Asymmetric dimethylarginine: a novel marker of risk and a potential target for therapy in chronic kidney disease

Endothelial function testing before conditioning therapy is useful for predicting transplant-related complications after allogeneic hematopoietic cell transplantation

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a useful tool for the treatment of hematologic malignancies. However, transplantation-related complications are the main cause of non-relapse mortality. Previous reports suggest that endothelial damage is related to early complications after HSCT. Non-invasive reactive hyperemia peripheral arterial tonometry (RH-PAT) was performed to evaluate endothelial function as a predictive marker for these complications.

METHODS

The reactive hyperemia index (RHI) obtained from RH-PAT was evaluated before the conditioning regimen. The relationship between the RHI and the appearance of engraftment syndrome, thrombotic microangiopathy, and acute graft-versus-host disease (aGVHD) was assessed. Receiver operating characteristic curve analysis showed that an RHI value of 1.58 was the optimal cut-off for predicting transplantation-related complications.

RESULTS

In total, 49 patients (22 acute myelogenous leukemia, 7 acute lymphocytic leukemia, 6 myelodysplastic syndrome, 6 adult T-cell leukemia, 6 non-Hodgkin lymphoma, and 2 others) were enrolled; 34 had a normal RHI (≥ 1.59), and 15 had an abnormally low RHI (≤ 1.58). Thrombotic microangiopathy (20.2% vs 0.0%, P = 0.025) and aGVHD (80.0% vs 41.2%, P = 0.015) were significantly more frequent in patients with a low RHI.

CONCLUSION

Endothelial dysfunction assessed by RH-PAT before HSCT was able to predict transplantation-related complications.

Associations of serum amino acids related to urea cycle with risk of chronic kidney disease in Chinese with type 2 diabetes

OBJECTIVE

Serum levels of amino acids related to urea cycle are associated with risk of type 2 diabetes mellitus (T2DM). Our study aimed to explore whether serum levels of amino acids related to urea cycle, i.e., arginine, citrulline, and ornithine, are also associated with increased risk of chronic kidney disease (CKD) in T2DM.

METHODS

We extracted medical records of 1032 consecutive patients with T2DM from the Electronic Administrative System of Liaoning Medical University First Affiliated Hospital (LMUFAH) system from May 2015 to August 2016. Of them, 855 patients with completed data available were used in the analysis. CKD was defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m². Serum amino acids were measured by mass spectrometry (MS) technology. Binary logistic regression was performed to obtain odds ratios (ORs) and their 95% confidence intervals (CIs).

RESULTS

52.3% of the 855 T2DM patients were male, and 143 had CKD. In univariable analysis, high serum citrulline, high ratio of arginine to ornithine, and low ratio of ornithine to citrulline were associated with markedly increased risk of CKD (OR of top vs. bottom tertile: 2.87, 95%CI, 1.79-4.62 & 1.98, 95%CI,1.25-3.14 & 2.56, 95%CI, 1.61-4.07, respectively). In multivariable analysis, the ORs of citrulline and ornithine/citrulline ratio for CKD remained significant (OR of top vs. bottom tertile: 2.22, 95%CI, 1.29-3.82 & 2.24, 1.29-3.87, respectively).

CONCLUSIONS

In Chinese patients with T2DM, high citrulline and low ornithine/citrulline ratio were associated with increased risk of CKD.

The Usefulness of Calcium/Magnesium Ratio in the Risk Stratification of Early Onset of Renal Replacement Therapy

Background: A growing number of studies have reported a close relationship between high serum calcium (Ca)/low serum magnesium (Mg) and vascular calcification. Endothelial dysfunction and vascular inflammation seem plausible risk factors for the enhanced progression of kidney disease. The aim of this study was to evaluate the role of the Ca/Mg ratio as a predictor of the early onset of renal replacement therapy (RRT). Methods: This was a prospective study conducted in an outpatient low-clearance nephrology clinic, enrolling 693 patients with stages 4−5 of CKD. Patients were divided into two groups according to the start of renal replacement therapy (RRT). Results: The kidney’s survival at 120 months was 60% for a Ca−Mg ratio < 6 and 40% for a Ca−Mg ratio ≥ 6 (p = 0.000). Patients who started RRT had lower levels of Hb, Ca, Mg, albumin, and cholesterol and higher values of phosphorus, the Ca/Mg ratio, and PTH. High values of phosphorus and the Ca/Mg ratio and low levels of Mg and GFR were independent predictors of entry into RRT. A high Ca/Mg ratio, high phosphorus levels, and low levels of GFR were associated with a cumulative risk for initiation of RRT. Conclusions: In our population, the Ca/Mg ratio is an independent predictive factor for the initiation of a depurative technique.

Endothelial cell dysfunction: a key determinant for the outcome of allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (alloSCT) carries the promise of cure for many malignant and non-malignant diseases of the lympho-hematopoietic system. Although outcome has improved considerably since the pioneering Seattle achievements more than 5 decades ago, non-relapse mortality (NRM) remains a major burden of alloSCT. There is increasing evidence that endothelial dysfunction is involved in many of the life-threatening complications of alloSCT, such as sinusoidal obstruction syndrome/venoocclusive disease, transplant-associated thrombotic microangiopathy, and refractory acute graft-versus host disease. This review delineates the role of the endothelium in severe complications after alloSCT and describes the current status of search for biomarkers predicting endothelial complications, including markers of endothelial vulnerability and markers of endothelial injury. Finally, implications of our current understanding of transplant-associated endothelial pathology for prevention and management of complications after alloSCT are discussed.

