Sterile inflammation in acute liver injury: myth or mystery?

Ccl2-Induced Regulatory T Cells Balance Inflammation Through Macrophage Polarization During Liver Reconstitution

Inflammation is highlighted as an initial factor that helps orchestrate liver reconstitution. However, the precise mechanisms controlling inflammation during liver reconstitution have not been fully elucidated. In this study, a clear immune response is demonstrated during hepatic reconstitution. Inhibition of the hepatic inflammatory response retards liver regeneration. During this process, Ccl2 is primarily produced by type 1 innate lymphoid cells (ILC1s), and ILC1-derived Ccl2 recruits peripheral ILC1s and regulatory T cells (Tregs) to the liver. Deletion of Ccl2 or Tregs exacerbates hepatic injury and inflammatory cytokine release, accelerating liver proliferation and regeneration. The adoption of Tregs and IL-10 injection reversed these effects on hepatocyte regenerative proliferation. Additionally, Treg-derived IL-10 can directly induce macrophage polarization from M1 to M2, which alleviated macrophage-secreted IL-6 and TNF-α and balanced the intrahepatic inflammatory milieu during liver reconstitution. This study reveals the capacity of Tregs to modulate the intrahepatic inflammatory milieu and liver reconstitution through IL-10-mediated macrophage polarization, providing a potential opportunity to improve hepatic inflammation and maintain homeostasis.

TRIM26 deficiency enhancing liver regeneration through macrophage polarization and β-catenin pathway activation

Liver regeneration is a complex process involving the crosstalk between parenchymal and non-parenchymal cells, especially macrophages. However, the underlying mechanisms remain incompletely understood. Here, we identify the E3 ubiquitin ligase TRIM26 as a crucial regulator of liver regeneration. Following partial hepatectomy or acute liver injury induced by carbon tetrachloride, Trim26 knockout mice exhibit enhanced hepatocyte proliferation compared to wild-type controls, while adeno-associated virus (AAV)-mediated overexpression of Trim26 reverses the promotional effects. Mechanistically, Trim26 deficiency promotes the recruitment of macrophages to the liver and their polarization towards pro-inflammatory M1 phenotype. These M1 macrophages secrete Wnts, including Wnt2, which subsequently stimulate hepatocyte proliferation through the activation of Wnt/β-catenin signaling. In hepatocytes, Trim26 knockdown reduces the ubiquitination and degradation of β-catenin, thereby further enhancing Wnt/β-catenin signaling. Pharmacological inhibition of Wnt/β-catenin pathway by ICG-001 or depletion of macrophages by clodronate liposomes diminishes the pro-regenerative effects of Trim26 deficiency. Moreover, bone marrow transplantation experiments provide evidence that Trim26 knockout in myeloid cells alone can also promote liver regeneration, highlighting the critical role of macrophage Trim26 in this process. Taken together, our study uncovers TRIM26 as a negative regulator of liver regeneration by modulating macrophage polarization and Wnt/β-catenin signaling in hepatocytes, providing a potential therapeutic target for promoting liver regeneration in clinical settings.

Hepatic Sirt6 activation abrogates acute liver failure

Acute liver failure (ALF) is a deadly illness due to insufficient detoxification in liver induced by drugs, toxins, and other etiologies, and the effective treatment for ALF is very limited. Among the drug-induced ALF, acetaminophen (APAP) overdose is the most common cause. However, the molecular mechanisms underlying APAP hepatoxicity remain incompletely understood. Sirtuin 6 (Sirt6) is a stress responsive protein deacetylase and plays an important role in regulation of DNA repair, genomic stability, oxidative stress, and inflammation. Here, we report that genetic and pharmacological activation of Sirt6 protects against ALF in mice. We first observed that Sirt6 expression was significantly reduced in the liver tissues of human patients with ALF and mice treated with an overdose of APAP. Then we developed an inducible Sirt6 transgenic mice for Cre-mediated overexpression of the human Sirt6 gene in systemic (Sirt6-Tg) and hepatic-specific (Sirt6-HepTg) manners. Both Sirt6-Tg mice and Sirt6-HepTg mice exhibited the significant protection against APAP hepatoxicity. In contrast, hepatic-specific Sirt6 knockout mice exaggerated APAP-induced liver damages. Mechanistically, Sirt6 attenuated APAP-induced hepatocyte necrosis and apoptosis through downregulation of oxidative stress, inflammation, the stress-activated kinase JNK activation, and apoptotic caspase activation. Moreover, Sirt6 negatively modulated the level and activity of poly (ADP-ribose) polymerase 1 (PARP1) in APAP-treated mouse liver tissues. Importantly, the specific Sirt6 activator MDL-800 exhibited better therapeutic potential for APAP hepatoxicity than the current drug acetylcysteine. Furthermore, in the model of bile duct ligation induced ALF, hepatic Sirt6-KO exacerbated, but Sirt6-HepTg mitigated liver damage. Collectively, our results demonstrate that Sirt6 protects against ALF and suggest that targeting Sirt6 activation could be a new therapeutic strategy to alleviate ALF.

