Hypothermic and Normothermic Machine Perfusion Differentially Shape the Renal Cellular Landscape
Using a murine model, this study demonstrates that while both hypothermic and normothermic machine perfusion improve upon static cold storage by inducing antioxidant and hypoxia-responsive genes, normothermic perfusion uniquely causes more severe tubular injury, heightened inflammation, and increased immune cell mobilization compared to hypothermic perfusion.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
When a person needs a new kidney, doctors rely on a donor. But there are not enough healthy kidneys to go around, so medical teams increasingly turn to organs from older donors or those who have died after their heart stopped beating. These "extended-criteria" kidneys are more fragile and often arrive damaged. To keep them alive and healthy between the moment of donation and the moment of transplant, surgeons use a technique called machine perfusion. Instead of simply wrapping the organ in ice and letting it sit in a cold solution, this method pumps a special oxygen-rich liquid through the kidney's blood vessels. This mimics the flow of blood, keeping the cells supplied with what they need to survive.
For years, the standard approach has been to keep the machine cold, chilling the kidney to about 4 degrees Celsius. This slows down the organ's metabolism, putting it into a state of deep rest. However, a newer, more ambitious approach keeps the kidney at normal body temperature, around 37 degrees Celsius. This warm method allows the organ to function almost as if it were still inside a body, potentially allowing doctors to check if the kidney is working before it is ever put into a patient. While the warm method has shown great promise for livers, scientists have been unsure if it is safe for kidneys, which are more delicate. The central question has been whether keeping a kidney warm and active actually helps it, or if the extra energy it burns causes more harm than good.
A team of researchers in Berlin set out to answer this by comparing the two methods side by side using a precise model. They took kidneys from mice and connected them to a machine that pumped oxygenated fluid through them for one hour. Some kidneys were kept cold, while others were kept warm. The researchers then looked very closely at what happened inside the organ, examining the tiny cells that make up the kidney and the immune cells that live within it. They wanted to see which method kept the tissue healthier and which one caused more stress or damage.
The results revealed that the two methods affect the kidney in very different ways. The warm, active perfusion caused more severe injury to the tubules, which are the tiny tubes inside the kidney that filter waste from the blood. When the kidney was kept warm, the researchers observed that immune cells, which act as the body's security team, were pushed out of the organ and into the circulating fluid. Specifically, the warm method caused a significant release of neutrophils, a type of white blood cell often associated with inflammation and tissue damage. In contrast, the cold method kept more of the organ's resident immune cells, such as certain types of T cells and macrophages, safely inside the kidney.
The study also looked at how the cells were dying. In the warm kidneys, the immune cells that stayed behind were more likely to be in the early stages of programmed cell death, a process where a cell shuts itself down in an orderly fashion. The cells that make up the blood vessels, known as endothelial cells, showed signs of dying later in the process under both warm and cold conditions, but the warm method seemed to trigger this more aggressively. Interestingly, the cells that line the kidney's filtering tubes did not show a major difference in how they died between the two methods, but the overall picture suggested that the warm environment was more stressful for the organ's internal structure.
On a molecular level, the researchers found that both methods helped the kidney prepare for the stress of being outside the body by turning on genes that protect against damage. However, the warm method turned on a much stronger inflammatory response. It increased the production of genes associated with inflammation and stress, suggesting that while the warm kidney is active, it is also fighting a battle against its own internal environment. The cold method, by keeping the organ in a state of rest, avoided this intense inflammatory flare-up.
To test if this model could be used to find new treatments, the team tried adding a drug called ABT-263 to the warm perfusion fluid. This drug is designed to clear out old, damaged cells. They found that the drug worked as intended in some areas, reducing the activation of blood vessel cells and changing the behavior of immune cells. However, it also increased stress in the kidney's filtering cells, showing that even a treatment designed to help can have complex side effects depending on the cell type.
Ultimately, this research suggests that while keeping a kidney warm allows it to function, it comes with a cost. The warm method accelerates injury to the filtering tubes and triggers a stronger inflammatory response than the cold method. The cold method, while less active, appears to preserve the kidney's internal cellular landscape better, keeping the immune system more contained and reducing the immediate stress on the organ's structure. These findings provide a clearer picture of how different preservation strategies change the biology of a donor kidney, helping scientists understand why one method might be better than the other for specific types of organs. The study confirms that the choice of preservation method is not just about temperature, but about how that temperature shapes the life and death of every cell inside the graft.
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