Fisher John P. e.a. (ed.) Tissue Engineering
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29-20 Tissue Engineering
[43] Tsuji, I., Ishida, H., and Fujieda, J. Experimental cystoplasty using preserved bladder graft. J. Urol.
1961; 85: 42.
[44] Kambic, H., Kay, R., Chen, J.F., Matsushita, M., Harasaki, H., and Zilber, S. Biodegradable
pericardial implants for bladder augmentation: a 2.5-year study in dogs. J. Urol. 1992; 148: 53943.
[45] Kelami, A., Ludtke-Handjery, A., Korb, G., Roll, J., Schnell, J., and Danigel, K.H. Alloplastic
replacement of the urinary bladder wall with lyophilized human dura. Eur. Surg. Res. 1970; 2: 195.
[46] Fishman, I.J., Flores, F.N., Scott, B., Spjut, H.J., and Morrow, B. Use of fresh placental membranes
for bladder reconstruction. J. Urol. 1987; 138: 1291.
[47] Probst, M., Dahiya, R., Carrier, S., and Tanagho, E.A. Reproduction of functional smooth muscle
tissue and partial bladder replacement. Br.J.Urol.1997; 79: 505.
[48] Sutherland, R.S., Baskin, L.S., Hayward, S.W., and Cunha, G.R. Regeneration of bladder urothe-
lium, smooth muscle, blood vessels, and nerves into an acellular tissue matrix. J. Urol. 1996; 156:
571–7.
[49] Kropp, B.P., Sawyer, B.D., Shannon, H.E., Rippy, M.K., Badylak, S.F., Adams, M.C., Keating, M.A.,
Rink, R.C., and Thor, K.B. Characterization of using small intestine submucosa regenerated canine
detrusor: assessment of reinnervaation, in vitro compliance and contractility. J. Urol. 1996; 156:
599–607.
[50] Vaught, J.D., Kroop, B.P., Sawyer, B.D., Rippy, M.K., Badylak, S.F., Shannon, H.E., and Thor, K.B.
Detrusor regeneration in the rat using porcine small intestine submucosal grafts: functional
innervation and receptor expression. J. Urol. 1996; 155: 374–8.
[51] Probst, M., Dahiya, R., Carrier, S., and Tanagho, E.A. Reproduction of functional smooth muscle
tissue and partial bladder replacement. Br.J.Urol.1997; 79: 505–15.
[52] Kropp, B.P., Rippy, M.K., Badylak, S.F., Adams, M.C., Keating, M.A., Rink, R.C., and Thor, K.B.
Small intestinal submucosa: urodynamic and histopahtologic evaluation in long term canine
bladder augmentations. J. Urol. 1996; 155: 2098–2104.
[53] Lai, J.Y., Yoo, J.J., Wulf, T., and Atala, A. Bladder augmentation using small intestinal submucosa
seeded with cells. [abstract]. J. Urol. 2002; 167(Suppl): 257.
[54] Brown, A.L., Farhat, W., Merguerian, P.A., Wilson, G.J., Khoury, A.E., and Woodhouse, K.A.
22 week assessment of bladder accellular matrix as a bladder augmentation material in a porcine
model. Biomaterials 2002; 23: 2179–90.
[55] Reddy, P.P., Barrieras, D.J., Wilson, G., Bagli, D.J., McLorie, G.A., Khoury, A.E., and
Merguerian, P.A. Regeneration of functional bladder substitutes using large segment acellular
matrix allografts in a porcine model. J. Urol. 2000; 164: 936–41.
[56] Merguerian, P.A., Reddy, P.P., Barrieras, D.J., Wilson, G.J., Woodhouse, K., Bagli, D.J.,
McLorie, G.A., and Khoury, A.E. Acellular bladder matrix allografts in the regeneration of func-
tional bladders: evaluation of large-segment (>24 cm) substitution in a porcine model. BJU Int.
2000; 85: 894–8.
[57] Portis, A.J., Elbahnasy, A.M., Shalhav, A.L., Brewer, A., Humphrey, P., McDougall, E.M., and
Clayman, R.V. Laparascopic augmentation cystoplasty with different biodegradable grafts in an
animal model. J. Urol. 2000; 164: 1405–11.
