SDMA is an early marker of change in GFR after living-related kidney donation

Serum symmetric dimethylarginine in older dogs: Reference interval and comparison of a gold standard method with the ELISA

BACKGROUND

Serum symmetric dimethylarginine (SDMA) is used to screen for renal dysfunction in dogs. The gold standard technique for measuring SDMA, liquid chromatography-tandem mass spectrometry (LC-MS/MS) is not widely available. Age-specific reference intervals for SDMA in older dogs are lacking.

OBJECTIVES

Prospective study in older dogs to validate a commercially available LC-MS/MS method for SDMA, compare SDMA concentrations with concentrations measured using ELISA and obtain a reference interval (RI) for older dogs using both methods.

ANIMALS

Client-owned older dogs undergoing health screening.

METHODS

The LC-MS/MS method was analytically validated (limit of detection, precision, and linearity). Serum was sent cooled overnight for ELISA or was frozen at -80°C until batch analysis using LC-MS/MS. Results of LC-MS/MS and ELISA were compared and RIs for older dogs were calculated according to international guidelines.

RESULTS

The LC-MS/MS method showed good linearity (r2  = .99) and precision (coefficient of variation <10%), with a laboratory RI between 8.0 and 14.0 μg/dL. Paired measurements were available from 118 different dogs. Median SDMA concentration were 9.4 (range, 5.0-21.2) using LC-MS/MS and 12.0 (range, 5.0-22.0) μg/dL using ELISA. Both methods significantly differed with a mean difference of 2.2 μg/dL. The RI for older dogs for LC-MS/MS was 4.4-15.0 μg/dL, and for ELISA was 6.4-17.4 μg/dL.

CONCLUSIONS AND CLINICAL IMPORTANCE

The ELISA provided significantly higher SDMA concentrations compared to the validated LC-MS/MS method, indicating the need for device- or assay-specific RI. The obtained age-specific RI for SDMA is considerably higher in older dogs compared to the general laboratory RI.

A systematic review of metabolomic findings in adult and pediatric renal disease

Chronic kidney disease (CKD) affects over 0.5 billion people worldwide across their lifetimes. Despite a growingly ageing world population, an increase in all-age prevalence of kidney disease persists. Adult-onset forms of kidney disease often result from lifestyle-modifiable metabolic illnesses such as type 2 diabetes. Pediatric and adolescent forms of renal disease are primarily caused by morphological abnormalities of the kidney, as well as immunological, infectious and inherited metabolic disorders. Alterations in energy metabolism are observed in CKD of varying causes, albeit the molecular mechanisms underlying pathology are unclear. A systematic indexing of metabolites identified in plasma and urine of patients with kidney disease alongside disease enrichment analysis uncovered inborn errors of metabolism as a framework that links features of adult and pediatric kidney disease. The relationship of genetics and metabolism in kidney disease could be classified into three distinct landscapes: (i) Normal genotypes that develop renal damage because of lifestyle and / or comorbidities; (ii) Heterozygous genetic variants and polymorphisms that result in unique metabotypes that may predispose to the development of kidney disease via synergistic heterozygosity, and (iii) Homozygous genetic variants that cause renal impairment by perturbing metabolism, as found in children with monogenic inborn errors of metabolism. Interest in the identification of early biomarkers of onset and progression of CKD has grown steadily in the last years, though it has not translated into clinical routine yet. This systematic review indexes findings of differential concentration of metabolites and energy pathway dysregulation in kidney disease and appraises their potential use as biomarkers.

The role of histone methylation in renal cell cancer: an update

Renal cell carcinoma accounts for 2-3% of all cancers. It is difficult to diagnose early. Recently, genome-wide studies have identified that histone methylation was one of the functional classes that is most frequently dysregulated in renal cell cancer. Mutation or mis-regulation of histone methylation, methyltransferases, demethylases are associated with gene expression and tumor progression in renal cell cancer. Herein, we summarize histone methylations, demethylases and their alterations and mechanisms in renal cell cancer.

EVALUATION OF SYMMETRIC DIMETHYLARGININE AS AN ENDOGENOUS MARKER OF RENAL DISEASE IN GREATER FLAMINGOS (PHOENICOPTERUS ROSEUS)

Detection of renal disease in birds is currently reliant on biochemical measures such as uric acid, which is only elevated after significant renal compromise has occurred. Symmetric dimethylarginine (SDMA) production has not been previously evaluated in birds and no reference intervals (RI) for measurement exist in avian species. This study aimed to develop an RI for SDMA in greater flamingos (Phoenicopterus roseus) and evaluate the association between SDMA levels and renal disease. Blood from 60 flamingos was collected for RI development and the RI of SDMA was found to be 11.8-34.2 µg/dl. Symmetric dimethylarginine showed a strong positive correlation with uric acid, a moderate positive correlation with creatine kinase, and moderate negative correlations with total protein, albumin, and glucose. No correlation was found with pododermatitis score or body condition. Using the SDMA RI, six clinical cases were included for assessment of the clinical relevance of SDMA in renally compromised patients. All birds that were euthanized had elevated SDMA levels and severe renal or systemic pathology on necropsy.

Dimethylarginines in Children after Anti-Neoplastic Treatment

Background and Objectives: According to a recent Cochrane systematic review, renal impairment can develop in 0–84% of childhood cancer survivors in the future. The renal function impairment in this patient group can be related to nephrectomy, nephrotoxic agents therapy, abdominal radiotherapy, and combinations of these treatment methods. In this study, in a population of patients after anti-neoplastic therapy, with particular emphasis on patients after Wilms’ tumour treatment, we compared new substances which play role in the chronic kidney disease (CKD) pathogenesis (asymmetric dimethylarginine—ADMA, symmetric dimethylarginine—SDMA) with standard renal function markers (e.g., creatinine and cystatin C in serum, creatinine in urine, etc.) to assess the usefulness of the former. Materials and Methods: Eighty-four children, without CKD, bilateral kidney tumours, congenital kidney defects, or urinary tract infections, with a minimum time of 1 year after ending anti-neoplastic treatment, aged between 17 and 215 months, were divided into three groups: group 1—patients after nephroblastoma treatment (n = 21), group 2—after other solid tumours treatment (n = 44), and group 3—after lymphoproliferative neoplasms treatment (n = 19). The patients’ medical histories were taken and physical examinations were performed. Concentrations of blood urea nitrogen (BUN), creatinine, cystatin C, C-reactive protein (CRP), ADMA, and SDMA in blood and albumin in urine were measured, and a general urine analysis was performed. The SDMA/ADMA ratio, albumin–creatine ratio, and estimated glomerular filtration rate (eGFR) were calculated. eGFR was estimated by three equations recommended to the paediatric population by the KDIGO from 2012: the Schwartz equation (eGFR1), equation with creatinine and urea nitrogen (eGFR2), and equation with cystatin C (eGFR3). Results: Both the eGFR1 and eGFR2 values were significantly lower in group 1 than in group 3 (eGFR1: 93.3 (83.1–102.3) vs. 116.5 (96.8–126.9) mL/min/1.73 m², p = 0.02; eGFR2: 82.7 (±14.4) vs. 94.4 (±11.9) mL/min/1.73 m², p = 0.02). Additionally, there were weak positive correlations between SDMA and creatinine (p < 0.05, r = 0.24), and cystatin C (p < 0.05, r = 0.32) and weak negative correlations between SDMA and eGFR1 (p < 0.05, r = −0.25), eGFR2 (p < 0.05, r = −0.24), and eGFR3 (p < 0.05, r = −0.32). Conclusions: The usefulness of ADMA and SDMA in the diagnosis of renal functional impairment should be assessed in further studies. eGFR, calculated according to equations recommended for children, should be used in routine paediatric practice.

