Selective priming to Toll-like receptor 4 (TLR4), not TLR2, ligands by P. acnes involves up-regulation of MD-2 in mice

To explore the mechanism of gypenosides in the treatment of liver injury in rats based on GC-MS metabolomics and bile acid metabolism pathway

Gynostemma pentaphyllum is a herbaceous vine of Cucurbitaceae family, and its principal pharmacological components, gypenosides (GPs), have been proved to be effective in various liver diseases. However, the mechanisms of GPs on liver injury are still to be studied for further. This investigation utilized the CCl4-induced liver injury rat model (LI) to comprehensively explore the mechanism of action of GPs in the treatment of chemical liver injury by comparing the metabolomic changes in four groups rats. In this study, the therapeutic efficacy of GPs in a liver injury rat model induced by weekly gavage of CCl4 was evaluated by inflammatory factors, oxidative damage indexes, and histopathological sections. Then, GC-MS technology was used to identify the metabolic profile of GPs in treating liver injury. Finally, the content variation of metabolites (BAs and SCFAs) was measured to elucidate the mechanism of GPs in the treatment of CCl4-induced liver injury. After 8 weeks of administration, GPs effectively reduced the degree of LI and appeared a substantial tendency of reversing in the levels of MDA, GSH, CYP7E1, CYP7A1 and CYP27A1. Untargeted metabolomics suggested that GPs may play a role in BAs and SCFAs metabolism. Targeted metabolomics and ELISA confirmed the key role of GPs in increasing SCFAs levels and regulating BAs metabolism. Overall, this study indicated that GPs can alleviate CCl4-induced liver injury. And GPs may exert beneficial effects on LI by affecting their metabolites (SCFAs and BAs).

The Intestinal Microbiota in the Development of Chronic Liver Disease: Current Status

Chronic liver disease (CLD) is a significant global health burden, leading to millions of deaths annually. The gut-liver axis plays a pivotal role in this context, allowing the transport of gut-derived products directly to the liver, as well as biological compounds from the liver to the intestine. The gut microbiota plays a significant role in maintaining the health of the digestive system. A change in gut microbiome composition as seen in dysbiosis is associated with immune dysregulation, altered energy and gut hormone regulation, and increased intestinal permeability, contributing to inflammatory mechanisms and damage to the liver, irrespective of the underlying etiology of CLD. The aim of this review is to present the current knowledge about the composition of the intestinal microbiome in healthy individuals and those with CLD, including the factors that affect this composition, the impact of the altered microbiome on the liver, and the mechanisms by which it occurs. Furthermore, this review analyzes the effects of gut microbiome modulation on the course of CLD, by using pharmacotherapy, nutrition, fecal microbiota transplantation, supplements, and probiotics. This review opens avenues for the translation of knowledge about gut-liver interplay into clinical practice as an additional tool to fight CLD and its complications.

Gut Microbiota at the Intersection of Alcohol, Brain, and the Liver

Over the last decade, increased research into the cognizance of the gut-liver-brain axis in medicine has yielded powerful evidence suggesting a strong association between alcoholic liver diseases (ALD) and the brain, including hepatic encephalopathy or other similar brain disorders. In the gut-brain axis, chronic, alcohol-drinking-induced, low-grade systemic inflammation is suggested to be the main pathophysiology of cognitive dysfunctions in patients with ALD. However, the role of gut microbiota and its metabolites have remained unclear. Eubiosis of the gut microbiome is crucial as dysbiosis between autochthonous bacteria and pathobionts leads to intestinal insult, liver injury, and neuroinflammation. Restoring dysbiosis using modulating factors such as alcohol abstinence, promoting commensal bacterial abundance, maintaining short-chain fatty acids in the gut, or vagus nerve stimulation could be beneficial in alleviating disease progression. In this review, we summarize the pathogenic mechanisms linked with the gut-liver-brain axis in the development and progression of brain disorders associated with ALD in both experimental models and humans. Further, we discuss the therapeutic potential and future research directions as they relate to the gut-liver-brain axis.

Bifidobacterium longum R0175 Protects Rats against d-Galactosamine-Induced Acute Liver Failure

Our research investigated the protective and preventive roles of B. longum R0175 in a rat model of acute liver failure. The results illustrated that this probiotic strain exhibited protective effects in rats with acute liver failure. Thus, B. longum R0175 showed clinical application prospects that required further exploration.

Acute liver failure is a severe liver disorder that poses considerable global challenges. Previous studies on Bifidobacterium longum R0175 have mainly focused on its psychotropic functions. The current research focused on the protective efficacy of B. longum R0175 against acute liver failure caused by d-galactosamine (d-GalN) in rats and further tested the hypothesis that B. longum R0175 exerted liver-protective effects by affecting the intestinal microbiota and fecal metabolites and by inhibiting inflammation. We found that oral gavage of B. longum R0175 markedly reduced the severity of liver injury in d-GalN-treated rats, as evidenced by decreased serum levels of aspartate aminotransferase (AST) and total bile acids (TBAs) (P < 0.05). Moreover, the plasma concentrations of proinflammatory cytokines (interleukin 1β [IL-1β] and tumor necrosis factor-α [TNF-α]) and chemokines (granulocyte-macrophage colony-stimulating factor [GM-CSF], macrophage chemoattractant protein 1 [MCP-1], chemokine [C-X-C motif] ligand 1 [CXCL1], chemokine [C-C motif] ligand 5 [CCL5], and macrophage inflammatory protein-1α [MIP-1α]) were also markedly reduced (P < 0.05). Pretreatment with B. longum R0175 partially reversed the gut microbiota dysbiosis in rats with liver injury by increasing the relative abundances of potentially beneficial bacteria, such as Alloprevotella spp., and decreasing the relative abundances of potentially harmful bacteria, such as Acetatifactor muris, Butyricimonas spp., and Oscillibacter spp. Furthermore, B. longum R0175 administration partially improved the metabolic function of the intestinal microbes, as indicated by the decreased level of lithocholic acid found in the feces.

IMPORTANCE Our research investigated the protective and preventive roles of B. longum R0175 in a rat model of acute liver failure. The results illustrated that this probiotic strain exhibited protective effects in rats with acute liver failure. Thus, B. longum R0175 showed clinical application prospects that required further exploration.

Dietary Toll-Like Receptor Stimulants Promote Hepatic Inflammation and Impair Reverse Cholesterol Transport in Mice via Macrophage-Dependent Interleukin-1 Production

Background: The mechanisms connecting dietary intake of processed foods with systemic inflammatory markers and cardiovascular risk remain poorly defined. We sought to compare the abundance of pro-inflammatory stimulants of innate immune receptors in processed foods with those produced by the murine ileal and caecal microbiota, and to explore the impact of their ingestion on systemic inflammation and lipid metabolism in vivo. Methods and results: Calibrated receptor-dependent reporter assays revealed that many processed foods, particularly those based on minced meats, contain pro-inflammatory stimulants of Toll-like receptor (TLR)-2 and TLR4 at concentrations which greatly exceed those produced by the endogenous murine ileal microbiota. Chronic dietary supplementation with these stimulants, at concentrations relevant to those measured in the Western diet, promoted hepatic inflammation and reduced several markers of reverse cholesterol transport (RCT) in mice. Hepatocytes were found to be insensitive to TLR2- and TLR4-stimulants directly, but their secretion of functional cholesterol acceptors was impaired by interleukin (IL)-1β released by TLR-responsive hepatic macrophages. Hepatic macrophage priming by high-fat diet enhanced the impairment of RCT by ingested endotoxin, and this was reversed by macrophage depletion via clodronate liposome treatment, or genetic deficiency in the IL-1 receptor. Conclusion: These findings reveal an unexpected mechanism connecting processed food consumption with cardiovascular risk factors, and introduce the food microbiota as a potential target for therapeutic regulation of lipid metabolism.

