Elevated plasma concentrations of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine predict adverse events in patients undergoing noncardiac surgery

A new perspective on NO pathway in sepsis and ADMA lowering as a potential therapeutic approach

The nitric oxide pathway plays a critical role in vascular homeostasis. Increased levels of systemic nitric oxide (NO) are observed in preclinical models of sepsis and endotoxemia. This has led to the postulation that vasodilation by inducible nitric oxide synthase (iNOS) generated NO may be a mechanism of hypotension in sepsis. However, contrary to the expected pharmacological action of a nitric oxide synthase (NOS) inhibitor, clinical studies with L-NAME produced adverse cardiac and pulmonary events, and higher mortality in sepsis patients. Thus, the potential adverse effects of NO in human sepsis and shock have not been fully established. In recent years, the emerging new understanding of the NO pathway has shown that an endogenously produced inhibitor of NOS, asymmetric dimethylarginine (ADMA), a host response to infection, may play an important role in the pathophysiology of sepsis as well as organ damage during ischemia–reperfusion. ADMA induces microvascular dysfunction, proinflammatory and prothrombotic state in endothelium, release of inflammatory cytokines, oxidative stress and mitochondrial dysfunction. High levels of ADMA exist in sepsis patients, which may produce adverse effects like those observed with L-NAME. Several studies have demonstrated the association of plasma ADMA levels with mortality in sepsis patients. Preclinical studies in sepsis and ischemia–reperfusion animal models have shown that lowering of ADMA reduced organ damage and improved survival. The clinical finding with L-NAME and the preclinical research on ADMA “bed to bench” suggest that ADMA lowering could be a potential therapeutic approach to attenuate progressive organ damage and mortality in sepsis. Testing of this approach is now feasible by using the pharmacological molecules that specifically lower ADMA.

The comparative and added prognostic value of biomarkers to the Revised Cardiac Risk Index for preoperative prediction of major adverse cardiac events and all-cause mortality in patients who undergo noncardiac surgery

BACKGROUND

The Revised Cardiac Risk Index (RCRI) is a widely acknowledged prognostic model to estimate preoperatively the probability of developing in-hospital major adverse cardiac events (MACE) in patients undergoing noncardiac surgery. However, the RCRI does not always make accurate predictions, so various studies have investigated whether biomarkers added to or compared with the RCRI could improve this.

OBJECTIVES

Primary: To investigate the added predictive value of biomarkers to the RCRI to preoperatively predict in-hospital MACE and other adverse outcomes in patients undergoing noncardiac surgery. Secondary: To investigate the prognostic value of biomarkers compared to the RCRI to preoperatively predict in-hospital MACE and other adverse outcomes in patients undergoing noncardiac surgery. Tertiary: To investigate the prognostic value of other prediction models compared to the RCRI to preoperatively predict in-hospital MACE and other adverse outcomes in patients undergoing noncardiac surgery.

SEARCH METHODS

We searched MEDLINE and Embase from 1 January 1999 (the year that the RCRI was published) until 25 June 2020. We also searched ISI Web of Science and SCOPUS for articles referring to the original RCRI development study in that period.

SELECTION CRITERIA

We included studies among adults who underwent noncardiac surgery, reporting on (external) validation of the RCRI and: - the addition of biomarker(s) to the RCRI; or - the comparison of the predictive accuracy of biomarker(s) to the RCRI; or - the comparison of the predictive accuracy of the RCRI to other models. Besides MACE, all other adverse outcomes were considered for inclusion.

DATA COLLECTION AND ANALYSIS

We developed a data extraction form based on the CHARMS checklist. Independent pairs of authors screened references, extracted data and assessed risk of bias and concerns regarding applicability according to PROBAST. For biomarkers and prediction models that were added or compared to the RCRI in ≥ 3 different articles, we described study characteristics and findings in further detail. We did not apply GRADE as no guidance is available for prognostic model reviews.

MAIN RESULTS

We screened 3960 records and included 107 articles.   Over all objectives we rated risk of bias as high in ≥ 1 domain in 90% of included studies, particularly in the analysis domain. Statistical pooling or meta-analysis of reported results was impossible due to heterogeneity in various aspects: outcomes used, scale by which the biomarker was added/compared to the RCRI, prediction horizons and studied populations.  Added predictive value of biomarkers to the RCRI Fifty-one studies reported on the added value of biomarkers to the RCRI. Sixty-nine different predictors were identified derived from blood (29%), imaging (33%) or other sources (38%). Addition of NT-proBNP, troponin or their combination improved the RCRI for predicting MACE (median delta c-statistics: 0.08, 0.14 and 0.12 for NT-proBNP, troponin and their combination, respectively). The median total net reclassification index (NRI) was 0.16 and 0.74 after addition of troponin and NT-proBNP to the RCRI, respectively. Calibration was not reported. To predict myocardial infarction, the median delta c-statistic when NT-proBNP was added to the RCRI was 0.09, and 0.06 for prediction of all-cause mortality and MACE combined. For BNP and copeptin, data were not sufficient to provide results on their added predictive performance, for any of the outcomes. Comparison of the predictive value of biomarkers to the RCRI  Fifty-one studies assessed the predictive performance of biomarkers alone compared to the RCRI. We identified 60 unique predictors derived from blood (38%), imaging (30%) or other sources, such as the American Society of Anesthesiologists (ASA) classification (32%). Predictions were similar between the ASA classification and the RCRI for all studied outcomes. In studies different from those identified in objective 1, the median delta c-statistic was 0.15 and 0.12 in favour of  BNP and NT-proBNP alone, respectively, when compared to the RCRI, for the prediction of MACE. For C-reactive protein, the predictive performance was similar to the RCRI. For other biomarkers and outcomes, data were insufficient to provide summary results. One study reported on calibration and none on reclassification. Comparison of the predictive value of other prognostic models to the RCRI   Fifty-two articles compared the predictive ability of the RCRI to other prognostic models. Of these, 42% developed a new prediction model, 22% updated the RCRI, or another prediction model, and 37% validated an existing prediction model. None of the other prediction models showed better performance in predicting MACE than the RCRI. To predict myocardial infarction and cardiac arrest, ACS-NSQIP-MICA had a higher median delta c-statistic of 0.11 compared to the RCRI. To predict all-cause mortality, the median delta c-statistic was 0.15 higher in favour of ACS-NSQIP-SRS compared to the RCRI. Predictive performance was not better for CHADS₂, CHA₂DS₂-VASc, R₂CHADS₂, Goldman index, Detsky index or VSG-CRI compared to the RCRI for any of the outcomes. Calibration and reclassification were reported in only one and three studies, respectively.

