Dendritic cell depletion exacerbates acetaminophen hepatotoxicity

Chitinase 3-like protein 1 deficiency ameliorates drug-induced acute liver injury by inhibition of neutrophil recruitment through lipocalin-2

Chitinase-3-like protein 1 (Chi3l1) is a member of the mammalian Chitinase-like protein family, and several studies reported that Chi3l1 is associated with various inflammatory diseases as well as liver diseases. Acetaminophen (APAP) is usually used for antipyretic drug, but its overdose induces acute liver injury (ALI). Several studies reported that subsequent inflammatory responses of the immune system play a critical role in the severity and outcome of APAP-induced ALI. In the present study, we investigated the role of Chi3l1 and its mechanism during APAP-induced ALI using Chi3l1 knock-out (KO) mice. We explored the function of Chi3l1 using APAP-injected KO mice and sought proteins associated with Chi3l1 through biological research data program for investigating mechanism. Liver histological analysis revealed that APAP-induced ALI was attenuated in KO mice compared to wild-type (WT) mice. We observed that APAP-induced neutrophil infiltration was decreased in the liver of KO mice compared to WT mice. To investigate this mechanism, we sought proteins potentially associated with Chi3l1 by mRNA sequencing and protein correlation analysis data. We found lipocalin-2 (Lcn2) and examined Chi3l1, Lcn2, and their relationship in the APAP-induced ALI model using recombinant proteins and antibodies. Our results suggest that Chi3l1 deficiency ameliorates APAP-induced liver injury through abrogating Lcn2-mediated neutrophil infiltration in the liver.

Innate immune regulation in inflammation resolution and liver regeneration in drug-induced liver injury

Drug-induced liver injury (DILI) is an acute liver injury that poses a significant threat to human health. In severe cases, it can progress into chronic DILI or even lead to liver failure. DILI is typically caused by either intrinsic hepatotoxicity or idiosyncratic metabolic or immune responses. In addition to the direct damage drugs inflict on hepatocytes, the immune responses and liver inflammation triggered by hepatocyte death can further exacerbate DILI. Initially, we briefly discussed the differences in immune cell activation based on the type of liver cell death (hepatocytes, cholangiocytes, and LSECs). We then focused on the role of various immune cells (including macrophages, monocytes, neutrophils, dendritic cells, liver sinusoidal endothelial cells, eosinophils, natural killer cells, and natural killer T cells) in both the liver injury and liver regeneration stages of DILI. This article primarily reviews the role of innate immune regulation mediated by these immune cells in resolving inflammation and promoting liver regeneration during DILI, as well as therapeutic approaches targeting these immune cells for the treatment of DILI. Finally, we discussed the activation and function of liver progenitor cells (LPCs) during APAP-induced massive hepatic necrosis and the involvement of chronic inflammation in DILI.

Effects of drug-induced liver injury on the in vivo fate of liposomes

Liposomes represent one of the most extensively studied nano-carriers due to their potential in targeted drug delivery. However, the complex in vivo fate, particularly under pathological conditions, presents challenges for clinical translation of liposomal therapeutics. Liver serves as the most important organ for liposome accumulation and metabolism. Unfortunately, the fate of liposomes under pathological liver conditions has been significantly overlooked. This study aimed to investigate the in vivo pharmacokinetic profile and biodistribution profile of liposomes under drug-induced liver injury (DILI) conditions. Two classic DILI animal models, i.e. acetaminophen-induced acute liver injury (AILI) and triptolide-induced subacute liver injury (TILI), were established to observe the effect of pathological liver conditions on the in vivo performance of liposomes. The study revealed significant changes in the in vivo fate of liposomes following DILI, including prolonged blood circulation and enhanced hepatic accumulation of liposomes. Changes in the composition of plasma proteins and mononuclear phagocyte system (MPS)-related cell subpopulations collectively led to the altered in vivo fate of liposomes under liver injury conditions. Despite liver injury, macrophages remained the primary cells responsible for liposomes uptake in liver, with the recruited monocyte-derived macrophages exhibiting enhanced ability to phagocytose liposomes under pathological conditions. These findings indicated that high capture of liposomes by the recruited hepatic macrophages not only offered potential solutions for targeted delivery, but also warned the clinical application of patients under pathological liver conditions.

Good Cells Go Bad: Immune Dysregulation in the Transition from Acute Liver Injury to Liver Failure After Acetaminophen Overdose

The role of inflammatory cells and other components of the immune system in acetaminophen (APAP)-induced liver injury and repair has been extensively investigated. Although this has resulted in a wealth of information regarding the function and regulation of immune cells in the liver after injury, apparent contradictions have fueled controversy around the central question of whether the immune system is beneficial or detrimental after APAP overdose. Ultimately, this may not be a simple assignment of "good" or "bad." Clinical studies have clearly demonstrated an association between immune dysregulation and a poor outcome in patients with severe liver damage/liver failure induced by APAP overdose. To date, studies in mice have not uniformly replicated this connection. The apparent disconnect between clinical and experimental studies has perhaps stymied progress and further complicated investigation of the immune system in APAP-induced liver injury. Mouse models are often dismissed as not recapitulating the clinical scenario. Moreover, clinical investigation is most often focused on the most severe APAP overdose patients, those with liver failure. Notably, recent studies have made it apparent that the functional role of the immune system in the pathogenesis of APAP-induced liver injury is highly context dependent and greatly influenced by the experimental conditions. In this review, we highlight some of these recent findings and suggest strategies seeking to resolve and build on existing disconnects in the literature. SIGNIFICANCE STATEMENT: Acetaminophen overdose is the most frequent cause of acute liver failure in the United States. Studies indicate that dysregulated innate immunity contributes to the transition from acute liver injury to acute liver failure. In this review, we discuss the evidence for this and the potential underlying causes.

Roles and therapeutic targeting of dendritic cells in liver fibrosis

Liver fibrosis is a common pathological condition marked by excessive accumulation of extracellular matrix proteins, resulting in irreversible cirrhosis and cancer. Dendritic cells (DCs) act as the crucial component of hepatic immunity and are believed to affect fibrosis by regulating the proliferation and differentiation of hepatic stellate cells (HSCs), a key mediator of fibrogenesis, and by interplaying with immune cells in the liver. This review concisely describes the process of fibrogenesis, and the phenotypic and functional characteristics of DCs in the liver. Besides, it focuses on the interaction between DCs and HSCs, T cells, and natural killer (NK) cells, as well as the dual roles of DCs in liver fibrosis, for the sake of exploring the potential of targeting DCs as a therapeutic strategy for the disease.

Single-cell RNA sequencing reveals the dynamics of hepatic non-parenchymal cells in autoprotection against acetaminophen-induced hepatotoxicity

Gaining a better understanding of autoprotection against drug-induced liver injury (DILI) may provide new strategies for its prevention and therapy. However, little is known about the underlying mechanisms of this phenomenon. We used single-cell RNA sequencing to characterize the dynamics and functions of hepatic non-parenchymal cells (NPCs) in autoprotection against DILI, using acetaminophen (APAP) as a model drug. Autoprotection was modeled through pretreatment with a mildly hepatotoxic dose of APAP in mice, followed by a higher dose in a secondary challenge. NPC subsets and dynamic changes were identified in the APAP (hepatotoxicity-sensitive) and APAP-resistant (hepatotoxicity-resistant) groups. A chemokine (C-C motif) ligand 2+ endothelial cell subset almost disappeared in the APAP-resistant group, and an R-spondin 3+ endothelial cell subset promoted hepatocyte proliferation and played an important role in APAP autoprotection. Moreover, the dendritic cell subset DC-3 may protect the liver from APAP hepatotoxicity by inducing low reactivity and suppressing the autoimmune response and occurrence of inflammation. DC-3 cells also promoted angiogenesis through crosstalk with endothelial cells via vascular endothelial growth factor-associated ligand-receptor pairs and facilitated liver tissue repair in the APAP-resistant group. In addition, the natural killer cell subsets NK-3 and NK-4 and the Sca-1-CD62L+ natural killer T cell subset may promote autoprotection through interferon-γ-dependent pathways. Furthermore, macrophage and neutrophil subpopulations with anti-inflammatory phenotypes promoted tolerance to APAP hepatotoxicity. Overall, this study reveals the dynamics of NPCs in the resistance to APAP hepatotoxicity and provides novel insights into the mechanism of autoprotection against DILI at a high resolution.

