Endothelin and hepatic wound healing

Targeting Hepatic Stellate Cells for the Prevention and Treatment of Liver Cirrhosis and Hepatocellular Carcinoma: Strategies and Clinical Translation

Hepatic stellate cells (HSC) are the major source of myofibroblasts (MFB) in fibrosis and cancer- associated fibroblasts (CAF) in both primary and metastatic liver cancer. Over the past few decades, there has been significant progress in understanding the cellular and molecular mechanisms by which liver fibrosis and HCC occur, as well as the key roles of HSC in their pathogenesis. HSC-targeted approaches using specific surface markers and receptors may enable the selective delivery of drugs, oligonucleotides, and therapeutic peptides that exert optimized anti-fibrotic and anti-HCC effects. Recent advances in omics, particularly single-cell sequencing and spatial transcriptomics, hold promise for identifying new HSC targets for diagnosing and treating liver fibrosis/cirrhosis and liver cancer.

Characterization of focal adhesion proteins in rodent hepatic stellate cells

Ongoing liver injury leads to fibrosis and ultimately cirrhosis, a leading cause of death worldwide. The primary mechanism underlying the fibrogenic response is the activation of cells known as hepatic stellate cells (HSCs) which are "quiescent" in the normal liver but become "activated" after injury by transdifferentiating into extracellular matrix-secreting myofibroblasts. Since integrins (extracellular matrix binding receptors) are important mediators of HSC activation and fibrogenesis, we hypothesized that focal adhesion (FA) proteins, which link integrins to the intracellular protein machinery, may be important in the activation process. Therefore, using both an in vitro model of activation in primary rat HSCs and an in vivo model of liver injury, we examined three FA proteins: vinculin, FAK, and talin. All three proteins were significantly upregulated during HSC activation at both the messenger RNA (mRNA) and protein levels. Confocal microscopy demonstrated that the proteins had a widespread expression throughout HSCs with prominent localization at the end of actin filaments. Finally, we stimulated HSCs with the profibrotic ligands endothelin-1 (ET-1) and transforming growth factor beta (TGF-β) and observed an increase in the size of vinculin-containing FAs and the cell area occupied by them. The data indicate that HSCs possess a broad array of FA proteins, and given their upregulation during activation, this raises the possibility that they play a role in the fibrogenic response to injury.

Targeting Oxidative Stress and Endothelial Dysfunction Using Tanshinone IIA for the Treatment of Tissue Inflammation and Fibrosis

Salvia miltiorrhiza Burge (Danshen), a member of the Lamiaceae family, has been used in traditional Chinese medicine for many centuries as a valuable medicinal herb with antioxidative, anti-inflammatory, and antifibrotic potential. Several evidence-based reports have suggested that Salvia miltiorrhiza and its components prevent vascular diseases, including myocardial infarction, myocardial ischemia/reperfusion injury, arrhythmia, cardiac hypertrophy, and cardiac fibrosis. Tanshinone IIA (TanIIA), a lipophilic component of Salvia miltiorrhiza, has gained attention because of its possible preventive and curative activity against cardiovascular disorders. TanIIA, which possesses antioxidative, anti-inflammatory, and antifibrotic properties, could be a key component in the therapeutic potential of Salvia miltiorrhiza. Vascular diseases are often initiated by endothelial dysfunction, which is accompanied by vascular inflammation and fibrosis. In this review, we summarize how TanIIA suppresses tissue inflammation and fibrosis through signaling pathways such as PI3K/Akt/mTOR/eNOS, TGF-β1/Smad2/3, NF-κB, JNK/SAPK (stress-activated protein kinase)/MAPK, and ERK/Nrf2 pathways. In brief, this review illustrates the therapeutic value of TanIIA in the alleviation of oxidative stress, inflammation, and fibrosis, which are critical components of cardiovascular disorders.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Application of ultrasound elastography for monitoring the effects of TβR1 shRNA therapy on hepatic fibrosis in a rat model

BACKGROUND

To investigate the application of ultrasound elastography in monitoring the effects of the transforming growth factor (TGF)-β1 signaling pathway-targeted combination therapy for hepatic fibrosis.

