Quantitative analysis of proliferating sinusoidal cells in dimethylnitrosamine-induced cirrhosis. An immunohistochemical study

Metabolism of N-nitrosodimethylamine, methylation of macromolecules, and development of hepatic fibrosis in rodent models

Hepatic fibrosis and cirrhosis are chronic diseases affecting liver and a major health problem throughout the world. The hallmark of fibrosis and cirrhosis is inordinate synthesis and deposition of fibril forming collagens in the extracellular matrix of the liver leading to nodule formation and loss of normal architecture. Hepatic stellate cells play a crucial role in the pathogenesis and progression of liver fibrosis through secretion of several potent fibrogenic factors that trigger hepatocytes, portal fibrocytes, and bone marrow-derived fibroblasts to synthesize and deposit several connective tissue proteins, especially collagens between hepatocytes and space of Disse. Regulation of various events involved in the activation and transformation of hepatic stellate cells seems to be an appropriate strategy for the arrest of hepatic fibrosis and liver cirrhosis. In order to unravel the molecular mechanisms involved in the pathogenesis and progression of hepatic fibrosis, to determine proper and potent targets to arrest fibrosis, and to discover powerful therapeutic agents, a quick and reproducible animal model of hepatic fibrosis and liver cirrhosis that display all decompensating features of human condition is required. This review thoroughly evaluates the biochemical, histological, and pathological features of N-nitrosodimethylamine-induced model of liver injury, hepatic fibrosis, and early cirrhosis in rodents.

Molecular mechanisms in the pathogenesis of N-nitrosodimethylamine induced hepatic fibrosis

Hepatic fibrosis is marked by excessive synthesis and deposition of connective tissue proteins, especially interstitial collagens in the extracellular matrix of the liver. It is a result of an abnormal wound healing in response to chronic liver injury from various causes such as ethanol, viruses, toxins, drugs, or cholestasis. The chronic stimuli involved in the initiation of fibrosis leads to oxidative stress and generation of reactive oxygen species that serve as mediators of molecular events involved in the pathogenesis of hepatic fibrosis. These processes lead to cellular injury and initiate inflammatory responses releasing a variety of cytokines and growth factors that trigger activation and transformation of resting hepatic stellate cells into myofibroblast like cells, which in turn start excessive synthesis of connective tissue proteins, especially collagens. Uncontrolled and extensive fibrosis results in distortion of lobular architecture of the liver leading to nodular formation and cirrhosis. The perpetual injury and regeneration process could also results in genomic aberrations and mutations that lead to the development of hepatocellular carcinoma. This review covers most aspects of the molecular mechanisms involved in the pathogenesis of hepatic fibrosis with special emphasize on N-Nitrosodimethylamine (NDMA; Dimethylnitorsmaine, DMN) as the inducing agent.

Overexpression of apelin receptor (APJ/AGTRL1) on hepatic stellate cells and sinusoidal angiogenesis in human cirrhotic liver

BACKGROUND

The apelin receptor (APJ) is related to angiotensin-like-receptor 1 (AGTRL1). This study was designed to elucidate the in vivo localization and changes of APJ in cirrhotic liver, and the in vitro changes of APJ expression in cultured hepatic stellate cells (HSCs) and capillarized sinusoidal endothelial cells (SECs) activated by growth factors.

METHODS

In vivo studies used control liver samples, cirrhotic liver samples from patients with Child's A cirrhosis undergoing surgical resection (Child-A-LC), and cirrhotic liver samples from autopsied cases of decompensated Child's C cirrhosis (Child-C-LC). Immunohistochemical (IHC), Western blot, laser-capture microdissection (LCM) coupled with reverse transcription -polymerase chain reaction (RT-PCR), and immunoelectron microscopic (IEM) studies for APJ expression were conducted. In vitro examinations used commercial human HSCs and SECs. APJ expression was examined in cultured HSCs activated by growth factors and in capillarized SECs activated by angiogenic factors.

RESULTS

The IHC study of liver samples revealed only slight APJ expression in hepatic sinusoids in control liver tissue. In cirrhotic liver (Child-A-LC and Child-C-LC), APJ expression was evident mainly along the sinusoids and on portal fibroblasts in fibrotic septa. Western blot analysis of whole-liver homogenate and LCM-PCR of sinusoids revealed overexpression of APJ in Child-C-LC samples. The results of IEM studies showed that APJ expression was increased significantly on HSCs, but it was sparse on SECs in Child-C-LC tissue. In vitro examination revealed that APJ was overexpressed in cultured HSCs activated by platelet-derived growth factor-β.

CONCLUSIONS

Enhanced expression of APJ on HSCs in cirrhosis indicates markedly increased vascular remodeling.

Transcriptional profiling and Wnt signaling activation in proliferation of human hepatic stellate cells induced by PDGF-BB

BACKGROUND/AIMS

This study aimed to better understand gene expression profiles of human hepatic stellate cell (HSC) activation and the relationship with the Wnt signaling pathway.

METHODS

The global transcript levels in platelet derived growth factor-BB (PDGF-BB)-stimulated hTERT HSCs were analyzed using oligonucleotide microarrays. Oligonucleotide microarrays with 19K human oligo chips were performed to obtain gene expression profiles associated with proliferation in human hTERT HSCs. The microarray data was verified by real time quantitative PCR and expression of the components of Wnt signaling was analyzed by Western blot.

