Advanced technology for extracorporeal liver support system devices

Transcription

1 The International Journal of Artificial Organs / Vol. 25 / no. 10, 2002 / pp Bioartificial Liver and Related Devices Advanced technology for extracorporeal liver support system devices M. BORRA 1, D. GALAVOTTI 1, C. BELLINI 1, L. FUMI 2, E. MORSIANI 3, G. BELLINI 1 1 RanD Biotech S.r.l., Medolla - Italy 2 Wyfold Consultancy Ltd., Goring-on-Thames - United Kingdom 3 Department of Surgery, Sant Anna University Hospital, Ferrara - Italy ABSTRACT: Acute Liver Failure (ALF) still presents high mortality rates, and liver transplant is the only treatment with proven efficacy. However transplant is not always possible and systems for Extracorporeal Liver Support (ELS) are being developed which can treat patients with ALF, for whom a transplant is not available, or is delayed. They can also treat patients with chronic liver disease who develop ALF. There are two types of ELS: artificial systems (hemoperfusion, plasmaperfusion, therapeutic plasma exchange, continuous hemodialysis and high volume continuous hemofiltration) and bioartificial systems. These are based on a biological component (animal or human hepatocytes) inserted into a bioreactor, whose main function is to perform the metabolic activity and synthesis that the liver can no longer perform. The results obtained in clinical trials have so far shown that the best results in terms of compensating for lost metabolic function and detoxification are obtained inserting artificial components in the bioartificial circuit. (Int J Artif Organs 2002; 25: ) KEY WORDS: Acute liver failure, Liver transplantation, Artificial liver, Bioartificial liver, Plasma exchange, Extracorporeal blood circulation INTRODUCTION Acute liver failure (ALF) still presents complex and multiple clinical challenges and above all, this condition has a high mortality rate, since emergency orthotopic liver transplantation (OLT) is the only treatment with proven efficacy (1). OLT is not however always possible, either because of the shortage of available organs for transplant, or because the patient is not a candidate for transplant as a result of the strict selection criteria. There exists also a significant proportion of patients whose liver can spontaneously recover adequate function; therefore there is a risk associated that a transplant would be inappropriate or at least not strictly necessary. In this scenario, considering the extreme shortage of organs available for OLT compared to the need, the development of systems for extracorporeal liver support is highly desirable. Such systems could treat patients with ALF for whom a transplant is not available. Alternatively, they could be used to prolong the waiting time for a transplant, avoiding irreversible damage during the time leading up to OLT, which even in urgent cases and where a suitable organ is available, can be in the range of hours. In particular, this applies to patients with fulminant hepatic failure (FHF), i.e. patients affected by ALF and in whom the liver was previously fully functioning. Moreover, there is also a major possibility for use in patients with chronic liver disease, in whom, because of various complications and/or intervening factors, ALF occurs. This group of patients, which is more numerous than the group with FHF, are Wichtig Editore, / $05.50/0

2 Liver support systems today not considered candidates for an urgent OLT, and could therefore benefit from treatment with a system of extracorporeal liver support, in addition to the usual intensive medical treatments. What is therefore the scope of extracorporeal liver support? First of all, the optimal outcome would be the regeneration of liver function, without the need for OLT. Further, the treatment could be a bridge to transplant, buying time before an acceptable OLT can be arranged, improving brain function, avoiding cerebral herniation, removing toxic metabolites, correcting metabolic anomalies. The principal methods for hepatic support can be subdivided into two groups: Artificial systems and hybrid or bioartificial systems (2). There have been many different types of artificial systems: hemoperfusion with absorbing filters, or plasma perfusion, preferred today, because of issues relating to biocompatibility. The first controlled clinical study at King s College in London was based on using active carbon (3), whilst today there is a tendency to use macroreticular resins. Other artificial techniques currently in use are therapeutic plasma exchange, continuous hemodialysis and high volume continuous hemofiltration (4). In spite of the many clinical reports, it should be noted that there is no proof of efficacy, defined in terms of critical outcomes including survival, for these techniques (4), even if there is certainly evidence of efficacy as measured by improvements in biochemical parameters. On the basis of our extensive experience in clinical trials in the field of