Zinc, iron, and peroxidation in liver tissue. Cumulative effects of alcohol consumption and virus-mediated damage--a preliminary report

Protective effect of inducible aldo-keto reductases on 4-hydroxynonenal- induced hepatotoxicity

4-Hydroxynonenal (HNE), an end-product of lipid peroxidation generated in response to oxidative stress, has been implicated in the pathophysiology of chronic liver diseases. HNE is very reactive that forms Michael adducts with nucleophilic sites in DNA, lipids and proteins. At high concentrations, HNE causes rapid cell death associated with depletion of sulfhydryl groups and inhibition of key metabolic enzymes. At low concentrations, HNE stimulates expression of genes that are part of an adaptive response. In this study, we show that sub-lethal concentrations of HNE induce mRNA expression levels of heme oxygenase-1 (HO-1) (2.5-fold), NADPH:quinone oxidoreductase (NQO1) (4.5-fold), AKR1C3 (2-fold) and AKR7A2 (3-fold) enzymes. Protein expression levels of AKR1C and AKR7A2 are induced by 2- and 1.5-fold following exposure to HNE. The role of AKR1C3 and AKR7A2 in protecting HepG2 cells against HNE toxicity was investigated through using RNAi. Results show that AKR7A2, but not AKR1C3 contributes to the protection against HNE toxicity in HepG2 cells. Moreover, transcriptional factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2) is activated by HNE through translocation to the nucleus. Overexpressing AKR7A2 could rescue the effect of knocking down Nrf2 on HNE-induced cytotoxicity. Furthermore, a natural compound 7-hydroxycoumain, an AKR7A2 inducer, shows hepatoprotection against HNE via AKR7A2 induction. Hence, the inducible AKR7A2 has provided a new therapeutic target to treat chronic liver disease.

Plasma levels of trace elements have an implication on interferon treatment of children with chronic hepatitis B infection

This study evaluated the plasma levels of trace elements in children with chronic hepatitis B virus (HBV) infection and assessed whether they can be a factor that affects the response to interferon alpha (IFN-alpha) treatment. The study included 35 cases (ten girls, 25 boys) aged 3-13 years with chronic HBV infection and the control group. Plasma levels of copper (Cu), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn) were measured before IFN-alpha treatment and biochemical, virological, and histopathologic response to treatment were assessed. Children were followed for at least 15 months. Although plasma Cu levels showed no difference between the groups, Mn, Mo, Se, and Zn levels were significantly lower in the study group before treatment. Fourteen cases (40%) showed biochemical response; 17 (48.6%) showed virological response; 16 (47.6%) showed histopathologic response, and ten (28.6%) showed response according to all three parameters. Plasma Cu and Mn levels of patients with triple response showed no difference; but Mo, Se, and Zn levels were significantly lower (p < 0.001) in the study group. No difference was observed between responders and nonresponders (p > 0.05). Plasma levels of Mn, Mo, Se, and Zn are lower in children with chronic HBV infection compared to healthy children. The pretreatment levels of these elements did not show difference between responders and nonresponders to IFN-alpha.

Elevated serum ALT levels during pegylated interferon monotherapy may be caused by hepatic iron overload

OBJECTIVE

Persistently elevated serum alanine aminotransferase (ALT) levels have been observed in chronic hepatitis C (CHC) patients during pegylated interferon (PEG-IFN) therapy. We investigated whether elevated serum ALT levels during PEG-IFN therapy are associated with iron overload.

METHODS

Sixty-three CHC patients treated with PEG-IFNalpha-2a monotherapy were evaluated. The associations between elevated serum ALT levels (> or =70 IU/l) were investigated before and 24 weeks after therapy. We classified patients as follows: patients with no elevated serum ALT levels (group NE: n = 35), patients with elevated serum ALT levels (group E: n = 28), and patients with no elevated serum ALT level and negative HCV RNA (group NE-: n = 24), and patients with elevated serum ALT level and negative HCV RNA (group E-: n = 19). We also compared total iron score (TIS) and fibrosis stage in liver specimens obtained before and during therapy from 3 patients with elevated serum ALT levels.

