Differential regulation of mitogen-activated protein kinase pathways by acetaminophen and its nonhepatotoxic regioisomer 3'-hydroxyacetanilide in TAMH cells

Acetaminophen overdose inhibits steroidogenic acute regulatory protein expression by reducing AKT-mediated SP1 expression in human granulosa-lutein cells

Overdose of acetaminophen (APAP) has been shown to adversely affect the outcome of pregnancy. The steroidogenic acute regulatory protein (StAR) plays a pivotal role in steroidogenesis, but the impact of APAP on StAR expression in adult human ovarian granulosa cells remains elusive. Here, we demonstrate that APAP overdose leads to the downregulation of StAR expression in the human granulosa cell tumor cell line, KGN, and in the primary culture of human granulosa-lutein (hGL) cells. Treatment of overdose APAP inhibits the activation of the AKT signaling pathway and downregulates the expression of transcription factor SP1. Using a small molecule of AKT activator and SP1 overexpression approaches, we show that the suppressive effect of APAP on StAR expression is mediated through the inhibition of AKT-mediated upregulation of SP1 expression. This study contributes to a deeper understanding of the pharmacological actions of APAP and its impacts on female reproductive health.

Identification of differentially expressed genes and pathways in diquat and paraquat poisoning using bioinformatics analysis

[Objective] In this study, differentially expressed genes (DEGs) and signaling pathways involved in diquat (DQ) and paraquat (PQ) poisoning were identified via bioinformatics analysis, in order to inform the development of novel clinical treatments. [Methods] Raw data from GSE153959 were downloaded from the Gene Expression Omnibus database. DEGs of the DQ vs. control (CON) and PQ vs. CON comparison groups were identified using R, and DEGs shared by the two groups were identified using TBtools. Subsequently, the shared DEGs were searched in the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, using the Database for Annotation, Visualization, and Integrated Discovery. A protein-protein interaction (PPI) network was constructed, and hub genes were identified using the cytoHubba plug-in in Cytoscape software. Finally, Circos and contrast plots showing the DEGs shared between mouse and human chromosomes were constructed using TBtools. [Results] Thirty- one DEGs shared by the DQ and PQ groups were identified. Enriched biological process terms included positive regulation of cell proliferation and translation. Enriched cellular component terms included extracellular region, intracellular membrane- bounded organelle and mitochondrion. Enriched molecular function terms included transcription factor activity and sequence-specific double-stranded DNA binding. Enriched KEGG pathways included the interleukin- 17 signaling pathway, tumor necrosis factor signaling pathway, and human T- cell leukemia virus 1 infection. The top ten hub genes in the PPI network were Ptgs2, Cxcl2, Csf2, Mmp13, Areg, Plaur, Fosl1, Ereg, Atf3, and Tfrc. Cxcl2, Csf2, and Atf3 played important roles in the mitogen- activated protein kinase signaling pathway. [Conclusions] These pathways and DEGs may serve as targets for gene therapy.

The dual role of immune response in acetaminophen hepatotoxicity: Implication for immune pharmacological targets

Acetaminophen (APAP), one of the most widely used antipyretic and analgesic drugs, principally contributes to drug-induced liver injury when taken at a high dose. APAP-induced liver injury (AILI) results in extensive necrosis of hepatocytes along with the occurrence of multiple intracellular events such as metabolic activation, cell injury, and signaling pathway activation. However, the specific role of the immune response in AILI remains controversial for its complicated regulatory mechanisms. A variety of inflammasomes, immune cells, inflammatory mediators, and signaling transduction pathways are activated in AILI. These immune components play antagonistic roles in aggravating the liver injury or promoting regeneration. Recent experimental studies indicated that natural products showed remarkable therapeutic effects against APAP hepatotoxicity due to their favorable efficacy. Therefore, this study aimed to review the present understanding of the immune response in AILI and attempted to establish ties among a series of inflammatory cascade reactions. Also, the immune molecular mechanisms of natural products in the treatment of AILI were extensively reviewed, thus providing a fundamental basis for exploring the potential pharmacological targets associated with immune interventions.

