Up-regulation of CD14 in liver caused by acute ethanol involves oxidant-dependent AP-1 pathway

Phorbal-12-mysristate-13-acetate-induced inflammation is restored by protectin DX through PPARγ in human promonocytic U937 cells

AIMS

Protectin DX (PDX), a specialized pro-resolving mediator, is an important pharmaceutical compound with potential antioxidant and inflammation-resolving effects. However, the fundamental mechanism by which PDX's ameliorate chronic inflammatory diseases has not yet been elucidated. This study aims to evaluate the anti-inflammatory properties and PPARγ-mediated mechanisms of PDX in phorbal-12-mysristate-13-acetate (PMA)-stimulated human promonocytic U937 cells.

MAIN METHODS

We confirmed the effects of PDX on expressions of pro-inflammatory cytokines, mediators, and CD14 using conventional PCR, RT-qPCR, ELISA, and flow cytometry. Using western blotting, immunofluorescence, and reactive oxygen species (ROS) determination, we observed that PDX regulated PMA-induced signaling cascades. Molecular docking analysis and a cellular thermal shift assay were conducted to verify the interaction between PDX and the proliferator-activated receptor-γ (PPARγ) ligand binding domain. Western blotting was then employed to explore the alterations in PPARγ expression levels and validate PDX as a PPARγ full agonist.

KEY FINDINGS

PDX attenuated protein and mRNA expression levels of interleukin-6, tumor necrosis factor-α, and cyclooxygenase-2 in PMA-treated U937 cells. PDX acts as a PPARγ agonist, exerting a modulating effect on the ROS/JNK/c-Fos signaling pathways. Furthermore, PDX reduced human monocyte differentiation antigen CD14 expression levels.

SIGNIFICANCE

PPARγ exhibits pro-resolving effects to regulate the excessive inflammation. These results suggest that PDX demonstrates the resolution of inflammation, indicating the potential for therapeutic targeting of chronic inflammatory diseases.

Molecular insights on intracellular Wnt/β-catenin signaling in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the most common health problems worldwide, especially in developing countries caused by chronic consumption of alcohol on a daily basis. The ALD spectrum is initiated with the early stages of alcoholic fatty liver (steatosis), progressing to alcoholic steatohepatitis, followed by the later stages of fibrosis and in some cases, cirrhosis and hepatocellular carcinoma (HCC). The Wnt/β-catenin signaling required for healthy liver development, function, and regeneration is found to be aberrated in ALD, attributed to its progression. This review is to elucidate the association of Wnt/β-catenin signaling with various stages of ALD progression. Alcohol causes downregulation of Wnt/β-catenin signaling components and thereby suppressing the pathway. Reports have been published that aberrated Wnt/β-catenin signaling, especially the absence of β-catenin, results in decreased alcohol metabolism, causing steatosis followed by steatohepatitis via lipid accumulation, lipid peroxidation, liver injury, increased oxidative stress and apoptosis of hepatocytes, contributing to the advancement of ALD. Contrastingly, the progression of later stages of ALD like fibrosis and HCC depends on the increased activation of Wnt/β-catenin signaling and its components. Existing studies reveal the varied expression of Wnt/β-catenin signaling in ALD. However, the dual role of the Wnt/β-catenin pathway in earlier and later stages of ALD is not clear. Therefore, studies on the Wnt/β-catenin pathway and its components in various manifestations of ALD might provide insight in targeting the Wnt/β-catenin pathway in ALD treatment.

Ambiguous Pathogenic Roles of Macrophages in Alcohol-Associated Liver Diseases

Alcohol-associated liver disease (ALD) represents a major public health issue worldwide and is a leading etiology of liver cirrhosis. Alcohol-related liver injuries include a range of manifestations including alcoholic hepatitis (AH), simple steatosis, steatohepatitis, hepatic fibrosis, cirrhosis and liver cancer. Liver disease occurs from several pathological disturbances such as the metabolism of ethanol, which generates reactive oxygen species (ROS) in hepatocytes, alterations in the gut microbiota, and the immune response to these changes. A common hallmark of these liver affections is the establishment of an inflammatory environment, and some (broad) anti-inflammatory approaches are used to treat AH (eg, corticosteroids). Macrophages, which represent the main innate immune cells in the liver, respond to a wide variety of (pathogenic) stimuli and adopt a large spectrum of phenotypes. This translates to a diversity of functions including pathogen and debris clearance, recruitment of other immune cells, activation of fibroblasts, or tissue repair. Thus, macrophage populations play a crucial role in the course of ALD, but the underlying mechanisms driving macrophage polarization and their functionality in ALD are complex. In this review, we explore the various populations of hepatic macrophages in alcohol-associated liver disease and the underlying mechanisms driving their polarization. Additionally, we summarize the crosstalk between hepatic macrophages and other hepatic cell types in ALD, in order to support the exploration of targeted therapeutics by modulating macrophage polarization.

Ethanol Metabolism in the Liver, the Induction of Oxidant Stress, and the Antioxidant Defense System

The liver metabolizes ethanol through three enzymatic pathways: alcohol dehydrogenase (ADH), cytochrome p450 (also called MEOS), and catalase. Alcohol dehydrogenase class I (ADH1) is considered the most important enzyme for the metabolism of ethanol, MEOS and catalase (CAT) are considered minor alternative pathways. However, contradicting experiments suggest that the non-ADH1 pathway may have a greater relevance for the metabolism of ethanol than previously thought. In some conditions, ethanol is predominately metabolized to acetaldehyde via cytochrome P450 family 2 (CYP2E1), which is involved in the generation of reactive oxygen species (ROS), mainly through electron leakage to oxygen to form the superoxide (O₂^•−) radical or in catalyzed lipid peroxidation. The CAT activity can also participate in the ethanol metabolism that produces ROS via ethanol directly reacting with the CAT-H₂O₂ complex, producing acetaldehyde and water and depending on the H₂O₂ availability, which is the rate-limiting component in ethanol peroxidation. We have shown that CAT actively participates in lactate-stimulated liver ethanol oxidation, where the addition of lactate generates H₂O₂, which is used by CAT to oxidize ethanol to acetaldehyde. Therefore, besides its known role as a catalytic antioxidant component, the primary role of CAT could be to function in the metabolism of xenobiotics in the liver.

Combined alcoholic and non-alcoholic steatohepatitis

While metabolic syndrome and alcohol consumption are the two main causes of chronic liver disease, one of the two conditions is often predominant, with the other acting as a cofactor of morbimortality. It has been shown that obesity and alcohol act synergistically to increase the risk of fibrosis progression, hepatic carcinogenesis and mortality, while genetic polymorphisms can strongly influence disease progression. Based on common pathogenic pathways, there are several potential targets that could be used to treat both diseases; based on the prevalence and incidence of these diseases, new therapies and clinical trials are needed urgently.

Complements are involved in alcoholic fatty liver disease, hepatitis and fibrosis

The complement system is a key component of the body's immune system. When abnormally activated, this system can induce inflammation and damage to normal tissues and participate in the development and progression of a variety of diseases. In the past, many scholars believed that alcoholic liver disease (ALD) is induced by the stress of ethanol on liver cells, including oxidative stress and dysfunction of mitochondria and protease bodies, causing hepatocyte injury and apoptosis. Recent studies have shown that complement activation is also involved in the genesis and development of ALD. This review focuses on the roles of complement activation in ALD and of therapeutic intervention in complement-activation pathways. We intend to provide new ideas on the diagnosis and treatment of ALD.

