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Biomedical subjects

J B Edwards

Publications and source records attributed to J B Edwards.

At least 37 records · Page 2Linked to original sources
PubMed1983

Preparation and characterization of a human serum matrix suitable for quality control or reference materials.

We describe the preparation of a human serum based matrix suitable for inclusion in long-term control materials. The procedure entails the removal of cells, fibrin and lipoproteins from blood to produce a clear, stable material which has been stored frozen at -70 degrees C for up to 14 mth without any apparent deterioration. When incorporated into a quality control material, storage at 4 degrees and -20 degrees C may cause a change in several unstable constituents, but the material remains optically clear. A noticeable reduction in lipoprotein as a result of the preparative procedure is probably responsible for the continued clarity of the matrix. The nature of the matrix has been examined by polyacrylamide gel electrophoresis and does not reveal any unusual protein bands, whereas commercially available materials when similarly examined often reveal protein bands not present in normal serum. The matrix has been used to prepare control material for the Chemical Pathology Quality Assurance Programme Group of the Royal College of Pathologists of Australasia/Australian Association of Clinical Biochemists.

Blood Chemical Analysis↗
PubMed1983

Urinary oxalate determination by use of immobilized oxalate oxidase in a continuous-flow system.

In this procedure, oxalate oxidase (EC 1.2.3.4) immobilized in a continuous-flow system is used to determine oxalate in urine. The hydrogen peroxide formed from oxalate is detected by use of a color reaction with peroxidase (EC 1.11.1.7), 3-methyl-2-benzothiazoline hydrazine, and N,N-dimethylalanine. However, urine contains an oxalate oxidase inhibitor, which cannot be removed by heating, ion-exchange resins, or cellulose columns. This makes it necessary to precipitate the oxalate before assay. The overall assay system is accurate (oxalate recovery, 95.9%), sensitive (less than or equal to 5 mumol/L), precise (within-batch CV less than 1.25%, between-batch CV less than 5%), and relatively rapid (60 samples per working day). The assay system has better accuracy than an established chemical method and a gas-chromatographic method, and is considerably less arduous than and correlates well (r = 0.94) with a modified chemical method. The reference interval for urinary oxalate excretion is 0.16-0.56 mmol per day (n = 97). Only nonphysiological concentrations of ascorbate interfere with the assay, by increasing the oxalate result in the overall assay, presumably by post-micturition formation of oxalate from ascorbate in the urine samples.

Adult↗
PubMed1982

Models for the metabolic production of oxalate from xylitol in humans: a role for fructokinase and aldolase.

It has been proposed previously that oxalate precursors may be formed in the transketolase reaction during the metabolism of xylitol. It is shown in this paper that fructokinase and aldolase, purified from human liver, provide an alternative model in that, in coupled sequence, they produce glycolaldehyde, an oxalate precursor, from D-xylulose via D-xylulose 1-phosphate; D-fructose does not give rise to glycolaldehyde. It is concluded that metabolic pathways based on a combination of the transketolase, fructokinase and aldolase reactions can account for the production of glucose, lactate, tetronates (C-threonic and D-erythronic acids) and oxalate (precursors) during the metabolism of xylitol administered parenterally.

Fructokinases↗
PubMed1982

A mechanism for the thiamin-sparing action of dietary xylitol in the rat.

The changes induced by dietary xylitol in the gastrointestinal tract of the rat were investigated in relation to the phenomenon of vitamin-sparing. Within 18 days of consuming a synthetic diet, deficient in thiamin, riboflavin and pyridoxine, rats ceased to grow and began to lose weight rapidly. If xylitol was then included in the diet (10% w/w), the effect of the vitamin-deficient diet on growth was reversed. Moreover, within 3 days of the rats ingesting xylitol, the metabolism of this sugar polyol by the caecal microflora was increased 17-fold and the caecal concentrations of thiamin and thiamin pyrophosphate were increased 5-fold. Increases were also observed in the caecal size, the weight of the caecal contents, and the weight of the caecal wall. In contrast to the rapid changes observed within the caecum, liver thiamin pyrophosphate levels did not rise until 6-12 days after the feeding of xylitol, at which time the rats had begun to gain weight. The caecal contents were shown to contain facultative bacteria which have the ability to metabolise and grow on xylitol and which can, at the same time, synthesise thiamin. Species of the genera Klebsiella, Serratia and Micrococcus which have this ability were isolated from the caecal contents of rats. It is assumed that coprophagy is the means by which the thiamin and other vitamins synthesised by enteral bacteria become available to the host, although some absorption from the caecum cannot be excluded.

Animals↗
PubMed1982

Creatine kinase.