METHODS

1. Short hairpin RNA (shRNA) constructs targeted towards TβR1 were designed, synthesized, and packaged using an adeno-associated virus (AAV), and the effective target shRNA was selected based on transfection results. 2. Fifty rats were randomly allocated (n = 10 per group) to the (A) control group, (B) model group, (C) 0-week therapy group, (D) 4-week therapy group, and (E) combination therapy group. At weeks 2, 4, 6, 8, 10, and 12, acoustic radiation force impulse (ARFI) elastography was used to measure the liver stiffness, inner diameter of the portal vein diameter, and blood velocity; radio frequency ultrasound imaging was used to measure the abdominal aortic elasticity parameter and pulse wave velocity (PWV) of the rats. 3. At week 12, portal vein puncture was performed to measure the portal venous pressure, and rat liver specimens were obtained for the pathological measurement of the degree of hepatic fibrosis.

RESULTS

1. An shRNA interference sequence targeted towards TβR1 was successfully designed, screened, and packaged using an AAV, and small-animal imaging results indicated expression of the specific shRNA in the liver. 2. At week 12, the ultrasound elastography results were significantly different between the experimental groups and the control group (p < 0.01); among the experimental groups, differences were significant between the therapy groups and the model group (p < 0.01). For groups C and E, the therapeutic effects on hepatic fibrosis in rats were significant, with the pathological results indicating a significant reduction in the degree of hepatic fibrosis (p < 0.01). The therapeutic effectiveness of group D was less than that of group C (p < 0.05). Significant differences existed between the portal venous pressure of the experimental groups and of the control group (p < 0.01). For the abdominal aortic elasticity parameter measured by radio frequency ultrasound imaging, differences existed between the values obtained from the experimental groups and from that of the control group (p < 0.05), while statistically significant differences were not found among the various experimental groups. 3. Continuous ultrasound examination results indicated that the elasticity value of group A was significantly different from those of the other groups after 2 weeks of model establishment (p < 0.01); after 6 weeks, the elasticity values of groups C and E were significantly different compared with those of groups B and D (p < 0.01). For the abdominal aortic elasticity parameter and pulse wave velocity (PWV), there were no significant differences among the various groups (p > 0.05).

CONCLUSION

CCl4-induced hepatic fibrosis can be treated through shRNA silencing of TβR1. Ultrasound ARFI elastography is superior to external force-assisted elastography as it can reflect the degree of fibrosis in moderate to severe hepatic fibrosis and the variations in the degree of fibrosis after treatment. Portal venous pressure was positively correlated with the degree of fibrosis; with early combination therapy, both the degree of fibrosis and portal venous pressure could be effectively reduced.

Endothelin-1 in portal hypertension: The intricate role of hepatic stellate cells

IMPACT STATEMENT

Portal hypertension is pathologically defined as increase of portal venous pressure, mainly due to chronic liver diseases such as fibrosis and cirrhosis. In fibrotic liver, activated hepatic stellate cells increase their contraction in response to endothelin-1 (ET-1) via autocrine and paracrine stimulation from liver sinusoidal endothelial cells and injured hepatocytes. Clinical studies are limited with ET receptor antagonists in cirrhotic patients with portal hypertension. Hence, studies are needed to find molecules that block ET-1 synthesis. Accumulation of extracellular matrix proteins in the perisinusoidal space, tissue contraction, and alteration in blood flow are prominent during portal hypertension. Therefore, novel matrix modulators should be tested experimentally as well as in clinical studies. Specifically, tumor necrosis factor-α, transforming growth factor-β1, Wnt, Notch, rho-associated protein kinase 1 signaling antagonists, and peroxisome proliferator-activated receptor α and γ, interferon-γ and sirtuin 1 agonists should be tested elaborately against cirrhosis patients with portal hypertension.

