- Email: [email protected]
Artificial Liver
Accepted Manuscript Artificial Liver Norman L. Sussman , MD James H. Kelly , PhD
PII: DOI: Reference:
S1542-3565(14)00820-9 10.1016/j.cgh.2014.06.002 YJCGH 53845
To appear in: Clinical Gastroenterology and Hepatology Accepted Date: 4 June 2014 Please cite this article as: Sussman NL, Kelly JH, Artificial Liver, Clinical Gastroenterology and Hepatology (2014), doi: 10.1016/j.cgh.2014.06.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. All studies published in Clinical Gastroenterology and Hepatology are embargoed until 3PM ET of the day they are published as corrected proofs on-line. Studies cannot be publicized as accepted manuscripts or uncorrected proofs.
ACCEPTED MANUSCRIPT
"Advances in Translational Science" Artificial Liver Authors: Norman L. Sussman, MD, Department of Surgery, Baylor College of Medicine, Houston, Texas. James H. Kelly, PhD, Cell Machines, Inc. Houston, TX
Conflict of interest:
• •
Norman Sussman and James Kelly were the founders of Hepatix Inc. (Houston, TX). Hepatix was subsequently acquired by Vitagen, and then by Vital Therapies. Neither Dr. Sussman nor Dr. Kelly has any ownership interest in either Vitagen or Vital Therapies. Norman Sussman is a board member for HepaHope, Inc. (Irvine, CA). James Kelly is the CEO of Cell Machines, a stem cell company based in Houston, TX.
RI PT
•
Abstract
SC
Artificial liver is generally classified as either inert or cell-based – only the latter is a true artificial liver. Despite some major achievements and investment, no device is currently available; devices have either not been tested rigorously, or have failed to meet expectations in clinical trials. A successful device will provide the appropriate level of liver function, but it must also be applied in the appropriate clinical setting. An extracorporeal device may be capable of supporting a failing liver, but it will not correct portal hypertension. The future of this field depends on both the technical aspects of the device(s) and their application to the appropriate clinical situation.
Technological primer
M AN U
Certain artificial organs have become commonplace in medical practice – hemodialysis is available in almost every mid-sized hospital, ventricular assist devices are implanted in over 200 centers in the United States and Europe (http://www.mylvad.com/living-lvad/hospital-supportcenter, accessed 6 April 2014), and extracorporeal membrane oxygenation for pulmonary support is increasingly within the reach of advanced community hospitals. An obvious deficiency in this lineup is liver support.
AC C
EP
TE D
Liver support has traditionally been closely associated with the management of acute liver failure (ALF). The initial description of ALF (then named fulminant hepatic failure) was followed by reports of its metabolic nature and the need for metabolic approaches to its management1,2. Despite these views, the field was subverted by the success of hemodialysis – clearance of toxins (ammonia in the case of liver failure), was thought to be the key to successful therapy. This proved disappointing – increasingly sophisticated devices and sorbents (materials that remove solutes by non-specific binding, e.g. charcoal) were used, culminating with two recent unsuccessful trials3,4. At the same time, liver transplantation has proven the benefit of swapping a failing liver for a viable one, and external liver perfusion proved the concept of extracorporeal liver support5. The issue remains whether we can produce a device that combines the convenience of hemodialysis with the effectiveness of liver transplantation6.
ACCEPTED MANUSCRIPT
Successful artificial organs mimic the function of the organ they are supporting – filtration in the case of the kidney, a pump in the case of the heart, and membrane oxygenation in the case of the lung. By this reasoning, an artificial liver has to replace the biological repertoire of the liver. The full range of this requirement is still incompletely understood, but it seems clear that liver cells of some type are the logical choice. Candidates include whole liver, liver slices, isolated primary hepatocytes, immortalized liver cells, and stem cells. Sorbent-based devices do not provide biologic support, and, not surprisingly, have not proven effective3,4.
