Asymmetric dimethylarginine is associated with macrovascular disease and total homocysteine in patients with type 2 diabetes

Asymmetric Dimethylarginine and NT-proBNP Levels Provide Synergistic Information in Pulmonary Arterial Hypertension

BACKGROUND

Plasma asymmetric dimethylarginine (ADMA) is elevated in pulmonary arterial hypertension (PAH) and is associated with unfavorable outcomes.

OBJECTIVES

The aim of this study was to assess changes in ADMA plasma levels for monitoring disease progression and outcomes during PAH-specific therapy.

METHODS

ADMA was measured at baseline and after at least 6 months of follow-up using enzyme-linked immunosorbent assay and high-performance liquid chromatography. Changes in ADMA were analyzed in relation to changes in established PAH markers, including hemodynamic status, N-terminal pro-brain natriuretic peptide (NT-proBNP) and risk assessment scores. Impact on survival was assessed using Kaplan-Meier curves and Cox proportional hazards models.

RESULTS

Between 2008 and 2019, ADMA samples were collected prospectively from 215 patients with PAH. Change in ADMA plasma level was a predictor of disease progression and survival. ΔADMA (median -0.03 μmol/L; 95% CI: -0.145 to 0.0135) was correlated with change in mean pulmonary arterial pressure (P < 0.005; rS = 0.287) but was not significantly correlated with ΔNT-proBNP (P = 0.056; rS = 0.135). Patients with decreased ADMA plasma levels at follow-up had better 3-year and 5-year survival rates (88% and 80%, respectively, vs 72% and 53% in those without decreases in ADMA) (P < 0.005; pulmonary hypertension-related mortality or lung transplantation). Patients with decreases in both ADMA and NT-proBNP had better survival rates compared with patients in whom only 1 parameter improved (P < 0.005). ΔADMA was a significant predictor of survival in Cox regression analysis and also when corrected for ΔNT-proBNP (HRs: 1.27 and 1.35, respectively; P < 0.005).

CONCLUSIONS

ADMA and NT-proBNP provide synergistic prognostic information for patients with PAH. ADMA could be used as an objective and distinct biomarker for monitoring treatment response in PAH.

Metabolomics Characterization of Disease Markers in Diabetes and Its Associated Pathologies

With the change in lifestyle of people, there has been a considerable increase in diabetes, which brings with it certain follow-up pathological conditions, which lead to a substantial medical burden. Identifying biomarkers that aid in screening, diagnosis, and prognosis of diabetes and its associated pathologies would help better patient management and facilitate a personalized treatment approach for prevention and treatment. With the advancement in techniques and technologies, metabolomics has emerged as an omics approach capable of large-scale high throughput data analysis and identifying and quantifying metabolites that provide an insight into the underlying mechanism of the disease and its progression. Diabetes and metabolomics keywords were searched in correspondence with the assigned keywords, including kidney, cardiovascular diseases and critical illness from PubMed and Scopus, from its inception to Dec 2023. The relevant studies from this search were extracted and included in the study. This review is focused on the biomarkers identified in diabetes, diabetic kidney disease, diabetes-related development of CVD, and its role in critical illness.

Metabolomics signature of cardiovascular disease in patients with diabetes, a narrative review

Objectives

The exact underlying mechanism of developing diabetes-related cardiovascular disease (CVD) among patients with type 2 diabetes (T2D) is not clear. Metabolomics can provide a platform enabling the prediction, diagnosis, and understanding of the risk of CVD in patients with diabetes mellitus. The aim of this review is to summarize the available evidence on the relationship between metabolomics and cardiovascular diseases in patients with diabetes.

Methods

The literature was searched to find out studies that have investigated the relationship between the alteration of specific metabolites and cardiovascular diseases in patients with diabetes.

Results

Evidence proposed that changes in the metabolism of certain amino acids, lipids, and carbohydrates, independent of traditional CVD risk factors, are associated with increased CVD risk.

Conclusions

Metabolomics can provide a platform to enable the prediction, diagnosis, and understanding of the risk of CVD in patients with diabetes mellitus. The association of the alteration in specific metabolites with CVD may be considered in the investigations for the development of new therapeutic targets for the prevention of CVD in patients with diabetes mellitus.

The effects of a comparatively higher dose of 1000 mg/kg/d of oral L- or D-arginine on the L-arginine metabolic pathways in male Sprague-Dawley rats

Oral L-arginine supplements are popular mainly for their nitric oxide mediated vasodilation, but their physiological impact is not fully known. L-arginine is a substrate of several enzymes including arginase, nitric oxide synthase, arginine decarboxylase, and arginine: glycine amidinotransferase (AGAT). We have published a study on the physiological impact of oral L- and D-arginine at 500 mg/kg/day for 4 wks in male Sprague-Dawley rats. We investigated the effects of oral L-arginine and D-arginine at a higher dose of 1000 mg/kg/d for a longer treatment duration of 16 wks in 9-week-old male Sprague-Dawley rats. We measured the expression and activity of L-arginine metabolizing enzymes, and levels of their metabolites in the plasma and various organs. L-arginine did not affect the levels of L-arginine and L-lysine in the plasma and various organs. L-arginine decreased arginase protein expression in the upper small intestine, and arginase activity in the plasma. It also decreased AGAT protein expression in the liver, and creatinine levels in the urine. L-arginine altered arginine decarboxylase protein expression in the upper small intestine and liver, with increased total polyamines plasma levels. Endothelial nitric oxide synthase protein was increased with D-arginine, the presumed metabolically inert isomer, but not L-arginine. In conclusion, oral L-arginine and D-arginine at a higher dose and longer treatment duration significantly altered various enzymes and metabolites in the arginine metabolic pathways, which differed from alterations produced by a lower dose shorter duration treatment published earlier. Further studies with differing doses and duration would allow for a better understanding of oral L-arginine uses, and evidence based safe and effective dose range and duration.

The impact of type 2 diabetes duration on serum asymmetric dimethylarginine and C-reactive protein concentration in Bosnian patients

Objective. The present study assessed the impact of type 2 diabetes mellitus (T2DM) duration on the serum asymmetric dimethylarginine (ADMA) and C-reactive protein (CRP) concentration in Bosnian patients.

