In vivo quantification of liver dialysis: comparison of albumin dialysis and fractionated plasma separation

Hepatobiliäre Funktionsstörungen und Leberversagen

Als »sepsisinduzierte Cholestase« bezeichnet man das Auftreten einer konjugierten Hyperbilirubinämie als Folge einer extrahepatischen bakteriellen Infektion ohne direkte Invasion der Leber durch Erreger.

[Evaluation of extracorporeal liver support systems in the treatment of liver failure. A systematic review]

OBJECTIVE

To evaluate the safety and efficacy of the MARS and Prometheus extracorporeal liver support systems in the treatment of liver failure.

DESIGN

We performed a systematic review of the literature from January 1999 to June 2009 in the Medline, Embase, HTA, DARE, NHSEED, Cochrane Library Plus, Clinical Trials Registry and HSRPROJ databases. Study selection was based on a series of previously established inclusion criteria related to the study design, population, type of intervention, language, and outcome measures.

PATIENTS AND INTERVENTIONS

Patients with acute liver failure or acute exacerbations of chronic liver failure treated with the MARS or Prometheus systems.

OUTCOME MEASURES

Data on safety, long-term survival, clinical effects and biochemical and hemodynamic variables.

RESULTS

We selected 22 studies evaluating the safety and efficacy of the MARS and Prometheus systems. Adequate evaluation of these techniques was hampered by the heterogeneity of the studies and their methodological limitations.

CONCLUSIONS

Extracorporeal liver support systems are able to purify both hydrosoluble and protein-bound substances. However, current data show that only the MARS system reduces mortality in acute liver failure and in acute exacerbations of chronic liver failure, although this reduction is non-significant. These techniques can be considered safe, with adverse effects similar to those of the control group. Their main indication is severe liver failure, for short periods while the liver recovers or a liver transplant becomes available.

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.

[Acute on chronic liver failure]

Acute-on-Chronic Liver Failure (ACLF) is a recently introduced term defined as severe acute deterioration of an established liver disease. This entity usually develops after an acute insult. The main clinical manifestations are hepatorenal syndrome, hepatic encephalopathy and organ failure, with a high risk of death in the short term. The true incidence of ACLF remains difficult to determine due to confusions surrounding the definition of this entity, but seems to be 40% at 5 years in patients with advanced cirrhosis, which translates into 4,000 cases in Europe within this time span. The treatment of choice is liver transplantation. However, due to the shortage of suitable organs and morbidity and mortality in these patients, other options must be used.

Treatment of hepatorenal syndrome

Hepatorenal syndrome (HRS) is a type of renal failure that occurs in patients with advanced cirrhosis. It is a result of splanchnic arterial vasodilation, renal vasoconstriction, reduced effective arterial volume, and potentially reduced cardiac output. Often, HRS is a fatal complication, and the only definitive treatment currently available is liver or liver-kidney transplantation. A number of other treatment modalities have been tested for the management of HRS, but most evidence is derived from small noncontrolled studies. The primary role of these treatment options is to provide a bridge to liver transplantation. Treatment may also provide acute reversal of renal failure and some symptomatic relief, but relapse is a common occurrence. The best therapeutic options appear to be those that reverse portal hypertension, splanchnic vasodilation, and/or renal vasoconstriction. Vasopressin analogs, particularly terlipressin, have emerged as the preferred pharmacologic therapies for management of HRS. Albumin is an appropriate adjunctive therapy to terlipressin and can be used to prevent HRS in patients with spontaneous bacterial peritonitis. Transjugular intrahepatic portosystemic shunt may provide a surgical option for qualified patients with HRS. Octreotide is ineffective as monotherapy but may be used as adjunctive therapy to other vasoactive agents. Dopamine agonists, endothelin antagonists, natriuretic peptides, and nitric oxide synthase inhibitors have not been effective for reversing HRS. Artificial hepatic support therapies have demonstrated the ability to improve laboratory abnormalities in patients with HRS, but their effect on clinical outcomes has not been determined. The role of renal replacement therapies or the newer artificial hepatic support therapies need further evaluation before they can be routinely recommended.

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.

Hepatic encephalopathy: pathophysiology and emerging therapies

Hepatic encephalopathy is characterized by neuropsychiatric abnormalities in patients with liver failure. Severe hepatic encephalopathy is an indication for liver transplantation as it portends poor outcome. Treatment of hepatic encephalopathy involves correction of precipitating factors such as sepsis, gastrointestinal bleeding, medications, and electrolyte imbalance. Effective therapies include lactulose and antibiotics such as neomycin, metronidazole, and rifaximin.

