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The next breakthrough in Alzheimer’s research could come from old and ‘cognitively impaired’ Chilean rats

December 22, 2022, 4:41 PM UTC
A Chilean degu rodent sitting on a forest branch
This small Chilean rodent could be the next boost to Alzheimer’s research.
Jayson Photography/Getty Images

Among the animals you might consider useful to understanding the degenerative effects of Alzheimer’s, a species of long-lived rodent found in the woodlands of Chile probably did not make the list.

Not as well-known as its cousins the chinchilla or the guinea pig, Octodon degus, also known as the common degu, is a rodent endemic to the forested valleys of central Chile with a propensity for especially long life spans among its kind, reaching up to eight years of age. 

But what the small rat lacks in fame it may more than make up for in its value to scientists studying the degenerative neurological symptoms of Alzheimer’s, one of the world’s most devastating ailments that causes irreversible cognitive decline and dementia, treatment for which has eluded medical researchers for more than a century since its discovery.

Elderly degus exhibiting signs of cognitive decline provide an ideal model for researchers to study the effects of one of the most common forms of Alzheimer’s disease or AD, scientists from the University of California at Irvine write in a new study published this week in the medical journal Acta Neuropathologica Communications.

The researchers observed a colony of 146 degus who were getting on in years and put them all through a test to evaluate their cognitive abilities. The experiment involved placing food pellets in an artificial burrow, and degus would pass or fail the test based on how many pellets they were able to retrieve in a given time. 

Degus who were unsuccessful in the pellet retrieval mission were designated as exhibiting “AD-like” behavior. Upon completion of the test, 12 unlucky degus, six with AD tendencies and six without, were euthanized before their brains were collected and analyzed by researchers. 

They concluded that, based on the behavior of AD-like degus, the species is a “natural model” for human Alzheimer’s disease, and specifically of “sporadic” Alzheimer’s, by far the most common form of the disease which does not run in families and can emerge as an unfortunate combination of genetics, environment, and lifestyle, making it much harder to identify before onset. Of the 44 million people suffering from Alzheimer’s worldwide, over 90% of cases occur sporadically, according to the study.

“We found robust neurodegenerative features in cognitively impaired aged degus,” Xiangmin Xu, a professor in anatomy and neurobiology at UCI and corresponding author for the study, said in a statement, adding the behavior was “consistent with the neural circuit hyperactivity that [is] commonly reported in human Alzheimer’s disease patients.”

Degus research will be useful in tracing the development and symptoms of sporadic Alzheimer’s, the authors wrote, adding it will help to understand comorbidities, diseases that can appear simultaneously with Alzheimer’s. The researchers identified evidence of Type 2 diabetes, macular degeneration affecting eyesight, and sclerosis in degus’ arteries.

Only symptomatic treatments that can temporarily dampen Alzheimer’s effects are currently available. There is no existing cure for the disease, and efforts and trials to cure or prevent the disease have so far mostly ended in failure

But earlier this year, hopes that the tragic disease could be reversed were revived when encouraging results from trials of a new medicine were published. The treatment, known as lecanemab, was found to reduce cognitive decline in patients exhibiting signs of Alzheimer’s by 27% compared with placebos.

Doubts remain about the new treatment’s safety, as three deaths have so far been tied to the experimental drug. Trial investigators found evidence of “brain swelling and microhemorrhages” that may have led to the deaths.

The drug is currently under FDA review.

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