RI PT
Whole liver: Extracorporeal human liver perfusion was used in three patients awaiting liver transplantation at the University of Nebraska – two of them improved neurologically, and were subsequently transplanted5. While this experience is important as a proof-of-principle, the shortage of human livers for transplantation makes their use for liver assist impractical. Animal livers are more plentiful, but suffer from problems of cross-species hyperacute rejection. An immunologically compatible pig that expressed human CD55 and CD59 proved effective in supporting two patients with ALF7. These animals are no longer commercially available. Liver slices: HepaHope, Inc. has pioneered the use of liver slices in a bioartificial liver. Several abstracts have been published, but no papers are available. The company has received FDA permission to proceed with clinical trials.
M AN U
SC
Isolated primary hepatocytes: Primary hepatocytes are cells that are isolated from whole liver. The technique for isolating these cells is well established although cumbersome. Purified hepatocytes have low immunogenicity, so hyperacute rejection does not occur, even with livers from widely divergent species. The problem with primary hepatocytes is their behavior in vitro. Although hepatocytes have nearly unlimited capacity to divide in vivo, they begin to dedifferentiate as soon as they are removed from their surrounding tissue support, and they do not divide in culture. This means that any device that depends on primary hepatocytes requires ongoing preparation from whole liver with attendant complexity of manufacturing, variability among source animals, and risks of contamination of the devices. Some problems related to availability have been addressed. For example, isolated porcine hepatocytes may be attached to collagen-coated dextran beads and cryopreserved for later use8. Although preliminary studies were promising, this device did not improve 30-day survival in a randomized clinical trial9, and was not approved by FDA.
AC C
EP
TE D
Cultured hepatocytes: Hepatocyte cell lines have the advantage of unlimited growth. One of the problems with this approach is that cells in continuous culture are eventually overgrown by rapidly dividing, but poorly differentiated variants, a condition known as genetic drift. For example, HepG2 is a very heterogeneous cell line, originally derived from a hepatoblastoma, and in continuous culture for decades. C3A, a subclone of HepG2, was selected by a number of biochemical criteria6,10, and its ability to perform as the metabolic core of an artificial liver was demonstrated in a model of lethal liver injury in dogs11,12. Elegant studies later questioned the ability of C3A cells to metabolize ammonia because of absence of ornithine transcarbamylase and arginase I13 . These studies were done in routine culture, so information on performance under clinical conditions is unknown. In addition, these studies are at odds with the animal data discussed above. The C3A-based liver assist device has been tested in a number of patients, but a definitive trial has not been published to date14,15.
ACCEPTED MANUSCRIPT
An interesting variation on the cell microenvironment is recent work on the Reuber H35 rat hepatoma line by creating suspended cell spheroids16. Primary porcine hepatocytes in the spheroid conformation appear to perform well in a porcine model of acute liver failure (Scott Nyberg, personal communication, abstract accepted, 2014 World Transplantation Congress, American Journal of Transplantation). Stem cells: Stem cells are the ideal solution for liver failure, either by repopulating the damaged liver, or by providing extracorporeal support. Approaches have included cultures of fetal and neonatal progenitors and directed differentiation of embryonic stem cells or pluripotent stem cells. Results have been disappointing so far, but two recent papers report a stem cell culture system that allows long-term expansion of cells into organoids17,18.
Findings
RI PT
An in depth reviews of artificial and bioartificial liver has been published recently, and covers the subject in detail19 – we will confine our comments to clinical trials using bioartificial livers.
SC
Only one randomized trial of artificial liver has been published, testing the HepatAssist device made by Circe Biomedical (no longer in existence). In this trial, 85 patients (86 controls) with acute liver failure or primary liver graft non-function were treat with a bioartificial liver (BAL) containing approximately 7 billion cryopreserved primary pig hepatocytes9. The study failed to meet its primary objective, improved 30-day survival, and therefore did not gain FDA approval. Several flaws in the study design were subsequently identified, but the company was never able to complete a second trial.
