The mitochondrial negative regulator MCJ is a therapeutic target for acetaminophen-induced liver injury

Molecular pathogenesis of acetaminophen-induced liver injury and its treatment options

Acetaminophen, also known as N-acetyl-p-aminophenol (APAP), is commonly used as an antipyretic and analgesic agent. APAP overdose can induce hepatic toxicity, known as acetaminophen-induced liver injury (AILI). However, therapeutic doses of APAP can also induce AILI in patients with excessive alcohol intake or who are fasting. Hence, there is a need to understand the potential pathological mechanisms underlying AILI. In this review, we summarize three main mechanisms involved in the pathogenesis of AILI: hepatocyte necrosis, sterile inflammation, and hepatocyte regeneration. The relevant factors are elucidated and discussed. For instance, N-acetyl-p-benzoquinone imine (NAPQI) protein adducts trigger mitochondrial oxidative/nitrosative stress during hepatocyte necrosis, danger-associated molecular patterns (DAMPs) are released to elicit sterile inflammation, and certain growth factors contribute to liver regeneration. Finally, we describe the current potential treatment options for AILI patients and promising novel strategies available to researchers and pharmacists. This review provides a clearer understanding of AILI-related mechanisms to guide drug screening and selection for the clinical treatment of AILI patients in the future.

Mitochondrial bioenergetics boost macrophage activation, promoting liver regeneration in metabolically compromised animals

BACKGROUND AND AIMS

Hepatic ischemia-reperfusion injury (IRI) is the leading cause of early posttransplantation organ failure as mitochondrial respiration and ATP production are affected. A shortage of donors has extended liver donor criteria, including aged or steatotic livers, which are more susceptible to IRI. Given the lack of an effective treatment and the extensive transplantation waitlist, we aimed at characterizing the effects of an accelerated mitochondrial activity by silencing methylation-controlled J protein (MCJ) in three preclinical models of IRI and liver regeneration, focusing on metabolically compromised animal models.

APPROACH AND RESULTS

Wild-type (WT), MCJ knockout (KO), and Mcj silenced WT mice were subjected to 70% partial hepatectomy (Phx), prolonged IRI, and 70% Phx with IRI. Old and young mice with metabolic syndrome were also subjected to these procedures. Expression of MCJ, an endogenous negative regulator of mitochondrial respiration, increases in preclinical models of Phx with or without vascular occlusion and in donor livers. Mice lacking MCJ initiate liver regeneration 12 h faster than WT and show reduced ischemic injury and increased survival. MCJ knockdown enables a mitochondrial adaptation that restores the bioenergetic supply for enhanced regeneration and prevents cell death after IRI. Mechanistically, increased ATP secretion facilitates the early activation of Kupffer cells and production of TNF, IL-6, and heparin-binding EGF, accelerating the priming phase and the progression through G1 /S transition during liver regeneration. Therapeutic silencing of MCJ in 15-month-old mice and in mice fed a high-fat/high-fructose diet for 12 weeks improves mitochondrial respiration, reduces steatosis, and overcomes regenerative limitations.

CONCLUSIONS

Boosting mitochondrial activity by silencing MCJ could pave the way for a protective approach after major liver resection or IRI, especially in metabolically compromised, IRI-susceptible organs.

Calpain-mediated cleavage of mitochondrial fusion/fission proteins in acetaminophen-induced mice liver injury

Mitochondrial dysfunction was considered to be a critical event in acetaminophen (APAP) -induced hepatotoxicity. Recent studies suggest that abnormal mitochondrial dynamics contributes to mitochondrial dysfunction in APAP-induced liver injury, yet the underlying mechanisms responsible for deregulated mitochondrial dynamics remains elusive. In this study, C57BL/6 mice were used to establish a model of acute liver injury via intraperitoneal (i.p.) injection with overdose of APAP. Furthermore, calpain intervention experiments were achieved by the inhibitors ALLN or calpeptin. The activity of serum enzymes and pathological changes of APAP-treated mice were evaluated, and the critical molecules in mitochondrial dynamics and calpain degradative pathway were determined by electron microscopy, immunoblot and calpain activity kit. The results demonstrated that APAP overdose resulted in a severe liver injury, mitochondrial damage and an obvious cleavage of fusion/fission proteins. Meanwhile, the activation of calpain degradative machinery in liver were observed following APAP. By contrast, pretreatment of calpain inhibitors significantly inhibited the activation of calpains. Our further investigation found that ALLN or calpeptin administration significantly suppresses the changes of mitochondrial dynamics in APAP-treated mice and finally protected against APAP-induced hepatoxicity. Overall, these results suggest that calpain-mediated cleavage of mitochondrial dynamics proteins was involved in the pathogenic process of mitochondrial dysfunction and thus present a potential molecular coupling APAP-induced hepatotoxicity.

Nano-selenium alleviating the lipid metabolism disorder of LMH cells induced by potassium dichromate via down-regulating ACACA and FASN

Chromium (Cr) VI is a common environmental contaminant highly toxic to livers. To explore the protective effect of nano-selenium (NANO-Se) on broiler liver damage caused by Cr (VI), this experiment was conducted with chicken hepatocellular carcinoma cell line (LMH) as the research object, using potassium dichromate (PDC) and NANO-Se gel for culturing cells. The results indicated that: (1) in the PDC-exposure group, LMH cells being treated with 20 μmol/L PDC for 24 h, IC50 (median inhibition concentration) = 23.427 could significantly reduce cell activity (p < 0.01) which decreased over time. PDC markedly increased the concentration of triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C) in LMH cells (p < 0.01), which increased over time. In addition, PDC could substantially augment the transcription and protein levels of acetyl-CoA carboxylases alpha (ACACA) and fatty acid synthase (FASN) in LMH cells (p < 0.01). (2) Compared with the PDC-exposure group, the addition of 8 μmol/L NANO-Se after 12 h of PDC treatment could significantly increase the cell viability (p < 0.01) but decreased over time; the levels of TG and LDL-C in LMH cells declined markedly (p < 0.01). In addition, the transcription and protein levels of ACACA and FASN in LMH cells were significantly reduced (p < 0.01). (3) The LMH cells were cultured in advance with 8 μmol/L NANO-Se for 12 h and then with PDC for 24 h. The obtained results were similar to the above. There were no obvious differences in TG and LDL-C levels (p > 0.05). However, significant differences were found in the activity of LMH cells and the expression of genes related to lipid metabolism (p < 0.05).All these results suggest that the exposure to PDC promotes the increase of lipid synthesis in LMH cells and causes disorders in the lipid metabolism. Moreover, NANO-Se can partially attenuate the damage caused by PDC through down-regulating of the lipid metabolism-related genes (ACACA and FASN) in LMH cells.

