Combination of plasma exchange and continuous hemofiltration as temporary metabolic support for patients with acute liver failure

Value of extracorporeal artificial liver support in pediatric acute liver failure: A single-center experience of over 10 years

PURPOSE

Acute liver failure (ALF) is a life-threatening disease characterized by rapid-onset liver dysfunction, coagulopathy, and encephalopathy in patients without chronic liver disease. Today, the combined application of continuous veno-venous hemodiafiltration (CVVHDF) and plasma exchange (PEX), which are forms of supportive extracorporeal therapy (SECT), with conventional liver therapy in ALF is recommended. This study aims to retrospectively analyze the effects of combined SECT in pediatric patients with ALF.

MATERIALS AND METHODS

We retrospectively analyzed 42 pediatric patients, followed in the liver transplantation intensive care unit. The patients had ALF and received PEX supportive therapy with combined CVVHDF. The biochemical lab values of the results for the patients before the first combined SECT and after the last combined SECT were analyzed comparatively.

RESULTS

Of the pediatric patients included in our study, 20 were girls and 22 were boys. Liver transplantation was performed in 22 patients, and 20 patients recovered without transplantation. After the discontinuation of combined SECT, all patients had significantly lower serum liver function test results (total bilirubin, alanine transaminase, aspartate transaminase), ammonia, and prothrombin time/international normalized ratio levels than the previous levels (p < 0.01). Hemodynamic parameters (i.e., mean arterial pressure) also improved significantly.

DISCUSSION AND CONCLUSION

Combined CVVHDF and PEX treatment significantly improved biochemical parameters and clinical findings, including encephalopathy, in pediatric patients with ALF. PEX therapy combined with CVVHDF is a proper supportive therapy for bridging or recovery.

Hemodiabsorption in Treatment of Hepatic Failure

Conducted at the University of California, Los Angeles, this randomized, prospectively controlled study was designed to measure the effects of a hemodiabsorption device in the treatment of 11 patients with hepatic failure and stage III to IV encephalopathy. The results of 5 days of treatment with the hemodiabsorption device were compared with those of standard intensive care procedures. The BioLogic-DT System, a simple sorbent-based system, demonstrated a slight improvement in the neurologic status of patients, a significant improvement in the physiologic status of patients, and an improved outcome for treated patients as opposed to nontreated patients.

Prediction value of model for end-stage liver disease scoring system on prognosis in the acute on chronic liver failure patients with plasma exchange treatment

Hepatitis B virus-related acute-on-chronic liver failure (AoCLF) is associated with a high mortality rate. Plasma exchange (PE) is useful to bridge patients with AoCLF to liver transplantation or recovery. The aim of this study was to analyze the impact of the model for end-stage liver disease (MELD) score on 30-day survival in patients with AoCLF treated with PE or conventional medications and to evaluate the therapeutic effectiveness of PE. In this study, 62 enrolled patients with AoCLF who received PE treatment were compared with 131 patients treated with conventional medications. The MELD scores were calculated according to the original formula, and the 30-day survival in patients was recorded. The 30-day survival rate of the patients who received PE versus controls was 41.9% versus 25.2% (p < 0.05). The 30-day survival rate of patients in the PE group (50.0%) with a MELD score from 20 to 30 was higher than that of the control group (31.7%, p < 0.05); for MELD scores more than 30, there was no significant difference in two groups (8.3% vs. 0%, p > 0.05). PE seems to be efficacious and safe for the treatment of patients with AoCLF and significantly increased the survival rates of patients with a MELD score of 20-30.

Hybrid artificial liver support system for treatment of severe liver failure

AIM: To construct a novel hybrid artificial liver support system (HALSS) and to evaluate its efficacy in patients with severe liver failure.

METHODS: Hepatocytes were isolated from suckling pig by the modified Seglen’s method. Isolated hepatocytes were cultured in a spinner flask for 24 h to form spheroids before use and the functions of spheroids were detected. HALSS consisted of a plasma separator, a hemo-adsorba and a bioreactor with hepatocytes spheroids in its extra-fiber space. HALSS was applied to 10 patients with severe liver failure. The general condition and the biochemical indexes of the patients were studied just before and after the treatment.

