ESAO - Liver Support Working Group

Recent reviews in the field of liver support

Recently several interesting reviews on liver support concepts have been published.

Roger Wiliams, Institute of Hepatology, University College London Medical School, London, UK, reported on "Acute liver failure--practical management".

John O'Grady, Institute of Liver Studies, King's College Hospital, London, UK, gave an overview on the management of acute or fulminant liver failure: "Modern management of acute liver failure".

J.P. Vacanti and H.I. Pryor, 2nd, reviewed the significant clinical findings of ALF, as well as, the non-biologic liver support systems and the bioartificial liver devices that have been clinically tested to support patients with this disease: "The promise of artificial liver replacement".

A.C. DuPont provides the critical care clinician with a comprehensive review entitled "Extracorporeal treatment of intoxications" reproting on the indications for extracorporeal elimination of toxic substances, summarizing the different techniques and the intoxications for which these techniques are suitable.

H.C Fiegel reviews latest developments in "Hepatic Tissue Engineering".

Two articles on liver tissue engineering in Nature Biotechnology

Two groups describe hepatic differentiation of mouse embryonic stem (ES) cells. Gouon-Evans et al. use knowledge of developmental pathways to produce immature hepatocytes that secrete albumin and store glycogen. Soto-Gutiérrez et al. show that ES cell-derived hepatocytes encapsulated in a bioartificial liver device are effective in treating mice with acute liver failure.

In order to generate an alternative source of cells for BAL support, American and Japanese scientist around Ira Fox and Naoya Kobayashi differentiated mouse embryonic stem (ES) cells into hepatocytes by coculture with a combination of human liver nonparenchymal cell lines and fibroblast growth factor-2, human activin-A and hepatocyte growth factor. Functional hepatocytes were isolated using albumin promoter–based cell sorting. ES cell–derived hepatocytes expressed liver-specific genes, secreted albumin and metabolized ammonia, lidocaine and diazepam. Treatment of 90% hepatectomized mice with a subcutaneously implanted BAL seeded with ES cell–derived hepatocytes or primary hepatocytes improved liver function and prolonged survival, whereas treatment with a BAL seeded with control cells did not. After functioning in the BAL, ES cell–derived hepatocytes developed characteristics nearly identical to those of primary hepatocytes.
Reversal of mouse hepatic failure using an implanted liver-assist device containing ES cell–derived hepatocytes
Nature Biotechnology - 24, 1412 - 1419 (2006)

Valerie Gouon-Evans and co-workers present their findings concerning the role of BMP-4 for hepatic specification of mouse embryonic stem cell–derived definitive endoderm. When differentiated in the presence of activin A in serum-free conditions, mouse embryonic stem cells efficiently generate an endoderm progenitor population defined by the coexpression of either Brachyury, Foxa2 and c-Kit, or c-Kit and Cxcr4. Specification of these progenitors with bone morphogenetic protein-4 in combination with basic fibroblast growth factor and activin A results in the development of hepatic populations highly enriched (45–70%) for cells that express the -fetoprotein and albumin proteins. These cells also express transcripts of Afp, Alb1, Tat, Cps1, Cyp7a1 and Cyp3a11; they secrete albumin, store glycogen, show ultrastructural characteristics of mature hepatocytes, and are able to integrate into and proliferate in injured livers in vivo and mature into hepatocytes expressing dipeptidyl peptidase IV or fumarylacetoacetate hydrolase. Together, these findings establish a developmental pathway in embryonic stem cell differentiation cultures that leads to efficient generation of cells with an immature hepatocytic phenotype.
BMP-4 is required for hepatic specification of mouse embryonic stem cell–derived definitive endoderm
Nature Biotechnology - 24, 1402 - 1411 (2006)

Recent relevant papers - Update August 2006

A. Jung et al. report on Bilirubin kinetic modeling for quantification of extracorporeal liver support (Blood Purif. 2006;24(4):413-422): The kinetics of conjugated bilirubin were described by a two-compartment model (V(c), V(p)) with central elimination (K) and constant generation rate (G). The transfer of solute between compartments was modeled by intercompartmental clearance (K(pc)). The central compartment (V(c)) was assumed as a constant fraction of total volume (V(c) = 0.3*V(t)). Eight patients were studied during 35 treatments lasting 6 h each. The average K, V(t), K(pc), 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. Kinetic analysis provides an improved measure of treatment dose as generation, distribution, and elimination of conjugated bilirubin are jointly considered.

