Activation of autophagy protects against cholestasis-induced hepatic injury

Vitamin D Receptor Activation Reduces Hepatic Inflammation via Enhancing Macrophage Autophagy in Cholestatic Mice

Macrophage autophagy dysfunction aggravates liver injury by activating inflammasomes, which can cleave pro-IL-1β to its active, secreted form. We investigated whether the vitamin D/vitamin D receptor (VDR) axis could up-regulate macrophage autophagy function to inhibit the activation of inflammasome-dependent IL-1β during cholestasis. Paricalcitol (PAL; VDR agonist) was intraperitoneally injected into bile duct-ligated mice for 5 days. Up-regulation of VDR expression by PAL reduced liver injury by reducing the oxidative stress-induced inflammatory reaction in macrophages. Moreover, PAL inhibited inflammasome-dependent IL-1β generation. Mechanistically, the knockdown of VDR increased IL-1β generation, whereas VDR overexpression exerted the opposite effect following tert-butyl hydroperoxide treatment. The inflammasome antagonist glyburide, the caspase-1-specific inhibitor YVAD, and the reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC) blocked the increase in Vdr shRNA-induced IL-1β production. Interestingly, up-regulation of VDR also enhanced macrophage autophagy. Autophagy reduction impaired the up-regulation of VDR-inhibited macrophage inflammasome-generated IL-1β, whereas autophagy induction showed a synergistic effect with VDR overexpression through ROS-p38 mitogen-activated protein kinase (MAPK) pathway. This result was confirmed by p38 MAPK inhibitor, MAPK activator, and ROS inhibitor NAC. Collectively, PAL triggered macrophage autophagy by suppressing activation of the ROS-p38 MAPK pathway, which, in turn, suppressed inflammasome-generated cleaved, active forms of IL-1β, eventually leading to reduced inflammation. Thus, triggering the VDR may be a potential target for the anti-inflammatory treatment of cholestatic liver disease.

The autophagic protein p62 is a target of reactive aldehydes in human and murine cholestatic liver disease

Inflammatory cholestatic liver diseases, including Primary Sclerosing Cholangitis (PSC), are characterized by periportal inflammation with progression to cirrhosis. The objective of this study was to examine interactions between oxidative stress and autophagy in cholestasis. Using hepatic tissue from male acute cholestatic (bile duct ligated) as well as chronic cholestatic (Mdr2KO) mice, localization of oxidative stress, the antioxidant response and induction of autophagy were analyzed and compared to human PSC liver. Concurrently, the ability of reactive aldehydes to post-translationally modify the autophagosome marker p62 was assessed in PSC liver tissue and in cell culture. Expression of autophagy markers was upregulated in human and mouse cholestatic liver. Whereas mRNA expression of Atg12, Lamp1, Sqstm1 and Map1lc3 was increased in acute cholestasis in mice, it was either suppressed or not significantly changed in chronic cholestasis. In human and murine cholestasis, periportal hepatocytes showed increased IHC staining of ubiquitin, 4-HNE, p62, and selected antioxidant proteins. Increased p62 staining colocalized with accumulation of 4-HNE-modified proteins in periportal parenchymal cells as well as with periportal macrophages in both human and mouse liver. Mechanistically, p62 was identified as a direct target of lipid aldehyde adduction in PSC hepatic tissue and in vitro cell culture. In vitro LS-MS/MS analysis of 4-HNE treated recombinant p62 identified carbonylation of His123, Cys128, His174, His181, Lys238, Cys290, His340, Lys341 and His385. These data indicate that dysregulation of autophagy and oxidative stress/protein damage are present in the same periportal hepatocyte compartment of both human and murine cholestasis. Thus, our results suggest that both increased expression as well as ineffective autophagic degradation of oxidatively-modified proteins contributes to injury in periportal parenchymal cells and that direct modification of p62 by reactive aldehydes may contribute to autophagic dysfunction.

Plumbagin ameliorates bile duct ligation-induced cholestatic liver injury in rats

Plumbagin, a natural bicyclic naphthoquinone, has diverse pharmacological properties and biological benefits against a number of disorders, including liver disease. Though plumbagin's hepatoprotective potential attracts attention, currently no experimental evidence exists on its effectiveness against cholestatic liver injury. The present study investigated its hepatoprotection in the rat model of extrahepatic cholestasis using Bile Duct Ligation (BDL). We found that daily plumbagin supplementation protected the liver from cholestatic damage. Hepatoprotective actions of plumbagin were accompanied by reduction of Transforming Growth Factor β1 (TGF-β1)/Smad, High Mobility Group Box-1 (HMGB1)/Toll-Like Receptor-4 (TLR4), Hypoxia-Inducible Factor-1α (HIF-1α), Aryl Hydrocarbon Receptor (AhR), Heat Shock Protein 90 (HSP90), caveolin-1, NF-κB/AP-1, Dynamin Related Protein-1 (Drp1), malondialdehyde level, Interleukin-1β (IL-1β), p62/SQSTM1, and caspase 3 as well as increase of Farnesoid X Receptor (FXR), bile acid efflux transporters, glutathione, LC3-II, Beclin1, and nuclear NF-E2-Related Factor-2 (Nrf2) and Transcription Factor EB (TFEB). The activation of nuclear Nrf2 caused by plumbagin correlated well with the improvement in bile acid retention, liver histology, serum biochemical, ductular reaction, mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, impaired autophagy, and fibrosis, involving interplay of multiple intracellular signaling pathways. Plumbagin is likely a candidate drug to protect the liver from cholestatic damages. Despite the promising findings from this study, translational implication of plumbagin on cholestatic liver injury warrants further investigation.