artificial systems, the so-called mixed therapies have also been developed, which combine dialysis with adsorption, by using resin and/or carbon, or coupled with a circuit for the infusion of albumin (5). A schematic view of the artificial system for the treatment of ALF by means of mixed therapies is summarized in Figures 1 A, B. The therapeutic modality defined as bioartificial liver (BAL) is based on a biological component, i.e. the hepatocytes of animal or human origin, which are seeded and perfused into a bioreactor and constitute the core of the system. The bioreactor s main function is to carry out the metabolic and synthetic activities which are deeply reduced when hepatic function is impaired, and therefore to have a positive effect in countering encephalopathy and cerebral edema, overall reducing the level of circulating toxins (6, 7). Although the efficacy of BAL systems based only on hepatocytes have been reported in phase I-II clinical trials (8), the controlled results obtained in a recent randomized clinical trial indicated that the best outcome in terms of compensating for lost metabolic function and comprehensive detoxification are obtained by inserting artificial components, e.g. an adsorbent charcoal column, in the BAL circuit (9) (Fig. 2). Extracorporeal liver support system The provision of the therapies described above, whether pure artificial or bioartificial, requires an extracorporeal support system which is primarily made up of one or more electromedical devices capable of carrying out and controlling extracorporeal blood circulation, the process of dialysis and/or plasma separation, the circulation of plasma through the related devices in the various phases, in particular filters, bioreactor and oxygenator. Equipment for hepatic support of this type, in addition to monitoring the base parameters such as pressure and flow rate, must also be capable of controlling temperature and fluid balance in the extracorporeal circuit and, through the use of innovative techniques, all of the functional phases and operations relative to each specific treatment. State-of-the-art technology allows equipment to be both modular and integrated at the same time, capable of supporting the different types of components both artificial and bioartificial, used in different techniques, by reducing the obstacles that currently impede the bringing about of a decisive increase in the use of these techniques in the treatment of ALF, in particular for the provision of a bridging therapy in patients awaiting OLT. This has now been realized in the pilot clinical trials and subsequently in the development of protocols for standard clinical practice (8). The availability of an integrated modular system, capable of a high level of computerized control (Performer-BAL, RanD, S.r.L., Medolla, Italy), can definitely contribute to the development and standardization of new techniques of liver support, with the goal of making available to physicians a flexible and safe tool for routine treatment. 940

3 Borra et al Fig. 1 - Artificial systems for the treatment of hepatic insufficiency: Mixed therapies. A: Continuous dialysis and plasma perfusion; B: Adsorption on albumin circuit and dialysis. A B Pulling together the general concepts described above, the extracorporeal system of liver support must provide the possibility to be configured in different ways, in order that it can be utilized both for well established standard techniques, as well as for more innovative experimental techniques. This can only be achieved if the operational system is kept simple. Where possible, the modular nature of the system should allow a straightforward upgrading over time, as well as updating the functional and operational characteristics, including the introduction of new techniques for hepatic support based on extracorporeal circulation (Fig. 3). Therapeutic modalities in liver support Table I reports the different therapeutic modalities commonly used to provide extracorporeal liver support. These modalities are carried out by using the many available standard devices for dialysis and plasmapheresis, either adapted for the purpose or combined (Tab. I). As the therapy involves extracorporeal circuits, they all require a blood circuit, for which the equipment must provide monitoring and control of important parameters, such as flow rate and pressure in the circuit, plus safety functions such as anti-embolic and blood leakage 941