Tolerizing CTL by Sustained Hepatic PD-L1 Expression Provides a New Therapy Approach in Mouse Sepsis

Cytotoxic T lymphocyte (CTL) activation contributes to liver damage during sepsis, but the mechanisms involved are largely unknown. Understanding the underlying principle will permit interference with CTL activation and thus, provide a new therapeutic option. Methods: To elucidate the mechanism leading to CTL activation we used the Hepa1-6 cell line in vitro and the mouse model of in vivo polymicrobial sepsis, following cecal-ligation and -puncture (CLP) in wildtype, myeloid specific NOX-2, global NOX2 and NOX4 knockout mice, and their survival as a final readout. In this in vivo setting, we also determined hepatic mRNA and protein expression as well as clinical parameters of liver damage - aspartate- and alanine amino-transaminases. Hepatocyte specific overexpression of PD-L1 was achieved in vivo by adenoviral infection and transposon-based gene transfer using hydrodynamic injection. Results: We observed downregulation of PD-L1 on hepatocytes in the murine sepsis model. Adenoviral and transposon-based gene transfer to restore PD-L1 expression, significantly improved survival and reduced the release of liver damage, as PD-L1 is a co-receptor that negatively regulates T cell function. Similar protection was observed during pharmacological intervention using recombinant PD-L1-Fc. N-acetylcysteine blocked the downregulation of PD-L1 suggesting the involvement of reactive oxygen species. This was confirmed in vivo, as we observed significant upregulation of PD-L1 expression in NOX4 knockout mice, following sham operation, whereas its expression in global as well as myeloid lineage NOX2 knockout mice was comparable to that in the wild type animals. PD-L1 expression remained high following CLP only in total NOX2 knockouts, resulting in significantly reduced release of liver damage markers. Conclusion: These results suggest that, contrary to common assumption, maintaining PD-L1 expression on hepatocytes improves liver damage and survival of mice during sepsis. We conclude that administering recombinant PD-L1 or inhibiting NOX2 activity might offer a new therapeutic option in sepsis.

Targeting the gut barrier for the treatment of alcoholic liver disease

Alcohol consumption remains one of the predominant causes of liver disease and liver-related death worldwide. Intriguingly, dysregulation of the gut barrier is a key factor promoting the pathogenesis of alcoholic liver disease (ALD). A functional gut barrier, which consists of a mucus layer, an intact epithelial monolayer and mucosal immune cells, supports nutrient absorption and prevents bacterial penetration. Compromised gut barrier function is associated with the progression of ALD. Indeed, alcohol consumption disrupts the gut barrier, increases gut permeability, and induces bacterial translocation both in ALD patients and in experimental models with ALD. Moreover, alcohol consumption also causes enteric dysbiosis with both numerical and proportional perturbations. Here, we review and discuss mechanisms of alcohol-induced gut barrier dysfunction to better understand the contribution of the gut-liver axis to the pathogenesis of ALD. Unfortunately, there is no effectual Food and Drug Administration-approved treatment for any stage of ALD. Therefore, we conclude with a discussion of potential strategies aimed at restoring the gut barrier in ALD. The principle behind antibiotics, prebiotics, probiotics and fecal microbiota transplants is to restore microbial symbiosis and subsequently gut barrier function. Nutrient-based treatments, such as dietary supplementation with zinc, niacin or fatty acids, have been shown to regulate tight junction expression, reduce intestinal inflammation, and prevent endotoxemia as well as liver injury caused by alcohol in experimental settings. Interestingly, saturated fatty acids may also directly control the gut microbiome. In summary, clinical and experimental studies highlight the significance and efficacy of the gut barrier in treating ALD.

Toll-like receptors in pathophysiology of liver diseases

Toll-like receptors (TLRs) are pattern recognition receptors that participate in host defense by recognizing pathogen-associated molecular patterns alongside inflammatory processes by recognizing damage associated molecular patterns. Given constant exposure to pathogens from gut, strict control of TLR-associated signaling pathways is essential in the liver, which otherwise may lead to inappropriate production of pro-inflammatory cytokines and interferons and may generate a predisposition to several autoimmune and chronic inflammatory diseases. The liver is considered to be a site of tolerance induction rather than immunity induction, with specificity in hepatic cell functions and distribution of TLR. Recent data emphasize significant contribution of TLR signaling in chronic liver diseases via complex immune responses mediating hepatocyte (i.e., hepatocellular injury and regeneration) or hepatic stellate cell (i.e., fibrosis and cirrhosis) inflammatory or immune pathologies. Herein, we review the available data on TLR signaling, hepatic expression of TLRs and associated ligands, as well as the contribution of TLRs to the pathophysiology of hepatic diseases.

Microbiota-based treatments in alcoholic liver disease

Gut microbiota plays a key role in the pathogenesis of alcoholic liver disease (ALD). Consumption of alcohol leads to increased gut permeability, small intestinal bacterial overgrowth, and enteric dysbiosis. These factors contribute to the increased translocation of microbial products to the liver via the portal tract. Subsequently, bacterial endotoxins such as lipopolysaccharide, in association with the Toll-like receptor 4 signaling pathway, induce a gamut of damaging immune responses in the hepatic milieu. Because of the close association between deleterious inflammation and ALD-induced microbiota imbalance, therapeutic approaches that seek to reestablish gut homeostasis should be considered in the treatment of alcoholic patients. To this end, a number of preliminary studies on probiotics have confirmed their effectiveness in suppressing proinflammatory cytokines and improving liver function in the context of ALD. In addition, there have been few studies linking the administration of prebiotics and antibiotics with reduction of alcohol-induced liver damage. Because these preliminary results are promising, large-scale randomized studies are warranted to elucidate the impact of these microbiota-based treatments on the gut flora and associated immune responses, in addition to exploring questions about optimal delivery. Finally, fecal microbiota transplant has been shown to be an effective method of modulating gut microbiota and deserve further investigation as a potential therapeutic option for ALD.

Toll-like Receptor 4 on Macrophage Promotes the Development of Steatohepatitis-related Hepatocellular Carcinoma in Mice

The role of Toll-like receptor (TLR) signaling has attracted much attention in the development of hepatic inflammation and hepatocellular carcinoma (HCC). We herein sought to determine the role of TLRs and responsible cells in steatohepatitis-related HCC. We used hepatocyte-specific Pten-deficient (Pten(Δ) (hep)) mice, which exhibit steatohepatitis followed by liver tumor formation, including HCC. We then generated Pten(Δ) (hep)/Tlr4(-/-) and Pten(Δ) (hep)/Tlr2(-/-) double-mutant mice and investigated the role of macrophages using reconstitution of bone marrow (BM)-derived cells, chemical depletion of macrophages, and isolated macrophages. Tlr4 but not Tlr2 deficiency in the Pten(Δ) (hep) mice suppressed tumor growth as well as hepatic inflammation. Gut sterilization by an antibiotic mixture reduced the portal LPS levels as well as tumor growth in the Pten(Δ) (hep) mice. Tumor growth was also decreased by reconstitution of BM-derived cells to Tlr4(-/-) BM cells. In addition, chemical depletion of macrophages significantly reduced tumor size and numbers. Macrophages expressing Ly6C were increased in number, which was associated with inflammation and tumor progression in the Pten(Δ) (hep) mice. Hepatic macrophages isolated from the Pten(Δ) (hep) mice abundantly expressed the Ly6C gene and produced much more IL-6 and TNFα in response to LPS. These proinflammatory cytokines induced the proliferation of HCC cells as well as oval cells, putative cancer progenitor cells. Indeed, putative cancer progenitor cells emerged before the development of macroscopic liver tumors and then increased in number under sustained inflammation. TLR4 on macrophages contributes to the development of steatohepatitis-related HCC in mice.

