Abstracts


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mTOR in Growth and Protection of Hypertrophying Myocardium
S. Balasubramanian, R.K. Johnston, P.C. Moschella, S.K. Mani, W.J. Tuxworth, Jr. and D. Kuppuswamy

In response to an increased hemodynamic load, such as pressure or volume overload, cardiac hypertrophy ensues as an adaptive mechanism. Although hypertrophy initially maintains ventricular function, a yet undefined derailment in this process eventually leads to compromised function (decompensation) and eventually culminates in congestive heart failure (CHF). Therefore, determining the molecular signatures induced during compensatory growth is important to delineate specific mechanisms responsible for the transition into CHF. Compensatory growth involves multiple processes. At the cardiomyocyte level, one major event is increased protein turnover where enhanced protein synthesis is accompanied by increased removal of deleterious proteins. Many pathways that mediate protein turnover depend on a key molecule, mammalian target of rapamycin (mTOR). In pressure-overloaded myocardium, adrenergic receptors, growth factor receptors, and integrins are known to activate mTOR in a PI3K-dependent and/or independent manner with the involvement of specific PKC isoforms. mTOR, described as a sensor of a cell's nutrition and energy status, is uniquely positioned to activate pathways that regulate translation, cell size, and the ubiquitin-proteasome system (UPS) through rapamycin-sensitive and -insensitive signaling modules. The rapamycin-sensitive complex, known as mTOR complex 1 (mTORC1), consists of mTOR, rapamycin-sensitive adaptor protein of mTOR (Raptor) and mLST8 and promotes protein translation and cell size via molecules such as S6K1. The rapamycin-insensitive complex (mTORC2) consists of mTOR, mLST8, rapamycin-insensitive companion of mTOR (Rictor), mSin1 and Protor. mTORC2 regulates the actin cytoskeleton in addition to activating Akt (Protein kinase B) for the subsequent removal of proapoptotic factors via the UPS for cell survival. In this review, we discuss pathways and key targets of mTOR complexes that mediate growth and survival of hypertrophying cardiomyocytes and the therapeutic potential of mTOR inhibitor, rapamycin.


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The Intermediate-Conductance Ca²⁺-Activated K⁺ Channel (K_Ca3.1) in Vascular Disease
D.L. Tharp and D.K. Bowles

The intermediate-conductance Ca²⁺-activated K⁺ channel (K_Ca3.1) was first described by Gardos in erythrocytes and later confirmed to play a significant role in T-cell activation and the immune response. More recently, K_Ca3.1 has been characterized in numerous cell types which contribute to the development of vascular disease, such as T-cells, B-cells, endothelial cells, fibroblasts, macrophages, and dedifferentiated smooth muscle cells (SMCs). Physiologically, K_Ca3.1 has been demonstrated to play a role in acetycholine and endothelium-derived hyperpolarizing factor (EDHF) induced hyperpolarization, and thus control of blood pressure. Pathophysiologically, K_Ca3.1 contributes to proliferation of T-cells, B-cells, fibroblasts, and vascular SMCs, as well as the migration of SMCs and macrophages and platelet coagulation. Recent studies have indicated that blockade of K_Ca3.1, by specific blockers such as TRAM-34, could prove to be an effective treatment for vascular disease by inhibiting T-cell activation as well as preventing proliferation and migration of macrophages, endothelial cells, and SMCs. This vasculoprotective potential of K_Ca3.1 inhibition has been confirmed in both rodent and swine models of restenosis. In this review, we will discuss the physiological and pathophysiological role of K_Ca3.1 in cells closely associated with vascular biology, and the effect of K_Ca3.1 blockers on the initiation and progression of vascular disease.


