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Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitamin E, can cause nerve problems. Vitamin E is a fat-soluble antioxidant protecting cell membranes from reactive oxygen species. Worldwide, government organizations recommend adults consume in the range of 7 to 15 mg per day. As of 2016, consumption was below recommendations according to a worldwide summary of more than one hundred studies that reported a median dietary intake of 6.2 mg per day for alpha-tocopherol.
CAS NUMBER: 10191-41-0
SYNONYM:
alpha-Tocopherol; VITAMIN E; D-alpha-Tocopherol; Trimethyltocol; alpha-Vitamin E; Aquasol E; Phytogermine; Eprolin; a-Tocopherol; dl-a-Tocopherol; Denamone; Viteolin; Esorb; Tocopherol alpha, Vitamin Ea; Mixed tocopherols; D-alpha tocopherol; Syntopherol; Tocopherol (R,S); Evitaminum; Profecundin; Waynecomycin; Almefrol; Emipherol; Epsilan; Etamican; Tokopharm; Vascuals; Vitayonon; Etavit; Ilitia; Evion; Vitaplex E; Eprolin S; Spavit E; ido-E; Endo E; Vita E; Lan-E; Med-E; Antisterility vitamin; Vi-E; Viprimol; Vitamin E alpha; Viterra E; E Prolin
Vitamin E (D-alpha-tocopherol; DL-alpha-tocopherol; tocopherol) is considered the most important oil-soluble anti-oxidant and freeradical scavenger. Studies indicate that vitamin e performs these functions when topically applied. Vitamin e is also a photoprotectant, and vitamin e helps protect the cellular membrane from free-radical damage. In addition, vitamin e serves a preservative function given vitamin e ability to protect against oxidation.This benefits not only the skin, but also the product in terms of longevity. As a moisturizer, vitamin e is well-absorbed through the skin, demonstrating a strong affinity with small blood vessels and an ability to enhance blood circulation in the skin.
Vitamin e is also thought to improve the skin’s water-binding ability. In addition, vitamin e emulsions have been found to reduce transepidermal water loss, thereby improving the appearance of rough, dry, and damaged skin. This vitamin is also believed to help maintain the connective tissue. There is evidence that vitamin e is effective in preventing irritation owing to sun exposure: studies show that vitamin e topically applied prior to uV irradiation is protective against epidermal cell damage caused by inflammation.
This indicates possible anti-inflammatory properties. Lipid peroxidation in tissues may be one cause of skin aging. Vitamin e, however, appears to counteract decreased functioning of the sebaceous glands and to reduce excessive skin pigmentation, which is found to increase almost linearly with age. Vitamin e is available also as a tocopherol-polypeptide complex that delivers the vitamin in a waterdispersable form. In this way, when incorporated into cosmetic formulations, vitamin e does not need other compounds to assist in vitamin e solubilization. Vitamin e is useful in anti-aging creams and lotions, and in uV protective products, tocopherol is a naturally occurring vitamin e found in a variety of cereal germ oils including wheat germ oil. Vitamin e can also be produced synthetically.
IUPAC NAME: (2R)-2,5,7,8-tetramethyl-2-[(4R,8R)-4,8,12-trimethyltridecyl]-3,4-dihydro-2H-1-benzopyran-6-ol
TRADE NAME: 5,7,8-Trimethyltocol; DL-alpha-Tocopherol; Vitamin E; Vitamin E DL alpha tocopherol.
OTHER NAME: 25094-97-7; 364-50-1; 364-50-1; 4072-33-7; 4072-33-7; 16826-11-2; 16826-11-2; 181591-70-8; 181591-70-8; 25094-97-7
Major sources of vitamin E in diet (‘RRR-alpha-tocopherol’, also referred to as ’natural‘ or ‘d-alpha-tocopherol’) include vegetable oils (olive, sunflower, and safflower oils), nuts, whole grains, and green leafy vegetables. All eight forms of vitamin E (alpha-, beta-, gamma-, and delta-tocopherols and tocotrienols) occur naturally in foods but in varying amounts.Many scientists believe vitamin e is difficult for an individual to consume more than 15 mg/day alpha-tocopherol from food (RRR-alpha-tocopherol) alone without increasing fat intake above recommended levels.Vitamin E supplements generally contain 100 IU to 1,000 IU alpha-tocopherol. While supplements made from entirely natural sources contain only RRR-alpha-tocopherol, synthetic alpha-tocopherol (‘all-rac-alpha-tocopherol’ or ‘dl-alpha-tocopherol’) is often found in fortified foods and nutritional supplements. All-rac-alpha-tocopherol is a mixture of eight forms (‘isomers’) of alpha-tocopherol; some of these isomers are less available to the body than the natural alpha-tocopherol. Therefore, all-rac-alpha-tocopherol is defined to be slightly less biologically active than RRR-alpha-tocopherol; a revision of this definition is currently being discussed.
