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Review article: liver support systems in acute hepatic failure
T. M. RAHMAN & H. J. F. HODGSON
Department of Gastroenterology, Imperial College School of Medicine, Hammersmith Hospital, London, UK
Accepted for publication 7 May 1999
INTRODUCTION
Hepatic failure has long been a challenge to the
physician. Both acute and chronic hepatic failure
present a spectrum of clinical problems associated with
high morbidity and mortality. This review surveys
changing perspectives in the treatment of acute hepatic
failure (AHF).
The development of hepatic encephalopathy, jaundice
and coagulopathy de®nes AHF. Following Lucke and
Mallory's description of two distinct clinical patterns
observed in acute hepatitis, Trey & Davidson1, 2 intro-
duced the terms fulminant and sub-fulminant hepatic
failure. These have since been modi®ed to make the
classi®cation more accurate and universal. Their series
and other similar reports have helped to inform and
familiarize clinicians. Early diagnosis, development of
specialist centres and better understanding has reduced
mortality. Advances in intensive care monitoring,
management and pharmacological therapy have made
a signi®cant impact on survival. Whilst liver transplan-
tation remains the only de®nitive treatment for patients,
improved techniques and immuno-suppressive regimes
have improved long-term survival post-transplantation.
Organ availability, however, remains a limiting factor.
The clinical aspects of the management of AHF have
recently been reviewed in this journal.3
Over the last 50 years there have been advances in the
understanding of the deranged pathophysiology encom-
passing the clinical features of AHF: encephalopathy,
cerebral oedema, haemorrhage, electrolyte and meta-
bolic disturbance, renal failure, cardiovascular instabil-
ity and increased risk of infection. The `toxin hypothesis'
and the `critical mass theory', originally thought to
explain the changes, have been modi®ed by the
realization that synergistic forces (endotoxin and cyto-
kines) are also involved in AHF, and these views have
led to a range of approaches to arti®cial liver support.
Advances taking place in the treatment of chronic
renal failure were trialled in patients with chronic liver
disease and began an era of `non-biological liver
support'. Areas investigated include haemodialysis,
haemo®ltration, the use of adsorbents, plasma exchange
and later plasmapheresis. With the limited impact that
these systems provided, alternative approaches were
also investigated. The use of extra-corporeal perfusion of
xenogeneic and allogeneic cadaveric organs marked the
SUMMARY
The treatment of acute hepatic failure has developed
rapidly over the last 40 years, reducing morbidity and
mortality from this syndrome. Whilst this has been
partly attributed to signi®cant improvements in the
specialist medical management of these patients,
advances in surgical techniques and pharmaceutical
developments have led to the establishment of
successful liver transplantation programmes, which
have improved mortality signi®cantly.
This review will examine the clinical impact of
alternative methods that have been used to provide
extra-corporeal hepatic support. Non-biological, bio-
logical and hybrid hepatic extra-corporeal support will
be explored, offering a comprehensive historical
overview and an appraisal of present and future
advances.
Correspondence to: Prof. H.J.F. Hodgson, Department of Gastroenterology,
Imperial College School of Medicine, Hammersmith Hospital, Du CaneRoad, London W12 0NN, UK.
E-mail: [email protected]
Aliment Pharmacol Ther 1999; 13: 1255±1272.
Ó 1999 Blackwell Science Ltd 1255
advent of `biological liver support'. The effects of
xenogeneic liver homogenate, fresh liver slices, freeze-
dried liver granules and whole organs on patients in
AHF have been reported. Subsequently, technological
advances in cell biology and biotechnology allowed
more sophisticated systems to be developed. More
recently a class of `hybrid liver support' has undergone
clinical trials involving the use of biological tissue with
non-biological materials. Several investigators have
devised complex systems that combine human and pig
cryopreserved hepatocytes, providing the synthetic,
metabolic and excretory functions of the failing liver
with advanced biotech constructs. Preliminary reports
have identi®ed the feasibility of the approach, but
effectiveness has not yet been proven.
Finally, also in its infancy, `hepatocyte transplantation'
has been shown in animal studies to be effective in the
treatment of AHF.
This review will summarize previous and current
endeavours in arti®cial liver support.
THE ROLE OF HEPATIC SUPPORT
The unique and complex architecture of the liver goes
some way to explaining its diverse involvement in
maintaining metabolic homeostasis within the body.
AHF leads to deranged intracellular metabolism and
failure of interconversion of carbohydrates, lipids and
amino acids, and reduced synthesis of plasma proteins,
coagulation factors and lipoproteins. The loss of detox-
i®cation and biotransformation increases susceptibility to
further damage and may lead to an increased incidence of
infection. These metabolic abnormalities are thought to
cause the unique clinical features seen in AHF.
Decades of investigation have focused on two hypoth-
eses that attempt to link the metabolic changes to the
clinical features of AHF. The `toxin hypothesis' suggests
that the failing organ is unable to clear toxins normally
processed by the healthy liver from the bloodstream.
Animal and human studies of AHF have identi®ed the
presence and deleterious effects of ammonia, phenols,
mercaptans, aromatic amino acids, fatty acids, cyto-
kines and nitric oxide moeities. The `critical mass
hypothesis' suggests that a profound loss of hepatocel-
lular metabolic capacity below a critical threshold leads
to end organ dysfunction and failure to support
peripheral organ function. More recent investigation
suggests that the hepatocyte itself, once injured,
contributes to the ampli®cation of liver injury. The
reduced integrity of the cell membrane, the loss of
intracellular homeostasis, imbalance of pro-oxidant and
antioxidant pathways, mitochondrial damage and de-
pletion of ATP all contribute to the generation of toxic
species, decreased cytoprotective capabilities and alter-
ations in cell-to-cell interactions. Both animal and
human studies have shown that, under extreme
circumstances, total hepatectomy improves the clinical
stability of the subject in AHF.4
The role of arti®cial hepatic support is therefore a
complex one. It must encompass several roles, i.e. the
removal of toxins incriminated in the pathobiology of
AHF, the synthesis of products such as coagulation
factors, albumin and other plasma proteins, and it must
also attempt to reverse the massive in¯ammatory
process taking place within the failing organ. Ideally,
hepatic support should provide metabolic, synthetic and
detoxi®cation functions, allowing time for recovery and
regeneration of the host organ. Where regeneration is
not possible, hepatic support may allow time for organ
transplantation to take place.
NON-BIOLOGICAL HEPATIC SUPPORT
Haemodialysis
Inspired by successful advances taking place in the
management of chronic renal failure in the 1950s,
extra-corporeal technology was applied to patients with
chronic liver disease. Haemodialysis requires a semi-
permeable dialysis membrane through which ¯uid and
small solutes may pass, whilst exchange occurs against
dialysis ¯uid. Transfer of solutes and molecules occurs
by diffusion.
