Oxidative stress in viral and alcoholic hepatitis

Free Radical Biology & Medicine, Vol. 34, No. 1, pp. 1–10, 2003 Copyright © 2002 Elsevier Science Inc. Printed in the USA. All rights reserved 0891-5849/02/$–see front matter

PII S0891-5849(02)01167-X

Serial Review: Reactive Oxygen and Nitrogen in Inflammation Guest Editor: Giuseppe Poli OXIDATIVE STRESS IN VIRAL AND ALCOHOLIC HEPATITIS CARMELA LOGUERCIO

and

ALESSANDRO FEDERICO

Gastroenterology School, 2nd University of Naples, and Inter-University Research Center of Alimentary Intake, Nutrition and Digestive Tract (CIRANAD), Naples, Italy (Received 7 February 2002; Revised 18 June 2002; Accepted 9 September 2002)

Abstract—Liver damage ranges from acute hepatitis to hepatocellular carcinoma, through apoptosis, necrosis, inflammation, immune response, fibrosis, ischemia, altered gene expression and regeneration, all processes that involve hepatocyte, Kupffer, stellate, and endothelial cells. Reactive oxygen and nitrogen species (ROS, RNS) play a crucial role in the induction and in the progression of liver disease, independently from its etiology. They are involved in the transcription and activation of a large series of cytokines and growth factors that, in turn, can contribute to further production of ROS and RNS. The main sources of free radicals are represented by hepatocyte mitochondria and cytochrome P450 enzymes, by endotoxin-activated macrophages (Kupffer cells), and by neutrophils. The consequent alteration of cellular redox state is potentiated by the correlated decrease of antioxidant and energetic reserves. Indices of free radical-mediated damage, such as the increase of malondialdehyde, 4-hydroxynonenal, protein-adducts, peroxynitrite, nitrotyrosine, etc., and/or decrease of glutathione, vitamin E, vitamin C, selenium, etc., have been documented in patients with viral or alcoholic liver disease. These markers may contribute to the monitoring the degree of liver damage, the response to antiviral therapies and to the design of new therapeutic strategies. In fact, increasing attention is now paid to a possible “redox gene therapy.” By enhancing the antioxidant ability of hepatocytes, through transgene vectors, one could counteract oxidative/nitrosative stress and, in this way, contribute to blocking the progression of liver disease. © 2002 Elsevier Science Inc. Keywords—Viral hepatitis, Alcohol, Antioxidants, Liver disease, Free radicals

INTRODUCTION

As a consequence, a large number of studies have focused on the pathogenetic significance of oxidative and nitrosative stress in liver injury as well as on therapeutic intervention with antioxidant and metabolic scavengers [1– 8].

Liver injury is a worldwide common pathology, both acute and chronic, quite often characterized in its chronic evolution by a progressive process from steatosis to hepatocellular carcinoma (HCC), through chronic hepatitis, fibrosis, and cirrhosis. Main etiology is represented by alcohol abuse and viral infection (HBV, HDV, and HCV). Other factors that could be simultaneously present, such as iron load, drugs, more than one virus infection, alteration of lipid and carbohydrate metabolism, etc., may exacerbate liver disease. Of note, in all types of liver damage there is consistent evidence of enhanced production of free radicals and/or significant decrease of antioxidant defense.

OXIDATIVE/NITROSATIVE STRESS IN THE LIVER

Mitochondria and cytochrome P450 enzymes are the main sources of reactive oxygen species (ROS) in hepatocytes acutely and/or chronically exposed to a “toxic” injury (environmental drugs, alcohol, therapeutical drugs, viruses, etc.). ROS also derive from Kupffer and inflammatory cells, in particular neutrophils. In hepatocytes, ROS may play a role in a very large cascade of reactions, such as Ca⫹⫹ accumulation, circulatory status and transport function, nitric oxide (NO) synthesis and metabolism, cytokine gene expression, caspase activity, growth factor synthesis and activity, DNA fragmenta-

