氯沙坦对心力衰竭大鼠心肌细胞凋亡和Ca2+变化的影响

目的:从细胞凋亡和细胞内钙调节的角度探讨血管紧张素ⅡⅠ型受体阻断剂--氯沙坦治疗心力衰竭(简称:心衰)的机制.方法:采用阿霉素腹腔注射造心衰模型,分为心衰组与治疗组,治疗组给予氯沙坦干预.同期选择8只正常大鼠为对照组.透射电镜观察心肌超微结构改变,检测血清中CPK、CK-MB及LDH的含量.检测大鼠心肌细胞凋亡及心肌组织匀浆中Ca2+的变化.结果:心衰组与治疗组相比,心肌细胞损伤明显,并可见凋亡小体.心肌组织中CPK、CK-MB和LDH活力降低.心肌细胞凋亡指数明显增加(P＜0.01).与对照组相比,心衰组心肌组织中的Ca2+含量升高(P＜0.01):治疗组与心衰组相比Ca2=显著降低(P＜0.01).结论:心力衰竭过程中发生了心肌细胞凋亡,氯沙坦可有效抑制心肌细胞凋亡,使心肌超微结构受损减轻,心肌酶外漏减少.心衰时心肌组织匀浆中Ca2+增加,可能是肌浆网钙泵活性受损.氯沙坦可抑制心肌细胞凋亡及Ca2+超载有积极逆转心肌受损,改善心衰进程作用.     

RyR2在心律失常中的研究进展

心脏的正常收缩舒张功能依赖于胞质内及肌质网内钙离子的稳态,当这种稳态被破坏会导致多种心脏疾病。RyR2是位于心肌细胞肌质网上的钙离子释放通道,其功能异常会导致胞质内钙离子稳态失衡,出现心律失常、心肌肥厚和心力衰竭等多种心脏疾病的发生。RyR2通过影响细胞内钙离子浓度介导心律失常的发生,但是具体作用机制尚不明了。本文对RyR2功能异常诱发心律失常的可能机制做一综述,为将来的临床治疗提供更可靠的依据。     

心力衰竭药物治疗研究进展

心力衰竭（心衰）是由于任何原因的初始心肌损伤引起的心脏结构和功能的变化。最终导致心室泵血功能低下。以前对心力衰竭的治疗主要是强心和减轻心脏负荷的对症治疗。目前治疗心力衰竭的目的以不仅是减轻心衰的症状，而且要逆转或延缓心衰病变的进展，治疗的重点是调节以被过度激活的交感神经、儿茶酚胺和肾素-血管紧张素-醛固酮的神经内分泌活性，从而阻止心肌的损害。在循证医学的指导下，心衰的治疗模式已由强心、利尿和改善血流动力学转变为干预神经体液机制，改善患者预后、提高生存率及生活质量的模式。当然，对晚期和顽固性心衰患者的强心和减轻心脏负荷的治疗仍是必不可少的措施。现对心力衰竭的药物治疗进展及评价作一简要介绍。     

肾上腺髓质素与心力衰竭的关系

肾上腺髓质素（ ＡＭ） 是一种由５２ 个氨基酸组成的血管活性肽,广泛分布在肾上腺髓质、肾、肺、心、脾、下丘脑、胰岛和胃肠道等许多组织器官中,具有扩张血管、降低血压、抑制醛固酮和调节胰岛素的合成和分泌等作用。心力衰竭患者血浆ＡＭ 水平随心衰的加重而显著升高,心肌ＡＭ 的合成和分泌也明显增加。给实验性肺动脉高压和右心室肥厚大鼠应用ＡＭ ,可明显降低肺动脉高压和减轻右心室肥厚。提示ＡＭ 参与心力衰竭的病理生理调节,在心力衰竭的治疗中可能具有一定的作用。     

新型钙增敏剂的研究现状及应用前景

钙增敏剂是在研究治疗充血性心力衰竭 (心衰 )的新型强心药时发现的一类作用机制完全不同于传统强心剂的强心药物。它们主要通过增加心肌收缩系统对 Ca2 的敏感性来发挥强心作用。近年来发现 ,钙增敏剂不仅在治疗心衰方面有着较好的应用前景 ,而且还有良好的抗休克以及调节外周血管反应性、改善器官组织血流量等作用。1　钙增敏剂的分类基础研究表明 ,正常情况下 ,机体细胞 Ca2 分布处于一种动态平衡状态 ,即所谓“钙稳态”(calcium hom eostasis)。细胞中 Ca2 分布是不均匀的 ,细胞外液和细胞内液 Ca2 浓度相差达 10 5倍 ,而细胞内 …     