Orchestrated regulation of immune inflammation with cell therapy in pediatric acute liver injury

Acute liver injury (ALI) in children, which commonly leads to acute liver failure (ALF) with the need for liver transplantation, is a devastating life-threatening condition. As the orchestrated regulation of immune hemostasis in the liver is essential for resolving excess inflammation and promoting liver repair in a timely manner, in this study we focused on the immune inflammation and regulation with the functional involvement of both innate and adaptive immune cells in acute liver injury progression. In the context of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic, it was also important to incorporate insights from the immunological perspective for the hepatic involvement with SARS-CoV-2 infection, as well as the acute severe hepatitis of unknown origin in children since it was first reported in March 2022. Furthermore, molecular crosstalk between immune cells concerning the roles of damage-associated molecular patterns (DAMPs) in triggering immune responses through different signaling pathways plays an essential role in the process of liver injury. In addition, we also focused on DAMPs such as high mobility group box 1 (HMGB1) and cold-inducible RNA-binding protein (CIRP), as well as on macrophage mitochondrial DNA-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway in liver injury. Our review also highlighted novel therapeutic approaches targeting molecular and cellular crosstalk and cell-based therapy, providing a future outlook for the treatment of acute liver injury.

Migration inhibitory factor and cluster of differentiation 74-mediated dendritic cell apoptosis exacerbates acute acetaminophen-induced liver injury

INTRODUCTION

We investigated the role of macrophage migration inhibitory factor (MIF) on dendritic cells (DC) during acetaminophen (APAP)-induced acute liver injury (ALI) in mice.

METHODS

First, we randomly divided the mice into experimental (ALI model) and control groups, then intraperitoneally injected 600 mg/kg of APAP or phosphate-buffered saline, respectively. Then, we collected liver tissue and serum samples to evaluate liver inflammation using serum alanine aminotransferase level and hematoxylin and eosin (H&E) staining of liver tissues. Flow cytometry was used to identify changes in the quantity and percentage of DCs, as well as the expression of cluster of differentiation (CD) 74 and other apoptosis-related markers in the liver. Next, we randomly divided the mice into APAP-vehicles, APAP-bone marrow-derived dendritic cells (BMDCs), APAP-MIF, APAP-IgG (isotype immunoglobin G antibody) groups (four mice per group), after APAP injection, we injected control extracts, BMDCs, mouse recombinant MIF antibodies, or IgG antibodies into the tail vein. Lastly, the severity of the liver injury and the number of DCs were assessed.

RESULTS

The APAP-induced ALI mice had increased hepatic MIF expression but significantly lower amounts of hepatic DCs and apoptotic DCs than healthy mice; CD74 expression on the HDCs also increased markedly. Supplementing APAP-induced ALI mice with BMDCs or MIF antibodies significantly increased the number of hepatic DCs compared with the control mice, alleviating liver damage.

CONCLUSION

The MIF/CD74 signaling pathway may mediate hepatic DC apoptosis and promote liver damage.

A dual role of inflammation in acetaminophen-induced liver injury

In many affluent nations, acetaminophen (APAP) overdose is the leading cause of drug-induced acute liver failure. The process of APAP-induced liver injury (AILI) is intimately tied to inflammation, including hepatocyte necrosis-caused initiation of inflammation, inflammation amplification that exacerbates liver injury, and the resolution of inflammation that triggers liver regeneration and repair. Excessive APAP metabolism in the liver eventually leads to hepatocyte necrosis and inflammation. Innate immune cells, such as neutrophils, eosinophils, monocytes, and gammadelta T cells, are recruited into the injured liver and release various cytokines. These immune cells and cytokines have been found to serve two purposes in AILI. In this review, we highlighted the dual role of inflammation, including inflammatory cytokines and inflammatory immune cells in AILI, and discussed possible explanations for contradictory findings.

The immunological mechanisms and therapeutic potential in drug-induced liver injury: lessons learned from acetaminophen hepatotoxicity

Acute liver failure caused by drug overdose is a significant clinical problem in developed countries. Acetaminophen (APAP), a widely used analgesic and antipyretic drug, but its overdose can cause acute liver failure. In addition to APAP-induced direct hepatotoxicity, the intracellular signaling mechanisms of APAP-induced liver injury (AILI) including metabolic activation, mitochondrial oxidant stress and proinflammatory response further affect progression and severity of AILI. Liver inflammation is a result of multiple interactions of cell death molecules, immune cell-derived cytokines and chemokines, as well as damaged cell-released signals which orchestrate hepatic immune cell infiltration. The immunoregulatory interplay of these inflammatory mediators and switching of immune responses during AILI lead to different fate of liver pathology. Thus, better understanding the complex interplay of immune cell subsets in experimental models and defining their functional involvement in disease progression are essential to identify novel therapeutic targets for the treatment of AILI. Here, this present review aims to systematically elaborate on the underlying immunological mechanisms of AILI, its relevance to immune cells and their effector molecules, and briefly discuss great therapeutic potential based on inflammatory mediators.

The Dual Role of Innate Immune Response in Acetaminophen-Induced Liver Injury

Acetyl-para-aminophenol (APAP), a commonly used antipyretic analgesic, is becoming increasingly toxic to the liver, resulting in a high rate of acute hepatic failure in Europe and the United States. Excessive APAP metabolism in the liver develops an APAP-protein adduct, which causes oxidative stress, MPTP opening, and hepatic necrosis. HMGB-1, HSP, nDNA, mtDNA, uric acid, and ATP are DMAPs released during hepatic necrosis. DMAPs attach to TLR4-expressing immune cells such KCs, macrophages, and NK cells, activating them and causing them to secrete cytokines. Immune cells and their secreted cytokines have been demonstrated to have a dual function in acetaminophen-induced liver injury (AILI), with a role in either proinflammation or pro-regeneration, resulting in contradicting findings and some research confusion. Neutrophils, KCs, MoMFs, NK/NKT cells, γδT cells, DCs, and inflammasomes have pivotal roles in AILI. In this review, we summarize the dual role of innate immune cells involved in AILI and illustrate how these cells initiate innate immune responses that lead to persistent inflammation and liver damage. We also discuss the contradictory findings in the literature and possible protocols for better understanding the molecular regulatory mechanisms of AILI.

Targeting innate immune responses to attenuate acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) hepatotoxicity is an important cause of acute liver failure, resulting in massive deaths in many developed countries. Currently, the metabolic process of APAP in the body has been well studied. However, the underlying mechanism of APAP-induced liver injury remains elusive. Increasing clinical and experimental evidences indicate that the innate immune responses are involved in the pathogenesis of APAP-induced acute liver injury (AILI), in which immune cells have dual roles of inducing inflammation to exacerbate hepatotoxicity and removing dead cells and debris to help liver regeneration. In this review, we summarize the latest findings of innate immune cells involved in AILI, particularly emphasizing the activation of innate immune cells and their different roles during the injury and repair phases. Moreover, current available treatments are discussed according to the different roles of innate immune cells in the development of AILI. This review aims to update the knowledge about innate immune responses in the pathogenesis of AILI, and provide potential therapeutic interventions for AILI.

Intrahepatic microbes govern liver immunity by programming NKT cells

The gut microbiome shapes local and systemic immunity. The liver is presumed to be a protected sterile site. As such, a hepatic microbiome has not been examined. Here, we showed a liver microbiome in mice and humans that is distinct from that of the gut and is enriched in Proteobacteria. It undergoes dynamic alterations with age and is influenced by the environment and host physiology. Fecal microbial transfer experiments revealed that the liver microbiome is populated from the gut in a highly selective manner. Hepatic immunity is dependent on the microbiome, specifically the bacteroidetes species. Targeting bacteroidetes with oral antibiotics reduced hepatic immune cells by approximately 90%, prevented antigen-presenting cell (APC) maturation, and mitigated adaptive immunity. Mechanistically, our findings are consistent with presentation of bacteroidetes-derived glycosphingolipids to NKT cells promoting CCL5 signaling, which drives hepatic leukocyte expansion and activation, among other possible host-microbe interactions. Collectively, we reveal a microbial/glycosphingolipid/NKT/CCL5 axis that underlies hepatic immunity.

