Brachial artery flow-mediated dilation and asymmetrical dimethylarginine in the cardiovascular risk in young Finns study

Asymmetric dimethyarginine as marker and mediator in ischemic stroke

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is known as mediator of endothelial cell dysfunction and atherosclerosis. Circulating ADMA levels are correlated with cardiovascular risk factors such as hypercholesterolemia, arterial hypertension, diabetes mellitus, hyperhomocysteinemia, age and smoking. Accordingly, clinical studies found evidence that increased ADMA levels are associated with a higher risk of cerebrovascular events. After the acute event of ischemic stroke, levels of ADMA and its analog symmetric dimethylarginine (SDMA) are elevated through augmentation of protein methylation and oxidative stress. Furthermore, cleavage of ADMA through dimethylarginine dimethylaminohydrolases (DDAHs) is reduced. This increase of dimethylarginines might be predictive for adverse clinical outcome. However, the definite role of ADMA after acute ischemic stroke still needs to be clarified. On the one hand, ADMA might contribute to brain injury by reduction of cerebral blood flow. On the other hand, ADMA might be involved in NOS-induced oxidative stress and excitotoxic neuronal death. In the present review, we highlight the current knowledge from clinical and experimental studies on ADMA and its role for stroke risk and ischemic brain injury in the hyperacute stage after stroke. Finally, further studies are warranted to unravel the relevance of the close association of dimethylarginines with stroke.

Translating metabolomics to cardiovascular biomarkers

Metabolomics is the systematic study of the unique chemical fingerprints of small molecules or metabolite profiles that are related to a variety of cellular metabolic processes in a cell, organ, or organism. Although messenger RNA gene expression data and proteomic analyses do not tell the whole story of what might be happening in a cell, metabolic profiling provides direct and indirect physiologic insights that can potentially be detectable in a wide range of biospecimens. Although not specific to cardiac conditions, translating metabolomics to cardiovascular biomarkers has followed the traditional path of biomarker discovery from identification and confirmation to clinical validation and bedside testing. With technological advances in metabolomic tools (such as nuclear magnetic resonance spectroscopy and mass spectrometry) and more sophisticated bioinformatics and analytical techniques, the ability to measure low-molecular-weight metabolites in biospecimens provides a unique insight into established and novel metabolic pathways. Systemic metabolomics may provide physiologic understanding of cardiovascular disease states beyond traditional profiling and may involve descriptions of metabolic responses of an individual or population to therapeutic interventions or environmental exposures.

Mechanism of cellular oxidation stress induced by asymmetric dimethylarginine

The mechanism by which asymmetric dimethylarginine (ADMA) induces vascular oxidative stress is not well understood. In this study, we utilized human umbilical vein endothelial cells (HUVEC) to examine the roles of ADMA cellular transport and the uncoupling of endothelial nitric oxide synthase (eNOS) in contributing to this phenomenon. Dihydroethidium (DHE) fluorescence was used as an index of oxidative stress. Whole cells and their isolated membrane fractions exhibited measureable increased DHE fluorescence at ADMA concentrations greater than 10 μM. ADMA-induced DHE fluorescence was inhibited by co-incubation with L-lysine, tetrahydrobiopterin (BH(4)), or L-nitroarginine methyl ester (L-NAME). Oxidative stress induced in these cells by angiotensin II (Ang II) were unaffected by the same concentrations of L-lysine, L-NAME and BH(4). ADMA-induced reduction in cellular nitrite or nitrite/nitrate production was reversed in the presence of increasing concentrations of BH(4). These results suggest that ADMA-induced DHE fluorescence involves the participation of both the cationic transport system in the cellular membrane and eNOS instead of the Ang II-NADPH oxidase pathway.

