Is reversal of endothelial dysfunction still an attractive target in modern cardiology?

Although the endothelium has a number of important functions, the term endothelial dysfunction is commonly used to describe impairment in its vasodilatory capacity. There have been numerous studies evaluating the relationship between endothelial dysfunction and cardiovascular disease, however assessment of endothelial function is perhaps still primarily thought of as a research tool and has not reached widespread clinical acceptance. In this review we explore the relationship between endothelial dysfunction and cardiovascular disease, its prognostic significance, methods of pharmacological reversal of endothelial dysfunction, and ask the question, is reversal of endothelial dysfunction still an attractive target in modern cardiology?     

Endothelial Dysfunction as an Early Sign of Atherosclerosis

The endothelium, the monolayer covering the inner surface of blood vessels, plays a pivotal role in the regulation of vascular tone and structure, as well as vascular inflammation and thrombosis, i.e., of key events of the atherosclerotic disease process and its clinical complications, such as myocardial infarction and stroke. In particular a reduced endothelial availability of nitric oxide (NO), in part due to increased vascular oxidant stress, has been shown to promote a pro-inflammatory and prothrombotic phenotype of the endothelium. More recently, it has been observed that cardiovascular risk factors reduce the number and impair the function of circulating bone marrow-derived endothelial progenitor cells (EPCs), thereby impairing the endogenous endothelial repair capacity.Importantly, endothelial dysfunction has been identified as a common link of all cardiovascular risk factors. Numerous clinical studies have further demonstrated a close association of the degree of endothelial dysfunction with the risk of future cardiovascular events. Whether endothelial dysfunction can improve cardiovascular risk prediction on top of a careful evaluation of classic cardiovascular risk factors is currently prospectively analyzed in several studies, i.e., in the PREVENT-it study. Furthermore, novel easier to use methods to assess endothelial function are currently explored, i.e., the Endo-PAT system, for their potential in improving cardiovascular risk prediction.At present, assessment of endothelial function and EPCs are highly valuable research tools to improve our understanding of mechanisms of vascular disease and to determine the impact of novel therapeutic approaches on vascular function. Before endothelial function measurements can, however, be recommended in clinical practice for cardiovascular risk assessment, the results of ongoing prospective studies assessing the additive value of these measurements for cardiovascular risk prediction should be awaited.     

Endothelial function and hypertension

PURPOSE OF REVIEW: Endothelial dysfunction, in particular a reduced vascular availability of endothelium-derived nitric oxide, has been analysed in numerous experimental and clinical studies as a potential mechanism mediating the adverse vascular effects of hypertension. This paper outlines some notable studies in this dynamic field published recently. RECENT FINDINGS: The understanding of mechanisms underlying endothelial dysfunction in hypertension has been substantially advanced recently. Increased oxidant stress is thought to represent a major mechanism leading to reduced vascular availability of endothelium-derived nitric oxide. Vascular nicotinamide adenine dinucleotide phosphate oxidases, uncoupled nitric oxide synthase and xanthine oxidase have been identified as major sources of reactive oxygen species in hypertension. Endothelial dysfunction has been implicated in the macrovascular complications of hypertension, such as stroke or myocardial infarction, coronary microvascular dysfunction and increased arterial stiffness, probably at least partly resulting from loss of the antiatherogenic and vasculoprotective effects of endothelium-derived nitric oxide. SUMMARY: Recent research on endothelial dysfunction supports its clinical significance in hypertension, and has led to important insights into the pathophysiology of the disease. These observations suggest that targeting endothelial dysfunction, in particular reduced nitric oxide availability, would exert beneficial effects in hypertensive patients. This concept needs further evaluation in clinical studies.     

Endothelial dysfunction in metabolic syndrome: Prevalence,pathogenesis and management

The metabolic syndrome (MetS) is characterized by the presence of central obesity, impaired glucose metabolism, dyslipidemia and hypertension. Several studies showed that MetS is associated with increased risk for type 2 diabetes mellitus (T2DM) and vascular events. All components of MetS have adverse effects on the endothelium. Endothelial dysfunction plays a role in the pathogenesis of atherosclerosis and might also increase the risk for insulin resistance and T2DM. We review the prevalence and pathogenesis of endothelial dysfunction in MetS. We also discuss the potential effects of lifestyle measures and pharmacological interventions on endothelial function in these patients. It remains to be established whether improving endothelial function in MetS will reduce the risk for T2DM and vascular events.     