The Immunological Mechanisms and Immune-Based Biomarkers of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) has become one of the major challenges of drug safety all over the word. So far, about 1,100 commonly used drugs including the medications used regularly, herbal and/or dietary supplements, have been reported to induce liver injury. Moreover, DILI is the main cause of the interruption of new drugs development and drugs withdrawn from the pharmaceutical market. Acute DILI may evolve into chronic DILI or even worse, commonly lead to life-threatening acute liver failure in Western countries. It is generally considered to have a close relationship to genetic factors, environmental risk factors, and host immunity, through the drug itself or its metabolites, leading to a series of cellular events, such as haptenization and immune response activation. Despite many researches on DILI, the specific biomarkers about it are not applicable to clinical diagnosis, which still relies on the exclusion of other causes of liver disease in clinical practice as before. Additionally, circumstantial evidence has suggested that DILI is mediated by the immune system. Here, we review the underlying mechanisms of the immune response to DILI and provide guidance for the future development of biomarkers for the early detection, prediction, and diagnosis of DILI.

The dual role of immune response in acetaminophen hepatotoxicity: Implication for immune pharmacological targets

Acetaminophen (APAP), one of the most widely used antipyretic and analgesic drugs, principally contributes to drug-induced liver injury when taken at a high dose. APAP-induced liver injury (AILI) results in extensive necrosis of hepatocytes along with the occurrence of multiple intracellular events such as metabolic activation, cell injury, and signaling pathway activation. However, the specific role of the immune response in AILI remains controversial for its complicated regulatory mechanisms. A variety of inflammasomes, immune cells, inflammatory mediators, and signaling transduction pathways are activated in AILI. These immune components play antagonistic roles in aggravating the liver injury or promoting regeneration. Recent experimental studies indicated that natural products showed remarkable therapeutic effects against APAP hepatotoxicity due to their favorable efficacy. Therefore, this study aimed to review the present understanding of the immune response in AILI and attempted to establish ties among a series of inflammatory cascade reactions. Also, the immune molecular mechanisms of natural products in the treatment of AILI were extensively reviewed, thus providing a fundamental basis for exploring the potential pharmacological targets associated with immune interventions.

Camellia japonica diminishes acetaminophen-induced acute liver failure by attenuating oxidative stress in mice

This experiment was to explore the possible defensive properties and potential molecular mechanisms of Camellia japonica (CJ) against APAP-stimulated acute liver failure (ALF) in mice. In this study, we investigated the effects of CJ on APAP-induced hepatotoxicity. Mice were orally treated with CJ before or after challenge with APAP. Both pretreatment and post-treatment with CJ attenuated APAP-induced hepatotoxicity, as confirmed by significantly reduced serum toxicity biomarkers and improved hepatic pathological damage. Pretreatment with CJ drastically decreased the rise of hepatic inflammatory cytokines levels and weakened neutrophil infiltration. Furthermore, pretreatment with CJ dramatically decreased the levels of hepatic oxidative stress markers such as hepatic malondialdehyde (MDA) and 4-Hydroxynonenal (4-HNE) expression and rescued the reduced hepatic level of GSH caused by APAP overdose. Additionally, CJ pretreatment markedly attenuated cyclooxygenase-2 (COX-2) activation, transcription factor nuclear factor-kappa B (NF-κB) phosphorylation, c-Jun-N-terminal kinase (JNK) phosphorylation, and activated AMP-activated protein kinase (AMPK) signaling pathway in the liver. The present study thus reveals that CJ attenuated APAP-induced ALF by inhibiting COX-2 activation, NF-κB, and JNK phosphorylation and activating the AMPK signaling pathway.

Emodin Attenuates Acetaminophen-Induced Hepatotoxicity via the cGAS-STING Pathway

Emodin is a natural bioactive compound from traditional Chinese herbs that exerts anti-inflammatory, antioxidant, anticancer, hepatoprotective, and neuroprotective effects. However, the protective effects of emodin in acetaminophen (APAP)-induced hepatotoxicity are not clear. The present study examined the effects of emodin on APAP-induced hepatotoxicity and investigated the potential molecular mechanisms. C57BL/6 mice were pretreated with emodin (15 and 30 mg/kg) for 5 consecutive days and then given APAP (300 mg/kg) to establish an APAP-induced liver injury model. Mice were sacrificed to detect the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and albumin (ALB) and the liver tissue levels of glutathione (GSH), malondialdehyde (MDA), and superoxide dismutase (SOD). Histological assessment, Western blotting, and ELISA were performed. Emodin pretreatment significantly reduced the levels of ALT, AST, and ALP; increased the levels of ALB; alleviated hepatocellular damage and apoptosis; attenuated the exhaustion of GSH and SOD and the accumulation of MDA; and increased the expression of antioxidative enzymes, including nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1), and NAD(P)H quinone dehydrogenase 1 (NQO1). Emodin also inhibited the expression of NLRP3 and reduced the levels of pro-inflammatory factors, including interleukin-1 beta (IL-1β), IL-6, and tumor necrosis factor-alpha (TNF-α). Emodin inhibited interferon (IFN)-α, cyclic GMP-AMP synthase (cGAS), and its downstream signaling effector stimulator of interferon genes (STING) expression to protect the liver against APAP-induced inflammatory responses and apoptosis. These results suggest that emodin protected hepatocytes from APAP-induced liver injury via the upregulation of the Nrf2-mediated antioxidative stress pathway, the inhibition of the NLRP3 inflammasome, and the downregulation of the cGAS-STING signaling pathway.

Myeloid DJ-1 deficiency protects acetaminophen-induced acute liver injury through decreasing inflammatory response

Background: DJ-1 (also known as PARK7), a noted protein implicated in modulating ROS production and immune response, has been observed to play critical roles in the pathogenesis of many forms of liver disease through multiple mechanisms. However, its role and specific mechanism in acetaminophen (APAP) -induced liver injury have not been explored.

Results: In this present study, by employing an acute liver injury induced by APAP overdose mouse model, we demonstrated that DJ-1 knockout (DJ-1^−/−) mice showed reduced liver injury and lower mortality. In accordance with these changes, there were also alleviating inflammatory responses in both the serum and the liver of the DJ-1^−/− mice compared to those of the wild-type (WT) mice. Functional experiments showed that APAP metabolism did not affected by DJ-1 deficiency. In addition, to investigate DJ-1 modulates which kind of cell types during APAP-overdose-induced acute liver injury, hepatocyte-specific DJ-1-knockout (Alb-DJ-1^−/−) and myeloid-specific DJ-1-knockout (Lysm-DJ-1^−/−) mice were generated. Interestingly, hepatic deletion of DJ-1 did not protect APAP-overdose induced hepatotoxicity and inflammation, whereas Lysm-DJ-1^−/− mice showed similar protective effects as DJ-1^−/− mice which suggest that the protective effects of deletion of DJ-1 was through modulating myeloid cell function. Consistently, there were alleviated pro-inflammatory cells infiltration and reduced reactive oxygen species (ROS) production in the liver of Lysm-DJ-1^−/− mice relative to control mice.

Conclusion: our findings clearly defined that deletion of DJ-1 protects APAP-induced acute liver injury through decreasing inflammatory response, and suggest DJ-1 as a potential therapeutic and/or prophylactic target of APAP-induced acute liver injury.