[58] Portis, A.J., Elbahnasy, A.M., Shalhav, A.L., Brewer, A.V., Olweny, E., Humphrey, P.A.,
McDougall, E.M., and Clayman, R.V. Laparoscopic midsagittal hemicystectomy and replacement
of bladder wall with small intestinal submucosa and reimplantation of ureter into graft. J. Endourol.
2000; 14: 203–11.
[59] Gleeson, M.J. and Griffith, D.P. The use of aloplastic biomaterials in bladder substitution. J. Urol.
1992; 148: 1377.
[60] Bona, A.V. and De Gresti, A. Partial substitution of urinary bladder with Teflon prothesis. Minerva
Urol. 1966; 18: 43.
[61] Monsour, M.J., Mohammed, R., Gorham, S.D., French, D.A., and Scott, R. An assessment of a
collagen/vicryl composite memebrane to repair defects of the urinary bladder in rabbits. Urology
1987; 15: 235.
mikos: “9026_c029” — 2007/4/9 — 15:53 — page 21 — #21
Stem Cells and Cloning 29-21
[62] Rohrmann, D., Albrecht, D., Hannappel, J., Gerlach, R., Schwarzkopp, G., and Lutzeyer, W.
Alloplastic replacement of the urinary bladder. J. Urol. 1996; 156: 2094.
Atala, A. Tissue engineering in the genitourinary system. In: Atala, Moone, D. (Eds.) Tissue
Engineering Boston: Birkhouser Press, 1997, p. 149.
[63] Atala, A., Freeman, M.R., Vacanti, J.P., Shepard, J., and Retik, A.B. Implantation in vivo and
retrieval of artificial structures consisting of rabbit and human urothelium and human bladder
muscle. J. Urol. 1993; 150: 608–12.
[64] Atala, A. Commentary on the replacement of urologic associated mucosa. J. Urol. 1995; 156: 338.
[65] De Boer, W.I., Schuller, A.G., Vermay, M., and van der Kwast, T.H. Expression of growth factors
and receptors during specific phases in regenerating urothelium after acute injury in vivo. Am.
J. Pathol. 1994; 145: 1199.
[66] Baker, R., Kelly, T., Tehan, T., Putman, C., and Beaugard, E. Subtotal cystectomy and total bladder
regeneration in treatment of bladder cancer. J. Am. Med. Assoc. 1955; 168: 1178.
[67] Gorham, S.D., French, D.A., Shivas, A.A., and Scott, R. Some observations on the regen-
eration of smooth muscle in the repaired urinary bladder of the rabbit. Eur. Urol. 1989;
16: 440.
[68] Oberpenning, F.O., Meng, J., Yoo, J., and Atala, A. De novo reconstitution of a functional urinary
bladder by tissue engineering. Nat. Biotechnol. 1999; 17: 2.
[69] Kershen, R.T., Yoo, J.J., Moreland, R.B., Krane, R.J., and Atala, A. Novel system for the formation
of human corpus cavernosum smooth muscle tissue in vivo. J. Urol. 1998; 159(Suppl): 156.
[70] Park, H.J., Kershen, R., Yoo, J., and Atala, A. Reconstitution of human corporal smooth muscle
and endothelial cells in vivo. J. Urol. 1999; 162: 1106–9.
[71] Falke, G., Yoo, J., Machado, M., Moreland, R., and Atala, A. Formation of corporal tissue in vivo
using human cavernosal muscle and endothelium cells seeded on collagen matrices. Tissue Eng.
2003; 9: 871–9.
[72] Kwon, T.G., Yoo, J.J., and Atala, A. Autologous penile corpora cavernosa replacement using tissue
engineering techniques. J. Urol. 2002; 168: 1754–58.
[73] Nukui, F., Okamoto, S., Nagata, M., Kurokawa, J., and Fukui, J. Complications and reimplantation
of penile implants. Int. J. Urol. 1997; 4: 52.
[74] Thomalla, J.V., Thompson, S.T., Rowland, R.G., and Mulcahy, J.J. Infectious complications of
penile prosthetic implants. J. Urol. 1987; 138: 65–7.
[75] Yoo, J.J., Lee, I., and Atala, A. Cartilage rods as a potential material for penile reconstruction.
