Mechanisms of hepatic fibrosis

Magnetic Fe3 O4 @graphene oxide improves the therapeutic effects of embryonic stem cells on acute liver damage

OBJECTIVE

Acute liver failure is usually associated with inflammation and oxidation of hepatocytes and has high mortality and resource costs. Mesenchymal stem cell (MSCs) has occasionally been reported to have no beneficial effect due to poor transplantation and the survival of implanted cells. Recent studies showed that embryonic stem cell (ESC)-derived MSCs are an alternative for regenerative medicine. On the other hand, graphene-based nanostructures have proven useful in biomedicine. In this study, we investigated whether magnetic graphene oxide (MGO) improved the effects of ESC-MSC conditioned medium (CM) on protecting hepatocytes and stimulating the regeneration of damaged liver cells.

MATERIALS AND METHODS

To provide a rat model of acute liver failure, male rats were injected intraperitoneally with carbon tetrachloride (CCl4 ). The rats were randomly divided into six groups, namely control, sham, CCl4 , ESC-MSC-CM, MGO and ESC-MSC-CM + MGO. In the experimental groups, the rats received, depending on the group, 2 ml/kg body weight CCl4 and either ESC-MSC-CM with 5 × 106 MSCs or 300 μg/kg body weight MGO or both. Symptoms of acute liver failure appeared 4 days after the injection. All groups were compared and analysed both histologically and biochemically 4 days after the injection. Finally, the results of ESC-MSC-CM and MSC-CM were compared.

RESULTS

The results indicated that the use of MGO enhanced the effect of ESC-MSC-CM on reducing necrosis, inflammation, aspartate transaminase, alanine aminotransferase and alkaline phosphatase in the CCl4 -induced liver failure of the rat model. Also, the expression of vascular endothelial growth factor and matrix metalloproteinase-9 (MMP-9) was significantly upregulated after treatment with MGO. Also, the results showed that the ESC-MSC-CM has more efficient effective compared to MSC-CM.

CONCLUSION

Magnetic graphene oxide improved the hepatoprotective effects of ESC-MSC-CM on acute liver damage, probably by suppressing necrosis, apoptosis and inflammation of hepatocytes.

Silica Magnetic Graphene Oxide Improves the Effects of Stem Cell-Conditioned Medium on Acute Liver Failure

OBJECTIVE

Acute liver failure (ALF) is usually associated with inflammation and oxidation of hepatocytes and has high mortality and resource costs. Although mesenchymal stem cell-conditioned medium (MSC-CM) has therapeutic effects similar to MSC transplant in treating liver failure, it may not increase survival. On the other hand, graphene-based nanostructures have been proven useful in biomedicine. In this study, we investigated whether silica magnetic graphene oxide (SMGO) improved the effects of MSC-CM in protecting hepatocytes and stimulating the regeneration of damaged liver cells.

MATERIALS AND METHODS

To provide a rat model of ALF, male rats were injected intraperitoneally with carbon tetrachloride (CCl₄). The rats were randomly divided into six groups, namely control, sham, CCl₄, MSC-CM, SMGO, and MSC-CM + SMGO. In the experimental groups, the rats received, depending on the group, 2 mL/kg body weight CCl₄ and either MSC-CM with 5 × 10⁶ MSCs or 300 μg/kg body weight SMGO or both. Symptoms of ALF appeared 4 days after the injection. All groups were compared and analyzed both histologically and biochemically 4 days after the injection.

RESULTS

The results indicated that the use of SMGO enhanced the effect of MSC-CM in reducing necrosis, inflammation, aspartate transaminase, alanine aminotransferase, and alkaline phosphatase in the CCl₄-induced liver failure of the rat model. Also, the expression of vascular endothelial growth factor and matrix metalloproteinase-9 (MMP-9) was significantly upregulated after treatment with SMGO.

CONCLUSION

SMGO improved the hepatoprotective effects of MSC-CM on acute liver damage, probably by suppressing necrosis, apoptosis, and inflammation of hepatocytes.

Effects of intraperitoneal injection of magnetic graphene oxide on the improvement of acute liver injury induced by CCl4

Background

Liver failure is usually associated with the inflammation and oxidation of hepatocytes. Due to their unique properties, graphene and graphene-based nanostructures such as magnetic graphene oxide (MGO) are useful in biomedicine and engineering. In this study, synthesized MGO was used to improve the liver failure induced by carbon tetrachloride (CCl₄). The hepatoprotective effects of intraperitoneal injection of MGO on the rat model of CCl₄-induced acute liver failure were investigated.

Materials and methods

In order to provide a rat model of acute liver failure, male rats were intraperitoneally injected with 2 ml/kg body weight CCl₄. In the experimental groups, rats received 2 ml/kg CCl₄ and 300 mg/kg MGO body weight simultaneously. Four days after injection, symptoms of acute liver failure appeared. The control, sham, CCl₄, and CCl₄ + MGO groups were compared and analyzed both histologically and biochemically.

Results

The results indicated that the MGO injection reduced all CCl₄-induced liver failure such as necrosis, fibrosis, inflammation, aspartate transaminase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) in the experimental groups of the rat model of acute liver failure.

Conclusion

The hepatoprotective effects of MGO might be due to histopathological suppression and inflammation inhibition in the liver.

Rap1 regulates hepatic stellate cell migration through the modulation of RhoA activity in response to TGF‑β1

Although the migration of hepatic stellate cells (HSCs) is important for hepatic fibrosis, the regulation of this migration is poorly understood. Notably, transforming growth factor (TGF)‑β1 induces monocyte migration to sites of injury or inflammation during the early phase, but inhibits cell migration during the late phase. In the present study, the role of transforming protein RhoA signaling in TGF‑β1‑induced HSC migration was investigated. TGF‑β1 was found to increase the protein and mRNA levels of smooth muscle actin and collagen type I in HSC‑T6 cells. The level of RhoA‑GTP in TGF‑β1‑stimulated cells was significantly higher than that in control cells. Furthermore, the phosphorylation of cofilin and formation of filamentous actin (F‑actin) were more marked in TGF‑β1‑stimulated cells than in control cells. Additionally, TGF‑β1 induced the activation of nuclear factor‑κB, and the expression of extracellular matrix proteins and several cytokines in HSC‑T6 cells. The active form of Rap1 (Rap1 V12) suppressed RhoA‑GTP levels, whereas the dominant‑negative form of Rap1 (Rap1 N17) augmented RhoA‑GTP levels. Therefore, the data confirmed that Rap1 regulated the activation of RhoA in TGF‑β1‑stimulated HSC‑T6 cells. These findings suggest that TGF‑β1 regulates Rap1, resulting in the suppression of RhoA, activation of and formation of F‑actin during the migration of HSCs.

