An antibiotic commonly used to treat acne may help slow or prevent the vision loss frequently associated with diabetes, a new study suggests.

Researchers found that rats treated with the antibiotic minocycline had about 50 percent less diabetes-induced damage to the retina -- the nerves in the back part of the eye that respond to light.

If further tests confirm these findings in humans, researchers say it may offer a new way to prevent diabetic retinopathy, a complication of diabetes that is the leading cause of blindness in people aged 20 to 74.

"Our studies in rats suggest that this antibiotic may be a strong candidate for further consideration as a therapeutic drug in reducing the retinal complications of diabetes," says researcher Kyle Krady, PhD, assistant professor of neural and behavioral sciences at Penn State College of Medicine, in a news release.

New Target in Diabetic Retinopathy

In the study, which appears in the May issue of the journal Diabetes, researchers looked at the role of microglia in diabetes-related blindness. Microglia are cells released by the central nervous system that destroy damaged cells by surrounding them and releasing a stream of toxins.

Researchers say previous studies have shown that changes that occur in diabetes cause the body to increase the production of inflammatory proteins called cytokines, which may damage nerves.

In this study, researchers showed that in rats with early diabetes, elevated levels of cytokines activate the microglia, leading to nerve cell death. Their results suggest that it's this nerve cell death that causes the vision loss associated with diabetic retinopathy.

In diabetic patients, inflammatory protein levels in the eye correlate with the degree of eye damage.

Antibiotic May Fight Blindness

Researchers compared the levels of cytokines in the retinas of healthy rats to rats with diabetes. They found there were four to six times higher levels of cytokines in the retinas of diabetic rats compared with healthy ones.

The researchers then treated the diabetic rats with the antibiotic and measured the levels of cytokines after treatment. Treatment with the antibiotic reduced the production of the inflammatory protein.

The results showed that minocycline reduced inflammation in the retina caused by the cytokines.

This in turn reduced the activation of microglia and prevented nerve cell death.

Researchers say this study shows that diabetes causes an increase in the production of inflammation-causing agents and treatment with the antibiotic minocycline appears to stop this inflammatory process.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Krady, K. Diabetes, May 2005; vol 54: pp 1559-1565. News release, Penn State College of Medicine.