Tocotrienol
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The vitamin E family comprise four tocotrienols (alpha, beta, gamma, delta) and four
tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...
s (alpha, beta, gamma, delta). The critical chemical structural difference between tocotrienols and tocopherols is that tocotrienols have unsaturated isoprenoid side chains with three carbon-carbon
double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...
s versus saturated side chains for tocopherols (see Figure). Tocotrienols are compounds naturally occurring at higher levels in some
vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or f ...
s, including
palm oil Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced from ...
,
rice bran oil Rice bran oil is the oil extracted from the hard outer brown layer of rice called bran. It is known for its high smoke point of and mild flavor, making it suitable for high-temperature cooking methods such as stir frying and deep frying. It i ...
,
wheat germ Cereal germ or Wheat germ: The germ of a cereal is the reproductive part that germinates to grow into a plant; it is the embryo of the seed. Along with bran, germ is often a by-product of the milling that produces refined grain products ...
,
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...
,
saw palmetto ''Serenoa repens'', commonly known as saw palmetto, is the sole species currently classified in the genus ''Serenoa''. It is a small palm, growing to a maximum height around . It is endemic to the subtropical and tropical Southeastern United S ...
,
annatto Annatto ( or ) is an orange-red condiment and food coloring derived from the seeds of the achiote tree (''Bixa orellana''), native to tropical America. It is often used to impart a yellow or orange color to foods, but sometimes also for its flav ...
, and certain other types of seeds, nuts and grains, and the oils derived from them. Chemically, different analogues of vitamin E all show some activity as a chemical
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
, but do not all have the same vitamin E equivalence. Tocotrienols demonstrate activity depending on the type of antioxidant performance being measured. All tocotrienols have some physical antioxidant activity due to an ability to donate a hydrogen atom (a proton plus electron) from the
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
group on the chromanol ring, to
free radical A daughter category of ''Ageing'', this category deals only with the biological aspects of ageing. Ageing Ailments of unknown cause Biogerontology Biological processes Causes of death Cellular processes Gerontology Life extension Metabo ...
and
reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...
. Historically studies of tocotrienols account for less than 1% of all research into vitamin E. A scientific compilation of tocotrienol research, ''Tocotrienols: Vitamin E Beyond Tocopherols'', was published in 2013.


Health effects

A number of health benefits of tocotrienols have been proposed, included decreased risk of heart disease and cancer. The Food and Nutrition Board of the Institute of Medicine of the
United States National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...
does not define a Recommended Dietary Allowance or Adequate Intake for tocotrienols.


Brain

A review of human studies in middle-aged and elderly stated "Evidence from prospective and case-control studies suggested that increased blood levels of tocotrienols were associated with favorable cognitive function outcomes." The review qualified this statement by noting that randomized, controlled clinical trials were needed to evaluate these observations.


Heart disease

Tocotrienols have been linked to improved markers of heart disease.


Side effects

Tocotrienols are generally well tolerated and without significant side effects.


History

The discovery of tocotrienols was first reported by Pennock and Whittle 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 Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
was first reported by Qureshi and Elson in the ''Journal of Medicinal Chemistry''. During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated. The current commercial sources of tocotrienol are rice and
palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae **List of Arecaceae genera * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...
. Other natural tocotrienol sources include rice bran oil, coconut oil, cocoa butter, barley, and wheat germ. 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 Annatto ( or ) is an orange-red condiment and food coloring derived from the seeds of the achiote tree (''Bixa orellana''), native to tropical America. It is often used to impart a yellow or orange color to foods, but sometimes also for its flav ...
, used in nutritional supplements,
functional food A functional food is a food claimed to have an additional (often one related to health promotion or disease prevention) by adding new ingredients or more of existing ingredients. The term may also apply to traits purposely bred into existing edib ...
s, and anti-aging cosmetics, are available in the market at 20%, 35%, 50%, and 70% total vitamin E content.