RESULTS

Microarray data showed 243 up-regulated and 265 down-regulated genes in PDGF-BB-treated HSCs. The changes in expression of glypican3 and BH3 interacting domain death agonist (BID) mRNA in real time quantitative PCR, especially among the highly up- or down-regulated genes, were statistically consistent with the microarray data. The Wnt signaling pathway components, frizzled10 (FZD10) and calcium/calmodulindependent protein kinase II alpha (CAMK2A), showed increased expression in the short time course microarray and the up-regulation of FZD10 also occurred at the protein level. Our data showed various gene expression profiles during activation of human HSC.

CONCLUSIONS

The up-regulated expression of FZD10 and CAMK2A suggests that the Wnt/Ca(2+) signaling pathway is active in hTERT HSCs and may participate in HSC activation and proliferation.

Pathophysiological characteristics of dimethylnitrosamine-induced liver fibrosis in acute and chronic injury models: a possible contribution of KLF5 to fibrogenic responses

Dimethylnitrosamine administration induces a rapid increase in collagen deposition with concomitant proliferation of hepatic stellate cells in rats. Here, we investigated the pathophysiological profiles of acute and chronic hepatic fibrosis states and attempted to determine the possible role of Kruppel-like factor-5 (KLF5) in this model. In acute study using a single drug injection, we observed a rapid transient increase of ALT and mRNA levels of KLF5 followed by increases in fibrosis-related genes. Repeated administration of dimethylnitrosamine once a week caused early damage with severe fibrosis and sustained hepatocyte injury, while intermittent injections at 2-week intervals induced only modest fibrosis from 3 weeks. Weekly administration also induced profound upregulation of collagen I, alpha-smooth muscle actin, and KLF5 mRNA. In contrast, such continued augmentation was not observed after intermittent injections; KLF5 increased only after 3 weeks. These results suggested that dimethylnitrosamine induced a rapid hepatic fibrogenic response with a possible participation of KLF5.

Preventive effect of Qianggan-Rongxian Decoction on rat liver fibrosis

AIM: To study the preventive effects of Qianggan-Rongxian Decoction on liver fibrosis induced by dimethylnitrosamine (DMN) in rats.

METHODS: Male Wistar rats were randomly divided into hepatic fibrosis model group, control group and 3 treatment groups (12 rats in each group). Except for the normal control group, all the rats received 1% DMN (10 &mgr;L/kg body weight, i.p), 3 times a week for 4 wk. The rats in the 3 treatment groups including a high-dose DMN group (10 mL/kg), a medium-dose DMN group (7 mL/kg), and a low-dose DMN group (4 mL/kg) were daily gavaged with Qianggan-Rongxian Decoction, and the rats in the model and normal control groups were given saline vehicle. Enzyme-linked immunosorbent assay (ELISA) was used to determine the changes in serum hyaluronic acid (HA), laminin (LN), and type IV collagen levels. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were measured using routine laboratory methods. Pathologic changes, particularly fibrosis, were examined by hematoxylin and eosin (HE) and Sirius red staining. Hepatic stellate cells (HSC) were examined by transmission electron microscopy.

RESULTS: Compared with the model control group, the serum levels of HA, LN, type IV collagen, ALT and AST were decreased markedly in the other groups after treatment with Qianggan-Rongxian Decoction, especially in the medium-dose DMN group (P < 0.05). Moreover, the area-density percentage of collagen fibrosis was lower in the Qianggan-Rongxian Decoction treatment groups than in the model group, and a more significant drop was observed in the medium-dose DMN group (P < 0.05).

CONCLUSION: Qianggan-Rongxian Decoction can inhibit hepatic fibrosis due to chronic liver injury, delay the development of cirrhosis, and notably ameliorate liver function. It may be used as a safe and effective thera-peutic drug for patients with fibrosis.

Baculovirus-mediated interferon alleviates dimethylnitrosamine-induced liver cirrhosis symptoms in a murine model

The wild-type baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) infects a range of mammalian cell types in vitro but does not replicate in these cells. The current study investigated the in vivo effect of AcMNPV in the mouse model of liver cirrhosis induced by the mutagen dimethylnitrosamine. Intraperitoneal injection of AcMNPV induced an immune response. The baculovirus was taken up by the liver and spleen where it suppressed liver injury and fibrosis through the induction of interferons. This study presents the first evidence of the feasibility of using baculovirus to treat liver cirrhosis.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

NOX in liver fibrosis

NADPH oxidase is a multi-protein complex producing reactive oxygen species (ROS) both in phagocytic cells, being essential in host defense, and in non-phagocytic cells, regulating intracellular signalling. In the liver, NADPH oxidase plays a central role in fibrogenesis. A functionally active form of the NADPH oxidase is expressed not only in Kupffer cells (phagocytic cell type) but also in hepatic stellate cells (HSCs) (non-phagocytic cell type), suggesting a role of the non-phagocytic NADPH oxidase in HSC activation. Consistent with this concept, profibrogenic agonists such as Angiotensin II (Ang II) and platelet derived growth factor (PDGF), or apoptotic bodies exert their activity through NADPH oxidase-activation in HSCs. Both pharmacological inhibition with DPI and genetic studies using p47(phox) knockout mice provided evidence for a central role of NADPH oxidase in the regulation of HSC-activity and liver fibrosis. In addition to the p47(phox) component, only Rac1 has been identified as a functional active component of the NADPH oxidase complex in HSCs.

