The concanavalin A model of acute hepatitis in mice

Pirfenidone alleviates concanavalin A-induced liver fibrosis in mice

AIMS

Liver fibrosis (LF) is a life-threatening complication of most chronic liver diseases resulting from a variety of injurious agents and hepatotoxic insults. To date, there are no specific therapies for LF, and all the currently available drugs have been developed for other indications. Thus, there is a pressing need to develop new drugs for treatment of LF. Therefore, the current study aimed to elucidate the potential antifibrotic effect of Pirfenidone (PFD) against concanavalin A (ConA)-induced immunological model of liver fibrosis in mice.

MAIN METHODS

Hepatic fibrosis was induced in mice by injecting ConA (10 mg/kg/wk./i.v) for 4 weeks. Then, the mice were treated with or without PFD (125 mg/kg/ip/day) for 2 weeks. Hepatic fibrosis was determined by Masson Trichrome staining; Haematoxylin & eosin (H&E) staining, immunohistochemistry staining of type II and IV collagens, and colorimetric assessment of hydroxyprolline (HP) content in the liver tissues. In addition, the expression of α-SMA mRNA was determined by real time RT-PCR. The serum levels of TGF-β, TNF-α, TIMP-1 and MMP-2 were measured by ELISA.

KEY FINDINGS

Treatment with PFD significantly reduced ConA-induced expression of type II and IV collagens, α-SMA mRNA expression, and HP content and decreased inflammatory cells infiltration in hepatic tissues. Furthermore, serum levels of TGF-β, TNF-α, and TIMP-1 were significantly reduced with concomitant increase in MMP-2 expression.

SIGNIFICANCE

Treatment with PFD ameliorates concanavalin A-induced hepatic inflammation and fibrosis in mice. Thus, PFD may represent a promising therapeutic option for hepatic fibrosis and its related complications.

Role of Oleic Acid in the Gut-Liver Axis: From Diet to the Regulation of Its Synthesis via Stearoyl-CoA Desaturase 1 (SCD1)

The consumption of an olive oil rich diet has been associated with the diminished incidence of cardiovascular disease and cancer. Several studies have attributed these beneficial effects to oleic acid (C18 n-9), the predominant fatty acid principal component of olive oil. Oleic acid is not an essential fatty acid since it can be endogenously synthesized in humans. Stearoyl-CoA desaturase 1 (SCD1) is the enzyme responsible for oleic acid production and, more generally, for the synthesis of monounsaturated fatty acids (MUFA). The saturated to monounsaturated fatty acid ratio affects the regulation of cell growth and differentiation, and alteration in this ratio has been implicated in a variety of diseases, such as liver dysfunction and intestinal inflammation. In this review, we discuss our current understanding of the impact of gene-nutrient interactions in liver and gut diseases, by taking advantage of the role of SCD1 and its product oleic acid in the modulation of different hepatic and intestinal metabolic pathways.

Retinoic acid modulates IL-4, IL-10 and MCP-1 pathways in immune mediated hepatitis and interrupts CD4+ T cells infiltration

AIMS

Immune mediated liver injury includes activation of different immune pathways that requires various modalities to control their consequences. The current study involves evaluation of retinoic acid (RA) modulatory effects on immune responses induced in concanavalin A (ConA) model of acute hepatitis.

MAIN METHODS

Mice were divided as follows: Control group; RA group: received 35 mg/kg RA; ConA group: received 15 mg/kg ConA; ConA + RA group: received ConA and RA as described. Liver function biomarkers were measured in addition to malondialdehyde as lipid peroxidation biomarker. Liver tissue sections were scored for necro-inflammation, neutrophils infiltration, CD4+ T cells infiltration and NF-κb positive cells. Effect on hepatic levels of TNF-α, IL-4, IL-10 and MCP-1 was evaluated as well.

KEY FINDINGS

Injection of RA before ConA significantly (p < 0.001) decreased ALT, AST and LDH levels compared to their levels in ConA group. Hepatic infiltration of neutrophils and CD4+ T cells was markedly (p < 0.001) reduced by RA. Hepatic injury, necrosis and expression of NF-κb were significantly decreased by RA when injected before ConA challenge. A significant decrease in the measured cytokines TNF-α and IL-4 was observed in ConA + RA group in addition to a decrease in MCP-1 level. On the other hand, IL-10 was significantly increased in the latter group compared to ConA group.

SIGNIFICANCE

RA can protect against ConA-induced hepatitis through: interrupting early inflammatory response as neutrophils, monocytes and CD4+ T cells infiltration, modulating IL-4 level and subsequent production of TNF-α and NF-κb activation, mitigating second inflammatory responses through increasing IL-10 liver production.

The upside-downside nature of Vitamin D signaling in liver

Discussion of the potential contradictory effects of vitamin D receptor signaling in a mouse model of autoimmune hepatitis.

Metabolomics profiling in a mouse model reveals protective effect of Sancao granule on Con A-Induced liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Sancao granule (SCG) is a traditional Chinese herb formula, which has been used for autoimmune liver disease for decades. Previous study demonstrated that there was an exactly therapeutic effect of SCG on autoimmune hepatitis (AIH) by improving liver function and alleviating the clinical symptoms. However, studies of the mechanism by which SCG alleviates Con A-induced liver injury (CILI) should be complemented.

MATERIALS AND METHODS

An ultraperformance liquid chromatography with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF/MS)-based metabolomics approach combined with principle component analysis (PCA) and orthogonal projection to latent structures discriminate analysis (OPLS-DA) were integrated applied to obtain metabolites for clarifying mechanisms of disease.

RESULTS

In accordance with previously study, the present study demonstrated that SCG could obviously improve the liver injury in mouse induced by Con A via downregulating serum biochemical indexes, alleviating the histological damage and inhibiting the neutrophil infiltration in liver tissues. Different expression of 9 metabolites related to 8 pathways, including fatty acid biosynthesis, arachidonic acid metabolisms, linoleic acid metabolisms, sphingolipid metabolisms, fatty acid elongation in mitochondria, glycerophospholipid metabolism, fatty acid metabolism, pyrimidine metabolism were demonstrated responsible for the efficacy of SCG in treating CILI.

CONCLUSION

In sum up, SCG has been indicated favorable therapeutic effect on Con A induced liver injury. And metabolomics could be a promising approach, which provide insights into mechanisms of SCG in treating CILI.

Overexpression of KLF14 protects against immune-mediated hepatic injury in mice

The underlying immunopathogenic mechanisms of autoimmune hepatitis (AIH) have not yet been well elucidated. An impairment in regulatory T cells (Tregs) is key to the development of AIH. Krüppel-like factors (KLFs) regulate a broad of cellular processes including immunocyte maturation. KLF14 may regulate Treg differentiation, but the biological functions remain far from elucidated. In this study, we identified the hepatic expression of KLF14 in human and murine liver diseases. Immune-mediated hepatitis was induced by concanavalin A (Con A). A KLF14 recombinant adenoviruses plasmid (Ad-KLF14) was constructed and injected into mice. Tregs were assessed by flow cytometry analysis; inflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), were tested by enzyme-linked immunosorbent assay (ELISA). The expression of KLF14 was suppressed in a time-and dose-dependent manner. Changes in cytokine levels were consistent with the degree of hepatic injury. Overexpression of KLF14 protected the liver from immune-mediated damage in vivo. Ad-KLF14 transfection before Con A challenge increased the frequency of Tregs in liver mononuclear cells (MNCs), and suppressed the expression of cytokines. All of these improvements were completely abrogated after Treg deletion in vivo by intraperitoneal injection of a CD25 antibody. In conclusion, these data suggest that KLF14 plays an as-yet unrecognized role in immune-mediated hepatitis mainly via induced Treg differentiation. Our findings extend the knowledge of the biological function of KLF14 to the autoimmune disease field, and indicate the possibility of KLF14 as a therapeutic target in AIH patients.

