Lethal toxicity of lipopolysaccharide and tumor necrosis factor in normal and D-galactosamine-treated mice

Fatty acid binding protein 7 regulates phagocytosis and cytokine production in Kupffer cells during liver injury

Kupffer cells (KCs) are involved in the progression of liver diseases such as hepatitis and liver cancer. Several members of the fatty acid binding proteins (FABPs) are expressed by tissue macrophages, and FABP7 is localized only in KCs. To clarify the role of FABP7 in the regulation of KC function, we evaluated pathological changes of Fabp7 knockout mice during carbon tetrachloride-induced liver injury. During liver injury in Fabp7 knockout mice, serum liver enzymes were increased, cytokine expression (tumor necrosis factor-α, monocyte chemoattractant protein-1, and transforming growth factor-β) was decreased in the liver, and the number of KCs in the liver necrotic area was significantly decreased. Interestingly, in the FABP7-deficient KCs, phagocytosis of apoptotic cells was impaired, and expression of the scavenger receptor CD36 was markedly decreased. In chronic liver injury, Fabp7 knockout mice showed less fibrogenic response to carbon tetrachloride compared with wild-type mice. Taken together, FABP7 is involved in the liver injury process through its regulation of KC phagocytic activity and cytokine production. Such modulation of KC function by FABP7 may provide a novel therapeutic approach to the treatment of liver diseases.

Balance of inflammatory pathways and interplay of immune cells in the liver during homeostasis and injury

Multiple potentially harmful stimuli challenge the liver, the chief metabolic and detoxifying organ of the human body. Due to its central anatomical location, continuous blood flow from the gastrointestinal tract through the hepatic sinusoids allows the metabolically active hepatocytes, the non-parenchymal cells and the various immune cell populations residing and patrolling in the liver to interact with antigens and microbiological components coming from the intestine. Cytokines are key mediators within the complex interplay of intrahepatic immune cells and hepatocytes, because they can activate effector functions of immune cells as well as hepatocytic intracellular signaling pathways controlling cellular homeostasis. Kupffer cells and liver-infiltrating monocyte-derived macrophages are primary sources of cytokines such as tumor necrosis factor (TNF). The liver is also enriched in natural killer (NK) and natural killer T (NKT) cells, which fulfill functions in pathogen defense, T cell recruitment and modulation of fibrogenic responses. TNF can activate specific intracellular pathways in hepatocytes that influence cell fate in different manners, e.g. pro-apoptotic signals via the caspase cascade, but also survival pathways, namely the nuclear factor (NF)-kappaB pathway. NF-kappaB regulates important functions in liver physiology and pathology. The exact dissection of the contribution of recruited and resident immune cells, their soluble cytokine and chemokine mediators and the intracellular hepatocytic response in liver homeostasis and injury could potentially identify novel targets for the treatment of acute and chronic liver disease, liver fibrosis or cirrhosis.

Bovine lactoferrin ingestion protects against inflammation via IL-11 induction in the small intestine of mice with hepatitis

Accumulating evidence suggests that orally ingested lactoferrin protects against inflammation. To assess the efficacy of orally administered bovine lactoferrin (bLF) against hepatitis and to identify the underlying mechanism, in the present study, we used four mouse models of hepatitis induced by d-galactosamine (GalN), carbon tetrachloride (CCl4), GalN plus lipopolysaccharide (LPS) and zymosan plus LPS. Intraperitoneal (i.p.) injection of GalN (500 mg/kg body weight) in mice treated with bovine serum albumin (BSA) for 14 d significantly increased serum aspartate aminotransferase (AST) concentrations compared with the untreated mice. However, orally administered bLF reduced AST concentrations compared with BSA treatment. In mice that received a single injection (0·4 ml/kg) and twice-weekly injections (0·08 ml/kg) of CCl4 for 24 weeks and pretreated with bLF for 14 d and 24 weeks, respectively, significantly suppressed alanine aminotransferase and AST concentrations were observed compared with the BSA-treated control. Oral administration of bLF for 14 d before i.p. injection of LPS (5 mg/kg) plus GalN (1 g/kg) significantly improved the survival rate. In mice that received intravenous injection of zymosan (25 mg/kg) and LPS (15 μg/kg) at 7 d intervals, bLF reduced the elevation of AST concentrations and enhanced the production of IL-11 and bone morphogenetic protein 2 in the small intestine compared with the BSA-treated control. To evaluate the effects of IL-11, we used IL-11 receptor α-null mice treated with GalN, CCl4 and zymosan plus LPS. In this group, the activity of bLF was not significantly different from that of BSA. These data indicate that orally ingested bLF enhances the expression of IL-11 in the small intestine and up-regulates protective activity in mice with hepatitis.

Altering the sphingolipid acyl chain composition prevents LPS/GLN-mediated hepatic failure in mice by disrupting TNFR1 internalization

The involvement of ceramide in death receptor-mediated apoptosis has been widely examined with most studies focusing on the role of ceramide generated from sphingomyelin hydrolysis. We now analyze the effect of the ceramide acyl chain length by studying tumor necrosis factor α receptor-1 (TNFR1)-mediated apoptosis in a ceramide synthase 2 (CerS2) null mouse, which cannot synthesize very-long acyl chain ceramides. CerS2 null mice were resistant to lipopolysaccharide/galactosamine-mediated fulminant hepatic failure even though TNFα secretion from macrophages was unaffected. Cultured hepatocytes were also insensitive to TNFα-mediated apoptosis. In addition, in both liver and in hepatocytes, caspase activities were not elevated, consistent with inhibition of TNFR1 pro-apoptotic signaling. In contrast, Fas receptor activation resulted in the death of CerS2 null mice. Caspase activation was blocked because of the inability of CerS2 null mice to internalize the TNFR1; whereas Fc-TNFα was internalized to a perinuclear region in hepatocytes from wild-type mice, no internalization was detected in CerS2 null mice. Our results indicate that altering the acyl chain composition of sphingolipids inhibits TNFR1 internalization and inhibits selective pro-apoptotic downstream signaling for apoptosis.

Ubiquitination-deubiquitination by the TRIM27-USP7 complex regulates tumor necrosis factor alpha-induced apoptosis

Tumor necrosis factor alpha (TNF-α) plays a role in apoptosis and proliferation in multiple types of cells, and defects in TNF-α-induced apoptosis are associated with various autoimmune diseases. Here, we show that TRIM27, a tripartite motif (TRIM) protein containing RING finger, B-box, and coiled-coil domains, positively regulates TNF-α-induced apoptosis. Trim27-deficient mice are resistant to TNF-α-d-galactosamine-induced hepatocyte apoptosis. Trim27-deficient mouse embryonic fibroblasts (MEFs) are also resistant to TNF-α-cycloheximide-induced apoptosis. TRIM27 forms a complex with and ubiquitinates the ubiquitin-specific protease USP7, which deubiquitinates receptor-interacting protein 1 (RIP1), resulting in the positive regulation of TNF-α-induced apoptosis. Our findings indicate that the ubiquitination-deubiquitination cascade mediated by the TRIM27-USP7 complex plays an important role in TNF-α-induced apoptosis.