Posttranslational Modifications Pattern in Clear Cell Renal Cell Carcinoma

Posttranslational modifications are dynamic enzymatic-mediated processes, regulated in time and space, associated with cancer development. We aimed to evaluate the significance of posttranslational modifications in the pathogenesis of clear cell renal cell carcinoma. The authors developed a prospective, observational study during a period of three years and included 55 patients with localized renal cell carcinoma and 30 heathy subjects. Glycosylation, nitration and carbonylation, thiol-disulfide homeostasis, methylation, phosphorylation and proteolytic cleavage were evaluated in the serum of the evaluated subjects in the present study. Our results showed some characteristics for early ccRCC: high production of cytokines, substrate hypersialylation, induced nitrosative and carbonylic stress, arginine hypermethylation, thiol/disulfide homeostasis (TDH) alteration, the regulatory role of soluble receptors (sRAGE, sIL-6R) in RAGE and IL-6 signaling, the modulatory effect of TK-1and TuM2-PK in controlling the level of phosphometabolites in neoplastic cells. These data could be the initial point for development of a panel of biomarkers such as total sialic acid, orosomucoids, nitrotyrosine, carbonylic metabolites, ADMA, SDMA, and thiol-disulfide equilibrium for early diagnosis of ccRCC. Moreover, they could be considered a specific disease PTM signature which underlines the transition from early to advanced stages in this neoplasia, and of a therapeutic target in kidney oncogenesis.

Dimethylarginines in acute myocardial infarction: Association with lifestyle, sociodemographic, and somatometric factors

BACKGROUND

Recent findings associate asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) with the prognosis of acute myocardial infarction (AMI). The purpose of the current study was to associate patients' lifestyle, sociodemographic, and somatometric characteristics with the time course of ADMA and SDMA concentrations in the serum of AMI patients.

PATIENTS AND METHODS

In the serum of 66 AMI patients, ADMA, SDMA, troponin T, and C-reactive protein (CRP) were measured upon hospital admission (<24 h) and on the 3rd day following. Lifestyle, sociodemographic, and somatometric characteristics were obtained through a questionnaire, filled on patient discharge.

RESULTS

ADMA concentrations on the 1st day positively correlated with daily reported hours of sleep (+0.497, P < 0.001) and delivery or eating out frequency (+0.285, P = 0.02), whereas it negatively correlated with reported physical condition (-0.304, P = 0.013). A personal history of hypertension indicated higher 1st-day ADMA concentration (1.818 vs 1.568, P = 0.042). Age positively correlated with 1st-day SDMA (+0.320, P = 0.009). All of the biomarker concentrations were reduced on the 3rd day measurements (P < 0.001). Self-reported lifetime minimum BMI positively correlated with either absolute (r = +0.366, P = 0.009) or percentage (r = +0.262, P = 0.045) ADMA reduction. A daily sleep in 5-8-h range was inversely correlated with percentage (-0.410, P = 0.001) or absolute (r = -0.369, P = 0.002) SDMA reduction.

CONCLUSIONS

Modifiable factors such as BMI, eating habits, physical condition, and sleep seem to affect the baseline levels or time course of ADMA and SDMA in AMI patients. Changes in these factors may affect AMI prognosis by altering dimethylarginine levels.

Serum symmetric dimethylarginine concentration in healthy horses and horses with acute kidney injury

BACKGROUND

There are limited options to diagnose acute kidney injury (AKI) in horses. Symmetric dimethylarginine (SDMA) is routinely used in human and small animal medicine. The aim of this study was to assess serum SDMA concentrations in healthy horses and horses with AKI. The objective of this study was to evaluate the association of: 1) age, 2) sex, 3) body weight and 4) serum creatinine and urea levels on serum SDMA concentrations. Fifty-three healthy horses, including 17 foals (2-6 months of age) and 36 adult horses (3-29 years of age), and 23 horses with AKI were included in the study based on history, physical examination, blood analysis, urinalysis and an ultrasonographic examination of the urinary tract. Serum SDMA concentrations were measured using a non-species specific commercial ELISA test.

RESULTS

In healthy adult horses, the value of SDMA was 0.53 ± 0.14 μmol/L. The value was higher in foals (1.5 ± 0.4 μmol/L, P < 0.001). Horses with AKI had significantly higher concentrations of SDMA compared to healthy horses (1.76 ± 1.05 μmol/L, P < 0.001). In the healthy adult horses, there was no association of sex, age or body weight on SDMA. However, a significant positive relationship was found between serum creatinine and SDMA concentrations.

CONCLUSIONS

Healthy adult horses had SDMA values similar to those of other species. Foals had higher SDMA values. Therefore, different reference values should be created for them. The study confirmed an increased SDMA in horses with AKI. This, as well as the low influence of extrarenal factors on the SDMA values, may confirm its usefulness in the diagnosis of kidney dysfunction. Higher SDMA values may also indicate a more advanced degree of kidney dysfunction. Further research is required to determine whether SDMA could be used to detect kidney dysfunction in the asymptomatic stage of AKI.

Symmetric dimethylarginine concentrations in dogs with International Renal Interest Society stage 4 chronic kidney disease undergoing intermittent hemodialysis

BACKGROUND

Symmetric dimethylarginine (SDMA) is a methylated arginine derived from intranuclear methylation of l-arginine by protein-arginine methyltransferase and released into circulation after proteolysis. It is primarily eliminated by renal excretion, and its concentration is highly correlated with glomerular filtration rate (GFR) in animals and humans and is an earlier indicator of kidney dysfunction than serum creatinine concentration (sCr).

