Reversibility of Liver Fibrosis and Inactivation of Fibrogenic Myofibroblasts

Tricyclic Antidepressants Promote Ceramide Accumulation to Regulate Collagen Production in Human Hepatic Stellate Cells

Activation of hepatic stellate cells (HSCs) in response to injury is a key step in hepatic fibrosis, and is characterized by trans-differentiation of quiescent HSCs to HSC myofibroblasts, which secrete extracellular matrix proteins responsible for the fibrotic scar. There are currently no therapies to directly inhibit hepatic fibrosis. We developed a small molecule screen to identify compounds that inactivate human HSC myofibroblasts through the quantification of lipid droplets. We screened 1600 compounds and identified 21 small molecules that induce HSC inactivation. Four hits were tricyclic antidepressants (TCAs), and they repressed expression of pro-fibrotic factors Alpha-Actin-2 (ACTA2) and Alpha-1 Type I Collagen (COL1A1) in HSCs. RNA sequencing implicated the sphingolipid pathway as a target of the TCAs. Indeed, TCA treatment of HSCs promoted accumulation of ceramide through inhibition of acid ceramidase (aCDase). Depletion of aCDase also promoted accumulation of ceramide and was associated with reduced COL1A1 expression. Treatment with B13, an inhibitor of aCDase, reproduced the antifibrotic phenotype as did the addition of exogenous ceramide. Our results show that detection of lipid droplets provides a robust readout to screen for regulators of hepatic fibrosis and have identified a novel antifibrotic role for ceramide.

Modulation of hepatic stellate cells and reversibility of hepatic fibrosis

Hepatic fibrosis (HF) is the pathological component of a variety of chronic liver diseases. Hepatic stellate cells (HSC) are the main collagen-producing cells in the liver and their activation promotes HF. If HSC activation and proliferation can be inhibited, HF occurrence and development can theoretically be reduced and even reversed. Over the past ten years, a number of studies have addressed this process, and here we present a review of HSC modulation and HF reversal.

Targeting Mechanotransduction at the Transcriptional Level: YAP and BRD4 Are Novel Therapeutic Targets for the Reversal of Liver Fibrosis

Liver fibrosis is the result of a deregulated wound healing process characterized by the excessive deposition of extracellular matrix. Hepatic stellate cells (HSCs), which are activated in response to liver injury, are the major source of extracellular matrix and drive the wound healing process. However, chronic liver damage leads to perpetual HSC activation, progressive formation of pathological scar tissue and ultimately, cirrhosis and organ failure. HSC activation is triggered largely in response to mechanosignaling from the microenvironment, which induces a profibrotic nuclear transcription program that promotes HSC proliferation and extracellular matrix secretion thereby setting up a positive feedback loop leading to matrix stiffening and self-sustained, pathological, HSC activation. Despite the significant progress in our understanding of liver fibrosis, the molecular mechanisms through which the extracellular matrix promotes HSC activation are not well understood and no effective therapies have been approved to date that can target this early, reversible, stage in liver fibrosis. Several new lines of investigation now provide important insight into this area of study and identify two nuclear targets whose inhibition has the potential of reversing liver fibrosis by interfering with HSC activation: Yes-associated protein (YAP), a transcriptional co-activator and effector of the mechanosensitive Hippo pathway, and bromodomain-containing protein 4 (BRD4), an epigenetic regulator of gene expression. YAP and BRD4 activity is induced in response to mechanical stimulation of HSCs and each protein independently controls waves of early gene expression necessary for HSC activation. Significantly, inhibition of either protein can revert the chronic activation of HSCs and impede pathological progression of liver fibrosis in clinically relevant model systems. In this review we will discuss the roles of these nuclear co-activators in HSC activation, their mechanism of action in the fibrotic process in the liver and other organs, and the potential of targeting their activity with small molecule drugs for fibrosis reversal.

