ADMA, proteinuria, and insulin resistance in non-diabetic stage I chronic kidney disease

Renal hypertrophy and hyperfiltration is enhanced in early acquired compared with a congenital solitary function kidney model in sheep

A congenital solitary functioning kidney (C-SFK) or an early acquired SFK (EA-SFK), due to childhood unilateral nephrectomy (UNX), increases the risk of hypertension and kidney disease early in life. Evidence suggests that children with an EA-SFK may have a higher risk of future kidney disease compared with those with a C-SFK, but the precise underlying mechanisms need further investigation. C-SFK was induced by fetal UNX at 100 days gestation (term=150 days) in male sheep fetuses, and a sham procedure was performed. At approximately one month of age, EA-SFK was induced by UNX in male lambs. At eight months of age, total kidney weight was similar in all groups due to marked hypertrophy in the C-SFK and EA-SFK groups. Blood pressure was similar in EA-SFK and sham groups but ~12 mmHg higher in the C-SFK group compared with sham. Compared with the sham group, glomerular filtration rate (GFR) was ~9% less in the EA-SFK group and ~26% less in the C-SFK. GFR was ~23% higher in EA-SFK compared with the C-SFK group. Albuminuria was ~67% higher in C-SFK sheep but similar in the EA-SFK group compared with sham sheep. However, like the C-SFK group, the renal blood flow response to nitric oxide blockade was attenuated in the EA-SFK group compared with sham. In conclusion, long-term studies are needed to determine whether the higher hyperfiltration and disturbed vasodilator balance observed in EA-SFK sheep will cause an accelerated decline in renal function with aging.

Unveiling Selected Influences on Chronic Kidney Disease Development and Progression

Currently, more and more people are suffering from chronic kidney disease (CKD). It is estimated that CKD affects over 10% of the population worldwide. This is a significant issue, as the kidneys largely contribute to maintaining homeostasis by, among other things, regulating blood pressure, the pH of blood, and the water-electrolyte balance and by eliminating unnecessary metabolic waste products from blood. What is more, this disease does not show any specific symptoms at the beginning. The development of CKD is predisposed by certain conditions, such as diabetes mellitus or hypertension. However, these disorders are not the only factors promoting the onset and progression of CKD. The primary purpose of this review is to examine renin-angiotensin-aldosterone system (RAAS) activity, transforming growth factor-β1 (TGF-β1), vascular calcification (VC), uremic toxins, and hypertension in the context of their impact on the occurrence and the course of CKD. We firmly believe that a deeper comprehension of the cellular and molecular mechanisms underlying CKD can lead to an enhanced understanding of the disease. In the future, this may result in the development of medications targeting specific mechanisms involved in the decline of kidney function. Our paper unveils the selected processes responsible for the deterioration of renal filtration abilities.

Plasma arginine metabolites in health and chronic kidney disease

BACKGROUND

Elevated plasma asymmetric and symmetric dimethylarginine (ADMA and SDMA) are risk factors for chronic kidney disease (CKD) and cardiovascular disease. Using plasma cystatin C (pCYSC)-based estimated glomerular filtration rate (eGFR) trajectories, we identified a cohort at high risk of poor kidney-related health outcomes amongst members of the Dunedin Multidisciplinary Health and Development Study (DMHDS). We therefore examined associations between methylarginine metabolites and kidney function in this cohort.

METHODS

ADMA, SDMA, L-arginine and L-citrulline were measured in plasma samples from 45-year-olds in the DMHDS cohort by liquid chromatography-tandem mass spectrometry.

RESULTS

In a healthy DMHDS subset (n = 376), mean concentrations were: ADMA (0.40 ± 0.06 µmol/L), SDMA (0.42 ± 0.06 µmol/L), L-arginine (93.5 ± 23.1 µmol/L) and L-citrulline (24.0 ± 5.4 µmol/L). In the total cohort (n = 857), SDMA correlated positively with serum creatinine (Pearson's r = 0.55) and pCYSC (r = 0.55), and negatively with eGFR (r = 0.52). A separate cohort of 38 patients with stage 3-4 CKD (eGFR 15-60 mL/min/1.73 m2) confirmed significantly higher mean ADMA (0.61 ± 0.11 µmol/L), SDMA (0.65 ± 0.25 µmol/L) and L-citrulline (42.7 ± 11.8 µmol/L) concentrations. DMHDS members classified as high-risk of poor kidney health outcomes had significantly higher mean concentrations of all four metabolites compared with individuals not at risk. ADMA and SDMA individually predicted high-risk of poor kidney health outcomes with areas under the ROC curves (AUCs) of 0.83 and 0.84, and together with an AUC of 0.90.

CONCLUSIONS

Plasma methylarginine concentrations facilitate stratification for risk of CKD progression.

Association between Proteinuria Status and Risk of Hypertension: A Nationwide Population-Based Cohort Study

Proteinuria is associated with cardiovascular disease. However, the relationship between changes in proteinuria status and hypertension remains unclear. This study aimed to explore the association between changes in proteinuria status and the risk of developing hypertension with the data from the Korean National Health Insurance Database. We included participants without prior hypertension history who underwent their first health examination in 2003-2004 and a second examination in 2005-2006. Based on their proteinuria status during these two examinations, participants were classified into four groups: the proteinuria-free, proteinuria-resolved, proteinuria-developed, and chronic proteinuria groups. The study outcome was the incidence of hypertension. The study included 935,723 participants followed for a median of 14.2 years (mean age: 40.96 ± 11.01, 62.5% male participants). During this period, 346,686 (37.1%) cases of hypertension were reported. The chronic proteinuria group had the highest hypertension risk, followed by the proteinuria-developed, proteinuria-resolved, and proteinuria-free groups (p < 0.001). Those who recovered from proteinuria had a lower risk of developing hypertension than those with chronic proteinuria (hazard ratio: 0.58; 95% confidence interval: 0.53-0.63, p < 0.001). In contrast, individuals who developed proteinuria had a higher risk of hypertension than proteinuria-free individuals (hazard ratio: 1.31; 95% confidence interval: 1.26-1.35, p < 0.001). Our findings suggest a significant association between proteinuria status changes and hypertension. Effective management of proteinuria may potentially decrease the risk of developing hypertension.