Methods. Participants for this cross-sectional study were randomly selected from the Family Medicine Clinic (Sarajevo, Bosnia and Herzegovina). Serum ADMA concentration was determined by ELISA. Serum high-sensitivity (hs-CRP) was determined by particle-enhanced immunonephelometry. ANOVA test followed by Scheffe post-hoc test or Kruskal-Wallis test followed by Man-Whitney test were used for statistical analysis.

Results. The study included 38 patients in up to 10 years diabetes duration (≤10 years T2DM) group, 22 patients in greater than 10 years diabetes duration (>10 years T2DM) group, and 60 controls. Serum ADMA concentration in the >10 years T2DM group (1.81±0.15 μmol/L) was significantly higher compared to serum ADMA concentration in the ≤10 years T2DM group (1.38±0.41 μmol/L; p<0.001) and in controls (0.62±0.15 μmol/L; p<0.001). A significant difference in serum ADMA concentration was found between the <10 years T2DM group and the controls (p<0.001). The serum CRP concentration in the >10 years T2DM group [5.95 (4.20–9.12) mg/L] was significantly higher compared to serum CRP concentration in the <10 years T2DM group [2.35 (1.40–4.30) mg/L; p<0.001] and controls [0.85 (0.50–1.30) mg/L; p<0.001]. Significant difference in serum CRP concentration was observed between the <10 years T2DM group and controls (p<0.001).

Conclusions. The present study showed an increase in the serum ADMA and CRP concentrations with the advancement of T2DM. These results suggest that ADMA and CRP may serve as indicators of endothelial dysfunction and chronic low-grade inflammation progression in patients with T2DM. Larger prospective studies are required to confirm the observed findings.

A Proinflammatory Diet Is Associated with Higher Risk of Peripheral Artery Disease

Peripheral arterial disease (PAD) has a strong relationship with inflammation. However, it is unclear whether the dietary inflammatory potential is associated with PAD. We aimed to address this knowledge gap. The dietary inflammatory index (DII) was obtained using a 24-h dietary recall interview for each individual. Logistic regression models and restricted cubic spline were performed to assess the relationship of DII with the prevalence of PAD. In addition, Spearman correlation analysis and subgroup analysis were also undertaken. In total, 5840 individuals from the 1999–2004 National Health and Nutrition Examination Survey (NHANES) were enrolled in our study. Participants in higher DII quartile tended to have higher rates of PAD. The increase in DII scores showed a positive association with PAD after fully multivariate adjustment (OR (odds ratios) = 1.094, 95% confidence interval (CI): 1.022–1.171). The multivariable-adjusted OR and 95% CI of the highest DII index quartile compared with the lowest quartile was 1.543 (95% CI: 1.116–2.133). Subgroup analysis demonstrated that the positive association between DII and PAD was persistent across population subgroups. In conclusion, we report that a proinflammatory dietary pattern is related to a higher risk of developing PAD among US adults.

Metabolomics in Diabetes and Diabetic Complications: Insights from Epidemiological Studies

The increasing prevalence of diabetes and its complications, such as cardiovascular and kidney disease, remains a huge burden globally. Identification of biomarkers for the screening, diagnosis, and prognosis of diabetes and its complications and better understanding of the molecular pathways involved in the development and progression of diabetes can facilitate individualized prevention and treatment. With the advancement of analytical techniques, metabolomics can identify and quantify multiple biomarkers simultaneously in a high-throughput manner. Providing information on underlying metabolic pathways, metabolomics can further identify mechanisms of diabetes and its progression. The application of metabolomics in epidemiological studies have identified novel biomarkers for type 2 diabetes (T2D) and its complications, such as branched-chain amino acids, metabolites of phenylalanine, metabolites involved in energy metabolism, and lipid metabolism. Metabolomics have also been applied to explore the potential pathways modulated by medications. Investigating diabetes using a systems biology approach by integrating metabolomics with other omics data, such as genetics, transcriptomics, proteomics, and clinical data can present a comprehensive metabolic network and facilitate causal inference. In this regard, metabolomics can deepen the molecular understanding, help identify potential therapeutic targets, and improve the prevention and management of T2D and its complications. The current review focused on metabolomic biomarkers for kidney and cardiovascular disease in T2D identified from epidemiological studies, and will also provide a brief overview on metabolomic investigations for T2D.

DDAH1 promoter -396 4N insertion variant is associated with increased risk of type 2 diabetes in a gender-dependent manner

Background

Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases, making it a contributing factor for diabetes. Endogenous ADMA is hydrolyzed by dimethylarginine dimethylaminohydrolase 1 (DDAH1), and a DDAH1 promoter ‐396 4N deletion/insertion polymorphism (DDAH1: ‐396_‐395insGCGT) regulates its transcriptional activity. This study aimed to explore the association between this polymorphism and type 2 diabetes (T2DM).

Methods

In a case–control study, all participants were genotyped for this polymorphism within two sets of populations (discovery: 1,227 T2DM patients and 1,339 controls; replication: 1,190 patients and 1,651 controls). The disease association was assessed by a unconditional logistic regression model. Homeostasis model assessment calculations were conducted among different genotypes.

Results

We identified that DDAH1: ‐396_‐395insGCGT insertion allele was significantly associated with increased risk of T2DM (discovery: adjusted odds ratio [OR] = 1.380, 95% CI = 1.128–1.687, p = .002; replication: OR = 1.231, 95% CI = 1.007–1.504, p = .043). The homeostasis model assessment of insulin resistance was increased in participants carrying Ins/Ins alleles (p = .0452). Interestingly, the insertion allele increased the risk of T2DM in males but not in females (male discovery: OR = 1.528, 95% CI = 1.141–2.047, p = .004; replication: OR = 1.439, 95% CI = 1.083–1.911, p = .012; female discovery: OR = 1.218, 95% CI = 0.913–1.626, p = .18; replication: OR = 1.161, 95% CI = 0.871–1.548, p = .308).

Conclusion

The DDAH1: ‐396_‐395insGCGT insertion allele is associated with increased risk of T2DM in a gender‐dependent manner, affects males but not females.

