Hepatitis C core protein inhibits induction of heme oxygenase-1 and sensitizes hepatocytes to cytotoxicity

Reactive oxygen species as potential antiviral targets

Reactive oxygen species (ROS) are by-products of cellular metabolism and can be either beneficial, at low levels, or deleterious, at high levels, to the cell. It is known that several viral infections can increase oxidative stress, which is mainly facilitated by viral-induced imbalances in the antioxidant defence mechanisms of the cell. While the exact role of ROS in certain viral infections (adenovirus and dengue virus) remains unknown, other viruses can use ROS for enhancement of pathogenesis (SARS coronavirus and rabies virus) or replication (rhinovirus, West Nile virus and vesicular stomatitis virus) or both (hepatitis C virus, human immunodeficiency virus and influenza virus). While several viral proteins (mainly for hepatitis C and human immunodeficiency virus) have been identified to play a role in ROS formation, most mediators of viral ROS modulation are yet to be elucidated. Treatment of viral infections, including hepatitis C virus, human immunodeficiency virus and influenza virus, with ROS inhibitors has shown a decrease in both pathogenesis and viral replication both in vitro and in animal models. Clinical studies indicating the potential for targeting ROS-producing pathways as possible broad-spectrum antiviral targets should be evaluated in randomized controlled trials.

HCV and Oxidative Stress: Implications for HCV Life Cycle and HCV-Associated Pathogenesis

HCV (hepatitis C virus) is a member of the Flaviviridae family that contains a single-stranded positive-sense RNA genome of approximately 9600 bases. HCV is a major causative agent for chronic liver diseases such as steatosis, fibrosis, cirrhosis, and hepatocellular carcinoma which are caused by multifactorial processes. Elevated levels of reactive oxygen species (ROS) are considered as a major factor contributing to HCV-associated pathogenesis. This review summarizes the mechanisms involved in formation of ROS in HCV replicating cells and describes the interference of HCV with ROS detoxifying systems. The relevance of ROS for HCV-associated pathogenesis is reviewed with a focus on the interference of elevated ROS levels with processes controlling liver regeneration. The overview about the impact of ROS for the viral life cycle is focused on the relevance of autophagy for the HCV life cycle and the crosstalk between HCV, elevated ROS levels, and the induction of autophagy.

Contradicting roles of miR-182 in both NK cells and their host target hepatocytes in HCV

BACKGROUND AND AIM

Natural killer cells are part of the innate immunity involved in viral eradication and were shown to be greatly affected by HCV infection. Epigenetic regulation of NK cell function by microRNAs was not efficiently studied before and was never studied in HCV infection; therefore the aim of this study was to assess for the first time the role of microRNAs in regulating the function of NK cells of HCV-infected patients and hence viral replication in the target HCV-infected Huh7 cells.

METHODOLOGY

NK cells were isolated from PBMCs of HCV-infected patients as well as controls, and HCV-infected liver biopsies as well as Huh7 cells infected with the virus were used. For the infection of Huh7 cells, first viral vector was in-vitro transcribed into viral RNA that was then used to infect naїve Huh7 cells. Supernatant from the infected cells was then collected and used for further infection. For manipulation of NK cells or Huh7 cells, miR-182 mimics and inhibitors were transfected via lipofection method. RNA was extracted from each cell population, reverse transcribed. Gene expression as well as viral load was quantified using qPCR.

RESULTS

Screening of NKG2A and NKG2D between patients and controls showed no difference in expression of NKG2A, while NKG2D was found to be downregulated. In view of that, bioinformatics analysis was performed and showed that miR-182 has potential binding sites on both the inhibitory receptor NKG2A and the activating receptor NKG2D, and on its ligand ULBP2, as well as on the viral genome itself. In NK cells of HCV-infected patients, miR-182 was found to be over-expressed compared to controls; its ectopic expression was found to decrease NKG2D mRNA level, while miR-182 inhibitors were able to decrease NKG2A mRNA compared to untransfected cells. In addition, co-culturing genotype 4 or 2 HCV-infected Huh7 cells with miR-182 mimicked NK cells of HCV-infected patients showed decreased viral replication, suggesting an enhanced NK cell function. On the other hand, miR-182 and ULBP2 were both found to be downregulated in HCV liver tissues and HCV-infected Huh7 cells compared to their controls. miR-182 mimics were found to decrease ULBP2 mRNA and increase viral replication in genotypes 4 and 2 HCV-infected target (Huh7) cells compared to controls, while miR-182 inhibitor decreased viral replication in the cell models.