Kaempferol from Penthorum chinense Pursh suppresses HMGB1/TLR4/NF-κB signaling and NLRP3 inflammasome activation in acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) is one of the safest and most effective over-the-counter (OTC) analgesics and antipyretics, but excessive doses of APAP will induce hepatotoxicity with high morbidity and mortality worldwide. Kaempferol (KA), a flavonoid compound derived from the medicinal and edible plant of Penthorum chinense Pursh, has been reported to exert a profound anti-inflammatory and antioxidant activity. In this study, we explored the protective effect and novel mechanism of KA against APAP-induced hepatotoxicity. The results revealed that KA pretreatment significantly reduced the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), relieved hepatocellular damage and apoptosis, attenuated the exhaustion of glutathione (GSH) and accumulation of malondialdehyde (MDA), increased the expression of antioxidative enzymes (e.g., heme oxygenase 1 (HO-1) and NADPH quinone oxidoreductase 1 (NQO1)), and thus restrained APAP-induced oxidative damage in the liver. KA suppressed the expression of NLRP3 and reduced the levels of pro-inflammatory factors, including interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6). Moreover, KA remarkably inhibited high-mobility group box 1 (HMGB1) and toll-like receptor 4 (TLR4) expression as well as nuclear factor kappa-B (NF-κB) activation for liver protection against APAP-induced inflammatory responses and apoptosis. Taken together, our findings suggested that KA could effectively protect hepatocytes from APAP hepatotoxicity through the up-regulation of HO-1 and NQO1 expression, the down-regulation of NLRP3 expression, and the inhibition of the HMGB1/TLR4/NF-κB signaling pathway.

The complex roles of neutrophils in APAP-induced liver injury

Acetaminophen (APAP) is a widely applied drug for the alleviation of pain and fever, which is also a dose‐depedent toxin. APAP‐induced acute liver injury has become one of the primary causes of liver failure which is an increasingly serious threat to human health. Neutrophils are the major immune cells in human serving as the first barrier against the invasion of pathogen. It has been reported that neutrophils patriciate in the occurrence and development of APAP‐induced liver injury. However, evolving evidences suggest that neutrophils also contribute to tissue repair and actively orchestrate resolution of inflammation. Here, we addressed the complex roles in APAP‐induced liver injury on the basis of brief introduction of neutrophil's activation, recruitment and migration.

Aedes aegypti mosquito saliva ameliorates acetaminophen-induced liver injury in mice

Acetaminophen (N-acetyl-p-aminophenol, APAP) overdose is the most common cause of drug-induced liver injury (DILI). Although the primary hepatic damage is induced by APAP-derived toxic intermediates resulting from cytochrome P450 metabolism, immune components also play an important role in DILI pathophysiology. Aedes aegypti saliva is a source of bioactive molecules with in vitro anti-inflammatory and immunomodulatory activities. However, evidences on the therapeutic use of Ae. aegypti salivary preparations in animal models of relevant clinical conditions are still scarce. Thus, the present study was designed to evaluate the protective role of Ae. aegypti saliva in a murine model of APAP-induced DILI. C57BL/6 mice were exposed to Ae. aegypti bites 2 hours after APAP overdose. Biochemical and immunological parameters were evaluated in blood and liver samples at different time points after APAP administration. Exposure to Ae. aegypti saliva attenuated liver damage, as demonstrated by reduced hepatic necrosis and serum levels of alanine aminotransferase in APAP-overdosed mice. The levels of hepatic CYP2E1, the major enzyme responsible for the bioactivation of APAP, were not changed in Ae. aegypti exposed animals, suggesting no effects in the generation of hepatotoxic metabolites. On the other hand, mice treated with Ae. aegypti saliva following APAP overdose presented lower serum concentration of TNF-α, IL-6, IL-1β and IL-10, as well as reduced frequency of inflammatory cell populations in the liver, such as NKT cells, macrophages and dendritic cells. These findings show that Ae. aegypti saliva has bioactive molecules with therapeutic properties and may represent a prospective source of new compounds in the management of DILI-associated inflammatory disorders and, perhaps, many other inflammatory/autoimmune diseases.

Macrophage-Inducible C-Type Lectin Signaling Exacerbates Acetaminophen-Induced Liver Injury by Promoting Kupffer Cell Activation in Mice

Overdose of acetaminophen (APAP) has become one of the most frequent causes of acute liver failure. Macrophage-inducible C-type lectin (Mincle) acts as a key moderator in immune responses by recognizing spliceosome-associated protein 130 (SAP130), which is an endogenous ligand released by necrotic cells. This study aims to explore the function of Mincle in APAP-induced hepatotoxicity. Wild-type (WT) and Mincle knockout (KO) mice were used to induce acute liver injury by injection of APAP. The hepatic expressions of Mincle, SAP130, and Mincle signaling intermediate (Syk) were markedly upregulated after the APAP challenge. Mincle KO mice showed attenuated injury in the liver, as shown by reduced pathologic lesions, decreased alanine aminotransferase and aspartate aminotransferase levels, downregulated levels of inflammatory cytokines, and decreased neutrophil infiltration. Consistently, inhibition of Syk signaling by GS9973 alleviated APAP hepatotoxicity. Most importantly, Kupffer cells (KCs) were found as the major cellular source of Mincle. The depletion of KCs abolished the detrimental role of Mincle, and the adoptive transfer of WT KC to Mincle KO mice partially reversed the hyporesponsiveness to hepatotoxicity induced by APAP. Furthermore, the expression levels of interleukin (IL)-1β and neutrophil-attractant CXC chemokines were substantially lower in KCs isolated from APAP-treated Mincle KO mice compared with those from WT mice. Similar results were found in primary Mincle KO KCs treated with a ligand of Mincle (trehalose-6,6-dibehenate) or in conditioned media obtained from APAP-treated hepatocytes. Collectively, Mincle can regulate the inflammatory response of KCs, which is necessary for the complete progression of hepatotoxicity induced by APAP. SIGNIFICANCE STATEMENT: Acetaminophen (APAP) overdose is becoming a main cause of drug-induced acute liver damage in the developed world. This study showed that macrophage-inducible C-type lectin (Mincle) deletion or inhibition of Mincle downstream signaling attenuates APAP hepatotoxicity. Furthermore, Mincle as a modulator of Kupffer cell activation contributes to the full process of hepatotoxicity induced by APAP. This mechanism will offer valuable insights to overcome the limitation of APAP hepatotoxicity treatment.

Inhibition of EZH2 ameliorates bacteria-induced liver injury by repressing RUNX1 in dendritic cells

Fulminant hepatic failure (FHF) is a clinical syndrome characterized by a sudden and severe impairment in liver function. However, the precise mechanism of immune dysregulation that is significant to FHF pathogenesis remains unclear. Enhancer of zeste homolog 2 (EZH2) has been implicated in inflammation as a regulator of immune cell function. In this study, we investigated the role of EZH2 in an animal model of human FHF induced by Propionibacterium acnes (P. acnes) and lipopolysaccharide (LPS). We demonstrated that EZH2 depletion in dendritic cells (DCs) and pharmacological inhibition of EZH2 using GSK126 both significantly ameliorated liver injury and improved the survival rates of mice with P. acnes plus LPS-induced FHF, which could be attributed to the decreased infiltration and activation of CD4⁺ T cells in the liver, inhibition of T helper 1 cells and induction of regulatory T cells. The expression of EZH2 in DCs was increased after P. acnes administration, and EZH2 deficiency in DCs suppressed DC maturation and prevented DCs from efficiently stimulating CD4⁺ T-cell proliferation. Further mechanistic analyses indicated that EZH2 deficiency directly increased the expression of the transcription factor RUNX1 and thereby suppressed the immune functions of DCs. The functional dependence of EZH2 on RUNX1 was further illustrated in DC-specific Ezh2-deficient mice. Taken together, our findings establish that EZH2 exhibits anti-inflammatory effects through inhibition of RUNX1 to regulate DC functions and that inhibition of EZH2 alleviates P. acnes plus LPS-induced FHF, probably by inhibiting DC-induced adaptive immune responses. These results highlight the effect of EZH2 on DCs, serving as a guide for the development of a promising immunotherapeutic strategy for FHF.

Hepatoprotective effect of apolipoprotein A4 against carbon tetrachloride induced acute liver injury through mediating hepatic antioxidant and inflammation response in mice

Apolipoprotein A4 (ApoA4) regulates lipid and glucose metabolism and exerts anti-inflammatory effects in atherogenesis and colitis. The present study explored the presumed protective role of ApoA4 in carbon tetrachloride (CCl4)-induced acute liver injury (ALI) in mice. The ALI model in wild type (WT), ApoA4 knock-out (ApoA4-KO) and ApoA4 transgenic (ApoA4-TG) mice was induced by a single intraperitoneal administration of CCl4. Liver and blood were harvested from mice to assess liver functions, immunohistological changes, immune cell populations and cytokine profiles. ApoA4 deficiency aggravated, and ApoA4 overexpression alleviated CCl4-inflicted liver damage by controlling levels of anti-oxidant enzymes. ApoA4 deletion increased the recruitment of monocytes/macrophages into the injured liver and upregulated the plasma levels of IL-6, TNF-α and MCP-1, but lower IL-10 and IFN-γ. ApoA4 over-expression rescued this effect and resulted in lower percentages of monocytes/macrophages and dendritic cells, the ratio of blood pro-inflammatory to anti-inflammatory monocytes and reduced plasma concentrations of IL-6, but enhanced IL-10 and IFN-γ. We propose ApoA4 as a potential new therapeutic target for the management of liver damage.

