This study investigates the effects of tocotrienol (TT) or alpha-tocopherol (TF) supplementation on corticosterone level, noradrenalin level and gastric lesions in rats exposed to restraint stress. Twenty-four male Sprague Dawley rats were randomly assigned into 4 equally sized groups; two control groups were given olive oil, while the treated group was supplemented with either tocotrienol of tocopherol orally at a dose of 60 mg/kg body weight. After 28 days of treatment, one control group, TT group and TF group were subjected to restraint stress, 2 hours daily for 4 consecutive days. After the last exposure to stress, plasma samples were taken to determine the corticosterone and noradrenalin levels, after which the rats were sacrificed. The stomach was excised for the evaluation of gastric lesions. Our findings showed that TT and TF were able to maintain the corticosterone level to the prestress values, while only TT was able to maintain the noradrenalin level in rats exposed to stress. Tocotrienol was found to be better in preventing formation of gastric lesions compared to TF. As a conclusion, the protective effect of vitamin E was related to the ability to inhibit stress induced elevation of corticosterone and noradrenalin levels.
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Gamma-tocotrienol suppresses prostate cancer cell proliferation and invasion through multiple-signalling pathways
Yap, W. N.,Chang, P. N.,Han, H. Y.,Lee, D. T.,Ling, M. T.,Wong, Y. C.,Yap, Y. L.
Br J Cancer, 2008; 99(11):1832-41
Tocotrienol-rich fraction (TRF) has demonstrated antiproliferative effect on prostate cancer (PCa) cells. To elucidate this anticancer property in PCa cells, this study aimed, first, to identify the most potent isomer for eliminating PCa cells; and second, to decipher the molecular pathway responsible for its activity. Results showed that the inhibitory effect of gamma-tocotrienol was most potent, which resulted in induction of apoptosis as evidenced by activation of pro-caspases and the presence of sub-G(1) cell population. Examination of the pro-survival genes revealed that the gamma-tocotrienol-induced cell death was associated with suppression of NF-kappaB, EGF-R and Id family proteins (Id1 and Id3). Meanwhile, gamma-tocotrienol treatment also resulted in the induction of JNK-signalling pathway and inhibition of JNK activity by a specific inhibitor (SP600125) was able to partially block the effect of gamma-tocotrienol. Interestingly, gamma-tocotrienol treatment led to suppression of mesenchymal markers and the restoration of E-cadherin and gamma-catenin expression, which was associated with suppression of cell invasion capability. Furthermore, a synergistic effect was observed when cells were co-treated with gamma-tocotrienol and Docetaxel. Our results suggested that the antiproliferative effect of gamma-tocotrienol act through multiple-signalling pathways, and demonstrated for the first time the anti-invasion and chemosensitisation effect of gamma-tocotrienol against PCa cells.
Dietary antioxidants as potential pharmacological agents for ischemic stroke
Cherubini A, Ruggiero C, Morand C, Lattanzio F, Dell'aquila G, Zuliani G, Di Iorio A, Andres-Lacueva C.
Curr Med Chem. 2008;15(12):1236-48.
Acute ischemic stroke is a leading cause of death and severe disability in industrialised countries and also in many developing countries. An excessive amount of free radicals is generated during cerebral ischemia, which significantly contributes to brain damage. Therefore, an increasing interest has been devoted to the potential benefits of antioxidant compounds in ischemic stroke patients. In this review, we examined the most relevant observational studies concerning the relationship between dietary antioxidants and ischemic stroke as well as clinical trials investigating the effects of single or multiple antioxidant supplementation in the prevention or treatment of acute ischemic stroke. Furthermore, we reviewed the most promising antioxidant compounds, i.e. dehydroascorbic acid, alpha-tocotrienol, gamma-tocopherol, flavonoids, resveratrol and gingko biloba, tested in animal models of acute ischemic stroke. Finally, we carefully evaluated the reasons for the discrepancy between experimental and clinical studies, and provided recommendations to improve the translation of the results obtained in animal models to patients with acute ischemic stroke.
Tocotrienol inhibits secretion of angiogenic factors from human colorectal adenocarcinoma cells by suppressing hypoxia-inducible factor-1alpha
Shibata A, Nakagawa K, Sookwong P, Tsuduki T, Tomita S, Shirakawa H, Komai M, Miyazawa T.
J Nutr. 2008 Nov;138(11):2136-42.
