A drug that appears to block the progression of Alzheimer's disease has been identified by scientists.
Alzheimer's is associated with tissue loss
In tests on mice, the drug, AF267B, reversed the symptoms of memory loss and problems with learning associated with Alzheimer's.
Further analysis showed it also reduced levels of protein clumps and tangles often found in Alzheimer's patients.
The study, by the University of California, Irvine, is published in the journal Neuron.
The drug was developed to activate receptors for a brain chemical called acetylcholine.
These receptors are abundant in two areas of the brain - the cortex and hippocampus.
Both are known to be particularly vulnerable to the build-up of the protein plaques and tangles that are so often found in the brains of Alzheimer's patients, and which are thought to destroy brain cells.
The researchers gave AF267B to mice engineered to show classic signs of Alzheimer's.
They found animals treated with the drug performed better at learning and memory tasks than untreated animals.
The drug also cut levels of both protein plaques - found outside brain cells - and tangles - found inside the cells - in the cortex and hippocampus.
However, it had no similar effect in another area, of the brain, called the amygdala.
The treated animals performed no better than their untreated peers in tests designed to assess amygdala function.
The researchers also showed that AF267B appears to mimic the action of acetylcholine, binding to its receptors and boosting levels of enzymes involved in breaking down the key protein that forms clumps and tangles in brain cells.
Lead researcher Professor Frank LaFerla said: "AF267B could be a tremendous step forward in the treatment of Alzheimer's disease.
"Not only does it appear to work on the pathology of Alzheimer's and ease its symptoms, it crosses the blood-brain barrier, which means it does not have to be directly administered to the brain, a significant advantage for a pharmaceutical product.
"Although we cannot determine what the effects of AF267B will be in humans until clinical trials are complete, we are very excited by the results our study has yielded."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said: "This research, which builds on earlier studies, is exciting as the scientists have overcome some of the problems seen in previous strains of this compound, including poor safety margins and lack of selectivity giving a higher potential for side-effects.
"It is very encouraging news that the drug was able to reduce some of the amyloid plaques and tau tangles in areas of the brain particularly affected by Alzheimer's - the hippocampus and cortex.
"It is also exciting that the mice experienced improved learning and memory, showing that, as well as affecting the pathology, the drug improved clinical symptoms."
But she added: "This drug would not be a complete solution to Alzheimer's, and more research is also needed to improve the drug's effectiveness, to ensure it is safe and to replicate the results in humans."