Alcohol Modulation of the Postburn Hepatic Response

The widespread and rapidly increasing trend of binge drinking is accompanied by a concomitant rise in the prevalence of trauma patients under the influence of alcohol at the time of their injury. Epidemiological evidence suggests up to half of all adult burn patients are intoxicated at the time of admission, and the presence of alcohol is an independent risk factor for death in the early stages post burn. As the major site of alcohol metabolism and toxicity, the liver is a critical determinant of postburn outcome, and experimental evidence implies an injury threshold exists beyond which burn-induced hepatic derangement is observed. Alcohol may lower this threshold for postburn hepatic damage through a variety of mechanisms including modulation of extrahepatic events, alteration of the gut-liver axis, and changes in signaling pathways. The direct and indirect effects of alcohol may prime the liver for the second-hit of many overlapping physiologic responses to burn injury. In an effort to gain a deeper understanding of how alcohol potentiates postburn hepatic damage, the authors summarize possible mechanisms by which alcohol modulates the postburn hepatic response.

Role of cytokines and chemokines in alcohol-induced tumor promotion

Excessive chronic alcohol consumption has become a worldwide health problem. The oncogenic effect of chronic alcohol consumption is one of the leading concerns. The mechanisms of alcohol-induced tumorigenesis and tumor progression are largely unknown, although many factors have been implicated in the process. This review discusses the recent progress in this research area with concentration on alcohol-induced dysregulation of cytokines and chemokines. Based on the available evidence, we propose that alcohol promotes tumor progression by the dysregulation of the cytokine/chemokine system. In addition, we discuss specific transcription factors and signaling pathways that are involved in the action of these cytokines/chemokines and the oncogenic effect of alcohol. This review provides novel insight into the mechanisms of alcohol-induced tumor promotion.

Potential Role of the Gut/Liver/Lung Axis in Alcohol-Induced Tissue Pathology

Both Alcoholic Liver Disease (ALD) and alcohol-related susceptibility to acute lung injury are estimated to account for the highest morbidity and mortality related to chronic alcohol abuse and, thus, represent a focus of intense investigation. In general, alcohol-induced derangements to both organs are considered to be independent and are often evaluated separately. However, the liver and lung share many general responses to damage, and specific responses to alcohol exposure. For example, both organs possess resident macrophages that play key roles in mediating the immune/inflammatory response. Additionally, alcohol-induced damage to both organs appears to involve oxidative stress that favors tissue injury. Another mechanism that appears to be shared between the organs is that inflammatory injury to both organs is enhanced by alcohol exposure. Lastly, altered extracellular matrix (ECM) deposition appears to be a key step in disease progression in both organs. Indeed, recent studies suggest that early subtle changes in the ECM may predispose the target organ to an inflammatory insult. The purpose of this chapter is to review the parallel mechanisms of liver and lung injury in response to alcohol consumption. This chapter will also explore the potential that these mechanisms are interdependent, as part of a gut-liver-lung axis.

A Central Role for JNK/AP-1 Pathway in the Pro-Oxidant Effect of Pyrrolidine Dithiocarbamate through Superoxide Dismutase 1 Gene Repression and Reactive Oxygen Species Generation in Hematopoietic Human Cancer Cell Line U937

Pyrrolidine dithiocarbamate (PDTC) known as antioxidant and specific inhibitor of NF-κB was also described as pro-oxidant by inducing cell death and reactive oxygen species (ROS) accumulation in cancer. However, the mechanism by which PDTC indices its pro-oxidant effect is unknown. Therefore, we aimed to evaluate the effect of PDTC on the human Cu/Zn superoxide dismutase 1 (SOD1) gene transcription in hematopoietic human cancer cell line U937. We herein show for the first time that PDTC decreases SOD1 transcripts, protein and promoter activity. Furthermore, SOD1 repression by PDTC was associated with an increase in oxidative stress as evidenced by ROS production. Electrophoretic mobility-shift assays (EMSA) show that PDTC increased binding of activating protein-1 (AP-1) in dose dependent-manner suggesting that the MAPkinase up-stream of AP-1 is involved. Ectopic NF-κB p65 subunit overexpression had no effect on SOD1 transcription. In contrast, in the presence of JNK inhibitor (SP600125), p65 induced a marked increase of SOD1 promoter, suggesting that JNK pathway is up-stream of NF-κB signaling and controls negatively its activity. Indeed, using JNK deficient cells, PDTC effect was not observed nether on SOD1 transcription or enzymatic activity, nor on ROS production. Finally, PDTC represses SOD1 in U937 cells through JNK/c-Jun phosphorylation. Taken together, these results suggest that PDTC acts as pro-oxidant compound in JNK/AP-1 dependent-manner by repressing the superoxide dismutase 1 gene leading to intracellular ROS accumulation.

Alcoholic liver disease: mechanisms of injury and targeted treatment

Alcoholic liver disease (ALD) is a complex process that includes a wide spectrum of hepatic lesions, from steatosis to cirrhosis. Cell injury, inflammation, oxidative stress, regeneration and bacterial translocation are key drivers of alcohol-induced liver injury. Alcoholic hepatitis is the most severe form of all the alcohol-induced liver lesions. Animal models of ALD mainly involve mild liver damage (that is, steatosis and moderate inflammation), whereas severe alcoholic hepatitis in humans occurs in the setting of cirrhosis and is associated with severe liver failure. For this reason, translational studies using humans and human samples are crucial for the development of new therapeutic strategies. Although multiple attempts have been made to improve patient outcome, the treatment of alcoholic hepatitis is still based on abstinence from alcohol and brief exposure to corticosteroids. However, nearly 40% of patients with the most severe forms of alcoholic hepatitis will not benefit from treatment. We suggest that future clinical trials need to focus on end points other than mortality. This Review discusses the main pathways associated with the progression of liver disease, as well as potential therapeutic strategies targeting these pathways.

An alteration of the gut-liver axis drives pulmonary inflammation after intoxication and burn injury in mice

Approximately half of all adult burn patients are intoxicated at the time of their injury and have worse clinical outcomes than those without prior alcohol exposure. This study tested the hypothesis that intoxication alters the gut-liver axis, leading to increased pulmonary inflammation mediated by burn-induced IL-6 in the liver. C57BL/6 mice were given 1.2 g/kg ethanol 30 min prior to a 15% total body surface area burn. To restore gut barrier function, the specific myosin light chain kinase inhibitor membrane-permeant inhibitor of kinase (PIK), which we have demonstrated to reduce bacterial translocation from the gut, was administered 30 min after injury. Limiting bacterial translocation with PIK attenuated hepatic damage as measured by a 47% reduction in serum alanine aminotransferase (P < 0.05), as well as a 33% reduction in hepatic IL-6 mRNA expression (P < 0.05), compared with intoxicated and burn-injured mice without PIK. This mitigation of hepatic damage was associated with a 49% decline in pulmonary neutrophil infiltration (P < 0.05) and decreased alveolar wall thickening compared with matched controls. These results were reproduced by prophylactic reduction of the bacterial load in the intestines with oral antibiotics before intoxication and burn injury. Overall, these data suggest that the gut-liver axis is deranged when intoxication precedes burn injury and that limiting bacterial translocation in this setting attenuates hepatic damage and pulmonary inflammation.