Endothelial Function: Strategies for Early Intervention

Assessment of endothelial function appears to be a valuable additional tool for diagnosing and therapeutic monitoring of coronary artery disease. The first part of this review discusses the biosynthesis, degradation, and antiatherosclerotic properties of nitric oxide, a major determinant of endothelial function. In the second part methods for assessing endothelial function and strategies for reversal of endothelial dysfunction are reviewed. Improvement of endothelial function may be obtained by lifestyle modifications, such as cessation of smoking, better blood glucose regulation, exercise, dietary measures, and pharmacological interventions, such as lipid lowering, antioxidant therapy, angiotensin-converting enzyme inhibition, and calcium channel blockers.     

Endothelial function and cerebrovascular disease: Implications for diagnosis and treatment

Opinion statement Cerebrovascular disease remains one of the most common causes of morbidity and mortality in the United States. There is strong evidence to implicate endothelial dysfunction in the initiation and progression of atherosclerosis and its complications. It is now well known that endothelial dysfunction represents a systemic syndrome involving multiple vascular beds, including the cerebral vasculature. Currently, no gold standard treatment for endothelial dysfunction exists. Nonetheless, several treatment strategies have been found to be helpful in improving endothelial function. A few of these strategies have been implicated in stroke risk reduction as well, adding another line of evidence to the relationship between endothelial function and cerebrovascular disease.     

Endothelial arginase: A new target in atherosclerosis

Decreased endothelial nitric oxide (NO) bioavailability as it relates to endothelial dysfunction plays an important role in various cardiovascular disorders, including atherosclerosis. Recent research has provided evidence that endothelial dysfunction in atherosclerosis is not primarily caused by decreased endothelial NO synthase (eNOS) gene expression, but rather deregulation of eNOS enzymatic activity, which contributes to the increased oxidative stress in atherosclerosis. Among other mechanisms, the substrate L-arginine is an important limiting factor for NO production. Emerging evidence demonstrates that L-arginine is not only converted to NO via eNOS, but also metabolized to urea and L-ornithine via arginase in endothelial cells. Hence, arginase competes with eNOS for the substrate L-arginine, resulting in deceased NO production. There are an increasing number of studies showing that enhanced arginase gene expression and/or activity contribute to endothelial dysfunction in various cardiovascular disorders, including atherosclerosis. Thus, endothelial arginase may represent a new therapeutic target in atherosclerosis.     

Endothelial cells, fibroblasts and vasculitis

One of the most important questions in vasculitis research is not why inflammation of blood vessels occurs but why it persists, often in a site-specific manner. In this review we illustrate how stromal cells, such as fibroblasts and pericytes, might play an important role in regulating the site at which vasculitis occurs. Smooth muscle cells and fibroblasts directly influence the behaviour of overlying vascular cells, amplifying the response of the endothelium to proinflammatory agents such as TNF-alpha and allowing enhanced and inappropriate leucocyte recruitment. An abnormal local vascular stromal environment can therefore influence local endothelial function and drive the persistence of local vascular inflammation. However, such local vascular inflammation can have distant effects on the systemic vascular system, leading to widespread endothelial cell dysfunction. Vascular endothelial dysfunction is common in a range of immune-mediated inflammatory diseases, is seen in multiple vascular beds, and is reversible following the induction of disease remission. The mechanisms that drive such systemic vascular endothelial dysfunction are unclear but factors such as TNF-alpha and CRP may play a role. Persistence of such widespread endothelial dysfunction in systemic vasculitis appears to have long-term consequences, leading to the acceleration of atherosclerosis and premature ischaemic heart disease. It may also underlie the accelerated atherosclerosis seen in other immune-mediated rheumatic diseases, such as rheumatoid arthritis.     

