Veronica persica ameliorates acetaminophen-induced murine hepatotoxicity via attenuating oxidative stress and inflammation

Excess acetaminophen (APAP) commonly causes severe acute liver injury (ALI), characterized by oxidative stress, pro-inflammatory responses, and hepatocyte damage. Veronica persica (VP) is a traditional medicine with antioxidant and anti-inflammatory properties. There is a paucity of information on its medicinal value, especially its potential mechanisms for alleviating ALI. This study aimed to clarify the ameliorative effects and intracellular mechanisms of VP on APAP-induced ALI via attenuating oxidative stress and inflammation. Mice were given VP for 7 days before exposure to APAP (300 mg/kg). The HPLC and radical scavenging assay found that VP contains 12 phenolic acids and 6 flavonoids, as well as show robust antioxidant capacity. In the APAP-induced ALI model, pre-treatment with VP significantly reduces APAP-induced hepatotoxicity by observing improved hepatocyte pathological injury and further confirmed by serum biochemical indicator. Also, the reduction of TUNEL-positive regions and the regulation of Bcl-2-associated X protein indicated that VP attenuates hepatocytotoxicity. Moreover, VP pre-intervention inhibits the formation of liver pro-inflammatory cytokines, the expression of inflammatory response genes, and increases in myeloperoxidase (MPO) in APAP-exposed mice. The elevated reduced glutathione (GSH) levels and decreased oxidative stress markers indicate that VP reduces APAP-promoted oxidative stress. Further study revealed that VP inhibited the phosphorylation of NF-κB/STAT3 cascade, blocked ERK and JNK phosphorylation, and activated AMP-activated protein kinase (AMPK). To sum up, this study demonstrated that VP exists hepatoprotective abilities on APAP-induced ALI, primarily by suppressing the phosphorylation of NF-κB/STAT3 cascade and ERK-JNK and inducing AMPK activation to alleviate oxidative stress and inflammation.

The hepatoprotective effect of Sophora viciifolia fruit extract against acetaminophen-induced liver injury in mice

This research demonstrated the protective effect and possible mechanism of the Sophora viciifolia extract (SVE) against acetaminophen-induced liver injury in mice. The levels of ALT and AST in the serum and antioxidant enzyme activity in the liver were measured. We used immunohistochemistry to detect CYP2E1, Nrf2, and Keap1 protein expression in the liver. The mRNA expression in the liver of TNF-α, NF-κB, and IL-6, Nrf2 and its downstream genes HO-1 and GCLC were measured by qRT-PCR. We found that SVE could decrease the ALT and AST levels, promote the activities of SOD, CAT, GSH-Px, and GSH, and ameliorate pathological liver lesions. SVE could down-regulate the mRNA expression of inflammatory factors and up-regulate Nrf2, HO-1 and GCLC. SVE reduced the protein expression of the CYP2E1 and increased the Nrf2 and Keap1. SVE has been shown to have a protective effect against APAP-induced liver injury, possibly through activation of the Keap1-Nrf2 pathway.

Fluorine-thiol displacement probes for acetaminophen's hepatotoxicity

Chemicals possessing reactive electrophiles can denature innate proteins leading to undesired toxicity, and the overdose-induced liver injury by drugs containing electrophiles has been one of the major causes of non-approval and withdraw by the US Food and Drug Administration (FDA). Elucidating the associated proteins could guide the future development of therapeutics to circumvent these drugs' toxicities, but was largely limited by the current probing tools due to the steric hindrance of chemical tags including the common "click chemistry" labels. Taking the widely used non-steroidal anti-inflammatory drug acetaminophen (APAP) as an example, we hereby designed and synthesized an APAP analogue using fluorine as a steric-free label. Cell toxicity studies indicated our analogue has similar activity to the parent drug. This analogue was applied to the mouse hepatocellular proteome together with the corresponding desthiobiotin-SH probe for subsequent fluorine-thiol displacement reactions (FTDRs). This set of probes has enabled the labeling and pull-down of hepatocellular target proteins of the APAP metabolite as validated by Western blotting. Our preliminary validation results supported the interaction of APAP with the thioredoxin protein, which is an important redox protein for normal liver function. These results demonstrated that our probes confer minimal steric perturbation and mimic the compounds of interest, allowing for global profiling of interacting proteins. The fluorine-thiol displacement probing system could emerge as a powerful tool to enable the investigation of drug-protein interactions in complex biological environments.

