Endothelin-A receptor antagonism modifies cardiovascular risk factors in CKD.

Arterial stiffness and impaired nitric oxide (NO) bioavailability contribute to the high risk for cardiovascular disease in CKD. Both asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO production, and endothelin-1 (ET-1) oppose the actions of NO, suggesting that ET-1 receptor antagonists may have a role in cardiovascular protection in CKD. We conducted a randomized, double-blind, three-way crossover study in 27 patients with proteinuric CKD to compare the effects of the ET(A) receptor antagonist sitaxentan, nifedipine, and placebo on proteinuria, BP, arterial stiffness, and various cardiovascular biomarkers. After 6 weeks of treatment, placebo and nifedipine did not affect plasma urate, ADMA, or urine ET-1/creatinine, which reflects renal ET-1 production; in contrast, sitaxentan led to statistically significant reductions in all three of these biomarkers. No treatment affected plasma ET-1. Reductions in proteinuria and BP after sitaxentan treatment was associated with increases in urine ET-1/creatinine, whereas reduction in pulse-wave velocity, a measure of arterial stiffness, was associated with a decrease in ADMA. Taken together, these data suggest that ET(A) receptor antagonism may modify risk factors for cardiovascular disease in CKD.

Blood pressure and not uraemia is the major determinant of arterial stiffness and endothelial dysfunction in patients with chronic kidney disease and minimal co-morbidity.

INTRODUCTION: Patients with chronic kidney disease (CKD) have increased risk of cardiovascular disease to which co-morbidity and associated conventional risk factors contribute. We hypothesised that arterial stiffness (AS) and endothelial dysfunction (ED), as surrogates of cardiovascular risk, would worsen as renal function declined even in patients without co-morbidity and that this would relate to emerging cardiovascular risk factors. METHODS: Carotid-femoral pulse wave velocity (PWV), as a measure of AS, and flow-mediated dilatation (FMD) of the brachial artery, as a measure of ED, were assessed in CKD patients without established cardiovascular disease or diabetes mellitus. RESULTS: PWV increased linearly as renal function declined (r(2) = 0.08, p < 0.01) whereas FMD was reduced only in patients with advanced kidney disease. In multivariable analysis, blood pressure was the major determinant of PWV and FMD. High-sensitivity C-reactive protein and asymmetric dimethylarginine, and isoprostanes and endothelin-1, were independent predictors of PWV and FMD, respectively. However, renal function did not independently predict either AS or ED. CONCLUSIONS: These findings suggest that declining renal function, in the absence of significant co-morbidity, is associated with progressive arterial stiffness, but only patients close to dialysis exhibit endothelial dysfunction. Whilst blood pressure remains the major determinant of PWV and FMD, inflammation, oxidative stress and endothelin-nitric oxide balance contribute to cardiovascular risk, in this non-comorbid cohort.

HPLC analysis of asymmetric dimethylarginine (ADMA) and related arginine metabolites in human plasma using a novel non-endogenous internal standard.

BACKGROUND: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthesis which has been implicated in the endothelial dysfunction. Methods for ADMA measurement often yield widely differing results, and few methods simultaneously offer satisfactory accuracy and precision. We describe a fully validated HPLC method for analysis of arginine and its methylated derivatives in human plasma using a novel internal standard. METHODS: Arginine and related metabolites are extracted from plasma by solid phase extraction (SPE), derivatised with ortho-phthaldialdehyde and separated by isocratic reverse phase chromatography. Monoethylarginine (MEA), which is not endogenously present in human plasma was used as internal standard. SPE and chromatographic procedures are optimised and recovery, precision, linearity and sensitivity of the assay established. The suitability and performance of MEA is compared with that of monomethylarginine (MMA), the internal standard most commonly used in HPLC methods. RESULTS: SPE yields high and reproducible recoveries (>90%). The analytes of interest are chromatographically well resolved. The method has high sensitivity (LOD, 0.01 micromol/L for arginine and 0.001 micromol/L for ADMA, SDMA and homoarginine) and good precision (CV, 2.5% for ADMA). The data obtained with the internal standards MEA and MMA is comparable in terms of assay precision and population reference intervals. CONCLUSIONS: We describe an optimised isocratic HPLC method for the simultaneous measurement of arginine and related metabolites in plasma which exhibits satisfactory precision and is suitable for routine use. Its main advantage over other published HPLC methods is the use of the novel internal standard, MEA, which unlike other commonly used internal standards is not inherent in human plasma.

