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Biomedical subjects

N B Roberts

Publications and source records attributed to N B Roberts.

At least 19 recordsLinked to original sources
PubMed2002

Activation of L-arginine transport in peripheral blood mononuclear cells in chronic renal failure.

Transport of LL-arginine, the precursor for nitric oxide (NO) synthesis, has been investigated in human peripheral blood mononuclear cells (PBMCs) obtained from healthy volunteers and chronic renal failure patients. Chronic renal failure patients were either on treatment by haemodialysis or continuous ambulatory peritoneal dialysis (CAPD). Saturable influx of L-arginine in PBMCs was mediated by the cationic amino acid transport systems y(+) and y(+)L. Initial rates of L-arginine transport (2 microM) via system y(+) were significantly increased in chronic renal failure patients, whereas transport via system y(+)L was unaffected. The increase in L-arginine transport via system y(+) was: 1.7-fold in uraemic patients on CAPD, 4.3-fold in uraemic patients pre-haemodialysis and 2.6-fold post-haemodialysis. When the intracellular PBMCs amino acid profile was analysed in chronic renal failure patients and control subjects, L-lysine and L-arginine concentrations were significantly increased in pre-haemodialysis uraemic patients and restored to normal values by haemodialysis and CAPD. The present study provides the first evidence that system y(+) mediates the increased transport of L-arginine in PBMCs from patients with chronic renal failure. The increased activity of system y(+) may provide the necessary supply of L-arginine to sustain NO synthesis in PBMCs exposed to increased levels of circulating cytokines in chronic renal failure.

Amino Acids↗
PubMed2002

Different Mg to Fe ratios in the mixed metal MgFe hydroxy-carbonate compounds and the effect on phosphate binding compared with established phosphate binders.

Due to the side effects of the current oral phosphate binders, there is a need for effective alternatives. A number of mixed metal hydroxy-carbonate compounds (MMHCs) based on Mg and Fe have recently been established as effective phosphate binders. We have now carried out further studies on the MMHCs with different ratios of Mg(2+):Fe(3+) in different forms to assess for phosphate binding efficacy and ionic release in aqueous solution and food slurries. The compounds that provide the most promise are those with Mg(2+):Fe(3+) ratios of 2:1 and 4:1 in the unaged/dry form. Their phosphate binding efficacy was compared with a wide range of established phosphate binders, such as aluminum hydroxide [Al(OH)(3)], calcium carbonate (CaCO(3)), calcium acetate (CaAc(2)), magnesium hydroxide [Mg(OH)(2)], and lanthanum carbonate [La(2)(CO(3))(3)] in various food slurries. The results showed that the MgFe compounds were much more effective (on a weight for weight basis) than the established binders, and their properties were relatively pH independent. Calcium compounds (CaCO(3) and CaAc(2)) were ineffective under the experimental conditions. Mg(OH)(2) was effective at low pH but not at pHs greater than 5.0, and also released two- to threefold more magnesium than the MgFe compounds. Al(OH)(3) showed some degree of efficacy, but the binding capacity was, at best, less than 50% of the MMHCs. La(2)(CO(3))(3) required at least a 10-fold increase in weight to give comparable binding to the MMHCs. In conclusion, MgFe hydroxy-carbonate compounds are effective phosphate binders and may provide a better alternative to both existing and emerging binders for combating hyperphosphataemia.

Binding Sites↗
PubMed2001

In-vitro studies of aluminium-induced toxicity on kidney proximal tubular cells.