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Insights Into the Role of microRNAs in Cardiac Diseases: From Biological Signalling to Therapeutic Targets
E. Zorio, P. Medina, J. Rueda, J.M. Millán, M.A. Arnau, M. Beneyto, F. Marín, J.R. Gimeno, J. Osca, A. Salvador, F. España and A. Estellés

microRNAs have recently opened new pathways to explain gene expression and disease biology in many scenarios, including cardiac diseases. microRNAs are endogenous small non-coding RNAs that mediate post-transcriptional repression or messenger RNA degradation. By annealing to inexactly complementary sequences in the 3’ untranslated region of the target messenger RNA, protein level is down-regulated. Several microRNAs appear to act cooperatively through multiple target sites in one gene and, conversely, most microRNAs can target several genes. miR-133 and miR-1 are specifically expressed in cardiac and skeletal muscle and control myogenesis, cardiac development, cardiac performance and cardiomyocyte hypertrophy (mainly by tuning transcription factors and other growth-related targets). They also modulate the expression of certain cardiac ion channels and related proteins with proarrhythmic effect. Besides them, other microRNAs have been shown to exert influence on the myocardial growth, the electrical balance and the angiogenesis processes that take place in the heart. Bioinformatics is a useful tool to identify potential targets of a given microRNA, although there is still substantial concern about their reliability. Experimental manipulation of microRNAs has provided a tantalizing basis to speculate that future research on microRNAs may yield important progress in the prevention of sudden cardiac death and in the treatment of cardiac heart failure. However, the final effect of the blockage of microRNAs in vivo remains unclear, since each of them can target hundreds of genes with different intensity. The era of the microRNAs in cardiovascular diseases has just started.


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Natriuretic Peptides in Cardiovascular Diseases of Fetus, Infants and Children
B.B. Das, S. Raj and R. Solinger Vol: 7-1

The natriuretic peptides (NP) appear to be functional by midgestation, respond to volume stimuli, and regulate blood pressure and salt and water balance in the developing embryo. In addition, the NP may help regulate the blood supply to the fetus, acting as vasodilators in the placental vasculature. Peaks of ANP and BNP expression during gestation coincide with significant events in cardiac organogenesis, suggesting a role for NP in the formation of the heart. Levels of atrial natriuretic peptide (ANP) are higher in the fetal circulation than in adults, and fetal ventricles express higher levels of ANP and B-type natriuretic peptide (BNP) than adult ventricles. In this comprehensive review we have discussed the role NP during development of the fetal heart and circulation and in various cardiovascular diseases of neonatal and pediatric age group.


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Circulating Biochemical Markers of Brain Damage in Infants Complicated by Ischemia Reperfusion Injury
Diego Gazzolo, Raul Abella, Emanuela Marinoni, Romolo Di Iorio, Giovanni Li Volti, Fabio Galvano, Giacomo Pongiglione, Alessandro Frigiola, Enrico Bertino and Pasquale Florio

Hypoxia-ischemia constitutes a risk in infants by altering cerebral blood flow regulatory mechanisms and causing loss of cerebral vascular auto-regulation. Hypotension, cerebral ischemia, and reperfusion are the main events involved in vascular auto-regulation leading to cell death and tissue damage. Reperfusion could be critical since organ damage, particularly of the brain, may be amplified during this period. An exaggerated activation of vasoactive agents of calcium mediated effects could be responsible for reperfusion injury, which, in turns, leads to cerebral hemorrhage and damage. These dramatic phenomena represent a common repertoire in infants complicated by perinatal acute or chronic hypoxia or cardiovascular disorders treated by risky procedures such as open heart surgery and cardiopulmonary by-pass (CPB). To date, despite accurate perinatal and intra-operative monitoring, the post-insult period is crucial, since clinical symptoms and monitoring parameters may be of no avail and therapeutic window for pharmacological intervention (6-12 hours) may be limited, at a time when brain damage is already occurring. Therefore, the measurement of circulating biochemical markers of brain damage, such as vasoactive agents and nervous tissue peptides is eagerly awaited in clinical practice to detect high risk infants.