J. Urol. 1998; 160: 1164.
[76] Yoo, J.J., Park, H., Lee, I., and Atala, A. Autologous engineered cartilage rods for penile
reconstruction. J. Urol. 1999; 162: 1119–21.
[77] Kershen, R.T. and Atala, A. Advances in injectable therapies for the treatment of incontinence and
vesicoureteral reflux. Urol. Clin. 1999; 26: 81–94.
[78] Atala, A., Cima, L.G., Kim, W., Paige, K.T., Vacanti, J.P., Retik, A.B., and Vacanti, C.A. Injectable
alginate seeded with chondrocytes as a potential treatment for vesicoureteral reflux. J. Urol. 1993;
150: 745–5.
[79] Atala, A., Kim, W., Paige, K.T., Vacanti, C.A., and Retik, A.B. Endoscopic treatment of
vesicoureteral reflux with chondrocyte-alginate suspension. J. Urol. 1994; 152: 641.
[80] Diamond, D.A., and Caldamone, A.A. Endoscopic correction of vesicoureteral reflux in children
using autologous chondrocytes: preliminary results. J. Urol. 1999; 162: 1185.
[81] Bent, A., Tutrone, R., McLennan, M., Lloyd, K., Kennelly, M., and Badlani, G. Treatment of
intrinsic sphincter deficiency using autologous ear chondrocytes as a bulking agent. Neurourol.
Urodynam 2001; 20: 157–65.
[82] Yokoyama, T., Chancellor, M.B., Watanabe, T., Ozawa, H., Yoshimura, N., de Groat, W.C., Qu, Z.,
and Huard, J. Primary myoblasts injection into the urethra and bladder as a potential treatment
of stress urinary incontinence and impaired detrusor contractility ; long term survival without
significant cytotoxicity. J. Urol. 1999; 161: 307.
mikos: “9026_c029” — 2007/4/9 — 15:53 — page 22 — #22
29-22 Tissue Engineering
[83] Chancellor, M.B., Yokoyama, T., Tirney, S., Mattes, C.E., Ozawa, H., Yoshimura, N., de Groat, W.C.,
and Huard, J. Preliminary results of myoblast injection into the urethra and bladder wall: a pos-
sible method for the treatment of stree urinary incontinence and impaired detrusor contractility.
Neurourol. Urodyn. 2000; 19: 279–87.
[84] Strasser, H., Marksteiner, R., Eva, M., Stanislav, B., Guenther, K., Helga, F. et al. Transurethral
Ultrasound Guided Injection of Clonally Cultured Autologous Myoblasts and Fibroblasts: Exper-
imental Results. In: Proceedings of the 2003 International Bladder Symposium, 2003 March 6–9;
Arlington, VA. Ridgefield, CT: National Bladder Foundation, 2003, p. 6.
[85] Bartsch, G., Yoo, J., Kim, B., and Atala, A. Stem cells in tissue engineering applications for
incontinence. J. Urol. 2000; 1009S: 227.
[86] Raya-Rivera, A., Yoo, J., and Atala, A. Hormone producing granulosa stem cells for intersex
disorders [abstract 29]. American Academy of Pediatrics Meeting, Urology section, Chicago, 2000.
[87] Lanza, R.P. et al. The ethical reasons for stem cell research. Science 2001; 293: 1299.
[88] Machluf, M. and Atala, A. Emerging concepts for tissue and organ transplantation. Graft 1998; 1:
31.
[89] Atala, A. and Lanza, R.P. Methods of Tissue Engineering. San Diego, CA: Academic Press, 2001.
[90] Atala, A. and Mooney, D. Synthetic Biodegradable Polymer Scaffolds. Boston, MA: Birkhaüser, 1997.
[91] Lanza, R.P., Cibelli, J.B., and West, M.D. Prospects for the use of nuclear transfer in human
transplantation. Nat. Biotechnol. 1999; 17: 1171–4.
[92] Evans, M.J. et al. Mitochondrial, DNA genotypes in nuclear transfer-derived cloned sheep. Nat.
Genet. 1999; 23: 90–3.
[93] Hiendleder, S., Schmutz, S.M., Erhardt, G., Green, R.D., and Plante, Y. Transmitochondrial differ-
ences and varying levels of heteroplasmy in nuclear transfer cloned cattle. Mol. Reprod. Dev. 1999;
54: 24–31.
