Clearance of transaminases during normothermic ex situ liver perfusion

Abstract

Background One of the most promising applications of liver normothermic machine perfusion (NMP) is the potential to directly assess graft viability and injury. In most NMP studies, perfusate transaminases are utilized as markers of graft injury. Our aim was to further elucidate the metabolism of transaminases by healthy porcine livers during NMP, specifically whether such livers could clear circuit perfusate transaminases. Methods A highly concentrated transaminase solution was prepared from homogenized liver, with an aspartate aminotransferase (AST) level of 107,427 U/L. Three livers in the treatment group were compared to three controls, during 48 hours of NMP. In the treatment group, the circuit perfusate was injected with the transaminase solution to artificially raise the AST level to a target of 7,500 U/L. Perfusate samples were taken at two-hour intervals and analyzed for biochemistry until NMP end. Graft oxygen consumption and vascular parameters were monitored. Results Compared to controls, treated perfusions demonstrated abrupt elevations in transaminase levels (p>0.0001) and lactate dehydrogenase (LDH) (p>0.0001), which decreased over time, but never to control baseline. Liver function, as demonstrated by lactate clearance and oxygen consumption was not different between groups. The treatment group demonstrated a higher portal vein resistance (p = 0.0003), however hepatic artery resistance was similar. Treated livers had higher bile production overall (p<0.0001). Conclusions Addition of high levels of transaminases and LDH to a healthy porcine liver during ex situ perfusion results in progressive clearance of these enzymes, suggesting preserved liver metabolism. Such tolerance tests may provide valuable indicators of prospective graft function.

Design, Analysis, and Pitfalls of Clinical Trials Using Ex Situ Liver Machine Perfusion: The International Liver Transplantation Society Consensus Guidelines

“…46,47 The ideal biomarker would be specific, easily processed and inexpensive with a quick "turn around" time that could be available before transplantation. 48 It would also have to predict long-term clinically relevant outcomes with a high degree of precision. Unfortunately, in MP trials, no single parameter (or combination of parameters) has been clearly established that meets strong criteria as a surrogate endpoint.…”

“…Unfortunately, in MP trials, no single parameter (or combination of parameters) has been clearly established that meets strong criteria as a surrogate endpoint. [46][47][48] Additionally, MP introduces many variables that may affect intra-and postoperative parameters. For example, size of the liver, volume of perfusate, and temperature of perfusion may all impact on machine and even postreperfusion transaminases levels.…”

“…65,66 Perfusate transaminases (as opposed to postoperative systemic levels of transaminase) have been used (typically in combination with graft lactate clearance and bile production) during NMP to determine the viability of a particular graft for implantation. 1,7,48,67 Transaminase levels may be influenced by the age of the donor, steatosis, ischemia time, among other factors. Perfusate transaminases should be normalized for liver weight and perfusate volume to allow comparability with other perfusion systems and different livers.…”

The Emerging Role of Viability Testing During Liver Machine Perfusion

“…( 43 ) Transaminases can also be cleared by the liver itself, further complicating the analysis. ( 44 ) In addition, reperfusion and oxygenation during machine perfusion lead to the release of accumulated transaminases in the organ to the perfusion solution. If perfusate transaminase levels are used as a marker for liver injury, they should be corrected for liver weight and perfusate volume to generalize cutoff values.…”

“…Instead of absolute transaminase levels, the clearance of endogenous or exogenous transaminases during NMP may be used to test liver function. ( 44 )…”