RESULTS: The number of cells per liver was about 2-4×10¹⁰ (mean, 3.1±1.5×10¹⁰). The cell viabilities were more than 95%. After 24 h of spheroid culture, most hepatocytes formed spheroids. The levels of albumin and urea in the medium of spheroid culture were higher than those in supernatant of petri dish culture (P = 0.0015 and 0.0001, respectively). The capacity of albumin production and urea synthesis remained stable for more than one wk and declined rapidly after two weeks in vitro. In HALSS group, the duration of HALSS treatment was 6-10 h each time. All patients tolerated the treatment well without any fatal adverse reaction. After HALSS treatment, the general condition, psychic state, encephalopathy and hepatic function of the patients were improved. The survival rate of the HALSS group, Plasmapheresis group and control group was 30% (3/10), 20% (2/10) and 0% (0/10), respectively (P = 0.024). Two weeks after treatment, Tbil and ALT decreased and the PTA level elevated in HALSS group and pasmapheresis group (P value: 0.015 vs 0.020, 0.009 vs 0.012 and 0.032 vs 0.041, respectively). But there was no significant change of blood albumin concentration before and after treatment in HALSS group and Plasmapheresis group.

CONCLUSION: The HALSS established by us is effective in supporting liver function of patients with severe liver failure.

Extracorporeal liver support: waiting for the deciding vote

Because acute liver cell failure is associated with an exceedingly high mortality, liver support has been proposed since the 1950s to improve patient outcome. Early devices, including hemodialysis, hemofiltration, exchange transfusion, plasmapheresis, hemoperfusion, plasma and cross-hemodialysis or cross-circulation, appeared inefficient. Meanwhile, documented results of extracorporeal liver perfusion (ECLP) suggested its superiority over conventional treatment. These devices were abandoned with the development of liver transplantation (LT), which allowed a better outcome and longer survival rate. In the present day, the fact that patients die while waiting for LT because of organ shortage led to a renewed interest in liver support as bridge to LT or regeneration. These devices can be classified according to the presence or lack of hepatocytes, whereas biologic devices refers to the presence of cells or other organic and biochemical component. The absence of individual success of early models led to the development of combined hepatocyte free devices, or artificial liver, which are based upon the hemodiabsorption principle (Biologic-DT) or on the "albumin bound toxin hypothesis" (Molecular Adsorbents Recirculating System) with encouraging results. Meanwhile, hepatocyte based bioartificial liver devices (BLD) were conceived for a global "metabolic support." BLD were developed with the use of human hepatoma cell line (C3A) or primary or cryopreserved porcine hepatocytes. Preliminary experience gave promising results bridging patients to LT. Based upon the same principle of global hepatocyte metabolic support, ECLP regained interest, particularly with the development of transgenic pigs. Several concerns were raised about these devices. Artificial livers lacked any metabolic synthetic activity, the use of human liver for ECLP seems hardly acceptable because of organ shortage, and the accepted use of borderline livers for transplantation is pending trials for the use of xenogenic livers. For BLD, the concerns were the low hepatocyte mass, the absence of accessory liver cells, and the potential risk of seeding tumor cells into patient with the use of human hepatoma cell line. The use of porcine hepatocytes (BLD or ECLP) raised physiologic and immunologic concerns and particularly the fear of a possible transfer of porcine viral material. Although recent studies clearly demonstrate clinical improvement of patients with the use of recently developed liver support devices, most of reported prospective, controlled, or randomized trials had a small number of patients. To give the deciding vote and avoid previous pitfalls, trials need to be developed with a larger number of patients based upon statistically significant models with the following characteristics: 1) comprehensive understanding of the acute liver cell failure mechanisms, 2) world wide classification of conditions that require liver support, and 3) a clear definition of treatment success pending patients to LT or recovery without transplantation. There has not yet been conclusive evidence to support the benefits of extracorporeal liver support. We are still waiting for the deciding vote.

Liver Regeneration Using a Hybrid Artificial Liver Support System

We have developed two types of hybrid artificial liver support system (HALSS) that use hepatocyte organoid culture: (1) a PUF-HALSS comprising an artificial liver module using polyurethane foam (PUF), in which hepatocytes form spheroids in its pores, and maintained liver-specific functions for at least ten days in vitro; (2) an LLS-HALSS that uses a liver lobule-like structure (LLS) module containing hollow fibers with a microregular arrangement in which hepatocytes in the extra-fiber space of the module form the organoids by centrifugation that maintain liver-specific functions for at least two months in vitro. In preclinical experiments, a PUF-HALSS was applied to a pig having liver failure. To evaluate the effect of liver regeneration, a PUF- and an LLS-HALSS were applied to a rat having reversible hepatic failure. Each HALSS was effective in supporting liver function, stabilization of general conditions and recovery from liver failure state. These results indicate that these HALSS may be useful to treat liver failure patients until liver transplantation or until regeneration of the native liver.

