Lactiplantibacillus plantarum P101 alleviates alcoholic liver injury by modulating the Nrf2/HO-1 pathway in mice

AIMS

The occurrence of alcoholic liver injury is related to the oxidative stress. Bacteria for alleviating alcoholic related liver injury have received widespread attention. Study aims to investigate the alleviated efficacy of Lactiplantibacillus plantarum (L. plantarum) P101 on alcohol-induced liver injury and its potential mechanism.

METHODS AND RESULTS

The model of alcoholic liver injury was obtained according to the NIAAA method and the mice were treated with L. plantarum P101 (108 CFU.mice-1). Results showed that treatment of L. plantarum P101 could significantly improve liver function and antioxidant capacity. Furthermore, L. plantarum P101 significantly up-regulated Nuclear factor erythroid 2-related factor (Nrf2) and its target molecule, Hemeoxygenase 1 (HO-1), by promoting nuclear translocation of Nrf2. Moreover, inflammatory factors and pro-apoptotic protein (Caspase3) levels were significantly decreased in mice treated with L. plantarum P101.

CONCLUSIONS

This study confirmed that the beneficial effect of L. plantarum P101 supplement was achieved via regulating Nrf2/HO-1 antioxidant pathway, and alleviated alcoholic liver injury.

Ameliorative Effects of Oyster Protein Hydrolysates on Cadmium-Induced Hepatic Injury in Mice

Cadmium (Cd) is a widespread environmental toxicant that can cause severe hepatic injury. Oyster protein hydrolysates (OPs) have potential effects on preventing liver disease. In this study, thirty mice were randomly divided into five groups: the control, Cd, Cd + ethylenediaminetetraacetic acid (EDTA, 100 mg/kg), and low/high dose of OPs-treatment groups (100 mg/kg or 300 mg/kg). After continuous administration for 7 days, the ameliorative effect of OPs on Cd-induced acute hepatic injury in Cd-exposed mice was assessed. The results showed that OPs significantly improved the liver function profiles (serum ALT, AST, LDH, and ALP) in Cd-exposed mice. Histopathological analysis showed that OPs decreased apoptotic bodies, hemorrhage, lymphocyte accumulation, and inflammatory cell infiltration around central veins. OPs significantly retained the activities of SOD, CAT, and GSH-Px, and decreased the elevated hepatic MDA content in Cd-exposed mice. In addition, OPs exhibited a reductive effect on the inflammatory responses (IL-1β, IL-6, and TNF-α) and inhibitory effects on the expression of inflammation-related proteins (MIP-2 and COX-2) and the ERK/NF-κB signaling pathway. OPs suppressed the development of hepatocyte apoptosis (Bax, caspase-3, and Blc-2) and the activation of the PI3K/AKT signaling pathway in Cd-exposed mice. In conclusion, OPs ameliorated the Cd-induced hepatic injury by inhibiting oxidative damage and inflammatory responses, as well as the development of hepatocyte apoptosis via regulating the ERK/NF-κB and PI3K/AKT-related signaling pathways.

Protective Effect and Mechanism of Placenta Extract on Liver

The placenta contains multiple biologically active substances, which exert antioxidation, anti-inflammatory, immunomodulatory, and delayed aging effects. Its extract can improve hepatic morphology and function: on the one hand, it can reduce liver interstitial collagen deposition, lipogenesis, and inflammatory cell infiltration and improve fibrosis; on the other hand, it can prevent hepatocellular degeneration by scavenging reactive oxygen species (ROS) and inhibiting inflammatory cytokine production, further improve hepatocyte apoptosis and necrosis, and promote hepatocyte regeneration, making it a promising liver-protective agent. Current research on placenta extract (PE) mainly focuses on treating a specific type of liver injury, and there are no systematic reports. Therefore, this review comprehensively summarizes the treatment reports of PE on liver injury and analyzes its mechanism of action.