In vivo nitric oxide synthesis, insulin sensitivity, and asymmetric dimethylarginine in obese subjects without and with metabolic syndrome

Metabolic syndrome (MetSyn) is associated with impaired endothelial function. Here the association between nitric oxide (NO) production and insulin sensitivity (Si) in obese subjects with and without MetSyn was evaluated. The relationship between NO production and asymmetric dimethylarginine (ADMA) was also explored. Seven healthy normal-weight subjects (male/female [M/F], 3/4; age, 27.4 ± 10.9 years; body mass index [BMI], 21.9 ± 2.2 kg/m(2)), 7 obese subjects without MetSyn (M/F, 1/6; age, 48.0 ± 8.0 years; BMI, 34.5 ± 2.3 kg/m(2)), and 7 with MetSyn (M/F, 3/4; age, 48.0 ± 10.7 years; BMI, 33.4 ± 2.9 kg/m(2)) were recruited. Body composition and cardiometabolic functions (blood pressure, glucose, insulin, triglycerides, total cholesterol, high-density lipoprotein, ADMA) were measured. A frequent sampling intravenous glucose tolerance test was performed to measure Si. A novel stable isotopic method was used to measure in vivo rates of NO production. The NO production was lower in obese subjects with MetSyn compared with normal-weight subjects and obese subjects without MetSyn. Similarly, Si was significantly lower in obesity, both without and with MetSyn, compared with the control group. A significant direct association was found between NO synthesis and Si (ρ = 0.47, P = .03). Circulating levels of ADMA were significantly higher in the obese group with MetSyn. A nonsignificant negative trend between ADMA and NO synthesis was observed. The association between Si and NO production suggests a close mechanistic link between endothelial function and insulin signaling. The results may be highly informative for the development of controlled longitudinal interventions to improve endothelial and metabolic regulation.

Endogenous nitric oxide synthase inhibitors in the biology of disease: markers, mediators, and regulators?

The asymmetric methylarginines inhibit nitric oxide synthesis in vivo by competing with L-arginine at the active site of nitric oxide synthase. High circulating levels of asymmetric dimethylarginine predict adverse outcomes, specifically vascular events but there is now increasing experimental and epidemiological evidence that these molecules, and the enzymes that regulate this pathway, play a mechanistic role in cardiovascular diseases. Recent data have provided insight into the impact of altered levels of these amino acids in both humans and rodents, however these reports also suggest a simplistic approach based on measuring, and modulating circulating asymmetric dimethylarginine alone is inadequate. This review outlines the basic biochemistry and physiology of endogenous methylarginines, examines both the experimental and observational evidence for a role in disease pathogenesis, and examines the potential for therapeutic regulation of these molecules.

Methods for evaluating endothelial function: a position statement from the European Society of Cardiology Working Group on Peripheral Circulation

The endothelium holds a pivotal role in cardiovascular health and disease. Assessment of its function was until recently limited to experimental designs due to its location. The advent of novel techniques has facilitated testing on a more detailed basis, with focus on distinct pathways. This review presents available in-vivo and ex-vivo methods for evaluating endothelial function with special focus on more recent ones. The diagnostic modalities covered include assessment of epicardial and microvascular coronary endothelial function, local vasodilation by venous occlusion plethysmography and flow-mediated dilatation, arterial pulse wave analysis and pulse amplitude tonometry, microvascular blood flow by laser Doppler flowmetry, biochemical markers and bioassays, measurement of endothelial-derived microparticles and progenitor cells, and glycocalyx measurements. Insights and practical information on the theoretical basis, methodological aspects, and clinical application in various disease states are discussed. The ability of these methods to detect endothelial dysfunction before overt cardiovascular disease manifests make them attractive clinical tools for prevention and rehabilitation.

Cellular biomarkers of endothelial health: microparticles, endothelial progenitor cells, and circulating endothelial cells

Endothelial dysfunction, the shift from a healthy endothelium to a damaged pro-coagulative, pro-inflammatory, and pro-vasoconstrictive phenotype, is an early event in many chronic diseases that frequently precedes cardiovascular complications. Functional assessment of the endothelium can identify endothelial damage and predict cardiovascular risk; however, this assessment provides little information as to the mechanisms underlying development of endothelial dysfunction. Changes in plasma asymmetric dimethyl arginine levels, markers of lipid peroxidation, circulating levels of inflammatory mediators, indices of coagulation and cellular surrogates such as microparticles, circulating endothelial cells, and endothelial progenitor cells may reflect alterations in endothelial status and as such have been defined as "biomarkers" of endothelial function. Biomarkers may be chemical or cellular. This review examines some markers of endothelial dysfunction, with a particular focus on cellular biomarkers of endothelial dysfunction and their diagnostic potential.

Where are we heading with noninvasive clinical vascular physiology? Why and how should we assess endothelial function?

