Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in patients with chronic kidney diseases

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.

Cardiovascular Risk in Women With PCOS

Polycystic ovary syndrome (PCOS), or Stein-Leventhal syndrome, is a common endocrine disorder defined by two of the three following features: i) oligoovulation or anovulation, ii) clinical and/or biochemical signs of hyperandrogenism, or iii) polycystic ovaries, once the related endocrinological and gynaecological disorders have been excluded. PCOS does not exclusively involve the reproductive apparatus , it has a complex number of systemic relevancy symptoms. It leads to Metabolic Syndrome, with severe consequences on the cardiovascular apparatus. Many clinical studies have underlined the connection between PCOS and the cardiovascular risk profile of such female patients, due to a lipid/glucose altered metabolism, hypertension, systemic inflammatory condition (assessable by markers such as VES, TNF-alfa, citokines and C-reactive protein (hsPCR) levels), and vascular injuries. Considering the early onset of the disease, PCOS could be considered as a real cardiovascular risk factor which affects the quality of life seriously. The current review aimed to point out the main connections between PCOS and cardiovascular risk factors according to the latest findings coming from literature data analysis, and try to depict the great influences that such a common disease can have on the patients' health integrity.

The biological effect of pharmacological treatment on dimethylaminohydrolases (DDAH-1) and cationic amino acid transporter-1 (CAT-1) expression in patients with acute congestive heart failure

AIM

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) which plays an important role in controlling vascular tone and regulates the contractile properties of cardiac myocytes. The aim of this study was to investigate the effect of pharmacological treatment on symmetric dimethylarginine (SDMA), ADMA and arginine plasma concentrations in patients with acute congestive heart failure (ACHF) through the evaluation of type-1 system cationic amino acid transporter-1/type 1 dimethylarginine dimethylaminohydrolases-1 (CAT-1/DDAH-1).

METHODS AND RESULTS

25 hospitalized cardiology patients with symptomatic acute congestive HF (NYHA Class III-IV) and impaired left ventricular (LV) function (ejection fraction<35%) were included in the study. ADMA, SDMA, and arginine plasma concentrations were assessed before and after pharmacological treatment by high performance liquid chromatography. All patients received an adequate pharmacological treatment for ACHF. ADMA and SDMA plasma levels were significantly higher after pharmacological treatment respect to baseline values (pre-treatment) (0.75 vs 0.48; 1.31 vs 1.03; p<0.01). Arginine plasma concentration was significantly lower after therapy respect to baseline values (0.78 vs 0.99; p<0.01). This is associated more with the modulation of DDAH-1 protein than with of CAT-1 system transport.

CONCLUSIONS

In patients with ACHF, acute renal impairment function and the modulation of metabolism and extracellular transport by the DDAH-1/CAT-1 system determine high ADMA and SDMA levels after therapy for acute congestive heart failure.

The role of asymmetric and symmetric dimethylarginines in renal disease

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases. By inhibiting nitric oxide formation, ADMA causes endothelial dysfunction, vasoconstriction, elevation of blood pressure, and aggravation of experimental atherosclerosis. Levels of ADMA and its isomer symmetric dimethylarginine (SDMA), which does not inhibit nitric oxide synthesis, are both elevated in patients with kidney disease. Currently available data from prospective clinical trials in patients with chronic kidney disease suggest that ADMA is an independent marker of progression of renal dysfunction, vascular complications and death. High SDMA levels also negatively affect survival in populations at increased cardiovascular risk, but the mechanisms underlying this effect are currently only partly understood. Beyond glomerular filtration, other factors influence the plasma concentrations of ADMA and SDMA. Elevated plasma concentrations of these dimethylarginines might also indirectly influence the activity of nitric oxide synthases by inhibiting the uptake of cellular L-arginine. Other mechanisms may exist by which SDMA exerts its biological activity. The biochemical pathways that regulate ADMA and SDMA, and the pathways that transduce their biological function, could be targeted to treat renal disease in the future.

The differences of asymmetric dimethylarginine removal by different dialysis treatments

BACKGROUND

Asymmetric dimethylarginine (ADMA) as a uremia toxin is accumulated in end-stage renal disease (ESRD) patients. Elevated ADMA level has been shown to be predictive of cardiovascular diseases (CVDs) and all-cause mortality in ESRD. Therefore, we investigated the removal of ADMA by different dialysis treatments.

METHODS

There were 30 each of hemodialysis (HD), hemodiafiltration (HDF), peritoneal dialysis (PD) patients, and healthy volunteers enrolled. The ADMA concentrations in serum, urine, and spent dialysate samples were determined. The urine and spent dialysate volumes were recorded. The ADMA removals by urine and spent dialysate in 1 week were calculated and compared among four groups. It was also analyzed for the correlations between the total removal of ADMA in 1 week and the parameters of age, durance of dialysis, glomerular filtration rate, urine volume, urinal ADMA level, spent dialysate volume, and spent dialysate ADMA level.

RESULTS

The serum levels of ADMA in dialysis patients were much higher than in healthy subjects (0.32 +/- 0.09 micromol/L), and their 1-week total removals of ADMA were much lower than healthy controls (249.21 +/- 57.04 micromol/week) (p-values all were less than 0.01). Among dialysis groups, serum ADMA levels decreased significantly in PD patients compared with HD or HDF patients (1.38 +/- 0.30 micromol/L vs. 1.82 +/- 0.38 micromol/L and 1.63 +/- 0.32 micromol/L, p < 0.01), and the total removal of ADMA diminished remarkably by turns of PD, HDF, and HD groups (47.79 +/- 8.20 micromol/week, 31.79 +/- 8.92 micromol/week, 14.63 +/- 6.53 micromol/week, respectively, p < 0.01). The total removal of ADMA in 1 week was related directly with the spent dialysate concentrations of ADMA, the spent dialysate volume, and the urine volume.

CONCLUSIONS

ADMA was mainly removed by dialysate in dialysis patients. Different dialysis models have different clearance capability on plasma ADMA. PD might be more effective on ADMA removal than HD and HDF, with HDF being more effective than HD.

