Vitamin E is a generic term for tocopherols and tocotrienols. This work is based on our striking evidence that, in neuronal cells, nanomolar concentrations of alpha-tocotrienol, but not alpha-tocopherol, block glutamate-induced death by suppressing early activation of c-Src kinase (Sen, C. K., Khanna, S., Roy, S., and Packer, L. (2000) J. Biol. Chem. 275, 13049-13055). This study on HT4 and immature primary cortical neurons suggests a central role of 12-lipoxygenase (12-LOX) in executing glutamate-induced neurodegeneration. BL15, an inhibitor of 12-LOX, prevented glutamate-induced neurotoxicity. Moreover, neurons isolated from 12-LOX-deficient mice were observed to be resistant to glutamate-induced death. In the presence of nanomolar alpha-tocotrienol, neurons were resistant to glutamate-, homocysteine-, and l-buthionine sulfoximine-induced toxicity. Long-term time-lapse imaging studies revealed that neurons and their axo-dendritic network are fairly motile under standard culture conditions. Such motility was arrested in response to glutamate challenge. Tocotrienol-treated primary neurons maintained healthy growth and motility even in the presence of excess glutamate. The study of 12-LOX activity and metabolism revealed that this key mediator of glutamate-induced neurodegeneration is subject to control by the nutrient alpha-tocotrienol. In silico docking studies indicated that alpha-tocotrienol may hinder the access of arachidonic acid to the catalytic site of 12-LOX by binding to the opening of a solvent cavity close to the active site. These findings lend further support to alpha-tocotrienol as a potent neuroprotective form of vitamin E.
Publications
Metabolic redesign of vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content
Cahoon EB, Hall SE, Ripp KG, Ganzke TS, Hitz WD, Coughlan SJ.
Nat Biotechnol. 2003 Sep;21(9):1082-7. Epub 2003 Aug 3.
Tocotrienols are the primary form of vitamin E in seeds of most monocot plants, including cereals such as rice and wheat. As potent antioxidants,tocotrienols contribute to the nutritive value of cereal grains in human and livestock diets. cDNAs encoding homogentisic acid geranylgeranyl transferase (HGGT), which catalyzes the committed step of tocotrienol biosynthesis, were isolated from barley, wheat and rice seeds. Transgenic expression of the barley HGGT in Arabidopsis thaliana leaves resulted in accumulation of tocotrienols, which were absent from leaves of nontransformed plants, and a 10- to 15-fold increase in total vitamin E antioxidants (tocotrienols plus tocopherols). Overexpression of the barley HGGT in corn seeds resulted in an increase in tocotrienol and tocopherol content of as much as six-fold. These results provide insight into the genetic basis for tocotrienol biosynthesis in plants and demonstrate the ability to enhance the antioxidant content of crops by introduction of an enzyme that redirects metabolic flux.
Nitric oxide synthase activity in blood vessels of spontaneously hypertensive rats: Antioxidant protection by gamma-tocotrienol
Newaz MA, Yousefipour Z, Nawal N, Adeeb N.
J Physiol Pharmacol. 2003 Sep;54(3):319-27.
Involvement of free radicals and nitric oxide (NO) has long been implicated to the pathogenesis of essential hypertension. Several studies using antioxidants as the radical scavenger have shown to confer protection against free radical mediated diseases. This study is designed to investigate the role of antioxidant gamma-tocotrienol on endothelial nitric oxide synthase (NOS) activity in spontaneously hypertensive rats (SHR). SHR’s were divided into four groups namely untreated SHR (HC), treatment with 15 mg gamma-tocotrienol/kg diet (gammal), 30 mg gamma-tocotrienol/kg diet (gamma2) and 150 mg gamma-tocotrienol/kg diet (gamma3) and studied for three months. Wister Kyoto (WKY) rats were used as the control (C). Blood pressure was recorded every fortnightly by tail plethysmography. Animals were sacrificed and NOS activity in blood vessels was measured by [3H]arginine radioactive assay. Nitrite concentration in plasma was determined by Greis assay and lipid peroxides in the blood vessels by spectrofluorometry. This study showed that gamma-tocotrienol significantly reduced systolic blood pressure (SBP) in SHRs with a maximum reduction in group treated with gamma-tocotrienol 15 mg/kg diet (HC: 210 +/- 9 mmHg, gammal:123 +/- 19 mmHg). Blood vessels from untreated SHR showed a reduced NOS activity compare to that of WKY rats (C: 1.54 +/- 0.26 pmol/mg protein, HC: 0.87 +/- 0.23 pmol/mg protein; p<0.001). Gamma-tocotrienol improves NOS activity in all the groups with more significance in group gamma2 (p<0.001) and gamma3 (p<0.05). Plasma level of nitrite was reduced in SHR from 55 +/- 3 microM/ml in WKY to 26+/-2 muM/ml (p<0.001). Plasma nitrite level was reversed by treatment with gamma-tocotrienol. (gammal: p<0.001, gamma2: p<0.005, gamma3: p<0.001, respectively). In all the treatment groups, NOS activity showed significant negative correlation with blood pressure (gammal: r=-0.716, p<0.05; gamma2: r=-0.709, p<0.05; gamma3: r=-0.789, p<0.05). For plasma nitrite, although it shows a negative correlation with blood pressure it was significant only in gammal (r=-0.676, p<0.05) and gamma2 (r=-0.721, p<0.05). From this study we found that compared to WKY rats, SHR has lower NOS activity in blood vessels, which upon treatment with antioxidant gamma-tocotrienol increased the NO activity and concomitantly reduced the blood pressure. These findings further strengthen the hypothesis that free radicals and NO play critical role in pathogenesis of essential hypertension.