Bioartificial liver inoculated with porcine hepatocyte spheroids for treatment of canine acute liver failure model

The aim of this study was to evaluate a novel bioartificial system in a canine model of acute liver failure. An acute liver failure model in canines was induced by an end-side portocaval shunt combined with common bile duct ligation and transection. The bioartificial liver system, which utilized blood perfusion through a hollow fiber bioreactor from BIOLIV A3A inoculated with 1.0 - 3.1 x 1010 porcine hepatocyte spheroids, was developed for the treatment of acute liver failure. Sixteen acute liver failure model canines were divided between a group treated with bioartificial liver (n=8) and a control group (n=8) for 5 h. Blood alanine aminotransferase (ALT), alkaline phosphatase (AKP), total bilirubin (TBi), direct bilirubin (DBi), prothrombin time (PT), ammonia levels, and the ratio of branched chain to aromatic amino acids (Fischer's ratio) were determined. ALT, AKP, TBi, DBi, and ammonia levels were significantly elevated, PT was significantly prolonged, and Fischer's ratio decreased significantly in the canine model of the two groups on day 14 after operation compared to baseline. There were no significant differences between the two groups in laboratory data before treatment. In canines treated with the bioartificial liver system, ALT, AKP, TBi, DBi, and ammonia levels decreased significantly, PT was significantly shortened, Fischer's ratio was significantly elevated after treatment, and the survival rate by day 7 after treatment was 100%. In canines in the control group, on the other hand, there were no significant differences in ALT, AKP, TBi, DBi, PT, and ammonia levels between pretreatment and posttreatment, though these indices decreased to a slight degree after treatment. The survival rate by day 7 after treatment was 62.5% in the control group. Fischer's ratio decreased after treatment. ALT, AKP, TBi, DBi, PT, and ammonia levels in the bioartificial liver system group were lower, and Fischer's ratio and survival rate were higher than those in the control group after treatment. These results indicate that the novel bioartificial liver system we developed has a significant impact on the course of canine acute liver failure model and has potential advantages for clinical use in patients with acute liver failure.

Generation of a novel apoptosis-resistant hepatoma cell line

The expansionable human hepatoma cell lines have potential for use in a bio-artificial liver (BAL) system for liver disease due to the shortage of donation. However, at present, bioartificial livers are incomplete and the functions need to be improved or at least maintained for a longer period. In the present study, the authors aimed to establish a novel hepatoma cell line for a longer-term or permanent artificial liver. For this purpose, bcl-2, an anti-apoptosis gene, was introduced into hepatoma HepG2 cells. Over-expression of Bcl-2 significantly inhibited apoptosis. After 15 d of serum-deprived culture, the viability of HepG2-Bcl2 was 51% while that of mock transfectant (HepG2-mock) was decreased to 14%. In the presence of hygromycin B, HepG2-mock were dead by day 6, while the HepG2-Bcl2 viability at day 9 was 65%. Over-expression of Bcl-2 prolonged the period of the stationary phase in the growth curve and did not affect the growth rate during the exponential phase. To test the liver function, albumin production was measured. After 10 d of culture, the albumin concentration in the culture supernatant of HepG2-Bcl2 was 30 ng ml(-1), while that of HepG2-mock was 23 ng ml(-1). The cytochrome P-450 activity per culture of 3-methyl-cholanthrene-treated HepG2-Bcl2 was double that of treated HepG2-mock. Introduction of Bcl-2 was effective for the generation of a novel hepatoma cell line for artificial livers.

Profound ionized hypomagnesemia induced by therapeutic plasma exchange in liver failure patients

BACKGROUND

Various adverse effects, including cardiac arrest, have been induced by plasma exchange (PE). Electrolyte derangement is frequently observed. The purpose of this study was to assess the effect of PE on the serum ionized magnesium (Mg2+) concentration in acute liver failure patients.

STUDY DESIGN AND METHODS

Seven liver failure patients requiring PE were enrolled in this study. PE was performed 21 times in total. Blood samples were drawn before PE and serially after the start of the PE. Serum Mg2+ was measured by the ion- selective electrode method.