Autophagic flux inhibition, apoptosis, and mitochondrial dysfunction in bile acids-induced impairment of human placental trophoblast

Intrahepatic cholestasis of pregnancy (ICP) is a common pregnancy-specific disease, characterized by increased bile acid levels and adverse fetal outcomes. We previously reported excessive bile acids led to dysfunction of placental trophoblasts in ICP. However, the detailed mechanism is still unclear. Autophagy is fundamental process for protecting cell survival against adverse conditions. Here, we evaluated the effect of increased concentration of bile acids on autophagy in trophoblasts in vitro and in vivo. First, we demonstrated that the autophagy substrate p62/sequestosome-1 was accumulated in placental tissues from patients with ICP and in human trophoblasts treated with hydrophobic bile acids, including chenodeoxycholic acid and deoxycholic acid. Furthermore, we found that treatment with hydrophobic bile acids impaired autophagic flux in both time- and concentration-dependent manners, by suppressing the AMP-activated protein kinase/unc-51-like kinase 1 autophagic signaling pathway. Notably, trophoblasts were prone to apoptotic cell death upon starvation along with bile-acids treatment in vitro or in an ICP mouse model in vivo. Additionally, we revealed mitochondrial dysfunction was the predominant biological process in excessive bile acids induced trophoblast impairment under starvation by proteomic assay. Collectively, our study proposed a complex interaction of excessive bile acids induced autophagic flux, mitochondrial dysfunction, and cellular apoptosis in placental trophoblasts may play a critical role in the pathogenesis of ICP.

Intestinal microbiota drives cholestasis-induced specific hepatic gene expression patterns

Intestinal microbiota regulates multiple host metabolic and immunological processes. Consequently, any difference in its qualitative and quantitative composition is susceptible to exert significant effects, in particular along the gut-liver axis. Indeed, recent findings suggest that such changes modulate the severity and the evolution of a wide spectrum of hepatobiliary disorders. However, the mechanisms linking intestinal microbiota and the pathogenesis of liver disease remain largely unknown. In this work, we investigated how a distinct composition of the intestinal microbiota, in comparison with germ-free conditions, may lead to different outcomes in an experimental model of acute cholestasis. Acute cholestasis was induced in germ-free (GF) and altered Schaedler's flora (ASF) colonized mice by common bile duct ligation (BDL). Studies were performed 5 days after BDL and hepatic histology, gene expression, inflammation, lipids metabolism, and mitochondrial functioning were evaluated in normal and cholestatic mice. Differences in plasma concentration of bile acids (BA) were evaluated by UHPLC-HRMS. The absence of intestinal microbiota was associated with significant aggravation of hepatic bile infarcts after BDL. At baseline, we found the absence of gut microbiota induced altered expression of genes involved in the metabolism of fatty and amino acids. In contrast, acute cholestasis induced altered expression of genes associated with extracellular matrix, cell cycle, autophagy, activation of MAPK, inflammation, metabolism of lipids, and mitochondrial functioning pathways. Ductular reactions, cell proliferation, deposition of collagen 1 and autophagy were increased in the presence of microbiota after BDL whereas GF mice were more susceptible to hepatic inflammation as evidenced by increased gene expression levels of osteopontin, interleukin (IL)-1β and activation of the ERK/MAPK pathway as compared to ASF colonized mice. Additonally, we found that the presence of microbiota provided partial protection to the mitochondrial functioning and impairment in the fatty acid metabolism after BDL. The concentration of the majority of BA markedly increased after BDL in both groups without remarkable differences according to the hygiene status of the mice. In conclusion, acute cholestasis induced more severe liver injury in GF mice compared to mice with limited intestinal bacterial colonization. This protective effect was associated with different hepatic gene expression profiles mostly related to tissue repair, metabolic and immune functions. Our findings suggest that microbial-induced differences may impact the course of cholestasis and modulate liver injury, offering a background for novel therapies based on the modulation of the intestinal microbiota.

Vitexin ameliorates glycochenodeoxycholate-induced hepatocyte injury through SIRT6 and JAK2/STAT3 pathways

Objectives

Vitexin, a natural flavonoid, is commonly found in many foods and traditional herbal medicines and has clear health benefits. However, the role of vitexin in cholestasis is presently unclear. This study investigated whether vitexin mitigated glycochenodeoxycholate (GCDC)-induced hepatocyte injury and further elucidated the underlying mechanisms.

