Endoplasmic Reticulum Stress-Induced Upregulation of STARD1 Promotes Acetaminophen-Induced Acute Liver Failure.

Acetaminophen (APAP) overdose is a major cause of acute liver failure (ALF). Mitochondrial SH3BP5 (also called SAB) and phosphorylation of c-Jun N-terminal kinase (JNK) mediate the hepatotoxic effects of APAP. We investigated the involvement of steroidogenic acute regulatory protein (STARD1), a mitochondrial cholesterol transporter, in this process and sensitization by valproic acid (VPA), which depletes glutathione and stimulates steroidogenesis. Nonfasted C57BL/6J mice (control) and mice with liver-specific deletion of STARD1 (Stard1ΔHep), SAB (SabΔHep), or JNK1 and JNK2 (Jnk1+2ΔHep) were given VPA with or without APAP. Liver tissues were collected and analyzed by histology and immunohistochemistry and for APAP metabolism, endoplasmic reticulum (ER) stress, and mitochondrial function. Adult human hepatocytes were transplanted into Fah-/-/Rag2-/-/Il2rg-/-/NOD (FRGN) mice to create mice with humanized livers. Administration of VPA before administration of APAP increased the severity of liver damage in control mice. The combination of VPA and APAP increased expression of CYP2E1, formation of NAPQI-protein adducts, and depletion of glutathione from liver tissues of control mice, resulting in ER stress and the upregulation of STARD1. Livers from control mice given VPA and APAP accumulated cholesterol in the mitochondria and had sustained mitochondrial depletion of glutathione and mitochondrial dysfunction. Inhibition of ER stress, by administration of tauroursodeoxycholic acid to control mice, prevented upregulation of STARD1 in liver and protected the mice from hepatoxicity following administration of VPA and APAP. Administration of N-acetylcysteine to control mice prevented VPA- and APAP-induced ER stress and liver injury. Stard1ΔHep mice were resistant to induction of ALF by VPA and APAP, despite increased mitochondrial levels of glutathione and phosphorylated JNK; we made similar observations in fasted Stard1ΔHep mice given APAP alone. SabΔHep mice or Jnk1+2ΔHep mice did not develop ALF following administration of VPA and APAP. The ability of VPA to increase the severity of APAP-induced liver damage was observed in FRGN mice with humanized liver. In studies of mice, we found that upregulation of STARD1 following ER stress mediates APAP hepatoxicity via SH3BP5 and phosphorylation of JNK1 and JNK2.

Torres S ，Baulies A ，Insausti-Urkia N ，Alarcón-Vila C ，Fucho R ，Solsona-Vilarrasa E ，Núñez S ，Robles D ，Ribas V ，Wakefield L ，Grompe M ，Lucena MI ，Andrade RJ ，Win S ，Aung TA ，Kaplowitz N ，García-Ruiz C ，Fernández-Checa JC ... -  《-》

CHOP is a critical regulator of acetaminophen-induced hepatotoxicity.

The liver is a major site of drug metabolism and elimination and as such is susceptible to drug toxicity. Drug induced liver injury is a leading cause of acute liver injury, of which acetaminophen (APAP) is the most frequent causative agent. APAP toxicity is initiated by its toxic metabolite NAPQI. However, downstream mechanisms underlying APAP induced cell death are still unclear. Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have recently emerged as major regulators of metabolic homeostasis. UPR regulation of the transcription repressor CHOP promotes cell death. We analyzed the role of UPR and CHOP in mediating APAP hepatotoxicity. A toxic dose of APAP was orally administered to wild type (wt) and CHOP knockout (KO) mice and damage mechanisms were assessed. CHOP KO mice were protected from APAP induced damage and exhibited decreased liver necrosis and increased survival. APAP metabolism in CHOP KO mice was undisturbed and glutathione was depleted at similar kinetics to wt. ER stress and UPR activation were overtly seen 12h following APAP administration, a time that coincided with strong upregulation of CHOP. Remarkably, CHOP KO but not wt mice exhibited hepatocyte proliferation at sites of necrosis. In vitro, large T immortalized CHOP KO hepatocytes were protected from APAP toxicity in comparison to wt control cells. CHOP upregulation during APAP induced liver injury compromises hepatocyte survival in various mechanisms, in part by curtailing the regeneration phase following liver damage. Thus, CHOP plays a pro-damage role in response to APAP intoxication.

