The Clinical Significance of Asymmetric Dimethylarginine

Dimethylarginines in patients with type 2 diabetes mellitus: relation with the glycaemic control

We tested the relationship between plasma levels of dimethylarginines (ADMA and SDMA) and glycaemic control in 43 type 2 diabetic patients. Type 2 diabetics with poor glycaemic control (HbA1c>6.5) had significantly lower SDMA and higher ADMA concentrations than those with well-controlled glycaemia (HbA1c<6.5).

Hypothermic renal perfusion during aortic surgery reduces the presence of lipocalin-2 and preserves renal extraction of dimethylarginines in rats

Cold perfusion through the renal arteries during renal ischemia has been suggested to diminish postoperative renal damage after juxtarenal aortic aneurysm repair. As the kidneys play a key role in dimethylarginine metabolism, which in turn is associated with renal hemodynamics, we hypothesized that the protective effect of cold perfusion is associated with a preserved renal extraction of dimethylarginines. Renal ischemia was induced in three groups of anesthetized Wistar rats ( n = 7/group), which underwent suprarenal aortic clamping (45 min) with no perfusion ( group 1), renal perfusion with 37°C saline ( group 2), or renal perfusion with 4°C saline ( group 3), respectively, followed by 90 min of renal reperfusion in all groups. The sham group had no clamping. In group 3 (renal ischemia with cold perfusion), postoperative serum creatinine levels as well as the presence of luminal lipocalin-2 and its associated brush-border damage were lower compared with groups 1 and 2 ( P < 0.05). Also, renal extraction of asymmetrical (ADMA) and symmetrical (SDMA) dimethylarginine as well as the arginine/ADMA ratio, which defines the bioavailability of nitric oxide, remained intact in group 3 only ( P < 0.04). The arginine/ADMA ratio correlated with cortical flow, lipocalin-2, and creatinine rises. Warm and cold renal perfusion ( groups 2 and 3) during ischemia were similarly effective in lowering protein nitrosylation levels, renal leukocyte accumulation, neutrophil gelatinase-associated lipocalin (NGAL) expression in distal tubules, and urine NGAL ( P < 0.05). These data support the use of cold renal perfusion during renal ischemia in situations where renal ischemia is inevitable, as it reduces tubular damage and preserves renal extraction of dimethylarginines. Renal perfusion with saline per se during renal ischemia is effective in diminishing renal leukocyte accumulation and oxidative stress.

Reference intervals for plasma L-arginine and the L-arginine:asymmetric dimethylarginine ratio in the Framingham Offspring Cohort

L-arginine, as a precursor of NO synthesis, has attracted much scientific attention in recent years. Experimental mouse models suggest that L-arginine supplementation can retard, halt, or even reverse atherogenesis. In human studies, supplementation with L-arginine improved endothelium-dependent vasodilation. However, L-arginine levels are best interpreted in the context of levels of asymmetric dimethylarginine (ADMA), a competitive inhibitor of NO synthase. Thus, reference limits for circulating L-arginine and the L-arginine:ADMA ratio may help to determine the nutritional state of individuals at high cardiovascular risk in light of increased ADMA levels. We defined reference limits for plasma L-arginine in 1141 people and for the L-arginine:ADMA ratio in 1138 relatively healthy individuals from the Framingham Offspring Cohort. Plasma L-arginine and ADMA concentrations were determined by using a stable isotope-based LC-MS/MS method. The reference limits (2.5th and 97.5th percentiles) for plasma L-arginine were 41.0 μmol/L (95% CI = 39.5-42.5 μmol/L) and 114 μmol/L (95% CI = 112-115 μmol/L), whereas corresponding reference limits (2.5th and 97.5th percentiles) for the L-arginine:ADMA ratio were 74.3 μmol/L (95% CI = 71.1-77.3 μmol/L) and 225 μmol/L (95% CI = 222-228 μmol/L). Plasma L-arginine was positively associated with the estimated glomerular filtration rate (eGFR) and blood glucose levels, whereas the L-arginine:ADMA ratio was positively associated with eGFR and diastolic blood pressure but inversely associated with homocysteine and (log)C-reactive protein. We report reference levels for plasma L-arginine and for the L-arginine:ADMA ratio that may be helpful for evaluation of the effects of L-arginine supplementation in participants with an impaired L-arginine/NO pathway.

Stimulus-specific blockade of nitric oxide-mediated dilatation by asymmetric dimethylarginine (ADMA) and monomethylarginine (L-NMMA) in rat aorta and carotid artery

Previous work on female rat aorta has shown that although monomethylarginine (L-NMMA) and asymmetric dimethylarginine (ADMA) each enhance submaximal phenylephrine-induced tone, consistent with blockade of basal nitric oxide activity, neither agent has any major effect on acetylcholine-induced relaxation. The aim of this study was to adopt a variety of different experimental approaches to test the hypothesis that these methylarginines block basal but not agonist-stimulated activity of nitric oxide. Basal activity of nitric oxide was assessed by observing the rise in submaximal phenylephrine-induced tone produced by nitric oxide synthase (NOS) inhibitors in male and female aorta and female carotid artery, and by monitoring the vasodilator actions of superoxide dismutase (SOD) or the PDE 5 inhibitor, T-0156. Agonist-stimulated activity of nitric oxide was assessed by observing the relaxant actions of acetylcholine or calcium ionophore A23187. L-NMMA, ADMA and L-NAME (100 μM) each enhanced submaximal phenylephrine-induced tone and inhibited SOD- or T-0156-induced relaxation, consistent with each NOS inhibitor blocking basal nitric oxide activity. In contrast, L-NMMA and ADMA had little effect on acetylcholine- or A23187-induced relaxation, while L-NAME produced powerful blockade. These observations provide support for the hypothesis that L-NMMA and ADMA selectively block basal over agonist-stimulated activity of nitric oxide in rat vessels.