M AN U
The other major bioartificial liver, the Extracorporeal Liver Assist Device (ELAD) was developed at Baylor College of Medicine, and contained the C3A cell line described above10,12. Any disadvantages of a tumor cell line were offset by the advantages of an unlimited supply of cultured human liver cells and the ability to treat patients indefinitely with a simple venous access catheter. The original design included perfusion with whole blood to assure adequate oxygenation. The design was changed to plasma infusion in later models, necessitating four cartridges and in-line oxygenation. The original Hepatix device supported dogs with lethal acetaminophen-induced liver failure until survival11,20, and suggested effectiveness in 23 patients with acute liver failure14,15. The modified device was tested in five patients in a pilot trial21, and in subsequent trials in China and the USA – these latter results have not been published to date.
Importance
AC C
EP
TE D
The benefit of artificial liver in acute liver failure (ALF) is undisputed – ALF is a potentially reversible disease caused by a critical loss of hepatocyte mass22. Although ALF remains an important clinical entity, its frequency is declining, and recovery is improving23. Chronic liver failure (CLF) is far more common, but the role of artificial liver is much less obvious. The clinical picture of CLF is usually dominated by the complications of portal hypertension, a problem not addressed by extracorporeal liver support. In addition, the underlying cirrhosis is not reversible – recovery from a decompensation episode leaves the patient in the same frail state, still in need of liver transplantation.
ACCEPTED Roadblocks/Limitations
MANUSCRIPT
Extracorporeal liver support has the potential to save lives in patients with ALF, but we cannot assume the same for patients with CLF. Since ALF is now relatively rare, and CLF is increasingly common, this may be the time to consider the next generation of artificial liver. Liver cells grow well in three dimensional structures like small cubes of loofa sponge24, but scaling up to the size of a liver creates a large central area that cannot be fed by diffusion alone. Printing a three dimensional (3-D) liver scaffold sounds appealing, but will have to include blood inflow and outflow conduits, and a drainage system for bile excretion. These obstacles aside, The New Organ Alliance (http://www.neworgan.org) has offered a prize of $1,000,000 for “the first team that creates a bioengineered replacement for the native liver of a large mammal, enabling it to recover in the absence of native function and survive three months with a normal lifestyle.“
RI PT
A more biologic approach may be an animal liver stripped of cells and repopulated with human liver cells. Two recent papers discuss reprogramming of human fibroblasts in mouse liver as a first step towards achieving a working human liver25,26.
Conclusions
M AN U
SC
Artificial liver requires a cellular component to mimic the function of the liver. Patients with ALF are extremely ill, but have the capacity to recover by liver regeneration. These patients may benefit from extracorporeal liver support. Patients with CLF are more challenging because an extracorporeal device does not improve portal hypertension, frequently the dominant component of their disease. We see a need for extracorporeal liver support, but the need has decreased with a declining number of acute liver failure cases. The real need is the growing number of patients with cirrhosis who, at best, will get partial benefit from extracorporeal liver support. An implantable artificial liver seems like science fiction at present, but initial results suggest that such an undertaking is feasible, and worth at least a million dollars.