Arginine Metabolites as Biomarkers of Myocardial Ischaemia, Assessed with Cardiac Magnetic Resonance Imaging in Chronic Kidney Disease

(1) Background: Cardiovascular disease (CVD) is the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Myocardial oxygenation and perfusion response to stress, using oxygen-sensitive cardiovascular magnetic resonance (OS-CMR) and stress T1 mapping respectively, are impaired in CKD patients with and without known coronary artery disease (CAD). Endothelial dysfunction, assessed by circulating levels of asymmetric dimethylarginine (ADMA) and homoarginine (HMA), promotes atherosclerosis. We hypothesized that in CKD patients, worsening endothelial dysfunction is associated with worsening myocardial oxygenation and perfusion as assessed by change in OS-CMR signal intensity (Δ OS-CMR SI) and stress T1 (ΔT1) values. (2) Methods: 38 patients with advanced CKD underwent cardiovascular magnetic resonance (CMR) scanning at 3 Tesla. OS-CMR and T1 mapping images were acquired both at rest and after adenosine stress and analyzed semi-quantitatively. Serum ADMA and HMA concentrations were assessed using mass spectrometry. (3) Results: There was no significant correlation between Δ OS-CMR SI and ADMA or HMA. Interestingly, there was a significant negative correlation seen between Δ T1 and ADMA (r = -0.419, p = 0.037, n = 30) but not between Δ T1 and HMA. (4) Conclusions: Stress T1 response is impaired in CKD patients and is independently associated with higher circulating ADMA concentrations.

Asymmetric (ADMA) and Symmetric (SDMA) Dimethylarginines in Chronic Kidney Disease: A Clinical Approach

Asymmetric dimethylarginine (ADMA) and its enantiomer, Symmetric dimethylarginine (SDMA), are naturally occurring amino acids that were first isolated and characterized in human urine in 1970. ADMA is the most potent endogenous inhibitor of nitric oxide synthase (NOS), with higher levels in patients with end-stage renal disease (ESRD). ADMA has shown to be a significant predictor of cardiovascular outcome and mortality among dialysis patients. On the other hand, although initially SDMA was thought to be an innocuous molecule, we now know that it is an outstanding marker of renal function both in human and in animal models, with ESRD patients on dialysis showing the highest SDMA levels. Today, we know that ADMA and SDMA are not only uremic toxins but also independent risk markers for mortality and cardiovascular disease (CVD). In this review, we summarize the role of both ADMA and SDMA in chronic kidney disease along with other cardiovascular risk factors.

Serum metabolites predict response to angiotensin II receptor blockers in patients with diabetes mellitus

Background

Individual patients show a large variability in albuminuria response to angiotensin receptor blockers (ARB). Identifying novel biomarkers that predict ARB response may help tailor therapy. We aimed to discover and validate a serum metabolite classifier that predicts albuminuria response to ARBs in patients with diabetes mellitus and micro- or macroalbuminuria.

Methods

Liquid chromatography-tandem mass spectrometry metabolomics was performed on serum samples. Data from patients with type 2 diabetes and microalbuminuria (n = 49) treated with irbesartan 300 mg/day were used for discovery. LASSO and ridge regression were performed to develop the classifier. Improvement in albuminuria response prediction was assessed by calculating differences in R² between a reference model of clinical parameters and a model with clinical parameters and the classifier. The classifier was externally validated in patients with type 1 diabetes and macroalbuminuria (n = 50) treated with losartan 100 mg/day. Molecular process analysis was performed to link metabolites to molecular mechanisms contributing to ARB response.

Results

In discovery, median change in urinary albumin excretion (UAE) was −42 % [Q1–Q3: −69 to −8]. The classifier, consisting of 21 metabolites, was significantly associated with UAE response to irbesartan (p < 0.001) and improved prediction of UAE response on top of the clinical reference model (R² increase from 0.10 to 0.70; p < 0.001). In external validation, median change in UAE was −43 % [Q1–Q35: −63 to −23]. The classifier improved prediction of UAE response to losartan (R² increase from 0.20 to 0.59; p < 0.001). Specifically ADMA impacting eNOS activity appears to be a relevant factor in ARB response.

Conclusions

A serum metabolite classifier was discovered and externally validated to significantly improve prediction of albuminuria response to ARBs in diabetes mellitus.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0960-3) contains supplementary material, which is available to authorized users.

New Developments in Our Understanding of Neointimal Hyperplasia

The vascular access remains the lifeline for the hemodialysis patient. The most common etiology of vascular access dysfunction is venous stenosis at the vein-artery anastomosis in arteriovenous fistula and at the vein-graft anastomosis in arteriovenous grafts (AVG). This stenotic lesion is typically characterized on histology as aggressive venous neointimal hyperplasia in both arteriovenous fistula and AVG. In recent years, we have advanced our knowledge and understanding of neointimal hyperplasia in vascular access and begun testing several novel therapies. This article will (1) review recent developments in our understanding of the pathophysiology of neointimal hyperplasia development in AVG and fistula failure, (2) discuss atypical factors leading to neointimal hyperplasia development, (3) highlight key novel therapies that have been evaluated in clinical trials, and (4) discuss future opportunities and challenges to improve our understanding of vascular access dysfunction and translate this knowledge into novel and innovative therapies.