OBJECTIVES

To evaluate and quantify the effects of IV fluid therapy (IF) or intermittent hemodialysis (IH) on renal function in a randomized group of dogs previously diagnosed with International Renal Interest Society (IRIS) stage 4 chronic kidney disease (CKD).

ANIMALS

Twenty-four client-owned dogs with naturally occurring CKD.

METHODS

Serum from 14 dogs treated by IH and 10 dogs treated with IF was submitted for measurement of sCr and SDMA. Dogs in each treatment group received up to 5 treatment sessions, administered 48 hours apart.

RESULTS

Significant differences (P ≤ .05) were seen between treatment groups, but dogs from the IH group were the most affected based on SDMA (P < .001), sCr (P < .001), and blood urea (P < .001) concentrations. Furthermore, for each 10% increase in urea reduction ratio, there was a 6.2 μg/dL decrease in SDMA (P = .002).

CONCLUSIONS AND CLINICAL IMPORTANCE

Although SDMA is dialyzable biomarker and despite its removal by IH, SDMA correlates better with renal function than does sCr in dogs with CKD undergoing IF and IH.

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.

Symmetric dimethylarginine is a stronger predictor of mortality risk than asymmetric dimethylarginine among older people with kidney disease

BACKGROUND

Circulating asymmetric dimethylarginine and symmetric dimethylarginine are increased in patients with kidney disease. Symmetric dimethylarginine is considered a good marker of glomerular filtration rate, while asymmetric dimethylarginine is a marker of cardiovascular risk. However, a link between symmetric dimethylarginine and all-cause mortality has been reported. In the present study, we evaluated both dimethylarginines as risk and glomerular filtration rate markers in a cohort of elderly white individuals, both with and without chronic kidney disease.

METHODS

Glomerular filtration rate was measured in 394 individuals aged >74 years using an iohexol clearance method. Plasma asymmetric dimethylarginine, symmetric dimethylarginine and iohexol were measured simultaneously using isotope dilution tandem mass spectrometry.

RESULTS

Plasma asymmetric dimethylarginine concentrations were increased ( P < 0.01) in people with glomerular filtration rate <60 mL/min/1.73 m² compared with those with glomerular filtration rate ≥60 mL/min/1.73 m², but did not differ ( P > 0.05) between those with glomerular filtration rate 30-59 mL/min/1.73 m² and <30 mL/min/1.73 m². Plasma symmetric dimethylarginine increased consistently across declining glomerular filtration rate categories ( P < 0.0001). Glomerular filtration rate had an independent effect on plasma asymmetric dimethylarginine concentration, while glomerular filtration rate, gender, body mass index and haemoglobin had independent effects on plasma symmetric dimethylarginine concentration. Participants were followed up for a median of 33 months. There were 65 deaths. High plasma asymmetric dimethylarginine ( P = 0.0412) and symmetric dimethylarginine ( P < 0.0001) concentrations were independently associated with reduced survival.

CONCLUSIONS

Among elderly white individuals with a range of kidney function, symmetric dimethylarginine was a better marker of glomerular filtration rate and a stronger predictor of outcome than asymmetric dimethylarginine. Future studies should further evaluate the role of symmetric dimethylarginine as a marker of outcome and assess its potential value as a marker of glomerular filtration rate.

Prospective comparison between DCE-MRR and 99m Tc-DTPA-based SPECT for determination of allograft renal function

BACKGROUND

Glomerular filtration rate (GFR) is a preferred indicator of allograft renal function, but direct measurement of GFR remains complicated.

PURPOSE

To prospectively compare dynamic contrast-enhanced MR renography (DCE-MRR) with ^99m Tc-DTPA-based single-photon emission computed tomography (SPECT) for determination of allograft renal function.

STUDY TYPE

Prospective.

POPULATION

Seventy kidney-transplant recipients FIELD STRENGTH: A low-dose DCE-MRR with a 3.0T scanner and a ^99m Tc-DTPA-based SPECT after renal transplantation were performed.

ASSESSMENT

A Baumann-Rudin (BR) and a modified two-compartment model (JZ2C) were used for DCE-MRR analysis. Standard Gate's method was used for SPECT analysis. An endogenous creatinine clearance rate (CCr) constituted the reference standard.

STATISTICAL TESTS

Pearson correlation test and Bland-Altman agreement analysis.

RESULTS

The reference CCr-GFR was 59.58 ± 23.72 mL/min/1.73 m² . GFR determined by eGFR, BR, JZ2C, and SPECT was 90.22 ± 34.38, 36.78 ± 14.46, 48.99 ± 23.88, and 67.32 ± 18.44 mL/min/1.73 m² , respectively. DCE-MRR using JZ2C had the best overall performance, with a Pearson correlation coefficient of 0.81, a bias of -10.58 mL/min/1.73 m² , and a precision of 14.61 mL/min/1.73 m² , as well as high accuracy (30-50% intervals: 74.3-90.0%). Although SPECT had a small bias (7.74 mL/min/1.73 m² ), it had a poor correlation coefficient (0.38), poor precision (23.93 mL/min/1.73 m² ), and low accuracy (64.3-72.3%) as compared with DCE-MRR using JZ2C.

DATA CONCLUSION

DCE-MRR using JZ2C is superior to ^99m Tc-DTPA-based SPECT to determine allograft renal function.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:262-269.

Prospective Comparison of Equations Based on Creatinine and Cystatin C for the Glomerular Filtration Rate Estimation in Chinese Renal Transplant Recipients

BACKGROUND

Currently, there is no dedicated equation to estimate glomerular filtration rate (GFR) for transplanted kidneys. This study aimed to compare the performance of serum creatinine (Scr)- and cystatin C (CysC)-based equations in Chinese renal transplant recipients.

METHODS

A total of 252 stable renal transplant recipients were enrolled in this study. The plasma clearance of ^99mTc-DTPA (rGFR) was used as a reference standard. The Scr, CysC, and rGFR of the patients were measured on the same day. The bias, precision, accuracy (percentage of estimates within 10%, 30%, and 50% of rGFR), and agreements of 8 Scr and 5 CysC eGFR equations were assessed. The factors affecting the accuracy were also evaluated.

