A 19th century scientific experiment is making a comeback, and results are showing it might have significant implications for how medicine approaches aging and Alzheimer’s disease. The procedure is called parabiosis and is performed on mice. The process involves making an incision on the right flank of one mouse and the left flank of another. Both mice are sutured together, and their paired front and rear legs are tied together. As the incisions heal together, the regrowth of capillaries combines their circulatory systems and they end up sharing the same blood much like conjoined twins or animals that share a placenta in the womb. The twist is that one mouse is always young and the other old.
Those early experiments showed that by sharing blood with the younger mouse, the old one had more energy and was clearly more alert, although scientists had no idea why. These experiments carried into the 20th century but were dropped in the 1970s. Now 45 years later, a resurgence of interest in these early findings is driving new research that is providing some very exciting results.
Much research has now shown that when old rats are exposed to young blood via parabiosis, they show significant improvement in brain function, muscle strength and heart health. Their fur even becomes shinier. After being joined for 9 to 18 months, the bones of older rats become similar in weight and density to their younger partner. The liver and muscles are restored as their dormant stem cells begin dividing again. There is even enhanced growth in brain cells after just five weeks. In addition, the older rats live 4 to 5 months longer than control rats suggesting that exposure to young blood may increase longevity.
In light of these incredible findings, researchers resist calling this phenomenon “rejuvenation” or “restarting the aging clock.” No one is turning old rats into young rats, but they do acknowledge that young blood exposure repairs tissue damage and restores function.
Among other intended uses, scientists hope to use these discoveries to help elderly people heal faster after surgery and devise new treatments for age-related diseases.
In spite of all this good news, the research hasn’t been without problems. A small percentage of the experimental rats died from what was called parabiotic illness, which researchers attributed to a sort of tissue rejection response.
Even so, the race is on to discover the specific components in young blood that contain these amazing healing properties. Research from the University of California Berkeley linked muscle rejuvenation to the act of Notch signaling, which promotes cell division. Last year, it was found that the hormone oxytocin in young blood was also responsible for much of its age-defying effects. Oxytocin exists in both men and women but is well known as the hormone that generates strong feelings of bonding and attachment between mother and child during and after birth. Although oxytocin declines with age, old mice injected systemically with the hormone experienced reactivation of their muscle stem cells and increased lean mass in just two weeks.
Further research out of Harvard University, the University of Cambridge, and Brigham and Women’s Hospital in Boston has demonstrated that young blood promotes the repair of damaged spinal cords in older mice, forms new neurons in the brain and olfactory system, as well as reverses age-related thickening of the heart walls. Of particular interest has been a protein called growth differentiation factor 11 or GDF11, which is abundant in young blood. Old mice receiving a direct injection of GDF11 experienced a significant increase in muscular strength and stamina, while DNA damage inside the muscle stem cells was reversed.
Because young blood consistently generates new neuron growth in the brains of older rats and mice, its application in Alzheimer’s disease and other dementia-related conditions has been a natural and new focus of this exciting research. It’s now been found that the exchange of the whole blood isn’t necessary to experience the benefits of parabiosis. Thank goodness for rats and humans. Experimentation has now shown that merely being exposed to young blood plasma activates brain plasticity (necessary for learning) and memory formation in older mice.
These results were so dramatic that many medical journals rejected the studies for publication deeming them too good to be true. After the results were repeated at the University of California San Francisco (UCSF) with a completely different staff, instruments and tools, the findings were finally published in Nature Medicine.
Promise for the Future
Even better, the journal article caught the eye of a company in Hong Kong, where the owner’s family has a history of Alzheimer’s disease. After experiencing a dramatic but unexplained improvement in a family member with Alzheimer’s disease when he received a plasma transfusion, the family contacted the researchers who conducted the study at UCSF. That family has now created a foundation and is currently funding the first human clinical trials where young blood plasma from men aged 30 or younger is being administered to older Alzheimer’s patients.
There has been some uncertainty regarding how young the blood needs to be to provide its rejuvenating effects. There is also concern that because receiving young blood activates stem cells, too much cell division over the long-term may raise cancer risk. Fortunately, parabiotic disease isn’t an issue because donors and recipients are no longer physically conjoined, and humans have been doing blood transfusions successfully for over 100 years. It is hoped that when further research is completed, young blood plasma will lead to powerful interventions not just with Alzheimer’s disease, but all age-related degenerative conditions.
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