Membrane pore size impacts performance of a xenogeneic bioartificial liver1

Novel spheroid reservoir bioartificial liver improves survival of nonhuman primates in a toxin-induced model of acute liver failure

This study aims to evaluate the effectiveness and safety of the spheroid reservoir bioartificial liver (SRBAL) with porcine hepatocyte organoids in a preclinical nonhuman primate model of acute liver failure (ALF). Methods: Thirty healthy rhesus monkeys were infused with α-amanitin and lipopolysaccharide and randomized into five groups (ALF alone control group; sham no-cell SRBAL treatment group; groups A, B and C with SRBAL treatment started at 12 h, 24 h and 36 h after induction of ALF, respectively). Animals were continuously treated with the SRBAL device for 6 h and followed for up to 336 h. Results: Survival of ALF monkeys improved with hepatocyte SRBAL treatment compared to control groups. Blood ammonia and total bilirubin were lower, and albumin levels were higher in all hepatocyte SRBAL treatment groups. No evidence of porcine endogenous retrovirus was identified in monkey liver or blood after SRBAL treatment. Titers of monkey antibody (IgG, IgM) did not rise after SRBAL treatment. In survival cases, the proportion of necrotic and apoptotic hepatocytes was lower in SRBAL-treated groups, with earlier liver regeneration leading to recovery. Cytokines TNF-α, IL-6, IL-12, IL-1β, IL-8, IFN-γ and IL-2 were ameliorated by the SRBAL treatment, while levels of M-CSF; HGF, EGF and VEGF; IL-1RA and MIF rose on priming, proliferation and the late phase of liver regeneration. Conclusions: The benefit of SRBAL therapy included preventive effects and therapeutic effects. SRBAL improved survival rate and prolonged median survival time in a nonhuman primate model of drug-induced ALF, and these benefits declined with a delay in the initiation of therapy. Improved survival and recovery of ALF monkeys was associated with a reduction in blood ammonia levels, inhibition of the pro-inflammatory response of ALF, and provided a microenvironment more suitable for regeneration of the injured liver.

Pivotal preclinical trial of the spheroid reservoir bioartificial liver

BACKGROUND & AIMS

The neuroprotective effect of the spheroid reservoir bioartificial liver (SRBAL) was evaluated in a porcine model of drug-overdose acute liver failure (ALF).

METHODS

Healthy pigs were randomized into three groups (standard therapy (ST) alone, ST+No-cell device, ST+SRBAL device) before placement of an implantable intracranial pressure (ICP) monitor and a tunneled central venous catheter. One week later, pigs received bolus infusion of the hepatotoxin D-galactosamine and were followed for up to 90h.

RESULTS

At 48h, all animals had developed encephalopathy and biochemical changes confirming ALF; extracorporeal treatment was initiated and pigs were observed up to 90h after drug infusion. Pigs treated with the SRBAL, loaded with porcine hepatocyte spheroids, had improved survival (83%, n=6) compared to ST alone (0%, n=6, p=0.003) and No-cell device therapy (17%, n=6, p=0.02). Ammonia detoxification, peak levels of serum ammonia and peak ICP, and pig survival were influenced by hepatocyte cell dose, membrane pore size and duration of SRBAL treatment. Hepatocyte spheroids remained highly functional with no decline in mean oxygen consumption from initiation to completion of treatment.

CONCLUSIONS

The SRBAL improved survival in an allogeneic model of drug-overdose ALF. Survival correlated with ammonia detoxification and ICP lowering indicating that hepatocyte spheroids prevented the cerebral manifestations of ALF (brain swelling, herniation, death). Further investigation of SRBAL therapy in a clinical setting is warranted.

Pig-to-baboon liver xenoperfusion utilizing GalTKO.hCD46 pigs and glycoprotein Ib blockade

BACKGROUND

Although transplantation of genetically modified porcine livers into baboons has yielded recipient survival for up to 7 days, survival is limited by profound thrombocytopenia, which becomes manifest almost immediately after revascularization, and by subsequent coagulopathy. Porcine von Willebrand's factor (VWF), a glycoprotein that adheres to activated platelets to initiate thrombus formation, has been shown to constitutively activate human platelets via their glycoprotein Ib (GPIb) receptors. Here, we report our pig-to-primate liver xenoperfusion model and evaluate whether targeting the GPIb-VWF axis prevents platelet sequestration.

