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Tocotrienol

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Not to be confused with the more common class of molecules that are also forms of vitamin E, the tocopherols.
General chemical structure of tocotrienols. alpha(α)-Tocotrienol: R1 = Me, R2 = Me, R3 = Me; beta(β)-Tocotrienol: R1 = Me, R2 = H, R3= Me; gamma(γ)-Tocotrienol: R1 = H, R2 = Me, R3= Me; delta(δ)-Tocotrienol: R1 = H, R2 = H, R3= Me

The vitamin E family comprises four tocotrienols (alpha, beta, gamma, delta) and four tocopherols (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 bonds versus saturated side chains for tocopherols (see Figure).[1][2]

Tocotrienols are compounds naturally occurring in some foods sources, the richest being palm oil, but to a lesser extent rice bran oil, barley, oats, and certain seeds, nuts and grains, and the oils derived from them.[3][4]

Chemically, different analogues of vitamin E all show some activity as a chemical antioxidant,[5] but do not all have the same vitamin E equivalence. Tocotrienols demonstrate activity depending on the type of antioxidant performance being measured.[6] All tocotrienols have some physical antioxidant activity due to an ability to donate a hydrogen atom (a proton plus electron) from the hydroxyl group on the chromanol ring, to free radical and reactive oxygen species. Historically studies of tocotrienols account for less than 1% of all research into vitamin E.[7] Tocotrienols are generally well tolerated and without significant side effects.

Medical applications

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The Food and Nutrition Board of the Institute of Medicine of the United States National Academy of Sciences does not define a Recommended Dietary Allowance or Adequate Intake for tocotrienols.[8]

Brain

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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.[9]

Disease biomarkers

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Reviews of human research linked tocotrienol threatment to improved biomarkers for inflammation and cardiovascular disease, although those did not report any information on clinically significant diease outcomes.[10][11] Biomarkers for other diseases were not affected by tocotrienol supplementation.[12]

History

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The discovery of tocotrienols was first reported by Pennock and Whittle in 1964, describing the isolation of tocotrienols from rubber.[13] The biological significance of tocotrienols was clearly delineated in the early 1980s, when its ability to lower cholesterol was first reported by Asaf Qureshi and Elson in the Journal of Medicinal Chemistry.[14] During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated.[15] The current commercial sources of tocotrienol are rice bran oil and palm oil.[4] Other natural tocotrienol sources include barley and oats.[4] Tocotrienols are safe and human studies show no adverse effects with consumption of 240 mg/day for 48 months.[16] Tocotrienol rich fractions from palm oil are used in nutritional supplements, functional foods, and topicallu applied anti-aging cosmetics.[citation needed]

Etymology

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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 the three double bonds to their side chains.

Comparison to tocopherols

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Tocotrienols have only a single chiral center—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 tail chain, the unsaturated chain of the tocotrienols instead have double-bonds at this sites. Tocotrienols extracted from plants are always dextrorotatory stereoisomers, signified as d-tocotrienols. In theory, (levorotatory; 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.[citation needed]

Research suggests tocotrienols are better antioxidants than tocopherols.[17][18][19][20] It has been proposed that the unsaturated side-chain in tocotrienols causes them to penetrate tissues with saturated fatty layers more efficiently than tocopherol.[21] 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."[22]

Metabolism and bioavailability

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Absorption and distribution

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As dietary supplements, tocotrienols are primarily administered orally and, due to their lipophilic nature, their absorption is significantly enhanced when taken with a fat-rich diet. These compounds are mainly absorbed in the small intestine, with absorption depending on adequate pancreatic function, bile secretion, and micelle formation in the intestines. Upon administration, tocotrienols are distributed throughout the body, with higher concentrations observed in plasma and adipose tissues.[23]

Bioavailability factors

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The short half-lives of tocotrienols are attributed to their low binding affinity for α-TTP, which maintains plasma levels of tocopherols. Specifically, α-tocopherol has a significantly higher binding affinity for α-TTP compared to tocotrienols. Relative to α-tocopherol's affinity, α-tocotrienol has about 9%, δ-tocotrienol 12%, and ɤ-tocotrienol 2% affinity for α-TTP. Consequently, δ-tocotrienol remains in plasma for a longer duration, offering greater bioavailability and slower biotransformation compared to other isomers. Human studies have indicated that δ-tocotrienol has a bioavailability of 28%, while ɤ- and α- isomers exhibit 9%.[23]