Effective bilirubin reduction by single-pass albumin dialysis in liver failure

Albumin dialysis is widely accepted as a liver-support technique for patients with liver failure. The Molecular Adsorbent Recirculating System, the widely accepted albumin dialysis technique, has limited use in developing countries because of its technical difficulties and high cost. Therefore, we assessed the efficacy of the more practical modality, the single-pass albumin dialysis (SPAD), in terms of bilirubin reduction, as a marker of albumin-bound toxins removal, as well as the patient outcomes. Twelve acute or acute-on-chronic patients with liver failure who had hyperbilirubinemia (total bilirubin > 20 mg/dL) were treated with SPAD by using 2% human serum albumin dialysate for 6 h. SPAD treatment significantly improved the levels of total bilirubin, conjugated bilirubin, urea, and creatinine (P < 0.001 for all parameters). The reduction ratios of these four parameters were 22.9 +/- 3.8%, 20.9 +/- 5%, 19.0 +/- 4.1%, and 27.7 +/- 3.2%, respectively. No significant difference was observed between serum ammonia before and after treatment. No significant changes in mean arterial pressures were noted during the maneuver, representing cardiovascular tolerability. No treatment-related complications were found. The 15-day in-hospital survival was 16.7%. However, a subgroup of the patients who had moderate severity showed 100% 15-day-survival rate (2 of 2 patients). In conclusion, SPAD is salutarily effective in reducing bilirubin in patients with liver failure. The procedure is safe and simply set up.

Role of artificial liver support in hepatic encephalopathy

Hepatic encephalopathy (HE) refers to the reversible neuropsychiatric disorders observed in acute liver failure and as a complication of cirrhosis and/or portal hypertension. This review aims to describe the pathophysiology of HE, the rationale for the use of artificial liver support in the treatment of HE, the different concepts of artificial liver support and the results obtained. Ammonia has been considered central to its pathogenesis but recently an important role for its interaction with inflammatory responses and auto-regulation of cerebral hemodynamics has been suggested. Artificial liver support might be able to decrease ammonia and modulate inflammatory mediators and cerebral hemodynamics. Bioartificial liver support systems use hepatocytes in an extracorporeal device connected to the patient's circulation. Artificial liver support is intended to remove protein-bound toxins and water-soluble toxins without providing synthetic function. Both systems improve clinical and biochemical parameters and can be applied safely to patients. Clinical studies have shown that artificial liver support, especially albumin dialysis, is able to improve HE in acute and acute-on-chronic liver failure. Further studies are required to better understand the mechanism, however, artificial liver support can be added to the therapeutic bundle in treating HE.

Extracorporeal treatment of acute liver failure

Acute liver failure (ALF) is a widespread problem with typically unfavorable prognosis. With the implementation of a liver support device in the clinical setting for treatment of patients with ALF, anticipated improvements include prolonging time available for spontaneous recovery and bridging to liver transplantation. Liver support could also serve to prevent systemic manifestations of ALF such as renal failure, pulmonary edema, systemic inflammatory response syndrome and cerebral edema evolving to brain death. Both non-cell based and cell based (bio-artificial) systems have been used in clinical trials. Systems with closed or open loop organization present different advantages and disadvantages; systems also differ in the membrane pore size for filtrate/dialysate exchange. Further optimization of liver assist devices is still required; when a system has proved to be successful in treating the debilitating results of ALF, the benefits will be enormous to liver failure patients.

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.

Thermodynamic considerations in solid adsorption of bound solutes for patient support in liver failure

New detoxification modes of treatment for liver failure that use solid adsorbents to remove toxins bound to albumin in the patient bloodstream are entering clinical evaluations, frequently in head-to-head competition. While generally effective in reducing toxin concentration beyond that obtainable by conventional dialysis procedures, the solid adsorbent processes are largely the result of heuristic development. Understanding the principles and limitations inherent in competitive toxin binding, albumin versus solid adsorbent, will enhance the design process and, possibly, improve detoxification performance. An equilibrium thermodynamic analysis is presented for both the molecular adsorbent recirculating system (MARS) and fractionated plasma separation, adsorption, and dialysis system (Prometheus), two advanced systems with distinctly different operating modes but with similar equilibrium limitations. The Prometheus analysis also applies to two newer approaches: sorbent suspension reactor and microsphere-based detoxification system. Primary results from the thermodynamic analysis are that: (i) the solute-albumin binding constant is of minor importance to equilibrium once it exceeds about 10(5) L/mol; (ii) the Prometheus approach requires larger solid adsorbent columns than calculated by adsorbent solute capacity alone; and (iii) the albumin-containing recycle stream in the MARS approach is a major reservoir of removed toxin. A survey of published results indicates that MARS is operating under mass transfer control dictated by solute-albumin equilibrium in the recycle stream, and Prometheus is approaching equilibrium limits under current clinical protocols.

Selective albumin exchange: a novel and simple method to remove bilirubin

PURPOSE

Owing to its non-selectivity, plasma exchange has limited use in the treatment of patients with hepatic failure, although it is effective in removal of protein-bound toxins. This study reports a novel way to perform selective albumin exchange (SAE) by using a secondary plasma separator and aims to study its depurative capacity in the removal of bilirubin.

