The role of extracellular matrix in normal liver

Microscale tissue engineering of liver lobule models: advancements and applications

The liver, as the body's primary organ for maintaining internal balance, is composed of numerous hexagonal liver lobules, each sharing a uniform architectural framework. These liver lobules serve as the basic structural and functional units of the liver, comprised of central veins, hepatic plates, hepatic sinusoids, and minute bile ducts. Meanwhile, within liver lobules, distinct regions of hepatocytes carry out diverse functions. The in vitro construction of liver lobule models, faithfully replicating their structure and function, holds paramount significance for research in liver development and diseases. Presently, two primary technologies for constructing liver lobule models dominate the field: 3D bioprinting and microfluidic techniques. 3D bioprinting enables precise deposition of cells and biomaterials, while microfluidics facilitates targeted transport of cells or other culture materials to specified locations, effectively managing culture media input and output through micro-pump control, enabling dynamic simulations of liver lobules. In this comprehensive review, we provide an overview of the biomaterials, cells, and manufacturing methods employed by recent researchers in constructing liver lobule models. Our aim is to explore strategies and technologies that closely emulate the authentic structure and function of liver lobules, offering invaluable insights for research into liver diseases, drug screening, drug toxicity assessment, and cell replacement therapy.

Whole Liver Derived Acellular Extracellular Matrix for Bioengineering of Liver Constructs: An Updated Review

Biomaterial templates play a critical role in establishing and bioinstructing three-dimensional cellular growth, proliferation and spatial morphogenetic processes that culminate in the development of physiologically relevant in vitro liver models. Various natural and synthetic polymeric biomaterials are currently available to construct biomimetic cell culture environments to investigate hepatic cell-matrix interactions, drug response assessment, toxicity, and disease mechanisms. One specific class of natural biomaterials consists of the decellularized liver extracellular matrix (dECM) derived from xenogeneic or allogeneic sources, which is rich in bioconstituents essential for the ultrastructural stability, function, repair, and regeneration of tissues/organs. Considering the significance of the key design blueprints of organ-specific acellular substrates for physiologically active graft reconstruction, herein we showcased the latest updates in the field of liver decellularization-recellularization technologies. Overall, this review highlights the potential of acellular matrix as a promising biomaterial in light of recent advances in the preparation of liver-specific whole organ scaffolds. The review concludes with a discussion of the challenges and future prospects of liver-specific decellularized materials in the direction of translational research.

Fibrogenic Pathways in Metabolic Dysfunction Associated Fatty Liver Disease (MAFLD)

The prevalence of nonalcoholic fatty liver disease (NAFLD), recently also re-defined as metabolic dysfunction associated fatty liver disease (MAFLD), is rapidly increasing, affecting ~25% of the world population. MALFD/NAFLD represents a spectrum of liver pathologies including the more benign hepatic steatosis and the more advanced non-alcoholic steatohepatitis (NASH). NASH is associated with enhanced risk for liver fibrosis and progression to cirrhosis and hepatocellular carcinoma. Hepatic stellate cells (HSC) activation underlies NASH-related fibrosis. Here, we discuss the profibrogenic pathways, which lead to HSC activation and fibrogenesis, with a particular focus on the intercellular hepatocyte–HSC and macrophage–HSC crosstalk.

Liver scaffolds obtained by decellularization: A transplant perspective in liver bioengineering

Liver transplantation is the only definitive treatment for many diseases that affect this organ, however, its quantity and viability are reduced. The study of liver scaffolds based on an extracellular matrix is a tissue bioengineering strategy with great application in regenerative medicine. Collectively, recent studies suggest that liver scaffold transplantation may assist in reestablishing hepatic function in preclinical diseased animals, which represents a great potential for application as a treatment for patients with liver disease in the future. This review focuses on useful strategies to promote liver scaffold transplantation and the main open questions about this context. We outline the current knowledge about ex vivo bioengineered liver transplantation, including the surgical techniques, recipient survival time, scaffold preparation before transplantation, and liver disease models. We also highlight the current limitations and future directions regarding in vivo bioengineering techniques.

Quantitative Analysis of Tissue Damage Evolution in Porcine Liver With Interrupted Mechanical Testing Under Tension, Compression, and Shear

In this study, the damage evolution of liver tissue was quantified at the microstructural level under tensile, compression, and shear loading conditions using an interrupted mechanical testing method. To capture the internal microstructural changes in response to global deformation, the tissue samples were loaded to different strain levels and chemically fixed to permanently preserve the deformed tissue geometry. Tissue microstructural alterations were analyzed to quantify the accumulated damages, with damage-related parameters such as number density, area fraction, mean area, and mean nearest neighbor distance (NND). All three loading states showed a unique pattern of damage evolution, in which the damages were found to increase in number and size, but decrease in NND as strain level increased. To validate the observed damage features as true tissue microstructural damages, more samples were loaded to the above-mentioned strain levels and then unloaded back to their reference state, followed by fixation. The most major damage-relevant features at higher strain levels remained after the release of the external loading, indicating the occurrence of permanent inelastic deformation. This study provides a foundation for future structure-based constitutive material modeling that can capture and predict the stress-state dependent damage evolution in liver tissue.

Collagen Gel Immobilisation Provides a Suitable Cell Matrix for Long Term Human Hepatocyte Cultures in Hybrid Reactors

An easy to apply culture technique is presented that protects a monolayer configuration of liver cells within an extracellular matrix. The Immobilising Gel (IG)-Technique not only preserves hepatocyte morphology and supports a variety of differentiated cell functions over long term periods, but also offers higher resistance of IG-culture systems against shear forces of fluids in a hybrid reactor device, as compared to other culture techniques. Human hepatocyte cultures in IG-Technique: DNA-normalised levels for the total production of cholinesterase, albumin, urea and lactate remained high throughout the investigational period (50 days). Glutamic-Pyruvic-Transaminase (GPT) release decreased after peak values during early culture adaptation. Electron Microscopic (EM) findings after the shear forces experiment revealed undisturbed subcellular structures and a preserved intercellular morphology, including bile canaliculi and desmosomes. We conclude that the IG-technique is of considerable advantage as compared to other culture systems, especially in the field of dynamic applications, e.g. hybrid reactors for artificial organ development.