Study of Serum Fibroblast Growth Factor 23 as a Predictor of Endothelial Dysfunction among Egyptian Patients with Diabetic Kidney Disease

Endothelial dysfunction in patients with diabetic nephropathy is caused by nontraditional factors in addition to common risk factors (e.g., hypertension) in people with normal kidney function. These nontraditional factors include factors involved in mineral bone disease in these patients. One of these factors is fibroblast growth factor 23 (FGF-23). We aimed to evaluate the relationship between flow-mediated dilatation (FMD) as a measure of endothelial dysfunction and FGF-23. This was a cross-sectional observational study that was conducted on 100 diabetic patients (Group I: 50 patients with nephropathy; Group II: 50 patients without nephropathy) and 50 healthy volunteers (Group III). Serum levels of intact FGF-23, interleukin-6, intact parathyroid hormone, and 25-hydroxyvitamin D (25-(OH)Vit D); estimated insulin resistance; and FMD were evaluated. FGF-23 was significantly higher in Group I (median: 101 pg/mL) and Group II (median: 101 pg/mL) than in Group III (median: 4 pg/mL) (P <0.001), but FGF-23 was not significantly different between Groups I and II. A significant positive correlation was found between serum levels of FGF-23 and phosphorus in Group I. A significant negative correlation was found between serum levels of FGF-23 and 25-(OH)Vit D in Group II. However, FGF-23 failed to show a significant correlation with FMD in patients with diabetic nephropathy. Our data suggest another factor that rises earlier than FGF-23 in diabetic nephropathy and causes endothelial dysfunction.

The Vascular Endothelium and Coagulation: Homeostasis, Disease, and Treatment, with a Focus on the Von Willebrand Factor and Factors VIII and V

The vascular endothelium has several important functions, including hemostasis. The homeostasis of hemostasis is based on a fine balance between procoagulant and anticoagulant proteins and between fibrinolytic and antifibrinolytic ones. Coagulopathies are characterized by a mutation-induced alteration of the function of certain coagulation factors or by a disturbed balance between the mechanisms responsible for regulating coagulation. Homeostatic therapies consist in replacement and nonreplacement treatments or in the administration of antifibrinolytic agents. Rebalancing products reestablish hemostasis by inhibiting natural anticoagulant pathways. These agents include monoclonal antibodies, such as concizumab and marstacimab, which target the tissue factor pathway inhibitor; interfering RNA therapies, such as fitusiran, which targets antithrombin III; and protease inhibitors, such as serpinPC, which targets active protein C. In cases of thrombophilia (deficiency of protein C, protein S, or factor V Leiden), treatment may consist in direct oral anticoagulants, replacement therapy (plasma or recombinant ADAMTS13) in cases of a congenital deficiency of ADAMTS13, or immunomodulators (prednisone) if the thrombophilia is autoimmune. Monoclonal-antibody-based anti-vWF immunotherapy (caplacizumab) is used in the context of severe thrombophilia, regardless of the cause of the disorder. In cases of disseminated intravascular coagulation, the treatment of choice consists in administration of antifibrinolytics, all-trans-retinoic acid, and recombinant soluble human thrombomodulin.

Methods to evaluate vascular function: a crucial approach towards predictive, preventive, and personalised medicine

Endothelium, the gatekeeper of our blood vessels, is highly heterogeneous and a crucial physical barrier with the ability to produce vasoactive and protective mediators under physiological conditions. It regulates vascular tone, haemostasis, vascular inflammation, remodelling, and angiogenesis. Several cardio-, reno-, and cerebrovascular diseases begin with the dysfunction of endothelial cells, and more recently, COVID-19 was also associated with endothelial disease highlighting the need to monitor its function towards prevention and reduction of vascular dysfunction. Endothelial cells are an important therapeutic target in predictive, preventive, and personalised (3P) medicine with upmost importance in vascular diseases. The development of novel non-invasive techniques to access endothelial dysfunction for use in combination with existing clinical imaging modalities provides a feasible opportunity to reduce the burden of vascular disease. This review summarises recent advances in the principles of endothelial function measurements. This article presents an overview of invasive and non-invasive techniques to determine vascular function and their major advantages and disadvantages. In addition, the article describes mechanisms underlying the regulation of vascular function and dysfunction and potential new biomarkers of endothelial damage. Recognising these biomarkers is fundamental towards a shift from reactive to 3P medicine in the vascular field. Identifying vascular dysfunction earlier with non-invasive or minimally invasive techniques adds value to predictive diagnostics and targeted prevention (primary, secondary, tertiary care). In addition, vascular dysfunction is a potential target for treatments tailored to the person.

Εndothelial and microvascular function in CKD: Evaluation methods and associations with outcomes

BACKGROUND

Cardiovascular disease is the major cause of morbidity and mortality in patients with chronic kidney disease (CKD). Endothelial dysfunction, the hallmark of atherosclerosis, is suggested to be involved pathogenetically in cardiovascular and renal disease progression in these patients.

METHODS

This is a narrative review presenting the techniques and markers used for assessment of microvascular and endothelial function in patients with CKD and discussing findings of the relevant studies on the associations of endothelial dysfunction with co-morbid conditions and outcomes in this population.

RESULTS

Venous Occlusion Plethysmography was the first method to evaluate microvascular function; subsequently, several relevant techniques have been developed and used in patients with CKD, including brachial Flow-Mediated Dilatation, and more recently, Near-Infrared Spectroscopy and Laser Speckle Contrast Analysis. Furthermore, several circulating biomarkers are commonly used in clinical research. Studies assessing endothelial function using the above techniques and biomarkers suggest that endothelial dysfunction occurs early in CKD and contributes to the target organ damage, cardiovascular events, death and progression towards end-stage kidney disease.

CONCLUSIONS

Older and newer functional methods and several biomarkers have assessed endothelial dysfunction in CKD; accumulated evidence supports an association of endothelial dysfunction with outcomes. Future research with new, non-invasive and easily applicable methods could further delineate the role of endothelial dysfunction on cardiovascular and renal disease progression in patients with CKD.

Uremic Toxins in the Progression of Chronic Kidney Disease and Cardiovascular Disease: Mechanisms and Therapeutic Targets

Chronic kidney disease (CKD) is a progressive loss of renal function. The gradual decline in kidney function leads to an accumulation of toxins normally cleared by the kidneys, resulting in uremia. Uremic toxins are classified into three categories: free water-soluble low-molecular-weight solutes, protein-bound solutes, and middle molecules. CKD patients have increased risk of developing cardiovascular disease (CVD), due to an assortment of CKD-specific risk factors. The accumulation of uremic toxins in the circulation and in tissues is associated with the progression of CKD and its co-morbidities, including CVD. Although numerous uremic toxins have been identified to date and many of them are believed to play a role in the progression of CKD and CVD, very few toxins have been extensively studied. The pathophysiological mechanisms of uremic toxins must be investigated further for a better understanding of their roles in disease progression and to develop therapeutic interventions against uremic toxicity. This review discusses the renal and cardiovascular toxicity of uremic toxins indoxyl sulfate, p-cresyl sulfate, hippuric acid, TMAO, ADMA, TNF-α, and IL-6. A focus is also placed on potential therapeutic targets against uremic toxicity.

