l-Arginine is related to endothelium-dependent vasodilation in resistance and conduit arteries in divergent ways—The Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study

Increased Plasma L-Arginine Levels and L-Arginine/ADMA Ratios after Twelve Weeks of Omega-3 Fatty Acid Supplementation in Amateur Male Endurance Runners

It is not fully understood how supplementation with omega-3 fatty acids affects the metabolism of amino acids required for the bioavailability/synthesis of NO, i.e., L-arginine (L-arg), asymmetric dimethylarginine (ADMA), their metabolites, and the L-arg/ADMA ratio and their impact on running economy (RE) in runners. Thus, 26 male amateur endurance runners completed a twelve-week study in which they were divided into two supplemented groups: the OMEGA group (n = 14; 2234 mg and 916 mg of eicosapentaenoic and docosahexaenoic acid daily) or the MCT group (n = 12; 4000 mg of medium-chain triglycerides daily). At the same time, all participants followed an endurance training program. Before and after the 12-week intervention, blood was collected from participants at two time points (at rest and immediately post-exercise) to determine EPA and DHA in red blood cells (RBCs) and plasma levels of L-arg, ADMA, and their metabolites. RBC EPA and DHA significantly increased in the OMEGA group (p < 0.001), which was related to the resting increase in L-arg (p = 0.001) and in the L-arg/ADMA ratio (p = 0.005) with no changes in the MCT group. No differences were found in post-exercise amino acid levels. A total of 12 weeks of omega-3 fatty acid supplementation at a dose of 2234 mg of EPA and 916 mg of DHA daily increased levels of L-arg and the L-arg/ADMA ratio, which indirectly indicates increased bioavailability/NO synthesis. However, these changes were not associated with improved RE in male amateur endurance runners.

Arginase: shedding light on the mechanisms and opportunities in cardiovascular diseases

Arginase, a binuclear manganese metalloenzyme in the urea, catalyzes the hydrolysis of L-arginine to urea and L-ornithine. Both isoforms, arginase 1 and arginase 2 perform significant roles in the regulation of cellular functions in cardiovascular system, such as senescence, apoptosis, proliferation, inflammation, and autophagy, via a variety of mechanisms, including regulating L-arginine metabolism and activating multiple signal pathways. Furthermore, abnormal arginase activity contributes to the initiation and progression of a variety of CVDs. Therefore, targeting arginase may be a novel and promising approach for CVDs treatment. In this review, we give a comprehensive overview of the physiological and biological roles of arginase in a variety of CVDs, revealing the underlying mechanisms of arginase mediating vascular and cardiac function, as well as shedding light on the novel and promising therapeutic approaches for CVDs therapy in individuals.

ADMA: A Key Player in the Relationship between Vascular Dysfunction and Inflammation in Atherosclerosis

Atherosclerosis is a chronic cardiovascular disease which increases risk of major cardiovascular events including myocardial infarction and stroke. Elevated plasma concentrations of asymmetric dimethylarginine (ADMA) have long been recognised as a hallmark of cardiovascular disease and are associated with cardiovascular risk factors including hypertension, obesity and hypertriglyceridemia. In this review, we discuss the clinical literature that link ADMA concentrations to increased risk of the development of atherosclerosis. The formation of atherosclerotic lesions relies on the interplay between vascular dysfunction, leading to endothelial activation and the accumulation of inflammatory cells, particularly macrophages, within the vessel wall. Here, we review the mechanisms through which elevated ADMA contributes to endothelial dysfunction, activation and reactive oxygen species (ROS) production; how ADMA may affect vascular smooth muscle phenotype; and finally whether ADMA plays a regulatory role in the inflammatory processes occurring within the vessel wall.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

SARCOPENIA: AN ENDOCRINE DISORDER?

