Apoptosis and necroptosis in the liver: a matter of life and death

Salidroside Inhibits CCl4-Induced Liver Fibrosis in Mice by Reducing Activation and Migration of HSC Induced by Liver Sinusoidal Endothelial Cell-Derived Exosomal SphK1

Sphingosine kinase 1 (SphK1)/Sphingosine-1-phosphate (S1P)/S1PRs signaling pathway is known to involve the advancement of liver fibrosis. Exosomal SphK1 promotes hepatic stellate cells (HSC) migration. Salidroside (Sal) inhibits liver fibrosis, but its mechanism is yet to be elucidated. This study was to explore the influences of Sal on the SphK/S1P/S1PRs signaling pathway in liver fibrosis induced by carbon tetrachloride (CCl₄) in vivo, and investigated the mechanism of Sal affecting the migration and activation of HSC triggered by exosomal SphK1 in vitro. Our data showed that Sal reduced the activities of alanine transaminase (ALT), aspartate aminotransferase (AST) in serum, and hydroxyproline (Hyp) content in the liver tissue. Sal subdued the expression of α-smooth muscle actin (α-SMA), fibronectin (FN) and type I collagen (Col I) of the liver. Sal also reduced mitochondria-induced hepatocyte apoptosis and to inhibit JNK activation. Furthermore, Sal remarkably eradicated the influence of SphK1, SphK2, S1P, and S1PRs triggered by CCl₄, whether stimulating or hindering. Compared with serum-derived exosomes from model group mice, serum-derived exosomes from Sal group mice expressed lower SphK1 and reduced JS 1 (mouse HSC cell line) migration. In addition, Sal was also observed to subdue Col I expression, AKT activation, and LX-2 migration induced by exosomal SphK1 from SK-HEP-1 (a kind of liver sinusoidal endothelial cells (LSEC) cell line). In conclusion, Sal could effectively alleviate liver injury, hepatocyte apoptosis, and liver fibrosis in vivo, providing supports that the protective effects of Sal might be realized by suppressing JNK activation and modulating the SphK/S1P/S1PRs axis. In vitro, it was observed that Sal might alleviate LX-2 migration and activation induced by exosomal SphK1 by inhibiting the AKT activation.

Mechanisms and disease consequences of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Its more advanced subtype, nonalcoholic steatohepatitis (NASH), connotes progressive liver injury that can lead to cirrhosis and hepatocellular carcinoma. Here we provide an in-depth discussion of the underlying pathogenetic mechanisms that lead to progressive liver injury, including the metabolic origins of NAFLD, the effect of NAFLD on hepatic glucose and lipid metabolism, bile acid toxicity, macrophage dysfunction, and hepatic stellate cell activation, and consider the role of genetic, epigenetic, and environmental factors that promote fibrosis progression and risk of hepatocellular carcinoma in NASH.

Targeting programmed cell death in metabolic dysfunction-associated fatty liver disease (MAFLD): a promising new therapy

Most currently recommended therapies for metabolic dysfunction-associated fatty liver disease (MAFLD) involve diet control and exercise therapy. We searched PubMed and compiled the most recent research into possible forms of programmed cell death in MAFLD, including apoptosis, necroptosis, autophagy, pyroptosis and ferroptosis. Here, we summarize the state of knowledge on the signaling mechanisms for each type and, based on their characteristics, discuss how they might be relevant in MAFLD-related pathological mechanisms. Although significant challenges exist in the translation of fundamental science into clinical therapy, this review should provide a theoretical basis for innovative MAFLD clinical treatment plans that target programmed cell death.

MicroRNAs in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), or, more accurately, metabolic associated fatty liver disease, accounts for a large proportion of chronic liver disorders worldwide and is closely associated with other conditions such as cardiovascular disease, obesity, and type 2 diabetes mellitus. NAFLD ranges from simple steatosis to nonalcoholic steatohepatitis (NASH) and can progress to cirrhosis and, eventually, also hepatocellular carcinoma. The morbidity and mortality associated with NAFLD are increasing rapidly year on year. Consequently, there is an urgent need to understand the etiology and pathogenesis of NAFLD and identify effective therapeutic targets. MicroRNAs (miRNAs), important epigenetic factors, have recently been proposed to participate in NAFLD pathogenesis. Here, we review the roles of miRNAs in lipid metabolism, inflammation, apoptosis, fibrosis, hepatic stellate cell activation, insulin resistance, and oxidative stress, key factors that contribute to the occurrence and progression of NAFLD. Additionally, we summarize the role of miRNA-enriched extracellular vesicles in NAFLD. These miRNAs may comprise suitable therapeutic targets for the treatment of this condition.

Yi-Qi-Jian-Pi Formula Suppresses RIPK1/RIPK3-Complex-Dependent Necroptosis of Hepatocytes Through ROS Signaling and Attenuates Liver Injury in Vivo and in Vitro

Acute-on-chronic liver failure (ACLF) is described as a characteristic of acute jaundice and coagulation dysfunction. Effective treatments for ACLF are unavailable and hence are urgently required. We aimed to define the effect of Yi-Qi-Jian-Pi Formula (YQJPF) on liver injury and further examine the molecular mechanisms. In this study, we established CCl₄-, LPS-, and d-galactosamine (D-Gal)-induced ACLF rat models in vivo and LPS- and D-Gal-induced hepatocyte injury models in vitro. We found that YQJPF significantly ameliorates liver injury in vivo and in vitro that is associated with the regulation of hepatocyte necroptosis. Specifically, YQJPF decreased expression of receptor-interacting protein kinase 1 (RIPK1), receptor-interacting protein kinase 3 (RIPK3) and pseudokinase mixed lineage kinase domain-like (MLKL) to inhibit the migration of RIPK1 and RIPK3 into necrosome. YQJPF also reduces the expression of inflammatory cytokines IL-6, IL-8, IL-1β, and TNF-α, which were regulated by RIPK3 mediates cell death. RIPK1 depletion was found to enhance the protective effect of YQJPF. Furthermore, we showed that YQJPF significantly downregulates the mitochondrial reactive oxygen species (ROS) production and mitochondrial depolarization, with ROS scavenger, 4-hydroxy-TEMPO treatment recovering impaired RIPK1-mediated necroptosis and reducing the expression of IL-6, IL-8, IL-1β, and TNF-α. In summary, our study revealed the molecular mechanism of protective effect of YQJPF on hepatocyte necroptosis, targeting RIPK1/RIPK3-complex-dependent necroptosis via ROS signaling. Overall, our results provided a novel perspective to indicate the positive role of YQJPF in ACLF.

Non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH)-related liver fibrosis: mechanisms, treatment and prevention

Liver fibrosis is the excessive expression and accumulation of extracellular matrix proteins in the liver. Fibrotic scarring occurs as the consequence of chronic injury and inflammation. While the successful treatment of hepatitis B and C reduced the burden of liver disease related to viral hepatitis, non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH) are nowadays the leading causes of hepatic fibrosis worldwide. Although basic research activities have significantly advanced our understanding of the molecular disease pathogenesis, the present therapeutic options for fibrosis are still limited. In advanced disease stages, liver transplantation often remains the only curative treatment. This highlights the necessity of preventive strategies to avoid complications of fibrosis, particularly cirrhosis, portal hypertension and liver cancer. Lifestyle modifications (weight loss, exercise, healthy diet) are the basis for prevention and treatment of NAFLD-associated fibrosis. In the present review, we discuss recent advances in antifibrotic prevention and therapy. In particular, we review the current concepts for antifibrotic drug candidates in the treatment of NAFLD and NASH. While some compounds aim at reverting pathogenic liver metabolism, an alternative approach is to disconnect the injury (e.g., NAFLD) from inflammation and/or fibrosis. Investigational drugs typically target metabolic pathways, insulin resistance, hepatocyte death, inflammatory cell recruitment or activation, the gut-liver axis, matrix expression or matrix turnover. While several promising drug candidates failed in phase 2 or 3 clinical trials (including elafibranor, emricasan and selonsertib), promising results with the farnesoid X receptor agonist obeticholic acid, the pan-PPAR agonist lanifibranor and the chemokine receptor CCR2/CCR5 inhibitor cenicriviroc support the expectation of an effective pharmacological therapy for liver fibrosis in the near future. Tackling NAFLD-associated fibrosis from different directions by combinatorial drug treatment and effective lifestyle changes hold the greatest prospects.