2016 Comprehensive Update of the Banff Working Group on Liver Allograft Pathology: Introduction of Antibody-Mediated Rejection

The Banff Working Group on Liver Allograft Pathology reviewed and discussed literature evidence regarding antibody-mediated liver allograft rejection at the 11th (Paris, France, June 5-10, 2011), 12th (Comandatuba, Brazil, August 19-23, 2013), and 13th (Vancouver, British Columbia, Canada, October 5-10, 2015) meetings of the Banff Conference on Allograft Pathology. Discussion continued online. The primary goal was to introduce guidelines and consensus criteria for the diagnosis of liver allograft antibody-mediated rejection and provide a comprehensive update of all Banff Schema recommendations. Included are new recommendations for complement component 4d tissue staining and interpretation, staging liver allograft fibrosis, and findings related to immunosuppression minimization. In an effort to create a single reference document, previous unchanged criteria are also included.

Prevention and treatment of liver allograft antibody-mediated rejection and the role of the 'two-hit hypothesis'

PURPOSE OF REVIEW

The review outlines the diagnosis, prevention strategies, and possible treatment options for acute and chronic antibody-mediated rejection (AMR).

RECENT FINDINGS

Although rare, severe acute AMR (aAMR) usually occurs in patients with high mean fluorescence intensity despite serial dilutions or high-titer preformed class I donor-specific alloantibodies (DSA). The diagnosis is suspected when allograft dysfunction occurs with DSA, diffuse C4d staining, and a microvascular injury, and may be aided by the aAMR score. However, the incidence of and treatment approach to combined T-cell-mediated rejection (TCMR) with DSA present and some but not all features of AMR is yet to be determined. Chronic liver allograft AMR is characterized by low-grade chronic inflammation and progressive fibrosis with DSA, the chronic AMR (cAMR) score may facilitate diagnosis. The 'two-hit' hypothesis, whereby a coexistent insult upregulates human leukocyte antigen class II target antigens on the microvascular endothelium, may explain why suboptimal donors with lower sensitization levels might suffer from acute AMR and those with chronic complications (e.g., recurrent original disease) might be more susceptible to chronic AMR. Although treatment algorithms are needed, prevention is preferable and at a minimum includes transfusion minimization, and medication adherence.

SUMMARY

Severe acute AMR is rare but diagnosable, and there is need to determine the incidence of and optimal therapy for less severe combined AMR and TCMR. Chronic AMR is likely more common and of significant relevance to long-term allograft survival improvement. The two-hit hypothesis may help to explain the rarity of both findings and shed insight onto future prevention and treatment strategies.

Relevance of activated hepatic stellate cells in predicting the development of pediatric liver allograft fibrosis

Activated hepatic stellate cells (HSCs) are the main collagen-producing cells in liver fibrogenesis. With the purpose of analyzing their presence and relevance in predicting liver allograft fibrosis development, 162 liver biopsies of 54 pediatric liver transplantation (LT) recipients were assessed at 6 months, 3 years, and 7 years after LT. The proportion of activated HSCs, identified by α-smooth muscle actin (ASMA) immunostaining, and the amount of fibrosis, identified by picrosirius red (PSR%) staining, were determined by computer-based morphometric analysis. Fibrosis was also staged by using the semiquantitative liver allograft fibrosis score (LAFSc), specifically designed to score fibrosis in the pediatric LT population. Liver allograft fibrosis displayed progression over time by PSR% (P < 0.001) and by LAFSc (P < 0.001). The ASMA expression decreased in the long term, with inverse evolution with respect to fibrosis (P < 0.01). Patients with ASMA-positive HSCs area ≥ 8% at 6 months (n = 20) developed a higher fibrosis proportion compared to those with ASMA-positive HSCs area ≤ 8% (n = 34) at the same period of time and in the long term (P = 0.03 and P < 0.01, respectively), but not at 3 years (P = 0.8). ASMA expression ≥ 8% at 6 months was found to be an independent risk factor for 7-year fibrosis development by PSR% (r(2) = 0.5; P < 0.01) and by LAFSc (r(2) = 0.3; P = 0.03). Furthermore, ASMA expression ≥ 8% at 3 years showed an association with the development of fibrosis at 7 years (P = 0.02). In conclusion, there is a high proportion of activated HSCs in pediatric LT recipients. ASMA ≥ 8% at 6 months seems to be a risk factor for early and longterm fibrosis development. In addition, activated HSCs showed inverse evolution with respect to fibrosis in the long term. Liver Transplantation 22 822-829 2016 AASLD.

