarization by an average of 10.4 ms (95% CI, 0.11–20.72) (n=9, P=0.047). Voltage‐clamp study showed that apamin‐sensitive SK current density was significantly larger in PCs compared with ventricular myocytes at potentials ≥0 mV. Western blotting of SK2 expression showed that the SK2 protein expression in the midmyocardium was 58% (P=0.028) and the epicardium was 50% (P=0.018) of that in the pseudotendons. Immunostaining of SK2 protein showed that PCs stained stronger than ventricular myocytes. Confocal microscope study showed SK2 protein was distributed to the periphery of the PCs.

Conclusions

SK2 proteins are more abundantly present in the PCs than in the ventricular myocytes of normal rabbit ventricles. Apamin‐sensitive SK current is important in ventricular repolarization of normal PCs.

Biodegradable Polymeric Nanocapsules Prevent Cardiotoxicity of Anti-Trypanosomal Lychnopholide

Chagas disease is a neglected parasitic disease caused by the protozoan Trypanosoma cruzi. New antitrypanosomal options are desirable to prevent complications, including a high rate of cardiomyopathy. Recently, a natural substance, lychnopholide, has shown therapeutic potential, especially when encapsulated in biodegradable polymeric nanocapsules. However, little is known regarding possible adverse effects of lychnopholide. Here we show that repeated-dose intravenous administration of free lychnopholide (2.0 mg/kg/day) for 20 days caused cardiopathy and mortality in healthy C57BL/6 mice. Echocardiography revealed concentric left ventricular hypertrophy with preserved ejection fraction, diastolic dysfunction and chamber dilatation at end-stage. Single cardiomyocytes presented altered contractility and Ca²⁺ handling, with spontaneous Ca²⁺ waves in diastole. Acute in vitro lychnopholide application on cardiomyocytes from healthy mice also induced Ca²⁺ handling alterations with abnormal RyR2-mediated diastolic Ca²⁺ release. Strikingly, the encapsulation of lychnopholide prevented the cardiac alterations induced in vivo by the free form repeated doses. Nanocapsules alone had no adverse cardiac effects. Altogether, our data establish lychnopholide presented in nanocapsule form more firmly as a promising new drug candidate to cure Chagas disease with minimal cardiotoxicity. Our study also highlights the potential of nanotechnology not only to improve the efficacy of a drug but also to protect against its adverse effects.

Beneficial Effect of Renal Denervation on Ventricular Premature Complex Induced Cardiomyopathy

Background

Frequent ventricular premature complexes (VPCs) can lead to the development of dilated cardiomyopathy and sudden cardiac death. Renal artery sympathetic denervation (RDN) may protect the heart from remodeling. This study aimed to investigate the effect of frequent VPCs on structural and electrical properties and whether RDN can protect the heart from remodeling.

Methods and Results

Eighteen rabbits were randomized to control (n=6), VPC (n=6), and VPC‐RDN (n=6) groups. Surgical and chemical RDNs were approached through bilateral retroperitoneal flank incisions in the VPC‐RDN group. Pacemakers were implanted to the left ventricular apex to produce 50% VPC burden for 5 weeks in the VPC and VPC‐RDN groups. In addition, ventricular myocardium was harvested for western blot and trichrome stain. Echocardiographic results showed left ventricular enlargement after 5‐week pacing in the VPC group, but not in the VPC‐RDN group, when compared to baseline. In biventricles, ion channel protein expressions of Nav1.5, Cav1.2, Kir2.1, and SERCA2 were similar among 3 groups. However, the degree of biventricular fibrosis was extensive in the VPC group, compared to the control and VPC‐RDN groups. Importantly, ventricular fibrillation inducibility was higher in the VPC group (41%) when comparing to the control (13%; P<0.05) and VPC‐RDN groups (13%; P<0.05), respectively.

Conclusions

Frequent VPCs are associated with the development of cardiac structural remodeling and high ventricular fibrillation inducibility. RDN prevents cardiac remodeling and the occurrence of ventricular arrhythmia through antifibrosis.

Murine Electrophysiological Models of Cardiac Arrhythmogenesis

Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.

Dietary Copper Restriction-Induced Changes in Myocardial Gene Expression and the Effect of Copper Repletion

Dietary copper (Cu) restriction leads to cardiac hypertrophy and failure in mice, and Cu repletion (CuR) reverses the hypertrophy and prevents the transition to heart failure. The present study was undertaken to determine changes in myocardial gene expression involved in Cu deficient (CuD) cardiomyopathy and its reversal by CuR. Analysis was performed on three groups of mice: 4-week-old CuD mice that exhibited signs of cardiac failure, their age-matched copper-adequate (CuA) controls, and the CuD mice that were re-fed adequate Cu for 2 weeks. Total RNA was isolated from hearts and subjected to cDNA microarray and real-time reverse transcription-polymerase chain reaction analysis. Dietary CuD caused a decrease in cardiac mRNA of β-MHC, L-type Ca2+ channel, K-dependent NCX, MMP-2, -8, and -13, NF-κB, and VEGF. The mRNA levels of ET-1, TGF-β, TNF-α, and procollagen-l-α1 and III-α1 were increased in the CuD cardiac tissue. Copper repletion resulted in cardiac mRNA levels of most of the genes examined returning to control levels, although the K-dependent NCX and MMP-2 values did not reach those of the CuA control. In addition, CuR caused an increase in β-MHC, L-type Ca2+channel, MMP-13 to levels surpassing those of CuA control, and a decrease in ET-1, and TNF-at mRNA levels. In summary, changes in gene expression of elements involved in contractility, Ca2+ cycling, and inflammation and fibrosis may account for the altered cardiac function found in CuD mice. The return to normal cardiac function by CuR may be a result of the favorable regression in gene expression of these critical components in myocardial tissue.

Atrial fibrillation in heart failure with preserved ejection fraction: Insights into mechanisms and therapeutics

Atrial fibrillation (AF) and heart failure (HF) often coexist, and the outcomes of patients who have both AF and HF are considerably worse than those with either condition in isolation. Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous clinical entity and accounts for approximately one-half of current HF. At least one-third of patients with HFpEF are burdened by comorbid AF. The current understanding of the relationship between AF and HFpEF is limited, but the clinical implications are potentially important. In this review, we explore 1) the pathogenesis that drives AF and HFpEF to coexist; 2) pharmacologic therapies that may attenuate the impact of AF in HFpEF; and 3) future directions in the management of this complex syndrome.

Muscarinic Stimulation Facilitates Sarcoplasmic Reticulum Ca Release by Modulating Ryanodine Receptor 2 Phosphorylation Through Protein Kinase G and Ca/Calmodulin-Dependent Protein Kinase II

Although the effects and the underlying mechanism of sympathetic stimulation on cardiac Ca handling are relatively well established both in health and disease, the modes of action and mechanisms of parasympathetic modulation are poorly defined. Here, we demonstrate that parasympathetic stimulation initiates a novel mode of excitation-contraction coupling that enhances the efficiency of cardiac sarcoplasmic reticulum Ca store utilization. This efficient mode of excitation-contraction coupling involves reciprocal changes in the phosphorylation of ryanodine receptor 2 at Ser-2808 and Ser-2814. Specifically, Ser-2808 phosphorylation was mediated by muscarinic receptor subtype 2 and activation of PKG (protein kinase G), whereas dephosphorylation of Ser-2814 involved activation of muscarinic receptor subtype 3 and decreased reactive oxygen species-dependent activation of CaMKII (Ca/calmodulin-dependent protein kinase II). The overall effect of these changes in phosphorylation of ryanodine receptor 2 is an increase in systolic Ca release at the low sarcoplasmic reticulum Ca content and a paradoxical reduction in aberrant Ca leak. Accordingly, cholinergic stimulation of cardiomyocytes isolated from failing hearts improved Ca cycling efficiency by restoring altered ryanodine receptor 2 phosphorylation balance.

