Zeaxanthin and Lutein: Photoprotectors, Anti-Inflammatories, and Brain Food

Abstract

This review compares and contrasts the role of carotenoids across the taxa of life-with a focus on the xanthophyll zeaxanthin (and its structural isomer lutein) in plants and humans. Xanthophylls' multiple protective roles are summarized, with attention to the similarities and differences in the roles of zeaxanthin and lutein in plants versus animals, as well as the role of meso-zeaxanthin in humans. Detail is provided on the unique control of zeaxanthin function in photosynthesis, that results in its limited availability in leafy vegetables and the human diet. The question of an optimal dietary antioxidant supply is evaluated in the context of the dual roles of both oxidants and antioxidants, in all vital functions of living organisms, and the profound impact of individual and environmental context.

Keywords: chronic inflammation; macular degeneration; meso-zeaxanthin; photosynthesis; radiation; redox regulation; signaling; thermal dissipation; vision; xanthophyll cycle.

Figure 1

Biosynthetic pathways for the formation of zeaxanthin, lutein, and meso-zeaxanthin. Pathways existing in plants only, area shaded in green only; pathways existing in both plants and cyanobacteria, area shaded in both green and blue; pathways existing in humans, area shaded in purple only; need for dietary acquisition of β-carotene, zeaxanthin, and lutein by humans, overlapping purple and green/blue areas. A, antheraxanthin, a zeaxanthin mono-epoxide; V, violaxanthin, a zeaxanthin di-epoxide.

Figure 2

Schematic depiction of the localization of carotenoids, vitamin E (tocopherol), and cholesterol in biological membranes. Moreover, β-carotene, zeaxanthin, lutein, and tocopherols dissolve in the phospholipid biolayer of the membranes of both plants and humans/animals; cholesterol only occurs in animal membranes. In addition, binding of carotenoids to multiple components of light-collecting, chlorophyll-binding proteins in the photosynthetic membrane of plants (green oval) and of zeaxanthin and meso-zeaxanthin to a protein in the retinal membrane of humans (purple oval) is shown. A, antheraxanthin; V, violaxanthin.

Figure 3

Schematic depiction of changes over the course of a clear day in (A) the fraction of light absorbed by a sun-exposed leaf that goes into photosynthesis (green), is dissipated harmlessly as heat (red), and is used by neither of the latter pathways (remainder; white). (B) shows corresponding changes in the level of the xanthophylls of the xanthophyll cycle, as well as the unchanged levels of lutein and β-carotene. Based on field data from evergreen shrubs reported in Adams et al. [18] and Demmig-Adams et al. [19]

Figure 4

Schematic depiction of the proportion of reactive oxygen (ROS) and antioxidants produced across environmental gradients for the example of exercise intensity in humans and light intensity in plants.