Abstract
The xanthophylls, lutein and zeaxanthin, are dietary carotenoids that selectively accumulate in the macula of the eye providing protection against age-related macular degeneration. To reach the macula, carotenoids cross the retinal pigment epithelium (RPE). Xanthophylls and β-carotene mostly associate with HDL and LDL, respectively. HDL binds to cells via a scavenger receptor class B1 (SR-B1)-dependent mechanism, while LDL binds via the LDL receptor. Using an in-vitro, human RPE cell model (ARPE-19), we studied the mechanisms of carotenoid uptake into the RPE by evaluating kinetics of cell uptake when delivered in serum or isolated LDL or HDL. For lutein and β-carotene, LDL delivery resulted in the highest rates and extents of uptake. In contrast, HDL was more effective in delivering zeaxanthin and meso-zeaxanthin leading to the highest rates and extents of uptake of all four carotenoids. Inhibitors of SR-B1 suppressed zeaxanthin delivery via HDL. Results show a selective HDL-mediated uptake of zeaxanthin and meso-zeaxanthin via SR-B1 and a LDL-mediated uptake of lutein. This demonstrates a plausible mechanism for the selective accumulation of zeaxanthin greater than lutein and xanthophylls over β-carotene in the retina. We found no evidence of xanthophyll metabolism to apocarotenoids or lutein conversion to meso-zeaxanthin.
Highlights
The xanthophylls, lutein and zeaxanthin, are dietary carotenoids that selectively accumulate in the macula of the eye providing protection against age-related macular degeneration
Xanthophylls preferentially accumulate in the macula of the eye despite higher levels of other carotenoids in the blood, indicating a selective mechanism of delivery in the retina
Using differentiated ARPE-19 cells as a model for the retinal pigment epithelium (RPE), we previously demonstrated that zeaxanthin delivered by detergent micelles is preferentially taken up compared with -carotene via scavenger receptor class B1 (SR-B1) [30]
Summary
The xanthophylls, lutein and zeaxanthin, are dietary carotenoids that selectively accumulate in the macula of the eye providing protection against age-related macular degeneration. Results show a selective HDL-mediated uptake of zeaxanthin and meso-zeaxanthin via SR-B1 and a LDL-mediated uptake of lutein. This demonstrates a plausible mechanism for the selective accumulation of zeaxanthin greater than lutein and xanthophylls over carotene in the retina. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The xanthophylls, lutein and zeaxanthin (Fig. 1A, B), are dietary carotenoids of interest because they accumulate in the retina of the eye and may provide protection from AMD. Meso-zeaxanthin (Fig. 1C), a stereoisomer of zeaxanthin, is present in the macula of the eye but is not a common dietary component
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