Metabolism and excretion

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Tocotrienols are primarily metabolized in the liver, undergoing ω-hydroxylation by the enzymes CYP3A4 and CYP4F2, followed by β-oxidation. The final metabolites, carboxyethyl-hydroxychromanols (CEHC) and carboxymethylbutyl hydroxychroman (CMBHC), are readily excreted in urine.[23]

Sources

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In nature, tocotrienols are present in many plants and fruits. The oil palm fruit (Elaeis guineensis) 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.[24]

Further reading

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  • Tan B, Watson RR, Preedy VR, eds. (2013). Tocotrienols: Vitamin E Beyond Tocopherols (2nd ed.). Boca Raton: CRC Press. ISBN 9781439884416.

References

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  1. ^ Kamal-Eldin A, Appelqvist LA (July 1996). "The chemistry and antioxidant properties of tocopherols and tocotrienols". Lipids. 31 (7): 671–701. doi:10.1007/BF02522884. PMID 8827691. S2CID 4052785.
  2. ^ Clarke MW, Burnett JR, Croft KD (2008). "Vitamin E in human health and disease". Critical Reviews in Clinical Laboratory Sciences. 45 (5): 417–50. doi:10.1080/10408360802118625. PMID 18712629. S2CID 85991655.
  3. ^ Tan B, Watson RR, Preedy VR, eds. (2013). Tocotrienols: Vitamin E Beyond Tocopherols (2nd ed.). Boca Raton: CRC Press. ISBN 9781439884416.
  4. ^ a b c Babura SR, Abdullah SN, Khaza Ai H (2017). "Advances in Genetic Improvement for Tocotrienol Production: A Review". J Nutr Sci Vitaminol (Tokyo). 63 (4): 215–221. doi:10.3177/jnsv.63.215. PMID 28978868.
  5. ^ Cerecetto H, López GV (March 2007). "Antioxidants derived from vitamin E: an overview". Mini Reviews in Medicinal Chemistry. 7 (3): 315–38. doi:10.2174/138955707780059871. PMID 17346221.
  6. ^ Fu JY, Che HL, Tan DM, Teng KT (January 2014). "Bioavailability of tocotrienols: evidence in human studies". Nutrition & Metabolism. 11 (1): 5. doi:10.1186/1743-7075-11-5. PMC 3895660. PMID 24410975.
  7. ^ Sen CK, Khanna S, Roy S (2007). "Tocotrienols in health and disease: the other half of the natural vitamin E family". Molecular Aspects of Medicine. 28 (5–6): 692–728. doi:10.1016/j.mam.2007.03.001. PMC 2435257. PMID 17507086.
  8. ^ Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals (Report). Food and Nutrition Board, Institute of Medicine, National Academies. 2004. Archived from the original on 2010-05-24. Retrieved 2009-06-09 – via www.iom.edu.
  9. ^ Georgousopoulou EN, Panagiotakos DB, Mellor DD, Naumovski N (January 2017). "Tocotrienols, health and ageing: A systematic review" (PDF). Maturitas. 95: 55–60. doi:10.1016/j.maturitas.2016.11.003. PMID 27889054.
  10. ^ Khor BH, Tiong HC, Tan SC, Wong SK, Chin KY, Karupaiah T, et al. (2021). "Effects of tocotrienols supplementation on markers of inflammation and oxidative stress: A systematic review and meta-analysis of randomized controlled trials". PLOS ONE. 16 (7): e0255205. doi:10.1371/journal.pone.0255205. PMC 8301652. PMID 34297765.
  11. ^ Rafique S, Khan DA, Farhat K, Khan MA, Noor M, Sharif M (June 2024). "Comparative efficacy of tocotrienol and tocopherol (vitamin E) on atherosclerotic cardiovascular diseases in humans". J Pak Med Assoc. 74 (6): 1124–29. doi:10.47391/JPMA.9227. PMID 38948984.