Sarcopenia is defined as low muscle function (walking speed or grip strength) in the presence of low muscle mass. A simple screening test-the SARC-F-is available to identify persons with sarcopenia. The major endocrine causes of sarcopenia are diabetes mellitus and male hypogonadism. Other causes are decreased physical activity, loss of motor neuron units, weight loss, inflammatory cytokines, reduced blood flow to muscles, very low 25(OH) vitamin D levels, and decreased growth hormone and insulin-like growth factor 1. Treatment for sarcopenia includes resistance and aerobic exercise, leucine-enriched essential amino acids, and vitamin D. In hypogonadal males, testosterone improves muscle mass, strength, and function. Selective androgen receptor molecules and anti-myostatin activin II receptor molecules are under development as possible treatments for sarcopenia.

ABBREVIATIONS

COPD = chronic obstructive pulmonary disease DHEA = dehydroepiandrosterone IGF-1 = insulin-like growth factor 1 GH = growth hormone mTOR = mammalian target of rapamycin SARM = selective androgen receptor molecule.

Multidisciplinary Treatment of the Metabolic Syndrome Lowers Blood Pressure Variability Independent of Blood Pressure Control

Blood pressure (BP) variability (BPV) contributes to target organ damage independent of BP. The authors examined the effect of a 1-year multidisciplinary intervention on BPV in patients with the metabolic syndrome (MetS) as defined by criteria from the Third Report of the Adult Treatment Panel. Forty-four nondiabetic patients underwent clinical and biochemical profiling, 24-hour ambulatory BP monitoring (ABPM), body composition, carotid intima-media thickness, and carotid-femoral pulse wave velocity (PWV). The intervention targeted all MetS components. BPV was assessed by the standard deviation of daytime systolic BP derived from ABPM. Patients with low and high BPV (lower or higher than the median daytime standard deviation of 11.6 mm Hg) did not differ in regards to systolic and diastolic BP, age, fasting glucose, glycated hemoglobin, and body mass index, but the high-variability group had higher values of low-density lipoprotein and leg fat. The 1-year intervention resulted in weight reduction but not BP-lowering. BPV declined in the high-variability group in association with lowering of PWV, C-reactive protein, glycated hemoglobin, alanine aminotransferase, asymmetric dimethylarginine, and increased high-density lipoprotein cholesterol. A multidisciplinary intervention independent of BP-lowering normalized BPV, lowered PWV, and enhanced metabolic control.

Plasma arginine/ADMA ratio as a sensitive risk marker for atherosclerosis: Shimane CoHRE study

BACKGROUND

Asymmetric dimethylarginine (ADMA), which acts an endogenous inhibitor of nitric oxide synthase (NOS), is involved in the pathogenesis of cardiovascular disease. Arginine (Arg) may regulate vascular endothelial function, since Arg is the substrate of NO competing with ADMA. In our previous study, low Arg/ADMA ratio is an independent risk for microangiopathy-related cerebral damage.

PURPOSE

Here, we performed a cross-sectional study to evaluate the association between the Arg/ADMA ratio and the maximal intima-media thickness (IMT) in the carotid artery.

SUBJECTS AND METHODS

Participants were 785 community-dwelling Japanese people without any severe disorders. Plasma concentration of Arg and ADMA in fasting blood sample was determined using HPLC. IMT was measured in the bilateral carotid artery by ultrasonography.

RESULTS

Among quartiles stratified by the Arg/ADMA ratio, ANOVA showed a significant difference in IMT and the IMT in Q1 (the lowest quartile) was significantly higher than that in Q4 (the highest quartile). In multiple linear regression analysis, age, the male gender, lower BMI, the presence of hypertension and lower Arg/ADMA ratio were independently correlated with IMT, while IMT was not correlated with Arg or ADMA alone. In addition, the Arg/ADMA ratio was associated with IMT independent of age, sex, BMI and the presence of hypertension with odds ratio 0.21 (95%CI: 0.05-0.88) in multiple logistic regression analysis for IMT 1.5 mm or more.

CONCLUSION

Imbalance of Arg and ADMA is independently involved in the progression of atherosclerosis, and the Arg/ADMA ratio may be a sensitive marker for atherosclerosis.

