3-nitrotyrosine and Carcinoma--Hepatocellular

One of the cancer hallmarks is mitochondrial dysfunction associated with oxidative stress. Among the first line of defense against oxidative stress is the dismutation of superoxide radicals, which in the mitochondria is carried out by manganese superoxide dismutase (MnSOD). Accordingly, carcinogenesis would be associated with a dysregulation in MnSOD expression. However, the association studies available so far are conflicting, and no direct proof concerning the role of MnSOD as a tumor promoter or suppressor has been provided. Therefore, we investigated the role of MnSOD in carcinogenesis by studying the effect of MnSOD deficiency in cells and in the livers of mice.. We found that loss of MnSOD in hepatoma cells contributed to their conversion toward a more malignant phenotype, affecting all cellular properties generally associated with metabolic transformation and tumorigenesis. In vivo, hepatocyte-specific MnSOD-deficient mice showed changed organ architecture, increased expression of tumor markers, and a faster response to carcinogenesis. Moreover, deficiency of MnSOD in both the in vitro and in vivo model reduced β-catenin and hypoxia-inducible factor-1α levels.. The present study shows for the first time the important correlation between MnSOD presence and the regulation of two major pathways involved in carcinogenesis, the Wnt/β-catenin and hypoxia signaling pathway.. Our study points toward a tumor suppressive role of MnSOD in liver, where the Wnt/β-catenin and hypoxia pathway may be crucial elements.

Topics: Animals; Carcinoma, Hepatocellular; Cell Hypoxia; Cell Proliferation; Cell Shape; Cell Transformation, Neoplastic; Diethylnitrosamine; Hep G2 Cells; Hepatocytes; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Liver Neoplasms, Experimental; Male; Mice, Knockout; Mitochondria; Reactive Oxygen Species; Superoxide Dismutase; Tyrosine; Wnt Signaling Pathway

Liver cancer, predominantly hepatocellular carcinoma (HCC), represents a complex and fatal malignancy driven primarily by oxidative stress and inflammation. Due to dismal prognosis and limited therapeutic intervention, chemoprevention has emerged as a viable approach to reduce the morbidity and mortality of HCC. Pomegranate fruit is a rich source of phytochemicals endowed with potent antioxidant and anti-inflammatory properties. We previously reported that pomegranate phytochemicals inhibit diethylnitrosamine (DENA)-initiated hepatocarcinogenesis in rats though nuclear factor E2-related factor 2 (Nrf2)-mediated antioxidant mechanisms. Since Nrf2 also acts as a key mediator of the nuclear factor-kappaB (NF-κB)-regulated inflammatory pathway, our present study investigated the anti-inflammatory mechanisms of a pomegranate emulsion (PE) during DENA-induced rat hepatocarcinogenesis. Rats were administered with PE (1 or 10 g/kg) 4 weeks before and 18 weeks following DENA initiation. There was a significant increase in hepatic expressions of inducible nitric oxide synthase, 3-nitrotyrosine, heat shock protein 70 and 90, cyclooxygenase-2 and NF-κB in DENA-exposed rat livers. PE dose-dependently suppressed all aforementioned elevated inflammatory markers. A conspicuous finding of this study involves lack of cardiotoxicity of PE as assessed by monitoring cardiac function using noninvasive echocardiography. Our results provide substantial evidence that suppression of the inflammatory cascade through modulation of NF-κB signaling pathway may represent a novel mechanism of liver tumor inhibitory effects of PE against experimental hepatocarcinogenesis. Data presented here coupled with those of our earlier study underline the importance of simultaneously targeting two interconnected molecular circuits, namely, Nrf2-mediated redox signaling and NF-κB-regulated inflammatory pathway, by pomegranate phytoconstituents to achieve chemoprevention of HCC.