P2rx1 deficiency alleviates acetaminophen-induced acute liver failure by regulating the STING signaling pathway

AIMS

Purinergic signaling-mediated mitochondria dysfunction and innate immune-mediated inflammation act as triggers during acetaminophen (APAP)-induced liver injury (AILI). However, the underlying mechanisms by which purinoceptor regulates mitochondria function and inflammation response in the progression of AILI remains unclear.

METHODS

First, the hepatic level of purinergic receptor P2X 1 (P2RX1) was identified in the DILI patients and APAP-induced WT mice. P2rx1 knockout (KO) mice (P2rx1-/-) with 300 mg/kg APAP challenge were used for the analysis of the potential role of P2RX1 in the progression of AILI. Administration of DMX, the activator of stimulator of interferon genes (STING), was performed to investigate the effects of the STING-related pathway on APAP-treated P2rx1-/- mice.

RESULTS

The elevated hepatic P2RX1 levels were found in DILI patients and the AILI mice. P2rx1 depletion offered protection against the initial stages of AILI, mainly by inhibiting cell death and promoting inflammation resolution, which was associated with alleviating mitochondria dysfunction. Mechanistically, P2rx1 depletion could inhibit STING-TANK-binding kinase 1 (TBK1)-P65 signaling pathways in vivo. We then showed that DMX-mediated STING activation could greatly aggravate the liver injury of P2rx1-/- mice treated with APAP.

CONCLUSION

Our data confirmed that P2RX1 was inducted during AILI, identified P2RX1 as a novel regulator in mitochondria dysfunction and STING pathways, and suggested a promising therapeutic approach for AILI involving the blockade of P2RX1. 1. It first demonstrated the protective effects of P2rx1 deficiency on acetaminophen-induced liver injury (AILI). 2. P2rx1 knockout alleviates mitochondria function and promotes inflammation resolution after APAP treatment. 3. It first reported the regulation of P2RX1 on the STING signaling pathway in the progress of AILI. 4. P2RX1 blockade is a promising therapeutic strategy for AILI.

Role of liensinine in sensitivity of activated macrophages to ferroptosis and in acute liver injury

Acute liver injury (ALI) is an acute inflammatory liver disease with a high mortality rate. Alternatively, activated macrophages (AAMs) have been linked to the inflammation and recovery of ALI. However, the mechanism underlying AAM death in ALI has not been studied sufficiently. We used liensinine (Lie) as a drug of choice after screening a library of small-molecule monomers with 1488 compounds from traditional Chinese remedies. In ALI, we evaluated the potential therapeutic effects and underlying mechanisms of action of the drug in ALI and found that it effectively inhibited RSL3-induced ferroptosis in AAM. Lie significantly reduced lipid peroxidation in RSL3-generated AAM. It also improved the survival rate of LPS/D-GalN-treated mice, reduced serum transaminase activity, suppressed inflammatory factor production, and may have lowered AAM ferroptosis in ALI. Lie also inhibited ferritinophagy and blocked Fe²⁺ synthesis. Following combined treatment with RSL3 and Lie, super-resolution microscopy revealed a close correlation between ferritin and LC3-positive vesicles in the AAM. The co-localization of ferritin and LC3 with LAMP1 was significantly reduced. These findings suggest that Lie may ameliorate ALI by inhibiting ferritinophagy and enhancing AMM resistance to ferroptosis by inhibiting autophagosome-lysosome fusion. Therefore, Lie may be used as a potential therapeutic agent for patients with ALI.

The role of macrophage TAM receptor family in the acute-to-chronic progression of liver disease: From friend to foe?

Hepatic macrophages, the key cellular components of the liver, emerge as essential players in liver inflammation, tissue repair and subsequent fibrosis, as well as tumorigenesis. Recently, the TAM receptor tyrosine kinase family, consisting of Tyro3, Axl and MerTK, was found to be a pivotal modulator of macrophages. Activation of macrophage TAM receptor signalling promotes the efferocytosis of apoptotic cells and skews the polarization of macrophages. After briefly reviewing the mechanisms of TAM receptor signalling in macrophage polarization, we focus on their role in liver diseases from acute injury to chronic inflammation, fibrosis and then to tumorigenesis. Notably, macrophage TAM receptor signalling seems to be a two-edged sword for liver diseases. On one hand, the activation of TAM receptor signalling inhibits inflammation and facilitates tissue repair during acute liver injury. On the other hand, continuous activation of the signalling contributes to the process of chronic inflammation into fibrosis and tumorigenesis by evoking hepatic stellate cells and inhibiting anti-tumour immunity. Therefore, targeting macrophage TAM receptors and clarifying its downstream pathways will be exciting prospects for the precaution and treatment of liver diseases, particularly at different stages or statuses.

