The researchers hope their findings will eventually lead to odor signatures of urine samples being used as biomarkers to identify early-stage Alzheimer's disease.
The team - including members from the Monell Chemical Sense Center in Philadelphia, PA, and the US Department of Agriculture (USDA) - describes the findings in the journal Scientific Reports.
One of the authors, Dr. Bruce Kimball - a chemical ecologist with the USDA National Wildlife Research Center (NWRC) , and who is based at the Monell Center - says before the new research, their work focused mostly on changes to body odor caused by factors that originate outside the body, such as viruses and vaccines. He notes:
"Now we have evidence that urinary odor signatures can be altered by changes in the brain characteristic of Alzheimer's disease. This finding may also have implications for other neurologic diseases."
While there are currently no treatments that stop or reverse the progression of Alzheimer's disease, an early, accurate diagnosis would give patients and their families time to plan for the future and their doctors time to find a treatment that gives symptom relief.
Alzheimer's disease affects around 5.1 million Americans over the age of 65. There is no definitive diagnostic test for this most common form of dementia, a hallmark of which is an excess of amyloid plaque deposits in the brain.
Alzheimer's mice have distinctly different urine odor signature
For their study, the team worked with mice bred to develop amyloid plaques in the brain similar to the ones that afflict humans. To breed the mice, scientists insert human genes into their genomes then activate them with drugs. The genes carry mutations that cause the mice's brain cells to make too much amyloid precursor protein.
The excess precursor protein forms amyloid plaques that clog up the brain in the modified mice in a similar way as seen in humans with Alzheimer's disease. The mice develop similar behavioral symptoms of mental deterioration. These types of mice are known as "amyloid precursor protein transgenic mouse models," or "APP mice."
The team used three separate strains of APP mice. Using behavioral and chemical analyses, they found each strain of APP mice had different urine odor signatures that were distinctly different from those of control mice.
The differences in odor signature between the APP and control mice were not due to different compounds, but to differences in concentrations of the same compounds.
The differences in odor signature did not vary much with age, and they preceded detectable amounts of amyloid plaque build-up in the brains of the APP mice, say the researchers. They suggest this means the odor signature is tied to the underlying gene, rather than the progress of changes in the brain.
Coauthor Dr. Daniel Wesson, a neuroscientist at Case Western Reserve University School of Medicine in Cleveland, OH, concludes:
"While this research is at the proof-of-concept stage, the identification of distinctive odor signatures may someday point the way to human biomarkers to identify Alzheimer's at early stages."
The findings follow another mouse study that Medical News Today reported recently about how brain inflammation may offer clues toward a potential treatment for Alzheimer's disease. The researchers suggest blocking a protein that regulates immune cells could be a way to stop the brain-wasting disease.