A review  MARS in the treatment of liver failure: Controversies and evidence (Int J Artif Organs. 2006 Jul;29(7):660-667)  is given by A. Chiu and S.T. Fan: Numerous studies have been published concerning the Molecular Adsorbent Recirculation System (MARS), with the majority of them describing the capability of MARS in removing albumin-bound toxins and improving systemic hemodynamics. Whether such improvement could be translated into survival benefit is still uncertain, given the paucity of randomized controlled trials available. The outcome of patients receiving MARS treatment is difficult to analyze because liver failure patients constitute a heterogeneous population and different subgroups carry different prognoses. An evidence-based recommendation on the timing of MARS initiation is not available and currently MARS is usually commenced for hyperbilirubinemia or presence of complications of liver failure. MARS is in general a safe procedure, but there are still potential complications that need to be cautioned, along with various operative issues that are worth attention. The future prospects of MARS would rely on the completion of adequately powered randomized controlled trials.

T. Naka et al. report on Acid-base balance during continuous veno-venous hemofiltration: The impact of severe hepatic failure   (Int J Artif Organs 2006; 29: 668 - 674): Continuous renal replacement therapy (CRRT) affects acid-base balance but the influence of severe hepatic failure (SHF) on this effect is unknown.  To assess the effect of SHF on acid-base balance in patients receiving CVVH. Design: Retrospective laboratory investigation. Forty patients with SHF and acute renal failure (ARF) treated with CVVH and 42 critically ill patients with severe ARF but no liver disease also treated with CVVH (controls). Intervention: Retrieval of clinical and laboratory data from prospective unit and laboratory databases. Quantitative acid-base status assessment using the Stewart-Figge methodology. Comparison of findings between the two groups. Results: Although CVVH had a major effect on acid base balance in both groups, patients with SHF had a higher mean lactate concentrations (4.8 vs. 3.1 mmol/L; p<0.0005), a greater base deficit compared to controls (-1 vs. 4.1 mEq/L; p<0.0001) and a lower PaCO 2 tension (36.8 vs. 42.5 mmHg; p<0.0001), despite the use of bicarbonate replacement fluid. The acidifying effect of hyperlactatemia was slightly worsened by an increased strong ion gap (9.3 vs. 4.9 mEq/L; p<0.0001). It was, however, attenuated by an increased strong ion difference apparent (SIDa) (43.6 vs. 41.9 mEq/L; p<0.05) secondary to hypochloremia (96 vs. 100 mmol/L; p<0.0001) and by hypoalbuminemia, although hypoalbuminemia in SHF patients (26 vs. 23; p<0.005) was less pronounced than in controls. The use of CVVH does not fully correct the independent acidifying effect of liver failure on acid-base status. Increased lactate and strong ion gap values maintain a persistent base deficit despite the alkalinizing effects of hypoalbuminemia and hypochloremia. The correction of acidosis in SHF patients may require more intensive CVVH.

New Microscope Sharpens Scientists' Focus

A new type of optical microscope was developed and tested by Howard Hughes Medical Institute's investigators. Offering resolutions of only 2 to 25 nanometers, the new microscopy technology is essentially not limited by the wavelength of the visible light:

A new light microscope so powerful that it allows scientists peering inside cells to discern the precise location of nearly each individual protein they are studying has been developed and successfully demonstrated by scientists at the Howard Hughes Medical Institute's Janelia Farm Research Campus in collaboration with researchers at the National Institutes of Health and Florida State University.

The new technique far surpasses the resolution of conventional optical microscopes, which are inherently limited by the wavelength of light. With these microscopes, objects separated by less than 200 nanometers cannot be distinguished from one another. While researchers can learn a lot by studying the arrangement of proteins inside cells at this resolution, it is insufficient to pinpoint the location of individual proteins - which are typically only one to two nanometers in diameter. The new approach, called photoactivated localization microscopy (PALM), brings scientists far closer to this goal - discriminating molecules that are only two to 25 nanometers apart.

