Carotenoid pigments: their possible role in protecting against photooxidation in eyes and photoreceptor cells

Abstract

The effect of light on animal tissues is ambivalent. Light is necessary for many functions, e. g. for vision and, as in the flagellate halobacterium, to gain energy. But light is potentially dangerous: it is capable of destroying cells or their components by photooxidation, especially in the presence of sensitizing pigments such as haems and cytochromes, which are ubiquitous in aerobic cells. Several different examples are discussed to show how a compromise is achieved in animal tissues that for functional reasons receive high exposure to light. Carotenoid pigments, present in many eyes and photoreceptors, seem especially suited to protect against the deleterious effects of light because they absorb the dangerous short wavelength part of the light spectrum. In plant tissue, carotenoids are also well known to be capable of ‘quenching’ photoexcited states of sensitizing pigments and of oxygen, a function that they might have also in animal tissues. A consequence of the considerations is that whenever animal tissues are exposed to higher than usual light levels and/or oxygen pressures cellular damage might occur. Examples are discussed; strategies to circumvent the deleterious effects by photooxidation follow directly from the arguments.

Dietary antioxidants and primary prevention of age related macular degeneration: systematic review and meta-analysis

“…Antioxidants are thought to prevent AMD by reducing the photo-oxidative damage from blue light in the oxygen filled environment of the retina, which is rich in polyunsaturated fatty acids that are highly susceptible to oxidation. 40 Previous studies and reviews have largely focused on the role of dietary antioxidants and supplements in the secondary prevention of AMD-that is, preventing progression to late AMD in people with signs of early disease. Our analysis examined the role of dietary antioxidants and supplements in primary prevention and found that a range of dietary antioxidants, including vitamins A, C, and E, zinc, lutein and zeaxanthin, α carotene, β carotene, β cryptoxanthin, and lycopene, have little or no effect: pooled odds ratios ranged from 0.91 to 1.11, with the exception of vitamin E, which had a modest borderline protective association (0.83, 95% confidence interval 0.69 to 1.01).…”

Insect retinal pigments: Spectral characteristics and physiological functions

“…Moreover, the rhabdomeric membrane of the housefly R7y photoreceptor houses another photostable pigment, a mixture of the carotenoids lutein and zeaxanthin (Kirschfeld, 1986;Hardie, 1986). These carotenoids may have an important function by quenching oxygen radicals so to protect the photoreceptor from photochemical damage (Kirschfeld, 1982). In any case, they act as a blue absorbance filter, so that ultimately the spectral sensitivity of R7y peaks at 355 nm.…”

Macular carotenoid supplementation in subjects with atypical spatial profiles of macular pigment

“…Their supply of readily available electrons enables these carotenoids to quench reactive oxidative intermediates (ROIs), thus limiting membrane phosopholipid peroxidation and attenuating oxidative injury (Sujak et al, 1999). Kirschfeld was the first to propose the idea that carotenoids protect the macula against oxidative stress, (Kirschfeld, 1982) and in 1997, Khachik et al confirmed the presence of direct oxidation products of L and Z in human retinal tissue, supporting the hypothesis that MP does indeed protect against oxidative damage in this tissue (Khachik et al, 1997).…”