心力衰竭患者三种心肌细胞应激标志物的临床意义

目的本研究旨在通过监测心衰患者及对照组非心衰患者NT-pro-BNP、BNP、ST2的血浓度水平,探讨心衰患者三种心肌细胞应激标志物血浓度水平的变化及其临床意义。方法选择2009-10-2010-03期间在广州市第一人民医院心内科住院心力衰竭的患者84例,无心力衰竭的患者95例。结果心力衰竭患者BNP、NT-pro-BNP、ST2血浓度水平较对照组明显升高(P<0.01)。心衰患者三种标志物血浓度水平在不同心功能分级组间差异均有统计学意义(P<0.001)。NT-pro-BNP诊断心衰的AUCROC为0.957(95%CI0.917~0.997),BNP诊断心衰的AUCROC为0.868(95%CI0.803~0.933),ST2诊断心衰的AUCROC为0.758(95%CI0.669~0.846)。结论心力衰竭组患者三种心肌应激标志物血浓度水平对不同程度的HF评估,指导HF治疗、评价预后均具有重要临床价值;其中NT-pro-BNP诊断参考价值较大,而BNP次之,ST2有一定的参考作用。     

浅谈儿茶酚胺在慢性充血性心力衰竭中的作用及其对策

心力衰竭 (心衰 )是由于不同原因的初始心肌损伤 (心肌梗死、血液动力负荷过重、炎症等 )引起心肌结构和功能的变化 ,最后导致心室泵血功能低下[1] 。慢性心衰中交感神经的兴奋性显著增高 ,且和心力衰竭的严重程度呈正相关 ,这有利于正常心肌和衰竭心脏早期调节的代偿机制 ,使心肌收缩力增强 ,心排出量增加 ,但交感神经张力的长期增高会产生有害的影响。1　慢性心力衰竭中儿茶酚胺的弊端高浓度的儿茶酚胺作用于心肌 ,具有直接的心肌毒性 ,因心肌细胞内钙超负荷和儿茶酚胺代谢产物自由基的产生使心肌受损 ;激活肾素 -血管紧张素系统 (RAAS)…     

慢性心力衰竭心肌纤维化与胞外信号调节激酶通路研究

慢性心力衰竭器质性病变难以逆转的根本原因是心室重构,心肌纤维化是心室重构的病变基础之一,其发展过程涉及复杂的神经-内分泌系统,具体生物学机制尚不明了。既往胞外信号调节激酶通路被认为是治疗肿瘤的经典通路,抑制该通路同样能够延缓心肌纤维化进程从而改善心力衰竭。为此,探究胞外信号调节激酶通路在心肌纤维化中的机制,或为临床拓展慢性心力衰竭防治提供新思路。该文就胞外信号调节激酶通路在心肌纤维化发生发展中的作用机制及其抑制药物进行阐述,以期为基于该通路防治慢性心力衰竭心肌纤维化提供依据。     

谈顽固性心衰的治疗

长期以来洋地黄治疗心力衰竭,都处于传统的支配地位,好象一提到心力衰竭,就意味着要用洋地黄,洋地黄也确实解决了不少心衰的问题,抢救了一些心衰垂危的病人,但洋地黄属于正性肌力作用的药物,可使心肌收缩加强、心率减慢、心博量增加、降低心室舒张未压,进而缓解全身的淤血状态,使心衰症状好转.当然这还要看心肌的储备能力,也就是心肌的代谢能量,如果心肌已趋耗竭状态,洋地黄不但不能增强其收缩力,反而还会加重其症状,所以应用药物还要特别注意其具体的适应症.     

利钠肽的研究进展

利钠肽家族作为内分泌激素，能够通过调节心脏和。肾脏的功能达到维持机体的内稳态。对利钠肽的最新研究表明，心力衰竭等心脏病患者的利钠肽水平升高，升高的利钠肽提示心血管事件的高危险性，监测利钠肽能够帮助诊断和判断预后。利钠肽能够抑制心肌的过度增殖和纤维化，具有改善心肌梗死和心衰时的心肌重构作用。脑钠肽是一种最重要的利钠肽，它可以作为心衰和其他心血管疾病的重要生物标记物，能够帮助我们了解肺动脉高压和粥样硬化性血管病等心血管疾病的进展。另外，合成的多种利钠肽如nesiritide已经被试验用来治疗急性充血性心衰。针对多种重组利钠肽的多个临床研究还在实验阶段，主要的方向包括它们在心脏手术中对心脏、肾脏的保护作用和抑制心肌重构的作用。     