[94] Steinborn, R., et al. Mitochondrial DNA heteroplasmy in cloned cattle produced by fetal and adult
cell cloning. Nat. Genet. 2000; 25: 255–7.
[95] Amiel, G.E. and Atala, A. Current and future modalities for functional renal replacement. Urol.
Clin. 1999; 26.
[96] Humes, H.D., Buffington, D.A., MacKay, S.M., Funke, A.J., and Weitzel, W.F. Replacement of renal
function in uremic animals with a tissue-engineered kidney. Nat. Biotechnol. 1999; 17: 451455.
[97] Cieslinsk, D.A. and Humes, H.D. Tissue engineering of a bioartificial kidney. Biotechnol. Bioeng.
1994; 43: 781–91.
[98] MacKay, S.M., Kunke, A.J., Buffington, D.A., and Humes, H.D. Tissue engineering of a bioartificial
renal tubule ASAIO J. 1998; 44: 179–83.
[99] Aebischer, P., Ip, T.K., Panol, G., and Galletti, P.M. The bioartificial kidney: progress towards an
ultrafiltration device with renal epithelial cells processing. Life Support Syst. 1987; 5: 159–68.
[100] Ip, T., Aebischer, P., and Galletti, P.M. Cellular control of membrane permeability. Implications
for a bioartificial renal tubule. ASAIO Trans. 1988; 34: 351–55.
[101] Humes, H.D. Renal replacement devices. In: Lanza, R.P., Langer, R., and Vacanti, J. Eds. Principles
of Tissue Engineering, 2nd ed. San Diego: Academic Press, 2000, pp. 645–653.
[102] Amiel, A., Yoo, J., and Atala, A. Renal therapy using tissue engineered constructs and gene delivery.
J. Urol. 2000; 18: 71–9.
[103] Lanz, R.P., Hayes, J.L., and Chick, W.L. Encapsulated cell technology. Nat. Biotechol. 1996; 14:
1107–11.
[104] Kuhtreiber, W.M., Lanza, R.P., and Chick, W.L. (Eds). Cell Encapsulation Technology and
Therapeutics. Boston: Birkhauser, 1998.
[105] Lanza, R.P. and Chick, W.L. (Eds.) Immunoisolation of Pancreatic Islets. Austin, TX: R.G. Landes,
1994.
[106] Joki, T., Machluf, M., Atala, A., Zhu, J., Seyfried, N.T., Dunn, I.F., Abe, T., Carroll, R.S., and
Black, P.M. Continuous release of endostatin from microencapsulated engineered cells for tumor
therapy. Nat. Biotechnol. 2001; 19: 35–9.
mikos: “9026_c029” — 2007/4/9 — 15:53 — page 23 — #23
Stem Cells and Cloning 29-23
[107] Lanza, R.P., Chung, H.Y., Yoo, J.J., Wettstein, P., Blackwell, C., Atala, A. et al. Generation of
histocompatible tissues using nuclear transplantation. Nat. Biotechnol. 2002; 20: 689.
[108] Lanza, R.P. et al. Cloning of an endangered species (Bos gaurus) using interspecies nuclear transfer.
Cloning 2000; 2: 79–90.
[109] Fischer Lindahl, K., Hermel, E., Loveland, B.E., and Wang, C.R. Maternally transmitted antigen of
mice. Ann. Rev. Immunol. 1991; 9: 351–72.
[110] Hadley, G.A., Linders, B., and Mohanakumar, T. Immunogenicity of MHC class I alloantigens
expressed on parenchymal cells in the human kidney. Transplantation 1992; 54: 537–42.
[111] Yard, B.A. et al. Analysis of T cell lines from rejecting renal allografts. Kidney Int. 1993; 43: S133–8.
[112] Bailey, D.W. Genetics of histocompatibility in mice. I. New loci and congenic lines. Immunogenetics
1975; 2: 249–56.
[113] Mohanakumar, T. The role of MHC and non-MHC antigens in allograft immunity. Austin, TX:
R.G. Landes Company, 1994, pp. 1–115.
