Asymmetric dimethylarginine in end-stage renal disease patients: a biomarker modifiable by calcium blockade and angiotensin II antagonism?

The nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is an emerging risk biomarker in cardiovascular and renal diseases. Apparently amlodipine and valsartan produce substantial reductions in the plasma concentration of this methylarginine in hemodialysis patients. These findings are of relevance for designing studies aimed at testing the etiologic relevance of ADMA to the high cardiovascular risk of ESRD.     

Handling of asymmetrical dimethylarginine and symmetrical dimethylarginine by the rat kidney under basal conditions and during endotoxaemia.

BACKGROUND: Asymmetrical dimethylarginine (ADMA) is capable of inhibiting nitric oxide synthase enzymes, whereas symmetrical dimethylarginine (SDMA) competes with arginine transport. The potential role of inflammation in the metabolism of ADMA has been elucidated in an in vitro model using tumour necrosis factor-alpha, resulting in a decreased activity of the ADMA-degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH). The kidney probably plays a crucial role in the metabolism of ADMA by both urinary excretion and degradation by DDAH. We aimed to further elucidate the role of the kidney in a rat model under basal conditions and during endotoxaemia. METHODS: Twenty-five male Wistar rats weighing 275-300 g were used for this study. The combination of arteriovenous concentration differences and kidney blood flow allowed calculation of net organ fluxes. Blood flow was measured using radiolabelled microspheres according to the reference sample method. Concentrations of ADMA, SDMA and arginine were measured by high-performance liquid chromatography. RESULTS: The kidney showed net uptake of both ADMA and SDMA and fractional extraction rates were 35% and 31%, respectively. Endotoxaemia resulted in a lower systemic ADMA concentration (P = 0.01), which was not explained by an increased net renal uptake. Systemic SDMA concentrations increased during endotoxaemia (P = 0.007), which was accompanied by increased creatinine concentrations. CONCLUSIONS: The rat kidney plays a crucial role in the regulation of concentrations of dimethylarginines, as both ADMA and SDMA were eliminated from the systemic circulation in substantial amounts. Furthermore, evidence for the role of endotoxaemia in the metabolism of dimethylarginines was obtained as plasma levels of ADMA were significantly lower in endotoxaemic rats.     

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 plasma concentrations differ in patients with end-stage renal disease: relationship to treatment method and atherosclerotic disease

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide (NO) synthase. Its concentration is elevated in patients with end-stage renal disease (ESRD), in part because it is excreted via the kidneys. In this study, the plasma concentrations of ADMA, symmetric dimethylarginine, and L-arginine were determined in relation to plasma nitrate levels (as an index of NO formation) for a group of 80 patients with ESRD. The effects of two treatment methods, i.e., hemodialysis (HD) and peritoneal dialysis (PD), and the role of the presence of atherosclerotic disease were evaluated. Forty-three patients receiving HD and 37 patients receiving PD were compared with healthy control subjects. Plasma L-arginine and dimethylarginine levels were determined by HPLC, using precolumn derivatization with o-phthaldialdehyde. Plasma nitrate levels were determined by gas chromatography-mass spectrometry. Predialysis ADMA concentrations in HD-treated patients were approximately sixfold higher than those in the control group (6.0+/-0.5 versus 1.0+/-0.1 micromol/L; P < 0.05). Plasma nitrate concentrations were significantly lower in HD-treated patients, which suggests that ADMA may inhibit NO synthase. In contrast, plasma ADMA levels and nitrate concentrations in PD-treated patients were similar to those in control subjects. Plasma L-arginine concentrations were not significantly decreased in patients with ESRD. ADMA concentrations were significantly decreased 5 h after HD, compared with baseline values. ADMA levels were significantly higher in HD-treated patients with manifest atherosclerotic disease than in HD-treated patients without atherosclerotic disease (7.31+/-0.70 versus 3.95+/-0.52 micromol/L; P < 0.05). This study confirms that ADMA is accumulated in ESRD. PD-treated patients exhibit significantly lower ADMA levels than do HD-treated patients. Accumulation of ADMA may be a risk factor for the development of endothelial dysfunction and cardiovascular disease in patients with ESRD.     

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.     

Effect of oxidized and reduced glutathione in liver preservation

Glutathione spontaneously oxidizes in the UW solution for organ preservation and reduced glutathione (GSH) is converted to oxidized (GSSG) glutathione. To determine the effects of the oxidized or reduced forms of glutathione on liver preservation dog livers were preserved for 24 and 48 hr with the UW solution containing either GSH or GSSG. After 24 hr of preservation the form of glutathione did not affect survival or the postoperative course of the animals. All animals survived (three per group) with near-normal liver functions by the third to fifth postoperative day. When preservation was extended to 48 hr survival was 100% (6/6) with GSH and 29% (2/7) with GSSG. The dogs that died developed primary nonfunction of the liver. This study shows that GSH is an important component of the UW solution for 48-hr preservation of the dog liver. The presence of GSSG does not prevent successful 24-hr preservation of the liver, which has been confirmed in clinical studies. However, for 48-hr preservation GSH is required and GSSG is not suitable.     

