This invention was made with U.S. Government support under
Grant #HD-31425 awarded by the National Institute of Health. The U. S. Government
has certain rights in the invention.
Field of the Invention
The present invention relates to a tissue graft composition
and methods for its preparation and use. More particularly, the present invention
is directed to non-immunogenic tissue graft compositions comprising the basement
membrane of liver and the use of same to promote endogenous tissue growth
in vivo and to support the growth and differentiation of eukaryotic cells
cultured in vitro.
Background and Summary of the Invention
There has been much research effort directed to finding
natural and synthetic materials having the requisite properties for use as tissue
grafts. Surprisingly, it has been found that basement membranes (stroma) prepared
from liver tissue of warm-blooded vertebrates by removing cellular components of
the liver tissue exhibit certain mechanical and biotropic properties similar to
that which has been reported for intestinal submucosal tissue in U.S. Patents 4,902,508;
5,281,422; and 5,275,826. It can be substituted for intestinal submucosa tissue
in most, if not all, of the applications previously reported for intestinal submucosa,
including enhancing wound healing, promoting endogenous tissue growth, stimulating
cell proliferation and inducing cell differentiation.
The basement membrane of the liver is an extracellular
matrix distinct from submucosal extracellular matrices. The liver basement membrane
does not support an overlaying mucosa and is devoid of the laminate tissue structure
in which submucosal extracellular matrices reside. The liver plays a central role
in numerous regulatory processes in the body, including glucose metabolism, insulin
regulation, anabolic processes for the musco-skeletal system and central nervous
system, and the maintenance of appropriate levels of circulating proteins essential
for day to day homeostasis.
B. Saad et al, in vitro cellular & developmental biology,
vol 2917, no 1, January 1993 and
B. Saad et al, European Journal of Biochemistry, vol 213, no 2, April 1993,
both citations teach the preparation of crude membrane fractions for use as a substrate
for the in vitro culture of rat hepatocytes. These crude liver membrane fractions
constitute a cellular membrane fraction.
In one embodiment of the present invention, liver basement
membranes are used to manufacture a non-immunogenic tissue graft composition for
use in the repair of damaged or diseased tissues. The tissue graft composition of
the present invention comprises the basement membrane of organ tissue of a warm-blooded
vertebrate, for example, liver tissue, substantially free, preferably devoid, of
all cells (e.g., hepatocytes and bile ductal cells) of said warm-blooded
vertebrate. The present tissue graft composition can be implanted, or fluidized
and injected, into a vertebrate host to contact damaged or defective tissues and
induce the repair or replacement of said tissues. The compositions of the present
invention can also be applied as a component of a wound dressing (ointment or bandage)
in fluidized or solid form for topical application to promote wound heating. Alternatively,
the liver tissue derived extracellular matrix can be utilized as a cell growth substrate
for growing eukaryotic cells in vitro.
Detailed Description of the Invention
The tissue graft composition of the present invention comprises
liver basement membrane prepared by separating same from the natively associated
cellular components of liver tissue of a warm-blooded vertebrate. The preparative
techniques described below provide an extracellular matrix composition consisting
essentially of liver basement membrane substantially free of any cellular components.
These compositions are referred to herein generically as liver basement membrane(s)
(LBM). Other organ tissue sources of basement membrane for use in accordance with
this invention include spleen, lymph nodes, salivary glands, prostate, pancreas
and other secreting glands.
Basement membrane for use in the graft composition of this
invention is typically prepared from liver tissue harvested from animals raised
for meat production, including, for example, pigs, cattle and sheep or other warm-blooded
vertebrates. Thus, there is an inexpensive commercial source of liver tissue for
use in preparation of the tissue graft compositions in accordance with the present
invention. In accordance with one embodiment, a composition comprising liver basement
membranes is prepared from liver tissue of a warm-blooded vertebrate. This composition
is useful as a non-immunogenic tissue graft capable of inducing endogenous tissue
growth when implanted in warm-blooded vertebrates. In one embodiment, the composition
comprises an extracellular matrix consisting essentially of liver basement membrane
devoid of endogenous cells associated with the source vertebrate liver tissue used
to prepared the composition.
