The role of apoptosis in acetaminophen-induced injury

Excessive N-acetylcysteine exaggerates glutathione redox homeostasis and apoptosis during acetaminophen exposure in Huh-7 human hepatoma cells

Acetaminophen (APAP) hepatotoxicity is one of the biggest drawbacks of this relatively safe and widely used drug. In addition to its hepatotoxicity, APAP also cause comparable levels of toxicity on human hepatoma cells. Here we show activation of the intrinsic caspase-9/3 pathway of apoptosis followed by gasdermin E (GSDME) cleavage and subsequent ballooning in APAP (10 mM, 72 h)-treated Huh-7 human hepatocarcinoma cells. N-acetylcysteine (NAC), an antioxidant currently used as an antidote for APAP overdose, does not alleviate APAP toxicity in Huh-7 cells; NAC overdose (10 mM) rather aggravates APAP toxicity. NAC overdose not only aggravates cell death, but also decreases the cellular GSH/GSSG ratio, an indicator of redox homeostasis of glutathione. These results show for the first time that APAP-induced apoptosis in hepatoma cells is followed by secondary necrosis via the caspase-3/GSDME pathway. NAC overdose (10 mM) not only worsens the glutathione redox status, but also accelerates this pathway.

The Performance of HepG2 and HepaRG Systems through the Glass of Acetaminophen-Induced Toxicity

Investigation of drug-induced liver injuries requires appropriate in vivo and in vitro toxicological model systems. In our study, an attempt was made to compare the hepatocarcinoma HepG2 and the stem cell-derived HepaRG cell lines both in two- and three-dimensional culture conditions to find the most suitable model. Comparison of the liver-specific characteristics of these models was performed via the extent and mechanism of acetaminophen (APAP)-induced hepatotoxicity. Investigating the detailed mechanism of APAP-induced hepatotoxicity, different specific cell death inhibitors were used: the pan-caspase inhibitor zVAD-fmk and dabrafenib significantly protected both cell lines from APAP-induced cell death. However, the known specific inhibitors of necroptosis (necrostatin-1 and MDIVI) were only effective in differentiated HepaRG, which suggest a differential execution of activated pathways in the two models. By applying 3D culture methods, CYP2E1 mRNA levels could be elevated, but we failed to achieve a significant increase in hepatocyte function; hence, the 3D cultivation especially in APAP toxicity studies is not necessarily worth the complicated maintenance. Based on our findings, the hepatocyte functions of HepaRG may stand between the properties of HepG2 cells and primary hepatocytes (PHHs). However, it should be noted that in contrast to PHHs having many limitations, HepaRG cells are relatively immortal, having a stable phenotype and CYP450 expression.

PYP1-4 peptide from Pyropia yezoensis protects against acetaminophen-induced hepatotoxicity in HepG2 cells

Acetaminophen (APAP) is a widely used analgesic and antipyretic. It is safe at normal treatment doses; however, APAP overdose is a major cause of acute liver and kidney failure. A variety of methods to reduce the damage caused by APAP overdose have previously been evaluated. The protein-rich seaweed Pyropia yezoensis has antioxidant, antitumor and anti-inflammatory activities, and protects against cytotoxicity. However, little is known regarding the protective effects of P. yezoensis peptide against APAP-induced hepatotoxicity. The present study investigated the ability of P. yezoensis peptide (PYP1-4) to ameliorate the damage caused by APAP-induced hepatotoxicity using HepG2 as the model cell line in addition to the signaling pathways involved. Briefly, cell viability, nitric oxide, reactive oxygen species and apoptosis assays were performed in conjunction with western blot analysis and reverse transcription-quantitative PCR. First, the present study revealed the minimum toxic concentration of APAP (15 mM) and the resting concentration of PYP1-4 (0–500 ng/ml). Administration of PYP1-4 to APAP-induced cells decreased the nitric oxide and reactive oxygen species levels, and restored the levels of antioxidant-associated proteins (catalase, heme oxygenase 1, superoxide dismutase 2 and quinone oxidoreductase 1). PYP1-4 increased the translocation of nuclear factor, erythroid 2 like 2 to the nucleus and the activities of glycogen synthase kinase-3β, Akt and AMP-activated protein kinase. In addition, APAP induced apoptosis; however, PYP1-4 inhibited apoptosis by modulating the levels of pro-apoptotic markers (Bad), anti-apoptotic markers (Bcl-2 and BH3 interacting domain death agonist), caspases and poly (ADP-ribose) polymerase 1. Subsequently, the insulin-like growth factor 1 receptor signaling pathway was investigated to determine whether PYP1-4 treatment restored the levels of cell growth-associated factors during APAP-induced hepatotoxicity. PYP1-4 treatment impacted the levels of components of the insulin receptor substrate 1/PI3K/Akt and Ras/Raf/ERK signaling pathways, and promoted cell survival. Therefore, the P. yezoensis peptide PYP1-4 may be useful for preventing APAP-induced hepatotoxicity.