Abnormal ryanodine receptor function in heart failure

The abnormally regulated release of Ca2+ from an intracellular Ca2+ store, the sarcoplasmic reticulum (SR), is the mechanism underlying contractile and relaxation dysfunctions in heart failure (HF). According to recent reports, protein kinase A (PKA)-mediated hyperphosphorylation of ryanodine receptor (RyR) in the SR has been shown to cause the dissociation of FK506 binding protein (FKBP) 12.6 from the RyR in heart failure. This causes an abnormal Ca2+ leak through the Ca2+ channel located in the RyR, leading to an increase in the cytosolic Ca2+ during diastole, prolongation of the Ca2+ transient, and delayed/slowed diastolic Ca2+ re-uptake. More recently, a considerable number of disease-linked mutations in the RyR have been reported in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) or arrhythmogenic right ventricular dysplasia type 2. An analysis of the disposition of these mutation sites within well-defined domains of the RyR polypeptide chain has led to the new concept that interdomain interactions among these domains play a critical role in channel regulation, and an altered domain interaction causes channel dysfunction in the failing heart. The knowledge gained from the recent literature concerning the critical proteins and the changes in their properties under pathological conditions has brought us to a better position to develop new pharmacological or genetic strategies for the treatment of heart failure or cardiac arrhythmia. A considerable body of evidence reviewed here indicates that abnormal RyR function plays an important role in the pathogenesis of heart failure. This review also covers some controversial issues in the literature concerning the involvement of phosphorylation and FKBP12.6.     

Differential regulation of two types of intracellular calcium release channels during end-stage heart failure.

The molecular basis of human heart failure is unknown. Alterations in calcium homeostasis have been observed in failing human heart muscles. Intracellular calcium-release channels regulate the calcium flux required for muscle contraction. Two forms of intracellular calcium-release channels are expressed in the heart: the ryanodine receptor (RyR) and the inositol 1,4,5-trisphosphate receptor (IP3R). In the present study we showed that these two cardiac intracellular calcium release channels were regulated in opposite directions in failing human hearts. In the left ventricle, RyR mRNA levels were decreased by 31% (P < 0.025) whereas IP3R mRNA levels were increased by 123% (P < 0.005). In situ hybridization localized both RyR and IP3R mRNAs to human cardiac myocytes. The relative amounts of IP3 binding sites increased approximately 40% compared with ryanodine binding sites in the failing heart. RyR down-regulation could contribute to impaired contractility; IP3R up regulation may be a compensatory response providing an alternative pathway for mobilizing intracellular calcium release, possibly contributing to the increased diastolic tone associated with heart failure and the hypertrophic response of failing myocardium.     

Molecular determinants of altered contractility in heart failure

Heart failure remains a leading cause of mortality in the Western world. An important hallmark of heart failure is reduced myocardial contractility. Alterations in intracellular Ca2+ handling play a major role in the pathophysiology of these contractile abnormalities. Several defects in the excitation-contraction (EC) coupling system have been identified in patients with heart failure. Alterations in the density and function of proteins relevant for EC coupling have been reported. Chronic stimulation of the beta-adrenergic signaling pathway leads to protein kinase A (PKA) hyperphosphorylation of the cardiac ryanodine receptor (RyR2), which dissociates FKBP12.6 from RyR2, thereby altering channel gating and promoting diastolic sarcoplasmic reticulum (SR) Ca2+ release. This may deplete the SR Ca2+ stores, which may reduce myocardial contractility. Clinical studies have demonstrated that beta-adrenergic receptor blockers reduce morbidity and mortality in all grades of congestive heart failure. Our experimental data indicate that beta-blockers reverse RyR2 hyperphosphorylation and normalize channel gating, which is associated with increased contractility in heart failure. In conclusion, chronic hyperactivity of the beta-adrenergic signaling pathway impairs intracellular Ca2+ handling, which leads to reduced contractility in patients with heart failure.     

