Asymmetric dimethylarginine (ADMA): the silent transition from an 'uraemic toxin' to a global cardiovascular risk molecule

Effect of advanced periodontal self-care in patients with early-stage periodontal diseases on endothelial function: An open-label, randomized controlled trial

Although a significant association between periodontal disease and atherosclerotic cardiovascular disease has been reported, their cause-to-effect relationship remains controversial. This randomized controlled clinical trial aimed to investigate the effect of advanced self-care on atherosclerotic cardiovascular disease-related vascular function markers flow-mediated brachial artery dilatation (FMD) and serum asymmetric dimethylarginine (ADMA) level in patients with early-stage periodontal disease. The study was designed as a parallel group, 3-month follow-up, open-label, randomized controlled trial. The control group received standard care for periodontal diseases, whereas the test group additionally applied disinfectant using a custom-fabricated prescription tray for advanced self-care twice a day. Overall, 110 patients provided data for FMD and serum ADMA level. No significant improvements in FMD were observed in the control (mean increase, −0.1%; 95% confidence interval [CI], −1.0–0.8; P = 0.805) or test (mean increase, −0.3%; 95% CI, −1.1–0.4; P = 0.398) group. No significant changes in serum ADMA levels were observed (mean reduction, 0.01 μmol/L; 95% CI, −0.00–0.02; P = 0.366 and mean reduction, 0.00 μmol/L; 95% CI, −0.01–0.01; P = 0.349, respectively). No significant between-group differences were found in FMD (mean difference, −0.2%; 95% CI, −1.4–0.9; p = 0.708) or serum ADMA levels (mean difference, 0.01 nmol/L; 95% CI, −0.00–0.03; p = 0.122). Significant improvements in the average probing pocket depth were observed in the control and test groups. The bleeding on probing score in the test group was significantly reduced, while that in the control group was reduced, although not significantly. Periodontal care for a 3-month duration did not provide better endothelial function although improvements of periodontal status in patients with early-stage periodontal diseases. This trial is registered in UMIN Clinical Trials Registry (www.umin.ac.jp/ctr/; ID: UMIN000023395).

Cardioprotective properties of leptin in patients with excessive body mass

Background

Adipose tissue is producing adipokines that play different roles in the pathophysiology of cardiovascular disease.

Aims

The study aimed to assess the role of selected biomarkers in hypertensive patients with overweight and obesity compared with those with normal body-mass index (BMI).

Methods

A total of 62 patients with BMI < 25 kg/m² (median age 54 (46–58) yrs., 57% males) and 51 with BMI ≥ 25 kg/m² (median age 53 (48–59) yrs., 37% males) were enrolled. Biochemical parameters, leptin, adiponectin, and resistin; asymmetric dimethylarginine; interleukin 6; and N-terminal propeptide of type III procollagen, were assessed in plasma. The evaluation of hemodynamic parameters was performed using SphygmoCor 9.0 tonometer. Echocardiography was performed using AlokaAlpha 10 Premier device.

Results

Overweight and obese patients had significantly higher concentration of leptin (34 vs 18 ng/ml; p = 0.03), ADMA (0.43 vs 0.38 μmol/l, p = 0.04), and lower concentration of adiponectin (5.3 vs 7 μg/ml, p = 0.01). The only significant difference in tonometry analysis was higher aortic pulse pressure (mmHg) in patients with BMI ≥ 25 kg/m² group (34 vs 30; p = 0.03). These patients had also significantly lower peak systolic velocity and early diastolic velocity in tissue Doppler imaging of the right ventricle free wall at the level of the tricuspid annulus compared with controls (p = 0.02 and p = 0.001, respectively). The level of leptin is correlated negatively with the left ventricular mass index (LVMI) (R Spearman = − 0.5; p = 0.002) and PWV (R = − 0.4; p = 0.01) and ADMA with total and LDL cholesterol (R = − 0.42; p = 0.008), and adiponectin is correlated positively with HDL cholesterol (R = 0.67; p = 0.0001).

Conclusions

Leptin concentrations were inversely proportional to LVMI and PWV in patients with BMI < 25 kg/m².

Trial registration

Clinicaltrials.gov study ID: NCT04175080.

Concentrations of representative uraemic toxins in a healthy versus non-dialysis chronic kidney disease paediatric population

Background

Chronic kidney disease (CKD) in childhood is poorly explained by routine markers (e.g. urea and creatinine) and is better depicted in adults by other uraemic toxins. This study describes concentrations of representative uraemic toxins in non-dialysis CKD versus healthy children.

Methods

In 50 healthy children and 57 children with CKD Stages 1-5 [median estimated glomerular filtration rate 48 (25th-75th percentile 24-71) mL/min/1.73 m2; none on dialysis], serum concentrations of small solutes [symmetric and asymmetric dimethyl-arginine (SDMA and ADMA, respectively)], middle molecules [β2-microglobuline (β2M), complement factor D (CfD)] and protein-bound solutes [p-cresylglucuronide (pCG), hippuric acid (HA), indole-acetic acid (IAA), indoxyl sulphate (IxS), p-cresyl sulphate (pCS) and 3-carboxy-4-methyl-5-propyl-furanpropionic acid (CMPF)] were measured. Concentrations in the CKD group were expressed as z-score relative to controls and matched for age and gender.

Results

SDMA, CfD, β2M, IxS, pCS, IAA, CMPF and HA concentrations were higher in the overall CKD group compared with controls, ranging from 1.7 standard deviations (SD) for IAA and HA to 11.1 SD for SDMA. SDMA, CfD, β2M, IxS and CMPF in CKD Stages 1-2 with concentrations 4.8, 2.8, 4.5, 1.9 and 1.6 SD higher, respectively. In contrast, pCS, pCG and IAA concentrations were only higher than controls from CKD Stages 3-4 onwards, but only in CKD Stage 5 for ADMA and HA (z-score 2.6 and 20.2, respectively).

Conclusions

This is the first study to establish reference values for a wide range of uraemic toxins in non-dialysis CKD and healthy children. We observed an accumulation of multiple uraemic toxins, each with a particular retention profile according to the different CKD stages.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

Symmetric dimethylarginine, high-density lipoproteins and cardiovascular disease

Aims

The vascular effects of high-density lipoproteins (HDL) differ under certain clinical conditions. The composition of HDL is modified in patients with chronic kidney disease (CKD). As a consequence, uremic HDL induces endothelial dysfunction. We have previously shown that accumulation of symmetric dimethylarginine (SDMA) in HDL causes these adverse effects of HDL in CKD. The aim of the study is to determine the impact of the accumulation of SDMA on the association between HDL and mortality.

Methods and results

Mortality, renal function, serum SDMA and HDL-cholesterol (HDL-C) were assessed in the LURIC study including 3310 subjects undergoing coronary angiography. All-cause mortality was 30.0% during median follow-up of 9.9 years. Serum SDMA levels significantly predicted all-cause and cardiovascular mortality, and were significantly correlated with SDMA accumulation in HDL. Notably, higher serum SDMA was independently associated with lower cholesterol efflux (P = 0.004) as a measure of HDL functionality. In subjects with low SDMA levels, higher HDL-C was associated with significantly lower mortality. In contrast, in subjects with high SDMA, HDL-C was associated with higher mortality. These findings were confirmed in 1424 participants of the MONICA/KORA S3 cohort. Of note, we derived an algorithm allowing for calculation of biologically effective HDL-C' based on measured HDL-C and SDMA. We corroborated these clinical findings with invitro evidence showing that SDMA accumulation abolishes the anti-inflammatory and regenerative properties of HDL.

Conclusion

The data identify SDMA as a marker of HDL dysfunction. These findings highlight on the pivotal role of SDMA accumulation in HDL as a mediator of pre-mature cardiovascular disease in patients with CKD.