Topics: Animals; Anticarcinogenic Agents; Carcinoma, Hepatocellular; Cyclooxygenase 2; Diethylnitrosamine; Echocardiography; Heart; HSP70 Heat-Shock Proteins; HSP90 Heat-Shock Proteins; Inflammation; Liver; Liver Neoplasms; Liver Neoplasms, Experimental; Lythraceae; Male; NF-kappa B; Nitric Oxide Synthase Type II; Plant Extracts; Rats; Rats, Sprague-Dawley; Tyrosine

Hepatocellular carcinoma (HCC), considered to be one of the most lethal cancers with almost > 1 million deaths reported annually worldwide, remains a devastating disease with no known effective cure. Hence, chemopreventive strategies come into play, offering an effective and safe mode of treatment, ideal to ward off potential cancer risks and mortality. A major predisposing condition, pertinent to the development and progression of HCC is oxidative stress. We previously reported a striking chemopreventive effect of anthocyanin-rich black currant skin extract (BCSE) against diethylnitrosamine (DENA)-initiated hepatocarcinogenesis in rats. The current study aims to elucidate the underlying antioxidant mechanisms of black currant anthocyanins implicated in the previously observed chemopreventive effects against experimental hepatocarcinogenesis. Dietary BCSE (100 and 500 mg/kg) administered four weeks before and 18 weeks after DENA challenge decreased abnormal lipid peroxidation, protein oxidation, and expression of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (3-NT) in a dose-responsive fashion. Mechanistic studies revealed that BCSE upregulated the gene expression of a number of hepatic antioxidant and carcinogen detoxifying enzymes, such as NAD(P)H:quinone oxidoreductase, glutathione S-transferase, and uridine diphosphate-glucuronosyltransferase isoenzymes, in DENA-initiated animals. Protein and mRNA expressions of nuclear factor E2-related factor 2 (Nrf2) were substantially elevated with BCSE treatment, providing a direct evidence of a coordinated activation of the Nrf2-regulated antioxidant pathway, which led to the upregulation of a variety of housekeeping genes. The results of our study provide substantial evidence that black currant bioactive anthocyanins exert chemopreventive actions against DENA-inflicted hepatocarcinogenesis by attenuating oxidative stress through activation of Nrf2 signaling pathway.

Topics: Alkylating Agents; Animals; Anthocyanins; Antioxidants; Blotting, Western; Carcinoma, Hepatocellular; Diet; Diethylnitrosamine; Glutathione Transferase; Immunoenzyme Techniques; Lipid Peroxidation; Liver Neoplasms, Experimental; Male; NF-E2-Related Factor 2; Nitric Oxide Synthase Type II; Oxidative Stress; Phytotherapy; Rats; Rats, Sprague-Dawley; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; Ribes; RNA, Messenger; Signal Transduction; Tyrosine

The aim of this study was to determine the effect of bicyclol against cisplatin-induced hepatotoxicity and the influence on the antitumour capacity of cisplatin in hepatocarcinoma 22 (H22) tumour-bearing mice. ICR mice were treated with bicyclol (250 mg/kg, orally) 2 hr before the injection of cisplatin (5 mg/kg, intraperitoneally) for 5 days (once daily) after H22 tumour cells were implanted. All animals were killed on the fifth day after cisplatin treatment and tumour weight of each animal was measured. Liver pathological changes were examined by light microscopy and biochemical assay. The expressions of liver inducible nitric oxide synthase (iNOS and nitric oxide synthase 2) and 3-nitrotyrosine were assessed by Western blotting. Bicyclol showed a significant protection as evidenced by the decrease of elevated serum aminotransferases and lactate dehydrogenase, and improvement of histopathological injury induced by cisplatin. The formation of liver malondialdehyde with a concomitant reduction of reduced glutathione was also inhibited by bicyclol, while the activities of liver superoxide dismutase, catalase and glutathione peroxidase were all increased, respectively. In addition, the over expressions of liver iNOS and 3-nitrotyrosine were suppressed by bicyclol. The administration of bicyclol had no affect on the anti-tumour capacity of cisplatin in mice bearing H22 tumour. The hepatoprotective action of bicyclol provides a new approach for preventing the hepatotoxicity induced by cisplatin in the clinic.

