Sep 8, 2009.
Australian researchers believe they have discovered why foods high in saturated fat increase the likelihood of developing Alzheimer's disease.
Researchers from Curtin University of Technology in Perth found that saturated dietary fat damages the lining of blood vessels in the brains of mice, allowing a protein called amyloid to enter the brain.
The study, to be published in the British Journal of Nutrition, is one of the first to demonstrate a scientific link between diet and Alzheimer's disease.
"In the past, population studies suggested that high fat diets may be a risk factor for Alzheimer's disease, but no-one really understood why," said Professor John Mamo, co-author of the study and national director of the Australian Technology Network's Centre for Metabolic Fitness.
"The brain has millions of blood vessels. Each vessel has a lining that is very selective about what is allowed to go in and out, and this keeps the brain in good health."
Professor Mamo and colleagues found this lining, called the blood-brain-barrier, is damaged by high saturated fat diets.
"This allows things to be getting in there that shouldn't be," he said.
A key feature of Alzheimer's disease is amyloid deposits in the brain, which cause inflammation and nerve cell death.
Amyloid is produced in the small intestine, and secreted into the blood where it attacks the blood-brain-barrier.
"When the blood vessel lining gets disrupted and deregulated you get delivery of amyloid into the brain," Professor Mamo said.
Past research has shown that saturated dietary fats increase the production of amyloid in the small intestine.
In the study, the researchers fed mice a diet of either saturated, monounsaturated or polyunsaturated fats, and compared them to mice genetically designed to develop Alzheimer's.
Within two months, the mice that were fed a saturated fat diet showed significant change in their blood vessels.
"We saw a very substantial deterioration in the mice blood vessel architecture," Professor Mamo said.
"But, we saw no deterioration in the mice fed monounsaturated or polyunsaturated diets."
The saturated fat mice also had more amyloid deposits in their brain than those fed the monounsaturated or polyunsaturated diets.
The researchers also found that the brains of the mice fed the saturated fat diet were remarkably similar to the Alzheimer's mouse models.
"In mice that have been genetically manipulated to overproduce amyloid, we find exactly the same kind of pathology," Professor Mamo said.
Using antibodies with a fluorescent tag the researchers were able to confirm that dietary fats are also found inside the amyloid deposits.
The researchers believe their study will provide a new target for Alzheimer's drug treatments, which are directed at improving nerve cells.
"We need to refocus our strategy to protect these vessel walls and to restore health to damaged vessels," he said.
The announcement comes at the same time as a French-led study announced the discovery of two genes associated with Alzheimer's.
The study, published in the journal Nature Genetics, is the largest ever genome study focused on Alzheimer's.
One of the genes, CLU, produces a protein called clusterin, which is known to reduce the inflammation caused by amyloid deposits.
The other gene, known as PICLAM, is important for maintaining communication between nerve cells in the brain.
Study co-author Dr Corinne Lendon of the Queensland Institute of Medical Research says the study should improve their understanding of Alzheimer's and will hopefully lead to better detection of the disease.