RETINAL AGING. The component of the retina which is essential for maintaining visual function and photoreceptor survival is the Retinal Pigment Epithelium (RPE).(1) The RPE provides the homeostasis of the retina, including phagocytosis, a process by which the shedding of the outer segments of photoreceptors is removed and properly disposed as waste products. It is critical that phagocytosis provide daily removal of the shedded segments to maintain vision. Phagocytosis denote a highly active lysosomal activity in the RPE of the retina. Aging of retinal results in a degression of lysosomal activity and accumulation of waste material (Lipofuscin). (2) Furthermore, age related photooxidation of the cellular membrane of the retina further damages the RPE and retinal function.
LIPOFUSCIN AND MACULAR DEGENERATION. Lipofuscin is generated through oxidative stress and a result of waste products. When the retina loses phagocytosis, there is photoreceptor degeneration.(1) Diminished phagocytosis results in increased lipofuscin accumulated in the RPE, which in turn negatively affects the RPE and photoreceptors. Lipofuscin levels also increase through oxidative stress in the retina. Accumulation of lipofuscin is an indicator of RPE atrophy and macular degeneration. As powerful antioxidants, lutein and zeaxanthin can reduce formation of lipofuscin. Zeaxanthin in particular can further help by supporting the phagocytosis removal of lipofuscin.(3,4)
The RPE contains the pigments melanin (in melanosomes) and lipofuscin. Melanin is an antioxidant pigment, whereas lipofucsin is the byproduct of waste material from photoreceptor removal and oxidative stress, which increases with dysfunction of phagocytosis. The accumulation of lipofuscin reduces the protection of melanin and increases oxidative stress of the RPE.(2)
While melanin is a powerful protector of the retina, aging affects the ability of melanin to protect the eye. Older melanosomes exposed to blue light, significantly inhibited phagocytosis - which accelerated degeneration of photoreceptors.. Therefore, the phototoxicity of melansomes increase with age. However, the antioxidant zeaxanthin has been shown to reduce the phototoxicity potential.(3)
ZEAXANTHIN HELPS PROTECTS AGAINST RETINAL DEGENERATION
(1) By reducing Phototoxicity / Photooxidation damage of retinal cellular membranes associated with aging.
(2) By supporting Phagocytosis.and the Maintenance of the RPE.
Meso zeaxanthin is the most powerful version of zeaxanthin, and is found in the central macula.
(1) Valiente-Soriano F, et al. Tracing the retina to analyze the integrity and phagocytic capacity of the retinal pigment epithelium.Sci Rep. 2020.
(2) Bonilha V.. Age and disease-related structural changes in the retinal pigment epithelium. Clin. Ophthalmol. 2008 Jun
(3) Olchawa M, et al. The effect of aging and antioxidants on photoreactivity and phototoxicity of human melanosomes; an in vitro study. Pigment Cell Melanoma Res, 2020 Jul 23.
(4) Olchawa M, et al. Zeaxanthin and α-tocopherol reduce the inhibitory effects of photodynamic stress on phagocytosis by ARPE-19 cells. Free Radic Biol Med. 2015 Dec.