Analysis of arginine and methylated metabolites in human plasma by field amplified sample injection capillary electrophoresis tandem mass spectrometry

A CE ion trap tandem MS method was optimised for the analysis of arginine, monomethyl- and (symmetric and asymmetric) dimethylarginines in human plasma after a very reduced sample pretreatment step involving a simple protein precipitation with ACN. Several parameters affecting the analytes MS ionization and the capillary electrophoretic separation were carefully studied and optimised. The complete separation of arginine, monomethylarginine and symmetric and asymmetric dimethylarginine was obtained in formic acid BGE in short analysis time with high specificity due to MS(2) detection of specific analytes fragments. In order to achieve the detection sensitivity suitable for the analysis of asymmetric and symmetric dimethylarginine in human plasma, the field amplified sample injection was applied. Due to stacking effects, this methodology allowed to operate a consistent on-line preconcentration of the analytes before running the electrophoresis. The method was validated for linearity, repeatability, recovery and accuracy and applied to the quantitative analysis of arginine, monomethyl- and dimethylarginines in human plasma of healthy subjects.

Dimethylarginine metabolism during acute and chronic rejection of rat renal allografts

Background. Dimethylarginines are inhibitors of NO synthesis and are involved in the pathogenesis of vascular diseases. In this study, we ask the question if asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels change during fatal and reversible acute rejection, and contribute to the pathogenesis of chronic vasculopathy.

Methods. The Dark Agouti to Lewis rat strain combination was used to investigate fatal acute rejection. Fischer 344 kidneys were transplanted to Lewis rats to study reversible acute rejection episode and the process of chronic rejection. Isograft recipients and untreated Lewis rats were used as controls. l-arginine derivatives were determined by HPLC, and ADMA-metabolizing enzymes were studied by quantitative RT–PCR and western blotting.

Results. Renal transplantation transiently increased dimethylarginine levels independent of acute rejection. ADMA plasma levels did not importantly differ between recipients undergoing fatal or reversible acute rejection, whereas SDMA was even lower in recipients of Fisher 344 grafts. In comparison to isograft recipients, ADMA and SDMA levels were slightly elevated during reversible, but not during the process of chronic rejection. Increased dimethylarginine levels, however, did not block NO synthesis. Interestingly, protein methylation, but not ADMA degradation, was increased in allografts.

Conclusions. Our data do not support the concept that renal allografts are protected from fatal rejection by dimethylarginines. Dimethylarginines may play a role in triggering chronic rejection, but a contribution to vascular remodelling itself is improbable. In contrast, differential arginine methylation of yet unknown proteins by PRMT1 may be involved in the pathogenesis of acute and chronic rejection.

Cardiovascular disease markers in women with polycystic ovary syndrome with emphasis on asymmetric dimethylarginine and homocysteine

BACKGROUND AND OBJECTIVES

Polycystic ovary syndrome (PCOS) is a disorder characterized by hyperandrogenism, ovulatory dysfunction, and polycystic ovaries. Little is known about cardiovascular risk factors in patients with PCOS. We investigated plasma markers of cardiovascular disease in Saudi women with PCOS, with an emphasis on asymmetric dimethylarginine (ADMA) and total homocysteine (tHcy).

PATIENTS AND METHODS

Fifty Saudi women with PCOS diagnosed by the Rotterdam criteria (mean age [SD] 30.2 [3.0] years) and 40 controls without PCOS (mean age 29.3 [2.5] years) had measyrements taken of clinical, metabolic, and hormonal parameters, including plasma ADMA, tHcy, lipoprotein (a) ([Lp(a)], and serum high sensitivity C-reactive protein (hs-CRP), nitric oxid, and fibrinogen. Insulin resistance was calculated by the homeostasis model assessment (HOMA-IR).

RESULTS

Women with PCOS had significantly higher fasting insulin, HOMA-IR, and luteinizing hormone (LH) levels than healthy controls (P P P CONCLUSION: Our study revealed that Saudi women with PCOS had a significantly different levels of plasma markers of cardiovascular disease compared with normal controls. Therefore, clinicians who manage women with PCOS should follow up on these markers to reduce the risk of cardiovascular disease.

Haemodialysis acutely reduces the plasma levels of ADMA without reversing impaired NO-dependent vasodilation

End-stage renal disease patients have endothelial dysfunction and high plasma levels of ADMA (asymmetric ω-NG,NG-dimethylarginine), an endogenous inhibitor of NOS (NO synthase). The actual link between these abnormalities is controversial. Therefore, in the present study, we investigated whether HD (haemodialysis) has an acute impact on NO-dependent vasodilation and plasma ADMA in these patients. A total of 24 patients undergoing maintenance HD (HD group) and 24 age- and gender-matched healthy controls (Control group) were enrolled. The increase in forearm SkBF (skin blood flow) caused by local heating to 41 °C (SkBF41), known to depend on endothelial NO production, was determined with laser Doppler imaging. SkBF41 was expressed as a percentage of the vasodilatory reserve obtained from the maximal SkBF induced by local heating to 43 °C (independent of NO). In HD patients, SkBF41 was assessed on two successive HD sessions, once immediately before and once immediately after HD. Plasma ADMA was assayed simultaneously with MS/MS (tandem MS). In the Control group, SkBF41 was determined twice, on two different days, and plasma ADMA was assayed once. In HD patients, SkBF41 was identical before (82.2±13.1%) and after (82.7±12.4%) HD, but was lower than in controls (day 1, 89.6±6.1; day 2, 89.2±6.9%; P<0.01 compared with the HD group). In contrast, plasma ADMA was higher before (0.98±0.17 μmol/l) than after (0.58±0.10 μmol/l; P<0.01) HD. ADMA levels after HD did not differ from those obtained in controls (0.56±0.11 μmol/l). These findings show that HD patients have impaired NO-dependent vasodilation in forearm skin, an abnormality not acutely reversed by HD and not explained by ADMA accumulation.

Dimethylarginines in complicated type 1 diabetes: roles of insulin, glucose, and oxidative stress

To investigate the roles of insulin, glucose, and oxidative stress on plasma asymmetric and symmetric dimethylarginine (ADMA, SDMA) levels in complicated diabetes, we studied patients with type 1 diabetes (T1D; n = 20), T1D + end-stage renal disease under hemodialysis (T1D + ESRD; n = 12), T1D + ESRD who received kidney transplant (KD; n = 16), and T1D + ESRD who received kidney-pancreas transplant (KP; n = 20) and healthy controls (n = 50). Levels of ADMA, SDMA, and free and total malondialdehyde (MDA) were increased in all patients, with the highest rises for SDMA and free MDA in T1D+ESRD. In KP, the normalized glycemia contributes to the recovery of ADMA, SDMA, and MDA levels toward normal values. From the covariance analyses, both glucose and insulin relate significantly to ADMA in T1D + ESRD (beta = +0.004, beta = -0.038, respectively) and in KP (beta = +0.032, beta = +0.032, respectively). Creatinine clearance and insulin relate to SDMA in all patient groups (beta = -0.006). Our results provide evidence for the effect of kidney-pancreas transplant on the recovery of ADMA, SDMA, and indexes of oxidative stress toward normal values. Only free MDA allows one to discriminate the magnitude of the oxidative status, as increased total MDA could also be attributable to a reduced renal function.