References
AC C
EP
TE D
1. Trey C, Burns DG, Saunders SJ. Treatment of hepatic coma by exchange blood transfusion. The New England journal of medicine 1966;274:473-81. 2. Eiseman B, Liem DS, Raffucci F. Heterologous liver perfusion in treatment of hepatic failure. Annals of surgery 1965;162:329-45. 3. Saliba F, Camus C, Durand F, et al. Albumin dialysis with a noncell artificial liver support device in patients with acute liver failure: a randomized, controlled trial. Annals of internal medicine 2013;159:522-31. 4. Banares R, Nevens F, Larsen FS, et al. Extracorporeal albumin dialysis with the molecular adsorbent recirculating system in acute-on-chronic liver failure: the RELIEF trial. Hepatology 2013;57:1153-62. 5. Fox IJ, Langnas AN, Fristoe LW, et al. Successful application of extracorporeal liver perfusion: a technology whose time has come. The American journal of gastroenterology 1993;88:1876-81. 6. Sussman NL, McGuire BM, Kelly JH. Hepatic assist devices: will they ever be successful? Current gastroenterology reports 2009;11:64-8. 7. Levy MF, Crippin J, Sutton S, et al. Liver allotransplantation after extracorporeal hepatic support with transgenic (hCD55/hCD59) porcine livers: clinical results and lack of
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
pig-to-human transmission of the porcine endogenous retrovirus. Transplantation 2000;69:272-80. 8. Rozga J. Liver support technology--an update. Xenotransplantation 2006;13:380-9. 9. Demetriou AA, Brown RS, Jr., Busuttil RW, et al. Prospective, randomized, multicenter, controlled trial of a bioartificial liver in treating acute liver failure. Annals of surgery 2004;239:660-7; discussion 7-70. 10. Kelly JH, Darlington GJ. Modulation of the liver specific phenotype in the human hepatoblastoma line Hep G2. In vitro cellular & developmental biology : journal of the Tissue Culture Association 1989;25:217-22. 11. Kelly JH, Koussayer T, He DE, et al. An improved model of acetaminophen-induced fulminant hepatic failure in dogs. Hepatology 1992;15:329-35. 12. Sussman NL, Chong MG, Koussayer T, et al. Reversal of fulminant hepatic failure using an extracorporeal liver assist device. Hepatology 1992;16:60-5. 13. Mavri-Damelin D, Damelin LH, Eaton S, Rees M, Selden C, Hodgson HJ. Cells for bioartificial liver devices: the human hepatoma-derived cell line C3A produces urea but does not detoxify ammonia. Biotechnology and bioengineering 2008;99:644-51. 14. Ellis AJ, Hughes RD, Wendon JA, et al. Pilot-controlled trial of the extracorporeal liver assist device in acute liver failure. Hepatology 1996;24:1446-51. 15. Sussman NL, Gislason GT, Conlin CA, Kelly JH. The Hepatix extracorporeal liver assist device: initial clinical experience. Artificial organs 1994;18:390-6. 16. Weeks CA, Newman K, Turner PA, et al. Suspension culture of hepatocyte-derived reporter cells in presence of albumin to form stable three-dimensional spheroids. Biotechnology and bioengineering 2013;110:2548-55. 17. Huch M, Boj SF, Clevers H. Lgr5(+) liver stem cells, hepatic organoids and regenerative medicine. Regenerative medicine 2013;8:385-7. 18. Huch M, Dorrell C, Boj SF, et al. In vitro expansion of single Lgr5+ liver stem cells induced by Wnt-driven regeneration. Nature 2013;494:247-50. 19. Nyberg SL. Bridging the gap: advances in artificial liver support. Liver transplantation : official publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society 2012;18 Suppl 2:S10-4. 20. Kelly JH, Koussayer T, He D, et al. Assessment of an extracorporeal liver assist device in anhepatic dogs. Artificial organs 1992;16:418-22. 21. Millis JM, Cronin DC, Johnson R, et al. Initial experience with the modified extracorporeal liver-assist device for patients with fulminant hepatic failure: system modifications and clinical impact. Transplantation 2002;74:1735-46. 22. Remien CH, Adler FR, Waddoups L, Box TD, Sussman NL. Mathematical modeling of liver injury and dysfunction after acetaminophen overdose: early discrimination between survival and death. Hepatology 2012;56:727-34. 23. Lee WM, Squires RH, Jr., Nyberg SL, Doo E, Hoofnagle JH. Acute liver failure: Summary of a workshop. Hepatology 2008;47:1401-15. 24. Chen JP, Yu SC, Hsu BR, Fu SH, Liu HS. Loofa sponge as a scaffold for the culture of human hepatocyte cell line. Biotechnology progress 2003;19:522-7. 25. Huang P, Zhang L, Gao Y, et al. Direct reprogramming of human fibroblasts to functional and expandable hepatocytes. Cell stem cell 2014;14:370-84. 26. Zhu S, Rezvani M, Harbell J, et al. Mouse liver repopulation with hepatocytes generated from human fibroblasts. Nature 2014;508:93-7.
