Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity

NLRP3 inflammasome activation triggers severe inflammatory liver injury in N, N-dimethylformamide-exposed mice

N,N-dimethylformamide (DMF) is a widely utilized chemical solvent with various industrial applications. Previous studies have indicated that the liver is the most susceptible target to DMF exposure, whereas the underlying mechanisms remain to be elucidated. This study aimed to investigate the role of NLRP3 inflammasome in DMF-induced liver injury in mice by using two NLRP3 inflammasome inhibitors, Nlrp3-/- mice, Nfe2l2-/- mice, and a macrophage-depleting agent. RNA sequencing revealed that endoplasmic reticulum (ER) stress and NLRP3 inflammasome-associated pathways were activated in the mouse liver after acute DMF exposure, which was validated by Western blotting. Interestingly, DMF-induced liver injury was effectively suppressed by two inflammasome inhibitors, MCC950 and Dapansutrile. In addition, knockout of Nlrp3 markedly attenuated DMF-induced liver injury without affecting the metabolism of DMF. Furthermore, silencing Nfe2l2 aggravated the liver injury and the NLRP3 inflammasome activation in mouse liver. Finally, the depletion of hepatic macrophages by clodronate liposomes significantly reduced the liver damage caused by DMF. These results suggest that NLRP3 inflammasome activation is the upstream molecular event in the development of acute liver injury induced by DMF.

Transcriptome Analysis Reveals Dynamic Microglial-Induced A1 Astrocyte Reactivity via C3/C3aR/NF-κB Signaling After Ischemic Stroke

Microglia and astrocytes are key players in neuroinflammation and ischemic stroke. A1 astrocytes are a subtype of astrocytes that are extremely neurotoxic and quickly kill neurons. Although the detrimental A1 astrocytes are present in many neurodegenerative diseases and are considered to accelerate neurodegeneration, their role in the pathophysiology of ischemic stroke is poorly understood. Here, we combined RNA-seq, molecular and immunological techniques, and behavioral tests to investigate the role of A1 astrocytes in the pathophysiology of ischemic stroke. We found that astrocyte phenotypes change from a beneficial A2 type in the acute phase to a detrimental A1 type in the chronic phase following ischemic stroke. The activated microglial IL1α, TNF, and C1q prompt commitment of A1 astrocytes. Inhibition of A1 astrocytes induction attenuates reactive gliosis and ameliorates morphological and functional defects following ischemic stroke. The crosstalk between astrocytic C3 and microglial C3aR contributes to the formation of A1 astrocytes and morphological and functional defects. In addition, NF-κB is activated following ischemic stroke and governs the formation of A1 astrocytes via direct targeting of inflammatory cytokines and chemokines. Taken together, we discovered that A2 astrocytes and A1 astrocytes are enriched in the acute and chronic phases of ischemic stroke respectively, and that the C3/C3aR/NF-κB signaling leads to A1 astrocytes induction. Therefore, the C3/C3aR/NF-κB signaling is a novel therapeutic target for ischemic stroke treatment.

NLRP3 deficiency protects against acetaminophen‑induced liver injury by inhibiting hepatocyte pyroptosis

Acetaminophen (APAP) overdose is the primary cause of drug‑induced acute liver failure in numerous Western countries. NLR family pyrin domain containing 3 (NLRP3) inflammasome activation serves a pivotal role in the pathogenesis of various forms of acute liver injury. However, the cellular source for NLRP3 induction and its involvement during APAP‑induced hepatotoxicity have not been thoroughly investigated. In the present study, hematoxylin and eosin staining was performed to assess histopathological changes of liver tissue. Immunohistochemistry staining(NLRP3, Caspase‑1, IL‑1β, GSDMD and Caspase‑3), western blotting (NLRP3, Caspase‑1, IL‑1β, GSDMD and Caspase‑3) and RT‑qPCR (NLRP3, Caspase‑1 and IL‑1β) were performed to assess the expression of NLRP3/GSDMD signaling pathway. TUNEL staining was performed to assess apoptosis of liver tissue. The serum expression levels of inflammatory factors (IL‑6, IL‑18, IL‑1β and TNF‑α) were assessed using ELISA and inflammation of liver tissue was assessed using immunohistochemistry (Ly6G and CD68) and RT‑qPCR (TNF‑α, Il‑6, Mcp‑1, Cxcl‑1, Cxcl‑2). A Cell Counting Kit‑8 was performed to assess cell viability and apoptosis. Protein and gene expression were analyzed by western blotting (PCNA, CCND1) and RT‑qPCR (CyclinA2, CyclinD1 and CyclinE1). Through investigation of an APAP‑induced acute liver injury model (AILI), the present study demonstrated that APAP overdose induced activation of NLRP3 and cleavage of gasdermin D (GSDMD) in hepatocytes, both in vivo and in vitro. Additionally, mice with hepatocyte‑specific knockout of Nlrp3 exhibited reduced liver injury and lower mortality following APAP intervention, accompanied by decreased infiltration of inflammatory cells and attenuated inflammatory response. Furthermore, pharmacological blockade of NLRP3/GSDMD signaling using MCC950 or disulfiram significantly ameliorated liver injury and reduced hepatocyte death. Notably, hepatocyte Nlrp3 deficiency promoted liver recovery by enhancing hepatocyte proliferation. Collectively, the present study demonstrated that inhibition of the NLRP3 inflammasome protects against APAP‑induced acute liver injury by reducing hepatocyte pyroptosis and suggests that targeting NLRP3 may hold therapeutic potential for treating AILI.

AIM2 regulates autophagy to mitigate oxidative stress in aged mice with acute liver injury

The cytoplasmic pattern recognition receptor, absent in melanoma 2 (AIM2), detects cytosolic DNA, activating the inflammasome and resulting in pro-inflammatory cytokine production and pyroptotic cell death. Recent research has illuminated AIM2's contributions to PANoptosis and host defense. However, the role of AIM2 in acetaminophen (APAP)-induced hepatoxicity remains enigmatic. In this study, we unveil AIM2's novel function as a negative regulator in the pathogenesis of APAP-induced liver damage in aged mice, independently of inflammasome activation. AIM2-deficient aged mice exhibited heightened lipid accumulation and hepatic triglycerides in comparison to their wild-type counterparts. Strikingly, AIM2 knockout mice subjected to APAP overdose demonstrated intensified liver injury, compromised mitochondrial stability, exacerbated glutathione depletion, diminished autophagy, and elevated levels of phosphorylated c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, our investigation revealed AIM2's mitochondrial localization; its overexpression in mouse hepatocytes amplified autophagy while dampening JNK phosphorylation. Notably, induction of autophagy through rapamycin administration mitigated serum alanine aminotransferase levels and reduced the necrotic liver area in AIM2-deficient aged mice following APAP overdose. Mechanistically, AIM2 deficiency exacerbated APAP-induced acute liver damage and inflammation in aged mice by intensifying oxidative stress and augmenting the phosphorylation of JNK and ERK. Given its regulatory role in autophagy and lipid peroxidation, AIM2 emerges as a promising therapeutic target for age-related acute liver damage treatment.

TLR9-independent CD8+ T cell responses in hepatic AAV gene transfer through IL-1R1-MyD88 signaling

Upon viral infection of the liver, CD8+ T cell responses may be triggered despite the immune suppressive properties that manifest in this organ. We sought to identify pathways that activate responses to a neoantigen expressed in hepatocytes, using adeno-associated viral (AAV) gene transfer. It was previously established that cooperation between plasmacytoid dendritic cells (pDCs), which sense AAV genomes by Toll-like receptor 9 (TLR9), and conventional DCs promotes cross-priming of capsid-specific CD8+ T cells. Surprisingly, we find local initiation of a CD8+ T cell response against antigen expressed in ∼20% of murine hepatocytes, independent of TLR9 or type I interferons and instead relying on IL-1 receptor 1-MyD88 signaling. Both IL-1α and IL-1β contribute to this response, which can be blunted by IL-1 blockade. Upon AAV administration, IL-1-producing pDCs infiltrate the liver and co-cluster with XCR1+ DCs, CD8+ T cells, and Kupffer cells. Analogous events were observed following coagulation factor VIII gene transfer in hemophilia A mice. Therefore, pDCs have alternative means of promoting anti-viral T cell responses and participate in intrahepatic immune cell networks similar to those that form in lymphoid organs. Combined TLR9 and IL-1 blockade may broadly prevent CD8+ T responses against AAV capsid and transgene product.

