Net renal extraction of asymmetrical (ADMA) and symmetrical (SDMA) dimethylarginine in fasting humans.

BACKGROUND: Recently, the potential importance of dimethylarginines as endogenously produced inhibitors of nitric oxide synthase has become clearer. Interestingly, elevated levels have been reported in patients with vascular disease, but especially in patients suffering end-stage renal disease. Although the kidney obviously seems to play a key role in the elimination of dimethylarginines, clear insight into the renal handling of these compounds is lacking. Thus, our aim was to investigate the renal extraction of dimethylarginines. METHODS: Plasma concentrations of dimethylarginines were determined in both arterial and renal venous blood in 20 fasting patients with normal renal function. Renal extraction was calculated as the arteriovenous concentration difference divided by the arterial concentration times 100%. RESULTS: A significant renal extraction was found for both dimethylarginines. Renal extraction was significantly higher for asymmetrical dimethylarginine (ADMA) when compared with symmetrical dimethylarginine (SDMA) (16.2 vs 10.5% respectively, P=0.001). In addition, arterial SDMA concentration, but not ADMA concentration, significantly correlated with arterial creatinine concentration. CONCLUSIONS: In healthy humans, the kidney contributes to the regulation of plasma levels of dimethylarginines, since both ADMA and SDMA were significantly extracted from the arterial supply. Interestingly, a higher renal extraction of ADMA was found when compared to SDMA extraction, which strongly suggests the presence of an additional catabolic pathway for ADMA in the kidney.     

The influence of acute renal injury on arginine and methylarginines metabolism

Abstract

Arginine (ARG) and its methylated analogs (methylarginines) are the crucial regulators of nitric oxide (NO) bioavailability. ARG is the substrate for NO synthesis, whereas monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA) are potent inhibitors. Symmetric dimethylarginine (SDMA) does not interfere with NO synthesis, but competes with ARG for the intracellular transport. The kidneys play the major role in ARG and methylarginines metabolism. They synthesize ARG de novo and eliminate methylarginines by excretion into urine and also by enzyme dimethylarginine dimethylaminohydrolase (DDAH) degrading only ADMA and MMA. Acute renal injury (ARI) is known to be accompanied by reduced NO production in the body. This study aimed to investigate the influence of ARI on ARG and methylarginines metabolism, and to establish the relationship between disturbances in the latter and reduced NO bioavailability in ARI. The rhabdomyolysis-related ARI model in rats was used. ARI reduced renal synthesis of ARG and its level in circulation as well as renal DDAH activity. However, ADMA did not accumulate because of its increased urinary excretion. Whole-body production of SDMA was increased significantly, whereas whole-body metabolism of MMA did not change. ARG and methylarginines content in renal tissue was decreased. Moreover, the balance between the substrate and inhibitors for NO synthesis was changed in favor of the inhibitors in renal tissue as well as in blood, and daily urinary excretion of NO metabolites was significantly decreased. Thus, ARI provokes severe disturbances in ARG and methylarginines metabolism that results in reduced NO bioavailability in the kidney and the whole body.     

Human recombinant erythropoietin augments serum asymmetric dimethylarginine concentrations but does not compromise nitric oxide generation in mice.

BACKGROUND: Patients with advanced chronic renal disease (CRD) suffer from excessive morbidity and mortality due to complications of accelerated atherosclerosis. Recombinant human erythropoietin (EPO), which is routinely used to treat the anaemia present in approximately 90% of dialysis-dependent patients with end-stage renal disease, may induce vascular dysfunction by reducing nitric oxide (NO) availability. Pathophysiologic concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), are found in patients with CRD and correlate with vascular disease and cardiovascular mortality. The aim of the current study was to investigate the effect of EPO on ADMA concentrations and NO generation in vitro and in vivo. Furthermore, we wanted to study the effect of EPO on the expression of the enzymes that regulate ADMA metabolism and NO generation. METHODS: Human umbilical vein endothelial cells (HUVECs) were exposed to therapeutic concentrations of EPO. The expression and metabolic activity of dimethylarginine dimethylaminohydrolase II (DDAH II), the enzyme that degrades ADMA, was evaluated. Following subcutaneous administration of EPO to Balb/c mice for 10 weeks, serum ADMA concentrations were determined. Systolic blood pressure was measured noninvasively. Urinary nitrite and nitrate (NOx) concentrations were assessed by Griess assay. Protein expression of DDAH and NOS in livers and kidneys was measured by western blotting. RESULTS: EPO suppressed ADMA elaboration by HUVECs. Systolic blood pressure and serum concentrations of ADMA were significantly elevated in EPO-treated mice. The protein expression of DDAH I in the kidney and liver was upregulated while hepatic expression of DDAH II was decreased and renal DDAH II expression remained unchanged by EPO administration. However, EPO augmented urinary NOx concentrations as well as the expression of NOS 1 and NOS 2 in the kidney. CONCLUSION: In spite of elevating serum ADMA concentrations, EPO does not appear to compromise overall NO generation in Balb/c mice.     

