Current Vascular Pharmacology - Volume 1, Issue 2, 2003

Endothelial dysfunction is thought to be an important factor in the development of atherosclerosis. Over the past decade, a non-invasive technique has evolved to evaluate flow-mediated vasodilation (FMD), an endothelium-dependent function, in the brachial artery. FMD decreases with increasing age and subjects with diabetes mellitus, hypercholesterolemia, smokers and hypertension have decreased FMD. There are a few concise studies reporting that FMD predicts cardiovascular events. However, the assumption that focal measurement of brachial artery FMD predicts coronary artery disease deserves further investigation.

Atherosclerosis is a chronic systemic disease of the vasculature with an inflammatory component. It accounts for the majority of cardiovascular morbidity and mortality in industrialized countries and its incidence is increasing in developing countries. The impairment of vascular endothelial cell function in atherosclerosis and in conditions associated with increased cardiovascular risk is an important determinant of disease progression. The reduction of endothelium-dependent relaxation in the coronary and systemic circulation in atherosclerosis is in part due to decreased bioavailability of nitric oxide and increased release of oxygen-derived free radicals. Atherosclerosis also increases the formation of vasoconstrictors and growth factors, adhesion of leukocytes, thrombosis, inflammation, cell proliferation, as well as increases in vascular tone. Here we review mechanisms and therapeutic approaches to improve endothelial pathways in atherosclerosis. Restoration of NO bioactivity through pharmacological inhibition of the renin-angiotensin system, statin therapy, or endothelin receptor blockade, ameliorates vascular function in experimental hypercholesterolemia, hypertension and heart failure. These treatments also have therapeutic benefit for patients at risk or with overt atherosclerosis, to reduce vascular and myocardial complications of this disease.

Before it gets to the development of manifest atherosclerotic lesions, all known risk factors primarily induce functional alterations in the vascular wall, namely in endothelial cells. Being termed endothelial dysfunction or endothelial activation, this condition is characterized by an altered availability of nitric oxide (NO). Under physiological conditions, NO is of unequivocal importance for the regulation of vascular homeostasis. Endothelium-derived NO released abluminally increases soluble guanylat cyclase activity in smooth muscle cells, thereby inducing relaxation and consequently vasodilatation. Intraluminally, NO inhibits the expression of adhesion molecules both on endothelial cells and neutrophils, thus preventing the adherence of cellular elements to the vascular wall. Furthermore, NO has antithrombotic effects by inhibiting platelet aggregation and directly influencing the synthesis of different factors involved in the coagulation cascade. Finally, in the long term, NO has been shown to exert antiproliferative properties.NO is generated intracellularly from L-arginine via NO-synthase with the help of several cofactors, including tetrahydobiopterin. Interestingly, it has recently become evident that under certain conditions, when there is a lack of tetrahydrobiopterin, NO-synthase produces reactive oxygen species instead of NO. Reactive oxygen species counteract the effects of NO and also scavenge NO resulting in the formation of peroxynitrite (ONOO). Peroxynitrite has been shown to have deleterious effects with respect to vascular function.The aim of the current review is to elucidate recent progress regarding the pathophysiological understanding of endothelial dysfunction. Furthermore, the significance of this condition for the evaluation and prognosis of patients is discussed. Finally, current therapeutical strategies in the treatment and improvement of endothelial dysfunction are highlighted.

A number of epidemiological studies have shown that diets rich in plant-derived phenolic compounds reduce the risk of coronary heart disease. The chronic antioxidant and hypolipidemic activities of these compounds have important roles in prevention of lipoprotein oxidation and atherosclerotic lesion development. In recent years, it has been recognized that inflammation is directly involved in development of cardiovascular disease and clinical events such as atherosclerotic plaque rupture (which is the trigger of acute coronary syndrome), arterial restenosis, and myocardial ischemia-reperfusion injury. Phenolic compounds have significant antiinflammatory effects, including inhibition of adhesion molecule, cytokine and chemokine gene expression; inhibition of platelet function; augmentation of endothelial nitric oxide release; suppression of smooth muscle activation; and other effects on proinflammatory factors such as endothelin and matrix metalloproteinases. However, direct evidence of acute therapeutic benefits of phenolic compounds in cardiovascular disorders remains sparse. This review attempts to integrate the inflammatory mechanisms involved in these cardiovascular diseases with recent findings on the antiinflammatory effects of phenolic compounds. Findings from the limited in vivo studies in this regard are discussed. It is suggested that searching for novel phenolic compounds with higher specificity and efficacy may represent a fruitful approach in development of new cardiovascular therapeutics.