NAD(P)H oxidase plays a crucial role in PDGF-induced proliferation of hepatic stellate cells

The proliferation of hepatic stellate cells (HSCs) is a critical step in hepatic fibrogenesis. Platelet-derived growth factor (PDGF) is the most potent mitogen for HSCs. We investigated the role of nonphagocytic NAD(P)H oxidase-derived reactive oxygen species (ROS) in PDGF-induced HSC proliferation. The human HSC line, LI-90 cells, murine primary-cultured HSCs, and PDGF-BB were used in this study. We examined the mechanism of PDGF-BB-induced HSC proliferation in relation to the role of a ROS scavenger and diphenylene iodonium, an inhibitor of NAD(P)H oxidase. We also measured ROS production with the aid of chemiluminescence. We showed that PDGF-BB induced proliferation of HSCs through the intracellular production of ROS. We also demonstrated that HSCs expressed key components of nonphagocytic NAD(P)H oxidase (p22phox, gp91phox, p47phox, and p67phox) at both the messenger RNA and protein levels. Diphenylene iodonium suppressed PDGF-BB-induced ROS production and HSC proliferation. Coincubation of H2O2 and PDGF-BB restored the proliferation of HSCs that was inhibited by diphenylene iodonium pretreatment. Phosphorylation of the mitogen-activated protein kinase (MAPK) family constitutes a signal transduction pathway of cell proliferation. Our data demonstrate that NAD(P)H oxidase-derived ROS induce HSC proliferation mainly through the phosphorylation of p38 MAPK. Moreover, an in vivo hepatic fibrosis model also supported the critical role of NAD(P)H oxidase in the activation and proliferation of HSCs. In conclusion, NAD(P)H oxidase is expressed in HSCs and produces ROS via activation of NAD(P)H oxidase in response to PDGF-BB. ROS further induce HSC proliferation through the phosphorylation of p38 MAPK.

Effects of lipopolysaccharides stimulated Kupffer cells on activation of rat hepatic stellate cells

AIM: To study the effects of Kupffer cell-conditioned medium (KCCM) derived from lipopolysaccharide (LPS) treatment on proliferation of rat hepatic stellate cells (HSC).

METHODS: HSC and Kupffer cells were isolated from the liver of Wistar rats by in situ perfusion with pronase and collagenase and density gradient centrifugation with Nycodenz and cultured. KCCM was prepared and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay was used to detect HSC proliferation. The content of type IV collagen and laminin secreted by HSC in the HSC-conditioned medium was determined by radioimmunoassay. TGF-β₁ production in the KCCM was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS: HSC and Kupffer cells isolated had high purity. One microgram per mililiter LPS-activated KCCM and unstimulated KCCM could significantly promote HSC proliferation [0.132 ± 0.005 and 0.123 ± 0.008 vs control group (0.100 ± 0.003), P < 0.01], and there was a difference between them (P < 0.05). Ten microgram per mililiter LPS-activated KCCM (0.106 ± 0.010) was unable to promote HSC proliferation (P > 0.05). Adding anti-TGF-β₁ antibodies could suppress the proliferation promoted by unstimulated KCCM and LPS (1 μg/ml)-activated KCCM (0.109 ± 0.009 vs 0.123 ± 0.008, 0.115 ± 0.008 vs 0.132 ± 0.005, P < 0.01). LPS (1 μg/ml or 10 μg/ml) could not promote HSC proliferation immediately (0.096 ± 0.003 and 0.101 ± 0.004 vs 0.100 ± 0.003, P > 0.05). There was a parallel behavior between HSC proliferation and increased ECM level. One microgram per mililiter LPS-activated KCCM contained a larger amount of TGF-β₁ than unstimulated KCCM.

CONCLUSION: The technique for isolation of HSC and Kupffer cells described here is simple and reliable. KCCM stimulated by LPS may promote HSC proliferation and collagen accumulation, which are associated with hepatic fibrogenesis.

Inhibition of the NA(+)/H(+) exchanger reduces rat hepatic stellate cell activity and liver fibrosis: an in vitro and in vivo study

BACKGROUND & AIMS

The Na(+)/H(+) exchanger is the main intracellular pH (pH(i)) regulator in hepatic stellate cells (HSCs) and plays a key role in regulating proliferation and gene expression. We evaluated the effect of specific inhibition of this exchanger on HSC proliferation and collagen synthesis in vivo and in vitro.

METHODS

Rat HSCs were incubated in the presence of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta1, iron ascorbate (FeAsc), and ferric nitrilotriacetate solution (FeNTA) with or without the Na(+)/H(+) exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (EIPA). pH(i) and Na(+)/H(+) exchanger activity, cell proliferation, and type I collagen accumulation were measured by using the fluorescent dye 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein, by immunohistochemistry for bromodeoxyuridine, and by enzyme-linked immunosorbent assay, respectively. In vivo liver fibrosis was induced by dimethylnitrosamine administration and bile duct ligation (BDL) in rats treated or not treated with amiloride.

RESULTS

PDGF, FeAsc, and FeNTA increased Na(+)/H(+) exchange activity and induced HSC proliferation. TGF-beta1 had no effect on the Na(+)/H(+) exchanger and was able, as for FeAsc and FeNTA, to induce type I collagen accumulation. EIPA inhibited all the effects determined by PDGF, FeAsc, and FeNTA and had no effect on TGF-beta1-induced collagen accumulation. In vivo, amiloride reduced HSC proliferation, activation, collagen deposition, and collagen synthesis.

CONCLUSIONS

The Na(+)/H(+) exchanger can play a key role in the development of liver fibrosis and in HSC activation in vivo.

