Competition Effects on Carotenoid Absorption by Caco-2 Cells - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 385

18.2.3 C OMPETITION BETWEEN C AROTENOIDS AND O THER F AT -S OLUBLE C OMPOUNDS
Plant sterols and stanols (phytosterols) effectively diminish exogenous (dietary) and endogenous
(biliary) cholesterol absorption in humans (Nguyen 1999). It is assumed that this is due to a com-
petition between these cholesterol and phytosterols with regard to their incorporation into mixed
micelles. Thus, it has been hypothesized that the absorption of carotenoids, which are also incor-
porated into mixed micelles during digestion, may also be impaired by phytosterols. Phytosterols
might also diminish cholesterol absorption by another mechanism. Indeed it has been shown that
these plant sterols may enhance cholesterol efl ux back to the apical side of the cell, that is, intestinal
lumen. It is tempting to suggest that such a mechanism works also for carotenoids. To support an
inhibitory effect of phytosterols on carotenoid absorption it has been shown that the cellular uptake
of 7.5 mM b-carotene was signii cantly reduced to about 50% in Caco-2 cells by the presence of
20 mM b-sitosterol in the medium (Fahy et al. 2004). Whatever the mechanism involved, that is,
competition for incorporation into micelles or net uptake by the enterocyte, the inhibitory effect
of phytosterols, in either free or ester form, on carotenoid bioavailability has been coni rmed in a
clinical study (Richelle et al. 2004).
In conclusion, the Caco-2 cell monolayer model has given original data on the competition effect
of several nutrients on carotenoid uptake. Most of these data have been coni rmed in several in vivo
studies, including clinical studies, coni rming that this model is a valuable tool to study competition
effects on carotenoid absorption.
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