More information via http://www.hhmi.org/news/palm20060810.html

Recent relevant papers - Update May 2006

A. Nüssler et al. summarise the present status of cell based therapies for liver diseases and to identify areas of future preclinical and clinical research (Present status and perspectives of cell-based therapies for liver diseases. J Hepatol, 2006, in press, available online 27 April 2006).
J. O'Grady gives his personal view on the current role of artificial liver support devices (Personal view: current role of artificial liver support devices. Aliment Pharmacol Ther. 2006 Jun 1;23(11):1549-1557): 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.
M.P. van de Kerkhove et al. studied subnormothermic culture conditions for porcine hepatocytes. This aspect is important when transporting cell charged bioreactors: Subnormothermic preservation maintains viability and function in a porcine hepatocyte culture model simulating bioreactor transport. Cell Transplant. 2006;15(2):161-168. In this study, the authors assessed the effect of subnormothermic preservation on freshly isolated porcine hepatocytes cultured in monolayer under oxygenation. Additionally, the effect of the University of Wisconsin (UW) preservation solution was compared with Williams' E (WE) culture medium at 4 degrees C. All groups were tested each day for cell damage and hepatic functions. Subnormothermic culture (i.e., 15 degrees C to 28 degrees C) for a period of 24 h did not reduce any hepatic function and did not increase cellular damage. In contrast, culture of hepatocytes in WE medium and preservation in UW solution at 4 degrees C significantly reduced hepatic function. In conclusion, freshly isolated porcine hepatocytes can be preserved for 24 h at subnormothermic temperatures as low as 15 degrees C.

Special issue of Therapeutic Apheresis and Dialysis: Cell-Free Artificial Liver Support

An ideal extracorporeal liver support system has to provide the main functions of the liver: detoxification, synthesis and regulation. But do we need such an ideal in all clinical situations and can we afford it? The critical issue of the clinical syndrome in liver failure is the accumulation of toxins not cleared by the failing liver. This understanding led to the development of cell-free artificial liver support systems.
This special issue of Therapeutic Apheresis and Dialysis is dedicated to cell-free artificial liver support, intended to give engineering scientists, inventors and clinical investigators an update and a better insight into the development and clinical evaluation of cell-free liver support systems. It gives an update on the status quo, both clinically and technically, of different concepts and discusses the current limitations as well as possible solutions. When compared to the cell-based systems, these devices are characterized by easier logistics, lower costs, and absence of hazards related to the cell source. These might be the reasons for being well ahead of the bioartificial concepts in terms of clinical evaluation and application.

Therapeutic Apheresis and Dialysis, April 2006 - Vol. 10 Issue 2:

S. Mitzner et al.: Albumin Regeneration in Liver Support—Comparison of Different Methods
J. Patzer: Principles of Bound Solute Dialysis
J. Vienken et al.: How Can Liver Toxins be Removed? Filtration and Adsorption With the Prometheus System
K. Rifai et al.: Review Article: Clinical Experience With Prometheus
J. Rozga et al.: A Novel Plasma Filtration Therapy for Hepatic Failure: Preclinical Studies
S.R. Ash: Sorbent Suspensions vs. Sorbent Columns for Extracorporeal Detoxification in Hepatic Failure
D. Falkenhagen: Fluidized Bed Adsorbent Systems for Extracorporeal Liver Support
L.J. Li: Artificial Liver Support System in China: A Review Over the Last 30 Years
R.A.F.M. Chamuleau: Bioartificial Liver: Its Pros and Cons
W. Bernal et al.: Cell-Free Artificial Liver Support: Design of Appropriate Clinical Studies
with a guest editorial by
I.M. Sauer and U. Baurmeister: Cell-Free Artificial Liver Support.

Recent relevant papers - Update April 2006

Prometheus versus molecular adsorbents recirculating system: comparison of efficiency in two different liver detoxification devices. (Artif Organs. 2006 Apr;30(4):276-284)
P. Evenepoel et al. compared the detoxification capacity of MARS and Prometheus. For this purpose, they 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.

A Modeling Study of Bilirubin Kinetics During Molecular Adsorbent Recirculating System Sessions (Artif Organs. 2006 Apr;30(4):285-300)
E. Magosso et al. present a quantitative description, by means of a mathematical model, of bilirubin removal during Molecular Adsorbent Recirculating System sessions. The model includes four compartments: two for the patient, and two for the albumin circuit. Equations in each compartment express mass preservation, mass exchange between compartments, and bilirubin–albumin binding kinetics. Model development and validation are based on in vivo data of bilirubin concentration acquired in eight sessions at different times during the session. The results suggest that the model may be used a priori (i.e., using a single set of parameters) to achieve a satisfactory prediction of the overall bilirubin removal, as well as a posteriori for the estimation of device parameters. The latter use may allow the investigation of the dependence of these parameters on the operative and clinical conditions, in the effort to arrive at a rationalization and optimization of the treatment.