Alpha-tocopherol supplements are available in two ester forms, ‘alpha-tocopheryl succinate’ and ‘alpha-tocopheryl acetate’, which are more resistant to oxidation during storage than unesterified tocopherols. The bioavailability of alpha-tocopherol from alpha-tocopheryl succinate and alpha-tocopheryl acetate is equivalent to that of free alpha-tocopherol.There is currently no published evidence that supplements containing ‘alpha-tocopheryl phosphates’ are more efficiently absorbed or have greater bioavailability in humans than supplements containing alpha-tocopherol.
Vitamin E consists of eight naturally occurring lipophilic compounds consisting of four tocopherols (α-, β-, γ-, and δ-) and four tocotrienols (α-, β-, γ-, and δ-) that differ in their side chain saturation and degree of methylation of their chromanol heads. Vitamin E is most widely recognized for vitamin e antioxidant function that terminates the self-perpetuating cycle of lipid peroxidation. Although α-tocopherol and γ-tocopherol are the most abundant vitamin E forms in the diet and in vivo, dietary requirements of vitamin E are currently limited to α-tocopherol because this is the only form that reverses vitamin E deficiency and no other vitamin E forms are interconverted to α-tocopherol in humans. This article will therefore discuss the mechanisms regulating vitamin E bioavailability and metabolism as well as vitamin e antioxidant function and dietary essentiality.
There are several naturally occurring forms of vitamin E in plants. Vitamin E is passively absorbed in conjunction with other lipid-soluble vitamins by the intestinal tract, and subsequently packaged into chylomicrons. Vitamin E is the first and selenium the second line of defense against peroxidation of lipids contained in cell membranes. Tocopherols act as antioxidants by breaking free-radical chain reactions. Vitamin C helps to regenerate the active form of vitamin E. Vitamin E deficiency can result in erythrocyte fragility, muscular degeneration, steatitis, retinopathy, and reproductive failure. Vitamin E excess appears to be non-toxic.
Vitamin E is the most potent, fat-soluble antioxidant in human plasma. Although vitamin E was first discovered in 1922, vitamin e metabolic function remains an enigma. There are eight different molecular forms with vitamin E antioxidant activity, yet the body preferentially retains the α-form of tocopherol. This preference for α-tocopherol has led the Food and Nutrition Board in vitamin e 2000 dietary reference intakes (DRIs) for vitamin E to recommend that only α-tocopherol, not the other forms, meets human requirements for vitamin E. Moreover, only α-tocopherol is recognized by the hepatic α-tocopherol transfer protein (α-TTP). This protein regulates plasma α-tocopherol concentrations. Abnormalities in the α-TTP gene lead to vitamin E deficiency in humans. Vitamin E metabolism is important for increasing excretion of excess α-tocopherol, as well as non-α-tocopherol forms of vitamin E.
The food constituent most closely identified with vitamin e properties is RRR-alpha-tocopherol with methyl groups in the side chain at positions 5, 7, and 8. The side chain of RRR-beta-tocopherol is methylated at positions 5 and 8, in RRR-gamma-tocopherol at positions 7 and 8. RRR-delta-tocopherol has only one methyl group in the side chain at position 8. The members of the analogous series of tocotrienols contain three double bonds in the side chain. All four members of the tocopherol series and the four members of the tocotrienol series are naturally present, though in varying amounts, in a wide range of foods.Synthetic production of vitamin e usually yields about equal amounts of the eight possible isomers, RRR, RSS, RRS, RSR, SRR, SRS, SSR, and SSS. The first three in this list of isomers are often called the 2R isomers because they are R-isomeric at position 2. The metabolic fate of the various isoforms differs and needs to be determined in every case.
