The effect of different isomers of tocotrienol was tested on myocardial ischemia reperfusion injury. Although all of the tocotrienol isomers offered some degree of cardioprotection, gamma-tocotrienol was the most protective as evident from the result of myocardial apoptosis. To study the mechanism of tocotrienol mediated cardioprotection, we examined the interaction and/or translocation of different signaling components to caveolins and activity of proteasome. The results suggest that differential interaction of MAP kinases with caveolin 1/3 in conjuncture with proteasome stabilization play a unique role in tocotrienol mediated cardioprotection possibly by altering the availability of pro-survival and anti-survival proteins.
Uncategorized
The familiar role of tocols (tocopherols and tocotrienols) as lipid-soluble chain-terminating inhibitors of lipid peroxidation is currently in the midst of a reinterpretation. New biological activities have been described for tocols that apparently are not dependent on their well-established antioxidant behaviour. These activities could well be real, but there remain large gaps in our understanding of the behaviour of tocols in membranes, especially when it comes to the alpha-, beta-, gamma-, delta-chroman methylation patterns and the seemingly special nature of tocotrienols. It is inappropriate to make conclusions and develop models based on in vivo (or cell culture) results with reference to in vitro measurements of antioxidant activity. When present in biological membranes, tocols will experience a large variation in the local composition of phospholipids and the presence of neutral lipids such as cholesterol, both of which would be expected to change the efficiency of antioxidant action. It is likely that tocols are not homogeneously dispersed in a membrane, but it is still not known whether any specific combination of lipid head group and acyl chains are conferred special protection from peroxidation, nor do we currently appreciate the structural role that tocols play in membranes. Tocols may enhance curvature stress or counteract similar stresses generated by other lipids such as lysolipids. This review will outline what is known about the location and behaviour of tocols in phospholipid bilayers. We will draw mainly from the biophysical literature, but will attempt to extend the discussion to biologically relevant phenomena when appropriate. We hope that it will assist researchers when designing new experiments and when critically assessing the results, in turn providing a more thorough understanding of the biochemistry of tocols.
Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C–H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol.
The common familial dysautonomia (FD) mutation results in tissue specific mis-splicing with reduced amount of wild-type (WT) IkappaB kinase associated protein gene (IKBKAP) mRNA and ELP1. ELP1 is a subunit of Elongator, formerly called the IkappaB kinase associated protein (IKAP) protein. We measured IKBKAP mRNA in peripheral blood leukocytes to determine whether FD subjects and carriers have characteristic levels. Estimated mean IKBKAP mRNA levels, measured by quantitative PCR and expressed as amount relative to the noncarrier average, were significantly different for the two groups when not adjusted for age and sex (p < 0.001): FD subjects 0.23, 95% confidence interval (CI) (0.19, 0.28); carriers 0.58, 95% CI (0.50, 0.68); or adjusted for age and sex (p < 0.001): FD subjects 0.21, 95% CI (0.16, 0.26); carriers 0.66, 95% CI (0.55, 0.79). Comparison of IKBKAP mRNA levels of the 22 FD subjects and their related carriers showed a strong correlation, providing evidence for genetic control of splicing efficiency. IKBKAP mRNA levels were not higher in those subjects using tocotrienols or epigallocatechin gallate. Levels of IKBKAP mRNA in peripheral blood leukocytes can be used to assess molecular response to therapies aimed at enhancing exon 20 inclusion and increasing cellular levels of ELP1/IKAP.
Vitamin E refers to a family of tocopherol and tocotrienol isomers discovered in 1922 as anti-infertility factor. Vitamin E deficiency causes infertility and delayed-onset ataxia in experimental animals, and it leads to neuronal dysfunctions in humans. However, based largely on its radical-scavenging antioxidant activity in vitro, vitamin E supplements are commonly thought to provide health benefits against diseases associated with oxidative damage, most notably cardiovascular diseases. Contrary to this belief, the outcome of recent large, prospective, randomized and placebo-controlled clinical studies does not encourage the use of vitamin E supplements. These overall disappointing results can be explained and substantiated by scientific data critically testing the strengths of evidence for many of the underlying assumptions and examining the possibility that in vivo vitamin E may have function(s) other than, or in addition to, acting as an antioxidant.