The role of bile acids in cholestatic liver injury

Clinical disorders that impair bile flow result in retention of bile acids and cholestatic liver injury, characterized by parenchymal cell death, bile duct proliferation, liver inflammation and fibrosis. However, the pathogenic role of bile acids in the development of cholestatic liver injury remains incompletely understood. In this review, we summarize the current understanding of this process focusing on the experimental and clinical evidence for direct effects of bile acids on each major cellular component of the liver: hepatocytes, cholangiocytes, stellate cells and immune cells. During cholestasis bile acids accumulated in the liver, causing oxidative stress and mitochondrial injury in hepatocytes. The stressed hepatocytes respond by releasing inflammatory cytokines through activation of specific signaling pathways and transcription factors. The recruited neutrophils and other immune cells then cause parenchymal cell death. In addition, bile acids also stimulate the proliferation of cholangiocytes and stellate cells that are responsible for bile duct proliferation and liver fibrosis. This review explores the evidence for bile acid involvement in these phenomena. The role of bile acid receptors, TGR5, FXR and the sphingosine-1-phosphate receptor 2 and the inflammasome are also examined. We hope that better understanding of these pathologic effects will facilitate new strategies for treating cholestatic liver injury.

Fungal-Induced Programmed Cell Death

Fungal infections are a cause of morbidity in humans, and despite the availability of a range of antifungal treatments, the mortality rate remains unacceptably high. Although our knowledge of the interactions between pathogenic fungi and the host continues to grow, further research is still required to fully understand the mechanism underpinning fungal pathogenicity, which may provide new insights for the treatment of fungal disease. There is great interest regarding how microbes induce programmed cell death and what this means in terms of the immune response and resolution of infection as well as microbe-specific mechanisms that influence cell death pathways to aid in their survival and continued infection. Here, we discuss how programmed cell death is induced by fungi that commonly cause opportunistic infections, including Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans, the role of programmed cell death in fungal immunity, and how fungi manipulate these pathways.

Cadmium induced skeletal underdevelopment, liver cell apoptosis and hepatic energy metabolism disorder in Bufo gargarizans larvae by disrupting thyroid hormone signaling

Cadmium (Cd) is hazardous to human health and it is also highly detrimental to amphibian life. In this study, Bufo gargarizans larvae were exposed to environmentally relevant Cd concentrations of 5, 100 and 200 μg L^-1 from Gosner stage (Gs) 26 to Gs 42 of metamorphic climax about 6 weeks. The results showed thyroid structural injuries and thyroid signaling disruption were induced by high Cd exposure (100 and 200 μg L^-1). Moreover, tadpole skeleton including whole body, vertebrata, forelimb and hindlimb was developmentally delayed by high Cd exposure through downregulating the mRNA expressions of genes involved with skeletal ossification and growth pathway. Moreover, liver histopathological injuries were caused by high Cd exposure featured by hepatocytes malformation, nuclear degeneration and increasing melanomacrophage centers. Meanwhile, liver apoptosis rate showed on the rise in a dose-dependent way and Cd stimulated liver apoptosis by upregulating mRNA expressions of genes related to extrinsic and intrinsic apoptosis pathways. Furthermore, high Cd caused hepatic glucometabolism disorder by decreasing the genetic expressions associated with glycolysis and mitochondrial oxidative phosphorylation. In addition, liver lipid metabolism was disrupted by high Cd exposure through downregulating mRNA levels of genes related to fatty oxidation and upregulating mRNA levels of genes related to fatty acid synthesis. We suggested that Cd did great harm to tadpole health by disturbing thyroid function, skeletal growth, liver cell apoptosis signaling and hepatic energy metabolism pathway.

Necroptosis Underlies Hepatic Damage in a Piglet Model of Lipopolysaccharide-Induced Sepsis

Background

Necroptosis is a newly recognized form of programmed cell death with characteristics of both necrosis and apoptosis. The role of necroptosis in hepatic damage during sepsis is poorly understood. In this study, we investigated the occurrence of necroptosis in hepatic damage, and its contribution to hepatic damage in a piglet model of lipopolysaccharide (LPS)-induced sepsis.

Methods

Two animal experiments were conducted. In trial 1, piglets were challenged with LPS and sacrificed at different time points after LPS challenge. In trial 2, piglets were pretreated with necrostatin-1, a specific inhibitor of necroptosis, prior to LPS challenge. Alterations in the hepatic structure and function, pro-inflammatory cytokine expression, and the necroptosis signaling pathway were investigated. Typical ultrastructural characteristics of cell necrosis was observed in the liver of LPS-challenged piglets.

Results

Expressions of critical components of necroptosis including kinases (RIP1, RIP3, and MLKL), mitochondrial proteins (PGAM5 and DRP1), and an intracellular damage-associated molecular pattern (HMGB1) were increased in the liver in a time-dependent manner, followed by hepatic inflammation, morphological damage, and dysfunction as manifested by elevated hepatic expression of IL-1β, IL-6 and TNF-α as well as increased serum AST and AKP activities and the AST/ALT ratio. Pretreatment with necrostatin-1 significantly reduced the expression of RIP1, RIP3 and MLKL as well as PGAM5, DRP1 and HMGB1, which subsequently led to obvious attenuation of hepatic inflammation and damage.

Conclusions

Our study demonstrates that necroptosis occurs in the liver during sepsis and contributes to septic hepatic injury.

Protective effects of gastrodin pretreatment on mouse hepatic ischemia-reperfusion occurring through antioxidant and anti-apoptotic mechanisms

Hepatic ischemia-reperfusion injury (HIRI) often occurs following surgical procedures such as liver resection and transplantation. However, despite its clinical prominence, to the best of our knowledge, there remain no effective strategies to treat HIRI. Therefore, the aim of present study was to identify therapeutic agents that can exert beneficial effects against HIRI. The present study found that following hepatic IR modeling in mice, gastrodin (Gas) pretreatment improved the IR outcomes in terms of the serum biochemical indexes (alanine transaminase and aspartate transaminase), tissue biochemical indexes (superoxide dismutase, malondialdehyde and reduced glutathione content) and tissue pathology (H&E staining). In addition, compared with those in the IR + vehicle group, the IR + Gas group showed upregulated expression levels of nuclear erythroid 2-related factor 2, heme oxygenase 1 and Bcl-2 as detected by western blotting and reverse transcription-quantitative PCR. The mRNA and protein expression levels of Bax and caspase-3 were downregulated in the IR + Gas group compared with the IR + vehicle group. Concurrently, no significant differences were observed in the parameters between the Sham + vehicle and the Sham + Gas groups, indicating that Gas pretreatment may not cause liver damage. In conclusion, the findings of the present study revealed that Gas pretreatment exerted a protective effect in HIRI through both antioxidant and anti-apoptotic mechanisms.

An Apoptotic Gene Signature for the Prognosis of Hepatocellular Carcinoma

Background

Hepatocellular carcinoma (HCC) is a major public health burden worldwide owing to high incidence and poor prognosis. Although numerous apoptotic genes were disclosed in HCC, the prognostic value and clinical utility of the genes remained unclear.

Methods

The differentially expressed genes (DEGs) were identified in the microarray and RNA sequencing data from public databases. The apoptosis-related differentially expressed genes (AR-DEGs) were selected to construct a Lasso-penalized Cox regression model. The signature including five apoptotic genes was used to calculate risk score. Then, the receiver operating characteristic (ROC) and survival analysis were conducted based on the signature. A nomogram containing the signature and clinical characteristics was plotted to visualized the prognosis prediction. Finally, the enrichment analysis was performed in the Gene Ontology (GO) to investigate the potential mechanism.

Results

Patients with high risk scores were related to worse overall survival than those with low risk. The 3-year and 5-year area under curve (AUC) values of the signature were above 0.7 in databases. And the nomogram presented reliable net benefits for the survival prediction. The nomogram was also tested by probability calibration curves and Decision Curve Analysis (DCA). Furthermore, the five differentially expressed genes were verified again in the HCC clinical specimens with real-time PCR and Western Blot.

Conclusion

Collectively, the present study formed a novel signature based on five apoptotic genes, and this possibly predicted prognosis and strengthened the communication with HCC patients about the likely treatment.

The Role of Diagnostic Biomarkers, Omics Strategies, and Single-Cell Sequencing for Nonalcoholic Fatty Liver Disease in Severely Obese Patients

Liver disease due to metabolic dysfunction constitute a worldwide growing health issue. Severe obesity is a particularly strong risk factor for non-alcoholic fatty liver disease, which affects up to 93% of these patients. Current diagnostic markers focus on the detection of advanced fibrosis as the major predictor of liver-related morbidity and mortality. The most accurate diagnostic tools use elastography to measure liver stiffness, with diagnostic accuracies similar in normal-weight and severely obese patients. The effectiveness of elastography tools are however hampered by limitations to equipment and measurement quality in patients with very large abdominal circumference and subcutaneous fat. Blood-based biomarkers are therefore attractive, but those available to date have only moderate diagnostic accuracy. Ongoing technological advances in omics technologies such as genomics, transcriptomics, and proteomics hold great promise for discovery of biomarkers and increased pathophysiological understanding of non-alcoholic liver disease and steatohepatitis. Very recent developments have allowed for single-cell sequencing and cell-type resolution of gene expression and function. In the near future, we will therefore likely see a multitude of breakthrough biomarkers, developed from a deepened understanding of the biological function of individual cell types in the healthy and injured liver.

