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Hepatic Fibrogenesis
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Purpose of Review
The dramatic increase in nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) fostered the development and evaluation of non-invasive, imaging based methods for diagnosing NAFLD, NASH, and its complications. We herein review different radiologic modalities in diagnosing steatosis, fibrosis, and liver cirrhosis.
Recent Findings
While routine abdominal ultrasound with hyperechogenic liver structure only detects moderate to severe steatosis, controlled attenuation parameter (CAP), magnetic resonance spectroscopy (MRS), and, especially, MRI-proton density fat fraction (MRI-PDFF) are more sensitive to diagnose and quantify steatosis. MRI-PDFF appears suitable to monitor treatment-related changes in liver fat in clinical trials. Liver fibrosis is related to hepatic and extrahepatic morbidity and mortality in NAFLD. Fibrosis and cirrhosis can be suspected by ultrasound-based elastography techniques (vibration-controlled transient elastography, VCTE; acoustic resonance forced impulse imaging, ARFI; shear wave elastography, SWE), which may be used to screen for fibrosis in high-risk patients. MR elastography (MRE) appears advantageous to quantify and stage fibrosis, while angiographic hepatic venous pressure gradient (HVPG) measurement can confirm portal hypertension in cirrhosis. Screening for hepatocellular carcinoma (HCC) in cirrhotic livers is done by ultrasound; suspicious nodules are followed by multiphasic CT/MRI, contrast-enhanced ultrasound (CEUS), or contrast-enhanced MRI.
Summary
Different radiologic modalities exist to screen, diagnose, stage, and monitor steatosis, steatohepatitis, fibrosis, and HCC, thereby complementing liver biopsy and blood biomarkers in the management of patients with NAFLD.
Hepatic fibrosis is characterized by the formation and deposition of excess fibrous connective tissue, leading to progressive architectural tissue remodeling. Irrespective of the underlying noxious trigger, tissue damage induces an inflammatory response involving the local vascular system and the immune system and a systemic mobilization of endocrine and neurological mediators, ultimately leading to the activation of matrix-producing cell populations. Genetic disorders, chronic viral infection, alcohol abuse, autoimmune attacks, metabolic disorders, cholestasis, alterations in bile acid composition or concentration, venous obstruction, and parasite infections are well-established factors that predispose one to hepatic fibrosis. In addition, excess fat and other lipotoxic mediators provoking endoplasmic reticulum stress, alteration of mitochondrial function, oxidative stress, and modifications in the microbiota are associated with non-alcoholic fatty liver disease and, subsequently, the initiation and progression of hepatic fibrosis. Multidisciplinary panels of experts have developed practice guidelines, including recommendations of preferred therapeutic approaches to a specific cause of hepatic disease, stage of fibrosis, or occurring co-morbidities associated with ongoing loss of hepatic function. Here, we summarize the factors leading to liver fibrosis and the current concepts in anti-fibrotic therapies.
Portal hypertension is one cause and a part of a dynamic process triggered by chronic liver disease, mostly induced by alcohol or incorrect nutrition and less often by viral infections and autoimmune or genetic disease. Adequate staging - continuously modified by current knowledge - should guide the prevention and treatment of portal hypertension with defined endpoints. The main goals are interruption of etiology and prevention of complications followed, if necessary, by treatment of these. For the past few decades, shunts, mostly as intrahepatic stent bypass between portal and hepatic vein branches, have played an important role in the prevention of recurrent bleeding and ascites formation, although their impact on survival remains ambiguous. Systemic drugs, such as non-selective beta-blockers, statins, or antibiotics, reduce portal hypertension by decreasing intrahepatic resistance or portal tributary blood flow or by blunting inflammatory stimuli inside and outside the liver. Here, the interactions among the gut, liver, and brain are increasingly examined for new therapeutic options. There is no general panacea. The interruption of initiating factors is key. If not possible or if not possible in a timely manner, combined approaches should receive more attention before considering liver transplantation.