AUTHORS' CONCLUSIONS

Studies included in this review suggest that the predictive performance of the RCRI in predicting MACE is improved when NT-proBNP, troponin or their combination are added. Other studies indicate that BNP and NT-proBNP, when used in isolation, may even have a higher discriminative performance than the RCRI. There was insufficient evidence of a difference between the predictive accuracy of the RCRI and other prediction models in predicting MACE. However, ACS-NSQIP-MICA and ACS-NSQIP-SRS outperformed the RCRI in predicting myocardial infarction and cardiac arrest combined, and all-cause mortality, respectively. Nevertheless, the results cannot be interpreted as conclusive due to high risks of bias in a majority of papers, and pooling was impossible due to heterogeneity in outcomes, prediction horizons, biomarkers and studied populations. Future research on the added prognostic value of biomarkers to existing prediction models should focus on biomarkers with good predictive accuracy in other settings (e.g. diagnosis of myocardial infarction) and identification of biomarkers from omics data. They should be compared to novel biomarkers with so far insufficient evidence compared to established ones, including NT-proBNP or troponins. Adherence to recent guidance for prediction model studies (e.g. TRIPOD; PROBAST) and use of standardised outcome definitions in primary studies is highly recommended to facilitate systematic review and meta-analyses in the future.

l-Citrulline supplementation during pregnancy improves perinatal and postpartum maternal vascular function in a mouse model of preeclampsia

Preeclampsia is a spontaneously occurring pregnancy complication diagnosed by new-onset hypertension and end-organ dysfunction with or without proteinuria. This pregnancy-specific syndrome contributes to maternal morbidity and mortality and can have detrimental effects on fetal outcomes. Preeclampsia is also linked to increased risk of maternal cardiovascular disease throughout life. Despite intense investigation of this disorder, few treatment options are available. The aim of this study was to investigate the potential therapeutic effects of maternal l-citrulline supplementation on pregnancy-specific vascular dysfunction in the male C57BL/6J × female C57BL/6J C1q-/- preeclampsia-like mouse model. l-Citrulline is a nonessential amino acid that is converted to l-arginine to promote smooth muscle and blood vessel relaxation and improve nitric oxide (NO)-mediated vascular function. To model a preeclampsia-like pregnancy, female C57BL/6J mice were mated to C1q-/- male mice, and a subset of dams was supplemented with l-citrulline throughout pregnancy. Blood pressure, systemic vascular glycocalyx, and ex vivo vascular function were investigated in late pregnancy, and postpartum at 6 and 10 mo of age. Main findings show that l-citrulline reduced blood pressure, increased vascular glycocalyx volume, and rescued ex-vivo vascular function at gestation day 17.5 in this preeclampsia-like model. The vascular benefit of l-citrulline also extended postpartum, with improved vascular function and glycocalyx measures at 6 and 10 mo of age. l-Citrulline-mediated vascular improvements appear, in part, attributable to NO pathway signaling. Taken together, l-citrulline supplementation during pregnancy appears to have beneficial effects on maternal vascular health, which may have translational implications for improved maternal cardiovascular health.

Asymmetric dimethylarginine predicts perioperative cardiovascular complications in patients undergoing medium-to-high risk non-cardiac surgery

Objectives

Perioperative cardiovascular events remain an important factor that affects surgery outcome. We assessed if asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, predicts perioperative risk, and if pre-operative supplementation with L-arginine/L-citrulline improves the plasma L-arginine/ADMA ratio.

Methods

In this prospective study, planned thoracic and/or abdominal surgery patients were randomized to receive L-arginine/L-citrulline (5 g/day) or placebo 1 to 5 days before surgery. We measured perioperative plasma ADMA and L-arginine levels. The primary outcome was a 30-day combined cardiovascular endpoint.

Results

Among 269 patients, 23 (8.6%) experienced a major adverse cardiovascular event. ADMA and C-reactive protein were significantly associated with the incidence of cardiovascular complications in the multivariable-adjusted analysis. The L-arginine plasma concentration was significantly higher on the day of surgery with L-arginine/L-citrulline supplementation compared with placebo. In patients with high pre-operative ADMA, there was a non-significant trend towards reduced incidence of the primary endpoint with L-arginine/L-citrulline supplementation (six vs. nine events).