METHODS

Twelve baboons underwent cross-circulation with the following extracorporeal livers: one allogeneic control with a baboon liver, 4 xenogeneic controls with a GalTKO.hCD46 pig liver, 3 GalTKO.hCD46 pig livers in recipients treated with αGPIb antibody during perfusion, and 4 GalTKO.hCD46 pig livers pre-treated with D-arginine vasopressin (DDAVP) in recipients treated with αGPIb antibody during perfusion.

RESULTS

All perfused livers appeared grossly and macroscopically normal and produced bile. Xenograft liver perfusion experiments treated with αGPIb antibody may show less platelet sequestration during the initial 2 h of perfusion. Portal venous resistance remained constant in all perfusion experiments. Platelet activation studies demonstrated platelet activation in all xenoperfusions, but not in the allogeneic perfusion.

CONCLUSION

These observations suggest that primate platelet sequestration by porcine liver and the associated thrombocytopenia are multifactorial and perhaps partially mediated by a constitutive interaction between porcine VWF and the primate GPIb receptor. Control of platelet sequestration and consumptive coagulopathy in liver xenotransplantation will likely require a multifaceted approach in our clinically relevant perfusion model.

Immunosafety evaluation of a multilayer flat-plate bioartificial liver

INTRODUCTION

To study and evaluate the immunosafety of our newly developed multilayer flat-plate bioartificial liver (BAL) in treatment of canines with acute liver failure.

METHODS

Fresh porcine hepatocytes and bone marrow mesenchymal stem cells were cocultured in new BAL. Ten canine models with acute liver failure were set up through D-galactosamine administration; 24 hours after administration, the beagles were randomly allocated to a 6-hour treatment with the BAL. The beagles were divided into 2 groups by treatment times. Group 1 beagles (n = 5) received a single BAL treatment. Group 2 beagles (n = 5) received 3 BAL treatments. The hemodynamic, hematologic response and humoral immune responses to BAL therapy were studied before and after treatments.

RESULTS

All beagles remained hemodynamically and hematologically stable during BAL treatments. The levels of IgG and IgM were similar before and after treatment after a single treatment. In addition, the level of CH50 in group 1 slightly decreased after the initiation of BAL treatment, and then the level recovered to baseline quickly after treatments. Time-course changes of the levels of antibodies and CH50 after 3 treatments in group 2 were similar to group 1. Only trace levels of IgG were detected in BAL medium after treatments.

CONCLUSION

The multilayer flat-plate BAL showed a great immunosafety in the treatment of canines with acute liver failure and exhibited a good prospect of its use in clinic.

The influence of membrane molecular weight cutoff on a novel bioartificial liver

Given the xenogeneic immune reaction relevant to the molecular weight cutoff of the membrane of a bioartificial liver (BAL) system, we investigated the influence of membrane molecular weight cutoff in our BAL system in this study. Acute liver failure in beagles was induced by d-galactosamine administration. Eight beagles were divided into two groups by the membrane molecular weight cutoff of the plasma component separator. Group 1 beagles were treated with BAL containing 200 kDa retention rating membrane. Group 2 beagles were treated with BAL containing 1200 kDa retention rating membrane. Each group underwent two 6-h BAL treatments that were performed on day 1 and day 21. The hemodynamic and hematologic response, humoral immune responses, and cytotoxic immune response to BAL therapy were studied before and after treatments. All beagles remained hemodynamically and hematologically stable during BAL treatments. BAL treatment was associated with a significant decline in levels of complement; however, a longer time of level maintenance was observed in Group 2. Group 2 beagles experienced a significant increase in levels of IgG and IgM after two BAL treatments. Significant levels of canine proteins were detected in BAL medium from Group 2; only trace levels of canine proteins were detected in BAL medium from Group 1. The posttreatment viability of co-culture cells in Group 2 was lower compared with Group 1, and the viability of co-culture cells after treatments was associated with deposition of canine proteins on the cells. Xenogeneic immune response was influenced by membrane molecular weight cutoff in the BAL.

