Carbenoxolone inhibits DNA synthesis and collagen gene expression in rat hepatic stellate cells in culture

Carbenoxolone mitigates extensive fibrosis formation in PLP-induced EAE model and multiple sclerosis serum-exposed pericyte culture

Introduction

Multiple sclerosis (MS) is one of the most common causes of disability in young adults. Nearly, 85% of MS cases start with attacks and remissions, classified as relapsing-remitting multiple sclerosis (RRMS). With repeating attacks, MS causes brain-spinal cord atrophy and enhanced disability as disease progresses. PLP-induced EAE is one of the most established models for pathophysiology and treatment of RRMS. Recent studies demonstrated the possible role of pericytes in perivascular and intra-lesional fibrosis in PLP-induced EAE, whose importance remains elusive. Hence, we have investigated the possible role of pericytes in fibrosis formation and amelioration with a hemichannel blocker, Carbenoxolone (CBX).

Methods

PLP-induced experimental autoimmune encephalitis (EAE) model is used and the effect of CBX is investigated. Clinical scores were recorded and followed. Perivascular Collagen 1 and 3 accumulations were demonstrated as markers of fibrosis in the spinal cord. To delineate the role of pericytes, human brain vascular pericytes (HBVP) were incubated with the sera of MS patients to induce in-vitro MS model and the fibrosis formation was investigated.

Results

In the PLP induced in-vivo model, both intracerebroventricular and intraperitoneal CBX have significantly mitigated the disease progression followed by clinical scores, demyelination, and fibrosis. Moreover, CBX significantly mitigated MS-serum-induced fibrosis in the HBVP cell culture.

Discussion

The study demonstrated two important findings. First, CBX decreases fibrosis formation in both in-vivo and in-vitro MS models. Secondly, it improves neurological scores and decreases demyelination in the EAE model. Therefore, CBX can be potential novel therapeutic option in treating Multiple Sclerosis.

Natural products in licorice for the therapy of liver diseases: Progress and future opportunities

Liver diseases related complications represent a significant source of morbidity and mortality worldwide, creating a substantial economic burden. Oxidative stress, excessive inflammation, and dysregulated energy metabolism significantly contributed to liver diseases. Therefore, discovery of novel therapeutic drugs for the treatment of liver diseases are urgently required. Licorice is one of the most commonly used herbal drugs in Traditional Chinese Medicine for the treatment of liver diseases and drug-induced liver injury (DILI). Various bioactive components have been isolated and identified from the licorice, including glycyrrhizin, glycyrrhetinic acid, liquiritigenin, Isoliquiritigenin, licochalcone A, and glycycoumarin. Emerging evidence suggested that these natural products relieved liver diseases and prevented DILI through multi-targeting therapeutic mechanisms, including anti-steatosis, anti-oxidative stress, anti-inflammation, immunoregulation, anti-fibrosis, anti-cancer, and drug-drug interactions. In the current review, we summarized the recent progress in the research of hepatoprotective and toxic effects of different licorice-derived bioactive ingredients and also highlighted the potency of these compounds as promising therapeutic options for the treatment of liver diseases and DILI. We also outlined the networks of underlying molecular signaling pathways. Further pharmacology and toxicology research will contribute to the development of natural products in licorice and their derivatives as medicines with alluring prospect in the clinical application.

TAT-Gap19 and Carbenoxolone Alleviate Liver Fibrosis in Mice

Although a plethora of signaling pathways are known to drive the activation of hepatic stellate cells in liver fibrosis, the involvement of connexin-based communication in this process remains elusive. Connexin43 expression is enhanced in activated hepatic stellate cells and constitutes the molecular building stone of hemichannels and gap junctions. While gap junctions support intercellular communication, and hence the maintenance of liver homeostasis, hemichannels provide a circuit for extracellular communication and are typically opened by pathological stimuli, such as oxidative stress and inflammation. The present study was set up to investigate the effects of inhibition of connexin43-based hemichannels and gap junctions on liver fibrosis in mice. Liver fibrosis was induced by administration of thioacetamide to Balb/c mice for eight weeks. Thereafter, mice were treated for two weeks with TAT-Gap19, a specific connexin43 hemichannel inhibitor, or carbenoxolone, a general hemichannel and gap junction inhibitor. Subsequently, histopathological analysis was performed and markers of hepatic damage and functionality, oxidative stress, hepatic stellate cell activation and inflammation were evaluated. Connexin43 hemichannel specificity of TAT-Gap19 was confirmed in vitro by fluorescence recovery after photobleaching analysis and the measurement of extracellular release of adenosine-5′-triphosphate. Upon administration to animals, both TAT-Gap19 and carbenoxolone lowered the degree of liver fibrosis accompanied by superoxide dismutase overactivation and reduced production of inflammatory proteins, respectively. These results support a role of connexin-based signaling in the resolution of liver fibrosis, and simultaneously demonstrate the therapeutic potential of TAT-Gap19 and carbenoxolone in the treatment of this type of chronic liver disease.