Materials and Methods

A cell counting kit-8 (CCK-8) assay was conducted to evaluate cell viability. The mitochondrial membrane potential (MMP, Δψm), reactive oxygen species (ROS) levels, and apoptosis rate of hepatocytes exposed to GCDC were detected by flow cytometry (FCM). We then measured the cytoprotective effects of vitexin against oxidative stress. The molecular signaling pathway was further investigated by using Western blotting and signaling pathway inhibitors.

Results

Here, we showed that vitexin increased cell viability and reduced cell apoptosis, necroptosis, and oxidative stress in a dose-dependent manner in GCDC-treated hepatocytes. In addition, by using selective inhibitors, we further confirmed that inhibition of the JAK2/STAT3 pathway by vitexin was mediated by prolonged activation of Sirtuin 6 (SIRT6).

Conclusion

Vitexin attenuated GCDC-induced hepatocyte injury via SIRT6 and the JAK2/STAT3 pathways.

Involvement of Autophagy in Ageing and Chronic Cholestatic Diseases

Autophagy is a “housekeeping” lysosomal degradation process involved in numerous physiological and pathological processes in all eukaryotic cells. The dysregulation of hepatic autophagy has been described in several conditions, from obesity to diabetes and cholestatic disease. We review the role of autophagy, focusing on age-related cholestatic diseases, and discuss its therapeutic potential and the molecular targets identified to date. The accumulation of toxic BAs is the main cause of cell damage in cholestasis patients. BAs and their receptor, FXR, have been implicated in the regulation of hepatic autophagy. The mechanisms by which cholestasis induces liver damage include mitochondrial dysfunction, oxidative stress and ER stress, which lead to cell death and ultimately to liver fibrosis as a compensatory mechanism to reduce the damage. The stimulation of autophagy seems to ameliorate the liver damage. Autophagic activity decreases with age in several species, whereas its basic extends lifespan in animals, suggesting that it is one of the convergent mechanisms of several longevity pathways. No strategies aimed at inducing autophagy have yet been tested in cholestasis patients. However, its stimulation can be viewed as a novel therapeutic strategy that may reduce ageing-dependent liver deterioration and also mitigate hepatic steatosis.

Farnesoid X Receptor as Target for Therapies to Treat Cholestasis-Induced Liver Injury

Recent studies on liver disease burden worldwide estimated that cirrhosis is the 11th most common cause of death globally, and there is a great need for new therapies to limit the progression of liver injuries in the early stages. Cholestasis is caused by accumulation of hydrophobic bile acids (BA) in the liver due to dysfunctional BA efflux or bile flow into the gall bladder. Therefore, strategies to increase detoxification of hydrophobic BA and downregulate genes involved in BA production are largely investigated. Farnesoid X receptor (FXR) has a central role in BA homeostasis and recent publications revealed that changes in autophagy due to BA-induced reactive oxygen species and increased anti-oxidant response via nuclear factor E2-related factor 2 (NRF2), result in dysregulation of FXR signaling. Several mechanistic studies have identified new dysfunctions of the cholestatic liver at cellular and molecular level, opening new venues for developing more performant therapies.

Prevention of D-GalN/LPS-induced ALI by 18β-glycyrrhetinic acid through PXR-mediated inhibition of autophagy degradation

Acute liver injury (ALI) has multiple causes and results in liver dysfunction. Severe or persistent liver injury eventually leads to liver failure and even death. Pregnane X receptor (PXR)-null mice present more severe liver damage and lower rates of autophagy. 18β-glycyrrhetinic acid (GA) has been proposed as a promising hepatoprotective agent. We hypothesized that GA significantly alleivates D-GalN/LPS-induced ALI, which involved in PXR-mediated autophagy and lysosome biogenesis. We found that GA can significantly decrease hepatocyte apoptosis and increase the hepatic autophagy marker LC3-B. Ad-mCherry-GFP-LC3 tandem fluorescence, RNA-seq and real-time PCR indicated that GA may stabilize autophagosomes and lysosomes and inhibit autophagosome-lysosome fusion. Simultaneously, GA markedly activates PXR, even reversing the D-GalN/LPS-induced reduction of PXR and its downstream genes. In contrast, GA has a weak protective effect in pharmacological inhibition of PXR and PXR-null mice, which significantly affected apoptosis- and autophagy-related genes. PXR knockout interferes with the stability of autophagosomes and lysosomes, preventing GA reducing the expression of lysosomal genes such as Cst B and TPP1, and suppressing autophagy flow. Therefore, we believe that GA increases autophagy by inhibiting autophagosome-lysosome fusion and blocked autophagy flux via activation of PXR. In conclusion, our results show that GA activates PXR to regulate autophagy and lysosome biogenesis, represented by inhibiting autophagosome-lysosome fusion and stabilization of lysosome. These results identify a new mechanism by which GA-dependent PXR activation reduces D-GalN/LPS-induced acute liver injury.

