INTESTINAL ABSORPTION AND METABOLISM OF CAROTENOIDS: INSIGHTS FROM CELL CULTURE

Authors: During, Alexandrine; Harrison, Earl

Submitted to: Archives of Biochemistry and Biophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2004
Publication Date: 10/25/2004
Citation: During, A., Harrison, E.H. 2004. Intestinal absorption and metabolism of carotenoids: insights from cell culture. Archives Of Biochemistry and Biophysics. 430:77-88.

Interpretive Summary: Several epidemiological studies have reported that consumption of carotenoid-rich foods is associated with a reduced risk of certain cancers, cardiovascular disease, and age-related macular degeneration. These preventive effects of carotenoids could be related to their major function as vitamin A precursors and/or their actions as antioxidants, modulators of the immune response, and inducers of gap-junction communications. In addition, carotenoids are generally recognized as safe for human health in contrast to vitamin A, which can be toxic at high doses. Thus, the potential use of carotenoids, as supplements or from natural food sources, to prevent certain chronic diseases in addition to vitamin A deficiency has stimulated a renewed interest in the carotenoid field. The recent advances that occurred in carotenoid absorption and metabolism are discussed with a special interest for studies that used cell culture as a tool to understand better the mechanisms on the molecular basis. The recent cloning of the enzyme involved in one of the main step of carotenoid metabolism, beta-carotene conversion to vitamin A, has opened wide perspectives for further studies, in particular to understand how nutritional factors regulate that enzyme reaction. Data generated from a promising cell culture model for studying intestinal absorption of carotenoids suggest the participation of a specific epithelial transporter. The identification of such transporters in humans represents an exciting challenge in carotenoid research to understand fully the intestinal transport process of those compounds. This review on carotenoids will be useful for nutritionists and biochemists.

Technical Abstract: Cell culture models are useful for studying intestinal absorption and metabolism of carotenoids. The human intestinal cell line, Caco-2, has been the most widely used model for these studies. The PF11 and TC7 clones of Caco-2 exhibit beta-carotene-15,15=-oxygenase activity, a key enzyme in the conversion of carotenoids to vitamin A. Studies on the recent cloning of this enzyme are discussed. An in vitro cell culture system used to study intestinal absorption of carotenoids is presented. Under conditions mimicking the postprandial state, Caco-2 cells on membranes take up carotenoids and secrete them incorporated into chylomicrons. Both the cellular uptake and secretion of beta-carotene are saturable, concentration dependent processes. The selective absorption of all-trans beta-carotene versus its cis isomers, the differential absorption of individual carotenoids and the specific interactions between carotenoids during their absorption are discussed. The participation of a specific epithelial transporter in the intestinal absorption of carotenoids is proposed.