RESULTS

After PE was started, Mg2+ concentrations began to fall significantly. The low Mg2+ blood concentration continued during PE. After PE, the Mg2+ level recovered to about 80 percent of the control value within 2 hours in six patients. However, in one patient, the Mg2+ concentration was still low even at 2 hours after PE. This patient complained of chest discomfort during PE and ECG analysis showed sporadic supraventricular premature contractions.

CONCLUSION

Profound ionized hypomagnesemia was induced by PE in liver failure patients.

Recovery of rats with fulminant hepatic failure by using a hybrid artificial liver support system with polyurethane foam/rat hepatocyte spheroids

We studied the recovery of rats with fulminant hepatic failure (FHF) by treating them with our original hybrid artificial liver support system (HALSS). FHF was induced by a two-thirds partial hepatectomy and 10 minutes of hepatic ischemia. Rats with FHF were treated with a polyurethane foam/spheroid HALSS including 2.0 x 10(8) hepatocytes for 1 hour (HALSS group, n = 5), and with the same system without hepatocytes in the artificial liver module as a control experiment (sham-HALSS group, n = 3). The level of blood constituents, ammonia, glucose and creatinine, showed no major difference between the two groups at the end of treatment. All rats in the sham-HALSS group died within 5 hours after treatment. However, the level of blood constituents of rats with FHF in the HALSS group improved with time, and all rats in the HALSS group recovered. Liver tissue of rats treated with HALSS showed cell mitosis and improvement from injury. These results indicated that our HALSS has a strong possibility to induce recovery from hepatic failure.

A case of acute hepatic insufficiency treated with novel plasmapheresis plasma diafiltration for bridge use until liver transplantation

A patient with acute hepatic insufficiency induced by a drug presented to our institution, and we performed a novel plasmapheresis that we call plasma dia-filtration (PDF). The patient was a 36 year old woman. She underwent 11 sessions of PDF for a duration of about 9 h for each procedure using the Evacure EC-2A filter together with 20 units of fresh frozen plasma and dialysate simultaneously. Serum levels of total bilirubin and prothrombin time were significantly improved after she underwent each procedure. However, after the third procedure the levels returned to the same level as on the previous day. Encephalopathy improved after the first procedure, and this improvement was maintained until the ninth procedure. The patient prepared to undergo liver transplantation after the tenth procedure because of the development of hepatic coma, but she died of respiratory insufficiency before undergoing the procedure. Accordingly in this case, PDF worked to maintain liver function in acute liver failure and may act as bridge therapy until the patient can undergo liver transplantation.

Effectiveness of combining plasma exchange and continuous hemodiafiltration (combined modality therapy in a parallel circuit) in the treatment of patients with acute hepatic failure

Plasma exchange has gained widespread acceptance as an effective mode of blood purification in patients suffering from acute hepatic failure. However, it is still undetermined whether a single use of plasma exchange is capable of removing inflammatory cytokines completely or of preventing the development of citrate toxicity inherent with fresh frozen plasma. To clarify these issues we developed combined plasma exchange and continuous hemodiafiltration (CHDF) modality in which CHDF is performed in an opposite direction to plasma exchange. This study was designed to assess the effectiveness of combined modality therapy. Fifteen patients with acute hepatic failure were treated with plasma exchange (plasma exchange group) or plasma exchange and CHDF (plasma exchange + CHDF group), and various biochemical parameters were determined before and after treatment. Although citrate levels increased significantly after treatment compared with pretreatment levels in both the plasma exchange group and the plasma exchange + CHDF group, the percentage of the increase in citrate levels was significantly higher in the plasma exchange group than in the plasma exchange + CHDF group. Bilirubin levels were significantly lower after treatment in both the plasma exchange and plasma exchange + CHDF groups. There were no significant differences in tumor necrosis factor-alpha levels before and after treatment in the plasma exchange group, but they were significantly lower after treatment in the plasma exchange + CHDF group. Interleukin-6 (IL-6) levels increased significantly after treatment in the plasma exchange group, but there were no significant differences in the IL-6 levels before and after treatment in the plasma exchange + CHDF group. Interleukin-8 levels increased significantly after treatment in the plasma exchange group while decreasing significantly after treatment in the plasma exchange + CHDF group. These results indicate that combining plasma exchange and CHDF in a parallel circuit is an effective modality for suppressing the elevation of blood citrate levels and for removing inflammatory cytokines. This finding may have important implications for the development of an effective treatment for patients with acute hepatic failure.