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30
Hepatic Tissue
Engineering for
Adjunct and
Temporary Liver
Support
François Berthiaume
Arno W. Tilles
Mehmet Toner
Martin L. Yarmush
Harvard Medical School
Shriners Hospital for Children
Christina Chan
Harvard Medical School
Shriners Hospital for Children
Michigan State University
30.1 Introduction.............................................. 30-1
30.2 Adjunct Internal Liver Support ......................... 30-2
Hepatocyte Transplantation • Implantable Devices •
Encapsulated Hepatocytes
30.3 Extracorporeal Temporary Liver Support .............. 30-3
Extracorporeal Whole Liver Perfusion • Dialysis and
Filtration Systems • Bioartificial Livers
30.4 Summary ................................................. 30-13
Acknowledgments............................................... 30-14
References ....................................................... 30-14
30.1 Introduction
Approximately 30,000 patients die each year from end-stage liver disease in the United States. About 80%
of these patients have decompensated chronic liver disease, typically caused by alcoholism or chronic
hepatitic C infection, and less commonly by a genetic — hepatocellular or anatomic — defect of liver
function, or cancer. The other 20% die of acute liver failure (without preexisting chronic liver disease),
which has various etiologies, including ischemia–reperfusion injury during liver surgery, acetaminophen
poisoning, viral hepatitis, severe sepsis, idiosyncratic drug reactions, etc. Acute liver failure symptoms
develop over a period of 6 weeks to 6 months and lead to death in over 80% of the cases, usually from
cerebral edema, complications due to coagulopathy, and renal dysfunction. A more severe form of acute
liver failure — fulminant hepatic failure — is characterized by a more rapid evolution (2 to 6 weeks).
Orthotopic liver transplantation (OLT) is the only clinically proven effective treatment for patients
with end-stage liver disease. The majority of donor livers are obtained from brain-dead cadavers that
still possess respiratory and circulatory functions at the time of organ retrieval. Expansion of the donor
pool to include living donors, marginal and domino livers, as well as using split livers has been a major
30-1
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30-2 Tissue Engineering
focus of transplant surgeons in the past few years. Although this may alleviate the donor organ shortage,
there still remains a great potential benefit to developing alternatives that could be more cost-effective
and less invasive, such as adjunct and temporary liver support. These approaches may find applications in
the treatment of acute liver failure by allowing endogenous liver regeneration, as well as in chronic liver
failure by ameliorating complications arising from the disease. Temporary liver support may also serve as
a bridge to OLT by allowing more time to find a better match between donor and recipient or stabilize the
patient prior to surgery.
30.2 Adjunct Internal Liver Support
A situation in which the native liver retains some functional capabilities is most amenable to adjunct liver
support. The concept of adjunct liver support has been validated by the success of auxiliary partial liver
transplantation [1,2]. However, primary nonfunction and vascular complications, for example, portal
vein thrombosis, are more frequent with auxiliary partial liver transplantation than with whole liver
transplantation. On the other hand, in certain situations, for example, fulminant hepatic failure (FHF),
the native liver recovered and the patients could be safely removed from immunosuppressive drug therapy.
Hepatocyte transplantation and hepatocyte-based implantable devices are an appealing alternative to
auxiliary partial liver transplantation for several reasons (a) several patients could be treatedwith one single
donor liver; (b) the implantation procedure could be performed using less invasive surgery; (c) isolated
liver cells can be cryopreserved for long times; and (d) the liver cells could be genetically engineered in vitro
to upregulate specific functions.
30.2.1 Hepatocyte Transplantation
Hepatocyte transplantation is the simplest form of adjunct internal liver support and has been investigated
for over 25 years. In general, the efficiency of engraftment has been found to be quite low and a lag time,
which may be as much as 48 h, is necessary before any clinical benefit occurs [3]. Thus, this approach
offers an attractive prospect for correcting mostly nonemergency conditions such as inherited metabolic
defects of the liver [4]. In early studies the choice of the transplantation site was dictated by accessibility
and ease of procedure, as well as by spatial considerations: the pulmonary vascular bed, dorsal and
inguinal fat pads, and peritoneal cavity. However, expression of liver-specific functions by transplanted
hepatocytes could not be achieved in most of these ectopic sites. A microenvironment resembling that
of liver, including a basement substrate to promote hepatocyte anchorage and a venous blood supply
mimicking the mechanical and biochemical environment of the hepatic sinusoid is required [5]. The
splenic pulp and the host liver itself are now the preferred sites for transplantation of hepatocytes [6].
