Caco-2 cells, carotenoid absorption

Independent Pathways of Retinol and Carotenoid Absorption in Caco-2 Cells ... 

Thus, in contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of the intestinal carotenoid absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (TC OA supplementation), differentiated Caco-2 cells were able (1) to take up carotenoids at the apical side and to incorporate them into CM and (2) to secrete them at the basolateral side, associated with CM fractions. In this model, no attempt has yet been made to reproduce the in vivo physiochemical conditions occurring in the intestinal lumen, such as carotenoid release from the food matrix and solubilization into mixed lipid micelles. Carotenoids were delivered to Caco-2 cells in aqueous suspension with Tween 40 (During et al., 2002). Using this cell culture system in conjunction with an in vitro... 

THE HUMAN CACO-2 INTESTINAL CELL MODEL A VALUABLE TOOL FOR STUDYING CAROTENOID ABSORPTION... 

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 confirmed in several in vivo studies, including clinical studies, confirming that this model is a valuable tool to study competition effects on carotenoid absorption. 

Carotenoids are highly lipophilic an active area of research concerns how carotenoids interact with and affect membrane systems (see Chapters 2 and 10). Also, the lipid solubility of these compounds has important implications for carotenoid intestinal absorption (see Chapter 17) models such as the Caco-2 cell model are being used to conduct detailed studies of carotenoid absorption/ competition for absorption (Chapter 18). The lipid solubility of these carotenoids also leads to the aggregation of carotenoids (see Chapter 3). Carotenoids aggregate both in natural and artificial systems, with implications for carotenoid excited states (see Chapter 8). This has implications for a new indication for carotenoids, namely, serving as potential materials for harnessing solar energy. 

In culture, the human colon carcinoma cell hne Caco-2 spontaneously differentiates at confluency into polarized cells with enterocyte-like characteristics. The principle of this approach consists of following the passage of the compound of interest from the apical or lumen-like sides to the basolateral or lymph-hke sides of Caco-2 cells, thus following the absorption of the compound per se. One obhgate step for fat-soluble nutrients such as carotenoids to cross the intestinal barrier is their incorporation into CMs assembled in the enterocytes. Under normal cell culture conditions, Caco-2 cells are unable to form CMs. When supplemented with taurocholate and oleic acid, Caco-2 cells were reported to assemble and secrete CMs. ... 

This in vitro approach thus has a great potential for studying the intestinal absorption processes of carotenoids and other pigments. It is important to note the existence of several clones isolated from the parent Caco-2 cell line that can be used for studying... 

Caco-2 cells and ezetimibe, a potent inhibitor of chloresterol absorption in humans, it was reported that (1) carotenoid transport was inhibited by ezetimibe up to 50% and the extent of that inhibition diminished with increasing polarity of the carotenoid molecule, (2) the inhibitory effects of ezetimibe and the antibody against SR-BI on P-carotene transport were additive, and (3) ezetimibe may interact physically with cholesterol transporters as previously suggested - and also down-regulate the gene expression of three surface receptors, SR-BI, NPCILI, and ABCAl. 

Reboul et al., 2007a,b). As mentioned earlier the competitive uptake occurs also in the presence of a mixture of carotenoids where absorption of lutein is inhibited by [1-carotene but not by lycopene (Reboul et al., 2005). This indicates that the presence of a mixture of different lipophilic substrates can strongly influence the uptake of certain carotenoids. It has also been demonstrated that cultured Caco-2 cells secrete (3-carotene, preferentially within micelles rich in long fatty acids (Yonekura et al., 2006), suggesting that carotenoids can be stored in the cell or secreted depending on the absence or presence of appropriate carotenoid acceptors. 

Ezetamibe Inhibits Carotenoid and Cholesterol Absorption in Caco-2 Cells but... 

Differential Absorption of Individual Carotenoids through Caco-2 Cell Monolayers... 

The first study was conducted to determine whether carotenoids and cholesterol share common pathways (transporters) for their intestinal absorption (During et al., 2005). Differentiated Caco-2 cells on membranes were incubated (16 h) with a carotenoid (1 pmol/L) with or without ezetimibe (EZ Zetia, an inhibitor of cholesterol transport), and with or without antibodies against the receptors, cluster determinant 36 (CD36) and scavenger receptor class B, type I (SR-BI). Carotenoid transport in Caco-2 cells (cellular uptake + secretion) was decreased by EZ (lOmg/L) as follows P-C and a-C (50% inhibition) P-cryptoxanthin and LYC (20%) LUT ZEA (1 1) (7%). EZ reduced cholesterol transport by 31%, but not retinol transport. P-Carotene transport was also inhibited by anti-SR-BI, but not by anti-CD36. The inhibitory effects of EZ and anti-SR-BI on P-C transport... 

As demonstrated above, the uptake of [1-C at the apical membrane of differentiated Caco-2 cells occurs via a saturable, facilitated mechanism and is inhibited by Ezetimibe, a clinically used inhibitor of cholesterol absorption. Carotenoids secreted at the basolateral membrane were associated... 

Another complicating factor in the intestinal mucosal cell is the partial conversion of provitamin A carotenoids (/3- and a-carotenes and cryptoxanthin) to vitamin A (primarily to retinyl esters). Therefore, in absorption studies these metabolic reactions must be accounted for in measuring intestinal transport. Nonprovitamin A carotenoids such as lycopene, lutein, and zeaxanthin are incorporated intact, although some cleavage can occur. Earlier studies on rats indicated that lycopene and /3-carotene are absorbed by passive diffusion. However, recent evidence from the kinetics of /3-carotene transport through Caco-2 cell... 

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