Infusing "old" blood into a young animal can have negative effects, according to researchers investigating the ageing process in blood.
The findings suggest the need for more detailed investigations to find how the ageing of blood contributes to brain ageing, according to the researchers.
Scientists investigated the effects of exposing young mice to the blood from older mice.
The team, led by Dr Irina Conboy of the University Of California - Berkeley, USA, were looking into the potential rejuvenating properties of young blood.
They had previously found evidence for tissue rejuvenation in older mice when they are surgically joined to younger mice so that blood is exchanged between the two.
However, the mechanism underlying this rejuvenation was unclear.
So they developed a technique to exchange blood between mice without joining them, so blood circulation could be precisely controlled.
This showed a rapid onset of the effects of blood on the health and repair of many tissues, including muscle, liver and brain, around 24 hours after exchange.
However, the team report in Nature Communications that older mice exposed to younger blood "saw either slight or no significant improvements compared to old mice with old blood".
Young mice that received older blood, however, showed a negative effect in most of their tissues and organs. Their neurons in particular showed a more than twofold drop in new cell development.
Dr Conboy and her team believe that any benefits in old mice after receiving young blood are probably due to the young blood diluting the concentration of ageing molecules in the old blood.
"What we showed previously was evidence that aging is reversible and is not set in stone," said Dr Conboy. "Under no circumstances were we saying that infusions of young blood into elderly is medicine.
"Old blood appears to have inhibitors of brain cell health and growth, which we need to identify and remove if we want to improve memory."
Reference: Rebo, J. et al. A single heterochronic blood exchange reveals rapid inhibition of multiple tissues by old blood. Nature Communications 22 November 2016; doi: 10.1038/ncomms13363
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