M. Visser

Imbalance of arginine and asymmetric dimethylarginine is associated with markers of circulatory failure, organ failure and mortality in shock patients

In shock, organ perfusion is of vital importance because organ oxygenation is at risk. NO, the main endothelial-derived vasodilator, is crucial for organ perfusion and coronary patency. The availability of NO might depend on the balance between a substrate (arginine) and an inhibitor (asymmetric dimethylarginine; ADMA) of NO synthase. Therefore, we investigated the relationship of arginine, ADMA and their ratio with circulatory markers, disease severity, organ failure and mortality in shock patients. In forty-four patients with shock (cardiogenic n 17, septic n 27), we prospectively measured plasma arginine and ADMA at intensive care unit admission, Acute Physiology and Chronic Health Evaluation (APACHE) II-(predicted mortality) and Sequential Organ Failure Assessment (SOFA) score, and circulatory markers to investigate their relationship. Arginine concentration was decreased (34·6 (SD 17·9) μmol/l) while ADMA concentration was within the normal range (0·46 (SD 0·18) μmol/l), resulting in a decrease in the arginine:ADMA ratio. The ratio correlated with several circulatory markers (cardiac index, disseminated intravascular coagulation, bicarbonate, lactate and pH), APACHE II and SOFA score, creatine kinase and glucose. The arginine:ADMA ratio showed an association (OR 0·976, 95 % CI 0·963, 0·997, P = 0·025) and a diagnostic accuracy (area under the curve 0·721, 95 % CI 0·560, 0·882, P = 0·016) for hospital mortality, whereas the arginine or ADMA concentration alone or APACHE II-predicted mortality failed to do so. In conclusion, in shock patients, the imbalance of arginine and ADMA is related to circulatory failure, organ failure and disease severity, and predicts mortality. We propose a pathophysiological mechanism in shock: the imbalance of arginine and ADMA contributes to endothelial and cardiac dysfunction resulting in poor organ perfusion and organ failure, thereby increasing the risk of death.

Role of dimethylarginine dimethylaminohydrolase activity in regulation of tissue and plasma concentrations of asymmetric dimethylarginine in an animal model of prolonged critical illness

High plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with adverse outcome in critically ill patients. Asymmetric dimethylarginine is released within cells during proteolysis of methylated proteins and is either degraded by dimethylarginine dimethylaminohydrolase (DDAH) or exported to the circulation via cationic amino acid transporters. We aimed to establish the role of DDAH activity in the regulation of tissue and plasma concentrations of ADMA. In 33 critically ill rabbits, we measured DDAH activity in kidney, liver, heart, and skeletal muscle and related these values to concentrations of ADMA in these tissues and in the circulation. Both DDAH activity and ADMA concentration were highest in kidney and lowest in skeletal muscle, with intermediate values for liver and heart. Whereas ADMA content was significantly correlated between tissues (r = 0.40-0.78), DDAH activity was not. Significant inverse associations between DDAH activity and ADMA content were only observed in heart and liver. Plasma ADMA was significantly associated with ADMA in the liver (r = 0.41), but not in the other tissues. In a multivariable regression model, DDAH activities in muscle, kidney, and liver, but not in heart, were negatively associated with plasma ADMA concentration, together explaining approximately 50% of its variation. In critical illness, plasma ADMA poorly reflects intracellular ADMA. Furthermore, tissue DDAH activity is a stronger predictor of plasma ADMA than of intracellular ADMA, indicating that, compared with DDAH activity, generation of ADMA and cationic amino acid transporter-mediated exchange may be more important regulators of intracellular ADMA.

Nutrition before, during, and after surgery increases the arginine:asymmetric dimethylarginine ratio and relates to improved myocardial glucose metabolism: a randomized controlled trial