Protective effects of curcumin and silymarin against paracetamol induced hepatotoxicity in adult male albino rats

BACKGROUND

Acute paracetamol (PCM) toxicity is a clinical problem; can result in a serious liver injury that finally may progress to acute liver failure. Curcumin (CUR) is a prevalent natural compound that can maintain prooxidant/antioxidant balance and thus can help in liver protection; also, Silymarin (SL) is a traditional antioxidant herb, used to treat liver disorders through scavenging free radicals. This study aimed to illustrate the histological, biochemical and molecular changes induced by acute PCM overdose on rats' liver to elucidate the effectiveness of CUR compared to SL in alleviating such changes.

MATERIALS AND METHODS

Male Wister Albino rats were divided into 6 groups each comprising 23 rats: control group, curcumin (CUR) treated group received (100 mg CUR/ kg), silymarin treated group received (100 mg SL/kg) for 7 successive days. Paracetamol (PCM) exposed group administered a single dose of PCM (200 mg/kg orally on 8th day). PCM + CUR group and PCM + SL group pretreated with CUR and SL respectively for 7 days then received single PCM dose (200 mg/kg) on the 8th day. Blood and liver tissues were collected for biochemical, histopathological and immunohistochemical analyses using anti-p53 antibody. In addition, real time polymerase chain reaction (RT- PCR) was used to measure Bax, bcl2 and Peroxisome proliferator-activated receptor-gamma (PPAR γ) mRNA expression levels.

RESULTS

In the paracetamol overdose group, the liver architecture showed necrotic changes, hydropic degeneration, congestion and dilatation of central veins. This hepatocellular damage was confirmed by a significant increase of AST, ALT levels and by an apparent increase in the number of p53 stained cells. PCM toxicity showed significant elevation of total oxidant status (TOS), oxidant status index (OSI) and decreased total antioxidant capacity (TAC) compared to controls (p < 0.001). Gene expression analysis showed that PCM caused an elevation of bcl2 and a reduction of both Bax and PPARγ mRNA expression. The histological alternation in the liver architecture was markedly improved in (PCM + CUR) group compared to (PCM+ SL) group, with an obvious decrease in the number of P53 stained cells. CUR pretreatment inhibited the elevation of TOS and OSI as well as the reduction of TAC caused by PCM toxicity compared to (PCM + SL) group.

CONCLUSION

Both SL and CUR pretreatment prevented the toxic effects of PCM, but CUR is more effective than SL in ameliorating acute PCM induced hepatotoxicity.

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.

Dimethyl fumarate ameliorates acetaminophen-induced hepatic injury in mice dependent of Nrf-2/HO-1 pathway

Drug-induced liver toxicity is the most frequent cause of acute liver failure worldwide. Hepatotoxicity caused by acetaminophen (ACT) overdose is mediated by its metabolic product promoting oxidative stress and activation of inflammatory mediators. Nuclear factor erythroid-related factor-2 (Nrf-2) induces the release of cytoprotective enzymes in response to electrophilic or oxidative stress and is considered a promising therapeutic target. Dimethyl fumarate (DMF) is a potent activator of (Nrf-2), its anti-inflammatory and antioxidant properties of DMF have been highlighted recently. We designed this study to explore the effect of DMF (100 mg/kg, orally) administered once and twice on hepatotoxicity induced by acetaminophen (ACT, 500 mg/kg, i.p.) in mice. DMF administration enhanced ACT-induced parameters in liver function, inhibited apoptosis and ameliorated the antioxidant machinery and inflammatory markers in a Nrf-2-dependent fashion. DMF elevated Nrf-2 and HO-1 levels and ameliorated liver injury as indicated by lowered levels of serum aminotransferases, ALP, GGT and bilirubin levels. Hepatic (Bcl-2) was elevated whereas hepatic caspase-3, NFκ-B, TNF-α and MPO were reduced. Hepatic levels of GSH, SOD, MDA and NO were altered promoting the antioxidant machinery. Histological examination of liver has further supported these results. These findings suggest that DMF can be employed in the treatment ACT-induced liver injury acting primarily through targeting Nrf-2/HO-1 pathway.

