Cardiovascular & Hematological Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Cardiovascular & Hematological Agents) - Volume 5, Issue 1, 2007

Apelin is a peptide recently isolated from bovine stomach extracts which appears to act as an endogenous ligand for the previously orphaned G-protein-coupled APJ receptor. The apelin gene encodes for a pre-propeptide consisting of 77 amino acids with mature apelin likely to be derived from the C-terminal region as either a 36, 17 or 13 amino acid peptide. Apelin mRNA expression and peptide immunoreactivity has been described in a variety of tissues including gastrointestinal tract, adipose tissue, brain, kidney, liver, lung and at various sites within the cardiovascular system. Apelin is strongly expressed in the heart with expression also present in the large conduit vessels, coronary vessels and endothelial cells. Message expression for the APJ receptor is similarly distributed throughout the brain and periphery, again including cardiovascular tissue. Consistent with this pattern of distribution, apelin and APJ have been shown to exhibit some role in the regulation of fluid homeostasis. In addition, a growing number of studies have reported cardiovascular actions of apelin. Not only has apelin been observed to alter arterial pressure, but the peptide also exhibits endotheliumdependent vasodilator actions in vivo and positive inotropic actions in the isolated heart. Furthermore, differences in apelin and APJ expression have been described in patients with congestive heart failure and circulating levels of apelin are also reported to change in heart failure. Taken together, these studies suggest a role for apelin in pressure/volume homeostasis and in the pathophysiology of cardiovascular disease. As such, manipulation of this peptide system may offer benefit to the syndrome of heart failure with potential clinical applications in humans.

Computational methods have been explored for predicting agents that produce therapeutic or adverse effects in cardiovascular and hematological systems. The quantitative structure-activity relationship (QSAR) method is the first statistical learning methods successfully used for predicting various classes of cardiovascular and hematological agents. In recent years, more sophisticated statistical learning methods have been explored for predicting cardiovascular and hematological agents particularly those of diverse structures that might not be straightforwardly modelled by single QSAR models. These methods include partial least squares, multiple linear regressions, linear discriminant analysis, k-nearest neighbour, artificial neural networks and support vector machines. Their application potential has been exhibited in the prediction of various classes of cardiovascular and hematological agents including 1, 4-dihydropyridine calcium channel antagonists, angiotensin converting enzyme inhibitors, thrombin inhibitors, AchE inhibitors, HERG potassium channel inhibitors and blockers, potassium channel openers, platelet aggregation inhibitors, protein kinase inhibitors, dopamine antagonists and torsade de pointes causing agents. This article reviews the strategies, current progresses and problems in using statistical learning methods for predicting cardiovascular and hematological agents. It also evaluates algorithms for properly representing and extracting the structural and physicochemical properties of compounds relevant to the prediction of cardiovascular and hematological agents.

The five current members of the thrombospondin (TSP) family can be divided in two subgroups according to their molecular architecture. TSP-1 and -2 (subgroup A) are trimeric matricellular proteins that do not contribute directly to tissue integrity, but influence cell function by modulating cell-matrix interactions, whereas TSP-3, -4 and -5 (subgroup B) are pentameric proteins. TSP-1 and TSP-2 are markedly induced in healing wounds and may regulate cellular responses important for tissue repair. TSP-1 is a crucial activator of TGF-β , whereas both TSP-1 and TSP-2 inhibit angiogenesis. This manuscript reviews our current knowledge on the expression and role of the TSPs in healing myocardial infarcts. In both canine and murine infarcts, TSP-1 shows a strikingly selective localization in the infarct border zone. In the absence of injury, TSP-1 -/- mice exhibit normal cardiac morphology and show no evidence of myocardial inflammation. Infarcted TSP-1 -/- mice have an enhanced and protracted inflammatory response with subsequent expansion of granulation tissue in the non-infarcted area, resulting in myofibroblast infiltration into the viable myocardium neighboring the infarct. Infarcted TSP-1 -/- animals have enhanced left ventricular remodeling compared with their wildtype littermates. We suggest that TSP-1 is a critical component of the protective mechanisms induced in the infarct border zone in order to limit expansion of fibrosis into the non-infarcted myocardium. Localized TSP-1 expression may suppress expansion of the inflammatory process by activating TGF-β or by inhibiting local angiogenesis. In addition, TSP-1-mediated inhibition of MMP activity may decrease adverse remodeling. TSP-2, on the other hand, appears to be a crucial regulator of the integrity of the cardiac matrix that is necessary for the myocardium to cope with increased loading. The expression and potential role of the pentameric TSPs in the infarcted heart remain unknown. Understanding the specific mechanisms responsible for the protective effects of TSP-1 and TSP-2 in healing infarcts may lead to novel therapeutic interventions aiming at attenuating adverse left ventricular remodeling.