Regulatory Effects and Mechanism of Adenovirus-Mediated PTEN Gene on Hepatic Stellate Cells

BACKGROUND

Tension homology deleted on chromosome ten (PTEN) is important in liver fibrosis.

AIMS

The purpose of this study was to evaluate the PTEN gene effects and mechanism of action on hepatic stellate cells (HSCs).

METHODS

The rat primary HSCs and human LX-2 cells were transfected by an adenovirus containing cDNA constructs encoding the wild-type PTEN (Ad-PTEN), the PTEN mutant G129E gene (Ad-G129E) and RNA interference targeting the PTEN sequence PTEN short hairpin RNA (PTEN shRNA), to up-regulate and down-regulate PTEN expression, respectively. The HSCs were assayed with a fluorescent microscope, real time PCR, Western blot, MTT, flow cytometry and Terminal-deoxynucleoitidyl transferase mediated nick end labeling. In addition, the CCl4 induced rat hepatic fibrosis model was also established to check the in vivo effects of the recombinant adenovirus with various levels of PTEN expression.

RESULTS

The data have shown that the over-expressed PTEN gene led to reduced HSCs activation and viability, caspase-3 activity and cell cycle arrest in the G0/G1 and G2/M phases, as well as negative regulation of the PI3K/Akt and FAK/ERK signaling pathways in vitro. The over-expressed PTEN gene improved liver function, inhibited proliferation and promoted apoptosis of HSCs both in vitro and in vivo.

CONCLUSIONS

These data have shown that gene therapy using the recombinant adenovirus encoding wild-type PTEN inhibits proliferation and induces apoptosis of HSCs, which is a potential treatment option for hepatic fibrosis.

Mechanisms of Lung Fibrosis Resolution

Fibrogenesis involves a dynamic interplay between factors that promote the biosynthesis and deposition of extracellular matrix along with pathways that degrade the extracellular matrix and eliminate the primary effector cells. Opposing the often held perception that fibrotic tissue is permanent, animal studies and clinical data now demonstrate the highly plastic nature of organ fibrosis that can, under certain circumstances, regress. This review describes the current understanding of the mechanisms whereby the lung is known to resolve fibrosis focusing on degradation of the extracellular matrix, removal of myofibroblasts, and the role of inflammatory cells. Although there are significant gaps in understanding lung fibrosis resolution, accelerated improvements in biotechnology and bioinformatics are expected to improve the understanding of these mechanisms and have high potential to lead to novel and effective restorative therapies in the treatment not only of pulmonary fibrosis, but also of a wide-ranging spectrum of chronic disorders.

Long noncoding RNAs expressed in human hepatic stellate cells form networks with extracellular matrix proteins

BACKGROUND

Hepatic fibrosis is the underlying cause of cirrhosis and liver failure in nearly every form of chronic liver disease, and hepatic stellate cells (HSCs) are the primary cell type responsible for fibrosis. Long noncoding RNAs (lncRNAs) are increasingly recognized as regulators of development and disease; however, little is known about their expression in human HSCs and their function in hepatic fibrosis.