The biological potency of vitamin e doses is often expressed as USP vitamin E units or International Units (IU). One such unit corresponds to 1.0 mg racemic (synthetic, all-rac) alpha-tocopheryl acetate (this is the original reference standard), or 1.1 mg all-rac alpha-tocopherol, or 1.36 mg RRR-alpha-tocopheryl acetate, or 1.49 mg RRR-alpha-tocopherol, or 0.89 mg all-rac-alpha-tocopheryl succinate, or 1.21 mg RRR-alpha-tocopheryl succinate. In the following vitamin e content will be expressed as alpha-tocopherol equivalents (ATE), which is the amount of RRR alpha-tocopherol that is expected to have the same potency as all vitamin e forms in a food combined.
There are only a few good sources that provide one serving with at least 2.5 mg (one-sixth of the recommended intake). Since gamma-tocopherol may differ in vitamin e action profile from gamma-tocopherol, the exact composition (which is often not reliably known) may be as important as the ATE figure. Vegetable oils with high to moderate content include wheat germ oil (1.9 mg ATE/g, more than half as alpha-tocopherol) and sunflower oil (0.5 mg/g, most as alpha-tocopherol). Most other commonly consumed oils have a much lower content, such as corn and soybean oil (0.2 mg/g, most as gamma-tocopherol), canola oil (0.2 mg/g, most as alpha-tocopherol), or olive oil (0.1 mg/g, most as alpha-tocopherol). Sunflower seeds (0.5 mg/g) are also a good source. Walnuts (0.03 mg ATE/g) contain nearly equal amounts of alpha-tocopherol, gamma-tocopherol, and delta-tocopherol.
American men have a daily vitamin e intake of about 8 mg, women get close to 6 mg (Phillips et al., 2000). American food consumption data indicate that only about 10% of men and virtually none of the women reach the recommended intake level (15 mg/day) with food alone (Food and Nutrition Board, Institute of Medicine, 2000: Appendix D).Vitamin E is a fat-soluble antioxidant that supports optimal glutathione levels. Research data on vitamin E in the setting of chronic hepatitis are mixed. Two small studies of CHC patients found vitamin E supplementation led to reduced ALT levels in roughly one-half of study participants. However, another study in which CHC patients took supplemental vitamin E, selenium, and vitamin C daily found no effect on ALT, HCV viral load, or oxidative markers after 6 months of treatment. Some studies have indicated that vitamin E may have a role in interrupting the fibrotic process.
Naturally occurring vitamin E is not one compound, but a family of 8 different isomers. Tocopherol or tocotrienol form the backbone structures and consist of a chromanol head and a phytyl or farnesyl tail, respectively. To either tocopherol or tocotrienol, there are 4 possible variations of methylation of the chromanol head, designated alpha, beta, delta, and gamma. All the members of the family of naturally occurring vitamin E isomers are well-established antioxidant compounds. They all derive their redox (antioxidant) capacity through the hydroxyl group at the C6 position of the chromanol ring. Analogues of vitamin E can be formed with a substitution at the site of the C6 hydroxyl group. Such analogues are popularly used in nutritional supplements due to their greater stability. However, regardless of the bond or group used for the substitution, loss of the hydroxyl moiety means there is no longer any redox (antioxidant) capacity.
The most common vitamin E analogues are made through substitution at C6 with an ester linkage of either acetate or succinate to form what is commonly known as “dry vitamin E.” These analogues of vitamin E are unique, semi-synthetic compounds with their own biological activities. One such analogue, dl-alpha tocopheryl succinate (a-TOS) has undergone extensive research as an anticancer compound both alone and with chemotherapy and/or radiation; studies suggest vitamin e has great promise as an anticancer agent.
Vitamin E” is a generic term that can represent any of the naturally occurring vitamers (tocopherols/ tocotrienols) or any of the semi-synthetic analogues of these vitamers. Further, medical literature does not always clearly distinguish between redox-sensitive tocopherols/tocotrienols and the redox-silent analogues such as aTOS. The lack of distinction between the various molecular forms may be a confounder when comparing various data sets. Further, extrapolation of information between the divergent compounds may lead to misinformation, as the redox-silent analogues are distinctly different from their redox-sensitive isomers, both in structure and biological activity. Even a single analogue such as aTOS can be variably referred to in medical literature as “alpha-tocopheryl succinate,” “vitamin E succinate (VES),” “vitamin E,” “alpha-tocopherol,” or simply “tocopherol.”
