Relationship between S-adenosylmethionine, S-adenosylhomocysteine, asymmetric dimethylarginine, and endothelial function in healthy human subjects during experimental hyper- and hypohomocysteinemia

Alterations in metabolome and lipidome in patients with in-stent restenosis

CONTEXT

In-stent restenosis (ISR) can lead to blood flow obstruction, insufficient blood supply to the brain, and may even result in serious complications such as stroke. Endothelial cell hyperproliferation and thrombosis are the primary etiologies, frequently resulting in alterations in intravascular metabolism. However, the metabolic changes related to this process are still undermined.

OBJECTIVE

We tried to characterize the serum metabolome of patients with ISR and those with non-restenosis (NR) using metabolomics and lipidomics, exploring the key metabolic pathways of this pathological phenomenon.

RESULTS

We observed that the cysteine and methionine pathways, which are associated with cell growth and oxidative homeostasis, showed the greatest increase in the ISR group compared to the NR group. Within this pathway, the levels of N-formyl-l-methionine and L-methionine significantly increased in the ISR group, along with elevated levels of downstream metabolites such as 2-ketobutyric acid, pyruvate, and taurocholate. Additionally, an increase in phosphatidylcholine (PC) and phosphatidylserine (PS), as well as a decrease in triacylglycerol in the ISR group, indicated active lipid metabolism in these patients, which could be a significant factor contributing to the recurrence of blood clots after stent placement. Importantly, phenol sulfate and PS(38:4) were identified as potential biomarkers for distinguishing ISR, with an area under the curve of more than 0.85.

CONCLUSIONS

Our study revealed significant metabolic alterations in patients with ISR, particularly in the cysteine and methionine pathways, with phenol sulfate and PS(38:4) showing promise for ISR identification.

Effects of tofacitinib therapy on arginine and methionine metabolites in association with vascular pathophysiology in rheumatoid arthritis: A metabolomic approach

Introduction

Rheumatoid arthritis (RA) has been associated with changes in lipid, arginine and NO metabolism with increased cardiovascular (CV) risk. The aim of this study is to evaluate the effect of tofacitinib, a Janus kinase (JAK) inhibitor, on arginine and methionine metabolism in correlation with inflammation, functional and pathological vascular changes during one-year treatment of patients with RA.

Materials and methods

Thirty RA patients with active disease were treated with either 5 mg bid or 10 mg bid tofacitinib for 12 months. We determined DAS28, CRP, IgM rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) levels. We assessed brachial artery flow-mediated vasodilation (FMD), carotid intima-media thickness (IMT) and pulse-wave velocity (PWV) by ultrasound at baseline and after 6 and 12 months. We also determined plasma L-arginine, L-citrulline, L-ornithine, inducible nitric oxide synthase (iNOS), asymmetric (ADMA) and symmetric dimethylarginine (SDMA), L-N-monomethyl-arginine (L-NMMA), cysteine, homocysteine, and methionine levels at these time points.

Results

Twenty-six patients (13 on each arm) completed the study. CRP, ESR and DAS28 decreased significantly during one-year treatment with tofacitinib. Arginine and ADMA showed a negative univariate correlation with CRP but not with FMD, PWV or IMT. Tofacitinib at 10 mg bid significantly increased L-arginine, L-ornithine, iNOS and methionine levels after 12 months. ADMA and SDMA levels did not change in our study. Methionine showed negative correlation with FMD at baseline and positive correlation with PWV after 12 months. No change was observed in FMD and PWV but a significant increase was measured in IMT at 6 and 12 months. Multivariate analysis indicated variable correlations of L-arginine, L-citrulline, ADMA, L-NMMA, homocysteine and methionine with DAS28, CRP, ESR and RF but not with anti-CCP after one-year treatment. With respect to vascular pathophysiology, only PWV and methionine correlated with each other.

Conclusion

One-year tofacitinib treatment suppressed systemic inflammation and improved functional status in RA. FMD, PWV have not been affected by one-year tofacitinib treatment., while IMT increased further despite treatment. Increased arginine and methionine might contribute to the anti-inflammatory effects of tofacitinib. Increased arginine availability with no changing ADMA may protect FMD and PWV from deterioration. The increase of IMT in the anti-inflammatory environment cannot be explained by arginine or methionine metabolism in this study.

Methionine adenosyltransferase 1a antisense oligonucleotides activate the liver-brown adipose tissue axis preventing obesity and associated hepatosteatosis

Altered methionine metabolism is associated with weight gain in obesity. The methionine adenosyltransferase (MAT), catalyzing the first reaction of the methionine cycle, plays an important role regulating lipid metabolism. However, its role in obesity, when a plethora of metabolic diseases occurs, is still unknown. By using antisense oligonucleotides (ASO) and genetic depletion of Mat1a, here, we demonstrate that Mat1a deficiency in diet-induce obese or genetically obese mice prevented and reversed obesity and obesity-associated insulin resistance and hepatosteatosis by increasing energy expenditure in a hepatocyte FGF21 dependent fashion. The increased NRF2-mediated FGF21 secretion induced by targeting Mat1a, mobilized plasma lipids towards the BAT to be catabolized, induced thermogenesis and reduced body weight, inhibiting hepatic de novo lipogenesis. The beneficial effects of Mat1a ASO were abolished following FGF21 depletion in hepatocytes. Thus, targeting Mat1a activates the liver-BAT axis by increasing NRF2-mediated FGF21 secretion, which prevents obesity, insulin resistance and hepatosteatosis.

Asymmetric Dimethylarginine (ADMA) and Symmetric Dimethylarginine (SDMA) Concentrations in Patients with Obesity and the Risk of Obstructive Sleep Apnea (OSA)

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are endogenous inhibitors of nitric oxide (NO) synthesis, and play a critical role in the process of endothelial dysfunction, and are considered markers of oxidative stress. The aim of the present study was to explore relationships between ADMA and/or SDMA and the occurrence of OSA in obese patients as well as the effect of the endothelial nitric oxide synthase (eNOS) gene polymorphism, which may modify the influence of ADMA or SDMA on NO production. A total of 518 unrelated obese subjects were included in this study. Body weight, height and blood pressure were measured and data on self-reported smoking status were collected. Obstructive sleep apnea (OSA) was assessed by the apnea hypopnea index (AHI). Blood samples were collected to measure serum concentrations of glucose, total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, creatinine, HbA1c (%), folic acid, vitamin B₁₂, C-reactive protein (CRP), aspartate aminotransferase (ASP), alanine aminotransferase (ALT) and IL-6 by routine methods. The NOS3 gene G894T and 4a/4b polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis. ADMA, SDMA and arginine concentrations were assessed simultaneously using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method. Adjusted multivariate logistic regression analysis showed a significant association between the occurrence of OSA and high serum ADMA levels, BMI above 40, age > 43 years, hypertension and male sex. Heterozygotes for the G894T eNOS polymorphism have the lowest serum concentrations of ADMA and SDMA, while no effect of the 4a/4b variants was observed. The results indicate that OSA in obese individuals can coexist with high ADMA levels, which appear as a potential OSA predictor.

