Identification and quantitation of novel vitamin E metabolites, sulfated long-chain carboxychromanols, in human A549 cells and in rats

The metabolism of vitamin E involves oxidation of the phytyl chain to generate the terminal metabolite 7,8-dimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (CEHC) via intermediate formation of 13'-hydroxychromanol and long-chain carboxychromanols. Conjugated (including sulfated) metabolites were reported previously but were limited to CEHCs. Here, using electrospray and inductively coupled plasma mass spectrometry, we discovered that gamma-tocopherol (gamma-T) and delta-T were metabolized to sulfated 9'-, 11'-, and 13'-carboxychromanol (9'S, 11'S, and 13'S) in human A549 cells. To further study the metabolites, we developed a HPLC assay with fluorescence detection that simultaneously analyzes sulfated and nonconjugated intermediate metabolites. Using this assay, we found that sulfated metabolites were converted to nonconjugated carboxychromanols by sulfatase digestion. In cultured cells, approximately 45% long-chain carboxychromanols from gamma-T but only 10% from delta-T were sulfated. Upon supplementation with gamma-T, rats had increased tissue levels of 9'S, 11'S, and 13'S, 13'-hydroxychromanol, 13'-carboxychromanol, and gamma-CEHC. The plasma concentrations of combined sulfated long-chain metabolites were comparable to or exceeded those of CEHCs and increased proportionally with the supplement dosages of gamma-T. Our study identifies sulfated long-chain carboxychromanols as novel vitamin E metabolites and provides evidence that sulfation may occur parallel with beta-oxidation. In addition, the HPLC fluorescence assay is a useful tool for the investigation of vitamin E metabolism.