Accumulation of uraemic toxins is reflected only partially by estimated GFR in paediatric patients with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) in childhood is characterised by the accumulation of uraemic toxins resulting in a multisystem disorder that has a negative impact on quality of life. Childhood CKD is predominantly defined by a decrease in glomerular filtration rate, estimated (eGFR) by a single serum measurement of endogenous biomarkers, e.g. creatinine. The objective of this study was to evaluate how accurately eGFR predicts the concentration of uraemic toxins in a paediatric CKD cohort.

METHODS

In 65 children (10.8 [5.1; 14.7] years) with CKD (eGFR 44 [20; 64] mL/min/1.73 m²), serum concentrations were determined of small solutes (uric acid [UA], urea, symmetric dimethylarginine [SDMA], asymmetric dimethylarginine [ADMA]), middle molecules (β2-microglobulin [β2M], complement factor D [CfD]) and protein-bound solutes (p-cresylglucuronide [pCG], hippuric acid, indole acetic acid, indoxyl sulphate [IxS], p-cresylsulfate [pCS] and 3-carboxy-4-methyl-5-propyl-furanpropionic acid [CMPF]). Spearman's correlation coefficients (r) were calculated to correlate uraemic toxin concentrations with three different eGFR equations, based on either serum creatinine or β2M.

RESULTS

Updated Schwartz eGFR was correlated reasonably well with concentrations of creatinine (r = -0.98), urea (r_s = -0.84), SDMA (r = -0.82) and middle molecules CfD and β2M (both r_s = -0.90). In contrast, poor correlation coefficients were found for CMPF (r_s = -0.32), UA (r_s = -0.45), ADMA (r_s = -0.47) and pCG (r_s = -0.48). The other toxins, all protein-bound, had r_s between -0.75 and -0.57. Comparable correlations were found between the three evaluated eGFR equations and uraemic toxin concentrations.

CONCLUSIONS

This study demonstrates that eGFR poorly predicts concentrations of protein-bound uraemic toxins, UA and ADMA in childhood CKD. Therefore, eGFR only partially reflects the complexity of the accumulation pattern of uraemic toxins in childhood CKD.

Increased circulating resistin is associated with insulin resistance, oxidative stress and platelet activation in type 2 diabetes mellitus

Resistin is an adipokine that promotes inflammation and insulin resistance by targeting several cells including platelets. We hypothesised that in type 2 diabetes (T2DM), resistin may foster in vivo oxidative stress, thromboxane-dependent platelet activation and platelet-derived inflammatory proteins release, key determinants of atherothrombosis. A cross-sectional comparison of circulating resistin, sCD40L, as a marker of platelet-mediated inflammation, asymmetric dimethylarginine (ADMA), endothelial dysfunction marker, Dickkopf (DKK)-1, reflecting the inflammatory interaction between platelets and endothelial cells, and urinary 8-iso-PGF_2α and 11-dehydro-TxB₂, reflecting in vivo lipid peroxidation and platelet activation, respectively, was performed between 79 T2DM patients and 30 healthy subjects. Furthermore, we investigated the effects of the α-glucosidase inhibitor acarbose and the PPARγ agonist rosiglitazone, targeting hyperglycaemia or insulin resistance, versus placebo, in 28 and 18 T2DM subjects, respectively. Age- and gender-adjusted serum resistin levels were significantly higher in patients than in controls. HOMA (β=0.266, p=0.017) and 11-dehydro-TXB₂ (β=0.354, p=0.002) independently predicted resistin levels. A 20-week treatment with acarbose was associated with significant reductions (p=0.001) in serum resistin, DKK-1, urinary 11-dehydro-TXB₂ and 8-iso-PGF_2α with direct correlations between the change in serum resistin and in other variables. A 24-week rosiglitazone treatment on top of metformin was associated with significant decreases in resistin, DKK-1, 11-dehydro-TXB₂ and 8-iso-PGF_2α, in parallel with HOMA decrease. In conclusion, resistin, antagonising insulin action in part through PPARγ activation, may favour insulin resistance and enhance oxidative stress, endothelial dysfunction and platelet activation. The adipokine-platelet interactions may be involved in platelet insulin resistance and their consequent pro-aggregatory phenotype in this setting.

Asymmetric dimethyl-arginine and coronary artery calcification in young adults entering middle age: the CARDIA Study

BACKGROUND

Normal endothelial function depends on nitric oxide (NO) release by endothelial cells. Asymmetric dimethylarginine (ADMA), by competing with L-arginine, inhibits NO production and may lead to endothelial dysfunction and atherosclerotic development. Our aim was to ascertain the association between ADMA and coronary artery calcification (CAC), a marker of atherosclerotic coronary disease burden.

DESIGN

A nested case-control study within the Coronary Artery Risk Development in Young Adults (CARDIA) cohort, an observational study among young adults residing in four US cities.

METHODS

Participants were 263 white and black male and female cases with the presence of CAC and 263 sex and race-matched controls without evidence of CAC by computed tomography, 33-47 years old in 2000-2001.

RESULTS

The median level (range) of ADMA was significantly higher in cases (0.55; 0.20-2.22 micromol/l) than in controls (0.53; 0.32-1.30 micromol/l; P=0.03). In conditional logistic regression adjusting for age, field center, educational attainment, smoking status, alcohol consumption, body mass index, waist circumference, hypertension, diabetes, low-density lipoprotein and high-density lipoprotein-cholesterol, triglycerides, renal function and C-reactive protein, the highest tertile of ADMA, compared with the lowest tertile, was associated with 1.80 (95% confidence interval 1.03-3.15) increased odds of the presence of any CAC. By linear regression, a significant independent relationship was also found between ADMA and the degree of CAC.

CONCLUSION

These results support a role for ADMA as a biochemical marker of CAC.

Impact of Continuous Erythropoietin Receptor Activator on Selected Biomarkers of Cardiovascular Disease and Left Ventricle Structure and Function in Chronic Kidney Disease

Background. Cardiovascular morbidity and mortality are very high in patients with chronic kidney disease (CKD). The purpose of this study is to evaluate the impact of continuous erythropoietin receptor activator (CERA) on selected biomarkers of cardiovascular disease, left ventricle structure, and function in CKD. Material and Methods. Peripheral blood was collected from 25 CKD patients before and after CERA treatment and 20 healthy subjects. In serum samples, we assessed inflammatory markers (IL-1β, TNF-RI, TNF-RII, sFas, sFasL, MMP-9, TIMP-1, and TGF-β1), endothelial dysfunction markers (sE-selectin, sICAM-1, and sVCAM-1), and volume-related marker (NT-proBNP). All subjects underwent echocardiography and were evaluated for selected biochemical parameters (Hb, creatinine, and CRP). Results. Evaluated biomarkers and echocardiographic parameters of left ventricle structure were significantly increased but left ventricle EF was significantly decreased in CKD patients compared to controls. After CERA treatment, we observed a significant increase of Hb and left ventricle EF and a significant decrease of NT-proBNP and MMP-9. There was a significant negative correlation between Hb and TNF-RI, sICAM-1, and IL-1β. Conclusions. Our results indicate that selected biomarkers related to cardiovascular risk are significantly increased in CKD patients compared to controls. CERA treatment has anti-inflammatory action, diminishes endothelial dysfunction, and improves left ventricle function in these patients.