CerefolinNAC Therapy of Hyperhomocysteinemia Delays Cortical and White Matter Atrophy in Alzheimer's Disease and Cerebrovascular Disease

We examined whether using a medical food therapy for hyperhomocysteinemia (HHcy) in patients with Alzheimer's disease (AD) or cognitive impairment due to cerebrovascular disease (CVD) with Cerefolin®/CerefolinNAC® (CFLN: L-methylfolate, methylcobalamin, and N-acetyl-cysteine) slowed regional brain atrophy. Thirty HHcy patients with AD and related disorders (ADRD) received CFLN (HHcy+CFLN: duration [μ ±  σ] = 18.6±16.1 months); a sub-sample of this group did not receive CFLN for varying periods of time (HHcy+NoCFLN: duration [μ ±  σ] = 12.6±5.6 months). Thirty-seven NoHHcy patients with ADRD did not receive CFLN (NoHHcy+NoCFLN: duration [μ ±  σ] = 13.3±17.7 months). No participant took supplemental B vitamins. Regional brain volumes were measured at baseline and end of study, and covariate-adjusted rates of hippocampal, cortical, and forebrain parenchymal (includes white matter) atrophy were predicted. The HHcy+CFLN group's hippocampal and cortical atrophy adjusted rates were 4.25 and 11.2 times slower than those of the NoHHcy+NoCFLN group (p < 0.024). The HHcy+CFLN group's forebrain parenchyma atrophy rate was significantly slower only for CVD; the rate of slowing was proportional to the degree of homocysteine lowering (p < 0.0001). CFLN was associated with significantly slowed hippocampal and cortical atrophy rates in ADRD patients with HHcy, and forebrain parenchymal atrophy rates in CVD patients with HHcy. The present results should be further validated.

Regulation of endothelial intracellular adenosine via adenosine kinase epigenetically modulates vascular inflammation

The molecular mechanisms underlying vascular inflammation and associated inflammatory vascular diseases are not well defined. Here we show that endothelial intracellular adenosine and its key regulator adenosine kinase (ADK) play important roles in vascular inflammation. Pro-inflammatory stimuli lead to endothelial inflammation by increasing endothelial ADK expression, reducing the level of intracellular adenosine in endothelial cells, and activating the transmethylation pathway through increasing the association of ADK with S-adenosylhomocysteine (SAH) hydrolase (SAHH). Increasing intracellular adenosine by genetic ADK knockdown or exogenous adenosine reduces activation of the transmethylation pathway and attenuates the endothelial inflammatory response. In addition, loss of endothelial ADK in mice leads to reduced atherosclerosis and affords protection against ischemia/reperfusion injury of the cerebral cortex. Taken together, these results demonstrate that intracellular adenosine, which is controlled by the key molecular regulator ADK, influences endothelial inflammation and vascular inflammatory diseases.

The molecular mechanisms underlying vascular inflammation are unclear. Here the authors show that pro-inflammatory stimuli lead to endothelial inflammation by increasing adenosine kinase expression, and that its knockdown in endothelial cells inhibits atherosclerosis and cerebral ischemic injury in mice.

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.

Homocysteinemia control by cysteine in cerebral vascular patients after methionine loading test: evidences in physiological and pathological conditions in cerebro-vascular and multiple sclerosis patients

The toxicity risk of hyperhomocysteinemia is prevented through thiol drug administration which reduces plasma total homocysteine (tHcy) concentrations by activating thiol exchange reactions. Assuming that cysteine (Cys) is a homocysteinemia regulator, the hypothesis was verified in healthy and pathological individuals after the methionine loading test (MLT). The plasma variations of redox species of Cys, Hcy, cysteinylglycine, glutathione and albumin (reduced, HS-ALB, and at mixed disulfide, XSS-ALB) were compared in patients with cerebral small vessels disease (CSVD) (n = 11), multiple sclerosis (MS) (n = 12) and healthy controls (n = 11) at 2-4-6 h after MLT. In MLT-treated subjects, the activation of thiol exchange reactions provoked significant changes over time in redox species concentrations of Cys, Hcy, and albumin. Significant differences between controls and pathological groups were also observed. In non-methionine-treated subjects, total Cys concentrations, tHcy and thiol-protein mixed disulfides (CSS-ALB, HSS-ALB) of CSVD patients were higher than controls. After MLT, all groups displayed significant cystine (CSSC) increases and CSS-ALB decreases, that in pathological groups were significantly higher than controls. These data would confirm the Cys regulatory role on the homocysteinemia; they also explain that the Cys-Hcy mixed disulfide excretion is an important point of hyperhomocysteinemia control. Moreover, in all groups after MLT, significant increases in albumin concentrations, named total albumin (tALB) and measured as sum of HS-ALB (spectrophometric), and XSS-ALB (assayed at HPLC) were observed. tALB increases, more pronounced in healthy than in the pathological subjects, could indicate alterations of albumin equilibria between plasma and other extracellular spaces, whose toxicological consequences deserve further studies.

Serum S-adenosylmethionine, but not methionine, increases in response to overfeeding in humans

BACKGROUND

Plasma concentration of the methyl donor S-adenosylmethionine (SAM) is linearly associated with body mass index (BMI) and fat mass. As SAM is a high-energy compound and a sensor of cellular nutrient status, we hypothesized that SAM would increase with overfeeding.

METHODS

Forty normal to overweight men and women were overfed by 1250 kcal per day for 28 days.

RESULTS

Serum SAM increased from 106 to 130 nmol/l (P=0.006). In stratified analysis, only those with weight gain above the median (high-weight gainers; average weight gain 3.9±0.3 kg) had increased SAM (+42%, P=0.001), whereas low-weight gainers (weight gain 1.5±0.2 kg) did not (Pinteraction=0.018). Overfeeding did not alter serum concentrations of the SAM precursor, methionine or the products, S-adenosyl-homocysteine and homocysteine. The SAM/SAH (S-adenosylhomocysteine) ratio was unchanged in the total population, but increased in high-weight gainers (+52%, P=0.006, Pinteraction =0.005). Change in SAM correlated positively with change in weight (r=0.33, P=0.041) and fat mass (r=0.44, P=0.009), but not with change in protein intake or plasma methionine, glucose, insulin or low-density lipoprotein (LDL)-cholesterol.