Fructose is one of the key dietary catalysts in the development of non-alcoholic fatty liver disease (NAFLD). NAFLD comprises a complex disease spectrum, including steatosis (fatty liver), non-alcoholic steatohepatitis, hepatocyte injury, inflammation, and fibrosis. It is also the hepatic manifestation of the metabolic syndrome, which covers abdominal obesity, insulin resistance, dyslipidemia, glucose intolerance, or type 2 diabetes mellitus. Commensal bacteria modulate the host immune system, protect against exogenous pathogens, and are gatekeepers in intestinal barrier function and maturation. Dysbalanced intestinal microbiota composition influences a variety of NAFLD-associated clinical conditions. Conversely, nutritional supplementation with probiotics and preobiotics impacting composition of gut microbiota can improve the outcome of NAFLD. In crosstalk with the host immune system, the gut microbiota is able to modulate inflammation, insulin resistance, and intestinal permeability. Moreover, the composition of microbiota of an individual is a kind of fingerprint highly influenced by diet. In addition, not only the microbiota itself but also its metabolites influence the metabolism and host immune system. The gut microbiota can produce vitamins and a variety of nutrients including short-chain fatty acids. Holding a healthy balance of the microbiota is therefore highly important. In the present review, we discuss the impact of long-term intake of fructose on the composition of the intestinal microbiota and its biological consequences in regard to liver homeostasis and disease. In particular, we will refer about fructose-induced alterations of the tight junction proteins affecting the gut permeability, leading to the translocation of bacteria and bacterial endotoxins into the blood circulation.
The aim of this study was to evaluate cenicriviroc (CVC), a dual antagonist of CC chemokine receptor types 2 and 5, for treatment of nonalcoholic steatohepatitis (NASH) with liver fibrosis (LF). A randomized, double-blind, multinational phase 2b study enrolled subjects with NASH, a nonalcoholic fatty liver disease activity score (NAS) ≥4, and LF (stages 1-3, NASH Clinical Research Network) at 81 clinical sites. Subjects (N = 289) were randomly assigned CVC 150 mg or placebo. Primary outcome was ≥2-point improvement in NAS and no worsening of fibrosis at year 1. Key secondary outcomes were: resolution of steatohepatitis (SH) and no worsening of fibrosis; improvement in fibrosis by ≥1 stage and no worsening of SH. Biomarkers of inflammation and adverse events were assessed. Full study recruitment was achieved. The primary endpoint of NAS improvement in the intent-to-treat population and resolution of SH was achieved in a similar proportion of subjects on CVC (N = 145) and placebo (N = 144; 16% vs. 19%, P = 0.52 and 8% vs. 6%, P = 0.49, respectively). However, the fibrosis endpoint was met in significantly more subjects on CVC than placebo (20% vs. 10%; P = 0.02). Treatment benefits were greater in those with higher disease activity and fibrosis stage at baseline. Biomarkers of systemic inflammation were reduced with CVC. Safety and tolerability of CVC were comparable to placebo.
Conclusion:
After 1 year of CVC treatment, twice as many subjects achieved improvement in fibrosis and no worsening of SH compared with placebo. Given the urgent need to develop antifibrotic therapies in NASH, these findings warrant phase 3 evaluation. (Hepatology 2018;67:1754-1767).
Hepatic fibrogenesis may gradually result to cirrhosis due to the accumulation of extracellular matrix components as a response to liver injury. Thus, therapeutic decisions in chronic liver disease, regardless of the cause, should first and foremost be guided by an accurate quantification of hepatic fibrosis. Detection and assessment of the extent of hepatic fibrosis represent a challenge in modern Hepatology. Although traditional histological staging systems remain the “best standard”, they are not able to quantify liver fibrosis as a dynamic process and may not accurately substage cirrhosis. This review aims to compare the currently used non-invasive methods of measuring liver fibrosis and provide an update in current tissue-based digital techniques developed for this purpose, that may prove of value in daily clinical practice.
The activation and transdifferentiation of hepatic stellate cells (HSCs) into contractile, matrix-producing myofibroblasts (MFBs) are central events in hepatic fibrogenesis. These processes are driven by autocrine- and paracrine-acting soluble factors (i.e., cytokines and chemokines). Proof-of-concept studies of the last decades have shown that both the deactivation and removal of hepatic MFBs as well as antagonizing profibrogenic factors are in principle suitable to attenuate ongoing hepatic fibrosis. Although several drugs show potent antifibrotic activities in experimental models of hepatic fibrosis, there is presently no effective pharmaceutical intervention specifically approved for the treatment of liver fibrosis. Pharmaceutical interventions are generally hampered by insufficient supply of drugs to the diseased liver tissue and/or by adverse effects as a result of affecting non-target cells. Therefore, targeted delivery systems that bind specifically to receptors solely expressed on activated HSCs or transdifferentiated MFBs and delivery systems that can improve drug distribution to the liver in general are urgently needed. In this review, we summarize current strategies for targeted delivery of drugs to the liver and in particular to pro-fibrogenic liver cells. The applicability and efficacy of sequestering molecules, selective protein carriers, lipid-based drug vehicles, viral vectors, transcriptional targeting approaches, therapeutic liver- and HSC-specific nanoparticles, and miRNA-based strategies are discussed. Some of these delivery systems that had already been successfully tested in experimental animal models of ongoing hepatic fibrogenesis are expected to translate into clinically useful therapeutics specifically targeting HSCs.