Metabolomic Profiling of Arginine Metabolome Links Altered Methylation to Chronic Kidney Disease Accelerated Atherosclerosis

Atherosclerotic cardiovascular disease is the leading cause of death in patients with chronic kidney disease (CKD), but the mechanisms underlying vascular disease has not been fully understood. As the nitrogen donor in nitric oxide (NO^·) synthesis, arginine and its metabolic products are integrally linked to vascular health and information. We hypothesized that derangements in this pathway could explain, in part, increased atherosclerotic risk in CKD. We developed a targeted metabolomic platform to profile quantitatively arginine metabolites in plasma by liquid chromatography tandem mass spectrometry (LC/MS). Male low-density lipoprotein receptor defcient (LDLr^−/−) mice at age 6 weeks were subjected to sham or 5/6 nephrectomy surgery to induce CKD. Subsequently, the animals were maintained on high fat diet for 24 weeks. Targeted metabolomic analysis of arginine metabolites in plasma was performed by isotope dilution LC/MS including asymmetric dimethyl arginine (ADMA), symmetric dimethyl arginine (SDMA), N-mono-methylarginine (NMMA), arginine and citrulline. Although elevated plasma levels of ADMA and SDMA were found in the CKD mice, only higher ADMA level correlated with degree of atherosclerosis. No significant differences were noted in levels of NMMA between the groups. CKD mice had high levels of citrulline and arginine, but ADMA levels had no correlation with either of these metabolites. These fndings strongly implicate altered arginine methylation and accumulation of ADMA, may in part contribute to CKD accelerated atherosclerosis. It raises the possibility that interrupting pathways that generate ADMA or enhance its metabolism may have therapeutic potential in mitigating atherosclerosis.

The role of asymmetric and symmetric dimethylarginine in acute deep vein thrombosis

BACKGROUND

In this study, we aimed to determine the importance of asymmetric dimethylarginine (ADMA), symmetric dimethyl arginine (SDMA), and l-arginine levels which are influenced by the endothelial dysfunction in acute deep vein thrombosis (DVT), and compare their pretreatment and post-treatment levels.

METHODS

A total of 34 cases (19 men and 15 women, age range 42 ± 14 years) diagnosed with acute DVT and 34 control subjects (22 men and 12 women, age range 45 ± 11 years) without any vascular disorders were included in the study. The patients were administered low-molecular-weight heparin subcutaneously. Blood samples were obtained to measure ADMA, SDMA, and arginine levels before treatment and during the treatment (on 10th day). ADMA, SDMA, and l-arginine levels were measured using high performance liquid chromatography method.

RESULTS

The ADMA and SDMA levels were significantly higher in acute DVT patients when compared with the controls (P = 0.001). Post-treatment decrease of ADMA and SDMA levels when compared with the pretreatment levels were found as statistically significant (P = 0.001). Increase in l-arginine levels were not found significant when compared with the control group (P = 0.12) or post-treatment levels (P = 0.16).

CONCLUSIONS

We concluded that ADMA and SDMA levels can be used as parameters in clinical follow-up for determining the efficacy of treatment in acute DVT patients, and further studies are needed to further clarify the subject.

Serum methylarginines and incident depression in a cohort of older adults

BACKGROUND

Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in depression. This study measured serum concentrations of l-arginine, asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in a representative sample of older community-dwelling adults and determined their association with incident depression over 6-years of follow-up.

METHODS

Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and l-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults (Median age=64 years; IQR=60-70) from the Hunter Community Study. Clinical depression was defined as a Centre for Epidemiological Studies Depression Scale (CES-D) score ≥16 or use of antidepressant medications.

RESULTS

In adjusted analyses ADMA (Q3), SDMA (Q2), l-arginine (Q2), gender, and asthma remained statistically significant predictors of incident depression at follow-up. Quartile 3 of ADMA concentration was associated with 3.5 times the odds of developing depression compared with Q1 (OR=3.54; 95% CI: 1.25-9.99).

LIMITATIONS

Limitations of our study include the use of a subjective self-reported questionnaire tool using a dichotomous cut-off, together with use of antidepressant medications, as proxies for clinical depression. Moreover, similarly to most population studies on methylated arginines, the measurement of ADMA and SDMA from blood does not necessarily reflect intracellular concentrations of these compounds. Finally, there were no measures of nitric oxide metabolites to determine if these levels were altered in the presence of elevated methylarginines and depression.

CONCLUSIONS

After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum ADMA was independently associated with incident depression at 6-years follow-up.

Evaluation of microvascular reactivity with laser Doppler flowmetry in chronic kidney disease

Cardiovascular diseases are the major causes of mortality in patients with chronic kidney disease (CKD). The complex process of accelerated athero- and arteriosclerosis in CKD is associated with this phenomenon, where endothelial dysfunction (ED) is one of the initial steps. Hence, the early diagnosis of ED can potentially lead to early interventions which could result in a better outcome for these patients. Several methodologies have been developed for the diagnosis of ED. Laser Doppler flowmetry (LDF) enables us to study the microcirculation continuously in a non-invasive manner. In our review we would like to focus on different tests developed for LDF, like postocclusive reactive hyperaemia, local heating, iontophoresis, microdialysis or analysis of flowmotion. We would also like to summarize the available data in CKD with these methodologies to enlighten their perspectives in the clinical use on this patient population.

Serum methylarginines and spirometry-measured lung function in older adults

Rationale

Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in animal models of lung disease but have not previously been examined for their association with spirometric measures of lung function in humans.

Objectives

This study measured serum concentrations of asymmetric and symmetric dimethylarginine in a representative sample of older community-dwelling adults and determined their association with spirometric lung function measures.

Methods

Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and L-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults from the Hunter Community Study. The five key lung function measures included as outcomes were Forced Expiratory Volume in 1 second, Forced Vital Capacity, Forced Expiratory Volume in 1 second to Forced Vital Capacity ratio, Percent Predicted Forced Expiratory Volume in 1 second, and Percent Predicted Forced Vital Capacity.

Measurements and Main Results

In adjusted analyses there were statistically significant independent associations between a) higher asymmetric dimethylarginine, lower Forced Expiratory Volume in 1 second and lower Forced Vital Capacity; and b) lower L-arginine/asymmetric dimethylarginine ratio, lower Forced Expiratory Volume in 1 second, lower Percent Predicted Forced Expiratory Volume in 1 second and lower Percent Predicted Forced Vital Capacity. By contrast, no significant associations were observed between symmetric dimethylarginine and lung function.

Conclusions

After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum asymmetric dimethylarginine was independently associated with a reduction in key measures of lung function. Further research is needed to determine if methylarginines predict the decline in lung function.

Nitric oxide and L-arginine metabolism in a devascularized porcine model of acute liver failure

In acute liver failure (ALF), the hyperdynamic circulation is believed to be the result of overproduction of nitric oxide (NO) in the splanchnic circulation. However, it has been suggested that arginine concentrations (the substrate for NO) are believed to be decreased, limiting substrate availability for NO production. To characterize the metabolic fate of arginine in early-phase ALF, we systematically assessed its interorgan transport and metabolism and measured the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) in a porcine model of ALF. Female adult pigs (23-30 kg) were randomized to sham (N = 8) or hepatic devascularization ALF (N = 8) procedure for 6 h. We measured plasma arginine, citrulline, ornithine levels; arginase activity, NO, and ADMA. Whole body metabolic rates and interorgan flux measurements were calculated using stable isotope-labeled amino acids. Plasma arginine decreased >85% of the basal level at t = 6 h (P < 0.001), whereas citrulline and ornithine progressively increased in ALF (P < 0.001 and P < 0.001, vs. sham respectively). No difference was found between the groups in the whole body rate of appearance of arginine or NO. However, ALF showed a significant increase in de novo arginine synthesis (P < 0.05). Interorgan data showed citrulline net intestinal production and renal consumption that was related to net renal production of arginine and ornithine. Both plasma arginase activity and plasma ADMA levels significantly increased in ALF (P < 0.001). In this model of early-phase ALF, arginine deficiency or higher ADMA levels do not limit whole body NO production. Arginine deficiency is caused by arginase-related arginine clearance in which arginine production is stimulated de novo.