The preparation of liver basement membrane from of liver
tissue of a warm-blooded vertebrate in accordance with the present invention is
carried out by removing the cellular components from liver tissue. Ideally the process
is carried out to separate the cells from the basement membranes without damaging,
or at least minimizing disruption or damage to, the basement membrane tissue. Removal
of the cellular components from the liver extracellular matrix allows the preparation
of a graft composition that is non-immunogenic, and thus does not induce a host
immune response when the graft composition is implanted into a host. In general,
the method for preparing a tissue graft composition from warm-blooded vertebrate
liver tissue comprising the steps of treating the liver tissue with a cell dissociation
solution for a period of time sufficient to release the cellular components of the
liver tissue from the extracellular components without substantial disruption of
the extracellular.components, and separating the cellular components from said extracellular
components. Typically the cell dissociation solution comprises a chaotropic agent
or an enzyme or both.
The first step in preparing LBM in accordance to one embodiment
of the present invention comprises slicing a segment of liver tissue into pieces
(e.g., strips or sheets) to increase the surface area-to-volume ratio of
the liver tissue. In one embodiment the liver tissue is sliced into a series of
sheets each having a thickness of about 50 to about 500 microns, more preferably
about 250 to about 300 microns. Freshly harvested liver tissue can be sliced using
a standard meat slicer, or the tissue can be frozen and sliced with a cryomicrotone.
The thin pieces of liver tissue are then treated with a solution that releases component
liver cells from the associated extracellular basement membrane matrix.
In accordance with one embodiment the liver tissue is treated
with a solution comprising an enzyme, for example, a protease, such as trypsin or
pepsin. Because of the collagenous structure of the liver basement membrane and
the desire to minimize degradation of the membrane structure during cell dissociation,
collagen specific enzyme activity should be minimized in the enzyme solutions used
in the cell-dissociation step. In addition, the liver tissue is typically also treated
with a calcium chelating agent or chaotropic agent such as a mild detergent such
as Triton 100. Thus, in one embodiment of this invention liver tissue is treated
by suspending slices or strips of the tissue in a cell-dissociation solution containing
enzyme(s) and chaotropic agent(s). However, the cell dissociation step can also
be conducted using a calcium chelating agent or chaotropic agent in the absence
of an enzymatic treatment of the tissue.
In one preferred embodiment the cell-dissociation step
is carried out by suspending liver tissue slices in an agitated solution containing
about 0.05 to about 2%, more typically about 0.1 to about 1% by weight protease,
optionally containing a chaotropic agent or a calcium chelating agent in an amount
effective to optimize release and separation of cells from the basement membrane
without substantial degradation of the membrane matrix.
After contacting the liver tissue with the cell-dissociation
solution for a time sufficient to release all cells from the matrix, the resulting
liver basement membrane is rinsed one or more times with saline and optionally stored
in a frozen hydrated state or a partially dehydrated state until used as described
below. The cell-dissociation step may require several treatments with the cell-dissociation
solution to release substantially all cells from the basement membrane. In one embodiment
liver tissue is treated with a protease solution to remove the component cells,
and the resulting extracellular matrix material (basement membrane) is further treated
to remove or inhibit any residual enzyme activity. For example, the resulting basement
membrane can be heated or treated with one or more protease inhibitors.
Liver basement membrane in accordance with this invention
can be fluidized (converted to an injectable or powder form) in a manner similar
to the preparation of fluidized intestinal submucosa, as described in U.S. Patent
No. 5,275,826 the disclosure of which is expressly incorporated herein by reference.
Liver basement membrane (devoid of cells from the source liver tissue) is comminuted
by tearing, cutting, grinding, shearing and the like. Grinding the liver basement
membrane in a frozen or freeze-dried state is preferred although good results can
be obtained as well by subjecting a suspension of liver basement membrane to treatment
in a high speed (high shear) blender and dewatering, if necessary, by centrifuging
and decanting excess water. Additionally, the comminuted fluidized tissue can be
solubilized by enzymatic digestion with a protease, for example a collagenase and
or other appropriate enzyme, such as glycanase, or other enzyme that disrupts the
matrix structural components, for a period of time sufficient to solubilize said
tissue and form a substantially homogeneous solution.
