Dimethylarginines in patients with type 2 diabetes mellitus: relation with the glycaemic control

SDMA as a marker and mediator in cerebrovascular disease

Symmetric dimethylarginine (SDMA) is a methylated derivative of arginine, generated by all cells as a by-product of cellular metabolism and eliminated via the kidney. For many years SDMA has been considered inert and of little biological significance. However, a growing body of evidence now suggests this view is outdated and that circulating SDMA levels may, in fact, be intricately linked to endothelial dysfunction and vascular risk. In this review, we specifically examine SDMA within the context of cerebrovascular disease, with a particular focus on ischaemic stroke. We first discuss pre-clinical evidence supporting the notion that SDMA has effects on nitric oxide signalling, inflammation, oxidative stress, and HDL function. We then appraise the most recent clinical studies that explore the relationship between circulating SDMA and cerebrovascular risk factors, such as chronic kidney disease, hypertension, atrial fibrillation, and atherosclerosis, exploring whether any associations may arise due to the existence of shared risk factors. Finally, we consider the evidence that elevated circulating SDMA is linked to poor outcomes following ischaemic and haemorrhagic stroke. We draw upon pre-clinical insights into SDMA function to speculate how SDMA may not only be a marker of cerebrovascular disease but could also directly influence cerebrovascular pathology, and we highlight the pressing need for more mechanistic pre-clinical studies alongside adequately powered, longitudinal clinical studies to fully evaluate SDMA as a marker/mediator of disease.

Associations of circulating dimethylarginines with the metabolic syndrome in the Framingham Offspring study

Background

Circulating levels of the endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA), are positively associated with the prevalence of metabolic syndrome (MetS) in cross-sectional investigations. It is unclear if circulating ADMA and other methylarginines are associated with incident MetS prospectively.

Methods

We related circulating ADMA, symmetric dimethylarginine (SDMA), L-arginine (ARG) concentrations (measured with a validated tandem mass spectrometry assay) and the ARG/ADMA ratio to MetS and its components in 2914 (cross-sectional analysis, logistic regression; mean age 58 years, 55% women) and 1656 (prospective analysis, Cox regression; mean age 56 years, 59% women) individuals from the Framingham Offspring Study who attended a routine examination.

Results

Adjusting for age, sex, smoking, and eGFR, we observed significant associations of ADMA (direct) and ARG/ADMA (inverse) with odds of MetS (N = 1461 prevalent cases; Odds Ratio [OR] per SD increment 1.13, 95%CI 1.04–1.22; and 0.89, 95%CI 0.82–0.97 for ADMA and ARG/ADMA, respectively). Upon further adjustment for waist circumference, systolic and diastolic blood pressure, glucose, high-density lipoprotein cholesterol, and triglycerides, we observed a positive relation between SDMA and MetS (OR per SD increment 1.15, 95% CI 1.01–1.30) but the other associations were rendered statistically non-significant. We did not observe statistically significant associations between any of the methylarginines and the risk of new-onset MetS (752 incident events) over a median follow-up of 11 years.

Conclusion

It is unclear whether dimethylarginines play an important role in the incidence of cardiometabolic risk in the community, notwithstanding cross-sectional associations. Further studies of larger samples are needed to replicate our findings.

Effects of AGXT2 variants on blood pressure and blood sugar among 750 older Japanese subjects recruited by the complete enumeration survey method

Background

Alanine:glyoxylate aminotransferase 2 (AGXT2; EC 2.6.1.44) is the only enzyme that degrades the R-form of 3-aminoisobutyrate, an intermediate metabolite of thymine. AGXT2, as well as diaminoarginine dimethylaminohydrolase 1 (DDAH1; EC 3.5.3.18), works as an enzyme that degrades asymmetric dimethylarginine (ADMA), which competitively inhibits the nitric oxide synthase family. Thus, these two enzyme activities may change vascular vulnerability for a lifetime via the nitric oxide (NO) system. We investigated the association between vascular conditions and diseases such as hypertension and diabetes mellitus and polymorphisms of these two genes in 750 older Japanese subjects (mean age ± standard deviation, 77.0 ± 7.6 years) recruited using the complete enumeration survey method in the Nakayama study. Demographic and biochemical data, such as blood pressure (BP) and casual blood sugar (CBS), were obtained. Four functional single nucleotide polymorphisms (SNPs; rs37370, rs37369, rs180749, and rs16899974) of AGXT2 and one functional insertion/deletion polymorphism in the promotor region with four SNPs (rs307894, rs669173, rs997251, and rs13373844) of DDAH1 were investigated. Plasma ADMA was also analyzed in 163 subjects.