Conclusions

ADMA is a predictor of major adverse cardiovascular complications in the perioperative period for patients who are undergoing major abdominal and/or thoracic surgery. Supplementation with L-arginine/L-citrulline increased the L-arginine plasma concentration, enhanced the L-arginine/ADMA ratio, and induced a trend towards fewer perioperative events.

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week-old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and N^G-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.

L-Arginine/NO Pathway Metabolites in Colorectal Cancer: Relevance as Disease Biomarkers and Predictors of Adverse Clinical Outcomes Following Surgery

The L-Arginine/NO pathway is involved in carcinogenesis and immunity. Its diagnostic and prognostic value in colorectal cancer (CRC) was determined using tandem mass spectrometry in 199 individuals (137 with CRC) and, during a three-day follow up, in 60 patients undergoing colorectal surgery. Citrulline was decreased and asymmetric (ADMA) and symmetric (SDMA) dimethylarginines and dimethylamine (DMA) were increased in CRC. The DMA increase corresponded with CRC advancement while arginine, ADMA, and SDMA levels were higher in left-sided cancers. Arginine, citrulline, ADMA, and DMA dropped and SDMA increased post incision. Females experienced a more substantial drop in arginine. The arginine and ADMA dynamics depended on blood loss. The initial SDMA increase was higher in patients requiring transfusions. Postoperative dynamics in arginine and dimethylarginines differed in robot-assisted and open surgery. Concomitant SDMA, citrulline, and DMA quantification displayed a 92% accuracy in detecting CRC. Monitoring changes in arginine, ADMA, and SDMA in the early postoperative period predicted postoperative ileus with 84% and surgical site infections with 90% accuracy. Changes in ADMA predicted operative morbidity with 90% and anastomotic leakage with 77% accuracy. If positively validated, L-arginine/NO pathway metabolites may facilitate CRC screening and surveillance, support differential diagnosis, and assist in clinical decision-making regarding patients recovering from colorectal surgery.

Protein Arginine Methyltransferases in Cardiovascular and Neuronal Function

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a type of post-translational modification which is important for numerous cellular processes, including mRNA splicing, DNA repair, signal transduction, protein interaction, and transport. PRMTs have been extensively associated with various pathologies, including cancer, inflammation, and immunity response. However, the role of PRMTs has not been well described in vascular and neurological function. Aberrant expression of PRMTs can alter its metabolic products, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). Increased ADMA levels are recognized as an independent risk factor for cardiovascular disease and mortality. Recent studies have provided considerable advances in the development of small-molecule inhibitors of PRMTs to study their function under normal and pathological states. In this review, we aim to elucidate the particular roles of PRMTs in vascular and neuronal function as a potential target for cardiovascular and neurological diseases.

Systematic Review of Comorbidity and Competing-risks Assessments for Bladder Cancer Patients

Context

Radical cystectomy continues to be associated with a significant risk of morbidity and all-cause mortality (ACM). Practice pattern data demonstrating underuse of surgery for patients with muscle-invasive and high-risk non-muscle invasive bladder cancer (BC) have been linked to the advanced age and higher comorbidity status of such patients, which suggests that rates of ACM as well as cancer-specific mortality should be incorporated into patient counseling and guideline recommendations.

Objective

To review the literature on risk assessment tools for preoperative comorbidity in BC that may aid in treatment decision-making.

Evidence acquisition

A systematic search was conducted using Ovid and Medline according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines to identify studies between 1970 and 2017 reporting on comorbidity risk assessment (CRA) tools for BC. Prospective and retrospective studies were included.

Evidence synthesis

There are no published randomized control trials comparing CRA tools for BC. Patients undergoing radical cystectomy with combined high-risk comorbidity and performance scores may face up to a sevenfold greater risk of other-cause mortality compared to those with low scores. The Charlson Comorbidity Index is one of the most widely studied indices for 90-d perioperative mortality and overall and cancer-specific survival, with an area under the receiver operating characteristic curve of up to 0.810. Prospective studies of CRA tools for BC have consistently shown that patients with higher comorbidity have worse outcomes. While not specific for BC, comorbidity indices provide useful assessment of competing risks. Competing-risks assessment tools are lacking, with limited studies assessing the impact of these tools on treatment decision-making by patients and providers. We provide the impetus for incorporation of comorbidity risks into practice guidelines when discussing treatment options with patients.

Conclusions

CRA tools should be incorporated into preoperative treatment counseling and the assessment of postoperative outcomes. While retrospective evidence supports the use of CRA tools for BC, further comparative studies evaluating the effectiveness of these tools and identifying the patients most likely to benefit from a treatment according to competing-risks assessment are needed.

Patient summary

In this review we explored the clinical evidence for comorbidity risk assessment tools in bladder cancer. We found evidence to support incorporation of comorbidity risks into practice guidelines when discussing treatment options with patients.

Arginine/Asymmetric Dimethylarginine Ratio in Colorectal Surgery

BACKGROUND

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid that inhibits the effects of nitric oxide synthetases, producing considerable effects on the vascular system. Recent studies have suggested that increased ADMA is a major contributor to endothelial dysfunction, resulting in significant effects on cardiovascular and renal function.

METHODS

The study sample consisted of five male and 11 female patients scheduled for elective laparoscopic colorectal surgery; patients were between 41 and 77 years of age. Venous whole blood (8 - 10 mL) was collected from patients prior to colorectal surgery, as well as on postoperative day 1 and 2. Arginine, citrulline, ADMA, and symmetric dimethylarginine levels were measured in collected blood using liquid chromatography coupled to mass spectrometry.