METHOD

In ex vivo experiments, the sieving coefficients (SCs) of plasma proteins for two secondary plasma separators, EC20W and EC30W (Asahi Medical, Tokyo, Japan), were measured. The EC20W membrane was chosen for use in clinical treatment because of its higher selectivity in separating albumin from plasma than the EC30W. The SCs of albumin, immunoglobumin G, A and M (IgG, IgA, IgM) for the EC20W were 0.3+/-0.021, 0.017+/-0.012, and 0, respectively. Five inpatients with plasma total bilirubin (TB) more than 200 micromol/L were enrolled in the present study and received a total of 10 SAE therapy sessions. Each session lasted 10 hours. SAE using the EC20W was conducted, making it similar to post-dilution continuous veno-venous hemofiltration (CVVH), with a filtrate rate of 2000 ml/h. Replacement fluid was composed by adding human albumin into conventional CVVH replacement fluid, with a final albumin concentration of 0.6%. During each treatment, the parameters of plasma and filtrate TB, direct bilirubin (DB), indirect bilirubin (IDB), and proteins were dynamically monitored. Hemostasis parameters were measured before and after sessions.

RESULTS

The reduction ratio of plasma TB, DB, and IDB after a single session was 29.1+/-3.0%, 31.3+/-4.5%, and 18.7+/-10.2%, respectively. The clearance of TB at initiation was 11.1+/-1.3 mL/min and declined to 4.4+/-0.5 ml/min at the end (p<0.01). This decline was accompanied by a reduction in albumin SC from 0.3+/-0.021 to 0.13+/-0.05. The molar ratio of bilirubin to albumin in filtrate was comparable to that in plasma. After a single treatment, plasma protein concentration including total protein, albumin, IgA and IgM remained unaffected, except for globulin and IgG, which were reduced by 11.5+/-7.8% and 11.1+/-2.3%, respectively. An improvement in hemostasis parameters, including plasma fibrinogen, prothrombase time and INR, was found after treatment. No obvious side effects were reported during any of the sessions.

CONCLUSION

Selective albumin exchange is a simple and effective method to remove bilirubin. However, further studies are required to verify its effects on clinical outcome.

Acute liver failure: Summary of a workshop

Acute liver failure (ALF) is a rare but challenging clinical syndrome with multiple causes; a specific etiology cannot be identified in 15% of adult and 50% of pediatric cases. The course of ALF is variable and the mortality rate is high. Liver transplantation is the only therapy of proven benefit, but the rapidity of progression and the variable course of ALF limit its use. Currently in the United States, spontaneous survival occurs in approximately 45%, liver transplantation in 25%, and death without transplantation in 30% of adults with ALF. Higher rates of spontaneous recovery (56%) and transplantation (31%) with lower rates of death (13%) occur in children. The outcome of ALF varies by etiology, favorable prognoses being found with acetaminophen overdose, hepatitis A, and ischemia (approximately 60% spontaneous survival), and poor prognoses with drug-induced ALF, hepatitis B, and indeterminate cases (approximately 25% spontaneous survival). Excellent intensive care is critical in management of patients with ALF. Nonspecific therapies are of unproven benefit. Future possible therapeutic approaches include N-acetylcysteine, hypothermia, liver assist devices, and hepatocyte transplantation. Advances in stem cell research may allow provision of cells for bioartificial liver support. ALF presents many challenging opportunities in both clinical and basic research.

Liver support devices

PURPOSE OF REVIEW

Liver support devices are used either as a bridge to liver transplantation or liver recovery in patients with acute or acute-on-chronic liver failure. The review analyzes the recent literature and asks if the current enthusiasm for these devices is justified.

RECENT FINDINGS

Many liver support devices exist and are discussed. Clinical data on artificial devices are rapidly emerging, especially on the molecular adsorbents recirculating system, and fractionated plasma separation and adsorption (Prometheus). While hepatic encephalopathy is improved by the molecular adsorbents recirculating system and probably Prometheus too, neither system has been shown to improve survival. Less clinical data exist for bioartificial support devices. These may use human hepatocytes, such as the extracorporeal liver assist device, although most devices use porcine hepatocytes, such as HepatAssist.

SUMMARY

Enthusiasm in liver support devices is justified as many nonrandomized studies have suggested some biochemical and clinical benefits. The results of several ongoing multicenter randomized controlled trials are anxiously awaited. Meanwhile, because mortality without liver transplantation remains high despite the use of liver support devices, these devices should only be used in the research setting or by experts proficient in their use and as a bridge to liver transplantation rather than liver recovery.