The toxicity of aluminium (Al) to various cells is well described. However, little is known about its effect on kidney cells, which can be exposed to relatively high concentrations. In this study, the effect of aluminium as the citrate complex in concentrations up to 100 microM/l was investigated using a monolayer cell culture of kidney proximal tubular cells (PTC). Aluminium was found to be slightly toxic; at 100 microM/l the PTCs lost viability by 15, 20 and 24% after incubation for 24, 48 and 72 h, respectively. Viability was significantly reduced (P<0.001) after 48 h incubation with aluminium concentrations of 25, 50, 75 and 100 microM/l compared with controls. Lactate dehydrogenase (LDH) release was significantly increased (P<0.001) with 100 microM/l Al to 44.67+/-1.76 and 50.33+/-0.88 compared with controls 24+/-1.00 and 28.33 2.34 U/l after 24 and 48 h incubation, respectively, indicating damage to the plasma membrane. However, N-acetyl-beta-D-glucosaminidase (NAG) release in the medium of cells exposed to aluminium showed no difference from control values (P>0.1). Glucose consumption in aluminium-exposed cells at 100 microM/l was slightly, but not significantly (P=0.14), increased during 48 h incubation. Electron micrographs of cells exposed to aluminium at 100 microM/l showed a slight reduction in microvilli density and the cell tight junctions were not as clear compared with the control cells. Pretreatment with protective agents glutathione and tiopronin partly restored the viability of kidney proximal tubular cells to control values, whereas vitamin C and/or cysteine showed no effect. This study indicates that aluminium may show toxicity to kidney cells in culture. Several sites on the cell, i.e. microvilli, membrane and the cell junction, seem to be affected, however the mechanism(s) of damage remain unclear.

Acetylglucosaminidase↗
PubMed2001

The development and in-vitro evaluation of novel mixed metal hydroxy-carbonate compounds as phosphate binders.

The currently available phosphate binders are relatively inefficient and suffer from clinical side-effects of increased absorption of calcium and aluminium and the diarrhoea-inducing effects of magnesium. A new class of compounds based on mixed metal hydroxides has been developed and evaluated for their potential as phosphate binders. The mixed metal hydroxides were prepared using a standard procedure for hydrotalcite (Al2Mg6(OH)16.CO3.4H2O) by substituting Fe3+ for Al3+, with Mg2+ or Ca2+ as the divalent metal ion. Phosphate precipitation (binding) was examined at different pH values in aqueous solution and in various food mixtures in comparison with hydrotalcite, Al(OH)3, CaCO3 and Mg(OH)2 on the same weight-to-weight basis. A series of compounds with differing ratios of metal ions (Fe:Mg/Ca 1:2 or 1:3) gave analytically similar ratios to those predicted from the initial amounts added. CTFeCa bound > 90% phosphate in aqueous solution compared with 65% binding with CTFeMg, 85% binding with Mg(OH)2, and less than 30% binding for CaCO3 and Al(OH)3. The mixed metal compounds also bound up to 80% phosphate in various food matrices, which was relatively independent of changes in pH, compared with Mg(OH)2, where binding decreased from 85% at pH 3.0 to 25% at pH 8.0. Al(OH)3 and CaCO3 were relatively ineffective phosphate binders under all the conditions tested. The mixed metal hydroxides compounds show considerable promise as phosphate binders over those currently available and warrant further patient-based in-vivo testing.

Aluminum↗
PubMed2001

The evaluation of novel mixed metal hydroxy-carbonates as phosphate binders: an in-vivo study in the rat.

A number of novel phosphate binders based on mixed metal hydroxide structures incorporating Fe and Ca, or Fe and Mg (classified as CT, Crosfield test compounds), were compared with the established phosphate binders Mg(OH)2, Al(OH)3, CaCO3 and a commercial hydrotalcite (Al- and Mg-based) using a rat model. The changes in urine and soluble faecal phosphate were used to evaluate efficacy of phosphate binding. The binders were mixed into a standard rat maintenance food at a concentration of 1% (w/w). Four rats were used for each binder study group and fed over 7 days. Urine and faeces were collected (in a metabolic cage) over the last 24-h study period and the phosphate content measured. The urinary phosphate was significantly reduced (P < 0.001) with CTFeCa (72+/-44 microm), CTFeMg (13+/-4 microm), CT100 (26+/-11 microm), and Mg(OH)2 (65+/-53 microm), compared with control (766+/-188 microm), Al(OH)3 (1,256+/-279 microm), and CaCO3 (857+/-25 microm). The soluble phosphate content of the faeces was significantly reduced (P < 0.05) by up to 60 % with CTFeCa, CTFeMg and Mg(OH)2, and up to 40% with CT100 and Al(OH)3, compared with 30% in controls and 10% with CaCO3. The new mixed metal hydroxy-carbonate compounds based on FeCa or FeMg are effective phosphate binders in-vivo and warrant further testing in patients.

