Researchers believed the proteins associated with Alzheimer's disease were largely produced by brain tissue but new research from the University of British Columbia shows proteins produced elsewhere in the body may also contribute to the development of the degenerative disease.

Alzheimer's, the slow disintegration of thinking ability, memory and behaviour, is incurable. It is a leading cause of dementia worldwide.

Dr. Weihong Song, a UBC psychiatry professor and a Canada Research Chair in Alzheimer's Disease, says his research team focused on the amyloid-β protein, a protein of unclear function which is normally produced everywhere in the body.

The neurons of the brain produce the amyloid-β protein in large amounts when a person has Alzheimer's, he said. The protein forms plaques which contributes to its development.

But the protein is also produced in other body tissues — like blood platelets, blood vessels and muscles.

Song said his team wanted to see whether these externally-produced proteins have any effect in the development of the disease.

He says the results show that they do.

"The main point of this study is to show the amyloid-β [from blood circulating outside of the brain] can get into the brain and deposit there and form the Alzheimer pathologies."

Study looked at conjoined mice

In the study, researchers surgically attached two sets of mice to one another: normal ones who don't naturally develop Alzheimer's disease and mice modified to produce high levels of the amyloid-β protein.

After conjoinment, the two mice shared a blood supply.

In the study, a mouse genetically-modified to create the protein associated with Alzheimer's disease was surgically attached to a normal mouse, both sharing the same blood supply. (University of British Columbia)

Song said researchers found the normal mice eventually ended up developing the protein plaques and Alzheimer's disease-like pathologies after a year of being conjoined.

They found the protein had traveled from the genetically-modified mice into the brains of their normal partners, where it accumulated and began to develop into the disease.

Implications for treatment

The results of the study, published in Molecular Psychiatry, could mean future drug therapies can target organs like the kidney or liver instead of brain tissue which can be more complex and sensitive, Song said.

"Because the amyloid-β can be cleared and excreted through the liver and kidneys ... [you can] reduce the blood level for amyloid-β and tip the balance between the brain's amyloid load," he said.

"That way you basically help with the clearance of amyloid-β inside of the brain [and reduce the buildup of Alzheimer's-forming plaques]."

Though estimates vary, Statistics Canada say the number of Canadians suffering from dementia is between 340,000 to 747,000 people.