Urinary excretion of 2,7, 8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman is a major route of elimination of gamma-tocopherol in humans

Abstract

Little is known of the post-absorptive, metabolic fate of gamma-tocopherol, the major form of vitamin E in North American diets. The objective of this study was to determine the extent of urinary excretion of 2,7, 8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a recently identified metabolite of gamma-tocopherol. A method for measurement of urinary gamma-CEHC was developed, using gas chromatography-mass spectrometry (GC-MS) with a deuterated internal standard, 2,7,8-trimethyl-2-(beta-carboxyethyl)-(3, 4-2H2)-6-hydroxychroman (d2-gamma-CEHC). This standard was synthesized by dehydrogenation of 6-acetyl-gamma-CEHC followed by deuteration of the resulting 3,4-double bond. The use of d2-gamma-CEHC resulted in accurate determinations of the concentration of d0-gamma-CEHC in human urine. Urine samples containing added d2-gamma-CEHC were treated with beta-glucuronidase, extracted with an organic solvent, and analyzed by GC-MS. Analysis of 24-h urine pools from healthy subjects revealed gamma-CEHC concentrations, normalized against creatinine, ranging from 2.5 to 31.5 micromol/g creatinine, or a total of 4.6 to 29.8 micromol per day. These results correspond to 2-12 mg gamma-tocopherol excreted daily as gamma-CEHC in the urine. Given an estimated mean intake of gamma-tocopherol of 20 mg/day, catabolism of gamma-tocopherol to gamma-CEHC, followed by glucuronide conjugation and urinary excretion, is a major pathway for elimination of gamma-tocopherol in humans.