Studies on the catabolism of Ng-methylarginine, Ng, Ng-dimethylarginine and Ng, Ng-dimethylarginine in the rabbit

SGLT2 inhibition improves coronary flow velocity reserve and contractility: role of glucagon signaling

BACKGROUND

SGLT2 inhibitors, a T2DM medication to lower blood glucose, markedly improve cardiovascular outcomes but the underlying mechanism(s) are not fully understood. SGLT2i's produce a unique metabolic pattern by lowering blood glucose without increasing insulin while increasing ketone body and glucagon levels and reducing body weight. We tested if glucagon signaling contributes to SGLT2i induced improvement in CV function.

METHODS

Cardiac contractility and coronary flow velocity reserve (CFVR) were monitored in ob/ob mice and rhesus monkeys with metabolic syndrome using echocardiography. Metabolic status was characterized by measuring blood ketone levels, glucose tolerance during glucose challenge and Arg and ADMA levels were measured. Baysian models were developed to analyse the data.

RESULTS

Dapagliflozin improved CFVR and contractility, co-application of a glucagon receptor inhibitor (GcgRi) blunted the effect on CFVR but not contractility. Dapagliflozin increased the Arg/ADMA ratio and ketone levels and co-treatment with GcgRi blunted only the Dapagliflozin induced increase in Arg/ADMA ratio but not ketone levels.

CONCLUSIONS

Since GcgRi co-treatment only reduced the Arg/ADMA increase we hypothesize that dapagliflozin via a glucagon-signaling dependent pathway improves vascular function through the NO-signaling pathway leading to improved vascular function. Increase in ketone levels might be a contributing factor in SGLT2i induced contractility increase and does not require glucagon signaling.

Successful endodontic treatment reduces serum levels of cardiovascular disease risk biomarkers-high-sensitivity C-reactive protein, asymmetric dimethylarginine, and matrix metalloprotease-2

AIM

To investigate serum biomarkers of inflammation 2 years following non-surgical root canal re-treatment (Re-RCT) and peri-apical surgery (PS). The results were correlated with signs and symptoms, treatment outcome, metabolic syndrome factors, infection with severe acute respiratory syndrome coronavirus 2 SARS-CoV-2 (COVID-19) infection and COVID-19 vaccination.

METHODOLOGY

Subjects from our previous study were recalled for 2 years post-treatment follow-up. Changes to the patient's history (medical, dental, social) were noted. Periapical health of the treated teeth was examined both clinically and radiographically. Blood pressure, fasting HbA1C and low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides and total cholesterol (TC) levels were measured. Serum inflammatory marker levels were assayed using a Bio-Rad Bio-Plex 200 analyser and values at different time points within the same group were compared using a Wilcoxon signed-rank test and differences between groups with a Mann-Whitney test. Linear associations were tested using Pearson's correlations.

RESULTS

The recall percentage at 2 years was 56.9% (n = 37), with a 100% radiographic success rate using periapical radiographs. In total, 21 cases (56.8%) were completely healed, and 16 cases (43.2%) were healing. Higher matrix metalloprotease 2 (MMP2) levels were present in the healing group compared to the healed group. Serum levels of high-sensitivity C-reactive protein (hs-CRP), asymmetric dimethylarginine (ADMA) and MMP-2 were significantly reduced (p ≤ .001) whereas other biomarkers showed significant increases at 2 year compared to pre-operative levels, while FGF-23 and ICAM-1 were not significantly increased. HbA1C (p = .015), TC (p = .003), LDL (p = .003) and HDL (p = .003) reduced significantly at 2 years post-treatment compared to their preoperative levels. COVID infection showed a significant association with MMP-9 (p = .048).

CONCLUSIONS

hs-CRP, ADMA and MMP-2 can be regarded as prognostic biomarkers of successful Re-RCT and PS as they reduced at 2 year recall in cases which showed evidence of clinical and radiographic success. The successful treatment of chronic apical periodontitis is correlated with improvements in metabolic syndrome indicators, better glycemic control, and reduction at 2 year of some systemic inflammatory markers which are related to risks of cardiovascular disease events.

Divergent Dimethylarginine Dimethylaminohydrolase Isoenzyme Expression in the Central Nervous System

The endogenous methylated derivative of ʟ-arginine, Nω,Nω'-dimethyl-ʟ-arginine (asymmetric dimethylarginine, ADMA), an independent risk factor in many diseases, inhibits the activity of nitric oxide synthases and, consequently, modulates the availability of nitric oxide. While most studies on the biological role of ADMA have focused on endothelial and inducible nitric oxide synthases modulation and its contribution to cardiovascular, metabolic, and renal diseases, a role in regulating neuronal nitric oxide synthases and pathologies of the central nervous system is less understood. The two isoforms of dimethylarginine dimethylaminohydrolase (DDAH), DDAH1 and DDAH2, are thought to be the main enzymes responsible for ADMA catabolism. A current impediment is limited knowledge on specific tissue and cellular distribution of DDAH enzymes within the brain. In this study, we provide a detailed characterization of the regional and cellular distribution of DDAH1 and DDAH2 proteins in the adult murine and human brain. Immunohistochemical analysis showed a wide distribution of DDAH1, mapping to multiple cell types, while DDAH2 was detected in a limited number of brain regions and exclusively in neurons. Our results provide key information for the investigation of the pathophysiological roles of the ADMA/DDAH system in neuropsychiatric diseases and pave the way for the development of novel selective therapeutic approaches.

Association between Endodontic Infection, Its Treatment and Systemic Health: A Narrative Review

The 'Focal Infection Era in Dentistry' in the late 19th and early 20th century resulted in widespread implementation of tooth extraction and limited the progress of endodontics. The theory proposed that bacteria and toxins entrapped in dentinal tubules could disseminate systemically to remote body parts, resulting in many types of degenerative systemic diseases. This theory was eventually refuted due to anecdotal evidence. However, lately there has been increased interest in investigating whether endodontic disease could have an impact on general health. There are reviews that have previously been carried out on this subject, but as new data have emerged since then, this review aims to appraise the available literature investigating the dynamic associations between apical periodontitis, endodontic treatment, and systemic health. The available evidence regarding focal infection theory, bacteraemia and inflammatory markers was appraised. The review also collated the available research arguing the associations of apical periodontitis with cardiovascular diseases, diabetes mellitus, adverse pregnancy outcome and autoimmune disorders, along with the effect of statins and immunomodulators on apical periodontitis prevalence and endodontic treatment prognosis. There is emerging evidence that bacteraemia and low-grade systemic inflammation associated with apical periodontitis may negatively impact systemic health, e.g., development of cardiovascular diseases, adverse pregnancy outcomes, and diabetic metabolic dyscontrol. However, there is limited information supporting the effect of diabetes mellitus or autoimmune disorders on the prevalence and prognosis post endodontic treatment. Furthermore, convincing evidence supports that successful root canal treatment has a beneficial impact on systemic health by reducing the inflammatory burden, thereby dismissing the misconceptions of focal infection theory. Although compelling evidence regarding the association between apical periodontitis and systemic health is present, further high-quality research is required to support and establish the benefits of endodontic treatment on systemic health.

