Immunohistochemical detection of Fas antigen in liver tissue of patients with chronic hepatitis C

Ethnopharmacological Approaches for Therapy of Jaundice: Part II. Highly Used Plant Species from Acanthaceae, Euphorbiaceae, Asteraceae, Combretaceae, and Fabaceae Families

In many developing countries, jaundice is the common symptom of hepatic diseases which are a major cause of mortality. The use of natural product-based therapies is very popular for such hepatic disorders. A great number of medicinal plants have been utilized for this purpose and some facilitated the discovery of active compounds which helped the development of new synthetic drugs against jaundice. However, more epidemiological studies and clinical trials are required for the practical implementation of the plant pharmacotherapy of jaundice. The focus of this second part of our review is on several of the most prominent plants used against jaundice identified in the analysis performed in the first part of the review viz. Andrographis paniculata (Burm.f.) Nees, Silybum marianum (L.) Gaertn., Terminalia chebula Retz., Glycyrrhiza glabra L. and some species of genus Phyllanthus. Furthermore, we discuss their physiological effects, biologically active ingredients, and the potential mechanisms of action. Some of the most important active ingredients were silybin (also recommended by German commission), phyllanthin and andrographolide, whose action leads to bilirubin reduction and normalization of the levels of relevant serum enzymes indicative for the pathophysiological status of the liver.

An Ingenol Derived from Euphorbia kansui Induces Hepatocyte Cytotoxicity by Triggering G0/G1 Cell Cycle Arrest and Regulating the Mitochondrial Apoptosis Pathway in Vitro

Natural product lingenol, a purified diterpenoid compound derived from the root of Euphorbia kansui, exerts serious hepatotoxicity; however, the molecular mechanisms remain to be defined. In the present study, cell counting Kit-8 (CCK-8), inverted phase contrast microscope and flow cytometry were used to demonstrate that lingenol significantly inhibited L-O2 cells proliferation, and induced cell cycle arrest and apoptosis. Moreover, the results investigated that lingenol markedly disrupted mitochondrial functions by high content screening (HCS). In addition, the up-regulation of cytochrome c, AIF and Apaf-1 and activation of caspases were found in L-O2 cells detected by Western blotting and ELISA assay, which was required for lingenol activation of cytochrome c-mediated caspase cascades and AIF-mediated DNA damage. Mechanistic investigations revealed that lingenol significantly down-regulated the Bcl-2/Bax ratio and enhanced the reactive oxygen species (ROS) in L-O2 cells. These data collectively indicated that lingenol modulation of ROS and Bcl-2/Bax ratio led to cell cycle arrest and mitochondrial-mediated apoptosis in L-O2 cells in vitro. All of these results will be helpful to reveal the hepatotoxicity mechanism of Euphorbia kansui and to effectively guide safer and better clinical application of this herb.

Role of fibrogenic and inflammatory cytokines in HCV-induced fibrosis

HCV is one of the main causative agents of liver fibrosis and hepatocellular carcinoma. Liver inflammation resulting from HCV infection triggers fibrosis. In HCV-related fibrosis, differentiated hepatic stellate cells (HSCs) known as myofibroblasts participate in the fibrogenic and inflammatory response. TGF-β1 and CTGF, released from these HSCs, have been implicated as master cytokines mediating HCV induced hepatic fibrosis. PDGF is another potent mitogen, which facilitates the progression of liver fibrosis by enhancing the proliferation and migration of HSCs. In addition to these major cytokines, the release of TNF-α, IL-6, IL-1b and IL-10 by immune cells also promotes the effect of HCV induced fibrosis. Targeting these cytokines may offer the potential for treatments to prevent or cure fibrosis.

Hepatic apoptotic markers are not predictors for the virological response to interferon-based therapy in chronic hepatitis C patients

INTRODUCTION

Chronic hepatitis C virus (HCV) infection is a major health problem worldwide. The majority of cases involving HCV infection develop into chronic hepatitis because of a failure to develop an effective immune response. Apoptosis of the hepatocytes plays a significant role in the pathogenesis of HCV infection: the interaction between the Fas antigen on hepatocytes and the Fas ligand on T cells corresponds to the main mechanism for hepatocyte damage. Interferon (IFN)-α has antiviral, immunoregulatory, and antiproliferative properties, and apoptosis seems to be a critical event in the action mechanisms of both IFNs. In this study, we aimed to detect any relationship between apoptotic markers in the liver and the response to the treatment.

MATERIALS AND METHODS

The study included 180 chronic HCV patients treated with IFN and ribavirin in four centers. Apoptotic markers (Fas, Fas ligand, Fas-associated death domain, caspases 3, 8, and 9, and in-situ apoptosis) were studied in the liver. The age, sex of the patients, response to therapy, ALT level, viral load, and genotype were recorded.

RESULTS

The results of the study showed that the histological activity index and fibrosis correlated with CD95 staining density, caspase-8 intensiveness, and portal and parenchymal Fas ligand scores. The apoptotic parameters of the responsive cases were not significantly different from those of the unresponsive cases.

CONCLUSION

The apoptotic parameters studied in liver tissue are associated with inflammation and fibrosis; however, these parameters may not predict response to treatment.

P53 rs1042522 and CD95 rs1800682 genetic variations in HCV-4a response to antiviral therapy

Current estimates indicate that the hepatitis C (HCV) is the leading cause of mortality around the world, with infection rates steadily increasing in Egypt. The dual therapy for this silent epidemic with pegylated-interferon-α2b/ribavirin has markedly improved the success rates in genotype-4 patients. It was reported that apoptosis plays a vital mechanistic role in limiting viral replication. P53, a key regulator of apoptosis, induces CD95 gene expression and subsequently initiates apoptotic cascade to be activated. The current study examined the impact of P53 rs1042522 and CD95 rs1800682 polymorphisms on the treatment response. Three groups of 240 volunteers were enrolled in this study; 86 in sustained virological responders group, 74 in non-responders group, and 80 in control group. All patients had HCV genotype-4a and were interferon treatment naïve. Quantizations of HCV-RNA by qRT-PCR and histological scores were performed for all patients. In addition, genotyping of HCV-RNA, P53 rs1042522 Arg/Pro and CD95 rs1800682 A/G polymorphisms were investigated in all subjects. It was resulted that P53 Pro/Pro homozygous genotype has high significant increase, while CD95 A/A homozygous genotype has high significant decrease when comparing non-responders with responders. Finally, it was concluded that Pro variant of P53 rs1042522 may be used as a genetic predictor for non-responsiveness, while A/A variant of CD95 rs1800682 may be used as a sensitive biomarker for responsiveness to antiviral therapy of HCV genotype-4a infection. In addition, low prolactin, high total testosterone, and high GH levels may provide promising biomarkers for early prediction of the response when associated with these genetic polymorphisms.

Inflammatory response of endothelial cells to hepatitis C virus recombinant envelope glycoprotein 2 protein exposure

The hepatitis C virus (HCV) encodes approximately 10 different structural and non-structural proteins, including the envelope glycoprotein 2 (E2). HCV proteins, especially the envelope proteins, bind to cell receptors and can damage tissues. Endothelial inflammation is the most important determinant of fibrosis progression and, consequently, cirrhosis. The aim of this study was to evaluate and compare the inflammatory response of endothelial cells to two recombinant forms of the HCV E2 protein produced in different expression systems (Escherichia coli and Pichia pastoris). We observed the induction of cell death and the production of nitric oxide, hydrogen peroxide, interleukin-8 and vascular endothelial growth factor A in human umbilical vein endothelial cells (HUVECs) stimulated by the two recombinant E2 proteins. The E2-induced apoptosis of HUVECs was confirmed using the molecular marker PARP. The apoptosis rescue observed when the antioxidant N-acetylcysteine was used suggests that reactive oxygen species are involved in E2-induced apoptosis. We propose that these proteins are involved in the chronic inflammation caused by HCV.