Methyl 6-O-cinnamoyl-α-d-glucopyranoside Ameliorates Acute Liver Injury by Inhibiting Oxidative Stress Through the Activation of Nrf2 Signaling Pathway

Excessive stimulation of hepatotoxins and drugs often lead to acute liver injury, while treatment strategies for acute liver injury have been limited. Methyl 6-O-cinnamoyl-α-d-glucopyranoside (MCGP) is a structure modified compound from cinnamic acid, a key chemical found in plants with significant antioxidant, anti-inflammatory, and antidiabetic effects. In this study, we investigated the effects and underlying mechanisms of MCGP on acetaminophen (APAP)- or carbon tetrachloride (CCl₄)-induced acute liver injury. As a result, MCGP inhibited cell death and apoptosis induced by APAP or CCl₄, and suppressed the reactive oxygen species (ROS) generation stimulated by H₂O₂ in liver AML12 cells. In vivo, MCGP alleviated APAP/CCl₄-induced hepatic necrosis and resumed abnormal aminotransferase activities and liver antioxidase activities. In addition, MCGP depressed APAP- or CCl₄-induced oxidative stress through the suppression of CYP2E1 and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. MCGP also enhanced the number of PCNA-positive hepatocytes, increased hepatic PCNA and Bcl-XL, and decreased BAX expression in APAP-/CCl₄-intoxicated mice. Furthermore, MCGP activated the GSDMD-N/cleaved caspase 1 pathway. In summary, MCGP might act as a potential therapeutic drug against drug-induced and chemical-induced acute liver injuries, and its underlying mechanisms might engage on the pressing of oxidative stress, refraining of hepatocyte apoptosis, and facilitating of liver regeneration.

Canonical Thyroid Hormone Receptor β Action Stimulates Hepatocyte Proliferation in Male Mice

CONTEXT

3,5,3'-L-triiodothyronine (T3) is a potent inducer of hepatocyte proliferation via the Wnt/β-catenin signaling pathway. Previous studies suggested the involvement of rapid noncanonical thyroid hormone receptor (TR) β signaling, directly activating hepatic Wnt/β-catenin signaling independent from TRβ DNA binding. However, the mechanism by which T3 increases Wnt/β-catenin signaling in hepatocytes has not yet been determined.

OBJECTIVE

We aimed to determine whether DNA binding of TRβ is required for stimulation of hepatocyte proliferation by T3.

METHODS

Wild-type (WT) mice, TRβ knockout mice (TRβ KO), and TRβ mutant mice with either specifically abrogated DNA binding (TRβ GS) or abrogated direct phosphatidylinositol 3 kinase activation (TRβ 147F) were treated with T3 for 6 hours or 7 days. Hepatocyte proliferation was assessed by Kiel-67 (Ki67) staining and apoptosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Activation of β-catenin signaling was measured in primary murine hepatocytes. Gene expression was analyzed by microarray, gene set enrichment analysis (GSEA), and quantitative reverse transcription polymerase chain reaction.

RESULTS

T3 induced hepatocyte proliferation with an increased number of Ki67-positive cells in WT and TRβ 147F mice (9.2% ± 6.5% and 10.1% ± 2.9%, respectively) compared to TRβ KO and TRβ GS mice (1.2% ± 1.1% and 1.5% ± 0.9%, respectively). Microarray analysis and GSEA showed that genes of the Wnt/β-catenin pathway-among them, Fzd8 (frizzled receptor 8) and Ctnnb1 (β-catenin)-were positively enriched only in T3-treated WT and TRβ 147F mice while B-cell translocation gene anti-proliferation factor 2 was repressed. Consequently, expression of Ccnd1 (CyclinD1) was induced.

CONCLUSIONS

Instead of directly activating Wnt signaling, T3 and TRβ induce key genes of the Wnt/β-catenin pathway, ultimately stimulating hepatocyte proliferation via CyclinD1. Thus, canonical transcriptional TRβ action is necessary for T3-mediated stimulation of hepatocyte proliferation.

Specnuezhenide reduces carbon tetrachloride-induced liver injury in mice through inhibition of oxidative stress and hepatocyte apoptosis

OBJECTIVES

This study aimed to investigate the hepatoprotective effects of specnuezhenide against carbon tetrachloride (CCl4)-induced liver injury in mice.

