Expression profiling of acetaminophen liver toxicity in mice using microarray technology

Multiorgan Metabolomics and Lipidomics Provide New Insights Into Fat Infiltration in the Liver, Muscle Wasting, and Liver-Muscle Crosstalk Following Burn Injury

Burn injury mediated hypermetabolic syndrome leads to increased mortality among severe burn victims, due to liver failure and muscle wasting. Metabolic changes may persist up to 2 years following the injury. Thus, understanding the underlying mechanisms of the pathology is crucially important to develop appropriate therapeutic approaches. We present detailed metabolomic and lipidomic analyses of the liver and muscle tissues in a rat model with a 30% body surface area burn injury located at the dorsal skin. Three hundred and thirty-eight of 1587 detected metabolites and lipids in the liver and 119 of 1504 in the muscle tissue exhibited statistically significant alterations. We observed excessive accumulation of triacylglycerols, decreased levels of S-adenosylmethionine, increased levels of glutamine and xenobiotics in the liver tissue. Additionally, the levels of gluconeogenesis, glycolysis, and tricarboxylic acid cycle metabolites are generally decreased in the liver. On the other hand, burn injury muscle tissue exhibits increased levels of acyl-carnitines, alpha-hydroxyisovalerate, ophthalmate, alpha-hydroxybutyrate, and decreased levels of reduced glutathione. The results of this preliminary study provide compelling observations that liver and muscle tissues undergo distinctly different changes during hypermetabolism, possibly reflecting liver-muscle crosstalk. The liver and muscle tissues might be exacerbating each other's metabolic pathologies, via excessive utilization of certain metabolites produced by each other.

Zebrafish as an integrative vertebrate model to identify miRNA mechanisms regulating toxicity

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Zebrafish are an established vertebrate model for toxicity studies.

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Zebrafish have a fully sequenced genome and the capability to create genetic models.

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Zebrafish have over 80 % homology for genes related to human disease.

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Functions of miRNAs in the zebrafish genome are being characterized.

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Zebrafish are ideal for mechanistic studies on how miRNAs regulate toxicity.

Zebrafish (Danio rerio) are an integrative vertebrate model ideal for toxicity studies. The zebrafish genome is sequenced with detailed characterization of all life stages. With their genetic similarity to humans, zebrafish models are established to study biological processes including development and disease mechanisms for translation to human health. The zebrafish genome, similar to other eukaryotic organisms, contains microRNAs (miRNAs) which function along with other epigenetic mechanisms to regulate gene expression. Studies have now established that exposure to toxins and xenobiotics can change miRNA expression profiles resulting in various physiological and behavioral alterations. In this review, we cover the intersection of miRNA alterations from toxin or xenobiotic exposure with a focus on studies using the zebrafish model system to identify miRNA mechanisms regulating toxicity. Studies to date have addressed exposures to toxins, particulate matter and nanoparticles, various environmental contaminants including pesticides, ethanol, and pharmaceuticals. Current limitations of the completed studies and future directions for this research area are discussed.

Identification of Novel Regulatory Genes in APAP Induced Hepatocyte Toxicity by a Genome-Wide CRISPR-Cas9 Screen

Acetaminophen (APAP) is a commonly used analgesic responsible for more than half of acute liver failure cases. Identification of previously unknown genetic risk factors would provide mechanistic insights and novel therapeutic targets for APAP-induced liver injury. This study used a genome-wide CRISPR-Cas9 screen to evaluate genes that are protective against, or cause susceptibility to, APAP-induced liver injury. HuH7 human hepatocellular carcinoma cells containing CRISPR-Cas9 gene knockouts were treated with 15 mM APAP for 30 minutes to 4 days. A gene expression profile was developed based on the 1) top screening hits, 2) overlap of expression data from APAP overdose studies, and 3) predicted affected biological pathways. We further demonstrated the implementation of intermediate time points for the identification of early and late response genes. This study illustrated the power of a genome-wide CRISPR-Cas9 screen to systematically identify novel genes involved in APAP-induced hepatotoxicity and to provide potential targets to develop novel therapeutic modalities.

SOCS2 Is Critical for the Balancing of Immune Response and Oxidate Stress Protecting Against Acetaminophen-Induced Acute Liver Injury

