Hyperhomocysteinemia, endothelial dysfunction, and cardiovascular risk: the potential role of ADMA

Hyperhomocysteinemia is an emerging risk factor for cardiovascular disease and stroke. The mechanisms underlying the pathophysiology of hyperhomocysteinemia are not completely defined, but endothelial dysfunction resulting from impaired bioavailability of nitric oxide is a consistent finding in experimental models. One potential mechanism for decreased nitric oxide bioavailability is inhibition of endothelial nitric oxide synthase by its endogenous inhibitor, asymmetric dimethylarginine (ADMA). Elevated plasma levels of ADMA have been found in association with hyperhomocysteinemia and endothelial dysfunction in both animals and humans. Additional studies are required to determine the mechanisms by which ADMA accumulates in hyperhomocysteinemia and to define the importance of ADMA in the endothelial dysfunction of hyperhomocysteinemia in vivo.     

氧化应激与血管内皮功能异常

氧化应激和人体内抗氧化系统功能处于动态平衡之中,如果抗氧化系统不能消除氧化应激,就会产生氧化损伤,导致内皮功能障碍.本文综述氧化应激的产生及其在内皮功能异常中的作用、抗氧化治疗的措施及可能机制.     

胰岛素抵抗与血管内皮功能障碍

胰岛素抵抗和血管内皮功能障碍之间有重要联系,两者相辅相成,共同在代谢综合征和心血管疾病的发生发展中起重要作用.高血糖导致的葡萄糖中毒、血中游离脂肪酸水平升高和血脂异常导致的脂质毒性增加、与代谢和心血管疾病有关的炎性状态是引起胰岛素抵抗和血管内皮功能障碍的共同机制.采用多种措施改善胰岛素抵抗和血管内皮功能障碍对预防和治疗代谢性疾病和心血管疾病具有重要意义.     

NADPH oxidase mediates vascular endothelial cadherin phosphorylation and endothelial dysfunction

Vascular endothelial activation is an early step during leukocyte/endothelial adhesion and transendothelial leukocyte migration in inflammatory states. Leukocyte transmigration occurs through intercellular gaps between endothelial cells. Vascular endothelial cadherin (VE-cadherin) is a predominant component of endothelial adherens junctions that regulates intercellular gap formation. We found that tumor necrosis factor (TNF) caused tyrosine phosphorylation of VE-cadherin, separation of lateral cell-cell junctions, and intercellular gap formation in human umbilical vein endothelial cell (HUVEC) monolayers. These events appear to be regulated by intracellular oxidant production through endothelial NAD(P)H (nicotinamide adenine dinucleotide phosphate) oxidase because antioxidants and expression of a transdominant inhibitor of the NADPH oxidase, p67(V204A), effectively blocked the effects of TNF on all 3 parameters of junctional integrity. Antioxidants and p67(V204A) also decreased TNF-induced JNK activation. Dominant-negative JNK abrogated VE-cadherin phosphorylation and junctional separation, suggesting a downstream role for JNK. Finally, adenoviral delivery of the kinase dead PAK1(K298A) decreased TNF-induced JNK activation, VE-cadherin phosphorylation, and lateral junctional separation, consistent with the proposed involvement of PAK1 upstream of the NADPH oxidase. Thus, PAK-1 acts in concert with oxidase during TNF-induced oxidant production and loss of endothelial cell junctional integrity.     

Glucocorticoid excess induces superoxide production in vascular endothelial cells and elicits vascular endothelial dysfunction

Glucocorticoid (GC) excess often elicits serious adverse effects on the vascular system, such as hypertension and atherosclerosis, and effective prophylaxis for these complications is limited. We sought to reveal the mechanism underlying GC-induced vascular complications. Responses in forearm blood flow to reactive hyperemia in 20 GC-treated patients were significantly decreased to 43+/-8.9% (mean+/-SEM) from the values obtained before GC therapy (130+/-14%). An administration of vitamin C almost normalized blood flow responses. In human umbilical vein endothelial cells (HUVECs), production of hydrogen peroxide was increased up to 166.5+/-3.3% of control values by 10(-7) mol/L dexamethasone (DEX) treatment (P<0.01). Concomitant with DEX-induced hydrogen peroxide production, intracellular amounts of peroxynitrite significantly increased and those of nitric oxide (NO) decreased, respectively (P<0.01). Immunoblotting analysis using anti-nitrotyrosine antibody showed that peroxynitrite formation was increased in DEX-treated HUVECs. Using inhibitors against metabolic pathways for generation of reactive oxygen species (ROS), we identified that the major production sources of ROS by DEX treatment were mitochondrial electron transport chain, NAD(P)H oxidase, and xanthine oxidase. These findings suggest that GC excess causes overproduction of ROS and thereby perturbs NO availability in the vascular endothelium, leading to vascular complications in patients with GC excess.     