Hepatic fibrosis and cirrhosis cause strong human suffering and necessitate a monetary burden worldwide. Therefore, there is an urgent need for the development of therapies. Pre-clinical animal models are indispensable in the drug discovery and development of new anti-fibrotic compounds and are immensely valuable for understanding and proofing the mode of their proposed action. In fibrosis research, inbreed mice and rats are by far the most used species for testing drug efficacy. During the last decades, several hundred or even a thousand different drugs that reproducibly evolve beneficial effects on liver health in respective disease models were identified. However, there are only a few compounds (e.g., GR-MD-02, GM-CT-01) that were translated from bench to bedside. In contrast, the large number of drugs successfully tested in animal studies is repeatedly tested over and over engender findings with similar or identical outcome. This circumstance undermines the 3R (Replacement, Refinement, Reduction) principle of Russell and Burch that was introduced to minimize the suffering of laboratory animals. This ethical framework, however, represents the basis of the new animal welfare regulations in the member states of the European Union. Consequently, the legal authorities in the different countries are halted to foreclose testing of drugs in animals that were successfully tested before. This review provides a synopsis on anti-fibrotic compounds that were tested in classical rodent models. Their mode of action, potential sources and the observed beneficial effects on liver health are discussed. This review attempts to provide a reference compilation for all those involved in the testing of drugs or in the design of new clinical trials targeting hepatic fibrosis.
Introduction: Chronic injury to the liver, such as viral hepatitis, alcoholism, non-alcoholic fatty liver disease (NAFLD) or nonalcoholic steatohepatitis (NASH), promotes extracellular matrix deposition and organ scarring, termed hepatic fibrosis. Fibrosis might progress to cirrhosis and predisposes to hepatocellular carcinoma (HCC), but is also associated with extrahepatic morbidity and mortality in NAFLD/NASH. The improved understanding of pathogenic mechanisms underlying chronic inflammation and fibrogenesis in the liver prompted recent advances in antifibrotic therapies.
Areas covered: We review recent advances in antifibrotic therapy, of which most are currently tested in clinical trials for NAFLD or NASH. This explains the manifold metabolic pathways as antifibrotic targets, including farnesoid X receptor (FXR) agonism (obeticholic acid, non-steroidal FXR agonists), acetyl-CoA carboxylase inhibition, peroxisome proliferator-activator receptor agonism (elafibranor, lanifibranor, saroglitazar) and fibroblast growth factor (FGF)-21 or FGF-19 activation. Other antifibrotic drug candidates target cell death or inflammation, such as caspase (emricasan) or ASK1 inhibitors (selonsertib), galectin-3 inhibitors and reducing inflammatory macrophage recruitment by blocking chemokine receptors CCR2/CCR5 (cenicriviroc).
Expert commentary: The tremendous advances in translational and clinical research fuels the hope for efficacious antifibrotic therapies within the next 5 years. Very likely, a combination of etiology-specific, metabolic, anti-inflammatory and direct anti-fibrotic interventions will be most effective.
Over the past 2 decades, nonalcoholic fatty liver disease (NAFLD) has grown from a relatively unknown disease to the most common cause of CLD in the world. In fact, 25% of the world's population is currently thought to have NAFLD. Non‐alcoholic steatohepatitis (NASH) is the subtype of NAFLD that can progress to cirrhosis, hepatocellular carcinoma, and death. NAFLD and NASH are found in not only adults—there is a high prevalence in children and adolescents. Due to NAFLD's close association with type 2 diabetes (T2DM) and obesity, the latest models predict the prevalence of NAFLD and NASH will increase, causing a tremendous clinical and economic burden and poor patient‐reported outcomes. Nonetheless, there is no accurate non‐invasive method to detect NASH and treatment is limited to life style modifications. To examine the state of NAFLD among different regions and understand the global trajectory of this disease, an international group of experts came together during 2017 AASLD Global NAFLD Forum. We provide a summary of this forum and an assessment of the current state of NAFLD and NASH worldwide. This article is protected by copyright. All rights reserved.