Blood content of asymmetric dimethylarginine: new insights into its dysregulation in renal disease

BACKGROUND

Plasma asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is significantly elevated in patients with kidney disease and is a potential risk factor for cardiovascular disease. Here, we tested whether human whole blood (WB), as in rodent blood, can accumulate free ADMA and whether this accumulation is a function of disease burden.

METHODS

In 16 healthy control subjects (CO), 18 patients with ESRD and 18 matched hypertensive patients with normal renal function (HTN), we compared using high-pressure liquid chromatography baseline plasma and WB supernatant (WBSUP) ADMA and symmetrical dimethylarginine (SDMA) concentrations and accumulation during a 5-h incubation. We measured protein turnover in incubated WBSUP to determine if proteolytic processes drive ADMA accumulation.

RESULTS

Elevated plasma ADMA was confirmed in ESRD and HTN populations while basal WBSUP ADMA was significantly higher in ESRD subjects than controls (P = 0.05 versus CO; P = 0.02 versus HTN). Plasma SDMA followed a similar pattern. Incubation of WBSUP resulted in ADMA release from protein-incorporated stores while SDMA was unaffected. ADMA accumulation in ESRD samples was significantly greater than that in HTN (P = 0.03). CO and HTN men showed significantly greater ADMA accumulation than women (P = 0.01 and P = 0.003, respectively) but no gender difference was observed in the ESRD group (P = 0.26). ADMA accumulation correlated with ex vivo protein turnover (R = 0.76, P < 0.0001).

CONCLUSIONS

Human blood is capable of releasing physiologically significant quantities of ADMA via proteolytic pathways. Dysregulated ADMA release from WB reservoirs may contribute to the distinctly high plasma ADMA levels in ESRD populations.

Development and validation of a fast quantitative method for plasma dimethylarginines analysis using liquid chromatography-tandem mass spectrometry

OBJECTIVES

The aim of this work was to implement a fast, accurate and simple method to quantify plasma ADMA and SDMA, in a run time suitable for routine analysis.

DESIGN AND METHODS

We developed and validated a hydrophilic interaction chromatographic method coupled to tandem mass spectrometry (HILIC-MS/MS) for separation and simultaneous quantification of Arginine (Arg) and its dimethylarginines, ADMA and SDMA, with a short run time (less than 5 min) using a small volume of human plasma (0.02 mL).

RESULTS

Correlation coefficients (r) of the calibration curves ranged from 0.9926 to 0.9984. Within-day and between-day imprecision (CV%) and inaccuracy (%), carry-over and recovery were also evaluated for validation. Preliminary data of Arg, ADMA and SDMA from 30 apparently healthy subjects and type 2 diabetic patients (n=33) with and without kidney dysfunction were calculated and some statistical differences occurred among them (p<0.05).

CONCLUSIONS

Data from calibration curves and quality controls reveal that the method is accurate and precise. Healthy subjects and diabetic patients' values are in agreement with those reported in other studies.

Symmetric dimethylarginine is an independent predictor of intradialytic hypotension

BACKGROUND

Hemodialysis (HD) is associated with significant reductions in the plasma concentrations of the nitric oxide (NO) inhibitors N(G)-monomethyl L-arginine (L-NMMA), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). We sought to determine whether elevated concentrations of these NO inhibitors pre-HD and/or their acute decrease during HD might mediate intradialytic hypotension (IDH).

METHODS

Systolic blood pressure (SBP), L-arginine, L-NMMA, ADMA, and SDMA were measured at the beginning (pre-HD) and at the end (end-HD) in 52 consecutive HD patients (age 64.4 +/- 13.4 years). IDH was defined as a SBP reduction of >20 mm Hg end-HD vs. pre-HD.

RESULTS

Fourteen patients demonstrated IDH. The mean SBP reduction during HD in this group was -35 +/- 13 mm Hg compared to an increase of +2 +/- 12 mm Hg among the 38 patients without IDH (no-IDH). Baseline demographic, clinical, and biochemical parameters did not differ between the IDH and no-IDH groups. However, the IDH group had higher pre-HD SBP (155 +/- 17 vs. 132 +/- 14 mm Hg, P < 0.001), pre-HD plasma SDMA concentrations (1.98 +/- 0.61 vs. 1.64 +/- 0.46 micromol/l, P = 0.04), and greater SDMA reductions during HD (-0.78 +/- 0.43 vs. -0.56 +/- 0.32 micromol/l, P = 0.06) than the no-IHD group. After adjusting for pre-HD SBP, the odds of IDH occurring were higher with increased pre-HD SDMA plasma concentrations (OR = 1.31 per 0.1 micromol/l SDMA increase; 95% CI = 1.04-1.65, P = 0.02) and with decreases in SDMA during HD (OR = 1.39 per 0.1 micromol/l SDMA decrease; 95% CI = 1.02-1.91, P = 0.04).

CONCLUSION

Increased pre-HD SDMA plasma concentrations and greater SDMA reductions during HD independently predict IDH after adjusting for demographic and clinical variables, pre-HD SBP, and other methylated forms of L-arginine.

The arginine-creatine pathway is disturbed in children and adolescents with renal transplants

Cardiovascular disease is an important cause of morbidity in recipients of renal transplants. The aim of the present study was to analyze the status of the arginine-creatine pathway in such patients, given the relationship between the arginine metabolism and both renal function and the methionine-homocysteine cycle. Twenty-nine children and adolescents (median age 13, range 6-18 years), who had received a renal allograft 14.5-82.0 months before, were recruited for the study. On immunosuppressive therapy, all patients evidenced an adequate level of renal function. Plasma concentrations of homocysteine and glycine were significantly higher, whereas urinary excretions of guanidinoacetate and creatine were significantly lower than controls. Urinary excretions of guanidinoacetate and creatine correlated positively with creatinine clearance. Urinary excretion of creatine was negatively correlated with plasma concentration of homocysteine. The demonstration of disturbances in the arginine-creatine pathway in patients with well-functioning renal transplants and in absence of chronic renal failure represents a novel finding. We speculate that the low urinary excretion of guanidinoacetate and creatine is probably related to the nephrotoxic effect of immunosuppressive therapy and to defective methylation associated with the presence of hyperhomocysteinemia.

Impact of asymmetric dimethylarginine on mortality after acute myocardial infarction

OBJECTIVE

Asymmetrical dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide (NO) synthases. From a prospective cohort of patients with acute myocardial infarction (MI), we aimed to analyze the predictive value of circulating ADMA concentrations on prognosis.