RESULTS

Among the Scr-based equations, the Japanese Society of Nephrology-Chronic Kidney Disease Initiatives (JSN-CKDI) equation had the best overall performance with a bias of -6.2 mL/min/1.73 m², and 96.1% of its estimates were within 30% of the rGFR. For the CysC-based equations, the Filler equation had the best performance with a bias of -3.9 mL/min/1.73 m², and 93.7% of its estimates were within 30% of the rGFR. Overall, the CysC-based equations showed better performance than the Scr-based equations. In addition, significant differences were observed between bias and gender and between bias and rGFR value in some equations, whereas transplantation time and immunosuppressive regimens were not correlated with the bias.

CONCLUSION

The JSN-CKDI equation provides the best estimation of the GFR equations, and the CysC-based equations performed better than the Scr-based equations in this population.

Plasma L-arginine levels distinguish pulmonary arterial hypertension from left ventricular systolic dysfunction

Pulmonary arterial hypertension (PAH) is a life-threatening condition, characterized by an imbalance of vasoactive substances and remodeling of pulmonary vasculature. Nitric oxide, formed from L-arginine, is essential for homeostasis and smooth muscle cell relaxation in PAH. Our aim was to compare plasma concentrations of L-arginine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) in PAH compared to left ventricular systolic dysfunction (LVSD) and healthy subjects. This was an observational, multicenter study comparing 21 patients with PAH to 14 patients with LVSD and 27 healthy subjects. Physical examinations were obtained and blood samples were collected. Plasma levels of ADMA, SDMA, L-arginine, L-ornithine, and L-citrulline were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Plasma levels of ADMA and SDMA were higher, whereas L-arginine and L-arginine/ADMA ratio were lower in PAH patients compared to healthy subjects (p < 0.001). Patients with PAH also had lower levels of L-arginine than patients with LVSD (p < 0.05). L-Arginine correlated to 6 min walking distance (6MWD) (r _s = 0.58, p = 0.006) and L-arginine/ADMA correlated to WHO functional class (r _s = -0.46, p = 0.043) in PAH. In conclusion, L-arginine levels were significantly lower in treatment naïve PAH patients compared to patients with LVSD. Furthermore, L-arginine correlated with 6MWD in PAH. L-arginine may provide useful information in differentiating PAH from LVSD.

Novel Biomarkers in the Diagnosis of Chronic Kidney Disease and the Prediction of Its Outcome

In its early stages, symptoms of chronic kidney disease (CKD) are usually not apparent. Significant reduction of the kidney function is the first obvious sign of disease. If diagnosed early (stages 1 to 3), the progression of CKD can be altered and complications reduced. In stages 4 and 5 extensive kidney damage is observed, which usually results in end-stage renal failure. Currently, the diagnosis of CKD is made usually on the levels of blood urea and serum creatinine (sCr), however, sCr has been shown to be lacking high predictive value. Due to the development of genomics, epigenetics, transcriptomics, proteomics, and metabolomics, the introduction of novel techniques will allow for the identification of novel biomarkers in renal diseases. This review presents some new possible biomarkers in the diagnosis of CKD and in the prediction of outcome, including asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), uromodulin, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), miRNA, ncRNA, and lincRNA biomarkers and proteomic and metabolomic biomarkers. Complicated pathomechanisms of CKD development and progression require not a single marker but their combination in order to mirror all types of alterations occurring in the course of this disease. It seems that in the not so distant future, conventional markers may be exchanged for new ones, however, confirmation of their efficacy, sensitivity and specificity as well as the reduction of analysis costs are required.

Plasma Symmetric Dimethylarginine Concentration in Dogs with Acute Kidney Injury and Chronic Kidney Disease

Background

Symmetric dimethylarginine (SDMA) is considered a biomarker for early detection of renal dysfunction in human patients with acute kidney injury (AKI). At present, no studies exist analyzing the relevance of SDMA in dogs with AKI.

Hypothesis/objectives

SDMA would correctly identify dogs with renal disease but would not be able to differentiate between AKI and CKD.

Animals

Eighteen healthy control dogs, 48 dogs with AKI, and 29 dogs with CKD.

Methods

Prospective study. Dogs with kidney disease were categorized as having AKI or CKD according to the history, clinical signs, laboratory findings, and results of diagnostic imaging. Plasma SDMA concentration was measured by IDEXX Laboratories. SDMA/creatinine ratio was calculated in dogs with AKI or CKD.

Results

Median SDMA concentrations were 8.5 μg/dL (6–12 μg/dL), 39.5 μg/dL (8–>100 μg/dL), and 35 μg/dL (12–>100 μg/dL), in healthy, AKI, and CKD, respectively. SDMA concentrations were significantly higher in dogs with AKI (P < .0001) or CKD (P < .0001) in comparison with healthy dogs. Median SDMA/creatinine ratio in dogs with AKI and CKD was 6.5 (1.7–20.9) and 10 (2.4–33.9) (P = .0004), respectively. Although there was overlap of the SDMA/creatinine ratio in dogs with AKI or CKD, it was significantly higher in dogs with CKD compared to dogs with AKI (P = .0004).

Conclusions and Clinical Importance

In this population, SDMA was suitable for identifying dogs affected by AKI or CKD, but could not differentiate between them.

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

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

Comparison of symmetric dimethylarginine with creatinine, cystatin C and their eGFR equations as markers of kidney function

OBJECTIVES

Symmetric dimethylarginine (SDMA) is a catabolic product of arginine-methylated proteins and is an emerging biomarker for kidney function. A limited number of studies in selected populations have shown good correlation between SDMA and a few known markers of glomerular filtration rate (GFR). However, a comprehensive comparison of SDMA with all existing serum endogenous markers in a population with varied kidney function and against measured GFR is lacking. The objective of this study was to compare the correlations of SDMA, creatinine, cystatin C and their eGFR equations against GFR measured by iothalamate clearance in an adult population with varied kidney function.

DESIGN & METHODS

Left-over serum and plasma specimens were collected from 40 adults with normal and reduced kidney function. GFR was measured using a radioactive iothalamate procedure. Creatinine and cystatin C were measured on Roche Cobas 8000. SDMA was measured by a published liquid chromatography-tandem mass spectrometry method.

RESULTS

SDMA correlated highly with measured GFR (r=-0.84), which was better than creatinine (r=-0.70) but equivalent to cystatin C (r=-0.86) and the eGFR equations [MDRD and CKD-EPI (separate and combined)].

CONCLUSIONS

SDMA is a strong marker of kidney function and further studies are needed to establish an eGFR formula that includes it for widespread clinical use.

