Tocotrienols are members of the vitamin E family. An essential nutrient for the body, vitamin E is made up of four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). The slight difference between tocotrienols and tocopherols lie in the unsaturated side chain having three double bonds in its farnesyl isoprenoid tail. Tocotrienols are natural compounds found in select vegetable oils, wheat germ, barley, saw palmetto, and certain types of nuts and grains. This variant of vitamin E typically only occurs at very low levels in nature.
Chemically, vitamin E in all of its forms functions as an antioxidant. All of the tocotrienol and tocopherol isomers have this antioxidant activity due to the ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to a free radical in the body. This process inactivates ("quenches") the free radical by effectively donating a single unpaired electron (which comes with the hydrogen atom) to the radical. Although the many vitamers of vitamin E have different distributions and metabolic fates, there is as yet no accepted evidence that any of the active forms of vitamin E are able to do any essential function in the body that each of the others is not also able to do. Specifically, 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. Thus, one model for the function of vitamin E in the body is that it protects cell membranes, active enzyme sites, and DNA from free radical damage.
While the majority of research on vitamin E has focused on alpha-tocopherol, studies into tocotrienols account for less than 1% of all research into vitamin E. More recently, tocotrienols have reached a new measure of scientific recognition, with nearly 30% of peer-reviewed research articles on the vitamin published within the last two years (2009–2010). The first-ever scientific compilation of tocotrienol research, Tocotrienols: Vitamin E Beyond Tocopherols, was published in 2008 by CRC and AOCS Press, while a second edition has been approved for publication in May 2012.
Tocotrienols are named by analogy to tocopherols (from Greek words meaning to bear a pregnancy (see tocopherol); but with this word changed to include the chemical difference that tocotrienols are trienes, meaning that they share identical structure with the tocopherols except for the addition of three double bonds to their side chains.
Tocotrienols extracted from natural sources are d-tocotrienols. Tocotrienols have only a single chiral center, which exists at the 2' chromanol ring carbon, at the point where the isoprenoid tail joins the ring; the other two corresponding centers in the phytyl tail of the corresponding tocopherols, do not exist due to tocotrienol's unsaturation at these sites. In theory, tocotrienol stereoisomers may thus exist in the natural d-tocotrienol form, or as the unnatural isomeric 'l-tocotrienols' which have a 2S (rather than 2R) configuration at the molecules' single chiral center. In practice, however, tocotrienols are extracted from natural sources, and synthetic l and d,l forms are not marketed as supplements.
- 1 Discovery of tocotrienols
- 2 Types
- 3 Comparison of tocotrienol and tocopherol
- 4 α-tocopherol interference
- 5 Synthetic tocotrienols
- 6 Health effects of tocotrienols
- 7 Tocotrienols and radiation countermeasures
- 8 No-observed-adverse-effect level
- 9 See also
- 10 References
- 11 External links
Discovery of tocotrienols
The discovery of tocotrienols was first reported by Pennock and Whittle (USDA, Liverpool) in 1964, describing the isolation of tocotrienols from rubber. The biological significance of tocotrienols was clearly delineated in the early 1980s, when its ability to lower cholesterol was first reported by Qureshi and Elson (UWisconsin/Madison). During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated.
The current commercial sources of tocotrienol are rice, palm, and annatto. The ratio of tocopherol-to-tocotrienol in rice, palm, and annatto is 50:50, 25:75, and 0.1:99.9, respectively. α-tocopherol makes up roughly 25–50% of palm and rice vitamin E mixtures, respectively, and has been shown to interfere with tocotrienol benefits. Annatto, on the other hand, naturally contains only δ- and γ-tocotrienols and is essentially tocopherol-free, hence not confined by α-tocopherol interference issues.
Other natural tocotrienol sources include rice bran oil, coconut oil, cocoa butter, barley, and wheat germ. Sunflower, peanut, walnut, sesame, and olive oils, however contain only tocopherols. Some vitamin E supplements supply 50–200 mg/day of mixed tocotrienols. In a number of clinical trials, doses of tocotrienols as low as 42 mg/day have shown to reduce blood cholesterol levels by 5–35%. Tocotrienols are safe and human studies show no adverse effects with consumption of 240 mg/day for 48 months.