METHODS AND RESULTS

Blood samples from 249 consecutive patients hospitalized for acute MI <24 hours were taken on admission. Serum levels of ADMA and its stereoisomer, symmetrical dimethylarginine (SDMA), were determined using high-performance liquid chromatography. The independent predictors of ADMA were glomerular filtration rate, female sex, and SDMA (R(2)=0. 25). Baseline ADMA levels were higher in patients who had died than in patients who were alive at 1 year follow-up (1.23 [0.98 to 1.56] versus 0.95 [0.77 to 1.20] micromol/L, P<0.001). By Cox multivariate analysis, the higher tertile of ADMA (median [interquartile range]: 1.45 [1.24 to 1.70] micromol/L) was a predictor for mortality (Hazard Ratio [95% CI], 4.83 [1.59 to 14.71]), when compared to lower tertiles, even when adjusted for potential confounders, such as acute therapy, biological, and clinical factors.

CONCLUSIONS

Our study suggests that the baseline ADMA level has a strong prognostic value for mortality after MI, beyond traditional risk factors and biomarkers.

Response of asymmetric dimethylarginine to hemodialysis-associated hypotension in end-stage renal disease patients

AIMS

To define the role of asymmetric dimethylarginine (ADMA) in the control of blood pressure (BP) during hemodialysis (HD).

METHODS

L-Arginine, ADMA and symmetric dimethylarginine (SDMA) levels of patients with (n = 18) or without (n = 13) hypotensive episodes during HD sessions were measured before and after HD treatment by liquid chromatography-mass spectrometry. Clinical variables, laboratory parameters and underlying pathologies of end-stage renal disease (ESRD) were comparable in the groups. BP was serially recorded.

RESULTS

In patients with ESRD, plasma dimethylarginines were markedly elevated and decreased significantly by the end of the HD sessions. ADMA levels in patients having hypotensive episodes during HD were significantly higher than in those maintaining their BP (before HD: 0.62 +/- 0.11 micromol/l vs. 0.71 +/- 0.13 micromol/l, p = 0.04; after HD: 0.31 +/- 0.11 micromol/l vs. 0.43 +/- 0.11 micromol/l, p = 0.01). There was a significant inverse relationship of the minimum systolic and diastolic BP during HD to the predialysis ADMA levels (for systolic BP r = -0.50, p < 0.01; for diastolic BP r = -0.59, p < 0.01) and to the postdialysis ADMA levels (for systolic BP r = -0.49, p < 0.01; for diastolic BP r = -0.51, p < 0.005), respectively.

CONCLUSIONS

It is suggested that excessive NO generation is involved in the HD-associated hypotension and induces an increase in plasma ADMA levels to prevent further fall in BP.

Nitric oxide deficiency in chronic kidney disease

The overall production of nitric oxide (NO) is decreased in chronic kidney disease (CKD) which contributes to cardiovascular events and further progression of kidney damage. There are many likely causes of NO deficiency in CKD and the areas surveyed in this review are: 1. Limitations on substrate (l-Arginine) availability, probably due to impaired renal l-Arginine biosynthesis, decreased transport of l-Arginine into endothelial cells and possible competition between NOS and competing metabolic pathways, such as arginase. 2. Increased circulating levels of endogenous NO synthase (NOS) inhibitors, in particular asymmetric dimethylarginine (ADMA). Increased methylation of proteins and their subsequent breakdown to release free ADMA may contribute but the major culprit is probably reduced ADMA catabolism by the enzymes dimethylarginine dimethylaminohydrolases. 3. Reduced renal cortex abundance of the neuronal NOS (nNOS)α protein correlates with injury while increasing nNOSβ abundance may provide a compensatory, protective response. Interventions that can restore NO production by targeting these various pathways are likely to reduce the cardiovascular complications of CKD as well as slowing the rate of progression.

Serum creatinine on admission predicts long-term mortality in acute myocardial infarction patients undergoing successful primary angioplasty: data from the Heart Institute of Japan Acute Myocardial Infarction (HIJAMI) Registry

BACKGROUND

Data about the long-term mortality of acute myocardial infarction (AMI) patients with renal insufficiency who received sufficient early revascularization are scant, so the present study evaluated the impact of serum creatinine levels on the long-term mortality in patients with AMI undergoing successful primary percutaneous coronary intervention (PCI).

METHODS AND RESULTS

The Heart Institute of Japan Acute Myocardial Infarction (HIJAMI) registry has 3,021 consecutive AMI patients. Primary PCI was attempted in 1,451 patients and successful revascularization was obtained in 1,359 patients (93.6%). An elevated serum creatinine level, defined as creatinine > or =1.2 mg/dl, was observed in 216 patients (15.8%). Univariate analyses showed statistical differences between normal and elevated serum creatinine groups in age, gender, hypertension, previous myocardial infarction, number of diseased vessels and Killip class. During a median follow-up period of 39 [32-49] months, the event-free survival rate was lower in elevated creatinine group than normal creatinine group. Multivariate Cox proportional hazards model showed that serum creatinine level was an independent predictor of long-term mortality (adjusted hazard ratio 1.43 [95% confidence interval 1.03-1.99]).

CONCLUSION

The serum creatinine level on admission in patients with AMI predicts long-term mortality, even in those with successful primary PCI.

Novel approaches to assessing renal function in cirrhotic liver disease

Renal dysfunction is common in patients with end-stage liver disease. Etiological factors include conditions as diverse as acute tubular necrosis, immunoglobulin A nephropathy and hepatorenal syndrome. Current standard tests of renal function, such as measurement of serum urea and creatinine levels, are inaccurate as the synthesis of these markers is affected by the native liver pathology. This article reviews novel markers of renal function and their potential use in patients with liver disease.

Reference values for plasma concentrations of asymmetrical dimethylarginine (ADMA) and other arginine metabolites in men after validation of a chromatographic method

BACKGROUND

Owing to the growing number of reports in the literature on ADMA as a possibly useful marker of endothelial health, its use in the clinical laboratory is of increasing interest. Age dependency and the small, but statistically significant differences between healthy subjects and disease groups are difficult to interpret. Additionally, levels of ADMA in comparable patient groups of different studies vary widely, even when similar methods have been used.

METHODS

After analytical evaluation of a chromatographic method according to international guidelines, we analysed asymmetrical (ADMA) and symmetrical dimethyl arginine (SDMA), homo-arginine and arginine in EDTA plasma of 292 healthy males aged 20 to 75 years (y) who had passed strict inclusion/exclusion criteria. For statistical analysis, 4 age groups were formed. Group differences were identified with the non-parametric Kruskal-Wallis test.