Role of chronic ryanodine receptor phosphorylation in heart failure and β-adrenergic receptor blockade in mice

Increased sarcoplasmic reticulum (SR) Ca2+ leak via the cardiac ryanodine receptor/calcium release channel (RyR2) is thought to play a role in heart failure (HF) progression. Inhibition of this leak is an emerging therapeutic strategy. To explore the role of chronic PKA phosphorylation of RyR2 in HF pathogenesis and treatment, we generated a knockin mouse with aspartic acid replacing serine 2808 (mice are referred to herein as RyR2-S2808D+/+ mice). This mutation mimics constitutive PKA hyperphosphorylation of RyR2, which causes depletion of the stabilizing subunit FKBP12.6 (also known as calstabin2), resulting in leaky RyR2. RyR2-S2808D+/+ mice developed age-dependent cardiomyopathy, elevated RyR2 oxidation and nitrosylation, reduced SR Ca2+ store content, and increased diastolic SR Ca2+ leak. After myocardial infarction, RyR2-S2808D+/+ mice exhibited increased mortality compared with WT littermates. Treatment with S107, a 1,4-benzothiazepine derivative that stabilizes RyR2-calstabin2 interactions, inhibited the RyR2-mediated diastolic SR Ca2+ leak and reduced HF progression in WT and RyR2-S2808D+/+ mice. In contrast, β-adrenergic receptor blockers improved cardiac function in WT but not in RyR2-S2808D+/+ mice.Thus, chronic PKA hyperphosphorylation of RyR2 results in a diastolic leak that causes cardiac dysfunction. Reversing PKA hyperphosphorylation of RyR2 is an important mechanism underlying the therapeutic action of β-blocker therapy in HF.     

Is ryanodine receptor phosphorylation key to the fight or flight response and heart failure?

In situations of stress the heart beats faster and stronger. According to Marks and colleagues, this response is, to a large extent, the consequence of facilitated Ca2+ release from intracellular Ca2+ stores via ryanodine receptor 2 (RyR2), thought to be due to catecholamine-induced increases in RyR2 phosphorylation at serine 2808 (S2808). If catecholamine stimulation is sustained (for example, as occurs in heart failure), RyR2 becomes hyperphosphorylated and "leaky," leading to arrhythmias and other pathology. This "leaky RyR2 hypothesis" is highly controversial. In this issue of the JCI, Marks and colleagues report on two new mouse lines with mutations in S2808 that provide strong evidence supporting their theory. Moreover, the experiments revealed an influence of redox modifications of RyR2 that may account for some discrepancies in the field.     

Agonists and antagonists of the cardiac ryanodine receptor: potential therapeutic agents?

This review addresses the potential use of the intracellular ryanodine receptor (RyR) Ca(2+) release channel as a therapeutic target in heart disease. Heart disease encompasses a wide range of conditions with the major contributors to mortality and morbidity being ischaemic heart disease and heart failure (HF). In addition there are many rare, but devastating conditions, some of which are either genetically linked to the RyR and its regulatory proteins or involve drug-induced modification of the proteins. The defects in Ca(2+) signalling vary with the nature of the heart disease and the stage in its progress and therefore specific corrections require different modifications of Ca(2+) signalling. Compounds that activate the RyR are potential inotropic agents to increase the Ca(2+) transient and strength of contraction. Compounds that reduce RyR activity are potentially useful in conditions where excess RyR activity initiates arrhythmias, or depletes the Ca(2+) store, as in end stage HF. It has recently been discovered that the cardio-protective action of the drug JTV519 can be attributed partly to its ability to stabilise the interaction between the RyR and the 12.6 kDa binding protein for the commonly used immunosuppressive drug FK506 (FKBP12.6, known as tacrolimus). This has established the credibility of the RyR as a therapeutic target. We explore the possibility that mutations causing the rare RyR-linked arrhythmias will open the door to identification of novel RyR-based therapeutic agents. The use of regulatory binding sites within the RyR complex or on its associated proteins as templates for drug design is discussed.     

Requirement for Ca2+/calmodulin–dependent kinase II in the transition from pressure overload–induced cardiac hypertrophy to heart failure in mice

Ca²⁺/calmodulin–dependent kinase II (CaMKII) has been implicated in cardiac hypertrophy and heart failure. We generated mice in which the predominant cardiac isoform, CaMKIIδ, was genetically deleted (KO mice), and found that these mice showed no gross baseline changes in ventricular structure or function. In WT and KO mice, transverse aortic constriction (TAC) induced comparable increases in relative heart weight, cell size, HDAC5 phosphorylation, and hypertrophic gene expression. Strikingly, while KO mice showed preserved hypertrophy after 6-week TAC, CaMKIIδ deficiency significantly ameliorated phenotypic changes associated with the transition to heart failure, such as chamber dilation, ventricular dysfunction, lung edema, cardiac fibrosis, and apoptosis. The ratio of IP₃R2 to ryanodine receptor 2 (RyR2) and the fraction of RyR2 phosphorylated at the CaMKII site increased significantly during development of heart failure in WT mice, but not KO mice, and this was associated with enhanced Ca²⁺ spark frequency only in WT mice. We suggest that CaMKIIδ contributes to cardiac decompensation by enhancing RyR2-mediated sarcoplasmic reticulum Ca²⁺ leak and that attenuating CaMKIIδ activation can limit the progression to heart failure.     

