Hepatocytes express nerve growth factor during liver injury: evidence for paracrine regulation of hepatic stellate cell apoptosis

Nerve growth factor-mediated paracrine regulation of hepatic stellate cells by multipotent mesenchymal stromal cells

AIMS

Multipotent mesenchymal stromal cells (MSC) have been reported to prevent the development of liver fibrosis and have emerged as a promising strategy for cell-based therapy. However, the underlying therapeutic mechanism remains unclear. Hepatic stellate cells (SC) activation is a pivotal event in the development of liver fibrosis.

MAIN METHODS

We hypothesized that MSC play an important role in regulating SC proliferation and apoptosis through paracrine mechanisms. To investigate the paracrine interactions between MSC and SC, a co-culture experimental model was developed using human MSC (hMSC) and human SC (hSC).

KEY FINDINGS

We demonstrate that hMSC and hSC both express nerve growth factor (NGF) receptor p75. Results acquired from transwell co-culture experiments using hSC and hMSC showed that hMSC secrete NGF, which enhances hSC apoptosis. Transcription factor nuclear factor kappa B (NF-KappaB) and B cell leukemia-xl (Bcl-xl) take part in the process.

SIGNIFICANCE

These findings demonstrated that hMSC indirectly modulate activated hSC in vitro via NGF-mediated signaling cascades and provide a potential mechanism of how transplanted MSC are effective in treating liver fibrosis.

p75 Neurotrophin receptor signaling regulates hepatic myofibroblast proliferation and apoptosis in recovery from rodent liver fibrosis

Hepatic myofibroblast apoptosis is critical to resolution of liver fibrosis. We show that human hepatic myofibroblasts co-express p75(NTR) (p75 neurotrophin receptor) and sortilin, thus facilitating differential responses to mature and pro nerve growth factor (proNGF). Although mature NGF is proapoptotic, proNGF protects human hepatic myofibroblasts from apoptosis. Moreover, in recovery from experimental liver fibrosis, the decrease in proNGF parallels loss of hepatic myofibroblasts by apoptosis. Macrophage-derived matrix metalloproteinase 7 (MMP7) cleaves proNGF in a concentration-dependent manner, and its expression in the liver coincides with falling proNGF levels. To define the dominant effect of p75(NTR)-mediated events in experimental liver fibrosis, we have used a mouse lacking the p75(NTR) ligand-binding domain but expressing the intracellular domain. We show that absence of p75(NTR) ligand-mediated signals leads to significantly retarded architectural resolution and reduced hepatic myofibroblast loss by apoptosis. Lack of the ligand-competent p75(NTR) limits hepatocyte and oval cell proliferative capacity in vivo without preventing hepatic stellate cell transdifferentiation.

CONCLUSION

NGF species have a differential effect on hepatic myofibroblast survival. Our data suggest that cleavage of proNGF by MMP7 during the early phase of recovery from liver fibrosis alters the pro/mature NGF balance to facilitate hepatic myofibroblast loss. Whereas fibrosis develops in the absence of p75(NTR) signaling, the dominant effects of loss of p75(NTR) ligand-mediated events are the retardation of liver fibrosis resolution via regulation of hepatic myofibroblast proliferation and apoptosis, and the reduction of hepatocyte and oval cell proliferation.

Advances in antifibrotic therapy

Sustained progress in defining the molecular pathophysiology of hepatic fibrosis has led to a comprehensive framework for developing antifibrotic therapies. Indeed, the single greatest limitation in bringing new drugs to the clinical setting is a lack of clarity regarding clinical trial and treatment end points, not a lack of promising agents. A range of treatments, including those developed for other indications, as well as those specifically developed for hepatic fibrosis, are nearing or in clinical trials. Most are focused on attacking features of either hepatic injury and/or activated stellate cells and myofibroblasts, which are the primary sources of extracellular matrix (scar) proteins. Thus, features of injury and stellate cell activation provide a useful template for classifying these emerging agents and point to a new class of therapies for patients with fibrosing liver disease.

NF-kappaB signaling, liver disease and hepatoprotective agents

The NF-kappaB signaling pathway has particular relevance to several liver diseases including hepatitis (liver infection by Helicobacter, viral hepatitis induced by HBV and HCV), liver fibrosis and cirrhosis and hepatocellular carcinoma. Furthermore, the NF-kappaB signaling pathway is a potential target for development of hepatoprotective agents. Several types of drugs including: selective estrogen receptor modulators (SERMs), antioxidants, proteasome inhibitors, IKK inhibitors and nucleic acid-based decoys have been shown to interfere with NF-kappaB activity at different levels and may be useful for the treatment of liver diseases. However, NF-kappaB also plays an important hepatoprotective function that needs to be taken into consideration during development of new therapeutic regimens.