Diacerein ameliorates acetaminophen hepatotoxicity in rats via inhibiting HMGB1/TLR4/NF-κB and upregulating PPAR-γ signal

BACKGROUND

Acetaminophen (APAP) is a worldwide antipyretic as well as an analgesic medication. It has been extensively utilized during the outbreak of coronavirus 2019 (COVID-19). APAP misuse would lead to liver injury. Diacerein (DIA), an anthraquinone derivative, has antioxidant and inflammatory properties. Hence, this study attempted to evaluate the impact of DIA treatment on liver injury induced by APAP and its influence on nuclear factor-κB (NF-κB) /toll-like receptor 4 (TLR4)/high mobility group box-1(HMGB-1) signaling as well as the expression of peroxisome proliferator-activated receptor-gamma (PPAR-γ) expression.

METHODS

Male albino rats received 25 as well as 50 mg/kg/day DIA orally for seven days. One hour after the last administration, rats received APAP (1gm/kg, orally). For histopathological analysis, liver tissues and blood were collected, immunohistochemical (IHC) assay, biochemical assay, as well as quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

DIA markedly reduced liver injury markers and ameliorated histopathological changes. Moreover, DIA dose-dependently alleviated oxidative stress status caused by APAP administration along with inflammatory markers, including the level of interleukin-1 beta (IL-1β), myeloperoxidase (MPO), tumor necrosis factor-alpha (TNF-α), and interleukin 6 (IL-6). Furthermore, DIA downregulated protein levels as well as mRNA of HMGB-1, TLR4, NF-κB p65 expression, and enhanced PPAR-γ expression. Moreover, DIA ameliorated apoptotic (Bax) and caspase-3 expressions and increased the anti-apoptotic (Bcl2) expression.

CONCLUSIONS

This study demonstrated that DIA exerts anti-apoptotic, anti-inflammatory, and antioxidant properties against liver injury induced by APAP that is attributed to inhibition of the HMGB1/TLR4/NF-κB pathway, besides upregulation of the expression of PPAR-γ.

Echinacoside alleviates acetaminophen-induced liver injury by attenuating oxidative stress and inflammatory cytokines in mice

This study evaluates the protective effect of Echinacoside on acute liver toxicity induced by acetaminophen in mice and the mechanism behind it. Echinacoside and N-Acetyl Cysteine were intragastrically administrated for 7 days, and acetaminophen was intraperitoneally injected into mice 1 h after the last treatment on day 7. At the end of the experimental period, histological examination, parameters for the level of oxidative damage, hepatic malondialdehyde, serum pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-6, and interleukin-1β), UDP-glucuronosyltransferases, and sulfotransferases changes were examined using enzyme-linked immunosorbent assay and standard biochemical procedures. The expression of cytochrome P450 2E1 protein was assessed by western blot, followed by in silico molecular docking. Acetaminophen treatment obviously increased the levels of ALT and AST, changed hepatic histopathology, promoted oxidative stress, decreased antioxidant enzyme activities, and elevated the pro-inflammatory cytokines. Echinacoside significantly attenuated Acetaminophen-induced liver damage in a dose-dependent manner, with the most effective dose at 100 mg/kg. The pretreatments of Echinacoside in different concentrations altered the Acetaminophen-induced hepatotoxicity levels by decreasing the level of liver enzymes, reducing the liver necrosis with vacuolization, decreasing the hepatic malondialdehyde formation, increasing hepatic antioxidants activities, suppressing the pro-inflammatory cytokines (Tumor Necrosis Factor, Interleukin-6 and Interleukin-1beta), inhibiting Nitric Oxide production, enhancing sulfotransferases and UDP-glucuronosyltransferases activities. Notably, the expression of cytochrome P450 2E1 was inhibited by Echinacoside in a dose-dependent manner and the binding energy was -214.3 MeV. Echinacoside showed a significant protective effect against Acetaminophen-induced hepatotoxicity through the inhibition of oxidative stress, the expression of pro-inflammatory cytokines and cytochrome P450 2E1 protein expression.