Moderate Hypothermia Effectively Alleviates Acetaminophen-Induced Liver Injury With Prolonged Action Beyond Cooling

Acetaminophen (APAP) overdose accounts for the highest incidence of acute liver failure, despite the availability of an antidote i.e. N-acetylcysteine. This calls for alternative strategies to manage APAP-induced liver injury (AILI). Therapeutic hypothermia has been explored in past studies for hepatoprotection, but these phenomenal reports lack clarification of its optimal window for application, and mechanistic effects in specific AILI. Hence, we conducted an in vitro study with transforming growth factor-α transgenic mouse hepatocytes cell line, TAMH, and human liver hepatocytes cell line, L-02, where cells were conditioned with deep (25°C) or moderate (32°C) hypothermia before, during or after APAP toxicity. Cell viability was evaluated as a hallmark of cytoprotection, along with cell death. Simultaneously, cold shock proteins (CSPs) and heat shock proteins expressions were monitored; key liver functions including drug-metabolizing ability and hepatic clearance were also investigated. Herein, we demonstrated significant hepatoprotection with 24-hour moderate hypothermic conditioning during AILI and this effect sustained for at least 24 hours of rewarming. Such liver preservation was associated with a CSP-RNA-binding motif protein 3 (RBM3) as its knockdown promptly abolished the cytoprotective effects of hypothermia. With mild and reversible liver perturbations, hypothermic therapy appears promising and its RBM3 involvement deserves future exploration.

Protection of mouse brain from paracetamol-induced stress by Centella asiatica methanol extract

ETHNOPHARMACOLOGICAL RELEVANCE

Centella asiatica (CA) is a medicinal herb traditionally used as a brain tonic in Ayurvedic medicine. Various ethnomedical leads revealed the effective use of CA in the treatment of symptoms associated to oxidative stress and inflammation.

AIM OF THE STUDY

The aim of this study was to evaluate the therapeutic ability of CA methanol extract (CAM) in protecting mouse brain and astrocytes from oxidative stress and inflammation induced by Paracetamol, and thus to substantiate the allied traditional/ethnomedical claims of CA.

MATERIALS AND METHODS

Chemical profiling of CAM and quantification of its major constituents were carried out by HPTLC-densitometry. Mice were administered with CAM and Paracetamol in various combinations, and oxidative stress parameters (lipid peroxidation, radical scavenging) as well as nitric oxide stress were estimated from isolated mouse brain. Cellular toxicity was investigated by apoptosis/necrosis in primary astrocytes isolated from brain tissues of mouse (which was challenged by CAM/Paracetamol) by flow cytometry and fluorescent microscopy. Expression of inflammatory cytokine mediators (monocyte chemo attractant protein 1, interleukin 1, interferon γ, tumor necrosis factor β, interleukin 10 and mitogen activated protein kinase 14 gene) in CAM/Paracetamol administered mouse brain tissues was analyzed by real time PCR. Mouse brain tissues challenged by CAM/Paracetamol were also assessed for gross and histopathology. In addition, staining with acridine orange was carried out in C6 cell lines treated with CAM, and viewed under fluorescent microscopy.

RESULTS

Paracetamol elicited reactive oxygen species generation was revealed through Ferric Reducing Antioxidant Power (FRAP) activity. CAM reversed the Paracetamol induced free radical and reactive nitrogen species production and increased the scavenging activity which was more pronounced at the higher dose (80 mg/kg b.wt). CAM negated the Paracetamol-induced damage by inhibiting expression of pro-inflammatory cytokines (MCP 1, IL 1, TNF β), and increasing the expression of the anti-inflammatory cytokine (IL 10) profoundly. Interestingly, MAPK 14 gene expression was decreased gradually and became same as normal control with increase in the dose of CAM. Also, it was evident that CAM protected mouse primary astrocytes from Paracetamol by maintaining a normal morphology. Similarly, apoptosis of primary astrocytes (treated with Paracetamol/CAM) decreased with the increase in CAM dose (80 mg/kg b.wt.) which was evident from flow cytometric data. Severe brain damage in the form of lesions was apparent from the histology of Paracetamol alone treated mouse brain. Whereas, CAM treated together with Paracetamol upturned these lesions. Surprisingly, CAM alone proved to be cytotoxic to C6 Glioma cells.