Uzi D ，Barda L ，Scaiewicz V ，Mills M ，Mueller T ，Gonzalez-Rodriguez A ，Valverde AM ，Iwawaki T ，Nahmias Y ，Xavier R ，Chung RT ，Tirosh B ，Shibolet O ... -  《-》

Combined Activities of JNK1 and JNK2 in Hepatocytes Protect Against Toxic Liver Injury.

c-Jun N-terminal kinase (JNK) 1 and JNK2 are expressed in hepatocytes and have overlapping and distinct functions. JNK proteins are activated via phosphorylation in response to acetaminophen- or carbon tetrachloride (CCl4)-induced liver damage; the level of activation correlates with the degree of injury. SP600125, a JNK inhibitor, has been reported to block acetaminophen-induced liver injury. We investigated the role of JNK in drug-induced liver injury (DILI) in liver tissue from patients and in mice with genetic deletion of JNK in hepatocytes. We studied liver sections from patients with DILI (due to acetaminophen, phenprocoumon, nonsteroidal anti-inflammatory drugs, or autoimmune hepatitis) or patients without acute liver failure (controls) collected from a DILI Biobank in Germany. Levels of total and activated (phosphorylated) JNK were measured by immunohistochemistry and Western blotting. Mice with hepatocyte-specific deletion of Jnk1 (Jnk1(Δhepa)) or combination of Jnk1 and Jnk2 (Jnk(Δhepa)), as well as Jnk1-floxed C57BL/6 (control) mice, were given injections of CCl4 (to induce fibrosis) or acetaminophen (to induce toxic liver injury). We performed gene expression microarray and phosphoproteomic analyses to determine mechanisms of JNK activity in hepatocytes. Liver samples from DILI patients contained more activated JNK, predominantly in nuclei of hepatocytes and in immune cells, than healthy tissue. Administration of acetaminophen to Jnk(Δhepa) mice produced a greater level of liver injury than that observed in Jnk1(Δhepa) or control mice, based on levels of serum markers and microscopic and histologic analysis of liver tissues. Administration of CCl4 also induced stronger hepatic injury in Jnk(Δhepa) mice, based on increased inflammation, cell proliferation, and fibrosis progression, compared with Jnk1(Δhepa) or control mice. Hepatocytes from Jnk(Δhepa) mice given acetaminophen had an increased oxidative stress response, leading to decreased activation of adenosine monophosphate-activated protein kinase, total protein adenosine monophosphate-activated protein kinase levels, and pJunD and subsequent necrosis. Administration of SP600125 before or with acetaminophen protected Jnk(Δhepa) and control mice from liver injury. In hepatocytes, JNK1 and JNK2 appear to have combined effects in protecting mice from CCl4- and acetaminophen-induced liver injury. It is important to study the tissue-specific functions of both proteins, rather than just JNK1, in the onset of toxic liver injury. JNK inhibition with SP600125 shows off-target effects.

Cubero FJ ，Zoubek ME ，Hu W ，Peng J ，Zhao G ，Nevzorova YA ，Al Masaoudi M ，Bechmann LP ，Boekschoten MV ，Muller M ，Preisinger C ，Gassler N ，Canbay AE ，Luedde T ，Davis RJ ，Liedtke C ，Trautwein C ... -  《-》

Sodium 4-phenylbutyric acid prevents murine acetaminophen hepatotoxicity by minimizing endoplasmic reticulum stress.

Kusama H ，Kon K ，Ikejima K ，Arai K ，Aoyama T ，Uchiyama A ，Yamashina S ，Watanabe S ... -  《-》

Editor's Highlight: Metformin Protects Against Acetaminophen Hepatotoxicity by Attenuation of Mitochondrial Oxidant Stress and Dysfunction.

Overdose of acetaminophen (APAP) causes severe liver injury and even acute liver failure in both mice and human. A recent study by Kim et al. (2015, Metformin ameliorates acetaminophen hepatotoxicity via Gadd45β-dependent regulation of JNK signaling in mice. J. Hepatol. 63, 75-82) showed that metformin, a first-line drug to treat type 2 diabetes mellitus, protected against APAP hepatotoxicity in mice. However, its exact protective mechanism has not been well clarified. To investigate this, C57BL/6J mice were treated with 400 mg/kg APAP and 350 mg/kg metformin was given 0.5 h pre- or 2 h post-APAP. Our data showed that pretreatment with metformin protected against APAP hepatotoxicity, as indicated by the over 80% reduction in plasma alanine aminotransferase (ALT) activities and significant decrease in centrilobular necrosis. Metabolic activation of APAP, as indicated by glutathione depletion and APAP-protein adducts formation, was also slightly inhibited. However, 2 h post-treatment with metformin still reduced liver injury by 50%, without inhibition of adduct formation. Interestingly, neither pre- nor post-treatment of metformin inhibited c-jun N-terminal kinase (JNK) activation or its mitochondrial translocation. In contrast, APAP-induced mitochondrial oxidant stress and dysfunction were greatly attenuated in these mice. In addition, mice with 2 h post-treatment with metformin also showed significant inhibition of complex I activity, which may contribute to the decreased mitochondrial oxidant stress. Furthermore, the protection was reproduced in JNK activation-absent HepaRG cells treated with 20 mM APAP followed by 0.5 or 1 mM metformin 6 h later, confirming JNK-independent protection mechanisms. Thus, metformin protects against APAP hepatotoxicity by attenuating the mitochondrial oxidant stress and subsequent mitochondrial dysfunction, and may be a potential therapeutic option for APAP overdose patients.

Du K ，Ramachandran A ，Weemhoff JL ，Chavan H ，Xie Y ，Krishnamurthy P ，Jaeschke H ... -  《-》