Interrelationship of Multiple Endothelial Dysfunction Biomarkers with Chronic Kidney Disease

The interrelationship of multiple endothelial biomarkers and chronic kidney disease (CKD) has not been well studied. We measured asymmetric dimethylarginine (ADMA), L-arginine, soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular adhesion molecule-1 (sVCAM-1), soluble E-selectin (sE-selectin), von Willebrand factor (vWF), flow-mediated dilation (FMD), and nitroglycerin-induced dilation (NID) in 201 patients with CKD and 201 community-based controls without CKD. Multivariable analyses were used to examine the interrelationship of endothelial biomarkers with CKD. The multivariable-adjusted medians (interquartile ranges) were 0.54 (0.40, 0.75) in patients with CKD vs. 0.25 (0.22, 0.27) μmol /L in controls without CKD (p<0.0001 for group difference) for ADMA; 67.0 (49.6, 86.7) vs. 31.0 (27.7, 34.2) μmol/L (p<0.0001) for L-arginine; 230.0 (171.6, 278.6) vs. 223.9 (178.0, 270.6) ng/mL (p=0.55) for sICAM-1; 981.7 (782.6, 1216.8) vs. 633.2 (507.8, 764.3) ng/mL (p<0.0001) for sVCAM-1; 47.9 (35.0, 62.5) vs. 37.0 (28.9, 48.0) ng/mL (p=0.01) for sE-selectin; 1320 (1044, 1664) vs. 1083 (756, 1359) mU/mL (p=0.008) for vWF; 5.74 (3.29, 8.72) vs. 8.80 (6.50, 11.39)% (p=0.01) for FMD; and 15.2 (13.5, 16.9) vs. 19.1 (17.2, 21.0)% (p=0.0002) for NID, respectively. In addition, the severity of CKD was positively associated with ADMA, L-arginine, sVCAM-1, sE-selectin, and vWF and inversely associated with FMD and NID. Furthermore, FMD and NID were significantly and inversely correlated with ADMA, L-arginine, sVCAM-1, sE-selectin, and vWF. In conclusion, these data indicate that multiple dysfunctions of the endothelium were present among patients with CKD. Interventional studies are warranted to test the effects of treatment of endothelial dysfunction on CKD.

A pharmaco-metabonomic study on chronic kidney disease and therapeutic effect of ergone by UPLC-QTOF/HDMS

Chronic kidney disease (CKD) is an important public health problem. Ergone has been proved to prevent the progression of CKD. UPLC-QTOF/HDMS was employed for metabolic profiling of adenine-induced CKD and to investigate the nephroprotective effects of ergone. Pharmacology parameters including blood biochemistry, histopathological evaluation and Western blot analysis were performed concurrently. The UPLC-MS data were analyzed by partial least squares-discriminate analysis, correlation analysis, heatmap analysis and mapped to KEGG pathways. Blood and serum biochemistry were observed to be significantly different in the CKD group than in the control group. In conjunction with biochemistry, histopathology and protein expression results, identified metabolites indicated perturbations in fatty acid metabolism, purine metabolism and amino acid metabolism as changes associated with adenine-induced CKD and the interventions of ergone. Upregulated expression of TGF-β1, ED-1, CTGF, bFGF and collagen I was observed in the CKD group. However, downregulated expression of these proteins was observed after oral administration of ergone. These results suggest that expression changes in these proteins had implications for fatty acid metabolism, purine metabolism and amino acid metabolism in the development of CKD and that ergone treatment could delay the development of CKD by normalizing or blocking abnormal changes in biomarker metabolites and protein expression in the CKD group.

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.

Neurological disorders in a murine model of chronic renal failure

Cardiovascular disease is highly prevalent in patients with chronic renal failure (CRF). However, data on the impact of CRF on the cerebral circulatory system are scarce—despite the fact that stroke is the third most common cause of cardiovascular death in people with CRF. In the present study, we examined the impact of CRF on behavior (anxiety), recognition and ischemic stroke severity in a well-defined murine model of CRF. We did not observe any significant increases between CRF mice and non-CRF mice in terms of anxiety. In contrast, CRF mice showed lower levels of anxiety in some tests. Recognition was not impaired (vs. controls) after 6 weeks of CRF but was impaired after 10 weeks of CRF. Chronic renal failure enhances the severity of ischemic stroke, as evaluated by the infarct volume size in CRF mice after 34 weeks of CRF. Furthermore, neurological test results in non-CRF mice tended to improve in the days following ischemic stroke, whereas the results in CRF mice tended to worsen. In conclusion, we showed that a murine model of CRF is suitable for evaluating uremic toxicity and the associated neurological disorders. Our data confirm the role of uremic toxicity in the genesis of neurological abnormalities (other than anxiety).

Asymmetric dimethylarginine and critical illness

PURPOSE OF REVIEW

Asymmetric dimethylarginine (ADMA) is an analog of arginine and functions as an endogenous inhibitor of the nitric oxide synthase, which forms nitric oxide. Nitric oxide is crucial for perfusion of vital organs and is an important signaling agent in the development of critical illness. The role of ADMA in the pathophysiological mechanisms underlying critical illness is widely studied in the last decades, and recently it has become clear that ADMA should not be overlooked by clinicians working at the ICU. The aim of this review is to describe new insights into the role of ADMA in critical illness and its clinical relevance.

