Topical [beta]-carotene is converted to retinyl esters in human skin ex vivo and mouse skin in vivo.
Antille, Christophe; Tran, Christian; Sorg, Olivier; Saurat, Jean-Hilaire
[Article] Experimental Dermatology. 13(9):558-561, September 2004.

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Human epidermis contains endogenous retinoids (retinol and retinyl esters) and carotenoids (mostly [beta]-carotene). Previous studies have shown that the enzymes involved in retinoid metabolism are present in human epidermis. There is still a controversy about the presence in the skin of the enzymes able to convert [beta]-carotene into vitamin A (retinol), although a recent study demonstrated the conversion of [beta]-carotene into retinol in human cultured epidermal cells. In this study, we addressed the question of the possible bioconversion of topical [beta]-carotene into vitamin A or derivatives by human and mouse skin. Surgically excised human abdominal skin was mounted on Franz perfusion chambers to assess the cutaneous penetration of topical [beta]-carotene as well as its metabolism, after a 24-h incubation period, whereas hairless mice received topical [beta]-carotene 24 h before assaying epidermal [beta]-carotene and retinoid concentrations. Epidermal retinoid and [beta]-carotene concentrations were determined by high-pressure liquid chromatography. Topical [beta]-carotene penetrated well into human and mouse epidermis and induced a 10-fold (human) and a threefold (mouse) increase of epidermal retinyl esters, which demonstrates that topical [beta]-carotene is converted into retinyl esters by human and mouse epidermis and thus appears as a precursor of epidermal vitamin A.

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