Plasma nitric oxide level is correlated with microvascular functions in the peripheral arterial disease

At present there is no widely accepted biomarker for monitoring of vascular functions. The purpose of this prospective study was to investigate the association of some blood biomarkers with vascular reactivity in patients with peripheral arterial diseases (PAD). A prospective evaluation was made of 3 groups comprising a control group of healthy individuals, and patients with PAD caused by either atherosclerosis or Buerger's disease. Microvascular perfusion was examined using laser Doppler imaging of cutaneous erythrocyte flux after iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP). The correlation of microvascular reactivity with endothelium-related biomarkers was assessed. ACh-induced and SNP-induced vasodilations were significantly diminished in the PAD groups. The plasma nitric oxide (NO) levels of PAD patients were significantly higher than those of the control group, but asymmetric dimethylarginine, total antioxidant capacity and hydrogen sulphide levels were similar. Plasma NO level was negatively correlated with ACh and SNP-stimulated microvascular flow increase, whereas a positive correlation was detected with blood glucose and glycated hemoglobin (HbA1c) levels in all groups. These results indicate that a high plasma level of NO in PAD patients is associated with diminished endothelium-dependent and independent flow increase in the microvascular bed. An excessive amount of NO-induced nitrosative stress in an inflammatory condition that might be a reason for vascular dysfunction should be taken into consideration in the diagnostic and therapeutic approaches to PAD.

HIV-infected persons with type 2 diabetes show evidence of endothelial dysfunction and increased inflammation

Background

Increased incidence of cardiovascular diseases (CVD) in both HIV infection and type 2 diabetes (T2D) compared to the general population has been described. Little is known about the combined effect of HIV infection and T2D on inflammation and endothelial function, both of which may contribute to elevated risk of CVD.

Methods

Cross-sectional study including 50 HIV-infected persons on combination anti-retroviral therapy (cART), with HIV RNA <200 copies/mL (n = 25 with T2D (HIV + T2D+), n = 25 without T2D (HIV + T2D-)) and 50 uninfected persons (n = 22 with T2D (HIV-T2D+) and n = 28 without T2D (HIV-T2D-)). Groups were matched on age and sex.

High sensitive C-reactive protein (hsCRP) was used to determine inflammation (cut-off 3 mg/L). The marker of endothelial dysfunction asymmetric dimethylarginine (ADMA) was measured using high performance liquid chromatography. Trimethylamine-N-oxide (TMAO), a microbiota-dependent, pro-atherogenic marker was measured using stable isotope dilution LC/MS/MS.

Results

The percentage of HIV + T2D+, HIV + T2D-, HIV-T2D+, and HIV-T2D- with hsCRP above cut-off was 50%, 19%, 47%, and 11%, respectively. HIV + T2D+ had elevated ADMA (0.67 μM (0.63-0.72) compared to HIV + T2D- (0.60 μM (0.57-0.64) p = 0.017), HIV-T2D+ (0.57 μM (0.51-63) p = 0.008), and HIV-T2D- (0.55 μM (0.52-0.58) p < 0.001). No differences in TMAO between groups were found. However, a positive correlation between ADMA and TMAO was found in the total population (r_s = 0.32, p = 0.001), which was mainly driven by a close correlation in HIV + T2D+ (r_s = 0.63, p = 0.001).

Conclusion

Elevated inflammation and evidence of endothelial dysfunction was found in HIV-infected persons with T2D. The effect on inflammation was mainly driven by T2D, while both HIV infection and T2D may contribute to endothelial dysfunction. Whether gut microbiota is a contributing factor to this remains to be determined.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2334-8) contains supplementary material, which is available to authorized users.

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.

Asymmetric dimethylarginine, a biomarker of cardiovascular complications in diabetes mellitus

Cardiovascular (CV) complications are an essential causal element of prospect in diabetes mellitus (DM), with carotid atherosclerosis being a common risk factor for prospective crisis of coronary artery diseases and/or cerebral infarction in DM subjects. From another point of view, asymmetric dimethylarginine (ADMA) has been established as an inhibitor of endogenous nitric oxide synthesis and the relationship between ADMA and arteriosclerosis has been reported. In our study with 87 type 2 DM (T2DM) patients, we have examined whether ADMA and other CV risk factors are the useful predictors of DMCV complications. After the measurement of the respective CV risk factors, we have followed the enrolled T2DM patients for 5 years. We have finally analyzed 77 patients. DMCV complications developed in 15 cases newly within 5 years, and 4 cases recurred. The concentrations of ADMA in plasma were markedly more elevated in 19 DM patients with CV complications than in 58 DM patients without CV complications. Urinary albumin (U-Alb), mean intimal-medial thickness (IMT) and ankle brachial index (ABI) were also higher in patients with CV complications. Multiple regression analyses showed that U-Alb had an influence on the high level of ADMA (standardized β = 6.59, P = 0.00014) independently of age, systolic BP, fibrinogen, mean IMT, plaque score, and ABI. The review indicates what is presently known regarding plasma ADMA that might be a new and meaningful biomarker of CV complications in DM subjects.

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.

Evaluation of cardiovascular biomarkers in patients with age-related wet macular degeneration

AIM

To evaluate levels of homocysteine, asymmetric dimethylarginine (ADMA), and nitric oxide (NO), as well as activity of endothelial NO synthase (eNOS), in patients with age-related macular degeneration (AMD).

METHODS

The levels of homocysteine, ADMA, and NO and activity of eNOS in patients who were diagnosed with wet AMD by fundus fluorescein angiography (n=30) were compared to a control group with no retinal pathology (n=30).

RESULTS

Levels of homocysteine and ADMA were found to be significantly higher in the wet AMD group than in the control group (P<0.001), whereas NO levels and eNOS activity were higher in the control group (P<0.001). In the wet AMD group, we detected a 2.64- and 0.33-fold increase in the levels of ADMA and homocysteine, respectively, and a 0.49- and 2.41-fold decrease in the eNOS activity and NO level, respectively.

CONCLUSION

Elevated levels of homocysteine and ADMA were observed in patients with wet AMD. Increased ADMA may be responsible for the diminished eNOS activity found in these patients, which in turn contributes to the decrease in NO levels, which likely plays a role in the pathogenesis of AMD.