RECENT FINDINGS

High levels of ADMA are found in critically ill patients, because of higher levels of protein methylation, increased rate of protein turnover, decreased activity of dimethylamine dimethylaminohydrolase, and impaired renal and hepatic clearance capacity. These high levels are an independent risk factor for cardiac dysfunction, organ failure, and ICU mortality. The arginine : ADMA ratio in particular is of clinical importance and the restoration of this ratio is expedient to restore several functions that are disturbed during critical illness.

SUMMARY

Elevated ADMA levels occur in critically ill patients, which is detrimental for morbidity and mortality. The arginine : ADMA ratio should be restored to maintain nitric oxide production and therewith improve the clinical outcome of the patient.

Measurement of renal function in patients with chronic kidney disease

Chronic kidney disease affects millions of people worldwide and is associated with an increased morbidity and mortality as a result of kidney failure and cardiovascular disease. Accurate assessment of kidney function is important in the clinical setting as a screening tool and for monitoring disease progression and guiding prognosis. In clinical research, the development of new methods to measure kidney function accurately is important in the search for new therapeutic targets and the discovery of novel biomarkers to aid early identification of kidney injury. This review considers different methods for measuring kidney function and their contribution to the improvement of detection, monitoring and treatment of chronic kidney disease.

Homoarginine and mortality in pre-dialysis chronic kidney disease (CKD) patients

Background and Aims

Homoarginine, a precursor of nitric oxide, is an inverse predictor of death in dialysis patients and in subjects with cardiovascular disease and normal kidney function but its relationship with clinical outcomes in chronic kidney disease (CKD) patients not yet on dialysis is unknown.

Design, setting, participants and measurements

We enrolled 168 consecutive predialysis CKD patients (Age: 70±11 yrs; 26% Diabetics; eGFR 34±18 ml/min/1.73 m²) referred to a tertiary care centre and measured laboratory data on kidney function and cardiovascular risk factors. We modeled progression to dialysis or death as a function of homoarginine, using Cox’s regression, accounting for clinical characteristics, baseline levels of kidney function, and markers of inflammation.

Results

On crude and adjusted analyses homoarginine was directly associated with the eGFR and patients with more compromised renal function exhibited lower homoarginine levels. Furthermore homoarginine was also independently related to L-arginine, serum albumin and body mass index, and inversely related to proteinuria, C-reactive protein and age. During the study (follow up median time 4 years, inter-quartile range 1.7 to 7.0 years) 56 patients started dialysis and 103 died and homoarginine was a strong inverse predictor of the incidence rate of both outcomes (P = 0.002 and P = 0.017).

Conclusions

Homoarginine declines with advancing renal disease and is inversely related to progression to dialysis and mortality. The nature of the link between homoarginine and clinical outcomes is amenable to testing in clinical trials.

Clinical and research markers of oxidative stress in chronic kidney disease

CONTEXT

Kidney-related pathologies have increasing prevalence rates, produce a considerable financial burden, and are characterized by elevated levels of oxidative stress (OS).

OBJECTIVE

This review examines relationships between chronic kidney disease (CKD) and markers of OS and antioxidant status (AS).

METHODS

A systematic review of MEDLINE-indexed clinical trials, randomized controlled trials and comparative studies that examined OS and AS was performed.

RESULTS AND CONCLUSION

Several markers emerged as well-suited indicators of OS and AS in CKD: malondialdehyde, F2-isoprostanes, lipid hydroperoxides, asymmetric dimethylarginine, 8-oxo-7,8-dihydro-2'-deoxyguanosine, protein carbonyls, advanced oxidation protein products and glutathione-related activity.

Asymmetric dimethylarginine, endothelial dysfunction and renal disease

l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review.

Elevated preoperative serum asymmetrical dimethylarginine (ADMA) is associated with poor outcomes after pediatric cardiac surgery

PURPOSE

Asymmetrical dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase, is elevated in vascular pathologies such as hypertension and chronic kidney disease. Children undergoing cardiac surgery are at high risk of poor hemodynamic and renal outcomes secondary to cardiopulmonary bypass (CPB). This study tested the hypothesis that elevated preoperative ADMA levels are associated with overall worse clinical outcomes after pediatric CPB.

METHODS

This was a prospective, observational study of 100 patients aged from 2 weeks to 18 years who underwent cardiac surgery involving CPB. Serum ADMA levels were obtained preoperatively and on postoperative days zero through four. Clinical outcomes measured included acute kidney injury (AKI) by pRIFLE criteria, low cardiac output syndrome (LCOS), length of mechanical ventilation, hospital and ICU length of stay, unplanned reoperation, and mortality.

RESULTS

The 29 patients with an elevated preoperative ADMA were more likely to have prolonged mechanical ventilation, increased ICU and hospital length of stay, unplanned reoperation, and LCOS than those with a normal preoperative level. ADMA levels inversely correlated with estimated glomerular filtration rate (eGFR), but did not differ between patients with and without AKI after CPB. Preoperative ADMA levels correlated with hospital length of stay (r(s) = 0.289), ICU length of stay (r(s) = 0.308), and length of mechanical ventilation (r(s) = 0.402); [all p < 0.05]. ADMA levels before surgery had good predictive power for prolonged mechanical ventilation (AUC-ROC 0.809; 95 % CI 0.704, 0.914; p < 0.001).