CONCLUSION

miR-182 was never investigated before, neither in HCV infection nor in NK cells, and we found it to have dysregulated expression in both liver tissues and NK cells of HCV-infected patients compared to control. In addition to that, miR-182 was found to have a contradicting effect in both effector cell and its HCV-infected target cell regarding HCV replication.

Induction of Heme Oxygenase-1 Deficiency and Associated Glutamate-Mediated Neurotoxicity Is a Highly Conserved HIV Phenotype of Chronic Macrophage Infection That Is Resistant to Antiretroviral Therapy

Expression of the cytoprotective enzyme heme oxygenase-1 (HO-1) is significantly reduced in the brain prefrontal cortex of HIV-positive individuals with HIV-associated neurocognitive disorders (HAND). Furthermore, this HO-1 deficiency correlates with brain viral load, markers of macrophage activation, and type I interferon responses. In vitro, HIV replication in monocyte-derived macrophages (MDM) selectively reduces HO-1 protein and RNA expression and induces production of neurotoxic levels of glutamate; correction of this HO-1 deficiency reduces neurotoxic glutamate production without an effect on HIV replication. We now demonstrate that macrophage HO-1 deficiency, and the associated neurotoxin production, is a conserved feature of infection with macrophage-tropic HIV-1 strains that correlates closely with the extent of replication, and this feature extends to HIV-2 infection. We further demonstrate that this HO-1 deficiency does not depend specifically upon the HIV-1 accessory genes nef, vpr, or vpu but rather on HIV replication, even when markedly limited. Finally, antiretroviral therapy (ART) applied to MDM after HIV infection is established does not prevent HO-1 loss or the associated neurotoxin production. This work defines a predictable relationship between HIV replication, HO-1 loss, and neurotoxin production in MDM that likely reflects processes in place in the HIV-infected brains of individuals receiving ART. It further suggests that correcting this HO-1 deficiency in HIV-infected MDM could provide neuroprotection above that provided by current ART or proposed antiviral therapies directed at limiting Nef, Vpr, or Vpu functions. The ability of HIV-2 to reduce HO-1 expression suggests that this is a conserved phenotype among macrophage-tropic human immunodeficiency viruses that could contribute to neuropathogenesis.

IMPORTANCE

The continued prevalence of HIV-associated neurocognitive disorders (HAND) underscores the need for adjunctive therapy that targets the neuropathological processes that persist in antiretroviral therapy (ART)-treated HIV-infected individuals. To this end, we previously identified one such possible process, a deficiency of the antioxidative and anti-inflammatory enzyme heme oxygenase-1 (HO-1) in the brains of individuals with HAND. In the present study, our findings suggest that the HO-1 deficiency associated with excess glutamate production and neurotoxicity in HIV-infected macrophages is a highly conserved phenotype of macrophage-tropic HIV strains and that this phenotype can persist in the macrophage compartment in the presence of ART. This suggests a plausible mechanism by which HIV infection of brain macrophages in ART-treated individuals could exacerbate oxidative stress and glutamate-induced neuronal injury, each of which is associated with neurocognitive dysfunction in infected individuals. Thus, therapies that rescue the HO-1 deficiency in HIV-infected individuals could provide additional neuroprotection to ART.

Ribavirin induced hemolysis: A novel mechanism of action against chronic hepatitis C virus infection

Hepatitis C virus (HCV) is not usually cleared by our immune system, leading to the development of chronic hepatitis C infection. Chronic HCV induces the production of various cytokines, predominantly by Kupffer cells (KCs), and creates a pro-inflammatory state in the liver. The chronic dysregulated production of interferon (IFN) and other cytokines by KCs also promotes innate immune tolerance. Ribavirin (RBV) monotherapy has been shown to decrease inflammation in liver of patients with chronic hepatitis C. Sustained virological response (SVR) is significantly higher when IFN is combined with RBV in chronic HCV (cHCV) infection. However, the mechanism of their synergy remains unclear. Previous theories have attempted to explain the anti-HCV effect based on direct action of RBV alone on the virus or on the immune system; however, these theories have serious shortcomings. We propose that hemolysis, which universally occurs with RBV therapy and which is considered a limiting side effect, is precisely the mechanism by which the anti-HCV effect is exerted. Passive hemolysis results in anti-inflammatory/antiviral actions within the liver that disrupt the innate immune tolerance, leading to the synergy of RBV with IFN-α. Ribavirin-induced hemolysis floods the hepatocytes and KCs with heme, which is metabolized and detoxified by heme oxygenase-1 (HMOX1) to carbon monoxide (CO), biliverdin and free iron (which induces ferritin). These metabolites of heme possess anti-inflammatory and antioxidant properties. Thus, HMOX1 plays an extremely important anti-oxidant, anti-inflammatory and cytoprotective role, particularly in KCs and hepatocytes. HMOX1 has been noted to have anti-viral effects in hepatitis C infected cell lines. Additionally, it has been shown to enhance the response to IFN-α by restoring interferon-stimulated genes (ISGs). This mechanism can be clinically corroborated by the following observations that have been found in patients undergoing RBV/IFN combination therapy for cHCV: (1) SVR rates are higher in patients who develop anemia; (2) once anemia (due to hemolysis) occurs, the SVR rate does not depend on the treatment utilized to manage anemia; and (3) ribavirin analogs, such as taribavirin and levovirin, which increase intrahepatic ribavirin levels and which produce lesser hemolysis, are inferior to ribavirin for treating cHCV. This mechanism can also explain the observed RBV synergy with direct antiviral agents. This hypothesis is testable and may lead to newer and safer medications for treating cHCV infection.