Repeated Transplantation of Microencapsulated Hepatocytes for Sustained Correction of Hyperbilirubinemia in Gunn Rats

In previous studies we demonstrated that transplantation of microencapsulated hepatocytes could correct congenital hyperbilirubinemia in Gunn rats for 4 to 6 wks. Reduction in hyperbilirubinemia followed a single transplantation of isolated encapsulated hepatocytes (IEH). After 4 to 6 wks of transplantation IEH gradually lose their functionality. To sustain long-term supplementation of liver function we have investigated the efficacy of monthly IEH transplantations for 6 mo. Hepatocytes, isolated from young Wistar rats, were microencapsulated with a collagen matrix within an alginate-poly L-lysine composite membrane. We transplanted IEH intraperitoneally into homozygous Gunn rats at monthly (4-wk) intervals for 6 mo. Control Gunn rats received intraperitoneal transplantations of empty microcapsules. Total serum bilirubin was measured in the IEH-transplanted and control Gunn rats at weekly intervals for the duration of the 6-month study. A significant (p < 0.01) and sustained decrease (by nearly 50%) in total serum bilirubin levels was observed following monthly IEH transplantations in Gunn rats for the duration of the study. No such decrease in total serum bilirubin levels was seen in the controls. The Gunn rats exhibited good tolerance for the multiple IEH transplantations. Thus, repeated IEH transplantations may be one strategy for providing long-term supplementation of liver function in congenital metabolic liver disease.

Hepatocyte Immobilization on Phema Microcarriers and its Biologically Modified Forms

Polyhydroxyethylmethacrylate (PHEMA) based microcarriers with different bulk structures were prepared by a phase inversion polymerization technique. PHEMA surfaces were further modified chemically by glow-discharge treatment, and biologically by covalent attachment of fibrinogen and collagen. Hepatocytes were isolated from young male Wistar rats using an in situ portal vein collagenase perfusion technique. Freshly isolated hepatocytes were seeded at 6 × 105 cells/mL and microcarrier concentration was 10 g/L. Stationary microcarrier cultures were carried out in standard (nontissue culture) polystyrene petri dishes in a humidified 5% CO2 incubator at 37 ± 0.5°C. Cell attachment was followed by light microscopy by taking samples from the culture medium every 30 min. Urea and protein syntheses by microcarrier-attached hepatocytes were determined by standard techniques. Nonswellable (highly cross-linked) hydrophilic PHEMA microcarriers did not support cell attachment and viability. However, swellable (low cross-linked) PHEMA microcarriers (pretreated in FBS) allowed high attachment and cell spreading. PHEMA microcarriers treated in dimethylaminoethylmethacrylate (DMAEMA) glow-discharge plasma also improved the cell attachment characteristics of the PHEMA microcarriers. The highest attachment efficiencies (immobilization yields) were observed with the biologically modified PHEMA microcarriers, especially modified with fibronectin. Metabolic activity, as estimated by urea and protein syntheses, was also higher in these microcarriers.

Spheroid organization kinetics of H35 rat hepatoma model cell system on elastin-like polypeptide-polyethyleneimine copolymer substrates

Though two-dimensional systems have yielded some success in deriving morphological and functional markers of hepatocyte culture, they largely fail to capture the three-dimensional organization, long-term viability, and functionality of the hepatic tissue. We have engineered a system for inducing self-assembly of model H35 rat hepatoma spheroids using a copolymer comprised of biocompatible elastin-like polypeptide (ELP) chemically conjugated to positively charged polyethyleneimine (PEI). We have achieved a conjugation ratio of 30 mol %, though our studies analyzing spheroid organization kinetics indicate conjugate ratios of 5 mol % and greater to be optimal for cell culture based on least variability in spheroid sizes and minimum incidence of overgrown aggregates. Furthermore, our ELP-PEI system indicated the potential for influencing ultimate spheroid dimensions, with spheroid size inversely related to polyelectrolyte conjugation. Overall, this study provides a good starting point to investigate functional correlations between spheroid size and functional markers and their future use as an in vitro diagnostic or tissue engineering tool.

Organotypic liver culture models: meeting current challenges in toxicity testing

Prediction of chemical-induced hepatotoxicity in humans from in vitro data continues to be a significant challenge for the pharmaceutical and chemical industries. Generally, conventional in vitro hepatic model systems (i.e. 2-D static monocultures of primary or immortalized hepatocytes) are limited by their inability to maintain histotypic and phenotypic characteristics over time in culture, including stable expression of clearance and bioactivation pathways, as well as complex adaptive responses to chemical exposure. These systems are less than ideal for longer-term toxicity evaluations and elucidation of key cellular and molecular events involved in primary and secondary adaptation to chemical exposure, or for identification of important mediators of inflammation, proliferation and apoptosis. Progress in implementing a more effective strategy for in vitro-in vivo extrapolation and human risk assessment depends on significant advances in tissue culture technology and increasing their level of biological complexity. This article describes the current and ongoing need for more relevant, organotypic in vitro surrogate systems of human liver and recent efforts to recreate the multicellular architecture and hemodynamic properties of the liver using novel culture platforms. As these systems become more widely used for chemical and drug toxicity testing, there will be a corresponding need to establish standardized testing conditions, endpoint analyses and acceptance criteria. In the future, a balanced approach between sample throughput and biological relevance should provide better in vitro tools that are complementary with animal testing and assist in conducting more predictive human risk assessment.

Curcumin protects against thioacetamide-induced hepatic fibrosis by attenuating the inflammatory response and inducing apoptosis of damaged hepatocytes

Inflammation and hepatic stellate cell (HSC) activation are the most crucial steps in the formation of hepatic fibrosis. Hepatocytes damaged by viral or bacterial infection, alcohol or toxic chemicals initiate an inflammatory response that activates collagen production by HSCs. Recent studies indicate curcumin has liver-protective effects due to its anti-inflammatory, antioxidant and anticancer activities; however, the mechanisms are not well understood. In this study, we show that curcumin protected against hepatic fibrosis in BALB/c mice in vivo by inhibiting HSC activation, inflammatory responses and inducing apoptosis of damaged hepatocytes. Using the thioacetamide (TAA)-induced hepatic fibrosis animal model, we found that curcumin treatment up-regulated P53 protein expression and Bax messenger RNA (mRNA) expression and down-regulated Bcl-2 mRNA expression. Together, these responses increased hepatocyte sensitivity to TAA-induced cytotoxicity and forced the damaged cells to undergo apoptosis. Enhancing the tendency of damaged hepatocytes to undergo apoptosis may be the protective mechanism whereby curcumin suppresses inflammatory responses and hepatic fibrogenesis. These results provide a novel insight into the cause of hepatic fibrosis and the cytoprotective effects curcumin has on hepatic fibrosis suppression.

