Metformin treatment lowers asymmetric dimethylarginine concentrations in patients with type 2 diabetes

Effect of metformin on arginine and dimethylarginines in patients with advanced type 2 diabetes: A post hoc analysis of a randomized trial

AIM

To study the effect of metformin on plasma levels of arginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), indicators of the nitric oxide pathway.

MATERIALS AND METHODS

In this post hoc analysis of the HOME trial, we analysed plasma levels of arginine, ADMA and SDMA during the 4.3-year follow-up (comparing the effects of metformin versus placebo on top of insulin therapy). Statistical analysis was performed with a mixed model approach, in which simultaneously constant treatment effects were estimated, as well as time-dependent treatment effects.

RESULTS

We found that metformin compared with placebo did not affect ADMA or SDMA plasma levels but rapidly decreased arginine plasma levels and hence the arginine to ADMA ratio. The constant treatment effect on ADMA was 0.99 (95% CI 0.97, 1.00) relative to placebo and the time-dependent treatment effect was 1.00 (95% CI 1.00, 1.01). By contrast, the constant treatment effect on arginine was 0.86 (95% CI 0.84, 0.88), with only a minimal time-dependent change of 1.01 (95% CI 1.00, 1.01).

CONCLUSIONS

The potential benefits of metformin on endothelial function cannot be explained by a decrease in ADMA or by improved global arginine availability. The clinical significance of the decreased arginine plasma levels is not clear and can be harmful or beneficial, depending on the mechanism involved. However, a potential effect of metformin on the nitric oxide pathway is not restricted to the studied metabolites.

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

Endothelium, the gatekeeper of our blood vessels, is highly heterogeneous and a crucial physical barrier with the ability to produce vasoactive and protective mediators under physiological conditions. It regulates vascular tone, haemostasis, vascular inflammation, remodelling, and angiogenesis. Several cardio-, reno-, and cerebrovascular diseases begin with the dysfunction of endothelial cells, and more recently, COVID-19 was also associated with endothelial disease highlighting the need to monitor its function towards prevention and reduction of vascular dysfunction. Endothelial cells are an important therapeutic target in predictive, preventive, and personalised (3P) medicine with upmost importance in vascular diseases. The development of novel non-invasive techniques to access endothelial dysfunction for use in combination with existing clinical imaging modalities provides a feasible opportunity to reduce the burden of vascular disease.

This review summarises recent advances in the principles of endothelial function measurements. This article presents an overview of invasive and non-invasive techniques to determine vascular function and their major advantages and disadvantages. In addition, the article describes mechanisms underlying the regulation of vascular function and dysfunction and potential new biomarkers of endothelial damage. Recognising these biomarkers is fundamental towards a shift from reactive to 3P medicine in the vascular field. Identifying vascular dysfunction earlier with non-invasive or minimally invasive techniques adds value to predictive diagnostics and targeted prevention (primary, secondary, tertiary care). In addition, vascular dysfunction is a potential target for treatments tailored to the person.

Cholecalciferol and metformin protect against lipopolysaccharide-induced endothelial dysfunction and senescence by modulating sirtuin-1 and protein arginine methyltransferase-1

Endothelial cell activation through nuclear factor-kappa-B (NFkB) and mitogen-activated protein kinases leads to increased biosynthesis of pro-inflammatory mediators, cellular injury and vascular inflammation under lipopolysaccharide (LPS) exposure. Recent studies report that LPS up-regulated global methyltransferase activity. In this study, we observed that a combination treatment with metformin (MET) and cholecalciferol (VD) blocked the LPS-induced S-adenosylmethionine (SAM)-dependent methyltransferase (SDM) activity in Eahy926 cells. We found that LPS challenge (i) increased arginine methylation through up-regulated protein arginine methyltransferase-1 (PRMT1) mRNA, intracellular concentrations of asymmetric dimethylarginine (ADMA) and homocysteine (HCY); (ii) up-regulated cell senescence through mitigated sirtuin-1 (SIRT1) mRNA, nicotinamide adenine dinucleotide (NAD+) concentration, telomerase activity and total antioxidant capacity; and (iii) lead to endothelial dysfunction through compromised nitric oxide (NOx) production. However, these LPS-mediated cellular events in Eahy926 cells were restored by the synergistic effect of MET and VD. Taken together, this study identified that the dual compound effect inhibits LPS-induced protein arginine methylation, endothelial senescence and dysfunction through the components of epigenetic machinery, SIRT1 and PRMT1, which is a previously unidentified function of the test compounds. In silico results identified the presence of vitamin D response element (VDRE) sequence on PRMT1 suggesting that VDR could regulate PRMT1 gene expression. Further characterization of the cellular events associated with the dual compound challenge, using gene silencing approach or adenoviral constructs for SIRT1 and/or PRMT1 under inflammatory stress, could identify therapeutic strategies to address the endothelial consequences in vascular inflammation-mediated atherosclerosis.

Plasma levels of Asymmetric Di Methyl Arginine and endothelial dysfunction in diabetic subjects with neuropathic foot ulcer

OBJECTIVE

Asymmetric dimethyl arginine (ADMA) is an amino acid that acts as an endogenous competitive inhibitor of Nitric oxide synthase, leading to endothelial dysfunction (ED). The aim of this study was to evaluate the relationship between plasma ADMA (p-ADMA) level and ED in diabetic subjects with neuropathic foot ulcer (NFU), and the possible predictors of p-ADMA level.

MATERIALS AND METHODS

80 diabetic subjects of matched age, sex and BMI were included; 40 with NFU (G1), 20 with peripheral nerve dysfunction (PND) (G2) and 20 without PND (G3), plus 20 matched healthy subjects (G4). Flow-mediated-dilatation (FMD) of brachial artery and Carotid-intima-media-thickness (CIMT) were measured to evaluate ED and subclinical atherosclerosis, respectively.

RESULTS

G1&2 had a significantly lower FMD than G3&4 [-5.09 (-22.5 to 22.92), 4.67 (-15 to 23.91) vs. 15.74 (8.33-36.59) and 20.1 (10.0-46.15)%, respectively] (p < 0.001), and higher CIMT [0.9 (0.6-1.5), 0.9 (0.6-1.3) vs. 0.6 (0.5-0.8) and 0.7 (0.5-0.9) cm, respectively] (p < 0.001, r = 0.237, p = 0.034, r = 0.330, p = 0.003, respectively), with no significant correlation with FMD (r = -0.176, p = 0.118). FMD was inversely and strongly related to CIMT (r = -0.520, p < 0.001). p-ADMA levels were significantly higher in uncontrolled hypertensive patients in comparison to controlled and normotensive subjects [717 (286-3611) vs. 648 (335-874) and 686 (526-857) ng/L, respectively] (p = 0.026). Metformin users and hypertensive subjects on ACEIs or ARBs had the lowest p-ADMA levels than the non-users (p < 0.001, p = 0.007, respectively).