Intracellular C3 prevents hepatic steatosis by promoting autophagy and very-low-density lipoprotein secretion

Complement component C3, mainly synthesized by hepatocytes, acts as the convergence point of three different pathways in activating the complement cascade. Besides its well-established roles in the extracellular milieu, C3 performs various intracellular functions such as immunomodulation and pathogen recognition. Although C3 is present at extremely high concentrations in hepatocytes, little is known about its intrahepatic function. In this study, we found that C3 knockout (C3^-/- ) mice displayed accelerated hepatic triglyceride (TG) accumulation compared with C57BL/6J wild type mice. Mechanistically, C3 deficiency impaired lipophagy in hepatocytes, owing to the disrupted interaction between C3 and autophagy-related 16 like 1, which is essential for autolysosome assembly. Furthermore, lipophagy deficiency affected the function of the endoplasmic reticulum in C3^-/- mice, subsequently affecting the expression of protein disulfide isomerase and activity of microsomal TG transfer protein, and ultimately impairing the production of hepatic very-low-density lipoproteins (VLDLs). Rapamycin and thapsigargin treatment accelerated VLDL secretion and alleviated hepatic lipid accumulation in C3^-/- mice. Our study demonstrates that C3 promotes lipophagy to facilitate VLDL secretion in hepatocytes, thus playing an essential role in balancing TG levels in the liver.

Neddylation inhibition ameliorates steatosis in NAFLD by boosting hepatic fatty acid oxidation via the DEPTOR-mTOR axis

OBJECTIVE

Neddylation is a druggable and reversible ubiquitin-like post-translational modification upregulated in many diseases, including liver fibrosis, hepatocellular carcinoma, and more recently, non-alcoholic fatty liver disease (NAFLD). Herein, we propose to address the effects of neddylation inhibition and the underlying mechanisms in pre-clinical models of NAFLD.

METHODS

Hepatic neddylation measured by immunohistochemical analysis and NEDD8 serum levels measured by ELISA assay were evaluated in NAFLD clinical and pre-clinical samples. The effects of neddylation inhibition by using a pharmacological small inhibitor, MLN4924, or molecular approaches were assessed in isolated mouse hepatocytes and pre-clinical mouse models of diet-induced NAFLD, male adult C57BL/6 mice, and the AlfpCre transgenic mice infected with AAV-DIO-shNedd8.

RESULTS

Neddylation inhibition reduced lipid accumulation in oleic acid-stimulated mouse primary hepatocytes and ameliorated liver steatosis, preventing lipid peroxidation and inflammation in the mouse models of diet-induced NAFLD. Under these conditions, increased Deptor levels and the concomitant repression of mTOR signaling were associated with augmented fatty acid oxidation and reduced lipid content. Moreover, Deptor silencing in isolated mouse hepatocytes abolished the anti-steatotic effects mediated by neddylation inhibition. Finally, serum NEDD8 levels correlated with hepatic neddylation during the disease progression in the clinical and pre-clinical models CONCLUSIONS: Overall, the upregulation of Deptor, driven by neddylation inhibition, is proposed as a novel effective target and therapeutic approach to tackle NAFLD.

Combined metabolic activators therapy ameliorates liver fat in nonalcoholic fatty liver disease patients

Nonalcoholic fatty liver disease (NAFLD) refers to excess fat accumulation in the liver. In animal experiments and human kinetic study, we found that administration of combined metabolic activators (CMAs) promotes the oxidation of fat, attenuates the resulting oxidative stress, activates mitochondria, and eventually removes excess fat from the liver. Here, we tested the safety and efficacy of CMA in NAFLD patients in a placebo-controlled 10-week study. We found that CMA significantly decreased hepatic steatosis and levels of aspartate aminotransferase, alanine aminotransferase, uric acid, and creatinine, whereas found no differences on these variables in the placebo group after adjustment for weight loss. By integrating clinical data with plasma metabolomics and inflammatory proteomics as well as oral and gut metagenomic data, we revealed the underlying molecular mechanisms associated with the reduced hepatic fat and inflammation in NAFLD patients and identified the key players involved in the host-microbiome interactions. In conclusion, we showed that CMA can be used to develop a pharmacological treatment strategy in NAFLD patients.

Microenvironment Activatable Nanoprodrug Based on Gripper-like Cyclic Phenylboronic Acid to Precisely and Effectively Alleviate Drug-induced Hepatitis

Drug-induced hepatitis (DIH), which seriously interferes with disease treatment, is one of the most common reasons for termination of new drugs during preclinical studies or post-marketing surveillance. Although antioxidants and anti-inflammatory agents are promising, their nonspecific distribution and insolubility limit their application. Therefore, precise drug release at the disease site is an important way to alleviate DIH and avoid side effects.

Methods: A gripper-like hydrophilic cyclic phenylboronic acid (cPBA) was synthesized and a nanoprodrug (cPBA-BE) was established by coupling cPBA with hydrophobic baicalein (BE). The stimuli-responsive release properties and therapeutic effect of cPBA-BE on drug-injured hepatocyte were investigated. The biodistribution and therapeutic effect of cPBA-BE both in acetaminophen-induced acute hepatitis model and rifampicin-induced chronic hepatitis model were further evaluated.

Results: cPBA-BE conjugate could self-assemble into nanoprodrug with cPBA as the hydrophilic external layer and BE as the hydrophobic core. In HepaRG cells, cPBA-BE showed stronger cellular uptake. Due to the H₂O₂- and acid-sensitivity, cPBA-BE could achieve adequate BE release, significantly resist the depletion of GSH, mitochondrial dysfunction, downregulation of inflammation and cell apoptosis in the acetaminophen injured HepaRG cells. Biodistribution showed that cPBA-BE specifically increased the concentration of BE in the liver of DIH mice. cPBA-BE could alleviate acetaminophen-induced acute hepatitis or rifampicin-induced chronic hepatitis more effectively through relieving the oxidative stress, inflammation and block the neutrophil infiltration in liver.

Conclusions: cPBA is expected to be a good platform for constructing injectable nanoprodrug with both H₂O₂ and pH-responsive properties by coupling a wide range of drugs containing o-diol. In this study, the nanoprodrug cPBA-BE was determined to be effective for alleviating the DIH.

Selenium Status in Diet Affects Acetaminophen-Induced Hepatotoxicity via Interruption of Redox Environment

Aims: Drug-induced liver injury, especially acetaminophen (APAP)-induced liver injury, is a leading cause of liver failure worldwide. Mouse models were used to evaluate the effect of microelement selenium levels on the cellular redox environment and consequent hepatotoxicity of APAP. Results: APAP treatment affected mouse liver selenoprotein thioredoxin reductase (TrxR) activity and glutathione (GSH) level in a dose- and time-dependent manner. Decrease of mouse liver TrxR activity and glutathione level was an early event, and occurred concurrently with liver damage. The decreases in the GSH/glutathione disulfide form (GSSG) ratio and TrxR activity, and the increase of protein S-glutathionylation were correlated with the APAP-induced hepatotoxicity. Moreover, in APAP-treated mice both mild deprivation and excess supplementation with selenium increased the severity of liver injury compared with those observed in mice with normal dietary selenium levels. An increase in the oxidation state of the TrxR-mediated system, including cytosolic thioredoxin1 (Trx1) and peroxiredoxin1/2 (Prx1/2), and mitochondrial Trx2 and Prx3, was found in the livers from mice reared on selenium-deficient and excess selenium-supplemented diets upon APAP treatment. Innovation: This work demonstrates that both Trx and GSH systems are susceptible to APAP toxicity in vivo, and that the thiol-dependent redox environment is a key factor in determining the extent of APAP-induced hepatotoxicity. Dietary selenium and selenoproteins play critical roles in protecting mice against APAP overdose. Conclusion: APAP treatment in mice interrupts the function of the Trx and GSH systems, which are the main enzymatic antioxidant systems, in both the cytosol and mitochondria. Dietary selenium deficiency and excess supplementation both increase the risk of APAP-induced hepatotoxicity.