CONCLUSIONS

Patients with elevated ADMA before surgery were more likely to have prolonged mechanical ventilation, develop LCOS, require an extended length of stay, and require reoperation. ADMA levels inversely correlated with eGFR, but did not predict AKI. Preoperative serum ADMA appears to identify pediatric cardiac surgery patients at risk of poor postoperative outcomes following CPB.

Nitric oxide synthase, ADMA, SDMA, and nitric oxide activity in the paraventricular nucleus throughout the etiology of renal wrap hypertension

Within the paraventricular nucleus (PVN), there is a balance between the excitatory and inhibitory neurotransmitters that regulate blood pressure; in hypertension, the balance shifts to enhanced excitation. Nitric oxide (NO) is an atypical neurotransmitter that elicits inhibitory effects on cardiovascular function. We hypothesized that reduced PVN NO led to elevations in blood pressure during both the onset and sustained phases of hypertension due to decreased NO synthase (NOS) and increased asymmetrical dimethylarginine (ADMA; an endogenous NOS inhibitor) and symmetric dimethylarginine (SDMA). Elevated blood pressure, in response to PVN bilateral microinjections of a NO inhibitor, nitro-L-arginine methyl ester, was blunted in renal wrapped rats during the onset of hypertension (day 7) and sustained renal wrap hypertension (day 28) compared with sham-operated rats. Adenoviruses (Ad) encoding endothelial NOS (eNOS) or LacZ microinjected into the PVN [1 × 10(9) plaque-forming units, bilateral (200 nl/site)] reduced mean arterial pressure compared with control (Day 7, Ad LacZ wrap: 144 ± 7 mmHg and Ad eNOS wrap: 117 ± 5 mmHg, P ≤ 0.05) throughout the study (Day 28, Ad LacZ wrap: 123 ± 1 mmHg and Ad eNOS wrap: 108 ± 4 mmHg, P ≤ 0.05). Western blot analyses of PVN NOS revealed significantly lower PVN neuronal NOS during the onset of hypertension but not in sustained hypertension. Reduced SDMA was found in the PVN during the onset of hypertension; however, no change in ADMA was observed. In conclusion, functional indexes of NO activity indicated an overall downregulation of NO in renal wrap hypertension, but the mechanism by which this occurs likely differs throughout the development of hypertension.

Actin cytoskeleton modulates ADMA-induced NF-kappaB nuclear translocation and ICAM-1 expression in endothelial cells

BACKGROUND

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, increases the activity of NF-κB (NF-κB) and then induces the expression of intercellular adhesion molecule-1 (ICAM-1). However, the mechanisms regulating ADMA-induced NF-κB activation are unknown. This study investigated the function of actin cytoskeleton for ADMA-induced NF-κB activation and ICAM-1 expression in endothelial cells.

MATERIAL/METHODS

Human umbilical vein endothelial cells (HUVEC) were cultured and left untreated or challenged for 24 h with 100 µM ADMA in the absence and presence of 5 µM cytochalasin D (Cyt D), or 1 µM Jasplakinolide (Jas). The form of actin cytoskeleton, the translocation of NF-κB, NF-κB DNA binding activity, and the expression of ICAM-1 were determined.

RESULTS

ADMA increased the formation of stress fiber in endothelial cells, and Cyt D clearly induced destabilization of the actin filaments. Either stabilizing or destabilizing the actin cytoskeleton prevented ADMA-induced NF-κB activation. It also showed that the inhibition of NF-κB activity was due to the impaired NF-κB nuclear translocation. Further, stabilizing or destabilizing the actin cytoskeleton inhibited the expression of the NF-κB target protein, ICAM-1.

CONCLUSIONS

Actin cytoskeleton may be engaged in modulated ADMA-induced NF-κB activation and thereby ICAM-1 expression in endothelial cells.

Sympathetic nerve traffic and asymmetric dimethylarginine in chronic kidney disease

BACKGROUND AND OBJECTIVES

Sympathetic overactivity and high levels of the endogenous inhibitor of NO synthase asymmetric dimethylarginine (ADMA) are prevalent risk factors in chronic kidney disease (CKD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 48 stage 2 to 4 CKD patients, we investigated the relationship between efferent postganglionic muscle sympathetic nerve traffic (microneurography) and circulating ADMA and analyzed the links between these risk factors and estimated GFR (eGFR), proteinuria, and different parameters of left ventricular (LV) geometry.

RESULTS

CKD patients characterized by sympathetic nerve traffic values in the third tertile showed the highest ADMA levels, and this association was paralleled by a continuous, positive relationship between these two risk factors (r = 0.32, P = 0.03) independent of other confounders. Both sympathetic nerve traffic and ADMA were inversely related to eGFR and directly to proteinuria and LV geometry. Remarkably, the variance of eGFR, proteinuria, and LV geometry explained by sympathetic nerve traffic and ADMA largely overlapped because sympathetic nerve traffic but not ADMA was retained as a significant correlate of the eGFR (P < 0.001) and of the relative wall thickness or the left ventricular mass index/LV volume ratio (P = 0.05) in models including both risk factors. ADMA, but not sympathetic nerve traffic, emerged as an independent correlate of proteinuria (P = 0.003) in a model including the same covariates.

CONCLUSIONS

Sympathetic activity and ADMA may share a pathway leading to renal disease progression, proteinuria, and LV concentric remodeling in CKD patients.

