Old Mice Could Live Longer by Sharing Young Blood, Study Finds

After surgically attaching pairs of mice, scientists suggest the procedure could rejuvenate the older individuals, slowing their aging

Blood Cells Flowing
Scientists are investigating how blood cells or other parts of blood might be responsible for aging. fotograzia via Getty Images

Connecting the bloodstreams of old and young mice can extend the lifespan of the older creatures by about six to nine percent, according to recent research.

In a procedure that sounds like a vampire’s dream, a team of scientists surgically connected pairs of living mice so that blood could circulate between them. After three months with their bodies fused together, the animals were unstitched and studied for the effects on their longevity.

The results, published late last month in the journal Nature Aging, show older mice’s lifespans tended to get a boost after the animals were linked to a young partner, when compared to older mice that had been connected to an old partner. Even two months after sharing the young blood, older mice had more youthful levels of molecules known to reflect aging.

“It’s a beautiful demonstration—it really shows that this effect is not transient,” says Tony Wyss-Coray, a parabiosis researcher at Stanford University who was not involved in the study, to the New York Times Carl Zimmer.

While this conjoining procedure, called parabiosis, is definitely not something you’ll see at your next spa day, connecting young and old individuals has shown promise for reducing aging in previous animal research. As far back as the 1800s, French scientists found that, after surgically attaching two rats, injecting a compound from a deadly nightshade plant into one rat could dilate the pupils of the other, the Times reports. Since the 2000s, researchers have found that the procedure seems to make several organs, including the brain and the heart, appear younger for their age in mice.

In the new study, undergoing a three-month period of parabiosis with a younger mouse resulted in older mice living about six weeks longer. “Based purely on this study, the extension in lifespan would equate to about five to seven human years,” says James White, senior author of the study and a cell biologist at Duke University, to Newsweek’s Pandora Dewan.

After the procedure ended, scientists looked at the animals’ biological age, or the age of their cells and tissues based on molecular markers in the blood, liver and DNA. The bodies of older mice that had been connected to a younger individual seemed to age less quickly than expected.

But Michael Conboy, a researcher studying aging at the University of California, Berkeley, tells the Times that this result is not necessarily the final word on the matter, as a similar experiment published last year did not extend the older mice’s lifespans by a statistically significant amount.

Parabiosis is a very extreme surgery, and during it, the mice share much more than blood. “It’s not just an infusion,” says co-lead author and researcher Vadim Gladyshev, at Harvard Medical School, to the Harvard Gazette’s Clea Simon. “Old mice have access to the younger organs, and… the damage accumulated with age is distributed.”

In this way, the procedure isn’t without a cost: The younger mice in the experiments showed signs of accelerated aging after being disconnected from their older counterparts. But this damage to the youngsters can disappear over time, while the rejuvenating effects on the older mice are permanent, Gladyshev tells the publication.

As to why parabiosis appeared to rejuvenate older mice’s bodies, scientists say that receiving young blood alone might not be the main restorative factor. Diluting the older mouse’s blood might be more important, if it contains cells or proteins that are causing aging, says White to New Scientist’s Alice Klein. Alternatively, when the mice are connected, the young mouse’s kidneys and liver might be helping the older one’s circulatory system.

“It’s probably a combination of different factors that leads to the rejuvenating effect,” Gladyshev tells the Harvard Gazette.

Importantly, the results are not ready to be applied to humans. Even if youthful blood is the key to slowing aging in an older mouse, scientists don’t currently have evidence that human biology works the same way, or that a less invasive blood transfusion could achieve similar results for us. In response to claims that blood plasma from young donors could treat dementia, the Food and Drug administration released a warning in 2019, saying that this technique has not been clinically proven to be beneficial or safe. A small trial testing weekly infusions of young plasma in Alzheimer’s patients resulted in “minimal benefits,” per New Scientist.

Blood itself is needed by cancer patients and victims of accidents. David Irving, director of product usage at Australian Red Cross Lifeblood, tells New Scientist that using donated blood in an attempt to extend lifespan is unethical, and that “[a] better focus would be on calorie restriction, for which there is much better evidence.” In a clinical trial published this year, eating fewer calories reduced DNA markers of aging in human participants’ blood.

Regardless, scientists still need to get more information on what influences aging. “It’s clearly not just that an infusion of young blood rejuvenates,” Gladyshev tells the Harvard Gazette. “It’s more complex than that.”

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