CONCLUSION

Overfeeding raised serum SAM in proportion to the fat mass gained. The increase in SAM may help stabilize methionine levels, and denotes a responsiveness of SAM to nutrient state in humans. The role of SAM in human energy metabolism deserves further attention.

Associations between asymmetric dimethylarginine, homocysteine, and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism (rs1801133) in rheumatoid arthritis

OBJECTIVES

The aim of our study was to determine whether asymmetric dimethylarginine (ADMA) levels are associated with homocysteine (Hcy) and methylenetetrahydrofolate reductase (MTHFR) C677T (rs1801133) gene variants in patients with rheumatoid arthritis (RA).

METHOD

Serum ADMA and Hcy levels were measured in 201 RA individuals [155 (77.1%) females, median age 67 years (interquartile range 59-73)]. The MTHFR C677T polymorphism was assessed by using the LightCyclerTM System. Initially, ADMA was compared across the categories of MTHFR using a one-way analysis of variance (ANOVA), followed by a multivariate model, which accounted for Hcy, age, erythrocyte sedimentation rate (ESR), and homeostatic model assessment (HOMA).

RESULTS

In univariable analysis, ADMA differed significantly across the categories of MTHFR (p = 0.037). Patients with the MTHFR 677TT genotype had the highest ADMA levels, with a mean of 0.62 (SE = 0.03), significantly higher than either those patients carrying the MTHFR 677CT (0.55, SE = 0.01) or the MTHFR 677CC (0.55, SE = 0.01) genotype (p = 0.042) in both cases. In the multivariable model, Hcy (p = 0.022) and ESR (p < 0.001) were found to have significant positive associations with ADMA but the relationship between MTHFR gene variants and ADMA was found to be non-significant (p = 0.102).

CONCLUSIONS

Hcy and ADMA are significantly associated in RA. It is plausible that abnormal Hcy metabolism plays an important role in premature atherosclerosis in RA by promoting ADMA accumulation and leading to the derangement of vascular haemostasis.

Role of S-adenosylhomocysteine in cardiovascular disease and its potential epigenetic mechanism

Transmethylation reactions utilize S-adenosylmethionine (SAM) as a methyl donor and are central to the regulation of many biological processes: more than fifty SAM-dependent methyltransferases methylate a broad spectrum of cellular compounds including DNA, histones, phospholipids and other small molecules. Common to all SAM-dependent transmethylation reactions is the release of the potent inhibitor S-adenosylhomocysteine (SAH) as a by-product. SAH is reversibly hydrolyzed to adenosine and homocysteine by SAH hydrolase. Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. However, a major unanswered question is if homocysteine is causally involved in disease pathogenesis or simply a passive and indirect indicator of a more complex mechanism. A chronic elevation in homocysteine levels results in a parallel increase in intracellular or plasma SAH, which is a more sensitive biomarker of cardiovascular disease than homocysteine and suggests that SAH is a critical pathological factor in homocysteine-associated disorders. Previous reports indicate that supplementation with folate and B vitamins efficiently lowers homocysteine levels but not plasma SAH levels, which possibly explains the failure of homocysteine-lowering vitamins to reduce vascular events in several recent clinical intervention studies. Furthermore, more studies are focusing on the role and mechanisms of SAH in different chronic diseases related to hyperhomocysteinemia, such as cardiovascular disease, kidney disease, diabetes, and obesity. This review summarizes the current role of SAH in cardiovascular disease and its effect on several related risk factors. It also explores possible the mechanisms, such as epigenetics and oxidative stress, of SAH. This article is part of a Directed Issue entitled: Epigenetic dynamics in development and disease.

Plasma asymmetric and symmetric dimethylarginine in a rat model of endothelial dysfunction induced by acute hyperhomocysteinemia

Hyperhomocysteinemia induces vascular endothelial dysfunction, an early hallmark of atherogenesis. While higher levels of circulating asymmetric dimethylarginine (ADMA) and symmetric dimethyl arginine (SDMA), endogenous inhibitors of nitric oxide synthesis, have been associated with increased cardiovascular risk, the role that ADMA and SDMA play in the initiation of hyperhomocysteinemia-induced endothelial dysfunction remains still controversial. In the present study, we studied the changes of circulating ADMA and SDMA in a rat model of acutely hyperhomocysteinemia-induced endothelial dysfunction. In healthy rats, endothelium-related vascular reactivity (measured as acetylcholine-induced transient decrease in mean arterial blood pressure), plasma ADMA and SDMA, total plasma homocysteine (tHcy), cysteine and glutathione were measured before and 2, 4 and 6 h after methionine loading or vehicle. mRNA expression of hepatic dimethylarginine dimethylaminohydrolase-1 (DDAH1), a key protein responsible for ADMA metabolism, was measured 6 h after the methionine loading or the vehicle. Expectedly, methionine load induced a sustained increase in tHcy (up to 54.9 ± 1.9 µM) and a 30 % decrease in vascular reactivity compared to the baseline values. Plasma ADMA and SDMA decreased transiently after the methionine load. Hepatic mRNA expression of DDAH1, cathepsin D, and ubiquitin were significantly lower 6 h after the methionine load than after the vehicle. The absence of an elevation of circulating ADMA and SDMA in this model suggests that endothelial dysfunction induced by acute hyperhomocysteinemia cannot be explained by an up-regulation of protein arginine methyltransferases or a down-regulation of DDAH1. In experimental endothelial dysfunction induced by acute hyperhomocysteinemia, down-regulation of the proteasome is likely to dampen the release of ADMA and SDMA in the circulation.

Plasma homoarginine, arginine, asymmetric dimethylarginine and total homocysteine interrelationships in rheumatoid arthritis, coronary artery disease and peripheral artery occlusion disease

Elevated circulating concentrations of total L-homocysteine (thCys) and free asymmetric dimethylarginine (ADMA) are long-established cardiovascular risk factors. Low circulating L-homoarginine (hArg) concentrations were recently found to be associated with increased cardiovascular morbidity and mortality. The biochemical pathways of these amino acids overlap and share the same cofactor S-adenosylmethionine (SAM). In the present study, we investigated potential associations between hArg, L-arginine (Arg), ADMA and thCys in plasma of patients suffering from rheumatoid arthritis (RA), coronary artery disease (CAD) or peripheral artery occlusive disease (PAOD). In RA, we did not find any correlation between ADMA or hArg and thCys at baseline (n = 100) and after (n = 83) combined add-on supplementation of omega-3 fatty acids, vitamin E, vitamin A, copper, and selenium, or placebo (soy oil). ADMA correlated with Arg at baseline (r = 0.446, P < 0.001) and after treatment (r = 0.246, P = 0.03). hArg did not correlate with ADMA, but correlated with Arg before (r = 0.240, P = 0.02) and after treatment (r = 0.233, P = 0.03). These results suggest that hArg, ADMA and Arg are biochemically familiar with each other, but unrelated to hCys in RA. In PAOD and CAD, ADMA and thCys did not correlate.