The potential impact of P53 and APO-1 genetic polymorphisms on hepatitis C genotype 4a susceptibility

The hepatitis C virus (HCV), the main cause of morbidity and mortality, is endemic worldwide. HCV causes cirrhosis and other complications that often lead to death. HCV is most common in underdeveloped nations, with the highest prevalence rates in Egypt. Tumor suppressor gene (P53) induces the expression of apoptotic antigen-1 gene (APO-1) by binding to its promoter for mediating apoptosis; an important mechanism for limiting viral replication. This study aims at investigating the impact of P53 72 Arg/Pro and APO-1 -670 A/G polymorphisms on HCV genotype 4a susceptibility. Two hundred and forty volunteers were enrolled in this study and divided into two major groups; 160 HCV infected patient group and 80 healthy control group. HCV patients were classified according to Metavir scoring system into two subgroups; 72 patients in F0/1-HCV subgroup (patients with no or mild fibrotic stages) and 38 patients in F3/4-HCV subgroup (patients with advanced fibrotic stages). Quantification of HCV-RNA by qRT-PCR and fibrotic scores as well as genotyping of HCV-RNA, P53 at 72 Arg/Pro, and APO-1 at -670 A/G were performed for all subjects. It was resulted that F0/1-HCV patients have significant differences of P53 at 72 (Pro/Pro and Arg/Arg) genotypes and dominant/recessive genetic models as well as APO-1 -670 A/A genotype and dominant genetic model as compared to F3/4-HCV patients. Moreover, HCV patients have significant differences of P53 at 72 (Pro/Pro) genotype and recessive genetic model as well as APO-1 -670 A/A genotype and dominant genetic model as compared to those of healthy individuals. Finally, it was concluded that P53 rs 1042522 (Pro/Pro and Arg/Arg) genotypes and APO-1 rs 1800682 A/A genotype may be potentially used as sensitive genetic markers for HCV genotype 4a susceptibility.

The role of fas/fas ligand system in the pathogenesis of liver cirrhosis and hepatocellular carcinoma

BACKGROUND

The Fas receptor/ligand system including soluble forms is the most important apoptotic initiator in the liver. Dysregulation of this pathway may contribute to abnormal cell proliferation and cell death and is regarded as one of the mechanisms preventing the immune system from rejecting the tumor cells.

OBJECTIVES

To analyze the role of Fas system Fas/ Fas ligand (Fas/ FasL) in the multi-step process of hepatic fibrosis/carcinogenesis, and to use of the serum markers as possible candidate biomarkers for early detection of hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

NINETY PATIENTS WERE ENROLLED: 30 cases of chronic hepatitis C (CHC) without cirrhosis, 30 cases of CHC with liver cirrhosis, and 30 cases of HCC and hepatitis V virus (HCV) infection. Ten wedge liver biopsies, taken during laparoscopic cholecystectomy, were served as normal controls. Serum soluble Fas (sFas) levels were measured using ELISA technique; Fas and FasL proteins were detected in hepatic tissue by indirect Immuno-histochemical technique (IHC); electron microscopic (EM) and immune electron microscopic examinations were performed for detection of Fas expression on lymphocytes.

RESULTS

Hepatic expression of both Fas and FasL as well as expression of Fas on separated lymphocytes were significantly increased in the diseased groups (P < 0. 01) compared to the control specimens. The highest expression was noticed in CHC specimens, particularly with the necro-inflammatory activity and advancement of the fibrosis. The sFas in cirrhotic patients and HCC were significantly higher than that in normal controls and CHC without cirrhosis group (P < 0.01).

CONCLUSIONS

Apoptosis and the Fas system were significantly involved in the process of converting liver cirrhosis into hepatocellular carcinoma. Down-regulation of Fas expression, up regulation of FasL expression in hepatocytes, and elevation of serum sFas levels were important in tumor evasion from immune surveillance, and in hepatic carcinogenesis.

Hepatitis C virus infection in the immunocompromised host: a complex scenario with variable clinical impact

The relationship between Hepatitis C Virus (HCV) infection and immunosuppression is complex and multifaceted. Although HCV-related hepatocytolysis is classically interpreted as secondary to the attack by cytotoxic T lymphocytes against infected cells, the liver disease is usually exacerbated and more rapidly evolutive in immunosuppressed patients. This generally occurs during the immunosuppression state, and not at the reconstitution of the host response after immunosuppressive therapy discontinuation. The field of immunosuppression and HCV infection is complicated both by the different outcome observed in different situations and/or by contrasting data obtained in the same conditions, with several still unanswered questions, such as the opportunity to modify treatment schedules in the setting of post-transplant follow-up. The complexity of this field is further complicated by the intrinsic tendency of HCV infection in itself to lead to disorders of the immune system. This review will briefly outline the current knowledge about the pathogenesis of both hepatic and extrahepatic HCV-related disorders and the principal available data concerning HCV infection in a condition of impairment of the immune system. Attention will be especially focused on some conditions - liver or kidney transplantation, the use of biologic drugs and cancer chemotherapy - for which more abundant and interesting data exist.

Bak deficiency inhibits liver carcinogenesis: a causal link between apoptosis and carcinogenesis

BACKGROUND & AIMS

Hepatocyte apoptosis is a key feature of chronic liver disease including viral hepatitis and steatohepatitis. A previous study demonstrated that absence of the Bcl-2 family protein Mcl-1 led to increased hepatocyte apoptosis and development of liver tumors in mice. Since Mcl-1 not only inhibits the mitochondrial pathway of apoptosis but can also inhibit cell cycle progression and promote DNA repair, it remains to be proven whether the tumor suppressive effects of Mcl-1 are mediated by prevention of apoptosis.

METHODS

We examined liver tumor development, fibrogenesis, and oxidative stress in livers of hepatocyte-specific knockout (KO) of Mcl-1 or Bcl-xL, another key antagonist of apoptosis in hepatocytes. We also examined the impact of additional KO of Bak, a downstream molecule of Mcl-1 towards apoptosis but not the cell cycle or DNA damage pathway, on tumor development, hepatocyte apoptosis, and inflammation.

RESULTS

Bcl-xL KO led to a high incidence of liver tumors in 1.5-year-old mice, similar to Mcl-1 KO. Bcl-xL- or Mcl-1-deficient livers showed higher levels of TNF-α production and oxidative stress than wild-type livers at as early as 6 weeks of age and oxidative DNA damage at 1.5 years. Deletion of Bak significantly inhibited hepatocyte apoptosis in Mcl-1 KO mice and reduced the incidence of liver cancer, coinciding with reduction of TNF-α production, oxidative stress, and oxidative DNA damage in non-cancerous livers.

CONCLUSIONS

Our findings strongly suggest that chronically increased apoptosis in hepatocytes is carcinogenic and offer genetic evidence that inhibition of apoptosis may suppress liver carcinogenesis in chronic liver disease.