Depletion of Kupffer cells modulates ethanol-induced hepatocyte DNA synthesis in C57Bl/6 mice

Kupffer cells (KCs) are important in hepatic homeostasis and responses to xenobiotics. KCs are activated on interaction with endotoxin, releasing cytokines, and reactive oxygen species normally associated with increased gene expression, cellular growth, or hepatic injury. Ethanol-induced endotoxemia is one means of KC activation. We propose that KC depletion attenuates the effect of EtOH-induced endotoxemia to impact the hepatic growth response. Hepatic DNA synthesis was examined in KC competent (KC+) or KC-depleted (KC-) C57BL/6 mice fed EtOH-containing diet in the presence or absence of polyphenol-60 antioxidant. KC depletion was assessed by F4/80 antigen, and DNA synthesis was assessed by 5-bromo-2'-deoxyuridine incorporation. Tumor necrosis factor alpha (TNF-α) messenger RNA released was quantified by RT-PCR/electrophoresis. ERK1/2 phosphorylation was evaluated by Western blotting, and Nrf2 and CYP2E1protein were also assayed. Apoptosis and hepatic injury were examined by the Tunnel assay and hepatic transaminases in serum, respectively. Hepatic transaminases in serum (AST and ALT) were within normal range. Over 90% of KC was depleted by clodronate treatment. KC depletion decreased TNF-α mRNA release, ERK1/2 phosphorylation, and hepatocyte DNA synthesis. KC depletion is associated with increased numbers of apoptotic cells bodies in KC- mice. Antioxidant treatment decreased DNA synthesis, Nrf2, and CYP2E1 protein expression in EtOH-consuming mice. Our data indicate that upon ethanol exposure, KC participates in hepatic DNA synthesis and growth responses. Collectively, these observations suggest that KC depletion attenuates the downstream effect of ethanol-induced endotoxemia by reduced cytokine and reactive oxygen species production with its concomitant effect on MAPK-signaling pathway on hepatocyte DNA synthesis.

Chinese medicinal formula, Qinggan Huoxue Recipe protects rats from alcoholic liver disease via the lipopolysaccharide-Kupffer cell signal conduction pathway

The Chinese medicinal formula, Qinggan (QG) Huoxue (HX) Recipe (R) exerts a range of pharmacological effects, including reversible steatosis, decreased levels of inflammatory cytokines and lipid peroxidation resistance. The aim of the present study was to determine the specific mechanisms of QGHXR hepatoprotection through the lipopolysaccharide-Kupffer cell (LPS-KC) signal conduction pathway in rats with alcoholic liver disease (ALD). ALD rats were exposed to the compound factors, QGR and HXR. Hematoxylin and eosin staining was conducted to evaluate the pathological changes in the liver following QGHXR treatment and an enzyme-linked immunosorbent assay was performed to measure the content of tumor necrosis factor (TNF)-α in the plasma. Immunohistochemical staining was conducted to examine the expression of cell differentiation antigen (CD) 68 and 14. In addition, western blot analysis and reverse transcription-polymerase chain reaction were used to measure the expression of Toll-like receptor 4 (TLR4), phosphorylated-extracellular regulated protein kinases (p-ERK), nuclear factor (NF)-κB, CD14 and TNF-α. Following stimulation with the compound factors, the rats exhibited increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, as well as marked pathological changes. Furthermore, the related molecules in the LPS-KC pathway were upregulated and QGHXR was identified to be effective in the LPS-KC signal conduction pathway in the ALD rats. QGHXR was superior to QGR and HXR in reducing the serum ALT and AST levels, regulating CD14, TLR4, NF-κB, ERK and TNF-α as well as improving the pathological changes. The results indicated that QGHXR therapy may provide a novel strategy for treating ALD via regulation of the related molecules in the LPS-KC signaling pathway.

Elevated activation of ERK1 and ERK2 accompany enhanced liver injury following alcohol binge in chronically ethanol-fed rats

BACKGROUND

Binge drinking after chronic ethanol consumption is one of the important factors contributing to the progression of steatosis to steatohepatitis. The molecular mechanisms of this effect remain poorly understood. We have therefore examined in rats the effect of single and repeat ethanol binge superimposed on chronic ethanol intake on liver injury, activation of mitogen-activated protein kinases (MAPKs), and gene expression.

METHODS

Rats were chronically treated with ethanol in liquid diet for 4 weeks followed by single ethanol binge (5 gm/kg body weight) or 3 similar repeated doses of ethanol. Serum alcohol and alanine amino transferase (ALT) levels were determined by enzymatic methods. Steatosis was assessed by histology and hepatic triglycerides. Activation of MAPK, 90S ribosomal kinase (RSK), and caspase 3 were evaluated by Western blot. Levels of mRNA for tumor necrosis factor alpha (TNFα), early growth response-1 (egr-1), and plasminogen activator inhibitor-1 (PAI-1) were measured by real-time qRT-PCR.

RESULTS

Chronic ethanol treatment resulted in mild steatosis and necrosis, whereas chronic ethanol followed by binge group exhibited marked steatosis and significant increase in necrosis. Chronic binge group also showed significant increase (compared with chronic ethanol alone) in the phosphorylation of extracellular regulated kinase 1 (ERK1), ERK2, and RSK. Phosphorylation of c-Jun N-terminal kinase (JNK) and p38 MAPK did not increase by the binge. Ethanol binge, after chronic ethanol intake, caused increase in mRNA for egr-1 and PAI-1, but not TNFα.

CONCLUSIONS

Chronic ethanol exposure increases the susceptibility of rat liver to increased injury by 1 or 3 repeat binge. Among other alterations, the activated levels of ERK1, and more so ERK2, were remarkably amplified by binge suggesting a role of these isotypes in the binge amplification of the injury. In contrast, p38 MAPK and JNK1/2 activities were not amplified. These binge-induced changes were also reflected in the increases in the RNA levels for egr-1 and PAI-1. This study offers chronic followed by repeat binge as a model for the study of progression of liver injury by ethanol and highlights the involvement of ERK1 and ERK2 isotypes in the amplification of liver injury by binge ethanol.

Long-term exogenous melatonin treatment modulates overall feed efficiency and protects ovarian tissue against injuries caused by ethanol-induced oxidative stress in adult UChB rats

BACKGROUND

Chronic ethanol intake leads to reproductive damage including reactive oxygen species formation, which accelerates the oxidative process. Melatonin is known to regulate the reproductive cycle, food/liquid intake, and it may also act as a potent antioxidant indoleamine. The aim of this study was to verify the effects of alcoholism and melatonin treatment on overall feed efficiency and to analyze its protective role against the oxidative stress in the ovarian tissue of UChB rats (submitted to 10% [v/v] voluntary ethanol consumption).

METHODS

Forty adult female rats (n = 10/group) were finally selected for this study: UChB Co: drinking water only; and UChB EtOH: drinking ethanol at 2 to 6 ml/100 g/d + water, both receiving 0.9% NaCl + 95% ethanol 0.04 ml as vehicle. Concomitantly, UChB Co + M and UChB EtOH + M groups were infused with vehicle + melatonin (100 μg/100 g body weight/d) intraperitoneally over 60 days. All animals were euthanized by decapitation during the morning estrus (4 am).

RESULTS

Body weight gain was reduced with ethanol plus melatonin after 40 days of treatment. In both melatonin-treated groups, it was observed a reduction in food-derived calories and liquid intake toward the end of treatment. The amount of consumed ethanol dropped during the treatment. Estrous cycle was longer in rats that received both ethanol and melatonin, with prolonged diestrus. Following to oxidative status, lipid hydroperoxide levels were higher in the ovaries of ethanol-preferring rats and decreased after melatonin treatment. Additionally, antioxidant activities of superoxide dismutase, glutathione peroxidase activity, and glutathione reductase activity were increased in melatonin-treated groups.

CONCLUSIONS

We suggest that melatonin is able to affect feed efficiency and, conversely, it protects the ovaries against the oxidative stress arising from ethanol consumption.

Mechanisms and cell signaling in alcoholic liver disease

Alcoholic liver disease (ALD) remains a major cause of morbidity and mortality worldwide. For example, the Veterans Administration Cooperative Studies reported that patients with cirrhosis and superimposed alcoholic hepatitis had a 4-year mortality of >60%. The poor prognosis of ALD implies that preventing disease progression would be more effective than treating end-stage liver disease. An obvious avenue of prevention would be to remove the damaging agent; however, the infamously high rate of recidivism in alcoholics makes maintaining abstinence a difficult treatment goal to prevent ALD. Indeed, although the progression of ALD is well-characterized, there is no universally accepted therapy available to halt or reverse this process in humans. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of ALD, rational targeted therapy can be developed to treat or prevent ALD. The purpose of this review is to summarize the established and proposed mechanisms by which chronic alcohol abuse damages the liver and to highlight key signaling events known or hypothesized to mediate these effects.