Results

The results of multiple regression analysis showed that a loss of the functional haplotype of AGXT2, CAAA, was significantly positively correlated with BP (systolic BP, p = 0.034; diastolic BP, p = 0.025) and CBS (p = 0.021). No correlation was observed between DDAH1 and either BP or CBS. ADMA concentrations were significantly elevated in subjects with two CAAA haplotypes compared with subjects without the CAAA haplotype (p = 0.033).

Conclusions

Missense variants of AGXT2, but not DDAH1, may be related to vulnerability to vascular diseases such as hypertension and DM via the NO system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07612-3.

The new age of renal biomarkers: does SDMA solve all of our problems?

Within clinical small animal practice, diagnosis of both chronic kidney disease and acute kidney injury is common. To assess renal function, measurement of glomerular filtration rate is considered the gold standard. Currently, routine tests of kidney function include surrogate markers of glomerular filtration rate such as serum creatinine, and urea, each with their own limitations, whilst urine protein to creatinine ratio gives an indication of glomerular and tubular handling of protein, and urine specific gravity information about urine concentrating ability by the kidney. These parameters are used together with historical and physical examination data to give a diagnosis of kidney disease following which creatinine, proteinuria and blood pressure are used to stage chronic kidney disease and, together with urine output, grade acute kidney injury according to the International Renal Interest Society. However, there has been much concern that creatinine is insensitive when used to indicate early decline in renal function and this has highlighted the need for additional methods of diagnosing and monitoring these patients, with the potential to allow earlier therapeutic intervention. Symmetric dimethylarginine is a novel biomarker, which has been shown to perform as a surrogate marker of glomerular filtration rate in small animals. This article will review current research on symmetric dimethylarginine and the ways in which it may be utilised in small animal practice; current research supports the use of symmetric dimethylarginine as a screening test for detection of early chronic kidney disease according to International Renal Interest Society guidelines, but further research is required in to the usefulness of symmetric dimethylarginine as a tool for monitoring disease and the effect of non-renal influences.

ADMA (asymmetric dimethylarginine) and angiogenic potential in patients with type 2 diabetes and prediabetes

Asymmetric dimethylarginine is an endogenous competitive inhibitor of nitric oxide synthase and marker of endothelial dysfunction, but the question remains as to whether asymmetric dimethylarginine is a marker of cardiovascular episodes or their independent risk factor. ADMA/DDAH (dimethylaminohydrolase) pathway regulates vascular endothelial growth factor (VEGF)-mediated angiogenesis due to its impact on the NO formation. The aim of the study was to assess the concentrations of asymmetric dimethylarginine and the angiogenic potential in the blood of subjects with type 2 diabetes (T2DM, n = 33) and patients with prediabetes (n = 32)-impaired fasting glycemia and/or impaired glucose tolerance (WHO criteria). The study found that both the prediabetes group and subjects with T2DM had significantly elevated concentrations of asymmetric dimethylarginine, significantly high levels of VEGF-A, low ratio of sVEGF-R1/VEGF-A, and sVEGF-R2/VEGF-A. This may suggest endothelial damage at early stages of carbohydrate metabolism dysfunction-before T2DM is diagnosed. Higher proangiogenic potential in prediabetes and T2DM patients than in healthy subjects, is not only the effect of an increase in VEGF-A levels, but also reduced inhibition of circulating receptors.

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.

