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

Optimizing environmental enrichment for Sprague Dawley rats: Exemplary insights into the liver proteome

BACKGROUND

Considering the expected increase in the elderly population and the growing emphasis on aging-related biomedical research, the demand for aged laboratory animals has surged, challenging established husbandry practices. Our objective was to establish a cost-effective method for environmental enrichment, utilizing the liver as a representative organ to assess potential metabolic changes in response to differing enrichment levels.

METHODS

We conducted a six-month study involving 24 male Sprague Dawley rats, randomly assigned to four environmental enrichment groups. Two groups were housed in standard cages, while the others were placed in modified rabbit cages. Half of the groups received weekly playtime in an activity focused rat housing unit. We evaluated hormone levels, playtime behavior, and subjective handling experience. Additionally, liver tissue proteomic analysis was performed.

RESULTS

Initial corticosterone levels and those after 3 and 6 months showed no significant differences. Yet, testosterone levels were lower in the control group by the end of the study (p = 0.007). We observed 1871 distinct proteins in liver tissue, with 77% being common across groups. In gene ontology analysis, no specific pathways were overexpressed. In semiquantitative analysis, we observed differences in proteins associated in lipid metabolism such as Apolipoprotein A-I and Acyl-CoA 6-desaturase, which were lower in the control group (p = 0.024 and p = 0.009). Rats in the intervention groups with weekly playtime displayed the least amount of reported distress during inspection or upon room entry and were less prone to accepting treats. Removing animals from their enclosure was most effortless for those in the large cage group. Over time, there was a decrease in conflicts among rats that interacted only twice weekly during playpen time.

DISCUSSION

In summary, refining husbandry practices for aging rats is both simple and budget-friendly, with no apparent adverse effects on stress levels, animal development, or relevant metabolic changes in the liver.

Incorporating a hemodialysis filter into a commercial normothermic perfusion system to facilitate long-term preservation of human split-livers

BACKGROUND

Normothermic machine perfusion (NMP) allows for the assessment and resuscitation of ex-vivo human livers prior to transplantation. Commercially available NMP systems are closed circuits that accumulate metabolic waste and cytokines over time, potentially limiting organ preservation times. Dialysis has been proposed as a method to remove waste and excess fluid from such systems. This study aimed to demonstrate the utility of integrating dialysis into a commercially available system by quantifying solute removal.

METHODS

A dialysis filter was attached in parallel to a commercially available liver perfusion system. Three livers declined for transplantation were split before undergoing long-term NMP with blood using the modified system. During perfusion, dialysate flow rates were set in the range of 100-600 mL/h for short periods of time. At each flow rate, perfusate and spent dialysate samples were collected and analyzed for solute clearance.

RESULTS

The addition of dialysis to a commercial NMP system removed water-soluble waste and helped regulate electrolyte concentrations. Interleukin-6 was successfully removed from the perfusate. Solute clearance was proportional to dialysate flow rate. A guide for our perfusion setup was created for the appropriate selection of dialysis flow rates and duration based on real-time perfusate composition.

CONCLUSIONS

Dialysis circuits can efficiently remove waste and regulate perfusate composition, and can be easily incorporated to improve the performance of commercially available systems. Quantification of the effect of dialysis on perfusate composition enables refined dialysis control to optimize electrolyte profiles and avoid the over- or under-correction of key solutes.

Hemofiltration Improves Blood Perfusate Conditions Leading to Improved Ex Situ Heart Perfusion

The aim was to optimize the perfusate composition by including a hemofiltrator to the PhysioHeartplatform for ex situ heart perfusion of porcine slaughterhouse hearts. Fourteen hearts were harvested from Dutch Landrace pigs and slaughtered for human consumption. All hearts were preserved for 4 hours using static cold storage before reperfusion for 4 hours on the PhysioHeart platform. Seven hearts were assigned to the hemofiltration group, where a hemofiltrator was added to the perfusion circuit, while the control group did not receive hemofiltration. In the hemofiltration group, the perfusion fluid was filtrated for 1 hour with a flow of 1 L/hour before reperfusion. After mounting the heart, hemofiltration was maintained at 1 L/hour, and cardiac function and blood samples were analyzed at multiple time points. Preserved cardiac function was defined as a cardiac output >3.0 L/min with a mean aortic pressure >60 mm Hg and a left atrial pressure <15 mm Hg. Hemofiltration resulted in a significantly reduced potassium concentration at all time points ( p < 0.001), while sodium levels remained at baseline values ( p < 0.004). Furthermore, creatinine and ammonia levels decreased over time. Functional assessment demonstrated a reduced left atrial pressure ( p < 0.04) and a reduction of the required dobutamine dose to support myocardial function ( p < 0.003) in the hemofiltration group. Preserved cardiac function did not differ between groups. Hemofiltration results in an improved biochemical composition of the whole blood perfusate and preserves cardiac function better during normothermic perfusion based on a reduced left atrial pressure (LAP) and dobutamine requirement to support function.