Fibrosis and cirrhosis reversibility - molecular mechanisms

The concept that liver fibrosis is a dynamic process with potential for regression as well as progression has emerged in parallel with clinical evidence for remodeling of fibrotic extracellular matrix in patients who can be effectively treated for their underlying cause of liver disease. This article reviews recent discoveries relating to the cellular and molecular mechanisms that regulate fibrosis regression, with emphasis on studies that have used experimental in vivo models of liver disease. Apoptosis of hepatic myofibroblasts is discussed. The functions played by transcription factors, receptor-ligand interactions, and cell-matrix interactions as regulators of the lifespan of hepatic myofibroblasts are considered, as are the therapeutic opportunities for modulating these functions. Growth factors, proteolytic enzymes, and their inhibitors are discussed in detail.

The therapeutic potential of bone marrow-derived mesenchymal stem cells on hepatic cirrhosis

Hepatic cirrhosis is the end-stage of chronic liver diseases. The majority of patients with hepatic cirrhosis die from life-threatening complications occurring at their earlier ages. Liver transplantation has been the most effective treatment for these patients. Since liver transplantation is critically limited by the shortage of available donor livers, searching for an effective alternative therapy has attracted great interest in preclinical studies. The transplantation of autologous bone marrow-derived mesenchymal stem cells holds great potential for treating hepatic cirrhosis. Mesenchymal stem cells can differentiate to hepatocytes, stimulate the regeneration of endogenous parenchymal cells, and enhance fibrous matrix degradation. Experimental and clinical studies have shown promising beneficial effects. This review is intended to translate the bench study results to the patients' bedside. The potential interventions of mesenchymal stem cells on cirrhosis are illustrated in terms of the cellular and molecular mechanisms of hepatic fibrogenesis.

Hepatic fibrosis -- overview

The study of hepatic fibrosis, or scarring in response to chronic liver injury, has witnessed tremendous progress in the past two decades. Clarification of the cellular sources of scar, and emergence of hepatic stellate cells not only as a fibrogenic cell type, but also as a critical immunomodulatory and homeostatic regulator are among the most salient advances. Activation of hepatic stellate cells remains a central event in fibrosis, complemented by evidence of additional sources of matrix-producing cells including bone marrow, portal fibroblasts, and epithelial-mesenchymal transition from both hepatocytes and cholangiocytes. A growing range of cytokines and their receptors and inflammatory cell subsets have further expanded our knowledge about this dynamic process. Collectively, these findings have laid the foundation for continued elucidation of underlying mechanisms, and more importantly for the implementation of rationally based approaches to limit fibrosis, accelerate repair and enhance liver regeneration in patients with chronic liver disease.

p75 Neurotrophin receptor is a marker for precursors of stellate cells and portal fibroblasts in mouse fetal liver

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) and portal fibroblasts (PFs) are 2 distinct mesenchymal cells in adult liver. HSCs in sinusoids accumulate lipids and express p75 neurotrophin receptor (p75NTR). HSCs and PFs play pivotal roles in liver regeneration and fibrosis. However, the roles of mesenchymal cells in fetal liver remain poorly understood. In this study, we aimed to characterize mesenchymal cells in mouse fetal liver.

METHODS

We prepared an anti-p75NTR monoclonal antibody applicable for flow cytometry and immunohistochemistry. p75NTR(+) cells isolated from fetal liver by flow cytometry were characterized by reverse-transcription polymerase chain reaction, immunohistochemistry, and cell cultivation. Lipid-containing cells were visualized by Oil-red O staining.

RESULTS

p75NTR(+) cells in fetal liver were clearly distinct from endothelial cells and showed characteristics of mesenchymal cells. At embryonic day (E) 10.5, p75NTR(+) cells were present at the periphery of the liver bud in close contact with endothelial cells, and spread over the liver at E11.5. With the formation of the liver architecture, they began to localize to 2 distinct areas, parenchymal and portal areas, and lipid-containing p75NTR(+) cells increased accordingly. p75NTR(+) cells around portal veins were adjacent to cholangiocytes and expressed Jagged1, a crucial factor for the commitment of hepatoblasts to cholangiocytes. By cultivation, p75NTR(+) cells showed features of adult HSCs with markedly increased expression of glial fibrillary acidic protein and alpha-smooth muscle actin.

CONCLUSIONS

p75NTR(+) mesenchymal cells in fetal liver include progenitors for HSCs and PFs, and the anti-p75NTR monoclonal antibody is useful for their isolation.

