The successful thawing and transplantation of a frozen pig's liver could bring the technique one step closer for humans.

Israeli scientists, reported New Scientist magazine, used a "slow freezing" method which preserved the organ without damaging it.

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A UK expert said more work would be needed to prove the method was safe.

Organ donation schemes have to work fast to match organs with patients who need them, as, even if kept chilled, they can become unusable within 24 hours.

Researchers have been looking for ways to preserve them by freezing, to cope with delays between donation and transplant operation.

The main problem with freezing is the formation of jagged ice crystals in the water inside cells, which can them and their contents.

The scientists from the Israeli Agricultural Research Organisation in Bet-Dagan employ a far slower system, cooling the organ by just 0.3 degrees celsius a minute.

This reduces the formation of crystals, and freezing an entire liver takes about an hour and a half.

A similar technique is used by some frog species during hibernation when some parts of their body are allowed to freeze.

In this experiment designed to test whether a liver could survive the method, the pig organs were frozen, then immediately thawed and transplanted into another animal alongside their existing liver.

Working together

Two hours later, the recipient pig was killed and the liver checked for signs of life.

The results were initially published in the journal Rejuvenation Research.

They found that the transplant liver had regained some signs of blood flow, and was producing a bile-like liquid, hinting that some of its functions had returned.

However, because it was working in tandem with the existing liver, and was only left working for a couple of hours, the research did not show whether it could recover all its functions, and work independently to keep the animal alive.

The researchers now plan to carry out further experiments to test this. Mr Keith Rigg, a transplant surgeon and vice president of the British Transplantation Society, said that the work was "interesting", but had not yet convinced him that it could work in humans.

"In terms of transplanting it into human patients, there is still some way to go."

He said that, with demand for donated livers exceeding supply in the UK, there was probably no need for a "bank" of frozen organs.

"We have fairly good transport time across the UK, so these delays are not so much of an issue - although this might be different across the rest of Europe."

(BBC)

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