Symmetric dimethylarginine as a proinflammatory agent in chronic kidney disease

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

Dimethylarginines in patients with intracerebral hemorrhage: association with outcome, hematoma enlargement, and edema

BACKGROUND

Asymmetric dimethylarginine (ADMA)--the most potent endogenous NO-synthase inhibitor, has been regarded as mediator of endothelial dysfunction and oxidative stress. Considering experimental data, levels of ADMA and its structural isomer symmetric dimethylarginine (SDMA) might be elevated after intracerebral hemorrhage (ICH) and associated with clinical outcome and secondary brain injury.

METHODS

Blood samples from 20 patients with acute ICH were taken at ≤ 24 h and 3 and 7 days after the event. Nine patients had favorable (modified Rankin Scale (mRS) at 90 days 0-2) outcome, and 11 patients unfavorable outcome (mRS 3-6). Patients' serum ADMA, SDMA, and L-arginine levels were determined by high-performance liquid chromatography-tandem mass spectrometry. Levels were compared to those of 30 control subjects without ICH. For further analysis, patients were grouped according to outcome, hematoma and perihematomal edema volumes, occurrence of hematoma enlargement, and cytotoxic edema as measured by computed tomography and serial magnetic resonance imaging.

RESULTS

Levels of ADMA--but not SDMA and L-arginine--were elevated in ICH patients compared to controls (binary logistic regression analysis: ADMA ≤ 24 h, p = 0.003; 3 days p = 0.005; 7 days p = 0.004). If patients were grouped according to outcome, dimethylarginines were increased in patients with unfavorable outcome. The binary logistic regression analysis confirmed an association of SDMA levels ≤ 24 h (p = 0.048) and at 3 days (p = 0.028) with unfavorable outcome. ADMA ≤ 24 h was increased in patients with hematoma enlargement (p = 0.003), while SDMA ≤ 24 h was increased in patients with large hematoma (p = 0.029) and perihematomal edema volume (p = 0.023).

CONCLUSIONS

Our data demonstrate an association between dimethylarginines and outcome of ICH. However, further studies are needed to confirm this relationship and elucidate the mechanisms behind.

Symmetric Dimethylarginine in Cats with Hypertrophic Cardiomyopathy and Diabetes Mellitus

Background

Symmetric dimethylarginine (SDMA) has been increasingly used as a marker of early chronic kidney disease (CKD) in cats, but little is known about the influence of comorbidities on SDMA in this species.

Hypothesis

Hypertrophic cardiomyopathy (HCM) and diabetes mellitus (DM), independently of CKD, are associated with changes in serum SDMA.

Animals

Ninety‐four cats (17 with CKD, 40 with HCM, 17 with DM, and 20 healthy controls).

Methods

Case‐control study. Clinical examination, echocardiography, ECG, blood pressure, CBC, biochemistry, thyroxine, and SDMA measurement were performed. Urinalysis was performed in controls and cats with CKD and DM. Analysis of variance was used to compare overall differences in the log‐transformed SDMA data among groups. A random forest algorithm was applied to explore which clinical and other factors influenced serum SDMA.

Results

Median (range) serum SDMA for the renal group (positive control) was 19 (10–93) μg/dL, whereas for the control group (negative control), it was 10 (5–15) μg/dL. For the cardiac and diabetic groups, serum SDMA was 9 (4–24) μg/dL and 7 (3–11) μg/dL, respectively. The renal group had significantly higher SDMA concentrations and the diabetic group significantly lower SDMA concentrations compared to all other groups.

Conclusions and Clinical Importance

Serum SDMA concentrations in cats with HCM were not significantly different from those of healthy control cats. Cats with DM, however, had significantly lower SDMA concentrations than controls, a finding that needs further investigation and should be kept in mind when evaluating renal function of cats with this endocrinopathy.

Does cardiac resynchronization therapy restore peripheral circulatory homeostasis?

Aims

To evaluate whether peripheral circulatory ‘remodelling’ as measured by changes in vascular compliance and in markers of nitric oxide signalling contributes to patient response to cardiac resynchronization therapy (CRT).

Methods and results

Effects of CRT were evaluated in 33 patients pre‐procedure and 6 months post‐procedure. Peak oxygen consumption, 6 min walk distance, New York Heart Association class, and quality of life score were evaluated. Augmentation index and its interactions with nitric oxide (NO) were evaluated by applanation tonometry. Platelet NO responsiveness and content of thioredoxin‐interacting protein were assessed. Plasma concentrations of N‐terminal proBNP, asymmetric and symmetric dimethylarginine (SDMA), high sensitivity C‐reactive protein, catecholamines, and matrix metalloproteinases‐2 and ‐9 were assessed. Despite significant improvement in 6 min walk distance (P = 0.005), New York Heart Association class (P < 0.001), quality of life (P = 0.001), and all echocardiographic parameters post‐CRT, there were no significant changes in augmentation index measurements, thioredoxin‐interacting protein content, and platelet NO response. Significant falls in N‐terminal proBNP (P = 0.008) and SDMA (P = 0.013; independent of renal function) occurred. Falls in SDMA predicted reduction in high‐sensitivity C‐reactive protein (P = 0.04) and increases in peak oxygen consumption (P = 0.04). There were no correlations between changes in echocardiographic parameters and those in vascular function.

Conclusions

These data suggest that the beneficial effects of CRT over 6 months are independent of any change in peripheral NO‐related signalling. However, there is evidence that suppression of inflammation occurs, and its magnitude predicts extent of clinical improvement.

Losartan for the nephropathy of sickle cell anemia: A phase-2, multicenter trial

Nephropathy is a common and progressive complication of sickle cell anemia (SCA). In SCA mice, we found that hyperangiotensinemia in the absence of hypertension underlies nephropathy, and its downregulation by losartan, an angiotensin-II-receptor-1 blocker, reduced albuminuria and progression of nephropathy. Therefore, we performed a phase-2 trial of oral losartan, given for 6 months, to explore whether it reduced albuminuria in children and adults with SCA. Participants were allocated to groups defined by class of baseline urinary albumin-to-creatinine ratio (UACR): no albuminuria (NoA), microalbuminuria (MicroA), and macroalbuminuria (MacroA). The primary endpoint was a ≥25% reduction UACR from baseline. There were 32 evaluable participants (mean age 24 years; NoA = 14, MicroA = 12, MacroA = 6). The primary endpoint was met in 83% of the MacroA group (P < 0.0001) and 58% of the MicroA group (P < 0.0001). Median fold-change in UACR was -0.74 for MacroA and -0.46 for MicroA. In MacroA and MicroA, UACR classification improved in 50% but worsened in 11%. Urine osmolality and estimated glomerular filtration rate (eGFR) did not change significantly. Losartan was discontinued in three participants [leg cramps, N = 1; decline in eGFR >25% (142➝104 mL/minute/1.73 m² ), N = 1; rise in serum creatinine >50% (0.2➝0.3 mg/dL), N = 1]. Albuminuria was associated with diastolic dysfunction and impaired functional capacity, although cardiopulmonary status was unchanged after 6 months of losartan therapy. In summary, losartan decreased urinary albumin excretion in most participants with albuminuria. Those with macroalbuminuria had the greatest benefit. This study forms the basis for a phase-3, randomized, placebo-controlled trial of losartan for the nephropathy of SCA.