Address correspondence to: Prof. Carmela Loguercio, Cattedra di Gastroenterologia II Universita` di Napoli, Via Pansini 5, 80131 Napoli, Italy; Tel: ⫹0039-81-5666718; Fax: ⫹0039-81-5666837; E-Mail: [email protected]. 1

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tion, Na⫹ influx, etc. Hence, a significant and sufficiently steady increase of ROS production leads to perturbation of the normal redox state and of the metabolism of the cell, with consequent impairment of various cell functions and activities, possibly until irreversible damage. The onset of liver damage depends on the length of the “toxic” insult. The consistent evidence of an increase level of malondialdehyde (MDA), 4-hydroxynonenal (4HNE), protein-adducts, etc. on liver and blood samples from patients with different degrees of chronic liver disease, supports the in vivo role of ROS as mediators of liver damage [9 –15]. More recently, ROS were also identified as involved in the response to interferon (IFN) therapy by patients with chronic HCV infection [16 –18]. ROS, in particular superoxide anion, rapidly react with nitric oxide (NO) to form peroxynitrite, that may act as a dangerous molecule by influencing some SH-related enzyme activities and by cooperating to induce membrane lipid peroxidation. The formation of peroxynitrite may also be considered as a “protective pathway” because through this mechanism NO acts as scavenger of ROS. Liver contains different forms of NO-synthase: the neuronal form (nNOS) in the peribiliar plexus; the inducible form (iNOS) in hepatocytes, cholangiocytes, Kupffer, and stellate cells; and the endothelial form (eNOS) in the endothelial cells. Liver iNOS is primarily regulated at the transcriptional level by cytokines and ROS, but NO could also derive directly from cytokineactivated neutrophils and/or lymphocytes in the circulation. NO is also regenerated by the reaction of glutathione (GSH) with peroxynitrite. Through the nitrosylation of free thiol groups, NO is stabilized by forming adducts, both directly and by the action of glutathione-S-transferase (GST) on GSH and organic nitrites. These reversible addition products act as the endogenous source, storage, and transport of NO in cells and circulation [1,19 –23]. In the liver, NO may have a protective role by maintaining perfusion and inhibiting thrombosis and apoptosis, but it still contributes to liver necrosis, immunomediated liver damage, and to DNA fragmentation by blocking mitochondrial function and depleting cellular pyridine nucleotides [24 –26]. In patients with chronic HCV infection, a direct correlation has been documented recently between iNOS induction and hepatitis C virus ribonucleic acid (HCV-RNA) titer, as well among hepatocyte nitrotyrosine, plasma nitrosothiols (S-NO) and histological severity of liver damage. Therefore, in addition to the “oxidative stress,” also the “nitrosative stress” may have a relevant role in the pathogenesis of chronic viral hepatitis [27–32]. Alcohol-related liver damage partly depends on endotoxin-mediated Kupffer cells activation, with second-