Boosting mitochondria activity by silencing MCJ overcomes cholestasis-induced liver injury

BACKGROUND & AIMS

Mitochondria are the major organelles for the formation of reactive oxygen species (ROS) in the cell, and mitochondrial dysfunction has been described as a key factor in the pathogenesis of cholestatic liver disease. The methylation-controlled J-protein (MCJ) is a mitochondrial protein that interacts with and represses the function of complex I of the electron transport chain. The relevance of MCJ in the pathology of cholestasis has not yet been explored.

METHODS

We studied the relationship between MCJ and cholestasis-induced liver injury in liver biopsies from patients with chronic cholestatic liver diseases, and in livers and primary hepatocytes obtained from WT and MCJ-KO mice. Bile duct ligation (BDL) was used as an animal model of cholestasis, and primary hepatocytes were treated with toxic doses of bile acids. We evaluated the effect of MCJ silencing for the treatment of cholestasis-induced liver injury.

RESULTS

Elevated levels of MCJ were detected in the liver tissue of patients with chronic cholestatic liver disease when compared with normal liver tissue. Likewise, in mouse models, the hepatic levels of MCJ were increased. After BDL, MCJ-KO animals showed significantly decreased inflammation and apoptosis. In an in vitro model of bile-acid induced toxicity, we observed that the loss of MCJ protected mouse primary hepatocytes from bile acid-induced mitochondrial ROS overproduction and ATP depletion, enabling higher cell viability. Finally, the in vivo inhibition of the MCJ expression, following BDL, showed reduced liver injury and a mitigation of the main cholestatic characteristics.

CONCLUSIONS

We demonstrated that MCJ is involved in the progression of cholestatic liver injury, and our results identified MCJ as a potential therapeutic target to mitigate the liver injury caused by cholestasis.

LAY SUMMARY

In this study, we examine the effect of mitochondrial respiratory chain inhibition by MCJ on bile acid-induced liver toxicity. The loss of MCJ protects hepatocytes against apoptosis, mitochondrial ROS overproduction, and ATP depletion as a result of bile acid toxicity. Our results identify MCJ as a potential therapeutic target to mitigate liver injury in cholestatic liver diseases.

Mitochondrial ATP fuels ABC transporter-mediated drug efflux in cancer chemoresistance

Chemotherapy remains the standard of care for most cancers worldwide, however development of chemoresistance due to the presence of the drug-effluxing ATP binding cassette (ABC) transporters remains a significant problem. The development of safe and effective means to overcome chemoresistance is critical for achieving durable remissions in many cancer patients. We have investigated the energetic demands of ABC transporters in the context of the metabolic adaptations of chemoresistant cancer cells. Here we show that ABC transporters use mitochondrial-derived ATP as a source of energy to efflux drugs out of cancer cells. We further demonstrate that the loss of methylation-controlled J protein (MCJ) (also named DnaJC15), an endogenous negative regulator of mitochondrial respiration, in chemoresistant cancer cells boosts their ability to produce ATP from mitochondria and fuel ABC transporters. We have developed MCJ mimetics that can attenuate mitochondrial respiration and safely overcome chemoresistance in vitro and in vivo. Administration of MCJ mimetics in combination with standard chemotherapeutic drugs could therefore become an alternative strategy for treatment of multiple cancers.

Quercitrin Attenuates Acetaminophen-Induced Acute Liver Injury by Maintaining Mitochondrial Complex I Activity

The flavonoid quercitrin has a strong antioxidant property. It is also reported to have a protective effect on the liver. However, the mechanism by which it exerts a protective effect on the liver is not fully understood. The objective of this article is to confirm the protective effect of quercitrin extracted from Albiziae flos on acetaminophen (APAP)-induced liver injury and to explain its mechanism. In the in vivo study, quercitrin was administered orally to BALB/c mice at a dose of 50, 100, and 200 mg/kg for seven consecutive days. APAP (300 mg/kg) was injected intraperitoneally after a last dose of quercitrin was administered. Determination of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-Px), catalase (CAT), and malondialdehyde (MDA) levels showed that quercitrin effectively attenuated APAP-induced acute liver injury in mice. Results of the in vitro study showed that quercitrin reduced the levels of ROS, protected mitochondria from damage, and restored the activity of mitochondrial complex I in APAP-treated L-02 cells. The addition of rotenone which is an inhibitor of complex I blocked the protective effect of quercitrin. The expression of mitochondrial complex I was also maintained by quercitrin. Our results suggest that quercitrin can maintain the level of mitochondrial complex I in injured cells and restore its activity, which reduces the production of ROS, protects the mitochondria from oxidative stress, and has a protective effect on the liver.

The complex roles of neutrophils in APAP-induced liver injury

Acetaminophen (APAP) is a widely applied drug for the alleviation of pain and fever, which is also a dose‐depedent toxin. APAP‐induced acute liver injury has become one of the primary causes of liver failure which is an increasingly serious threat to human health. Neutrophils are the major immune cells in human serving as the first barrier against the invasion of pathogen. It has been reported that neutrophils patriciate in the occurrence and development of APAP‐induced liver injury. However, evolving evidences suggest that neutrophils also contribute to tissue repair and actively orchestrate resolution of inflammation. Here, we addressed the complex roles in APAP‐induced liver injury on the basis of brief introduction of neutrophil's activation, recruitment and migration.

Nano-designed carbon monoxide donor SMA/CORM2 exhibits protective effect against acetaminophen induced liver injury through macrophage reprograming and promoting liver regeneration

Acetaminophen (APAP) induced liver injury is the most common drug-induced liver injury, accounting for the top cause of acute liver failure in the United State, however the therapeutic options for it is very limited. Excess generation of reactive oxygen species (ROS) and the subsequent inflammatory responses are the major factors of the liver injury. Carbon monoxide (CO) is an important gaseous molecule with versatile functions including anti-oxidation and anti-inflammation, and we previous reported the therapeutic potential of a nano-designed CO donor SMA/CORM2 in a dextran sulphate sodium (DSS) induced mouse colitis model. In this context, we investigated the effect of SMA/CORM2 in an APAP-induced mouse acute liver injury model and tackled the mechanisms involved. We found upregulation of heme oxygenase-1 (HO-1, endogenous CO generating enzyme) and the dynamic changes of macrophage polarization (pro-inflammatory M1/anti-inflammatory M2), which played important roles in the process of live injury. SMA/CORM2 treatment remarkably increased the CO levels in the liver and circulation, by which oxidative stresses in the liver were significantly reduced, and more importantly, it remarkably suppressed the expression of M1 macrophages but alternatively increased M2 polarization. Consequently the liver injury was significantly ameliorated, and the proliferation and regeneration were greatly promoted through the Pi3k/Akt/mTOR signaling pathway. The shift of macrophage polarization accompanied with the downregulated hypoxia-inducible factor-1α (HIF-1α) level. These findings suggested CO released from SMA/CORM2 manipulated the macrophage reprogramming toward M2 phenotype by inhibiting HIF-1α, which subsequently protected liver against inflammatory injury and benefited tissue repair. Moreover, compared to native CORM2, SMA/CORM2 exhibited superior bioavailability and protective effect. We thus anticipate the application of SMA/CORM2 as a therapeutic regimen for APAP induced liver injury as well as other inflammatory diseases and disorders.