Duodenal L cell density correlates with features of metabolic syndrome and plasma metabolites

BACKGROUND

Enteroendocrine cells are essential for the regulation of glucose metabolism, but it is unknown whether they are associated with clinical features of metabolic syndrome (MetS) and fasting plasma metabolites.

OBJECTIVE

We aimed to identify fasting plasma metabolites that associate with duodenal L cell, K cell and delta cell densities in subjects with MetS with ranging levels of insulin resistance.

RESEARCH DESIGN AND METHODS

In this cross-sectional study, we evaluated L, K and delta cell density in duodenal biopsies from treatment-naïve males with MetS using machine-learning methodology.

RESULTS

We identified specific clinical biomarkers and plasma metabolites associated with L cell and delta cell density. L cell density was associated with increased plasma metabolite levels including symmetrical dimethylarginine, 3-aminoisobutyric acid, kynurenine and glycine. In turn, these L cell-linked fasting plasma metabolites correlated with clinical features of MetS.

CONCLUSIONS

Our results indicate a link between duodenal L cells, plasma metabolites and clinical characteristics of MetS. We conclude that duodenal L cells associate with plasma metabolites that have been implicated in human glucose metabolism homeostasis. Disentangling the causal relation between L cells and these metabolites might help to improve the (small intestinal-driven) pathophysiology behind insulin resistance in human obesity.

Symmetric Dimethylarginine in Cats with Hypertrophic Cardiomyopathy and Diabetes Mellitus

Background

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

Hypothesis

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

Animals

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

Methods

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

Results

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

Conclusions and Clinical Importance

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

Effects of betaine supplementation on nitric oxide metabolism, atherosclerotic parameters, and fatty liver in guinea pigs fed a high cholesterol plus methionine diet

OBJECTIVE

The aim of this study was to investigate the effect of high cholesterol (CHOL) and CHOL + methionine (MET) diets on atherogenic and oxidative index parameters and on the factors that influence nitric oxide (NO) bioavailability. Also, attempts were made to determine whether dietary betaine (BET) resulted in any improvement in the changes that occurred after CHOL + MET administration.

METHODS

Guinea pigs were fed chow containing 1.5% CHOL with or without 2% MET for 10 wk. A third group received the CHOL + MET + BET diet. Control groups were given standard chow or standard chow + BET. Arginine, NO, nitrotyrosine (NT), and asymmetric dimethylarginine (ADMA) levels; lipid profile; and dimethylarginine dimethylaminohydrolase (DDAH) activity were measured. The liver and aorta were subjected to histopathologic analysis.

RESULTS

The CHOL + MET diet caused higher serum CHOL and homocysteine levels, but no further increases were seen in aortic CHOL and diene conjugate (DC) levels and histopathologic lesions as compared with the CHOL group. Hepatic lipids and DC levels were also higher, and histopathologic lesions were more severe. CHOL + MET feeding increased ADMA and NT levels as compared with those of the CHOL-fed group. When BET (1 g/kg body weight/d) was added to the CHOL + MET diet, homocysteine and lipid levels decreased and histopathologic changes were reversed. BET diet decreased serum ADMA and hepatic and aortic DC levels and partly restored DDAH activity.

CONCLUSIONS

BET supplementation may be effective in preventing hyperlipidemia, disturbed NO availability, oxidative stress, and the development of fatty liver and atherosclerotic lesions that might result from excess amounts of cholesterol and methionine in the diet.

Assessment of asymmetrical dimethylarginine metabolism in patients with critical illness

BACKGROUND

Critically ill patients experience metabolic disorders including hypercatabolic state and hyperglycaemia, and these are associated with poor outcome. Hyperglycaemia and asymmetrical dimethylarginine (ADMA) are reported to have significant influences on endothelial dysfunction. The aim of this study was to examine the relationship between plasma ADMA and related arginine metabolism in patients with critical illness.

