A group of scientists has successfully extended the lifespan of aging mice by connecting their blood vessels to younger mice. According to the study, the infusions of youthful blood increased the older mice’s lifespan by 6 to 9 percent, which is equivalent to six additional years for the average human.
Although the study does not provide a definitive anti-aging treatment for humans, it does suggest that the blood of young mice contains compounds that promote longevity, according to the researchers.
James White, a cell biologist at Duke University School of Medicine and one of the study’s authors, referred to the combination of compounds as a “useful cocktail.”
The practice of connecting animals together, known as parabiosis, has a long history in scientific research. In the 19th century, French scientists connected the blood vessels of rats to demonstrate a shared circulatory system. They injected a compound from the deadly nightshade plant into one of the rats and observed that both rats’ pupils dilated.
In the 1950s, Clive McCay of Cornell University and his colleagues used parabiosis to study aging. By joining the flanks of young and old rats, they merged the capillaries of their skin. Dr. McCay and his team later found that the cartilage in the old rats appeared younger.
Parabiosis experienced a resurgence in the early 2000s when researchers used modern techniques to investigate the effects of animals of different ages sharing the same bloodstream. They discovered that the muscles and brains of old mice were rejuvenated, while younger mice showed signs of accelerated aging.
Some doctors took advantage of these initial results and began offering blood plasma injections from young individuals as a treatment for dementia and other age-related diseases. However, the Food and Drug Administration warned against these treatments in 2019, stating that they had no proven clinical benefits and could be potentially harmful.
Dr. White and his team have been refining parabiosis procedures in mice in order to better understand its anti-aging effects. They joined an old and young mouse together for three months, twice as long as typical experiments, before separating them and observing their subsequent lifespans.
The researchers not only observed that the old mice lived longer, but also noted changes in the aging process. After detaching the mice, they examined molecular markers in their blood and liver that act as indicators of biological age. Two months later, these markers indicated that the older mice appeared “younger” than untreated mice of the same age.
“We reset the trajectory of aging,” said Dr. White.
The union also affected the young mice, causing them to rapidly age and then revert to their original state upon separation, as noted by Vadim Gladyshev, an expert on biological clocks at Harvard Medical School and one of the study’s authors.
The study was published in the journal Nature Aging, and Tony Wyss-Coray, a parabiosis expert at Stanford University, hailed it as a “beautiful demonstration” of the lasting effect on aging.
However, Michael Conboy, a research scientist at the University of California, Berkeley, cautioned that a similar experiment conducted by Ukrainian scientists last year did not show increased lifespan in old mice after parabiosis.
Dr. David Glass, the vice president for research on age-related disorders at Regeneron, a pharmaceutical company, noted that the new report used a different strain of mice compared to the previous year’s study, highlighting the need for caution in generalizing the findings.
Dr. White and his colleagues are now conducting further experiments to uncover the mechanisms behind the slowing down of aging in the old mice. They aim to understand the “hows and whys” of the process.
According to Dr. White, the long-term effects of the experiment suggest that the cause cannot be solely attributed to the rejuvenation of old mice through cells from young mice. When the mice were separated, the old mice did not return to their original state despite losing their supply of young cells.
One possibility is that harmful compounds in the old animals are diluted by the young blood, potentially reprogramming the cells in the old mice to exhibit youthful behavior even after detachment.
Dr. Gladyshev, however, does not view the study as a justification for receiving injections of young human serum. Firstly, the specific factors comprising the life-extending cocktail for mice, let alone humans, remain unknown. Secondly, injections differ greatly from the prolonged connection of animals in parabiosis.
“To me, it’s just very strange to think it could work,” commented Dr. Gladyshev.
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