Hemodynamic forces in endothelial dysfunction and vascular aging

Aging is a key risk factor associated with the onset of cardiovascular disease. Notably, vascular aging and cardiovascular disease are both associated with endothelial dysfunction, or a marked decrease in production and bioavailability the vasodilator of nitric oxide (NO). As a result of decreased nitric oxide availability, aging vessels often exhibit endothelial cell senescence and increased oxidative stress. One of the most potent activators of NO production is fluid shear stress produced by blood flow. Interestingly, age-related decrease in NO production partially results from endothelial insensitivity to shear stress. While the endothelial cell response to fluid shear stress has been well characterized in recent years, the exact mechanisms of how the mechanical force of fluid shear stress is converted into intracellular biochemical signals are relatively unknown. Therefore, gaining a better knowledge of mechanosignaling events in endothelial cells may prove to be beneficial for developing potential therapies for cardiovascular diseases.     

肺血管内皮细胞功能障碍与肺动脉高压

肺动脉高压的发病机制是一个复杂的、多因素参与的过程.近年来,逐步形成内皮功能紊乱学说,认为肺血管内皮是引起血管收缩和特征性病理改变的首要因素.本文就肺血管内皮细胞功能障碍和肺动脉高压的研究进展作一综述.     

Oxidative stress and endothelial dysfunction in vascular disease

In response to physiologic stimuli, endothelial cells dynamically regulate arterial vascular tone by producing vasodilators and vasoconstrictors. Risk factors for atherosclerosis, such as diabetes, smoking, hypercholesterolemia, and hypertension, interfere with this response, promoting endothelial dysfunction and atherosclerosis. This review explores whether oxidative stress might be a common feature of both endothelial dysfunction and atherosclerosis. Using biomarkers to assess endothelial function might provide insights into the pathways for oxidative stress in vascular disease. However, currently available markers of oxidative stress and endothelial function are unsuitable for routine clinical use because they are too expensive and inadequately validated. Thus, there is a need to develop and validate new markers that could be used to both measure oxidative stress and monitor therapies that specifically interrupt oxidative pathways in vascular tissue. Such markers might eventually help to identify susceptible individuals at a stage when cardiovascular complications could be prevented.     

Genetic determinants of vascular oxidant stress and endothelial dysfunction

Reactive oxygen species are products of cellular metabolism and function as normal signaling molecules in the vasculature. Overproduction of reactive oxygen species that outstrips antioxidant defenses generates oxidant stress that can lead to nitric oxide depletion and endothelial cell injury, and contributes to the pathophysiology of cardiovascular disease and myocardial dysfunction. Antioxidant enzymes that are important in limiting vascular oxidant stress include superoxide dismutases, catalase, glutathione peroxidases, and glucose-6-phosphate dehydrogenase. The relevance of deficiencies in glutathione peroxidase and glucose-6-phosphate dehydrogenase on endothelial and myocardial dysfunction will be reviewed.     

Peripheral vascular endothelial dysfunction and apoptosis in old monkeys

To determine the effects of aging on vasoactivity in a primate model (Macaca fascicularis), 13 young male monkeys (aged 7.1+/-0.4 years) and 9 old male monkeys (aged 19.8+/-0.6 years) were chronically instrumented for measurement of left ventricular and aortic pressures and cardiac output. Total cholesterol, triglyceride, and fasting blood sugar levels were not different between the 2 groups. There were no significant differences in baseline mean aortic pressure and total peripheral resistance (TPR) in the young monkeys versus the old monkeys. TPR fell less (P<0.05) with acetylcholine (1 microg/kg) in old monkeys (-25+/-1%) than in young monkeys (-34+/-2%), whereas decreases in TPR with sodium nitroprusside were similar in old and young monkeys. There was no evidence of atherosclerosis, but apoptosis of endothelial cells was enhanced (P<0.05) in the aortas and femoral arteries, but not in the media, of the old monkeys. There was a relationship (r=0.62, P=0.013) between the incidence of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive endothelial cells and endothelial cell density in the femoral artery. The reduced endothelial cell density was also correlated (r=0.82, P<0.01) with depressed TPR responses to acetylcholine. Thus, vascular endothelial dysfunction was present in old monkeys without evidence of atherosclerosis, which may be due to endothelial apoptosis and reduced endothelial cell density.     