Acetaminophen (APAP) is usually safe when administrated in therapeutic doses; however, APAP overdose can lead to severe liver injury. APAP can cause direct hepatocyte damage, and stimulates an inflammatory response leading to oxidative stress. Supressor of Cytokine Signaling (SOCS) 2 modulates cytokine and growth factor signaling, and plays a role in the regulation of hepatic cellular processes. Our study evaluated the role of SOCS2 in APAP liver injury. The administration of a toxic dose (600 mg/kg) of APAP caused significant liver necrosis in WT mice. In SOCS2^−/− mice, there was significantly more necrosis, neutrophil recruitment, and expression of the neutrophil-active chemokine CXCL-1. Expression of proinflammatory cytokines, such as TNF-α and IL-6, was elevated, while expression of anti-inflammatory cytokines, IL-10 and TGF-β, was diminished. In vitro, SOCS2^−/− hepatocytes expressed more p-NF-kB and produced more ROS than WT hepatocytes when exposed to APAP. SOCS2^−/− hepatocytes were more sensitive to cell death in the presence of IL-6 and hydrogen peroxide. The administration of catalase in vitro and in vivo resulted in a pronounced reduction of cells/mice death and necrosis in the SOCS2^−/− group. We have demonstrated that SOCS2 has a protective role in the liver by controlling pro-oxidative and inflammatory mechanisms induced by APAP.

Synthesis, characterization and cytotoxicity of boron nitride nanoparticles: emphasis on toxicogenomics

Nanotechnology is increasingly developing area including more than 700 commercial products such as clothing, food preparation, cosmetics, mechanics, electronics and also health industry. People generally contact with nanoparticles by inhaling from air. Thus, it is becoming important issue to understand harmful effects of nanoparticles on human health and prepare risk reports for common nano-sized materials. In this paper, synthesis, characterization and cytotoxicity evaluation of boron nitride (BN) nanoparticles were performed on human primary alveolar epithelial cells (HPAEpiC) since, main exposure to nanoparticles would generally happen through lung via inhalation. Chemically synthetized BN nanoparticles were characterized by using X-ray crystallography, transmission electron microscope, scanning electron microscope and energy-dispersive X-ray spectroscopy techniques. 3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide, neutral red and lactate dehydrogenase release assays were used to analyze cytotoxicity after nanoparticles exposure. Whole genome microarray analysis was used to find out the effects of BN NPs on gene expressions of HPAEpiC cells. Finally, the database for annotation, visualization and integrated discovery analysis was used to reveal relationships between different cellular pathways and nanoparticle exposure. According to cytotoxicity analysis LC₂₀ value for BN nanoparticles was 125.051 mg/L. Microarray results showed that 2159 genes expression change (FC ≥ 2) significantly over 40,000 genes analysis. When the gene pathways were analyzed, it was seemed that BN nanoparticles mostly affect cell cycle, cell-cell interactions, cancer affecting genes and signal transduction. In a conclusion, our results supported for the first time that BN nanoparticles could be used as a safe nanomaterial in both pharmacological and medical applications.

Liquid chromatography mass spectrometry-based profiling of phosphatidylcholine and phosphatidylethanolamine in the plasma and liver of acetaminophen-induced liver injured mice

Background

Acetaminophen (APAP) overdose is one of the most common causes of acute liver failure in many countries. The aim of the study was to describe the profiling of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in the plasma and liver of Acetaminophen -induced liver injured mice.

Methods

A time course study was carried out using C57BL/6 mice after intraperitoneal administration of 300 mg/kg Acetaminophen 1 h, 3 h, 6 h, 12 h and 24 h. A high-throughput liquid chromatography mass spectrometry (LC-MS) lipidomic method was utilized to detect phosphatidylcholine and phosphatidylethanolamine species in the plasma and liver. The expressions of phosphatidylcholine and phosphatidylethanolamine metabolism related genes in liver were detected by quantitative Reverse transcription polymerase chain reaction (qRT-PCR) and Western-blot.

Results

Following Acetaminophen treatment, the content of many PC and PE species in plasma increased from 1 h time point, peaked at 3 h or 6 h, and tended to return to baseline at 24 h time point. The relative contents of almost all PC species in liver decreased from 1 h, appeared to be lowest at 6 h, and then return to normality at 24 h, which might be partly explained by the suppression of phospholipases mRNA expressions and the induction of choline kinase (Chka) expression. Inconsistent with PC profile, the relative contents of many PE species in liver increased upon Acetaminophen treatment, which might be caused by the down-regulation of phosphatidylethanolamine N-methyltransferase (Pemt).

Conclusions

Acetaminophen overdose induced dramatic change of many PC and PE species in plasma and liver, which might be caused by damaging hepatocytes and interfering the phospholipid metabolism in Acetaminophen -injured liver.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0540-4) contains supplementary material, which is available to authorized users.