Folic acid supplementation on homocysteine levels in children taking antiepileptic drugs: A randomized controlled trial

OBJECTIVES

To assess the level of homocysteine (tHcy) in children taking AEDs and to study whether daily oral supplementation of folic acid for 1 month will reduce the tHcy level.

MATERIALS AND METHODS

This was a double-blinded, randomized control trial conducted in Institute of Maternal and Child Health, Kozhikode, India. Totally 60 children were recruited and of them, 48 were enrolled. Of these children, 32 were assigned to the experimental group and 16 to the control group. Baseline data collection and tHcy estimation were done. One mg folic acid tablets were given to the experimental group and placebo tablets to the control group for 30 days. tHcy levels were re-estimated after 1 month follow-up. Statistical significance was tested by χ(2) test, and paired and unpaired t-tests, as appropriate. Correlation was tested by Pearson correlation test and P value less than 0.05 was taken as the cut-off for statistical significance.

RESULTS

Baseline plasma tHcy concentrations in both groups were comparable [11.90 (6.3) and 13.02 (2.4) μmol/l, respectively]. During the follow-up period, no increase in seizure episodes or no serious adverse reactions were noticed in either group. The reduction of tHcy in the experimental group was 1.92 μmol/l (P = 0.04) and in the control group, there was an increase of 1.05 μmol/l (P = 0.16).

CONCLUSIONS

In children on AED treatment, folic acid supplementation may reduce tHcy level and thus reduce CVD risk.

Effect of taurine and N-acetylcysteine on methionine restriction-mediated adiposity resistance

OBJECTIVES

Methionine-restricted (MR) rats, which are lean and insulin sensitive, have low serum total cysteine (tCys) and taurine and decreased hepatic expression and activity indices of stearoyl-coenzyme A desaturase-1 (SCD1). These effects are partly or completely reversed by cysteine supplementation. We investigated whether reversal of MR phenotypes can be achieved by other sulfur compounds, namely taurine or N-acetylcysteine (NAC).

METHODS

MR and control-fed (CF) rats were supplemented with taurine (0.5%) or NAC (0.5%) for 12weeks. Adiposity, serum sulfur amino acids (SAA), Scd1 gene expression in liver and white adipose tissue, and SCD1 activity indices (calculated from serum fatty acid profile) were monitored.

RESULTS

Taurine supplementation of MR rats did not restore weight gain or hepatic Scd1 expression or indices to CF levels, but further decreased adiposity. Taurine supplementation of CF rats did not affect adiposity, but lowered triglyceridemia. NAC supplementation in MR rats raised tCys and partly or completely reversed MR effects on weight, fat %, Scd1 expression in liver and white adipose tissue, and estimated SCD1 activity. In CF rats, NAC decreased body fat % and lowered SCD1-18 activity index (P<0.001). Serum triglycerides and leptin were over 40% lower in CF+NAC relative to CF rats (P≤0.003 for both). In all groups, change in tCys correlated with change in SCD1-16 index (partial r=0.60, P<0.001) independent of other SAA.

CONCLUSION

The results rule out taurine as a mediator of increased adiposity produced by cysteine in MR, and show that NAC, similar to L-cysteine, blocks anti-obesity effects of MR. Our data show that dietary SAA can influence adiposity in part through mechanisms that converge on SCD1 function. This may have implications for understanding and preventing human obesity.

In vivo nitric oxide synthesis, insulin sensitivity, and asymmetric dimethylarginine in obese subjects without and with metabolic syndrome

Metabolic syndrome (MetSyn) is associated with impaired endothelial function. Here the association between nitric oxide (NO) production and insulin sensitivity (Si) in obese subjects with and without MetSyn was evaluated. The relationship between NO production and asymmetric dimethylarginine (ADMA) was also explored. Seven healthy normal-weight subjects (male/female [M/F], 3/4; age, 27.4 ± 10.9 years; body mass index [BMI], 21.9 ± 2.2 kg/m(2)), 7 obese subjects without MetSyn (M/F, 1/6; age, 48.0 ± 8.0 years; BMI, 34.5 ± 2.3 kg/m(2)), and 7 with MetSyn (M/F, 3/4; age, 48.0 ± 10.7 years; BMI, 33.4 ± 2.9 kg/m(2)) were recruited. Body composition and cardiometabolic functions (blood pressure, glucose, insulin, triglycerides, total cholesterol, high-density lipoprotein, ADMA) were measured. A frequent sampling intravenous glucose tolerance test was performed to measure Si. A novel stable isotopic method was used to measure in vivo rates of NO production. The NO production was lower in obese subjects with MetSyn compared with normal-weight subjects and obese subjects without MetSyn. Similarly, Si was significantly lower in obesity, both without and with MetSyn, compared with the control group. A significant direct association was found between NO synthesis and Si (ρ = 0.47, P = .03). Circulating levels of ADMA were significantly higher in the obese group with MetSyn. A nonsignificant negative trend between ADMA and NO synthesis was observed. The association between Si and NO production suggests a close mechanistic link between endothelial function and insulin signaling. The results may be highly informative for the development of controlled longitudinal interventions to improve endothelial and metabolic regulation.

Asymmetric dimethylarginine in adults with cystathionine β-synthase deficiency

In hyperhomocysteinemia (HHcy), an independent risk factor for cardiovascular diseases, endothelial dysfunction due to reduced bioavailability of nitric oxide is a consistent finding. However, the underlying mechanisms remain unknown. Increased levels of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) have been associated with HHcy, and may contribute, at least in part, for the homocysteine-induced endothelial dysfunction, but whether cystathionine β-synthase (CBS) deficiency is associated with increased ADMA has hardly been investigated. To address this question, we measured total homocysteine (tHcy), ADMA and symmetric dimethylarginine (SDMA) in plasma of 22 adult CBS deficient patients, using established HPLC techniques. Results showed that in CBS deficient patients with elevated levels of tHcy (median (total range): 33 (14-237) μmol/L), both ADMA and SDMA levels were normal. Moreover, tHcy and ADMA concentrations were not correlated (r(s)=0.017, p=0.94). Our results favor the hypothesis that the negative vascular effects of HHcy have an ADMA-independent etiology.