MATERIALS AND METHOSDS

Two venous blood samples (EDTA) (104 patients), on admission and follow-up sample in the last day in intensive care unit (ICU) (died or discharge sample median 7, interquartile range (IQR) 6-8, range 5-15). Plasma ADMA, arginine, homoarginine and SDMA were measured by high-performance liquid chromatography (HPLC).

RESULT

ADMA (P < 0·01) and SDMA (P < 0·05) were elevated, and homoarginine was decreased (P < 0·05) in nonsurvivors and was directly associated with predicted mortality rate (P < 0·05 and P < 0·001), Sequential Organ Failure Assessment (SOFA) (P < 0·05, P < 0·001), ICU stay (P < 0·05, P < 0·001) and mortality (P < 0·01, P < 0·05). ADMA was directly associated with SDMA (P < 0·001), albumin (P < 0·05), ICU stay and mortality (P < 0·01). SDMA was directly associated with creatinine (P < 0·001) and Acute physiology and Chronic Health Evaluation II score (P < 0·001). In the follow-up measurements, there was a significant decrease in SOFA score (P < 0·01), homoarginine (P < 0·01), aminotransferase (P < 0·01), Laboratory Glucose (P < 0·01) and albumin (P < 0·01). In contrast, there was an increase in arginine (P < 0·01), ADMA (P < 0·01), ADMA:SDMA ratio (P < 0·01) and the norepinephrine administration (P < 0·01).

CONCLUSION

In the present longitudinal study, ADMA metabolism was altered in patients with critical illness and was associated with disease severity and mortality.

Supplementation with Phycocyanobilin, Citrulline, Taurine, and Supranutritional Doses of Folic Acid and Biotin-Potential for Preventing or Slowing the Progression of Diabetic Complications

Oxidative stress, the resulting uncoupling of endothelial nitric oxide synthase (eNOS), and loss of nitric oxide (NO) bioactivity, are key mediators of the vascular and microvascular complications of diabetes. Much of this oxidative stress arises from up-regulated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. Phycocyanobilin (PhyCB), the light-harvesting chromophore in edible cyanobacteria such as spirulina, is a biliverdin derivative that shares the ability of free bilirubin to inhibit certain isoforms of NADPH oxidase. Epidemiological studies reveal that diabetics with relatively elevated serum bilirubin are less likely to develop coronary disease or microvascular complications; this may reflect the ability of bilirubin to ward off these complications via inhibition of NADPH oxidase. Oral PhyCB may likewise have potential in this regard, and has been shown to protect diabetic mice from glomerulosclerosis. With respect to oxidant-mediated uncoupling of eNOS, high-dose folate can help to reverse this by modulating the oxidation status of the eNOS cofactor tetrahydrobiopterin (BH4). Oxidation of BH4 yields dihydrobiopterin (BH2), which competes with BH4 for binding to eNOS and promotes its uncoupling. The reduced intracellular metabolites of folate have versatile oxidant-scavenging activity that can prevent oxidation of BH4; concurrently, these metabolites promote induction of dihydrofolate reductase, which functions to reconvert BH2 to BH4, and hence alleviate the uncoupling of eNOS. The arginine metabolite asymmetric dimethylarginine (ADMA), typically elevated in diabetics, also uncouples eNOS by competitively inhibiting binding of arginine to eNOS; this effect is exacerbated by the increased expression of arginase that accompanies diabetes. These effects can be countered via supplementation with citrulline, which efficiently enhances tissue levels of arginine. With respect to the loss of NO bioactivity that contributes to diabetic complications, high dose biotin has the potential to "pinch hit" for diminished NO by direct activation of soluble guanylate cyclase (sGC). High-dose biotin also may aid glycemic control via modulatory effects on enzyme induction in hepatocytes and pancreatic beta cells. Taurine, which suppresses diabetic complications in rodents, has the potential to reverse the inactivating impact of oxidative stress on sGC by boosting synthesis of hydrogen sulfide. Hence, it is proposed that concurrent administration of PhyCB, citrulline, taurine, and supranutritional doses of folate and biotin may have considerable potential for prevention and control of diabetic complications. Such a regimen could also be complemented with antioxidants such as lipoic acid, N-acetylcysteine, and melatonin-that boost cellular expression of antioxidant enzymes and glutathione-as well as astaxanthin, zinc, and glycine. The development of appropriate functional foods might make it feasible for patients to use complex nutraceutical regimens of the sort suggested here.

