The Carotenoids of Macular Pigment and Bisretinoid Lipofuscin Precursors in Photoreceptor Oute Segments - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 355

16 The Carotenoids of Macular

Pigment and Bisretinoid
Lipofuscin Precursors in
Photoreceptor Outer
Segments

Janet R. Sparrow and So Ra Kim

CONTENTS
16.1 Introduction .......................................................................................................................... 355
16.2 Light Filtering and Antioxidant Properties of Macular Pigment ......................................... 356
16.3 Photoreactive Bisretinoid Compounds in Photoreceptor Outer Segments ........................... 357
16.4 Lutein and Zeaxanthin Attenuate A2PE Photooxidation ..................................................... 359
16.5 Zeaxanthin and Lutein Quench Singlet Oxygen .................................................................. 359
16.6 Structural Features of Zeaxanthin and Lutein versus A2PE................................................ 361
16.7 Summary .............................................................................................................................. 361
Acknowledgments .......................................................................................................................... 362
References ...................................................................................................................................... 362

16.1 INTRODUCTION
The oxygen atom-containing carotenoids (xanthophylls), zeaxanthin and lutein, Figure 16.1, are
obtained by humans through the dietary intake of fruits and vegetables and become incorporated
in the retina as macroscopically visible macular pigment. These yellow-colored pigments are par-
ticularly abundant in the fovea, their concentration declining steeply toward the peripheral retina.
Of the two carotenoids, zeaxanthin is more concentrated in the central 10° of the retina while lutein
dominates at eccentricities greater than 35° (Bone et al., 1988; Snodderly et al., 1991). The specii city
of this distribution indicates the selective uptake of macular pigments by specii c binding proteins
(Bhosale et al., 2004). Nevertheless, the concentration of lutein and zeaxanthin in the macula varies
among individuals (Bone et al., 1997) and it is likely that the extent of oral intake is responsible for
these differences (Hammond et al., 1997; Landrum et al., 1997). Indeed, the long-term intake of the
dietary supplements of lutein increases the levels of macular pigment (Bhosale et al., 2007). The
highest levels of lutein and zeaxanthin are present in photoreceptor cell axonal processes (Henle's
i bers) (Snodderly et al., 1984) but 25% of total retinal carotenoids are present within photorecep-
tor outer segments (Rapp et al., 2000; Sommerburg et al., 1999). Given their hydrophobicity, lutein
and zeaxanthin readily integrate into the lipophilic compartment of cell membranes (Landrum and
Bone, 2001).

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