Association between brachial-ankle pulse wave velocity and the ratio of l-arginine to asymmetric dimethylarginine in patients undergoing coronary angiography

BACKGROUND

Endothelial dysfunction causes vasomotor dysregulation and vascular stiffening in addition to structural changes. By influencing NO synthesis, deficiency of l-arginine relative to asymmetric dimethylarginine (ADMA), which is an l-arginine derivative that acts as a competitive NO synthase inhibitor, may lead to the promotion of arterial stiffness. This study investigated the relationship between the l-arginine/ADMA ratio and brachial-ankle pulse wave velocity (baPWV), an indicator of arterial stiffness.

METHODS AND RESULTS

This cross-sectional study enrolled 74 patients (62 men, 12 women; mean age, 67±10 years) undergoing elective coronary angiography. A total of 54 (73%) patients had coronary artery disease. Serum l-arginine and ADMA were measured by high-performance liquid chromatography with fluorescence detection. The ratio of l-arginine to ADMA and the serum l-arginine level was associated with baPWV in univariate regression analysis (l-arginine/ADMA ratio: β=-0.323, p=0.005; l-arginine: β=-0.247, p=0.034). In addition, baPWV was related to blood hemoglobin concentration, hematocrit, brain natriuretic peptide level, symmetric dimethylarginine, renal function, blood pressure, and heart rate. In multivariate analysis, the l-arginine/ADMA ratio was a significant predictor of baPWV (β=-0.310, p<0.001). In subgroup analyses, the l-arginine/ADMA ratio was associated with baPWV in elderly patients (n=46, β=-0.359, p=0.004), and in younger patients (n=28, β=-0.412, p=0.006).

CONCLUSION

A low l-arginine/ADMA ratio may be associated with high baPWV in patients undergoing coronary angiography.

L-arginine, asymmetric dimethylarginine, and symmetric dimethylarginine in plasma and synovial fluid of patients with knee osteoarthritis

BACKGROUND

The aim of this study was to investigate the involvement of the nitric oxide (NO) pathway in osteoarthritis (OA).

MATERIAL AND METHODS

The study groups consisted of 32 patients with knee OA and 31 healthy controls. In peripheral venous blood samples (from the OA patients and the controls) and in synovial fluid samples (from the OA patients), the concentrations of L-arginine (ARN), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) were evaluated. In plasma samples, thiobarbituric acid reactive substances (TBARS) were also measured.

RESULTS

Plasma ARN concentrations were lower in the OA patients than in controls (53.55 ± 16.37 vs. 70.20 ± 25.68 µmol/l) (P<0.05), while plasma ADMA concentrations were similar. Accordingly, the ARN/ADMA ratio was lower in the OA patients than in the control group (80.85 ± 29.58 vs. 110.51 ± 30.48, P<0.05). Plasma SDMA and TBARS concentrations were higher in the OA patients than in controls (0.69 ± 0.15 vs. 0.60 ± 0.10 µmol/l, P<0.05 and 1.21 ± 0.29 vs. 0.55 ± 0.12, respectively) (P<0.001). In the OA patients, ADMA concentrations were significantly higher in the synovial fluid than in plasma (0.75 ± 0.09 vs. 0.69 ± 0.14 µmol/l, P<0.05), as were ARN concentrations (76.96 ± 16.73 vs. 53.55 ± 16.73 µmol/l) (P<0.00001). Conclusions These results indicate a poor availability of NO in the synovial fluid of the OA patients, which may contribute to the progression of OA. The decreased ARN/ADMA ratio and the increased SDMA and TBARS in the plasma of the OA patients suggest an impairment of endothelial function in these subjects.

Genetic variation in the dimethylarginine dimethylaminohydrolase 1 gene (DDAH1) is related to asymmetric dimethylarginine (ADMA) levels, but not to endothelium-dependent vasodilation

Objectives:

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase. The breakdown of ADMA is mainly governed by the activity of dimethylarginine dimethylaminohydrolases (DDAHs). We investigated if genetic variation in the DDAH1 and DDAH2 genes were related to ADMA and l-arginine levels, as well as measures of endothelium-dependent vasodilation.