The present invention also contemplates the use of powder
forms of liver basement membrane. In one embodiment a powder form of liver basement
membrane is prepared by pulverizing liver basement membrane submucosa tissue under
liquid nitrogen to produce particles ranging in size from 0.1 to 1 mm2.
The particulate composition is then lyophilized overnight and sterilized to form
a solid substantially anhydrous particulate composite. Alternatively, a powder form
of liver basement membrane can be formed from fluidized liver basement membranes
by drying the suspensions or solutions of comminuted/liver basement membrane. The
dehydrated forms have been rehydrated and used as cell culture substrates as described
below without any apparent loss of their ability to support cell growth.
To determine the components of the isolated liver basement
membranes of the present invention, the membranes have been extracted and the isolated
fractions analyzed by Western blot analysis. LBM was extracted with guanidine hydrochloride
or urea, as described in Example 4 and Western blot analysis, using antibodies directed
against various specific growth factors, indicated the presence of basic growth
fibroblast growth factor (bFGF), hepatocyte growth factor (HGF) and epidermal growth
The present liver basement membrane compositions may be
sterilized using conventional sterilization techniques including tanning with glutaraldehyde,
formaldehyde tanning at acidic pH, ethylene oxide treatment, propylene oxide treatment,
gas plasma sterilization, gamma radiation, and peracetic acid sterilization. A sterilization
technique which does not significantly weaken the mechanical strength and biotropic
properties of the material is preferably used. For instance, it is believed that
strong gamma radiation may cause loss of strength in the graft material. Preferred
sterilization techniques include exposing the graft to peracetic acid, low dose
gamma irradiation and gas plasma sterilization; peracetic acid sterilization being
the most preferred method. In particular, LBM has been disinfected and sterilized
through the use of either peracetic acid or one megarad of gamma irradiation without
adversely effecting the mechanical properties or biological properties of the tissue.
The treatment with peracetic acid is conducted at a pH of about 2 to about 5 in
an aqueous ethanolic solution (2-10% ethanol by volume) at a peracid concentration
of about 0.03 to about 0.5% by volume. Typically, after the graft composition has
been sterilized, the composition is wrapped in a porous plastic wrap and sterilized
again using electron beam or gamma irradiation sterilization techniques.
In accordance with one embodiment, liver basement membrane
is used as, or used to prepare, tissue graft compositions of the present invention.
Such tissue graft compositions lend themselves to a wide variety of surgical applications
relating to the repair or replacement of damaged tissues, including, for example
the repair of connective tissues. Connective tissues for the purposes of the present
invention includes bone, cartilage, muscle, tendons, ligaments, and fibrous tissue
including the dermal layer of skin.
In accordance with this invention, the present tissue graft
compositions are used advantageously to induce the formation of endogenous tissue
at a desired site in a warm blooded vertebrate. Compositions comprising an extracellular
matrix, consisting essentially of liver basement membrane, can be administered to
a vertebrate host in an amount effective to induce endogenous tissue growth at a
site in the host in need of same due to the presence of damaged or diseased tissue.
The present liver tissue derived tissue graft compositions can be administered to
the host in either solid form, by surgical implantation, or in fluidized form, by
The liver basement membrane segments can be used in accordance
with this invention as a tissue graft construct for use in the repair or replacement
of connective tissues using the same procedures described for use of intestinal
submucosa in U.S. Patent Nos. 5,281,422 and 5,352,463, each expressly incorporated
herein by reference.
The tissue graft compositions formed and used in accordance
with this invention, upon implantation, undergo biological remodeling. They serve
as a rapidly vascularized matrix for supporting the growth of new endogenous connective
tissue. When used as a tissue graft material liver basement membrane is expected
to be trophic for host tissues with which it is attached or otherwise associated
in its implanted environment.
The liver basement membrane graft composition can be formed
in a variety of shapes and configurations, for example, to serve as a ligament or
tendon replacement or a patch for a broken or severed tendon or ligament. Preferably,
the segment is shaped and formed to have a layered or even a multilayered configuration
with at least the opposite end portions and/or opposite lateral portions being formed
to have multiple layers of the graft material to provide reinforcement for attachment
to physiological structures, including bone, tendon, ligament, cartilage and muscle.
