Retinyl palmitate

Retinyl palmitate, or vitamin A palmitate, is the ester of retinol (vitamin A) and palmitic acid, with formula C36H60O2. It is the most abundant form of vitamin A storage in animals.[1]

Retinyl palmitate
Names
IUPAC name
[(2E,4E,6E,8E)-3,7-Dimethyl-9-(2,6,6-trimethylcyclohex-1-en-1-yl)nona-2,4,6,8-tetraenyl] hexadecanoate
Other names
Retinol palmitate
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.001.117
UNII
Properties
C36H60O2
Molar mass 524.86 g/mol
Hazards
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

An alternate spelling, retinol palmitate, which violates the -yl organic chemical naming convention for esters, is also frequently seen.

Biology

Animals use long-chain esters of vitamin A, most abundantly the palmitate form, as a form of vitamin A storage. The storage reaction is catalyzed by LRAT, and the inverse is catalyzed by REH.[1] The esters are also intermediates in the visual cycle: RPE65 isomerizes the retinyl part to 11-cis-retinal.[1]

Uses

Vitamin A palmitate is a common vitamin supplement, available in both oral and injectable forms for treatment of vitamin A deficiency, under the brand names Aquasol A, Palmitate A and many others. It is a constituent of intra ocular treatment for dry eyes at a concentration of 138 μg/g (VitA-Pos) by Ursapharm. It is a pre-formed version of vitamin A; therefore, the intake should not exceed the Recommended Dietary Allowance (RDA). Overdosing preformed Vitamin A forms such as retinyl palmitate leads to adverse physiological reactions (hypervitaminosis A).[2]

Retinyl palmitate is used as an antioxidant and a source of vitamin A added to low fat milk and other dairy products to replace the vitamin content lost through the removal of milk fat. Palmitate is attached to the alcohol form of vitamin A, retinol, in order to make vitamin A stable in milk.

Retinyl palmitate is also a constituent of some topically applied skin care products. After its absorption into the skin, retinyl palmitate is converted to retinol, and ultimately to retinoic acid (the active form of vitamin A present in Retin-A), though neither its skin absorption [3] nor its conversion [4] is very effective.

Carcinogenicity controversy

New York Senator Chuck Schumer has called attention to the fact that high doses of topical retinyl palmitate were shown to accelerate cancer in lab animals,[5] fueling the sunscreen controversy in the popular press.[6] One toxicological analysis determined that "there is no convincing evidence to support the notion that [retinyl palmitate] in sunscreens is carcinogenic."[7] A technical report issued thereafter by the National Toxicology Program concluded that diisopropyl adipate increased incidence of skin tumors in mice, and the addition of either retinoic acid or retinyl palmitate both exacerbated the rate and frequency of tumors.[8]

Teratogenicity

World Health Organization recommendation on Maternal Supplementation During Pregnancy states that "health benefits are expected for the mother and her developing fetus with little risk of detriment to either, from a daily supplement not exceeding 10,000 IU [preformed] vitamin A (3000 μg RE) at any time during pregnancy."[9] Preformed Vitamin A refers to retinyl palmitate and retinyl acetate.

See also

References
  1. O'Byrne, SM; Blaner, WS (July 2013). "Retinol and retinyl esters: biochemistry and physiology". Journal of Lipid Research. 54 (7): 1731–43. doi:10.1194/jlr.R037648. PMC 3679378. PMID 23625372.
  2. Vitamin A, Linus Pauling Institute
  3. E. A. Duell, S. Kang & J. J. Voorhees (1997). "Unoccluded retinol penetrates human skin in vivo more effectively than unoccluded retinyl palmitate or retinoic acid". The Journal of Investigative Dermatology. 109 (3): 301–305. doi:10.1111/1523-1747.ep12335788. PMID 9284094.
  4. Boehnlein, James; Sakr, Adel; Lichtin, J. Leon; Bronaugh, Robert L. (1994). "Characterization of Esterase and Alcohol Dehydrogenase Activity in Skin. Metabolism of Retinyl Palmitate to Retinol (Vitamin A) During Percutaneous Absorption". Pharmaceutical Research. 11 (8): 1155–1159. doi:10.1023/A:1018941016563. ISSN 0724-8741. PMID 7971717. S2CID 25458156.
  5. "Possible link between ingredient in sunscreen and skin cancer: Schumer". New York Daily News. June 14, 2010.
  6. Wang, SQ; Dusza, SW; Lim, HW (2010). "Safety of retinyl palmitate in sunscreens: a critical analysis". Journal of the American Academy of Dermatology. 63 (5): 903–6. doi:10.1016/j.jaad.2010.07.015. PMID 20692724.
  7. Wang, SQ; Dusza, SW; Lim, HW (2010). "Safety of retinyl palmitate in sunscreens: a critical analysis". Journal of the American Academy of Dermatology. 63 (5): 903–6. doi:10.1016/j.jaad.2010.07.015. PMID 20692724.
  8. National Toxicology Program. (2012). NTP technical report on the photocarcinogenesis study of retinoic acid and retinyl palmitate [CAS Nos. 302-79-4 (All-trans-retinoic acid) and 79-81-2 (All-trans-retinyl palmitate)] in SKH-1 mice (Simulated solar light and topical application study). Available at http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/TR568_508.pdf. Accessed September 19, 2013.
  9. Safe vitamin A dosage during pregnancy and lactation (PDF), WHO, 1998.


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