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Laurence M. Rapp, Seema S. Maple, Jung H. Choi; Lutein and Zeaxanthin Concentrations in Rod Outer Segment Membranes from Perifoveal and Peripheral Human Retina. Invest. Ophthalmol. Vis. Sci. 2000;41(5):1200-1209.
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purpose. In addition to acting as an optical filter, macular (carotenoid)
pigment has been hypothesized to function as an antioxidant in the
human retina by inhibiting the peroxidation of long-chain
polyunsaturated fatty acids. However, at its location of highest
density in the inner (prereceptoral) layers of the foveal retina, a
specific requirement for antioxidant protection would not be predicted.
The purpose of this study was to determine whether lutein and
zeaxanthin, the major carotenoids comprising the macular pigment, are
present in rod outer segment (ROS) membranes where the concentration of
long-chain polyunsaturated fatty acids, and susceptibility to
oxidation, is highest.
methods. Retinas from human donor eyes were dissected to obtain two regions: an
annular ring of 1.5- to 4-mm eccentricity representing the area
centralis excluding the fovea (perifoveal retina) and the remaining
retina outside this region (peripheral retina). ROS and residual
(ROS-depleted) retinal membranes were isolated from these regions by
differential centrifugation and their purity checked by polyacrylamide
gel electrophoresis and fatty acid analysis. Lutein and zeaxanthin were
analyzed by high-performance liquid chromatography and their
concentrations expressed relative to membrane protein. Preparation of
membranes and analysis of carotenoids were performed in parallel on
bovine retinas for comparison to a nonprimate species. Carotenoid
concentrations were also determined for retinal pigment epithelium
harvested from human eyes.
results. ROS membranes prepared from perifoveal and peripheral regions of human
retina were found to be of high purity as indicated by the presence of
a dense opsin band on protein gels. Fatty acid analysis of human ROS
membranes showed a characteristic enrichment of docosahexaenoic
acid relative to residual membranes. Membranes prepared from bovine
retinas had protein profiles and fatty acid composition similar to
those from human retinas. Carotenoid analysis showed that lutein and
zeaxanthin were present in ROS and residual human retinal membranes.
The combined concentration of lutein plus zeaxanthin was 70% higher in
human ROS than in residual membranes. Lutein plus zeaxanthin in human
ROS membranes was 2.7 times more concentrated in the perifoveal than
the peripheral retinal region. Lutein and zeaxanthin were consistently
detected in human retinal pigment epithelium at relatively low
conclusions. The presence of lutein and zeaxanthin in human ROS membranes raises the
possibility that they function as antioxidants in this cell
compartment. The finding of a higher concentration of these carotenoids
in ROS of the perifoveal retina lends support to their proposed
protective role in age-related macular
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