Huang Qi Decoction Prevents BDL-Induced Liver Fibrosis Through Inhibition of Notch Signaling Activation

Notch signaling has been demonstrated to be involved in ductular reactions and fibrosis. Previous studies have shown that Huang Qi Decoction (HQD) can prevent the progression of cholestatic liver fibrosis (CLF). However, whether HQD affects the Notch signaling pathway is unclear. In this study, CLF was established by common bile duct ligation (BDL) in rats. At the end of the first week, the rats were randomly divided into a model group (i.e., BDL), an HQD group, and a sorafenib positive control group (SORA) and were treated for 3 weeks. Bile duct proliferation and liver fibrosis were determined by tissue staining. Activation of the Notch signaling pathway was evaluated by analyzing expressions of Notch-1, -2, -3, and -4, Jagged (JAG) 1, and Delta like (DLL)-1, -3, and -4. The results showed that HQD significantly reduced the deposition of collagen and the Hyp content of liver tissue and inhibited the activation of HSCs compared with the BDL group. In addition, HQD significantly decreased the protein and mRNA expressions of TGF-[Formula: see text]1 and [Formula: see text]-SMA. In contrast, HQD significantly enhanced expression of the Smad 7 protein. HQD also reduced biliary epithelial cell proliferation, and reduced the mRNA levels of CK7, CK8, CK18, SRY-related high mobility group-box gene (SOX) 9, epithelial cell adhesion molecule (EpCAM) and the positive areas of CK19 and OV6. In addition, the mRNA and protein expressions of Notch-3, -4, JAG1, and DLL-1, -3 were significantly reduced in the HQD compared to the BDL group. These results demonstrated that HQD may prevent biliary liver fibrosis through inhibition of the Notch signaling pathway, and it may be a potential treatment for cholestatic liver disease.

Connexins, Pannexins, and Their Channels in Fibroproliferative Diseases

Cellular and molecular mechanisms of wound healing, tissue repair, and fibrogenesis are established in different organs and are essential for the maintenance of function and tissue integrity after cell injury. These mechanisms are also involved in a plethora of fibroproliferative diseases or organ-specific fibrotic disorders, all of which are associated with the excessive deposition of extracellular matrix components. Fibroblasts, which are key cells in tissue repair and fibrogenesis, rely on communicative cellular networks to ensure efficient control of these processes and to prevent abnormal accumulation of extracellular matrix into the tissue. Despite the significant impact on human health, and thus the epidemiologic relevance, there is still no effective treatment for most fibrosis-related diseases. This paper provides an overview of current concepts and mechanisms involved in the participation of cellular communication via connexin-based pores as well as pannexin-based channels in the processes of tissue repair and fibrogenesis in chronic diseases. Understanding these mechanisms may contribute to the development of new therapeutic strategies to clinically manage fibroproliferative diseases and organ-specific fibrotic disorders.

Astragaloside prevents BDL-induced liver fibrosis through inhibition of notch signaling activation

ETHNOPHARMACOLOGICAL RELEVANCE

Huangqi decoction was first described in Prescriptions of the Bureau of Taiping People׳s Welfare Pharmacy in the Song Dynasty (AD1078). It consists of Radix Astragali (Astragalus membranceus (Fisch.) Bge. Root, Huangqi) and Radix Glycyrrhizae (Glycyrrhiza uralensis Fisch., root and rhizome, Gancao), and it is an effective recipe that is usually used to treat consumptive disease and chronic liver diseases. Astragaloside (AS) is a main component of Radix Astragali had an effect similar to the Huangqi decoction on hepatic fibrosis.

