Dehydroascorbic acid (DHA) is an oxidized form of ascorbic acid (vitamin C). It is actively imported into the endoplasmic reticulum of cells via glucose transporters.[1] It is trapped therein by reduction back to ascorbate by glutathione and other thiols.[2] The (free) chemical radical semidehydroascorbic acid (SDA) also belongs to the group of oxidized ascorbic acids.
Although a sodium-dependent transporter for vitamin C exists, it is present mainly in specialized cells, whereas the glucose transporters, the most notable being GLUT1, transport Vitamin C (in its oxidized form, DHA)[3] in most cells, where recycling back to ascorbate generates the necessary enzyme cofactor and intracellular antioxidant, (see Transport to mitochondria).
The structure shown here for DHA is the commonly shown textbook structure. This 1,2,3-tricarbonyl is too electrophilic to survive more than a few milliseconds in aqueous solution, however. The actual structure shown by spectroscopic studies is the result of rapid hemiketal formation between the 6-OH and the 3-carbonyl groups. Hydration of the 2-carbonyl is also observed.[4] The lifetime of the stabilized species is commonly said to be about 6 minutes under biological conditions.[1] Destruction results from irreversible hydrolysis of the lactone bond, with additional degradation reactions following.[5] Crystallization of solutions of DHA gives a pentacyclic dimer structure of indefinite stability. Recycling of ascorbate via active transport of DHA into cells, followed by reduction and reuse, mitigates the inability of humans to synthesize it from glucose.[6]
Hydration equilibria of DHA - center hemiketal structure is the predominant species in aqueous solutions.[7]
Vitamin C does not pass from the bloodstream into the brain, although the brain is one of the organs that have the greatest concentration of vitamin C. Instead, DHA is transported through the blood–brain barrier via GLUT1 transporters, and then converted back to ascorbate.[8]
Dehydroascorbic acid has been used as a vitamin C dietary supplement.[9]
As a cosmetic ingredient, dehydroascorbic acid is used to enhance the appearance of the skin.[10] It may be used in a process for permanent waving of hair[11] and in a process for sunless tanning of skin.[12]
In a cell culturegrowth medium, dehydroascorbic acid has been used to assure the uptake of vitamin C into cell types that do not contain ascorbic acid transporters.[13]
As a pharmaceutical agent, some research has suggested that administration of dehydroascorbic acid may confer protection from neuronal injury following an ischemic stroke.[8] The literature contains many reports on the antiviral effects of vitamin C,[14] and one study suggests dehydroascorbic acid has stronger antiviral effects and a different mechanism of action than ascorbic acid.[15] Solutions in water containing ascorbic acid and copper ions and/or peroxide, resulting in rapid oxidation of ascorbic acid to dehydroascorbic acid, have been shown to possess powerful but short-lived antimicrobial, antifungal, and antiviral properties, and have been used to treat gingivitis, periodontal disease, and dental plaque.[16][17] A pharmaceutical product named Ascoxal is an example of such a solution used as a mouth rinse as an oral mucolytic and prophylactic agent against gingivitis.[17][18] Ascoxal solution has also been tested with positive results as a treatment for recurrent mucocutaneous herpes,[18] and as a mucolytic agent in acute and chronic pulmonary disease such as emphysema, bronchitis, and asthma by aerosol inhalation.[19]
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Kerber, R. C. (2008). ""As Simple as Possible, but Not Simpler"—The Case of Dehydroascorbic Acid". Journal of Chemical Education. 85 (9): 1237. Bibcode:2008JChEd..85.1237K. doi:10.1021/ed085p1237.
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Kimoto, E.; Tanaka, H.; Ohmoto, T.; Choami, M. (1993). "Analysis of the transformation products of dehydro-L-ascorbic acid by ion-pairing high-performance liquid chromatography". Analytical Biochemistry. 214 (1): 38–44. doi:10.1006/abio.1993.1453. PMID8250252.
^Jariwalla, R.J. & Harakeh S. (1997). Mechanisms underlying the action of vitamin C in viral and immunodeficiency disease. In L. Packer & J. Fuchs (Eds.), Vitamin C in health and disease (pp. 309-322). New York:Marcell Dekker, Inc.
^ abHovi T, Hirvimies A, Stenvik M, Vuola E, Pippuri R (1995). "Topical treatment of recurrent mucocutaneous herpes with ascorbic acid-containing solution". Antiviral Res. 27 (3): 263–70. doi:10.1016/0166-3542(95)00010-j. PMID8540748.