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Biomedical subjects

Masaaki Korenaga

Publications and source records attributed to Masaaki Korenaga.

9 recordsLinked to original sources
PubMed2006

Hepatitis C virus core protein inhibits deoxycholic acid-mediated apoptosis despite generating mitochondrial reactive oxygen species.

BACKGROUND: Hepatitis C virus (HCV) core protein is known to cause oxidative stress and alter apoptosis pathways. However, the apoptosis results are inconsistent, and the real significance of oxidative stress is not well known. The aim of this study was twofold. First, we wanted to confirm whether core-induced oxidative stress was really significant enough to cause DNA damage, and whether it induced cellular antioxidant responses. Second, we wanted to evaluate whether this core-induced oxidative stress and the antioxidant response to it was responsible for apoptosis changes. METHODS: HCV core protein was expressed under control of the Tet-Off promoter in Huh-7 cells and HeLa cells. We chose to use deoxycholic acid (DCA) as a model because it is known to produce both reactive oxygen species (ROS) and apoptosis. RESULTS: Core expression uniformly increased ROS and 8-hydroxy-2'-deoxyguanosine (8-OHdG) under basal and DCA-stimulated conditions. Core protein expression also increased manganese superoxide dismutase levels. Core protein inhibited DCA-mediated mitochondrial membrane depolarization and DCA-mediated activation of caspase-9 and caspase-3, despite the increase in ROS by DCA. Core protein inhibited DCA-mediated apoptosis by increasing Bcl-x(L) protein and decreasing Bax protein, without affecting the proportion of Bax between mitochondria and cytosol, resulting in suppression of cytochrome c release from mitochondria into cytoplasm. CONCLUSIONS: HCV core protein induces oxidative DNA damage, whereas it inhibits apoptosis that is accompanied by enhancement of ROS production. Thus, oxidative stress and apoptosis modulation by core protein are independent of each other.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2006

Hepatic iron overload induces hepatocellular carcinoma in transgenic mice expressing the hepatitis C virus polyprotein.

BACKGROUND & AIMS: Despite the evidence of hepatic iron overload in patients with chronic hepatitis C, it remains unknown if iron overload is related to hepatocarcinogenesis in this condition. The aim of this study was to determine whether iron overload contributes to development of hepatocellular carcinoma (HCC) in transgenic mice expressing the hepatitis C virus (HCV) polyprotein. METHODS: Male C57BL/6 transgenic mice expressing the HCV polyprotein and nontransgenic littermates were fed an excess-iron diet or control diet. Mice in each group were assessed for altered liver morphology and function and the development of liver tumors. RESULTS: Hepatic iron concentrations in mice fed the excess-iron diet were comparable to those of patients with chronic hepatitis C. There was no inflammation in transgenic and nontransgenic livers. Compared with mice in 3 other groups, transgenic mice fed the excess-iron diet showed marked hepatic steatosis including the centrilobular microvesicular type, ultrastructural alterations of the mitochondria and decreased degradation activity of fatty acid at 6 months, and greater hepatic content of lipid peroxidation products and 8-hydroxy-2'-deoxyguanosine at 12 months after initiation of feeding. The number of proliferating hepatocytes was significantly increased in mice fed the excess-iron diet but was not different between transgenic and nontransgenic mice. Hepatic tumors including HCC developed in 5 of 11 (45%) transgenic mice fed the excess-iron diet but not in mice in other groups at 12 months after initiation of feeding. CONCLUSIONS: Iron overload induces mitochondrial injury and increases the risk of HCC development in transgenic mice expressing the HCV polyprotein.

Animals↗
PubMed2006

[Insulin sensitizer--anti-diabetic drugs, metformin and pioglitazone that can improve insulin resistance].

