A rapid capillary electrochromatographic (CEC) method for the analysis of vitamin E in vegetable oils is reported. Vitamin E consists of a group of eight isomers, tocopherols (TOHs) and tocotrienols. The separation of four TOHs (alpha-, gamma-, delta-TOH), alpha-tocopherol acetate (alpha-TOH-Ac), and an antioxidant compound, butylated hydroxytoluene (BHT) used to prevent TOH autoxidation, was optimized. The CEC experiments were carried out in a 75 microm inner diameter (ID) fused-silica capillary, partially packed with 3 microm C(18 )stationary phase (33 cm total length, 8.4 cm and 7 cm effective and packed lengths, respectively). The optimum mobile phase was a polar organic phase composed of a mixture of methanol-acetonitrile in the ratio 50/50 v/v containing 0.01% ammonium acetate, applying a voltage and temperature set at -25 kV and 20 degrees C, respectively. The tocopherols and the BHT were successfully separated within 2.5 min using the short-end injection method. Under these experimental conditions, repeatability of retention time and peak area, analyte detection and quantitation limits, linearity, precision, and accuracy were studied. The CEC method was applied to determine the content of TOHs in different commercially available oils of virgin olive, hazelnut, sunflower, and soybean. The extraction of vitamin E isomers from oil samples was achieved using methanol and a methanol-isopropanol mixture.
Metabolism of vitamin E is initiated by cytochrome P450 (CYP) enzymes usually involved in the metabolism of xenobiotics. Like other CYP substrates, vitamin E induced a reporter gene under the control of the pregnane X receptor (PXR) which regulates the expression of CYPs including CYP3A4. gamma-Tocotrienol, the most effective PXR activator, also induced endogenous CYP3A4 mRNA in HepG2 cells. Since these findings imply an interference of vitamin E with drug metabolism it was deemed necessary to investigate their in vivo relevance. Therefore, mice were grown for 3 months with alpha-tocopherol-deficient, -adequate, and -supranutritional diet, i.e. 2, 20 and 200 mg RRR-alpha-tocopheryl acetate/kg diet, respectively. Half of them received 250 microg gamma-tocotrienol/day for the last 7 days. After 3 months, hepatic levels of Cyp3a11 mRNA, the murine homolog to human CYP3A4, were about 2.5-fold higher in the 20 and 200 mg alpha-tocopherol groups than in the 2 mg group. After feeding 200 mg alpha-tocopherol for 9 months, Cyp3a11 mRNA was 1.7-fold higher than after 3 months. In contrast, gamma-tocotrienol did not induce Cyp3a11 mRNA. This could be explained by its high metabolism as demonstrated by the 20- to 25-fold increase in the urinary excretion of gamma-CEHC, the final metabolite of gamma-tocotrienol degradation. In conclusion, alpha-tocopherol maintains an adequate level of xenobiotic-metabolizing enzymes. If fed in supranutritional dosages, especially for longer times, alpha-tocopherol induces Cyp3a11 to levels which might interfere with drug metabolism.
Human lung type II cell derived A549 epithelial cancer cells and HepG2 hepatocytes constitutively express cytochrome P4504F2, a P450 we previously identified as a tocopherol-omega-hydroxylase. To determine if A549 cells would metabolize tocochromanols via the omega-hydroxylase pathway, we compared the metabolism of tocopherols (alpha-, gamma-, delta-TOH) and tocotrienols (alpha-, gamma-, delta-T3) in these 2 cell lines. Cultures were incubated with alpha-, gamma-, or delta-TOH, or the analogous T3s, and synthesis of their metabolites quantitated by GC-MS. A549 cells metabolized all tocochromanols 2-3 times more extensively than HepG2 cells (P < 0.001) except alpha-TOH, a difference not related to cell uptake of substrate but rather was reflective of greater microsomal TOH-omega-hydroxylase enzyme activity. Notably, 9′-carboxychromanols were the major metabolites of all gamma- and delta-TOHs and T3s in A549 cultures, whereas 3′- and 5′-carboxychromanols predominated in HepG2 cultures. Accumulation of 9′-carboxychromanols in A549 cultures was due to their inefficient conversion to 7′-carboxychromanols relative to HepG2 cells. Sesamin inhibited tocochromanol metabolism in both cells types, and neither cell type exhibited evidence of alternative (sesamin-insensitive) pathways of metabolism. TOH-omega-hydroxylase activity was undetectable in rat primary lung type II cells, suggesting that expression of activity was associated with transformation of normal type II cells to cancer cells. Long-chain carboxychromanol metabolites of gamma-TOH and other forms of vitamin E can be biosynthesized in A549 cultures for assessment of their biological activity, including their potential inhibition of synthesis of inflammatory mediators.
Tocotrienols, a class of vitamin E analogs, modulate several mechanisms associated with the aging process and aging-related diseases. Most studies compare the activities of tocotrienols with those of tocopherols (“classical vitamin E”). However, some biological effects were found to be unique for tocotrienols. Although the absorption mechanisms are essentially the same for all vitamin E analogs, tocotrienols are degraded to a greater extent than tocopherols. The levels of tocotrienols in the plasma of animals and humans were estimated to reach low micromolar concentrations. One hallmark in the origin of disease and aging is the overproduction of reactive oxygen species (ROS). Tocotrienols possess excellent antioxidant activity in vitro and have been suggested to suppress ROS production more efficiently than tocopherols. In addition, tocotrienols show promising nonantioxidant activities in various in vitro and in vivo models. Most notable are the interactions of tocotrienols with the mevalonate pathway leading to the lowering of cholesterol levels, the prevention of cell adhesion to endothelial cells, and the suppression of tumor cell growth. Furthermore, glutamate-induced neurotoxicity is suppressed in the presence of tocotrienols. This review summarizes the main antioxidant and nonantioxidant effects of tocotrienols and assesses their potential as health-maintaining compounds.
Tocotrienols and tocopherols represent the 2 subgroups within the vitamin E family of compounds, but tocotrienols display significantly greater apoptotic activity against a variety of cancer cell types. However, the exact mechanism mediating tocotrienol-induced apoptosis is not understood. Studies were conducted to determine the effects of tocotrienols on mitochondrial-stress-mediated apoptotic signaling in neoplastic +SA mammary epithelial cells grown in vitro. Exposure for 24 h to 0-20 micromol/L gamma-tocotrienol resulted in a dose-responsive increase in +SA cells undergoing apoptosis, as determined by flow cytometric analysis of Annexin V staining. However, tocotrienol-induced apoptosis was not associated with a disruption or loss of mitochondrial membrane potential, or the release of mitochondrial cytochrome c into the cytoplasm, as determined by JC-1 flow cytometric staining and ELISA assay, respectively. Interestingly, apoptotic +SA cells showed a paradoxical decrease in mitochondrial levels of pro-apoptotic proteins Bid, Bax, and Bad, and a corresponding increase in mitochondrial levels of anti-apoptotic proteins, Bcl-2 and Bcl-xL, suggesting that mitochondrial membrane stability and integrity might actually be enhanced for a limited period of time following acute tocotrienol exposure. In summary, these findings clearly demonstrate that tocotrienol-induced apoptosis occurs independently of mitochondrial stress apoptotic signaling in neoplastic +SA mammary epithelial cells.