ary production of proinflammatory cytokines, which induce iNOS expression. In these conditions, NO may reduce or even enhance the toxicity of ethanol by interfering with the activity of some alcohol-metabolizing enzymes [33,34]. It has been outlined recently that the toxic or protective function of this molecule is dependent on the entity of ROS production, as well as the amount of cell antioxidants, in particular GSH. Low levels of ROS and high content of GSH facilitate the protective effects of NO. In these conditions, NO inhibits lipid peroxidation and liver necrosis. In opposite conditions, i.e., high levels of ROS and low GSH, NO can be deleterious, by enhancing lipid peroxidation and apoptosis [1,2,6,23]. Hepatocytes contain about 10% of total body pool of GSH [35]. A normal homeostasis of this tripeptide is necessary for the activity of the cytochrome P450 enzyme system and of mitochondria, for the “traffic” from cytoplasm and nucleus and finally for the maintenance of a normal cellular redox status. GSH also affects the transcription of proinflammatory/anti-inflammatory cytokine genes, liver regeneration through cytokine-mediated nuclear factor ␬ binding (NF-␬B) induction, NO bioavailability, and energy metabolism. By inducing GSH depletion, ROS induce oxidative stress and reduce the antioxidant capability of other antioxidants [36 –39]. Depletion of GSH may also be a consequence of liver damage. Indeed, a large literature documented the decrease of GSH in liver and circulation in patients with alcoholic and viral cirrhosis, and, more recently, in those with HCV-related chronic hepatitis. In this last group the bioavailability of GSH influences both the entity of liver apoptosis and necrosis and the response to antiviral therapies [13–15,40 – 44]. Other antioxidant systems are involved in the induction and progression of chronic liver damage. In rats, ethanol significantly alters the GSH-peroxidase system by contributing to mitochondria dysfunction [45]. Particularly in presence of vitamin E, superoxide dismutase (SOD) is a primary defense mechanism against the damaging effect of ROS. In experimental animals, the induction by diet and alcohol of a SOD-catalase insensitive free radical species facilitates liver damage [46,47]. Selenium also represents a protective agent against lipid peroxidation, liver injury, and HCC, and its circulating levels are decreased in cirrhotic patients, in which also a decrease of retinol serum levels is associated to the risk of HCC. It has recently been suggested that measurement of plasma levels of GSH, vitamin A, ␤-carotene, SOD, GSH-peroxidase, catalase, and markers of lipid peroxidation may represent a useful marker to monitor the progression of liver damage and the response to therapy in patients with viral and alcoholic disease [48 –55]. The GST family represents one of the main detoxifying sys-

0.12 ⫾ 0.02* 6.6 ⫾ 0.5 0.13 ⫾ 0.03* 6.8 ⫾ 0.4 0.16 ⫾ 0.02 6.7 ⫾ 0.9 0.18 ⫾ 0.03 6.2 ⫾ 0.7

* p ⬍ .05 and ** p ⬍ .01 vs. controls. Values are mean ⫾ SD. See references [13–15,30,40,41,54,55,59 – 61]. GSH ⫽ glutathione; CYS ⫽ cysteine; MDA ⫽ malondialdehyde; LPO ⫽ lipoperoxides; ␥GCs ⫽ gamma-glutamylcysteine synthetase; GSHs ⫽ glutathione synthetase; S-NO ⫽ nitroso-thiols; ␣GST ⫽ glutathione-S-transferase alpha.