Testing in vitro tools for the prediction of cholestatic liver injury induced by non-pharmaceutical chemicals

Bile acid accumulation and subsequent liver damage is a frequent adverse effect induced by drugs. Considerable efforts have therefore been focused on the introduction and characterization of tools that allow reliable prediction of this type of drug-induced liver injury. Among those are the cholestatic index and transcriptomic profiling, which are typically assessed in in vitro settings. The present study was set up to test the applicability of both tools to non-pharmaceutical compounds with cholestatic potential, including the industrial compound bis(2-ethylhexyl)phthalate, the cosmetic ingredients triclosan and octynoic acid, the herbicides paraquat and quizalofop-para-ethyl, and the food additives sunset yellow and tartrazine, in a human hepatoma cell culture model of cholestatic liver injury. The cholestatic index method showed cholestatic liability of sunset yellow, tartrazine and triclosan. Of those, tartrazine induced transcriptional changes reminiscent of the transcriptional profile of cholestatic drugs. Furthermore, a number of genes were found to be uniquely modulated by tartrazine, in accordance with the cholestatic drugs atazanavir, cyclosporin A and nefazodone, which may have potential as novel transcriptomic biomarkers of chemical-induced cholestatic liver injury. In conclusion, unambiguous identification of the non-pharmaceutical compounds tested in this study as inducers of cholestasis could not be achieved.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms. Damaged organelles, lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell. Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports. In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy. Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma. We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases. We analyzed autophagy not only in well studied diseases, like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis, biliary diseases, autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity. We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells, sinusoidal endothelial cells or hepatic stellate cells. Finally, we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Regulation of autophagy by bile acids and in cholestasis - CholestoPHAGY or CholeSTOPagy

Autophagy is a lysosomal degradation pathway in which the cell self-digests its own components to provide nutrients in harsh environmental conditions. It also represents an opportunity to rid the cell of superfluous and damaged organelles, misfolded proteins or invaded microorganisms. Liver autophagy contributes to basic hepatic functions such as lipid, glycogen and protein turnover. Deregulated hepatic autophagy has been linked to many liver diseases including alpha-1-antitrypsin deficiency, alcoholic and non-alcoholic fatty liver diseases, hepatitis B and C infections, liver fibrosis as well as liver cancer. Recently, bile acids and the bile acid receptor FXR have been implicated in the regulation of hepatic autophagy, which implies a role of autophagy also for cholestatic liver diseases. This review summarizes the current evidence of bile acid mediated effects on autophagy and how this affects cholestatic liver diseases. Although detailed studies are lacking, we suggest a concept that the activity of autophagy in cholestasis depends on the disease stage, where autophagy may be induced at early stages ("cholestophagy") but may be impaired in prolonged cholestatic states ("cholestopagy").

FXR-dependent Rubicon induction impairs autophagy in models of human cholestasis

BACKGROUND & AIMS

Cholestasis comprises a spectrum of liver diseases characterized by the accumulation of bile acids. Bile acids and activation of the farnesoid X receptor (FXR) can inhibit autophagy, a cellular self-digestion process necessary for cellular homeostasis and regeneration. In mice, autophagy appears to be impaired in cholestasis and induction of autophagy may reduce liver injury.

METHODS

Herein, we explored autophagy in human cholestasis in vivo and investigated the underlying molecular mechanisms in vitro. FXR chromatin immunoprecipitation-sequencing and qPCR were performed in combination with luciferase promoter studies to identify functional FXR binding targets in a human cholestatic liver sample.

RESULTS

Autophagic processing appeared to be impaired in patients with cholestasis and in individuals treated with the FXR ligand obeticholic acid (OCA). In vitro, chenodeoxycholic acid and OCA inhibited autophagy at the level of autophagosome to lysosome fusion in an FXR-dependent manner. Rubicon, which inhibits autophago-lysosomal maturation, was identified as a direct FXR target that is induced in cholestasis and by FXR-agonistic bile acids. Genetic inhibition of Rubicon reversed the bile acid-induced impairment of autophagic flux. In contrast to OCA, ursodeoxycholic acid (UDCA), which is a non-FXR-agonistic bile acid, induced autophagolysosome formation independently of FXR, enhanced autophagic flux and was associated with reduced Rubicon levels.

CONCLUSION

In models of human cholestasis, autophagic processing is impaired in an FXR-dependent manner, partly resulting from the induction of Rubicon. UDCA is a potent inducer of hepatic autophagy. Manipulating autophagy and Rubicon may represent a novel treatment concept for cholestatic liver diseases.

LAY SUMMARY

Autophagy, a cellular self-cleansing process, is impaired in various forms of human cholestasis. Bile acids, which accumulate in cholestatic liver disease, induce Rubicon, a protein that inhibits proper execution of autophagy. Ursodeoxycholic acid, which is the first-line treatment option for many cholestatic liver diseases, induces hepatic autophagy along with reducing Rubicon.