TNFR2 maintains adequate IL-12 production by dendritic cells in inflammatory responses by regulating endogenous TNF levels

Sepsis-induced immune reactions are reduced in TNF receptor 2 (TNFR2)-deficient mice as previously shown. In order to elucidate the underlying mechanisms, the functional integrity of myeloid cells of TNFR2-deficient mice was analyzed and compared to wild type (WT) mice. The capacity of dendritic cells to produce IL-12 was strongly impaired in TNF-deficient mice, mirroring impaired production of IL-12 by WT dendritic cells in sepsis or after LPS or TNF pre-treatment. In addition, TNFR2-deficient mice were refractory to LPS pre-treatment and also to hyper-sensitization by inactivated Propionibacterium acnes, indicating habituation to inflammatory stimuli by the immune response when TNFR2 is lacking. Constitutive expression of TNF mRNA in kidney, liver, spleen, colon and lung tissue, and the presence of soluble TNFR2 in urine of healthy WT mice supported the conclusion that TNF is continuously present in naïve mice and controlled by soluble TNFR2. In TNFR2-deficient mice endogenous TNF levels cannot be balanced and the continuous exposure to enhanced TNF levels impairs dendritic cell function. In conclusion, TNF pre-exposure suppresses secondary inflammatory reactions of myeloid cells; therefore, continuous control of endogenous TNF by soluble TNFR2 seems to be essential for the maintenance of adequate sensitivity to inflammatory stimuli.

Beta-catenin-NF-κB interactions in murine hepatocytes: a complex to die for

Wnt/β-catenin signaling plays an important role in hepatic homeostasis, especially in liver development, regeneration, and cancer, and loss of β-catenin signaling is often associated with increased apoptosis. To elucidate how β-catenin may be regulating hepatocyte survival, we investigated the susceptibility of β-catenin conditional knockout (KO) mice and their wild-type (WT) littermates to Fas and tumor necrosis factor-α (TNF-α), two common pathways of hepatocyte apoptosis. While comparable detrimental effects from Fas activation were observed in WT and KO, a paradoxical survival benefit was observed in KO mice challenged with D-galactosamine/lipopolysaccharide. KO mice showed significantly lower morbidity and liver injury due to early, robust, and protracted activation of NF-κB in the absence of β-catenin. Enhanced NF-κB activation in KO mice was associated with increased basal inflammation and Toll-like receptor 4 expression and lack of the p65/β-catenin complex in hepatocytes. The p65/β-catenin complex in WT livers underwent temporal dissociation allowing for NF-κB activation to regulate hepatocyte survival following TNF-α-induced hepatic injury. Decrease of total β-catenin protein but not its inactivation induced p65 activity, whereas β-catenin stabilization either chemically or due to mutations repressed it in hepatomas in a dose-dependent manner, whereas β-catenin stabilization repressed it either chemically or due to mutations.

CONCLUSION

The p65/β-catenin complex in hepatocytes undergoes dynamic changes during TNF-α-induced hepatic injury and plays a critical role in NF-κB activation and cell survival. Modulation of β-catenin levels is a unique mode of regulating NF-κB activity and thus may present novel opportunities in devising therapeutics in specific hepatic injuries.

Human liver stem cell-derived microvesicles inhibit hepatoma growth in SCID mice by delivering antitumor microRNAs

Microvesicles (MVs) play a pivotal role in cell-to-cell communication. Recent studies demonstrated that MVs may transfer genetic information between cells. Here, we show that MVs derived from human adult liver stem cells (HLSC) may reprogram in vitro HepG2 hepatoma and primary hepatocellular carcinoma cells by inhibiting their growth and survival. In vivo intratumor administration of MVs induced regression of ectopic tumors developed in SCID mice. We suggest that the mechanism of action is related to the delivery of microRNAs (miRNAs) from HLSC-derived MVs (MV-HLSC) to tumor cells on the basis of the following evidence: (a) the rapid, CD29-mediated internalization of MV-HLSC in HepG2 and the inhibition of tumor cell growth after MV uptake; (b) the transfer by MV-HLSC of miRNAs with potential antitumor activity that was downregulated in HepG2 cells with respect to normal hepatocytes; (c) the abrogation of the MV-HLSC antitumor effect after MV pretreatment with RNase or generation of MVs depleted of miRNAs; (d) the relevance of selected miRNAs was proven by transfecting HepG2 with miRNA mimics. The antitumor effect of MV-HLSC was also observed in tumors other than liver such as lymphoblastoma and glioblastoma. These results suggest that the delivery of selected miRNAs by MVs derived from stem cells may inhibit tumor growth and stimulate apoptosis. Stem Cells2012;30:1985–1998

Human liver stem cells improve liver injury in a model of fulminant liver failure

Liver transplantation is currently the only effective therapy for fulminant liver failure, but its use is limited by the scarcity of organs for transplantation, high costs, and lifelong immunosuppression. Here we investigated whether human liver stem cells (HLSCs) protect from death in a lethal model of fulminant liver failure induced by intraperitoneal injection of D-galactosamine and lipopolysaccharide in SCID mice. We show that injection of HLSCs and of HLSC-conditioned medium (CM) significantly attenuates mouse mortality in this model. Histopathological analysis of liver tissue showed reduction of liver apoptosis and enhancement of liver regeneration. By optical imaging we observed a preferential localization of labeled HLSCs within the liver. HLSCs were detected by immunohistochemistry in large liver vessels (at 24 hours) and in the liver parenchyma (after day 3). Fluorescence in situ hybridization analysis with the human pan-centromeric probe showed that positive cells were cytokeratin-negative at 24 hours. Coexpression of cytokeratin and human chromosome was observed at 7 and, to a lesser extent, at 21 days. HLSC-derived CM mimicked the effect of HLSCs in vivo. Composition analysis of the HLSC-CM revealed the presence of growth factors and cytokines with liver regenerative properties. In vitro experiments showed that HLSC-CM protected human hepatocytes from apoptosis and enhanced their proliferation.

CONCLUSION

These data suggest that fulminant liver failure may potentially benefit from treatment with HLSCs or HLSC-CM.

Linear bactenecin analogs with cell selectivity and anti-endotoxic activity

Bactenecin (Bac) is a 12-residue disulfide-linked antimicrobial peptide isolated from the granules of bovine neutrophils. In this study, to develop novel linear Bac analogs with cell selectivity and anti-endotoxic activity, we designed and synthesized a series of linear Bac analogs with amino acid substitution in Cys3,11 and/or Val6,7 of Bac. Among Bac analogs, some analogs (Bac-W, Bac-KW, Bac-L, Bac-KL, Bac-LW, and Bac-KLW) with higher hydrophobicity showed the amalgamated property of cell selectivity and anti-endotoxic activity. Furthermore, Bac-W, Bac-KW, Bac-LW, and Bac-KLW showed serum stability comparable with that of disulfide-bonded Bac. Therefore, these Bac analogs (Bac-W, Bac-KW, Bac-LW, and Bac-KLW) can serve as promising antibiotics for the development of therapeutic agents for treatment against endotoxic shock and bacterial infection. In addition, our results suggest that a little increase in hydrophobicity may be responsible for the decreased cell selectivity of the multiple Arg-containing peptides (Bac-W, Bac-L, and Bac-LW) over the multiple Lys-containing peptides (Bac-KW, Bac-KL, and Bac-KLW).