0.09 ⫾ 0.01* 6.9 ⫾ 0.3

45 ⫾ 9*

182 ⫾ 76 18.4 ⫾ 7.2* 0.06 ⫾ 0.01* 0.8 ⫾ 0.3* 30.6 ⫾ 12.4* 48 ⫾ 12*

190 ⫾ 91 12.2 ⫾ 6.2* 0.07 ⫾ 0.04* 0.7 ⫾ 0.2* 43.5 ⫾ 3.8** 35 ⫾ 4

210 ⫾ 68 62.8 ⫾ 24.6** 0.8 ⫾ 0.02* 0.9 ⫾ 0.2* 45 ⫾ 12** 28 ⫾ 5 30 ⫾ 4

165 ⫾ 49 7.4 ⫾ 1.5 0.10 ⫾ 0.01 1.1 ⫾ 0.1 ⱕ8

0.65 ⫾ 0.04 22.3 ⫾ 4.0 20.6 ⫾ 13.5 270 ⫾ 65

185 ⫾ 38 27.9 ⫾ 8.4** 0.12 ⫾ 0.03 1.2 ⫾ 0.1 57.4 ⫾ 16.2**

2.1 ⫾ 1.3* 15 ⫾ 2.9 0.38 ⫾ 0.05* .33 ⫾ 0.10* 1.27 ⫾ 0.12 24.6 ⫾ 2.4* 230 ⫾ 58 1.1 ⫾ 0.3* 140 ⫾ 28 0.37 ⫾ 0.03* 0.40 ⫾ 0.08* 1.17 ⫾ 0.15* 0.27 ⫾ 0.02* 68 ⫾ 14* 2.0 ⫾ 1.0* 10 ⫾ 2.9* 0.39 ⫾ 0.04* 0.34 ⫾ 0.10* 1.16 ⫾ 0.16* 21.5 ⫾ 1.4* 280 ⫾ 67 1.9 ⫾ 0.4* 80 ⫾ 25* 0.40 ⫾ 0.04* 0.37 ⫾ 0.06* 1.18 ⫾ 0.14* 0.27 ⫾ 0.03* 60 ⫾ 6.5* 2.7 ⫾ 1.2* 12 ⫾ 7.5 0.38 ⫾ 0.04* 0.35 ⫾ 0.03* 1.14 ⫾ 0.12* 28.4 ⫾ 2.9* 300 ⫾ 50 4.2 ⫾ 3.0 26 ⫾ 8 0.29 ⫾ 0.05 0.28 ⫾ 0.02

4.7 ⫾ 0.2 21 ⫾ 5 0.21 ⫾ 0.01 0.24 ⫾ 0.02 1.29 ⫾ 0.12 0.54 ⫾ 0.03 21 ⫾ 5

GSH (nmol/ml) CYS (nmol/ml) MDA (nmol/ml) LPO (nmol/ml) ␥GCs (nmol/ml) GSHs (nmol/ml) Glutamic acid (nmol/ml) Glycine (nmol/ml) S-NO (␮M/l) Selenium (␮g/ml) Zinc (␮g/ml) ␣GST (ng/ml)

8.5 ⫾ 2.6 17 ⫾ 4.1 0.26 ⫾ 0.33 0.28 ⫾ 0.02 1.28 ⫾ 0.16 12.6 ⫾ 6.8 219 ⫾ 70

8.0 ⫾ 2.0 14 ⫾ 5.2 .24 ⫾ 0.05 0.27 ⫾ 0.04

E P E P E P E P

Chronic Hepatitis Controls

Oxidative and nitrosative stress initiate and regulate the transcription and activation of a large series of other mediators in all liver cells, which culminate in common mechanisms of liver damage: apoptosis, necrosis, inflammation, immune response, fibrosis, ischemia, altered gene expression, and regeneration. The prevalence and the persistence of one or more of these aspects may influence the occurrence of the different types of liver diseases. Enhanced production of ROS and altered GSH pool contribute to death programs by activating the gene expression of transcription factors such as NF-␬B, leading to upregulation of proinflammatory cytokines (IL-1␤, IL-6, IL-18, etc.), chemokines, adhesion molecules, Fas ligands, survival genes, etc., which consecutively activate the cascade of caspases [apoptosis] or induce the release of cytochrome c and the depletion of ATP at mitochondrial level (necrosis) [2,39,62,63]. GSH-dependent mechanisms are also required for the expression of protective signaling proteins and transcriptional factors such as those of Bcl-2 family [38]. The link between oxidative stress and apoptosis is documented by the antiapoptotic effect of some antioxidants, such as n-acetyl-cysteine and thioredoxin [64,65]. The induction of the cytochrome P450 enzyme system, the endotoxin-induced cytokine expression in Kupffer cells and the neutrophil infiltration further enhance the production of ROS and deplete ATP reserves in hepatocytes. In fact, ROS generated from neutrophils, migrate into the hepatocytes and potentiate the shift of apoptosis to necrosis. [66]. Another contribution to cell death derives from the adhesion of cytotoxic lymphocytes, that release proteases (granzymes) and perforin from cytotoxic granules, particularly in presence of ROS, which mediate the interaction lymphocyte-Fas/Fas ligands [67]. In different known clinical conditions, such as diabetes, obesity, exposition to toxic agents, drugs, ethanol, and HCV infection, but also in unknown, fatty liver represents the first step of chronic liver damage. The induction of CYP2E1 and of other CYP enzymes,