Endothelial function and cardiovascular prevention: role of blood lipids, exercise, and other risk factors

Multifactorial risk factor modification is proven to positively influence morbidity and mortality from both cardiovascular disease and stroke. The vascular endothelium has recently been a focus of interest in cardiovascular prevention. Data suggest that vascular endothelial dysfunction may contribute to the pathophysiology of clinical ischemia, especially angina, myocardial infarction, and sudden death. Endothelial dysfunction includes abnormalities of vasomotor tone (constriction and dilation), balance between fibrinolysis and thrombosis, control of the inflammatory response, and growth of vascular smooth muscle. Cardiovascular prevention interventions have been studied extensively and there are considerable data supporting a beneficial effect on endothelial dysfunction. The interventions that are clearly effective in improving endothelial function are diet and lipid-lowering therapy (especially with statin drugs), use of angiotensin-converting enzyme inhibitors, hormone replacement therapy, vitamin E, and proper physical exercise. Many challenging issues remain unsolved, however, and the endothelium at both the molecular and cellular levels must be further investigated for both research and clinical interests.     

Endothelial dysfunction in the pulmonary vascular bed

The pulmonary endothelium modulates vascular tone by the release of endothelium-derived constricting (EDCF) and relaxing (EDRF) factors, among them endothelin-1, nitric oxide, prostacyclin, and putative endothelium-derived hyperpolarizing factors. Abnormalities in EDCF and EDRF generation have been demonstrated in a number of cardiopulmonary disease states, such as primary and secondary pulmonary hypertension, chronic obstructive lung disease, cardiopulmonary bypass, and congestive heart failure. An imbalance between EDCF and EDRF, termed "pulmonary endothelial dysfunction," may contribute to the alteration in vascular tone characteristic of pulmonary disease. The following review summarizes the present knowledge of the role of EDCF and EDRF in such processes with major focus on pulmonary endothelial dysfunction in hypoxia-induced pulmonary hypertension.     

Endothelial dysfunction: its role in hypertensive coronary disease

PURPOSE OF REVIEW: Coronary artery disease is the major cause of death worldwide. Hypertension is a major risk factor for developing coronary disease. It is now recognized that endothelial dysfunction is an early marker of coronary artery disease before structural changes to the vessel wall are apparent on angiography or intravascular ultrasound and that it has a prognostic value in predicting cardiovascular events in hypertensive patients. This review addresses recent developments in hypertension-induced endothelial dysfunction. RECENT FINDINGS: Hyperaldosteronism causes endothelial dysfunction independent of high blood pressure. Exaggerated exercise blood pressure response has been related to endothelial dysfunction. Cyclosporin-A-induced endothelial dysfunction is related to reduced cholesterol content in caveolae. Chronic kidney disease induces changes in caveoli-1 and thus contributes to the reduced nitric oxide bioavailability, and causes oxidative stress independent of the high blood pressure. Asymmetric dimethylarginine plays a role in endothelial dysfunction in hypertensive patients independent of insulin resistance. 20-Hydroxyeicosatetraenoic acid is an independent predictor of hypertension in postmenopausal women. Endothelial dysfunction precedes and predicts the development of hypertension in postmenopausal women. Oral treatment with L-arginine improves endothelial dysfunction in hypertensives and lowers the blood pressure. SUMMARY: The pathophysiology of endothelial dysfunction in hypertension is multifactorial. Recent findings have contributed to our understanding of mechanisms of endothelial dysfunction and support a role for early intervention to prevent irreversible vascular and organ damage.     

硫化氢与血管内皮细胞的功能

血管内皮细胞参与血管内多种生理活动,内皮功能障碍将导致各种心血管疾病的发生.近几年来,研究发现新型气体信号分子硫化氢具有抗动脉粥样硬化等心血管疾病的效应:硫化氢促进内皮细胞增殖迁移诱导血管新生;抑制黏附分子分泌;通过打开平滑肌上ATP依赖性K+通道调节血管紧张度;抵抗氧化应激对内皮细胞的损伤等.随着其保护机制的不断发现与证实,硫化氢将有望逐渐应用于临床治疗,其.对内皮的保护作用仍需要做进一步的研究.     