The present review is aimed at investigating the role as circulating biochemical markers such as adrenomedullin, a vasoactive peptide; S100B, a calcium binding protein, activin A, a glycoprotein; neuronal specific enolase (NSE), a dimeric isoenzyme; glial fibrillary acid protein (GFAP), a astroglial protein, in the cascade of events leading to ischemia reperfusion injury in infants complicated by perinatal asphyxia or cardiovascular disorders requiring risky therapeutic strategies such as CPB and/or extracorporeal membrane oxygenation.

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Immunomodulator Activity of 3-Hydroxy-3-Methilglutaryl-CoA Inhibitors
C. Smaldone, S. Brugaletta, V. Pazzano and G. Liuzzo

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-CoA are best known for their lipid-lowering effects but they also possess immunomodulatory properties that are, at least in part, independent of changes in serum cholesterol. Some recent clinical trials (eg. PROVE-IT) have shown that statins exert beneficial cardiovascular effects independently of the resultant level of LDL cholesterol.

These “pleiotropic” effects seem to be due to inhibition of prenylation of several proteins such as the small GTP-binding proteins Ras and Rho, and to the disruption, or depletion, of cholesterol rich membrane micro-domains (membrane rafts). Through these pathways statins are able to modulate immune responses by modulating cytokine levels and by affecting the function of cells involved in both innate and adaptive responses. Over the past decade, a large number of studies reported a prominent role of inflammation and immune response in atherosclerosis, thus, the ability of statins to modulate immune-inflammatory processes could explain their cardiovascular beneficial effects beyond lipid-lowering effects. Moreover, various studies demonstrated beneficial effects of statins in inflammatory and auto-immune diseases, such as rheumatoid arthritis, multiple sclerosis, and others.

The purpose of this review is to summarize clinical and experimental evidence of immunomodulatory properties of these drugs, highlighting their clinical and, thus, therapeutic implications.


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Antiarrhythmic Drug Therapy for Atrial Fibrillation: Focus on Atrial Selectivity and Safety
D. Li, H. Sun and P. Levesque

Atrial fibrillation (AF) is a highly prevalent arrhythmia and responsible for significant morbidity, mortality and health care cost. The prevalence of AF is expected to increase markedly with the aging population. The use of conventional antiarrhythmic agents has been limited by potentially fatal ventricular proarrhythmia. Rhythm control could become the preferred treatment strategy for AF if antiarrhythmic agents that are similarly or more effective, but safer, than currently approved AF agents become available. A subanalysis of the Atrial Fibrillation Follow-Up Investigation of Rhythm Management (AFFIRM) trial data showed that normal sinus rhythm confers a survival benefit in AF, suggesting that rhythm control, if achieved without the adverse effects related to current antiarrhythmic medications, may offer a significant survival advantage over rate control. Considerable work has been performed to explore novel, potentially safer antiarrhythmic drug targets for AF therapy, and some of these drug targets are currently being tested in experimental and clinical proof of concept studies. This article summarizes relevant aspects of the cellular electrophysiology of AF and re-views the actions of pharmacological agents being considered for the prevention and treatment of AF, focusing on atrial selective antiarrhythmic agents. A variety of drugs that inhibit the atrium-specific ultra rapid delayed rectifier potassium current (IKur) are being evaluated pre-clinically, but human experience with these agents is limited. The acetylcholine-activated current (IKACh) is another novel candidate target for atrial-specific drug therapy. The constitutively active form of this current is increased in human AF and pharmacological inhibition might be of therapeutic value. Certain drugs have IKACh blocking properties, but similar to IKur-blockers, none have been shown to have pure selectivity for this current. Newer agents being studied also include gap junction modulators and angiotensin-converting enzyme inhibitors. There is great hope that at least some of these agents will ultimately be available for effective and safer clinical treatment and prevention of AF.


