Impact of Machine Perfusion on Sinusoid Microcirculation of Liver Graft Donated After Cardiac Death

Machine perfusion preservation with hemoglobin based oxygen vesicles alleviate ultrastructural damages in porcine liver donated after cardiac death

Midthermic machine perfusion (MMP) of post-circulatory arrest donor liver grafts has the advantage of preserving the functional ultrastructure of hepatocytes in donor grafts. It was reported that oxygenation during MMP reduces portal venous resistance and increases bile production. The MMP with hemoglobin-based oxygen vesicles (HbV) keeps the lower aspartate aminotransferase level (an indicator of liver injury) and maintains the functional ultrastructure of mitochondria in the hepatocytes. To evaluated differences of ultrastructural damages in donor livers between the MMP with and without HbV, porcine liver grafts after 60 min of warm ischemia were perfused at 22°C for 4 h with or without HbV, and a part of liver grafts were analyzed by transmission electron microscopy (TEM) and osmium-maceration scanning electron microscopy (OM-SEM). The remaining grafts were perfused with autologous blood at 38°C for 2 h in an isolated liver reperfusion model (IRM) that mimics the inside of the body after transplantation, and then analyzed by TEM and OM-SEM. Hepatocytes after MMP had small round mitochondria with rod-shaped cristae and reticulovesicular rough endoplasmic reticulum (rER) in both HbV(+) and HbV(-) livers. After IRM of HbV(+) livers, the well-developed lamellar rER was often found in hepatocytes. Liver sinusoidal endothelial cells (LSECs) after MMP contained some large vacuolar structures containing amorphous garbage in the cytoplasm, and their size along with appearance frequency were smaller and lower, respectively, in HbV(+) livers than HbV(-). Oxygenation during the MMP by using HbV suppressed the ultrastructural damages in donor livers, in particular for the LSECs. RESEARCH HIGHLIGHTS: Liver sinusoidal endothelial cells after midthermic machine perfusion had large vacuolar organelles with amorphous garbage. Oxygenation during the perfusion made them less and smaller, ultrastructurally supporting its utility.

Preservation Efficacy of a Quercetin and Sucrose Solution for Warm Ischemically Damaged Porcine Liver Grafts

BACKGROUND

The University of Wisconsin (UW) solution is the gold standard for preserving the liver, kidneys, and pancreas. For renal preservation, the addition of the flavonoid, quercetin (QE), to the preservation solution reduces damage to renal tubular cells, and the addition of sucrose (Suc) is also beneficial for preservation. The aim of this study was to investigate the protective effects of QE and Suc on porcine livers in terms of warm and cold injury and to evaluate whether their use improves ischemia-reperfusion (I/R) injury after simple cold storage (CS).

METHODS

We tested porcine livers procured after 30 minutes of warm ischemia followed by preservation for 6 hours under the following 2 conditions: group 1, preserved with the CS/UW solution (n = 4); group 2, preserved with the CS/UW solution containing Que 33.1 μM and Suc 0.1 M (n = 6). All livers were evaluated using an ex vivo isolated liver reperfusion model with saline-diluted autologous blood.

RESULTS

Aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase levels in group 2 were significantly lower at 30 minutes of reperfusion than in group 1. Furthermore, histologic evaluation by hematoxylin and eosin staining showed significantly fewer morphologic changes in group 2 than in group 1, as indicated by the total Suzuki score. Group 2 also had significantly better scores for sinusoidal congestion and hepatocyte cytoplasmic vacuolization.

CONCLUSION

Adding Que and Suc to the UW solution can effectively prevent cold injury in livers donated after circulatory death.

Endothelial Cells and Mitochondria: Two Key Players in Liver Transplantation

Building the inner layer of our blood vessels, the endothelium forms an important line communicating with deeper parenchymal cells in our organs. Previously considered passive, endothelial cells are increasingly recognized as key players in intercellular crosstalk, vascular homeostasis, and blood fluidity. Comparable to other cells, their metabolic function strongly depends on mitochondrial health, and the response to flow changes observed in endothelial cells is linked to their mitochondrial metabolism. Despite the direct impact of new dynamic preservation concepts in organ transplantation, the impact of different perfusion conditions on sinusoidal endothelial cells is not yet explored well enough. This article therefore describes the key role of liver sinusoidal endothelial cells (LSECs) together with their mitochondrial function in the context of liver transplantation. The currently available ex situ machine perfusion strategies are described with their effect on LSEC health. Specific perfusion conditions, including perfusion pressure, duration, and perfusate oxygenation are critically discussed considering the metabolic function and integrity of liver endothelial cells and their mitochondria.

Ultrastructural changes in porcine liver sinusoidal endothelial cells of machine perfused liver donated after cardiac death

BACKGROUND

The machine perfusion (MP) preservation including hypothermic MP (HMP) and midthermic MP (MMP) has been considered as a promising strategy to preserve the functions of liver donated after cardiac death. The importance of understanding liver sinusoidal endothelial cells (LSEC) damage in regulating liver injury during MP has been emphasized. However, the ultrastructural changes in the LSEC and sinusoids around them after MP are unclear.