Toxicological Property of Acetaminophen: The Dark Side of a Safe Antipyretic/Analgesic Drug?

Acetaminophen (paracetamol, N-acetyl-p-aminophenol; APAP) is the most popular analgesic/antipyretic agent in the world. APAP has been regarded as a safer drug compared with non-steroidal anti-inflammatory drugs (NSAIDs) particularly in terms of lower risks of renal dysfunction, gastrointestinal injury, and asthma/bronchospasm induction, even in high-risk patients such as the elderly, children, and pregnant women. On the other hand, the recent increasing use of APAP has raised concerns about its toxicity. In this article, we review recent pharmacological and toxicological findings about APAP from basic, clinical, and epidemiological studies, including spontaneous drug adverse events reporting system, especially focusing on drug-induced asthma and pre-and post-natal closure of ductus arteriosus. Hepatotoxicity is the greatest fault of APAP and the most frequent cause of drug-induced acute liver failure in Western countries. However, its precise mechanism remains unclear and no effective cure beyond N-acetylcysteine has been developed. Recent animal and cellular studies have demonstrated that some cellular events, such as c-jun N-terminal kinase (JNK) pathway activation, endoplasmic reticulum (ER) stress, and mitochondrial oxidative stress may play important roles in the development of hepatitis. Herein, the molecular mechanisms of APAP hepatotoxicity are summarized. We also discuss the not-so-familiar "dark side" of APAP as an otherwise safe analgesic/antipyretic drug.

circ-CBFB upregulates p66Shc to perturb mitochondrial dynamics in APAP-induced liver injury

p66Shc, a master regulator of mitochondrial reactive oxygen species (mtROS), is a crucial mediator of hepatocyte oxidative stress. However, its functional contribution to acetaminophen (APAP)-induced liver injury and the mechanism by which it is modulated remain unknown. Here, we aimed to assess the effect of p66Shc on APAP-induced liver injury and to evaluate if circular RNA (circRNA) functions as a competitive endogenous RNA (ceRNA) to mediate p66Shc in APAP-induced liver injury. p66Shc-, miR-185-5p-, and circ-CBFB-silenced mice were injected with APAP. AML12 cells were transfected with p66Shc, miR-185-5p, and circ-CBFB silencing or overexpression plasmids or siRNAs prior to APAP stimulation. p66Shc was upregulated in liver tissues in response to APAP, and p66Shc silencing in vivo protected mice from APAP-induced mitochondrial dynamics perturbation and liver injury. p66Shc knockdown in vitro attenuated mitochondrial dynamics and APAP-induced hepatocyte injury. Mechanically, p66Shc perturbs mitochondrial dynamics partially by inhibiting OMA1 ubiquitination. miR-185-5p, which directly suppressed p66Shc translation, was identified by microarray and bioinformatics analyses, and its overexpression attenuated mitochondrial dynamics and hepatocyte injury in vitro. Furthermore, luciferase, pull-down and RNA immunoprecipitation assays demonstrated that circ-CBFB acts as a miRNA sponge of miR-185-5p to mediate p66Shc in APAP-induced liver injury. circ-CBFB knockdown also alleviated APAP-induced mitochondrial dynamics perturbation and hepatocyte injury. More importantly, we found that the protective effects of circ-CBFB knockdown on p66Shc, mitochondrial dynamics and liver injury were abolished by miR-185-5p inhibition both in vivo and in vitro. In conclusion, p66Shc is a key regulator of APAP-induced liver injury that acts by triggering mitochondrial dynamics perturbation. circ-CBFB functions as a ceRNA to regulate p66Shc during APAP-induced liver injury, which may provide a potential therapeutic target.

Preexisting diabetes mellitus had no effect on the no-observed-adverse-effect-level of acetaminophen in rats

Information on the safety of chemical substances in patients with various preexisting conditions remains limited. Acetaminophen was added to the basal diet at 0, 80, 253, 800, 2530, or 8000 ppm and administered to type 2 diabetes mellitus rats (GK/Jcl) and the control male rats (Wistar) for 13 weeks. Both strains treated with 8000 ppm acetaminophen (561.4 and 567.7 mg/kg body weight/day, GK/Jcl and Wistar rats, respectively) showed decreased levels of red blood cell counts, blood urea nitrogen, creatinine, and total bilirubin compared to those of non-treated rats. Treatment with 8000 ppm of acetaminophen reduced the blood glucose and hemoglobin A1c levels of GK/Jcl rats. An increase in the relative weights of the kidneys and liver, and a decrease in the weight of the salivary glands were observed in both GK/Jcl and Wistar rats treated with 8000 ppm acetaminophen relative to those of non-treated control rats. Microscopically, both strains treated with 2530 (174.3 and 164.2 mg/kg body weight/day, GK/Jcl and Wistar rats, respectively) or 8000 ppm acetaminophen showed hepatocellular hypertrophy and degenerative lesions in the salivary glands, whereas similar lesions were not observed in non-treated rats. In conclusion, the no-observed-adverse-effect-level of acetaminophen was 800 ppm in both diabetic and control rats.

Acetaminophen-induced apoptosis: Facts versus fiction

An overdose of the widely used analgesic acetaminophen (APAP) is the most common cause of acute liver failure in the western world and hence is a clinically significant problem. Thus, mechanisms of APAP-induced hepatotoxicity have been the focus of extensive investigation for decades and it was established that APAP induces hepatocyte cell death by necrosis. Although APAP-induced necrosis shares some features of apoptosis induced by the intrinsic pathway, apoptotic cell death in this context was ruled out due to the absence of caspase activation and lack of protection by caspase inhibitors and missing morphological characteristics of apoptotic cells. Deeper mechanistic understanding of the cell death process after APAP in recent years has now revealed that cells die by programmed necrosis and apoptosis is not a relevant mode of cell death in this context. Hence, it is alarming to note that an increasing number of studies are being published purporting to indicate that APAP induces apoptotic cell death. These papers broadly measure "apoptotic markers" with questionable specificity such as Bax, Bcl-2 and caspase-3 protein expression, or use the terminal deoxynucleotidyl transferase dUTP nick end labeling assay as basis for the conclusion that there is apoptosis after APAP overdose. The misguided use of these apoptosis parameters in correlative studies without context or scientific rationale confuses the field and threatens to undo decades of careful mechanistic investigation into this topic. This review examines this emerging problem in detail and recommends approaches to correct it.

RELEVANCE FOR PATIENTS

Hepatotoxicity and acute liver failure caused by an acetaminophen overdose is a serious clinical problem in western countries. Understanding the mode of cell death and the signaling pathways involved is critical for developing new therapeutic approaches. Recent trends to claim that apoptosis is a relevant mode of cell death in acetaminophen hepatotoxicity are not justified by sound scientific data and will not lead to effective new drug development.