Topics: Animals; Antineoplastic Agents; Biphenyl Compounds; Blotting, Western; Carcinoma, Hepatocellular; Cell Line, Tumor; Chemical and Drug Induced Liver Injury; Cisplatin; Drug Interactions; Gene Expression Regulation; L-Lactate Dehydrogenase; Liver; Liver Diseases; Liver Neoplasms, Experimental; Male; Mice; Mice, Inbred ICR; Nitric Oxide Synthase Type II; Transaminases; Tyrosine

In addition to serving as a biomarker of oxidative/nitrative stress, elevated levels of nitrotyrosine have been shown to cause DNA damage or trigger apoptosis. Whether the body is equipped with mechanisms for protecting against the potentially harmful nitrotyrosine remains unknown. The present study was designed to investigate the possibility that sulfation serves as a pathway for the metabolism/regulation of nitrotyrosine. Using metabolic labelling, nitrotyrosine O-[35S]sulfate was found to be produced and released into the medium of HepG2 human hepatoma cells labelled with [35S]sulfate in the presence of nitrotyrosine. To identify the enzyme(s) responsible for nitrotyrosine sulfation, a systematic study of all eleven known human cytosolic SULTs (sulfotransferases) was performed. Of the 11 enzymes tested, only SULT1A3 displayed sulfating activity toward nitrotyrosine. The pH-dependence and kinetic constants of SULT1A3 with nitrotyrosine or dopamine as substrate were determined. To examine whether the sulfation of nitrotyrosine occurs in the context of cellular physiology, HepG2 cells labelled with [35S]sulfate were treated with SIN-1 (morpholinosydnonimine), a peroxynitrite generator. Increments of nitrotyrosine O-[35S]sulfate were detected in the medium of HepG2 cells treated with higher concentrations of SIN-1. To gain insight into the physiological relevance of nitrotyrosine sulfation, a time-course study was performed using [3H]tyrosine-labelled HepG2 cells treated with SIN-1. The findings confirm that the bulk of free [3H]nitrotyrosine inside the cells was present in the unconjugated form. The proportion of sulfated [3H]nitrotyrosine increased dramatically in the medium over time, implying that sulfation may play a significant role in the metabolism of free nitrotyrosine.

Topics: Arylsulfotransferase; Carcinoma, Hepatocellular; Cell Line, Tumor; Dopamine; Humans; Kinetics; Molsidomine; Sulfotransferases; Tyrosine

We recently developed a sensitive method using biotin-N-maleimide (biotin-NM) as a probe to positively identify oxidized mitochondrial proteins. In this study, biotin-NM was used to identify oxidized cytosolic proteins in alcohol-fed mouse livers. Alcohol treatment for 6 wk elevated the levels of CYP2E1 and nitrotyrosine, a marker of oxidative stress. Markedly increased levels of oxidized proteins were detected in alcohol-fed mouse livers compared to pair-fed controls. The biotin-NM-labeled oxidized proteins from alcohol-exposed mouse livers were subsequently purified with streptavidin-agarose and resolved on 2-DE. More than 90 silver-stained protein spots that displayed differential intensities on 2-D gels were identified by MS. Peptide sequence analysis revealed that many enzymes or proteins involved in stress response, chaperone activity, intermediary metabolism, and antioxidant defense systems such as peroxiredoxin were oxidized after alcohol treatment. Smaller fragments of many proteins were repeatedly detected only in alcohol-fed mice, indicating that many oxidized proteins after alcohol exposure were degraded. Immunoblot results showed that the level of oxidized peroxiredoxin (inactivated) was markedly increased in the alcohol-exposed mouse livers and ethanol-sensitive hepatoma cells compared to the corresponding controls. Our results may explain the underlying mechanism for cellular dysfunction and increased susceptibility to other toxic agents following alcohol-mediated oxidative stress.