First detection and quantification of N(δ)-monomethylarginine, a structural isomer of N(G)-monomethylarginine, in humans using MS(3)

The L-arginine metabolites methylated at the guanidino moiety, such as N(G)-monomethyl-L-arginine (LNMMA), asymmetric N(G),N(G)-dimethyl-L-arginine (ADMA), and symmetric N(G),N(G')-dimethyl-L-arginine (SDMA), are long known to be present in human plasma. Far less is known about the structural isomer of LNMMA, N(δ)-monomethyl-L-arginine (δ-MMA). In prior work, it has been detected in yeast proteins, but it has not been investigated in mammalian plasma or cells. In this work, we present a method for the simultaneous and unambiguous quantification of LNMMA and δ-MMA in human plasma that is capable of detecting δ-MMA separately from LNMMA. The method comprises a simple protein precipitation sample preparation, hydrophilic interaction liquid chromatography (HILIC) gradient elution on an unmodified silica column, and triple stage mass spectrometric detection. Stable isotope-labeled D6-SDMA was used as internal standard. The calibration ranges were 25-1000 nmol/L for LNMMA and 5-350 nmol/L for δ-MMA. The intra- and inter-batch precision determinations resulted in relative standard deviations of less than 12% for both compounds with accuracies of less than 6% deviation from the expected values. In a pilot study enrolling 10 healthy volunteers, mean concentrations of 48.0 ± 7.4 nmol/L for LNMMA and 27.4 ± 7.7 nmol/L for δ-MMA were found.

Dimethylarginines as biomarkers for the kidney transplant management in methylmalonic aciduria

Methylmalonic aciduria (MMA) is an inborn error of metabolism associated with many complications despite treatment. Chronic renal failure is the most common problem, and patients may eventually require kidney transplant. Therefore, it is worth investigating whether living donor kidney transplant offers a better option than deceased kidney donors; and the value of novel vascular risk biomarkers in the assessment of transplanted MMA patients. We report a case of a 26-year-old man with MMA, who progressed to end-stage renal disease and received kidney transplant from a heterozygous next-of-kin living donor at 20 years of age. Although post-transplant urinary levels of methylmalonic acid decreased, this reduction was lower than previously reported for deceased donors. No episodes of metabolic decompensation were observed after transplantation. During his clinical progress, vascular complications appeared; and finally, pancreatitis was the cause of death. After kidney transplant, we evaluated novel vascular risk factors, such as asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), which were used as early biomarkers of progression and metabolic management for this transplanted patient. This case report illustrates the disadvantage of transplantation with an allograft from a heterozygous living donor, and the utility of vascular risk biomarkers in renal transplant assessment.

Oxidative and Nitrosative Stress in Stable Renal Transplant Recipients with Respect to the Immunosuppression Protocol - Differences or Similarities?

Background

The aim of the study was to evaluate parameters of oxidative and nitrosative stress as well as antioxidative parameters in a group of renal transplant recipients with stable graft function and no clinical signs of cardiovascular disease. We also aimed to determine the correlations among these parameters and to evaluate potential differences in all the biomarkers with regard to the immunosuppression protocol.

Methods

We enrolled 57 renal transplant recipients and 31 controls who were age and sex matched with the renal transplant recipients. All of the patients included in this study had post-renal transplant surgery at least 12 months earlier and were on standard immunosuppressive therapy. In this study, we determined thiobarbituric acid-reactive substances in plasma and red blood cells and advanced oxidation protein products, nitrosative stress parameters (asymmetric and symmetric dimethylarginine – ADMA and SDMA), and antioxidative parameters (total SH groups and catalase activity).

Results

The results of our study demonstrated that the levels of oxidative and nitrosative stress were significantly increased compared to the healthy population (p<0.01 except for plasma catalase activity p<0.05). Correlation analysis showed significant positive correlations between: ADMA and SDMA (p<0.01); ADMA and nitrates (p<0.05); SDMA and nitrates (p<0.05); between OS parameters in the experimental group; AOPP and SH groups (p<0.05) and TBARS in plasma and SH groups (p<0.01), SDMA and AOPP (p< 0.05); SDMA and TBARS in plasma (p<0.05); SDMA and SH groups (p<0.01); nitrates and SH groups (p<0.05).

Conclusion

There was no significant difference in oxidative and nitrosative stress parameters with respect to the immunosuppressive protocol.

Residual Cardiovascular Risk in Chronic Kidney Disease: Role of High-density Lipoprotein

Although reducing low-density lipoprotein-cholesterol (LDL-C) levels with lipid-lowering agents (statins) decreases cardiovascular disease (CVD) risk, a substantial residual risk (up to 70% of baseline) remains after treatment in most patient populations. High-density lipoprotein (HDL) is a potential contributor to residual risk, and low HDL-cholesterol (HDL-C) is an established risk factor for CVD. However, in contrast to conventional lipid-lowering therapies, recent studies show that pharmacologic increases in HDL-C levels do not bring about clinical benefits. These observations have given rise to the concept of dysfunctional HDL where increases in serum HDL-C may not be beneficial because HDL loss of function is not corrected by or even intensified by the therapy. Chronic kidney disease (CKD) increases CVD risk, and patients whose CKD progresses to end-stage renal disease (ESRD) requiring dialysis are at the highest CVD risk of any patient type studied. The ESRD population is also unique in its lack of significant benefit from standard lipid-lowering interventions. Recent studies indicate that HDL-C levels do not predict CVD in the CKD population. Moreover, CKD profoundly alters metabolism and composition of HDL particles and impairs their protective effects on functions such as cellular cholesterol efflux, endothelial protection, and control of inflammation and oxidation. Thus, CKD-induced perturbations in HDL may contribute to the excess CVD in CKD patients. Understanding the mechanisms of vascular protection in renal disease can present new therapeutic targets for intervention in this population.

Genome-wide association study of L-arginine and dimethylarginines reveals novel metabolic pathway for symmetric dimethylarginine

BACKGROUND

Dimethylarginines (DMA) interfere with nitric oxide formation by inhibiting nitric oxide synthase (asymmetrical DMA [ADMA]) and l-arginine uptake into the cell (ADMA and symmetrical DMA [SDMA]). In prospective clinical studies, ADMA has been characterized as a cardiovascular risk marker, whereas SDMA is a novel marker for renal function and associated with all-cause mortality after ischemic stroke. The aim of the current study was to characterize the environmental and genetic contributions to interindividual variability of these biomarkers.