Evaluation of Asymmetric Dimethylarginine Serum Level and Left Ventricular Function by 2D Speckle Tracking Echocardiography in Children on Regular Hemodialysis

Cardiovascular disease is the leading cause of morbidity and mortality in children with chronic kidney disease. Asymmetric dimethylarginine (ADMA) is thought to be related to chronic kidney disease patients' adverse cardiovascular effects. Our study is to assess ADMA concentrations in children on hemodialysis (HD) as a marker of cardiovascular risk and detect the relation to the left ventricular (LV) function by traditional and speckled tracking echo. Forty children with end-stage renal disease on regular HD were enrolled in the study and selected from the nephrology HD unit of Al-Zahraa Hospital, Al-Azhar University. Another group of 40 healthy children matches age and sex with the patient's group as a control. ADMA serum level, traditional echo, and tissue Doppler imaging spackled tracking were performed to assess: LV functions for both groups in the same line with the routine laboratory investigations. Moreover, bioimpedance was assessed after the HD session. Children on regular HD have a significantly higher (ADMA) serum level compared to their controls; the median is (72.5 ng/mL) and (25 ng/mL), respectively (P = 0.001) and a significant increase in high-sensitivity C-reactive protein and the median is (3.6 ng/mL) and (2.5 ng/mL), respectively (P = 0.001). Moreover, conventional echo detects 27 (67.5%) patients out of 40 had an impaired LV function; meanwhile, 33 (82.5%) had a global LV strain (LV GLS) detected by 2D (Speckle echo), a negative correlation between LV ejection fraction with serum (urea, cholesterol, and triglyceride) and a positive correlation between ADMA and LV systolic diameter. LV GLS (Speckle echo) is negatively correlated with LV end-diastolic diameter, LV end-systolic diameter and positively correlated with LV inter ventricular septum in diastole and reduced average systolic velocity (ml). The sensitivity and specificity of (ADMA), high-sensitivity C-reactive protein (hs-CRP), traditional, and Speckle echo for early left ventricular (LV) dysfunction were 92.50, 92, and 67.50, 97 and 67.50, 90.00, and 80.00, 92, respectively. An ADMA emerges as a sensitive and specific marker for early LV dysfunction in children on hemodialysis (HD); drugs targeting ADMA isessential in the future direction after clinical approval, to avoid early LV changes, furthermore (Speckle echo) is superior to the traditional echo for early detection of LV changes in chronic kidney disease (CKD) children.

Bariatric Surgery Improves the Atherogenic Profile of Circulating Methylarginines in Obese Patients: Results from a Pilot Study

Bariatric surgery improves obesity-related comorbidities. Methylarginines are biomarkers of cardiometabolic risk, liver steatosis, and insulin resistance. Here, we aimed to investigate methylarginines in obese patients undergoing bariatric surgery and compared them to age- and sex-matched healthy subjects. Thirty-one obese patients who underwent bariatric surgery and 31 healthy individuals were used for this retrospective study. The basal serum methylarginine levels were determined in the healthy individuals and the obese patients, before surgery and 6 and 12 months after surgery, by mass spectrometry. Compared with the healthy individuals, the obese patients displayed elevated monomethylarginine (mean change: +95%, p < 0.001), asymmetric-dimethylarginine (+105%, p < 0.001), symmetric-dimethylarginine (+25%, p = 0.003), and dimethylguanidino valerate (+32%, p = 0.008) concentrations. Bariatric surgery durably reduced the body mass index by 28% (12 months, 95%CI: 24–33, p = 0.002) and improved plasma lipids, insulin resistance, and liver function. Bariatric surgery reduced the serum levels of monomethylarginine and asymmetric-dimethylarginine by 12% (95%CI: 6–17) and 36% (95%CI: 27–45) (12 months, p = 0.003), respectively, but not symmetric-dimethylarginine or dimethylguanidino valerate. The monomethylarginine and asymmetric-dimethylarginine concentrations were strongly correlated with markers of dyslipidemia, insulin resistance, and a fatty liver. Serum dimethylguanidino valerate was primarily correlated with glycemia and renal function, whereas serum symmetric-dimethylarginine was almost exclusively associated with renal function. In conclusion, the monomethylarginine and asymmetric-dimethylarginine levels are efficiently decreased by bariatric surgery, leading to a reduced atherogenic profile in obese patients. Methylarginines follow different metabolic patterns, which could help for the stratification of cardiometabolic disorders in obese patients.

Asymmetric Dimethylarginine (ADMA) in Pediatric Renal Diseases: From Pathophysiological Phenomenon to Clinical Biomarker and Beyond

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide (NO) synthase inhibitor, inhibits NO synthesis and contributes to the pathogenesis of many human diseases. In adults, ADMA has been identified as a biomarker for chronic kidney disease (CKD) progression and cardiovascular risk. However, little attention is given to translating the adult experience into the pediatric clinical setting. In the current review, we summarize circulating and urinary ADMA reported thus far in clinical studies relating to kidney disease in children and adolescents, as well as systematize the knowledge on pathophysiological role of ADMA in the kidneys. The aim of this review is also to show the various analytical methods for measuring ADMA and the issues tht need to be addressed before transforming to clinical practice in pediatric medicine. The last task is to suggest that ADMA may not only be suitable as a diagnostic or prognostic biomarker, but also a promising therapeutic strategy to treat pediatric kidney disease in the future.

Reduced L-Arginine and L-Arginine-ADMA-Ratio, and Increased SDMA after Norseman Xtreme Triathlon

Endothelial vasodilatory function is dependent on the NO synthesis from L-arginine by endothelial NO-synthetase (eNOS). eNOS can be inhibited by asymmetric dimethylarginine (ADMA) by competitive inhibition on the binding site, and symmetric dimethylarginine (SDMA) can reduce the L-arginine availability intracellularly through competing for transport over the cellular membrane. To study the NO synthesis after prolonged exercise, we assessed circulatory L-arginine, the L-arginine/ADMA ratio, and SDMA before, after, and on the day after the Norseman Xtreme triathlon, an Ironman distance triathlon. We found significantly reduced levels of L-arginine and the L-arginine/ADMA ratio and increased levels of SDMA after the race (all p < 0.05). L-arginine rose toward baseline levels the day after the race, but ADMA increased beyond baseline levels, and SDMA remained above baseline the day after the race. The reduced levels of L-arginine and the L-arginine/ADMA ratio, and increased SDMA, after the race indicate a state of reduced capability of NO production. Increased levels of ADMA and SDMA, and reduced L-arginine/ADMA ratio, as seen the day after the race, are known risk markers of atherosclerosis and warrant further studies.

Impact of Physical Activity and Natural Bioactive Compounds on Endothelial Dysfunction in Chronic Kidney Disease

Chronic kidney disease (CKD) represents a world-wide public health problem. Inflammation, endothelial dysfunction (ED) and vascular calcifications are clinical features of CKD patients that increase cardiovascular (CV) mortality. CKD-related CV disease pathogenic mechanisms are not only associated with traditional factors such as arterial hypertension and dyslipidemia, but also with ED, oxidative stress and low-grade inflammation. The typical comorbidities of CKD contribute to reduce the performance and the levels of the physical activity in nephropathic patients compared to healthy subjects. Currently, the effective role of physical activity on ED is still debated, but the available few literature data suggest its positive contribution. Another possible adjuvant treatment of ED in CKD patients is represented by natural bioactive compounds (NBCs). Among these, minor polar compounds of extra virgin olive oil (hydroxytyrosol, tyrosol and oleocanthal), polyphenols, and vitamin D seem to exert a beneficial role on ED in CKD patients. The objective of the review is to evaluate the effectiveness of physical exercise protocols and/or NBCs on ED in CKD patients.