Plasma ADMA associates with all-cause mortality in renal transplant recipients

Asymmetric dimethylarginine (ADMA) is a key endogenous inhibitor of endothelial NO synthase that affects endothelial function, blood pressure and vascular remodeling. Increased plasma levels of ADMA are associated with worse outcome from cardiovascular disease. Due to endothelial dysfunction before and after kidney transplantation, renal transplant recipients (RTR) are at high risk for the alleged deleterious effects of ADMA. We investigated the associations of ADMA levels with all-cause mortality and graft failure in RTR. Plasma ADMA levels were determined in 686 stable outpatient RTR (57 % male, 53 ± 13 years), with a functioning graft for ≥1 year. Determinants of ADMA were evaluated with multivariate linear regression models. Associations between ADMA and mortality were assessed using multivariable Cox regression analyses. The strongest associations with plasma ADMA in the multivariable analyses were male gender, donor age, parathyroid hormone, NT-pro-BNP and use of calcium supplements. During a median follow-up of 3.1 [2.7–3.9] years, 79 (12 %) patients died and 45 (7 %) patients developed graft failure. ADMA was associated with increased all-cause mortality [HR 1.52 (95 % CI 1.26–1.83] per SD increase, P < 0.001], whereby associations remained upon adjustment for confounders. ADMA was associated with graft failure [HR 1.41 (1.08–1.83) per SD increase, P = 0.01]; however, upon addition of eGFR significance was lost. High levels of plasma ADMA are associated with increased mortality in RTR. Our findings connect disturbed NO metabolism with patient survival after kidney transplantation.

The relationship between serum asymmetric dimethylarginine levels and subjective sleep quality in normotensive patients with type 2 diabetes mellitus

BACKGROUND/AIMS

Poor sleep quality (SQ) is associated with increased cardiovascular mortality and morbidity. Additionally, asymmetric dimethylarginine (ADMA) is an independent predictor of cardiovascular mortality and morbidity. However, no sufficient data regarding the relationship between ADMA levels and SQ have been reported. The goal of the current study was to evaluate the association between SQ and ADMA levels in normotensive patients with type 2 diabetes mellitus.

METHODS

The study participants consisted of 78 normotensive type 2 diabetics. The SQ of all participants was assessed using the Pittsburgh Sleep Quality Index (PSQI). Patients with a global PSQI score > 5 were defined as "poor sleepers." Factors associated with poor SQ were analyzed using a multiple regression model. Serum ADMA levels were measured using high performance liquid chromatography.

RESULTS

The median ADMA levels of the poor sleepers were increased compared with patients defined as good sleepers (5.5 [4.2 to 6.6] vs. 4.4 [2.9 to 5.4], p < 0.01, respectively). However, the L-arginine/ADMA ratio was decreased in poor sleepers (p < 0.01). Global PSQI scores were positively correlated with ADMA levels (p < 0.01) and negatively correlated with the L-arginine/ADMA ratio (p = 0.02). ADMA levels were correlated with sleep latency (p < 0.01) and sleep efficiency (p = 0.01). Logistic regression analysis showed that ADMA levels (odds ratio [OR], 1.68; 95% confidence interval [CI], 1.16 to 2.44; p = 0.01) and body mass index (OR, 1.15; 95% CI, 1.01 to 1.31; p = 0.04) were associated with poor SQ independently of glomerular filtration rate, sex, age, duration of diabetes, hemoglobin A1c, total cholesterol, and systolic blood pressure.

CONCLUSIONS

Self-reported SQ was independently associated with ADMA levels in normotensive patients with diabetes mellitus.