Nonalcoholic steatohepatitis (NASH), which is considered the hepatic manifestation of the metabolic syndrome is an increasingly cause of chronic liver disease in Japan. NASH is finally lead to liver cirrhosis and hepatocellular carcinoma as viral hepatitis, therefore, medical treatment should be considered, when NASH occurs. Treatment of patients with metabolic syndrome has been focused on the management of associated conditions such as obesity, hyperlipidemia, hypertension and hyperinsulinemia. Insulin resistance, that could accelerate liver inflammation and fibrosis by up-regulation of TNFa seems to be most important factor in many cases of NASH. The insulin-sensitizing drugs, which were biguanides (metformin) and thiazolidinediones (pioglitazone) have been shown to correct not only insulin resistance but also steatosis and inflammation in the liver. Metformin and pioglitazone might be useful drugs against NASH, however further investigations were needed.

Fatty Liver↗
PubMed2005

Hepatitis C virus core protein inhibits mitochondrial electron transport and increases reactive oxygen species (ROS) production.

Hepatitis C infection causes a state of chronic oxidative stress, which may contribute to fibrosis and carcinogenesis in the liver. Previous studies have shown that expression of the HCV core protein in hepatoma cells depolarized mitochondria and increased reactive oxygen species (ROS) production, but the mechanisms of these effects are unknown. In this study we examined the properties of liver mitochondria from transgenic mice expressing HCV core protein, and from normal liver mitochondria incubated with recombinant core protein. Liver mitochondria from transgenic mice expressing the HCV proteins core, E1 and E2 demonstrated oxidation of the glutathione pool and a decrease in NADPH content. In addition, there was reduced activity of electron transport complex I, and increased ROS production from complex I substrates. There were no abnormalities observed in complex II or complex III function. Incubation of control mitochondria in vitro with recombinant core protein also caused glutathione oxidation, selective complex I inhibition, and increased ROS production. Proteinase K digestion of either transgenic mitochondria or control mitochondria incubated with core protein showed that core protein associates strongly with mitochondria, remains associated with the outer membrane, and is not taken up across the outer membrane. Core protein also increased Ca(2+) uptake into isolated mitochondria. These results suggest that interaction of core protein with mitochondria and subsequent oxidation of the glutathione pool and complex I inhibition may be an important cause of the oxidative stress seen in chronic hepatitis C.

Animals↗
PubMed2005

Hepatitis C virus core protein, cytochrome P450 2E1, and alcohol produce combined mitochondrial injury and cytotoxicity in hepatoma cells.

BACKGROUND & AIMS: Alcohol consumption exacerbates liver injury in chronic hepatitis C, and enhanced mitochondrial oxidative stress is one possible mechanism. The aim of this study was to determine whether hepatitis C virus core protein and alcohol-inducible cytochrome P450 2E1 contribute to reactive oxygen species production and cytotoxicity in human hepatoma cells. METHODS: Huh-7 cells expressing core protein, cytochrome P450 2E1, or both were exposed to 0.1 mmol/L tertiary butyl hydroperoxide, tumor necrosis factor alpha, and/or 25 mmol/L ethanol. Cytotoxicity, reactive oxygen species production, glutathione content, and mitochondrial membrane potential were measured. RESULTS: Expression of core/cytochrome P450 2E1 synergistically enhanced cell death induced by either tertiary butyl hydroperoxide or tumor necrosis factor alpha. After tertiary butyl hydroperoxide treatment, total reactive oxygen species production was increased more than 3-fold compared with cells that did not express core and cytochrome P450 2E1. Mitochondrial depolarization and reduced glutathione depletion occurred as well, and cell death was prevented by inhibition of mitochondrial permeability transition or caspase activity. Confocal microscopy showed that the mitochondria themselves were the origin of the reactive oxygen species. In the absence of core/cytochrome P450 2E1 expression, mitochondrial changes and cell death did not occur. Ethanol treatment further decreased mitochondrial reduced glutathione content and exacerbated mitochondrial reactive oxygen species production, depolarization, and cell death. All these effects were prevented by the antioxidant N -acetylcysteine. CONCLUSIONS: Mitochondrial reactive oxygen species production is induced by hepatitis C virus core and cytochrome P450 2E1, resulting in a reduction of mitochondrial antioxidant capacity and sensitivity to oxidants and tumor necrosis factor alpha. Alcohol further depletes mitochondrial reduced glutathione, which exacerbates depolarization and cell death. Sensitization of mitochondria to oxidative insults is thus a potential mechanism for alcohol-related exacerbation of liver injury in chronic hepatitis C.