4 Liver support systems Fig. 2 - Fluid path of the Bioartificial support system, according to Demetriou et al (9). monitoring. Other vital monitoring and control will depend on the techniques being followed by the producer. Together, therefore, the ideal and complete system for the support of an extracorporeal hepatic function must have the features indicated in Table II. Blood circuit The base circuit of the system provides a vascular access in the patient, a pump, generally peristaltic, that pumps the blood to a filter for dialysis and plasma perfusion and a return line that completes the circuit returning the blood from the filter into the peripheral circulation of the patient. Attention must be paid to the choice of the positioning of the catheters utilized to take and to return blood from and to the patient, in order to avoid problems arising from too elevated pressure resistances, which might compromise the efficacy of the treatment and the safety of the patient. Blood flow TABLE I - DIFFERENT BLOOD PURIFICATION TECHNIQUES IN EXTRACORPOREAL LIVER SUPPORT SYSTEMS Standard techniques Mixed techniques - Hemoperfusion - Hemodialysis + plasma adsorption - Plasma perfusion/adsorption - Dialysis with albumin + adsorption - Plasma exchange - Plasmafiltration + recirculation - Continuous hemodialysis on a bioartificial cartridge - High volume hemofiltration is generally comprised in a range of ml/min, depending on the therapeutic mode and therefore on the filter used. It is very important to have a good quality control of the flow generated by the peristaltic pump, both in terms of precision (max. 5%) and of variation (2-5 ml/min steps), in order to maintain a good pressure stability in the filter and at the patient vascular access points. Pressure monitoring In a system of extracorporeal circulation, which is mainly controlled by peristaltic pumps, the monitoring of pressure is particularly important. This will need not only to guarantee the safety of the patient, but also allow for the physician full information in order to manage the therapy in the best way, by avoiding possible problems during the treatment. Pressure monitoring in a particularly complex liver support technique, for example a mixed therapy, can require monitoring at up to 8 defined points in the circuit. The operator must always have up to date information on the pressure throughout the system (e.g. pressure in the blood circuit, in the plasma circuit, in the dialysis circuit, etc.), with the possibility to modify ranges and operating limits, both in the pre-treatment phase and during the following treatment. If possible, the physician will be able to monitor the data in graphic form (Fig. 4). It is also important that the monitoring of pressure levels that are critical, for example the withdrawal 942

5 Borra et al Fig. 3 - Modular nature of the BAL support system used in a phase I clinical trial (8). This configuration allows a straightforward upgrading over time, as well as updating the functional and operational characteristics, including the introduction of new techniques for hepatic support based on extracorporeal circulation. pressure from the patient, or the dialysis or plasma filtration trans-membrane pressure, should be included in a control and self-adjusting loop, so that the machine will automatically adjust the values in the first instance, usually by reducing the flow rates, to correct dangerous situations, whilst at the same time alerting the physician. Dosing the anticoagulant In each of the therapies involving the circulation of blood in an extracorporeal circuit it is important to maintain control of coagulation factors relative to patient condition, to the total volume of blood and to the flow rate. As regards the system of liver support, in addition to the use of heparin as the standard anticoagulant, it is necessary to consider the use also of other types of anticoagulant, such as citrate and prostacyclin. The reasons for this use of alternative anticoagulants often relate to the hematological condition of the patient, or to the incompatibility of biological components, such as isolated cells, with heparin (6). The control system for the anticoagulant should therefore be sufficiently flexible and accurate for the dosing of small volumes, i.e. 3 to 4 ml/h in the case of heparin or higher volumes (usually 50 to 70 ml/h) in the case of citrate, by maintaining at all times a direct relationship between the parameter controlling blood circulation and those of the anticoagulant. Continuous hemodialysis / hemofiltration Amongst the standard techniques for providing extracorporeal liver support, continuous veno-venous hemodialysis (CVVHD) and continuous veno-venous hemofiltration (CVVH), including high volume hemofiltration (HVHF), are the best known and most frequently used. This is partly a result of the availability of equipment in the intensive care setting, where a patient with ALF would normally be treated. The accepted technique of CVVH or HVHF involves the removal of a fraction of plasma water (max %) 943