METHODS

We performed RNA sequencing and ab initio assembly of RNA transcripts to define the lncRNAs expressed in human HSC myofibroblasts. We analyzed chromatin immunoprecipitation data and expression data to identify lncRNAs that were regulated by transforming growth factor beta (TGF-β) signaling, associated with super-enhancers and restricted in expression to HSCs compared with 43 human tissues and cell types. Co-expression network analyses were performed to discover functional modules of lncRNAs, and principle component analysis and K-mean clustering were used to compare lncRNA expression in HSCs with other myofibroblast cell types.

RESULTS

We identified over 3600 lncRNAs that are expressed in human HSC myofibroblasts. Many are regulated by TGF-β, a major fibrotic signal, and form networks with genes encoding key components of the extracellular matrix (ECM), which is the substrate of the fibrotic scar. The lncRNAs directly regulated by TGF-β signaling are also enriched at super-enhancers. More than 400 of the lncRNAs identified in HSCs are uniquely expressed in HSCs compared with 43 other human tissues and cell types and HSC myofibroblasts demonstrate different patterns of lncRNA expression compared with myofibroblasts originating from other tissues. Co-expression analyses identified a subset of lncRNAs that are tightly linked to collagen genes and numerous proteins that regulate the ECM during formation of the fibrotic scar. Finally, we identified lncRNAs that are induced during progression of human liver disease.

CONCLUSIONS

lncRNAs are likely key contributors to the formation and progression of fibrosis in human liver disease.

New Developments on the Treatment of Liver Fibrosis

Liver fibrosis results from many chronic injuries and often progresses to cirrhosis, liver failure, portal hypertension, and hepatocellular carcinoma. Liver transplantation is the only treatment available for patients with advanced stages of liver fibrosis. Therefore, new strategies for anti-fibrotic therapy are required. Various kinds of hepatocyte damage result in inflammation, which leads to the activation of hepatic stellate cells (HSCs), which are the major source of myofibroblasts in the liver. Myofibroblasts proliferate in response to various kinds of cytokines, chemokines, and growth factors and produce extracellular matrix proteins, which forms the fibrous scar. Myofibroblasts undergo apoptosis and inactivation when the underlying causative etiologies are cleared. Here we describe our current knowledge of targeting the steps in HSC activation as therapeutic target for liver fibrosis.

Reversibility of Stricturing Crohn's Disease-Fact or Fiction?

Intestinal fibrosis is a common feature of Crohn's disease and may appear as a stricture, stenosis, or intestinal obstruction. Fibrostenosing Crohn's disease leads to a significantly impaired quality of life in affected patients and constitutes a challenging treatment situation. In the absence of specific medical antifibrotic treatment options, endoscopic or surgical therapy approaches with their potential harmful side effects are frequently used. However, our understanding of mechanisms of fibrogenesis in general and specifically intestinal fibrosis has emerged. Progression of fibrosis in the liver, lung, or skin can be halted or even reversed, and possible treatment targets have been identified. In face of this observation and given the fact that fibrotic alterations in various organs of the human body share distinct core characteristics, this article aims to address whether reversibility of intestinal fibrosis may be conceivable and to highlight promising research avenues and therapies.

Protective effect of gastrodin on bile duct ligation-induced hepatic fibrosis in rats