Table 1. Data of Our Group on Plasma (P) and Erythrocyte (E) Samples

FROM OXIDATIVE/NITROSATIVE STRESS TO LIVER DAMAGE AND CLINICAL DISEASE OUTCOMES

Alcoholics Without Cirrhosis

Alcoholic Cirrhosis

P

Viral Cirrhosis

E

tems in the hepatocytes, because these enzymes bind GSH with a large series of hydroperoxides, toxic substances, etc. GST regulates apoptosis by influencing the lipid peroxidation pathway [56]. Ethanol and virus infections cause a liver induction of GST and their plasma variations are a good predictive response index to IFN therapy [57– 61]. Table 1 summarizes the data of our group on a series of markers of oxidative and nitrosative stress in various types of chronic liver damage (see [13–15,30,40,41,54,55,59– 61]).

3 1.5 ⫾ 0.3* 75 ⫾ 18* 0.42 ⫾ 0.04* 0.38 ⫾ 0.04* 1.23 ⫾ 0.07 0.37 ⫾ 0.03 68 ⫾ 13*

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through an increased production of ROS, membrane lipid peroxidation and ATP depletion, promotes the progression of fatty liver to steatohepatitis, and therefore fibrosis and cirrhosis [68 –71]. It has been well known for many years that oxidative damage is a substrate for fibrogenesis [72]. Fibrosis, always defined as a “passive” and irreversible chronic liver damage, is now considered a dynamic process, in part reversible [73]. During a chronic liver insult, hepatic stellate cells are activated and assume the typology of active fibroblasts, particularly those next to necrotic areas. ROS generated by CYP2E1 in hepatocytes, but also by Kupffer and inflammatory cells, TGF-␤ activation, 4-HNE, cytokines, GSH depletion, directly and/or indirectly increase procollagen type 1 gene expression and synthesis (for a review see [74]). The persistence of profibrogenic factors, the progressive decrease of antioxidant reserves, the dysfunction of liver microcirculation through NO-mediated pathways, determine the shift to liver regeneration and cirrhosis. In this context, the activation of several CYP forms directly takes part in the carcinogenesis process because of the metabolic activation of procarcinogens to reactive, DNA-binding intermediates, and the quenching or inhibition of oxidative stress-related pathways may be suggested as a mechanism to arrest cancer cell proliferation [75]. Role of viral hepatitis In viral hepatitis, cellular damage is predominantly determined by the immune response and, although the pathophysiology is very complex, there are a very large number of data demonstrating that the persistence of infection, the progression of liver damage and carcinogenesis are all steps in which oxidative-mediated pathways are involved [76]. Immunohistochemical analyses in biopsies from patients with acute hepatitis demonstrated the expression of vascular cell adhesion molecules ICAM-1, ELAM-1, and VCAM-1 and T-cell homing receptor in sinusoids and areas of parenchymal necrosis. This supports the understanding of cytokine-induced upregulation of adhesiveness and recruitment of cytotoxic CD8⫹ lymphocytes, with subsequent T-cell mediated cell death through the release of cytotoxic substances such as perforin and proteases (granzymes) or the induction of apoptosis via the FAS/Apo-1/CD 95 receptor system and mitochondrial dysfunction [77]. Viral infection promotes apoptosis (in human liver diseases Councilman bodies are the expression of apoptosis). By this way the virus can inhibit or reduce the host immune response and therefore allow viral replication and propagation. X protein of HBV and HCV core regulates apoptosis through TNF-␣, TGF-␤, IFN-␥, and

