WASHINGTON U. – ST. LOUIS (US) — Drugs prescribed to lower cholesterol may also be effective against age-related macular degeneration, the leading cause of vision loss in Americans over the age of 50.
New research finds the eye disease shares a common link with atherosclerosis—both problems have the same underlying defect: the inability to remove a buildup of fat and cholesterol.
Working in mice and in human cells, researchers shed new light on how deposits of cholesterol contribute to macular degeneration and atherosclerosis and even blood vessel growth in some types of cancer.
Patients who have atherosclerosis often are prescribed medications to lower cholesterol and keep arteries clear. The new study suggests that some of those same drugs could be evaluated in patients with macular degeneration.
“Based on our findings, we need to investigate whether vision loss caused by macular degeneration could be prevented with cholesterol-lowering eye drops or other medications that might prevent the buildup of lipids beneath the retina,” says senior investigator Rajendra S. Apte, professor of ophthalmology and visual sciences at Washington University in St. Louis.
Published in the journal Cell Metabolism, the new research centers on macrophages, key immune cells that remove cholesterol and fats from tissues. In macular degeneration, the excessive buildup of cholesterol begins to occur as we age, and our macrophages begin to malfunction.
In the “dry” form of age-related macular degeneration, doctors examining the eye can see lipid deposits beneath the retina. As those deposits become larger and more numerous, they slowly begin to destroy the central part of the eye, interfering with the vision needed to read a book or drive a car.
As aging macrophages clear fewer fat deposits beneath the retina, the macrophage cells themselves can become bloated with cholesterol, creating an inflammatory process that leads to the formation of new blood vessels that can cause further damage. Those vessels characterize the later “wet” form of the disease.
“Ultimately, that inflammation creates a toxic mix of things that leads to new blood vessel growth,” Apte says. “Most of the vision loss from ‘wet’ macular degeneration is the result of bleeding and scar-tissue formation related to abnormal vessel growth.”
As part of their research, scientists identified a protein that macrophages need to clear fats and cholesterol. As mice and humans age, they make less of the protein, and macrophages become less effective at engulfing and removing fat and cholesterol.
Apte and colleagues found that macrophages, from old mice and in patients with macular degeneration, have inadequate levels of the protein, called ABCA1, which transports cholesterol out of cells. As a result, the old macrophages accumulated high levels of cholesterol and couldn’t inhibit the growth of the damaging blood vessels that characterize the “wet” form of the disorder.
But when the researchers treated the macrophages with a substance that helped restore levels of ABCA1, the cells could remove cholesterol more effectively, and the development of new blood vessels was slowed.
“We were able to deliver the drug, called an LXR agonist, in eye drops,” says first author Abdoulaye Sene, PhD, a postdoctoral fellow in the Apte lab. “And we found that we could reverse the macular degeneration in the eye of an old mouse. That’s exciting because if we could use eye drops to deliver drugs that fight macular degeneration, we could focus therapy only on the eyes, and we likely could limit the side effects of drugs taken orally.”
Since macrophages are important in atherosclerosis and in the formation of new blood vessels around certain types of cancerous tumors, the same pathway also might provide a target for more effective therapies for those diseases, the researchers say.
“We have shown that we can reverse the disease cascade in mice by improving macrophage function, either with eye drops or with systemic treatments,” Apte says. “Some of the therapies already being used to treat atherosclerosis target this same pathway, so we may be able to modify drugs that already are available and use them to deliver treatment to the eye.”