Alpha-tocopherol (α-Toc) is a member of the vitamin E family and is lipid soluble. Vitamin e biosynthesis is by the reaction of isopentyl diphosphate and homogentisic acid in plastid membranes. The putative biochemical activities of tocopherols are linked with the formation of tocopherol quinone species, which subsequently undergo degradation and recycling within cells/tissues. α-Toc plays a key role in a variety of plant metabolic processes throughout the ontogeny of plants. Vitamin e can maintain the integrity and fluidity of photosynthesizing membranes. Vitamin e can also neutralize lipid peroxy radicals, consequently blocking lipid peroxidation by quenching oxidative cations.
Vitamin e preserves membrane integrity by retaining membranous structural components under environmental constraints such as water deficiency, high salt content, toxic metals, high/low temperatures, and radiations. α-Toc also induces cellular signalling pathways within biological membranes. Vitamin e biosynthesis varies during growth and developmental stages as well as under different environmental conditions. The current review primarily focuses on how α-Toc can regulate various metabolic processes involved in promoting plant growth and development under stress and non-stress and how vitamin e can effectively counteract the stress-induced high accumulation of reactive oxygen species (ROS). Currently, exogenous application of α-Toc has been widely reported as a potential means of promoting resistance in plants to a variety of stressful environments.
Consumers have long trusted and understood the importance of vitamin e the name given to a group of fat-soluble compounds offering proven anti-oxidant properties and often wish to supplement what they consume in naturally occurring sources in order to meet their needs. With more consumers than ever looking for plant-based solutions, our naturally sourced vitamin e and mixed tocopherols deliver a clean label that can support your desired front-of-package claims.
Along with other chemicals tocopherols are also include in the list of such chemicals that found effective for induction of stress tolerance in plants through vitamin e internal accumulation or through vitamin e exogenous application. Vitamin e is a family of lipid soluble compounds, which have great role in different cellular activities. These include the tocopherol and tocotrienols. Among them α-Toc is consider the most important one. The important tocochromanol that are present in leaves are tocopherol. Tocopherol (vitamin E) is a lipid-soluble antioxidant synthesized only by all plants and is an essential part of human nutrition and health. Vitamin e levels are tissue specific and mainly fluctuate under stressful conditions, where vştamin e actively takes part in different metabolic activities. Mainly they are present in the chloroplast of leaf as a defensive compound.
Vitamin e plays a major role in ROS scavenging, membrane stabilization while interacting with the polyunsaturated acyl groups of lipids and protects polyunsaturated fatty acids from lipid peroxidation and regulates varying signal transduction pathways. Tocopherols perform like a terminator in chain reaction for polyunsaturated fatty acids removal by scavenging and quenching of oxygen. Where they show significant defensive responses in different stresses especially in abiotic ones (salt, drought, & light etc.) and provide protection against oxidation damages to defend plant chloroplast membrane and to maintain the integrity of chloroplast.
Vitamin e has been found to play various metabolic roles in plants through endogenous synthesis or through the exogenous application. Vitamin e was found that leaf transpiration and respiration rate affected significantly with the level of cellular tocopherol that effectively improved the tolerance to various stresses. In sunflower enhanced photosynthesis was found after tocopherol application that was associated with decreased ABA content. Similarly in sunflower and faba bean α-Toc improved the leaf chlorophyll content.
Vitamin e is used for treating vitamin e deficiency, which is rare, but can occur in people with certain genetic disorders and in very low-weight premature infants.Some people use vitamin e for treating and preventing diseases of the heart and blood vessels including hardening of the arteries, heart attack, chest pain, stroke, irregular heart beat (atrial fibrillation), heart failure, leg pain due to blocked arteries, and high blood pressure.
Vitamin e is also used for treating diabetes and vitamin E complications, liver disease, kidney disease, Peyronie's disease (painful erection in men), and enlarged prostate (BPH). Vitamin e is used for preventing cancer, particularly lung and oral cancer in smokers; colorectal cancer and polyps; and gastric, skin, bladder, breast, head and neck, prostate, and pancreatic cancers. Vitamin e is also used decrease side effects of chemotherapy.
Some people use vitamin e for diseases of the brain and nervous system including Alzheimer's disease and other dementias, Parkinson's disease, night cramps, restless leg syndrome, and for epilepsy, along with other medications. Vitamin e is also used for Huntington's chorea, and other disorders involving nerves and muscles. Women use vitamin e for preventing complications in late pregnancy due to high blood pressure (pre-eclampsia), for preventing preterm labor, premenstrual syndrome (PMS), benign breast disease, weak bones (osteoporosis), painful periods, menopausal syndrome, hot flashes associated with breast cancer, and breast cysts.