6 Liver support systems Fig. 4 - Pressure s graphic trend visualization on the Performer equipment. from the blood that crosses a capillary filter. This is achieved by means of a porous membrane with high permeability cut-off. The liquid ultra-filtrated across the membrane during the therapy is replaced fully or partially with an appropriate replacement solution, in order to obtain, in addition to blood purification, control of the volume of the fluid exchanged. The therapeutic goal in liver support is blood detoxification by associating the capabilities of dialytic techniques, by removing hydrophilic molecules with low molecular weight (<400 Daltons) and medium molecular weight ( Daltons), with the performance of an adsorption system through resinmediated removal of hydrophobic molecules and protein-bound molecules, without having to alternate the two treatments. Plasma separation Plasma separation by filtration, also called plasma filtration, is a procedure where separation of plasma is achieved by passing the blood in an extracorporeal circuit through a filter made up of microporous synthetic capillary membranes (nominal cut-off 0.4 to 0.5 µm). These, in relation to their specific cut-off, can be crossed by the plasma protein molecules, but not by the blood cells. The procedure of filtration of plasma across a membrane is mainly determined by two factors: the pressure across the membrane (TMP) and the shear rate. The first of these pushes the plasma through the membrane and is measured by the difference between the average pressure of the plasma compartment and the average pressure of the blood compartment. The shear rate measures the orthogonal action of the membrane wall, which acts on the blood cells and pushes them away from the membrane wall towards the axis of the capillary where the flow rate is greatest. This action depends on the blood flow rate, the number of capillaries in the filter and the radius of the capillaries. The surface area of filters used is 0.2 m 2, though this is not a clear indication of the useful surface area, as the principal limitation is the vascular 944

7 Borra et al access of the patient from which the patient s blood is drawn. The use of filters with larger surface area (0.4 to 0.5 m 2 ) is indicated only for patients with high blood viscosity, or when vascular access is available to allow flow rates ranging ml/min (artero-venous fistula, femoral vein, jugular or subclavian vein). Control of fluid balance During extracorporeal therapies providing liver support for a period up to 24 h, it is possible to note variations in volume, as well as enforced interruptions, for example in the plasma separation circuit or in the recirculation circuit for a mixed therapy. It is therefore important that the system should be capable of replenishing and maintaining the initial volume by way of providing feedback to one or more peristaltic pumps for plasma return and replacement solution with electrolytes. Some types of equipment have one or more control points for weight, (gravimetric control) therefore also volume, sensitive enough to detect changes of a few grams (usually <5 g). The bags containing the solutions to be used for dialysis, or a reservoir that collects the filtered plasma from the plasma separation procedure, can be hung on these control points. Temperature control Temperature is an indispensable function in any therapy with extracorporeal circulation of blood, where there are significant volumes exposed to thermal dispersion, and above all in fluid-exchange techniques. In the specific case of a device for liver support, the control of temperature is very important in the technique of dialysis and that of plasma exchange where there is a fluid exchange, but it becomes vital when the mixed technique is used, which includes a biological component. Here the cells must absolutely be kept within a normal range of body temperature (37 to 38 C). The ideal device would therefore need to be sufficiently efficient at providing warming in the case of replacement of large volumes, but also accurate in the control and regulation of temperature, within the safety limits. At the present time invasive temperaturemeasuring devices are not used, however the possibility to use techniques and components already in use in other medical fields, could contribute to an improvement in the way in which patients are monitored (Fig. 5). Modular components for BAL support system Bioreactor Independently of type of hepatocyte, i.e. of human, porcine or cell line origin, and BAL design, an ideal bioreactor should: i) be ready for use at the patient s bedside within a few hours; ii) have a configuration that allows an easy loading of hepatocytes, and the even distribution and immobilization of the cells inside the module; iii) accommodate at least 150 grams of cells, a cell mass that is considered sufficient to replace the liver function (6); iv) maintain hepatocyte viability and the expression of highly differentiated metabolic functions for the expected duration of the clinical treatment. Commercially available hollow-fiber bioreactors show limitations in mass transfer capacity and trans-fiber fluid convection, when axial flow geometry is applied. On the other hand, cross-flow hydraulic geometry, though able to significantly increase the overall transport of solutes across the membranes, involves cell leakage through the lateral ports, unless a coarse screen is placed on the extrafiber space outlets. The radial-flow bioreactor configuration allows full contact between tissue culture medium and hepatocytes at a physiologic perfusion flow rate, and a homogeneous distribution of solutes TABLE II - PARTICULAR FEATURES OF AN IDEAL EXTRACORPOREAL LIVER SUPPORT SYSTEM BASED ON ISOLATED HEPA- TOCYTES Blood circuit control Pressure monitoring Dosing of anti-coagulant Continuous hemodialysis / hemofiltration (option) Plasma separation (option) Control of fluid balance Bioartificial component circuit (modular) Oxygenator Temperature control 945