Endothelial dysfunction in insulin resistance and type 2 diabetes

Macrovascular disease is the number one killer in type 2 diabetes patients. The cluster of risk factors in the insulin resistance syndrome (IRS) partly explains this notion. Insulin action in muscle, liver or adipose tissue has been thoroughly described in the literature, whilst this has been less described for the endothelium. Insulin stimulates nitric oxide (NO) production in the endothelium and reduced bioavailability of NO is usually defined as endothelial dysfunction. This impairment might be related to defective insulin signalling in the endothelial cell. Therefore, insulin resistance mechanisms in the endothelial cell will be emphasized in this review. Imbalance between the vasodilating agent NO and the vasoconstrictor endothelin-1 (ET-1) contributes to endothelial dysfunction. Different methods and circulating markers to assess endothelial function will be outlined. Circulating markers of an activated endothelium appear long before type 2 diabetes develops suggesting a unique role of the endothelium in the pathophysiology of the disease. Hampered blood flow in nutritive capillaries due to endothelial dysfunction is coupled with decreased glucose uptake and hyperglycemia. The forearm model combined with muscle microdialysis enables us to measure interstitial glucose and an index for capillary recruitment, the permeability surface area (PS). Available data from this method suggest that capillary recruitment in response of insulin is impaired in insulin resistant human subjects.     

血管内皮细胞损伤与高血压

近年来很多研究表明内皮细胞损伤导致的功能障碍与多种心血管疾病的发生发展有着密切相关,包括高血压、冠状动脉性心脏病、糖尿病等。深入探讨血管内皮细胞损伤的机制、评估,保护和修复内皮细胞功能,对改善心血管疾病的预后有积极的意义。现就血管内皮细胞损伤引起的内皮功能障碍和高血压发病机制之间的关系进行综述。     

Endothelial dysfunction in hypercholesterolemia: mechanisms, pathophysiological importance, and therapeutic interventions

Since the demonstration of the obligatory role of the endothelium in arterial relaxation by Furchgott and Zawadzki (1980), there has been great interest in the role of the endothelium in vascular disease. Apart from endothelium-dependent vasodilation, other important functions of the endothelium have now been studied, that is, the regulation of adhesion and infiltration of leukocytes and inhibition of platelet adhesion and aggregation. Many functions of the endothelium are influenced by nitric oxide (NO), which is synthesized by endothelial NO synthase. Endothelial dysfunction in hypercholesterolemic patients is in large part due to a reduced bioavailability of NO. Multiple factors contribute to this, including increased inactivation of NO by radicals and inhibition of NO formation by different mechanisms. The functional implications of endothelial dysfunction are not completely defined. However, recent studies suggest that endothelial dysfunction contributes to myocardial perfusion abnormalities. Furthermore, endothelial dysfunction may play an important role with respect to development and progression of atherosclerosis because the endothelium is involved in the regulation of key events of the atherosclerotic process. Endothelial dysfunction in hypercholesterolemia is reversible by cholesterol-lowering treatment, that is treatment with HMG-CoA-reductase inhibitors. First experimental data suggest that maneuvers that increase the bioavailability of NO in hypercholesterolemia may even result in regression of preexisting atherosclerotic lesions.     

Vascular Endothelial Function and Hypertension: Insights and Directions

Hypertension contributes significantly to worldwide cardiovascular morbidity and mortality. Hypertension appears to have a complex association with endothelial dysfunction, a phenotypical alteration of the vascular endothelium that precedes the development of adverse cardiovascular events and portends future cardiovascular risk. This review concentrates on recent findings with respect to the mechanisms of hypertension-associated endothelial dysfunction, the interrelationship between these two entities, and the relationship of the efficacy of antihypertensive therapies to improvements in vascular homeostasis beyond blood pressure reduction. Current evidence suggests that hypertension and endothelial dysfunction are integrally related with respect to pathophysiologic mechanisms. Future studies will need to identify the key connections between hypertension and endothelial dysfunction to allow novel interventions to be designed and promulgated.     