The role of apoptosis in acetaminophen hepatotoxicity

Although necrosis is recognized as the main mode of cell death induced by acetaminophen (APAP) overdose in animals and humans, more recently an increasing number of publications, especially in the herbal medicine and dietary supplement field, claim an important contribution of apoptotic cell death in the pathophysiology. However, most of these conclusions are based on parameters that are not specific for apoptosis. Therefore, the objective of this review was to re-visit the key signaling events of receptor-mediated apoptosis and APAP-induced programmed necrosis and critically analyze the parameters that are being used as evidence for apoptotic cell death. Both qualitative and quantitative comparisons of parameters such as Bax, Bcl-2, caspase processing and DNA fragmentation in both modes of cell death clearly show fundamental differences between apoptosis and cell death induced by APAP. These observations together with the lack of efficacy of pan-caspase inhibitors in the APAP model strongly supports the conclusion that APAP hepatotoxicity is dominated by necrosis or programmed necrosis and does not involve relevant apoptosis. In order not to create a new controversy, it is important to understand how to use these "apoptosis" parameters and properly interpret the data. These issues are discussed in this review.

Natural Dietary Pigments: Potential Mediators against Hepatic Damage Induced by Over-The-Counter Non-Steroidal Anti-Inflammatory and Analgesic Drugs

Over-the-counter (OTC) analgesics are among the most widely prescribed and purchased drugs around the world. Most analgesics, including non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen, are metabolized in the liver. The hepatocytes are responsible for drug metabolism and detoxification. Cytochrome P450 enzymes are phase I enzymes expressed mainly in hepatocytes and they account for ≈75% of the metabolism of clinically used drugs and other xenobiotics. These metabolic reactions eliminate potentially toxic compounds but, paradoxically, also result in the generation of toxic or carcinogenic metabolites. Cumulative or overdoses of OTC analgesic drugs can induce acute liver failure (ALF) either directly or indirectly after their biotransformation. ALF is the result of massive death of hepatocytes induced by oxidative stress. There is an increased interest in the use of natural dietary products as nutritional supplements and/or medications to prevent or cure many diseases. The therapeutic activity of natural products may be associated with their antioxidant capacity, although additional mechanisms may also play a role (e.g., anti-inflammatory actions). Dietary antioxidants such as flavonoids, betalains and carotenoids play a preventive role against OTC analgesics-induced ALF. In this review, we will summarize the pathobiology of OTC analgesic-induced ALF and the use of natural pigments in its prevention and therapy.

Hepatoprotective Effect of Polyphenol-Enriched Fraction from Folium Microcos on Oxidative Stress and Apoptosis in Acetaminophen-Induced Liver Injury in Mice

Folium Microcos (FM), the leaves of Microcos paniculata L., shows various biological functions including antioxidant activity and α-glucosidase inhibitory effect. However, its therapeutic potential in acute liver injury is still unknown. This study investigated the hepatoprotective effect and underlying mechanisms of the polyphenol-enriched fraction (FMF) from Folium Microcos. FMF exhibited strong free radical scavenging activities and prevented HepG2/Hepa1-6 cells from hydrogen peroxide- (H₂O₂-) induced ROS production and apoptosis in vitro. Antioxidant activity and cytoprotective effects were further verified by alleviating APAP-induced hepatotoxicity in mice. Western blot analysis revealed that FMF pretreatment significantly abrogated APAP-mediated phosphorylation of MAPKs, activation of proapoptotic protein caspase-3/9 and Bax, and restored expression of antiapoptotic protein Bcl2. APAP-intoxicated mice pretreated with FMF showed increased nuclear accumulation of nuclear factor erythroid 2-related factor (Nrf2) and elevated hepatic expression of its target genes, NAD(P)H:quinine oxidoreductase 1 (NQO1) and hemeoxygenase-1(HO-1). HPLC analysis revealed the four predominantly phenolic compounds present in FMF: narcissin, isorhamnetin-3-O-β-D-glucoside, isovitexin, and vitexin. Consequently, these findings indicate that FMF possesses a hepatoprotective effect against APAP-induced hepatotoxicity mainly through dual modification of ROS/MAPKs/apoptosis axis and Nrf2-mediated antioxidant response, which may be attributed to the strong antioxidant activity of phenolic components.