There are several invasive and noninvasive methods available to the clinical researcher for the assessment of endothelial function. The first investigations in humans involved invasive pharmacological vascular function testing, which have been used to gain a detailed understanding of the mechanisms involved in the pathogenesis of endothelial dysfunction and atherosclerosis as well as novel targets for intervention. Techniques for endothelial function testing have evolved over time from these invasive methods, which, by their nature, are restricted to small studies in the research laboratory, to more standardized noninvasive methods, which are suitable for use in large prospective cohort studies and clinical trials. This paper describes currently available methods for assessment of endothelial function and their potential application in cardiovascular research and clinical practice.

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.

Peripheral vascular dysfunction in chronic kidney disease

There is an increased prevalence of cardiovascular disease- (CVD-) related mortality in patients with chronic kidney disease (CKD). Endothelial dysfunction is a primary event in the development of atherosclerosis and hypertension and likely contributes to the elevated cardiovascular risk in CKD. Endothelial dysfunction has been shown to occur in the peripheral vasculature of patients with both severe and moderate CKD. Mechanisms include oxidative stress, L-arginine deficiency, and elevated plasma levels of ADMA. Interventions designed to restore vascular function in patients with CKD have shown mixed results. Evidence from cell culture studies suggest that the accumulation of uremic toxins inhibits L-arginine transport and reduces nitric oxide production. The results of these studies suggest that endothelial dysfunction may become less reversible with advancing kidney disease. The purpose of this paper is to present the current literature pertaining to potential mechanisms of peripheral vascular dysfunction in chronic kidney disease and to identify possible targets for treatment.

Role of asymmetrical dimethylarginine in inflammation-induced endothelial dysfunction in human atherosclerosis

We explored the role of asymmetrical dimethylarginine (ADMA) as a cause of endothelial dysfunction induced by systemic inflammation. In vitro data suggest that ADMA bioavailability is regulated by proinflammatory stimuli, but it is unclear whether ADMA is a link between inflammation and endothelial dysfunction in humans. In study 1 we recruited 351 patients with coronary artery disease (CAD) and 87 healthy controls. In study 2 we recruited 69 CAD, 69 healthy, and 10 patients with rheumatoid arthritis, whereas in study 3, 22 healthy and 70 CAD subjects were randomly assigned to Salmonella typhii vaccination (n=11 healthy and n=60 CAD) or placebo (n=11 healthy and n=10 CAD). Circulating interleukin 6/ADMA and flow-mediated dilation (FMD) were measured at 0 and 8 hours. In study 1, ADMA was inversely correlated with FMD in healthy individuals and CAD patients (P<0.0001 for both). However, interleukin 6 was inversely correlated with FMD (P<0.0001) in healthy subjects but not in CAD patients. The positive correlation between ADMA and interleukin 6 was stronger in healthy (r=0.515; P<0.0001) compared with CAD (r=0.289; P=0.0001) subjects. In study 2, both patients with rheumatoid arthritis and CAD had higher interleukin 6 (P<0.0001) and ADMA (P=0.004) but lower FMD (P=0.001) versus healthy subjects. In study 3, vaccination increased interleukin 6 in healthy (P<0.001) and CAD (P<0.001) subjects. FMD was reduced in healthy subjects (P<0.05), but its reduction in CAD was borderline. Vaccination increased ADMA only in healthy subjects (P<0.001). Systemic, low-grade inflammation leads to increased ADMA that may induce endothelial dysfunction. This study demonstrated that ADMA may be a link between inflammation and endothelial dysfunction in humans.

Endothelial mechanisms of endothelial dysfunction in patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) occurs in 2% of middle-aged women and 4% of middle-aged men in the general population and the prevalence is much higher in specific patient groups. Intermittent hypoxia (IH, oxygen desaturation and re-oxygenation) cycle, a major pathophysiologic character of OSA, and the physiological responses this evokes are thought to be responsible for its association with increased cardiovascular morbidity and mortality. Endothelial dysfunction, resulting from IH and as a key early event in atherosclerosis, was demonstrated repeatedly in patients with OSA and in animal models of IH, providing an important mechanistic link between the acute cyclical IH during sleep and the increased prevalence of chronic vascular diseases.