Sorbent-based artificial liver devices: principles of operation, chemical effects and clinical results

Devices for support of patients with liver failure are of two types: bioartificial livers and artificial livers. Bioartificial livers include hepatocytes in bioreactors to provide both excretory and synthetic liver functions. Artificial livers use nonliving components to remove toxins of liver failure, supply nutrients and macromolecules. Current artificial liver devices use columns or suspensions of sorbents (including adsorbents and absorbents) to selectively remove toxins and regenerate dialysate, albumin-containing dialysate, plasma filtrate or plasma. This article reviews three artificial liver devices. Liver Dialysis uses a suspension of charcoal and cation exchangers to regenerate dialysate. MARS uses charcoal and an anion exchanger to regenerate dialysate with albumin. Prometheus uses neutral and anion exchange resins to regenerate a plasma filtrate containing albumin and small globulins. We review the operating principles, chemical effects, clinical effects and complications of use of each type of artificial liver. These devices clearly improve the clinical condition of patients with acute or acute-on-chronic liver failure. Further randomized outcome studies are necessary to prove clinical outcome benefit of the artificial liver support devices, and define what types of patients appear most amenable to therapy.

Transdifferentiation in developmental biology, disease, and in therapy

Transdifferentiation (or metaplasia) refers to the conversion of one cell type to another. Because transdifferentiation normally occurs between cells that arise from the same region of the embryo, understanding the molecular and cellular events in cell type transformations may help to explain the mechanisms underlying normal development. Here we review examples of transdifferentiation in nature focusing on the possible role of cell type switching in metamorphosis and regeneration. We also examine transdifferentiation in mammals in relation to disease and the use of transdifferentiated cells in cellular therapy.

The therapeutical efficiency of the newest extracorporal elimination procedure (Prometheus® treatment) in acute liver failure caused by intoxication

Az akut májelégtelenség mortalitása az intenzív terápia ellenére májtranszplantáció nélkül 60–90%. Az átültethető szervek korlátozott száma miatt azonban a betegek jelentős része a várólistán exitál. A mortalitás csökkentése érdekében számos próbálkozás történt a májelégtelenségben felhalmozódó albuminhoz kötött és vízoldékony méreganyagok eltávolítására, elősegítve ezzel a máj spontán regenerációját, illetve a beteg életben tartását a májtranszplantációig. A Prometheus®-kezelés egy viszonylag új technika, a frakcionált plazmaszeparáció és -adszorpció (FPSA) és egy high-flux dialízis kombinációja. Az eljárás során a beteg saját, szeparált, albuminban gazdag plazmája speciális adszorbereken halad keresztül, lehetővé téve az albuminhoz kötött toxinok eliminációját, miközben a vízoldékony toxinok eltávolítása hemodialízissel történik. Célkitűzés: A szerzők szándéka az volt, hogy a Prometheus®-kezelés hatékonyságát igazolják mérgezés okozta akut májelégtelenségben. Betegek és módszer: A Prometheus®-kezelést három, konzervatív kezeléssel nem uralható akut májelégtelenségben szenvedő, súlyos, paracetamol-, káliumpermanganát- és Amanita phalloides-mérgezett beteg esetében alkalmazták. Eredmények: A három nőbetegnél 10 kezelés történt. Súlyos szövődményt nem észleltek. A kezelések során az albuminhoz kötött (indirekt bilirubin p = 0,048; epesav p = 0,001) és a vízoldékony (direkt bilirubin p = 0,002; kreatinin p = 0,007) toxinok szignifikáns csökkenését tapasztalták. Az ammónia, a karbamid, a fibrinogén és az antitrombin III szint szignifikánsan nem változott. Mindhárom beteg májtranszplantáció nélkül meggyógyult. Következtetés: A Prometheus®-kezelés hatékonyan távolítja el az akut májelégtelenségben akkumulálódó toxinokat. Biztonságos eljárás. Konzervatív terápiával nem uralható esetekben lehetővé teszi a beteg életben tartását a máj spontán regenerációjáig vagy a májtranszplantációig.

Removal of bile acids by two different extracorporeal liver support systems in acute-on-chronic liver failure

Acute-on-chronic liver failure (ACLF) is accompanied by marked intrahepatic cholestasis leading to accumulation of cytotoxic bile acids. Extracorporeal liver support systems efficiently remove bile acids, but their effect on bile acid composition in ACLF is unknown. The aim of the present study was to compare elimination of individual plasma bile acids by albumin dialysis (Molecular Adsorbents Recirculating System, MARS) and fractionated plasma separation (Prometheus). Eight consecutive patients with ACLF underwent alternating 6-hour sessions with MARS or Prometheus in a randomized, cross-over design. Serum samples were obtained before, during, and after each treatment, and individual bile acids including cholic acid and chenodeoxycholic acid (CDCA) were measured by gas chromatography. MARS and Prometheus removed total bile acids to a similar extent (reduction ratio, 45% and 46%, respectively). Both devices cleared cholic acid more efficiently than did CDCA. The molar fraction of CDCA (fCDCA) was elevated at baseline and correlated with the degree of liver dysfunction. Prometheus but not MARS treatments further increased fCDCA. Although both devices eliminate total bile acids to a similar extent, clearance of individual bile acids is different, leading to a slight change of the bile acid profile toward hydrophobic bile acids during Prometheus treatments.