Tocotrienol rich fractions from rice, palm, or annatto, used in nutritional supplements, functional foods, and anti-aging cosmetics, are available in the market at 20%, 35%, 50%, and 70% total vitamin E content. Molecular distillation occurs at lower temperatures and reduces the problem of thermal decomposition. High vacuum also eliminates oxidation that might occur in the presence of air. For the utility and quality it is desired for the absolute tocotrienol concentration to be highest, tocopherol to be the lowest, and the process used to be solvent-free. Annatto tocotrienol has the highest tocotrienol concentrations, and is tocopherol-free.
Vitamin E, be it tocopherols or tocotrienols, is extremely sensitive to heat.
Comparison of tocotrienol and tocopherol
Tocotrienols are forms of natural vitamin E that can protect against brain cell damage, prevent cancer and reduce cholesterol. These biological characteristics, however, are not present in tocopherols.
Since the 1980s, there have been more studies proving tocotrienols are more potent in their anti-oxidation and anti-cancer effect than the common forms of tocopherol due their chemical structure. The unsaturated side-chain in tocotrienols causes them to penetrate tissues with saturated fatty layers more efficiently, making them ideal for anti-aging oral supplements and the skincare range. Tocotrienols are better able than tocopherols at combating oxidative stress of skin that had been exposed to UV rays of the sunlight.
Vitamin E has long been known for its antioxidative properties against lipid peroxidation in biological membranes and alpha-tocopherol is considered to be the most active form. In vivo, tocotrienols are more powerful antioxidants, and lipid ORAC values are highest for δ-tocotrienol. Since 2000, scientists have suggested tocotrienols are better antioxidants than tocopherols at preventing cardiovascular diseases and cancer. From the pharmacological standpoint, current formulation of vitamin E supplements, composed mainly of alpha- tocopherol, seems questionable.
Various studies have shown that alpha-tocopherol interferes with tocotrienol benefits. This was first published by Qureshi et al. in 1996, where researchers administered varying amounts of α-tocopherol and/or tocotrienol to six groups of chickens. The group that received only a minimal amount of α-tocopherol showed the greatest reduction in lipid parameters, while the group with the highest amount of alpha-tocopherol had an increase in cholesterol production. A separate study confirmed that high levels of α-tocopherol increase cholesterol production. α-tocopherol interference with tocotrienol absorption was described previously by Ikeda et al., who showed that α-tococopherol interfered with absorption of α-tocotrienol, but not γ-tocotrienol. More recently, Japanese researchers found that tocopherols, and α-tocopherol in particular, interfered with δ-tocotrienol’s ability to induce apoptosis in cancer cells, while blocking the absorption of δ-tocotrienol. Finally, α-tocopherol was shown to interfere with tocotrienols by increasing their catabolism.
Curiously, synthetic tocotrienol is not commonly available despite the ability to generate the compounds through chemical reactions. Depending on the route of synthesis, the product may result in a racemic mix of dl-tocotrienol which consists of a mix of d and l (left and right) forms that are lateral inversions of one another. However, pure isomers of either the d or l tocotrienol forms should also be possible using the right chemistry. In theory these would then likely confer many of the clinical benefits claimed for natural tocotrienol while being extremely pure in comparison and relatively cheap to produce.
Health effects of tocotrienols
Many research claims of tocotrienols' health benefits for human beings have been made. The toxicity levels for humans are presently unknown. The no-observed-adverse-effect level (NOAEL) for rats is estimated at 120–130 mg/kg body weight/day. As of 2004, the Food and Nutrition Board of the Institute of Medicine of the United States National Academy of Sciences did not define either the health benefits or the health risks, i.e. the Estimated Average Requirement, the Recommended Dietary Allowance, the Adequate Intake and the Tolerable Upper Intake Level (UL) were defined for alpha-tocopherol (except the ULs for infants) but not for tocotrienols.
Tocotrienol is more effective antioxidant than tocopherol because its unsaturated side chain facilitates better penetration into saturated fatty layers of the brain and liver. Tocotrienols can lower tumor formation, DNA damage and cell damage.