High Risk of Hepatocellular Carcinoma Development in Fibrotic Liver: Role of the Hippo-YAP/TAZ Signaling Pathway

Liver cancer is the fourth leading cause of cancer-related death globally, accounting for approximately 800,000 deaths annually. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, making up about 80% of cases. Liver fibrosis and its end-stage disease, cirrhosis, are major risk factors for HCC. A fibrotic liver typically shows persistent hepatocyte death and compensatory regeneration, chronic inflammation, and an increase in reactive oxygen species, which collaboratively create a tumor-promoting microenvironment via inducing genetic alterations and chromosomal instability, and activating various oncogenic molecular signaling pathways. In this article, we review recent advances in fields of liver fibrosis and carcinogenesis, and consider several molecular signaling pathways that promote hepato-carcinogenesis under the microenvironment of liver fibrosis. In particular, we pay attention to emerging roles of the Hippo-YAP/TAZ signaling pathway in stromal activation, hepatic fibrosis, and liver cancer.

Development of a peptide-modified siRNA nanocomplex for hepatic stellate cells

Insulin-like growth factor 2 receptor (IGF2R) is overexpressed in activated hepatic stellate cells (HSCs) and therefore can be utilized for HSC-specific drug delivery. We recently discovered an IGF2R-specific peptide using a novel biopanning. Here, we adopted biotin-conjugated IGF2R-specific peptide, cholesterol, and vitamin A as the targeting ligands for the neutravidin-based siRNA nanocomplex to deliver PCBP2 siRNA, a potentially antifibrotic agent, to HSCs. Compared to vitamin A and cholesterol, the IGF2R-specific peptide exhibited the highest targeting effect to human LX-2 HSC, rat HSC-T6 cell line, and activated primary rat HSCs. Accordingly, the IGF2R-specific peptide coupled nanocomplex demonstrated higher silencing activity of PCBP2 and better inhibition on the migration of activated HSCs. Compared to free siRNA and the nanocomplexes coupled with vitamin A and cholesterol, the IGF2R-specific peptide coupled nanocomplex showed the highest uptake in the liver and lowest uptake in the lung and kidney of the rats with CCl4-induced liver fibrosis.

The pH sensitivity of murine heat shock protein 47 (HSP47) binding to collagen is affected by mutations in the breach histidine cluster

Heat shock protein 47 (HSP47) is a single-substrate molecular chaperone crucial for collagen biosynthesis. Although its function is well established, the molecular mechanisms that govern binding to procollagen peptides and triple helices in the endoplasmic reticulum (followed by controlled release in the Golgi) are unclear. HSP47 binds procollagen at a neutral pH but releases at a pH similar to the pK(a) of the imidazole side chain of histidine residues. It thus seems likely that these residues are involved in this pH-dependent mechanism. Murine HSP47 has 14 histidine residues grouped into three clusters, known as the breach, gate, and shutter. Here, we report the use of histidine mutagenesis to demonstrate the relative contribution of these three clusters to HSP47 structure and the "pH switch." Many of the tested mutants are silent; however, breach mutants H197A and H198A show binding but no apparent pH switch and are unable to control release. Another breach mutant, H191A, shows perturbed collagen release characteristics, consistent with observed perturbations in pH-driven trans-conformational changes. Thus, His-198, His-197 and His-191 are important (if not central) to HSP47 mechanism of binding/release to collagen. This is consistent with the breach cluster residues being well conserved across the HSP47 family.

Histopathological and ultrastructural studies on the effects of electromagnetic fields on the liver of preincubated white Leghorn chicken embryo

There are several reports indicating a linkage between exposures to 50-60 Hz electromagnetic fields and abnormalities in the early stages of embryonic development of chicken embryos. The present study was designed to demonstrate whether electromagnetic fields could be an environmental factor invoking histopathological and ultra-structural changes in livers of preincubated chicken embryos exposed to EMFs. Following other researchers and our previous results from different groups of Developmental Biology at the Animal Sciences, Faculty of Biological Sciences, Shahid-Beheshti University, effects of most effective intensities (1.33, 2.66, 5.52, and 7.32 mT) of electromagnetic fields (EMFs, 50 Hz ) on livers of pre-incubated white leghorn chicken embryos were investigated . 150 healthy, fresh, and fertilized eggs (55-65 gr) were divided into 6 groups of experimental(1-4, n = 30), control (n = 60), and sham (n = 50). Experimental eggs (inside coil) were exposed to 4 different intensities (1.33, 2.66, 5.52, and 7.32 mT). Sham groups were located inside same coil, with no exposure, for 24 h before incubation. Control, sham, and experimental groups (1-4) were then incubated in an incubator (38 +/- 0.5 degrees C, 60% humidity) for 17 days. At the end of this period, livers of experimental, sham, and control groups were processed for light and transmission electrom microscopes (TEM and SEM) studies. So, livers of 17-day old chicken embryos were removed by C-sections, fixed in formalin 10%, stained with H&E and reticulin, and studied under light microscope. Others were prepared for electron microscopes (TEM and SEM) investigations. Morphological observations indicated exencephalic embryos, embryos with asymmetrical faces, crossed beak, shorter upper beak, deformed hind limbs, gastroschesis, anophthalmia, and microphthalmia. H&E and reticulin stainings, TEMS, and SEMs studies indicated EMFs would create hepato-cytes with fibrotic bands, severe steatohepatitis, vacuolizations, swollen and extremely electron-dense mitochondria, reduced invisible cristae, crystalized mitochondria with degenerated cristae, myelin-like figures, macrophages engulfing adjacent cells, dentated nuclei, nuclei with irregular envelopes, degenerated hepatocytes, abnormal lipid accumulations, lipid droplets pushing hepatocytes' nuclei to the corner of the cells, abundant cellular infiltrations cellular infiltrations inside sinusoid and around central veins, disrupted reticulin plexus, and release of chromatin into cytosol,, with partially regular water layers. An elevated oxyradical generation and, subsequently, cell membrane disruptions were the reasons for electromagnetic fields inducing cell damages.