Asymmetric dimethylarginine in young people with Type 1 diabetes: a paradoxical association with HbA(1c)

AIMS

Asymmetric dimethylarginine (ADMA) is an independent risk factor for cardiovascular disease and its concentrations are increased in several diseases, including diabetes. However, there is limited information on this plasma marker in young people, particularly in those with Type 1 diabetes. The aim of the present study was therefore to perform a longitudinal evaluation of plasma ADMA and of its determinants in young people with childhood-onset Type 1 diabetes.

METHODS

For measurement of ADMA using mass spectrometry, 1018 longitudinal stored blood samples were available from 330 young people with Type 1 diabetes followed in the Oxford Regional Prospective Study. Additional data concerning annual assessments of HbA(1c) , height, weight, insulin dose and three early morning urine samples for measurement of the albumin/creatinine ratio were available.

RESULTS

ADMA levels were significantly higher in males than in females (mean ± SD: 0.477 ± 0.090 vs. 0.460 ± 0.089 μmol/l, P=0.002) and declined with chronological age (estimate ± SE: -0.0106 ± 0.0008, P<0.001). A significant inverse association was detected between ADMA and HbA(1c) (estimate ± SE:-0.0113 ± 0.001, P<0.001). ADMA levels were lower in subjects developing microalbuminuria (mean ± SD: 0.455 ± 0.093 vs. 0.476 ± 0.087 μmol/l, P=0.001) than in subjects with normoalbuminuria, but this difference disappeared after adjusting for HbA(1c) .

CONCLUSIONS

In this longitudinal study, ADMA concentrations decreased with age and were significantly higher in males and lower in subjects developing microalbuminuria. These associations were largely explained by a paradoxical negative association between HbA(1c) and ADMA. We suggest that chronic hyperglycaemia might down-regulate mechanisms implicated in ADMA production or stimulate its metabolism confounding short-term associations with complications risk.

Infrarenal aortic-clamping after renal ischaemia aggravates acute renal failure

BACKGROUND

Renal failure is a frequent complication of juxtarenal abdominal aortic aneurysm (JAA)-repair. During this operation, suprarenal aortic-clamping is followed by infrarenal aortic-clamping (below renal arteries) to restore renal flow, while performing the distal anastomosis. We hypothesized that infrarenal aortic-clamping, despite restoring renal perfusion provokes additional renal damage.

MATERIALS AND METHODS

We studied three groups of rats. After 45min of suprarenal aortic-clamping, group 1 had renal reperfusion for 90min without aortic-clamps (n=7). In group 2, 45min of suprarenal aortic-clamping with a distal clamp on the aortic-bifurcation was followed by 20min of infrarenal aortic-clamping. Renal reperfusion was continued for 70min without aortic-clamps (i.e. 90 min of renal reperfusion; n=8). The sham-group had no clamps (n=7). We measured renal haemodynamics, functional parameters and tissue damage.

RESULTS

On suprarenal aortic-clamp removal, renal artery flow, cortical flow and arterial pressures were higher in group 2 than in group 1. We detected increased tubular brush border damage, luminal lipocalin-2 and 30-60% higher renal protein nitrosylation in group 2 when compared to group 1 (P<0·05). Group 2 showed more release of asymmetrical dimethylarginine (ADMA) from the kidneys in the renal vein, therefore indicating diminished clearing capacity (P<0·001). Arginine/ADMA-ratio, which defines the bio-availability of nitric oxide, tended to be lower in group 2 and correlated with renal flow. Furthermore, there were no significant differences found in creatinine levels and renal leucocyte accumulation between group 1 and 2.

CONCLUSIONS

Additional infrarenal aortic-clamping leads to increased renal damage and oxidative stress, despite adequate perfusion of kidneys after suprarenal aortic-clamping. This study indicates that the clamping sequence used in JAA-repair causes more than simple renal I/R-injury.

Plasma levels of asymmetric dimethylarginine in patients with biopsy-proven nonalcoholic fatty liver disease

Asymmetric (ADMA) and symmetric dimethylarginine (SDMA) are produced by breakdown of proteins that have been methylated posttranslationally at an arginine residue. Plasma levels of ADMA are elevated in insulin resistance states. Nonalcoholic fatty liver disease (NAFLD) is associated with insulin resistance and varying degrees of hepatic dysfunction. Because ADMA is metabolized in the liver, we hypothesized that ADMA levels will be high in patients with NAFLD as a consequence of hepatic dysfunction and insulin resistance. Plasma levels of ADMA, SDMA, total homocysteine, glucose, and insulin were measured in nondiabetic patients with biopsy-proven NAFLD (11 steatosis and 24 nonalcoholic steatohepatitis) and 25 healthy subjects. Plasma ADMA levels were significantly higher (P = .029) in patients with biopsy-proven NAFLD (0.43 ± 0.21 μmol/L) compared with controls (0.34 ± 0.10 μmol/L). However, when adjusted for insulin resistance (homeostasis model assessment), the difference between 2 groups was not evident. Plasma SDMA levels were similar in all 3 groups. Plasma levels of ADMA were positively correlated with plasma total homocysteine levels (P = .003). Plasma levels of SDMA were negatively correlated with estimated glomerular filtration rate (P = .016) and positively correlated with plasma total homocysteine levels (P = .003). The ratio of ADMA/SDMA was positively correlated with body mass index (P = .027). Elevated plasma concentrations of ADMA in biopsy-proven NAFLD were primarily related to insulin resistance. Hepatic dysfunction in NAFLD does not appear to make significant contribution to changes in plasma methylarginine levels.

