Drug could mean fewer needle sticks in eye
JOHNS HOPKINS (US) — A new drug encased in a two-layer, time-release coating may mean far fewer injections to the eye for patients with “wet” age-related macular degeneration.
Biomedical engineers teamed up with clinicians to create the new drug-delivery strategy for wet AMD, a type of central vision loss caused by blood vessel growth at the back of the eye, where such growth should not occur.
If proven effective in humans, the technique could mean only two or three injections in the eye each year instead of shots as often as once a month. So far, the procedure has only been tested in mice with abnormalities similar to those in people with what is formally known as neovascular AMD.
“The frequent visits for injections are a burden and each injection carries a small risk of infection, so one of our goals is to find new approaches that allow for fewer visits and injections,” says Peter Campochiaro. (Credit: Jonathan Bennett/Flickr)
“If you lose central vision, you can’t drive a car and you can’t see your grandchildren,” says Jordan Green, assistant professor of biomedical engineering and ophthalmology at Johns Hopkins University. “You’re willing to do what it takes to keep your sight.
“We hope that our system will work in people and make invasive treatments much less frequent, and, therefore, easier to comply with, and safer.”
The study is currently available online and will be published in the October issue of the journal Biomaterials.
About 200,000 Americans suffer from central vision loss caused by wet AMD, says Peter Campochiaro, professor of ophthalmology and neuroscience.
The macula is a few square centimeters of tissue in the center of the retina at the back of the eye. It is responsible for the majority of a person’s high-resolution vision, especially the high-res vision needed for driving and reading.
There are normally no blood vessels in the outer part of the retina because it needs to be unobstructed to capture complete images. In patients with wet AMD, blood vessels from behind the retina can break through into the macula and leak fluid that reduces vision. This loss is initially reversible, but, if left untreated, becomes permanent.
Currently, wet AMD patients are treated with frequent injections into the eye of a drug that blocks one of the major stimulators of abnormal blood vessel growth.
“Patients are given localized antibacterial and pain-numbing agents, and then a very fine needle is passed through the white of the eye into the central cavity where the drug is injected. It’s not painful, but it isn’t something that patients enjoy,” Campochiaro says.
“The frequent visits for injections are a burden and each injection carries a small risk of infection, so one of our goals is to find new approaches that allow for fewer visits and injections.”
Green’s laboratory, which specializes in designing new drug-delivery systems, worked with Campochiaro and Aleksander Popel, professor of biomedical engineering. Popel’s lab discovered the new drug, a short piece of protein that blocks the growth of unwanted blood vessels.
When injected into the eyes of mice with abnormal blood vessels like those seen in wet AMD, the drug was only effective for about four weeks since the watery contents inside the eye gradually flushed it out.
The team’s solution, Green says, was to slow the release and depletion of the drug by covering it in nontoxic biodegradable coatings. They first created “nanoparticles,” tiny little spheres filled with the drug. When the spheres are placed in a watery environment, the water gradually breaks down the coating and releases the drug a little at a time.
Gumball ice cream
To maximize this effect, the team created larger spheres, called microparticles, filled with about a hundred nanoparticles per microparticle, and held together by another type of biodegradable “glue.”
The end result is something like a scoop of gumball ice cream. As the ice cream “glue” gets licked away, more and more “gumballs” (nanoparticles) are exposed.
The microparticle-encased drug persisted in mice eyes for at least 14 weeks, more than three times as long as the current treatment. The treatments may last longer in humans than in mice, but clinical trials will not begin before further testing in other animals.
(Drugs now used to treat wet AMD are longer protein pieces or full-length proteins that could become inactive if given a biodegradable coating.)
The National Eye Institute, the Wallace H. Coulter Foundation, and the Edward N. and Della L. Thome Memorial Foundation supported the research.
Source: Johns Hopkins University
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