Liposome cocktail activator modulates hepatocytes and remodels the microenvironment to mitigate acute liver failure

Acute liver failure (ALF) is a mortal and critical hepatic disease, in which oxidative stress, inflammation storm and hepatocyte death are crucial in the pathogenesis. Hence, in contrast to the control of a single link, a combination therapy targeting multiple pathogenic links of the disease will be a favorable means to control the progression of the disease. In this study, we constructed dimethyl itaconate-loaded liposomes modified with dodecyl gallate as a cocktail activator to investigate its functional role in acetaminophen (APAP)-induced ALF. Our results demonstrated that the cocktail activator acted on hepatocytes and triggered cocktail efficacy, thereby simultaneously attenuating APAP-induced hepatocyte damage and remodeling the damage microenvironment. The cocktail activator could effectively scavenge reactive oxygen species, inhibit excessive inflammatory responses and reduce cell death in impaired hepatocytes for detoxification. More importantly, the cocktail activator could remodel the damage microenvironment, thus further promoting hepatocyte expansion and specifically switching macrophages from the M1 to M2 phenotype for a favorable liver regeneration of ALF. Furthermore, in APAP-induced ALF mouse model, the cocktail activator improved liver function, alleviated histopathological damage and increased survival rate. In summary, these findings indicate that the cocktail activator may provide a promising therapeutic approach for ALF treatment as a nanomedicine.

Particulate and drug-induced toxicity assessed in novel quadruple cell human primary hepatic disease models of steatosis and pre-fibrotic NASH

In an effort to replace, reduce and refine animal experimentation, there is an unmet need to advance current in vitro models that offer features with physiological relevance and enhanced predictivity of in vivo toxicological output. Hepatic toxicology is key following chemical, drug and nanomaterials (NMs) exposure, as the liver is vital in metabolic detoxification of chemicals as well as being a major site of xenobiotic accumulation (i.e., low solubility particulates). With the ever-increasing production of NMs, there is a necessity to evaluate the probability of consequential adverse effects, not only in health but also in clinically asymptomatic liver, as part of risk stratification strategies. In this study, two unique disease initiation and maintenance protocols were developed and utilised to mimic steatosis and pre-fibrotic NASH in scaffold-free 3D liver microtissues (MT) composed of primary human hepatocytes, hepatic stellate cells, Kupffer cells and sinusoidal endothelial cells. The characterized diseased MT were utilized for the toxicological assessment of a panel of xenobiotics. Highlights from the study included: 1. Clear experimental evidence for the pre-existing liver disease is important in the augmentation of xenobiotic-induced hepatotoxicity and 2. NMs are able to activate stellate cells. The data demonstrated that pre-existing disease is vital in the intensification of xenobiotic-induced liver damage. Therefore, it is imperative that all stages of the wide spectrum of liver disease are incorporated in risk assessment strategies. This is of significant consequence, as a substantial number of the general population suffer from sub-clinical liver injury without any apparent or diagnosed manifestations.

Liquiritigenin protects against arsenic trioxide-induced liver injury by inhibiting oxidative stress and enhancing mTOR-mediated autophagy

Liquiritigenin (LQ) has protective effects against various hepatotoxicities. However, its specific role on arsenic trioxide (ATO)-induced hepatotoxicity and the related biomolecular mechanisms remain unclear. The purpose of this study is to explore the protective actions of LQ on ATO-induced hepatotoxicity and its biomolecular mechanisms in mice. LQ was administered orally at 20 and 40 mg/kg per day for seven consecutive days with an intraperitoneal injection of ATO (5 mg/kg). Liver injury was induced by ATO and was alleviated by treatment with LQ as reflected by reduced histopathological damage of liver and decreased serum ALT, AST, and ALP levels. The generation of intracellular ROS induced by ATO was attenuated after LQ treatment. The levels of SOD, CAT, and GSH were elevated with LQ administration while MDA levels decreased. LQ mitigated elevated TNF-α and IL-6 levels as well as the hepatic mitochondrial damage caused by ATO. Moreover, LQ upregulated the expression of LC3-II and enhanced autophagy in the liver of ATO-induced mice. Further studies indicated that LQ significantly suppressed the expression of p-PI3K, p-AKT, and p-mTOR in ATO-induced mice. In conclusion, our findings show that LQ protects against ATO-induced hepatotoxicity due to its antioxidant and anti-inflammatory activities and enhancement of autophagy mediated by the PI3K/AKT/mTOR signaling pathway in mice.

Modulation of HMGB1 Release in APAP-Induced Liver Injury: A Possible Strategy of Chikusetsusaponin V Targeting NETs Formation

