Asymmetric dimethylarginine and reactive oxygen species: unwelcome twin visitors to the cardiovascular and kidney disease tables

L-Arginine and its metabolites in kidney and cardiovascular disease

L-Arginine is a semi essential amino acid synthesised from glutamine, glutamate and proline via the intestinal-renal axis in humans and most mammals. L-Arginine degradation occurs via multiple pathways initiated by arginase, nitric-oxide synthase, Arg: glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine and agmatine with each having enormous biological importance. Several disease are associated to an L-arginine impaired levels and/or to its metabolites: in particular various L-arginine metabolites may participate in pathogenesis of kidney and cardiovascular disease. L-Arginine and its metabolites may constitute both a marker of pathology progression both the rationale for manipulating L-arginine metabolism as a strategy to ameliorate these disease. A large number of studies have been performed in experimental models of kidney disease with sometimes conflicting results, which underlie the complexity of Arg metabolism and our incomplete knowledge of all the mechanisms involved. Moreover several lines of evidence demonstrate the role of L-arg metabolites in cardiovascular disease and that L-arg administration role in reversing endothelial dysfunction, which is the leading cause of cardiovascular diseases, such as hypertension and atherosclerosis. This review will discuss the implication of the mains L-arginine metabolites and L-arginine-derived guanidine compounds in kidney and cardiovascular disease considering the more recent literature in the field.

Systemic and renal oxidative stress in the pathogenesis of hypertension: modulation of long-term control of arterial blood pressure by resveratrol

Hypertension affects over 25% of the global population and is associated with grave and often fatal complications that affect many organ systems. Although great advancements have been made in the clinical assessment and treatment of hypertension, the cause of hypertension in over 90% of these patients is unknown, which hampers the development of targeted and more effective treatment. The etiology of hypertension involves multiple pathological processes and organ systems, however one unifying feature of all of these contributing factors is oxidative stress. Once the body's natural anti-oxidant defense mechanisms are overwhelmed, reactive oxygen species (ROS) begin to accumulate in the tissues. ROS play important roles in normal regulation of many physiological processes, however in excess they are detrimental and cause widespread cell and tissue damage as well as derangements in many physiological processes. Thus, control of oxidative stress has become an attractive target for pharmacotherapy to prevent and manage hypertension. Resveratrol (trans-3,5,4'-Trihydroxystilbene) is a naturally occurring polyphenol which has anti-oxidant effects in vivo. Many studies have shown anti-hypertensive effects of resveratrol in different pre-clinical models of hypertension, via a multitude of mechanisms that include its function as an anti-oxidant. However, results have been mixed and in some cases resveratrol has no effect on blood pressure. This may be due to the heavy emphasis on peripheral vasodilator effects of resveratrol and virtually no investigation of its potential renal effects. This is particularly troubling in the arena of hypertension, where it is well known and accepted that the kidney plays an essential role in the long term regulation of arterial pressure and a vital role in the initiation, development and maintenance of chronic hypertension. It is thus the focus of this review to discuss the potential of resveratrol as an anti-hypertensive treatment via amelioration of oxidative stress within the framework of the fundamental physiological principles of long term regulation of arterial blood pressure.

Time course of asymmetric dimethylarginine and symmetric dimethylarginine levels after successful renal transplantation

BACKGROUND

Although renal transplantation (Tx) improves the outcome of patients with renal disease, cardiovascular (CV) risk remains high. Recently, it was demonstrated that asymmetric dimethylarginine (ADMA) levels predict CV events and graft survival in renal transplant recipients (RTRs). Little is known about the impact of renal Tx on the plasma levels of ADMA and symmetric dimethylarginine (SDMA). The present study aimed to define the time course of ADMA and SDMA after Tx.

METHODS

We prospectively followed 167 incident RTRs with visits at the time of Tx and 3 and 12 months thereafter. At all visits, demographics and relevant biochemistry were recorded and blood was sampled for analysis of ADMA and SDMA (high-performance liquid chromatography). Eighty-four patients had an additional sampling in the immediate postoperative period. In a case-controlled substudy (n = 31), we compared ADMA and SDMA levels between RTRs and chronic kidney disease (CKD) patients, matched for glomerular filtration rate, gender, age, CV history and diabetes.

RESULTS

Overall, plasma ADMA and SDMA levels decreased after Tx. The decline of SDMA was more pronounced and paralleled the recovery of renal function. Interestingly, the decline of ADMA was preceded by an increase in the immediate postoperative period. In the case-controlled substudy, SDMA levels were similar, whereas ADMA levels were significantly higher in RTRs compared with the CKD counterparts (P = 0.003).