CONCLUSION

The remarkable ED in diabetic subjects with NFU is unlikely to be due to alteration in p-ADMA. Further studies are needed in order to conclude a causal association between p-ADMA and ED in this group of patients.

A Cross-Talk between the Erythrocyte L-Arginine/ADMA/Nitric Oxide Metabolic Pathway and the Endothelial Function in Subjects with Type 2 Diabetes Mellitus

(1) Background: Type-2-diabetes-mellitus (DM) is one the most important cardiovascular-risk-factors. Among many molecules regulating vascular tone, nitric oxide appears to be the most pivotal. Although micro- and macrovascular-abnormalities are extensively studied, the alterations in the nitric-oxide-metabolic-pathway require further investigations. Additionally, the role of erythrocytes in the vascular tone regulation has not been extensively explored. The aim of this study was to evaluate the endothelial-function and the nitric-oxide-metabolic-pathway in erythrocytes and plasma of diabetic individuals. (2) Methods: A total of 80 subjects were enrolled in this cross-sectional study, including 35 patients with DM and 45 healthy individuals. The endothelial-function was evaluated in response to different stimuli. (3) Results: In the DM group, decreased Arginine and citrulline concentrations in the plasma compartment with reduced Arginine/ADMA and ADMA/DMA-ratios were observed. Preserved nitric-oxide-metabolism in erythrocytes with reduced citrulline level and significantly higher NO-bioavailability were noted. Significant endothelial dysfunction in DM individuals was proved in response to the heat-stimulus. (4) Conclusions: DM patients at an early stage of disease show significant differences in the nitric-oxide-metabolic-pathway, which are more pronounced in the plasma compartment. Erythrocytes constitute a buffer with a higher nitric-oxide-bioavailability, less affected by the DM-related deviations. Patients at an early-stage of DM reveal endothelial-dysfunction, which could be diagnosed earlier using the laser-Doppler-flowmetry.

Review - Nutraceuticals Can Target Asthmatic Bronchoconstriction: NADPH Oxidase-Dependent Oxidative Stress, RhoA and Calcium Dynamics

Activation of various isoforms of NADPH oxidase contributes to the pathogenesis of asthma at multiple levels: promoting hypercontractility, hypertrophy, and proliferation of airway smooth muscle; enabling lung influx of eosinophils via VCAM-1; and mediating allergen-induced mast cell activation. Free bilirubin, which functions physiologically within cells as a feedback inhibitor of NADPH oxidase complexes, has been shown to have a favorable impact on each of these phases of asthma pathogenesis. The spirulina chromophore phycocyanobilin (PhyCB), a homolog of bilirubin’s precursor biliverdin, can mimic the inhibitory impact of biliverdin/bilirubin on NADPH oxidase activity, and spirulina’s versatile and profound anti-inflammatory activity in rodent studies suggests that PhyCB may have potential as a clinical inhibitor of NADPH oxidase. Hence, spirulina or PhyCB-enriched spirulina extracts merit clinical evaluation in asthma. Promoting biosynthesis of glutathione and increasing the expression and activity of various antioxidant enzymes – as by supplementing with N-acetylcysteine, Phase 2 inducers (eg, lipoic acid), selenium, and zinc – may also blunt the contribution of oxidative stress to asthma pathogenesis. Nitric oxide (NO) and hydrogen sulfide (H₂S) work in various ways to oppose pathogenic mechanisms in asthma; supplemental citrulline and high-dose folate may aid NO synthesis, high-dose biotin may mimic and possibly potentiate NO’s activating impact on soluble guanylate cyclase, and NAC and taurine may boost H₂S synthesis. The amino acid glycine has a hyperpolarizing effect on airway smooth muscle that is bronchodilatory. Insuring optimal intracellular levels of magnesium may modestly blunt the stimulatory impact of intracellular free calcium on bronchoconstriction. Nutraceutical regimens or functional foods incorporating at least several of these agents may have utility as nutraceutical adjuvants to standard clinical management of asthma.

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.

Metabolite Profiles of Incident Diabetes and Heterogeneity of Treatment Effect in the Diabetes Prevention Program

Novel biomarkers of type 2 diabetes (T2D) and response to preventative treatment in individuals with similar clinical risk may highlight metabolic pathways that are important in disease development. We profiled 331 metabolites in 2,015 baseline plasma samples from the Diabetes Prevention Program (DPP). Cox models were used to determine associations between metabolites and incident T2D, as well as whether associations differed by treatment group (i.e., lifestyle [ILS], metformin [MET], or placebo [PLA]), over an average of 3.2 years of follow-up. We found 69 metabolites associated with incident T2D regardless of treatment randomization. In particular, cytosine was novel and associated with the lowest risk. In an exploratory analysis, 35 baseline metabolite associations with incident T2D differed across the treatment groups. Stratification by baseline levels of several of these metabolites, including specific phospholipids and AMP, modified the effect that ILS or MET had on diabetes development. Our findings highlight novel markers of diabetes risk and preventative treatment effect in individuals who are clinically at high risk and motivate further studies to validate these interactions.

Asymmetric (ADMA) and Symmetric (SDMA) Dimethylarginines in Chronic Kidney Disease: A Clinical Approach

Asymmetric dimethylarginine (ADMA) and its enantiomer, Symmetric dimethylarginine (SDMA), are naturally occurring amino acids that were first isolated and characterized in human urine in 1970. ADMA is the most potent endogenous inhibitor of nitric oxide synthase (NOS), with higher levels in patients with end-stage renal disease (ESRD). ADMA has shown to be a significant predictor of cardiovascular outcome and mortality among dialysis patients. On the other hand, although initially SDMA was thought to be an innocuous molecule, we now know that it is an outstanding marker of renal function both in human and in animal models, with ESRD patients on dialysis showing the highest SDMA levels. Today, we know that ADMA and SDMA are not only uremic toxins but also independent risk markers for mortality and cardiovascular disease (CVD). In this review, we summarize the role of both ADMA and SDMA in chronic kidney disease along with other cardiovascular risk factors.

