Extracorporeal Liver Support Research Articles

Lidocaine/Monoethylglycinexylidide Test, Galactose Elimination Test, and Sorbitol Elimination Test for Metabolic Assessment of Liver Cell Bioreactors

Various metabolic tests were compared for the performance characterization of a liver cell bioreactor as a routine function assessment of cultures in a standby for patient application in clinical studies. Everyday quality assessment (QA) is essential to ensure a continuous level of cellular functional capacity in the development of hepatic progenitor cell expansion systems providing cells for regenerative medicine research; it is also of interest to meet safety requirements in bioartificial extracorporeal liver support systems under clinical evaluation. Quality criteria for the description of bioreactor cultures were developed using primary porcine liver cells as a model. Porcine liver cells isolated by collagenase perfusion with an average of 3 x 10(9) primary cells were used in 39 bioreactors for culture periods up to 33 days. Measurements of monoethylglycinexylidide synthesis and elimination of lidocaine, galactose elimination, and sorbitol elimination proved to be useful for routine QA of primary liver cell cultures. We demonstrate two methods for dispensing test substances, bolus administration and continuous, steady-state administration. Bolus test data were grouped in Standard, Therapy, Infection/Contamination, and Cell-free control groups. Statistical analyses show significant differences among all groups for every test substance. Post hoc comparisons indicated significant differences between Standard and Cell-free groups for all elimination parameters. For continuous tests, results were categorized according to number of culture days and time-dependent changes were analyzed. Continuous administration enables a better view of culture health and the time dependency of cellular function, whereas bolus administration is more flexible. Both procedures can be used to define cell function. Assessment of cellular function and bioreactor quality can contribute significantly to the quality of experimental or clinical studies in the field of hepatic bioreactor development.

Three-Dimensional Perfusion Bioreactor Culture Supports Differentiation of Human Fetal Liver Cells

The ability of human fetal liver cells to survive, expand, and form functional tissue in vitro is of high interest for the development of bioartificial extracorporeal liver support systems, liver cell transplantation therapies, and pharmacologic models. Conventional static two-dimensional culture models seem to be inadequate tools. We focus on dynamic three-dimensional perfusion technologies and developed a scaled-down bioreactor, providing decentralized mass exchange with integral oxygenation. Human fetal liver cells were embedded in a hyaluronan hydrogel within the capillary system to mimic an in vivo matrix and perfusion environment. Metabolic performance was monitored daily, including glucose consumption, lactate dehydrogenase activity, and secretion of alpha-fetoprotein and albumin. At culture termination cells were analyzed for proliferation and liver-specific lineage-dependent cytochrome P450 (CYP3A4/3A7) gene expression. Occurrence of hepatic differentiation in bioreactor cultures was demonstrated by a strong increase in CYP3A4/3A7 gene expression ratio, lower alpha-fetoprotein, and higher albumin secretion than in conventional Petri dish controls. Cells in bioreactors formed three-dimensional structures. Viability of cells was higher in bioreactors than in control cultures. In conclusion, the culture model implementing three-dimensionality, constant perfusion, and integral oxygenation in combination with a hyaluronan hydrogel provides superior conditions for liver cell survival and differentiation compared to conventional culture.

Removal of asymmetric dimethylarginine during artificial liver support using fractionated plasma separation and adsorption

Objective. Asymmetric dimethylarginine (ADMA) is the most potent endogenous nitric oxide synthase inhibitor. Elevated ADMA levels have been linked to increased mortality in different patient populations. Key regulation of ADMA levels mainly takes place in the liver. Hence, ADMA is elevated in liver disease. There is no specific pharmacological treatment to lower the elevated ADMA levels. Hemodialysis is of limited efficiency in removing ADMA as it is highly protein bound. Prometheus® is an extracorporeal liver support system which allows the removal of protein-bound toxins. We assessed the efficiency of the Prometheus® system in reducing high ADMA levels in patients with liver failure. Material and methods. We studied nine patients with acute-on-chronic liver failure and concomitant renal failure already necessitating hemodialysis. Seven patients needed intensive care treatment. Two consecutive sessions of Prometheus® therapy of each 4 h were performed in all patients. ADMA and its structural isomer symmetrical dimethylarginine (SDMA) were determined using liquid chromatography–mass spectrometry. Results. ADMA levels correlated to model for end stage liver disease (MELD) score (rs = 0.62; p < 0.0001). Before Prometheus® was started, levels of ADMA and SDMA were elevated (1.36 ± 0.5 μmol/l and 1.90 ± 0.4 μmol/l, respectively). During Prometheus® treatments, plasma levels of ADMA dropped by a mean 25% (p < 0.0001) and SDMA levels by 22% (p < 0.0001). However, there was a significant rebound of ADMA levels between the two therapy sessions (p < 0.01). Conclusions. This study shows for the first time that plasma levels of ADMA can be effectively lowered by an artificial liver support system (Prometheus®). Effective elimination of ADMA might explain some of the beneficial clinical effects of these systems in patients with liver failure.