AIM

To investigate the ultrastructural changes in the LSEC and sinusoids around them after MP.

METHODS

Porcine liver grafts undergo a warm ischemia time of 60 minutes perfused for 4 h with modified University of Wisconsin gluconate solution. Group A grafts were preserved with HMP at 8 °C constantly for 4 h. Group B grafts were preserved with a rewarming solution at 22 °C by MMP for 4 h. Then the ultrastructural changes in the LSEC and sinusoids in Group A and B were comparatively analyzed by using osmium-maceration scanning electron microscopy with complementary transmission electron microscopy methods.

RESULTS

An analysis of the LSEC after warm ischemia revealed that mitochondria with condensed-shaped cristae, abnormal vesicles, reduction of ribosomes and the endoplasmic reticulum (ER) surround the mitochondria appeared. The MP subsequent after warm ischemia alleviate the abnormal vesicles and reduction of ribosomes in LSEC, which indicated the reduction of the ER damage. However, MMP could restore the tubular mitochondrial cristae, while after HMP the condensed and narrow mitochondrial cristae remained. In addition, the volume of the sinusoidal space in the liver grafts after MMP were restored, which indicated a lower risk of pressure injury than HMP.

CONCLUSION

MMP alleviates the ER damage of LSEC by warm ischemia, additionally restore the metabolism of LSEC via the normalization of mitochondria and prevent the share stress damage of liver grafts.

The Use of Hemoglobin-Based Oxygen Carriers in Ex Vivo Machine Perfusion of Donor Organs for Transplantation

There has been significant progress in the development of ex vivo machine perfusion for the nonischemic preservation of donor organs. However, several complications remain, including the logistics of using human blood for graft oxygenation and hemolysis occurring as a result of mechanical technology. Recently, hemoglobin-based oxygen carriers, originally developed for use as blood substitutes, have been studied as an alternative to red blood cell-based perfusates. Although research in this field is somewhat limited, the findings are promising. We offer a brief review of the use of hemoglobin-based oxygen carriers in ex vivo machine perfusion and discuss future directions that will likely have a major impact in progressing oxygen carrier use in clinical practice.

The Prognostic Utility of Intraoperative Allograft Vascular Inflow Measurements in Donation After Circulatory Death Liver Transplantation

Donation after circulatory death (DCD) liver transplantation improves deceased donor liver use and decreases waitlist burden, albeit at an increased risk of biliary complications and inferior graft survival. Employing liver vascular inflow measurements intraoperatively permits allograft prognostication. However, its use in DCD liver transplantation is hitherto largely unknown and further explored here. DCD liver transplantation patient records at a single center from 2005 to 2018 were retrospectively scrutinized. Intraoperative flow data and relevant donor parameters were analyzed against endpoints of biliary events and graft survival. A total of 138 cases were chosen. The incidence of cumulative biliary complications was 38%, the majority of which were anastomotic strictures and managed successfully by endoscopic means. The ischemic cholangiopathy rate was 6%. At median thresholds of a portal vein (PV) flow rate of <92 mL/minute/100 g and buffer capacity (BC) of >0.04, both variables were independently associated with risk of biliary events (P = 0.01 and 0.04, respectively). Graft survival was 90% at 12 months and 75% at 5 years. Cox regression analysis revealed a PV flow rate of <50 mL/minute/100 g as predictive of poorer graft survival (P = 0.01). Furthermore, 126 of these DCD livers were analyzed against a propensity-matched group of 378 contemporaneous donation after brain death liver allografts (1:3), revealing significantly higher rates (P < 0.001) of both early allograft dysfunction (70% versus 30%) and biliary complications (37% versus 20%) in the former group. Although flow data were comparable between both sets, PV flow and BC were predictive of biliary events only in the DCD cohort. Intraoperative inflow measurements therefore provide valuable prognostication on biliary/graft outcomes in DCD liver transplantation, can help inform graft surveillance, and its routine use is recommended.

Current review of machine perfusion in liver transplantation from the Japanese perspective

In light of the present evidence, machine perfusion is opening up new horizons in the field of liver transplantation. Although many advances have been made in liver transplantation, organ preservation methods have so far changed very little. Static cold storage is universally used for graft preservation in liver transplantation; however, there is a need for better preservation methods, such as ex vivo machine perfusion, to improve the outcomes by decreasing warm ischemic damage. Based on the findings of basic and clinical trials, hypothermic and normothermic machine perfusion techniques are now commercially available and include the OrganOx metra, Liver Assist, Cleveland NMP device, Organ Care System, and LifePort Liver. Recent clinical trials have provided further evidence for the potential role of normothermic machine perfusion to resuscitate and subsequently improve utilization of marginal or currently discarded livers. Further studies are required to explore the longer-term outcomes, late biliary complications, outcomes in specific high-risk groups, viability biomarkers, optimum and maximum perfusion duration, perfusate composition, and liver-directed therapeutic interventions during normothermic machine perfusion. The use of organs from marginal donors after brain death, such as fatty livers and the livers from elderly donors with multiple comorbidities, may be accepted for machine perfusion in Japan in the near future.

