Australians will be among the first in the world to test new drugs hoped to ward off Alzheimer's disease after doctors discovered the illness takes decades to develop in people's brains before symptoms appear.
Director of nuclear medicine at the Austin Hospital, Professor Chris Rowe, said Australians aged over 60 were now being invited to trial drugs which could prevent the build-up of proteins in the brain believed to cause the disease.
Trials on participants whose scans show early signs of dementia are likely to begin in Melbourne later this year.
The call for volunteers comes as a study by Professor Rowe and his colleagues revealed the build-up of these proteins could be seen on scans of people's brains over about four years, allowing doctors to model the natural development of the disease before it becomes detectable.
The findings pave the way for preventative drugs that would act like anti-cholesterol or blood-pressure drugs that help prevent heart disease.
Professor Rowe said although post-mortem studies suggested the build-up of this destructive protein, known as amyloid beta, occurred over several years, his study was the first to use brain scans on a large group of people to show Alzheimer's disease was a 30-year process.
"If we put it into a patient scenario, if someone develops dementia at the age of 75, our study shows that the amyloid which is thought to be the cause of Alzheimer's disease started building up at the age of 45 and by the age of 60, there was enough to detect it with an amyloid PET scan. Then at the age of 70 – about five years before dementia – the patient would have started to notice their memory beginning to fail and if you did an MRI scan at that time, you would start to see shrinkage of the brain. Over the last five years there would be fairly rapid decline of memory and worsening of the brain shrinkage to the point where they develop dementia," he said.
The study, which was part of the Australian Imaging Biomarkers and Lifestyle Study of Ageing, involved 200 people in Victoria and Western Australia aged 55 to 89. The participants included healthy people with no symptoms of dementia, some with mild cognitive impairment and some with Alzheimer's disease. The results were published online in The Lancet Neurology medical journal on Friday.
Professor Rowe said mapping the natural progression of Alzheimer's disease was crucial for testing preventative drugs which dozens of pharmaceutical companies were working on.
He said if the drugs, which are showing positive results in animal studies, could clear the amyloid beta or adjust the production of it in people's brains, they could prevent dementia.
"The good news about this study is that it gives us a large window for therapy," he said.
Professor Rowe said while one or two clinical trials were already starting in other parts of the world, the Melbourne clinical trial inviting participants now would be the first opportunity for Australians to test a potentially preventative drug. He said although animal studies suggest the drugs were safe, he could not say if it would cause side effects in humans.
"They seem fine in animals but it can be a different story once you start doing large-scale trials in lots of people," he said.
Participants would have a PET scan to map levels of amyloid beta in their brains. The scan involves an injection of a small amount of radioactive material which will stick to the protein so it can be seen on a CT scan. If someone qualifies for the study, they may be selected for the drug treatment over several years.
In the US, people are paying about $3000 for PET scans to find out if they are likely to get Alzheimer's disease, but Professor Rowe said this was discouraged in Australia until there was a treatment available. While more educated people and those with bigger brains seemed less likely to get Alzheimer's disease or to get it later than others, he said evidence showed physical exercise, particularly in mid-life, was associated with a reduced risk, along with controlling risk factors for heart disease including cholesterol and high blood pressure.
About 280,000 Australians have dementia, however almost 1 million are predicted to have it by 2050 as the population ages. The World Health Organisation estimates that worldwide, 35.6 million people have the illness.
People interested in the study can call the Austin Hospital on 9496 3326 or 9496 5953.