When implanted into the spleen, hepatocytes may engraft locally or migrate into the liver. Some of the
successes with hepatocyte transplantation in experimental animals, although often not very dramatic,
have prompted clinical studies. The best results have been obtained in the treatment of specific metabolic
disorders; however, except for one case with Crigler–Najjar syndrome type I, there was no detectable
long-term function of transplanted human hepatocytes [7].
30.2.2 Implantable Devices
To improve the survival and function of implanted hepatocytes, the latter have been incorporated into
biocompatible support materials, effectively constituting an implantable device. There are two major types
of implantables devices (a) hepatocytes in open matrices that allow tissue — especially blood vessels —
ingrowth from the host, thus leading to integration with the surrounding tissue, and (b) hepatocytes
isolated from the surrounding environment in the host by a selective membrane barrier.
In early studies, isolated hepatocytes attached to collagen-coated dextran microcarriers were trans-
planted by intraperitoneal injection in two rat models of liver dysfunction (a) the Nagase analbuminemic
rat, and (b) the Gunn rat, which has and inherited deficiency of bilirubin–uridine disphosphate
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Adjunct and Temporary Liver Support 30-3
glucuronosyltransferase activity causing a lack of conjugated bilirubin in the bile [8]. In both models,
microcarriers promoted cell attachment, survival, and function of the transplanted hepatocytes.
Prevascularizing the cell polymer devices in combination with hepatotrophic stimulation have been
used to encourage liver tissue regeneration around the implant [9]. Furthermore, materials that bio-
degrade at controlled rates in vivo (such as collagen and poly-lactic-glycolic co-polymers) can be used
[10,11], and novel techniques, such as solid freeform fabrication can be used to reproducibly manufacture
three-dimensional porous materials of well-defined pore size, distribution and interconnectivity [12,13].
Recently, novel biomaterials that are bioactive as well as resorbable have been developed [14]. For example,
biomaterials are being designed to stimulate tissue repair through the release of factors that elicit specific
cellular responses, such as cell proliferation, differentiation, and synthesis of extracellular matrix. Thus
far, one of the more common approaches is to incorporate growth factors into tissue-engineering scaffolds
[15,16]. There is also an interest in using “smart” materials consisting of stimuli-responsive polymers that
change their properties in response to changes in the external environment [17].
30.2.3 Encapsulated Hepatocytes
A limitation of hepatocyte-based devices using open matrices is the need to use the host’s own cells or at
the very least an allogeneic cell source, both of which are very difficult to obtain, which seriously limits the
usefulness of these devices. To circumvent this problem, there is great interest in using hepatocytes from
xenogeneic sources. Since there is no immunosuppressive regimen that currently exists to prevent rejection
of xenografts, hepatocytes have been encapsulated into small microspheres as well as into hollow fibers.
In theory, encapsulating with a synthetic, permeable membrane provides a physical separation which
protects the cells from the immune system of the host by excluding high molecular weight immunocom-
petent proteins (e.g., antibodies and complement) as well as leukocytes, while allowing free exchange of
nutrients and oxygen. Nevertheless, if the microcapsule causes complement activation after implantation,
the breakdown complement products could be small enough to enter the microcapsules and damage the
transplanted cells. Initial applications of semipermeable microcapsules contained hemoglobin as blood
substitute, enzymes to treat inborn errors of metabolism or absorbents to treat drug overdoses [18]. With
advances in genetically engineered cells, microencapsulated cells have been used to remove ammonia
in liver failure and amino acids such as phenylalanine in phenylketonuria [19]. Numerous studies have
been performed with encapsulated hepatocytes without immunosuppressive drugs. Transplantation of
microencapsulated xenogeneic hepatocytes into Gunn rats without immunosuppression reduced serum
bilirubin levels for up to 9 weeks before returning to control rat levels, possibly due to the deterioration
of the biomaterial [20]. The viability and function of encapsulated hepatocytes is highly dependent on
the composition of the hollow fiber material [21]. Better results may be possible if angiogenesis near the
capsule surface can be promoted [22], and the formation of a fibrotic layer around the capsule can be
avoided [23].