CONCLUSIONS

From this work, we conclude that IH from OSA may result in endothelial dysfunction, as a potential promoter of atherosclerosis, through nitric oxide unavailability, oxidative stress and inflammation, cell apoptosis, the crosstalk between endothelial cells and circulating inflammatory cells, microparticles, and damage repairing process. Though effective continuous positive airway pressure (CPAP) may specifically improve endothelial function, more controlled larger interventional trials that will include multiple centers and randomized allocation of CPAP therapy are needed to see if such changes are reversible before cause and effect can be implied finally, while further studies on cellular and animal level are also needed to elucidate molecular biologic/pathologic pathways.

Asymmetric dimethylarginine, endothelial nitric oxide bioavailability and mortality in sepsis

Background

Plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, are raised in patients with chronic vascular disease, causing increased cardiovascular risk and endothelial dysfunction, but the role of ADMA in acute inflammatory states is less well defined.

Methods and Results

In a prospective longitudinal study in 67 patients with acute sepsis and 31 controls, digital microvascular reactivity was measured by peripheral arterial tonometry and blood was collected at baseline and 2–4 days later. Plasma ADMA and L-arginine concentrations were determined by high performance liquid chromatography. Baseline plasma L-arginine: ADMA ratio was significantly lower in sepsis patients (median [IQR] 63 [45–103]) than in hospital controls (143 [123–166], p<0.0001) and correlated with microvascular reactivity (r = 0.34, R² = 0.12, p = 0.02). Baseline plasma ADMA was independently associated with 28-day mortality (Odds ratio [95% CI] for death in those in the highest quartile (≥0.66 µmol/L) = 20.8 [2.2–195.0], p = 0.008), and was independently correlated with severity of organ failure. Increase in ADMA over time correlated with increase in organ failure and decrease in microvascular reactivity.

Conclusions

Impaired endothelial and microvascular function due to decreased endothelial NO bioavailability is a potential mechanism linking increased plasma ADMA with organ failure and death in sepsis.

Oxidant/antioxidant status in obese children compared to pediatric patients with type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes (T1D) mellitus and obesity are recognized risk factors for cardiovascular disease (CVD). A common mechanism underlying an increased risk for endothelial dysfunction in these two metabolic diseases is oxidative stress.

OBJECTIVE

To evaluate and compare the oxidant/antioxidant defense systems in children affected with T1D or obesity in order to determine the importance of oxidative stress before the emergence of complications.

SUBJECTS

Children with T1D (n = 20) or obesity (n = 22), without comorbidities, and age- and sex-matched controls (n = 16).

METHODS

We assessed lipid peroxidation by circulating levels of lipoperoxides and malondialdehyde, as well as protein oxidation by the concentration of plasma carbonyl groups. The endogenous antioxidative defense system was evaluated by the red cell glutathione peroxidase and reduced glutathione. The serum levels of alpha-tocopherol and beta-carotene were determined to assess exogenous antioxidants.

RESULTS

Lipid peroxidation was significantly higher in both T1D and obese children when compared with control children. However, T1D patients showed a more elevated level, because their malondialdehyde values were significantly increased with respect to obese children. Protein oxidation was present in both groups of children and did not differ between them. With respect to obese children, the glutathione peroxidase activity and exogenous antioxidants were decreased in T1D patients.

CONCLUSION

Oxidative stress is present in both children with T1D and obesity, although it is more pronounced in the former. Obese children may suffer an additional oxidative stress in the case of developing impaired glucose metabolism.

Reduced proteinuria using ramipril in diabetic CKD stage 1 decreases circulating cell death receptor activators concurrently with ADMA. A novel pathophysiological pathway?

BACKGROUND

Renin-angiotensin system (RAS) blockade improves proteinuria and the endothelial functions in diabetic nephropathy. Plasma asymmetric dimethylarginine (ADMA), abundant in the cell than in the plasma, is also improved by RAS blockage. We hypothesized that RAS blockade may reduce ADMA by reducing injurious cell death.

