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Contents

Platelet Signaling Induced by Lipoproteins Pp. 93-109
S.J.A. Korporaal and J.W.N. Akkerman
[Abstract]

Pathophysiology of Platelet Resistance to Anti- Aggregating Agents in Insulin Resistance and Type 2 Diabetes: Implications for Anti-Aggregating Therapy Pp. 111-128
G. Anfossi and M. Trovati
[Abstract]

Aldosterone Receptor Antagonists and Cardiovascular Disease: Do We Need a Change of the Guard? Pp. 129-153
C.W. Jewell, L.E. Watson, J. Mock and D.E. Dostal
[Abstract]

COX-Inhibiting Nitric Oxide Donors (CINODs): Potential Benefits on Cardiovascular and Renal Function Pp. 155-164
M.N. Muscará and J.L. Wallace
[Abstract]

Inflammation in Cardiovascular Disease and Regulation of the Actin Cytoskeleton in Inflammatory Cells: The Actin Cytoskeleton as a Target Pp. 165-182
T.H. Thomas and A. Advani
[Abstract]

The Role of Thrombomodulin in Atherosclerosis: From Bench to Bedside Pp. 183-187
Y.-H. Li, G.-Y. Shi and H.-L. Wu
[Abstract]

Abstracts

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Platelet Signaling Induced by Lipoproteins
S.J.A. Korporaal and J.W.N. Akkerman

Cardiovascular disease is the main cause of death and disability in the Western society. Lipoproteins play an important role in the development of this disease and affect different cell types involved in atherosclerosis and thrombosis. Based on their density, five classes of lipoproteins have been identified which all influence cells via distinct mechanisms. Modification turns lipoproteins into atherogenic particles with a prominent role in atherogenesis.

The interaction of lipoproteins with platelets has been under investigation for a number of years. Especially the role of LDL in platelet signaling has been studied intensively as platelets of hypercholesterolemic patients are hyperreactive and show hyperaggregability in vitro and enhanced activity in vivo, suggesting that LDL enhances platelet responsiveness. Several signaling pathways induced by LDL have been revealed in vitro, such as signaling via p38 mitogen-activated protein kinase (p38_^MAPK) and p125 focal adhesion kinase (p125_^FAK). HDL opposes the activating properties of LDL on platelets, whereas the effects of chylomicrons, VLDL or IDL on platelet function are controversial. Modification of lipoproteins is associated with the generation of new constituents with new signaling properties. In particular, the platelet-activating properties of lysophosphatidic acid, which is a constituent of atherosclerotic plaques and is generated upon oxidation of LDL, have been investigated intensively.

This review provides a summary of the activation of signaling pathways after platelet-lipoprotein interactions, with special emphasis on the role of these interactions in the development of thrombosis and atherosclerosis.

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Pathophysiology of Platelet Resistance to Anti- Aggregating Agents in Insulin Resistance and Type 2 Diabetes: Implications for Anti-Aggregating Therapy
G. Anfossi and M. Trovati

The insulin resistance syndrome, which presents among its many facets obesity and type 2 diabetes mellitus, is a major risk factor for cardiovascular events. Thus, therapeutic guidelines recommend multifactorial treatment programs including, especially in the presence of type 2 diabetes, antiplatelet drugs. Few data, however, are available about the protective effect of antiplatelet therapy in both obese and type 2 diabetic patients. Furthermore, some reports showed a decreased sensitivity to the platelet antiaggregating effect of acetylsalicylic acid in diabetic patients. In the first part of this review, we focused our attention to alterations of platelets from insulin resistant subjects with or without type 2 diabetes, underlining that platelet hyperactivation is explained, at least in part, by: i) a reduced sensitivity to agents exerting an inhibitory modulation of platelet responses, ii) an altered intracellular milieu with elevated cytosolic Ca_²⁺, iii) an enhanced thromboxane A₂ synthesis, and iv) an increased number and/or function of GPIIb/IIIa complexes on platelet membranes. Furthermore, oxidative stress, which increases isoprostane production from arachidonic acid, may be involved in platelet hyperactivation, since isoprostanes activate platelets by interplaying with thromboxane receptors. These defects explain why antiplatelet therapy for both chronic atherosclerotic vascular disease and acute coronary syndromes should be specifically tailored in obese, insulin resistant subjects, especially in the presence of type 2 diabetes mellitus. Thus, in the second part of this review we carried out a critical overview of the clinical trials in subjects with metabolic syndrome and type 2 diabetes mellitus with or without macroangiopathy.