CONCLUSION

ADMA levels follow a biphasic pattern after successful renal Tx with a transient rise in the immediate postoperative period followed by a decline. Levels remain elevated compared with CKD patients, matched for age, gender, diabetes, CV history and renal function.

Protective effect of ginseng against gamma-irradiation-induced oxidative stress and endothelial dysfunction in rats

This study investigated the potential protective effects of ginseng on gamma-irradiation-induced oxidative stress and endothelial dysfunction in rats. Twenty four male albino rats were divided into four groups. In the control group, rats were administered vehicle by tube for 7 consecutive days. The second group was administered ginseng extract (100 mg/kg, by gavage) for 7 consecutive days. Animals in the third group were administered vehicle by tube for 7 consecutive days, then exposed to single dose gamma-irradiation (6 Gy). The Fourth group received ginseng extract for 7 consecutive days, one hour later rats were exposed to gamma-irradiation. Oral administration of ginseng extract prior to irradiation produced a significant protection which was evidenced by a significant reduction in serum creatine kinase (CPK) and lactate dehydrogenase (LDH) activities and asymmetric dimethylarginine (ADMA), urea and creatinine levels with significant increase in serum total nitrate/nitrite (NO(x)) level. Moreover, ginseng significantly increased cardiac and renal superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities, and reduced glutathione (GSH) content, associated with a significant depletion in malondialdehyde (MDA) and NO(x) levels compared to irradiated group. This study suggests that ginseng may serve as a potential protective agent against gamma-irradiation-induced cardio-nephrotoxicity via enhancing the antioxidant activity and inhibition of endothelial dysfunction.

Renal dopamine receptors, oxidative stress, and hypertension

Dopamine, which is synthesized in the kidney, independent of renal nerves, plays an important role in the regulation of fluid and electrolyte balance and systemic blood pressure. Lack of any of the five dopamine receptor subtypes (D1R, D2R, D3R, D4R, and D5R) results in hypertension. D1R, D2R, and D5R have been reported to be important in the maintenance of a normal redox balance. In the kidney, the antioxidant effects of these receptors are caused by direct and indirect inhibition of pro-oxidant enzymes, specifically, nicotinamide adenine dinucleotide phosphate, reduced form (NADPH) oxidase, and stimulation of anti-oxidant enzymes, which can also indirectly inhibit NADPH oxidase activity. Thus, stimulation of the D2R increases the expression of endogenous anti-oxidants, such as Parkinson protein 7 (PARK7 or DJ-1), paraoxonase 2 (PON2), and heme oxygenase 2 (HO-2), all of which can inhibit NADPH oxidase activity. The D5R decreases NADPH oxidase activity, via the inhibition of phospholipase D2, and increases the expression of HO-1, another antioxidant. D1R inhibits NADPH oxidase activity via protein kinase A and protein kinase C cross-talk. In this review, we provide an overview of the protective roles of a specific dopamine receptor subtype on renal oxidative stress, the different mechanisms involved in this effect, and the role of oxidative stress and impairment of dopamine receptor function in the hypertension that arises from the genetic ablation of a specific dopamine receptor gene in mice.

Left ventricular hypertrophy and endothelial dysfunction in chronic kidney disease

Aim Mortality, predominantly due to cardiovascular events, is high in patients with chronic kidney disease (CKD) and left ventricular hypertrophy (LVH) is a strong risk factor. Vascular endothelial dysfunction (ED) is common in CKD, but its potential contribution to LVH in non-dialysis CKD is unknown. This study investigated the association of ED with LVH in non-dialysis CKD patients.

METHODS AND RESULTS

We studied 30 CKD patients (17 pre-dialysis and 13 renal transplant recipients) and 29 age-gender-matched controls. In both groups, high-sensitivity C-reactive protein (hsCRP) levels, systemic ED (brachial artery flow-mediated dilatation, FMD), and LVH using two-dimensional echocardiography were measured. LV mass index (LVMI) was calculated using Penn formula and indexed by height. CKD patients had higher CRP levels (3.9 ± 2.8 vs. 1.0 ± 0.7 mg/L; P < 0.001), reduced FMD (3.2 ± 2.1 vs. 6.1 ± 1.9%; P < 0.001), and increased LVMI (146.1 ± 40.2 vs. 105.3 ± 26.2 g/m; P < 0.001), compared with controls. In CKD patients, LVMI increased with decreasing FMD (r = -0.371; P = 0.043) and FMD decreased with increasing CRP (r = -0.741; P < 0.001). Patients with low FMD <2.3% had higher CRP and LVMI (161.9 ± 48.9 vs. 130.4 ± 20.7 g/m; P = 0.033), compared with CKD patients with FMD ≥2.3%. There was no significant difference in age, blood pressure, cholesterol, FMD, and LVMI between pre-dialysis and post-renal transplant CKD patients. In multivariate regression, the relationship between LVMI and FMD remained significant after adjusting for age, diabetes, and smoking (adjacent beta = -0.396; P = 0.004).

