Slices of mouse brain that were kept at -150掳C for up to a week have shown near-normal electrical activity after being warmed up. The results could take us a step closer towards cooling and reviving entire brains for purposes such as putting for space flights.
鈥淎t the moment, it is not possible, but I think there are existing techniques that can be combined to achieve this, and there is room for careful optimism,鈥� says at the University of Erlangen-Nuremberg in Germany.
The key to cryopreserving living tissues is to avoid the formation of ice crystals. These rip up molecules in cells and even larger structures like blood vessels as they grow, and as the remaining liquid in a tissue becomes more concentrated, that does damage as well. Some insects and a few amphibians and reptiles produce cryoprotectants that inhibit ice crystal formation, allowing them to survive in below-zero temperatures.
Advertisement
In the 1980s, , now scientific head of California-based company Intervene Immune, and , then at the Cryobiology Laboratory in Maryland, showed that mammalian cells by adding cryoprotectants that result in fluids turning into a so-called amorphous solid when cooled rather than crystallising 鈥� a process known as vitrification.
This works by largely replacing the water in cells with cryoprotectants, says German. 鈥淔or conventional biologists, it鈥檚 often hard to believe that it is possible to replace the majority of water molecules in the tissue with different polar solvents.鈥�
In 2006, Fahy and his colleagues reported after cooling them to -130掳C for short periods. But the limited test results they described didn鈥檛 convince neuroscientists that the slices had regained normal activity, says German.
Now, German and his team have gone further. They first experimented with different combinations of cryoprotectants and varying methods for applying them to minimise adverse effects 鈥� for instance, cryoprotectants can be toxic at the high concentrations required and they can cause cells to swell or shrink.
The researchers then used their optimised technique to cool slices of the hippocampi of mouse brains to -196掳C with liquid nitrogen, before storing them in a freezer at -150掳C for up to a week. After reviving them, the team did a battery of tests, including measuring electrical activity. All the results were similar to those seen in non-cryopreserved brain slices.
In particular, there was no damage to the delicate synapses that connect nerve cells to each other. In a whole brain, this degree of recovery should preserve memories. 鈥淭hat would be expected, but this needs to be confirmed,鈥� says German.
In 2021, rat hearts were revived after vitrification, he says. This was achieved in rat livers in 2022 and in 聽in 2023.
鈥淎nd our work now shows that it is also possible to cryopreserve rodent brain tissue slices,鈥� says German. 鈥淪o this is leaving some room for optimism that it would be possible to cryopreserve the whole brain, and also the whole rodent organism, at some point. I personally do believe that it is possible to cryopreserve a whole human and that this could have beneficial applications if done responsibly.鈥�
Even if it becomes possible to cryopreserve and revive healthy brains, this doesn鈥檛 mean that people cryopreserved after death with these improved methods could be revived. Significant damage can occur after death, says German.
鈥淚t鈥檚 an exciting piece of research that pushes the boundaries in the fascinating area of brain cryopreservation,鈥� says at the University of Birmingham in the UK. 鈥淥f course, there is still a lot more research needed before we can cryopreserve human organs, including brains, but it is a step in the right direction.鈥�
at Binghamton University in New York state says the work is a step forward, but the findings need to be independently verified. He also isn鈥檛 convinced that this approach will help with entire brains. 鈥淲hole-organ vitrification and long-term functional recovery is an entirely different ballgame,鈥� he says.
Even if the improved method works only with slices of brain tissue rather than whole brains, being able to store and revive brain slices will in itself be a very useful tool, as the slices usually survive for only 10 or so hours.
For instance, small living slices of human brains are sometimes removed during surgery, says German. If these could be stored and transported, it would greatly increase the opportunities for using them to study brain conditions and test treatments.
鈥淭here are immense potential applications of brain slice vitrification for the sharing of valuable materials between different laboratories and for preserving valuable brain samples for later analysis,鈥� says Fahy.
bioRxiv