Interleukin-1 participates in the progression from liver injury to fibrosis

Interleukin-1 (IL-1) is rapidly expressed in response to tissue damage; however, its role in coordinating the progression from injury to fibrogenesis is not fully understood. Liver fibrosis is a consequence of the activation of hepatic stellate cells (HSCs), which reside within the extracellular matrix (ECM) of subsinusoids. We have hypothesized that, among the hepatic inflammatory cytokines, IL-1 may directly activate HSCs through autocrine signaling and stimulate the matrix metalloproteinases (MMPs) produced by HSCs within the space of Disse, resulting in liver fibrogenesis. In this study, we first established a temporal relationship between IL-1, MMPs, HSC activation, and early fibrosis. The roles of IL-1 and MMP-9 in HSC activation and fibrogenesis were determined by mice deficient of these genes. After liver injury, IL-1, MMP-9, and MMP-13 levels were found to be elevated before the onset of HSC activation and fibrogenesis. IL-1 receptor-deficient mice exhibited ameliorated liver damage and reduced fibrogenesis. Similarly, advanced fibrosis, as determined by type-I and -III collagen mRNA expression and fibrotic septa, was partially attenuated by the deficiency of IL-1. In the early phase of liver injury, the MMP-9, MMP-13, and TIMP-1 expression correlated well with IL-1 levels. In injured livers, MMP-9 was predominantly colocalized to desmin-positive cells, suggesting that HSCs are MMP-producing cells in vivo. MMP-9-deficient mice were partially protected from liver injury and HSC activation. Thus IL-1 is an important participant, along with other cytokines, and controls the progression from liver injury to fibrogenesis through activation of HSCs in vivo.

Interleukin-1 participates in the progression from liver injury to fibrosis

Interleukin-1 (IL-1) is rapidly expressed in response to tissue damage; however, its role in coordinating the progression from injury to fibrogenesis is not fully understood. Liver fibrosis is a consequence of the activation of hepatic stellate cells (HSCs), which reside within the extracellular matrix (ECM) of subsinusoids. We have hypothesized that, among the hepatic inflammatory cytokines, IL-1 may directly activate HSCs through autocrine signaling and stimulate the matrix metalloproteinases (MMPs) produced by HSCs within the space of Disse, resulting in liver fibrogenesis. In this study, we first established a temporal relationship between IL-1, MMPs, HSC activation, and early fibrosis. The roles of IL-1 and MMP-9 in HSC activation and fibrogenesis were determined by mice deficient of these genes. After liver injury, IL-1, MMP-9, and MMP-13 levels were found to be elevated before the onset of HSC activation and fibrogenesis. IL-1 receptor-deficient mice exhibited ameliorated liver damage and reduced fibrogenesis. Similarly, advanced fibrosis, as determined by type-I and -III collagen mRNA expression and fibrotic septa, was partially attenuated by the deficiency of IL-1. In the early phase of liver injury, the MMP-9, MMP-13, and TIMP-1 expression correlated well with IL-1 levels. In injured livers, MMP-9 was predominantly colocalized to desmin-positive cells, suggesting that HSCs are MMP-producing cells in vivo. MMP-9-deficient mice were partially protected from liver injury and HSC activation. Thus IL-1 is an important participant, along with other cytokines, and controls the progression from liver injury to fibrogenesis through activation of HSCs in vivo.

Scaffolding in tissue engineering: general approaches and tissue-specific considerations

Scaffolds represent important components for tissue engineering. However, researchers often encounter an enormous variety of choices when selecting scaffolds for tissue engineering. This paper aims to review the functions of scaffolds and the major scaffolding approaches as important guidelines for selecting scaffolds and discuss the tissue-specific considerations for scaffolding, using intervertebral disc as an example.

Growth inhibitory actions of prothrombin on normal hepatocytes: influence of matrix

Most hepatomas have a defect in prothrombin carboxylation, and can secrete under-carboxylated prothrombin or des-gamma-carboxy-prothrombin (DCP), the function of which is unknown. We considered that the prothrombin-DCP axis might also be involved in growth control. Hepatocytes and hepatoma cells were treated with prothrombin and DNA synthesis and cytoskeletal changes were studied. Prothrombin inhibited DNA synthesis in hepatocytes on fibronectin, but not collagen matrix. Hepatoma cell lines were not inhibited. We found that hepatoma cell matrix conferred resistance to hepatocytes. Prothrombin decreased fibronectin but not collagen amounts, but only in the presence of hepatocytes and not hepatoma cells, indicating that it has a differential action on matrix proteins. It also caused changes in cell shape and actin depolymerization. In vivo, there was a decrease in plasma prothrombin activity after a partial hepatectomy (PH), concomitant with the peak of DNA synthesis in the hepatocytes at 24h after PH. Injection of warfarin at the time of PH, further inhibited PT activity and enhanced this 24h peak of DNA synthesis. Furthermore, repeated injection of prothrombin lowered the peak DNA synthesis after PH. The data support the hypothesis that prothrombin can act as a hepatocyte growth inhibitor, likely at the level of fibronectin loss and result in cytoskeletal changes. Hepatomas resist this action, possibly due to their different matrix proteins. This represents a novel mechanism for growth regulation and provides a possible biological significance for the tumor marker DCP.

Effect of Chinese traditional compound, Gan-fu-kang, on CCl(4)-induced liver fibrosis in rats and its probable molecular mechanisms

AIM

To explore the antifibrotic effect of traditional Chinese medicine compound Gan-fu-kang (GFK) on CCl(4)-induced liver fibrosis in rats and its probable mechanisms.

METHODS

The effects of GFK on CCl(4)-induced liver fibrosis were tested in rats. The liver histopathology was examined by light microscope, polaring microscope and electron microscope. The activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were assayed and the content of albumin (ALB) and hydroxyproline in the liver was measured. The expression of transforming growth factor-beta(1) (TGF-beta(1)) and laminin (LN) was determined by immunohistochemistry. Semi-quantitive computation of collagen types I and III and laminin was done. The expression of MMP-2 and TIMP-1 was assayed by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Upon pathological examination, GFK treatment had significantly reversed liver fibrosis. Hepatic extracellular matrix (ECM) deposition was significantly reduced, as evidenced by the reduction of the content of hydroxyproline, collagen types I and III, and laminin. Hepatic function was improved by GFK treatment, as evidenced by the increase of plasma ALB and A/G, and by the decrease of serum ALT and AST. TGF-beta(1) in liver was significantly reduced. A significant expression of MMP-2 and TIMP-1 mRNA in liver were downregulated after GFK treatment.

CONCLUSION

The traditional Chinese medicine compound recipe GFK has an antifibrotic effect on CCl(4)-induced liver fibrosis in rats, which improves hepatic function and lessens the deposition of collagen in the liver. The probable antifibrotic mechanisms were: inhibiting the expression of TGF-beta(1) and decreasing expressions of MMP-2 and TIMP-1.

