Preface - Ous-research.no

Cell Transplantation
have been treated with hepatocyte transplantation.
In principle, the procedures for islet isolation, culture and
transplantation may also be applied for hepatocytes. The liver
tissue is digested with a two-step collagenase perfusion,
followed by continuous-density Ficoll gradient purification
in a refrigerated COBE 2991 centrifuge. Hepatocyte preparations
are maintained in culture medium supplemented
with ABO-identical serum. Data confirm that isolation of
hepatocytes from the liver tissue is easier to perform than
islet isolation and the isolation technique produces large
quantities of viable hepatocytes. Thus, islet isolation facilities
can be used also for hepatocyte isolation.
Routes of hepatocyte transplantation
As in islet transplantation, hepatocytes may be transplanted
into the liver via the portal vein and it has been demonstrated
that hepatocytes then translocate from the portal
pedicle into the space of Disse by disrupting the sinusoidal
endothelium and then join with adjacent host hepatocytes.
Hepatocytes are regularly well engrafted in the liver (better
than islets). Other potential implantation sites are striated
musculature, peritoneal cavity, mesenteric leaves, the
spleen, lung parenchyma, under the kidney capsule, and in
the subcutaneous space.
Therapeutic hepatocyte mass
Hepatocytes occupy almost 80% of the total liver volume.
The cell mass required to restore adequate liver function
in a patient is dependent on the underlying disease. The
cell mass needed to correct a single enzymatic defect e.g.
familial hypercholesterolemia, is significantly less than for
treatment of either acute or chronic liver failure. Thus, it has
been suggested that 1- 5% of normal liver mass may be
sufficient to restore adequate function of a single enzymatic
liver defect, while a considerably larger hepatocyte mass is
required for the treatment end stage liver failure. 10% of the
liver mass (150 g) can be transplanted safely as hepatocytes
via the intraportal route into the diseased liver. Since both
fulminant and chronic liver failure require replacement of
more than 10% of functional hepatocytes into the liver,
additional ectopic sites such as the peritoneal cavity or
musculature, may provide alternative sites for hepatocyte
implantation. To correct enzymatic defects or to bridge a
patient to Ltx or liver recovery 10 % functional hepatocytes
from a normal liver may sufficient.
An important distinction from islets is that there exists a
wide range of endogenous hepatic growth stimulators
which increase the mitotic activity of transplanted hepatocytes
and thus increases total hepatic mass. Several growth
factors such as insulin and hepatocyte growth factor (HGF)
can be injected and thereby could speed up the mitotic
activity further. Interestingly, it has been shown that low
molecular weight dextran sulfate (LMW-DS), a newly developed
drug (within the Nordic Network for Islet Transplantation)
used to counteract islet-blood interactions in clinical
islet transplantation, induces a100-fold increase in the
patient’s level of HGF. Interaction between foreign material
and blood is a universal reaction following infusion, thus
the inflammatory response elicited by hepatocyte-blood
interactions may probably be diminished by LMW-DS, as it
does in islet transplantation. Thus, the potential of LMW-DS
in hepatocyte transplantation is promising. These hypotheses
need further investigation.
Sources of hepatocytes
A limiting factor of clinical hepatocyte transplantation is
shortage of mature functioning human hepatocytes, which
currently are obtained from livers rejected for Ltx. The most
common cause for rejecting a donor liver for Ltx is excessive
steatosis. Other potential sources of hepatocytes are
part of livers after reduced sized Ltx, fetal livers and livers
from patients transplanted for other causes than disordered
hepatocytes such as polycystic livers and livers explanted
due to hemangiomas. An other important source of hepatocytes
could be livers from PSC patients (without cirrhosis)
transplanted due to risk of developing malignancy in the
liver. PSC is the most common cause of Ltx in Scandinavia,
comprising more than 20% of all Ltxs. The suitability of such
livers for hepatocyte transplantation should be explored,
and if suitable, a significant number of livers will be available
for hepatocyte transplantation in the Nordic countries.
Furthermore, hepatocytes derived from bone marrow stem
cells, immortalized hepatocyte cell lines and xenogenic
hepatocytes should be investigated further.
Banking of hepatocytes
The most important indications for hepatocyte transplantation
beyond enzymatic defects in children, are acute fulminant
hepatic failure and liver failure following too extensive
liver resections in patients with liver malignancy. In these
acute situations, stored hepatocytes should be available.
Therefore, in order to achieve this goal, a functional freezing
protocol needs to be developed for maintenance of hepatocyte
viability and metabolic capacity for a long period of
time. In this aspect several cryopreservation techniques are
developed but need further refinement.
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