Induction and progression of cholangiofibrosis in rat liver injured by oral administration of furan

Cholangiofibrosis is a structural anomaly that precedes the development of cholangiocarcinoma in some rodent models. In this article, the authors examine the contribution of the epithelial and mesenchymal cells in the pathogenesis of this complex lesion. Furan was administered to rats by gavage in corn oil at 30 mg/kg b.w. (five daily doses per week) and livers were sampled between eight hr to three months. Characteristically the administration of furan caused centrilobular injury, and restoration was accomplished by proliferation of hepatocytes. Some areas of the liver were, however, more severely affected, and here, injury extended into portal and capsular areas, which resulted in a rapid proliferation of ductular cells that extended into the parenchyma accompanied by a subtype of liver fibroblasts. These ductules either differentiated into hepatocytes, with loss of the associated fibroblasts, or progressed to form tortuous ductular structures that replaced much of the parenchyma, leading to cholangiofibrosis. Although it is unclear what determines the difference in the hepatic response, a loss of micro-environmental cues that instigate hepatocyte differentiation and termination of the hepatocyte stem cell repair response may be perturbed by continual furan administration that results in an irreversible expansile lesion that may mimic the features of cholangiocarcinoma.

Biochemical characterization of the binding of cyclic RGDyK to hepatic stellate cells

Activated hepatic stellate cells (HSCs) play a crucial role in the development of liver fibrosis. Noninvasive monitoring of the activation of HSCs has been challenging due to the lack of specific receptors or motifs on the cells. The present study provides the evidence that integrin alpha v beta 3 expressed on HSCs is a biomarker reflecting the activation of HSCs. Solid-phase synthesis of cRGDyK (Arg-Gly-Asp-(D)Tyr-Lys) peptide and FAM-conjugated peptide were employed for binding to integrin alpha v beta 3. The increased expression of integrin alpha v and beta 3 at mRNA and protein levels was detected during HSC activation. The affinity of cRGDyK to integrin alpha v beta 3 was examined by both radioligand binding assay and FAM-conjugated peptide binding measurements. Quantitative RT-PCR and Western blotting showed a less dramatic, but significant increase in alpha v and beta 3 integrin mRNA and protein expression following activation of rat HSCs. Radioiodinated cRGDyK binds to both purified and membrane-bound integrin alpha v beta 3 with high affinity in a dissociable manner. FAM-conjugated cRGDyK was coupled to activated HSCs in a time- and dose-dependent, receptor-mediated manner. Activated HSCs express sufficient number of integrin alpha v beta 3 receptor. cRGDyK peptide binds to both purified and membrane-bound integrin alpha v beta 3 with high affinity in a reversible fashion. Thus, the cRGDyK peptide represented a new agent potentially useful for the diagnosis of liver fibrosis.

Neutrophil depletion blocks early collagen degradation in repairing cholestatic rat livers

Biliary obstruction results in a well-characterized cholestatic inflammatory and fibrogenic process; however, the mechanisms and potential for liver repair remain unclear. We previously demonstrated that Kupffer cell depletion reduces polymorphonuclear cell (neutrophil) (PMN) and matrix metalloproteinase (MMP)8 levels in repairing liver. We therefore hypothesized that PMN-dependent MMP activity is essential for successful repair. Male Sprague-Dawley rats received reversible biliary obstruction for 7 days, and the rat PMN-specific antibody RP3 was administered 2 days before biliary decompression (repair) and continued daily until necropsy, when liver underwent morphometric analysis, immunohistochemistry, quantitative RT-PCR, and in situ zymography. We found that RP3 treatment did not reduce Kupffer cell or monocyte number but significantly reduced PMN number at the time of decompression and 2 days after repair. RP3 treatment also blocked resorption of type I collagen. In addition, biliary obstruction resulted in increased expression of MMP3, MMP8, and tissue inhibitor of metalloproteinase 1. Two days after biliary decompression, both MMP3 and tissue inhibitor of metalloproteinase 1 expression declined toward sham levels, whereas MMP8 expression remained elevated and was identified in bile duct epithelial cells by immunohistochemistry. PMN depletion did not alter the hepatic expression of these genes. Conversely, collagen-based in situ zymography demonstrated markedly diminished collagenase activity following PMN depletion. We conclude that PMNs are essential for collagenase activity and collagen resorption during liver repair, and speculate that PMN-derived MMP8 or PMN-mediated activation of intrinsic hepatic MMPs are responsible for successful liver repair.

Albumin mediates PPAR-gamma or C/EBP-alpha-induced phenotypic changes in pancreatic stellate cells

Activation of quiescent hepatic stellate cells (HSCs) into myofibroblast-like cells is a key event of liver fibrosis, and adipogenic transcription factors, PPAR-gamma and C/EBP-alpha, reverse HSC activation. As albumin was reported to maintain the quiescent phenotype of stellate cells, we examined whether it plays a role in PPAR-gamma and C/EBP-alpha-mediated effects. Pancreatic stellate cells (PSCs) were isolated from rat pancreas and used in their culture-activated phenotype. Forced expression of PPAR-gamma or C/EBP-alpha in PSCs increased albumin mRNA and protein levels by >2.5-fold, which is accompanied with increased C/EBP-beta binding to albumin promoter. PPAR-gamma and C/EBP-alpha also induced a phenotypic switch from activated to quiescent cells and, interestingly, suppression of albumin using short-hairpin RNA (shRNA) blocked their effects. Therefore, our findings suggest that albumin may be a downstream effector of PPAR-gamma and C/EBP-alpha in PSCs and that it can be an attractive molecular target for anti-fibrotic therapies.

Evaluation of hepatic fibrosis with portal pressure gradient in rats

MRI has the potential of providing a noninvasive assessment of liver pathology. This work introduces a portal pressure gradient (PPG) model derived from fluid mechanics, where the PPG is proportional to the average velocity and inversely proportional to the vessel area in the upper part of portal vein. Using a phase-contrast spoiled gradient echo sequence, the PPG model was verified in a phantom study and was tested in an animal study using 35 rats with various degrees of hepatic fibrosis induced by carbon tetrachloride (CCl(4)). Histological examination was conducted to determine the severity of hepatic fibrosis. The fibrosis score monotonically increased with the duration of CCl(4) treatment. The PPG was highly correlated with nonzero fibrosis scores (r(2) = 0.90, P < 0.05). There was a significant difference between control and cirrhosis groups (P < 0.0006, alpha < 0.0018). The difference between control and fibrosis (noncirrhosis) groups (P < 0.002, alpha < 0.006) was also significant. Without the administration of any contrast agent, the MRI-PPG approach shows promise as a noninvasive means of evaluating liver fibrosis.