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Alcoholic liver disease and the gut-liver axis

Alcoholic liver disease (ALD) is one of the leading causes of liver diseases and liver-related death worldwide. Of the many factors that contribute to the pathogenesis of ALD, gut-derived lipopolysaccharide (LPS) plays a central role in induction of steatosis, inflammation, and fibrosis in the liver. In this review, we discuss the mechanisms by which alcohol contributes to increased gut permeability, the activation of Kupffer cells, and the inflammatory cascade by LPS. The role of the Toll-like receptor 4 (TLR4) complex in LPS recognition and the importance of the TLR4-induced signaling pathways are evaluated in ALD.

Alcohol, signaling, and ECM turnover

Alcohol is recognized as a direct hepatotoxin, but the precise molecular pathways that are important for the initiation and progression of alcohol-induced tissue injury are not completely understood. The current understanding of alcohol toxicity to organs suggests that alcohol initiates injury by generation of oxidative and nonoxidative ethanol metabolites and via translocation of gut-derived endotoxin. These processes lead to cellular injury and stimulation of the inflammatory responses mediated through a variety of molecules. With continuing alcohol abuse, the injury progresses through impairment of tissue regeneration and extracellular matrix (ECM) turnover, leading to fibrogenesis and cirrhosis. Several cell types are involved in this process, the predominant being stellate cells, macrophages, and parenchymal cells. In response to alcohol, growth factors and cytokines activate many signaling cascades that regulate fibrogenesis. This mini-review brings together research focusing on the underlying mechanisms of alcohol-mediated injury in a number of organs. It highlights the various processes and molecules that are likely involved in inflammation, immune modulation, susceptibility to infection, ECM turnover and fibrogenesis in the liver, pancreas, and lung triggered by alcohol abuse.

The opposite effects of acute and chronic alcohol on lipopolysaccharide-induced inflammation are linked to IRAK-M in human monocytes

Impaired host defense after alcohol use is linked to altered cytokine production, however, acute and chronic alcohol differently modulate monocyte/macrophage activation. We hypothesized that in human monocytes, acute alcohol induces hyporesponsiveness to LPS, resulting in decreased TNF-alpha, whereas chronic alcohol increases TNF-alpha by sensitization to LPS. We found that acute alcohol increased IL-1R-associated kinase-monocyte (IRAK-M), a negative regulator of IRAK-1, in human monocytes. This was associated with decreased IkappaB alpha kinase activity, NFkappaB DNA binding, and NFkappaB-driven reporter activity after LPS stimulation. In contrast, chronic alcohol decreased IRAK-M expression but increased IRAK-1 and IKK kinase activities, NFkappaB DNA binding, and NFkappaB-reporter activity. Inhibition of IRAK-M in acute alcohol-exposed monocytes using small interfering RNA restored the LPS-induced TNF-alpha production whereas over-expression of IRAK-M in chronic alcohol macrophages prevented the increase in TNF-alpha production. Addition of inhibitors of alcohol metabolism did not alter LPS signaling and TNF-alpha production during chronic alcohol exposure. IRAK-1 activation induces MAPKs that play an important role in TNF-alpha induction. We determined that acute alcohol decreased but chronic alcohol increased activation of ERK in monocytes and ERK inhibitor, PD98059, prevented the chronic alcohol-induced increase in TNF-alpha. In summary, inhibition of LPS-induced NFkappaB and ERK activation by acute alcohol leads to hyporesponsiveness of monocytes to LPS due to increased IRAK-M. In contrast, chronic alcohol sensitizes monocytes to LPS through decreased IRAK-M expression and activation of NFkappaB and ERK kinases. Our data indicate that IRAK-M is a central player in the opposite regulation of LPS signaling by different lengths of alcohol exposure in monocytes.

Signalling pathways in alcohol-induced liver inflammation

The pathogenesis of alcoholic liver injury involves interactions of several intracellular signalling pathways in different cell types of the liver. Alcohol-induced sensitization of liver macrophages to portal endotoxin/lipopolysaccharide (LPS) is considered a hallmark of alcoholic liver disease (ALD). Intracellular mechanisms associated with LPS-induced signalling play a crucial role in the initiation and progression of alcoholic liver injury, and are being extensively explored. LPS recognition by Toll-like receptor 4 (TLR4) on macrophages and other cell types in the liver, activation of downstream signalling pathways culminating in activation of transcription factors such as NFkappaB, AP-1 leads to increased inflammatory cytokine production in ALD. In addition, LPS-induced MAPK such as ERK and p38 also contribute to liver injury. The importance of alcohol-induced reactive oxygen species and interactions with TLR pathways in macrophages leading to inflammation is becoming increasingly evident. Collectively, these signalling pathways induce pro- and anti-inflammatory cytokines that play an important role in ALD. In this review we describe the key signalling intermediates leading to alcohol-induced inflammation in alcoholic liver disease.

Polyenephosphatidylcholine prevents alcoholic liver disease in PPARalpha-null mice through attenuation of increases in oxidative stress

BACKGROUND/AIMS

Alcoholic liver disease (ALD) is one of the leading causes of cirrhosis and yet efficient therapeutic strategies are lacking. Polyenephosphatidylcholine (PPC), a major component of essential phospholipids, prevented alcoholic liver fibrosis in baboons, but its precise mechanism remains uncertain. We aimed to explore the effects of PPC on ALD using ethanol-fed peroxisome proliferator-activated receptor alpha (Ppara)-null mice, showing several similarities to human ALD.

METHODS

Male wild-type and Ppara-null mice were pair-fed a Lieber-DeCarli control or 4% ethanol-containing diet with or without PPC (30 mg/kg/day) for 6 months.

RESULTS

PPC significantly ameliorated ethanol-induced hepatocyte damage and hepatitis in Ppara-null mice. These effects were likely a consequence of decreased oxidative stress through down-regulation of reactive oxygen species (ROS)-generating enzymes, including cytochrome P450 2E1, acyl-CoA oxidase, and NADPH oxidases, in addition to restoration of increases in Toll-like receptor 4 and CD14. PPC also decreased Bax and truncated Bid, thus inhibiting apoptosis. Furthermore, PPC suppressed increases in transforming growth factor-beta1 expression and hepatic stellate cell activation, which retarded hepatic fibrogenesis.

CONCLUSIONS

PPC exhibited anti-inflammatory, anti-apoptotic, and anti-fibrotic effects on ALD as a result of inhibition of the overexpression of ROS-generating enzymes. Our results demonstrate detailed molecular mechanisms of the anti-oxidant action of PPC.

In vitro and in vivo models of acute alcohol exposure

Alcohol abuse is a global problem due to the financial burden on society and the healthcare system. While the harmful health effects of chronic alcohol abuse are well established, more recent data suggest that acute alcohol consumption also affects human wellbeing. Thus, there is a need for research models in order to fully understand the effect of acute alcohol abuse on different body systems and organs. The present manuscript summarizes the interdisciplinary advantages and disadvantages of currently available human and non-human models of acute alcohol abuse, and identifies their suitability for biomedical research.

The impact of CYP2E1 on the development of alcoholic liver disease as studied in a transgenic mouse model

BACKGROUND/AIMS

CYP2E1 metabolizes ethanol, generates reactive oxygen species, and is suggested to be important for development of alcoholic liver disease. The present study aims to evaluate the role of CYP2E1 in combination with ethanol for development of alcoholic liver disease using mice transgenic for the human CYP2E1 gene.