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.     

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.     

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.     

流行性乙型脑炎患者机体氧化还原态初探

目的探讨流行性乙型脑炎患者机体氧化还原态。方法选取40例流行性乙型脑炎患儿为研究对象,分别测定发病极期和恢复期血浆还原型谷胱甘肽（GSH）与氧化型谷胱甘肽（GSSG）,还原型辅酶Ⅱ（NADPH）与氧化型辅酶Ⅱ（NADP^＋）,计算GSH／GSSG和NADPH／NADP^＋比值,评价HIV／AIDS患者机体氧化还原态。结果流行性乙型脑炎患儿发病极期血浆氧化还原态向氧化方向偏移。结论氧化还原态失衡、氧化还原态向氧化方向偏移与流行性乙型脑炎疾病进展有一定相关性。     

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.     

Effect of the transdermal low-level laser therapy on endothelial function

The effect of low-level laser therapy (LLLT) on the cardiovascular system is not fully established. Since the endothelium is an important endocrine element, establishing the mechanisms of LLLT action is an important issue.The aim of the study was to evaluate the effect of transdermal LLLT on endothelial function.In this study, healthy volunteers (n?=?40, age?=?20–40 years) were enrolled. N?=?30 (14 female, 16 male, mean age 30?±?5 years) constituted the laser-irradiated group (LG). The remaining 10 subjects (6 women, 4 men, mean age 28?±?5 years) constituted the control group (CG). Participants were subjected to LLLT once a day for three consecutive days. Blood for biochemical assessments was drawn before the first irradiation and 24 h after the last session. In the LG, transdermal illumination of radial artery was conducted (a semiconductor laser λ?=?808 nm, irradiation 50 mW, energy density 1.6 W/cm² and a dose 20 J/day, a total dose of 60 J). Biochemical parameters (reflecting angiogenesis: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), angiostatin; antioxidative status: glutathione (GSH) and the nitric oxide metabolic pathway: symmetric dimethylarginine (SDMA), asymmetric dimethylarginine (ADMA) and l-arginine) were assessed. In the LG, a significant increase in GSH levels and considerable decrease in angiostatin concentration following the LLLT were observed. No significant differences in levels of the VEGF, FGF, SDMA, ADMA were observed.LLLT modifies vascular endothelial function by increasing its antioxidant and angiogenic potential. We found no significant differences in levels of the nitric oxide pathway metabolites within 24 h following the LLLT irradiation.     

Low dialysance of asymmetric dimethylarginine (ADMA)--in vivo and in vitro evidence of significant protein binding

BACKGROUND: Increased blood levels of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) predict cardiovascular mortality in patients with end-stage renal disease. Despite its low molecular weight, available information on the impact of hemodialysis (HD) on ADMA plasma levels is controversial. METHODS: We assessed plasma concentrations, dialyzer clearance and total amount of ADMA removed in 30 patients with end-stage renal disease during regular HD. In addition, plasma ADMA levels were assessed in 10 patients with acute renal failure treated with extended HD. RESULTS: Regular HD decreased plasma creatinine (from 774 +/- 42 to 312 +/- 17 micromol/l) and urea (from 24.5 +/- 1.5 to 8.4 +/- 0.5 mmol/l) concentrations significantly (both p < 0.001), whereas plasma ADMA remained unchanged (4.35 +/- 0.19 vs. 4.76 +/- 0.24 micromol/l). ADMA clearance was 92 +/- 6 ml/min, and the total amount removed in the spent dialysate was 37 +/- 4 micromol. The clearances of creatinine (161 +/- 3 ml/min) and of urea (173 +/- 3 ml/min) were significantly higher. Furthermore, even during extended HD, plasma ADMA concentrations did not decrease significantly (1.73 +/- 0.22 vs. 1.63 +/- 0.18 micromol/l). CONCLUSION: In conclusion, dialysance of ADMA is markedly lower than expected from its molecular weight because of significant protein binding of the substance. Since markedly increased ADMA blood concentrations have been linked to cardiovascular complications due to atherosclerosis in patients with ESRD, new strategies should be evaluated to remove this putative uremic toxin.     

Glutathione and glutathione peroxidase in sputum samples of adult patients with cystic fibrosis.