Assessment of Endothelial and Microvascular Function in CKD: Older and Newer Techniques, Associated Risk Factors, and Relations with Outcomes

BACKGROUND

Endothelium is the inner cellular lining of the vessels that modulates multiple biological processes including vasomotor tone, permeability, inflammatory responses, hemostasis, and angiogenesis. Endothelial dysfunction, the basis of atherosclerosis, is characterized by an imbalance between endothelium-derived relaxing factors and endothelium-derived contracting factors.

SUMMARY

Starting from the semi-invasive venous occlusion plethysmography, several functional techniques have been developed to evaluate microvascular function and subsequently used in patients with CKD. Flow-mediated dilatation of the forearm is considered to be the "gold standard," while in the last years, novel, noninvasive methods such as laser speckle contrast imaging and near-infrared spectroscopy are scarcely used. Moreover, several circulating biomarkers of endothelial function have been used in studies in CKD patients. This review summarizes available functional methods and biochemical markers for the assessment of endothelial and microvascular function in CKD and discusses existing evidence on their associations with comorbid conditions and outcomes in this population. Key Messages: Accumulated evidence suggests that endothelial dysfunction occurs early in CKD and is associated with target organ damage, progression of renal injury, cardiovascular events, and mortality. Novel methods evaluating microvascular function can offer a detailed, real-time assessment of underlying phenomena and should be increasingly used to shed more light on the role of endothelial dysfunction on cardiovascular and renal disease progression in CKD.

Maternal serum levels of asymmetric dimethylarginine in normal and preeclamptic pregnancies

The study aims to investigate maternal serum levels of asymmetric dimethylarginine (ADMA) in preeclampsia. Serum samples were collected from 57 women with preeclamptic pregnancies and 30 women with normal pregnancies during the third trimester. ADMA levels were measured with the ELISA method. ADMA levels in preeclamptic pregnancies were significantly higher when compared with normal pregnancies (2.35 ± 3.20 nmol/l versus 0.35 ± 0.10 nmol/l; p < .05). ADMA levels show a significant positive correlation with systolic and diastolic pressure, urea, and creatinine but a negative correlation with proteinuria. ADMA levels have a significant strong correlation with PE. ADMA levels are significantly higher in preeclamptic pregnancy compared with normal pregnancy.

Enhancing kidney DDAH-1 expression by adenovirus delivery reduces ADMA and ameliorates diabetic nephropathy

Endothelial dysfunction, characterized by reduced bioavailability of nitric oxide and increased oxidative stress, is a hallmark characteristic in diabetes and diabetic nephropathy (DN). High levels of asymmetric dimethylarginine (ADMA) are observed in several diseases including DN and are a strong prognostic marker for cardiovascular events in patients with diabetes and end-stage renal disease. ADMA, an endogenous endothelial nitric oxide synthase (NOS3) inhibitor, is selectively metabolized by dimethylarginine dimethylaminohydrolase (DDAH). Low DDAH levels have been associated with cardiac and renal dysfunction, but its effects on DN are unknown. We hypothesized that enhanced renal DDAH-1 expression would improve DN by reducing ADMA and restoring NOS3 levels. DBA/2J mice injected with multiple low doses of vehicle or streptozotocin were subsequently injected intrarenally with adenovirus expressing DDAH-1 (Ad-h-DDAH-1) or vector control [Ad-green fluorescent protein (GFP)], and mice were followed for 6 wk. Diabetes was associated with increased kidney ADMA and reduced kidney DDAH activity and DDAH-1 expression but had no effect on kidney DDAH-2 expression. Ad-GFP-treated diabetic mice showed significant increases in albuminuria, histological changes, glomerular macrophage recruitment, inflammatory cytokine and fibrotic markers, kidney ADMA levels, and urinary thiobarbituric acid reactive substances excretion as an indicator of oxidative stress, along with a significant reduction in kidney DDAH activity and kidney NOS3 mRNA compared with normal mice. In contrast, Ad-h-DDAH-1 treatment of diabetic mice reversed these effects. These data indicate, for the first time, that DDAH-1 mediates renal tissue protection in DN via the ADMA-NOS3-interaction. Enhanced renal DDAH-1 activity could be a novel therapeutic tool for treating patients with diabetes.

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 Levels of Protein-Bound Methylglyoxal-Derived Hydroimidazolone-1 are Independently Correlated with Asymmetric Dimethylarginine

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase, being involved in endothelial dysfunction. Furthermore, ADMA levels have been shown to predict future cardiovascular events in patients with coronary risk factors, such as diabetes and hypertension. We have previously found that glyceraldehyde-derived advanced glycation end products (glycer-AGEs) stimulate ADMA generation in vitro and the levels are associated with ADMA, endothelial dysfunction, and vascular inflammation in humans. However, it remains unclear what structurally distinct glycer-AGEs are independent correlates of ADMA. In this study, we addressed the issue. We measured serum levels of protein-bound and free methylglyoxal-derived hydroimidazolone-1 (MG-H1) and argpyrimidine, two major structurally identified glycer-AGEs by liquid chromatography-tandem mass spectrometry in 128 outpatients, and examined the correlations of these AGEs, vascular stiffness, and inflammation with ADMA. Moreover, we examined whether the changes in serum MG-H1 and argpyrimidine levels after 4-month treatment with oral hypoglycemic agents (OHAs) were associated with those of ADMA in other 44 patients with impaired glucose tolerance or type 2 diabetes. Multiple stepwise regression analysis revealed that protein-bound MG-H1, high-density lipoprotein cholesterol (inversely), high-sensitivity C-reactive protein, and cardio-ankle vascular index were independently correlated with ADMA (R² = 0.259). Treatment with OHAs significantly decreased ADMA levels in 44 glucose-intolerant or type 2 diabetic patients, and the changes in protein-bound MG-H1 levels were positively associated with those in ADMA values (p < 0.05). This study demonstrates that serum levels of protein-bound MG-H1 are independently correlated with ADMA and may be a therapeutic target for cardiovascular disease.