Liver Transplantation for Acute Liver Failure: A Spanish Perspective

The Spanish characteristics of organ donation (high accessibility to a transplant) and the different proportion in the etiologies of acute liver failure (ALF), namely, the very low incidence of paracetamol overdose causing this syndrome in contrast with other Western countries, are the causes of some specific features of emergency liver transplantation for ALF. The most relevant are the short time between the need for a graft and effective urgent liver transplant, and the high proportion of patients who undergo this therapy. This paper analyzes these characteristics and provides information about the use of biological and nonbiological extracorporeal liver support devices in acute liver failure, suggesting that these systems should be tested in countries with a long waiting times for urgent liver transplantation, or in patients with ALF and contraindications for transplantation.

Changes in Plasma Amino Acids During Extracorporeal Liver Support by Fractionated Plasma Separation and Adsorption

In patients with liver failure, amino acid dysbalance is common and associated with hepatic encephalopathy. Prometheus is a newly designed extracorporeal liver support system based upon fractionated plasma separation and adsorption (FPSA). We evaluated the influence of FPSA on plasma amino acid patterns in patients with liver failure and hepatic encephalopathy. We studied nine patients with acute-on-chronic liver failure, hepatic encephalopathy, and concomitant renal failure. A single session of FPSA therapy for 5 +/- 1 h was performed in all patients. Twenty-six different plasma amino acids were measured by high-performance liquid chromatography before and after FPSA treatment. Total amino acids as well as Fischer index were calculated. Additionally, a variety of clinical and biochemical parameters were assessed. Before FPSA was started, plasma levels of most amino acids were elevated. Plasma ammonia levels correlated with glutamine levels (P < 0.04). During FPSA, plasma levels of nearly all amino acids significantly decreased except for branched-chain amino acids. The Fischer index improved without reaching statistical significance. FPSA therapy tends to normalize plasma amino acids in patients with combined liver and renal failure. This may contribute to positive pathophysiologic effects, especially on hepatic encephalopathy. However, the clinical significance of these findings needs to be further evaluated.

Use of a Rotary Bioartificial Liver in the Differentiation of Human Liver Stem Cells

The use of bioartificial livers (BALs) for the expansion of human adult liver stem cells and the production of growth factors could be a potential strategy for cell-based extracorporeal liver support. The present study aimed to assessing the differentiation of human adult liver stem cells in a rotary BAL. Liver stem cells were seeded into a polysulphone membrane filter at a density of 3 x 10(8) cells, and the filter was connected to a rotary bioreactor perfusion system (37 degrees C, 50 mL/min, 48 h). Viability, cell differentiation, and metabolic performances were evaluated at 24 and 48 h. Hepatocyte growth factor production from human adult liver stem cells, mature hepatocytes, and mesenchymal stem cells in adhesion and in the rotary BAL conditions was compared. Liver stem cells cultured in the rotary BAL produced the highest amounts of albumin (p = 0.002) and ammonia-induced urea (p = 0.0001), and had an increased cytochrome P450 expression in respect to liver stem cells in adhesion. Remarkably, liver stem cells in the rotary BAL produced very high amounts of hepatocyte growth factor (p = 0.005) in respect to hepatocytes and mesenchymal stem cells. Moreover, the cells lost their stem cell markers and acquired several markers of mature hepatocytes. In conclusion, the rotary BAL favored liver stem cell differentiation into mature hepatocyte-like cells.