N-acetyl-serotonin protects HepG2 cells from oxidative stress injury induced by hydrogen peroxide

Oxidative stress plays an important role in the pathogenesis of liver diseases. N-Acetyl-serotonin (NAS) has been reported to protect against oxidative damage, though the mechanisms by which NAS protects hepatocytes from oxidative stress remain unknown. To determine whether pretreatment with NAS could reduce hydrogen peroxide- (H₂O₂-) induced oxidative stress in HepG2 cells by inhibiting the mitochondrial apoptosis pathway, we investigated the H₂O₂-induced oxidative damage to HepG2 cells with or without NAS using MTT, Hoechst 33342, rhodamine 123, Terminal dUTP Nick End Labeling Assay (TUNEL), dihydrodichlorofluorescein (H2DCF), Annexin V and propidium iodide (PI) double staining, immunocytochemistry, and western blot. H₂O₂ produced dramatic injuries in HepG2 cells, represented by classical morphological changes of apoptosis, increased levels of malondialdehyde (MDA) and intracellular reactive oxygen species (ROS), decreased activity of superoxide dismutase (SOD), and increased activities of caspase-9 and caspase-3, release of cytochrome c (Cyt-C) and apoptosis-inducing factor (AIF) from mitochondria, and loss of membrane potential (ΔΨ_m). NAS significantly inhibited H₂O₂-induced changes, indicating that it protected against H₂O₂-induced oxidative damage by reducing MDA levels and increasing SOD activity and that it protected the HepG2 cells from apoptosis through regulating the mitochondrial apoptosis pathway, involving inhibition of mitochondrial hyperpolarization, release of mitochondrial apoptogenic factors, and caspase activity.

Hepatitis C and alcohol exacerbate liver injury by suppression of FOXO3

Hepatitis C virus (HCV) infection exacerbates alcoholic liver injury by mechanisms that include enhanced oxidative stress. The forkhead box transcription factor FOXO3 is an important component of the antioxidant stress response that can be altered by HCV. To test whether FOXO3 is protective for alcoholic liver injury, we fed alcohol to FOXO3(-/-) mice. After 3 weeks, one third of these mice developed severe hepatic steatosis, neutrophilic infiltration, and >10-fold alanine aminotransferase (ALT) elevations. In cell culture, either alcohol or HCV infection alone increased FOXO3 transcriptional activity and expression of target genes, but the combination of HCV and alcohol together caused loss of nuclear FOXO3 and decreased its transcriptional activity. This was accompanied by increased phosphorylation of FOXO3. Mice expressing HCV structural proteins on a background of reduced expression of superoxide dismutase 2 (SOD2; Sod2(+/-)) also had increased liver sensitivity to alcohol, with elevated ALT, steatosis, and lobular inflammation. Elevated ALT was associated with an alcohol-induced decrease in SOD2 and redistribution of FOXO3 to the cytosol. These results demonstrate that FOXO3 functions as a protective factor preventing alcoholic liver injury. The combination of HCV and alcohol, but not either condition alone, inactivates FOXO3, causing a decrease in expression of its target genes and an increase in liver injury. Modulation of the FOXO3 pathway is a potential therapeutic approach for HCV-alcohol-induced liver injury.