Disordered Myocardial Ca2+ Homeostasis Results in Substructural Alterations That May Promote Occurrence of Malignant Arrhythmias

We aimed to determine the impact of Ca2+-related disorders induced in intact animal hearts on ultrastructure of the cardiomyocytes prior to occurrence of severe arrhythmias. Three types of acute experiments were performed that are known to be accompanied by disturbances in Ca2+ handling. Langedorff-perfused rat or guinea pig hearts subjected to K+-deficient perfusion to induce ventricular fibrillation (VF), burst atrial pacing to induce atrial fibrillation (AF) and open chest pig heart exposed to intramyocardial noradrenaline infusion to induce ventricular tachycardia (VT). Tissue samples for electron microscopic examination were taken during basal condition, prior and during occurrence of malignant arrhythmias. Cardiomyocyte alterations preceding occurrence of arrhythmias consisted of non-uniform sarcomere shortening, disruption of myofilaments and injury of mitochondria that most likely reflected cytosolic Ca2+ disturbances and Ca2+ overload. These disorders were linked with non-uniform pattern of neighboring cardiomyocytes and dissociation of adhesive junctions suggesting defects in cardiac cell-to-cell coupling. Our findings identified heterogeneously distributed high [Ca2+]i-induced subcellular injury of the cardiomyocytes and their junctions as a common feature prior occurrence of VT, VF or AF. In conclusion, there is a link between Ca2+-related disorders in contractility and coupling of the cardiomyocytes pointing out a novel paradigm implicated in development of severe arrhythmias.

Post-extrasystolic Potentiation: Link between Ca(2+) Homeostasis and Heart Failure?

Post-extrasystolic potentiation (PESP) describes the phenomenon of increased contractility of the beat following an extrasystole and has been attributed to changes in Ca(2+) homeostasis. While this effect has long been regarded to be a normal physiological phenomenon, a number of reports describe an enhanced potentiation of the post-extrasystolic beat in heart failure patients. The exact mechanism of this increased PESP is unknown, but disruption of normal Ca(2+) handling in heart failure may be the underlying cause. The use of PESP as a prognostic marker or therapeutic intervention have recently regained new attention, however, the value of the application of PESP in the clinic is still under debate. In this review, the mechanism of PESP with regard to Ca(2+) in the normal and failing heart will be discussed and the possible diagnostic and therapeutic role of this phenomenon will be explored.

Potassium Channel Interacting Protein 2 (KChIP2) is not a transcriptional regulator of cardiac electrical remodeling

The heart-failure relevant Potassium Channel Interacting Protein 2 (KChIP2) augments Ca_V1.2 and K_V4.3. KChIP3 represses Ca_V1.2 transcription in cardiomyocytes via interaction with regulatory DNA elements. Hence, we tested nuclear presence of KChIP2 and if KChIP2 translocates into the nucleus in a Ca²⁺ dependent manner. Cardiac biopsies from human heart-failure patients and healthy donor controls showed that nuclear KChIP2 abundance was significantly increased in heart failure; however, this was secondary to a large variation of total KChIP2 content. Administration of ouabain did not increase KChIP2 content in nuclear protein fractions in anesthetized mice. KChIP2 was expressed in cell lines, and Ca²⁺ ionophores were applied in a concentration- and time-dependent manner. The cell lines had KChIP2-immunoreactive protein in the nucleus in the absence of treatments to modulate intracellular Ca²⁺ concentration. Neither increasing nor decreasing intracellular Ca²⁺ concentrations caused translocation of KChIP2. Microarray analysis did not identify relief of transcriptional repression in murine KChIP2^−/− heart samples. We conclude that although there is a baseline presence of KChIP2 in the nucleus both in vivo and in vitro, KChIP2 does not directly regulate transcriptional activity. Moreover, the nuclear transport of KChIP2 is not dependent on Ca²⁺. Thus, KChIP2 does not function as a conventional transcription factor in the heart.

Arrhythmogenic and metabolic remodelling of failing human heart

Heart failure (HF) is a major cause of morbidity and mortality worldwide. The global burden of HF continues to rise, with prevalence rates estimated at 1-2% and incidence approaching 5-10 per 1000 persons annually. The complex pathophysiology of HF impacts virtually all aspects of normal cardiac function - from structure and mechanics to metabolism and electrophysiology - leading to impaired mechanical contraction and sudden cardiac death. Pharmacotherapy and device therapy are the primary methods of treating HF, but neither is able to stop or reverse disease progression. Thus, there is an acute need to translate basic research into improved HF therapy. Animal model investigations are a critical component of HF research. However, the translation from cellular and animal models to the bedside is hampered by significant differences between species and among physiological scales. Our studies over the last 8 years show that hypotheses generated in animal models need to be validated in human in vitro models. Importantly, however, human heart investigations can establish translational platforms for safety and efficacy studies before embarking on costly and risky clinical trials. This review summarizes recent developments in human HF investigations of electrophysiology remodelling, metabolic remodelling, and β-adrenergic remodelling and discusses promising new technologies for HF research.

Liraglutide protects cardiac microvascular endothelial cells against hypoxia/reoxygenation injury through the suppression of the SR-Ca(2+)-XO-ROS axis via activation of the GLP-1R/PI3K/Akt/survivin pathways

Microvascular endothelial cells (CMECs) oxidative damage resulting from hypoxia/reoxygenation (H/R) injury is responsible for microcirculation perfusion disturbances and the progression of cardiac dysfunction. However, few strategies are available to reverse such pathologies. Here, we studied the effects and mechanisms of liraglutide on CEMCs oxidative damage, focusing in particular on calcium overload-triggered free radical injury signals and the GLP-1R/PI3K/Akt/survivin survival pathways. The results indicate that H/R increased IP3R expression but reduced SERCA2a expression, which rapidly raised intracellular Ca(2+) levels, subsequently leading to Ca(2+)-dependent xanthine oxidase (XO) activation, reactive oxygen species (ROS) production and the cellular apoptosis of CMECs. However, liraglutide pretreatment abrogated Ca(2+)-mediated oxidative apoptosis. Furthermore, liraglutide regulated the rate of IP3R/SERCA2a gene transcription and conserved SERCA2a-ATPase activity via the maintenance of ATP production under H/R, which drove excessive Ca(2+) reflux to the sarcoplasmic reticulum (SR) and inhibited Ca(2+) release from the SR, ultimately restoring Ca(2+) homeostasis. Furthermore, the regulatory role of liraglutide on Ca(2+) balance in conjunction with its up-regulation of superoxide dismutase, glutathione and glutathione peroxidase collectively scavenged the excess ROS under H/R. Moreover, we showed that liraglutide strengthened Akt phosphorylation and subsequently survivin expression. In addition, both the blockade of the GLP-1R/PI3K/Akt pathways and the siRNA-mediated knockdown of survivin abolished the protective effects of liraglutide on SR-Ca(2+) function and CMECs oxidative apoptosis. In summary, this study confirmed that H/R induced CMECs oxidative damage through the SR-Ca(2+)-XO-ROS injury signals and that liraglutide pretreatment may suppress such CMECs damage through the PI3K/Akt/survivin pathways.