CONCLUSIONS

CAM showed antioxidant and anti-inflammatory effects (which were pronounced at higher doses) against Paracetamol-induced oxidative stress and associated inflammation in mouse brain. The underlying mechanisms may be mediated by inhibiting the pro-inflammatory cytokines TNF β, IL 1 and MCP 1 via regulation of the antioxidant mediated INF γ and MAPK 14 gene signalling pathways. The major bioactive constituents in CAM are the triterpenoid saponins, asiaticoside and madecassoside. The present results provide pharmacological evidence that CAM acts as an antioxidant and anti-inflammatory agent. Furthermore, this study validates the use of CA as an antioxidant and anti-inflammatory agent in ethnomedicine.

Chlorpromazine protects against acetaminophen-induced liver injury in mice by modulating autophagy and c-Jun N-terminal kinase activation

BACKGROUND AND AIM

Overdose of acetaminophen (APAP) leads to liver injury, which is one of the most common causes of liver failure in the United States. We previously demonstrated that pharmacological activation of autophagy protects against APAP-induced liver injury in mice via removal of damaged mitochondria and APAP-adducts (APAP-ADs). Using an image-based high-throughput screening for autophagy modulators, we recently identified that chlorpromazine (CPZ), a dopamine inhibitor used for anti-schizophrenia, is a potent autophagy inducer in vitro. Therefore, the aim of the present study is to determine whether CPZ may protect against APAP-induced liver injury via inducing autophagy.

METHODS

Wild type C57BL/6J mice were injected with APAP to induce liver injury. CPZ was administrated either at the same time with APAP (co-treatment) or 2 h later after APAP administration (post-treatment). Hemotoxyline and eosin (H&E) staining of liver histology, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) staining of necrotic cell death as well as serum levels of alanine aminotransferase (ALT) were used to monitor liver injury.

RESULTS

We found that CPZ markedly protected against APAP-induced liver injury as demonstrated by decreased serum levels of ALT, liver necrotic areas as well as TUNEL-positive cells in mice that were either co-treated or post-treated with CPZ. Mechanistically, we observed that CPZ increased the number of autolysosomes and decreased APAP-induced c-Jun N-terminal kinase activation without affecting the metabolic activation of APAP. Pharmacological inhibition of autophagy by chloroquine partially weakened the protective effects of CPZ against APAP-induced liver injury.

CONCLUSIONS

Our results indicate that CPZ ameliorates APAP-induced liver injury partially via activating hepatic autophagy and inhibiting JNK activation.

Polyphenols reported to shift APAP-induced changes in MAPK signaling and toxicity outcomes

Due to its widespread availability, acetaminophen (APAP) is the leading cause for drug-induced liver injury in many countries including United States and United Kingdom. When used as recommended, APAP is relatively safe. However, in overdose cases, increased metabolism of APAP to N-acetyl-para-benzoquinoneimine (NAPQI), a reactive metabolite, leads to glutathione (GSH) depletion, oxidative stress, and cellular injury. Throughout this process, a variety of factors play important roles in propagating toxicity, including c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family. Because of its involvement in multiple cellular processes, biomarkers associated with MAPK signaling have generated interest as a mechanistic target for protecting against APAP-induced liver injury and hepatocellular injury, in general. This review summarizes mechanistic details by which natural products, specifically those containing polyphenolic moieties, are capable of attenuating APAP-induced toxicity, at least in part through an ability to modulate MAPKs. These compounds include carnosic acid, chlorogenic acid, davallialactone, extracts from Hibiscus sabdariffa, quercetin-based compounds, and resveratrol. Despite variations in the experimental designs across these studies, common pathways and biomarkers were implicated in cytoprotection when polyphenolic compounds were given with APAP, such as enhanced antioxidant gene expression and reversal of APAP-induced changes in oxidative stress markers and MAPK signaling. Overall, an emphasis should be placed on method standardization for future studies if we are to gain a more in-depth understanding of how polyphenolic moieties contribute to cytoprotection during an APAP overdose event.

