Submitted on January 19, 2007
Revised on February 12, 2007
Accepted on February 13, 2007
Identification and quantitation of novel vitamin E metabolites, sulfated long-chain carboxychromanols, in human A549 cells and in rats
Qing Jiang, Helene Freiser, Karl V. Wood, and Xinmin Yin
Foods and Nutrition, Purdue University, West Lafayette, IN 47907
Corresponding Author: qjiang{at}purdue.edu
Metabolism of vitamin E involves oxidation of the phytyl chain to generate terminal metabolite CEHCs [(2-carboxyethyl)-hydroxychroman], via intermediate formation of 13-hydroxychromanol and long-chain carboxychromanols. Conjugated (including sulfated) metabolites were previously reported, but were limited to CEHCs. Here, employing electrospray and inductively-coupled plasma mass spectrometry, we discovered that
-tocopherol and
-tocopherol were metabolized to sulfated 9-, 11- and 13-carboxychromanols in human A549 cells. To further study the metabolites, we developed a HPLC assay with fluorescent detection that simultaneously analyzes sulfated and non-conjugated intermediate metabolites. Using this assay, we found that sulfated metabolites were converted to non-conjugated carboxychromanols by sulfatase digestion. In cultured cells, approximately 45% long-chain carboxychromanols from
-tocopherol but only 10% from
-tocopherol were sulfated. Upon supplementation with
-tocopherol, rats had elevated tissue levels of sulfated 9-, 11- and 13-carboxychromanols, 13-hydroxychromanol, 13-carboxychromanol and
-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
-tocopherol. Our study identified sulfated long-chain carboxychromanols as novel vitamin E metabolites, and provided evidence that sulfation may occur parallel with
-oxidation. In addition, the HPLC-fluorescent assay is a useful tool for investigation of vitamin E metabolism.