PII: DOI: Reference:
S1542-3565(14)00820-9 10.1016/j.cgh.2014.06.002 YJCGH 53845
To appear in: Clinical Gastroenterology and Hepatology Accepted Date: 4 June 2014 Please cite this article as: Sussman NL, Kelly JH, Artificial Liver, Clinical Gastroenterology and Hepatology (2014), doi: 10.1016/j.cgh.2014.06.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. All studies published in Clinical Gastroenterology and Hepatology are embargoed until 3PM ET of the day they are published as corrected proofs on-line. Studies cannot be publicized as accepted manuscripts or uncorrected proofs.
ACCEPTED MANUSCRIPT
"Advances in Translational Science" Artificial Liver Authors: Norman L. Sussman, MD, Department of Surgery, Baylor College of Medicine, Houston, Texas. James H. Kelly, PhD, Cell Machines, Inc. Houston, TX
Conflict of interest:
• •
Norman Sussman and James Kelly were the founders of Hepatix Inc. (Houston, TX). Hepatix was subsequently acquired by Vitagen, and then by Vital Therapies. Neither Dr. Sussman nor Dr. Kelly has any ownership interest in either Vitagen or Vital Therapies. Norman Sussman is a board member for HepaHope, Inc. (Irvine, CA). James Kelly is the CEO of Cell Machines, a stem cell company based in Houston, TX.
RI PT
•
Abstract
SC
Artificial liver is generally classified as either inert or cell-based – only the latter is a true artificial liver. Despite some major achievements and investment, no device is currently available; devices have either not been tested rigorously, or have failed to meet expectations in clinical trials. A successful device will provide the appropriate level of liver function, but it must also be applied in the appropriate clinical setting. An extracorporeal device may be capable of supporting a failing liver, but it will not correct portal hypertension. The future of this field depends on both the technical aspects of the device(s) and their application to the appropriate clinical situation.
Technological primer
M AN U
Certain artificial organs have become commonplace in medical practice – hemodialysis is available in almost every mid-sized hospital, ventricular assist devices are implanted in over 200 centers in the United States and Europe (http://www.mylvad.com/living-lvad/hospital-supportcenter, accessed 6 April 2014), and extracorporeal membrane oxygenation for pulmonary support is increasingly within the reach of advanced community hospitals. An obvious deficiency in this lineup is liver support.
AC C
EP
TE D
Liver support has traditionally been closely associated with the management of acute liver failure (ALF). The initial description of ALF (then named fulminant hepatic failure) was followed by reports of its metabolic nature and the need for metabolic approaches to its management1,2. Despite these views, the field was subverted by the success of hemodialysis – clearance of toxins (ammonia in the case of liver failure), was thought to be the key to successful therapy. This proved disappointing – increasingly sophisticated devices and sorbents (materials that remove solutes by non-specific binding, e.g. charcoal) were used, culminating with two recent unsuccessful trials3,4. At the same time, liver transplantation has proven the benefit of swapping a failing liver for a viable one, and external liver perfusion proved the concept of extracorporeal liver support5. The issue remains whether we can produce a device that combines the convenience of hemodialysis with the effectiveness of liver transplantation6.
ACCEPTED MANUSCRIPT
Successful artificial organs mimic the function of the organ they are supporting – filtration in the case of the kidney, a pump in the case of the heart, and membrane oxygenation in the case of the lung. By this reasoning, an artificial liver has to replace the biological repertoire of the liver. The full range of this requirement is still incompletely understood, but it seems clear that liver cells of some type are the logical choice. Candidates include whole liver, liver slices, isolated primary hepatocytes, immortalized liver cells, and stem cells. Sorbent-based devices do not provide biologic support, and, not surprisingly, have not proven effective3,4.