METHODS

In a hypothesis-generating study, we assessed circulating levels of apoptotic signalling peptides in incident chronic kidney disease (CKD) stage 1 patients (aged >18 years with diabetes mellitus type 2 as the only cause of nephropathy) not previously prescribed statins or RAS blockade. Ninety-three (29 M, 47 ± 5 years) patients with CKD 1 diabetic nephropathy and 38 healthy subjects (20 M, 47 ± 5 years) were enrolled. Ramipril was given (5 mg daily for 12 weeks), and circulating ADMA, soluble Fas (sFas), myostatin and endothelial function [flow-mediated vasodilation (FMD); ultrasound)] were measured.

RESULTS

After the study, ADMA, sFas, myostatin, insulin resistance, high-sensitive C-reactive protein (hsCRP), estimated glomerular filtration rate (eGFR), blood pressure and proteinuria levels were decreased, and FMD and serum albumin levels increased (P < 0.05 for all). ADMA and sFas levels were independently related to FMD levels both before (rho = -0.33; P < 0.005 and rho = -0.26; P < 0.02, respectively) and after (rho = -0.39; P < 0.001 and rho = -0.28; P < 0.002, respectively) ramipril treatment. Changes in sFas and ADMA were related to the change in FMD (-0.32; P > 0.004 and -0.31; P < 0.004, respectively).

CONCLUSION

A reduction of proteinuria in CKD 1 diabetic kidney disease is accompanied by lower circulating sFas, myostatin and ADMA, suggesting that increased cell death may contribute to ADMA formation and endothelial dysfunction in diabetic CKD.

Asymmetric dimethylarginine reference intervals determined with liquid chromatography-tandem mass spectrometry: results from the Framingham offspring cohort

BACKGROUND

Accumulating evidence links higher circulating asymmetric dimethylarginine (ADMA) to greater risk of cardiovascular disease (CVD). Relatively small differences in ADMA concentrations between healthy individuals and those with disease underscore the need to formulate reference intervals that may aid risk stratification of individuals.

METHODS

We formulated reference intervals for plasma ADMA concentrations using a community-based reference sample from the Framingham Offspring Study consisting of 1126 nonsmoking individuals [mean (SD) age 56 (9) years; 60% women] who were free of clinical CVD, hypertension, diabetes, and obesity and who attended a routine examination at which ADMA was assayed. ADMA concentrations were determined using a validated tandem mass spectrometry-liquid chromatography assay.

RESULTS

In the study sample, the mean ADMA concentration was 0.52 (0.11) micromol/L, and the reference limits were 0.311 and 0.732 (2.5th and 97.5th percentile). The sex-specific reference limits were 0.310 and 0.745 in men and 0.313 and 0.721 micromol/L in women. In multivariable regression analysis, ADMA plasma concentrations were positively correlated with age and total plasma homocysteine (both P < 0.001).

CONCLUSIONS

Reference limits calculated for circulating ADMA in our large community-based healthy reference sample confirm the previous observation of a relatively narrow distribution of concentrations. This suggests a tight physiological control of ADMA plasma concentrations, presumably by dimethylarginine dimethylaminohydrolase (DDAH) metabolism of ADMA.

Targeted metabolomic evaluation of arginine methylation and cardiovascular risks: potential mechanisms beyond nitric oxide synthase inhibition

BACKGROUND

We examine the relationship of related posttranslational modification products of arginine methylation and coronary artery disease (CAD) phenotypes.

METHODS AND RESULTS

Plasma was isolated from 1011 consecutive consenting subjects undergoing elective diagnostic cardiac catheterization, and future major adverse cardiac events (MACE, including myocardial infarction, stroke, and death) at 3 years were investigated. Plasma levels of asymmetrical dimethylarginine (ADMA, endogenous nitric oxide synthase [NOS] inhibitor), symmetrical dimethylarginine (SDMA, which lacks NOS inhibitory activity), N-mono-methylarginine (MMA, a potent NOS inhibitor), methyl-lysine (Methyl-Lys, an unrelated methylated amino acid), arginine, and its major catabolites (citrulline and ornithine) were quantified simultaneously by stable isotope dilution HPLC with online electrospray ionization tandem mass spectrometry and adjusted for traditional risk factors, C-reactive protein, and estimated creatinine clearance. High SDMA levels (adjusted odds ratio [OR] 1.6, 95%CI, 1.1 to 2.6, P<0.001), low MMA (adjusted OR 0.5, 95%CI 0.4 to 0.8, P=0.007), but not ADMA (adjusted OR 1.3, 95%CI 0.88 to 2.0, P=0.177) were associated with increased prevalence of significantly obstructive CAD. Elevated levels of SDMA (adjusted Hazard Ratio [HR] 2.4, 95%CI 1.2 to 4.6, P=0.009), ADMA (adjusted HR 2.2, 95%CI 1.2 to 4.0, P=0.015), as well as an integrated index of arginine methylation [ArgMI=(ADMA+SDMA)/MMA] (adjusted HR 2.4, 95%CI 1.3 to 4.5, P=0.006) were significant independent predictors of incident MACE. ArgMI was predictive of incident MACE even following adjustments for global arginine bioavailability, particularly within secondary prevention patients.