Gastrodin has been showed to possess many beneficial physiological functions, including protection against inflammation and oxidation and apoptosis. Studies showed inflammation and oxidation play important roles in producing liver damage and initiating hepatic fibrogenesis. However, it has not been reported whether gastrodin has a protective effect against hepatic fibrosis or not. This is first ever made attempts to test gastrodin against liver fibrosis in bile duct ligation (BDL) rats. The aim of the present study is to evaluate the effect of gastrodin on BDL-induced hepatic fibrosis in rats. BDL rats were divided into two groups, BDL alone group, and BDL-gastrodin group treated with gastrodin (5 mg/ml in drinking water). The effects of gastrodin on BDL-induced hepatic injury and fibrosis in rats were estimated by assessing serum, urine, bile and liver tissue biochemistry followed by liver histopathology (using hematoxylin & eosin and sirius red stain) and hydroxyproline content measurement. The results showed that gastrodin treatment significantly reduced collagen content, bile duct proliferation and parenchymal necrosis after BDL. The serum alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST) decreased with gastrodin treatment by 15.1 and 23.6 percent respectively in comparison to BDL group did not receive gastrodin. Gastrodin also significantly increased the level of serum high density lipoprotein (HDL) by 62.5 percent and down-regulated the elevated urine total bilirubin (TBIL) by 56.5 percent, but had no effect on total bile acid (TBA) in serum, bile and liver tissues. The immunohistochemical assay showed gastrodin remarkably reduced the expressions of CD68 and NF-κB in BDL rats. Hepatic SOD levels, depressed by BDL, were also increased by gastrodin by 8.4 percent. In addition, the increases of hepatic MDA and NO levels in BDL rats were attenuated by gastrodin by 31.3 and 38.7 percent separately. Our results indicate that gastrodin significantly attenuated the severity of BDL-induced hepatic injury and fibrosis by attenuating oxidative stress and inflammation. Taken together, these findings suggest that gastrodin might be an effective antifibrotic drug in cholestatic liver disease.

New therapies for hepatic fibrosis

Liver fibrosis is an outcome of many chronic diseases, and often results in cirrhosis, liver failure, and portal hypertension. Liver transplantation is the only treatment available for patients with advanced stages of liver cirrhosis. Therefore, alternative methods are required to develop new strategies for anti-fibrotic therapy. Various kinds of hepatocyte injuries cause inflammatory reactions, which lead to activation of hepatic stellate cells (HSCs). Continuous liver injuries maintain these activated HSCs, and they are called as myofibroblasts. Myofibroblasts proliferate in response to various kinds of cytokines and produce extracellular matrix proteins (ECMs). Myofibroblasts undergo apoptosis and inactivation when the underlying causative etiologies are cleared. Here, we describe the current knowledge of targeting the activated HSCs as a therapeutic target for liver fibrosis.

Reversibility of liver fibrosis

Liver fibrosis is a serious health problem worldwide, which can be induced by a wide spectrum of chronic liver injuries. However, until today, there is no effective therapy available for liver fibrosis except the removal of underlying etiology or liver transplantation. Recent studies indicate that liver fibrosis is reversible when the causative agent(s) is removed. Understanding of mechanisms of liver fibrosis regression will lead to the identification of new therapeutic targets for liver fibrosis. This review summarizes recent research progress on mechanisms of reversibility of liver fibrosis. While most of the research has been focused on HSCs/myofibroblasts and inflammatory pathways, the crosstalk between different organs, various cell types and multiple signaling pathways should not be overlooked. Future studies that lead to fully understanding of the crosstalk between different cell types and the molecular mechanism underlying the reversibility of liver fibrosis will definitely give rise to new therapeutic strategies to treat liver fibrosis.

ABO-compatible liver allograft antibody-mediated rejection: an update

PURPOSE OF REVIEW

Liver allograft antibody-mediated rejection (AMR) studies have lagged behind parallel efforts in kidney and heart because of a comparative inherent hepatic resistance to AMR. Three developments, however, have increased interest: first, solid phase antibody testing enabled more precise antibody characterization; second, increased expectations for long-term, morbidity-free survival; and third, immunosuppression minimization trials.

RECENT FINDINGS

Two overlapping liver allograft AMR phenotypic expressions are beginning to emerge: acute and chronic AMR. Acute AMR usually occurs within the several weeks after transplantation and characterized clinically by donor-specific antibodies (DSA) persistence, allograft dysfunction, thrombocytopenia, and hypocomplementemia. Acute AMR appears histopathologically similar to acute AMR in other organs: diffuse microvascular endothelial cell hypertrophy, C4d deposits, neutrophilic, eosinophilic, and macrophag-mediated microvasculitis/capillaritis, along with liver-specific ductular reaction, centrilobular hepatocyte swelling, and hepatocanalicular cholestasis often combined with T-cell-mediated rejection (TCMR). Chronic AMR is less well defined, but strongly linked to serum class II DSA and associated with late-onset acute TCMR, fibrosis, chronic rejection, and decreased survival. Unlike acute AMR, chronic AMR is a slowly evolving insult with a number of potential manifestations, but most commonly appears as low-grade lymphoplasmacytic portal and perivenular inflammation accompanied by unusual fibrosis patterns and variable microvascular C4d deposition; capillaritis can be more difficult to identify than in acute AMR.