Relation of asymmetric dimethylarginine levels to macrovascular disease and inflammation markers in type 2 diabetic patients

AIM. We aimed to determine the relation of asymmetric dimethyl arginine (ADMA) levels to atherosclerotic vascular disease and inflammation markers in type 2 diabetes. METHODS. We recruited 50 type 2 diabetic patients with atherosclerosis, 50 type 2 diabetic patients without atherosclerosis, and 31 healthy control patients into our study. We obtained fasting serum and plasma samples and measured HbA1c, fasting blood glucose, C-peptide, creatinine, total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, hsCRP, fibrinogen, erythrocyte sedimentation rate, total homocysteine, and ADMA levels. In addition, all of the patients were evaluated for carotid artery intima media thickness by ultrasound. We evaluated ADMA levels in healthy controls, diabetic patients with macrovascular complications, and diabetic patients without macrovascular complications and evaluated the relationship between ADMA levels and total homocysteine, inflammation markers, and macrovascular disease. RESULTS. Mean ADMA values in non-MVD and control groups were significantly lower than in MVD group (0.39 ± 0.16, 0.32 ± 0.13, 0.52 ± 0.23, P < 0.05, resp.). These three variables (carotid intima-media thickness, inflammatory markers, and ADMA levels) were significantly higher in diabetes group than control (P < 0.05). CONCLUSION. There is a relationship between ADMA and macrovascular disease in type 2 diabetes, but further studies are needed to understand whether increased ADMA levels are a cause of macrovascular disease or a result of macrovascular disease.

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.

Contribution of arginase activation to vascular dysfunction in cigarette smoking

BACKGROUND

Cigarette smoke increases the risk of several cardiovascular diseases and has synergistic detrimental effects when present with other risks that contribute to its pathogenesis. Oxidative injury to the endothelium via reactive oxygen species (ROS) and nitric oxide (NO) dysregulation is a common denominator of smoking-induced alterations in vascular function. However, the mechanisms underlying ROS and NO dysregulation due to smoking remain unclear. We tested if arginase (Arg) activation/upregulation contributes to this phenomenon by constraining nitric oxide synthase (NOS) activity.

METHODS

Arg2 knockout (Arg2(-/-)) and control C57BL/6J mice were either exposed to cigarette smoke, 6 h/day/2 weeks (Second Hand Smoking; SHS) or housed in normal environment (Non Smoking; NS). Arg activity, NO and ROS levels were determined by measuring urea production, fluorescent dye (DAF), and dihydroethedium (DHE) respectively in isolated mouse aorta.

RESULTS

Arg activity and ROS levels were higher NO lower in SHS compared to NS mice. SHS failed to lower NO levels in Arg2(-/-) mice. Endothelial dependent vasodilation (EDV) was attenuated in SHS mice as compared to controls (78.80% ± 8 vs 46.58% ± 5). This impaired EDV was abolished in Arg2(-/-) mice (67.48% ± 7 in SHS vs. 78.80% ± 8 in NS). Vascular stiffness was increased in SHS mice as compared to NS controls but remained unchanged in Arg2(-/-) mice.

CONCLUSION

Endothelial NOS is uncoupled by smoking exposure, leading to endothelial dysfunction and vascular stiffness, a process that is prevented by Arg2 deletion. Hence, we identify Arg2 upregulation as a critical pathogenic factor and target for therapy in oxidative injury following smoking exposure through reciprocal regulation of endothelial NOS.

Direct and indirect antioxidant properties of α-lipoic acid and therapeutic potential

Diabetes has emerged as a major threat to worldwide health. The exact mechanisms underlying the disease are unknown; however, there is growing evidence that the excess generation of reactive oxygen species (ROS) associated with hyperglycemia, causes oxidative stress in a variety of tissues. In this context, various natural compounds with pleiotropic actions like α-lipoic acid (LA) are of interest, especially in metabolic diseases such as diabetes. LA, either as a dietary supplement or a therapeutic agent, modulates redox potential because of its ability to match the redox status between different subcellular compartments as well as extracellularly. Both the oxidized (disulfide) and reduced (di-thiol: dihydro-lipoic acid, DHLA) forms of LA show antioxidant properties. LA exerts antioxidant effects in biological systems through ROS quenching but also via an action on transition metal chelation. Dietary supplementation with LA has been successfully employed in a variety of in vivo models of disease associated with an imbalance of redox status: diabetes and cardiovascular diseases. The complex and intimate association between increased oxidative stress and increased inflammation in related disorders such as diabetes, makes it difficult to establish the temporal sequence of the relationship.

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.

Red cell distribution width and risk of peripheral artery disease: Analysis of National Health and Nutrition Examination Survey 1999–2004

Red cell distribution width (RDW) is an independent predictor of the 10-year estimated risk of coronary heart disease (CHD) events. However, RDW’s association with peripheral artery disease (PAD) – a CHD risk equivalent – has not been evaluated to date. In this cross-sectional study, we examined 6950 participants of the National Health and Nutrition Examination Survey, 1999–2004. PAD was defined as an ankle–brachial index below 0.9 ( n = 618). RDW was divided into quartiles (Q) (Q1: ≤ 12.2; Q2: 12.3–12.5; Q3: 12.6–13.0; Q4: ≥ 13.1) and PAD risk was compared across these quartiles using adjusted multivariate logistic regression. A graded increase in prevalent PAD with increasing RDW quartiles was observed (4.2% in Q1 vs 13.9% in Q4; test of trend p < 0.001). Risk of PAD was significantly higher (odds ratio (OR) 1.19, 95% confidence interval (CI): 1.06–1.34; p = 0.003) after adjusting for age, sex, race, body mass index, hypertension, hyperlipidemia, diabetes, smoking, estimated glomerular filtration rate, C-reactive protein, hemoglobin, mean corpuscular volume, and nutritional factors (folate, iron and vitamin B12) deficiencies with each unit (0.1) increase in RDW. Upon receiver-operating characteristics analysis, the predictive accuracy of the American College of Cardiology / American Heart Association (ACC/AHA)-defined PAD screening criteria (for a high-risk population) was 0.657 at best, but improved significantly (0.727) after addition of RDW ( p < 0.0001). In conclusion, higher levels of RDW are independently associated with a higher risk of PAD and can significantly improve the risk prediction beyond that estimated by ACC/AHA-defined PAD screening criteria.

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.

Relationship between DDAH gene variants and serum ADMA level in individuals with type 1 diabetes

Asymmetric dimethylarginine (ADMA) levels are elevated in diabetes and likely contribute to diabetic complications such as retinopathy and nephropathy. The DDAH enzymes are primarily responsible for ADMA metabolism. Polymorphisms in the dimethylarginine dimethylaminohydrolase (DDAH) 1 and 2 genes have been previously associated with serum ADMA levels in type 2 diabetes (T2DM). We sought to determine whether they are also associated with ADMA levels in individuals with type 1 diabetes (T1DM). Serum ADMA concentrations were measured in 196 individuals with T1DM. Twenty-six tag SNPs in the DDAH1 gene and 10 in the DDAH2 gene were genotyped. One SNP in the DDAH1 gene (rs3738111) and one in the DDAH2 gene (rs805293) showed a correlation with serum ADMA levels; however, neither survived correction for multiple testing. We found limited evidence that genetic polymorphisms in DDAH genes influence serum ADMA levels in individuals with T1DM. This differs to findings in T2DM and may be due to underlying differences in the cohorts or to fundamental differences in the pathogenesis of the two types of diabetes.