Technology Insight: artificial extracorporeal liver support—how does Prometheus® compare with MARS®?

Artificial extracorporeal liver support or 'liver dialysis' has been used in patients with severe liver failure with increasing frequency since the Molecular Adsorbents Recirculating System (MARS), a variant of albumin dialysis, was introduced in 1999. Nevertheless, liver dialysis must still be thought of as experimental because its contribution to improved patient survival has not been proven in large randomized trials. Prometheus is a novel device for fractionated plasma separation via an albumin-permeable filter that was developed to improve removal of albumin-bound toxins. Initial studies have proven clinical use of Prometheus to be feasible and safe. Head-to-head comparisons of Prometheus and MARS have shown treatment with the former to be more efficient with respect to removal of most albumin-bound and water-solved markers. As controlled studies with clinical end points are lacking, it is not known whether the observed greater detoxification capacity of Prometheus will translate into clinical benefit; two small studies indicate that there might be a beneficial effect in hepatic encephalopathy and pruritus. In a recent randomized comparison of MARS and Prometheus, however, hemodynamic improvement was observed in response to MARS, but not Prometheus, treatment. A large randomized controlled trial investigating the effect of Prometheus on survival--the HELIOS study--has been initiated. First results are expected in 2008 and will be crucial to establishing a role for Prometheus in the field of extracorporeal liver support.

Acute liver failure: liver support therapies

PURPOSE OF REVIEW

We summarize the therapeutic approach to patients with acute liver failure with the main focus on bioartificial and artificial liver support. We also describe specific and general therapeutic approaches based upon recent advances in the understanding of the pathophysiology of acute liver failure.

RECENT FINDINGS

Bioartificial liver support systems use hepatocytes in an extracorporeal device connected to the patient's circulation. Artificial liver support is intended to remove protein-bound toxins and water-soluble toxins without providing synthetic function. Both systems improve clinical and biochemical parameters and can be applied safely to patients. Although bioartificial liver-assist devices have not been shown to improve the survival of patients with acute liver failure, further development is underway. Artificial liver support systems have been shown to alter several pathophysiological mechanisms involved in the development of acute liver failure but survival data are still limited.

SUMMARY

Mortality in patients with acute liver failure is still unacceptably high. The most effective treatment, liver transplantation, is a limited resource and so other therapeutic options to bridge patients to recovery or stabilization have to be considered. Better understanding of the pathophysiology of acute liver failure and device development is necessary to achieve the elusive goal of effective extracorporeal liver assist.

Effect of extracorporeal liver support by MARS and Prometheus on serum cytokines in acute-on-chronic liver failure

Introduction

Cytokines are believed to play an important role in acute-on-chronic liver failure (ACLF). Extracorporeal liver support systems may exert beneficial effects in ACLF via removal of cytokines. At present, two systems are commercially available, the Molecular Adsorbent Recirculating System (MARS™) and Fractionated Plasma Separation, Adsorption and Dialysis (Prometheus™). The aim of this study was to compare the effects of MARS and Prometheus treatments on serum cytokine levels and their clearances.

Methods

Eight patients with ACLF underwent alternating treatments with either MARS or Prometheus in a randomized cross-over design. Thirty-four treatments (17 MARS, 17 Prometheus) were available for analysis. Serum cytokines were measured before and after each treatment, and cytokine clearance was calculated from paired arterial and venous samples and effective plasma flow one hour after the start of treatment.

Results

Baseline serum levels of interleukin (IL)-6, IL-8, IL-10, tumor necrosis factor-alpha (TNF-α), and soluble TNF-α receptor 1 were significantly elevated in patients with ACLF. Measurable plasma clearances were detected for all cytokines tested, but no significant changes in serum levels of any cytokine were found after treatments with MARS or Prometheus. In MARS treatments, IL-10 was cleared from plasma more efficiently than IL-6. Clearance of IL-10 was higher in Prometheus than in MARS treatments.

Conclusion

Cytokines are cleared from plasma by both MARS and Prometheus, but neither system is able to change serum cytokine levels. This discrepancy is probably due to a high rate of cytokine production in patients with ACLF.

Effect of the molecular adsorbent recirculating system and Prometheus devices on systemic haemodynamics and vasoactive agents in patients with acute-on-chronic alcoholic liver failure

Introduction

Patients with acute-on-chronic liver failure show an aggravated hyperdynamic circulation. We evaluated, in a controlled manner, potential changes in systemic haemodynamics induced by the molecular adsorbent recirculating system (MARS) and the Prometheus system liver detoxification devices in a group of patients with acute-on-chronic liver failure.