RESULTS

Data from the amino-acid blood analysis demonstrated that the levels of L-citrulline and L-arginine decreased on postoperative days 1, coinciding with an increase of ADMA levels. The overall result of these changes was a decrease in the arginine to ADMA ratio by 21% from the preoperative period to postoperative day 2 (P = 0.02).

CONCLUSIONS

The data collected through this study demonstrate a significant increase in systemic ADMA levels following major laparoscopic colorectal surgery.

Caveolin1/protein arginine methyltransferase1/sirtuin1 axis as a potential target against endothelial dysfunction

Endothelial dysfunction (ED), an established response to cardiovascular risk factors, is characterized by increased levels of soluble molecules secreted by endothelial cells (EC). Evidence suggest that ED is an independent predictor of cardiac events and that it is associated with a deficiency in production or bioavailability of nitric oxide (NO) and/or an imbalance in the relative contribution of endothelium-derived relaxing and contracting factors. ED can be reversed by treating cardiovascular risk factors, hence, beyond ambiguity, ED contributes to initiation and progression of atherosclerotic disease. Majority of cardiovascular risk factors act by a common pathway, oxidative stress (OS), characterized by an imbalance in bioavailability of NO and reactive oxygen species (ROS). Enhanced ROS, through several mechanisms, alters competence of EC that leads to ED, reducing its potential to maintain homeostasis and resulting in development of cardiovascular disease (CVD). Influential mechanisms that have been implicated in the development of ED include (i) presence of elevated levels of NOS inhibitor, asymmetric dimethylarginine (ADMA) due to augmented enzyme activity of protein arginine methyl transferase-1 (PRMT1); (ii) decrease in NO generation by endothelial nitric oxide synthase (eNOS) uncoupling, or by reaction of NO with free radicals and (iii) impaired post translational modification of protein (PTM) such as eNOS, caveolin-1 (cav1) and sirtuin-1 (SIRT1). However, the inter-related mechanisms that concur to developing ED is yet to be understood. The events that possibly overlay include OS-induced sequestration of SIRT1 to caveolae facilitating cav1-SIRT1 association; potential increase in lysine acetylation of enzymes such as eNOS and PRMT1 leading to enhanced ADMA formation; imbalance in acetylation-methylation ratio (AMR); diminished NO generation and ED. Here we review current literature from research showing interdependent association between cav1-PRMT1-SIRT1 to the outcomes of experimental and clinical research aiming to preserve endothelial function with gene- or pharmaco-therapy.

Asymmetric and Symmetric Dimethylarginine as Risk Markers for Total Mortality and Cardiovascular Outcomes: A Systematic Review and Meta-Analysis of Prospective Studies

Background

A growing number of studies linked elevated concentrations of circulating asymmetric (ADMA) and symmetric (SDMA) dimethylarginine to mortality and cardiovascular disease (CVD) events. To summarize the evidence, we conducted a systematic review and quantified associations of ADMA and SDMA with the risks of all-cause mortality and incident CVD in meta-analyses accounting for different populations and methodological approaches of the studies.

Methods

Relevant studies were identified in PubMed until February 2015. We used random effect models to obtain summary relative risks (RR) and 95% confidence intervals (95%CIs), comparing top versus bottom tertiles. Dose-response relations were assessed by restricted cubic spline regression models and potential non-linearity was evaluated using a likelihood ratio test. Heterogeneity between subgroups was assessed by meta-regression analysis.

Results

For ADMA, 34 studies (total n = 32,428) investigating associations with all-cause mortality (events = 5,035) and 30 studies (total n = 30,624) investigating the association with incident CVD (events = 3,396) were included. The summary RRs (95%CI) for all-cause mortality were 1.52 (1.37–1.68) and for CVD 1.33 (1.22–1.45), comparing high versus low ADMA concentrations. Slight differences were observed across study populations and methodological approaches, with the strongest association of ADMA being reported with all-cause mortality in critically ill patients. For SDMA, 17 studies (total n = 18,163) were included for all-cause mortality (events = 2,903), and 13 studies (total n = 16,807) for CVD (events = 1,534). High vs. low levels of SDMA, were associated with increased risk of all-cause mortality [summary RR (95%CI): 1.31 (1.18–1.46)] and CVD [summary RR (95%CI): 1.36 (1.10–1.68) Strongest associations were observed in general population samples.

Conclusions

The dimethylarginines ADMA and SDMA are independent risk markers for all-cause mortality and CVD across different populations and methodological approaches.

Asymmetric dimethylarginine, related arginine derivatives, and incident atrial fibrillation

BACKGROUND

Oxidative stress plays an important role in the development of atrial fibrillation (AF). Arginine derivatives including asymmetric dimethylarginine (ADMA) are central to nitric oxide metabolism and nitrosative stress. Whether blood concentrations of arginine derivatives are related to incidence of AF is uncertain.

METHODS AND RESULTS

In 3,310 individuals (mean age 58 ± 10 years, 54% women) from the community-based Framingham Study, we prospectively examined the relations of circulating levels of ADMA, l-arginine, symmetric dimethylarginine (SDMA), and the ratio of l-arginine/ADMA to incidence of AF using proportional hazards regression models. Over a median follow-up time of 10 years, 247 AF cases occurred. Using age- and sex-adjusted regression models, ADMA was associated with a hazard ratio of 1.15 per 1-SD increase in loge-biomarker concentration (95% CI 1.02-1.29, P = .02) for AF, which was no longer significant after further risk factor adjustment (hazard ratio 1.09, 95% CI 0.97-1.23, P = .15). Neither l-arginine nor SDMA was related to new-onset AF. A clinical model comprising clinical risk factors for AF (for age, sex, height, weight, systolic blood pressure, diastolic blood pressure, current smoking, diabetes, hypertension treatment, myocardial infarction, and heart failure; c statistic = 0.781; 95% CI 0.753-0.808) was not improved by the addition of ADMA (0.782; 95% CI 0.755-0.809).