The transplanted liver graft is capable of clearing asymmetric dimethylarginine.

Asymmetric dimethylarginine (ADMA) has been recognized as an endogenous inhibitor of the arginine-nitric oxide (NO) pathway. Its concentration is tightly regulated by urinary excretion and degradation by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), which is highly expressed in the liver. Considering the liver as a crucial organ in the clearing of ADMA, we hypothesized increased ADMA levels during hepatic failure and, consequently, a decline of ADMA concentrations after successful liver transplantation. The aim of the present study was to investigate the role of the liver in the metabolism of ADMA in patients undergoing liver transplantation. In this prospective study, we investigated the course of ADMA concentrations in 42 patients undergoing liver transplantation and results showed that preoperative ADMA concentrations were higher in patients with acute (1.26 micromol/L, P < .001) and in patients with chronic (.69 micromol/L, P < .001) hepatic failure compared with healthy volunteers (.41 micromol/L). In addition, ADMA concentrations decreased from the preoperative day to the first postoperative day in both the acute (Delta(ADMA): -.63 micromol/L, P = .005) and the chronic hepatic failure group (Delta(ADMA): -0.15 micromol/L, P < .001). Furthermore, in patients who experienced acute rejection, ADMA concentrations were higher during the whole first postoperative month compared with nonrejectors (P = .012). Moreover, in 11 of 13 rejectors (85%) a clear increase in ADMA concentration preceded the onset of the first episode of rejection, which was confirmed by liver biopsy. In conclusion, our results indicate that the transplanted liver graft is quickly capable of clearing ADMA, suggesting preservation of DDAH. In addition, increased ADMA concentrations in the posttransplantation period reflect serious dysfunction of the liver graft during acute rejection.     

Impact of vitamin E on plasma asymmetric dimethylarginine (ADMA) in chronic kidney disease (CKD): a pilot study.

BACKGROUND: Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of endothelial nitric oxide synthase and a proposed cardiovascular risk factor, is elevated in chronic kidney disease (CKD). Pharmacological strategies that lower plasma concentration of ADMA may be expected to increase nitric oxide (NO.) bioavailability and potentially limit atherosclerosis. We hypothesized that the antioxidant alpha-tocopherol (vitamin E) reduces ADMA levels in CKD. METHODS: An open-label pilot interventional study using 800 IU of vitamin E was undertaken in eight stable out-patients with non-diabetic CKD (creatinine clearance <30 ml/min/1.73 m(2)) and six healthy controls, with the objective of measuring plasma ADMA levels at baseline and after 8 weeks of treatment. Plasma ADMA, symmetric dimethylarginine (SDMA) and alpha-tocopherol concentrations were determined at study entry and exit using high-performance liquid chromatography, while plasma total F2-isoprostanes, an index of oxidative stress, were measured using a commercially available enzyme-linked immunosorbent assay kit. RESULTS: ADMA and SDMA concentrations were significantly higher in the plasma of patients compared with that of controls (P 相似文献   

Erythropoietin increases asymmetric dimethylarginine in endothelial cells: role of dimethylarginine dimethylaminohydrolase