METHODS

Male C57BL/6 mice were intraperitoneally injected with 10 ml/kg body weight of CCl4 (0.5% diluted in arachis oil) for acute liver injury after oral administration of specnuezhenide for 7 days. Twenty-four hours after the final CCl4 injection, mice were euthanized and plasma and liver samples were collected.

KEY FINDINGS

The results showed that specnuezhenide markedly and dose-dependently reduced serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) activity and relative liver weight, as well as ameliorated histopathological damage caused by CCl4 and decreased malondialdehyde (MDA) levels, and increased the activity of antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Moreover, specnuezhenide promoted the expression and nuclear translocation of the nuclear factor erythroid 2-related factor 2 (Nrf2) and increased the mRNA and protein expression of Nrf2 signalling-related genes heme oxygenase-1 (HO-1), glutamate-cysteine ligase catalytic subunit (GCLC) and NAD(P)H:quinone oxidoreductase 1 (NQO1). Finally, TUNEL staining and immunohistochemistry indicated that specnuezhenide prevented CCl4-induced hepatocytic apoptosis by up-regulating B-cell lymphoma 2 (Bcl-2) expression and downregulating Bcl-2-associated X (Bax) expression.

CONCLUSIONS

Specnuezhenide reduced CCl4-induced liver injury in mice by inhibiting oxidative stress via activation of Nrf2 signalling and decreasing hepatocyte apoptosis.

Aberrant expression of SNHG12 contributes to N, N-dimethylformamide-induced hepatic apoptosis both in short-term and long-term DMF exposure

N, N-Dimethylformamide (DMF) can cause liver damage in occupationally exposed workers, but the molecular mechanism of DMF-induced liver damage has not been fully elucidated. Researches have proved that lncRNA plays a major function in chemical-induced liver toxicity and can be used as a biomarker and therapeutic target for liver injury. In order to verify that lncRNA also participates in DMF-induced liver damage, we treated HL-7702 cells with 75 or 150 mM DMF, and obtained lncRNA expression profiles through high-throughput sequencing. Among the differentially expressed lncRNAs, lncRNA SNHG12 was proved to be significantly downregulated in DMF-treated HL-7702 cells and participate in DMF-mediated apoptosis, even under long-term low-dose DMF exposure (5-10 mM, 8 weeks). In addition, according to bioinformatics analysis, miR-218-5p is expected to be a potential target of SNHG12, which was verified by the dual luciferase reporter assay in HEK293FT cells. MiR-218-5p mimic can induce apoptosis in HL-7702 cells. Among the predicted targets of miR-218-5p, protein kinase C epsilon (PRKCE) was reported to be involved in apoptosis, and was indeed downregulated by miR-218-5p mimic in our study. Further experiments showed that changes of the expression of SNHG12 can affect the expression of PRKCE. In the epidemiological study of occupational population, we also found that SNHG12 was downregulated in the serum exosomes of workers exposed to DMF. These results indicated that SNHG12 can mediate DMF-induced apoptosis of HL-7702 cells through miR-218-5p/PRKCE pathway.

Role of inhibiting Chk1-p53 pathway in hepatotoxicity caused by chronic arsenic exposure from coal-burning

Arsenic is a naturally occurring environmental toxicant, chronic exposure to arsenic can cause multiorgan damage, except for typical skin lesions, liver damage is the main problem for health concern in population with arsenic poisoning. Abnormal apoptosis is closely related to liver-related diseases, and p53 is one of the important hallmark proteins in apoptosis progression. This study was to investigate whether arsenic poisoning-induced hepatocyte apoptosis and the underlying role of p53 signaling pathway. A rat model of arsenic poisoning was established by feeding corn powder for 90 days, which was baked with high arsenic coal, then were treated with Ginkgo biloba extract (GBE) for 45 days by gavage. The results showed that arsenic induced liver damage, increased hepatocyte apoptosis and elevated the expression level of Chk1 and the ratios of p-p53/p53 and Bax/Bcl-2 in liver tissues, which were significantly attenuated by GBE. Additionally, to further demonstrate the potential apoptosis-associated mechanism, L-02 cells were pre-incubated with p53 inhibitor pifithrin-α (PFTα), ataxia telangiectasia-mutated (ATM)/ataxia telangiectasia-mutated and Rad3-related (ATR) inhibitor (CGK733) or GBE, then treated with sodium arsenite (NaAsO₂) for 24 h. The results showed that GBE, PFTα or CGK733 significantly reduced arsenic-induced Chk1 expression and the ratios of p-p53/p53 and Bax/Bcl-2. In conclusion, Chk1-p53 pathway was involved in arsenic poisoning-induced hepatotoxicity, and inhibiting of Chk1-p53 pathway ameliorated hepatocyte apoptosis caused by coal-burning arsenic poisoning. The study provides a pivotal clue for understanding of the mechanism of arsenic poisoning-induced liver damage, and possible intervention strategies.