Haemodialysis had been shown to improve survival in
patients with chronic renal failure and other diseases
such as porphyria.5, 6 Zysno et al.7, 8 demonstrated
improvements in EEG recordings that correlated with
clinical improvement in severely uraemic patients. This
principle was applied to a group of chronic cirrhotic
patients, demonstrating improved encephalopathy and
an associated decrease in arterial ammonia levels.9 In
1968 a patient in acute liver failure was treated with
haemodialysis and showed temporary improvement in
their clinical status following treatment.10 (Table 1
illustrates the various studies discussed.)
Success was also reported by Oules et al.,11 who
suggested that removal of soluble, uncharacterized
compounds in the `middle' molecular weight range
1256 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
(400±2000 Da) improved encephalopathy in patients
with chronic liver disease and also the clinical status of
patients with chronic renal failure.12 However, these
observations were challenged by several investigators,
who suggested that the toxaemia of AHF was not due to
middle molecules, based on the results of a larger trial
showing minimal improvement in clinical state.
Application of haemodialysis became more widespread
in the early 1970s and reports of improvement in lactic
acidosis13 and of improved survival (individual case
reports) following paracetamol, salicylate and ben-
zodiazepine overdoses also appeared. Advances in
membrane technology allowed Opolon et al.12 to dem-
onstrate improved neurological status in animal models
of AHF using polyacrylonitrile (PAN) membranes. This
was followed by a clinical trial using PAN membranes
in 1975,14 in which ®ve complete neurological and two
partial recoveries were reported in a group of nine non-
decerebrate patients in coma due to `acute hepatic
atrophy'. No improvement in survival was demonstrated.
Similar ®ndings were reported by Denis et al.15 in 41
patients with fulminant hepatic failure who had
between them 180 treatment periods. Seventeen
patients had complete neurological recovery from coma
and seven had partial recovery. Of those that had
complete neurological recovery, nine survived.
Whilst PAN membranes allowed increasing solute
removal, it and other similar polymers such as polysul-
phone were unable to remove protein-bound and
lipophilic substances. An alternative approach was
developed using a liquid membrane that allowed the
removal of lipophilic toxins but prevented the removal
of physiological substances such as hormones. The
structure consisted of a hydrophobic polysulphone
membrane with large voids containing paraf®n oil.
Blood passed through the liquid membrane ®lter with a
sodium hydroxide acceptor solution on the other side.
Protein-bound toxins contacting the membrane were
released into the oily layer, diffused through the
membrane and became water-soluble due to a reaction
with the accepting solution. Application in pigs has
shown improvement in neurological function.16
Haemodialysis was further adapted by Stange &
Mitzner,17 who introduced the Molecular Adsorbents
Recirculating System (MARS) in 1993. It had been well
known that some toxins were avidly protein bound and
that standard haemodialysis membranes did not remove
these. The polysulphone membrane was impregnated
on both sides with albumin and dialysis took place
against a closed loop dialysate also containing 10±20%
albumin. In vitro studies have shown enhanced removal
of protein-bound toxins such as bilirubin, bile acids,
Table 1. Non-biological hepatic support in man
Non-biological hepatic support Subjects Outcome
Haemodialysis (Acute and chronic hepatic failure)
Kiley et al.9 Improved neurological
Keynes10 outcome. Improved
Opolon et al.14 9 patients encephalopathy
Denis et al.15 41 patients (AHF)
Klammt et al.18; Mitzner et al.19 Decreased urea, creatinine, bilirubin
Haemo®ltration
Bellomo et al.28 Animal and human sepsis Reduced IL-6, IL-1, TNFa,
Ronco & Bellomo26 C1q, C3a, C5a. Improved clinical status
Adsorbents (Acute and chronic hepatic failure)
Charcoal
Gazzard et al.35 22 patients Improved neurological status/survival
O'Grady et al.42 137 patients No bene®t in survival
Haemodiabsorption
Ash et al.57, 58 Acute and chronic hepatic failure Decreased bilirubin, lactate, creatinine. No
survival bene®t
Plasmapheresis
Larsen et al.68 12 patients (AHF) Increased survival
Clemmesen et al.20 16 AHF 11 chronics Improved ICP, CBF, CPP,
Larsen et al.67 40 AHF and chronics CMRO2, CO, MAP
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1257
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
tryptophan and fatty acids. The success of this tech-
nique is dependent on complex physiochemical processes
involving speci®c trilateral interactions between ligands,
binding proteins and the polymer. More recent clinical
studies have demonstrated improved clinical parameters
(encephalopathy and renal function) with reductions in
bilirubin, urea and creatinine in eight patients with
decompensated chronic liver disease following a total of
47 single treatments.18, 19
Despite the improvements in technology and apparent
effects on encephalopathy, there is no proof of effective-
ness in altering survival. Haemodialysis is therefore not
currently recommended for use in the treatment of
AHF. Haemodynamic instability may occur, as well as
electrolyte and ¯uid shifts, and these changes can
exacerbate cerebral oedema, leading to increased intra-
cranial pressure; they may also have adverse effects on
cardiac output and other haemodynamic parame-
ters.20, 21 High-volume haemodialysis has, however,
been used together with plasma exchange in AHF, as
discussed below.
Haemo®ltration
Haemo®ltration has been shown to be more suitable
than haemodialysis for the treatment of some patients
in renal failure following sepsis, trauma and liver
failure. Haemo®ltration uses a permeable membrane
and relies on continuous convective solute removal,
avoiding large volume and electrolyte shifts. There is no
dialysate ¯uid, only a substitution solution replacing the
ultra®ltrate. Convective removal of solutes has been
shown to be more ef®cient than haemodialysis for the
removal of molecules with molecular weights of 2000±
3000 Da. This range corresponds to the `middle'
molecules thought to be involved in encephalopathy
and liver failure.
Continuous venous±venous haemo®ltration is pre-
ferred in AHF because it offers haemodynamic stability
and allows predictable and gradual control of metabolic
disturbance.21, 22 The substitution solution for AHF can
be lactate-free and bene®ts have been observed using a
bicarbonate-buffered solution.23 Venous±venous circuits
are commonly used and require anticoagulation with
heparin, low molecular weight heparin or prostacyclin if
the platelet count is low.24 Potentially, the bene®cial
effects include ef®cient removal of middle and indeed
larger molecules, allowing immuno-modulation with the
removal of vaso-active substances from the circulation,
including immunoglobulins, IL-1, IL-6, TNF-a, C1q, C3a,
C5a and platelet activating factor.25±27 Removal of these
may be advantageous in sepsis, multi-organ failure and
systemic in¯ammatory response syndrome, all variants
of that seen in AHF. Bellomo et al. described high-
volume exchange haemo®ltration of up to 6 L/h, which
has demonstrated improved survival in animal studies of
sepsis.27 This has recently been demonstrated in a
clinical setting.28
Haemodia®ltration
There are advantages also in haemodia®ltration, which
combines the advantages of both convection (removal of
larger molecules, 2000±3000 Da) and diffusion (re-
moval of smaller molecules, 400 Da or less). Yoshiba
et al.29 used this technique in an uncontrolled series of
patients with AHF, sub-acute hepatic failure and late
onset hepatic failure, demonstrating survival rates of
85, 54 and 50%, respectively. Adverse effects included
complement activation, activation of the coagulation
cascade and release of vaso-active and chemo-attractant
fragments.