Transcriptome analysis of the brain of the sea bream (Sparus aurata) after exposure to human pharmaceuticals at realistic environmental concentrations

Human pharmaceuticals such as Acetaminophen, Atenolol and Carbamazepine are pseudo persistent aquatic pollutants with yet unknown sub-lethal effects at environmentally relevant concentrations. Gilthead seabream (Sparus aurata) were exposed to Acetaminophen: 31.90 ± 11.07 μg L^-1; Atenolol: 0.95 ± 0.38 μg L^-1 and Carbamazepine: 6.95 ± 0.13 μg L^-1 in a 28 day flow through experiment to (1) determine whether exposure to low concentrations in the μg·L^-1 range of the pharmaceuticals alters the brain transcriptome and, (2) identify different expression profiles and treatment specific modes of action and pathways. Despite low exposure concentrations, 411, 7 and 612 differently expressed transcripts were identified in the individual treatments with Acetaminophen, Atenolol and Carbamazepine, respectively. Functional analyses of differentially expressed genes revealed a significant over representation of several biological processes, cellular compartment features and molecular functions for both Acetaminophen and Carbamazepine treatments. Overall, the results obtained in seabream brain suggest similar physiological responses to those observed in humans also at environmental concentrations, as well as the existence of treatment specific processes that may be useful for the development of biomarkers of contamination.

In vivo imaging of leucine aminopeptidase activity in drug-induced liver injury and liver cancer via a near-infrared fluorescent probe

The liver, a main detoxification organ, has evolved a complex enzymatic system to respond to multiple pathological conditions, in which leucine aminopeptidase (LAP) has been reported to participate in detoxifying cisplatin in hepatoma cells and contribute to the intrinsic drug resistance. In vivo imaging of LAP activity in liver disease models is thus helpful to further understand the function of LAP in detoxification and medicine, but such an imaging approach is still lacking. Herein, we develop a selective and sensitive near-infrared fluorescent probe (HCAL) for this purpose. Using the probe, combined with confocal fluorescence imaging, we disclose the upregulations of LAP in acetaminophen-induced liver injury and tumor-bearing mice models. Supplementary acetylcysteine can suppress this upregulation, revealing that the LAP increase may be connected with a deficiency in biothiols. Moreover, HCAL has been used to image LAP in hepatoma cells, tumor tissues and xenograft tumor mice models successfully. These results demonstrate that HCAL may be a promising tool for studying the function of LAP in LAP-associated liver diseases.

Microvesicular Steatosis Induced by a Short Chain Fatty Acid: Effects on Mitochondrial Function and Correlation with Gene Expression

Hepatotoxicity characterized by microvesicular steatosis (MVS) is characterized by an abnormal accumulation of numerous small cytoplasmic lipid droplets in hepatocytes. Fulminant or progressive cases of microvesicular steatosis may lead to liver failure and death. Experimentally, short-chain carboxylic acids are known to induce microvesicular steatosis. The identification of gene changes that correlate with MVS concomitant with biochemical and histological indices could provide a better understanding of how this toxicity occurs as well as biomarkers that could be used to avoid this toxicity in the future. Sprague—Dawley rats were dosed days with cyclopropane carboxylic acid (CPCA) a short-chain fatty acid that can induce microvesicular steatosis, and with butyrate, a short chain fatty acid that served as a negative control. CPCA initiated microvesicular steatosis while butyrate did not. In addition, CPCA inhibited beta-oxidation in a concentration-dependent manner in vitro and caused a reduction in mitochondrial respiration ex vivo; no inhibition was evident with butyrate. Microarray results showed that gene expression changes with CPCA resulted in regulation of genes involved in beta-oxidation, as well as other genes associated with mitochondrial function. Overall, these results support altered hepatic mitochondrial function as a mechanism of the toxicity induced by a short-chain fatty acid and may provide potential biomarkers for this toxicity.

Translational biomarkers of acetaminophen-induced acute liver injury

Acetaminophen (APAP) is a commonly used analgesic drug that can cause liver injury, liver necrosis and liver failure. APAP-induced liver injury is associated with glutathione depletion, the formation of APAP protein adducts, the generation of reactive oxygen and nitrogen species and mitochondrial injury. The systems biology omics technologies (transcriptomics, proteomics and metabolomics) have been used to discover potential translational biomarkers of liver injury. The following review provides a summary of the systems biology discovery process, analytical validation of biomarkers and translation of omics biomarkers from the nonclinical to clinical setting in APAP-induced liver injury.

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.

Establishment of a model of acetaminophen-induced hepatotoxicity in different weekly-aged ICR mice

Acetaminophen (APAP), a widely used analgesic and antipyretic drug, has the potential to cause lethal hepatotoxicity. Mice are widely used for developing murine models of APAP-induced hepatotoxicity, and many researchers have used these models for APAP-related studies including the fields of biology, pharmacology and toxicology. Although drug-induced hepatotoxicity is dependent on a number of factors (species, gender and age), very few studies have investigated the effect of aging on APAP hepatotoxicity. In this study, we evaluated the effect of age on APAP-induced hepatotoxicity in different weekly-aged mice to establish a model of APAP-induced hepatotoxicity that is an accurate reflection of general experimental conditions. Male ICR mice 4, 6, 8, 10 and 12 weeks old were given APAP intraperitoneally, and mortality, hepatic damage and the plasma concentration of APAP metabolites were evaluated. It was found that younger male ICR mice were relatively resistant to hepatotoxicity induced by intraperitoneal APAP administration. In addition, the APAP-glucuronide concentration in plasma remained essentially the same among the differently-aged mice, while APAP-sulfate levels were dramatically decreased in an age-dependent manner. Thus, it is recommended that mice of the same ages be used in studies related to APAP-induced hepatotoxixity. These results provide evidence in support of not only the age-related changes in susceptibility to APAP-derived hepatotoxicity in mice but also in developing mouse models for APAP-related studies.