Increased protection from vaccinia virus infection in mice genetically prone to lymphoproliferative disorders

Mutations in the genes that encode Fas or Fas ligand (FasL) can result in poor restraints on lymphocyte activation and in increased susceptibility to autoimmune disorders. Because these mutations portend a continuously activated immune state, we hypothesized that they might in some cases confer resistance to infection. To examine this possibility, the immune response to, morbidity caused by, and clearance of vaccinia virus (VACV) Western Reserve was examined in 5- to 7-week-old Fas mutant (lpr) mice, before an overt lymphoproliferative disorder was observable. On day 6 after VACV infection, C57BL/6-lpr (B6-lpr) mice had decreased morbidity, decreased viral titers, and an increased percentage and number of CD4(+) and CD8(+) T cells. As early as day 2 after infection, B6-lpr mice had decreased liver and spleen viral titers and increased numbers of and increased gamma interferon (IFN-γ) production by several different effector cell populations. Depletion of individual effector cell subsets did not inhibit the resistance of B6-lpr mice. Uninfected B6-lpr mice also had increased numbers of NK cells, γδ(+) T cells, and CD44(+) CD4(+) and CD44(+) CD8(+) T cells compared to uninfected B6 mice. Antibody to IFN-γ resulted in increased virus load in both B6 and B6-lpr mice and eliminated the differences in viral titers between them. These results suggest that IFN-γ produced by multiple activated leukocyte populations in Fas-deficient hosts enhances resistance to some viral infections.

Delayed-onset caspase-dependent massive hepatocyte apoptosis upon Fas activation in Bak/Bax-deficient mice

The proapoptotic Bcl-2 family proteins Bak and Bax serve as an essential gateway to the mitochondrial pathway of apoptosis. When activated by BH3-only proteins, Bak/Bax triggers mitochondrial outer membrane permeabilization leading to release of cytochrome c followed by activation of initiator and then effector caspases to dismantle the cells. Hepatocytes are generally considered to be type II cells because, upon Fas stimulation, they are reported to require the BH3-only protein Bid to undergo apoptosis. However, the significance of Bak and Bax in the liver is unclear. To address this issue, we generated hepatocyte-specific Bak/Bax double knockout mice and administered Jo2 agonistic anti-Fas antibody or recombinant Fas ligand to them. Fas-induced rapid fulminant hepatocyte apoptosis was partially ameliorated in Bak knockout mice but not in Bax knockout mice, and was completely abolished in double knockout mice 3 hours after Jo2 injection. Importantly, at 6 hours, double knockout mice displayed severe liver injury associated with repression of XIAP, activation of caspase-3/7 and oligonucleosomal DNA breaks in the liver, without evidence of mitochondrial disruption or cytochrome c-dependent caspase-9 activation. This liver injury was not ameliorated in a cyclophilin D knockout background nor by administration of necrostatin-1, but was completely inhibited by administration of a caspase inhibitor after Bid cleavage.

CONCLUSION

Whereas either Bak or Bax is critically required for rapid execution of Fas-mediated massive apoptosis in the liver, delayed onset of mitochondria-independent, caspase-dependent apoptosis develops even in the absence of both. The present study unveils an extrinsic pathway of apoptosis, like that in type I cells, which serves as a backup system even in type II cells.

Adoptive transfer of splenocytes to study cell-mediated immune responses in hepatitis C infection using HCV transgenic mice

Background

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and a health problem affecting over 170 million people around the world. We previously studied transgenic mice that express HCV Core, Envelope 1 and Envelope 2 proteins predominantly in the liver, resulting in steatosis, liver and lymphoid tumors, and hepatocellular carcinoma. Herein, the immune-mediated cell response to hepatitis C antigens was evaluated by adoptive transfers of carboxyfluorescein succinimidyl ester (CFSE) labelled splenocytes from HCV immunized mice into HCV transgenic mice.

Results

In comparison to non-transgenic mice, there was a significant decrease in the percentage of CFSE-labeled CD4⁺ and CD8⁺ T cells in transgenic mouse peripheral blood receiving adoptive transfers from immunized donors. Moreover, the percentage of CFSE-labeled CD4⁺ and CD8⁺ T cells were significantly higher in the spleen of transgenic and non-transgenic mice when they received splenocytes from non-immunized than from immunized mice. On the other hand, the percentages of CD4⁺ and CD8⁺ T cells in the non-transgenic recipient mouse lymph nodes were significantly higher than the transgenic mice when they received the adoptive transfer from immunized donors. Interestingly, livers of transgenic mice that received transfers from immunized mice had a significantly higher percentage of CFSE labeled T cells than livers of non-transgenic mice receiving non-immunized transfers.

Conclusions

These results suggest that the T cells from HCV immunized mice recognize the HCV proteins in the liver of the transgenic mouse model and homed to the HCV antigen expression sites. We propose using this model system to study active T cell responses in HCV infection.

Hepatocyte death: a clear and present danger

The hepatocyte is especially vulnerable to injury due to its central role in xenobiotic metabolism including drugs and alcohol, participation in lipid and fatty acid metabolism, its unique role in the enterohepatic circulation of bile acids, the widespread prevalence of hepatotropic viruses, and its existence within a milieu of innate immune responding cells. Apoptosis and necrosis are the most widely recognized forms of hepatocyte cell death. The hepatocyte displays many unique features regarding cell death by apoptosis. It is quite susceptible to death receptor-mediated injury, and its death receptor signaling pathways involve the mitochondrial pathway for efficient cell killing. Also, death receptors can trigger lysosomal disruption in hepatocytes which further promote cell and tissue injury. Interestingly, hepatocytes are protected from cell death by only two anti-apoptotic proteins, Bcl-x(L) and Mcl-1, which have nonredundant functions. Endoplasmic reticulum stress or the unfolded protein response contributes to hepatocyte cell death during alterations of lipid and fatty acid metabolism. Finally, the current information implicating RIP kinases in necrosis provides an approach to more fully address this mode of cell death in hepatocyte injury. All of these processes contributing to hepatocyte injury are discussed in the context of potential therapeutic strategies.

Hepatocyte growth factor protects against Fas-mediated liver apoptosis in transgenic mice

BACKGROUND

Apoptosis via the Fas/Fas ligand signalling system plays an important role in the development of various liver diseases. The administration of an agonistic anti-Fas antibody to mice causes massive hepatic apoptosis and fulminant hepatic failure. Several growth factors including hepatocyte growth factor (HGF) have been found to prevent apoptosis.

METHODS

In this study, we demonstrated the overexpression of HGF to have a protective effect on Fas-mediated hepatic apoptosis using a transgenic mice (Tg mice) model.

RESULTS

In HGF Tg mice, the elevation of alanine aminotransferase was dramatically inhibited at 12 and 24 h after the administration of 0.15 mg/kg anti-Fas antibody. HGF Tg mice showed a significantly lower number of apoptotic hepatocytes at 12 h compared with wild-type (WT) mice. Furthermore, 85% (six of seven) HGF Tg mice were able to survive after the administration of 0.3 mg/kg anti-Fas antibody, while none of the WT mice survived. The Bcl-xL expression was increased in HGF Tg mice, while there was no difference in the expression of Bax, Bid, Mcl-1 and bcl-2 between WT mice and HGF Tg mice. In addition, the HGF Tg mice showed more Akt phosphorylation than the WT mice both before and after the anti-Fas antibody injection.

CONCLUSIONS

Taken together, our findings suggest that HGF protects against Fas-mediated liver apoptosis in vivo, and the upregulation of Bcl-xL via Akt activation may also play a role in the protective effects of HGF.