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Aldosterone Receptor Antagonists and Cardiovascular Disease: Do We Need a Change of the Guard?
C.W. Jewell, L.E. Watson, J. Mock and D.E. Dostal

Aldosterone is a mineralocorticoid primarily produced in the zona glomerulosa of the adrenal gland. For many years, aldosterone (Aldo) was thought to have its sole site of action in the kidney, where it regulated sodium excretion and potassium reabsorption. It is now known that Aldo is produced in cardiovascular tissues, and has been implicated in the development of ventricular hypertrophy and cardiac fibrosis. The precise mechanisms whereby Aldo acts in cardiac tissues are diverse. It was assumed that Aldo production could be limited by angiotensin-converting enzyme (ACE) inhibition, but serial measurements during therapy reveal only a transient decrease in Aldo levels. Moreover, the effects of Aldo on cardiac tissues occur even when angiotensin II (Ang II) has been suppressed or eliminated. Multiple investigators have examined effects of Aldo receptor blockade in human subjects and various animal models using the two Aldo receptor antagonists (ARAs), spironolactone and eplerenone. Major clinical trials involving spironolactone (RALES) and eplerenone (EPHESUS) ARAs have shown significant benefits in the treatment of congestive heart failure (CHF). In RALES, patients with New York Heart Association (NYHA) Class III or IV systolic heart failure treated with spironolactone had a 30% relative risk decrease in mortality. Although spironolactone is an effective competitive inhibitor of the mineralocorticoid receptor (MR), progestational and antiandrogenic side effects limit its use in some patients. Eplerenone, a more selective ARA, lacks these undesirable side effects. Although eplerenone is 20-fold less potent at the MR, it demonstrates efficacy similar to spironolactone, possibly due to decreased protein binding. Eplerenone has fewer side effects than spironolactone, which has been attributed to the low cross-reactivity with androgen and progesterone receptors. In EPHESUS, patients with left ventricular systolic dysfunction [Ejection Fraction (EF) <40%] and CHF following an acute myocardial infarction (AMI), were treated with eplerenone, resulting in a 17% reduction in cardiovascular mortality. However, these studies were limited in that diastolic function was not evaluated, although approximately 1/2 of CHF is due to diastolic dysfunction alone. To date, neither ARA has been studied for the treatment of diastolic dysfunction in a major clinical trial. However, numerous animal studies employing ARAs have shown a decrease in cardiac hypertrophy and fibrosis, indicating the potential benefits of these agents in the treatment of diastolic heart failure. In this review, we discuss possible underlying mechanisms responsible for Aldo effects on cardiovascular function and compare the beneficial effects of spironolactone and eplerenone in the treatment of heart disease.