Adsorbents
There has been considerable focus on the use of different
adsorbents as a part of non-biological hepatic support
systems to remove toxins or middle molecules thought
to contribute to the clinical manifestations of AHF. Most
work in this area has involved the study of three major
types of sorbents, including activated charcoal in
various forms, synthetic neutral resins (XAD-2,4,7)
and anion exchange resins (Dowex-1). This work has
recently been further developed with the combination of
charcoal and a cation exchange resin in the form of the
Biologic-DT system.55±58
Charcoal. Yatzidis30 demonstrated the adsorbent prop-
erties of coconut charcoal in a haemoperfusion circuit.
This provided effective removal of creatinine, uric acid
and guanidine from uraemic dogs. Removal of pheno-
barbitone in dogs and in vitro and in vivo work in pigs
demonstrating the removal of paracetamol using char-
coal haemoperfusion led to isolated clinical case
reports.31±33 Problems with biocompatibility of charcoal
encouraged adaptations of its use. Chang34 used
microencapsulated charcoal for haemoperfusion in
AHF, recording complete recovery of consciousness
1258 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
from hepatic coma in a patient with alcoholic hepatitis.
Microencapsulation stops ®ne particles of charcoal
escaping into the circulation, thus improving its bio-
compatibility. Gazzard et al.35 reported the use of
charcoal haemoperfusion in 22 cases of AHF with
grade IV hepatic coma in an uncontrolled trial.
Recovery of consciousness and improved survival was
demonstrated. Subsequently several groups attempted
to repeat these observations, but were unsuccessful,
encountering problems such as intractable hypotension,
charcoal particle emboli, and thrombocytopaenia.36, 37
To improve the biocompatibility of charcoal Weston
et al.38 examined the advantages of coated and uncoated
charcoal. However, little difference in leucocyte and
platelet loss was demonstrated. Gelfrand et al.39 exam-
ined the use of charcoal coated with acrylic hydrogel,
which resulted in improved clinical tolerance to
haemoperfusion. Uncontrolled clinical trials showed
improved levels of consciousness in 9 of 10 patients in
hepatic coma and complete recovery in 40%.
Gimson et al.40, 41 used prostacyclin to prevent plate-
let activation in clinical trials of charcoal haemoper-
fusion. Two groups were studied, those in grade III and
those in grade IV encephalopathy. The use of charcoal
haemoperfusion in the grade III group led to a better
rate of survival (65%) and a reduced incidence of
cerebral oedema (49%) as opposed to those in the
grade IV group (20% survival, 78% cerebral oedema).
Contrasting ®ndings were reported in the largest
controlled trial of charcoal haemoperfusion undertaken
by O'Grady et al.42 One hundred and thirty-seven
patients were entered into two controlled trials run
concurrently. Trial A randomized 75 patients in grade
III encephalopathy to 5 or 10 h of charcoal haemo-
perfusion. There was no signi®cant bene®t seen in
survival, incidence of renal failure or cerebral oedema
in the two groups. Trial B randomized 62 patients in
grade IV encephalopathy to charcoal haemoperfusion
or no haemoperfusion. Survival rates were similar
(39.3 and 34.5%, respectively). The conclusion was
that charcoal haemoperfusion had little in¯uence on
survival or incidence of cerebral oedema and renal
failure. The additional conclusion was reached that the
apparent effectiveness of the approach, noted in
uncontrolled trials during the 1970s and early
1980s, was due to the use of historical controls and
in particular re¯ected the progressive general enhance-
ment of intensive care of patients in severe liver
failure.
Other adsorbents. The properties of other adsorbents
have been explored in an attempt to overcome the
biocompatibility problems encountered with charcoal.
The use of Dowex 50-X8, a cation exchange resin, was
reported in dogs with hepatic coma.43 Blood ammonia
levels were reduced by 50% and concurrent clinical
improvement encouraged its use in humans. Small
uncontrolled trials showed reversal in coma and
reduction of ammonia levels in 20% of patients.44
Dowex 50-X8 and Amberlite IR 120 (another cation
exchange resin) were trialled in 13 patients with
hepatic failure, with reports of improvement in con-
scious level in 54% of patients.45±47 Amberlite XAD-7,
an albumin-coated macro-reticular resin, was shown to
reduce plasma total bilirubin in 19 patients with AHF, of
whom eight left hospital.48 Its ability to remove TNF-a,
IL-6 and IFN-a, as compared with charcoal, was also
demonstrated.49, 50
More speci®c resins have been developed and tested
with recorded improvement in clinical parameters and
survival. Examples include polyamine triglycidylisocy-
anurate (PAT) resin, polylysine-immobilized chitosan
beads for removal of bilirubin, and polymyxin B
immobilized on polystyrene ®bres for the removal of
endotoxin.51±54 The last two in particular have been
associated with biocompatibility problems and despite,
or perhaps re¯ecting, the multiple types trialled, no
adsorbents have come into widespread clinical usage.
Haemodiabsorption
The Biologic-DT system55 is currently in use at a small
number of centres. This system combines charcoal and
cation exchanger in a system called `haemodiabsorp-
tion'. Blood is dialysed across a parallel plate dialyser
with a cellulose membrane that has sorbent present at
the membrane surface. The sorbent contains powdered
charcoal, sodium and a loaded cation exchange resin.
Animal studies have examined the effect of the
Biologic-DT system in dogs with AHF induced by a
two-step devascularization procedure. Following 6 h of
treatment the treated animals were more physiologically
stable, developed less lactic acidosis, had reduced
transaminase increases and also maintained higher
blood glucose levels than the untreated controls.56
Uncontrolled clinical trials in patients with hepatic
failure have recorded improved neurological status and
normalization of diastolic blood pressure in treated
patients.57, 58 Controlled trials, however, have shown
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1259
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
no bene®t in survival in AHF but plasma lactate,
creatinine and bilirubin were reduced. Increased
thrombocytopaenia, decreased ®brinogen and an
increase in the activated clotting time were, however,
seen in the Biologic-DT treated group. Neurological
improvement has been recorded in chronic decompen-
sated patients.59
Plasma exchange and plasmapheresis
The removal of toxins from plasma and replacement
with plasma from healthy individuals was ®rst performed
by Lepore et al.60, 61 They reported neurological im-
provement prior to death in two patients out of nine
with AHF. This followed one to 12 treatments with 10±
83 L of plasma exchanged. Patient survival was dem-
onstrated by Buckner et al.,62 who treated four patients
with 10 L exchanges per day for 3±36 days. Three
patients survived in this uncontrolled trial. The devel-
opment of membrane separators led to several groups
claiming increased survival.63, 64
In 1985, Winikoff et al.65 suggested that plasmaphere-
sis was only a bridge to liver transplantation (OLT).
