Submitted on December 13, 2007
Revised on April 18, 2008
Accepted on April 18, 2008
Xanthophylls are preferentially taken up compared to 
-carotene by retinal cells via a scavenger receptor BI-dependent mechanism
Alexandrine During, Sundari Doraiswamy, and Earl H. Harrison
Sciences de la Vie, Universite catholique de Louvain, Louvain-La-Neuve B-1348
Corresponding Author: Alexandrine.During{at}uclouvain.be
The purpose of this study was to investigate mechanisms by which carotenoids (xanthophylls versus ß-carotene) 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 and zeaxanthin were taken up by cells to an extent two-fold higher than ß-carotene (P < 0.05). At 9 weeks, cellular uptakes were 1.6%, 2.5%, and 3.2%, respectively for ß-carotene, lutein, and zeaxanthin. Similar extents were observed when carotenoids were delivered either in Tween40 or in “chylomicrons” produced by Caco-2 cells. Differentiated ARPE-19 cells did not exhibit any detectable ß-carotene 15,15’-oxygenase activity or convert exogenous ß-carotene into vitamin A. When using specific antibodies against the lipid transporters CD36 and SR-BI, cellular uptake of ß-carotene and zeaxanthin were significantly decreased (40-60%) with anti-SR-BI, but not with anti-CD36. siRNA transfection for SR-BI led to marked knock-down of SR-BI protein expression (~90%), which resulted in decreased ß-carotene and zeaxanthin 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 zeaxanthin and partly so for ß-carotene. This mechanism may explain, in part, the preferential accumulation of xanthophylls in the macula of the retina.
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