Systemic inflammation is linked to low arginine and high ADMA plasma levels resulting in an unfavourable NOS substrate-to-inhibitor ratio: the Hoorn Study

Inflammation is associated with a reduced availability of NO in the vasculature. We investigated the possible involvement of altered levels of the substrate (arginine) and the inhibitor [ADMA (asymmetric ω-NG,NG-dimethylarginine)] of NOS (NO synthase). Plasma concentrations of arginine and ADMA, the inflammatory markers CRP (C-reactive protein) and MPO (myeloperoxidase), and oxLDL [oxidized LDL (low-density lipoprotein)] were measured in 369 male and 377 female participants (aged 50–87 years) of a population-based cohort study. The arginine/ADMA ratio decreased significantly across increasing tertiles of CRP and MPO. These negative associations remained significant in a linear regression model with both MPO (P=0.002) and CRP (P<0.001) as independent variables and adjusted for age, sex and cardiovascular risk factors. In a fully adjusted regression model, MPO was positively associated with ADMA {5.4 [95% CI (confidence interval), 1.3–9.4] nmol/l change of ADMA per S.D. increase in MPO; P=0.010}, whereas CRP was not (P=0.36). Conversely, in a fully adjusted model, CRP was negatively associated with arginine [−2.8 (95% CI, −4.0 to −1.6) μmol/l arginine per S.D. of CRP; P<0.001], without a significant contribution of MPO (P=0.23). The relationship between MPO and ADMA became stronger with increasing levels of oxLDL (1.8, 5.2 and 8.7 nmol/l ADMA per S.D. of MPO for increasing tertiles of oxLDL), consistent with the ability of MPO to amplify oxidative stress. In contrast, the relationship between CRP and arginine was not modified by levels of oxLDL. In conclusion, an unfavourable NOS substrate/inhibitor ratio may contribute to the reduced NO bioavailability associated with inflammation.

Asymmetric dimethylarginine in normotensive pregnant women with isolated fetal intrauterine growth restriction: a comparison with preeclamptic women with and without intrauterine growth restriction

OBJECTIVE

The aim of this study was to evaluate maternal asymmetric dimethylarginine (ADMA) levels in pregnancies complicated by isolated fetal intrauterine growth restriction (IUGR), in preeclamptic pregnancies with and without IUGR, and in healthy normotensive pregnant women with proper weight fetuses.

PATIENTS AND METHODS

The study was carried out on 54 normotensive pregnant patients with pregnancy complicated by IUGR, 35 patients with IUGR in the course of preeclampsia, 29 preeclamptic patients with appropriate-for-gestational-age weight infants and 54 healthy normotensive pregnant patients. The ADMA concentrations were evaluated using an ELISA assay.

RESULTS

The preeclamptic women and normotensive patients with pregnancy complicated by isolated IUGR revealed higher levels of maternal serum ADMA. The mean values of maternal serum ADMA were 0.5730 ± 0.1769 μmol/l in the P group, 0.5727 ± 0.1756 μmol/l in the PI group, 0.6129 ± 0.1517 μmol/l in the IUGR group, and 0.5017 ± 0.1116 μmol/l in the control group. The levels of ADMA were additionally higher in the patients with HELLP syndrome and in patients with pregnancy complicated by eclampsia.

CONCLUSIONS

It seems that ADMA is an active agent not only in preeclamptic patients, but also in normotensive pregnant women with isolated fetal IUGR and could be a marker of severity of preeclampsia.

Capillary electrophoresis-mass spectrometry for the analysis of amino acids

In this review, the recent contribution of CE-MS technology to the analysis of amino acids, as well as the advantages of the hyphenation and the technologies involved in the instrumental coupling are reported. Different sections are dedicated to the recent contributions of CE-MS to the analysis of protein amino acids and their post-translational modifications, such as phosphorylation and sulfation. CE-MS analysis of some amino acid derivatives, such as the free methylated-derivatives of arginine is also discussed. A section is specifically devoted to the CE-MS applications in the field of chiral separation of D- and L-amino acid enantiomers.

Dietary nitrate attenuates oxidative stress, prevents cardiac and renal injuries, and reduces blood pressure in salt-induced hypertension

AIMS

Reduced bioavailability of endogenous nitric oxide (NO) is a central pathophysiological event in hypertension and other cardiovascular diseases. Recently, it was demonstrated that inorganic nitrate from dietary sources is converted in vivo to form nitrite, NO, and other bioactive nitrogen oxides. We tested the hypothesis that dietary inorganic nitrate supplementation may have therapeutic effects in a model of renal and cardiovascular disease.

METHODS AND RESULTS

Sprague-Dawley rats subjected to unilateral nephrectomy and chronic high-salt diet from 3 weeks of age developed hypertension, cardiac hypertrophy and fibrosis, proteinuria, and histological as well as biochemical signs of renal damage and oxidative stress. Simultaneous nitrate treatment (0.1 or 1 mmol nitrate kg⁻¹ day⁻¹), with the lower dose resembling the nitrate content of a diet rich in vegetables, attenuated hypertension dose-dependently with no signs of tolerance. Nitrate treatment almost completely prevented proteinuria and histological signs of renal injury, and the cardiac hypertrophy and fibrosis were attenuated. Mechanistically, dietary nitrate restored the tissue levels of bioactive nitrogen oxides and reduced the levels of oxidative stress markers in plasma (malondialdehyde) and urine (Class VI F2-isoprostanes and 8-hydroxy-2-deoxyguanosine). In addition, the increased circulating and urinary levels of dimethylarginines (ADMA and SDMA) in the hypertensive rats were normalized by nitrate supplementation.

CONCLUSION

Dietary inorganic nitrate is strongly protective in this model of renal and cardiovascular disease. Future studies will reveal if nitrate contributes to the well-known cardioprotective effects of a diet rich in vegetables.

Differential sensitivity of basal and acetylcholine-induced activity of nitric oxide to blockade by asymmetric dimethylarginine in the rat aorta

BACKGROUND AND PURPOSE

Previous work has shown that N(G)-monomethyl-l-arginine (l-NMMA) paradoxically inhibits basal, but not ACh-stimulated activity of nitric oxide in rat aorta. The aim of this study was to determine if the endogenously produced agent, asymmetric N(G), N(G)-dimethyl-l-arginine (ADMA), also exhibits this unusual selective blocking action.

