There is a fair amount of interest in finding out whether the observations derived from heterochronic parabiosis, where the circulatory systems of an old and a young mouse are linked, can be reproduced by transferring whole blood or blood plasma from a young individual to an old individual. In theory the introduction of young signals into an old environment may adjust cellular behavior for the better, analogous to the effects produced by some forms of stem cell transplant. So far the results are mixed, however, with some studies showing no benefit - it is quite possible that transfer doesn't recreate all of the effects of a fully joined circulation for one reason or another. That said, researchers with Alkahest, involved in trials of plasma transfer as a human therapy, are now presenting initial results from introducing young human blood plasma into old mice, in which benefits were observed:
Blood plasma from young people has been found to rejuvenate old mice, improving their memory, cognition, and physical activity. The method has the potential to be developed into a treatment for people. Previous research has found that stitching old and young mice together has an interesting effect. While sharing a blood system works out well for the older mouse, the younger one isn't so lucky. The young animals started to show signs of brain ageing, while the brains of the older mice started to look younger. The key to youth appears to be in the blood plasma - the liquid part of blood. Several studies have found that injecting plasma from young mice into old mice can help rejuvenate the brain and other organs, including the liver, heart, and muscle.
Could blood plasma from young people have the same benefits? To find out, researchers took blood samples from 18-year-olds, and injected them into 12-month-old mice. At this age, the equivalent of around age 50 for people, the mice start to show signs of ageing - they move more slowly, and perform badly on memory tests. The mice were given twice-weekly injections of the human plasma. After three weeks of injections, they were submitted to a range of tests. The treated mice's performance was compared to young, 3-month-old mice, as well as old mice who had not received injections. Treated mice ran around an open space like young mice. Their memories also seemed to improve, and they were much better at remembering their way around a maze than untreated mice.
The team then examined the brains of the treated and untreated mice. They looked for clues on the birth of new neurons in the hippocampus - a process called neurogenesis, which is thought to be important for memory and learning. Sure enough, the treated mice appeared to have created more new cells in their brain. The researchers have identified some factors in young blood that might be responsible for these benefits, but that won't reveal what they are yet. Some of them seem to be crossing into the brain, while others may be acting remotely, elsewhere in the body.