Deficiency of interleukin-15 enhances susceptibility to acetaminophen-induced liver injury in mice

Hepatocytes have a direct necrotic role in acetaminophen (APAP)-induced liver injury (AILI), prolonged secondary inflammatory response through innate immune cells and cytokines also significantly contributes to APAP hepatotoxicity. Interleukin 15 (IL-15), a multifunction cytokine, regulates the adaptive immune system and influences development and function of innate immune cells. To better understand the role of IL-15 in liver injury, we treated wild-type (WT) and IL-15-knockout (Il15⁻/⁻) mice with a hepatotoxic dose of APAP to induce AILI and evaluated animal survival, liver damage, APAP metabolism in livers and the inflammatory response. Production of pro-inflammatory cytokines/chemokines was greater in Il15⁻/⁻ than WT mice. Subanalysis of hepatic infiltrated monocytes revealed greater neutrophil influx, along with greater hepatic induction of inducible nitric oxide synthase (iNOS), in Il15⁻/⁻ than WT mice. In addition, the level of hepatic hemeoxygenase 1 (HO-1) was partially suppressed in Il15⁻/⁻ mice, but not in WT mice. Interestingly, elimination of Kupffer cells and neutrophils did not alter the vulnerability to excess APAP in Il15⁻/⁻ mice. However, injection of galactosamine, a hepatic transcription inhibitor, significantly reduced the increased APAP sensitivity in Il15⁻/⁻ mice but had minor effect on WT mice. We demonstrated that deficiency of IL-15 increased mouse susceptibility to AILI. Moreover, Kupffer cell might affect APAP hepatotoxicity through IL-15.

Bacterial endotoxins: biological properties and mechanisms of action

Endotoxins (lipopolysaccharides, LPS) are agents of pathogenicity of Gram-negative bacteria, implicated in the development of Gram-negative shock. Endotoxin reacts with lipopolysaccharide-sensitive cells producing endogenous mediators such as tumour necrosis factor alpha (TNFα). Macrophages are cells mediating the toxic activities of LPS and TNFα is the primary mediator of the lethal action of endotoxin. This review article discusses the various mechanisms by which endotoxin hypersensitivity in bacteria-sensitized animals develops. The paper concludes with a discussion on the possible protective effect of carnitine congeners against the lethal action of LPS.

Defense peptides secreted by helminth pathogens: antimicrobial and/or immunomodulator molecules?

Host defense peptides (HDPs) are an evolutionarily conserved component of the innate immune response found in all living species. They possess antimicrobial activities against a broad range of organisms including bacteria, fungi, eukaryotic parasites, and viruses. HDPs also have the ability to enhance immune responses by acting as immunomodulators. We discovered a new family of HDPs derived from pathogenic helminth (worms) that cause enormous disease in animals and humans worldwide. The discovery of these peptides was based on their similar biochemical and functional characteristics to the human defense peptide LL-37. We propose that these new peptides modulate the immune response via molecular mimicry of mammalian HDPs thus providing a mechanism behind the anti-inflammatory properties of helminth infections.

The role of innate immunity in HBV infection

Hepatitis B virus (HBV) infection is one of the main causes of chronic liver diseases. Whether HBV infection is cleared or persists is determined by both viral factors and host immune responses. It becomes clear that innate immunity is of importance in protecting the host from HBV infection and persistence. However, HBV develops strategies to suppress the antiviral immune responses. A combined therapeutic strategy with both viral suppression and enhancement of antiviral immune responses is needed for effective long-term clearance and cure for chronic HBV infection. We and others confirmed that bifunctional siRNAs with both gene silencing and innate immune activation properties are beneficial for inhibition of HBV and represent a potential approach for treatment of viral infection. Understanding the nature of liver innate immunity and their roles in chronic HBV progression and HBV clearance may aid in the design of novel therapeutic strategies for chronic HBV infection.

Hepatoprotective effect and mechanistic insights of deoxyelephantopin, a phyto-sesquiterpene lactone, against fulminant hepatitis

Deoxyelephantopin (DET) is an abundant sesquiterpene lactone isolated from an anecdotally hepatoprotective phytomedicine, Elephantopus scaber. Our objective in this study was to provide scientific evidence for the in vivo efficacy and the underlying mechanisms of action of DET in lipopolysaccharide/d-galactosamine (LPS/D-GalN)-induced fulminant hepatitis. We investigated both the protective effect of pretreatment with DET (10 mg/kg body weight, Pre-DET10) prior to administration of LPS/D-GalN and the therapeutic effect of treatment with 10 mg/kg DET (Post-DET10) or the hepatoprotective drug silymarin (Post-SM10) following the administration of LPS/D-GalN. Our data showed that Pre-DET10 prevented LPS/D-GalN-induced infiltration of F4/80 monocytes/macrophages and an increase of nitrotyrosine and cyclooxygenase-2 protein in liver tissues. Further, Post-DET10 and Psot-SM10 treatments protected against liver cell apoptosis. All three treatments suppressed serum aminotransferase activities, tumor necrosis factor-alpha and interleukin-6 levels, and serum and hepatic matrix metalloproteinase-9 activity. The Pre-DET10 or Post-DET10 and Post-SM10 treatments in combination with inhibition of heme oxygenase-1 expression ultimately decreased protection of mice from LPS/D-GalN-induced mortality, with decreased survival from 75% and 62.5% to 50%, respectively. Results obtained from serial liver scintigraphy with (99m)Tc-diisopropyl iminodiacetic acid (DISIDA) on single-photon emission computed tomography analysis showed that both liver uptake and excretion times of DISIDA were significantly delayed in LPS/D-GalN-treated animals and were effectively recovered by DET and silymarin treatment. This report demonstrates that DET functions in the modulating multiple molecular targets or signaling pathways that counteract inflammation during the progression of fulminant hepatitis and may serve as a novel lead compound for future development of anti-inflammatory or hepatoprotective agents.

Cutting edge: Divergent cell-specific functions of MyD88 for inflammatory responses and organ injury in septic peritonitis

Although global MyD88 deficiency attenuates lethal inflammation in sepsis, cell-specific functions of MyD88 remain largely unknown. Using mice with selective expression of MyD88 in myeloid cells (Myd88(MYEL)), we show that, during polymicrobial septic peritonitis, both myeloid and nonmyeloid cells contribute to systemic inflammation, whereas myeloid cell MyD88 was sufficient to fully establish the peritoneal cytokine response. Importantly, Myd88(MYEL) mice developed markedly aggravated liver injury that was linked to impaired upregulation of cellular inhibitor of apoptosis protein 2 and an excessive production of TNF-α. Upregulation of inducible cAMP early repressor (ICER), a known transcriptional repressor of the Tnfa gene, was impaired in Myd88(MYEL) mice. Moreover, Myd88(MYEL) mice showed enhanced transcription of the Tnfa gene and an excessive production of CCL3, which is also negatively regulated by ICER, but they had normal levels of CXCL1, which is expressed in an ICER-independent manner. Together, these findings suggest a novel protective role for nonmyeloid cell MyD88 in attenuating liver injury during septic peritonitis.