The oral administration of Lacticaseibacillus casei Shirota alleviates acetaminophen-induced liver injury through accelerated acetaminophen metabolism via the liver-gut axis in mice

Acetaminophen is a widely used antipyretic and analgesic drug, and its overdose is the leading cause of drug-induced acute liver failure. This study aimed to investigate the effect and mechanism of Lacticaseibacillus casei Shirota (LcS), an extensively used and highly studied probiotic, on acetaminophen-induced acute liver injury. C57BL/6 mice were gavaged with LcS suspension or saline once daily for 7 days before acute liver injury was induced via intraperitoneal injection of 300 mg/kg acetaminophen. The results showed that LcS significantly decreased acetaminophen-induced liver and ileum injury, as demonstrated by reductions in the increases in aspartate aminotransferase, total bile acids, total bilirubin, indirect bilirubin, and hepatic cell necrosis. Moreover, LcS alleviated acetaminophen-induced intestinal mucosal permeability, decreased serum IL-1α and lipopolysaccharide levels, and elevated serum eosinophil chemokine (eotaxin) and hepatic glutathione levels. Furthermore, analysis of the gut microbiota and metabolome showed that LcS reduced the acetaminophen-enriched levels of Cyanobacteria, Oxyphotobacteria, long-chain fatty acids, cholesterol, and sugars in the gut. Additionally, the transcriptomic and proteomic results showed that LcS mitigated the decrease in metabolic and immune pathways as well as glutathione formation during acetaminophen-induced acute liver injury. This is the first study showing that pretreatment with LcS alleviates acetaminophen-enriched acute liver injury, and it provides a reference for the application of LcS.IMPORTANCEAcetaminophen is the most frequently used antipyretic analgesic worldwide. As a result, overdoses easily occur and lead to drug-induced acute liver injury, which quickly progresses to liver failure with a mortality of 60%-80% if not corrected in time. The current emergency treatment for overused acetaminophen needs to be administered within 8 hours to avoid liver injury or even liver failure. Therefore, developing preventive strategies for liver injury during planned acetaminophen medication is particularly important, preferably nonpharmacological methods. Lacticaseibacillus casei Shirota (LcS) is a famous probiotic that has been used for many years. Our study found that LcS significantly alleviated acetaminophen-induced acute liver injury, especially acetaminophen-induced liver injury toward fulminant hepatic failure. Here, we elucidated the function and potential mechanisms of LcS in alleviating acetaminophen-induced acute liver injury, hoping it will provide preventive strategies to people during acetaminophen treatment.

Acetaminophen Hepatotoxicity: Paradigm for Understanding Mechanisms of Drug-Induced Liver Injury

Acetaminophen (APAP) overdose is the clinically most relevant drug hepatotoxicity in western countries, and, because of translational relevance of animal models, APAP is mechanistically the most studied drug. This review covers intracellular signaling events starting with drug metabolism and the central role of mitochondrial dysfunction involving oxidant stress and peroxynitrite. Mitochondria-derived endonucleases trigger nuclear DNA fragmentation, the point of no return for cell death. In addition, adaptive mechanisms that limit cell death are discussed including autophagy, mitochondrial morphology changes, and biogenesis. Extensive evidence supports oncotic necrosis as the mode of cell death; however, a partial overlap with signaling events of apoptosis, ferroptosis, and pyroptosis is the basis for controversial discussions. Furthermore, an update on sterile inflammation in injury and repair with activation of Kupffer cells, monocyte-derived macrophages, and neutrophils is provided. Understanding these mechanisms of cell death led to discovery of N-acetylcysteine and recently fomepizole as effective antidotes against APAP toxicity.

Ethyl gallate concurrent administration protects against acetaminophen-induced acute liver injury in mice: An in vivo and in silico approach

Acetaminophen (APAP) in high doses causes acute liver injury and acute liver failure. Ethyl gallate (EG) is a natural polyphenol, possessing antioxidant, anti-inflammatory, and anti-microbial properties. Therefore, in this study, we evaluated the protective role of EG against APAP-induced acute liver injury in mice. Acute liver injury was induced by a single dose of APAP (400 mg/kg., i.p.). In separate groups, EG (10 mg/kg), EG (20 mg/kg), and N-acetylcysteine (NAC; 1200 mg/kg., i.p.) were administered concurrently with APAP. The mice were sacrificed after 24 h of treatment. Liver marker enzymes of hepatotoxicity, antioxidant markers, inflammatory markers, and histopathological studies were done. APAP administration caused a significant elevation of marker enzymes of hepatotoxicity and lipid peroxidation. APAP administration also decreased enzymic and nonenzymic antioxidants. Acute APAP intoxication induced nuclear factor κ B, tumor necrosis factor-α, interleukin-1, p65, and p52 and downregulated IκB gene expressions. Our histopathological studies have confirmed the presence of centrilobular necrosis, 24 h after APAP intoxication. All the above abnormalities were significantly inhibited in groups of mice that were concurrently administered with APAP + EG and APAP + NAC. Our in silico analysis further confirms that hydroxyl groups of EG interact with the above inflammatory proteins at the 3,4,5-trihydroxybenzoic acid region. These effects of EG against APAP-induced acute liver injury could be attributed to its antioxidative, free radical scavenging, and anti-inflammatory potentials. Therefore, this study suggests that EG can be an efficient therapeutic approach to protect the liver from APAP intoxication.

Therapeutic modulation of the liver immune microenvironment

Inflammation is a hallmark of progressive liver diseases such as chronic viral or immune-mediated hepatitis, alcohol-associated liver disease, and NAFLD. Preclinical and clinical studies have provided robust evidence that cytokines and related cellular stress sensors in innate and adaptive immunity orchestrate hepatic disease processes. Unresolved inflammation and liver injury result in hepatic scarring, fibrosis, and cirrhosis, which may culminate in HCC. Liver diseases are accompanied by gut dysbiosis and a bloom of pathobionts, fueling hepatic inflammation. Anti-inflammatory strategies are extensively used to treat human immune-mediated conditions beyond the liver, while evidence for immunomodulatory therapies and cell therapy-based strategies in liver diseases is only emerging. The development and establishment of novel immunomodulatory therapies for chronic liver diseases has been dampened by several clinical challenges, such as invasive monitoring of therapeutic efficacy with liver biopsy in clinical trials and risk of DILI in several studies. Such aspects prevented advancements of novel medical therapies for chronic inflammatory liver diseases. New concepts modulating the liver immune environment are studied and eagerly awaited to improve the management of chronic liver diseases in the future.

Neutrophils exacerbate acetaminophen-induced liver injury by producing cytotoxic interferon-γ

BACKGROUND

Drug (e.g., acetaminophen, APAP)-associated hepatotoxicity is the major cause of acute liver failure. Emerging evidence shows that initial tissue damage caused by APAP triggers molecular and cellular immune responses, which can modulate the severity of hepatoxicity. The pro-inflammatory and cytotoxic cytokine interferon (IFN)-γ has been reported as a key molecule contributing to APAP-induced liver injury (AILI). However, its cellular source remains undetermined.

RESULTS

In the current study, we show that elevation of serum IFN-γ in patients with drug hepatotoxicity correlates with disease severity. Neutralization of IFN-γ in a mouse model of AILI effectively reduces hepatotoxicity. Strikingly, we reveal that IFN-γ is expressed primarily by hepatic neutrophils, not by conventional immune cells with known IFN-γ-producing capability, e.g., CD8+ T cells, CD4+ T cells, natural killer cells, or natural killer T cells. Upon encountering APAP-injured hepatocytes, neutrophils secrete cytotoxic IFN-γ further causing cell stress and damage, which can be abrogated in the presence of blocking antibodies for IFN-γ or IFN-γreceptor. Furthermore, removal of neutrophils in vivo substantially decreases hepatic IFN-γ levels concomitantly with reduced APAP hepatotoxicity, whereas adoptive transfer of IFN-γ-producing neutrophils confers IFN-γ-/- mice susceptibility to APAP administration.

CONCLUSIONS

Our findings uncover a novel mechanism of neutrophil action in promoting AILI and provide new insights into immune modulation of the disease pathogenesis.