Cerebral changes occurring in arginase and dimethylarginine dimethylaminohydrolase (DDAH) in a rat model of sleeping sickness

Background

Involvement of nitric oxide (NO) in the pathophysiology of human African trypanosomiasis (HAT) was analyzed in a HAT animal model (rat infected with Trypanosoma brucei brucei). With this model, it was previously reported that trypanosomes were capable of limiting trypanocidal properties carried by NO by decreasing its blood concentration. It was also observed that brain NO concentration, contrary to blood, increases throughout the infection process. The present approach analyses the brain impairments occurring in the regulations exerted by arginase and N^G, N^G–dimethylarginine dimethylaminohydrolase (DDAH) on NO Synthases (NOS). In this respect: (i) cerebral enzymatic activities, mRNA and protein expression of arginase and DDAH were determined; (ii) immunohistochemical distribution and morphometric parameters of cells expressing DDAH-1 and DDAH-2 isoforms were examined within the diencephalon; (iii) amino acid profiles relating to NOS/arginase/DDAH pathways were established.

Methodology/Principal Findings

Arginase and DDAH activities together with mRNA (RT-PCR) and protein (western-blot) expressions were determined in diencephalic brain structures of healthy or infected rats at various days post-infection (D5, D10, D16, D22). While arginase activity remained constant, that of DDAH increased at D10 (+65%) and D16 (+51%) in agreement with western-blot and amino acids data (liquid chromatography tandem-mass spectrometry). Only DDAH-2 isoform appeared to be up-regulated at the transcriptional level throughout the infection process. Immunohistochemical staining further revealed that DDAH-1 and DDAH-2 are contained within interneurons and neurons, respectively.

Conclusion/Significance

In the brain of infected animals, the lack of change observed in arginase activity indicates that polyamine production is not enhanced. Increases in DDAH-2 isoform may contribute to the overproduction of NO. These changes are at variance with those reported in the periphery. As a whole, the above processes may ensure additive protection against trypanosome entry into the brain, i.e., maintenance of NO trypanocidal pressure and limitation of polyamine production, necessary for trypanosome growth.

Characterization of C-alkyl amidines as bioavailable covalent reversible inhibitors of human DDAH-1

C-Alkyl amidine analogues of asymmetric N(ω),N(ω)-dimethyl-L-arginine are dual-targeted inhibitors of both human DDAH-1 and nitric oxide (NO) synthase, and provide a promising scaffold for the development of therapeutics to control NO overproduction in a variety of pathologies including septic shock and some cancers. Using a two-part click-chemistry-mediated activity probe, a homologated series of C-alkyl amidines were ranked for their ability to inhibit DDAH-1 within cultured HEK 293T cells. N⁵-(1-Iminopentyl)-L-ornithine was determined to be the most potent compound in vitro (K(d)=7 μM) as well as in cultured cells, and the binding conformation and covalent reversible mode of inhibition was investigated by comparison of interactions made with DDAH-1 and a catalytically inactive C274S variant, as gauged by X-ray crystallography and isothermal titration calorimetry. By interrupting the ability of the inhibitor to form a covalent bond, the contribution of this interaction could be estimated. These results suggest that further stabilization of the covalent adduct is a promising strategy for lead optimization in the design of effective reagents to block NO synthesis.

Dimethylarginine metabolism during acute and chronic rejection of rat renal allografts

Background. Dimethylarginines are inhibitors of NO synthesis and are involved in the pathogenesis of vascular diseases. In this study, we ask the question if asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels change during fatal and reversible acute rejection, and contribute to the pathogenesis of chronic vasculopathy.

Methods. The Dark Agouti to Lewis rat strain combination was used to investigate fatal acute rejection. Fischer 344 kidneys were transplanted to Lewis rats to study reversible acute rejection episode and the process of chronic rejection. Isograft recipients and untreated Lewis rats were used as controls. l-arginine derivatives were determined by HPLC, and ADMA-metabolizing enzymes were studied by quantitative RT–PCR and western blotting.

Results. Renal transplantation transiently increased dimethylarginine levels independent of acute rejection. ADMA plasma levels did not importantly differ between recipients undergoing fatal or reversible acute rejection, whereas SDMA was even lower in recipients of Fisher 344 grafts. In comparison to isograft recipients, ADMA and SDMA levels were slightly elevated during reversible, but not during the process of chronic rejection. Increased dimethylarginine levels, however, did not block NO synthesis. Interestingly, protein methylation, but not ADMA degradation, was increased in allografts.

Conclusions. Our data do not support the concept that renal allografts are protected from fatal rejection by dimethylarginines. Dimethylarginines may play a role in triggering chronic rejection, but a contribution to vascular remodelling itself is improbable. In contrast, differential arginine methylation of yet unknown proteins by PRMT1 may be involved in the pathogenesis of acute and chronic rejection.

Postprandial hyperglycemia is a determinant of platelet activation in early type 2 diabetes mellitus

BACKGROUND

Chronic hyperglycemia is a major contributor to in vivo platelet activation in diabetes mellitus.

OBJECTIVES

To evaluate the effects of acarbose, an alpha-glucosidase inhibitor, on platelet activation and its determinants in newly diagnosed type 2 diabetic patients.

METHODS

Forty-eight subjects (26 males, aged 61 +/- 8 years) with early type 2 diabetes (baseline hemoglobin A(1c) < or = 7% and no previous hypoglycemic treatment) were randomly assigned to acarbose up to 100 mg three times a day or placebo, and evaluated every 4 weeks for 20 weeks. The main outcome measures were urinary 11-dehydro-thromboxane (TX)B(2) (marker of in vivo platelet activation) and 8-iso-prostaglandin (PG)F(2alpha) (marker of in vivo lipid peroxidation) excretion rate, 2-h postprandial plasma glucose (PPG) after a test meal, and assessment of glucose fluctuations by mean amplitude of glycemic excursions (MAGE).

RESULTS

Baseline measurements revealed biochemical evidence of enhanced lipid peroxidation and platelet activation. As compared with the placebo group, patients treated with acarbose had statistically significant reductions in urinary 11-dehydro-TXB(2) and 8-iso-PGF(2alpha) excretion rate as early as after 8 weeks and at each subsequent time point (between-group P < 0.0001 at 12, 16 and 20 weeks), following earlier decreases in PPG and MAGE. Multiple regression analyses in the acarbose group revealed that PPG was the only significant predictor of 11-dehydro-TXB(2) urinary excretion rate (beta = 0.39, P = 0.002) and MAGE the only predictor of 8-iso-PGF(2alpha) urinary excretion rate (beta = 0.42, P = 0.001).

CONCLUSIONS

Postprandial hyperglycemia is associated with enhanced lipid peroxidation and platelet activation in early type 2 diabetes. A moderate decrease in PPG achieved with acarbose causes time-dependent downregulation of these phenomena, suggesting a causal link between early metabolic abnormalities and platelet activation in this setting.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Characterization and expression of two amphioxus DDAH genes originating from an amphioxus-specific gene duplication

Two dimethylarginine dimethylaminohydrolase (DDAH) homologous genes in amphioxus are identified and cloned. The phylogenetic analysis indicates two DDAHs in amphioxus originated by independent duplication specific in cephalochordate lineage. Analysis of AmphiDDAHa and AmphiDDAHb genomic structure shows their comparability with the DDAH in vertebrate and aboriginality which is consistent with animal classification. To explore the function relationship of AmphiDDAHa and AmphiDDAHb with AmphiNOS, the nitric oxide synthase homologue in amphioxus, we investigate the three genes expression patterns in embryos and adult tissues. The results indicate that these three genes possess different spatial and temporal expression patterns during embryogenesis. AmphiDDAHa transcripts are detected extensively in the differentiating ectoderm, mesendoderm in gastrula/early neurula, the developing and newly formed neural tube, somites, notochord, alimentary canal and epidermis at neurula stage, as well as in the differentiating pharynx and tailbud at early larval stage. While AmphiDDAHb is expressed in the differentiating non-neural ectoderm at the gastrla/early neurula stage, then locates abroad in the developing and formed neural tube, notochord, somites and alimentary canal. AmphiNOS is expressed weakly but widely from early neurula stage to at least 72-h larva stage. In adult, AmphiDDAHa and AmphiNOS share similar expression patterns in diverse adult tissues and cells such as the neural cord, gut, midgut diverticulum, wheel organ, gill, blood vessels, endostyle, oocytes and macrophages. But no expression of AmphiDDAHb is detected in tissues mentioned above. The results suggest that AmphiDDAHa and AmphiDDAHb should be two homologous genes with different functions in amphioxus. AmphiDDAHa may play a conserved role in the regulation of NO synthesis and immune defense, whereas AmphiDDAHb may mainly play the roles in the cell movement or differentiation of embryonic non-neural ectoderm cells during gastrulation and early neurulation.