IL-2 pathways; these cytokines also affect the progression of liver damage to chronicity. On the contrary, the immune-mediated response of Th0/Th1 cytokines, such as IL-4 and IL-10, protects from the persistence of viruses and the appearance of fibrosis [78,79]. In vitro, the adhesion of HBV antigen depends on oxidative stress; the intracellular pathways that inhibit HBV gene expression and replication are mediated by IFN-␥ and TNF-␣, which also activate the post-transcriptional degradation of viral RNA in the nucleus. Both HCV and HBV are able to induce, via IFN-␥, hepatic iNOS, which mediates cellular damage through the production of TNF-␣ and IL-␤ [27,28]. Role of ethanol The big “love” between ethanol and liver is due to the fact that more than 80% of ingested ethanol is metabolized in the liver, without a feedback mechanism. In an early phase, oxygen and NO-radicals derive from the complete oxidation of ethanol, and acetaldehyde in excess markedly alters the intracellular redox status, induces fat deposits, triggers the inflammatory and immune response [80] (see Fig. 1). The increased generation of mitochondrial oxidants, secondary to ROS-mediated membrane perturbation, is firstly utilized from healthy hepatocytes to activate the oxidantsensitive transcription factors (such as NF-␬B, antiapoptotic proteins Bfl-1 and Bcl-xl or SOD) that limit the entity of apoptosis. Even when the adaptation is successful, hepatocytes are extremely susceptible to other insults that partially depolarize the mitochondrial membranes, until collapse, facilitating ATP and GSH depletion [81– 83]. In a last phase the cytokine-mediated (particularly increase of TNF-␣ and decrease of IL-10) oxidative/nitrosative stress depends on endotoxin-activated Kupffer cells. A genetically induced insufficient production of TNF-␣ and the use of intestinal antibiotics that decrease Kupffer cells activation, actually prevent alcohol-related liver damage in animals [84]. In alcoholic patients there is a direct relationship among cytokine production, degree of liver damage and survival; based on this evidence, recent therapies are aimed to inhibit TNF-␣ actions [81,85– 87]. The progression of liver damage is also affected by the generation of addition products between acetaldehyde and cytochrome c oxidase and/or P450 2E1 [88,89]. Excessive production of ROS, depletion of GSH and ATP, adducts with acetaldehyde, rise of lipid peroxidation markers, are all documented findings in alcoholics [7,12–15,69,85,89]. Role of cofactors The interaction between viruses and ethanol significantly affects viral replication and potentiates the appear-

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Fig. 1. Pathophysiology of ethanol-induced liver damage.

ance and the progression of liver damage via oxidative/ nitrosative stress [90,91]. Females are more susceptible than males to development of alcohol-related liver damage. In female animals, activity of P450-system including CYP2E1 and phagocytosis are reduced, estrogens increase endotoxin in the circulation and CD14-expression in the liver, the transcription factor NF-␬B is more sensitive to oxidative stress, the expression of ICAM-1 protein, the lipid binding to protein and the production of ROS and TNF-␣ and IL-6 increase, with a consequent more marked inflammation and fibrosis [92–96]. The different body composition between male and female affects the pharmacocynetic and therefore the distribution and bioavailability of ethanol, and it is currently known that the expression of TNF-␣ and other cytokines is related to the quantity of adipose tissue. This influences the degree of fat accumulation in the liver [97–99]. In old rats ethanol causes enhanced oxidative damage and structural integrity of mitochondrial DNA, while in human liver, age affects the cytochrome P450 system [74,100]. Iron and other metals potentiate liver damage, particularly in presence of ethanol or HCV infection [3,5,74]. Food available for human consumption contains molecules (lipid, DNA, proteins, vitamins, and carbohydrates) that are susceptible to the oxidative damage [101]. In rats, a reduction of dietary carbohydrate intake, affecting CYP2E1 activity, accelerates the progression of ethanol-mediated liver damage. Rats fed with diets high in polyunsaturated fatty acids or low vitamin E show a

more marked ethanol-induced liver damage while a diet enriched with cholesterol prevents necrosis and inflammation, but enhances fibrosis. A high-fat diet enhances the expression of GSH-synthesizing enzymes in the liver, but it is unable to restore GSH content in presence of ethanol. On the contrary, olive oil reduces the entity of lipid peroxidation and therefore liver damage [102–106]. In humans, the role of dietary lipids on the progression of alcoholic liver disease is debated, while low vegetable consumption is a risk factor for the appearance of HCC [107,108]. Our group recently documented that, in early stage of HCV-related chronic liver disease, the overexpression of a protein p53 is significantly affected by ethanol and quality of foods [109]. SHOULD THE MODULATION OF OXIDATIVE OR NITROSATIVE STRESS MODIFY THE NATURAL HISTORY OF LIVER DAMAGE?