Glycochenodeoxycholic acid impairs transcription factor E3 -dependent autophagy-lysosome machinery by disrupting reactive oxygen species homeostasis in L02 cells

Cholestasis represents pathophysiologic syndromes defined as impaired bile flow from the liver. As an outcome, bile acids accumulate and promote hepatocyte injury, followed by liver cirrhosis and liver failure. Glycochenodeoxycholic acid (GCDCA) is relatively toxic and highly concentrated in bile and serum after cholestasis. However, the mechanism underlying GCDCA-induced hepatotoxicity remains unclear. In this study, we found that GCDCA inhibits autophagosome formation and impairs lysosomal function by inhibiting lysosomal proteolysis and increasing lysosomal pH, contributing to defects in autophagic clearance and subsequently leading to the death of L02 human hepatocyte cells. Notably, through tandem mass tag (TMT)-based quantitative proteomic analysis and database searches, 313 differentially expressed proteins were identified, of which 71 were increased and 242 were decreased in the GCDCA group compared with those in the control group. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that GCDCA suppressed the signaling pathway of transcription factor E3 (TFE3), which was the most closely associated with autophagic flux impairment. In contrast, GCDCA-inhibited lysosomal function and autophagic flux were efficiently attenuated by TFE3 overexpression. Specifically, the decreased expression of TFE3 was closely related to the disruption of reactive oxygen species (ROS) homeostasis, which could be prevented by inhibiting intracellular ROS with N-acetyl cysteine (NAC). In summary, our study is the first to demonstrate that manipulation of ROS/TFE3 signaling may be a therapeutic approach for antagonizing GCDCA-induced hepatotoxicity.

Hepatitis C virus core or NS3/4A protein expression preconditions hepatocytes against oxidative stress and endoplasmic reticulum stress

Objectives: The occurrence of oxidative stress and endoplasmic reticulum (ER) stress in hepatitis C virus (HCV) infection has been demonstrated and play an important role in liver injury. During viral infection, hepatocytes must handle not only the replication of the virus, but also inflammatory signals generating oxidative stress and damage. Although several mechanisms exist to overcome cellular stress, little attention has been given to the adaptive response of hepatocytes during exposure to multiple noxious triggers.

Methods: In the present study, Huh-7 cells and hepatocytes expressing HCV Core or NS3/4A proteins, both inducers of oxidative and ER stress, were additionally challenged with the superoxide anion generator menadione to mimic external oxidative stress. The production of reactive oxygen species (ROS) as well as the response to oxidative stress and ER stress were investigated.

Results: We demonstrate that hepatocytes diminish oxidative stress through a reduction in ROS production, ER-stress markers (HSPA5 [GRP78], sXBP1) and apoptosis (caspase-3 activity) despite external oxidative stress. Interestingly, the level of the autophagy substrate protein p62 was downregulated together with HCV Core degradation, suggesting that hepatocytes can overcome excess oxidative stress through autophagic degradation of one of the stressors, thereby increasing cell survival.

Duscussion: In conclusion, hepatocytes exposed to direct and indirect oxidative stress inducers are able to cope with cellular stress associated with viral hepatitis and thus promote cell survival.

Robustness testing and optimization of an adverse outcome pathway on cholestatic liver injury

Adverse outcome pathways (AOPs) have been recently introduced as tools to map the mechanisms underlying toxic events relevant for chemical risk assessment. AOPs particularly depict the linkage between a molecular initiating event and an adverse outcome through a number of intermediate key events. An AOP has been previously introduced for cholestatic liver injury. The objective of this study was to test the robustness of this AOP for different types of cholestatic insult and the in vitro to in vivo extrapolation. For this purpose, in vitro samples from human hepatoma HepaRG cell cultures were exposed to cholestatic drugs (i.e. intrahepatic cholestasis), while in vivo samples were obtained from livers of cholestatic mice (i.e. extrahepatic cholestasis). The occurrence of cholestasis in vitro was confirmed through analysis of bile transporter functionality and bile acid analysis. Transcriptomic analysis revealed inflammation and oxidative stress as key events in both types of cholestatic liver injury. Major transcriptional differences between intrahepatic and extrahepatic cholestatic liver insults were observed at the level of cell death and metabolism. Novel key events identified by pathway analysis included endoplasmic reticulum stress in intrahepatic cholestasis, and autophagy and necroptosis in both intrahepatic as extrahepatic cholestasis. This study demonstrates that AOPs constitute dynamic tools that should be frequently updated with new input information.