The systemic nature of CKD

The accurate definition and staging of chronic kidney disease (CKD) is one of the major achievements of modern nephrology. Intensive research is now being undertaken to unravel the risk factors and pathophysiologic underpinnings of this disease. In particular, the relationships between the kidney and other organs have been comprehensively investigated in experimental and clinical studies in the last two decades. Owing to technological and analytical limitations, these links have been studied with a reductionist approach focusing on two organs at a time, such as the heart and the kidney or the bone and the kidney. Here, we discuss studies that highlight the complex and systemic nature of CKD. Energy balance, innate immunity and neuroendocrine signalling are highly integrated biological phenomena. The diseased kidney disrupts such integration and generates a high-risk phenotype with a clinical profile encompassing inflammation, protein-energy wasting, altered function of the autonomic and central nervous systems and cardiopulmonary, vascular and bone diseases. A systems biology approach to CKD using omics techniques will hopefully enable in-depth study of the pathophysiology of this systemic disease, and has the potential to unravel critical pathways that can be targeted for CKD prevention and therapy.

Toxic Dimethylarginines: Asymmetric Dimethylarginine (ADMA) and Symmetric Dimethylarginine (SDMA)

Asymmetric and symmetric dimethylarginine (ADMA and SDMA, respectively) are toxic, non-proteinogenic amino acids formed by post-translational modification and are uremic toxins that inhibit nitric oxide (NO) production and play multifunctional roles in many human diseases. Both ADMA and SDMA have emerged as strong predictors of cardiovascular events and death in a range of illnesses. Major progress has been made in research on ADMA-lowering therapies in animal studies; however, further studies are required to fill the translational gap between animal models and clinical trials in order to treat human diseases related to elevated ADMA/SDMA levels. Here, we review the reported impacts of ADMA and SDMA on human health and disease, focusing on the synthesis and metabolism of ADMA and SDMA; the pathophysiological roles of these dimethylarginines; clinical conditions and animal models associated with elevated ADMA and SDMA levels; and potential therapies against ADMA and SDMA. There is currently no specific pharmacological therapy for lowering the levels and counteracting the deleterious effects of ADMA and SDMA. A better understanding of the mechanisms underlying the impact of ADMA and SDMA on a wide range of human diseases is essential to the development of specific therapies against diseases related to ADMA and SDMA.

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.

Coronary artery calcification scores improve contrast-induced nephropathy risk assessment in chronic kidney disease patients

BACKGROUND

Coronary artery calcification (CAC) is an independent predictor of cardiovascular morbidity and mortality in chronic kidney disease (CKD) patients. The aim of the present study was to evaluate the predictive value of CAC scores for the incidence of contrast-induced nephropathy (CIN) after cardiac catheterization in non-dialyzed CKD patients.

METHODS

The present study evaluated a total of 140 CKD patients who underwent cardiac catheterization. Patients were stratified into two groups based on the optimal cut-off value of the CAC score, which was graded by a non-triggered, routine diagnostic chest computed tomography scan: CAC score ≥8 (high CAC group); and CAC score <8 (low CAC group). CIN was defined as an increase of >10 % in the baseline serum cystatin C level at 24 h after contrast administration.

RESULTS

The mean estimated glomerular filtration rate levels were 41.1 mL/min/1.73 m², and the mean contrast dose administered was 37.5 mL. Patients with high CAC scores exhibited a higher incidence of CIN than patients with low CAC scores (25.5 vs. 3.2 %, p < 0.001). After multivariate adjustment for confounders, the CAC score predicted CIN (odds ratio 1.68, 95 % confidence interval 1.28-2.21, p < 0.001). Moreover, the C-index for CIN prediction significantly increased when the CAC scores were added to the Mehran risk score (0.855 vs. 0.760, p = 0.023).

CONCLUSION

CAC scores, as evaluated using semi-quantitative methods, are a simple and powerful predictor of CIN. Incorporating the CAC score in the Mehran risk score significantly improved the predictive ability to predict CIN incidence.

Determination of Asymmetric and Symmetric Dimethylarginine in Serum from Patients with Chronic Kidney Disease: UPLC-MS/MS versus ELISA

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis, and its structural isomer symmetric dimethylarginine (SDMA) are uremic toxins accumulating in chronic kidney disease (CKD) patients. The objective of this study was to develop and validate a robust UPLC-MS/MS method for the simultaneous determination of ADMA and SDMA in human serum. Chromatographic separation after butyl ester derivatization was achieved on an Acquity UPLC BEH C18 column, followed by tandem mass spectrometric detection. After validation, the applicability of the method was evaluated by the analysis of serum samples from 10 healthy controls and 77 CKD patients on hemodialysis (CKD5HD). Both ADMA (0.84 ± 0.19 µM vs. 0.52 ± 0.07 µM) and SDMA concentrations (2.06 ± 0.82 µM vs. 0.59 ± 0.13 µM) were significantly (p < 0.001) elevated in CKD5HD patients compared to healthy controls. In general, low degrees of protein binding were found for both ADMA and SDMA. In addition, an established commercially available ELISA kit was utilized on the same samples (n = 87) to compare values obtained both with ELISA and UPLC-MS/MS. Regression analysis between these two methods was significant (p < 0.0001) but moderate for both ADMA (R = 0.78) and SDMA (R = 0.72).

Kt/Vurea and Nonurea Small Solute Levels in the Hemodialysis Study

The Hemodialysis (HEMO) Study showed that high-dose hemodialysis providing a single-pool Kt/V_urea of 1.71 provided no benefit over a standard treatment providing a single-pool Kt/V_urea of 1.32. Here, we assessed whether the high-dose treatment used lowered plasma levels of small uremic solutes other than urea. Measurements made ≥3 months after randomization in 1281 patients in the HEMO Study showed a range in the effect of high-dose treatment compared with that of standard treatment: from no reduction in the level of p-cresol sulfate or asymmetric dimethylarginine to significant reductions in the levels of trimethylamine oxide (-9%; 95% confidence interval [95% CI], -2% to -15%), indoxyl sulfate (-11%; 95% CI, -6% to -15%), and methylguanidine (-22%; 95% CI, -18% to -27%). Levels of three other small solutes also decreased slightly; the level of urea decreased 9%. All-cause mortality did not significantly relate to the level of any of the solutes measured. Modeling indicated that the intermittency of treatment along with the presence of nondialytic clearance and/or increased solute production accounted for the limited reduction in solute levels with the higher Kt/V_urea In conclusion, failure to achieve greater reductions in solute levels may explain the failure of high Kt/V_urea treatment to improve outcomes in the HEMO Study. Furthermore, levels of the nonurea solutes varied widely among patients in the HEMO Study, and achieved Kt/V_urea accounted for very little of this variation. These results further suggest that an index only on the basis of urea does not provide a sufficient measure of dialysis adequacy.

Ageing/Menopausal Status in Healthy Women and Ageing in Healthy Men Differently Affect Cardiometabolic Parameters

BACKGROUND

Gender medicine requires a global analysis of an individual's life. Menopause and ageing induce variations of some cardiometabolic parameters, but, it is unknown if this occurs in a sex-specific manner. Here, some markers of oxidative stress, systemic inflammation, and endothelial dysfunction are analysed in men younger and older than 45 years and in pre- and postmenopausal women.

METHODS

Serum and plasma sample were assayed for TNF-α and IL-6, malondialdehyde and protein carbonyls and for methylated arginines using ELISA kits, colorimetric methods and capillary electrophoresis.

RESULTS

Before body weight correction, men overall had higher creatinine, red blood cells and haemoglobin and lower triglycerides than women. Men younger than 45 years had lower levels of TNF-α and malondialdehyde and higher levels of arginine than age-matched women, while postmenopausal women had higher IL-6 concentrations than men, and higher total cholesterol, triglycerides, creatinine and IL-6 levels than younger women. Men younger than 45 years had lower total cholesterol and malondialdehyde than older men. After correction, some differences remained, others were amplified, others disappeared and some new differences emerged. Moreover, some parameters showed a correlation with age, and some of them correlated with each other as functions of ageing and ageing/menopausal status.

