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

Ethanol-induced liver injury: potential roles for egr-1

Chronic ethanol-induced liver injury follows a typical progression from its earliest stage of steatosis to more advanced injury, characterized by the development of inflammation, hepatocyte necrosis/apoptosis, fibrosis and finally cirrhosis. Kupffer cells, the resident macrophage in the liver, play a critical role in the progression of liver injury. Increased exposure of Kupffer cells to lipopolysaccharide (LPS) during chronic ethanol exposure leads to the production of a number of inflammatory mediators, including tumor necrosis factor alpha (TNF-alpha). Recent evidence indicates that in addition to increased exposure to LPS, Kupffer cells also develop an enhanced sensitivity to LPS after chronic ethanol feeding. We have recently identified early growth response-1 (Egr-1), an immediate-early gene transcription factor, as an important contributor to increased LPS-stimulated TNF-alpha secretion by Kupffer cells after chronic ethanol exposure. In other models of tissue injury, such as ischemia-reperfusion in the lung, Egr-1 acts as a coordinator of the complex response to stress. Here we review the literature regarding the role of EGR-1 in regulation of a number of genes implicated in each of the stages of chronic ethanol-induced liver injury. In addition to the critical role of Egr-1 in generating maximal LPS-stimulated TNF-alpha expression, Egr-1 also controls the expression of a number of inflammatory mediators, including intercellular adhesion molecule (ICAM)-1, monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-2, as well as genes contributing to fibrosis, such as transforming growth factor (TFG)-beta1, platelet-derived growth factor PDGF-A chain and fibroblast growth factor (FGF). Understanding the contribution of Egr-1 to the expression of genes involved in the development of chronic ethanol-induced liver injury may lead to the development of improved therapies designed to prevent and/or reverse alcohol-induced liver injury.

Modulation of non-alcoholic steatohepatitis by pattern recognition receptors in mice: the role of toll-like receptors 2 and 4

Toll-like receptors (TLR) recognize pathogen-derived molecules and induce downstream activation of inflammatory pathways. Fatty liver has been shown to result in increased sensitivity to lipopolysaccharide (LPS), a TLR4 ligand. In this study, we investigated the roles of TLR2 and TLR4 in liver damage and on cytokine induction in a methionine-choline deficient (MCD) diet-induced model of nonalcoholic steatohepatitis. We found that mice with nonalcoholic fatty liver had increased liver injury and inflammatory cytokine induction after challenge with a TLR4 but not with a TLR2 ligand. TLR2 deficient mice were not protected against the development of steatohepatitis after MCD diet feeding. On the contrary, TLR2 mice had significantly higher levels of serum ALT and greater TNF-alpha levels after LPS challenge suggesting increased liver injury. This was associated with reduced production of IL-6, a cytokine with hepatoprotective effects in fatty liver. Increased liver injury in the MCD diet-fed TLR2 mice was associated with reduced baseline and LPS-induced NF-kB and PPRE binding compared to MCS controls. These results demonstrate that TLR2 deficiency results in increased liver injury in association with nonalcoholic steatohepatitis and may suggest a protective role for TLR2-mediated signals in liver injury.

Temporal differences in the ability of ethanol to modulate endotoxin-induced increases in inflammatory cytokines in muscle under in vivo conditions

BACKGROUND

Acute alcohol (EtOH) intoxication may both antagonize and potentiate the ability of monocytes/macrophages to respond to endotoxin (lipopolysaccharide [LPS]). The suppressive effects of EtOH predominate when the duration between EtOH and LPS administration is relatively short, whereas sensitization is observed under conditions when there is a relatively longer delay between EtOH and LPS exposure. Striated muscle is now recognized to possess components of both the afferent and efferent limbs of the innate immune system. The aim of the present study was to determine whether the interval between EtOH and LPS administration differentially affects the mRNA content for selected elements of the innate immune response in skeletal and cardiac muscle and to compare such changes with those occurring in liver and spleen.

METHODS

The content of mRNA for interleukin (IL)-6, IL-1beta, tumor necrosis factor (TNF)-alpha, and high-mobility group box (HMGB)-1, as well as toll-like receptors (TLRs)-2 and -4, were measured in gastrocnemius, heart, liver and spleen from rats orally gavaged with EtOH and then injected with LPS either two or 24 hr thereafter.