Artificial liver support devices for fulminant liver failure

Artificial liver-support devices attempt to bridge patients with fulminant hepatic failure until either a suitable liver allograft is obtained for transplantation or the patient's own liver regenerates sufficiently to resume normal function. It is thought that toxins contribute to the clinical picture of fulminant hepatic failure. The earliest reports of successful toxin removal were blood- and plasma-exchange transfusions. Given these successful case reports, mechanical liver-support devices were designed to filter toxins. These mechanical devices used hemodialysis, charcoal hemoperfusion, hemoperfusion through cation-exchange resins, hemodiabsorption, and combinations of all of these techniques as in the MARS liver-support device. Despite promising case reports and small series, no controlled studies of mechanical devices have ever showed a long-term survival benefit. Thus, the removal of presumed toxins seems to be insufficient to support patients with fulminant hepatic failure, and the biologic function of the liver must also be replaced. Attempts at replacing the biologic function have included extracorporeal liver perfusion, cross-circulation, and hepatocyte transplantation. Current technologies have combined mechanical and biologic support systems in hybrid liver-support devices. The mechanical component of these hybrid devices serves both to remove toxins and to create a barrier between the patient's serum and the biologic component of the liver-support device. The biologic component of these hybrid liver support devices may consist of liver slices, granulated liver, or hepatocytes from low-grade tumor cells or porcine hepatocytes. These biologic components are housed within bioreactors. Currently the most clinically studied bioreactors are those that use capillary hollow-fiber systems. Both the bioartificial liver by Demetrious and the extracorporeal liver-assist device by Sussman and Kelly are in clinical trials. Although the trials seemed to have yielded good survival data when the devices are used as a bridge to transplantation, the type and degree of liver support provided by these devices remains uncertain. Thus, despite decades of great progress in the field of artificial liver support, no one technique alone yet provides sufficient liver support. A hybrid system seems to be the best option at present. Still to be determined is the best tissue to use, how much liver tissue should be used, and the optimal design of the bioreactor.

Hybrid artificial liver using hepatocyte organoid culture

We developed 2 types of hybrid artificial liver modules using hepatocyte organoid culture. One was a polyurethane foam (PUF)/hepatocyte spheroid packed-bed module. Hepatocytes spontaneously formed spheroids in the PUF pores, and they maintained liver-specific functions well for at least 2 weeks in vitro. As a preclinical experiment, a hybrid artificial liver with 200 g porcine hepatocytes was applied to a pig (25 kg) with liver failure and showed that the hybrid artificial liver was effective in support of liver functions and stabilization of general conditions. We established a new technique of hepatocyte organoid formation using centrifugal force. A hepatocyte organoid formed by centrifugation in hollow fibers maintained functions for more than 4 months in vitro. We developed a new sinusoid-like structure module having hollow fibers arranged by spacers in a micro-regular arrangement. Inoculated hepatocytes in the extra-fiber space of the module formed the organoid by centrifugation, and they maintained the functions for at least 1 month in vitro. The results indicated that this module seems to be promising as a hybrid artificial liver.

Push-pull sorbent-based pheresis and hemodiabsorption in the treatment of hepatic failure: preliminary results of a clinical trial with the BioLogic-DTPF System

The BioLogic-DTPF System combines hemodiabsorption (the BioLogic-DT System with dialysis against powdered sorbent) with push-pull sorbent-based pheresis (the BioLogic-PF System with powdered sorbent surrounding plasma filters). At blood flow rates of 200 ml/min, the system clears creatinine and aromatic amino acids at 120-160 ml/min, unconjugated bilirubin at 20-40 ml/min, and cytokines at 15-25 ml/min. This article outlines a study of the DTPF System in treatment of patients with hepatic failure with Grade 3 or 4 encephalopathy and respiratory and kidney insufficiency. Treatment appeared to be safe, and there are no significant hematologic changes. Physiologic changes include improved blood pressure and encephalopathy and stable urine output. Chemical changes include decrease in plasma levels of bilirubin, aromatic amino acids, ammonium, creatinine, and interleukin-3 (IL-1beta). The BioLogic-DT System is now marketed for treatment of acute hepatic failure with encephalopathy. The BioLogic-DTPF System adds the capability of removing bilirubin and other strongly protein-bound toxins from treated patients and may be of clinical benefit in management of patients with the most severe hepatic failure and encephalopathy.