The Protective Effect of Sheep Placental Extract on Concanavalin A-induced Liver Injury in Mice

Though the biological effects of human placental extract have been widely studied, it has limited availability and its use poses ethical problems. Thus, domestic animal placental extracts are suggested as alternatives. In this study, the protective effect of sheep placental extract (SPE) on concanavalin A (Con A)-induced liver injury was investigated. BALB/c mice were randomly divided into six groups, including one normal group and five experimental groups, which received different oral doses of SPE (0, 5, 10 and 50 mg/kg) or a mixture of amino acids for 3 days before Con A injection. Compared with Con A-induced model group, the SPE administration significantly decreased serum aminotransaminase activity, alleviated pathological changes, recovered liver antioxidant capacity and prevented the increase of nitric oxide. Secretion of pro-inflammatory cytokines in serum decreased and mRNA expression of hepatic intercellular adhesion molecule-1, interferon-inducible chemokine 10 and inducible nitric oxide synthase were downregulated, while B-cell lymphoma-2 expression increased. The administration of amino acids mixture had no significant effect in most measurements compared with the model group, which indicated proteins and peptides, rather than individual amino acid, were largely responsible for the bioactivity of SPE. The results indicate SPE has potential therapeutic effects against immune-mediated hepatitis.

Mechanisms of concanavalin A-induced cytokine synthesis by hepatic stellate cells: Distinct roles of interferon regulatory factor-1 in liver injury

Mice depleted of hepatic stellate cells (HSCs) are protected from concanavalin A (ConA)-induced liver injury that is mediated by the activation of interferon regulatory factor 1 (IRF1). The aim of this study was to determine the mechanisms of ConA-mediated signaling and synthesis/release of mediators by HSCs that damage hepatocytes. Primary cultures of wildtype (WT) and IRF1-knockout (KO) HSCs and hepatocytes were used, and ConA-induced liver damage in interferon (IFN)αβ receptor-deficient (IFNαβR-KO) mice was determined. Specific binding of ConA to HSCs induced rapid activation of JAK2 and STAT1. ConA-induced expression of IRF1, IFNβ, tumor necrosis factor α, and CXCL1 was abrogated by selective inhibition of JAK2 and STAT1. Despite activating JAK2/STAT1, ConA failed to stimulate expression of inflammatory cytokines in HSCs from IRF1-KO mice. ConA-conditioned WT-HSC medium caused activation of JNK and caspase 3, and apoptosis of hepatocytes from WT but not from IRF1-KO or IFNαβR-KO mice. Conversely, ConA-conditioned medium of IRF1-KO HSCs failed to cause apoptosis of WT or IRF1-KO hepatocytes. IFNαβR-KO mice were protected from ConA-induced liver damage, and ConA-induced hepatic expression of IRF1 and pro-inflammatory cytokines and chemokines, and infiltration of neutrophils were significantly lower in IFNαβR-KO than in WT mice. These results demonstrate distinct roles of IRF1 in hepatic inflammation (HSCs) and injury (hepatocytes) and can be an important target for intervention in acute liver injury.

CEACAM1 in Liver Injury, Metabolic and Immune Regulation

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein that is expressed on epithelial, endothelial and immune cells. CEACAM1 is a differentiation antigen involved in the maintenance of epithelial polarity that is induced during hepatocyte differentiation and liver regeneration. CEACAM1 regulates insulin sensitivity by promoting hepatic insulin clearance, and controls liver tolerance and mucosal immunity. Obese insulin-resistant humans with non-alcoholic fatty liver disease manifest loss of hepatic CEACAM1. In mice, deletion or functional inactivation of CEACAM1 impairs insulin clearance and compromises metabolic homeostasis which initiates the development of obesity and hepatic steatosis and fibrosis with other features of non-alcoholic steatohepatitis, and adipogenesis in white adipose depot. This is followed by inflammation and endothelial and cardiovascular dysfunctions. In obstructive and inflammatory liver diseases, soluble CEACAM1 is shed into human bile where it can serve as an indicator of liver disease. On immune cells, CEACAM1 acts as an immune checkpoint regulator, and deletion of Ceacam1 gene in mice causes exacerbation of inflammation and hyperactivation of myeloid cells and lymphocytes. Hence, hepatic CEACAM1 resides at the central hub of immune and metabolic homeostasis in both humans and mice. This review focuses on the regulatory role of CEACAM1 in liver and biliary tract architecture in health and disease, and on its metabolic role and function as an immune checkpoint regulator of hepatic inflammation.

Deficient O-GlcNAc Glycosylation Impairs Regulatory T Cell Differentiation and Notch Signaling in Autoimmune Hepatitis

Post-translational modifications such as glycosylation play an important role in the functions of homeostatic proteins, and are critical driving factors of several diseases; however, the role of glycosylation in autoimmune hepatitis is poorly understood. Here, we established an O-GlcNAc glycosylation-deficient rat model by knocking out the Eogt gene by TALEN-mediated gene targeting. O-GlcNAc glycosylation deficiency overtly aggravated liver injury in concanavalin-A induced autoimmune hepatitis, and delayed self-recovery of the liver. Furthermore, flow cytometry analysis revealed increased CD4⁺ T cell infiltration in the liver of rats with O-GlcNAc glycosylation deficiency, and normal differentiation of regulatory T cells (Tregs) in the liver to inhibit T cell infiltration could not be activated. Moreover, in vitro experiments showed that O-GlcNAc glycosylation deficiency impaired Treg differentiation to inhibit the Notch signaling pathway in CD4⁺ T cells. These finding indicate that O-GlcNAc glycosylation plays a critical role in the activation of Notch signaling, which could promote Treg differentiation in the liver to inhibit T cell infiltration and control disease development in autoimmune hepatitis. Therefore, this study reveals a regulatory role for glycosylation in the pathogenesis of autoimmune hepatitis, and highlights glycosylation as a potential treatment target.

Role of hepatic stellate cell (HSC)-derived cytokines in hepatic inflammation and immunity

In their quiescent state, Hepatic stellate cells (HSCs), are present in the sub-endothelial space of Disse and have minimal interaction with immune cells. However, upon activation following injury, HSCs directly or indirectly interact with various immune cells that enter the space of Disse and thereby regulate diverse hepatic function and immune physiology. Other than the normal physiological functions of HSCs such as hepatic homeostasis, maturation and differentiation, they also participate in hepatic inflammation by releasing a battery of inflammatory cytokines and chemokines and interacting with other liver cells. Here, we have reviewed the role of HSC in the pathogenesis of liver inflammation and some infectious diseases in order to understand how the interplay between immune cells and HSCs regulates the overall outcome and disease pathology.