IFATS collection: in vivo therapeutic potential of human adipose tissue mesenchymal stem cells after transplantation into mice with liver injury

Mesenchymal stem cells (MSCs), largely present in the adult human body, represent an attractive tool for the establishment of a stem cell-based therapy for liver diseases. Recently, the therapeutic potential and immunomodulatory activity of MSCs have been revealed. Adipose tissue-derived mesenchymal stem cells (AT-MSCs), so-called adipose-derived stem cells or adipose stromal cells, because of their high accessibility with minimal invasiveness, are especially attractive in the context of future clinical applications. The goal of the present study was to evaluate the therapeutic potential of AT-MSCs by their transplantation into nude mice with CCl(4)-caused liver injury. We observed that after transplantation, AT-MSCs can improve liver functions, which we verified by changes in the levels of biochemical parameters. Ammonia, uric acid, glutamic-pyruvic transaminase, and glutamic-oxaloacetic transaminase concentrations returned to a nearly normal level after AT-MSC transplantation. These results raised the question of how AT-MSCs can achieve this. To discover the possible mechanisms involved in this therapeutic ability of AT-MSCs, in vitro production of cytokines and growth factors was analyzed and compared with MSCs from bone marrow (BM-MSCs) and normal human dermal fibroblasts (NHDFs). As a result we observed that AT-MSCs secrete interleukin 1 receptor alpha (IL-1Ralpha), IL-6, IL-8, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), monocyte chemotactic protein 1, nerve growth factor, and hepatocyte growth factor in a volume higher than both BM-MSCs and NHDFs. Thus, our findings suggest that AT-MSCs may account for their broad therapeutic efficacy in animal models of liver diseases and in the clinical settings for liver disease treatment. Disclosure of potential conflicts of interest is found at the end of this article.

Wound healing and local neuroendocrine regulation in the injured liver

The hepatic wound-healing response is a complex process involving many different cell types and factors. It leads to the formation of excessive matrix and a fibrotic scar, which ultimately disrupts proper functioning of the liver and establishes cirrhosis. Activated hepatic myofibroblasts, which are derived from cells such as hepatic stellate cells (HSCs), play a key role in this process. Upon chronic liver injury, there is an upregulation in the local neuroendocrine system and it has recently been demonstrated that activated HSCs express specific receptors and respond to different components of this system. Neuroendocrine factors and their receptors participate in a complex network that modulates liver inflammation and wound healing, and controls the development and progression of liver fibrosis. The first part of this review provides an overview of the molecular mechanisms governing hepatic wound healing. In the second section, we explore important components of the hepatic neuroendocrine system and their recently highlighted roles in HSC biology and hepatic fibrogenesis. We discuss the therapeutic interventions that are being developed for use in antifibrotic therapy.

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.

Nerve growth factor involvement in liver cirrhosis and hepatocellular carcinoma

AIM: To define NGF (nerve growth factor) and its high-affinity receptor trkA^NGF presence and distribution in fibrotic liver and in HCC, and to verify if NGF might have a role in fibrosis and HCC.

METHODS: Intracellular distribution of NGF and trkA^NGF were assessed by immunohistochemistry and immuno-electron microscopy in liver specimens from HCC, cirrhosis or both. ELISA was used to measure circulating NGF levels.

RESULTS: NGF and trkA^NGF were highly expressed in HCC tissue, mainly localized in hepatocytes, endothelial and some Kupffer cells. In the cirrhotic part of the liver they were also markedly expressed in bile ducts epithelial and spindle-shaped cells. Surprisingly, in cirrhotic tissue from patients without HCC, both NGF and trkA^NGF were negative. NGF serum levels in cirrhotic and/or HCC patient were up to 25-fold higher than in controls.

CONCLUSION: NGF was only detected in liver tissue with HCC present. Intracellular distribution suggests paracrine and autocrine mechanisms of action. Better definition of mechanisms may allow for therapeutic and diagnostic/prognostic use of NGF.

The simple truth is seldom true and never simple: dual role for p75(NTR) in transdifferentation and cell death of hepatic stellate cells

Differentiation of hepatic stellate cells (HSCs) to extracellular matrix- and growth factor-producing cells supports liver regeneration through promotion of hepatocyte proliferation. We show that the neurotrophin receptor p75(NTR), a tumor necrosis factor receptor superfamily member expressed in HSCs after fibrotic and cirrhotic liver injury in humans, is a regulator of liver repair. In mice, depletion of p75(NTR) exacerbated liver pathology and inhibited hepatocyte proliferation in vivo. p75 (NTR-/-) HSCs failed to differentiate to myofibroblasts and did not support hepatocyte proliferation. Moreover, inhibition of p75(NTR) signaling to the small guanosine triphosphatase Rho resulted in impaired HSC differentiation. Our results identify signaling from p75(NTR) to Rho as a mechanism for the regulation of HSC differentiation to regeneration-promoting cells that support hepatocyte proliferation in the diseased liver.