With an estimated prevalence of ≈25% in Western and Asian countries, non alcoholic fatty liver disease (NAFLD), caused by chronic excessive caloric intake, is the emerging as the most prevalent liver disorder worldwide. NAFLD exists in two clinical entities, non-alcoholic fatty liver disease (NAFL), a relative benign disease that carry on minimal risk of liver-related morbidity but significant risk of cardiovascular complications, and non-alcoholic steatohepatitis (NASH), a progressive liver disorder with a significant risk for development of liver-related morbidities and mortality. While, liver injury in NASH is contributed by lipid overload in hepatocytes, lipotoxicity, the main determinant of disease progression is an inflammation-driven fibrotic response. Here, we review the landscape of emerging pharmacological interventions in the treatment of NAFL and NASH. A consensus exists that, while treating the liver component of NASH requires development of novel pharmacological approaches, the future therapy of NASH needs to be tailored to the single patient and most likely will be a combination of agents acting on specific pathogenic mechanisms at different disease stage.
Fibrosis denotes excessive scarring, which exceeds the normal wound healing response to injury in many tissues. Although the extracellular matrix deposition appears unstructured disrupting the normal tissue architecture and subsequently impairing proper organ function, fibrogenesis is a highly orchestrated process determined by defined sequences of molecular signals and cellular response mechanisms. Persistent injury and parenchymal cell death provokes tissue inflammation, macrophage activation and immune cell infiltration. The release of biologically highly active soluble mediators (alarmins, cytokines, chemokines) lead to the local activation of collagen producing mesenchymal cells such as pericytes, myofibroblasts or Gli1 positive mesenchymal stem-like cells, to a transition of various cell types into myofibroblasts as well as to the recruitment of fibroblast precursors. Clinical observations and experimental models highlighted that fibrosis is not a one-way road. Specific mechanistic principles of fibrosis regression involve the resolution of chronic tissue injury, the shift of inflammatory processes towards recovery, deactivation of myofibroblasts and finally fibrolysis of excess matrix scaffold. The thorough understanding of common principles of fibrogenic molecular signals and cellular mechanisms in various organs - such as liver, kidney, lung, heart or skin - is the basis for developing improved diagnostics including biomarkers or imaging techniques and novel antifibrotic therapeutics.
NASH/NAFLD is rapidly becoming one of top causes of cirrhosis, hepatocellular carcinoma and indication for liver transplantation. Except for life style modification through diet and exercise, there are currently no other approved treatments for NASH/NAFLD. Although weight loss can be effective, it is hard to achieve and sustain. In contrast, bariatric surgery can improve metabolic conditions associated with NAFLD and has been shown to improve liver histology. In order to have approved regimens for treatment of NASH/NAFLD, a number of issues that must be addressed. First, all stakeholders must agree on the most appropriate clinical trial endpoints for NASH. Currently, resolution of NASH (without worsening fibrosis) or reduction of fibrosis stage (without worsening NASH) are the accepted endpoints by the regulatory authorities. It is important to recognize the prognostic implication of histologic features of NASH. In this context, although histologic NASH has been associated with advanced stage of fibrosis, it is not an independent predictor of long term mortality. In contrast, there is significant data to suggest that stage of fibrosis is the only robust and independent predictor of liver-related mortality. In addition to the primary endpoints, a number of important secondary endpoints, including non-invasive biomarkers, long term outcomes, and patient reported outcomes, must be considered. In 2017, a few phase 3 clinical trials for treatment of NASH are in progress. Additionally, a number of phase 2a and 2b clinical trials targeting different pathogenic pathways in NASH enriches the pipeline of emerging therapies.
Conclusion:
Over the next 5 years, some of these regimens are expected to provide potential new treatment options for patients with NASH/NAFLD. This article is protected by copyright. All rights reserved.