30.3 Extracorporeal Temporary Liver Support
Extracorporeal temporary liver support systems are life-support systems that are analogous in concept to
kidney dialysis machines, but specifically designed for liver failure patients. Since the liver has the ability
to regenerate, temporary liver support may be sufficient to prevent patient death during the most severe
phase of the illness, and allow regeneration of the host liver. The other main purpose of liver support
systems is to provide a bridge to transplantation while awaiting a suitable donor. Table 30.1 provides a
listing of the various techniques and systems currently being tested in a clinical setting.
30.3.1 Extracorporeal Whole Liver Perfusion
This technique was first used in humans in 1964 [24]. Xenogeneic (pig) livers were used for the first time
in human studies in 1965 [25]. Although it fell out of favor due to the development of OLT, extracorporeal
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30-4 Tissue Engineering
TABLE 30.1
Clinical Trials for Temporary Extracorporeal Liver Support
Device
a
Configuration
Cell mass and source Perfusate and treatment prot
ocol Trial phase Refs.
Whole liver perfusion
Whole pig, baboon, or human liver
Whole blood
,5hmedian
perfusion time, most
patients received
1 or 2 perfusions
I/II
[26,36]
Dialysis and filtration systems
MARS (Teraklin AG, Rostock,
Germany)
Albumin-loaded hemofilter, 60-kDa
cut-off
None
Whole blood, 12–132 h I/II
[123,124]
Liver Dialysis Unit (HemoCleanse
Technologies, West Lafayette, IN)
Hemodiabsorption across 5-kDa cut-off
cellulosic membranes
None
Whole blood, 6 h/day;
upto5days
FDA approved [38,39]
Prometheus (Fresenius Medical Care
AG, Bad Homburg, Germany)
Hemofilter, 250-kD a cut-off, connected to
two adsorber cartridges, in series with
conventional dialyser
None
Whole blood, up to 12 h
divided into 2 treatments
over2days
I
[40,125]
Bioartificial livers
HepatAssist (Circe Biomedical,
Lexington, MA)
Hollow-fiber, polysulphone, 0.15–0.20
µm
pore size
50 g cryopreserved primary porcine
hepatocytes on microcarrier beads
b
Plasma, 6 h/session; up to
14 sessions
II/III
[126–
128]
BLSS (Excorp Medical, Oakdale,
MN)
Hollow-fiber, cellulose acetate, 100-kDa
cut-off
70–100 g primary porcine
hepatocytes
Whole blood, 12 h/session;
up to 2 sessions
I/II
[129,130]
MELS (Charité Virchow, Berlin,
Germany)
Hollow-fiber (Interwoven,
multi-compartment)
250–500 g primary porcine or human
hepatocytes
Plasma, continuous up to
3days
I/II
[131]
ELAD (Vital Therapies, La Jolla, CA) Hollow-fiber, c
ellulose acetate, 120-kDa
cut-off
100 g human hepatoblastoma C3A
cells per cartridge, up to
4 cartridges/device
Plasma, continuous up to
107 h
II (due to resume
in 2004)
[132]
AMC-BAL (Hep-Art Medical
Devices, B.V., Amsterdam, The
Netherlands)
Spirally wound, nonwoven polyester
matrix, no membrane
70–150 g
b
primary porcine
hepatocytes
Plasma, up to 18 h/session;
up to 2 sessions
I
[99,133]
Radial-flow bioreactor (Sant’Anna
University Hospital, Italy)
Radial-flow bioreactor
230 g primary porcine hepatocytes Plasma, 6–24 h t
reatments,
mostly in one session
I/II
[134]
LiverX-2000 (Algenix, Inc.,
Minneapolis, MN)
Cells embedded in collagen matrix within
hollow-fibers
40 g primary porcine hepatocytes per
cartridge, 2 cartridges/device
Blood
I/II
[135]
c
Hybrid bioartificial liver
(Hepatobiliary Institute of Nanjing
University, China)
Polysulfone hollow-fiber cartridge with
100-kDa cut-off combined with
adsorption column
100 g primary porcine hepatocytes
b
Plasma, on
e6htreatment,
except one patient with
2 ×6 h treatments
I
[136]
a
ELAD, Extracorporeal liver assist device; BLSS, bioartificial
liver support system; MELS, modular extracorporeal liver syst
em; AMC–BAL, Amsterda
m bioartificial liver system; MARS,
molecular adsorbent recycling system; FDA, Food and Drug A
dministration.
b
Basedon10
8
hepatocytes/g liver tissue.
c
Clinical data not yet published, reference describes device desig
n.
mikos: “9026_c030” — 2007/4/9 — 15:53 — page5—#5
Adjunct and Temporary Liver Support 30-5
whole liver perfusion has experienced renewed interest in recent years. Pascher et al. [26] analyzed data
from nearly 200 patients from studies conducted from 1964 to 2000, and overall the study concluded that
extracorporeal whole liver perfusion was not superior to conventional intensive care treatment approaches.