Calcium cycling proteins and heart failure: mechanisms and therapeutics

Ca²⁺-dependent signaling is highly regulated in cardiomyocytes and determines the force of cardiac muscle contraction. Ca²⁺ cycling refers to the release and reuptake of intracellular Ca²⁺ that drives muscle contraction and relaxation. In failing hearts, Ca²⁺ cycling is profoundly altered, resulting in impaired contractility and fatal cardiac arrhythmias. The key defects in Ca²⁺ cycling occur at the level of the sarcoplasmic reticulum (SR), a Ca²⁺ storage organelle in muscle. Defects in the regulation of Ca²⁺ cycling proteins including the ryanodine receptor 2, cardiac (RyR2)/Ca²⁺ release channel macromolecular complexes and the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a)/phospholamban complex contribute to heart failure. RyR2s are oxidized, nitrosylated, and PKA hyperphosphorylated, resulting in “leaky” channels in failing hearts. These leaky RyR2s contribute to depletion of Ca²⁺ from the SR, and the leaking Ca²⁺ depolarizes cardiomyocytes and triggers fatal arrhythmias. SERCA2a is downregulated and phospholamban is hypophosphorylated in failing hearts, resulting in impaired SR Ca²⁺ reuptake that conspires with leaky RyR2 to deplete SR Ca²⁺. Two new therapeutic strategies for heart failure (HF) are now being tested in clinical trials: (a) fixing the leak in RyR2 channels with a novel class of Ca²⁺-release channel stabilizers called Rycals and (b) increasing expression of SERCA2a to improve SR Ca²⁺ reuptake with viral-mediated gene therapy. There are many potential opportunities for additional mechanism-based therapeutics involving the machinery that regulates Ca²⁺ cycling in the heart.     

Dysregulated sarcoplasmic reticulum calcium release: potential pharmacological target in cardiac disease

In the heart, Ca(2+) released from the intracellular Ca(2+) storage site, the sarcoplasmic reticulum (SR), is the principal determinant of cardiac contractility. SR Ca(2+) release is controlled by dedicated molecular machinery, composed of the cardiac ryanodine receptor (RyR2) and a number of accessory proteins, including FKBP12.6, calsequestrin (CASQ2), triadin (TRD) and junctin (JN). Acquired and genetic defects in the components of the release channel complex result in a spectrum of abnormal Ca(2+) release phenotypes ranging from arrhythmogenic spontaneous Ca(2+) releases and Ca(2+) alternans to the uniformly diminished systolic Ca(2+) release characteristic of heart failure. In this article, we will present an overview of the structure and molecular components of the SR and Ca(2+) release machinery and its modulation by different intracellular factors, such as Ca(2+) levels inside the SR as well as phosphorylation and redox modification of RyR2s. We will also discuss the relationships between abnormal SR Ca(2+) release and various cardiac disease phenotypes, including, arrhythmias and heart failure, and consider SR Ca(2+) release as a potential therapeutic target.     

Chain-reaction Ca(2+) signaling in the heart

Mutations in Ca(2+) -handling proteins in the heart have been linked to exercise-induced sudden cardiac death. The best characterized of these have been mutations in the cardiac Ca(2+) release channel known as the ryanodine receptor type 2 (RyR2). RyR2 mutations cause "leaky" channels, resulting in diastolic Ca(2+) leak from the sarcoplasmic reticulum (SR) that can trigger fatal cardiac arrhythmias during stress. In this issue of the JCI, Song et al. show that mutations in the SR Ca(2+)-binding protein calsequestrin 2 (CASQ2) in mice result not only in reduced CASQ2 expression but also in a surprising, compensatory elevation in expression of both the Ca(2+)-binding protein calreticulin and RyR2, culminating in premature Ca(2+) release from cardiac myocytes and stress-induced arrhythmia (see the related article beginning on page 1814). In the context of these findings and other recent reports studying CASQ2 mutations, we discuss how CASQ2 influences the properties of Ca(2+)-dependent regulation of RyR2 and how this contributes to cardiac arrhythmogenesis.