Xanthophylls are preferentially taken up compared with beta-carotene by retinal cells via a SRBI-dependent mechanism.
The purpose of this study was to investigate the mechanisms by which carotenoids [xanthophylls vs. beta-carotene(beta-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 beta-C (P < 0.05). At 9 weeks, cellular uptakes were 1.6, 2.5, and 3.2%, respectively, for beta-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 beta-C 15,15'-oxygenase activity or convert exogenous beta-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 beta-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 (approximately 90%), which resulted in decreased beta-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 beta-C. This mechanism may explain, in part, the preferential accumulation of xanthophylls in the macula of the retina.
During
Alexandrine
A
Phytonutrients Laboratory, US Department of Agriculture-Agricultural Research Service, Beltsville Human Nutrition Research Center, Beltsville, MD 20705, USA. alexandrine.during@uclouvain.be
Doraiswamy
Sundari
S
Harrison
Earl H
EH
D001692:Biological Transport; D002454:Cell Differentiation; D002478:Cells, Cultured; D006801:Humans; D014975:Lutein / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism*; D051122:Scavenger Receptors, Class B / Q000276:immunology / Q000502:physiology*; D024341:Xanthophylls / Q000378:metabolism*; D065146:Zeaxanthins; D019207:beta Carotene / Q000378:metabolism*
C495124:SCARB1 protein, human; D051122:Scavenger Receptors, Class B; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D014975:Lutein