Expression Levels of GABA-A Receptor Subunit Alpha 3, Gabra3 and Lipoprotein Lipase, Lpl Are Associated with the Susceptibility to Acetaminophen-Induced Hepatotoxicity

Drug-induced liver injury (DILI) is the serious and fatal drug-associated adverse effect, but its incidence is very low and individual variation in severity is substantial. Acetaminophen (APAP)-induced liver injury accounts for >50% of reported DILI cases but little is known for the cause of individual variations in the severity. Intrinsic genetic variation is considered a key element but the identity of the genes was not well-established. Here, pre-biopsy method and microarray technique was applied to uncover the key genes for APAP-induced liver injury in mice, and a cause and effect experiment employing quantitative real-time PCR was conducted to confirm the correlation between the uncovered genes and APAP-induced hepatotoxicity. We identified the innately and differentially expressed genes of mice susceptible to APAP-induced hepatotoxicity in the pre-biopsied liver tissue before APAP treatment through microarray analysis of the global gene expression profiles (Affymetrix GeneChip® Mouse Gene 1.0 ST for 28,853 genes). Expression of 16 genes including Gdap10, Lpl, Gabra3 and Ccrn4l were significantly different (t-test: FDR <10%) more than 1.5 fold in the susceptible animals than resistant. To confirm the association with the susceptibility to APAP-induced hepatotoxicity, another set of animals were measured for the expression level of selected 4 genes (higher two and lower two genes) in the liver pre-biopsy and their sensitivity to APAP-induced hepatotoxicity was evaluated by post hoc. Notably, the expressions of Gabra3 and Lpl were significantly correlated with the severity of liver injury (p<0.05) demonstrating that these genes may be linked to the susceptibility to APAP-induced hepatotoxicity.

TAMH: A Useful In Vitro Model for Assessing Hepatotoxic Mechanisms

In vitro models for hepatotoxicity can be useful tools to predict in vivo responses. In this review, we discuss the use of the transforming growth factor-α transgenic mouse hepatocyte (TAMH) cell line, which is an attractive model to study drug-induced liver injury due to its ability to retain a stable phenotype and express drug-metabolizing enzymes. Hepatotoxicity involves damage to the liver and is often associated with chemical exposure. Since the liver is a major site for drug metabolism, drug-induced liver injury is a serious health concern for certain agents. At the molecular level, various mechanisms may protect or harm the liver during drug-induced hepatocellular injury including signaling pathways and endogenous factors (e.g., Bcl-2, GSH, Nrf2, or MAPK). The interplay between these and other pathways in the hepatocyte can change upon drug or drug metabolite exposure leading to intracellular stress and eventually cell death and liver injury. This review focuses on mechanistic studies investigating drug-induced toxicity in the TAMH line and how alterations to hepatotoxic mechanisms in this model relate to the in vivo situation. The agents discussed herein include acetaminophen (APAP), tetrafluoroethylcysteine (TFEC), flutamide, PD0325901, lapatinib, and flupirtine.