Li-Dan-He-Ji Improves Infantile Cholestasis Hepatopathy Through Inhibiting Calcium-Sensing Receptor-Mediated Hepatocyte Apoptosis

Infantile cholestatic hepatopathy (ICH) is a clinical syndrome characterized by the accumulation of cytotoxic bile acids in infancy, leading to serious liver cirrhosis or liver failure. The aetiology of ICH is complicated and some of them is unknown. Regardless of the aetiology, the finial pathology of ICH is hepatocyte apoptosis caused by severe and persistent cholestasis. It is already known that activation of calcium-sensing receptor (CaSR) could lead to the apoptosis of cardiomyocytes. However, the mechanism by CaSR-mediated cholestasis-related hepatocyte apoptosis is not fully understood. Li-Dan-He-Ji (LDHJ), a Traditional Chinese Medicine prescription, was developed to treat ICH. Another aim of this study was to investigate the possible mechanisms of LDHJ in cholestasis-related hepatocyte apoptosis. Using the primary hepatocytes, we first investigated the molecular mechanism of CaSR-mediated hepatocyte apoptosis in cholestasis. Then we prepared LDHJ granules and used ultra-high-performance liquid chromatography to identify the predominant drugs; confirmed the stability of the main substances; and for cell experiments screened forsythoside-A, emodin and chlorogenic acid as the three active substances of LDHJ granules. In the young rats with ANIT-induced intrahepatic cholestasis and the primary hepatocytes with TCDC-induced cholestasis-related hepatocyte apoptosis, the levels of liver injury and cholestasis-related biomarkers, calcium-sensing receptor (CaSR), hepatocyte apoptosis, Bax/Bcl-2 ratio, Cytochrome-C, caspase-3, phosphorylated-c-Jun NH₂-terminal kinase (p-JNK)/JNK, and p-P38/P38 were all increased, while the levels of p-extracellular signal-regulated kinase (p-ERK)/ERK were decreased. However, LDHJ granules and its three active substances effectively reversed these changes. Furthermore, the three active substances reduced the increases in the intracellular calcium concentration ([Ca²⁺]_i) and ROS levels and attenuated the dissipation of the mitochondria membrane potential in the TCDC-induced primary hepatocytes. The opposite results were obtained from the TCDC-induced primary hepatocytes treated with an agonist of CaSR (GdCl₃) plus forsythoside-A, emodin or chlorogenic acid. Based on the results from in vivo and in vitro studies, LDHJ functions as an antagonist of CaSR to regulate hepatocyte apoptosis in cholestasis through the mitochondrial pathway and mitogen-activated protein kinase pathway.

Inhibition of lncRNA HULC improves hepatic fibrosis and hepatocyte apoptosis by inhibiting the MAPK signaling pathway in rats with nonalcoholic fatty liver disease