β-Glucan from Lentinus edodes inhibits nitric oxide and tumor necrosis factor-α production and phosphorylation of mitogen-activated protein kinases in lipopolysaccharide-stimulated murine RAW 264.7 macrophages

Lentinan (LNT), a β-glucan from the fruiting bodies of Lentinus edodes, is well known to have immunomodulatory activity. NO and TNF-α are associated with many inflammatory diseases. In this study, we investigated the effects of LNT extracted by sonication (LNT-S) on the NO and TNF-α production in LPS-stimulated murine RAW 264.7 macrophages. The results suggested that treatment with LNT-S not only resulted in the striking inhibition of TNF-α and NO production in LPS-activated macrophage RAW 264.7 cells, but also the protein expression of inducible NOS (iNOS) and the gene expression of iNOS mRNA and TNF-α mRNA. It is surprising that LNT-S enhanced LPS-induced NF-κB p65 nuclear translocation and NF-κB luciferase activity, but severely inhibited the phosphorylation of JNK1/2 and ERK1/2. The neutralizing antibodies of anti-Dectin-1 and anti-TLR2 hardly affected the inhibition of NO production. All of these results suggested that the suppression of LPS-induced NO and TNF-α production was at least partially attributable to the inhibition of JNK1/2 and ERK1/2 activation. This work discovered a promising molecule to control the diseases associated with overproduction of NO and TNF-α.

Cell signals influencing hepatic fibrosis

Liver fibrosis is the result of the entire organism responding to a chronic injury. Every cell type in the liver contributes to the fibrosis. This paper first discusses key intracellular signaling pathways that are induced during liver fibrosis. The paper then examines the effects of these signaling pathways on the major cell types in the liver. This will provide insights into the molecular pathophysiology of liver fibrosis and should identify therapeutic targets.

Whole-body deletion of LPS-induced TNF-α factor (LITAF) markedly improves experimental endotoxic shock and inflammatory arthritis

LPS-induced TNF-α factor (LITAF) mediates cytokine expression in response to endotoxin challenge. Previously, we reported that macrophage-specific LITAF-deficient (macLITAF-/-) mice exposed to LPS have a delayed onset in the serum levels of proinflammatory cytokines and prolonged persistence of anti-inflammatory cytokines, but only partial protection from endotoxic shock. We postulated that greater protection might be achieved if LITAF were deleted from all LITAF-producing cells, including macrophages. Using a Cre-loxP system, we engineered a tamoxifen-induced recombination mouse [tamLITAF(i)-/-] that resulted in whole-body LITAF deficiency. Our findings demonstrate that (i) tamLITAF(i)-/- mice are more resistant to systemic Escherichia coli LPS-induced lethality than our previous macLITAF-/- mice, providing evidence that LITAF-producing cells other than LysMCre-positive cells play an important role in mediating endotoxic shock; (ii) tamLITAF(i)-/- mice show a similar pattern of cytokine expression with decreased proinflammatory and prolonged anti-inflammatory mediators compared with WT mice; and (iii) tamLITAF(i)-/- mice, compared with WT mice, display a significant reduction in bone resorption and inflammation associated with a local chronic inflammatory disease--namely, collagen antibody-induced arthritis. Our findings offer a unique model to study the role of LITAF in systemic and chronic local inflammatory processes, and pave the way for anti-LITAF therapeutic approaches for the treatment of TNF-mediated inflammatory diseases.

Cyclooxygenase inhibitors protect D-galactosamine/lipopolysaccharide induced acute hepatic injury in experimental mice model

We investigated the protective effects of two non-steroid anti-inflammatory drugs, indomethacin (COX-1 and COX-2 inhibitors) and nimesulide (specific COX-2 inhibitor) on the hepatic injury induced by lipopolysaccharide in d-galactosamine sensitized (Gal/LPS) mice. ICR male mice were injected with a single dose of Gal/LPS with or without pre-treatment of 3mg/kg indomethacin or 30 mg/kg nimesulide (single i.p. injection). Sixteen hours later, blood and liver tissues of mice were collected for histological, molecular, and biochemical analyses. Our results showed marked reduction of hepatic necrosis, serum ALT, and tissue TBARS levels in both indomethacin- and nimesulide-pre-treated mice when compared with Gal/LPS-treated mice. Western blot and RT-PCR analysis showed decreased levels of iNOS mRNA, iNOS protein, and nitrotyrosine formation in both COX inhibitor pre-treated groups when compared with Gal/LPS-treated group. There was an inverse relationship between COX-1 and COX-2 expressions, as well as between COX-2 and C/EBP-α expressions in COX inhibitors groups, Gal/LPS and control groups. COX inhibitors reduced the expression of TNF-α mRNA and the activity of NF-κB which were elevated by Gal/LPS treatment. We conclude that COX inhibitors protected the liver from Gal/LPS-induced hepatotoxicity. COX inhibitors could be considered as potential agents in the prevention of acute liver failure and sepsis.

Bioactive phytochemicals of leaf essential oils of Cinnamomum osmophloeum prevent lipopolysaccharide/D-galactosamine (LPS/D-GalN)-induced acute hepatitis in mice

The purpose of this study was to investigate the bioactive phytochemicals of leaf essential oils of Cinnamomum osmophloeum on lipopolysaccharide/D-galactosamine (LPS/D-GalN)-induced acute hepatitis. The results revealed that post-treatment with 100 μmol/kg trans-cinnamaldehyde, (-)-aromadendrene, T-cadinol, or α-cadinol significantly decreased the aspartate aminotransferase (AST), alanine aminotransferase (ALT), tumor necrosis factor-α (TNF-α), and interleukin 6 (IL-6) levels in serum. Moreover, both T-cadinol and α-cadinol treatments decreased the expressions of cleaved caspase-3 and cleaved poly-ADP ribose polymerase (PARP) in the liver tissues when compared with the LPS/D-GalN group. Liver histopathology also showed that silymarin, trans-cinnamaldehyde, (-)-aromadendrene, T-cadinol, or α-cadinol significantly reduced the incidence of liver lesions induced by LPS/D-GalN. These results suggest that the above phytochemicals exhibit potent hepatoprotection against LPS/D-GalN-induced liver damage in mice, and their hepatoprotective effects may be due to the modulation of anti-inflammatory activities.