BACKGROUND: Reduced glutathione (GSH) is a major antioxidant in the lung. In cystic fibrosis (CF) patients, extracellular GSH levels of lower airways, obtained by bronchoalveolar lavage (BAL), were reported to be lower than non-CF individuals. METHODS: Upper airway secretions of stable adult CF patients (29 spontaneous and 13 induced sputum) and non-CF individuals (14 healthy and 12 asthmatics; all induced sputum) were analyzed for total glutathione (i.e. the sum of reduced, GSH, and oxidized, GSSG, forms), GSH and GSSG levels by enzymatic kinetic assay. RESULTS: In CF, both spontaneous and induced sputum samples were comparable in total glutathione levels which were surprisingly high (median concentration of 9.2 (range 1.4-65.2) and 11.6 (1.1-69.8) microM, respectively). In non-CF individuals, total glutathione levels were significantly lower (healthy 2.8 (1.0-12.3), asthmatics (5.3 (1.3-19.2) microM; p<0.001, both vs. CF). In CF, more than 90% of total glutathione was represented by GSH, whereas in non-CF controls, GSH made up less than 50% of total glutathione (p<0.001). CONCLUSIONS: In contrast to BAL, CF sputum contains high levels of GSH. Sputum induction is a potentially useful procedure to monitor antioxidant levels in upper airways of CF patients.     

Hepatorenal interaction in glutathione redox state during partial hepatic ischemia-reperfusion in rats.

The hepatic glutathione metabolism during partial hepatic ischemia-reperfusion was studied in a rat model with special reference to the hepatorenal glutathione metabolism system. Bile samples, and in- and outflow blood and tissue samples of the rat liver, kidney and small intestine were collected during 60 min of 70% partial liver ischemia and reperfusion. Both reduced and oxidized glutathione levels were determined by HPLC. The tissue ratio of reduced to oxidized glutathione (GSH/GSSG ratio) decreased significantly in the ischemic hepatic lobe at 60 min after reperfusion. The GSH/GSSG ratio in bile from the ischemic hepatic lobes decreased significantly after 60 min of ischemia and gradually recovered after reperfusion. The net release of GSH from the nonischemic hepatic lobe increased at 60 min after reperfusion, since the calculated net release of GSH from the whole liver increased significantly whereas there was no change in the net release from the ischemic hepatic lobe. The tissue GSH level in the kidney increased significantly at 180 min after reperfusion. The calculated net uptake of GSH into the kidney, and the net release of total cysteine from the kidney, tended to decrease at the end of 60 min of ischemia, to increase at 60 min after reperfusion and then decrease at 180 min after reperfusion. We found that the hepatorenal glutathione metabolism was changed by partial hepatic ischemia-reperfusion. These changes might reflect a hepatorenal interaction to maintain the glutathione redox state of the vital organs.     

Oxidative stress, hepatocellular integrity, and hepatic function after initial reperfusion in human hepatic transplantation

BACKGROUND: The mechanisms underlying liver graft dysfunction are not completely defined, although much of the injury derives from oxidative stress in organ reperfusion. The antioxidant glutathione in its reduced form (GSH) is an important agent to detoxify oxygen species after reperfusion. However, this effect might be limited by low concentrations at the end of cold storage. The objective of this study was to evaluate GSH and glutathione oxidized (GSSG) hepatic levels pre- and postreperfusion and correlate with hepatocellular injury and liver function in the 5 subsequent days after transplantation. METHODS: Liver biopsies were taken immediately before implant and 2 hours after venous reperfusion in 34 grafts, determining GSH, GSSG levels, and GSSG/GSH ratio. Aminotransferases (ALT, AST) and PT were measured for 5 days. RESULTS: There was a strong decrease in GSH concentration (P <.0001), increase of GSSG levels (P <.01), and increase of the GSSG/GSH ratio (P <.0001). No correlations were found between GSH, GSSG, or GSH/GSSH levels and AST, ALT, and PT. CONCLUSION: Glutathione levels showed significant changes after 2 hours of reperfusion, due to intense oxidative stress. Therapies to replenish GSH should be considered as a protective measure to avoid liver graft dysfunction after transplantation.     

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   

Oxidative stress markers in pre-uremic patients.

AIM: The present study was designed to investigate a complex of oxidative stress (OS) markers in patients with chronic renal failure (CRF) and to study the relationship between different OS markers and degree of renal failure. The following indices of OS were measured in plasma: oxidized glutathione (GSSG), reduced glutathione (GSH), total glutathione (TGSH), glutathione redox ratio (GSSG/GSH) and resistance of lipoprotein fraction to oxidation (lag phase of LPF). Baseline diene conjugation level of lipoprotein fraction (BDC-LPF), total antioxidative activity (TAA), diene conjugates (DC), lipid hydroperoxides (LOOH) and thiobarbituric acid-reactive substances (TBARS) were measured in serum. All markers in plasma and serum were measured both in patients with CRF and in healthy controls. SUBJECTS AND METHODS: Blood samples were obtained from 38 patients with CRF and from 61 healthy controls. Routine biochemical analyses were performed by using commercially available kits. RESULTS: Levels of DC, BDC-LPF, LOOH, GSSG and GSSG/GSH ratio were significantly increased and lag phase of LPF was significantly shortened in patients with CRF compared with healthy controls. Serum creatinine and urea levels correlated significantly with GSSG level and GSSG/GSH in patients with CRF. A significant inverse correlation was found between glutathione redox ratio and lag phase of LPF and between GSSG level and BDC-LPF. CONCLUSIONS: The findings suggest that renal patients are in a state of oxidative stress compared with healthy controls. The most informative indices to evaluate the degree of OS in CRF were: GSSG level, GSSG/GSH status, lag phase of LPF and BDC-LPF.     