NAFLD is a spectrum comprised of isolated steatosis, NASH, advanced fibrosis, and cirrhosis. The majority of NAFLD subjects do not have NASH and don't carry a significant risk for adverse outcomes (cirrhosis and mortality). Globally, the prevalence of NAFLD is approximately 25%. In Asia, a gradient of high prevalence rates to low rates are noted from urban to rural areas. Given the prevalence of NAFLD, the clinical and economic burden of NAFLD and NASH can be substantial. With increasing recognition as an important liver disease, the diagnosis of NASH still requires a liver biopsy which is suboptimal. Although liver biopsy is the most accurate modality to diagnose and stage the severity of NASH, it suffers from being invasive, costly, associated with potential complications, and plagued with interobserver variability of individual pathologic features. A number of non-invasive modalities to diagnose NASH and stage liver fibrosis are being developed. These include predictive models (NAFLD fibrosis score) and serum biomarkers such as Enhanced Liver Fibrosis, (ELF). Other tests are based on radiologic techniques such as transient or MR elastography (MRE) which are used to estimate liver stiffness as a potential surrogate of hepatic fibrosis. Although a dynamic field of research, most of these diagnostic modalities have AUROC between 0.76 to 0.90% with MRE having the best predictive performance. In summary, developing accurate, safe and easily accessible non-invasive modalities to accurately diagnose and monitor NASH and associated fibrosis is of utmost importance in clinical practice and clinical research. These tests are not only important to risk stratify subjects at the greatest risk for progressive liver disease but to serve as appropriate surrogate endpoints for therapeutic clinical trials of NASH. This article is protected by copyright. All rights reserved.
Fibrosis plays an important role in many different pathologies. It results from tissue injury, chronic inflammation, autoimmune reactions and genetic alterations, and it is characterized by the excessive deposition of extracellular matrix components. Biopsies are routinely employed for fibrosis diagnosis, but they suffer from several drawbacks, including their invasive nature, sampling variability and limited spatial information. To overcome these limitations, multiple different imaging tools and technologies have been evaluated over the years, including x-ray imaging, computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), positron emission tomography (PET) and single-photon emission computed tomography (SPECT). These modalities can provide anatomical, functional and molecular imaging information which is useful for fibrosis diagnosis and staging, and they may also hold potential for the longitudinal assessment of therapy responses. Here, we summarize the use of non-invasive imaging techniques for monitoring fibrosis in systemic autoimmune diseases, in parenchymal organs (such as liver, kidney, lung and heart), and in desmoplastic cancers. We also discuss how imaging biomarkers can be integrated in (pre-) clinical research to individualize and improve anti-fibrotic therapies.
Progressive liver fibrosis, induced by chronic viral and metabolic disorders, leads to more than one million deaths annually via development of cirrhosis, although no antifibrotic therapy has been approved to date. Transdifferentiation (or “activation”) of hepatic stellate cells is the major cellular source of matrix protein-secreting myofibroblasts, the major driver of liver fibrogenesis. Paracrine signals from injured epithelial cells, fibrotic tissue microenvironment, immune and systemic metabolic dysregulation, enteric dysbiosis, and hepatitis viral products can directly or indirectly induce stellate cell activation. Dysregulated intracellular signaling, epigenetic changes, and cellular stress response represent candidate targets to deactivate stellate cells by inducing reversion to inactivated state, cellular senescence, apoptosis, and/or clearance by immune cells. Cell type- and target-specific pharmacological intervention to therapeutically induce the deactivation will enable more effective and less toxic precision antifibrotic therapies.
Macrophages represent a key cellular component of the liver, and are essential for maintaining tissue homeostasis and ensuring rapid responses to hepatic injury. Our understanding of liver macrophages has been revolutionized by the delineation of heterogeneous subsets of these cells. Kupffer cells are a self-sustaining, liver-resident population of macrophages and can be distinguished from the monocyte-derived macrophages that rapidly accumulate in the injured liver. Specific environmental signals further determine the polarization and function of hepatic macrophages. These cells promote the restoration of tissue integrity following liver injury or infection, but they can also contribute to the progression of liver diseases, including hepatitis, fibrosis and cancer. In this Review, we highlight novel findings regarding the origin, classification and function of hepatic macrophages, and we discuss their divergent roles in the healthy and diseased liver.
Lay summary:
Macrophages (greek for "big eaters") are a frequent non-parenchymal cell type of the liver that ensures homeostasis, antimicrobial defense and proper metabolism. However, liver macrophages consist of different subtypes regarding their ontogeny (developmental origin), differentiation and function. Understanding this heterogeneity and the critical regulation of inflammation, fibrosis and cancer by macrophage subsets opens promising new options for treating liver diseases.