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Nucleotide-Derived Thrombin Inhibitors: A New Tool for an Old Issue
Stefano Lancellotti and Raimondo De Cristofaro

Aptamer molecules represent an attractive approach in pharmacological therapy. Thrombin is a plasma serine protease that plays a key role in coagulation and haemostasis, also playing a relevant role in endothelial and smooth muscle cell functions. Thus, the development and use of direct thrombin inhibitors represents a potent tool in cardiovascular therapeutics. This review describes the status of direct thrombin inhibitors, focusing on aptamer-based drug candidates, that are at present in pre-clinical and in clinical trials. In addition, more recent research strategies in the design of novel aptamer thrombin inhibitors are presented and discussed. In particular, their structural, conformational, pharmacokinetic and pharmacodynamic properties are discussed in relation with the specificity of their binding to relevant thrombin exosites, which regulate the enzyme interaction with natural substrates and cellular receptors. Despite the addition of new effective anticoagulants to the therapeutic armoury, there remains a need for safer and effective anticoagulants. The aptamer- based thrombin inhibitors may represent an attractive approach for future developments of more potent and safer anticoagulants.

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Human Plasma Kallikrein-Kinin System: Physiological and Biochemical Parameters
J.W. Bryant and Z. Shariat-Madar

The plasma kallikrein-kinin system (KKS) plays a critical role in human physiology. The KKS encompasses coagulation factor XII (FXII), the complex of prekallikrein (PK) and high molecular weight kininogen (HK). The conversion of plasma prekallikrein to kallikrein by the activated FXII and in response to numerous different stimuli leads to the generation of bradykinin (BK) and activated HK (HKa, an antiangiogenic peptide). BK is a proinflammatory peptide, a pain mediator and potent vasodilator, leading to robust accumulation of fluid in the interstitium. Systemic production of BK, HKa with the interplay between BK bound-BK receptors and the soluble form of HKa are key to angiogenesis and hemodynamics. KKS has been implicated in the pathogenesis of inflammation, hypertension, endotoxemia, and coagulopathy. In all these cases increased BK levels is the hallmark. In some cases, the persistent production of BK due to the deficiency of the blood protein C1-inhibitor, which controls FXII, is detrimental to the survival of the patients with hereditary angioedema (HAE). In others, the inability of angiotensin converting enzyme (ACE) to degrade BK leads to elevated BK levels and edema in patients on ACE inhibitors. Thus, the mechanisms that interfere with BK liberation or degradation would lead to blood pressure dysfunction. In contrast, anti-kallikrein treatment could have adverse effects in hemodynamic changes induced by vasoconstrictor agents. Genetic models of kallikrein deficiency are needed to evaluate the quantitative role of kallikrein and to validate whether strategies designed to activate or inhibit kallikrein may be important for regulating whole-body BK sensitivity.


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Cardiotoxicity of Tyrosine-Kinase-Targeting Drugs
A. Garcia-Alvarez, X. Garcia-Albeniz, J. Esteve, M. Rovira and X. Bosch

The development of the so-called "targeted therapies", particularly those drugs that inhibit the activity of tyrosine kinases, has become a remarkable progress in the treatment of neoplastic diseases. The small molecule tyrosine kinase inhibitor (TKI) imatinib has revolutionized the treatment of chronic myeloid leukemia, and trastuzumab, the humanized monoclonal antibody against the ERBB2 receptor tyrosine kinase, has proved to have a high efficacy in 25% of breast cancers. On the basis of treatment success it is expected that targeted therapies will spread its use in the future.

Recent data has shown that some of these therapies are associated with certain cardiotoxicity ranging from asymptomatic mild left ventricular dysfunction to congestive heart failure through different mechanisms. However, rates of cardiotoxicity associated with TKI are not well known mainly because clinical trials usually do not include predefined cardiac endpoints or the assessment of left ventricular function before and during treatment. In addition, it is especially difficult to diagnose heart failure in patients with some kinds of cancer who have many reasons to develop dyspnoea. Here we summarize what is known up to date about the cardiotoxicity of drugs targeting the tyrosine kinases. Being aware of the risk of using these drugs is particularly important to early detect and institute the appropriate treatment to prevent irreversible myocardial injury, especially when some neoplastic diseases, as hematological or breast cancers, can affect young people with an estimated long-term survival.