α- and γ-Tocotrienols are metabolized to carboxyethyl-hydroxychroman derivatives and excreted in human urine

Abstract

Limited information is available regarding metabolism of vitamin E forms, especially the tocotrienols. Carboxyethyl-hydroxychromans (α- and γ-CEHC) are human urinary metabolites of α- and γ-tocopherols, respectively. To evaluate whether tocotrienols are also metabolized and excreted as urinary CEHC, urine was monitored following tocotrienol supplementation. Complete (24 h) urine collections were obtained for 2 d prior to (baseline), the day of, and 2 d after human subjects (n = 6) ingested tocotrienol supplements. The subjects consumed 125 mg γ-tocotrienyl acetate the first week, then the next week 500 mg; then 125 mg α-tocotrienyl acetate was administered the third week, followed by 500 mg the fourth week. Urinary α- and γ-CEHC were measured by high-performance liquid chromatography with electrochemical detection. Urinary γCEHC levels rose about four- to sixfold in response to the two doses of γ-tocotrienol and then returned to baseline the following day. Significant (P < 0.0001) increases in urinary α-CEHC were observed only following ingestion of 500 mg α-tocotrienyl acetate. Typically, 1-2% of α-tocotrienyl acetates or 4-6% of γ-tocotrienyl acetates were recovered as their respective urinary CEHC metabolites. A γ-CEHC excretion time course showed an increase in urinary γ-CEHC at 6 h and a peak at 9 h following ingestion of 125 mg γ-tocotrienyl acetate. In summary, tocotrienols, like tocopherols, are metabolized to CEHC; however, the quantities excreted in human urine are small in relation to dose size.