Kazuhiko Onodera et al. are presenting a review Artificial liver support at present and in the future in Journal of Artificial Organs (J Artif Organs. 2006;9(1):17-28)

Recent relevant papers - Update March 2006

J.F. Patzer 2nd et al. discuss "Slow continuous ultrafiltration with bound solute dialysis." (ASAIO J. 2006 Jan-Feb;52(1):47-58). Bound solute dialysis (BSD), often referred to as "albumin dialysis" (practiced clinically as the molecular adsorbents recirculating system, MARS, or single-pass albumin dialysis, SPAD) or "sorbent dialysis" (practiced clinically as the charcoal-based Biologic-DT), is based upon the thermodynamic principle that the driving force for solute mass transfer across a dialysis membrane is the difference in free solute concentration across the membrane. The clinically relevant practice of slow continuous ultrafiltration (SCUF) for maintenance of patients with liver failure is analyzed in conjunction with BSD. Results from mathematical modeling of solute removal during a single pass through a dialyzer and solute removal from a one-compartment model indicate that solute removal is remarkably insensitive to the ultrafiltration/blood flow rate ratio. The results of experimental observations over a range of blood flow rates, 100 to 180 mL/min, dialysate flow rates, 600 to 2150 mL/h, ultrafiltration rates, 0 to 220 mL/h, and dialysate/blood albumin concentration ratios, beta = 0.01 to 0.04, were independently predicted remarkably well by the one-compartment model (with no adjustable parameters) based on BSD principles.
H. Vogelsinger et al. describe the "Pharmacokinetics of liposomal amphotericin B during extracorporeal albumin dialysis." (Artif Organs. 2006 Feb;30(2):118-121) Extracorporeal blood purification techniques such as hemofiltration or albumin dialysis can exert a significant, but not easily predictable influence on plasma pharmacokinetics of antimicrobial agents. The effect of albumin dialysis on the pharmacokinetics of liposomal amphotericin B (AMB) and other lipid-formulated drugs has not been investigated so far. Therefore, plasma concentrations of liberated and liposomal AMB were measured in a patient, who obtained liposomal AMB for suspected invasive mycosis and required albumin dialysis because of cholestatic liver failure caused by graft versus host disease after bone marrow transplantation. Liberated and liposomal AMB were separated by solid phase extraction and measured by high performance liquid chromatography. No excessive AMB elimination took place during albumin dialysis. Plasma levels of liposomal AMB exceeded those of liberated AMB. Pharmacokinetic data were comparable to those obtained previously in patients on hemofiltration and in critically ill patients without extracorporeal blood purification.
K.Rifai et al. address a similar topic: "Removal selectivity of Prometheus: A new extracorporeal liver support device." (World J Gastroenterol. 2006 Feb 14;12(6):940-944)The authors evaluated whether treatment with the Prometheus reg system significantly affects cytokines, coagulation factors and other plasma proteins.They studied nine patients with acute-on-chronic liver failure and accompanying renal failure and observed a significant decrease of both protein-bound (e.g. bile acids) and water-soluble (e.g. ammonia) substances after Prometheus reg therapy. Despite significant removal of protein-bound and water-soluble substances, Prometheus reg therapy did not affect the level of cytokines, coagulation factors or other plasma proteins. Thus, the filters and adsorbers used in the system are highly effective and specific for water-soluble substances and toxins bound to the albumin fraction.
The article The management of severe alcoholic liver disease and variceal bleeding in the intensive care unit. by P.A. Berry and J.A. Wendon (Curr Opin Crit Care. 2006 Apr;12(2):171-177) addresses recent advances in the understanding and management of alcohol-related chronic liver disease and its acute complications. 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.
Z. Chen et al. evaluated the functions of a new bioartificial liver (BAL) system in vitro ("Functional evaluation of a new bioartificial liver system in vitro and in vitro" (World J Gastroenterol. 2006 Feb 28;12(8):1312-1316)
P.S. Pahlavan et al. review recent findings concerning the capacity to regenerate after injury or resection ("Prometheus' Challenge: Molecular, Cellular and Systemic Aspects of Liver Regeneration" - J Surg Res. 2006, Epub ahead of print). A variety of genes, cytokines, growth factors, and cells are involved in liver regeneration. The exact mechanism of regeneration and the interaction between cells and cytokines are not fully understood. There seems to exist a sequence of stages that result in liver regeneration, while at the same time inhibitors control the size of the regenerated liver. It has been proven that hepatocyte growth factor, transforming growth factor, epidermal growth factor, tumor necrosis factor-alpha, interleukins -1 and -6 are the main growth and promoter factors secreted after hepatic injury, partial hepatectomy and after a sequence of different and complex reactions to activate transcription factors, mainly nuclear factor kappaB and signal transduction and activator of transcription-3, affects specific genes to promote liver regeneration. Unraveling the complex processes of liver regeneration may provide novel strategies in the management of patients with end-stage liver disease. In particular, inducing liver regeneration should reduce morbidity for the donor and increase faster recovery for the liver transplantation recipient.