A new experimental murine model for lipopolysaccharide-mediated lethal shock with lung injury

We have recently established a new experimental murine model for lipopolysaccharide (LPS)-mediated lethal shock with lung-specific injury. Severe lung injury is induced by administration of LPS into α-galactosylceramide (α-GalCer)-sensitized mice; the mice died with acute lung injury and respiratory distress within 24 h. α-GalCer activates natural killer T (NKT) cells in the lungs and liver, and induces the production of interferon (IFN)-γ. However, IFN-γ signaling is only triggered in the lungs and makes them susceptible to LPS. On the other hand, IFN-γ signaling is inhibited in liver and results in few hepatic lesions. Unlike liver NKT cells, lung NKT cells fail to produce interleukin (IL)-4, which down-regulates the IFN-γ signaling, in response to α-GalCer. The differential cytokine profile between lung and liver NKT cells may lead to organ-specific lung lesions. The experimental system using α-GalCer sensitization could be a useful experimental model for clinical endotoxic or septic shock as it presents respiratory failure, a typical manifestation in severe septic patients. In this review, key evidence and the introducuction of the detailed mechanism of LPS-mediated lung-specific injury in α-GalCer-sensitized mice is provided. In particular, the molecular background of organ-specific development of lung injury in the model is focused on.

Effect of intestinal microflora on the production of interleukin 10 and prostaglandin e(2) in serum and kupffer cells from germfree and conventional mice

To determine why germfree (GF) mice are less productivity of proinflammatory cytokines than conventional (CV) mice, we studied serum levels of interleukin 10 (IL-10) and prostaglandin E₂ (PGE₂) in mice after treatment with lipopolyssacharide (LPS). A single injection of LPS caused an elevation of IL-10 in serum from GF, LPS-GF (germfree mice given drinking water containing LPS) and CV mice. The response was highest in serum from GF mice, and was lower in serum from LPS-GF mice compared with GF mice. Before LPS injection, serum PGE₂ was significantly higher in CV and LPS-GF mice than in GF ones. After LPS injection, a higher level of PGE₂ was maintained over 12 h in CV mice after LPS injection, while the LPS treatment reduced the level in LPS-GF mice and increased the level in GF mice. The levels of IL-10 in culture medium from Kupffer cells treated with LPS showed similar results to serum in GF and CV mice. These results suggest that high levels of IL-10 in serum from germfree mice may be partly responsible for the lower in vivo responsiveness of these proinflammatory cytokines to LPS in these mice, although PGE₂ was not responsible for the lower responsiveness of these inflammatory cytokines to LPS.

A family of helminth molecules that modulate innate cell responses via molecular mimicry of host antimicrobial peptides

Over the last decade a significant number of studies have highlighted the central role of host antimicrobial (or defence) peptides in modulating the response of innate immune cells to pathogen-associated ligands. In humans, the most widely studied antimicrobial peptide is LL-37, a 37-residue peptide containing an amphipathic helix that is released via proteolytic cleavage of the precursor protein CAP18. Owing to its ability to protect against lethal endotoxaemia and clinically-relevant bacterial infections, LL-37 and its derivatives are seen as attractive candidates for anti-sepsis therapies. We have identified a novel family of molecules secreted by parasitic helminths (helminth defence molecules; HDMs) that exhibit similar biochemical and functional characteristics to human defence peptides, particularly CAP18. The HDM secreted by Fasciola hepatica (FhHDM-1) adopts a predominantly α-helical structure in solution. Processing of FhHDM-1 by F. hepatica cathepsin L1 releases a 34-residue C-terminal fragment containing a conserved amphipathic helix. This is analogous to the proteolytic processing of CAP18 to release LL-37, which modulates innate cell activation by classical toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS). We show that full-length recombinant FhHDM-1 and a peptide analogue of the amphipathic C-terminus bind directly to LPS in a concentration-dependent manner, reducing its interaction with both LPS-binding protein (LBP) and the surface of macrophages. Furthermore, FhHDM-1 and the amphipathic C-terminal peptide protect mice against LPS-induced inflammation by significantly reducing the release of inflammatory mediators from macrophages. We propose that HDMs, by mimicking the function of host defence peptides, represent a novel family of innate cell modulators with therapeutic potential in anti-sepsis treatments and prevention of inflammation.

G-protein coupled receptor kinase 5 mediates lipopolysaccharide-induced NFκB activation in primary macrophages and modulates inflammation in vivo in mice

G-protein coupled receptor kinase-5 (GRK5) is a serine/threonine kinase discovered for its role in the regulation of G-protein coupled receptor signaling. Recent studies have shown that GRK5 is also an important regulator of signaling pathways stimulated by non-GPCRs. This study was undertaken to determine the physiological role of GRK5 in Toll-like receptor-4-induced inflammatory signaling pathways in vivo and in vitro. Using mice genetically deficient in GRK5 (GRK5(-/-) ) we demonstrate here that GRK5 is an important positive regulator of lipopolysaccharide (LPS, a TLR4 agonist)-induced inflammatory cytokine and chemokine production in vivo. Consistent with this role, LPS-induced neutrophil infiltration in the lungs (assessed by myeloperoxidase activity) was markedly attenuated in the GRK5(-/-) mice compared to the GRK5(+/+) mice. Similar to the in vivo studies, primary macrophages from GRK5(-/-) mice showed attenuated cytokine production in response to LPS. Our results also identify TLR4-induced NFκB pathway in macrophages to be selectively regulated by GRK5. LPS-induced IκBα phosphorylation, NFκB p65 nuclear translocation, and NFκB binding were markedly attenuated in GRK5(-/-) macrophages. Together, our findings demonstrate that GRK5 is a positive regulator of TLR4-induced IκBα-NFκB pathway as well as a key modulator of LPS-induced inflammatory response.

A humanized anti-osteopontin antibody protects from Concanavalin A induced-liver injury in mice

Osteopontin has been implicated in various inflammatory diseases including rheumatoid arthritis, multiple sclerosis, Crohn's disease, and fulminant hepatitis. Increased expression of osteopontin has been detected in pathological foci of these diseases. RA and fulminant hepatitis have been successfully treated by administration of neutralizing anti-osteopontin antibody in mice. However, rodent antibodies are highly immunogenic in humans and therefore limited in their clinical application. Here, a murine monoclonal antibody 23C3 against human osteopontin, was humanized by complementarity-determining region grafting method based on computer-assisted molecular modeling. The humanized version of 23C3, denoted as Hu23C3, was shown to possess affinity comparable to that of its parental antibody. Hu23C3 could also inhibit monocyte migration in response to osteopontin in vitro. Furthermore, in vivo data showed that Hu23C3 significantly protects mice from Concanavalin A (Con A) induced-liver injury in association with the reduction of transaminase activities and improvement of liver injury. Mechanistic studies demonstrated that Hu23C3 inhibited T and NKT cell infiltration, and activation of nuclear factor κB (NF-κB) in the liver, resulting in reduction of TNF-α and IFN-γ production. Thus, our data strongly support that the humanized anti-osteopontin antibody, Hu23C3, may have a potential for the treatment of T cell mediated-hepatitis in human.