Myocardin and myocardin-related transcription factor-A synergistically mediate actin cytoskeletal-dependent inhibition of liver fibrogenesis

Activation of hepatic stellate cells (HSCs), characterized by development of a robust actin cytoskeleton and expression of abundant extracellular matrix (ECM) proteins, such as type 1 collagen (COL.1), is a central cellular and molecular event in liver fibrosis. It has been demonstrated that HSCs express both myocardin and myocardin-related transcription factor-A (MRTF-A). However, the biological effects of myocardin and MRTF-A on HSC activation and liver fibrosis, as well as the molecular mechanism under the process, remain unclear. Here, we report that myocardin and MRTF-A's expression and nuclear accumulation are prominently increased during the HSC activation process, accompanied by robust activation of actin cytoskeleton dynamics. Targeting myocardin and MRTF-A binding and function with a novel small molecule, CCG-203971, led to dose-dependent inhibition of HSC actin cytoskeleton dynamics and abrogated multiple functional features of HSC activation (i.e., HSC contraction, migration and proliferation) and decreased COL.1 expression in vitro and liver fibrosis in vivo. Mechanistically, blocking the myocardin and MRTF-A nuclear translocation pathway with CCG-203971 directly inhibited myocardin/MRTF-A-mediated serum response factor (SRF), and Smad2/3 activation in the COL.1α2 promoter and indirectly abrogated actin cytoskeleton-dependent regulation of Smad2/3 and Erk1/2 phosphorylation and their nuclear accumulation. Finally, there was no effect of CCG-203971 on markers of inflammation, suggesting a direct effect of the compound on HSCs and liver fibrosis. These data reveal that myocardin and MRTF-A are two important cotranscriptional factors in HSCs and represent entirely novel therapeutic pathways that might be targeted to treat liver fibrosis.NEW & NOTEWORTHY Myocardin and myocardin-related transcription factor-A (MRTF-A) are upregulated in activated hepatic stellate cells (HSCs) in vitro and in vivo, closely associated with robustly increased actin cytoskeleton remodeling. Targeting myocardin and MRTF-A by CCG-203971 leads to actin cytoskeleton-dependent inhibition of HSC activation, reduced cell contractility, impeded cell migration and proliferation, and decreased COL.1 expression in vitro and in vivo. Dual expression of myocardin and MRTF-A in HSCs may represent novel therapeutic targets in liver fibrosis.

Restoration of liver sinusoidal cell phenotypes by statins improves portal hypertension and histology in rats with NASH

Non-alcoholic steatohepatitis (NASH) is a common chronic liver disorder in developed countries, with the associated clinical complications driven by portal hypertension (PH). PH may precede fibrosis development, probably due to endothelial dysfunction at early stages of the disease. Our aim was to characterize liver sinusoidal endothelial cell (LSEC) dedifferentiation/capillarization and its contribution to PH in NASH, together with assessing statins capability to revert endothelial function improving early NASH stages. Sprague-Dawley rats were fed with high fat glucose-fructose diet (HFGFD), or control diet (CD) for 8 weeks and then treated with simvastatin (sim) (10 mg·kg⁻¹·day⁻¹), atorvastatin (ato) (10 mg·kg⁻¹·day⁻¹) or vehicle during 2 weeks. Biochemical, histological and hemodynamic determinations were carried out. Sinusoidal endothelial dysfunction was assessed in individualized sorted LSEC and hepatic stellate cells (HSC) from animal groups and in whole liver samples. HFGFD rats showed full NASH features without fibrosis but with significantly increased portal pressure compared with CD rats (10.47 ± 0.37 mmHg vs 8.30 ± 0.22 mmHg; p < 0.001). Moreover, HFGFD rats showed a higher percentage of capillarized (CD32b⁻/CD11b⁻) LSEC (8% vs 1%, p = 0.005) showing a contractile phenotype associated to HSC activation. Statin treatments caused a significant portal pressure reduction (sim: 9.29 ± 0.25 mmHg, p < 0.01; ato: 8.85 ± 0.30 mmHg, p < 0.001), NASH histology reversion, along with significant recovery of LSEC differentiation and a regression of HSC activation to a more quiescent phenotype. In an early NASH model without fibrosis with PH, LSEC transition to capillarization and HSC activation are reverted by statin treatment inducing portal pressure decrease and NASH features improvement.