A narrative review of the role of necroptosis in liver disease: a double-edged sword

Acute and chronic liver injuries lead to hepatocyte death and turnover. When injuries become chronic, continuous cell death and transformation lead to chronic inflammation, fibrosis, cirrhosis, and eventually carcinoma. A therapeutic strategy of great significance for liver disease is to control hepatocyte death in acute and chronic injuries. This strategy prevents hepatocytes from causing liver failure and inhibits both secondary inflammation and fibrosis. Both apoptosis and necrosis have been proven to occur in the liver, but the role of necroptosis in liver diseases is controversial. Necroptosis, which has features of necrosis and apoptosis, is a regulatory process that occurs in some cell types when caspases are inhibited. The signaling pathway of necroptosis is characterized by the activation of receptor-interacting proteins kinase (RIPK) and mixed lineage kinase domain-like (MLKL). Necroptosis is associated with a variety of inflammatory diseases and has been the focus of research in recent years. The incidence of necroptosis in liver tissues has been studied recently in several liver injury models, but the results of the studies are not consistent. The purpose of this review is to summarize the published data on the involvement of necroptosis in liver injury, focusing on the controversies, issues remaining to be discussed, and potential therapeutic applications in this area.

How Diet-Induced Changes in the “Gut-Liver” Axis Affect Chronic Liver Disease Outcome?

Hepatocellular carcinoma (HCC) occurs in patients with chronic liver damage, inflammation and cirrhosis. The facilitators involved in increasing the HCC risk in the damaged liver are yet to be discovered. Diet and lifestyle have a profound effect on the liver inflammation and HCC. The term “gut liver axis” describes the bidirectional relationship between the liver and the gut, which are both anatomically and functionally related. Chronic liver damage is characterised by increased intestinal permeability that allows the translocation of various components and metabolites from the gut microbiota to the liver, resulting in liver inflammation and fibrosis. In this review, we discuss how diet-induced changes in gut microbiome composition, such as lipopolysaccharide and lipoteichoic acid, and its metabolites, such as bile acids, play a role in the pathogenesis of liver fibrosis and HCC.

Differential role of MLKL in alcohol-associated and non-alcohol-associated fatty liver diseases in mice and humans

Hepatocellular death contributes to progression of alcohol-associated (ALD-associated) and non-alcohol-associated (NAFL/NASH) liver diseases. However, receptor-interaction protein kinase 3 (RIP3), an intermediate in necroptotic cell death, contributes to injury in murine models of ALD but not NAFL/NASH. We show here that a differential role for mixed-lineage kinase domain-like protein (MLKL), the downstream effector of RIP3, in murine models of ALD versus NAFL/NASH and that RIP1-RIP3-MLKL can be used as biomarkers to distinguish alcohol-associated hepatitis (AH) from NASH. Phospho-MLKL was higher in livers of patients with NASH compared with AH or healthy controls (HCs). MLKL expression, phosphorylation, oligomerization, and translocation to plasma membrane were induced in WT mice fed diets high in fat, fructose, and cholesterol but not in response to Gao-binge (acute on chronic) ethanol exposure. Mlkl-/- mice were not protected from ethanol-induced hepatocellular injury, which was associated with increased expression of chemokines and neutrophil recruitment. Circulating concentrations of RIP1 and RIP3, but not MLKL, distinguished patients with AH from HCs or patients with NASH. Taken together, these data indicate that MLKL is differentially activated in ALD/AH compared with NAFL/NASH in both murine models and patients. Furthermore, plasma RIP1 and RIP3 may be promising biomarkers for distinguishing AH and NASH.

Roles of Ceramides in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease is one of the most common chronic liver diseases, ranging from simple steatosis to steatohepatitis, fibrosis, and cirrhosis. Its prevalence is rapidly increasing and presently affects around 25% of the general population of Western countries, due to the obesity epidemic. Liver fat accumulation induces the synthesis of specific lipid species and particularly ceramides, a sphingolipid. In turn, ceramides have deleterious effects on hepatic metabolism, a phenomenon called lipotoxicity. We review here the evidence showing the role of ceramides in non-alcoholic fatty liver disease and the mechanisms underlying their effects.

The Role of Necroptosis: Biological Relevance and Its Involvement in Cancer

Simple Summary

A new form of programmed necrosis called necroptosis has emerged. This new and well-documented type of programmed cell death is involved in several human diseases, including cancer. RIPK1, the main mediator of necroptosis, in response to different stimuli, activates several molecular pathways leading to inflammation, cell survival, or cell death. Targeting necroptosis could be a new strategy for advanced therapies. In this review, we focus on the biological relevance of this type of programmed cell death and its main executor RIPK1 in pathogenesis to find novel potential clinical intervention strategies.

Abstract

Regulated cell death mechanisms are essential for the maintenance of cellular homeostasis. Evasion of cell death is one of the most important hallmarks of cancer. Necroptosis is a caspase independent form of regulated cell death, investigated as a novel therapeutic strategy to eradicate apoptosis resistant cancer cells. The process can be triggered by a variety of stimuli and is controlled by the activation of RIP kinases family as well as MLKL. The well-studied executor, RIPK1, is able to modulate key cellular events through the interaction with several proteins, acting as strategic crossroads of several molecular pathways. Little evidence is reported about its involvement in tumorigenesis. In this review, we summarize current studies on the biological relevance of necroptosis, its contradictory role in cancer and its function in cell fate control. Targeting necroptosis might be a novel therapeutic intervention strategy in anticancer therapies as a pharmacologically controllable event.

How does hepatic lipid accumulation lead to lipotoxicity in non-alcoholic fatty liver disease?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD), characterized as excess lipid accumulation in the liver which is not due to alcohol use, has emerged as one of the major health problems around the world. The dysregulated lipid metabolism creates a lipotoxic environment which promotes the development of NAFLD, especially the progression from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH).

PURPOSEAND AIM

This review focuses on the mechanisms of lipid accumulation in the liver, with an emphasis on the metabolic fate of free fatty acids (FFAs) in NAFLD and presents an update on the relevant cellular processes/mechanisms that are involved in lipotoxicity. The changes in the levels of various lipid species that result from the imbalance between lipolysis/lipid uptake/lipogenesis and lipid oxidation/secretion can cause organellar dysfunction, e.g. ER stress, mitochondrial dysfunction, lysosomal dysfunction, JNK activation, secretion of extracellular vesicles (EVs) and aggravate (or be exacerbated by) hypoxia which ultimately lead to cell death. The aim of this review is to provide an overview of how abnormal lipid metabolism leads to lipotoxicity and the cellular mechanisms of lipotoxicity in the context of NAFLD.

Protective effect of rapamycin against acrylamide-induced hepatotoxicity: The associations between autophagy, apoptosis, and necroptosis

Acrylamide (ACRL) was demonstrated to induce hepatotoxicity and programmed cell death (PCD). Rapamycin (RAPA)-induced autophagy had been reported to limit the progression of hepatocellular injury in experimental models. This research was designed to study two death pathways involved in ACRL-induced hepatotoxicity and the modulating effect of RAPA on the resulting hepatic injury. Thirty-six adult male rats were divided into three groups: control group, ACRL-treated group (20 mg kg/day), and the last group co-treated with ACRL plus RAPA (0.5 mg kg/day). Drugs were administered for 21 days via oral gavage. Blood samples were collected to assess alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Livers were dissected; parts were used for detection of superoxide dismutase (SOD) and malondialdehyde (MDA) tissue levels. Other parts were processed for hematoxylin and eosin, Masson's trichrome staining, immunostaining for microtubule-associated proteins 1A/1B light chain 3B (LC3), ubiquitin-binding protein (p62), caspase-3, and receptor-interacting protein kinase 1 (RIPK1). ACRL induced a significant elevation in ALT, AST, MDA levels, and reduction in the SOD level. ACRL also induced hepatocellular injury, fibrosis, and defective autophagy indicated by elevation of LC3 and p62 and increased p62/LC3 ratio. Moreover, it increased the apoptotic (caspase-3) and necroptotic (RIPK1) markers expression. RAPA significantly reduced liver enzymes, oxidative stress, fibrosis, and improved liver histology. Moreover, RAPA decreased p62/LC3 ratio indicated enhanced autophagy, and significantly reduced caspase-3 and RIPK1 expression. In conclusion, RAPA maintained autophagic activity which may save the hepatocytes from PCD and enhance cell viability.