Expression of Biliverdin Reductase A in peripheral blood leukocytes is associated with treatment response in HCV-infected patients

BACKGROUND AND AIMS

Hepatitis C virus (HCV) infection is associated with systemic oxidative stress. Since the heme catabolic pathway plays an important role in antioxidant protection, we attempted to assess the gene expression of key enzymes of heme catabolism, heme oxygenase 1 (HMOX1), heme oxygenase 2 (HMOX2), and biliverdin reductase A (BLVRA) in the liver and peripheral blood leukocytes (PBL) of patients chronically infected with HCV.

METHODS

Gene expressions (HMOX1, HMOX2, BLVRA) and HCV RNA were analyzed in PBL of HCV treatment naïve patients (n = 58) and controls (n = 55), with a subset of HCV patients having data on hepatic gene expression (n = 35). Based upon the therapeutic outcome, HCV patients were classified as either responders (n = 38) or treatment-failure patients (n = 20). Blood samples in HCV patients were collected at day 0, and week 12, 24, 36, and 48 after the initiation of standard antiviral therapy.

RESULTS

Compared to the controls, substantially increased BLVRA expression was detected in PBL (p<0.001) of therapeutically naïve HCV patients. mRNA levels of BLVRA in PBL closely correlated with those in liver tissue (r2 = 0.347,p = 0.03). A marked difference in BLVRA expression in PBL between the sustained responders and patients with treatment failure was detected at week 0 and during the follow-up (p<0.001). Multivariate analysis revealed that BLVRA basal expression in PBL was an independent predictor for sustained virological response (OR 15; 95% CI 1.05-214.2; P = 0.046). HMOX1/2 expression did not have any effect on the treatment outcome.

CONCLUSION

Our results suggest that patients with chronic HCV infection significantly upregulate BLVRA expression in PBL. The lack of BLVRA overexpression is associated with non-responsiveness to standard antiviral therapy; whereas, HMOX1/2 does not seem to have any predictive potential.

HCV and oxidative stress in the liver

Hepatitis C virus (HCV) is the etiological agent accounting for chronic liver disease in approximately 2-3% of the population worldwide. HCV infection often leads to liver fibrosis and cirrhosis, various metabolic alterations including steatosis, insulin and interferon resistance or iron overload, and development of hepatocellular carcinoma or non-Hodgkin lymphoma. Multiple molecular mechanisms that trigger the emergence and development of each of these pathogenic processes have been identified so far. One of these involves marked induction of a reactive oxygen species (ROS) in infected cells leading to oxidative stress. To date, markers of oxidative stress were observed both in chronic hepatitis C patients and in various in vitro systems, including replicons or stable cell lines expressing viral proteins. The search for ROS sources in HCV-infected cells revealed several mechanisms of ROS production and thus a number of cellular proteins have become targets for future studies. Furthermore, during last several years it has been shown that HCV modifies antioxidant defense mechanisms. The aim of this review is to summarize the present state of art in the field and to try to predict directions for future studies.

Reduced heme oxygenase-1 expression in steatotic livers infected with hepatitis C virus

Hepatic nonalcoholic fatty liver disease (NAFLD) is known to exacerbate liver injury due to chronic hepatitis C infection. Heme oxygenase-1 (HO-1) is an important protective antioxidative defense enzyme that is known to be induced in response to NAFLD and other liver injuries. The aim of this study was to evaluate HO-1 expression in HCV infected human livers with concomitant NAFLD.

METHODS

We compared levels of HO-1 in NAFLD liver biopsies from patients with or without chronic HCV infection using immunohistochemistry, immunoblots and real time RT-PCR. We also evaluated frozen sections of liver with dihydroethidium (DHE) or dichlorofluorescein (DCF) fluorescence staining to evaluate O(2)(-) and peroxide production respectively.

RESULTS

HO-1 expression was only increased in NAFLD livers without HCV infection, while HCV infected livers showed reduced HO-1 levels, regardless whether NAFLD was present. In uninfected livers with NAFLD, HO-1 expression was primarily localized in hepatocytes containing fat and areas of injury around the central vein. However, both NAFLD with and without concomitant HCV infection showed high levels of O(2)(-) or peroxide production compared to normal human liver control samples.

CONCLUSIONS

These findings support the hypothesis that NAFLD is an important process for hepatocyte oxidative stress and injury in liver diseases. They also suggest that HCV can repress HO-1 induction in vivo even when other inducers of HO-1 are present.