Caspase inhibitors for the treatment of hepatitis C

Decreasing hepatocyte injury and death is an attractive therapeutic target in chronic hepatitis C and other liver diseases. Apoptotic cell death is a critical mechanism responsible for liver injury in hepatitis C, and contributes to hepatic fibrogenesis. At the cellular level, apoptosis is executed by a family of cysteine proteases termed caspases. Caspase inhibitors have been developed to inhibit these proteases and attenuate cellular apoptosis in vivo. By reducing hepatocyte apoptosis these agents have the potential to serve as hepatoprotective agents, minimizing liver injury and fibrosis. Studies on a variety of animal models, and time-limited studies in human patients with hepatitis C suggest these are promising therapeutic agents. However, although these agents hold promise, their usefulness requires further studies, especially longer duration studies using hepatic fibrogenesis as the end point before they can be considered further for the treatment of patients infected with the hepatitis C virus.

Ultra-structural localisation of hepatocellular PKR protein using immuno-gold labelling in chronic hepatitis C virus disease

The greater resistance of HCV genotype 1 infection to IFN therapy has been partially attributed to functional inhibition of the type 1 interferon induced anti-viral protein PKR in vitro. Whether PKR has antiviral activity against HCV in vivo is unknown. Whilst the ultra-structural localisation of PKR is known in vitro, it is not defined in chronic hepatitis C disease. Using a novel immuno-gold technique we characterised the expression of intrahepatic PKR protein at the ultra-structural level in four patients with chronic HCV disease compared to normal human PBMCs, HepG2 cells and a normal human liver biopsy. All four HCV patients labelled for PKR protein, localising to the nucleus, nucleolus and cytoplasm. Nuclear labelling was confined mainly to the nucleolus and euchromatin. Cytoplasmic labelling was evident within smooth vesicles. Strong immunogold labelling was also evident within the cisternae of the rough endoplasmic reticulum. A similar pattern of ultra-structural nuclear and cytoplasmic PKR protein labelling was seen in PBMCs from healthy donors, HepG2 cells and a normal liver biopsy. The mean nuclear and cytoplasmic count for PKR protein in the HCV group was 21 +/- 4 and 18 +/- 3 gold particles/microm(2), respectively. This represented an increase, though not statistically significant, in nuclear and cytoplasmic labelling for PKR protein in HCV biopsies relative to normal liver tissue.

Using high-throughput genomics to study hepatitis C: what determines the outcome of infection?

High-throughput genomic methods are now being used to study a wide variety of viral diseases, in an effort to understand how host responses to infection can lead either to efficient elimination of the pathogen or the development of severe disease. This article reviews how gene expression studies are addressing important clinical issues related to hepatitis C virus infection, in which some 15-25% of infected individuals are able to clear the virus without treatment, while the remainder progress to chronic liver disease that can lead to cirrhosis and death. Similar methods are also being used in an effort to identify the mechanisms underlying the failure of some hepatitis C patients to respond to interferon-alpha/ribavirin therapy. By providing a detailed picture of virus-host interactions, high-throughput genomics could potentially lead to the identification of novel cellular targets for the treatment of hepatitis C.

Adiponectin inhibits steatotic CD95/Fas up-regulation by hepatocytes: therapeutic implications for hepatitis C

BACKGROUND/AIMS

Steatosis may trigger hepatocytes to up-regulate CD95/Fas thereby increasing susceptibility to apoptosis, inflammation and fibrosis. We investigated this concept and potential roles of adiponectin and its receptors (AdipoR1; AdipoR2) in chronically HCV-infected patients.

METHODS

In 98 HCV+ patients and 20 controls, sera were tested for HCV genotypes, FFAs, adiponectin and the M30 apoptosis indicator, and biopsies were evaluated for steatosis/inflammation/fibrosis, CD95/Fas (mRNA/protein), adiponectin (mRNA/protein), AdipoR1/-R2 (mRNA) and M30 (protein). We also questioned whether adiponectin protects HepG2 hepatoblastoma cells from FFA-triggered CD95/Fas up-regulation and apoptosis.

RESULTS

Patients [HCV clades 1 (78%), 2 (3%) and 3 (19%)] revealed increased FFA and adiponectin serum levels (p = .005). Hepatocyte CD95/Fas up-regulation correlated with steatosis, inflammation and fibrosis (p = .004). Advanced fibrosis correlated significantly (p = .05) with serum M30. Liver adiponectin correlated with steatosis (p = .016), CD95/Fas (p < .001) and inflammation/fibrosis. Hepatocyte AdipoR2 mRNA specifically correlated with serum adiponectin and steatosis (p = .003), while hepatocyte AdipoR1 mRNA dropped in pronounced fibrosis (p = .060). Finally, adiponectin protected HepG2 cells from FFA-triggered CD95/Fas expression and induction of apoptosis (p = .0396).

CONCLUSIONS

In chronic HCV infection, steatosis up-regulates hepatocyte CD95/Fas and thus increases apoptosis, which facilitates inflammation and fibrosis. The physiologic countermeasure of adiponectin up-regulation may offer clues for future therapeutic intervention.

Disease-specific mechanisms of fibrosis: hepatitis C virus and nonalcoholic steatohepatitis

Our mechanistic understanding of liver fibrosis has increased dramatically in recent years for all liver diseases and for hepatitis C and nonalcoholic steatohepatitis (NASH) in particular. Hepatitis C causes liver injury and fibrosis through direct cytopathic means, direct and indirect interactions with hepatic stellate cells, and activation of the immune system. Steatosis and insulin resistance, which are intrinsic deficits in NASH, are also of great importance in hepatitis C and may be induced by viral or host metabolic factors. For NASH, the key mediators of damage include oxidative stress, fat compartmentalization, visceral fat, apoptosis, and adipokine derangement. This article explores in depth the disease-specific mechanisms of fibrosis in hepatitis C and NASH, with a focus on recent developments.

Fas / FasL system, IL-1beta expression and apoptosis in chronic HBV and HCV liver disease

The Fas / Fas-ligand (FasL) system is an important death signal pathway in the liver. An enhanced local inflammatory response prompted by FasL expression, which contributes to neutrophil recruitment and interleukin-1 beta (IL-1beta) release, seems to be crucial to chronic liver damage, persistence of viral infections, and probably initiation and / or promotion of HCC. In order to evaluate the expression of Fas, FasL, and IL-1beta in different stages of human liver disease and to determine whether hepatitis B virus (HBV) and hepatitis C virus (HCV) infections modulate their expression, also in relation to apoptosis, we examined 87 liver samples obtained from patients with: chronic hepatitis (CH) (n.42), cirrhosis (n.9) and hepatocellular carcinoma (HCC) (n.16) and corresponding peritumoural tissues (n.16); histologically-normal liver (n.4) as controls. Fas, FasL and IL-1beta mRNA were quantified using reverse transcriptase-polymerase chain reaction. The apoptotic index was evaluated by TUNEL analysis. Our data showed a progressive Fas / FasL increase from CH to cirrhosis followed by a decline from the latter to HCC. In histological sections apoptosis was detected in HCC. A significant difference emerged between HCV and HBV-related disease for IL-1beta expression only in CH. A significant positive correlation between IL-1beta and FasL in HCV-related disease (P = 0.014) and an inverse correlation between IL-1beta and Fas in HBV-related disease (P = 0.021) were observed. The different pattern of IL-1beta, Fas and FasL expression found in HCV- and HBV-mediated liver disease, points to a different modulation of immune response B and C virus induced, while the decline in Fas / FasL expression in HCC may be related to defence mechanisms adopted by HCC cells against the immune system.