Liver-specific deletion of mechanistic target of rapamycin does not protect against acetaminophen-induced liver injury in mice

BACKGROUND

Acetaminophen (APAP) overdose can cause liver injury and liver failure, which is one of the most common causes of drug-induced liver injury in the United States. Pharmacological activation of autophagy by inhibiting mechanistic target of rapamycin (mTOR) protects against APAP-induced liver injury likely via autophagic removal of APAP-adducts and damaged mitochondria. In the present study, we aimed to investigate the role of genetic ablation of mTOR pathways in mouse liver in APAP-induced liver injury and liver repair/regeneration.

METHODS

Albumin-Cre (Alb-Cre) mice, mTOR^f/f and Raptor^f/f mice (C57BL/6J background) were crossbred to produce liver-specific mTOR knockout (L-mTOR KO, Alb Cre+/-, mTOR^f/f) and liver-specific Raptor KO (L-Raptor, Alb Cre+/-, Raptor ^f/f) mice. Alb-Cre littermates were used as wild-type (WT) mice. These mice were treated with APAP for various time points for up to 48 h. Liver injury, cell proliferation, autophagy and mTOR activation were determined.

RESULTS

We found that genetic deletion of neither Raptor, an important adaptor protein in mTOR complex 1, nor mTOR, in the mouse liver significantly protected against APAP-induced liver injury despite increased hepatic autophagic flux. Genetic deletion of Raptor or mTOR in mouse livers did not affect APAP metabolism and APAP-induced c-Jun N-terminal kinase (JNK) activation, but slightly improved mouse survival likely due to increased hepatocyte proliferation.

CONCLUSIONS

Our results indicate that genetic ablation of mTOR in mouse livers does not protect against APAP-induced liver injury but may slightly improve liver regeneration and mouse survival after APAP overdose.

The role of Neu1 in the protective effect of dipsacoside B on acetaminophen-induced liver injury

Background

Pharmacological induction of autophagy can protect against acetaminophen (APAP) induced acute liver failure (ALF) by removing APAP adducts (APAP-AD), but its mechanism is not well understood. Hepatoprotective effect of saponins from traditional Chinese medicine has attracted widespread attention from all over the world. The content of saponins in Lonicerae Flos (Shanyinhua in Chinese) is up to 15–25%. Dipsacoside B (DB) is a common bioactive ingredient of different Shanyinhua, but its hepatoprotective effect and mechanism are still unknown. The present investigation aimed to study the benefit of DB in APAP-induced hepatotoxicity mouse model and different cell model.

Methods

Mice were treated with DB by intraperitoneal injection 1 h before treated with 500 mg/kg APAP, which caused ALF after 4 h. HepG2 cells were treated with DB for 1 h before treated with 10 mM APAP for 12 h. Hepatotoxicity was assessed via ALT and AST. Neuraminidase 1 (Neu1), lysosomal autophagy marker LC3 and P62 were examined by western blot. Neu1 activity was assayed using its substrate 2-(4-methylumbelliferyl)-D-N-acetylneuraminic acid. Apoptosis level was examined by TUNEL and caspase 3 activity. Molecular docking was used to predict the interaction between DB and protein Neu1.

Results

Our results demonstrated that pretreatment with 0.5 μM DB (in vitro) and 50 mg/kg DB (in vivo) respectively reversed increased level of AST and ALT induced by APAP. Histopathological examinations showed reduced necrosis and apoptosis in the liver of DB-treated APAP mice. DB promoted the removal of APAP-AD by lysosomal autophagy. These effects were associated with significant decrease in the level of Neuraminidase 1 (Neu1), a negative regulator of lysosomal exocytosis. Molecular docking results showed that DB could bind to Neu1 protein (binding energy =−7.86 kcal/mol). Akt/mTOR-mediated autophagy and inhibition of apoptosis may be the main mechanisms for the hepatoprotective effects of DB in acetaminophen-induced liver injury.

