Young blood has no rejuvenating effect

In contrast, a study shows that young mice that receive large amounts of aged blood suffer a significant deterioration of their organs and tissues.

In 2005, a team of researchers from the University of California published a study showing that continuous transfusion of blood from a young mouse to an old mouse while the latter was surgically operated made it possible for the older animal to experience a rejuvenation of its tissues. A “vampiric” effect that, in addition to total surprise, gave the starting signal to an unbridled search to try to find if the “young blood” encloses the secret of eternal youth. Since then millions of dollars have been spent on a multitude of studies without any satisfactory results being obtained. And now, the researchers themselves have published a new study that shuts down any hope that someday this might be so.

Specifically, the study published in the journal Nature Communications, shows that young mice in which half of their blood is replaced with that obtained from older animals suffer a very significant deterioration of their tissues and regeneration capacity Tissue. The ‘young blood’ does not have rejuvenation power observed in the first study, as well as that the ‘aged blood’, or rather its cells and molecules, are responsible for directing the natural process of aging.

This work suggests that young blood itself does not work as an effective medicine. Or rather it would be more accurate to say that there are inhibitors in the aged blood on which we need to act to reverse the aging.

The exchange of blood between humans nowadays is already contemplated in the treatment of some very specific and potentially deadly diseases, in case of some autoimmune pathologies. However, this is a measure that can only be carried out limited number of times, since repeated administration of blood or its components between two genetically different people carries typical side effects and immune rejection as in the case Of organ transplants. But, according to what was observed in the 2005 study, is there not a possibility that young blood could be used as a medicine?

What we saw in 2005 is an evidence that the aging is reversible. But under no circumstances infusions of young blood in older people were a medicine. What was seen in the first study is that when two living organisms, in this case mice, are ‘stitched’ together, a technique called ‘parabiosis‘, not only share their blood but also their organs. Thus, the older animal benefits from its young partner’s lungs, heart, immune system, liver and kidneys. Also, how long should they remain united? And what is the amount of blood that is required to be shared so that rejuvenation is possible?

In the new study, the authors have used an experimental technique that allows animals to share their blood without having to ‘lend’ the remaining organs. Thus, animals, young and old, have remained separated, which has made it possible to quantify the amount of blood transferred between them and their effects, especially those related to aging: cell growth in liver and adipose tissue, cellular development in the brain areas involved in memory and learning, and the ability to recover muscle tissue.

The experiment was stopped when the animals shared half of their blood with their neighbors. And according to the results, it only took 24 hours to see the effects of ‘transfusion’. However, the elderly mice that received the blood of the young did not get any benefit. On the contrary, the young mice experienced a deterioration, and very remarkable, in the majority of their organs and tissues.

The greatest effect was observed at the brain level, more specifically in the number of new neurons in the areas involved in memory and learning. In fact, the young mice that received the blood of their elders suffered a very remarkable reduction (about two times lower) in the production of new neurons from the stem cells. And what about the older animals that received ‘young blood’? Well, nothing at all. Or at least, no apparent effect. Young blood did not improve cerebral neurogenesis in any circumstance. It appears that the aged blood contains inhibitors of neuronal growth. Therefore, in order to improve memory, we have to identify and eliminate these inhibitors.