Assessment of vascular and endothelial dysfunction in nutritional studies

Vascular and endothelial dysfunction (VED) is emerging as a potential set of early markers of cardiovascular disease risk and tests for its measurement have been widely used in clinical research. The aim of this viewpoint is to describe and discuss the current usage of these measures in well-designed nutritional trials, using the potential relationship between fruit juice intake and VED as example. A search was conducted using the NHS evidence portal including studies published in English between January 1980 and October 2013. Only 10 suitable studies were selected, which investigated the effect of fruit juice intake on VED, among which 4 interventions used flow-mediated dilatation, 2 arterial stiffness, 2 a combination of arterial stiffness and flow-mediated dilatation, 2 carotid intimal media thickness and 1 iontophoresis with laser Doppler. Despite minimal effects reported on classical CVD markers, such as lipids, 8 out of the 10 identified studies reported an effect on endothelial function following juice consumption, indicating that VED tests can be effectively used in human dietary interventions to identify relationships between bioactive compounds from fruit and CVD risk. However, paucity of available data, scarcity of compound bioavailability and metabolism information, strong heterogeneity among experimental methodologies and a number of limitations to study designs, still limit the interpretation of the results obtained through these measures. Future, well-designed studies with greater attention to consider use of VED measures are needed to strengthen the utility of VED tests in nutrition research such as those investigating the impact of polyphenol-rich juices and CVD risk.     

Disturbed-flow-mediated vascular reactive oxygen species induce endothelial dysfunction

Emerging evidence is revealing the different roles of steady laminar flow (s-flow) and disturbed flow (d-flow) in the regulation of the vascular endothelium. s-flow is atheroprotective while d-flow creates an atheroprone environment. Most recently, we found unique atheroprone signals, which involve protein kinase C (PKC)ζ activation, elicited by d-flow. We and others have defined a novel role for PKCζ as a shared mediator for tumor necrosis factor alpha (TNF alpha) and d-flow, which cause pro-inflammatory and pro-apoptotic events in endothelial cells (ECs) in the atheroprone environment. Under such conditions, ONOO(-) formation is increased in a d-flow-mediated PKCζ-dependent manner. Here, we propose a new signaling pathway involving d-flow-induced EC inflammation via PKCζ-ERK5 interaction-mediated downregulation of KLF2/eNOS stability, which leads to PKCζ-mediated p53-SUMOylation and EC apoptosis. In addition, we highlight several mechanisms contributing to endothelial dysfunction, focusing on the relations between flow patterns and activation of reactive oxygen species generating enzymes.     

Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction

CONTEXT: Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation. OBJECTIVE: We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans. DESIGN AND SETTING: We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital. PATIENTS AND INTERVENTIONS: Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations. MAIN OUTCOME MEASURES: Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion. RESULTS: Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline). CONCLUSIONS: Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.     

Hyperhomocysteinemia,vascular function and atherosclerosis: effects of vitamins

Homocysteine is a metabolic product of methyl group donation by the amino acid methionine. Moderate elevation of plasma homocysteine (>15 M) is most commonly caused by B-vitamin deficiencies, especially folic acid, B₆ and B₁₂. Genetic factors, certain drugs and renal impairment may also contribute. Homocysteine has several potentially deleterious vascular actions. These include increased oxidant stress, impaired endothelial function, stimulation of mitogenesis, and induction of thrombosis. Homocysteine also appears to increase arterial pressure. In humans, experimental induction of hyperhomocysteinemia by methionine loading rapidly causes profound impairment of endothelium-dependent dilatation in both resistance and conduit arteries. This endothelial dysfunction can be reversed by administration of antioxidants. Epidemiological evidence suggests that homocysteine acts as an independent risk factor for atherosclerosis, thrombosis and hypertension. Prospective studies have shown that elevated plasma homocysteine concentrations in the top quintile of the population (>12 M) increase risk of cardiovascular disease by about 2-fold. There are currently no data available from randomized, controlled trials of the effects of lowering plasma homocysteine on atherothrombotic events. Nonetheless, it would seem appropriate to screen for and treat hyperhomocysteinemia in individuals with progressive or unexplained atherosclerosis. Folic acid and vitamins B₆ and B₁₂ are the mainstay of therapy. Treatment of moderately elevated plasma homocysteine in patients without atherosclerosis should be deferred until the completion of randomized outcome trials.     