Caspase-3/7-mediated Cleavage of β2-spectrin is Required for Acetaminophen-induced Liver Damage

The ubiquitously expressed β2-spectrin (β2SP, SPTBN1) is the most common non-erythrocytic member of the β-spectrin gene family. Loss of β2-spectrin leads to defects in liver development, and its haploinsufficiency spontaneously leads to chronic liver disease and the eventual development of hepatocellular cancer. However, the specific role of β2-spectrin in liver homeostasis remains to be elucidated. Here, we reported that β2-spectrin was cleaved by caspase-3/7 upon treatment with acetaminophen which is the main cause of acute liver injury. Blockage of β2-spectrin cleavage robustly attenuated β2-spectrin-specific functions, including regulation of the cell cycle, apoptosis, and transcription. Cleaved fragments of β2-spectrin were physiologically active, and the N- and C-terminal fragments retained discrete interaction partners and activity in transcriptional regulation and apoptosis, respectively. Cleavage of β2-spectrin facilitated the redistribution of the resulting fragments under conditions of liver damage induced by acetaminophen. In contrast, downregulation of β2-spectrin led to resistance to acetaminophen-induced cytotoxicity, and its insufficiency in the liver promoted suppression of acetaminophen-induced liver damage and enhancement of liver regeneration.

CONCLUSIONS

β2-Spectrin, a TGF-β mediator and signaling molecule, is cleaved and activated by caspase-3/7, consequently enhancing apoptosis and transcriptional control to determine cell fate upon liver damage. These findings have extended our knowledge on the spectrum of β2-spectrin functions from a scaffolding protein to a target and transmitter of TGF-β in liver damage.

Experimental models of hepatotoxicity related to acute liver failure

Acute liver failure can be the consequence of various etiologies, with most cases arising from drug-induced hepatotoxicity in Western countries. Despite advances in this field, the management of acute liver failure continues to be one of the most challenging problems in clinical medicine. The availability of adequate experimental models is of crucial importance to provide a better understanding of this condition and to allow identification of novel drug targets, testing the efficacy of new therapeutic interventions and acting as models for assessing mechanisms of toxicity. Experimental models of hepatotoxicity related to acute liver failure rely on surgical procedures, chemical exposure or viral infection. Each of these models has a number of strengths and weaknesses. This paper specifically reviews commonly used chemical in vivo and in vitro models of hepatotoxicity associated with acute liver failure.

Models of drug-induced liver injury for evaluation of phytotherapeutics and other natural products

Extracts from medicinal plants, many of which have been used for centuries, are increasingly tested in models of hepatotoxicity. One of the most popular models to evaluate the hepatoprotective potential of natural products is acetaminophen (APAP)-induced liver injury, although other hepatotoxicity models such as carbon tetrachloride, thioacetamide, ethanol and endotoxin are occasionally used. APAP overdose is a clinically relevant model of drug-induced liver injury. Critical mechanisms and signaling pathways, which trigger necrotic cell death and sterile inflammation, are discussed. Although there is increasing understanding of the pathophysiology of APAP-induced liver injury, the mechanism is complex and prone to misinterpretation, especially when unknown chemicals such as plant extracts are tested. This review discusses the fundamental aspects that need to be considered when using this model, such as selection of the animal species or in vitro system, timing and dose-responses of signaling events, metabolic activation and protein adduct formation, the role of lipid peroxidation and apoptotic versus necrotic cell death, and the impact of the ensuing sterile inflammatory response. The goal is to enable researchers to select the appropriate model and experimental conditions for testing of natural products that will yield clinically relevant results and allow valid interpretations of the pharmacological mechanisms.

Circulating apoptotic and necrotic cell death markers in patients with acute liver injury

BACKGROUND

The host response to cell death underpins the immune activation that follows acute liver injury, and measurement of circulating cell death markers could therefore aid prognostication following paracetamol overdose. Nucleosomes, formed during apoptosis, can complex with high-mobility group box 1 (HMGB1) protein and may play a pathogenic role in liver injury.

AIMS

To explore the levels and prognostic significance of nucleosomes, HMGB1, and other cell death markers following acute liver injury.

