In the study, published April 19 in the journal Nature, researchers from Stanford University found that plasma from blood in human umbilical cords had a stimulatory effect on the brains of mice. Researchers have discovered hundreds of compounds that babies produce in abundance and that adult bodies seem to barely make at all.
A specific protein called TIMP2 was found to mimic the same beneficial results as the umbilical cord blood.
There are lots of caveats. They examined the mouse brains and investigated the hippocampi.
Researchers at Stanford had first noted that injecting middle-aged mice with plasma from human cord blood could boost activity in their hippocampi, an area of the brain critical for creating and banking memories.
"It was all mouse to mouse".
The team then analyzed protein changes in human umbilical cord, young adult, and elderly adult plasma, as well as in plasma from mice of different ages, identifying TIMP2 as a candidate plasticity-promoting factor. Wyss-Coray wondered if TIMP2 suppresses signals from senescent cells, including microglia and astrocytes, which help drive the aging process.
Researchers used immune-deficient mice during their experiments and repeatedly injected them with human plasma without negative immune reactions.
But what component of the serum was doing it? Her own work suggests that the apparent antiaging effects of young blood may reflect the fact that it contains less of certain factors in old blood that her lab and others have reported contribute to aging.
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Earlier studies have turned up youthful effects of young mice's blood on old mice (SN: 12/27/14, p. 21). The mice also got better at memory tests. The researchers suggest that it is likely that similar beneficial effects would be seen in humans.
Valdez said that the therapeutic potential could extend beyond TIMP2-to endogenous factors that cause levels of the protein to decrease with aging. It's not practical to do large-scale blood transfusions, even if they could be shown to help - which they haven't been.
That runs counter to the argument made by Castellano and colleagues that TIMP2 is associated with improved memory and learning, and that TIMP2 levels would drop as people age. "We are not saying we've found the protein that's responsible for brain aging". The lower the age at which the plasma is collected, the higher are its benefits.
What's more, antibodies against TIMP2 suppressed LTP in hippocampal slices from wild-type mice, and worsened their performance in an object-recognition task. "That will be a much better intervention because you're actually working with the endogenous protein, rather than having to administer [TIMP2] and dealing with side effects of too much or too little".
The science is in very early stages now.
"We need to find out if it works in serious human trials", Wyss-Coray says.
"This is exciting", said Roberta Diaz Brinton of the University of Southern California and the University of Arizona, who was not involved in the work.
Decades ago in somewhat grisly experiments, researchers found that sewing together the circulatory systems of an old and young mouse so that they shared the same blood supply rejuvenated the old animals.
Castellano concedes that "further studies will be needed to comprehensively characterize TIMP2 [levels and expression] over more precise age ranges and over varied demographic" groups, but defends its use in their study, as its effect on neuroplasticity appear positive and haven't been studied before.