Recent relevant papers - Update January 2006

Two articles deal with the effect of albumin dialysis on the intracranial pressure: Sen et al. report on the Effect of albumin dialysis on intracranial pressure increase in pigs with acute liver failure: a randomized study (Crit Care Med. 2006 Jan;34(1):158-164) and S. Mitzner gives a comment in the same issue (Drain the brain: albumin dialysis for intracranial hypertension (Crit Care Med. 2006 Jan;34(1):254-255). Increased intracranial pressure (ICP) worsens the outcome of acute liver failure (ALF). This study investigates the underlying pathophysiological mechanisms and evaluates the therapeutic effect of albumin dialysis in ALF with use of the Molecular Adsorbents Recirculating System without hemofiltration/dialysis (modified, M-MARS). Pigs were randomized into three groups: sham, ALF, and ALF + M-MARS. ICP and arterial ammonia increased significantly over 6 hrs in the ALF group, in comparison with the sham group. M-MARS attenuated (did not normalize) the increased ICP in the ALF group, whereas arterial ammonia was unaltered by M-MARS. Brain water in the frontal cortex (grey matter) and in the subcortical white matter at 6 hrs was significantly higher in the ALF group than in the sham group. M-MARS prevented a rise in water content, but only in white matter. CBF and inflammatory mediators remained unchanged in all groups. The auhors concluded that the initial development of cerebral edema and increased ICP occurs independently of CBF changes in this noninflammatory model of ALF. Factor(s) other than or in addition to hyperammonemia are important, however, and may be more amenable to alteration by albumin dialysis.

Shibata et al. report on Liver repopulation and long-term function of rat small hepatocyte transplantation as an alternative cell source for hepatocyte transplantation (Liver Transpl. 2006 Jan;12(1):78-87). Hepatocyte transplantation (HT) is an attractive therapeutic modality for liver disease as an alternative for liver organ transplantation. Primary fresh hepatocytes (FHs) are the exclusive cell source that has been used for clinical HT. However, the use of FHs is limited due to a shortage of donor cells. Small hepatocytes (SHs) are hepatic progenitor cells and can be isolated not only from rodents but also from humans. SHs can proliferate in vitro and express liver functions, although conventional hepatocytes lose them within a short period after culture. The authors investigated HT using SHs to evaluate cell engraftment and function compared to HT using FHs. The donor cell number in the SH group was smaller than that in the FH group at HT. The cell engraftment in the SH group was smaller in the liver and larger in the spleen than in the FH group. The cell engraftment in the liver increased after HT; however, that in the spleen decreased after HT in both groups. HT using SHs supported the serum albumin level in the NAR experiment as well as that using FH, and albumin mRNA was detectable in the recipients' tissues at 12 weeks after HT. In conclusion, HT using SHs showed hepatic repopulation similar to that using FHs. This suggests that both SHs and FHs can repopulate the liver as if they were hepatic stem cells. In addition, HT using SHs supported liver functions such as albumin correction at the same level as that using FHs. These observations strongly support the idea that SHs could be an alternative to primary FHs as a novel cell source for future HT.

Two review articles concerning artificial liver support concepts were published: Laleman et al.: Review article: non-biological liver support in liver failure (Aliment Pharmacol Ther. 2006 Feb;23(3):351-363) and Pless et al.: Bioartificial liver: current status (Transplant Proc. 2005 Nov;37(9):3893-2895)

HubMed: PubMed rewired

HubMed is found at http://www.hubmed.org and serves an alternative interface to the PubMed medical literature database. Any search strategies you use in PubMed may be used in HubMed and once you have the core skills for efficient searching of PubMed, HubMed offers many options that are not found in the original PubMed:

• Daily updates of search results via web feeds.
• Export citations in RIS, BibTeX, RDF and MODS formats, or directly to RefWorks.
• Unzip HubMed's import filter into Endnote's Filters folder for direct import into Endnote, or install the RIS Export plugin for direct import into ProCite, RefMan and older versions of Endnote.
• Use the Citation Finder to convert reference lists from PDFs into search results.
• Create lists of closely related papers using Rank Relations, then visualise and browse clusters of related papers using TouchGraph (requires Java).
• Graph occurrences of keywords in published papers over time.
• Tag and store annotated metadata for articles of interest.