Comparative metabonomic analysis of hepatotoxicity induced by acetaminophen and its less toxic meta-isomer

The leading cause of drug-induced liver injury in the developed world is overdose with N-acetyl-p-aminophenol (APAP). A comparative metabonomic approach was applied to the study of both xenobiotic and endogenous metabolic profiles reflective of in vivo exposure to APAP (300 mg/kg) and its structural isomer N-acetyl-m-aminophenol (AMAP; 300 mg/kg) in C57BL/6J mice, which was anchored with histopathology. Liver and urine samples were collected at 1 h, 3 h and 6 h post-treatment and analyzed by ¹H nuclear magnetic resonance (NMR) spectroscopy and gas chromatography–mass spectrometry (liver only). Histopathology revealed the presence of centrilobular necrosis from 3 h post-APAP treatment, while an AMAP-mediated necrotic endpoint was not observed within the timescale of this study, yet two of five treated mice showed minimal centrilobular eosinophilia. The ¹H-NMR xenobiotic metabolic profile of APAP-treated animals comprised of mercapturate (urine and liver) and glutathionyl (liver) conjugates detected at 1 h post-treatment. This finding corroborated the hepatic endogenous metabolic profile which showed depletion of glutathione from 1 h onwards. In contrast, AMAP glutathionyl conjugates were not detected, nor was AMAP-induced depletion of hepatic glutathione observed. APAP administration induced significant endogenous hepatic metabolic perturbations, primarily linked to oxidative and energetic stress, and perturbation of amino acid metabolism. Early depletion of glutathione was followed by depletion of additional sulfur-containing metabolites, while altered levels of mitochondrial and glycolytic metabolites indicated a disruption of energy homeostasis. In contrast, AMAP administration caused minimal, transient, distinct metabolic perturbations and by 6 h the metabolic profiles of AMAP-treated mice were indistinguishable from those of controls.

Altered protein S-glutathionylation identifies a potential mechanism of resistance to acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) is the most commonly used over-the-counter analgesic. However, hepatotoxicity induced by APAP is a major clinical issue, and the factors that define sensitivity to APAP remain unclear. We have previously demonstrated that mice nulled for glutathione S-transferase Pi (GSTP) are resistant to APAP-induced hepatotoxicity. This study aims to exploit this difference to delineate pathways of importance in APAP toxicity. We used mice nulled for GSTP and heme oxygenase-1 oxidative stress reporter mice, together with a novel nanoflow liquid chromatography-tandem mass spectrometry methodology to investigate the role of oxidative stress, cell signaling, and protein S-glutathionylation in APAP hepatotoxicity. We provide evidence that the sensitivity difference between wild-type and Gstp1/2(-/-) mice is unrelated to the ability of APAP to induce oxidative stress, despite observing significant increases in c-Jun N-terminal kinase and extracellular signal-regulated kinase phosphorylation in wild-type mice. The major difference in response to APAP was in the levels of protein S-glutathionylation: Gstp1/2(-/-) mice exhibited a significant increase in the number of S-glutathionylated proteins compared with wild-type animals. Remarkably, these S-glutathionylated proteins are involved in oxidative phosphorylation, respiratory complexes, drug metabolism, and mitochondrial apoptosis. Furthermore, we found that S-glutathionylation of the rate-limiting glutathione-synthesizing enzyme, glutamate cysteine ligase, was markedly increased in Gstp1/2(-/-) mice in response to APAP. The data demonstrate that S-glutathionylation provides an adaptive response to APAP and, as a consequence, suggest that this is an important determinant in APAP hepatotoxicity. This work identifies potential novel avenues associated with cell survival for the treatment of chemical-induced hepatotoxicity.

