The effect of decreasing the concentration of urinary urate on the crystallization of calcium oxalate in undiluted human urine.

The effect of lowering the urate concentration, using uricase immobilized on to nylon tubing, on the nucleation, growth and aggregation of calcium oxalate crystals in undiluted human urine was examined. The median urate concentration was significantly (p less than 0.01) reduced from 2.8 to 0.55 mmol/l., but this had no reproducible effect on the metastable limits, the volume of crystalline calcium oxalate deposited and the size of the crystals and aggregates produced from the 10 urine samples examined. It was concluded that further studies aimed at testing the effects of a raised urinary urate concentration on the crystallization of calcium oxalate should be made a matter of high priority.

The long-term effect of dietary administration of refined sugars and sugar alcohols on plasma biochemistry, urine biochemistry and tissue histology in mice given a limited degree of dietary self-selection.

A prototype animal feeding model is described in which mice were meal-fed a balanced diet but were given free access to water (controls) or 20% (w/v) solutions of glucose, sucrose, fructose, xylitol or sorbitol. Under these conditions it was found that the provision of an alternative energy source, in the form of a refined carbohydrate, produced marked effects on total energy intake, mouse cube (i.e. balanced energy) intake and body weight. There were also changes in the metabolic states of the animals as assessed by serum levels of glucose, urea and cholesterol, plasma levels of lactate and D-3-hydroxybutyrate, and urinary excretion of urea and oxalate. Histological examinations of tissue indicated that the sucrose-fed mice had a tendency to suffer from acute congestion of the lungs and liver steatosis. Given a limited degree of dietary self-selection it appears that mice are more likely to be at risk of excessive food consumption and obesity when given glucose- or sucrose-containing diets than they are when fructose-, xylitol- or sorbitol-containing diets are given.

Urinary glycolate measured by use of (S)-2-hydroxy-acid oxidase.

Glycolate can be determined in urine by using (S)-2-hydroxy-acid oxidase (EC 1.1.3.15; formerly called "glycolate oxidase"), either immobilized in a continuous-flow system or in a semiautomated procedure for the centrifugal analyzer. In the presence of peroxidase (EC 1.11.1.7), the hydrogen peroxide formed from glycolate is detected by use of a peroxide indicator reaction. Before the analysis, urine must be treated with charcoal to remove reducing substances such as ascorbic acid, which interfere with the assay by decreasing the color of the indicator reaction. Lactate also interferes with the determination of glycolate because it also is a substrate for this oxidase; thus a correction has to be made for the lactate content of urine. The system with (S)-2-hydroxy-acid oxidase immobilized to the inner surface of nylon tubing is accurate, precise, and sensitive but unsuitable for routine use because, even immobilized, the oxidase is unstable and can only be used for 12 days. We have used the semiautomated assay routinely: it has a mean analytical recovery of 96% (SD 4.2%), a within-batch CV less than 2%, and a between-batch CV less than 5%. The normal reference interval for urinary excretion of glycolate so measured is 0.13 to 1.31 mmol per day (n = 55).

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.

The inhibition of bacterial cell growth by ketone bodies.

The effect of ketone bodies on the growth, in culture, of Escherichia coli was investigated. Both growth and glucose utilisation were inhibited in the presence of 20 mmol/l D-3-hydroxybutyrate. Lower concentrations of D-3-hydroxybutyrate caused proportionally less inhibition of growth. Acetoacetate also inhibited growth but other glycolytic inhibitors and chemical analogues of D-3-hydroxybutyrate either did not inhibit or proved to be too toxic for bacterial growth. Citrate enhanced the ketone body effect. D-3-hydroxybutyrate also inhibited the growth of Klebsiella pneumoniae, Enterobacter aerogenes, Citrobacter freundii and Salmonella typhimurium. The possible relationship between ketone body inhibition of cell growth and oxygen limitation is discussed.

The inhibition of malignant cell growth by ketone bodies.

The effect of ketone bodies on the growth, in culture, of transformed lymphoblasts (Raji cells) was investigated. Cell growth was inhibited and this effect was reversible, non-toxic, and proportional to the concentration of D-beta-hydroxybutyrate up to 20mM. The total glucose utilisation and the total lactate production were reduced in proportion to the inhibition of cell proliferation. D-beta-hydroxybutyrate was not metabolised by the cells. Other glycolytic inhibitors and chemical analogues of D-beta-hydroxybutyrate either did not inhibit or proved to be too toxic for cell growth. D-beta-hydroxybutyrate also inhibited the growth of rabbit kidney (RK13), HeLa, mouse melanoma (B16), fibroblast and trypsin-dispersed human thyroid and beef testis cells. Moreover, in vivo dietary-induced ketosis reduced the number of B16 melanoma deposits in the lungs of C57BL/6 mice by two-thirds. The significance of these results in the clinical management of cancer cachexia is discussed.

Assessment of the Beckman System 1.

The System 1 produced results for glucose and urea which were precise and accurate. It proved suitable as a general laboratory instrument as it samples 28 mul of specimen, is able to calibrate itself, produces results in three minutes, and has the capacity to analyse 56 samples an hour.