Atherogenic cofactors, such as altered cholesterol metabolism, may impact locally on inflammatory responses in atherosclerotic lesions. Blood levels of inflammatory markers (e.g., C-reactive protein, fibrinogen) have been associated with hypercholesterolemia and with overt atherothrombotic disorders. More recently, cytokines (e.g., interleukin-6, interleukin-1β) and soluble adhesion molecules (e.g., selectins, intercellular adhesion molecule-1, vascular cell adhesion molecule-1) have been associated with both hypercholesterolemia and atherosclerotic disease, suggesting their use as potential therapeutic targets for the non-specific “anti-inflammatory” treatment of atherosclerosis.The inflammatory response associated with hypercholesterolemia involves not only the intrinsic cells of the artery wall, but also circulating cells. Platelets participate in this disease process through the release of a wide variety of biologically active substances. An imbalance of the hemostatic system and persistent in vivo platelet activation can be observed in hypercholesterolemia and may have pathophysiological implications in the development and progression of atherosclerotic plaques. Recent findings on the inflammatory actions of platelets have esta blished the potential for a pr eviously unr ecognize d biologic role for plate le ts in inflammation a nd va scula r injury, and have opened new perspectives in the comprehension of the pathogenetic mechanism(s) of atherosclerosis. Stimulated platele ts ac tively synthesize proinflammatory cytokines ( e.g., CD40L, IL-1 β) and are able to r ele ase c he mokines (i.e., platelet factor-4, RANT ES) which have been all involved in the inflammatory process associated with hyper cholesterole mia .This review will summarize the present understanding of the interplay between hypercholesterolemia, inflammation and platelet activation in the development and progression of atherosclerosis, and we also discuss the effects of lipid-lowering treatment on these phenomena.

Pulmonary arterial hypertension (PAH) is associated with changes in vascular tone as well as vascular structure, with the relative contribution of each dependent upon the etiology of the increased vascular resistance. Prostacyclin treatment has markedly improved both the therapeutic options and the prognosis of PAH. The beneficial effect of prostacyclin in PAH is linked to the powerful vasodilating capacity and, even more importantly, to the inhibition of platelet aggregation, smooth muscle proliferation and antiinflammatory actions. Since prostacyclin has a very short plasma half-life, continuous intravenous administration via a portable infusion pump must be carried out. Because of the complexity of the delivery and the associated complications, intravenous prostacyclin (epoprostenol) therapy is restricted to patients with late NYHA Class III and Class IV and thus alternative modes of delivery in less advanced PAH are desirable. Recent clinical studies with more stable prostacyclin analogs such as subcutaneously delivered treprostinil, orally active beraprost and aerosolized iloprost have demonstrated beneficial effects of each of these prostanoids, especially in NYHA Class II and III patients and, therefore, these agents should be considered first for prostanoid therapy in the early stages of PAH. Prostaglandins may be more effective in conjunction with endothelin receptor antagonists or phosphodiesterase inhibitors and an increasing number of studies are now addressing the combined efficiency and safety of these combinations.This update will focus on the current development status of PAH therapy with prostacyclin and its analogs. Special attention will be accorded to the selection of patients for prostanoid therapy, therapy monitoring and improvement of therapeutic efficacy by addition of other new therapeutic agents to prostaglandins. Survival benefits and special aspects of bridging-to-transplant therapy are also important aspects of the review.

Coronary Artery Disease (CAD) remains globally the leading cause of death and long-term morbidity. Among the many manifestations of CAD, acute coronary syndrome (ACS), ranging from unstable angina to acute myocardial infarction, is the most catastrophic event due to our inability to predict its occurrence. Despite improved treatments of CAD, ACS results in sudden death or permanent disability in a substantial percentage of patients. If we could predict the timing of ACS or better yet prevent its occurrence, we could alter the otherwise unfavorable course of CAD.Several studies have convincingly demonstrated that majority of all ACS develops from previously mild to moderate stenoses. Thus, based on these and autopsy studies, sudden disruption or rupture of the non-obstructive “vulnerable”atherosclerotic lesion is currently considered the cause of ACS. Recent clinical studies have substantiated earlier autopsy observations that plaque vulnerability is a systemic process, involving multiple locations concurrently. Although the exact inciting factors of the vulnerable plaque rupture are unknown, inflammation is accepted to be a pivotal event. The possibility of stabilizing the vulnerable plaques has strongly been supported by the lipid lowering trials, in which dramatic reduction of the acute coronary events was noted despite subtle improvements in luminal diameter. Furthermore, antiplatelet therapies have become an important preventative therapy due to the essential role of platelets in the aftermath of plaque rupture. Finally, various imaging modalities to diagnose the plaque vulnerability could help prevent the acute coronary events in the future.

