A 鈥淏ANK鈥� of donated organs ready for use is one step closer thanks to the successful freezing, thawing and transplantation of a pig鈥檚 liver. If human livers, which are about the same size, can survive this process, more people in need of transplants could receive them.
The vast majority of donated livers find a home. But they deteriorate rapidly without a blood supply, becoming useless between 12 and 24 hours later, so getting them to recipients on time is a logistical nightmare.
Amir Arav, who pioneered the new freezing method at the Israeli in Bet-Dagan, says the key to limiting cell damage during freezing is to cool the liver very slowly, as this prevents the formation of jagged ice crystals. Some frog species employ a similar technique when they allow parts of their bodies to freeze during hibernation. 鈥淲e didn鈥檛 invent this process, nature did,鈥� says Arav.
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鈥淪ome frog species employ a similar technique when they allow parts of their bodies to freeze during hibernation鈥�
Arav and his colleagues flushed the blood from the pig鈥檚 liver, cooled it, and then encased it in a pair of hollow brass cooling blocks attached to a supply of liquid nitrogen. The device was developed by , a company Arav co-founded in Ness Ziona, Israel. This cooled the liver at a rate of 0.3 掳C per minute bringing it to a temperature of -20 掳C in about an hour and a half.
The team then immediately let the liver thaw for 20 minutes before transplanting it into another pig, plumbing it in as a second liver. There it rapidly recovered its red colour, an indication of blood flowing through it, and began producing bile 鈥� both signs of health and normal function. The pig was then killed after about 2 hours and the auxiliary liver analysed, revealing that the cells were alive (Rejuvenation Research, ).
Liver researchers welcome the work, but say it would be more convincing if Arav鈥檚 team had left the liver in the pig for longer and disconnected the existing organ, forcing the auxiliary to take over. 鈥淥ne pig liver in a piggyback transplant is not very convincing, as there鈥檚 no evidence the thawed liver can really support the animal,鈥� says David Winter, president of , a company in Palo Alto, California, which has successfully thawed and transplanted rat kidneys that had been frozen for three months.
Arav says he was not allowed to do more than a temporary piggyback transplant because of restrictions imposed by animal welfare regulators, but he hopes the positive results from this limited experiment will allow the restrictions to be eased. 鈥淲e hope to repeat it and do those other tests next time,鈥� he says. He plans to evaluate how long livers can be stored, as well as the optimal storage temperature.
The team also found that rat livers stored at -80 掳C for up to three weeks regained function, although they were not transplanted into living animals. Arav has also frozen rat hearts, human ovaries connected to fallopian tubes, and parts of human knee joints. He has successfully transplanted the joints into about 20 people.