Efficacy and Safety of Anticoagulation With Heparin Versus Heparin Plus Epoprostenol in Patients Undergoing Extracorporeal Liver Support With Prometheus

Anticoagulation for extracorporeal liver support is delicate due to underlying coagulation disorders in patients with liver failure and to the associated elevated bleeding risk. To date, there has been no detailed report on anticoagulation issues in patients treated with Prometheus, a device based on the principle of fractionated plasma separation and adsorption. We studied 17 patients from two centers treated with Prometheus, comparing standard anticoagulation with heparin (15 treatments) and a combination of heparin and the synthetic prostacyclin epoprostenol (22 treatments). Standard coagulation tests, proteins C and S, and thrombin-antithrombin (TAT) complex were determined, and adverse events were recorded. All but two treatments could be completed as scheduled, although filter exchange due to filter clotting was required in 24% of the treatments. Three out of 17 patients developed severe bleeding complications within 24 h of treatment. There were no overt thrombotic events. Addition of epoprostenol neither reduced coagulation-related adverse events nor improved standard coagulation parameters. Protein C, but not protein S, showed a significant reduction (23 +/- 18%) after Prometheus treatments, but levels rebounded to baseline within 18 h. TAT levels--a measure for activation of coagulation--were only altered by Prometheus in patients where TAT was already elevated before treatment. In conclusion, anticoagulation of Prometheus with heparin is feasible but still associated with a relatively high frequency of filter clotting and a considerable risk of severe bleeding in this high-risk patient population. As addition of epoprostenol did not prove beneficial, other strategies, such as regional anticoagulation with citrate, should be further evaluated.

Characterization of peptides and proteins in commercial HSA solutions

HSA solutions account for 14% of the world market for plasma products. Albumin is indicated for reestablishing and maintaining circulatory volume in situations resulting from traumatic shock, surgery, or blood loss. Albumin is also used in extracorporeal liver support devices that perform blood dialysis against this protein. However, the protein composition of therapeutic albumin is only partially known. We performed an exhaustive analysis of albumin composition using a proteomic approach. Low abundance proteins and peptides in these samples were concentrated using a strong anion exchange resin. The absorbed material was eluted with a stepwise gradient of ammonium trifluoroacetate and the protein fraction was digested and analyzed by multidimensional liquid chromatography coupled to ESI-MS/MS using a linear ion trap. A total of 1219 peptides corresponding to 141 proteins different from albumin were identified with a false discovery rate <1%. Near 50% of these proteins have been described previously as forming part of the albuminome. Some of these proteins are proteases (kallikrein) or protease inhibitors (kininogen and SRPK1) or have relevant functions in cell surface adhesion (selectin, cadherins, and ICAMs) or in immunity and defense (molecules of the complement system and attractin). Characterization of these proteins and peptides is crucial in order to understand the therapeutic and possible deleterious effects of albumin therapies, in which this solution is infused to treat different pathological conditions.

Preclinical characterization of primary porcine hepatocytes in a clinically relevant flat membrane bioreactor

Using primary porcine hepatocytes, artificial extracorporeal liver support (AEL) is a therapy that carries out the liver functions of liver failure patients until their own organs have been regenerated or until whole organ transplantation. Significant variation exists with regard to current bioreactor designs for AEL, and they may not reflect the in vivo architecture of the liver since each individual hepatocyte has its own direct contact with blood plasma for oxygen and nutrient supply and detoxification. The present study, based on our flat membrane bioreactor (FMB), aimed at in vivo liver architecture and to meet authentic clinical levels of human plasma exposure. Since many existing preclinical AELs are based on commercial culture medium with or without nonhuman serum, they may not authentically reflect the clinical situation in human patients, and little research has been done on human plasma exposure in in vitro culture-based bioreactors. To address this situation, herein we examined liver-specific functions such as albumin secretion, urea synthesis, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), cell membrane stability by lactate dehydrogenase (LDH) test and ammonia clearance by using human plasma and serum-free medium in long-term culture of primary porcine hepatocytes to show the potential of our clinically relevant FMB. We observed that the organotypical double-gel (DG) culture is superior to conventional collagen-coated single-gel (SG) cultures. The performance of liver-specific functions by the FMB has long-term stability with intact cell morphology for up to 20 days under both plasma exposure and serum-free media. Our three focus points (long-term culture that correlates with the generation time of spontaneous regeneration, high-density culture, organotypical culture model using human plasma) may provide valuable clinical clues for AEL.