CONCLUSION

This pilot study demonstrates for the first time a relationship of ED with LVH in non-dialysis CKD patients; suggesting but not proving a cause-effect relationship.

Impact of high salt independent of blood pressure on PRMT/ADMA/DDAH pathway in the aorta of Dahl salt-sensitive rats

Endothelial dysfunction participates in the development and progression of salt-sensitive hypertension. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS). The objectives of this study were to investigate the impact of a high salt diet on the PRMT/ADMA/DDAH (protein arginine methyltransferases; dimethylarginine dimethylaminohydrolase) pathway in Dahl salt-sensitive (DS) rats and SS-13^BN consomic (DR) rats, and to explore the mechanisms that regulate ADMA metabolism independent of blood pressure reduction. Plasma levels of nitric oxide (NO) in DS rats given a high salt diet and subjected to intragastric administration of hydralazine (SH + HYD group) were lower than those given a normal salt diet (SN group). There were significant decreases in expression and activity of dimethylarginine dimethylaminohydrolase (DDAH) and endothelial NO synthase (eNOS) in DS rats given a high diet (SH group) in comparison to the SN group. The activity of DDAH and expression of eNOS in the SH + HYD group decreased more significantly than SN group. The mRNA expression of DDAH-1 and DDAH-2 were lowest in the SH group. The results suggest that salt, independent of blood pressure, can affect the PRMT-1/ADMA/DDAH system to a certain degree and lead to endothelial dysfunction in Dahl salt-sensitive rats.

The methylarginines NMMA, ADMA, and SDMA are ubiquitous constituents of the main vegetables of human nutrition

Endogenous methylarginines, N(G),N(G)-dimethyl-L-arginine (asymmetric dimethylarginine, ADMA), N(G)-N('G)-dimethyl-L-arginine (symmetric dimethylarginine; SDMA), and N(G)-monomethyl-L-arginine (monomethylarginine; NMMA) are supposed to be produced in human body through the methylation of protein arginine residues by protein arginine methyltransferases (PRMT) and released during proteolysis of the methylated proteins. Micromolar concentration of ADMA and NMMA can compete with arginine for nitric oxide synthase (NOS) reducing nitric oxide (NO) formation, whereas SDMA does not. Indeed, increased ADMA and SDMA plasma levels or a decreased arginine/ADMA ratio is related with risk factors for chronic kidney disease and cardiovascular disease. To the best of our knowledge the exogenous presence of methylarginines, like that in fruits and vegetables, has never been described so far. Here, we report the finding that methylarginines are ubiquitous in vegetables which represent an important part of human daily diet. Some of these vegetables contain discrete amounts of ADMA, SDMA, and NMMA. Specifically, among the vegetables examined, soybean, rye, sweet pepper, broad bean, and potato contain the highest ADMA and NMMA mean levels. Our results establish that the three methylarginines, in addition to being produced endogenously, can also be taken daily through the diet in conspicuous amounts. We propose that the contribution of the methylarginines contained in the vegetables of daily diet should be taken into account when the association between vegetable assumption and their levels is evaluated in clinical studies. Furthermore, a comprehensive understanding on the role of the digestive breakdown process and intestinal absorption grade of the methylarginines contained in vegetables is now needed.

Plasma metabolomic profiles in different stages of CKD

BACKGROUND AND OBJECTIVES

CKD is a common public health problem. Identifying biomarkers adds prognostic/diagnostic value by contributing to an understanding of CKD at the molecular level and possibly defining new drug targets. Metabolomics provides a snapshot of biochemical events at a particular time in the progression of CKD. This cross-sectional metabolomics study ascertained whether plasma metabolite profiles are significantly different in CKD stages 2, 3, and 4.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

An analysis of plasma metabolites, using gas and liquid chromatography coupled to mass spectrometry, was conducted on 30 nondiabetic men ages 40-52 years, with 10 participants each in CKD stages 2, 3, and 4 based on their estimated GFR (calculated by the Modified Diet in Renal Disease formula). Participants were recruited in late 2008, and plasma samples were tested at Metabolon Inc and analyzed in 2012.