Mitochondrial protein adducts formation and mitochondrial dysfunction during N-acetyl-m-aminophenol (AMAP)-induced hepatotoxicity in primary human hepatocytes

3'-Hydroxyacetanilide orN-acetyl-meta-aminophenol (AMAP) is generally regarded as a non-hepatotoxic analog of acetaminophen (APAP). Previous studies demonstrated the absence of toxicity after AMAP in mice, hamsters, primary mouse hepatocytes and several cell lines. In contrast, experiments with liver slices suggested that it may be toxic to human hepatocytes; however, the mechanism of toxicity is unclear. To explore this,we treated primary human hepatocytes (PHH) with AMAP or APAP for up to 48 h and measured several parameters to assess metabolism and injury. Although less toxic than APAP, AMAP dose-dependently triggered cell death in PHH as indicated by alanine aminotransferase (ALT) release and propidium iodide (PI) staining. Similar to APAP, AMAP also significantly depleted glutathione (GSH) in PHH and caused mitochondrial damage as indicated by glutamate dehydrogenase (GDH) release and the JC-1 assay. However, unlike APAP, AMAP treatment did not cause relevant c-jun-N-terminal kinase (JNK) activation in the cytosol or phospho-JNK translocation to mitochondria. To compare, AMAP toxicity was assessed in primary mouse hepatocytes (PMH). No cytotoxicity was observed as indicated by the lack of lactate dehydrogenase release and no PI staining. Furthermore, there was no GSH depletion or mitochondrial dysfunction after AMAP treatment in PMH. Immunoblotting for arylated proteins suggested that AMAP treatment caused extensive mitochondrial protein adduct formation in PHH but not in PMH. In conclusion, AMAP is hepatotoxic in PHH and the mechanism involves the formation of mitochondrial protein adducts and mitochondrial dysfunction.

p53 Contributes to Differentiating Gene Expression Following Exposure to Acetaminophen and Its Less Hepatotoxic Regioisomer Both In Vitro and In Vivo

The goal of the present study was to compare hepatic toxicogenomic signatures across in vitro and in vivo mouse models following exposure to acetaminophen (APAP) or its relatively nontoxic regioisomer 3′-hydroxyacetanilide (AMAP). Two different Affymetrix microarray platforms and one Agilent Oligonucleotide microarray were utilized. APAP and AMAP treatments resulted in significant and large changes in gene expression that were quite disparate, and likely related to their different toxicologic profiles. Ten transcripts, all of which have been implicated in p53 signaling, were identified as differentially regulated at all time-points following APAP and AMAP treatments across multiple microarray platforms. Protein-level quantification of p53 activity aligned with results from the transcriptomic analysis, thus supporting the implicated mechanism of APAP-induced toxicity. Therefore, the results of this study provide good evidence that APAP-induced p53 phosphorylation and an altered p53-driven transcriptional response are fundamental steps in APAP-induced toxicity.

Transcriptomic studies on liver toxicity of acetaminophen

Acetaminophen is widely used as a pain reliever and to reduce fever. At high doses, it can cause severe hepatotoxicity. Acetaminophen overdose has become the leading cause of acute liver failure in the US. The mechanisms for acetaminophen-induced liver injury are unclear. Transcriptomic studies can identify the changes in expression of thousands of genes when exposed to supratherapeutic doses of acetaminophen. These studies elucidated the mechanism of acetaminophen-induced hepatotoxicity and also provide insight into future development of diagnosis and treatment options for acetaminophen-induced acute liver failure. The following is a brief overview of some recent transcriptomic studies and gene-expression-based prediction models on liver toxicity induced by acetaminophen.

A new polymorph of metacetamol

The existence of a new polymorph of metacetamol together with its properties are reported for the first time.

Cyclooxygenase inhibitors inhibit antibody response through interference with MAPK/ERK pathways and BLIMP-1 inhibition

Fever is a common symptom of illness in children, and although not harmful in itself, fever and its associated symptoms are often treated with antipyretic drugs. A number of national and other guidelines now recommend against their routine use; a conclusion that was initially supported by a study showing that the prophylactic use of paracetamol might reduce antibody response to some vaccine antigens, although data from booster vaccinations are more equivocal. Although in vivo data on the cause of this inhibition are scarce, in vitro data suggests that the cause may be due to inhibition of the mitogen activated protein kinase/extracellular regulated protein kinase pathways, and a subsequent reduction in the process of plasma cell differentiation at the beginning of the antibody response. This suggests that in high-risk patients these drugs could be avoided in the early part of an infection when plasma-cell differentiation is occurring. More data are needed to define this period; until then existing data support the recommendation against the routine use of these drugs.