The role of asymmetric and symmetric dimethylarginines in renal disease

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthases. By inhibiting nitric oxide formation, ADMA causes endothelial dysfunction, vasoconstriction, elevation of blood pressure, and aggravation of experimental atherosclerosis. Levels of ADMA and its isomer symmetric dimethylarginine (SDMA), which does not inhibit nitric oxide synthesis, are both elevated in patients with kidney disease. Currently available data from prospective clinical trials in patients with chronic kidney disease suggest that ADMA is an independent marker of progression of renal dysfunction, vascular complications and death. High SDMA levels also negatively affect survival in populations at increased cardiovascular risk, but the mechanisms underlying this effect are currently only partly understood. Beyond glomerular filtration, other factors influence the plasma concentrations of ADMA and SDMA. Elevated plasma concentrations of these dimethylarginines might also indirectly influence the activity of nitric oxide synthases by inhibiting the uptake of cellular L-arginine. Other mechanisms may exist by which SDMA exerts its biological activity. The biochemical pathways that regulate ADMA and SDMA, and the pathways that transduce their biological function, could be targeted to treat renal disease in the future.

No gross abnormality of plasma homocysteine after acute methionine loading in clinically stabilized patients with schizophrenia

Homocysteine is reported to be a risk factor for schizophrenia. The methionine loading test evaluates the summation of a multitude of enzymatic pathways associated with homocysteine metabolism. Using a challenge paradigm, we measured homocysteine levels in 10 chronic schizophrenia patients and five controls at baseline and 3h after 100mg/kg oral methionine. This pilot study failed to detect a gross abnormality of plasma homocysteine level after acute methionine load in patients with schizophrenia. Elevations in plasma homocysteine reported in schizophrenia do not derive from a dynamic abnormality in methionine metabolism in this challenge paradigm.

Association between exaggerated blood pressure response to exercise and serum asymmetric dimethylarginine levels

BACKGROUND

The exaggerated blood pressure response to exercise (EBPR) is an independent predictor of hypertension. Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide inhibitor and higher plasma levels of ADMA are related to increased cardiovascular risk. The aim of this study is to identify the relationship between ADMA and EBPR.

METHODS AND RESULTS

A total of 66 patients (36 with EBPR and 30 as controls) were enrolled in the study. EBPR is defined as blood pressure (BP) measurements > or =200/100 mmHg during the treadmill test. All the subjects underwent 24-h ambulatory BP monitoring. L-arginine and ADMA levels were measured using a high performance lipid chromatography technique. The serum ADMA levels were increased in the EBPR group compared to the healthy controls (4.0+/-1.4 vs 2.6+/-1.1 micromol/L respectively, P=0.001), but L-arginine levels were similar in the 2 groups (P=0.19). The serum ADMA levels were detected as an independent predictor of EBPR (odds ratio 2.28; 95% confidence interval 1.22-4.24; P=0.002).

CONCLUSIONS

Serum ADMA levels might play a role in EBPR to exercise.

Alpha-lipoic acid induces elevated S-adenosylhomocysteine and depletes S-adenosylmethionine

Lipoic acid is a disulfhydryl-containing compound used in clinical medicine and in experimental models as an antioxidant. We developed a stable isotope dilution capillary gas chromatography/mass spectrometry assay for lipoic acid. We assayed a panel of the metabolites of transmethylation and transsulfuration 30 min after injecting 100 mg/kg lipoic acid in a rat model. Lipoic acid values rose 1000-fold in serum and 10-fold in liver. A methylated metabolite of lipoic acid was also detected but not quantitated. Lipoic acid injection caused a massive increase in serum S-adenosylhomocysteine and marked depletion of liver S-adenosylmethionine. Serum total cysteine was depleted but liver cysteine and glutathione were maintained. Serum total homocysteine doubled, with increases also in cystathionine, N,N-dimethylglycine, and alpha-aminobutyric acid. In contrast, after injection of 2-mercaptoethane sulfonic acid, serum total cysteine and homocysteine were markedly depleted and there were no effects on serum S-adenosylmethionine or S-adenosylhomocysteine. We conclude that large doses of lipoic acid displace sulfhydryls from binding sites, resulting in depletion of serum cysteine, but also pose a methylation burden with severe depletion of liver S-adenosylmethionine and massive release of S-adenosylhomocysteine. These changes may have previously unrecognized deleterious effects that should be investigated in both human disease and experimental models.

Reference values for plasma concentrations of asymmetrical dimethylarginine (ADMA) and other arginine metabolites in men after validation of a chromatographic method

BACKGROUND

Owing to the growing number of reports in the literature on ADMA as a possibly useful marker of endothelial health, its use in the clinical laboratory is of increasing interest. Age dependency and the small, but statistically significant differences between healthy subjects and disease groups are difficult to interpret. Additionally, levels of ADMA in comparable patient groups of different studies vary widely, even when similar methods have been used.

METHODS

After analytical evaluation of a chromatographic method according to international guidelines, we analysed asymmetrical (ADMA) and symmetrical dimethyl arginine (SDMA), homo-arginine and arginine in EDTA plasma of 292 healthy males aged 20 to 75 years (y) who had passed strict inclusion/exclusion criteria. For statistical analysis, 4 age groups were formed. Group differences were identified with the non-parametric Kruskal-Wallis test.

RESULTS

Calibration curves were linear throughout the selected ranges; the standard deviation for the regression line, recovery, imprecision, and accuracy results were all highly satisfactory. The reference ranges of ADMA for the 4 age groups are presented as age (mean+/-SD of age group, y); number of subjects; median, 2.5th-97.5th percentile: group <35 y: 26.7+/-4.0 y; n=78; 0.58, 0.43-0.69 micromol/L; group 35-49 y: 41.6+/-4.0 y; n=93; 0.59, 0.45-0.73 micromol/L; group 50-65 y: 57.5+/-4.2 y; n=82; 0.61, 0.46-0.78 micromol/L; and group >65 y: 69.6+/-3.3 y; n=39; 0.64, 0.54-0.79 micromol/L.

CONCLUSIONS

Only highly precise methods are able to detect small differences between groups. The application of an evaluated method to a well defined group of healthy subjects should provide a basis for comparison of ADMA concentrations in different patient populations of future studies.