RESULTS

EtOH intoxication two hr before LPS acutely suppressed the increased IL-6 mRNA in all tissues and antagonized the increase in plasma and tissue IL-6 protein concentration. Similarly, EtOH blunted the LPS-induced increase in tissue mRNA expression of TNF-alpha and IL-1beta. In contrast, when LPS was given 24 hr after EtOH, the increased IL-6 in striated muscle, but not in liver or spleen, was selectively potentiated. An enhanced LPS responsiveness was also observed for the late-phase cytokine HMGB1 in all tissues; however, the increased tissue expression of TNF-alpha and IL-1beta induced by LPS was not augmented. TLR4 mRNA was decreased in both heart and spleen (but unaltered in skeletal muscle and liver) of rats injected with LPS, and this change was prevented by pretreatment with EtOH. In contrast, EtOH alone increased TLR-2 mRNA content of heart, liver, and spleen but not muscle. LPS also markedly increased TLR2 mRNA in the same three tissues under control conditions, but this increase was attenuated by EtOH administered either two or 24 hr before LPS.

CONCLUSIONS

Under in vivo conditions, the interval between EtOH exposure and LPS differentially affected the synthesis of various cytokines. In this regard, EtOH administered within two hr of LPS generally suppressed IL-6, IL-1beta, and TNF-alpha mRNAs in muscle, heart, liver, and spleen. Delaying the exposure of animals to LPS for 24 hr after EtOH, however, accentuated the increase in IL-6 and HMGB1, and for IL-6, this increased sensitivity appeared localized to striated muscle.

Kupffer cell function during the erythocytic stage of malaria

BACKGROUND AND AIM

Previous studies using isolated perfused rat liver in vivo have suggested that during the erythrocytic phase of malaria infection, overall phagocytosis by Kupffer cells is enhanced. The aim of the present study was to further investigate the individual phagocytic capacity and prostaglandin E(2) (PGE(2)) secretion of isolated Kupffer cells in vitro, and the immunohistochemical characteristics of Kupffer cells in vivo.

METHODS

Malaria was induced in male Sprague-Dawley rats (n = 12) by inoculation with parasitized red cells containing Plasmodium berghei. Kupffer cells were isolated by centrifugal elutriation.

RESULTS

A significantly increased yield of Kupffer cells was obtained from malaria-infected livers compared to controls (36.7 +/- 4.5 vs 11.8 +/- 1.1 x10(6) cells, P < 0.0001, n = 12). There was an increased internalization by phagocytosis of [(3)H]-BSA latex microspheres after 60 min in malaria-infected Kupffer cells compared to controls (65.05 +/- 1.5 vs 48.6 +/- 0.7, P < 0.001, n = 12). PGE(2) secretion into the cell culture medium was significantly suppressed in malaria-infected Kupffer cells compared to controls (1167 +/- 88 vs 4537 +/- 383 pg per 10(6) cells, P < 0.001, n = 5). Staining of ED1, ED2 and PCNA was greater in malaria-infected livers compared to control.

CONCLUSION

The results indicate that the number of Kupffer cells is significantly increased and their phagocytic activity on a cell-by-cell basis is enhanced during the erythrocytic stage of malaria.

Drug abuse, innate immunity and hepatitis C virus

Since its discovery in 1989, hepatitis C virus (HCV) has become a major public health problem. HCV chronically infects an estimated 170 million people worldwide. The seroprevalence of anti-HCV antibody in the United States has been estimated at 1.8%, which corresponds to approximately 4 million people. HCV is the most common chronic blood borne infection in the United States, and the leading cause of liver transplantation in developed countries. Injection drug use is the dominant mode of HCV transmission and accounts for up to 90% of current infections. Opiates and other drug abuse, such as alcohol, have been implicated as cofactors in the pathogenesis of HCV disease. Injection drug use has been the most common risk factor identified in alcoholics with HCV infection. Both opiates and alcohol contribute significantly to morbidity and mortality from HCV disease. These drugs most likely act synergistically to promote the development and progression of HCV disease. However, there is limited information available concerning the interaction of the drug abuse with the host cell innate immunity against HCV infection, which is a major barrier to fundamental understanding of the immunopathogenesis of HCV disease. Therefore, defining the role of the drug abuse in the development of chronic HCV infection is of crucial importance and should provide practical guidance toward the reduction of risk factors that interfere with therapeutic approaches for HCV infection and disease. This review paper focuses on the interplay between drug abuse (opiates and alcohol), innate immunity and HCV in the context of the development of HCV disease.

Identification of novel transcriptional networks in response to treatment with the anticarcinogen 3H-1,2-dithiole-3-thione

3H-1,2-dithiole-3-thione (D3T), an inducer of antioxidant and phase 2 genes, is known to enhance the detoxification of environmental carcinogens, prevent neoplasia, and elicit other protective effects. However, a comprehensive view of the regulatory pathways induced by this compound has not yet been elaborated. Fischer F344 rats were gavaged daily for 5 days with vehicle or D3T (0.3 mmol/kg). The global changes of gene expression in liver were measured with Affymetrix RG-U34A chips. With the use of functional class scoring, a semi-supervised method exploring both the expression pattern and the functional annotation of the genes, the Gene Ontology classes were ranked according to the significance of the impact of D3T treatment. Two unexpected functional classes were identified for the D3T treatment, cytosolic ribosome constituents with 90% of those genes increased, and cholesterol biosynthesis with 91% of the genes repressed. In another novel approach, the differentially expressed genes were evaluated by the Ingenuity computational pathway analysis tool to identify specific regulatory networks and canonical pathways responsive to D3T treatment. In addition to the known glutathione metabolism pathway (P = 0.0011), several other significant pathways were also revealed, including antigen presentation (P = 0.000476), androgen/estrogen biosynthesis (P = 0.000551), fatty acid (P = 0.000216), and tryptophan metabolism (P = 0.000331) pathways. These findings showed a profound impact of D3T on lipid metabolism and anti-inflammatory/immune-suppressive response, indicating a broader cytoprotective effect of this compound than previously expected.

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.

Signal transduction in alcohol-related diseases

This article summarizes the proceedings of a symposium presented at the 12th World Congress on Biomedical Alcohol Research, organized by the International Society for Biomedical Research on Alcoholism, held at the University of Heidelberg in Mannheim, Germany, in September and October 2004. The organizers and chairpersons were Manfred V. Singer and Stephen J. Pandol. The presentations were (1) Ethanol‐induced acinar cell injury, by Minoti V. Apte; (2) Oxidants and antioxidants: signal transduction and alcohol, by Thomá Zima; (3) Anti–TGF‐β strategies for the treatment of chronic liver disease, by Steven Dooley; (4) Immune mechanisms in alcohol‐induced liver disease, by Sören V. Siegmund; and (5) Alcoholic pancreatitis: insights from animal models, by Steven J. Pandol.

Alcohol and the liver

PURPOSE OF REVIEW

To highlight salient recent discoveries and results of clinical trials in alcoholic liver disease (ALD). The burden of care for ALD patients is hefty and the prevalence of alcohol abuse may be increasing in both the developed and the underdeveloped world.

RECENT FINDINGS

Molecular mechanisms of alcoholism are being identified but not of the predisposition to alcoholic liver injury, except perhaps for polymorphism of a cytotoxic T-cell antigen. The Mayo End-stage Liver Disease (MELD) score performs well in assessing the prognosis of ALD; serological biomarkers for predicting ALD outcome are of uncertain value. Concomitant liver disease (e.g., obesity, hepatitis C, and iron overload) aggravates the severity of ALD; conversely, alcohol abuse may be a cryptic co-factor in some cases of non-alcoholic fatty liver. For alcoholic hepatitis, nutritional support is the mainstay of treatment; steroids are considered by some (but not all) as safe and effective therapy, whereas manipulations of tumor necrosis factor-alpha activity have been disappointing, or of unproven benefit at best. In liver transplantation for ALD, methods are being devised to monitor recidivism and to ameliorate its risk and that of co-morbid psychiatric conditions.

SUMMARY

Much of the pathogenesis of ALD has been identified and headway has been made in predicting its prognosis. However, much remains to be done to elucidate the molecular genetics of the risk of developing ALD and in formulating safe, effective therapies for alcoholic hepatitis.

Cytochrome P450 CYP2E1, but not nicotinamide adenine dinucleotide phosphate oxidase, is required for ethanol-induced oxidative DNA damage in rodent liver

The occurrence of malignant tumors of the upper gastrointestinal tract and liver is, based largely on epidemiological evidence, causally related to the consumption of ethanol. It is widely recognized that oxidants play a key role in alcohol-induced liver injury; however, it is unclear how oxidants may be involved in DNA damage. We asked whether nicotinamide adenine dinucleotide phosphate oxidase, cytochrome P450 CYP2E1, or both are responsible for the production of DNA damage. The rodent Tsukamoto-French model of intragastric ethanol infusion was used. Wistar rats, Cyp2e1-, p47(phox)-null, and hCyp2e1 transgenic mice were used. The abundance of oxidative DNA adducts, mutagenic apurinic/apyrimidinic sites, and expression of base excision DNA repair genes was determined. In rats and wild-type mice, ethanol treatment for 4 weeks led to an increase in oxidative DNA damage and induction of expression of the base excision DNA repair genes that are known to remove oxidative DNA lesions. No increase in either of the endpoints was observed in ethanol-treated Cyp2e1-null mice, whereas the magnitude of response in p47(phox)-null mice and transgenic hCyp2e1 was identical to that in wild types. The increase in expression of DNA repair genes was completely abolished by treatment with the P450 inhibitor 1-aminobenzotriazole. In conclusion, the data support the hypothesis that oxidative stress to DNA is induced in liver by ethanol. Furthermore, although it was shown that nicotinamide adenine dinucleotide phosphate oxidase-derived oxidants are critical for the development of ethanol-induced liver injury, CYP2E1 is required for the induction of oxidative stress to DNA, and thus may play a key role in ethanol-associated hepatocarcinogenesis.