CONCLUSIONS

Ageing/menopausal status increased many more cardiovascular risk factors in women than ageing in men, confirming that postmenopausal women had increased vascular vulnerability and indicating the need of early cardiovascular prevention in women. Sex-gender differences are also influenced by body weight, indicating as a matter of debate whether body weight should be seen as a true confounder or as part of the causal pathway.

Challenges and opportunities for stem cell therapy in patients with chronic kidney disease

Chronic kidney disease (CKD) is a global health care burden affecting billions of individuals worldwide. The kidney has limited regenerative capacity from chronic insults, and for the most common causes of CKD, no effective treatment exists to prevent progression to end-stage kidney failure. Therefore, novel interventions, such as regenerative cell-based therapies, need to be developed for CKD. Given the risk of allosensitization, autologous transplantation of cells to boost regenerative potential is preferred. Therefore, verification of cell function and vitality in CKD patients is imperative. Two cell types have been most commonly applied in regenerative medicine. Endothelial progenitor cells contribute to neovasculogenesis primarily through paracrine angiogenic activity and partly by differentiation into mature endothelial cells in situ. Mesenchymal stem cells also exert paracrine effects, including proangiogenic, anti-inflammatory, and antifibrotic activity. However, in CKD, multiple factors may contribute to reduced cell function, including older age, coexisting cardiovascular disease, diabetes, chronic inflammatory states, and uremia, which may limit the effectiveness of an autologous cell-based therapy approach. This Review highlights current knowledge on stem and progenitor cell function and vitality, aspects of the uremic milieu that may serve as a barrier to therapy, and novel methods to improve stem cell function for potential transplantation.

Serum amine-based metabolites and their association with outcomes in primary prevention implantable cardioverter-defibrillator patients

AIMS

Heart failure patients are at increased risk of ventricular arrhythmias and all-cause mortality. However, existing clinical and serum markers only modestly predict these adverse events. We sought to use metabolic profiling to identify novel biomarkers in two independent prospective cohorts of patients with implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden cardiac death (SCD).

METHODS AND RESULTS

Baseline serum was quantitatively profiled for 42 known biologically relevant amine-based metabolites among 402 patients from the Prospective Observational Study of Implantable Cardioverter-Defibrillators (PROSE-ICD) Study (derivation group) and 240 patients from the Genetic Risk Assessment of Defibrillator Events (GRADE) Study (validation group) for ventricular arrhythmia-induced ICD shocks and all-cause mortality. Three amines, N-methyl-l-histidine, symmetric dimethylarginine (SDMA), and l-kynurenine, were derived and validated to be associated with all-cause mortality. The hazard ratios of mortality in PROSE-ICD and GRADE were 1.48 (95% confidence interval 1.14-1.92) and 1.67 (1.22-2.27) for N-methyl-l-histidine, 1.49 (1.17-1.91) and 1.77 (1.27-2.45) for SDMA, 1.31 (1.06-1.63) and 1.73 (1.32-2.27) for l-kynurenine, respectively. l-Histidine, SDMA, and l-kynurenine were associated with ventricular arrhythmia-induced ICD shocks in PROSE-ICD, but they did not reach statistical significance in the GRADE cohort.

CONCLUSION

Utilizing metabolic profiling in two independent prospective cohorts of patients undergoing ICD implantation for primary prevention of SCD, we identified several novel amine markers that were associated with appropriate shock and mortality. These findings shed insight into the potential biologic pathways leading to adverse events in ICD patients. Further studies are needed to confirm the prognostic value of these findings.

Future Avenues to Decrease Uremic Toxin Concentration

In this article, we review approaches for decreasing uremic solute concentrations in chronic kidney disease and in particular, in end-stage renal disease (ESRD). The rationale to do so is the straightforward relation between concentration and biological (toxic) effect for most toxins. The first section is devoted to extracorporeal strategies (kidney replacement therapy). In the context of high-flux hemodialysis and hemodiafiltration, we discuss increasing dialyzer blood and dialysate flows, frequent and/or extended dialysis, adsorption, bioartificial kidney, and changing physical conditions within the dialyzer (especially for protein-bound toxins). The next section focuses on the intestinal generation of uremic toxins, which in return is stimulated by uremic conditions. Therapeutic options are probiotics, prebiotics, synbiotics, and intestinal sorbents. Current data are conflicting, and these issues need further study before useful therapeutic concepts are developed. The following section is devoted to preservation of (residual) kidney function. Although many therapeutic options may overlap with therapies provided before ESRD, we focus on specific aspects of ESRD treatment, such as the risks of too-strict blood pressure and glycemic regulation and hemodynamic changes during dialysis. Finally, some recommendations are given on how research might be organized with regard to uremic toxins and their effects, removal, and impact on outcomes of uremic patients.

Symmetric Dimethylarginine Is Not Associated with Cumulative Inflammatory Load or Classical Cardiovascular Risk Factors in Rheumatoid Arthritis: A 6-Year Follow-Up Study

Symmetric dimethylarginine (SDMA) indirectly inhibits nitric oxide (NO) synthesis and predicts cardiovascular and all-cause mortality in high-risk patients. The aim of our study was to investigate the associations of cumulative inflammatory burden (assessed by serial measurements of inflammatory markers) and classical cardiovascular (CV) disease risk factors with SDMA in RA patients. 201 RA patients (155 females, median age 67 (59–73)) were assessed at baseline (2006). Classical CV disease risk factors were recorded and systemic inflammation was determined by the measurement of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). At follow-up (2012) SDMA levels were measured by enzyme-linked immunosorbent assay. Mean SDMA levels in RA population were 0.40 (0.40–0.53) μmol/L. No significant association between SDMA and cumulative inflammatory load was established in the analysis. SDMA levels were not found to be significantly related to CV disease risk factors. We explored the potential relationship between SDMA and cumulative inflammatory burden in patients with RA and obtained negative results. SDMA did not relate to CV disease risk factors in our population and its clinical significance as a surrogate marker of endothelial dysfunction in patients with RA remains to be determined.

Subtle renal dysfunction and bleeding risk in atrial fibrillation: symmetric dimethylarginine predicts HAS-BLED score

BACKGROUND

Risk of substantial haemorrhage represents a critically important limitation to effective anti-thrombotic treatment in patients with atrial fibrillation (AF). While it is known that this risk is increased in anticoagulated patients either in the presence of anti-aggregatory drugs or concomitant renal insufficiency, there are currently few data on the potential interactions between endogenous platelet aggregability and bleeding risk.

OBJECTIVE

We therefore evaluated in a cohort of AF patients: (1), the putative relationship between platelet aggregability and HAS-BLED score; (2), the potential biochemical bases for such a relationship.

METHODS

Patients were included as part of SAFETY, a randomised controlled trial evaluating outpatient management of AF patients. Platelet response to ADP was evaluated via whole blood impedance aggregometry; clinical and biochemical correlates of platelet aggregation were sought via univariate and multivariate analysis.

RESULTS

Platelet aggregation correlated inversely (r=-0.220, p<0.05) with HAS-BLED score. Univariate biochemical correlates of decreased platelet aggregation were plasma concentrations of symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA). On multivariate analyses, plasma SDMA concentration (β=-0.318, p<0.01), platelet content of thioredoxin-interacting protein (Txnip, β=0.261, p<0.05) and plasma thrombospondin-1 (TSP-1, β=0.249, p<0.05) concentration were predictive of platelet ADP response. Consistent with previous reports, plasma SDMA concentrations were strongly and inversely correlated with estimated glomerular filtration rate (eGFR, r=-0.780, p<0.001).

CONCLUSIONS

These data therefore suggest that (1), physiologically impaired, like pharmacologically impaired, platelet aggregability may increase bleeding risk in anticoagulated AF patients; (2), the biochemical basis for this may include impaired effects of nitric oxide (via Txnip, TSP-1) but also concomitant renal dysfunction.

