Measurement of -Tocopherol Turnover in Plasma and in Lipoproteins Using Stable Isotopes and Gas Chromatography/Mass Spectrometry

As the primary fat-soluble antioxidant in human tissues, α-tocopherol absorption and metabolism have been the focus of active investigation, as reviewed recently (
1
,
2
). Although the concentration of any metabolite measured in plasma or tissue at a given time can be used as an indicator of the status of that pool, the true biological activity of molecules is better represented by their turnover. The use of stable isotopes in biological research has expanded steadily since the 1950s. The availability of methods has also increased as a result of improvements in instrument sensitivity and automation. Vitamin E studies utilizing gas chromatography-mass spectrometry (GC-MS) have aided in the elucidation of vitamin E absorption and transport, as well as the identification of vitamin E oxidation byproducts (
3
). Human vitamin E studies using stable isotopes of α-tocopherol (deuterated molecules) have evaluated plasma α-tocopherol levels in response to increasing vitamin E doses (
4
) and the selective secretion of RRR-α-tocopherol from the liver out in nascent very low-density lipoproteins (VLDL) (
5
,
6
).