Matrix metalloproteinase gene delivery for liver fibrosis

The resolution of advanced liver fibrosis has been recently recognized to be possible, if the causative stimuli are successfully removed. However, whether complete resolution from cirrhosis, the end stage of liver fibrosis, can be achieved is still questionable. Delivery of interstitial collagenases, such as matrix metalloproteinase (MMP)-1, in the liver could be an attractive strategy to treat advanced hepatic fibrosis from the view point that the imbalance between too few interstitial collagenases and too many of their inhibitors is the main obstacle to the resolution from fibrosis. Remodeling of hepatic extracellular matrix by delivered interstitial collagenases also facilitates the disappearance of activated hepatic stellate cells, the main matrix-producing cells in the liver, and promotes the proliferation of hepatocytes. This review will focus on the impact of the gene delivery of MMPs for the treatment of advanced liver fibrosis while discussing other current therapeutic strategies for liver fibrosis, and on the need for the development of a safe and effective delivery system of MMPs.

Hyperthyroidism induces apoptosis in rat liver through activation of death receptor-mediated pathways

BACKGROUND/AIMS

The molecular basis of hepatic dysfunction in thyrotoxicosis is not fully understood. Here, we investigated the effect of altered thyroidal status on death receptor pathways including p75 neurotrophin receptor (p75NTR), a member of tumor necrosis factor (TNF) receptor superfamily, in rat liver.

METHODS

Hyperthyroidism was induced in Sprague-Dawley rats by daily injections of triiodothyronine in a dose of 12.5 microg/100 g body weight for 10 days.

RESULTS

Terminal deoxynucleotide-transferase-mediated dUTP nick end labeling assay and caspase-3 activation data confirmed apoptosis in hyperthyroid rat liver. We observed the elevated levels of death ligands, TNF-alpha, Fas ligand and their cognate receptors, TNF-receptor-1 and Fas, and 8-fold increase in caspase-8 activation in hyperthyroid rat liver (p<0.001). We demonstrated for the first time that hyperthyroidism elevates p75NTR levels and its ligands, pro-nerve growth factor and pro-brain-derived neurotrophic factor, in rat liver. Further we showed that most of the apoptotic cells in hyperthyroid liver express p75NTR. We also demonstrated that triiodothyronine administration to rats causes NF-kappaB activation, but persistent exposure (10 days) to triiodothyronine deactivates NF-kappaB leading to sustained c-Jun N-terminal kinase (JNK) activation.

CONCLUSIONS

This study showed that hyperthyroidism-induced apoptosis in rat liver involves the activation of death receptor-mediated pathways, including p75NTR.

Regulation of hepatic stellate cell differentiation by the neurotrophin receptor p75NTR

Differentiation of hepatic stellate cells (HSCs) to extracellular matrix- and growth factor-producing cells supports liver regeneration through promotion of hepatocyte proliferation. We show that the neurotrophin receptor p75NTR, a tumor necrosis factor receptor superfamily member expressed in HSCs after fibrotic and cirrhotic liver injury in humans, is a regulator of liver repair. In mice, depletion of p75NTR exacerbated liver pathology and inhibited hepatocyte proliferation in vivo. p75NTR-/- HSCs failed to differentiate to myofibroblasts and did not support hepatocyte proliferation. Moreover, inhibition of p75NTR signaling to the small guanosine triphosphatase Rho resulted in impaired HSC differentiation. Our results identify signaling from p75NTR to Rho as a mechanism for the regulation of HSC differentiation to regeneration-promoting cells that support hepatocyte proliferation in the diseased liver.

Stellate cell apoptosis by a soluble mediator from immortalized human hepatocytes

Activated hepatic stellate cells (HSCs) are the major source of extracellular matrix in fibrosis and cirrhosis. In this study, we have investigated the role of hepatitis C virus (HCV) core protein induced immortalized human hepatocytes (IHH) on HSC growth. Preferential growth of IHH and apoptosis of activated human hepatic stellate cells (LX2) were observed upon coculture of these two cell types in a dual chamber or in the presence of conditioned medium (CM) from IHH. CM did not display a growth inhibitory role on other hepatic (Huh-7, HepG2, Hep3B and THLE) and non-hepatic (HeLa, MCF-7, and BHK) epithelial cells, indicating that the soluble mediator from IHH does not have a generalized effect on cell lines examined in our study. Further studies suggested that CM from IHH increased the expression of TRAIL receptors on LX2 cell surface, and induced apoptosis by a caspase dependent mechanism. Peptide mass fingerprinting of the purified soluble mediator from CM suggested that gelsolin fragments may play a role in apoptosis of LX2 cells. Taken together, our results suggested that a soluble mediator secreted from immortalized human hepatocytes plays an important role in hepatic stellate cell growth regulation.

