The last thing the field of gene therapy needs is another setback. Two studies, not yet peer-reviewed, point to adeno-associated virus (AAV)…
Transplant medicine could take a giant leap forward if donor organs could soak up oxygen for longer and decay delayed. A technology called OrganEx, described in Nature from a team at Yale, promises to do just that. The researchers stopped the hearts of pigs and an hour later used OrganEx, then cataloged the return of bodily functions. The new approach far exceeded the ability of existing technology to prolong organ viability.
Pigs have long been a popular animal model of human disease because they are about our size and their hearts and blood vessels are quite similar. They have also had fictional roles in medicine.
In the Twilight Zone episode Eye of the Beholder, Janet Tyler has undergone multiple procedures to replace the “pitiful twisted lump of flesh” that is her face with something more acceptable. At the end, as the bandages are slowly unrolled from yet another failed procedure, we see that she naturally looks like us, considered hideous in her world where most people, including the nurse and doctor, have pig faces. Janet and others like her are sent to live among themselves.
Arnold Ziffel, aka Arnold the Pig, served as a child substitute on the TV show Green Acres, which ran from 1965 to 1971.
In a 1993 episode of Seinfeld, Kramer, visiting a friend at a hospital, thinks he sees a Pigman running through the hallway, the result of an experiment gone awry on an upper floor.
In real life, in 1997 a 15-week-old, 118-pound pig named Sweetie Pie made medical history. A 19-year-old suffering from liver failure desperately needed a transplant. He survived for 6 hours awaiting a donor organ with his blood circulating outside of his body through Sweetie Pie’s disembodied liver. Sweetie Pie was no ordinary pig, not even one as wonderful as Arnold. Her cells were festooned with human proteins, which shielded her liver from the patient’s immune system.
The Twilight Zone pigfaces were a metaphor, Arnold a child stand-in, Pigman a mystery, and Sweetie Pie a temporary liver replacement. But the pigs in the new study promise to be much more.
A characteristic chemical choreography sets in upon brain death or the heart stopping. In just minutes after oxygen ebbs, acids build up as cells swell, injuring delicate membranes and organelles. The distinct events of cell death begin to unfold.
At the whole-body level a flood of hormones and cytokines alerts cells and triggers inflammation. The nervous and immune systems, as well as blood clotting, go into overdrive as organs shut down. But even organs in their death throes have some viable cells that can be scooped out and nurtured in laboratory glassware. Isolated, entire organs, including hearts, livers, kidneys and lungs, can be kept going if a proper soup is sent (perfused) through their vessels.
These observations led to the Yale team’s developing BrainEx technology in 2019. That kept alive pig brains, the organ most vulnerable to damage from lack of oxygen.
“OrganEX is a continuation of our BrainEx, adjusted from an isolated brain to a whole body. Similar to the previous study, this study showed we can restore certain cell functions after death and we see similar cell recovery in other organ systems. Cells don’t die as quickly as we assumed, which opens up the possibility for intervention,” said Zvonimir Vrselja in a webinar that Nature held just before the paper published. The researchers induced heart attacks to kill the pigs used in the BrainEx experiments, followed by up to six hours of oxygen deprivation.
Both BrainEx and OrganEx use a “cryoprotective perfusate,” a cold elixir packed with synthetic hemoglobin to carry oxygen. The brew also includes antibiotics, anti-inflammatories, suppressors of cell death, and various molecules to keep cells safe and able to withstand freezing while quelling clotting.
While the OrganEx recipe was tweaked to cover a whole pig body, the key change was computer control of a pump to send the stuff through the circulatory system of an entire large mammal. The set-up resembles a heart-lung machine. An illustration in the Nature paper depicts a splayed cartoon pig hooked up to various sensors (hemoglobin, heartbeat, blood flow, and pressure), pumps, a tank of drugs including heparin to maintain blood flow, an oxygenator, and a dialysis unit to maintain electrolytes.
A bioethicist was on board to ensure that the pigs – females 10 to 12 weeks old – didn’t suffer. They were given fentanyl patches, deep anesthesia, and then their hearts stopped with 9-volt batteries.
Better than ECMO
An hour after death, some pigs were placed on OrganEx and some on ECMO (extracorporeal membrane oxygenation), an existing technique that recirculates an animal’s oxygenated blood and can keep it going for maybe 20 minutes. Instead, OrganEx replaces the blood – and the different recipe works better.
After six hours, ECMO hadn’t reached all the pig organs, and many smaller blood vessels had collapsed. But OrganEx pigs had full reperfusion and stable oxygen consumption, plus no electrolyte disturbances and acidic body fluids that result from lack of oxygen. The pigs passed various tests of their returning physiology: glucose, blood clotting, kidney function, EEG, and EKG.
When the researchers looked closely at bits of major organs – brain, heart, lung, liver, kidney, and pancreas – they found less damage and more repair and recovery after OrganEx than after ECMO. The kidneys on OrganEx even showed signs of cell division.
Analyzing gene expression drilled down even further, probing which genes were being turned on or off in individual cells sampled from the kidneys, liver, and heart. The findings echoed those seen at the tissue and organ levels, validating the approach. The key differences between OrganEx and ECMO to emerge from all the testing were in extent of inflammation and cell death.
Nenad Sestan summed up the findings. “OrganEx restored function in numerous organs hours after they should have been dead. The demise of cells can be halted, and cells can restart, even an hour after death induced by circulatory arrest.”
The demonstration of OrganEx’s superiority may open doors to future treatments, said David Andrijevic. “Our findings highlight a previously unappreciated capacity of a large mammalian body to recover after cessation of life. The findings have the potential to increase organ availability for transplant or treat local organ ischemia,” which causes clotting problems such as strokes and heart attacks.
What’s ahead for OrganEx? Testing in specific clinical situations.
OrganEx could expand the donor organ pool. An individual who is brain dead and has circulation to perfuse the organs can be a donor, but that’s not so for a person who is brain dead but whose circulation has ceased. Lack of oxygen ignites the cascade of organ damage and demise.
The precious coolers with organ decals that festoon the surgical suites of TV medical shows can only buy a bit of time. OrganEx could greatly extend that. But that brings me back to the realm of the Twilight Zone.
What if OrganEx works too well?
Could cerebral neurons of a heart-stopped, brain-dead organ donor suddenly start firing action potentials and then connect as new synapses form? Imagine a car accident victim splayed on a table, hooked up to machines, awaiting organ harvesting. And suddenly the brain starts to awaken.
That’s what happens in one of my favorite novels, Kazuo Ishiguro’s 2005 Never Let Me Go, also a 2010 film.
At a creepy boarding school in England, young students are groomed to “make donations” to wealthy people of their organs, “completing” by young adulthood. The plot unspools from a blabbing teacher, who tells the kids how their livers, kidneys, spleens, and all parts will be plucked out, one by one, until they “complete.”
The new work has a bioethicist aboard to ensure that the pigs die painlessly. I hope he will stay around to consider all possibilities for the aftermath of the well-meant and very promising OrganEx. For in science, results aren’t always what we expect.