TGF-beta and mesenchymal hepatic involvement after visceral leishmaniasis

The liver involvement in the human visceral leishmaniasis (VL) has been related to parasitism and activated Kupffer cells with further occasional fibrotic alterations, especially after long-term disease without treatment. However, fibrotic alterations have been reported after therapy, whose clinical finding is the persistence of hepatomegaly. Fibrotic involvement of the liver after therapy was never well understood, and the aim of this study was to evaluate this finding through ultrastructural and morphometric analysis. A case-control study was performed with 20 patients (15 cases and five controls). Cases included patients with persistent hepatomegaly (residual) after treatment of VL submitted to liver biopsy to exclude other causes of liver enlargement, including serum tests of viral hepatitis. The material was evaluated by electron microscopy allowing ultrastructural with morphometric analysis of medium portion of hepatic lobule. Narrow sinusoidal lumen and prominent Kupffer cells were found with insignificant alterations of hepatocytes, pit, and endothelial cells. On ultrastructural analysis, the enlargement of the space of Disse was due to fibrous collagen, increase of number of Ito cells, and nonfibrous extracellular matrix that were associated with Kupffer cells enlargement. Immunohistochemistry showed an intense expression of TGF-beta in patients with VL. These findings suggest a production of TGF-beta by Kupffer cells that resulted in the characteristic fibrotic involvement of the liver. Residual hepatomegaly in visceral leishmaniasis could result from sustained Kupffer cell activation with perihepatocytic fibrosis.

Experimental poisoning by Senecio brasiliensis in calves: quantitative and semi-quantitative study on changes in the hepatic extracellular matrix and sinusoidal cells

Extracellular matrix plays an important role in chronic hepatic lesions and has been studied in experimental intoxication models. However in cattle, studies on chronic disease have focused on the hepatocellular damage and extracellular matrix (ECM) changes are usually overlooked. There are no specific studies on the hepatic ECM in either normal or chronically damaged bovine liver. Thus an experimental model of hepatic toxicity model using Senecio brasiliensis poisoned calves was designed. Senecio brasiliensis contains pyrrolizidine alkaloids which cause either acute or chronic progressive dose dependent liver damage. Five calves were orally fed with 0.38g of dry leaves of S. brasiliensis/kg/day for 24 days. Liver needle biopsy specimens were obtained every 15 days for 60 days. Clinical signs of digestive complications appeared at 3rd week. One calf died on 45th day and four were evaluated up to 60th day. Biopsy samples were processed for routine light microscopy, immuno-histochemistry and transmission electron microscopy. From 30th day on progressive liver damage characterized by hepatocellular ballooning, necrosis, apoptosis and megalocytosis, centrilobular, pericellular and portal fibrosis were seen by light microscopy. Quantitative and semi-quantitative measurements of hepatic ECM components were performed before and after the onset of lesions. Morphometric analysis of total collagen and elastic fiber system was conducted. Total collagen and I and III collagen types progressively increased in throughout the liver of affected calves. Changes in location, amount and disposition of the elastic fiber system were also observed. Then numbers of Kupffer cells were significantly increased at 30th day and total numbers of sinusoidal cells were significantly increased at 45th and 60th days. Liver damage was progressive and irreversible even after the exposure to the plant was discontinued. Severe fibrotic lesions occurred mainly in portal tracts, followed by veno-occlusive and pericellular fibrosis. Collagen types I and III s were present in every normal and damaged liver, with predominance of type I. In affected calves the increase of total collagen and elastic fibers system paralleled the number of total sinusoidal cells.

Antioxidant and anti-inflammatory properties of curcumin

Curcumin, a yellow pigment from Curcuma longa, is a major component of turmeric and is commonly used as a spice and food-coloring agent. It is also used as a cosmetic and in some medical preparations. The desirable preventive or putative therapeutic properties of curcumin have also been considered to be associated with its antioxidant and anti-inflammatory properties. Because free-radical-mediated peroxidation of membrane lipids and oxidative damage of DNA and proteins are believed to be associated with a variety of chronic pathological complications such as cancer, atherosclerosis, and neurodegenerative diseases, curcumin is thought to play a vital role against these pathological conditions. The anti-inflammatory effect of curcumin is most likely mediated through its ability to inhibit cyclooxygenase-2 (COX-2), lipoxygenase (LOX), and inducible nitric oxide synthase (iNOS). COX-2, LOX, and iNOS are important enzymes that mediate inflammatory processes. Improper upregulation of COX-2 and/or iNOS has been associated with the pathophysiology of certain types of human cancer as well as inflammatory disorders. Because inflammation is closely linked to tumor promotion, curcumin with its potent anti-inflammatory property is anticipated to exert chemopreventive effects on carcinogenesis. Hence, the past few decades have witnessed intense research devoted to the antioxidant and anti-inflammatory properties of curcumin. In this review, we describe both antioxidant and anti-inflammatory properties of curcumin, the mode of action of curcumin, and its therapeutic usage against different pathological conditions.

PAI-1 deficiency reduces liver fibrosis after bile duct ligation in mice through activation of tPA

Plasminogen activator inhibitor-1 (PAI-1) increases injury in several liver, lung and kidney disease models. The objective of this investigation was to assess the effect of PAI-1 deficiency on cholestatic liver fibrosis and determine PAI-1 influenced fibrogenic mechanisms. We found that PAI-1(-/-) mice had less fibrosis than wild type (WT) mice after bile duct ligation. This change correlated with increased tissue-type plasminogen activator (tPA) activity, and increased matrix metalloproteinase-9 (MMP-9), but not MMP-2 activity. Furthermore, there was increased activation of the tPA substrate hepatocyte growth factor (HGF), a known anti-fibrogenic protein. In contrast, there was no difference in hepatic urokinase plasminogen activator (uPA) or plasmin activities between PAI-1(-/-) and WT mice. There was also no difference in the level of transforming growth factor beta 1 (TGF-beta1), stellate cell activation or collagen production between WT and PAI-1(-/-) animals. In conclusion, PAI-1 deficiency reduces hepatic fibrosis after bile duct obstruction mainly through the activation of tPA and HGF.

Is cirrhosis of the liver reversible?

