Carotenoids and other dietary antioxidants in free radical research : protection of human retina homogenate against photochemical and metal-induced lipid autoxidation
Year: 1994
Type: dissertation
Abstract: Carotenoids and other dietary antioxidants in free radical research: Protection of human retina homogenate against photochemical and metal-induced lipid autoxidation.Dietary antioxidants including, carotenoids, tocopherols, ascorbate, and retinol are of current interest as "chemopreventive" agents in cancer, coronary heart disease, agerelated macular degeneration, and other diseases.The human retina is an important target in free radical pathology, due to its anatomy, biochemistry, fbnction, and its constant exposure to photochemically-induced oxidative stress.Lipid peroxidation of human retina homogenate can be induced by either photo-sensitization (rose Bengal and light) or metalcatalysis (iron and ascorbate).Tissue injury was estimated by the formation of lipid peroxides as assessed by the thiobarbituric acid (TBA) assay.The systems chosen are potential models for certain eye injuries, diseases, or the natural processes of aging.Ascorbate ( 1mM) is the superior antioxidant in oxidative stress protecting human retina homogenate against metal-induced injury by 98% and against photosensitized injury by 68%.a-Tocopherol (1 mM) and P-carotene (.05 mM) protected against irodascorbateinduced damage by 34% and 18% and against photosensitized damage by 37% and 26%.Retinol(O.1 mM) protected only against the photosensitized system.Potencies of the carotenoids varied widely, with a-carotene > canthaxanthin > astaxanthin > lycopene > p-carotene > lutein 2 zeaxanthin.The relatively low protection by p-carotene confirms suggestions that other carotenoids have been neglected in studies of protection and in chemoprevention trials.Lutein and zeaxanthin did not reach significance (p 5 0.05) at . . .111.05 mM, however they did reach significance at .O1 rnM.Lutein and zeaxanthin, the two major carotenoids of the retina accumulate especially at the macula Iutea (or "yellow spot").Their relative lack of antioxidant activity or singlet oxygen quenching ability would serve to ensure their conservation, preserving them to hnction as filters.By attenuating light in the macular area, they would decrease production of the species that initiate light-induced lipid peroxidation.a-Tocopherol was a more effective antioxidant at the higher partial pressures of oxygen.Oxidized p-carotene at ambient PO, increased production of MDA.This finding may have particular importance to studies finding a higher incidence of cancer in subjects receiving P-carotene supplementation.Endogenous lutein is positively correlated with zeaxanthin, as are total carotenoids and y-tocopherol, but not a-tocopherol or retinol.Our results encourage speculation that, in the human retina, phototoxic reactions and free radical-mediated damage would be attenuated by the presence of high levels of ascorbate.Tocopherols, carotenoids, and retinol may protect to a lesser degree.In either event, the current data support and provide a mechanistic basis for epidemiological studies of protective actions of antioxidants in visual disorders.
Source: Summit (Simon Fraser University)
Author: Eunice Joy Natsuko Rousseau
Language: English
Subfield: Biochemistry (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W176844800