Leonurine alleviates acetaminophen-induced acute liver injury by regulating the PI3K/AKT signaling pathway in mice

Leonurine (Leo) is a natural alkaloid isolated from the herb Leonurus japonicus Houtt. (Leonuri) that has been shown to inhibit oxidative stress and inflammation. However, the role and mechanism of Leo in acetaminophen (APAP)-induced acute liver injury (ALI) remain unknown. In this study, we investigated the protective effect of Leo against APAP-induced ALI and elucidated the molecular mechanism. Here, we showed that the damage to mouse primary hepatocytes (MPHs) induced by APAP was attenuated by treatment with Leo, which promoted proliferation and inhibited oxidative stress injury, and Leo significantly improved APAP-induced ALI in mice. Leo could protect against APAP-induced ALI by reducing serum aspartate aminotransferase (AST) and alanine transaminase (ALT) levels, hepatic histopathological damage, liver cell necrosis, inflammation, and oxidative stress-induced damage in vivo and in vitro. Moreover, the results indicated that Leo relieved APAP-induced liver cell necrosis by reducing the expression of Bax and cleaved caspase-3 and increasing Bcl-2 expression. Leo alleviated APAP-induced oxidative stress-induced damage by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, which facilitated Nrf2 nuclear translocation and upregulated oxidative stress-related protein expression in liver tissues. Moreover, the results suggested that APAP-induced inflammation in the liver was suppressed by Leo by suppressing the Toll-like receptor 4 (TLR4) and NLR family pyrin domain containing 3 (NLRP3) pathways. In addition, Leo facilitated the activation of the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway in the liver tissue of ALI mice. Network pharmacology, molecular docking, and western blotting showed that PI3K was a potential target of Leo in the treatment of ALI. Molecular docking and cellular thermal shift assay (CETSA) indicated that Leo could stably bind to the PI3K protein. In conclusion, Leo attenuated ALI, and reversed liver cell necrosis, the inflammatory response and oxidative stress-induced damage by regulating the PI3K/AKT signaling pathway.

Celastrol-loaded biomimetic nanodrug ameliorates APAP-induced liver injury through modulating macrophage polarization

Drug-induced liver injury (DILI) is a major concern in clinical treatment as well as postmarketing surveillance, showing an urgent requirement for the development of protective medications. Celastrol (Cel), a highly active natural product extracted from the roots of Tripterygium wilfordii, has a potential liver protective activity due to its antioxidant and anti-inflammatory effects. However, the further application of Cel to DILI remains a challenge because of its short half-life, low solubility, and toxic side effects. Herein, we developed a Cel-loaded biomimetic nanodrug based on erythrocyte membrane vesicles (EMV) for protecting the liver from acetaminophen (APAP)-induced liver injury. The Cel-loaded EMV (C-EMV) with lower cytotoxicity had a well-sustained release effect and exhibited excellent ability for liver accumulation under physiological and pathological conditions. By suppressing the inflammatory response of pro-inflammatory macrophage M1 polarization while stimulating anti-inflammatory macrophage M2 polarization, C-EMV could significantly alleviate the primary pathological manifestations related to liver injury, including aberrant elevation of biochemical indicators, histopathological alterations, neutrophil infiltration as well as hepatocyte DNA fragmentation. The macrophage depletion experiment further demonstrated that the protective effect of C-EMV on APAP-induced liver injury appeared to be dependent on hepatic macrophages. Therefore, C-EMV as a biomimetic nanodrug exhibits great potential for attenuating the progress of DILI, providing a new approach to protecting the liver from DILI as well as other liver inflammatory diseases through a targeted nanodelivery system. KEY MESSAGES: EMV biomimetic nanocarrier has good monodispersity and sustained-release property. EMV biomimetic nanocarrier displays excellent liver-targeting capability under physiological and pathological conditions. C-EMV biomimetic nanodrug with lower cytotoxicity regulates macrophage polarization in vitro and in vivo. C-EMV biomimetic nanodrug can significantly alleviate APAP-induced liver injury. The protective effect of C-EMV on APAP-induced liver injury is dependent on hepatic macrophages.

Dose-dependent pleiotropic role of neutrophils during acetaminophen-induced liver injury in male and female mice

Acetaminophen (APAP) overdose is the leading cause of acute liver failure in western countries. APAP can cause extensive hepatocellular necrosis, which triggers an inflammatory response involving neutrophil and monocyte recruitment. Particularly the role of neutrophils in the injury mechanism of APAP hepatotoxicity has been highly controversial. Thus, the objective of the current study was to assess whether a potential contribution of neutrophils was dependent on the APAP dose and the sex of the animals. Male and female C57BL/6 J mice were treated with 300 or 600 mg/kg APAP and the injury and inflammatory cell recruitment was evaluated between 6 and 48 h. In both male and female mice, ALT plasma levels and the areas of necrosis peaked at 12-24 h after both doses with more severe injury at the higher dose. In addition, Ly6g-positive neutrophils started to accumulate in the liver at 6 h and peaked at 6-12 h after 300 mg/kg and 12-24 h after 600 mg/kg for both sexes; however, the absolute numbers of hepatic neutrophils in the liver were significantly higher after the 600 mg/kg dose. Neutrophil infiltration correlated with mRNA levels of the neutrophil chemoattractant Cxcl2 in the liver. Treating mice with an anti-Cxcl2 antibody at 2 h after APAP significantly reduced neutrophil accumulation at 24 h after both doses and in both sexes. However, the injury was significantly reduced only after the high overdose. Thus, neutrophils, recruited through Cxcl2, have no effect on APAP-induced liver injury after 300 mg/kg but aggravate the injury only after severe overdoses.

Temporal analysis of paracetamol-induced hepatotoxicity

Paracetamol-induced hepatotoxicity (APAP) causes severe damage that may be irreversible. Understanding the evolution of liver injury caused by overdose of the drug is important to assist in the treatment. In the present study, we evaluated the acute intoxication by APAP (500 mg/kg) in periods of 3 and 12 hours in C57BL/6 mice through biochemical, histological, inflammatory parameters, and the redox status. The results showed that in the 3-hour period there was an increase in creatinine dosage and lipid peroxidation (TBARS) compared to the control group. In the period of 12 hours after APAP intoxication all parameters evaluated were altered; there was an increase of ALT, AST, and necrosis, besides the increase of redox status biomarkers as carbonylated protein, TBARS, and MMP-9. We also observed activation of the inflammasome pathway as well as a reduction in the regenerative capacity of hepatocytes with a decrease in binucleated liver cells. In cytochrome gene expression, the mRNA level increased in CYP2E1 isoenzyme and reduced CYP1A2 expression. This study indicated that early treatment is necessary to mitigate APAP-induced acute liver injury, and alternative therapies capable of controlling the progression of intoxication in the liver are needed.

IL-33/ST2 antagonizes STING signal transduction via autophagy in response to acetaminophen-mediated toxicological immunity

BACKGROUND

Interleukin-33 (IL-33), defined as "alarming", exert diverse functions through signaling via the suppression of tumorigenicity 2 (ST2). However, the physiological roles of IL-33/ST2 signaling during acetaminophen (APAP)-induced liver injury are still poorly understood by modern medicine (AILI). This research aims to explore the relationship between IL-33/ST2 and stimulator of interferon (IFN) response cGAMP interactor 1 (STING)-mediated signal transduction.

METHODS

C57BL/6N mice (WT) and IL-33-deficient mice (KO) were intraperitoneally injected with APAP (250 mg/kg). Recombinant IL-33 (500 ng/mouse) and the cGAS/STING inhibitor RU.521 (200 g/kg) were combined to treat AILI. For mechanistic research in vitro, CRISPR-mediated KD technology, immunoprecipitation, mass spectrometry, and immunofluorescence were utilized.

RESULTS

We discovered that IL-33 deficient mice had increased APAP-induced hepatotoxicity, DNA accumulation, and type 1 IFN production. Mechanistic analysis revealed that IL-33/ST2 enhanced the interaction between Beclin-1 and STING, disrupting STING dimerization, IRF3 phosphorylation, nuclear transport, and IFN-1 gene transcription in HepaRG and Huh7 cells. Beclin-1 interacted with the C-terminus of STING, causing Lys338 acetylation and autophagy degradation of STING. ST2 depletion increased STING signal transduction and IFN-1 promoter activity. Surprisingly, the cGAS/STING inhibitor RU.521 and recombinant IL-33 together improved AILI in vivo.