Berk53 demonstrated the theoretical advantage of high-
volume plasmapheresis, suggesting that the volume of
distribution of toxins would correspond to the extracel-
lular space. The development and subsequent use of
high-volume plasmapheresis (HVP) for the treatment of
AHF has since been re®ned.
Kondrup et al.66 investigated the effect of HVP in 11
patients with AHF, all initially in grade III or IV
encephalopathy. An average of 2.6 exchanges, each
with a mean volume equivalent to 16% of body weight,
were performed. Five of the 11 patients, all with
acetaminophen poisoning, survived. The six non-survi-
vors remained haemodynamically stable during treat-
ment for a mean of 6.9 days. The conclusion was that
HVP could be used as a bridge to transplantation, and
also that patients who have residual liver function may
be supported until their own organs recover.
A larger series of 40 patients (mixed aetiologies)
receiving HVP reported 28 survivors (54%). Seventeen
patients received OLT, of whom three later died. The
documented improvement was in parameters of cerebral
blood ¯ow (CBF), cerebral perfusion pressure (CPP),
cerebral metabolic rate for oxygen (CMRO2), and mean
arterial pressure (MAP). No episodes of raised intracra-
nial pressure (ICP) were reported. Systemic vascular
resistance (SVR) increased and cardiac output (CO)
appropriately decreased, an effect lasting 12 h. These
changes imply improved tissue oxygen extraction
systemically and in the brain.67 Similar haemodynamic
®ndings were reported by Clemmesen et al.20 who
suggested that the removal of a humoral factor by
HVP may explain these results.
The effect of HVP on intracranial parameters, CBF,
CMRO2 and oxygen extraction has been reported in 12
patients with AHF. Encephalopathy was seen to im-
prove in four patients and improvements in CBF and
CMRO2 were statistically signi®cant.68 This improve-
ment was thought to re¯ect partial removal of neuro-
inhibitory plasma factors.
There is therefore currently some evidence that HVP
improves haemodynamic parameters, reduces cerebral
oedema and prolongs survival in those awaiting OLT. It
may be that it can be effectively used to sustain life in a
small group of patients that have some recovering
hepatic function, and might be of bene®t in patients
who are not awaiting transplantation.
BIOLOGICAL HEPATIC SUPPORT
Xenogeneic and allogeneic extra-corporeal support have
been investigated for 50 years. Several techniques have
been used, all of which have had only limited success
(Table 2). Approaches that have been explored include
cross-haemodialysis with animals, and extra-corporeal
haemoperfusion with pig, baboon and human livers.
Haemoperfusion has been extended to pass blood over
liver fragments and also liver cells. All techniques
performed have shown some improvement in clinical
and/or physiological parameters but not improvement
of survival in controlled trials.
Xenogeneic support has the disadvantage that naturally
occurring antibodies in the human recipient will react
with endothelial expressed antigens in the perfused liver.
This rapidly leads to complement activation, activation of
the clotting cascade, and haemodynamic instability.
Cross-haemodialysis
Kimoto performed a technique called cross-heterohae-
modialysis in 1957, which involved haemodialysis in a
man in hepatic failure against the circulation of a live
dog.85 This resulted in improvement of ammonia levels.
This technique was further adapted with the addition of
an ion exchange column by Hori et al.69,70 who
performed cross-haemodialysis between a man in AHF
1260 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
and a dog separated by a semi-permeable membrane.
This was associated with recovery from hepatic coma
and a corresponding reduction in blood ammonia.
Extra-corporeal haemoperfusion
Eiseman et al.71 in 1965 described the ®rst experience of
heterologous liver perfusion in the treatment of liver
failure. This technique demonstrated bile ¯ow, galactose
elimination, clearance of ammonia and bilirubin in a
pig liver extra-corporeally perfused with human blood.
Abouna72, 73 repeated this technique using pig livers on
10 patients with AHF, seven with acute hepatitis and
liver cell necrosis and three with pre-existing liver
disease. Improvements in conscious state and survival
greater than 4 days was recorded, but only two patients
survived.73 Waldschmidt et al. haemoperfused nine
patients with AHF using isolated pig livers and reported
one survivor, and transiently improved conscious levels
of the other patients who later died.74
Isolated baboon livers were also used to provide extra-
corporeal support in the treatment of 14 grade IV
encephalopathic patients. Thirteen patients had viral
hepatitis and one had developed drug-induced AHF.
Thirty perfusions were performed (29 baboon livers and
1 human cadaveric liver) each lasting 5±27 h, with 1±4
perfusions per patient. Bile excretion peaked at 7±8 h
and was used as a marker for successful perfusion. Lie
et al.75±77 claim a 50% survival rate of patients with
AHF, when perfused by this technique. Baboon livers
were also used by other groups who have claimed
survival rates of 34±45%. No controlled trials exist to
compare treatment regimes.78
Extra-corporeal liver perfusion using human livers
procured and unused by the United Network for Organ
Sharing was reported in three patients with AHF in
1993.79 All patients showed improved serial serum
bilirubin and arterial ammonia values, while two of three
patients also showed marked neurological improvement.
These patients were later successfully transplanted. The
third patient failed to show clinical improvement and died
7 days after the treatment was discontinued.
Common problems encountered with xenogeneic
haemoperfusion were: activation of the clotting cascade,
antibody and immune complex formation, and the
expected sequelae. This limited the length of perfusion
time per session and its repeated use. Technical
problems also include the requirements of large num-
bers of trained surgical, nursing, technical and ancillary
staff and the supply of animals for each haemoperfusion
session. In the case of cadaveric human liver extra-
corporeal perfusions, organs and transplant surgeons
are of limited availability.