Silencing hepatic MCJ attenuates non-alcoholic fatty liver disease (NAFLD) by increasing mitochondrial fatty acid oxidation

Nonalcoholic fatty liver disease (NAFLD) is considered the next major health epidemic with an estimated 25% worldwide prevalence. No drugs have yet been approved and NAFLD remains a major unmet need. Here, we identify MCJ (Methylation-Controlled J protein) as a target for non-alcoholic steatohepatitis (NASH), an advanced phase of NAFLD. MCJ is an endogenous negative regulator of the respiratory chain Complex I that acts to restrain mitochondrial respiration. We show that therapeutic targeting of MCJ in the liver with nanoparticle- and GalNAc-formulated siRNA efficiently reduces liver lipid accumulation and fibrosis in multiple NASH mouse models. Decreasing MCJ expression enhances the capacity of hepatocytes to mediate β-oxidation of fatty acids and minimizes lipid accumulation, which results in reduced hepatocyte damage and fibrosis. Moreover, MCJ levels in the liver of NAFLD patients are elevated relative to healthy subjects. Thus, inhibition of MCJ emerges as an alternative approach to treat NAFLD.

Non-alcoholic fatty liver (NAFLD) disease causes degeneration of the liver, affects about 25% of people globally, and has no approved treatment. Here, the authors show that the therapeutic siRNA-driven silencing of MCJ in the liver is an effective and safe treatment for NAFLD in multiple mouse models.

DLL4 restores damaged liver by enhancing hBMSC differentiation into cholangiocytes

BACKGROUND & AIMS

Biliary injury is one of the main pathological mechanisms of fulminant hepatic failure (FHF). Delta-like ligand 4 (DLL4)-mediated Notch activation contributes to reversing biliary injury; however, the specific role of DLL4 in biliary restoration is still unclear. This study aimed to determine whether human bone marrow mesenchymal stem cells (hBMSCs) can differentiate into biliary epithelial cells (cholangiocytes) in vitro and in vivo and to clarify the role of DLL4 in restoring damaged liver by enhancing cholangiocyte differentiation.

METHODS

hBMSCs were transplanted into immunodeficient mice (FRGS) with FHF induced by the hamster-anti-mouse CD95 antibody JO2. The appearance of human cholangiocytes was evaluated in the generated hBMSC-FRGS mice by q-PCR expression, flow cytometry and immunohistochemistry. The potency of DLL4 in inducing cholangiocyte differentiation from hBMSCs was assessed by observing the cell morphology and measuring the expression of cholangiocyte-specific genes and proteins.

RESULTS

Human KRT19- and KRT7-double-positive cholangiocyte-like cells appeared in hBMSC-FRGS mice at 12 weeks after transplantation. After these cells were separated and collected by fluorescent-activated cell sorting (FACS), there were high levels of expression of eight typical human cholangiocyte-specific genes and proteins (e.g., KRT19 and KRT7). Furthermore, hBMSC-derived cholangiocytes induced by DLL4 had a better shape with higher nucleus/cytoplasm ratios and showed a specific increase in the expression of cholangiocyte-specific genes and proteins (e.g., KRT19, KRT7, SOX9 and CFTR).

CONCLUSIONS

Cholangiocytes can be efficiently differentiated from hBMSCs in vivo and in vitro. DLL4 restores damaged liver by enhancing cholangiocyte differentiation from hBMSCs and has the potential to be used in future clinical therapeutic applications.

Autophagy: a promising process for the treatment of acetaminophen-induced liver injury

Toxicity from drugs has become an important cause of acute liver failure. Acetaminophen, a commonly used analgesic, can cause severe acute liver injury that can worsen into acute liver failure. Autophagy, a protective cell programme, has been reported to have protective effects in a variety of diseases such as cancer, immune diseases, neurodegenerative diseases, and inflammatory diseases. In this review, we describe how an excess of acetaminophen causes liver injury step by step, from the formation of the initial protein adduct to the final hepatocyte necrosis, as well as the induction of autophagy and its beneficial effects on diseases. Emphasis is placed on the potential effect of autophagy on improving the damage of acetaminophen to hepatocytes. Finally, we are committed to providing insights into the treatment of acute liver failure through the mechanism of acetaminophen induced liver injury, the mechanism of autophagy, and the link between autophagy and liver injury.

Inflammatory injury and mitophagy induced by Cr(VI) in chicken liver

Cr(VI) is a widely used chemical. Excessive Cr(VI) exposure not only causes inflammatory damage but also induces mitophagy. This study aimed to demonstrate the effect of Cr(VI) on inflammatory injury and mitophagy in chicken liver. A total of 120 Hyland Brown cockerels (1 day old) were randomly divided into four groups and orally treated with different Cr(VI) doses (10% median lethal dose, 6% median lethal dose, 2% median lethal dose, and 0% median lethal dose) daily for 45 days to explore the underlying mechanism. Results showed that excessive Cr(VI) increased tumor necrosis factor-α, interleukin-6, and heat shock protein but decreased interferon-γ expression and adenosine triphosphate content in chicken liver. Cr(VI) significantly increased reactive oxygen species production, induced mitochondrial membrane potential collapse, and promoted autophagosome formation. Cr(VI) treatment also caused an increase in LC3-II, stimulated Parkin translocation, and inhibited the expression of p62/SQSTM1 and translocase of outer mitochondrial membrane 20. Therefore, excessive Cr(VI) caused inflammatory damage and mitophagy in chicken liver.

A mitochondrial journey through acetaminophen hepatotoxicity

Acetaminophen (APAP) overdose is the leading cause of acute liver failure in the United States and APAP-induced hepatotoxicity is initiated by formation of a reactive metabolite which depletes hepatic glutathione and forms protein adducts. Studies over the years have established the critical role of c-Jun N terminal kinase (JNK) and its mitochondrial translocation, as well as mitochondrial oxidant stress and subsequent induction of the mitochondrial permeability transition in APAP pathophysiology. However, it is now evident that mitochondrial responses to APAP overdose are more nuanced than appreciated earlier, with multiple levels of control, for example, to dose of APAP. In addition, mitochondrial dynamics, as well as the organelle's importance in recovery and regeneration after APAP-induced liver injury is also being recognized, which are exciting new areas with significant therapeutic potential. Thus, this review examines the temporal course of hepatocyte mitochondrial responses to an APAP overdose with an emphasis on mechanistic response to various trigger checkpoints such as NAPQI-mitochondrial protein adduct formation and activated JNK translocation. Mitochondrial dynamics, the organelle's role in recovery after APAP and emerging areas of research which promise to provide further insight into modulation of APAP pathophysiology by these fascinating organelles will also be discussed.