Estrogen receptor agonists protect against acetaminophen-induced hepatorenal toxicity in rats

AIMS

Acetaminophen-induced hepatorenal toxicity varies among sexes with controversial results among species. The aim was to compare the impact of sex and ovarian hormones on hepatorenal toxicity and to elucidate protective effects of estrogen and estrogen receptor (ER) agonists.

MAIN METHODS

Under anesthesia, female rats underwent ovariectomy (OVX) or sham-OVX. Starting at postsurgical 40th day, OVX-rats received subcutaneously (each, 1 mg/kg/day) 17β-estradiol (E₂), ERβ-agonist (DPN) or ERα-agonist (PPT) for 10 days, while male and sham-OVX rats received vehicle for 10 days. Then, rats received either acetaminophen (3 g/kg) or saline by orogastric gavage and were decapitated at 24th h. Blood samples were obtained to measure serum ALT, AST, BUN, creatinine levels. Liver and kidney samples were obtained for histopathologic examination and for analyzing levels of luminol- and lucigenin-chemiluminescence, glutathione and myeloperoxidase activity.

KEY FINDINGS

Compared to their control groups, levels of AST, ALT, BUN, creatinine, hepatic and renal myeloperoxidase activity and chemiluminescence levels were increased, and hepatic glutathione level was decreased in acetaminophen-administered male groups, while ALT and hepatic chemiluminescence levels were not elevated in sham-OVX-rats. Both ER-agonists and E₂ reduced BUN, creatinine and reversed all oxidative parameters in renal tissues of OVX-rats. Additionally, ERα-agonist reversed all hepatic injury parameters, while ERβ-agonist elevated hepatic glutathione level.

SIGNIFICANCE

Acetaminophen toxicity in female rats presented with a more preserved hepatic function, while renal toxicity was not influenced by sex or by the lack of ovarian hormones. Pretreatment with estrogen or ER agonists, via their antioxidant actions, provided protective effects on acetaminophen-induced hepatorenal toxicity.

New insights in acetaminophen toxicity: HMGB1 contributes by itself to amplify hepatocyte necrosis in vitro through the TLR4-TRIF-RIPK3 axis

Extracellular release of HMGB1 contributes to acetaminophen-induced liver injury. HMGB1 acts as a danger-associated molecular patterns during this toxic process but the mechanisms of action and targeted cells are incompletely defined. Here we studied, in vitro, the role of HMGB1 in amplifying the acetaminophen-induced hepatocyte necrosis process. Using cultured HepaRG cells, primary human hepatocytes and selective chemical inhibitors we evaluated acetaminophen-induced toxicity. We confirmed that addition of acetaminophen induced HepaRG cell death and HMGB1 release. We showed that inhibition of HMGB1 decreased acetaminophen-induced HepaRG cell death, suggesting a feedforward effect. We provide the first evidence that exposure of HepaRG cells to recombinant human HMGB1 (rhHMGB1) also resulted in cell death. Moreover, we found that both acetaminophen and rhHMGB1 induced programmed HepaRG cell necrosis through a RIPK3-dependent mechanism. By using TLR4 blocking antibody, we demonstrated the reduction of the HepaRG cell death induced by acetaminophen and rhHMGB1. Furthermore, inhibition of TRIF, known to induce a RIPK3-dependent cell death, reduced rhHMGB1-induced HepaRG cell death. Our data support that released HMGB1 from acetaminophen-stressed hepatocytes induced necrosis of neighboring hepatocytes by TLR4-TRIF-RIPK3- pathway. This in vitro study gives new insights in the role of HMGB1 in the amplification of acetaminophen-induced toxicity.

Critical roles of conventional dendritic cells in autoimmune hepatitis via autophagy regulation

Autoimmune hepatitis (AIH) is a necroinflammatory disease associated with interactive cell populations of the innate and adaptive immune systems. The contribution of conventional dendritic cells (cDCs) to AIH and the underlying mechanism remain poorly understood. The frequency of peripheral mature cDCs increased in AIH patients and was positively correlated with disease severity. In experimental autoimmune hepatitis (EAH), hepatic accumulation of mature cDCs was observed, along with an increase in the periphery. Sequentially, bone marrow-derived dendritic cells (BMDC) from EAH mice exhibit more proinflammatory function than those from control mice. In vitro, ConA treatment promotes the maturation of BMDCs, which are characterized by higher expression of MHC-II, costimulatory molecules and cytokine secretion. ConA also induced the expression of autophagy-related protein and the formation of autophagosomes in DCs. To further investigate whether ConA-induced DC activation is associated with autophagy, we utilized 3-MA and bafilomycin A1 to block autophagy flux and accessed the maturation and function of DCs induced by ConA. 3-MA and bafilomycin A1 inhibited the mature status and proinflammatory cytokine secretion and diminished the proliferation and differentiation of CD4+ T cells when ConA-induced BMDCs cocultured CD4+ T cells. We demonstrated that cDCs contribute to the pathogenesis of AIH through excessive maturation. Aberrant autophagy flux plays a vital role in the immunogenic maturation of cDCs in AIH, and tolerogenic cDCs by inhibition of autophagy flux can be exploited as a new therapeutic approach for AIH.

CX3CR1 Mediates the Development of Monocyte-Derived Dendritic Cells during Hepatic Inflammation

Recent evidence suggests that hepatic dendritic cells (HDCs) contribute to the evolution of chronic liver diseases. However, the HDC subsets involved and the mechanisms driving these responses are still poorly understood. In this study, we have investigated the role of the fractalkine receptor CX3CR1 in modulating monocyte-derived dendritic cell (moDC) differentiation during liver inflammation. The phenotype of HDC and functional relevance of CX3CR1 was assessed in mice following necro-inflammatory liver injury induced by the hepatotoxic agent carbon tetrachloride (CCl4) and in steatohepatitis caused by a methionine/choline-deficient (MCD) diet. In both the experimental models, hepatic inflammation was associated with a massive expansion of CD11c+/MHCIIhigh/CD11b+ myeloid HDCs. These cells also expressed the monocyte markers Ly6C, chemokine (C-C Motif) receptor 2 (CCR2), F4/80 and CD88, along with CX3CR1, allowing their tentative identification as moDCs. Mice defective in CX3CR1 showed a reduction in liver-moDC recruitment following CCl4 poisoning in parallel with a defective maturation of monocytes into moDCs. The lack of CX3CR1 also affected moDC differentiation from bone marrow myeloid cells induced by granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin-4 (IL-4) in vitro. In wild-type mice, treatment with the CX3CR1 antagonist CX3-AT (150 µg, i.p.) 24 h after CCl4 administration reduced liver moDCS and significantly ameliorated hepatic injury and inflammation. Altogether, these results highlight the possible involvement of moDCs in promoting hepatic inflammation following liver injury and indicated a novel role of CX3CL1/CX3CR1 dyad in driving the differentiation of hepatic moDCs.

Liver DCs in health and disease

Hepatic dendritic cells represent a unique and multifaceted subset of antigen-presenting leukocytes that orchestrate specified immune responses in the liver. They are constantly exposed to antigens and signals derived not only from the hepatic microenvironment and the systemic circulation but also from the portal vein draining the gut and conveying food antigens as well as microbial compounds. Modulated by these various factors they shape intrahepatic immune responses during acute and chronic liver diseases, hepatocellular carcinoma and allograft tolerance as well as systemic responses to gut-derived components. Hence, hepatic DC are central targets to decipher and fine-tune innate and adaptive hepatic immune responses as well as tolerance. This review focuses on the origin of hepatic DC, the different DC subsets present in the liver and their functionality during different acute and chronic liver diseases in mice and men and will discuss potential DC directed therapeutic interventions in liver disease.