Animals↗
PubMed2001

Homocysteine and thiol metabolites in vitamin B12 deficiency.

Homocysteine metabolism is increasingly implicated in a diverse group of clinical disorders, including atheromatous vascular disease. We studied the disposition of homocysteine via the trans-sulphuration pathway, plasma glutathione peroxidase (GPx) activity and plasma levels of the sulphated hormone dehydro-epiandrosterone sulphate (DHEAS) in six vitamin B(12)-deficient human subjects before and after 2 weeks of vitamin B(12) repletion, both in the fasting state and following an oral methionine load (0.1 g/kg body weight). Fasting plasma total homocysteine concentrations fell (P=0.03) and total cysteine concentrations rose significantly (P=0.048) after treatment for 2 weeks with vitamin B(12) injections. The magnitude of the mean fall in the fasting concentration of homocysteine (38.8 micromol/l) was similar to the mean rise in cysteine levels (36.0 micromol/l) following vitamin B(12) therapy. Circulating levels of homocysteine were increased at 4 h after a methionine load when compared with fasting levels, both before and after vitamin B(12) repletion (P=0.003 for both). Total cysteinyl-glycine was lower post-methionine than in the fasting state following vitamin B(12) therapy (P=0.007). Fasting plasma GPx fell significantly after 2 weeks of vitamin B(12) therapy (P=0.05). The change in plasma GPx between the fasting state and 4 h after methionine loading was significantly different pre- and post-vitamin B(12) therapy (P=0.05). The present study provides indirect support to the hypothesis that defects in the trans-sulphuration and remethylation of homocysteine produce hyperhomocysteinaemia in vitamin B(12) deficiency in human subjects. Elevated homocysteine levels directly or indirectly may up-regulate GPx. Sulphation status, as measured by plasma DHEAS, was unchanged.

Aged↗
PubMed2001

Long-term evaluation of electrospray ionization mass spectrometric analysis of glycated hemoglobin.

BACKGROUND: Electrospray ionization mass spectrometry (ESIMS) has been successfully applied to the identification of hemoglobin (Hb) variants and the presence of glucose adducts (mass difference of 162 Da) on the separate Hb alpha and beta chains. To establish the potential of ESIMS as a routine and/or a reference method for the quantification of glycohemoglobin (HbA1c), we carried out a detailed evaluation over a 4-month period in a routine laboratory environment. METHODS: We optimized a procedure using ESIMS suitable for the routine quantitative analysis of HbA1c. We determined reliability and reproducibility over 4 months and assessed the potential for automated sample injection. We then compared values of 1022 blood samples from diabetic patients with a routine HPLC-based ion-exchange procedure (HA-8140; Menarini). RESULTS: Results of HbA1c measurement by ESIMS were available within 3 min. The analytical imprecision (CV) was 1.6-5.0% for both manual and automated injections. Data collection over the m/z 980-1400 range confirmed lower glycation of the alpha chain relative to the beta chain (0.66:1). Only one glycation was observed per globin chain. The overall glycohemoglobin (i.e., the average of alpha- and beta-chain glycations) measured by ESIMS (x) on 1022 blood samples was lower than by HPLC (y): y = 1.0432x + 0.4815. However, the ss-chain glycation measured by ESIMS was up to 20% higher than the value measured by ion-exchange HPLC and showed a close conformity, particularly at 5-10% HbA1c, with the ion-exchange Diabetes Control and Complications Trial (DCCT)-corrected and the United Kingdom National External Quality Assessment Scheme DCCT mean return values. CONCLUSIONS: ESIMS provides a precise measurement of HbA1c and, in particular, glycation of the beta chain. The method is robust and could be proposed as a procedure to substantiate HbA1c measurement and/or calibration.

Autoanalysis↗
PubMed2001

Mucosal protective effects of ecabet sodium: pepsin inhibition and interaction with mucus.