METHODS

Changes in hepatic gene expression were monitored in controls and mice transgenic for human CYP2E1, treated with ethanol or isocaloric dextrose intragastrically for 4 weeks, and related to pathology using Affymetrix microarrays and TaqMan RealTime PCR.

RESULTS

Presence of the CYP2E1 transgene increased liver injury and increased expression of stress related genes. Microarray analyses revealed the expression of structural genes, particularly cytokeratin 8 and 18, to be highly related to pathology.

CONCLUSIONS

This in vivo study confirms several findings regarding CYP2E1 and alcohol previously found only in vitro. These results provide in vivo evidence that CYP2E1 overexpression aggravates hepatic injury, and suggest that expression of cytokeratins 8 and 18 can be considered as biomakers for the progression of alcoholic liver disease.

Role of increased ROS dissipation in prevention of T1D

Protection of pancreatic beta cells is an approach to prevent autoimmune type 1 diabetes (T1D) and to protect transplanted islets. Reactive oxygen species (ROS) are important mediators of beta cell death during the development of T1D. We have examined the role of elevated ROS dissipation in the prevention of T1D using the ALR mouse strain. The selection of ALR, for resistance against alloxan-induced free radical-mediated diabetes, led to a strain of mice with an elevated systemic as well as pancreatic ROS dissipation. Independent genetic mapping studies have identified ALR-derived diabetes protective loci. Conplastic and congenic mouse as well as cell line studies have confirmed the genetic mapping and demonstrated that the elevated ROS dissipation protects ALR beta cells from autoimmune destruction. Our data support the hypothesis that elevated ROS dissipation protects beta cells against autoimmune destruction and prevents T1D development.

Toll-like receptors and adaptor molecules in liver disease: update

Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen-associated molecular patterns and signal through adaptor molecules, myeloid differentiation factor 88 (MyD88), Toll/IL-1 receptor domain containing adaptor protein (TIRAP), Toll/IL-1 receptor domain containing adaptor inducing interferon-beta (TRIF), and TRIF-related adaptor molecule (TRAM) to activate transcription factors, nuclear factor (NF)-kappaB, activator protein 1 (AP-1), and interferon regulatory factors (IRFs) leading to the initiation of innate immunity. This system promptly initiates host defenses against invading microorganisms. Endogenous TLR ligands such as the products from dying cells may also engage with TLRs as damage-associated molecular patterns. Although Kupffer cells are considered the primary cells to respond to pathogen associated molecular patterns in the liver, recent studies provide evidence of TLR signaling in hepatic nonimmune cell populations, including hepatocytes, biliary epithelial cells, endothelial cells, and hepatic stellate cells. This review highlights advances in TLR signaling in the liver, the role of TLRs in the individual hepatic cell populations, and the implication of TLR signaling in acute and chronic liver diseases. We further discuss recent advances regarding cytosolic pattern recognition receptors, RNA helicases that represents a new concept in chronic hepatitis C virus infection.

Nuclear factor-eythroid 2-related factor 2 prevents alcohol-induced fulminant liver injury

BACKGROUND & AIMS

The transcription factor nuclear factor-eythroid 2-related factor 2 (Nrf2(-/-)) is essential for protecting cells against xenobiotic and oxidative stress. Increased oxidative stress has been implicated in the pathophysiology of many diseases including ethanol-induced liver disease. Therefore, the role of Nrf2(-/-) in ethanol-induced liver injury was investigated.

METHODS

Wild-type and Nrf2(-/-) mice were fed with the ethanol diet, followed by examination of liver pathology, mortality, and ethanol metabolism.

RESULTS

Nrf2(-/-) mice displayed a dramatically increased mortality associated with liver failure when fed doses of ethanol that were tolerated by WT mice. Nrf2(-/-) mice showed a significantly reduced ability to detoxify acetaldehyde, leading to an accumulation of the toxic metabolite. Loss of Nrf2(-/-) caused a marked steatosis in livers of ethanol-fed mice, and Srebp1 was identified as a candidate transcription factor responsible for lipogenic enzyme induction. Furthermore, ethanol consumption led to a progressive depletion of total and mitochondrial reduced glutathione, which was associated with more pronounced structural and functional changes to mitochondria of Nrf2(-/-) mice. In addition, ethanol feeding elicited an aggravated inflammatory response mediated by Kupffer cells in Nrf2(-/-) mice as shown by an increased tumor necrosis factor-alpha secretion and activation of the interleukin-6/Stat-3 pathway. Together these changes lead to a vicious cycle of accumulating hepatocellular damage, ultimately leading to liver failure and death of Nrf2(-/-) mice.

CONCLUSIONS

Our data establish a central role for Nrf2(-/-) in the protection against ethanol-induced liver injury.

Innate immunity and alcoholic liver fibrosis

The hepatic innate immune system consists of predominant innate immunity, which plays an important role in innate defense against infection and tumor transformation. Emerging evidence suggests that innate immunity also contributes to liver injury, repair, and fibrosis. The present review summarizes the recent findings on the role of innate immunity in liver fibrosis. In general, Kupffer cells stimulate liver fibrosis via production of reactive oxygen species and pro-inflammatory cytokines, whereas natural killer (NK) cells inhibit liver fibrosis by directly killing activated hepatic stellate cells and production of gamma-interferon (IFN-gamma). Complement components, interferons, and Toll-like receptors have also been shown to regulate liver fibrosis. Recent evidence also suggests that modulation of innate immunity by alcohol plays an important role in the pathogenesis of alcoholic liver fibrosis. These include alcohol amplification of the profibrotic effects of Kupffer cells and suppression of the antifibrotic effects of NK/IFN-gamma.

Protective effect of bicyclol on acute alcohol-induced liver injury in mice

Oxidative stress, cytokine over expression and Kupffer cell activation are well-documented pathological factors in the development of alcoholic liver disease. Bicyclol is a novel synthetic anti-hepatitis drug with anti-oxidative and anti-inflammatory property. The present study was to investigate the effect of bicyclol on acute alcohol-induced liver injury and related mechanisms in mice. Bicyclol (200, 300 mg/kg) was given to mice by gavage for three times. Alcohol (6 g/kg) was administered orally 1 h after the last dose of bicyclol. All animals were sacrificed at different time points after alcohol administration. Liver injury was evaluated by biochemical and histopathological examination. Lipid peroxidation and the activity of antioxidants were measured by spectrophotometric method. Expression of cytokines and CD14 were determined by enzyme-linked immunosorbent assay, reverse transcriptional-polymerase chain reaction and immunohistochemical staining. As a result, bicyclol pretreatment significantly protected against acute alcohol-induced liver injury as evidenced by the decrease of elevated serum alanine aminotransferase and hepatic triglyceride, and the attenuation of histopathological changes in mice. In addition, bicyclol remarkably alleviated the formation of thiobarbituric acid-reactive substance and restored impaired antioxidants, including glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase. Over-expression of cytokines, such as tumor necrosis factor alpha and interleukin 1beta, elevated plasma endotoxin level, and up-regulation of CD14 were also suppressed by bicyclol in alcohol-intoxicated mice. The protective effect of bicyclol on alcohol-induced hepatotoxicity was mainly due to its ability to attenuate oxidative stress, suppress the cytokine expression at both protein and gene level, and inhibit the activation of Kupffer cells by decreasing plasma endotoxin level and CD14 expression.