Pathogenesis of drug-resistant hypertension

More is known about the epidemiology of drug-resistant hypertension than particular pathogenic factors and pathways. Several recurring themes, however, seem evident on using insight from epidemiology and general knowledge of the pathophysiology of hypertension. Specifically, 4 main pathways converge on drug resistance including sodium handling, sympathetic nervous system activation, endothelial dysfunction, and arterial stiffness. These factors, and the various pathways and elements contributing to them, are reviewed. In addition to describing how these factors exert their individual influences on resistant hypertension, several examples of how interactions between these factors, particularly in the case of chronic kidney disease, are included. At the conclusion of this review some thoughts are offered on additional mechanisms and areas for potential research.

Platelet hyperaggregability in patients with atrial fibrillation. Evidence of a background proinflammatory milieu

OBJECTIVE

Atrial fibrillation (AF) is a condition where platelet hyperaggregability is commonly present. We examined potential physiological bases for platelet hyperaggregability in a cohort of patients with acute and chronic AF. In particular, we sought to identify the impact of inflammation [myeloperoxidase (MPO) and C-reactive protein (CRP)] and impaired nitric oxide (NO) signaling.

METHODS

Clinical and biochemical determinants of adenosine diphosphate (ADP)-induced platelet aggregation were sought in patients (n = 106) hospitalized with AF via univariate and multivariate analysis.

RESULTS

Hyper-responsiveness of platelets to ADP was directly (r = 0.254, p < 0.01) correlated with plasma concentrations of thrombospondin-1 (TSP-1), a matricellular protein that impairs NO responses and contributes to development of oxidative stress. In turn, plasma TSP-1 concentrations were directly correlated with MPO concentrations (r = 0.221, p < 0.05), while MPO concentrations correlated with those of asymmetric dimethylarginine (ADMA, r = 0.220, p < 0.05), and its structural isomer symmetric dimethylarginine (SDMA, r = 0.192, p = 0.05). Multivariate analysis identified TSP-1 (β = 0.276, p < 0.05) concentrations, as well as female sex (β = 0.199, p < 0.05), as direct correlates of platelet aggregability, and SDMA concentrations (β = - 0.292, p < 0.05) as an inverse correlate.

CONCLUSION

We conclude that platelet hyperaggregability, where present in the context of AF, may be engendered by impaired availability of NO, as well as via MPO-related inflammatory activation.

Symmetric Dimethylarginine Assay Validation, Stability, and Evaluation as a Marker for the Early Detection of Chronic Kidney Disease in Dogs

BACKGROUND

Symmetric dimethylarginine (SDMA) is a small molecule formed by methylation of arginine, and released into blood during protein degradation. SDMA is primarily eliminated by renal excretion and is a promising endogenous marker of glomerular filtration rate (GFR).

OBJECTIVES

To validate an assay for SDMA measurement, determine stability of SDMA in blood, and compare SDMA with serum creatinine concentration (sCr) and GFR for early detection of decreasing kidney function in dogs with chronic kidney disease (CKD).

ANIMALS

Eight male dogs affected with X-linked hereditary nephropathy and 4 unaffected male littermates.

METHODS

Prospective study validating SDMA measurement using liquid chromatography-mass spectrometry, assessing stability of SDMA in serum and plasma, and serially determining sCr, SDMA, and GFR (using iohexol clearance) in dogs during progression from preclinical disease to end-stage renal failure. Correlations were determined using linear regression. Timepoints at which sCr, SDMA, and GFR identified decreased renal function were compared using defined cutoffs, trending in an individual dog, and comparison with unaffected littermates.

RESULTS

Symmetric dimethylarginine was highly stable in serum and plasma, and the assay demonstrated excellent analytical performance. In unaffected dogs, SDMA remained unchanged whereas in affected dogs, SDMA increased during disease progression, correlating strongly with an increase in sCr (r = 0.95) and decrease in GFR (r = -0.95). Although trending improved sCr's sensitivity, SDMA identified, on average, <20% decrease in GFR, which was earlier than sCr using any comparison method.

CONCLUSIONS AND CLINICAL IMPORTANCE

Symmetric dimethylarginine is useful for both early identification and monitoring of decreased renal function in dogs with CKD.

Uraemic toxins and new methods to control their accumulation: game changers for the concept of dialysis adequacy

The current concept of an adequate dialysis based only on the dialysis process itself is rather limited. We now have considerable knowledge of uraemic toxicity and improved tools for limiting uraemic toxin accumulation. It is time to make use of these. A broader concept of adequacy that focusses on uraemic toxicity is required. As discussed in the present review, adequacy could be achieved by many different methods in combination with, or instead of, dialysis. These include preservation of renal function, dietary intake, reducing uraemic toxin generation rate and intestinal absorption, isolated ultrafiltration and extracorporeal adsorption of key uraemic toxins. A better measure of the quality of dialysis treatment would quantify the uraemic state in the patient using levels of a panel of key uraemic toxins. Treatment would focus on controlling uraemic toxicity while reducing harm or inconvenience to the patient. Delivering more dialysis might not be the best way to achieve this.

Transcriptome analysis in patients with chronic kidney disease on hemodialysis disclosing a key role for CD16+CX3CR1+ monocytes

The risk for cardiovascular morbidity and mortality is increased in chronic kidney disease; in this process micro-inflammation plays an essential role. Responsible mechanisms remain to a large extent unidentified. In this pilot study transcriptome analysis of peripheral blood monocytes was used to identify in an unprejudiced manner which factors could be discriminative for cardiovascular disease in patients with chronic kidney disease on hemodialysis. Forty gender- and age-matched, non-diabetic, non-smoking subjects with CRP < 20 mg/L were recruited: 9 healthy controls, 11 patients with eGFR > 60 mL/min/1.73m² and a history of cardiovascular event (CVE), 10 patients with chronic kidney disease stage 5 on hemodialysis without previous cardiovascular event (CKD5HD) and 10 with a previous cardiovascular event (CKD5HD/CVE). Monocytes were isolated and their mRNA was submitted to focused transcriptome analysis using a macroarray platform containing ca. 700 genes associated with macrophage functional capacity. The macroarray data indicated 9 genes (8 upregulated and 1 downregulated) with a significant differential expression in CKD5HD/CVE vs. CVE alone, after excluding genes differentially expressed in CKD5HD vs. control. For FCGR3A (CD16) and CX3CR1 (chemokine receptor) the upregulation vs. control and vs. CVE could be confirmed by quantitative RT-PCR for all CKD5HD patients. Furthermore, CX3CR1 relative expression on monocytes correlated with CRP. Flow cytometric analysis of purified monocytes confirmed a significant increase in the percentage of CD16 positive monocytes in all CKD5HD patients vs. control and CVE. The present study indicates the importance of a specific pro-inflammatory monocyte subpopulation, positive for CD16 and the co-expressed chemokine receptor, CX3CR1, discriminative for CKD5HD patients.

Symmetric dimethylarginine as predictor of graft loss and all-cause mortality in renal transplant recipients

Supplemental digital content is available in the text.

Background

Elevated symmetric dimethylarginine (SDMA) has been shown to predict cardiovascular events and all cause mortality in diverse populations. The potential role of SDMA as a risk marker in renal transplant recipients (RTR) has not been investigated.

Methods

We analyzed SDMA in the placebo arm of the Assessment of Lescol in Renal Transplantation study, a randomized controlled trial of fluvastatin in RTR. Mean follow-up was 5.1 years. Patients were grouped into quartiles based on SDMA levels at study inclusion. Relationships between SDMA and traditional risk factors for graft function and all-cause mortality were analyzed in 925 RTR using univariate and multivariate survival analyses.