NF-κB in the liver--linking injury, fibrosis and hepatocellular carcinoma

Hepatic cirrhosis and hepatocellular carcinoma (HCC) are the most common causes of death in patients with chronic liver disease. Chronic liver injury of virtually any etiology triggers inflammatory and wound-healing responses that in the long run promote the development of hepatic fibrosis and HCC. Here, we review the role of the transcription factor nuclear factor-κB (NF-κB), a master regulator of inflammation and cell death, in the development of hepatocellular injury, liver fibrosis and HCC, with a particular focus on the role of NF-κB in different cellular compartments of the liver. We propose that NF-κB acts as a central link between hepatic injury, fibrosis and HCC, and that it may represent a target for the prevention or treatment of liver fibrosis and HCC. However, NF-κB acts as a two-edged sword and inhibition of NF-κB may not only exert beneficial effects but also negatively impact hepatocyte viability, especially when NF-κB inhibition is pronounced. Finding appropriate targets or identifying drugs that either exert only a moderate effect on NF-κB activity or that can be specifically delivered to nonparenchymal cells will be essential to avoid the increase in liver injury associated with complete NF-κB blockade in hepatocytes.

Dectin-1 targeting delivery of TNF-α antisense ODNs complexed with β-1,3-glucan protects mice from LPS-induced hepatitis

Antisense therapy, the first concept of oligonucleotide therapeutics, was proposed more than two decades ago. However, the lack of suitable delivering carriers continues to be a major obstacle to practical therapy. In this study, we present a novel complex consisting of β-1,3-glucan and antisense oligonucleotide (AS-ODN) as a new candidate of the carriers. We used schizophyllan (SPG) as a β-1,3-glucan and an AS-ODN sequence to suppress tumor necrosis factor alpha (TNF-α), where the AS-ODN has a (dA)(60) tail to induce complex with SPG. When the complexes were applied to peritoneal macrophages, they were incorporated into the cells via dectin-1 (a β-1,3-glucan receptor expressed on antigen presenting cells) and suppressed lipopolysaccharide (LPS)-induced TNF-α secretion. In-vivo, AS-ODN/SPG decreased the secretion of TNF-α in serum and drastically reduced the inflammation of LPS-induced hepatitis. This new complex could overcome the long outstanding problem for antisense therapy because of its complexation ability, non-toxicity and high target specificity.

Fulminant liver failure model with hepatic encephalopathy in the mouse

AIM

To develop a reliable murine model for fulminant liver failure (FLF).

MATERIAL AND METHODS

We treated three groups of male C57BL/6 mice:as controls, with azoxymethane (AOM), and with galactosamine (Gal) and tumor necrosis factor-alpha (TNFα). Effects of body temperature (BT) control on survival, in all three groups were investigated. Using BT control, survival, histopathological findings and biochemical/coagulation profiles were compared between the experimental groups. Effects of hydration on international normalized ratios of prothrombin time (PT-INR) were also checked. Dose-dependent survival curves were made for both experimental groups. Neurological behaviors were assessed using a coma scale.

RESULTS

No unexpected BT effects were seen in the control group. The AOM group, but not the Gal+TNFα group, showed significant differences in survival curves between those with and without BT care. Histopathological assessment showed consistent FLF findings in both experimental groups with BT care. Between the experimental groups, there were significant differences in aspartate aminotransferase levels and PT-INR; and significant differences in PT-INRs between sufficiently- and insufficiently-hydrated groups. There were significant differences between FLF models, in the duration of each coma stage, with significant differences in stages 1 and 3 as percentages of the diseased state (stages 1-4). The two FLF models with BT care showed different survival curves in the dose-dependent survival study.

CONCLUSION

Azoxymethane can provide a good FLF model, but requires a specialized environment and careful BT control. Other FLF models may also be useful, depending on research purpose. Thoughtful attention to caregiving and close observation are indispensable for successful FLF models.

Effect of lactobacilli on paracellular permeability in the gut

Paracellular permeability is determined by the complex structures of junctions that are located between the epithelial cells. Already in 1996, it was shown that the human probiotic strain Lactobacillus plantarum 299v and the rat-originating strain Lactobacillus reuteri R2LC could reduce this permeability in a methotrexate-induced colitis model in the rat. Subsequently, many animal models and cell culture systems have shown indications that lactobacilli are able to counteract increased paracellular permeability evoked by cytokines, chemicals, infections, or stress. There have been few human studies focusing on the effect of lactobacilli on intestinal paracellular permeability but recently it has been shown that they could influence the tight junctions. More precisely, short-term administration of L. plantarum WCSF1 to healthy volunteers increased the relocation of occludin and ZO-1 into the tight junction area between duodenal epithelial cells.

Regulation of lipopolysaccharide-induced inflammatory response and endotoxemia by beta-arrestins

Beta-arrestins are scaffolding proteins implicated as negative regulators of TLR4 signaling in macrophages and fibroblasts. Unexpectedly, we found that beta-arrestin-1 (beta-arr-1) and -2 knockout (KO) mice are protected from TLR4-mediated endotoxic shock and lethality. To identify the potential mechanisms involved, we examined the plasma levels of inflammatory cytokines/chemokines in the wild-type (WT) and beta-arr-1 and -2 KO mice after lipopolysaccharide (LPS, a TLR4 ligand) injection. Consistent with lethality, LPS-induced inflammatory cytokine levels in the plasma were markedly decreased in both beta-arr-1 and -2 KO, compared to WT mice. To further explore the cellular mechanisms, we obtained splenocytes (separated into CD11(b+) and CD11(b-) populations) from WT, beta-arr-1, and -2 KO mice and examined the effect of LPS on cytokine production. Similar to the in vivo observations, LPS-induced inflammatory cytokines were significantly blocked in both splenocyte populations from the beta-arr-2 KO compared to the WT mice. This effect in the beta-arr-1 KO mice, however, was restricted to the CD11(b-) splenocytes. Our studies further indicate that regulation of cytokine production by beta-arrestins is likely independent of MAPK and IkappaBalpha-NFkappaB pathways. Our results, however, suggest that LPS-induced chromatin modification is dependent on beta-arrestin levels and may be the underlying mechanistic basis for regulation of cytokine levels by beta-arrestins in vivo. Taken together, these results indicate that beta-arr-1 and -2 mediate LPS-induced cytokine secretion in a cell-type specific manner and that both beta-arrestins have overlapping but non-redundant roles in regulating inflammatory cytokine production and endotoxic shock in mice.

Tumor suppressor ras association domain family 5 (RASSF5/NORE1) mediates death receptor ligand-induced apoptosis

Epigenetic silencing of RASSF (Ras association domain family) genes RASSF1 and RASSF5 (also called NORE1) by CpG hypermethylation is found frequently in many cancers. Although the physiological roles of RASSF1 have been studied in some detail, the exact functions of RASSF5 are not well understood. Here, we show that RASSF5 plays an important role in mediating apoptosis in response to death receptor ligands, TNF-α and TNF-related apoptosis-inducing ligand. Depletion of RASSF5 by siRNA significantly reduced TNF-α-mediated apoptosis, likely through its interaction with proapoptotic kinase MST1, a mammalian homolog of Hippo. Consistent with this, siRNA knockdown of MST1 also resulted in resistance to TNF-α-induced apoptosis. To further study the role of Rassf5 in vivo, we generated Rassf5-deficient mouse. Inactivation of Rassf5 in mouse embryonic fibroblasts (MEFs) resulted in resistance to TNF-α- and TNF-related apoptosis-inducing ligand-mediated apoptosis. Importantly, Rassf5-null mice were significantly more resistant to TNF-α-induced apoptosis and failed to activate Mst1. Loss of Rassf5 also resulted in spontaneous immortalization of MEFs at earlier passages than the control MEFs, and Rassf5-null immortalized MEFs, but not the immortalized wild type MEFs, were fully transformed by K-RasG12V. Together, our results demonstrate a direct role for RASSF5 in death receptor ligand-mediated apoptosis and provide further evidence for RASSF5 as a tumor suppressor.