Acetaminophen (APAP), one of the most common antipyretic analgesics, which is safe at therapeutic dose, cause acute liver injury and even death at overdose. However, the mechanism of APAP-induced inflammation in liver injury is still controversial. Therefore, effective drug intervention is urgently needed. The aim of this study was to explore the inflammatory exact mechanism of APAP, especially on neutrophils, and to study the intervention effect of Chikusetsusaponin V (CKV) derived from Panax japonicus. Establishment of hepatotoxicity model of APAP in vitro and in vivo. In vitro, HepG2 cells, AML12 cells, primary mouse hepatocytes and neutrophils were used to mimic APAP-affected hepatocytes and neutrophil. In vivo, C57BL/6 mice were administrated overdose of APAP with or without neutrophil depletion or abolishing neutrophil extracellular traps (NETs) formation. In this study, APAP stimulation increased the level of HMGB1, IL-1β and Caspase-1 in mouse liver, especially hepatocytes, which had a synergistic effect with LPS/ATP combination. NETs were formatted at early stage of APAP or HMGB1-stimulated neutrophils’ damage. Conditioned mediums from APAP-treated hepatocytes induced more significant NETs than direct APAP stimulation. Neutrophil depletion or abolishing NETs formation decreased HMGB1 level, eventually blocked hepatocytes necrosis. CKV pretreatment interfered Caspase-1 activation and HMGB1 release in APAP-damaged hepatocytes. CKV also prevented NETs formation. These results indicate that the production of HMGB1 may depend on the activation of Caspase-1 and play a key role in liver inflammation caused by APAP. The cross-dialogue between hepatocytes and neutrophils can be mediated by HMGB1. Therefore, CKV has a positive intervention effect on NETs-related inflammation in APAP-damaged liver, targeting Caspase-1-HMGB1.

Disturbed mitochondrial redox state and tissue energy charge in cholestasis

The liver is the primary organ affected by cholestasis. However, the brain, skeletal muscle, heart, and kidney are also severely influenced by cholestasis/cirrhosis. However, little is known about the molecular mechanisms of organ injury in cholestasis. The current study was designed to evaluate the mitochondrial glutathione redox state as a significant index in cell death. Moreover, tissue energy charge (EC) was calculated. Rats underwent bile duct ligation (BDL) and the brain, heart, liver, kidney, and skeletal muscle mitochondria were assessed at scheduled time intervals (3, 7, 14, and 28 days after BDL). A significant decrease in mitochondrial glutathione redox state and EC was detected in BDL animals. Moreover, disturbed mitochondrial indices were evident in different organs of BDL rats. These data could offer new insight into the mechanisms of organ injury and the source of oxidative stress during cholestasis and might provide novel therapeutic strategies against these complications.

The cross-talk of NLRP3 inflammasome activation and necroptotic hepatocyte death in acetaminophen-induced mice acute liver injury

Overdose acetaminophen (APAP) can result in severe liver injury, which is responsible for nearly half of drug-induced liver injury in western countries. Previous studies have found that there existed massive hepatocellular necrosis and severe inflammatory response in APAP-induced liver injury. However, the mechanistic linkage between necroptosis and NLRP3 inflammasome pathway in APAP-induced hepatotoxicity remains poorly understood. In order to investigate the relationship between inflammation and hepatocytes death in APAP hepatotoxicity, a time-course model for APAP hepatotoxicity in C57/BL6 mice was established by intraperitoneal (i.p) injection of 300 mg/kg APAP in this study. The activity of serum enzymes and pathological changes of APAP-treated mice were evaluated, and the critical molecules in necroptosis and NF-κB-NLRP3 inflammasome signaling pathway were determined by immunoblot and immunofluorescence analysis. The results demonstrated that APAP overdose resulted in a severe liver injury. Furthermore, the expression of critical molecules in NLRP3 inflammasome and necroptosis pathways peaked at 12-24 h, and then was decreased gradually, which is consistent with the pattern of pathological injury induced by APAP. Our further investigation found that the level of IL-1β in mouse liver was closely correlated with the level of phosphorylated MLKL following exposure to APAP. Furthermore, inhibition of necroptosis with necrostatin-1 significantly suppressed the activation of NLRP3 inflammasome signaling. Taken together, our results highlighted that the cross-talk between necroptosis and NLRP3 inflammasome played a critical role for promoting APAP-induced liver injury. Inhibition of the interaction of inflammation and necroptosis by pharmaceutical methods may represent a promising therapeutic strategy for APAP-induced liver injury.

The platelet receptor CLEC-2 blocks neutrophil mediated hepatic recovery in acetaminophen induced acute liver failure

Acetaminophen (APAP) is the main cause of acute liver failure in the West. Specific efficacious therapies for acute liver failure (ALF) are limited and time-dependent. The mechanisms that drive irreversible acute liver failure remain poorly characterized. Here we report that the recently discovered platelet receptor CLEC-2 (C-type lectin-like receptor) perpetuates and worsens liver damage after toxic liver injury. Our data demonstrate that blocking platelet CLEC-2 signalling enhances liver recovery from acute toxic liver injuries (APAP and carbon tetrachloride) by increasing tumour necrosis factor-α (TNF-α) production which then enhances reparative hepatic neutrophil recruitment. We provide data from humans and mice demonstrating that platelet CLEC-2 influences the hepatic sterile inflammatory response and that this can be manipulated for therapeutic benefit in acute liver injury. Since CLEC-2 mediated platelet activation is independent of major haemostatic pathways, blocking this pathway represents a coagulopathy-sparing, specific and novel therapy in acute liver failure.