Development of a high-affinity peptide that prevents phospholemman (PLM) inhibition of the sodium/calcium exchanger 1 (NCX1)

NCX1 (Na⁺/Ca²⁺ exchanger 1) is an important regulator of intracellular Ca²⁺ and a potential therapeutic target for brain ischaemia and for diastolic heart failure with preserved ejection fraction. PLM (phospholemman), a substrate for protein kinases A and C, has been suggested to regulate NCX1 activity. However, although several studies have demonstrated that binding of phosphorylated PLM (pSer⁶⁸-PLM) leads to NCX1 inhibition, other studies have failed to demonstrate a functional interaction of these proteins. In the present study, we aimed to analyse the biological function of the pSer⁶⁸-PLM–NCX1 interaction by developing high-affinity blocking peptides. PLM was observed to co-fractionate and co-immunoprecipitate with NCX1 in rat left ventricle, and in co-transfected HEK (human embryonic kidney)-293 cells. For the first time, the NCX1–PLM interaction was also demonstrated in the brain. PLM binding sites on NCX1 were mapped to two regions by peptide array assays, containing the previously reported PASKT and QKHPD motifs. Conversely, the two NCX1 regions bound identical sequences in the cytoplasmic domain of PLM, suggesting that NCX1-PASKT and NCX1-QKHPD might bind to each PLM monomer. Using two-dimensional peptide arrays of the native NCX1 sequence KHPDKEIEQLIELANYQVLS revealed that double substitution of tyrosine for positions 1 and 4 (K1Y and D4Y) enhanced pSer⁶⁸-PLM binding 8-fold. The optimized peptide blocked binding of NCX1-PASKT and NCX1-QKHPD to PLM and reversed PLM(S68D) inhibition of NCX1 activity (both forward and reverse mode) in HEK-293 cells. Altogether our data indicate that PLM interacts directly with NCX1 and inhibits NCX1 activity when phosphorylated at Ser⁶⁸.

The role of CaMKII in diabetic heart dysfunction

Diabetes mellitus (DM) is an increasing epidemic that places a significant burden on health services worldwide. The incidence of heart failure (HF) is significantly higher in diabetic patients compared to non-diabetic patients. One underlying mechanism proposed for the link between DM and HF is activation of calmodulin-dependent protein kinase (CaMKIIδ). CaMKIIδ mediates ion channel function and Ca(2+) handling during excitation-contraction and excitation-transcription coupling in the myocardium. CaMKIIδ activity is up-regulated in the myocardium of diabetic patients and mouse models of diabetes, where it promotes pathological signaling that includes hypertrophy, fibrosis and apoptosis. Pharmacological inhibition and knockout models of CaMKIIδ have shown some promise of a potential therapeutic benefit of CaMKIIδ inhibition, with protection against cardiac hypertrophy and apoptosis reported. This review will highlight the pathological role of CaMKIIδ in diabetes and discuss CaMKIIδ as a therapeutic target in DM, and also the effects of exercise on CaMKIIδ.

Calcium upregulation by percutaneous administration of gene therapy in patients with cardiac disease (CUPID 2): a randomised, multinational, double-blind, placebo-controlled, phase 2b trial

BACKGROUND

Sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a) activity is deficient in the failing heart. Correction of this abnormality by gene transfer might improve cardiac function. We aimed to investigate the clinical benefits and safety of gene therapy through infusion of adeno-associated virus 1 (AAV1)/SERCA2a in patients with heart failure and reduced ejection fraction.

METHODS

We did this randomised, multinational, double-blind, placebo-controlled, phase 2b trial at 67 clinical centres and hospitals in the USA, Europe, and Israel. High-risk ambulatory patients with New York Heart Association class II-IV symptoms of heart failure and a left ventricular ejection fraction of 0·35 or less due to an ischaemic or non-ischaemic cause were randomly assigned (1:1), via an interactive voice and web-response system, to receive a single intracoronary infusion of 1 × 10(13) DNase-resistant particles of AAV1/SERCA2a or placebo. Randomisation was stratified by country and by 6 min walk test distance. All patients, physicians, and outcome assessors were masked to treatment assignment. The primary efficacy endpoint was time to recurrent events, defined as hospital admission because of heart failure or ambulatory treatment for worsening heart failure. Primary efficacy endpoint analyses and safety analyses were done by modified intention to treat. This trial is registered with ClinicalTrials.gov, number NCT01643330.

FINDINGS

Between July 9, 2012, and Feb 5, 2014, we randomly assigned 250 patients to receive either AAV1/SERCA2a (n=123) or placebo (n=127); 243 (97%) patients comprised the modified intention-to-treat population. Patients were followed up for at least 12 months; median follow-up was 17·5 months (range 1·8-29·4 months). AAV1/SERCA2a did not improve time to recurrent events compared with placebo (104 vs 128 events; hazard ratio 0·93, 95% CI 0·53-1·65; p=0·81). No safety signals were noted. 20 (16%) patients died in the placebo group and 25 (21%) patients died in the AAV1/SERCA2a group; 18 and 22 deaths, respectively, were adjudicated as being due to cardiovascular causes.

INTERPRETATION

CUPID 2 is the largest gene transfer study done in patients with heart failure so far. Despite promising results from previous studies, AAV1/SERCA2a at the dose tested did not improve the clinical course of patients with heart failure and reduced ejection fraction. Although we did not find evidence of improved outcomes at the dose of AAV1/SERCA2a studied, our findings should stimulate further research into the use of gene therapy to treat patients with heart failure and help inform the design of future gene therapy trials.

FUNDING

Celladon Corporation.

Nuclear calcium in cardiac myocytes

Calcium (Ca) is a universal second messenger involved in the regulation of various cellular processes, including electrical signaling, contraction, secretion, memory, gene transcription, and cell death. In heart, Ca governs cardiomyocyte contraction, is central in electrophysiological properties, and controls major signaling pathway implicated in gene transcription. How cardiomyocytes decode Ca signal to regulate gene expression without interfering with, or being controlled by, "contractile" Ca that floods the entire cytosol during each heartbeat is still elusive. In this review, we summarize recent findings on nuclear Ca regulation and its downstream signaling in cardiomyocytes. We will address difficulties in reliable quantification of nuclear Ca fluxes and discuss its role in the development and progression of cardiac hypertrophy and heart failure. We also point out key open questions to stimulate future work.