RI PT
Whole liver: Extracorporeal human liver perfusion was used in three patients awaiting liver transplantation at the University of Nebraska – two of them improved neurologically, and were subsequently transplanted5. While this experience is important as a proof-of-principle, the shortage of human livers for transplantation makes their use for liver assist impractical. Animal livers are more plentiful, but suffer from problems of cross-species hyperacute rejection. An immunologically compatible pig that expressed human CD55 and CD59 proved effective in supporting two patients with ALF7. These animals are no longer commercially available. Liver slices: HepaHope, Inc. has pioneered the use of liver slices in a bioartificial liver. Several abstracts have been published, but no papers are available. The company has received FDA permission to proceed with clinical trials.
M AN U
SC
Isolated primary hepatocytes: Primary hepatocytes are cells that are isolated from whole liver. The technique for isolating these cells is well established although cumbersome. Purified hepatocytes have low immunogenicity, so hyperacute rejection does not occur, even with livers from widely divergent species. The problem with primary hepatocytes is their behavior in vitro. Although hepatocytes have nearly unlimited capacity to divide in vivo, they begin to dedifferentiate as soon as they are removed from their surrounding tissue support, and they do not divide in culture. This means that any device that depends on primary hepatocytes requires ongoing preparation from whole liver with attendant complexity of manufacturing, variability among source animals, and risks of contamination of the devices. Some problems related to availability have been addressed. For example, isolated porcine hepatocytes may be attached to collagen-coated dextran beads and cryopreserved for later use8. Although preliminary studies were promising, this device did not improve 30-day survival in a randomized clinical trial9, and was not approved by FDA.
AC C
EP
TE D
Cultured hepatocytes: Hepatocyte cell lines have the advantage of unlimited growth. One of the problems with this approach is that cells in continuous culture are eventually overgrown by rapidly dividing, but poorly differentiated variants, a condition known as genetic drift. For example, HepG2 is a very heterogeneous cell line, originally derived from a hepatoblastoma, and in continuous culture for decades. C3A, a subclone of HepG2, was selected by a number of biochemical criteria6,10, and its ability to perform as the metabolic core of an artificial liver was demonstrated in a model of lethal liver injury in dogs11,12. Elegant studies later questioned the ability of C3A cells to metabolize ammonia because of absence of ornithine transcarbamylase and arginase I13 . These studies were done in routine culture, so information on performance under clinical conditions is unknown. In addition, these studies are at odds with the animal data discussed above. The C3A-based liver assist device has been tested in a number of patients, but a definitive trial has not been published to date14,15.
ACCEPTED MANUSCRIPT
An interesting variation on the cell microenvironment is recent work on the Reuber H35 rat hepatoma line by creating suspended cell spheroids16. Primary porcine hepatocytes in the spheroid conformation appear to perform well in a porcine model of acute liver failure (Scott Nyberg, personal communication, abstract accepted, 2014 World Transplantation Congress, American Journal of Transplantation). Stem cells: Stem cells are the ideal solution for liver failure, either by repopulating the damaged liver, or by providing extracorporeal support. Approaches have included cultures of fetal and neonatal progenitors and directed differentiation of embryonic stem cells or pluripotent stem cells. Results have been disappointing so far, but two recent papers report a stem cell culture system that allows long-term expansion of cells into organoids17,18.
Findings
RI PT
An in depth reviews of artificial and bioartificial liver has been published recently, and covers the subject in detail19 – we will confine our comments to clinical trials using bioartificial livers.
SC
Only one randomized trial of artificial liver has been published, testing the HepatAssist device made by Circe Biomedical (no longer in existence). In this trial, 85 patients (86 controls) with acute liver failure or primary liver graft non-function were treat with a bioartificial liver (BAL) containing approximately 7 billion cryopreserved primary pig hepatocytes9. The study failed to meet its primary objective, improved 30-day survival, and therefore did not gain FDA approval. Several flaws in the study design were subsequently identified, but the company was never able to complete a second trial.
