Vitamin E (a-tocopherol) is the major lipid soluble antioxidant in vivo and is important for maintaining the integrity of cell membranes. Oxidative stress, defined as an imbalance between oxidants and antioxidants, has been implicated in the aetiology of numerous diseases. There is, therefore, interest in establishing methods to measure oxidative stress. It has been suggested that metabolites of vitamin E such as atocopheronolactone (a-TL), with an oxidised chroman ring, may be an indicator of in vivo oxidative stress and that the carboxyethyl-hydroxychromans (CEHCs), with a shortened phytyl side chain, may provide a measure of adequate or excess vitamin E status. However, doubts have been raised about the authenticity of a-TL since a-CEHC has been shown to be artefactually oxidised to a-TL in many of the procedures described. In the course of the current study a relatively simple method using gas chromatographymass spectrometry (GC-MS) was developed which allowed the reproducible measurement of a wide range of deconjugated vitamin E metabolites in urine. This method was used to study the urinary metabolites produced by normal subjects before and after supplementation with vitamin E. The CEHCs were confirmed as the major urinary metabolites of vitamin E, a-TL was detected and a novel group of metabolites, the carboxymethylbutyl-hydroxychromans (CMBHCs), was also tentatively identified. A range of conjugated (sulphated and glucuronidated) and free metabolites of vitamin E were synthesised chemically and used to a) confirm the identity of (x-CMBHC, b) provide standards for GC-MS and tandem mass spectrometry, c) elucidate the mechanism of artefactual oxidation and to develop new methods for the precise measurement of endogenously produced a-TL and d) investigate the type of conjugation of the various metabolites of vitamin E in human urine.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:247078 |
| Date | January 2001 |
| Creators | Pope, Simon Alexander Samuel |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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