Sometimes vitamin e is used to lessen the harmful effects of medical treatments such as dialysis and radiation. Vitamin e is also used to reduce unwanted side effects of drugs such as hair loss in people taking doxorubicin and lung damage in people taking amiodarone. Vitamin e is sometimes used for improving physical endurance, increasing energy, reducing muscle damage after exercise, and improving muscle strength.
Vitamin e is also used for cataracts, age-related vision loss (age-related macular degeneration), asthma, respiratory infections, skin disorders, aging skin, sunburns, cystic fibrosis, infertility, impotence, chronic fatigue syndrome (CFS), neurodegenerative disease called Lou Gherig's disease (ALS), leg cramps, peptic ulcers, H pylori, swelling in the middle layer of the eye (uveitis), mouth sores (oral mucosal lesions), movement and coordination disorder called dyspraxia, kidney problems in children (glomerulosclerosis), movement disorder (ataxia) associated with vitamin e deficiency (AVED), rheumatoid arthritis, for certain inherited diseases and to prevent allergies. Finally, vitamin e is used for preventing death. Some people apply vitamin E to their skin to keep vitamin e from aging, sunburn, scarring, lice, stretch marks, and to protect against the skin effects of chemicals used for cancer therapy (chemotherapy).
Some people apply vitamin e to their skin to keep vitamin e from aging, sunburn, scarring, lice, stretch marks, and to protect against the skin effects of chemicals used for cancer therapy (chemotherapy). The American Heart Association recommends obtaining antioxidants, including vitamin e, by eating a well-balanced diet high in fruits, vegetables, and whole grains rather than from supplements until more is known about the risks and benefits of taking supplements. Movement disorder (ataxia) associated with vitamin e deficiency. The genetic movement disorder called ataxia causes severe vitamin e deficiency. Vitamin e supplements are used as part of the treatment for ataxia.
Vitamin e deficiency. Taking vitamin e by mouth is effective for preventing and treating vitamin e deficiency. Alzheimer's disease. Some early research suggests that dietary intake of vitamin e is linked to a lower chance of developing Alzheimer's disease. But not all research agrees. Taking vitamin e supplements doesn't seem to prevent Alzheimer's disease from developing. In people who already have Alzheimer's disease, taking vitamin e along with some anti-Alzheimer's medicines might slow down the worsening of memory loss. Vitamin e might also delay the loss of independence and the need for caregiver assistance in people with mild-to-moderate Alzheimer's disease.
Anemia. Some research shows that that taking vitamin e improves the response to the drug erythropoietin, which affects red blood cell production, in adults and children on hemodialysis. Blood disorder (beta-thalassemia). Taking vitamin e by mouth seems to benefit children with the blood disorder called beta-thalessemia and vitamin e deficiency. Leakage of chemotherapy drug into surrounding tissue. Applying vitamin e to the skin together with dimethylsulfoxide (DMSO) seems to be effective for treating leakage of chemotherapy into surrounding tissues. Chemotherapy-related nerve damage. Taking vitamin e (alpha-tocopherol) before and after treatment with cisplatin chemotherapy might reduce the risk of nerve damage. Painful menstruation (dysmenorrhea). Taking vitamin e for 2 days before and for 3 days after bleeding begins seems to decrease pain severity and duration, and reduce menstrual blood loss. Movement and coordination disorder called dyspraxia. Taking vitamin e by mouth together with evening primrose oil, thyme oil, and fish oils seems to improve movement disorders in children with dyspraxia.
Kidney problems in children (glomerulosclerosis). There is some evidence that taking vitamin e by mouth might improve kidney function in children with glomerulosclerosis. An inherited disorder called G6PD deficiency. Some research shows that taking vitamin e by mouth, alone or together with selenium, might benefit people with an inherited disorder called G6PD deficiency. Healing a type of skin sore called granuloma annulare. Applying vitamin e to the skin seems to clear up skin sores called granuloma annulare. Huntington's disease. Natural vitamin e (RRR-alpha-tocopherol) can improve symptoms in people with early Huntington's disease. However, vitamin e does not seem to help people with more advanced disease. Male infertility. Taking vitamin e by mouth improves pregnancy rates for men with fertility problems.
