Delivery of orally supplemented alpha-tocotrienol to vital organs of rats and tocopherol-transport protein deficient mice

Nanomolar vitamin E alpha-tocotrienol inhibits glutamate-induced activation of phospholipase A2 and causes neuroprotection

Our previous works have elucidated that the 12-lipoxygenase pathway is directly implicated in glutamate-induced neural cell death, and that such that toxicity is prevented by nM concentrations of the natural vitamin E alpha-tocotrienol (TCT). In the current study we tested the hypothesis that phospholipase A(2) (PLA(2)) activity is sensitive to glutamate and mobilizes arachidonic acid (AA), a substrate for 12-lipoxygenase. Furthermore, we examined whether TCT regulates glutamate-inducible PLA(2) activity in neural cells. Glutamate challenge induced the release of [(3)H]AA from HT4 neural cells. Such response was attenuated by calcium chelators (EGTA and BAPTA), cytosolic PLA(2) (cPLA(2))-specific inhibitor (AACOCF(3)) as well as TCT at 250 nM. Glutamate also caused the elevation of free polyunsaturated fatty acid (AA and docosahexaenoic acid) levels and disappearance of phospholipid-esterified AA in neural cells. Furthermore, glutamate induced a time-dependent translocation and enhanced serine phosphorylation of cPLA(2) in the cells. These effects of glutamate on fatty acid levels and on cPLA(2) were significantly attenuated by nM TCT. The observations that AACOCF(3), transient knock-down of cPLA(2) as well as TCT significantly protected against the glutamate-induced death of neural cells implicate cPLA(2) as a TCT-sensitive mediator of glutamate induced neural cell death. This work presents first evidence recognizing glutamate-induced changes in cPLA(2) as a novel mechanism responsible for neuroprotection observed in response to nanomolar concentrations of TCT.

Id1, inhibitor of differentiation, is a key protein mediating anti-tumor responses of gamma-tocotrienol in breast cancer cells

Gamma-tocotrienol has demonstrated anti-proliferative effect on breast cancer (BCa) cells, but mechanisms involved are largely unknown. This study aimed at deciphering the molecular pathways responsible for its activity. Our results showed that treatment of BCa cells with gamma-tocotrienol resulted in induction of apoptosis as evidenced by activation of pro-caspases, accumulation of sub-G1 cells and DNA fragmentations. Examination of the pro-survival genes revealed that the gamma-tocotrienol-induced cell death was associated with suppression of Id1 and NF-kappaB through modulation of their upstream regulators (Src, Smad1/5/8, Fak and LOX). Meanwhile, gamma-tocotrienol treatment also resulted in the induction of JNK signaling pathway and inhibition of JNK activity by specific inhibitor partially blocked the effect of gamma-tocotrienol. Furthermore, synergistic effect was observed when cells were co-treated with gamma-tocotrienol and Docetaxel. Interestingly, in cells that treated with gamma-tocotrienol, alpha-tocopherol or beta-aminoproprionitrile were found to partially restore Id1 expression. Meanwhile, this restoration of Id1 was found to protect the cells from gamma-tocotrienol induced apoptosis. Consistent outcome was observed in cells ectopically transfected with the Id-1 gene. Our results suggested that the anti-proliferative and chemosensitization effect of gamma-tocotrienol on BCa cells may be mediated through downregulation of Id1 protein.

Evidence of gamma-tocotrienol as an apoptosis-inducing, invasion-suppressing, and chemotherapy drug-sensitizing agent in human melanoma cells

To date, the most effective cure for metastatic melanoma remains the surgical resection of the primary tumor. Recently, tocotrienol-rich-fraction has shown antiproliferative effect on cancer cells. To elucidate this anticancer property in malignant melanoma, this study aimed, first, to identify the most potent isomer for eliminating melanoma 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 procaspases and the accumulation of sub-G1 cell population. Examination of the prosurvival genes revealed that the gamma-tocotrienol-induced cell death was associated with suppression of NF-kappaB, EGF-R, and Id family proteins. Meanwhile, gamma-tocotrienol treatment also resulted in induction of JNK signaling pathway, and inhibition of JNK activity by selective inhibitor 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, synergistic effect was observed when cells were cotreated with gamma-tocotrienol and chemotherapy drugs. Together, our results demonstrated for the first time the anti-invasion and chemonsensitization effect of gamma-tocotrienol against human malignant melanoma cells.