Imaging-based vascular-related biomarkers for early detection of acetaminophen-induced liver injury

Acetaminophen (APAP) is the foremost cause of drug-induced liver injury in the Western world. Most studies of APAP hepatotoxicity have focused on the hepatocellular injury, but current hepatocyte-related biomarkers have delayed presentation time and a lack of sensitivity. APAP overdose can induce hepatic microvascular congestion, which importantly precedes the injury of hepatocytes. However, the underlying molecular mechanisms remain unclear. It is imperative to discover and validate sensitive and specific translational biomarkers of APAP-induced liver injury. Methods: In this study, we assessed APAP toxicity in sinusoidal endothelial cells and hepatocytes in mice treated with overdose APAP at different time points. The underlying mechanisms of APAP overdose induced sinusoidal endothelial cell injury were investigated by RT2 Profiler PCR arrays. The impact of APAP overdose on endothelial cell function was assessed by pseudovessel formation of endothelial cells in 2D Matrigel and in vivo hepatic vascular integrity using multiphoton microscopy. Finally, the effects of APAP overdose on oxygen levels in the liver and hepatic microcirculation were evaluated by contrast enhanced ultrasonography. Potential imaging-based vascular-related markers for early detection of APAP induced liver injury were assessed. Results: Our study confirmed that hepatic endothelial cells are an early and direct target for APAP hepatotoxicity. ICAM1-related cellular adhesion pathways played a prominent role in APAP-induced endothelial cell injury, which was further validated in primary human sinusoidal endothelial cells and human livers after APAP overdose. APAP overdose impacted pseudovessel formation of endothelial cells and in vivo hepatic vascular integrity. Use of ultrasound to detect APAP-induced liver injury demonstrated that mean transit time, an imaging-based vascular-related biomarker, was more sensitive and precise for early detection of APAP hepatotoxicity and monitoring the treatment response in comparison with a conventional blood-based biomarker. Conclusion: Imaging-based vascular-related biomarkers can identify early and mild liver injury induced by APAP overdose. With further development, such biomarkers may improve the assessment of liver injury and the efficacy of clinical decision-making, which can be extended to other microvascular dysfunction of deep organs.

THE ROLE OF OXIDANT STRESS IN ACETAMINOPHE-INDUCED LIVER INJURY

Acetaminophen is a widely used analgesic and antipyretic, which can cause liver injury after an overdose. Although a controversial topic for some time, solid evidence for a critical role of oxidative and nitrosative stress has emerged during the last two decades. This review will discuss the cellular sources, amplification mechanisms and the consequences of the excessive formation of reactive oxygen and nitrogen species in the clinically relevant mouse model of acetaminophen hepatotoxicity. This new mechanistic insight contributes to the better understanding of the mechanism of action of N-acetylcysteine, the only clinically approved antidote. In addition, it provides the rationale for the development of new antidotes that target the formation or metabolism of mitochondrial superoxide.

Ccrn4l as a pre-dose marker for prediction of cisplatin-induced hepatotoxicity susceptibility

Clinical cisplatin use is often limited by its drug-induced liver injury (DILI). Particularly, individual differences in susceptibility to DILI can cause life-threatening medical conditions. This study aimed to uncover the inherent genetic factors determining individual variations in hepatotoxicity susceptibility. Rats were subjected to liver biopsy and a 3-week postoperative recovery period before cisplatin administration. At 2 days post-treatment with cisplatin, the rats exhibited histopathological and serum biochemical alterations in the liver, and changes in hydrogen peroxide and cytochrome P450-2E1 levels. Based on these results of liver-related biochemical markers, 32 rats were grouped into the susceptible (top five) and resistant (bottom five) groups. Using RNA-sequencing, we compared gene expressions in the liver pre-biopsied from these two groups before cisplatin treatment and found 161 differently expressed genes between the Susceptible and Resistant groups. Among them, the clock-controlled Ccrn4l responsible for 'rhythmic process' was identified as a common gene downregulated inherently prior to drug exposure in both cisplatin- and acetaminophen-sensitive animals. Additionally, low Ccrn4l levels before cisplatin treatment in the Susceptible group were maintained even after treatment, with decreased antioxidants, increased nitration, and apoptosis. The relationship of Ccrn4l with catalase and mitochondrial RNAs in the liver was confirmed by correlation of their hepatic levels among individuals and similar patterns of circadian variation in their mRNA expression. Remarkably, Ccrn4l knockdown promoted cisplatin-induced mitochondrial dysfunction in WB-F344 cells with antioxidant catalase and apoptosis-related Bax changes. Inherent individual hepatic Ccrn4l level might be a novel factor affecting cisplatin-induced hepatotoxicity susceptibility, possibly through regulation of mitochondrial and antioxidant functions.

Sonoporation as an Approach for siRNA delivery into T cells

Delivery of small interfering RNAs (siRNAs) into primary T cells is quite challenging because they are non-proliferating cells and are difficult to transfect with non-viral approaches. Because sonoporation is independent of the proliferation status of cells and siRNA acts in the cell cytoplasm, we investigated whether sonoporation could be used to deliver siRNA into mouse and human T cells. Cells mixed with Definity microbubbles and siRNA were sonicated with a non-focused transducer of center frequency 2.20 MHz producing ultrasound at a 10% duty cycle, pulse repetition frequency of 2.20 kHz and spatial average temporal average ultrasound intensity of 1.29 W/cm² for 5 s and then examined for siRNA fluorescence by flow cytometry analysis. These sonoporation conditions resulted in high-efficiency transfection of siRNA in mouse and human T cells. Further, the efficacy of siRNA delivery by sonoporation was illustrated by the successful visualization of decreased methylation-controlled J protein expression in mouse and human CD8 T cells via Western blot analysis. The results provide the first evidence that sonoporation is a novel approach to delivery of siRNA into fresh isolated mouse and human T cells in vitro, and might be used for in vivo studies in the future.

miR-873-5p targets mitochondrial GNMT-Complex II interface contributing to non-alcoholic fatty liver disease

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) is a complex pathology in which several dysfunctions, including alterations in metabolic pathways, mitochondrial functionality and unbalanced lipid import/export, lead to lipid accumulation and progression to inflammation and fibrosis. The enzyme glycine N-methyltransferase (GNMT), the most important enzyme implicated in S-adenosylmethionine catabolism in the liver, is downregulated during NAFLD progression. We have studied the mechanism involved in GNMT downregulation by its repressor microRNA miR-873-5p and the metabolic pathways affected in NAFLD as well as the benefit of recovery GNMT expression.

METHODS

miR-873-5p and GNMT expression were evaluated in liver biopsies of NAFLD/NASH patients. Different in vitro and in vivo NAFLD murine models were used to assess miR-873-5p/GNMT involvement in fatty liver progression through targeting of the miR-873-5p as NAFLD therapy.

RESULTS

We describe a new function of GNMT as an essential regulator of Complex II activity in the electron transport chain in the mitochondria. In NAFLD, GNMT expression is controlled by miR-873-5p in the hepatocytes, leading to disruptions in mitochondrial functionality in a preclinical murine non-alcoholic steatohepatitis (NASH) model. Upregulation of miR-873-5p is shown in the liver of NAFLD/NASH patients, correlating with hepatic GNMT depletion. Importantly, NASH therapies based on anti-miR-873-5p resolve lipid accumulation, inflammation and fibrosis by enhancing fatty acid β-oxidation in the mitochondria. Therefore, miR-873-5p inhibitor emerges as a potential tool for NASH treatment.

CONCLUSION

GNMT participates in the regulation of metabolic pathways and mitochondrial functionality through the regulation of Complex II activity in the electron transport chain. In NAFLD, GNMT is repressed by miR-873-5p and its targeting arises as a valuable therapeutic option for treatment.