Modulation of Th1/Th2 immune responses by killed Propionibacterium acnes and its soluble polysaccharide fraction in a type I hypersensitivity murine model: induction of different activation status of antigen-presenting cells

Propionibacterium acnes (P. acnes) is a gram-positive anaerobic bacillus present in normal human skin microbiota, which exerts important immunomodulatory effects, when used as heat- or phenol-killed suspensions. We previously demonstrated that heat-killed P. acnes or its soluble polysaccharide (PS), extracted from the bacterium cell wall, suppressed or potentiated the Th2 response to ovalbumin (OVA) in an immediate hypersensitivity model, depending on the treatment protocol. Herein, we investigated the mechanisms responsible for these effects, using the same model and focusing on the activation status of antigen-presenting cells (APCs). We verified that higher numbers of APCs expressing costimulatory molecules and higher expression levels of these molecules are probably related to potentiation of the Th2 response to OVA induced by P. acnes or PS, while higher expression of toll-like receptors (TLRs) seems to be related to Th2 suppression. In vitro cytokines production in cocultures of dendritic cells and T lymphocytes indicated that P. acnes and PS seem to perform their effects by acting directly on APCs. Our data suggest that P. acnes and PS directly act on APCs, modulating the expression of costimulatory molecules and TLRs, and these differently activated APCs drive distinct T helper patterns to OVA in our model.

Host-microbiome interactions in alcoholic liver disease

Alcoholic liver disease is a leading cause of morbidity and liver-related death worldwide. Intestinal bacterial overgrowth and dysbiosis induced by ethanol ingestion play an important role in the pathogenesis of alcoholic liver disease. After exposure to alcohol in the lumen, enteric bacteria alter their metabolism and thereby disturb intestinal homeostasis. Disruption of the mucosal barrier results in the translocation of microbial products that contribute to liver disease by inducing hepatic inflammation. In this review, we will discuss the effects of alcohol on the intestinal microbiome, and in particular, its effects on bacterial metabolism, bacterial translocation and ecological balance. A better understanding of the interactions among alcohol, the host and the microbiome will reveal new targets for therapy and lead to new treatments.

Alterations of the gut microbiome and metabolome in alcoholic liver disease

Alcohol consumption is one of the leading causes of liver diseases and liver-related death worldwide. The gut is a habitat for billions of microorganisms which promotes metabolism and digestion in their symbiotic relationship with the host. Alterations of gut microbiome by alcohol consumption are referred to bacterial overgrowth, release of bacteria-derived products, and/or changed microbiota equilibrium. Alcohol consumption also perturbs the function of gastrointestinal mucosa and elicits a pathophysiological condition. These adverse effects caused by alcohol may ultimately result in a broad change of gastrointestinal luminal metabolites such as bile acids, short chain fatty acids, and branched chain amino acids. Gut microbiota alterations, metabolic changes produced in a dysbiotic intestinal environment, and the host factors are all critical contributors to the development and progression of alcoholic liver disease. This review summarizes recent findings of how alcohol-induced alterations of gut microbiota and metabolome, and discusses the mechanistic link between gastrointestinal dyshomeostasis and alcoholic liver injury.

Developmental origins of nonalcoholic fatty liver disease

Obese pregnant women may transmit their metabolic phenotype to offspring, leading to a cycle of obesity and diabetes over generations. Early childhood obesity predicts nonalcoholic fatty liver disease (NAFLD), the most common chronic human liver disease. The fetus may be vulnerable to steatosis because immature fetal adipose depots are not available to buffer the excess transplacental lipid delivery in maternal obesity. In animal models, in utero high-fat diet exposure results in an increase in the accumulation of liver triglycerides in offspring and increased hepatic oxidative stress and apoptosis, perhaps priming the liver for later development of NAFLD. Innate immune dysfunction and necroinflammatory changes have been observed in postnatal offspring liver of animals born to high-fat-fed dams. Postweaning, livers of offspring exposed to maternal high-fat feeding in utero share pathophysiologic features with human NAFLD, including increased de novo lipogenesis and decreased free fatty acid oxidation. Human studies using magnetic resonance imaging have shown that maternal BMI predicts infant intrahepatocellular lipid storage, as seen in animal models. The generational transfer of NAFLD may occur via epigenetic changes in offspring liver. Transmission of microbiota from mother to infant may impact energy retention and immune function that contribute to a predisposition to NAFLD.

Developmental programming of pediatric nonalcoholic fatty liver disease: redefining the"first hit"

The incidence of pediatric nonalcoholic fatty liver disease has increased dramatically, and growing evidence indicates that the pathophysiology may be unique from the adult form, suggesting a role for early-life events. Recent radiologic techniques have now demonstrated that maternal obesity contributes to hepatic fat storage in newborn infants. In this review, we will explore how maternal obesity and a hyperlipidemic environment can initiate liver histopathogenesis in utero, including steatosis, mitochondrial dysfunction, oxidative stress, and inflammatory priming. Thus, early exposure to excess lipids may represent the "first hit" for the fetal liver, placing it on a trajectory toward future metabolic disease.

Toll-like receptors in alcoholic liver disease, non-alcoholic steatohepatitis and carcinogenesis

Activation of innate immune systems including Toll-like receptor (TLR) signaling is a key in chronic liver disease. Recent studies suggest that gut microflora-derived bacterial products (i.e. lipopolysaccharide [LPS], bacterial DNA) and endogenous substances (i.e. high-mobility group protein B1 [HMGB1], free fatty acids) released from damaged cells activate hepatic TLRs that contribute to the development of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH) and liver fibrosis. The crucial role of TLR4, a receptor for LPS, has been implicated in the development of ASH, NASH, liver fibrosis, and hepatocellular carcinoma. However, the role of other TLRs, such as TLR2 and TLR9 in chronic liver disease remains less clear. In this review, we will discuss the role of TLR2, 4, and 9 in Kupffer cells and hepatic stellate cells in the development of ASH, NASH, and hepatocarcinogenesis.

Late recognition and illness severity are determinants of early death in severe septic patients

OBJECTIVE

To identify the independent variables associated with death within 4 days after the first sepsis-induced organ dysfunction.

METHODS

In this prospective observational study, severe sepsis and septic shock patients were classified into 3 groups: Group 1, survivors; Group 2, late non-survivors; and Group 3, early non-survivors. Early death was defined as death occurring within 4 days after the first sepsis-induced organ dysfunction. Demographic, clinical and laboratory data were collected and submitted to univariate and multinomial analyses.

RESULTS

The study included 414 patients: 218 (52.7%) in Group 1, 165 (39.8%) in Group 2, and 31 (7.5%) in Group 3. A multinomial logistic regression analysis showed that age, Acute Physiology and Chronic Health Evaluation II score, Sepsis-related Organ Failure Assessment score after the first 24 hours, nosocomial infection, hepatic dysfunction, and the time elapsed between the onset of organ dysfunction and the sepsis diagnosis were associated with early mortality. In contrast, Black race and a source of infection other than the urinary tract were associated with late death. Among the non-survivors, early death was associated with Acute Physiology and Chronic Health Evaluation II score, chronic renal failure, hepatic dysfunction Sepsis-related Organ Failure Assessment score after 24 hours, and the duration of organ dysfunction.