Diabetes and alpha lipoic Acid

Diabetes mellitus is a multi-faceted metabolic disorder where there is increased oxidative stress that contributes to the pathogenesis of this debilitating disease. This has prompted several investigations into the use of antioxidants as a complementary therapeutic approach. Alpha lipoic acid, a naturally occurring dithiol compound which plays an essential role in mitochondrial bioenergetic reactions, has gained considerable attention as an antioxidant for use in managing diabetic complications. Lipoic acid quenches reactive oxygen species, chelates metal ions, and reduces the oxidized forms of other antioxidants such as vitamin C, vitamin E, and glutathione. It also boosts antioxidant defense system through Nrf-2-mediated antioxidant gene expression and by modulation of peroxisome proliferator activated receptors-regulated genes. ALA inhibits nuclear factor kappa B and activates AMPK in skeletal muscles, which in turn have a plethora of metabolic consequences. These diverse actions suggest that lipoic acid acts by multiple mechanisms, many of which have only been uncovered recently. In this review we briefly summarize the known biochemical properties of lipoic acid and then discussed the oxidative mechanisms implicated in diabetic complications and the mechanisms by which lipoic acid may ameliorate these reactions. The findings of some of the clinical trials in which lipoic acid administration has been tested in diabetic patients during the last 10 years are summarized. It appears that the clearest benefit of lipoic acid supplementation is in patients with diabetic neuropathy.

Quantitation of L-arginine and asymmetric dimethylarginine in human plasma by LC-selective ion mode-MS for Type 2 diabetes mellitus study

The article reports a simple, sensitive and fast LC/MS method for the analysis of L-arginine (L-Arg), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in human plasma. The homoarginine was used as the internal standard (IS). The chromatographic separation was achieved on C₁₈(150 mm×2.1 mm, 5 µm) column with a mobile phase consisting of ammonium acetate (0.25 mmol/l) and methanol (93 : 7, v/v), at a flow rate of 0.2 ml/min. L-Arg, ADMA and SDMA were well separated by LC/MS with selective ion mode (SIM). The method was successfully applied to type 2 diabetes mellitus (T2DM) study. Twenty-one healthy controls and twenty-two T2DM patients before and after treatment two years were investigated. The results indicated that the level of ADMA in T2DM was significantly higher than that in healthy controls. Furthermore, ADMA has important association with the development of cardiovascular diseases.

Asymmetric dimethylarginine in young people with Type 1 diabetes: a paradoxical association with HbA(1c)

AIMS

Asymmetric dimethylarginine (ADMA) is an independent risk factor for cardiovascular disease and its concentrations are increased in several diseases, including diabetes. However, there is limited information on this plasma marker in young people, particularly in those with Type 1 diabetes. The aim of the present study was therefore to perform a longitudinal evaluation of plasma ADMA and of its determinants in young people with childhood-onset Type 1 diabetes.

METHODS

For measurement of ADMA using mass spectrometry, 1018 longitudinal stored blood samples were available from 330 young people with Type 1 diabetes followed in the Oxford Regional Prospective Study. Additional data concerning annual assessments of HbA(1c) , height, weight, insulin dose and three early morning urine samples for measurement of the albumin/creatinine ratio were available.

RESULTS

ADMA levels were significantly higher in males than in females (mean ± SD: 0.477 ± 0.090 vs. 0.460 ± 0.089 μmol/l, P=0.002) and declined with chronological age (estimate ± SE: -0.0106 ± 0.0008, P<0.001). A significant inverse association was detected between ADMA and HbA(1c) (estimate ± SE:-0.0113 ± 0.001, P<0.001). ADMA levels were lower in subjects developing microalbuminuria (mean ± SD: 0.455 ± 0.093 vs. 0.476 ± 0.087 μmol/l, P=0.001) than in subjects with normoalbuminuria, but this difference disappeared after adjusting for HbA(1c) .

CONCLUSIONS

In this longitudinal study, ADMA concentrations decreased with age and were significantly higher in males and lower in subjects developing microalbuminuria. These associations were largely explained by a paradoxical negative association between HbA(1c) and ADMA. We suggest that chronic hyperglycaemia might down-regulate mechanisms implicated in ADMA production or stimulate its metabolism confounding short-term associations with complications risk.

Asymmetric dimethylarginine as a risk factor for cardiovascular disease in Japanese patients with type 2 diabetes mellitus

AIMS

Although asymmetric dimethylarginine (ADMA) is known to be involved in the developing process of cardiovascular diseases (CVD), little is known about the effects of ADMA on atherosclerosis in Asian patients with diabetes, who have the racial feature of lower body mass index (BMI) and decreased capacity of insulin secretion and sensitivity.

METHODS

We employed 55 Japanese patients with type 2 diabetes mellitus (mean age, 64·2 years; 56% men) in a 6-month-longitudinal study and 450 patients (mean age, 62·7 years; 56% men) in a cross-sectional study and examined the association of serum ADMA with atherosclerosis parameters [intima-media thickness (IMT) and brachial-ankle pulse wave velocity (baPWV)] as well as with the presence of CVD.

RESULTS

In the longitudinal study, multiple regression analysis showed that basal serum ADMA level had a significantly positive association with changes in IMT (β=0·35, P=0·03) independently of age, duration of diabetes, BMI, blood pressure, low-density lipoprotein and high-density lipoprotein (LDL and HDL) cholesterol, HbA(1c) , and renal function. In the cross-sectional study, the serum ADMA level was significantly and positively associated with the presence of CVD (odds ratio=7·22, 95% confidence interval 1·29-40·40, P=0·02, by logistic analysis) and with baPWV (β=0·14, P <0·01, by multiple regression analysis). In contrast, serum symmetric dimethylarginine level, a structural isomer of ADMA, was associated neither with parameters for atherosclerosis nor with the presence of CVD in both studies.

CONCLUSIONS

Serum ADMA is a predictor of atherosclerosis and associated with the presence of CVD in Japanese patients with type 2 diabetes mellitus.