EXPERIMENTAL APPROACH

The effect of ADMA on basal nitric oxide activity was assessed by examining its ability to enhance phenylephrine (PE)-induced tone in endothelium-containing rings. Its effect on ACh-induced relaxation was assessed both in conditions where ADMA greatly enhanced PE tone and where tone was carefully matched with control tissues at a range of different levels.

KEY RESULTS

ADMA (100 microM) potentiated PE-induced contraction, consistent with inhibition of basal nitric oxide activity. Higher concentrations (300-1000 microM) had no greater effect. Although ADMA (100 microM) also appeared to block ACh-induced relaxation when it enhanced PE tone to maximal levels, virtually no block was seen at intermediate levels of tone in the presence of ADMA. Even ADMA at 1000 microM had no effect on the maximal relaxation to ACh, although it produced a small (two- to threefold) reduction in sensitivity. ADMA and l-NMMA, like l-arginine (all at 1000 microM), protected ACh-induced relaxation against blockade by l-NAME (30 microM).

CONCLUSIONS AND IMPLICATIONS

In the rat aorta, ADMA, like l-NMMA, blocks basal activity of nitric oxide, but has little effect on that stimulated by ACh. Further studies are required to explain these seemingly anomalous actions of ADMA and l-NMMA.

The role of asymmetric dimethylarginine and arginine in the failing heart and its vasculature

Nitric oxide (NO) is formed from arginine by the enzyme nitric oxide synthase (NOS). Asymmetric dimethylarginine (ADMA) can inhibit NO production by competing with arginine for NOS binding. Therefore, the net amount of NO might be indicated by the arginine/ADMA ratio. In turn, arginine can be metabolized by the enzyme arginase, and ADMA by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). While ADMA has been implicated as a cardiovascular risk factor, arginine supplementation has been indicated as a treatment in cardiac diseases. This review discusses the roles of ADMA and arginine in the failing heart and its vasculature. Furthermore, it proposes nutritional therapies to improve NO availability.

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.

The T1405N carbamoyl phosphate synthetase polymorphism does not affect plasma arginine concentrations in preterm infants

Background

A C-to-A nucleotide transversion (T1405N) in the gene that encodes carbamoyl-phosphate synthetase 1 (CPS1) has been associated with changes in plasma concentrations of L-arginine in term and near term infants but not in adults. In preterm infants homozygosity for the CPS1 Thr1405 variant (CC genotype) was associated with an increased risk of having necrotizing enterocolitis (NEC). Plasma L-arginine concentrations are decreased in preterm infants with NEC.

Aim

To examine the putative association between the CPS1 T1405N polymorphism and plasma arginine concentrations in preterm infants.

Methods

Prospective multicenter cohort study. Plasma and DNA samples were collected from 128 preterm infants (<30 weeks) between 6 and 12 hours after birth. Plasma amino acid and CPS1 T1405N polymorphism analysis were performed.

Results

Distribution of genotypes did not differ between the preterm (CC∶CA∶AA = 55.5%∶33.6%∶10.9%, n = 128) and term infants (CC∶CA∶AA = 54.2%∶35.4%∶10.4%, n = 96). There was no association between the CPS1 genotype and plasma L-arginine or L-citrulline concentration, or the ornithine to citrulline ratio, which varies inversely with CPS1 activity. Also the levels of asymmetric dimethylarginine, and symmetric dimethylarginine were not significantly different among the three genotypes.

Conclusions

The present study in preterm infants did not confirm the earlier reported association between CPS1 genotype and L-arginine levels in term infants.

Asymmetric dimethylarginine in the maternal and fetal circulation in preeclampsia

Preeclampsia is a leading cause of intrauterine growth restriction and preterm birth. Endothelial dysfunction is the common final pathway leading to clinical signs of preeclampsia including hypertension and proteinuria. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NOS and induces endothelial dysfunction by reversibly inhibiting NO production from l-arginine. The purpose of this study was to investigate maternal and fetal concentrations of ADMA, l-arginine, and symmetric dimethylarginine (SDMA). Women with preeclampsia (n = 47) and controls (n = 51) who gave birth by cesarean section were included in the study. We analyzed the maternal plasma and umbilical vein and artery plasma. We found that not only maternal concentrations of ADMA and SDMA but also l-arginine were significantly higher in women with preeclampsia than in controls. In fetal samples, only SDMA concentrations were higher in the preeclampsia group than in controls. The median ADMA concentration was three times higher in the fetal circulation than in the maternal circulation, but there was no difference between the preeclampsia group and the control group, and the veno-arterious gradient indicated that the placenta was the source of ADMA.

Cellular ADMA: regulation and action

Asymmetric (N(G),N(G)) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitric oxide synthase (NOS) that generates nitric oxide (NO) and cationic amino acid transporters (CATs) that supply intracellular NOS with its substrate, l-arginine, from the plasma. Therefore, ADMA and its transport mechanisms are strategically placed to regulate endothelial function. This could have considerable clinical impact since endothelial dysfunction has been detected at the origin of hypertension and chronic kidney disease (CKD) in human subjects and may be a harbinger of large vessel disease and cardiovascular disease (CVD). Indeed, plasma levels of ADMA are increased in many studies of patients at risk for, or with overt CKD or CVD. However, the levels of ADMA measured in plasma of about 0.5micromol.l(-1) may be below those required to inhibit NOS whose substrate, l-arginine, is present in concentrations many fold above the Km for NOS. However, NOS activity may be partially inhibited by cellular ADMA. Therefore, the cellular production of ADMA by protein arginine methyltransferase (PRMT) and protein hydrolysis, its degradation by N(G),N(G)-dimethylarginine dimethylaminohydrolase (DDAH) and its transmembrane transport by CAT that determines intracellular levels of ADMA may also determine the state of activation of NOS. This is the focus of the review. It is concluded that cellular levels of ADMA can be 5- to 20-fold above those in plasma and in a range that could tonically inhibit NOS. The relative importance of PRMT, DDAH and CAT for determining the intracellular NOS substrate:inhibitor ratio (l-arginine:ADMA) may vary according to the pathophysiologic circumstance. An understanding of this important balance requires knowledge of these three processes that regulate the intracellular levels of ADMA and arginine.