Macrophage markers soluble CD163 and soluble mannose receptor are associated with liver injury in patients with paracetamol overdose

The macrophage activation markers, soluble CD163 (sCD163) and soluble mannose receptor (sMR), are associated with liver disease severity and prognosis. We aimed to investigate macrophage activation reflected by sMR and sCD163 in patients with mild and severe paracetamol (PCM) intoxication and effects of antidote treatment in patients and healthy controls. We measured sMR and sCD163 levels by in-house enzyme-linked immunosorbent assays in two independent prospective cohorts of PCM overdosed patients: 49 patients with early mild PCM overdose from Aarhus University Hospital and 30 patients with severe acute liver injury included at the Royal Infirmary of Edinburgh. Furthermore, we investigated sMR and sCD163 in 14 healthy controls during N-acetylcysteine treatment. Within the mild PCM cohort, patients with elevated alanine transaminase on admission had significantly higher levels of sCD163 compared with patients with normal alanine transaminase (2.92[2.00-5.75] versus 1.29[1.02-1.69] mg/L, p = .009), whereas sMR showed no significant difference. In patients with acute liver injury, both markers were markedly higher compared to the mild PCM cohort (sCD163: 10.73[5.79-14.62] versus 1.34[1.06-1.96], p < .001; sMR: 0.80[0.63-1.14] versus 0.18[0.14-0.25], p < .001). Antidote treatment significantly reduced sCD163 levels in both PCM overdosed patients and healthy controls. In conclusion, macrophage activation assessed by the levels of sMR and sCD163 is associated with the degree of liver injury in patients with PCM intoxication and is ameliorated by antidote treatment, suggesting macrophage involvement in PCM-induced liver injury.

The Role of Myeloid-Derived Cells in the Progression of Liver Disease

Control of homeostasis and rapid response to tissue damage in the liver is orchestrated by crosstalk between resident and infiltrating inflammatory cells. A crucial role for myeloid cells during hepatic injury and repair has emerged where resident Kupffer cells, circulating monocytes, macrophages, dendritic cells and neutrophils control local tissue inflammation and regenerative function to maintain tissue architecture. Studies in humans and rodents have revealed a heterogeneous population of myeloid cells that respond to the local environment by either promoting regeneration or driving the inflammatory processes that can lead to hepatitis, fibrogenesis, and the development of cirrhosis and malignancy. Such plasticity of myeloid cell responses presents unique challenges for therapeutic intervention strategies and a greater understanding of the underlying mechanisms is needed. Here we review the role of myeloid cells in the establishment and progression of liver disease and highlight key pathways that have become the focus for current and future therapeutic strategies.

Network pharmacology oriented study reveals inflammatory state-dependent dietary supplement hepatotoxicity responses in normal and diseased rats

Rhubarb, a well-used herbal and dietary supplement, has been widely used as a laxative in many countries.

FGF21 mediates the protective effect of fenofibrate against acetaminophen -induced hepatotoxicity via activating autophagy in mice

Overdose of acetaminophen (APAP) induces acute liver injury due in part to destruction of mitochondria and resulted oxidative stress. Recently, FGF21 has been demonstrated to be an endocrine factor to protect liver from oxidative stress. The aim of present study is to explore the role of fibroblast growth factor 21 (FGF21) in the protective effect of fenofibrate, an agonist of peroxisome proliferator-activated receptor alpha (PPARα), against acetaminophen (APAP)-induced liver injury. Mice and primary cultured hepatocytes were used to test the potential hepatoprotective effect of fenofibrate against APAP-induced hepatotoxicity. FGF21 deficient mice were used to evaluate the role of FGF21 in fenofibrate against APAP-induced acute liver injury. Post-treatment with fenofibrate significantly inhibits APAP-induced hepatotoxicity, as evidenced by decreased serum ALT and AST levels and hepatic necrosis in liver tissue as well as increased the surviving rate in response to APAP overdose, whereas this protective effect of fenofibrate is largely attenuated in FGF21 KO mice. Interestingly, administration of fenofibrate efficiently increases autophagy, which was companied with alleviating hepatotoxicity in APAP-treated WT mice. However, such effect is significantly attenuated in APAP-treated FGF21 KO mice. In conclusion, our findings suggest that fenofibrate against APAP-induced hepatotoxicity is at least in part mediated by up-regulating the expression of FGF21, which in turn promotes autophagy-mediated hepatoprotective effects.

Autophagy and acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug. APAP overdose can induce acute liver injury in humans, which is responsible for approximately 50% of total cases of acute liver failure in the United States and some European countries. Currently, the metabolism of APAP in the body has been extensively investigated; however, the exact mechanisms for APAP hepatotoxicity are not well understood. Recent studies have shown that mitochondrial dysfunction, oxidative stress and inflammatory responses play a critical role in the pathogenesis of APAP hepatotoxicity. Autophagy is a catabolic machinery aimed at recycling cellular components and damaged organelles in response to a variety of stimuli, such as nutrient deprivation and toxic stress. Increasing evidence supports that autophagy is involved in the pathophysiological process of APAP-induced liver injury. In this review, we summarized the changes of autophagy in the liver following APAP intoxication and discussed the role and its possible mechanisms of autophagy in APAP hepatotoxicity. Furthermore, this review highlights the crosstalk between mitophagy, oxidative stress and inflammation in APAP-induced liver injury and presents some possible molecular mechanisms by which activated autophagy protects against APAP-induced liver injury.

CX3CR1 modulates the anti-inflammatory activity of hepatic dendritic cells in response to acute liver injury

The chemokine fractalkine (CX3CL1) and its receptor CX3CR1 are known to mediate leukocyte chemotaxis, adhesion and survival. In the liver, CX3CR1 is expressed on multiple cell types including monocytes and dendritic cells. However, the function of CX3CR1 on hepatic dendritic cells (HDCs) is still poorly understood. In this study, we investigated the role of CX3CR1 on mouse HDCs during homeostasis and following acute liver injury. At homeostasis, CX3CR1-expression was detected among CD11b+/CD103- type 2 myeloid HDCs (mHDCs) and these cells were characterized by the production of IL-10.   Mice treatment with the hepatotoxic agent CCl4 up-regulated liver IL-10 expression and stimulated the expansion of CX3CR1+ mHDCs which also showed a more mature phenotype. The absence of CX3CR1 in naïve CX3CR1gfp/gfp mice specifically reduced the CD11b+/IL-10+ mHDCs as compared to CX3CR1-proficient animals (CX3CR1+/gfp).  Following CCl4 poisoning, the liver recruitment and maturation of CD11b+ mHDCs was significantly attenuated in CX3CR1gfp/gfp mice. Furthermore, these mice suffered more severe hepatic injury and inflammation than CX3CR1+/gfp mice and showed a delated recovery from liver damage. Such a worsening of liver injury in CX3CR1gfp/gfp mice was associated with an impaired up-regulation of hepatic IL-10 expression and a lower number of IL-10 producing CD11b+ mHDCs. Consistently, IL-10 inactivation enhanced hepatic injury and inflammation in CX3CR1+/gfp mice receiving CCl4 Altogether, these data indicate a novel role of the CX3CL1/CX3CR1 axis in liver type 2 mHDC functions, pointing out the importance of CX3CR1 in promoting IL-10-mediated anti-inflammatory actions of HDCs.

Glycyrrhetinic acid prevents acetaminophen-induced acute liver injury via the inhibition of CYP2E1 expression and HMGB1-TLR4 signal activation in mice

Acetaminophen (APAP) is a widely used antipyretic and analgesic drug, which is safe and effective at the therapeutic dose. Unfortunately, excessive dosage of APAP could cause severe liver injury due to lack of effective therapy. Successful therapeutic strategies are urgently requested in clinic. Glycyrrhetinic acid (GA), derived from a traditional medicine licorice, has been shown to exert anti-inflammatory and antioxidant actions. In this study, the effect and the underlying mechanism of GA on APAP-induced hepatotoxicity were explored. Our results showed that pretreatment with GA significantly reduced serum ALT and AST activities, alleviated hepatic pathological damages with hepatocellular apoptosis, down-regulated expression of CYP2E1 mRNA and protein, increased GSH levels, and reduced reactive oxygen species (ROS) productions in the liver of APAP-exposed mice. Furthermore, GA obviously inhibited APAP-induced HMGB1-TLR4 signal activation, as evaluated by reduced hepatic HMGB1 release, p-IRAK1, p-MAPK and p-IκB expression as well as the productions of TNF-α and IL-1β. In addition, GA attenuated hepatic neutrophils recruitment and macrophages infiltration caused by APAP. These findings reflected that GA could alleviate APAP-induced hepatotoxicity, the possible mechanism is associated with down-regulation of CYP2E1 expression and deactivation of HMGB1-TLR4 signal pathway.