Maturation-induces endothelial dysfunction via vascular inflammation in diabetic mice

We hypothesized that maturation-induced vascular inflammation produces endothelial dysfunction in type II diabetes and TNFalpha plays a key role in triggering inflammation in the development of diabetes. In control (Db/db) mice aged 6, 12, 18 and 24 weeks, sodium nitroprusside (SNP) and acetylcholine (ACh) induced dose-dependent vasodilation, and dilation to ACh was blocked by the NO synthase inhibitor N (G)-monomethyl-L: -arginine. In type II diabetic (db/db) mice at age of 12, 18 and 24 weeks, ACh or flow-induced dilation was blunted compared to Db/db; endothelial function is normal at 6 weeks of age in db/db Vs. control mice, but SNP produced comparable dilation at age of 6, 12, 18 and 24 weeks. Decrements in endothelial function in db/db mice progressively increased from 6-12 to 18-24 weeks. Administration of neutralizing antibodies to TNFalpha ameliorated endothelial dysfunction in db/db mice aged 12, 18 and 24 weeks. The effect was most prominent in the younger animals. Plasma concentration, expression of TNFalpha and TNFalpha receptor 1 (TNFR1) were elevated in coronary arterioles, even at the age of 6 weeks before the development of diabetes in db/db mice compared to control mice. Superoxide production was lower in Db/db mice compared to db/db mice and increments in superoxide production in db/db mice progressively increased from 6-12 to 18-24 weeks. NAD(P)H oxidase inhibitor apocynin attenuated superoxide production in db/db mice at 12 weeks of age, mitochondria respiratory chain inhibitor rotenone attenuated superoxide production at 24 weeks in db/db and Db/db mice, but the combination of apocynin and rotenone reduced superoxide production at 18 weeks for db/db and Db/db mice. The expression of TNFalpha and its receptors increase progressively with maturation in concert with the development of diabetes. Incremental increases in TNFalpha/TNFR1 expression induces activation and production of superoxide via NAD(P)H oxidase and/or mitochondria respiratory chain, leading to endothelial dysfunction progressing to the development of type II diabetes.     

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.     

Arterial ageing: from endothelial dysfunction to vascular calcification

Complex structural and functional changes occur in the arterial system with advancing age. The aged artery is characterized by changes in microRNA expression patterns, autophagy, smooth muscle cell migration and proliferation, and arterial calcification with progressively increased mechanical vessel rigidity and stiffness. With age the vascular smooth muscle cells modify their phenotype from contractile to ‘synthetic’ determining the development of intimal thickening as early as the second decade of life as an adaptive response to forces acting on the arterial wall. The increased permeability observed in intimal thickening could represent the substrate on which low‐level atherosclerotic stimuli can promote the development of advanced atherosclerotic lesions. In elderly patients the atherosclerotic plaques tend to be larger with increased vascular stenosis. In these plaques there is a progressive accumulation of both lipids and collagen and a decrease of inflammation. Similarly the plaques from elderly patients show more calcification as compared with those from younger patients. The coronary artery calcium score is a well‐established marker of adverse cardiovascular outcomes. The presence of diffuse calcification in a severely stenotic segment probably induces changes in mechanical properties and shear stress of the arterial wall favouring the rupture of a vulnerable lesion in a less stenotic adjacent segment. Oxidative stress and inflammation appear to be the two primary pathological mechanisms of ageing‐related endothelial dysfunction even in the absence of clinical disease. Arterial ageing is no longer considered an inexorable process. Only a better understanding of the link between ageing and vascular dysfunction can lead to significant advances in both preventative and therapeutic treatments with the aim that in the future vascular ageing may be halted or even reversed.