A role for serotonin (5-HT) in hepatic stellate cell function and liver fibrosis

Hepatic stellate cells (HSCs) are key cellular components of hepatic wound healing and fibrosis. There is emerging evidence that the fibrogenic function of HSCs may be influenced by neurochemical and neurotrophic factors. This study addresses the potential for the serotonin (5-HT) system to influence HSC biology. Rat and human HSCs express the 5-HT1B, 5-HT1F 5-HT2A 5-HT2B, and 5-HT7 receptors, with expression of 5-HT1B 5-HT2A and 5-HT2B being induced on HSC activation. Induction of 5-HT2A and 5-HT2B was 106+/-39- and 52+/-8.5-fold that of quiescent cells, respectively. 5-HT2B was strongly associated with fibrotic tissue in diseased rat liver. Treatment of HSCs with 5-HT2 antagonists suppressed proliferation and elevated their rate of apoptosis; by contrast 5-HT was protective against nerve growth factor-induced apoptosis. 5-HT synergized with platelet-derived growth factor to stimulate increased HSC proliferation. HSCs were shown to express a functional serotonin transporter and to participate in both active uptake and release of 5-HT. We conclude that HSCs express key regulatory components of the 5-HT system enabling them to store and release 5-HT and to respond to the neurotransmitter in a profibrogenic manner. Antagonists that selectively target the 5-HT class of receptors may be exploited as antifibrotic drugs.

Resolving fibrosis in the diseased liver: translating the scientific promise to the clinic

Liver fibrosis and its end-stage disease cirrhosis are a major cause of mortality and morbidity throughout the world. Fibrosis is a response to chronic liver injury or infection that if unabated leads to the replacement of normal functional liver tissue with scar tissue. Basic research over the past decade has generated a vastly improved knowledge of the cell and molecular biology of liver fibrosis that provides a framework on which to design and develop therapeutics. The field has also witnessed a genuine paradigm shift from the original dogma that liver fibrosis is only ever a progressive process, to the new understanding that liver fibrosis even in an advanced stage can be reversible. There is therefore renewed optimism that liver fibrosis may be cured providing that we develop therapies that halt the fibrogenic process and encourage the natural regenerative properties of the liver. The key to the design of effective therapeutics will be to exploit the ongoing discoveries pertaining to the biology and function of fibrogenic hepatic myofibroblasts and their interplay with other liver cells and with the hepatic extracellular matrix. This review provides a critique of those discoveries in basic research that provide the most promise for translation to the clinic. In addition, we review the latest developments in the search for minimal invasive diagnostic tests for fibrosis that will be essential for determining the efficacy of anti-fibrotic drugs.

Reversal of fibrosis: no longer a pipe dream?

The reversal of liver fibrosis is not a new phenomenon. Treatment of the primary disease remains the most effective strategy, but new approaches to promote resolution of fibrosis are being built on the foundations that were provided by research into the basic mechanisms of fibrogenesis. A return to normal hepatic architecture from advanced fibrosis is achievable in some cases, and cirrhosis itself may be partly remediable.

Activated hepatic stellate cells overexpress p75NTR after partial hepatectomy and undergo apoptosis on nerve growth factor stimulation

BACKGROUND

Expression of neurotrophins (NTs) and their receptors is increased during hepatic regeneration, but their role is not well understood.

METHODS

NTs and their receptors were investigated by RT-PCR and immunostaining in regenerating livers after two-thirds hepatectomy (PH) and in hepatocytes and hepatic stellate cells (HSCs) isolated from regenerating livers in mice. Induction of apoptosis after treatment with NGF and the expression of alpha-smooth muscle actin (SMA), interleukin 6 (IL-6) and hepatocyte growth factor (HGF) were also investigated in regenerating HSCs.

RESULTS

Nerve growth factor (NGF) and p75 NT receptor (p75NTR) mRNA were elevated after PH, while other NTs and NT receptors showed no remarkable change. NGF was detected in regenerating hepatocytes, but not in normal hepatocytes. Regenerating HSCs expressed increased p75NTR and SMA in vivo and showed an activated phenotype and the high expression of HGF and IL-6 in vitro. Enhanced cell death was seen in HSCs, both from normal and regenerating liver, after treatment with NGF.

CONCLUSIONS

Although activated HSCs may produce the factors that regulate liver regeneration, the de novo NGF production by regenerating hepatocytes may induce the death of activated HSCs via p75NTR, leading to termination of hepatic regeneration.