Pepsin, acid and Helicobacter pylori are major factors in the pathophysiology of peptic ulcer disease and reflux oesophagitis. Ecabet sodium reduces the survival of H. pylori in the stomach and inhibits pepsin activity in the gastric juice of experimental animals. Here we have investigated the effects of ecabet sodium on some of the factors involved in the dynamics of the mucosal barrier, i.e. pepsins and mucins. This study used gastric juice obtained from 12 non-symptomatic volunteers and nine patients with reflux oesophagitis. Ecabet sodium significantly inhibited pepsin activity in human gastric juice, with a maximum inhibition of 78%. Pepsin 1, the ulcer-associated pepsin, was inhibited to the greatest extent. The ability of gastric juice to digest mucin was significantly inhibited by ecabet. As with gastric juice proteolytic activity, the inhibitory effect of ecabet on mucolysis was greater in gastric juice from patients with reflux oesophagitis than in that from controls. Ecabet sodium showed a positive interaction with gastric mucin, as assessed by an increase in viscosity. Thus ecabet sodium may reduce the aggressive potential of gastric juice towards the mucosa, which may be relevant in the treatment of reflux oesophagitis and peptic ulcer disease. In addition, it may strengthen the mucus barrier in peptic ulcer disease and gastritis.

Abietanes↗
PubMed2000

Human erythrocyte and plasma amino acid concentrations during exercise.

PURPOSE: This investigation examined the effects of exercise and maltodextrin (Md) or placebo (Pl) ingestion on plasma and erythrocyte concentrations of amino acids. METHODS: The erythrocyte and plasma concentrations of 17 amino acids, as well as plasma glucose and insulin, were analyzed in eight healthy trained male subjects before, during, and 25 min after 90-min cycle ergometer exercise at 65% peak oxygen uptake. The two treatments involved ingestion of orange-flavored water (Pl) or orange-flavored 10% maltodextrin solution (Md). RESULTS: Two-way ANOVA revealed 1) that plasma concentrations of alanine and tyrosine changed significantly during the treatments, 2) that the plasma concentrations were significantly different between treatments for glycine and threonine, 3) that all erythrocyte concentrations increased significantly throughout the treatments except for arginine and tyrosine, and 4) that there were no significant differences in erythrocyte concentrations between the treatments. Three-way ANOVA highlighted the significant differences in the time responses between plasma and erythrocyte concentrations; the changes in erythrocyte levels from rest being significantly different from plasma for all amino acids except aspartic acid, glycine, and ornithine. Plasma glucose concentrations became elevated and remained above rest values in Md but fell below rest values in Pl: the differences in concentration between treatments were significant. Correspondingly, plasma insulin was significantly higher in Md during exercise. CONCLUSION: These results highlight that far from being slow in the uptake of amino acids, the erythrocyte in fact sequesters amino acids at an appreciable rate during exercise without a corresponding elevation in the plasma amino acids. For a greater understanding of amino acid changes during exercise, the analysis of both plasma and erythrocytes is recommended.

Administration, Oral↗
PubMed1999

Age does not influence levels of HbA1c in normal subject.

To resolve whether haemoglobin A1c(HbA1c) levels in normal subjects increase with age, we measured HbA1c in 399 patients undergoing routine oral glucose tolerance test (OGTT). The OGTT results categorized the patients into 127 normal, 94 impaired glucose tolerance (IGT) and 178 diabetic. None of these groups showed a significant correlation between HbA1c and age and we cannot, therefore, see a need for age-specific reference ranges for HbA1c. Some of the confusion in the literature may have arisen from less rigorous categorization of subjects than we used, resulting in the inclusion of some individuals with IGT or diabetes in the 'normal' groups of other studies. The prevalence of such abnormality would be expected to be greater amongst older subjects, falsely suggesting a correlation between HbA1c and age, and we were able to demonstrate this with our own data when insufficiently rigorous criteria were applied for the selection of normal subjects.

Adolescent↗
PubMed1999

Urinary catecholamine excretion in relation to renal function.