Chronic liver injury is accompanied by a dysbalanced scarring process, termed fibrosis. This process is mainly driven by chronic inflammation and an altered activity of a multitude of different chemokines and cytokines, resulting in the infiltration by immune cells (especially macrophages) and increase of matrix-expressing cell types. These processes might lead to cirrhosis representing the end-stage of fibrosis. Recent clinical studies comprising patients successfully treated for viral hepatitis showed that liver fibrogenesis and even cirrhosis may be reverted. The hepatic capacity to remodel scar tissue and to revert into a normal liver follows specific mechanistic principles that include the termination of chronic tissue damage, shifting the cellular bias from inflammation to resolution, initiation of myofibroblast apoptosis or senescence and, finally, fibrinolysis of excess scar tissue. The plurality of molecular and cellular triggers involved in initiation, progression and resolution of hepatic fibrogenesis offers an infinite number of therapeutic possibilities. For instance, inflammatory macrophages can be targeted via inhibition of chemokine CCL2 or its receptor CCR2 (e.g., by cenicriviroc) as well as by transfer of restorative macrophage subsets. Another target is galectin-3 that acts at various stages along the continuum from acute to chronic inflammation. Profibrogenic cytokines (e.g., transforming growth factor-β), matricellular proteins (e.g., CCN1/CYR61) or signaling pathways involved in fibrogenesis offer further possible targets. Other options are the application of therapeutic antibodies directed against components involved in biogenesis or remodeling of connective tissue such as lysyl oxidase-like-2 or synthetic bile acids like obeticholic acid that activate the farnesoid X receptor and was antifibrotic in a phase 2 study (FLINT trial). Factors affecting the gut barrier function or the intestinal microbiome further expanded the repertoire of drug targets. In this review, we discuss novel concepts in resolution of hepatic fibrosis and focus on drug targets that might be suitable to trigger resolution of fibrosis.
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Sustained hepatic inflammation promotes progression of liver diseases, including hepatitis and nonalcoholic steatohepatitis. Liver inflammation is regulated by chemokines, which regulate the migration and activities of hepatocytes, Kupffer cells, hepatic stellate cells, endothelial cells, and circulating immune cells. However, the effects of the different chemokines and their receptors vary during pathogenesis of different liver diseases. During development of chronic viral hepatitis, CCL5 and CXCL10 regulate the cytopathic versus antiviral immune responses of T cells and natural killer cells. During development of nonalcoholic steatohepatitis, CCL2 and its receptor are up-regulated in the liver, where they promote inflammation, fibrosis, and steatosis, as well as in adipose tissue. CCL2 signaling thereby links hepatic and systemic inflammation related to metabolic disorders and insulin resistance. Several chemokine signaling pathways also promote hepatic fibrosis. Recent studies have shown that other chemokines and immune cells have anti-inflammatory and antifibrotic activities. Chemokines and their receptors can also contribute to the pathogenesis of hepatocellular carcinoma, promoting proliferation of cancer cells, the inflammatory microenvironment of the tumor, evasion of the immune response, and angiogenesis. We review the roles of different chemokines in the pathogenesis of liver diseases and their potential use as biomarkers or therapeutic targets.
Hepatic stellate cells (HSCs), also called Ito cells or lipocytes, are vitamin A-storing cells located in the Dissé space between hepatocytes and sinusoidal endothelial cells. Upon liver injury, these cells transdifferentiate into extracellular matrix-producing, highly proliferative myofibroblasts that promote hepatic fibrogenesis. Other possible collagen-producing cells in liver fibrosis include portal fibroblasts, bone marrow-derived cells (mesenchymal stem cells, fibrocytes and hematopoietic cells) and parenchymal cells undergoing epithelial-to-mesenchymal transition. Important factors and signaling pathways for HSC activation, as well as different functions of HSC during homeostasis and fibrosis, such as collagen production, secretion of cytokines and chemokines, immune modulation and changes in contractile features, as well as vitamin A storage capacity, have been identified in vitro and in vivo. Novel isolation techniques, specifically HSC sorting by FACS via autofluorescence and antibodies, will provide us with further opportunities to advance our understanding of HSC biology in health and disease.
Objectives:
Needle liver biopsy has been shown to have a high rate of sampling error in patients with diffuse parenchymal liver diseases. In these cases, the sample of liver tissue does not reflect the true degree of inflammation, fibrosis, or cirrhosis, despite an adequate sample size. The aim of this study was to determine the rate and extent of sampling error in patients with chronic hepatitis C virus infection, and to assess the intraobserver variation with the commonly used scoring system proposed by Scheuer and modified by Batts and Ludwig.