Topics: Animals; Bacterial Proteins; Biomarkers, Tumor; Biotin; Carcinoma, Hepatocellular; Central Nervous System Depressants; Computational Biology; Cytochrome P-450 CYP2E1; Cytosol; Electrophoresis, Gel, Two-Dimensional; Ethanol; Liver; Liver Extracts; Liver Neoplasms; Male; Mice; Mice, Inbred C57BL; Oxidation-Reduction; Peroxidases; Peroxiredoxins; Sepharose; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Tyrosine

Chronic ethanol consumption causes increased oxidative damage in the liver. Induction of CYP2E1 is one pathway involved in how ethanol produces oxidative stress. Ethanol can cause protein accumulation, decreased proteolysis, and decreased proteasome activity. The objective of this study was to investigate the effect of inhibition of the proteasome activity on CYP2E1-dependent toxicity. HepG2 cells over-expressing CYP2E1 (E47 cells) were treated with arachidonic acid (AA) plus iron, agents important in development of alcoholic liver injury and which are toxic to E47 cells by a mechanism dependent on CYP2E1, oxidative stress, and lipid peroxidation. Addition of various proteasome inhibitors was associated with significant potentiation of the loss of cell viability caused by AA plus iron. Potentiation of toxicity was associated with increased oxidative damage as reflected by an increase in lipid peroxidation and accumulation of oxidized and nitrated proteins in E47 cells and an enhanced decline in mitochondrial membrane potential. Antioxidants prevented the loss of viability and the potentiation of this loss of viability by proteasome inhibition. CYP2E1 levels were elevated about 3-fold by the proteasome inhibitors. Inhibition of proteasome activity also potentiated toxicity of AA alone and toxicity after treatment to remove glutathione (GSH). Similar results were found in hepatocytes from pyrazole-treated rats with high levels of CYP2E1. In conclusion, proteasome activity plays an important role in modulating CYP2E1-mediated toxicity in HepG2 cells by regulating CYP2E1 levels and by removal of oxidized proteins. Such interactions may be important in CYP2E1-catalyzed toxicity of hepatotoxins and in alcohol-induced liver injury.

Topics: Antioxidants; Arachidonic Acid; Buthionine Sulfoximine; Carcinoma, Hepatocellular; Cysteine Endopeptidases; Cytochrome P-450 CYP2E1; Drug Synergism; Endopeptidases; Humans; Iron; Leupeptins; Lipid Peroxides; Liver Neoplasms; Lysosomes; Membrane Potentials; Mitochondria, Liver; Multienzyme Complexes; Proteasome Endopeptidase Complex; Tumor Cells, Cultured; Tyrosine

Human liver cancers have been associated mainly with chronic inflammations such as viral hepatitis B or C. This suggests that prolonged cell damage by chronic inflammation is critical in cancer development. Overproduction of nitric oxide (NO.) and its derivative (NOx, peroxynitrite) has been implicated as a cause of tissue damage by inflammation, thus contributing to tumor promotion. We have demonstrated the expression of the inducible isoform of nitric oxide synthase (iNOS) and 3-nitrotyrosine, a marker of peroxynitrite formation, by immunohistochemistry in preneoplastic and neoplastic rat liver tissues induced by continuous infusion of N-nitrosodiethylamine with mini-pumps. The preneoplastic lesions were characterized by proliferation of phenotypically altered hepatic foci (PAHF), dysplastic hepatocytes and oval cells. Histologically, the tumors were hepatocellular carcinomas (HCCs) of trabecular, (pseudo)glandular and solid types with or without cholangiocellular involvement. iNOS was located mainly in oval cells, capillary endothelial and muscular cells, epithelia of cholangiomas and glandular HCCs. 3-Nitrotyrosine was observed in the cytoplasms of PAHF and dysplastic hepatocytes in preneoplasias and in the cytoplasms of some living or apoptotic HCC cells, connective tissues, proteinaceous fluids, sinusoidal endothelia of tumorous hepatocytes and cholangiomas in tumors. From these observations, we suggest that: (i) chronic tissue damage by chemical carcinogens may act to induce iNOS and peroxynitrite formation; (ii) oval cells play a key role in development and/or growth of tumor tissues by producing NO. via iNOS, which may also cause tissue damage by peroxynitrite; (iii) iNOS can be considered as a phenotypic marker in cells of oval cell lineage and neovascularized capillaries in tumor tissues.

Topics: Adenoma, Bile Duct; Animals; Apoptosis; Carcinoma, Hepatocellular; Diethylnitrosamine; Immunohistochemistry; Liver; Liver Neoplasms; Male; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Precancerous Conditions; Rats; Rats, Inbred F344; Rats, Sprague-Dawley; Tyrosine