Murine CD103+ dendritic cells protect against steatosis progression towards steatohepatitis

BACKGROUND & AIMS

Non-alcoholic fatty liver (NAFL) is the hepatic consequence of metabolic syndrome and can progress to non-alcoholic steatohepatitis (NASH). The identification of molecular and cellular factors that determine the progression of NASH and lead to irreversible hepatocellular damage are crucial. Dendritic cells (DCs) represent a heterogeneous cell population among which CD103⁺ DCs play a significant role in immunity and tolerance. We aimed to clarify the role of this DC subset in the pathomechanism of NASH.

METHODS

Steatosis progression towards steatohepatitis was analysed using multicolor FACS analyses, cytokine and qPCR array in high sucrose diet (HSD) and methionine and choline deficient diet (MCD) fed wild-type and basic leucine zipper transcription factor, ATF-Like-3 (Batf3) deficient animals, which lack CD103⁺ DCs (classical type-1 DC, cDC1s).

RESULTS

Metabolic challenge of Batf3^-/- animals resulted in the progression of steatosis towards steatohepatitis, manifesting by an increased influx of inflammatory cells into the liver and elevated inflammatory cytokine production of myeloid cells upon innate stimuli. However, the lack of cDC1s did not affect cellular apoptosis and fibrosis progression but altered genes involved in lipid metabolism. The adoptive transfer of CD103⁺ cDC1s to Batf3 deficient animals reversed these observed changes and more importantly could attenuate cellular damage and inflammation in established murine steatohepatitis.

CONCLUSION

Here, we have identified the murine CD103⁺ cDC1s as a protective DC subtype that influences the pro-anti-inflammatory balance and protects the liver from metabolic damage. As guardians of liver integrity, they play a key role in the inflammatory process during the development of steatohepatitis in mice.

LAY SUMMARY

Non-alcoholic fatty liver (NAFL) is the hepatic consequence of metabolic syndrome and can lead to non-alcoholic steatohepatitis (NASH). The current study demonstrated that a specific murine dendritic cell subtype possesses a potent regulatory role to influence the inflammatory milieu of the liver in this process.

Inhibition of pannexin1 channels alleviates acetaminophen-induced hepatotoxicity

Pannexins constitute a relatively new family of transmembrane proteins that form channels linking the cytoplasmic compartment with the extracellular environment. The presence of pannexin1 in the liver has been documented previously, where it underlies inflammatory responses, such as those occurring upon ischemia-reperfusion injury. In the present study, we investigated whether pannexin1 plays a role in acute drug-induced liver toxicity. Hepatic expression of pannexin1 was characterized in a mouse model of acetaminophen-induced hepatotoxicity. Subsequently, mice were overdosed with acetaminophen followed by treatment with the pannexin1 channel inhibitor 10Panx1. Sampling was performed 1, 3, 6, 24 and 48 h after acetaminophen administration. Evaluation of the effects of pannexin1 channel inhibition was based on a number of clinically relevant readouts, including protein adduct formation, measurement of aminotransferase activity and histopathological examination of liver tissue as well as on a series of markers of inflammation, oxidative stress and regeneration. Although no significant differences were found in histopathological analysis, pannexin1 channel inhibition reduced serum levels of alanine and aspartate aminotransferase. This was paralleled by a reduced amount of neutrophils recruited to the liver. Furthermore, alterations in the oxidized status were noticed with upregulation of glutathione levels upon suppression of pannexin1 channel opening. Concomitant promotion of regenerative activity was detected as judged on increased proliferating cell nuclear antigen protein quantities in 10Panx1-treated mice. Pannexin1 channels are important actors in liver injury triggered by acetaminophen. Inhibition of pannexin1 channel opening could represent a novel approach for the treatment of drug-induced hepatotoxicity.

The impact of sterile inflammation in acute liver injury

BACKGROUND

The liver has a number of functions in innate immunity. These functions predispose the liver to innate immune-mediated liver injury when inflammation goes unchecked. Significant progress has been made in the last 25 years on sterile inflammatory liver injury in a number of models; however, a great deal of controversy and many questions about the nature of sterile inflammation still exist.

AIM

The goal of this article is to review sterile inflammatory liver injury using both a basic approach to what constitutes the inflammatory injury, and through examination of current models of liver injury and inflammation. This information will be tied to human patient conditions when appropriate.

RELEVANCE FOR PATIENTS

Inflammation is one of the most critical factors for managing in-patient liver disease in a number of scenarios. More information is needed for both scientists and clinicians to develop rational treatments.

Critical roles of conventional dendritic cells in promoting T cell-dependent hepatitis through regulating natural killer T cells

Dendritic cells (DCs) play critical roles in initiating and regulating innate immunity as well as adaptive immune responses. However, the role of conventional dendritic cells (cDCs) in concanavalin A (ConA)-induced fulminant hepatitis is unknown. In this study, we demonstrated that depletion of cDCs using either CD11c-diphtheria toxin receptor transgenic mice (DTR Tg) mice or anti-CD11c antibody reduced the severity of liver injury significantly, indicating a detrimental role of cDCs in ConA-induced hepatitis. We elucidated further the pathological role of cDCs as being the critical source of interleukin (IL)-12, which induced the secretion of interferon (IFN)-γ by natural killer (NK) T cells. Reconstitution of cDCs-depleted mice with IL-12 restored ConA-induced hepatitis significantly. Furthermore, we determined that NK T cells were the target of DC-derived IL-12, and NK T cells contributed to liver inflammation and injury through production of IFN-γ. In summary, our study demonstrated a novel function of cDCs in mediating ConA-induced hepatitis through regulating IFN-γ secretion of NK T cells in an IL-12-dependent fashion. Targeting cDCs might provide potentially therapeutic applications in treating autoimmune related liver diseases.

Combination of Mass Cytometry and Imaging Analysis Reveals Origin, Location, and Functional Repopulation of Liver Myeloid Cells in Mice

BACKGROUND & AIMS

Resident macrophages are derived from yolk sac precursors and seed the liver during embryogenesis. Native cells may be replaced by bone marrow precursors during extensive injuries, irradiation, and infections. We investigated the liver populations of myeloid immune cells and their location, as well as the dynamics of phagocyte repopulation after full depletion. The effects on liver function due to the substitution of original phagocytes by bone marrow-derived surrogates were also examined.

METHODS

We collected and analyzed liver tissues from C57BL/6 (control), LysM-EGFP, B6 ACTb-EGFP, CCR2^-/-, CD11c-EYFP, CD11c-EYFP-DTR, germ-free mice, CX3CR1^gfp/gfp, CX3CR1^gpf/wt, and CX3CR1-DTR-EYFP. Liver nonparenchymal cells were immunophenotyped using mass cytometry and gene expression analyses. Kupffer and dendritic cells were depleted from mice by administration of clodronate, and their location and phenotype were examined using intravital microscopy and time-of-flight mass cytometry. Mice were given acetaminophen gavage or intravenous injections of fluorescently labeled Escherichia coli, blood samples were collected and analyzed, and liver function was evaluated. We assessed cytokine profiles of liver tissues using a multiplexed array.

RESULTS

Using mass cytometry and gene expression analyses, we identified 2 populations of hepatic macrophages and 2 populations of monocytes. We also identified 4 populations of dendritic cells and 1 population of basophils. After selective depletion of liver phagocytes, intravascular myeloid precursors began to differentiate into macrophages and dendritic cells; dendritic cells migrated out of sinusoids, after a delay, via the chemokine CX3CL1. The cell distribution returned to normal in 2 weeks, but the repopulated livers were unable to fully respond to drug-induced injury or clear bacteria for at least 1 month. This defect was associated with increased levels of inflammatory cytokines, and dexamethasone accelerated the repopulation of liver phagocytes.