Involvement of reactive oxygen species and nitric oxide radicals in activation and proliferation of rat hepatic stellate cells

BACKGROUND/AIMS

Reactive oxygen species (ROS) induce HSCs activation, proliferation and collagen gene expression in vitro. Nitric oxide (NO) represents a reactive molecule that reacts with ROS, yielding peroxynitrite. We thus verified the effect of NO on ROS-induced HSCs proliferation in vitro and correlated iNOS expression and ROS formation to HSCs activation in the early phase of liver injury leading to hepatic fibrosis in vivo.

METHODS/RESULTS

HSCs were incubated with iron ascorbate (FeAsc) in vitro, which induced ROS production, ERK1/2 phosphorylation and increased cell proliferation. This effect was significantly reduced by the presence of the NO donor S-nitroso-N-acetylpenicillamine. Liver injury was induced in vivo in rats by dimethylnitrosamine administration. HSCs activation started 6 h after DMN administration and peaked at 1 week. ROS generation and neutrophil infiltration were evident for at least 48 h after DMN treatment, showing an identical distribution pattern. Only a few inflammatory cells expressed iNOS 6 h after DMN administration.

CONCLUSIONS

we have shown that NO acts as a ROS scavenger in vitro, thus inhibiting HSCs proliferation. ROS production by infiltrating neutrophils occurs in the early phase of liver fibrosis and can represent a stimulus to HSCs activation in vivo. The reduced iNOS expression may account for the low NO levels and the inability to prevent the ROS-induced HSC activation in vivo.

Interaction between hyaluronan and CD44 in the development of dimethylnitrosamine-induced liver cirrhosis

BACKGROUND

A significant increase in serum hyaluronan (HA) levels has been reported in patients with liver cirrhosis. This mechanism is not yet clear, and receptors for HA have not been characterized. In this study, we examined the expression of both HA and its receptors, CD44 and intercellular adhesion molecule-1 (ICAM-1), in dimethylnitrosamine-induced liver cirrhosis.

METHODS AND RESULTS

Using biotinylated HA binding protein, HA was detected in the area of periportal fibrosis and around the sinusoidal wall where hepatic fibrosis was developing. Electron microscopy revealed that HA was localized on Ito cells and sinusoidal endothelial cells (SEC). Conversely, CD44, which was only expressed weakly in normal liver, was present in large amounts in cirrhotic liver. The distribution pattern of CD44 was similar to that of HA, however, CD44 was mainly localized on the infiltrating lymphocytes and Kupffer cells. Moreover, CD44 was detected on part of factor VIII-positive SEC. Intercellular adhesion molecule-1, another receptor for HA, was detected on the surface of hepatocytes and around the sinusoidal wall in cirrhotic liver, but its distribution was not accompanied by expression of HA. With respect to CD44 isoforms, the standard form m-RNA predominated in both normal and cirrhotic liver. Variant pMeta-1 mRNA was detected at low levels.

CONCLUSIONS

An interaction between HA and CD44 may play a role in the recruitment of numerous infiltrating cells and HA accumulation in hepatic sinusoids. Together with phenotypic changes in the SEC, these results may lead to a disturbance in the elimination of HA during the progression of liver cirrhosis.

Biological effects of C-type natriuretic peptide in human myofibroblastic hepatic stellate cells

During chronic liver diseases, hepatic stellate cells (HSC) acquire a myofibroblastic phenotype, proliferate, and synthetize fibrosis components. Myofibroblastic HSC (mHSC) also participate to the regulation of intrahepatic blood flow, because of their contractile properties. Here, we examined whether human mHSC express natriuretic peptide receptors (NPR). Only NPR-B mRNA was identified, which was functional as demonstrated in binding studies and by increased cGMP levels in response to C-type natriuretic peptide (CNP). CNP inhibited mHSC proliferation, an effect blocked by the protein kinase G inhibitor 8-(4 chlorophenylthio)-cGMP and by the NPR antagonist HS-142-1 and reproduced by analogs of cGMP. Growth inhibition was associated with a reduction of extracellular signal-regulated kinase and c-Jun N-terminal kinase and with a blockade of AP-1 DNA binding. CNP and cGMP analogs also blunted mHSC contraction elicited by thrombin, by suppressing calcium influx. The relaxing properties of CNP were mediated by a blockade of store-operated calcium channels, as demonstrated using a calcium-free/calcium readdition protocol. These results constitute the first evidence for a hepatic effect of CNP and identify mHSC as a target cell. Activation of NPR-B by CNP in human mHSC leads to inhibition of both growth and contraction. These data suggest that during chronic liver diseases, CNP may counteract both liver fibrogenesis and associated portal hypertension.

The Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat hepatic stellate cells

BACKGROUND/AIMS

Oxidative stress is associated with liver fibrosis in vivo and with hepatic stellate cell (HSC) activation in vitro, but the intracellular mechanisms mediating these effects are mostly unknown. The Na+/H+ exchanger plays a key role in regulating the cell cycle, and is involved in HSC proliferation. Its role in different HSC features, such as collagen accumulation, is still unknown. We thus evaluated if the Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat HSC.

METHODS

HSC were incubated with 0.1 mM ferric nitrilotriacetate complex (FeNTA). Intracellular hydroperoxides and malonildialdehyde (MDA) levels in the culture media were measured by the dichlorofluorescein and TBARS method, respectively. Intracellular pH and Na+/H+ exchanger activity were measured using the fluorescent dye BCECF. Cell proliferation was measured by immunohistochemistry for bromodeoxyuridine incorporation. Collagen type I accumulation in the culture media was measured by ELISA.

