Proteomic Insights from Thrombolytic Ex-Vivo Machine Perfusion in an Extended uDCD Porcine Model

Every year, thousands of people die waiting for a kidney transplant. A significant portion of these potential donors are individuals who have suffered a sudden cardiac arrest. In these cases, the heart stops beating, and the body's organs begin to suffer from a lack of oxygen and blood flow. This period of deprivation, known as warm ischemia, is particularly damaging to the kidneys. Unlike a brain-dead donor whose heart is still beating and circulating oxygenated blood, a donor after circulatory death has kidneys that have been starved of oxygen for a critical window of time before they can be retrieved. During this time, the tiny blood vessels inside the kidney become clogged with a sticky mixture of blood cells and clotting proteins. It is as if the organ's internal plumbing has been blocked by a thick sludge, preventing blood from reaching the delicate filtering units even after the kidney is placed in a new body. Because of this damage, many of these kidneys are simply discarded, and the patients waiting for them remain on dialysis.

Scientists have long known that simply washing these organs with cold fluid is not enough to clear the blockage. A more promising approach involves using a machine to pump a special solution through the kidney outside the body, mimicking the flow of blood. However, standard machine perfusion often fails to dissolve the stubborn clots that form during the initial period of oxygen deprivation. Researchers have been working on a method to actively break down these clots using enzymes that act like molecular scissors, cutting the proteins that hold the blockages together. The goal is to restore the kidney's internal plumbing so that it can function once transplanted. While early experiments in pigs showed that this method could save kidneys that would otherwise be lost, the biological story of how the organ actually recovered remained a mystery. Did the treatment simply wash away the debris, or did it trigger a complex healing process within the organ's cells?

A team of researchers at the Sahlgrenska Academy in Sweden set out to answer this question by looking inside the kidneys at the molecular level. They used a technique called proteomics, which allows scientists to take a snapshot of every protein present in a tissue sample at a specific moment. Proteins are the workhorses of the body, carrying out almost every function, from building structures to fighting infection. By measuring thousands of these proteins, the researchers could see exactly how the kidney was changing over time. They studied kidneys from pigs that had undergone the same procedure as human donors: the heart stopped for four to five hours, the kidneys were treated with clot-busting enzymes, and then they were placed on a machine perfusion system before being transplanted back into the animals. They compared these treated kidneys to a control group of kidneys that were transplanted without any of the special treatment or machine perfusion, representing a healthy, standard transplant.

The researchers took tiny samples of the kidney tissue at several key moments: right after the kidney was retrieved from the donor, at the end of each phase of the machine perfusion, and again three months after the transplant. In total, they analyzed more than eight thousand different proteins. When they looked at the kidneys immediately after retrieval, the picture was stark. The tissue was dominated by proteins associated with blood clots, red blood cells, and inflammation. It was a molecular signature of a kidney in distress, clogged and overwhelmed by the aftermath of the heart stopping. The treated kidneys looked completely different from the healthy controls at this stage, confirming that the damage was severe.

However, as the treatment progressed, the story changed. During the machine perfusion, the researchers watched the levels of clotting proteins and red blood cell debris drop sharply. The enzymes successfully dissolved the blockages, and the machine washed the debris away. But the most surprising findings emerged three months later, after the kidneys had been living inside the pigs for a quarter of a year. By this time, the molecular profile of the treated kidneys had shifted dramatically. The chaotic signature of clots and inflammation had largely vanished. Instead, the proteins present in the treated kidneys began to resemble those in the healthy, control kidneys, showing a significant move toward a normal state. The organ had not just survived; it had healed.

Crucially, the study revealed what the kidney was not doing. There was a concern that treating these damaged kidneys might lead to a specific type of cell death driven by iron overload, a process that had been observed in other types of machine perfusion. The researchers looked carefully for signs of this iron toxicity and found none. The proteins that would indicate such damage were absent. Instead, the treated kidneys showed signs of active repair. They were building new structural components, such as collagen, which forms the scaffolding of the organ, and they were managing their energy use efficiently. The cells were not frantically trying to survive a crisis; they were settling into a state of stable recovery. The treatment appeared to guide the kidney through a process of structural adaptation rather than leaving it in a state of chronic injury or scarring.

The researchers also tracked a specific set of ninety-three proteins that were known to be involved in clotting, inflammation, and kidney stress. This targeted analysis confirmed the broader findings. The proteins that indicated blockage and damage disappeared quickly during the perfusion phase. Meanwhile, proteins associated with healing and tissue repair increased over the long term. The study showed that the treatment did not just clear the immediate obstruction; it allowed the kidney to reset its internal environment. The organ moved from a state of acute injury to a state of functional recovery, with its molecular machinery returning to a pattern that closely matched a healthy, transplanted kidney, although the study noted that this normalization was not yet complete.

This work provides a detailed map of how a damaged kidney can be rescued. It demonstrates that the blockage caused by a lack of oxygen is not necessarily permanent. By using enzymes to dissolve the clots and a machine to wash the organ, it is possible to reverse the molecular chaos of ischemia. The study suggests that the key to saving these marginal kidneys lies in addressing the physical blockages that prevent blood flow, rather than just trying to cool the organ down. While the research was conducted in pigs, the findings offer a strong biological basis for moving this approach into human trials. The data suggests that kidneys which were previously considered too damaged to use can be reconditioned to function normally, potentially opening the door to saving many more lives. The molecular evidence shows that the organ does not just survive the ordeal; it heals, returning to a state of health that is very close to, though not yet fully identical to, a standard transplant.