RESULTS

Serum ferritin levels were significantly increased after 24 weeks compared to baseline levels in group E (218 +/- 273 vs. 438 +/- 308 ng/ml; p < 0.0001) and group E- (146 +/- 152 vs. 410 +/- 291 ng/ml; p < 0.0001). Serum ALT and ferritin levels were significantly correlated after 24 weeks. The liver specimens revealed that TIS and fibrosis progressed during therapy.

CONCLUSION

Our findings suggest that the elevation in serum ALT levels during therapy is caused by iron overload which may be induced by PEG-IFNalpha-2a.

Zinc and the liver: an active interaction

Zinc is an essential trace element, exerting important antioxidant, anti-inflammatory, and antiapoptotic effects. It affects growth and development and participates in processes such as aging and cancer induction. The liver is important for the regulation of zinc homeostasis, while zinc is necessary for proper liver function. Decreased zinc levels have been implicated in both acute and chronic liver disease states, and zinc deficiency has been implicated in the pathogenesis of liver diseases. Zinc supplementation offers protection in experimental animal models of acute and chronic liver injury, but these hepatoprotective properties have not been fully elucidated. In the present review, data on zinc homeostasis, its implication in the pathogenesis of liver diseases, and its effect on acute and chronic liver diseases are presented. It is concluded that zinc could protect against liver diseases, although up to now the underlying pathophysiology of zinc and liver interactions have not been defined.

Influence of zinc sulfate intake on acute ethanol-induced liver injury in rats

AIM: To investigate the role of metallothionein and proliferating cell nuclear antigen (PCNA) on the morphological and biochemical effects of zinc sulfate in ethanol-induced liver injury.

METHODS: Wistar albino rats were divided into four groups. Group I; intact rats, group II; control rats given only zinc, group III; animals given absolute ethanol, group IV; rats given zinc and absolute ethanol. Ethanol-induced injury was produced by the 1 mL of absolute ethanol, administrated by gavage technique to each rat. Animals received 100 mg/kg per day zinc sulfate for 3 d 2 h prior to the administration of absolute ethanol.

RESULTS: Increases in metallothionein immunoreactivity in control rats given only zinc and rats given zinc and ethanol were observed. PCNA immunohistochemistry showed that the number of PCNA-positive hepatocytes was increased significantly in the livers of rats administered ethanol + zinc sulfate. Acute ethanol exposure caused degenerative morphological changes in the liver. Blood glutathione levels decreased, serum alkaline phosphatase and aspartate transaminase activities increased in the ethanol group when compared to the control group. Liver glutathione levels were reduced, but lipid peroxidation increased in the livers of the group administered ethanol as compared to the other groups. Administration of zinc sulfate in the ethanol group caused a significant decrease in degenerative changes, lipid peroxidation, and alkaline phosphatase and aspartate transaminase activities, but an increase in liver glutathione.

CONCLUSION: Zinc sulfate has a protective effect on ethanol-induced liver injury. In addition, cell proliferation may be related to the increase in metallothionein immunoreactivity in the livers of rats administered ethanol + zinc sulfate.

Prevalence of liver steatosis in patients with chronic hepatitis B: a study of associated factors and of relationship with fibrosis

OBJECTIVES

The clinical significance of hepatic steatosis in chronic hepatitis B virus patients is poorly understood. The purpose of this study was to determine risk factors for liver steatosis in chronic hepatitis B patients and its relationship with fibrosis.

METHODS

We retrospectively evaluated liver biopsies from patients with chronic hepatitis B treated in our department. Patients co-infected with other viruses (hepatitis C virus, HIV) or suffering from liver disease of any other cause were excluded from the study, as well as patients consuming alcohol above 30 g/day for males or 20 g/day for females. Liver steatosis, necroinflammation and fibrosis were assessed.