CONCLUSION

Factors related to patients' intrinsic characteristics and disease severity as well as the promptness of sepsis recognition are associated with early death among severe septic patients.

Blockade of B-cell-activating factor signaling enhances hepatic steatosis induced by a high-fat diet and improves insulin sensitivity

Chronic inflammation is an important contributor to the development and progression of metabolic syndrome. Recent evidence indicates that, in addition to innate immune cells, adaptive immune cells have an important role in this process. We previously showed that the serum level of B-cell-activating factor (BAFF) was increased in patients with nonalcoholic steatohepatitis. However, it is currently unknown whether BAFF and BAFF-R (BAFF-R) have a role in lipid metabolism in the liver. To address this issue, the role played by BAFF and BAFF-R signaling in the development of insulin resistance and hepatic steatosis was examined in BAFF-R(-/-) mice fed a high-fat diet (HFD). Furthermore, the effect of BAFF on lipid metabolism in hepatocytes was analyzed in vitro. BAFF-R(-/-) mice showed improvements in HFD-induced obesity and insulin resistance. In addition, the number of B cells, levels of serum IgG, and inflammation of visceral fat were reduced in these mice. However, the expression of steatogenic genes and fatty acid deposition in the liver was higher in these mice than in control mice. BAFF was also found to downregulate the expression of steatogenesis genes and enhance steatosis in hepatocytes through BAFF-R. Collectively, these data indicated that, in addition to its known functions in inflammation and glucose metabolism, BAFF has a protective role in hepatic steatosis by regulating lipid metabolism in the liver.

Inflammasomes in liver diseases

Inflammation is a common element in the pathogenesis of most chronic liver diseases that lead to fibrosis and cirrhosis. Inflammation is characterized by activation of innate immune cells and production of pro-inflammatory cytokines IL-1α, IL-1β, and TNFα. Inflammasomes are intracellular multiprotein complexes expressed in both parenchymal and non-parenchymal cells of the liver that in response to cellular danger signals activate caspase-1, and release IL-1β and IL-18. The importance of inflammasome activation in various forms of liver diseases in relation to liver damage, steatosis, inflammation and fibrosis is discussed in this review.

Microfluidically-unified cell culture, sample preparation, imaging and flow cytometry for measurement of cell signaling pathways with single cell resolution

We have developed a microfluidic platform that enables, in one experiment, monitoring of signaling events spanning multiple time-scales and cellular locations through seamless integration of cell culture, stimulation and preparation with downstream analysis. A combination of two single-cell resolution techniques-on-chip multi-color flow cytometry and fluorescence imaging provides multiplexed and orthogonal data on cellular events. Automated, microfluidic operation allows quantitatively- and temporally-precise dosing leading to fine time-resolution and improved reproducibility of measurements. The platform was used to profile the toll-like receptor (TLR4) pathway in macrophages challenged with lipopolysaccharide (LPS)-beginning with TLR4 receptor activation by LPS, through intracellular MAPK signaling, RelA/p65 translocation in real time, to TNF-α cytokine production, all in one small macrophage population (< 5000 cells) while using minute reagent volume (540 nL/condition). The platform is easily adaptable to many cell types including primary cells and provides a generic platform for profiling signaling pathways.

Beneficial effect of garlic on D-galactosamine and lipopolysaccharide-induced acute hepatic failure in male albino rats

BACKGROUND AND AIMS

Activation of the pro-inflammatory and anti-inflammatory cytokine cascade, including tumour necrosis factor (TNF)-alpha and interleukin (IL)-4, is considered to play an important role in severe liver injury. Kupffer cells, resident macrophages of the liver, activated with lipopolysaccharide (LPS) release pro-inflammatory cytokine. D-Galactosamine (D-GalN), a hepatocyte-specific inhibitor of RNA synthesis, is known to sensitise animals to the lethal effects of LPS. In the present study we seek to reverse some altered parameters, immunological and histopathological, to normal values of rats pre-treated with garlic.

METHODS

Acute hepatic failure was induced in male albino rats by the intraperitoneal injection of 500 mg D-GalN and 50 μg LPS/kg body weight. Expression levels of TNF-α and IL-4 were detected by ELISA. Leukocytes proliferation was carried out by differential count. For histopathology, liver sections were stained with haematoxylin and eosin. Data were analysed by SPSS program version 13.0.

RESULTS

The data showed significant increase in the numbers of granulocytes, but with significant decreases in lymphocyte and monocytes proliferation and the TNF-alpha and IL-4 levels in D-GalN/LPS-induced group. Garlic pre-treatment of liver-injured rats induced significant amelioration in the numbers of monocytes and lymphocytes, with significant increase in granulocytes numbers, TNF-α level and IL-4 level.

CONCLUSIONS

Results of this study revealed that garlic could afford a significant protection in the alleviation of D-GalN/LPS-induced hepatocellular injury.

Plasmodium yoelii blood-stage primes macrophage-mediated innate immune response through modulation of toll-like receptor signalling

BACKGROUND

Toll-like receptors (TLRs) signalling is reported to be primed by the infection of human malaria parasite, Plasmodium falciparum. However, little is known about the regulation of macrophages TLR signalling by the infection of lethal or non-lethal strain of rodent malaria parasites.

METHODS

BALB/c mice were infected with non-lethal strain Plasmodium yoelii 17XNL or lethal strain P. yoelii 17XL. Peritoneal macrophages were isolated to study its immune response to pRBC lysate, and TLRs (TLR2, TLR4, and TLR9) agonists, and the expression of TLRs and intracellular signalling molecules were also investigated by flow cytometry and semi-quantitive RT-PCR.

RESULTS

The reactivity of peritoneal macrophages from the mice infected with lethal strain P. y 17XL or non-lethal strain P. y 17XNL were enhanced to pRBC lysate, and TLR2, TLR4, and TLR9 agonists at one, three and five days post-infection. Of all the tested TLRs, only TLR2 was up-regulated on peritoneal macrophages of mice infected with either strain. However, transcription of intracellular signalling molecules MyD88, IRAK-1, and TRAF-6 was significantly up-regulated in peritoneal macrophages from mice infected either with P. yoelii 17XL or P. yoelii 17XNL at one, three and five days post-infection. However, the enhanced TLRs response of macrophage from P. yoelii 17XNL-infected mice persisted for a much longer time than that from P. yoelii 17XL-infected mice.

CONCLUSION

Both P. yoelii 17XL and 17XNL strains could enhance the response of peritoneal macrophages to pRBC lysate and TLR agonists, through up-regulating the expression of TLR2 and intracellular signalling molecules MyD88, IRAK-1, and TRAF-6. In addition, prolonged high response of macrophage from P. yoelii 17XNL-infected mice might be associated with the more efficiently controlling of P. yoelii 17XNL growth in mice at early stage.

Clearance of Propionibacterium acnes by kupffer cells is regulated by osteopontin through modulating the expression of p47phox

Osteopontin (OPN) is a cytokine with multiple functions, including the regulation of innate immune response. However, the detailed function and mechanism of OPN in host defense against invaded microorganisms remain unclear. In this report, we revealed that OPN could affect the clearance of Propionibacterium acnes in kupffer cells. In a murine model of P. acnes induced hepatic granuloma, OPN-deficient mice or wild-type (WT) mice treated with anti-OPN mAb exhibited more hepatic granuloma formation than WT mice. Increased infiltration of intrahepatic leukocytes, higher expression of TLRs, and significantly upregulated level of proinflammatory cytokines of liver tissue were observed in OPN-deficient mice after P. acnes challenge. Moreover, in vitro assay showed that kupffer cells isolated from OPN(-/-) mice exhibited impairment in clearance of P. acnes. Kupffer cells isolated from OPN(-/-) mice showed reduced level of NADPH oxidase-mediated reactive oxygen species (ROS) in response to P. acnes, which was regulated by NADPH oxidase subunit p47phox. Further investigation revealed that OPN interaction with αvβ3 integrin activated PI3K and ERK signal pathways, leading to the expression of p47phox. Taken together, these data demonstrated an important role of OPN in enhancing the antimicrobial innate immune response by modulation of bacterium clearance activity in kupffer cells.