SUMMARY

More precise DSA characterization, increasing expectations for long-term survival, and immunosuppression weaning precipitated a re-emergence of liver allograft AMR interest. Pathophysiological similarities exist between heart, kidney, and liver allografts, but liver-specific considerations may prove critical to our ultimate understanding of all solid organ AMR.

In vitro reversion of activated primary human hepatic stellate cells

Background

Liver fibrosis is characterized by the excessive formation and accumulation of matrix proteins as a result of wound healing in the liver. A main event during fibrogenesis is the activation of the liver resident quiescent hepatic stellate cell (qHSC). Recent studies suggest that reversion of the activated HSC (aHSC) phenotype into a quiescent-like phenotype could be a major cellular mechanism underlying fibrosis regression in the liver, thereby offering new therapeutic perspectives for the treatment of liver fibrosis. Whether human HSCs have the ability to undergo a similar reversion in phenotype is currently unknown. The aim of the present study is to identify experimental conditions that can revert the in vitro activated phenotype of primary human HSCs and consequently to map the molecular events associated with this reversion process by gene expression profiling.

Results

We find that epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2) synergistically downregulate the expression of ACTA2 and LOX in primary human aHSCs. Their combination with oleic acid, palmitic acid, and retinol further potentiates a more quiescent-like phenotype as demonstrated by the abundant presence of retinyl ester-positive intra-cytoplasmic lipid droplets, low expression levels of activation markers, and a reduced basal as well as cytokine-stimulated proliferation and matrix metalloproteinase activity. Gene expression profiling experiments reveal that these in vitro reverted primary human HSCs (rHSCs) display an intermediary phenotype that is distinct from qHSCs and aHSCs. Interestingly, this intermediary phenotype is characterized by the increased expression of several previously identified signature genes of in vivo inactivated mouse HSCs such as CXCL1, CXCL2, and CTSS, suggesting also a potential role for these genes in promoting a quiescent-like phenotype in human HSCs.

Conclusions

We provide evidence for the ability of human primary aHSCs to revert in vitro to a transitional state through synergistic action of EGF, FGF2, dietary fatty acids and retinol, and provide a first phenotypic and genomic characterization of human in vitro rHSCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13069-015-0031-z) contains supplementary material, which is available to authorized users.

Reversibility and heritability of liver fibrosis: Implications for research and therapy

Liver fibrosis continues to be a major health problem worldwide due to lack of effective therapy. If the etiology cannot be eliminated, liver fibrosis progresses to cirrhosis and eventually to liver failure or malignancy; both are associated with a fatal outcome. Liver transplantation, the only curative therapy, is still mostly unavailable. Liver fibrosis was shown to be a reversible process; however, complete reversibility remains debatable. Recently, the molecular markers of liver fibrosis were shown to be transmitted across generations. Epigenetic mechanisms including DNA methylation, histone posttranslational modifications and noncoding RNA have emerged as major determinants of gene expression during liver fibrogenesis and carcinogenesis. Furthermore, epigenetic mechanisms have been shown to be transmitted through mitosis and meiosis to daughter cells and subsequent generations. However, the exact epigenetic regulation of complete liver fibrosis resolution and inheritance has not been fully elucidated. This communication will highlight the recent advances in the search for delineating the mechanisms governing resolution of liver fibrosis and the potential for multigenerational and transgenerational transmission of fibrosis markers. The fact that epigenetic changes, unlike genetic mutations, are reversible and can be modulated pharmacologically underscores the unique opportunity to develop effective therapy to completely reverse liver fibrosis, to prevent the development of malignancy and to regulate heritability of fibrosis phenotype.