RESULTS

A total of 233 patients with chronic hepatitis B were included in the study. The mean age was 44.7+/-16.2 years. There were 164 men (70.4%) and 69 women (29.6%). The majority of patients were HbeAg-negative, 196/233 (84.1%). Thirty-seven patients had cirrhosis (15.9%). Steatosis was present in 42 patients (18%). Steatosis was independently associated with fasting glucose level (P=0.019) and being overweight (body mass index >or=25; P=0.021). No correlation was found with stage of fibrosis, grade of inflammation, alcohol use or other parameters. Ninety-four out of 233 patients (40.3%) had advanced fibrosis. Patients with advanced fibrosis were older than those with minimal or no fibrosis (47.6+/-17 versus 42.3+/-15.2 years, P=0.024) and more frequently had a higher grade of necroinflammation activity (57/94 (60.6%) versus 26/139 (18.7%), P<0.0001). There was no significant association between advanced fibrosis and the presence of steatosis or mild alcohol consumption.

CONCLUSION

Hepatic steatosis is present in 18% of our patients with biopsy-proven chronic hepatitis B. Steatosis is independently associated only with body mass index and fasting glucose level, risk factors for metabolic steatohepatitis, and was not correlated with the degree of fibrosis.

Structure and dynamics of a predicted ferredoxin-like selenoprotein in Japanese encephalitis virus

Homologues of the selenoprotein glutathione peroxidase (GPx) have been previously identified in poxviruses and in RNA viruses including HIV-1 and hepatitis C virus (HCV). Sequence analysis of the NS4 region of Japanese encephalitis virus (JEV) suggests it may encode a structurally related but functionally distinct selenoprotein gene, more closely related to the iron-binding protein ferredoxin than to GPx, with three highly conserved UGA codons that align with essential Cys residues of ferredoxin. Comparison of the probe JEV sequence to an aligned family of ferredoxin sequences gave an overall 30.3% identity and 45.8% similarity, and was statistically significant at 4.9 S.D. (P < 10(-6)) above the average score computed for randomly shuffled sequences. A 3-dimensional model of the hypothetical JEV protein (JEV model) was constructed by homology modeling using SYBYL, based upon a high resolution X-ray structure of ferredoxin (PDB code: 1awd). The JEV model and the model from 1awd were subsequently subjected to molecular dynamics simulations in aqueous medium using AMBER 6. The solution structure of the JEV model indicates that it could fold into a tertiary structure globally similar to ferredoxin 1awd, with RMSD between the averaged structures of 1.8 A for the aligned regions. The modeling and MD simulations data also indicate that this structure for the JEV protein is energetically favorable, and that it could be quite stable at room temperature. This protein might play a role in JEV infection and replication via TNF and other cellular stimuli mediated via redox mechanisms.

Zinc treatment prevents lipid peroxidation and increases glutathione availability in Wilson's disease

Oxidative and reductive mechanisms are important in Wilson's disease. In this study, we sought to evaluate tissue levels of glutathione and cysteine, an important detoxification system, and of malondialdehyde, a marker of lipoperoxidation, in patients with Wilson's disease receiving penicillamine or zinc treatment, in comparison with patients with chronic liver disease of different origin. Concentrations of cysteine, reduced/oxidized glutathione, malondialdehyde, zinc, and copper were determined (with the use of high-pressure liquid chromatography, fluorimetry and atomic-absorption spectrophotometry) in liver-biopsy specimens from 24 patients with Wilson's disease (18 treated with zinc, 6 with penicillamine), 34 patients with chronic viral hepatitis, and 10 patients with alcoholic liver disease. In patients with Wilson's disease, the concentration of reduced glutathione was lower than that in patients with viral hepatitis and as high as that in subjects with alcoholic liver damage. The cysteine level was significantly lower than those in the control groups, and the percentage of oxidized glutathione/total glutathione was higher than that in viral or alcoholic disease. Malondialdehyde levels were low, but when zinc- and penicillamine-treated patients were considered separately, only the former had low malondialdehyde levels. Zinc-treated patients had higher concentrations of reduced glutathione and a lower percentage of oxidized glutathione. In summary, patients with Wilson's disease have relevant glutathione depression, with low levels of reduced glutathione and cysteine and high concentrations of oxidized glutathione: This is prevented by zinc administration, which inhibits lipid peroxidation and increases glutathione availability.