CONCLUSIONS

These results shed insight on the potential of inhibiting cGAS/STING as a therapy for AILI and emphasize the crucial role of IL-33/ST2 signaling in the regulation of APAP-induced STING signaling. Video Abstract.

Retracted and Republished from: "Gut Microbiota Mediates the Therapeutic Effect of Monoclonal Anti-TLR4 Antibody on Acetaminophen-Induced Acute Liver Injury in Mice"

Acetaminophen (APAP) overdose is one of the most common causes of acute liver injury (ALI) in Western countries. Many studies have shown that the gut microbiota plays an important role in liver injury. Currently, the only approved treatment for APAP-induced ALI is N-acetylcysteine; therefore, it is essential to develop new therapeutic agents and explore the underlying mechanisms. We developed a novel monoclonal anti-Toll-like receptor 4 (TLR4) antibody (ATAB) and hypothesized that it has therapeutic effects on APAP-induced ALI and that the gut microbiota may be involved in the underlying mechanism of ATAB treatment. Male C57BL/6 mice were treated with APAP and ATAB, which produced a therapeutic effect on ALI and altered the members of the gut microbiota and their metabolic pathways, such as Roseburia, Lactobacillus, Akkermansia, and the fatty acid pathway, etc. Furthermore, we verified that purified short-chain fatty acids (SCFAs) could alleviate ALI. Moreover, a separate group of mice that received feces from the ATAB group showed less severe liver injury than mice that received feces from the APAP group. ATAB therapy also improved gut barrier functions in mice and reduced the expression of the protein zonulin. Our results revealed that the gut microbiota plays an important role in the therapeutic effect of ATAB on APAP-induced ALI. IMPORTANCE In this study, we found that a monoclonal anti-Toll-like receptor 4 antibody can alleviate APAP-induced acute liver injury through changes in the gut microbiota, metabolic pathways, and gut barrier function. This work suggested that the gut microbiota can be a therapeutic target of APAP-induced acute liver injury, and we performed foundation for further research.

Sterile liver injury induces a protective tissue-resident cDC1-ILC1 circuit through cDC1-intrinsic cGAS-STING-dependent IL-12 production

Tissue-resident immune cells are critical to the initiation and potentiation of inflammation. However, the tissue-protective cellular communication networks initiated by resident immunity during sterile inflammation are not well understood. Using single-cell transcriptomic analysis, we show the liver-resident cell connectome and signalome during acute liver injury. These analyses identify Il12b as a central regulator of liver injury-associated changes in gene expression. Interleukin (IL)-12 produced by conventional type 1 dendritic cells (cDC1s) is required for protection during acute injury through activation of interferon (IFN)-γ production by liver-resident type 1 innate lymphoid cells (ILC1s). Using a targeted in vivo CRISPR-Cas9 screen of innate immune sensing pathways, we find that cDC1-intrinsic cGAS-STING signaling acts upstream of IL-12 production to initiate early protective immune responses. Our study identifies the core communication hubs initiated by tissue-resident innate immune cells during sterile inflammation in vivo and implicates cDC1-derived IL-12 as an important regulator of this process.

Role of NADPH Oxidase-Derived ROS-Mediated IL-6/STAT3 and MAPK/NF-κB Signaling Pathways in Protective Effect of Corilagin against Acetaminophen-Induced Liver Injury in Mice

Acetaminophen (APAP) overdose causes acute liver injury via oxidative stress, uncontrolled inflammatory response, and subsequent hepatocyte death. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is a potent source of cellular reactive oxygen species (ROS) and may contribute to oxidative stress in many inflammatory processes. Corilagin, a component of Phyllanthus urinaria, possesses antioxidant, anti-inflammatory, and hepatoprotective effects. We evaluated the mechanisms underlying the protective effect of corilagin against acetaminophen-induced liver injury. Mice were intraperitoneally administrated 300 mg/kg APAP or equal volume of saline (control), with or without various concentrations of corilagin (0, 1, 5, or 10 mg/kg) administered after 30 min. All animals were sacrificed 16 h after APAP administration, and serum and liver tissue assays including histology, immunohistochemistry, and Western blot assay were performed. Corilagin post-treatment significantly attenuated APAP-induced liver injury (p < 0.005), inflammatory cell infiltration, hepatic proinflammatory cytokine levels, and hepatic oxidative stress. Furthermore, corilagin attenuated the protein levels of NOX1, NOX2, signal transducer and activator of transcription 3 (STAT3), and nuclear factor kappa B (NF-κB) in APAP-induced liver injury. These results indicated that the antioxidant, anti-inflammatory, and protective effects of corilagin in APAP-induced liver injury might involve the regulation of interleukin (IL)-6/STAT3 and mitogen-activated protein kinase (MAPK)/NF-κB signaling pathways through NOX-derived ROS.

Role of Pyroptosis in Acetaminophen-Induced Hepatotoxicity

Acetaminophen (APAP) is a widely used pain reliever that can cause liver injury or liver failure in response to an overdose. Understanding the mechanisms of APAP-induced cell death is critical for identifying new therapeutic targets. In this respect it was hypothesized that hepatocytes die by oncotic necrosis, apoptosis, necroptosis, ferroptosis and more recently pyroptosis. The latter cell death is characterized by caspase-dependent gasdermin cleavage into a C-terminal and an N-terminal fragment, which forms pores in the plasma membrane. The gasdermin pores can release potassium, interleukin-1β (IL-1β), IL-18, and other small molecules in a sublytic phase, which can be the main function of the pores in certain cell types such as inflammatory cells. Alternatively, the process can progress to full lysis of the cell (pyroptosis) with extensive cell contents release. This review discusses the experimental evidence for the involvement of pyroptosis in APAP hepatotoxicity as well as the arguments against pyroptosis as a relevant mechanism of APAP-induced cell death in hepatocytes. Based on the critical evaluation of the currently available literature and understanding of the pathophysiology, it can be concluded that pyroptotic cell death is unlikely to be a relevant contributor to APAP-induced liver injury.

Generation of pro-and anti-inflammatory mediators after acetaminophen overdose in surviving and non-surviving patients

Acetaminophen (APAP) overdose causes liver injury in animals and humans. Although well-studied in animals, limited longitudinal data exist on cytokine release after APAP overdose in patients. The purpose of this study was to quantify concentrations of cytokines in APAP overdose patients to determine if early cytokine or complement measurements can distinguish between surviving and non-surviving patients. Plasma was obtained from healthy controls, APAP overdose patients with no increase in liver transaminases, and surviving and non-surviving APAP overdose patients with severe liver injury. Interleukin-10 (IL-10), and CC chemokine ligand-2 (CCL2, MCP-1) were substantially elevated in surviving and non-surviving patients, whereas IL-6 and CXC chemokine ligand-8 (CXCL8, IL-8) had early elevations in a subset of patients only with liver injury. Day 1 IL-10 and IL-6 levels, and Day 2 CCL2, levels correlated positively with survival. There was no significant increase in IL-1α, IL-1β or TNF-α in any patient during the first week after APAP. Monitoring cytokines such as CCL2 may be a good indicator of patient prognosis; furthermore, these data indicate the inflammatory response after APAP overdose in patients is not mediated by a second phase of inflammation driven by the inflammasome.

Sapidolide A alleviates acetaminophen-induced acute liver injury by inhibiting NLRP3 inflammasome activation in macrophages

Macrophages play a critical role in the pathogenesis of acetaminophen (APAP)-induced liver injury (AILI), a major cause of acute liver failure or even death. Sapidolide A (SA) is a sesquiterpene lactone extracted from Baccaurea ramiflora Lour., a folk medicine used in China to treat inflammatory diseases. In this study, we investigated whether SA exerted protective effects on macrophages, thus alleviated the secondary hepatocyte damage in an AILI. We showed that SA (5-20 μM) suppressed the phosphorylated activation of NF-κB in a dose-dependent manner, thereby inhibiting the expression and activation of the NOD-like receptor protein 3 (NLRP3) inflammasome and pyroptosis in LPS/ATP-treated mouse bone marrow-derived primary macrophages (BMDMs). In human hepatic cell line L02 co-cultured with BMDMs, SA (10 μM) protected macrophages from the pyroptosis induced by APAP-damaged L02 cells. Moreover, SA treatment reduced the secondary liver cell damage aggravated by the conditioned medium (CM) taken from LPS/ATP-treated macrophages. The in vivo assessments conducted on mice pretreated with SA (25, 50 mg/kg, ip) then with a single dose of APAP (400 mg/kg, ip) showed that SA significantly alleviated inflammatory responses of AILI by inhibiting the expression and activation of the NLRP3 inflammasome. In general, the results reported herein revealed that SA exerts anti-inflammatory effects by regulating NLRP3 inflammasome activation in macrophages, which suggests that SA has great a potential for use in the treatment of AILI patients.