CONCLUSIONS

Asymmetric dimethylarginine and related arginine derivatives were not associated with incident AF in the community after accounting for other clinical risk factors and confounders. Its role in the pathogenesis of AF needs further refinement.

Nebivolol ameliorates asymmetric dimethylarginine-induced vascular response in rat aorta via β3 adrenoceptor-mediated mechanism

BACKGROUND

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, induces endothelial dysfunction. Nebivolol, a highly selective β1-adrenergic receptor (AR) blocker, is the only beta-blocker known to induce vascular production of nitric oxide.

OBJECTIVE

The present study was designed to evaluate the effect and mechanism of nebivolol on ADMA-induced vascular response in rat aorta in vitro.

METHODS

In vitro, the effects of nebivolol and ADMA on resting tone or contraction induced by phenylephrine (PE, 10(-6 )mol/L) and relaxation induced by acetylcholine (Ach, 10(-10)-10(-5 )mol/L) were evaluated.

RESULTS

ADMA in a concentration-dependent manner increased the resting and PE-induced tone and reduced Ach-induced relaxation. Nebivolol inhibited the ADMA-induced enhancements in tone and reversed the effects of ADMA on Ach-induced relaxation. These effects of nebivolol were blocked by selective β3 receptor blocker cyanopindolol (1 μM), but not by selective β2 receptor blocker butoxamine (50 μM).

CONCLUSIONS

Nebivolol ameliorates the ADMA-induced vascular responses in rat aorta, at least in part, by mechanisms involving β3 adrenoceptor.

Asymmetric dimethylarginine and cardiovascular risk: systematic review and meta-analysis of 22 prospective studies

BACKGROUND

Asymmetric dimethylarginine (ADMA) inhibits the production of nitric oxide, a key regulator of the vascular tone, and may be important in the development of cardiovascular disease (CVD). Our aim was to reliably quantify the association of ADMA and its isomer symmetric dimethylarginine (SDMA) with the risk of CVD outcomes in long-term cohort studies.

METHODS AND RESULTS

Data were collated from 22 prospective studies involving a total of 19 842 participants, which have recorded 2339 CVD, 997 coronary heart disease, and 467 stroke outcomes during a mean follow-up of 7.1 years. In a comparison of individuals in the top with those in the bottom third of baseline ADMA values, the combined risk ratios were 1.42 (95% confidence interval: 1.29 to 1.56) for CVD, 1.39 for coronary heart disease (1.19 to 1.62), and 1.60 for stroke (1.33 to 1.91). Broadly similar results were observed according to participants' baseline disease status (risk ratios for CVD: 1.35 [1.18 to 1.54] in general populations; 1.47 [1.16 to 1.87] in individuals with pre-existing CVD; and 1.52 [1.26 to 1.84] in individuals with pre-existing kidney disease) and by different study characteristics, including geographical location, sample type, assay method, number of incident outcomes, and level of statistical adjustment (all P values>0.05). In contrast, in 8 prospective studies involving 9070 participants and 848 outcomes, the corresponding estimate for SDMA concentration was 1.32 (0.92 to 1.90) for CVD.

CONCLUSIONS

Available prospective studies suggest associations between circulating ADMA concentration and CVD outcomes under a broad range of circumstances. Further research is needed to better clarify these associations, particularly in large general population studies.

Asymmetric dimethylarginine and oxidative stress following coronary artery bypass grafting: associations with postoperative outcome

OBJECTIVES

Elevated asymmetric dimethylarginine (ADMA) is associated with an increased risk of coronary artery disease. A prognostic value of ADMA following coronary artery bypass grafting (CABG) is unknown. The aim of the current study was to assess the effect of CABG on ADMA and oxidative stress and determine their associations with postoperative complications.

METHODS

In 158 consecutive patients (35 women, 123 men, aged 65.2 ± standard deviation 8.2 years) undergoing isolated, elective CABG procedure, we measured plasma ADMA and 8-iso-prostaglandin F2α (8-iso-PGF2α) preoperatively and twice postoperatively: 18-36 h and 5-7 days after surgery. The primary end points were postoperative myocardial infarction (PMI) and in-hospital cardiovascular death.

RESULTS

ADMA increased from 0.56 ± 0.06 μmol/l at baseline by 68% to 0.94 ± 0.11 μmol/l at 18-36 h after CABG, and then decreased by 20% to 0.75 ± 0.12 μmol/l on 5-7 days postoperatively (P = 0.0001 for all comparisons). A similar pattern of changes was observed for 8-iso-PGF2α. Thirteen (8.2%) patients developed PMI, and 6 patients (3.8%) died during the early postoperative period because of extensive PMI. PMI and early perioperative mortality were positively associated with ADMA and 8-iso-PGF2α.

CONCLUSIONS

A marked increase of ADMA and oxidative stress is observed within the first days following CABG, and is associated with unfavourable early post-CABG outcomes, including PMI and in-hospital cardiovascular death.