METHODS

Levels of plasma nucleosomes, HMGB1, caspase-cleaved cytokeratin-18 (M30) and total cytokeratin-18 (M65) were measured by immunoassay, in a cohort of 33 patients with paracetamol- and non-paracetamol-induced acute liver injury.

RESULTS

Admission nucleosome levels in paracetamol overdose patients were significantly higher than in chronic liver disease and healthy control subjects, but were similar in paracetamol and non-paracetamol patients (P=0.11). Nucleosome levels were not associated with death or requirement for liver transplantation, fulfillment of poor prognostic criteria or organ failure in paracetamol patients. Nucleosome levels correlated with levels of HMGB1 (r=0.500, P=0.009), alanine aminotransferase (r=0.410, P=0.038) and M65 (r=0.709, P<0.001), but not with M30 (r=0.309, P=0.124). None of the cell death markers analysed improved prognostication in paracetamol patients beyond the King's College criteria.

CONCLUSIONS

Plasma nucleosomes are significantly elevated following acute liver injury. Neither apoptotic nor necrotic cell death markers accurately predict survival following paracetamol-induced hepatotoxicity, suggesting that the extent and type of cell death play a limited role in determining outcome.

Apoptosis versus necrosis rate as a predictor in acute liver failure following acetaminophen intoxication compared with acute-on-chronic liver failure

Cell death is known to play a crucial role in liver diseases. We compared the clinical courses of two cases of liver failure of different origins correlated with the extent of cell death (apoptosis and/or necrosis), measured in the patient's blood. Patient 1 was admitted with acute liver failure following acetaminophen intoxication. Intravenous therapy with acetylcysteine was performed. The percentage of apoptotic cell death measured by M30 was three times higher than normal and the overall cell death measured by M65 was more than 30 x higher than normal. High levels of aminotransferases were detected, indicating high rates of necrosis. M30 and M65 values rapidly returned to normal levels, while the liver function test (LFT) levels decreased with latency. Patient 2 was admitted with acute-on-chronic liver failure with known liver fibrosis. M30 values were 16 x higher than normal. In contrast, M65 values were lower than in the first case. This time, no movement in M30 levels was seen until the M30 levels rapidly increased indicating the inevitable death of the patient, while LFTs did not change. These results indicate the role of M30 and M65 immunoexpression as markers for functioning liver cell mass, capacity for recovery and therefore as predictive markers in acute liver failure.

Caspase-cleaved cytokeratin 18 and 20 S proteasome in liver degeneration

Apoptosis of epithelial hepatocytes plays a pivotal role in acute as well as in chronic liver diseases. The cleavage of cytokeratin-18 (CK-18) by caspases is an early event in the apoptotic process. We therefore sought to investigate serum levels of CK-18 and 20S proteasome in patients with liver cirrhosis, primary graft dysfunction (PDF), and acute liver failure (ALF), and in healthy volunteers. Enzyme-linked immunosorbent assay (ELISA) was utilized to measure the concentration of M30, a fragment of CK-18 cleaved at Asp396 (M30 neoantigen), and the concentration of 20S proteasome. Serum levels of the CK-18 neoepitope M30 were significantly increased in ALF, primary graft dysfunction, and liver cirrhosis vs. healthy controls (1,993.6+/-124.7 U/L, 2,238.1+/-235.9 U/L, and 673.6+/-86.5 U/L vs. 66.8+/-29.1 U/L, respectively, P<0.001). Similar results were detected with the evaluation of 20S proteasome (124,014.5+/-13,235.6 ng/mL, 76,993.2+/-15,720.1 ng/mL, and 2,395.9+/-1,098.2 ng/mL vs. 1,074.5+/-259.4 ng/mL, respectively; P<0.001). Detection of CK-18 neoepitope M30 and 20S proteasome may represent a novel marker of tracing apoptotic epithelium, respectively mirroring degenerative liver processes in affected patient population.

Serum apoptosis markers in acute liver failure: a pilot study

BACKGROUND & AIMS

We sought to determine whether circulating apoptotic markers are altered in acute liver failure (ALF), differ with etiology, or predict clinical outcome in this condition.

METHODS

Serum levels of soluble Fas (sFas), tumor necrosis factor-alpha (TNF-alpha), hepatocyte growth factor (HGF), and interleukin-6 (IL-6) were measured in 67 acute liver failure patients, as well as controls. In a subset of the groups, we measured serum M-30 antigen, an exposed neoepitope from caspase cleavage. We also assessed M-30 immunoreactivity in liver tissue of ALF patients and controls.