Taking high doses of vitamin e together with vitamin C does not seem to provide the same benefits. Bleeding within the skull. Taking vitamin e by mouth seems to be effective for treating bleeding in the skull in premature infants. Bleeding within the ventricular system of the brain. Taking vitamin e by mouth seems to be effective for treating bleeding within the ventricular system of the brain in premature infants. Liver disease (nonalcoholic steatohepatitis, NASH). Taking vitamin e daily seems to improve inflammation and liver markers of this form of liver disease in adults and children.Nitrate tolerance. There is some evidence that taking vitamin e daily can help prevent nitrate tolerance. Parkinson's disease.
Early evidence suggests that vitamin e intake in the diet might be linked with a decreased risk of Parkinson's disease. However, taking all-rac-alpha-tocopherol (synthetic vitamin e) does not seem to have any benefit for people with Parkinson's disease. Laser eye surgery (photoreactive keratectomy). Taking high doses of vitamin A along with vitamin e (alpha-tocopheryl nicotinate) daily seems to improve healing and vision in people undergoing laser eye surgery. Premenstrual syndrome (PMS). Taking vitamin e by mouth seems to reduce anxiety, craving, and depression in some women with PMS.
Physical performance. Research suggests that increasing vitamin e intake in the diet is linked with improved physical performance and muscle strength in older people. Fibrosis caused by radiation. Taking vitamin e by mouth with the drug pentoxifylline seems to treat fibrosis caused by radiation. However, taking vitamin e alone does not seem to be effective. An eye disease in newborns called retinopathy of prematurity. Taking vitamin e by mouth seems to be effective for treating an eye disease cause retinopathy of prematurity in newborns. Rheumatoid arthritis (RA).
Vitamin e taken along with standard treatment is better than standard treatment alone for reducing pain in people with RA. However, this combination does not reduce swelling. Sunburn. Taking high doses of vitamin e (RRR-alpha-tocopherol) by mouth together with vitamin C protects against skin inflammation after exposure to UV radiation. However, vitamin e alone does not provide the same benefit. Applying vitamin e to the skin, together with vitamin C and melatonin, provides some protection when used before UV exposure. Movement disorder (tardive dyskinesia). Taking vitamin e by mouth seems to improve symptoms associated with the movement disorder called tardive dyskinesia. However, some other research suggests that vitamin e does not improve symptoms, but may prevent symptoms from worsening. Swelling in the middle layer of the eye (uveitis). Taking vitamin e with vitamin C by mouth seems to improve vision, but does not reduce swelling, in people with uveitis.
In 1922, Evans and Bishop demonstrated the existence of a hitherto unrecognized dietary factor essential for normal reproduction in the rat. Vitamin e was accepted at that time that the most striking function of vitamin e was to provide a normal gestation in a pregnant rat to prevent the resorption of the embryos which invariably occurred in Vitamin e absence. This unknown dietary factor X was found to be present in green lettuce, dried alfalfa leaves, wheat, and oats. Evans isolated the factor X from wheat germ oil, provided the chemical formula C29H50O2 and proposed the name α-tocopherol in 1936. The structural formula for α-tocopherol was provided by Fernholz in 1938.
Tocotrienols were discovered much later than tocopherol and named in the early 1960s. Olcott found that the lipid fractions of vegetable oils contained antioxidants against the oxidative deterioration of lard. Since then, Vitamin e has been unequivocally demonstrated that vitamin e acts as an essential antioxidant in vivo as well as in vitro and plays an important role in the prevention of detrimental oxidative damage of biological molecules. More recently, the non-antioxidant functions of vitamin e, including cellular signaling, gene regulation, membrane processes, and nerve functions, have also received much attention. However, many issues are still controversial and remain to be elucidated. Sound information based on solid chemical evidence is essential for understanding the role of vitamin e in vivo as well as in vitro.
In addition to tocopherols and tocotrienols, tocomonoenols and tocodienols containing a single and two double bond unsaturation, respectively, have also been found in nature. For example, a tocomonoenol with a single double bond at carbon 11′, 2,5,7,8-tetramethy1-2-(4′,8′,12′-trimethyltrideca-11′-enyl)-6-chromanol, was isolated from palm and rice bran oils. Since then, several groups have detected tocomonoenols in plants and plant foods, such as α-tocomonoenol in palm oil, pumpkin seed oil (Cucurbita pepo L.),23 and sunflower oil (Helianthus annuus), γ-tocomonoenol in pumpkin seed oil,22,23 δ-tocomonoenol in kiwi (Actinidia chinensis), and β-, γ-, and δ-tocomonoenol in the leaves of Kalanchoe daigremontiana and Phaseolus coccineus. A tocomonoenol with an unsaturation at the isoprenoid-chain terminus was also found in the tissues of salmon.