Fatty acid and endotoxin activate inflammasomes in mouse hepatocytes that release danger signals to stimulate immune cells

The pathogenesis of nonalcoholic steatohepatitis (NASH) and inflammasome activation involves sequential hits. The inflammasome, which cleaves pro-interleukin-1β (pro-IL-1β) into secreted IL-1β, is induced by endogenous and exogenous danger signals. Lipopolysaccharide (LPS), a toll-like receptor 4 ligand, plays a role in NASH and also activates the inflammasome. In this study, we hypothesized that the inflammasome is activated in NASH by multiple hits involving endogenous and exogenous danger signals. Using mouse models of methionine choline-deficient (MCD) diet-induced NASH and high-fat diet-induced NASH, we found up-regulation of the inflammasome [including NACHT, LRR, and PYD domains-containing protein 3 (NALP3; cryopyrin), apoptosis-associated speck-like CARD-domain containing protein, pannexin-1, and pro-caspase-1] at the messenger RNA (mRNA) level increased caspase-1 activity, and mature IL-1β protein levels in mice with steatohepatitis in comparison with control livers. There was no inflammasome activation in mice with only steatosis. The MCD diet sensitized mice to LPS-induced increases in NALP3, pannexin-1, IL-1β mRNA, and mature IL-1β protein levels in the liver. We demonstrate for the first time that inflammasome activation occurs in isolated hepatocytes in steatohepatitis. Our novel data show that the saturated fatty acid (FA) palmitic acid (PA) activates the inflammasome and induces sensitization to LPS-induced IL-1β release in hepatocytes. Furthermore, PA triggers the release of danger signals from hepatocytes in a caspase-dependent manner. These hepatocyte-derived danger signals, in turn, activate inflammasome, IL-1β, and tumor necrosis factor α release in liver mononuclear cells.

CONCLUSION

Our novel findings indicate that saturated FAs represent an endogenous danger in the form of a first hit, up-regulate the inflammasome in NASH, and induce sensitization to a second hit with LPS for IL-β release in hepatocytes. Furthermore, hepatocytes exposed to saturated FAs release danger signals that trigger inflammasome activation in immune cells. Thus, hepatocytes play a key role in orchestrating tissue responses to danger signals in NASH.

Toll-like receptors in acute liver injury and regeneration

Liver is the lymphoid organ with an overwhelming innate immune system, which functions as a filter organ at the first line between the digestive tract and the rest of the body, with receiving 80% of the blood supply through portal vein. TLRs are widely expressed on parenchymal and non-parenchymal cells in the liver, which play critical roles for the liver health. Recent studies indicate that TLR-medicated signals have been involved in almost all liver diseases such as acute and chronic hepatitis, liver fibrosis and cirrhosis, alcoholic and non-alcoholic liver disease, ischemia/reperfusion liver injury, liver regeneration and hepatocellular carcinoma. In this review, the expressions of TLRs in hepatic cell populations including hepatocytes, LSECs, Kupffer cells, lymphocytes, DCs, biliary epithelial cells and HSCs, and TLR ligands and signaling in the liver are summarized. Further, recent advances in the roles of TLRs in acute liver injury and regeneration as mediator and regulator, and their potential therapeutic targets are discussed.

Hepatoprotective effects of Sedum sarmentosum on D-galactosamine/lipopolysaccharide-induced murine fulminant hepatic failure

The hepatoprotective effects of sarmentosin-containing extracts of Sedum sarmentosum (SS) in D-galactosamine (D-GalN) / lipopolysaccharide (LPS)-induced fulminant hepatic failure mouse model. Pretreatment with SS markedly protected mice from lethal liver injury, which has known to be associated with an abrupt elevation of serum tumor necrosis factor (TNF)-α level. Indeed, SS significantly blocked the elevation of TNF-α and alanine aminotransferase and aspartate aminotransferase as well. SS also remarkably reduced number of apoptotic hepatocytes and DNA fragmentation in the liver, which correlated with blockade of caspase-3 activation. In addition, SS suppressed the increased expression of toll-like receptor 4 (TLR4). The activation of c-Jun NH(2)-terminal kinase, extracellular signal-regulated kinase, and p38 induced by D-GalN/LPS was also significantly suppressed by SS treatment. Furthermore, SS significantly inhibited the activation of nuclear factor-κB. In RAW 264.7 cells stimulated with LPS, TNF-α release and TLR4 expression was suppressed by SS pretreatment, which was in line with in vivo results. These findings suggested that SS prevents D-GalN/LPS-induced fulminant hepatic failure, and this protection is likely associated with its anti-apoptotic activity and the down-regulation of mitogen activated protein kinase activity associated at least in part with suppressing the transcription of LPS receptors.

Toll-like receptors in the pathogenesis of alcoholic liver disease

In the multifactorial pathophysiology of alcoholic liver disease (ALD), inflammatory cascade activation plays a central role. Recent studies demonstrated that Toll-like Receptors, the sensors of microbial and endogenous danger signals, are expressed and activated in innate immune cells as well as in parenchymal cells in the liver and thereby contribute to ALD. In this paper, we discuss the importance of gut-derived endotoxin and its recognition by TLR4. The significance of TLR-induced intracellular signaling pathways and cytokine production as well as the contribution of reactive oxygen radicals is evaluated. The contribution of TLR signaling to induction of liver fibrosis and hepatocellular cancer is reviewed in the context of alcohol-induced liver disease.

The TLR4/TRIF-Mediated Activation of NLRP3 Inflammasome Underlies Endotoxin-Induced Liver Injury in Mice

Administration of heat-killed Propionibacterium acnes renders mice highly susceptible to LPS. After LPS challenge P. acnes-primed mice promptly show hypothermia, hypercoagulation (disseminated intravascular coagulation), elevation of serum proinflammatory cytokine levels, and high mortality. The surviving mice develop liver injury. As previously reported, IL-18 plays a pivotal role in the development of this liver injury. Many cell types including macrophages constitutively store IL-18 as biologically inactive precursor (pro) form. Upon appropriate stimulation exemplified by TLR4 engagement, the cells secrete biologically active IL-18 by cleaving pro-IL-18 with caspase-1. Caspase-1 is also constitutively produced as a zymogen in macrophages. Recently, NLRP3, a cytoplasmic pathogen sensor, has been demonstrated to be involved in the activation of caspase-1. Here, we review the molecular mechanisms for the liver injuries, particularly focusing on the TLR4/NLRP3-mediated caspase-1 activation process, with a brief introduction of the mechanism underlying P. acnes-induced sensitization to LPS.

Salvage effect of E5564, Toll-like receptor 4 antagonist on d-galactosamine and lipopolysaccharide-induced acute liver failure in rats

BACKGROUND AND AIMS

The transmembrane protein Toll-like receptor 4 (TLR4), which exists mainly in macrophages such as Kupffer cells of the liver, plays an important role in recognizing and mediating macrophage activation and pro-inflammatory cytokine release. Activation of the pro-inflammatory cytokine cascade, including tumor necrosis factor-alpha (TNF-alpha), has a pivotal role in the progression of severe liver injury. D-galactosamine (GalN) and lipopolysaccharide (LPS)-induced liver injury in rats is an experimental model of fulminant hepatic failure, where TNF-alpha plays a central role in the progression of liver injury. E5564, a synthetic analogue of the lipid A component of endotoxin, inhibits endotoxin-stimulated inflammation and is under study for patients with sepsis. In the present study, we sought to explore the salvage effect of TLR4 antagonist E5564 on GalN+LPS-induced acute liver failure (ALF) in rats.