Results

In univariate analysis, SDMA was significantly associated with renal graft loss, all-cause death, and major cardiovascular events. After adjustment for established risk factors including estimated glomerular filtration rate, an elevated SDMA-level (4th quartile, >1.38 μmol/L) was associated with renal graft loss; hazard ratio (HR), 5.51; 95% confidence interval (CI), 1.95–15.57; P=0.001, compared to the 1st quartile. Similarly, SDMA in the 4th quartile was independently associated with all-cause mortality (HR, 4.56; 95% CI, 2.15–9.71; P<0.001), and there was a strong borderline significant trend for an association with cardiovascular mortality (HR, 2.86; 95% CI, 0.99–8.21; P=0.051).

Conclusion

In stable RTR, an elevated SDMA level is independently associated with increased risk of all-cause mortality and renal graft loss.

Pro-inflammatory cytokines and leukocyte oxidative burst in chronic kidney disease: culprits or innocent bystanders?

BACKGROUND

Pro-inflammatory cytokines are elevated in chronic kidney disease (CKD), a condition characterized by microinflammation with oxidative stress as key feature. However, their role in the inflammatory response at uraemic concentrations has not yet been defined. In this study, the contribution of cytokines on induction of leukocyte oxidative stress was investigated.

METHODS

Whole blood from healthy donors was incubated with 20-1400 pg/mL TNFα, 5-102.8 pg/mL IL-6, 20-400 pg/mL IL-1β and 75-1200 pg/mL IL-18 separately or in combination. Oxidative burst was measured, at baseline and after stimulation with fMLP (Phagoburst™). The effect of the TNFα blocker, adalimumab (Ada), was evaluated on TNFα-induced ROS production. Finally, the association between TNFα and the composite end point all-cause mortality or first cardiovascular event was analysed in a CKD population stage 4-5 (n = 121).

RESULTS

While interleukin (IL)-6, IL-1β and IL-18 alone induced no ROS activation of normal leukocytes, irrespective of concentrations, TNFα induced ROS activation at baseline (P < 0.01) and after fMLP stimulation (P < 0.05), but only at uraemic concentrations in the high range (400 and 1400 pg/mL). A similar pattern was observed with all cytokines in combination, but already at intermediate uraemic concentrations (all P < 0.05, except for monocytes after fMLP stimulation: n.s.), suggesting synergism between cytokines. ROS production induced by TNFα (400 pg/mL) and the cytokine combination was blocked with Ada. Uraemia-related oxidative stress in leukocytes of haemodialysis patients was however not blocked by Ada. In patients, TNFα was not associated to adverse events (HR: 1.52, 95% CI 0.81-2.85, P = 0.13).

CONCLUSION

Among several pro-inflammatory cytokines, TNFα alone was pro-oxidative but only at high-range uraemic concentrations. Adding a TNFα blocker, Ada, blocked this ROS production, but not the oxidative stress in blood samples from haemodialysis patients, suggesting that other uraemic toxins than TNFα are more crucial in this process. However, the lack of association between TNFα and mortality suggests that the role of TNFα-linked oxidative stress is limited.

The L-arginine pathway in acute ischemic stroke and severe carotid stenosis: temporal profiles and association with biomarkers and outcome

BACKGROUND

Endothelial dysfunction is associated with increased levels of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) resulting in a decreased production of nitric oxide, which regulates the vascular tone.

METHODS

Patients with acute ischemic stroke (AIS, n = 55) and asymptomatic significant carotid stenosis (AsCS, n = 44) were prospectively investigated. L-arginine, ADMA, SDMA, S100 B, and high-sensitivity C-reactive protein (hsCRP) were serially measured within 6 hours after the onset of stroke, at 24 and 72 poststroke hours. All markers were compared with healthy subjects (n = 45). The severity of AIS was daily assessed by National Institute of Health Stroke Scale scoring.

RESULTS

Even within 6 hours after the onset of stroke, L-arginine, ADMA, and SDMA were significantly higher in patients with AIS compared with both AsCS and healthy subjects. S100 B reflecting infarct size, positively correlated with the level of SDMA at 72 poststroke hours; changes in concentration of S100 B positively correlated with changes in the concentration of ADMA by 72 hours. Change in concentration of both ADMA and SDMA correlated with the change in concentration of hsCRP. Concentrations of L-arginine and hsCRP at 72 poststroke hours, respectively, were independent predictors of poststroke infection. S100 B level measured within 6 hours after the onset of AIS and hsCRP at 72 poststroke hours were independent predictors of death.

CONCLUSIONS

Metabolites of the L-arginine pathway were elevated in the very acute phase of ischemic stroke indicating a more pronounced endothelial dysfunction compared with AsCS. An increased basal L-arginine level in patients with AIS might be an adaptive mechanism; such transient elevation of the L-arginine/ADMA ratio at 24 poststroke hours may suggest that a temporary increase of L-arginine along with decrease of ADMA might be related to the protective role of L-arginine. Changes in the L-arginine pathway are predictive of poststroke infections.

Is symmetric dimethylarginine a sensitive biomarker of subclinical kidney injury in children born with low birth weight?

OBJECTIVE

The aim of this study was to investigate if Symmetric Dimethylarginine (SDMA) is a sensitive biomarker of renal function and may predict subclinical kidney injury in low birth weight (LBW) children.

METHODS

We studied 68 LBW children and 20 children as reference group. An enzyme-linked immunosorbent assay was used to measure serum SDMA and Cystatin C (Cys C).

RESULTS

SDMA levels were higher in study groups compared to reference groups. There was a strong correlation between SDMA and Cys C, also SDMA negatively correlated with eGFR.

CONCLUSION

Elevated SDMA concentration may play an important role in pathogenesis of chronic kidney disease.

Dimethylarginines: endogenous inhibitors of nitric oxide synthesis in children with falciparum malaria

BACKGROUND

Nitric oxide (NO) bioavailability is impaired in children and adults with severe falciparum malaria (SM). Asymmetric-dimethylarginine (ADMA) limits NO production by inhibiting NO synthase and is increased in adult SM. The role of ADMA in the pathogenesis of childhood SM is unknown.

METHODS

We studied Tanzanian children ages 4-8 years with malaria. Plasma levels of arginine, arginase, cell-free hemoglobin, ADMA, symmetric-dimethylarginine (SDMA), histidine-rich protein-2, and angiopoietin-2 were measured.

RESULTS

ADMA was low in children with SM relative to controls. Nevertheless, arginine and arginine:ADMA ratios were very low in SM. SDMA was high in children with SM. With treatment, arginine and the arginine:ADMA ratio normalized, but SDMA did not. Arginine:ADMA ratios, but not arginine, were significantly and inde-pendent-ly inversely associated with lactate and angiopoietin-2. Plasma arginase was not elevated in those with malaria, and plasma free hemoglobin was elevated only in patients with cerebral malaria.

CONCLUSIONS

In contrast to adults, plasma ADMA is reduced in SM in children, but hypoargininemia is more severe. Arginine bioavailability (reflected by low arginine:ADMA ratios) is therefore comparably low in SM in children as in adults. Therapies to increase NO bioavailability in malaria may be useful as adjunctive treatment of severe malaria in children.

Dimethylarginines ADMA and SDMA: the real water-soluble small toxins?

Uremia occurs if the kidney loses the ability to eliminate toxic compounds at a sufficient rate into the urine. In 1970, N-N, N-G- and N-G,N׳-G-dimethyl-arginine (asymmetric dimethylarginine [ADMA] and symmetric dimethylarginine) were isolated from human urine. It was anticipated that both substances might be important in the pathophysiology and for the diagnosis of various pathologic states. It took 22 years, however, before this idea materialized when it was found that ADMA, which is increased in hemodialysis patients, inhibits the synthesis of the endothelial-derived relaxing factor, identified as nitric oxide. ADMA correlates with traditional and nontraditional cardiovascular risk factors and is a strong predictor of cardiovascular events and death in both patients with chronic kidney disease and in the general population. It also seems to mediate adverse cardiovascular effects of drugs such as proton pump inhibitors. To date, we have no specific pharmacologic therapy at hand to neutralize the deleterious effects of ADMA, curbing the enthusiasm for this marker and mediator of cardiovascular disease.