Conclusions

These data indicate that DB alleviated hepatotoxicity caused by APAP at least in part via Neu1 inhibition, Akt/mTOR pathway is involved in the detoxification effect of DB on acetaminophen-induced hepatotoxicity.

Plasma membrane vesicles of human umbilical cord mesenchymal stem cells ameliorate acetaminophen-induced damage in HepG2 cells: a novel stem cell therapy

BACKGROUND

Acetaminophen (APAP) overdose is the common cause of acute liver failure (ALF) due to the oxidative damage of multiple cellular components. This study aimed to investigate whether plasma membrane vesicles (PMVs) from human umbilical cord mesenchymal stem cells (hUCMSCs) could be exploited as a novel stem cell therapy for APAP-induced liver injury.

METHODS

PMVs from hUCMSCs were prepared with an improved procedure including a chemical enucleation step followed by a mechanical extrusion. PMVs of hUCMSCs were characterized and supplemented to hepatocyte cultures. Rescue of APAP-induced hepatocyte damage was evaluated.

RESULTS

The hUCMSCs displayed typical fibroblastic morphology and multipotency when cultivated under adipogenic, osteogenic, or chondrogenic conditions. PMVs of hUCMSCs maintained the stem cell phenotype, including the presence of CD13, CD29, CD44, CD73, and HLA-ABC, but the absence of CD45, CD117, CD31, CD34, and HLA-DR on the plasma membrane surface. RT-PCR and transcriptomic analyses showed that PMVs were similar to hUCMSCs in terms of mRNA profile, including the expression of stemness genes GATA4/5/6, Nanog, and Oct1/2/4. GO term analysis showed that the most prominent reduced transcripts in PMVs belong to integral membrane components, extracellular vesicular exosome, and extracellular matrix. Immunofluorescence labeling/staining and confocal microscopy assays showed that PMVs enclosed cellular organelles, including mitochondria, lysosomes, proteasomes, and endoplasmic reticula. Incorporation of the fusogenic VSV-G viral membrane glycoprotein stimulated the endosomal release of PMV contents into the cytoplasm. Further, the addition of PMVs and a mitochondrial-targeted antioxidant Mito-Tempo into cultures of APAP-treated HepG2 cells resulted in reduced cell death, enhanced viability, and increased mitochondrial membrane potential. Lastly, this study demonstrated that the redox state and activities of aminotransferases were restored in APAP-treated HepG2 cells.

CONCLUSIONS

The results suggest that PMVs from hUCMSCs could be used as a novel stem cell therapy for the treatment of APAP-induced liver injury.

Human multidrug resistance protein 4 (MRP4) is a cellular efflux transporter for paracetamol glutathione and cysteine conjugates

Paracetamol (acetaminophen, APAP) overdose is a leading cause of acute drug-induced liver failure. APAP hepatotoxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI). NAPQI is inactivated by conjugation with glutathione (GSH) to APAP-GSH, which is further converted into its cysteine derivative APAP-CYS. Before necrosis of hepatocytes occurs, APAP-CYS is measurable in plasma of the affected patient and it has been proposed as an early biomarker of acetaminophen toxicity. APAP-GSH and APAP-CYS can be extruded by hepatocytes, but the transporters involved are unknown. In this study we examined whether ATP-binding cassette (ABC) transporters play a role in the cellular efflux of APAP, APAP-GSH, and APAP-CYS. The ABC transport proteins P-gp/ABCB1, BSEP/ABCB11, BCRP/ABCG2, and MRP/ABCC1-5 were overexpressed in HEK293 cells and membrane vesicles were produced. Whereas P-gp, BSEP, MRP3, MRP5, and BCRP did not transport any of the compounds, uptake of APAP-GSH was found for MRP1, MRP2 and MRP4. APAP-CYS appeared to be a substrate of MRP4 and none of the ABC proteins transported APAP. The results suggest that the NAPQI metabolite APAP-CYS can be excreted into plasma by MRP4, where it could be a useful biomarker for APAP exposure and toxicity. Characterization of the cellular efflux of APAP-CYS is important for its development as a biomarker, because plasma concentrations might be influenced by drug-transporter interactions and upregulation of MRP4.