Creatine kinase is present in significant concentrations in skeletal muscle and cardiac muscle and to a lesser extent in gastrointestinal tract and brain tissue. The enzyme has been purified from a variety of tissues and an examination of its kinetic and physical properties reveal that the enzyme consists of two subunits and can exist as three isoenzymes containing essential cysteine residues. These properties are important in understanding its stability, the assay conditions, and the techniques used to identify the different isoenzymes. The relationship between the properties and the determination of the enzyme in biological fluids will be a main thrust of the review. Creatine kinase activity in serum rises rapidly in conditions such as acute myocardial infarction and trauma to skeletal muscle. However, the interpretation of such increases is dependent upon a sound knowledge of the factors which influence both the total and isoenzyme activities. The nature of these factors will be discussed in detail.

Animals↗
PubMed1980

The production of (14C) oxalate during the metabolism of (14C) carbohydrates in isolated rat hepatocytes.

Oxalate (14C) was produced during the metabolism of (U-14C) carbohydrates in hepatocytes isolated from normal rats. At 10 mM, the order of oxalate production was fructose > glycerol > xylitol > sorbitol greater than or equal to glucose in the ratio 10 : 4 : 3 : 1 : 1. This difference between oxalate production from fructose and glucose was reflected in their rates of utilisation, glucose being poorly metabolised in hepatocytes from fasted rats. Fructose was rapidly metabolised, producing glucose, lactate and pyruvate as the major metabolites. Glycerol, xylitol and sorbitol were metabolised at half the rate of fructose, the major metabolites being glucose, lactate and glycerophosphate. The marked similarity in the pattern of intermediary metabolites produced by these polyols was not, however, reflected in the rates of oxalate production. Hepatic polyol metabolism resulted in high levels of cytosolic NADH, as indicated by elevated lactate : pyruvate and glycerophosphate : dihydroxyacetone phosphate ratios. The artificial electron acceptor, phenazine methosulphate (PMS) stimulated oxalate production from the polyols, particularly xylitol. In the presence of PMS, the order of oxalate production was fructose greater than or equal to xylitol > glycerol > sorbitol in the ratio 10 : 10 : 6 : 2. The production of glucose, lactate and pyruvate from the polyols was also stimulated by PMS, whereas the general metabolism of fructose, including oxalate production, was little affected. Oxalate (14C) was produced from (1-14C), (2-14C) and (6-14C) but not (3,4-14C) glucose in hepatocytes isolated from non-fasted, pyridoxine-deficient rats. Whilst this labelling pattern is consistent with oxalate being produced by a number of pathways, it is suggested that metabolism via hydroxypyruvate is a major route for oxalate production from various carbohydrates, with perhaps the exception of xylitol, which appears to have an alternative mechanism for oxalate production. The observation that carbohydrates, particularly fructose, contribute to endogenous oxalate production lends support to the hypothesis that a high sucrose consumption contributes to the formation of renal oxalate stones in man.

Animals↗
PubMed1980

Some biochemical studies on the adaptation associated with xylitol ingestion in rats.

The mechanism of adaptation to dietary carbohydrates was investigated by examining cellular metabolism in the liver and gut lumen. The inclusion of 10% (w/w) glucose, fructose, sucrose, xylose, sorbitol, xylitol or arabitol in the diet of rats for 7 days had essentially no effect on the ability of liver homogenates to produce 14CO2 from labelled glucose, fructose, xylose, sorbitol or xylitol. Moreover, no major changes were observed in the activities of hepatic enzymes. In these studies, diarrhoea and caecal distension were only observed in those rats receiving dietary sugar alcohols. Rats were also fed 0, 2.5, 5, 10, and 20% (w/w) xylitol in their diets for periods ranging from 1 to 14 days. These diets caused no significant changes in 16 of the commonly assessed blood parameters which included liver function tests. Xylitol feeding, however, caused distension, caecal gas production, decreases in the pH of caecal contents, the appearance of a fluffy layer in the centrifuged specimens of caecal contents, and diarrhoea. These changes were directly related to the concentration of xylitol in the caecal contents. After various periods, and depending on the concentration of xylitol in the diet, the rats underwent an adaptation which reduced the incidence of diarrhoea. In the short term, dietary xylitol does not affect the function of the liver or the gut wall, but causes an adaptation within the gut microflora. This adaptation leads to the increased ability of gut microflora to utilise xylitol, followed by a subsequent reduction in the caecal osmotic load and diarrhoea.

Adaptation, Physiological↗
PubMed1980

The effect of dietary xylitol on the ability of rat caecal flora to metabolise xylitol.