RESULTS

HSC incubation with FeNTA resulted in a significant production of intracellular hydroperoxides and MDA, associated with increased Na+/H+ exchange activity and baseline intracellular pH (pHi). Exposure of HSC to FeNTA significantly enhanced the number of proliferating HSC and collagen type I levels in the culture medium. All these effects were reversed by the antioxidant resveratrol and by the Na+/H+ exchanger inhibitor amiloride.

CONCLUSIONS

This study indicates that the Na+/H+ exchanger might represent a common mediator of the different effects induced by oxidative stress on HSC. The reduction in cell proliferation and collagen synthesis induced by amiloride could represent a new therapeutic challenge in liver fibrosis.

Expression of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 in acute liver injury

BACKGROUND/AIMS

Matrix metalloproteinase-13, one of the principal neutral proteinases capable of cleaving native fibrillar collagens, is important in the degradation and remodeling of extracellular matrix. However, its precise expression in liver injury has not been characterized. We examined the kinetics of the expression of matrix metalloproteinase-13 and one of its specific inhibitors, tissue inhibitor of metalloproteinase-1, in acute liver injury in rats.

METHODS

Acute liver injury was induced by administration of carbon tetrachloride or two different doses of D-galactosamine hydrochloride in Wistar rats. Hepatic matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 mRNA levels were then examined by Northern blotting.

RESULTS

All rats survived after liver injury induced by carbon tetrachloride or low doses of D-galactosamine hydrochloride. However, rats died 5 days after induction of liver injury by high doses of D-galactosamine hydrochloride. In carbon tetrachloride-induced liver injury, matrix metalloproteinase-13 mRNA was transiently increased between 6 h and 1 day after injury. Tissue inhibitor of metalloproteinase-1 mRNA expression was increased between 6 h and 3 days after the peak of matrix metalloproteinase-13 expression. Similar patterns of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 expression were observed in low-dose D-galactosamine hydrochloride-induced liver injury. In contrast, in high-dose D-galactosamine hydrochloride-induced liver injury, tissue inhibitor of metalloproteinase-1 expression peaked before matrix metalloproteinase-13 expression, which was increased 2 days after injury. Both mRNA levels continued to increase until death.

CONCLUSIONS

Transient expression of matrix metalloproteinase-13, followed by that of tissue inhibitor of metalloproteinase-1, was observed during recovery from acute liver injury induced by carbon tetrachloride and low-dose D-galactosamine hydrochloride. In contrast, disordered expression of matrix metalloproteinase-13 was observed in fatal liver injury caused by high-dose D-galactosamine hydrochloride. These results indicate that matrix metalloproteinase13 plays an important role in the early phase of recovery from liver injury.

Quantitative analysis of liver fibrosis and stellate cell changes in patients with chronic hepatitis C after interferon therapy

OBJECTIVE

The proliferation and differentiation of stellate (Ito, or fat-storing) cells into myofibroblast-like cells is responsible for the development of liver fibrosis. Using computer image analysis, we evaluated the changes of alpha smooth muscle actin-positive stellate cells and liver fibrosis after interferon-alpha or -beta (IFN-alpha, beta) therapy in patients with chronic hepatitis C.

METHODS

Patients with chronic hepatitis C were treated with IFN-alpha or -beta and were divided into three groups on the basis of clinical criteria; a complete responder group (CR, 18 of 51), a partial responder group (PR, 17 to 51), and a nonresponder group (NR, 16 of 51). Liver fibrosis was assessed from specimens stained with Sirius red and was quantitated by computer image analysis. We also evaluated alpha-smooth muscle actin expression in the liver before and after IFN therapy by a semiquantitative scoring method (the alpha-smooth muscle actin index).

RESULTS

Before IFN therapy, a large number of stellate cells expressing a-smooth muscle actin were present in the liver biopsy specimens. There was a significant correlation (r = 0.699, p < 0.05) between the change in the percent area of fibrosis and the alpha-smooth muscle actin index before and after IFN therapy in all groups. The complete responder group also showed a significant reduction of a-smooth muscle actin-expressing cells that was correlated with the reduction of serum ALT (r = 0.686, p < 0.05).

CONCLUSION

These results suggest a-smooth muscle actin-expressing cells are responsible for liver fibrosis, and the elimination of factors stimulating matrix synthesis (e.g., hepatitis virus) may decrease liver fibrosis.

Platelet-derived growth factor-BB and thrombin generate positive and negative signals for human hepatic stellate cell proliferation. Role of a prostaglandin/cyclic AMP pathway and cross-talk with endothelin receptors

Proliferation of myofibroblastic hepatic stellate cells (HSC) in response to growth factors is essential for the development of liver fibrosis. We have reported that prostaglandins (PG) and cyclic AMP (cAMP) inhibit growth of human HSC. This PG/cAMP pathway transduces the endothelin (ET) B-mediated antiproliferative effect of endothelin-1 (ET-1) and up-regulates ETB receptors. Here, we show that platelet-derived growth factor (PDGF)-BB and thrombin, although mitogenic, generate growth inhibitory PGE2 in myofibroblastic human HSC. The two peptides elicit early PGE2 and cAMP synthesis, and also promote delayed induction of cyclooxygenase (COX)-2. Both early and delayed production of PGE2 counteract the mitogenic effect of PDGF-BB and thrombin because: (i) pretreatment with the COX inhibitor ibuprofen markedly enhances the mitogenic effect of both peptides; (ii) blocking early synthesis of PGE2 greatly enhances extracellular signal-regulated kinase (ERK) activation by both growth factors; (iii) enhancement of DNA synthesis by ibuprofen is only lost when the inhibitor is added after COX-2 induction has occurred. Finally, PDGF-BB and thrombin raise ETB receptors through the PG pathway. Thus, ibuprofen blunts growth factor-induced increase in ETB receptors. Up-regulation of the growth inhibitory ETB receptors by both mitogens may enhance the antiproliferative effect of ET-1 and thereby establish a negative feedback of their mitogenic effect. Our results shed light on novel growth inhibitory signals evoked by two mitogenic growth factors expressed during liver injury.