Tocotrienols and stroke-induced Injuries
In the peer-reviewed Stroke journal (Oct 2005), oral supplementation of a natural full spectrum palm tocotrienol complex to spontaneously hypertensive rats led to increased tocotrienol levels in the brain. The rats, supplemented with tocotrienols, showed more protection against stroke-induced injury compared to controls (non-supplemented group). This study demonstrated that oral supplementation of the palm tocotrienol complex acts on key molecular checkpoints (c-Src and 12-Lipoxygenase) to protect against glutamate- and stroke-induced neurodegeneration and ultimately protect against stroke in vivo. The protective effects of tocotrienols are independent of their antioxidant activity because tocopherols were effective only at higher concentrates.
In 2005, a study jointly undertaken at Wayne State University and Ohio State University Medical Center showed that tocotrienol can be efficiently delivered to organs and could therefore offer the health benefits suggested by in vitro and in vivo studies. "Our results demonstrate that tocotrienols is efficiently delivered to the bloodstream despite the fact that the transfer protein has a lower affinity for tocotrienols than it has for tocopherols," said Chandan Sen of Ohio State University and senior author of the study.[this quote needs a citation]
The researchers recruited women with normal cholesterol levels (average age of 23.5 years old) and gave them a fat-rich strawberry smoothie containing 400 mg of vitamin E containing 77 mg alpha-tocotrienol, 96 mg delta-tocotrienol, and 3 mg gamma-tocotrienol, plus tocopherols. Since vitamin E is a fat-soluble vitamin, the researchers chose to deliver the micronutrient in a fat-loaded meal in order to improve absorption. Blood measurements in the post-prandial period showed that maximal alpha-tocotrienol levels averaged almost 3 micromoles in blood plasma, 1.7 micromoles in low density lipoproteins, and 0.5 micromoles in high density lipoproteins. "This work presented first evidence demonstrating the post-absorptive fate of tocotrienol isomers and their association with lipoprotein subfractions in humans," wrote lead author Pramod Khosla of Wayne State University.[this quote needs a citation]
These concentrations, say the researchers, are sufficient to support the proposed neuro-protective functions of tocotrienol. "We have determined that when administered orally, tocotrienol can reach concentrations needed to serve these… protective functions," said Sen. "It is a regular dietary ingredient in Asia, so it can safely be a part of a daily diet within prepared foods or as a supplement in the United States." Can it be therapeutically used to prevent stroke? "Results from animal studies are encouraging, but it is still too soon to tell for humans," he added.[this quote needs a citation]
Tocotrienols and pancreatic cancer
Pancreatic cancer represents the fourth-leading cause of cancer death in the United States, with a dismal 5-year survival rate of less than 5%. Early detection and screening for pancreatic cancer in the current state should be limited to high-risk patients, although hereditary/familial factors account for only 10% of patients with pancreatic cancer.
In a 2009 in-vitro study, scientists at Department of Nutrition and Food Sciences, Texas Woman's University evaluated the impact of d-delta-tocotrienol, a potent vitamin E isomer, on human MIA PaCa-2 and PANC-1 pancreatic carcinoma cells and BxPC-3 pancreatic ductal adenocarcinoma cells. They concluded suppression of mevalonate pathway activities, be it by modulators of HMG CoA reductase (statins, tocotrienols, and farnesol), farnesyl transferase (farnesyl transferase inhibitors), and/or mevalonate pyrophosphate decarboxylase (phenylacetate) activity, have a potential in pancreatic cancer chemotherapy. Moreover, a Phase I dose-escalating clinical study evaluating the effect of pure δ-tocotrienol towards individuals with pancreatic cancer is running from 2009 to 2013 at the Moffitt Cancer Centre, and is the first tocotrienol study that is being clinically evaluated in humans towards cancer.[dated info]
Tocotrienols and breast cancer
In the 1990s, studies showed tocotrienols are the components of vitamin E responsible for growth inhibition in human breast cancer cells in vitro, through estrogen-independent mechanisms. Tocotrienols work synergistically with tamoxifen, a commonly used breast cancer medicine, in killing cancer cells.
Tocotrienols can also affect cell homeostasis, possibly independently of their antioxidant activity. Anti-cancer effects of α- and γ-tocotrienol have been reported, although δ-tocotrienol was verified to be the most effective tocotrienol in inducing apoptosis (cell death) in estrogen-responsive and estrogen-nonresponsive human breast cancer cells. Based on these results on cells in culture, investigators have hypothesised that a mixture of α- and γ-tocotrienols might reduce breast cancer risk.