Homocysteine-induced endothelial cell adhesion is related to adenosine lowering and is not mediated byS-adenosylhomocysteine

Hyperhomocysteinemia is a cardiovascular risk factor and may contribute to the pathogenesis of atherosclerosis by altering endothelial functions. The mechanism of homocysteine-induced cell adhesion has been here investigated using EA.hy 926 cells. Homocysteine induces a stereospecific, time- and dose-dependent cell adhesion which is prevented by adenosine. The dramatic increase of S-adenosylhomocysteine induced by adenosine-2',3'-dialdehyde does not cause cell adhesion, indicating that no apparent relationship exists between this process and intracellular S-adenosylhomocysteine content. Homocysteine-induced cell adhesion is abolished by pre-treatment with adenosine-2',3'-dialdehyde, demonstrating that the adenosine depletion caused by reversal of S-adenosylhomocysteine hydrolase reaction is responsible for homocysteine-induced cell damage.

Improvement in central arterial pressure waveform during hemodialysis is related to a reduction in asymmetric dimethylarginine (ADMA) levels

BACKGROUND

Cardiovascular mortality is high in hemodialysis (HD) patients. Early arterial pressure wave reflections, reflecting arterial stiffness and the endogenous nitric oxide synthesis inhibitor asymmetric dimethylarginine (ADMA) levels predict mortality in HD patients. Therefore, we aimed to study changes in ADMA levels and central arterial pressure waveform during HD.

METHODS

Thirty-two chronic HD patients were studied before and after a HD session. In a subset of 22 patients without arrhythmias, pulse wave analysis was performed on radial artery (SphygmoCor). Augmentation index (AIx), defined as difference between the second and first systolic peak divided by central pulse pressure, was used as a measure of arterial stiffness. ADMA was measured in plasma with the ELISA technique. Homocysteine was measured in plasma using the EIA technique.

RESULTS

HD reduced both AIx (19%; p = 0.003) and ADMA levels (17%; p < 0.001). The magnitudes of changes in AIx and ADMA during HD were correlated (r = 0.44; p = 0.045). Mean arterial pressure change was not significant. HD reduced homocysteine levels, but homocysteine was not related to ADMA or AIx.

CONCLUSION

The reduction in ADMA level seen after HD was associated with improvement in the central arterial pressure waveform, suggesting involvement of nitric oxide in the regulation of arterial stiffness in HD patients.

Nontraditional atherosclerotic risk factors and extent of coronary atherosclerosis in patients with combined impaired fasting glucose and impaired glucose tolerance

Partially inconsistent data exist on mutual relations between nontraditional atherosclerotic risk factors, including the magnitude of insulin resistance (IR), as well as on their relevance for atherogenesis in the metabolic syndrome. Subjects exhibiting combined impaired fasting glucose and impaired glucose tolerance (IFG/IGT) are exposed to an exceptionally high risk for atherogenesis and development of type 2 diabetes mellitus. Because of islet Beta-cell dysfunction, the usefulness of commonly used indices of IR is limited in IFG/IGT. Our aim was to assess the relationship between extent of angiographic coronary artery disease (CAD) and nontraditional atherosclerotic risk factors (including IR by a clamp-based golden standard method) in IFG/IGT. Fifty-three subjects (32 men, 21 women; mean age, 55 +/- 11 years) with stable angina, preserved left ventricular systolic function, and IFG/IGT were divided into 3 groups: group A (no coronary stenoses >50%, n = 22), group B (1-vessel CAD, n = 15), and group C (2/3-vessel CAD, n = 16). Insulin sensitivity was quantified by a hyperinsulinemic euglycemic clamp technique and expressed as M. M value, plasma homocysteine (Hcy) level, and asymmetric dimethyl-L-arginine (ADMA)/L-arginine ratio were independent determinants of CAD extent as shown by forward stepwise discriminant function analysis. Compared with group A (M = 32.7 +/- 9.3 micromol/kg fat-free mass [FFM] per minute; Hcy, 8.1 +/- 1.4 micromol/L), lower M and higher Hcy levels were found in group B (M = 16.9 +/- 8.2 micromol/kg FFM per minute, P < .001; Hcy, 11.2 +/- 2.9 micromol/L, P = .003) and C (M = 16.4 +/- 7.8 micromol/kg FFM per minute, P < .001; Hcy, 12.8 +/- 3.9 micromol/L, P < .001). The ADMA/L-arginine ratio was increased in group C (0.0078 +/- 0.0011) compared with group A (0.0063 +/- 0.0013, P = .03) and B (0.0058 +/- 0.0012, P = .01). Multivariate correlates (P < .05) of plasma Hcy concentrations were M (beta = -.34 +/- .12, P = .008), creatinine clearance (beta = -.23 +/- .10, P = .03) and fasting insulin (beta = .25 +/- .12, P = .04). This indicates an additive contribution of IR, plasma Hcy, and elevated ADMA/L-arginine ratio to the extent of angiographic CAD in combined IFG/IGT.

Asymmetrical dimethylarginine independently predicts total and cardiovascular mortality in individuals with angiographic coronary artery disease (the Ludwigshafen Risk and Cardiovascular Health study)

BACKGROUND

Asymmetrical dimethylarginine (ADMA) is increased in conditions associated with increased risk of atherosclerosis. We investigated the use of ADMA to predict total and cardiovascular mortality in patients scheduled for coronary angiography.

METHODS

In 2543 persons with and 695 without coronary artery disease (CAD) identified by angiography we measured ADMA and recorded total and cardiovascular mortality during a median follow-up of 5.45 years.

RESULTS

ADMA was correlated positively to age, female sex, diabetes mellitus, former and current smoking, and C-reactive protein and inversely to HDL cholesterol and triglycerides. ADMA was not associated with body mass index, hypertension, LDL cholesterol, or the presence or absence of angiographic CAD. Glomerular filtration rate and homocysteine were the strongest predictors of ADMA. At the 2nd, 3rd and 4th quartile of ADMA, hazard ratios for all-cause mortality adjusted for age, sex, and cardiovascular risk factors were 1.12 [95% confidence interval (CI) 0.83-1.52], 1.35 (95% CI 1.01-1.81), and 1.87 (95% CI 1.43-2.44), respectively, compared with the 1st quartile. Hazard ratios for cardiovascular death were 1.13 (95% CI 0.78-1.63), 1.42 (95% CI 1.00-2.02), and 1.81 (95% CI 1.31-2.51). ADMA in the highest quartile remained predictive of mortality after accounting for medication at baseline. The predictive value of ADMA was similar to that in the entire cohort in persons with CAD, stable or unstable, but was not statistically significant in persons without angiographic CAD.

CONCLUSIONS

ADMA concentration predicts all-cause and cardiovascular mortality in individuals with CAD independently of established and emerging cardiovascular risk factors.