Early on, a major challenge of this technique was the relatively poor and unstable function of the
extracorporeal liver and hemodynamic instability of the patient, which have been improved by using dual
vessel (hepatic artery and portal vein) perfusion [27]. Studies in the period ranging from 1990 to 2000
have shown that patients treated with an extracorporeal liver and that survived all eventually received
OLT; thus, the extracorporeal liver was potentially effective as a bridge to transplantation, but not as a
substitute.
The shortage of human donors provides a strong motivation for the use of xenogeneic livers. Transgenic
pigs and immunoabsorption techniques have been used to reduce the effects of hyperacute rejection
[28–30]. Given that immune function is severely depressed in acute liver failure patients, this may not be
necessary for perfusions lasting 24 to 36 h [31–33]. Borie et al. [34] described an alternative approach to
isolate the xenogeneic liver from the host whereby a pig liver is perfused with pig blood in a secondary
circuit which is separated from the host’s blood by a microporous membrane. Although it appears that
immune incompatibilities could be addressed, some of the data suggest that baboon and human livers
may be more effective than livers from other species, suggesting an important role for proper matching of
the metabolic and physiological activities of the extracorporeal liver and host [35,36].
30.3.2 Dialysis and Filtration Systems
The first attempts at developing devices for temporary and adjunct liver support consisted of nonbiolo-
gical devices incorporating hemodialysis, hemofiltration, and/or plasma exchangeunits aimed at removing
toxins accumulating in the patient’s blood. Charcoal perfusion, the most extensively characterized non-
biological method, showed benefits in various animal models, but no survival benefit was reported in
the only one reported randomized clinical trial [37]. Recently, there has been renewed interest in further
refining these approaches, with three different systems at various stages of clinical assessment.
The Liver Dialysis Unit (Hemocleanse Technologies, West Lafayette, IN), an approved device in the
United States since 1996, is a modified dialysis machine wherein blood is dialyzed against a solution that
is continuously recycled through a mixture of sorbents including activated charcoal and an ion-exchange
resin. In several small randomized prospectively controlled trials carried out from 1992 to 1998, patients
were treated 6 h/day for 1 to 5 days, and the results showed a better outcome with patients with acute on
chronic liver failure, although there was no benefit for patients with FHF [38]. The lack of benefit in FHF
patients was attributed to the inability to clear strongly protein- or lipid-bound toxins, including bilirubin,
endotoxin, and inflammatory cytokines, that are too big to go across the 5 kDa molecular weight cut-off
of the dialysis module. A modified version of the device includes a plasma filter module wherein plasma
interacts directly with the sorbent particles, thus eliminating this barrier. In preliminary clinical studies,
including the plasma filter module resulted in decreases in bilirubin, aromatic amino acids, ammonium,
creatinine, and inflammatory mediators such as interleukin-1β [39], but not enough information was
available to make conclusions on the overall clinical benefit. A “second-generation” system is currently
being designed as kit to convert an existing kidney dialysis into a liver dialysis system, and being touted as
a more cost-effective system than its predecessor.
The Prometheus System (Fresenius Medical Care AG, Bad Homburg, Germany) is conceptually very
similar to the competing system described above, in that it also includes of two separate modules (a) a high-
flux dialyzer that removes water soluble toxins, and (b) a plasma filter module. The latter consists of a
large pore (250 kDa) hollow-fiber module that enables albumin along with hydrophobic toxins bound
to it to enter a closed loop circuit that contains sorbent materials that strip off the toxins and free up
the binding sites on albumin before it is returned to the blood stream. A clinical study in patients with
acute-on-chronic liver failure with accompanying hepatorenal syndrome shows that treatment decreased
circulating levels of many toxins, such as ammonia, bilirubin, bile acids, etc. although there was no