Asymmetric dimethylarginine and the effect of folate substitution in children with familial hypercholesterolemia and diabetes mellitus type 1

A recently discussed cardiovascular risk factor, asymmetric dimethylarginine (ADMA), is known to act as an endogenous inhibitor of endothelial nitric oxide synthase. The aim of this study was to establish 1) the relationship between ADMA and ultrasonographically or biochemically determined endothelial dysfunction in children, and 2) the effect of folate supplementation on these parameters. The study cohort included 32 children with familial hypercholesterolemia (FH), 30 with diabetes mellitus type 1 (DM1) and 30 age-matched healthy children as the control group. Furthermore, twenty-eight randomly selected FH and DM1 children were re-examined after 3-months supplementation with folic acid. Baseline levels of ADMA and oxidized low density lipoproteins (oxLDL) were significantly higher in FH group than in DM1 and healthy children. Children in DM1 group had significantly lower concentration of homocysteine, but ADMA levels were normal. Folic acid supplementation significantly lowered homocysteine and hsCRP levels in both FH and DM1 group; however, ADMA and oxLDL concentrations remained unaltered. In conclusion, ADMA and oxLDL appear to be associated with endothelial dysfunction in children with FH. Administration of folic acid did not influence these markers in both FH and DM1 children.     

Asymmetric dimethylarginine is not involved in ovariectomy-induced osteopenia in rats

Previous studies have indicated that the plasma concentration of nitric oxide synthase inhibitor, asymmetric dimethylarginine (ADMA), was increased in postmenopausal women. In the study reported here, we tested the relationship between the decrease of bone mineral density (BMD) and ADMA concentration in ovariectomized (OVX) rats. Ovariectomized rats at 8 months of age were treated with 17beta-estradiol (10 or 30 microg/kg of body weight/day, s.c.) or L-arginine (300 mg/kg/day, i.p.) for 12 weeks (n = 10 for each group). Pre- and posttreatment total BMD, posttreatment plasma nitrite/nitrate and ADMA concentrations, and posttreatment BMD in the lumbar part of the spine (L4-L6), femurs, and tibias were examined. Ovariectomy caused a significant decrease in several BMD indexes, which was reversed by estrogen treatment (P < 0.05). Plasma nitrite/nitrate concentration was significantly decreased in OVX rats, but was restored by estrogen treatment (P < 0.05). There were no differences in the plasma concentration of ADMA in OVX or estrogen-treated rats. L-Arginine had no effect on plasma nitrite/nitrate concentration and BMD in OVX rats. These results suggest that ovariectomy does not influence the plasma concentration of ADMA, and that ADMA is not involved in ovariectomy-induced osteopenia in rats.     

Asymmetric dimethylarginine: metabolism, arginine paradox, pathophysiology

Pathophysiology of asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of NO synthase, has been a subject of intensive research activity during last years. The ways of ADMA synthesis and degradation were studied. It was suggested that ADMA plays a considerable role in the realization of so called "Arginine paradox". This paradox refers to the dependence of cellular NO production on exogenous L-arginine despite the saturation of NOS enzymes with intracellular L-arginine. Close association was described between increase in blood ADMA level and endothelial dysfunction accompanied by related pathologies like atherosclerosis, renal insufficiency, hypertension and some others. Some studies have represented ADMA as a strong independent risk factor for cardiovascular complications. Possible reasons are discussed of some experimental data ambiguity as well as the limits of confidence in clinical ADMA analysis.     

Asymmetric dimethylarginine, endothelial nitric oxide bioavailability and mortality in sepsis

Background

Plasma concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, are raised in patients with chronic vascular disease, causing increased cardiovascular risk and endothelial dysfunction, but the role of ADMA in acute inflammatory states is less well defined.