Glucocorticoid-induced leucine zipper: A key protein in the sensitization of monocytes to lipopolysaccharide in alcoholic hepatitis

Glucocorticoid-induced leucine zipper (GILZ), a recently identified protein induced by glucocorticoids (GCs), inhibits the nuclear factor kappaB pathway and the activation of monocytes/macrophages by lipopolysaccharides (LPS). This study aimed to elucidate the contribution of GILZ to the pathogenesis of alcoholic hepatitis (AH): we (1) assessed GILZ expression in the livers of patients with AH and (2) treated patients with severe AH with GCs (prednisolone 40 mg/day) and studied the effect of GILZ modulation on circulating monocyte function. We quantified GILZ expression in the livers of 42 consecutive alcoholic patients (21 with and 21 without AH). GILZ messenger RNA (mRNA) levels were lower in the livers of patients with AH versus those without AH (P < 0.05). We collected circulating monocytes from patients with severe AH before and 48 hours after GC treatment to quantify GILZ expression and cytokine secretion. GC treatment induced significantly higher levels of GILZ mRNA than that observed before treatment and impaired LPS-induced tumor necrosis factor-alpha (TNF-alpha) and regulated upon activation, normal T cell-expressed secretion (RANTES) by these monocytes. We transfected circulating monocytes with GILZ small interfering RNA (siRNA), specifically blocking GILZ expression, to demonstrate the role of GILZ in mediating GC effect. GILZ siRNA abrogated the effect of GC treatment on LPS-induced TNF-alpha and RANTES secretion.

CONCLUSION

Low expression of GILZ may contribute to liver inflammation in AH. GCs enhance GILZ expression, abrogating macrophage sensitivity to LPS and proinflammatory cytokine secretion. These findings may explain the beneficial effect of GC treatment in patients with severe AH.

Selenium supplementation increases liver MnSOD expression: molecular mechanism for hepato-protection

Selenium is recognized as essential in animal and human nutrition. Several hypotheses have been advanced for its biological activity. The aim of this study was to investigate the in vivo effect of selenium on rat liver manganese superoxide dismutase (MnSOD), a key antioxidant enzyme, under naïve and inflammatory conditions. Rats received sodium selenite supplementation and LPS injection. Whole-liver samples, isolated hepatocytes, Kupffer cells and blood samples were subjected to protein, RNA and biochemical analysis. Liver enrichment with selenium increased whole-liver MnSOD levels due to an increase in MnSOD transcription in hepatocytes. This was due to an increase in the ratio of specificity protein 1 to activating enhancer binding protein 2 DNA-binding activity. The inflammatory stimulus further elevated MnSOD levels in the whole-liver that was abrogated in sodium selenite supplementation due to reduced transcription of MnSOD in Kupffer cells. Moreover, selenium enrichment decreased Kupffer cells IL-6 transcription in LPS-injected animals. Anti-inflammatory activity of selenium was demonstrated by normalized blood levels of ALT and IL-6 in LPS-injected animals. In conclusion, selenium up-regulates hepatocytes MnSOD expression, probably improving their anti-oxidant defense, while decreasing MnSOD and IL-6 transcription in Kupffer cells in the presence of inflammatory stimuli, attenuating their inflammatory response. This selective mechanism may explain the anti-inflammatory and hepato-protective effect of selenium.

Alcohol-induced oxidative stress

Alcohol-induced oxidative stress is linked to the metabolism of ethanol involving both microsomal and mitochondrial systems. Ethanol metabolism is directly involved in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). These form an environment favourable to oxidative stress. Ethanol treatment results in the depletion of GSH levels and decreases antioxidant activity. It elevates malondialdehyde (MDA), hydroxyethyl radical (HER), and hydroxynonenal (HNE) protein adducts. These cause the modification of all biological structures and consequently result in serious malfunction of cells and tissues.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Essential roles of ERKs and p38K in up-regulation of GST A1 expression by Maotai content in human hepatoma cell line Hep3B

It is widely accepted that the consumption of alcohol may lead to hepatic injuries such as hepatic fibrosis and cirrhosis. However, consumption of Maotai, one of the famous liquors in China, is found to have no obvious relevance with hepatic injury as ordinary white wine does in both epidemiological and histopathological studies. Present study used human hepatoma cell line Hep3B to address the mechanisms involved in the resistance of alcohol-induced hepatic injury by Maotai liquor. We found that exposure of Hep3B cells to Maotai residue without ethanol (MRWE) resulted in the increased GST A1 anti-oxidant responsive element (ARE) transcriptional expression, while MRWE treatment did not affect Nrf-2-dependent transcriptional activity. Those findings were further confirmed at all time points and doses tested, suggesting that GST A1 transcription was regulated by MRWE via an Nrf-2-independent pathway. Consistent with GST A1 induction, the phosphorylation of c-Jun, extracellular signal-regulated kinases (ERKs) and p38 kinase (p38 K), were also observed in MRWE-treated Hep3B cells. Furthermore, pretreatment of cells with either PD98059 (an inhibitor specific for MEK1/2-ERKs pathway) or SB202190 (an inhibitor specific for p38 K) led to a significant decrease in the induction of GST A1 transcriptional expression by MRWE treatment. Our results indicate that certain content in MRWE is able to induce GST A1 ARE transcriptional expression, which may provide protective effects for hepatic cells by antagonizing the oxidative stress derived from ethanol via an ERKs- and p38 K-dependent pathway.

Alcoholic pancreatitis: mechanisms of viral infections as cofactors in the development of acute and chronic pancreatitis and fibrosis

Acute and chronic pancreatitis is associated with alcohol abuse, but symptomatic pancreatitis develops in only a small proportion of persons (10-20%) who abuse alcohol. This apparent paradox has led to the notion that additional cofactors are involved in the development of alcoholic pancreatitis. Potential cofactors, such as diet and smoking, have been suggested, but there are no compelling epidemiologic data to support this idea. A number of viruses and some bacteria have been shown to infect the pancreas and produce pancreatitis. One important mediator of pancreatitis in persons with a compromised immune system is a viral infection. The increased susceptibility of immunocompromised persons to viral pancreatitis led to the hypothesis, described in this paper, that the well-known immunosuppression associated with alcohol abuse would result in a more severe viral pancreatitis in mice, which are provided ethanol, than in control animals. To test this hypothesis, C57BL/6 mice were infected with a virulent strain of coxsackievirus B3, which preferentially induces pancreatitis, or with a strain that is naturally avirulent. The study findings presented in this paper show that ethanol consumption alone does not produce pancreas damage but results in a more severe and prolonged pancreatitis after infection with a virulent virus and interestingly, after infection with the avirulent strain of virus. This was associated with an increased number of viruses in the pancreas and spleen, which correlated with decreased humoral immune responses to the virus.

Tumor necrosis factor-alpha down-regulates human Cu/Zn superoxide dismutase 1 promoter via JNK/AP-1 signaling pathway

Overexpression of Cu/Zn superoxide dismutase 1 (SOD1) in monocytes blocks reactive oxygen species-induced inhibition of cell growth and apoptosis and renders cells resistant to the toxic effect of tumor necrosis factor (TNF)-alpha, suggesting that TNF-alpha represses the SOD1 gene in these cells. We herein show that TNF-alpha decreases SOD1 mRNA, protein, and promoter activity in U937 cells. Electrophoretic mobility-shift assays (EMSA) show that TNF-alpha decreased binding of three different complexes. Ectopic Sp1 overexpression markedly increased SOD1-basal promoter activity and partially antagonized the TNF-alpha inhibitory effect. In contrast, ectopic c-Jun overexpression mimics TNF-alpha inhibitory effects and antagonizes Sp1 stimulatory effects. In agreement with these findings, EMSA shows a TNF-alpha-induced increase in AP-1 and a decrease in Sp1 DNA binding. Disruption of the C/EBP site decreases, whereas mutation in the Sp1/Egr-1 site completely abolishes DNA-binding and promoter activity. A JNK inhibitor antagonized the negative effects of TNF-alpha on SOD1 promoter activity, suggesting that JNK signaling through c-Jun protein activation is critical for the TNF-alpha-dependent SOD1 repression. A greater understanding of the mechanisms of TNF-alpha-induced SOD1 repression could facilitate the design and development of novel therapeutic drugs for inflammatory conditions.