Enhanced hepatic lipid peroxidation in patients with primary biliary cirrhosis

OBJECTIVE

The mechanisms responsible for hepatic injury have not been fully clarified in primary biliary cirrhosis (PBC). It has recently been suggested that hepatic lipid peroxidation may be involved in the pathogenesis of PBC. The aims of the current study were to determine whether patients with PBC have evidence of enhanced hepatic lipid peroxidation and to evaluate its relationship to clinicopathological features.

METHODS

Immunohistochemical detection of 4-hydroxynonenal (HNE) protein adducts was performed in the liver biopsies of 20 patients with PBC. Histological stages of PBC were evaluated. Orcein or Victoria blue staining was performed for detection of copper-associated proteins. The size of bile ducts was defined as the smallest diameter between the subepithelial basement membranes.

RESULTS

All 20 patients had immunodetectable HNE protein adducts in the cytoplasm of damaged, but also intact, biliary cells. The mean diameter of bile ducts with HNE protein adducts was smaller than those without the adducts (61.0 +/- 1.9 vs 122.5 +/- 24.4 microm, respectively, p < 0.01). Out of 20 patients, 6 (30%) also had immunodetectable HNE protein adducts in hepatocytes preferentially located around the portal tracts. Most of the patients with hepatocytic HNE protein adducts had copper-associated protein granules in hepatocytes around the portal tracts and were classified as histological stage 3, whereas all of the patients without the adducts lacked copper-associated protein granules and were classified as histological stage 1 or 2. The patients with hepatocytic HNE protein adducts had higher levels of serum total bilirubin than did those without the adducts (2.9 +/- 0.9 vs 0.7 +/- 0.1 mg/dl, respectively, p < 0.01).

CONCLUSIONS

Hepatic lipid peroxidation can occur in PBC and may be an early event in bile duct destruction. At advanced stages of PBC, hepatocellular lipid peroxidation may play a role in hepatocyte injury during cholestasis.

Low hepatic iron concentration: evaluation of two complementary methods, colorimetric assay and iron histological scoring

AIMS

To validate a method of assessment of low hepatic iron concentration based on a biochemical colorimetric assay plus histological scoring.

METHODS

The within-day and day to day precision of the iron colorimetric assay was determined on frozen rat liver. The coefficient of variation (CV) of iron measurement in two separate samples from the same liver was determined for 21 deparaffinised human biopsies. The intra- and interlaboratory variability of the colorimetric assay and histological scoring were assessed on 38 deparaffinised liver biopsies.

RESULTS

For the within-day test, the CV was 11% (5.1 (0.6) mumol/g dry weight (dw), mean (SD) iron concentration). For the day to day test, the CV was 19.5% (8.2 (1.6) mumol/g dw). The CV was 14.7% for iron concentration determined in two separate samples from the same liver. By correlation and kappa concordance tests, the intra- and interlaboratory variability of the hepatic iron colorimetric assay and iron histological scoring was slight. Absence of stainable iron corresponded to a liver iron concentration < or = 20 mumol/g dw.

CONCLUSIONS

A combination of two complementary methods, colorimetric measurement and histological scoring, is an accurate and reliable way of determining low iron concentrations in deparaffinised human liver biopsies. In secondary haemosiderosis, such methods would be essential for investigating the role of low iron overload in fibrogenesis and during the response to antiviral treatment in chronic viral hepatitis.