3, 5, 3'-Triiodothyroacetic acid (TRIAC) is an anti-inflammatory drug that targets toll-like receptor 2

Drug repositioning is a strategy that explores new pharmaceutical applications of previously launched or failed drugs, and is advantageous since it saves capital and time. In this study, we examined the inhibition of TLR2 signaling by drug candidates. HEK-Blue™-hTLR2 cells were pretreated with drugs and stimulated using the TLR2 ligand, Pam3CSK4. Among the drugs that inhibited TLR2 signaling, we selected TRIAC, which is yet to be patented. Pretreatment with TRIAC decreased the TLR2 level and the phosphorylation of Akt and MAPKs in HEK-Blue™-hTLR2 cells. Since TLR2 is overexpressed in patients with acute hepatitis, we confirmed that TRIAC alleviates necrosis in a mouse model of Con A-induced acute hepatitis. The serum AST and ALT levels are indicators of liver damage, and are increased in Con A-induced hepatitis. Additionally, TLR2 and inflammatory cytokine levels are increased following administration of Con A and lead to liver damage. TRIAC decreased the serum levels of AST and ALT, and reduced liver tissue necrosis in mice with Con A-induced acute fulminant liver damage, by reducing the levels of inflammatory cytokines. In conclusion, TRIAC alleviates inflammation in mouse models of Con A-induced hepatitis by inhibiting the phosphorylation of Akt and MAPKs, the sub-mechanisms underlying TLR2 signaling.

Expression of microRNA-155 in inflammatory cells modulates liver injury

MicroRNA 155 (miR-155) is involved in immune and inflammatory diseases and is associated with liver fibrosis and steatohepatitis. However, the mechanisms involved in miR-155 regulation of liver injury are largely unknown. The role of miR-155 in acute liver injury was assessed in wild-type (WT), miR-155^-/- , and miR-155^-/- mice transplanted with WT bone marrow. Additionally, miR-155 expression was evaluated in liver tissue and peripheral blood mononuclear cells of patients with autoimmune hepatitis. Concanavalin A, but not acetaminophen, treatment increased the expression of miR-155 in liver tissue of WT mice. Concanavalin A induced increases in cell death, liver aminotransferases, and expression of proinflammatory cytokines (chemokine [C-X-C motif] ligands 1, 5, 9, 10, and 11; chemokine [C-C motif] ligands 2 and 20; and intercellular cell adhesion molecule 1) in miR-155^-/- compared to WT mice. Importantly, these animals showed a significant decrease in cluster of differentiation 4-positive/chemokine (C-X-C motif) receptor 3-positive and forkhead box p3-positive cell recruitment but no changes in other inflammatory cell populations. Mechanistically, miR-155-deficient regulatory T cells showed increased SH2 domain-containing inositol 5-phosphatase 1 expression, a known target of miR-155. Inhibition of SH2 domain-containing inositol 5-phosphatase 1 in miR-155^-/- mice restored forkhead box p3 recruitment and reduced liver cytokine expression. Transplantation of bone marrow from WT animals into miR-155^-/- mice partially reversed the effect of concanavalin A on miR-155^-/- mice as assessed by proinflammatory cytokines and cell death protein expression. Patients with autoimmune hepatitis showed a marked increase in miR-155 expression in the liver but reduced expression of miR-155 in peripheral blood mononuclear cells.

CONCLUSION

miR-155 expression is altered in both liver tissue and circulating inflammatory cells during liver injury, thus regulating inflammatory cell recruitment and liver damage; these results suggest that maintaining miR-155 expression in inflammatory cells might be a potential strategy to modulate liver injury. (Hepatology 2018).

Fucosterol Protects against Concanavalin A-Induced Acute Liver Injury: Focus on P38 MAPK/NF-κB Pathway Activity

Objective

Fucosterol is derived from the brown alga Eisenia bicyclis and has various biological activities, including antioxidant, anticancer, and antidiabetic properties. The aim of this study was to investigate the protective effects of fucosterol pretreatment on Concanavalin A- (ConA-) induced acute liver injury in mice, and to understand its molecular mechanisms.

Materials and Methods

Acute liver injury was induced in BALB/c mice by ConA (25 mg/kg), and fucosterol (dissolved in 2% DMSO) was orally administered daily at doses of 25, 50, and 100 mg/kg. The levels of hepatic necrosis, apoptosis, and autophagy associated with inflammatory cytokines were measured at 2, 8, and 24 h.

Results

Fucosterol attenuated serum liver enzyme levels and hepatic necrosis and apoptosis induced by TNF-α, IL-6, and IL-1β. Fucosterol also inhibited apoptosis and autophagy by upregulating Bcl-2, which decreased levels of functional Bax and Beclin-1. Furthermore, reduced P38 MAPK and NF-κB signaling were accompanied by PPARγ activation.

Conclusion

This study showed that fucosterol could alleviate acute liver injury induced by ConA by inhibiting P38 MAPK/PPARγ/NF-κB signaling. These findings highlight that fucosterol is a promising potential therapeutic agent for acute liver injury.

Hepatoprotective Effect of San-Cao Granule on Con A-Induced Liver Injury in Mice and Mechanisms of Action Exploration

Objective: San-Cao granule (SCG), a traditional Chinese herb formula, has been used for treating autoimmune hepatitis (AIH) in our clinics for a long time. However, its active ingredients and mechanisms of action were still unknown due to its complicated chemical compositions. In the present study, the pharmacological study of SCG on acute liver injury induced by Concanavalin A (Con A) was performed to provide a scientific evidence for SCG against liver injury. Methods: In order to screen active components and predicate mechanisms of action, an "ingredients-target-disease" interaction network was constructed by network pharmacology. Then, the pharmacological study was performed to evaluate the therapeutic effect and the underlying mechanisms of SCG on Con A-induced liver injury in mice. Results: This research demonstrated the pharmacological effect of SCG on Con A-induced liver injury, which was through improving the liver function, relieving the pathological changes of liver tissue, decreasing the level of pro-inflammatory cytokines, and thus balancing the pro- and anti-inflammatory cytokines. And the anti-inflammatory of SCG may advantage over the ursodeoxycholic acid (UDCA). Network pharmacology analysis revealed that the pharmacological effect of SCG might be related to its active ingredients of taraxanthin, dihydrotanshinone I, isotanshinone I, γ-sitosterol, 3β-acetyl-20,25-epoxydammarane-24α, and δ-7-stigmastenol. The hepatoprotective effect of SCG was reflected by suppressing Con A-induced apoptosis which was mediated by TRAIL and FASL. Conclusion: The combination of network pharmacology and experimental data has revealed the anti-apoptotic effect of SCG against Con A-induced liver injury.

Salidroside mediates apoptosis and autophagy inhibition in concanavalin A-induced liver injury

Salidroside (Sal) is a glycoside extract from Rhodiola rosea L. with anti-inflammatory, antioxidant, anticancer and cardioprotective properties. The present study explored the protective effects and the possible mechanisms of Sal on concanavalin A (ConA)-induced liver injury in mice. Balb/C mice were divided into five groups: Normal control (injected with normal saline), ConA (25 mg/kg), Sal (10 mg/kg) +ConA, Sal (20 mg/kg) + ConA (Sal injected 2 h prior to ConA injection) and Sal (20 mg/kg) only. The serum levels of liver enzymes, pro-inflammatory cytokines, and apoptosis- and autophagy-associated marker proteins were determined at 2, 8 and 24 h after ConA injection. LY294002 was further used to verify whether the phosphoinositide 3-kinase (PI3K)/Akt pathway was activated. Primary hepatocytes were isolated to verify the effect of Sal in vitro. The results indicated that Sal was a safe agent to reduce pathological damage and serum liver enzymes in ConA-induced liver injury. Sal suppressed inflammatory reactions in serum and liver tissues, and activated the PI3K/Akt signaling pathway to inhibit apoptosis and autophagy in vivo and in vitro, which could be reversed by LY294002. In conclusion, Sal attenuated ConA-induced liver injury by modulating PI3K/Akt pathway-mediated apoptosis and autophagy in mice.