Roles of Insulin,Age, and Asymmetric Dimethylarginine on Nitric Oxide Synthesis In Vivo

We tested the effects of insulin on production of nitrous oxide (NO)-related substances (nitrites and nitrates [NOx]) after ¹⁵N-arginine intravenous infusion and on asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) concentrations in conditions reportedly associated with altered NO availability, i.e., aging, hypertension, hypercholesterolemia, and type 2 diabetes mellitus (T2DM). A total of 26 male subjects (age 23–71 years, BMI 23–33 kg/m²), some of whom were affected by mixed pathologic features, were enrolled. NOx fractional synthesis rate (FSR) was lower in elderly (P < 0.015) and T2DM subjects (P < 0.03) than in matched control subjects. Hyperinsulinemia generally increased both NOx FSR and absolute synthesis rate (ASR) and reduced NOx, ADMA, and SDMA concentrations. Insulin sensitivity was impaired only in T2DM. With use of simple linear regression analysis across all subjects, age was inversely correlated with both NOx FSR (R² = 0.23, P < 0.015) and ASR (R² = 0.21, P < 0.02). NOx FSR inversely correlated with both ADMA and SDMA. With use of multiple regression analysis and various models, NOx FSR remained inversely associated with age and ADMA, whereas ASR was inversely associated with age and diabetes. No association with insulin sensitivity was found. We conclude that whole-body NOx production is decreased in aging and T2DM. Age, ADMA concentration, and T2DM, but not insulin resistance, appear as negative regulators of whole-body NOx production.Nitric oxide (NO) is a molecule with key functions in the cardiovascular, immune, and nervous systems (1). NO production is modified during physical exercise (2) and is altered in aging (3), diabetes (4,5), hypertension (6,7), and hypercholesterolemia (8,9). The understanding of the pathophysiological mechanism(s) underlying the altered NO metabolism in these diseases is important also for the development of therapeutic interventions aimed at improving vascular function.NO is synthesized from the guanidine group of arginine via the enzyme family NO synthases (NOS), which include three isoforms (10). One of these, the constitutive endothelial NOS (eNOS) enzyme, is stimulated by hormones (insulin and estrogens), physical exercise, and cofactors such as tetrahydrobiopterin (10). Conversely, it is inhibited by the endogenous methylarginines asymmetric dimethylarginine (ADMA), l-monomethylarginine (LMMA), and symmetric dimethylarginine (SDMA) (11,12). ADMA and LMMA inhibit both eNOS and arginine cellular transport, whereas SDMA inhibits arginine transport (11,12). Dimethylarginines are increasingly recognized as important markers or factors of endothelial dysfunction and cardiovascular disease (11). ADMA concentration is increased in diabetes, hypertension, hypercholesterolemia, and aging (11,13).Insulin is an important regulator of NO production, and insulin resistance is frequently associated with endothelial dysfunction (14). Insulin mediates both glucose entry into insulin-sensitive tissues and NO production via stimulation of protein kinase B/Akt (15), translocation of GLUT4 on cell membrane, and stimulation of eNOS (16). Since in insulin-resistant states insulin signaling is altered at the Akt level (17), any pathway downstream of Akt (including glucose metabolism and NOS activity) should be concomitantly affected. Furthermore, in many insulin-resistant states, ADMA levels are increased, too (18), and they may thus interfere with the insulin signaling on NOS activity and NO production.The relative roles of insulin sensitivity and of ADMA and SDMA concentrations, as well as of other potential interfering factors such as age, on NO production in vivo have never been comprehensively investigated. Therefore, this study was designed to measure whole-body insulin sensitivity (i.e., the insulin-stimulated glucose disposal), ADMA and SDMA concentrations, and basal and insulin-stimulated NO production (19) in human subjects over a wide range of insulin sensitivity and age either healthy or affected by hypertension, hypercholesterolemia, or type 2 diabetes mellitus (T2DM). NO production was determined by a precursor product, isotope dilution technique (5). A key target of this study was also to examine the possible correlates between production of nitrites and nitrates (NOx) and ADMA, SDMA, insulin sensitivity, and age.