AIM OF THE STUDY

Cholestasis is associated with a number of chronic liver diseases and Notch signaling has been demonstrated to be involved in ductular reaction. Previous studies have shown that AS can prevent the progression of cholestatic liver fibrosis, however, whether AS affects the Notch signaling pathway is unclear.

MATERIALS AND METHODS

Cholestatic liver fibrosis was established by common bile duct ligation (BDL) in rats. At first weekend, the rats were randomly divided into a model group (BDL), an AS group, and a Sorafenib positive control group (SORA) and treated for 3 weeks. Bile duct proliferation and liver fibrosis were determined by tissue staining. Activation of the Notch signaling pathway was evaluated by analyzing expressions of Notch-1, -2, -3, -4, Jagged 1 (JAG1), Delta-like (DLL)-1, -3, -4, Hes1, Numb and RBP-Jκ. Activation of the Wnt signaling pathway was evaluated by analyzing expressions of Wnt-4, -5a, -5b, Frizzled (Fzd)-2, -3, -6 and β-catenin.

RESULTS

(1) Compared with the BDL group, AS significantly reduced the deposition of collagen and the Hyp content of liver tissue and inhibited the activation of HSCs. In addition, AS significantly decreased the protein and mRNA expressions of TGF-β1 and α-SMA. In contrast, AS significantly enhanced expression of the Smad 7 protein. AS also reduced biliary epithelial cell proliferation, and reduced the mRNA and protein expressions of CK7, CK8, CK18, CK19, OV6, Sox9 and EpCAM. (2) The mRNA and protein expressions of Notch-2, -3, -4 and JAG1 were significantly reduced in the AS compared to the BDL group. In contrast, the mRNA and protein level of Numb was clearly enhanced after AS treatment.

CONCLUSION

AS may prevent biliary liver fibrosis via inhibition of the Notch signaling pathway, thereby inhibiting the abnormal proliferation of biliary epithelial cells. Results indicate that AS may be a potential therapeutic drug for cholestatic liver disease.

[Effects of Chinese herbal medicine Xiaopi Pill in preventing rats from dimethylnitrosamine-induced liver fibrosis]

OBJECTIVE

To explore the intervention effects of Xiaopi Pill (XPW), a compound traditional Chinese herbal medicine, on the development progress of dimethylnitrosamine (DMN)-induced liver fibrosis in rats.

METHODS

Liver fibrosis model was established by intraperitoneal injection of 0.5% DMN 2 mL/kg thrice a week for 4 weeks. Rats were divided into control group given saline and treatment group given XPW during the 3rd week of DMN injections. Rats were sacrificed at the end of the experiment, and then liver histological changes, liver function and mRNA expression of the liver fibrosis-associated markers were observed.

RESULTS

(1) At the end of the 2nd and 4th weeks of DMN injection, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) increased significantly in rats (P<0.01 or P<0.05); content of total bilirubin (TBil) increased significantly compared with the normal group until the end of the 4th week (P<0.05); compared with the model group after 4 weeks of DMN injection, the serum levels of ALT, AST, ALP and TBil were decreased remarkably in the XPW-treated group (P<0.01 or P<0.05). (2) The hepatic inflammation and collagen deposition in hepatic tissues increased by different degrees in experimental rats. Parts of pathological changes in the rat liver were found at the end of the 4th week, including a complete round structure of false flocculus round, meantime, the hydroxyproline content of hepatic tissue was increased significantly at the end of the 2nd and 4th weeks (P<0.05). Compared with the 4-week model group, the hepatic inflammation, collagen deposition and hydroxyproline content in hepatic tissues were alleviated dramatically (P<0.05). (3) Compared with the normal and 2nd week groups, protein expression of alpha-smooth muscle actin (α-SMA) was gradually increased, and that of the 4th week group were aggrandized significantly (P<0.01). Compared with the normal group, the mRNA expression of α-SMA, transforming growth factor-β1 (TGF-β1), tissue inhibitor of metalloproteinase-1 (TIMP-1), and heme oxygenase-1 (HO-1) was gradually increased. Further changes in above-mentioned abnormalities were found in the model rats at the end of the 4th week (P<0.01); while compared to the 4th week group, protein and mRNA levels of α-SMA and mRNA levels of TGF-β1, TIMP-1, and HO-1 were decreased significantly in the XPW group (P<0.01 or P<0.05).

CONCLUSION

Progressive DMN-induced liver fibrosis in rats can be suppressed by XPW; the mechanism may be associated with inhibition of the activated hepatic stellate cells.