Plasma concentrations of the cardiovascular risk factor asymmetric dimethylarginine (ADMA) are increased in patients with HIV-1 infection and correlate with immune activation markers

OBJECTIVE

Higher concentrations of inflammation and immune activation markers as well as the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) are associated with an increased cardiovascular risk. In vitro, parallel formation of ADMA and macrophage marker neopterin was found in stimulated human peripheral blood mononuclear cells.

METHODS

In 112 HIV-1 infected patients, concentrations of ADMA, SDMA and arginine were compared to C-reactive protein and neopterin concentrations before they were referred to antiretroviral therapy. Disease activity was determined by viral load (qPCR), CD4(+) cell counts (FACS) and neopterin concentrations in plasma and urine (HPLC and ELISA). Additionally, concentrations of lipids were determined.

RESULTS

HIV-1 infected patients presented with increased neopterin, ADMA and SDMA concentrations, whereas CD4(+) counts and arginine and plasma lipid concentrations were low. ADMA and SDMA concentrations significantly correlated with markers of immune activation, but not with plasma lipids.

CONCLUSIONS

Results of this study indicate that increased ADMA and SDMA production may be related to an increased activity of immune activation pathways.

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.

The prominent role of the liver in the elimination of asymmetric dimethylarginine (ADMA) and the consequences of impaired hepatic function

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS), the enzyme which converts the amino acid arginine into nitric oxide (NO). ADMA has been identified as an important risk factor for cardiovascular diseases. Besides the role of ADMA in cardiovascular diseases, it also seems to be an important determinant in the development of critical illness, (multiple) organ failure, and the hepatorenal syndrome. ADMA is eliminated from the body by urinary excretion, but it is mainly metabolized by the dimethylarginine dimethylaminohydrolase (DDAH) enzymes that convert ADMA into citrulline and dimethylamine. DDAH is highly expressed in the liver, which makes the liver a key organ in the regulation of the plasma ADMA concentration. The prominent role of the liver in the elimination of ADMA and the consequences of impaired hepatic function on ADMA levels will be discussed in this article.

Differential effects of cross-sex hormonal treatment on plasma asymmetric dimethylarginine (ADMA) in healthy male-to-female and female-to-male transsexuals

OBJECTIVE

Sex hormone administration affects plasma levels of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). We investigated the effects of cross-sex hormone treatment (CHT) on plasma ADMA concentration in an open-label study in 40 male-to-female (M-F) and 14 female-to-male (F-M) transsexuals.

METHODS

M-F received (1) cyproterone acetate (CA) 50mg bid (n=10), (2) CA 50mg bid+ethinyl estradiol (EE) 50 microg bid (n=15), or (3) CA 50mg bid+transdermal estradiol (tE(2)) patches daily delivering 100 microg 17beta-estradiol (n=15). F-M received 250 mg mixed testosterone esters intramuscularly every 2 weeks (n=14).

RESULTS

All M-F treatment arms showed a decrease in plasma ADMA concentration after 16 weeks of CHT (mean percentage change from pre-treatment (95% confidence interval)): -26.2% (-30.9 to -21.5%) for EE+CA, -8.9% (-13.4 to -4.3%) for tE(2)+CA, and -11.3% (-17.4 to -5.2%) for CA. Testosterone administration to females increased ADMA by 9.4% (2.6 to 16.3%). The change in the EE+CA treated group was still significant after 52 weeks of CHT. In M-F and F-M, CHT had opposite effects on concentrations of other plasma amino acids as well, with EE+CA treatment causing a decrease and testosterone administration resulting in an increase.

CONCLUSION

Administration of anti-androgens alone or combined with estrogens to males decreases and testosterone administration to females increases the plasma ADMA concentration, possibly reflecting a general effect of sex hormones on amino acid metabolism.

Effect of acute variations of insulin and glucose on plasma concentrations of asymmetric dimethylarginine in young people with Type 1 diabetes

ADMA (asymmetric dimethylarginine), an endogenous inhibitor of nitric oxide synthase, is considered a major risk factor for cardiovascular disease and progression of renal disease. In the present study we aim to investigate the effect of acute variations in plasma glucose and insulin on plasma ADMA levels in young people with T1D (Type 1 diabetes). Fifteen young patients (ten males) with T1D, median age 18.3 (13.2–24.4) years, HbA1c (glycated haemoglobin) 9% (6.4–13.6%), underwent an overnight (18:00–08:00 hours) variable insulin infusion for euglycaemia, followed by a hyperinsulinaemic–euglycaemic clamp (08:00–12:00 hours). Blood samples were collected every 15 min for determination of ADMA, SDMA (symmetric dimethylarginine), valine, phenylalanine, arginine, creatinine and glucose. Insulin levels were assessed every 30 min. During the overnight period, glucose levels increased following the evening meal. In response to the protein intake there was a significant increase in ADMA, arginine, valine, phenylalanine and creatinine. For the remaining part of the night, glucose levels progressively decreased reaching 5 mmol/l by 04:00 hours. ADMA and SDMA did not change significantly. During the hyperinsulinaemic clamp, a significant fall in ADMA was observed, from 0.468±0.056 to 0.364±0.050 μmol/l (P<0.001). A significant fall was also found in SDMA, valine, phenylalanine, arginine and the ADMA/SDMA ratio (all P<0.001), but not in creatinine levels. No correlation was found between insulin sensitivity and ADMA. We conclude that acute changes in glycaemia do not significantly affect plasma ADMA levels whereas infusion of insulin significantly reduces ADMA, suggesting an important role for insulin in the regulation of this cardiovascular risk factor.