In a ligament replacement application, opposite ends are attached using standard
surgical technique to first and second bones, respectively, the bones typically
being articulated as in the case of a knee joint.
The end portions of the liver basement membrane graft composition
can be formed, manipulated or shaped to be attached, for example, to a bone structure
in a manner that will reduce the possibility of graft tearing at the point of attachment.
Preferably the material can be folded or to provide multiple layers for gripping,
for example, with spiked washers or staples.
Alternatively, the liver basement membrane graft material
may be folded back on itself to join the end portions to provide a first connective
portion to be attached, for example, to a first bone and a bend in the intermediate
portion to provide a second connective portion to be attached to a second bone articulated
with respect to the first bone. For example, one of the end portions may be adapted
to be pulled through a tunnel in, for example, the femur and attached thereto, while
the other of the end portions may be adapted to be pulled through a tunnel in the
tibia and attached thereto to provide a substitute for the natural cruciate ligament,
the segment being adapted to be placed under tension between the tunnels to provide
a ligament function, i.e., a tensioning and positioning function provided
by a normal ligament.
The liver basement membranes of the present invention have
been implanted in rabbits and in dogs to serve as Achilles tendon replacement graft
constructs. Two rabbits and two dogs were each implanted with Achilles tendon replacement
LBM graft constructs using a similar procedure as used for intestinal submucosal
tissue as describe in U.S. Patent No. 4,902,508. The experiments demonstrated that
LBM graft constructs could support the regeneration of the Achilles tendon.
During preparation of the liver basement membrane, the
tissue is cut or sliced into pieces/slices. After the cell-dissociation processing
step the individual segments of liver basement membrane can be overlapped with one
another and bonded together using standard techniques known to those skilled in
the art, including the use of sutures, crosslinking agents, and adhesives or pastes.
Alternatively, in one embodiment, the overlapped layers of submucosal tissue are
fused to one another by applying pressure to the overlapped regions under dehydrating
conditions. The term "dehydrating conditions" is defined to include any mechanical
or environmental condition which promotes or induces the removal of water from the
submucosal tissue. To promote dehydration of the compressed submucosal tissue, at
least one of the two surfaces compressing the tissue is water permeable. Dehydration
of the tissue can optionally be further enhanced by applying blotting material,
heating the tissue or blowing air across the exterior of the compressing surfaces.
Accordingly, multilayer liver basement membrane constructs can be prepared to provide
tissue graft compositions of enhanced strength.
In addition, by overlapping a portion of one piece of liver
basement membrane with a portion of at least one additional piece of liver basement
membrane and bonding the overlapped layers to one another, large area sheets of
liver basement membrane can be formed. In one embodiment, during formation of the
large area sheets of tissue, pressure is applied to the overlapped portions under
dehydrating conditions by compressing the overlapped tissue segments between two
surfaces. The two surfaces can be formed from a variety of materials and in any
shape depending on the desired form and specification of the targeted graft construct.
Typically the two surfaces are formed as flat plates but they can also include other
shapes such as screens, opposed cylinders or rollers and complementary nonplanar
surfaces. Each of these surfaces can optionally be heated or perforated. In preferred
embodiments at least one of the two surfaces is water permeable. The term water
permeable surface as used herein includes surfaces that are water absorbent, microporous
or macroporous. Macroporous materials include perforated plates or meshes made of
plastic, metal, ceramics or wood.
The liver basement membrane can be compressed in accordance
with one embodiment by placing the overlapped portions of the strips of cell-dissociated
liver membrane on a first surface and placing a second surface on top of the exposed
membrane surface. A force is then applied to bias the two surfaces towards one another,
compressing the membrane composition between the two surfaces. The biasing force
can be generated by any number of methods known to those skilled in the art including
the passage of the apparatus through a pair of pinch rollers (the distance between
the surface of the two rollers being less than the original distance between the
two plates), the application of a weight on the top plate, and the use of a hydraulic
press or the application of atmospheric pressure on the two surfaces.
In one preferred embodiment, a multi-layered liver basement
membrane graft material is prepared without the use of adhesives or chemical pretreatments
by compressing at least the overlapped portions of submucosal tissue under conditions
that allow dehydration of the material concurrent with the compression of the tissue.