Tocotrienols are a group of natural vitamin E compounds with patent antitumoral effects, mostly based on their ability to induce apoptosis in cancer cells. In activated pancreatic stellate cells (PSCs) we have determined that tocotrienols elicit a dramatic mitochondrial destabilization followed by initiation of non-necrotic forms of programmed cell death, namely apoptosis and autophagy. PSCs are the main cell type involved in the generation of pancreatic fibrosis, and their removal is critical to limit the fibrogenic process. Noteworthy, tocotrienol death-promoting actions are exclusively directed to activated PSCs, but not to their quiescent counterparts nor to terminally differentiated acinar cells. Here, we hypothesize that the transformed phenotype of PSCs may include “activated” mitochondria, which can be used by tocotrienols to trigger autophagic and apoptotic signaling. We propose that mitochondria are the cornerstone of cell sensitivity to tocotrienols, and suggest possible mechanisms, that may be interconnected, on how tocotrienols may govern mitochondrial death pathways.
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.
This study reports the effect of physical refining on palm vitamin E including α−tocopherol, α−, γ− and δ−tocotrienols as well as α−tocomonoenol. A method using HPLC with fluorescence detector using normal phase silica column is described. An isocratic elution with n-hexane/THF/2-propanol (1000:60:4, by vol.) as mobile phase was used. The structure of the α−tocomonoenol was determined using gas chromatography coupled with mass spectrometry. The composition of the vitamers were α−tocopherol (14–17%), α−tocotrienol (22–24%), γ−tocotrienol (49–53%), δ−tocotrienol (6–7%) and α−tocomonoenol (3%) throughout the physical refining. The concentration of all vitamers in crude palm oil was 1273±18 ppm. The concentrations of all vitamers in degummed palm oil, bleached palm oil and deodorized palm oil were 1134±20 ppm, 1095±18 ppm and 1029±18 ppm, respectively. This method provides fast and valuable information with minimal analysis time and no sample pre-treatment.
Rice bran is a rich natural source of vitamin E and gamma-oryzanol, which have been extensively studied and reported to possess important health-promoting properties. However, commercial rice bran is a mixture of rice bran and germ, and profiles of vitamin E and gamma-oryzanol components in these two different materials are less well-studied. In the current study, vitamin E and gamma-oryzanol components in rice bran and germ were analyzed by liquid chromatography/mass spectrometry/mass spectrometry. The components were identified by electrospray ionization mass spectrometry (ESI-MS) with both positive- and negative-ion modes. Both deprotonated molecular ion [M – H](-) and protonated molecular ion [M + H](+) found as the base peaks in spectra of vitamin E components made ESI-MS a valuable analytic method in detecting vitamin E compounds, especially when they were at very low levels in samples. Ultraviolet absorption was used for quantification of vitamin E and gamma-oryzanol components. While the level of vitamin E in rice germ was 5 times greater than in rice bran, the level of gamma-oryzanol in rice germ was 5 times lower than in rice bran. Also, the major vitamin E component was alpha-tocopherol in rice germ and gamma-tocotrienol in rice bran. These data suggest that rice bran and germ have significantly different profiles of vitamin E and gamma-oryzanol components. The method enables rapid and direct on-line identification and quantification of the vitamin E and gamma-oryzanol components in rice bran and germ.
The present paper describes the development and validation of a normal-phase liquid chromatography-mass spectrometry (NP-HPLC-MS) method for the screening and quantification of vitamin E constituents in human plasma and food matrixes. Liquid-liquid extraction combined with isotope dilution was applied to extract the lipophilic target analytes. Baseline separation of alpha-tocopherylacetate, alpha-tocopherol, alpha-tocotrienol, alpha-tocopherylquinone, beta-tocopherol, gamma-tocopherol, beta-tocotrienol, gamma-tocotrienol, delta-tocopherol, and delta-tocotrienol was achieved utilizing a normal-phase amine column operated with n-hexane and 1,4-dioxane as solvents. Detection was achieved by positive-ion atmospheric-pressure chemical ionization (APCI). Key features of the method are lower limits of detection, 3-51 nmoles/L; lower limits of quantification, 8-168 nmoles/L; linearity coefficients, 0.9778-0.9989; linear ranges, 0.01-29 micromol/L; recoveries, 53-92%; accuracies, 99-103%; intraday precisions, 2-17%; interday precisions, 5-18%; and suppression values, 0-29%. Fragmentation of tocopherols was studied by tandem mass spectrometry, and a fragmentation scheme for tocotrienols/tocopherols is postulated. Neutral-loss and precursor-ion scan experiments were performed for targeted discovery of oxidation products of tocopherols in human blood and fish oil, the latter being an important food component. The presented data suggest that this method will help to expand the number of quantified/discovered vitamin E constituents detected in food products and analyzed during human/animal trials in order to give a more comprehensive picture to nutritionists about the fate of vitamin E.