Methods:
A total of 124 patients with chronic hepatitis C virus infection underwent simultaneous laparoscopy-guided biopsies of the right and left hepatic lobes. Formalin-fixed paraffin-embedded sections were stained with hematoxylin and eosin and with trichrome. The slides were blindly coded and randomly divided among two hepatopathologists. Inflammation and fibrosis were scored according to the standard grading (inflammation) and staging (fibrosis) method based on the modified Scheuer system. Following the interpretation, the slides were uncoded to compare the results of the right and left lobes. Fifty of the samples were blindly resubmitted to each of the pathologists to determine the intraobserver variation.
Results:
Thirty of 124 patients (24.2%) had a difference of at least one grade, and 41 of 124 patients (33.1%) had a difference of at least one stage between the right and left lobes. In 18 patients (14.5%), interpretation of cirrhosis was given in one lobe, whereas stage 3 fibrosis was given in the other. A difference of two stages or two grades was found in only three (2.4%) and two (1.6%) patients, respectively. Of the 50 samples that were examined twice, the grading by each pathologist on the second examination differed from the first examination in 0% and 4%, and the staging differed in 6% and 10%, respectively. All observed variations were of one grade or one stage.
Conclusions:
Liver biopsy samples taken from the right and left hepatic lobes differed in histological grading and staging in a large proportion of chronic hepatitis C virus patients; however, differences of more than one stage or grade were uncommon. A sampling error may have led to underdiagnosis of cirrhosis in 14.5% of the patients. These differences could not be attributed to intraobserver variation, which appeared to be low.
Hepatic fibrosis is a scarring process that is associated with an increased and altered deposition of extracellular matrix in liver. At the cellular and molecular level, this progressive process is mainly characterized by cellular activation of hepatic stellate cells and aberrant activity of transforming growth factor-beta1 and its downstream cellular mediators. Although the cellular responses to this cytokine are complex, the signalling pathways of this pivotal cytokine during the fibrogenic response and its connection to other signal cascades are now understood in some detail. Based on the current advances in understanding the pleiotropic reactions during fibrogenesis, various inhibitors of transforming growth factor-beta were developed and are now being investigated as potential drug candidates in experimental models of hepatic injury. Although it is too early to favour one of these antagonists for the treatment of hepatic fibrogenesis in human, the experimental results obtained yet provide stimulatory impulses for the development of an effective treatment of choice in the not too distant future. The present review summarises the actual knowledge on the pathogenesis of hepatic fibrogenesis, the role of transforming growth factor-beta and its signalling pathways in promoting the fibrogenic response, and the therapeutic modalities that are presently in the spotlight of many investigations and are already on the way to take the plunge into clinical studies.
Introduction
Pathways, cells and molecular mediators in liver fibrogenesis
Classification of biomarkers of fibrosis
Class I biomarkers of fibrosis
Class II fibrosis biomarkers
Genetic pre‐disposition biomarkers
Future developments
Abstract
Fibrosis is a frequent, life‐threatening complication of most chronic liver diseases. Despite major achievements in the understanding of its pathogenesis, the translation of this knowledge into clinical practice is still limited. In particular, non‐invasive and reliable (serum‐) biomarkers indicating the activity of fibrogenesis are scarce. Class I biomarkers are defined as serum components having a direct relation to the mechanism of fibrogenesis, either as secreted matrix‐related components of activated hepatic stellate cells and fibroblasts or as mediators of extracellular matrix (ECM) synthesis or turnover. They reflect primarily the activity of the fibrogenic process. Many of them, however, proved to be disappointing with regard to sensitivity and speci‐ficity. Up to now hyaluronan turned out to be the relative best type I serum marker. Class II biomarkers comprise in general rather simple standard laboratory tests, which are grouped into panels. They fulfil most criteria for detection and staging of fibrosis and to a lesser extent grading of fibrogenic activity. More than 20 scores are currently available, among which Fibrotest™ is the most popular one. However, the diagnostic use of many of these scores is still limited and standardization of the assays is only partially realized. Combining of panel markers in sequential algorithms might increase their diagnostic validity. The translation of genetic pre‐disposition biomarkers into clinical practice has not yet started, but some polymorphisms indicate a link to progression and outcome of fibrogenesis. Parallel to serum markers non‐invasive physical techniques, for example, transient elastography, are developed, which can be combined with serum tests and profiling of serum proteins and glycans.