Effects of single and combined metformin and L-citrulline supplementation on L-arginine-related pathways in Becker muscular dystrophy patients: possible biochemical and clinical implications

The L-arginine/nitric oxide synthase (NOS) pathway is considered to be altered in muscular dystrophy such as Becker muscular dystrophy (BMD). We investigated two pharmacological options aimed to increase nitric oxide (NO) synthesis in 20 male BMD patients (age range 21-44 years): (1) supplementation with L-citrulline (3 × 5 g/d), the precursor of L-arginine which is the substrate of neuronal NO synthase (nNOS); and (2) treatment with the antidiabetic drug metformin (3 × 500 mg/d) which activates nNOS in human skeletal muscle. We also investigated the combined use of L-citrulline (3 × 5 g/d) and metformin (3 × 500 mg/d). Before and after treatment, we measured in serum and urine samples the concentration of amino acids and metabolites of L-arginine-related pathways and the oxidative stress biomarker malondialdehyde (MDA). Compared to healthy subjects, BMD patients have altered NOS, arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) pathways. Metformin treatment resulted in concentration decrease of arginine and MDA in serum, and of homoarginine (hArg) and guanidinoacetate (GAA) in serum and urine. L-Citrulline supplementation resulted in considerable increase of the concentrations of amino acids and creatinine in the serum, and in their urinary excretion rates. Combined use of metformin and L-citrulline attenuated the effects obtained from their single administrations. Metformin, L-citrulline or their combination did not alter serum nitrite and nitrate concentrations and their urinary excretion rates. In conclusion, metformin or L-citrulline supplementation to BMD patients results in remarkable antidromic changes of the AGAT and GAMT pathways. In combination, metformin and L-citrulline at the doses used in the present study seem to abolish the biochemical effects of the single drugs in slight favor of L-citrulline.

Asymmetric Dimethyl Arginine as a Biomarker of Atherosclerosis in Rheumatoid Arthritis

Cardiovascular disease is the main cause of morbidity and mortality in rheumatoid arthritis (RA). Despite the advent on new drugs targeting the articular manifestations, the burden of cardiovascular disease is still an unmet need in the management of RA. The pathophysiology of accelerated atherosclerosis associated to RA is not yet fully understood, and reliable and specific markers of early cardiovascular involvement are still lacking. Asymmetric dimethylarginine is gaining attention for its implication in the pathogenesis of endothelial dysfunction and as biomarkers of subclinical atherosclerosis. Moreover, the metabolic pathway of methylarginines offers possible targets for therapeutic interventions to decrease the cardiovascular risk. The purpose of this review is to describe the main causes of increased methylarginine levels in RA, their implication in accelerated atherosclerosis, the possible role as biomarkers of cardiovascular risk, and finally the available data on current pharmacological treatment.

Polycystic ovarian syndrome-associated cardiovascular complications: An overview of the association between the biochemical markers and potential strategies for their prevention and elimination

Polycystic ovarian syndrome (PCOS) is associated with multiple cardiovascular risk factors (CVRF) including endothelial dysfunction (ED) and presence of metabolic syndrome (MS). The probable reason suggested for elevated CVRF in PCOS is oxidative stress (OS), which is an integral factor in cardiometabolic complications (CMC) seen in PCOS women. The interrelated mechanisms by which CVRF instigate clinical manifestation plays a crucial role in identification of a strategy to treat different comorbidities in PCOS. The existing treatment for PCOS mostly focuses on management of individual disorders, however, therapeutic strategies or novel targets to address cardiovascular complications in PCOS deserve extensive analysis.

Vitamin D and methylarginines in chronic kidney disease (CKD)

Background

Vitamin D associates with the plasma concentration of the endogenous inhibitor of the nitric oxide system asymmetric dimethyl arginine (ADMA) and cross-sectional studies in CKD patients treated with the vitamin D receptor activator paricalcitol show that plasma ADMA is substantially less than in those not receiving this drug.

Methods

In the frame of a randomized, double-blind, placebo controlled trial, the Paracalcitol and ENdothelial fuNction in chronic kidneY disease (PENNY), we investigated whether vitamin D receptor activation by paricalcitol (2 μg/day x 12 weeks) affects the plasma concentration of ADMA and symmetric dimethyl arginine (SDMA) in 88 patients with stage 3 to 4 CKD.

Results

Paricalcitol produced the expected small rise in serum calcium and phosphate and a marked PTH suppression. However, ADMA [Paricalcitol: baseline 0.75 μMol/L (95%CI: 0.70–0.81), 12 week 0.72 μMol/L (95%CI: 0.66–0.78); Placebo: baseline 0.75 μMol/L (95%CI: 0.70–0.90) 12 weeks 0.70 μMol/L (95%CI: 0.66–0.74)] and SDMA [Paricalcitol: baseline 0.91 μMol/L (95%CI: 0.82–1.00), 12 week 0.94 μMol/L (95%CI: 0.82–0.1.06); Placebo: baseline 0.91 μMol/L (95%CI: 0.82–1.06) 12 weeks 0.99 μMol/L (95%CI: 0.88–1.10)] remained unchanged during the trial and 2 weeks after stopping these treatments.

Conclusions

Paricalcitol does not modify plasma ADMA and SDMA in patients with stage 3–4 CKD. The apparent beneficial effects of paricalcitol on ADMA registered in cross-sectional studies is likely attributable to confounding by indication rather than to a true effect of this drug on ADMA metabolism.

Analysis of risk factors in patients with leukoaraiosis

To investigate the risk factors for leukoaraiosis (LA) and the correlation between risk factors and LA.The study comprised 92 patients with diagnoses of LA (LA group) and 56 non-LA individuals (control group). Data were collected for the following: age, gender, fasting blood glucose, total cholesterol, triglyceride, high- and low-density lipoprotein cholesterol, uric acid, creatinine, and histories of smoking, hypertension, and diabetes. Levels of serum asymmetric dimethylarginine (ADMA) were detected by enzyme-linked immunosorbent assay.Univariate analysis showed statistical significance between the 2 groups in age, histories of hypertension and smoking, uric acid, creatinine, and levels of serum ADMA (P < 0.05). Binary logistic analysis showed that age (P < 0.0001), hypertension (P = 0.0101), and serum ADMA (P = 0.0206) were related to LA. Pearson correlation analysis showed that levels of serum ADMA correlated with uric acid (r = 0.184, P = 0.025) and creatinine (r = 0.169, P = 0.04).Age, hypertension, and levels of serum ADMA were independent risk factors for LA. Serum ADMA levels may be related to uric acid and creatinine.

ADMA and oxidative stress may relate to the progression of renal disease: rationale and design of the VIVALDI study

The renin angiotensin system has been shown to be involved in the patho genesis of vascular and renal sequelae of diabetes mellitus. In type 2 diabetes mel litus, angiotensin receptor blockers have been shown to exert clinical benefit by reducing the progression of diabetic nephropathy. They also improve endothelium- mediated vascular function. The latter effect is partly due to the reduction of angiotensin II-associated oxidative stress. Moreover, small clinical studies have shown that treatment with angiotensin receptor blockers also reduces the circulating levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthase.