Serum symmetric dimethylarginine shows a relatively consistent long-term concentration in healthy dogs with a significant effect of increased body fat percentage

Symmetric dimethylarginine (SDMA) is a promising renal marker that correlates well with the glomerular filtration rate and could allow earlier detection of impaired renal function. The main objectives of this study were to assess the long-term variability of SDMA in healthy dogs and examine the influence of an increased body fat percentage on the level of SDMA. Sixteen lean Beagles were randomly assigned to the control group or weight-change group in age- and gender-matched pairs. The energy intake of the control group (n = 8) was strictly regulated to maintain an ideal body weight for 83 weeks, while the weight-change group (n = 8) was fed to induce weight gain (week 0–47), to maintain stable excessive body weight (week 47–56) and to lose weight (week 56–83), consecutively. At 8 specified time points, the body condition score, body composition, glomerular filtration rate, serum concentration of SDMA and creatinine were analyzed. In the control group, the within-subject coefficient of variation, between-subject coefficient of variation, reference change value (type I error = 5%) and index of individuality were 0.16, 0.22, 0.43 and 0.73, respectively. The control group and weight-change group did not differ significantly in SDMA concentration. SDMA showed a significant negative association (coefficient = -0.07) with body fat percentage (p<0.01) in the weight-change group and a significant positive association (coefficient = 7.79) with serum creatinine (p<0.01) in the entire study population. In conclusion, SDMA concentration has high long-term stability in healthy adult dogs. For the evaluation of SDMA concentrations, subject-specific reference values are preferred over a population-based reference value seen their higher sensitivity. Moreover, an increased body fat percentage does seem to affect the serum SDMA concentration of otherwise healthy dogs, but its clinical relevance has to be clarified in further research.

Raised Plasma Levels of Asymmetric Dimethylarginine Are Associated with Pathological Type and Predict the Therapeutic Effect in Lupus Nephritis Patients Treated with Cyclophosphamide

BACKGROUND

Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE). Asymmetric dimethylarginine (ADMA) has been associated with cardiovascular events in SLE patients and is a strong predictor of the progression of chronic kidney disease. However, whether ADMA can provide a predictive value for the diagnosis and treatment of LN patients remains unclear. This study evaluated the clinical significance of ADMA in LN patients.

METHODS

Blood samples of 114 patients with LN, 52 patients with primary glomerular disease, and 20 healthy people were collected. Plasma ADMA was measured via enzyme-linked immunosorbent assay. The relationship between plasma ADMA levels and pathological types and renal function and efficacy in LN patients were further analyzed.

RESULTS

There was no significant difference in plasma ADMA levels between LN and primary glomerular disease, but both were significantly higher than the values in healthy people (p < 0.05). Plasma ADMA levels in LN patients were negatively correlated with baseline estimated glomerular filtration rate (eGFR) and serum superoxide dismutase and positively correlated with serum cystatin C and serum β2-microglobulin (p < 0.05). The plasma ADMA levels of diffuse proliferative LN patients were significantly higher than those of other histopathological classes of LN. High plasma ADMA levels in LN patients (OR = 1.012; 95% CI 1.003-1.022; p = 0.010) is a risk factor for diffuse proliferative LN. The area under the receiver operating characteristic (ROC) curve of diagnosing diffuse proliferative LN by plasma ADMA was 0.707 (95% CI 0.610-0.805). The area under the ROC curve of combination with plasma ADMA, serum complement C3, and eGFR for diffuse proliferative LN was 0.796 (95% CI 0.713-0.879), which was significantly higher than that of ADMA, complement C3, and eGFR for diffuse proliferative LN alone, respectively (p < 0.05). Low plasma ADMA is an independent protective factor for proliferative LN patients achieving complete remission with cyclophosphamide as induction therapy (OR = 0.978; 95% CI 0.961-0.996; p < 0.05).

CONCLUSION

High plasma ADMA levels in combination with eGFR and complement C3 may be useful to diagnose diffuse proliferative LN. Low plasma ADMA may help to predict complete remission in proliferative LN patients treated with cyclophosphamide as induction therapy. Plasma ADMA may be a new biomarker to determine the pathological type of LN and predict the therapeutic effect.

Increased Serum Levels of Asymmetric Dimethylarginine and Symmetric Dimethylarginine and Decreased Levels of Arginine in Sudanese Patients with Essential Hypertension

INTRODUCTION

Essential hypertension (EH) is a disease caused by various environmental and genetic factors. Nitric oxide (NO) is important for the functional integrity of the endothelium. It is produced in endothelial cells by endothelial NO synthase (eNOS) that mediates the conversion of the amino acid arginine into NO and citrulline. Asymmetric dimethylarginine (ADMA) acts as an inhibitor of eNOS. In contrast, symmetric dimethylarginine (SDMA) has no direct effect on eNOS but plays an important role competing with arginine for transport across the amino acid transporter. ADMA and SDMA have been found to play a central role in the development of cardiovascular diseases. Serum ADMA levels may serve as a future diagnostic marker and a target of therapy in hypertensive patients in the Sudanese population. This study aimed to investigate the relation between serum arginine, ADMA, and SDMA levels with EH in the Sudanese population.

METHODS

Patients (n = 260) with established hypertension and controls (n = 144) with normal blood pressure were included in this case-control study. Serum blood samples were analyzed for arginine, ADMA, and SDMA, using high-performance liquid chromatography-tandem mass spectrometry. Other laboratory data were measured using routine methods. Mann-Whitney's U test and χ2 tests were used for continuous and categorical data, respectively. A multivariate logistic regression analysis was conducted to investigate the independent effect of multiple variables on the development of hypertension.

RESULTS

Serum arginine levels were significantly lower in the patient group than in the control group (p < 0.001). ADMA and SDMA levels were significantly higher in the patient group than the control group (p < 0.001, p = 0.001, respectively). Multivariate logistic regression analysis showed that only older age, being a male, and arginine levels are independent factors controlling the development of hypertension (p < 0.001, p < 0.001, and p = 0.046, respectively). ADMA and SDMA levels were not independent factors for the development of hypertension.

CONCLUSIONS

This study demonstrated increased serum levels of ADMA and SDMA and decreased arginine levels in Sudanese patients with EH. Lowering serum ADMA levels or increasing the arginine levels might be a novel therapeutic target in these individuals.

Inhibition of Dimethylarginine Dimethylaminohydrolase (DDAH) Enzymes as an Emerging Therapeutic Strategy to Target Angiogenesis and Vasculogenic Mimicry in Cancer

The small free radical gas nitric oxide (NO) plays a key role in various physiological and pathological processes through enhancement of endothelial cell survival and proliferation. In particular, NO has emerged as a molecule of interest in carcinogenesis and tumor progression due to its crucial role in various cancer-related events including cell invasion, metastasis, and angiogenesis. The dimethylarginine dimethylaminohydrolase (DDAH) family of enzymes metabolize the endogenous nitric oxide synthase (NOS) inhibitors, asymmetric dimethylarginine (ADMA) and monomethyl arginine (L-NMMA), and are thus key for maintaining homeostatic control of NO. Dysregulation of the DDAH/ADMA/NO pathway resulting in increased local NO availability often promotes tumor growth, angiogenesis, and vasculogenic mimicry. Recent literature has demonstrated increased DDAH expression in tumors of different origins and has also suggested a potential ADMA-independent role for DDAH enzymes in addition to their well-studied ADMA-mediated influence on NO. Inhibition of DDAH expression and/or activity in cell culture models and in vivo studies has indicated the potential therapeutic benefit of this pathway through inhibition of both angiogenesis and vasculogenic mimicry, and strategies for manipulating DDAH function in cancer are currently being actively pursued by several research groups. This review will thus provide a timely discussion on the expression, regulation, and function of DDAH enzymes in regard to angiogenesis and vasculogenic mimicry, and will offer insight into the therapeutic potential of DDAH inhibition in cancer based on preclinical studies.