Chronic renal failure alters endothelial function in cerebral circulation in mice

We examined structure, composition, and endothelial function in cerebral arterioles after 4 wk of chronic renal failure (CRF) in a well-defined murine model (C57BL/6J and apolipoprotein E knockout female mice). We also determined quantitative expression of endothelial nitric oxide synthase (eNOS), phosphorylated eNOS (on serine 1177 and threonine 495), and caveolin-1; quantitative expression of markers of vascular inflammation or oxidative stress [Rock-1, Rock-2, VCAM-1, and peroxisome proliferator-activated receptor-γ (PPARγ)]; and the plasma concentration of l-arginine and asymmetric dimethylarginine (ADMA). Our hypothesis was that endothelial function would be impaired in cerebral arterioles during CRF following either a decrease in NO production (through alteration of eNOS expression or regulation) or an increase in NO degradation (due to oxidative stress or vascular inflammation). Endothelium-dependent relaxation was impaired during CRF, but endothelium-independent relaxation was not. CRF had no effect on cerebral arteriolar structure and composition. Quantitative expressions of eNOS, eNOS phosphorylated on serine 1177, caveolin-1, Rock-1, Rock-2, and VCAM-1 were similar in CRF and non-CRF mice. In contrast, quantitative expression of PPARγ (which exercises a protective role on blood vessels) was significantly lower in CRF mice, whereas quantitative expression of eNOS phosphorylated on the threonine 495 (the inactive form of eNOS) was significantly higher. Lastly, the plasma concentration of ADMA (a uremic toxin and an endogenous inhibitor of eNOS) was elevated and plasma concentration of l-arginine was low in CRF. In conclusion, endothelial function is impaired in a mouse model of early stage CRF. These alterations may be related (at least in part) to a decrease in NO production.

Methionine-induced homocysteinemia impairs endothelial function in hypertensives: the role of asymmetrical dimethylarginine and antioxidant vitamins

BACKGROUND

Nitric oxide synthase (NOS) inhibitor asymmetrical dimethylarginine (ADMA) is synthesized by the methylation of arginine as part of the methionine/homocysteine cycle. However, the mechanisms regulating ADMA synthesis in hypertension are unclear.

METHODS

We investigated the role of ADMA and antioxidants in endothelial dysfunction during methionine-induced homocysteinemia in hypertensives. Thirty-nine hypertensives and forty-nine normotensive controls underwent methionine loading (100 mg methionine/kg BW), after being randomized to receive vitamin C (2 g) and E (800 IU) or placebo. Endothelium-dependent dilation (EDD) was evaluated by plethysmography (baseline and 4-h post-methionine loading (4-h PML)).

RESULTS

Hypertensives had higher homocysteine at baseline (P < 0.001) and 4-h PML (P < 0.05), whereas methionine increased homocysteine in all groups. EDD was decreased in both vitamins and placebo groups in controls (P < 0.01 for both) and vitamins- and placebo-treated hypertensives (P < 0.05 and P < 0.01, respectively). In controls, ADMA was increased in both vitamin- and placebo groups (P < 0.01 for both) at 4-h PML. Hypertensives had higher ADMA at baseline (P < 0.01 vs. normotensive) and remained unchanged at 4-h PML (P = NS in placebo and vitamins treated).

CONCLUSIONS

ADMA is elevated in hypertensives but remains unchanged after methionine loading, suggesting that ADMA plays an important role in endothelial dysfunction in hypertensives, but it is not responsible for homocysteine-induced endothelial dysfunction in these patients.

Inflammation and asymmetric dimethylarginine for predicting death and cardiovascular events in ESRD patients

BACKGROUND

Endothelial dysfunction as assessed by asymmetric dimethylarginine (ADMA) and inflammation has been consistently linked to atherosclerosis, death, and cardiovascular (CV) events in ESRD patients. Inflammation amplifies the effect of ADMA on the severity of atherosclerosis in ESRD patients, but it is still unknown whether inflammation and ADMA interact in the high risk of death and CV events in this population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cohort of 225 hemodialysis patients, we investigated the interaction between inflammatory biomarkers (C-reactive protein and IL-6) and ADMA as predictors of death and CV events over an extended follow-up (13 years).

RESULTS

During follow-up, 160 patients died, and 123 had CV events. With crude and multiple Cox regression analyses, an interaction was found between inflammation biomarkers and ADMA for explaining death and CV events in ESRD patients. The adjusted hazard ratios (HRs) for death (HR, 2.18; 95% confidence interval [CI], 1.34 to 3.54) and CV outcomes (HR, 2.59; 95% CI, 1.47 to 4.55) of patients with C-reactive protein and ADMA above the median were higher than expected in the absence of interaction under the additive model (1.15 and 1.97, respectively) and significantly higher than in patients with only one biomarker above the median. Data analyses carried out by stratifying patients according to IL-6 provided similar results.

CONCLUSIONS

These data support the hypothesis that inflammation amplifies the risk of death and CV events associated with high ADMA levels in ESRD. These analyses further emphasize the need for intervention studies to attenuate inflammation and high ADMA levels in this population.

