Medical ultrasound can help to rid the brain of the toxic protein that builds up to cause Alzheimer's Disease, research from Australia has shown.
With 40 million people worldwide currently affected by Alzheimer's, and the number of affected individuals expected to triple in the next 50 years as the world population ages, finding a way to halt or even reverse the debilitating symptoms of this dementing disease is a major priority.
Alzheimer's is caused by the accumulation in the brain of a protein called beta-amyloid, which builds up to form aggregates called plaques that are toxic to nerve cells. This leads to a progressive loss of mental faculties, robbing victims of their memory and independence and ultimately leaves patients fully dependent on others to care for them. The only treatments currently available for the condition tackle some of the symptoms but do not halt the progression of the disease itselt.
Instead, scientists speculate that reducing the build up of beta-amyloid in the brain is one way to achieve this. Previous attempts to do this have included developing a vaccine to immunise individuals against their own beta-amyloid, but these had to be abandoned when patients in a clinical trial developed signs of inflammation in their nervous systems.
Now University of Queensland researchers Gerhard Leinenga and Jurgen Gotz, writing in Science Translational Medicine, have shown that a simple medical ultrasound might be all that's needed to reverse beta-amyloid accumulation. The duo reasoned that it might be possible to wash out the amyloid from the brain if the blood brain barrier, which isolates the brain from the bloodstream, could be opened up temporarily.
To do this, they injected mice with a mixture of "microbubbles". These circulate harmlessly in the bloodstream, but when the are hit by ultrasound waves they collapse in on themselves and create a miniature shock wave. If the ultrasound is directed at the head, the researchers showed, the blood brain barrier becomes leaky for a short while but without apparent harm to the surround nervous tissue.
Next, working with mice that develop the rodent equivalent of Alzheimer's, the duo gave their ultrasound treatment to one group of mice and compared them with an identical untreated control group. In tests, the brains of animals treated for a month with the new therapy showed 58% lower concentrations of beta-amyloid than the control cases.Moreover, in tests designed to probe memory function the treated mice showed significantly improved cognitive function compared with the untreated animals.
Leinenga and Gotz think that the treatment works by allowing proteins from the blood called albumins to get into the brain where they bind to beta-amyloid and encourage it to be taken up and disposed of by immune "microglial" cells.
However, despite the apparent effectiveness of the approach, mice are not humans, and it's not clear whether the technique would work for an Alzheimer's patient like it does for the experimental mice. The greater thickness of bone in a human skull can make it difficult for the ultrasound waves to reach the brain, which is also much larger.