Hepatoprotective Effect of Wedelolactone against Concanavalin A-Induced Liver Injury in Mice

Eclipta prostrata L. is a traditional Chinese herbal medicine that has been used in the treatment of liver diseases. However, its biological mechanisms remain elusive. The current study aimed to investigate the hepatoprotective effect of wedelolactone, a major coumarin ingredient of Eclipta prostrata L., on immune-mediated liver injury. Using the well-established animal model of Concanavalin A (ConA)-induced hepatitis (CIH), we found that pretreatment of mice with wedelolactone markedly reduced both the serum levels of transaminases and the severity of liver damage. We further investigated the mechanisms of the protective effect of wedelolactone. In mice treated with wedelolactone prior to the induction of CIH, increases of serum concentrations of tumor necrosis factor (TNF)-[Formula: see text], interferon (IFN)-[Formula: see text], and interleukin (IL)-6 were dramatically attenuated. Additionally, expressions of the interferon-inducible chemokine (C-X-C motif) ligand 10 gene CXCL10 and intercellular adhesion molecule 1 gene ICAM1 were lower in livers of the treated mice. Moreover, wedelolactone-treated CIH mice exhibited reduced leukocyte infiltration and T-cell activation in liver. Furthermore, wedelolactone suppressed the activity of nuclear factor-kappa B (NF-[Formula: see text]B), a critical transcriptional factor of the above-mentioned inflammatory cytokines by limiting the phosphorylation of I kappa B alpha (I[Formula: see text]B[Formula: see text] and p65. In conclusion, these findings demonstrate the inhibitory potential of wedelolactone in immune-mediated liver injury in vivo, and show that this protection is associated with modulation of the NF-[Formula: see text]B signaling pathway.

N-Glycosylation of Lipocalin 2 Is Not Required for Secretion or Exosome Targeting

Lipocalin 2 (LCN2) is a highly conserved secreted adipokine acting as a serum transport protein for small hydrophobic molecules such as fatty acids and steroids. In addition, LCN2 limits bacterial growth by sequestering iron-containing siderophores and further protects against intestinal inflammation and tumorigenesis associated with alterations in the microbiota. Human LCN2 contains one N-glycosylation site conserved in other species. It was postulated that this post-translational modification could facilitate protein folding, protects from proteolysis, is required for proper trafficking from the Golgi apparatus to the cell surface, and might be relevant for effective secretion. We here show that the homologous nucleoside antibiotic tunicamycin blocks N-linked glycosylation but not secretion of LCN2 in primary murine hepatocytes, derivatives thereof, human lung carcinoma cell line A549, and human prostate cancer cell line PC-3. Moreover, both the glycosylated and the non-glycosylated LCN2 variants are equally targeted to exosomes, demonstrating that this post-translational modification is not necessary for proper trafficking of LCN2 into these membranous extracellular vesicles. Furthermore, a hydrophobic cluster analysis revealed that the N-glycosylation site is embedded in a highly hydrophobic evolutionarily conserved surrounding. In sum, our data indicate that the N-glycosylation of LCN2 is not required for proper secretion and exosome cargo recruitment in different cell types, but might be relevant to increase overall solubility.

The Hepatoprotection by Oleanolic Acid Preconditioning: Focusing on PPARα Activation

OBJECTIVE

Previous studies have characterized the hepatoprotective and anti-inflammatory properties of oleanolic acid (OA). This study aimed to investigate the molecular mechanisms of OA hepatoprotection in concanavalin A- (ConA-) induced acute liver injury.

MATERIALS AND METHODS

ConA (20 mg/kg) was intravenously injected to induce acute liver injury in Balb/C mice. OA pretreatment (20, 40, and 80 mg/kg) was administered subcutaneously once daily for 3 consecutive days prior to treatment with ConA; 2, 8, and 24 h after ConA injection, the levels of serum liver enzymes and the histopathology of major factors and inflammatory cytokines were determined.

RESULTS

OA reduced the release of serum liver enzymes and inflammatory factors and prevented ConA mediated damage to the liver. OA elevated the expression levels of peroxisome proliferator-activated receptor alpha (PPARα) and decreased the phosphorylation of c-Jun NH2-terminal kinase (JNK).

CONCLUSION

OA exhibits anti-inflammatory properties during ConA-induced acute liver injury by attenuating apoptosis and autophagy through activation of PPARα and downregulation of JNK signaling.

Pristimerin as a Novel Hepatoprotective Agent Against Experimental Autoimmune Hepatitis

Pristimerin (Pris) is bioactive natural quinonoid triterpene that has anti-inflammatory and anti-cancer activities. Meanwhile, its effect against hepatitis needs to be elucidated. This investigation aimed to evaluate the ability of Pris to protect against autoimmune hepatitis (AIH). A mouse model of AIH was established using single concanavalin A (Con A) intravenous injection. Mice were treated with Pris at two different doses (0.4 and 0.8 mg/kg) for 5 days prior to Con A challenge. Markers of hepatic injury, oxidative, inflammatory, and apoptotic damage were estimated. Results have revealed that Pris pretreatment ameliorated Con A-induced hepatic damage. There was decrease in the elevated serum indices of hepatic damage (ALT, AST, ALP, and LDH) and improvement of the histopathological picture of the liver. Pris effectively decreased Con A-induced neutrophil infiltration into the hepatic tissue as presented by amelioration of the level and immuno-expression of myeloperoxidase (MPO). Additionally, Pris attenuated Con A-induced increase in CD4+ T-cells in hepatic tissue. Lipid peroxidation was significantly depressed simultaneously with enhancement of the antioxidant capacity in Pris pretreated animals. Pris also enhanced nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expression and its binding capacity. In addition, Pris increased mRNA expression of heme-oxygenase-1 (HO-1) and restored its normal level. Furthermore, Pris decreased the level and immuno-expression of nuclear factor kappa-B (NF-κB) as well as the downstream inflammatory cascade (TNF-α, IL-6, and IL-1β). Finally, Pris showed inhibitory effect on Con A-induced apoptotic alteration in liver as it decreased the mRNA expression and levels the apoptotic markers (Bax and caspase-3) and increased mRNA expression and level of the anti-apoptotic protein (Bcl2). In conclusion, this study demonstrates the potent hepatoprotective efficacy of Pris against Con A-induced hepatitis which may be related to anti-oxidative, anti-inflammatory, and anti-apoptotic pathways. Pris could serve as a new candidate for the management of hepatitis.

Liver inflammation and regeneration in drug-induced liver injury: sex matters!

Drug-induced liver injury (DILI) remains a clinical challenge due to the poorly predictable outcomes. Accordingly, considerable efforts have been devoted to unravel the risk factors responsible for DILI worsening toward acute liver failure (ALF), liver transplantation (LT), and/or death. From a pathogenic point of view, exhaustion of drug metabolizing pathways, cell death mechanisms, activation of local immune cells, such as Kupffer cells, and recruitment of inflammatory leukocytes including monocytes and lymphocytes are key drivers of DILI progression. Taking into account that the liver is a sexually dimorphic organ, in the recent past several studies aimed to investigate the implications of gender differences in promoting DILI. While sex discrepancies in DILI include the hepatic drug metabolism or direct effects of steroid hormones (e.g. androgens and estrogens) on signaling pathways in the liver, relatively little is known on gender differences in modulating liver innate immune responses. In a previous issue of Clinical Science, Bizzaro and co-workers, analyzed sex-dependent differences in experimental acute liver injury and regeneration in mice. The authors observed a time-delay in the recovery process in male animals associated with a higher recruitment of monocytes expressing the androgen receptor (AR) as compared with females. Treatment of male mice with the pharmacological AR antagonist flutamide reduced monocyte recruitment in mice. Likewise, human male patients suffering from DILI displayed higher circulating immature and potentially more inflammatory monocytes. Altogether, these observations provide new insights into sex-dependent immune mechanisms in the context of acute liver injury, suggesting gender disparate inflammatory and regenerative responses following DILI.