Phospholamban ablation rescues the enhanced propensity to arrhythmias of mice with CaMKII-constitutive phosphorylation of RyR2 at site S2814

KEY POINTS

Mice with Ca(2+) -calmodulin-dependent protein kinase (CaMKII) constitutive pseudo-phosphorylation of the ryanodine receptor RyR2 at Ser2814 (S2814D(+/+) mice) exhibit a higher open probability of RyR2, higher sarcoplasmic reticulum (SR) Ca(2+) leak in diastole and increased propensity to arrhythmias under stress conditions. We generated phospholamban (PLN)-deficient S2814D(+/+) knock-in mice by crossing two colonies, S2814D(+/+) and PLNKO mice, to test the hypothesis that PLN ablation can prevent the propensity to arrhythmias of S2814D(+/+) mice. PLN ablation partially rescues the altered intracellular Ca(2+) dynamics of S2814D(+/+) hearts and myocytes, but enhances SR Ca(2+) sparks and leak on confocal microscopy. PLN ablation diminishes ventricular arrhythmias promoted by CaMKII phosphorylation of S2814 on RyR2. PLN ablation aborts the arrhythmogenic SR Ca(2+) waves of S2814D(+/+) and transforms them into non-propagating events. A mathematical human myocyte model replicates these results and predicts the increase in SR Ca(2+) uptake required to prevent the arrhythmias induced by a CaMKII-dependent leaky RyR2.

ABSTRACT

Mice with constitutive pseudo-phosphorylation at Ser2814-RyR2 (S2814D(+/+) ) have increased propensity to arrhythmias under β-adrenergic stress conditions. Although abnormal Ca(2+) release from the sarcoplasmic reticulum (SR) has been linked to arrhythmogenesis, the role played by SR Ca(2+) uptake remains controversial. We tested the hypothesis that an increase in SR Ca(2+) uptake is able to rescue the increased arrhythmia propensity of S2814D(+/+) mice. We generated phospholamban (PLN)-deficient/S2814D(+/+) knock-in mice by crossing two colonies, S2814D(+/+) and PLNKO mice (SD(+/+) /KO). SD(+/+) /KO myocytes exhibited both increased SR Ca(2+) uptake seen in PLN knock-out (PLNKO) myocytes and diminished SR Ca(2+) load (relative to PLNKO), a characteristic of S2814D(+/+) myocytes. Ventricular arrhythmias evoked by catecholaminergic challenge (caffeine/adrenaline) in S2814D(+/+) mice in vivo or programmed electric stimulation and high extracellular Ca(2+) in S2814D(+) /(-) hearts ex vivo were significantly diminished by PLN ablation. At the myocyte level, PLN ablation converted the arrhythmogenic Ca(2+) waves evoked by high extracellular Ca(2+) provocation in S2814D(+/+) mice into non-propagated Ca(2+) mini-waves on confocal microscopy. Myocyte Ca(2+) waves, typical of S2814D(+/+) mice, could be evoked in SD(+/+) /KO cells by partially inhibiting SERCA2a. A mathematical human myocyte model replicated these results and allowed for predicting the increase in SR Ca(2+) uptake required to prevent the arrhythmias induced by a Ca(2+) -calmodulin-dependent protein kinase (CaMKII)-dependent leaky RyR2. Our results demonstrate that increasing SR Ca(2+) uptake by PLN ablation can prevent the arrhythmic events triggered by SR Ca(2+) leak due to CaMKII-dependent phosphorylation of the RyR2-S2814 site and underscore the benefits of increasing SERCA2a activity on SR Ca(2+) -triggered arrhythmias.

Comorbidity of atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are evolving epidemics, together responsible for substantial human suffering and health-care expenditure. Ageing, improved cardiovascular survival, and epidemiological transition form the basis for their increasing global prevalence. Although we now have a clear picture of how HF promotes AF, gaps remain in our knowledge of how AF exacerbates or even causes HF, and how the development of HF affects the outcome of patients with AF. New data regarding HF with preserved ejection fraction and its unique relationship with AF suggest a possible role for AF in its aetiology, possibly as a trigger for ventricular fibrosis. Deciding on optimal treatment strategies for patients with both AF and HF is increasingly difficult, given that results from trials of pharmacological rhythm control are arguably obsolete in the age of catheter ablation. Restoring sinus rhythm by catheter ablation seems successful in the medium term and improves HF symptoms, functional capacity, and left ventricular function. Long-term studies to examine the effect on rates of stroke and death are ongoing. Guidelines continue to evolve to keep pace with this rapidly changing field.

Small-conductance Ca2+-activated K+ current is upregulated via the phosphorylation of CaMKII in cardiac hypertrophy from spontaneously hypertensive rats

Left ventricular hypertrophy is associated with an increased risk of ventricular arrhythmias. However, the underlying molecular basis is poorly understood. It has been reported that small-conductance Ca2+-activated K+ (SK) channels are involved in the pathogenesis of ventricular arrhythmias in heart failure. The present study aimed to test the hypothesis that SK channel activity is increased via the Ca2+/calmodulin-dependent protein kinase II (CaMKII)-dependent pathway in hypertensive cardiac hypertrophy. Normotensive Wistar-Kyoto (WKY) rats and spontaneous hypertensive rats (SHRs) were used. Whole cell membrane currents were recorded in isolated ventricular myocytes by the patch-clamp method, and apamin-sensitive K+ current ( IKAS), which is inhibited by apamin (100 nM), an SK channel blocker, was evaluated. IKAS at 40 mV was present in SHRs, whereas it was hardly detectable in WKY rats (0.579 ± 0.046 vs. 0.022 ± 0.062 pA/pF, both n = 6, P < 0.05). IKAS was almost completely abolished by 1 μM KN-93, a CaMKII inhibitor, in SHRs. Optical recordings of left ventricular anterior wall action potentials revealed that apamin prolonged the late phase of repolarization only in SHRs. Western blot analysis of SK channel protein isoforms demonstrated that SK2 was significantly increased in SHRs compared with WKY rats (SK2/GAPDH: 0.66 ± 0.07 vs. 0.40 ± 0.02, both n = 6, P < 0.05), whereas SK1 and SK3 did not differ between groups. In addition, autophosphorylated CaMKII was significantly increased in SHRs (phosphorylated CaMKII/GAPDH: 0.80 ± 0.06 vs. 0.58 ± 0.06, both n = 6, P < 0.05) despite a comparable total amount of CaMKII between groups. In conclusion, SK channels are upregulated via the enhanced activation of CaMKII in cardiac hypertrophy in SHRs.

Representing variability and transmural differences in a model of human heart failure

During heart failure (HF) at the cellular level, the electrophysiological properties of single myocytes get remodeled, which can trigger the occurrence of ventricular arrhythmias that could be manifested in many forms such as early afterdepolarizations (EADs) and alternans (ALTs). In this paper, based on experimentally observed human HF data, specific ionic and exchanger current strengths are modified from a recently developed human ventricular cell model: the O'Hara-Virág-Varró-Rudy (OVVR) model. A new transmural HF-OVVR model is developed that incorporates HF changes and variability of the observed remodeling. This new heterogeneous HF-OVVR model is able to replicate many of the failing action potential (AP) properties and the dynamics of both [Ca(2+)]i and [Na(+)]i in accordance with experimental data. Moreover, it is able to generate EADs for different cell types and exhibits ALTs at modest pacing rate for transmural cell types. We have assessed the HF-OVVR model through the examination of the AP duration and the major ionic currents' rate dependence in single myocytes. The evaluation of the model comes from utilizing the steady-state (S-S) and S1-S2 restitution curves and from probing the accommodation of the HF-OVVR model to an abrupt change in cycle length. In addition, we have investigated the effect of chosen currents on the AP properties, such as blocking the slow sodium current to shorten the AP duration and suppress the EADs, and have found good agreement with experimental observations. This study should help elucidate arrhythmogenic mechanisms at the cellular level and predict unseen properties under HF conditions. In addition, this AP cell model might be useful for modeling and simulating HF at the tissue and organ levels.