Oxidative stress, endogenous antioxidants, alcohol, and hepatitis C: pathogenic interactions and therapeutic considerations

Hepatitis C virus (HCV) is a blood-borne pathogen that was identified as an etiologic agent of non-A, non-B hepatitis in 1989. HCV is estimated to have infected at least 170 million people worldwide. The majority of patients infected with HCV do not clear the virus and become chronically infected, and chronic HCV infection increases the risk for hepatic steatosis, cirrhosis, and hepatocellular carcinoma. HCV induces oxidative/nitrosative stress from multiple sources, including inducible nitric oxide synthase, the mitochondrial electron transport chain, hepatocyte NAD(P)H oxidases, and inflammation, while decreasing glutathione. The cumulative oxidative burden is likely to promote both hepatic and extrahepatic conditions precipitated by HCV through a combination of local and more distal effects of reactive species, and clinical, animal, and in vitro studies strongly point to a role of oxidative/nitrosative stress in HCV-induced pathogenesis. Oxidative stress and hepatopathogenesis induced by HCV are exacerbated by even low doses of alcohol. Alcohol and reactive species may have other effects on hepatitis C patients such as modulation of the host immune system, viral replication, and positive selection of HCV sequence variants that contribute to antiviral resistance. This review summarizes the current understanding of redox interactions of HCV, outlining key experimental findings, directions for future research, and potential applications to therapy.

Hepatitis C virus infection: molecular pathways to insulin resistance

Chronic Hepatitis C virus has the potential of inducing insulin resistance and type 2 Diabetes Mellitus in vitro as well as in vivo . Structural and non-structural proteins of HCV modulate cellular gene expression in such a way that insulin signaling is hampered, concomitantly leads toward diabetes mellitus. A number of mechanisms have been proposed in regard to the HCV induced insulin resistance involving the upregulation of Inflammatory cytokine TNF-α, hypophosphorylation of IRS-1 and IRS-2, phosphorylation of Akt, up-regulation of gluconeogenic genes, accumulation of lipids and targeting lipid storage organelles. This review provides an insight of molecular mechanisms by which HCV structural and non-structural proteins can induce insulin resistance.

NK cells prevalence, subsets and function in viral hepatitis C

Innate immunity appears to play an important role in the pathogenesis of viral hepatitis C. Among various cell subsets of this immunity natural killer (NK) cells raised particular interest. These cells are abundant in liver, possess significant cytotoxic potential and show links with adaptive immunity. They play important role, particularly in the acute phase of viral infections, including hepatitis C. They exhibit various types of receptors, either inhibitory or activating, that are able to react with distinct ligands on infected cells. Homozygosity of some receptors, namely KIR2DL3 reacting with recipient HLA-C1 antigens is a herald of good prognosis in hepatitis C virus (HCV) infection. In the early stage of the latter, both the prevalence and the cytotoxicity of NK cells are increased. Their inhibitory receptors are down regulated whereas activating ones are up regulated. Interferon-γ secreted by NK56(+bright) NK cells has a direct cytotoxic effect on infected hepatocytes. In contrast, in the chronic phase of HCV liver disease both, the prevalence and function of NK cells are impaired. Nevertheless, their cytotoxicity contributes to liver injury. Cells show change in the polarization profile from NK1 to NK2, manifested by secretion of immunosuppressive cytokines. Some HCV peptides are inhibitory for NK cells leading to the reduction of their antiviral activity. The unwanted effects of HCV peptides can be at least partly reversed by the antiviral therapy.

Biliverdin inhibits hepatitis C virus nonstructural 3/4A protease activity: mechanism for the antiviral effects of heme oxygenase?

Induction of heme oxygenase-1 (HO-1) inhibits hepatitis C virus (HCV) replication. Of the products of the reaction catalyzed by HO-1, iron has been shown to inhibit HCV ribonucleic acid (RNA) polymerase, but little is known about the antiviral activity of biliverdin (BV). Herein, we report that BV inhibits viral replication and viral protein expression in a dose-dependent manner in replicons and cells harboring the infectious J6/JFH construct. Using the SensoLyte 620 HCV Protease Assay with a wide wavelength excitation/emission (591 nm/622 nm) fluorescence energy transfer peptide, we found that both recombinant and endogenous nonstructural 3/4A (NS3/4A) protease from replicon microsomes are potently inhibited by BV. Of the tetrapyrroles tested, BV was the strongest inhibitor of NS3/4A activity, with a median inhibitory concentration (IC(50)) of 9 μM, similar to that of the commercial inhibitor, AnaSpec (Fremont, CA) #25346 (IC(50) 5 μM). Lineweaver-Burk plots indicated mixed competitive and noncompetitive inhibition of the protease by BV. In contrast, the effects of bilirubin (BR) on HCV replication and NS3/4A were much less potent. Because BV is rapidly converted to BR by biliverdin reductase (BVR) intracellularly, the effect of BVR knockdown on BV antiviral activity was assessed. After greater than 80% silencing of BVR, inhibition of viral replication by BV was enhanced. BV also increased the antiviral activity of α-interferon in replicons.

