Factors Differentiating the Antioxidant Activity of Macular Xanthophylls in the Human Eye Retina

Abstract

Macular xanthophylls, which are absorbed from the human diet, accumulate in high concentrations in the human retina, where they efficiently protect against oxidative stress that may lead to retinal damage. In addition, macular xanthophylls are uniquely spatially distributed in the retina. The zeaxanthin concentration (including the lutein metabolite meso-zeaxanthin) is ~9-fold greater than lutein concentration in the central fovea. These numbers do not correlate at all with the dietary intake of xanthophylls, for which there is a dietary zeaxanthin-to-lutein molar ratio of 1:12 to 1:5. The unique spatial distributions of macular xanthophylls—lutein, zeaxanthin, and meso-zeaxanthin—in the retina, which developed during evolution, maximize the protection of the retina provided by these xanthophylls. We will correlate the differences in the spatial distributions of macular xanthophylls with their different antioxidant activities in the retina. Can the major protective function of macular xanthophylls in the retina, namely antioxidant actions, explain their evolutionarily determined, unique spatial distributions? In this review, we will address this question.

Light-Modulated Sunscreen Mechanism in the Retina of the Human Eye

“…Besides, retinal tissues are highly vascularized, resulting in relatively high molecular oxygen partial pressure, which further increases the risk of photooxidative damage. The macular xanthophylls were shown to be potent antioxidants, protecting membranes through combined activity of different molecular mechanisms: physical quenching of singlet oxygen, modification of structural and dynamic properties of lipid bilayers, and sacrificial chemical reactions leading to the pigment oxidation. ,− An important aspect of the photoprotective activity of xanthophylls in the macula lutea is the ability to filter out the short-wavelength radiation due to the high molecular extinction coefficients of this group of pigments. , The most plausible physiological role of this mechanism is to enable color and high-acuity vision at dim light while protecting photoreceptors against photodamage at high light. Using an analogy to the macro-scale, we like to refer to this mechanism as “molecular blinds” (Figure ).…”

“…Photooxidative damage of biomolecules in the retina is recognized as one of the leading causes of AMD . Despite a general agreement regarding the protective activity of the macular xanthophylls against photodegradation, ,− the specific molecular mechanisms involved in this activity in the retina are still not fully understood. In the present work, we address this problem both in the human retina and in the model membrane systems, providing a multiangle picture in which xanthophyll chromatography and molecular simulations complement the insights from spectroscopic imaging techniques based on time-resolved fluorescence and resonance Raman scattering.…”

Coenzyme Q10 in the eye isomerizes by sunlight irradiation

“…Macular xanthophylls are well-known to prevent retinal photodamage by absorbing the blue light and removing the reactive oxygen species 44 . In addition, it has been shown that CoQ10 protects several parts of the eyes from light-induced damage.…”

Natural Antioxidant Evaluation: A Review of Detection Methods

“…Usually, carotenoids are located inside cell membranes as highly lipophilic molecules. While strict hydrocarbons, such as lycopene or β-carotene, are arranged exclusively in the inner part of the lipid bilayer, molecules with a more polar configuration containing oxygen atoms attached (like lutein or zeaxanthin) are oriented roughly perpendicular to the membrane surface with their hydrophilic parts oriented to the aqueous environment [ 29 , 30 ].…”