MicroRNA 15a/16-1 suppresses aryl hydrocarbon receptor-dependent interleukin-22 secretion in CD4+ T cells and contributes to immune-mediated organ injury

Interleukin-22 (IL-22), as a link between leukocytic and nonleukocytic cells, has gained increasing attention for its pronounced tissue-protective properties. MicroRNAs, emerging as crucial immune modulators, have been reported to be involved in the production and action of various cytokines. However, the precise control of IL-22 by microRNAs and its subsequent actions remained to be elucidated. In this study, we found a negative correlation between the expression of microRNA 15a/16-1 (miR-15a/16-1) and IL-22 in the model of concanavalin A-induced, immune-mediated liver injury. Knockout of miR-15a/16-1 ameliorated liver injury in an IL-22-dependent manner. Further results revealed that cluster of differentiation 4-positive (CD4+ ) T cells were the major source of IL-22 during liver injury and that the aryl hydrocarbon receptor was the direct target of miR-15a/16-1 in CD4+ T cells. In vivo and in vitro data showed that miR-15a/16-1 knockout CD4+ T cells produced more IL-22, while overexpression of miR-15a/16-1 down-regulated the IL-22 production by inhibiting the aryl hydrocarbon receptor. Moreover, transfer of miR-15a/16-1 knockout CD4+ T cells promoted tissue repair compared to wild-type CD4+ T cells by up-regulating IL-22. In addition, as a synergistic effect, IL-22 could down-regulate miR-15a/16-1 expression by activating phosphorylated signal transducer and activator of transcription 3-c-myc signaling, and the decrease of miR-15a/16-1 in damaged hepatocytes contributed to IL-22-mediated tissue repair by reducing cell apoptosis and promoting cell proliferation. As further proof, we demonstrated the role of miR-15a/16-1 in controlling IL-22 production and IL-22-mediated reconstruction of the intestinal epithelial barrier in a dextran sodium sulfate-induced colitis model.

CONCLUSION

Our results suggest that miR-15a/16-1 acts as a essential regulator of IL-22 and that the miR-15a/16-1-aryl hydrocarbon receptor-IL-22 regulatory axis plays a central role in tissue repair; modulation of miR-15a/16-1 might hold promise in developing new strategies to enhance IL-22-mediated tissue repair. (Hepatology 2018;67:1027-1040).

The Receptor Interacting Protein Kinases in the Liver

The receptor interacting serine/threonine kinase1 and 3 (RIPK1, RIPK3) are regulators of cell death and survival. RIPK1 kinase activity is required for necroptosis and apoptosis, while its scaffolding function is necessary for survival. Although both proteins can mediate apoptosis, RIPK1 and RIPK3 are most well-known for their role in the execution of necroptosis via the mixed lineage domain like pseudokinase. Necroptosis is a caspase-independent regulated cell death program which was first described in cultured cells with unknown physiologic relevance in the liver. Many recent reports have suggested that RIPK1 and/or RIPK3 participate in liver disease pathogenesis and cell death. Notably, both proteins have been shown to mediate inflammation independent of cell death. Whether necroptosis occurs in hepatocytes, and how it is executed in the presence of an intact caspase machinery is controversial. In spite of this controversy, it is evident that RIPK1 and RIPK3 participate in many experimental liver disease models. Therefore, in addition to cell death signaling, their necroptosis-independent role warrants further examination.

Hepatoprotective and inhibiting HBV effects of polysaccharides from roots of Sophora flavescens

Roots of Sophora flavescens is an important herbal medicine for treatment of HBV and hepatic carcinoma in China. Alkaloids in the root were well known for exhibiting good hepato-protective and anti-HBV effects. However, polysaccharides as main components in the root remained unknown. In the studies, we investigated the chemical features and hepatoprotective effects of Sophora flavescens polysaccharides (SFP-100 and its active fractions) with ConA-induced hepatitis mice, human liver LO2 cells and HepG2.2.15 cells. The results showed that SFP-100 was composed of arabinose, glucose, galactose and galacturonic acid, SFP-100-A mainly contained glucose. SFP-100-B and SFP-100-C were acidic polysaccharides. SFP-100 significantly decreased hepatocytes apoptosis, inhibited the infiltration of neutrophils and macrophages into liver, and improved the production of IFN-γ and IL-6 of splenocytes in ConA-induced hepatitis mice. SFP-100 and its two sugar fractions increased LO2 cell proliferation and reduced cell apoptosis induced by ConA. SFP-100, SFP-100-A and SFP-100-C remarkedly inhibited the secretion of HBsAg and HBeAg by HepG2.2.15 cells.These results suggested Sophora flavescens polysaccharides exerts significant hepatoprotective and anti-HBV roles, and further is used for treatment of immune-mediated liver disease in the future.

Immunomodulatory Therapy of Inflammatory Liver Disease Using Selectin-Binding Glycopolymers

Immunotherapies have the potential to significantly advance treatment of inflammatory disease and cancer, which are in large part driven by immune cells. Selectins control the first step in immune cell adhesion and extravasation, thereby guiding leukocyte trafficking to tissue lesions. We analyzed four different highly specific selectin-binding glycopolymers, based on linear poly(2-hydroxypropyl)-methacrylamide (PHPMA) polymers. These glycopolymers contain either the tetrasaccharide sialyl-Lewis^X (SLe^X) or the individual carbohydrates fucose, galactose, and sialic acids mimicking the complex SLe^X binding motive. The glycopolymers strongly bind to primary human macrophages, without activating them, and also to primary human blood leukocytes, but poorly to fibroblasts and endothelial cells in vitro. After intravenous injection in mice, all glycopolymers accumulated in the liver without causing hepatotoxicity. The glycosylated binder most potently targeted resident hepatic macrophages (Kupffer cells) and protected mice from acute toxic liver injury in the two different experimental models, carbon tetrachloride (CCl₄) or Concanavalin A (ConA)-based hepatitis. Its sulfated counterpart, on the other hand, induced a decrease in infiltrating and resident macrophages, increased T helper cells, and aggravated immune-mediated liver injury. We demonstrate that, in the context of selectin-binding glycopolymers, minor modifications strongly impact leukocyte influx and macrophage activation, thereby ameliorating or aggravating liver inflammation depending on the underlying immunopathology. The nonsulfated random glycopolymer is a promising candidate for the treatment of inflammatory disease. The modulation of hepatic immune cells by selectin-binding glycopolymers might breach the immunosuppressive hepatic microenvironment and could improve efficacy of immunotherapies for inflammatory disease and cancer.

Molecular Imaging with Kupffer Cell-Targeting Nanobodies for Diagnosis and Prognosis in Mouse Models of Liver Pathogenesis

PURPOSE

Kupffer cells (KCs), the liver resident macrophages, are important mediators of tissue homeostasis and pathogen clearance. However, depending on the inflammatory stimuli, KCs have been involved in divergent hepato-protective or hepato-destructive immune responses. The versatility of KCs in response to environmental triggers, in combination with the specific biomarkers they express, make these macrophages attractive in vivo targets for non-invasive monitoring of liver inflammation or pathogenicity. This study aims to determine whether V-set and Ig domain-containing 4 (Vsig4) and C-type lectin domain family (Clec) 4, member F (Clec4F) can be used as imaging biomarkers for non-invasive monitoring of KCs during distinct liver inflammation models.

