Α-Tocopheryl acetate explained

α-Tocopheryl acetate (alpha-tocopherol acetate), also known as vitamin E acetate, is a form of vitamin E with D-Alpha Tocpheryl Acetate as the natural form and DL-Alpha Tocopheryl Acetate as the synthetic form. DL-indicates the synthetic form where as D- indicates the natural form. It is the ester of acetic acid and .

The U.S. Centers for Disease Control and Prevention says that vitamin E acetate is a very strong culprit of concern in the 2019 outbreak of vaping-associated pulmonary injury (VAPI), but there is not yet sufficient evidence to rule out contributions from other chemicals.[1] Vaporization of this ester produces toxic pyrolysis products.

Use in cosmetics

α-Tocopheryl acetate is often used in dermatological products such as skin creams. It is not oxidized and can penetrate through the skin to the living cells, where about 5% is converted to free tocopherol. Claims are made for beneficial antioxidant effects. α-Tocopheryl acetate is used as an alternative to tocopherol itself because the phenolic hydroxyl group is blocked, providing a less acidic product with a longer shelf life. It is believed that the acetate is slowly hydrolyzed after it is absorbed into the skin, regenerating tocopherol and providing protection against the sun's ultraviolet rays.[2] Tocopheryl acetate was first synthesized in 1963 by workers at Hoffmann-La Roche.[3]

Although there is widespread use of tocopheryl acetate as a topical medication, with claims for improved wound healing and reduced scar tissue,[4] reviews have repeatedly concluded that there is insufficient evidence to support these claims.[5] [6] There are reports of vitamin E-induced allergic contact dermatitis from use of vitamin E derivatives such as tocopheryl linoleate and tocopherol acetate in skin care products. Incidence is low despite widespread use.[7]

Misuse

Ingredient in vape liquids

On September 5, 2019, the United States Food and Drug Administration (US FDA) announced that 10 out of 18, or 56% of the samples of vape liquids sent in by states, linked to the recent vaping-related lung disease outbreak in the United States, tested positive for vitamin E acetate[8] which had been used as a thickening agent by illicit THC vape cartridge manufacturers.[9] On November 8, 2019, the Centers for Disease Control and Prevention (CDC) identified vitamin E acetate as a very strong culprit of concern in the vaping-related illnesses, but has not ruled out other chemicals or toxicants as possible causes. The CDC's findings were based on fluid samples from the lungs of 29 patients with vaping-associated pulmonary injury, which provided direct evidence of vitamin E acetate at the primary site of injury in all the 29 lung fluid samples tested.[10] Research suggests when vitamin E acetate is inhaled, it may interfere with normal lung functioning.[11] A 2020 study found that vaporizing vitamin E acetate produced carcinogenic alkenes and benzene, but also exceptionally toxic ketene gas, which may be a contributing factor to the pulmonary injuries.[12]

Chemistry

At room temperature, α-tocopheryl acetate is a fat-soluble liquid. It has 3 chiral centers and thus 8 stereoisomers. It is made by esterifying α-tocopherol with acetic acid. 2R,4R,8R-isomer, also known as RRR-α-tocopheryl acetate, is the most common isomer used for various purposes. This is because α-tocopherol occurs in nature primarily as RRR-α-tocopherol.[13]

α-Tocopherol acetate does not boil at atmospheric pressure and begins to degrade at 240 °C.[13] It can be vacuum distilled: it boils at 184 °C at 0.01 mmHg, at 194 °C (0.025 mmHg) and at 224 °C (0.3 mmHg). In practice, it is not degraded notably by air, visible light or UV-radiation. It has a refractive index of 1.4950–1.4972 at 20 °C.[14]

α-Tocopherol acetate is hydrolyzed to α-tocopherol and acetic acid under suitable conditions or when ingested by people.[13]

Notes and References

  1. Feldman. Ryan. Meiman. Jonathan. Stanton. Matthew. Gummin. David D.. June 2020. Culprit or correlate? An application of the Bradford Hill criteria to Vitamin E acetate. Archives of Toxicology. 94. 6. 2249–2254. 10.1007/s00204-020-02770-x. 1432-0738. 32451600. 218878143.
  2. Beijersbergen van Henegouwen G, Junginger H, de Vries H . Hydrolysis of RRR-alpha-tocopheryl acetate (vitamin E acetate) in the skin and its UV protecting activity (an in vivo study with the rat) . J Photochem Photobiol B . 29 . 1 . 45–51 . 1995 . 7472802 . 10.1016/1011-1344(95)90251-1.
  3. Mayer. H.. Schudel. P.. Rüegg. R.. Isler. O.. Über die Chemie des Vitamins E. 3. Mitteilung. Die Totalsynthese von (2R, 4′R, 8′R)- und (2S, 4′R, 8′R)-α-Tocopherol. Helvetica Chimica Acta. 46. 2. 1963. 650–671. 0018-019X. 10.1002/hlca.19630460225.
  4. Panin G, Strumia R, Ursini F . Topical alpha-tocopherol acetate in the bulk phase: eight years of experience in skin treatment . Ann. N. Y. Acad. Sci. . 1031 . 443–447 . 2004 . 1 . 15753192 . 10.1196/annals.1331.069 . 2004NYASA1031..443P . 45771699 . free .
  5. Sidgwick GP, McGeorge D, Bayat A . A comprehensive evidence-based review on the role of topicals and dressings in the management of skin scarring . Arch. Dermatol. Res. . 307 . 6 . 461–477 . 2015 . 26044054 . 4506744 . 10.1007/s00403-015-1572-0 . free .
  6. Tanaydin V, Conings J, Malyar M, van der Hulst R, van der Lei B . The Role of Topical Vitamin E in Scar Management: A Systematic Review . Aesthet Surg J . 36 . 8 . 959–965 . 2016 . 26977069 . 10.1093/asj/sjw046. free .
  7. Kosari P, Alikhan A, Sockolov M, Feldman SR . Vitamin E and allergic contact dermatitis . Dermatitis . 21 . 3 . 148–153 . 2010 . 20487657 . 10.2310/6620.2010.09083. 38212099 .
  8. News: Contaminant found in marijuana vaping products linked to deadly lung illnesses, tests show. Sun. Lena. September 6, 2019. Washington Post. en. September 9, 2019.
  9. Three Companies Subpoenaed in Weed Vape Illness Investigation. September 10, 2019. Rolling Stone. en.
  10. Web site: Transcript of CDC Telebriefing: Update on Lung Injury Associated with E-cigarette Use, or Vaping. Centers for Disease Control and Prevention. November 8, 2019.
  11. Web site: Outbreak of Lung Injury Associated with E-Cigarette Use, or Vaping. Centers for Disease Control and Prevention. November 8, 2019.
  12. Wu. D. O'Shea. DF. March 24, 2020. Potential for release of pulmonary toxic ketene from vaping pyrolysis of vitamin E acetate. Proceedings of the National Academy of Sciences of the United States of America. 117. 12. 6349–6355. 10.1073/pnas.1920925117. 7104367. 32156732. free. 2020PNAS..117.6349W.
  13. 2016. Safety assessment of the substance α-tocopherol acetate for use in food contact materials. EFSA Journal. 14. 3. 4412. 10.2903/j.efsa.2016.4412. free.
  14. Book: The Merck index. 1996. Merck. 9780911910124. 12th. 1580. et al.