M2-like macrophages exert hepatoprotection in acute-on-chronic liver failure through inhibiting necroptosis-S100A9-necroinflammation axis

Necroptosis has emerged as a novel and crucial player in acute and chronic liver diseases. Necroptotic cells lead to the release of DAMPs including S100A9, followed by the development of necroinflammation. We previously have documented the beneficial hepatoprotection conferred by M2-like macrophages in acute-on-chronic liver failure (ACLF) in vitro and in vivo, namely, M2-like macrophages protect hepatocytes against apoptosis. Herein, we integrated necroptosis, S100A9, and necroinflammation into this hepatoprotection, and hypothesized M2-like macrophages exert a hepatoprotective effect through inhibiting necroptosis-S100A9-necroinflammation axis. To testify this hypothesis, control mice were pre-treated with necroptosis or S100A9 inhibitors followed by D-GalN/LPS challenge. The extent of liver injury and M1/M2 macrophage activation was assessed. Necroptosis signaling and S100A9 expression were analysed and compared in control and fibrotic mice with or without acute insult. To document the pivotal role of M2-like macrophages in necroptosis and S100A9 inhibition, loss-of-function and gain-of-function experiments were performed. In addition, necroinflammation and its dependence on necroptosis and S100A9 were analysed. Moreover, the inhibitory effects of M2-like macrophages on necroinflammation were investigated in vivo and in vitro. We found that: firstly, the inhibition of necroptosis signaling and S100A9 expression alleviated D-GalN/LPS-induced hepatic damage, which was accompanied by M2-like macrophage activation; secondly, fibrosis inhibited necroptosis signaling and S100A9 expression, which could be attributed to M2-like macrophage activation; thirdly, S100A9 may function as a downstream player of necroptosis signaling; fourthly, fibrosis suppressed necroptosis- and S100A9-dependent necroinflammation; and finally, M2-like macrophages inhibited NLRP3 inflammasome activation and resultant necroinflammation via IL-10. Therefore, M2-like macrophages exert a beneficial hepatoprotection by inhibiting necroptosis-S100A9-necroinflammation axis in ACLF. Our findings provide novel insight for treating ACLF patients by specially targeting this signaling axis.

Phosphorylation of eIF2α mitigates endoplasmic reticulum stress and hepatocyte necroptosis in acute liver injury

INTRODUCTION AND OBJECTIVES

Necroptosis and endoplasmic reticulum (ER) stress has been implicated in acute and chronic liver injury. Activated eukaryotic initiation factor 2 alpha (eIF2α) attenuates protein synthesis and relieves the load of protein folding in the ER. In this study, we aimed to analyze the impact of eIF2α phosphorylation on hepatocyte necroptosis in acute liver injury.

MATERIALS AND METHODS

Male BALB/c mice were injected with tunicamycin or d-galactosamine, and LO2 cells were incubated with tunicamycin to induce acute liver injury. 4-Phenylbutyric acid (PBA) and salubrinal were used to inhibit ER stress and eIF2α dephosphorylation, respectively. We analyzed the eIF2α phosphorylation, ER stress, and hepatocyte necroptosis in mice and cells model.

RESULTS

Tunicamycin or d-galactosamine significantly induced ER stress and necroptosis, as well as eIF2α phosphorylation, in mice and LO2 cells (p<0.05). ER stress aggravated tunicamycin-induced hepatocyte necroptosis in mice and LO2 cells (p<0.05). Elevated eIF2α phosphorylation significantly mitigated hepatocyte ER stress (p<0.05) and hepatocyte necroptosis in mice (34.37±3.39% vs 22.53±2.18%; p<0.05) and LO2 cells (1±0.11 vs 0.33±0.05; p<0.05). Interestingly, tumor necrosis factor receptor (TNFR) 1 protein levels were not completely synchronized with necroptosis. TNFR1 expression was reduced in d-galactosamine-treated mice (p<0.05) and cells incubated with tunicamycin for 12 and 24h (p<0.05). ER stress partially restored TNFR1 expression and increased necroptosis in tunicamycin-incubated cells (p<0.05).

CONCLUSIONS

These results imply that ER stress can mediate hepatocyte necroptosis independent of TNFR1 signaling and elevated eIF2α phosphorylation can mitigate ER stress during acute liver injury.

Design and synthesis of 7-O-1,2,3-triazole hesperetin derivatives to relieve inflammation of acute liver injury in mice

Based on the previous research results of our research group, to further improve the anti-inflammatory activity of hesperetin, we substituted triazole at the 7-OH branch of hesperetin. We also evaluated the anti-inflammatory activity of 39 new hesperetin derivatives. All compounds showed inhibitory effects on nitric oxide (NO) and inflammatory factors in lipopolysaccharide-induced RAW264.7 cells. Compound d5 showed a strong inhibitory effect on NO (half maximal inhibitory concentration = 2.34 ± 0.7 μM) and tumor necrosis factor-α, interleukin (IL)-1β, and (IL-6). Structure-activity relationships indicate that 7-O-triazole is buried in a medium-sized hydrophobic cavity that binds to the receptor. Compound d5 can also reduce the reactive oxygen species production and significantly inhibit the expression of inducible NO synthase and cyclooxygenase-2 through the nuclear factor-κB signaling pathway. In vivo results indicate that d5 can reduce liver inflammation in mice with acute liver injury (ALI) induced by CCI₄. In conclusion, d5 may be a candidate drug for treating inflammation associated with ALI.

Complement-5 Inhibition Deters Progression of Fulminant Hepatitis to Acute Liver Failure in Murine Models

BACKGROUND & AIMS

Acute liver failure (ALF) is a life-threatening condition with limited treatment alternatives. ALF pathogenesis seemingly involves the complement system. However, no complement-targeted intervention has been clinically applied. In this study, we aimed to investigate the potential of Complement-5 (C5)-targeted ALF treatment.

METHODS

ALF was induced in C5-knockout (KO, B10D2/oSn) mice and their wild-type (WT) counterparts (B10D2/nSn) through intraperitoneal lipopolysaccharide (LPS) and d-galactosamine (D-GalN) administration. Thereafter, monoclonal anti-C5 antibody (Ab) or control immunoglobulin was administered intravenously. Furthermore, a selective C5a-receptor (C5aR) antagonist was administered to WT mice to compare its efficacy with that of anti-C5-Ab-mediated total C5 inhibition. We clarified the therapeutic effect of delayed anti-C5-Ab administration after LPS/D-GalN challenge. We also assessed the efficacy of anti-C5-Ab in another ALF model, using concanavalin-A.

RESULTS

Liver injury was evident 6 hours after LPS/D-GalN administration. C5-KO and anti-C5-Ab treatment significantly improved overall animal survival and significantly reduced serum transaminase and high-mobility group box-1 release with decreased histological tissue damage. This improvement was characterized by significantly reduced CD41+ platelet aggregation, maintained F4/80+ cells, and less infiltration of CD11+/Ly6-G+ cells with lower cytokine/chemokine expression. Furthermore, C5-KO and anti-C5-Ab downregulated tumor necrosis factor-α production by macrophages before inducing marked liver injury. Moreover, single-stranded-DNA cells and caspase activation were reduced, indicating significant attenuation of apoptosis. Anti-C5-Ab treatment protected the liver more effectively than the C5aR antagonist, and its delayed doses were hepatoprotective. In addition, anti-C5-Ab treatment was effective against concanavalin-A-induced ALF.

CONCLUSIONS

C5 inhibition effectively suppresses progression to ALF in mice models of fulminant hepatitis, serving as a new potential treatment strategy for ALF.

IOX1 protects from TGF-β induced fibrosis in LX-2 cells via the regulation of extracellular matrix protein expression

The aim of the present study was to investigate the effect of the histone H3K9 demethylase inhibitor, IOX1, on the mechanism of hepatic fibrosis in TGF-β-induced human hepatic stellate LX-2 cells. Cellular proliferation, apoptosis, histone H3K9 dimethylation (H3K9me2), protein expression of extracellular matrix (ECM)-related proteins α-smooth muscle actin (SMA), type I collagen (Col I), MMP-1 and TIMP-1 were measured. H3K9me2 levels in the promoter region of ECM-related genes were detected by real-time cell analysis (RTCA), flow cytometry, western blotting and chromatin immunoprecipitation (ChIP) in LX-2 cells. IOX1 significantly inhibited cell proliferation and the IC₅₀ of IOX1 was 100 µM in cells treated with IOX1 for 48 h. IOX1 significantly induced apoptosis in LX-2 cells in a concentration-dependent manner. In addition, different concentration of IOX1 increased the level of H3K9me2 and downregulated the expression of α-SMA, Col I, MMP-1 and TIMP-1 in TGF-β-induced LX-2 cells. ChIP measurements indicated that H3K9me2 levels in the promotor region of the corresponding genes were increased in TGF-β-induced LX-2 cells. IOX1 may elevate H3K9me2 in the promotor region of Col I, MMP-1, and TIMP-1 genes to regulate α-SMA, Col I, MMP-1 and TIMP-1 protein expression to induce cell apoptosis, inhibit LX-2 cell proliferation and oppose hepatic fibrotic activity.

