Vitamin E, an essential nutrient with powerful antioxidant activity, is the mixture of two classes of compounds, tocopherols (TPs) and tocotrienols (TTs). Although TTs exhibit better bone protective activity than α-TP, the underlying mechanism is poorly understood. In this study, we investigated whether α-TT and α-TP can modulate osteoclastic bone resorption. We found that α-TT but not α-TP inhibits osteoclastogenesis in coculture of osteoblasts and bone marrow cells induced by either IL-1 or combined treatment with 1α,25(OH)(2) vitamin D(3) and prostaglandin E(2). In accordance with this, only α-TT inhibited receptor activator of NF-κB ligand (RANKL) expression in osteoblasts. In addition, α-TT but not α-TP inhibited RANKL-induced osteoclast differentiation from precursors by suppression of c-Fos expression, possibly through inhibiting ERK and NF-κB activation. This anti-osteoclastogenic effect was reversed when c-Fos or an active form of NFATc1, a critical downstream of c-Fos during osteoclastogenesis, was overexpressed. Furthermore, only α-TT reduced bone resorbing activity of mature osteoclasts without affecting their survival. Overall, our results demonstrate that α-TT but not α-TP has anti-bone resorptive properties by inhibiting osteoclast differentiation and activation, suggesting that α-TT may have therapeutic value for treating and preventing bone diseases characterized by excessive bone destruction.
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Paradoxically, meta-analysis of human randomized controlled trials revealed that natural but not synthetic α-tocopherol supplementation significantly increases all-cause mortality at 95% confidence interval. The root cause was that natural α-tocopherol supplementation significantly depressed bioavailability of other forms of vitamin E that have better chemo-prevention capability. Meta-analysis outcome demonstrated flaws in the understanding of vitamin E. Reinterpretation of reported data provides plausible explanations to several important observations. While α-tocopherol is almost exclusively secreted in chylomicrons, enterocytes secrete tocotrienols in both chylomicrons and small high-density lipoproteins. Vitamin E secreted in chylomicrons is discriminately repacked by α-tocopherol transfer protein into nascent very low-density lipoproteins in the liver. Circulating very low-density lipoproteins undergo delipidation to form intermediate-density lipoproteins and low-density lipoproteins. Uptake of vitamin E in intermediate-density lipoproteins and low-density lipoproteins takes place at various tissues via low-density lipoproteins receptor-mediated endocytosis. Small high-density lipoproteins can deliver tocotrienols upon maturation to peripheral tissues independent of α-tocopherol transfer protein action, and uptake of vitamin E takes place at selective tissues by scavenger receptor-mediated direct vitamin E uptake. Dual absorption pathways fortocotrienols are consistent with human and animal studies. α-Tocopherol depresses the bioavailability of α-tocotrienol and has antagonistic effect ontocotrienols in chemo-prevention against degenerative diseases. Therefore, it is an undesirable component for chemo-prevention. Future research directions should be focused on tocotrienols, preferably free from α-tocopherol, for optimum chemo-prevention and benefits to mankind.
Tocochromanols are potent lipid-soluble antioxidants and essential nutrients for human health. Genetic engineering techniques were used to develop soybeans with enhanced vitamin E levels, including tocotrienols, which are not found in soybean. The gene encoding rice homogentisate geranylgeranyl transferase (HGGT) was overexpressed in soybeans using seed-specific and constitutive promoters. The association between abundance of vitamin E isomers and antioxidant activity was investigated during seed germination. With the exception of β-tocotrienol, all vitamin E isomers were detected in germinating seeds expressing OsHGGT. The antioxidant properties of germinating seed extracts were determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radicals and lipid peroxidation (TBARS). Compared with intact wild-type seeds, transgenic seeds showed increases in radical scavenging of 5.4-17 and 23.2-35.3% in the DPPH and ABTS assays, respectively. Furthermore, the lipid peroxidation levels were 2.0-4.5-fold lower in germinating seeds from transgenic lines than in wild-type seeds. Therefore, it appears that the antioxidant potential of transgenic oil-producing plants such as soybean, sunflower, and corn may be enhanced by overexpressing OsHGGT during seed germination.