CONCLUSIONS

ADMA, SDMA, and the integrated quantification of arginine methylation (in the form of a methylation index) provided independent risk prediction for both significantly obstructive CAD and incident MACE in stable patients undergoing cardiac evaluation. These results suggest that factors beyond direct NOS inhibition contribute to the clinical associations between methylarginines and CAD outcomes.

The endothelial-erectile dysfunction connection: an essential update

INTRODUCTION

The endothelial monolayer plays a crucial role in the vasodilation and hemodynamic events involved in erection physiology. Due to its relevant functions, a close link has been established between endothelial integrity and erectile dysfunction (ED). Endothelial dysfunction is induced by the detrimental actions of vascular risk factors (VRFs), identified as common correlates for the development of cardiovascular disease and ED. It is currently recognized that ED is the early harbinger of a more generalized vascular systemic disorder, and, therefore, an evaluation of endothelial health in ED patients should be of prime relevance. Several noninvasive methods for endothelial function assessment have been proposed, including the Penile Nitric Oxide Release Test (PNORT).

AIM

To highlight the most recent gathered knowledge on basic and clinical mechanisms underlying loss of cavernosal endothelial function promoted by VRFs and to discuss local and systemic methods for endothelial function assessment in ED individuals, focusing on the PNORT.

MAIN OUTCOME MEASURES

A complete revision on the novel basic and clinical links between endothelial and ED.

METHODS

A systematic review of the literature regarding the aforementioned issues.

RESULTS

Risk factor-associated cavernosal endothelial dysfunction is mostly induced by unifying mechanisms, including oxidative stress and impaired endothelial nitric oxide functional activities, which present clinically as ED. Several techniques to evaluate endothelial dysfunction were revised, with advantages and limitations debated, focusing on our detailed expertise using the PNORT method.

CONCLUSIONS

The established endothelial-erectile dysfunction connection was thoroughly revised, from basic mechanisms to the clinical importance of endothelial dysfunction assessment as diagnosis for generalized vascular disease. Further studies are required to disclose efficient approaches to repair disabled endothelium and both restore and prevent endothelial dysfunction.

HDL-Cholesterol, Blood Pressure, and Asymmetric Dimethylarginine Are Significantly Associated With Arterial Wall Thickness in Children

Objective— Atherosclerosis is found at autopsy in the arteries of adolescents and young adults. Arterial wall thickening may be assessed in vivo by ultrasound measurement of the carotid intima media thickness (CIMT), a marker of subclinical atherosclerosis. As the determinants of arterial wall thickness in childhood are unknown, we assessed the influence of cardiovascular risk factors on CIMT in 8-year-old children.

Methods and Results— A community-based sample of 405 children (age 8.0±0.1 years, 49% girls) had anthropometry, family history, blood pressure (BP), and CIMT measured. A blood sample was collected for HDL and non-HDL cholesterol, apolipoproteins A1 and B, high-sensitivity C-reactive protein, bilirubin, and asymmetric dimethylarginine (ADMA, an endogenous nitric oxide inhibitor). CIMT was significantly associated with systolic BP ( r =0.17, P <0.001), diastolic BP ( r =0.10, P =0.04), HDL ( r =−0.13, P =0.02), and ADMA ( r =0.18, P =0.001). CIMT was significantly higher in children with premature parental CHD (0.63±0.07 versus 0.59±0.06 mm, P =0.03). On multivariate analysis, HDL (β coefficient=−0.02, P =0.04), ADMA (β coefficient=0.05, P <0.001), and systolic BP (β coefficient=0.001, P =0.003) were significantly and independently associated with CIMT.