Hepatic recruitment of eosinophils and their protective function during acute liver injury

BACKGROUND & AIMS

Beyond the classical description of eosinophil functions in parasite infections and allergic diseases, emerging evidence supports a critical role of eosinophils in resolving inflammation and promoting tissue remodeling. However, the role of eosinophils in liver injury and the underlying mechanism of their recruitment into the liver remain unclear.

METHODS

Hepatic eosinophils were detected and quantified using flow cytometry and immunohistochemical staining. Eosinophil-deficient (ΔdblGata1) mice were used to investigate the role of eosinophils in 3 models of acute liver injury. In vivo experiments using Il33-/- mice and macrophage-depleted mice, as well as in vitro cultures of eosinophils and macrophages, were performed to interrogate the mechanism of eotaxin-2 (CCL24) production.

RESULTS

Hepatic accumulation of eosinophils was observed in patients with acetaminophen (APAP)-induced liver failure, whereas few eosinophils were detectable in healthy liver tissues. In mice treated with APAP, carbon tetrachloride or concanavalin A, eosinophils were recruited into the liver and played a profound protective role. Mice deficient of macrophages or IL-33 exhibited impaired hepatic eosinophil recruitment during acute liver injury. CCL24, but not CCL11, was increased after treatment of each hepatotoxin in an IL-33 and macrophage-dependent manner. In vitro experiments demonstrated that IL-33, by stimulating IL-4 release from eosinophils, promoted the production of CCL24 by macrophages.

CONCLUSIONS

This is the first study to demonstrate that hepatic recruitment of and protection by eosinophils occur commonly in various models of acute liver injury. Our findings support further exploration of eosinophils as a therapeutic target to treat APAP-induced acute liver injury.

LAY SUMMARY

The current study unveils that eosinophils are recruited into the liver and play a protective function during acute liver injury caused by acetaminophen overdose. The data demonstrate that IL-33-activated eosinophils trigger macrophages to release high amounts of CCL24, which promotes hepatic eosinophil recruitment. Our findings suggest that eosinophils could be an effective cell-based therapy for the treatment of acetaminophen-induced acute liver injury.

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.

Gut Microbiota Mediates the Therapeutic Effect of Monoclonal Anti-TLR4 Antibody on Acetaminophen-Induced Acute Liver Injury in Mice

Acetaminophen (APAP) overdose is one of the most common causes of acute liver injury (ALI) in Western countries. Many studies show that the gut microbiota plays an important role in liver injury. Currently, the only approved treatment for APAP-induced ALI is N-acetylcysteine; therefore, it is essential to develop new therapeutic agents and explore the underlying mechanisms. We developed a novel monoclonal anti-Toll-like receptor 4 (TLR4) antibody (ATAB) and hypothesized that it has therapeutic effects on APAP-induced ALI and that gut microbiota may be involved in the underlying mechanism of ATAB treatment. Male C57BL/6 mice were treated with APAP and ATAB, which produced a therapeutic effect on ALI and altered the gut microbiota and their metabolic pathway, such as Roseburia, Lactobacillus, Akkermansia, and the fatty acid pathway, etc. Furthermore, we verified that purified short-chain fatty acids (SCFAs) could alleviate ALI. Moreover, a separate group of mice that received feces from the ATAB group showed less severe liver injury compared with the mice receiving feces from the APAP group. ATAB therapy also improved the gut barrier functions in mice and reduced the expression of protein zonulin. Our results revealed that gut microbiota plays an important role in the therapeutic effect of ATAB on APAP-induced ALI. IMPORTANCE In this study, we found the monoclonal anti-Toll-like receptor 4 antibody can alleviate APAP-induced acute liver injury through the change of the gut microbiota, metabolic pathways, and gut barrier function. This work suggested the gut microbiota can be the therapeutic target of the APAP-induced acute liver injury, and we performed the fundamental research for further research.

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.

Roles of heterogenous hepatic macrophages in the progression of liver diseases

Hepatic macrophages are key immune cells associated with the broad ranges of liver diseases including steatosis, inflammation and fibrosis. Hepatic macrophages interact with other immune cells and orchestrate hepatic immune circumstances. Recently, the heterogenous populations of hepatic macrophages have been discovered termed residential Kupffer cells and monocyte-derived macrophages, and identified their distinct population dynamics during the progression of various liver diseases. Liver injury lead to Kupffer cells activation with induction of inflammatory cytokines and chemokines, which triggers recruitment of inflammatory monocyte-derived macrophages. To understand liver pathology, the functions of different subtypes of liver macrophages should be regarded with different perspectives. In this review, we summarize recent advances in the roles of hepatic macrophages under liver damages and suggest hepatic macrophages as promising therapeutic targets for treating liver diseases.

Molecular pathogenesis of acetaminophen-induced liver injury and its treatment options

Acetaminophen, also known as N-acetyl-p-aminophenol (APAP), is commonly used as an antipyretic and analgesic agent. APAP overdose can induce hepatic toxicity, known as acetaminophen-induced liver injury (AILI). However, therapeutic doses of APAP can also induce AILI in patients with excessive alcohol intake or who are fasting. Hence, there is a need to understand the potential pathological mechanisms underlying AILI. In this review, we summarize three main mechanisms involved in the pathogenesis of AILI: hepatocyte necrosis, sterile inflammation, and hepatocyte regeneration. The relevant factors are elucidated and discussed. For instance, N-acetyl-p-benzoquinone imine (NAPQI) protein adducts trigger mitochondrial oxidative/nitrosative stress during hepatocyte necrosis, danger-associated molecular patterns (DAMPs) are released to elicit sterile inflammation, and certain growth factors contribute to liver regeneration. Finally, we describe the current potential treatment options for AILI patients and promising novel strategies available to researchers and pharmacists. This review provides a clearer understanding of AILI-related mechanisms to guide drug screening and selection for the clinical treatment of AILI patients in the future.

Imatinib-induced hepatotoxicity via oxidative stress and activation of NLRP3 inflammasome: an in vitro and in vivo study

Imatinib (IM), a milestone drug used in the field of molecular targeted therapy, has been reported to cause serious adverse liver effects, including liver failure and even death. Immune-mediated injury and mitochondrial dysfunction are involved in drug-induced liver injury. However, the mechanism of IM-induced hepatotoxicity remains unclear and warrants further study. In our study, Sprague Dawley rats were administered IM by gavage with 50 mg/kg body weight (BW) once daily for 10 days. Drug-induced liver injury accompanied by inflammatory infiltration was observed in rats following IM exposure, and the expression of NOD-like receptor protein 3 (NLRP3) inflammasome-related proteins was significantly increased compared with that of the control. HepG2 cells were exposed to 0-100 μM IM for 24 h. The results showed that IM decreased cell viability in a dose-dependent manner. Moreover, IM induced a state of obvious oxidative stress and activation of nuclear factor kappa B (NF-κB) in cells, which resulted in the activation of NLRP3 inflammasomes, including caspase 1 cleavage and IL-1β release. These results were significantly reduced after the use of the antioxidants N-acetyl-l-cysteine or the NF-κB inhibitor pyrrolidine di-thio-carbamate. Furthermore, NLRP3 knockdown significantly reduced the release of inflammatory cytokines and improved cell viability. In summary, our data demonstrated that oxidative stress and NLRP3 inflammasome activation are involved in the process of IM-induced hepatotoxicity. The results of this study provide a reference for the prevention and treatment of IM-induced hepatotoxicity.

