Spinach could offer new hope for the blind

SPINACH, TOUTED in the Popeye cartoon for its ability to strengthen the body, may prove even more valuable for restoring vision to people who are legally blind.

Researchers at the Department of Energy's Oak Ridge National Laboratory and the University of Southern California hope to learn whether a protein from spinach could replace a non- functioning light receptor in the eye.

``Although the neural wiring from the eye to brain is intact in people with these diseases, their eyes lack photoreceptor activity,''said Eli Greenbaum of ORNL's Chemical Technology Division. Greenbaum and colleagues propose replacing these non- functioning photoreceptors with a spinach protein that gives off a small electrical voltage after capturing the energy of incoming photons.

The main function of Photosystem I, a photosynthetic reaction centre protein, is to perform photosynthesis in leaves using the energy of the sun to make plant tissue.

Greenbaum's collaborator is Mark Humayun, a professor in the University of Southern California's Doheny Eye Institute. Humayun and his research team showed that if retinal tissue is stimulated electrically using pinhead- sized electrodes implanted in the eyes of legally blind patients, many can see image patterns that mimic the effects of stimulation by light. Greenbaum believes that it might be possible to use Photosystem I protein to restore photoreceptor activity.

Experiments by Greenbaum's team showed that Photosystem I protein can capture photon energy and generate electric voltages of up to 1 volt. ``What we need to find out is whether these voltages can trigger neural events and allow the brain to interpret the images,'' Greenbaum said.

In recent research, the team showed that Photosystem I reaction centres protein could be incorporated into the membrane of an artificial liposome, a tiny spherical particle formed by a fatty (lipid) membrane enclosing a watery compartment. Artificial membrane mimics that of a living cell.

Greenbaum's team also showed that the Photosystem I reaction centres can work inside a liposome, which means it produces the experimental equivalent of a voltage when it comes into contact with light.

A liposome will likely be used to deliver Photosystem I reaction centres protein to a retinal cell. Retinitis pigmentosa is an inherited condition of the retina in which specific photoreceptor cells, called rods, degenerate.

The loss of function of these rod cells diminishes a person's ability to see in dim light and gradually can reduce peripheral vision.

Age-related macular degeneration is a disease that affects the centre of vision. It rarely leads to blindness but people with the disease have difficulty reading, driving and performing other activities that require fine, sharp straight-ahead vision. The disease affects the macula- centre of the retina.

The project builds upon work using the technique of Kelvin force microscopy, in which Greenbaum and his team performed the first measurements of voltages induced by photons of light from single photosynthetic reaction centres.

The work was published in the Journal of Physical Chemistry.

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