Hepatocyte-specific IL11 cis-signaling drives lipotoxicity and underlies the transition from NAFLD to NASH

IL11 is important for fibrosis in non-alcoholic steatohepatitis (NASH) but its role beyond the stroma in liver disease is unclear. Here, we investigate the role of IL11 in hepatocyte lipotoxicity. Hepatocytes highly express IL11RA and secrete IL11 in response to lipid loading. Autocrine IL11 activity causes hepatocyte death through NOX4-derived ROS, activation of ERK, JNK and caspase-3, impaired mitochondrial function and reduced fatty acid oxidation. Paracrine IL11 activity stimulates hepatic stellate cells and causes fibrosis. In mouse models of NASH, hepatocyte-specific deletion of Il11ra1 protects against liver steatosis, fibrosis and inflammation while reducing serum glucose, cholesterol and triglyceride levels and limiting obesity. In mice deleted for Il11ra1, restoration of IL11 cis-signaling in hepatocytes reconstitutes steatosis and inflammation but not fibrosis. We found no evidence for the existence of IL6 or IL11 trans-signaling in hepatocytes or NASH. These data show that IL11 modulates hepatocyte metabolism and suggests a mechanism for NAFLD to NASH transition.

Efficacy and Safety of Emricasan in Liver Cirrhosis and/or Fibrosis

This study aimed to perform a meta-analysis to determine the efficacy and safety of emricasan. Nine databases were searched for clinical trials investigating the efficacy of emricasan treatment in patients with liver cirrhosis or fibrosis. A manual search was conducted to identify the missing trials. The quality of the included studies was assessed using the revised Cochrane risk of bias tool. Efficacy of emricasan treatment was defined as a positive change in apoptosis-related parameters from baseline to the last follow-up visit. Overall, emricasan treatment is more effective in patients with liver cirrhosis or fibrosis than placebo (standardized mean difference [SMD] [95% confidence intervals (CI)]=0.28 [0.14; 0.41]). No significant change in model for end-stage liver disease (MELD) score between the emricasan and placebo groups was noted (SMD [95% CI]=0.18 [-0.01; 0.36]; p=0.058). A 50 mg dose of emricasan had the highest efficacy rate compared to placebo (SMD [95% CI]=0.28 [0.06; 0.50]; p=0.012), followed by the 5 mg dosing regimen (SMD [95% CI]=0.28 [0.06; 0.50]; p=0.012). Treatment with emricasan resulted in significant reductions in ALT (mean difference (MD) [95% CI]=-5.89 [-10.59; -1.20]; p=0.014) and caspase3/7 levels (MD [95%CI]=-1215.93 [-1238.53; -1193.33]; p<0.001), respectively. No significant increase in the rate of overall adverse events was noted (OR [95% CI]=1.52 [0.97; 2.37]; p=0.069). Treatment with emricasan is more effective in improving liver function and apoptosis parameters compared to placebo, with a well-tolerated safety profile. However, due to the poor quality of the analyzed studies, the small number of trials and patients, and the short follow-up periods, more robust trials are still warranted.

Therapeutic potential of bicyclol in liver diseases: Lessons from a synthetic drug based on herbal derivative in traditional Chinese medicine

Bicyclol, an innovative chemical drug with proprietary intellectual property rights in China, is based on derivative of traditional Chinese medicine (TCM) Schisandra chinensis (Wuweizi) of North. Mounting data has proved that bicyclol has therapeutic potential in various pathological conditions in liver. In this narrative review, we provide the first summary of pharmacological activities, pharmacokinetic characteristics and toxicity of bicyclol, and discuss future research perspectives. Our results imply that bicyclol has a wide spectrum of pharmacological properties, including anti-viral, anti-inflammatory, immuno-regulatory, anti-oxidative, antisteatotic, anti-fibrotic, antitumor, cell death regulatory effects and modulation of heat shock proteins. Pharmacokinetic studies have indicated that bicyclol is the main substrate of CYP3A/2E1. Additionally, no obvious drug interactions have been found when bicyclol is administered simultaneously with other prescriptions. Furthermore, the results of chronic toxicity have strongly addressed that bicyclol has no noticeable toxic effects on all biochemical indices and pathological examinations of the main organs. In view of good pharmacological actions and safety, bicyclol is anticipated to be a potential candidate for various liver diseases, including acute liver injury, fulminant hepatitis, non-alcoholic fatty liver disease, fibrosis and hepatocellular carcinoma. Further studies are therefore required to delineate its molecular mechanisms and targets to confer this well-designed drug a far greater potency. We hope that bicyclol-based therapeutics for liver diseases might be broadly used in clinical practice worldwide.

Study on the protective effect and mechanism of Dicliptera chinensis (L.) Juss (Acanthaceae) polysaccharide on immune liver injury induced by LPS

The purpose of this study is to use Dicliptera chinensis (L.) Juss (Acanthaceae) polysaccharide (DCP) to act on the NF-κB inflammatory pathway and Fas/FasL ligand system, in order to find a new method to improve immune liver injury. Lipopolysaccharide (LPS) was used to establish an injury model in vivo (Kunming mice) and in vitro (LO2 cells). In this experiment, hematoxylin-eosin (H&E) staining and related biochemical indicators were used to observe the pathological changes of liver tissues, oxidative stress and inflammatory reactions. Immunohistochemistry, ELISA, RT-PCR and Western blot were used to detect protein or mRNA expressions associated with inflammation response and apoptosis. The experimental results show that the model group has obvious liver cell damage and inflammatory infiltration. After DCP intervention, it could significantly reduce the levels of ALT, AST, ALP, TBIL and MDA in serum, and increase the content of SOD and GSH-Px. In addition, DCP can reduce the expression level of NF-κB in the liver and reduce the release of downstream inflammatory factors TNF-α, IL-6 and IL-1β, thereby reducing the inflammation. At the same time, DCP can significantly inhibit the expression of Fas/FasL ligand system and apoptosis related-proteins and mRNA, which in turn can reduce cell apoptosis. In conclusion, DCP can alleviate liver injury by inhibiting liver inflammation and apoptosis, which provides a new strategy for clinical treatment of immune liver injury.

Mitochondrial Mechanisms of Necroptosis in Liver Diseases

Cell death represents a basic biological paradigm that governs outcomes and long-term sequelae in almost every hepatic disease. Necroptosis is a common form of programmed cell death in the liver. Necroptosis can be activated by ligands of death receptors, which then interact with receptor-interactive protein kinases 1 (RIPK1). RIPK1 mediates receptor interacting receptor-interactive protein kinases 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL) and necrosome formation. Regarding the molecular mechanisms of mitochondrial-mediated necroptosis, the RIPK1/RIPK3/MLKL necrosome complex can enhance oxidative respiration and generate reactive oxygen species, which can be a crucial factor in the susceptibility of cells to necroptosis. The necrosome complex is also linked to mitochondrial components such as phosphoglycerate mutase family member 5 (PGAM5), metabolic enzymes in the mitochondrial matrix, mitochondrial permeability protein, and cyclophilin D. In this review, we focus on the role of mitochondria-mediated cell necroptosis in acute liver injury, chronic liver diseases, and hepatocellular carcinoma, and its possible translation into clinical applications.

Altered mitochondrial calcium handling and cell death by necroptosis: An emerging paradigm

The classical necroptosis signaling is mediated by death receptors (DRs) that work in synergy with traditional caspase inhibitory signals. Currently, potential therapeutic molecules are in various phases of clinical trials for a spectrum of pathological conditions associated with necroptosis. However, a non-classical model of necroptosis has also emerged over the last decade with a relatively unexplored molecular mechanism. Although in vitro studies and preclinical models have shown its close association with mitochondrial dysfunction (mito-dysfunction), contradictory reports have emerged which complicate its definitiveness. Though impaired mitochondrial calcium ([Ca²⁺]_m) handling is established in necrotic cell death, how this interplay regulates necroptosis is yet to be elucidated. Taking these questions into consideration, we have discussed various molecular aspects of necroptosis with the emerging role of mito-dysfunction. Based on the central role of altered [Ca²⁺]_m handling in mito-dysfunction mediated necroptosis, we have provided a comprehensive molecular insight into this emerging paradigm. Potential reasons for the contradictory findings regarding the role of mito-dysfunction in necroptosis in general and mitochondrial-dependent necroptosis in specific are discussed. We also provide insights into the current understanding of how [Ca²⁺]_m can be a critical determinant in deciding the cell fate under certain pathological conditions, while under others it may be dispensable. Lastly, we have highlighted the key molecular targets which have a direct implication for therapeutic intervention in conditions that are associated with impaired [Ca²⁺]_m handling and cell death by necroptosis.