Caspase activation is associated with spontaneous recovery from acute liver failure

Acute liver failure (ALF) has various causes and is characterized by rapid hepatocyte dysfunction with development of encephalopathy in the absence of preexisting liver disease. Whereas most patients require liver transplantation to prevent the high mortality, some patients recover spontaneously and show complete liver regeneration. Because of the low incidence of ALF, however, the molecular mechanisms of liver dysfunction and regeneration are largely unknown. In this study, we investigated the role of apoptosis and caspases in 70 ALF patients using novel biomarkers that allow the detection of caspase activation in serum samples. Compared with healthy individuals, activation of caspases was strongly enhanced in ALF patients. Interestingly, patients with spontaneous recovery from ALF revealed a significantly higher activation of caspases than patients that required transplantation or died, although in the latter patients extensive DNA fragmentation and signs of nonapoptotic cell death were observed. In the spontaneous survivors, increased caspase activation was accompanied by elevated levels of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6), important cytokines involved in liver regeneration.

CONCLUSION

Our data suggest that caspase activation and apoptosis are involved in ALF of patients with spontaneous recovery, whereas caspase-independent cell death might be more relevant in irreversible forms of liver failure. These findings might be important for therapeutic options of ALF but also suggest that measurement of caspase activation might be of prognostic value to predict the outcome of acute liver failure.

Cellular and molecular mechanisms of liver injury

Derangements in apoptosis of liver cells are mechanistically important in the pathogenesis of end-stage liver disease. Vulnerable hepatocytes can undergo apoptosis via an extrinsic, death receptor-mediated pathway, or alternatively intracellular stress can activate the intrinsic pathway of apoptosis. Both pathways converge on mitochondria, and mitochondrial dysfunction is a prerequisite for hepatocyte apoptosis. Persistent apoptosis is a feature of chronic liver diseases, and massive apoptosis is a feature of acute liver diseases. Fibrogenesis is stimulated by ongoing hepatocyte apoptosis, eventually resulting in cirrhosis of the liver in chronic liver diseases. Endothelial cell apoptosis occurs in ischemia-reperfusion injury. Natural killer and natural killer T cells remove virus-infected hepatocytes by death receptor-mediated fibrosis. Lastly, activated stellate cell apoptosis leads to slowing and resolution of apoptosis. This review summarizes recent cellular and molecular advances in the understanding of the injury mechanisms leading to end-stage liver disease.

Modulation of signaling pathways by RNA virus capsid proteins

Capsid proteins are structural components of virus particles. They are nucleic acid-binding proteins whose main recognized function is to package viral genomes into protective structures called nucleocapsids. Research over the last 10 years indicates that in addition to their role as genome guardians, viral capsid proteins modulate host cell signaling networks. Disruption or alteration of intracellular signaling pathways by viral capsids may benefit replication of the virus by affecting innate immunity and in some cases, may underlie disease progression. In this review, we describe how the capsid proteins from medically relevant RNA viruses interact with host cell signaling pathways.

Putative association of Fas and FasL gene polymorphisms with clinical outcomes of hepatitis B virus infection

OBJECTIVE

Fas/FasL polymorphisms, which are related to apoptosis, might influence the clearance of hepatitis B virus (HBV) infection and the occurrence of hepatocellular carcinoma (HCC). This study was performed to determine whether Fas and FasL promoter polymorphisms are associated with clinical outcome in chronic HBV infection.

METHODS

A total of 1,095 Korean subjects were prospectively allocated to two different groups: 'the chronic carrier group' (CC; n = 666), who were repeatedly hepatitis B surface antigen (HBsAg)-positive, and 'the spontaneous recovery group' (SR; n = 429), who were HBsAg-negative with antibodies to HBsAg and hepatitis B core antigen. In addition, the CC group was subcategorized into chronic hepatitis and HCC subgroups. Fas promoter polymorphisms at -1377G>A and -670A>G and the FasL promoter polymorphism at -844C>T were analyzed for and the genotype distributions of subjects were compared.

RESULTS

There were no significant associations between Fas or FasL promoter polymorphism with the HBV clearance and HBeAg clearance. However, -1377G>A in Fas promoter region showed protective effect to HCC occurrence (RH = 0.70, p = 0.03).

CONCLUSIONS

Fas-1377G>A polymorphisms might be involved in the pathogenesis of human HCC.

Autoimmune cholangitis in NOD.c3c4 mice is associated with cholangiocyte-specific Fas antigen deficiency

A major handicap in understanding the pathogenesis of autoimmune cholangitis has been the absence of an informative mouse model. Recently, autoimmune cholangitis, with several features similar to PBC, has been described in NOD.c3c4 mice, including anti-mitochondrial antibodies, lymphocytic portal tract infiltrates, biliary destruction and the adoptive transfer of disease to naïve recipients using liver-derived lymphocytes. A unique feature, and a characteristic quite distinct from human PBC, is the presence of bile cyst formation. We have addressed the issue of cysts in NOD.c3c4 mice by performing comprehensive microarray analysis using cholangiocytes from NOD.c3c4 mice compared to NOD controls. Several key differences in gene expression were noted in NOD.c3c4 cholangiocytes. First, there was consistent impairment in the expression of Fas antigen (CD95). Second, cholangiocytes were PCNA positive but TUNEL negative, suggesting an absence of apoptosis despite abnormal proliferation. In conclusion, we propose that autoimmune cholangitis develops in NOD.c3c4 mice secondary to impaired biliary cell apoptosis with exposure of mitochondrial antigens, loss of tolerance and subsequent development of multi-lineage anti-mitochondrial responses.

Met signals hepatocyte survival by preventing Fas-triggered FLIP degradation in a PI3k-Akt-dependent manner

The FasL-Fas couple is a general death mediator whose activated signals lead to caspase-8 activation and apoptosis in adult hepatocytes. Suppression of caspase-8 activation and cell death is a protective mechanism modulated by the FLICE-Like Inhibitory Protein (FLIP). Although hepatocyte growth factor (HGF) and its receptor Met are known to mediate cell survival in developing livers, the molecular mechanisms involved in this process are poorly understood. We show here that Met activation by HGF impairs Fas-triggered apoptosis of primary embryonic hepatocytes and cell survival correlates with inhibition of caspase-8 and caspase-3 activities. Furthermore, we found that HGF treatment prevents degradation of FLIPL triggered by Fas activation. In contrast to this, Met activation does not modulate FLIPL levels and its stability in untreated cells, thus showing the specificity of this regulatory mechanism for embryonic hepatocyte survival. Knocking down FLIP expression abolishes the ability of Met to inhibit Fas-triggered hepatocyte death, demonstrating the functional requirement of FLIP in HGF anti-apoptotic signals. By combining genetic and pharmacological approaches, we also demonstrate that the PI3K-Akt pathway is required in embryonic hepatocytes to prevent Fas-triggered FLIP degradation and death. Thus, Met acting on PI3K and Akt ensures high levels of FLIPL, and disruption of this pathway contributes to hepatic apoptosis and possibly to Fas-related liver diseases.

Immunopathogenesis in hepatitis C virus cirrhosis

HCV (hepatitis C virus) has a high propensity to persist and to cause chronic hepatitis C, eventually leading to cirrhosis. Since HCV itself is not cytopathic, liver damage in chronic hepatitis C is commonly attributed to immune-mediated mechanisms. HCV proteins interact with several pathways in the host's immune response and disrupt pathogen-associated pattern recognition pathways, interfere with cellular immunoregulation via CD81 binding and subvert the activity of NK (natural killer) cells as well as CD4(+) and CD8(+) T-cells. Finally, HCV-specific T-cells become increasingly unresponsive and apparently disappear, owing to several possible mechanisms, such as escape mutations in critical viral epitopes, lack of sufficient help, clonal anergy or expansion of regulatory T-cells. The role of neutralizing antibodies remains uncertain, although it is still possible that humoral immunity contributes to bystander damage of virally coated cells via antibody-dependent cellular cytotoxicity. Cytotoxic lymphocytes kill HCV-infected cells via the perforin/granzyme pathway, but also release Fas ligand and inflammatory cytokines such as IFNgamma (interferon gamma). Release of soluble effector molecules helps to control HCV infection, but may also destroy uninfected liver cells and can attract further lymphocytes without HCV specificity to invade the liver. Bystander damage of these non-specific inflammatory cells will expand the tissue damage triggered by HCV infection and ultimately activate fibrogenesis. A clear understanding of these processes will eventually help to develop novel treatment strategies for HCV liver disease, independent from direct inhibition of HCV replication.

