A new study using mice suggests that carefully timed pulses of ultrasound waves could dramatically improve survival rates after a type of stroke known as a hemorrhagic stroke. This approach, which enhances the brain’s natural cleansing mechanisms, might also hold promise for treating Alzheimer’s disease in the future.
Hemorrhagic strokes occur when a blood vessel within the brain bursts, disrupting oxygen flow and damaging brain cells. These strokes account for about 15% of all strokes, often leading to debilitating movement and cognitive impairments. Current treatment typically involves sealing the ruptured blood vessel with a small metal clip followed by removing dead red blood cells from the brain. This process is often invasive, carrying risks such as further brain damage and infection.
Dr. Raag Airan at Stanford University wondered if ultrasound could offer a less invasive solution. While experimenting with ultrasound-activated drugs in mice brains, he accidentally left the device on for longer than intended. What he observed was surprising: instead of remaining localized, the drug seemed to spread throughout the brain, carried by cerebrospinal fluid – the very fluid responsible for clearing waste from the brain.
This serendipitous discovery sparked an idea: could ultrasound be used to actively clear debris from the brain?
To test this theory, Airan’s team induced hemorrhagic stroke-like conditions in mice by injecting their own blood into their brains. Half of the mice received daily 10-minute pulses of ultrasound for three days; the other half served as a control group. Three days later, the researchers tested both groups using a behavioral test that assessed motor function and cognitive abilities.
Mice treated with ultrasound showed significantly improved performance compared to the untreated group. They turned more consistently in all directions within a tank and demonstrated stronger grip strength – clear indicators of reduced brain damage. These findings were confirmed when scientists examined slices of their brains after euthanasia, revealing less tissue damage in the ultrasound-treated mice.
Importantly, survival rates also differed dramatically: by one week after the initial blood injection, half of the untreated mice had died, while only a fifth of those treated with ultrasound had succumbed to the stroke-like condition. This translated to a 30% increase in survival thanks to just three brief ultrasound sessions.
Further investigation revealed that ultrasound pulses activated pressure-sensitive proteins on microglia – the brain’s resident immune cells. This activation reduced inflammation and boosted the microglia’s ability to engulf and eliminate dead red blood cells. Additionally, the ultrasound enhanced cerebrospinal fluid flow through the brain, further aiding in clearing cellular debris to lymph nodes in the neck where waste is processed.
The implications of this research extend beyond hemorrhagic stroke. Dr. Airan believes that if ultrasound can effectively remove relatively large dead red blood cells from the brain, it could potentially clear smaller toxic proteins implicated in neurodegenerative diseases like Alzheimer’s and Parkinson’s. Dr. Kathleen Caron at the University of North Carolina at Chapel Hill shares this optimism.
While human trials are still underway, early results indicate that ultrasound exposure is safe, minimizing concerns about unexpected side effects. The team plans to begin a trial with people diagnosed with Alzheimer’s disease next year due to the less urgent need for immediate treatment compared to hemorrhagic stroke victims.
If successful, this non-invasive approach could revolutionize the treatment of stroke and potentially reshape the landscape of neurodegenerative diseases.