Anti-inflammatory effects of the immobilization of SEMA4D on titanium surfaces in an endothelial cell/macrophage indirect coculture model

In this study, we established a procedure to prepare a Semaphorin4D (SEMA4D)-immobilized titanium surface and explored its effects on macrophage behaviors in an endothelial cell/macrophage indirect coculture model. The SEMA4D-bovine serum albumin complex was immobilized onto a preprocessed poly L-lysine titanium surface through NaOH hydrothermal treatment and self-assembly technology. All titanium specimens were examined for surface microstructure, surface element composition, and surface wettability by field emission scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and water contact angle measurement, respectively. Subsequently, we constructed an endothelial cell/macrophage indirect coculture model and evaluated the activation of NF-κB signaling pathway and the expression of proinflammatory cytokines (TNFα, IL-6, and IL-1β) in macrophages. In XPS analysis, the SEMA4D-immobilized titanium surface appeared as a loose porous structure covered with uniform film, which exhibited better hydrophilicity than the control smooth titanium surface. In the indirect coculture model, SEMA4D attenuated the activation of NF-κB signaling pathway of lipopolysaccharide-stimulated THP-1 macrophages, thereby downregulating the expression of proinflammatory cytokines in macrophages. In conclusion, SEMA4D could be immobilized on titanium surfaces through NaOH hydrothermal treatment and self-assembly technology. Meanwhile, SEMA4D immobilization altered the characteristics of the titanium surfaces, which negatively regulated macrophage behaviors in the endothelial cell/macrophage indirect coculture model.

CD5L deficiency attenuate acetaminophen-induced liver damage in mice via regulation of JNK and ERK signaling pathway

CD5 molecule like (CD5L), a member of the scavenger receptor cysteine-rich domain superfamily, plays a critical role in immune homeostasis and inflammatory disease. Acetaminophen (APAP) is a safe and effective antipyretic analgesic. However, overdose may cause liver damage or even liver failure. APAP hepatotoxicity is characterized by extensive necrotic cell death and a sterile inflammatory response, in which the role of CD5L remains to be investigated. In this study, we found that the expression of CD5L was increased in the livers of mice after APAP overdose. Furthermore, CD5L deficiency reduced the increase of alanine transaminase (ALT) level, histopathologic lesion area, c-Jun N-terminal kinase (JNK)/extracellular signal-regulated kinase (ERK) phosphorylation level, Transferase-Mediated dUTP Nick End-Labeling positive (TUNEL⁺) cells proportion, vascular endothelial cell permeability and release of inflammatory cytokines induced by excess APAP. Therefore, our findings reveal that CD5L may be a potential therapeutic target for prevention and treatment of APAP-induced liver injury.

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.

Pyroptosis in Steatohepatitis and Liver Diseases

Pyroptosis is an inflammatory form of regulated cell death, which functions in the clearance of intracellularly replicating pathogens by cell lysis in order to induce further immune response. Since the discovery of the gasdermin (GSDM) family, pyroptosis has attracted attention in a wide range of inflammatory diseases such as nonalcoholic steatohepatitis and other liver diseases. Due to the cleavage of GSDMs by different caspases, the amino-terminal GSDM fragments form membrane pores essential for pyroptosis that facilitate the release of inflammatory cytokines by loss of ionic gradient and membrane rupture. In this review, we address the key molecular and cellular processes that induce pyroptosis in the liver and its significance in the pathogenesis of common liver diseases in different human and experimental mice studies.

Targeting Gut–Liver Axis for Treatment of Liver Fibrosis and Portal Hypertension

Antifibrotic therapies for the treatment of liver fibrosis represent an unconquered area of drug development. The significant involvement of the gut microbiota as a driving force in a multitude of liver disease, be it pathogenesis or fibrotic progression, suggest that targeting the gut–liver axis, relevant signaling pathways, and/or manipulation of the gut’s commensal microbial composition and its metabolites may offer opportunities for biomarker discovery, novel therapies and personalized medicine development. Here, we review potential links between bacterial translocation and deficits of host-microbiome compartmentalization and liver fibrosis that occur in settings of advanced chronic liver disease. We discuss established and emerging therapeutic strategies, translated from our current knowledge of the gut–liver axis, targeted at restoring intestinal eubiosis, ameliorating hepatic fibrosis and rising portal hypertension that characterize and define the course of decompensated cirrhosis.

Omega‑3 polyunsaturated fatty acids inhibit IL‑11/STAT3 signaling in hepatocytes during acetaminophen hepatotoxicity

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert a negative effect on IL-6 production in several liver disorders, including cirrhosis, acute liver failure and fatty liver disease. However, its effect on the production of IL-11, another important IL-6 family cytokine, remains unclear. IL-11 was found to be significantly elevated in acetaminophen (APAP)-induced liver damage. The aim of the present study was to investigate whether and how n-3 PUFAs modulate IL-11 production during APAP-induced liver injury. For that purpose, wild-type (WT) and fat-1 transgenic mice were intraperitoneally injected with APAP to induce liver injury. Serum was collected for ELISA and alanine aminotransferase assay. The hepatocytes of APAP-injected mice were isolated for reverse transcription-quantitative PCR and western blot analyses. For the in vitro study, primary hepatocytes isolated from WT or fat-1 mice were stimulated with APAP. The results revealed that both endogenous and exogenous n-3 PUFAs significantly aggravated APAP-induced liver damage via the downregulation of STAT3 signaling. Notably, n-3 PUFAs inhibited IL-11 expression, but not IL-6 expression in hepatocytes during the APAP challenge. Furthermore, it was demonstrated that limited phosphorylation of ERK1/2 and Fos-like-1 (Fra-1) expression are responsible for the n-3 PUFA-mediated inhibitory effect on IL-11 production in APAP-treated hepatocytes. It was concluded that n-3 PUFAs inhibit IL-11 production and further STAT3 activation in hepatocytes during APAP-induced liver injury. Therefore, ERK1/2-mediated Fra-1 expression is responsible for the effect of n-3 PUFAs on IL-11 expression.

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.

Immune-Mediated Drug-Induced Liver Injury: Immunogenetics and Experimental Models

Drug-induced liver injury (DILI) is a challenging clinical event in medicine, particularly because of its ability to present with a variety of phenotypes including that of autoimmune hepatitis or other immune mediated liver injuries. Limited diagnostic and therapeutic tools are available, mostly because its pathogenesis has remained poorly understood for decades. The recent scientific and technological advancements in genomics and immunology are paving the way for a better understanding of the molecular aspects of DILI. This review provides an updated overview of the genetic predisposition and immunological mechanisms behind the pathogenesis of DILI and presents the state-of-the-art experimental models to study DILI at the pre-clinical level.

Interleukin 33 mediates hepatocyte autophagy and innate immune response in the early phase of acetaminophen-induced acute liver injury

Despite interleukin 33 (IL-33) functions as an "alarmin" released from hepatic dead cells in response to tissue damages, the interrelationship between IL-33-mediated hepatocyte autophagy and innate immune response in the acetaminophen (APAP)-induced liver injury (AILI) process remains obscure. This study aimed to explore the regulation of IL-33 on hepatocyte autophagy and macrophage polarization after APAP challenge in vivo and vitro. We found IL-33 released from hepatic necrosis was elevated in the AILI mouse model. Blockage of IL-33 exacerbated liver injury by consuming liver-resident macrophages cells (Kupffer cells, KCs) and promoting hepatic inflammatory factors secretion, such as TNF-α, IL-6 and IL-1β in the early phase of liver injury. Interestingly, IL-33 deficiency further activated hepatocyte autophagy and disrupted M2 macrophage polarization post-APAP challenge in vivo and vitro, which can be reversed by recombinant IL-33 treatment. Mechanistically, administration of IL-33 can directly enhance M2 polarization via PI3K/Akt signaling pathway and activate protective hepatocyte autophagy via AMPKα/mTOR signaling pathway in the AILI process. In conclusion, our data firstly demonstrates that IL-33 exerts protective effects on hepatocytes through the activation of autophagy and functions as an innate immunity regulator mediating macrophage polarization in the early phase of AILI.

Lycopene alleviates hepatic ischemia reperfusion injury via the Nrf2/HO-1 pathway mediated NLRP3 inflammasome inhibition in Kupffer cells

Background

Lycopene is a naturally occurring carotenoid found in many fruits and vegetables, which has antioxidant effects. Although lycopene’s protective effect has been observed on ischemia reperfusion (IR) injury in different organs, the effect of lycopene on Kupffer cells (KCs) has not been clearly elucidated in IR-induced acute hepatic inflammatory injury.