The ADAM (a disintegrin and metalloprotease) family of proteins possess multi-domain structures composed of a signal peptide, a prodomain, a metalloprotease domain, a disintegrin-like domain, a cysteine rich domain, an epidermal growth factor-like domain, a transmembrane domain and cytoplasmic tail. The disintegrin-like domain shares sequence similarity with the soluble venom disintegrins, a family of proteins which are potent inhibitors of integrinmediated platelet aggregation and cell adhesion. Several ADAMs have been reported to interact with integrins, and the disintegrin-like domain may be crucial part in this respect. A description of structure-activity relationship of ADAM proteins interacting with integrin is outlined in this review. The review highlights recent reports on potential integrin family for ADAMs and how ADAMs selectively modulate interaction for integrin mediated cell function. Lastly, it describes progress in understanding the structural features and functional roles of the ADAMs in normal and pathological conditions and how this insight may assist the development of new therapeutic approaches.

Myocardial sarcolemmal ATP-dependent potassium (KATP) channels, which are normally closed by high ATP concentration, open during ischemia when ATP generation decreases favoring K+ efflux. This reduces action potential duration (APD) decreasing the time of Ca2+ influx and Ca2+ overload. This behavior suggested that they might be involved in the protection against stunning and arrhythmias and in the mechanism of ischemic preconditioning. Sulfonylureas, used as hypoglycemic agents for the treatment of type 2 diabetes also block myocardial KATP channels prolonging APD during ischemia, which by allowing Ca2+ entry for a longer period of time, is potentially harmful to the heart. Controversial findings have been reported regarding the protective effect of sulfonylureas. Due to their importance in the clinical setting, their action on the heart of large conscious animal models is relevant. The effect of glibenclamide, a representative sulfonylurea, has been studied in a conscious sheep model submitted to regional 12 min ischemia. Glibenclamide (0.4 mg/kg) completely blocked KATP channels, as assessed by monophasic APD, producing a deleterious effect on reperfusion-induced arrhythmias and myocardial recovery from stunning in normal animals. This adverse effect was more noticeable in alloxan-induced diabetic sheep, where a lower dose (0.1 mg/kg) inhibited KATP channel opening worsening mechanical recovery and arrhythmia incidence. However, glibenclamide did not abolish ischemic late preconditioning against stunning and arrhythmias in normal animals. Because diabetic sheep do not develop this cardioprotective phenomenon, probably due to KATP channel dysfunction, it was not possible to assess glibenclamide effect on preconditioning in this pathological condition. In conclusion, in large conscious animals, glibenclamide interferes with the beneficial action of KATP channel opening during acute ischemia-reperfusion events both in normal and diabetic animals. Therefore, despite some studies claiming no added cardiovascular risk due to glibenclamide treatment, this pharmacological agent should be further investigated to ensure its safe administration in patients with concurrent heart disease.

High plasma levels of LDL cholesterol, triglycerides and low levels of HDL cholesterol are strong and independent risk factors of coronary heart disease (CHD). The first two abnormalities are addressed by a variety of drugs including statins, cholesterol absorption inhibitors, fibrates and niacin. Some of these drugs also elevate HDL albeit weakly. Thus treatments optimized for HDL elevation are still an unmet medical need. Low HDL-C is the most common lipoprotein abnormality in patients with CHD and the body of evidence showing an inverse relationship between HDL-C levels and risk for CHD has grown large. Research in the past decade not only greatly enhanced our understanding of HDL metabolism but also offered potential therapeutic targets to address low HDL syndrome. There are two classes of these ‘HDL drugs’ - those that elevate plasma HDL (e.g. cholesteryl ester transfer protein - CETP and ligands of transcription factors such as peroxisome proliferator activated receptor PPAR α/δ, liver X receptor (LXR)) and those that mimic HDL and facilitate reverse cholesterol transport (RCT) a key function of plasma HDL. HDL mimetics, which include ApoA1 mutants and peptide mimetics of ApoA1, are thought to be ‘fast acting’ and may show greater benefits especially in acute coronary syndromes. The purpose of this review is to examine key players in HDL metabolism and therapeutics that modulate/ mimic these targets. The prospect of these approaches in the prevention of cardiovascular disease is also discussed.