Antioxidant activities of natural vitamin E formulations
Naguib Y, Hari SP, Passwater R Jr, Huang D.
J Nutr Sci Vitaminol (Tokyo). 2003 Aug;49(4):217-20.
The antioxidant activities of natural d-alpha-tocopherol, mixed tocopherols and tocotrienols, and formulations comprising all forms of vitamin E, providing 400 IU, were determined employing an improved oxygen radical absorbance capacity (ORAC) assay using fluorescein (FL) as the fluorescent probe, randomly methylated beta-cyclodextrin (RMCD), 2,2′-azobis(2-amidino-propane)dihydrochloride (AAPH) as the peroxyl radical generator, and Trolox as the standard in 75 mM phosphate buffer. The antioxidant activities, expressed in micromol Trolox equivalent per gram, of d-alpha-tocopherol (87%), mixed tocopherols (70%), and tocotrienols (30%) were found to be 1,293, 1,948, and 1,229, respectively. Some of the vitamin E formulations showed antioxidant activities superior to d-alpha-tocopherol.
Anti-angiogenic activity of tocotrienol
Inokuchi H, Hirokane H, Tsuzuki T, Nakagawa K, Igarashi M, Miyazawa T.
Biosci Biotechnol Biochem. 2003 Jul;67(7):1623-7.
The anti-angiogenic property of vitamin E compounds, with particular emphasis on tocotrienol, has been investigated in vitro. Tocotrienol, but not tocopherol, inhibited both the proliferation and tube formation of bovine aortic endothelial cells, with delta-tocotrienol appearing the highest activity. Also, delta-tocotrienol reduced the vascular endothelial growth factor-stimulated tube formation by human umbilical vein endothelial cells. Our findings suggest that tocotrienol has potential use as a therapeutic dietary supplement for minimizing tumor angiogenesis.
Vitamin E analogues as inducers of apoptosis: Structure-function relation
Birringer M, EyTina JH, Salvatore BA, Neuzil J.
Br J Cancer. 2003 Jun 16;88(12):1948-55.
Recent results show that alpha-tocopheryl succinate (alpha-TOS) is a proapoptotic agent with antineoplastic activity. As modifications of the vitamin E (VE) molecule may affect its apoptogenic activity, we tested a number of newly synthesised VE analogues using malignant cell lines. Analogues of alpha-TOS with lower number of methyl substitutions on the aromatic ring were less active than alpha-TOS. Replacement of the succinyl group with a maleyl group greatly enhanced the activity, while it was lower for the glutaryl esters. Methylation of the free succinyl carboxyl group on alpha-TOS and delta-TOS completely prevented the apoptogenic activity of the parent compounds. Both Trolox and its succinylated derivative were inactive. alpha-tocotrienol (alpha-T3 H) failed to induce apoptosis, while gamma-T3 H was apoptogenic, and more so when succinylated. Shortening the aliphatic side chain of gamma-T3 by one isoprenyl unit increased its activity. Neither phytyl nor oleyl succinate caused apoptosis. These findings show that modifications of different functional moieties of the VE molecule can enhance apoptogenic activity. It is hoped that these observations will lead to the synthesis of analogues with even higher apoptogenic and, consequently, antineoplastic efficacy.
Inhibition of THP-1 cell adhesion to endothelial cells by alpha-tocopherol and alpha-tocotrienol is dependent on intracellular concentration of the antioxidants
Noguchi N, Hanyu R, Nonaka A, Okimoto Y, Kodama T.
Free Radic Biol Med. 2003 Jun 15;34(12):1614-20.
