Date Published: April 24, 2019
Publisher: Public Library of Science
Author(s): Mariusz Bral, Nader Aboelnazar, Sanaz Hatami, Aducio Thiesen, David L. Bigam, Darren H. Freed, A. M. James Shapiro, Akshay Chauhan.
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.
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.
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). 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.
Due to a worldwide shortage of organs available for transplantation, there is increasing pressure to consider more marginal and ‘extended criteria’ liver grafts, in hopes of expanding the donor pool. It is well recognized that such grafts are not optimally preserved with current static cold storage (SCS), resulting in increased instances of both short and long term post-transplant complications. It is increasingly important that such grafts undergo some form of functional assessment before transplant to minimize any adverse outcomes.
The ex situ circuit was primed concomitantly with donor procurement surgery and NMP was established in all cases without difficulty. Mean starting hemoglobin concentration of the perfusates was 62.8 ± 8.7 g/L. There were no technical complications during the machine perfusions for any of the livers. The starting enzyme values in the prepared concentrated supernatant were as follows: AST 107,427 U/L, ALT 2,788 U/L and LDH 28,050 U/L. Tissue concentrate biochemistry from other solid abdominal organs, not used in any perfusions, was as follows: Kidney- AST 44,383 U/L, ALT 2,128 U/L, LDH 23,995 U/L, Lac 6.41 mmol/L; Spleen- AST 9,004 U/L, ALT 273 U/L, LDH 26,041 U/L, Lac 10.57 mmol/L.
Liver ex situ NMP has previously demonstrated the potential to resuscitate donor livers that would otherwise be discarded from the transplant process . Functional evaluation of such livers is necessary prior to implantation, in order to minimize the possibility of the catastophic outcome of primary non-function (PNF). Ex situ NMP offers a potentially ideal temperature modality, as it allows for viability assessment occur in the setting of physiologic metabolism.