Lutein & Zeaxanthin Protect Lens Cells from Oxidative Damage

Background: Lutein, Zeaxanthin & Cataract

Epidemiologic studies indicate that high dietary intake or blood levels of lutein or zeaxanthin may decrease the risk of cataract. The most recent study reports that subjects with the highest plasma concentrations of lutein and zeaxanthin had 42% and 41% lower risk of nuclear cataract, respectively (see EduFacts Vol 13, No 5).

Lutein and zeaxanthin are the only carotenoids detected in the lens. While their role in the lens and the mechanism by which they may reduce the risk for cataract aren’t fully understood, it has been proposed that the benefit of these two carotenoids is related, at least in part, to their antioxidant properties.

Oxidative stress is, in fact, a major risk factor for age-related cataract, particularly nuclear cataract. One of the major oxidants in the lens and aqueous humor is H₂0₂ (hydrogen peroxide), and levels of H₂0₂ in the aqueous humor of those with cataracts have been shown to be higher than in the aqueous humor of normal individuals.

In a recently published study, researchers from Tufts University and Sun Yat-sen University in China used cultured lens epithelial cells exposed to H₂0₂ as a model system to study the effects of supplemental lutein or zeaxanthin on oxidative damage, and their interaction with intracellular glutathione – an antioxidant enzyme that prevents damage by peroxides.

Study Design

Human lens epithelial cells were pre-incubated with or without 5 μM lutein, zeaxanthin, or α-tocopherol for 48 hours, and then exposed to 100 μM H₂0₂ for 1 hour. Alpha tocopherol ( vitamin E) was used as a positive control because the same researchers previously demonstrated that adding α-tocopherol to cultured rabbit lens epithelial cells can improve cellular redox status and restore the resistance of glutathione-depleted cells to H₂0₂. Markers of damage to proteins (protein carbonyls), lipids (maldonaldehyde) and DNA (damaged nuclei), were assessed by western-blotting analysis, HPLC, and comet assay, respectively. Glutathione (reduced and oxidized) were measured by HPLC.

Results

Exposure of the lens cells to H₂0₂ significantly increased levels of oxidized proteins, lipid peroxidation, and DNA damage. Pre-incubation with lutein, zeaxanthin, or α-tocopherol dramatically reduced the levels of H₂0₂ -induced protein carbonyl, MDA, and DNA damage.

The addition of lutein, zeaxanthin, or α-tocopherol increased glutathione levels and the ratio of reduced to oxidized glutathione, particularly in response to oxidative stress. Alpha tocopherol, but not lutein or zeaxanthin, partially restored the resistance of glutathione-depleted cells to H₂0₂.

Figure courtesy of Molecular Vision

Figure 5. Supplementation with lutein, zeaxanthin or α-tocopherol suppressed H2O2-induced DNA damage in human lens epithelial cells (HLEC). Subconfluent HLEC were incubated with or without 5 μM of lutein, zeaxanthin or α-tocopherol for 48 h and then exposed to 100 μM H2O2 for 1 h. A: Fluorescence micrograph of nuclei of normal HLEC. B: Fluorescence micrograph of nuclei of oxidative insulted HLEC.

Comment

These findings imply that sufficient intake of lutein and zeaxanthin may reduce the risk for senile cataract via protecting the lens from oxidative damage. They also suggest that vitamin E is important in protecting lens cells when glutathione levels are depleted.

References

1. Gao S, et al. Lutein and zeaxanthin supplementation reduces H202-induced oxidative damage in human lens epithelial cells. Mol Vis 17:3180-90, Dec, 2011.