Response of asymmetric dimethylarginine to hemodialysis-associated hypotension in end-stage renal disease patients

AIMS

To define the role of asymmetric dimethylarginine (ADMA) in the control of blood pressure (BP) during hemodialysis (HD).

METHODS

L-Arginine, ADMA and symmetric dimethylarginine (SDMA) levels of patients with (n = 18) or without (n = 13) hypotensive episodes during HD sessions were measured before and after HD treatment by liquid chromatography-mass spectrometry. Clinical variables, laboratory parameters and underlying pathologies of end-stage renal disease (ESRD) were comparable in the groups. BP was serially recorded.

RESULTS

In patients with ESRD, plasma dimethylarginines were markedly elevated and decreased significantly by the end of the HD sessions. ADMA levels in patients having hypotensive episodes during HD were significantly higher than in those maintaining their BP (before HD: 0.62 +/- 0.11 micromol/l vs. 0.71 +/- 0.13 micromol/l, p = 0.04; after HD: 0.31 +/- 0.11 micromol/l vs. 0.43 +/- 0.11 micromol/l, p = 0.01). There was a significant inverse relationship of the minimum systolic and diastolic BP during HD to the predialysis ADMA levels (for systolic BP r = -0.50, p < 0.01; for diastolic BP r = -0.59, p < 0.01) and to the postdialysis ADMA levels (for systolic BP r = -0.49, p < 0.01; for diastolic BP r = -0.51, p < 0.005), respectively.

CONCLUSIONS

It is suggested that excessive NO generation is involved in the HD-associated hypotension and induces an increase in plasma ADMA levels to prevent further fall in BP.

ADMA levels correlate with proteinuria, secondary amyloidosis, and endothelial dysfunction

Asymmetric dimethyl-arginine (ADMA), a residue of the proteolysis of arginine-methylated proteins, is a potent inhibitor of nitric oxide synthesis. The increased protein turnover that accompanies proteinuric secondary amyloidosis may increase circulating levels of ADMA, and this may contribute to endothelial dysfunction. We performed a cross-sectional study of 121 nondiabetic proteinuric patients with normal GFR (including 39 patients with nephrotic-range proteinuria and secondary amyloidosis) and 50 age-, sex-, and BMI-matched healthy controls. The proteinuric patients had higher levels of serum ADMA, symmetric dimethyl-arginine (SDMA), high-sensitivity C-reactive protein (hsCRP), and insulin resistance (homeostasis model assessment index) than controls. Compared with controls, brachial artery flow-mediated dilatation (FMD), serum L-Arginine, and the L-Arginine/ADMA ratio were significantly lower among proteinuric patients, suggesting greater endothelial dysfunction. When patients with secondary amyloidosis were compared with patients with glomerulonephritis who had similar levels of proteinuria, those with amyloidosis had higher ADMA and SDMA levels and lower L-Arginine/ADMA ratios and FMD measurements (P < 0.001 for all). Finally, even after adjusting for confounders, ADMA level correlated with both proteinuria and the presence of secondary amyloidosis, and was an independent predictor of FMD. We propose that ADMA synthesis may be increased in chronic kidney disease, especially in secondary amyloidosis, and this may explain part of the mechanism by which proteinuria increases cardiovascular morbidity and mortality.

Decreased plasma soluble RAGE in patients with hypercholesterolemia: effects of statins

The receptor for advanced glycation endproducts (RAGE) is overexpressed at sites of vascular pathology. A soluble RAGE isoform (sRAGE) neutralizes the ligand-mediated damage by acting as a decoy. We hypothesized that in hypercholesterolemia up-regulation of the ligand-RAGE axis may bridge impairment of nitric oxide biosynthesis with oxidative stress. We measured in 60 hypercholesterolemic patients and 20 controls plasma total sRAGE levels, urinary 8-iso-prostaglandin (PG) F(2alpha) excretion, and plasma levels of asymmetric dimethylarginine (ADMA). The effects of two structurally different statins (pravastatin and atorvastatin) on these parameters were analyzed in 20 hypercholesterolemic subjects free of vascular disease. Plasma sRAGE was significantly lower, ADMA and urinary 8-iso-PGF(2alpha) were higher, in hypercholesterolemic versus normocholesterolemic patients. Patients on statin treatment with previous myocardial infarction had lower 8-iso-PGF(2alpha), higher sRAGE, and unchanged ADMA levels compared to subjects free of vascular disease. On multivariate regression analysis only 8-iso-PGF(2alpha) and ADMA predicted sRAGE levels. An 8-week treatment with either statin was associated with a significant reduction in urinary 8-iso-PGF(2alpha), whereas only atorvastatin raised sRAGE levels near to normal values, with no change in ADMA levels. sRAGE might serve as an endogenous protecting factor for accelerated atherosclerosis mediated by oxidative stress and endothelial dysfunction in hypercholesterolemia.

Soluble RAGE in type 2 diabetes: association with oxidative stress

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

Effects of combined supplementation with B vitamins and antioxidants on plasma levels of asymmetric dimethylarginine (ADMA) in subjects with elevated risk for cardiovascular disease

Elevated plasma asymmetric dimethylarginine (ADMA) concentrations have been suggested as a potential risk factor for cardiovascular disease (CVD). Studies indicate a linkage between hyperhomocysteinemia, oxidative stress and ADMA metabolism. We tested the hypothesis that combined supplementation of B vitamins and antioxidants reduces ADMA concentrations in subjects with at least two CVD risk factors. A total of 123 men and women (58+/-8.1 years) were randomly assigned to take either a preparation including B vitamins and antioxidants (verum) or placebo for 6 months in a double-blind design. Blood concentrations of ADMA, symmetric dimethylarginine (SDMA), L-arginine, B vitamins, total homocysteine (tHcy), alpha-tocopherol, antioxidant capacity (TEAC), and oxLDL were measured pre- and post-intervention. Treatment with verum significantly decreased tHcy (-2.14 micromol/L; P<0.001) and significantly increased TEAC values (+39.3 microM; P<0.022), but no effect on ADMA was observed. OxLDL was significantly reduced in verum (-7.3 U/L; P=0.001) and placebo (-9.2U/L; P<0.001). At baseline, significant correlations were found only between ADMA and SDMA (r=0.281; P=0.002), L-arginine/ADMA and SDMA (r=-0.294; P<0.001), L-arginine/ADMA and oxLDL (r=-0.281; P=0.016), and L-arginine/ADMA and age (r=-0.231; P=0.010). Our results indicate that combined supplementation of B vitamins and antioxidants is not an adequate strategy to reduce ADMA plasma levels in subjects with elevated CVD risk.