The association of dimethylarginine dimethylaminohydrolase 1 gene polymorphism with type 2 diabetes: a cohort study

BACKGROUND

Elevated plasma levels of asymmetric dimethylarginine (ADMA) has been reported to be associated with insulin resistance and micro/macrovascular diabetic complications, and may predict cardiovascular events in type 2 diabetic patients. Dimethylarginine dimethylaminohydrolase 1 (DDAH1) is the major enzyme eliminating ADMA in humans, but the effect of genetic variations in DDAH1 on type 2 diabetes and its long-term outcome are unknown.

METHODS

From July 2006 to June 2009, we assessed the association between polymorphisms in DDAH1 and type 2 diabetes in 814 consecutive unrelated subjects, including 309 type 2 diabetic patients and 505 non-diabetic individuals. Six single nucleotide polymorphisms (SNPs) in DDAH1, rs233112, rs1498373, rs1498374, rs587843, rs1403956, and rs1241321 were analyzed. Plasma ADMA levels were determined by high performance liquid chromatography. Insulin sensitivity was assessed by the homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

Among the 6 SNPs, only rs1241321 was significantly associated with a decreased risk of type 2 diabetes (AA vs GG+AG, OR = 0.64, 95% CI 0.47-0.86, p = 0.004). The association remained unchanged after adjustment for plasma ADMA level. The fasting plasma glucose and log HOMA-IR tended to be lower in subjects carrying the homozygous AA genotype of rs1241321 compared with the GG+AG genotypes. Over a median follow-up period of 28.2 months, there were 44 all-cause mortality and 50 major adverse cardiovascular events (MACE, including cardiovascular death, non-fatal myocardial infarction and stroke). Compared with the GG and AG genotypes, the AA genotype of rs1241321 was associated with reduced risk of MACE (HR = 0.31, 95% CI: 0.11-0.90, p = 0.03) and all-cause mortality (HR = 0.18, 95% CI: 0.04-0.80, p = 0.02) only in subgroup with type 2 diabetes. One common haplotype (GGCAGC) was found to be significantly associated with a decreased risk of type 2 diabetes (OR = 0.67, 95% CI = 0.46-0.98, p = 0.04).

CONCLUSIONS

Our results provide the first evidence that SNP rs1241321 in DDAH1 is associated with type 2 diabetes and its long-term outcome.

Endothelial progenitor cells in long-standing asymptomatic type 1 diabetic patients with or without diabetic nephropathy

A decrease in the number and dysfunction of endothelial progenitor cells (EPC) may increase the risk for progression of cardiovascular disease (CVD) in type 1 diabetic patients with diabetic nephropathy (DN). Our aim was to evaluate EPC numbers in asymptomatic CVD type 1 diabetic patients with or without DN and to study the effect of CVD and medication on EPC numbers.

METHODS

We examined EPC numbers in 37 type 1 diabetic patients with DN and 35 type 1 diabetic patients with long-standing normoalbuminuria. Patients were without symptoms of CVD and the prevalence of CVD was previously shown to be very low. EPC number was assessed in in vitro cultures by fluorescent staining of attached cells.

RESULTS

There was no difference in EPC numbers between patients with DN (mean ± SD 120 ± 49 cells/field) and normoalbuminuria (108 ± 41 cells/field; p = 0.25). Furthermore, EPC number was not associated with CVD (p > 0.05). Conventional risk factors were significantly higher in patients with DN and they received more CVD-preventive treatment. All patients receiving simvastatin or calcium-channel blockers had higher numbers of EPC compared to patients not treated with these drugs.

CONCLUSIONS

Asymptomatic patients with DN had EPC numbers similar to normoalbuminuric patients, which was related to aggressive CVD intervention therapy. This may have contributed to the low prevalence of CVD.

Biomarkers of peripheral arterial disease

Atherosclerotic arterial occlusive disease affecting the lower extremities is also known as peripheral artery disease (PAD). This disorder affects 8 to 12 million individuals in the U.S. and is increasingly prevalent in Europe and Asia. Unfortunately, most patients are not diagnosed and are not optimally treated. A blood test for PAD, if sufficiently sensitive and specific, would be expected to improve recognition and treatment of these individuals. Even a biomarker panel of moderate sensitivity and specificity for PAD could refine risk stratification to select individuals for diagnostic vascular examination. Alternatively, biomarkers for PAD may be useful in determining prognosis, the risk for progression, or the response to therapy. Finally, the discovery of biomarkers associated with PAD may provide novel insights into the pathophysiology of PAD and new therapeutic avenues to pursue. Biomarkers may be derived from studies of the genome, transcriptome, proteome, or metabolome. The focus of this review is on proteomic biomarkers associated with PAD.

Asymmetric dimethylarginine correlates with measures of disease severity, major adverse cardiovascular events and all-cause mortality in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is associated with major cardiovascular morbidity and mortality. Abnormalities in nitric oxide metabolism due to excess of the NO synthase inhibitor asymmetric dimethylarginine (ADMA) may be pathogenic in PAD. We explored the association between ADMA levels and markers of atherosclerosis, function, and prognosis. A total of 133 patients with symptomatic PAD were enrolled. Ankle-brachial index (ABI), walking time, vascular function measures (arterial compliance and flow-mediated vasodilatation) and plasma ADMA level were assessed for each patient at baseline. ADMA correlated inversely with ABI (r = -0.238, p = 0.003) and walking time (r = -0.255, p = 0.001), independent of other vascular risk factors. We followed up 125 (94%) of our 133 initial subjects with baseline measurements (mean 35 months). Subjects with ADMA levels in the highest quartile (> 0.84 mumol/l) showed a significantly greater occurrence of a major adverse cardiovascular event (MACE) compared to those with ADMA levels in the lower three quartiles (p = 0.001). Cox proportional-hazards regression analysis revealed that ADMA was a significant predictor of MACE, independent of other risk factors including age, sex, blood pressure, smoking history, diabetes and ABI (hazard ratio = 5.1, p < 0.001). Measures of vascular function, such as compliance, flow-mediated vasodilatation (FMVD) and blood pressure, as well as markers of PAD severity, including ABI and walking time, were not predictive. In conclusion, circulating levels of ADMA correlate independently with measures of disease severity and major adverse cardiovascular events. Agents that target this pathway may be useful for this patient population. Clinical Trial Registration - URL: http:// www.clinicaltrials.gov. Unique identifier: NCT00284076.