Alteration of mitochondrial DNA homeostasis in drug-induced liver injury

Mitochondrial DNA (mtDNA) encodes for 13 proteins involved in the oxidative phosphorylation (OXPHOS) process. In liver, genetic or acquired impairment of mtDNA homeostasis can reduce ATP output but also decrease fatty acid oxidation, thus leading to different hepatic lesions including massive necrosis and microvesicular steatosis. Hence, a severe impairment of mtDNA homeostasis can lead to liver failure and death. An increasing number of investigations report that some drugs can induce mitochondrial dysfunction and drug-induced liver injury (DILI) by altering mtDNA homeostasis. Some drugs such as ciprofloxacin, antiretroviral nucleoside reverse-transcriptase inhibitors and tacrine can inhibit hepatic mtDNA replication, thus inducing mtDNA depletion. Drug-induced reduced mtDNA levels can also be the consequence of reactive oxygen species-mediated oxidative damage to mtDNA, which triggers its degradation by mitochondrial nucleases. Such mechanism is suspected for acetaminophen and troglitazone. Other pharmaceuticals such as linezolid and tetracyclines can impair mtDNA translation, thus selectively reducing the synthesis of the 13 mtDNA-encoded proteins. Lastly, some drugs might alter the mtDNA methylation status but the pathophysiological consequences of such alteration are still unclear. Drug-induced impairment of mtDNA homeostasis is probably under-recognized since preclinical and post-marketing safety studies do not classically investigate mtDNA levels, mitochondrial protein synthesis and mtDNA oxidative damage.

CCL5 deficiency promotes liver repair by improving inflammation resolution and liver regeneration through M2 macrophage polarization

Despite the diverse etiologies of drug-induced liver injury (DILI), innate immunity activation is a common feature involved in DILI progression. However, the involvement of innate immunity regulation in inflammation resolution and liver regeneration in DILI remains obscure. Herein, we identified the chemokine CCL5 as a central mediator of innate immunity regulation in the pathogenesis of DILI. First, we showed that serum and hepatic CCL5 levels are elevated in both DILI patients and an APAP-induced liver injury (AILI) mouse model. Interestingly, both nonparenchymal cells and stressed hepatocytes are cell sources of CCL5 induction in response to liver injury. Functional experiments showed that CCL5 deficiency has no effect on the early phase of AILI but promotes liver repair in the late phase mainly by promoting inflammation resolution and liver regeneration, which are associated with an increased number of hepatic M2 macrophages. Mechanistically, CCL5 can directly activate M1 polarization and impede M2 polarization through the CCR1- and CCR5-mediated activation of the MAPK and NF-κB pathways. We then showed that CCL5 inhibition mediated by either a CCL5-neutralizing antibody or the antagonist Met-CCL5 can greatly alleviate liver injury and improve survival in an AILI mouse model. Our data demonstrate CCL5 induction during DILI, identify CCL5 as a novel innate immunity regulator in macrophage polarization, and suggest that CCL5 blockage is a promising therapeutic strategy for the treatment of DILI.

A comprehensive review of cytochrome P450 2E1 for xenobiotic metabolism

Cytochrome P450 2E1 (CYP2E1) plays a vital role in drug-induced hepatotoxicity and cancers (e.g. lung and bladder cancer), since it is responsible for metabolizing a number of medications and environmental toxins to reactive intermediate metabolites. CYP2E1 was recently found to be the highest expressed CYP enzyme in human livers using a proteomics approach, and CYP2E1-related toxicity is strongly associated with its protein level that shows significant inter-individual variability related to ethnicity, age, and sex. Furthermore, the expression of CYP2E1 demonstrates regulation by extensive genetic polymorphism, endogenous hormones, cytokines, xenobiotics, and varying pathological states. Over the past decade, the knowledge of pharmacology, toxicology, and biology about CYP2E1 has grown remarkably, but the research progress has yet to be summarized. This study presents a timely systematic review on CYP2E1's xenobiotic metabolism, genetic polymorphism, and inhibitors, with the focus on their clinical relevance for the efficacy and toxicity of various CYP2E1 substrates. Moreover, several knowledge gaps have been identified towards fully understanding the potential interactions among different CYP2E1 substrates in clinical settings. Through in-depth analyses of these knowns and unknowns, we expect this review will aid in future drug development and improve management of CYP2E1 related clinical toxicity.

Acetaminophen Hepatotoxicity

Acetaminophen (APAP) is one of the most popular and safe pain medications worldwide. However, due to its wide availability, it is frequently implicated in intentional or unintentional overdoses where it can cause severe liver injury and even acute liver failure (ALF). In fact, APAP toxicity is responsible for 46% of all ALF cases in the United States. Early mechanistic studies in mice demonstrated the formation of a reactive metabolite, which is responsible for hepatic glutathione depletion and initiation of the toxicity. This insight led to the rapid introduction of N-acetylcysteine as a clinical antidote. However, more recently, substantial progress was made in further elucidating the detailed mechanisms of APAP-induced cell death. Mitochondrial protein adducts trigger a mitochondrial oxidant stress, which requires amplification through a MAPK cascade that ultimately results in activation of c-jun N-terminal kinase (JNK) in the cytosol and translocation of phospho-JNK to the mitochondria. The enhanced oxidant stress is responsible for the membrane permeability transition pore opening and the membrane potential breakdown. The ensuing matrix swelling causes the release of intermembrane proteins such as endonuclease G, which translocate to the nucleus and induce DNA fragmentation. These pathophysiological signaling mechanisms can be additionally modulated by removing damaged mitochondria by autophagy and replacing them by mitochondrial biogenesis. Importantly, most of the mechanisms have been confirmed in human hepatocytes and indirectly through biomarkers in plasma of APAP overdose patients. The extensive necrosis caused by APAP overdose leads to a sterile inflammatory response. Although recruitment of inflammatory cells is necessary for removal of cell debris in preparation for regeneration, these cells have the potential to aggravate the injury. This review touches on the newest insight into the intracellular mechanisms of APAP-induced cells death and the resulting inflammatory response. Furthermore, it discusses the translation of these findings to humans and the emergence of new therapeutic interventions.

The Relationship Between Circulating Acetaminophen-Protein Adduct Concentrations and Alanine Aminotransferase Activities in Patients With and Without Acetaminophen Overdose and Toxicity

INTRODUCTION

Measurement of serum acetaminophen-protein adducts (APAP-CYS) has been suggested to support or refute a diagnosis of acetaminophen (APAP)-induced hepatotoxicity when ingestion histories are unreliable or unavailable and when circulating APAP concentrations are low or undetectable. Non-APAP overdose patients commonly have used APAP products in non-toxic quantities and, thus, will have measurable APAP-CYS concentrations, even when hepatic injury results from other causes, such as ischemic hepatitis. The relationship between alanine aminotransferase (ALT) activity and APAP-CYS concentration might assist in distinguishing between toxic and non-toxic APAP doses in patients suspected of drug overdose.

METHODS

We measured serial levels of serum APAP-CYS and ALT activities in 500 overdose patients in whom APAP toxicity was suspected on inpatient admission, but who were then classified at time of discharge and before results of APAP-CYS concentrations were available into three groups: 1) definite APAP group; 2) definitely not APAP group; and 3) indeterminate group. Subjects in the definite and definitely not APAP groups were selected in whom a plasma ALT activity was measured within ± 4 h of a serum APAP-CYS concentration. Regressions with correlation coefficients between APAP-CYS and ALT were calculated for repeat measures in the 335 subjects (908 blood samples) in the definite APAP group and 79 subjects (231 samples) in the definitely not APAP group, with an emphasis on APAP-CYS concentrations and calculation of 95% prediction intervals when ALT was ≥ 1000 IU/L.