METHODS

ALF was induced in male Wistar rats by the intraperitoneal injection of GalN (500 mg/kg) and LPS (50 microg/kg). Immediately after GalN+LPS injection, rats were treated with intravenous injection of E5564 (3 mg/kg). The cumulative survival rates of GalN+LPS-induced ALF rats were compared between those with and without E5564 treatment.

RESULTS

The intravenous injection of E5564 reduced the elevation of serum total bilirubin, aspartate aminotransferase, alanine aminotransferase and TNF-alpha levels in rats at 3 h after GalN+LPS injection, and improved the survival rate of GalN+LPS-induced ALF rats at 24 h (8% vs 43%).

CONCLUSIONS

TLR4 antagonist E5564 reduced GalN+LPS-induced acute liver injury in rats and improved the overall survival rate of GalN+LPS-induced ALF rats. It may contribute to the treatment of ALF through blocking endotoxin-induced TNF-alpha overproduction of macrophages.

18Beta-glycyrrhetinic acid ameliorates acute Propionibacterium acnes-induced liver injury through inhibition of macrophage inflammatory protein-1alpha

18Beta-glycyrrhetinic acid (GA), the major bioactive component of licorice root extract, has a protective effect on hepatic injury and exhibits antiinflammatory activity. Here, we investigate the effect of GA in Propionibacterium acnes-induced acute inflammatory liver injury. C57BL/6 mice were primed with P. acnes followed by lipopolysaccharide challenge to induce fulminant hepatitis. GA (75 mg/kg) or vehicle control was administered intraperitoneally daily 1 day after P. acnes priming, and GA significantly improved mouse mortality. Then, to investigate the underlying mechanisms of GA in this acute inflammatory liver injury model, we primed C57BL/6 mice with P. acnes only. We propose that GA ameliorates acute P. acnes-induced liver injury through reduced macrophage inflammatory protein (MIP)-1alpha expression in Kupffer cells by down-regulating MyD88 expression and inhibiting NF-kappaB activation. Reduced MIP-1alpha expression lowered the recruitment of CD11c(+)B220(-) dendritic cell precursors into the liver. Consequently, GA treatment inhibits the activation and proliferation of liver-infiltrating CD4(+) T cells and reduces the production of serum alanine aminotransferase and proinflammatory cytokines such as interferon-gamma and tumor necrosis factor-alpha. Moreover, anti-MIP-1alpha treatment in P. acnes-primed mice inhibits the recruitment of dendritic cell precursors into the liver and suppresses mouse mortality as GA does. Taken together, our results suggest that GA exhibits antiinflammatory effects through inhibition of MIP-1alpha in a mouse model of acute P. acnes-induced inflammatory liver injury.

Therapeutic approach to regulate innate immune response by Toll-like receptor 4 antagonist E5564 in rats with D-galactosamine-induced acute severe liver injury

BACKGROUND AND AIMS

Toll-like receptor 4 (TLR4) is a transmembrane protein, existing mainly in macrophages, such as Kupffer cells of the liver. It plays an important role in recognizing and mediating macrophage activation and pro-inflammatory cytokine release. Activation of pro-inflammatory cytokines, including tumor necrosis factor (TNF)-alpha is pivotal in the progression of liver injury. Gut-derived endotoxin has been considered to play an important role in the development and progression of a D-galactosamine (GalN)-induced acute severe liver injury (ALI) model. E5564, a synthetic analog of the lipid A component of endotoxin, inhibits endotoxin-stimulated inflammation and is under study for patients with sepsis. In this study, we seek to explore the effect of TLR4 antagonist E5564 on GalN-induced ALI in rats.

METHODS

ALI was induced in male Wistar rats by the i.p. injection of 1 g/kg bodyweight of GalN and immediately after GalN injection they were treated with an i.v. injection of 3 mg/kg bodyweight of E5564. At 24 h after GalN injection with or without E5564, serum levels of total bilirubin (T.Bil), alanine aminotransferase (ALT) and TNF-alpha were analyzed. Expression levels of TNF-alpha, TLR4 and CD14 mRNA in the whole liver of rats was detected by reverse transcription polymerase chain reaction analysis.

RESULTS

The i.v. injection of E5564 reduced the elevation of serum T.Bil, ALT and TNF-alpha levels in rats treated with GalN. The expression level of TNF-alpha mRNA in the whole liver, which was increased at 24 h after GalN injection, was also reduced by i.v. injection of E5564.

CONCLUSION

TLR4 antagonist E5564 reduced GalN-induced ALI in rats. It may contribute to the treatment of acute liver failure through blocking endotoxin-induced TNF-alpha overproduction of macrophages.

VSL#3 probiotic treatment attenuates fibrosis without changes in steatohepatitis in a diet-induced nonalcoholic steatohepatitis model in mice

Nonalcoholic fatty liver disease (NAFLD) and its advanced stage, nonalcoholic steatohepatitis (NASH), are the most common causes of chronic liver disease in the United States. NASH features the metabolic syndrome, inflammation, and fibrosis. Probiotics exhibit immunoregulatory and anti-inflammatory activity. We tested the hypothesis that probiotic VSL#3 may ameliorate the methionine-choline-deficient (MCD) diet-induced mouse model of NASH. MCD diet resulted in NASH in C57BL/6 mice compared to methionine-choline-supplemented (MCS) diet feeding evidenced by liver steatosis, increased triglycerides, inflammatory cell accumulation, increased tumor necrosis factor alpha levels, and fibrosis. VSL#3 failed to prevent MCD-induced liver steatosis or inflammation. MCD diet, even in the presence of VSL#3, induced up-regulation of serum endotoxin and expression of the Toll-like receptor 4 signaling components, including CD14 and MD2, MyD88 adaptor, and nuclear factor kappaB activation. In contrast, VSL#3 treatment ameliorated MCD diet-induced liver fibrosis resulting in diminished accumulation of collagen and alpha-smooth muscle actin. We identified increased expression of liver peroxisome proliferator-activated receptors and decreased expression of procollagen and matrix metalloproteinases in mice fed MCD+VSL#3 compared to MCD diet alone. MCD diet triggered up-regulation of transforming growth factor beta (TGFbeta), a known profibrotic agent. In the presence of VSL#3, the MCD diet-induced expression of TGFbeta was maintained; however, the expression of Bambi, a TGFbeta pseudoreceptor with negative regulatory function, was increased. In summary, our data indicate that VSL#3 modulates liver fibrosis but does not protect from inflammation and steatosis in NASH. The mechanisms of VSL#3-mediated protection from MCD diet-induced liver fibrosis likely include modulation of collagen expression and impaired TGFbeta signaling.

Statins inhibit toll-like receptor 4-mediated lipopolysaccharide signaling and cytokine expression

OBJECTIVE

Toll-like receptor 4 (TLR4) is the main receptor for Lipopolysaccharide (LPS). Two relatively common variants of the TLR4 gene are present, resulting in changes from aspartic acid (D) to glycine (G) at residue 299 and from threonine (T) to isoleucine (I) at residue 399, respectively. It has been shown that statins have a greater effect on lowering risk of cardiovascular events in individuals carrying the 299G allele than in those not carrying this allele. We investigated possible mechanisms underlying this synergy of statin treatment and TLR4 genotype.