Smooth Muscle α-Actin Deficiency Leads to Decreased Liver Fibrosis via Impaired Cytoskeletal Signaling in Hepatic Stellate Cells

In the liver, smooth muscle α-actin (SM α-actin) is up-regulated in hepatic stellate cells (HSCs) as they transition to myofibroblasts during liver injury and the wound healing response. Whether SM α-actin has specific functional effects on cellular effectors of fibrosis such as HSC is controversial. Here, the relationship between SM α-actin and type 1 collagen expression (COL1A1), a major extracellular matrix protein important in liver fibrosis, is investigated with the results demonstrating that knockout of SM α-actin leads to reduced liver fibrosis and COL1 expression. The mechanism for the reduction in fibrogenesis in vivo is multifactorial, including not only a reduction in the number of HSCs, but also an HSC-specific reduction in COL1 expression in Acta2-deficient HSCs. Despite a compensatory increase in expression of cytoplasmic β-actin and γ-actin isoforms in Acta2^-/- HSCs, defects were identified in each transforming growth factor beta/Smad2/3 and ET-1/Erk1/2 signaling in Acta2^-/- HSCs. These data not only suggest a molecular link between the SM α-actin cytoskeleton and classic fibrogenic signaling cascades, but also emphasize the relationship between SM α-actin and fibrogenesis in hepatic myofibroblasts in vivo.

Mechanisms and treatment of liver fibrosis

Hepatic fibrosis is a characteristic consequence of multiple chronic liver injuries. However, there are currently no specific drugs that can effectively reverse or prevent liver fibrosis progression. Liver fibrosis is a complex pathological process attributable to a variety of cytokines and molecular pathways. Therefore, further exploring the cellular and molecular mechanisms of liver fibrosis, unearthing specific anti-fibrosis targeted therapies and translation of the potential findings into clinical treatment are of great significance.

Impaired wound healing: facts and hypotheses for multi-professional considerations in predictive, preventive and personalised medicine

Whereas the physiologic wound healing (WH) successfully proceeds through the clearly defined sequence of the individual phases of wound healing, chronic non-healing wounds/ulcers fail to complete the individual stages and the entire healing process. There are many risk factors both modifiable (such as stress, smoking, inappropriate alcohol consumption, malnutrition, obesity, diabetes, cardio-vascular disease, etc.) and non-modifiable (such as genetic diseases and ageing) strongly contributing to the impaired WH. Current statistics demonstrate that both categories are increasingly presented in the populations, which causes dramatic socio-economic burden to the healthcare sector and society at large. Consequently, innovative concepts by predictive, preventive and personalised medicine are crucial to be implemented in the area. Individual risk factors, causality, functional interrelationships, molecular signature, predictive diagnosis, and primary and secondary prevention are thoroughly analysed followed by the expert recommendations in this paper.

Biomarkers for Diabetic Retinopathy - Could Endothelin 2 Be Part of the Answer?

Purpose

The endothelins are a family of three highly conserved and homologous vasoactive peptides that are expressed across all organ systems. Endothelin (Edn) dysregulation has been implicated in a number of pathophysiologies, including diabetes and diabetes-related complications. Here we examined Edn2 and endothelin receptor B (Endrb) expression in retinae of diabetic mouse models and measured serum Edn2 to assess its biomarker potential.

Materials and Methods

Edn2 and Ednrb mRNA and Edn2 protein expression were assessed in young (8wk) and mature (24wk) C57Bl/6 (wild type; wt), Kimba (model of retinal neovascularisation, RNV), Akita (Type 1 diabetes; T1D) and Akimba mice (T1D plus RNV) by qRT-PCR and immunohistochemistry. Edn2 protein concentration in serum was measured using ELISA.