Role of NF-kappaB in the antiproliferative effect of endothelin-1 and tumor necrosis factor-alpha in human hepatic stellate cells. Involvement of cyclooxygenase-2

During chronic liver diseases, hepatic stellate cells (HSC) acquire an activated myofibroblast-like phenotype and proliferate and synthesize fibrosis components. Endothelin-1 (ET-1), which inhibited the growth of human myofibroblastic HSC, increased the formation of two NF-kappaB DNA binding complexes; this effect was also observed with tumor necrosis factor-alpha (TNF-alpha). The complexes were identified as the p50/p50 and p50/p65 NF-kappaB dimers. Activation of NF-kappaB was associated with the degradation of the inhibitory protein IkappaB-alpha; no IkappaB-beta was detected. Activation of NF-kappaB and degradation of IkappaB-alpha were prevented by the NF-kappaB inhibitors sodium salicylate and MG-132. In addition to cyclooxygenase-1 (COX-1), COX-2 is also constitutively expressed in human HSC, and the use of dexamethasone and of SC-58125, a selective COX-2 inhibitor, revealed that COX-2 accounts for basal COX activity. Moreover, COX-2 mRNA and protein were up-regulated by ET-1 and TNF-alpha, whereas COX-1 was unaffected. Induction of COX-2 and stimulation of COX activity by ET-1 and TNF-alpha were prevented by sodium salicylate and MG-132, suggesting that activation of NF-kappaB by either factor is needed for stimulation of COX-2. Finally, SC-58125 and dexamethasone reduced the growth inhibitory effect of ET-1 and TNF-alpha, indicating that activation of COX-2 is required for inhibition of HSC proliferation. Taken together, our results suggest that NF-kappaB, by inducing COX-2 expression, may play an important role in the negative regulation of human myofibroblastic HSC proliferation.

Fibrogenic effect of oxidative stress on rat hepatic stellate cells

Oxidative stress is associated with liver fibrosis and with hepatic stellate cell (HSC) activation in vivo. However, it remains controversial whether oxidative stress contributes to HSC activation either directly or through a paracrine stimulation by damaged hepatocytes. A medium containing products released from cells undergoing oxidative stress was obtained after incubation of hepatocytes with (HCM/Fe) or without (HCM) 0.1 mmol/L ferric nitrilotriacetate complex (FeNTA). Exposure of HSC to HCM/Fe for 24 hours significantly increased the number of proliferating HSC compared with HCM and to controls at all dilutions tested. The simultaneous coincubation of HSC with HCM/Fe and desferrioxamine (50 micromol/L) did not reduce the observed increase in cell proliferation, thus excluding a role for eventually contaminating iron in HCM/Fe. HCM/Fe induced also a significant increase in collagen type I accumulation in HSC culture media. To study the cellular mechanism underlying HCM/Fe effects, we evaluated the activity of the Na+/H+ exchanger, which plays a role in regulating HSC proliferation. The incubation of HSC for 24 hours with HCM/Fe significantly increased baseline intracellular pH (pHi) and Na+/H+ exchanger activity, indicating a plausible role of this antiport in mediating cell response. In conclusion, hepatocytes undergoing oxidative stress release factors which are fibrogenic for HSC, thereby, confirming what has been only hypothesized in vivo. In addition, HSC proliferation is associated with changes in the Na+/H+ exchanger activity, thus providing a useful target for the evaluation of inhibitors of this pathway for the treatment of hepatic fibrosis.

Hepatic stellate cells (Ito cells) but not collagen IV may partly be responsible for lower portal pressure after reversing secondary biliary cirrhosis in the rat

BACKGROUND/AIMS

Chronic bile duct obstruction in the rat leads to biliary cirrhosis and portal hypertension. Biliary decompression with Rouxen-Y choledocho-jejunostomy (RY) reverses most but not all of these changes. The aim of the present study was to determine whether hepatic stellate cells, as a main source of extracellular matrix proteins, participate in this process.

METHODS

Sprague-Dawley rats were allocated to one of three groups: Bile duct ligation (BDL) for 3 weeks, BDL followed by RY and sham-operated animals as controls (SHAM). At the end of the experimental period, portal pressure was measured, livers subjected to random sampling and hepatocytes, bile ducts/ductules, hepatic stellate cells and collagen IV determined stereologically. Hepatic stellate cells and collagen IV were characterized immunohistochemically with an antibody against desmin and collagen IV, respectively.