Transcriptomics of Hepatocytes Treated with Toxicants for Investigating Molecular Mechanisms Underlying Hepatotoxicity

Transcriptomics is a powerful tool for high-throughput gene expression profiling. Transcriptome microarray experiments conducted with RNA isolated from hepatocytes after exposure to toxicants enable a deep insight into the molecular mechanisms of hepatotoxicity. This understanding, along with structure-activity relationships underlying hepatotoxicity, will provide a novel strategy to design cost-effective and safer therapeutics. Transcriptomics studies conducted with established hepatotoxic drugs in various in vitro and in vivo hepatotoxicity test systems have contributed to the elucidation of the mechanistic basis of liver insults, which were later on substantiated at the proteomics and metabolomics levels. The present chapter is focused on comprehensive transcriptomics of cultured primary hepatocytes treated with chemicals by applying Affymetrix microarray technology. It also describes the detailed protocol for culturing of hepatocytes, their exposure to toxicants as well as sample collection, including RNA isolation, RNA target preparation and finally the hybridization to gene chips for microarray expression analysis.

Hepatic proteome analysis of Atlantic salmon (Salmo salar) after exposure to environmental concentrations of human pharmaceuticals

Pharmaceuticals are pseudopersistent aquatic pollutants with unknown effects at environmentally relevant concentrations. Atlantic salmon (Salmo salar) were exposed to Acetaminophen: 54.77 ± 34.67; Atenolol: 11.08 ± 7.98, and Carbamazepine: 7.85 ± 0.13 μg·L(-1) for 5 days. After Acetaminophen treatment, 19 proteins were differently expressed, of which 11 were significant with respect to the control group (eight up-regulated and three down-regulated). After Atenolol treatment, seven differently expressed proteins were obtained in comparison with the control, of which six could be identified (four up-regulated and two down-regulated). Carbamazepine exposure resulted in 15 differently expressed proteins compared with the control, with 10 of them identified (seven up-regulated and three down-regulated). Out of these, three features were common between Acetaminophen and Carbamazepine and one between Carbamazepine and Atenolol. One feature was common across all treatments. Principal component analysis and heat map clustering showed a clear grouping of the variability caused by the applied treatments. The obtained data suggest (1) that exposure to environmentally relevant concentrations of the pharmaceuticals alters the hepatic protein expression profile of the Atlantic salmon; and (2) the existence of treatment specific processes that may be useful for biomarker development.

A Txnrd1-dependent metabolic switch alters hepatic lipogenesis, glycogen storage, and detoxification

Besides helping to maintain a reducing intracellular environment, the thioredoxin (Trx) system impacts bioenergetics and drug metabolism. We show that hepatocyte-specific disruption of Txnrd1, encoding Trx reductase-1 (TrxR1), causes a metabolic switch in which lipogenic genes are repressed and periportal hepatocytes become engorged with glycogen. These livers also overexpress machinery for biosynthesis of glutathione and conversion of glycogen into UDP-glucuronate; they stockpile glutathione-S-transferases and UDP-glucuronyl-transferases; and they overexpress xenobiotic exporters. This realigned metabolic profile suggested that the mutant hepatocytes might be preconditioned to more effectively detoxify certain xenobiotic challenges. Hepatocytes convert the pro-toxin acetaminophen (APAP, paracetamol) into cytotoxic N-acetyl-p-benzoquinone imine (NAPQI). APAP defenses include glucuronidation of APAP or glutathionylation of NAPQI, allowing removal by xenobiotic exporters. We found that NAPQI directly inactivates TrxR1, yet Txnrd1-null livers were resistant to APAP-induced hepatotoxicity. Txnrd1-null livers did not have more effective gene expression responses to APAP challenge; however, their constitutive metabolic state supported more robust GSH biosynthesis, glutathionylation, and glucuronidation systems. Following APAP challenge, this effectively sustained the GSH system and attenuated damage.

Acetaminophen induced cytotoxicity and altered gene expression in cultured cardiomyocytes of h(9)c(2) cells

OBJECTIVES

Hepatotoxicity of acetaminophen has been widely studied. However, the adverse effects on the heart have not been sufficiently evaluated. This study was performed to investigate cytotoxicity and alterations of gene expression in cultured cardiomyocytes (H(9)C(2) cells) after exposure to acetaminophen.