Connexins regulate cell functions in pancreatic stellate cells

OBJECTIVES

Pancreatic stellate cells (PSCs) play a pivotal role in pancreatic fibrosis associated with chronic pancreatitis and pancreatic cancer. Connexins (Cxs) allow direct intercellular communications as components of gap junction but also play important roles in the regulation of cell proliferation, cell differentiation, and tissue development. We here examined the expression of Cxs and Cx-mediated regulation of cell functions in PSCs.

METHODS

Human PSCs were isolated from patients undergoing operation for chronic pancreatitis or pancreatic cancer. The expression of Cxs was examined by reverse transcription polymerase chain reaction, Western blotting, and immunofluorescent staining. The roles of Cxs in PSC functions were examined by using carbenoxolone, a broad-spectrum Cx inhibitor, and small interfering RNA for Cx43.

RESULTS

Human activated PSCs expressed a variety of Cxs including Cx43 both in vitro and in vivo. Carbenoxolone inhibited platelet-derived growth factor-BB-induced proliferation and migration, and type I collagen expression in PSCs. In addition, carbenoxolone inhibited the activation of quiescent PSCs to a myofibroblastlike phenotype. Decreased Cx43 expression by small interfering RNA resulted in decreased proliferation and type I collagen expression.

CONCLUSIONS

Pancreatic stellate cells expressed a variety of Cxs. Connexins, especially Cx43, might regulate the cell functions and activation of PSCs.

Gap junctions and non-neoplastic liver disease

Because of their critical role as goalkeepers of hepatic homeostasis, gap junctions are frequent targets in liver disease. This concept has been demonstrated on many occasions in the light of hepatocarcinogenesis. Relatively little focus has been put on the fate of gap junctions in other liver pathologies, including hepatitis, liver fibrosis and cirrhosis, cholestasis and hepatic ischemia and reperfusion injury. The present paper provides an in-depth description of the multiple changes in expression, localization and function of connexins, the molecular constituents of gap junctions. The use of connexins as biomarkers and therapeutic targets in liver disease is also illustrated.

Biological role of connexin intercellular channels and hemichannels

Gap junctions (GJ) and hemichannels (HC) formed from the protein subunits called connexins are transmembrane conduits for the exchange of small molecules and ions. Connexins and another group of HC-forming proteins, pannexins comprise the two families of transmembrane proteins ubiquitously distributed in vertebrates. Most cell types express more than one connexin or pannexin. While connexin expression and channel activity may vary as a function of physiological and pathological states of the cell and tissue, only a few studies suggest the involvement of pannexin HC in acquired pathological conditions. Importantly, genetic mutations in connexin appear to interfere with GJ and HC function which results in several diseases. Thus connexins could serve as potential drug target for therapeutic intervention. Growing evidence suggests that diseases resulting from HC dysfunction might open a new direction for development of specific HC reagents. This review provides a comprehensive overview of the current studies of GJ and HC formed by connexins and pannexins in various tissue and organ systems including heart, central nervous system, kidney, mammary glands, ovary, testis, lens, retina, inner ear, bone, cartilage, lung and liver. In addition, present knowledge of the role of GJ and HC in cell cycle progression, carcinogenesis and stem cell development is also discussed.

Antifibrotic activity of coumarins from Cnidium monnieri fruits in HSC-T6 hepatic stellate cells

The CHCl(3) fraction of Cnidium monnieri fruits significantly inhibited the proliferation of hepatic stellate cells in an in-vitro assay system employing HSC-T6 hepatic stellate cell lines. Activity-guided fractionation of the CHCl(3) fraction of C. monnieri led to the isolation of ten coumarins: osthol (1), meranzin (2), auraptenol (3), meranzin hydrate (4), 7-hydroxy-8-methoxy coumarin (5), imperatorin (6), xanthotoxol (7), xanthotoxin (8), bergapten (9) and isopimpinellin (10). Of these, compounds 1 and 6 significantly inhibited proliferation of HSCs in a time- and concentration-dependent manner. In addition, compounds 1 and 6 significantly reduced collagen content in HSC-T6 cells.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Proanthocyanidin derived from the leaves of Vaccinium virgatum suppresses platelet-derived growth factor-induced proliferation of the human hepatic stellate cell line LI90

AIM

Hepatic stellate cell (HSC) proliferation plays a pivotal role in liver fibrogenesis, and agents that suppress HSC activation, including platelet-derived growth factor (PDGF)-induced HSC proliferation, are good candidates for antifibrogenic therapies. In this report, we use the LI90 HSC line to elucidate the antifibrogenic effects of proanthocyanidin derived from the leaves of Vaccinium virgatum.