The urinary excretions of the free catecholamines noradrenaline, adrenaline and dopamine were measured in 50 patients (33 men and 17 women) with chronic renal failure. Stability studies showed that the catecholamines were stable in unacidified urine as long as the pH was not greater than 7.5 and the urine was acidified within 2-3 h of collection. The outputs of noradrenaline and dopamine correlated positively with creatinine clearance and in patients with clearances above 40 mL/min were similar to those in healthy volunteers (n = 20). However, adrenaline output was not correlated with creatinine clearance although it was lower in patients with renal failure compared with healthy volunteers. The urinary free catecholamine output during the first 10 days after a renal transplant was significantly less than normal, presumably because renal function was still impaired. However, in patients treated with cyclosporin A (CyA) combined with prednisolone the catecholamine excretion was lower compared with those treated with CyA and azathioprine. Impairment in renal function can have a marked effect on the output of free catecholamines and must be borne in mind when interpreting values that may have pathological significance.

Case-Control Studies↗
PubMed1999

Measurement of platinum in saliva of patients treated with cisplatin.

A procedure for the measurement of platinum (Pt) in the saliva of patients treated with cisplatin has been developed. The saliva is collected and solubilized in hyamine hydroxide before analysis by graphite furnace atomic absorption spectrometry using assay by standard additions. The method has an analytical detection limit of 0.025 microgram/mL and is precise, with coefficients of variation of 3-10.0% over a range of 0.05-2.0 micrograms/mL. Platinum was measured in saliva collected during an 8-h infusion of cisplatin from five patients, at the end of a 30-min infusion in nine, and 24 and 48 h later from a further 15 patients, all of whom were treated with cisplatin for squamous cell carcinoma of the neck. The platinum concentration in saliva taken at the end of a 30-min infusion was 0.27 +/- 0.23 microgram/mL (mean +/- 1 SD) but was below the detection limit of 0.025 microgram/mL at 24 and 48 h. After an 8-h infusion the salivary Pt was significantly less (0.12 +/- 0.04 microgram/mL; P < 0.05). The plasma Pt concentrations after 30-min and 8-h infusions were 2.98 +/- 1.03 and 2.54 +/- 0.59 micrograms/mL, respectively, and were not significantly different. The results indicate higher concentrations of free platinum in plasma after 30 min compared with an 8-h infusion. The monitoring of salivary concentrations of platinum may therefore provide a non-invasive way to study the unbound fraction of cisplatin in blood and facilitate optimization of cisplatin treatment.

Adult↗
PubMed1999

Evaluation of a new method for the analysis of free catecholamines in plasma using automated sample trace enrichment with dialysis and HPLC.

BACKGROUND: Analysis of urinary free catecholamines was automated recently, but analysis of plasma samples posed special difficulties. The present study was undertaken to evaluate a new method for the automated analysis of plasma catecholamines. METHODS: The procedure is based on an improved sample handling system that includes dialysis and sample clean-up on a strong cation trace-enrichment cartridge. The catecholamines norepinephrine, epinephrine, and dopamine are then separated by reversed-phase ion-pair chromatography and quantified by electrochemical detection. RESULTS: Use of a 740- microL sample is required to give the catecholamine detection limit of 0.05 nmol/L and analytical imprecision (CV) between 1.1% and 9.3%. The assay can be run unattended, although >12 h of analysis time is not recommended without cooling of the autosampler rack. Comparison (n = 68) of the automated cation-exchange clean-up with the well-established manual alumina procedure gave excellent agreement (mean, 3.78 +/- 2.76 and 3.8 +/- 2.89 nmol/L for norepinephrine and 0.99 +/- 1.72 and 1.08 +/- 1.78 nmol/L for epinephrine). Hemodialysis had no clear effect on plasma norepinephrine. Epinephrine concentrations were similar (0.05 < P < 0.1) in chronic renal failure patients (0.24 +/- 0.3 nmol/L; n = 15) and healthy controls (0.5 +/- 0.24 nmol/L; n = 31). Dopamine was not quantified, being usually <0.2 nmol/L. CONCLUSION: The availability of such a fully automated procedure should encourage the more widespread use of plasma catecholamine estimation, e.g., after dialysis, exercise, or trauma/surgery and in the investigation of catecholamine-secreting tumors, particularly in the anuric patient.

Autoanalysis↗