CONCLUSION

BV is a potent inhibitor of HCV NS3/4A protease, which likely contributes to the antiviral activity of HO-1. These findings suggest that BV or its derivatives may be useful in future drug therapies targeting the NS3/4A protease.

Parallel microRNA and mRNA expression profiling of (genotype 1b) human hepatoma cells expressing hepatitis C virus

BACKGROUND & AIMS

MicroRNAs (miRNAs) are members of a class of small noncoding functional RNAs that modulate gene regulation at the post-transcriptional level in a sequence specific manner. miRNA dysfunction has been linked to the pathophysiology of human diseases including those resulting from viral infections. The objective of this study was to investigate changes in miRNA profiles that occur in hepatoma cells expressing hepatitis C virus (HCV) and identify anticorrelated mRNAs, which may be their regulatory targets.

METHODS

Microarrays were used to perform global miRNA and mRNA expression analysis. Fold changes and pairwise statistics were computed for the resulting datasets. Hierarchical cluster and pathway analyses were performed to assess the degree of differential expression and identify regulatory networks. Bioinformatics tools were used to integrate mRNA profiling results with miRNA target predictions.

RESULTS

Replication of the Con1 strain of HCV virus in hepatoma cells elicited extensive differential expression of both miRNAs and mRNAs. Forty-three differentially expressed miRNAs (P≤0.001) were identified by microarray analysis in HCV expressing cells. Six thousand eight hundred and fifteen differentially expressed mRNAs (P≤0.05) were identified. Computational analyses revealed anticorrelated miRNA:mRNA pairs for each target prediction algorithm used. Pathway analysis generated a filtered pathway with 120 entities, including seven major regulators and nine major targets potentially under the control of at least 11 miRNAs.

CONCLUSIONS

The expression of a number of anticorrelated miRNAs:mRNA pairs are affected by the presence of HCV. These miRNAs and their putative targets are attractive candidates for being involved in the pathogenesis and/or progression of HCV-induced chronic hepatitis.

MicroRNA-196 represses Bach1 protein and hepatitis C virus gene expression in human hepatoma cells expressing hepatitis C viral proteins

Hepatitis C virus (HCV) directly induces oxidative stress and liver injury. Bach1, a basic leucine zipper mammalian transcriptional repressor, negatively regulates heme oxygenase 1 (HMOX1), a key cytoprotective enzyme that has antioxidant and anti-inflammatory activities. microRNAs (miRNAs) are small noncoding RNAs ( approximately 22 nt) that are important regulators of gene expression. Whether and how miRNAs regulate Bach1 or HCV are largely unknown. The aims of this study were to determine whether miR-196 regulates Bach1, HMOX1, and/or HCV gene expression. HCV replicon cell lines (Con1 and 9-13) of the Con1 isolate and J6/JFH1-based HCV cell culture system were used in this study. The effects of miR-196 mimic on Bach1, HMOX1, and HCV RNA, and protein levels were measured by way of quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting, respectively. The Dual Glo Luciferase Assay System was used to determine reporter activities. miR-196 mimic significantly down-regulated Bach1 and up-regulated HMOX1 gene expression and inhibited HCV expression. Dual luciferase reporter assays demonstrated that transfection of miR-196 mimic resulted in a significant decrease in Bach1 3'-untranslated region (UTR)-dependent luciferase activity but not in mutant Bach1 3'-UTR-dependent luciferase activity. Moreover, there was no detectable effect of mutant miR-196 on Bach1 3'-UTR-dependent luciferase activity.

CONCLUSION

miR-196 directly acts on the 3'-UTR of Bach1 messenger RNA and translationally represses the expression of this protein, and up-regulates HMOX1. miR-196 also inhibits HCV expression in HCV replicon cell lines (genotype 1b) and in J6/JFH1 (genotype 2a) HCV cell culture system. Thus, miR-196 plays a role in both HMOX1/Bach1 expression and the regulation of HCV expression in human hepatocytes. Overexpression of miR-196 holds promise as a potential novel strategy to prevent or ameliorate hepatitis C infection, and to protect against liver injury in chronic HCV infection.

