Long-term glucocorticoid treatment is associated with severe side effects, such as obesity and osteoporosis. A palm oil-derived vitamin E mixture had been shown previously to be protective against osteoporosis in rats given 120 microg/kg dexamethasone daily for 12 weeks. In this study we determined the effects of two isomers of vitamin E (i.e., palm oil-derived gamma-tocotrienol and the commercially available alpha-tocopherol, 60 mg/kg of body weight/day) on body composition and bone calcium content in adrenalectomized rats replaced with two doses of dexamethasone, 120 microg/kg and 240 microg/kg daily. Treatment period was 8 weeks. gamma-Tocotrienol (60 mg/kg of body weight/day) was found to reduce body fat mass and increase the fourth lumbar vertebra bone calcium content in these rats, while alpha-tocopherol (60 mg/kg of body weight/day) was ineffective. Therefore, in conclusion, palm oil-derived gamma-tocotrienol has the potential to be utilized as a prophylactic agent in prevention of the side effects of long-term glucocorticoid use.
Vitamin E derivative, RRR-alpha-tocopheryl succinate (vitamin E succinate, VES), is a potent pro-apoptotic agent, inducing apoptosis by restoring both transforming growth factor-beta (TGF-beta) and Fas (CD95) apoptotic signaling pathways that contribute to the activation of c-Jun N-terminal kinase (JNK)-mediated apoptosis. Objectives of these studies were to characterize signaling events involved in the pro-apoptotic actions of a naturally occurring form of vitamin E, delta-tocotrienol, and a novel vitamin E analog, alpha-tocopherol ether acetic acid analog [alpha-TEA; 2,5,7,8-tetramethyl-2R-(4R,8R,12-trimethyltridecyl)chroman-6-yloxyacetic acid]. Like VES, alpha-TEA and delta-tocotrienol induced estrogen-nonresponsive MDA-MB-435 and estrogen-responsive MCF-7 human breast cancer cells to undergo high levels of apoptosis in a concentration- and time-dependent fashion. Like VES, the two compounds induced either no or lower levels of apoptosis in normal human mammary epithelial cells and immortalized but nontumorigenic human MCF-10A cells. The pro-apoptotic mechanisms triggered by the structurally distinct alpha-TEA and delta-tocotrienol were identical to those previously reported for VES, that is, alpha-TEA- and delta-tocotrienol-induced apoptosis involved up-regulation of TGF-beta receptor II expression and TGF-beta-, Fas- and JNK-signaling pathways. These data provide a better understanding of the anticancer actions of a dietary form of vitamin E (delta-tocotrienol) and a novel nonhydrolyzable vitamin E analog (alpha-TEA).
Two xanthones, namely virgataxanthone A and B, have been isolated from the stem bark of Garcinia virgata, together with two formylated tocotrienolsand the known delta-tocotrienol, griffipavixanthone and 2,6-dihydroxy-4-methoxybenzophenone (cotoin). Their structures were mainly established using one and two-dimensional NMR and mass spectroscopies. When sufficient material was available, the antioxidant activities of the crude extracts as well as the isolated compounds were evaluated.
Tocotrienols are lipophilic antioxidants belonging to the tocochromanols, better known as vitamin E. Although present in cereal grains in high quantities not much is known about their function in plants. In a detailed study the temporal and spatial accumulation of tocotrienols and tocopherols during grain development in two barley cultivars was analyzed. Tocochromanols and lipids accumulated in parallel until 80% of the final dry weight of the kernels was reached. Later on the tocochromanol content did not change while the lipid content decreased. Generally, only about 13% of the tocochromanols were found in the germ fraction, whereas the pericarp fraction contained about 50% and the endosperm fraction about 37% of the tocochromanols. Altogether, about 85% of the tocochromanols were tocotrienols in both cultivars. In case of the tocopherols about 80% were found in the germ fraction and the remaining 20% in the pericarp fraction. Tocotrienols were almost equally present in the pericarp and the endosperm fraction. Individual forms of tocopherols and tocotrienols accumulated with different kinetics during barley grain development. The differences in distribution and accumulation indicate different functions of the individual tocochromanols during grain development.
Inhibition of angiogenesis and telomerase activity with vitamin E compounds, especially for tocotrienol (T3), has been investigated. Nutrigenomic tools have been used for elucidating the bioactive mechanisms of T3. In the cell culture experiments, T3 reduced the vascular endothelial growth factor (VEGF)-stimulated tube formation by human umbilical vein endothelial cells (HUVEC). Among T3 isomers, delta-T3 appeared the highest activity. The T3 inhibited the new blood vessels formation on the growing chick embryo chorioallantoic membrane (CAM assay for an in vivo model of angiogenesis). In contrast, tocopherol did not. The findings suggested that the T3 has potential use for reducing angiogenic disorder. DNA chip analysis revealed that T3 specifically down-regulates the expression of VEGF receptor (VEGFR) in endothelial cells. It is well-known that VEGF regulates angiogenesis by binding to VEGFR. Therefore, T3 could block the intracellular signaling of VEGF via down-regulation of VEGFR, which resulted in the inhibition of angiogenesis. On the other hand, DNA chip analysis also revealed that T3 down-regulates the expression of protein kinase C (PKC) in the cultured HUVEC. Since PKC is involved with the control of telomerase activity, T3 has potential to act as anti-telomerase inhibitor via PKC inhibition. In this manner, DNA chip technology provides efficient access to genetic information regarding food function and its mechanism.
Crude palm oil contains 600 to 1000 ppm of tocols in the form of tocopherols and tocotrienols. These palm tocols have been isolated and analyzed in the past by various chromatographic techniques such as open column chromatography, high-performance liquid chromatography, as well as thin-layer chromatography. Supercritical fluid chromatography (SFC) has emerged as a more advanced chromatographic technique in recent years. The tocols present in palm oil are successfully isolated using SFC. Identification of these tocols is supported by various spectroscopic techniques such as 1H NMR, 13C NMR, and mass spectrometry.
Oxidative stress and apoptosis play pivotal roles in the pathogenesis of neurodegenerative diseases. We investigated the effects of vitamin E analogs on oxidative stress and apoptosis using primary neuronal cultures of rat striatum. A tocotrienol-rich fraction of edible oil derived from palm oil (Tocomin 50%), which contains alpha-tocopherol, and alpha-, gamma- and delta-tocotrienols, significantly inhibited hydrogen peroxide (H2O2)-induced neuronal death. Each of the tocotrienols, purified from Tocomin 50% by high-performance liquid chromatography, significantly attenuated H2O2-induced neurotoxicity, whereas alpha-tocopherol did not. alpha-, gamma- and delta-Tocotrienols also provided significant protection against the cytotoxicity of a superoxide donor, paraquat, and nitric oxide donors, S-nitrosocysteine and 3-morpholinosydnonimine. Moreover, tocotrienols blocked oxidative stress-mediated cell death with apoptotic DNA fragmentation caused by an inhibitor of glutathione synthesis, L-buthionine-[S,R]-sulfoximine. In addition, alpha-tocotrienol, but not gamma- or delta-tocotrienol, prevented oxidative stress-independent apoptotic cell death, DNA cleavage and nuclear morphological changes induced by a non-specific protein kinase inhibitor, staurosporine. These findings suggest that alpha-tocotrienol can exert anti-apoptotic neuroprotective action independently of its antioxidant property. Among the vitamin E analogs examined, alpha-tocotrienol exhibited the most potent neuroprotective actions in rat striatal cultures.