Hesperetin attenuated acetaminophen-induced hepatotoxicity by inhibiting hepatocyte necrosis and apoptosis, oxidative stress and inflammatory response via upregulation of heme oxygenase-1 expression

Acetaminophen (APAP) is a common antipyretic and analgesic drug, but its overdose can induce acute liver failure with lack of effective therapies. Hesperetin, a dihydrogen flavonoid compound, has been revealed to exert multiple pharmacological activities. Here, we explored the protective effects and mechanism of hesperetin on APAP-induced hepatotoxicity. The results showed that pretreatment with hesperetin dose-dependently attenuated APAP-induced acute liver injury in mice, as measured by alleviated serum enzymes activities, hepatic pathological damage and apoptosis. Moreover, hesperetin mitigated APAP-induced oxidative stress and inflammatory response in mice by inhibiting oxidative molecules but increasing antioxidative molecules production, reducing inflammatory cells infiltration and proinflammatory cytokines production, blocking Toll-like receptor (TLR)-4 signal activation. In vitro experiment indicated that hesperetin dose-dependently inhibited APAP-primed cytotoxicity, apoptosis, and reactive oxygen species (ROS) in murine AML12 hepatocytes. Notably, hesperetin up-regulated expression of heme oxygenase-1 (HO-1) mRNA and protein in the liver of mice and AML12 cells exposed to APAP. Furthermore, knockdown of HO-1 by adenovirus-mediated HO-1 siRNA reverted these beneficial effects of hesperetin on APAP-induced hepatocytotoxicity as well as ROS and inflammatory response in vivo and in vitro. These findings demonstrated that hesperetin exerted a protective prophylaxis on APAP-induced acute liver injury by inhibiting hepatocyte necrosis and apoptosis, oxidative stress and inflammatory response via up-regulating HO-1 expression.

Acetaminophen toxicity induces mitochondrial complex I inhibition in human liver tissue

Acetaminophen (APAP) is used worldwide and is regarded as safe in therapeutic concentrations but can cause acute liver failure in higher doses. High doses of APAP have been shown to inhibit complex I and II mitochondrial respiratory capacity in mouse hepatocytes, but human studies are lacking. Here, we studied mitochondrial respiratory capacity in human hepatic tissue ex vivo with increasing doses of APAP. Hepatic biopsies were obtained from 12 obese patients who underwent a Roux-en-Y gastric bypass (RYGB) or a sleeve gastrectomy surgery. Mitochondrial respiration was measured by high-resolution respirometry. Therapeutic concentrations (≤0.13 mmol/L) of APAP did not inhibit state 3 complex I-linked respiration. APAP concentrations of ≥2.0 mmol/L in the medium significantly reduced hepatic mitochondrial respiration in a dose-dependent manner. Complex II-linked mitochondrial respiration was not inhibited by APAP. We conclude that the mitochondrial respiratory capacity is affected by a hepato-toxic effect of APAP, which involved complex I, but not complex II.

Granzyme B and miR-378a Interaction in Acetaminophen Toxicity in Children

BACKGROUND AND AIM

Hepatic phase I drug-metabolizing enzymes CYP2E1, CYP1A2 and CYP3A4 catalyze the biotransformation of Acetaminophen (APAP) and are important in the mediation of toxicity. The potential role of other hepatic and non-hepatic Phase I enzymes in APAP toxicity has not been established.

METHODS

PCR array containing 84 genes involved in phase I drug metabolism was examined in subgroups of hospitalized children for APAP overdose, categorized as no toxicity (ALT ≤ 45 IU/L, n=5) and moderate toxicity (ALT ≥ 500 IU/L, n=5).

RESULTS

Significant downregulation was observed for ALDH6A1, CYP4F12 and GZMB in the no toxicity subgroup and ALDH1A1, CYP27A1 and GZMB in the moderate toxicity subgroup. qRTPCR confirmed significant downregulation for ALDH1A1, CYP4F12, and GZMB. In-silico analysis identified GZMB 3'UTR to be a target of miR-378a-5p. Overexpression of miR-378a-5p reduced the luciferase activity of GZMB 3'UTR reporter plasmid reportedly by 50%. NK-92 cells transfected with the miR-378a-5p mimic extended the effect of APAP on GZMB protein expression compared to mimic controls. In addition, miR-378a-5p was significantly upregulated in blood samples of children with APAP overdose undergoing NAC treatment.

