Ultrasound focused on lipid-skinned “bubbles” could be used to deliver potent drugs to some parts of the brain without disturbing others, say US researchers. The technique works by making a tiny hole in the blood brain barrier – the membrane that usually prevents large molecules from crossing from the bloodstream into the brain.
The blood-brain barrier prevents researchers from using big molecules to treat a range of brain disorders, including Alzheimer’s, Parkinson’s, epilepsy and schizophrenia. But because different parts of the brain have very different functions, small molecules meant for one area can cause unwanted side-effects in another.
Researchers at Brigham and Women’s Hospital in Boston wondered whether they could breach the blood brain barrier by focusing ultrasound to a discrete point. As part of their experiments, they injected rabbits with a stream of lipid-skinned bubbles containing saline. These bubbles are conventionally used to improve the quality of magnetic resonance images.
To their delight, the team found that a low power ultrasound beam could vibrate and pop any bubble it was focused on, leaving a tiny hole in the blood brain barrier. The hole repaired within a couple of days and there was no collateral damage, says Kullervo Hynynen, who led the research.
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Other researchers say the work is especially exciting because the bubbles are already approved for use in people by the US Food and Drug Administration.
Marc Mayberg, who leads a group researching the science of the blood brain barrier at the Cleveland Clinic Foundation in Ohio, says the new technology is very likely to have clinical applications. “There’s currently no way to deliver drugs to a small volume of the brain without an invasive injection,” he says.
Ferenc Jolesz of the Brigham and Women’s Hospital says the bubbles could be filled with any drug. This drug would then be released directly into the brain through the hole made when the bubble pops. This could deliver a discrete dose that wouldn’t spread to other parts of the brain.
“The drug molecules become less concentrated as it diffuses out,” Jolesz says. He’s currently working on the idea of delivering tiny doses of a toxin to the malfunctioning neurons that cause epilepsy without killing other healthy neurons.
The team presented their research at the Acoustical Society of America’s annual meeting in Fort Lauderdale, Florida.