RESULTS

A strong correlation was found between APAP-CYS and ALT in the definite APAP group over all ALT activities (r = 0.93, p < 0.001; N = 335), and when ALT was > 1000 IU/L (r = 0.82, p < 0.001, N = 144). In the 79 definitely not APAP subjects, no significant correlation was found when ALT exceeded 1000 IU/L (r = 0.04; p = 0.84, N = 32). All subjects in the definitely not APAP group displayed APAP-CYS concentrations < 3 μM. In definitely not APAP subjects, the great majority of APAP-CYS levels were below the 95% prediction interval for APAP-CYS concentrations in definite APAP group subjects when ALT was ≥ 1000 IU/L. However, some definitely not APAP group subjects who had ingested non-toxic doses of APAP displayed APAP-CYS concentrations as high as 2.8 μM in the face of ALT elevation from ischemic hepatitis.

CONCLUSION

The interpretation of serum APAP-CYS concentrations must always be made in light of detailed clinical information and the population being tested, especially because of some overlap in APAP-CYS levels in subjects with and without APAP toxicity.

Acetaminophen hepatotoxicity: A mitochondrial perspective

Acetaminophen (APAP) is a highly effective analgesic, which is safe at therapeutic doses. However, an overdose can cause hepatotoxicity and even liver failure. APAP toxicity is currently the most common cause of acute liver failure in the United States. Decades of research on mechanisms of liver injury have established the role of mitochondria as central players in APAP-induced hepatocyte necrosis and this chapter examines the various facets of the organelle's involvement in the process of injury as well as in resolution of damage. The injury process is initiated by formation of a reactive metabolite, which binds to sulfhydryl groups of cellular proteins including mitochondrial proteins. This inhibits the electron transport chain and leads to formation of reactive oxygen species, which induce the activation of redox-sensitive members of the MAP kinase family ultimately causing activation of c-Jun N terminal kinase, JNK. Translocation of JNK to the mitochondria then amplifies mitochondrial dysfunction, ultimately resulting in mitochondrial permeability transition and release of mitochondrial intermembrane proteins, which trigger nuclear DNA fragmentation. Together, these events result in hepatocyte necrosis, while adaptive mechanisms such as mitophagy remove damaged mitochondria and minimize the extent of the injury. This oscillation between recovery and necrosis is predominant in cells at the edge of the necrotic area in the liver, where induction of mitochondrial biogenesis is important for liver regeneration. All these aspects of mitochondria in APAP hepatotoxicity, as well as their relevance to humans with APAP overdose and development of therapeutic approaches will be examined in detail in this chapter.

Abundance of Cytochromes in Hepatic Extracellular Vesicles Is Altered by Drugs Related With Drug-Induced Liver Injury

Drug‐induced liver injury (DILI) is a serious worldwide health problem that accounts for more than 50% of acute liver failure. There is a great interest in clinical diagnosis and pharmaceutical industry to elucidate underlying molecular mechanisms and find noninvasive biomarkers for this pathology. Cell‐secreted extracellular vesicles (EVs) have provided a new biological source to identify low disease invasive markers. Despite the intense research developed on these vesicles, there is currently a gap on their patho‐physiological effects. Here, we study EVs secreted by primary rat hepatocytes challenged with galactatosamine (GalN), acetaminophen, or diclofenac as DILI in vitromodels. Proteomics analysis of these EVs revealed an increase in enzymes already associated with liver damage, such as catecholamine‐methyl transferase and arginase 1. An increase in translation‐related proteins and a decrease in regulators of apoptosis were also observed. In addition, we show the presence of enzymatic activity of P450 cytochrome 2d1 in EVs. The activity specifically is decreased in EVs secreted by hepatocytes after acetaminophen treatment and increased in EVs derived from GalN‐treated hepatocytes. By using in vivo preclinical models, we demonstrate the presence of this cytochrome activity in circulation under normal conditions and an increased activity after GalN‐induced injury. Conclusion: Hepatocyte‐secreted EVs carry active xenobiotic‐metabolizing enzymes that might be relevant in extracellular metabolism of drugs and be associated with DILI. (Hepatology Communications 2018;0:00‐00)

Mitochondrial dysfunction as a mechanism of drug-induced hepatotoxicity: current understanding and future perspectives

Mitochondria are critical cellular organelles for energy generation and are now also recognized as playing important roles in cellular signaling. Their central role in energy metabolism, as well as their high abundance in hepatocytes, make them important targets for drug-induced hepatotoxicity. This review summarizes the current mechanistic understanding of the role of mitochondria in drug-induced hepatotoxicity caused by acetaminophen, diclofenac, anti-tuberculosis drugs such as rifampin and isoniazid, anti-epileptic drugs such as valproic acid and constituents of herbal supplements such as pyrrolizidine alkaloids. The utilization of circulating mitochondrial-specific biomarkers in understanding mechanisms of toxicity in humans will also be examined. In summary, it is well-established that mitochondria are central to acetaminophen-induced cell death. However, the most promising areas for clinically useful therapeutic interventions after acetaminophen toxicity may involve the promotion of adaptive responses and repair processes including mitophagy and mitochondrial biogenesis, In contrast, the limited understanding of the role of mitochondria in various aspects of hepatotoxicity by most other drugs and herbs requires more detailed mechanistic investigations in both animals and humans. Development of clinically relevant animal models and more translational studies using mechanistic biomarkers are critical for progress in this area.

Relevance for patients:This review focuses on the role of mitochondrial dysfunction in liver injury mechanisms of clinically important drugs like acetaminophen, diclofenac, rifampicin, isoniazid, amiodarone and others. A better understanding ofthe mechanisms in animal models and their translation to patients will be critical for the identification of new therapeutic targets.

Oxidant Stress and Lipid Peroxidation in Acetaminophen Hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of liver injury and acute liver failure in many western countries. The mechanism of APAP-induced hepatocyte necrosis has been investigated extensively. The formation of a reactive metabolite and its binding to cellular proteins was initially thought to be responsible for cell death. A competing hypothesis was introduced that questioned the relevance of protein binding and instead suggested that P450-derived oxidant stress and lipid peroxidation causes APAP-induced liver injury. However, work over the last 15 years has reconciled some of these apparent contradictory hypotheses. This review summarizes the present state of knowledge on the role of reactive oxygen species (ROS) in APAP hepatotoxicity. Detailed investigations into the sources and relevance of the oxidant stress have clearly shown the critical role of the electron transport chain of mitochondria as main source of the oxidant stress. Other potential sources of ROS such as cytochrome P450 enzymes or NADPH oxidase on phagocytes are of limited relevance. The mitochondria-derived superoxide and peroxynitrite formation is initiated by the binding of the reactive metabolite to mitochondrial proteins and the amplification by mitogen activated protein kinases. The consequences of this oxidant stress are the opening of the mitochondrial membrane permeability transition pore with cessation of ATP synthesis, nuclear DNA fragmentation and ultimately cell necrosis. Lipid peroxidation is not a relevant mechanism of cell death but can be a marker of ROS formation. These mechanistic insights suggest that targeting mitochondrial oxidant stress is a promising therapeutic option for APAP hepatotoxicity.