RIP1 kinase activity promotes steatohepatitis through mediating cell death and inflammation in macrophages

Hepatocyte cell death and liver inflammation have been well recognized as central characteristics of nonalcoholic steatohepatitis (NASH), however, the underlying molecular basis remains elusive. The kinase receptor-interacting protein 1 (RIP1) is a multitasking molecule with distinct functions in regulating apoptosis, necroptosis, and inflammation. Dissecting the role of RIP1 distinct functions in different pathophysiology has absorbed huge research enthusiasm. Wild-type and RIP1 kinase-dead (Rip1^K45A/K45A) mice were fed with high-fat diet (HFD) to investigate the role of RIP1 kinase activity in the pathogenesis of NASH. Rip1^K45A/K45A mice exhibited significantly alleviated NASH phenotype of hepatic steatosis, liver damage, fibrosis as well as reduced hepatic cell death and inflammation compared to WT mice. Our results also indicated that both in vivo lipotoxicity and in vitro saturated fatty acids (palmitic acid) treatment were able to induce the kinase activation of RIP1 in liver macrophages. RIP1 kinase was required for mediating inflammasome activation, apoptotic and necrotic cell death induced by palmitic acid in both bone marrow-derived macrophage and mouse primary Kupffer cells. Results from chimeric mice established through lethal irradiation and bone marrow transplantation further confirmed that the RIP1 kinase in hematopoietic-derived macrophages contributed mostly to the disease progression in NASH. Consistent with murine models, we also found that RIP1 kinase was markedly activated in human NASH, and the kinase activation mainly occurred in liver macrophages as indicated by immunofluorescence double staining. In summary, our study indicated that RIP1 kinase was phosphorylated and activated mainly in liver macrophages in both experimental and clinical NASH. We provided direct genetic evidence that the kinase activity of RIP1 especially in hematopoietic-derived macrophages contributes to the pathogenesis of NASH, through mediating inflammasome activation and cell death induction. Macrophage RIP1 kinase represents a specific and potential therapeutic target for NASH.

The dichotomous role of TGF-β in controlling liver cancer cell survival and proliferation

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer and one of the most prevalent and life-threatening malignancies globally. One of the hallmarks in HCC is the sustained cell survival and proliferative signals, which are determined by the balance between oncogenes and tumor suppressors. Transforming growth factor beta (TGF-β) is an effective growth inhibitor of epithelial cells including hepatocytes, through induction of cell cycle arrest, apoptosis, cellular senescence, or autophagy. The antitumorigenic effects of TGF-β are bypassed during liver tumorigenesis via multiple mechanisms. Furthermore, along with malignant progression, TGF-β switches to promote cancer cell survival and proliferation. This dichotomous nature of TGF-β is one of the barriers to therapeutic targeting in liver cancer. Thereafter, understanding the underlying molecular mechanisms is a prerequisite for discovering novel antitumor drugs that may specifically disable the growth-promoting branch of TGF-β signaling or restore its tumor-suppressive arm. This review summarizes how TGF-β inhibits or promotes liver cancer cell survival and proliferation, highlighting the functional switch mechanisms during the process.

Methionine selenium antagonizes LPS-induced necroptosis in the chicken liver via the miR-155/TRAF3/MAPK axis

Organic selenium has antioxidation and disease treatment effects. To explore the mechanisms of how methionine selenium alleviates necroptosis in the liver and whether this process is related to microRNA (miRNA) and the mitogen-activated protein kinase (MAPK) pathway, an animal model of methionine selenium and the lipopolysaccharide (LPS) interaction was established. The morphology, inflammatory factor (tumor necrosis factor-α [TNF-α]), necroptosis-related genes (RIP1, RIP3, MLKL, and caspase 8), MAPK pathway-related genes (JNK, ERK, and p38, p-JNK, p-ERK, and p-p38), gga-miR-155, TRAF3 (predicted target of gga-miR-155), and oxidative stress-related indicators (SOD, MDA, CAT, GSH, and GSH-Px) were analyzed from the perspective of the miR-155/TRAF3/MAPK axis to elucidate the mechanism of methionine selenium on the LPS-induced necroptosis mechanism in the chicken liver. The current results suggested that methionine selenium antagonizes oxidative stress, inflammation, and the MAPK pathway, thereby antagonizing the occurrence of necroptosis through multiple mechanisms. At the same time, methionine selenium affects miR-155/TRAF3/MAPK signaling, reduces miR-155 expression, and upregulates TRAF3 expression to inhibit necroptosis. This information provided new ideas and a theoretical basis for the practical application of methionine selenium, and it also enriched the study of miRNAs in birds and provided a reference for comparative medicine.

Cell Death and Liver Disease

Cell death is now reclassified into several types based on the mechanisms and morphologic phenotype. Understanding of such classifications offers insights into the pathogenesis of liver disease, as well as diagnostic or therapeutic implications. Apoptosis is recognized relatively easily due to its unique morphology, but lytic cell death may occur in the form of accidental necrosis, mitochondria permeability transition-driven necrosis, necroptosis, pyroptosis, ferroptosis, and parthanatos. The cell may be engulfed by neighboring cells due to a loss of integrin signaling or cancer cell competition by entosis, a type of cell death. The classification also includes mechanistically termed cell death such as autophagy-dependent cell death and lysosome-dependent cell death. These different types of cell death may occur uniquely in certain liver diseases but may coexist in the evolution of the disease. They occur in parenchymal and non-parenchymal liver cells, as well as inflammatory cells, causing distinct pathologic consequences. This review briefly covers the recently revised classifications of cell death and discusses their relevance to liver diseases of different etiologies.

Pathophysiological mechanisms underlying MAFLD

BACKGROUND AND AIMS

The pathophysiology underlying metabolic associated fatty liver disease (MAFLD) involves a multitude of interlinked processes, including insulin resistance (IR) underlying the metabolic syndrome, lipotoxicity attributable to the accumulation of toxic lipid species, infiltration of proinflammatory cells causing hepatic injury and ultimately leading to hepatic stellate cell (HSC) activation and fibrogenesis. The proximal processes, such as IR, lipid overload and lipotoxicity are relatively well established, but the downstream molecular mechanisms, such as inflammatory processes, hepatocyte lipoapoptosis, and fibrogenesis are incompletely understood.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases till June 2020, using relevant keywords (nonalcoholic fatty liver disease; metabolic associated fatty liver disease; nonalcoholic steatohepatitis; NASH pathogenesis) to extract relevant studies describing pathogenesis of MAFLD/MASH.

RESULTS

Several studies have reported new concepts underlying pathophysiology of MAFLD. Activation of HSCs is the common final pathway for diverse signals from damaged hepatocytes and proinflammatory cells. Activated HSCs then secrete excess extracellular matrix (ECM) which accumulates and impairs structure and function of the liver. TAZ (a transcriptional regulator), hedgehog (HH) ligands, transforming growth factor-β (TGF-β), bone morphogenetic protein 8B (BMP8B) and osteopontin play important roles in activating these HSCs. Dysfunctional gut microbiome, dysregulated bile acid metabolism, endogenous alcohol production, and intestinal fructose handling, modify individual susceptibility to MASH.

CONCLUSIONS

Newer concepts of pathophysiology underlying MASH, such as TAZ/Ihh pathway, extracellular vesicles, microRNA, dysfunctional gut microbiome and intestinal fructose handling present promising targets for the development of therapeutic agents.

Polydeoxyribonucleotide Exerts Protective Effect Against CCl4-Induced Acute Liver Injury Through Inactivation of NF-κB/MAPK Signaling Pathway in Mice

Acute liver injury (ALI) causes life-threatening clinical problem, and its underlying etiology includes inflammation and apoptosis. An adenosine A_2A receptor agonist, polydeoxyribonucleotide (PDRN), exhibits anti-inflammatory and anti-apoptotic effects by inhibiting the secretion of pro-inflammatory cytokines. In the current study, the protective effect of PDRN against carbon tetrachloride (CCl₄)-induced ALI was investigated using mice. For the induction of ALI, mice received intraperitoneal injection of CCl₄ twice over seven days. Mice from the PDRN-treated groups received an intraperitoneal injection of 200 μL saline containing PDRN (8 mg/kg), once a day for seven days, starting on day 1 after the first CCl₄ injection. In order to confirm that the action of PDRN occurs through the adenosine A_2A receptor, 8 mg/kg 3,7-dimethyl-1-propargylxanthine (DMPX), an adenosine A_2A receptor antagonist, was treated with PDRN. Administration of CCl₄ impaired liver tissue and increased the liver index and histopathologic score. The expression of pro-inflammatory cytokines was increased, and apoptosis was induced by the administration of CCl₄. Administration of CCl₄ activated nuclear factor-kappa B (NF-κB) and facilitated phosphorylation of signaling factors in mitogen-activated protein kinase (MAPK). In contrast, PDRN treatment suppressed the secretion of pro-inflammatory cytokines and inhibited apoptosis. PDRN treatment inactivated NF-κB and suppressed phosphorylation of signaling factors in MAPK. As a result, liver index and histopathologic score were reduced by PDRN treatment. When PDRN was treated with DMPX, the anti-inflammatory and anti-apoptotic effect of PDRN disappeared. Therefore, PDRN can be used as an effective therapeutic agent for acute liver damage.