Absorption, transport, and bioavailability of vitamin e and its role in pregnant women

Vitamin E is an important lipophilic antioxidant. The term refers to eight essential naturally occurring fat-soluble nutrients called tocopherols or tocotrienols. Among these isomers, alpha-tocopherol has the highest biologically active form and is found in all lipoprotein fractions. Vitamin E deficiency during pregnancy may cause miscarriage, preterm birth, preeclampsia, and intrauterine growth restriction. This review highlights recent findings that have led to a better understanding of vitamin E absorption, transport, bioavailability, and its role in pregnancy, and that underline the need for re-evaluation of the potential benefits of vitamin E supplementation in pregnant women.

Chemical reactivities and physical effects in comparison between tocopherols and tocotrienols: physiological significance and prospects as antioxidants

Vitamin E is a generic term for all tocopherol and tocotrienol derivatives. The most abundant and active form of vitamin E isoforms in vivo is alpha-tocopherol, but recently the roles of other forms of vitamin E have received renewed attention. In this review, we summarize the differences among alpha-, beta-, gamma-, delta-tocopherols and tocotrienols specifically regarding the following points; (i) their radical-scavenging efficacies and chemical reactivity with metal ions in solution, (ii) their physical effects at the liposomal membrane interior, and (iii) their protective effects against cell toxicity. Moreover, the physiological significance and future prospects for using vitamin E, especially tocotrienols, for the prevention and treatment of disease are discussed.

Vitamin E: An overview of major research directions

During the last 90 years since the discovery of vitamin E, research has focused on different properties of this molecule, the focus often depending on the specific techniques and scientific knowledge present at each time. Originally discovered as a dietary factor essential for reproduction in rats, vitamin E has revealed in the meantime many more important molecular properties, such as the scavenging of reactive oxygen and nitrogen species with consequent prevention of oxidative damage associated with many diseases, or the modulation of signal transduction and gene expression in antioxidant and non-antioxidant manners. Research over the last 30 years has also resolved the biosynthesis and occurrence of vitamin E in plants, the proteins involved in the cellular uptake, tissue distribution and metabolism, and defined a congenital recessive neurological disease, ataxia with vitamin E deficiency (AVED), characterized by impaired enrichment of alpha-tocopherol in plasma as a result of mutations in the liver alpha-tocopherol transfer gene. This review is giving a brief introduction about vitamin E by following the major research directions since its discovery with a historical perspective.

Vitamin E and mast cells

Mast cells play an important role in the immune system by interacting with B and T cells and by releasing several mediators involved in activating other cells. Hyperreactivity of mast cells and their uncontrolled accumulation in tissues lead to increased release of inflammatory mediators contributing to the pathogenesis of several diseases such as rheumatoid arthritis, atherosclerosis, multiple sclerosis, and allergic disorders such as asthma and allergic rhinitis. Interference with mast cell proliferation, survival, degranulation, and migration by synthetic or natural compounds may represent a preventive strategy for the management of these diseases. Natural vitamin E covers a group of eight analogues-the alpha-, beta-, gamma-, and delta-tocopherols and the alpha-, beta-, gamma-, and delta-tocotrienols, but only alpha-tocopherol is efficiently retained by the liver and distributed to peripheral tissues. Mast cells preferentially locate in the proximity of tissues that interface with the external environment (the epithelial surface of the skin, the gastrointestinal mucosa, and the respiratory system), what may render them accessible to treatments with inefficiently retained natural vitamin E analogues and synthetic derivatives. In addition to scavenging free radicals, the natural vitamin E analogues differently modulate signal transduction and gene expression in several cell lines; in mast cells, protein kinase C, protein phosphatase 2A, and protein kinase B are affected by vitamin E, leading to the modulation of proliferation, apoptosis, secretion, and migration. In this chapter, the possibility that vitamin E can prevent diseases with mast cells involvement by modulating signal transduction and gene expression is evaluated.