ADMA correlates with portal pressure in patients with compensated cirrhosis

BACKGROUND

Chronic liver diseases are frequently complicated by portal hypertension, an important component of which is the increased intrahepatic vascular resistance, in part related to endothelial dysfunction. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, is an established mediator and marker of endothelial dysfunction. We therefore investigated the possible implication of ADMA in chronic liver diseases-induced portal hypertension.

MATERIALS AND METHODS

We studied 39 consecutive patients with compensated hepatitis C virus (HCV) related chronic liver diseases. All patients underwent hepatic venous pressure gradient (HVPG) measurement, and simultaneous blood sampling from the hepatic vein and the pulmonary artery, for ADMA and nitrite/nitrate (NOx) plasma level determinations.

RESULTS

A positive correlation between HVPG and ADMA concentrations in hepatic veins (ADMA-h) was found (r = 0.77, P < 0.0001). Moreover, a negative correlation between HVPG and NOx concentrations in the hepatic veins (NO-h) (r = -0.50, P = 0.005), and between ADMA-h and NO-h was observed (r = -0.40, P = 0.02). ADMA concentrations in pulmonary artery (ADMA-p) (0.55 +/- 0.13 micromol L(-1)) were significantly higher than in hepatic veins (0.47 +/- 0.09 micromol L(-1)) (P < 0.0001).

CONCLUSIONS

These results suggest that ADMA may play a pathophysiological role in portal hypertension by contributing to the relative intrahepatic NO deficiency typical of endothelial dysfunction.

Biological variation of asymmetric dimethylarginine and related arginine metabolites and analytical performance goals for their measurement in human plasma

BACKGROUND

Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide synthase which is believed to be a cause of endothelial dysfunction and has been shown to predict the occurrence of acute coronary events. Data regarding the biological variation of arginine and its methylated derivatives are conspicuously absent from the literature. Such data are important in setting analytical quality specifications, assessing the utility of population reference intervals and assessing the significance of changes in serial results from an individual.

MATERIALS AND METHODS

Arginine, homoarginine, ADMA and symmetric dimethylarginine (SDMA) are measured in plasma by high performance liquid chromatography. Twelve healthy volunteers underwent weekly blood sampling for 20 weeks in order to determine the intra- and inter-individual biological variation of these analytes, from which analytical quality specifications, indices of individuality (II) and reference change values (RCV) are derived. Plasma samples from 100 healthy individuals were obtained in order to determine population reference intervals.

RESULTS

ADMA and symmetric dimethylarginine (SDMA) exhibit low intra-individual biological variation of 7.4% and 5.8%, respectively, imposing desirable imprecision goals (CV(A)) of < or = 3.7% and 2.9% for these analytes. The described methodology achieves these goals, with analytical CVs of < 3.5% for all analytes. Goals for bias and total error were 3.1-10.1% and 7.2-16.0%, respectively. Reference intervals for ADMA and SDMA were 0.29-0.63 micromol L(-1) and 0.24-0.55 micromol L(-1), but have IIs < 1. RCVs were at least 20% for all analytes studied.

CONCLUSIONS

Dimethylarginine concentrations are tightly controlled in health, with the result that imprecision goals for laboratory methods require to be low. Relatively large differences are required between serial results to denote a significant change. Population reference intervals for dimethylarginines are likely to be of limited value in detecting 'abnormality' in an individual from a single result.

Serum asymmetric dimethylarginine negatively correlates with intima-media thickness in early-onset atherosclerosis

BACKGROUND

Asymmetric dimethylarginine (ADMA) assumes a significant role in atherosclerosis by inhibiting the endothelial nitric oxide synthase (eNOS). Moreover, ADMA inhibits the inducible NOS (iNOS), the isoform that triggers atherosclerosis via peroxynitrite formation. Therefore, we investigated whether ADMA is a risk or protective factor in the atherosclerotic process. Intima-media thickness (IMT) of the common carotid artery, a surrogate for vascular diseases, was chosen as the outcome variable of interest.

METHODS

Sixty patients younger than 55 years having at least 30% stenosis of the internal carotid artery and 30 age- and gender-matched controls were recruited at a community-based neurosonological laboratory. We investigated relatively young patients to circumvent the confounding effect age has in the development of atherosclerosis.

RESULTS

The IMT showed a negative correlation with ADMA upon analysis of the pooled data (Spearman correlation coefficient -0.300, p = 0.0041) and the atherosclerotic stratum (Spearman correlation coefficient -0.323, p = 0.012). A multiple linear regression model containing all determinant factors of IMT previously identified by simple regression was used to further quantify the relationship between IMT and ADMA. The negative association between IMT and ADMA remained statistically significant (beta: -0.510, CI: -0.894, -0.127; p = 0.010), furthermore it was even stronger in the atherosclerotic stratum (beta: -0.67, CI: -1.16, -0.18; p = 0.008).

CONCLUSIONS

A minimal increase in ADMA concentration may be protective by inhibiting iNOS but not eNOS in states where iNOS is induced, e.g. inflammation accompanying atherosclerosis.

Endogenous inhibitors of nitric oxide and preeclampsia: a review

Nitric oxide (NO) is a potent vasodilator. NO is synthesized by NO synthases (NOS) and NOS are inhibited by asymmetrical dimethylarginine (ADMA). ADMA is metabolized by dimethylarginine dimethylaminohydrolase (DDAH) and excreted in the kidneys. Lower ADMA levels in pregnant women compared to non-pregnant controls suggest that ADMA has a role in vascular dilatation and blood pressure changes. Several studies show an increase in ADMA levels in pregnancies complicated with preeclampsia. Elevated ADMA levels in preeclampsia are seen before clinical symptoms have developed; these findings suggest that ADMA has a role in the pathogenesis of preeclampsia.

Contribution of whole blood to the control of plasma asymmetrical dimethylarginine

The endogenous nitric oxide (NO) synthase (NOS) inhibitor asymmetrical dimethylarginine (ADMA) is elevated in many patients and may contribute to the initiation and progression of their disease. While some mechanistic pathways have been identified, tissue-specific contributions to ADMA control remain unclear. We sought to determine if whole blood (WB) could participate in ADMA control ex vivo. Anesthetized male Sprague-Dawley rats underwent exsanguinations, and WB preparations were incubated at 37°C for 5 h. ADMA and symmetrical dimethylarginine were analyzed by high-pressure liquid chromatography. Incubation of lysed red blood cell (RBC) supernatant yielded a significant decrease in ADMA that was blocked by 4124W, a synthetic inhibitor of dimethylarginine dimethylaminohydrolase, the only reported enzyme to hydrolyze ADMA. Hydrolysis of ADMA was diminished by addition of physiologically relevant concentrations of zinc (i.e., 20 μM). Conversely, when rat WB or WB supernatant was incubated at 37°C, it liberated quantities of free ADMA (1–2 μM) that in vivo would likely have pathological consequences. Addition of arginine methyltransferase inhibitors to these incubations did not reduce ADMA release, indicating no dominant role for active protein methylation during these incubations. This ADMA liberation was significantly reduced by addition of protease inhibitors, indicating a dependence on peptide bond hydrolysis. Total ADMA (protein incorporated plus free) was determined by acid hydrolysis and found to be 43.18 ± 4.79 μM in WB with ∼95% of this in RBCs. These ex vivo data demonstrate the potential of blood to control the NO-NOS system by modulating free ADMA.

Why don't fistulas mature?

