Association of asymmetric dimethylarginine and endothelial dysfunction.

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), which has been characterized as an "endogenous anti-atherosclerotic molecule". Synthesis of NO can be selectively inhibited by guanidino-substituted analogs of L-arginine, which act as competitive inhibitors at the active site of the enzyme. One such analog is asymmetric dimethylarginine (ADMA), a compound that has been found in human plasma and urine and exerts the activity of an endogenous inhibitor of NO synthase. In contrast to ADMA, its regioisomer symmetric dimethylarginine (SDMA) does not inhibit NO synthase. The methyl groups contained within the dimethylarginine molecules are derived from S-adenosylmethionine, an intermediate in the homocysteine/methionine pathway. There is experimental evidence that homocysteine may affect endothelium-dependent vascular function by increasing the formation of ADMA. Both ADMA and SDMA are eliminated from the body by renal excretion. In addition, the metabolism of ADMA, but not SDMA, occurs via hydrolytic degradation to citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Data from experimental studies suggest that ADMA inhibits vascular NO elaboration at concentrations found in pathophysiological conditions (i.e., 3-15 microM). ADMA likely acts as an autocrine regulator of endothelial NO synthase activity. When rabbits are placed on a diet enriched with 1% cholesterol, ADMA levels are increased within 4 weeks of dietary intervention as compared to control animals. Elevated plasma concentrations of ADMA are also present in hypercholesterolemic and hypertensive patients, in patients with chronic heart failure, and in other patient groups at high risk of developing cardiovascular disease. Elevation of ADMA induces dysfunction of the endothelium, which becomes clinically evident by impaired endothelium-dependent vasodilation, hyperaggregability of platelets, and enhanced monocyte adhesion. Recent prospective studies suggest that endothelial dysfunction indicates an increased risk of future cardiovascular events. In line with these observations, we and others found evidence that ADMA is a novel cardiovascular risk factor.     

Markers of myocardial injury and dysfunction

Acute coronary syndrome (ACS) is defined as the spectrum of diagnoses from angina to sudden cardiac death caused by ischemic coronary artery disease. Although cardiovascular disease is the leading cause of death of adults in the United States, the ability to diagnose ACS is not always definitive. Cardiac markers are laboratory tests that are used to assist in the diagnosis. Research continues to develop new and refine "old" cardiac markers to improve diagnostic testing that then leads to appropriate and timely interventions for patients with ACS. The purpose of this article is to review the cardiac markers and their role in the diagnosing, as well as predicting the risk of ACS.     

Testing for endothelial dysfunction

Endothelial health is a key factor in normal cardiovascular homeostasis, and recent studies have revealed several important functions of the vascular endothelium that protect against atherothrombosis. These include control over arterial tone, coagulation, fibrinolysis, and vascular growth. Consequently, endothelial dysfunction has been implicated as an important event in the pathogenesis of atherosclerosis, coronary vasoconstriction, hypertension, and myocardial ischaemia. Therefore, there has been considerable research interest in diagnostic assays for the assessment of endothelium. This review outlines the current status of markers of endothelial dysfunction, particularly those related to vasomotor control, as well as circulating markers of vascular health.     

Testing for endothelial dysfunction

Endothelial health is a key factor in normal cardiovascular homeostasis, and recent studies have revealed several important functions of the vascular endothelium that protect against atherothrombosis. These include control over arterial tone, coagulation, fibrinolysis, and vascular growth. Consequently, endothelial dysfunction has been implicated as an important event in the pathogenesis of atherosclerosis, coronary vasoconstriction, hypertension, and myocardial ischaemia. Therefore, there has been considerable research interest in diagnostic assays for the assessment of endothelium. This review outlines the current status of markers of endothelial dysfunction, particularly those related to vasomotor control, as well as circulating markers of vascular health.     

Oxidative stress and endothelial dysfunction

This review focuses on the role of vascular oxidative stress in the development and progression of endothelial dysfunction. We discuss different sources of oxidative stress in the vessel wall, oxidative stress and coagulation, the role of oxidative stress and vascular function in arteries and veins, the flow-dependent regulation of reactive oxygen species, the putative impact of oxidative stress on atherosclerosis, the interaction of angiotensin II, oxidative stress and endothelial dysfunction, and clinical implications.     