Research highlights: aptamers on a chip

Aptamers, oligonucleic acid or peptide molecules with binding affinity to a specific molecule, have gained broad scientific attention due to their stability, ease of production and modification, and durability, and therefore have been employed in a wide range of applications both in basic research and clinical science. Recent advances in high-throughput sequencing are poised to revolutionize the selection of aptamers, while microfluidic and microarray approaches have helped automate these processes of selection. Here we highlight work addressing several challenges in using aptamers more widely. We discuss array-based discovery of multivalent aptamers which is used to develop high affinity or paired aptamers by cleverly selecting new aptamers that bind to previously aptamer-bound proteins. Other highlighted work is addressing problems in analyzing local cell secretions, as well as refreshable sensors that detect signals over hundreds of cycles and can be refreshed with DI water scavenged from the air, leading to less reagent storage towards wearable sensors.

Inhibition of acidic sphingomyelinase reduces established hepatic fibrosis in mice

AIM

Liver fibrosis occurs as a result of several chronic liver diseases and leads to portal hypertension, cirrhosis and liver failure, often requiring liver transplantation. Activated hepatic stellate cells (HSC) are known to contribute to liver fibrosis, but currently there are no effective therapies for the treatment of established liver fibrosis. Activation of the acidic sphingomyelinase (ASM) has been shown to be involved in HSC activation. In the present study we investigated whether treatment with the ASM inhibitor, amitriptyline (TCA), could prevent and/or reverse fibrosis induced in mice by carbon tetrachloride (CCl4 ).

METHODS

Mice were treated with CCl4 for 8 weeks to induce fibrosis. Concurrently, mice received drinking water with or without 180 mg/L TCA.

RESULTS

Mice receiving TCA in the water had decreased hepatic collagen deposition and reduced liver mRNA expression of the fibrogenic mediators, transforming growth factor (TGF)-β1, tissue inhibitor of matrix metalloproteinase-1, collagen and tumor necrosis factor-α. TCA treatment also reduced HSC activation determined by α-smooth muscle actin staining. In a separate set of experiments, mice were treated with CCl4 for 5 weeks prior to treatment with TCA, to test whether TCA had any effect on established fibrosis. Remarkably, in mice with established fibrosis, treatment with TCA significantly reduced collagen deposition, HSC activation, and prevented portal hypertension and improved hepatic architecture. Treatment of isolated HSC in vitro with TCA completely inhibited TGF-β1-induced collagen expression and platelet-derived growth factor-β-β-induced proliferation.

CONCLUSION

The data suggest that ASM is a critical signaling component in HSC for the development of liver fibrosis and represents an important therapeutic target.

Early to Phase II drugs currently under investigation for the treatment of liver fibrosis

INTRODUCTION

Chronic liver diseases represent a high unmet medical need and are characterized by persistent inflammation, parenchymal damage and fibrotic remodeling, leading eventually to cirrhosis and hepatic failure. Besides the persisting high prevalence of chronic viral hepatitis B and C, the dramatic increase in nonalcoholic steatohepatitis is now considered to be a major pathophysiologic driver for fibrosis development and subsequently cirrhosis. Increasing evidence suggests that also liver cirrhosis can regress when treated adequately.

AREAS COVERED

Herein, the authors review the underlying pathophysiologic mechanisms leading to fibrotic remodeling in the liver. They also highlight the options for novel treatment strategies by using molecular targeted agents.

EXPERT OPINION

New in vitro and preclinical animal models, and the careful selection of patients with high disease dynamics for clinical studies, provide a sound basis for the clinical development of antifibrotic agents in humans. Surrogate parameters of liver function, inflammation, tissue remodeling and damage, as well as noninvasive imaging techniques, can be applied in clinical trials to provide fast readouts and novel and reliable endpoints for trial design, and provide an attractive regulatory environment for this emerging disease area.

