Associations of metabolomic profiles with circulating vitamin E and urinary vitamin E metabolites in middle-aged individuals

Vitamin E (α-tocopherol, α-TOH) is transported in lipoprotein particles in blood, but little is known about the transportation of its oxidized metabolites. In the Netherlands Epidemiology of Obesity Study, we aimed to investigate the associations of 147 circulating metabolomic measures obtained through targeted nuclear magnetic resonance (NMR) with serum α-TOH and its urinary enzymatic (α-CEHC) and oxidized (α-TLHQ) metabolites from 24-hour urine quantified by LC/MS-MS. Multivariable linear regression analyses, in which multiple testing was taken into account, were performed to assess associations between metabolomic measures (determinants; standardized to mean = 0, SD = 1) with vitamin E metabolites (outcomes), adjusted for demographic factors. We analyzed 474 individuals (45% men) with mean (SD) age of 55.7 (6.0) years. Out of 147 metabolomic measures, 106 were associated (p < 1.34E-3) with serum α-TOH [median beta (IQR): 0.416 (0.383, 0.466)], predominantly lipoproteins associated with higher α-TOH. The associations of metabolomic measures with urinary α-CEHC are with similar directions as those with α-TOH, but effect sizes were smaller and non-significant [median beta (IQR):0.065 (0.047, 0.084)]. However, associations of metabolomic measures with urinary α-TLHQ were markedly different from the associations of metabolomic measures with both serum α-TOH and urinary α-CEHC, with negative and small-to-null relations to most VLDL and amino acids. Therefore, our results highlight the differences of the lipoproteins involved in the transportation of circulating α-TOH and oxidized vitamin E metabolites. This indicates that circulating α-TOH may be representative of the enzymatic but not to antioxidative function of vitamin E