CONCLUSIONS

In studies of hepatic phagocyte depletion in mice, we found that myeloid precursors can differentiate into liver macrophages and dendritic cells, which each localize to distinct tissue compartments. During replenishment, macrophages acquire the ability to respond appropriately to hepatic injury and to remove bacteria from the blood stream.

Update on innate immunity and perspectives on metabolite regulation in acute pancreatitis

PURPOSE OF REVIEW

Acute pancreatitis is a major cause of gastrointestinal morbidity for which specific therapy is greatly needed to prevent progression to and induce resolution of severe disease.

RECENT FINDINGS

Innate immune components and metabolite signaling are recently identified as strong determinants of disease severity and resolution in acute pancreatitis and this work will be discussed herein.

SUMMARY

Targeting innate immune cell populations and metabolite signaling pathways in acute pancreatitis may result in broader and ultimately more efficacious re-direction of the inflammatory programme toward disease resolution and improved clinical outcomes.

Blood transcript immune signatures distinguish a subset of people with elevated serum ALT from others given acetaminophen

The diagnosis of drug-induced liver injury is hindered by the limited utility of clinical chemistries. We have shown that hepatotoxicants can produce peripheral blood transcriptome "signatures" (PBTS) in rodents and humans. In this study, 42 adults were treated with acetaminophen (APAP; 1 g every 6 hours) for seven days, followed by three days of placebo. Eleven subjects received only placebo. After five days, 12 subjects (30%) had increases in serum alanine aminotransferase (ALT) levels ("responders"). PBTS of 707 and 760 genes, respectively, could distinguish responders and nonresponders from placebos. Functional analysis of the responder PBTS revealed increased expression of genes involved in TH2-mediated and innate immune responses, whereas the nonresponders demonstrated increased gene expression consistent with a tolerogenic immune response. Taken together, these observations suggest that the clinical subjects with transient increases in serum ALT failed to maintain or intensify a hepatic tolerogenic immune response.

CX3CR1-expressing inflammatory dendritic cells contribute to the progression of steatohepatitis

Liver monocytes play a major role in the development of NASH (non-alcoholic steatohepatitis). In inflamed tissues, monocytes can differentiate in both macrophages and dendritic cells. In the present study, we investigated the role of moDCs (monocyte-derived inflammatory dendritic cells) in experimental steatohepatitis induced in C57BL/6 mice by feeding on a MCD (methionine/choline-deficient) diet. The evolution of steatohepatitis was characterized by an increase in hepatic CD45+ / CD11b+ myeloid cells displaying the monocyte/macrophage marker F4-80(+). In the early phases (4 weeks of treatment), Ly6C(high)/CD11b(+)/F4-80(+) inflammatory macrophages predominated. However, their frequency did not grow further with the disease progression (8 weeks of treatment), when a 4-fold expansion of CD11b(+)/F4-80(+) cells featuring the fractalkine receptor (CX3CR1) was evident. These CX3CR1+ cells were also characterized by the combined expression of inflammatory monocyte (Ly6C, CD11b) and dendritic cell (CD11c, MHCII) markers as well as by a sustained TNFα (tumour necrosis factor α) production, suggesting monocyte differentiation into inflammatory moDCs. The expansion of TNFα-producing CX3CR1+ moDCs was associated with an elevation in hepatic and circulating TNFα level and with the worsening of parenchymal injury. Hydrogen sulfide (H2S) has been shown to interfere with CX3CR1 up-regulation in monocyte-derived cells exposed to pro-inflammatory stimuli. Treating 4-week-MCD-fed mice with the H2S donor NaHS while continuing on the same diet prevented the accumulation of TNFα-producing CX3CR1+ moDCs without interfering with hepatic macrophage functions. Furthermore, NaHS reduced hepatic and circulating TNFα levels and ameliorated transaminase release and parenchymal injury. Altogether, these results show that inflammatory CX3CR1+ moDCs contributed in sustaining inflammation and liver injury during steatohepatitis progression.

Xenobiotic and Endobiotic Mediated Interactions Between the Cytochrome P450 System and the Inflammatory Response in the Liver

The liver is a unique organ in the body as it has significant roles in both metabolism and innate immune clearance. Hepatocytes in the liver carry a nearly complete complement of drug metabolizing enzymes, including numerous cytochrome P450s. While a majority of these enzymes effectively detoxify xenobiotics, or metabolize endobiotics, a subportion of these reactions result in accumulation of metabolites that can cause either direct liver injury or indirect liver injury through activation of inflammation. The liver also contains multiple populations of innate immune cells including the resident macrophages (Kupffer cells), a relatively large number of natural killer cells, and blood-derived neutrophils. While these cells are primarily responsible for clearance of pathogens, activation of these immune cells can result in significant tissue injury during periods of inflammation. When activated chronically, these inflammatory bouts can lead to fibrosis, cirrhosis, cancer, or death. This chapter will focus on interactions between how the liver processes xenobiotic and endobiotic compounds through the cytochrome P450 system, and how these processes can result in a response from the innate immune cells of the liver. A number of different clinically relevant diseases, as well as experimental models, are currently available to study mechanisms related to the interplay of innate immunity and cytochrome P450-mediated metabolism. A major focus of the chapter will be to evaluate currently understood mechanisms in the context of these diseases, as a way of outlining mechanisms that dictate the interactions between the P450 system and innate immunity.

Divergent effects of RIP1 or RIP3 blockade in murine models of acute liver injury

Necroptosis is a recently described Caspase 8-independent method of cell death that denotes organized cellular necrosis. The roles of RIP1 and RIP3 in mediating hepatocyte death from acute liver injury are incompletely defined. Effects of necroptosis blockade were studied by separately targeting RIP1 and RIP3 in diverse murine models of acute liver injury. Blockade of necroptosis had disparate effects on disease outcome depending on the precise etiology of liver injury and component of the necrosome targeted. In ConA-induced autoimmune hepatitis, RIP3 deletion was protective, whereas RIP1 inhibition exacerbated disease, accelerated animal death, and was associated with increased hepatocyte apoptosis. Conversely, in acetaminophen-mediated liver injury, blockade of either RIP1 or RIP3 was protective and was associated with lower NLRP3 inflammasome activation. Our work highlights the fact that diverse modes of acute liver injury have differing requirements for RIP1 and RIP3; moreover, within a single injury model, RIP1 and RIP3 blockade can have diametrically opposite effects on tissue damage, suggesting that interference with distinct components of the necrosome must be considered separately.

Application of IL-36 receptor antagonist weakens CCL20 expression and impairs recovery in the late phase of murine acetaminophen-induced liver injury

Overdosing of the analgesic acetaminophen (APAP, paracetamol) is a major cause of acute liver injury. Whereas toxicity is initiated by hepatocyte necrosis, course of disease is regulated by mechanisms of innate immunity having the potential to serve in complex manner pathogenic or pro-regenerative functions. Interleukin (IL)-36γ has been identified as novel IL-1-like cytokine produced by and targeting epithelial (-like) tissues. Herein, we investigated IL-36γ in acute liver disease focusing on murine APAP-induced hepatotoxicity. Enhanced expression of hepatic IL-36γ and its prime downstream chemokine target CCL20 was detected upon liver injury. CCL20 expression coincided with the later regeneration phase of intoxication. Primary murine hepatocytes and human Huh7 hepatocellular carcinoma cells indeed displayed enhanced IL-36γ expression when exposed to inflammatory cytokines. Administration of IL-36 receptor antagonist (IL-36Ra) decreased hepatic CCL20 in APAP-treated mice. Unexpectedly, IL-36Ra likewise increased late phase hepatic injury as detected by augmented serum alanine aminotransferase activity and histological necrosis which suggests disturbed tissue recovery upon IL-36 blockage. Finally, we demonstrate induction of IL-36γ in inflamed livers of endotoxemic mice. Observations presented introduce IL-36γ as novel parameter in acute liver injury which may contribute to the decision between unleashed tissue damage and initiation of liver regeneration during late APAP toxicity.