Increase of Octanoate Concentrations During Extracorporeal Albumin Dialysis Treatments

Extracorporeal liver support procedures based on albumin dialysis require the use of pharmaceutical-grade human serum albumin (HSA). Those preparations contain octanoate, which is added as stabilizer during the production process. For octanoate, a direct involvement in the pathogenesis of liver failure complications as well as an indirect influence by competitive displacement effects at the albumin molecule have been described. During five Single Pass Albumin Dialysis (SPAD) and three Molecular Adsorbent Recirculating System (MARS) treatments the changes of octanoate concentrations in blood and dialysate were investigated. An octanoate increase in patient blood was observed during passage of the filter for both SPAD (585 micromol/L [338-1022 micromol/L]) (median [range]) and MARS (182 micromol/L [71-437 micromol/L]) during the first three hours of treatment. The molar ratio of octanoate/albumin at the blood outflow was significantly higher during SPAD treatments (1.73 [0.86-2.64] vs. 0.54 [0.31-1.1]; P = 0.001) during MARS. Changes of octanoate blood levels during SPAD were significantly higher than during MARS (P < 0.001). The shift of octanoate from the dialysate to the patient was persistent during SPAD (median 67.6 micromol/min), whereas during MARS a decrease over time was observed (from 25.5 to 7.5 micromol/min). During albumin dialysis procedures a transfer of octanoate into patient blood occurs. The time-course and extent are different between both albumin dialysis procedures. Given the positive clinical effects reported mainly for MARS, the clinical impact of albumin dialysis-associated transfer of octanoate during extracorporeal liver support needs to be evaluated further.

Effect of Extracorporeal Liver Support by Molecular Adsorbents Recirculating System and Prometheus on Redox State of Albumin in Acute‐on‐Chronic Liver Failure

Oxidative stress is believed to play an important role in acute-on-chronic liver failure (AoCLF). Albumin, an important transport vehicle, was found to be severely oxidized in AoCLF patients. Extracorporeal liver support systems may exert beneficial effects in AoCLF via removal of albumin-bound toxins. At present, two systems are commercially available, the molecular adsorbents recirculating system (MARS) and fractionated plasma separation, adsorption and dialysis (FPAD, also known as Prometheus). The aim of this study was to compare the effect of MARS and Prometheus treatments on the redox state of human serum albumin. Eight patients with AoCLF underwent alternating treatments with either MARS or Prometheus in a randomized cross-over design. Sixteen treatments (eight MARS and eight Prometheus) were available for analysis. The fraction of human mercaptalbumin (HMA), human nonmercaptalbumin-1 (HNA1), and human nonmercaptalbumin-2 (HNA2) were measured before and after single MARS and Prometheus treatments and during follow-up. In AoCLF patients the oxidized fractions of albumin, HNA1, and HNA2 were markedly increased. Both MARS and Prometheus treatments resulted in a shift of HNA1 to HMA, while HNA2 was not significantly affected. This shift in albumin fractions was transient and disappeared within 24 h after treatment. There were no significant differences between MARS and Prometheus treatments with respect to the redox state of albumin. Both MARS and Prometheus treatments lead to transient improvements of the redox state of albumin, which could be beneficial in the treatment of AoCLF.

Albumin Dialysis in Liver Failure: Comparison of Molecular Adsorbent Recirculating System and Single Pass Albumin Dialysis—A Retrospective Analysis