Differential liver sensitization to toll-like receptor pathways in mice with alcoholic fatty liver

Gut-derived, endotoxin-mediated hepatocellular damage has been postulated to play a crucial role in the pathogenesis of alcohol-induced liver injury in rodents. Endotoxins induce production of tumor necrosis factor alpha (TNF-alpha) by Kupffer cells via Toll-like receptor (TLR) 4 and contribute to liver injury. This study addressed the contribution of other TLRs and ligands to alcoholic fatty liver. C57Bl6/J mice were fed a modified Lieber-DeCarli diet. Serum aminotransferase measurements, histological analysis, and quantification of liver TNF-alpha and TLR1-9 messenger RNA (mRNA) were performed. The effect of TLR ligands on liver injury was assessed in vivo. Neomycin and metronidazole or diphenyleneiodonium sulfate (DPI) were administered to evaluate the role of gut bacteria and NADPH oxidase activity, respectively, in hepatic TLR expression. Enteral ethanol (EtOH) exposure induced steatosis and increased liver weight, aminotransferase levels, and expression of TLR1, 2, 4, 6, 7, 8, and 9 liver mRNA. Injection of lipoteichoic acid, peptidoglycan (PGN), lipopolysaccharide (LPS), loxoribine, and oligonudeotide containing CpG (ISS-ODN) increased TNF-alpha mRNA expression more in the livers of EtOH-fed mice than in control mice. PGN, LPS, flagellin, and ISS-ODN induced liver inflammatory infiltrate in EtOH-fed mice but not control mice. Addition of antibiotics reduced the severity of alcoholic fatty liver without affecting TLR expression, whereas daily DPI injections reduced the EtOH-mediated upregulation of TLR2, 4, 6, and 9 mRNA. In conclusion, EtOH-fed mice exhibited an oxidative stress dependent on upregulation of multiple TLRs in the liver and are sensitive to liver inflammation induced by multiple bacterial products recognized by TLRs.

Glycine as a therapeutic immuno-nutrient for alcoholic liver disease

Activation of Kupffer cells by gut-derived endotoxin is an important factor in ethanol hepatotoxicity. Further, it was shown that ethanol modulates both the expression and activity of several intracellular signaling molecules and transcription factors in Kupffer cells and chronic ethanol treatment enhances Kupffer cell sensitivity to endotoxin. These findings suggest that inhibition of Kupffer cell activation is effective for clinical application in alcoholic hepatitis. Recently, accumulating lines of evidence suggest a possibility that glycine is useful as an immuno-modulating amino acid. It has been shown that a diet containing glycine improved survival in endotoxin shock by preventing Kupffer cell activation. Glycine most likely prevents the LPS-induced elevation of intracellular Ca concentration in Kupffer cells, thereby minimizing LPS receptor signaling and cytokine production. Indeed, glycine prevents alcohol-induced liver injury in a long-term enteral ethanol feeding rats (Tsukamoto-French) by decreasing production of TNF-alpha in the liver. Moreover, glycine is protective against apoptosis of sinusoidal endothelial cells (SECs) that is one of the initial events in the development of liver injury. On the other hand, epidemiologic data have identified chronic alcohol consumption as a significant risk factor for carcinogenesis. Interestingly, glycine inhibits growth of tumor in vivo most likely because of the inhibition of angiogenesis. It was shown that the inhibitory effect of glycine on growth and migration of endothelial cells is due to activation of a glycine-gated Cl channel. It is hypothesized that the opening of this anion channel hyperpolarizes the cell membrane, blocks influx of Ca through voltage-dependent Ca channel, thereby blunting growth factor-mediated signaling. Therefore, glycine can be used not only for treatment of alcoholic hepatitis, but also for chemoprevention and treatment of hepatocellular carcinoma in alcoholic cirrhosis. Taken together, it is concluded that glycine is a potent therapeutic immuno-nutrient for various kinds of chronic liver diseases including alcoholic liver disease (ALD).

Oxidative stress and signal transduction pathways in alcoholic liver disease

Ethanol is linked to several pathologies like alcohol liver injury, neurotoxicity, cardiomyopathy, fetal alcoholic syndrome or cancer. It is generally accepted that oxidative stress plays a central role in their pathogenesis. After chronic and excessive consumption, alcohol may accelerate oxidative mechanisms both directly via increased production of reactive oxygen species and indirectly by impairing protective mechanisms against them. Ethanol, its metabolites arising during its metabolic degradation as well as novel compounds formed via ethanol induced oxidative stress, especially during the action of the ethanol inducible microsomal cytochrome CYP2E1, may apart from direct damage to biological structures affect signal transduction pathways thus modulating and potentiating damage. Alteration of the redox status of cells following chronic ethanol misuse may have profound effects on cellular function and viability and lead to cell death and tissue damage. These changes linked to pathologic processes in the organism, are related to alteration of intracellular signaling pathways associated with protein kinases and transcription factor activation. Mainly mitogen activated protein kinase (MAPK) family, transcription factors-nuclear factor kappaB (NF-kappaB) and activating protein 1 (AP-1) are involved in the deterioration of cells and organs. The response is cell-type specific and depends on the dose of ethanol. Oxido-reduction balance, regulatory disturbances and signal transduction cascades responsible for alcoholic damage have been partially described, nevertheless, further studies are required to allow future novel diagnostic and therapeutical strategies. We are only at the beginning ...

Increased lipopolysaccharide sensitivity in alcoholic fatty livers is independent of leptin deficiency and toll-like receptor 4 (TLR4) or TLR2 mRNA expression

BACKGROUND

Both alcoholic (AFL) and nonalcoholic (NAFL) fatty livers show increased sensitivity to endotoxin-induced injury. Lipopolysaccharide (LPS) is recognized by toll-like receptor 4 (TLR4), whereas lipopeptide triggers TLR2 to induce common downstream activation of nuclear factor (NF)-kappaB and pro-inflammatory pathways that are activated in AFL and NAFL.

METHODS

Serum alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 levels; hepatic NF-kappaB activity; and expression of TLR2, TLR4, inducible nitric oxide synthase (iNOS), and heme oxygenase (HO)-1 mRNAs were investigated in lean and leptin-deficient ob/ob mice after LPS challenge in combination with acute or chronic alcohol feeding.

RESULTS

Increased LPS sensitivity in AFL and NAFL was characterized by elevated serum TNF-alpha and IL-6 induction. However, there was no difference in TLR2 and TLR4 mRNA levels between lean and ob/ob livers at baseline and after acute or chronic alcohol treatment. LPS increased TLR2, but not TLR4, mRNA levels in all groups. Chronic alcohol feeding and LPS increased serum ALT and TNF-alpha levels in lean but not in ob/ob mice compared with pair-fed controls. Hepatic NF-kappaB activation was increased in both ob/ob and lean mice after chronic alcohol feeding compared with pair-fed controls. Expression of iNOS, an inducer of oxidative stress, and HO-1, a cytoprotective protein, were higher in ob/ob compared with lean mice after chronic alcohol feeding. However, LPS-induced HO-1, but not iNOS, expression was attenuated in ob/ob compared with lean mice.

CONCLUSION

These results imply that the increased sensitivity of AFL to LPS occurs without up-regulation of TLR2 or TLR4 genes and may be related to an imbalance of pro-inflammatory/oxidative and cytoprotective mechanisms.