CONCLUSION

Overall, our study suggests the presence of a novel signaling pathway, whereby miR- 378a-5p inhibits GZMB expression in children with APAP overdose.

Human amniotic mesenchymal stromal cells alleviate acute liver injury by inhibiting the pro-inflammatory response of liver resident macrophage through autophagy

Background

The activation and polarization of macrophages are crucial during the pathogenesis of liver injury induced by the toxin. Human amniotic mesenchymal stromal cells (hAMSCs) are newly identified mesenchymal stem cells and have been shown to have an immunoregulatory ability for multiple autoimmune diseases.

Methods

Mice were intraperitoneally injected with Acetaminophen (APAP) to establish a liver injury model. hAMSCs were injected through the tail vein, and the liver function was observed through a liver function and pathology analysis. To test the regulative ability of hAMSCs in vitro, the supernatant of hAMSCs were collected and co-cultured with Kupffer cells (KCs). Liposome was used to abolish the function of KCs in vivo.

Results

Infusion of hAMSCs reduced the level of liver function injury and inflammation expression in APAP-induced liver injury. hAMSCs markedly promoted M2 polarization of KCs instead of M1 polarization in vitro. Furthermore, the mechanism study also proved that hAMSCs reduced autophagy, as revealed by down-regulated LC3B-II levels. The elimination of KCs in vivo abolished the protective ability of hAMSCs in liver injury, which resulted in a significant increase of liver pathogenesis along with an increase in alanine aminotransaminase (ALT) and aspartate aminotransaminase (AST) levels.

Conclusions

Our results proved that hAMSCs suppressed M1 polarization and promoted M2 polarization of KCs through regulating autophagy in the model of APAP-treated livers. Thus, the injury of the liver was attenuated. This study provides us a new therapeutic strategy for the disease of acute liver injury.

Dihydromyricetin alleviates acetaminophen-induced liver injury via the regulation of transformation, lipid homeostasis, cell death and regeneration

AIMS

We previously reported that Hovenia dulcis Thunb. extract, a traditional Chinese medicine rich in dihydromyricetin (DHM), exhibited a significant hepatoprotective effect against acetaminophen (APAP)-induced liver injury. However, whether DHM plays a protective role in APAP hepatotoxicity and what mechanisms are involved remain unclear. In this study, we evaluated the hepatoprotective effects of DHM against APAP-induced liver injury.

MAIN METHODS

Male C57BL/6 mice were used for the experiment. LC-MS, q-PCR, immunochemistry and western blot analysis were employed to mechanism analysis.

KEY FINDINGS

DHM exhibited a protective effect against APAP-induced liver injury. Further mechanistic investigations revealed that the protective effect of DHM against APAP hepatotoxicity had multi-target and multi-pathway characteristics involving APAP metabolism, lipid regulation, and hepatocyte death and regeneration. DHM pretreatment resulted in cytochrome P450 2E1 inhibition and UDP-glucuronosyltransferase 1A1 activation, affecting APAP biotransformation. Moreover, DHM pretreatment significantly ameliorated lipid dysregulation via peroxisome proliferator-activated receptor and sterol regulatory element-binding protein-1c (SREBP-1c) signalling pathways. Furthermore, DHM regulated the expression of cell death- and liver regeneration-associated proteins.

SIGNIFICANCE

These results suggested that DHM alleviated APAP-induced liver injury in mice by inhibiting hepatocyte death, promoting p53-related regeneration, and regulating lipid homeostatic imbalance and APAP transformation. Based on these findings, DHM provides a potential and novel approach for preventing and treating APAP-induced liver damage, and SREBP-1c signalling might be a new therapeutic target for APAP hepatotoxicity.