The role of hepatic sinusoidal obstruction in the pathogenesis of the hepatic involvement in HELLP syndrome: Exploring the literature

AIM

This study aims to determine, based on existing data, whether the mechanism resulting in liver dysfunction in HELLP syndrome resembles that in Sinusoidal Obstruction Syndrome (SOS).

BACKGROUND

HELLP syndrome is a serious pregnancy disorder with high maternal and perinatal morbidity and mortality rates. Because of poor insight in its pathophysiology, particularly that of the liver involvement, clinical management is limited to symptomatic treatment, often followed by termination of pregnancy. SOS is a rare, potentially life-threatening complication of radio and/ or chemotherapy in the preparation of hematopoietic cell transplantation. The etiology of liver dysfunction in SOS is - unlike that in HELLP syndrome - better-understood and seems to be initiated by direct toxic damage and demise of endothelial cells, causing hepatic sinusoidal obstruction and ischemia.

METHODS

We searched Pubmed, Embase and Cochrane for reports on the etiology of HELLP and SOS. This yielded 73 articles, with 14 additional reports from the references listed in these articles.

RESULTS

The dysfunctional placenta in women developing HELLP initiates a cascade of events that eventually results in liver dysfunction. The placenta releases, besides anti-angiogenetic factors, also necrotic debris and cell-free DNA, a mixture that not only induces systemic endothelial dysfunction as in preeclampsia, but also a systemic inflammatory response. The latter aggravates the endothelio-toxic effects in the systemic cardiovascular bed, amplifying the already increased pro-thrombotic conditions. Particularly in microcirculations with extremely low shear forces, such as in the hepatic sinusoids, this will facilitate microthrombi formation and fibrin deposition eventually resulting in obstruction of the sinusoids similar as in SOS. The latter causes ischemic damage and progressive demise of hepatocytes.

CONCLUSION

The available information supports the concept that the liver damage in HELLP and SOS results from sinusoidal ischemia, presumably resulting from partially overlapping pathophysiological mechanisms.

Protective role of N-acetyl-l-tryptophan against hepatic ischemia-reperfusion injury via the RIP2/caspase-1/IL-1β signaling pathway

Context: Hepatic ischemia-reperfusion injury (HIRI) is a complex process observed during liver resection and transplantation. N-acetyl-l-tryptophan (l-NAT), an antagonist of neurokinin 1 receptor, has been used for the treatment of nausea and neurodegenerative diseases. Objective: This study investigates the protective effect of l-NAT against HIRI and explores the potential underlying mechanisms. Materials and methods: Adult male Sprague-Dawley (SD) rats were randomly divided into three groups: sham, I/R and I/R + l-NAT. HIRI model was generated by clamping the hepatic artery, portal vein and common bile duct with a microvascular bulldog clamp for 45 min, and then removing the clamp and allowing reperfusion for 6 h. BRL cells were exposed to 200 µM H2O2 with or without 10 µM l-NAT for 6 h. Results: After l-NAT intervention, the structure of hepatic lobules was intact, and no swelling was noted in the cells. Furthermore, cell viability was found to be significantly enhanced when compared with the controls (p < 0.05). The mRNA and protein expression levels of serine-threonine kinase 2 (RIP2) and interleukin-1β (IL-1β) were significantly increased in the I/R and H2O2 groups when compared with the controls; however, these levels were significantly decreased after l-NAT intervention. Similarly, IL-1β activity and caspase-1 activity were significantly decreased in the H2O2 group when compared with the controls, after l-NAT intervention. Conclusions: Our findings indicated that l-NAT may exert a hepatoprotective role in HIRI through inhibiting RIP2/caspase-1/IL-1β signaling pathway, which can provide evidence for l-NAT to be a potential effective drug against HIRI during clinical practice.

CCL5 deficiency promotes liver repair by improving inflammation resolution and liver regeneration through M2 macrophage polarization

Despite the diverse etiologies of drug-induced liver injury (DILI), innate immunity activation is a common feature involved in DILI progression. However, the involvement of innate immunity regulation in inflammation resolution and liver regeneration in DILI remains obscure. Herein, we identified the chemokine CCL5 as a central mediator of innate immunity regulation in the pathogenesis of DILI. First, we showed that serum and hepatic CCL5 levels are elevated in both DILI patients and an APAP-induced liver injury (AILI) mouse model. Interestingly, both nonparenchymal cells and stressed hepatocytes are cell sources of CCL5 induction in response to liver injury. Functional experiments showed that CCL5 deficiency has no effect on the early phase of AILI but promotes liver repair in the late phase mainly by promoting inflammation resolution and liver regeneration, which are associated with an increased number of hepatic M2 macrophages. Mechanistically, CCL5 can directly activate M1 polarization and impede M2 polarization through the CCR1- and CCR5-mediated activation of the MAPK and NF-κB pathways. We then showed that CCL5 inhibition mediated by either a CCL5-neutralizing antibody or the antagonist Met-CCL5 can greatly alleviate liver injury and improve survival in an AILI mouse model. Our data demonstrate CCL5 induction during DILI, identify CCL5 as a novel innate immunity regulator in macrophage polarization, and suggest that CCL5 blockage is a promising therapeutic strategy for the treatment of DILI.