Transgenic organ transplantation
Despite problems with organ availability, immunolog-
ical incompatibility, hyperacute rejection and ethical
dilemmas, the role of xenogeneic transplantation is an
area of current interest. The development of trans-
genic animals with genetically modi®ed immune
expression to reduce incompatibility for use in organ
transplantation is now the subject of ethical debate
and approval. Manipulation of the animals' genome
involves the insertion of human anti-complement
genes and modi®cation of their xenoantigens. Prelim-
inary studies have perfused human blood into isolated
transgenic pig livers expressing human complement-
ary±regulatory protein, human CD59 and human
decay-accelerating factor (hDAF). Results show
Table 2. Biological hepatic support in man
Biological hepatic support Technique No. of patients Outcome
Hori et al.70 Cross-heterohaemodialysis 1 patient Improved neurological status
Dog/man Decreased NH3
Eiseman et al.71 Heterologous liver perfusion 10 patients Bile ¯ow, galactose elimination,
Pig/man decreased NH3
Abouna72 Heterologous liver perfusion 10 patients Improved neurological status and
Pig/man survival
Lie et al.75 Heterologous liver perfusion 14 patients 50% survival
Baboon/man
Fox et al.79 Extra-corporeal human cadaveric 3 patients Decreased NH3, bilirubin.
Survival 2/3
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1261
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
reduced complement and TNF-a expression and
reduced activation of the hyperacute rejection pro-
cess.80±82 Expression of porcine MHC class II is a
potent stimulator of human CD4+ T-cells and is
thought to be dependent on class II transactivator
(CIITA), a bi- or multifactorial domain protein.
Manipulation of this protein has successfully demon-
strated potent suppression of MHC class II expression
and may lead to prolonged graft survival.83
Practical use at present still remains some way off.
Even without the complexities that xenotransplantation
introduces (such as the potential for spread of viruses
from animal to man), there is much that needs to be
addressed with respect to perfusion of whole livers
extra-corporeally, necrosis, apoptosis, ischaemia and
reperfusion injury, and allogeneic rejection.84
HYBRID HEPATIC SUPPORT
Hybrid hepatic support combines the use of biological
tissue with the use of non-biological materials. The use
of hepatic tissue may provide synthetic, excretory and
biotransformational functions, which combined with
membranes removing cytokines and other toxins, is
thought to be bene®cial in AHF.
Recent advances in the isolation and characterization
of hepatocyte function and growth, and the require-
ments for in vitro function, have allowed the use of
colonies of cells in hybrid liver support. Bioreactor
designs have changed to allow for optimum integrity
and function of cells taking into account the complex
biophysics involved in oxygenation, removal of waste
products and ¯ow dynamics.
The concept of hybrid support was introduced in the
last section, and was developed by the pioneers Kimoto
and Hori.85, 86 Their techniques were used by others
and cleverly adapted by Mikami et al.87 and Nose
et al.88 An extra-corporeal circuit was used to assess
the function of liver tissue homogenate, fresh liver slices
and freeze-dried granules of liver tissue in clinical trials.
Patients were connected to a dialysis circuit, and blood
was then passed to a `metabolic circuit' which con-
tained a gel-type cellulose membrane, a bubble oxygen-
ator and a chamber or `bioreactor' containing either
liver homogenate, liver slices or freeze-dried granules.
Limited clinical application demonstrated stable glucose
and lactate levels and a reduction in ammonia levels.
The use of liver fragments has been further developed
and now colonies of cells are being used in similar but
more sophisticated arti®cial liver support systems.
Parallel advances have been taking place in biotech-
nology, study of cell growth, function, integrity and
manipulation. Cells may now be genetically manipulat-
ed, cell lines immortalized and cryopreserved.
Hepatocytes
Ideally, liver cells maintained in an extra-corporeal
environment should express the full functional reper-
toire of the normal liver. As the liver contains various
sub-populations, not only the major metabolically
active cells, i.e. the hepatocytes, but also Kupffer cells,
sinusoidal endothelial cells and stellate (mesenchymal-
derived) cells providing extracellular matrix and growth
factors should ideally be present. This is clearly a major
challenge. However, there is general consensus that the
most important functions of an extra-corporeal liver
circuit, i.e. detoxi®cation and synthesis, are largely
(although not totally) ful®lled by the hepatocytes.
Calculations indicate that there are of the order of
1±2 ´ 1011 hepatocytes in a normal adult human liver.
Data from surgical resections indicate that probably
one-third of this number is suf®cient for normal survival,
but of course a larger number may be required to reverse
the changes of hepatic failure. Of course, data from
surgical experience also de®nes the numbers of cells that
are adequate when they are in the optimum, i.e. natural,
con®guration as components of a normal liver.
The ®rst major issue in providing hepatocytes for such
systems is that the mature adult hepatocyte is a non-
dividing cell. It is capable of entering DNA synthesis and
dividing in vivo, but in vitro there are only specialized
circumstances in which limited rounds of cell division
can be achieved. The option of taking a limited number
of adult human hepatocytes and letting them proliferate
in culture to provide the number required, is currently
not available. Scienti®c approaches to the limited
replicative potential of adult hepatocytes in vitro involve
identifying growth factors and media that will allow
proliferation, and/or genetically manipulating cells to
remove the normal checks to division in the adult cell.89
The use of foetal or neonatal hepatocytes with a greater
proliferative rate is also being explored.90 However,
until such techniques are truly successful, workers have
to use one of two optionsÐeither utilizing cell lines from
human livers, or using primary cells from other species.
Current evidence indicates that any proliferating
hepatocyte cell line from a human liver falls short in
1262 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
some respects from a fully functional repertoire. On the
other hand the use of xenogeneic cells has the same
problems as have been alluded to under xenogeneic
haemoperfusion, due to naturally occurring antibodies.
It is possible, however, with the use of diffusion barriers
to prevent direct exposure of xenogeneic cells to human
antibodies and cells. This should delay immediate
deleterious immune responses whilst a patient is
connected to an extra-corporeal circuit, but the diffu-
sion barriers which prevent exchange of proteins and
protein-bound small molecules will also limit the
effectiveness of functional replacement.
The second set of issues in providing adequately
functioning hepatocytes derives from our expanding
knowledge of the requirement for maintenance and
expression of fully differentiated function. Primary
hepatocytes in the most straightforward con®guration
of tissue cultureÐas a monolayerÐrapidly lose differ-
entiated function. A variety of techniques can maintain
function: co-culture with non-parenchymal cells, cul-
ture as multilayer spheroids and exposure of cells to
extracellular matrix proteins. In essence, maintaining
hepatocytes with normal occupancy of their surface
integrin receptors,91 and normal cell-to-cell contact, is
probably the critical feature for maintaining function.
This can be achieved by, for example, encapsulating
cells in substances such as alginates;92 such techniques
also tend, by producing compact cell masses, to reduce
the volume required to hold 3 ´ 1010 cells and thus
render extra-corporeal circuits practicable. However,
too compact a cell mass imperils transfer of nutrients,
cell products, and, perhaps most importantly, oxygen.
Thus the micro-design of the cell aggregates, and the
macro-design of the bioreactor, are of fundamental
importance.