Recombinant human erythropoietin therapy frequently causes hypertension in humans and animals with chronic renal failure. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase, and its accumulation has been associated with reducing NO bioavailability and increasing superoxide generation. Whether epoetin beta (EPO) or darbepoetin alpha (NESP) can modify the levels of ADMA in endothelial cells was investigated. Endothelial cells from the third passage were incubated for 24 h in the presence of various concentrations of EPO or NESP (0, 0.1, 1, 10, 50, 100, and 200 U/ml). The levels of ADMA, allantoin, nitrate, and nitrite in conditioned media and the activity of dimethylarginine dimethylaminohydrolase (DDAH), the content of thiols and reactive oxygen species in endothelial cells, were determined. When endothelial cells were exposed to EPO or NESP, ADMA concentration in the cell culture medium increased significantly in a dose-dependent manner versus control. This effect was associated with a reduced activity of DDAH, the enzyme that degrades ADMA. Furthermore, EPO- or NESP-induced accumulation of ADMA was accompanied by a significant reduction of NO synthesis and an increase in oxidative stress. Both allantoin, a marker of oxygen free radical generation, and reactive oxygen species increased significantly after EPO or NESP treatment compared with control. The antioxidant pyrrolidine dithiocarbamate preserved DDAH activity and reduced ADMA accumulation in the same way as the co-incubation with anti-EPO neutralizing antibody. EPO and NESP posttranslationally impair DDAH activity via increased oxidative stress, causing ADMA as an important cardiovascular risk factor to accumulate and inhibit NO synthesis.     

Intravenous N-acetylcysteine during hemodialysis reduces asymmetric dimethylarginine level in end-stage renal disease patients

AIM: Cardiovascular disease is the main cause of mortality in chronic kidney disease patients. Moreover, uremic patients are in a pro-oxidant state and show an increase in asymmetric dimethylarginine (ADMA) levels due to inhibition of the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Asymmetric dimethylarginine per se seems responsible for a 52% increase in the risk of death and for a 34% increase in the risk of cardiovascular events in dialysis patients. N-acetylcysteine (NAC) is a thiol molecule that has direct and indirect antioxidant effects which decrease reactive oxidant species and increase the bioavailability of the DDAH enzyme. The aim of the current study was to determine the effect of intravenous NAC on plasma ADMA level when administered during hemodialysis in end-stage renal disease (ESRD) patients. MATERIALS AND METHODS: 40 patients with ESRD were randomized to receive a 4-hour intravenous infusion of NAC or placebo during a 4-hour hemodialysis session. There were 3 diabetic patients (15%) in the treatment group and 6 patients in the control group. Plasma ADMA levels were measured before and immediately after hemodialysis. Hemodynamic parameters, including pulse pressure, were also measured. The paired t-test was used to compare the difference of ADMA levels before and after hemodialysis in each group, while the independent t-test was used to compare the difference of ADMA levels between the groups. RESULTS: Compared with the pre-dialysis condition, there was a decrease of ADMA level in the control group (1.1253 +/- 0.1797 microM to 0.8676 +/- 0.1449 microM) (p < 0.001), and in the NAC group (1.1522 +/- 0.1737 microM to 0.7844 +/- 0.1586 microM) (p < 0.001). Compared with hemodialysis alone, NAC had a greater lowering effect on the ADMA level (21.3 vs. 31.9%, p < 0.05). CONCLUSION: N-acetylcysteine (NAC) administered intravenously during hemodialysis reduced asymmetric dimethylarginine (ADMA) levels more significantly than hemodialysis alone.     

Symmetrical dimethylarginine: a new combined parameter for renal function and extent of coronary artery disease

Symmetrical dimethylarginine (SDMA) is the structural isomer of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine. Whereas the major route of asymmetric dimethylarginine elimination is the hydrolytic degradation by dimethylarginine dimethylaminohydrolase, SDMA is eliminated by renal excretion. SDMA does not directly inhibit NOS but is a competitor of arginine transport. This study showed for the first time that measurement of SDMA can be a marker of estimated GFR and extent of coronary artery disease (CAD). In 97 patients with CAD, SDMA was a marker of estimated GFR. On multiple regression analysis of the CAD parameter stenosis score, SDMA was the only parameter retained. In addition, endothelial cells from the third passage were cultured in medium that contained 70 micromol/L arginine and was incubated for 24 h in the presence of various concentration of SDMA (0, 2, 5, 10, and 100 micromol/L). The levels of nitrate and nitrite in conditioned media, the protein expression of NOS, and the content of reactive oxygen species in endothelial cells were determined. SDMA inhibited dose dependently the NO synthesis in intact endothelial cells, whereas it had no effect on protein expression of NOS. This effect was associated with an increase in reactive oxygen species. Co-incubation with L-arginine but not D-arginine reversed the effect of SDMA on NOS pathway. Our data suggest that SDMA reduced the endothelial NO synthesis, probably by limiting L-arginine supply to NOS. It is concluded that SDMA might be a useful parameter for detecting patients in very early stages of chronic kidney disease and for determining their risk for developing cardiovascular disease.     

