Monthly Archives: January 2001

We have investigated the pharmacokinetics and bioavailability of α-, γ- and δ-tocotrienolsmunder fed and fasted conditions in eight healthy volunteers. The volunteers were administered a single oral dose of mixed tocotrienols (300 mg) undermfed or fasted conditions. The bioavailability of tocotrienols under the two conditions wasmcompared using the parameters peak plasma concentration (Cmax), time to reach peak plasmaconcentration (Tmax) and total area under the plasma concentration±time curve (AUCo-α). A statistically significant difference was observed between the fed and fasted logarithmic transformed values of Cmax (P<0.01) and AUCo-α (P <0.01) for all three tocotrienols. In addition, the 90% confidence intervals for the ratio of the logarithmic transformed AUCo-α values of α-, γ- and δ-tocotrienols under the fed state over those of the fasted state were found to lie between 2.24±3.40, 2.05±4.09 and 1.59±3.81, respectively, while those of the Cmax were between 2.28±4.39, 2.31±5.87 and 1.52±4.05, respectively. However, no statistically significant difference was observed between the fed and fasted Tmax values of the three homologues. The mean apparent elimination half-life (t1/2) of α-, γ- and δ-tocotrienols was estimated to be 4.4, 4.3 and 2.3 h, respectively, being between 4.5- to 8.7-fold shorter than that reported for α-tocopherol. No statistically significant difference was observed between the fed and fasted t ½ values. The mean apparent volume of distribution (Vd/f) values under the fed state were significantly smaller than those of the fasted state, which could be attributed to increased absorption of the tocotrienols in the fed state.

Limited information is available regarding metabolism of vitamin E forms, especially the tocotrienols. Carboxyethyl-hydroxychromans (alpha- and gamma-CEHC) are human urinary metabolites of alpha- and gamma-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 gamma-tocotrienyl acetate the first week, then the next week 500 mg; then 125 mg alpha-tocotrienyl acetate was administered the third week, followed by 500 mg the fourth week. Urinary alpha- and gamma-CEHC were measured by high-performance liquid chromatography with electrochemical detection. Urinary gamma-CEHC levels rose about four- to sixfold in response to the two doses of gamma-tocotrienol and then returned to baseline the following day. Significant (P < 0.0001) increases in urinary alpha-CEHC were observed only following ingestion of 500 mg alpha-tocotrienyl acetate. Typically, 1-2% of alpha-tocotrienyl acetates or 4-6% of gamma-tocotrienyl acetates were recovered as their respective urinary CEHC metabolites. A gamma-CEHC excretion time course showed an increase in urinary gamma-CEHC at 6 h and a peak at 9 h following ingestion of 125 mg gamma-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.