Methods and Results

In a prospective longitudinal study in 67 patients with acute sepsis and 31 controls, digital microvascular reactivity was measured by peripheral arterial tonometry and blood was collected at baseline and 2–4 days later. Plasma ADMA and L-arginine concentrations were determined by high performance liquid chromatography. Baseline plasma L-arginine: ADMA ratio was significantly lower in sepsis patients (median [IQR] 63 [45–103]) than in hospital controls (143 [123–166], p<0.0001) and correlated with microvascular reactivity (r = 0.34, R² = 0.12, p = 0.02). Baseline plasma ADMA was independently associated with 28-day mortality (Odds ratio [95% CI] for death in those in the highest quartile (≥0.66 µmol/L) = 20.8 [2.2–195.0], p = 0.008), and was independently correlated with severity of organ failure. Increase in ADMA over time correlated with increase in organ failure and decrease in microvascular reactivity.

Conclusions

Impaired endothelial and microvascular function due to decreased endothelial NO bioavailability is a potential mechanism linking increased plasma ADMA with organ failure and death in sepsis.     

Plasma molybdenum concentrations in children with and without phenylketonuria

Plasma molybdenum concentrations were determined in children, ages two to 12 yr, with and without phenylketonuria (PKU). Mean plasma molybdenum concentrations did not differ significantly between the children with PKU (1.33±0.5 μg/L) and without PKU (1.75±0.8 μg/L). Plasma molybdenum concentrations in both groups of children ranged from <1 to 3 μg/L. When data from all children were combined and then separated based on gender, mean plasma molybdenum levels did not differ significantly between 9 females (1.56±0.68 μg/L) and 12 males (1.58±0.76 μg/L). Data were also combined and mean (±SD) plasma molybdenum concentrations calculated for age groups. Two children aged 1 to <4 yr had plasma molybdenum concentrations of 1.0 μg/L, and six children aged 4 to <7 yr had mean (±SD) plasma molybdenum concentrations of 1.5±0.8 μg/L. Eleven children aged 7 to <11 yr had a mean plasma molybdenum concentration of 1.7±0.7 μg/L, and two children 11 to <14 yr had plasma molybdenum concentrations of 1 μg/L and 2 μg/L. Plasma molybdenum concentrations did not differ significantly among children in the age groups.     

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

Patients with type 2 diabetes are at a high risk for acute cardiovascular events, which usually arise from the rupture of a vulnerable coronary lesion characterized by specific morphological plaque features. Thus, the identification of vulnerable plaques is of utmost clinical importance in patients with type 2 diabetes. However, there is currently no scoring system available to identify vulnerable lesions based on plaque characteristics. Thus, we aimed to characterize the diagnostic value of optical coherence tomography (OCT) - derived lesion characteristics to quantify plaque vulnerability both as individual parameters and when combined to a score in patients with type 2 diabetes. OCT was performed in the coronary culprit lesions of 112 patients with type 2 diabetes. The score, which quantifies plaque vulnerability, was defined as the predicted probability that a lesion is the cause for an acute coronary syndrome (ACS) (vs. stable angina (SAP)) based on its specific plaque morphology. Multivariable logistic regression analysis demonstrated that plaque vulnerability was independently predicted by the minimal fibrous cap thickness overlying a lesion’s lipid core (odds ratio (OR) per 10 μm 0.478, p = 0.002), the medium lipid arc (OR per 90° 13.997, p < 0.001), the presence of macrophages (OR 4.797, p = 0.015) and the lipid plaque length (OR 1.290, p = 0.098). Receiver-operating-characteristics (ROC) analyses demonstrated that these parameters combined to a score demonstrate an excellent diagnostic efficiency to identify culprit lesions of patients with ACS (vs. SAP, AUC 0.90, 95% CI 0.84-0.96). This is the first study to present a score to quantify lesion vulnerability in patients with type 2 diabetes. This score may be a valuable adjunct in decision-making and useful in guiding coronary interventions.     

