Protein Discovered Protects From Macular Degeneration

Scientists have identified a protein responsible for transporting nutrients such as Lutein and Zeaxanthin to the eye, and believe that these nutrients protect against macular degeneration. Light sensitive tissue in the macula at the back of the eye responsible for sending signals to the brain gradually die or are damaged, depending on the type of macular degeneration a person has.

The nutrients Lutein and Zeaxanthin are thought to move along the bloodstream to the eye, but exactly how this occurs was unknown.

Lutien and Zeaxanthin are known as xanthophylls, and have been shown in previous studies to have certain properties that can lower the risk of macular degeneration. These two nutrients are not made by the body and must be obtained directly through diet. Leafy green vegetables such as kale, spinach, brocolli, zucchine and peas, as well as yellow or orange fruits such as carrots, squash and peaches contain high amounts of Lutein and Zeaxanthin.

The study which appears in the August 2008 issue of the Journal of Lipid Rsearch, has shown that a protein known as SR-B1, plays a role in transporting Lutein and Zeaxanthin from the bloodstream into the cells in the eye.

According to Earl Harrison, Dean’s Distinguished Professor and chair of human nutrition at the Ohio State University, “Our research to understand this mechanism might provide a greater appreciation for how one could intervene to possibly slow macular degeneration.”

In the United States alone, there are an estimated 10 million people with macular degeneration, and depending on whether a person has wet macular degeneration or dry macular degeneration, treatment options can slow vision loss, but does not have the ability to restore vision.

Xantophylls are a class of carotenoids and have the ability to absorb blue light. These also act as antioxidants in the body.

Previous studies have suggested that these two nutrients might provide protection from macular degeneration because of the ability of Lutein and Zeaxanthin to fliter the damaging blue light and their strong antioxidant properties.

Xantophylls have been shown to accumulate in the retina and form yellow spots known as macular pigments. Such concentrations have been observed and associated with a lower risk of macular degeneration, but how these nutrients protect the eye is unknown.

Previous research by Harrison and his colleagues had shown that SR-B1 was involved when Lutein and Zeaxanthin were digested, and they believed that the same protein may be involved with transporting the nutrients to the eye. Working with a line of human retinal pigment epithelial cells that line the retina, researchers introduced three types of carotenoids – Lutein, Zeaxanthin and beta carotene. As expected, the retinal pigment epithelial cells absorbed more of the xanthophylls than the beta carotene.

By blocking the SR-B1 protein using two different methods, researchers showed that the cells’ absorbtion of the two xanthophylls was reduced by 41 percent and 87 percent compared to absorption when SR-B1 was not blocked.

“It’s fairly safe to say that if you inhibit this transporter, you inhibit the uptake of xanthophylls. So that certainly suggests that this transporter is involved in that process,” Harrison said.

This research was supported by grants from the National Institutes of Health.