Extensive and persistent hepatic fibrosis has for a long time been considered irreversible. Accumulating evidence suggests that liver fibrosis is reversible and that recovery from cirrhosis may be possible. The application of molecular techniques to models of reversible fibrosis are helping to establish the events and processes that are critical to recovery. The problem consists in identifying and eliminating its cause. Although fibrosis in the liver has little functional significance by itself, its severity derives from associated vascular changes. Disappearance of fibrosis can be accompanied by remodeling of vascular changes. However, depending on its duration, the fibrosis may be irreversible.

Influence of different intravenous lipid emulsions on hepatobiliary dysfunction in a rabbit model

OBJECTIVES

Long-term total parenteral nutrition (TPN) in children is often complicated by the development of cholestasis, liver fibrosis, and liver failure. High doses of intravenous lipids may be involved in the pathogenesis of hepatobiliary dysfunction. The purpose of this study was to determine whether the use of 2 newly developed lipid emulsions could reduce liver damage.

MATERIALS AND METHODS

Three groups of prepubescent rabbits received TPN including a lipid emulsion either based on soybean oil, olive oil, or soybean oil with n-3 fatty acids added. Enterally fed animals served as controls. After 21 d the animals were killed. Serum samples were obtained at the beginning and end of the study period. Specimens were processed for histological evaluation using a specific score to assess the severity of liver damage.

RESULTS

Biochemical parameters did not predict the extent of liver damage. Hydropic degeneration as an indicator of toxic liver injury was the predominant histological alteration regardless of the type of lipids infused. The extent of fibrosis did not significantly differ among treatment groups except for animals infused with n-3 fatty acids exhibiting increased fibrotic transformation as compared with controls.

CONCLUSION

In our animal model, the use of a lipid emulsion with a reduced amount of polyunsaturated fatty acids was not superior to a lipid emulsion based on soybean oil. Long-term application of n-3 fatty acids was associated with more extensive fibrosis. Therefore, intravenous n-3 fatty acids containing lipid preparations (fish oil) should not be used in patients for long-term TPN.

[Immunohistochemical analysis of alpha-SMA and GFAP expression in liver stellate cells]

BACKGROUND/AIM

Liver stellate cells play an important role in hepatic fibrosis, and its progression to cirrhosis. These cells show immunoreactivity with different monoclonal antibodies amongst which the commonest are alpha-smooth muscle actin (alpha-SMA) and glial fibrillary acid protein (GFAP). The aim of this study was to analyze stellate cell immunoreactivity for alpha-SMA and GFAP in tissue sections showing the signs of chronic viral B-hepatitis and compare it with those without histopathological changes.

METHODS

We included 12 tissue samples showing chronic viral B hepatitis in the different stages of fibrosis and 7 tissue samples showing no histopathological changes. Immunohistochemical staining was performed using the streptavidin-biotin method.

RESULTS

There was a regular presence of alpha-SMA immunoreactivity in tissue sections without histopathological changes in the portal tracts and also in liver parenchyma, while GFAP expression was noted in the periportal cavity. Tissue sections with the signs of chronic viral B hepatitis displayed very strong alpha-SMA expression in the portal tracts. A statistical analysis showed a positive correlation between the degree of liver fibrosis and alpha-SMA expression along the fibrous septa, whereas a negative correlation between the degree of liver fibrosis and alpha-SMA expression was present in the portal zone.

CONCLUSION

This study showed the existance of two different stellate cell subpopulations in liver tissue. Differentiation between them was possible on the basis of SMA/GFAP expression.

Inhibition of CCl4-induced liver fibrosis by Piper longum Linn.?

This study was carried out to evaluate the antifibrotic effect of ethanol extract of the fruits of Indian herb Piper longum Linn. Liver fibrosis was induced in rats by CCl(4) administration. The extent of liver fibrosis was assessed by measuring the level of liver hydroxy proline (HP) and serum enzyme levels. Following CCl(4) administration HP was significantly increased and serum enzyme levels were elevated. Treatment with the ethanol extract of Piper longum Linn. reduced the HP and also the serum enzymes. The liver weight that increased following CCl(4) administration due to the deposition of collagen was reduced by the ethanol extract. Hence, it is concluded that this extract inhibits liver fibrosis induced by CCl(4).

Repair after cholestatic liver injury correlates with neutrophil infiltration and matrix metalloproteinase 8 activity

BACKGROUND

Although timely surgical treatment of liver disease can interrupt inflammation and reduce fibrosis, the mechanisms of repair are unknown. We questioned whether these mechanisms of repair include changes in the inflammatory infiltrate and associated biological activity of matrix metalloproteinases (MMPs) 8 and 2.

METHODS

Rats (n >or= 3) underwent biliary ductal suspension for 7 days followed by decompression. Livers were collected after 7 days of obstruction (d0) and after 2, 5, and 7 days of repair (d2, d5, d7, respectively), and assessed morphometrically for collagen, polymorphonuclear cells (PMNs), Kupffer cells (KCs), and inflammatory mononuclear phagocytes (MNPs). In situ zymography was performed by using fluorogenic substrates for MMP-8 and MMP-2 to spatially localize enzymatic activity.

RESULTS

Cholestatic injury resulted in significantly elevated (P <or= .001) collagen deposition (3-fold), and elevated numbers of MNPs (10-fold), KCs (5-fold), and PMNs (4-fold), compared with shams. PMNs remained elevated through d7, while collagen deposition, KCs, and MNPs returned to sham levels by d2. In situ zymography showed no significant changes in MMP-2 activity after cholestatic injury and repair. MMP-8 activity was significantly (P <or= .05) elevated only during repair. Activity was localized to fibrotic portal triads containing PMNs.

CONCLUSIONS

Cholestatic injury results in increased fibrosis, MNPs, KCs, and PMNs but no MMP-2 or MMP-8 activity. Biliary decompression results in increased MMP-8 activity co-localized to areas of portal fibrosis and PMN accumulation. We conclude that secretion of MMP-8 by neutrophils may play a critical role in resolving the fibrotic scar generated during cholestasis.