Methods

Eighteen patients (51.2 ± 2.3 years old; Child–Pugh score, 12.5 ± 0.2; Maddrey score, 63.1 ± 5.0; hepatic venous pressure gradient, 17.6 ± 0.9 mmHg) with biopsy-proven alcoholic cirrhosis and superimposed alcoholic hepatitis were either treated with standard medical therapy (SMT) combined with MARS (n = 6) or Prometheus (n = 6) or were treated with SMT alone (n = 6) on three consecutive days (6 hours/session). Liver tests, systemic haemodynamics and vasoactive substances were determined before and after each session.

Results

Groups were comparable for baseline haemodynamics and levels of vasoactive substances. Both MARS and Prometheus decreased serum bilirubin levels (P < 0.005 versus SMT), the Prometheus device being more effective than MARS (P = 0.002). Only MARS showed significant improvement in the mean arterial pressure (Δchange, +9 ± 2.4 mmHg versus -0.3 ± 2.4 mmHg with Prometheus and -5.2 ± 2.1 mmHg with SMT, P < 0.05) and in the systemic vascular resistance index (Δchange, +131.5 ± 46.2 dyne.s/cm⁵/m² versus -92.8 ± 85.2 dyne.s/cm⁵/m²with Prometheus and -30.7 ± 32.5 dyne.s/cm⁵/m² with SMT; P < 0.05), while the cardiac index and central filling remained constant. This circulatory improvement in the MARS group was paralleled by a decrease in plasma renin activity (P < 0.05), aldosterone (P < 0.03), norepinephrine (P < 0.05), vasopressin (P = 0.005) and nitrate/nitrite levels (P < 0.02).

Conclusion

The MARS device, and not the Prometheus device, significantly attenuates the hyperdynamic circulation in acute-on-chronic liver failure, presumably by a difference in removal rate of certain vasoactive substances. These findings suggest conspicuous conceptual differences among the albumin dialysis devices.

Albumin regeneration in liver support-comparison of different methods

Albumin is the most abundant human plasma protein. Among many other functions it is an important transporter of hydrophobic internal and external substances such as intermediate and end products of metabolism and drugs. In liver failure the albumin binding capacity is decreased because of a disproportion between available albumin molecules caused by decreased hepatic synthesis and hydrophobic toxins because of decreased hepatic clearance. The resulting increase in plasma and tissue concentrations of these substances is associated with multiple organ dysfunctions frequently seen in severe liver failure. The scope of the present article is to compare different liver support strategies with regard to their ability to regenerate the patients albumin pool by removing albumin-bound toxins. Most prominent technique in this group is the molecular adsorbent recirculating system (MARS). It will be compared with single pass albumin dialysis (SPAD), fractionated plasma separation and adsorption system (FPSA, Prometheus), and plasma perfusion/bilirubin adsorption with special regard to efficacy and selectivity.

How can liver toxins be removed? Filtration and adsorption with the Prometheus system

The application of extracorporeal blood circuits in liver failure therapy has its roots in the two functions of the liver, first as a detoxifying and second as a synthetizing organ. In contrast to hydrophilic uremic toxins, most liver toxins are hydrophobic and bind preferentially to blood proteins. Consequently, the majority of these compounds cannot be removed by hemodialysis or similar dialytic procedures. Current systems use albumin as a transport vehicle for hydrophobic compounds across high flux membranes (e.g. albumin-dialysis, molecular adsorbent recirculating system (MARS)). In contrast to these devices, the Prometheus system (Fresenius Medical Care, Bad Homburg, Germany) applies filtration across highly permeable membranes with a molecular weight cut-off of >300.000. These membranes facilitate a direct filtration of most of the toxin-bearing proteins. In a secondary circuit these toxins are then removed by adsorber beads assembled in specially designed cartridges. The protein-containing toxin-free solution returns to the primary circuit. Clinical testing of the Prometheus system's safety and efficacy parameters showed that cell counts and coagulation factors were not significantly affected. Total bilirubin-, bile acid- and plasma ammonia-levels were reduced in vivo by -21%, -43% and -40%, respectively. First successful therapeutic results have been obtained for patients treated for drug abuse and for patients waiting for transplantation. Thus, a combination of plasma fractionation with highly permeable membranes followed by a secondary circuit with adsorber cartridges proves to be the most effective method of removing toxic waste in liver failure. Further investigations will follow in order to extend the application of the Prometheus system to larger cohorts of patients.

Review article: clinical experience with Prometheus

Prometheus is a new extracorporeal liver support device which facilitates the combined removal of both albumin-bound and water-soluble toxins based upon the method of fractionated plasma separation and adsorption (FPSA). The pilot trial included 11 patients with acute-on-chronic liver failure and concomitant renal failure. Prometheus therapy was found to be safe except for a reversible decrease of blood pressure. In three patients, clotting of the secondary system occurred. Prometheus treatment significantly improved blood levels of protein-bound (conjugated bilirubin, bile acids, ammonia) and water-soluble (creatinine, urea) substances. Thus, Prometheus might be a new therapeutic option in patients with severe hepatorenal syndrome. Furthermore, there is some preliminary experience with Prometheus in the treatment of refractory cholestatic pruritus and in successful bridging to liver transplantation. In order to compare extraction capacities of Prometheus and the molecular adsorbent recirculating system (MARS), five patients were crossover-treated with both systems. Prometheus resulted in significantly higher reduction ratios of bilirubin, ammonia and urea. Another study closely monitored whether the device causes an unselective removal. Neither important cytokines nor coagulation factors were found to be removed. In conclusion, Prometheus seems to be a new therapeutic option in artificial liver support. A significant improvement of the biochemical milieu was already observed after two treatments. The potential to remove protein-bound and water-soluble substances has been shown without signs of a significant unselective removal.