Results

Fold-changes in Edn2 and Ednrb mRNA were seen only in young Kimba (Edn2: 5.3; Ednrb: 6.0) and young Akimba (Edn2: 7.9, Ednrb: 8.8) and in mature Kimba (Edn2:9.2, Ednrb:11.2) and mature Akimba (Edn2:14.0, Ednrb:17.5) mice. Co-localisation of Edn2 with Müller-cell-specific glutamine synthetase demonstrated Müller cells and photoreceptors as the major cell types for Edn2 expression in all animal models. Edn2 serum concentrations in young Kimba, Akita and Akimba mice were not elevated compared to wt. However, in mature mice, Edn2 serum concentration was increased in Akimba (6.9pg/mg total serum protein) compared to wt, Kimba and Akita mice (3.9, 4.6, and 3.8pg/mg total serum protein, respectively; p<0.05).

Conclusions

These results demonstrated that long-term hyperglycaemia in conjunction with VEGF-driven RNV increased Edn2 serum concentration suggesting Edn2 might be a candidate biomarker for vascular changes in diabetic retinopathy.

Strategies and endpoints of antifibrotic drug trials: Summary and recommendations from the AASLD Emerging Trends Conference, Chicago, June 2014

There is an urgent need to develop antifibrotic therapies for chronic liver disease, and clarify which endpoints in antifibrotic trials will be acceptable to regulatory agencies. The American Association for the Study of Liver Diseases sponsored an endpoints conference to help accelerate the efficient testing of antifibrotic agents and develop recommendations on clinical trial design for liver fibrosis. In this review, we summarize the salient and novel elements of this conference and provide directions for future clinical trial design. The article follows the structure of the conference and is organized into five areas: (1) antifibrotic trial design; (2) preclinical proof-of-concept studies; (3) pharmacological targets, including rationale and lessons to learn; (4) rational drug design and development; and (5) consensus and recommendations on design of clinical trials in liver fibrosis. Expert overviews and collaborative discussions helped to summarize the key unmet needs and directions for the future, including: (1) greater clarification of at-risk populations and study groups; (2) standardization of all elements of drug discovery and testing; (3) standardization of clinical trial approaches; (4) accelerated development of improved noninvasive markers; and (5) need for exploration of potential off-target toxicities of future antifibrotic drugs.

Eggshell membrane ameliorates hepatic fibrogenesis in human C3A cells and rats through changes in PPARγ-Endothelin 1 signaling

Our previous nutrigenomic findings indicate that eggshell membrane (ESM) may prevent liver fibrosis. Here we investigated the effects and mechanisms underlying ESM intervention against liver injury by using DNA microarray analysis and comparative proteomics. In vitro hydrolyzed ESM attenuated the TGFβ1-induced procollagen production of human hepatocyte C3A cells and inhibited the expression of Endothelin 1 (EDN1) and its two receptors, and extracellular matrix components. In vivo male Wistar rats were allocated into a normal control group, a CCl4 group (hypodermic injection of 50% CCl4 2×/wk) and an ESM group (20 g ESM/kg diet with CCl4 injection) for 7 wks. Dietary ESM ameliorated the elevated activity of ALT/AST, oxidative stress and collagen accumulation in liver, accompanied by the down-regulated expression of Edn1 signaling and notable profibrogenic genes and growth factors as well as peroxisome proliferator-activated receptor gamma (PPARγ). Concomitantly, the decreased expressions of Galectin-1 and Desmin protein in the ESM group indicated the deactivation of hepatic stellate cells (HSCs). Through a multifaceted integrated omics approach, we have demonstrated that ESM can exert an antifibrotic effect by suppressing oxidative stress and promoting collagen degradation by inhibiting HSCs' transformation, potentially via a novel modulation of the PPARγ-Endothelin 1 interaction signaling pathway.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

Regulator of G-protein signaling-5 is a marker of hepatic stellate cells and expression mediates response to liver injury