Therapeutic strategies for endothelial dysfunction

INTRODUCTION: A functionally compromised vascular endothelium is associated with tissue-damaging responses including inflammation, immune stimulation, oxidative stress and platelet activation/aggregation and can lead to severe end-organ damage, as implicated in the pathology of several cardiac, cerebral and renal disorders. Multiple noninvasive techniques are available for assessing endothelial dysfunction in clinical settings. Diverse interventions have been identified as having therapeutic potential for treating endothelial dysfunction and preventing its pathophysiological sequellae. AREAS COVERED: Evaluation techniques and interventional treatment approaches for endothelial dysfunction, with particular reference to prevalent cardiovascular and metabolic disorders such as coronary artery disease and diabetes. Limitations of the current treatments and avenues for improved endothelium-targeted therapies. EXPERT OPINION: Beneficial pleiotropic effects of various agents (cardiovascular medicines, antioxidants, nutritional supplements) on vascular endothelial function in humans notwithstanding, a growing body of preclinical data suggests that protein-, cell- and gene-based approaches hold promise for selective therapeutic targeting of the dysfunctional vascular endothelium. Additional efficacy data in appropriate animal models of vascular injury and cardiometabolic disease, further refinement of delivery modalities and continued investigation of the mechanisms underlying endothelial repair and regeneration should help identify the most promising therapeutic approaches for improving endothelial function that merit evaluation in human trials.     

Simvastatin improves diabetes-induced coronary endothelial dysfunction

3-Hydroxy-3-methylglutaryl CoA reductase inhibitors decrease cardiovascular morbidity in diabetic patients, but the mechanism is unclear. We studied the actions of simvastatin (SIM) in enhancing NO bioavailability and reducing oxidative stress in coronary vessels from diabetic rats and in rat coronary artery endothelial cells (RCAEC) exposed to high glucose. Coronary arteries isolated from diabetic rats showed decreases in acetylcholine (ACh)-mediated maximal relaxation from 81.0 +/- 4.5% in controls to 43.5 +/- 7.6% at 4 weeks and 22.3 +/- 0.6% at 10 weeks of diabetes. This effect was associated with oxidative stress in coronary vessels as shown by dichlorofluorescein (DCF) imaging and nitrotyrosine labeling. Diabetes also reduced trans-coronary uptake of [(3)H]l-arginine. Supplemental l-arginine (50 mg/kg/day p.o.) did not improve coronary vasorelaxation to ACh. However, SIM treatment (5 mg/kg/day subcutaneously) improved maximal ACh relaxation to 65.8 +/- 5.1% at 4 weeks and 47.1 +/- 3.9% at 10 weeks. Coronary arteries from rats treated with both SIM and l-arginine demonstrated the same maximal relaxation to ACh (66.1 +/- 3%) as SIM alone. Mevalonate and l-NAME (N(omega)-nitro-l-arginine methyl ester hydrochloride) inhibited the response to ACh in SIM-treated diabetic rats. Coronary arteries from all groups relaxed similarly to sodium nitroprusside. SIM increased endothelial NO synthase protein levels and blocked diabetes-induced increases in DCF and nitrotyrosine labeling in diabetic coronary vessels. SIM treatment restored normal NO levels in media from high-glucose-treated RCAEC and plasma of diabetic rat. Treatment with SIM or the NADPH oxidase inhibitor apocynin also blocked high-glucose-induced increases in reactive oxygen species and superoxide formation in RCAEC. Taken together, these data suggest that SIM improves diabetes-induced coronary dysfunction by reducing oxidative stress and increasing NO bioavailability.     