PROCEDURE

Flow cytometry (FACS), immuno-histochemistry (IHC), and single-photon emission computed tomography (SPECT) with Tc-99m labeled anti-Vsig4 or anti-Clec4F nanobodies (Nbs) was performed to evaluate in mice KC dynamics in concanavalin A (ConA)-induced hepatitis and in non-alcoholic steatohepatitis induced via methionine choline deficiency (MCD).

RESULTS

In homeostatic mice, Nbs targeting Clec4F were found to accumulate and co-localize with Vsig4-targeting Nbs only in the liver. Upon induction of acute hepatitis using ConA, down-regulation of the in vivo Nb imaging signal was observed, reflecting reduction in KC numbers as confirmed by FACS and IHC. On the other hand, induction of steatohepatitis resulted in higher signals in the liver corresponding to higher density of KCs. The Nb-imaging signals returned to normal levels after resolution of the investigated liver diseases.

CONCLUSIONS

Anti-Clec4F and anti-Vsig4 Nbs targeting KCs as molecular imaging biomarkers could allow non-invasive monitoring/staging of liver pathogenesis.

Protective Effect of Akkermansia muciniphila against Immune-Mediated Liver Injury in a Mouse Model

Accumulating evidence indicates that gut microbiota participates in the pathogenesis and progression of liver diseases. The severity of immune-mediated liver injury is associated with different microbial communities. Akkermansia muciniphila can regulate immunologic and metabolic functions. However, little is known about its effects on gut microbiota structure and function. This study investigated the effect of A. muciniphila on immune-mediated liver injury and potential underlying mechanisms. Twenty-two C57BL/6 mice were assigned to three groups (N = 7-8 per group) and continuously administrated A. muciniphila Muc^T or PBS by oral gavage for 14 days. Mouse feces were collected for gut microbiota analysis on the 15th day, and acute liver injury was induced by Concanavalin A (Con A, 15 mg/kg) injection through the tail vein. Samples (blood, liver, ileum, colon) were assessed for liver injury, systemic inflammation, and intestinal barrier function. We found that oral administration of A. muciniphila decreased serum ALT and AST and alleviated liver histopathological damage induced by Con A. Serum levels of pro-inflammatory cytokines and chemokines (IL-2, IFN-γ, IL-12p40, MCP-1, MIP-1a, MIP-1b) were substantially attenuated. A. muciniphila significantly decreased hepatocellular apoptosis; Bcl-2 expression increased, but Fas and DR5 decreased. Further investigation showed that A. muciniphila enhanced expression of Occludin and Tjp-1 and inhibited CB1 receptor, which strengthened intestinal barriers and reduced systemic LPS level. Fecal 16S rRNA sequence analysis indicated that A. muciniphila increased microbial richness and diversity. The community structure of the Akk group clustered distinctly from that of mice pretreated with PBS. Relative abundance of Firmicutes increased, and Bacteroidetes abundance decreased. Correlation analysis showed that injury-related factors (IL-12p40, IFN-γ, DR5) were negatively associated with specific genera (Ruminococcaceae_UCG_009, Lachnospiraceae_UCG_001, Akkermansia), which were enriched in mice pretreated with A. muciniphila. Our results suggested that A. muciniphila Muc^T had beneficial effects on immune-mediated liver injury by alleviating inflammation and hepatocellular death. These effects may be driven by the protective profile of the intestinal community induced by the bacteria. The results provide a new perspective on the immune function of gut microbiota in host diseases.

Mesenchymal Stem Cell-Dependent Modulation of Liver Diseases

Acute liver failure and cirrhosis display sequential and overlapping severe pathogenic processes that include inflammation, hepatocyte necrosis, and fibrosis, carrying a high mortality rate. Mesenchymal stem cells (MSCs) are a heterogeneous subset of stromal stem cells with immunonodulatory characteristics. MSCs are considered to act through multiple mechanisms to coordinate a dynamic, integrated response to liver inflammation and fibrosis, which prevents the progressive distortion of hepatic architecture. Accordingly, MSCs as well as their products have been investigated as a novel therapeutic approach for the treatment of inflammatory and fibrotic liver diseases.

In this review, we highlight the current findings on the MSC-based modulation of liver inflammation and fibrosis, and the possible use of MSCs in the therapy of immune-mediated liver pathology. We briefly describe the cellular and molecular mechanisms involved in MSC-dependent modulation of cytokine production, phenotype and function of liver infiltrated inflammatory cells and compare effects of engrafted MSCs versus MSC-generated conditioned medium (MSC-CM) in the therapy of acute liver injury. In order to elucidate therapeutic potential of MSCs and their products in modulation of chronic liver inflammation and fibrosis, we present the current findings regarding pathogenic role of immune cells in liver fibrosis and describe mechanisms involved in MSC-dependent modulation of chronic liver inflammation with the brief overview of on-going and already published clinical trials that used MSCs for the treatment of immune mediated chronic liver diseases. The accumulating evidence shows that MSCs had a significant beneficial effect in the treatment of immune-mediated liver diseases.

CD24 aggravates acute liver injury in autoimmune hepatitis by promoting IFN-γ production by CD4+ T cells

The T-cell-mediated immune response is implicated in many clinical hepatic injuries, such as autoimmune hepatitis and acute virus hepatitis. CD24 is widely expressed by different immune cells and plays an important role in the pathogenesis of many autoimmune diseases. However, the role of CD24 in T-cell-mediated liver injury has not been elucidated until now. Here we showed that CD24 deficiency protects mice from concanavalin A (ConA)-induced fulminant liver injury by reducing serum interferon-γ (IFN-γ) levels. CD24 expression by hepatic T cells was markedly increased following ConA challenge. Moreover, decreased IFN-γ production by hepatic CD4⁺ T cells in CD24-deficient mice was detected, which was correlated with downregulated phosphorylation of STAT1 in hepatic tissue. In vitro experiments also supported the conclusion that CD24 deficiency impaired IFN-γ production by CD4⁺ T cells following ConA, CD3/CD28 and phorbol myristate acetate/ionomycin stimulation. Our study suggests that CD24 deficiency confers hepatoprotection by decreasing CD4⁺ T-cell-dependent IFN-γ production in vivo, which suggests that CD24 might be a potential target molecule for reducing clinical hepatitis.

Naturally Occurring Nrf2 Activators: Potential in Treatment of Liver Injury

Oxidative stress plays a major role in acute and chronic liver injury. In hepatocytes, oxidative stress frequently triggers antioxidant response by activating nuclear erythroid 2-related factor 2 (Nrf2), a transcription factor, which upregulates various cytoprotective genes. Thus, Nrf2 is considered a potential therapeutic target to halt liver injury. Several studies indicate that activation of Nrf2 signaling pathway ameliorates liver injury. The hepatoprotective potential of naturally occurring compounds has been investigated in various models of liver injuries. In this review, we comprehensively appraise various phytochemicals that have been assessed for their potential to halt acute and chronic liver injury by enhancing the activation of Nrf2 and have the potential for use in humans.