Conclusions— Lower HDL-cholesterol, higher levels of ADMA, and systolic BP are significantly associated with greater arterial wall thickness in early childhood.

Association of plasma asymmetrical dimethylarginine (ADMA) with elevated vascular superoxide production and endothelial nitric oxide synthase uncoupling: implications for endothelial function in human atherosclerosis

BACKGROUND

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase (eNOS), is considered to be a risk factor for atherosclerosis. However, the mechanisms relating ADMA with vascular function have been evaluated in vitro and in animal models, but its effect in human vasculature is unclear.

AIMS

We examined the impact of serum ADMA on endothelial nitric oxide (NO) bioavailability and vascular superoxide radical (O2-) production in patients with advanced atherosclerosis.

METHODS AND RESULTS

Paired samples of saphenous veins (SVs) and internal mammary arteries (IMAs) were collected from 201 patients undergoing coronary bypass surgery, and serum ADMA was measured pre-operatively. The vasomotor responses of SV segments to acetylcholine (ACh) and bradykinin (Bk) were evaluated ex vivo. Vascular O2- was measured in paired SV and IMA by lucigenin-enhanced chemiluminescence. The l-NAME-inhibitable as well as the NADPH-stimulated vascular O2- generation was also determined by chemiluminescence. High serum ADMA levels were associated with decreased vasorelaxation of SV to ACh (P < 0.05) and Bk (P < 0.05). Similarly, high serum ADMA was associated with higher total O2- production in both SVs and IMAs (P < 0.05) and greater L-NAME-inhibitable vascular O2- (P < 0.05). However, serum ADMA was not associated with NADPH-stimulated vascular O2-. In multivariable linear regression, serum ADMA was independently associated with vascular O2- in both SVs [beta (SE): 0.987 (0.412), P = 0.019] and IMAs [beta (SE): 1.905 (0.541), P = 0.001]. Asymmetrical dimethylarginine was also independently associated with maximum vasorelaxation in response to both ACh [beta (SE): 14.252 (3.976), P = 0.001] and Bk [beta (SE): 9.564 (3.762), P = 0.013].

CONCLUSION

This is the first study that demonstrates an association between ADMA and important measures of vascular function, such as vascular O2- production and NO bioavailability directly in human vessels. Although serum ADMA has no effect on NADPH-stimulated superoxide in intact vessels, it is associated with greater eNOS uncoupling in the human vascular endothelium of patients with coronary artery disease.

Differential effects of cross-sex hormonal treatment on plasma asymmetric dimethylarginine (ADMA) in healthy male-to-female and female-to-male transsexuals

OBJECTIVE

Sex hormone administration affects plasma levels of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). We investigated the effects of cross-sex hormone treatment (CHT) on plasma ADMA concentration in an open-label study in 40 male-to-female (M-F) and 14 female-to-male (F-M) transsexuals.

METHODS

M-F received (1) cyproterone acetate (CA) 50mg bid (n=10), (2) CA 50mg bid+ethinyl estradiol (EE) 50 microg bid (n=15), or (3) CA 50mg bid+transdermal estradiol (tE(2)) patches daily delivering 100 microg 17beta-estradiol (n=15). F-M received 250 mg mixed testosterone esters intramuscularly every 2 weeks (n=14).

RESULTS

All M-F treatment arms showed a decrease in plasma ADMA concentration after 16 weeks of CHT (mean percentage change from pre-treatment (95% confidence interval)): -26.2% (-30.9 to -21.5%) for EE+CA, -8.9% (-13.4 to -4.3%) for tE(2)+CA, and -11.3% (-17.4 to -5.2%) for CA. Testosterone administration to females increased ADMA by 9.4% (2.6 to 16.3%). The change in the EE+CA treated group was still significant after 52 weeks of CHT. In M-F and F-M, CHT had opposite effects on concentrations of other plasma amino acids as well, with EE+CA treatment causing a decrease and testosterone administration resulting in an increase.

CONCLUSION

Administration of anti-androgens alone or combined with estrogens to males decreases and testosterone administration to females increases the plasma ADMA concentration, possibly reflecting a general effect of sex hormones on amino acid metabolism.

