Rice bran is a rich natural source of vitamin E and gamma-oryzanol, which have been extensively studied and reported to possess important health-promoting properties. However, commercial rice bran is a mixture of rice bran and germ, and profiles of vitamin E and gamma-oryzanol components in these two different materials are less well-studied. In the current study, vitamin E and gamma-oryzanol components in rice bran and germ were analyzed by liquid chromatography/mass spectrometry/mass spectrometry. The components were identified by electrospray ionization mass spectrometry (ESI-MS) with both positive- and negative-ion modes. Both deprotonated molecular ion [M – H](-) and protonated molecular ion [M + H](+) found as the base peaks in spectra of vitamin E components made ESI-MS a valuable analytic method in detecting vitamin E compounds, especially when they were at very low levels in samples. Ultraviolet absorption was used for quantification of vitamin E and gamma-oryzanol components. While the level of vitamin E in rice germ was 5 times greater than in rice bran, the level of gamma-oryzanol in rice germ was 5 times lower than in rice bran. Also, the major vitamin E component was alpha-tocopherol in rice germ and gamma-tocotrienol in rice bran. These data suggest that rice bran and germ have significantly different profiles of vitamin E and gamma-oryzanol components. The method enables rapid and direct on-line identification and quantification of the vitamin E and gamma-oryzanol components in rice bran and germ.
Monthly Archives: September 2007
The present paper describes the development and validation of a normal-phase liquid chromatography-mass spectrometry (NP-HPLC-MS) method for the screening and quantification of vitamin E constituents in human plasma and food matrixes. Liquid-liquid extraction combined with isotope dilution was applied to extract the lipophilic target analytes. Baseline separation of alpha-tocopherylacetate, alpha-tocopherol, alpha-tocotrienol, alpha-tocopherylquinone, beta-tocopherol, gamma-tocopherol, beta-tocotrienol, gamma-tocotrienol, delta-tocopherol, and delta-tocotrienol was achieved utilizing a normal-phase amine column operated with n-hexane and 1,4-dioxane as solvents. Detection was achieved by positive-ion atmospheric-pressure chemical ionization (APCI). Key features of the method are lower limits of detection, 3-51 nmoles/L; lower limits of quantification, 8-168 nmoles/L; linearity coefficients, 0.9778-0.9989; linear ranges, 0.01-29 micromol/L; recoveries, 53-92%; accuracies, 99-103%; intraday precisions, 2-17%; interday precisions, 5-18%; and suppression values, 0-29%. Fragmentation of tocopherols was studied by tandem mass spectrometry, and a fragmentation scheme for tocotrienols/tocopherols is postulated. Neutral-loss and precursor-ion scan experiments were performed for targeted discovery of oxidation products of tocopherols in human blood and fish oil, the latter being an important food component. The presented data suggest that this method will help to expand the number of quantified/discovered vitamin E constituents detected in food products and analyzed during human/animal trials in order to give a more comprehensive picture to nutritionists about the fate of vitamin E.
2R-gamma-Tocotrienol (gamma-T3) is currently receiving attention because it has beneficial effects not observed with alpha-tocopherol. To achieve the effective delivery of gamma-T3, we synthesized three kinds of ester derivatives of gamma-T3 and evaluated their use as hydrophilic prodrugs for gamma-T3 in vitro and in vivo. 2R-gamma-Tocotrienyl N,N-dimethylamino-acetate hydrochloride (compound 3) was a solid compound, with high solubility and stability in water, and was converted to gamma-T3 by esterases in rat and human liver. Intravenous administration of 3 in rats led to a rapid increase in the plasma, liver, heart, and kidney levels of gamma-T3. The bioavailability (plasma level) after intravenous administration was 82.5 +/- 13.4% and 100 +/- 11.3% for 3 and gamma-T3 in surfactant, respectively, and the availability in liver was 213 +/- 47.6% and 100 +/- 4.8% for 3 and gamma-T3 in surfactant, respectively. Furthermore, the systemic availability of 2,7,8-trimethyl-2S-(beta-carboxyethyl)-6-hydroxychroman (S-gamma-CEHC), a metabolite of gamma-T3, was 78.6% for compound 3, 47.1% for gamma-T3 in surfactant, and 100% for racemic gamma-CEHC. Based on these results, we identified compound 3 as the most promising water-soluble prodrug of gamma-T3 and two-step prodrug of S-gamma-CEHC.
Brown rice is a valuable source of lipid-soluble antioxidants including ferulated phytosterols (i.e., gamma-oryzanol), tocopherols, and tocotrienols. To evaluate the impact of temperature on the accumulation of these compounds, seeds from six different rice lines grown to maturity in replicate greenhouses in Gainesville, FL, were analyzed. The lines represented Oryza sativa indica, O. sativa japonica, and Oryza glaberrima of different origins. Temperatures were maintained near ambient at one end of each greenhouse and at approximately 4.5 degrees C above ambient at the other end. gamma-Oryzanols, tocopherols, and tocotrienols were extracted from whole seed (i.e., brown rice) and analyzed by HPLC. Tocotrienols and tocopherols varied widely between lines but changed only slightly with respect to temperature. In general, the proportions of alpha-tocotrienol and/or alpha-tocopherol increased at elevated temperature, whereas gamma-tocopherol and gamma-tocotrienol decreased. Six gamma-oryzanol peaks, identified on the basis of absorbance maxima at 330 nm and HPLC-mass spectrometry, were quantified. The most abundant component was 24-methylenecycloartanyl ferulate, present at 40-62% of total. Its levels increased 35-57% at elevated temperature in five of six lines, accounting for most of the change in total gamma-oryzanol. The results suggest that the physiological action of individual ferulated phytosterols should be investigated because their relative proportions in gamma-oryzanol can change.