Antioxidants, both natural and synthetic, have been proposed and utilized as therapeutic agents in liver damage. In vitro and in vivo, activation of Kupffer cells, collagen gene expression, HBV and HCV replication, are counteracted by N-acetyl-cysteine, ␣-tocopherol, phenols, selenium, vitamin C and E, etc. [110 –119]. Antioxidants deriving from plants, such as Sylibum marianum, Salvia milthiorriza, Psyllantus amarum, etc. have been proposed in the treatment of viral and alcoholic liver diseases [120 –124]. Indeed, antioxidant drugs such as GSH, S-adenosylmethionine, sylimarin, vitamin E, N-acetyl-cysteine, ur-

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sodeoxycholic acid, etc. reduce oxidative and nitrosative stress, increase GSH pool, improve the activity of P450enzymes, and therefore counteract the progression of liver disease in liver patients [125–129]. More recently, the antioxidant treatment of liver disease was focused on NO pathway, cytokine expression and on “redox gene therapy.” NO donors have been suggested for their immunoregulatory ability on Th1-like cytokine production [74,130]. NO may also be endogenously enhanced through the use of adenovirus transgene vectors or a gene transfer of recombinant NOsynthases [131,132]. Gene delivery of antioxidant enzymes (particularly of SOD) and the use of retroviral vectors, as well as the induction of detoxifying enzymes such as GST and catalases are actually a promising new approach to attenuate intrahepatic inflammatory and fibrotic processes [133–135]. Anti-TNF-␣ and caspase antibodies, singularly used or associated to IFN and ribavirine treatment, are able to reduce fibrosis [136 – 139].

[8]

[9]

[10]

[11]

[12]

[13]

CONCLUSIONS [14]

The actual knowledge on the various steps that initiate and regulate the progression of liver damage clearly demonstrates that both hepatitis viruses and ethanol cause a marked perturbation of the cellular redox status, with consequent oxidative and nitrosative stress. Oxygen and NO radicals may affect the respiratory, energetic, and regenerative pathways in hepatocytes, the proinflammatory/anti-inflammatory cytokine imbalance in inflammatory and immune cells, the expression of collagen genes, and angiogenesis in stellate and endothelial cells. On the basis of these data, a high number of recent investigations are aimed at discovering treatments that could restore the antioxidant potential of cells and therefore improve liver damage and/or prevent liver cirrhosis and HCC.

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ABBREVIATIONS

ATP—adenosine triphosphate CD— cluster of differentiation

CYP— cytochrome P450 DNA— deoxyribonucleic acid ELAM— endothelial/leukocyte adhesion molecule eNOS— endothelial form GSH— glutathione GSNO—nitrosoglutathione GST— glutathione-S-transferase HBV— hepatitis B virus HCC— hepatocellular carcinoma HCV— hepatitis C virus HCV-RNA— hepatitis virus C ribonucleic acid HDV— hepatitis D virus 4-HNE— 4-hydroxynonenal ICAM—intercellular adhesion molecule IFN—interferon IL—interleukin iNOS—inducible form LPO—lipoperoxides MDA—malondialdehyde NF-␬B—nuclear factor ␬ binding nNOS—neuronal form NO—nitric oxide NOS—NO-synthase PDGF—platelet-derived growth factor ROS—reactive oxygen species S-NO—nitrosothiols SOD—superoxide dismutase TGF—transforming growth factor Th—T helper TNF—tumor necrosis factor VCAM—viral cell adhesion molecule