NOD1, a new player in cardiac function and calcium handling

AIMS

Inflammation is a significant contributor to cardiovascular disease and its complications; however, whether the myocardial inflammatory response is harmonized after cardiac injury remains to be determined. Some receptors of the innate immune system, including the nucleotide-binding oligomerization domain-like receptors (NLRs), play key roles in the host response after cardiac damage. Nucleotide-binding oligomerization domain containing 1 (NOD1), a member of the NLR family, is expressed in the heart, but its functional role has not been elucidated. We determine whether selective NOD1 activation modulates cardiac function and Ca(2+) signalling.

METHODS AND RESULTS

Mice were treated for 3 days with the selective NOD1 agonist C12-iE-DAP (iE-DAP), and cardiac function and Ca(2+) cycling were assessed. We found that iE-DAP treatment resulted in cardiac dysfunction, measured as a decrease in ejection fraction and fractional shortening. Cardiomyocytes isolated from iE-DAP-treated mice displayed a decrease in the L-type Ca(2+) current, [Ca(2+)]i transients and Ca(2+) load, and decreased expression of phospho-phospholamban, sarcoplasmic reticulum-ATPase, and Na(+)-Ca(2+) exchanger. Furthermore, iE-DAP prompted 'diastolic Ca(2+) leak' in cardiomyocytes, resulting from increased Ca(2+) spark frequency and RyR2 over-phosphorylation. Importantly, these iE-DAP-induced changes in Ca(2+) cycling were lost in NOD1(-/-) mice, indicating that iE-DAP exerts its actions through NOD1. Co-treatment of mice with iE-DAP and a selective inhibitor of NF-κB (BAY11-7082) prevented cardiac dysfunction and Ca(2+) handling impairment induced by iE-DAP.

CONCLUSION

Our data provide the first evidence that NOD1 activation induces cardiac dysfunction associated with excitation-contraction coupling impairment through NF-κB activation and uncover a new pro-inflammatory player in the regulation of cardiovascular function.

Hypoxia-driven sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2) downregulation depends on low-density lipoprotein receptor-related protein 1 (LRP1)-signalling in cardiomyocytes

The maintenance of sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) activity is crucial for cardiac function and SERCA2 is dramatically reduced in the heart exposed to hypoxic/ischemic conditions. Previous work from our group showed that hypoxia upregulates the phosphorylated form of the Ca(2+)-dependent nonreceptor protein tyrosine kinase (PTK) proline-rich tyrosine kinase 2 (pPyk2) protein levels in a low-density lipoprotein receptor-related protein (LRP1)-dependent manner. Pyk2 in turn may modulate SERCA2 in cardiomyocytes although this remains controversial. We therefore aimed to investigate the role of LRP1 on hypoxia-induced SERCA2 depletion in cardiomyocytes and to establish LRP1 signalling mechanisms involved. Western blot analysis showed that hypoxia reduced SERCA2 concomitantly with a sustained increase in LRP1 and pPyk2 protein levels in HL-1 cardiomyocytes. By impairing hypoxia-induced Pyk2 phosphorylation and HIF-1α accumulation, LRP1 deficiency prevented SERCA2 depletion and reduction of the sarcoplasmic reticulum calcium content in cardiomyocytes. Moreover, the inhibition of Pyk2 phosphorylation (with the Src-family inhibitor PP2) or the specific silencing of Pyk2 (with siRNA-anti Pyk2) preserved low HIF-1α and high SERCA2 levels in HL-1 cardiomyocytes exposed to hypoxia. We determined that the LRP1/Pyk2 axis represses SERCA2 mRNA expression via HIF-1α since HIF-1α overexpression abolished the protective effect of LRP1 deficiency on SERCA2 depletion. Our findings show a crucial role of LRP1/Pyk2/HIF-1α in hypoxia-induced cardiomyocyte SERCA2 downregulation, a pathophysiological process closely associated with heart failure.

Gene expression network analysis reveals new transcriptional regulators as novel factors in human ischemic cardiomyopathy

BACKGROUND

Ischemic cardiomyopathy (ICM) is characterized by transcriptomic changes that alter cellular processes leading to decreased cardiac output. Because the molecular network of ICM is largely unknown, the aim of this study was to characterize the role of new transcriptional regulators in the molecular mechanisms underlying the responses to ischemia.

METHODS

Myocardial tissue explants from ICM patients and control (CNT) subjects were analyzed by RNA-Sequencing (RNA-Seq) and quantitative Real-Time PCR.

RESULTS

Enrichment analysis of the ICM transcriptomic profile allowed the characterization of novel master regulators. We found that the expression of the transcriptional regulators SP100 (-1.5-fold, p < 0.05), CITED2 (-3.8-fold, p < 0.05), CEBPD (-4.9-fold, p < 0.05) and BCL3 (-3.3-fold, p < 0.05) were lower in ICM than in CNT. To gain insights into the molecular network defined by the transcription factors, we identified CEBPD, BCL3, and HIF1A target genes in the RNA-Seq datasets. We further characterized the biological processes of the target genes by gene ontology annotation. Our results suggest that CEBPD-inducible genes with roles in the inhibition of apoptosis are downregulated and that BCL3-repressible genes are involved in the regulation of cellular metabolism in ICM. Moreover, our results suggest that CITED2 downregulation causes increased expression of HIF1A target genes. Functional analysis of HIF1A target genes revealed that hypoxic and stress response genes are activated in ICM. Finally, we found a significant correlation between the mRNA levels of BCL3 and the mRNA levels of both CEBPD (r = 0.73, p < 0.001) and CITED2 (r = 0.56, p < 0.05). Interestingly, CITED2 mRNA levels are directly related to ejection fraction (EF) (r = 0.54, p < 0.05).

CONCLUSIONS

Our data indicate that changes in the expression of SP100, CITED2, CEBPD, and BCL3 affect their transcription regulatory networks, which subsequently alter a number of biological processes in ICM patients. The relationship between CITED2 mRNA levels and EF emphasizes the importance of this transcription factor in ICM. Moreover, our findings identify new mechanisms used to interpret gene expression changes in ICM and provide valuable resources for further investigation of the molecular basis of human cardiac ischemic response.

[New therapy concepts for heart failure with preserved ejection fraction]

The management of patients with heart failure and preserved ejection fraction (HFpEF) remains challenging and requires an accurate diagnosis. Although currently no convincing therapy that can prolong survival in patients with HFpEF has been established, treatment of fluid retention, heart rate and control of comorbidities are important cornerstones to improve the quality of life and symptoms. In recent years many new therapy targets have been tested for development of successful interventional strategies for HFpEF. Insights into new mechanisms of HFpEF have shown that heart failure is associated with dysregulation of the nitric oxide-cyclic guanosine monophosphate-protein kinase (NO-cGMP-PK) pathway. Two new drugs are currently under investigation to test whether this pathway can be significantly improved by either the neprilysin inhibitor LCZ 696 due to an increase in natriuretic peptides or by the soluble guanylate cyclase stimulator vericiguat, which is also able to increase cGMP. In addition, several preclinical or early phase studies which are currently investigating new mechanisms for matrix, intracellular calcium and energy regulation including the role of microRNAs and new devices are presented and discussed.