The heme oxygenase 1 product biliverdin interferes with hepatitis C virus replication by increasing antiviral interferon response

The anti-inflammatory and antiapoptotic heme degrading enzyme heme oxygenase-1 (HO-1) has been shown recently to interfere with replication of hepatitis C virus (HCV). We investigated the effect of HO-1 products carbon monoxide (CO), iron and biliverdin on HCV replication using the replicon cell lines Huh-5-15 and LucUbiNeo-ET, stably expressing HCV proteins NS3 through NS5B. Incubation of these cell lines in the presence of the CO donor methylene chloride transiently reduced HCV replication, whereas an increase of iron in cell culture by administration of FeCl(3) or iron-saturated lactoferrin did not interfere with HCV replication. Likewise, depletion of iron by deferoxamine during induction of HO-1 by cobalt-protoporphyrin IX did not restore HCV replication. The most prominent effect was observed after incubation of replicon cell lines in the presence of biliverdin. Biliverdin seems to interfere with HCV replication-mediated oxidative stress by inducing expression of antiviral interferons, such as interferon alpha2 and alpha17.

CONCLUSION

The antioxidant biliverdin reduces HCV replication in vitro by triggering the antiviral interferon response and might improve HCV therapy in the future.

Carbon monoxide in biology and microbiology: surprising roles for the "Detroit perfume"

Carbon monoxide (CO) is a colorless, odorless gas with a reputation for being an anthropogenic poison; there is extensive documentation of the modes of human exposure, toxicokinetics, and health effects. However, CO is also generated endogenously by heme oxygenases (HOs) in mammals and microbes, and its extraordinary biological activities are now recognized and increasingly utilized in medicine and physiology. This review introduces recent advances in CO biology and chemistry and illustrates the exciting possibilities that exist for a deeper understanding of its biological consequences. However, the microbiological literature is scant and is currently restricted to: 1) CO-metabolizing bacteria, CO oxidation by CO dehydrogenase (CODH) and the CO-sensing mechanisms that enable CO oxidation; 2) the use of CO as a heme ligand in microbial biochemistry; and 3) very limited information on how microbes respond to CO toxicity. We demonstrate how our horizons in CO biology have been extended by intense research activity in recent years in mammalian and human physiology and biochemistry. CO is one of several "new" small gas molecules that are increasingly recognized for their profound and often beneficial biological activities, the others being nitric oxide (NO) and hydrogen sulfide (H2S). The chemistry of CO and other heme ligands (oxygen, NO, H2S and cyanide) and the implications for biological interactions are briefly presented. An important advance in recent years has been the development of CO-releasing molecules (CO-RMs) for aiding experimental administration of CO as an alternative to the use of CO gas. The chemical principles of CO-RM design and mechanisms of CO release from CO-RMs (dissociation, association, reduction and oxidation, photolysis, and acidification) are reviewed and we present a survey of the most commonly used CO-RMs. Amongst the most important new applications of CO in mammalian physiology and medicine are its vasoactive properties and the therapeutic potentials of CO-RMs in vascular disease, anti-inflammatory effects, CO-mediated cell signaling in apoptosis, applications in organ preservation, and the effects of CO on mitochondrial function. The very limited literature on microbial growth responses to CO and CO-RMs in vitro, and the transcriptomic and physiological consequences of microbial exposure to CO and CO-RMs are reviewed. There is current interest in CO and CO-RMs as antimicrobial agents, particularly in the control of bacterial infections. Future prospects are suggested and unanswered questions posed.

Peripheral blood gene expression profile associated with sustained virologic response after peginterferon plus ribavirin therapy for chronic hepatitis-C genotype 1

We investigated the relationship between global gene expression in peripheral blood mononuclear cells (PBMCs) during the first 4 weeks of peginterferon alfa and ribavirin therapy and long-term eradication of hepatitis-C genotype 1 infections in 23 patients. A sustained virologic response (SVR), defined as an undetected serum HCV ribonucleic acid (RNA) at week 72, was the virologic response endpoint. PBMC RNA was prepared at week 0 and week 4 from 23 patients (17 black and 6 white Americans), and hybridized to Affymetrix GeneChip HG-U133 plus 2.0 arrays. Compared to week 0, 269 genes were differentially expressed at week 4 of treatment, including many genes regulated by alpha interferons and associated with host immunity (p<0.0001), cell signal transduction (p<0.001) and cellular protein metabolism (p<0.001). Expression of these 269 genes at week 0 and week 4 did not differ significantly between patients with and without a SVR. In contrast, SVR was associated with differential expression of 98 genes at week 4 (false discovery rate <0.01). Many of the genes have been implicated in control of HCV lifecycle and thus may play important roles in HCV clearance during peginterferon and ribavirin therapy.