To promote dehydration of the compressed material, at least one of the two surfaces
compressing the tissue is water permeable. Dehydration can optionally be further
enhanced by applying blotting material, heating the material or blowing air across
the exterior of the two compressing surfaces. The compressed multi-layered liver
basement membrane material can be removed from the two surfaces as a unitary compliant
large area graft construct. The construct can be further manipulated (i.e., cut,
folded, sutured, etc.) to suit various medical applications where the liver basement
membrane material is required.
A vacuum can optionally be applied to liver basement membrane
during the compression procedure. The applied vacuum enhances the dehydration of
the tissue and may assist the compression of the tissue. Alternatively the application
of a vacuum may provide the sole compressing force for compressing the overlapped
portions of the multiple layers of liver basement membranes. For example, in one
embodiment the overlapped liver basement membrane is laid out between two surfaces,
preferably one of which is water permeable. The apparatus is covered with blotting
material, to soak up water, and a breather blanket to allow air flow. The apparatus
is then placed in a vacuum chamber and a vacuum is applied, generally ranging from
35.6-177.8 cm ofHg (0.49-2.46 Kg/cm2) and more preferably the vacuum
applied is approximately 129.5 cm of Hg (1.76 Kg/cm2). Optionally a heating
blanket can be placed on top of the chamber to heat the liver basement membrane
during compression. Chambers suitable for use in this embodiment are known to those
skilled in the art and include any device that is equipped with a vacuum port. The
resulting drop in atmospheric pressure coacts with the two surfaces to compress
the tissue and simultaneously dehydrate the compressed tissue.
In an alternative embodiment of the present invention,
liver basement membrane can be utilized in a method and composition for supporting
the proliferation and induction of tissue differentiation of eukaryotic cells cultured
in vitro. Generally the method comprises the step of contacting eukaryotic
cells, in vitro, with a liver basement membrane composition under conditions
conducive to eukaryotic cell growth. The term "contacting" as used herein with reference
to cell culture is intended to include both direct and indirect contact, for example
in fluid communication, of the liver basement membrane composition and the cultured
cells. The term "conditions conducive to eukaryotic cell growth" as used herein
refers to the environmental conditions, such as sterile technique, temperature and
nutrient supply, that are considered optimal for eukaryotic cell growth under currently
available cell culture procedures. Although optimum cell culture conditions used
for culturing eukaryotic cells depend somewhat on the particular cell type, cell
growth conditions are generally well known in the art. However a number of differentiated
cell types are still considered difficult to culture (i.e., islets
ofLangerhans, hepatocytes, chondrocytes, osteoblasts, etc.).
Applicants have discovered that compositions comprising
liver basement membrane prepared in accordance with this invention can be used for
supporting growth or proliferation of eukaryotic cells in vitro. In accordance
with one embodiment a liver tissue derived composition for supporting the growth
of a cell population is prepared from liver tissue of a warm-blooded vertebrate.
The composition comprises isolated liver basement membrane devoid of source liver
tissue endogenous cells and added nutrients to support the growth of said cell population
in vitro. In addition fluidized forms of liver basement membrane can be used
to coat culture-ware with a matrix comprising liver basement membrane devoid of
source liver tissue endogenous cells. Thus liver basement membrane can be used as
a cell growth substrate in a variety of forms, including a sheet-like configuration,
as a gel matrix, as an additive for art-recognized cell/tissue culture media, or
as coating for culture-ware to provide a more physiologically relevant substrate
that supports and enhances the proliferation of cells.
The liver basement membrane, due to its honeycomb-like
structure (that which remains after cell-dissociation) provides a high surface area
for cell adhesion and also induces cell differentiation. Scanning electron images
indicate that the isolated liver basement membrane is very porous. When fetal rat
cells are cultured on liver basement membranes that are retained in their nature
three dimensional shape, scanning electron images reveal that the fetal rat cells
form confluent sheets on the liver cell substrate and also invade into the LBM matrix.
The membrane material is preferably sterilized prior to use in cell culture applications,
however nonsterile material can be used if antibiotics are included in the cell
In one preferred embodiment cells are seeded directly onto
sheets of liver basement membrane under conditions conducive to eukaryotic cell
proliferation. The highly porous nature of the liver basement membrane allow diffusion
of cell nutrients throughout the membrane matrix. Thus, cells can be cultured on
or within the liver basement membrane matrix.