Tocotrienols in health and disease: the other half of the natural vitamin E family

Tocochromanols encompass a group of compounds with vitamin E activity essential for human nutrition. Structurally, natural vitamin E includes eight chemically distinct molecules: alpha-, beta-, gamma- and delta-tocopherol; and alpha-, beta-, gamma- and delta-tocotrienol. Symptoms caused by alpha-tocopherol deficiency can be alleviated by tocotrienols. Thus, tocotrienols may be viewed as being members of the natural vitamin E family not only structurally but also functionally. Palm oil and rice bran oil represent two major nutritional sources of natural tocotrienol. Taken orally, tocotrienols are bioavailable to all vital organs. The tocotrienol forms of natural vitamin E possesses powerful hypocholesterolemic, anti-cancer and neuroprotective properties that are often not exhibited by tocopherols. Oral tocotrienol protects against stroke-associated brain damage in vivo. Disappointments with outcomes-based clinical studies testing the efficacy of alpha-tocopherol need to be handled with caution and prudence recognizing the untapped opportunities offered by the other forms of natural vitamin E. Although tocotrienols represent half of the natural vitamin E family, work on tocotrienols account for roughly 1% of the total literature on vitamin E. The current state of knowledge warrants strategic investment into investigating the lesser known forms of vitamin E.

Tocotrienols: the emerging face of natural vitamin E

Natural vitamin E includes eight chemically distinct molecules: alpha-, beta-, gamma-, and delta-tocopherols and alpha-, beta-, gamma-, and delta-tocotrienols. More than 95% of all studies on vitamin E are directed toward the specific study of alpha-tocopherol. The other forms of natural vitamin E remain poorly understood. The abundance of alpha-tocopherol in the human body and the comparable efficiency of all vitamin E molecules as antioxidants led biologists to neglect the non-tocopherol vitamin E molecules as topics for basic and clinical research. Recent developments warrant a serious reconsideration of this conventional wisdom. The tocotrienol subfamily of natural vitamin E possesses powerful neuroprotective, anticancer, and cholesterol-lowering properties that are often not exhibited by tocopherols. Current developments in vitamin E research clearly indicate that members of the vitamin E family are not redundant with respect to their biological functions. alpha-Tocotrienol, gamma-tocopherol, and delta-tocotrienol have emerged as vitamin E molecules with functions in health and disease that are clearly distinct from that of alpha-tocopherol. At nanomolar concentration, alpha-tocotrienol, not alpha-tocopherol, prevents neurodegeneration. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. Recently, it has been suggested that the safe dose of various tocotrienols for human consumption is 200-1000/day. A rapidly expanding body of evidence supports that members of the vitamin E family are functionally unique. In recognition of this fact, title claims in publications should be limited to the specific form of vitamin E studied. For example, evidence for toxicity of a specific form of tocopherol in excess may not be used to conclude that high-dosage "vitamin E" supplementation may increase all-cause mortality. Such conclusion incorrectly implies that tocotrienols are toxic as well under conditions where tocotrienols were not even considered. The current state of knowledge warrants strategic investment into the lesser known forms of vitamin E. This will enable prudent selection of the appropriate vitamin E molecule for studies addressing a specific health need.