Plasma concentrations of asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, are elevated in sickle cell patients but do not increase further during painful crisis

Plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are elevated in the clinically asymptomatic state of sickle cell disease (SCD). However, the role of ADMA during vaso-occlusive complications has not been defined. ADMA concentrations were determined in HbSS (n = 43) and HbSC (n = 25) patients with healthy blood donors (HbAA) as controls. In the clinically asymptomatic state ADMA concentrations were elevated in sickle cell patients as compared to healthy controls (HbSS 0.70 micromol/L, HbSC 0.54 micromol/L, HbAA 0.39 micromol/L) (P < 0.001). Yet plasma ADMA concentrations did not increase further at presentation with a painful crisis implicating no role of primary importance during vaso-occlusive crises.

Glycemic control modulates arginine and asymmetrical-dimethylarginine levels during critical illness by preserving dimethylarginine-dimethylaminohydrolase activity

In the context of the hypercatabolic response to stress, critically ill patients reveal hyperglycemia and elevated levels of asymmetrical-dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthases. Both hyperglycemia and elevated ADMA levels predict increased morbidity and mortality. Tight glycemic control by intensive insulin therapy lowers circulating ADMA levels, and improves morbidity and mortality. Methylarginines are released from proteins during catabolism. ADMA is predominantly cleared by the enzyme dimethylarginine-dimethylaminohydrolase (DDAH) in different tissues, whereas its symmetrical isoform (SDMA) is cleared via the kidneys. Therefore, glycemic control or glycemia-independent actions of insulin on protein breakdown and/or on DDAH activity resulting in augmented ADMA levels may explain part of the clinical benefit of intensive insulin therapy. Therefore, we investigated in our animal model of prolonged critical illness the relative impact of maintaining normoglycemia and of glycemia-independent action of insulin over 7 d in a four-arm design on plasma and tissue levels of ADMA and SDMA, on proteolysis as revealed by surrogate parameters as changes of body weight, plasma urea to creatinine ratio, and plasma levels of SDMA, and on tissue DDAH activity. We found that ADMA levels remained normal in the two normoglycemic groups and increased in hyperglycemic groups. SDMA levels in the investigated tissues remained largely unaffected. The urea to creatinine ratio indicated reduced proteolysis in all but normoglycemic/normal insulin animals. DDAH activity deteriorated in hyperglycemic compared with normoglycemic groups. Insulin did not affect this finding independent of glycemic control action. Conclusively, maintenance of normoglycemia and not glycemia-independent actions of insulin maintained physiological ADMA plasma and tissue levels by preserving physiological DDAH activity.

Tight glycemic control does not affect asymmetric-dimethylarginine in septic patients

OBJECTIVE

We investigated whether preventing hyperglycemia in septic patients affected the plasma concentration of asymmetric-dimethylarginine and if this was associated with clinical benefit.

DESIGN

A prospective, multicenter, randomized, controlled, clinical study.

SETTING

Intensive care units (ICU) in three university hospitals.

PATIENTS

A total of 72 patients admitted for severe sepsis or septic shock, who stayed at least 3 days in the ICU. At admission the patients were assigned to receive either tight or conventional glycemic control.

INTERVENTIONS

Determination of circulating levels of asymmetric-dimethylarginine, arginine, interleukin-6, C-reactive-protein and tumor-necrosis-factor-alpha.

MEASUREMENTS AND RESULTS

Blood was sampled at admission (no differences between groups), and on the 3rd, 6th, 9th, and 12th (T12) days. Sequential organ failure assessment was scored at each sampling time. All the data were analyzed on an intention-to-treat basis. The control and treatment groups received the same energy intake, glycemia (110.4 +/- 17.3 vs. 163.0 +/- 28.9 mg/dL, P < 0.001) and insulin (P = 0.02) supply differed. No differences were found in high plasma levels of asymmetric-dimethylarginine (P = 0.812) at any time during the ICU stay. The clinical course, as indicated by markers of inflammation, average and maximum organ failure score, ICU stay and ICU and 90-day mortality, was the same.

CONCLUSIONS

Intensive insulin treatment, while achieving glucose control, did not reduce asymmetric-dimethylarginine in high-risk septic patients fed with no more than 25 kcal/kg per day to limit ventilatory demand and to simplify glucose control.

DESCRIPTOR

45 (SIRS/sepsis: clinical studies).

Specific amino acids in the critically ill patient--exogenous glutamine/arginine: a common denominator?

OBJECTIVE

Glutamine and arginine are both used as nutritional supplements in critically ill patients. Although glutamine has been shown to be beneficial for the metabolically stressed patient, considerations about arginine supplementation are not unanimously determined. Our aim is to review the current knowledge on the possible interplay between glutamine and arginine generation in the stressed patient and to elaborate on whether these amino acids may function as a common denominator. Because glutamine can be given by the parenteral and enteral routes, possible different actions on the metabolic fate (e.g., generation of citrulline) with both routes are analyzed.

DATA SOURCE

A summary of data on the clinical effect of glutamine and arginine metabolism is given, incorporating data on glutamine and arginine supplementation. Differences between the route of administration, parenteral or enteral, and the molecular form of supplied glutamine, free or as dipeptide, on citrulline generation by the gut and production of arginine are discussed.