RESULTS

Comparison of stage 3/stage 2 identified 62 metabolites that differed (P ≤ 0.05), with 39 higher and 23 lower in stage 3 compared with stage 2; comparisons of stage 4/stage 2 identified 111 metabolites, with 66 higher and 45 lower; and comparisons of stage 4/stage 3 identified 11 metabolites, with 7 higher and 4 lower. Major differences in metabolite profiles with increasing stage of CKD were observed, including altered arginine metabolism, elevated coagulation/inflammation, impaired carboxylate anion transport, and decreased adrenal steroid hormone production.

CONCLUSIONS

Global metabolite profiling of plasma uncovered potential biomarkers of stages of CKD. Moreover, these biomarkers provide insight into possible pathophysiologic processes that may contribute to progression of CKD.

Cardiovascular risk in autoimmune disorders: role of asymmetric dimethylarginine

Mounting evidence indicates that cardiovascular events are a main cause of excessive mortality of autoimmune disorders like type I diabetes mellitus and rheumatic diseases. Inflammation and endothelial dysfunction, independent predictors to cardiovascular disease, are hallmarks of autoimmunity. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, can cause or contribute to the inflammatory syndrome and endothelial dysfunction. Recently, elevated ADMA levels have been demonstrated in many autoimmune diseases, suggesting that ADMA might play an important role for the associated manifestations of cardiovascular disease. In the review, we discuss the role of ADMA in the excessive cardiovascular morbidity and mortality associated with autoimmune diseases.

Chronic kidney disease and vascular remodelling: molecular mechanisms and clinical implications

CKD (chronic kidney disease) is a severe and complex disease with a very high prevalence of CV (cardiovascular) complications. CKD patients are exposed to haemodynamic disturbances in addition to severe metabolic abnormalities that lead to a specific form of arterial remodelling, which contributes to the development of CV disease. Arterial calcification is a major event in the arterial remodelling process and is strongly linked to mineral metabolism abnormalities associated with CKD. Arterial remodelling is not limited to arterial calcification and modifications in arterial wall composition are also observed. Activation of the RAS (renin-angiotensin system), ET-1 (endothelin-1), endothelial dysfunction, oxidative stress and ADMA (asymmetric ω-NG,NG-dimethylarginine), as well as the anti-aging molecule Klotho, are implicated in this process. The present review details the mechanisms involved in arterial calcification and arterial remodelling associated with CKD, and provides the clinical consequences of large and small artery stiffness and remodelling in CKD patients.

Reduced renal plasma clearance does not explain increased plasma asymmetric dimethylarginine in hypertensive subjects with mild to moderate renal insufficiency

Plasma concentrations of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) increase already in the early stages of renal insufficiency. There is no agreement as to whether reduced renal plasma clearance (RPCL) contributes to this increase. Therefore, we investigated the relationship between estimated glomerular filtration rate (eGFR), RPCL, and plasma ADMA and SDMA in essential hypertensive patients with mild to moderate renal insufficiency. In 171 patients who underwent renal angiography, we drew blood samples from the aorta and both renal veins and measured mean renal blood flow (MRBF) using the (133)Xe washout technique. RPCL was calculated using arteriovenous concentration differences and MRBF. After correction for potential confounders, reduced eGFR was associated with higher plasma ADMA and SDMA [standardized regression coefficient (β) = -0.22 (95% confidence intervals: -0.41, -0.04) and β = -0.66 (95% confidence intervals: -0.83, -0.49), respectively]. However, eGFR was not independently associated with RPCL of ADMA. Moreover, reduced RPCL of ADMA was not associated with higher plasma ADMA. Contrary to ADMA, reduced eGFR was indeed associated with lower RPCL of SDMA [β = 0.21 (95% confidence intervals: 0.02, 0.40)]. In conclusion, our findings indicate that RPCL of ADMA is independent of renal function in hypertensive patients with mild to moderate renal insufficiency. Unlike the case for SDMA, reduced RPCL of ADMA is of minor importance for the increase in plasma ADMA in these patients, which indicates that increased plasma ADMA in this population is not a direct consequence of the kidneys failing as a plasma ADMA-regulating organ.