Willem J. Serfontein

Stability of pyridoxal-5-phosphate semicarbazone: applications in plasma vitamin B6 analysis and population surveys of vitamin B6 nutritional status

The determination of pyridoxal-5-phosphate (PLP) and pyridoxal (PL) in plasma requires the availability of dark room facilities, due to the photosensitivity of these vitamin B6 vitamers. The fact that the semicarbazone forms of PL and PLP are more strongly fluorescent than the underivatized B6 vitamers has been exploited in plasma analyses, but it was not previously realised that these semicarbazone forms are also very stable even under conditions that lead to rapid decomposition of free PL and PLP. The stabilisation of PLP and PL obtained in this manner is sufficient and fully adequate to meet the practical requirements of clinical field studies. We report a high-performance liquid chromatographic method for plasma PLP and PL determinations based on precolumn semicarbazone formation and fluorescence detection. The method is sensitive enough for quantitative plasma PLP determinations even in B6-deficient patients.

Plasma pyridoxal-5-phosphate level as risk index for coronary artery disease

Preliminary evidence is presented that plasma pyridoxal-5-phosphate levels are considerably and significantly reduced (P less than 0.0001) in patients suffering from myocardial infarction when compared to a healthy control group.

The Relationship between Vitamin B6 Metabolism, Asthma, and Theophylline Therapy

Asthma can be broadly defined as enhanced reactivity of the airways to specific and nonspecific stimuli, resulting in diffuse airways obstruction with clinical symptoms like dyspnea, cough, and a tight chest. Stimuli that may provoke asthmatic responses include environmental allergens, respiratory infection, certain drugs such as nonsteroidal anti-inflammatory drugs, and exercise.’ An important aspect of asthma treatment is the administration of bronchodilators of which theophylline is most commonly used.2 As will be reviewed in this paper, vitamin B, status and asthma have been studied by several researchers3^’; however, the effect of medication per se on vitamin B, status has not been investigated. Because it would be practically impossible to study vitamin B, status in asthmatics without the use of bronchodilators, we opted for the alternative: to study the effect of bronchodilators on vitamin B, metabolism in healthy volunteers. We therefore investigated the effect of theophylline on vitamin B, metabolism in healthy volunteers, and our results are summarized and reviewed in the second part of this paper.

The direct quantification in whole serum of HDL subfractions

A method is described for the direct electrophoretic separation in human serum of three HDL subfractions and the quantification of the cholesterol content of these by means of gas-liquid chromatography. Used in conjunction with established procedures for the separation of total HDL, VLDL and LDL on agarose gels (with gas-liquid chromatography quantification of cholesterol in each band) the procedure affords comprehensive information on lipoprotein metabolism in patients. Two technicians can process 10 samples per day, making the method suitable for semi-large scale screening of patients such as may occur in clinical trials or to evaluate in greater detail lipoprotein patterns of patients suspected of having lipoprotein abnormalities on the basis of simpler screening methods. Results obtained by the method correlate well with those obtained by means of ultracentrifugation.

A rapid g.l.c. procedure for the determination of codeine and norcodeine in biological fluids based on micro-phase extraction techniques.

Therapeutic serum concentrations of codeine can be virtually completely extracted and obtained sufficiently concentrated for g.c. measurement without distillation, by acid extraction of the drug from the initial crude organic extracts of alkalinized serum followed by a micro‐phase back extraction step. The procedure has simplicity, rapidity and eliminates concentration by distillation and background interference. The method can be readily adapted for the separate measurement of codeine and norcodeine and it can also be used for similar analyses of other body fluids.

A new g.c. procedure, based on nitrosation, for the simultaneous determination of propoxyphene and norpropoxyphene in biological material

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