8 Liver support systems Fig. 5 - Temperature monitoring module and visualization on the Performer equipment. and O 2 within the module, demonstrating long-term survival of the liver cells and proving useful for extracorporeal liver support (7). A scaled-up version of the radial-flow bioreactor conceived for human plasma perfusion and accommodating a suitable cell mass, is presently under study to assess the clinical efficacy of an extracorporeal BAL system for long-term support of ALF patients (8). During liver support using the bioartificial component, the control of circulation, or rather the recirculation is fundamental. The full circuit includes an oxygenator to allow the cell metabolic activity and a device called bioreactor, in which these liver cells have been seeded and cultivated with the goal of developing a significant and viable cellular mass with a residual cellular viability 90% after the trypan blue exclusion test. With regards to the type of bioreactor, a soft reservoir included in the circuit allows for the perfusion of the cells contained in it at a physiological flow rate, normally in the range of 1 to 1.5 ml/min/g of liver cells. By taking into account that in the BAL system the cell mass could reach a mass of g, it is clear that this flow rate is significantly greater than the amount of plasma obtainable through an on-line filter in the plasma filter placed in the blood circuit (max ml/min). The high flow, controlled by a dedicated peristaltic pump, is required to establish a regime of optimal biochemical exchange between the cells and the patient s plasma. In an integrated liver support system, a particularly important function is maintaining the bioreactor circuit completely independent from the rest of the extracorporeal circuit, i.e. the blood and plasma circuits, in this way reducing to a minimum any interruption of the flow and therefore of the bioreactor oxygenation. Oxygenator In currently available systems for continuous cell culture perfusion, oxygenation of the hepatocytes is performed by an oxygenator, which, depending on the technology, could be integral to the bioreactor or positioned upstream from it. In the clinical setting, the oxygenator is fed with a mixture of gases comprising different components of air/co 2 /O 2 or air/o 2. The technology to achieve extracorporeal blood oxygenation is well known, even if its use with plasma and over the long periods of time necessary for these treatments require the use of equipment whose reliability must be studied in parallel with the study of the technique. Only two types of membrane for the oxygenator are currently commercially available: 1) the microporous and 2) the continuous, non-microporous, usually silicon-based. The continuous membranes are highly permeable to gas, but are expensive and difficult 946

9 Borra et al to produce without micro pores. In addition silicon membranes are very flexible and therefore tend to expand when the pressure is high; this in turn increases the phenomenon of volume compliance, making the priming volume requirements and the gas transfer constancy dependent on the internal pressure losses. The pressure of the ventilation gas has also a fundamental importance since it is a function of the quantity of O 2 and CO 2 required to be exchanged. On the other hand, the microporous membranes have minuscule micro pores that are formed through the chemical processes during manufacturing. These conditions can be reproduced to provide a constant density and shape to the pores of the hollow fiber and they are generally much more permeable to gas. The microporous membranes are generally made of polypropylene or polyethylene, and they have an average pore size ranging between 0,005 and 0,2 µm. A red blood cell is roughly 80 times larger than the micro pore and it cannot pass across the membrane. Immediately after the perfusion starts, the small amount of platelets and proteins coats the internal surface of the membrane, in this way the gas is passing across the membrane material after having primarily crossed a layer constituted by plasma, protein, platelets, etc. In this way, the total absence of a gas directly in contact with the blood interface results more physiological and is less traumatic for the blood cells. The main limitation on the use of conventional membranes is represented