RESULTS

Calibration curves were linear throughout the selected ranges; the standard deviation for the regression line, recovery, imprecision, and accuracy results were all highly satisfactory. The reference ranges of ADMA for the 4 age groups are presented as age (mean+/-SD of age group, y); number of subjects; median, 2.5th-97.5th percentile: group <35 y: 26.7+/-4.0 y; n=78; 0.58, 0.43-0.69 micromol/L; group 35-49 y: 41.6+/-4.0 y; n=93; 0.59, 0.45-0.73 micromol/L; group 50-65 y: 57.5+/-4.2 y; n=82; 0.61, 0.46-0.78 micromol/L; and group >65 y: 69.6+/-3.3 y; n=39; 0.64, 0.54-0.79 micromol/L.

CONCLUSIONS

Only highly precise methods are able to detect small differences between groups. The application of an evaluated method to a well defined group of healthy subjects should provide a basis for comparison of ADMA concentrations in different patient populations of future studies.

The past, presence and future of ADMA in nephrology

Kakimoto and Akazawa, first isolated and identified asymmetric dimethylarginine (ADMA) from human urine in 1970. They speculated that ADMA, and its structural isomer symmetrical dimethylarginine (SDMA), "may be important for the study of various pathological states". It took 22 years before this hypothesis materialized in form of the seminal paper by Vallance et al. who advanced the idea that ADMA accumulation may be a cardiovascular risk factor in chronic kidney disease (CKD). In the last 15 years the relationship between ADMA and adverse cardiovascular outcomes has been thoroughly investigated in more than 600 published reports. These studies have shown that ADMA does not only correlate with traditional and non-traditional risk factors but also, independently of other risk factors, is strongly associated with clinical measures of cardiovascular burden such as intima-media thickness (IMT) of the carotid artery and left ventricular mass. Furthermore, cohort studies in both the general population and the dialysis population demonstrated a strong and independent link between ADMA, all-cause mortality and cardiovascular events. Last but not least, ADMA predicts the progression of CKD. This burgeoning body experimental and clinical studies form a fairly coherent framework indicating that ADMA is not only a marker but also a potent mediator of endothelial dysfunction and atherosclerosis as well as a solid predictor of mortality in selected patient populations. This article reviews the role of ADMA as a marker and mediator in cardiovascular disease in the setting of CKD and summarizes the effect of different renal replacement therapies as well as the effect on ADMA levels of commonly used drugs in nephrology. We conclude with remarks on the usefulness of ADMA as a marker in the clinical setting as well as for emerging therapeutic strategies.

Dimethylarginines at the crossroad of insulin resistance and atherosclerosis

We tested if asymmetric dimethylarginine (ADMA) contributes to the simultaneous evolution of atherosclerosis and insulin resistance. We investigated the significant predictors of insulin resistance in the context of atherosclerosis, focusing on the role ADMA, symmetric dimethylarginine (SDMA), and l-arginine play in a cohort of young atherosclerotic patients and their age-matched controls. In a case-control study, 60 patients younger than 55 years having at least 30% stenosis of the internal carotid artery and 30 age- and sex-matched controls were recruited at a community-based neurosonologic laboratory. We found a strong positive association between the homeostasis model assessment of beta-cell function and insulin resistance and the ADMA/SDMA ratio that remained statistically significant even after adjusting for all significant and a priori identified determinants (beta = 6.76; 95% confidence interval [CI], 2.13-11.39; P = .005). Interestingly, this relationship was even more pronounced in the atherosclerotic stratum (beta = 8.29; 95% CI, 1.43-15.15; P = .019), whereas, on multiple linear regression, lack of association was seen in subjects free of carotid atherosclerosis (beta = 1.39; 95% CI, -5.46 to 8.26; P = .671). We conclude that ADMA/SDMA ratio is a significant determinant of insulin resistance and may be a better parameter to monitor than ADMA alone. By accounting for the competition at the y+ transporters, ADMA/SDMA ratio could be an indicator of intracellular ADMA level.

Asymmetric dimethylarginine (ADMA) and hyperhomocysteinemia in patients with acute myocardial infarction

OBJECTIVES

We sought to investigate the association between increased levels of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, and total plasma homocysteinemia (tHcy) in patients with acute myocardial infarction (AMI).

DESIGN AND METHODS

In 138 patients hospitalized for AMI <24 h on admission, serum levels of ADMA, its symmetric stereoisomer (SDMA) and tHcy were measured.

RESULTS

ADMA was positively associated with SDMA (p<0.001) and tHcy (p=0.03) but not with estimated glomerular filtration rates (eGFR, p=0.96), while tHcy strongly correlated with eGFR (p=0.002) and SDMA (p<0.001). By multiple linear regression, SDMA but not ADMA was independently associated with tHcy (p=0.005).

CONCLUSION

Our findings suggest that, in AMI patients, hyperhomocysteinemia is indirectly related to ADMA levels via renal function. Moreover, ADMA level was independent of traditional cardiovascular risk factors in AMI patients. Interestingly, our findings suggest that SDMA could be a good risk indicator for cardiovascular disease in AMI patients.

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.

Asymmetrical (ADMA) and symmetrical dimethylarginine (SDMA) as potential risk factors for cardiovascular and renal outcome in chronic kidney disease - possible candidates for paradoxical epidemiology?

BACKGROUND

Asymmetrical dimethylarginine (ADMA) is an inhibitor of nitric-oxide synthase. It has been linked to atherosclerotic risk in the general population as well as in end-stage renal disease patients (ESRD), whereas symmetrical dimethylarginine (SDMA) is thought to be biological inactive. Prospective data concerning the role of both dimethylarginines are rare in patients with chronic kidney disease.

METHODS

200 Patients with chronic kidney disease (mean age 57.6 +/- 13.0 years, 69 female, 131 male); 82 with chronic renal failure (CRF), 81 on maintenance haemodialysis (HD) and 37 renal transplant recipients (RTR) were prospectively followed for 24 months. ADMA and SDMA were measured by HPLC. The relation of plasma levels of ADMA and SDMA together with conventional risk factors for the cardiovascular and renal outcome was investigated with Cox proportional hazards model.