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COX-Inhibiting Nitric Oxide Donors (CINODs): Potential Benefits on Cardiovascular and Renal Function
M.N. Muscará and J.L. Wallace

The COX-inhibiting nitric oxide donors (CINODs) are a new class of agents designed for the treatment of pain and inflammation. CINODs have a multi-pathway mechanism of action that involves COX inhibition and nitric oxide donation. The anti-inflammatory and analgesic effects of COX inhibition are reinforced through inhibition of caspase-1 regulated cytokine production, while nitric oxide donation provides multiorgan protection. Whereas both conventional nonsteroidal anti-inflammatory drugs (NSAIDs) and COX-2-selective NSAIDs are associated with a variety of adverse effects on the renal system, such as hypertension and edema, CINODs may offer an improved renal safety profile. These agents are devoid of hypertensive effects in animal models and their mechanism of action suggests that they may not cause edema. CINODs also have other renal-sparing effects, being better tolerated than NSAIDs in models of kidney failure. CINODs have been shown to prevent platelet activation in vitro and exhibit anti-thrombotic activity in vivo. In animal models of ischemia/reperfusion, CINODs treatment results in improved recovery of heart contractility and reduced left ventricular end-diastolic pressure, in contrast to the effects of aspirin. The combination of improved analgesia, reduced gastrointestinal toxicity and cardiorenal protection has been established in animal models, and early clinical results suggest a favourable gastrointestinal safety profile in humans. The potential for CINODs to provide cardiorenal protection in humans is currently being investigated.

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Inflammation in Cardiovascular Disease and Regulation of the Actin Cytoskeleton in Inflammatory Cells: The Actin Cytoskeleton as a Target
T.H. Thomas and A. Advani

Cardiovascular disease is prevalent in developed countries causing very large burdens to health services. The underlying pathology is atheromatous plaque in the sub-endothelial region of the vascular wall. High levels of low density lipoprotein cholesterol and high blood pressure cause endothelial damage. Atheroma develop from a response to this injury that is perpetuated to chronic inflammation. The invasion of inflammatory leukocytes into atheroma during its development and in the precipitation of acute thrombotic events is mediated by adhesion molecules on the cell surface. These are regulated by the actin filament cytoskeleton which also mediates intracellular signalling from them. The actin cytoskeleton is central to NADPH oxidase activation that produces superoxide which is an intracellular signalling molecule for the hypertensive and inflammatory actions of angiotensin II. There are polymorphisms in actin filament proteins such as adducin and caldesmon and in the promoter regions of tropomyosins that may cause individual variation in these processes. Many signalling molecules in the actin filament response to inflammatory stimuli and in signalling downstream from actin filaments are small G-proteins that require post-transcriptional modification by isoprenoids from the cholesterol synthetic pathway. Statins deplete the isoprenoids and so down regulate G-proteins that mediate the inflammatory response. Angiotensin converting enzyme inhibitors and angiotensin II receptor type 1 antagonists decrease angiotensin II stimulated superoxide production thus decreasing not only blood pressure but also inflammation. The anti-inflammatory effects of these drugs, involving altered actin filament function, are a major contributor to their benefits in the treatment of cardiovascular disease. The feasibility of modifying the behaviour of actin filament proteins as a therapeutic approach for cardiovascular disease is considered.

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The Role of Thrombomodulin in Atherosclerosis: From Bench to Bedside
Y.-H. Li, G.-Y. Shi and H.-L. Wu

Atherosclerosis remains a leading cause of morbidity and mortality worldwide. In addition to the deposition of cholesterol in the arterial wall, inflammation, cell proliferation and migration play important roles in the pathogenesis of atherosclerosis. Thrombomodulin (TM) is a cell surface-expressed glycoprotein which is predominantly synthesized by vascular endothelial cells and a critical cofactor for thrombin-mediated activation of protein C. Activated protein C is best known for its natural anticoagulant and anti-inflammatory properties. Recent evidence has revealed that TM also has protein C- and thrombin-independent physiological function. This review summarizes recent investigations of TM, giving an overview on the TM unique effects on cellular proliferation, adhesion and inflammation, all of which are important steps in atherosclerosis. The current evidence of TM in the pathogenesis of atherosclerosis will be reviewed, and the associations of TM gene polymorphisms with atherosclerosis are presented. Newly emerging data of the TM in mouse atherosclerosis model demonstrates that TM potentially may have therapeutic role in atherosclerosis.

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