Circulating Peroxiredoxin-1 is a novel damage-associated molecular pattern and aggravates acute liver injury via promoting inflammation

Sterile inflammation is initiated by damage-associated molecular patterns (DAMPs) and a key contributor to acute liver injury (ALI). However, the current knowledge on those DAMPs that activate hepatic inflammation under ALI remains incomplete. We report here that circulating peroxiredoxin-1 (Prdx1) is a novel DAMP for ALI. Intraperitoneal injection of acetaminophen (APAP) elicited a progressive course of ALI in mice, which was developed from 12 to 24 h post injection along with liver inflammation evident by macrophage infiltration and upregulations of cytokines (IL-1β, IL-6 and TNF-α); these alterations were concurrently occurred with a robust and progressive production of serum Prdx1. Similar observations were also obtained in carbon tetrachloride (CCl₄)-induced ALI in mice. Removal of the source of serum Prdx1 protected mice deficient in Prdx1 from APAP and CCl₄-induced liver injury, and decreased macrophage infiltration, IL-1β, IL-6 and TNF-α production. As a result, Prdx1^-/- mice were strongly protected from APAP-induced death that was likely progressed from ALI. Additionally, intravenous re-introduction of recombinant Prdx1 (rPrdx1) in Prdx1^-/- mice reversed or reduced all the above events, demonstrating an important contribution of circulating Prdx1 to ALI. rPrdx1 potently induced in primary macrophages the expression of pro-IL-1β, IL-6, TNF-α, and IL-1β through the NF-κB signaling as well as the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome signaling, evident by caspase-1 activation. Furthermore, a significant elevation of serum Prdx1 was demonstrated in patients (n = 15) with ALI; the elevation is associated with ALI severity. Collectively, we provide the first demonstration for serum Prdx1 contributing to ALI.

Zerumbone Protects against Carbon Tetrachloride (CCl4)-Induced Acute Liver Injury in Mice via Inhibiting Oxidative Stress and the Inflammatory Response: Involving the TLR4/NF-κB/COX-2 Pathway

The natural compound Zerumbone (hereinafter referred to as ZER), a monocyclic sesquiterpenoid, has been reported to possess many pharmacological properties, including antioxidant and anti-inflammatory properties. This study aimed to investigate the underlying mechanism of ZER against acute liver injury (ALI) in CCl₄-induced mice models. ICR mice were pretreated intraperitoneally with ZER for five days, then received a CCl₄ injection two hours after the last ZER administration and were sacrificed 24 h later. Examination of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and the histopathological analysis confirmed the hepatoprotective effect of ZER. Biochemical assays revealed that ZER pretreatment recovered the activities of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), restored the glutathione (GSH) reservoir, and reduced the production of malondialdehyde (MDA), all in a dose-dependent manner. Furthermore, administration of ZER in vivo reduced the release amounts of pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and inhibited the increased protein levels of Toll-like receptor 4 (TLR4), nuclear factor-kappaB (NF-κB) p-p65, and cyclooxygenase (COX-2). Further studies in lipopolysaccharide (LPS)-induced Raw264.7 inflammatory cellular models verified that ZER could inhibit inflammation via inactivating the TLR4/NF-κB/COX-2 pathway. Thus, our study indicated that ZER exhibited a hepatoprotective effect against ALI through its antioxidant and anti-inflammatory activities and the possible mechanism might be mediated by the TLR4/NF-κB/COX-2 pathway. Collectively, our studies indicate ZER could be a potential candidate for chemical liver injury treatment.

Autophagy in liver diseases: Time for translation?

Autophagy is a self-eating catabolic pathway that contributes to liver homeostasis through its role in energy balance and in the quality control of the cytoplasm, by removing misfolded proteins, damaged organelles and lipid droplets. Autophagy not only regulates hepatocyte functions but also impacts on non-parenchymal cells, such as endothelial cells, macrophages and hepatic stellate cells. Deregulation of autophagy has been linked to many liver diseases and its modulation is now recognized as a potential new therapeutic strategy. Indeed, enhancing autophagy may prevent the progression of a number of liver diseases, including storage disorders (alpha-1 antitrypsin deficiency, Wilson's disease), acute liver injury, non-alcoholic steatohepatitis and chronic alcohol-related liver disease. Nevertheless, in some situations such as fibrosis, targeting specific liver cells must be considered, as autophagy displays opposing functions depending on the cell type. In addition, an optimal therapeutic time-window should be identified, since autophagy might be beneficial in the initial stages of disease, but detrimental at more advanced stages, as in the case of hepatocellular carcinoma. Finally, identifying biomarkers of autophagy and methods to monitor autophagic flux in vivo are important steps for the future development of personalized autophagy-targeting strategies. In this review, we provide an update on the regulatory role of autophagy in various aspects of liver pathophysiology, describing the different strategies to manipulate autophagy and discussing the potential to modulate autophagy as a therapeutic strategy in the context of liver diseases.