Mitochondrial Consequences of Organ Preservation Techniques during Liver Transplantation

Allograft ischemia during liver transplantation (LT) adversely affects the function of mitochondria, resulting in impairment of oxidative phosphorylation and compromised post-transplant recovery of the affected organ. Several preservation methods have been developed to improve donor organ quality; however, their effects on mitochondrial functions have not yet been compared. This study aimed to summarize the available data on mitochondrial effects of graft preservation methods in preclinical models of LT. Furthermore, a network meta-analysis was conducted to determine if any of these treatments provide a superior benefit, suggesting that they might be used on humans. A systematic search was conducted using electronic databases (EMBASE, MEDLINE (via PubMed), the Cochrane Central Register of Controlled Trials (CENTRAL) and Web of Science) for controlled animal studies using preservation methods for LT. The ATP content of the graft was the primary outcome, as this is an indicator overall mitochondrial function. Secondary outcomes were the respiratory activity of mitochondrial complexes, cytochrome c and aspartate aminotransferase (ALT) release. Both a random-effects model and the SYRCLE risk of bias analysis for animal studies were used. After a comprehensive search of the databases, 25 studies were enrolled in the analysis. Treatments that had the most significant protective effect on ATP content included hypothermic and subnormothermic machine perfusion (HMP and SNMP) (MD = −1.0, 95% CI: (−2.3, 0.3) and MD = −1.1, 95% CI: (−3.2, 1.02)), while the effects of warm ischemia (WI) without cold storage (WI) and normothermic machine perfusion (NMP) were less pronounced (MD = −1.8, 95% CI: (−2.9, −0.7) and MD = −2.1 MD; CI: (−4.6; 0.4)). The subgroup of static cold storage (SCS) with shorter preservation time (< 12 h) yielded better results than SCS ≥ 12 h, NMP and WI, in terms of ATP preservation and the respiratory capacity of complexes. HMP and SNMP stand out in terms of mitochondrial protection when compared to other treatments for LT in animals. The shorter storage time at lower temperatures, together with the dynamic preservation, provided superior protection for the grafts in terms of mitochondrial function. Additional clinical studies on human patients including marginal donors and longer ischemia times are needed to confirm any superiority of preservation methods with respect to mitochondrial function.

Research progress on hepatic machine perfusion

Nowadays, liver transplantation is the most effective treatment for end-stage liver disease. However, the increasing imbalance between growing demand for liver transplantation and the shortage of donor pool restricts the development of liver transplantation. How to expand the donor pool is a significant problem to be solved clinically. Many doctors have devoted themselves to marginal grafting, which introduces livers with barely passable quality but a high risk of transplant failure into the donor pool. However, existing common methods of preserving marginal grafts lead to both high risk of postoperative complications and high mortality. The application of machine perfusion allows surgeons to make marginal livers meet the standard criteria for transplant, which shows promising prospect in preserving and repairing donor livers and improving ischemia reperfusion injury. This review summarizes the progress of recent researches on hepatic machine perfusion.

A Novel Preservation Solution Containing Quercetin and Sucrose for Porcine Kidney Transplantation

In organ transplantation, the University of Wisconsin (UW) solution has been the gold standard for organ preservation. Quercetin (Que) has numerous antioxidant and anti-inflammatory activities, and sucrose (Suc) may be effective for cold storage (CS). This study aimed to investigate the in vitro protective effect of Que and Suc on cold injury to the kidney and to determine whether Que + Suc could improve ischemia-reperfusion injury during CS and hypothermic oxygenated perfusion (HOPE) in autologous transplantation models.

METHODS

BHK-21 cells were stored at 4°C for 3 days in UW solution for CS/machine perfusion (CS/MP-UW) with Que (33.1 μM, 3.3 μM, 0.33 μM) and Suc (0.1 M). In a porcine model of renal autologous transplantation, left kidney grafts were preserved under 3 conditions: group 1, CS preservation for 24 hours; group 2, CS preservation for 22 hours and HOPE with CS/MP-UW solution for 2 hours; and group 3, identical preservation as group 2, with Que and Suc added to the solution. Animals were euthanized on day 7 after autologous transplantation.

RESULTS

After 3 days of CS preservation, the CS/MP-UW solution with Que (33.1 μM, 3.3 μM) and Suc showed significant cell protection against cold injury. In the porcine model of renal autologous transplantation, the last blood Cre level and the blood lipid hydroperoxide on posttransplantation day 2 were significantly different between group 1 and group 3. Moreover, the total endothelial, glomerular, tubular, interstitial (EGTI) histology score in the kidney tissue was also significantly different. Regarding the change in renal resistance in HOPE, the decrease observed in group 3 was significantly larger than that in group 2.

CONCLUSIONS

Our results suggest that the addition of Que and Suc to a UW solution can improve kidney preservation and could potentially enhance the outcome of kidney transplantation.