Vitamin E analogs such as alpha-tocopherol and alpha-tocotrienol have been shown to reduce endothelial expression of adhesion molecules. The reactivity of alpha-tocopherol and alpha-tocotrienol in inhibiting lipid peroxidation in vitro was essentially identical but the inhibition of adhesion of THP-1 cells, a monocytic-“like” cell line, to endothelial cells differs substantially. To determine the mechanism underlying this response, human umbilical vein endothelial cells (HUVECs) were assessed for their ability to accumulate vitamin E analogs. alpha-Tocotrienol accumulated in HUVECs to levels approximately 10-fold greater than that of alpha-tocopherol. The decrease in expression of vascular cell adhesion molecule-1 (VCAM-1) and the adhesion of THP-1 cells to HUVECs by alpha-tocopherol and alpha-tocotrienol was also determined. Both alpha-tocopherol and alpha-tocotrienol suppressed VCAM-1 expression and adhesion of THP-1 cells to HUVECs in a concentration-dependent manner. The efficacy of tocotrienol for reduction of VCAM-1 expression and adhesion of THP-1 cells to HUVECs was also 10-fold higher than that of tocopherol. The inhibitory effects of vitamin E analogs on the adhesiveness of endothelial cells clearly correlated with their intracellular concentrations. The data demonstrated that, in assessing the biological responses of antioxidants, intracellular accumulation and metabolism were additional important factors that must be considered.
Tocotrienols induce IKBKAP expression: a possible therapy for familial dysautonomia
Anderson SL, Qiu J, Rubin BY.
Biochem Biophys Res Commun. 2003 Jun 20;306(1):303-9.
Familial dysautonomia (FD), a neurodegenerative genetic disorder primarily affecting individuals of Ashkenazi Jewish descent, is caused by mutations in the IKBKAP gene which encodes the IkappaB kinase complex-associated protein (IKAP). The more common or major mutation causes aberrant splicing, resulting in a truncated form of IKAP. Tissues from individuals homozygous for the major mutation contain both mutant and wild-type IKAP transcripts. The apparent leaky nature of this mutation prompted a search for agents capable of elevating the level of expression of the wild-type IKAP transcript. We report the ability of tocotrienols, members of the vitamin E family, to increase transcription of IKAP mRNA in FD-derived cells, with corresponding increases in the correctly spliced transcript and normal protein. These findings suggest that in vivo supplementation with tocotrienols may elevate IKBKAP gene expression and in turn increase the amount of functional IKAP protein produced in FD patients.
The use of antioxidant therapies during chemotherapy
Drisko JA, Chapman J, Hunter VJ.
Gynecol Oncol. 2003 Mar;88(3):434-9.
OBJECTIVE: At the present time, many cancer patients combine some form of complementary and alternative medicine therapies with their conventional therapies. The most common choice of these therapies is the use of antioxidants.
RESULTS: A review of four common antioxidants is undertaken, which includes vitamin E (mixed tocopherols and tocotrienols), beta-carotene (natural mixed carotenoids), vitamin C (ascorbic acid), and vitamin A (retinoic acid). Antioxidants act as electron acceptors as well as therapeutic biologic response modifiers. Despite the fact that chemotherapy-induced formation of free radicals is well-demonstrated, chemotherapy-induced cytotoxicity in general does not seem to depend on formation of reactive oxygen species.
CONCLUSIONS: Currently, evidence is growing that antioxidants may provide some benefit when combined with certain types of chemotherapy. Because of the potential for positive benefits, a randomized controlled trial evaluating the safety and efficacy of adding antioxidants to chemotherapy in newly diagnosed ovarian cancer is underway at the University of Kansas Medical Center.
Role of caspase-8 activation in mediating vitamin E-induced apoptosis in murine mammary cancer cells
Shah S, Gapor A, Sylvester PW.
Nutr Cancer. 2003;45(2):236-46. March-April
The vitamin E family of compounds is divided into two subgroups, tocopherols and tocotrienols. However, tocotrienols display more potent apoptotic activity in mammary cancer cells. Although the mechanism(s) mediating tocotrienol-induced apoptosis is presently unknown, apoptosis is carried out by activation of initiator caspases (caspase-8 or -9) that subsequently activate effector caspases (caspase-3, -6, or -7). Studies were conducted to determine whether tocotrienol-induced apoptosis is mediated by activation of the caspase-8 and/or caspase-9 pathway. Highly malignant +SA mouse mammary epithelial cells were grown in culture and maintained on serum-free media. Treatment with tocotrienol-rich-fraction of palm oil (TRF) and g-tocotrienol, but not a-tocopherol, induced a dose-dependent decrease in +SA cell viability. TRF- and g-tocotrienol-induced cell death resulted from apoptosis, as determined by DNA fragmentation and positive TUNEL assay staining. Additional studies showed that treatment with 50 mM TRF or 20 mM g-tocotrienol increased intracellular activity and levels of processed caspase-8 and -3 but not caspase-9. Furthermore, treatment with specific caspase-8 or -3 inhibitors, but not caspase-9 inhibitor, completely blocked the tocotrienol-induced apoptosis in +SA cells. These findings demonstrate that tocotrienol-induced apoptosis in +SA mammary cancer cells is mediated through activation of the caspase-8 signaling pathway and is independent of caspase-9 activation.