Symmetrical Dimethylarginine Predicts Mortality in the General Population

Objective—

Increased asymmetrical dimethylarginine (ADMA), a NO synthase inhibitor, and its congener symmetrical dimethylarginine (SDMA), predict cardiovascular and all-cause mortality in at-risk populations. Their prognostic value in the general population remains uncertain. We investigated the correlations of SDMA and ADMA with atherosclerosis and cardiovascular/all-cause mortality in the Dallas Heart Study, a multiethnic probability-based cohort aged 30 to 65 years.

Approach and Results—

SDMA and ADMA were measured by liquid chromatography-tandem mass-spectrometry (n=3523), coronary artery calcium by electron-beam computed tomography, and abdominal aortic wall thickness by MRI. In unadjusted analyses, categories of increasing SDMA and ADMA were associated with higher prevalence of cardiovascular risk factors, increased risk markers, and all-cause and cardiovascular mortality (median follow-up, 7.4 years). After adjustment for age, sex, and race, traditional cardiovascular risk factors, and renal function, SDMA and ADMA analyzed as continuous variables were associated with coronary artery calcium >10, but only SDMA was associated with abdominal aortic wall thickness. SDMA, but not ADMA, was associated with cardiovascular mortality (hazard ratio per log unit change, 3.36 [95% confidence interval, 1.49–7.59]; P =0.004). SDMA and ADMA were both associated with all-cause mortality, but after further adjustment for N-terminal pro–brain-type natriuretic peptide, high-sensitivity C-reactive protein, and high-sensitivity cardiac troponin T, only SDMA was associated with all-cause mortality (hazard ratio per log unit change, 1.86 [95% confidence interval, 1.04–3.30]; P =0.01).

Conclusions—

SDMA, but not ADMA, was an independent predictor of all-cause and cardiovascular mortality in a large multiethnic population-based cohort.

What evidence is there for intraoperative predictors of perioperative cardiac outcomes? A systematic review

Background

Patients undergo cardiac preoperative evaluation to identify those at risk of adverse perioperative cardiac events. The Revised Cardiac Risk index is commonly used for this task, although it is unable to accurately risk stratify in all patients. This may be partly a result of intraoperative events which significantly modify preoperative risk.

Methods

We conducted a systematic review to identify independent intraoperative predictors of adverse cardiac events in patients undergoing non-cardiac surgery. Four databases (Ovid Healthstar 1966 to Jan 2012, Ovid Medline 1946 to 6 March 2012, EMBASE 1974 to March 05 2012 and The Cochrane Library to March 06 2012) were searched.

Results

Fourteen eligible studies were identified. The need for intraoperative blood transfusion (odds ratio (OR), 2.3; 95% confidence interval (CI), 1.4-3.3), vascular surgery (OR, 2.3; 95% CI, 1.2-3.4) and emergent/urgent surgery (OR, 2.3; 95% CI, 1.1-3.5) were the only independent intraoperative risk predictors identified in more than study. Other independent intraoperative factors identified included a >20 mmHg fall in mean arterial blood pressure for > 60 min (OR, 3.0; 95% CI, 1.8-4.9), >30% increase in baseline systolic pressure (OR, 8.0; 95% CI, 1.3-50), tachycardia in the recovery room (>30 beats per min (bpm) from baseline for >5 min) (OR, 7; 95% CI, 1.9-26), new onset atrial fibrillation (OR, 6.6; 95% CI, 2.5-20), hypothermia (OR, 2.2; 95% CI, 1.1-5) and remote ischemic preconditioning (OR, 0.22; 95% CI, 0.07-0.67). Other markers of surgical complexity were not independently associated with postoperative adverse cardiac outcomes. None of these studies controlled for blood transfusion.

Conclusions

Intraoperative events significantly increase the risk for postoperative cardiac complications, although only intraoperative blood transfusion has strong evidence supporting this finding. It is possible that modification of these intraoperative risk factors by anesthetists and surgeons may reduce postoperative cardiac events and improve outcome. The Vascular Events in Noncardiac Surgery Patients Cohort Evaluation (VISION) Study will add important information to understanding intraoperative risk factors for adverse cardiac events.

Circulating levels of dimethylarginines, chronic kidney disease and long-term clinical outcome in non-ST-elevation myocardial infarction

BACKGROUND

Mechanisms linking chronic kidney disease (CKD) and adverse outcomes in acute coronary syndromes (ACS) are not fully understood. Among potential key players, reduced nitric oxide (NO) synthesis due to its endogenous inhibitors, asymmetric (ADMA) and symmetric (SDMA) dimethylarginine could be involved. We measured plasma concentration of arginine, ADMA and SDMA and investigated their relationship with CKD and long-term outcome in non-ST-elevation myocardial infarction (NSTEMI).

METHODOLOGY/PRINCIPAL FINDINGS

We prospectively measured arginine, ADMA, and SDMA at hospital admission in 104 NSTEMI patients. CKD was defined as an estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2). We considered a primary end point of combined cardiac death and re-infarction at a median follow-up of 21 months. In CKD (n = 33) and no-CKD (n = 71) patients, arginine and ADMA were similar, whereas SDMA was significantly higher in CKD patients (0.65±0.23 vs. 0.42±0.12 µmol/L; P<0.0001). Twenty-four (23%) patients had an adverse cardiac event during follow-up: 12 (36%) were CKD and 12 (17%) no-CKD patients (P = 0.02). When study population was stratified according to arginine, ADMA and SDMA median values, only SDMA (median 0.46 µmol/L) was associated with the primary end-point (P = 0.0016). In models adjusted for age, hemoglobin and left ventricular ejection fraction, the hazard ratio (HR) for CKD and SDMA were high (HR 2.93, interquartile range [IQR] 1.15-7.53; P = 0.02 and HR 6.80, IQR 2.09-22.2; P = 0.001, respectively) but, after mutual adjustment, only SDMA remained significantly associated with the primary end point (HR 5.73, IQR 1.55-21.2; P = 0.009).