Methods:

In 1016 70-year-old participants of the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study (50% women), we measured endothelium-dependent vasodilation (EDV) using the invasive forearm technique with acetylcholine given in the brachial artery and the brachial artery ultrasound technique with measurement of flow-mediated dilatation (FMD). Plasma l-arginine and ADMA levels were measured by high-performance liquid chromatography and 55 single nucleotide polymorphisms (SNPs) in the DDAH1 and DDAH2 genes were genotyped.

Results:

Several of the genotypes in the DDAH1 gene were highly significantly related to ADMA levels ( p = 10−7 at best), but not to the l-arginine levels. No relationships between the genotypes in the DDAH2 gene and ADMA or l-arginine levels were found. None of the DDAH1 genotypes being closely related to ADMA levels were significantly related to EDV or FMD. Neither were any of the DDAH2 genotypes closely related to any of the measurements of vasoreactivity.

Conclusion:

A close relationship was seen between SNPs in the DDAH1, but not DDAH2, gene and ADMA levels. However, variation in those genes was not related to measures of EDV in this elderly population.

Role of endothelin receptor A and NADPH oxidase in vascular abnormalities

Vascular dilatation is critically impaired in many diseases and is encountered by an upregulated endothelin receptor A (ETA) in the vasculature in association with a decline in nitric oxide bioavailability. Diabetic vasculopathy is characterized as a compromised vascular dilatation, implicated in many diabetic complications. It appears to be activated ETA and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase in the vasculature. Glucose-lowering agents do not always blunt these changes, as these changes may be progressive leading to the end stage of renal disease. The vascular insults by hypertension, hyperglycemia and aging may share the changes with diabetic vascular beds. Endothelin receptor antagonist CPU0213 and ingredients from plant origins such as CPU86017, p-benzyl-tetra-hydro-berberine are effective in attenuating vascular abnormality by normalizing changes of biomarkers in the vascular wall. The early sign of subclinical atherosclerosis presented as an intima media thickness in the carotid may indicate endothelium dysfunction. The reduced ABI (ankle brachial index) has been taken to predict patients at risk for cardiovascular and cerebrovascular events, and an increased risk of mortality from all causes and cardiovascular disease. An application of agents which suppress the activated ET-NADPH oxidase in the vascular wall is beneficial to attenuate vascular abnormalities. It is worth testing the activity of these agents further for the potential in relieving abnormal vascular activity, reducing the risk of morbidity and mortality in patients at risk.

Oral L-arginine supplementation improves endothelial function and ameliorates insulin sensitivity and inflammation in cardiopathic nondiabetic patients after an aortocoronary bypass

It is known that L-arginine treatment can ameliorate endothelial dysfunction and insulin sensitivity in type 2 diabetes mellitus patients, but little is known on L-arginine effects on these variables in nondiabetic patients with stable cardiovascular disease (coronary artery disease). We evaluated the effects of long-term oral L-arginine treatment on endothelial dysfunction, inflammation, adipokine levels, glucose tolerance, and insulin sensitivity in these patients. Sixty-four patients with cardiovascular disease previously submitted to an aortocoronary bypass and not known for type 2 diabetes mellitus had an oral glucose load to define their glucose tolerance. Thirty-two patients with nondiabetic response were eligible to receive, in a double-blind randomized parallel order, L-arginine (6.4 g/d) or placebo for 6 months. An evaluation of insulin sensitivity index during the oral glucose load, markers of systemic nitric oxide bioavailability and inflammation, and blood flow was performed before and at the end of the treatment in both groups. Compared with placebo, L-arginine decreased asymmetric dimethylarginine levels (P < .01), indices of endothelial dysfunction, and increased cyclic guanosine monophosphate (P < .01), L-arginine to asymmetric dimethylarginine ratio (P < .0001), and reactive hyperemia (P < .05). Finally, L-arginine increased insulin sensitivity index (P < .05) and adiponectin (P < .01) and decreased interleukin-6 and monocyte chemoattractant protein-1 levels. In conclusion, insulin resistance, endothelial dysfunction, and inflammation are important cardiovascular risk factors in coronary artery disease patients; and L-arginine seems to have anti-inflammatory and metabolic advantages in these patients.