Effect of endurance exercise training on liver gene expression in male and female mice

Chronic endurance exercise is a therapeutic strategy in the treatment of many chronic diseases in humans, including the prevention and treatment of metabolic diseases such as diabetes mellitus. Metabolic, cardiorespiratory, and endocrine pathways targeted by chronic endurance exercise have been identified. In the liver, however, the cellular and molecular pathways that are modified by exercise and have preventive or therapeutic relevance to metabolic disease need to be elucidated. The mouse model used in the current study allows for the quantification of a human-relevant exercise "dosage". In this study we show hepatic gene expression differences between sedentary female and sedentary male mice and that chronic exercise modifies the transcription of hepatic genes related to metabolic disease and steatosis in both male and female mice. Chronic exercise induces molecular pathways involved in glucose tolerance, glycolysis, and gluconeogenesis while producing a decrease in pathways related to insulin resistance, steatosis, fibrosis, and inflammation. Given these findings, this mouse exercise model has potential to dissect the cellular and molecular hepatic changes following chronic exercise with application to understanding the role that chronic exercise plays in preventing human diseases. Novelty: Exercise modifies the hepatic gene expression and hepatic pathways related to metabolic disease in male and female mice. Sex differences were seen in hepatic gene expression between sedentary and exercised mice. The mouse exercise model used in this study allows for application and evaluation of exercise effects in human disease.

Stoking the Fire: How Dying Cells Propagate Inflammatory Signalling through Extracellular Vesicle Trafficking

Communication between dying cells and their environment is a critical process that promotes tissue homeostasis during normal cellular turnover, whilst during disease settings, it can contribute to inflammation through the release of intracellular factors. Extracellular vesicles (EVs) are a heterogeneous class of membrane-bound cell-derived structures that can engage in intercellular communication via the trafficking of bioactive molecules between cells and tissues. In addition to the well-described functions of EVs derived from living cells, the ability of dying cells to release EVs capable of mediating functions on target cells or tissues is also of significant interest. In particular, during inflammatory settings such as acute tissue injury, infection and autoimmunity, the EV-mediated transfer of proinflammatory cargo from dying cells is an important process that can elicit profound proinflammatory effects in recipient cells and tissues. Furthermore, the biogenesis of EVs via unique cell-death-associated pathways has also been recently described, highlighting an emerging niche in EV biology. This review outlines the mechanisms and functions of dying-cell-derived EVs and their ability to drive inflammation during various modes of cell death, whilst reflecting on the challenges and knowledge gaps in investigating this subgenre of extracellular vesicles research.

Hepatic inflammation after burn injury is associated with necroptotic cell death signaling

BACKGROUND

Burn injury still has a high attributable mortality. The elevated mortality rate of severe burns is still concerning. Hepatic inflammation and injury are common after burns and are associated with poor outcomes. Necroptosis is a programmed cell death linked with inflammation. Thus, assessing necroptotic pathways in the liver can lead to new therapeutic modalities to improve mortality after severe burns.

METHODS

Mice underwent 15% total body surface area burn or sham injury. Three hours after burn, the mice were euthanized to collect blood and livers. Histology, injury markers, genes expression, and tissue protein levels were compared between groups.

RESULTS

Compared with sham, burned mice had heightened liver inflammatory cell infiltration and edema. Serum aspartate aminotransferase and alanine aminotransferase were increased by 4.9- and 3.4-fold, respectively, in burned mice relative to sham (p < 0.05). Expression of tumor necrosis factor α, interleukin-6, interleukin-1β, and CXCL1 (KC) genes were elevated in livers of burned mice by 10-, 86-, 10-, and 828-fold, respectively, compared with sham (p < 0.05). Expression of necroptotic genes, namely, receptor-interacting protein kinases 1 and 3, and mixed lineage kinase domain-like in livers of burned mice were increased by 10-, 13-, and 4.5-fold, respectively, relative to sham (p < 0.05). Receptor-interacting protein kinase 1 and phosphorylated mixed lineage kinase domain-like protein levels measured by Western-blot in livers after burn injury were elevated by 22- and 17-fold, respectively, compared with sham (p < 0.05).

CONCLUSION

Liver damage occurs early after burns in mice and is associated with elevation of proinflammatory cytokines, chemokine, and proteins involved in the necroptotic pathway. This study suggests that necroptosis plays a role in the pathogenesis of liver failure secondary to burn injury.

Cisplatin induced testicular damage through mitochondria mediated apoptosis, inflammation and oxidative stress in rats: impact of resveratrol

The target of this study was to explore the role of mitochondria mediated apoptosis and inflammation in cisplatin-induced testicular damage and to evaluate the ameliorative effect of resveratrol. Adult male Wistar rats were randomly allocated to 4 groups. Group I (Control) received normal saline, Group II (Resveratrol) received resveratrol (50 mg/kg/day), Group III (Cisplatin) received cisplatin (7.5 mg/kg/week, i.p.) and Group IV (Resveratrol + Cisplatin) received resveratrol and cisplatin in the same regimen of treatment. Treatment with resveratrol in Groups II and IV started 48h before cisplatin injection and continued for further 4 successive weeks. Cisplatin-treated rats showed reduced body weight, absolute testes weight and sperm count, motility and viability. On the other hand, cisplatin treatment increased the percentage of sperm abnormalities. It also decreased serum testosterone level, mitochondrial membrane potential while, increased cytochrome C liberation from the mitochondria into the cytosol. The activities of caspase-3 & -9 were increased. The level of TNF-α, IL-6 and Bax were increased whereas Bcl-2 was decreased. Oxidative stress markers were found to increase with a concomitant reduction in the antioxidant enzymes and GSH levels. These results were confirmed by immunohistochemical and histopathological analysis. Contrary to all these results, there were improvements in cisplatin induced testicular damage through attenuation of mitochondria mediated apoptosis, inflammation, and oxidative stress owing to resveratrol pretreatment. Thus, resveratrol, as a potential therapeutic agent, may hold promise in preventing mitochondria mediated apoptosis and inflammation in cisplatin-induced testicular damage in rats.

Artesunate induces autophagy dependent apoptosis through upregulating ROS and activating AMPK-mTOR-ULK1 axis in human bladder cancer cells

Artesunate is a kind of derivative of artemisinin, which possesses potent anti-cancer effect in addition to its anti-malarial property. And autophagy was a highly conserved process, exerting a double-edged effect in cancer cell survival. Besides, apoptosis is a programmed cell death program, crucial to cell homeostasis. However, the relations between autophagy and apoptosis, and the role of artesunate in this interaction have not been elucidated in bladder cancer. In present study, we used human bladder cancer cells (T24 and EJ cell lines) to investigate that how artesunate would influence autophagy and apoptosis processes. We found that artesunate could inhibit the viability, proliferation and migration of bladder cancer cells, as well as induce autophagy in a time and dose dependent manner, in addition, the artesunate induced autophagy subsequently activated cells apoptosis. Furthermore, we pretreated T24 and EJ cells with 3-Methyladenine or Rapamycin to inhibit or promote autophagy, respectively, leading to inhibited or increased apoptosis. Moreover, pretreatment of these cell lines with Acadesine or Dorsomorphin to activate or inhibit the AMPK-mTOR-ULK1 pathway, respectively, also resulting in promotion or suppression in both autophagy and apoptosis. In the upstream, ROS upregulation triggered by ART initiated AMPK-mTOR-ULK1 axis. However, this initiative effect of ROS can be reversed by N-Acetyl-l-cysteine. Therefore, this study indicated that Artesunate induces autophagy dependent apoptosis through upregulating ROS and activating AMPK-mTOR-ULK1 pathway in human bladder cancer cells.

Programmed cell death in alcohol-associated liver disease

Alcohol-associated liver disease (ALD), which ranges from mild disease to alcohol-associated hepatitis and cirrhosis, is the most prevalent type of chronic liver disease and a leading cause of morbidity and mortality worldwide. Accumulating evidence reveals that programmed cell death (PCD) plays a crucial role in progression of ALD involving crosstalk between hepatocytes and immune cells. Multiple pathways of PCD, including apoptosis, necroptosis, autophagy, pyroptosis and ferroptosis, are reported in ALD. Interestingly, PCD pathways are intimately linked and interdependent, making it difficult to therapeutically target a single pathway. This review clarifies the multiple types of PCD occurring in liver and focuses on crosstalk between hepatocytes and innate immune cells in ALD.