Tocotrienol (T3), unsaturated vitamin E, has recently gained considerable attention as a potent antiangiogenic agent minimizing tumor growth, the exact intracellular mechanisms of which remain poorly understood. Because hypoxia-inducible factor-1alpha (HIF-1alpha), its downstream target vascular endothelial growth factor (VEGF), and other angiogenic factors such as interleukin-8 (IL-8) and cyclooxygenase 2 (COX-2) play critical roles in neovascularization, we tested the hypothesis that the inhibitory effect of T3 on tumor angiogenesis is via regulation of these angiogenic factors. We used 2 cancer cell lines, human colorectal adenocarcinoma cells (DLD-1) and human hepatoma cells (HepG2). T3 isomers (2 micromol/L) inhibited hypoxia-induced VEGF secretion from DLD-1, with delta-T3 showing potent inhibition. Delta-T3 suppressed hypoxia-induced VEGF and IL-8 expression in DLD-1 at both mRNA and protein levels, and we found the inhibitory mechanism of delta-T3 by reducing HIF-1alpha protein expression or increasing HIF-1alpha degradation. Also, delta-T3 (2 micromol/L) did not affect hypoxia-induced COX-2 mRNA expression; however, delta-T3 tended to suppress (P = 0.044) hypoxia-induced COX-2 protein expression, implying a possible post-transcriptional mechanism by delta-T3. Overall, our results confirmed that T3 has an inhibitory effect on angiogenic factor secretion from cancer cells and revealed the possible mechanisms, providing new information about the antiangiogenic effects of T3.
Vitamin E in nature is comprised of a family of tocopherols and tocotrienols. The most studied of these is alpha-tocopherol (alpha-TOH), because this form is retained within the body, and vitamin E deficiency is corrected with this supplement. alpha-TOH is a lipid-soluble antioxidant required for the preservation of cell membranes, and it potentially acts as a defense against oxidative stress. Many studies have investigated the metabolism, transport, and efficacy alpha-TOH in the prevention of sequelae associated with cardiovascular disease (CVD). Supplementation with vitamin E is considered to provide health benefits against CVD through its antioxidant activity, the prevention of lipoprotein oxidation, and the inhibition of platelet aggregation. However, the results from large prospective, randomized, placebo-controlled clinical trials with alpha-TOH have been largely negative. A recent meta-analysis suggests that alpha-TOH supplements may actually increase all-cause mortality; however, the mechanism for this increased risk is unknown. In vitro studies performed in human cell cultures and animal models suggest that vitamin E might increase the hepatic production of cytochrome P450s and MDR1. Induction of CYP3A4 or MDR1 by vitamin E could potentially lower the efficacy of any drug metabolized by CYP3A4 or MDR1. Other possibilities include an adverse effect of alpha-TOH on blood pressure in high-risk populations. Because of the wide popularity and use of vitamin E supplements, further research into potential adverse effects is clearly warranted.
Tocopherol and tocotrienol compositions were studied in 175 genotypes of different wheat types grown under similar conditions to screen for natural diversity. The main focus was on bread wheats, including 130 and 20 winter and spring types, respectively. The average total content of tocopherols and tocotrienols was 49.4 microg/g of dm, with a range of 27.6-79.7 microg/g of dm, indicating a 2.9-fold variation among genotypes. Beta-tocotrienol and alpha-tocopherol were the major vitamers, and in general there were more tocotrienols than tocopherols. In the early cultivated forms of wheat the proportion of tocotrienols was especially high, at >or=62.5%. In conclusion, there was a large variation in total tocopherol and tocotrienol contents in bread wheats and this, along with the high proportions of tocotrienols in other types of wheat, demonstrates the great genetic potential of genotypes to be exploited by plant breeders.
Multitargeted therapy of cancer by tocotrienols
Nesaretnam K
Cancer Lett. 2008 Oct 8;269(2):388-95. Epub 2008 May 27.
Natural compounds with possible health benefits have become attractive targets for research in areas pertaining to human health. For both prevention and therapy of various human ailments, such compounds are preferred over synthetic ones due to their lesser toxicity. They are also easily absorbed and processed by our body. Vitamins are prominent among natural or endogenous compounds that are considered to be beneficial. The vitamin E group of compounds is among the better known of the vitamins due to their suggested health benefits including antioxidant and related protective properties. Among these, tocotrienols have gained prominence in recent years due to their potential applications and better protective effects in certain systems. These tocotrienols are vitamin E derivatives that are analogs of the more established forms of vitamin E namely tocopherols. In addition to their potent antioxidant activity, tocotrienols have other important functions, especially in maintaining a healthy cardiovascular system and a possible role in protection against cancer and other ailments.