RESULTS

Volume fraction of hepatocytes decreased from 65.6 +/- 5.3 in sham-operated animals to 27.9 +/- 8.8% in bile duct ligated animals (p < 0.05). In contrast, volume fraction of bile ducts/ductules increased from 0.4 +/- 0.2 in sham-operated animals to 25.3 +/- 8.6% in bile duct ligated ones; similarly, hepatic stellate cells increased from 0.4 +/- 0.2 in sham-operated animals to 2.6 +/- 0.9% in bile duct ligated ones (p < 0.01) and collagen IV from 10.0 +/- 2.3 in sham-operated animals to 24.5 +/- 8.0% (p < 0.01) in bile duct ligated animals. These changes were partially reversed by Roux-en-Y choledocho-jejunostomy; hepatocytes, bile ducts/ductules, hepatic stellate cells and collagen IV averaging 54.8 +/- 13.1, 6.1 +/- 6.8, 1.6 +/- 0.6 and 14.5 +/- 3.6%, respectively (p < 0.05 RY vs. BDL). Portal pressure in sham-operated animals, bile duct ligated animals and those with a Roux-en-Y choledocho-jejunostomy averaged 13.4 +/- 0.7, 20.1 +/- 2.7 and 16.9 +/- 1.6 cm H2O, respectively, and correlated significantly with the volume fraction of hepatic stellate cells (rS = 0.96; p < 0.001) and less with collagen IV (rS = 0.61; p < 0.007). However, by stepwise regression, collagen IV did not significantly add to the ability of the equation to predict portal pressure.

CONCLUSIONS

These results lend further support to the notion that hepatic stellate cells are prominently involved in fibrogenesis and in the reversibility of these changes, but hepatic stellate cells do not completely revert to normal even 4 weeks after successful decompression. Furthermore, our data suggest that hepatic stellate cells may be related to maintenance of portal hypertension.

Growth inhibitory properties of endothelin-1 in activated human hepatic stellate cells: a cyclic adenosine monophosphate-mediated pathway. Inhibition of both extracellular signal-regulated kinase and c-Jun kinase and upregulation of endothelin B receptors

During chronic liver diseases, hepatic stellate cells (HSC) acquire an activated myofibroblast-like phenotype, proliferate, and synthetize fibrosis components. We have shown that endothelin-1 (ET-1) inhibits the proliferation of activated human HSC via endothelin B (ETB) receptors. We now investigate the transduction pathway involved in the growth inhibitory effect of ET-1 in activated HSC. Endothelin-1 and the ETB receptor agonist, sarafotoxin-S6C, increased synthesis of PGI2 and PGE2, leading to elevation of cAMP. The cyclooxygenase inhibitor ibuprofen and the adenylyl cyclase inhibitor SQ22536 both blunted the growth inhibitory effect of ET-1. Analysis of early steps associated with growth inhibition indicated that: (a) similar to ET-1, forskolin decreased c-jun mRNA induction without affecting c-fos and krox 24 mRNA expression; (b) ET-1, sarafotoxin-S6C, as well as forskolin, reduced activation of both c-Jun kinase and extracellular signal-regulated kinase. Finally, forskolin, PGI2, and PGE2 raised by fivefold the number of ET binding sites after 6 h, and increased the proportion of ETB receptors from 50% in control cells to 80% in treated cells. In conclusion, ET-1 inhibits proliferation of activated HSC via ETB receptors, through a prostaglandin/cAMP pathway that leads to inhibition of both extracellular signal-regulated kinase and c-Jun kinase activities. Upregulation of ETB receptors by prostaglandin/cAMP raises the possibility of a positive feedback loop that would amplify the growth inhibitory response. These results suggest that ET-1 and agents that increase cAMP might be of interest to limit proliferation of activated HSC during chronic liver diseases.

Bromodeoxyuridine: a diagnostic tool in biology and medicine, Part III. Proliferation in normal, injured and diseased tissue, growth factors, differentiation, DNA replication sites and in situ hybridization

This paper is a continuation of parts I (history, methods and cell kinetics) and II (clinical applications and carcinogenesis) published previously (Dolbeare, 1995 Histochem. J. 27, 339, 923). Incorporation of bromodeoxyuridine (BrdUrd) into DNA is used to measure proliferation in normal, diseased and injured tissue and to follow the effect of growth factors. Immunochemical detection of BrdUrd can be used to determine proliferative characteristics of differentiating tissues and to obtain birth dates for actual differentiation events. Studies are also described in which BrdUrd is used to follow the order of DNA replication in specific chromosomes, DNA replication sites in the nucleus and to monitor DNA repair. BrdUrd incorporation has been used as a tool for in situ hybridization experiments.

Liver stellate cells in chronic viral hepatitis: the effect of interferon therapy

BACKGROUND/AIMS

Liver stellate cell proliferation and differentiation into myofibroblast-like cells is related to the development of liver fibrosis. Several cytokines, including interferons, regulate liver stellate cell proliferation and phenotypic modulation. Recent studies indicate that human liver stellate cells express the alpha-isotype of actin, specific to smooth muscle cell differentiation. We aimed to evaluate the expression of alpha-smooth muscle actin-positive liver stellate cells in patients with chronic viral hepatitis and to evaluate whether and how such expression can be modified by alpha-interferon treatment.

METHODS

Using immunohistochemistry, and a semi-quantitative scoring method, we evaluated alpha-smooth muscle actin expression in liver stellate cells before and after alpha-interferon therapy in a series of liver biopsies from 44 patients with chronic viral hepatitis.

RESULTS

Before therapy, a large number of liver stellate cells expressing alpha-smooth muscle actin were present throughout all acinar zones. A significant reduction in alpha-smooth muscle actin expression by liver stellate cells was demonstrated in biopsies performed after suspending the interferon treatment. The drop in the number of alpha-smooth muscle actin-labelled cells after therapy correlated closely with the improvement in the histological index of activity.

CONCLUSIONS

The results suggest a specific effect of interferon on liver stellate cells, possibly related to its anti-inflammatory action.

