A new ultrasound technique uses microbubbles and focused sound waves to help chemo medication sneak past the the stubborn blood-brain barrier. Developed by Canadian surgeons, the technique could eventually be used to treat such conditions as Alzheimer's and depression.
The blood-brain barrier (BBB) protects the brain from all sorts of nasty things, like disruptive hormones, neurotransmitters, and foreign substances. Unfortunately, this same barrier also prevents doctors from using the bloodstream as a conduit for delivering essential medicines.
Artist's impression of the blood-brain barrier (Credit: University of Alberta)
Last year, doctors from Pitié-Salpêtrière Hospital in Paris were the first to use an innovative technique in which microbubbles were used to open a rift in the BBB with ultrasound waves. This surgery was used on patients with glioblastoma — an aggressive type of brain tumour — to deliver chemotherapy drugs directly into the brain. The technique, though promising, wasn't very targeted, and it required an ultrasound inducer to be implanted into the skull during surgery.
The revised technique, developed by Dr. Todd Mainprize, Dr. Kullervo Hynynen, and their team at Sunnybrook Hospital in Toronto, is very similar to the one developed in Europe, but it's more targeted and much less invasive.
The procedure involves three steps. The first is the introduction of the chemotherapy medication liposomal doxorubicin into the patient's bloodstream. For the second stage, tiny air bubbles, or microbubbles, are intravenously delivered into the patient's bloodstream. Then, after using MRI scanners to locate the target area, a focused beam of ultrasound is used to expand the microbubbles within the brain's capillaries. This creates tiny tears in the cellular sheath of the BBB, allowing the chemo to seep through the barrier and into the targeted neural areas.
The bubbles themselves do not cross the BBB, and are eventually absorbed in the lungs. As for the tiny fissures in the barrier, they heal and close up in as little as 8 to 12 hours. The procedure was performed last week for the very first time on a 56-year-old female patient with a brain tumour.
"Our surgery was done in a highly focused and precise fashion," Mainprize told Gizmodo. What's more, "it did not require a surgical craniotomy upfront and was minimally invasive."
The next day, doctors performed traditional surgery on the patient to remove the tumour. It will be carefully analysed to determine how much of the chemo effectively passed through the BBB. The team is planning on replicating this process nine more times before formally publishing their results.
In the future, such a technique could be used to deliver new chemicals and therapies for depression, Alzheimer's disease, and even stem cells.
"With...this technique, you can selectively open almost anywhere in the brain and deliver whatever you want," noted Mainprize in a Globe & Mail article. "Essentially, whatever you can think of is a potential study that may help in the future."