The effect of three-dimensional co-culture of hepatocytes and hepatic stellate cells on key hepatocyte functions in vitro

In this study, we demonstrate the ability of a three-dimensional co-culture model to preserve some key aspects of differentiated hepatocyte function in vitro. Freshly isolated rat hepatocytes in co-culture with activated stellate cells rapidly aggregate to form well-defined viable spheroids. After 5 days in culture, the spheroids have a complex extracellular matrix support and hepatic ultrastructure including bile canaliculi, tight junctions, desmosomes and lipid storage. Co-culture spheroids have superior cytochrome P450 (CYP450) 3A and 2B function, and increased inducibility of 2B function, relative to a range of hepatocyte monoculture techniques (high-performance liquid chromatography of testosterone metabolites). Increased function in co-culture is supported by greater expression of CYP450 3A23, 1A2, and 2E1 mRNA relative to monoculture (reverse transcriptase quantitative polymerase chain reaction). Also, high hepatocyte growth factor mRNA expression in co-culture suggests a post-traumatic, or possibly regenerative, environment. A preliminary study of human hepatocytes co-cultured with rat stellate cells demonstrated prolonged function of CYP450 3A4, 2C19 and 2C9. This study shows that stellate cells facilitate spheroid formation, influence spheroid architecture, and are an effective method of preserving some aspects of hepatocyte function in the early stage of culture.

Reversal of hepatic fibrosis -- fact or fantasy?

The prospect of reversing hepatic fibrosis has generated great interest now that basic science advances are being translated into promising new antifibrotic therapies. It is appropriate to recognize both the historical advances that created the framework for these successes, and the important role that Hepatology has played in disseminating them. A sense of urgency underlies this effort as the epidemics of HCV and NASH are becoming associated with advancing fibrosis. To maintain progress and minimize confusion among investigators and clinicians it is essential to standardize terms referring to fibrosis 'reversal' and 'regression.' There must also be rapid optimization of non-invasive markers of fibrosis to relieve this current bottleneck to conducting clinical trials. Progress in identifying genetic determinants of fibrosis could further refine patient selection for clinical trials and shorten their duration, as well as unearthing new directions of scientific inquiry. Realistic expectations for successful anti-fibrotic therapies reflect solid evidence of fibrosis regression in patients treated effectively for viral liver disease, as well as growing clarity in the understanding mechanisms of extracellular matrix production and degradation. The paradigms of stellate cell activation and apoptosis remain valuable frameworks for understanding pathways of hepatic fibrogenesis and fibrosis regression, respectively. Continued progress is essential in order to identify the determinants and dynamics of fibrosis reversibility, to discover additional targets for anti-fibrotic therapy, and to develop customized multi-drug regimens. These advances are sure to be captured in the next 25 years by Hepatology , and to profoundly impact the prognosis of patients with chronic liver disease.

The role and regulation of hepatic stellate cell apoptosis in reversal of liver fibrosis

Liver fibrosis and its end-stage disease cirrhosis are major world health problems arising from chronic injury of the liver by a variety of etiological factors including viruses, alcohol and drug abuse, the metabolic syndrome, autoimmune disease and hereditary disorders of metabolism. Fibrosis is a progressive pathological process in which wound-healing myofibroblasts of the liver respond to injury by promoting replacement of the normal hepatic tissue with a scar-like matrix composed of cross-linked collagen. Until recently it was believed that this process was irreversible. However emerging experimental and clinical evidence is starting to show that even cirrhosis is potentially reversible. Key to this is the discovery that reversion of fibrosis is accompanied by clearance of hepatic stellate cells (HSC) by apoptosis. Furthermore, proof-of-concept studies in rodents have demonstrated that experimental augmentation of HSC apoptosis will promote the resolution of fibrosis. Consequently there is now considerable interest in determining the molecular events that regulate HSC apoptosis and the discovery of drugs that will stimulate HSC apoptosis in a selective manner. This review will consider the regulatory role played by growth factors (e.g. NGF, IGF-1, TGFbeta), death receptor ligands (TRAIL, FAS), components and regulators of extracellular matrix (integrins, collagen, matrix metalloproteinases and their tissue inhibitors) and signal transduction proteins and transcription factors (Rho/Rho kinase, Jun N-terminal Kinase (JNK), IkappaKinase (IKK), NF-kappa B). The potential for known pharmacological agents such as gliotoxin, sulfasalazine, benzodiazepine ligands, curcumin and tanshinone I to induce HSC apoptosis and therefore to be used therapeutically will be explored.