Asymmetric dimethylarginine, oxidative stress, and vascular nitric oxide synthase in essential hypertension

We reported impaired endothelium-derived relaxation factor/nitric oxide (EDRF/NO) responses and constitutive nitric oxide synthase (cNOS) activity in subcutaneous vessels dissected from patients with essential hypertension (n = 9) compared with normal controls (n = 10). We now test the hypothesis that the patients in this study have increased circulating levels of the cNOS inhibitor, asymmetric dimethylarginine (ADMA), or the lipid peroxidation product of linoleic acid, 13-hydroxyoctadecadienoic acid (HODE), which is a marker of reactive oxygen species. Patients had significantly (P < 0.001) elevated (means +/- SD) plasma levels of ADMA (P(ADMA), 766 +/- 217 vs. 393 +/- 57 nmol/l) and symmetric dimethylarginine (P(SDMA): 644 +/- 140 vs. 399 +/- 70 nmol/l) but similar levels of L-arginine accompanied by significantly (P < 0.015) increased rates of renal ADMA excretion (21 +/- 9 vs. 14 +/- 5 nmol/mumol creatinine) and decreased rates of renal ADMA clearance (18 +/- 3 vs. 28 +/- 5 ml/min). They had significantly increased plasma levels of HODE (P(HODE): 309 +/- 30 vs. 226 +/- 24 nmol/l) and renal HODE excretion (433 +/- 93 vs. 299 +/- 67 nmol/micromol creatinine). For the combined group of normal and hypertensive subjects, the individual values for plasma levels of ADMA and HODE were both significantly (P < 0.001) and inversely correlated with microvascular EDRF/NO and positively correlated with mean blood pressure. In conclusion, elevated levels of ADMA and oxidative stress in a group of hypertensive patients could contribute to the associated microvascular endothelial dysfunction and elevated blood pressure.     

Asymmetric dimethylarginine, an endogenous NOS inhibitor, is actively metabolized in rat erythrocytes

N(G), N(G)-Dimethyl-L-arginine (asymmetric dimethylarginine: ADMA) is an endogenous competitive inhibitor of nitric oxide synthase (NOS). Plasma ADMA concentrations have been reported to increase in connection with diseases associated with an impaired endothelial L-arginine/NO pathway. In this study, we investigated the metabolism of ADMA in circulating blood cell populations to elucidate the regulatory mechanism of elevation of plasma ADMA, a novel risk factor for cardiovascular disease. We found by RT-PCR and Western blot analyses that protein arginine methyltransferase (PRMT)1 and dimethylarginine dimethylaminohydrolase (DDAH)-1, responsible for the biosynthesis and degradation of ADMA respectively, are expressed in erythrocytes (ECs), leukocytes, and platelets. We also identified a major ADMA-containing protein in ECs as catalase, confirmed by GST-pull down assay to bind to PRMT1 in vitro. This is the first report that the ADMA-metabolizing system, including the arginine methylation of proteins and the breakdown of free ADMA, occurs in circulating blood cell-populations, and that catalase in ECs might be a potential protein targeted by PRMT1.     

Asymmetric division in mouse oocytes: with or without Mos

In both vertebrates and invertebrates, meiotic divisions in oocytes are typically asymmetric, resulting in the formation of a large oocyte and small polar bodies. The size difference between the daughter cells is usually a consequence of asymmetric positioning of the spindle before cytokinesis. Spindle movements are often related to interactions between the cell cortex and the spindle asters [1,2]. The spindles of mammalian oocytes are, however, typically devoid of astral microtubules, which normally connect the spindle to the cortex, suggesting that another mechanism is responsible for the unequal divisions in these oocytes. We observed the formation of the first polar body in wild-type oocytes and oocytes derived from c-Mos knockout mice [3]. In wild-type oocytes, the meiotic spindle formed in the centre of the cell and migrated to the cortex just before polar-body extrusion. The spindle did not elongate during anaphase. In mos-/- oocytes, the spindle formed centrally but did not migrate, although an asymmetric division still took place. In these oocytes, the spindle elongated during anaphase and the pole closest to the cortex moved while the other remained in place. Thus, a compensation mechanism exists in mouse oocytes and formation of the first polar body can be achieved in two ways: either after migration of the spindle to the cortex in wild-type oocytes, or after elongation, without migration, of the first meiotic spindle in mos-/- oocytes.     