In the VIVALDI trial, the ability of the angiotensin receptor blocker telmisartan to reduce the progression of diabetic nephropathy (associated with proteinuria) in com parison with valsartan in more than 800 patients with type 2 diabetes during 1 year of treatment is being studied. In order to gain more detailed insight into the poten tial pathomechanisms associated with this effect, further end-points have been defined. Among these are the circulating levels of ADMA and the urinary excretion rate of 8-iso-prostaglandin F2α (8-iso-PGF 2α). The former is an endogenous inhibitor of NO-mediated vascular function(s) and a prospectively determined marker of major cardiovascular events and mortality; the latter is a lipid peroxidation product resulting from the nonenzymatic peroxidation of arachidonic acid, which exerts detrimental vascular effects similar to those of thromboxane A2. Urinary 8-iso-PGF 2α has been shown in clinical studies to be an independent marker of cardiovascular disease.

Highlighting the effects of telmisartan on ADMA and 8-iso-PGF levels in such a large cohort of diabetic patients will enhance our understanding of the roles of dys functional NO metabolism and redox mechanisms in the pathogenesis of end-organ damage and its prevention by pharmacotherapy with angiotensin receptor blockers.

Pharmacotherapies and their influence on asymmetric dimethylargine (ADMA)

Elevated plasma concentrations of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) are found in various clinical settings, including renal failure, coronary heart disease, hypertension, diabetes and pre eclampsia. In healthy people acute infusion of ADMA promotes vascular dysfunc tion, and in mice chronic infusion of ADMA promotes progression of atherosclerosis. Thus, ADMA may not only be a marker but also an active player in cardiovascular disease, which makes it a potential target for therapeutic interventions. This review provides a summary and critical discussion of the presently available data concern ing the effects on plasma ADMA levels of cardiovascular drugs, hypoglycemic agents, hormone replacement therapy, antioxidants, and vitamin supplementation. We assess the evidence that the beneficial effects of drug therapies on vascular func tion can be attributed to modification of ADMA levels. To develop more specific ADMA-lowering therapies, mechanisms leading to elevation of plasma ADMA con centrations in cardiovascular disease need to be better understood. ADMA is formed endogenously by degradation of proteins containing arginine residues that have been methylated by S-adenosylmethionine-dependent methyltransferases (PRMTs). There are two major routes of elimination: renal excretion and enzymatic degrada tion by the dimethylarginine dimethylaminohydrolases (DDAH-1 and -2). Oxidative stress causing upregulation of PRMT expression and/or attenuation of DDAH activity has been suggested as a mechanism and possible drug target in clinical conditions associated with elevation of ADMA. As impairment of DDAH activity or capacity is associated with substantial increases in plasma ADMA concentrations, DDAH is likely to emerge as a prime target for specific therapeutic interventions.

Insulin resistance: potential role of the endogenous nitric oxide synthase inhibitor ADMA

The insulin resistance syndrome (IRS) is considered to be a new target of risk-reduction therapy. The IRS is a cluster of closely associated and interdependent abnormalities and clinical outcomes that occur more commonly in insulin-resistant/hyperinsulinemic individuals. This syndrome predisposes individuals to type 2 diabetes, cardiovascular diseases, essential hypertension, certain forms of cancer, polycystic ovary syndrome, nonalcoholic fatty liver disease, and sleep apnea. In patients at high risk for cardiovascular diseases, endothelial dysfunction is observed in morphologically intact vessels even before the onset of clinically manifest vascular disease. Indeed, there are several lines of evidence that indicate that endothelial function is compromised in situations where there is reduced sensitivity to endogenous insulin. It is well established that a decreased bioavailability of nitric oxide (NO) contributes to endothelial dysfunction. Furthermore, NO may modulate insulin sensitivity. Activation of NO synthase (NOS) augments blood flow to insulin-sensitive tissues (i.e. skeletal muscle, liver, adipose tissue), and its activity is impaired in insulin resistance. Inhibition of NOS reduces the microvascular delivery of nutrients and blunts insulin-stimulated glucose uptake in skeletal muscle. Furthermore, induction of hypertension by administration of the NOS inhibitor NG-monomethyl-L-arginine is also associated with insulin resistance in rats. Increased levels of asymmetric dimethylarginine (ADMA) are associated with endothelial vasodilator dysfunction and increased risk of cardiovascular diseases. An intriguing relationship exists between insulin resistance and ADMA. Plasma levels of ADMA are positively correlated with insulin resistance in nondiabetic, normotensive people. New basic research insights that provide possible mechanisms underlying the development of insulin resistance in the setting of impaired NO bioavailability will be discussed.

Review: 50 years later: is metformin a vascular drug with antidiabetic properties?

Since the clinical demonstration of a protective effect of metformin against chronic diabetic angiopathy in the United Kingdom Prospective Diabetes Study, many data have accumulated which confirm such effects in acute or chronic situations as diverse as ischaemia, non-diabetic insulin resistant states and diabetes. Recent years have provided several mechanisms of action and further documented some unique properties of this compound such as improvements in microcirculatory flow, glycation and oxidative stress. In particular, the latter effect could be shown in mitochondria, i.e. the most important sources of reactive oxygen species in diabetes. Specific, non-toxic actions of metformin at the level of the mitochondrial respiratory chain also prevent apoptosis, another mechanism to explain the long-term protection afforded by metformin. Noteworthy, most of these effects of metformin are unrelated to drug dosage and largely independent of its antihyperglycaemic effect (intrinsic properties). These new data open potential avenues for larger therapeutic utilisations of this drug, 50 years after its launch for the treatment of type 2 diabetes.

Asymmetric dimethylarginine (ADMA) elevation and arginase up-regulation contribute to endothelial dysfunction related to insulin resistance in rats and morbidly obese humans

KEY POINTS

The presence of insulin resistance (IR) is determinant for endothelial dysfunction associated with obesity. Although recent studies have implicated the involvement of mitochondrial superoxide and inflammation in the defective nitric oxide (NO)-mediated responses and subsequent endothelial dysfunction in IR, other mechanisms could compromise this pathway. In the present study, we assessed the role of asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of endothelium-dependent vasodilatation in human morbid obesity and in a non-obese rat model of IR. We show that both increased ADMA and up-regulated arginase are determinant factors in the alteration of the l-arginine/NO pathway associated with IR in both models and also that acute treatment of arteries with arginase inhibitor or with l-arginine significantly alleviate endothelial dysfunction. These results help to expand our knowledge regarding the mechanisms of endothelial dysfunction that are related to obesity and IR and establish potential therapeutic targets for intervention.