Total parenteral nutrition induced liver pathology: an autopsy series of 24 newborn cases

Total parenteral nutrition (TPN)-induced liver injury is a common complication in neonates managed with newborn intensive care. In several of these cases, irreversible and even fatal liver damage may develop, with patients dying of liver failure. In spite of multiple studies over several years, the pathogenesis of TPN-induced liver damage remains poorly understood. Clinical data from 24 neonates with clinical history of receiving TPN who died at Yale-New Haven Children's Hospital and had autopsies performed, were collected by medical record review without knowledge of liver pathology findings. Liver histological sections from these patients were evaluated for multiple parameters without knowledge of the clinical course. Continuous data were analyzed by Wilcoxon signed-rank test and Mann-Whitney test, and dichotomous data by Fisher's exact test; P < 0.05 was considered significant. Different histopathological abnormalities with varying degrees of severity were observed. A progression in the severity of histopathological changes in relation to duration of TPN administration (DTPN) was found. While patients with DTPN of < 2 wk had no fibrosis or only mild degrees of fibrosis, patients with more than 6 wk of DTPN developed moderate-to-severe fibrosis. Similar results were observed for cholestasis and bile duct proliferation. We did not find significant differences for birth weight, gestational age, occurrence of necrotizing enterocolitis, sepsis, or enteral feedings between the group with normal-to-mild liver changes ( n = 16), and the group with moderate-to-severe liver changes ( n = 8). On the other hand, DTPN was significantly different between these two groups ( P = 0.008). Also, patients small for gestational age ( P = 0.003) and patients with bronchopulmonary dysplasia ( P = 0.001) were more commonly seen in the group with moderate-to-severe histopathological findings. Intracellular copper was detected in 12.5% of patients with moderate-to-severe liver changes, and was found in 50% of patients with normal-to-mild liver findings ( P = 0.04). Detection of copper from tissue sections also decreased with DTPN, being observed in 57% of patients with < 2 wk DTPN and in none of the patients with > 12 wk DTPN. Our findings confirm the known significant relationship between the duration of TPN and liver injury. While previously described associations with birth weight, gestational age, enteral feedings, necrotizing enterocolitis, and sepsis were not noted, our study suggests that poor intrauterine growth may be a significant clinical risk factor for TPN-induced liver injury. In addition, our findings suggest that copper may have a protective effect against the development of TPN-induced liver damage.

Biliary intervention augments chemotactic reaction and aggravates cholestatic liver injury in rats

BACKGROUND

Intervention of the biliary system is frequently done in patients with obstructive jaundice and is associated with significant morbidity and mortality. The pathogenesis is unknown.

MATERIALS AND METHODS

A rat model of bile duct ligation (BDL) for 2 weeks was established in which biliary intervention was feasible by injection of normal saline through an indwelling catheter in the bile ducts. Plasma levels of C-C chemokine MCP-1 and C-X-C chemokine MIP-2 were measured by using ELISA. Blood monocytes, Kupffer cells, and neutrophils in the liver were characterized with antibodies to ED1, ED2, and myeloperoxidase (MPO). Lipid peroxidation was measured by malondialdehyde contents and apoptosis by TUNEL stain of the liver.

RESULTS

Biliary intervention resulted in an increase of plasma MCP-1 and MIP-2 proteins by 1 h, which declined to normal level by 3 h in both sham and BDL rats. The levels in BDL rats were significantly higher than in sham at most points. There was a transient increase of ED1- and ED2-positive cells and MPO-staining cells in sham rat liver by 1 h after intervention. ED2-positive cells increased significantly by 1 h, while ED1- and MPO-positive cells decreased, yet insignificantly after intervention in BDL rats. The cell counts in BDL were constantly higher than in sham. Malondialdehyde increased precipitously in BDL by 3 h and was significantly higher than in sham throughout the study period. Parenchymal liver injury, manifested by elevated ALT, as well as apoptosis and necrosis of liver cells, was significantly increased in BDL rats, but not in sham rats.

CONCLUSION

Biliary intervention augments chemokine expression, precipitates lipid peroxidation, and aggravates liver injury in cholestatic rats.

Identification of transforming growth factors actively transcribed during the progress of liver fibrosis in biliary atresia

BACKGROUND/PURPOSE

Transforming growth factor-beta (TGF-beta) 1 and 2 and their receptors TbetaR-I, TbetaR-II, and TbetaR-III are powerful profibrogenic mediators in the body. Their expression has not been completely elucidated in the progress of liver fibrosis associated with biliary atresia (BA).

METHODS

The authors compared the cytokine expression in the liver of 3 patients with BA at Kasai's procedure (KP) and in 3 patients at liver transplantation (LT). Two liver samples from children with no liver disorders served as normal controls (CO). Real-time quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) was used to confirm the findings of relative mRNA expression of TGF-beta1 and 2 and their receptors. An immunohistochemistry and an enzyme-linked immunoassay (ELISA) were used to localize the liver cells that express TGF-beta2 and to quantitate the protein expression among groups.

RESULTS

Compared with controls, both TGF-beta1 and TGF-beta2 mRNA expression increased in the liver during the progress of liver fibrosis in patients with KP and LT on the array. Only TGF-beta2 showed a significant increase in expression in LT compared with KP and CO (P =.001 for TGF-beta2 and P = 0.054 for TGF-beta1). Both TbetaR-I and TbetaR-II showed no significant change among groups; TbetaR-III decreased significantly in LT compared with CO (P =.011). TGF-beta2 immunostaining was mainly localized in the bile duct epithelium and was remarkably higher in LT in which the proliferating bile ductules and the hepatocytes contributed to the increase in immunostaining and possibly to significantly higher plasma TGF-beta2 protein levels in LT than in KP.

CONCLUSIONS

This study identified TGF-beta2 as the most actively transcribed TGF-beta gene during the progress of liver fibrosis in BA and found a reciprocal relationship of upregulation of TGF-beta2 with downregulation of TbetaR-III in LT.

Identification of expressed sequence tags of genes expressed highly in the activated hepatic stellate cell

Expressed sequence tags (ESTs) were generated from two 3'-directed cDNA libraries constructed from quiescent and activated rat hepatic stellate cell (HSC) to analyze the expression profiles of active genes in both cells. From quiescent and activated HSC, 694 ESTs and 779 ESTs, respectively, were obtained after excluding those having shorter than 30 bp. Among ESTs obtained from quiescent and activated HSC, 68 and 73 kinds of ESTs (186 clones and 236 clones), respectively, appeared more than once, implying that their genes are expressed highly in each cell type. 52 among 73 ESTs appeared only in the activated HSC, 47 among 68 ESTs only in the normal HSC, and 21 in both cells. The genes of these 52 ESTs were assumed to be expressed more highly in the activated HSC. To confirm the high expression of genes of which the ESTs appeared more than twice in the activated HSC, northern hybridization was carried out with RNAs derived from rat normal and fibrotic liver using each of 18 EST DNAs as probe. 13 ESTs showed more intense bands with RNA isolated from the fibrotic liver than normal liver. From these results, we confirm the positive correlation between abundance of transcript in activated HSCs and the expression level in fibrotic liver. The expression profile of the transcripts serves as an important tool in understanding the biological properties of HSC.