Fistula maturation requires a compliant and responsive vasculature capable of dilating in response to the increased velocity of blood flowing into the newly created low-resistance circuit. Successful maturation to a high volume flow circuit capable of sustaining hemodialysis typically occurs within the first few weeks after creation. Failure to achieve maturation within 4-8 weeks should prompt a search for reversible etiologies; however, an accepted definition of maturation, particularly for patients not yet on dialysis remains elusive. The most commonly identified etiology is neointimal hyperplasia typically occurring in the juxta-anastomotic vein. However, failed maturation has also been reported secondary to impaired arterial and venous dilation and accessory veins. The exact frequency of each of these etiologies is unclear. Understanding the etiologies of impaired fistula maturation will focus future studies of targeted interventions to improve the rate of fistula maturation and increase the number of dialysis patients with a functioning autogenous fistula.

CHARACTERIZATION OF CATIONIC AMINO ACID TRANSPORT SYSTEMS IN RAT ERYTHROCYTES: LACK OF EFFECT OF URAEMIA ON l-ARGININE INFLUX

1. Chronic renal failure (CRF) is associated with the abnormal regulation of nitric oxide (NO) synthesis at the systemic level. The transport of L-arginine, upregulated in blood cells from uraemic patients, modulates NO synthesis in this pathological condition. The model of partial nephrectomy in rats is widely accepted as a valid model of uraemia. Because there are no reports of L-arginine transport in blood cells from uraemic rats, the aim of the present study was to investigate L-arginine transport in red blood cells (RBCs) from these rats. 2. The kinetics of L-arginine transport in RBC and plasma and the amino acid profiles of RBC were investigated in control, sham-operated and subtotally nephrectomized rats. 3. L-Arginine transport was mediated via the cationic amino acid transport system y+ and a transport system with kinetics resembling the human system y+L. In control RBC, the apparent Ki for L-leucine inhibition of L-arginine transport via system y+L was 0.16 +/- 0.02 and 4.8 +/- 2 mmol/L in the presence of Li+ and Na+, respectively. 4. The Vmax values for L-arginine transport via system y+L and system y+ were similar in RBC from control sham-operated and uraemic rats. Moreover, L-arginine concentrations in plasma and RBC were not affected by uraemia. 5. The findings of the present study provide the first evidence that L-arginine transport in rat erythrocytes is mediated by two distinct cationic transport systems with characteristics of systems y+ and y+L, which accept neutral amino acids only in the presence of Li+. In contrast with previous studies in uraemic patients, plasma levels and maximal transport rates of L-arginine were not altered in this rat model of CRF.

[Thrombocytopathy and blood complications in uremia]

Bleeding diathesis and thrombotic tendencies are characteristic findings in patients with end-stage renal disease. The pathogenesis of uremic bleeding tendency is related to multiple dysfunctions of the platelets. The platelet numbers may be reduced slightly, while platelet turnover is increased. The reduced adhesion of platelets to the vascular subendothelial wall is due to reduction of GPIb and altered conformational changes of GPIIb/IIIa receptors. Alterations of platelet adhesion and aggregation are caused by uremic toxins, increased platelet production of NO, PGI(2), calcium and cAMP as well as renal anemia. Correction of uremic bleeding is caused by treatment of renal anemia with recombinant human erythropoietin or darbepoetin alpha, adequate dialysis, desmopressin, cryoprecipitate, tranexamic acid, or conjugated estrogens. Thrombotic complications in uremia are caused by increased platelet aggregation and hypercoagulability. Erythrocyte-platelet-aggregates, leukocyte-platelet-aggregates and platelet microparticles are found in higher percentage in uremic patients as compared to healthy individuals. The increased expression of platelet phosphatidylserine initiates phagocytosis and coagulation. Therapy with antiplatelet drugs does not reduce vascular access thrombosis but increases bleeding complications in endstage renal disease patients. Heparin-induced thrombocytopenia (HIT type II) may develop in 0-12 % of hemodialysis patients. HIT antibody positive uremic patients mostly develop only mild thrombocytopenia and only very few thrombotic complications. Substitution of heparin by hirudin, danaparoid or regional citrate anticoagulation should be decided based on each single case.

The cardiovascular risk marker asymmetrical dimethylarginine is not affected by venous thromboembolism

Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase, causes vasoconstriction, impairs cardiac function, and may predict cardiovascular risk. The prognostic value of plasma ADMA concentrations in acute vascular situations may be confounded by concomitant factors such as clot formation. In an effort to address the effect of hemostatic system activation, the authors have measured plasma concentrations of ADMA, its stereoisomer symmetrical dimethylarginine (SDMA), and L-arginine in 74 patients with suspected deep vein thrombosis (DVT). DVT was confirmed by sonography or venography in 39 subjects. There was no difference of L-arginine, ADMA, or SDMA (all P > 0.05) between subjects with or without DVT. ADMA correlated with SDMA, L-arginine, and plasma creatinine (all P < 0.05) but not with age, body mass index, D-dimer, thrombus extension, or history of symptoms. Venous thrombembolism does not influence circulating ADMA concentrations. The lack of association between ADMA and DVT argues against a contribution of endogenous NO synthase inhibition in hemostatic systemic activation.

Laser Doppler flowmetry detection of endothelial dysfunction in end-stage renal disease patients: correlation with cardiovascular risk

Prediction of cardiovascular (CV) complications represents the Achilles' heel of end-stage renal disease. Surrogate markers of endothelial dysfunction have been advocated as predictors of CV risk in this cohort of patients. We have recently adapted a noninvasive laser Doppler flowmetry (LDF) functional testing of endothelium-dependent microvascular reactivity and demonstrated that end-stage renal disease patients are characterized by profound alterations in thermal hyperemic responsiveness. We hypothesized that such functional assessment of the cutaneous microcirculation may offer a valid, noninvasive test of the severity of endothelial dysfunction and CV risk. To test this hypothesis, we performed a cross-sectional study, in which we compared LDF measurements to conventional risk factors, and performed a pilot longitudinal study. LDF studies were performed in 70 patients and 33 controls. Framingham and Cardiorisk scores were near equivalent for low-risk patients, but more divergent as risk increased. C reactive protein (CRP) levels and LDF parameters (amplitude of thermal hyperemia (TH), area under the curve of TH) showed significant abnormality in high-risk vs low-risk patients calculated using either Framingham or Cardiorisk scores. Patients who had abnormal LDF parameters showed increased CV mortality, however, had similar risk assessments (Framingham, Cardiorisk, CRP, and homocysteine) to those with unimpaired LDF tracings. In conclusion, LDF parameters of microvascular reactivity offer a sensitive characterization of endothelial dysfunction, which may improve CV risk assessment through incorporation into the Framingham or Cardiorisk algorithm.

L-Arginine supplementation or arginase inhibition augments reflex cutaneous vasodilatation in aged human skin

Full expression of reflex cutaneous vasodilatation is dependent on nitric oxide (NO) and vasodilatation is attenuated in healthy older humans. NO bioavailability in aged skin may be decreased by an age-related upregulation of arginase, which reciprocally regulates the NO-synthase (NOS) substrate L-arginine (L-Arg). We hypothesized that increased arginase activity contributes to attenuated vasodilatation in aged skin by limiting L-Arg for NOS-mediated NO synthesis. Five microdialysis fibres were placed in forearm skin of 10 young (Y, 23 +/- 1 years) and 9 older (O, 68 +/- 1 years) human subjects, serving as control (C, Ringer solution), NOS-inhibited (10.0 mM NG-nitro-L-arginine), arginase-inhibited (5.0 mM (S)-(2-boronoethyl)-L-cysteine + 5.0 mM Nomega-hydroxy-nor-L-arginine), L-arg supplemented (L-Arg; 10.0 mM L-arginine) and combined arginase-inhibited + L-Arg sites. After 20 min thermoneutral baseline, cutaneous vasodilatation was induced by passive whole-body heating to increase oral temperature (Tor) by 1.0 degrees C. Red blood cell flux was measured by laser-Doppler flowmetry over each microdialysis site. Cutaneous vascular conductance was calculated (CVC = flux/mean arterial pressure) and normalized to maximal CVC (CVCmax, 28.0 mM sodium nitroprusside + local heating to 43 degrees C). Cutaneous vasodilatation during heating was attenuated in O (Y, 42 +/- 1, versus O, 30 +/- 1%CVCmax, P < 0.001) at control sites. NOS inhibition decreased vasodilatation in both age groups compared to C (Y, 22 +/- 2; O, 18 +/- 2%CVCmax; P < 0.001). Arginase inhibition, L-Arg supplementation, and arginase inhibition + L-Arg supplementation augmented vasodilatation in O (arginase-inhibited, 46 +/- 4; L-Arg, 44 +/- 4; arginase-inhibited + L-arg, 46 +/- 5%CVCmax; P < 0.001 versus C) but not in Y (arginase-inhibited, 46 +/- 4; L-Arg, 38 +/- 4; arginase-inhibited + L-Arg, 44 +/- 4%CVCmax; P > 0.05 versus C). Increasing L-Arg for NO synthesis by either arginase inhibition or direct L-Arg supplementation restores the age-related deficit in reflex cutaneous vasodilatation.