ABSTRACT

Insulin resistance (IR) is determinant for endothelial dysfunction in human obesity. Although we have previously reported the involvement of mitochondrial superoxide and inflammation, other mechanisms could compromise NO-mediated responses in IR. We evaluated the role of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) and arginase with respect to IR-induced impairment of l-arginine/NO-mediated vasodilatation in human morbid obesity and in a non-obese rat model of IR. Bradykinin-induced vasodilatation was evaluated in microarteries derived from insulin-resistant morbidly obese (IR-MO) and non-insulin-resistant MO (NIR-MO) subjects. Defective endothelial vasodilatation in IR-MO was improved by l-arginine supplementation. Increased levels of ADMA were detected in serum and adipose tissue from IR-MO. Serum ADMA positively correlated with IR score and negatively with pD2 for bradykinin. Gene expression determination by RT-PCR revealed not only the decreased expression of ADMA degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH)1/2 in IR-MO microarteries, but also increased expression of arginase-2. Arginase inhibition improved endothelial vasodilatation in IR-MO. Analysis of endothelial vasodilatation in a non-obese IR model (fructose-fed rat) confirmed an elevation of circulating and aortic ADMA concentrations, as well as reduced DDAH aortic content and increased aortic arginase activity in IR. Improvement of endothelial vasodilatation in IR rats by l-arginine supplementation and arginase inhibition provided functional corroboration. These results demonstrate that increased ADMA and up-regulated arginase contribute to endothelial dysfunction as determined by the presence of IR in human obesity, most probably by compromising arginine availability. The results provide novel insights regarding the mechanisms of endothelial dysfunction related to obesity and IR and establish potential therapeutic targets for intervention.

Serum apelin and ADMA levels in type 2 diabetics with and without vascular complications

AIMS

Type 2 diabetes mellitus (T2DM) is a metabolic and chronic disease which is characterized by hyperglycemia, and that is the major causes of various micro and macrovascular complications. Asymmetrical dimethylarginine (ADMA), formed by the hydrolysis of proteins containing methylated arginine residues, is an endogenous inhibitor of nitric oxide synthase (NOS), which oxidize l-arginine to citruline and nitric oxide (NO), related to hyperinsulinaemia and hyperlipidaemia. Apelin is a recently discovered peptide, present in a number of tissues and play role in insulin sensitivity improvement. In this study, our aim was to determine the levels of apelin and ADMA with glycated haemoglobin (HbA1c) in type 2 diabetic patients with or without vascular complications.

METHODS

This study included (a total of) 59 diabetic patients. Of the patients, 30 were diabetic with complications, and 29 without complications. In serum samples obtained from the patients, serum ADMA and apelin levels were measured with Enzyme Linked Immunosorbent Assay (ELISA) method.

RESULTS

Our study totally enrolled 59 patients in two groups. No significant differences were found in sex, age, HbA1c and glucose levels among groups. Apelin and ADMA levels of group with complications were lower than those of group without complications, but no statistically significant difference of apelin and ADMA levels (p>0.05).

CONCLUSION

The results of this study have been showed no statistically significant relationship present between ADMA-apelin levels and complications of T2DM. Further studies involving larger patients populations and healthy controls should be done to clarify the pathogenetic significance of apelin and ADMA in diabetic vascular complications.

Effects of metformin on metabolite profiles and LDL cholesterol in patients with type 2 diabetes

OBJECTIVE

Metformin is used as a first-line oral treatment for type 2 diabetes (T2D). However, the underlying mechanism is not fully understood. Here, we aimed to comprehensively investigate the pleiotropic effects of metformin.

RESEARCH DESIGN AND METHODS

We analyzed both metabolomic and genomic data of the population-based KORA cohort. To evaluate the effect of metformin treatment on metabolite concentrations, we quantified 131 metabolites in fasting serum samples and used multivariable linear regression models in three independent cross-sectional studies (n = 151 patients with T2D treated with metformin [mt-T2D]). Additionally, we used linear mixed-effect models to study the longitudinal KORA samples (n = 912) and performed mediation analyses to investigate the effects of metformin intake on blood lipid profiles. We combined genotyping data with the identified metformin-associated metabolites in KORA individuals (n = 1,809) and explored the underlying pathways.

RESULTS

We found significantly lower (P < 5.0E-06) concentrations of three metabolites (acyl-alkyl phosphatidylcholines [PCs]) when comparing mt-T2D with four control groups who were not using glucose-lowering oral medication. These findings were controlled for conventional risk factors of T2D and replicated in two independent studies. Furthermore, we observed that the levels of these metabolites decreased significantly in patients after they started metformin treatment during 7 years' follow-up. The reduction of these metabolites was also associated with a lowered blood level of LDL cholesterol (LDL-C). Variations of these three metabolites were significantly associated with 17 genes (including FADS1 and FADS2) and controlled by AMPK, a metformin target.

CONCLUSIONS

Our results indicate that metformin intake activates AMPK and consequently suppresses FADS, which leads to reduced levels of the three acyl-alkyl PCs and LDL-C. Our findings suggest potential beneficial effects of metformin in the prevention of cardiovascular disease.

Asymmetric dimethylarginine as a mediator of vascular dysfunction in cirrhosis

Cirrhosis is associated with marked abnormalities in the circulatory function that involve a reduction in systemic vascular resistance. An important cause of this vasodilatation is the increased production or activity of nitric oxide (NO) in the splanchnic circulation. During portal hypertension and cirrhosis an increased endothelial NO synthase (eNOS) activity is demonstrated in splanchnic vessels. In contrast, the activity of eNOS in the cirrhotic liver is decreased, which suggests a different regulation of eNOS in the liver and in the splanchnic vessels. Asymmetric dimethylarginine (ADMA) is an endogenous NO inhibitor and higher plasma levels of ADMA are related to increased cardiovascular risk in both the general population and among patients with cirrhosis. It has been demonstrated that the liver is a key player in the metabolism of ADMA. This observation was further supported by investigations in human patients, showing a close correlation between ADMA plasma levels and the degree of hepatic dysfunction. ADMA is degraded to citrulline and dimethylamine by dimethylarginine dimethylaminohydrolases (DDAHs). DDAHs are expressed as type 1 and 2 isoforms and are widely distributed in various organs and tissues, including the liver. In this review, we discuss experimental and clinical data that document the effects of dimethylarginines on vascular function in cirrhosis. Our increasing understanding of the routes of synthesis and metabolism of methylarginines is beginning to provide insights into novel mechanisms of liver disease and allowing us to identify potential therapeutic opportunities.