  12. ^ Li F, Xu B, Soltanieh S, Zanghelini F, Abu-Zaid A, Sun J (2022). "The effects of tocotrienols intake on obesity, blood pressure, inflammation, liver and glucose biomarkers: a meta-analysis of randomized controlled trials". Crit Rev Food Sci Nutr. 62 (26): 7154–67. doi:10.1080/10408398.2021.1911926. PMID 33909529.
  13. ^ Dunphy PJ, Whittle KJ, Pennock JF, Morton RA (1965). "Identification and Estimation of Tocotrienols in Hevea Latex". Nature. 207 (4996): 521–522. Bibcode:1965Natur.207..521D. doi:10.1038/207521a0. S2CID 4214464.
  14. ^ Pearce BC, Parker RA, Deason ME, Qureshi AA, Wright JJ (October 1992). "Hypocholesterolemic activity of synthetic and natural tocotrienols". Journal of Medicinal Chemistry. 35 (20): 3595–606. doi:10.1021/jm00098a002. PMID 1433170.
  15. ^ Schauss AG (2008). "Tocotrienols: A Review". In Watson RR, Preedy VR (eds.). Tocotrienols: Vitamin E Beyond Tocopherols. CRC Press. p. 6. ISBN 978-1-4200-8037-7.
  16. ^ Tomeo AC, Geller M, Watkins TR, Gapor A, Bierenbaum ML (December 1995). "Antioxidant effects of tocotrienols in patients with hyperlipidemia and carotid stenosis". Lipids. 30 (12): 1179–83. doi:10.1007/BF02536621. PMID 8614310. S2CID 4038103.
  17. ^ Müller L, Theile K, Böhm V (May 2010). "In vitro antioxidant activity of tocopherols and tocotrienols and comparison of vitamin E concentration and lipophilic antioxidant capacity in human plasma". Molecular Nutrition & Food Research. 54 (5): 731–42. doi:10.1002/mnfr.200900399. PMID 20333724.
  18. ^ Yoshida Y, Niki E, Noguchi N (March 2003). "Comparative study on the action of tocopherols and tocotrienols as antioxidant: chemical and physical effects". Chemistry and Physics of Lipids. 123 (1): 63–75. doi:10.1016/S0009-3084(02)00164-0. PMID 12637165.
  19. ^ Schaffer S, Müller WE, Eckert GP (February 2005). "Tocotrienols: constitutional effects in aging and disease". The Journal of Nutrition. 135 (2): 151–4. doi:10.1093/jn/135.2.151. PMID 15671205.
  20. ^ Theriault A, Chao JT, Wang Q, Gapor A, Adeli K (July 1999). "Tocotrienol: a review of its therapeutic potential". Clinical Biochemistry. 32 (5): 309–19. doi:10.1016/S0009-9120(99)00027-2. PMID 10480444.
  21. ^ Suzuki YJ, Tsuchiya M, Wassall SR, Choo YM, Govil G, Kagan VE, et al. (October 1993). "Structural and dynamic membrane properties of alpha-tocopherol and alpha-tocotrienol: implication to the molecular mechanism of their antioxidant potency". Biochemistry. 32 (40): 10692–9. doi:10.1021/bi00091a020. PMID 8399214.
  22. ^ Müller L, Theile K, Böhm V (May 2010). "In vitro antioxidant activity of tocopherols and tocotrienols and comparison of vitamin E concentration and lipophilic antioxidant capacity in human plasma". Molecular Nutrition & Food Research. 54 (5): 731–42. doi:10.1002/mnfr.200900399. PMID 20333724.
  23. ^ a b c Sharif M, Khan DA, Farhat K, Mudassar Noor, Mohammad Asghar Khan, Saima Rafique (2023-02-15). "Pharmacokinetics and bioavailability of tocotrienols in healthy human volunteers: a systematic review". Journal of the Pakistan Medical Association. 73 (3): 603–610. doi:10.47391/JPMA.6008. ISSN 0030-9982. PMID 36932765. S2CID 257423183. Archived from the original on 2023-03-26.
  24. ^ Tocopherol and tocotrienol contents of raw and processed fruits and vegetables in the United States diet p.199
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