Effects of N-acetylcysteine on ethanol-induced hepatotoxicity in rats fed via total enteral nutrition

The effects of the dietary antioxidant N-acetylcysteine (NAC) on alcoholic liver damage were examined in a total enteral nutrition (TEN) model of ethanol toxicity in which liver pathology occurs in the absence of endotoxemia. Ethanol treatment resulted in steatosis, inflammatory infiltrates, occasional foci of necrosis, and elevated ALT in the absence of increased expression of the endotoxin receptor CD 14, a marker of Kupffer cell activation by LPS. In addition, ethanol treatment induced CYP 2 E1 and increased TNFalpha and TGFbeta mRNA expression accompanied by suppressed hepatic IL-4 mRNA expression. Ethanol treatment also resulted in the hepatic accumulation of malondialdehyde (MDA) and hydroxynonenal (HNE) protein adducts, decreased antioxidant capacity, and increased antibody titers toward serum hydroxyethyl radical (HER), MDA, and HNE adducts. NAC treatment increased cytosolic antioxidant capacity, abolished ethanol-induced lipid peroxidation, and inhibited the formation of antibodies toward HNE and HER adducts without interfering with CYP 2 E1 induction. NAC also decreased ethanol-induced ALT release and inflammation and prevented significant loss of hepatic GSH content. However, the improvement in necrosis score and reduction of TNFalpha mRNA elevation did not reach statistical significance. Although a direct correlation was observed among hepatic MDA and HNE adduct content and TNFalpha mRNA expression, inflammation, and necrosis scores, no correlation was observed between oxidative stress markers or TNFalpha and steatosis score. These data suggest that ethanol-induced oxidative stress can contribute to inflammation and liver injury even in the absence of Kupffer cell activation by endotoxemia.

Proinflammatory synergism of ethanol and HIV-1 Tat protein in brain tissue

Human immunodeficiency virus type 1 (HIV-1) Tat protein is a potent transactivator of viral replication. It is actively released from HIV-infected cells and has been shown to induce cell injury effects. Alcohol abuse is a risk factor of HIV infection and we hypothesize that alcohol and Tat may interact in an additive or synergistic fashion to influence molecular processes which can contribute to their toxic effects. To study this possibility, we investigated the effects of two intraperitoneal injections of ethanol (EtOH, 3 g/kg each, 16 h apart) and a single intracerebral injection of Tat (25 microg/microl into the right hippocampus, injected 12 h after the first EtOH injection) on generation of cellular oxidative stress, DNA binding activity of redox-responsive transcription factors, and induction of inflammatory genes in the hippocampus and corpus striatum of mouse brain. As compared to control animals, treatment with EtOH plus Tat resulted in increased production of reactive oxygen species in both brain regions. In addition, DNA binding activities of nuclear factor-kappaB (NF-kappaB) and CREB in both brain regions and SP-1 in the hippocampus were more pronounced in mice injected with Tat plus EtOH as compared to the effects of Tat or EtOH alone. Among studied inflammatory genes, induction of IL-1beta and MCP-1 was potentiated in animals injected with EtOH plus Tat. These results indicate that Tat and EtOH can cross-amplify their cellular effects, leading to alterations of redox-regulated inflammatory pathways in the brain. Such potentiation of proinflammatory stimulation may further contribute to CNS pathology in HIV-infected patients who are alcohol abusers.

CD14-dependent alterations in c-Jun expression in the liver after burn injury

BACKGROUND

Burn injury-triggered activation of lipopolysaccharide signaling via the CD14 pathway alters the expression of a variety of downstream genes contributing to pathogenic changes in distant organs. The regulation of CD14 and its role in the immediate-early response of c-Jun in the liver after burn injury were investigated in this study.

MATERIALS AND METHODS

An incidental identification of the differential induction of CD14 mRNA after an approximately 18% TBSA burn injury in mice was confirmed by RT-PCR and immunohistochemical analyses of CD14 expression. Subsequently, CD14's role in the immediate-early regulation of c-Jun expression in the liver after injury was examined by Western blot analysis using CD14 knockout (KO) mice.

RESULTS

RT-PCR analysis demonstrated a rapid and transient induction of CD14 mRNA in the liver and lungs of mice after injury. Immunohistochemical analysis revealed a peak induction of CD14 reactivity in cells appearing to be Kupffer cells at day 1 after injury. Furthermore, an augmented and delayed induction of c-Jun mRNA was observed in the liver of CD14 KO mice after injury compared to wild-type controls. The induction of phosphorylated (serine 63 or serine 73) forms of c-Jun after injury was lower in the livers of CD14 KO mice than that in WT controls.

CONCLUSIONS

This study provides evidence that injury elicits CD14 induction as well as hyperphosphorylation of the c-Jun N-terminus activation domain and that CD14 is involved in the modulation of c-Jun's transactivation potential via phosphorylation, which may be associated with hepatic pathogenesis after injury.

Potential Role of Endotoxin as a Proinflammatory Mediator of Atherosclerosis

Atherosclerosis is increasingly recognized as a chronic inflammatory disease. Although a variety of inflammatory markers (ie, C-reactive protein) have been associated with atherosclerosis and its consequences, it is important to identify principal mediators of the inflammatory responses. One potentially important source of vascular inflammation in atherosclerosis is bacterial endotoxin. Mutations in Toll-like receptor 4 (TLR-4), an integral component of the endotoxin signaling complex, are fairly common in the Caucasian population and have recently been associated with reduced incidence of atherosclerosis and other cardiovascular diseases in some studies. Moreover, epidemiological studies suggest that endotoxemia at levels as low as 50 pg/mL constitutes a strong risk factor for the development of atherosclerosis. Endotoxin concentrations in this range may be produced by a variety of common subclinical Gram-negative infections. In this article, we outline the main elements of the endotoxin signaling receptor complex that initiates proinflammatory signaling (lipopolysaccharide binding protein [LBP], CD14, TLR-4, and MD-2) and discuss how changes in expression of these molecules may affect proatherogenic responses in the vessel wall. We also describe some of the proinflammatory effects of endotoxin that may be relevant to atherosclerosis, and discuss how serum lipoproteins, especially high-density lipoprotein, may modulate endotoxin-induced inflammatory responses. Further, we discuss recent findings suggesting that the lipid-lowering statins may have an additional protective role in blocking at least some of these proinflammatory signaling pathways. Finally, we discuss species diversity with regard to endotoxin signaling that should be considered when extrapolating experimental data from animal models to humans.

Molecular aspects of alcohol metabolism: transcription factors involved in early ethanol-induced liver injury

Alcohol metabolism takes place primarily in the liver. Initial exposures to ethanol have a major impact on the hepatic redox state and intermediary metabolism as a consequence of ethanol metabolism via alcohol dehydrogenase. However, upon continued exposure to ethanol, the progression of liver injury involves ethanol metabolism via CYP2E1 and consequent oxidant stress, as well as potential direct effects of ethanol on membrane proteins that are independent of ethanol metabolism. Multiple organ systems contribute to liver injury, including the innate immune system and adipose tissue. In response to ethanol exposure, specific signal transduction pathways, including NFkappaB and the mitogen-activated protein kinase family members ERK1/2, JNK, and p38, are activated. These complex responses to ethanol exposure translate into activation of nuclear transcription factors and altered gene expression within the liver, leading to the development of steatosis and inflammation in the early stages of alcohol-induced liver injury.

Recent advances in alcoholic liver disease III. Role of the innate immune response in alcoholic hepatitis

Ethanol consumption is known to cause significant acute liver damage resulting in hepatic fibrosis and eventual cirrhosis when consumed chronically. The mechanism(s) by which ethanol exerts its damaging effects on the liver are not well understood; however, recent scientific investigation has begun to delineate the earliest events in alcoholic liver disease. From these studies, it is apparent that components of the innate immune system and, in particular, Kupffer cells, play a significant role in this process. It is also becoming clear that other parts of the immune system including T cells may also be responsible for mediating the devastating effects of chronic alcohol consumption on the liver. This review will highlight recent experiments demonstrating a role for the innate immune response in the initiation and progression of alcohol-induced liver hepatitis and subsequent organ damage.