Further studies on tocotrienol and breast cancer indicated that gamma-tocotrienol targets cancer cells by inhibiting Id1, a key cancer-promoting protein. Gamma-tocotrienol was shown to trigger cell apoptosis as well as anti-proliferation of cancer cells. This mechanism for δ- and γ-tocotrienol was also observed in separate prostate cancer and melanoma cell line studies.
In 2009, a study by scientists at the College of Pharmacy, University of Louisiana at Monroe, showed that lower level statin treatment in combination with γ-tocotrienol inhibits growth of highly malignant +SA mammary epithelial cells in culture (suggesting the possibility of avoiding myotoxicity associated with high dose statin monotherapy).
Tocotrienols and prostate cancer
Investigation of the antiproliferative effect of tocotrienols in PC3 and LNCaP prostate cancer cells suggests that the transformation of vitamin E to carboxyethyl-hydroxychroman (CEHC) is mostly a detoxification mechanism, useful to maintain the malignant properties of prostate cancer cells. However, various research studies suggest that both δ- and γ-tocotrienol potently suppressed prostate cancer cell proliferation. In one study, the antiproliferative effects of γ-tocotrienol were found to act through multiple-signalling pathways (NF-B, EGF-R and Id family proteins). In addition, the same study demonstrated the anti-invasion and chemosensitisation effect of γ-tocotrienol against PCa cells. In another study, δ-tocotrienol was at least equally or more potent than γ-tocotrienol in prostate cancer cells, and showed that alpha-tocopherol enhanced cancer cell growth.
Tocotrienols and skin cancer
In a 2009 study at the Li Ka Shing Faculty of Medicine, The University of Hong Kong, scientists found reduction in skin cancer cells when treated with gamma-tocotrienol with chemotherapy drugs. For the first time, researchers recorded the anti-invasion and chemonsensitization effect of gamma-tocotrienol against human malignant melanoma cells. In cell line and animal studies, δ- and γ- tocotrienols have been shown to suppress the growth of melanoma.
Tocotrienols and cholesterol reduction
The human body makes cholesterol from the liver, producing about 1g of cholesterol each day or 80% of the needed total body cholesterol. The remaining 20% comes from what we eat. Excessive cholesterol is a health risk because gradual fatty deposits clog up the arteries. This will cause blood flow to the brain, heart, kidneys and other parts of the body to become less efficient.
Cholesterol, though needed metabolically, is not essential in diet. Tocotrienols can decrease the liver's capacity to manufacture cholesterol. They do so by dialing down HMG-CoA reductase, the enzyme in the liver responsible for cholesterol synthesis.
In 1993, American scientists conducted a double-blind placebo controlled study of 50 volunteers at the Kenneth Jordan Heart Foundation and Elmhurst Medical Center. Their results suggested that tocotrienols (from palm and rice) could ease clogged arteries. Seven high cholesterol patients with narrowing arteries experienced reversal of arterial blockage of the carotid artery after consuming tocotrienols, while in two the condition worsened. This was compared to the control group, where none improved and ten worsened. Tocotrienols, especially δ- and γ-tocotrienols, were shown to be effective nutritional agents in treating high cholesterol. In particular, they act on a specific enzyme called 3-hydroxy-3-methylglutaryl-coenzyme A reductase and dial down the production of the enzyme, resulting in less cholesterol being manufactured by liver cells. . Both δ- and γ-tocotrienols degraded the enzyme, but only δ-tocotrienol was shown to block production fully. A 1996 study in chickens indicated that the presence of dietary alpha-tocopherol may interfere with tocotrienol's ability to lower cholesterol  Investigation on FeAOX-6, which combines antioxidant structural features of both tocopherols and carotenoids into a single molecule, on macrophage functions involved in foam cell formation showed that both FeAOX-6 or alpha-tocotrienol induce a strong dose-dependent reduction of cholesterol and reduce cholesterol accumulation in human macrophages. The extent of the reduction found with alpha-tocotrienol was greater than that induced by FeAOX-6 and did not correlate with their respective antioxidant capacities.