RESULTS

Mean serum levels of SDMA were significantly increased in all groups compared to the control group (P <or= 0.0005), ADMA was increased only in HD and RTR (P <or= 0.004). Forty-seven cardiovascular events (CVE) occurred during follow-up, 35 patients died, and 39 patients reached ESRD. Multivariate analysis showed diabetes (RR 3.072, P = 0.01), ESRD (RR 11.915, P < 0.0005), elevated CRP levels (RR 3.916, P < 0.0005) and surprisingly a lower ADMA level (RR 0.271, P = 0.008) as independent risk factors for CVE. Serum creatinine (RR 11.378, P = 0.001), haemoglobin (RR 0.710, P = 0.038 for an increment of 1 mmol/l), and SDMA levels (RR 1.633, P = 0.006, per 1 micromol/l increment) were predictors for the progression to ESRD.

CONCLUSIONS

Data from a heterogeneous group of patients with chronic kidney disease provide evidence that conventional risk factors seem to play a more important role than elevated serum levels of ADMA or SDMA for cardiovascular events. Increasing serum SDMA concentration seems to play an additive role for the renal outcome besides serum creatinine and haemoglobin levels. Whether ADMA might possibly be a candidate for the phenomenon of "paradoxical epidemiology" in chronic kidney disease needs further investigation.

Asymmetric dimethyl arginine levels correlate with cardiovascular risk factors in patients with erectile dysfunction

BACKGROUND

Erectile dysfunction is related to penile arterial endothelial nitric oxide production. Asymmetric dimethylarginine (ADMA) and E-selectin are often considered plasma markers of endothelial function.

OBJECTIVE

This study investigated the relationship between these plasma markers and cardiovascular risk factors in patients with erectile dysfunction.

METHODS AND RESULTS

Cardiovascular risk factors, ADMA and E-selectin were assessed in 45 patients with erectile dysfunction. Plasma markers showed associations with baseline risk factors. E-selectin levels showed an inverse relationship with age (p = 0.005) and statin therapy (p = 0.03) and a weak association with concomitant beta-blocker therapy (p = 0.05). Compared to these relatively weak associations with cardiovascular risk factors, ADMA levels showed strong associations with pulse pressure (p < 0.001), lack of smoking (p = 0.002) and lipoprotein (a) (p = 0.004) concentrations and weak associations with LDL-cholesterol (p = 0.02), and C-reactive protein levels (p = 0.04). ADMA levels correlated with E-selectin (partial r = 0.76; p < 0.001) after adjustment for lipoprotein (a), pulse pressure and smoking. No change in E-selectin or ADMA levels was seen after 70 days therapy with sildenafil and no relationship was found between either plasma marker and the acute pulse wave response to a single challenge dose of sildenafil.

CONCLUSION

ADMA levels correlate at baseline with some cardiovascular risk factors including inflammatory markers and lipoprotein (a) in patients with erectile dysfunction.

The determinants of endothelial dysfunction in CKD: oxidative stress and asymmetric dimethylarginine

BACKGROUND

Oxidative stress is related to endothelial dysfunction (ED) and cardiovascular outcomes in patients with chronic kidney disease. Increased asymmetric dimethylarginine (ADMA) levels are among the main causes of ED. We aim to investigate any association between ED and ADMA levels, as well as levels of oxidative stress markers, in patients with chronic kidney disease.

METHODS

One hundred fifty-nine patients without diabetes with chronic kidney disease were studied. Staging was performed according to glomerular filtration rate, determined as stages 1 to 5 according to the Kidney Disease Outcomes Quality Initiative (n = 30, 33, 28, 32, and 36, respectively). The control group consisted of 30 healthy subjects. Oxidative stress markers (plasma malondialdehyde [MDA], erythrocyte superoxide dismutase [SOD], glutathione peroxidase [GSH-Px]), trace elements (erythrocyte zinc [EZn], erythrocyte copper [ECu]), plasma selenium (Se), and serum ADMA were studied. Brachial artery endothelium-dependent vasodilatation (FMD) was calculated for all.

RESULTS

FMD, SOD, GSH-Px, EZn, ECu, and Se values were lower, whereas MDA and ADMA levels were higher in patients than controls. Glomerular filtration rate correlated negatively with MDA and ADMA levels and positively with FMD, SOD, and GSH-Px values. These parameters were significantly different among patients with stages 2, 3, 4, and 5 (hemodialysis group; P < 0.001 for all). Regression analysis showed that ADMA (beta = -0.228; P < 0.01), SOD (beta = 0.405; P < 0.001), and oxidized low-density lipoprotein levels (beta = -0.428; P < 0.001) were related independently to FMD, whereas glomerular filtration rate was not involved in the model.

CONCLUSION

The present results imply that FMD, oxidative stress, and ADMA levels all are associated with stage of chronic kidney disease. Additionally, levels of oxidative stress markers and ADMA independently determine endothelial function.

Plasma asymmetric dimethylarginine (ADMA) concentration is independently associated with carotid intima-media thickness and plasma soluble vascular cell adhesion molecule-1 (sVCAM-1) concentration in patients with mild-to-moderate renal failure

BACKGROUND

Patients with renal insufficiency have an increased risk of cardiovascular disease that is not fully explained by the presence of known cardiovascular risk factors. In patients with end-stage renal disease, increased serum concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), has been linked to excess cardiovascular morbidity. We investigated, in patients with mild-to-moderate renal failure, the relationship between plasma ADMA and three surrogate markers of atherosclerosis that have been shown to have prognostic value, namely carotid intima-media thickness (IMT), plasma soluble vascular cell adhesion molecule-1 (sVCAM-1), and plasma C-reactive protein (CRP).

METHODS

We used baseline data of an ongoing randomized trial in which the effects of oxidative stress-lowering treatment on vascular function and structure are studied in patients with chronic nondiabetic renal failure without clinical evidence of atherosclerosis (GFR 15 to 70 mL/min/per 1.73 m(2) according to the Cockcroft-Gault equation; ATIC study).

RESULTS

Data from 93 patients were used. Creatinine clearance was inversely related to plasma ADMA concentration (standardized beta after adjustment = -0.342, P = 0.023). Plasma ADMA was strongly related to carotid IMT in univariate (beta = 0.459, P < 0.0001) and multivariate analysis (beta= 0.444, P < 0.0001). Plasma ADMA was also significantly related with plasma soluble vascular cell adhesion molecule-1 (sVCAM-1) in univariate (beta = 0.260, P = 0.010) and multivariate (beta = 0.242, P = 0.022) analysis. Plasma ADMA was not significantly related to C-reactive protein (beta = -0.134, P = 0.204).

CONCLUSION

In patients with mild-to-moderate renal failure, renal function is inversely associated with plasma ADMA, which, in turn, is positively associated with carotid IMT and plasma sVCAM-1 concentration. Increased plasma ADMA may be a link between renal function and cardiovascular disease in patients with mild-to-moderate renal failure.