Albuminuria, Reduced Kidney Function, and the Risk of ST - and non-ST-segment-elevation myocardial infarction

Background Chronic kidney disease is a recognized independent risk factor for cardiovascular disease, but whether the risks of ST-segment-elevation myocardial infarction ( STEMI ) and non-ST-segment-elevation myocardial infarction ( NSTEMI ) differ in the chronic kidney disease population is unknown. Methods and Results Using administrative data from Ontario, Canada, we examined patients ≥66 years of age with an outpatient estimated glomerular filtration rate ( eGFR ) and albuminuria measure for incident myocardial infarction from 2002 to 2015. Adjusted Fine and Gray subdistribution hazard models accounting for the competing risk of death were used. In 248 438 patients with 1.2 million person-years of follow-up, STEMI , NSTEMI , and death occurred in 1436 (0.58%), 4431 (1.78%), and 30 015 (12.08%) patients, respectively. The highest level of albumin-to-creatinine ratio (>30 mg/mmol) was associated with a 2-fold higher adjusted risk of both STEMI and NSTEMI among patients with eGFR ≥60 mL/(min·1.73 m2) compared to albumin-to-creatinine ratio <3 mg/mmol. The lowest level of eGFR (<30 mL/[min·1.73 m2]) was not associated with higher STEMI risk but with a 4-fold higher risk of NSTEMI compared to those with eGFR ≥60 mL/(min·1.73 m2). The lowest eGFR (<30 mL/[min·1.73 m2]) and highest albumin-to-creatinine ratio (>30 mg/mmol) were associated with a greater than 4-fold higher risk of both STEMI and NSTEMI (subdistribution hazard models [95% confidence interval] 4.53 [3.30-6.21] and 4.42 [3.67-5.32], respectively) compared to albumin-to-creatinine ratio <3 mg/mmol and eGFR ≥60 mL/(min·1.73 m2). Conclusions Elevations in albuminuria are associated with a higher risk of both NSTEMI and STEMI , regardless of kidney function, whereas reduced kidney function alone is associated with a higher NSTEMI risk.

Serum concentrations of asymmetric and symmetric dimethylarginine are associated with mortality in acute heart failure patients

BACKGROUND

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine are established predictors of total and cardiovascular mortality. However, the predictive capacity of ADMA and SDMA for hospital and 3-months mortality of patients with acute heart failure (AHF) is unknown.

METHODS & RESULTS

Out of 152 included AHF patients, 79 (52%) were female, and the mean patient age was 75.2 ± 10.3 years. Hospital and three-month mortality rates were 14.5% and 27.4%, respectively. Serum ADMA and SDMA levels at admission, determined by reversed phase high performance liquid chromatography, were higher in patients having at least one of the three signs implying venous volume overload (enlarged liver, ascites, peripheral edema), a consequence of right-sided heart failure, compared to patients without those signs. Univariable logistic regression analyses revealed a significant positive association of ADMA and SDMA concentrations with hospital mortality [odds ratio (OR) and 95% confidence interval (CI) per standard deviation (SD) increase: 2.22 (1.37-3.79), p = 0.002, and 2.04 (1.34-3.18), p = 0.001, respectively], and 3-months mortality [2.06 (1.36-3.26), p = 0.001, and 2.52 (1.67-4.04), p < 0.001, respectively]. These associations remained significant after adjusting for age, sex, mean arterial pressure, low-density lipoprotein cholesterol, glomerular filtration rate, and N-terminal pro-brain natriuretic peptide.

CONCLUSIONS

We conclude that ADMA and SDMA concentrations are associated with hospital and 3-month mortality and are increased by venous volume overload in AHF patients.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

Relation of asymmetrical dimethylarginine levels with renal outcomes in hypertensive patients with and without type 2 diabetes mellitus

AIM

The aim of the study was to evaluate the association between high plasma ADMA levels, a biomarker of endothelial dysfunction, with the progression of albuminuria and chronic kidney disease (CKD) in hypertensive patients, with and without type 2 diabetes mellitus.

METHODS

We successfully contacted 213 of 644 patients who had been evaluated between 2004 and 2005 and for whom basal data were available. After the exclusion of 51 patients, 162 hypertensive patients who were free from albuminuria were stratified into the following 4 groups according to the presence of diabetes and plasma ADMA percentiles: general hypertensive patients with high levels of plasma ADMA (>P4 or ADMA > 0.61 μmol/L), general hypertensive patients with low levels of plasma ADMA (≤P4), diabetic hypertensive patients with high levels of plasma ADMA (>P4), and diabetic hypertensive patients with low levels of plasma ADMA (≤P4).

RESULTS

The patients were prospectively evaluated over 5.8 years. High ADMA levels were associated with the progression of albuminuria in hypertensive patients, with and without type 2 diabetes. Major increases in the ADMA value during follow-up were associated with the progression of CKD, and direct correlations between ADMA changes and GFR changes were observed in the whole group and in the subgroup of diabetic patients.

CONCLUSIONS

We suggest that high plasma ADMA levels might be a biomarker of renal disease progression and might even be an early predictor of albuminuria and its progression to the late stages of renal disease in hypertensive and diabetic hypertensive patients.

ADMA predicts major adverse renal events in patients with mild renal impairment and/or diabetes mellitus undergoing coronary angiography

Asymmetric dimethylarginine (ADMA) is a competitive inhibitor of the nitric oxide (NO)-synthase and a biomarker of endothelial dysfunction (ED). ED plays an important role in the pathogenesis of contrast-induced nephropathy (CIN). The aim of our study was to evaluate serum ADMA concentration as a biomarker of an acute renal damage during the follow-up of 90 days after contrast medium (CM) application.Blood samples were obtained from 330 consecutive patients with diabetes mellitus or mild renal impairment immediately before, 24 and 48 hours after the CM application for coronary angiography. The patients were followed for 90 days. The composite endpoints were major adverse renal events (MARE) defined as occurrence of death, initiation of dialysis, or a doubling of serum creatinine concentration.Overall, ADMA concentration in plasma increased after CM application, although, there was no differences between ADMA levels in patients with and without CIN. ADMA concentration 24 hours after the CM application was predictive for dialysis with a specificity of 0.889 and sensitivity of 0.653 at values higher than 0.71 μmol/L (area under the curve: 0.854, 95% confidential interval: 0.767-0.941, P < 0.001). This association remained significant in multivariate Cox regression models adjusted for relevant factors of long-term renal outcome. 24 hours after the CM application, ADMA concentration in plasma was predictive for MARE with a specificity of 0.833 and sensitivity of 0.636 at a value of more than 0.70 μmol/L (area under the curve: 0.750, 95% confidence interval: 0.602-0.897, P = 0.004). Multivariate logistic regression analysis confirmed that ADMA and anemia were significant predictors of MARE. Further analysis revealed that increased ADMA concentration in plasma was highly significant predictor of MARE in patients with CIN. Moreover, patients with CIN and MARE had the highest plasma ADMA levels 24 hours after CM exposure in our study cohort. The impact of ADMA on MARE was independent of such known CIN risk factors as anemia, pre-existing renal failure, pre-existing heart failure, and diabetes.ADMA concentration in plasma is a promising novel biomarker of major contrast-induced nephropathy-associated events 90 days after contrast media exposure.