Transcriptome correlation analysis identifies two unique craniosynostosis subtypes associated with IRS1 activation

The discovery of causal mechanisms associated with nonsyndromic craniosynostosis has proven to be a difficult task due to the complex nature of the disease. In this study, differential transcriptome correlation analysis was used to identify two molecularly distinct subtypes of nonsyndromic craniosynostosis, termed subtype A and subtype B. In addition to unique correlation structure, subtype A was also associated with high IGF pathway expression, whereas subtype B was associated with high integrin expression. To identify a pathologic link between altered gene correlation/expression and the disease state, phosphorylation assays were performed on primary osteoblast cell lines derived from cases within subtype A or subtype B, as well as on primary osteoblast cell lines with novel IGF1R variants previously reported by our lab (Cunningham ML, Horst JA, Rieder MJ, Hing AV, Stanaway IB, Park SS, Samudrala R, Speltz ML. Am J Med Genet A 155A: 91-97, 2011). Elevated IRS1 (pan-tyr) and GSK3β (ser-9) phosphorylation were observed in two novel IGF1R variants with receptor L domain mutations. In subtype A, a hypomineralization phenotype coupled with decreased phosphorylation of IRS1 (ser-312), p38 (thr-180/tyr-182), and p70S6K (thr-412) was observed. In subtype B, decreased phosphorylation of IRS1 (ser-312) as well as increased phosphorylation of Akt (ser-473), GSK3β (ser-9), IGF1R (tyr-1135/tyr-1136), JNK (thr-183/tyr-187), p70S6K (thr-412), and pRPS6 (ser-235/ser-236) was observed, thus implicating the activation of IRS1-mediated Akt signaling in potentiating craniosynostosis in this subtype. Taken together, these results suggest that despite the stimulation of different pathways, activating phosphorylation patterns for IRS1 were consistent in cell lines from both subtypes and the IGF1R variants, thus implicating a key role for IRS1 in the pathogenesis of nonsyndromic craniosynostosis.

AMAP, the alleged non-toxic isomer of acetaminophen, is toxic in rat and human liver

N-acetyl-meta-aminophenol (AMAP) is generally considered as a non-toxic regioisomer of the well-known hepatotoxicant acetaminophen (APAP). However, so far, AMAP has only been shown to be non-toxic in mice and hamsters. To investigate whether AMAP could also be used as non-toxic analog of APAP in rat and human, the toxicity of APAP and AMAP was tested ex vivo in precision-cut liver slices (PCLS) of mouse, rat and human. Based on ATP content and histomorphology, APAP was more toxic in mouse than in rat and human PCLS. Surprisingly, although AMAP showed a much lower toxicity than APAP in mouse PCLS, AMAP was equally toxic as or even more toxic than APAP at all concentrations tested in both rat and human PCLS. The profile of proteins released into the medium of AMAP-treated rat PCLS was similar to that of APAP, whereas in the medium of mouse PCLS, it was similar to the control. Metabolite profiling indicated that mouse PCLS produced the highest amount of glutathione conjugate of APAP, while no glutathione conjugate of AMAP was detected in all three species. Mouse also produced ten times more hydroquinone metabolites of AMAP, the assumed proximate reactive metabolites, than rat or human. In conclusion, AMAP is toxic in rat and human liver and cannot be used as non-toxic isomer of APAP. The marked species differences in APAP and AMAP toxicity and metabolism underline the importance of using human tissues for better prediction of toxicity in man.

