The so-called focused ones, with low intensity, they have already been successfully tested in several clinical studies to make the blood-brain barrier permeable to drugs
In our brain there is a kind of palisade. It’s called the blood-brain barrier. It means that here, in the nervous tissue, the carpet of cells that lines the internal surface of the blood capillaries is so thick and tight as to allow the diffusion of only a few, selected substances. Nature has devised such a device for prevent potentially toxic molecules circulating in the blood from leaking from the vessels and damaging the neurons
. The other side of the coin? that this rigid barrier hinders the profession of doctors, because the drugs intended to treat brain tumors and neurodegenerative pathologies may be unable to cross the blockade and reach their destination.
Widen the meshes of the net
One possibility to work around this problem is represented by ultrasounds, which have been shown to be able to widen the meshes of this compact cellular network, as needed and in a highly selective way. And they could, in the near future, in selected cases, facilitate the therapy of various conditions: from tumors to Alzheimer’s, from stroke to depression. One of the main references of these innovative applications Francesco Prada, neurosurgeon at the Carlo Besta Neurological Institute in Milan where he is director of the Acoustic Neuro-Imaging and Therapy Lab (ANTY-Lab). The ultrasounds in question are defined as focused, the researcher intervenes, and they are already being exploited, at high intensity, to produce targeted lesions, like a scalpel
. They are used and are approved to treat movement disorders, and also studied for psychiatric disorders and epilepsy.
The advantages
The target is perfectly visualized and framed by the magnetic resonance and the ultrasound beams emitted by a helmet, in the center of which is the patient’s head, are conveyed to this precise point. The advantages are obvious: the heated and destroyed area without invasive manoeuvressurgical incisions or deep instrument insertions. And therefore preserving the surrounding tissues. But, as we said, focused ultrasound can not only destroy pathological tissue: at low intensity they also know how to make the blood-brain barrier permeable.
Different methods of hitting the target
Ultrasounds on the brain are focused in different ways. In addition to the helmet that spreads the beams while the patient is on the magnetic resonance bed, there is an alternative, says Francesco Prada, the neuronavigation: a three-dimensional reconstruction of the neuro-anatomical images is carried out and then we pilot the ultrasounds with an external probe. A third implantable method. In someone undergoing surgery (for example, to remove a brain tumor), a temporary window is created on the head: a piece of bone is removed and in some cases we attach the wave emitter to the skull, activated when you have to open the barrier for healing. The window can be left open, replacing the bone plug with a plastic inlay, through which the ultrasounds are then transmitted. The first three strategies have already been tested with positive results in various clinical studies.
Engineered microbubbles
This effect can be amplified by inoculating a solution based on engineered microbubbles, consisting of a shell of phospholipids enclosing a gas: with the subsequent emission of the ultrasounds, the microscopic spheres focally affected by the ultrasounds “stir” and the vibration temporarily opens the locks, so to speak, of the barrier. Prada has established a solid collaboration with various research groups thanks to the support of Focused Ultrasound Foundation, a reality created in 2006 in Charlottesville, Virginia, to accelerate the application of the revolutionary focused ultrasound in the world. Research in the sector is covering different fronts. In Canada and France the opening of the barrier is studied in patients with Alzheimer’s disease, in Spain for tissue regeneration in Parkinson’s, in the United States ultrasound is used to treat drug addiction and treat adult brain tumors (and, in England, in children), and again in France, the aim is to alleviate depression in this way. These are preliminary results, but certainly encouraging.
April 9, 2023 (change April 9, 2023 | 09:42)
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