Plasma levels of dimethylarginines in preterm very low birth weight neonates: its relation with perinatal factors and short-term outcome

Endogenously produced inhibitors of nitric oxide (NO) synthase, in particular asymmetric dimethylarginine (ADMA), are currently considered of importance in various disease states characterized by reduced NO availability. We investigated the association between plasma levels of ADMA, symmetric dimethylarginine (SDMA), l-arginine, and citrulline and perinatal factors and outcome in 130 preterm (gestational age ≤30 weeks) very low birth weight (VLBW, <1500 g) infants. Plasma samples were collected 6–12 h after birth. We did not find significant correlations between ADMA, SDMA, l-arginine, and citrulline levels and gestational age or birth weight. However, the arginine:ADMA ratio (AAR, a better indicator of NO availability than either arginine or ADMA separately) was positively correlated with gestational age. ADMA and arginine levels were not significantly different between males and females but males showed a negative correlation between ADMA levels and gestational age. Perinatal factors such as preeclampsia, chrorioamnionitis, prolonged rupture of membranes, or form of delivery did not significantly alter dimethylarginine levels or AAR. In contrast, the AAR was significantly reduced in the infants with respiratory distress, mechanical ventilation, and systemic hypotension Therefore, our data suggest that altered NO availability may play a role in the respiratory and cardiovascular adaptation in preterm VLBW infants.

Asymmetric dimethylarginine and long-term adverse cardiovascular events in patients with type 2 diabetes: relation with the glycemic control

Background and aims

Elevated plasma asymmetric dimethylarginine (ADMA) levels have been observed in patients with insulin resistance and diabetes, and have been reported to predict adverse cardiovascular events in type 2 diabetic patients. However, the relationship between ADMA and glycemic control in patients with type 2 diabetes remained controversial.

Methods and results

We evaluated 270 patients with type 2 diabetes and measured their plasma ADMA and hemoglobin A1c (HbA1c) levels by high performance liquid chromatography. The mean age was 67 ± 12 years. The mean plasma ADMA and HbA1c level were 0.46 ± 0.09 μmol/l and 7.8 ± 1.6%, respectively. There was no significant correlation between plasma ADMA level and HbA1c level (r = −0.09, p = 0.13). During the median follow-up period of 5.7 years (inter-quartile range: 5.0 − 7.3 years), major adverse cardiovascular event (MACE, including cardiovascular death, myocardial infarction and stroke) was observed in 55 patients (20.4%). Multivariate Cox regression analysis revealed that the ADMA tertile was an independent risk factor for MACE (ADMA tertile III versus ADMA tertile I: p = 0.026, HR: 2.31, 95% CI: 1.10 − 4.81). The prognosis predictive power of ADMA disappeared in patients with well glycemic control (HbA1c ≤6.5%), and the ADMA-HbA1c interaction p value was 0.01.

Conclusions

In patients with type 2 diabetes, ADMA might be an independent risk factor for long-term adverse cardiovascular events. However, ADMA was not correlated with serum HbA1c level, and in diabetic patients with HbA1c ≤6.5%, elevated ADMA level was no longer associated with increased risk of long-term prognosis. Our findings suggested that the prognosis predictive value of ADMA in type 2 diabetes might be modified by the glycemic control.

Antidiabetic drug metformin is effective on the metabolism of asymmetric dimethylarginine in experimental liver injury

AIMS

We aimed to investigate the pharmacological efficiency of metformin on asymmetric dimethylarginine (ADMA) metabolism in inflammation caused by the lipopolysaccharide (LPS)/D-galactosamine (D-GalN) treatment.

METHODS

Adult Sprague-Dawley rats were injected LPS/D-GalN intraperitoneally. One half of the animals was injected metformin (250 mg kg(-1) body mass for one week) prior to LPS/D-GalN treatment. Six hours after the LPS/D-GalN injection, livers were removed, and used for the measurements of dimethylarginine dimethylaminohydrolase (DDAH) and myeloperoxidase (MPO) activities, glutathione (GSH), ADMA and arginine levels. Liver tissues were examined histopathologically. The Kruskal-Wallis (posthoc Mann-Whitney U) test was used for the statistics. LPS/D-GalN injections caused liver injury as evidenced by the activities of aminotransferases and arginase. GSH level and DDAH activity were decreased in the liver. Metformin pretreatment alleviated the activity of serum enzymes, and attenuated histopathological lesions caused by LPS/D-GalN injections. LPS/D-GalN-induced inflammation, as confirmed by the increased MPO activity, created an asymmetrical distribution of arginine and ADMA between the tissue and plasma. Metformin decreased tissue ADMA level while it restored the DDAH activity and GSH.