METHODS

H(9)C(2) cells were incubated in a 10 mM concentration of acetaminophen for the designated times (6, 12, and 24 hours), and cytotoxicity was determined by the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. Alteration of gene expression was observed by microarray analysis, and RT-PCR was performed for the three representative oxidative stress-related genes at 24 hours after treatment.

RESULTS

It revealed that acetaminophen was toxic to cardiomyocytes, and numerous critical genes were affected. Induced genes included those associated with oxidative stress, DNA damage, and apoptosis. Repressed genes included those associated with cell proliferation, myocardial contraction, and cell shape control.

CONCLUSIONS

These findings provide the evidences of acetaminophen-induced cytotoxicity and changes in gene expression in cultured cardiomyocytes of H(9)C(2) cells.

Fibrin(ogen)-independent role of plasminogen activators in acetaminophen-induced liver injury

Hepatic fibrin(ogen) has been noted to occur after acetaminophen (APAP)-induced liver injury in mice. Deficiency in plasminogen activator inhibitor-1 (PAI-1), an endogenous inhibitor of fibrinolysis, increases APAP-induced liver injury in mice. However, the roles of fibrinogen and fibrinolysis in APAP-induced liver injury are not known. We tested the hypothesis that hepatic fibrin(ogen) deposition reduces severity of APAP-induced liver injury. APAP-induced (300 mg/kg) liver injury in mice was accompanied by thrombin generation, consumption of plasma fibrinogen, and deposition of hepatic fibrin. Neither fibrinogen depletion with ancrod nor complete fibrinogen deficiency [via knockout of the fibrinogen alpha chain gene (Fbg(-/-))] affected APAP-induced liver injury. PAI-1 deficiency (PAI-1(-/-)) increased APAP-induced liver injury and hepatic fibrin deposition 6 hours after APAP administration, which was followed by marked hemorrhage at 24 hours. As in PAI-1(-/-) mice, administration of recombinant tissue plasminogen activator (tenecteplase, 5 mg/kg) worsened APAP-induced liver injury and hemorrhage in wild-type mice. In contrast, APAP-induced liver injury was reduced in both plasminogen-deficient mice and in wild-type mice treated with tranexamic acid, an inhibitor of plasminogen activation. Activation of matrix metalloproteinase 9 (MMP-9) paralleled injury, but MMP-9 deficiency did not affect APAP-induced liver injury. The results indicate that fibrin(ogen) does not contribute to development of APAP-induced liver injury and suggest rather that plasminogen activation contributes to APAP-induced liver injury.

Gene expression in rat hearts following oral administration of a single hepatotoxic dose of acetaminophen

PURPOSE

Toxicity caused by acetaminophen and its toxic mechanisms in the liver have been widely studied, including effects involving metabolism and oxidative stress. However, its adverse effects on heart have not been sufficiently investigated. This study evaluated the cardiac influence and molecular events occurring within the myocardium in rats treated with a dose of acetaminophen large enough to induce conventional liver damage.

MATERIALS AND METHODS

Male rats were orally administered a single dose of acetaminophen at 1,000 mg/kg-body weight, and subsequently examined for conventional toxicological parameters and for gene expression alterations to both the heart and liver 24 hours after administration.

RESULTS

Following treatment, serum biochemical parameters including aspartate aminotransferase and alanine aminotransferase were elevated. Histopathological alterations of necrosis were observed in the liver, but not in the heart. However, alterations in gene expression were observed in both the liver and heart 24 hours after dosing. Transcriptional profiling revealed that acetaminophen changed the expression of genes implicated in oxidative stress, inflammatory processes, and apoptosis in the heart as well as in the liver. The numbers of up-regulated and down-regulated genes in the heart were 271 and 81, respectively, based on a two-fold criterion.

CONCLUSION

The induced expression of genes implicated in oxidative stress and inflammatory processes in the myocardium reflects molecular levels of injury caused by acetaminophen (APAP), which could not be identified by conventional histopathology.

Up-regulation of the lysyl hydroxylase 2 gene by acetaminophen and isoniazid is modulated by transcription factor c-Myb

OBJECTIVES

Lysyl hydroxylase 2 (LH2), an isoform of hydroxylase, catalyses the hydroxylation of lysine residues in the telopeptide of collagen to form stable and irreversible cross-linkages in collagen. Increased activity of this enzyme in activated stellate cells in human liver has been proposed to relate to the promotion of hepatic fibrosis. In the present study, we examined the regulation of LH2 expression in drug-induced liver injury in order to clarify the mechanisms behind the hepatic fibrosis caused by certain drugs.

METHODS

The mRNA and protein expression of the target gene were detected by real-time reverse transcription-polymerase chain reaction (RT-PCR) with specific primers and Western blotting with a specific antibody, respectively.