METHODS AND RESULTS

This study comprised a genome-wide association analysis of 3 well-characterized population-based cohorts (Framingham Heart Study [FHS; n=2992], Gutenberg Health Study [GHS; n=4354], and Multinational Monitoring of Trends and Determinants in Cardiovascular Disease Study [MONICA]/Cooperative Health Research in the Augsburg Area, Augsburg, Bavaria, Germany [KORA] F3 [n=581]) and identified replicated loci (DDAH1, MED23, Arg1, and AGXT2) associated with the interindividual variability in ADMA, l-arginine, and SDMA. Experimental in silico and in vitro studies confirmed functional significance of the identified AGXT2 variants. Clinical outcome analysis in 384 patients of the Leeds stroke study demonstrated an association between increased plasma levels of SDMA, AGXT2 variants, and various cardiometabolic risk factors. AGXT2 variants were not associated with poststroke survival in the Leeds study or were they associated with incident stroke in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium.

CONCLUSIONS

These genome-wide association study support the importance of DDAH1 and MED23/Arg1 in regulating ADMA and l-arginine metabolism, respectively, and identify a novel regulatory renal pathway for SDMA by AGXT2. AGXT2 variants might explain part of the pathogenic link between SDMA, renal function, and outcome. An association between AGXT2 variants and stroke is unclear and warrants further investigation.

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.

Association of angiopoietin-2 and dimethylarginines with complicated course in patients with leptospirosis

Leptospirosis is one of the most relevant zoonosis worldwide and a potentially life-threatening infectious disease. While it is frequent in tropic regions, it is uncommon in European industrialized countries. Angiopoietin-2 (Angpt-2) and asymmetric and symmetric dimethylarginine (ADMA and SDMA) are markers of endothelial activation and systemic inflammation. These parameters have been studied recently in the context of sepsis and MODS showing potential to determine disease severity and outcome specific parameters like acute kidney injury (AKI) and survival. These biomarkers were measured in 13 patients with leptospirosis. High levels of Angpt-2 were statistically significant associated with a complicated clinical course with occurrence of AKI, Sepsis and intensive care unit treatment. ADMA was significantly associated with occurrence of AKI and ICU treatment whereas SDMA was associated with AKI. Therefore these endothelial markers may serve as additional tools for risk stratification in these patients.

[Management of patients with EHEC/HUS. Lessons and perspectives from clinical infectious disease specialists]

The 2011 EHEC/HUS outbreak created uncertainty regarding the previous recommendations of withholding antibiotic therapy and regarding rational measures for prevention of invasive meningococcal disease after treatment with the monoclonal antibody eculizumab. For both these areas, an expert panel of the German Society for Infectious Diseases in cooperation with representatives of other learned societies and health institutions has drafted and consented guidelines that were published online on 1 June 2011 (i.e., ~10 days after the peak of the epidemic) and 4 June 2011. A summary of the guidelines in English was made available online on 4 June 2011. The time until ad hoc guidelines are made publicly available should and can be shortened in similar scenarios in the future. To this end-among other things-scientific societies in Germany linked to infectious diseases and medical microbiology have established a permanent working group called AFIM. This working group will facilitate timely identification and appointment of experts and expert panels, and will make use of new ways of rapid and effective sharing and dissemination of knowledge and ad hoc guidelines in the medical community and public domain if needed. In the case of disease outbreaks, immediate telephone conferences among all professionals involved, close cooperation between institutions and expert groups, and avoidance of premature unconsented information and press releases will be critical. We expect that proceeding in this way will also have a major impact on proper planning, professional design, and adequate analysis of clinical studies and endpoints appropriate for the outbreak situation.

Mass spectrometric quantification of L-arginine and its pathway related substances in biofluids: the road to maturity

The amino acid L-arginine together with its metabolites and related substances is in the center of many biologically important pathways, especially the urea cycle and the nitric oxide (NO) synthesis. Therefore, the concentrations of these substances in various biological fluids are of great interest as predictive markers for health and disease. Yet, they provide major analytical difficulties as they are very polar in nature and therefore not easily to be separated on standard reversed phase HPLC stationary phases. Furthermore, as endogenous substances, no analyte-free matrix is available, a fact that results in complicated calibration procedures. This review evaluates the analytical literature for the determination of L-arginine, symmetric dimethylarginine, asymmetric dimethylarginine, monomethylarginine, L-citrulline, L-ornithine, L-homoarginine, agmatine and dimethylguanidinovaleric acid in biological fluids. Papers are discussed, which were published since 2007 and describe methods applying capillary electrophoresis (CE), gas chromatography (GC), reversed phase HPLC or polar phase HPLC, coupled to mass spectrometric quantification. Nowadays, many carefully developed and validated methods for L-arginine and its related substances are available to the scientific community. The use of stable isotope labeled internal standards enables high precision and accuracy in mass spectrometry-based quantitative analysis.

Plasma concentrations of arginine and asymmetric dimethylarginine do not reflect their intracellular concentrations in peripheral blood mononuclear cells

OBJECTIVE

Production of nitric oxide (NO) from arginine is inhibited by endogenously produced monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA). Elevated levels of ADMA, by limiting NO production, may lead to endothelial dysfunction and cardiovascular disease. Symmetric dimethylarginine (SDMA) and the arginine homolog homoarginine have also been associated with cardiovascular disease. Although NO synthesis, as well as generation of MMA, ADMA, SDMA and homoarginine, occurs intracellularly, these biomarkers are usually measured in plasma. Despite extensive transmembrane transport, it is not clear whether plasma levels of these biomarkers are a valid proxy for their intracellular levels in the cardiovascular system. Since it is difficult to obtain vascular tissue from healthy humans, we explored the relations between concentrations of these biomarkers in plasma and intracellular concentrations in peripheral blood mononuclear cells (PBMC).

METHODS

In PBMC and plasma of 27 healthy subjects, concentrations of arginine, MMA, ADMA, SDMA, and homoarginine were determined using stable isotope dilution liquid chromatography tandem mass spectrometry.

RESULTS

In PBMC, significant positive correlations were observed among arginine and its methylated forms (ρ = 0.43 to 0.81) and these correlations were slightly less pronounced in plasma. Homoarginine was not significantly correlated with (methylated) arginine in either PBMC or plasma. Plasma concentrations of arginine and its methylated forms showed non-significant inverse associations with their respective intracellular concentrations in PBMC and only for homoarginine was a weak positive association observed (ρ = 0.37).

CONCLUSION

In healthy individuals, plasma levels of arginine, MMA, ADMA, and SDMA poorly reflect their intracellular levels in PBMC.