Autophagy in Triptolide-Mediated Cytotoxicity in Hepatic Cells

Triptolide is a major active ingredient isolated from the traditional Chinese herb Tripterygium wilfordii Hook F. However, its use in clinical practice is limited due to its severe hepatotoxicity. Autophagy, a highly conserved intracellular process, is essential for maintaining cytoplasmic homeostasis. Considering that abnormalities in autophagy are closely associated with drug-mediated hepatotoxicity, we applied human normal liver HL7702 cells to elucidate the roles of autophagy in triptolide-induced hepatotoxicity. Our study revealed that triptolide was cytotoxic to HL7702 cells. It markedly increased autophagosome formation and expression of autophagy-related proteins, namely Beclin1 and microtubule-associated protein 1 light chain 3II, and induced oxidative stress. These proautophagic effects were counteracted by pretreatment with N-acetylcysteine, a reactive oxygen species scavenger. Moreover, the pharmacological suppression of autophagy further exacerbated triptolide-elicited decrease in cell viability, increase in lactate dehydrogenase leakage, and activation of apoptosis proteases (caspase 3 and caspase 9). Our findings suggest that triptolide-induced oxidative stress consequently enhances autophagic activity, and autophagy is a cytoprotective mechanism against triptolide-induced cytotoxicity in HL7702 cells.

The Role of Phospho-c-Jun N-Terminal Kinase Expression on hepatocyte Necrosis and Autophagy in the Cholestatic Liver

BACKGROUND

Clinically, liver fibrosis and cholestasis are two major disease entities, ultimately leading to hepatic failure. Although autophagy plays a substantial role in the pathogenesis of these diseases, its precise mechanism has not been determined yet.

MATERIALS AND METHODS

Mouse models of liver fibrosis or cholestasis were obtained after the serial administration of thioacetamide (TAA) or surgical bile duct ligation (BDL), respectively. Then, after obtaining liver specimens at specific time points, we compared the expression of makers related to apoptosis (cleaved caspases), inflammation (CD68), necrosis (high-mobility group box 1), phospho-c-Jun N-terminal kinase (p-JNK), and autophagy (microtubule-associated protein light chain 3B and p62) in the fibrotic or cholestatic mouse livers, by polymerase chain reaction, Western blot analysis, immunohistochemistry, and immunofluorescence.

RESULTS

Although cholestatic livers exhibited the tendency of progressively increasing the expression of most apoptosis-related markers (cleaved caspases), it was not prominent when it was compared with the tendency found in the livers of TAA-treated mice. Contrastingly, the necrosis-related factor (high-mobility group box 1) was significantly increased in the livers of BDL mice over time, reaching their peak values on day 7 after BDL. In addition, the inflammation-related factor (CD68) was highly expressed in BDL mice compared with TAA-treated mice over time. Autophagy marker studies indicated that autophagy was upregulated in fibrotic livers, whereas it was downregulated in cholestatic livers. We also observed mild to moderate activation of p-JNK in the livers of TAA-treated mice, whereas significantly higher p-JNK activation was detected in the livers of BDL mice.

CONCLUSIONS

Unlike TAA-treated mice, BDL mice exhibited higher expression of the markers related with inflammation and necrosis, especially including p-JNK, while maintaining low levels of autophagic process. Therefore, obstructive cholestasis is characterized by higher p-JNK activation, which could be related with marked necrotic cell death resulting from extensive inflammation and little chance of compensatory autophagy.

Glycochenodeoxycholate promotes hepatocellular carcinoma invasion and migration by AMPK/mTOR dependent autophagy activation

Metastasis and recurrence severely impact the treatment effect of hepatocellular carcinoma (HCC). HCC complicated with cholestasis is more prone to recurrence and metastasis. Previous studies have implicated pathogenesis of HCC by bile acid; however, the underlying mechanism is unknown yet. Glycochenodeoxycholate (GCDC) is one of most important component of bile acid (BA). In the present study, the role of GCDC in HCC cells invasion was detected by in vitro and in vivo assays. GCDC was found to significantly enhance the invasive potential of HCC cells; Further studies showed that GCDC could induce autophagy activation and higher invasive capability in HCC cells. Interestingly, inhibition of autophagy by chloroquine (CQ) reversed this phenomenon. Subsequently, the correlation between TBA expression level and clinicopathological characteristics was analyzed in HCC patients. Clinically, high TBA level in HCC tissue was found to be associated with more invasive and poor survival in HCC patients. Mechanistic study showed that bile acid induced autophagy by targeting the AMPK/mTOR pathway in HCC cells. Therefore, our results suggest that bile acid may promote HCC invasion via activation of autophagy and the level of bile acid may serve as a potential useful indicator for prognosis of HCC patients.

Mechanisms and in vitro models of drug-induced cholestasis

Cholestasis underlies one of the major manifestations of drug-induced liver injury. Drug-induced cholestatic liver toxicity is a complex process, as it can be triggered by a variety of factors that induce 2 types of biological responses, namely a deteriorative response, caused by bile acid accumulation, and an adaptive response, aimed at removing the accumulated bile acids. Several key events in both types of responses have been characterized in the past few years. In parallel, many efforts have focused on the development and further optimization of experimental cell culture models to predict the occurrence of drug-induced cholestatic liver toxicity in vivo. In this paper, a state-of-the-art overview of mechanisms and in vitro models of drug-induced cholestatic liver injury is provided.