Role of endothelial progenitor cells in diabetes mellitus

Endothelial progenitor cells (EPCs) are bone marrow-derived cells involved in endothelial healing and angiogenesis. EPCs are considered an integrated component of the cardiovascular system, which promotes vascular health. Derangement of EPC biology in diabetes has been hailed as a novel concept in the pathogenesis of micro- and macro-vascular complications. Additionally, EPCs are considered to be disease biomarkers, as they provide an index of cardiovascular risk. The mechanisms leading to EPC dysfunction in diabetes may include defective mobilization from bone marrow to peripheral blood and reduced half-life. Hyperglycemia is considered the major determinant of microvascular complications, while other mechanisms concur to increase the risk of cardiovascular disease in diabetic patients. EPCs may represent a novel pathophysiological connection to understand development and progression of diabetic complications.

Regulation of peripheral blood flow in complex regional pain syndrome: clinical implication for symptomatic relief and pain management

BACKGROUND

During the chronic stage of Complex Regional Pain Syndrome (CRPS), impaired microcirculation is related to increased vasoconstriction, tissue hypoxia, and metabolic tissue acidosis in the affected limb. Several mechanisms may be responsible for the ischemia and pain in chronic cold CPRS.

DISCUSSION

The diminished blood flow may be caused by either sympathetic dysfunction, hypersensitivity to circulating catecholamines, or endothelial dysfunction. The pain may be of neuropathic, inflammatory, nociceptive, or functional nature, or of mixed origin.

SUMMARY

The origin of the pain should be the basis of the symptomatic therapy. Since the difference in temperature between both hands fluctuates over time in cold CRPS, when in doubt, the clinician should prioritize the patient's report of a persistent cold extremity over clinical tests that show no difference. Future research should focus on developing easily applied methods for clinical use to differentiate between central and peripheral blood flow regulation disorders in individual patients.

ADMA, cardiovascular disease and diabetes

The endogenous competitive nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is an emerging risk marker for future cardiovascular events. Elevated ADMA concentrations have been described in patients with an adverse cardiovascular risk profile. Recently, various studies investigated the independent role of ADMA as a cardiovascular risk predictor in several patient cohorts. In addition, ADMA might not only be a risk marker but also a causative factor for cardiovascular disease. This review summarizes the literature on the relationship between ADMA, cardiovascular disease and diabetes.

Tissue-specific downregulation of dimethylarginine dimethylaminohydrolase in hyperhomocysteinemia

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase, has been proposed to be a mediator of vascular dysfunction during hyperhomocysteinemia. Levels of ADMA are regulated by dimethylarginine dimethylaminohydrolase (DDAH). Using both in vitro and in vivo approaches, we tested the hypothesis that hyperhomocysteinemia causes downregulation of the two genes encoding DDAH (Ddah1 and Ddah2). In the MS-1 murine endothelial cell line, the addition of homocysteine decreased NO production but did not elevate ADMA or alter levels of Ddah1 or Ddah2 mRNA. Mice heterozygous for cystathionine beta-synthase (Cbs) and their wild-type littermates were fed either a control diet or a high-methionine/low-folate (HM/LF) diet to produce varying degrees of hyperhomocysteinemia. Maximal relaxation of the carotid artery to the endothelium-dependent dilator acetylcholine was decreased by approximately 50% in Cbs(+/-) mice fed the HM/LF diet compared with Cbs(+/+) mice fed the control diet (P < 0.001). Compared with control mice, hyperhomocysteinemic mice had lower levels of Ddah1 mRNA in the liver (P < 0.001) and lower levels of Ddah2 mRNA in the liver, lung, and kidney (P < 0.05). Downregulation of DDAH expression in hyperhomocysteinemic mice did not result in an increase in plasma ADMA, possibly due to a large decrease in hepatic methylation capacity (S-adenosylmethionine-to-S-adenosylhomocysteine ratio). Our findings demonstrate that hyperhomocysteinemia causes tissue-specific decreases in DDAH expression without altering plasma ADMA levels in mice with endothelial dysfunction.

Overexpression of Dimethylarginine Dimethylaminohydrolase Inhibits Asymmetric Dimethylarginine–Induced Endothelial Dysfunction in the Cerebral Circulation

Background and Purpose— Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS). An elevation of plasma ADMA levels is associated with cardiovascular disease. ADMA is hydrolyzed by dimethylarginine dimethylaminohydrolases (DDAHs). The goal of this study was to determine whether overexpression of human DDAH-1 in transgenic (DDAH-1–Tg) mice inhibits the vascular effects of ADMA.

Methods— Using nontransgenic (non-Tg) and DDAH-1–Tg mice, we compared responses of the carotid artery and aorta (in vitro) and of the cerebral arterioles (in vivo) in the absence or presence of ADMA. DDAH-1 expression and plasma levels of ADMA were also measured.

Results— Western blotting indicated that vascular expression of DDAH-1 was increased markedly in DDAH-1–Tg mice. Plasma levels of ADMA were reduced by ≈50% in DDAH-1–Tg mice compared with non-Tg mice (0.19±0.02 vs 0.37±0.04 μmol/L, P <0.05). Contraction of the aorta to nitro- l -arginine methyl ester (an inhibitor of NOS), an index of basal production of NO, was increased in DDAH-1–Tg mice compared with controls (50±4% vs 34±4%, P <0.05). Relaxation of the carotid artery to acetylcholine (an endothelium-dependent agonist) was enhanced in DDAH-1–Tg animals compared with control mice (relaxation of 74±6% vs 59±5%, respectively, in response to 10 μmol/L acetylcholine, P <0.05). ADMA (100 μmol/L) impaired the vascular response to acetylcholine in both non-Tg and DDAH-1–Tg mice, but the relative difference between the 2 strains remained. Responses to the endothelium-independent NO donor nitroprusside were similar in all groups. In vivo, ADMA (10 μmol/L) reduced responses of the cerebral arterioles to acetylcholine by ≈70% in non-Tg mice ( P <0.05), and this inhibitory effect was largely absent in DDAH-1–Tg mice.

Conclusions— These findings provide the first evidence that overexpression of DDAH-1 increases basal levels of vascular NO and protects against ADMA-induced endothelial dysfunction in the cerebral circulation.