M AN U
The other major bioartificial liver, the Extracorporeal Liver Assist Device (ELAD) was developed at Baylor College of Medicine, and contained the C3A cell line described above10,12. Any disadvantages of a tumor cell line were offset by the advantages of an unlimited supply of cultured human liver cells and the ability to treat patients indefinitely with a simple venous access catheter. The original design included perfusion with whole blood to assure adequate oxygenation. The design was changed to plasma infusion in later models, necessitating four cartridges and in-line oxygenation. The original Hepatix device supported dogs with lethal acetaminophen-induced liver failure until survival11,20, and suggested effectiveness in 23 patients with acute liver failure14,15. The modified device was tested in five patients in a pilot trial21, and in subsequent trials in China and the USA – these latter results have not been published to date.
Importance
AC C
EP
TE D
The benefit of artificial liver in acute liver failure (ALF) is undisputed – ALF is a potentially reversible disease caused by a critical loss of hepatocyte mass22. Although ALF remains an important clinical entity, its frequency is declining, and recovery is improving23. Chronic liver failure (CLF) is far more common, but the role of artificial liver is much less obvious. The clinical picture of CLF is usually dominated by the complications of portal hypertension, a problem not addressed by extracorporeal liver support. In addition, the underlying cirrhosis is not reversible – recovery from a decompensation episode leaves the patient in the same frail state, still in need of liver transplantation.
ACCEPTED Roadblocks/Limitations
MANUSCRIPT
Extracorporeal liver support has the potential to save lives in patients with ALF, but we cannot assume the same for patients with CLF. Since ALF is now relatively rare, and CLF is increasingly common, this may be the time to consider the next generation of artificial liver. Liver cells grow well in three dimensional structures like small cubes of loofa sponge24, but scaling up to the size of a liver creates a large central area that cannot be fed by diffusion alone. Printing a three dimensional (3-D) liver scaffold sounds appealing, but will have to include blood inflow and outflow conduits, and a drainage system for bile excretion. These obstacles aside, The New Organ Alliance (http://www.neworgan.org) has offered a prize of $1,000,000 for “the first team that creates a bioengineered replacement for the native liver of a large mammal, enabling it to recover in the absence of native function and survive three months with a normal lifestyle.“
RI PT
A more biologic approach may be an animal liver stripped of cells and repopulated with human liver cells. Two recent papers discuss reprogramming of human fibroblasts in mouse liver as a first step towards achieving a working human liver25,26.
Conclusions
M AN U
SC
Artificial liver requires a cellular component to mimic the function of the liver. Patients with ALF are extremely ill, but have the capacity to recover by liver regeneration. These patients may benefit from extracorporeal liver support. Patients with CLF are more challenging because an extracorporeal device does not improve portal hypertension, frequently the dominant component of their disease. We see a need for extracorporeal liver support, but the need has decreased with a declining number of acute liver failure cases. The real need is the growing number of patients with cirrhosis who, at best, will get partial benefit from extracorporeal liver support. An implantable artificial liver seems like science fiction at present, but initial results suggest that such an undertaking is feasible, and worth at least a million dollars.