Despite improvement in critical care, liver failure is still associated with high mortality. Therapeutic concepts are aimed at restoring endogenous liver function or to bridge the time to liver transplantation. In addition to standard medical treatment, extracorporeal liver support with albumin dialysis is used for this purpose. The aim of this study was to analyze the efficacy of single pass albumin dialysis (SPAD) in comparison to the molecular adsorbent recirculating system (MARS) in patients treated at our university hospital intensive care unit between July 2004 and August 2008. In this retrospective analysis we studied patients presenting with liver failure who were treated with albumin dialysis. Laboratory parameters, daily health scoring, the number of transfusions, and mortality were recorded. The (paired) t-test, Mann-Whitney U-test, and Wilcoxon test were used for statistical analysis. In all, 163 albumin dialysis treatments, 126 with MARS and 37 with SPAD, in 57 patients were performed. MARS resulted in a significant decrease in bilirubin (-38 +/- 66.5 micromol/L from a baseline of 301 +/- 154.6 micromol/L), gamma-glutamyltransferase (gamma-GT), alanine aminotransferase, creatinine, and urea. SPAD resulted in a significant decrease in bilirubin (-41 +/- 111.2 micromol/L from a baseline of 354 +/- 189.4 micromol/L) and gamma-GT, while lactate levels increased. No differences in the need for blood transfusion, health scoring, or mortality between the two treatment modalities were detected. This retrospective analysis suggests equal efficacy of MARS and SPAD; however, prospective assessment to further define the role of SPAD in the treatment of acute or acute-on-chronic liver failure is needed.

Hemodynamic Effects of Albumin Dialysis in Patients With Liver Failure: For Better or For Worse?

Liver failure, irrespective of is cause, is frequently associated with multi-organ dysfunction, including hemodynamic instability, and renal and cerebral insufficiency. As a result of the combined impact of these complications, liver failure carries an exceptionally high risk of mortality. A central role in the etiopathogenesis of different end-organ manifestations, as well as in the aggravation of the underlying liver failure, has been attributed to the hyperdynamic (hypotensive) state, which is characterized by a reduced systemic vascular resistance and mean arterial pressure, as well as an increased cardiac index, heart rate, and total plasma volume. Since the accumulation of toxins due to the decreased detoxification capacity by the failing liver is considered vital herein, the emergence of extracorporeal liver support has provided a rational basis for the potential reversal of these phenomena. The present article critically reviews data with regard to the hemodynamic effects of artificial liver support in the context of liver failure. Although these are scarce for acute liver failure, several uncontrolled series and small randomized trials have clearly documented that artificial liver support is able to improve both portal hypertension and the associated systemic circulatory dysfunction in patients with acute-on-chronic liver failure. The molecular basis for these effects have been related to temporary changes and/or elimination in endogenous vasoactive substances, improved albumin binding capacity, or restoration of oxidative stress-mediated damage to albumin.

Extracorporeal Liver Support Therapy With Prometheus in Patients With Liver Failure in the Intensive Care Unit

Acute liver failure (ALF) and acute-on-chronic liver failure (AoCLF) are associated with a high mortality. In these patients an accumulation of both water-soluble and water-insoluble, protein-bound, metabolic waste products occurs. Conventional extracorporeal blood purification techniques based on diffusion and/or convection such as hemodialysis or hemofiltration may only eliminate small molecular weight, water-soluble compounds. In recent years, fractionated plasma separation and adsorption (FPSA) with the Prometheus system has been introduced for extracorporeal liver support therapy. To date, however, only limited data is available regarding the effect of this treatment on mortality and outcome of patients with advanced liver disease. Here we report on our experience with 23 patients with severe liver failure who were treated with Prometheus in our medical intensive care unit. Fourteen patients had AoCLF, and nine patients experienced ALF. The median bilirubin level at the start of Prometheus therapy was 30.5 mg/dL and the median Acute Physiology and Chronic Health Evaluation II (APACHE II) score was 26. During 40 individual treatment sessions lasting 5-6 h, Prometheus therapy reduced serum bilirubin levels from 23.7 mg/dL to 15.0 mg/dL (median values) (P < 0.001), and the overall survival was 26%. ALF patients had a better survival compared to AoCLF patients (44% vs. 22%; P = 0.022). Apart from one patient who developed hemodynamic instability during a treatment session, Prometheus therapy was well tolerated without relevant side-effects. In conclusion, extracorporeal liver support therapy with Prometheus is a novel and safe treatment option in patients with severe liver failure. In this series, patients with ALF showed a significantly better outcome with Prometheus therapy compared to AoCLF patients.