Peripheral arterial disease (PAD) is a common but under-recognized problem. Intermittent claudication is the most frequent symptom of PAD, although the diagnosis of PAD is often overlooked until the patient is presented with limb-threatening ischemia. Importantly, PAD is a marker of generalized atherosclerosis and is closely associated with coronary and cerebrovascular disease. The primary causes of death in patients with PAD are myocardial infarction and stroke. Reducing risk factors is an integral and aggressive part of the treatment regimen. The recognition and diagnosis of PAD, combined with its appropriate medical management, may well reduce the overall risk of cardiovascular morbidity. When diagnosed early, both exercise and pharmacotherapy can ameliorate symptoms of claudication, augment functional performance, and improve quality of life. This review focuses on the general medical management and specific therapeutic options. Because PAD is a manifestation of generalized atherosclerosis, the principal issue in medical management of PAD is a treatment plan that modifies known risk factors for atherosclerosis and its atherothrombotic complications. All patients with PAD should be receiving antiplatelet therapy to prevent ischemic events and ACE inhibitors should be used if appropriate. Medical treatment for patients with claudication includes exercise in rehabilitation and drug therapy. It is also recognized that selected patients with claudication symptoms may benefit from catheter-based interventions, and most PAD patients with critical leg ischemia require revascularization procedures. Although many therapies for claudication have been thoroughly investigated, research continues on new treatments. In contrast, more prospective, randomized trials are needed to evaluate various therapies for treating patients with PAD.

In vascular tissues, angiotensin II is potentially cleaved from angiotensin I by chymase and angiotensin converting enzyme (ACE). In the normal state, ACE regulates angiotensin II formation and plays a crucial role in the regulation of blood pressure, whereas chymase is stored in mast cells and has no angiotensin II-forming activity. Chymase is activated immediately upon its release into the extracellular matrix in vascular tissues after mast cells have been activated by local stimuli such as vessel injury by grafting or a balloon catheter. In dog grafted veins, vascular proliferation, chymase activity, angiotensin II concentration and mRNA levels of fibronectin, collagen I and collagen III were significantly increased after the operation, while they were significantly suppressed by a chymase inhibitor. A clinical trial of an angiotensin II receptor blocker (ARB) for preventing restenosis after percutaneous transluminal coronary angioplasty was successful, but that of an ACE inhibitor was not. After balloon injury in dog vessels, chymase activity was signifcantly increased in the injured artery, and a chymase inhibitor and an ARB were effective in preventing the vascular proliferation, but an ACE inhibitor was ineffective. On the other hand, a chymase inhibitor, unlike an ACE inhibitor and an ARB, did not affect blood pressure. These reports indicate that local angiotensin II production by chymase is involved only in the intimal hyperplasia seen in the injured vessels. Therefore, chymase inhibitors may be useful for preventing vascular disoders without affecting blood pressure.

Despite recent advances, cardiovascular disease continues to be the leading cause of death among patients with diabetes. Diabetes-related heart disease makes up the majority of the cardiovascular morbidity and mortality and this clinical entity results from synergistic interaction amongst various overlapping mechanisms. Diabetes-related heart disease is characterised by a propensity to develop premature, diffuse atherosclerotic disease, structural and functional abnormalities of the microvasculature, autonomic dysfunction and intrinsic myocardial dysfunction (the so-called diabetic ‘cardiomyopathy’), all of which are exacerbated by hypertension and diabetic nephropathy. The renin-angiotensinaldosterone system possesses various autocrine and paracrine effects which drive most of the pathophysiological mechanisms in diabetes-related heart disease. This review aims to describe the expanding role of the renin-angiotensinaldosterone system, the complex entity of diabetes-related heart disease and the (emerging) evidence for specific inhibition of the renin-angiotensin-aldosterone system in diabetes.