Mechanisms of Drug-Induced Cholestasis

Cholestasis can be defined as any situation of impaired bile secretion with concomitant accumulation of bile acids in the liver or in the systemic circulation. A variety of factors may evoke cholestasis, including genetic disorders, metabolic pathologies, infectious diseases, immunogenic stimuli, and drugs. Drug-induced cholestasis is a mechanistically complex process. At least three triggering factors of drug-induced cholestasis have been described, including effects on drug transporters, various hepatocellular changes, and altered bile canaliculi dynamics. These stimuli induce two cellular responses, each typified by a number of key events, namely a deteriorative response activated by bile acid accumulation and an adaptive response aimed at decreasing the uptake and increasing the export of bile acids into and from the liver, respectively. The mechanistic scenario of drug-induced cholestasis is described in this chapter.

Autophagy May Protect Against Parenteral Nutrition-Associated Liver Disease by Suppressing Endoplasmic Reticulum Stress

BACKGROUND

The objectives of this study were to address the role of autophagy in the pathogenesis of parenteral nutrition (PN)-associated liver disease (PNALD) and its possible mechanism in vivo.

METHODS

Five-week-old male Sprague Dawley rats were fed Shoobree chow (Xietong Organism, Jiangsu, China) and administered intravenous 0.9% saline (sham group), PN (PN group), PN plus rapamycin (1 mg/kg; PN + Rapa group), or rapamycin (Rapa group) for 7 days. Before and after study, body weight, biochemical indicators, hepatic histology, level of autophagy, hepatocyte apoptosis, reactive oxygen species (ROS), and endoplasmic reticulum (ER) stress indicators including binding immunoglobulin protein (BIP), spliced X-box-binding protein-1 (sXBP1), and CCAAT-enhancer-binding protein homologous protein (CHOP) were measured.

RESULTS

Autophagy was suppressed in the PNALD model, which was demonstrated by less light chain 3 fluorescence (LC3) puncta and lower LC3II expression. Rapamycin effectively induced hepatic autophagy in PN rats. The PN + Rapa group presented improved hepatic function, decreased pathology scores, and less steatosis than the PN group. In addition, rapamycin treatment decreased terminal deoxynucleotidyl transferase dUTP nick end labeling and cleaved-caspase 3 expression, indicating a lower level of hepatocyte apoptosis. Compared with the PN group, the PN + Rapa group had lower levels of ROS and reduced expression of ER stress-related protein markers, such as BIP, sXBP1 and CHOP.

CONCLUSIONS

Autophagy was suppressed in the PNALD model. Rapamycin treatment induced autophagy and protected against PNALD, possibly by suppressing ROS-induced ER stress.

Zebrafish abcb11b mutant reveals strategies to restore bile excretion impaired by bile salt export pump deficiency

Bile salt export pump (BSEP) adenosine triphosphate-binding cassette B11 (ABCB11) is a liver-specific ABC transporter that mediates canalicular bile salt excretion from hepatocytes. Human mutations in ABCB11 cause progressive familial intrahepatic cholestasis type 2. Although over 150 ABCB11 variants have been reported, our understanding of their biological consequences is limited by the lack of an experimental model that recapitulates the patient phenotypes. We applied CRISPR/Cas9-based genome editing technology to knock out abcb11b, the ortholog of human ABCB11, in zebrafish and found that these mutants died prematurely. Histological and ultrastructural analyses showed that abcb11b mutant zebrafish exhibited hepatocyte injury similar to that seen in patients with progressive familial intrahepatic cholestasis type 2. Hepatocytes of mutant zebrafish failed to excrete the fluorescently tagged bile acid that is a substrate of human BSEP. Multidrug resistance protein 1, which is thought to play a compensatory role in Abcb11 knockout mice, was mislocalized to the hepatocyte cytoplasm in abcb11b mutant zebrafish and in a patient lacking BSEP protein due to nonsense mutations in ABCB11. We discovered that BSEP deficiency induced autophagy in both human and zebrafish hepatocytes. Treatment with rapamycin restored bile acid excretion, attenuated hepatocyte damage, and extended the life span of abcb11b mutant zebrafish, correlating with the recovery of canalicular multidrug resistance protein 1 localization.

CONCLUSIONS

Collectively, these data suggest a model that rapamycin rescues BSEP-deficient phenotypes by prompting alternative transporters to excrete bile salts; multidrug resistance protein 1 is a candidate for such an alternative transporter. (Hepatology 2018;67:1531-1545).

Liver Disease in Alpha-1 Antitrypsin Deficiency: Current Approaches and Future Directions

Purpose of Review

The aim of the study is to review the liver disease caused by alpha-1 antitrypsin deficiency (A1ATD), including pathogenesis, epidemiology, diagnostic testing, and recent therapeutic developments.