The management of severe alcoholic liver disease and variceal bleeding in the intensive care unit

PURPOSE OF REVIEW

To address recent advances in the understanding and management of alcohol-related chronic liver disease and its acute complications.

RECENT FINDINGS

Refinements have been made in the prognosis and treatment of alcoholic hepatitis, and new insights have been gained into the pathophysiology of the hepatorenal syndrome. Further trial evidence has emerged concerning therapy in the hepatorenal syndrome, and there has been some clarification of the benefits and risks relating to albumin dialysis/extracorporeal liver support, and consensus in the early management of variceal haemorrhage.

SUMMARY

Recent developments have led to modifications in the standard of care of patients with severe alcoholic liver disease, many of which are highly applicable to the general critical care setting. These changes apply specifically to alcoholic hepatitis, the hepatorenal syndrome and variceal bleeding, common conditions with a high mortality rate, upon which changes in practice can have a significant impact.

Prometheus versus molecular adsorbents recirculating system: comparison of efficiency in two different liver detoxification devices

Albumin dialysis by the molecular adsorbents recirculating system (MARS) and by fractionated plasma separation, adsorption, and dialysis (Prometheus[PROM]) represent novel nonbiological liver support systems specifically designed to remove albumin-bound substances. Preliminary evidence suggests a favorable impact of MARS on the course and outcome of liver failure. This study aimed at comparing the detoxification capacity of both devices. For this purpose, we performed a retrospective analysis on data prospectively collected in patients with acute-on-chronic liver failure treated with either the MARS (n = 9) or the PROM (n = 9) device on 2-5 consecutive days. Each treatment was performed for at least 5 h at identical blood and dialysate flows. Blood clearances were calculated during the first treatment session for urea nitrogen, creatinine, total bilirubin, and bile acids from paired arterial and venous line samples after 1, 4, and 6 h of treatment. Reduction ratios for all single-treatment sessions, and the overall treatment phase, were calculated from pretreatment and post-treatment values. For all markers but bile acids, the single-treatment as well as the overall treatment phase reduction ratios obtained with PROM were significantly higher compared with those obtained with MARS. PROM led at all time points to higher clearances for all evaluated solutes. Blood clearances of protein-bound substances declined over time with MARS, but not with PROM. In conclusion, a significant decline in the serum level of water-soluble and protein-bound toxins was achieved with both devices. PROM produces higher blood clearances for most toxins, which results in higher delivered treatment doses compared with a matching treatment with MARS.

Treatment of severe refractory pruritus with fractionated plasma separation and adsorption (Prometheus)

OBJECTIVE

Severe pruritus is a serious complication of cholestatic liver disease. Prometheus is a recently introduced extracorporeal liver support system with direct toxin adsorption of the patient's albumin fraction (FPSA; fractionated plasma separation and adsorption). Here we report on the effect of Prometheus therapy in patients with intractable cholestatic pruritus.

MATERIAL AND METHODS

Seven patients with different liver diseases and severe pruritus refractory to all medical treatment efforts for more than 4 weeks were treated with Prometheus (3-5 times, 18+/-3 h total). Pruritus intensity was assessed using the visual analogue scale (VAS; from 0 = no pruritus to 10 = unbearable pruritus), and VAS, serum bile acids and total bilirubin were evaluated directly before and after Prometheus treatment, as well as 4 weeks later.

RESULTS

After Prometheus therapy, VAS values had dropped significantly from 9+/-1 to 3+/-3 (p<0.001). Likewise, serum bile acids decreased (from 248+/-192 to 101+/-85 micromol/l; p<0.03). All patients, with the exception of one with no initial bile acid elevation, reported a pronounced improvement in pruritus with Prometheus therapy, although in two anicteric patients the amelioration lasted only a few days. In the other four patients a distinct benefit was still observed 4 weeks after the treatment.

CONCLUSIONS

Prometheus therapy significantly improved refractory pruritus in all patients with elevated bile acid levels, but in some patients the clinical benefit was of short duration. The clinical findings suggest that we have to better characterize those patients who might derive a long-lasting benefit from this invasive and expensive treatment.

Bilirubin Kinetic Modeling for Quantification of Extracorporeal Liver Support

BACKGROUND/AIM

To provide a measure of treatment dose for extracorporeal liver support (ELS).