The biosynthesis of the tocotrienol and tocopherol forms of vitamin E is initiated by prenylation of homogentisate. Geranylgeranyl diphosphate (GGDP) is the prenyl donor for tocotrienol synthesis, whereas phytyl diphosphate (PDP) is the prenyl donor for tocopherol synthesis. We have previously shown that tocotrienol synthesis is initiated in monocot seeds by homogentisate geranylgeranyl transferase (HGGT). This enzyme is related to homogentisate phytyltransferase (HPT), which catalyzes the prenylation step in tocopherol synthesis. Here we show that monocot HGGT is localized in the plastid and expressed primarily in seed endosperm. Despite the close structural relationship of monocot HGGT and HPT, these enzymes were found to have distinct substrate specificities. Barley (Hordeum vulgare cv. Morex) HGGT expressed in insect cells was six times more active with GGDP than with PDP, whereas the Arabidopsis HPT was nine times more active with PDP than with GGDP. However, only small differences were detected in the apparent Km values of barley HGGT for GGDP and PDP. Consistent with its in vitro substrate properties, barley HGGT generated a mixture of tocotrienols and tocopherols when expressed in the vitamin E-null vte2-1 mutant lacking a functional HPT. Relative levels of tocotrienols and tocopherols produced in vte2-1 differed between organs and growth stages, reflective of the composition of plastidic pools of GGDP and PDP. In addition, HGGT was able to functionally substitute for HPT to rescue vte2-1-associated phenotypes, including reduced seed viability and increased fatty acid oxidation of seed lipids. Overall, we show that monocot HGGT is biochemically distinct from HPT, but can replace HPT in important vitamin E-related physiological processes.
BACKGROUND/OBJECTIVES: Vitamin E is an essential fat-soluble vitamin that has been shown to induce favorable effects on animal and human immune systems. The objective of this study was to assess the effects of tocotrienol-rich fraction (TRF) supplementation on immune response following tetanus toxoid (TT) vaccine challenge in healthy female volunteers.
SUBJECTS/METHODS: In this double-blinded, placebo-controlled clinical trial, participants were randomly assigned to receive either placebo (control group) or 400 mg of TRF (study group) supplementation daily. Over the 2-month period of the study, volunteers were asked to attend three clinical sessions (that is, on days 0, 28 and 56) and blood samples were obtained from the volunteers during the follow-up. On day 28, all volunteers were also vaccinated with the TT vaccine (20 Lf) intramuscularly.
RESULTS:The results from the clinical trial showed that TRF supplementation significantly increased the total vitamin E level in the plasma of the TRF-supplemented volunteers compared with the placebo group, indicating overall compliance. Volunteers supplemented with TRF showed a significantly (P < 0.05) enhanced production of interferon-γ and interleukin (IL)-4 by the mitogen or TT-stimulated leukocytes compared with the control group. Volunteers from the TRF group produced significantly (P < 0.05) lower amounts of IL-6 compared with the placebo group. Anti-TT IgG production was also significantly (P < 0.05) augmented in the TRF-supplemented group compared with the placebo group.
CONCLUSIONS: We conclude that TRF has immunostimulatory effects and potential clinical benefits to enhance immune response to vaccines.
AIMS: Vitamin E is an antioxidant that may protect bone against oxidative stress-induced osteoporosis. This in vitro study was conducted to determine the protective effects of a-tocopherol and γ-tocotrienol on osteoblasts, the bone forming cells, against oxidative stress.
MATERIALS AND METHODS: Toxicity tests were carried out on hydrogen peroxide (H(2)O(2)), a-tocopherol and γ-tocotrienol and their inhibitory concentration 50 (IC(50)) on osteoblasts were determined if any. Osteoblast cultures were then pretreated with different concentrations of a-tocopherol or γ-tocotrienol for 24 hours before incubated with the IC50 of H(2)O(2) for 2 hours. Cell viability was determined by using MTS assay to compare the protective effects of both vitamin E on osteoblast exposed to H(2)O(2).
RESULTS: The IC(50) after 2 hours and 24 hours incubation time for H(2)O(2) were 490 µM and 280 µM respectively. γ-Tocotrienol was found to be toxic to osteoblasts with the IC(50) of 290 µM after 24 hours incubation time while a-tocopherol was not toxic to osteoblasts at any doses. However, γ-tocotrienol was able to protect osteoblasts from H(2)O(2) toxicity at low concentration (1 µM), whereras a-tocopherol was not able to offer protection against H2O2 toxicity.
CONCLUSIONS: γ-tocotrienol was found to be toxic to osteoblasts at high concentrations but at much lower concentration, it has better antioxidant activity than a-tocopherol to protect osteoblasts from oxidative stress.