Impaired proteolysis of collagen I inhibits proliferation of hepatic stellate cells: implications for regulation of liver fibrosis

Myofibroblastic-activated hepatic stellate cells are the major source of the collagen I-rich extracellular matrix in liver fibrosis but also produce matrix metalloproteinases, which remodel this protein. We have investigated the role of collagen I proteolysis in both regulating proliferation and maintaining the activated myofibroblastic phenotype of stellate cells in vitro. Compared with stellate cells plated on normal collagen I, those plated on a collagenase-resistant form of collagen I (r/r collagen) had reduced thymidine incorporation and proliferating cell nuclear antigen expression but increased p21 expression. Collagen I was shown to be rendered resistant to matrix metalloproteinases by artificial cross-linking in vitro using tissue transglutaminase exerted similar antiproliferative effects on stellate cells to r/r collagen. Of the stellate cell activation markers examined (tissue inhibitor of metalloproteinases-1, alpha-smooth muscle actin, matrix metalloproteinases-2 and -9, and procollagen I) only the last was decreased by culture on r/r collagen relative to normal collagen I. Antagonists of integrin alphavbeta3, an integrin reported to stimulate stellate cell proliferation, significantly inhibited adhesion, proliferation, and procollagen I synthesis of stellate cells plated on normal collagen I but had reduced effectiveness on these parameters in cells on r/r collagen. We conclude that proliferation of stellate cells is promoted by pericellular collagen I proteolysis acting via alphavbeta3 integrin. Cross-linking of collagen I by tissue transglutaminase, a process known to occur in chronic liver fibrosis, might not only increase its resistance to matrix metalloproteinases thereby inhibiting resolution of fibrosis but also functions to constrain the fibroproliferative process.

Phenobarbital responsiveness as a uniquely sensitive indicator of hepatocyte differentiation status: requirement of dexamethasone and extracellular matrix in establishing the functional integrity of cultured primary rat hepatocytes

We used a serum-free, highly defined primary hepatocyte culture model to investigate the mechanisms whereby dexamethasone (Dex) and extracellular matrix (ECM) coordinate cell differentiation and transcriptional responsiveness to the inducer, phenobarbital (PB). Low nanomolar levels of Dex and dilute concentrations of ECM overlay were essential in the maintenance of normal hepatocyte physiology, as assessed by cell morphology, LDH release, expression of the hepatic nuclear factors C/EBPalpha, -beta, -gamma, HNF-1alpha, -1beta, -4alpha, and RXRalpha, expression of prototypical hepatic marker genes, including albumin and transferrin, and ultimately, cellular capacity to respond to PB. The loss of hepatocyte integrity produced by deficiency of these components correlated with the activation of several stress signaling pathways including the MAPK, SAPK/JNK, and c-Jun signaling pathways, with resulting nuclear recruitment of the activated protein-1 (AP-1) complex. In Dex-deficient cultures, normal cellular function, including the PB induction response, was largely restored in a dose-dependent manner by reintroduction of nanomolar additions of the hormone, in the presence of ECM. Our results demonstrate critical and cooperative roles for Dex and ECM in establishing hepatocyte integrity and in the coordination of an array of liver-specific functions. These studies further establish the PB gene induction response as an exceptionally sensitive indicator of hepatocyte differentiation status.

Extracellular matrix regulates the hepatocellular heat shock response

BACKGROUND

Cirrhosis is characterized by the accumulation of collagen within the extracellular matrix (ECM) of the liver and progressive hepatocellular dysfunction. Since recent studies have shown that the ECM can modulate cellular function, we examined whether the ECM could contribute to hepatocellular dysfunction. To address this question we examined hepatocyte behavior in two different ECM environments.

MATERIALS AND METHODS

Primary rat hepatocytes were cultured as a monolayer on collagen or as multicellular aggregates (spheroids) within a laminin-rich ECM. Hepatocytes were then compared for viability, response to proinflammatory cytokines, and their capacity to activate a heat shock response and adopt a thermotolerant phenotype. In addition, we compared the ability of prior heat shock exposure to protect hepatocytes from tumor necrosis factor (TNF) alpha/actinomycin-D-induced apoptosis in the two different ECM environments.

RESULTS

Hepatocytes cultured as a monolayer on collagen exhibited decreased viability, underwent spontaneous apoptosis, and displayed an attenuated cytokine-stimulated nitric oxide production compared to hepatocytes cultured as spheroids. In response to heat, hepatocytes in both ECM environments expressed inducible heat shock protein 70 (hsp72). But, only the hepatocyte spheroids exhibited thermotolerance in response to a subsequent thermal challenge. In contrast to previous reports, induction of the heat shock response failed to protect hepatocytes against TNFalpha-induced apoptosis.

CONCLUSIONS

These data demonstrate that the ECM can play an integral role in specific hepatocellular behaviors. Furthermore, the progressive deposition of collagen within the ECM, which is characteristic of fibrotic liver diseases, may directly contribute to the progressive hepatocellular dysfunction observed in cirrhosis. Hepatocellular viability, response to proinflammatory cytokines, heat shock response, and thermotolerance were all altered depending on the composition of the ECM. In contrast, TNFalpha-induced apoptosis was independent of the composition of the ECM.

Decorin and actin expression and distribution in patients with chronic hepatitis C following interferon-alfa-2b treatment

BACKGROUND/AIMS

Chronic hepatitis C can lead to cirrhosis and hepatocellular carcinoma. Interferon-alfa therapy may prevent the progression of the disease. The expressions of decorin and alfa-smooth muscle cell actin of the extracellular matrix play a central role in liver fibrosis. We set out to assess the expressions of these proteins in chronic hepatitis C patients, and to evaluate how they can be modified by interferon-alfa therapy.

METHODS

Twenty chronic hepatitis C patients received interferon-alfa-2b therapy for 6 months (group I) or 12 months (group II). Liver biopsy samples were taken before and after the therapy. The alfa-smooth muscle actin-positive cells were determined with a monoclonal antibody, and decorin expression was detected with a polyclonal antibody. The cells were evaluated with a semiquantitative scoring method. For statistical analysis, non-parametric methods were used.

RESULTS

Before the therapy, alfa-smooth muscle actin-labeled cells and marked decorin expression were present throughout all the acinar zones. Interferon-alfa-2b therapy resulted in significant decreases in both the number of alfa-smooth muscle actin-positive cells and the decorin expression. The alfa-smooth muscle actin-positive cells and decorin expression correlated with the histological activity index (R=0.72, p<0.03, R=0.68, p<0.05).

CONCLUSIONS

This study demonstrates that a large number of alfa-smooth muscle actin-positive cells and a marked decorin expression are frequent findings in chronic hepatitis C. Treatment with interferon-alfa-2b for 12 months reduced the number of labeled cells and the decorin expression. The results suggest that interferon-alfa-2b is capable of interfering with fibrogenesis in an early and presumably still reversible phase of chronic hepatitis C.