KEY FINDINGS

The expression of LH2 was increased in HepG2 cells incubated with acetaminophen and isoniazid. This increase was accompanied by an increase in the expression of c-myeloblastosis viral oncogene homolog (Myb) mRNA. Over-expression of c-Myb in cells transfected with a c-Myb expression plasmid, pMbm I, caused an increase in the expression of LH2 mRNA. Mutation of the Myb-binding site in the promoter region of the LH2 gene resulted in a loss of transcriptional activation in the reporter gene assay.

CONCLUSIONS

These results suggest that c-Myb modulates the expression of the LH2 gene in HepG2 cells incubated with drugs causing hepatic fibrosis.

Application of toxicogenomics in hepatic systems toxicology for risk assessment: acetaminophen as a case study

Hepatic systems toxicology is the integrative analysis of toxicogenomic technologies, e.g., transcriptomics, proteomics, and metabolomics, in combination with traditional toxicology measures to improve the understanding of mechanisms of hepatotoxic action. Hepatic toxicology studies that have employed toxicogenomic technologies to date have already provided a proof of principle for the value of hepatic systems toxicology in hazard identification. In the present review, acetaminophen is used as a model compound to discuss the application of toxicogenomics in hepatic systems toxicology for its potential role in the risk assessment process, to progress from hazard identification towards hazard characterization. The toxicogenomics-based parallelogram is used to identify current achievements and limitations of acetaminophen toxicogenomic in vivo and in vitro studies for in vitro-to-in vivo and interspecies comparisons, with the ultimate aim to extrapolate animal studies to humans in vivo. This article provides a model for comparison of more species and more in vitro models enhancing the robustness of common toxicogenomic responses and their relevance to human risk assessment. To progress to quantitative dose-response analysis needed for hazard characterization, in hepatic systems toxicology studies, generation of toxicogenomic data of multiple doses/concentrations and time points is required. Newly developed bioinformatics tools for quantitative analysis of toxicogenomic data can aid in the elucidation of dose-responsive effects. The challenge herein is to assess which toxicogenomic responses are relevant for induction of the apical effect and whether perturbations are sufficient for the induction of downstream events, eventually causing toxicity.

Validation of reference gene stability for APAP hepatotoxicity studies in different in vitro systems and identification of novel potential toxicity biomarkers

Liver cell lines and primary hepatocytes are becoming increasingly valuable for in vitro toxicogenomic studies, with RT-qPCR enabling the analysis of gene expression profiles following exposure to potential hepatotoxicants. Supporting the accurate normalisation of RT-qPCR data requires the identification of reference genes which have stable expression during in vitro toxicology studies. Therefore, we performed a comprehensive analysis of reference gene stability in two routinely used cell types, (HepG2 cells and primary rat hepatocytes), and two in vitro culture systems, (2D monolayer and 3D scaffolds). A robust reference gene validation strategy was performed, consisting of geNorm analysis, to test for pair wise variation in gene expression, and statistical analysis using analysis of variance. This strategy identified stable reference genes with respect to acetaminophen treatment and time in HepG2 cells (GAPDH and PPIA), and with respect to acetaminophen treatment and culture condition in primary hepatocytes (18S rRNA and α-tubulin). Following the selection of reference genes, the novel target genes E2F7 and IL-11RA were identified as potential toxicity biomarkers for acetaminophen treatment. We conclude that accurate quantification of gene expression requires the use of a validated normalisation strategy for each species and experimental system employed.

Use of transcriptomics in understanding mechanisms of drug-induced toxicity

Adverse drug reactions (ADRs) are an important clinical issue and a serious public health risk. Understanding the underlying mechanisms is critical for clinical diagnosis and management of different ADRs. Toxicogenomics can reveal impacts on biological pathways and processes that had not previously been considered to be involved in a drug response. Mechanistic hypotheses can be generated that can then be experimentally tested using the full arsenal of pharmacology, toxicology, molecular biology and genetics. Recent transcriptomic studies on drug-induced toxicity, which have provided valuable mechanistic insights into various ADRs, have been reviewed with a focus on nephrotoxicity and hepatotoxicity. Related issues have been discussed, including extrapolation of mechanistic findings from experimental model systems to humans using blood as a surrogate tissue for organ damage and comparative systems biology approaches.