High clinical accuracy of asymmetric dimethylarginine and symmetric dimethylarginine in patients with ischemic heart disease

Elevated plasma concentrations of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) were found in various clinical settings including coronary heart disease. To assess ADMA and SDMA diagnostic validity in patients with different stages of ischemic heart disease, we studied these markers in patients having stable angina pectoris (SAP), unstable angina (USAP), and acute myocardial infarction (AMI). The results were compared with the values of healthy individuals. Plasma ADMA and SDMA levels were measured by high-performance liquid chromatography. In all patient groups both markers were significantly elevated in comparison with control ones (p?<?0.001). In SAP patients, the median ADMA value was 0.75 (0.31–2.73)?μmol/L, and SDMA 1.11 (0.69–0.1.42)?μmol/L, in USAP patients, the marker values were 0.94 (0.34–3.13)?μmol/L and 1.23 (0.88–4.72)?μmol/L, and in AMI patients, 0.98 (0.48–2.01)?μmol/L and 1.26 (0.75–2.93)?μmol/L, while in healthy subjects they were 0.31 (0.17–0.87)?μmol/L and 0.29 (0.20–0.83)?μmol/L, respectively. SDMA was found significantly different in SAP and AMI patients (p?<?0.05). Diagnostic accuracy was determined by receiver operating characteristic (ROC) curve analysis. The highest area under the ROC (AUC) for ADMA was obtained in AMI patients (0.976), while for SDMA in USAP patients (1.000). There was no significant difference between the AUCs. The greatest sensitivity and specificity were found in the USAP group (95.65 and 96.30?% for ADMA, and 100?% for each characteristic of SDMA). Considering these results, SDMA showed better clinical accuracy in assessing ischemic disease, where it could be used as a valid marker and a therapeutic target.     

Effect of stopping low-phenylalanine diet on intellectual progress of children with phenylketonuria.

Forty-seven patients at the Hospital for Sick Children, London, who had phenylketonuria and were on a low-phenylalanine diet (21 early-treated--that is, treatment started before the age of 4 months--and 26 late-treated) were placed on a normal diet between the ages of 5 and 15 years. They showed significant falls in mean IQ of about six points after the diet was withdrawn. Twenty-two similar patients (five early-treated and 17 late-treated) at the Universitäts-Kinderklinik, Heidelberg, who were placed on a relaxed low-phenylalanine rather than a normal diet, showed smaller and non-significant falls in mean IQ. During the period of strict diet none of the patients in London or Heidelberg showed any consistent falls in IQ. These results suggest that complete withdrawal of the low-phenylalanine diet during childhood leads to a fall in intellectual progress in many patients.     

Oxidative stress in patients with phenylketonuria

Phenylketonuria (PKU) is an autossomal recessive disease caused by phenylalanine-4-hydroxylase deficiency, which is a liver-specific enzyme that catalyzes the hydroxylation of l-phenylalanine (Phe) to l-tyrosine (Tyr). The deficiency of this enzyme leads to the accumulation of Phe in the tissues and plasma of patients. The clinical characterization of this disease is mental retardation and other neurological features. The mechanisms of brain damage are poorly understood. Oxidative stress is observed in some inborn errors of intermediary metabolism owing to the accumulation of toxic metabolites leading to excessive free radical production and may be a result of restricted diets on the antioxidant status. In the present study we evaluated various oxidative stress parameters, namely thiobarbituric acid-reactive species (TBA-RS) and total antioxidant reactivity (TAR) in the plasma of PKU patients. The activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were also measured in erythrocytes from these patients. It was observed that phenylketonuric patients present a significant increase of plasma TBA-RS measurement, indicating a stimulation of lipoperoxidation, as well as a decrease of plasma TAR, reflecting a deficient capacity to rapidly handle an increase of reactive species. The results also showed a decrease of erythrocyte GSH-Px activity. Therefore, it is presumed that oxidative stress is involved in the pathophysiology of the tissue damage found in PKU.     

Defective DNA excision repair in cells of patients with homocystinuria

Fibroblasts obtained from biopsied material and lymphocytes from patients with homocystinuria were studied for repair activity using the criterion of repair of DNA breaks induced by 4-nitroquinoline 1-oxide and gamma-irradiation and criteria of reactivation and induced mutagenesis of vaccinia virus. Lymphocytes showed defective DNA repair for all these criteria. In fibroblast cultures, the inhibition of cell-repair activity for the gamma-type was retained. The number of spontaneous and gamma-induced virus mutations increased as passaging of fibroblasts proceeded.