Anti-apoptotic activity of gentiopicroside in D-galactosamine/lipopolysaccharide-induced murine fulminant hepatic failure

This study investigated the hepatoprotective effects of gentiopicroside on d-galactosamine (d-GalN) and lipopolysaccharide (LPS)-induced fulminant hepatic failure. Mice were administrated orally with gentiopicroside (40 or 80 mg/kg body weight) at 12h and 1h before d-GalN (700 mg/kg)/LPS (10 microg/kg) injection. Gentiopicroside markedly reduced the increases in serum aminotransferase activities and lipid peroxidation. The glutathione content decreased in d-GalN/LPS alone group, and this decrease was attenuated by gentiopicroside. Increases in serum tumor necrosis factor-alpha (TNF-alpha), which were observed in d-GalN/LPS alone group, were significantly reduced by gentiopicroside. Importantly, gentiopicroside attenuated d-GalN/LPS-induced apoptosis of hepatocytes, as estimated by the caspase-3 cleavage, poly(ADP-ribose) polymerase (PARP) cleavage, and DNA fragmentation. d-GalN/LPS-induced caspase-8 and -9 activation was significantly suppressed by gentiopicroside. Moreover, increased cytosolic cytochrome c protein was reduced by gentiopicroside. Also, the increased ratio of Bax and Bcl-2 protein was significantly attenuated by gentiopicroside. After 6h of d-GalN/LPS injection, phosphorylated c-jun N-terminal kinase (JNK) and extracellular signal regulated kinase (ERK) was significantly increased, whereas phosphorylation JNK and ERK were attenuated by gentiopicroside. Our results suggest that gentiopicroside offers remarkable hepatoprotection against damage induced by d-GalN/LPS related with its anti-apoptotic activities.

Beneficial dysregulation of the time course of inflammatory mediators in lipopolysaccharide-induced tumor necrosis factor alpha factor-deficient mice

To begin to understand the surprising survival of macrophage-specific lipopolysaccharide-induced tumor necrosis factor alpha factor-deficient (macLITAF(-/-)) animals after a lethal dose of lipopolysaccharide (LPS), as reported earlier, the present follow-up study focuses on the role of LITAF in the regulation of inflammatory cytokines secreted in response to lethal or sublethal doses of LPS administered to wild-type (WT) and macLITAF(-/-) mice. A time course study of kinase expression in peritoneal macrophages revealed increased phosphorylation of prosurvival kinases Akt, Erk1/2, and ribosomal S6 kinase (RSK) in macLITAF(-/-) mice compared to that in WT mice (n = 8), confirming their role in LPS-mediated diseases. macLITAF(-/-) mice (n = 8) survived a lethal dose of LPS plus d-galactosamine (d-GalN), expressing lower serum levels of pro- and anti-inflammatory cytokines than the WT levels. To extend our knowledge on LPS-induced inflammatory events, an effective sublethal dose of LPS was administered to the animals (n = 14). WT animals exhibited an acute inflammatory response that decreased after 4 h. Interestingly, macLITAF(-/-) mice exhibited an initial delay in the secretion of proinflammatory cytokines that peaked after 8 h and reached WT levels after 18 h. Anti-inflammatory cytokine secretions were initially delayed but increased after 4 h and remained elevated compared to WT levels, even after 18 h. Our results demonstrate that LITAF deficiency in vivo affects cytokines other than TNF-alpha and influences the balance between the pro- and anti-inflammatory cytokines, which protects the animals from the deleterious effects of an LPS-induced inflammatory response, resulting in a beneficial host regulation of inflammatory cytokines and in enhanced survival. Therapeutic intervention aimed at reducing LITAF via kinase modulators may prove useful in preventing LPS-induced mortality.

NETWORKS, BIOLOGY AND SYSTEMS ENGINEERING: A CASE STUDY IN INFLAMMATION

Biological systems can be modeled as networks of interacting components across multiple scales. A central problem in computational systems biology is to identify those critical components and the rules that define their interactions and give rise to the emergent behavior of a host response. In this paper we will discuss two fundamental problems related to the construction of transcription factor networks and the identification of networks of functional modules describing disease progression. We focus on inflammation as a key physiological response of clinical and translational importance.

Bach1 deficiency ameliorates hepatic injury in a mouse model

Bach1 is a basic region-leucine zipper (bZip) protein that forms heterodimers with the small Maf proteins and functions as a repressor of gene expression. One of the target genes of Bach1 is Hmox-1 that encodes heme oxygenase-1 (HO-1). HO-1 degrades heme into carbon monoxide (CO), biliverdin, and iron. HO-1 is strongly induced by various stresses as well as its substrate heme, and protects cells and tissues against insults through diverse cytoprotective functions of the reaction products CO and biliverdin. Bach1-deficiency in mice leads to higher expression of Hmox-1 in various tissues. Here we investigated the effects of Bach1-deficiency in mice on tissue injuries: hepatic injury induced by D-galactosamine (GalN) and lipopolysaccharide (LPS), and mouse paw edema induced by carrageenin, polysaccharide derived from various seaweeds. Bach1-deficiency suppressed induction of plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in response to the GalN/LPS-treatment. However, production of tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO), both being cytotoxic mediators in LPS-induced hepatic injury, in Bach1-deficient mice and their peritoneal macrophages was similar to wild type controls. In contrast, Bach1-deficiency did not affect extent of mouse paw edema induced by carrageenin, which enhances vascular permeability by activating kinin release. These results indicate that Bach1 plays an inhibitory role in the cytoprotection of LPS-induced liver injury but not in the kinin-mediated inflammatory edema. The inhibitory role for Bach1 may stem from its activity to repress gene expression including HO-1.

Indirect action of tumor necrosis factor-alpha in liver injury during the CD8+ T cell response to an adeno-associated virus vector in mice

CD8+ T cells can cause hepatocellular injury by two distinct mechanisms. In addition to their direct cytotoxic effect, there is also collateral liver injury, which occurs when cells are killed in an antigen-independent manner. Whereas immune effector cytokines interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) have both been implicated in various forms of hepatitis, their respective roles in direct and/or collateral liver damage remains unclear. In order to investigate these elements of liver injury, we developed a new experimental model of CD8+ T-cell-mediated hepatitis based on an adeno-associated virus-based gene therapy vector. This vector is used to deliver antigen to hepatocytes, and CD8+ T cells specific for the vector-encoded transgene are adoptively transferred to produce liver immunopathology. In this experimental model, CD8+ T-cell IFNgamma acts on Kupffer cells, inducing TNFalpha secretion and liver injury. Both IFNgamma and TNFalpha are important in this injury process, but TNFalpha acts as an autocrine amplifier of Kupffer cell function, rather than as a direct effector of hepatocellular damage.

