The aim of the work described in this thesis was to evaluate the potential for using stable isotope <SUP>13</SUP>C labelled tracer, 1-<SUP>13</SUP>C -AA, in studies of AA kinetics in humans. To this end a method of measuring AA isotope enrichment in plasma samples using gas chromatography and mass spectrometry, (GC/MS), was developed. Derivatisation of AA was required for gas chromatographic separation, and the trimethylsilyl, (TMS), ether derivative, AA-tetra-TMS, was found to be the most compatible with subsequent mass spectrometric quantitation of isotope enrichment. A method was developed to prepare lyophilized plasma samples for TMS derivatisation. Two studies of AA kinetics in human volunteers were than carried out in which a dose of stable isotope labelled 1-<SUP>13</SUP>C-AA was administered orally. The enrichment of AA was measured in plasma samples collected for 24 and 48 hours after dosing. In the second study, investigation of isoascorbic acid, (IAA), kinetics was also undertaken. IAA concentration in plasma samples was measured by high performance liquid chromatography, HPLC. Compartment models of AA and IAA handling in man were constructed and described as a series of mathematical expressions containing kinetic parameters. Kinetic analysis was achieved by fitting theoretical values calculated from the mathematical expressions describing the models to the observed (time course) data. This produced estimates of kinetic parameters, (flow constants and pool sizes), describing AA and IAA handing in man. These were compared with those obtained in other studies. The method is now being applied to further studies into the bioavailability, metabolism and utilization of AA in humans and has the potential to be a useful non-invasive technique which may provide an invaluable insight into the vitamin C status of individuals in a variety of populations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:604981 |
| Date | January 1998 |
| Creators | Izzard, A. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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