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

Acetaminophen (APAP), a widely used analgesic and antipyretic that is considered to be relatively safe at recommended doses, is the leading cause of drug-induced liver failure in the United States. 3'-Hydroxyacetanilide (AMAP), a regioisomer of APAP, is useful as a comparative tool for studying APAP-induced toxicity because it is nontoxic relative to APAP. Transforming growth factor-alpha transgenic mouse hepatocytes were treated with both isomers to investigate mitogen-activated protein kinase (MAPK) cascades in order to differentiate their toxicological outcomes. Posttranslational modifications of MAPK signaling were assessed using immunoblotting and Bioplex technology, whereas gene expression changes were measured using Affymetrix Mouse Gene 1.0 ST arrays. APAP treatment led to higher levels of glutathione depletion at 6 and 24 h compared with AMAP in mitochondria. Glutathione depletion was preceded by increased levels of c-Jun N-terminal kinase (JNK) phosphorylation at 2 and 6 h after APAP treatment compared with AMAP, whereas AMAP treatment led to increased extracellular signal-regulated protein kinase (ERK) phosphorylation at 2 and 6 h compared with APAP. Furthermore, APAP treatment significantly upregulated jun oncogene (c-Jun) gene expression, which was confirmed by Western blotting for both the phosphorylated and the nonphosphorylated forms of c-Jun protein. Transfection with JNK siRNA attenuated APAP toxicity after 24 h, suggesting that higher levels of APAP-induced activation of JNK were related to higher rates of cell death. In summary, genomic regulation of MAPK-related transcription factors coupled with posttranslational activation of their upstream kinases is critical in differentiating the toxicities of APAP and AMAP.

Acute exposure to ozone exacerbates acetaminophen-induced liver injury in mice

Ozone (O(3)), an oxidant air pollutant in photochemical smog, principally targets epithelial cells lining the respiratory tract. However, changes in gene expression have also been reported in livers of O(3)-exposed mice. The principal aim of the present study was to determine if acute exposure to environmentally relevant concentrations of O(3) could cause exacerbation of drug-induced liver injury in mice. Overdose with acetaminophen (APAP) is the most common cause of drug-induced liver injury in developed countries. In the present study, we examined the hepatic effects of acute O(3) exposure in mice pretreated with a hepatotoxic dose of APAP. C57BL/6 male mice were fasted overnight and then given APAP (300 mg/kg ip) or saline vehicle (0 mg/kg APAP). Two hours later, mice were exposed to 0, 0.25, or 0.5 ppm O(3) for 6 h and then sacrificed 9 or 32 h after APAP administration (1 or 24 h after O(3) exposure, respectively). Animals euthanized at 32 h were given 5-bromo-2-deoxyuridine 2 h before sacrifice to identify hepatocytes undergoing reparative DNA synthesis. Saline-treated mice exposed to either air or O(3) had no liver injury. All APAP-treated mice developed marked centrilobular hepatocellular necrosis that increased in severity with time after APAP exposure. O(3) exposure increased the severity of APAP-induced liver injury as indicated by an increase in necrotic hepatic tissue and plasma alanine aminotransferase activity. O(3) also caused an increase in neutrophil accumulation in livers of APAP-treated animals. APAP induced a 10-fold increase in the number of bromodeoxyuridine-labeled hepatocytes that was markedly attenuated by O(3) exposure. Gene expression analysis 9 h after APAP revealed differential expression of genes involved in inflammation, oxidative stress, and cellular regeneration in mice treated with APAP and O(3) compared to APAP or O(3) alone, providing some indications of the mechanisms behind the APAP and O(3) potentiation. These results suggest that acute exposure to near ambient concentrations of this oxidant air pollutant may exacerbate drug-induced liver injury by delaying hepatic repair.

An integrative genomic analysis identifies Bhmt2 as a diet-dependent genetic factor protecting against acetaminophen-induced liver toxicity

Acetaminophen-induced liver toxicity is the most frequent precipitating cause of acute liver failure and liver transplant, but contemporary medical practice has mainly focused on patient management after a liver injury has been induced. An integrative genetic, transcriptional, and two-dimensional NMR-based metabolomic analysis performed using multiple inbred mouse strains, along with knowledge-based filtering of these data, identified betaine-homocysteine methyltransferase 2 (Bhmt2) as a diet-dependent genetic factor that affected susceptibility to acetaminophen-induced liver toxicity in mice. Through an effect on methionine and glutathione biosynthesis, Bhmt2 could utilize its substrate (S-methylmethionine [SMM]) to confer protection against acetaminophen-induced injury in vivo. Since SMM is only synthesized in plants, Bhmt2 exerts its beneficial effect in a diet-dependent manner. Identification of Bhmt2 and the affected biosynthetic pathway demonstrates how a novel method of integrative genomic analysis in mice can provide a unique and clinically applicable approach to a major public health problem.

Simultaneous application of t-test and fold change criteria to identify acetaminophen and carbon tetrachloride affected genes in mice liver

t-Test and fold change criteria were employed simultaneously following acute exposure to acetaminophen and carbon tetrachloride to provide high statistical confidence in the identification of affected genes in mice livers. Furthermore, gene expression data was also investigated with either t-test or fold change criteria alone. Gene expression studies were also accompanied by liver histological and serum biochemical studies for toxicity evaluation. We identified a large number of affected genes using both filtering criteria (p<0.01 and twofold) simultaneously following both the hepatotoxicants. In some cases gene expression studies provided the earliest evidence of tissue response in the absence of traditional markers at histological and biochemical level. We conclude that simultaneous application of t-test and fold change criteria helps to identify important genes with greater statistical confidence than the use of either of them alone, however, this approach results in the reduction of identified probes. Thus, data analysis at different statistical stringencies is needed to know exact outcome of any toxicological event.