Assessment of dietary intake and trace element status in patients with ileal pouch-anal anastomosis.

PURPOSE: Panproctocolectomy and ileal pouch-anal anastomosis is the operation of choice for patients with ulcerative colitis and familial polyposis. The long-term nutritional consequences after pouch surgery are unknown. We have assessed the nutritional status of the essential trace elements-zinc, copper, manganese, and selenium-in patients several years (median, 10 (range, 2-15) years) after surgery. METHODS: Fifty-five patients with uncomplicated ileal pouch-anal anastomosis and 46 healthy control subjects were studied. A dietary assessment of trace element intake was undertaken by using a semiquantitative food frequency questionnaire. The patients' trace elements status for zinc, copper, manganese, and selenium was assessed by measuring their concentrations in blood. RESULTS: The dietary intake of individual trace elements was similar in both groups (all P values > 0.4). There was no significant difference in the concentrations of plasma copper, zinc, and selenium between patients and healthy control subjects (all P values > 0.07). The concentration of whole blood manganese was significantly higher (P = 0.004) in patients (median, 178.5 nmol/l; range, 59-478 nmol/l) compared with healthy control subjects (median, 140 nmol/l; range, 53-267 nmol/l). Four (7 percent) patients had manganese concentrations more than three standard deviations of the mean of control group (>255 nmol/l). CONCLUSIONS: This study shows that patients who have had uncomplicated pouch surgery have a normal dietary intake of trace elements and do not develop deficiencies in copper, zinc, manganese, and selenium. However, these patients may be at increased risk of manganese toxicity.

Biological variation of vitamins in blood of healthy individuals.

BACKGROUND: Components of biological variation can be used to define objective quality specifications (imprecision, bias, and total error), to assess the usefulness of reference values [index of individuality (II)], and to evaluate significance of changes in serial results from an individual [reference change value (RCV)]. However, biological variation data on vitamins in blood are limited. The aims of the present study were to determine the intra- and interindividual biological variation of vitamins A, E, B(1), B(2), B(6), C, and K and carotenoids in plasma, whole blood, or erythrocytes from apparently healthy persons and to define quality specifications for vitamin measurements based on their biology. METHODS: Fasting plasma, whole blood, and erythrocytes were collected from 14 healthy volunteers at regular weekly intervals over 22 weeks. Vitamins were measured by HPLC. From the data generated, the intra- (CV(I)) and interindividual (CV(G)) biological CVs were estimated for each vitamin. Derived quality specifications, II, and RCV were calculated from CV(I) and CV(G). RESULTS: CV(I) was 4.8%-38% and CV(G) was 10%-65% for the vitamins measured. The CV(I)s for vitamins A, E, B(1), and B(2) were lower (4.8%-7.6%) than for the other vitamins in blood. For all vitamins, CV(G) was higher than CV(I), with II <1.0 (range, 0.36-0.95). The RCVs for vitamins were high (15.8%-108%). Apart from vitamins A, B(1), and erythrocyte B(2), the imprecision of our methods for measurement of vitamins in blood was within the desirable goal. CONCLUSIONS: For most vitamin measurements in plasma, whole blood, or erythrocytes, the desirable imprecision goals based on biological variation are obtainable by current methodologies. Population reference intervals for vitamins are of limited value in demonstrating deficiency or excess.