Animal Models and Renal Biomarkers of Diabetic Nephropathy

Diabetes mellitus (DM) is the first cause of end stage chronic kidney disease (CKD). Animal models of the disease can shed light on the pathogenesis of the diabetic nephropathy (DN) and novel and earlier biomarkers of the condition may help to improve diagnosis and prognosis. This review summarizes the most important features of animal models used in the study of DN and updates the most recent progress in biomarker research.

An update of urine and blood metabolomics in chronic kidney disease

Chronic kidney disease is considered as a serious obstacle in global health, with increasing incidence and prevalence. In spite of numerous attempts by using recent omics technologies, specially metabolomics, for understanding pathophysiology, molecular mechanism and identification reliable consensus biomarkers for diagnosis and prognosis of this complex disease, the current biomarkers are still insensitive and many questions about its pathomechanism are still to be unanswered. This review is focused on recent findings about urine and serum/plasma metabolite biomarkers and changes in the pathways that occurs in the disease conditions. The urine and blood metabolome content in the normal and disease state is investigated based on the current metabolomics studies and well known metabolite candidate biomarkers for chronic kidney disease are discussed.

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.

Comparison of the diagnostic value of symmetric dimethylarginine, cystatin C, and creatinine for detection of decreased glomerular filtration rate in dogs

BACKGROUND

Early detection of decreased glomerular filtration rate (GFR) in dogs is challenging. Current methods are insensitive and new biomarkers are required.

OBJECTIVE

To compare overall diagnostic performance of serum symmetric dimethylarginine (SDMA) and serum cystatin C to serum creatinine, for detection of decreased GFR in clinically stable dogs, with or without chronic kidney disease (CKD).

ANIMALS

Ninety-seven client-owned dogs: 67 dogs with a diagnosis or suspicion of CKD and 30 healthy dogs were prospectively included.

METHODS

Prospective diagnostic accuracy study. All dogs underwent physical examination, systemic arterial blood pressure measurement, urinalysis, hematology and blood biochemistry analysis, cardiac and urinary ultrasound examinations, and scintigraphy for estimation of glomerular filtration rate (mGFR). Frozen serum was used for batch analysis of SDMA and cystatin C.

RESULTS

The area under the curve of creatinine, SDMA, and cystatin C for detection of an mGFR <30.8 mL/min/L was 0.98 (95% confidence interval [CI], 0.93-1.0), 0.96 (95% CI, 0.91-0.99), and 0.87 (95% CI, 0.79-0.93), respectively. The sensitivity of both creatinine and SDMA at their prespecified cutoffs (115 μmol/L [1.3 mg/dL] and 14 μg/dL) for detection of an abnormal mGFR was 90%. The specificity was 90% for creatinine and 87% for SDMA. When adjusting the cutoff for cystatin C to correspond to a diagnostic sensitivity of 90% (0.49 mg/L), specificity was lower (72%) than that of creatinine and SDMA.

CONCLUSIONS AND CLINICAL IMPORTANCE

Overall diagnostic performance of creatinine and SDMA for detection of decreased mGFR was similar. Overall diagnostic performance of cystatin C was inferior to both creatinine and SDMA.

AGXT2 and DDAH-1 genetic variants are highly correlated with serum ADMA and SDMA levels and with incidence of coronary artery disease in Egyptians

Dimethylarginine aminodehydrolase (DDAH1) and alanine glyoxylate aminotransferase2 (AGXT2) are two enzymes that contribute in asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) metabolism. Hence they affect production and bioavailability of eNOS-derived nitric oxide (NO) and consequently healthy blood vessels. The major aims of the current study were to investigate the association of genetic variants of AGXT2 rs37369, AGXT2 rs16899974 and DDAH1 rs997251 SNPs with incidence of coronary artery disease (CAD) in Egyptians and to correlate these variants with the serum levels of ADMA and SDMA. The study included 150 subjects; 100 CAD patients and 50 healthy controls. Genotyping was performed by qPCR while the ADMA and SDMA concentrations were assayed by ELISA. Both serum ADMA and SDMA concentrations were significantly higher in CAD patients compared to controls (both p < 0.0001). Genotype distributions for all studied SNPs were significantly different between CAD patients and controls. Carriers of AGXT2 rs37369-T allele (CT + TT genotypes) and AGXT2 rs16899974-A allele (CA + AA genotypes) had 2.4- and 2.08-fold higher risk of having CAD than CC genotype in both SNPs (p = 0.0050 and 0.0192, respectively). DDAH1 rs997251 TC + CC genotypes were associated with 2.3-fold higher risk of CAD than TT genotype (p = 0.0063). Moreover, the AGXT2 rs37369 TT and AGXT2 rs16899974 AA genotypes were associated with the highest serum ADMA and SDMA while DDAH1 rs997251 CC genotype was associated with the highest ADMA. AGXT2 rs37369-T, AGXT2 rs16899974-A, and DDAH1 rs997251-C alleles represent independent risk factors for CAD in the Egyptians.

Reliability of symmetric dimethylarginine in dogs with myxomatous mitral valve disease as kidney biomarker

The most common cause of heart failure in the canine population is myxomatous mitral valve disease, sometimes complicated by chronic kidney disease. Many studies have been done on the use of symmetric dimethylarginine as biomarker of renal impairment in dogs affected by chronic kidney disease, few studies have examined his reliability as biomarker in dogs affected by heart diseases. Aim of this study was to evaluate symmetric dimethylarginine in dogs affected by mitral valve disease in order to assess his reliability in heart diseases. This was a retrospective case-control study on a clinical population of dogs affected by mitral valve disease (cases) vs healthy dogs (controls). Both groups underwent a complete physical evaluation, echocardiographic examination, complete blood count, biochemical panel, including serum creatinine and urea and urine analysis with protein-to-creatinine ratio. Serum was frozen and sent to IDEXX laboratories for symmetric dimethylarginine determination. General linear model was applied to data. A total number of 24 cases and 7 controls were included. Symmetric dimethylarginine value was in the reference value in the 75% (n=18) of cases, and in the 43% (n=3) of controls. Once set symmetric dimethylarginine as dependent variable, no statistical significant differences were found for each variable considered (breed, age, sex, weight, class of cardiomyopathy, presence/absence of valvular disease, presence/absence of congestive heart failure, pharmacological therapy, creatinine and urea concentration). Blood concentration of SDMA resulted not influenced by the variables mentioned above, so it could be considered a reliable marker of early renal impairment in dogs affected by mitral valve disease.

