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

Abstract

The metabolism of vitamin E involves oxidation of the phytyl chain to generate the terminal metabolite 7,8-dimethyl-2-(β-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 γ-tocopherol (γ-T) and δ-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, ∼45% long-chain carboxychromanols from γ-T but only 10% from δ-T were sulfated. Upon supplementation with γ-T, rats had increased tissue levels of 9′S, 11′S, and 13′S, 13′-hydroxychromanol, 13′-carboxychromanol, and γ-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 γ-T. Our study identifies sulfated long-chain carboxychromanols as novel vitamin E metabolites and provides evidence that sulfation may occur parallel with β-oxidation. In addition, the HPLC fluorescence assay is a useful tool for the investigation of vitamin E metabolism.

Keywords

• tocopherol
• tocotrienol
• 7,8-dimethyl-2-(β-carboxyethyl)-6-hydroxychroman
• sulfation
• metabolism
• high-performance liquid chromatography