Asymmetric Dimethylarginine and Its Relation As a Biomarker in Nephrologic Diseases

It is encouraging to observe that a search for publications on "asymmetric dimethylarginine (ADMA)" in PubMed, as updated on June 2016, yielded >2500 items, 24 years after a splendid paper published by Vallance et al in which the authors proposed that ADMA accumulation could be a cardiovascular risk factor in chronic kidney diseases. ADMA is the endogenous inhibitor of nitric oxide synthase and is related to endothelial dysfunction, which plays an important role in vascular damage elicited by various cardiometabolic risk factors. Although current knowledge suggests that ADMA has critical central roles in renal diseases, there are still unexplained details. The present article aims to provide a review on ADMA and its relation as a biomarker in nephrologic diseases. We aimed to systematize articles in which ADMA levels were assessed in order to clarify its role in many diseases and establish its reference values in different populations.

The influence of renin angiotensin aldosterone system blockers on asymmetric dimethylarginine levels in patients with chronic glomerulonephritis

Endothelial dysfunction could be related to the limited availability of nitric oxide (NO). NO is synthesized with the participation of an NO synthase whose activity is inhibited by asymmetric dimethylarginine (ADMA). The synthesis of ADMA is exacerbated by oxidative stress, and several studies have shown the efficacy of drugs acting on the renin-angiotensin-aldosterone system (RAAS) (converting enzyme inhibitors and angiotensin II receptor antagonists) in reducing the level of ADMA. The probable mechanism of drug action is a reduction of oxidative stress through a decrease of angiotensin II formation. The aim of this study was to assess the influence of RAAS blockers on the plasma concentration of ADMA in patients with chronic glomerulonephritis (ChGN). The study included 37 patients, placed into group A and group B, depending on the treatment. Both groups were treated with RAAS blockers. In group B, immunosuppressive drugs were additionally administered. The control visits were at the 0, 6 and 12 months of observation. In both the studied groups (A+B), a significant reduction of ADMA (0.77 vs 0.4 μmol/l; p<0.05) was noticed. In patients suffering from ChGN, the use of RAAS blockers resulted in a significant decrease of plasma ADMA concentration, independently of immunosupressive treatment.

1 H NMR-based metabolomics exploring urinary biomarkers correlated with proteinuria in focal segmental glomerulosclerosis: a pilot study

Focal segmental glomerulosclerosis (FSGS) is a common glomerulonephritis, and its rates of occurrence are increasing worldwide. Proteinuria is a clinical defining feature of FSGS which correlates with the severity of podocyte injury in patients with nephrotic-range protein excretion. Metabolite biomarkers corresponding with the level of proteinuria could be considered as non-invasive complementary prognostic factors to proteinuria. The urine samples of 15 patients (n = 6 women and n = 9 men) with biopsy-proven FSGS were collected and subjected to nuclear magnetic resonance (NMR) analysis for metabolite profiling. Multivariate statistical analyses, including principal component analysis and orthogonal projection to latent structure discriminant analysis, were applied to construct a predictive model based on patients with proteinuria >3000 mg/day and <3000 mg/day. In addition, random forest was performed to predict differential metabolites, and pathway analysis was performed to find the defective pathways responsible for proteinuria. Ten metabolites, significant in both statistical methods (orthogonal projection to latent structure discriminant analysis and random forest), were considered as prognostic biomarkers for FSGS: citrulline, dimethylamine, proline, acetoacetate, alpha-ketoisovaleric acid, valine, isobutyrate, D-Palmitylcarnitine, histidine, and N-methylnicotinamide. Pathway analysis revealed impairment of the branched-chain amino acid degradation pathways in patients with massive proteinuria. This study shows that metabolomics can reveal the molecular changes corresponding with disease progression in patients with FSGS and provide a new insight for pathogenic pathways. Copyright © 2016 John Wiley & Sons, Ltd.

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).

Metabolomic Profiling of Arginine Metabolome Links Altered Methylation to Chronic Kidney Disease Accelerated Atherosclerosis

Atherosclerotic cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD), but the mechanisms underlying vascular disease has not been fully understood. As the nitrogen donor in nitric oxide (NO^·) synthesis, arginine and its metabolic products are integrally linked to vascular health and information. We hypothesized that derangements in this pathway could explain, in part, increased atherosclerotic risk in CKD. We developed a targeted metabolomic platform to profile quantitatively arginine metabolites in plasma by liquid chromatography tandem mass spectrometry (LC/MS). Male low-density lipoprotein receptor defcient (LDLr^−/−) mice at age 6 weeks were subjected to sham or 5/6 nephrectomy surgery to induce CKD. Subsequently, the animals were maintained on high fat diet for 24 weeks. Targeted metabolomic analysis of arginine metabolites in plasma was performed by isotope dilution LC/MS including asymmetric dimethyl arginine (ADMA), symmetric dimethyl arginine (SDMA), N-mono-methylarginine (NMMA), arginine and citrulline. Although elevated plasma levels of ADMA and SDMA were found in the CKD mice, only higher ADMA level correlated with degree of atherosclerosis. No significant differences were noted in levels of NMMA between the groups. CKD mice had high levels of citrulline and arginine, but ADMA levels had no correlation with either of these metabolites. These fndings strongly implicate altered arginine methylation and accumulation of ADMA, may in part contribute to CKD accelerated atherosclerosis. It raises the possibility that interrupting pathways that generate ADMA or enhance its metabolism may have therapeutic potential in mitigating atherosclerosis.