Emerging therapies for liver fibrosis

Liver fibrosis occurs as a result of a wide range of injurious processes and in its end-stage results in cirrhosis. This gross disruption of liver architecture is associated with impaired hepatic function, portal hypertension and significant resultant morbidity and mortality. Indeed, liver fibrosis and cirrhosis represent a major worldwide healthcare burden. Recent progress in liver transplantation, the management of portal hypertension and the treatment of chronic viral hepatitis have had an important impact. However, these approaches are not without their limitations - in particular, issues regarding organ availability for transplantation - and serve to highlight the urgent requirement to influence pharmacologically the underlying fibrotic process in many patients. Liver fibrosis has been shown to be a bidirectional process and increasing data from laboratory and clinical studies reveal that even advanced fibrosis and cirrhosis are potentially reversible. Exploration of the molecular mechanisms underlying this bi-directionality will lead to char acterisation of the essential attributes of an antifibrotic therapy. In this review, these mechanisms are highlighted and the growing number of emerging antifibrotic agents discussed.

Upregulation of pleiotrophin expression in rat hepatic stellate cells by PDGF and hypoxia: Implications for its role in experimental biliary liver fibrogenesis

Pleiotrophin (PTN) is a secretory heparin binding protein with various biological activities including mitogenesis, angiogenesis, and tissue repair after injury. Recent studies have shown that PTN is a strong mitogen of hepatocytes and involved in liver regeneration. In adult liver cells Ptn gene is mainly expressed by quiescent hepatic stellate cells (HSCs). Although we have been able to demonstrate mRNA and protein expression of the anaplastic lymphoma kinase-the receptor tyrosine kinase for PTN-on HSCs, PTN did not act as a mitogen of HSCs in contrast to hepatocytes. PTN immunoreactivity was markedly increased in experimental fibrogenesis by common bile duct ligation and observed in sinusoidal HSCs. In primary HSC cultures, Ptn transcription was significantly increased by PDGF-BB, and under hypoxic atmosphere. Mechanistically, hypoxia and PDGF mediated induction of PTN expression in sinusoidal HSCs may provide a strong mitogenic signal for hepatocytes to limit the damage to the parenchymal cells in biliary-type liver fibrogenesis.

Tissue and intracellular reorganization of rat liver during total body hypothermia

We studied tissue and intracellular reorganization of the liver during total body hypothermia and evaluated regeneration strategies at different levels of structural organization. Hypothermia results in morphofunctional changes in the liver (degeneration, lysis, necrobiosis, and focal necrosis of hepatocytes developing against the background of disorders in blood and lymph circulation). Decreased sinusoid/hepatocyte volume ratio is the key factor in tissue reorganization of the liver. Intracellular reorganization of hepatocytes is characterized by dysproportional changes in the volume and surface densities of the main cytoplasmic organelles involved in biosynthesis and energy production.

Targeted treatments for cirrhosis

The causes of hepatic scarring (fibrosis) are protean but, unchecked, all result in a common fate--the development of cirrhosis--with gross disruption of the normal liver architecture. Subsequent liver cell dysfunction and portal hypertension give rise to major systemic complications and premature death. Cirrhosis and its sequelae represent a huge, and global, healthcare burden. The success of liver transplantation and the development of efficacious antiviral regimens for hepatitis B and C should not be underestimated, but they also serve to highlight our current inability to manipulate the underlying fibrotic process in many patients with liver disease. Moreover, transplantation as a treatment is limited by organ availability, among other factors. The development of antifibrotic therapies is urgently needed and for this we require a mechanistic and evidence-based approach. Accumulating data from clinical and laboratory studies demonstrate that even advanced fibrosis and cirrhosis are potentially reversible. The hepatic stellate cells have been identified as the pivotal effector cells orchestrating the fibrotic process and, furthermore, reversibility appears to hinge upon their elimination. This review draws on recent scientific advances, and highlights emerging therapeutic interventions in liver fibrosis.

New insights into functional aspects of liver morphology

The liver is structurally and functionally complex and has been considered second only to brain in its complexity. Many mysteries still exist in this heterogeneous tissue whose functional unit of the lobule has continued to stump morphologists for over 300 years. The primary lobule, proposed by Matsumoto in 1979, has been gaining acceptance as the functional unit of the liver over other conceptual views because it's based on vessel architecture and includes the classic lobule as a secondary feature. Although hepatocytes comprise almost 80% of the liver, there are at least another dozen cell types, many of which provide "cross-talk" and play important functional roles in the normal and diseased liver. The distribution and functional roles of all cells in the liver must be carefully considered in both the analysis and interpretation of research data, particularly data in the area of genomics and "phenotypic anchoring" of gene expression results. Discoveries regarding the functional heterogeneity of the various liver cell types, including hepatocytes, hepatic stellate cells, sinusoidal endothelia, and Kupffer cells, are providing new insights into our understanding of the development, prevention and treatment of liver disease. For example, functional differences along zonal patterns (centrilobular or periportal) have been demonstrated for sinusoidal endothelium, Kupffer cells, and hepatocytes and can explain the gradients and manifestations of disease observed within lobules. Intralobular gradients of bile uptake, glycogen depletion, glutamine synthetase, and carboxylesterase by hepatocytes; widened fenestrations in centrilobular sinusoidal lining cells; and differences in the components of centrilobular extracellular matrix or function of Kupffer cells have been demonstrated. Awareness of the complexities and heterogeneity of the liver will add to a greater understanding of liver function and disease processes that lead to toxicity, cancer, and other diseases.