METHODS AND RESULTS

In cells expressing the 299D-399T TLR4, LPS activated the transcription factor NFkappaB and increased the expression of interleukin-6 and tumor necrosis factor-alpha, and these effects were reduced by pretreatment of the cells with pravastatin or simvastatin. LPS-induced NFkappaB activation and interleukin-6 and tumor necrosis factor-alpha expression were substantially reduced in cell expressing the 299G-399T or 299D-399I variant, and undetectable in cells expressing the 299G-399I TLR4. The 3-hydroxy-3-methylglutaryl coenzyme A pathway inhibitors, Y27632 and GGTI-286, exhibited a similar effect to statins, suggesting that the inhibitory effect of statins was mediated by the 3-hydroxy-3-methylglutaryl coenzyme A pathway.

CONCLUSION

The results of this study indicate that the TLR4 variations and statins have an additive inhibitory effect on TLR4-mediated inflammatory response, providing a potential explanation for the finding that the beneficial effect of statins on cardiovascular risk is dependent on TLR4 genotype.

Bone marrow-derived immune cells mediate sensitization to liver injury in a myeloid differentiation factor 88-dependent fashion

Toll-like receptors (TLRs) expressed on both immune cells and hepatocytes recognize microbial danger signals and regulate immune responses. Previous studies showed that TLR9 and TLR2 mediate Propionibacterium acnes-induced sensitization to lipopolysaccharide-triggered acute liver injury in mice. Ligand-specific activation of TLR2 and TLR9 are dependent on the common TLR adaptor, myeloid differentiation factor 88 (MyD88). Here, we dissected the role of MyD88 in parenchymal and bone marrow (BM)-derived cells in liver sensitization. Using chimeric mice with green fluorescent protein-expressing BM cells, we identified that P. acnes-induced liver inflammatory foci are of BM origin. Chimeras with MyD88-deficient BM showed no inflammatory foci after P. acnes or TLR2+TLR9 challenge, suggesting that recruitment of inflammatory cells to the liver required MyD88 expression in BM-derived cells. Further, selective MyD88 deficiency in parenchymal cells in mice with wild-type BM failed to prevent inflammatory cell infiltration. These results demonstrate that MyD88 in immune cells rather than in liver parenchymal cells plays an important role in inflammatory cell recruitment and liver injury.

Expression of Toll-like receptor 4 in various organs in rats with D-galactosamine-induced acute hepatic failure

BACKGROUND AND AIMS

Activation of the pro-inflammatory cytokine cascade, including tumor necrosis factor alpha (TNF-alpha) is considered to play an important role in the pathophysiology and clinical outcome of severe liver injury. Kupffer cells, resident macrophages of the liver, have a transmembrane protein Toll-like receptor 4 (TLR4), which recognizes endotoxin (lipopolysaccharide; LPS) or LPS-CD14 complex and mediates macrophage activation and pro-inflammatory cytokine release. D-Galactosamine (GalN), a hepatocyte-specific inhibitor of RNA synthesis, is known to sensitize animals to the lethal effects of LPS and TNF-alpha. In the present study we seek to address TLR4-signaling in the development of GalN-induced acute hepatic failure (AHF) and explore the expression of TLR4 mRNA as compared to TNF-alpha mRNA and CD14 mRNA in the liver, spleen and lung of rats with GalN-induced hepatitis.

METHODS

AHF was induced in male Wistar rats by the intraperitoneal injection of 1 g/kg bodyweight GalN. Expression levels of TNF-alpha, TLR4 and CD14 mRNA in the whole liver, spleen and lung of rats were detected by reverse transcription-polymerase chain reaction analysis.

RESULTS

Expression level of TLR4 mRNA in the liver of rats with GalN-induced AHF was increased parallel with that of TNF-alpha and CD14 mRNA as compared to the control rats. However, expression levels of TNF-alpha, TLR4 and CD14 mRNA in the whole spleen and lung were not different between rats with AHF and control.

CONCLUSIONS

There may be a difference of stimulatory effects of endotoxin on the innate immunity between the liver and other organs of rats with GalN-induced AHF.

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

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

Skin microbiota: a source of disease or defence?

Microbes found on the skin are usually regarded as pathogens, potential pathogens or innocuous symbiotic organisms. Advances in microbiology and immunology are revising our understanding of the molecular mechanisms of microbial virulence and the specific events involved in the host-microbe interaction. Current data contradict some historical classifications of cutaneous microbiota and suggest that these organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic. This review will summarize current information on bacterial skin flora including Staphylococcus, Corynebacterium, Propionibacterium, Streptococcus and Pseudomonas. Specifically, the review will discuss our current understanding of the cutaneous microbiota as well as shifting paradigms in the interpretation of the roles microbes play in skin health and disease.

c-Jun N-terminal kinase 1 is required for Toll-like receptor 1 gene expression in macrophages

The regulation of innate immune responses to pathogens occurs through the interaction of Toll-like receptors (TLRs) with pathogen-associated molecular patterns and the activation of several signaling pathways whose contribution to the overall innate immune response to pathogens is poorly understood. We demonstrate a mechanism of control of murine macrophage responses mediated by TLR1/2 heterodimers through c-Jun N-terminal kinase 1 (JNK1) activity. JNK controls tumor necrosis factor alpha production and TLR-mediated macrophage responses to Borrelia burgdorferi, the causative agent of Lyme disease, and the TLR1/TLR2-specific agonist PAM(3)CSK(4). JNK1, but not JNK2, activity regulates the expression of the tlr1 gene in the macrophage cell line RAW264.7, as well as in primary CD11b(+) cells. We also show that the proximal promoter region of the human tlr1 gene contains an AP-1 binding site that is subjected to regulation by the kinase and binds two complexes that involve the JNK substrates c-Jun, JunD, and ATF-2. These results demonstrate that JNK1 regulates the response to TLR1/2 ligands and suggest a positive feedback loop that may serve to increase the innate immune response to the spirochete.

Plasmodium falciparum infection causes proinflammatory priming of human TLR responses

TLRs are a major group of pattern recognition receptors that are crucial in initiating innate immune responses and are capable of recognizing Plasmodium ligands. We have investigated TLR responses during acute experimental P. falciparum (P.f.) infection in 15 malaria-naive volunteers. TLR-4 responses in whole blood ex vivo stimulations were characterized by significantly (p < 0.01) up-regulated proinflammatory cytokine production during infection compared with baseline, whereas TLR-2/TLR-1 responses demonstrated increases in both proinflammatory and anti-inflammatory cytokine production. Responses through other TLRs were less obviously modified by malaria infection. The degree to which proinflammatory TLR responses were boosted early in infection was partially prognostic of clinical inflammatory parameters during the subsequent clinical course. Although simultaneous costimulation of human PBMC with P.f. lysate and specific TLR stimuli in vitro did not induce synergistic effects on cytokine synthesis, PBMC started to respond to subsequent TLR-4 and TLR-2 stimulation with significantly (p < 0.05) increased TNF-alpha and reduced IL-10 production following increasing periods of preincubation with P.f. Ag. In contrast, preincubation with preparations derived from other parasitic, bacterial, and fungal pathogens strongly suppressed subsequent TLR responses. Taken together, P.f. primes human TLR responses toward a more proinflammatory cytokine profile both in vitro and in vivo, a characteristic exceptional among microorganisms.

Critical role of toll-like receptors and the common TLR adaptor, MyD88, in induction of granulomas and liver injury

BACKGROUND/AIMS

Toll-like receptors (TLR) recognize pathogens and regulate innate immune activation. Here, we investigated the roles of TLR9 and the common TLR adaptor, MyD88, in liver injury.