Effect of human patient plasma ex vivo treatment on gene expression and progenitor cell activation of primary human liver cells in multi‐compartment 3D perfusion bioreactors for extra‐corporeal liver support

Cultivation of primary human liver cells in innovative 3D perfusion multi-compartment capillary membrane bioreactors using decentralized mass exchange and integral oxygenation provides in vitro conditions close to the physiologic environment in vivo. While a few scale-up bioreactors were used clinically, inoculated liver progenitors in these bioreactors were not investigated. Therefore, we characterized regenerative processes and expression patterns of auto- and paracrine mediators involved in liver regeneration in bioreactors after patient treatment. Primary human liver cells containing parenchymal and non-parenchymal cells co-cultivated in bioreactors were used for clinical extra-corporeal liver support to bridge to liver transplantation. 3D tissue re-structuring in bioreactors was studied; expression of proteins and genes related to regenerative processes and hepatic progenitors was analyzed. Formation of multiple bile ductular networks and colonies of putative progenitors were observed within parenchymal cell aggregates. HGF was detected in scattered cells located close to vascular-like structures, expression of HGFA and c-Met was assigned to biliary cells and hepatocytes. Increased expression of genes associated to hepatic progenitors was detected following clinical application. The results confirm auto- and paracrine interactions between co-cultured cells in the bioreactor. The 3D bioreactor provides a valuable tool to study mechanisms of progenitor activation and hepatic regeneration ex vivo under patient plasma treatment.

Proteomic Analysis of Proteins Bound to Adsorption Units of Extracorporeal Liver Support System under Clinical Conditions

Fractionated Plasma Separation, Adsorption and Dialysis (Prometheus) has a well-documented capacity to remove protein-bound organic toxins in patients with liver failure. However, the compositions of adsorbed proteins remain unknown. Elution of both adsorbers constituting Prometheus system was performed following a 6-h session in a patient with acute on chronic liver failure. Sodium dodecylsulphate was employed to elute proteins from the neutral adsorber (P1), while acetic acid was applied to the cationic one (P2). Eluted proteins were resolved by two-dimensional gel electrophoresis (2-DE) and identified by mass spectrometry (MS). Totally, 4113 and 8280 mg of proteins were obtained from P1 and P2 eluates, 2-DE yielded 148 and 163 protein fractions in P1 and P2, respectively. MS identified 18 unique proteins in P1, and 30 unique proteins in P2 sample. Proteins with the highest selective adsorption (as determined by eluate to plasma ratio) included transthyretin (37), trypsin-2 (29), prothrombin (23), hyaluronan-binding protein 2 (13) and plasma retinol-binding protein (8.7), all of which adsorbed to P2. We identified a large number of proteins removed by extracorporeal liver support system. A selective adsorption was demonstrated in a subset of proteins depending on the type of adsorber and proteins' characteristics.

Usefulness and Safety of Extracorporeal Liver Support Therapy Using MARS® for Patients with Liver Failure: A Preliminary Report

The molecular adsorbent recirculating system (MARSR) is a form of artificial extracorporeal liver support and can be used for a bridge to spontaneous recovery of hepatic function or liver transplantation in patients with liver failure. This study evaluated the usefulness of MARSR in patients with liver failure. Between January 2004 and July 2007, 30 patients (21 males and 7 females; age 48.9+/-12.9 years) with acute or acute-on-chronic liver failure were managed using MARSR. We assessed laboratory data, the grade of hepatic encephalopathy, Child-Turcotte-Pugh class, and Model for End-Stage Liver Disease (MELD) score. The number of patients with acute liver failure and acute-on-chronic liver failure was 16 and 14, respectively. The mean cycle of MARSR in patients with liver failure was 2.2 sessions. After MARSR had been performed, serum total bilirubin, alanine aminotransferase (ALT), BUN, creatinine, ammonia level, daily urine output, and MELD score were improved (p<0.05). In contrast, MARSR failed to improve Child-Turcotte-Pugh score and the grade of hepatic encephalopathy. Liver transplantation was performed in 8 patients. Among them, 5 (62.5%) patients survived and 3 (37.5%) patients died. Twenty two patients underwent MARSR without liver transplantation and 4 (18.2%) of them survived. In patients with liver failure, MARSR improved the laboratory data and hepatic and renal function associated clinical characteristics. However, MARSR without liver transplantation did not improve survival. MARSR may be useful as a bridge therapy to liver transplantation in patients with liver failure.