L-Arginine and its metabolites in kidney and cardiovascular disease

L-Arginine is a semi essential amino acid synthesised from glutamine, glutamate and proline via the intestinal-renal axis in humans and most mammals. L-Arginine degradation occurs via multiple pathways initiated by arginase, nitric-oxide synthase, Arg: glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine and agmatine with each having enormous biological importance. Several disease are associated to an L-arginine impaired levels and/or to its metabolites: in particular various L-arginine metabolites may participate in pathogenesis of kidney and cardiovascular disease. L-Arginine and its metabolites may constitute both a marker of pathology progression both the rationale for manipulating L-arginine metabolism as a strategy to ameliorate these disease. A large number of studies have been performed in experimental models of kidney disease with sometimes conflicting results, which underlie the complexity of Arg metabolism and our incomplete knowledge of all the mechanisms involved. Moreover several lines of evidence demonstrate the role of L-arg metabolites in cardiovascular disease and that L-arg administration role in reversing endothelial dysfunction, which is the leading cause of cardiovascular diseases, such as hypertension and atherosclerosis. This review will discuss the implication of the mains L-arginine metabolites and L-arginine-derived guanidine compounds in kidney and cardiovascular disease considering the more recent literature in the field.

Elevated asymmetric dimethylarginine is associated with oxidant stress aggravation in patients with early stage autosomal dominant polycystic kidney disease

BACKGROUND/AIMS

In experimental models of polycystic kidney disease impaired bioavailability of nitric oxide (NO) and elevated mRNA expression of oxidative stress markers at the kidney level was noted. However, clinical studies investigating the potential role of endothelial dysfunction and oxidative stress in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD) are limited. We evaluated asymmetric dimethylarginine (ADMA) as marker of NO synthase inhibitor as well as 15-F2t-Isoprostane and oxidized-low density lipoprotein (oxidized-LDL) as measures of oxidative stress in patients with early stages ADPKD.

METHODS

We recruited 26 ADPKD patients (Group A) with modestly impaired renal function (eGFR 45-70 ml/min/1.73 m(2)), 26 age- and sex-matched ADPKD patients (Group B) with relatively preserved renal function (eGFR)>70 ml/min/1.73 m(2)), and 26 age- and sex-matched controls (Group C). Determination of circulating levels of ADMA, 15-F2t-Isoprostane, oxidized-LDL and routine biochemistry was performed.

RESULTS

Group A and B had significantly higher ADMA levels as compared to controls (1.68 ± 0.7 vs 0.51 ± 0.2 μmol/l, P<0.001 and 1.26 ± 0.7 vs 0.51 ± 0.2 μmol/l, P<0.001, respectively). 15-F2t-IsoP and oxidized-LDL levels were also significantly higher in Group B relative to controls (788.8 ± 185.0 vs 383.1 ± 86.0 pgr/ml, P<0.001 and 11.4 ± 6.6 vs 6.4 ± 2.6 EU/ml, P<0.05 respectively) and were further elevated in Group A. In correlation analysis, ADMA levels exhibited strong associations with levels of 15-F2t-Isoprostane (r=0.811, P<0.001) and oxidized-LDL (r=0.788, P<0.001), whereas an inverse correlation was evident between ADMA and eGFR (r=-0.460, P<0.001).

CONCLUSION

This study shows elevation in circulating levels of ADMA along with aggravation of oxidative stress from the early stages of ADPKD. © 2014 S. Karger AG, Basel.

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.

Asymmetric dimethylarginine accumulates in the kidney during ischemia/reperfusion injury

Ischemia/reperfusion injury is the leading cause of acute tubular necrosis. Nitric oxide has a protective role against ischemia/reperfusion injury; however, the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in ischemia/reperfusion injury remains unclear. ADMA is produced by protein arginine methyltransferase (PRMT) and is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). Here we examined the kinetics of ADMA and PRMT and DDAH expression in the kidneys of ischemia/reperfusion-injured mice. After the injury, DDAH-1 levels were decreased and renal and plasma ADMA values were increased in association with renal dysfunction. Renal ADMA was correlated with 8-hydroxy-2'-deoxyguanosine, a marker of oxidative stress. An antioxidant, N-acetylcysteine, or a proteasomal inhibitor, MG-132, restored these alterations. Infusion of subpressor dose of ADMA exacerbated renal dysfunction, capillary loss, and tubular necrosis in the kidneys of ischemia/reperfusion-injured wild mice, while damage was attenuated in DDAH transgenic mice. Thus, ischemia/reperfusion injury-induced oxidative stress may reduce DDAH expression and cause ADMA accumulation, which may contribute to capillary loss and tubular necrosis in the kidney.

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.

Homeostatic model assessment indices in evaluation of insulin resistance and secretion in hemodialysis patients

Background

Some previous observations suggest that insulin resistance and glucose metabolism disturbances are frequent complications of chronic kidney disease. However, there are no conclusive studies on other indices of the effectiveness of insulin action in end-stage renal disease (ESRD) patients, including chronically hemodialysed (HD) ones.

Material/Methods

The groups comprised 33 non-diabetic ESRD hemodialysed patients and 33 healthy controls matched for age, sex, and body mass index (BMI). In both groups, HOMA-%B, HOMA-%S, HOMA-IR indices, and DI were calculated using HOMA1 and HOMA2 as measures of insulin resistance. The indices were also assessed in subgroups divided according to BMI.

Results

Mean fasting plasma glucose concentrations were lower in ESRD patients than in healthy persons (82.4±10.4 vs. 93.9±11.6, p=0.001). Fasting serum insulin concentrations were similar in both groups (median 6.8 vs. 6.0 mU/l, p=0.698). HOMA1-%B values were higher in ESRD patients than controls (median 137.1 vs. 81.6, p=0.002). HOMA1-%S (median 75.6 vs. 71.5) and HOMA1-IR (median 1.3 vs. 1.4) values were not significantly different (p=0.264 and p=0.189, respectively). DI1 levels were higher for HD patients than for healthy subjects (median 1.16 vs. 0.53, p<0.001). In subgroup analysis, all statistically significant differences were restricted mainly to persons with BMI <25 kg/m². Similar results as for the HOMA1 model were obtained for HOMA2.

Conclusions

1. HOMA beta-cell function is strongly correlated with HOMA insulin resistance in HD patients. 2. In non-diabetic ESRD hemodialysed patients, the HOMA indices and DI may be useful and important models in interpretation of glucose metabolism disturbances.