Bioreactor design
The successful development of the arti®cial liver is
dependent on the hepatocyte component, matrix sup-
port and bioreactor design. Much has been invested in
the design of the `bioreactor', which will allow optimum
cell culture, storage and cell integrity allowing its
practical use in the circuit designed for support.
Three general forms of hepatocyte culture have been
identi®ed: suspension culture, attachment culture and
hepatocyte spheroid culture. Suspension culture is the
least effective method as hepatocytes lose function
rapidly.93 Advantages, however, include low gradients
of nutrients, metabolites, toxins and oxygen, allowing
high transfer ef®ciency.94, 95
Attachment culture has been shown to maintain cell
integrity and function.96 This has been used extensively
in arti®cial liver support systems that use hollow ®bre
ultra®ltration cartridges. These devices rely on trans-
membrane diffusion for exchange of metabolites and
this may lead to reduced ef®ciency.
Hepatocyte spheroid culture allows optimal distribu-
tion of media around hepatocytes, allowing high mass
transfer ef®ciency. This may be reduced when cells have
been encapsulated and/or coated.93, 97, 98
The choice of culture suspension will in¯uence the
design, materials and construction of the bioreactor as
ef®cient attachment and growth will be required. Three
basic designs have emerged; bioreactors for use with
suspension culture, bioreactors based on cell immobili-
zation and those with membranes.
Most bioreactors have used capillary membranes
within a cartridge for cell attachment. Capillary mem-
branes allow a number of other functions to take place
(gas exchange, substrate supply and waste removal)
ef®ciently and with practical ease. Hepatocytes may be
seeded, cultured and grown within capillary mem-
branes and perfused in the extra-capillary space pro-
viding mechanical and physiological protection from
toxic blood or plasma. This approach has been used by
Nyberg et al.99, 100 in the three-compartment gel
entrapment bioreactor. This entraps porcine hepato-
cytes in a collagen matrix inoculated into the capillary
lumen spaces of two 100 kDa molecular mass cut-off
hollow ®bre bioreactors.
An alternative approach is to construct a bioreactor
with hepatocytes in the extra-capillary space with
capillary membranes providing the in-¯ow and out-
¯ow of media, oxygen, nutrients, toxins and waste.
Capillary membrane constructions rely on transmem-
brane diffusion for mass transfer and so choice of
materials is also of paramount importance.
Construction of the three arti®cial liver support devices
that have had clinical exposure will be reviewed:
Sussman's Extra-corporeal Liver Assist Device (ELAD),
Demetriou's Bioarti®cial Liver (BAL) and Gerlach's
hybrid liver support system.
ELAD, developed by Sussman et al.101 in 1992, incor-
porates the C3A cell line. This is a highly differentiated
clonal population isolated from a human hepatoblas-
toma cell line, HepG2. Two hundred grams of cells were
originally seeded and grown in the extra-capillary space
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1263
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
of a haemodialysis cartridge containing » 10 000 hollow
®bres with a surface area of 2 m2. Two to four weeks is
required for adequate numbers of cells to have grown for
clinical use. They may then be stored and studies have
shown good function (glucose, albumin secretion) after
8 months. The intra-capillary space is used in the growth
period for culture medium and oxygen supply and later in
clinical use this space is used for perfusion of blood.
Diffusion gradients and mass transfer is felt to be ef®cient
as ®bres are approximately four cells apart, allowing
adequate oxygenation and waste removal. The mem-
brane has a molecular weight cut-off of 70 000 kDa,
protecting hepatocytes from ¯ow trauma, white cells and
immunoglobulins, but allowing middle molecules and
ammonia to pass across the membrane.
Recent modi®cations include two main design chan-
ges, i.e. increased cell numbers used per cartridge
(700 g) and adaptation of the circuit so that it can be
perfused with plasma and not blood (1999).
The BAL system, developed by Demetriou and
co-workers, is conceptually very similar to ELAD but
originally had three major differences: the cell source,
i.e. primary pig hepatocytes rather than a human
tumour derived cell line; the perfusate, which is plasma
rather than blood; and the presence of a charcoal
column ®ltering the plasma prior to its entry to the
bioreactor.102, 103
Hepatocytes are isolated from pigs and attached to
collagen-coated dextran microcarriers. More recently
cryopreserved cells have been used. The hollow ®bre
bioreactor consists of a polycarbonate cylinder contain-
ing cellulose nitrate/cellulose acetate porous ®bres.
Fibres have a pore size of 0.2 lm and a total internal
surface area of about 6000 cm2. The total extra-
capillary surface area is 7000 cm2.
The BAL system comprises a plasma separator, gener-
ating plasma (80±105 mL/min) from venous blood and
passing this to the charcoal column. The plasma is then
directed across the bioreactor at high ¯ow rates (220±
500 mL/min) which allows several passes before it is
passed back to the individual.
Gerlach et al.97, 98, 104 described a more sophisticated
hybrid liver support system. The structure is housed in a
polyurethane PUR 725 case. The bioreactor is made up
of several interwoven, independent polyurethane capil-
lary systems, entering and leaving the bioreactor in four
discrete bundles and each serving a different function.
The four capillary bundles provide plasma in-¯ow,
oxygen supply and carbon dioxide removal, plasma
out-¯ow, and sinusoidal endothelial co-culture. Hepa-
tocytes (pig hepatocytes) are seeded in the extra-
capillary space and ®nd all types of bundles locally,
thus reducing transmembrane diffusion gradients. The
design can be adapted by the addition of further
bundles, allowing additional functions to be incorpo-
rated. The design is such that many identical capillary
units supply only a few hepatocytes, thus allowing small
diffusion gradients.
Trials
Both ELAD and BAL have been trialled extensively
in vitro, in vivo animal work and also in clinical trials.
(Table 3 illustrates the clinical trials.)
ELAD. Kelly et al.105 performed the ®rst in vivo trials in
1992. Six male beagles had portacaval shunts inserted
and then underwent a total hepatectomy. Dogs were
kept sedated and were given sodium bicarbonate and
glucose maintenance infusions to avoid hypoglycaemia.
ELAD was perfused by vascular access via the internal
carotid artery and the external jugular vein. Blood was
driven through ELAD solely by arterial pressure and
maintained at a ¯ow rate of 80±100 mL/min. The
circuit was heparinized to avoid clot formation. Of the
six beagles, three control dogs lived for 3±5 h after
surgery but did not awake from the anaesthesia. Two of
the three hepatectomized dogs also died within 3±5 h of
surgery but some did require extra sedation. The third
hepatectomized dog survived 125 h post-surgery. Plas-
ma ammonia levels were seen to increase following
surgery in control animals, and this was felt to be a pre-
terminal event. This was not seen in the ELAD-treated
dogs.