Methylated arginine derivatives in children and adolescents with chronic kidney disease

Asymmetric dimethylarginine (ADMA), a methylated L: -arginine (Arg) derivative is associated with endothelial dysfunction, vasoconstriction, and hypertension in animals and humans. We examined the relationship between these derivatives, estimated glomerular filtration rate (eGFR), and awake (AW) and asleep (AS) blood pressure (BP) load in children and adolescents (n = 28) with stage 2-3 chronic kidney disease (CKD) and in matched intra-familial controls (n = 10). Plasma L: -Arg, ADMA, and symmetric dimethylarginine (SDMA) levels were measured by high-performance liquid chromatography-tandem mass spectrometry. Subjects wore a 24-hr ambulatory BP monitor with BP load >95th percentile. ADMA, SDMA/ADMA ratio and SDMA were 38-200% higher in CKD patients while L: -Arg/ADMA and L: -Arg/SDMA ratios and the L: -Arg level were 11-64% lower. The eGFR explained 42-60% of L: -Arg/SDMA, SDMA/ADMA, and SDMA variability (n = 38). Using linear regression, SDMA and SDMA/ADMA separately explained 15-38% of AW and AS systolic (S) BP and diastolic (D) BP load variability (p < 0.001-0.022). Using multivariate stepwise regression with eGFR held constant, SDMA/ADMA was a significant independent variable for AW DBP load (p = 0.03). In conclusion, BP load and a disproportionate elevation of SDMA are seen in children and adolescents with stage 2-3 (mild-moderate) CKD. SDMA is a strong marker for reduced eGFR and serves as a moderate but significant indicator of 24-hr BP load variability.     

Asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and L-arginine in patients with arteriogenic and non-arteriogenic erectile dysfunction

The plasma concentration of asymmetrical dimethylarginine (ADMA), an inhibitor of nitric oxide synthase, has been linked to endothelial dysfunction. We investigated the relation between ADMA, symmetric dimethylarginine (SDMA) and L-arginine concentrations and erectile dysfunction. We compared plasma levels of ADMA, SDMA and L-arginine in 61 men in good health with erectile dysfunction of arteriogenic and non-arteriogenic origin. Diagnosis of erectile dysfunction was based on the International Index of Erectile Function Score and its aetiology was classified with penile echo-colour-Doppler in basal condition and after intracavernous injection of prostaglandin E1. The ADMA and SDMA concentrations were significantly higher in men with arteriogenic erectile dysfunction compared with those with erectile dysfunction of non-arteriogenic origin (p??0.05) nor between each of the two erectile dysfunction subgroups and controls (p?>?0.05). The L-arginine/ADMA and the L-arginine/SDMA ratios in arteriogenic erectile dysfunction subgroups were significantly lower than both in controls (p??0.05). We conclude that ADMA and SDMA concentrations are significantly higher and L-arginine/ADMA ratio lower in patients who have arteriogenic erectile dysfunction compared with both patients with non-arteriogenic erectile dysfunction and controls. The negative correlation between ADMA and severity of erectile dysfunction is present only in patients with arteriogenic erectile dysfunction. This study supports the importance to always distinguish arteriogenic from non-arteriogenic erectile dysfunction patients to study the complicate erectogenic mechanisms that lead to erectile dysfunction and also to provide potential therapeutic agents for patients with arteriogenic erectile dysfunction.     

PROGRESS IN UREMIC TOXIN RESEARCH: Asymmetric Dimethylarginine and Symmetric Dimethylarginine: Axis of Evil or Useful Alliance?

Almost 40 years ago, in 1970, Kakimoto and Akazawa were the first to isolate and describe N‐N, N‐G‐ and N‐G,N′‐G‐dimethyl‐arginine from human urine. Today, these substances are known as asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). In their detailed and meticulous publication, Kakimoto and Akazawa speculated about these two compounds: “They may have functional importance in proteins in which they are formed. If they are excreted into the urine as metabolites of body proteins, amounts of these substances in human urine may reflect methylation rate of body proteins and their turnover rates and determination of these substances might be important for the study of various pathological states.” The following decades proved them to be right. ADMA, the most potent endogenous nitric oxide synthase (NOS) inhibitor was first found to be elevated in hemodialysis patients. It has been shown to correlate with traditional and nontraditional cardiovascular risk factors. ADMA is also a strong predictor of cardiovascular events and death in both patients with chronic kidney disease (CKD, stage 2–5) and in the general population. Moreover, ADMA predicts the progression of CKD. SDMA, the structural isomer of ADMA, has been shown to be an excellent marker of renal function in human and animal studies. There is emerging evidence that SDMA might also be involved in inflammation and atherosclerosis although it is only thought to be a (weak) indirect inhibitor of NOS. There is burgeoning evidence that these two substances may indeed damage normal physiological functions, or interfere with physiological defense mechanisms in CKD, play a role in the progression of renal disease, induce uremic symptoms, and may even contribute to dialysis‐related complications. Hence these compounds are considered uremic toxins. This review summarizes our current concept how these two compounds might play a crucial part in the pathophysiology of uremia, either alone or in their combination. We also allude to the potential physiological role these substances might have.     