Adiponectin agonist ADP355 attenuates CCl4-induced liver fibrosis in mice

Liver fibrosis is a growing global health problem characterized by excess deposition of fibrillar collagen, and activation of hepatic stellate cells (HSCs). Adiponectin is known to possess anti-fibrotic properties; however a high physiological concentration and multiple forms circulating in blood prohibit clinical use. Recently, an adiponectin-like small synthetic peptide agonist (ADP355: H-DAsn-Ile-Pro-Nva-Leu-Tyr-DSer-Phe-Ala-DSer-NH2) was synthesized for the treatment of murine breast cancer. The present study was designed to evaluate the efficacy of ADP355 as an anti-fibrotic agent in the in vivo carbon tetrachloride (CCl4)-induced liver fibrosis model. Liver fibrosis was induced in eight-week old male C57BL/6J mice by CCl4-gavage every other day for four weeks before injection of a nanoparticle-conjugated with ADP355 (nano-ADP355). Control gold nanoparticles and nano-ADP355 were administered by intraperitoneal injection for two weeks along with CCl4-gavage. All mice were sacrificed after 6 weeks, and serum and liver tissue were collected for biochemical, histopathologic and molecular analyses. Biochemical studies suggested ADP355 treatment attenuates liver fibrosis, determined by reduction of serum aspartate aminotransferase (AST), alanine aminotransferase ALT) and hydroxyproline. Histopathology revealed chronic CCl4-treatment results in significant fibrosis, while ADP355 treatment induced significantly reversed fibrosis. Key markers for fibrogenesis-α-smooth muscle actin (α-SMA), transforming growth factor-beta1 (TGF-β1), connective tissue growth factor (CTGF), and the tissue inhibitor of metalloproteinase I (TIMP1) were also markedly attenuated. Conversely, liver lysates from ADP355 treated mice increased phosphorylation of both endothelial nitric oxide synthase (eNOS) and AMPK while AKT phosphorylation was diminished. These findings suggest ADP355 is a potent anti-fibrotic agent that can be an effective intervention against liver fibrosis.

The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies

Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.

Bone marrow derived stem cells for the treatment of end-stage liver disease

End-stage disease due to liver cirrhosis is an important cause of death worldwide. Cirrhosis results from progressive, extensive fibrosis and impaired hepatocyte regeneration. The only curative treatment is liver transplantation, but due to the several limitations of this procedure, the interest in alternative therapeutic strategies is increasing. In particular, the potential of bone marrow stem cell (BMSC) therapy in cirrhosis has been explored in different trials. In this article, we evaluate the results of 18 prospective clinical trials, and we provide a descriptive overview of recent advances in the research on hepatic regenerative medicine. The main message from the currently available data in the literature is that BMSC therapy is extremely promising in the context of liver cirrhosis. However, its application should be further explored in randomized, controlled trials with large cohorts and long follow-ups.

Liver renewal: detecting misrepair and optimizing regeneration

Cirrhosis and liver cancer, the main causes of liver-related morbidity and mortality, result from defective repair of liver injury. This article summarizes rapidly evolving knowledge about liver myofibroblasts and progenitors, the 2 key cell types that interact to orchestrate effective repair, because deregulation of these cells is likely to be central to the pathogenesis of both cirrhosis and liver cancer. We focus on cirrhosis pathogenesis because cirrhosis is the main risk factor for primary liver cancer. Emerging evidence suggests that the defective repair process has certain characteristics that might be exploited for biomarker development. Recent findings in preclinical models also indicate that the newly identified cellular and molecular targets are amenable to therapeutic manipulation. Thus, recent advances in our understanding about key cell types and fundamental mechanisms that regulate liver regeneration have opened new avenues to improve the outcomes of liver injury.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01899859.