Iron increases HMOX1 and decreases hepatitis C viral expression in HCV-expressing cells

AIM: To investigate effects of iron on oxidative stress, heme oxygenase-1 (HMOX1) and hepatitis C viral (HCV) expression in human hepatoma cells stably expressing HCV proteins.

METHODS: Effects of iron on oxidative stress, HMOX1, and HCV expression were assessed in CON1 cells. Measurements included mRNA by quantitative reverse transcription-polymerase chain reaction, and protein levels by Western blots.

RESULTS: Iron, in the form of ferric nitrilotriacetate, increased oxidative stress and up-regulated HMOX1 gene expression. Iron did not affect mRNA or protein levels of Bach1, a repressor of HMOX1. Silencing the up-regulation of HMOX1 nuclear factor-erythroid 2-related factor 2 (Nrf2) by Nrf2-siRNA decreased FeNTA-mediated up-regulation of HMOX1 mRNA levels. These iron effects were completely blocked by deferoxamine (DFO). Iron also significantly decreased levels of HCV core mRNA and protein by 80%-90%, nonstructural 5A mRNA by 90% and protein by about 50% in the Con1 full length HCV replicon cells, whereas DFO increased them.

CONCLUSION: Excess iron up-regulates HMOX1 and down-regulates HCV gene expression in hepatoma cells. This probably mitigates liver injury caused by combined iron overload and HCV infection.

Heme oxygenase-1 suppresses hepatitis C virus replication and increases resistance of hepatocytes to oxidant injury

Oxidative injury to hepatocytes occurs as a result of hepatitis C virus (HCV) infection and replication. Modulation of host cell antioxidant enzymes such as heme oxygenase-1 (HO-1) may be useful therapeutically to minimize cellular injury, reduce viral replication, and attenuate liver disease. In this report, we evaluated the effects of HO-1 overexpression on HCV replication and hepatocellular injury. Full-length (FL) (Con1) or nonstructural (NS) replicons (I 389 NS3-3') were transfected with complete human HO-1 sequences or empty vector for control. Cell lines overexpressing HO-1 (twofold to sixfold above basal values) or empty vector were isolated, and their HCV RNA synthesis, pro-oxidant levels, and resistance to oxidative injury were assessed. HO-1 overexpression decreased HCV RNA replication in both FL and NS replicons without affecting cellular growth or DNA synthesis. The attenuation of HCV replication was significantly reversed in both replicon systems with HO-1 small interfering RNA (siRNA) knockdown. Both FL and NS replicons that overexpress HO-1 showed reduced prooxidant levels at baseline and increased resistance to oxidant-induced cytotoxicity. HO-1 induction with hemin also markedly decreased HCV replication in both parental FL and NS replicon cell lines. Conversely, knockdown of HO-1 messenger RNA (mRNA) by siRNA in parental FL or NS replicons did not significantly affect HCV replication, suggesting that less than basal levels of HO-1 had minimal effect on HCV replication.

CONCLUSION

Overexpression or induction of HO-1 results in decreased HCV replication as well as protection from oxidative damage. These findings suggest a potential role for HO-1 in antiviral therapy and therapeutic protection against hepatocellular injury in HCV infection.

Natural heme oxygenase-1 inducers in hepatobiliary function

Many physiological effects of natural antioxidants, their extracts or their major active components, have been reported in recent decades. Most of these compounds are characterized by a phenolic structure, similar to that of α-tocopherol, and present antioxidant properties that have been demonstrated both in vitro and in vivo. Polyphenols may increase the capacity of endogenous antioxidant defences and modulate the cellular redox state. Changes in the cellular redox state may have wide-ranging consequences for cellular growth and differentiation. The majority of in vitro and in vivo studies conducted so far have attributed the protective effect of bioactive polyphenols to their chemical reactivity toward free radicals and their capacity to prevent the oxidation of important intracellular components. However, in recent years a possible novel aspect in the mode of action of these compounds has been suggested; that is, the ultimate stimulation of the heme oxygenase-1 (HO-1) pathway is likely to account for the established and powerful antioxidant/anti-inflammatory properties of these polyphenols. The products of the HO-catalyzed reaction, particularly carbon monoxide (CO) and biliverdin/bilirubin have been shown to exert protective effects in several organs against oxidative and other noxious stimuli. In this context, it is interesting to note that induction of HO-1 expression by means of natural compounds contributes to protection against liver damage in various experimental models. The focus of this review is on the significance of targeted induction of HO-1 as a potential therapeutic strategy to protect the liver against various stressors in several pathological conditions.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.