METHODS

The kinetics of conjugated bilirubin were described by a two-compartment model (Vc, Vp) with central elimination (K) and constant generation rate (G). The transfer of solute between compartments was modeled by intercompartmental clearance (Kpc). The central compartment (Vc) was assumed as a constant fraction of total volume (Vc = 0.3*Vt).

RESULTS

Eight patients were studied during 35 treatments lasting 6 h each. The average K, Vt, Kpc, G, and mass of conjugated bilirubin removed were 18.6 +/- 3.9 ml/min, 9.1 +/- 3.8 liters, 103 +/- 108 ml/min, 0.33 +/- 0.15 mg/min, and 641 +/- 275 mg, respectively. The reduction ratio (48 +/- 10%) measured as the change in post- to pre-treatment concentrations underestimated the modeled fraction of bilirubin mass removed (54 +/- 13%) essentially because of significant conjugated bilirubin appearance during treatments.

CONCLUSIONS

Kinetic analysis provides an improved measure of treatment dose as generation, distribution, and elimination of conjugated bilirubin are jointly considered.

Personal view: current role of artificial liver support devices

Enthusiasm for liver support devices, particularly cell-based biological systems and albumin dialysis, increased over the last decade and there has been considerable clinical activity both within and without the construct of clinical trials. Most data have been generated on patients with acute liver failure or in patients with decompensation of chronic liver disease, often referred to as acute-on-chronic liver failure. In acute liver failure liver, liver support devices are more realistically being used as a 'bridge' to liver transplantation rather than to transplant-free survival. In acute-on-chronic liver failure the clinical objective of attaining clinical stability with treatment appears more achievable. The so-called bioartificial liver device, based on porcine hepatocytes, is the most extensively evaluated biological device. A sizeable clinical trial failed to demonstrate efficacy, but secondary analyses suggest it would be unwise to assume futility had been established with this device. Molecular adsorbent recirculating system leads the way in the non-biological category in terms of the number of patients treated, but data from large clinical trials are not yet available. One of the strongest conclusions of this review is that the amount of high-quality data available on liver support devices dramatically understates the effort and money that have been expended in their assessment. It is very clear that randomized controlled trials are mandatory to establish clinical efficacy, but it is less clear how the ideal trial should be constructed.

Prometheus System: A Technological Support in Liver Failure

The Prometheus system is a plasma filtration treatment coupling adsorption and hemodialysis (FPSA) aimed to blood purification in liver failure. After separation through an albumin-permeable membrane, plasma enters a secondary circuit where protein-bound toxic substances are removed by two adsorbers; p01, a neutral resin, and p02, an anion exchanger. Plasma is then returned to the venous line, where a high-flux hemodialyzer removes water-soluble substances. We used the Prometheus system in 12 patients with acute or acute-on-chronic liver insufficiency: eight cirrhosis, one posttransplant dysfunction, and three secondary liver insult (two cardiogenic shock and one rhabdomyolysis). All patients were severely hyperbilirubinemic, hypercholemic, and hyperammonemic. Twenty-eight sessions each lasting 340 +/- 40 minutes were performed (2.5/patient). The mean total bilirubin decreased from 33.6 +/- 20 to 22.2 +/- 13.6 mg/dL (P < .001); the reduction ratios for cholic acid and ammonia were 48.6% and 51.6%, respectively. The pre- to postsession urea reduction was 57.6% +/- 9.5% and creatinine 42.7% +/- 10%. A significant reduction was observed in the circulating levels of soluble interleukin (IL) 2 receptor (pre: 2687.2 +/- 1434.7; post: 1977.1 +/- 602 Ul/ml; P < .001) and in IL 6 (pre: 56.1 +/- 11.1; post: 35.9 +/- 10.3 pg/mL, P = .05). During treatments the hemodynamics were stable. Two patients received liver transplantations. The secondary liver insult was completely overcome in all three patients. The overall survival at 30 days was 41.6% (5/12 patients). Prometheus, based on FPSA, produced high clearance for protein-bound and water soluble markers, which resulted in high treatment efficacy.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

Review article: non-biological liver support in liver failure

Liver failure, whether acute or acute-on-chronic, remains an important cause of morbidity and mortality. The lack of liver detoxification, metabolic and regulatory functions of the liver leads to life-threatening complications, such as renal failure, altered immune response, hepatic coma and systemic haemodynamic dysfunction, eventually culminating in multiorgan failure. Current medical therapy involves the management of the precipitating event and treatment of complications until the liver eventually recovers, leaving us with no other treatment options than transplantation if these attempts fail. However, the shortage in cadaveric organs and other transplant-related problems, have prompted the need for alternative methods to provide liver support. As liver failure is often potentially reversible, considerable effort has been invested in the development of liver support systems. Currently, most of the experience is available for non-biological support systems. They represent the focus of this review, which aims to define the goals of liver support, to describe the design of the different existing devices and to analyse the available data to determine their current status in the management of patients with liver failure.