Asymmetric dimethylarginine (ADMA) as an important risk factor for the increased cardiovascular diseases and heart failure in chronic kidney disease

Patients with chronic kidney disease have an increased cardiovascular morbidity and mortality. It has been recognized that the traditional cardiovascular risk factors could only partially explain the increased cardiovascular morbidity and mortality in patients with chronic kidney disease. Asymmetric dimethylarginine (ADMA) and N-monomethy l-arginine (L-NMMA) are endogenous inhibitors of nitric oxide synthases that attenuate nitric oxide production and enhance reactive oxidative specie generation. Increased plasma ADMA and/or L-NMMA are strong and independent risk factor for chronic kidney disease, and various cardiovascular diseases such as hypertension, coronary artery disease, atherosclerosis, diabetes, and heart failure. Both ADMA and L-NMMA are also eliminated from the body through either degradation by dimethylarginine dimethylaminohydrolase-1 (DDAH1) or urine excretion. This short review will exam the literature of ADMA and L-NMMA degradation and urine excretion, and the role of chronic kidney diseases in ADMA and L-NMMA accumulation and the increased cardiovascular disease risk. Based on all available data, it appears that the increased cardiovascular morbidity in chronic kidney disease may relate to the dramatic increase of systemic ADMA and L-NMMA after kidney failure.

Contribution of symmetric dimethylarginine to GFR decline in pediatric chronic kidney disease

BACKGROUND

In pediatric chronic kidney disease (pCKD), traditional factors (proteinuria, etiology, and race) do not fully explain disease progression. The levels of methylated arginine derivatives (MADs: asymmetric and symmetric dimethylarginine, respectively) rise in CKD and increase with CKD progression. The impact of MADs on glomerular filtration rate (GFR) decline has not been examined in pCKD. The aim of this study was to examine the additive impact of baseline (BL) levels of MADs on directly measured GFR (mGFR) decline per year (ml/min/1.73 m²/year) for a period of up to 4 years.

METHODS

Plasma and data, including mGFR by plasma iohexol clearance, were provided by the prospective, observational Chronic Kidney Disease in Children study. BL MADs were analyzed by high-performance liquid chromatography-tandem mass spectrometry.

RESULTS

For 352 pCKD subjects, the median [interquartile range] BL mGFR was 45 [35, 57] ml/min/1.73 m². The levels of BL MADs were inversely related to the initial mGFR and its decline over time (p < 0.0005) but not to the rate of decline. Covariates, non-glomerulopathy and Tanner stage of ≥ 3 demonstrated weaker relationships between BL levels and beginning mGFR (p = 0.004 and p = 0.002, respectively).

CONCLUSIONS

In pCKD, higher concentrations of BL MADs were inversely related to BL mGFR. MADs did not affect the CKD progression rate. Quantification of this relationship is novel to the pCKD literature.

AGXT2: An unnegligible aminotransferase in cardiovascular and urinary systems

Cardiovascular diseases (CVDs) and renal impairment interact in a complex and interdependent manner, which makes clarification of possible pathogenesis between CVDs and renal diseases very challenging and important. There is increasing evidence showing that both asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) play a crucial role in the development of CVDs as well as in the prediction of cardiovascular events. Also, the plasma levels of ADMA and SDMA were reported to be significantly associated with renal function. Alanine-glyoxylate aminotransferase 2 (AGXT2) is reported to be involved in ADMA and SDMA metabolism, thus deficiency in the expression or activity of AGXT2 may play a part in the progression of cardiovascular or renal diseases through affecting ADMA/SDMA levels. Here, we focused our attention on AGXT2 and discussed its potential impact on CVDs and renal diseases. Meanwhile, the review also summarized the functions and recent advances of AGXT2, as well as the clinical association studies of AGXT2 in cardiovascular and urinary systems, which might arouse the interest of researchers in these fields.

AGXT2 rs37369 polymorphism predicts the renal function in patients with chronic heart failure

Patients with chronic heart failure (CHF) are often accompanied with varying degrees of renal diseases. The purpose of this study was to identify rs37369 polymorphism of AGXT2 specific to the renal function of CHF patients. A total of 1012 southern Chinese participants, including 487 CHF patients without history of renal diseases and 525 healthy volunteers, were recruited for this study. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine the genotypes of AGXT2 rs37369 polymorphism. Levels of blood urea nitrogen (BUN) and serum creatinine (SCr) were detected to indicate the renal function of the participants. BUN level was significantly higher in CHF patients without history of renal diseases compared with healthy volunteers (p=0.000). And the similar result was also obtained for SCr (p=0.000). Besides, our results indicated that the level of BUN correlated significantly with SCr in both the CHF patients without renal diseases (r=0.4533, p<0.0001) and volunteers (r=0.2489, p<0.0001). Furthermore, we found that the AGXT2 rs37369 polymorphism could significantly affect the level of BUN in CHF patients without history of renal diseases (p=0.036, AA+AG vs GG). Patients with rs37369 GG genotype showed a significantly reduced level of BUN compared to those with the AA genotype (p=0.024), and the significant difference was still observed in the smokers of CHF patients without renal diseases (p=0.023). In conclusion, we found that CHF might induce the impairment of kidney and cause deterioration of renal function. AGXT2 rs37369 polymorphism might affect the renal function of CHF patients free from renal diseases, especially in patients with cigarette smoking.

Evidence-Based Advances in Rabbit Medicine

Rabbit medicine has been continuously evolving over time with increasing popularity and demand. Tremendous advances have been made in rabbit medicine over the past 5 years, including the use of imaging tools for otitis and dental disease management, the development of laboratory testing for encephalitozoonosis, or determination of prognosis in rabbits. Recent pharmacokinetic studies have been published, providing additional information on commonly used antibiotics and motility-enhancer drugs, as well as benzimidazole toxicosis. This article presents a review of evidence-based advances for liver lobe torsions, thymoma, and dental disease in rabbits and controversial and new future promising areas in rabbit medicine.

DdaR (PA1196) Regulates Expression of Dimethylarginine Dimethylaminohydrolase for the Metabolism of Methylarginines in Pseudomonas aeruginosa PAO1

Dimethylarginine dimethylaminohydrolases (DDAHs) catalyze the hydrolysis of methylarginines to yield l-citrulline and methylamines as products. DDAHs and their central roles in methylarginine metabolism have been characterized for eukaryotic cells. While DDAHs are known to exist in some bacteria, including Streptomyces coelicolor and Pseudomonas aeruginosa, the physiological importance and genetic regulation of bacterial DDAHs remain poorly understood. To provide some insight into bacterial methylarginine metabolism, this study focused on identifying the key elements or factors regulating DDAH expression in P. aeruginosa PAO1. First, results revealed that P. aeruginosa can utilize N^G ,N^G -dimethyl-l-arginine (ADMA) as a sole source of nitrogen but not carbon. Second, expression of the ddaH gene was observed to be induced in the presence of methylarginines, including N^G -monomethyl-l-arginine (l-NMMA) and ADMA. Third, induction of the ddaH gene was shown to be achieved through a mechanism consisting of the putative enhancer-binding protein PA1196 and the alternative sigma factor RpoN. Both PA1196 and RpoN were essential for the expression of the ddaH gene in response to methylarginines. On the basis of the results of this study, PA1196 was given the name DdaR, for dimethylarginine dimethylaminohydrolase regulator. Interestingly, DdaR and its target ddaH gene are conserved only among P. aeruginosa strains, suggesting that this particular Pseudomonas species has evolved to utilize methylarginines from its environment.IMPORTANCE Methylated arginine residues are common constituents of eukaryotic proteins. During proteolysis, methylarginines are released in their free forms and become accessible nutrients for bacteria to utilize as growth substrates. In order to have a clearer and better understanding of this process, we explored methylarginine utilization in the metabolically versatile bacterium Pseudomonas aeruginosa PAO1. Our results show that the transcriptional regulator DdaR (PA1196) and the sigma factor RpoN positively regulate expression of dimethylarginine dimethylaminohydrolases (DDAHs) in response to exogenous methylarginines. DDAH is the central enzyme of methylarginine degradation, and its transcriptional regulation by DdaR-RpoN is expected to be conserved among P. aeruginosa strains.