Liver fibrosis is mediated by hepatic stellate cells (HSCs), which respond to a variety of cytokine and growth factors to moderate the response to injury and create extracellular matrix at the site of injury. G-protein coupled receptor (GPCR)-mediated signaling, via endothelin-1 (ET-1) and angiotensin II (AngII), increases HSC contraction, migration and fibrogenesis. Regulator of G-protein signaling-5 (RGS5), an inhibitor of vasoactive GPCR agonists, functions to control GPCR-mediated contraction and hypertrophy in pericytes and smooth muscle cells (SMCs). Therefore we hypothesized that RGS5 controls GPCR signaling in activated HSCs in the context of liver injury. In this study, we localize RGS5 to the HSCs and demonstrate that Rgs5 expression is regulated during carbon tetrachloride (CCl₄)-induced acute and chronic liver injury in Rgs5^LacZ/LacZ reporter mice. Furthermore, CCl₄ treated RGS5-null mice develop increased hepatocyte damage and fibrosis in response to CCl₄ and have increased expression of markers of HSC activation. Knockdown of Rgs5 enhances ET-1-mediated signaling in HSCs in vitro. Taken together, we demonstrate that RGS5 is a critical regulator of GPCR signaling in HSCs and regulates HSC activation and fibrogenesis in liver injury.

Substance P stimulates endothelin 1 secretion via endothelin-converting enzyme 1 and promotes melanogenesis in human melanocytes

Substance P (SP) is a well-known neuropeptide implicated in the wound-healing process. The wound occasionally causes a pigmented scar. In the present study, we examined whether increased levels of SP affected melanogenesis. When human melanocytes were treated with SP, the melanin content increased and the pigmentation process accelerated in a dose-dependent manner. In addition to melanogenesis-related genes, the expression of neurokinin 1 receptor, endothelin 1 (EDN1), and EDN receptor type B (EDNRB) also increased at both the messenger RNA and protein levels. Interestingly, secreted EDN1 was observed in the melanocyte culture medium, and this phenomenon was significantly enhanced by SP treatment. Through knockdown experiments using small interfering RNAs (siRNAs), we confirmed that endothelin-converting enzyme 1 (ECE1), EDN1, and EDNRB were involved in SP-induced pigmentation and found that EDN1 secretion was affected by ECE1 and EDN1 siRNAs, but not by EDNRB siRNA. These findings indicate that ECE1 is essential for EDN1 secretion in melanocytes and that EDNRB functions downstream of secreted EDN1 to increase the cAMP levels and activate the melanogenesis-related phosphorylation cascade. This study provides in vitro evidence for a melanogenic function of SP in the skin and suggests that the SP-related signal is a potent target for regulating stress- or wound-induced pigmentation.

Cellular and molecular mechanisms in the pathogenesis of liver fibrosis: An update

There have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying liver fibrogenesis. Recent data indicate that the termination of fibrogenic processes and the restoration of deficient fibrolytic pathways may allow the reversal of advanced fibrosis and even cirrhosis. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in liver fibrosis. Activation of hepatic stellate cells (HSCs) remains a central event in fibrosis, complemented by other sources of matrix-producing cells, including portal fibroblasts, fibrocytes and bone marrow-derived myofibroblasts. These cells converge in a complex interaction with neighboring cells to provoke scarring in response to persistent injury. Defining the interaction of different cell types, revealing the effects of cytokines on these cells and characterizing the regulatory mechanisms that control gene expression in activated HSCs will enable the discovery of new therapeutic targets. Moreover, the characterization of different pathways associated with different etiologies aid in the development of disease-specific therapies. This article outlines recent advances regarding the cellular and molecular mechanisms involved in liver fibrosis that may be translated into future therapies. The pathogenesis of liver fibrosis associated with alcoholic liver disease, non-alcoholic fatty liver disease and viral hepatitis are also discussed to emphasize the various mechanisms involved in liver fibrosis.

The profibrotic role of endothelin-1: is the door still open for the treatment of fibrotic diseases?