Influence of oxygen uptake through the liver surface on the metabolism of ex vivo perfused liver during hypoxia

The low quality of transplants having undergone hypoxic injury can lead to postoperative complications. The aim of the present research is to estimate, by means of mathematical modeling, how the process of oxygen uptake through the liver surface influences the metabolism of ex vivo perfused liver under hypoxia. The value of oxygen uptake through the surface was established to depend on the degree of oxygenation of the perfusion medium. A decrease in the oxygenation of the perfusion medium resulted in a decreased oxygen uptake through the liver surface. Stoichiometric modeling of the liver metabolism shows that upon the decreased oxygenation of the perfusion medium more energy is required for the process of oxygen uptake through the surface even at a lower level as compared to the normal oxygen supply. The application of the Pareto optimality allows estimating the optimum distribution of the energy resources in liver under ex vivo conditions. Both upon the normal and decreased oxygenation of the perfusion medium, the phenomenon of "free competition" for the resource was observed, with the energy being optimally distributed among all the metabolic fluxes. Moreover, this energy is also spent on the accompanying processes, e.g. for the transport of interstitial fluid.

Advancing Perfusion Models: Dual-Vessel Ex Vivo Rat Liver Perfusion Based on a Clinical Setup

Normothermic ex vivo liver machine perfusion (NEVLP) has been developed to address the increasing organ shortage in liver transplantation, through optimal preservation, assessment, and conditioning of grafts from extended criteria donors. There remains a need to establish simple and standardized animal models that simulate clinical NEVLP to test novel therapies. Liver grafts from 36 Sprague-Dawley rats were perfused for 6 h in a dual-vessel NEVLP system with a Dulbecco's modified Eagles medium-based perfusate supplemented with rat plasma and erythrocytes. Varying doses of the clinically used vasodilator epoprostenol, Kupffer cell inhibitor glycine, and a Steen™-based perfusate were assessed. Perfusion pressures and bile production were recorded, and perfusate was analyzed for transaminase secretion. Tissue samples were evaluated histologically, and levels of cytokines and 8-Isoprostane were measured. Increasing levels of epoprostenol and the addition of glycine resulted in a stepwise decrease of transaminase secretion and improved bile production. Steen further decreased transaminase release and interleukin 1 beta levels. Liver grafts perfused with the optimized Steen-based protocol exhibited lowest levels of oxidative stress and best-preserved liver integrity. In conclusion, epoprostenol seemed to ameliorate liver function and prevent cellular damage beyond its vasodilatory effect, with glycine acting synergistically. The anti-inflammatory and antioxidative properties of Steen further improved the outcome of perfusion. Our rodent NEVLP system may be used to rapidly test new agents for the pharmacologic conditioning of livers and help translate findings from bench-to-bedside.

Assessing Donor Liver Quality and Restoring Graft Function in the Era of Extended Criteria Donors

Liver transplantation (LT) is the final treatment option for patients with end-stage liver disease. The increasing donor shortage results in the wide usage of grafts from extended criteria donors across the world. Using such grafts is associated with the elevated incidences of post-transplant complications including initial nonfunction and ischemic biliary tract diseases, which significantly reduce recipient survival. Although several clinical factors have been demonstrated to impact donor liver quality, accurate, comprehensive, and effective assessment systems to guide decision-making for organ usage, restoration or discard are lacking. In addition, the development of biochemical technologies and bioinformatic analysis in recent years helps us better understand graft injury during the perioperative period and find potential ways to restore graft function. Moreover, such advances reveal the molecular profiles of grafts or perfusate that are susceptible to poor graft function and provide insight into finding novel biomarkers for graft quality assessment. Focusing on donors and grafts, we updated potential biomarkers in donor blood, liver tissue, or perfusates that predict graft quality following LT, and summarized strategies for restoring graft function in the era of extended criteria donors. In this review, we also discuss the advantages and drawbacks of these potential biomarkers and offer suggestions for future research.

Long-term normothermic machine preservation of human livers: what is needed to succeed?

Although short-term machine perfusion (≤24 h) allows for resuscitation and viability assessment of high-risk donor livers, the donor organ shortage might be further remedied by long-term perfusion machines. Extended preservation of injured donor livers may allow reconditioning, repairing, and regeneration. This review summarizes the necessary requirements and challenges for long-term liver machine preservation, which requires integrating multiple core physiological functions to mimic the physiological environment inside the body. A pump simulates the heart in the perfusion system, including automatically controlled adjustment of flow and pressure settings. Oxygenation and ventilation are required to account for the absence of the lungs combined with continuous blood gas analysis. To avoid pressure necrosis and achieve heterogenic tissue perfusion during preservation, diaphragm movement should be simulated. An artificial kidney is required to remove waste products and control the perfusion solution's composition. The perfusate requires an oxygen carrier, but will also be challenged by coagulation and activation of the immune system. The role of the pancreas can be mimicked through closed-loop control of glucose concentrations by automatic injection of insulin or glucagon. Nutrients and bile salts, generally transported from the intestine to the liver, have to be supplemented when preserving livers long term. Especially for long-term perfusion, the container should allow maintenance of sterility. In summary, the main challenge to develop a long-term perfusion machine is to maintain the liver's homeostasis in a sterile, carefully controlled environment. Long-term machine preservation of human livers may allow organ regeneration and repair, thereby ultimately solving the shortage of donor livers.