METHODS

Proanthocyanidin (PAC) was extracted from the leaves of blueberry V. virgatum (BB-PAC), grape seeds (GS-PAC) and Croton lechleri (CL-PAC). These extracts were examined for their effects on PDGF-BB-induced LI90 cell proliferation and DNA synthesis. Extracellular signal-regulated kinase (ERK) and Akt phosphorylation and PDGF receptor-beta (PDGFR-beta) expression were evaluated by western blot analysis.

RESULTS

BB-PAC potently suppressed PDGF-BB-induced proliferation and DNA synthesis of LI90 cells. BB-PAC also suppressed PDGF-BB-induced DNA synthesis in primary cultured rat HSC. Moreover, GS-PAC and CL-PAC suppressed PDGF-BB-induced DNA synthesis in LI90 cells. In contrast, the monomeric PAC catechin and epicatechin and dimeric PAC procyanidin B2 only slightly suppressed PDGF-BB-induced DNA synthesis. Western blot analysis showed that BB-PAC completely or partially inhibited PDGF-BB-induced ERK and Akt phosphorylation, respectively. In addition, BB-PAC partially inhibited the PDGF-BB-induced degradation of PDGFR-beta.

CONCLUSION

Our results suggest that BB-PAC suppresses activated HSC by inhibiting the PDGF signaling pathway. In addition, these results provide novel findings that may facilitate the development of antifibrogenic agents.

Reversibility of fibrosis, inflammation, and endoplasmic reticulum stress in the liver of rats fed a methionine-choline-deficient diet

Fatty liver disease has become a health problem related to metabolic syndrome worldwide, although its molecular pathogenesis requires further study. It is also unclear whether advanced fibrosis of steatohepatitis will regress when diet is controlled. The aim of this study was to investigate whether the resolution of fibrosis occurs in steatohepatitis induced by a methionine-choline-deficient diet (MCDD). Manifestation of endoplasmic reticulum (ER) stress in this model was also studied. Nonalcoholic steatohepatitis with advanced fibrosis was induced in rats by feeding them an MCDD for 10 weeks. Instead of MCDD, a methionine-choline control diet (CD) was given for the last 2 weeks to the experimental group. Fibrosis and inflammation were determined by tissue staining. Protein and gene expressions were determined by immunoblotting and quantitative reverse transcription-PCR (RT-PCR), respectively. Expressions of caspase-7, caspase-12, glucose-regulated protein 78 (GRP78), and protein disulfide isomerase were evaluated to clarify the presence of ER stress. Changing the diet from MCDD to CD triggered the reduction of fat in hepatocytes, a decrease in inflammatory gene expression and oxidative stress, and regression of fibrosis accompanied by the disappearance of activated stellate cells and macrophages. Immunohistochemistry, immunoblotting, and RT-PCR analysis all indicated the occurrence of ER stress in steatohepatitis, while it recovered immediately after changing the diet from MCCD to CD. The ratio of hepatocyte proliferation/apoptotis increased significantly during the recovery stage. This simple experiment clearly shows that changing the diet from MCDD to a normal diet (CD) triggers the resolution of hepatic inflammatory and fibrotic reactions and hepatocyte apoptosis, suggesting that MCDD-induced steatohepatitis is also reversible. ER stress appears and disappears in association with the generation and regression of steatohepatitis, respectively, with fibrosis.

Antiproliferative activity of triterpenoids from Eclipta prostrata on hepatic stellate cells

Hepatic stellate cells (HSCs) have been known to play a key role in the pathogenesis of liver fibrosis. In the course of screening antifibrotic activity of natural products employing HSC-T6, a rat hepatic stellate cell line as an in vitro assay system, the methanolic extract of aerial parts of Eclipta prostrata L. showed significant inhibitory activity on HSCs proliferation. Activity-guided fractionation led to the isolation of five oleanane-type triterpenoids, echinocystic acid (1), eclalbasaponin II (2), eclalbasaponin V (3), eclalbasaponin I (4) and eclalbasaponin III (5), which are all echinocystic acid derivatives. Among the five echinocystic acid derivatives isolated, echinocystic acid (1) and eclalbasaponin II (2) significantly inhibited the proliferation of HSCs in dose- and time-dependent manners. Our present study also suggests the importance of free carboxylic acid at C-28 position in echinocystic acid derivatives for the antifibrotic activity. Taken together, antifibrotic activity of E. prostrata and its triterpenoids might suggest the therapeutic potentials against liver fibrosis.