Further work was carried out on an improved model of
AHF using intravenously administered acetaminop-
hen.106 Control animals developed AHF with worsening
encephalopathy, hypoglycaemia, prolonged prothrom-
bin time and severe transaminitis. Death occurred in
all controls at 15±30 h. Dogs treated with ELAD for
42±48 h had a survival rate of 80%.
Technical modi®cations were made before the system
underwent trials in man. These included a switch to a
venous±venous circuit and also an increase in ¯ow rate
that allowed the formation of an ultra®ltrate, which
would then bathe the cells within the extra-capillary
space. Filters were inserted to stop any cell debris
entering the patient's circulation, as some concern was
1264 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
raised over the use of a hepatoblastoma cell line
metastasizing in the patient.
Initial trials between 1991 and 1993107±109 were
carried out in four centres and 11 AHF patients were
treated with ELAD. All patients were in grade III/IV
encephalopathy, nine of whom required mechanical
ventilation. One patient had been made anhepatic
following primary graft failure. The age range was
9±63 years old and treatment times ranged between 9 h
and 144 h. Encephalopathy improved in eight out of 11
patients and renal function was preserved in those who
were not anuric at the start of treatment. Improvement
in the galactose elimination capacity was demonstrated.
Of the 11, six patients died, four received liver trans-
plantation and one survived without transplantation.
Following the initial studies, a controlled clinical trial
containing 24 patients in two risk-strati®ed groups was
initiated. Groups I and II had predicted survivals of 50%
and less than 10%, respectively. Patients were then
randomly allocated intensive care only or intensive care
and ELAD treatment within each group. Patients were
treated for a mean period of 72 h (3±168 h). Results
showed improved galactose elimination time, and
encephalopathy, but no survival changes; Group I had
78% survival compared with 75% in the control group;
group II also showed no difference, with 33% survival
compared to 25% in controls.110
BAL. Rozga et al. reported the use of BAL in the
treatment of an animal model of AHF. Dogs were
ventilated, had portacaval shunts inserted and then
hepatic and gastroduodenal arteries were occluded.
They were divided into three groups. Group 1, the
control, received treatment with BAL containing no
cells. Group 2 received BAL containing dog hepatocytes
and group 3 received BAL with pig hepatocytes. Within
5 h of devascularization all animals in the control group
demonstrated increases in lactate, transaminases, lac-
tate dehydrogenase and a signi®cant decrease was seen
in the blood glucose, pH and mean arterial blood
pressure as compared to the BAL/hepatocyte treated
animals.102
This study demonstrated that there was no signi®cant
difference in the use of allogeneic or xenogeneic cells
Table 3. Hybrid hepatic support in man
Hybrid hepatic support Bioreactor Subjects Parameters Outcome
BAL (Uncontrolled trials)
Chen et al.113 Plasma perfused
cryopreserved pig
hepatocytes (6 ´ 109) attached
to dextran-coated microcarrier
beads packed into
extracapillary space of a
hollow ®bre bioreactor
Group 1: 12 patients
(AHF)
Group 2: 8 patients
(chronics)
Improved ICP, CPP
Improved NH3, bilirubin
and glucose
12 patients to OLT
6/8 died
Watanabe et al.114 Group 1: 18 patients
(AHF)
Improved ICP, CPP 16/18 to OLT
Group 2: 3 patients
(Primary graft
non-function)
Improved NH3, bilirubin
and glucose
3 patients to OLT
Group 3: 10 patients
(chronics)
2 patients to OLT
ELAD (Pilot controlled
trial)
Survival
Group 1: 50% chance
of survival on
admission Blood perfused.
Group 1: ELAD 9
patients, control
5 patients
1 patient decreased ICP
Galactose elimination
after the ®rst 6 h was
8/9 patients (89%)
4/5 patients (80%)
Ellis et al.110 200g of C3A
hepatoblastoma cells
no different between
groups, as was NH3,
Group 2: met criteria for
OLT on admission
in attachment culture
on outer surface of
hollow ®bre membranes
Group 2: ELAD
3 patients, control
3 patients
factor V levels and
arterial ketone
body ratios
1/3 patients (33%)
1/3 patients (33%)
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1265
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
within the BAL bioreactor. However, only single
treatments lasting 4±6 h were performed and the effect
of xenogeneic hepatocytes might have become more
apparent upon subsequent use. BAL and charcoal
perfusion were compared in a canine model of hepatic
ischaemia in 1993. Group 1 (n � 7) was treated with
BAL; group 2 was plasmapheresed and treated via a
charcoal column only. After 6 h group 1 had signi®-
cantly lower blood ammonia and normalized prothrom-
bin times. Blood glucose was also signi®cantly higher in
group 1 than in group 2.103
BAL was soon clinically applied and an early case
report demonstrated signi®cant improvements in hae-
modynamic stability, increased presence of clotting
factors, reduction in serum ammonia levels and also
improved mental state following a single period of BAL
treatment lasting 6 h in a patient with severe decom-
pensated alcoholic liver disease.111 This demonstrated
that BAL could be used safely in man and in 1993, 10
patients were treated with BAL for AHF. Eight patients
showed improvement in ICP, CPP, transaminases,
ammonia levels and clinical encephalopathic state
leading to OLT.112
In 1996 Chen et al.113 examined the effect of BAL on
two groups of patients. Group 1 consisted of 12 patients
with AHF all of whom were bridged to OLT. Biochemical
parameters, blood glucose, ammonia and bilirubin
improved signi®cantly in this group, as did ICP and
CPP. Group 2 contained eight patients with acute
decompensation of chronic liver disease of whom six
patients died.
Watanabe et al.114 presented similar ®ndings with three
groups of patients treated with BAL: group 1, patients
with AHF (n � 18); group 2, three patients with primary
non-function of transplanted grafts; and group 3, 10
patients with decompensation of chronic liver disease
(not regarded as candidates for OLT). Analysis of the
results revealed signi®cant improvements in bio-
chemical and clinical parameters as seen previously
(Chen et al.113). All but two patients in groups 1 and 2
went on to have OLT. Two surviving patients from group
3 also went forward for OLT at a later date.
A multicentre controlled trial of the use of BAL in AHF
is currently taking place, the results of which are
eagerly awaited.
Limitations. The use of isolated primary cryopreserved
hepatocytes presents some immunological and micro-
biological concerns. Immunological attack will come
from the host, by both cellular and humoral mecha-
nisms. Naturally occurring antibodies will attack the pig
cells. The synthesis of foreign plasma proteins, coagu-
lation factors and transport factors by the pig hepato-
cytes have signi®cant immunological effects on the host,
including antibody formation. Patients have been
shown to develop type III hypersensitivity (serum
sickness). Coagulation factors produced by the pig
hepatocytes used in the BAL have been shown to cause
immune complex deposition in animal and human
studies and may contribute to end organ dysfunc-
tion.115 Some investigators have avoided this problem
by manipulating cell lines and abrogating protein
production.116, 117
The use of xenogeneic material also raises the possibility
of the transfer of viral or prion disease to the host. Recent
reports of pig endogenous retrovirus (PERV) infections
in man led to concern over the use of pig hepatocytes in
bioarti®cial support systems. Retrospective studies of
patients treated with BAL have shown no evidence
of PERV DNA in blood samples. Similar results have been
found in patients who have received other forms of
porcine tissue (pancreatic islets and heart valves).118±120
However, the long-term aetiology of viral or prion
transfer in immuno-compromised patients is still an area
that is unclear and highly controversial.