Endothelial dysfunction in African-Americans

The journey of atherosclerosis begins with endothelial dysfunction and culminates into its most fearful destination producing ischemia, myocardial infarction and death. The excess cardiovascular disease morbidity and mortality in African-Americans is one of the major public health problems. In this review, we discuss vascular endothelial dysfunction as a key element for excess cardiovascular disease burden in this target population. It can be logical window of future atherosclerotic outcomes, and further efforts should be made to detect it at the earliest in African American individuals even if they are appearing healthy as the therapeutic interventions if instituted early, might prevent the subsequent cardiac events.

Obstructive sleep apnea: the new cardiovascular disease. Part I: Obstructive sleep apnea and the pathogenesis of vascular disease

Obstructive sleep apnea (OSA) is increasingly recognized as a novel cardiovascular risk factor. OSA is implicated in the pathogenesis of hypertension, left ventricular dysfunction, coronary artery disease and stroke. OSA exerts its negative cardiovascular consequences through its unique pattern of intermittent hypoxia. Endothelial dysfunction, oxidative stress, and inflammation are all consequences of OSA directly linked to intermittent hypoxia and critical pathways in the pathogenesis of cardiovascular disease in patients with OSA. This review will discuss the known mechanisms of vascular dysfunction in patients with OSA and their implications for cardiovascular disease.

Asymmetric dimethylarginine (ADMA) has a role in regulating systemic vascular tone in young healthy subjects: the cardiovascular risk in young Finns study

BACKGROUND

This study was designed to evaluate whether plasma asymmetric dimethylarginine (ADMA) has any role in predicting hemodynamic responses in clinically healthy young subjects. ADMA, as an endogenous nitric oxide (NO) synthase inhibitor, has been demonstrated to associate with hypertension and vascular reactivity in experimental but not undoubtedly in physiological settings.

METHODS

A total of 199 subjects aged 31.4 years (range 24-39 years) were studied. Plasma ADMA and symmetric dimethylarginine (SDMA) were assessed by isocratic high-pressure liquid chromatography using precolumn derivatization with o-phtaldialdehyde at baseline. Blood pressure (BP) was measured by casual measurements in the beginning of the study and after a follow-up period of 2.45 +/- 0.42 years (range, 1.86-3.19 years). Hemodynamic regulation was assessed by noninvasive methods after a follow-up.

RESULTS

Plasma ADMA had a negative association with resting systemic vascular resistance index (SVRI) (r = -0.23, P < 0.01) and pulse wave velocity (PWV) (r = -0.17, P < 0.05) and positive association with cardiac index (CI) (r = 0.21, P < 0.01) after the follow-up. Plasma ADMA had also negative association with responses of SVRI (r = -0.19, P < 0.01) and positive association with CI (r = 0.25, P < 0.001) in a hemodynamic reactivity test. In a multivariate linear model (R2 = 0.20, P < 0.00001), diastolic BP (R = 0.37, P < 0.00001) and ADMA (R = -0.20, P < 0.01) were significant predictors of SVRI.

CONCLUSIONS

These results suggest that plasma ADMA seems to play a role in the regulation of vascular tone in young healthy subjects.

Pathophysiology, diagnosis and prognostic implications of endothelial dysfunction

Endothelial dysfunction (ED) in the setting of cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, chronic smoking as well as in patients with heart failure has been shown to be at least in part dependent on the production of reactive oxygen species (ROS) such as superoxide and the subsequent decrease in vascular bioavailability of nitric oxide (NO). Methods to quantify endothelial dysfunction include forearm plethysmography, flow-dependent dilation of the brachial artery, finger-pulse plethysmography, pulse curve analysis, and quantitative coronary angiography after intracoronary administration of the endothelium-dependent vasodilator acetylcholine. Superoxide sources include the NADPH oxidase, xanthine oxidase, and mitochondria. Superoxide produced by the NADPH oxidase may react with NO released by the endothelial nitric oxide synthase (eNOS) thereby generating peroxynitrite (ONOO-), leading to eNOS uncoupling and therefore eNOS-mediated superoxide production. The present review will discuss current concepts of how to assess endothelial function, prognostic implications of ED, mechanisms underlying ED with focus on oxidative stress and circulating biomarkers, which have been proposed to indicate endothelial dysfunction and/or damage, respectively.