Role of asymmetrical dimethylarginine in the progression of renal disease

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid found in tissues and cells that circulates in plasma and is excreted in urine. It inhibits nitric oxide synthases (NOs) and produces considerable cardiovascular biological effects. Several studies have suggested that plasma concentrations of ADMA provide a marker of risk for endothelial dysfunction and cardiovascular disease. In animal and in population studies ADMA has been associated with progression of CKD. Several mechanisms may be involved in this association, such as compromise of the integrity of the glomerular filtration barrier and development of renal fibrosis. This review summarizes the existing literature on the biology and physiology of ADMA focusing on its role in the progression of renal disease.

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.

Glucagon-like peptide-1 receptor agonist inhibits asymmetric dimethylarginine generation in the kidney of streptozotocin-induced diabetic rats by blocking advanced glycation end product-induced protein arginine methyltranferase-1 expression

Advanced glycation end products (AGEs) and their receptor (RAGE) play a role in diabetic nephropathy. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, contributes to diabetic nephropathy. We have found that glucagon-like peptide-1 (GLP-1) inhibits the AGE-induced inflammatory reactions in endothelial cells. However, effects of GLP-1 on the AGE-RAGE-ADMA axis are unknown. This study examined the effects of GLP-1 on reactive oxygen species (ROS) generation, gene expression of protein arginine methyltransfetase-1 (PRMT-1), an enzyme that mainly generates ADMA, and ADMA levels in human proximal tubular cells. Streptozotocin-induced diabetic rats received continuous i.p. infusion of 0.3 μg of vehicle or 1.5 μg of the GLP-1 analog exendin-4 per kilogram of body weight for 2 weeks. We further investigated whether and how exendin-4 treatment reduced ADMA levels and renal damage in streptozotocin-induced diabetic rats. GLP-1 inhibited the AGE-induced RAGE and PRMT-1 gene expression, ROS, and ADMA generation in tubular cells, which were blocked by small-interfering RNAs raised against GLP-1 receptor. Exendin-4 treatment decreased gene expression of Rage, Prmt-1, Icam-1, and Mcp-1 and ADMA level; reduced urinary excretions of 8-hydroxy-2'-deoxyguanosine and albumin; and improved histopathologic changes of the kidney in diabetic rats. Our present study suggests that GLP-1 receptor agonist may inhibit the AGE-RAGE-mediated ADMA generation by suppressing PRMT-1 expression via inhibition of ROS generation, thereby protecting against the development and progression of diabetic nephropathy.

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.

Biomarkers in hemodialysis patients

Patients with chronic kidney disease (CKD) are, compared to the general population, at higher risk of cardiovascular disease (CVD), including sudden death, coronary artery disease (CAD), congestive heart failure (HF), stroke, and peripheral artery disease. The presence of CVD is independently associated with kidney function decline. Renal insufficiency is a strong and independent predictor of mortality in patients with different CKD stages. The interplay of traditional and nontraditional risk factors is complex such that risk factor profiles are different in CKD patients. Seemingly, paradoxical associations between traditional risk factors and cardiovascular outcome complicate efforts to identify real cardiovascular etiology in these patients. Additional tools are often required to aid clinical assessment of cardiovascular risk. Recently, a number of cardiovascular biomarkers were identified as predictors of outcome in CVD. These may be used to guide early diagnosis and therapy for CVD or may predict outcome in CKD. This review focuses on the potential diagnostic and prognostic use of some important new biomarkers including brain natriuretic peptide (BNP), cardiac troponins (cTns), inflammatory markers, adhesion molecules, and asymmetric dimethylarginine (ADMA) in CKD as well as those patients with end-stage renal failure.

Proteinuria elevates asymmetric dimethylarginine levels via protein arginine methyltransferase-1 overexpression in a rat model of nephrotic syndrome

AIMS

Proteinuria is an independent risk factor for cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Asymmetric dimethylarginine (ADMA) is a mediator of endothelial dysfunction and is associated with proteinuria in CKD patients. Thus, ADMA can partially account for the increased risk of CVD in CKD patients presenting proteinuria. However, a causal relationship between proteinuria and ADMA remains to be demonstrated.

MAIN METHODS

We first investigated whether and how proteinuria might increase ADMA levels in adriamycin (ADR)-treated rats. Next, we examined the effects of human serum albumin (HSA) on ADMA production by human renal proximal tubular epithelial cells (RPTECs) cultured in vitro.

KEY FINDINGS

Proteinuria was associated with ADMA levels in ADR treated rats. Although ADR treatment did not affect the expression levels of the dimethylarginine dimethylaminohydrolase (DDAH)-1 or -2 enzymes that degrade ADMA, it significantly increased the expression levels of protein arginine methyltransferase-1 (PRMT-1) that facilitates the production of ADMA. HSA increased the generation of reactive oxygen species in RPTECs, which was blocked by the anti-oxidant N-acetylcysteine (NAC) or an inhibitor of NADPH oxidase. Furthermore, HSA increased ADMA generation by RPTECs in a dose- and time-dependent manner and induced gene expression of PRMT-1 but not DDAHs, which were also suppressed by NAC.

SIGNIFICANCE

Our data suggest that proteinuria might enhance ADMA generation in tubular cells, at least in part via the overexpression of PRMT-1 triggered by oxidative stress. Our findings thereby propose a mechanistic link between proteinuria and ADMA levels in CKD patients.

Reduced renal plasma clearance does not explain increased plasma asymmetric dimethylarginine in hypertensive subjects with mild to moderate renal insufficiency

Plasma concentrations of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) increase already in the early stages of renal insufficiency. There is no agreement as to whether reduced renal plasma clearance (RPCL) contributes to this increase. Therefore, we investigated the relationship between estimated glomerular filtration rate (eGFR), RPCL, and plasma ADMA and SDMA in essential hypertensive patients with mild to moderate renal insufficiency. In 171 patients who underwent renal angiography, we drew blood samples from the aorta and both renal veins and measured mean renal blood flow (MRBF) using the (133)Xe washout technique. RPCL was calculated using arteriovenous concentration differences and MRBF. After correction for potential confounders, reduced eGFR was associated with higher plasma ADMA and SDMA [standardized regression coefficient (β) = -0.22 (95% confidence intervals: -0.41, -0.04) and β = -0.66 (95% confidence intervals: -0.83, -0.49), respectively]. However, eGFR was not independently associated with RPCL of ADMA. Moreover, reduced RPCL of ADMA was not associated with higher plasma ADMA. Contrary to ADMA, reduced eGFR was indeed associated with lower RPCL of SDMA [β = 0.21 (95% confidence intervals: 0.02, 0.40)]. In conclusion, our findings indicate that RPCL of ADMA is independent of renal function in hypertensive patients with mild to moderate renal insufficiency. Unlike the case for SDMA, reduced RPCL of ADMA is of minor importance for the increase in plasma ADMA in these patients, which indicates that increased plasma ADMA in this population is not a direct consequence of the kidneys failing as a plasma ADMA-regulating organ.