Understanding and managing HELLP syndrome: the integral role of aggressive glucocorticoids for mother and child

Antepartum or postpartum HELLP syndrome constitutes an obstetric emergency that requires expert knowledge and management skills. The insidious and variable nature of disease presentation and progression challenges the clinician and complicates consensus on universally accepted diagnostic and classification criteria. A critical review of published research about this variant form of severe preeclampsia, focused primarily on what is known about the pathogenesis of this disorder as it relates to patient experience with corticosteroids for its management, leads to the conclusion that there is maternal-fetal benefit realized when potent glucocorticoids are aggressively used for its treatment. Although acknowledging the need for definitive multicenter trials to better define the limits of benefit and the presence of any maternal or fetal risk, and given an understanding of the nature of the disorder with its potential to cause considerable maternal morbidity and mortality, we recommend for the present that aggressively used potent glucocorticoids constitute the cornerstone of management for patients considered to have HELLP syndrome.

Non-structural protein 4A of Hepatitis C virus accumulates on mitochondria and renders the cells prone to undergoing mitochondria-mediated apoptosis

Non-structural protein 4A (NS4A) of Hepatitis C virus (HCV) functions as a cofactor for NS3 by forming a complex with it to augment its enzymic activities. NS4A also forms a complex with other HCV proteins, such as NS4B/NS5A, to facilitate the formation of the viral RNA replication complex on the endoplasmic reticulum (ER) membrane. In addition to its essential role in HCV replication, NS4A is thought to be involved in viral pathogenesis by affecting cellular functions. In this study, it was demonstrated that NS4A was localized not only on the ER, but also on mitochondria when expressed either alone or together with NS3 in the form of the NS3/4A polyprotein and in the context of HCV RNA replication in Huh7 cells harbouring an HCV RNA replicon. Moreover, NS4A expression altered the intracellular distribution of mitochondria significantly and caused mitochondrial damage, as evidenced by the collapsed mitochondrial transmembrane potential and release of cytochrome c into the cytoplasm, which led ultimately to induction of apoptosis through activation of caspase-3, but not caspase-8. Consistently, Huh7 cells expressing NS3/4A and those harbouring an HCV RNA replicon were shown to be more prone to undergoing actinomycin D-induced, mitochondria-mediated apoptosis, compared with the control Huh7 cells. Taken together, these results suggest the possibility that HCV exerts cytopathic effect (CPE) on the infected cells under certain conditions and that NS4A is responsible, at least in part, for the conditional CPE in HCV-infected cells.

HBV and HCV infections and acute rejection differentially modulate CD95 and CD28 expression on peripheral blood lymphocytes after liver transplantation

Hepatitis B virus (HBV) and hepatitis C virus (HCV) generally reinfect liver graft early posttransplantation and lead to poorer graft and patient survivals. In the present study the influence of acute rejection (AR), HBV and HCV infections, and human leukocyte antigen (HLA) class-I compatibility on the expression of CD28 (in 237 liver recipients) and CD95 (in 114 liver recipients) on peripheral blood cells were evaluated by flow cytometry during the first month after transplantation. HBV/HCV infections induced strong CD95 upregulation on CD3+ lymphocytes. Maximal CD95 upmodulation was found in infected recipients showing partial HLA class-I compatibility. AR and virus reinfection could be distinguished because CD28 was upregulated on CD4+ lymphocytes only in recipients with AR, irrespective of their status regarding HBV/HCV infections. In conclusion, cytometric co-evaluation of CD95 and CD28 expression on peripheral blood lymphocytes could be useful to discriminate AR from cellular activation induced by viral reinfection of the liver graft.

Paraoxonase-1 is associated with oxidative stress, fibrosis and FAS expression in chronic liver diseases

BACKGROUND/AIMS

We previously reported that paraoxonase-1 activity measurement may be useful for the evaluation of liver diseases. Because oxidative stress plays a role in liver apoptosis, and lipid peroxides are hydrolyzed by paraoxonase-1, we have extended our studies to explore the relationships between this enzyme and oxidative stress, fibrosis and apoptosis.

METHODS

We measured paraoxonase-1 activity and concentration, soluble FAS concentration, serum fibrosis markers, and total peroxides in a group of patients with minimal hepatic changes (n=25), chronic hepatitis (n=51), or liver cirrhosis (n=17). We also measured the Knodell activity index in liver biopsies and performed FAS and PON1 immunostaining.

RESULTS

Patients with liver diseases showed an increase in soluble FAS, fibrosis markers and paraoxonase-1 concentrations, as well as a decrease in PON1 activity. Paroxonase-1 activity and concentration were correlated with soluble FAS (r=-0.43, P<0.001 and r=0.27, P=0.007, respectively). Paraoxonase-1 concentration showed a significant inverse association with FAS immunostaining (P=0.013) and a direct association with PON1 immunostaining (P<0.001).

CONCLUSIONS

These results suggest an active role of PON1 in the regulation of oxidative stress, fibrosis and hepatic cell apoptosis in chronic liver diseases.

Identification of a specific gene expression pattern associated with HCV-induced pathogenesis in HCV- and HCV/HIV-infected individuals

Gene expression profiling was performed on liver biopsies from 28 patients (12 HCV and 16 HCV/HIV infected) in an attempt to understand the mechanisms of HCV liver disease in the presence and absence of HIV coinfection. The data were compared with clinical observations and a gene expression database obtained for transplant HCV-infected samples. This is the first report of functional genomics being used to compare intrahepatic gene expression profiles of HCV- and HCV/HIV-infected individuals. Significantly, the intrahepatic global gene expression profiles do not differ between HCV- and HCV/HIV-infected individuals. However, a subset of patients was identified who share a specific pattern of gene expression, termed the enhanced gene expression (EGE) pattern. Specifically, the EGE (+) patients show a dramatic decreased expression of multiple genes associated with the FAS-apoptosis pathway and increased expression of lymphocyte adhesion molecules and lymphocyte-specific genes. The EGE (+) patients also have partially impaired Type I and II IFN-mediated antiviral responses, including a lack of induction of the anti-fibrogenic cytokine IFN-gamma. Importantly, the pattern of gene expression observed in EGE (+) patients has similarities to patients who developed fibrosis within 1 year of receiving a liver transplant.

Modulation of apoptosis as a target for liver disease

Apoptosis mediated via extrinsic or intrinsic pathways is essential for maintaining cellular homeostasis in the liver. The extrinsic pathway is triggered from the cell surface by engagement of death receptors as CD95, TRAIL (TNF-related apoptosis inducing ligand) and TNF (tumour necrosis factor) or TGF-beta (transforming growth factor beta) receptors. The intrinsic pathway is initiated from the mitochondria and can be influenced by Bcl-2 family members. Both pathways are intertwined and play a physiological role in the liver. Dysregulation of apoptosis pathways contributes to diseases as hepatocellular carcinoma, viral hepatitis, autoimmune hepatitis, ischaemia-reperfusion injury, iron or copper deposition disorders, toxic liver damage and acute liver failure. The apoptosis defects are often central pathogenetic events; hence molecular mechanisms of apoptosis give not only insight into disease mechanisms but also provide potential corresponding therapeutic candidates in liver disease. The focus of this review is the identification of apoptotic signalling components in the liver as therapeutic targets.

