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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #204021
Title: The Bioconversion of Carotenoids into Vitamin A: Implications for Cancer Prevention

Author
item Wang, Xiang-Dong
item MERNITZ, HEATHER - HNRCA AT TUFTS

Submitted to: Vitamin A: New Research
Publication Type: Book / Chapter
Publication Acceptance Date: 12/1/2006
Publication Date: 6/6/2007
Citation: Wang, X., Mernitz, H. 2007. The Bioconversion of Carotenoids into Vitamin A: Implications for Cancer Prevention. In: Columbus, F., Loessing, I. T. editors. Vitamin A: New Research. Hauppauge, NY: Nova Science Publishers, Inc. p. 1-19.

Interpretive Summary:

Technical Abstract: Carotenoids are lipophilic plant pigments with polyisoprenoid structures, typically containing a series of conjugated double bonds in the central chain of the molecule, which makes them susceptible to oxidative cleavage and isomerization from trans to cis forms. This cleavage can result in the formation of potentially bioactive metabolites, such as retinoids (vitamin A and its derivatives) and other biological compounds. For provitamin A carotenoids, such as beta-carotene, alpha-carotene, and beta-cryptoxanthin, central cleavage is a major pathway leading to vitamin A formation. This pathway has been substantiated by the cloning of a central cleavage enzyme, beta-carotene 15,15'-monooxygenase (CMO1, formerly called beta-carotene 15,15'-dioxygenase), which can cleave carotenoids at their 15,15’-double bond. In addition to being cloned in several different species, further classification of this enzyme as a non-heme iron monooxygenase and recent biochemical and structural characterization have been carried out. An alternative pathway for carotenoid metabolism into vitamin A in mammals, the excentric cleavage pathway, was confirmed by the molecular identification of beta-carotene 9’,10’-monooxygenase (CMO2) in humans and animals. Recent biochemical characterization of CMO2 demonstrates that this enzyme catalyzes the excentric cleavage of both provitamin A carotenoids and non-provitamin A carotenoids. Further characterization and determination of the biological functions of central and excentric cleavage metabolites of carotenoids, and an understanding of the regulation of CMO1 and CMO2, will provide invaluable insights into the mechanisms underlying the bioconversion of carotenoids to vitamin A. Since disruption in retinoid metabolism and signaling may play a key role in the process of carcinogenesis, understanding the molecular details behind the actions of these carotenoid oxidative metabolites may yield insights into both physiological and pathophysiological processes in human health and disease, particularly the potential for beneficial effects of small quantities and harmful effects of large quantities of carotenoid metabolites.