Cardiovascular risk factors and endothelial dysfunction

Endothelial dysfunction is a feature of atherosclerosis and is associated with CHD (coronary heart disease) risk factors. This study aimed to determine the relationship between the degree of endothelial dysfunction and calculated cardiovascular risk. Endothelial function, as determined by the ACh/NP (acetycholine/sodium nitroprusside response) ratio on brachial plethysmography, was compared with cardiovascular risk as calculated from the Framingham, PROCAM (Prospective Cardiovascular Munster) and MRFIT (Multiple Risk Factor Intervention Trial) algorithms in 246 (187 male) patients, including 44 (22%) with established CHD. Endothelial dysfunction correlated with the total number of risk factors (r2=0.22; P=0.002) and was related to LDL (low-density lipoprotein)-cholesterol in men and triacylglycerols (triglycerides) in women. The ACh/NP ratio correlated with the occurrence of diabetes, CHD and the LDL-cholesterol concentration (r2=0.58; P<0.001). Endothelial dysfunction was associated with presence of CHD on receiver-operating characteristic plot analysis (area=0.706+/-0.04; P=0.001). There was no correlation between ACh/NP ratio and CHD risk calculated with the Framingham algorithm in men, although both ACh and NP response correlated separately with risk in women. The endothelial ACh/NP ratio correlated with absolute risk in the PROCAM algorithm (r2=0.41; P<0.005). Intermediate results were obtained with MRFIT. Individual risk factors make different contributions to endothelial dysfunction compared with their role in risk calculators. The stronger relationship of endothelial dysfunction with PROCAM risk reflects the contribution of male sex, LDL-cholesterol and triacylglycerols to risk calculated by this algorithm.     

Role of endothelial dysfunction in sepsis mortality

During the past decade, a unifying hypothesis has been developed to explain the vascular changes that occur in septic shock on the basis of the effect of inflammatory mediators on the vascular endothelium. The vascular endothelium plays a central role in the control of microvascular flow, and it has been proposed that widespread vascular endothelial activation, dysfunction and eventually injury occur in septic shock, ultimately resulting in multiorgan failure. This has been characterised in various models of experimental septic shock. Now, direct and indirect evidence for endothelial cell alteration in humans during septic shock is emerging. The present review details recently published literature on this rapidly evolving topic.     

Modulation of pain-induced endothelial dysfunction by hypnotisability

Mental stress induces endothelial dysfunction, that is a reduction of the post-occlusion brachial artery flow-mediated vasodilation (FMD). This does not occur in subjects highly susceptible to hypnosis (Highs) in either the waking or hypnotic state. The aim of the present experiment was to assess whether endothelial dysfunction is also induced by acute nociceptive stimulation and whether high hypnotisability and/or the specific instruction of analgesia prevent its occurrence in awake highly hypnotizable individuals. Thus, nine Highs and nine subjects with low susceptibility to hypnosis (Lows) underwent an experimental session including the administration of pressor pain and of pressor pain associated with the instruction of analgesia. Heart rate, basal artery diameters and brachial artery flow-mediated vasodilation were measured during stimulation and rest conditions. Heart rate exhibited slight changes not modulated by hypnotisability. During painful stimulation both Highs and Lows showed a decrease of FMD, but it was significantly less pronounced in Highs. During the administration of painful stimulation together with the instruction of analgesia, only Highs reported analgesia and their FMD no longer decreased. This study provides the first evidence of pain-related endothelial dysfunction and extends previous findings concerning a sort of natural protection of Highs against the vascular effects of mental stress to acute pain.     

Vascular endothelial cell dysfunction in diabetes mellitus

Diabetes mellitus is complicated with vascular disorders such as atherosclerosis (macroangiopathy) and retinopathy (microangiopathy). In macroangiopathy, AGE plays an important role in atherogesis through NF-kappa B activation, that induces VCAM-1 and MCP-1. Diabetic retinopathy is based on the microangiopathy characteristic of angiogenesis. VEGF is a key substance in the angiogenesis in the retina. VEGF is produced from retinal cells exposed to AGE, adenosine, bFGF. VEGF elictes angiogenesis and increased vascular permeability (retinal edema). I consider that AGE is the most important substance in diabetic vascular disorder. Therefore, I expect a new application for diabetic angiopathy to suppress the effect of AGE.     