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 is negatively correlated with hyperglycemia in children

Asymmetric dimethylarginine (ADMA) is a nonselective nitric oxide (NO) synthase inhibitor associated with cardiovascular and metabolic disorders. In several prospective and cross-sectional studies, ADMA has evolved as a marker of cardiovascular risk. However, there is limited information on this serum marker in young people, particularly in those with obesity, type 1 diabetes (DM1) and type 2 diabetes (DM2). We investigated ADMA concentrations in children and adolescents with hyperglycemia as compared with healthy age- and sex-matched individuals. The subjects were 21 simple obesity [male 13, female 8; aged 11.7±4.3 years], 18 with DM1 [male 4, female 14; aged 12.9±4.2 years, duration of disease 3.4±2.1 years], 10 with DM2 [male 5, female 5; aged 13.9±3.4 years, duration of disease 2.8±1.4 years] and 21 controls [male 12, female 9; aged 11.1±2.7 years]. ADMA levels were analyzed in a cross-sectional study. Concentrations of serum ADMA were determined using an enzyme-linked immunosorbent assay. Circulating levels of ADMA were significantly lower in subjects with DM1, DM2 or obesity. In all subjects, ADMA levels were inversely correlated with glycated hemoglobin A1c concentrations (r=-0.401, p=0.0003) and serum glucose levels (r=-0.341, p=0.0023). Low circulating ADMA levels are directly associated with glucose levels, suggesting that ADMA production is suppressed in childhood in order to compensate and protect vasculopathy due to hyperglycemia.

Metformin reduces asymmetric dimethylarginine and prevents hypertension in spontaneously hypertensive rats

Elevated asymmetric dimethylarginine (ADMA) levels and nitric oxide (NO) deficiency are associated with the development of hypertension. Metformin, an antidiabetic agent, is a structural analog of ADMA. We examined whether metformin can prevent the development of hypertension in spontaneously hypertensive rats (SHRs) by restoration of ADMA-NO balance. SHRs and control normotensive Wistar-Kyoto (WKY) rats were assigned to 4 groups (N = 8 for each group): untreated SHRs and WKY rats, metformin-treated SHRs and WKY rats. Metformin-treated rats received metformin 500 mg/kg per day via oral gavage for 8 weeks. All rats were sacrificed at the age of 12 weeks. We found an increase in the blood pressure of SHRs was prevented by metformin. ADMA levels in the plasma and lung were elevated in SHRs, which metformin prevented. Lung dimethylarginine dimethylaminohydrolase (DDAH, ADMA-metabolizing enzyme) activity was lower in SHRs than WKY rats. Next, metformin had no effect on protein arginine methyltransferase 1 (ADMA-synthesizing enzyme), DDAH-1, DDAH-2, NO synthase enzymes, and DDAH activity in the kidney. Moreover, metformin increased the levels of NO in kidney. Conclusively, the observed antihypertensive effect of metformin in SHRs is because of the restoration of the ADMA-NO pathway. Our findings support the consideration of metformin as an antihypertensive agent for diabetic patients with prehypertension.

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.

Clinical evaluation of extracellular ADMA concentrations in human blood and adipose tissue

Circulating asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, has been proposed as a biomarker for clinical outcome. Dimethylarginine dimethylaminohydrolase (DDAH) is the main enzyme responsible for ADMA metabolism and elimination. Adipose tissue ADMA concentrations and DDAH activity and their role in diabetes and obesity have not yet been investigated. In this study, we evaluated clinical microdialysis in combination with a sensitive analytical method (GC-MS/MS) to measure ADMA concentrations in extracellular fluid. Adipose tissue ADMA concentrations were assessed before and during an oral glucose tolerance test in lean healthy subjects and subjects with diabetes (n = 4 each), and in morbidly obese subjects before and after weight loss of 30 kg (n = 7). DDAH activity was determined in subcutaneous and visceral adipose tissue obtained during laparoscopic surgery (n = 5 paired samples). Mean interstitial ADMA concentrations did not differ between study populations (healthy 0.17 ± 0.03 μM; diabetic 0.21 ± 0.03 μM; morbidly obese 0.16 ± 0.01 and 0.17 ± 0.01 μM before and after weight loss, respectively). We did not observe any response of interstitial ADMA concentrations to the oral glucose challenge. Adipose tissue DDAH activity was negligible compared to liver tissue. Thus, adipose tissue ADMA plays a minor role in NO-dependent regulation of adipose tissue blood flow and metabolism.

Asymmetric dimethylarginine attenuates serum starvation-induced apoptosis via suppression of the Fas (APO-1/CD95)/JNK (SAPK) pathway

Asymmetric dimethylarginine (ADMA) is synthesized by protein arginine methyltransferases during methylation of protein arginine residues and released into blood upon proteolysis. Higher concentrations of ADMA in blood have been observed in patients with metabolic diseases and certain cancers. However, the role of ADMA in colon cancer has not been well investigated. ADMA serum levels in human patients diagnosed with colon cancer were found to be higher than those present in healthy subjects. ADMA treatment of LoVo cells, a human colon adenocarcinoma cell line, attenuated serum starvation-induced apoptosis and suppressed the activation of the Fas (APO-1/CD95)/JNK (SAPK) (c-Jun N terminal protein kinase/stress-activated protein kinase)pathway. ADMA also suppressed the activation of JNK triggered by death receptor ligand anti-Fas mAb and exogenous C₂-ceramide. Moreover, we demonstrated that ADMA pretreatment protected LoVo cells from doxorubicin hydrochloride-induced cell death and activation of the Fas/JNK pathway. In summary, our results suggest that the elevated ADMA in colon cancer patients may contribute to the blocking of apoptosis of cancer cells in response to stress and chemotherapy.

Impact of ADMA, endothelial progenitor cells and traditional cardiovascular risk factors on pulse wave velocity among prediabetic individuals

Background

Central arterial stiffness represents a well-established predictor of cardiovascular disease. Decreased circulating endothelial progenitor cells (EPCs), increased asymmetric dimethyl-arginine (ADMA) levels, traditional cardiovascular risk factors and insulin resistance have all been associated with increased arterial stiffness. The correlations of novel and traditional cardiovascular risk factors with central arterial stiffness in prediabetic individuals were investigated in the present study.

Methods

The study population consisted of 53 prediabetic individuals. Individuals were divided into groups of isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT) and combined IGT-IFG. Age, sex, family history of diabetes, smoking history, body mass index (BMI), waist to hip ratio (WHR), waist circumference (WC), blood pressure, lipid profile, levels of high sensitive C-reactive protein (hsCRP), glomerular filtration rate (GFR), and history of antihypertensive or statin therapy were obtained from all participants. Insulin resistance was evaluated using the Homeostatic Model Assessment (HOMA-IR). Carotid -femoral pulse wave velocity was used as an index of arterial stiffness. Circulating EPC count and ADMA serum levels were also determined.

Results

Among studied individuals 30 (56.6%) subjects were diagnosed with isolated IFG, 9 (17%) with isolated IGT (17%) and 14 with combined IFG-IGT (26.4%). In univariate analysis age, mean blood pressure, fasting glucose, total cholesterol, LDL cholesterol, and ADMA levels positively correlated with pulse-wave velocity while exercise and GFR correlated negatively. EPC count did not correlate with PWV. In multivariate stepwise regression analysis PWV correlated independently and positively with LDL-Cholesterol (low density lipoprotein) and ADMA levels and negatively with exercise.

