An asthma drug can reverse memory loss caused by Alzheimer's and remove toxic build-ups of a protein in the brain, a study suggests.

Trials on mice engineered to have the disease revealed that zileuton helped them to perform significantly better on memory tests.

Scientists also found the drug also reversed the accumulation of tau proteins in the brain – long considered a hallmark of Alzheimer's.

Temple University experts claimed their findings open up a potential new route to stop the aggressive progression of the disease.

An estimated 850,000 people in the UK and five million in the US have dementia, of which Alzheimer's is the most common form.

Trials on mice engineered to have the disease revealed that zileuton helped them to perform significantly better on memory tests (stock)

Dr Domenico Praticò, senior author, said: 'This is an old drug for a new disease. The research could soon be translated to the clinic, to human patients with Alzheimer's.

'We show that we can intervene after disease is established and pharmacologically rescue mice that have tau-induced memory deficits.'

The researchers found inflammatory molecules, called leukotrienes, are deregulated in animals with Alzheimer's.

Further experiments then revealed that the leukotriene pathway plays an important role in the later stages of the disease.

Dr. Praticò said: 'At the onset of dementia, leukotrienes attempt to protect nerve cells, but over the long term, they cause damage.'

This discovery then led them to the new study, published in the journal Molecular Neurobiology.

They wanted to understand whether or not blocking leukotrienes could fix memory impairments in mice with brain build-ups of tau.

Two groups of mice were compared for the study. One were genetically engineered to develop build-ups of tau proteins in their brains.

The genetically engineered mice were treated with doses of zileuton when they were 12 months old – the equivalent of 60 human years.

The drug, which is available on prescription in the UK but costs roughly $32 for one pill at pharmacies in the US, inhibits leukotriene formation by blocking the 5-lipoxygenase enzyme and is approved for long-term use in asthma patients in the UK and US.

Maze tests were undertaken after 16 weeks of treatment to assess their working and spatial memory – both of which decline in Alzheimer's.

The zileuton mice performed better – which the scientists said was suggestive of a successful reversal of memory impairment.

Further tests revealed the rodents given the drug had 50 per cent less tau – which is believed to trigger the death of nerve cells.

Microscopic inspections of the brains of the mice revealed vast differences in the quality of synapses between the two groups.

Those not given zileuton had severely deteriorated synapses - connections between neurons that die off in Alzheimer's.

However, the mice which received the drug had synapses indistinguishable of those from ordinary mice without the most common form of dementia.

Dr. Praticò, director of the Alzheimer's Center at Temple, said: 'Inflammation was completely gone from tau mice treated with the drug.

'The therapy shut down inflammatory processes in the brain, allowing the tau damage to be reversed.'