Genetic and environmental determinants of dimethylarginines and association with cardiovascular disease in patients with type 2 diabetes

OBJECTIVE

To investigate determinants of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), including single nucleotide polymorphisms (SNPs), in the DDAH1, DDAH2, and AGXT2 genes and their associations with prevalent and incident cardiovascular disease (CVD) in older adults with type 2 diabetes mellitus.

RESEARCH DESIGN AND METHODS

Prevalent CVD was assessed in men and women aged 60-75 years with type 2 diabetes as part of the Edinburgh Type 2 Diabetes Study (ET2DS), and the participants were prospectively followed up for 4 years for incident CVD. Dimethylarginines were measured in 783 of these subjects, and genotyping for tag SNPs in the DDAH1, DDAH2, and AGXT2 genes was performed in 935 subjects.

RESULTS

Plasma ADMA levels were significantly associated with SNPs in DDAH1 (top SNP rs1554597; P = 9.0E-09), while SDMA levels were associated with SNPs in AGXT2 (top SNP rs28305; P = 1.3E-04). Significant, independent determinants of plasma ADMA were sex, L-arginine, creatinine, fasting glucose, and rs1554597 (all P < 0.05; combined R(2) = 0.213). Determinants of SDMA were age, sex, creatinine, L-arginine, diabetes duration, prevalent CVD, and rs28305 (all P < 0.05; combined R(2) = 0.425). Neither dimethylarginine was associated with incident CVD. None of the investigated SNPs were associated with overall CVD, although subgroup analysis revealed a significant association of AGXT2 rs28305 with intermittent claudication.

CONCLUSIONS

Our study in a well-characterized population with type 2 diabetes does not support reported associations or causal relationship between ADMA and features of diabetes or CVD.

The physical basis of renal fibrosis: effects of altered hydrodynamic forces on kidney homeostasis

Healthy kidneys are continuously exposed to an array of physical forces as they filter the blood: shear stress along the inner lumen of the tubules, distension of the tubular walls in response to changing fluid pressures, and bending moments along both the cilia and microvilli of individual epithelial cells that comprise the tubules. Dysregulation of kidney homeostasis via underlying medical conditions such as hypertension, diabetes, or glomerulonephritis fundamentally elevates the magnitudes of each principle force in the kidney and leads to fibrotic scarring and eventual loss of organ function. The purpose of this review is to summarize the progress made characterizing the response of kidney cells to pathological levels of mechanical stimuli. In particular, we examine important, mechanically responsive signaling cascades and explore fundamental changes in renal cell homeostasis after cyclic strain or fluid shear stress exposure. Elucidating the effects of these disease-related mechanical imbalances on endogenous signaling events in kidney cells presents a unique opportunity to better understand the fibrotic process.

Protein-bound uremic toxins stimulate crosstalk between leukocytes and vessel wall

Leukocyte activation and endothelial damage both contribute to cardiovascular disease, a major cause of morbidity and mortality in CKD. Experimental in vitro data link several protein-bound uremic retention solutes to the modulation of inflammatory stimuli, including endothelium and leukocyte responses and cardiovascular damage, corroborating observational in vivo data. However, the impact of these uremic toxins on the crosstalk between endothelium and leukocytes has not been assessed. This study evaluated the effects of acute and continuous exposure to uremic levels of indoxylsulfate (IS), p-cresylsulfate (pCS), and p-cresylglucuronide (pCG) on the recruitment of circulating leukocytes in the rat peritoneal vascular bed using intravital microscopy. Superfusion with IS induced strong leukocyte adhesion, enhanced extravasation, and interrupted blood flow, whereas pCS caused a rapid increase in leukocyte rolling. Superfusion with pCS and pCG combined caused impaired blood flow and vascular leakage but did not further enhance leukocyte rolling over pCS alone. Intravenous infusion with IS confirmed the superfusion results and caused shedding of heparan sulfate, pointing to disruption of the glycocalyx as the mechanism likely mediating IS-induced flow stagnation. These results provide the first clear in vivo evidence that IS, pCS, and pCG exert proinflammatory effects that contribute to vascular damage by stimulating crosstalk between leukocytes and vessels.

Genome-wide association study on dimethylarginines reveals novel AGXT2 variants associated with heart rate variability but not with overall mortality

AIMS

The purpose of this study was to identify novel genetic variants influencing circulating asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels and to evaluate whether they have a prognostic value on cardiovascular mortality.

METHODS AND RESULTS

We conducted a genome-wide association study on the methylarginine traits and investigated the predictive value of the new discovered variants on mortality. Our meta-analyses replicated the previously known locus for ADMA levels in DDAH1 (rs997251; P = 1.4 × 10(-40)), identified two non-synomyous polymorphisms for SDMA levels in AGXT2 (rs37369; P = 1.4 × 10(-40) and rs16899974; P = 1.5 × 10(-38)) and one in SLC25A45 (rs34400381; P = 2.5 × 10(-10)). We also fine-mapped the AGXT2 locus for further independent association signals. The two non-synonymous AGXT2 variants independently associated with SDMA levels were also significantly related with short-term heart rate variability (HRV) indices in young adults. The major allele (C) of the novel non-synonymous rs16899974 (V498L) variant associated with decreased SDMA levels and an increase in the ratio between the low- and high-frequency spectral components of HRV (P = 0.00047). Furthermore, the SDMA decreasing allele (G) of the non-synomyous SLC25A45 (R285C) variant was associated with a lower resting mean heart rate during the HRV measurements (P = 0.0046), but not with the HRV indices. None of the studied genome-wide significant variants had any major effect on cardiovascular or total mortality in patients referred for coronary angiography.

CONCLUSIONS

AGXT2 has an important role in SDMA metabolism in humans. AGXT2 may additionally have an unanticipated role in the autonomic nervous system regulation of cardiac function.

Asymmetric and symmetric dimethylarginine in adolescents with hyperuricemia

The purpose of this work was to investigate if in adolescents with hyperuricemia serum levels of asymmetric and symmetric dimethylarginine (ADMA, SDMA) are increased and if their levels correlate with serum uric acid (UA). Patients and Methods. The study group consisted of 58 hyperuricemic patients aged median 16.15 Q1–Q3 (14–17). The reference group contained 27 healthy individuals with normal serum UA level. ADMA and SDMA were measured by immunoenzymatic ELISA commercial kits and expressed in μmol/L. Serum UA was measured by the colorimetric method. Results. In hyperuricemic patients serum ADMA values did not differ between two estimated groups (P > 0.05); however, SDMA was significantly higher than in reference group (P < 0.01). Serum ADMA and SDMA correlated positively with UA (r = 0.34, P < 0.01) (r = 0.31, P < 0.01) and hs-CRP (r = 0.20, P < 0.05) (r = 0.36, P < 0.01), respectively. Conclusion. We demonstrated increased SDMA but not ADMA levels in adolescents with hyperuricemia and their correlation with serum uric acid levels. However, at the moment it is difficult to answer the question if it is just coexistence of these factors or any mechanism linking uric acid and methylated arginines really exists.

Uremia-related oxidative stress in leukocytes is not triggered by β2-microglobulin

BACKGROUND

Chronic kidney disease (CKD) is characterized by low-grade inflammation and increased risk for cardiovascular disease. The interest in β2-microglobulin (B2M) as a marker for cardiovascular outcome with and without CKD has grown. Clinical studies suggested that B2M could be involved in the pathogenesis of vascular disease, for which chronic leukocyte activation is a pathogenic factor. We investigated whether B2M is proinflammatory by inducing oxidative burst in leukocytes.