Cell Therapy for Acute Liver Failure - Ideal source of cell

Liver is the central metabolic organ that regulates body’s energy supply, secretes several essential compounds and clears substances by several methods, including recycling, inactivation andexcretion. Global loss of the liver function results in profound metabolic instability and disruption of essential functions such as acid-base balance and thermoregulation leading to acute liver failure (ALF). If this is not rapidly reversed, complications such as uncontrolled bleeding occur, and dependent organs such as brain and kidneys begin to fail, reducing the chance of recovery even further. Acute liver failure (ALF) carries high morbidity and mortality (>80%) even in the best centres. Presently, orthotopic liver transplantation (OLTx) is the only treatment that improves the survival rate in patients with ALF. Advent of various immunosuppressive agents has improved the success rate of this procedure by preventing rejection. Non availability of donor organs however remained a major limitation. Two approaches viz., (i) hepatocyte transplantation (ii) extracorporeal liver support system, have been attempted to provide temporary liver support to failing liver till a suitable organ becomes available. These approaches have demonstrated their efficacy in the pre-clinical and clinical studies.

Extracorporeal albumin dialysis

Patients with liver failure still present a high mortality. It can only be significantly improved by the rare resource of liver transplantation. Extracorporeal liver support devices have been developed to temporarily support liver detoxification. Artificial devices without hepatocytes ("liver dialysis" or "albumin dialysis") are already widely used in Europe. The two best-known systems, MARS and Prometheus, use a different technical approach to remove water-soluble as well as albumin-bound toxins from the blood. In MARS, toxins diffuse along a concentration gradient through an albumin-impermeable membrane into a secondary circuit that is pre-filled with an albumin solution. The albumin is continuously "recycled" inside the secondary circuit by different adsorber and low flux dialysis. In contrast, Prometheus includes an albumin-permeable filter allowing separation of the albumin fraction into the secondary circuit where the albumin-bound toxins are directly removed by two adsorbers. Thereafter, high flux dialysis is performed inside the primary circuit. For both extracorporeal systems, an improvement of hepatic encephalopathy and biochemical markers such as bilirubin is consistently reported. In-vivo comparisons of both systems showed significantly higher extraction capacities for protein-bound and water-soluble substances under Prometheus than under MARS treatment. Possible pathophysiological mechanisms could be a reduction of portal pressure or a removal of vasoactive cytokines. However, only few randomised controlled trials with low patient numbers and conflictive results regarding patient survival exist. Nevertheless, a Cochrane meta-analysis revealed a significant survival benefit for extracorporeal liver support devices in patients with acute-on-chronic liver failure. Other promising indications are severe refractory cholestatic pruritus, intoxication with protein-bound substances and graft dysfunction after liver transplantation. As large randomised controlled multi-center trials are currently underway, better evidence will be available soon to define the clinical role of extracorporeal liver support devices.

Albumin dialysis has a favorable effect on amino acid profile in hepatic encephalopathy

According to one popular theory, hepatic encephalopathy (HE) is partly caused by an imbalance in plasma amino acid levels. The Fischer's ratio between branched chain amino acids (BCAAs) and aromatic amino acids (AAAs) correlates with the degree of HE; the lower Fischer's ratio, the higher the grade of HE. Extra-corporeal liver support systems, like MARS(R)-albumin dialysis (Molecular Adsorbents Recirculating System), can improve HE. The MARS(R) system uses a hyperosmolar albumin circuit to remove both water-soluble and albumin-bound substances. Plasma levels of neuroactive amino acids were analyzed in 82 consecutive patients with life-threatening liver failure admitted to our ICU. All patients fulfilled our indications for MARS treatment and most also fulfilled the criteria for liver transplantation (LTx). In patients with acute liver failure (ALF), as compared to those with acute decompensation of chronic liver failure (AcOChr), levels of leucine and isoleucine were significantly higher before MARS(R) treatment. In all patients, before MARS(R) treatment the higher the grade of HE grade the lower was the Fischer's ratio and higher were the levels of inhibitory neuroactive amino acids. During MARS(R) treatments the Fischer's ratio increased, and the grade of HE decreased. The increase in Fischer's ratio was mainly due to the decrease in AAAs. The plasma levels of neuroactive amino acids, methionine, glutamine, glutamate, histidine and taurine decreased during MARS(R)-treatment. In this study MARS(R)-albumin dialysis had a favorable effect on the plasma amino acid profile of patients with HE.