Matrix-mediated changes in the expression of HNF-4alpha isoforms and in DNA-binding activity of ARP-1 in primary cultures of rat hepatocytes

Recently, we have developed a culture system in which rat hepatocytes dedifferentiate and proliferate and after the addition of EHS-gel redifferentiate. During both developmental stages HNF-4alpha2 mRNA was more abundant than HNF-4alpha1 mRNA. However, Western blot analysis using COS-7 cell-expressed HNF-4alpha1 and HNF-4alpha2 proteins as standards revealed that (i) HNF-4alpha2 protein was not expressed in dedifferentiated hepatocytes and (ii) either HNF-4alpha2 protein or a highly phosphorylated HNF-4alpha1 protein was the dominating isoform in redifferentiated hepatocytes. The changes in HNF4-isoform expression could not be mimicked by DMSO, suggesting them to be matrix specific. Furthermore, DMSO was less efficient than EHS-gel in reinducing liver-specific gene expression. EHS-gel overlay also led to reduction of ARP-1 DNA binding activity, while overall ARP-1 protein levels did not change. These results suggest that EHS-matrix overlay regulates the expression of different HNF-4alpha isoforms on a posttranscriptional level while ARP-1 DNA binding activity is regulated by posttranslational mechanisms.

Xenotransplantation of fetal porcine hepatocytes in rats using a tissue engineering approach

Hepatocytes can be successfully transplanted into highly vascular sites such as the spleen, liver, and lungs. Subcutaneous sites lack adequate vascularization to nutritionally support transplanted hepatocytes. We recently reported that matrix-immobilized angiogenic growth factors, e.g., endothelial cell growth factor (ECGF), can induce a high degree of neovascularization. Using this technique, we explored the possibility of transplanting isolated fetal porcine hepatocytes to create liver tissue organoids at a specific subcutaneous site. We evaluated chitosan as a scaffold biomaterial because of its structural similarity to glycosaminoglycans; glycosaminoglycans play a critical role in cell attachment, differentiation, and morphogenesis. Freshly isolated fetal porcine hepatocytes (FPH) (viability greater than 97%) were cultured on modified chitosan scaffolds and transplanted into rat groin fat pads with or without ECGF-induced neovascularization. Cell density and attachment kinetics on chitosan were examined by scanning electron microscopy (SEM) and quantified using a flavianic acid binding assay. Hepatocyte viability and liver organoid formation were examined immunohistochemically. FPH transplanted without prior neovascularization died within 1 day post-transplantation. When transplanted after ECGF-induced neovascularization, FPH thrived for at least 2 weeks and formed liver tissue like structures. Immunohistochemical analysis revealed the presence of hepatocyte-specific cytokeratin staining as well as the presence of alpha-fetoprotein. Light microscopy and SEM revealed that FPH did not change their morphology after attachment to the chitosan surfaces. Thus, chitosan-based biomaterial surfaces have good hepatocyte attachment properties. However, extensive neovascularization is essential for hepatocyte survival and organoid formation. In the future, chitosan-based biomaterials may be useful as scaffolds for creating liver tissue organoids.

Dedifferentiation of human hepatocytes by extracellular matrix proteins in vitro: quantitative and qualitative investigation of cytokeratin 7, 8, 18, 19 and vimentin filaments

BACKGROUND/AIMS

Liver cirrhosis and carcinogenesis are accompanied by an alteration in extracellular matrix material. Histological studies reveal upregulation of the intermediate filaments cytokeratins 8 and 18 and de novo synthesis of vimentin, and cytokeratin 7 or 19 in hepatocytes. The aim of this study was to investigate how these two processes are linked.

METHODS

Human hepatocytes were seeded: (i) on the matrix components collagen I, IV, laminin, or fibronectin; (ii) on stoichiometrically different complete matrices, derived from human placenta (matrix I) or the Englebreth-Holm-Swarm tumor (matrix II), and (iii) inside a three-dimensional collagen I sandwich. Filament expression and assembly were measured by cytofluor analysis or confocal laserscan microscopy.

RESULTS

The matrix components or complete matrices triggered enhancement of cytokeratins 8 and 18 and de novo synthesis of cytokeratins 7, 19 and vimentin in a characteristic way. Confocal images demonstrated a dense and uniform network of cytokeratin 18 in freshly isolated cells, which was "replaced" by a few, thick protein bundles within 20 days. Interestingly, newly synthesized cytokeratin 19 structurally resembled the cytokeratin 19 organization in biliary epithelial cells. Marked cytokeratin alterations could be partially prevented when hepatocytes were grown in a three-dimensional collagen sandwich.

CONCLUSIONS

Pathological alterations to the chemical composition, molecular structure, or spatial arrangement of the liver matrix lead to specific changes in the intermediate filament pattern in human hepatocytes. We assume that degradation of the matrix results in pathological alterations to the hepatocyte-receptor matrix-ligand ratio, followed by a switch from physiological to pathological cell-activation.

Toward development of an implantable tissue engineered liver

Hepatocyte transplantation on implantable devices is a tissue engineering approach to improve the treatment of liver disease and the efficacy of ex vivo gene therapy. Diverse physiological functions and high metabolic activity of the liver represent significant challenges to engineering implantable devices that provide long-term hepatic support. Liver tissue engineering research has explored alternatives to direct hepatocyte injection that include hepatocyte attachment to microcarriers, encapsulation and transplantation on biodegradable polymer scaffolds. Successful function of hepatocytes transplanted on implantable devices in animal models has been documented by production of albumin and other liver-specific markers, and clearance of bilirubin and urea metabolites. Strategies used to achieve these successes are reviewed, with particular emphasis on biodegradable polymer scaffolds, and two areas of investigation that may improve the function of implantable tissue engineered liver devices are highlighted.

The mesentery as a laminated vascular bed for hepatocyte transplantation

The small bowel mesentery provides a unique structure of a large vascularized surface area to support hepatocyte transplantation. Cell-seeded polymeric matrices can be juxtaposed in a relatively atraumatic manner between leaves of mesentery such that adequate exchange of nutrients and diffusion of gases can proceed in the interim while neovascularization occurs. Hepatocytes obtained from (RHA) Wistar rats by collagenase perfusion were seeded onto non-woven filamentous sheets of polyglycolic acid 1 x 3 cm in size and 2 mm thickness to a density of 500,000 cells/cm2. Twenty-six recipient Gunn rats (UDP-glucuronyl transferase deficient) underwent laparotomy. Hepatocyte-ladened polymer sheets were placed between leaves of mesentery. Eight sheets were placed per animal and the leaves were approximated, creating a functional implant 1 x 3 x 2 cm. Biopsies between 5-99 days after implantation revealed neovascularization, moderate inflammatory reaction and the presence of viable hepatocytes in 96% (25/26). Immunoperoxidase studies using anti-albumin antibody substantiated hepatocyte specific function in implants. HPLC profiles of bile from Gunn rats transplanted with hepatocytes from congeneic (RHA) rats demonstrated the presence of bilirubin conjugates. There were no conjugation fractions seen in control gunn rats without hepatocyte transplantation. Although total serum bilirubin did not significantly decrease, conjugated bilirubin was identified in 46% (12/26) animals after transplantation with congeneic hepatocytes. We conclude that the mesentery of the small bowel provides a large vascularized surface for cell transplantation. Large numbers of metabolically active hepatocytes can engraft, vascularize, and show function. The mesentery may be a potential bed for clinical hepatocyte transplantation.