METHODS

Oxidative burst was measured at baseline and after stimulation with N-formyl-methionine-leucine-phenylalanine (fMLP), Escherichia coli, or phorbol-12-myristate-acetate (PMA) in the whole blood of healthy volunteers in the absence (saline) and presence of human B2M (hB2M; 10 and 50 mg/L) versus uremic whole blood. Because of suspicion of contamination, hB2M was dialyzed for purification and purified B2M (dB2M) and dialysates were tested in the burst test. As a comparator, reactive oxygen species (ROS) in response to lipopolysaccharide (LPS) was measured.

RESULTS

Unpurified hB2M strongly enhanced ROS in monocytes and granulocytes after E. coli and PMA and moderately after fMLP stimulation compared with control (P < .01) and uremia (P < .01) whereas at baseline hB2M only induced ROS in granulocytes (P < .05). After purification, dB2M no longer increased burst activity, suggesting that contamination was responsible for the initial effect. An endotoxin concentration of less than 1.5 EU/mL, as observed in hB2M, could not induce oxidative stress.

CONCLUSION

This study suggests that B2M, a traditional marker for middle molecule retention and a novel marker for cardiovascular outcome, may not by itself cause vascular damage by influencing inflammatory response due to induction of leukocyte free radical production. However, an effect on other cell types involved cannot be excluded. Our data further reveal that this type of research might be skewed by non-LPS contaminants, and that care should be taken to exclude this bias.

Changes in biomarkers associated with living kidney donation

Living donor kidneys have been associated with better graft and overall survival in kidney transplant recipients. Although a living kidney donation is generally considered safe in carefully selected living donors, concerns of possible adverse effects related to kidney donation remain, especially in younger and high-risk donors. In this study, we examined the changes in a panel of traditional and novel serum biomarkers linked with cardiovascular conditions in a cohort of 34 healthy living kidney donors with a mean age ± SD of 40 ± 10 years and estimated predonation glomerular filtration rate (GFR) of 86 ± 10 ml/min/1.73 m(2). At 6 months after donation, there were no significant changes in the clinical parameters including body mass index and blood pressure despite a significant decline in the mean estimated GFR to 60 ml/min/1.73 m(2). Among the panel of markers, the levels of symmetric dimethylarginine and fibroblast growth factor 23 increased significantly compared to baseline, suggesting that living kidney donation may result in changes in biomarkers that are associated with cardiovascular risk in other cohorts.

Regular cigarette smoking influences the transsulfuration pathway, endothelial function, and inflammation biomarkers in a sex-gender specific manner in healthy young humans

Cigarette smoking (CS) is the primary cause of preventable morbidity and mortality. Abundant clinical evidence suggests that CS is more harmful to women; however, the mechanisms responsible for these differences are not yet known. CS alters endothelial function, the redox state, inflammation, and global DNA methylation, which is associated with one-carbon metabolism and the transsulfuration pathway. However, it is not known whether the previously identified alterations are sex-gender related. Healthy adult men and oral contraceptive-free women with regular menstrual cycles were enrolled; women were examined during the follicular phase. Men had higher plasma levels of uric acid, total bilirubin, homocysteine, glutamylcysteine, total glutathione, cysteinylglycine; had more monocytes and released more TNF-alpha from human monocytes derived macrophages (hMDMs), but they had fewer platelets and lower levels of DNA methylation, and their hMDMs released less TNF-alpha after LPS stimulation. MDA, taurine, cysteine, arginine, ADMA, and SDMA were not different. CS decreased global DNA methylation more in women and increased the platelet, monocyte, and lymphocyte counts and the homocysteine, arginine, and ADMA levels only in women, whereas increased the neutrophil and eosinophil counts only in men. Additionally, CS reduced the sex-gender differences in total bilirubin, basal and LPS-induced TNF-alpha release, total glutathione, and glutamylcysteine, leaving unchanged cysteinylglycine, taurine, SDMA, MDA, and cysteine. These data suggest that cardiovascular risk factors seem to come earlier in young healthy female smokers than in young healthy male smokers, supporting the greater alarmism regarding the effects of CS in women and providing a basis for understanding the sex-gender differences. These results also suggest that cessation programs targeting women are needed.

Assessment of endothelial dysfunction: the role of symmetrical dimethylarginine and proinflammatory markers in chronic kidney disease and renal transplant recipients

OBJECTIVES

The study was designed to evaluate associations between symmetric dimethylarginine (SDMA), inflammation, and superoxide anion (O2∙-) with endothelial function and to determine their potential for screening of endothelial dysfunction in patients with chronic kidney disease (CKD) and renal transplant (RT) recipients.

MATERIALS AND METHODS

We included 64 CKD and 52 RT patients. Patients were stratified according to brachial artery flow-mediated dilation (FMD).

RESULTS

Logistic regression analysis showed that high SDMA and high sensitive C-reactive protein (hs-CRP) were associated with impaired FMD in CKD and RT patients, after adjustment for glomerular filtration rate. The ability of inflammation, SDMA, and O2∙- to detect impaired FMD was investigated by receiving operative characteristic analysis. Hs-CRP (area under the curves (AUC) = 0.754, P < 0.001), IL-6 (AUC = 0.699, P = 0.002), and SDMA (AUC = 0.689, P = 0.007) had the highest ability to detect impaired FMD. SDMA in combination with inflammatory parameters and/or O2∙- had better screening performance than SDMA alone.

CONCLUSIONS

Our results indicate a strong predictable association between hs-CRP, SDMA, and endothelial dysfunction in CKD patients and RT recipients. The individual marker that showed the strongest discriminative ability for endothelial dysfunction is hs-CRP, but its usefulness as a discriminatory marker for efficient diagnosis of endothelial dysfunction should be examined in prospective studies.

A zebrafish model for uremic toxicity: role of the complement pathway

Many organic solutes accumulate in end-stage renal disease (ESRD) and some are poorly removed with urea-based prescriptions for hemodialysis. However, their toxicities have been difficult to assess. We have employed an animal model, the zebrafish embryo, to test the toxicity of uremic serum compared to control. Serum was obtained from stable ESRD patients predialysis or from normal subjects. Zebrafish embryos 24 h postfertilization were exposed to experimental media at a water:human serum ratio of 3:1. Those exposed to serum from uremic subjects had significantly reduced survival at 8 h (19 ± 18 vs. 94 ± 6%, p < 0.05, uremic serum vs. control, respectively). Embryos exposed to serum from ESRD subjects fractionated at 50 kDa showed significantly greater toxicity with the larger molecular weight fraction (83 ± 11 vs. 7 ± 17% survival, p < 0.05, <50 vs. >50 kDa, respectively). Heating serum abrogated its toxicity. EDTA, a potent inhibitor of complement by virtue of calcium chelation, reduced the toxicity of uremic serum compared to untreated uremic serum (96 ± 5 vs. 28 ± 20% survival, p < 0.016, chelated vs. nonchelated serum, respectively). Anti-factor B, a specific inhibitor of the alternative complement pathway, reduced the toxicity of uremic serum, compared to untreated uremic serum (98 ± 6 vs. 3 ± 9% survival, p < 0.016, anti-factor B treated vs. nontreated, respectively). Uremic serum is thus more toxic to zebrafish embryos than normal serum. Furthermore, this toxicity is associated with a fraction of large size, is inactivated by heat, and is reduced by both specific and nonspecific inhibitors of complement activation. Together these data lend support to the hypothesis that at least some uremic toxicities may be mediated by complement.