Methods

Mice were administered with either olive oil (10 mL/kg body weight) as the control or lycopene (20 mg/kg body weight) by gavage for 2 weeks before undergoing hepatic IR injury.

Results

In this study, we observed that the levels of aspartate aminotransferases (AST), alanine aminotransferase (ALT), and the percentages of hepatocellular apoptosis in mice pretreated with lycopene were significantly lower than control mice. Lycopene inhibited F4/80+ macrophage and Ly6G+ neutrophil accumulation, which further decreased the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin 6 (IL-6). Interestingly, lycopene induced increased autophagy in KCs, which was evidenced by elevated autophagosomes and the increased protein level of LC3B. In these KCs, lycopene-induced upregulation of autophagy inhibited NOD-like receptor family pyrin domain-containing 3 protein (NLRP3) inflammasome activation, which was demonstrated by the reduced mRNA and protein levels of NLRP3, cleaved caspase-1, an apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and IL-1β. Furthermore, 3-methyladenine, an autophagy inhibitor, abolished lycopene’s inhibitory effect on the NLRP3 inflammasome in KCs, which led to increased hepatic IR injury. Intriguingly, we identified that the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) were elevated in KCs isolated from IR-stressed mice pretreated with lycopene. Nrf2-siRNA or HO-1-siRNA could block the autophagy activation enhanced by lycopene in KCs, resulting in the activation of the NLRP3 inflammasome and aggravated hepatic IR injury.

Conclusions

Our findings demonstrated that lycopene promoted Nrf2/HO-1 pathway activation and further suppressed the NLRP3 inflammasome via enhancing KC autophagy, which alleviated hepatic IR injury.

Pentoxifylline Can Reduce the Inflammation Caused by LPS after Inhibiting Autophagy in RAW264.7 Macrophage Cells

Pentoxifylline (PTX), as a methylxanthine derivative and nonspecific phosphodiesterase inhibitor, has the characteristics of anti-inflammatory and partial inflammatory process inhibition. However, the regulatory effect of PTX on inflammatory cytokines is unclear. Autophagy can regulate the activation of inflammasomes and then inhibit inflammation as previously described. Our study attempts to explore the relationship between autophagy and PTX-mediated regulation of inflammasome suppression. Macrophage-like RAW264.7 cells were studied as the in vitro macrophage model. We investigated the anti-inflammatory effect caused by PTX with time and dose response against the LPS-induced inflammatory factors (TNF-α, IL-1β). Western blot detected the levels of autophagy-related proteins Beclin-1 and LC3, as well as the signal pathways of AMPK and p-AMPK. Fluorescence microscope and transmission electron microscope were used to observe the autophagy bodies in cells influenced by PTX. The autophagy in cells inhibited by PTX exhibited dose- and time-dependent effects, and PTX alleviated LPS-induced inflammation caused by retarded autophagy. Furthermore, in RAW264.7 macrophage cells, our data indicated that AMPK signaling perhaps functioned importantly in repressed autophagy. In addition, in RAW264.7 macrophages, our data suggested that AMPK signaling might play an important role in inhibiting autophagy during the process of PTX ameliorating LPS-mediated inflammation.

Mapping of Translocator Protein (18 kDa) in Peripheral Sterile Inflammatory Disease and Cancer through PET Imaging

Positron emission tomography (PET) imaging of the translocator 18 kDa protein (TSPO) with radioligands has become an effective means of research in peripheral inflammatory conditions that occur in many diseases and cancers. The peripheral sterile inflammatory diseases (PSIDs) are associated with a diverse group of disorders that comprises numerous enduring insults including the cardiovascular, respiratory, gastrointestinal, or musculoskeletal system. TSPO has recently been introduced as a potential biomarker for peripheral sterile inflammatory diseases (PSIDs). The major critical issue related to PSIDs is its timely characterization and localization of inflammatory foci for proper therapy of patients. As an alternative to metabolic imaging, protein imaging expressed on immune cells after activation is of great importance. The five transmembrane domain translocator protein-18 kDa (TSPO) is upregulated on the mitochondrial cell surface of macrophages during inflammation, serving as a potential ligand for PET tracers. Additionally, the overexpressed TSPO protein has been positively correlated with various tumor malignancies. In view of the association of escalated TSPO expression in both disease conditions, it is an immensely important biomarker for PET imaging in oncology and PSIDs. In this review, we summarize the most outstanding advances on TSPO-targeted PSIDs and cancer in the development of TSPO ligands as a potential diagnostic tool, specifically discussing the last five years.

Cell Death in Liver Diseases: A Review

Regulated cell death (RCD) is pivotal in directing the severity and outcome of liver injury. Hepatocyte cell death is a critical event in the progression of liver disease due to resultant inflammation leading to fibrosis. Apoptosis, necrosis, necroptosis, autophagy, and recently, pyroptosis and ferroptosis, have all been investigated in the pathogenesis of various liver diseases. These cell death subroutines display distinct features, while sharing many similar characteristics with considerable overlap and crosstalk. Multiple types of cell death modes can likely coexist, and the death of different liver cell populations may contribute to liver injury in each type of disease. This review addresses the known signaling cascades in each cell death pathway and its implications in liver disease. In this review, we describe the common findings in each disease model, as well as the controversies and the limitations of current data with a particular focus on cell death-related research in humans and in rodent models of alcoholic liver disease, non-alcoholic fatty liver disease and steatohepatitis (NASH/NAFLD), acetaminophen (APAP)-induced hepatotoxicity, autoimmune hepatitis, cholestatic liver disease, and viral hepatitis.

Immunopathobiology and therapeutic targets related to cytokines in liver diseases

Chronic liver injury with any etiology can progress to fibrosis and the end-stage diseases cirrhosis and hepatocellular carcinoma. The progression of liver disease is controlled by a variety of factors, including liver injury, inflammatory cells, inflammatory mediators, cytokines, and the gut microbiome. In the current review, we discuss recent data on a large number of cytokines that play important roles in regulating liver injury, inflammation, fibrosis, and regeneration, with a focus on interferons and T helper (Th) 1, Th2, Th9, Th17, interleukin (IL)-1 family, IL-6 family, and IL-20 family cytokines. Hepatocytes can also produce certain cytokines (such as IL-7, IL-11, and IL-33), and the functions of these cytokines in the liver are briefly summarized. Several cytokines have great therapeutic potential, and some are currently being tested as therapeutic targets in clinical trials for the treatment of liver diseases, which are also described.

Therapeutic Role of Inducible Nitric Oxide Synthase Expressing Myeloid-Derived Suppressor Cells in Acetaminophen-Induced Murine Liver Failure

Background

Acetaminophen (APAP) overdose is one of the major etiologies of liver failure. Hepatocyte necrosis induced by toxic metabolites of APAP can activate proinflammatory responses, including elastase-expressing neutrophils, to exacerbate liver injury. Myeloid-derived suppressor cells (MDSCs) increased in inflammation can inhibit proinflammatory responses. Our aim is to investigate the role of MDSC in APAP-induced liver failure and the possible therapeutic application.

Methods

BLAB/c mice were injected with a sublethal/lethal dose of APAP as the murine model of liver failure. MDSCs were defined as CD11b⁺Gr-1⁺ cells with the ability of T-cell suppression.

Results

A sublethal challenge of APAP could increase the intrahepatic MDSC and protect mice against subsequent lethal challenge of APAP, lipopolysaccharide (LPS)/D-galatosamine or concanavalin A. This protection was lost if MDSCs were depleted and inducible nitric oxide synthase (iNOS) was the key molecule in this MDSC-mediated protection. Taking advantage of these observations, different bone marrow-derived MDSCs (BM-MDSCs) were generated. Among different cytokine-treated BM-MDSCs, tumor necrosis factor alpha/LPS-primed MDSCs (TNF-α/LPS MDSCs) had the strongest liver-protection ability after adoptive transfer. Further mechanistic explorations showed, iNOS-expressing TNF-α/LPS MDSCs induced the apoptosis of activated neutrophil and decreased the intrahepatic infiltration of elastase-expressing neutrophil. Moreover, we generated MDSCs from human peripheral blood mononuclear cells (PBMCs) with similar phenotype.