Fucoidans -- sulphated polysaccharides extracted from brown algae - could be beneficial in patients with ischemic diseases. Their antithrombotic and proangiogenic properties promote in animals, neovascularization and angiogenesis which prevent necrosis of ischemic tissue. In 1997, endothelial progenitor cells were first identified in human peripheral blood. They are recruited from bone marrow and contribute to neovascularization after ischemic injury. Mobilization of these cells in ischemic sites is an important step in new vessel formation. It is thought that the progenitors interact with endothelial cells, then extravasate and reach ischemic sites, where they proliferate and differentiate into new blood vessels. Although chemokines, cytokines and adhesion molecules are thought to be involved, the precise mechanism of progenitor mobilization is not fully understood. Recent studies suggest that stromal-derived factor 1 plays a critical role at several steps of progenitor mobilization. Given the role of proteoglycans within bone marrow, at the endothelium surface, and in growth factor and chemokine binding, fucoidans might influence the mobilization of endothelial progenitor cells and their incorporation in ischemic tissue. This review provides an update on circulating endothelial progenitors and their role in neovascularization. It focuses on recent advances in our understanding of interactions between these progenitor cells and exogenous sulphated polysaccharides, and their implications for understanding the fucoidan mechanism of action.

Brief periods of ischaemia induce in the myocardium an increased resistance to the injury due to a subsequent, more prolonged ischaemic episode. This phenomenon, known as ischaemic pre-conditioning (IPC), articulated in two distinct phases (an early and a delayed one), is ensured by different biological mechanisms. Although an exhaustive comprehension of these mechanisms has not yet been reached, it is widely accepted that among the various signals involved as triggers and/or end-effectors, an important role is undoubtedly played by the activation of cardiac ATP-sensitive potassium channels (KATP). In the myocardial cells, KATP channels have been identified both in the sarcolemmal membrane (sarc-KATP) and in the mitochondrial inner membrane (mito-KATP). Although many experimental findings suggest that a role of sarc-KATP channel activation in IPC cannot be excluded, in the last few years, many authors have indicated that this phenomenon could be attributed to the exclusive (or at least prevalent) activation of the mito-KATP channels. Conversely, drugs modulating the KATP channels (as activators or blockers), on one hand, have been employed as useful experimental tools for basic studies on IPC. On the other hand, KATP-openers have been viewed as promising possible therapeutic agents for limiting the myocardial injury due to ischaemic episodes. In particular, those molecules exhibiting a good degree of selectivity towards the mito-KATP channels have been indicated as potential anti-ischaemic cardio-protective pharmacological tools, devoid of other biological effects (such as negative inotropic activity, hypotension or hyperglycaemia) linked to the activation of cardiac and non-cardiac sarcKATP channels. In this paper, we wish to report the experimental evidence supporting the role of sarc- and mito-KATP channels in IPC, the relative signalling pathways potentially involved in the mechanisms of cardio-protection and, finally, an overview of the most important molecules acting as activators or blockers of KATP channels, with their selectivity profiles.

Leukocyte recruitment and the expression of pro-inflammatory cytokines are prevalent characteristics of early atherogenesis [1]. Recently, several inflammatory mediators have been linked to atheroma formation and inflammatory pathways have been shown to promote thrombosis [1]. The discovery of mast cells, activated T lymphocytes and macrophages in atherosclerotic lesions, the detection of human leukocyte antigen class II expression, and the finding of local secretion of several cytokines all suggest the involvement of immune and inflammatory mechanisms in the pathogenesis of atherosclerosis [2-5]. Recent research suggests activation of protease activated receptors (PAR) on the surface of endothelial cells may play a role in general mechanisms of inflammation. In previous studies, our laboratory has demonstrated that thrombin (which activates PAR-1) and tryptase (which activates PAR-2) stimulation of endothelial cells results in activation of calcium-independent phospholipase A2 (iPLA2) [6,7]. iPLA2 plays a critical role in the synthesis of membrane phospholipid-derived inflammatory mediators such as arachidonic acid, platelet activating factor (PAF), and prostaglandins, all demonstrated to be central in both the initiation and propagation of the inflammatory response. Activation of iPLA2 results in release of choline lysophospholipids from endothelial cells, these metabolites may contribute to the initiation of ventricular arrhythmias following myocardial ischemia as a direct result of incorporation into the myocyte sarcolemma. This biochemical event represents a direct link between occlusion of a coronary vessel and the nearly immediate initiation of arrhythmogenesis often seen in myocardial ischemia.