The effect of dietary xylitol on the ability of the rat caecal flora to metabolise xylitol was investigated. Xylitol metabolism in micro-organisms has generally been assessed in terms of pH change and acid production which are often insensitive in demonstrating low rates of substrate utilisation. Using a rapid and sensitive radioisotopic assay, in which 14CO2 production from [U-14C] xylitol was measured, it was possible to show that the caecal microflora obtained from rats can metabolise xylitol. This activity was increased 10, 15, 30 and 40-fold in the caecal flora taken from rats fed diets containing 2.5,5,10 and 20% xylitol, respectively. Using the caecal microflora of normally fed rats, the order of 14CO2 production from 14C-labelled sugars and sugar alcohols was glucose greater than fructose greater than xylose greater than sorbitol greater than or equal to xylitol. The feeding of glucose and fructose did not alter the 14CO2 producing activities, whereas xylose feeding increased xylose metabolism, sorbitol feeding increased sorbitol and xylitol metabolism, xylitol feeding increased sorbitol, xylose and its own metabolism and arabitol feeding increased xylose and sorbitol metabolism. Marked changes were also observed in the population of the caecal flora of xylitol-fed rats, with increases in the number of gram-positive bacteria, compared to rats on a normal diet. Possible mechanisms for these effects involve mutation, selection of micro-organisms capable of metabolising sugar alcohols, and the induction of enzymes involved in sugar alcohol metabolism.

Adaptation, Physiological↗
PubMed1980

Metabolic and cardiovascular side effects of the beta 2-adrenoceptor agonists salbutamol and rimiterol.

The metabolic and cardiovascular side-effects of intravenous infusions of therapeutic doses of beta 2-adrenoceptor agonists salbutamol and rimiterol have been determined in four healthy male subjects. There were dose-related increases in plasma glucose, renin activity, serum insulin and heart rate, and significant hyperlactataemia and ketonaemia. There were dose-related decreases in plasma potassium, phosphate and corticosteroids and significant hypocalcaemia and hypomagnesaemia. The effects of equivalent molar amounts of salbutamol and rimiterol were similar. Whichever drug is used, special care is required with patients who may have abnormal glucose tolerance, potassium depletion, or be predisposed to lactic acidosis. Rimiterol may be preferable for infusion because of its short plasma half-life.

Albuterol↗
PubMed1980

Increased creatine kinase activities associated with haemolysis.

The effect of haemolysis on creatine kinase activity has been investigated. The presence of adenylate kinase released from erythrocytes increases the apparent creatine kinase activity. This can be overcome by the addition of 10 mumol/l of diadenosine pentaphosphate to the reagents.

Adenine Nucleotides↗
PubMed1979

Oxalate excretion in rats injected with xylitol or glycollate: stimulation by phenobarbitone pre-treatment.

The hypothesis that the prior intake of barbiturates may predispose patients to form increased amounts of oxalate following the intravenous infusion of xylitol was investigated in the rat. Phenobarbitone pre-treatment resulted in a 2-3 fold increase in urinary [14C] oxalate concentration following the intraperitoneal injection of [U-14C] xylitol or [l -14C] glycollate. The absence of any marked changes in urine volumes and creatinine excretion implied that this increase in urinary oxalate excretion was due to the enhanced synthesis of oxalate. The activities of key enzymes in hepatic oxalate synthesis, glycollate oxidase, lactate dehydrogenase, catalase and alanine aminotransferase were not altered by phenobarbitone pre-treatment. It is suggested that the increased activity of the microsomal mixed function oxidases, following phenobarbitone treatment, may facilitate the oxidation of glycollate and possibly xylitol. This communication leads experimental support to the concept that the prior intake of drugs, such as barbiturates, may predispose patients to form increased amounts of oxalate.

Animals↗
PubMed1979

Nalidixic acid and lactic acidosis.

Nalidixic acid may cause severe acidosis and we report a fatal case of lactic acidosis assocaited with nalidixic acid therapy. Studies in normal volunteers showed drug related impairment of lactate metabolism. We question whether the drug should be used in patients who may accumulate the drug or be predisposed to lactic acidosis.

Acidosis↗
PubMed1977

Formation of oxalate in pyridoxine or thiamin deficient rats during intravenous xylitol infusions.

Glucose, fructose, sorbitol and xylitol were assessed as precursors of oxalate in normal rats and rats deficient in thiamin or vitamin B-6. Urinary excretions of oxalate, glyoxylate and glycine were increased significantly in vitamin B-6 deficient rats infused with xylitol when compared with all other groups. Using [U-14C]xylitol, oxalate was shown to be derived directly from this polyalcohol in vitamin B-6 deficient rats. These results suggest that vitamin B-6 deficiency may be a factor contributing to oxalate crystal deposition seen in some patients infused with xylitol.

Animals↗