Effects of membrane molecular weight cutoff on performance of a novel bioartificial liver

Immunoisolation using semipermeable membranes has been incorporated into bioartificial liver (BAL) devices to separate cellular components of the recipient's immune system from the cells within the BAL device. This study was designed to explore the influence of membrane molecular weight cutoff on performance of the multilayer radial-flow BAL using porcine hepatocytes cocultured with mesenchymal stem cells. In this study, healthy beagles underwent 6-h treatment with a BAL containing membrane with 200 kDa retention rating or 1200 kDa retention rating. Functional markers of BAL performance were monitored before and after treatment, as well as cytotoxic immune response to BAL therapy. The results showed that hepatocyte performance levels such as albumin secretion, urea synthesis, and viability were all significantly higher in 200 kDa retention rating group compared with the 1200 kDa retention rating group after treatment (P <  0.05). Significant levels of canine proteins were detected in BAL medium from the 1200 kDa retention rating group. Fluorescence microscopy further verified that heavy deposition of canine IgG, IgM, and complement (C3) on coculture cells was obtained after BAL treatment in the 1200 kDa retention rating group. However, only trace deposits of canine immunoproteins were observed on coculture cells obtained from BAL in the 200 kDa retention rating group. Small membrane molecular weight cutoff of the BAL could reduce the transfer of xenoreactive antibodies into the BAL medium and improve the performance of the BAL.

Optimization of mass transfer for toxin removal and immunoprotection of hepatocytes in a bioartificial liver

This study was designed to determine optimal operating conditions of a bioartificial liver (BAL) based on mass transfer of representative hepatotoxins and mediators of immune damage. A microprocessor-controlled BAL was used to study mass transfer between patient and cell compartments separated by a hollow fiber membrane. Membrane permeability (70, 150, or 400 kDa molecular weight cut-off-MWCO), membrane convection (high: 50 mL/min; medium: 25 mL/min; low: 10 mL/min; diffusion: 0 mL/min), and albumin concentration in the cell compartment (0.5 or 5 g%) were considered for a total of 24 test conditions. Initially, the patient compartment contained pig plasma supplemented with ammonia (0.017 kDa), unconjugated bilirubin (0.585 kDa), conjugated bilirubin (0.760 kDa), TNF-alpha (17 kDa), pig albumin (67 kDa), pig IgG (147 kDa), and pig IgM (900 kDa). Mass transfer of each substance was determined by its rate of appearance in the cell compartment. Membrane fouling was assessed by dextran polymer technique. Of the three tested variables (membrane pore size, convection, and albumin concentration), membrane permeability had the greatest impact on mass transfer (P < 0.001). Mass transfer of all toxins was greatest under high convection with a 400 kDa membrane. Transfer of IgG and IgM was insignificant under all conditions. Bilirubin transfer was increased under high albumin conditions (P = 0.055). Fouling of membranes ranged from 7% (400 kDa), 24% (150 kDa) to 62% (70 kDa) during a 2-h test interval. In conclusion, optimal toxin removal was achieved under high convection with a 400-kDa membrane, a condition which should provide adequate immunoprotection of hepatocytes in the BAL.

Functional evaluation of a new bioartificial liver system in vitro and in vitro

AIM

To evaluate the functions of a new bioartificial liver (BAL) system in vitro and in vitro.

METHODS

The BAL system was configured by inoculating porcine hepatocyte spheroids into the cell circuit of a hollow fiber bioreactor. In the experiments of BAL in vitro, the levels of alanine aminotransferase (ALT), total bilirubin (TB), and albumin (ALB) in the circulating hepatocyte suspension and RPMI-1640 medium were determined during 6 h of circulation in the BAL device. In the experiments of BAL in vitro, acute liver failure (ALF) model in canine was induced by an end-side portocaval shunt combined with common bile duct ligation and transaction. Blood ALT, TB and ammonia levels of ALF in canines were determined before and after BAL treatment.

RESULTS

During 6 h of circulation in vitro, there was no significant change of ALT, whereas the TB and ALB levels gradually increased with time both in the hepatocyte suspension and in RPMI-1640 medium. In the BAL treatment group, blood ALT, TB and ammonia levels of ALF in canines decreased significantly.