Exercise Training and Endothelial Function

Vascular endothelium is a key determinant of circulatory homeostasis because it coordinates tissue perfusion and modulates arterial compliance. Endothelial dysfunction is considered to be a very early indication of atherosclerosis, being detectable even in childhood. Later on in life, endothelial dysfunction in large conduit arteries has been consistently shown to be a significant predictor of cardiovascular events. Elegantly conducted innovative studies have demonstrated the efficacy of physical exercise in improving endothelial dysfunction. Randomized controlled trials with parallel group design with adequate statistical power have consistently shown the therapeutic efficacy of both aerobic and resistance exercise training as physiologic means to improve, and even normalize, vascular endothelial function in patients with cardiovascular diseases. On the contrary, few data of comparable quality are available from randomized controlled trials among asymptomatic subjects or in those with metabolic disturbances. In addition, female participants are clearly under-represented in exercise training studies with vascular function as the key outcome measure.     

Endothelial dysfunction in uraemia

Cardiovascular disease is a major cause of morbidity and mortality in chronic renal failure (CRF). The endothelium plays a central role in the control of many aspects of vascular function, and abnormalities may contribute to the generation of atherosclerosis. The endothelium produces a wide range of regulatory molecules which, in health, function in concert to provide a carefully balanced anti-atherogenic environment. Endothelial dysfunction has been repeatedly demonstrated in renal failure, is present in the absence of anatomically obvious disease and appears to be useful in the prediction of morbidity and mortality in other cardiovascular risk groups. One of the most intensively studied and important mediators of endothelial function is nitric oxide (NO), whose production is reduced in CRF. A number of possible mechanisms for reduced NO bioavailability have been investigated including substrate limitation, competitive inhibition of NO synthase by endogenous NO synthase inhibitors known to accumulate in renal failure, and premature quenching of NO by free radicals present in high concentrations in this group. A clearer understanding of the pathogenesis of endothelial dysfunction in CRF has potential clinical implications. It may provide avenues for therapeutic interventions before the onset of clinically obvious cardiovascular disease in this high-risk patient group.     

The Role of Asymmetric Dimethylarginine (ADMA) in Endothelial Dysfunction and Cardiovascular Disease

Endothelium plays a crucial role in the maintenance of vascular tone and structure. Endothelial dysfunction is known to precede overt coronary artery disease. A number of cardiovascular risk factors, as well as metabolic diseases and systemic or local inflammation cause endothelial dysfunction. Nitric oxide (NO) is one of the major endothelium derived vaso-active substances whose role is of prime importance in maintaining endothelial homeostasis. Low levels of NO are associated with impaired endothelial function. Asymmetric dimethylarginine (ADMA), an analogue of L-arginine, is a naturally occurring product of metabolism found in human circulation. Elevated levels of ADMA inhibit NO synthesis and therefore impair endothelial function and thus promote atherosclerosis. ADMA levels are increased in people with hypercholesterolemia, atherosclerosis, hypertension, chronic heart failure, diabetes mellitus and chronic renal failure. A number of studies have reported ADMA as a novel risk marker of cardiovascular disease. Increased levels of ADMA have been shown to be the strongest risk predictor, beyond traditional risk factors, of cardiovascular events and all-cause and cardiovascular mortality in people with coronary artery disease. Interventions such as treatment with L-arginine have been shown to improve endothelium-mediated vasodilatation in people with high ADMA levels. However the clinical utility of modifying circulating ADMA levels remains uncertain.     

Endothelial Dysfunction in Hypertension

Hypertension is an important risk factor for the development of atherosclerosis and endothelial dysfunction may be a key mechanism. The nitric oxide mediated vasodilator function of the endothelium has been widely studied as a test of endothelial integrity in patients with hypertension and impaired basal and muscarinic agonist stimulated components of nitric oxide mediated vascular tone have been found in coronary, forearm and cutaneous resistance vessels and in coronary and forearm conduit vessels. The underlying abnormalities of these changes are unknown but it is likely to be a secondary phenomenon due to increased blood pressure. However, endothelial dysfunction as assessed by response to muscarinic agonists does not occur in all patients and antihypertensive therapy so far has been mostly unable to reverse it. Although widely used the response to acetylcholine has some shortcomings and it remains to be established what parameter best reflects endothelial dysfunction. The relationship of such abnormalities to the present or future atherosclerosis needs to be defined.