HEPATOCYTE TRANSPLANTATION
Injection of hepatocytes into an individual with AHF
has the potential to replace detoxifying and synthetic
function, provided cells access blood or tissue ¯uid in
equilibrium with plasma. Sutherland et al.121 in 1977
demonstrated improved survival following transplanta-
tion of 1.5±2.0 g hepatocytes intra-portally or intra-
peritoneally after dimethylnitrosamine toxicity in rats as
compared to controls. Sommer et al.122 used D-galactos-
amine in rats as the AHF model and showed similar
survival. However, the bene®ts of transplantation could
also be obtained by injection of irradiated hepatocytes,
hepatocyte supernatants and homogenates, suggesting
that substances other than the hepatocyte itself may be
eliciting bene®cial effects.
Surgical models of AHF (90% hepatectomy) in animals
were also used to demonstrate improved survival.123, 124
As with previous experiments, improved survival was
evident if transplantation was carried out prior to or at
the same time as the original insult. Advances in
biotechnology have led to the concept of encapsulation
1266 T. M. RAHMAN & H. J. F. HODGSON
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
of hepatocytes. This protects the hepatocytes by reducing
immunogenicity, mechanical trauma and also allows
three-dimensional structures to develop within the semi-
permeable capsules.125 Improved results are also found if
the hepatocytes are co-cultured and transplanted with
non-parenchymal cells. These developments may en-
hance cell-to-cell interactions, improve cell viability and
may reduce the incidence of host rejection.
The clinical use of hepatocyte transplantation has been
limited due to the dif®culty of providing adequate and as
yet unknown quantities of hepatocytes. These trans-
planted cells are required to function optimally in a toxic
environment. Both Mito and Kusano126, 127 demon-
strated little bene®t from intrasplenic transplantation of
hepatocytes isolated from nine chronic hepatitics and
cirrhotics (their own left lateral segments). Habibullah
et al.128 delivered 60 ´ 106 cells/kg body weight of
human foetal hepatocytes (isolated from 2 to 34 week
gestational foetuses) intra-peritoneally into seven AHF
patients. Overall survival was 43% compared with 33%
in matched controls. Further small studies have been
reported. Soriano et al.129 reported three children in
AHF who were treated with intra-portal injection of
cryopreserved hepatocytes taken from unused donor
segments. One out of three children survived and some
biochemical parameters improved post-transplantation.
Bilir et al.130 showed improved encephalopathy, serum
ammonia levels and prothrombin times, following
percutaneous cryopreserved human hepatocyte trans-
plantation in three patients with AHF. Strom et al.131
performed a prospective controlled trial of transplanted
isolated fresh and cryopreserved human hepatocytes as
a bridge to transplantation. Five hepatocyte transplant
recipients with grade IV encephalopathy and multi-
organ failure and four patients of equal illness severity
with AHF were studied. Medical treatment resulted in
signi®cant improvements in the biochemical markers of
AHF, including blood ammonia. No improvement was
seen in haemodynamic stability or cerebral stability and
all died within 3 days. Those receiving hepatocyte
transplants maintained normal cerebral perfusion and
haemodynamic stability with signi®cant reductions in
blood ammonia and liver injury markers. All were
transplanted within 2±10 days.
This area requires further re®nement and investigation
to demonstrate de®nite clinical impact. Overall, it seems
challenging to develop techniques for acute failure, if
the estimate of » 3 ´ 1010 fully functioning hepatocytes
are required is correct, due to the dif®culties of
establishing the conditions for effective function imme-
diately. On the other hand the technique may be of
greater potential in chronic disease, and can also be
modi®ed for gene transfer.
CONCLUSION
The clinical sequelae of AHF re¯ect the multi-faceted
dysfunction that takes place once the liver fails.
Recognition of the extreme nature of these problems
has led to the development of specialist centres, which
have been instrumental in reducing the mortality
associated with this devastating syndrome. Treatment
of clinical problems in AHF such as cerebral oedema,
systemic hypotension and renal failure may be tempo-
rarily valuable until either transplantation takes place
or the organ begins to regenerate. Greater understand-
ing of the biochemistry of systemic in¯ammatory
response syndrome, sepsis and AHF have led to
evidence-based treatment of clinical problems. The
complexities of liver function and dysfunction are still
not completely understood and therefore it is naive to
expect arti®cial support systems to correct and/or
replace the synthetic, metabolic and excretory functions
that are associated with a healthy organ.
Currently, arti®cial support systems demonstrate im-
provements in some clinical and biochemical parame-
ters. Effects on survival are still not clear and the results
of multicentre randomized controlled trials are awaited.
The design of such trials poses several problems. AHF is
a rare disease and therefore to recruit the appropriate
number of patients into both the control and active
treatment arms will take some time unless the multi-
centre approach is used. Problems will arise in the
matching of patients within the trial, as the syndrome is
both disparate and varied in its pattern and presenta-
tion. Present treatment for AHF is liver transplantation,
which is well established with low morbidity and
mortality. Following patient recruitment, it would be
unethical to deny or delay transplantation if available.
This may result in signi®cant loss of numbers. The
varying aetiology of AHF has a great in¯uence on
patient survival. Therefore groups will have to be
subdivided according to aetiology and controlled studies
will have to examine the differences within each group.
Separate studies will have to take place to look at the
decompensated chronic liver disease group. These
patients may also have to be studied according to the
aetiology of their disease.
REVIEW: SUPPORT SYSTEMS IN LIVER FAILURE 1267
Ó 1999 Blackwell Science Ltd, Aliment Pharmacol Ther 13, 1255±1272
The nature of international multicentre trials raises
issues such as the fact that AHF classi®cation differs
between countries, as does the incidence, epidemiology
and treatment of different aetiologies. Intensive care
units and specialist centres have differences in medical
and nursing standards as well as marked differences in
management of the critically ill. Evidence exists that
genotypic variation amongst patients may introduce
degrees of susceptibility to the immune and physiological
response seen in AHF and sepsis. This may have an as
yet unexplained effect on individual patient survival.132
It is clear that precise end-points are required for such
a trial. Design of a multicentre controlled trial will be a
dif®cult task, the results will take time to accrue and
must in the ®rst instance be carefully interpreted.
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