Transient expression of tenascin in experimentally induced cholestatic fibrosis in rat liver: an immunohistochemical study

This study describes the sequential changes in tenascin expression in hepatic fibrosis induced by bile duct ligation (BDL) in the rat. Two days after BDL, tenascin was strongly expressed in the matrix surrounding interlobular bile ducts and also between proliferating ductules. From day 7 onwards, its distribution was restricted to the connective tissue-parenchymal interfaces where ductular proliferation was still active. A markedly increased number of desmin- and alpha-smooth muscle actin (alpha-smA)-positive cells, considered myofibroblasts, was noted around interlobular bile ducts and between proliferating ductules during periductal fibrogenesis. Type IV collagen and laminin were strongly expressed on the basement membranes of proliferating ductules, and contributed to the development of newly formed fibrous septa. The transient expression of tenascin around interlobular bile ducts in the early phase of BDL may be related to the onset of periductal fibrosis or to the mitogenic response of the biliary epithelium. The expression of tenascin between 'proliferating' ductules in contrast to its absence from 'mature' fibrous areas suggests a transient role in early matrix organization. Furthermore, alpha-smA-positive cells may modulate the synthesis of extracellular matrix components.

A morphological and functional evaluation of transplanted isolated encapsulated hepatocytes following long-term transplantation in Gunn rats

In this study we investigated the fate of microencapsulated hepatocytes following long-term (6 months) transplantation in Gunn rats. Isolated hepatocytes were microencapsulated with a collagen matrix within an alginate-poly L-lysine composite membrane. Isolated, encapsulated hepatocytes (IEH) or free (unencapsulated) isolated hepatocytes were intraperitoneally transplanted into homozygous Gunn rats that exhibit congenital hyperbilirubinemia. Control Gunn rats received empty microcapsules. Total serum bilirubin was measured at weekly intervals for one month post-IEH transplantation, every two weeks for the next month, and monthly thereafter for up to six months. IEH samples were biopsied from the Gunn rats at monthly intervals and analyzed by light and electron microscopy. A significant (p < 0.01) decrease in total serum bilirubin was observed in IEH transplanted animals during the first month of transplantation. Thereafter, total serum bilirubin levels gradually returned to pre-transplantation levels. A mild, transient decrease in total serum bilirubin was seen in animals transplanted with free (unencapsulated) hepatocytes. No decrease in total serum bilirubin levels was seen in the Gunn rats transplanted with control (empty) microcapsules. Transplanted IEH retained its normal ultrastructure for up to one month and intact microcapsules showed no evidence of hepatocyte rejection, at this time. Degenerative changes observed in the IEH beginning at 2 months post-transplantation, suggests that repeated transplantations may be necessary for long-term effectiveness of IEH therapy.

Morphological assessment of hepatoma cells (HepG2) microencapsulated in a HEMA-MMA copolymer with and without Matrigel

Hepatoma cells (HepG2), an anchorage-dependent cell line, were microencapsulated in a HEMA-MMA polyacrylate membrane to which the cells do not adhere. This environment was altered by the coencapsulation of Matrigel, a reconstituted extracellular matrix derived from the Engelbreth-Holm-Swarm (EHS) mouse tumor basement membrane, to provide sites for cell attachment. The effect on the cells of these two capsule microenvironments during a 2-week in vitro culture period was assessed by examining the spatial arrangement, morphology, and viability of the cells using light microscopy and scanning electron microscopy (SEM). In preparation for microscopy, dissolution of the polymer was prevented by the use of frozen sections embedded in a water-soluble compound. Similarly, freeze cleavage of conductively stained capsules permitted SEM observation of the capsule interior along with ultrastructural detail of the cells. In the absence of Matrigel, cells in HEMA-MMA capsules were found to form aggregates in intracapsular pockets with central necrosis occurring at day 7 in large aggregates. The coencapsulation of HepG2 cells with Matrigel, resulted in an initially uniform distribution of essentially individual cells with aggregates appearing later within the Matrigel. Many cells within these capsules had remained viable when examined up to day 14 with only limited cellular necrosis, implying a favorable environment for microencapsulated HepG2 cells.

Light microscopic and ultrastructural distribution of type VI collagen in human liver: alterations in chronic biliary disease

We have investigated the distribution of type VI collagen in normal human liver obtained from cadaveric renal transplant donors, using a peroxidase-antiperoxidase method for light microscopic visualization, and an immunogold labelling method for ultrastructural localization. The distribution was compared with that of the more abundant interstitial collagen type III, using antibodies to amino terminal procollagen type III. Staining for type VI collagen was identified in Glisson's capsule, in portal tract stroma and within the space of Disse. Perisinusoidal staining showed intra-acinar heterogeneity with the intensity in acinar zones 2 and 3 being greater than in zone 1. Type III collagen was also found in the space of Disse although no significant intra-acinar variation in staining intensity was noted. Immuno-gold labelling for type VI collagen was demonstrated on amorphous or microfilamentous material lying between, and occasionally appearing to interconnect, cross-striated collagen fibrils, whereas labelling for amino terminal procollagen type III was exclusively on fibrils. Intracellular staining for type VI collagen was noted in perisinusoidal (lto) cells. These results confirm that type VI collagen is a ubiquitous constituent of the normal hepatic extracellular matrix and suggest that it may be synthesized by perisinusoidal (lto) cells. The distribution of type VI collagen was also studied in biopsy material from patients with different histological stages of primary biliary cirrhosis. Intense staining was noted around proliferating bile ductules within developing fibrous septa and in established septa of cirrhotic liver. These observations indicate that this 'minor' matrix component may play an important role in hepatic fibrogenesis.

