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Journal of Lipid Research, Vol. 49, 1715-1724, August 2008
Copyright © 2008 by American Society for Biochemistry and Molecular Biology

Xanthophylls are preferentially taken up compared with β-carotene by retinal cells via a SRBI-dependent mechanism^*,1

Alexandrine During^2,*,, Sundari Doraiswamy^* and Earl H. Harrison^*,

^* Phytonutrients Laboratory, U.S. Department of Agriculture-Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville, MD 20705
Laboratoire de Biochimie Cellulaire, Université Catholique de Louvain, Louvain-La-Neuve B1348, Belgium
Department of Human Nutrition, Ohio State University, Columbus, OH 43210

^* The authors acknowledge with thanks the financial support of National Institutes of Health Grants R01 DK-044498 and R01 HL-49879.

¹ This work was presented in part at the Annual Meeting of FASEB, Experimental Biology '03, San Diego, CA, April 2003 (abstract No. 456.16).

Published, JLR Papers in Press, April 19, 2008.

²To whom correspondence should be addressed. e-mail: alexandrine.during{at}uclouvain.be

The purpose of this study was to investigate the mechanisms by which carotenoids [xanthophylls vs. β-carotene(β-C)] are taken up by retinal pigment epithelial (RPE) cells. The human RPE cell line, ARPE-19, was used. When ARPE-19 cells were fully differentiated (7–9 weeks), the xanthophylls lutein (LUT) and zeaxanthin (ZEA) were taken up by cells to an extent 2-fold higher than β-C (P < 0.05). At 9 weeks, cellular uptakes were 1.6, 2.5, and 3.2%, respectively, for β-C, LUT, and ZEA. Similar extents were observed when carotenoids were delivered in either Tween 40 or "chylomicrons" produced by Caco-2 cells. Differentiated ARPE-19 cells did not exhibit any detectable β-C 15,15'-oxygenase activity or convert exogenous β-C into vitamin A. When using specific antibodies against the lipid transporters cluster determinant 36 (CD36) and scavenger receptor class B type I (SR-BI), cellular uptake of β-C and ZEA were significantly decreased (40–60%) with anti-SR-BI but not with anti-CD36. Small interfering RNA transfection for SR-BI led to marked knockdown of SR-BI protein expression (90%), which resulted in decreased β-C and ZEA uptakes by 51% and 87%, respectively. Thus, the present data show that RPE cells preferentially take up xanthophylls versus the carotene by a process that appears to be entirely SR-BI-dependent for ZEA and partly so for β-C. This mechanism may explain, in part, the preferential accumulation of xanthophylls in the macula of the retina.

Supplementary key words carotenoids • xanthophylls • cellular uptake • scavenger receptor class B type I • small interfering RNAs • ARPE-19 cells

Abbreviations: AMD, age-related macular degeneration; β-C, β-carotene; BCO1, β-carotene 15,15'-oxygenase; CD36, cluster determinant 36; LP2000, Lipofectamine 2000; LUT, lutein; RNAi, RNA interference; RPE, retinal pigment epithelium; siRNA, small interfering RNA; SR-BI, scavenger receptor class B type I; ZEA, zeaxanthin

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