In another embodiment of the present invention, cell growth
substrates are formed from fluidized forms of liver basement membrane. The fluidized
tissue can be gelled to form a solid or semi-solid matrix. The viscosity of fluidized
tissue for use in accordance with this invention can be manipulated by controlling
the concentration of the tissue component and the degree of hydration. The viscosity
can be adjusted to a range of about 2 to about 300,000 cps at 25°C. Higher
viscosity formulations, for example, gels, can be prepared from the digest solutions
by adjusting the pH of such solutions to about 6.0 to about 7.4. Eukaryotic or prokaryotic
cells can then be seeded directly on the surface of the matrix and cultured under
conditions conducive to eukaryotic cell proliferation.
The cell growth substrates of the present invention can
be combined with nutrients, including minerals, amino acids, sugars, peptides, proteins,
or glycoproteins that facilitate cellular proliferation, such as laminin and fibronectin
and growth factors such as epidermal growth factor, platelet-derived growth factor,
transforming growth factor beta, or fibroblast growth factor. In one embodiment
fluidized or powder forms of liver basement membrane can be used to supplement standard
eukaryotic culture media to enhance the standard media's capacity for sustaining
and inducing the proliferation of cells cultured in vitro.
In accordance with the present invention there is provided
a cell culture composition for supporting growth in vitro of an eukaryotic
cell population in combination with liver basement membrane of a warm-blooded vertebrate.
The composition comprises liver basement membrane substantially free of the original
associated endogenous cells. The composition can further comprise nutrients, and
growth factors required for optimal growth of the cultured cells. The liver basement
membrane cell culture substrate can be used with commercially available cell culture
liquid media (both serum based and serum free). Proliferating cells can either be
in direct contact with the liver basement membrane or they can simply be in fluid
communication with the liver basement membrane.
It is anticipated that cell growth compositions utilizing
the liver basement membrane composition of the present invention can be used to
stimulate proliferation of undifferentiated stems cells as well as differentiated
cells such as islets of Langerhans, hepatocytes and chondrocytes. Furthermore, the
described cell growth composition is believed to support the growth of differentiated
cells while maintaining the differentiated state of such cells. Several primary
cell lines have been grown on LBM derived cell culture substrates in vitro,
including primary cell lines derived from the cruciate ligament. Primary cell lines
derived from the cruciate ligament show an approximate doubling of the growth rate
compared to when these cells are grown on plastic.
It is anticipated that liver basement membrane is capable
of inducing host tissue proliferation, remodeling and regeneration of appropriate
tissue structures upon implantation in a number of microenvironments in vivo
(e.g., tendon, ligament; bone, articular cartilage, artery, and vein). In one embodiment
of the present invention the tissue replacement capabilities of graft compositions
comprising liver basement membrane of warm-blooded vertebrates are further enhanced
or expanded by seeding the tissue with various cell types, prior to implantation.
For example, a liver basement membrane derived cell culture substrate may be seeded
with endothelial cells or keratinocytes for use as a vascular graft or skin replacement,
respectively. Alternatively, the liver basement membrane can be seeded with mesenchymal
cells (stem cells) initially for expansion of the cell population and thereafter
for implantation into a host. Liver basement membrane can also serve as a delivery
vehicle, either in fluidize form or in its native solid form, for introducing various
cell populations, including genetically modified cells, to a specific location in
a host. Optionally, after the liver basement membrane have been seeded with eukaryotic
cells, the graft composition can be subjected to conditions conducive to the proliferation
of eukaryotic cells to further expand the population of the seeded cells prior to
implantation of the graft into the host.
In another embodiment, compositions comprising liver basement
membrane and a proliferating cell population can be encapsulated in a biocompatible
matrix for implantation into a host. The encapsulating matrix can be configured
to allow the diffusion of nutrients to the encapsulated cells while allowing the
products of the encapsulated cells to diffuse from the encapsulated cells to the
host cells. Suitable biocompatible polymers for encapsulating living cells are known
to those skilled in the art. For example a polylysine/alginate encapsulation process
has been previously described by F. Lim and A. Sun (Science Vol. 210 pp. 908-910).