Total homocysteine, folate, and cobalamin, and their relation to genetic polymorphisms, lifestyle and body mass index in healthy children and adolescents

We investigated total homocysteine (tHcy) concentrations and relations between tHcy and folate, cobalamin (Cbl), genetic polymorphisms (MTHFR 677C > T, MTHFR 1298A > C, MTHFR 1793G > A), blood pressure (BP), body mass index (BMI), cholesterol, triglycerides, sports activities, family and individual history of cardiovascular disease (CVD) and lifestyle issues in 264 healthy children and adolescents (2-17 y). THcy concentrations significantly increased while folate and Cbl decreased with age without gender differences. Age, folate and Cbl were significant predictors for tHcy concentrations. THcy was higher but within normal ranges in MTHFR 677TT homozygotes (10.6%) and carriers of the MTHFR 1793A allele (8%). Only two individuals (0.8%), both with low tHcy concentrations, were homozygous for MTHFR 1793AA. THcy concentration correlated positively with creatinine, triglycerides, BMI and systolic BP and was not related to cholesterol, sports activities and family history of CVD. In conclusion, tHcy concentrations in this pediatric population were significantly influenced by age, folate and Cbl concentrations. No gender differences for tHcy, folate or Cbl concentrations were observed. Both the MTHFR 677TT genotype and the MTHFR 1793A allele were not associated with hyperhomocysteinemia. The prevalence of the MTHFR 1793AA genotype was too low for meaningful interpretation.

Synergy of genes and nutrients: the case of homocysteine

PURPOSE OF REVIEW

Folic acid is now considered an important functional food component: it lowers potentially toxic homocysteine, prevents birth defects and modulates the risk of several cancers. The complexity of interactions involved, however, means we still have much to learn about the role of folate and homocysteine in both health and disease.

RECENT FINDINGS

This review examines the emergence of homocysteine as a public health issue, and places this in context by exploring recent developments in the field of homocysteine as a vasculo, neuro and embryotoxic thiol. The paper also examines the homocysteine nexus in relation to mood disorders and cancer. It ends with an assessment of the issues associated with government-mandated folate fortification.

SUMMARY

Folate fortification as a population measure may mask B12 deficiency, affect antiepileptic drug seizure control, and influence the genetic selection of a potentially deleterious genotype, albeit over a number of generations. It is likely that only large studies with a comprehensive battery of endpoints that fully address the complexity of nutrient-gene and gene-gene interactions will be able to answer all the necessary questions fully.

Medium-term methionine supplementation increases plasma homocysteine but not ADMA and improves blood pressure control in rats fed a diet rich in protein and adequate in folate and choline

BACKGROUND

Hyperhomocysteinemia (HHcy) is associated with cardiovascular risk, possibly because it increases asymmetric dimethyl-arginine (ADMA), but the general association remains unclear and may vary with nutritional and physiological conditions.

AIM OF THE STUDY

We aimed to monitor the effect of methionine supplementation, and subsequent HHcy, on plasma ADMA and hemodynamics in the context of a diet rich in protein and adequate in folic acid and choline.

METHODS

For 6 weeks, rats were fed a 29% protein diet supplemented (M) or not (C) with 8 g/kg L: -methionine. Blood pressure and plasma amino acids, including homocysteine and ADMA, were measured throughout the experiment and additional parameters, including in vivo hemodynamic response to acetylcholine, were measured at week 5-6.

RESULTS

As compared to the C diet, the M diet induced a marked HHcy during the first 3 weeks, which lessened at week 5. In contrast, plasma ADMA stayed similar in the C and M diet. Paradoxically, M rats had lower mean and diastolic blood pressure values over the experiment, together with a lower left ventricular mass at week 6, when compared with C rats. No difference was observed between groups regarding vascular reactivity and plasma NOx at week 6.

CONCLUSIONS

In a context of a diet rich in protein and adequate in methyl donors, rats exhibit a complex adaptation to the medium-term methionine supplementation, with improvement in blood pressure control despite marked HHcy. The lack of increase in plasma ADMA may account for the absence of detrimental effects of HHcy on hemodynamics.

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 dysfunction, 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 concerning 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 function can be attributed to modification of ADMA levels. To develop more specific ADMA-lowering therapies, mechanisms leading to elevation of plasma ADMA concentrations 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 degradation 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.

Acute effect of folic acid, betaine, and serine supplements on flow-mediated dilation after methionine loading: a randomized trial

OBJECTIVES

We investigated whether reducing post-methionine homocysteine concentrations via various treatments other than folic acid affects vascular function, as measured through flow-mediated dilation (FMD) of the brachial artery. High fasting and post-methionine homocysteine concentrations are associated with cardiovascular disease risk, but homocysteine might be a surrogate marker for low folate status.

DESIGN

This was a randomized, placebo-controlled, double-blind, crossover study.

SETTING

The study took place at Wageningen University in Wageningen in the Netherlands.

PARTICIPANTS

Participants were 39 apparently healthy men and women, aged 50-70 y.

INTERVENTIONS

Participants ingested 10 mg of folic acid, 3 g of betaine, 5 g of serine, and placebo together with an oral methionine load. Each supplement was tested on two different days.

OUTCOME MEASURES

On each of the eight treatment days, plasma homocysteine concentrations and FMD were measured before (t = 0 h, fasting) and 6 h (t = 6 h) after methionine loading.

RESULTS

The mean (+/- SD) fasting homocysteine concentrations averaged over the eight test days were 9.6 +/- 2.1 micromol/l. Mean fasting FMD was 3.1 +/- 2.4 FMD%. A methionine load with placebo increased homocysteine concentrations by 17.2 +/- 9.3 micromol/l at 6 h after loading, similar to the increase following methionine loading with folic acid. A methionine load together with betaine and with serine increased homocysteine by 10.4 +/- 2.8 micromol/l (p < 0.001 relative to placebo) and by 12.1 +/- 8.2 micromol/l (p < 0.001 relative to placebo), respectively. Methionine loading with placebo did not affect FMD, and neither did methionine loading with folic acid, betaine, or serine; differences relative to placebo were +0.7 FMD% (95%CI, -0.6; 1.9), +0.2 FMD% (-1.0; 1.3), and +0.3 FMD% (-0.8; 1.4), respectively.

CONCLUSIONS

Experimentally induced acute changes in homocysteine concentrations did not affect FMD in healthy volunteers. This implies that potential adverse effects of high homocysteine concentrations on the cardiovascular system are not mediated through vascular function. However, homocysteine or folate may affect cardiovascular disease risk through other mechanisms.