Intracerebral Administration of S-Adenosylhomocysteine or S-Adenosylmethionine Attenuates the Increases in the Cortical Extracellular Levels of Dimethylarginines Without Affecting cGMP Level in Rats with Acute Liver Failure

Alterations in brain nitric oxide (NO)/cGMP synthesis contribute to the pathogenesis of hepatic encephalopathy (HE). An increased asymmetrically dimethylated derivative of L-arginine (ADMA), an endogenous inhibitor of NO synthases, was observed in plasma of HE patients and animal models. It is not clear whether changes in brain ADMA reflect its increased local synthesis therefore affecting NO/cGMP pathway, or are a consequence of its increased peripheral blood content. We measured extracellular concentration of ADMA and symmetrically dimethylated isoform (SDMA) in the prefrontal cortex of control and thioacetamide (TAA)-induced HE rats. A contribution of locally synthesized dimethylarginines (DMAs) in their extracellular level in the brain was studied after direct infusion of the inhibitor of DMAs synthesizing enzymes (PRMTs), S-adenosylhomocysteine (AdoHcy, 2 mM), or the methyl donor, S-adenosylmethionine (AdoMet, 2 mM), via a microdialysis probe. Next, we analyzed whether locally synthesized ADMA attains physiological significance by determination of extracellular cGMP. The expression of PRMT-1 was also examined. Concentration of ADMA and SDMA, detected by positive mode electrospray LC-DMS-MS/MS, was greatly enhanced in TAA rats and was decreased (by 30 %) after AdoHcy and AdoMet infusion. TAA-induced increase (by 40 %) in cGMP was unaffected after AdoHcy administration. The expression of PRMT-1 in TAA rat brain was unaltered. The results suggest that (i) the TAA-induced increase in extracellular DMAs may result from their effective synthesis in the brain, and (ii) the excess of extracellular ADMA does not translate into changes in the extracellular cGMP concentration and implicate a minor role in brain NO/cGMP pathway control.

DDAH gene and cardiovascular risk

The crucial role of nitric oxide (NO) for normal endothelial function is well known. In many conditions associated with increased risk of cardiovascular diseases such as hypercholesterolemia, hypertension, abdominal obesity, diabetes and smok ing, NO biosynthesis is dysregulated, leading to endothelial dysfunction. The grow ing evidence from animal and human studies indicates that endogenous inhibitors of endothelial NO synthase such as asymmetric dimethylarginine (ADMA) and NG-monomethyl-L-arginine (L-NMMA) are associated with the endothelial dysfunc tion and potentially regulate NO synthase. The major route of elimination of ADMA is metabolism by the enzymes dimethylarginine dimethylaminohydrolase-1 and -2 (DDAH). In our recent study 16 men with either low or high plasma ADMA concen trations were screened to identify DDAH polymorphisms that could potentially be associated with increased susceptibility to cardiovascular diseases. In that study a novel functional mutation of DDAH-1 was identified; the mutation carriers had a significantly elevated risk for cardiovascular disease and a tendency to develop hypertension. These results confirmed the clinical role of DDAH enzymes in ADMA metabolism. Furthermore, it is possible that more common variants of DDAH genes contribute more widely to increased cardiovascular risk.

ADMA and hyperhomocysteinemia

Hyperhomocysteinemia is a risk factor for cardiovascular disease and stroke. Like many other cardiovascular risk factors, hyperhomocysteinemia produces endothelial dysfunction due to impaired bioavailability of endothelium-derived nitric oxide (NO). The molecular mechanisms responsible for decreased NO bioavailabil ity in hyperhomocysteinemia are incompletely understood, but emerging evidence suggests that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, may be a key mediator. Homocysteine is produced during the synthesis of ADMA and can alter ADMA metabolism by inhibiting dimethylarginine dimethy laminohydrolase (DDAH). Several animal and clinical studies have demonstrated a strong association between plasma total homocysteine, plasma ADMA, and endothelial dysfunction. These observations suggest a model in which elevation of ADMA may be a unifying mechanism for endothelial dysfunction during hyper homocysteinemia. The recent development of transgenic mice with altered ADMA metabolism should provide further mechanistic insights into the role of ADMA in hyperhomocysteinemia.

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

Background

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

Methods

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

Results

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

Conclusions

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

A pilot study of l-arginine supplementation on functional capacity in peripheral arterial disease

Peripheral arterial disease (PAD) impairs walking capacity and is often associated with a profound endothelial vasodilator dysfunction, characterized by reduced bioactivity and/or synthesis of endothelium-derived nitric oxide (NO). Previous studies have suggested that dietary supplementation of L-arginine, the precursor of NO, improves endothelium-dependent vasodilation, limb blood flow and walking distance. However, these studies have been small, and have used large intravenous doses of L-arginine. The optimal dose of L-arginine has not been determined. Accordingly, this pilot study was conducted to establish the lowest effective oral dose of L-arginine to improve walking distance in preparation for the definitive study. Patients with PAD and intermittent claudication ( n = 80) participated in this study. Eligibility criteria included: (1) ankle-brachial index (ABI) at rest ≤0.90; (2) post-exercise reduction in ABI ≥25%; and (3) difference in absolute claudication distance of ≤25% between two consecutive treadmill tests. Treadmill testing was performed using the Skinner-Gardner protocol and community-based walking was assessed using the walking impairment questionnaire. Patients were randomly assigned to oral doses of 0, 3, 6 or 9 g of L-arginine daily in three divided doses for 12 weeks. Treadmill testing was performed prior to administration of the study drug and again after 12 weeks of treatment. The study drug was well tolerated, with no significant adverse effects of L-arginine therapy. The safety laboratory studies were unremarkable, except for a statistically significant reduction in hematocrit in the L-arginine-treated groups. There was no significant difference observed in absolute claudication distance between the groups. However, a trend was observed for a greater increase in walking distance in the group treated with 3 g L-arginine daily, and there was a trend for an improvement in walking speed in patients treated with L-arginine. This pilot study provided data for safety, for power calculation and for dosing for the larger definitive trial that is now underway.

Arginine dimethylation products in pediatric patients with chronic kidney disease

Background

arginine and its metabolites have been linked to pediatric chronic kidney disease (CKD). We aimed to estimate serum levels of argninine (Arg), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in pediatric CKD patients and its relation to altered kidney function.

Patients and methods

132 pediatric patients with CKD and 120 healthy age and sex matched controls were compared regarding; serum Arg, ADMA and SDMA levels.

Results

In comparison to their values in control subjects, serum Arg levels were significantly lower; serum ADMA levels were non-significantly higher, but serum SDMA levels were significantly higher in CKD patients (p values: < 0.000; = 0.054; <0.000, respectively).

Calculated Arg/ADMA and Arg/SDMA ratios were significantly higher in patients compared to controls (p values: 0.001, and <0.000, respectively). However ADMA/SDMA ratio was significantly lower in patients compared to controls (p = 0.001. Serum Arg levels showed positive significant correlation, while serum ADMA and SDMA levels showed negative significant correlation with eGFR. Moreover, Arg/ADMA ratio showed negative significant correlation, while ADMA/SDMA ratio showed positive significant correlation with eGFR of patients. Regression analysis defined high serum SDMA level as persistently significant predictor for low eGFR.