Engagement of alphavbeta3 integrin regulates proliferation and apoptosis of hepatic stellate cells

Hepatic stellate cells are the major source of the extracellular matrix that accumulates in fibrotic liver. During progressive liver fibrosis, hepatic stellate cells proliferate, but during resolution of fibrosis there is extensive stellate cell apoptosis that coincides with degradation of the liver scar. We have examined the possibility that the fate of stellate cells is influenced by the extracellular matrix through the intermediary of alpha(v)beta(3) integrin. alpha(v)beta(3) integrin was expressed by activated, myofibroblastic rat and human stellate cells in culture. Antagonism of this integrin using neutralizing antibodies, echistatin, or small inhibitory RNA to silence alpha(v) subunit expression inhibited stellate cell proliferation and their expression of proliferating cell nuclear antigen and activated forms of p44 and p42 MAPK. These alpha(v)beta(3) antagonists also increased apoptosis of cultured stellate cells, and this was associated with an increase in the BAX/BCL-2 protein ratio, induction of nuclear DNA fragmentation, and activation of intracellular caspase-3. Expression of tissue inhibitor of metalloproteinases-1 by activated stellate cells was reduced by the alpha(v)beta(3) antagonists, while matrix metalloproteinase-9 synthesis was enhanced. Stellate cells incubated with active recombinant matrix metalloproteinase-9 showed enhanced apoptosis, while cells treated with a synthetic inhibitor of this protease showed increased survival. Our studies suggest that alpha(v)beta(3) integrin regulates the fate of hepatic stellate cells. Degradation of alpha(v)beta(3) ligands surrounding activated stellate cells during resolution of liver fibrosis might decrease alpha(v)beta(3) integrin ligation, suppressing stellate cell proliferation and inducing a fibrolytic, matrix metalloproteinase-secreting phenotype that may prime stellate cells for apoptosis.

The human Delta-like 1 homologue is implicated in the progression of liver fibrosis in biliary atresia

Advanced liver cirrhosis frequently occurs in infants with biliary atresia despite early surgical correction. The aetiology is unknown, but may involve many cytokines and liver cells including hepatic stellate cells (HSCs). A cytokine expression array and real-time quantitative reverse transcription-polymerase chain reaction (QRT-PCR) were used to study cytokine expression during the progression of liver fibrosis in biliary atresia. A Delta-like 1 homologue (DLK1) gene was identified and this gene was up-regulated during the early stage, and down-regulated during the late stage, of biliary atresia, similar to the expression pattern of the procollagen alpha1(I) gene. Further characterization with immunohistochemistry, confocal microscopy, and in situ hybridization revealed that the DLK1 protein was mainly present in the cytoplasm of smooth muscle actin-positive mesenchymal cells that were morphologically and immunohistochemically identical to activated HSCs/myofibroblasts, whereas DLK1 mRNA was present only in hepatocytes. As DLK1 is a negative regulator of adipocyte differentiation and may control cell fate during differentiation, overexpression of DLK1 protein in HSCs in the early stage of biliary atresia suggests that DLK1 may be implicated in the transformation of HSCs from fat-storing cells to myofibroblasts and in fibrogenesis associated with biliary atresia.

Transcriptional reprogramming in murine liver defines the physiologic consequences of biliary obstruction

BACKGROUND/AIMS

While the metabolic and histological responses to cholestasis are recognized, the consequences of impaired biliary flow on liver gene expression are largely undefined. We hypothesized that biliary obstruction results in transcriptional reprogramming that dictates the physiologic response.

METHODS

We determined global gene expression in murine livers 1-21 days following bile duct ligation. Total hepatic cRNA from experimental and sham mice was hybridized to Affymetrix gene chips. Gene expression data was analyzed by GeneSpring software and validated by Northern analysis.

RESULTS

We found 92 genes over-expressed > or =2-fold at one or more time points following bile duct ligation. Functional classification of these genes revealed the activation of three main biological processes in a sequential and time-restricted fashion. At day 1, genes involved in sterol metabolism were uniquely over-expressed, including HMG-CoA reductase, the rate-limiting enzyme of cholesterol biosynthesis. This was followed by an increased expression of growth-promoting genes at day 7, the time point coinciding with peak cholangiocyte proliferation. In later phases (days 14-21), the liver over-expressed genes encoding structural proteins and proteases.

CONCLUSIONS

Transcriptional reprogramming in the liver following biliary obstruction favors the activation of genes regulating metabolism, cell proliferation, and matrix remodeling in a time-restricted and sequential fashion.

Basement membrane-like matrix inhibits proliferation and collagen synthesis by activated rat hepatic stellate cells: evidence for matrix-dependent deactivation of stellate cells

During liver fibrosis hepatic stellate cells become activated, transforming into proliferative myofibroblastic cells expressing type I collagen and alpha-smooth muscle actin. They become the major producers of the fibrotic neomatrix in injured liver. This study examines if activated stellate cells are a committed phenotype, or whether they can become deactivated by extracellular matrix. Stellate cells isolated from normal rat liver proliferated and expressed mRNA for activation markers, alpha-smooth muscle actin, type I procollagen and tissue inhibitor of metalloproteinases-1 following 5-7 day culture on plastic, but culture on Matrigel suppressed proliferation and mRNA expression. Activated stellate cells were recovered from plastic by trypsinisation and replated onto plastic, type I collagen films or Matrigel. Cells replated on plastic and type I collagen films proliferated and remained morphologically myofibroblastic, expressing alpha-smooth muscle actin and type I procollagen. However, activated cells replated on Matrigel showed <30% of the proliferative rate of these cells, and this was associated with reduced cellular expression of proliferating cell nuclear antigen and phosphorylation of mitogen-activated protein kinase in response to serum. Activated HSC replated on Matrigel for 3-7 days progressively reduced their expression of mRNA for type I procollagen and alpha-smooth muscle actin and both became undetectable after 7 days. We conclude that basement membrane-like matrix induces deactivation of stellate cells. Deactivation represents an important potential mechanism mediating recovery from liver fibrosis in vivo where type I collagen is removed from the liver and stellate cells might re-acquire contact with their normal basement membrane-like pericellular matrix.