Adjuvant strategies for prevention of glomerulosclerosis

The glomerulosclerosis which frequently complicates diabetes and severe hypertension is mediated primarily by increased mesangial production and activation of transforming growth factor-beta (TGF-beta), which acts on mesangial cells to boost their production of matrix proteins while suppressing extracellular proteolytic activity. Hyperglycemia and glomerular hypertension work in various complementary ways to stimulate superoxide production via NADPH oxidase in mesangial cells; the resulting oxidant stress results in the induction and activation of TFG-beta. Nitric oxide, generated by glomerular capillaries and by mesangial cells themselves, functions physiologically to oppose mesangial TGF-beta overproduction; however, NO bioactivity is compromised by oxidant stress. In addition to low-protein diets and drugs that suppress angiotensin II activity, a variety of other agents and measures may have potential for impeding the process of glomerulosclerosis. These include vitamin E, which blunts the rise in mesangial diacylglycerol levels induced by hyperglycemia; statins and (possibly) policosanol, which down-regulate NADPH oxidase activity by diminishing isoprenylation of Rac1; lipoic acid, whose potent antioxidant activity antagonizes the impact of oxidant stress on TGF-beta expression; pyridoxamine, which inhibits production of advanced glycation endproducts; arginine, high-dose folate, vitamin C, and salt restriction, which may support glomerular production of nitric oxide; and estrogen and soy isoflavones, which may induce nitric oxide synthase in glomerular capillaries while also interfering with TGF-beta signaling. Further research along these lines may enable the development of complex nutraceuticals which have important clinical utility for controlling and preventing glomerulosclerosis and renal failure. Most of these measures may likewise reduce risk for left ventricular hypertrophy in hypertensives, inasmuch as the signaling mechanisms which mediate this disorder appear similar to those involved in glomerulosclerosis.

Body size, but neither age nor asymptomatic mitral regurgitation, influences plasma concentrations of dimethylarginines in dogs

Asymmetric dimethylarginine (ADMA) is a marker of various cardiovascular diseases in man. The aim of the present study was to test if Cavalier King Charles Spaniels (CKCS) with varying degrees of mitral regurgitation (MR) had increased plasma concentration of ADMA and furthermore, characterize the plasma level of ADMA and symmetric dimethylarginine (SDMA) in normal dogs. Seventy-six dogs were included (44 CKCS and 32 dogs of other breeds). The CKCS had various degrees of MR, whereas the remaining dogs had either no or minimal MR. Apart from cardiac murmurs, no dogs showed signs of cardiac or systematic disease. The degree of MR had no significant influence on ADMA (P = 0.33). Body weight was directly associated with ADMA (P = 0.0004) and creatinine was directly associated with SDMA (P<0.0001). Furthermore, the plasma concentration of ADMA was three to four times higher than found in healthy humans.

High-performance liquid chromatographic assay of N(G)-monomethyl-L-arginine, N(G),N(G)-dimethyl-L-arginine, and N(G),N(G)'-dimethyl-L-arginine using 4-fluoro-7-nitro-2, 1,3-benzoxadiazole as a fluorescent reagent

N(G)-Monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (ADMA), and N(G),N(G)'-dimethyl-L-arginine (SDMA) are emerging cardiovascular risk factors. A high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of L-NMMA, ADMA and SDMA is described. The assay employed 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as a fluorescent derivatization reagent. After solid phase extraction with cation-exchange column, the methylated arginines were converted to fluorescent derivatives with NBD-F, and the derivatives were separated within 32 min on a reversed-phase column. Nomega-Propyl-L-arginine was Used as an internal standard. Extrapolated detection limits were 12 nM (12 fmol per injection) for L-NMMA and 20 nM (20 fmol per injection) for ADMA and SDMA, respectively, with a signal-to-noise ratio of 3. The calibration curves for L-NMMA, ADMA and SDMA were linear within the range of 50-5000 fmol. The method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in 200 microl of rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.03, 0.80 +/- 0.25 and 0.40 +/- 0.21 microM, respectively (n = 5).

The human liver clears both asymmetric and symmetric dimethylarginine

Asymmetric (ADMA) and symmetric dimethylarginine (SDMA) inhibit production of nitric oxide. The concentration of both dimethylarginines is regulated by urinary excretion, although ADMA, but not SDMA, is also subject to degradation by dimethylarginine dimethylaminohydrolase, which is highly expressed in the liver but also present in the kidney. The exact roles of the human liver and kidney in the metabolism of dimethylarginines are currently unknown. Therefore, we aimed to investigate renal and hepatic handling of ADMA and SDMA in detail in 24 patients undergoing hepatic surgery. To calculate net organ fluxes and fractional extraction (FE) rates, blood was collected from an arterial line, the portal vein, hepatic vein, and renal vein, and blood flow of the hepatic artery, portal vein, and renal vein was determined using Doppler ultrasound techniques. Results showed a significant net uptake (median [IQR]) of ADMA in both the liver (9.6 nmol/min [5.6-13.2]) and the kidney (12.1 nmol/min [1.3-17.1]). SDMA uptake was present not only in the kidney (12.7 nmol/min [3.5-25.4]), but also in the liver (7.7 nmol/min [2.8-16.4]). FE rates of ADMA for the liver and kidney were 5.0% (3.5%-7.4%) and 8.4% (1.3%-13.9%), respectively. For SDMA, hepatic and renal FE rates were 3.4% (2.1%-7.5%) and 12.5% (3.6%-16.2%), respectively. In conclusion, this study gives a detailed description of the hepatic and renal elimination of dimethylarginines and shows that the clearing of SDMA is not only confined to the kidney, but the human liver also takes up substantial amounts of SDMA from the portal and systemic circulation.

Determination of methylated arginines by column-switching high-performance liquid chromatography-fluorescence detection

A column-switching high-performance liquid chromatography (HPLC)-fluorescence detection method for the determination of three methylated arginines, N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetric dimethyl-L-arginine, ADMA), and N(G),N(G)'-dimethyl-L-arginine (symmetric dimethyl-L-arginine, SDMA), which are endogenous nitric oxide synthase inhibitors, was developed. After fluorescence derivatization of plasma samples with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), the samples were injected into the HPLC system. The NBD-derivatized methylated arginines were trapped on a cation exchange column with filter to remove proteins, separated within 42 min on a reversed-phase column, and detected at an emission wavelength of 530 nm with excitation at 470 nm. The detection limits were 10 fmol for L-NMMA and 20 fmol for ADMA and SDMA with a signal-to-noise ratio of 3. A good linearity for calibration curves for each methylated arginine was observed within the range of 50-5000 fmol using homoarginine as an internal standard. The proposed method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.01, 0.73 +/- 0.02 and 0.41 +/- 0.05 micromol l(-1), respectively (n= 5).