Protein-energy wasting and mortality in chronic kidney disease

Protein-energy wasting (PEW) is common in patients with chronic kidney disease (CKD) and is associated with an increased death risk from cardiovascular diseases. However, while even minor renal dysfunction is an independent predictor of adverse cardiovascular prognosis, PEW becomes clinically manifest at an advanced stage, early before or during the dialytic stage. Mechanisms causing loss of muscle protein and fat are complex and not always associated with anorexia, but are linked to several abnormalities that stimulate protein degradation and/or decrease protein synthesis. In addition, data from experimental CKD indicate that uremia specifically blunts the regenerative potential in skeletal muscle, by acting on muscle stem cells. In this discussion recent findings regarding the mechanisms responsible for malnutrition and the increase in cardiovascular risk in CKD patients are discussed. During the course of CKD, the loss of kidney excretory and metabolic functions proceed together with the activation of pathways of endothelial damage, inflammation, acidosis, alterations in insulin signaling and anorexia which are likely to orchestrate net protein catabolism and the PEW syndrome.

Effects of long-term disease-modifying antirheumatic drugs on endothelial function in patients with early rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with enhanced atherosclerosis and impaired endothelial function early after the onset of the disease and cardiovascular (CV) disease represents one of the leading causes of morbidity and mortality. It is well known that disease modifying antirheumatic drugs (DMARDs) are able to improve the course of the disease and the quality of life of these patients, but little is known about the effects of DMARDs on CV risk and endothelial dysfunction. Our goal was to examine the effects of long-term therapy with DMARDs on endothelial function and disease activity in early RA (ERA). Twenty-five ERA patients (mean age 52 ± 14.6 years, disease duration 6.24 ± 4.10 months) without evidence of CV involvement were evaluated for disease activity score (DAS-28), 2D-echo derived coronary flow reserve (CFR), common carotid intima-media thickness (IMT) and plasma asymmetric dimethylarginine (ADMA) levels at baseline and after 18 months of treatment with DMARDs (10 patients with methotrexate and 10 with adalimumab). DMARDs significantly reduced DAS-28 (6.0 ± 0.8 vs. 2.0 ± 0.7; P < 0.0001) and improved CFR (2.4 ± 0.2 vs. 2.7 ± 0.5; P < 0.01). Common carotid IMT and plasma ADMA levels did not show significant changes. The present study shows that DMARDs, beyond the well known antiphlogistic effects, are able to improve coronary microcirculation without a direct effect on IMT and ADMA, clinical markers of atherosclerosis. Treatment strategies in ERA patients with high inflammatory activity must be monitored to identify beneficial effects on preclinical markers of vascular function.

The use of targeted biomarkers for chronic kidney disease

There is a paucity of sensitive and specific biomarkers for the early prediction of CKD progression. The recent application of innovative technologies such as functional genomics, proteomics, and biofluid profiling has uncovered several new candidates that are emerging as predictive biomarkers of CKD. The most promising among these include urinary proteins such as neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and liver-type fatty acid binding protein. In addition, an improved understanding of the complex pathophysiologic processes underlying CKD progression has also provided discriminatory biomarkers of CKD progression that are being actively evaluated. Candidates included in this category are plasma proteins such as asymmetric dimethylarginine, adiponectin, apolipoprotein A-IV, fibroblast growth factor 23, neutrophil gelatinase-associated lipocalin, and the natriuretic peptides, as well as urinary N-acetyl-β-d-glucosaminidase. This review represents a critical appraisal of the current status of these emerging CKD biomarkers. Currently, none of these are ready for routine clinical use. Additional large, multicenter prospective studies are needed to validate the biomarkers, identify thresholds and cut-offs for prediction of CKD progression and adverse events, assess the effects of confounding variables, and establish the ideal assays.

Removal of asymmetric dimethylarginine during artificial liver support using fractionated plasma separation and adsorption

OBJECTIVE

Asymmetric dimethylarginine (ADMA) is the most potent endogenous nitric oxide synthase inhibitor. Elevated ADMA levels have been linked to increased mortality in different patient populations. Key regulation of ADMA levels mainly takes place in the liver. Hence, ADMA is elevated in liver disease. There is no specific pharmacological treatment to lower the elevated ADMA levels. Hemodialysis is of limited efficiency in removing ADMA as it is highly protein bound. Prometheus is an extracorporeal liver support system which allows the removal of protein-bound toxins. We assessed the efficiency of the Prometheus system in reducing high ADMA levels in patients with liver failure.

MATERIAL AND METHODS

We studied nine patients with acute-on-chronic liver failure and concomitant renal failure already necessitating hemodialysis. Seven patients needed intensive care treatment. Two consecutive sessions of Prometheus therapy of each 4 h were performed in all patients. ADMA and its structural isomer symmetrical dimethylarginine (SDMA) were determined using liquid chromatography-mass spectrometry.

RESULTS

ADMA levels correlated to model for end stage liver disease (MELD) score (r(s) = 0.62; p < 0.0001). Before Prometheus was started, levels of ADMA and SDMA were elevated (1.36 +/- 0.5 micromol/l and 1.90 +/- 0.4 micromol/l, respectively). During Prometheus treatments, plasma levels of ADMA dropped by a mean 25% (p < 0.0001) and SDMA levels by 22% (p < 0.0001). However, there was a significant rebound of ADMA levels between the two therapy sessions (p < 0.01).

CONCLUSIONS

This study shows for the first time that plasma levels of ADMA can be effectively lowered by an artificial liver support system (Prometheus). Effective elimination of ADMA might explain some of the beneficial clinical effects of these systems in patients with liver failure.