METHODS

C57BL6, TLR9(-/-), IFNgamma(-/-) or MyD88(-/-) mice were primed with Propionibacterium acnes, TLR9 (CpG) or TLR2 (lipoteichoic acid) ligands followed by LPS challenge. ALT, cytokines and liver histology were assessed.

RESULTS

Selective priming through TLR9 but not TLR2 induced granulomas, elevated serum ALT, and sensitized C57BL6 mice to increased LPS-induced serum IL-6, IL-12 and IFNgamma levels. Further, TLR2 and TLR9 ligands synergized in induction of granulomas and sensitization to LPS-induced inflammation. IFNgamma induction by P. acnes, TLR2 and TLR9 ligands required MyD88. In MyD88(-/-) mice P. acnes failed to induce granulomas and both MyD88 and TLR9 deficiency prevented P. acnes-induced sensitization to LPS. Increased mRNA expression of genes of the TLR4 signaling complex (TLR4, CD14, MD-2, and MyD88) and the NADPH complexes (p47phox, p67phox, gp91phox, and p22phox) was induced by priming with P. acnes or TLR9 plus TLR2 suggesting mechanisms for LPS sensitization and liver injury.

CONCLUSIONS

TLR9+/-TLR2 activation via MyD88-dependent pathways plays a pivotal role in liver sensitization and granuloma formation.

Pretreatment with soluble ST2 reduces warm hepatic ischemia/reperfusion injury

The interleukin-1 receptor-like protein ST2 exists in both membrane-bound (ST2L) and soluble form (sST2). ST2L has been found to play an important regulatory role in Th2-type immune response, but the function of soluble form of ST2 remains to be elucidated. In this study, we report the protective effect of soluble ST2 on warm hepatic ischemia/reperfusion injury. We constructed a eukaryotic expression plasmid, psST2-Fc, which expresses functional murine soluble ST2-human IgG1 Fc (sST2-Fc) fusion protein. The liver damage after ischemia/reperfusion was significantly attenuated by the expression of this plasmid in vivo. sST2-Fc remarkably inhibited the activation of Kupffer cells and the production of proinflammatory mediators TNF-alpha and IL-6. Furthermore, the levels of TLR4 mRNA and the nuclear translocation of NF-kappaB were also suppressed by pretreatment with sST2-Fc. These results thus identified soluble ST2 as a negative regulator in hepatic I/R injury, possibly via ST2-TLR4 pathway.

Pattern recognition receptors: a contemporary view on liver diseases

Pattern recognition receptors (PRRs) function as sensors of microbial danger signals enabling the vertebrate host to initiate an immune response. PRRs are present not only in immune cells but also in liver parenchymal cells and the complexity of the cell populations provide unique aspects to pathogen recognition and tissue damage in the liver. This review discusses the role of different PRRs in pathogen recognition in the liver, and focuses on the role of PRRs in hepatic inflammation, cholestasis, ischemia, repair and fibrosis. PRRs as novel therapeutic targets are evaluated.

Hepatic stellate cells primed with cytokines upregulate inflammation in response to peptidoglycan or lipoteichoic acid

Gram-positive bacterial products such as peptidoglycan (PGN) and lipoteichoic acid (LTA) are potent stimulators of innate inflammatory responses. We previously reported that lipopolysaccharide (LPS), a major biologically active agent of gram-negative bacteria, induces a proinflammatory response via the Toll-like receptor (TLR) 4 in hepatic stellate cells (HSCs). Here we investigated the mechanism of proinflammatory action by PGN and LTA in activated human HSCs. Following treatment with either TNF-alpha or IL-1beta, expression of TLR2 and CD14 was determined by real-time PCR and Western blotting. NF-kappaB activation was assessed by NF-kappaB-driven luciferase assay and electrophoretic mobility shift assay. Interleukin-8 (IL-8) from culture supernatant was measured by ELISA. Activated human HSCs express TLR2 and CD14, which are receptors for PGN and LTA signaling. TNF-alpha and IL-1beta significantly upregulated the expression of TLR2 mRNA and protein in HSCs. PGN and LTA induced NF-kappaB activation and stimulated production of IL-8 in HSCs. Pretreatment with TNF-alpha or IL-1beta augmented NF-kappaB activation and IL-8 production in response to PGN or LTA. Both PGN- and LTA-induced NF-kappaB activation and IL-8 secretion were completely inhibited by anti-TLR2 blocking antibody (T2.5). These findings suggest that TNF-alpha or IL-1beta primed HSCs enhance the production of IL-8 in response to PGN and LTA through augmentation of the TLR2 system.

RSA 2004: Combined Basic Research Satellite Symposium-Mechanisms of Alcohol-Mediated Organ and Tissue Damage: Inflammation and Immunity and Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death Session One: Alcohol, Cellular and Organ

This article summarizes content proceedings of a satellite meeting held at the 2004 Research Society on Alcoholism Annual Scientific Meeting in Vancouver, Canada. The aim of the satellite conference was to facilitate the interaction of scientists investigating the mechanisms of alcohol-mediated organ or tissue damage, and enable the discussion and sharing of new ideas and concepts that may be common in each of the organs or tissues affected by chronic ethanol consumption. The original planned program on immunity was expanded to incorporate a session on a closely related topic "Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death" organized by Dr. Jan Hoek and Dr. Sam Zakhari. The conference was arranged into four sessions: 1) Alcohol, Cellular and Organ Damage 2) Toll-like receptors and Organ Damage 3) Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death and 4) Hepatitis virus and alcohol interactions in Immunity and Liver Disease. The keynote address was given by Dr. Bruce Beutler from the Scripps Institute on "TLRs in Inflammation and Immunity."The Combined Basic Research Satellite Symposium entitled, "Mechanisms of Alcohol-Mediated Organ and Tissue Damage: Inflammation and Immunity and Alcohol and Mitochondrial Metabolism: At the Crossroads of Life and Death" was convened at the 2004 Research Society on Alcoholism meeting in Vancouver, BC. Session One featured five speakers who discussed various aspects of the role of the immune system in initiating or exacerbating cellular and organ damage following alcohol consumption. The presentations were (1) Innate Immune responses of Alcohol-exposed mice and macrophage-like cells following infections with Listeria monocytogenes by Robert T. Cook 2) Alcohol, cytokines and host defense by Kyle Happel 3) Decreased antigen presentation and anergy induced by alcohol in myeloid dendritic cells by Pranoti Mandrekar 4) Transcriptional regulation of TNF-alpha in human monocytes by chronic ethanol: role of the cellular redox state by Jay Kolls 5) Estrogen and gender differences in inflammatory responses after alcohol and burn injury by Elizabeth Kovacs. This session highlighted the growing information on the role of pattern recognition molecules in alcohol-mediated tissue damage or dysfunction. The new techniques and ideas presented will be helpful in future studies in this area of research, and should result in some exciting avenues of study.

RSA 2004: Combined Basic Research Satellite Symposium - Session Two: Toll-Like Receptors and Organ Damage

This article summarizes the proceedings of the RSA 2004 Combined Basic Research Satellite Meeting convened at the Westin Bayshore Resort and Marina, Vancouver, BC. The session "Toll-like receptors and organ damage" featured three speakers and was chaired by Drs. Steve Nelson and Craig McClain. The presentations were 1) Toll-like receptor mediated macrophage activation-modulation by acute alcohol administration in mice by Stephen Pruett, 2) Alcoholic liver disease: Crossroads of TLRs and oxidative stress by Gavin Arteel, and 3) The role of TLR2 and TLR4-mediated signals in liver injury by Gyongyi Szabo.

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

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