Determination of arginine and asymmetric dimethylarginine (ADMA) in human plasma by liquid chromatography/mass spectrometry with the isotope dilution technique

Arginine (ARG) is a substrate for endogenous nitric oxide (NO) production whereas its metabolite, asymmetric dimethylarginine (ADMA), acts as an inhibitor. Sufficient NO production is essential for cardiovascular key functions, thus elevated concentration levels of ADMA are related to a range of cardiovascular diseases. Owing to the lack of reliable methods for the measurement of ARG and ADMA in human plasma, concentration values determined with these methods can differ considerably. We present here a simple and very robust liquid chromatographic/mass spectrometric method for the determination of ARG and ADMA utilizing isotope-labeled internal standards. Sample preparation requires only protein precipitation; the analytes were derivatized with o-phthalaldehyde-mercaptoethanol and separated on a reversed-phase C(18) column with gradient elution. The analytes were detected with an electrospray ionization ion trap instrument working in the full-scan single mass spectrometry mode. Concentration values obtained with this method for healthy controls were ARG = 63.9 +/- 23.9 microM and ADMA = 0.355 +/- 0.066 microM, with a normal range for ADMA from 0.225 to 0.485 microM. The corresponding values for end-stage chronic renal failure patients are ARG = 48.1 +/- 18.5 microM, p < 0.01 and ADMA = 0.673 +/- 0.134 M, p < 0.001.

PRMT7, a new protein arginine methyltransferase that synthesizes symmetric dimethylarginine

The cDNA for PRMT7, a recently discovered human protein-arginine methyltransferase (PRMT), was cloned and expressed in Escherichia coli and mammalian cells. Immunopurified PRMT7 actively methylated histones, myelin basic protein, a fragment of human fibrillarin (GAR) and spliceosomal protein SmB. Amino acid analysis showed that the modifications produced were predominantly monomethylarginine and symmetric dimethylarginine (SDMA). Examination of PRMT7 expressed in E. coli demonstrated that peptides corresponding to sequences contained in histone H4, myelin basic protein, and SmD3 were methylated. Furthermore, analysis of the methylated proteins showed that symmetric dimethylarginine and relatively small amounts of monomethylarginine and asymmetric dimethylarginine were produced. SDMA was also formed when a GRG tripeptide was methylated by PRMT7, indicating that a GRG motif is by itself sufficient for symmetric dimethylation to occur. Symmetric dimethylation is reduced dramatically compared with monomethylation as the concentration of the substrate is increased. The data demonstrate that PRMT7 (like PRMT5) is a Type II methyltransferase capable of producing SDMA modifications in proteins.

Vascular biology in uremia: insights into novel mechanisms of vascular injury

Cardiovascular disease is the leading cause of death in patients with end-stage renal disease. Although the prevalence of traditional atherosclerotic risk factors is increased in patients with chronic kidney disease, these traditional risk factors alone do not seem to account for the increased cardiovascular mortality. It has been proposed that additional risk factors may play a role in vascular injury. Among nontraditional risk factors, chronic inflammation, oxidative stress, and vascular calcification have been implicated in the accelerated athersclerosis of chronic kidney disease. Uremia is a proinflammatory state. Elevated levels of the proinflammatory cytokine interleukin-6 and suppressed levels of the anti-inflammatory cytokine interleukin-10 are present in chronic kidney disease and have been implicated in accelerated atherosclerosis. Uremia also results in increased oxidative stress. Asymmetric dimethyl arginine and myeloperoxidase may be critical mediators of the endothelial damage that results from oxidative stress. Finally, the uremic milieu seems to promote vascular calcification. The abundance of proinflammatory cytokines, the possible deficiency in calcification inhibitory proteins and the high phosphorus that are often present in uremia contribute to vascular calcification. Smooth muscle cells in calcifying lesions undergo phenotypic changes and molecular reprogramming that are reminiscent of endochondral bone formation during embryogenesis.

Prognostic significance of serum creatinine concentration for in-hospital mortality in patients with acute myocardial infarction who underwent successful primary percutaneous coronary intervention (from the Heart Institute of Japan Acute Myocardial Infarction [HIJAMI] Registry)

This study evaluated the impact of serum creatinine levels on in-hospital mortality in 1,359 consecutive patients with acute myocardial infarction (from a Japanese prospective multicenter registry) who underwent successful primary percutaneous coronary intervention (PCI). Even in the patients who underwent successful primary PCI, the in-hospital mortality of patients with mild (1.2 </= creatinine < 2.0 mg/dl) and severe (creatinine >/=2.0 mg/dl) renal dysfunction was greater (17.1% and 34.5%, respectively) than that of patients without renal dysfunction (3.9%) (relative risk [RR] 1.72, 95% confidence interval [CI] 0.94 to 3.14, p = 0.080; and RR 4.26, 95% CI 1.48 to 12.27, p <0.0001, respectively).

Decreased number and impaired angiogenic function of endothelial progenitor cells in patients with chronic renal failure

OBJECTIVE

Increased risk of cardiovascular disease in patients with chronic renal failure (CRF) has been explained by accelerated atherosclerosis and impaired angiogenesis, in which endothelial progenitor cells (EPCs) may play key roles. We hypothesized that altered EPC biology may contribute to the pathophysiology of CRF.

METHODS AND RESULTS

EPCs were isolated from CRF patients on maintenance hemodialysis (n=44) and from a normal control group (n=30). CRF patients showed markedly decreased numbers of EPC (44.6%) and colonies (75.3%) when compared with the controls (P<0.001). These findings were corroborated by 30.5% decrease in EPC migratory function in response to vascular endothelial growth factor (VEGF) (P=0.040) and 48.8% decrease in EPC incorporation into human umbilical vein endothelial cells (HUVEC) (P<0.001). In addition, Framingham's risk factor score of both CRF (r=-0.461, P=0.010) and normal group (r=-0.367, P=0.016) significantly correlated with the numbers of EPC. Indeed, the number of circulating EPC was significantly lower in CRF patients than in normal group under the same burden of risk factors (P<0.001). A significant correlation was also observed between dialysis dose (Kt/V) and EPC incorporation into HUVEC (r=0.427, P=0.004).

CONCLUSIONS

EPC biology, which is critical for neovascularization and the maintenance of vascular function, is altered in CRF. Our data strongly suggest that dysfunction of circulating EPC has a role in the progression of cardiovascular disease in patients with CRF.