Oximetry of the human T-Lymphoblastoid (CEM) cells was measured using (19)F magnetic resonance imaging ((19)F MRI). The cells were treated with the analogues of vitamin E, alpha-, gamma-, delta-tocopherols and corresponding tocotrienols, ex vivo in three-dimensional (3D) cell culture. The study showed that (19)F MRI allows to measure the effect of the analogues due to changes of oxygenation, which were detected using MRI. Hexafluorobenzene was used as a (19)F MRI probe sensitive to oxygen concentrations. After 72h of treatment in HFBR with alpha-, gamma-, delta-tocopherols the oxygen concentration was 19.9+/-0.8%, 19.3+/-1.4%, 16+/-3.5%, respectively. The oxygen concentration in cells treated with alpha-, gamma-, delta-tocotrienols was found to be 14+/-1.5%, 10+/-1.2% and 8.8+/-1.1%, respectively whereas for the control cells it was 22.1+/-1%. The results show that delta-tocopherol and delta-tocotrienol are the most effective treatments in CEM cells among all the tested analogues.
This study compared two dietary phytochemicals, grape-derived resveratrol and palm oil-derived γ-tocotrienol, either alone or in combination, on the contribution of autophagy in cardioprotection during ischaemia and reperfusion. Sprague-Dawley rats weighing between 250 and 300 g were randomly assigned to one of the following groups: vehicle, ischaemia/reperfusion (I/R), resveratrol + I/R, γ-tocotrienol + I/R, resveratrol +γ-tocotrienol + I/R. For resveratrol treatments, the rats were gavaged with resveratrol (2.5 mg/kg) for 15 days while for γ-tocotrienol experiments the rats were gavaged with γ-tocotrienol (0.3 mg/kg) for 30 days. For the combined resveratrol +γ-tocotrienol experiments, the rats were gavaged with γ-tocotrienol for 15 days, and then gavaging continued with resveratrol along with γ-tocotrienol for a further period of 15 days. After 30 days, isolated perfused hearts were subjected to 30 min. of global ischaemia followed by 2 hrs of reperfusion. Our results showed for the first time that at least in part, the cardioprotection (evidenced from the ventricular performance, myocardial infarct size and cardiomyocyte apoptosis) with resveratrol and γ-toctrienol was achieved by their abilities to induce autophagy. Most importantly, resveratrol and γ-tocotrienol acted synergistically providing greater degree of cardioprotection simultaneously generating greater amount of survival signal through the activation of Akt-Bcl-2 survival pathway. Autophagy was accompanied by the activation of Beclin and LC3-II as well as mTOR signalling, which were inhibited by either 3-methyl adenine (3-MA) or Wortmannin. The autophagy was confirmed from the results of transmission electron microscopy and light microscopy as well as with confocal microscopy. It is tempting to speculate that during ischaemia and reperfusion autophagy along with enhanced survival signals helps to recover the cells from injury.
Tocol composition was studied in 26 genotypes of wheat grown in one location for three years and in three other locations for one year. Special emphasis was placed on evaluating the variation of tocols within wheat genotypes and among various growing conditions. In general, both genetic and environmental effects had a strong impact on tocols in wheat genotypes. Because the growing locations and years differed considerably, greater variation due to the environment was found in this study than in earlier ones. Some of the genotypes were more sensitive to the impact of the environment, whereas others were relatively stable. Of the wheat genotypes with an average total tocol content of >or=55 microg/g of dry matter, five genotypes showed relatively low variation: Claire, Cadenza, Lynx, Atlas 66, and Disponent. These genotypes could be potential candidates for the breeding of stable and high-tocol content wheat cultivars.
Bone is a specialized connective tissue that functions as the load-bearing structure of the body. Free radicals may affect bone remodeling by regulating osteoclast activity in either the physiological or pathological condition. Vitamin E, a lipid-soluble antioxidant, has been demonstrated to offer protection against osteoporosis and to improve the bone material and structure of animal models. The aim of this study was to observe and compare the effects of alpha-tocopherol (alpha-tocopherol), delta-tocotrienol (delta-tocotrienol), and gamma-tocotrienol (gamma-tocotrienol) on the static and dynamic bone histomorphometric parameters in normal male rats. Thirty-two normal Sprague-Dawley male rats aged 3 months and weighing 200-250 g were randomly divided into four groups. The control group was supplemented with oral gavages of olive oil (vehicle), whereas the alpha-tocopherol, delta-tocotrienol, and gamma-tocotrienol groups were given oral gavages of 60 mg/kg alpha-tocopherol, delta-tocotrienol, and gamma-tocotrienol, respectively. The rats were injected twice with calcein to fluorochrome-label the bones. After 4 months of treatment, the rats were killed, and the left femurs were dissected out and prepared for bone histomorphometry. Both the static and dynamic parameters of the vitamin E-treated groups were better than those of the normal control group. Among the vitamin E-treated groups, the tocotrienol groups showed better histomorphometry results compared to the α-tocopherol group, with the γ-tocotrienol group demonstrating the best effects on both sets of parameters. We concluded that vitamin E can promote bone formation in normal rats, with gamma-tocotrienol being the most potent form of vitamin E.