Inhibition of inhibitor of kappaB kinases stimulates hepatic stellate cell apoptosis and accelerated recovery from rat liver fibrosis

BACKGROUND & AIMS

Resolution of liver fibrosis is associated with clearance of hepatic myofibroblasts by apoptosis; development of strategies that promote this process in a selective way is therefore important. The aim of this study was to determine whether the inhibitor of kappaB kinase suppressor sulfasalazine stimulates hepatic myofibroblast apoptosis and recovery from fibrosis.

METHODS

Hepatic myofibroblasts were generated by culture activation of rat and human hepatic stellate cells. Fibrosis was established in rat livers by chronic injury with carbon tetrachloride followed by recovery with or without sulfasalazine (150 mg/kg) treatment.

RESULTS

Treatment of hepatic stellate cells with sulfasalazine (0.5-2.0 mmol/L) induced apoptosis of activated rat and human hepatic stellate cells. A single in vivo administration of sulfasalazine promoted accelerated recovery from fibrosis as assessed by improved fibrosis score, selective clearance of smooth muscle alpha-actin-positive myofibroblasts, reduced hepatic procollagen I and tissue inhibitor of metalloproteinase 1 messenger RNA expression, and increased matrix metalloproteinase 2 activity. Mechanistic studies showed that sulfasalazine selectively blocks nuclear factor-kappaB-dependent gene transcription, inhibits hepatic stellate cell expression of Gadd45beta, stimulates phosphorylation of Jun N-terminal kinase 2, and promotes apoptosis by a mechanism that is prevented by the Jun N-terminal kinase inhibitor SP600125. As further evidence for a survival role for the inhibitor of kappaB kinase/nuclear factor-kappaB pathway in activated hepatic stellate cells, a highly selective cell-permeable peptide inhibitor of kappaB kinase activation also stimulated hepatic stellate cell apoptosis via a Jun N-terminal kinase-dependent mechanism.

CONCLUSIONS

Inhibition of the inhibitor of kappaB kinase/nuclear factor-kappaB pathway is sufficient to increase the rate at which activated hepatic stellate cells undergo apoptosis both in vitro and in vivo, and drugs that selectively target inhibitor of kappaB kinase have potential as antifibrotics.

Capsule oxymatrine in treatment of hepatic fibrosis due to chronic viral hepatitis: A randomized, double blind, placebo-controlled, multicenter clinical study

AIM: To evaluate the efficacy and safety of oxymatrine capsule in treatment of hepatic fibrosis in patients with chronic viral hepatitis.

METHODS: It was a randomized, double blind, placebo-controlled, multicenter clinical study. One hundred and forty-four patients were divided into oxymatrine capsule group(group A) and placebo group (group B).The course was 52 wk. Patients were visited once every 12 wk and the last visit was at 12 wk after cessation of the treatment. All patients had liver biopsy before treatment. part of them had a second biopsy at the end of therapy. Clinical symptoms, liver function test, serum markers of hepatic fibrosis were tested. Ultrasound evaluation was performed before, during and at the end of therapy.

RESULTS: One hundred and forty-four patients enrolled in the study. Of them 132 patients completed the study according to the protocol,49 patients had liver biopsy twice (25 patients in group A and 24 in group B). At the end of therapy, significant improvements in hepatic fibrosis and inflammatory activity based on Semi-quantitative scoring system (SSS) were achieved in group A. The total effective rate of the treatment was 48.00%, much higher than that of 4.17% in group B (P < 0.05). Significant improvement in serum markers of hepatic fibrosis such as hyaluronic acid (HA) and type III procollagenic peptide (P III P) in group A was seen (P < 0.05). The total effective rate of serum markers at the end of therapy in group A was 68.19%, much higher than that of 34.85% in group B (P < 0.05). The total effective rate of noninvasive markers at the end of therapy in group A was 66.67%, much higher than that of 30.30% in group B (P < 0.05). The rate of adverse events was similar in two groups.

CONCLUSION: Oxymatrine capsule is effective and safe in treatment of hepatic fibrosis due to chronic viral hepatitis.