Abnormal high-density lipoprotein induces endothelial dysfunction via activation of Toll-like receptor-2

Endothelial injury and dysfunction (ED) represent a link between cardiovascular risk factors promoting hypertension and atherosclerosis, the leading cause of death in Western populations. High-density lipoprotein (HDL) is considered antiatherogenic and known to prevent ED. Using HDL from children and adults with chronic kidney dysfunction (HDL(CKD)), a population with high cardiovascular risk, we have demonstrated that HDL(CKD) in contrast to HDL(Healthy) promoted endothelial superoxide production, substantially reduced nitric oxide (NO) bioavailability, and subsequently increased arterial blood pressure (ABP). We have identified symmetric dimethylarginine (SDMA) in HDL(CKD) that causes transformation from physiological HDL into an abnormal lipoprotein inducing ED. Furthermore, we report that HDL(CKD) reduced endothelial NO availability via toll-like receptor-2 (TLR-2), leading to impaired endothelial repair, increased proinflammatory activation, and ABP. These data demonstrate how SDMA can modify the HDL particle to mimic a damage-associated molecular pattern that activates TLR-2 via a TLR-1- or TLR-6-coreceptor-independent pathway, linking abnormal HDL to innate immunity, ED, and hypertension.

Transsulfuration pathway thiols and methylated arginines: the Hunter Community Study

Background

Serum homocysteine, when studied singly, has been reported to be positively associated both with the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine [ADMA, via inhibition of dimethylarginine dimethylaminohydrolase (DDAH) activity] and with symmetric dimethylarginine (SDMA). We investigated combined associations between transsulfuration pathway thiols, including homocysteine, and serum ADMA and SDMA concentrations at population level.

Methods

Data on clinical and demographic characteristics, medication exposure, C-reactive protein, serum ADMA and SDMA (LC-MS/MS), and thiols (homocysteine, cysteine, taurine, glutamylcysteine, total glutathione, and cysteinylglycine; capillary electrophoresis) were collected from a sample of the Hunter Community Study on human ageing [n = 498, median age (IQR) = 64 (60–70) years].

Results

Regression analysis showed that: a) age (P = 0.001), gender (P = 0.03), lower estimated glomerular filtration rate (eGFR, P = 0.08), body mass index (P = 0.008), treatment with beta-blockers (P = 0.03), homocysteine (P = 0.02), and glutamylcysteine (P = 0.003) were independently associated with higher ADMA concentrations; and b) age (P = 0.001), absence of diabetes (P = 0.001), lower body mass index (P = 0.01), lower eGFR (P<0.001), cysteine (P = 0.007), and glutamylcysteine (P<0.001) were independently associated with higher SDMA concentrations. No significant associations were observed between methylated arginines and either glutathione or taurine concentrations.

Conclusions

After adjusting for clinical, demographic, biochemical, and pharmacological confounders the combined assessment of transsulfuration pathway thiols shows that glutamylcysteine has the strongest and positive independent associations with ADMA and SDMA. Whether this reflects a direct effect of glutamylcysteine on DDAH activity (for ADMA) and/or cationic amino acid transport requires further investigations.

Effects of asymmetric dimethylarginine on inflammatory cytokines (TNF-α, IL-6 and IL-10) in rats

This study is intended to examine the effects of administration of asymmetric dimethylarginine (ADMA) on the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-10. A total of 30 Wistar adult albino rats were used. Group I was administrated ( n = 10) with 1 mg/kg/day of ADMA, group II ( n = 10) was administrated with 2 mg/kg/day of ADMA and the control group was administrated ( n = 10) with 0.9% sodium chloride. ADMA was intraperitoneally administrated for 7 days. The serum levels of IL-6, TNF-α and IL-10 were measured. There was a significant decrease in the levels of TNF-α, IL-6 and IL-10 in group I compared with that of the control group ( p < 0.001 ). There was also a significant decrease in the levels of IL-10 in group II compared with that of the control group ( p < 0.05) but the increase was much more distinct in the levels of IL-6 and TNF-α ( p < 0.001). When comparing the groups by the doses given, no difference between the levels of IL-6 and IL-10 in groups I and II ( p > 0.05) was observed; the levels of TNF-α in group II were significantly lower than those of group I (p < 0.05). A significant decrease in the serum levels of inflammatory cytokines IL-6, TNF-α and IL-10, after administration of 1 mg/kg/day and 2 mg/kg/day of ADMA, indicates that ADMA has an effect on inflammation. Increase in ADMA levels in the rats shows that the effects of inflammatory cytokines were suppressed.

Asymmetric dimethyarginine as marker and mediator in ischemic stroke

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, is known as mediator of endothelial cell dysfunction and atherosclerosis. Circulating ADMA levels are correlated with cardiovascular risk factors such as hypercholesterolemia, arterial hypertension, diabetes mellitus, hyperhomocysteinemia, age and smoking. Accordingly, clinical studies found evidence that increased ADMA levels are associated with a higher risk of cerebrovascular events. After the acute event of ischemic stroke, levels of ADMA and its analog symmetric dimethylarginine (SDMA) are elevated through augmentation of protein methylation and oxidative stress. Furthermore, cleavage of ADMA through dimethylarginine dimethylaminohydrolases (DDAHs) is reduced. This increase of dimethylarginines might be predictive for adverse clinical outcome. However, the definite role of ADMA after acute ischemic stroke still needs to be clarified. On the one hand, ADMA might contribute to brain injury by reduction of cerebral blood flow. On the other hand, ADMA might be involved in NOS-induced oxidative stress and excitotoxic neuronal death. In the present review, we highlight the current knowledge from clinical and experimental studies on ADMA and its role for stroke risk and ischemic brain injury in the hyperacute stage after stroke. Finally, further studies are warranted to unravel the relevance of the close association of dimethylarginines with stroke.

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.

Association of dimethylarginines and mediators of inflammation after acute ischemic stroke

Background

Elevated levels of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are accompanied by endothelial dysfunction and predict adverse outcome after ischemic stroke. Via induction of oxidative stress, dimethylarginines are possibly linked to the inflammatory cascade after stroke that is known to considerably contribute to secondary progression of brain injury. We sought to investigate the association between dimethylarginines and inflammatory mediators in patients with acute ischemic stroke.

Methods

Plasma levels of ADMA and SDMA were measured in prospectively collected blood samples of 58 patients with acute ischemic stroke. Blood samples were taken at 6 hours, 12 hours, 24 hours, 3 days and 7 days after onset of symptoms. Analyses of ADMA and SDMA were done by high-performance liquid chromatography-tandem mass spectrometry. Monocyte chemotactic protein-1 (MCP-1), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), interleukin-6 (IL-6), C-reactive protein (CRP) and S100B as markers of inflammation and brain damage were determined by commercially available immunometric assays. Patient data were compared with control data from 32 age-adjusted healthy volunteers. Baseline stroke severity was evaluated by the National Institutes of Health Stroke Scale (NIHSS) (NIHSS 0 to 1: mild stroke; NIHSS 2 to 8: moderate stroke; NIHSS ≥9: severe stroke).

Results

Plasma ADMA and SDMA levels significantly correlated with blood levels of inflammatory mediators up to day 7 after stroke. On multiple stepwise linear regression analysis ADMA correlated with TIMP-1 at 6 hours, 24 hours, 3 days and 7 days, MMP-9 at 12 hours and IL-6 at 7 days (P <0.05) while SDMA correlated with MCP-1 at 6 hours, 24 hours, 3 days and 7 days as well as IL-6 at 3 days and 7 days (P <0.05).

Conclusions

The levels of the vasoactive compound ADMA as well as levels of its structural isomer SDMA are associated with levels of inflammatory mediators after acute ischemic stroke. Further studies need to elucidate the cause and effect relationship of these crucial players.