by the constancy of the performance characteristics through the period of use. In case of liver support systems, it must be underlined that, whether the oxygenator is integrated to the circuit or not, an adequate membrane performance must be guaranteed for a minimum of h. In cases in which the design of the bioreactor has been developed with an integral hollow fiber oxygenator, a period of incubation, which actually could take hours to allow cell attachment to the matrix, must be taken into account before starting treatment of patients. It is generally recognized amongst researchers in this field that the average life of microporous membranes is limited to a few hours. The prolonged contact of this membrane with blood and/or plasma determines the effect known as plasma breakthrough, which is caused by the contact hydrophylization of the membrane. In fact, the water plasma component gradually closes the membrane pores by compromising the efficiency of the gas exchange and allowing even in short periods of 6 to 8 h the leakage of plasma and proteins. This will end up in loss of device function and could generate a source of contamination, for instance in patients affected by viral hepatitis. In recent years, new membranes have appeared on the market, which combine the advantages of both the micro-porous and the continuous membranes. They are multilayer membranes, developed in sheet and, more recently in hollow fiber configuration, which combine the high permeability of polypropylene/polyethylene with the resistance to hydrophilization of continuous membranes. The working examples most often used are co- extrusions of polypropylene and polymethylpentene, and a sandwich of polyethylene / polyurethane / polyethylene. The uncertainty regarding the medium-term reliability of the performances of gas transfer in membranes normally used in artificial support systems for respiratory assistance, and the greater flexibility of a non integrated system, has led us to prefer a configuration where the cell bioreactor is not integrated with an oxygenator in a single device (7, 8). This choice not only simplifies the device design, but it also leaves the physician the opportunity to replace just the oxygenator in cases where the membrane used for the gas exchange looses its characteristics of initial permeability, which is mandatory for the preservation of cell oxygenation and therefore cell viability. In Tables III and IV, a directory of the main systems currently in use, together with a brief technical description is reported. The list includes all the positive and negative aspects that have arisen in respect of safety, economy and functionality of the systems. In fact, when considering the integration or not of an oxygenator in the bioreactor for BAL support, one should consider many aspects in order to gange the functionality, safety, economy, easy of use and versatility (Tab. V). Monitoring of CO 2 and O 2 production and consumption by the cell bioreactor during BAL support treatment is mandatory in order to check viability and function of the bioartificial system. Even if it is not possible to give a rule about O 2 requirement and consumption by the bioreactor, depending on the 947

10 Liver support systems TABLE III - LIVER SUPPORT SYSTEMS WITH AN OXYGENATOR INTEGRATED IN THE BIOREACTOR Virchow Klinik, Berlin (Dr. J. Gerlach) Research Teams ACAD. MED. CTR., Amsterdam (Dr. R. Chamuleau) Material Polypropylene Polypropylene Supplier Acordis GmbH Acordis GmbH Geometry microporous microporous hollow fibers hollow fibers (bundle) (bundle) Integration microporous spirally wound nonwowen architecture hollow fibers polyester plus hollow fiber (bundle) TABLE IV - LIVER SUPPORT SYSTEMS WITHOUT AN OXYGENATOR INTEGRATED IN THE BIOREACTOR Research Teams Circe, Vitagen, RanD, Lexington La Jolla Medolla (Dr. A. Demetriou) (Dr. M. Millis) (Dr. E. Morsiani) Material Polypropylene Polypropylene Polypropylene and Polymethylpentene Supplier Terumo Spectrum Acordis GmbH Geometry microporous microporous microporous hollow fibers hollow fibers hollow fibers (bundle) (bundle) (monolayer warp) Integration N/A N/A N/A architecture N/A: not applicable TABLE V - EXTRACORPOREAL LIVER SUPPORT SYSTEMS INCORPORATING A BIO- REACTOR WITH INTEGRATED OXY- GENATOR VERSUS SYSTEMS WITH COMBINED OXYGENATOR Integrated oxygenator Non-integrated oxygenator Functionality Safety Economy Easy of use Versatility device geometry, the extracellular attachment matrix, the perfusion flow rate, the initially seeded cell mass and the perfusion media, it is advisable to keep a po 2 >150 mm Hg in the gas mixture perfusing the bioreactor, i.e. with a FiO 2 of 21% that is equivalent to air ventilation. Otherwise, the pco 2 is easily controlled by tuning up the ventilation gas mixture in order to maintain the medium ph neutral. In our experience, the use of a gas mixture of air, CO 2 and O 2, previously prepared and checked in the experimental laboratory setting, allowed for