The inhibitor of glycerol 3-phosphate acyltransferase FSG67 blunts liver regeneration after acetaminophen overdose by altering GSK3β and Wnt/β-catenin signaling

Repair mechanisms after acetaminophen (APAP) hepatotoxicity are poorly understood. We recently discovered that phosphatidic acid (PA) increases in mice and humans after APAP overdose, and is critical for liver regeneration. Here, we hypothesized that PA inhibits glycogen synthase kinase-3β (GSK3β), a component of canonical Wnt/β-catenin signaling, after APAP overdose. To test that, we treated mice with 300 mg/kg APAP at 0 h followed by vehicle or 20 mg/kg of the glycerol 3-phosphate acyltransferase inhibitor FSG67 at 3, 24 and 48 h. Some mice also received the GSK3 inhibitor L803-mts. Blood and liver were collected at multiple time points. Consistent with our earlier results, FSG67 did not affect toxicity (ALT, histology), APAP bioactivation (total glutathione), or oxidative stress (oxidized glutathione), but did reduce expression of proliferating cell nuclear antigen (PCNA) at 52 h. We then measured GSK3β phosphorylation and found it was dramatically decreased by FSG67 at 24 h, before PCNA dropped. Expression of cyclin D1, downstream of Wnt/β-catenin, was also reduced. To determine if the effect of FSG67 on GSK3β is important, we treated mice with FSG67 and L803-mts after APAP. Importantly, L803-mts rescued hepatocyte proliferation and survival. Our data indicate PA and lysoPA may support recovery after APAP overdose by inhibiting GSK3β.

Therapeutic Potential of Plants and Plant Derived Phytochemicals against Acetaminophen-Induced Liver Injury

Acetaminophen (APAP), which is also known as paracetamol or N-acetyl-p-aminophenol is a safe and potent drug for fever, pain and inflammation when used at its normal therapeutic doses. It is available as over-the-counter drug and used by all the age groups. The overdose results in acute liver failure that often requires liver transplantation. Current clinical therapy for APAP-induced liver toxicity is the administration of N-acetyl-cysteine (NAC), a sulphydryl compound an approved drug which acts by replenishing cellular glutathione (GSH) stores in the liver. Over the past five decades, several studies indicate that the safety and efficacy of herbal extracts or plant derived compounds that are used either as monotherapy or as an adjunct therapy along with conventional medicines for hepatotoxicity have shown favorable responses. Phytochemicals mitigate necrotic cell death and protect against APAP-induced liver toxicityby restoring cellular antioxidant defense system, limiting oxidative stress and subsequently protecting mitochondrial dysfunction and inflammation. Recent experimental evidences indicat that these phytochemicals also regulate differential gene expression to modulate various cellular pathways that are implicated in cellular protection. Therefore, in this review, we highlight the role of the phytochemicals, which are shown to be efficacious in clinically relevant APAP-induced hepatotoxicity experimental models. In this review, we have made comprehensive attempt to delineate the molecular mechanism and the cellular targets that are modulated by the phytochemicals to mediate the cytoprotective effect against APAP-induced hepatotoxicity. In this review, we have also defined the challenges and scope of phytochemicals to be developed as drugs to target APAP-induced hepatotoxicity.

Danger-Associated Molecular Patterns (DAMPs): Molecular Triggers for Sterile Inflammation in the Liver

Inflammatory liver diseases in the absence of pathogens such as intoxication by xenobiotics, cholestatic liver injury, hepatic ischemia-reperfusion injury (I/R), non-alcoholic steatohepatitis (NASH), or alcoholic liver disease (ALD) remain threatening conditions demanding specific therapeutic options. Caused by various different noxae, all these conditions have been recognized to be triggered by danger- or death-associated molecular patterns (DAMPs), discompartmentalized self-structures released by dying cells. These endogenous, ectopic molecules comprise proteins, nucleic acids, adenosine triphosphate (ATP), or mitochondrial compounds, among others. This review resumes the respective modes of their release—passively by necrotic hepatocytes or actively by viable or apoptotic parenchymal cells—and their particular roles in sterile liver pathology. It addresses their sensors and the initial inflammatory responses they provoke. It further addresses a resulting second wave of parenchymal death that might be of different mode, boosting the release of additional, second-line DAMPs. Thus, triggering a more complex and pronounced response. Initial and secondary inflammatory responses comprise the activation of Kupffer cells (KCs), the attraction and activation of monocytes and neutrophil granulocytes, and the induction of type I interferons (IFNs) and their effectors. A thorough understanding of pathophysiology is a prerequisite for identifying rational therapeutic targets.