Mechanisms of SR calcium release in healthy and failing human hearts

Normal heart contraction and rhythm relies on the proper flow of calcium ions (Ca2+) into cardiac cells and between their intracellular organelles, and any disruption can lead to arrhythmia and sudden cardiac death. Electrical excitation of the surface membrane activates voltage-dependent L-type Ca2+ channels to open and allow Ca2+ to enter the cytoplasm. The subsequent increase in cytoplasmic Ca2+ concentration activates calcium release channels (RyR2) located at specialised Ca2+ release sites in the sarcoplasmic reticulum (SR), which serves as an intracellular Ca2+ store. Animal models have provided valuable insights into how intracellular Ca2+ transport mechanisms are altered in human heart failure. The aim of this review is to examine how Ca2+ release sites are remodelled in heart failure and how this affects intracellular Ca2+ transport with an emphasis on Ca2+ release mechanisms in the SR. Current knowledge on how heart failure alters the regulation of RyR2 by Ca2+ and Mg2+ and how these mechanisms control the activity of RyR2 in the confines of the Ca2+ release sites is reviewed.

Force-interval relationship predicts mortality in survivors of myocardial infarction with atrial fibrillation

BACKGROUND

RR interval variations lead to beat-to-beat blood pressure differences through the myocardial force-interval relationship (FIR). In sinus rhythm, an altered FIR leads to post-extrasystolic potentiation (PESP) of systolic blood pressure, which has been shown to predict adverse outcome in survivors of acute myocardial infarction (MI). The purpose of this study was (1) to develop a parameter to assess the FIR in patients with atrial fibrillation (AF) and (2) to investigate its association with mortality in MI survivors suffering from AF.

METHODS AND RESULTS

Thirty-two patients with acute MI and AF underwent 30-min recordings of ECG and continuous blood pressure. Episodes of a short RR interval (<80% of mean interval, RRi) preceding a long interval (>140%, RRi+1) were identified. The systolic pressures of the pulse waves following RRi and RRi+1 were labeled Pi and Pi+1. PESPAfib was calculated as (Pi+1-Pi)/(RRi+1-RRi). During 5years of follow-up, 13 patients died. When PESPAfib was dichotomized at the median, mortality rates were 63% and 19% in patients with high and low PESPAfib. Hazard ratio for mortality was 4.88 for patients with high PESPAfib (1.33-17.84, p=0.004). The association of PESPAfib and mortality was independent from LVEF, age, diabetes mellitus or mean heart rate.

CONCLUSIONS

PESPAfib, a measure for the FIR in patients with AF, can be derived from simultaneous ECG and blood pressure recordings. The results of this pilot study indicate that PESPAfib may be useful to predict adverse outcome in survivors of myocardial infarction suffering from AF.

Regulation of RYR2 by sarcoplasmic reticulum Ca(2+)

Ca(2+) is arguably the most important ion involved in the contraction of the heart. The cardiac ryanodine receptor (RyR2), the major Ca(2+) release channel located in the sarcoplasmic reticulum (SR) membrane, is responsible for releasing the bulk of Ca(2+) required for contraction. Moreover, RyR2 is also crucial for maintaining SR Ca(2+) homeostasis by releasing Ca(2+) from the SR when it becomes overloaded with Ca(2+) . During normal contraction, RyR2 is activated by cytosolic Ca(2+) , whereas during store overload conditions, the opening of RyR2 is governed by SR Ca(2+) . Although the process of the cytosolic control of RyR2 is well established, the molecular mechanism by which SR luminal Ca(2+) regulates RyR2 has only recently been elucidated and remains controversial. In addition to the activation of RyR2, SR luminal Ca(2+) also determines when the RyR2 channel closes. RyR2-mediated Ca(2+) release from the SR does not continue until the SR is completely depleted. Rather, it ceases when SR luminal Ca(2+) falls below a certain level. Given the importance of SR Ca(2+) , it is not surprising that the SR luminal Ca(2+) level is tightly controlled by SR Ca(2+) -buffering proteins. Consequently, the opening and closing of RyR2 is heavily influenced by the presence of such proteins, particularly those associated with RyR2, such as calsequestrin and the histidine-rich Ca(2+) -binding protein. These proteins appear to indirectly alter RyR2 activity by modifying the microdomain SR Ca(2+) level surrounding RyR2.

Impaired oxidative metabolism and calcium mishandling underlie cardiac dysfunction in a rat model of post-acute isoproterenol-induced cardiomyopathy

Stress-induced cardiomyopathy, triggered by acute catecholamine discharge, is a syndrome characterized by transient, apical ballooning linked to acute heart failure and ventricular arrhythmias. Rats receiving an acute isoproterenol (ISO) overdose (OV) suffer cardiac apex ischemia-reperfusion damage and arrhythmia, and then undergo cardiac remodeling and dysfunction. Nevertheless, the subcellular mechanisms underlying cardiac dysfunction after acute damage subsides are not thoroughly understood. To address this question, Wistar rats received a single ISO injection (67 mg/kg). We found in vivo moderate systolic and diastolic dysfunction at 2 wk post-ISO-OV; however, systolic dysfunction recovered after 4 wk, while diastolic dysfunction worsened. At 2 wk post-ISO-OV, cardiac function was assessed ex vivo, while mitochondrial oxidative metabolism and stress were assessed in vitro, and Ca(2+) handling in ventricular myocytes. These were complemented with sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), phospholamban (PLB), and RyR2 expression studies. Ex vivo, basal mechanical performance index (MPI) and oxygen consumption rate (MVO2) were unchanged. Nevertheless, upon increase of metabolic demand, by β-adrenergic stimulation (1-100 nM ISO), the MPI versus MVO2 relation decreased and shifted to the right, suggesting MPI and mitochondrial energy production uncoupling. Mitochondria showed decreased oxidative metabolism, membrane fragility, and enhanced oxidative stress. Myocytes presented systolic and diastolic Ca(2+) mishandling, and blunted response to ISO (100 nM), and all these without apparent changes in SERCA, PLB, or RyR2 expression. We suggest that post-ISO-OV mitochondrial dysfunction may underlie decreased cardiac contractility, mainly by depletion of ATP needed for myofilaments and Ca(2+) transport by SERCA, while exacerbated oxidative stress may enhance diastolic RyR2 activity.

Dantrolene rescues aberrant N-terminus intersubunit interactions in mutant pro-arrhythmic cardiac ryanodine receptors

AIMS

The ryanodine receptor (RyR2) is an intracellular Ca(2+) release channel essential for cardiac excitation-contraction coupling. Abnormal RyR2 channel function results in the generation of arrhythmias and sudden cardiac death. The present study was undertaken to investigate the mechanistic basis of RyR2 dysfunction in inherited arrhythmogenic cardiac disease.

METHODS AND RESULTS

We present several lines of complementary evidence, indicating that the arrhythmia-associated L433P mutation disrupts RyR2 N-terminus self-association. A combination of yeast two-hybrid, co-immunoprecipitation, and chemical cross-linking assays collectively demonstrate that a RyR2 N-terminal fragment carrying the L433P mutation displays substantially reduced self-interaction compared with wild type. Moreover, sucrose density gradient centrifugation reveals that the L433P mutation impairs tetramerization of the full-length channel. [(3)H]Ryanodine-binding assays demonstrate that disrupted N-terminal intersubunit interactions within RyR2(L433P) confer an altered sensitivity to Ca(2+) activation. Calcium imaging of RyR2(L433P)-expressing cells reveals substantially prolonged Ca(2+) transients and reduced Ca(2+) store content indicating defective channel closure. Importantly, dantrolene treatment reverses the L433P mutation-induced impairment and restores channel function.