BACKGROUND Nitric oxide (NO) is essential for the optimal perfusion of the heart and its vasculature. NO may be insufficient in surgical patients because its precursor arginine is decreased, and the inhibitor of NO synthesis asymmetric dimethylarginine (ADMA) is increased. Besides arginine, the presence of other amino acids essential for the proper metabolism of cardiac cells may be decreased too. Supplementation of these amino acids with enteral and parenteral nutrition before, during, and after surgery may augment the myocardial and plasma arginine:ADMA ratio and availability of amino acids. Myocardial glucose metabolism and nutritional conditioning may result in a reduction of cardiac injury and support rapid recovery after major surgery. OBJECTIVE We investigated the effect of nutrition before, during, and after surgery on amino acids and the myocardial arginine:ADMA ratio and its relation to myocardial glucose metabolism. DESIGN In this trial, 33 patients who were undergoing off-pump coronary artery bypass grafting (CABG) were randomly assigned between enteral, parenteral, or no nutrition (control) from 2 d before, during, and until 2 d after surgery. Both enteral and parenteral solutions were prepared with commercially available products and included proteins or amino acids, glucose, vitamins, and minerals. Concentrations of amino acids including ADMA were analyzed in myocardial tissue and plasma samples. ¹⁸F-fluorodeoxyglucose positron emission tomography was performed before and after surgery to assess myocardial glucose metabolism. RESULTS The myocardial arginine:ADMA ratio increased during surgery and was significantly higher in the enteral and parenteral groups than in the control group [median (IQR): 115.0 (98.0-142.2) (P = 0.012), 116.9 (100.3-135.3) (P = 0.004), and 93.3 (82.7-101.1), respectively]. Furthermore, the change in the preoperative to postoperative plasma arginine:ADMA ratio correlated with the change in myocardial glucose metabolism in positron emission tomography (r = 0.427, P = 0.033). CONCLUSION Enteral or parenteral nutrition before, during, and after CABG may positively influence myocardial glucose metabolism by increasing the plasma and myocardial arginine:ADMA ratio.

The effect of rosiglitazone on asymmetric dimethylarginine (ADMA) in critically ill patients

Asymmetric dimethylarginine (ADMA) plays a crucial role in the arginine-nitric oxide pathway. Critically ill patients have elevated levels of ADMA which proved to be a strong and independent risk factor for ICU mortality. The aim of this study was to investigate the effect of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist rosiglitazone on ADMA plasma levels in critically ill patients. In a randomized controlled pilot study, ADMA, arginine and symmetric dimethylarginine (SDMA) were measured in 21 critically ill patients on the intensive care unit (ICU). Twelve patients received 4mg rosiglitazone once a day for a maximum of 6 weeks or until discharge or death. Nine patients served as control patients. In addition, total sequential organ failure assessment (SOFA score), kidney function and liver function were determined. Compared to the ADMA levels of healthy individuals as specified in earlier studies, ADMA plasma levels of critically ill patients were significantly higher (0.42+/-0.06 versus 0.73+/-0.2micromol/L, respectively; p<0.001). Both ADMA (B=3.5; 95% CI: 0.5-6.5; p=0.023) and SDMA (B=1.7; 95% CI: 0.7-2.7; p=0.001) were independently related to SOFA scores. Overall, rosiglitazone treatment had no effect on ADMA levels, which only significantly differed between the rosiglitazone and control groups at day 7 (p=0.028). The SOFA score in the rosiglitazone group was lower compared to the control group but the difference was only statistically significant at day 10 (p=0.01). In conclusion, in critically ill patients plasma ADMA levels were elevated and associated with the extent of multiple organ failure, but no significant ADMA-lowering effect of the PPAR-gamma agonist rosiglitazone was observed.

O016 ARGININE/ADMA IS A PREDICTOR FOR CARDIAC OUPUT IN SEPTIC SHOCK PATIENTS

Rationale: Critical illness may impair liver mitochondrial function. We hypothesised that i.v. glutamine reverses hepatic mitochondrial dysfunction in critically-ill adults. Methods: After ethics approval, 43 critically-ill adults were randomised to receive 0.5 (n = 16), 0.3 (n = 14) or 0 g/kg/d (n = 13) i.v. alanyl-glutamine as a standalone infusion. A [1-13C]methionine breath test was performed by administering 2mg/kg [1-13C]methionine and measuring breath CO2/CO2 ratio every 15min for 3h. The test was performed at ICU admission and repeated on d5 or day of discharge from ICU, if sooner. 8 Healthy adults were tested as controls. [1-13C]methionine oxidation, reflecting hepatic mitochondrial function, was calculated as cumulative percentage dose recovered (CPDR) over 3h. Data (mean±SEM) are compared by one-way ANOVA or paired or unpaired t-tests as appropriate. Results: At ICU admission, patients had a significantly lower CPDR than controls (34.7±3.4 vs. 59.8±6.0, p = 0.005, reflecting impaired liver mitochondrial function). At d5/ICU discharge, patients who did not receive glutamine had a significantly lower CPDR compared with healthy controls (Table; p < 0.05). At d5/ICU discharge, patients receiving 0.5 g/kg/d alanyl-glutamine had a significant improvement in CPDR compared with baseline (p < 0.05), and a significantly higher CPDR than patients receiving 0 g/kd/d (Table, p < 0.05), such that their CPDR was similar to controls. Patients receiving 0.3 g/kg/d had a CPDR intermediate between the placebo group and the 0.3 g/kg/d group.