Glycyrrhizin and its metabolite inhibit Smad3-mediated type I collagen gene transcription and suppress experimental murine liver fibrosis

AIMS

Glycyrrhizin has been widely used for the treatment of chronic hepatitis C. It decreases the serum levels of aminotransferases, and suppresses progression of liver fibrosis as well as subsequent occurrence of hepatocellular carcinoma. Although previous studies have shown that glycyrrhizin and its metabolite inhibit collagen gene expression, its underlying mechanisms are virtually unknown. This study was aimed to explore molecular mechanisms responsible for the inhibitory effect of glycyrrhizin on type I collagen gene transcription.

MAIN METHODS

Effects of glycyrrhizin and its metabolite, glycyrrhetinic acid, on collagen promoter activity were examined by using transgenic reporter mice harboring alpha2(I) collagen gene (COL1A2) promoter. Their effects on the TGF-beta/Smad signaling pathway were studied by cell transfection assays and immunofluorescence studies using cultured hepatic stellate cells.

KEY FINDINGS

Administration of glycyrrhizin or its metabolite, glycyrrhetinic acid, significantly suppressed COL1A2 promoter activation and progression of liver fibrosis induced by repeated carbon tetrachloride injections. In cultured hepatic stellate cells, glycyrrhetinic acid, but not glycyrrhizin, inhibited type I collagen synthesis mostly at the level of gene transcription. This inhibitory effect of glycyrrhetinic acid was abolished by a mutation introduced into a Smad3-binding region within the COL1A2 promoter. Glycyrrhetinic acid did not affect gene expression of TGF-beta receptors or Smad proteins, but inhibited nuclear accumulation of Smad3 in activated hepatic stellate cells. In addition to those direct inhibitory effects on COL1A2 transcription, glycyrrhetinic acid also suppressed activation of quiescent hepatic stellate cells in primary culture.

SIGNIFICANCE

The results provide a molecular basis for the anti-fibrotic effect of glycyrrhizin treatment.

Erythrophagocytosis by liver macrophages (Kupffer cells) promotes oxidative stress, inflammation, and fibrosis in a rabbit model of steatohepatitis: implications for the pathogenesis of human nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive fibrotic disease, the pathogenesis of which has not been fully elucidated. Here, we report a molecular aspect of this disease elucidated using rabbits fed a cholesterol-rich high-fat diet and exhibiting insulin resistance. The liver in this model showed steatohepatitis with fibrosis and high mRNA expression for some cytokines, heme oxygenase-1, transforming growth factor-beta1, and collagen alpha1(I). Erythrocytes isolated from the model showed marked fragility and the externalization of phosphatidylserine (PS) on the outer leaflet of the membrane and were frequently engulfed by Kupffer cells/macrophages in the hepatic sinusoids. Expression of milk fat globule-epidermal growth factor (EGF)-factor 8, a PS-binding protein, was augmented in the liver. In culture, RAW 264.7 cells engulfed erythrocytes oxidized by tert-butyl hydroperoxide, a process that was inhibited by anti-milk fat globule-EGF-factor 8 antibody. In addition, PS-positive erythrocytes appeared entrapped in the model liver in ex vivo perfusion experiments. Finally, in specimens from NASH patients, the aggregation of erythrocytes in inflammatory hepatic sinusoids was notable. These results indicate that the engulfment of PS-externalized, apoptotic signal-positive, erythrocytes by hepatic macrophages may lead to the deposition of iron derived from hemoglobin in the liver and be involved in the pathogenesis of steatohepatitis.

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

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

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

Tetrandrine inhibits activation of rat hepatic stellate cells in vitro via transforming growth factor-β signaling

AIM: To investigate the effect of various concentrations of tetrandrine on activation of quiescent rat hepatic stellate cells (HSCs) and transforming growth factor-β (TGF-β) signaling in vitro.

