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 ... -  《-》

The transcription factor CHOP, a central component of the transcriptional regulatory network induced upon CCl4 intoxication in mouse liver, is not a critical mediator of hepatotoxicity.

Campos G ，Schmidt-Heck W ，Ghallab A ，Rochlitz K ，Pütter L ，Medinas DB ，Hetz C ，Widera A ，Cadenas C ，Begher-Tibbe B ，Reif R ，Günther G ，Sachinidis A ，Hengstler JG ，Godoy P ... -  《-》

Protection afforded by pre- or post-treatment with 4-phenylbutyrate against liver injury induced by acetaminophen overdose in mice.

Acetaminophen (paracetamol, N-acetyl-p-aminophenol; APAP) is a widely used analgesic/antipyretic drug with few adverse effects at therapeutic doses; suicidal or unintentional overdose of APAP frequently induces severe hepatotoxicity. To explore a new and effective antidote for APAP hepatotoxicity, this study examined the effects of sodium 4-phenylbutyrate (4-PBA) on liver injury induced by APAP overdose in mice. Liver injury was induced in C57BL/6 male mice by intraperitoneal injection of APAP (400mg/kg). The effects of 4-PBA (100-200mg/kg) treatment at 1h before the APAP injection were evaluated with serum alanine aminotransferase (ALT) and blood ammonia levels, hepatic pathological changes, including histopathology, DNA damage, nitrotyrosine formation, and mRNA or protein expression involved in the development of hepatotoxicity, such as X-box binding protein-1 (XBP1), c-Jun N-terminal kinase (JNK), C/EBP homologous protein (CHOP) and B-cell lymphoma 2 interacting mediator of cell death (Bim). In addition, glutathione depletion and CYP2E1 protein expression, which are measures of the metabolic conversion of APAP to a toxic metabolite, were examined. Furthermore, we examined the effects of post-treatment with 4-PBA against APAP-induced hepatotoxicity in mice. When administered at 1h before APAP injection, 4-PBA significantly prevented the increase in serum ALT and blood ammonia levels, centrilobular necrosis of hepatocytes, DNA fragmentation, and nitrotyrosine formation induced by APAP in mice. 4-PBA also inhibited hepatic Xbp1 mRNA splicing and JNK phosphorylation induced by APAP, but did not suppress CHOP and Bim mRNA and protein expression. In addition, 4-PBA had little effect on hepatic glutathione depletion and CYP2E1 expression, parameters of toxic APAP metabolite production. Post-treatment with 4-PBA administration at 1 or 2h after APAP injection also attenuated the increase in serum ALT and blood ammonia levels and hepatic pathological changes in APAP-induced hepatotoxicity in mice. Although post-treatment with 4-PBA did not show any effects on hepatic Xbp1 mRNA splicing and JNK phosphorylation, it drastically attenuated the DNA fragmentation induced by APAP. The precise molecular mechanisms of the protection afforded by 4-PBA against APAP hepatotoxicity in mice are unclear, but they seem to involve inhibition of hepatocellular DNA fragmentation. We suggest that 4-PBA is a promising candidate as an antidote against APAP-induced liver injury.

Shimizu D ，Ishitsuka Y ，Miyata K ，Tomishima Y ，Kondo Y ，Irikura M ，Iwawaki T ，Oike Y ，Irie T ... -  《-》

Metformin ameliorates acetaminophen hepatotoxicity via Gadd45β-dependent regulation of JNK signaling in mice.

Acetaminophen (APAP) overdose is a leading cause of drug-induced acute liver failure. Prolonged c-Jun N-terminal kinase (JNK) activation plays a central role in APAP-induced liver injury and growth arrest, and DNA damage-inducible 45 beta (Gadd45β) is known to inhibit JNK phosphorylation. Metformin has recently been shown to have hepatoprotective effects. The aim of the present study is to investigate whether metformin mitigates APAP-induced hepatotoxicity and to ascertain the molecular basis of this effect. We used APAP- and/or metformin-treated Gadd45β knockout (KO) mice and wild type (WT) C57BL/6J control mice. Primary mouse hepatocytes were isolated from WT and Gadd45β KO mice were used for in vitro study. Metformin pretreatment protected against APAP toxicity with decreased liver damage, and inhibited APAP-induced prolonged hepatic JNK phosphorylation in WT mice. Gadd45β expression was increased after APAP treatment, and the expression of Gadd45β was further enhanced by metformin. The effects of metformin on APAP-induced liver injury and JNK phosphorylation were abolished in Gadd45β KO mice. Notably, subtoxic doses of APAP caused cell death and sustained JNK phosphorylation in Gadd45β-deficient primary hepatocytes. In parallel, APAP increased mortality, severe liver injury, and JNK activation in Gadd45β KO mice. Interestingly, metformin administered after APAP treatment protected against APAP-evoked hepatotoxicity in WT mice, but not in Gadd45β KO mice. This study is the first to demonstrate that metformin shows protective and therapeutic effects against APAP overdose-evoked hepatotoxicity via Gadd45β-dependent JNK regulation. Metformin would be a promising therapeutic strategy for treatment of APAP overdose.

Kim YH ，Hwang JH ，Kim KS ，Noh JR ，Choi DH ，Kim DK ，Tadi S ，Yim YH ，Choi HS ，Lee CH ... -  《-》

FGF21 mediates the protective effect of fenofibrate against acetaminophen -induced hepatotoxicity via activating autophagy in mice.

Overdose of acetaminophen (APAP) induces acute liver injury due in part to destruction of mitochondria and resulted oxidative stress. Recently, FGF21 has been demonstrated to be an endocrine factor to protect liver from oxidative stress. The aim of present study is to explore the role of fibroblast growth factor 21 (FGF21) in the protective effect of fenofibrate, an agonist of peroxisome proliferator-activated receptor alpha (PPARα), against acetaminophen (APAP)-induced liver injury. Mice and primary cultured hepatocytes were used to test the potential hepatoprotective effect of fenofibrate against APAP-induced hepatotoxicity. FGF21 deficient mice were used to evaluate the role of FGF21 in fenofibrate against APAP-induced acute liver injury. Post-treatment with fenofibrate significantly inhibits APAP-induced hepatotoxicity, as evidenced by decreased serum ALT and AST levels and hepatic necrosis in liver tissue as well as increased the surviving rate in response to APAP overdose, whereas this protective effect of fenofibrate is largely attenuated in FGF21 KO mice. Interestingly, administration of fenofibrate efficiently increases autophagy, which was companied with alleviating hepatotoxicity in APAP-treated WT mice. However, such effect is significantly attenuated in APAP-treated FGF21 KO mice. In conclusion, our findings suggest that fenofibrate against APAP-induced hepatotoxicity is at least in part mediated by up-regulating the expression of FGF21, which in turn promotes autophagy-mediated hepatoprotective effects.

Zhang Y ，Pan Y ，Xiong R ，Zheng J ，Li Q ，Zhang S ，Li X ，Pan X ，Yang S ... -  《-》