Mice lacking both TNFα receptors show increased constitutive expression of IFNγ: A possible reason for lack of protection from fumonisin B1 hepatotoxicity☆

Fumonisin B1 is a mycotoxin prevalent in corn that produces species-, gender-, and organ-specific diseases. Mice lacking TNFalpha receptor (TNFR) 1 or 2 exhibited a diminished hepatotoxic response to fumonisin B1; however, the protection was lost when both TNFRs were deleted. We therefore investigated the constitutive expression of selected apoptotic factors and their response to fumonisin B1 in the liver from mice lacking both TNFRs (DRKO). Compared to their wild-type (WT) counterparts the DRKO strain had a higher constitutive mRNA expression of interferon (IFN)gamma, Fas, and interleukin (IL)-18. The mRNA expression of Bcl-2 was also higher in DRKO than in WT mice. The mRNA expression of IL-1 receptor antagonist (IL-1Ra) was decreased; that of TNF-related apoptosis-inducing ligand (TRAIL) was dramatically reduced. Induction of most apoptotic genes in response to fumonisin B1 was similar in both WT and DRKO strains; except in DRKO mice it was greater for Max and lesser for IL-1Ra than that in WT strain. Fumonisin B1 hepatotoxicity in DRKO mice was reduced by pretreatment with anti-IFNgamma antibody. It appears that in the absence of TNFalpha signaling other apoptotic pathways become operative; particularly the increase of IFNgamma, Fas and IL-18 may compensate for the loss of TNFalpha effects. Fumonisin B1 toxicity therefore appears to be a complex phenomenon that may utilize more than one cytotoxic pathway consequent to sphingoid deregulation; a higher expression of IFNgamma and other apoptotic factors in DRKO may be responsible for the observed fumonisin hepatotoxicity.

Host-specific response to HCV infection in the chimeric SCID-beige/Alb-uPA mouse model: role of the innate antiviral immune response

The severe combined immunodeficiency disorder (SCID)-beige/albumin (Alb)-urokinase plasminogen activator (uPA) mouse containing a human-mouse chimeric liver is currently the only small animal model capable of supporting hepatitis C virus (HCV) infection. This model was utilized to characterize the host transcriptional response to HCV infection. The purpose of these studies was to investigate the genetic component of the host response to HCV infection and also to distinguish virus-induced gene expression changes from adaptive HCV-specific immune-mediated effects. Gene expression profiles from HCV-infected mice were also compared to those from HCV-infected patients. Analyses of the gene expression data demonstrate that host factors regulate the response to HCV infection, including the nature of the innate antiviral immune response. They also indicate that HCV mediates gene expression changes, including regulation of lipid metabolism genes, which have the potential to be directly cytopathic, indicating that liver pathology may not be exclusively mediated by HCV-specific adaptive immune responses. This effect appears to be inversely related to the activation of the innate antiviral immune response. In summary, the nature of the initial interferon response to HCV infection may determine the extent of viral-mediated effects on host gene expression.

Caspase activation is required for antiviral treatment response in chronic hepatitis C virus infection

Only half of patients with chronic hepatitis C virus (HCV) infection and genotype-1 show a sustained antiviral response to the current antiviral therapy. The reason this treatment fails is unclear, and no reliable marker exists that predicts the treatment outcome. In the present study, we investigated the apoptotic activation of caspases in HCV patients undergoing antiviral therapy with regard to the treatment outcome. We determined caspase activation in sera from patients who were either responding or nonresponding to antiviral therapy by using two novel caspase assays, an immunological and a luminometric enzyme test. We found that compared with nonresponding individuals, responding patients showed significantly (P < .05) increased caspase activity, which was closely correlated with virus elimination (r = 0.81). The cutoff value of serum caspase activity was determined, which correctly predicted the treatment outcome with a sensitivity of 70% and a specificity of 82% (area under the curve 0.845; 95% CI). In conclusion, hepatic caspase activity might play a role in HCV clearance and could also predict the efficacy of antiviral therapy.

HCV E2 may induce apoptosis of Huh-7 cells via a mitochondrial-related caspase pathway

INTRODUCTION

One unusual characteristic of HCV is to establish chronic infection and the precise mechanisms remain unclear.

MATERIALS AND METHODS

Huh-7 cells were transiently transfected with E2 and subjected to MTT assay, DNA fragmentation assay, and Western blotting to see the impact of E2 protein on apoptosis.

RESULTS AND DISCUSSION

E2 may inhibit cell proliferation by inducing apoptosis and pro-caspases 3, 8, and 9 were cleaved and activated to result in the presence of active forms in a time-dependent fashion, which suggest that E2-induced apoptosis is caspase-dependent. Furthermore, the cytosolic level of cytochrome c was increased together with a gradually down-regulated Bcl-2 and up-regulated Bax protein expression. The continuing reduction of Bid protein and the gradual increase of tBid protein also indicated that a time-dependent increased turn-over of Bid protein into tBid. Taken together, our data suggested that HCV E2 may induce apoptosis through a mitochondrial damage-mediated caspase pathway.

Ellipticine induces apoptosis through p53-dependent pathway in human hepatocellular carcinoma HepG2 cells

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), one of the simplest naturally occurring alkaloids, was isolated from the leaves of the evergreen tree Ochrosia elliptica Labill (Apocynaceae). Here, we reported that ellipticine inhibited the cell growth of human hepatocellular carcinoma cell line HepG2 and provided molecular understanding of this effect. The XTT assay results showed that ellipticine decreased the cell viability of HepG2 cells in a dose- and time-dependent manner, and the IC50 value was 4.1 microM. Furthermore, apoptosis induction by ellipticine in HepG2 cells was verified by the appearance of DNA fragmentation and annexin V-FITC/propidium iodide (PI) staining assay. Ellipticine treatment was found to result in the upregulation of p53, Fas/APO-1 receptor and Fas ligand. Besides, ellipticine also initiated mitochondrial apoptotic pathway through regulation of Bcl-2 family proteins expression, alteration of mitochondrial membrane potential (DeltaPsim), and activation of caspase-9 and caspase-3. Taken together, ellipticine decreased the cell growth and induced apoptosis in HepG2 cell.

L’apoptose hépatique

Apoptosis or programmed cell death occurs in the liver as in other organs. In the normal state it is not a frequent mode of hepatic cell destruction. Morphological and biochemical characteristics of liver cell apoptosis do not differ from what is observed in other cells. The Fas receptor pathway, a frequent hepatic apoptotic pathway among various others, involves intra-cellular signals amplified by mitochondria. Although hepatic apoptosis may occur by following several others pathways, Fas, which is abundantly expressed in the plasma membrane of hepatocytes, is very often involved in hepatocyte demise during B or C viral hepatitis irrespective of their clinical form, alcoholic hepatitis, cholestasis due to accumulation of hepatic biliary salts, or certain types of drug-induced hepatitis. Fas is also probably responsible for the death of biliary cells in primary biliary cirrhosis. In contrast one of the causes of resistance to apoptosis of hepatic cancerous cells could be related to an alteration of the Fas receptor. This is why much experimental work is presently performed to achieve inhibition of the Fas receptor either at the mRNA level or at the level of Fas-inductible proteolytic enzymes called caspases. One perspective is a specific treatment of apoptosis as an adjuvant treatment of liver diseases.