Improved function of microencapsulated hepatocytes in a hybrid bioartificial liver support system

Conventional methods of microencapsulating isolated hepatocytes with Type I collagen matrix have provided metabolic liver support in experimental animal models of acute liver failure and congenital metabolic liver disease. We compared the biological function of transplanted microencapsulated hepatocytes cultured on standard Type I collagen (Vitrogen) and a commercially available liver basement-membrane-like extract from a mouse sarcoma (Matrigel). Isolated hepatocytes were microencapsulated with Matrigel and Vitrogen within an alginate-poly-L-lysine composite membrane. Isolated encapsulated hepatocytes (IEH) were transplanted intraperitoneally into homozygous Gunn rats that exhibit congenital hyperbilirubinemia. Control Gunn rats received empty or no microcapsules. Total serum bilirubin and conjugated bilirubin in bile were measured at weekly intervals for one month. Significant (p < 0.01) decreases in total serum bilirubin were observed in all IEH transplanted animals. No such decrease was seen in control animals. Gunn rats that received Matrigel had significantly (p < 0.05) lower serum bilirubin values and significantly (p < 0.05) higher conjugated bilirubin in bile than those that received Vitrogen. We conclude that hepatocytes microencapsulated with Matrigel functioned better than those with Vitrogen. This improved in vivo biological response underscores the importance of using the appropriate cell attachment substratum to enhance the function of a hybrid bioartificial liver support system based on transplanted hepatocytes.

Significance of serum type-IV collagen levels in various liver diseases. Measurement with a one-step sandwich enzyme immunoassay using monoclonal antibodies with specificity for pepsin-solubilized type-IV collagen

Serum type-IV collagen levels determined with a one-step sandwich enzyme immunoassay (EIA) using monoclonal antibodies with specificity for pepsin-solubilized type-IV collagen were compared with histologic changes in liver biopsy specimens from 107 patients with various liver diseases. Serum type-IV collagen levels were increased in the groups with liver diseases compared with controls. The serum type-IV collagen levels in the group with alcoholic cirrhosis showed significantly higher values than the other groups (P less than 0.05). A significant positive correlation was found between the serum type-IV collagen level and the degree of fibrosis or cell infiltration in 107 patients. Immunolocalization of type-IV collagen was observed around blood vessels and bile ducts increased in number in the portal tracts, with cell infiltration and fibrosis, increased around vessels in fibrous septa, and sinusoidal walls of areas with cell infiltration or necrosis in hepatic lobules, and along the boundary between fibrous septa and hepatocytes. The present data indicate that serum type-IV collagen may be a sensitive marker for active fibrosis and that the elevation of serum type-IV collagen level primarily reflects the enhancement of type-IV collagen synthesis and deposition in the liver tissue at the stage of active fibrosis in liver disease.

Localization and cellular source of the extracellular matrix protein tenascin in normal and fibrotic rat liver

The distribution and the cellular source of the novel extracellular matrix glycoprotein tenascin were studied in normal and fibrotic rat liver. Cryostat sections of normal rat livers, livers of rats treated with intraperitoneal injections of CCl4 and 4-day-old and 8-day-old primary fat-storing cell cultures were stained for tenascin and desmin using an immunoperoxidase procedure or a double-label immunofluorescence technique. Fat-storing cell cultures were metabolically labeled with 3H-proline. Radiolabeled proteins were immunoprecipitated from the supernatant with antitenascin antiserum and subjected to polyacrylamide gel electrophoresis. In normal rat livers, tenascin was detected discontinuously along the sinusoids, whereas portal tracts were devoid of staining. In fibrotic rat livers, tenascin was preferentially expressed in areas of cell damage, in slender septa or at connective tissue-parenchymal interfaces. The middle region of broad septa was negative. Desmin-positive fat-storing cells accumulated in areas strongly immunoreactive for tenascin, and double-label immunofluorescence showed cells positive for both tenascin and desmin. In fat-storing cell cultures, both intracellular positivity for tenascin and staining of extracellular fibers were seen. Gel electrophoresis of immunoprecipitated proteins revealed two major and three minor bands with molecular weights consistent with tenascin. We conclude that tenascin is a component of the extracellular matrix of both normal and fibrotic rat livers. The strong expression of tenascin in areas of cell damage, in "early" septa or at septal-parenchymal interfaces, in contrast to its absence from the middle region of mature septa, suggests a role in early matrix organization. Fat-storing cells synthesize and secrete tenascin.

Vitronectin in liver disorders: biochemical and immunohistochemical studies

The concentration of plasma vitronectin was determined and compared with various parameters of liver function including the blood coagulation system in patients with liver diseases. The severity of cirrhosis was graded according to Child's criteria and compared with the plasma vitronectin level. Furthermore, the distribution of vitronectin in the liver of patients with liver diseases was studied by light and electron microscopy using the indirect immunoperoxidase method. The plasma vitronectin level was low in all liver disease groups as compared with the healthy controls. The difference from the controls was significant in patients with hepatocellular carcinoma and decompensated cirrhosis. Moreover, the plasma vitronectin level was positively correlated with the levels of serum cholinesterase, albumin, plasma alpha 2 plasmin inhibitor-plasmin complex and the prothrombin time and results of the hepatoplastin test. Plasma vitronectin decreased with increasing severity of cirrhosis according to Child's criteria. These results suggest that the plasma vitronectin level is a useful parameter of hepatic synthetic function in patients with liver diseases; it may also reflect the severity of cirrhosis. Light microscopy revealed vitronectin in the area of focal necrosis and the portal tracts in the liver of patients with acute viral hepatitis, in the area of piecemeal necrosis in the liver of patients with chronic hepatitis and along the area of fiber deposition in the liver of patients with cirrhosis. Immunoelectron microscopy showed vitronectin in the rough endoplasmic reticulum of hepatocytes. Moreover, vitronectin was seen around inflammatory cells, endothelial cells, Ito cells and hepatocytes in the perisinusoidal area near focal necrosis and piecemeal necrosis and on collagen fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfation and glucuronidation of acetaminophen by cultured hepatocytes reproducing in vivo sex-differences in conjugation on Matrigel and type 1 collagen

The sulfate and glucuronide conjugation of acetaminophen (APAP) by hepatocytes cultured on Matrigel or type 1 collagen was compared to APAP metabolism in vivo. The metabolic fate of low (15 mg/kg), medium (125 mg/kg), and high (300 mg/kg) doses of APAP injected intraperitoneally were determined in male and female rats. Males excreted more APAP as the sulfate conjugate than females, which correlated with the twofold greater APAP sulfotransferase activity in the male vs. females (301 +/- 24 vs. 156 +/- 18 pmol.mg-1 protein.min-1). Also, as sulfate conjugation became saturated, there was a dose-related shift in APAP metabolism from sulfate to glucuronide conjugation in both sexes. After death, the livers of the same animals were perfused with collagenase and the hepatocytes cultured in modified Waymouth's medium on either Matrigel or rat-tail collagen, with various doses of APAP (0, 0.125, 0.25, 0.5, and 1.0 mM). Sex differences in APAP sulfation and glucuronidation persisted in culture for up to 4 days, with sulfation predominating in the male similar to in vivo. With increasing APAP concentration (dose), there was a saturation of sulfate conjugation and a shift to glucuronidation as observed in vivo. Sex differences in APAP sulfation and glucuronidation were no longer significant by Day 4 in culture. Sulfation, and to a lesser extent, glucuronidation, were more stable on Matrigel than collagen. We concluded that APAP metabolism of freshly isolated hepatocytes could replicate in vivo sex differences in conjugation, and that Matrigel was superior to collagen as substrate.

