Vibrating Micro-Bubbles Let Drugs Sneak Across the Blood-Brain Barrier

Ultrasound technology and micro-bubbles together have pried open one of the most resistant barriers in the body

brain MRI
MRI scan of a brain Larry Mulvehill/Corbis

In the late 19th century, a bacteriologist exploring the intricacies of biology found that if he injected a colored dye into the bloodstream of an animal, all the tissues of the body were stained that same color. All except for the brain, that is. The researcher, Paul Ehrlich, had just observed the effects of something called the blood-brain barrier.

This barrier is important. It protects the brain and spinal cord from toxins, viruses and bacteria that have breached the body. But it also keeps out medicines we’d like to use to treat disease in the brain.

Until now, because researchers have figured out how to pry open that barrier on demand using sound waves, reports Helen Thompson for New Scientist. First, the researchers inject microbubbles into the patient and then they switch on an implanted ultrasound device. "When ultrasound waves meet micro-bubbles in the blood, they make the bubbles vibrate," Thompson writes. "This pushes apart the cells of the [blood-brain barrier]."

Brain tumors make the barrier leaky and this lets small amounts of chemotherapy drugs through, Michael Cannery, of Paris-based medical start-up CarThera, told New Scientist. If more drug could slip between the cracks created by their technology, treatments might work better. 

The experimental trial just started in July, and results aren’t ready yet. However, the scientists involved did see a marker chemical injected with the micro-bubbles crossing the barrier in MRI scans. Other groups are also testing the same idea.

This isn’t the first time ultrasound has been used to do more than peek at unborn babies. A meeting at Stanford University earlier this month showcased the ultrasound in medicine. Sara Wykes for the Stanford Medicine News Center writes:

Since the 1970s, however, ultrasound has become, quietly and steadily, the Swiss Army knife of health care, with an ever-expanding repertoire of functions, based on the ability of sound waves to travel through the body and bounce back when they hit something. Now the technology has been developed into a high-resolution, often pocket-sized aid for the diagnosis and treatment of many types of injuries and medical conditions.

Ultrasound has been wielded to get quick, relatively inexpensive answers to patients in emergency care and during surgery. The air-filled spaces of the lungs have been hard to image, but in diseases where the lungs fill with fluids, such as pneumonia and cystic fibrosis, ultrasound can be more accurate than X-rays and faster than CT scans.

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