Conclusion

Disturbed serum levels of arginine and its dimethyl derivatives may underlie development and/or progression of CKD. Elevated serum SDMA level is strongly correlated with impaired kidney functions and could be considered as a predictor for kidney functions deterioration and CKD progression.

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The underlying pathogenic mechanisms for pediatric CKD are multiple and interlocking.

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Disturbed serum levels of Arg and its dimethyl derivatives may underlie development and/or progression of CKD.

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Elevated serum SDMA level is strongly correlated with impaired kidney functions.

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Elevated SDMA level can be a predictor for kidney functions deterioration and CKD progression.

Effect of asymmetric dimethylarginine (ADMA) on heart failure development

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases that limits nitric oxide bioavailability and can increase production of NOS derived reactive oxidative species. Increased plasma ADMA is a one of the strongest predictors of mortality in patients who have had a myocardial infarction or suffer from chronic left heart failure, and is also an independent risk factor for several other conditions that contribute to heart failure development, including hypertension, coronary artery disease/atherosclerosis, diabetes, and renal dysfunction. The enzyme responsible for ADMA degradation is dimethylarginine dimethylaminohydrolase-1 (DDAH1). DDAH1 plays an important role in maintaining nitric oxide bioavailability and preserving cardiovascular function in the failing heart. Here, we examine mechanisms of abnormal NO production in heart failure, with particular focus on the role of ADMA and DDAH1.

Changes in serum asymmetric dimethylarginine and endothelial markers levels with varying periods of hemodialysis

Asymmetric dimethylarginine (ADMA) as a uremia toxin is accumulated in end-stage renal disease (ESRD) patients. Elevated ADMA level has been shown to be predictive of cardiovascular diseases (CVDs) and all-cause mortality in ESRD. Therefore, we investigated the effect of prolonged hemodialysis (HD) treatment on the levels of serum ADMA, arginine, nitric oxide (NO), soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1). Seventy-five patients (M/F = 40/35) with chronic renal failure (CRF) and who were on HD were divided into five groups with differing treatment periods of HD; from 6 to 24 months to 97-120 months. Fifteen apparently healthy subjects acted as controls. The serum levels of ADMA, sICAM-1 and sVCAM-1 were increased in all patient groups compared to the control group. No significant difference was observed when the patient groups were compared in terms of HD treatment periods. Nitric oxide levels were lower in the three groups who were treated for periods of 49-72, 73-96, 97-120 months compared to the control group. The L-arginine to ADMA ratio was decreased in all patient groups compared to controls. Consequently, our investigations have shown that in HD continued for more than 4 years NO levels began to decrease significantly and the levels of serum ADMA, sICAM-1 and sVCAM-1 levels increased although this increase was not affected by the period in which hemodialysis treatment was applied.

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

BACKGROUND

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

OBJECTIVES

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

ANIMALS

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

METHODS

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

RESULTS

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

CONCLUSIONS AND CLINICAL IMPORTANCE

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

Changes in plasma levels of asymmetric dimethylarginine, symmetric dimethylarginine, and arginine after a single dose of vardenafil in patients with pulmonary hypertension

OBJECTIVE

We investigated whether vardenafil, a phosphodiesterase-5 inhibitor, alters plasma levels of asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and arginine.

PATIENTS AND METHODS

ADMA, SDMA, and arginine were measured (0-540 min) in 12 patients with pulmonary hypertension after a single oral dose of vardenafil. Invasive hemodynamic data were collected at baseline and after 60 min.

RESULTS

A reduction in ADMA was observed at 30 and 45 min with a median change of -11.1% (P=0.021) and -12.5% (P=0.002). SDMA decreased with a median -5.3% change (P=0.032) at 45 min. An increase in arginine, median 40.3% (P=0.002), 45.0% (P=0.010), and 77.1% (P=0.008) was observed at 120, 300, and 540 min respectively. An increase in the arginine/ADMA ratio, median 11.7% (P=0.012), 32.5% (P=0.003), 26.5% (P=0.021), 33% (P=0.007), 48.5% (P=0.007), and 63.1% (P=0.008) was observed at 15, 45, 60, 120, 300, and 540 min respectively. There was a positive correlation between vardenafil exposure and the percent change in the arginine/ADMA ratio from baseline to 540 min (r=0.80; P=0.01). A correlation between baseline mean right atrial pressure (mRAP) and baseline ADMA (r=0.65; P=0.023), and baseline SDMA (r=0.61; P=0.035) was observed. A correlation between the baseline arginine/ADMA ratio and baseline cardiac output (CO) (r=0.59; P=0.045) and baseline cardiac index (CI) (r=0.61; P=0.036) was observed. Baseline arginine/ADMA ratio correlated with baseline mRAP (r=-0.79; P=0.002). A correlation between change (0-60 min) in CI and change in arginine (r=0.77; P=0.003) as well as change in the arginine/ADMA ratio (r=0.61; P=0.037) was observed.

CONCLUSIONS

Vardenafil induced changes in ADMA, SDMA, arginine, and the arginine/ADMA ratio in patients with PH. An increase in arginine and the arginine/ADMA ratio was associated with improvement in CI.

Predictive Potential of Twenty-Two Biochemical Biomarkers for Coronary Artery Disease in Type 2 Diabetes Mellitus

We investigated the potential of a panel of 22 biomarkers to predict the presence of coronary artery disease (CAD) in type 2 diabetes mellitus (DM2) patients. The study enrolled 96 DM2 patients with (n = 75) and without (n = 21) evidence of CAD. We assessed a biochemical profile that included 22 biomarkers: total cholesterol, LDL, HDL, LDL/HDL, triglycerides, glucose, glycated hemoglobin, fructosamine, homocysteine, cysteine, methionine, reduced glutathione, oxidized glutathione, reduced glutathione/oxidized glutathione, L-arginine, asymmetric dimethyl-L-arginine, symmetric dimethyl-L-arginine, asymmetric dimethyl-L-arginine/L-arginine, nitrate plus nitrite, S-nitrosothiols, nitrotyrosine, and n-acetyl-β-glucosaminidase. Prediction models were built using logistic regression models. We found that eight biomarkers (methionine, nitratate plus nitrite, n-acetyl-β-glucosaminidase, BMI, LDL, HDL, reduced glutathione, and L-arginine/asymmetric dimethyl-L-arginine) along with gender and BMI were significantly associated with the odds of CAD in DM2. These preliminary findings support the notion that emerging biochemical markers might be used for CAD prediction in patients with DM2. Our findings warrant further investigation with large, well-designed studies.

N(G)-Methylarginines: Biosynthesis, biochemical function and metabolism

N(G)-Methylarginines (N(G)-monomethylarginine, N(G), N(G)-dimethylarginine and N(G), N'(G)-dimethylarginine) occur widely in nature in either proteinbound or in free states. They are posttranslationally synthesized by a group of enzymes called protein methylase I with S-adenosyl-L-methionine as the methyl donor. The enzymes are highly specific not only towards arginine residues but also towards the protein species. Since transmethylation reaction is energy-dependent in the form of S-adenosyl-L-methionine and is catalyzed a group of highly specific enzymes, it is quite logical to assume that the enzymatic methylation of protein-bound arginine residues play an important role in the regulation of the function and/or metabolism of the protein. When determined with histones asin vitro substrates, protein methylase I activity parallels closely the degree of cell proliferation, and the myelin basic protein (MBP)-specific protein methylase I activity decreases drastically in dysmyelinating mutant mouse brain during myelinating period, suggesting an important role played in the formation and/or maintenance of myelin. When the methylated proteins are degraded by intracellular proteolytic enzymes, free N(G)-methylarginines are generated. Some of these free N(G)-methylarginines, particularly N(G)-monomethylarginine, are extensively metabolized by decarboxylation, hydrolysis, transfer of methylamidine and deimination reaction. Recent experiment demonstrates that some of the N(G)-methylarginines may be involved in the neutralization of activity of nitric oxide (NO) which has attracted a great deal of attention as vascular smooth muscle relaxation factor.