Changes in biomarkers associated with living kidney donation

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

Comparison of seven estimated glomerular filtration rate equations in kidney patients

Introduction: The degree of glomerular filtration rate determines the stages of chronic renal disease and, therefore, knowledge on its estimation is essential. Aims: Two standardized creatinine based estimated glomerular filtration rate equations and five equations based on the immunoturbidimetric determination of cystatin C were compared. Methods: The distribution of the analytes and the equations, their relations, as well as the differences among the estimated glomerular filtration rates and their chronic kidney disease stages assignments were studied. Results: The equations based on cystatin C classified more patient into stage 1, while the creatinine based ones more into stages 2, 3 and 4. The equations published as Grubb1, Grubb2 and Larsson classified more patients while the equations created by Tan and Sjöström classified fewer into stage 5 compared to the creatinine based equations. The equations of Grubb1 and Grubb2 resulted in the most similar stage assignment. The occurence of stages between 3 and 5 was the lowest using the equation of Sjöström. Conclusions: The different equations for the estimation of glomerular filtration rate modify significantly the chronic kidney disease stage assignment which may have an influence on the treatment and outcome measures of the patients. Orv. Hetil., 2013, 154, 415–425.

Dimethylarginine dimethylaminohydrolase1 is an organ-specific mediator of end organ damage in a murine model of hypertension

BACKGROUND

The endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is an independent predictor of cardiovascular and overall mortality. Moreover, elevated ADMA plasma concentrations are associated with the extent of hypertension. However, data from small-sized clinical trials and experimental approaches using murine transgenic models have revealed conflicting results regarding the impact of ADMA and its metabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) in the pathogenesis of hypertension.

METHODOLOGY/PRINCIPAL FINDINGS

Therefore, we investigated the role of ADMA and DDAH1 in hypertension-induced end organ damage using the uninephrectomized, deoxycorticosterone actetate salt, and angiotensin II-induced hypertension model in human DDAH1 (hDDAH1) overexpressing and wild-type (WT) mice. ADMA plasma concentrations differed significantly between hDDAH1 and WT mice at baseline, but did not significantly change during the induction of hypertension. hDDAH1 overexpression did not protect against hypertension-induced cardiac fibrosis and hypertrophy. In addition, the hypertension-induced impairment of the endothelium-dependent vasorelaxation of aortic segments ex vivo was not significantly attenuated by hDDAH1 overexpression. However, hDDAH1 mice displayed an attenuated hypertensive inflammatory response in renal tissue, resulting in less hypertensive renal injury.

CONCLUSION/SIGNIFICANCE

Our data reveal that hDDAH1 organ-specifically modulates the inflammatory response in this murine model of hypertension. The lack of protection in cardiac and aortic tissues may be due to DDAH1 tissue selectivity and/or the extent of hypertension by the used combined model. However, our study underlines the potency of hDDAH1 overexpression in modulating inflammatory processes as a crucial step in the pathogenesis of hypertension, which needs further experimental and clinical investigation.

Osteopontin and symmetric dimethylarginine plasma levels in solitary functioning kidney in children

AIM

The present study aimed to examine whether plasma osteopontin (pOPN) and symmetric dimethylarginine (pSDMA) are useful biomarkers of renal dysfunction in children with solitary functioning kidney (SFK).

METHODS

We measured circulating pOPN and pSDMA in 51 patients with SFK and no other urinary defects. Patients were subdivided into two groups: primary SFK (pSFK) - unilateral renal agenesis (URA), and secondary SFK (sSFK) - unilateral nephrectomy. The control group (C) contained 21 healthy children, with mean age 9.92 ± 4.85 years. Immunoenzymatic ELISA commercial kits were used to measure pOPN and pSDMA concentrations.

RESULTS

Plasma osteopontin and pSDMA levels in children with SFK were higher than those in healthy participants (p < 0.05). There was no difference in pOPN and pSDMA concentrations between patients with pSFK and those with sSFK (p > 0.05). Receiver operator characteristic analyses performed to define the diagnostic efficiency of serum creatinine, pOPN and pSDMA in identifying children with C(cr)  < 90 mL/min/1.73 m(2) among all examined children revealed no differences between all three AUCs (p > 0.05).

CONCLUSION

Increased pOPN and pSDMA levels were observed in children with SFK. Both pOPN and pSDMA correlated with eGFR; however, the sensitivity and specificity of those markers were not better than those of creatinine.

Quantification of L-arginine, asymmetric dimethylarginine and symmetric dimethylarginine in human plasma: a step improvement in precision by stable isotope dilution mass spectrometry

The amino acid L-arginine and its metabolites ADMA and SDMA are important markers for a range of diseases in humans. Increased levels of ADMA and SDMA in plasma point to endothelial dysfunction, hypertension, renal impairment and other pathological states. We present here a method to quantify L-arginine, ADMA and SDMA in human plasma, which is suitable to support clinical research in this field. Sample preparation consisted only of protein precipitation and the analytes were separated using a silica based HILIC column. The analytes were detected by ESI MS/MS, providing high selectivity and sensitivity. The calibration functions were linear in the ranges of 7.5-150 μmol/l for l-arginine, 0.15-3 μmol/l for ADMA and 0.2-4 μmol/l for SDMA. These ranges cover the concentrations encountered in healthy and pathological human plasma. The method employs (13)C(6)-arginine, D(7)-ADMA and, for the first time in LC-MS/MS, D(6)-SDMA as internal standards for L-arginine, ADMA and SDMA. Therefore, matrix independency and a high intra-day precision of 0.82% for L-arginine, 2.12% for ADMA and 2.83% for SDMA, were achieved at basal plasma concentrations. The respective inter-day precision values were 4.01% for l-arginine, 3.77% for ADMA and 3.86% for SDMA.

Renal comorbidity after solid organ and stem cell transplantation

After transplantation of solid organs or hematopoietic stem cells, a significant acute decrease in renal function occurs in the majority of patients. Depending on the degree of kidney injury, a large number of patients develop chronic kidney disease (CKD) and some develop end-stage renal disease requiring renal replacement therapy. The incidence varies depending on the transplanted organ, but important risk factors for the development of CKD are preexisting renal disease, hepatitis C, diabetes, hypertension, age, sex, posttransplant acute kidney injury and thrombotic microangiopathy. This review article focuses on the risk factors of posttransplant chronic kidney disease after organ transplantation, considering the current literature and integrates the incidence and the associated mortality rates of acute and chronic kidney disease. Furthermore, we introduce the RECAST (REnal Comorbidity After Solid organ and hematopoietic stem cell Transplantation) registry.

Asymmetric dimethylarginine may mediate increased heat pain threshold in experimental chronic kidney disease

BACKGROUND

Thermal sensitivity in uraemia is decreased. Non-selective synthetic nitric oxide synthase (NOS) inhibitors significantly attenuate thermal hyperalgesia in preclinical models. The aim of our study was to evaluate the effect of experimental uraemia, which is associated with an increase of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA), on thermal sensitivity in rats. Furthermore, we intended to study the effect of chronic ADMA infusion alone on thermal sensitivity.