METHODS: HSCs were isolated from rats by in situ perfusion of liver and 18% Nycodenz gradient centrifugation, and primarily cultured on uncoated plastic plates for 24 h with DMEM containing 20% fetal bovine serum (FBS/DMEM) before the culture medium was substituted with 2% FBS/DMEM for another 24 h. Then, the HSCs were cultured in 2% FBS/DMEM with tetrandrine (0.25, 0.5, 1, 2 mg/L, respectively). Cell morphological features were observed under an inverted microscope, smooth muscle-α-actin (α-SMA) was detected by immunocytochemistry and image analysis system, laminin (LN) and type III procollagen (PCIII) in supernatants were determined by radioimmunoassay. TGF-β₁ mRNA, Smad 7 mRNA and Smad 7 protein were analyzed with RT-PCR and Western blotting, respectively.

RESULTS: Tetrandrine at the concentrations of 0.25-2 mg/L prevented morphological transformation of HSC from the quiescent state to the activated one, while α-SMA, LN and PCIII expressions were inhibited. As estimated by gray values, the expression of α-SMA in tetrandrine groups (0.25, 0.5, 1, 2 mg/L) was reduced from 21.3% to 42.2% (control: 0.67, tetrandrine groups: 0.82, 0.85, 0.96, or 0.96, respectively, which were statistically different from the control, P<0.01), and the difference was more significant in tetrandrine at 1 and 2 mg/L. The content of LN in supernatants was significantly decreased in tetrandrine groups to 58.5%, 69.1%, 65.8% or 60.0% that of the control respectively, and that of PCIII to 84.6%, 81.5%, 75.7% or 80.7% respectively (P<0.05 vs control), with no significant difference among tetrandrine groups. RT-PCR showed that TGF-β₁ mRNA expression was reduced by tetrandrine treatments from 56.56% to 87.90% in comparison with the control, while Smad 7 mRNA was increased 1.4-4.8 times. The TGF-β₁ mRNA and Smad 7 mRNA expression was in a significant negative correlation (r = -0.755, P<0.01), and both were significantly correlated with α-SMA protein expression (r = -0.938, P<0.01; r = 0.938, P<0.01, respectively). The up-regulation of Smad 7 protein by tetrandrine (1 mg/L) was confirmed by Western blotting as well.

CONCLUSION: Tetrandrine has a direct inhibiting effect on the activation of rat HSCs in culture. It up-regulates the expression of Smad 7 which in turn blocks TGF-β₁ expression and signaling.

Rapid hepatic metabolism of 7-ketocholesterol by 11beta-hydroxysteroid dehydrogenase type 1: species-specific differences between the rat, human, and hamster enzyme

The role of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in the local activation of the glucocorticoid receptor by converting inactive 11-ketoglucocorticoids to active 11beta-hydroxyglucocorticoids is well established. Currently, 11beta-HSD1 is considered a promising target for treatment of obese and diabetic patients. Here, we demonstrate a role of 11beta-HSD1 in the metabolism of 7-ketocholesterol (7KC), the major dietary oxysterol. Comparison of recombinant 11beta-HSD1, transiently expressed in human embryonic kidney 293 cells, revealed the stereo-specific interconversion of 7KC and 7beta-hydroxycholesterol by rat and human 11beta-HSD1, whereas the hamster enzyme interconverted 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, and 7KC. In contrast to lysates, which efficiently catalyzed both oxidation and reduction, intact cells exclusively reduced 7KC. These findings were confirmed using rat and hamster liver homogenates, intact rat hepatocytes, and intact hamster liver tissue slices. Reduction of 7KC was abolished upon inhibition of 11beta-HSD1 by carbenoxolone (CBX) or 2'-hydroxyflavanone. In vivo, after gavage feeding rats, 7KC rapidly appeared in the liver and was converted to 7beta-hydroxycholesterol. CBX significantly decreased the ratio of 7beta-hydroxycholesterol to 7KC, supporting the evidence from cell culture experiments for 11beta-HSD1-dependent reduction of 7KC to 7beta-hydroxycholesterol. Upon inhibition of 11beta-HSD1 by CBX, 7KC tended to accumulate in the liver, and plasma 7KC concentration increased. Together, our results suggest that 11beta-HSD1 efficiently catalyzes the first step in the rapid hepatic metabolism of dietary 7KC, which may explain why dietary 7KC has little or no effect on the development of atherosclerosis.