CONCLUSION

The new BAL system has the ability to perform liver functions and can be used to treat ALF.

Functional evaluation of a new bioartificial liver system in vivo and in vivo

AIM: To evaluate the functions of a new bioartificial liver (BAL) system in vitro and in vitro.

MEHTODS: The BAL system was configurated by inoculating porcine hepatocyte spheroids into the cell circuit of a hollow fiber bioreactor. In the experiments of BAL in vitro, the levels of alanine aminotransferase (ALT), total bilirubin (TB), and albumin (ALB) in the circulating hepatocyte suspension and RPMI-1640 medium were determined during 6 h of circulation in the BAL device. In the experiments of BAL in vitro, acute liver failure (ALF) model in canine was induced by an end-side portocaval shunt combined with common bile duct ligation and transaction. Blood ALT, TB and ammonia levels of ALF in canines were determined before and after BAL treatment.

RESULTS: During 6 h of circulation in vitro, there was no significant change of ALT, whereas the TB and ALB levels gradually increased with time both in the hepatocyte suspension and in RPMI-1640 medium. In the BAL treatment group, blood ALT, TB and ammonia levels of ALF in canines decreased significantly.

CONCLUSION: The new BAL system has the ability to perform liver functions and can be used to treat ALF.

Rapid, large-scale formation of porcine hepatocyte spheroids in a novel spheroid reservoir bioartificial liver

We have developed a novel bioreactor based on the observation that isolated porcine hepatocytes rapidly and spontaneously aggregate into spheroids under oscillation conditions. The purpose of this study was to characterize the influence of oscillation frequency (0.125 Hz, 0.25 Hz), cell density (1-10 x 10(6) cells/mL), and storage condition (fresh, cryopreserved) of porcine hepatocytes on the kinetics of spheroid formation. The viability and metabolic performance of spheroid hepatocytes was also compared to monolayer culture. We observed that both fresh and cryopreserved porcine hepatocytes began formation of spheroids spontaneously at the onset of oscillation culture. Spheroid size was directly related to cell density and time in culture, though inversely related to oscillatory frequency. Spheroid formation by fresh porcine hepatocytes was associated with decreased cell death (lactate dehydrogenase release, 1.3 +/- 1.0 vs. 3.1 +/- 0.7 U/mL, P < 0.05) and increased metabolic performance (albumin production, 14.7 +/- 3.3 vs. 4.6 +/- 1.4 fg/c/h, P < 0.0001; ureagenesis from ammonia, 267 +/- 63 vs. 92 +/- 13 micromol/L/h, P < 0.001) compared with monolayer culture. In conclusion, based on the favorable properties of rapid spheroid formation, increased hepatocellular function, and ease of scale-up, the spheroid reservoir bioreactor warrants further investigation as a bioartificial liver for support of liver failure.

Cytotoxic immune response to a xenogeneic bioartificial liver

Prior studies have suggested the possibility of immune-mediated death of xenogeneic hepatocytes in a bioartificial liver (BAL) during hemoperfusion. This study was designed to elucidate how immunity may cause death of xenogeneic hepatocytes in the BAL. Healthy dogs were treated with a BAL containing hollow fiber membranes with large pores (200 nm) or small pores (400 kDa). The immune response of recipient dogs to BAL therapy was monitored over 3 h of treatment. We observed significantly greater loss of viability of hepatocytes in the 200 nm group compared with the 400 kDa group (p < 0.001). Low viability after treatment with the large pore membrane was associated with positive staining for dog IgG, dog IgM, and dog complement on dead hepatocytes. Significant levels of dog antibody were detected in samples of BAL medium from the 200 nm group. These canine antibodies were cytotoxic to porcine hepatocytes. In contrast, medium from the 400 kDa group contained only trace levels of dog IgG and were noncytotoxic. We conclude that antibody-mediated cytotoxicity contributed to the death of hepatocytes during treatment with a xenogeneic BAL. Immune-mediated death of hepatocytes was reduced by increasing selectivity of the BAL membrane.

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