Management of osteoporosis in CKD Stages 3 to 5

Osteoporosis and chronic kidney disease (CKD) are both common conditions of older adults and both may be associated with substantial morbidity. However, biochemical and histologic changes that occur with progressive kidney disease require specific interventions, some of which may be concordant with osteoporosis management in the general population, whereas others may be less relevant or perhaps even harmful. In this article, we review the diagnosis of and management strategies for osteoporosis in individuals with CKD, placing these into perspective with the recently published KDIGO (Kidney Disease: Improving Global Outcomes) guidelines for treatment of CKD-mineral and bone disorder (CKD-MBD). Specifically, we highlight osteoporosis treatment recommendations by CKD stage and discuss new avenues for osteoporosis treatment that may be useful in individuals with CKD.

Characterization of a model of an arteriovenous fistula in the rat: the effect of L-NAME

Vascular access dysfunction contributes to the mortality of patients undergoing chronic hemodialysis. The present study analyzed the changes that evolve in a femoral arteriovenous fistula in the rat. The venous segment of this model exhibited, at 1 week, activation of pro-inflammatory transcription factors and up-regulation of pro-inflammatory, proliferative, procoagulant, and profibrotic genes; and at 4 weeks, the venous segment displayed neointimal hyperplasia, smooth muscle proliferation, and thrombus formation. These changes were accompanied by endothelial (e) nitric oxide synthase (NOS) and inducible (i) NOS up-regulation. The administration of NG-nitro-L-arginine methyl ester, an inhibitor of NOS activity, increased venous neointimal hyperplasia and pro-inflammatory gene expression (monocyte chemoattractant protein-1 and cytokine-induced neutrophil chemoattractant-1), increased systolic blood pressure, and decreased blood flow through the fistula. In another hypertensive model, the rat subtotal nephrectomy model, venous neointimal hyperplasia in the arteriovenous fistula was also exacerbated. We conclude that this arteriovenous fistula model recapitulates the salient features observed in dysfunctional, hemodialysis arteriovenous fistulas, and that venous neointimal hyperplasia is exacerbated when this model is superimposed in two different models of systemic hypertension. Since the uremic milieu contains increased amounts of asymmetric dimethylarginine, we speculate that such accumulation of this endogenous inhibitor of NOS, by virtue of its pressor or nitric oxide-depleting effects, or a combination thereof, may contribute to the limited longevity of arteriovenous fistulas used for hemodialysis.

Amino acid and protein metabolism in the human kidney and in patients with chronic kidney disease

The progressive loss of kidney function in patients with chronic kidney disease (CKD) is associated with a number of complications, including cardiovascular diseases, anemia, hyperparathyroidism, inflammation, metabolic acidosis, malnutrition and protein-energy wasting. The excess cardiovascular risk related to CKD is due in part to a higher prevalence of traditional atherosclerotic risk factors, in part to non-traditional, emerging risk factors peculiar to CKD. While even minor renal dysfunction is an independent predictor of adverse cardiovascular prognosis, nutritional changes are more often observed in an advanced setting. In addition, factors related to renal-replacement treatment may be implicated in the pathogenesis of heart disease and protein-energy wasting in dialysis-treated patients. Progressive alterations in kidney metabolism may cause progressive effects on cardiovascular status and nutrition. Altered kidney amino acid/protein metabolism and or excretion may be a key factor in the homeostasis of several vasoactive compounds and hormones in patients with more advanced disease. In this discussion recent research regarding the kidney handling of amino acids and protein turnover and their potential link with cardiovascular disease, progressive kidney dysfunction and nutritional status are reviewed.

Emerging risk factors and markers of chronic kidney disease progression

Chronic kidney disease (CKD) is a common condition with an increasing prevalence. A number of comorbidities are associated with CKD and prognosis is poor, with many patients experiencing disease progression. Recognizing the factors associated with CKD progression enables high-risk patients to be identified and given more intensive treatment if necessary. The identification of new predictive markers might improve our understanding of the pathogenesis and progression of CKD. This Review discusses a number of emerging factors and markers for which epidemiological evidence from prospective studies indicates an association with progression of CKD. The following factors and markers are discussed: asymmetric dimethylarginine, factors involved in calcium-phosphate metabolism, adrenomedullin, A-type natriuretic peptide, N-terminal pro-brain natriuretic peptide, liver-type fatty acid binding protein, kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, apolipoprotein A-IV, adiponectin and some recently identified genetic polymorphisms. Additional epidemiological and experimental data are required before these markers can be broadly used for the prediction of CKD progression and before the risk factors can be considered as potential drug targets in clinical interventional trials.

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.

SLCO4C1 transporter eliminates uremic toxins and attenuates hypertension and renal inflammation

Hypertension in patients with chronic kidney disease (CKD) strongly associates with cardiovascular events. Among patients with CKD, reducing the accumulation of uremic toxins may protect against the development of hypertension and progression of renal damage, but there are no established therapies to accomplish this. Here, overexpression of human kidney-specific organic anion transporter SLCO4C1 in rat kidney reduced hypertension, cardiomegaly, and inflammation in the setting of renal failure. In addition, SLCO4C1 overexpression decreased plasma levels of the uremic toxins guanidino succinate, asymmetric dimethylarginine, and the newly identified trans-aconitate. We found that xenobiotic responsive element core motifs regulate SLCO4C1 transcription, and various statins, which act as inducers of nuclear aryl hydrocarbon receptors, upregulate SLCO4C1 transcription. Pravastatin, which is cardioprotective, increased the clearance of asymmetric dimethylarginine and trans-aconitate in renal failure. These data suggest that drugs that upregulate SLCO4C1 may have therapeutic potential for patients with CKD.