Challenging the Ex Vivo Lung Perfusion Procedure With Continuous Dialysis in a Pig Model

BACKGROUND

Normothermic ex vivo lung perfusion (EVLP) increases the pool of donor lungs by requalifying marginal lungs refused for transplantation through the recovery of macroscopic and functional properties. However the cell response and metabolism occurring during EVLP generate a nonphysiological accumulation of electrolytes, metabolites, cytokines and other cellular byproducts which may have deleterious effects both at the organ and cell levels, with impact on transplantation outcomes.

METHODS

We analyzed the physiological, metabolic and genome-wide response of lungs undergoing a 6-hour EVLP procedure in a pig model in 4 experimental conditions: without perfusate modification, with partial replacement of fluid, and with adult or pediatric dialysis filters.

RESULTS

Adult and pediatric dialysis stabilized the electrolytic and metabolic profiles while maintaining acid-base and gas exchanges. Pediatric dialysis increased the level of IL-10 and IL-6 in the perfusate. Despite leading to modification of the perfusate composition, the 4 EVLP conditions did not affect the gene expression profiles which were associated in all cases with increased cell survival, cell proliferation, inflammatory response and cell movement, and with inhibition of bleeding.

CONCLUSIONS

Management of EVLP perfusate by periodic replacement and continuous dialysis has no significant effect on the lung function nor on the gene expression profiles ex vivo. These results suggest that the accumulation of dialysable cell products does not significantly alter the lung cell response during EVLP, a finding that may have impact on EVLP management in the clinic.

Evaluation of the ex vivo liver viability using a nuclear magnetic resonance relaxation time-based assay in a porcine machine perfusion model

There is a dearth of effective parameters for selecting potentially transplantable liver grafts from expanded-criteria donors. In this study, we used a nuclear magnetic resonance (NMR) relaxation analyzer-based assay to assess the viability of ex vivo livers obtained via porcine donation after circulatory death (DCD). Ex situ normothermic machine perfusion (NMP) was utilized as a platform for viability test of porcine DCD donor livers. A liver-targeted contrast agent, gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA), was injected into the perfusate during NMP, and the dynamic biliary excretion of the Gd-EOB-DTPA was monitored by measuring the longitudinal relaxation time (T1). The longitudinal relaxation rate (R1) of the bile was served as a parameter. The delay of increase in biliary R1 during early stage of NMP indicated the impaired function of liver grafts in both warm and cold ischemia injury, which was correlated with the change of alanine aminotransferase. The preservative superiority in cold ischemia of dual hypothermic oxygenated machine perfusion could also be verified by assessing biliary R1 and other biochemical parameters. This study allows for the dynamic assessment of the viability of porcine DCD donor livers by combined usage of ex situ NMP and NMR relaxation time based assay, which lays a foundation for further clinical application.

Dual versus single vessel normothermic ex vivo perfusion of rat liver grafts using metamizole for vasodilatation

Background

Normothermic ex vivo liver perfusion (NEVLP) is a promising strategy to increase the donor pool in liver transplantation. Small animal models are essential to further investigate questions regarding organ preservation and reconditioning by NEVLP. A dual vessel small animal NEVLP (dNEVLP) model was developed using metamizole as a vasodilator and compared to conventional portovenous single vessel NEVLP (sNEVLP).

Methods

Livers of male Wistar rats were perfused with erythrocyte-supplemented culture medium for six hours by either dNEVLP via hepatic artery and portal vein or portovenous sNEVLP. dNEVLP was performed either with or without metamizole treatment. Perfusion pressure and flow rates were constantly monitored. Transaminase levels were determined in the perfusate at the start and after three and six hours of perfusion. Bile secretion was monitored and bile LDH and GGT levels were measured hourly. Histopathological analysis was performed using liver and bile duct tissue samples after perfusion.

Results

Hepatic artery pressure was significantly lower in dNEVLP with metamizole administration. Compared to sNEVLP, dNEVLP with metamizole treatment showed higher bile production, lower levels of transaminases during and after perfusion as well as significantly lower necrosis in liver and bile duct tissue. Biochemical markers of bile duct injury showed the same trend.

Conclusion

Our miniaturized dNEVLP system enables normothermic dual vessel rat liver perfusion. The administration of metamizole effectively ameliorates arterial vasospasm allowing for six hours of dNEVLP, with superior outcome compared to sNEVLP.