This study is conducted to investigate the role of long noncoding RNA highly upregulated in liver cancer (lncRNA HULC) on hepatic fibrosis and hepatocyte apoptosis by inhibiting the mitogen-activated protein kinase (MAPK) signaling pathway in rats with nonalcoholic fatty liver disease (NAFLD). The successfully modeled rats were injected with HULC siRNA or small interfering RNA (siRNA) negative control into the tail vein. The expression of HULC in liver tissues was detected by reverse transcription quantitative polymerase reaction chain. The role of HULC in pathological state and liver function-related indexes of liver lipid deposition, the degree of hepatic fibrosis and hepatocyte apoptosis in rats with NAFLD were also investigated through a series of experiments. Increased expression of HULC was found in liver tissue of NAFLD rats. Inhibition of HULC improved the pathological state and liver function-related indexes of liver lipid deposition, improved the degree of hepatic fibrosis, reduced hepatocyte apoptosis, and inhibited the MAPK signaling pathway in the liver tissue of NAFLD rats. The inhibition of p38 and JNK improved the pathological state of liver lipid deposition and liver function to some extent, improved the degree of hepatic fibrosis, and reduced the apoptosis of hepatocytes in NAFLD rats. Collectively, this present study provides evidence that inhibition of lncRNA HULC improves hepatic fibrosis and decrease hepatocyte apoptosis in rats with NAFLD by inhibiting the MAPK signaling pathway.

AKT activator SC79 protects hepatocytes from TNF-α-mediated apoptosis and alleviates d-Gal/LPS-induced liver injury

Tumor necrosis factor-α (TNF-α) is a highly pleiotropic cytokine executing biological functions as diverse as cell proliferation, metabolic activation, inflammatory responses, and cell death. TNF-α can induce multiple mechanisms to initiate apoptosis in hepatocytes leading to the subsequent liver injury. Since the phosphoinositide-3-kinase/protein kinase B (PI3K/Akt) pathway is known to have a protective role in death factor-mediated apoptosis, it is our hypothesis that activation of Akt may represent a therapeutic strategy to alleviate TNF-α-induced hepatocyte apoptosis and liver injury. We report here that the Akt activator SC79 protects hepatocytes from TNF-α-induced apoptosis and protects mice from d-galactosamine (d-Gal)/lipopolysaccharide (LPS)-induced TNF-α-mediated liver injury and damage. SC79 not only enhances the nuclear factor-κB (NF-κB) prosurvival signaling in response to TNF-α stimulation, but also increases the expression of cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein L and S (FLIP_L/S), which consequently inhibits the activation of procaspase-8. Furthermore, pretreatment of the PI3K/Akt inhibitor LY294002 reverses all the SC79-induced hepatoprotective effects. These results strongly indicate that SC79 protects against TNF-α-induced hepatocyte apoptosis and suggests that SC79 is likely a promising therapeutic agent for ameliorating the development of liver injury. NEW & NOTEWORTHY SC79 protects hepatocytes from TNF-α-mediated apoptosis and mice from Gal/LPS-induced liver injury and damage. Cytoprotective effects of SC79 against TNF-α act through both AKT-mediated activation of NF-κB and upregulation of FLIP_L/S.

[Protective effect of earthworm active ingredients against endoplasmic reticulum stress induced L-02 hepatocyte apoptosis]

This study focused on the protective effect of earthworm active ingredients (EWAs) on hepatocyte apoptosis induced by endoplasmic reticulum stress (ERS) in L-02 cells. The L-02 cells were cultured in vitro. The cell viability was measured with CCK-8, the apoptosis of L-02 cells was detected by flow cytometry, and the relevant protein and mRNA expressions were detected by Western blot and qPCR. According to the findings, tunicamycin (TM) could obviously reduce the survival rate of L-02 cells in a time-dependent and dose-dependent manner. Compared with normal group, the apoptosis rate in model group was significantly increased (P<0.05 or P<0.01). The protein and mRNA expressions of ERS-related signal molecules, such as GRP78, PERK, eLF2α, ATF4, CHOP and Bax, were significantly up-regulated (P<0.05 or P<0.01), while Bcl-2 was significantly down-regulated (P<0.05 or P<0.01). After the administration with different concentrations of EWAs, compared with model group, EWAs could significantly increase the survival rate ofL-02 hepatocyte and decrease the cell apoptosis rates. It could also reduce the protein and mRNA expressions of ERS-related signal molecules, such as GRP78, PERK, eLF2α, ATF4, CHOP and Bax, in a dose-dependent manner (P<0.05 or P<0.01) and increased the protein and mRNA expressions of Bcl-2(P<0.05 or P<0.01). These results showed that EWAs had a significantly protective effect on hepatocyte apoptosis induced by ERS in L-02 cells. Its mechanism may be related to the down-regulation of mRNA and protein expressions of GRP78, PERK, ATF4, eLF2α, CHOP and Bax, and the up-regulation, the relief of ERS and the promotion of the proliferation of impaired L-02 cells.