Comparative study of bioartificial liver support and plasma exchange for treatment of pigs with fulminant hepatic failure

Recently, bioartificial liver (BAL) treatment was reported to provide beneficial effects for patients with fulminant hepatic failure (FHF). Some success in experimental or clinical trials has been reported; however, the evaluation of BAL efficacy remains unclear, especially in comparison with other treatments for FHF. The purpose of this study was to compare the efficacy between BAL and plasma exchange (PE) in experimentally induced FHF in pigs. Pigs undergoing hepatic devascularization (HD) were placed into the following groups: no treatment (control; n = 6), BAL treatment (BAL; n = 5), and plasma exchange (PE; n = 5). Each treatment was initiated 6 h after HD and lasted for 4 h. BAL treatment significantly improved liver functions in FHF pigs. The decrease in cerebral perfusion pressure was also significantly suppressed in the pigs with BAL, and their survival time was prolonged compared with the results in pigs with PE. The effects of BAL outperform those of PE in the treatment of experimental FHF model.

Hyperbaric oxygenation, plasma exchange, and hemodialysis for treatment of acute liver failure in a 3-year-old child

A girl aged 3 years and 4 months weighing 16 kg was treated with plasma exchange (PE), hemodialysis (HD), and hyperbaric oxygenation (HBO) for acute hepatic failure and coma. She was given a total of 13 PEs, 13 HD sessions, and 9 HBO treatments over a period of 1 month. The initial 4 PEs were followed by HD sessions while the other 8 PE treatments were given simultaneously with HD. There was no renal failure; HD was instituted to improve ammonia elimination. In 1 HD session, 20% human albumin (370 ml) was used as the dialysate to enhance bilirubin elimination. Three volumes of plasma (2,000 ml) per PE were exchanged and replaced with fresh frozen plasma (FFP). The Bellco BL 791 plasmapheresis monitor and Gambro PF1000 and PF2000 plasma filters were used. Heparin was added to prevent clotting. A dual lumen pediatric HD catheter (7 Fr) placed percutaneously into the femoral vein was used as a blood access. The Fresenius 2008 C HD monitor and the Filtral 10 dialyzer were used for HD. PE and HD were instituted simultaneously to prevent the tetanic (hypocalcemic) cramps observed with 2 previous PEs due to citrate in the FFP. The extracorporeal circuit was primed with a mixture of concentrated red cells, human albumin, and saline solution and was discarded at the end of the procedure. The average blood flow rate in PE and/or HD circuits was 80 ml/min. During HBO, the girl breathed 100% oxygen at 2.5 atm for 90 min. Throughout the treatment, the patient was in good clinical, physical, and mental condition, but she was dependent on blood purification procedures. She was referred to a liver transplant center and successfully transplanted. The etiology of liver failure has not been clarified.

Function of culturing monolayer hepatocytes by collagen gel coating and coculture with nonparenchymal cells

Since 1987, we have been developing a bioartificial liver (BAL) using multiplated cultured hepatocyte monolayers. With the goal of promoting hepatic functions of cultured hepatocyte monolayers, we combined the use of a collagen gel layer over the monolayers of hepatocytes and/or cocultured hepatocytes with nonparenchymal cells (NPCs). The study was divided into four groups according to culture configurations: Group 1: hepatocyte monolayer culture (control); Group 2; coculture of hepatocytes and NPCs; Group 3: hepatocyte monolayer with a overlaid collagen gel layer; and Group 4: coculture with a overlaid collagen gel layer. The culture continued for 14 days. Morphological changes and hepatic functions were evaluated by urea and albumin syntheses. The morphological status of the hepatocytes remained for 2 weeks in Groups 3 and 4. Deterioration and detachment of hepatocytes and/or NPCs started in Group 1 and 2 on the third day in culture. Significantly high urea synthesis was noted in Group 4 (p < 0.001 compared with Group 1 and 2: p = 0.0014 compared with Group 3). Although there was no significant difference in albumin synthesis among the four groups, those hepatocytes covered by the collagen gel (Groups 3 and 4) tended to secrete albumin throughout the observation period. These results indicted that the environment, although artificial (but close to the in vivo state), supplied with collagen gel and the coculture, enhanced the activities of the cultured hepatocyte monolayers. We suggest that use of cocultured hepatocytes under a collagen gel is a promising candidate for a bioreactor of multiplated BAL.