Transdermal nicotine mimics the smoking-induced endothelial dysfunction

BACKGROUND: Cigarette smoking is a major risk factor for coronary artery disease and causes endothelial dysfunction, perhaps by decreasing the availability of nitric oxide availability in arteries and veins. Nicotine in cigarette smoke may be responsible for this impaired endothelial response. METHODS: We studied nine healthy nonsmokers and 12 healthy mild to moderate smokers by use of the dorsal hand vein compliance technique. Dose-response curves to bradykinin and sodium nitroprusside were obtained to test the endothelium-dependent and endothelium-independent vasorelaxation before and during the use of a nicotine (21 mg) patch. Mean arterial blood pressure and heart rate were measured beat-to-beat during the 4-hour study and serial blood samples were drawn to assay plasma thromboxane B2 levels. RESULTS: Transdermal nicotine reduced the venous responsiveness to bradykinin in nonsmokers (Emax = 88.0% +/- 17.9% and 54.3% +/- 14.9%, respectively, before and after the nicotine patch; P < .05); the latter response was similar to that in smokers (Emax = 56.3% +/- 16.6%). Sodium nitroprusside-induced venodilation was unaltered. Mean arterial blood pressure increased in both smokers and nonsmokers. Transdermal nicotine increased the plasma thromboxane B2 concentrations only among nonsmokers. CONCLUSION: These findings indicate that nicotine can have a major role in the impaired endothelial function in smokers. The results probably also reflect what occurs in arterial beds because the nicotine patches increased the mean arterial blood pressure in both smokers and nonsmokers.     

Staphylococcus aureus alpha toxin mediates polymorphonuclear leukocyte-induced vasocontraction and endothelial dysfunction.

The effect of Staphylococcus aureus alpha toxin (alpha-toxin) on selectin-mediated neutrophil adhesion was investigated in polymorphonuclear leukocyte- (PMN) induced vasocontraction and endothelial dysfunction. Adherence of human PMNs to rat aortic endothelium increased significantly following stimulation of the endothelium with alpha-toxin (0.1, 0.5, and 1 microg/mL). This effect could be significantly attenuated by monoclonal antibodies directed against P-selectin or fucoidin, a carbohydrate known to block selectins. Unstimulated human PMNs (10(6)cells/mL) were added to organ chambers containing rat aortic rings stimulated with alpha-toxin (0.5 microg/mL). PMNs elicited a significant vasocontraction in alpha-toxin-stimulated, but not in control aortic, rings (142+/-12 mg versus 12+/-4 mg, P < 0.05). This PMN-induced vasocontraction was virtually blunted by pretreatment with MAb directed against P-selectin or fucoidin (P < 0.05). Endothelial function as assessed by endothelium-dependent vasorelaxation to acetylcholine was substantially inhibited after induction of PMN-induced vasocontraction in alpha-toxin-stimulated aortic rings. This endothelial dysfunction was reduced by P-selectin MAb or fucoidin. In contrast, endothelium-independent relaxation to sodium nitrite was not altered by PMN incubation, indicating that vascular smooth muscle function was unaffected. Thus, PMN-endothelial interaction following S. aureus a-toxin activation of the vascular endothelium is at least, in part, mediated by selectins. As a consequence, PMN-induced vasocontraction and endothelial dysfunction occur. Such mechanisms may be involved in microcirculation abnormalities encountered in sepsis or septic shock due to S. aureus infection.     

Pioglitazone ameliorates endothelial dysfunction and restores ischemia-induced angiogenesis in diabetic mice.

Angiogenesis, the formation of new blood vessels, is a physiological response to tissue ischemia. Clinical evidence suggests that diabetic patients have endothelial dysfunction and impaired angiogenesis in response to ischemia. Here, we investigated the impact of diabetes on ischemia-induced collateral growth, and tested the hypothesis that peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist augments collateral flow to ischemic tissue. We conducted unilateral hindlimb ischemia surgery in KKAy mice. Blood flow recovery was markedly impaired in diabetic mice compared with that in wild-type mice as determined by laser Doppler imaging. Treatment of KKAy mice with pioglitazone partially restored the blood flow recovery. Anti-CD31 immunostaining revealed that pioglitazone also significantly improved the capillary density in ischemic limb muscle. Endothelial NO synthase (eNOS) activity was ameliorated in diabetic mice treated with pioglitazone as determined by vasorelaxation in response to acetylcholine. Pioglitazone normalized vascular endothelial growth factor (VEGF) protein levels, which was decreased in ischemic muscle of KKAy mice, and up-regulated eNOS phosphorylation at Ser-1177 and Akt phosphorylation at Ser-473 in ischemic muscle. Pioglitazone had no beneficial effects on blood flow recovery in diabetic mice treated with N(G)-nitro-l-arginine methyl ester (L-NAME). Our findings demonstrate that pioglitazone significantly ameliorates endothelial dysfunction and enhances blood flow recovery after tissue ischemia in diabetic mice. Activation of eNOS appears to be essential for pioglitazone to promote angiogenesis in ischemic tissue.