Nitric oxide synthase derangements and hypertension in kidney disease

PURPOSE OF REVIEW

Nitric oxide deficiency occurs by multiple mechanisms and contributes to the pathogenesis of progression of chronic kidney disease (CKD) and its cardiovascular complications. This article concentrates on recent developments on the regulation of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) in CKD and on the importance of the nitric oxide synthases in kidney disease progression, particularly in diabetic nephropathy.

RECENT FINDINGS

The increased plasma ADMA seen in renal disease is generally predictive of severity of CKD progression and cardiovascular risk. However, some assumptions about the control of ADMA have been challenged: the primacy of the kidney as a metabolic organ for plasma ADMA regulation has come under scrutiny and the relative importance of the two isoforms of the ADMA-metabolizing enzymes dimethylarginine dimethylaminohydrolases (DDAHs) is being re-evaluated. Alterations in NOS also contribute to CKD progression with the endothelial isoform playing a major role in diabetic nephropathy.

SUMMARY

Improving our understanding of ADMA regulation is important since pharmacologic targeting of DDAH is underway. The major role of endothelial NOS-derived nitric oxide in diabetic nephropathy should lead to novel therapies. The beneficial actions of dietary nitrate supplementation on blood pressure and kidney disease are of considerable clinical relevance.

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.

Symmetric dimethylarginine as a proinflammatory agent in chronic kidney disease

BACKGROUND & OBJECTIVES

Chronic kidney disease (CKD) is characterized by chronic inflammation, considered a nontraditional risk factor for cardiovascular disease, the major cause of death in CKD. Symmetric dimethylarginine (SDMA) was recently demonstrated to induce reactive oxygen species in monocytes. The present study further investigates the inflammatory character of SDMA compared with its structural counterpart asymmetric dimethylarginine (ADMA).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In vitro, the effect of SDMA on intracellular monocytic expression of IL-6 and TNF-α was studied followed by an evaluation of nuclear factor (NF)-κB activation. Additionally, an association of SDMA with inflammatory parameters in consecutive stages of CKD was evaluated in vivo.

RESULTS

Monocytes incubated with SDMA showed increased IL-6 and TNF-α expression and a rise in active NF-κB. N-acetylcysteine abrogated both these effects. No significant effects were observed with ADMA. In vivo, 142 patients (67 ± 12 years) at different stages of CKD showed an inverse association between serum SDMA and ADMA and renal function. Correlations between SDMA and IL-6, TNF-α, and albumin were more significant than for ADMA, while multiple regression analysis only retained TNF-α at a high significance for SDMA (P < 0.0001). In receiver operating characteristic analysis for inflammation, defined as an IL-6 level above 2.97 pg/ml (median), the discriminative power of SDMA (area under the curve [AUC]: 0.69 ± 0.05) directly followed that of C-reactive protein (AUC: 0.82 ± 0.04) and albumin (AUC: 0.72 ± 0.05; for all, P < 0.0001) and preceded that of ADMA (P = 0.002).

CONCLUSIONS

The present study shows that SDMA is involved in the inflammatory process of CKD, activating NF-κB and resulting in enhanced expression of IL-6 and TNF-α, which is corroborated by the clinical data pointing to an in vivo association of SDMA with inflammatory markers in CKD at different stages.

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.

Asymmetric dimethylarginine and clinical outcomes in chronic kidney disease

BACKGROUND AND OBJECTIVES

Elevated plasma level of asymmetric dimethylarginine (ADMA) have been reported to be associated with endothelial dysfunction and atherosclerosis risk factors, and may predict cardiovascular events in patients with ESRD. In this study, we aimed to assess the association between plasma ADMA and long-term outcome in a cohort of patients with stage 3 to 4 chronic kidney disease (CKD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

From July 2006 to June 2009, 298 consecutive patients with stage 3 to 4 CKD scheduled to undergo coronary angiography were recruited. Plasma ADMA levels were determined using HPLC.

RESULTS

The mean age was 73 ± 10 years. Approximately half of the patients had diabetes and 88 patients had proteinuria. The baseline estimated GFR (eGFR) was 44 ± 13 ml/min per 1.73 m². The plasma ADMA levels of the patients with proteinuria were significantly higher than those without. The plasma ADMA levels correlated significantly with eGFR. During the median follow-up period of 2.7 years, we observed 26 all-cause deaths, 12 nonfatal myocardial infarctions, and 2 strokes. Multivariate Cox analysis revealed that an increase of 0.1 μmol/L in plasma ADMA level was associated with a 37% increased risk of the composite outcomes of all-cause deaths, nonfatal myocardial infarctions, and strokes.

CONCLUSIONS

In this elder and high-risk population with stage 3 to 4 CKD, high plasma ADMA level was associated with low eGFR and macroalbuminuria. Furthermore, high plasma ADMA level appeared to be an independent predictor of long-term outcome.

The role of asymmetric and symmetric dimethylarginines in renal disease

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases. By inhibiting nitric oxide formation, ADMA causes endothelial dysfunction, vasoconstriction, elevation of blood pressure, and aggravation of experimental atherosclerosis. Levels of ADMA and its isomer symmetric dimethylarginine (SDMA), which does not inhibit nitric oxide synthesis, are both elevated in patients with kidney disease. Currently available data from prospective clinical trials in patients with chronic kidney disease suggest that ADMA is an independent marker of progression of renal dysfunction, vascular complications and death. High SDMA levels also negatively affect survival in populations at increased cardiovascular risk, but the mechanisms underlying this effect are currently only partly understood. Beyond glomerular filtration, other factors influence the plasma concentrations of ADMA and SDMA. Elevated plasma concentrations of these dimethylarginines might also indirectly influence the activity of nitric oxide synthases by inhibiting the uptake of cellular L-arginine. Other mechanisms may exist by which SDMA exerts its biological activity. The biochemical pathways that regulate ADMA and SDMA, and the pathways that transduce their biological function, could be targeted to treat renal disease in the future.