Protein-tyrosine Phosphatase 1B Deficiency Protects against Fas-induced Hepatic Failure

Genetic disruption of protein-tyrosine phosphatase 1B (PTP1B) in mice leads to increased insulin sensitivity and resistance to weight gain. Although PTP1B has been implicated as a regulator of multiple signals, its function in other physiological responses in vivo is poorly understood. Here we demonstrate that PTP1B-null mice are resistant to Fas-induced liver damage and lethality, as evident by reduced hepatic apoptosis in PTP1B-null versus wild type mice and reduced levels of circulating liver enzymes. Activation of pro-apoptotic caspases-8, -9, -3, and -6 was attenuated in livers from PTP1B-null mice following Fas receptor stimulation, although components of the death-inducing signaling complex were intact. Activation of anti-apoptotic regulators, such as the hepatocyte growth factor/Met receptor tyrosine kinase, as well as Raf, ERK1/2, FLIP(L), and the NF-kappaB pathway, was elevated in response to Fas activation in livers from PTP1B-null mice. Using PTP1B-deficient primary hepatocytes, we show that resistance to Fas-mediated apoptosis is cell autonomous and that signals involving the Met, ERK1/2, and NF-kappaB pathways are required for cytoprotection. This study identifies a previously unknown physiological role for PTP1B in Fas-mediated liver damage and points to PTP1B as a potential therapeutic target against hepatotoxic agents.

Ticlopidine-Induced Cholestatic Inflammatory Hepatitis: New Insights into Pathogenetic Mechanisms of Drug-Related Hepatotoxicity

In immune-induced liver damage the reactive metabolites may covalently bind or alter liver proteins such as cytochrome P450 enzymes, which leads to activation of the immune system. Ticlopidine is an inhibitor of CYP2C19 human liver cytochrome. We attempted to analyse the role of cytochrome CYP2C19 genetic polymorphism in the development of ticlopidine-induced cholestatic hepatitis and relate it with the specific immune reactivity to ticlopidine, different cytokine profiles and induction of necrosis and apoptosis within the liver tissue. Three patients with cholestatic hepatitis with ticlopidine-related liver injury, 3 patients with obstructive jaundice due to choledocholithiasis, 3 patients treated with ticlopidine without liver damage and 10 healthy individuals were studied. Genotyping for the following genotypes CYP2C19 (CYP2C19*1–3) were tested after polymerase chain reaction (PCR) by restriction fragment length polymorphism (RFLP) with Sma I and BamH I enzymes. The T cell reactivity to ticlopidine was analysed by T cell proliferation assay in PBMC against ticlopidine, tetanus toxoid antigen and phytohemagglutinin on days 0, 90, 150 and 210 after therapy withdrawal. The serum levels of INF-γ, IL-2, IL-4, IL-10, TNF-α, sFas and sFasL were measured by ELISA at the same time points. Apoptosis was analysed by TUNEL assay. All patients with cholestatic hepatitis had “slow metabolizers” genotypes in contrast to other groups. The T cell reactivity to ticlopidine was present only in all the cholestatic hepatitis patients together with substantial decrease in levels of INF-γ, IL-2 and TNF-α during all of the follow-up period. Cholestatic hepatitis patients had high apoptotic index in TUNEL assay. The genetic polymorphism of the cytochrome CYP2C19 gene is directly responsible for the susceptibility to the ticlopidine-induced liver damage. Th1 type of immune reactivity plays the key role in the pathogenesis of drug-induced hepatotoxicity.

Structural proteins of Hepatitis C virus induce interleukin 8 production and apoptosis in human endothelial cells

Hepatitis C virus (HCV) infection is associated with inflammation of liver endothelium, which contributes to the pathogenesis of chronic hepatitis. The mechanism of this endothelitis is not understood, since the virus does not appear to infect endothelial cells productively. Here, an 'innocent bystander' mechanism related to HCV proteins was hypothesized and it was investigated whether the binding of HCV particles to human endothelium induced functional changes in the cells. Exposure of human umbilical vein endothelial cells (HUVECs) to HCV-like particles (HCV-LPs) resulted in increased interleukin 8 (IL8) production and induction of apoptosis. The IL8 supernatants collected after stimulation of HUVECs with HCV-LPs, BV-GUS (control baculovirus containing beta-glucuronidase) and appropriate controls were used to assay the transendothelial migration of neutrophils. This assay confirmed that HCV-LP-induced IL8 was functionally active. Using specific NF-kappaB inhibitors, it was also shown that HCV-LP-induced NF-kappaB activity mediated IL8 production in HUVECs. Apoptosis appeared to be mediated by the Fas/Fas-L pathway, as neutralizing antibodies for Fas and Fas-L significantly protected HUVECs against HCV-LP-induced apoptosis. Treatment of HUVECs with HCV-LPs also enhanced cellular Fas-L expression and augmented caspase-3 activation. This was confirmed by using a specific caspase-3 inhibitor, Z-Asp-Glu-Val-Asp-fluoromethyl ketone. As shown by blocking of specific chemokine receptors for IL8 on HUVECs, the induction of IL8 did not appear to contribute to HCV-LP-induced apoptosis. These results suggest that HCV proteins can trigger the release of inflammatory chemokines such as IL8 and cause endothelial apoptosis, thereby facilitating endothelitis.

Apoptosis of activated CD4+ and CD8+ T cells is enhanced by co-culture with hepatocytes expressing hepatitis C virus (HCV) structural proteins through FasL induction

A central unresolved issue in hepatitis C virus (HCV) infection is how the virus establishes chronic infection. Recent studies suggest that the liver microenvironment leads to apoptosis of activated T cells, which may be involved in the tolerance to liver allograft. Here, We report that murine hepatocytes expressing a transgene encoding the HCV structural proteins core, envelope 1 (E1) and envelope 2 (E2) enhance apoptosis of activated T cells. Unlike normal liver, which appears to selectively remove only activated CD8+ T cells, enhanced apoptosis was seen for both CD4+ and CD8+ T cells. Enhanced apoptosis of activated T lymphocytes was associated with upregulation of FasL by HCV transgenic hepatocytes and was specifically inhibited by anti-FasL blocking antibody. Increased apoptosis of activated T cells induced by HCV structural proteins could amplify the ability of the liver to down-modulate T cell responses, leading to attenuation of anti-viral responses and facilitating viral persistence.

Hepatitis C virus and the immune system: a concise review

Hepatitis C Virus (HCV) induces a chronic infection in 50%-80% of infected individuals, which can lead to cirrhosis and hepatocellular carcinoma. The inefficiency of the immune system in eliminating the virus is not well understood as humoral and cellular immune responses are induced. While a persistent infection is generally associated with a weak CD4+ and CD8+ T cell response during the acute phase, there is no good explanation as to why this response is strong enough in 20% of acutely infected people such that they spontaneously resolve the infection. However, the immune system partially controls the viral infection but due to a long-lasting inflammatory milieu, hepatic damage occurs. During the chronic phase of the infection, HCV does not seem to be cytopathic. This aspect is still controversial as the virus was linked to the development of cholestatic syndrome or acute lobular hepatitis after liver transplant in HCV infected patients. The development of new experimental systems such as HCV pseudoparticles, genomic replicon and transfected cell lines have improved our vision of the virus cycle as well as the understanding of the mechanism of persistence. However, a convincing explanation for the chronicity of the infection in the presence of a functional immune response is still missing and is an important area of research to understand HCV immune pathogenesis. Future research should dissect mechanisms that lead to quantitatively or qualitatively inadequate immune responses, the role of the high variability of the virus, the relevance of host's genetic factors and mechanisms of immunosuppression induced by the virus.