Deletion of endoplasmic reticulum stress-responsive co-chaperone p58IPK protects mice from diet-induced steatohepatitis

AIM

Activation of PKR-like endoplasmic reticulum kinase (PERK), an endoplasmic reticulum stress sensor, is a feature of non-alcoholic steatohepatitis (NASH), yet regulators of PERK signaling remain undefined in this context. The protein p58^IPK regulates PERK; however, its role in NASH has not been examined. The aim of this study was to assess the in vivo role of p58^IPK in the pathogenesis of dietary NASH.

METHODS

Parameters of hepatocyte cell death, liver injury, inflammation, fibrosis, indirect calorimetry and PERK activation were assessed in p58^IPK knockout (p58^ipk-/- ) mice and their wild-type littermate controls. All animals were fed a diet enriched in fat, fructose, and cholesterol (FFC) for 20 weeks.

RESULTS

Activation of PERK was attenuated in FFC-fed p58^ipk-/- mice. Accordingly, FFC-fed p58^ipk-/- mice showed a reduction in hepatocyte apoptosis and death receptor expression, with a significant reduction in serum alanine transaminase values. Correspondingly, macrophage accumulation and fibrosis were significantly lower in FFC-fed p58^ipk-/- mice.

CONCLUSION

We have shown that, in an in vivo dietary NASH model, p58^IPK mediates hepatocyte apoptosis and liver injury, likely through PERK phosphorylation. In the absence of p58^IPK , PERK phosphorylation and NASH are attenuated. Inhibition of hepatic p58^IPK could be a future target for NASH therapy.

Silica nanoparticles induce liver fibrosis via TGF-β1/Smad3 pathway in ICR mice

The liver is one of the target organs of silica nanoparticles (SiO₂ NPs) but the toxic mechanism on the liver still remains unclear. This study aimed to explore the hepatic toxicity and its mechanism through repeated intravenous exposure to SiO₂ NPs in ICR mice. Results indicated that SiO₂ NPs could be distributed in hepatocytes, Kupffer cells, and hepatic stellate cells, and induce hepatic dysfunction as well as granuloma formation in the liver. The increase of lipid peroxide level and decrease of antioxidant enzyme activities in the liver indicated that SiO₂ NPs could induce hepatic oxidative damage. SiO₂ NPs induced hepatocytes’ apoptosis shown by morphological examination and TUNEL assay. The results of Masson’s trichrome staining and hydroxyproline assay showed hyperplasia of collagen fibers in the liver, suggesting SiO₂ NPs caused liver fibrosis, and it was promoted by oxidative damage and hepatocytes’ apoptosis. The results of Western blot analysis and immunohistochemical staining indicated that the activation of TGF-β₁/Smad3 signaling pathway played an important role in this pathophysiological process. The results suggested that oxidative damage and hepatocyte apoptosis activated TGF-β₁/Smad3 signaling pathway, and thus promoted the process of liver fibrosis induced by intravenous injection of SiO₂ NPs in mice. This study, for the first time, investigated liver fibrosis and its related mechanism induced by repeated intravenous exposure of amorphous SiO₂ NPs, and provides important experimental evidence for safety evaluation of SiO₂ NPs, especially in biomedical application.