Recent Findings

Therapeutic approaches target several intracellular pathways to reduce the cytotoxic effects of the misfolded mutant globular protein (ATZ) on the hepatocyte. These include promoting ATZ transport out of the endoplasmic reticulum (ER), enhancing ATZ degradation, and preventing ATZ globule-aggregation.

Summary

A1ATD is the leading genetic cause of liver disease among children. It is a protein-folding disorder in which toxic insoluble ATZ proteins aggregate in the ER of hepatocytes leading to inflammation, fibrosis, cirrhosis, and increased risk of hepatocellular carcinoma. The absence of the normal A1AT serum protein also predisposes patients to pan lobar emphysema as adults. At this time, the only approved therapy for A1ATD-associated liver disease is orthotopic liver transplantation, which is curative. However, there has been significant recent progress in the development of small molecule therapies with potential both to preserve the native liver and prevent hepatotoxicity.

Bile Duct Ligation Induces ATZ Globule Clearance in a Mouse Model of α-1 Antitrypsin Deficiency

α-1 Antitrypsin deficiency (A1ATD) can progress to cirrhosis and hepatocellular carcinoma; however, not all patients are susceptible to severe liver disease. In A1ATD, a toxic gain-of-function mutation generates insoluble ATZ "globules" in hepatocytes, overwhelming protein clearance mechanisms. The relationship between bile acids and hepatocytic autophagy is less clear but may involve altered gene expression pathways. Based on previous findings that bile duct ligation (BDL) induces autophagy, we hypothesized that retained bile acids may have hepatoprotective effects in PiZZ transgenic mice, which model A1ATD. We performed BDL and partial BDL (pBDL) in PiZZ mice, followed by analysis of liver tissues. PiZZ liver subjected to BDL showed up to 50% clearance of ATZ globules, with increased expression of autophagy proteins. Analysis of transcription factors revealed significant changes. Surprisingly nuclear TFEB, a master regulator of autophagy, remained unchanged. pBDL confirmed that ATZ globule clearance was induced by localized stimuli rather than diet or systemic effects. Several genes involved in bile metabolism were overexpressed in globule-devoid hepatocytes, compared to globule-containing cells. Retained bile acids led to a dramatic reduction of ATZ globules, with enhanced hepatocyte regeneration and autophagy. These findings support investigation of synthetic bile acids as potential autophagy-enhancing agents.

Lithocholic acid induces endoplasmic reticulum stress, autophagy and mitochondrial dysfunction in human prostate cancer cells

Lithocholic acid (LCA) is a secondary bile acid that is selectively toxic to human neuroblastoma, breast and prostate cancer cells, whilst sparing normal cells. We previously reported that LCA inhibited cell viability and proliferation and induced apoptosis and necrosis of androgen-dependent LNCaP and androgen-independent PC-3 human prostate cancer cells. In the present study, we investigated the roles of endoplasmic reticulum (ER) stress, autophagy and mitochondrial dysfunction in the toxicity of LCA in PC-3 and autophagy deficient, androgen-independent DU-145 cells. LCA induced ER stress-related proteins, such as CCAAT-enhancer-binding protein homologous protein (CHOP), and the phosphorylation of eukaryotic initiation factor 2-alpha (p-eIF2α) and c-Jun N-terminal kinases (p-JNK) in both cancer cell-types. The p53 upregulated modulator of apoptosis (PUMA) and B cell lymphoma-like protein 11 (BIM) levels were decreased at overtly toxic LCA concentrations, although PUMA levels increased at lower LCA concentrations in both cell lines. LCA induced autophagy-related conversion of microtubule-associated proteins 1A/1B light chain 3B (LC3BI-LC3BII), and autophagy-related protein ATG5 in PC-3 cells, but not in autophagy-deficient DU-145 cells. LCA (>10 µM) increased levels of reactive oxygen species (ROS) concentration-dependently in PC-3 cells, whereas ROS levels were not affected in DU-145 cells. Salubrinal, an inhibitor of eIF2α dephosphorylation and ER stress, reduced LCA-induced CHOP levels slightly in PC-3, but not DU-145 cells. Salubrinal pre-treatment increased the cytotoxicity of LCA in PC-3 and DU-145 cells and resulted in a statistically significant loss of cell viability at normally non-toxic concentrations of LCA. The late-stage autophagy inhibitor bafilomycin A1 exacerbated LCA toxicity at subtoxic LCA concentrations in PC-3 cells. The antioxidant α-tocotrienol strongly inhibited the toxicity of LCA in PC-3 cells, but not in DU-145 cells. Collectively, although LCA induces autophagy and ER stress in PC-3 cells, these processes appear to be initially of protective nature and subsequently consequential to, but not critical for the ROS-mediated mitochondrial dysfunction and cytotoxicity of LCA. The full mechanism of LCA-induced mitochondrial dysfunction and cytotoxicity in the similarly sensitive DU-145 cells remains to be elucidated.