Magazine article Drug Topics

Researchers Try New Angle in Treatment of Glaucoma

Magazine article Drug Topics

Researchers Try New Angle in Treatment of Glaucoma

Article excerpt

The diuretic ethacrynic acid is being revived as a possible treatment for glaucoma. Unlike current therapies, which affect either the flow or production of fluid in the eye, the drug targets a cellular network that serves as a sort of drainage system.

Normally, aqueous humor, a liquid substance manufactured in the eye, makes its way though a web of cells between the cornea and the iris, to a structure known as Schlemm's canal. From there, it is ultimately carried to the bloodstream.

In glaucoma, that web, called the trabecular meshwork, becomes somewhat impassable. Fluid is trapped, and pressure climbs within the eye, causing permanent injury to the optic nerve. Left unchecked, the disease will lead to blindness.

The best analogy is really to the kitchen sink and the drain," David Epstein, professor and chairman of ophthalmology at Duke University Medical Center, told Drug Topics. "In the most common kind, open-angle glaucoma, there's something deep down within the drain that you can't see that's impairing the drainage of fluid. In angle-closure glaucoma, it would be as if there were a plate floating around in the water in the sink, and the plate could come over the top of the drain and prevent access to it."

While there are some 40 different kinds of glaucoma, each type can be sorted into one of the two main categories, Epstein said. In the early stages, he added, angle-closure glaucoma can be cured by making an opening with a laser in the iris or plate" portion of the eye. Open-angle varieties are managed with chronic drug therapy.

Each of the agents used now offers a "very nonspecific type of remedy," Epstein remarked. "They cut down the inflow of fluid into the eye. But we know that glaucoma is not a disease of making too much fluid." With ethacrynic acid, researchers are, for the first time, going after a drug that's directed at the diseased tissue, he said.

Epstein, who first identified ethacrynic acid's potential value in glaucoma therapy, explained that the drug seems to exert two use effects on the trabecular meshwork. In some forms of open-angle glaucoma, he said, extracellular materials clog the tissue. Ethacrynic acid causes the cells in the network to change shape, allowing the matter to be flushed out.

"The other thing with this medication is that it makes the cells in the 'drain' more permeable," Epstein said. …

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