Article

Mechanisms of provitamin A (carotenoid) and vitamin A (retinol) transport into and out of intestinal Caco-2 cells

Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA.
The Journal of Lipid Research (Impact Factor: 4.42). 11/2007; 48(10):2283-94. DOI: 10.1194/jlr.M700263-JLR200
Source: PubMed

ABSTRACT

The purpose of this study was to compare the mechanisms of intestinal retinol (ROL) and carotenoid transport. When differentiated Caco-2 cells were incubated with ROL for varying times, cellular ROL plateaued within 2 h, whereas retinyl ester (RE) formation increased continuously. ROL and RE efflux into basolateral medium (BM) increased linearly with time, ROL in the nonlipoprotein fraction and REs in chylomicrons (CMs). In contrast to carotenoids, ROL uptake was proportional to ROL concentration (0.5-110 microM). ROL efflux into BM occurred via two processes: a) a saturable process at low concentrations (<10 microM) and b) a nonsaturable process at higher concentrations. When ROL-loaded cells were maintained on retinoid-free medium, free ROL, but not REs, was secreted into BM. Glyburide significantly reduced ROL efflux but not ROL uptake. Inhibition of ABCA1 protein expression by small interfering RNAs decreased ROL efflux but not carotenoid efflux. Scavenger receptor class B type I (SR-BI) inhibition did not affect ROL transport but decreased carotenoid uptake. The present data suggest that a) ROL enters intestinal cells by diffusion, b) ROL efflux is partly facilitated, probably by the basolateral transporter ABCA1, and c) newly synthesized REs, but not preformed esters, are incorporated into CM and secreted. In contrast to ROL transport, carotenoid uptake is mediated by the apical transporter SR-BI, and carotenoid efflux occurs exclusively via their secretion in CM.

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    • "Lin et al. (2007) reported a better uptake of lycopene into DU145 prostate cancer cells from FCS-compared to THF-supplemented media. Lipoproteins appear to play an important role in the cellular uptake of carotenoids (During and Harrison 2007; O'Sullivan et al. 2007). The involvement of the scavenger receptor class B type I (SR-BI) in carotenoid uptake has been demonstrated (van Bennekum et al. 2005; During and Harrison 2007). "
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