Liver fibrosis: insights into migration of hepatic stellate cells in response to extracellular matrix and growth factors

BACKGROUND & AIMS

In liver fibrosis, alterations within the space of Disse microenvironment occur and facilitate further progression of chronic liver disease. The normal basement membrane-like matrix present within the space of Disse converts to a matrix rich in fibril-forming collagens during fibrosis.

METHODS

To further understand the pathogenesis of liver fibrosis, we modified an in vitro Boyden chamber system to partially mimic in vivo conditions of hepatic stellate cells (HSCs) during health and disease.

RESULTS

Stimulation of HSCs with platelet-derived growth factor (PDGF)-BB, transforming growth factor (TGF)-beta1, and/or epithelial growth factor (EGF) resulted in an increase in their migratory capacity and up-regulated matrix metalloproteinase (MMP)-2 activity. Migration induced by PDGF-BB was associated with increased proliferation, whereas TGF-beta1/EGF-induced migration was proliferation independent. COL-3, an inhibitor of MMP-2 and MMP-9, inhibited migration of HSCs induced by direct activation of PDGF-BB or TGF-beta1 but had no effect on migration induced by chemotactic stimuli without direct contact, suggesting 2 distinct MMP-dependent and MMP-independent mechanisms of PDGF-BB- or TGF-beta1-induced migration. Additionally, we show that type I collagen by itself induced migration of HSCs. Migration induced by PDGF-BB, TGF-beta1, and collagen I could be inhibited by alpha(1)- and/or alpha(2)-integrin blocking antibodies, collectively suggesting an integrin-dependent, MMP-2-mediated migration of HSCs.

CONCLUSIONS

Basement membrane matrix integrity, composition, and cell-matrix interactions play an important role in anchoring HSCs and preventing them from spreading within the space of Disse and potentially elsewhere in the liver. Additionally, our data provide strong evidence for MMPs in regulation of HSCs migration.

Matrix metalloproteinase-2 from bronchial epithelial cells induces the proliferation of subepithelial fibroblasts

BACKGROUND

In bronchial asthma, subepithelial fibrosis in the conducting airways is associated with increased numbers of subepithelial fibroblasts.

OBJECTIVE

This study examined the hypothesis that MMP-2 from airway epithelial cells induces the proliferation of subepithelial fibroblasts.

METHODS

Using primary bronchial epithelial cells MMP-2, MT1-MMP and TIMP-2 mRNA expression were assessed by Northern blotting and RT-PCR. Primary bronchial epithelial cells transfected with constructs encoding pro-MMP-2 and MT1-MMP (MMP-14).

RESULTS

Transfected cells showed enhanced expression of the appropriate mRNA species by RT-PCR and enhanced MMP-2 or MT1-MMP activity by zymography. Active MMP-2 levels in epithelial supernatants were increased most by cotransfection with pro-MMP-2 and MT1-MMP encoding constructs. By measuring tritiated thymidine incorporation, supernatants from transfected cells were found to enhance DNA synthesis of primary airway fibroblast cultures compared with controls. There was a strong correlation (r = 0.9, P < 0.01) between MMP-2 levels in epithelial cell conditioned media and fibroblast proliferation as indicated by DNA synthesis. The MMP inhibitor 1,10-phenanthroline attenuated the increased proliferation, while the addition of exogenous purified MMP-2 alone also increased fibroblast proliferation.

CONCLUSIONS

Our results support a role for MMP-2 in mediating cross-talk between epithelial cells and myofibroblasts.

Transcriptional regulation of fibronectin gene by phorbol myristate acetate in hepatoma cells: a negative role for NF-kappaB

The transcriptional regulation of the fibronectin (FN) gene in hepatoma cells by phorbol myristate acetate (PMA) was investigated. PMA increased the synthesis and mRNA levels of FN and its promoter activity in Hep3B hepatoma cells. The PMA-induced activation of FN expression was blocked by a protein kinase C (PKC) inhibitor and did not require a new protein synthesis. Deletion analysis revealed that the sequence between positions -69 and +136 of the FN gene was responsible for the PMA induction. Two PMA-inducible nuclear protein complexes were found to bind to a putative NF-kappaB site at -41 and were identified as a p65/p50 heterodimer and a p50/50 homodimer of NF-kappaB family. Mutations in the -41 NF-kappaB site, however, did not block the PMA induction of the FN promoter but rather enhanced it. Overexpression of p65 increased the FN promoter activity. While overexpression of p50 alone did not affect the promoter activity, it decreased the p65-induced activation of the FN promoter. Mutations in the -41 NF-kappaB site attenuated the p50-mediated suppression of the p65 transactivation of the FN promoter. Deletion of the sequence between +1 and +136 decreased the basal and PMA-induced activities of the FN promoter. This study shows that PMA induces the transcription of the FN gene in hepatoma cells via the PKC pathway. The DNA sequence between +1 and +136 is responsible, at least in part, for the PMA-induced activation of the FN gene, while the -41 NF-kappaB binding site plays as a negative regulatory element for it. In addition, this study is the first to show a role for NF-kappaB p65 in the transcriptional activation of the FN gene.

Plasminogen deficiency leads to impaired remodeling after a toxic injury to the liver

Cellular proliferation and tissue remodeling are central to the regenerative response after a toxic injury to the liver. To explore the role of plasminogen in hepatic tissue remodeling and regeneration, we used carbon tetrachloride to induce an acute liver injury in plasminogen-deficient (Plg(o)) mice and nontransgenic littermates (Plg(+)). On day 2 after CCl(4), livers of Plg(+) and Plg(o) mice had a similar diseased pale/lacy appearance, followed by restoration of normal appearance in Plg(+) livers by day 7. In contrast, Plg(o) livers remained diseased for as long as 2.5 months, with a diffuse pale/lacy appearance and persistent damage to centrilobular hepatocytes. The persistent centrilobular lesions were not a consequence of impaired proliferative response in Plg(o) mice. Notably, fibrin deposition was a prominent feature in diseased centrilobular areas in Plg(o) livers for at least 30 days after injury. Nonetheless, the genetically superimposed loss of the Aalpha fibrinogen chain (Plg(o)/Fib(o) mice) did not correct the abnormal phenotype. These data show that plasminogen deficiency impedes the clearance of necrotic tissue from a diseased hepatic microenvironment and the subsequent reconstitution of normal liver architecture in a fashion that is unrelated to circulating fibrinogen.