Arginine, arginine analogs and nitric oxide production in chronic kidney disease

Nitric oxide (NO) production is reduced in renal disease, partially due to decreased endothelial NO production. Evidence indicates that NO deficiency contributes to cardiovascular events and progression of kidney damage. Two possible causes of NO deficiency are substrate (L-arginine) limitation and increased levels of circulating endogenous inhibitors of NO synthase (particularly asymmetric dimethylarginine [ADMA]). Decreased L-arginine availability in chronic kidney disease (CKD) is due to perturbed renal biosynthesis of this amino acid. In addition, inhibition of transport of L-arginine into endothelial cells and shunting of L-arginine into other metabolic pathways (e.g. those involving arginase) might also decrease availability. Elevated plasma and tissue levels of ADMA in CKD are functions of both reduced renal excretion and reduced catabolism by dimethylarginine dimethylaminohydrolase (DDAH). The latter might be associated with loss-of-function polymorphisms of a DDAH gene, functional inhibition of the enzyme by oxidative stress in CKD and end-stage renal disease, or both. These findings provide the rationale for novel therapies, including supplementation of dietary L-arginine or its precursor L-citrulline, inhibition of non-NO-producing pathways of L-arginine utilization, or both. Because an increase in ADMA has emerged as a major independent risk factor in end-stage renal disease (and probably also in CKD), lowering ADMA concentration is a major therapeutic goal; interventions that enhance the activity of the ADMA-hydrolyzing enzyme DDAH are under investigation.     

Role of asymmetrical dimethylarginine in the progression of renal disease

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid found in tissues and cells that circulates in plasma and is excreted in urine. It inhibits nitric oxide synthases (NOs) and produces considerable cardiovascular biological effects. Several studies have suggested that plasma concentrations of ADMA provide a marker of risk for endothelial dysfunction and cardiovascular disease. In animal and in population studies ADMA has been associated with progression of CKD. Several mechanisms may be involved in this association, such as compromise of the integrity of the glomerular filtration barrier and development of renal fibrosis. This review summarizes the existing literature on the biology and physiology of ADMA focusing on its role in the progression of renal disease.     

Inhibition of eNOS phosphorylation mediates endothelial dysfunction in renal failure: new effect of asymmetric dimethylarginine

Patients with chronic kidney disease have elevated circulating asymmetric dimethylarginine (ADMA). Recent studies have suggested that ADMA impairs endothelial nitric oxide synthase (eNOS) by effects other than competition with the substrate L-arginine. Here, we sought to identify the molecular mechanism by which increased ADMA causes endothelial dysfunction in a chronic kidney disease model. In wild-type mice with remnant kidney disease, blood urea nitrogen, serum creatinine, and ADMA were increased by 2.5-, 2-, and 1.2-fold, respectively, without any change in blood pressure. Nephrectomy reduced endothelium-dependent relaxation and eNOS phosphorylation at Ser1177 in isolated aortic rings. In transgenic mice overexpressing dimethylarginine dimethylaminohydrolase-1, the enzyme that metabolizes ADMA, circulating ADMA was not increased by nephrectomy and was decreased to half that of wild-type mice. These mice did not exhibit the nephrectomy-induced inhibition of both endothelium-dependent relaxation and eNOS phosphorylation. In cultured human endothelial cells, agonist-induced eNOS phosphorylation and nitric oxide production were decreased by ADMA at concentrations less than that of L-arginine in the media. Thus, elevated circulating ADMA may be a cause, not an epiphenomenon, of endothelial dysfunction in chronic kidney disease. This effect may be attributable to inhibition of eNOS phosphorylation.     