Hepatitis C Virus Nonstructural 5A Protein (HCV-NS5A) Inhibits Hepatocyte Apoptosis through the NF-κb/miR-503/bcl-2 Pathway

The nonstructural protein 5A (NS5A) encoded by the human hepatitis C virus (HCV) RNA genome is a multifunctional phosphoprotein. To analyse the influence of NS5A on apoptosis, we established an Hep-NS5A cell line (HepG2 cells that stably express NS5A) and induced apoptosis using tumour necrosis factor (TNF)-α. We utilised the MTT assay to detect cell viability, real-time quantitative polymerase chain reaction and Western blot to analyse gene and protein expression, and a luciferase reporter gene experiment to investigate the targeted regulatory relationship. Chromatin immunoprecipitation was used to identify the combination of NF-κB and miR-503. We found that overexpression of NS5A inhibited TNF-αinduced hepatocellular apoptosis via regulating miR-503 expression. The cell viability of the TNF-α induced Hep-mock cells was significantly less than the viability of the TNF-α induced Hep-NS5A cells, which demonstrates that NS5A inhibited TNF-α-induced HepG2 cell apoptosis. Under TNF-α treatment, miR-503 expression was decreased and cell viability and B-cell lymphoma 2 (bcl-2) expression were increased in the Hep-NS5A cells. Moreover, the luciferase reporter gene experiment verified that bcl-2 was a direct target of miR-503, NS5A inhibited TNF-α-induced NF-κB activation and NF-κB regulated miR-503 transcription by combining with the miR-503 promoter. After the Hep-NS5A cells were transfected with miR-503 mimics, the data indicated that the mimics could reverse TNF-α-induced cell apoptosis and blc-2 expression. Collectively, our findings suggest a possible molecular mechanism that may contribute to HCV treatment in which NS5A inhibits NF-κB activation to decrease miR-503 expression and increase bcl-2 expression, which leads to a decrease in hepatocellular apoptosis.

Reduced SHARPIN and LUBAC Formation May Contribute to CCl₄- or Acetaminophen-Induced Liver Cirrhosis in Mice

Linear ubiquitin chain assembly complex (LUBAC), composed of SHARPIN (SHANK-associated RH domain-interacting protein), HOIL-1L (longer isoform of heme-oxidized iron-regulatory protein 2 ubiquitin ligase-1), and HOIP (HOIL-1L interacting protein), forms linear ubiquitin on nuclear factor-κB (NF-κB) essential modulator (NEMO) and induces NF-κB pathway activation. SHARPIN expression and LUBAC formation were significantly reduced in the livers of mice 24 h after the injection of either carbon tetrachloride (CCl₄) or acetaminophen (APAP), both of which produced the fulminant hepatitis phenotype. To elucidate its pathological significance, hepatic SHARPIN expression was suppressed in mice by injecting shRNA adenovirus via the tail vein. Seven days after this transduction, without additional inflammatory stimuli, substantial inflammation and fibrosis with enhanced hepatocyte apoptosis occurred in the livers. A similar but more severe phenotype was observed with suppression of HOIP, which is responsible for the E3 ligase activity of LUBAC. Furthermore, in good agreement with these in vivo results, transduction of Hepa1-6 hepatoma cells with SHARPIN, HOIL-1L, or HOIP shRNA adenovirus induced apoptosis of these cells in response to tumor necrosis factor-α (TNFα) stimulation. Thus, LUBAC is essential for the survival of hepatocytes, and it is likely that reduction of LUBAC is a factor promoting hepatocyte death in addition to the direct effect of drug toxicity.

Mechanism of Hepatocyte Apoptosis

Hepatocyte apoptosis plays important roles in both the removal of external microorganisms and the occurrence and development of liver diseases. Different conditions, such as virus infection, fatty liver disease, hepatic ischemia reperfusion, and drug-induced liver injury, are accompanied by hepatocyte apoptosis. This review summarizes recent research on the mechanism of hepatocyte apoptosis involving the classical extrinsic and intrinsic apoptotic pathways, endoplasmic reticulum stress, and oxidative stress-induced apoptosis. We emphasized the major causes of apoptosis according to the characteristics of different liver diseases. Several concerns regarding future research and clinical application are also raised.

Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells

The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.