CONCLUSIONS/SIGNIFICANCE

In NSTEMI patients, elevated SDMA plasma levels are associated with CKD and worse long-term prognosis.

Asymmetric dimethylarginine, an endogenous NOS inhibitor, is actively metabolized in rat erythrocytes

N(G), N(G)-Dimethyl-L-arginine (asymmetric dimethylarginine: ADMA) is an endogenous competitive inhibitor of nitric oxide synthase (NOS). Plasma ADMA concentrations have been reported to increase in connection with diseases associated with an impaired endothelial L-arginine/NO pathway. In this study, we investigated the metabolism of ADMA in circulating blood cell populations to elucidate the regulatory mechanism of elevation of plasma ADMA, a novel risk factor for cardiovascular disease. We found by RT-PCR and Western blot analyses that protein arginine methyltransferase (PRMT)1 and dimethylarginine dimethylaminohydrolase (DDAH)-1, responsible for the biosynthesis and degradation of ADMA respectively, are expressed in erythrocytes (ECs), leukocytes, and platelets. We also identified a major ADMA-containing protein in ECs as catalase, confirmed by GST-pull down assay to bind to PRMT1 in vitro. This is the first report that the ADMA-metabolizing system, including the arginine methylation of proteins and the breakdown of free ADMA, occurs in circulating blood cell-populations, and that catalase in ECs might be a potential protein targeted by PRMT1.

The Role of Asymmetric Dimethylarginine (ADMA) in Endothelial Dysfunction and Cardiovascular Disease

Endothelium plays a crucial role in the maintenance of vascular tone and structure. Endothelial dysfunction is known to precede overt coronary artery disease. A number of cardiovascular risk factors, as well as metabolic diseases and systemic or local inflammation cause endothelial dysfunction. Nitric oxide (NO) is one of the major endothelium derived vaso-active substances whose role is of prime importance in maintaining endothelial homeostasis. Low levels of NO are associated with impaired endothelial function. Asymmetric dimethylarginine (ADMA), an analogue of L-arginine, is a naturally occurring product of metabolism found in human circulation. Elevated levels of ADMA inhibit NO synthesis and therefore impair endothelial function and thus promote atherosclerosis. ADMA levels are increased in people with hypercholesterolemia, atherosclerosis, hypertension, chronic heart failure, diabetes mellitus and chronic renal failure. A number of studies have reported ADMA as a novel risk marker of cardiovascular disease. Increased levels of ADMA have been shown to be the strongest risk predictor, beyond traditional risk factors, of cardiovascular events and all-cause and cardiovascular mortality in people with coronary artery disease. Interventions such as treatment with L-arginine have been shown to improve endothelium-mediated vasodilatation in people with high ADMA levels. However the clinical utility of modifying circulating ADMA levels remains uncertain.

Role of dimethylarginine dimethylaminohydrolases in the regulation of endothelial nitric oxide production

Reduced NO is a hallmark of endothelial dysfunction, and among the mechanisms for impaired NO synthesis is the accumulation of the endogenous nitric-oxide synthase inhibitor asymmetric dimethylarginine (ADMA). Free ADMA is actively metabolized by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH), which catalyzes the conversion of ADMA to citrulline. Decreased DDAH expression/activity is evident in disease states associated with endothelial dysfunction and is believed to be the mechanism responsible for increased methylarginines and subsequent ADMA-mediated endothelial nitric-oxide synthase impairment. Two isoforms of DDAH have been identified; however, it is presently unclear which is responsible for endothelial ADMA metabolism and NO regulation. The current study investigated the effects of both DDAH-1 and DDAH-2 in the regulation of methylarginines and endothelial NO generation. Results demonstrated that overexpression of DDAH-1 and DDAH-2 increased endothelial NO by 24 and 18%, respectively. Moreover, small interfering RNA-mediated down-regulation of DDAH-1 and DDAH-2 reduced NO bioavailability by 27 and 57%, respectively. The reduction in NO production following DDAH-1 gene silencing was associated with a 48% reduction in l-Arg/ADMA and was partially restored with l-Arg supplementation. In contrast, l-Arg/ADMA was unchanged in the DDAH-2-silenced cells, and l-Arg supplementation had no effect on NO. These results clearly demonstrate that DDAH-1 and DDAH-2 manifest their effects through different mechanisms, the former of which is largely ADMA-dependent and the latter ADMA-independent. Overall, the present study demonstrates an important regulatory role for DDAH in the maintenance of endothelial function and identifies this pathway as a potential target for treating diseases associated with decreased NO bioavailability.