RESULTS

Glutamine and arginine influence similar organ systems; however, they differ in their targets. For example, glutamine serves as fuel for the immune cells, increases human leukocyte antigen-DR expression on monocytes, enhances neutrophil phagocytosis, and increases heat shock protein expression. Arginine affects the immune system by stimulating direct or indirect proliferation of immune cells. This indirect effect is possibly mediated by nitric oxide, which also enhances macrophage cytotoxicity. Furthermore, glutamine serves as a precursor for the de novo production of arginine through the citrulline-arginine pathway. Glutamine has shown to be beneficial in the surgical and critically ill patient, whereas arginine supplementation is still under debate. The route of glutamine administration (parenteral or enteral) determines the effect on citrulline and on the de novo arginine generation. There is a marked difference between the administration of free glutamine and dipeptide enterally or parenterally. Splanchnic extraction of the hydrolyzed glutamine in mice when administering the dipeptide enterally is higher compared with administering free glutamine from the enteral site. In patients, splanchnic extraction of the dipeptide given enterally is 100% when comparing supplementation of the dipeptide intravenously.

CONCLUSIONS

The beneficial effects of free glutamine or dipeptide may depend on the route of administration but also on the metabolic fate of amino acids generated (e.g., citrulline, arginine). Glutamine serves as a substrate for de novo citrulline and arginine synthesis. More research needs to be done to establish the direct clinical relevance of the different metabolic pathways. Future perspectives might include combining enteral and parenteral routes of administrating free glutamine or dipeptide.

Insulin therapy in the pediatric intensive care unit

BACKGROUND & AIMS

Hyperglycemia is a major risk factor for increased morbidity and mortality in the intensive care unit. Insulin therapy has emerged in adult intensive care units and several pediatric studies are currently being conducted. This review discusses hyperglycemia and the effects of insulin on metabolic and non-metabolic pathways, with a focus on pediatric critical illness.

METHODS

A PubMed search was performed by using the following keywords and limits (("hyperglycemia"[MeSH terms] or ("insulin resistance"[MeSH major topic]) and ("critical care"[MeSH terms] or "critical illness"[MeSH terms])) in different combinations with ("metabolism"[MeSH terms] or "metabolic networks and pathways"[MeSH terms]) and ("outcome"[all fields]) and ("infant"[MeSH terms] or "child"[MeSH terms] or "adolescent"[MeSH terms]). Quality assessment of selected studies included clinical pertinence, publication in peer-reviewed journals, objectivity of measurements and techniques used to minimize bias. Reference lists of such studies were included.

RESULTS

The magnitude and duration of hyperglycemia are associated with increased morbidity and mortality in the pediatric intensive care unit (PICU), but prospective, randomized controlled studies with insulin therapy have not been published yet. Evidence concerning the mechanism and the effect of insulin on glucose and lipid metabolism in pediatric critical illness is scarce. More is known about the positive effect on protein homeostasis, especially in severely burned children. The effect in septic children is less clear and seems age dependent. Some non-metabolic properties of insulin such as the modulation of inflammation, endothelial dysfunction and coagulopathy have not been fully investigated in children.

CONCLUSION

Future studies on the effect of insulin on morbidity and mortality as well as on the mechanisms through which insulin exerts these effects are necessary in critically ill children. We propose these studies to be conducted under standardized conditions including precise definitions of hyperglycemia and rates of glucose intake.

Asymmetric dimethylarginine (ADMA) in vascular, renal and hepatic disease and the regulatory role of L-arginine on its metabolism

Asymmetric dimethylarginine (ADMA), an inhibitor of nitric oxide synthase (NOS), has been identified as a new and emerging contributor to, or marker for, cardiovascular risk. The ADMA-mediated regulation of nitric oxide (NO) production is determined by the quantitative bioavailability of intracellular and extracellular ADMA. Dimethylarginine dimethylaminohydrolase (DDAH), which is ubiquitously expressed in tissues, especially liver and kidney, converts the majority of the ADMA to citrulline. In this review, we discuss a new regulatory mechanism for the metabolism of ADMA in which L-arginine acts as a competitive inhibitor of DDAH activity. This novel regulatory pathway is consistent with ADMA contributing to cardiovascular risk when levels are increased but not when levels are within the normal range. The pathway then has a physiological role in the regulation of NO production by preventing overproduction of NO. The regulatory role of L-arginine on ADMA may explain the unexpected outcomes in some L-arginine supplementation studies. This paper also reviews associations between the metabolism of ADMA and insulin resistance, smoking and homocysteine which are all associated with an increased risk of vascular disease.

Increased asymmetric dimethylarginine concentrations in stimulated peripheral blood mononuclear cells

Elevated concentrations of total homocysteine as well as of asymmetric dimethylarginine (ADMA) in the blood have been reported to reflect an increased cardiovascular risk. ADMA is formed by endothelial cells and is an endogenous inhibitor of NO synthase. Earlier we have found that human peripheral blood mononuclear cells (PBMC) produce homocysteine upon stimulation with mitogens concanavalin A, phytohaemagglutinin and pokeweed mitogen. In this study, the ability of PBMC to form ADMA and symmetric dimethylarginine (SDMA) was determined. Effects were compared with levels of cysteine, homocysteine and arginine in cultures. Increased concentrations of ADMA and SDMA were found in mitogen-stimulated compared with unstimulated PBMC. Arginine and cysteine concentrations did not differ between stimulated and unstimulated PBMC. There existed significant associations between concentrations of homocysteine and ADMA (Spearman rank correlation (rs) = 0.575) as well as SDMA (rs = 0.436, both P < 0.001). Treatment of stimulated PBMC with the anti-inflammatory compounds salicylic acid (5 mm) and atorvastatin (25 microm) decreased the rate of ADMA and SDMA formation. Results of these in vitro studies show that ADMA and SDMA formation coincides with homocysteine production in human PBMC. Activated PBMC not only release Th1-type cytokine gamma-interferon, which is the most important inducer of nitric oxide synthase, but also ADMA, a natural inhibitor of the enzyme.