Emerging role of epoxyeicosatrienoic acids in coronary vascular function

The importance of endothelium-derived nitric oxide in coronary vascular regulation is well-established and the loss of this vasodilator compound is associated with endothelial dysfunction, tissue hypoperfusion and atherosclerosis. Numerous studies indicate that the endothelium produces another class of compounds, the epoxyeicosatrienoic acids (EETs), which may partially compensate for the loss of nitric oxide in cardiovascular disease. The EETs are endogenous lipids which are derived through the metabolism of arachidonic acid by cytochrome P450 epoxygenase enzymes. Also, EETs hyperpolarize vascular smooth muscle and induce dilation of coronary arteries and arterioles, and therefore may be endogenous mediators of coronary vasomotor tone and myocardial perfusion. In addition, EETs have been shown to inhibit vascular smooth muscle migration, decrease inflammation, inhibit platelet aggregation and decrease adhesion molecule expression, therefore representing an endogenous protective mechanism against atherosclerosis. Endogenous EETs are degraded to less active dihydroxyeicosatrienoic acids by soluble epoxide hydrolase. Pharmacological inhibition of soluble epoxide hydrolase has received considerable attention as a potential approach to enhance EET-mediated vascular protection, and several compounds have appeared promising in recent animal studies. The present review discusses the emerging role of EETs in coronary vascular function, as well as recent advancements in the development of pharmacological agents to enhance EET bioavailability.

[Sequelae of hypertenson: kidney disease]

Nephropathy is one of the frequent sequelae of hypertension. Arterial hypertension causes both arterial and capillary changes in the kidneys as well as development of interstitial fibrosis. Systemic or intraglomerular pressure increase leads to albuminuria and proteinuria, which in turn contributes to further damage of the kidneys. Impairment of the kidneys due to hypertension can ultimately result in terminal renal insufficiency necessitating dialysis. Metabolic factors such as hyperlipidemia, hyperuricemia, hyperhomocysteinemia, and insulin resistance can aggravate renal lesions. Effective lowering of blood pressure in conjunction with management of the metabolic risk factors is decisive for prevention of chronic kidney disease, which in turn must be considered a factor involved in exacerbation of the hypertension.

Nitric oxide and the vascular endothelium

The vascular endothelium synthesises the vasodilator and anti-aggregatory mediator nitric oxide (NO) from L-arginine. This action is catalysed by the action of NO synthases, of which two forms are present in the endothelium. Endothelial (e)NOS is highly regulated, constitutively active and generates NO in response to shear stress and other physiological stimuli. Inducible (i)NOS is expressed in response to immunological stimuli, is transcriptionally regulated and, once activated, generates large amounts of NO that contribute to pathological conditions. The physiological actions of NO include the regulation of vascular tone and blood pressure, prevention of platelet aggregation and inhibition of vascular smooth muscle proliferation. Many of these actions are a result of the activation by NO of the soluble guanylate cyclase and consequent generation of cyclic guanosine monophosphate (cGMP). An additional target of NO is the cytochrome c oxidase, the terminal enzyme in the electron transport chain, which is inhibited by NO in a manner that is reversible and competitive with oxygen. The consequent reduction of cytochrome c oxidase leads to the release of superoxide anion. This may be an NO-regulated cell signalling system which, under certain circumstances, may lead to the formation of the powerful oxidant species, peroxynitrite, that is associated with a variety of vascular diseases.

Cerebrocellular Swelling in the Presence of Uraemic Guanidino Compounds: Ameliorative Effects of Taurine

Cell volumes (equilibrium non-inulin spaces) have been measured in slices of rat cerebral cortex incubated in the presence of uraemic guanidino compounds. Of 5 guanidino compounds tested, all but one caused significant cell swelling. This was most pronounced for guanidinosuccinic acid (GSA, 40 micromol/l)(+22%) and guanidine hydrochloride (G, 3 micromol/l)(+13%). Swelling was reduced by taurine in a dose-dependent manner, being completely abolished at 20 mmol/l. Swelling was also abolished by the antioxidants ascorbic acid (0.4 mmol/l) and butylated hydroxytoluene (0.5 mmol/l), the free radical scavenger N-acetyl-L-cysteine (10 mmol/l) and the lipid peroxidase inhibitor desmethyl tirilazad (100 micromol/l). The remission of swelling by 20 mmol/l taurine was reduced by 50% by the taurine transport inhibitor guanidinoethylsulphonate (GES, 1 mmol/l). This figure was not significantly altered when the concentration of GES was increased to 10 mmol/l. It was also reduced by 45% by the GABAA receptor antagonist bicuculline (100 micromol/l). It was completely abolished when both GES and bicuculline were present. It is suggested that guanidino compounds result in cells undergoing oxidative-nitrosative stress, and that taurine protects against the resultant cell swelling by 2 mechanisms One (intracellular) requires taurine transport and depends on its role as an antioxidant, with lipid peroxidation being probably a significant factor. The other (extracellular) is associated with activation of GABAA receptors.

Asymmetrical dimethylarginine plasma clearance persists after acute total nephrectomy in rats

Elevated plasma concentrations of symmetrical dimethylarginine (SDMA) and asymmetrical dimethylarginine (ADMA) are repeatedly associated with kidney failure. Both ADMA and SDMA can be excreted in urine. We tested whether renal excretion is necessary for acute, short-term maintenance of plasma ADMA and SDMA. Sprague-Dawley rats underwent sham operation, bilateral nephrectomy (NPX), ureteral ligation, or ureteral section under isoflurane anesthesia. Tail-snip blood samples (250 microl) were taken before and at 6- or 12-h intervals for 72 h after operation. Plasma clearance was assessed in intact and NPX rats. High-performance liquid chromatography determined SDMA and ADMA concentrations. Sodium, potassium, creatinine, blood urea nitrogen (BUN), and body weight were also measured. Forty-eight hours after NPX, SDMA increased 25 times (0.23 +/- 0.03 to 5.68 +/- 0.30 microM), whereas ADMA decreased (1.17 +/- 0.08 to 0.73 +/- 0.08 microM) by 38%. Creatinine and BUN increased, paralleling SDMA. Sham-operated animals showed no significant changes. Increased SDMA confirms continuous systemic production of SDMA and its obligatory renal excretion, much like creatinine. In contrast, decreased plasma ADMA suggests that acute total NPX either reduced systemic ADMA formation and/or systemic hydrolysis of ADMA increased 48-h post-NPX. However, plasma clearance of ADMA appeared unchanged 48 h after NPX. We conclude that renal excretory function is needed for SDMA elimination but not needed for acute, short-term ADMA elimination in that systemic hydrolysis is fully capable of clearing plasma ADMA.