METHODS

Male Sprague-Dawley rats (n = 54), 10 weeks old, weight 370-430 g, were randomly assigned to three groups receiving either (i) isotonic saline or (ii) ADMA via osmotic mini pumps or (iii) underwent 5/6 nephrectomy (Nx). After 14 days, 50% of all animals from all groups underwent thermal sensitivity testing and terminal blood draw. After 28 days, the remaining animals underwent the same procedures. Thermal sensitivity examination was performed by the hot-plate test, measuring time from heat exposition to first paw licking or jumping of the animal.

RESULTS

While the median [interquartile range] latency time between heat exposition to first paw licking or jumping of the animal in the NaCl infusion group remained unchanged between Day 14 (8.4 [6.75-11.50] s) and Day 28 (7.35 [6.10-7.90] s) both, ADMA infusion and 5/6 nephrectomy tended to increase the thermal pain threshold at Day 14 (9.25 [6.55-12.18] s) and (9.50 [5.8 ± 11.0] s), respectively, compared to NaCl on Day 14 (8.4 [6.75-11.50] s). This difference became statistical significant at Day 28 where the median latency time in the ADMA group (13.10 [11.85-15.95] s) and in the 5/6 Nx group (13.50 [10.85-17.55] s) were significantly higher than in the NaCl group (7.35 [6.10-7.90] s).

CONCLUSIONS

Induction of progressive renal failure in rats by 5/6 nephrectomy, which is accompanied by a marked increase of the serum levels of the endogenous NOS inhibitor ADMA, leads to a significantly increased heat pain threshold at 28 days. The sole infusion of ADMA into healthy rats leads to the same increase in heat pain threshold.

Is plasma symmetric dimethylarginine a suitable marker of renal function in children and adolescents?

OBJECTIVE

The purpose of this cross-sectional study was to identify whether plasma symmetric dimethylarginine (pSDMA) is a useful marker of renal function in children.

MATERIAL AND METHODS

The study group consisted of 35 patients with chronic kidney disease (CKD) stages 1-5 (median age 11.5 years), classified on the basis of estimated glomerular filtration rate (eGFR) and divided into three groups: group A, patients with CKD stages 1 and 2; group B, CKD stage 3; and group C, CKD stages 4 and 5. A control group included 42 age-matched healthy children. Commercial enzyme-linked immunosorbent assay kits were used to measure pSDMA and serum cystatin C (sCysC) concentrations.

RESULTS

The pSDMA and sCysC levels were significantly elevated in all CKD patients in comparison with healthy controls (p < 0.05). The pSDMA level in children was increased in the mild CKD (group A) (p < 0.01). There were also a significant difference in pSDMA concentration between groups A and B (p < 0.01). No differences in pSDMA levels were found between groups B and C. Receiver operating characteristics analyses showed that pSDMA was a better diagnostic tool than sCysC for identifying CKD stage among all the examined children and for detecting patients from group A (eGFR >60 ml/min/1.73 m(2)).

CONCLUSIONS

Increased pSDMA and sCysC levels were found in CKD children. Further studies are required to confirm potential applications of pSDMA and CysC as useful biomarkers for the diagnosis and progression of CKD.

Symmetric dimethylarginine is a marker of detrimental outcome in the acute phase after ischaemic stroke: role of renal function

Methylarginines have been shown to interfere with NO (nitric oxide) formation by inhibiting NOS (NO synthase)–ADMA (asymmetric dimethylarginine) and cellular L-arginine uptake into the cell [ADMA and SDMA (symmetric dimethylarginine)]. In a recent study, elevation of SDMA was related to long-term mortality in patients recruited 30 days after a stroke event. In the present study, we aimed at investigating the association of SDMA and adverse clinical outcome in the early phase (first 30 days) after acute ischaemic stroke. A total of 137 patients were recruited immediately upon admission to the emergency unit with an acute ischaemic stroke. Plasma levels of methylarginines were determined by a validated LC–MS/MS (liquid chromatography–tandem MS) method. Patients were prospectively followed for 30 days. A total of 25 patients (18.2%) experienced the primary composite endpoint [death, recurrent stroke, MI (myocardial infarction) and rehospitalization]. SDMA plasma levels were significantly higher in stroke patients compared with patients without event (0.89±0.80 compared with 0.51±0.24 μmol/l; P<0.001). SDMA levels were significantly correlated with markers of renal function. Kaplan–Meier survival analysis demonstrated that cumulative survival decreased significantly with ascending tertiles of SDMA (P<0.001). Our study provides the first data indicating that SDMA is strongly associated with adverse clinical outcome during the first 30 days after ischaemic stroke. Our results strengthen the prognostic value of renal function in patients with stroke and confirm the hypothesis that SDMA is a promising marker for renal function.

Unilateral nephrectomy causes an abrupt increase in inflammatory mediators and a simultaneous decrease in plasma ADMA: a study in living kidney donors

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases (NOS). Reducing inducible NOS activity in acute inflammation seems to be desirable. In vitro data show that ADMA increases in response to inflammatory mediators, yet the effect of acute inflammation in vivo is scarcely studied. The aim of the study was to evaluate ADMA plasma levels before, during, and after the acute (nonbacterial) inflammatory-like state. Plasma ADMA, l-arginine, C-reactive protein, and IL-6 were determined in 24 healthy subjects undergoing living related kidney donation before as well as 1, 6, 12, 24, 72, and 168 h thereafter. Six hours after nephrectomy, ADMA levels decreased compared with baseline (0.488 ± 0.075 vs. 0.560 ± 0.060 μmol/l, P < 0.05). This difference became even more marked 24 h after the operation (0.478 ± 0.083 μmol/l, P < 0.01 vs. baseline), when the proinflammatory cytokine IL-6 peaked. Seven days after unilateral nephrectomy, ADMA levels were elevated above baseline (0.63 ± 0.05 μmol/l, P < 0.001 vs. baseline). l-Arginine levels decreased already 1 h after nephrectomy (97.5 ± 22.5 μmol/l, P < 0.01 vs. baseline) and paralleled the change in ADMA thereafter. At the end of the observation period when inflammation markers were regressing, l-arginine levels were significantly elevated above baseline (160.6 ± 25.1 μmol/l, P < 0.001 vs. baseline). In summary, this is the first study showing that both ADMA and l-arginine decrease temporarily after unilateral nephrectomy coinciding with the increase in inflammatory mediators. The l-arginine/ADMA ratio, a surrogate for NO production capacity, was only altered for <24 h.