Alcohols↗
PubMed2005

Mitochondrial dysfunction in hepatitis C.

Chronic hepatitis C induces a state of hepatic oxidative stress that is more pronounced than that present in many other inflammatory liver diseases. This review summarizes recent information that the hepatitis C virus (HCV) core protein plays an important role in this phenomenon. Core protein localizes to mitochondria, particularly at the points of contact between mitochondrial outer membrane and endoplasmic reticulum. Its expression causes inhibition of electron transport at complex I, increased complex I reactive oxygen species (ROS) production, decreased mitochondrial glutathione, and increased mitochondrial permeability transition in response to exogenous oxidants and tumor necrosis factor-alpha. Possible mechanisms of the core protein effects include direct interaction with electron carriers and indirect effects mediated by changes in mitochondrial calcium. These results suggest that antioxidant approaches may prove beneficial for patients with chronic hepatitis C.

Hepacivirus↗
PubMed2003

Hepatic expression of type I interferon receptor for predicting response to interferon therapy in chronic hepatitis C patients: a comparison of immunohistochemical method vs. competitive polymerase chain reaction assay.

The focus of this study is to determine both mRNA and protein expression levels of the type I interferon (IFN) receptor subunits, IFNalpha receptor (IFNAR1) and IFNalpha/beta receptor (IFNAR2), in the liver, and to assess which quantification method is most useful in predicting response to IFN in chronic hepatitis C patients. Liver biopsy specimens from 41 chronic hepatitis C patients subsequently treated with IFN were immunostained with IFNAR1 and IFNAR2 antibodies, and also analyzed for both receptor subunit mRNA levels, using competitive polymerase chain reaction. Immunostaining of IFNAR1 and IFNAR2 was observed in the cell membrane and cytoplasm of hepatocytes in all liver specimens. Hepatic expression of IFNAR1 (r=0.45, P=0.012) or IFNAR2 mRNA (r=0.46, P=0.009) was weakly correlated with their protein expression in hepatocytes. The labeling indexes of IFNAR1 (136.7+/-94.1 vs. 77.4+/-76.8, P=0.032) and IFNAR2 (153.1+/-80.2 vs. 87.2+/-75.5, P=0.011) in liver specimens were significantly higher in sustained virologic responders (n=17) than in non-sustained virologic responders (n=24), while mRNA levels of either receptor subunit did not differ between response groups. These results suggest that protein expression of the type I IFN receptor in liver is a more useful measure than its mRNA expression in predicting response to IFN in chronic hepatitis C patients.

Journal Article↗
PubMed2003

Hepatitis C virus infection upregulates expression of the type I interferon receptor in human peripheral blood mononuclear cells.

To assess whether hepatitis C virus infection (HCV) affects type I interferon (IFN) receptor expression, the expression levels of two subunits of this receptor, IFNAR1 and IFNAR2, in peripheral blood mononuclear cells (PBMCs) were determined by flow-cytometric assay in 68 anti-HCV antibody-positive patients (47 positive for HCV RNA and 21 negative for HCV RNA) and 14 healthy controls. The percentages of IFNAR1- and IFNAR2-expressing cells were significantly higher in HCV RNA-positive patients than in HCV RNA-negative patients or healthy controls. In multiple regression analysis, the presence of HCV RNA in serum was independently associated with the expression of both IFNAR1 and IFNAR2 in PBMCs (P=0.007 for IFNAR1 and P=0.003 for IFNAR2). The frequency of IFN-gamma-producing peripheral CD4(+) and CD8(+) cells was also significantly higher in HCV RNA-positive patients than in HCV RNA-negative patients or healthy controls and there was a significant correlation between IFN receptor expression and the frequency of IFN-gamma-producing cells. These results suggest that HCV infection upregulates the expression of the type I IFN receptor in PBMCs through enhanced IFN-gamma production by peripheral CD4(+) and CD8(+) cells as one of mechanisms that regulate the expression of the type I IFN receptor.

Journal Article↗