CONCLUSIONS

TNFalpha indirectly promotes liver damage and is not a direct hepatotoxic agent. IFNgamma also indirectly contributes to liver injury through Kupffer cell activation while, in parallel, directly promoting hepatitis through induction of hepatocyte major histocompatability complex class I. In principle, it may be possible to ameliorate this immunopathologic indirect mechanism by developing therapies that target Kupffer cells, without impairing CD8+ T-cell-mediated antiviral immunity. This would have great therapeutic potential in chronic viral hepatitis.

In silico simulation of corticosteroids effect on an NFkB- dependent physicochemical model of systemic inflammation

BACKGROUND

During the onset of an inflammatory response signaling pathways are activated for "translating" extracellular signals into intracellular responses converging to the activation of nuclear factor (NF)-kB, a central transcription factor in driving the inflammatory response. An inadequate control of its transcriptional activity is associated with the culmination of a hyper-inflammatory response making it a desired therapeutic target. Predicated upon the nature of the response, a systems level analysis might provide rational leads for the development of strategies that promote the resolution of the response.

METHODOLOGY AND FINDINGS

A physicochemical host response model is proposed to integrate biological information in the form of kinetic rules and signaling cascades with pharmacokinetic models of drug action for the modulation of the response. The unifying hypothesis is that the response is triggered by the activation of the NFkB signaling module and corticosteroids serve as a template for assessing anti-inflammatory strategies. The proposed in silico model is evaluated through its ability to predict and modulate uncontrolled responses. The pre-exposure of the system to hypercortisolemia, i.e. 6 hr before or simultaneously with the infectious challenge "reprograms" the dynamics of the host towards a balanced inflammatory response. However, if such an intervention occurs long before the inflammatory insult a symptomatic effect is observed instead of a protective relief while a steroid infusion after inducing inflammation requires much higher drug doses.

CONCLUSIONS AND SIGNIFICANCE

We propose a reversed engineered inflammation model that seeks to describe how the system responds to a multitude of external signals. Timing of intervention and dosage regimes appears to be key determinants for the protective or symptomatic effect of exogenous corticosteroids. Such results lie in qualitative agreement with in vivo human studies exposed both to LPS and corticosteroids under various time intervals thus improving our understanding of how interacting modules generate a behavior.

NKG2D-retinoic acid early inducible-1 recognition between natural killer cells and Kupffer cells in a novel murine natural killer cell-dependent fulminant hepatitis

Increasing evidence suggests the contribution of natural killer (NK) cells to pathogenesis of human hepatitis, but the detailed mechanisms have yet to be clearly elucidated. In this study, injection of polyinosinic:polycytidylic acid (poly I:C) and D-galactosamine (D-GalN) was used to establish a novel murine fulminant hepatitis model: results showed that predepletion of either NK cells or Kupffer cells could completely abolish the liver injury. Injection of poly I:C/D-GalN into mice could promote tumor necrosis factor-alpha production and surface retinoic acid early inducible-1 (Rae1) protein expression by Kupffer cells, which then activated NK cells to produce interferon-gamma via NKG2D-Rae1 recognition. NK cell-derived interferon-gamma and Kupffer cell-derived tumor necrosis factor-alpha synergistically mediated the severe liver injury. Moreover, Kupffer cell-derived interleukin-12 and interleukin-18 were also found to improve cross talk between NK cells and Kupffer cells.

CONCLUSION

These results provide the first in vivo evidence that NKG2D/ligand interaction is involved in the synergic effects of NK cells and Kupffer cells on acute liver injury.

Inflammatory pathways in liver homeostasis and liver injury

The liver is a unique organ with respect to its anatomical location, allowing continuous blood flow from the gastrointestinal tract through the sinusoids, and its cellular composition, comprising metabolically active hepatocytes, nonhepatocytic parenchymal cells, and various immune cell populations. Cytokines are key mediators within the complex interplay of intrahepatic immune cells and hepatocytes, as they can activate effector functions of immune cells, as well as hepatocytic intracellular signaling pathways controlling cellular homeostasis. Kupffer cells and liver-infiltrating monocyte-derived macrophages are primary sources of cytokines such as tumor-necrosis factor-alpha (TNF-alpha) and interleukin-6. The liver is also enriched in natural killer (NK) and NK T cells, which fulfill functions in pathogen defense, T cell recruitment, and modulation of liver injury. TNF-alpha can activate specific intracellular pathways in hepatocytes that influence cell fate in different manners, e.g., proapoptotic signals via the caspase cascade, but also survival pathways, namely the nuclear factor (NF)-kappaB pathway. NF-kappaB regulates important functions in liver physiology and pathology. Recent experiments with genetically modified mice demonstrated important and partly controversial functions of this pathway, e.g., in cytokine-mediated hepatocyte apoptosis or ischemia-reperfusion injury. The exact dissection of the contribution of recruited and resident immune cells, their soluble cytokine and chemokine mediators, and the intracellular hepatocytic response in liver homeostasis and injury could potentially identify novel targets for the treatment of acute and chronic liver disease, liver fibrosis, or cirrhosis.

Transgenic expression of cyclooxygenase-2 in hepatocytes accelerates endotoxin-induced acute liver failure

Bacterial LPS (endotoxin) is implicated in the pathogenesis of acute liver failure and several chronic inflammatory liver diseases. To evaluate the effect of hepatocyte cyclooxygenase (COX)-2 in LPS-induced liver injury, we generated transgenic mice with targeted expression of COX-2 in the liver by using the albumin promoter-enhancer driven vector and the animals produced were subjected to a standard experimental protocol of LPS-induced acute fulminant hepatic failure (i.p. injection of low dose of LPS in combination with d-galactosamine (d-GalN)). The COX-2 transgenic mice exhibited earlier mortality, higher serum aspartate aminotransferase and alanine aminotransferase levels and more prominent liver tissue damage (parenchymal hemorrhage, neutrophilic inflammation, hepatocyte apoptosis, and necrosis) than wild-type mice. Western blot analysis of the liver tissues showed that LPS/d-GalN treatment for 4 h induced much higher cleavage of poly(ADP-ribose) polymerase, caspase-3, and caspase-9 in COX-2 transgenic mice than in wild-type mice. Increased hepatic expression of JNK-2 in COX-2 transgenic mice suggest that up-regulation of JNK-2 may represent a potential mechanism for COX-2-mediated exacerbation of liver injury. Blocking the prostaglandin receptor, EP(1), prevented LPS/d-GalN-induced liver injury and hepatocyte apoptosis in COX-2 transgenic mice. Accordingly, the mice with genetic ablation of EP(1) showed less LPS/d-GalN-induced liver damage and less hepatocyte apoptosis with prolonged survival when compared with the wild-type mice. These findings demonstrate that COX-2 and its downstream prostaglandin receptor EP(1) signaling pathway accelerates LPS-induced liver injury. Therefore, blocking COX-2-EP(1) pathway may represent a potential approach for amelioration of LPS-induced liver injury.