Etymology

Tocotrienols are named by analogy to tocopherols (from Greek words meaning ''to bear a pregnancy'' (see
tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...
); 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 the three
double bonds In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
to their
side chain In organic chemistry and biochemistry, a side chain is a chemical group that is attached to a core part of the molecule called the "main chain" or backbone. The side chain is a hydrocarbon branching element of a molecule that is attached to a ...
s.


Comparison to tocopherols

Tocotrienols have only a single
chiral center In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups ...
—the 2' carbon on the chromanol ring, which is where the isoprenoid tail is attached. Unlike the tocopherols, which have additional chiral centers along their
saturated Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds ** Saturated and unsaturated compounds **Degree of unsaturation ** Saturated fat or fatty ac ...
tail chain, the unsaturated chain of the tocotrienols instead have double-bonds at this sites. Tocotrienols extracted from plants are always
dextrorotatory Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
stereoisomers, signified as d-tocotrienols. In theory, (
levorotatory Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
; l-tocotrienol) forms of tocotrienols could exist as well, which would have a 2S rather than 2R configuration at the molecules' single chiral center, but unlike synthetic, dl-alpha-tocopherol, the marketed tocotrienol dietary supplements are all d-tocotrienol extracts from palm or annatto oils. Tocotrienol studies confirm anti-oxidation, anti-inflammatory potentials and suggest anti-cancer effects better than the common forms of tocopherol due to their chemical structure. Scientists have suggested tocotrienols are better antioxidants than tocopherols. It has been proposed that the unsaturated side-chain in tocotrienols causes them to penetrate tissues with saturated fatty layers more efficiently than tocopherol. Lipid ORAC values are highest for δ-tocotrienol. However that study also says: "Regarding α-tocopherol equivalent antioxidant capacity, no significant differences in the antioxidant activity of all vitamin E isoforms were found."


Metabolism and bioavailability

The
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
and thus the
bioavailability In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. Ho ...
of tocotrienols are not well understood and simply increasing the intake of tocotrienols might not increase tocotrienol levels in the body.


α-Tocopherol interference

Various studies have shown that alpha-tocopherol interferes with tocotrienol benefits. High levels of α-tocopherol increase cholesterol production. α-Tocopherol interference with tocotrienol absorption was described previously by scientists, who showed that α-tococopherol interfered with absorption of α-tocotrienol, but not γ-tocotrienol. Finally, α-tocopherol was shown to interfere with tocotrienols by increasing catabolism.


Sources

In nature, tocotrienols are present in many plants and fruits. The palm fruit (''
Elaeis guineensis ''Elaeis guineensis'' is a species of palm commonly just called oil palm but also sometimes African oil palm or macaw-fat. It is the principal source of palm oil. It is native to west and southwest Africa, specifically the area between Angola an ...
'') is particularly high in tocotrienols, primarily gamma-tocotrienol, alpha-tocotrienol and delta-tocotrienol. Other cultivated plants high in tocotrienols includes rice, wheat, barley, rye and oat.Tocopherol and tocotrienol contents of raw and processed fruits and vegetables in the United States diet
p.199


Research


Radiation countermeasures

Following exposure to
gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...
, hematopoietic stem cells (HSCs) in the bone marrow, which are important for producing blood cells, rapidly undergo
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
(cell death). There are no known treatments for this acute effect of radiation. Two studies conducted by the U.S. Armed Forces Radiobiology Research Institute (AFRRI) found that treatment with γ-tocotrienol or δ-tocotrienol enhanced survival of hematopoietic stem cells, which are essential for renewing the body's supply of blood cells. Based on these successful results of studies in mice, γ-tocotrienol is being studied for its safety and efficacy as a radioprotective measure in nonhuman primates. No human trials have yet been completed.


References


External links


Vitamin E factsheet
— Office of Dietary Supplements, National Institutes of Health * * {{vitamin Vitamers Vitamin E