Conclusion

We demonstrated the protective role of MDSCs and therapeutic effect of TNF-α/LPS MDSCs in APAP-induced liver failure. MDSC might protect against the APAP-induced liver failure by reducing the intrahepatic infiltration of activated neutrophil to limit inflammation. Therefore, a therapeutic role of MDSCs for APAP-induced liver failure was proposed.

Live Imaging of Innate and Adaptive Immune Responses in the Liver

Immune response in the liver is determined by the spatial organization and cellular dynamics of hepatic immune cells. The liver vasculature accommodates abundant tissue-resident innate immune cells, such as Kupffer cells, natural killer cells, and natural killer T cells, to ensure efficient intravascular immunosurveillance. The fenestrated sinusoids also allow direct contact between circulating T cells and non-canonical antigen-presenting cells, such as hepatocytes, to instruct adaptive immune responses. Distinct cellular behaviors are exploited by liver immune cells to exert proper functions. Intravital imaging enables real-time visualization of individual immune cell in living animals, representing a powerful tool in dissecting the spatiotemporal features of intrahepatic immune cells during steady state and liver diseases. This review summarizes current advances in liver immunology prompted by in vivo imaging, with a particular focus on liver-resident innate immune cells and hepatic T cells.

Hepatic macrophages in liver homeostasis and diseases-diversity, plasticity and therapeutic opportunities

Macrophages, which are key cellular components of the liver, have emerged as essential players in the maintenance of hepatic homeostasis and in injury and repair processes in acute and chronic liver diseases. Upon liver injury, resident Kupffer cells (KCs) sense disturbances in homeostasis, interact with hepatic cell populations and release chemokines to recruit circulating leukocytes, including monocytes, which subsequently differentiate into monocyte-derived macrophages (MoMϕs) in the liver. Both KCs and MoMϕs contribute to both the progression and resolution of tissue inflammation and injury in various liver diseases. The diversity of hepatic macrophage subsets and their plasticity explain their different functional responses in distinct liver diseases. In this review, we highlight novel findings regarding the origins and functions of hepatic macrophages and discuss the potential of targeting macrophages as a therapeutic strategy for liver disease.

T. gondii infection induces IL-1R dependent chronic cachexia and perivascular fibrosis in the liver and skeletal muscle

Cachexia is a progressive muscle wasting disease that contributes to death in a wide range of chronic diseases. Currently, the cachexia field lacks animal models that recapitulate the long-term kinetics of clinical disease, which would provide insight into the pathophysiology of chronic cachexia and a tool to test therapeutics for disease reversal. Toxoplasma gondii (T. gondii) is a protozoan parasite that uses conserved mechanisms to infect rodents and human hosts. Infection is lifelong and has been associated with chronic weight loss and muscle atrophy in mice. We have recently shown that T. gondii-induced muscle atrophy meets the clinical definition of cachexia. Here, the longevity of the T. gondii-induced chronic cachexia model revealed that cachectic mice develop perivascular fibrosis in major metabolic organs, including the adipose tissue, skeletal muscle, and liver by 9 weeks post-infection. Development of cachexia, as well as liver and skeletal muscle fibrosis, is dependent on intact signaling through the type I IL-1R receptor. IL-1α is sufficient to activate cultured fibroblasts and primary hepatic stellate cells (myofibroblast precursors in the liver) in vitro, and IL-1α is elevated in the sera and liver of cachectic, suggesting a mechanism by which chronic IL-1R signaling could be leading to cachexia-associated fibrosis.

Capsaicin alleviates acetaminophen-induced acute liver injury in mice

Overdose of N-acetyl-para-aminophenol (APAP) can induce acute liver injury (ALI). We evaluated the potential protective effect of 8-methyl-N-geranyl-6-nonamide (capsaicin (CAP)) in APAP-induced ALI in mice. ALI was induced by APAP (150 mg/kg, i.p.) administration; CAP pretreatment (1 mg/kg) was undertaken before APAP injection for 3 consecutive days. We found that CAP pretreatment attenuated ALI significantly; improve the oxidative stress-associated indicators (hepatic expression of malondialdehyde (MDA) superoxide dismutase (SOD) and glutathione (GSH)); downregulate expression of proinflammatory cytokines (interleukin (IL)-6, IL-1β, tumor necrosis factor-α) through the high-mobility group box 1/toll-like receptor-4/nuclear factor-kappa B (HMGB1/TLR4/NF-κB) signaling pathway; alleviate hepatocyte apoptosis by inhibiting expression of B-cell lymphoma-2-associated X, caspase-3 and cleaved caspase-3. CAP pretreatment reduced expression of B-cell lymphoma-2, which served as a hepatotoxic factor rather than an anti-apoptotic protein in our mouse model. We propose that CAP can alleviate APAP-induced ALI by inhibiting the inflammatory response, attenuating oxidative stress, and reducing hepatocyte apoptosis.

Activation of Farnesoid X Receptor by Schaftoside Ameliorates Acetaminophen-Induced Hepatotoxicity by Modulating Oxidative Stress and Inflammation

Aims: Acetaminophen (APAP) overdose leads to acute liver injury by inducing hepatic mitochondrial oxidative stress and inflammation. However, the molecular mechanisms involved are still unclear. Farnesoid X receptor (FXR) serves as a therapeutic target for the treatment of liver disorders, whose activation has been proved to protect APAP-induced hepatotoxicity. In this study, we examined whether FXR activation by schaftoside (SS), a naturally occurring flavonoid from Desmodium styracifolium, could protect mice against APAP-induced hepatotoxicity via regulation of oxidative stress and inflammation. Results: We first found that SS exhibited potent protective effects against APAP-induced hepatotoxicity in mice. The study reveals that SS is a potential agonist of FXR, which protects mice from hepatotoxicity mostly via regulation of oxidative stress and inflammation. Mechanistically, the hepatoprotective SS is associated with the induction of the genes of phase II detoxifying enzymes (e.g., UGT1A1, GSTα1), phase III drug efflux transporters (e.g., bile salt export pump, organic solvent transporter protein β), and glutathione metabolism-related enzymes (e.g., glutamate-cysteine ligase modifier subunit [Gclm], glutamate-cysteine ligase catalytic subunit [Gclc]). More importantly, SS-mediated FXR activation could fine-tune the pro- and anti-inflammatory eicosanoids generation via altering eicosanoids metabolic pathway, thereby resulting in decrease of hepatic inflammation. In contrast, FXR deficiency can abrogate the above effects. Innovation and Conclusion: Our results provided the direct evidence that FXR activation by SS could attenuate APAP-induced hepatotoxicity via inhibition of nuclear factor kappa-B signaling and fine-tuning the generation of proinflammatory mediators' eicosanoids. Our findings indicate that strategies to activate FXR signaling in hepatocytes may provide a promising therapeutic approach to alleviate liver injury induced by APAP overdose.

Interleukin-22 ameliorated acetaminophen-induced kidney injury by inhibiting mitochondrial dysfunction and inflammatory responses

Acetaminophen (APAP) overdose can lead to acute, severe kidney injury, which has recently attracted considerable attention among researchers and clinicians. Unfortunately, there are no well-established treatments for APAP-induced renal injury, and the molecular mechanism of APAP-induced kidney injury is still unclear. Herein, we explored the protective effects of interleukin (IL)-22 on APAP-induced renal injury and the underlying molecular basis. We found that IL-22 could significantly alleviate the accumulation of reactive oxygen species (ROS) and ameliorate mitochondrial dysfunction, reducing APAP-induced renal tubular epithelial cell (TEC) death in vitro and in vivo. Furthermore, IL-22 could downregulate the APAP-induced NLRP3 inflammasome activation and mature IL-1β release in kidney injury. Additionally, the APAP-mediated upregulation of the serum levels of IL-18, TNF-α, IL-6, and IL-1β was obviously decreased, suggesting IL-22 has inhibitory effects on inflammatory responses. Conclusively, our study demonstrated that IL-22 exerted ameliorative effects on APAP-induced kidney injury by alleviating mitochondrial dysfunction and NLRP3 inflammasome activation, suggesting that IL-22 represents a potential therapeutic approach to treat APAP-induced kidney injury. KEY POINTS: • IL-22 could ameliorate APAP that triggered oxidative stress and mitochondrial dysfunction. • IL-22 could reduce APAP that caused inflammatory responses. Graphical abstract.