The endothelin (ET) system consists of two G-protein-coupled receptors (ETA and ETB), three peptide ligands (ET-1, ET-2 and ET-3), and two activating peptidases (endothelin-converting enzyme-, ECE-1 and ECE-2). While initially described as a vasoregulatory factor, shown to influence several cardiovascular diseases, from hypertension to heart failure, ET-1, the predominant form in most cells and tissues, has expanded its pathophysiological relevance by recent evidences implicating this factor in the regulation of fibrosis. In this article, we review the current knowledge of the role of ET-1 in the development of fibrosis, with particular focus on the regulation of its biosynthesis and the molecular mechanisms involved in its profibrotic actions. We summarize also the contribution of ET-1 to fibrotic disorders in several organs and tissues. The development and availability of specific ET receptor antagonists have greatly stimulated a number of clinical trials in these pathologies that unfortunately have so far given negative or inconclusive results. This review finally discusses the circumstances underlying these disappointing results, as well as provides basic and clinical researchers with arguments to keep exploring the complex physiology of ET-1 and its therapeutic potential in the process of fibrosis.

Influence of block of NF-kappa B signaling pathway on oxidative stress in the liver homogenates

The aim of the present study was to assess whether BAY 11-7082, a nuclear factor-kappaB (NF-κB) inhibitor, influences the level of reactive oxygen species (ROS), tumor necrosis factor alpha (TNF-α), and NF-κB related signaling pathways in the liver. The animals were divided into 4 groups: I: saline; II: saline + endothelin-1 (ET-1) (1.25 μg/kg b.w., i.v.); III: saline + ET-1 (12.5 μg/kg b.w., i.v.); and IV: BAY 11-7082 (10 mg/kg b.w., i.v.) + ET-1 (12.5 μg/kg b.w., i.v.). Injection of ET-1 alone at a dose of 12.5 μg/kg b.w. showed a significant (P < 0.001) increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H₂O₂) level and decrease (P < 0.01) in GSH level (vs. control). ET-1 administration slightly downregulated gene expression of p65 of NF-κB but potently and in a dose-dependent way downregulated p21-cip gene expression in the liver. BAY 11-7082 significantly decreased TBARS (P < 0.001), H₂O₂ (P < 0.01) and improved the redox status (P < 0.05), compared to ET-1 group. The concentration of TNF-α was increased in the presence of ET-1 (P < 0.05), while BAY 11-7082 decreased TNF-α concentration (P < 0.01). Inhibition of IkBα before ET-1 administration downregulated gene expression of p21-cip but had no effect on p65.

Comparison of endothelin receptors in normal versus cirrhotic human liver and in the liver from endothelial cell-specific ETB knockout mice

AIMS

Endothelin (ET) antagonists show promise in animal models of cirrhosis and portal hypertension. The aim was to pharmacologically characterise the expression of endothelin receptors in human liver, hepatic artery and portal vein.

MAIN METHODS

Immunofluorescence staining, receptor autoradiography and competition binding assays were used to localise and quantify ET receptors on hepatic parenchyma, hepatic artery and portal vein in human cirrhotic or normal liver. Additional experiments were performed to determine the affinity and selectivity of ET antagonists for liver ET endothelin receptors. An endothelial cell ET(B) knockout murine model was used to examine the function of sinusoid endothelial ET(B) receptors.

KEY FINDINGS

ET(B) receptors predominated in normal human liver and displayed the highest ratio (ET(B):ET(A) 63:47) compared with other peripheral tissues. In two patients examined, liver ET(B) expression was up-regulated in cirrhosis (ET(B):ET(A) 83:17). Both sub-types localised to the media of normal portal vein but ET(B) receptors were downregulated fivefold in the media of cirrhotic portal vein. Sinusoid diameter was fourfold smaller in endothelial cell ET(B) knockout mice. The liver morphology of ET(B) knockout mice was markedly different to normal murine liver, with loss of the wide spread sinusoidal pattern. In the knockout mice, sinusoids were reduced in both number and absolute diameter, while large intrahepatic veins were congested with red blood cells.

SIGNIFICANCE

These data support a role for the ET system in cirrhosis of the liver and suggest that endothelial ET(B) blockade may cause sinusoidal constriction which may contribute to hepatotoxicity associated with some endothelin antagonists.