Oral, more than transdermal, oestrogen therapy lowers asymmetric dimethylarginine in healthy postmenopausal women: a randomized, placebo-controlled study

OBJECTIVE

To compare the effects of oral and transdermal hormone therapy (HT) on asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, in postmenopausal women.

DESIGN

In a multicentre, placebo-controlled, double-blind study, 152 hysterectomized healthy women were randomized to receive daily transdermal 17beta-oestradiol (tE2, n = 33), or oral micronized 17beta-oestradiol either unopposed (oE2, n = 37), or continuous combined with gestodene (oE2 + G, n = 33), or placebo (n = 49) for 13, 28-day treatment cycles. Plasma concentrations of ADMA, arginine and symmetric dimethylarginine (SDMA) were measured at baseline and in treatment cycles 4 and 13 with a high-performance liquid chromatography method.

RESULTS

After 13 cycles all active treatment groups showed a significant reduction in ADMA compared with placebo: tE2, -4.0% (95% CI: -7.5 to -0.6%); oE2, -7.7% (95% CI: -10.9 to -4.4%) and oE2 + G, -7.5% (95% CI: -10.8 to -4.3%). ancova showed a significantly larger reduction in the oral groups compared with the transdermal group (tE2 vs. oE2 and tE2 vs. oE2 + G, both P < 0.01). Oral, but not transdermal treatment, significantly reduced arginine compared with placebo. All active treatments reduced SDMA; however, this was only statistically significant in the oE2 group.

CONCLUSION

Reduction of ADMA was more pronounced after oral than after tE2 administration. Adding gestodene to oral 17beta-oestradiol did not alter the reduction of ADMA. The clinical implications of these findings remain uncertain; however, the decrease of ADMA by 17beta-oestradiol could be a key phenomenon in the modulation of nitric oxide synthesis by postmenopausal HT.

Asymmetric dimethylarginine in homocystinuria due to cystathionine beta-synthase deficiency: relevance of renal function

OBJECTIVE

Vascular disease is associated with increased plasma asymmetric dimethylarginine (ADMA) and homocysteine, and both are increased in renal failure. In cystathionine beta-synthase deficiency (CBS) there is severe hyperhomocysteinaemia, precocious vascular disease, and endothelial dysfunction. We investigated whether ADMA levels are elevated in CBS patients with and without renal impairment, and whether lowering plasma homocysteine also lowers ADMA.

METHODS

We measured plasma homocysteine, arginine, asymmetric and symmetric dimethylarginines, nitrate + nitrite, creatinine and cystatin C in 23 CBS-deficient patients and 24 age-matched controls.

RESULTS

In the patients, nitrate + nitrite and the ratio L: -arginine/ADMA were markedly reduced (21.6 +/- 6.1 vs 57.7 +/- 7.5 micromol/L and 132.9 +/- 24.7 vs 181.9 +/- 56.1, respectively, p < 0.001 for both), reflecting endothelial dysfunction. Plasma ADMA for the group was moderately increased (0.55 +/- 0.08 vs 0.49 +/- 0.07 micromol/L, p = 0.018), but this was due to significantly higher levels than controls in only those 7 of the 23 patients who had elevated cystatin C levels (0.59 +/- 0.08 vs 0.49 +/- 0.07 mg/L, p = 0.007). Posttreatment total homocysteine in patients varied widely (15-285, median 92 micromol/L), but was not correlated with ADMA or other measured variables. In three newly-diagnosed patients, marked reduction of total homocysteine during treatment produced minimal changes in ADMA.

CONCLUSIONS

ADMA levels were significantly increased only in the CBS-deficient patients with elevated cystatin C levels, and not in those with normal renal function. The reported relationship between hyperhomocysteinaemia and ADMA may not be direct, but could be secondary to reduced renal function.

Measurement of asymmetric dimethylarginine in plasma: methodological considerations and clinical relevance

Asymmetric dimethylarginine (ADMA) is a potent inhibitor of nitric oxide synthase and is regarded as a novel risk factor for cardiovascular disease. The metabolic pathways of ADMA and homocysteine are strongly intertwined. First, during synthesis of ADMA, two equivalents of homocysteine are formed. Second, homocysteine has been shown to inhibit the ADMA-degrading enzyme dimethylarginine dimethylaminohydrolase. Finally, homocysteine, either directly or by increasing oxidative stress, may promote release of free ADMA by accelerating protein degradation. Currently used techniques for the quantification of ADMA in plasma are mostly based on liquid chromatography with fluorimetric or mass spectrometric detection. Plasma ADMA has a very narrow concentration distribution, with an inter-individual coefficient of variation of approximately 12%, and even slightly elevated ADMA concentrations are associated with increased cardiovascular disease risk. Therefore, to generate useful results in clinical research, high precision of the assay used for the quantification of ADMA assay is a matter of prime importance. Assays with a high coefficient of variation may lead to low statistical power in clinical trials and to a severe underestimation of the strength of associations in epidemiological studies.

Hyperhomocysteinemia in Children Treated with Antiepileptic Drugs Is Normalized by Folic Acid Supplementation

PURPOSE

To assess the prevalence of hyperhomocysteinemia in pediatric patients treated with antiepileptic drugs (AEDs) and to evaluate the effect of folic acid supplementation on plasma total homocysteine (tHcy) concentrations in hyperhomocysteinemic patients.

METHODS

123 patients from three regional hospitals participated in the study. Patients with hyperhomocysteinemia were included in a 3-month double-blind randomized trial testing oral folic acid supplementation (1 mg/day) versus placebo.

RESULTS

Hyperhomocysteinemia (tHcy >10.4 micromol/L) was present in 19 of 123 patients. Patients with hyperhomocysteinemia were older (13.7 +/- 4 vs. 11.0 +/- 3.9 years) and had significantly lower folate and cobalamin concentrations. Multidrug (two or more) AED treatment and duration of therapy correlated significantly with elevated total homocysteine (tHcy) and low folate. In contrast, polymorphisms in the methylene tetrahydrofolate reductase gene (MTHFR 677 C-->T, 1298 A-->C, 1793 G-->A) had no significant impact on tHcy. Nine of 19 patients with hyperhomocysteinemia were randomized to placebo, whereas the remaining 10 patients received folic acid supplementation. Folic acid supplementation resulted in a significant increase of folate and decrease of tHcy, whereas both parameters remained unchanged in the placebo group.

CONCLUSIONS

Hyperhomocysteinemia is present in 15.5% of children receiving long-term AED treatment. Multidrug treatment and long duration of therapy enhance the risk for hyperhomocysteinemia. Folic acid supplementation significantly reduces tHcy. We recommend assessment of serum folate and plasma tHcy in children receiving AEDs.