A Novel 5′-Carboxychroman Metabolite of γ-Tocopherol Secreted by HepG2 Cells and Excreted in Human Urine

Abstract

HepG2 cells were incubated with a medium containing fetal bovine serum enriched with RRR-γ-tocopherol (γ-TOH). After 48 h the medium was extracted and analyzed for γ-TOH metabolites by gas chromatography-mass spectrometry. In addition to γ-CEHC, the 3′-carboxychroman metabolite of γ-TOH previously reported in human urine, these cells secreted a second substance whose extraction and mass spectral characteristics were consistent with those of the 5′-carboxychroman analog of γ-CEHC, 2,7,8-trimethyl-2-(δ-carboxymethylbutyl)-6-hydroxychroman. This is the first report of metabolism of γ-TOH to carboxychroman metabolites in cell culture. Analysis of human urine samples revealed the consistent presence of the novel 5′-carboxychroman metabolite, along with that of γ-CEHC. Oral supplementation with purified RRR-γ-TOH resulted in elevated urinary concentrations of both metabolites, although the concentration of the 5′-γ-carboxychroman metabolite was consistently and substantially less than that of γ-CEHC. The presence of both metabolites is consistent with the involvement of an ω-oxidation-like process in the phytyl tail shortening of γ-TOH to water soluble metabolites excreted in urine.