Natural vitamin E alpha-tocotrienol: retention in vital organs in response to long-term oral supplementation and withdrawal

The natural vitamin E tocotrienol (TCT) possesses biological properties not shared by tocopherols (TCP). Nanomolar alpha-TCT, not alpha-TCP, is potently neuroprotective (JBC 275:13049; 278:43508; Stroke 36:2258). The report that the affinity of TTP to bind (alpha-TCT is an order of magnitude lower than that for alpha-TCP questions the bioavailability of orally taken TCT to tissues. Oral supplementation of TCT for 3 years in nine generations of female and male rat was studied. Ten vital organs were examined. To gain insight into the turnover of alpha-TCT in tissues, a subset of supplemented rats was moved to vitamin E deficient diet for 7 weeks. Orally supplemented alpha-TCT was delivered to all vital organs including the brain and spinal cord in significant amounts. In organs such as the skin, adipose and gonads the maximum level of alpha-TCT achieved in response to supplementation was folds higher than baseline values of alpha-TCP in rats maintained on laboratory chow. Females had higher levels of alpha-TCT compared to matched tissues of corresponding males. To gain insight into how quickly alpha-TCT is metabolized in the tissues, washout of alpha-TCT from vital organs was examined. alpha-TCT accumulated in vital organs over more than 2 years was almost completely lost in less than 2 months when the supplementation was stopped. This is in sharp contrast with findings related to alpha-TCP retention. The ability of long-term oral supplementation to maintain and elevate alpha-TCT levels in vital organs together with the rapid elimination of the intact vitamin from all organs studied underscores the need for continuous oral supplementation of TCT.

Characterization of the potent neuroprotective properties of the natural vitamin E alpha-tocotrienol

The natural vitamin E tocotrienols possess properties not shared by tocopherols. Nanomolar alpha-tocotrienol, not alpha-tocopherol, is potently neuroprotective. On a concentration basis, this finding represents the most potent of all biological functions exhibited by any natural vitamin E molecule. We sought to dissect the antioxidant-independent and -dependent neuroprotective properties of alpha-tocotrienol by using two different triggers of neurotoxicity, homocysteic acid (HCA) and linoleic acid. Both HCA and linoleic acid caused neurotoxicity with comparable features, such as increased ratio of oxidized to reduced glutathione GSSG/GSH, raised intracellular calcium concentration and compromised mitochondrial membrane potential. Mechanisms underlying HCA-induced neurodegeneration were comparable to those in the path implicated in glutamate-induced neurotoxicity. Inducible activation of c-Src and 12-lipoxygenase (12-Lox) represented early events in that pathway. Overexpression of active c-Src or 12-Lox sensitized cells to HCA-induced death. Nanomolar alpha-tocotrienol was protective. Knock-down of c-Src or 12-Lox attenuated HCA-induced neurotoxicity. Oxidative stress represented a late event in HCA-induced death. The observation that micromolar, but not nanomolar, alpha-tocotrienol functions as an antioxidant was verified in a model involving linoleic acid-induced oxidative stress and cell death. Oral supplementation of alpha-tocotrienol to humans results in a peak plasma concentration of 3 microm. Thus, oral alpha-tocotrienol may be neuroprotective by antioxidant-independent as well as antioxidant-dependent mechanisms.

Postprandial levels of the natural vitamin E tocotrienol in human circulation

Compared to tocopherols, tocotrienols are poorly understood. The postabsorptive fate of tocotrienol isomers and their association with lipoprotein subfractions was examined. Normocholesterolemic women were subjected to an oral fat challenge supplemented with vitamin E (capsule containing 77 mg alpha-tocotrienol, 96 mg alpha-tocotrienol, 3 mg gamma-tocotrienol, 62 mg alpha-tocopherol, and 96 mg gamma-tocopherol). Plasma samples were collected at every 2 h intervals for up to 8 h following a one-time supplementation. Lipoproteins were measured by NMR spectroscopy, and subfractions of lipoproteins were isolated by density gradient ultracentrifugation. The maximal alpha-tocotrienol concentrations in supplemented individuals averaged approximately 3 microM in blood plasma, 1.7 microM in LDL, 0.9 microM in triglyceride-rich lipoprotein, and 0.5 microM in HDL. The peak plasma level corresponded to 12- to 30-fold more than the concentration of alpha-tocotrienol required to completely prevent stroke-related neurodegeneration. Tocotrienols were detected in the blood plasma and all lipoprotein subfractions studied postprandially.