CONCLUSION

The N-terminus domain constitutes an important structural determinant for the functional oligomerization of RyR2. Our findings are consistent with defective N-terminus self-association as a molecular mechanism underlying RyR2 channel deregulation in inherited arrhythmogenic cardiac disease. Significantly, the therapeutic action of dantrolene may occur via the restoration of normal RyR2 N-terminal intersubunit interactions.

Pharmacogenetics of cardiac inotropy

The ability to stimulate cardiac contractility is known as positive inotropy. Endogenous hormones, such as adrenaline and several natural or synthetic compounds possess this biological property, which is invaluable in the modern cardiovascular therapy setting, especially in acute heart failure or in cardiogenic shock. A number of proteins inside the cardiac myocyte participate in the molecular pathways that translate the initial stimulus, that is, the hormone or drug, into the effect of increased contractility (positive inotropy). Genetic variations (polymorphisms) in several genes encoding these proteins have been identified and characterized in humans with potentially significant consequences on cardiac inotropic function. The present review discusses these polymorphisms and their effects on cardiac inotropy, along with the individual pharmacogenomics of the most important positive inotropic agents in clinical use today. Important areas for future investigations in the field are also highlighted.

Calcium handling proteins: structure, function, and modulation by exercise

Heart failure is a serious public health issue with a growing prevalence, and it is related with the aging of the population. Hypertension is identified as the main precursor of left ventricular hypertrophy and therefore can lead to diastolic dysfunction and heart failure. Scientific studies have confirmed the beneficial effects of the physical exercise by reducing the blood pressure and improving the functional status of the heart in hypertension. Several proteins are involved in the mobilization of calcium during the coupling excitation-contraction process in the heart among those are sarcoplasmic reticulum Ca(2+)-ATPase, phospholamban, calsequestrin, sodium-calcium exchanger, L-type calcium's channel, and ryanodine receptors. Our goal is to address the beneficial effects of exercise on the calcium handling proteins in a heart with hypertension.

New strategies for heart failure with preserved ejection fraction: the importance of targeted therapies for heart failure phenotypes

The management of heart failure with reduced ejection fraction (HF-REF) has improved significantly over the last two decades. In contrast, little or no progress has been made in identifying evidence-based, effective treatments for heart failure with preserved ejection fraction (HF-PEF). Despite the high prevalence, mortality, and cost of HF-PEF, large phase III international clinical trials investigating interventions to improve outcomes in HF-PEF have yielded disappointing results. Therefore, treatment of HF-PEF remains largely empiric, and almost no acknowledged standards exist. There is no single explanation for the negative results of past HF-PEF trials. Potential contributors include an incomplete understanding of HF-PEF pathophysiology, the heterogeneity of the patient population, inadequate diagnostic criteria, recruitment of patients without true heart failure or at early stages of the syndrome, poor matching of therapeutic mechanisms and primary pathophysiological processes, suboptimal study designs, or inadequate statistical power. Many novel agents are in various stages of research and development for potential use in patients with HF-PEF. To maximize the likelihood of identifying effective therapeutics for HF-PEF, lessons learned from the past decade of research should be applied to the design, conduct, and interpretation of future trials. This paper represents a synthesis of a workshop held in Bergamo, Italy, and it examines new and emerging therapies in the context of specific, targeted HF-PEF phenotypes where positive clinical benefit may be detected in clinical trials. Specific considerations related to patient and endpoint selection for future clinical trials design are also discussed.

Paradoxical effects of KB-R7943 on arrhythmogenicity in a chronic myocardial infarction rabbit model

BACKGROUND

Na(+)/Ca(2+) exchanger blockade has been reported to be anti-arrhythmic in different models. The effects of KB-R7943, a Na(+)/Ca(2+) exchanger blocker, on arrhythmogenesis in hearts with chronic myocardial infarction (MI) remain unclear.

METHODS

Dual voltage and intracellular Ca(2+) (Cai) optical mapping was performed in nine rabbit hearts with chronic MI and four control hearts. Electrophysiology studies including inducibility of ventricular tachyarrhythmias, ventricular fibrillation dominant frequency, action potential, Cai alternans, Cai decay, and conduction velocity were performed. The same protocol was repeated in the presence of KB-R7943 (0.5, 1, and 5μM) after the baseline studies.

RESULTS

KB-R7943 was effective in suppressing afterdepolarizations and spontaneous ventricular tachyarrhythmias in hearts with chronic MI. Surprisingly, KB-R7943 increased the inducibility of ventricular tachyarrhythmias in a dose-dependent manner (11%, 11%, 22%, and 56% at baseline and with 0.5, 1, and 5μM KB-R7943, respectively, p=0.02). Optical mapping analysis revealed that the underlying mechanisms of the induced ventricular tachyarrhythmias were probably spatially discordant alternans with wave breaks and rotors. Further analysis showed that KB-R7943 significantly enhanced both action potential (p=0.033) and Cai (p=0.001) alternans, prolonged Cai decay (tau value) in a dose-dependent manner (p=0.004), and caused heterogeneous conduction delay especially at peri-infarct zones during rapid burst pacing. In contrast, KB-R7943 had insignificant effects in control hearts.

CONCLUSIONS

In this chronic MI rabbit model, KB-R7943 has contrasting effects on arrhythmogenesis, suppressing afterdepolarizations and spontaneous ventricular tachyarrhythmias, but enhancing the inducibility of tachyarrhythmias. The mechanism is probably the enhanced spatially discordant alternans because of prolonged Cai decay and heterogeneous conduction delay.

New therapeutic options in heart failure. What's on the horizon? An overview

Heart failure is a complex clinical syndrome responsible for high morbidity and mortality in the world. Despite advances in the management of heart failure, the prognosis of these patients remains poor and there is a critical need for new treatment strategies improving the clinical outcomes. New approaches in heart failure therapies target cellular mechanisms, as well as mechanical and structural aspects of heart failure that are not addressed by recent therapies. These include abnormalities in molecular mechanisms, electrical conduction and ventricular remodeling. This review presents the pathophysiological basis, mechanisms of action and available clinical efficacy and safety data of drugs and mechanical therapies that are currently under development.

Decrease in sarcoplasmic reticulum calcium content, not myofilament function, contributes to muscle twitch force decline in isolated cardiac trabeculae

We set out to determine the factors responsible for twitch force decline in isolated intact rat cardiac trabeculae. The contractile force of trabeculae declined over extended periods of isometric twitch contractions. The force-frequency relationship within the frequency range of 4-8 Hz, at 37 °C, became more positive and the frequency optimum shifted to higher rates with this decline in baseline twitch tensions. The post-rest potentiation (37 °C), a phenomenon highly dependent on calcium handling mechanisms, became more pronounced with decrease in twitch tensions. We show that the main abnormality during muscle run-down was not due to a deficit in the myofilaments; maximal tension achieved using a K(+) contracture protocol was either unaffected or only slightly decreased. Conversely, the sarcoplasmic reticulum (SR) calcium content, as assessed by rapid cooling contractures (from 27 to 0 °C), decreased, and had a close association with the declining twitch tensions (R(2) ~ 0.76). SR Ca(2+)-ATPase, relative to Na(+)/Ca(2+) exchanger activity, was not altered as there was no significant change in paired rapid cooling contracture ratios. Furthermore, confocal microscopy detected no abnormalities in the overall structure of the cardiomyocytes and t-tubules in the cardiac trabeculae (~23 °C). Overall, the data indicates that the primary mechanism responsible for force run-down in multi-cellular cardiac preparations is a decline in the SR calcium content and not the maximal tension generation capability of the myofilaments.