Down's syndrome, neuroinflammation, and Alzheimer neuropathogenesis

Down syndrome (DS) is the result of triplication of chromosome 21 (trisomy 21) and is the prevailing cause of mental retardation. In addition to the mental deficiencies and physical anomalies noted at birth, triplication of chromosome 21 gene products results in the neuropathological and cognitive changes of Alzheimer's disease (AD). Mapping of the gene that encodes the precursor protein (APP) of the β-amyloid (Aβ) present in the Aβ plaques in both AD and DS to chromosome 21 was strong evidence that this chromosome 21 gene product was a principal neuropathogenic culprit in AD as well as DS. The discovery of neuroinflammatory changes, including dramatic proliferation of activated glia overexpressing a chromosome 2 gene product--the pluripotent immune cytokine interleukin-1 (IL-1)--and a chromosome 21 gene product--S100B--in the brains of fetuses, neonates, and children with DS opened the possibility that early events in Alzheimer pathogenesis were driven by cytokines. The specific chromosome 21 gene products and the complexity of the mechanisms they engender that give rise to the neuroinflammatory responses noted in fetal development of the DS brain and their potential as accelerators of Alzheimer neuropathogenesis in DS are topics of this review, particularly as they relate to development and propagation of neuroinflammation, the consequences of which are recognized clinically and neuropathologically as Alzheimer's disease.

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.

Mechanism of cellular oxidation stress induced by asymmetric dimethylarginine

The mechanism by which asymmetric dimethylarginine (ADMA) induces vascular oxidative stress is not well understood. In this study, we utilized human umbilical vein endothelial cells (HUVEC) to examine the roles of ADMA cellular transport and the uncoupling of endothelial nitric oxide synthase (eNOS) in contributing to this phenomenon. Dihydroethidium (DHE) fluorescence was used as an index of oxidative stress. Whole cells and their isolated membrane fractions exhibited measureable increased DHE fluorescence at ADMA concentrations greater than 10 μM. ADMA-induced DHE fluorescence was inhibited by co-incubation with L-lysine, tetrahydrobiopterin (BH(4)), or L-nitroarginine methyl ester (L-NAME). Oxidative stress induced in these cells by angiotensin II (Ang II) were unaffected by the same concentrations of L-lysine, L-NAME and BH(4). ADMA-induced reduction in cellular nitrite or nitrite/nitrate production was reversed in the presence of increasing concentrations of BH(4). These results suggest that ADMA-induced DHE fluorescence involves the participation of both the cationic transport system in the cellular membrane and eNOS instead of the Ang II-NADPH oxidase pathway.

Nitric oxide (NO) and asymmetric dimethylarginine (ADMA): their pathophysiological role and involvement in intracerebral hemorrhage

OBJECTIVE

Nitric oxide (NO) has a variety of functions in physiological systems, particularly in the vasculature and the central nervous system. Currently, the imbalance of the pathway involving nitric oxide, nitric oxide synthase, and asymmetric dimethylarginine (NO-NOS-ADMA) is increasingly discussed in connection with endothelial dysfunction. Knowledge about the role of this pathway in intracerebral hemorrhage (ICH), which represents the most devastating stroke subtype, is increasing but still sparse. This article aims to review the current knowledge about the role and metabolism of NO and ADMA. It will also address the role of the NO-NOS-ADMA pathway in ICH and delineate some questions that should be addressed by future studies.

METHODS

A literature search regarding the data about NO, NOS, and ADMA and its role in ICH was conducted in PubMed.

RESULTS

Experimental data from cell culture and animal models indicate that, after the occurrence of ICH, neuronal and inducible nitric oxide synthases (nNOS and iNOS) are both overexpressed and uncoupled through the induction of blood compound metabolites, including thrombin and inflammatory mediators. ADMA, the most potent endogenous inhibitor of NOS, is also overproduced following dysregulation of its metabolizing enzymes. Dysfunction of the NO-NOS-ADMA pathway results in cell death, blood-brain barrier (BBB) disruption, and brain edema via different pathological mechanisms. However, the available data from clinical studies are still rare and partially contradictory.

CONCLUSION

Experimental data suggest an important role for the NO-NOS-ADMA pathway for secondary injury after ICH. Since the literature shows contradictory results, further studies are needed to address current confusion.

[Methylarginies-induced endothelial dysfunction in chronic kidney disease]

Chronic kidney disease (CKD), defined as low glomerular filtration rates and/or the presence of albuminuria, is considered a risk factor for cardiovascular disease (CVD). In recent years, increasing emphasis has been placed on endothelial dysfunction as a key element underlying the relationship between CKD and CVD. Endothelial cells play a pivotal role in many aspects of vascular function by generating nitric oxide (NO). However, NO production is reduced in CKD patients, partially due to decreased endothelial NO production. One possible cause of NO deficiency is increased levels of endogenous NO synthase inhibitors, in particular asymmetric dimethylarginine (ADMA). Elevated plasma levels of ADMA are consequence of increased synthesis and reduced degradation. Accumulation of ADMA and inhibition of NO production might contribute to endothelial dysfunction, hypertension, initiation of atherosclerosis, and incidence of CVD. Clinical studies revealed that ADMA plasma concentration is increased in populations with renal disease, vascular diseases, and high cardiovascular risks. In this regard, ADMA is increasingly recognized as a biomarker of CKD and CVD. This review discusses ADMA-mediated endothelial dysfunction in CKD, especially focusing on the link between CKD and CVD.

Role of dimethylarginine dimethylaminohydrolase activity in regulation of tissue and plasma concentrations of asymmetric dimethylarginine in an animal model of prolonged critical illness

High plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with adverse outcome in critically ill patients. Asymmetric dimethylarginine is released within cells during proteolysis of methylated proteins and is either degraded by dimethylarginine dimethylaminohydrolase (DDAH) or exported to the circulation via cationic amino acid transporters. We aimed to establish the role of DDAH activity in the regulation of tissue and plasma concentrations of ADMA. In 33 critically ill rabbits, we measured DDAH activity in kidney, liver, heart, and skeletal muscle and related these values to concentrations of ADMA in these tissues and in the circulation. Both DDAH activity and ADMA concentration were highest in kidney and lowest in skeletal muscle, with intermediate values for liver and heart. Whereas ADMA content was significantly correlated between tissues (r = 0.40-0.78), DDAH activity was not. Significant inverse associations between DDAH activity and ADMA content were only observed in heart and liver. Plasma ADMA was significantly associated with ADMA in the liver (r = 0.41), but not in the other tissues. In a multivariable regression model, DDAH activities in muscle, kidney, and liver, but not in heart, were negatively associated with plasma ADMA concentration, together explaining approximately 50% of its variation. In critical illness, plasma ADMA poorly reflects intracellular ADMA. Furthermore, tissue DDAH activity is a stronger predictor of plasma ADMA than of intracellular ADMA, indicating that, compared with DDAH activity, generation of ADMA and cationic amino acid transporter-mediated exchange may be more important regulators of intracellular ADMA.