Mouse hepatocyte overexpression of NF-κB-inducing kinase (NIK) triggers fatal macrophage-dependent liver injury and fibrosis

Damaged, necrotic, or apoptotic hepatocytes release damage-associated molecular patterns that initiate sterile inflammation, and liver inflammation drives liver injury and fibrosis. Here we identified hepatic nuclear factor kappa B (NF-κB)-inducing kinase (NIK), a Ser/Thr kinase, as a novel trigger of fatal liver inflammation. NIK is activated by a broad spectrum of stimuli. It was up-regulated in injured livers in both mice and humans. In primary mouse hepatocytes, NIK overexpression stimulated, independently of cell injury and death, release of numerous chemokines and cytokines that activated bone marrow-derived macrophages (BMDMs). BMDMs in turn secreted proapoptotic molecules that stimulated hepatocyte apoptosis. Hepatocyte-specific expression of the NIK transgene triggered massive liver inflammation, oxidative stress, hepatocyte apoptosis, and liver fibrosis, leading to weight loss, hypoglycemia, and death. Depletion of Kupffer cells/macrophages reversed NIK-induced liver destruction and death.

CONCLUSION

the hepatocyte NIK-liver immune cell axis promotes liver inflammation, injury, and fibrosis, thus driving liver disease progression.

Low dose of carbon monoxide intraperitoneal injection provides potent protection against GalN/LPS-induced acute liver injury in mice

Carbon monoxide (CO) is an important effector-signaling molecule involved in various pathophysiological processes. Here we investigated the protective effects of exogenous CO in a murine model of acute liver damage induced by d-galactosamine (GalN) and lipopolysaccharide (LPS). Exogenous CO gas was administered to mice via intraperitoneal injection (first at a dose of 15 ml kg(-1) and then, 6 h later, 8 ml kg(-1)), which caused a significant elevation of blood carboxyhemoglobin levels of up to 12-14% for more than 12 h. GalN/LPS were given to induce acute liver damage in mice 30 min prior to CO exposure. This showed that GalN/LPS induced severe liver injury in mice, whereas CO injection remarkably improved the survival rate of mice and led to attenuated hepatocellular damage. CO exhibited anti-oxidative capabilities by inhibiting hepatic malondialdehyde contents and restoring superoxide dismutase and glutathione, as well as by reducing inducible NOS/NO production. The anti-apoptotic and anti-inflammatory effects of CO were substantial, characterized by a notable inhibition of hepatocyte apoptosis and a reduction of pro-inflammatory cytokines in mice. Our findings thus supported the hypothesis that exogenous CO provides protective effects against acute liver damage in mice, mainly dependent on its anti-oxidative, anti-inflammatory and anti-apoptotic properties.

Liver fibrosis and hepatocyte apoptosis are attenuated by GKT137831, a novel NOX4/NOX1 inhibitor in vivo

Reactive oxygen species (ROS) play a key role in chronic liver injury and fibrosis. Homologs of NADPH oxidases (NOXs) are major sources of ROS, but the exact role of the individual homologs in liver disease is unknown. Our goal was to determine the role of NOX4 in liver fibrosis induced by bile duct ligation (BDL) with the aid of the pharmacological inhibitor GKT137831, and genetic deletion of NOX4 in mice. GKT137831 was either applied for the full term of BDL (preventive arm) or started at 10 day postoperatively (therapeutic arm). Primary hepatic stellate cells (HSC) from control mice with and without BDL were analyzed and the effect of NOX4 inhibition on HSC activation was also studied. FasL or TNFα/actinomycin D-induced apoptosis was studied in wild-type and NOX4(-/-) hepatocytes. NOX4 was upregulated by a TGF-β/Smad3-dependent mechanism in HSC. Downregulation of NOX4 decreased ROS production and the activation of NOX4(-/-) HSC was attenuated. NOX4(-/-) hepatocytes were more resistant to FasL or TNFα/actinomycin D-induced apoptosis. Similarly, after pharmacological NOX4 inhibition, ROS production, the expression of fibrogenic markers, and hepatocyte apoptosis were reduced. NOX4 was expressed in human livers with stage 2-3 autoimmune hepatitis. Fibrosis was attenuated by the genetic deletion of NOX4. BDL mice gavaged with GKT137831 in the preventive or the therapeutic arm displayed less ROS production, significantly attenuated fibrosis, and decreased hepatocyte apoptosis. In conclusion, NOX4 plays a key role in liver fibrosis. GKT137831 is a potent inhibitor of fibrosis and hepatocyte apoptosis; therefore, it is a promising therapeutic agent for future translational studies.