Questions and controversies: the role of necroptosis in liver disease

Acute and chronic liver injury results in hepatocyte death and turnover. If injury becomes chronic, the continuous cell death and turnover leads to chronic inflammation, fibrosis and ultimately cirrhosis and hepatocellular carcinoma. Controlling liver cell death both in acute injury, to rescue the liver from acute liver failure, and in chronic injury, to curb secondary inflammation and fibrosis, is of paramount importance as a therapeutic strategy. Both apoptosis and necrosis occur in the liver, but the occurrence of necroptosis in the liver and its contribution to liver disease is controversial. Necroptosis is a form of regulated necrosis which occurs in certain cell types when caspases (+/-cIAPs) are inhibited through the RIPK1-RIPK3 activation of MLKL. The occurrence of necroptosis in the liver has recently been examined in multiple liver injury models with conflicting results. The aim of this review is to summarize the published data with an emphasis on the controversies and remaining questions in the field.

The pseudokinase MLKL mediates programmed hepatocellular necrosis independently of RIPK3 during hepatitis

Although necrosis and necroinflammation are central features of many liver diseases, the role of programmed necrosis in the context of inflammation-dependent hepatocellular death remains to be fully determined. Here, we have demonstrated that the pseudokinase mixed lineage kinase domain-like protein (MLKL), which plays a key role in the execution of receptor-interacting protein (RIP) kinase-dependent necroptosis, is upregulated and activated in human autoimmune hepatitis and in a murine model of inflammation-dependent hepatitis. Using genetic and pharmacologic approaches, we determined that hepatocellular necrosis in experimental hepatitis is driven by an MLKL-dependent pathway that occurs independently of RIPK3. Moreover, we have provided evidence that the cytotoxic activity of the proinflammatory cytokine IFN-γ in hepatic inflammation is strongly connected to induction of MLKL expression via activation of the transcription factor STAT1. In summary, our results reveal a pathway for MLKL-dependent programmed necrosis that is executed in the absence of RIPK3 and potentially drives the pathogenesis of severe liver diseases.

Mincle Signaling Promotes Con A Hepatitis

Con A hepatitis is regarded as a T cell-mediated model of acute liver injury. Mincle is a C-type lectin receptor that is critical in the immune response to mycobacteria and fungi but does not have a well-defined role in preclinical models of non-pathogen-mediated inflammation. Because Mincle can ligate the cell death ligand SAP130, we postulated that Mincle signaling drives intrahepatic inflammation and liver injury in Con A hepatitis. Acute liver injury was assessed in the murine Con A hepatitis model using C57BL/6, Mincle(-/-), and Dectin-1(-/-) mice. The role of C/EBPβ and hypoxia-inducible factor-1α (HIF-1α) signaling was assessed using selective inhibitors. We found that Mincle was highly expressed in hepatic innate inflammatory cells and endothelial cells in both mice and humans. Furthermore, sterile Mincle ligands and Mincle signaling intermediates were increased in the murine liver in Con A hepatitis. Most significantly, Mincle deletion or blockade protected against Con A hepatitis, whereas Mincle ligation exacerbated disease. Bone marrow chimeric and adoptive transfer experiments suggested that Mincle signaling in infiltrating myeloid cells dictates disease phenotype. Conversely, signaling via other C-type lectin receptors did not alter disease course. Mechanistically, we found that Mincle blockade decreased the NF-κβ-related signaling intermediates C/EBPβ and HIF-1α, both of which are necessary in macrophage-mediated inflammatory responses. Accordingly, Mincle deletion lowered production of nitrites in Con A hepatitis and inhibition of both C/EBPβ and HIF-1α reduced the severity of liver disease. Our work implicates a novel innate immune driver of Con A hepatitis and, more broadly, suggests a potential role for Mincle in diseases governed by sterile inflammation.

Opposing role of tumor necrosis factor receptor 1 signaling in T cell-mediated hepatitis and bacterial infection in mice

Death receptor (DR) ligands such as tumor necrosis factor (TNF) have been identified as fundamental mediators of liver damage both in mouse models and in humans. While the essential site of function of DR signaling is conceivably the hepatocyte, a systematic analysis is missing. Using mice with conditional gene ablation, we analyzed the tissue-specific function of DR signaling in T cell-dependent (concanavalin A) and independent (lipopolysaccharide/galactosamine) hepatitis and in models of bacterial infection (Listeria monocytogenes, lipopolysaccharide). We report that lipopolysaccharide/galactosamine-induced liver injury depends on hepatocyte-intrinsic TNF receptor 1 (p55, TNFR1). In contrast, we show that T cell-induced hepatitis was independent of TNFR1 signaling in hepatocytes, T cells, or endothelial cells. Moreover, T cell-induced hepatitis was independent of hepatocyte-intrinsic Fas-associated protein with death domain, TNF-related apoptosis-inducing ligand receptor, or Fas signaling. Instead, concanavalin A-induced hepatitis was completely prevented in mice with myeloid-derived cell (MDC)-specific deletion of TNFR1. Significantly, however, mice lacking TNFR1 in MDCs succumbed to listeria infection, although they displayed similar sensitivity toward endotoxin-induced septic shock when compared to control mice. These results suggest that TNFR1 signaling in MDCs is a critical mediator of both the detrimental and the protective functions of TNF in T cell-induced hepatitis and bacterial infection, respectively.

CONCLUSION

The critical site of action of DRs is completely dependent on the nature of hepatitis; the data specify MDCs as the essential cell type of TNFR1 function in T cell-mediated hepatitis and in the response to listeria, thereby identifying the opposing role of MDC TNFR1 in autoimmunity and bacterial infection. (Hepatology 2016;64:508-521).

Modulation of liver tolerance by conventional and nonconventional antigen-presenting cells and regulatory immune cells

The liver is a tolerogenic organ with exquisite mechanisms of immune regulation that ensure upkeep of local and systemic immune tolerance to self and foreign antigens, but that is also able to mount effective immune responses against pathogens. The immune privilege of liver allografts was recognized first in pigs in spite of major histo-compatibility complex mismatch, and termed the "liver tolerance effect". Furthermore, liver transplants are spontaneously accepted with only low-dose immunosuppression, and induce tolerance for non-hepatic co-transplanted allografts of the same donor. Although this immunotolerogenic environment is favorable in the setting of organ transplantation, it is detrimental in chronic infectious liver diseases like hepatitis B or C, malaria, schistosomiasis or tumorigenesis, leading to pathogen persistence and weak anti-tumor effects. The liver is a primary site of T-cell activation, but it elicits poor or incomplete activation of T cells, leading to their abortive activation, exhaustion, suppression of their effector function and early death. This is exploited by pathogens and can impair pathogen control and clearance or allow tumor growth. Hepatic priming of T cells is mediated by a number of local conventional and nonconventional antigen-presenting cells (APCs), which promote tolerance by immune deviation, induction of T-cell anergy or apoptosis, and generating and expanding regulatory T cells. This review will focus on the communication between classical and nonclassical APCs and lymphocytes in the liver in tolerance induction and will discuss recent insights into the role of innate lymphocytes in this process.

Roles of hepatic stellate cells in liver inflammation: a new perspective

Connected with the intestinal tract through the portal circulation, liver sinusoids function as the first line of defense against extrahepatic stimuli such as bacterial products and other toxic substances. Hepatic stellate cells (HSCs) are pericytes residing in the perisinusoidal space, between sinusoidal endothelial cells and hepatocytes, store vitamin A, and regulate sinusoidal circulation. Following chronic hepatitis, HSCs actively produce extracellular matrices and cause liver fibrosis. In spite of their close position to the liver sinusoids, however, whether HSCs contribute to liver inflammation has remained elusive. Evidence now accumulates to suggest that HSCs actively take part in the regulation of various forms of liver inflammation. Upon inflammatory stimuli from the sinusoids, HSCs produce various inflammatory molecules and interact with other liver cells, thereby recruiting and then activating infiltrating leukocytes and ultimately causing hepatocyte death. On the other hand, HSCs also exert hepatoprotective effects through inhibition of cytokine and chemokine production or induction of immunosuppressive cell population. HSCs therefore integrate cytokine-mediated inflammatory responses in the sinusoids and relay them to the liver parenchyma, either amplifying liver inflammation or suppressing parenchymal damage through immunoregulatory signaling depending on the context.

