Competition Effects on Carotenoid Absorption by Caco-2 Cells - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 383

also assessed in this work, we cannot make conclusions regarding competition between carotenoids
during the incorporation into chylomicrons. Indeed, decreased secretion could also be the conse-
quence of competition at the level of cellular uptake.
In a third study performed in our laboratory in 2005, lutein absorption was measured after lutein-
rich mixed micelles were mixed either with carotenoid-free mixed micelles or with mixed micelles
containing b-carotene and/or lycopene (Reboul et al. 2005). The carotenoids were provided at phys-
iological concentrations (i.e., 0.90, 0.2, and 0.13 mM for lutein, b-carotene, and lycopene, respec-
tively) while the mixed micelles contained lipids from the digestion process and biliary salts. Lutein
absorption was signii cantly decreased when micellar lutein was co-incubated for 3 h with micellar
b-carotene (approx. 20%) or with both micellar b-carotene and lycopene, but not with micellar lyco-
pene alone (Figure 18.1). Although it is unclear if signii cant competition could have been observed
at a reduced, more physiological time of incubation (i.e., 30 min), this last result is in agreement
with human studies in which b-carotene signii cantly affected lutein absorption (Kostic et al. 1995,
van den Berg 1998, van den Berg and van Vliet 1998, Tyssandier et al. 2002). In contrast to what
was observed in humans (Tyssandier et al. 2002), the fact that lycopene did not signii cantly affect
lutein absorption was explained either by the lower concentration of lycopene that could have been
incorporated into micelles (0.13 mM instead of 0.2 mM for b-carotene), or by the fact that this caro-
tenoid has no b-ionone rings (in contrast with b-carotene and lutein). Note that the different results
obtained in this study and in the study from During et al. (2002) can be explained by the vehicle
used to deliver the carotenoids (Tween 40 micelles vs. the physiological mixed micelles).
In summary, Caco-2 cells studies strongly suggest that carotenoids interact with each other at the
level of cellular uptake by the enterocyte. This phenomenon has been explained by the fact that the
uptake of several carotenoids involves, at least in part, the same intestinal membrane transporter:
the scavenger receptor class B type I SR-BI (Reboul et al. 2005, van Bennekum et al. 2005, Moussa
et al. 2008).

120

100

*

80

*

60

40

20

0

Lutein
(control)

Lutein +
lycopene

Lutein +
β-carotene

Lutein +
lycopene +
β-carotene

FIGURE 18.1 Competitive effects of β-carotene and lycopene on lutein absorption. The effects of β- carotene
and lycopene on lutein absor ption were observed in conl uent Caco-2 cells. The apical side of the cells received
FBS-free medium containing lutein-rich micelles (0.90 mM), or lutein-rich micelles (0.90 mM) plus lycopene-
rich micelles (0.13 mM), or lutein-rich micelles (0.90 mM) plus β-carotene-rich micelles (0.20 mM), or lutein-
rich micelles (0.90 mM) plus β-carotene-rich micelles (0.90 mM) plus lycopene-rich micelles (0.13 mM). The
basolateral side received complete medium. Incubation time was 180 min. Data are mean ± SEM of three
assays. An asterisk indicates a signii cant difference with control (0.90 mM lutein-rich micelles alone).