Effects of amlodipine and valsartan on oxidative stress and plasma methylarginines in end-stage renal disease patients on hemodialysis

Patients with end-stage renal disease (ESRD) receiving hemodialysis (HD) treatment have a markedly shortened life expectancy in large part owing to cardiovascular disease (CVD), not explained by established risk factors. We tested the hypothesis that therapy with valsartan, an angiotensin receptor blocker and amlodipine, an antioxidant calcium channel blocker will reduce oxidative stress and the plasma levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase. We confirmed that compared with age- and gender-matched healthy controls, ESRD patients have excessive oxidative stress and arginine methylation as indexed by elevated plasma levels of oxidation products of lipids (13-hydroxyoctadecadienoic acid (13-HODE)), thiols (oxidized:reduced glutathione, oxidized glutathione (GSSG):GSH), proteins, and nucleic acids, and the methylation products ADMA and symmetric dimethylarginine (SDMA). We undertook a double blind, crossover study of equi-antihypertensive treatment with amlodipine and valsartan for 6 weeks each to test our hypothesis. Both treatments significantly reduced GSSG:GSH, 8-hydroxy 2-deoxyguanosine, ADMA, and SDMA levels and amlodipine reduced 13-HODE. We conclude that hypertensive patients with ESRD receiving HD have evidence of extensive oxidation of lipids, thiols, proteins, and nucleic acids and methylation of arginine that could contribute to CVD. Many of these changes can be reduced by short-term treatment with amlodipine and valsartan.     

Total nitric oxide production is low in patients with chronic renal disease

BACKGROUND: A deficiency of the endogenous vasodilator nitric oxide (NO) has been implicated as a potential cause of hypertension in chronic renal disease (CRD) patients. This study was conducted to determine whether 24-hour NOX (NO2 and NO3) excretion (a qualitative index of total NO production) is reduced in patients with CRD. METHODS: Measurements were made in 13 CRD patients and 9 normotensive healthy controls after 48 hours on a controlled low-NOX diet. Urine was collected over the second 24-hour period for analysis of 24-hour NOX, and cGMP and blood drawn at the completion. Plasma levels of arginine (the substrate for endogenous renal NO synthesis), citrulline (substrate for renal arginine synthesis), and the endogenous NO synthesis inhibitor asymmetrical dimethylarginine (ADMA) and its inert isomer and symmetrical dimethylarginine (SDMA) were also determined. RESULTS: Systolic blood pressure was higher in CRD patients (12 of whom were already on antihypertensive therapy) than in controls (P < 0.05). Twenty-four-hour urinary NOX excretion was low in CRD patients compared with controls despite similar dietary NO intake, suggesting that net endogenous NO production is decreased in renal disease. In contrast, the 24-hour urinary cGMP did not correlate with UNOXV. Plasma citrulline was increased in CRD patients, possibly reflecting reduced conversion of citrulline to arginine. Plasma arginine was not different, and plasma ADMA levels were elevated in CRD versus controls, changes that would tend to lower NO synthase. CONCLUSION: These results suggest that NO production is low in CRD patients and may contribute to hypertension and disease progression in CRD.     

Symmetric dimethylarginine (SDMA) as endogenous marker of renal function--a meta-analysis.

BACKGROUND: Dosing of most drugs must be adapted in renal insufficiency, making accurate assessment of renal function essential in clinical medicine. Furthermore, even modest impairment of renal function has been recognized as a cardiovascular risk factor. The purpose of this analysis was to identify the role of symmetric dimethylarginine (SDMA), the structural isomer of the cardiovascular risk marker asymmetric dimethylarginine, as an endogenous marker of renal function. METHODS: Comprehensive searches of Medline and the Cochrane Library from 1970 to February 2006 were performed to identify studies that evaluated the correlation between SDMA and renal function. The search was augmented by scanning references of identified articles and reviews. The correlation coefficients (R) were recorded from each study for the values of 1/SDMA and clearance estimates and for SDMA and creatinine levels. The summary correlation coefficients with 95% confidence intervals (CIs) were pooled using the random-effects method. RESULTS: In 18 studies involving 2136 patients systemic SDMA concentrations correlated highly with inulin clearance [R = 0.85 (CI 0.76-0.91, P < 0.0001)], as well as with various clearance estimates combined [R = 0.77 (CI 0.65-0.85, P < 0.0001)] and serum creatinine [R = 0.75 (CI 0.46-089, P < 0.0001)]. CONCLUSIONS: SDMA exhibits some properties of a reliable marker of renal function. Future studies have to clarify whether SDMA is indeed suited to improve diagnosis and eventually optimize care of patients.