CONCLUSION

Our findings showed that metformin administration for one week has a potency to protect liver through regulating ADMA metabolism in LPS/D-GalN-induced injury.

Time course of asymmetric dimethylarginine and symmetric dimethylarginine levels after successful renal transplantation

BACKGROUND

Although renal transplantation (Tx) improves the outcome of patients with renal disease, cardiovascular (CV) risk remains high. Recently, it was demonstrated that asymmetric dimethylarginine (ADMA) levels predict CV events and graft survival in renal transplant recipients (RTRs). Little is known about the impact of renal Tx on the plasma levels of ADMA and symmetric dimethylarginine (SDMA). The present study aimed to define the time course of ADMA and SDMA after Tx.

METHODS

We prospectively followed 167 incident RTRs with visits at the time of Tx and 3 and 12 months thereafter. At all visits, demographics and relevant biochemistry were recorded and blood was sampled for analysis of ADMA and SDMA (high-performance liquid chromatography). Eighty-four patients had an additional sampling in the immediate postoperative period. In a case-controlled substudy (n = 31), we compared ADMA and SDMA levels between RTRs and chronic kidney disease (CKD) patients, matched for glomerular filtration rate, gender, age, CV history and diabetes.

RESULTS

Overall, plasma ADMA and SDMA levels decreased after Tx. The decline of SDMA was more pronounced and paralleled the recovery of renal function. Interestingly, the decline of ADMA was preceded by an increase in the immediate postoperative period. In the case-controlled substudy, SDMA levels were similar, whereas ADMA levels were significantly higher in RTRs compared with the CKD counterparts (P = 0.003).

CONCLUSION

ADMA levels follow a biphasic pattern after successful renal Tx with a transient rise in the immediate postoperative period followed by a decline. Levels remain elevated compared with CKD patients, matched for age, gender, diabetes, CV history and renal function.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Transsulfuration pathway thiols and methylated arginines: the Hunter Community Study

Background

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

Methods

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

Results

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

Conclusions

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

Elevated asymmetric dimethylarginine in plasma: an early marker for endothelial dysfunction in non-alcoholic fatty liver disease?

AIMS

Non-alcoholic fatty liver disease (NAFLD) is associated with cardiovascular disease. Asymmetric dimethylarginine (ADMA) is a novel marker of endothelial dysfunction and atherosclerosis. We aimed to investigate circulating ADMA concentrations in biopsy proven NAFLD and also to search its association with carotid atherosclerosis.

METHODS

Sixty-seven nondiabetic and normotensive patients with NAFLD and 35 healthy controls were enrolled. Plasma ADMA was measured along with glucose, lipids and insulin levels. Insulin resistance (IR) was assessed by homeostasis model assessment-estimated insulin resistance (HOMA-IR) method. Carotid atherosclerosis was evaluated by carotid artery intima-media thickness (CIMT) using carotid ultrasonography.

RESULTS

ADMA levels and CIMT measurements were significantly higher in NAFLD group than the controls. However, the difference regarding the CIMT disappeared when the findings were adjusted according to the metabolic parameters and insulin sensitivity. In contrast, the difference for ADMA remained significant between two groups. No significant association was found between ADMA, CIMT and histopathological findings.

CONCLUSIONS

Plasma ADMA levels are increased in subjects with NAFLD. This increase seems to be independent from traditional cardiovascular risk factors, insulin resistance and liver histology. Circulating ADMA may be an earlier marker of vascular damage with respect to CIMT in subjects with NAFLD.