References
AC C
EP
TE D
1. Trey C, Burns DG, Saunders SJ. Treatment of hepatic coma by exchange blood transfusion. The New England journal of medicine 1966;274:473-81. 2. Eiseman B, Liem DS, Raffucci F. Heterologous liver perfusion in treatment of hepatic failure. Annals of surgery 1965;162:329-45. 3. Saliba F, Camus C, Durand F, et al. Albumin dialysis with a noncell artificial liver support device in patients with acute liver failure: a randomized, controlled trial. Annals of internal medicine 2013;159:522-31. 4. Banares R, Nevens F, Larsen FS, et al. Extracorporeal albumin dialysis with the molecular adsorbent recirculating system in acute-on-chronic liver failure: the RELIEF trial. Hepatology 2013;57:1153-62. 5. Fox IJ, Langnas AN, Fristoe LW, et al. Successful application of extracorporeal liver perfusion: a technology whose time has come. The American journal of gastroenterology 1993;88:1876-81. 6. Sussman NL, McGuire BM, Kelly JH. Hepatic assist devices: will they ever be successful? Current gastroenterology reports 2009;11:64-8. 7. Levy MF, Crippin J, Sutton S, et al. Liver allotransplantation after extracorporeal hepatic support with transgenic (hCD55/hCD59) porcine livers: clinical results and lack of
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
pig-to-human transmission of the porcine endogenous retrovirus. Transplantation 2000;69:272-80. 8. Rozga J. Liver support technology--an update. Xenotransplantation 2006;13:380-9. 9. Demetriou AA, Brown RS, Jr., Busuttil RW, et al. Prospective, randomized, multicenter, controlled trial of a bioartificial liver in treating acute liver failure. Annals of surgery 2004;239:660-7; discussion 7-70. 10. Kelly JH, Darlington GJ. Modulation of the liver specific phenotype in the human hepatoblastoma line Hep G2. In vitro cellular & developmental biology : journal of the Tissue Culture Association 1989;25:217-22. 11. Kelly JH, Koussayer T, He DE, et al. An improved model of acetaminophen-induced fulminant hepatic failure in dogs. Hepatology 1992;15:329-35. 12. Sussman NL, Chong MG, Koussayer T, et al. Reversal of fulminant hepatic failure using an extracorporeal liver assist device. Hepatology 1992;16:60-5. 13. Mavri-Damelin D, Damelin LH, Eaton S, Rees M, Selden C, Hodgson HJ. Cells for bioartificial liver devices: the human hepatoma-derived cell line C3A produces urea but does not detoxify ammonia. Biotechnology and bioengineering 2008;99:644-51. 14. Ellis AJ, Hughes RD, Wendon JA, et al. Pilot-controlled trial of the extracorporeal liver assist device in acute liver failure. Hepatology 1996;24:1446-51. 15. Sussman NL, Gislason GT, Conlin CA, Kelly JH. The Hepatix extracorporeal liver assist device: initial clinical experience. Artificial organs 1994;18:390-6. 16. Weeks CA, Newman K, Turner PA, et al. Suspension culture of hepatocyte-derived reporter cells in presence of albumin to form stable three-dimensional spheroids. Biotechnology and bioengineering 2013;110:2548-55. 17. Huch M, Boj SF, Clevers H. Lgr5(+) liver stem cells, hepatic organoids and regenerative medicine. Regenerative medicine 2013;8:385-7. 18. Huch M, Dorrell C, Boj SF, et al. In vitro expansion of single Lgr5+ liver stem cells induced by Wnt-driven regeneration. Nature 2013;494:247-50. 19. Nyberg SL. Bridging the gap: advances in artificial liver support. Liver transplantation : official publication of the American Association for the Study of Liver Diseases and the International Liver Transplantation Society 2012;18 Suppl 2:S10-4. 20. Kelly JH, Koussayer T, He D, et al. Assessment of an extracorporeal liver assist device in anhepatic dogs. Artificial organs 1992;16:418-22. 21. Millis JM, Cronin DC, Johnson R, et al. Initial experience with the modified extracorporeal liver-assist device for patients with fulminant hepatic failure: system modifications and clinical impact. Transplantation 2002;74:1735-46. 22. Remien CH, Adler FR, Waddoups L, Box TD, Sussman NL. Mathematical modeling of liver injury and dysfunction after acetaminophen overdose: early discrimination between survival and death. Hepatology 2012;56:727-34. 23. Lee WM, Squires RH, Jr., Nyberg SL, Doo E, Hoofnagle JH. Acute liver failure: Summary of a workshop. Hepatology 2008;47:1401-15. 24. Chen JP, Yu SC, Hsu BR, Fu SH, Liu HS. Loofa sponge as a scaffold for the culture of human hepatocyte cell line. Biotechnology progress 2003;19:522-7. 25. Huang P, Zhang L, Gao Y, et al. Direct reprogramming of human fibroblasts to functional and expandable hepatocytes. Cell stem cell 2014;14:370-84. 26. Zhu S, Rezvani M, Harbell J, et al. Mouse liver repopulation with hepatocytes generated from human fibroblasts. Nature 2014;508:93-7.