Suitability of livers for transplantation when treated by normothermic machine perfusion

Contemporary strategies to assess and manage liver donor steatosis: a review

PURPOSE OF REVIEW

Due to a persistent shortage of donor livers, attention has turned toward ways of utilizing marginal grafts, particularly those with steatosis, without incurring inferior outcomes. Here we review the evaluation and utilization of steatotic liver allografts, highlight recently published data, and discuss novel methods of graft rehabilitation.

RECENT FINDINGS

Although severe liver allograft (>60%) steatosis has been associated with inferior graft and recipient outcomes, mild (<30%) steatosis has not. There is ongoing debate regarding safe utilization of grafts with moderate (30-60%) steatosis. Presently, no established protocols for evaluating steatosis in donor candidates or utilizing such grafts exist. Liver biopsy is accepted as the gold standard technique, though noninvasive methods have shown promise in accurately predicting steatosis. More recently, machine perfusion has been shown to enhance ex situ liver function and reduce steatosis, emerging as a potential means of optimizing steatotic grafts prior to transplantation.

SUMMARY

Steatotic liver allografts constitute a large proportion of deceased donor organs. Further work is necessary to define safe upper limits for the acceptable degree of steatosis, develop standardized evaluation protocols, and establish utilization guidelines that prioritize safety. Machine perfusion has shown promise in rehabilitating steatotic grafts and offers the possibility of expanding the deceased donor pool.

A Novel Oxygen Carrier (M101) Attenuates Ischemia-Reperfusion Injuries during Static Cold Storage in Steatotic Livers

The combined impact of an increasing demand for liver transplantation and a growing incidence of nonalcoholic liver disease has provided the impetus for the development of innovative strategies to preserve steatotic livers. A natural oxygen carrier, HEMO2life^®, which contains M101 that is extracted from a marine invertebrate, has been used for static cold storage (SCS) and has shown superior results in organ preservation. A total of 36 livers were procured from obese Zucker rats and randomly divided into three groups, i.e., control, SCS-24H and SCS-24H + M101 (M101 at 1 g/L), mimicking the gold standard of organ preservation. Ex situ machine perfusion for 2 h was used to evaluate the quality of the livers. Perfusates were sampled for functional assessment, biochemical analysis and subsequent biopsies were performed for assessment of ischemia-reperfusion markers. Transaminases, GDH and lactate levels at the end of reperfusion were significantly lower in the group preserved with M101 (p < 0.05). Protection from reactive oxygen species (low MDA and higher production of NO2-NO3) and less inflammation (HMGB1) were also observed in this group (p < 0.05). Bcl-1 and caspase-3 were higher in the SCS-24H group (p < 0.05) and presented more histological damage than those preserved with HEMO2life^®. These data demonstrate, for the first time, that the addition of HEMO2life^® to the preservation solution significantly protects steatotic livers during SCS by decreasing reperfusion injury and improving graft function.

Changing Trends in Liver Transplantation: Challenges and Solutions

Despite improvements in postliver transplant outcomes through refinements in perioperative management and surgical techniques, several changing trends in liver transplantation have presented challenges. Mortality on the waitlist remains high. In the United States, Europe, and the United Kingdom, there is an increasing need for liver transplantation, primarily as a result of increased incidence of nonalcoholic steatohepatitis-related cirrhosis and cancer indications. Meanwhile, donor suitability has decreased, as donors are often older and have more comorbidities. Despite a mismatch between organ need and availability, many organs are discarded. Notwithstanding this, many solutions have been developed to overcome these challenges. Innovative techniques in allograft preservation, viability assessment, and reconditioning have allowed the use of suboptimal organs with adequate results. Refinements in surgical procedures, including live donor liver transplantations, have increased the organ pool and are decreasing the time and mortality on the waitlist. Despite many challenges, a similar number of solutions and prospects are on the horizon. This review seeks to explore the changing trends and challenges in liver transplantation and highlight possible solutions and future directions.

Cold-to-warm machine perfusion of the liver: a novel circuit for an uninterrupted combined perfusion protocol

BACKGROUND

Ex-vivo perfusion of liver grafts is associated with promising results for the preservation of marginal grafts. Recent studies highlight the need for a combination of perfusion conditions, such as hypothermic followed by normothermic perfusion. While comprehensive machines dedicated to liver perfusion have been developed, these systems remain costly and poorly adaptable to perfusion condition switch, which requires a complete interruption of the perfusion process. Our team aimed at developing an adaptable and simple circuit for uninterrupted ex-vivo liver perfusion.

METHODS

Together with specialized bioengineers, we developed a highly adaptable circuit that can fit on already pre-existing extracorporeal oxygenation machines routinely used in cardiovascular surgery. This circuit, owing to its reservoir, allows any type of perfusion conditions without interrupting the perfusion process.

RESULTS

In a preliminary study, to assess the technical feasibility of liver perfusion using our circuit under different conditions, we performed 7 perfusions of discarded liver grafts. HOPE and DHOPE hypothermic perfusion could be performed, and a switch to normothermia was easily possible within seconds. From there, a dynamic perfusion sequence model was developed.

CONCLUSION

This circuit may represent a simpler alternative or a new refinement to existing perfusion systems allowing uninterrupted combined perfusion protocols.