Tocotrienols and diabetes
According to the World Health Organization (WHO), 170 million people were affected by diabetes in the year 2002, and this number is likely to increase to 366 million by the year 2030. Diabetes mellitus (DM) has been recognized as the sole independent risk factor for the development of any cardiovascular disease. Cardiovascular complications such as stroke and heart attack are increasingly causing death in diabetic patients. Alarmingly, literature statistics indicate that atherosclerosis accounts for about 8 to 10% of all diabetic deaths.
Recent studies are showing that vitamin E intake significantly reduced risk of type 2 diabetes. The relative risk (RR) of type 2 diabetes between the extreme quartiles of the intake was 0.69 (95% CI 0.51-0.94, P for trend=0.003). Intakes of alpha-tocopherol, gamma-tocopherol, delta-tocopherol, and beta-tocotrienol were inversely related to a risk of type 2 diabetes. While correlation does not imply causation, these data suggest the possibility that the development of type 2 diabetes might be modified by the intake of antioxidants in the diet.
In 2009, animal trials carried out in India and Malaysia revealed palm tocotrienols improved blood glucose, dyslipidemia and oxidative stress in diabetic rats. It is able to prevent the progression of vascular wall changes occurring in DM. Moreover, tocotrienols alone and in mixture with alpha-tocopherol had the capability to enhance lymphocyte proliferation among streptozotocin-induced diabetic rats.
Tocotrienols and radiation countermeasures
When radiation strikes, be it from warfare, disaster (as in Japan’s recent earthquake and tsunami), or therapy (as in cancer), the bone marrow is the first to be compromised. Those lethally affected die immediately, whereas those who are critically affected may survive the first 30 days, and survival is predominantly dependent on the bone marrow regenerating itself. Severe side effects include acute radiation syndrome (ARS) and bone marrow failure syndrome (BMFS). If the bone marrow regenerates fast enough, new blood from the marrow will replenish arteries and veins, replacing old blood that was extremely compromised. This is true for radiation in warfare, disaster or cancer.
In the past six years, the Armed Forces Radiobiology Research Institute (AFRRI) has performed extensive research on tocotrienol —a form of vitamin E — as radiation countermeasure agent. Tocotrienols occur naturally as four distinct molecules designated α-, β-, γ- and δ-tocotrienol. Of these, δ- and γ-tocotrienol are the most effective radioactive countermeasure agents. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the primary source of radiation-induced damage, and – as potent antioxidants – tocotrienols are effective radioprotectors, supporting the hypothesis that “strong antioxidants make strong radioprotectors”. However, amelioration of radiation lethality goes beyond tocotrienol’s antioxidant properties. δ- and γ-tocotrienol display an unambiguous stimulatory effect on hematopoietic (blood-forming) tissue, with delta-tocotrienol performing better than gamma-tocotrienol. Following total body irradiation of mice, both δ- and γ-tocotrienol regenerated blood-borne cells by increasing the total white blood cell count; only δ-tocotrienol regenerated lymphocytes. Tocotrienols almost fully restored bone marrow cellularity to normal levels following radiation, while overall cellularity in untreated controls remained depleted. In both cases, prophylactic treatment 24 hours pre-radiation was more effective than post-radiation treatment. These results suggest that tocotrienols, especially of the δ- and γ-isoforms, could be used as powerful radioprotectors in first responders to nuclear fallout areas, radiation workers, and cancer radiotherapy patients. Annatto tocotrienol is the only source containing exclusively δ-tocotrienol (90%) and γ-tocotrienol (10%) that may be useful for radiation countermeasures, tocotrienols from rice bran contain all four: alpha, beta, gamma and delta.
A 13-week study by H. Nakamura and colleagues at the National Institute of Health Sciences (Japan) of tocotrienols' toxicity in rats found significant changes in several blood components, increases in liver weights and (in females) reductions in ovary and uterus weights, depending on the dosages. The authors estimated the no-observed-adverse-effect level (NOAEL) to be 120 mg per kg of body weight per day for males and 130 mg per kg of body weight per day for females. Since effects on the blood components were observed in all cases with non-placebos, a no-observed-effect level (NOEL) could not be determined.
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