Epigallocatechin-3-gallate attenuates apoptosis and autophagy in concanavalin A-induced hepatitis by inhibiting BNIP3

Background

Epigallocatechin-3-gallate (EGCG) is the most effective compound in green tea, and possesses a wide range of beneficial effects, including anti-inflammatory, antioxidant, antiobesity, and anticancer effects. In this study, we investigated the protective effects of EGCG in concanavalin A (ConA)-induced hepatitis in mice and explored the possible mechanisms involved in these effects.

Methods

Balb/C mice were injected with ConA (25 mg/kg) to induce acute autoimmune hepatitis, and EGCG (10 or 30 mg/kg) was administered orally twice daily for 10 days before ConA injection. Serum liver enzymes, proinflammatory cytokines, and other marker proteins were determined 2, 8, and 24 hours after the ConA administration.

Results

BNIP3 mediated cell apoptosis and autophagy in ConA-induced hepatitis. EGCG decreased the immunoreaction and pathological damage by reducing inflammatory factors, such as TNF-α, IL-6, IFN-γ, and IL-1β. EGCG also exhibited an antiapoptotic and antiautophagic effect by inhibiting BNIP3 via the IL-6/JAKs/STAT3 pathway.

Conclusion

EGCG attenuated liver injury in ConA-induced hepatitis by downregulating IL-6/JAKs/STAT3/BNIP3-mediated apoptosis and autophagy.

Immunology in the liver--from homeostasis to disease

The liver is a central immunological organ with a high exposure to circulating antigens and endotoxins from the gut microbiota, particularly enriched for innate immune cells (macrophages, innate lymphoid cells, mucosal-associated invariant T (MAIT) cells). In homeostasis, many mechanisms ensure suppression of immune responses, resulting in tolerance. Tolerance is also relevant for chronic persistence of hepatotropic viruses or allograft acceptance after liver transplantation. The liver can rapidly activate immunity in response to infections or tissue damage. Depending on the underlying liver disease, such as viral hepatitis, cholestasis or NASH, different triggers mediate immune-cell activation. Conserved mechanisms such as molecular danger patterns (alarmins), Toll-like receptor signalling or inflammasome activation initiate inflammatory responses in the liver. The inflammatory activation of hepatic stellate and Kupffer cells results in the chemokine-mediated infiltration of neutrophils, monocytes, natural killer (NK) and natural killer T (NKT) cells. The ultimate outcome of the intrahepatic immune response (for example, fibrosis or resolution) depends on the functional diversity of macrophages and dendritic cells, but also on the balance between pro-inflammatory and anti-inflammatory T-cell populations. As reviewed here, tremendous progress has helped to understand the fine-tuning of immune responses in the liver from homeostasis to disease, indicating promising targets for future therapies in acute and chronic liver diseases.

Hepatoprotective and Anti-fibrotic Agents: It's Time to Take the Next Step

Hepatic fibrosis and cirrhosis cause strong human suffering and necessitate a monetary burden worldwide. Therefore, there is an urgent need for the development of therapies. Pre-clinical animal models are indispensable in the drug discovery and development of new anti-fibrotic compounds and are immensely valuable for understanding and proofing the mode of their proposed action. In fibrosis research, inbreed mice and rats are by far the most used species for testing drug efficacy. During the last decades, several hundred or even a thousand different drugs that reproducibly evolve beneficial effects on liver health in respective disease models were identified. However, there are only a few compounds (e.g., GR-MD-02, GM-CT-01) that were translated from bench to bedside. In contrast, the large number of drugs successfully tested in animal studies is repeatedly tested over and over engender findings with similar or identical outcome. This circumstance undermines the 3R (Replacement, Refinement, Reduction) principle of Russell and Burch that was introduced to minimize the suffering of laboratory animals. This ethical framework, however, represents the basis of the new animal welfare regulations in the member states of the European Union. Consequently, the legal authorities in the different countries are halted to foreclose testing of drugs in animals that were successfully tested before. This review provides a synopsis on anti-fibrotic compounds that were tested in classical rodent models. Their mode of action, potential sources and the observed beneficial effects on liver health are discussed. This review attempts to provide a reference compilation for all those involved in the testing of drugs or in the design of new clinical trials targeting hepatic fibrosis.

MORPHOLOGICAL CHANGES IN MICE LIVER IN DYNAMICS OF CONCANAVALIN A - INDUCED HEPATITIS

The injure of the liver tissue and its infiltration by cells of the innate and adaptive immunity in dynamics of Con A-induced hepatitis in mice was studied. The semiquantitative method of damage rate of microcirculation channel and liver parenchyma was used, leukocyte liver infiltration and cellular composition of infiltrates were investigated also. Primary liver reaction to the Con-A was the inflammatory changes in the vascular bed, followed by disturbances in the parenchyma.The sufficient increasing of leukocyte migration to the liver was revealed. Besides, the neutrophile infiltration was increased first with a maximum at 6 hours of the experiment (63,9 ±4,6%, p<0,001 to the control level) ,and then the lymphocyte infiltration was increased with creation of manycellular lymphocytemacrophage infiltrates (62% at 48 hours comparing to 6 hours of experiment) and sufficient quantity of plasma cells population (4,9%, p<0,05 comparing to 6 hours of experiment). The obtained data gives the base to suggest that the elevated infiltration of liver tissue by leukocytes, particularly by lymphocytes and monocytes, together with necrotic death increasing creats the conditions for effective intracellular interaction and immune response to autoantigenes. This can be the essential pathogenic mechanism of development of autoimmune liver deseases.

Experimental models of hepatotoxicity related to acute liver failure

Acute liver failure can be the consequence of various etiologies, with most cases arising from drug-induced hepatotoxicity in Western countries. Despite advances in this field, the management of acute liver failure continues to be one of the most challenging problems in clinical medicine. The availability of adequate experimental models is of crucial importance to provide a better understanding of this condition and to allow identification of novel drug targets, testing the efficacy of new therapeutic interventions and acting as models for assessing mechanisms of toxicity. Experimental models of hepatotoxicity related to acute liver failure rely on surgical procedures, chemical exposure or viral infection. Each of these models has a number of strengths and weaknesses. This paper specifically reviews commonly used chemical in vivo and in vitro models of hepatotoxicity associated with acute liver failure.

B cells expressing CD11b effectively inhibit CD4+ T-cell responses and ameliorate experimental autoimmune hepatitis in mice

Increasing evidence in recent years has suggested that B cells act as a crucial regulator in autoimmune diseases. However, little is known about their role in autoimmune hepatitis (AIH) and the underlying regulatory mechanisms. In this study, we show that B cells ameliorated experimental AIH (EAH) by suppressing CD4+ T-cell responses and that CD11b expression on B cells was required for the regulatory function of B cells. In vitro studies reveal that the suppressive function of CD11b was mediated by the impairment of T-cell antigen receptor (TCR) signaling transduction and the promotion of TCR down-regulation. Moreover, we show that the increased CD11b expression on B cells was interleukin (IL)-10 dependent and that additional IL-10 stimulation promoted CD11b expression on B cells, thereby enhancing B-cell regulatory effects.

CONCLUSION

These findings reveal a previously unrecognized role for CD11b in B-cell regulatory function and its protective effect on EAH.