A “reversible” form of death? Scientists are reviving cells from dead pig organs.

The pigs lay dead in the laboratory for an hour – no blood circulating in their bodies, their hearts still, their brain waves flat. Then, a team of Yale scientists injected a special solution into the bodies of the dead pigs using a device similar to a heart-lung machine.

What happened next raises questions about what science considers the wall between life and death. Although the pigs were not considered conscious in any way, their seemingly dead cells were revived. Their hearts began to beat as the solution, which the scientists called OrganEx, circulated through their veins and arteries. The cells in their organs, including the heart, liver, kidneys and brain, were still functional and the animals never languished like a typical dead pig.

Other pigs that were dead within an hour were treated with ECMO, a machine that pumped blood through their bodies. They stiffened, their organs became swollen and damaged, their blood vessels collapsed, and they had purple spots on their backs where blood pooled.

The team reported their results Wednesday in Nature.

Researchers say their goal is to one day increase the supply of human organs for transplant, allowing doctors to obtain viable organs long after death. And, they say, they hope their technology can also be used to prevent severe heart damage after a devastating heart attack or serious stroke.

But the findings are just the first step, said Stephen Latham, a bioethicist at Yale University who worked closely with the team. The technology, he stressed, “is a long way from being used in humans.”

The team, led by Dr. Nenad Sestan, a professor of neuroscience, comparative medicine, genetics and psychiatry at the Yale School of Medicine, was amazed by the cells’ ability to regenerate.

“We didn’t know what to expect,” said Dr. David Andreevich, also a Yale neuroscientist and one of the authors of the paper. “Everything we’ve recovered has been incredible to us.”

Others not connected to the work were also surprised.

“It’s mind-boggling, it’s mind-boggling,” said Nita Farahani, a Duke law professor who studies the ethical, legal and social implications of emerging technologies.

And Dr. Farahani added that the paper raises questions about the definition of death.

“We assume that death is a thing, it’s a state of being,” he said. “There are forms of death that are reversible. If no?”

The work began a few years ago, when the group conducted a similar experiment on the brains of dead pigs from the slaughterhouse. Four hours after the pigs died, the team injected an OrganEx-like solution called BrainEx and saw that brain cells that were supposed to be dead could be regenerated.

That led them to ask whether they could revive the whole body, said Dr. Zvonimir Vrsela, another member of the Yale team.

The OrganEx solution contained nutrients, anti-inflammatory drugs, drugs to prevent cell death, nerve blockers—substances that slow down the activity of neurons and prevent the pigs from regaining consciousness—and artificial hemoglobin mixed with each animal’s blood.

As they treated the slaughtered pigs, investigators took precautions to ensure the animals were not harmed. Pigs were anesthetized before they were killed by cardiac arrest, and deep anesthesia continued throughout the experiment. In addition, the nerve blockers in the OrganEx solution stop the nerve firing to make sure the brain is not active. The researchers also chilled the animals to slow the chemical reactions. Individual brain cells were alive, but there was no sign of organized global neural activity in the brain.

There was one startling finding: Pigs treated with OrganEx turned their heads when researchers injected iodine contrast solution for imaging. Dr. Latham emphasized that while the cause of the movement was not known, there was no indication of any brain involvement.

Yale filed a patent on the technology. The next step, Dr. Sestan said, will be to see if the organs are functioning properly and can be successfully transplanted. Over time, the researchers hope to test whether this method can repair damaged hearts or brains.

The journal Nature asked two independent experts to comment on the study. In one, Dr. Robert Port, a transplant surgeon at the University of Groningen in the Netherlands, discussed the possible use of the system to expand organs available for transplant.

In a phone interview, he explained that OrganEx could be used in the future in situations where patients are not brain dead, but brain damaged to the point where life support is ineffective.

In most countries, Dr. Port said, there is a five-minute “no-touch” policy after the respirator is turned off and before transplant surgeons remove organs. But, he said, “it’s extra minutes before you rush to the OR,” and by then organs can be damaged beyond repair.

And sometimes patients don’t die immediately when life support goes off, but their hearts beat too weakly for their organs to be healthy.

“In most countries, transplant teams wait two hours for patients to die,” Dr. Porte said. Then, he said, if the patient is not already dead, they don’t try to remove the organs.

As a result, 50 to 60 percent of patients who die after life has ended and whose families would like to donate their organs cannot be donors.

If OrganEx could regenerate these organs, Dr. Port said, the effect would be “huge” — a huge increase in the number of organs available for transplant.

Another comment was by Brendan Parent, a lawyer and ethicist who is director of transplant ethics and policy research at New York University’s Grossman School of Medicine.

In a phone interview, he discussed what he said were “tough life-and-death questions” that OrganEx poses.

“By the accepted medical and legal definition of death, these pigs were dead,” Mr Parent said. But, he added, “the critical question is: What function and what kind of function would change things?”

Would the pigs be dead if the group hadn’t used the nerve blockers in his solution and their brains would still be functioning? This would create ethical problems if the goal was to preserve organs for transplantation and the pigs gained some degree of intelligence in the process.

But restoring brain function may be a goal if the patient has had a severe stroke or drowning victim.

“If we’re going to get this technology to the point where it can help people, we need to see what happens in the brain without nerve blockers,” Mr. Parent said.

In his view, the method should eventually be tested on people who could benefit, such as stroke or drowning victims. But this will require a lot of deliberation by ethicists, neurologists and neuroscientists.

“How we get there will be the critical question,” Mr. Parent said. “When does the data we have justify it?”

Another question is what impact OrganEx might have on the definition of death.

If OrganEx continues to show that the length of time it takes for cells to recover after a lack of blood and oxygen is much longer than previously thought, then the time when a person is determined to be dead needs to change.

“It’s strange, but no different than what we went through when developing the ventilator,” Mr. Parent said.

“There’s a whole population of people that in another era could be called dead,” he said.

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