The innate immune receptor TREM-1 promotes liver injury and fibrosis

Inflammation occurs in all tissues in response to injury or stress and is the key process underlying hepatic fibrogenesis. Targeting chronic and uncontrolled inflammation is one strategy to prevent liver injury and fibrosis progression. Here, we demonstrate that triggering receptor expressed on myeloid cells 1 (TREM-1), an amplifier of inflammation, promotes liver disease by intensifying hepatic inflammation and fibrosis. In the liver, TREM-1 expression was limited to liver macrophages and monocytes and was highly upregulated on Kupffer cells, circulating monocytes, and monocyte-derived macrophages in a mouse model of chronic liver injury and fibrosis induced by carbon tetrachloride (CCl4) administration. TREM-1 signaling promoted proinflammatory cytokine production and mobilization of inflammatory cells to the site of injury. Deletion of Trem1 reduced liver injury, inflammatory cell infiltration, and fibrogenesis. Reconstitution of Trem1-deficient mice with Trem1-sufficient Kupffer cells restored the recruitment of inflammatory monocytes and the severity of liver injury. Markedly increased infiltration of liver fibrotic areas with TREM-1-positive Kupffer cells and monocytes/macrophages was found in patients with hepatic fibrosis. Our data support a role of TREM-1 in liver injury and hepatic fibrogenesis and suggest that TREM-1 is a master regulator of Kupffer cell activation, which escalates chronic liver inflammatory responses, activates hepatic stellate cells, and reveals a mechanism of promotion of liver fibrosis.

Review article: therapeutic bile acids and the risks for hepatotoxicity

BACKGROUND

Bile acids play important roles in cholesterol metabolism and signal through farnesoid X receptor and G protein-coupled receptors. Given their importance in liver biology, bile acid therapy enables therapeutic applications beyond the treatment of cholestatic liver disease. However, predicting hepatotoxicity of bile acids in humans is obscured due to inconsistent extrapolations of animal data to humans.

AIM

To review the evidence that could explain discordant bile acids hepatotoxicity observed in humans and animals.

METHOD

Literature search was conducted in PubMed using keywords "bile acid," "transporter," "hepatotoxicity," "clinical study," "animal study," "species difference," "mechanism," "genetic disorder." Relevant articles were selected for review.

RESULTS

Clinically significant hepatotoxicity was reported in response to certain bile acids, namely chenodeoxycholic acid, which was given a boxed warning for potential hepatotoxicity. The chemical structure, specifically the number and orientation of hydroxyl groups, significantly affects their hydrophobicity, an important factor in bile acid toxicity. Experimental studies show that hydrophobic bile acids can lead to liver injury through various mechanisms, such as death receptor signalling, mitochondrial dysfunction and inflammation. Although animal studies play a central role in investigating bile acid safety, there are considerable differences in bile acid composition, metabolism and hepatobiliary disposition across species. This does not allow appropriate safety inference, especially for predicting hepatotoxicity in humans. Exploring evidences stemming from inborn errors, genetic models of disease and toxicology studies further improves an understanding of bile acid hepatotoxicity.

CONCLUSION

Species differences should be considered in the development of bile acid related therapeutics. Although the mechanism of bile acid hepatotoxicity is still not fully understood, continued mechanistic studies will deepen our understanding.

Ethyl pyruvate attenuates acetaminophen-induced liver injury and prevents cellular injury induced by N-acetyl-p-benzoquinone imine

Acetaminophen, a common analgesic/antipyretic, is a frequent cause of acute liver failure in Western countries. The development of an effective cure against acetaminophen hepatotoxicity is crucial. Ethyl pyruvate, an ethyl ester derivative of pyruvic acid, has been identified as a possible candidate against acetaminophen hepatotoxicity in animal experiments. However, the mode of the hepatoprotective action of ethyl pyruvate remains unclear. We examined the hepatoprotective effect of ethyl pyruvate against hepatocyte injury and oxidative stress in a mouse model of acetaminophen hepatotoxicity. In addition, to examine whether ethyl pyruvate has direct hepatocellular protection against acetaminophen hepatotoxicity to counteract the influence of inflammatory cells, such as macrophages, we examined the effects of ethyl pyruvate on cellular injury induced by N-acetyl-p-benzoquinone imine, a toxic metabolite of acetaminophen, in a human hepatocyte cell line, HepG2 cells. Treatment with ethyl pyruvate significantly prevented increases in serum transaminase levels and hepatic centrilobular necrosis induced with an acetaminophen overdose in mice in a dose-dependent manner. Although hepatic DNA fragmentation induced by acetaminophen was also attenuated with ethyl pyruvate, nitrotyrosine formation was not inhibited. Ehyl pyruvate significantly attenuated mitochondria dehydrogenase inactivity induced by N-acetyl-p-benzoquinone imine in HepG2 cells. The attenuating effect was also observed in a rat hepatocyte cell line. Increases in annexin V and propidium iodide-stained cells induced by N-acetyl-p-benzoquinone imine were prevented with ethyl pyruvate in HepG2 cells. Pyruvic acid, a parent compound of ethyl pyruvate, tended to attenuate these changes. The results indicate that ethyl pyruvate has direct hepatocellular protection against N-acetyl-p-benzoquinone imine induced injury observed in acetaminophen overdose. The in vivo and in vitro results suggest that ethyl pyruvate attenuates acetaminophen-induced liver injury via, at least in part, its cellular protective potential.

The impact of sterile inflammation in acute liver injury

BACKGROUND

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

AIM

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

RELEVANCE FOR PATIENTS

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