Spred-2 deficiency exacerbates acetaminophen-induced hepatotoxicity in mice

MAPKs are involved in acetaminophen (APAP)-hepatotoxicity, but the regulatory mechanism remains unknown. Here, we explored the role of Spred-2 that negatively regulates Ras/ERK pathway in APAP-hepatotoxicity. Spred-2 knockout (KO) mice demonstrated exacerbated liver injury, an event that was associated with increased numbers of CD4(+) T, CD8(+) T and NK cells in the liver compared to the control. Levels of CXCL9/CXCL10 that attract and activate these cells were increased in Spred-2 KO-liver. Kupffer cells isolated from Spred-2 KO mice after APAP challenge expressed higher levels of CXCL9/CXCL10 than those from the control. Upon stimulation with APAP or IFNγ, naïve Kupffer cells from Spred-2 KO mice expressed higher levels of CXCL9/CXCL10. NK cell-depletion attenuated APAP-hepatotoxicity with lowered hepatic IFNγ and decreased numbers of not only NK cells but also CD4(+) T and CD8(+) T cells in the liver. These results suggest that Spred-2 negatively regulates APAP-hepatotoxicity under the control of Kupffer cells and NK cells.

Acetaminophen overdose-induced liver injury in mice is mediated by peroxynitrite independently of the cyclophilin D-regulated permeability transition

Acetaminophen (APAP) is safe at therapeutic dosage but can cause severe hepatotoxicity if used at overdose. The mechanisms of injury are not yet fully understood, but previous reports had suggested that the mitochondrial permeability transition (mPT) may be involved in triggering hepatocellular necrosis. We aimed at inhibiting mitochondrial cyclophilin D (CypD), a key regulator of the mPT, as a potential therapeutic target in APAP hepatotoxicity. Wildtype mice treated with a high dose of APAP (600 mg/kg, intraperitoneal) developed typical centrilobular necrosis, which could not, however, be prevented by cotreatment with the selective CypD inhibitor, Debio 025 (alisporivir, DEB025, a nonimmunosuppressive cyclosporin A analog). Similarly, genetic ablation of mitochondrial CypD in Ppif-null mice did not afford protection from APAP hepatotoxicity. To determine whether APAP-induced peroxynitrite stress might directly activate mitochondrial permeabilization, independently of the CypD-regulated mPT, we coadministered the peroxynitrite decomposition catalyst Fe-TMPyP (10 mg/kg, intraperitoneal, 90 minutes prior to APAP) to CypD-deficient mice. Liver injury was greatly attenuated by Fe-TMPyP pretreatment, and mitochondrial 3-nitrotyrosine adduct levels (peroxynitrite marker) were decreased. Acetaminophen treatment increased both the cytosolic and mitochondria-associated P-JNK levels, but the c-jun-N-terminal kinase (JNK) signaling inhibitor SP600125 was hepatoprotective in wildtype mice only, indicating that the JNK pathway may not be critically involved in the absence of CypD.

CONCLUSION

These data support the concept that an overdose of APAP results in liver injury that is refractory to pharmacological inhibition or genetic depletion of CypD and that peroxynitrite-mediated cell injury predominates in the absence of CypD.

Proteomic analysis of acetaminophen-induced changes in mitochondrial protein expression using spectral counting

Comparative proteomic analysis following treatment with acetaminophen (APAP) was performed on two different models of APAP-mediated hepatocellular injury in order to both identify common targets for adduct formation and track drug-induced changes in protein expression. Male C57BL/6 mice were used as a model for APAP-mediated liver injury in vivo, and TAMH cells were used as a model for APAP-mediated cytotoxicity in vitro. SEQUEST was unable to identify the precise location of sites of adduction following treatment with APAP in either system. However, semiquantitative analysis of the proteomic data sets using spectral counting revealed a downregulation of P450 isoforms associated with APAP bioactivation and an upregulation of proteins related to the electron transport chain by APAP compared to the control. Both mechanisms are likely compensatory in nature as decreased P450 expression is likely to attenuate toxicity associated with N-acetyl-p-quinoneimine (NAPQI) formation, whereas APAP-induced electron transport chain component upregulation may be an attempt to promote cellular bioenergetics.