Furthermore, tocodienols with two double bonds at carbon 7′ and 11′ were identified in palm oil. Tocopherols contain three chiral carbons, one at C2 in the chromanol ring and two in the side chain at C4′ and C8′. Naturally occurring α-tocopherol contains chiral carbons in the R-conformation, 2R, 4′R, and 8′R-α-tocopherol. α-Tocotrienol has one chiral center at C2 in the chromanol ring and natural tocotrienols occur as the R-isoform. On the other hand, the chemical synthesis of α-tocopherol produces an equimolar mixture of eight different stereoisomers: RRR, SRR, RSR, RRS, RSS, SSR, SRS, and SSS. The synthetic α-tocopherol is called all-rac-α-tocopherol. An equimolar mixture of RRR-α-tocopherol and SRR-α-tocopherol is called 2-ambo-α-tocopherol. The IUPAC names of RRR-α-tocopherol and RRR-α-tocotrienol are (2R)-2,5,7,8-tetramethyl-2-[(4R,8R)-(4,8,12-trimethyltridecyl)]chroman-6-ol and (2R)-2,5,7,8-tetramethyl-2-[(3E,7E)-4,8,12-trimethyltrideca-3,7,11-trienyl]-3,4-dihydrochromen-6-ol, respectively.
Ester forms of tocopherol and tocotrienols, including acetate, nicotinate, succinate, and phosphate, have been prepared and their action and potential applications have been studied. Vitamin e is easily oxidized when subjected to heat, light, and alkaline conditions, but esters are less susceptible to oxidation and therefore more appropriate for food, cosmetic, and pharmaceutical applications compared to the free form. Polyethylene glycol conjugates of tocopherols and tocotrienols have the ability to form miscible micelles in water due to amphiphilic properties and enhance bioavailability in animals and humans via improving their water solubility and absorption. Vitamin e was reported that RRR-α-tocopheryl polyethylene glycol 1000 succinate acted as a safe and effective form of vitamin e for reversing or preventing vitamin e deficiency during chronic childhood cholestasis. The tocopherols are viscous oils at room temperature, insoluble in water but soluble in ethanol and aprotic solvents.
Vitamin e is a slightly yellow to amber, nearly odorless, clear, viscous oil, which darkens on exposure to air or light by oxidation. The physicochemical properties of α-tocopherol, the most abundant and active form of vitamin e in humans, are summarized in Table 1.1.30 The melting point of RRR-α-tocopherol is 3 °C. The optical rotations of tocopherols are very small and depend on the nature of the solvent. The ultraviolet absorption spectra of tocopherols and tocotrienols in ethanol show an absorption maximum at 292–298 nm, while the infrared spectra show OH (2.8 ± 3.0 µm) and CH (3.4 ± 3.5 µm) stretching and a characteristic band at 8.6 µm. α-Tocopherol is fluorescent with an emission maximum about 325 nm in a hydrophobic solution.
The bond dissociation energy of α-tocopherol's O–H bond is 77.1 kcal mol−1.31 The pKa values for α-, β-, γ-, and δ-tocopherol in a micellar solution were reported as 13.1, 12.8, 12.7, and 12.6 respectively. The contents and composition of tocopherols and tocotrienols in natural oils vary markedly between the plant species and even within the same species. Tocopherols are widely distributed in higher plants, whereas tocotrienols occur only in some non-photosynthetic tissues. Some examples of the contents in natural edible oils adopted from several reports36–41 are shown in Table 1.2. α-Tocopherol is the major tocopherol in palm, olive, and sunflower oils, whereas the contents of γ-tocopherol in some edible oils such as corn, rapeseed, and soybean oils are higher than α-tocopherol.
The major sources of tocotrienols are palm, rice, and annatto, the ratio of tocopherol–tocotrienol in each being 25 : 75, 50 : 50, and 0.1 : 99.9, respectively.42 Palm oil contains considerable amounts of α-, γ-, and δ-tocotrienols. γ-Tocotrienol is the major vitamin e isoform in the oil extracted from rice bran39,43 while β-tocopherol is one of the major isoforms found in wheat germ oil.36,37 Interestingly, the lipid fraction of annatto (Bixa orellana L.) seeds contained only tocotrienols, mainly δ-tocotrienol, but no tocopherols.