Ultrastructural localization of type IV collagen and laminin in the Disse space of rat liver with carbon tetrachloride induced fibrosis

Monospecific antibodies, directed against type IV collagen and laminin, were used to clarify the process of sinusoidal capillarization in rats after carbon tetrachloride (CCl4) intoxication by the direct immunoperoxidase method. After acute intoxication, both type IV collagen and laminin were increased in the area of hepatic necrosis, adjacent to the central veins; however, sinusoidal capillarization was not found. During chronic intoxication, deposition of laminin was co-distributed with that of type IV collagen, but deposition proceeded more slowly than that of the type IV collagen. Deposition of laminin was increased in the Disse space. Sinusoidal capillarization was noted as thick deposition of both antigens by light microscopy. Immunoelectron microscopy showed that both components were continuously present in the Disse space. Intracellularly, both antigens were found in the rough endoplasmic reticulum (RER) of fat-storing cells (FSC) and endothelial cells, and these cells showed morphological changes, becoming slender and flattened. In contrast, few immunoreactive products of the two components were observed in the hepatocytes. These findings suggest that type IV collagen and laminin are indispensable for the establishment of sinusoidal capillarization, and that FSC play an important role in the production of both components.

Restoration of liver function in Gunn rats without immunosuppression using transplanted microencapsulated hepatocytes

Microencapsulation of cells within synthetic semipermeable membranes is a novel technique that enables the transplantation of cell cultures without the need for immunosuppression. We have previously shown that transplanted isolated encapsulated hepatocytes can provide sufficient short-term metabolic support to improve the survival of animals with galactosamine-induced fulminant hepatic failure. Here we have demonstrated the feasibility of isolated encapsulated hepatocyte transplantation in providing long-term metabolic liver support in Gunn rats. Gunn rats have a congenital inability to conjugate bilirubin and thus exhibit lifelong hyperbilirubinemia. We studied the feasibility of isolated encapsulated hepatocyte transplantation in restoring this specific liver function. Free hepatocytes, isolated from male Wistar rats, were microencapsulated with collagen within a trilayered sodium alginate-poly-L-lysine-sodium alginate membrane using techniques developed in our laboratory. A total of 45 Gunn rats underwent intraperitoneal transplantation with free hepatocytes (5 x 10(7], isolated encapsulated hepatocytes (5 x 10(7], control (empty) microcapsules or no transplant (untreated controls). Serum bilirubin levels were monitored daily for 10 days after transplantation, and subsequent weekly samples were obtained for up to 1 mo. Microcapsules were studied by light and electron microscopy 1 mo after transplantation. During the first week after transplantation, the mean maximum reduction in serum bilirubin levels for the isolated encapsulated hepatocytes, free hepatocytes and control microcapsule transplanted groups was 45.7%, 18.6% and 14.3%, respectively. For up to 1 mo thereafter the mean reduction in serum bilirubin levels in these respective groups was 34.8%, 13.5% and 3.3%.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of extracellular matrix components during dimethylnitrosamine-induced cirrhosis

Liver fibrosis was induced in rats after administration of dimethylnitrosamine (DMN) intraperitoneally three times a week for 3 weeks. Incomplete septa appeared after 7 days and evidence of nodulation of the parenchyma was observed after 21 days. Both distribution of extracellular matrix components (collagen type I, type III and type IV, laminin, fibronectin, heparan sulphate proteoglycan) and the distribution of desmin as a marker of lipocytes (Ito cells) and of iso-alpha-smooth muscle actin were studied with immunoperoxidase. Changes in the distribution of extracellular matrix components outlined both the formation of septa and the development of nodules with changes in the sinusoidal pattern evoking aspects of capillarization. The number of desmin-positive cells increased in DMN-treated animals, showing a prominent reaction in the fibrous septa. In the normal liver, lipocytes were positive for laminin and negative for actin, but septal and juxta-septal lipocytes were positive for both antigens, suggesting the presence of transitional cells with mixed immunoreactivity. This was confirmed by ultrastructural studies which showed typical intraseptal myofibroblasts and other elements exhibiting the structural features of both myofibroblasts and lipocytes.

Immunohistochemistry of the hepatic extracellular matrix in acute viral hepatitis

The distribution of several extracellular matrix components in the liver of patients with acute viral hepatitis was studied by light and electron microscopy using indirect immunoperoxidase methods. Light microscopy revealed type III and type V collagen and fibronectin in the portal tracts and the area of focal necrosis, showing cell infiltration. Type III and type V collagen were more strongly stained in the periphery of focal necrosis. Type IV collagen was seen around the vessels and hepatocytes near the focal necrosis. Electron microscopy showed many transitional Ito cells in the area of focal necrosis and fibroblasts were observed in the portal tracts, showing collagen fiber deposition. Numerous collagen fibrils were observed around fibroblasts, Ito cells and hepatocytes. Using immunoelectron microscopy, type III and type IV collagen and fibronectin were observed in the rough endoplasmic reticulum of Ito cells and hepatocytes localized near the area of focal necrosis or fiber deposition. In addition, type IV collagen was seen in the rough endoplasmic reticulum of endothelial cells forming capillary vessels. These results suggest that several extracellular matrix components such as types III, IV and V collagen and fibronectin, produced by Ito cells, hepatocytes or endothelial cells, play important roles in the healing of liver damage in acute viral hepatitis.

Expression of the novel extracellular matrix component tenascin in normal and diseased human liver. An immunohistochemical study

The novel extracellular matrix glycoprotein tenascin was studied immunohistochemically in normal and fibrotic human liver. Its localization was compared to that of laminin, fibronectin and collagen type IV. In the normal liver, a weak staining for tenascin was detected along sinusoids, while portal tracts were negative. In both alcoholic and cholestatic liver disease and acute and chronic hepatitis, sinusoidal immunoreactivity for tenascin was variably increased as compared to the normal liver. Most striking, however, was the preferential accumulation of tenascin at connective tissue-parenchymal interfaces between proliferating ductules and in areas of piecemeal necrosis. As compared to laminin, fibronectin and collagen type IV, tenascin has the most restricted distribution. Our findings indicate that tenascin is a component of the extracellular matrix of the human liver. Its preferential expression at connective tissue-parenchymal interfaces in fibrosing areas in contrast to its absence from mature fibrous septa suggest a transient role in early matrix organization.