Chlorpromazine protects against acetaminophen-induced liver injury in mice by modulating autophagy and c-Jun N-terminal kinase activation

BACKGROUND AND AIM

Overdose of acetaminophen (APAP) leads to liver injury, which is one of the most common causes of liver failure in the United States. We previously demonstrated that pharmacological activation of autophagy protects against APAP-induced liver injury in mice via removal of damaged mitochondria and APAP-adducts (APAP-ADs). Using an image-based high-throughput screening for autophagy modulators, we recently identified that chlorpromazine (CPZ), a dopamine inhibitor used for anti-schizophrenia, is a potent autophagy inducer in vitro. Therefore, the aim of the present study is to determine whether CPZ may protect against APAP-induced liver injury via inducing autophagy.

METHODS

Wild type C57BL/6J mice were injected with APAP to induce liver injury. CPZ was administrated either at the same time with APAP (co-treatment) or 2 h later after APAP administration (post-treatment). Hemotoxyline and eosin (H&E) staining of liver histology, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) staining of necrotic cell death as well as serum levels of alanine aminotransferase (ALT) were used to monitor liver injury.

RESULTS

We found that CPZ markedly protected against APAP-induced liver injury as demonstrated by decreased serum levels of ALT, liver necrotic areas as well as TUNEL-positive cells in mice that were either co-treated or post-treated with CPZ. Mechanistically, we observed that CPZ increased the number of autolysosomes and decreased APAP-induced c-Jun N-terminal kinase activation without affecting the metabolic activation of APAP. Pharmacological inhibition of autophagy by chloroquine partially weakened the protective effects of CPZ against APAP-induced liver injury.

CONCLUSIONS

Our results indicate that CPZ ameliorates APAP-induced liver injury partially via activating hepatic autophagy and inhibiting JNK activation.

GADD45α alleviates acetaminophen-induced hepatotoxicity by promoting AMPK activation

As an analgesic and antipyretic drug, acetaminophen (APAP) is commonly used and known to be safe at therapeutic doses. In many countries, the overuse of APAP provokes acute liver injury and even liver failure. APAP-induced liver injury (AILI) is the most used experimental model of drug-induced liver injury (DILI). Here, we have demonstrated elevated levels of growth arrest and DNA damage-inducible 45α (GADD45α) in the livers of patients with DILI/AILI, in APAP-injured mouse livers and in APAP-treated hepatocytes. GADD45α exhibited a protective effect against APAP-induced liver injury and alleviated the accumulation of small lipid droplets in vitro and in vivo. We found that GADD45α promoted the activation of AMP-activated protein kinase α and induced fatty acid beta-oxidation, tricarboxylic acid cycle (TCA) and glycogenolysis-related gene expression after APAP exposure. Liquid chromatography-mass spectrometry (LC-MS) analysis showed that GADD45α increased the levels of TCA cycle metabolites. Co-immunoprecipitation analysis showed that Ppp2cb, a catalytic subunit of protein phosphatase 2A, could interact directly with GADD45α. Our results indicate that hepatocyte GADD45α might represent a therapeutic target to prevent and rescue liver injury caused by APAP.

Ginsenoside Rg1 protects against acetaminophen-induced liver injury via activating Nrf2 signaling pathway in vivo and in vitro

Acetaminophen (APAP) is a worldwide used drug for treating fever and pain. However, APAP overdose is the leading cause of drug-induced liver injury. The purpose of the current study is to evaluate the hepatoprotective effect of ginsenoside Rg1 (Rg1), the main pharmacologically active compounds of Panax ginseng, against APAP-induced acute liver injury, and further to elucidate the involvement of Nrf2 signaling pathway by in vivo and in vitro experiments. Male C57BL/6 mice were treated with Rg1 for 3 days before injection of APAP. Serum and liver tissue samples were collected 6 h later. The results indicated that Rg1 significantly attenuated APAP-induced hepatotoxicity and oxidative stress in a dose-dependent manner. Rg1 effectively enhanced antioxidant and detoxification capacity, which is largely dependent on up-regulating Nrf2 nuclear translocation, reducing Keap1 protein expression and up-regulating Nrf2 target genes including GCLC, GCLM, HO-1, NQO1, Ugt1a1, Ugt1a6, Ugt2b1, Sult2a1, Mrp2, Mrp3 and Mrp4. Furthermore, Rg1 repressed the activities of Cyp2e1, Cyp3a11, Cyp1a2, which are important enzymes in the formation of APAP toxic metabolite N-acetyl-p-benzoquinone imine. However, the changes in transporters and enzymes, as well as ameliorative liver histology induced by Rg1 were abrogated by Nrf2 antagonist all-transretinoic acid in vivo and Nrf2 siRNA in vitro. In conclusion, Rg1 produced hepatoprotective effects against APAP-induced acute liver injury via Nrf2 signaling pathway. Rg1 might be an effective approach for the prevention against acute liver injury.

