Development of a normothermic extracorporeal liver perfusion system toward improving viability and function of human extended criteria donor livers

Abstract

Donor organ shortages have led to an increased interest in finding new approaches to recover organs from extended criteria donors (ECD). Normothermic extracorporeal liver perfusion (NELP) has been proposed as a superior preservation method to reduce ischemia/reperfusion injury (IRI), precondition suboptimal grafts, and treat ECD livers so that they can be successfully used for transplantation. The aim of this study was to investigate the beneficial effects of a modified NELP circuit on discarded human livers. Seven human livers that were rejected for transplantation were placed on a modified NELP circuit for 8 hours. Perfusate samples and needle core biopsies were obtained at hourly intervals. A defatting solution that contained exendin-4 (50 nM) and L-carnitine (10 mM) was added to the perfusate for 2 steatotic livers. NELP provided normal temperature, electrolytes, and pH and glucose levels in the perfusate along with physiological vascular flows and pressures. Functional, biochemical, and microscopic evaluation revealed no additional injuries to the grafts during NELP with an improved oxygen extraction ratio (>0.5) and stabilized markers of hepatic injury. All livers synthesized adequate amounts of bile and coagulation factors. We also demonstrated a mild reduction (10%) of macroglobular steatosis with the use of the defatting solution. Histology demonstrated normal parenchymal architecture and a minimal to complete lack of IRI at the end of NELP. In conclusion, a modified NELP circuit preserved hepatocyte architecture, recovered synthetic functions, and hepatobiliary parameters of ECD livers without additional injuries to the grafts. This approach has the potential to increase the donor pool for clinical transplantation. The major limiting factor of using extended criteria donor (ECD) grafts is their greater susceptibility to injury during cold preservation and lower tolerance for ischemia/reperfusion injury (IRI) upon reperfusion. Therefore, ECD grafts have been associated with a higher risk of posttransplant complications such as primary graft nonfunction and chronic cholangiopathy.(1-4) Machine perfusion has been investigated both as a preservation method to reduce IRI in ECD livers and as a method to assess the viability and function of suboptimal grafts prior to transplantation.(5-7)Currently, there are 3 variants of liver machine perfusion that are distinguished by the perfusate temperature: hypothermic, subnormothermic, and normothermic.

The future of organ perfusion and re‐conditioning

“…Banan et al . have reported results from two human livers which were preserved normothermically with the addition of de‐fatting agents, namely l‐carnitine and exendin‐4. However, in the two treated livers, only one showed a minimal reduction in the degree of macrovesicular steatosis (10%) after 8 h NMP .…”

Improvement of Normothermic Ex Vivo Machine Perfusion of Rat Liver Grafts by Dialysis and Kupffer Cell Inhibition With Glycine

“…The need of plasma volume expansion may be due to suboptimal perfusion conditions in our experimental setup because it is not integrated to most of the clinically used systems. However, Banan et al used a dialyzer to maintain the perfusate pH and electrolyte profiles within physiologic ranges throughout the 8‐hour NEVLP of human liver grafts . Rigo et al recently reported on escalating transaminase release during 4 hours of normothermic perfusion of rat livers without dialysis, resulting in significant damage of the liver architecture …”

Combined liver‐kidney perfusion enhances protective effects of normothermic perfusion on liver grafts from donation after cardiac death

“…Additional to an osmotic effect, it has been shown that a high concentration of urea (100 mmol/L) negatively affects hepatic metabolism via proteolysis inhibition . For this reason, Banan et al incorporated a dialyzer to clear the urea and glucose in the circuit, but it would not be feasible in a portable system. Also, the costs of adding a dialyzer to the system will be $20,000–$30,000 …”