The biosynthesis of natural products in a fast growing and easy to manipulate heterologous host system, such as Escherichia coli, is of increasing interest in biotechnology. This procedure allows the investigation of complex natural product biosynthesis and facilitates the engineering of pathways. Here we describe the cloning and the heterologous expression of tocochromanol (vitamin E) biosynthesis genes in E. coli. Tocochromanols are synthesized solely in photosynthetic organisms (cyanobacteria, algae, and higher green plants). For recombinant tocochromanol biosynthesis, the genes encoding hydroxyphenylpyruvate dioxygenase (hpd), geranylgeranylpyrophosphate synthase (crtE), geranylgeranylpyrophosphate reductase (ggh), homogentisate phytyltransferase (hpt), and tocopherol-cyclase (cyc) were cloned in a stepwise fashion and expressed in E. coli. Recombinant E. coli cells were cultivated and analyzed for tocochromanol compounds and their biosynthesis precursors. The expression of only hpd from Pseudomonas putida or crtE from Pantoea ananatis resulted in the accumulation of 336 mg L(-1) homogentisate and 84 microg L(-1) geranylgeranylpyrophosphate in E. coli cultures. Simultaneous expression of hpd, crtE, and hpt from Synechocystis sp. under the control of single tac-promoter resulted in the production of methyl-6-geranylgeranyl-benzoquinol (67.9 microg g(-1)). Additional expression of the tocopherol cyclase gene vte1 from Arabidopsis thaliana resulted in the novel formation of a vitamin E compound-delta-tocotrienol (15 microg g(-1))-in E. coli.
Suppression of cell proliferation and gene expression by combinatorial synergy of EGCG, resveratrol and gamma-tocotrienol in estrogen receptor-positive MCF-7 breast cancer cells
Hsieh TC, Wu JM.
Int J Oncol. 2008 Oct;33(4):851-9.
Numerous dietary phytochemicals have shown anti-breast carcinogenic activities when tested in vitro; however, in most cases, the demonstrated efficacy of individual phytochemicals requires doses not readily achievable in vivo. Therefore, whether diets might exert translational promises and benefits in clinical settings and prevention of breast cancer remain unclear. Since cancer cells are endowed with complex, redundant, converging and diverging pathways spanning both the genetic and metabolic networks that are not merely replicates of those in normal cells, it is of interest to test whether a multicomponent approach involving lower, physiologically relevant doses of natural dietary agents may be developed as a chemopreventive strategy for breast cancer. Herein, we investigated, using the estrogen receptor-positive MCF-7 breast cancer cells as a model, whether the combination of epigallocatechin gallate (EGCG), resveratrol and gamma-tocotrienol at suboptimal doses elicits synergism in suppressing cell proliferation, modulating gene expression, and increasing antioxidant activity, as compared to each of the three phytochemicals added alone. The results showed that there was a approximately 33, 50 and 58% inhibition of cell proliferation by > or =50 microM EGCG, > or =25 microM resveratrol and > or =10 microM gamma-tocotrienol, respectively, added as a single agent. When a suboptimal dose (10 microM) of each phytochemical was used, a significant additive effect in suppression of cell proliferation was observed with the combination of resveratrol and gamma-tocotrienol whereas the three phytochemicals added together did not produce more pronounced inhibition of cell proliferation. A significant additive effect in reducing cyclin D1 and bcl-2 expression was found when gamma-tocotrienol was added with either EGCG or resveratrol. Functional synergism among the three phytochemicals was only observed in the induction of quinone reductase NQO1. These results suggest that diet-based protection against breast cancer may partly derive from synergy amongst dietary phytochemicals directed against specific molecular targets in responsive breast cancer cells, and provide support for the feasibility of the development of a diet-based combinatorial approach in the prevention and treatment of breast cancer.
Tocochromanols, plastoquinol, and other biological prenyllipids as singlet oxygen quenchers-determination of singlet oxygen quenching rate constants and oxidation products
Gruszka J, Pawlak A, Kruk J.
Free Radic Biol Med. 2008 Sep 15;45(6):920-8. Epub 2008 Jun 30.
Singlet oxygen quenching rate constants for tocopherol and tocotrienol homologues have been determined in organic solvents of different polarities, as well as for other biological prenyllipids such as plastoquinol, ubiquinol, and alpha-tocopherolquinol. The obtained results showed that the quenching activity of tocochromanols was mainly due to the chromanol ring of the molecule and the activity increased with the number of the methyl groups in the ring and solvent polarity. Among prenylquinols, alpha-tocopherolquinol was the most active scavenger of singlet oxygen followed by ubiquinol and plastoquinol. The oxidation products of tocopherols were identified as 8a-hydroperoxy-tocopherones which are converted to the corresponding tocopherolquinones under acidic conditions. The primary oxidation products of prenylquinols, containing unsaturated side chains, were the corresponding prenylquinones that were further oxidized to hydroxyl side-chain derivatives. In the case of plastochromanol, the gamma-tocotrienol homologue found in some seed oils, mainly the hydroxyl derivatives were formed, although 8a-hydroperoxy-gamma-tocopherones were also formed to a minor extent, both from plastochromanol and from its hydroxyl, side-chain derivatives. The obtained results were discussed in terms of the activity of different prenyllipids as singlet oxygen scavengers in vivo.