Thrombin stimulates proliferation of liver fat-storing cells and expression of monocyte chemotactic protein-1: potential role in liver injury

Liver fat-storing cells (FSC) proliferate and secrete extracellular matrix in experimental models of liver injury. In this study, we determined if thrombin, a serine protease produced during acute and chronic tissue injury, modulates the functions of FSC. Thrombin stimulated DNA synthesis and proliferation of FSC, as assessed by [3H]-thymidine incorporation assay and measurement of cell number, respectively. Thrombin also increased the secretion of monocyte chemotactic protein-1 (MCP-1) in a time- and dose-dependent fashion. The effect of thrombin on both DNA synthesis and MCP-1 secretion was neutralized by pretreatment of thrombin with hirudin. The increased MCP-1 secretion was associated with increased steady-state levels of MCP-1 messenger RNA. Pretreatment of FSC with 5 mumol/retinol for 48 hours inhibited the mitogenic effects of thrombin but not the induction of MCP-1 secretion. FSC express specific transcripts encoding for the human thrombin receptor, as shown by Northern blot analysis of poly(A)+ RNA. Proteolytic activation of the thrombin receptor results in the formation of a new N-terminus that functions as a tethered ligand. We studied the effects of a thrombin receptor activating peptide (TRAP) corresponding to the newly formed N-terminus on FSC. TRAP mimicked the effects of thrombin on [3H]-thymidine incorporation, MCP-1 secretion, and MCP-1 gene expression. This study suggest that thrombin may be involved in modulating FSC proliferation and monocyte chemotaxis during human liver disease, through proteolytic activation of its receptor.

Regulation of platelet-derived growth factor secretion and gene expression in human liver fat-storing cells

BACKGROUND/AIMS

Liver fat-storing cells (FSCs) actively proliferate and secrete extracellular matrix during liver injury. Platelet-derived growth factor (PDGF) is a potent mitogen for cultured FSCs. In the present study, we investigated the regulation of PDGF gene expression and production in cultured human liver FSCs.

METHODS

PDGF A-chain and B-chain expression was analyzed by Northern blotting and ribonuclease protection assay, respectively. Secretion of PDGF was evaluated by immunoprecipitation and immunoblotting of conditioned medium and metabolic labeling of FSC followed by immunoprecipitation.

RESULTS

Three PDGF A-chain transcripts were detectable. Stimulation of FSC with phorbol myristate acetate (10(-7) mol/L) or PDGF BB (20 ng/mL) increased steady-state levels of PDGF A-chain and B-chain messenger RNA. PDGF AA had a small stimulatory effect on A-chain but not B-chain messenger RNA levels. FSCs secrete PDGF in the conditioned medium. The secreted protein is bioactive, because concentrated conditioned medium induced an increase in thymidine incorporation that was inhibited by anti-PDGF antibodies.

CONCLUSIONS

This study shows that cultured FSCs express PDGF A- and B-chain genes and release bioactive PDGF in the culture medium. These data raise the possibility of an autocrine or short-loop paracrine effect of PDGF in FSCs as a mechanism contributing to the maintenance of the proliferative state during liver injury.

Hepatic sinusoidal endothelial cell G1/S arrest correlates with severity of alcoholic liver injury in the rat

BACKGROUND/AIMS

Capillarization of the hepatic sinusoid occurs in alcoholic liver disease. Because endothelial cell proliferation is relevant to capillarization, we used the intragastric feeding rat model to evaluate the relationship between pathological liver injury and endothelial cell proliferation.

METHODS

Male Wistar rats (225-250 g) were fed liquid diets containing corn oil and ethanol for periods ranging between 1 week and 2 months. At the time the rats were killed, the severity of pathological injury and endothelial cell proliferation using anti-rat proliferating cell nuclear antigen/antibody was evaluated.

RESULTS

Two distinctly different populations of proliferating sinusoidal lining cells were identified; one population showed relatively weak granular staining consistent with cells arrested at the G1/S boundary. The other population of cells showed strong granular staining of the nucleoplasm and nucleoli (cells in mid to late S phase). A strong correlation (r = 0.85; P < 0.01) was obtained between pathological severity and G1/S-arrested endothelial cells. There was no correlation between cells in S phase.

CONCLUSIONS

The presence of an increased number of G1/S-arrested endothelial cells in animals with severe pathological change suggests that stimuli are present for both endothelial cell proliferation and G1/arrest. The identification of these stimuli could lead to a better understanding of the pathogenesis of alcoholic liver disease.

An interleukin-1 receptor antagonist decreases fibrosis induced by dimethylnitrosamine in rat liver

The main pathological feature of liver fibrosis is the accumulation of extracellular matrix associated with hyperplasia and activation of perisinusoidal (Ito) cells (PSC) to myofibroblast-like cells. Interleukin-1 enhances collagen synthesis by increasing the proliferative activity of cultured PSC and has been implicated in the pathogenesis of hepatic fibrosis. Interleukin-1 receptor antagonist (IL-1ra) can block the binding of IL-1 to its receptors and act as a natural inhibitor of IL-1. We have examined whether the administration of IL-1ra can interfere with the development of experimental cirrhosis induced by dimethylnitrosamine (DMN). Rats were divided in three groups and received respectively DMN, DMN + IL-1ra and IL-1ra. For each group the collagen content of the hepatic tissue and the volume density of the inflammatory infiltrate were measured. Immunostaining for laminin and alpha-smooth muscle actin were also performed. In animals given DMN + IL-1ra we observed a decreased deposition of laminin and collagen, and a decreased number of laminin-positive PSC and of alpha-smooth muscle actin reactive cells, compared with animals receiving DMN alone. The present findings suggest that the early activation of PSC in vivo is at least in part mediated by IL-1 and confirm that the administration of IL-1ra may be of interest in modifying the biological effects of IL-1.