the easy administration of gas to the bioreactor, only by regulating the flow rate. The BAL configuration allowed for the maintenance of a po 2 ranging between mmhg at the bioreactor inlet, which was effective in allowing hepatocyte respiratory functions. CO 2 levels, as detected at the bioreactor outlet, increased throughout the clinical treatment periods, while oxygen total consumption (OTC) decreased with time. In particular, 24-h continuous perfusion of the bioreactor resulted in OTC decline at the end of the treatment period (8). CONCLUSIONS In the western countries, millions of people are affected by acute or chronic organ failure but only about 10% will receive a new organ by means of an allogeneic transplantation, such as the kidney, the liver, the heart, the pancreas replacement, or by temporary artificial organ substitution. Tissue engineering might soon support conventional therapies and in the long run these technologies could replace the transplantation of organs. A recent overview of the literature in the field of tissue engineering showed that skin only ranks second on the priority list of German industry, is first on the publication list and on the patent list cartilage and bone ranks third on the industry list, is second on both publication and patents lists, and liver is only fourth on the industry list but third on both publication and patent lists (12). Taking into account that publications and patents are the crucial basis for future industry products, it is obvious that liver is not getting enough attention from R&D managers (12). Although the results of the use of extracorporeal liver support systems for the treatment of ALF are still 948

11 Borra et al preliminary, the clinical efficacy of BAL support systems in FLF patients has been established in a phase III trial conducted in the USA and Europe (9). More recently, a phase I-II clinical trial in FLF patients waiting for an OLT showed the safety and the effectiveness of a BAL support system based only on porcine hepatocytes (8), and the contribution of the RanD Company in this field has been recognized worldwide. As reported in the present paper, new modular support systems are expected to be used in the near future, in order to combine technologies incorporating liver cells in an artificial liver. In particular, the current apheresis technologies and methods of hemodialysis, hemadsorption, plasma exchange and blood purification require more attention in view of the treatment of chronic liver diseases (13). ACKNOWLEDGEMENTS The RanD-Ferrara University research project was supported by a grant from MURST, Ministero dell Università e della Ricerca Scientifica e Tecnologica, Rome. The authors wish to express their gratitude. Address for correspondence: G. Bellini, MD RanD S.r.L. Via Sparato, 60 I Medolla Modena, Italy gianni.bellini@rand-biotech.com REFERENCES 1. Bismuth H, Samuel D, Gugenheim J, et al. Emergency liver transplantation for fulminant hepatitis. Ann Intern Med 1987; 107: Dixit V, Gitnick G. Artificial liver support: State of the art. Scand J Gastroenterol 1996; 31: (suppl 220) S O Grady JG, Gimson AES, O Brien CJ, Pucknell A, Hughes RD, Williams R. Controlled trial of charcoal hemoperfusion and prognostic factors in fulminant hepatic failure. Gastroenterology 1988; 94: Lee WM, Williams R. Acute liver failure. Cambridge: Cambridge University Press, Awad SS, Swaniker F, Magee J, Punch J, Bartlett RH, Results of a phase I trial evaluating a liver support device utilizing albumin dialysis. Surgery 2001; 130: Rozga J, Morsiani E, LePage H, Moscioni AD, Giorgio T, Demetriou AA. Isolated hepatocytes in a bioartificial liver: A single group view and experience. Biotechnol Bioengin 1994; 43: Morsiani E, Brogli M, Galavotti D, et al. Long-term expression of highly differentiated functions by isolated porcine hepatocytes perfused in a radial-flow bioreactor. Artif Organs 2001; 25: Morsiani E, Pazzi P, Puviani AC, et al. Early experiences with a porcine hepatocyte-based bioartificial liver in acute hepatic failure patients. Int J Artif Organs 2002; 25: Stevens AC, Busuttil R, Han S, et al. An interim analysis of a phase II/III prospective randomized, multicenter, controlled trial of the hepatassists bioartificial liver support system for the treatment of fulminant hepatic failure. Hepatology 2001; 34: 299A. 10. Morsiani E, Galavotti D, Puviani AC, et al. Radial flow bioreactor outperforms hollow-fiber modules as a perfusing culture system for primary porcine hepatocytes. Transplant Proc 2000; 32: Falkenhagen D, Klinkmann H, Piskin E, Opatrny K. Bloodmaterial interaction. A basic guide from polymer science to clinical application. Glasgow, Krems, INFA Ed., Marx U, Bushnaq H, Yalcin E. European research and commercialization activities in the field of tissue engineering and liver support in the wide competition. Int J Artif Organs 1998; 21; Takahashi T, Malchesky PS, Nosè Y. Artificial liver. State of the art. Dig Dis Sci 1991; 9: