Long-term alcohol exposure changes sensitivity of rat Kupffer cells to lipopolysaccharide

Acetaldehyde exposure underlies functional defects in monocytes induced by excessive alcohol consumption

Increased intestinal permeability and hepatic macrophage activation by endotoxins are involved in alcohol-induced liver injury pathogenesis. Long-term alcohol exposure conversely induces endotoxin immune tolerance; however, the precise mechanism and reversibility are unclear. Seventy-two alcohol-dependent patients with alcohol dehydrogenase-1B (ADH1B, rs1229984) and aldehyde dehydrogenase-2 (ALDH2, rs671) gene polymorphisms admitted for alcohol abstinence were enrolled. Blood and fecal samples were collected on admission and 4 weeks after alcohol cessation and were sequentially analyzed. Wild-type and ALDH2*2 transgenic mice were used to examine the effect of acetaldehyde exposure on liver immune responses. The productivity of inflammatory cytokines of peripheral CD14⁺ monocytes in response to LPS stimulation was significantly suppressed in alcohol dependent patients on admission relative to that in healthy controls, which was partially restored by alcohol abstinence with little impact on the gut microbiota composition. Notably, immune suppression was associated with ALDH2/ADH1B gene polymorphisms, and patients with a combination of ALDH2*1/*2 and ADH1B*2 genotypes, the most acetaldehyde-exposed group, demonstrated a deeply suppressed phenotype, suggesting a direct role of acetaldehyde. In vitro LPS and malondialdehyde-acetaldehyde adducted protein stimulation induced direct cytotoxicity on monocytes derived from healthy controls, and a second LPS stimulation suppressed the inflammatory cytokines production. Consistently, hepatic macrophages of ethanol-administered ALDH2*2 transgenic mice exhibited suppressed inflammatory cytokines production in response to LPS compared to that in wild-type mice, reinforcing the contribution of acetaldehyde to liver macrophage function. These results collectively provide new perspectives on the systemic influence of excessive alcohol consumption based on alcohol-metabolizing enzyme genetic polymorphisms.

Panaxynol from Saposhnikovia diviaricata exhibits a hepatoprotective effect against lipopolysaccharide + D-Gal N induced acute liver injury by inhibiting Nf-κB/IκB-α and activating Nrf2/HO-1 signaling pathways

We investigated the mechanism of action of panaxynol (PAL) extract from the root of Saposhnikovia diviaricata (Turcz.) Schischk for treating acute liver injury caused by lipopolysaccharide (LPS) and D-galactosamine (D-Gal N) in mice. A mouse model of acute liver failure induced by LPS/D-Gal N was established. Mice were divided randomly into three equal groups: control group, LPS/D-Gal N group and PAL group. After seven days of continuous PAL administration, all animals except controls were injected with 50 μg/kg LPS and 800 mg/kg D-Gal N; blood and liver samples were collected after 8 h. Compared to the LPS/D-Gal N group, the levels of catalase, glutathione and superoxide dismutase were increased in the liver of the PAL group. The inflammatory response index indicated that PAL attenuated LPS/D Gal N-induced liver pathological injury and decreased levels of hepatic malondialdehyde, serum alanine aminotransferase, aspartate transaminase, tumor necrosis factor-α, and interleukins 1β and 6. PAL also inhibited LPS/D-Gal N induced nuclear factor-kappa B (Nf-κB), inhibitor kappa B-α (IκB-α) activation, and up-regulated Nrf2 and heme oxygenase-1 (HO-1) expression. PAL can prevent LPS/D-Gal N induced acute liver injury by activating Nrf2/HO-1 to stimulate antioxidant defense and inhibit the IkB-α/NF-κB signaling pathway.

Murine macrophage autophagy protects against alcohol-induced liver injury by degrading interferon regulatory factor 1 (IRF1) and removing damaged mitochondria

Excessive alcohol consumption induces intestinal dysbiosis of the gut microbiome and reduces gut epithelial integrity. This often leads to portal circulation-mediated translocation of gut-derived microbial products, such as lipopolysaccharide (LPS), to the liver, where these products engage Toll-like receptor 4 (TLR4) and initiate hepatic inflammation, which promotes alcoholic liver disease (ALD). Although the key self-destructive process of autophagy has been well-studied in hepatocytes, its role in macrophages during ALD pathogenesis remains elusive. Using WT and myeloid cell-specific autophagy-related 7 (Atg7) knockout (Atg7 ^ΔMye) mice, we found that chronic ethanol feeding for 6 weeks plus LPS injection enhances serum alanine aminotransferase and IL-1β levels and augments hepatic C-C motif chemokine ligand 5 (CCL5) and C-X-C motif chemokine ligand 10 (CXCL10) expression in WT mice, a phenotype that was further exacerbated in Atg7 ^ΔMye mice. Atg7 ^ΔMye macrophages exhibited defective mitochondrial respiration and displayed elevated mitochondrial reactive oxygen species production and inflammasome activation relative to WT cells. Interestingly, compared with WT cells, Atg7 ^ΔMye macrophages also had a drastically increased abundance and nuclear translocation of interferon regulatory factor 1 (IRF1) after LPS stimulation. Mechanistically, LPS induced co-localization of IRF1 with the autophagy adaptor p62 and the autophagosome, resulting in subsequent IRF1 degradation. However, upon p62 silencing or Atg7 deletion, IRF1 started to accumulate in autophagy-deficient macrophages and translocated into the nucleus, where it induced CCL5 and CXCL10 expression. In conclusion, macrophage autophagy protects against ALD by promoting IRF1 degradation and removal of damaged mitochondria, limiting macrophage activation and inflammation.

Taurine alleviates lipopolysaccharide‑induced liver injury by anti‑inflammation and antioxidants in rats

The aim of the present study was to investigate the protective effect of taurine on lipopolysaccharide (LPS)-induced liver injury and its mechanisms. Male rats were randomly divided into three groups: Normal saline, LPS model and taurine treatment. Experimental animals were treated with saline or taurine (dissolved in saline, 200 mg/kg/day) via intravenous injection. After 2 h, saline or LPS (0.5 mg/kg) was administrated via intraperitoneal injection. Markers of liver injury, pro-inflammatory cytokines and superoxide dismutase (SOD) activity were determined in plasma. Liver tissues were removed for morphological analysis and determination by western blot analysis. Taurine significantly reduced the elevation in the levels of LPS-induced aspartate transaminase and alanine transaminase and decreased the concentrations of LPS-induced inflammatory factors including tumor necrosis factor-α and interleukin-6. Taurine also increased the activity of SOD in serum and the expression of heme oxygenase-1 protein in liver tissue. Taurine pretreatment also reduced the elevated expression levels of LPS-induced cyclooxygenase-2, nuclear factor κB and extracellular regulated protein kinase. The results from the present study demonstrated that taurine alleviates LPS-induced liver injury. The beneficial role of taurine may be associated with its reduction of pro-inflammatory response and oxidative stress.

Fever onset is linked to the appearance of lipopolysaccharide in the liver

To assess the relative contributions of different phagocytes to the febrile response of guinea pigs to intravenous (i.v.) and intraperitoneal (i.p.) bacterial endotoxic lipopolysaccharide (LPS), we injected fluorescein isothiocyanate (FITC)-labeled LPS at doses of 37.5, 75, 150, 300 and 900 μg/kg, and measured its distribution and corresponding core temperature (Tc) changes before and at 15, 30, 60, 90, and 120 min after injection. At all times, i.v. FITC-LPS appeared as granular fluorescent patches in circulating leukocytes and hepatic macrophages; its density was proportional to dose. At all doses, the density of i.v. FITC-LPS labeling decreased from its peak 15 min after injection at a rate commensurate with its dose. Intraperitoneal FITC-LPS was also present dose- and time-dependently in peritoneal macrophages, but it appeared later and accumulated more slowly except at the highest dose. Compared with i.v. FITC-LPS, its maximal appearance was always lower in density. No labeling was found at any time in brain and kidney following any dose of i.v. or i.p. FITC-LPS injection. The initiation of Tc rises was best correlated with the presence of FITC-LPS in liver, irrespective of its route of injection. Pretreatment with gadolinium chloride 3 days before LPS injection attenuated the febrile response and reduced FITC-LPS labels in liver. These results suggest that the Kupffer cells may be central to the initiation of the febrile response of guinea pigs to i.v. and i.p. LPS.

Adipose tissue-liver axis in alcoholic liver disease

Alcoholic liver disease (ALD) remains an important health problem worldwide. The disease spectrum is featured by early steatosis, steatohepatitis (steatosis with inflammatory cells infiltration and necrosis), with some individuals ultimately progressing to fibrosis/cirrhosis. Although the disease progression is well characterized, no effective therapies are currently available for the treatment in humans. The mechanisms underlying the initiation and progression of ALD are multifactorial and complex. Emerging evidence supports that adipose tissue dysfunction contributes to the pathogenesis of ALD. In the first part of this review, we discuss the mechanisms whereby chronic alcohol exposure contributed to adipose tissue dysfunction, including cell death, inflammation and insulin resistance. It has been long known that aberrant hepatic methionine metabolism is a major metabolic abnormality induced by chronic alcohol exposure and plays an etiological role in the pathogenesis of ALD. The recent studies in our group documented the similar metabolic effect of chronic alcohol drinking on methionine in adipose tissue. In the second part of this review, we also briefly discuss the recent research progress in the field with a focus on how abnormal methionine metabolism in adipose tissue contributes to adipose tissue dysfunction and liver damage.

Lactobacillus fermentum ZYL0401 Attenuates Lipopolysaccharide-Induced Hepatic TNF-α Expression and Liver Injury via an IL-10- and PGE2-EP4-Dependent Mechanism

Lipopolysaccharide (LPS) has essential role in the pathogenesis of D-galactosamine-sensitized animal models and alcoholic liver diseases of humans, by stimulating release of pro-inflammatory mediators that cause hepatic damage and intestinal barrier impairment. Oral pretreatment of probiotics has been shown to attenuate LPS-induced hepatic injury, but it is unclear whether the effect is direct or due to improvement in the intestinal barrier. The present study tested the hypothesis that pretreatment with probiotics enables the liver to withstand directly LPS-induced hepatic injury and inflammation. In a mouse model of LPS-induced hepatic injury, the levels of hepatic tumor necrosis factor-alpha (TNF-α) and serum alanine aminotransferase (ALT) of mice with depleted intestinal commensal bacteria were not significantly different from that of the control models. Pre-feeding mice for 10 days with Lactobacillus fermentum ZYL0401 (LF41), significantly alleviated LPS-induced hepatic TNF-α expression and liver damage. After LF41 pretreatment, mice had dramatically more L.fermentum-specific DNA in the ileum, significantly higher levels of ileal cyclooxygenase (COX)-2 and interleukin 10 (IL-10) and hepatic prostaglandin E2 (PGE₂). However, hepatic COX-1, COX-2, and IL-10 protein levels were not changed after the pretreatment. There were also higher hepatic IL-10 protein levels after LPS challenge in LF41-pretreaed mice than in the control mice. Attenuation of hepatic TNF-α was mediated via the PGE₂/E prostanoid 4 (EP4) pathway, and serum ALT levels were attenuated in an IL-10-dependent manner. A COX-2 blockade abolished the increase in hepatic PGE₂ and IL-10 associated with LF41. In LF41-pretreated mice, a blockade of IL-10 caused COX-2-dependent promotion of hepatic PGE₂, without affecting hepatic COX-2levels. In LF41-pretreated mice, COX2 prevented enhancing TNF-α expression in both hepatic mononuclear cells and the ileum, and averted TNF-α-mediated increase in intestinal permeability. Together, we demonstrated that LF41 pre-feeding enabled the liver to alleviate LPS-induced hepatic TNF-α expression and injury via a PGE₂-EP4- and IL-10-dependent mechanism.

Mechanisms of action of acetaldehyde in the up-regulation of the human α2(I) collagen gene in hepatic stellate cells: key roles of Ski, SMAD3, SMAD4, and SMAD7

Alcohol-induced liver fibrosis and eventually cirrhosis is a leading cause of death. Acetaldehyde, the first metabolite of ethanol, up-regulates expression of the human α2(I) collagen gene (COL1A2). Early acetaldehyde-mediated effects involve phosphorylation and nuclear translocation of SMAD3/4-containing complexes that bind to COL1A2 promoter to induce fibrogenesis. We used human and mouse hepatic stellate cells to elucidate the mechanisms whereby acetaldehyde up-regulates COL1A2 by modulating the role of Ski and the expression of SMADs 3, 4, and 7. Acetaldehyde induced up-regulation of COL1A2 by 3.5-fold, with concomitant increases in the mRNA (threefold) and protein (4.2- and 3.5-fold) levels of SMAD3 and SMAD4, respectively. It also caused a 60% decrease in SMAD7 expression. Ski, a member of the Ski/Sno oncogene family, is colocalized in the nucleus with SMAD4. Acetaldehyde induces translocation of Ski and SMAD4 to the cytoplasm, where Ski undergoes proteasomal degradation, as confirmed by the ability of the proteasomal inhibitor lactacystin to blunt up-regulation of acetaldehyde-dependent COL1A2, but not of the nonspecific fibronectin gene (FN1). We conclude that acetaldehyde up-regulates COL1A2 by enhancing expression of the transactivators SMAD3 and SMAD4 while inhibiting the repressor SMAD7, along with promoting Ski translocation from the nucleus to cytoplasm. We speculate that drugs that prevent proteasomal degradation of repressors targeting COL1A2 may have antifibrogenic properties.

Inhibition of heat shock protein (molecular weight 90 kDa) attenuates proinflammatory cytokines and prevents lipopolysaccharide-induced liver injury in mice

Endotoxin-mediated proinflammatory cytokines play a significant role in the pathogenesis of acute and chronic liver diseases. Heat shock protein 90 (molecular weight, 90 kDa) (hsp90) functions as an important chaperone of lipopolysaccharide (LPS) signaling and is required for the production of proinflammatory cytokines. We hypothesized that inhibition of hsp90 would prevent LPS-induced liver injury by decreasing proinflammatory cytokines. C57BL/6 mice were injected intraperitoneally with an hsp90 inhibitor, 17-dimethylamino-ethylamino-17-demethoxygeldanamycin (17-DMAG), and LPS. Parameters of liver injury, proinflammatory cytokines, and associated mechanisms were studied by in vivo and in vitro experiments. Inhibition of hsp90 by 17-DMAG prevented LPS-induced increases in serum alanine aminotransferase activity and significantly reduced serum tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6) protein as well as messenger RNA (mRNA) in liver. Enhanced DNA-binding activity of heat shock transcription factor 1 (HSF1) and induction of target gene heat shock protein 70 (molecular weight, 70 kDa) confirmed hsp90 inhibition in liver. 17-DMAG treatment decreased cluster of differentiation 14 mRNA and LPS-induced nuclear factor kappa light-chain enhancer of activated B cells (NFκB) DNA binding without affecting Toll-like receptor 4 mRNA in liver. Mechanistic studies revealed that 17-DMAG-mediated inhibition of TNFα showed no effect on LPS-induced NFκB promoter-driven reporter activity, but significantly decreased TNFα promoter-driven reporter activity. Chromatin immunoprecipitation assays showed that 17-DMAG enhanced HSF1 binding to the TNFα promoter, but not the IL-6 promoter, suggesting HSF1 mediated direct inhibition of TNFα, but not IL-6. We show that HSF1 indirectly regulates IL-6 by the induction of another transcription factor, activating transcription factor 3. Inhibition of HSF1, using small interfering RNA, prevented 17-DMAG-mediated down-regulation of NFκB-binding activity, TNFα, and IL-6 induction, supporting a repressive role for HSF1 on proinflammatory cytokine genes during hsp90 inhibition.

CONCLUSION

Hsp90 inhibition in vivo reduces proinflammatory cytokines and prevents LPS-induced liver injury likely through repressive action of HSF1. Our results suggest a novel application for 17-DMAG in alleviating LPS-induced liver injury.

Inflammation in alcoholic liver disease

Frank Burr Mallory's landmark observation in 1911 on the histopathology of alcoholic liver disease (ALD) was the first identification of a link between inflammation and ALD. In this review, we summarize recent advances regarding the origins and roles of various inflammatory components in ALD. Metabolism of ethanol generates a number of metabolites, including acetate, reactive oxygen species, acetaldehyde, and epigenetic changes, that can induce inflammatory responses. Alcohol and its metabolites can also initiate and aggravate inflammatory conditions by promoting gut leakiness of microbial products, by sensitizing immune cells to stimulation, and by activating innate immune pathways, such as complement. Chronic alcohol consumption also sensitizes nonimmune cells, e.g., hepatocytes, to inflammatory signals and impairs their ability to respond to protective signals. Based on these advances, a number of inflammatory targets have been identified with potential for therapeutic intervention in ALD, presenting new opportunities and challenges for translational research.

Chronic ethanol feeding accelerates hepatocellular carcinoma progression in a sex-dependent manner in a mouse model of hepatocarcinogenesis

BACKGROUND

Chronic ethanol consumption increases the risk of hepatic cirrhosis and hepatocellular carcinoma (HCC). While sex differences exist in susceptibility to ethanol-induced liver damage/HCC development, little is known about the effects of ethanol on tumor progression.

METHODS

Neonatal male and female mice were initiated with a single dose of diethylnitrosamine (DEN). Sixteen or 40 weeks later, animals were placed on a 10/20% (v/v) ethanol-drinking water (EtOH-DW; alternate days) regime for 8 weeks. At study end, liver tissue and serum were analyzed for liver pathology/function and cytokine expression.

RESULTS

DEN reproducibly induced hepatic foci/tumors in male and female mice. Ethanol diminished hepatic function and increased liver damage, but ethanol alone did not induce hepatic foci/HCC formation. In DEN-initiated EtOH-DW animals, ethanol significantly increased tumor incidence and burden, but only in male mice. Male and female mice (±DEN) demonstrated comparable blood alcohol content at necropsy, yet increased hepatic damage and diminished hepatic function/antioxidant capacity were significantly greater in males. Analysis of liver mRNA for Th1, Th2, or T-regulatory factors demonstrated significantly elevated SMAD3 in male compared to female mice in response to EtOH, DEN initiation, and DEN + EtOH-DW.

CONCLUSIONS

These data demonstrate male mice are more susceptible to HCC incidence and progression in the setting of chronic ethanol feeding than females. Differences in markers of hepatic immune response in male mice suggest that increased TGFβ-SMAD3 signaling may enhance promotion in this model of HCC progression, effects modulated by chronic ethanol feeding.

The impact of alcohol on BCG-induced immunity against Mycobacterium tuberculosis

BACKGROUND

Alcoholics are at heightened risk for developing active tuberculosis. This study evaluates chronic alcohol consumption in a murine model of vaccination with Mycobacterium bovis Bacille Calmette-Guèrin (BCG) and subsequent pulmonary infection with virulent Mycobacterium tuberculosis.

METHODS

BALB/c mice were administered the Lieber-DeCarli liquid ethanol diet or pair-fed the liquid control diet for 3 weeks either before or after subcutaneous vaccination with M. bovis BCG. At least 3 weeks after BCG vaccination, groups of mice on the aforesaid diets were challenged with intratracheal infection with M. tuberculosis H37Rv. Lung mycobacterial burden, and lung and lung-associated lymph node CD4(+) lymphocyte production of tuberculosis-specific interferon (IFN)-γ were assayed. Popliteal lymph node lymphocytes from both dietary regimens undergoing BCG vaccination (in the absence of M. tuberculosis infection) were also evaluated for purified protein derivative-induced IFN-γ production by ELISpot assay.

RESULTS

Mice begun on alcohol prior to vaccination with M. bovis BCG demonstrated impaired control of pulmonary challenge with virulent M. tuberculosis, as well as impaired lung CD4(+) and popliteal lymph node T-cell IFN-γ responses. If BCG vaccination was delivered prior to initiation of alcohol feeding, the mice remained protected against a subsequent challenge with M. tuberculosis, and BCG-induced immunity was not impaired in either the lung or the popliteal lymph nodes.

CONCLUSIONS

Alcohol consumption blunts the development of the adaptive immune response to M. bovis BCG vaccination, which impairs the control of a secondary challenge with M. tuberculosis, but only if the alcohol exposure is begun prior to BCG vaccination. These results provide insight into mechanisms by which alcohol consumption impairs antimycobacterial immunity, including in response to vaccination and subsequent pathogenic challenge.

Pathogenesis of the hyperlipidemia of Gram-negative bacterial sepsis may involve pathomorphological changes in liver sinusoidal endothelial cells

The Gram-negative bacterium Pseudomonas aeruginosa is one of the most common opportunistic pathogens, especially after liver transplantation. Pathophysiological alterations of liver sinusoidal endothelial cells (LSECs) have far-reaching repercussions on the liver and on metabolism. LSECs are perforated with fenestrations, pores that facilitate the transfer of lipoproteins and macromolecules between blood and hepatocytes. Gram-negative bacterial endotoxin (lipopolysaccharide, LPS) and the P. aeruginosa toxin, pyocyanin, have marked effects on LSECs. Initial loss of LSEC porosity (defenestration) induced by P. aeruginosa pyocyanin and LPS may confer subsequent immune tolerance to circulating bacterial antigens and toxins. This review collates the known immune responses of the liver to Gram-negative bacterial toxins, with a focus on LSECs. Hyperlipidemia is an important response to Gram-negative bacterial sepsis. The mechanisms proposed for sepsis-associated hyperlipidemia include tissue lipoprotein lipase inhibition and upregulated hepatic triglyceride production. In this review, we propose defenestration of the LSECs by bacterial toxins as an additional mechanism for the hyperlipidemia of sepsis. Given the role of LSECs in hyperlipidemia and liver allograft rejection, LSEC changes induced by P. aeruginosa toxins including LPS and pyocyanin may have significant clinical implications.

Different effects of acute and chronic ethanol on LPS-induced cytokine production and TLR4 receptor behavior in mouse peritoneal macrophages

Both binge and chronic heavy drinking can adversely affect the immune system, but the effects seem to be at least partly dependent on the manner of ethanol (EtOH) consumption. Previous study results from several labs have clearly demonstrated that acute administration of EtOH interferes with innate immune responses. Specifically, EtOH has a general inhibitory effect on cytokine and chemokine production induced by various Toll-like receptor (TLR) ligands, and it suppresses signaling on several levels along the TLR signaling pathways. However, it is not clear whether chronic exposure to ethanol has the same effects or not. The purpose of this study was to investigate the difference between the effect of chronic versus acute EtOH exposure on LPS-induced cytokine production and clustering of components of the TLR4 complex, which is an important early signaling event. Some groups of mice received acute EtOH by oral gavage using our binge drinking model and/or chronic administration of EtOH at 20% (w/v) in the drinking water as the sole liquid source for 4 wk. The cellular distribution of CD14 and TLR4 were studied by confocal microscopy following exposure of peritoneal cells to LPS locally in vivo, and cytokine production in peritoneal fluid and serum was measured by ELISA after LPS injection via a tail vein. Chronic EtOH exposure did not consistently cause significant changes in LPS-induced cytokine production. However, mice previously exposed to chronic EtOH treatment became partially resistant to the suppressive effects of acute EtOH administration with regard to cytokine production. As we have reported previously, acute EtOH treatment suppressed the LPS-induced clustering of TLR4 and CD14 in peritoneal macrophages. However, peritoneal cells from mice treated with chronic EtOH exhibited a greater amount of intracellular expression of CD14 instead of CD14/TLR4 clustering on the membrane following LPS exposure. The results demonstrate different effects of chronic versus acute EtOH treatment on LPS-induced cytokine production in mice. Partial tolerance to the effect of acute EtOH administration caused by chronic EtOH treatment suggests a compensatory mechanism is induced by chronic EtOH administration. Acute EtOH exposure acts probably by disrupting the receptor clustering following LPS recognition, whereas adaptations induced by chronic EtOH treatment seem to involve alteration of LPS receptor expression.

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.

Cell type-dependent pro- and anti-inflammatory role of signal transducer and activator of transcription 3 in alcoholic liver injury

BACKGROUND & AIMS

Signal transducer and activator of transcription 3 (STAT3) is known to be activated in human alcoholic liver disease, but its role in the pathogenesis of alcoholic liver injury remains obscure.

METHODS

The role of STAT3 in alcoholic liver injury was investigated in hepatocyte-specific STAT3 knockout (H-STAT3KO) mice and macrophage/neutrophil-specific STAT3 KO (M/N-STAT3KO) mice. Alcoholic liver injury was achieved by feeding mice a liquid diet containing 5% ethanol for up to 8 weeks.

RESULTS

Compared with wild-type mice, feeding H-STAT3KO mice with an ethanol-containing diet induced greater hepatic steatosis, hypertriglyceridemia, and hepatic expression of lipogenic genes (sterol regulatory element-binding protein, fatty acid synthase, acetyl-CoA carboxylase-1, and stearoyl-CoA desaturase 1), but less inflammation and lower expression of hepatic proinflammatory cytokines. In contrast, ethanol-fed M/N-STAT3KO mice showed more hepatic inflammation, worse injury, and increased hepatic expression of proinflammatory cytokines compared with wild-type mice. Kupffer cells isolated from ethanol-fed H-STAT3KO mice produced similar amounts of reactive oxygen species and tumor necrosis factor alpha, whereas Kupffer cells from M/N-STAT3KO mice produced more reactive oxygen species and tumor necrosis factor alpha compared with wild-type controls.

CONCLUSIONS

These findings suggest that STAT3 regulates hepatic inflammation in a cell type-dependent manner during alcoholic liver injury: STAT3 in hepatocytes promotes whereas STAT3 in macrophages/Kupffer cells suppresses inflammation. In addition, activation of hepatocellular STAT3 ameliorates alcoholic fatty liver via inhibition of sterol regulatory element-binding protein 1c expression.

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.

Thymocytes, pre-B cells, and organ changes in a mouse model of chronic ethanol ingestion--absence of subset-specific glucocorticoid-induced immune cell loss

BACKGROUND

The well-known immune deficiency of the chronic alcoholic dictates the need for a long-term rodent ethanol administration model to evaluate the baseline immunologic effects of chronic ethanol abuse, and investigate the genetic determinants of those effects. Much published work with rodents has shown clearly that acute ethanol administration and short-term ethanol-containing liquid diets both cause elevated corticosterone and can cause significant thymocyte, pre-B cell and peripheral lymphocyte losses. Such losses may mask more subtle alterations in immune homeostasis, and in any case are generally short-lived compared with the span of chronic ethanol abuse. Thus, it is important to have a model in which long-term immune alterations can be studied free of corticosteroid-induced cell losses.

METHODS

We have utilized chronic 20% (w/v) ethanol in water administration to several mouse strains for prolonged periods of time and evaluated serum corticosterone, immunologic stress parameters, and other organ changes by standard methods.

RESULTS

We now confirm earlier reports that chronic ethanol in water administration to mice does not produce net elevations of corticosterone, although diurnal variation is altered. Importantly, there is neither selective loss of immune cell populations known to be corticosteroid sensitive, CD4+CD8+ thymocytes and pre-B cells, nor are changes observed in the histologic appearance of the thymus. Nonetheless, there are significant chronic ethanol effects in other tissues, including reduced heart weight, mild hepatic steatosis, alterations of gut flora, increased serum peptidoglycan, and as published elsewhere, immune system abnormalities.

CONCLUSIONS

This model of ethanol administration is convenient, sustainable for up to 1 year, demonstrably feasible in several mouse strains, permits good weight gains in most strains, and results in significant changes in a number of organs. The administration method also will permit modeling of long-term steady abuse punctuated by major binges, and is suitable for supplementation studies using water soluble additives. Overall, the method is useful for a wide range of studies requiring a chronic low-stress method of ethanol administration.

Effect of ethanol on inflammatory responses. Implications for pancreatitis

BACKGROUND/AIMS

Alcohol use alters inflammatory cell responses. While alcohol has direct effects on pancreatic acinar cells, activation of inflammatory cells is a major component of the pathology of alcoholic pancreatitis.

METHODS

The effects of acute or chronic alcohol exposure were evaluated in human monocytes on the production of TNFalpha or IL-10 production, pro-inflammatory gene and nuclear factor-kappaB (NF-kappaB) activation.

RESULTS

Moderate, acute alcohol consumption or equivalent doses of alcohol in vitro had anti-inflammatory effects on monocyte activation via inhibition of pro-inflammatory genes and NF-kappaB activation, inhibition of TNFalpha production and augmentation of the anti-inflammatory cytokine, IL-10. In contrast, acute alcohol treatment augmented NF-kappaB activation and TNFalpha production and inhibited IL-10 levels in the presence of complex stimulation with combined TLR2 and TLR4 ligands. Prolonged alcohol exposure also resulted in an increase in NF-kappaB and TNFalpha production in response to TLR4 stimulation with LPS.

CONCLUSION

These results suggest that alcohol can either attenuate or promote inflammatory responses that are critical in pancreatitis. Our results support the hypothesis that both acute alcohol intake in the presence of complex stimuli (such as necrotic cells) and chronic alcohol exposure result in hyper-responsiveness of monocytes to inflammatory signals and may contribute to increased inflammation in pancreatitis.

Expression of Toll-like receptor 4 in rat liver during the course of carbon tetrachloride-induced liver injury

BACKGROUND AND AIM

It has recently been reported that Toll-like receptor 4 (TLR4) is involved in cellular responses to lipopolysaccharides (LPS) and early liver injury induced by LPS. The aim of the present study was to investigate the alterations of TLR4 gene expression in liver tissues and Kupffer cells during the course of carbon tetrachloride (CCl(4))-induced chronic liver injury and fibrosis and its role in liver injury.

METHODS

Rats were induced with liver injury and fibrosis by CCl(4) administered subcutaneously twice weekly for up to 8 weeks. The Kupffer cells were isolated by the combined collagenase-pronase perfusion method and incubated with varying doses of LPS. The mRNA expression of TLR4 in liver tissues and Kupffer cells was measured by reverse transcriptase polymerase chain reaction. The levels of tumor necrosis factor (TNF)-alpha in Kupffer cell culture supernatants were determined by enzyme-linked immunosorbent assay. The plasma levels of the endotoxin were determined by chromogenic substrate limulus amebocyte lysate assay. The association of the endotoxin receptor expression with plasma endotoxin levels was assessed.

RESULTS

CCl(4) administration elicited extensive changes in liver morphology, including steatosis, inflammation, necrosis, and fibrosis. Low levels of TLR4 mRNA were detected in normal rat liver tissues, but no expression was detected in the Kupffer cells. The expression of TLR4 mRNA in liver tissues and Kupffer cells was increased 2 weeks after CCl(4) administration, peaked at 4 and 6 weeks, and declined at 8 weeks. Basic TNF-alpha production of Kupffer cells isolated from CCl(4)-treated rats at 4 and 6 weeks was significantly higher than that of normal rats (P < 0.05). Upon LPS stimulation, production of TNF-alpha was markedly increased in Kupffer cells isolated from normal and 2-,4-, and 6-week CCl(4)-treated rats. Moreover, LPS-induced TNF-alpha production was dose-dependent. The plasma levels of the endotoxin were increased during the time of liver injury. There was a correlation between plasma endotoxin levels and TLR4 gene expression in the early and middle stage of liver injury.

CONCLUSION

The gene expression of TLR4 was upregulated during the course of CCl(4)-induced liver injury, which is associated with the degree of liver injury and Kupffer cell activation. The gut-derived endotoxin may be involved in the upregulation of TLR4 expression.

Involvement of TLR4/type I IL-1 receptor signaling in the induction of inflammatory mediators and cell death induced by ethanol in cultured astrocytes

Activated astroglial cells are implicated in neuropathogenesis of many infectious and inflammatory diseases of the brain. A number of inflammatory mediators and cytokines have been proposed to play a key role in glial cell-related brain damage. Cytokine production seems to be initiated by signaling through TLR4/type I IL-1R (IL-1RI) in response to their ligands, LPS and IL-1beta, playing vital roles in innate host defense against infections, inflammation, injury, and stress. We have shown that glial cells are stimulated by ethanol, up-regulating cytokines and inflammatory mediators associated with TLR4 and IL-1RI signaling pathways in brain, suggesting that ethanol may contribute to brain damage via inflammation. We explore the possibility that ethanol, in the absence of LPS or IL-1beta, triggers signaling pathways and inflammatory mediators through TLR4 and/or IL-1RI activation in astrocytes. We show in this study that ethanol, at physiologically relevant concentrations, is capable of inducing rapid phosphorylation within 10 min of IL-1R-associated kinase, ERK1/2, stress-activated protein kinase/JNK, and p38 MAPK in astrocytes. Then an activation of NF-kappaB and AP-1 occurs after 30 min of ethanol treatment along with an up-regulation of inducible NO synthase and cyclooxygenase-2 expression. Finally, we note an increase in cell death after 3 h of treatment. Furthermore, by using either anti-TLR4- or anti-IL-1RI-neutralizing Abs, before and during ethanol treatment, we inhibit ethanol-induced signaling events, including NF-kappaB and AP-1 activation, inducible NO synthase, and cyclooxygenase-2 up-regulation and astrocyte death. In summary, these findings indicate that both TLR4 and IL-1RI activation occur upon ethanol treatment, and suggest that signaling through these receptors mediates ethanol-induced inflammatory events in astrocytes and brain.

Lipopolysaccharide is a cofactor for malondialdehyde-acetaldehyde adduct-mediated cytokine/chemokine release by rat sinusoidal liver endothelial and Kupffer cells

BACKGROUND

The nonparenchymal cells of the liver have been suggested to play a significant role in the inflammatory processes observed in the development and/or progression of alcoholic liver disease. Our laboratories have shown that malondialdehyde-acetaldehyde (MAA)-modified proteins can induce immune responses, cytokine/chemokine secretion, and antigen processing and presentation by liver sinusoidal endothelial cells (SECs). Another molecule that has been shown to induce similar types of responses in Kupffer cells (KCs) is lipopolysaccharide (LPS). Because these materials induce similar responses, it was the purpose of this study to investigate the relationship between LPS and MAA-modified proteins in the development of proinflammatory responses by SECs and KCs.

METHODS

For these studies, SECs and KCs were isolated from chow-fed, pair-fed, and ethanol-fed rats. Cells were stimulated with media alone, bovine serum albumin (Alb), or MAA-modified Alb (MAA-Alb) in the presence or absence of LPS 1 ng/ml, and the supernatants were assayed by enzyme-linked immunosorbent assay for tumor necrosis factor alpha, macrophage chemotactic protein 1, and macrophage inhibitory protein.

RESULTS

All three cytokines/chemokines were 3 to 5 times higher when SECs or KCs were stimulated by MAA-Alb in the presence of LPS, in contrast to cells stimulated with Alb or media in the presence of LPS. Chronic ethanol consumption (6 weeks) had variable effects on the secretion of these cytokines/chemokines but in general did not alter the increased secretion in response to MAA-Alb in the presence of LPS.

CONCLUSIONS

These studies strongly suggest that the sensitization of SECs and KCs by LPS plays a significant role in the development and/or progression of alcoholic liver disease, and the subsequent activation by MAA-modified proteins may be a mechanism by which proinflammatory processes are initiated.

CD14 expression in Kupffer cells of ischemia-reperfusion injury after rat liver transplantation

AIM: To study the expression of lipopolysaccharide receptor CD14 mRNA and protein in Kupffer cells and its role in ischemia-reperfusion injury (IRI) in rat liver graft.

METHODS: The Kupffer cells were isolated and divided into control, ischemia-reperfusion (IR), and anti CD14 antibody groups. The CD14 mRNA, CD14 protein, nuclear factor kappa B (NF-κB) activity, and TNF-α and IL-1 level in the culture supernatant were measured.

RESULTS: The CD14 mRNA, and protein in IR group were significantly higher than those in control group (mRNA 1.28±0.12 vs 0.42±0.02, protein 23.7±2.36 vs 6.3±1.27, P < 0.01). The NF-κB activity, TNF-α and IL-1 level in IR group were significantly higher than those in control group (NF-κB 2.79±0.48 vs 0.27±0.01, TNF-α 205.9±12.04 ng/L vs 57.4±4.35 ng/L, IL-1 176.8±8.94 ng/L vs 37.6±3.47 ng/L, P < 0.01), and they greatly decreased after anti-CD14 antibody treatment compared with IR group (NF-κB 1.34±0.24 vs 2.79±0.48, TNF-α 129.6±6.48 ng/L vs 205.9±12.04 ng/L, IL-1 103.4±5.74 ng/L vs 176.8±8.94 ng/L, P < 0.05), but still significantly higher than those in control group (NF-κB 1.34±0.24 vs 0.27±0.01, TNF-α 129.6±6.48 ng/L vs 57.4±4.35 ng/L, IL-1 103.4±5.74 ng/L vs 37.6±3.47 ng/L, P < 0.01).

CONCLUSION: LPS following IR can up-regulate the expression of CD14 mRNA and protein in Kupffer cells, and subsequently activate NF-κB to produce cytokines. But other signal transduction pathways might also participate in the NF-κB activation and IRI.

Toll-like receptor 4 mediates inflammatory signaling by bacterial lipopolysaccharide in human hepatic stellate cells

Bacterial lipopolysaccharide (LPS) stimulates Kupffer cells and participates in the pathogenesis of alcohol-induced liver injury. However, it is unknown whether LPS directly affects hepatic stellate cells (HSCs), the main fibrogenic cell type in the injured liver. This study characterizes LPS-induced signal transduction and proinflammatory gene expression in activated human HSCs. Culture-activated HSCs and HSCs isolated from patients with hepatitis C virus-induced cirrhosis express LPS-associated signaling molecules, including CD14, toll-like receptor (TLR) 4, and MD2. Stimulation of culture-activated HSCs with LPS results in a rapid and marked activation of NF-kappaB, as assessed by in vitro kinase assays for IkappaB kinase (IKK), IkappaBalpha steady-state levels, p65 nuclear translocation, NF-kappaB-dependent luciferase reporter gene assays, and electrophoretic mobility shift assays. Lipid A induces NF-kappaB activation in a similar manner. Both LPS- and lipid A-induced NF-kappaB activation is blocked by preincubation with either anti-TLR4 blocking antibody (HTA125) or Polymyxin B. Lipid A induces NF-kappaB activation in HSCs from TLR4-sufficient (C3H/OuJ) mice but not from TLR4-deficient (C3H/HeJ) mice. LPS also activates c-Jun N-terminal kinase (JNK), as assessed by in vitro kinase assays. LPS up-regulates IL-8 and MCP-1 gene expression and secretion. LPS-induced IL-8 secretion is completely inhibited by the IkappaB super repressor (Ad5IkappaB) and partially inhibited by a specific JNK inhibitor, SP600125. LPS also up-regulates cell surface expression of ICAM-1 and VCAM-1. In conclusion, human activated HSCs utilize components of TLR4 signal transduction cascade to stimulate NF-kappaB and JNK and up-regulate chemokines and adhesion molecules. Thus, HSCs are a potential mediator of LPS-induced liver injury.