Organ transplantation is a critical medical procedure, but the current methods for preserving donor organs have significant limitations. The field of transplantation is facing a serious donor shortage crisis, with more than five times the number of patients on the waiting list than those who will receive a donor organ in the USA. One of the major limitations is the current preservation times for whole organs, which is typically limited to 8-10 hours using the standard method of static cold storage at 4°C. Researchers have been exploring new strategies to extend organ preservation times, including metabolic support through machine perfusion and metabolic depression through cryopreservation techniques.
In this groundbreaking study, a team of researchers from the Massachusetts General Hospital and Shriners Hospitals for Children have developed an optimized partial freezing protocol that enables the storage of rat livers for up to 10 days – a significant advancement in the field of organ preservation. The researchers leveraged a bioinspired technique called “partial freezing,” which takes advantage of subzero preservation with controlled ice formation to avoid the damaging effects of full freezing. By precisely controlling the ice nucleation and the unfrozen fraction, the researchers were able to extend the viable preservation time of rodent livers from 5 days to 10 days, outperforming the current gold standard of static cold storage. This study represents a significant step forward in addressing the donor organ shortage and revolutionizing the field of transplant medicine.
Overcoming the Limitations of Static Cold Storage
The standard method of static cold storage (SCS) at 4°C imposes a preservation time limit of 8-10 hours, which can have significant implications for organ allocation, handling, and transplantation. Longer preservation times could shift surgeries from emergency to planned, resulting in reduced transplantation costs and improved matching based on human leukocyte antigen (HLA) compatibility. Additionally, prolonged preservation could enable the implementation of immune tolerance protocols, which promise to eliminate rejection and weaning patients off immunosuppressive regimens, ultimately enhancing recipients’ quality of life and improving patient survival.
To address these limitations, researchers have explored two main strategies: metabolic support and metabolic depression. Metabolic support involves providing essential nutrients and oxygen to maintain the viability of organs, as seen in the advancement of machine perfusion technology. While machine perfusion has demonstrated success in extending preservation time up to 7 days, it is limited by high costs, challenging logistics, and labor-intensive equipment.
Harnessing the Power of Partial Freezing
Metabolic depression, on the other hand, aims to prolong organ storage by lowering the temperature and depressing metabolism. This approach has led to the development of various preservation strategies, such as supercooling, isochoric preservation, and vitrification. However, these techniques have their own limitations, including the need for highly stable storage conditions, technologically advanced storage systems, and complex warming processes.
The researchers in this study have introduced an attractive alternative called “partial freezing” (PF), which takes advantage of subzero preservation with controlled ice formation. Inspired by the freeze-tolerance strategies observed in the Sylvatica wood frog (Rana Sylvatica), the PF technique leverages specialized storage solutions to promote extracellular ice nucleation while avoiding damaging intracellular ice formation. This allows for deeper storage temperatures, as low as -15°C, compared to the limitations of supercooling.
Optimizing the Partial Freezing Protocol
The researchers’ initial PF protocol was able to store rat livers for 5 days, but they identified the need for further improvements to extend the viable preservation time. To achieve this, they adopted several key optimizations:
1. Increased the concentration of polyethylene glycol (PEG) to 10% in the storage solution to enhance membrane stability and minimize shear stress during cryoprotectant unloading.
2. Introduced a 20-minute acclimation period during the thawing phase to gradually unload the cryoprotectants and prevent potential damage.
3. Increased the concentration of bovine serum albumin (BSA) in the recovery solution to maintain the precise balance of fluid dynamics between the cell’s interior and exterior, ensuring proper cellular hydration and function.
Figure 2
Remarkable Results: 10-Day Liver Storage
The optimized PF protocol demonstrated significant improvements in liver function and viability. During the recovery phase, the 10% PEG group showed reduced vascular resistance, increased oxygen uptake, and decreased tissue edema compared to the previous 5% PEG protocol.
When the researchers tested the efficacy of the optimized protocol for 10-day storage, the results were truly remarkable. The partially frozen livers stored for 10 days (PF10) outperformed the time-matched static cold stored (SCS10) livers in several key metrics:
– Vascular resistance was significantly lower in PF10 compared to SCS10 throughout the simulated transplantation.
– Oxygen uptake rate was higher in PF10, indicating better mitochondrial function.
– Liver transaminases (ALT and AST) were lower in PF10, suggesting less cellular damage.
– Edema was greatly reduced in PF10, with only a 3% increase in weight compared to 83% in SCS10.
– Bile production was sustained in PF10, but not in SCS10, indicating better overall liver function.
Figure 3
Transforming Transplant Medicine
This study represents a significant advancement in expanding organ availability through prolonged preservation. By extending the viable storage time of rat livers from 5 days to 10 days using the optimized partial freezing protocol, the researchers have taken a crucial step towards revolutionizing the field of transplant medicine.
The ability to store organs for up to 10 days could have a profound impact on organ allocation, handling, and transplantation. It would allow for better matching, reduced transplantation costs, and the implementation of promising immune tolerance protocols, ultimately improving the quality of life and survival rates for transplant recipients.
Figure 4
Future Directions and Broader Implications
While this study was conducted using rat livers, the researchers plan to explore the application of the optimized partial freezing protocol to larger animal models and, eventually, human livers. Successful translation to human organs would be a game-changer, as it could dramatically increase the donor pool and transform the landscape of transplant medicine.
Furthermore, the insights gained from this research could have broader implications beyond organ transplantation. The principles of controlled ice formation and metabolic depression could potentially be applied to the preservation of other tissues and cells, opening up new avenues for regenerative medicine and personalized therapies.
As the scientific community continues to push the boundaries of organ preservation, studies like this one offer hope for a future where the donor organ shortage is a thing of the past, and transplant recipients can look forward to longer, healthier lives.
Meta description: Researchers develop an optimized partial freezing protocol that enables 10-day storage of rat livers, a revolutionary advancement in organ preservation that could transform the field of transplant medicine.
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