Glutathione depletion is associated with decreased Bcl-2 expression and increased apoptosis in cholangiocytes

Cholangiocytes are the target of a group of liver diseases termed the cholangiopathies that include conditions characterized by periductal inflammation and cholangiocyte apoptosis. Because inflammation is associated with oxidative stress, we developed the hypothesis that cholangiocytes exposed to oxidative stress will be depleted of endogenous cytoprotective molecules, leading to cholangiocyte apoptosis. To begin to test this hypothesis, we explored the relationships among glutathione (GSH) depletion, expression of Bcl-2 (a protooncogene that inhibits apoptosis), and apoptosis in a nonmalignant human cholangiocyte cell line. Monolayers of human bile duct epithelial cells, derived from normal liver and immortalized by SV40 transformation, were depleted of GSH using buthionine sulfoximine (BSO). Bcl-2 expression was assessed by quantitative immunoblot analysis, and apoptosis quantified by fluorescence microscopy using the DNA binding dye 4', 6'-diamidino-2-phenylindole. Bcl-2 message was assessed by RNase protection assay, and Bcl-2 protein synthesis and half-life by pulse-chase analysis. Exposure of human cholangiocytes in culture to BSO reduced GSH levels by 93 +/- 3% (P < 0.01). In addition, treatment of cholangiocytes with BSO reduced Bcl-2 levels by 87 +/- 2% (P < 0.01) and was associated with a time-dependent increase in the number of cells undergoing apoptosis; approximately 11 +/- 1% of cultured cells demonstrated morphological changes of apoptosis by 72 h compared with 1.5 +/- 0.1% in untreated cholangiocytes (P < 0. 01). Maintenance of GSH levels by addition of glutathione ethyl ester in the presence of BSO blocked the BSO-associated increase in apoptosis in BSO-treated cholangiocytes and also prevented the decrease in Bcl-2 protein. BSO treatment of cholangiocytes did not change steady-state levels of bcl-2 mRNA or Bcl-2 protein synthesis. However, Bcl-2 protein half-life decreased 57% in BSO-treated vs. untreated cells. Our results using a human cholangiocyte cell line demonstrate that reduction in the cellular levels of an antioxidant such as GSH results in increased degradation of Bcl-2 protein and an increase in apoptosis. These data provide a mechanistic link between the consequences of oxidative stress and cholangiocyte apoptosis, an observation that may be important in the pathogenesis of the inflammatory cholangiopathies.

In situ detection of lipid peroxidation in chronic hepatitis C: correlation with pathological features

AIMS

To assess the occurrence of lipid peroxidation in chronic hepatitis C and to evaluate its relation to pathological features and liver iron concentrations.

METHODS

Liver biopsy samples of 43 patients with untreated chronic hepatitis C were studied by immunohistochemistry using specific antibodies directed against two major aldehyde metabolites of lipid peroxidation, malondialdehyde (MDA), and 4-hydroxynonenal (HNE).

RESULTS

MDA and HNE adducts (aldehydes covalently linked to another molecule) were detected in the liver samples in 77% and 30% of cases, respectively. MDA adducts were detected both in the extracellular matrix and sinusoidal cells localised in areas of periportal and lobular necrosis. HNE adducts appeared in the cytoplasm of only a few hepatocytes. Comparison of the semiquantitative assessment of adducts (MDA and HNE indexes) with the grading and the staging of chronic hepatitis showed that the MDA index was correlated with fibrosis score (p < 0.001) and the grade of activity (p < 0.01). There was also a tendency to correlation with liver iron concentration (p = 0.09). No correlation was observed between the HNE index and pathological features or liver iron concentration.

CONCLUSION

Lipid peroxidation products are detectable in the liver of chronic hepatitis C patients. The presence of MDA adducts in areas of active fibrogenesis and the correlation between the MDA index and fibrosis score suggest a role for lipid peroxidation in liver fibrosis.