RESULTS

Median levels for TNF-alpha, HGF, IL-6, and M-30 antigen were at least 10-fold greater in ALF than in hepatitis C virus or normal controls (P < .0001). Median day 1 sFas, day 3 sFas, and day 1 HGF levels varied according to etiology of acute liver failure (P = .004, P = .011, and P = .019, respectively), with values for drug-induced liver injury and acetaminophen-related ALF higher than other etiologies. Median M-30 antigen levels were significantly higher in patients who were transplanted and/or died (2183 U/L) than spontaneous survivors (1004 U/L) (P = .026). M-30 immunoreactivity in liver tissue was significantly greater in ALF patients than HCV controls (P = .004).

CONCLUSIONS

TNF-alpha, HGF, IL-6, and M-30 antigen were significantly elevated in ALF. High levels of sFas and HGF might help to confirm a diagnosis of drug-induced liver injury or acetaminophen-related ALF. Higher levels of M-30 antigen are associated with poor clinical outcomes in ALF.

Chromatin breakdown by deoxyribonuclease1 promotes acetaminophen-induced liver necrosis: an ultrastructural and histochemical study on male CD-1 mice

We analyzed in male wild-type (WT) and Dnase1 knockout (KO) CD-1 mice after acetaminophen (APAP)-intoxication the hepatolobular distribution of APAP-adducts in relation to DNA-damage by terminal deoxyribonucleotidyl-transferase dUTP nick end-labeling (TUNEL), the ultrastructural alterations of hepatocellular morphology and the intracellular localization of Dnase1. Treatment of WT-mice with 600 mg/kg APAP led to extensive pericentral necrosis. Electron microscopy (EM) demonstrated vesiculation of the rough endoplasmatic reticulum and swelling of mitochondria. Pericentral WT-hepatocyte nuclei exhibited pyknosis, karyorrhexis and karyolysis. In contrast, livers from treated KO-mice exhibited almost normal light microscopical structure and EM revealed only mild signs of hepatocellular damage. In WT-mice several layers of pericentral hepatocytes displayed APAP-adduct formation and subsequent DNA-damage, whereas in KO-animals only few cells were affected. Serum aminotransferases rose similarly in both mouse strains up to 12 h, thereafter increased only in WT-mice. Immunogold-EM revealed the translocation of Dnase1 from the rER into the nuclei of treated WT-mice. In KO-mice, APAP-adduct formation was retarded and less extensive suggesting that detoxification of APAP must have been more effective in KO-mice possibly due to the lack of energy depletion otherwise caused by Dnase1-induced DNA-damage in WT-mice.

Acetaminophen induces ER dependent signaling in mouse liver

Role of endoplasmic reticulum (ER) in liver injury by acetaminophen (AAP) was studied in vivo in mice. Sublethal dose of AAP resulted in a decrease in microsomal total glutathione and in the reduced-to-total glutathione ratio; redox state of thiols of ER resident oxidoreductases ERp72, PDI was shifted towards the oxidized form; ER stress-responsive transcription factor ATF6 was activated. Transcriptional activation and elevated expression of GADD153/CHOP, an ER stress-responsive proapoptotic transcription factor, was observed upon AAP addition. Transient activation of the ER-resident caspase-12 was shown followed by an elevation in procaspase-12 level. Caspase-3 and caspase-8 activation could not be detected. AAP treatment resulted in an increased apoptosis of hepatocytes. Buthionine-sulfoximine treatment was unable to mimic the effects by AAP indicating that glutathione depletion itself is insufficient to provoke apoptosis. The results show that intraluminal redox imbalance of the ER and consequential activation of signaling processes and proapoptotic events are involved in hepatocellular damage caused by AAP overdose.

Mechanistic classification of liver injury

Toxic injury occurs in the liver more often than any other organ. This can be attributed to the fact that virtually all ingested substances that are absorbed are first presented to the liver and that the liver is responsible for the metabolism and elimination of many substances. Drug-induced liver injury has become a serious health problem in contemporary society. Moreover, liver toxicity is a significant impediment to development of new pharmaceuticals. A classification of liver injury is presented as a means to better understand the spectrum of known mechanisms of liver injury and to assist in discovering novel pathways of toxic liver injury.