Conclusions

Elevated ADMA and LDL-C levels are strongly associated with increased arterial stiffness among pre-diabetic subjects. In contrast exercise inversely correlated with arterial stiffness.

Endothelial dysfunction and insulin resistance

In this article, we review several mechanisms by which insulin resistance is related to endothelial dysfunction. The mechanisms we discuss may explain the high prevalence of cardiovascular disease found in people with the metabolic syndrome and diabetes mellitus.

Cardiovascular risk in autoimmune disorders: role of asymmetric dimethylarginine

Mounting evidence indicates that cardiovascular events are a main cause of excessive mortality of autoimmune disorders like type I diabetes mellitus and rheumatic diseases. Inflammation and endothelial dysfunction, independent predictors to cardiovascular disease, are hallmarks of autoimmunity. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, can cause or contribute to the inflammatory syndrome and endothelial dysfunction. Recently, elevated ADMA levels have been demonstrated in many autoimmune diseases, suggesting that ADMA might play an important role for the associated manifestations of cardiovascular disease. In the review, we discuss the role of ADMA in the excessive cardiovascular morbidity and mortality associated with autoimmune diseases.

Restoration of impaired nitric oxide production in MELAS syndrome with citrulline and arginine supplementation

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is one of the most common mitochondrial disorders. Although the pathogenesis of stroke-like episodes remains unclear, it has been suggested that mitochondrial proliferation may result in endothelial dysfunction and decreased nitric oxide (NO) availability leading to cerebral ischemic events. This study aimed to assess NO production in subjects with MELAS syndrome and the effect of the NO precursors arginine and citrulline. Using stable isotope infusion techniques, we assessed arginine, citrulline, and NO metabolism in control subjects and subjects with MELAS syndrome before and after arginine or citrulline supplementation. The results showed that subjects with MELAS had lower NO synthesis rate associated with reduced citrulline flux, de novo arginine synthesis rate, and plasma arginine and citrulline concentrations, and higher plasma asymmetric dimethylarginine (ADMA) concentration and arginine clearance. We conclude that the observed impaired NO production is due to multiple factors including elevated ADMA, higher arginine clearance, and, most importantly, decreased de novo arginine synthesis secondary to decreased citrulline availability. Arginine and, to a greater extent, citrulline supplementation increased the de novo arginine synthesis rate, the plasma concentrations and flux of arginine and citrulline, and NO production. De novo arginine synthesis increased markedly with citrulline supplementation, explaining the superior efficacy of citrulline in increasing NO production. The improvement in NO production with arginine or citrulline supplementation supports their use in MELAS and suggests that citrulline may have a better therapeutic effect than arginine. These findings can have a broader relevance for other disorders marked by perturbations in NO metabolism.

Vascular effects of nebivolol added to hydrochlorothiazide in African Americans with hypertension and echocardiographic evidence of diastolic dysfunction: the NASAA study

BACKGROUND

African Americans have greater risk of cardiovascular events than comparator populations of white European origin. A potential reason for this is reduced nitric oxide bioavailability in African Americans, resulting in increased prevalence of factors that contribute to ventricular dysfunction. We investigated the effects of nebivolol with the diuretic hydrochlorothiazide (HCTZ) in hypertensive African Americans with echocardiographic evidence of diastolic dysfunction.

METHODS

A total of 42 African American patients were assigned to nebivolol and HCTZ in an open-label fashion for a 24-week period. Changes in blood pressure (BP), echocardiographic parameters, and success in attaining target BP were determined. As an indirect determinant of endothelial function, serum total nitric oxide (NOx) levels and asymmetric dimethyl arginine (ADMA) levels were performed at baseline and after the treatment period.

RESULTS

The systolic BP decreased from 150 ± 13 to 136 ± 16 mm Hg (P < .005). Diastolic BP decreased from 94 ± 13 to 84 ± 9 mm Hg (P = .008). Of the patients that completed the study, 77% achieved a combined target BP of systolic BP <140 mm Hg and a diastolic BP <90 mm Hg. Serum NOx increased by 41% and 39% in patients that were treated with 10 mg and 20 mg daily nebivolol, respectively. The ADMA levels decreased by 44% following treatment. The change in systolic BP was strongly correlated to the change in ADMA (r = .54; P = .024). Furthermore, in comparison to a group of age-matched patients controlled with diuretic therapy only, the ADMA levels were significantly lower in the nebivolol posttreatment group (controlled BP with diuretic: 0.32 ± 0.07μmol/L; nebivolol posttreatment: 0.24 ± 0.06 μmol/L; P < .05).

CONCLUSION

Reduced BP with nebivolol in hypertensive African Americans and echocardiographic evidence of diastolic dysfunction correlates with improved endothelial function. Furthermore, improvement in endothelial function and increased nitric oxide bioavailability suggests a potential mechanism of efficacy of nebivolol in these patients.

Metformin restores endothelial function in aorta of diabetic rats

BACKGROUND AND PURPOSE

The effects of metformin, an antidiabetic agent that improves insulin sensitivity, on endothelial function have not been fully elucidated. This study was designed to assess the effect of metformin on impaired endothelial function, oxidative stress, inflammation and advanced glycation end products formation in type 2 diabetes mellitus.

EXPERIMENTAL APPROACH

Goto-Kakizaki (GK) rats, an animal model of nonobese type 2 diabetes, fed with normal and high-fat diet during 4 months were treated with metformin for 4 weeks before evaluation. Systemic oxidative stress, endothelial function, insulin resistance, nitric oxide (NO) bioavailability, glycation and vascular oxidative stress were determined in the aortic rings of the different groups. A pro-inflammatory biomarker the chemokine CCL2 (monocyte chemoattractant protein-1) was also evaluated.

KEY RESULTS

High-fat fed GK rats with hyperlipidaemia showed increased vascular and systemic oxidative stress and impaired endothelial-dependent vasodilatation. Metformin treatment significantly improved glycation, oxidative stress, CCL2 levels, NO bioavailability and insulin resistance and normalized endothelial function in aorta.

CONCLUSION AND IMPLICATIONS

Metformin restores endothelial function and significantly improves NO bioavailability, glycation and oxidative stress in normal and high-fat fed GK rats. This supports the concept of the central role of metformin as a first-line therapeutic to treat diabetic patients in order to protect against endothelial dysfunction associated with type 2 diabetes mellitus.