Soluble RAGE in type 2 diabetes: association with oxidative stress

Advanced glycation end products (AGEs) contribute to diabetic vascular complications by engaging the AGE receptor (RAGE). A soluble RAGE form (sRAGE) acts as a decoy domain receptor, thus decreasing AGE cellular binding. A cross-sectional comparison of sRAGE, asymmetric dimethylarginine (ADMA) plasma levels (index of endothelial dysfunction), and urinary 8-iso-prostaglandin (PG)F(2alpha) (marker of oxidative stress) was performed between 86 diabetic patients and 43 controls. Plasma sRAGE levels were significantly lower and ADMA levels were significantly higher in diabetic patients as compared to controls (P<0.0001). HbA1c and urinary 8-iso-PGF(2alpha) were correlated inversely with sRAGE and directly with ADMA. On multivariate analysis HbA1c was independently related to sRAGE levels in diabetic patients. Twenty-four of 86 patients with newly diagnosed diabetes and 12 patients in poor metabolic control were reevaluated after treatment with a hypoglycemic agent or insulin, respectively. Improvement in metabolic control by oral agents or insulin resulted in a significant increase in sRAGE and decrease in ADMA levels (P<0.0001). Thus, poor glycemic control reduces sRAGE levels, in association with enhanced oxidative stress and endothelial dysfunction in diabetes. These abnormalities are susceptible to modulation by improvement in metabolic control.

Asymmetric dimethylarginine predicts cardiovascular events in patients with type 2 diabetes

OBJECTIVE

Circulating concentrations of an endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA), are elevated in patients with increased cardiovascular risk. We hypothesized that ADMA predicts cardiovascular events and enhances risk prediction independent of established risk markers in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

This prospective cohort study included 125 patients with type 2 diabetes. ADMA, L-arginine, high-sensitivity C-reactive protein (CRP), and routine clinical parameters were determined at baseline. First occurrence of cardiovascular events (myocardial infarction, percutaneous coronary intervention, coronary artery bypass graft, stroke, carotid revascularization, or all-cause mortality) was defined as a composite end point.

RESULTS

During a median follow-up of 21 (interquartile range 11-27) months, 84 events occurred in 48 patients. According to multivariate Cox regression analysis, patients with baseline ADMA or CRP in the highest tertile had a significantly increased hazard ratio for incident cardiovascular events compared with those with ADMA or CRP in tertile 1 (2.37 [95% CI 1.05-5.35], P = 0.038, and 3.63 [1.59-8.28], P = 0.002). Assessing the joint effect of ADMA and CRP revealed that patients with either ADMA or CRP or both in the highest tertile had increased hazard ratios for cardiovascular events compared with patients with neither ADMA nor CRP in the highest tertile before and after adjustment for possible confounders (hazard ratio 4.59 [95% CI 2.07-10.15], P < 0.001).

CONCLUSIONS

ADMA predicted cardiovascular events and enhanced the predictive role of CRP in patients with type 2 diabetes. ADMA therefore could improve cardiovascular risk assessment in patients with type 2 diabetes.

Uncomplicated type 1 diabetes is associated with increased asymmetric dimethylarginine concentrations

CONTEXT

Asymmetric dimethylarginine (ADMA) has recently emerged as an independent risk marker for cardiovascular disease, but studies investigating the ADMA levels in type 1 diabetes mellitus (DM) are scarce.

OBJECTIVE

We aimed to evaluate plasma ADMA, L-arginine concentrations, and L-arginine to ADMA ratio in uncomplicated type 1 diabetic patients and controls.

DESIGN AND SUBJECTS

Forty patients with type 1 DM who did not have clinical evidence of vascular complications and 35 healthy controls were included in the study.

RESULTS

Plasma ADMA concentrations were higher (2.6 +/- 1.9 vs. 1.7 +/- 0.7 micromol/liter, P < 0.01), and L-arginine levels were lower (79.3 +/- 22.6 vs. 89.6 +/- 19.4 micromol/liter, P < 0.05) in the diabetic group, compared with controls. The L-arginine to ADMA ratio was also lower in the diabetic group (38.7 +/- 17.1 vs. 62.0 +/- 27.9, P < 0.0001). In diabetic patients, logADMA correlated positively with body mass index (BMI) (P = 0.01), fasting blood glucose (P = 0.006), and low-density lipoprotein cholesterol (LDL-c) (P = 0.01) and negatively with high-density lipoprotein cholesterol (P = 0.03). L-arginine to ADMA ratio correlated negatively with BMI (P = 0.004), fasting blood glucose (P = 0.02), and LDL-c (P = 0.01) and positively with high-density lipoprotein cholesterol (P = 0.04). In controls, logADMA and L-arginine to ADMA ratio correlated with BMI and LDL-c (P < 0.05). In regression analysis, BMI predicted 15% variance of ADMA levels (P = 0.02).

CONCLUSIONS

We demonstrated that ADMA increases and L-arginine to ADMA ratio decreases, even before the development of vascular complications in type 1 DM.

Elevated concentrations of asymmetric dimethylarginine are associated with deterioration of glucose tolerance in women with previous gestational diabetes mellitus

OBJECTIVE

Women with previous gestational diabetes mellitus (GDM) have a high risk for development of type 2 diabetes mellitus. The endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) could be related to disorders of the glucose metabolism. To evaluate if ADMA predicts deterioration of glucose tolerance in women with previous GDM and to assess concentration changes we analysed ADMA in women with previous GDM after delivery and after a median follow-up of 2.75 years (interquartile range: 1.47-4.60).

DESIGN

Prospective cohort study. Subjects and methods. ADMA, symmetric dimethylarginine (SDMA) and L-arginine were determined in 77 women with previous GDM who underwent a 75-g oral glucose tolerance test 4 months after delivery and at follow-up.

RESULTS

Deterioration in glucose tolerance was observed in 36% of the women with ADMA above and 11% of those with ADMA below the median (0.56 micromol L(-1); P = 0.008, log-rank test). ADMA correlated significantly with mean arterial blood pressure and nonsignificantly with body mass index (P = 0.050) but not with insulin resistance, fasting glucose, lipids or glomerular filtration rate. The fully adjusted hazard ratio for a decline of glucose tolerance during follow-up was 3.94 (95% CI: 1.16-13.37; P = 0.028) for subjects with ADMA above the median. SDMA and L-arginine were not associated with changes in the glucose tolerance status. ADMA and L-arginine decreased significantly during follow-up.

CONCLUSIONS

High serum ADMA after delivery is associated with deterioration in glucose tolerance in women with previous GDM and declines in the following years.