Early remodeling of perinuclear Ca2+ stores and nucleoplasmic Ca2+ signaling during the development of hypertrophy and heart failure

BACKGROUND

A hallmark of heart failure is impaired cytoplasmic Ca(2+) handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca(2+) handling via altered excitation-transcription coupling contribute to the development and progression of heart failure.

METHODS AND RESULTS

Using tissue and isolated cardiomyocytes from nonfailing and failing human hearts, as well as mouse and rabbit models of hypertrophy and heart failure, we provide compelling evidence for structural and functional changes of the nuclear envelope and nuclear Ca(2+) handling in cardiomyocytes as remodeling progresses. Increased nuclear size and less frequent intrusions of the nuclear envelope into the nuclear lumen indicated altered nuclear structure that could have functional consequences. In the (peri)nuclear compartment, there was also reduced expression of Ca(2+) pumps and ryanodine receptors, increased expression of inositol-1,4,5-trisphosphate receptors, and differential orientation among these Ca(2+) transporters. These changes were associated with altered nucleoplasmic Ca(2+) handling in cardiomyocytes from hypertrophied and failing hearts, reflected as increased diastolic Ca(2+) levels with diminished and prolonged nuclear Ca(2+) transients and slowed intranuclear Ca(2+) diffusion. Altered nucleoplasmic Ca(2+) levels were translated to higher activation of nuclear Ca(2+)/calmodulin-dependent protein kinase II and nuclear export of histone deacetylases. Importantly, the nuclear Ca(2+) alterations occurred early during hypertrophy and preceded the cytoplasmic Ca(2+) changes that are typical of heart failure.

CONCLUSIONS

During cardiac remodeling, early changes of cardiomyocyte nuclei cause altered nuclear Ca(2+) signaling implicated in hypertrophic gene program activation. Normalization of nuclear Ca(2+) regulation may therefore be a novel therapeutic approach to prevent adverse cardiac remodeling.

Postextrasystolic blood pressure potentiation predicts poor outcome of cardiac patients

Background

Postextrasystolic blood pressure potentiation (PESP), the pulse wave augmentation after an extrasystolic beat, is typically enhanced in heart failure (HF) patients. This study prospectively tested the association of PESP and mortality in cardiac patients.

Methods and Results

Consecutive patients (n=941; mean age, 61 years; 19% female) presenting with acute myocardial infarction were enrolled between May 2000 and March 2005 and followed up until August 2010. The main study outcome was 5‐year all‐cause mortality. Patients underwent noninvasive 30‐minute recordings of ECG and continuous blood pressure. PESP presence was based on the ratio between the first postectopic pulse wave amplitude and the mean of the subsequent 9 pulse wave amplitudes. A ratio above 1 was prospectively defined as PESP present. Ventricular premature complexes (VPCs) suitable for PESP quantification were present in recordings of 220 patients. PESP was present in 62 of these patients. Patients without suitable VPCs were classified as PESP absent.

During the follow‐up, 72 patients died. Among the 220 patients in whom PESP was measurable, 27 died. Under univariable analysis, PESP was a significant predictor of death (P<0.001) as were GRACE score (P<0.001), left ventricular ejection fraction (LVEF) (P<0.001), and the number of recorded VPCs (P<0.001). Under multivariable analysis, PESP (P<0.001), GRACE score (P<0.001), and LVEF (P=0.001) were independently associated with outcome. The combination of PESP presence and LVEF ≤35% identified a subgroup of patients with a particularly high mortality of 46.7%. Separate validation reproduced the finding in an unrelated population of 146 HF patients.

Conclusions

PESP, which likely reflects abnormalities of myocardial calcium cycling, predicts the mortality risk in postinfarction patients.

Clinical Trial Registration

URL: ClinicalTrials.gov. Unique identifier: NCT00196274.

Progressive decay of Ca2+ homeostasis in the development of diabetic cardiomyopathy

Background

Cardiac dysfunction in diabetic cardiomyopathy may be associated with abnormal Ca²⁺ homeostasis. This study investigated the effects of alterations in Ca²⁺ homeostasis and sarcoplasmic reticulum Ca²⁺-associated proteins on cardiac function in the development of diabetic cardiomyopathy.

Methods

Sprague–Dawley rats were divided into 4 groups (n = 12, each): a control group, and streptozotocin-induced rat models of diabetes groups, examined after 4, 8, or 12 weeks. Evaluations on cardiac structure and function were performed by echocardiography and hemodynamic examinations, respectively. Cardiomyocytes were isolated and spontaneous Ca²⁺ spark images were formed by introducing fluorescent dye Fluo-4 and obtained with confocal scanning microscopy. Expressions of Ca²⁺-associated proteins were assessed by Western blotting.

Results

Echocardiography and hemodynamic measurements revealed that cardiac dysfunction is associated with the progression of diabetes, which also correlated with a gradual but significant decline in Ca²⁺ spark frequency (in the 4-, 8- and 12-week diabetic groups). However, Ca²⁺ spark decay time constants increased significantly, relative to the control group. Expressions of ryanodine receptor 2 (RyR2), sarcoplasmic reticulum Ca²⁺-2ATPase (SERCA) and Na⁺/Ca²⁺ exchanger (NCX1) were decreased, together with quantitative alterations in Ca²⁺regulatory proteins, FKBP12.6 and phospholamban progressively and respectively in the diabetic rats.

Conclusions

Ca²⁺ sparks exhibited a time-dependent decay with progression of diabetic cardiomyopathy, which may partly contribute to cardiac dysfunction. This abnormality may be attributable to alterations in the expressions of some Ca²⁺-associated proteins.

Differential effects of S100 proteins A2 and A6 on cardiac Ca(2+) cycling and contractile performance

Defective intracellular calcium (Ca(2+)) handling is implicated in the pathogenesis of heart failure. Novel approaches targeting both cardiac Ca(2+) release and reuptake processes, such as S100A1, have the potential to rescue the function of failing cardiac myocytes. Here, we show that two members of the S100 Ca(2+) binding protein family, S100A2 and S100A6 that share high sequence homology, differentially influence cardiac Ca(2+) handling and contractility. Cardiac gene expression of S100A2 significantly enhanced both contractile and relaxation performance of rodent and canine cardiac myocytes, mimicking the functional effects of its cardiac homologue, S100A1. To interrogate mechanism, Ca(2+) spark frequency, a measure of the gating of the ryanodine receptor Ca(2+) release channel, was found to be significantly increased by S100A2. Therapeutic testing showed that S100A2 rescued the contractile defects of failing cardiac myocytes. In contrast, cardiac expression of S100A6 had no significant effects on contractility or Ca(2+) handling. These data reveal novel differential effects of S100 proteins on cardiac myocyte performance that may be useful in application to diseased cardiac muscle.