The Role of Asymmetric Dimethylarginine (ADMA) in Endothelial Dysfunction and Cardiovascular Disease

Endothelium plays a crucial role in the maintenance of vascular tone and structure. Endothelial dysfunction is known to precede overt coronary artery disease. A number of cardiovascular risk factors, as well as metabolic diseases and systemic or local inflammation cause endothelial dysfunction. Nitric oxide (NO) is one of the major endothelium derived vaso-active substances whose role is of prime importance in maintaining endothelial homeostasis. Low levels of NO are associated with impaired endothelial function. Asymmetric dimethylarginine (ADMA), an analogue of L-arginine, is a naturally occurring product of metabolism found in human circulation. Elevated levels of ADMA inhibit NO synthesis and therefore impair endothelial function and thus promote atherosclerosis. ADMA levels are increased in people with hypercholesterolemia, atherosclerosis, hypertension, chronic heart failure, diabetes mellitus and chronic renal failure. A number of studies have reported ADMA as a novel risk marker of cardiovascular disease. Increased levels of ADMA have been shown to be the strongest risk predictor, beyond traditional risk factors, of cardiovascular events and all-cause and cardiovascular mortality in people with coronary artery disease. Interventions such as treatment with L-arginine have been shown to improve endothelium-mediated vasodilatation in people with high ADMA levels. However the clinical utility of modifying circulating ADMA levels remains uncertain.

Serum asymmetric dimethylarginine levels in diabetic patients with neuropathy

OBJECTIVE

The goal of our study was to evaluate the role of asymmetric dimethylarginine (ADMA) in patients with diabetic neuropathy.

MATERIALS AND METHODS

In this study, 58 diabetic patients and 26 healthy volunteers were included. In both groups ADMA measurements were performed together with other biochemical examinations. Nerve conduction studies and Neuropathy Symptom Score (NSS) were administered to the diabetic patients.

RESULTS

ADMA levels were found significantly higher in diabetic patients compared to the control group (p = 0.0001). However, ADMA levels were not statistically significant between diabetic patients with neuropathy and without neuropathy (p = 0.86 and p = 0.47).

CONCLUSION

These results demonstrate that there is not any significant relationship between ADMA and diabetic neuropathy.

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.

Increased plasma level of asymmetric dimethylarginine in hypertensive rats facilitates platelet aggregation: role of plasma tissue factor

This study was designed to explore the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, in platelet aggregation in hypertension and its possible mechanisms. Spontaneously hypertensive rats (SHR) and L-NAME-induced hypertensive rats were orally administered with L-arginine (1 g/(kg·day) for 14 days. Systolic blood pressure, platelet aggregation, and plasma tissue factor (TF) level and activity were measured. The plasma concentration of ADMA in SHR was determined. In vitro, platelet-rich plasma isolated from Wistar rats was prepared in order to observe the effect of exogenous ADMA on platelet aggregation and TF level and (or) activity in platelet-rich plasma. In both types of hypertensive rats, systolic blood pressure, platelet aggregation, and the level and activity of plasma TF were elevated compared with corresponding control animals. Plasma ADMA level was also increased in SHR. Treatment with L-arginine, a competitor of ADMA, lowered blood pressure and inhibited platelet aggregation concomitantly with a decrease in plasma TF level and activity in both types of hypertensive rats. We also found that exogenous ADMA promoted platelet aggregation and increased TF level and (or) activity in platelet-rich plasma, an effect that was inhibited by pretreatment with L-arginine. Importantly, the enhanced platelet aggregation induced by exogenous ADMA was reduced by pretreatment with anti-TF antibody. The results suggest that endogenous ADMA may be involved in platelet hyperaggregation status in hypertension, and the facilitation of platelet aggregation by ADMA is related to upregulation of the level and activity of plasma TF.

Asymmetrical dimethylarginine and severity of erectile dysfunction and their impact on cardiovascular events in patients with acute coronary syndrome

INTRODUCTION

Coronary artery disease (CAD) and vascular erectile dysfunction (ED) are related to endothelial dysfunction. Elevated asymmetrical dimethylarginine (ADMA) levels and ED are common in patients with increased cardiovascular risk. Our aim was to investigate whether ADMA has a predictive role for major adverse cardiovascular events (MACE) in acute coronary syndrome (ACS). The secondary aim of this study was to investigate whether severity of ED predicts MACE in these patients.

MATERIAL AND METHODS

Follow-up data were available for severity of ED in 71 patients with ACS. Plasma ADMA levels were determined by ELISA in 57 patients. Erectile dysfunction was assessed by the International Index of Erectile Function-6 (IIEF-6) score. Major adverse cardiovascular events (reinfarction, all-cause hospitalisation, stroke and all-cause death) was evaluated after a median of 10 months.

RESULTS

Severe ED had no significantly increased hazard ratio for cardiovascular events compared with mild, mild to moderate, and moderate ED (0.259 [95% CI 0.041-1.6], p = 0.147; 0.605 [95% CI 0.095-3.8], p = 0.594; 0.980 [95% CI 0.233-4.1], p = 0.978; and 0.473 [95% CI 0.052-1.3], p = 0.508). The patients who had ADMA levels ≥ 0.32 µmol/l had no significantly increased hazard ratio for cardiovascular events compared with patients who had ADMA levels < 0.32 µmol/l (2.018 [95% CI 0.615-6.6], p = 0.247).

CONCLUSIONS

Severity of ED and ADMA did not increase the risk of cardiovascular events in follow-up patients with ACS in our study. Larger prospective studies are necessary to evaluate whether ADMA predicts cardiovascular events in patients with ACS.

Asymmetric dimethylarginine as a mediator of vascular dysfunction and a marker of cardiovascular disease and mortality: an intriguing interaction with diabetes mellitus

Asymmetric dimethylarginine (ADMA) has evolved as an important regulator of nitric oxide (NO) synthesis in recent years. Elevated levels of ADMA have been reported in many conditions associated with a high cardiovascular risk. Moreover, ADMA is a biomarker for major cardiovascular events and mortality in cohorts with high, intermediate and low overall cardiovascular risk. Discrepant data have been reported on cardiovascular risk in people with and without diabetes mellitus, and the association of ADMA with diabetes mellitus per se has also remained controversial, possibly relating to type and stage of diabetes. Clinical and experimental data suggest that there is a multifaceted link between ADMA and insulin metabolism and action on one hand, and ADMA and glucose utilisation on the other. This interplay may be regulated by the enzyme involved in the metabolic degradation of ADMA, dimethylarginine dimethylaminohydrolase (DDAH). Recent data from prospective clinical studies suggest that whilst ADMA may be a marker for total mortality in patients without diabetes, elevated ADMA may exert beneficial effects in patients with diabetes. In this respect, ADMA could serve as a re-coupling agent overcoming endothelial nitric oxide synthase (eNOS) uncoupling in patients with diabetes. Anticipated advances in clinical and experimental investigation will help us to better understand this complex interrelationship between diabetes, eNOS, DDAH and ADMA.