Toxicogenomics-based prediction of acetaminophen-induced liver injury using human hepatic cell systems

Primary human hepatocytes (hHEP), human HepaRG and HepG2 cell lines are the most used human liver-based in vitro models for hepatotoxicity testing, including screening of drug-induced liver injury (DILI)-inducing compounds. hHEP are the reference hepatic in vitro system, but their availability is limited and the cells available for toxicology studies are often of poor quality. Hepatic cell lines on the other hand are highly proliferative and represent an inexhaustible hepatic cell source. However, these hepatoma-derived cells do not represent the population diversity and display reduced hepatic metabolism. Alternatively, stem cell-derived hepatic cells, which can be produced in high numbers and can differentiate into multiple cell lineages, are also being evaluated as a cell source for in vitro hepatotoxicity studies. Human skin-derived precursors (hSKP) are post-natal stem cells that, after conversion towards hepatic cells (hSKP-HPC), respond to hepatotoxic compounds in a comparable way as hHEP. In the current study, four different human hepatic cell systems (hSKP-HPC, hHEP, HepaRG and HepG2) are evaluated for their capacity to predict hepatic toxicity. Their hepatotoxic response to acetaminophen (APAP) exposure is compared to data obtained from patients suffering from APAP-induced acute liver failure (ALF). The results indicate that hHEP, HepaRG and hSKP-HPC identify comparable APAP-induced hepatotoxic functions and that HepG2 cells show the slightest hepatotoxic response. Pathway analyses further points out that HepaRG cells show the highest predicted activation of the functional genes related to 'damage of liver', followed by hSKP-HPC and hHEP cells that generated similar results. HepG2 did not show any activation of this function.

Immune mechanisms in acetaminophen-induced acute liver failure

An overdose of acetaminophen (N-acetyl-p-aminophenol, APAP), also termed paracetamol, can cause severe liver damage, ultimately leading to acute liver failure (ALF) with the need of liver transplantation. APAP is rapidly taken up from the intestine and metabolized in hepatocytes. A small fraction of the metabolized APAP forms cytotoxic mitochondrial protein adducts, leading to hepatocyte necrosis. The course of disease is not only critically influenced by dose of APAP and the initial hepatocyte damage, but also by the inflammatory response following acetaminophen-induced liver injury (AILI). As revealed by mouse models of AILI and corresponding translational studies in ALF patients, necrotic hepatocytes release danger-associated-molecular patterns (DAMPs), which are recognized by resident hepatic macrophages, Kupffer cell (KC), and neutrophils, leading to the activation of these cells. Activated hepatic macrophages release various proinflammatory cytokines, such as TNF-α or IL-1β, as well as chemokines (e.g., CCL2) thereby further enhancing inflammation and increasing the influx of immune cells, like bone-marrow derived monocytes and neutrophils. Monocytes are mainly recruited via their receptor CCR2 and aggravate inflammation. Infiltrating monocytes, however, can mature into monocyte-derived macrophages (MoMF), which are, in cooperation with neutrophils, also involved in the resolution of inflammation. Besides macrophages and neutrophils, distinct lymphocyte populations, especially γδ T cells, are also linked to the inflammatory response following an APAP overdose. Natural killer (NK), natural killer T (NKT) and T cells possibly further perpetuate inflammation in AILI. Understanding the complex interplay of immune cell subsets in experimental models and defining their functional involvement in disease progression is essential to identify novel therapeutic targets for human disease.