Indeed, the present liver basement membrane composition itself could be used advantageously
to encapsulate a proliferating cell population in accordance with this invention
for implantation as an artificial organ.
Preparation of Liver Basement Membrane
Preparation of liver slices:
2 mM EDTA Chaotropic Solution Used In The Experiment
Liver frozen in -70°C was sliced with a cryomicrotone
to a thickness of about 50µM. The slices of liver tissue were then subjected
to enzymatic treatment (trypsin) with a chaotropic solution (samples 1 and 2), with
enzyme alone (samples 3 and 4), or with a chaotropic solution alone (sample 5),
as indicated below.
Trypsin in 2mM EDTA solution
Trypsin in 2mM EDTA solution
Trypsin in 2mM PBS
Trypsin in 2mM PBS
Liver slices were placed in five 50ml tubes, each of which
contained 25mL of a different buffered enzyme treatment solution. The liver tissue
was incubated at 37°C in water bath with gentle shaking for 1 hour. The liver
slices were washed twice with PBS with agitation/shaking for 1 hour at room temperature.
The above enzymatic treatment steps were repeated three times.
The wash buffers were collected and spin them down in 2000rpm
for 10 min. The pellet was suspended and an equal amount of trypan blue was added
to identify any remaining cells. The material was checked for presence of cells
Mechanical Properties of Isolated Liver Basement Membrane
Porosity of a graft material is typically measured in terms
of ml of water passed per cm2min-1 at a pressure of 120 mm
Hg. The average "porosity index" established for two separate specimens of LBM was
1162. The suture retention strength of LBM is approximately 68 grams. The material
appears to be anisotropic, with the suture strength being approximately the same
in all directions.
Growth and Differentiation of Various Cell Lines on Liver Basement Membrane
In the present study, the growth and differentiation of
three different cell lines on liver basement membrane (LBM) was investigated. These
tested cell lines included Swiss 3T3, a fibroblast cell line, ROS. 17/2.8, an osteosarcoma
cell line and PC12, a neuronal cell line. All cells were seeded on a collagen coated
plate. The seeding densities for Swiss 3T3 and ROS cells was 20 x 104
cells/ml, whereas the PC12 was seeded at 5 x 104 cells/ml. In order to
compare the growth and differentiation of these cells lines on LBM and small intestinal
submucosa (SIS), the same cells with same densities were also seeded on SIS. In
addition, a positive control for PC12 cells was achieved by adding nerve growth
factor (NGF) 50ng/ml to the cells. All experiments were carried out in duplicate.
After five days one sample from each cell line seeded on SIS and LBM was prepared
Preliminary observations indicate growth of all three cell
lines and differentiation of ROS and PC12 cell lines on both substrates. A light
microscopic observation of PC12 cells indicated a greater degree of differentiation
on LBM compared to the cells grown on SIS. In addition, ROS and 3T3 cells appeared
to grow/differentiate as well as they do on SIS. Due to the transparent nature of
LBM, it was difficult to quantify the growth and differentiation of the cells, but
the histological examination will allow a more detailed assessment.
Preparation of Extracts of LBM
Extraction buffers used for these studies included 4 M
guanidine and 2 M urea each prepared in 50 mM Tris-HCl, pH 7.4. The powder form
of LBM was suspended in the relevant extraction buffer (25% w/v) containing phenylmethyl
sulphonyl fluoride, N-ethylmaleimide, and benzamidine (protease inhibitors) each
at 1 mM and vigorously stirred for 24 hours at 4°C. The extraction mixture
was then centrifuged at 12,000xg for 30 minutes at 4°C and the supernatant
collected. The insoluble material was washed briefly in the extraction buffer, centrifuged,
and the wash combined with the original supernatant. The supernatant was dialyzed
extensively in Spectrapor tubing (MWCO 3500, Spectrum Medical Industries, Los Angeles,
CA) against 30 volumes of deionized water (9 changes over 72 hours). The dialysate
was centrifuged at 12,000xg to remove any insoluble material and the supernatant
was used immediately or lyophilized for long term storage.
Western blot analysis with antibodies specific for bFGF
HGF and EGF detected a corresponding reactive band for each of the antibodies, confirming
the presence of these growth factors in LBM.