HPLC analysis of ADMA and other methylated l-arginine analogs in biological fluids

Post-translational methylation of arginine residues in proteins leads to generation of N(G)-monomethylarginine (MMA) and both symmetric and asymmetric dimethylarginine (SDMA and ADMA), that are released into the cytosol upon proteolysis. Both MMA and ADMA are inhibitors of nitric oxide synthase and especially elevated levels of ADMA are associated with endothelial dysfunction and cardiovascular disease. Plasma concentrations of ADMA and SDMA are very low, typically between 0.3 and 0.8 microM, making their quantification by HPLC an analytical challenge. Sample preparation usually involves a cleanup step by solid-phase extraction on cation-exchange columns followed by derivatization of amino acids into fluorescent adducts. Because ADMA and SDMA concentrations in healthy subjects show a very narrow distribution, with a between-subject variability of 13% for ADMA and 19% for SDMA, very low imprecision is an essential assay feature. Procedures for sample cleanup, derivatization, and chromatographic separation of arginine and its methylated analogs are the main topics of this review. In addition, important aspects of method validation, pre-analytical factors, and reference values are discussed.

Low plasma concentrations of arginine and asymmetric dimethylarginine in premature infants with necrotizing enterocolitis

Several studies have described reduced plasma concentrations of arginine, the substrate for nitric oxide synthase (NOS) in infants with necrotizing enterocolitis (NEC). No information on the plasma concentrations of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) in patients with NEC is currently available. We investigated whether plasma concentrations of arginine, ADMA, and their ratio differ between premature infants with and without NEC, and between survivors and non-survivors within the NEC group. In a prospective case–control study, arginine and ADMA concentrations were measured in ten premature infants with NEC (median gestational age 193 d, birth weight 968 g), and ten matched control infants (median gestational age 201 d, birth weight 1102 g), who were admitted to the Neonatal Intensive Care Unit. In the premature infants with NEC, median arginine and ADMA concentrations (μmol/l), and the arginine:ADMA ratio were lower compared to the infants without NEC: 21·4 v. 55·9, P = 0·001; 0·59 v. 0·85, P = 0·009 and 36·6 v. 72·3, P = 0·023 respectively. In the NEC group, median arginine (μmol/l) and the arginine:ADMA ratio were lower in non-surviving infants than in surviving infants: 14·7 v. 33·8, P = 0·01 and 32·0 v. 47·5, P = 0·038 respectively. In premature infants with NEC not only the NOS substrate arginine, but also the endogenous NOS inhibitor ADMA and the arginine:ADMA ratio were lower than in infants without NEC. In addition, low arginine and arginine:ADMA were associated with mortality in infants with NEC. Overall, these data suggest that a diminished nitric oxide production may be involved in the pathophysiology of NEC, but this needs further investigation.

Preferential response of glutathione-related enzymes to folate-dependent changes in the redox state of rat liver

BACKGROUND

Oxidative stress likely constitutes an important contributing factor in the onset of degenerative diseases associated with folate deficiency. Direct, as well as homocysteine-linked, antioxidant properties of folate could explain its preventive effect on these pathologies.

AIM OF THE STUDY

Our study aimed at determining the changes in the redox status of adult rats as a function of folate intake.

METHODS

Adult male rats were pair-fed for 4 weeks with a semi-synthetic diet containing 0, 0.5, 1.5, 8 or 20 mg of folic acid/kg. Folate and homocysteine concentrations, redox status markers and antioxidant enzyme activities were measured in the plasma and/or liver of the rats. A principal component analysis of the overall data was performed to draw a general scheme of the changes observed between the conditions.

RESULTS

Folate deficiency caused increased homocysteinemia and features of oxidative stress including reduced plasma antioxidant capacity together with increased lipid peroxidation in liver and heart. This was associated with an increase in the specific activity of several enzymes involved in liver glutathione metabolism (glutathione peroxidase, glutathione reductase and glutathione S-transferase), suggesting an adaptive tissue response to the oxidative stress induced by folate deficiency. In contrast, no such variation was observed for hepatic superoxide dismutase and catalase.

CONCLUSION

Despite no changes in hepatic levels of total glutathione, our findings indicate that glutathione-dependent antioxidant pathways could be particularly involved in the compensatory mechanism committed by liver to counteract the oxidative stress induced by folate deficiency. They also suggest that folate supplementation may not be associated with a better antioxidant protection of rats.

Increasing dimethylarginine levels are associated with adverse clinical outcome in severe alcoholic hepatitis

Previous studies suggest reduced hepatic endothelial nitric oxide synthase activity contributes to increased intrahepatic resistance. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, undergoes hepatic metabolism via dimethylarginine-dimethylamino-hydrolase, and is derived by the action of protein-arginine-methyltransferases. Our study assessed whether ADMA, and its stereo-isomer symmetric dimethylarginine (SDMA), are increased in alcoholic hepatitis patients, and determined any relationship with severity of portal hypertension (hepatic venous pressure gradient measurement) and outcome. Fifty-two patients with decompensated alcoholic cirrhosis were studied, 27 with acute alcoholic hepatitis and cirrhosis, in whom hepatic venous pressure gradient was higher (P = 0.001) than cirrhosis alone, and correlated with ADMA measurement. Plasma ADMA and SDMA were significantly higher in alcoholic hepatitis patients and in nonsurvivors. Dimethylarginine-dimethylamino-hydrolase protein expression was reduced and protein-arginine-methyltransferase-1 increased in alcoholic hepatitis livers. ADMA, SDMA and their combined sum, which we termed a dimethylarginine score, were better predictors of outcome compared with Pugh score, MELD and Maddrey's discriminant-function.

CONCLUSION

Alcoholic hepatitis patients have higher portal pressures associated with increased ADMA, which may result from both decreased breakdown (decreased hepatic dimethylarginine-dimethylamino-hydrolase) and/or increased production. Elevated dimethylarginines may serve as important biological markers of deleterious outcome in alcoholic hepatitis.