Mesenchymal stem cell-based cell-free strategies: safe and effective treatments for liver injury

Various hepatoxic factors, such as viruses, drugs, lipid deposition, and autoimmune responses, induce acute or chronic liver injury, and 3.5% of all worldwide deaths result from liver cirrhosis, liver failure, or hepatocellular carcinoma. Liver transplantation is currently limited by few liver donors, expensive surgical costs, and severe immune rejection. Cell therapy, including hepatocyte transplantation and stem cell transplantation, has recently become an attractive option to reduce the overall need for liver transplantation and reduce the wait time for patients. Recent studies showed that mesenchymal stem cell (MSC) administration was a promising therapeutic approach for promoting liver regeneration and repairing liver injury by the migration of cells into liver sites, hepatogenic differentiation, immunoregulation, and paracrine mechanisms. MSCs secrete a large number of molecules into the extracellular space, and soluble proteins, free nucleic acids, lipids, and extracellular vesicles (EVs) effectively repair tissue injury in response to fluctuations in physiological states or pathological conditions. Cell-free-based therapies avoid the potential tumorigenicity, rejection of cells, emboli formation, undesired differentiation, and infection transmission of MSC transplantation. In this review, we focus on the potential mechanisms of MSC-based cell-free strategies for attenuating liver injury in various liver diseases. Secretome-mediated paracrine effects participate in the regulation of the hepatic immune microenvironment and promotion of hepatic epithelial repair. We look forward to completely reversing liver injury through an MSC-based cell-free strategy in regenerative medicine in the near future.

MLKL-dependent signaling regulates autophagic flux in a murine model of non-alcohol-associated fatty liver and steatohepatitis

BACKGROUND & AIMS

Autophagy maintains cellular homeostasis and plays a critical role in the development of non-alcoholic fatty liver and steatohepatitis. The pseudokinase mixed lineage kinase domain-like (MLKL) is a key downstream effector of receptor interacting protein kinase 3 (RIP3) in the necroptotic pathway of programmed cell death. However, recent data reveal that MLKL also regulates autophagy. Herein, we tested the hypothesis that MLKL contributes to the progression of Western diet-induced liver injury in mice by regulating autophagy.

METHODS

Rip3^+/+, Rip3^-/-, Mlkl^+/+ and Mlkl^-/- mice were fed a Western diet (FFC diet, high in fat, fructose and cholesterol) or chow for 12 weeks. AML12 and primary mouse hepatocytes were exposed to palmitic acid (PA).

RESULTS

The FFC diet increased expression, phosphorylation and oligomerization of MLKL in the liver. Mlkl, but not Rip3, deficiency protected mice from FFC diet-induced liver injury. The FFC diet also induced accumulation of p62 and LC3-II, as well as markers of endoplasmic reticulum stress, in Mlkl^+/+ but not Mlkl^-/- mice. Mlkl deficiency in mice also prevented the inhibition of autophagy by a protease inhibitor, leupeptin. Using an mRFP-GFP-LC3 reporter in cultured hepatocytes revealed that PA blocked the fusion of autophagosomes with lysosomes. PA triggered MLKL expression and translocation, first to autophagosomes and then to the plasma membrane, independently of Rip3. Mlkl, but not Rip3, deficiency prevented inhibition of autophagy in PA-treated hepatocytes. Overexpression of Mlkl blocked autophagy independently of PA. Additionally, pharmacologic inhibition of autophagy induced MLKL expression and translocation to the plasma membrane in hepatocytes.

CONCLUSIONS

Taken together, these data indicate that MLKL-dependent, but RIP3-independent, signaling contributes to FFC diet-induced liver injury by inhibiting autophagy.

LAY SUMMARY

Autophagy is a regulated process that maintains cellular homeostasis. Impaired autophagy contributes to cell injury and death, thus playing a critical role in the pathogenesis of a number of diseases, including non-alcohol-associated fatty liver and steatohepatitis. Herein, we show that Mlkl-dependent, but Rip3-independent, signaling contributed to diet-induced liver injury and inflammatory responses by inhibiting autophagy. These data identify a novel co-regulatory mechanism between necroptotic and autophagic signaling pathways in non-alcoholic fatty liver disease.

Mechanisms of nonalcoholic fatty liver disease and implications for surgery

Background

Nonalcoholic fatty liver disease (NAFLD) has become the most common form of chronic liver disease in both adults and children worldwide. Understanding the pathogenic mechanisms behind NAFLD provides the basis for identifying risk factors, such as metabolic syndrome, pancreatoduodenectomy, and host genetics, that lead to the onset and progression of the disease. The progression from steatosis to more severe forms, such as steatohepatitis, fibrosis, and cirrhosis, leads to an increased number of liver and non-liver complications.

Purpose

NAFLD-associated end-stage liver disease (ESLD) and hepatocellular carcinoma (HCC) often require surgery as the only curative treatment. In particular, the presence of NAFLD together with the coexisting metabolic comorbidities that usually occur in these patients requires careful preoperative diagnosis and peri-/postoperative management. Bariatric surgery, liver resection, and liver transplantation (LT) have shown favorable results for weight loss, HCC, and ESLD in patients with NAFLD. The LT demand and the increasing spread of NAFLD in the donor pool reinforce the already existing lack of donor organs.

Conclusion

In this review, we will discuss the diverse mechanisms underlying NAFLD, its implications for surgery, and the challenges for patient management.

Comprehensive analysis of transcriptomics and metabolomics to understand triptolide-induced liver injury in mice

Triptolide, a major active component of Triptergium wilfordii Hook. f, is used in the treatment of autoimmune disease. However, triptolide is associated with severe adverse reactions, especially hepatotoxicity, which limits its clinical application. To examine the underlying mechanism of triptolide-induced liver injury, a combination of dose- and time-dependent toxic effects, RNA-seq and metabolomics were employed. Triptolide-induced toxicity occurred in a dose- and time-dependent manners and was characterized by apoptosis and not necroptosis. Transcriptomics profiles of the dose-dependent response to triptolide suggested that PI3K/AKT, MAPK, TNFα and p53 signaling pathways were the vital steps in triptolide-induced hepatocyte apoptosis. Metabolomics further revealed that glycerophospholipid, fatty acid, leukotriene, purine and pyrimidine metabolism were the major metabolic alterations after triptolide exposure. Finally, acylcarnitines were identified as potential biomarkers for the early detection of triptolide-induced liver injury.

Deficiency of CD147 Attenuated Non-alcoholic Steatohepatitis Progression in an NLRP3-Dependent Manner

Cluster of differentiation 147 (CD147) is a transmembrane glycoprotein belonging to the immunoglobulin superfamily. CD147 overexpression has been reported to facilitate the development of hepatocellular carcinoma (HCC) and influence immunologic disorders. Although increased expression of CD147 was reported in non-alcoholic steatohepatitis (NASH), functions of CD147 in NASH have not been evaluated. Firstly, we confirmed that CD147 expression was increased in the liver tissues from methionine-choline-deficient (MCD) diet-induced NASH model mice and NASH patients. Mice with hepatocyte-specific CD147 deletion exhibited attenuated NASH phenotypes, including reduced steatosis, liver injury, hepatocyte apoptosis and inflammatory cytokines IL-1β/IL-18 secretion. Following the administration of the MCD diet, NLRP3 expression was increased gradually along with CD147 expression. Furthermore, CD147 deletion inhibited the NF-κB/NLRP3 signaling pathway in both MCD diet-induced mice and primary hepatocytes. Finally, CypA inhibitor TMN355 attenuated liver steatosis and injury and inhibited NF-κB/NLRP3 signaling pathway. Therefore, our results suggest that CD147 played a vital role in NASH pathogenesis by regulating the inflammatory response, and CypA/CD147 could be attractive therapeutic targets for NASH treatment.

Lytic cell death in metabolic liver disease

Regulated cell death is intrinsically associated with inflammatory liver disease and is pivotal in governing outcomes of metabolic liver disease. Different types of cell death may coexist as metabolic liver disease progresses to inflammation, fibrosis, and ultimately cirrhosis. In addition to apoptosis, lytic forms of hepatocellular death, such as necroptosis, pyroptosis and ferroptosis elicit strong inflammatory responses due to cell membrane permeabilisation and release of cellular components, contributing to the recruitment of immune cells and activation of hepatic stellate cells. The control of liver cell death is of fundamental importance and presents novel opportunities for potential therapeutic intervention. This review summarises the underlying mechanism of distinct lytic cell death modes and their commonalities, discusses their relevance to metabolic liver diseases of different aetiologies, and acknowledges the limitations of current knowledge in the field. We focus on the role of hepatocyte necroptosis, pyroptosis and ferroptosis in non-alcoholic fatty liver disease, alcohol-associated liver disease and other metabolic liver disorders, as well as potential therapeutic implications.