Regulation of the ADMA-DDAH system in endothelial cells: a novel mechanism for the sterol response element binding proteins, SREBP1c and -2

Asymmetric dimethylarginine (ADMA) has been implicated in the progression of cardiovascular disease as an endogenous inhibitor of nitric oxide synthase. The regulation of dimethylarginine dimethylaminohydrolase (DDAH), the enzyme responsible for metabolizing ADMA, is poorly understood. The transcription factor sterol response element binding protein (SREBP) is activated by statins via a reduction of membrane cholesterol content. Because the promoters of both DDAH1 and DDAH2 isoforms contain sterol response elements, we tested the hypothesis that simvastatin regulates DDAH1 and DDAH2 transcription via SREBP. In cultured endothelial cells, simvastatin increased DDAH1 mRNA expression compared with vehicle. In an ADMA loading experiment, simvastatin treatment resulted in a decrease in ADMA content, an indication of increased DDAH activity. The knockdown of SREBP1c protein led to an increase in DDAH1 mRNA expression and activity, whereas the knockdown of SREBP2 led to a decrease in DDAH1 mRNA expression. The role of SREBP2 in the activation of the DDAH1 was supported by chromatin immunoprecipitation studies demonstrating increased binding of SREBP2 to the DDAH1 promoter upon simvastatin stimulation. These data indicate that SREBP1c might act as a repressor and SREBP2 as an activator of DDAH transcription and activity. This study describes a novel mechanism of reciprocal regulation by the SREBP family members of the DDAH-ADMA system, which represents a potential link between cellular cholesterol content and endothelial dysfunction observed in cardiovascular disease.

Role of the PRMT-DDAH-ADMA axis in the regulation of endothelial nitric oxide production

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), formed in healthy vascular endothelium from the amino acid precursor l-arginine. Endothelial dysfunction is increased by various cardiovascular risk factors, metabolic diseases, and systemic or local inflammation. One mechanism that has been implicated in the development of endothelial dysfunction is the presence of elevated levels of asymmetric dimethylarginine (ADMA). Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH) which catalyzes the conversion of ADMA to citrulline and dimethylamine. It has been estimated that more than 70% of ADMA is metabolized by DDAH (Achan et al. [1]). Decreased DDAH expression/activity is evident in disease states associated with endothelial dysfunction and is believed to be the mechanism responsible for increased methylarginines and subsequent ADMA mediated eNOS impairment. However, recent studies suggest that DDAH may regulate eNOS activity and endothelial function through both ADMA-dependent and -independent mechanisms. In this regard, elevated plasma ADMA may serve as a marker of impaired methylarginine metabolism and the pathology previously attributed to elevated ADMA may be manifested, at least in part, through altered activity of the enzymes involved in ADMA regulation, specifically DDAH and PRMT.

Asymmetric dimethylarginine (ADMA) as a prospective marker of cardiovascular disease and mortality--an update on patient populations with a wide range of cardiovascular risk

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthases. By inhibiting NO formation, ADMA causes endothelial dysfunction, vasoconstriction, elevation of blood pressure, and aggravation of experimental atherosclerosis. Cross-sectional studies in humans have revealed that ADMA plasma concentration is elevated in numerous populations with vascular diseases or at high cardiovascular risk. However, the potential causal relationship between elevated ADMA and cardiovascular events and mortality in humans can only be revealed in prospective clinical studies. This review gives an overview of currently available data from prospective clinical studies in which ADMA has been measured in populations at high, intermediate, or low global vascular risk. Although the analytical methods used to quantify ADMA varied and statistical approaches to assess the association of ADMA with risk differed, these data reveal that ADMA is significantly associated with an increased risk of incident cardiovascular events and total mortality in subjects at a broad range of global risk. Hazard ratios were mostly in a range comparable to that of traditional cardiovascular risk markers even after multivariable adjustments, suggesting that ADMA may be suitable as a diagnostic marker for risk assessment, and that the biochemical pathways that regulate ADMA may be promising therapeutic approaches to treat cardiovascular disease in the future.

Plasma asymmetric dimethylarginine and incidence of cardiovascular disease and death in the community

BACKGROUND

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, induces endothelial dysfunction. Although elevated ADMA has been associated with an increased risk of cardiovascular disease events and death in referral samples, the prognostic significance of ADMA in the community has not been adequately evaluated.

METHODS AND RESULTS

We related plasma ADMA, l-arginine (Arg), and the ratio of Arg to ADMA to the incidence of cardiovascular disease (fatal or nonfatal myocardial infarction, coronary insufficiency, angina pectoris, stroke or transient ischemic attack, intermittent claudication, or heart failure) and death in 3320 Framingham Offspring Study participants (1769 women; mean age, 59 years). Over a follow-up period of 10.9 years, 281 individuals of 2956 free of cardiovascular disease at baseline developed incident cardiovascular disease, and 285 participants died. In multivariable models adjusting for established risk factors and other biomarkers (B-type natriuretic peptide, renin, homocysteine, urine albumin excretion, and C-reactive protein), ADMA and the ratio of Arg to ADMA were significantly associated with all-cause mortality (adjusted-hazard ratio [HR] per 1-SD increment, 1.21; 95% CI, 1.07 to 1.37; and HR per 1-SD increment, 0.80; 95% CI, 0.69 to 0.93, respectively), whereas Arg was not (HR per 1-SD increment, 0.89; 95% CI, 0.77 to 1.02). We noted effect modification by diabetes status; ADMA was associated with death in individuals without diabetes (adjusted HR per 1-SD increment, 1.30; 95% CI, 1.13 to 1.50) but not in individuals with diabetes (adjusted HR per 1-SD increment, 0.85; 95% CI, 0.62 to 1.16). ADMA, Arg, and the ratio of Arg to ADMA were not associated with cardiovascular disease incidence (P>0.10).

CONCLUSIONS

In our large community-based sample, ADMA was significantly associated with all-cause mortality, particularly in nondiabetic individuals.

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).