Application of stable isotope-labeled compounds in metabolism and in metabolism-mediated toxicity studies

Stable isotope-labeled compounds have been synthesized and utilized by scientists from various areas of biomedical research during the last several decades. Compounds labeled with stable isotopes, such as deuterium and carbon-13, have been used effectively by drug metabolism scientists and toxicologists to gain better understanding of drugs' disposition and their potential role in target organ toxicities. The combination of stable isotope-labeling techniques with mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, which allows rapid acquisition and interpretation of data, has promoted greater use of these stable isotope-labeled compounds in absorption, distribution, metabolism, and excretion (ADME) studies. Examples of the use of stable isotope-labeled compounds in elucidating structures of metabolites and delineating complex metabolic pathways are presented in this review. The application of labeled compounds in mechanistic toxicity studies will be discussed by providing an example of how strategic placement of a deuterium atom in a drug molecule mitigated specific-specific renal toxicity. Other examples from the literature demonstrating the application of stable isotope-labeled compounds in understanding metabolism-mediated toxicities are presented. Furthermore, an example of how a stable isotope-labeled compound was utilized to better understand some of the gene changes in toxicogenomic studies is discussed. The interpretation of large sets of data produced from toxicogenomics studies can be a challenge. One approach that could be used to simplify interpretation of the data, especially from studies designed to link gene changes with the formation of reactive metabolites thought to be responsible for toxicities, is through the use of stable isotope-labeled compounds. This is a relatively unexplored territory and needs to be further investigated. The employment of analytical techniques, especially mass spectrometry and NMR, used in conjunction with stable isotope-labeled compounds to establish and understand mechanistic link between reactive metabolite formation, genomic, and proteomic changes and onset of toxicity is proposed. The use of stable isotope-labeled compounds in early human ADME studies as a way of identifying and possibly quantifying all drug-related components present in systemic circulation is suggested.

Neuroinflammatory response to lipopolysaccharide is exacerbated in mice genetically deficient in cyclooxygenase-2

Background

Cyclooxygenases (COX) -1 and -2 are key mediators of the inflammatory response in the central nervous system. Since COX-2 is inducible by inflammatory stimuli, it has been traditionally considered as the most appropriate target for anti-inflammatory drugs. However, the specific roles of COX-1 and COX-2 in modulating a neuroinflammatory response are unclear. Recently, we demonstrated that COX-1 deficient mice show decreased neuroinflammatory response and neuronal damage in response to lipopolysaccharide (LPS).

Methods

In this study, we investigated the role of COX-2 in the neuroinflammatory response to intracerebroventricular-injected LPS (5 μg), a model of direct activation of innate immunity, using COX-2 deficient (COX-2^-/-) and wild type (COX-2^+/+) mice, as well as COX-2^+/+ mice pretreated for 6 weeks with celecoxib, a COX-2 selective inhibitor.

Results

Twenty-four hours after LPS injection, COX-2^-/- mice showed increased neuronal damage, glial cell activation, mRNA and protein expression of markers of inflammation and oxidative stress, such as cytokines, chemokines, iNOS and NADPH oxidase. Brain protein levels of IL-1β, NADPH oxidase subunit p67^phox, and phosphorylated-signal transducer and activator of transcription 3 (STAT3) were higher in COX-2^-/- and in celecoxib-treated mice, compared to COX-2^+/+ mice. The increased neuroinflammatory response in COX-2^-/- mice was likely mediated by the upregulation of STAT3 and suppressor of cytokine signaling 3 (SOCS3).

Conclusion

These results show that inhibiting COX-2 activity can exacerbate the inflammatory response to LPS, possibly by increasing glial cells activation and upregulating the STAT3 and SOCS3 pathways in the brain.

Plasminogen activator inhibitor-1 limits liver injury and facilitates regeneration after acetaminophen overdose

Deficiency in plasminogen activator inhibitor-1 (PAI-1) gene expression is known to promote growth factor activation and regeneration in a number of hepatotoxicity models. To evaluate if PAI-1 has similar effects in acetaminophen (APAP) hepatotoxicity, wild-type (WT) and PAI-1 gene knockout mice (PAI-KO) were treated with 200 mg/kg APAP and liver injury and its repair were assessed. In WT animals, plasma alanine aminotransferase (ALT) activities increased during the first 12 h and then returned to baseline within 48 h. The area of necrosis increased in parallel to the ALT values, peaked between 12 and 24 h and was completely resolved by 96 h. The regenerative response of cells outside the necrotic area, as indicated by proliferating cell nuclear antigen protein and cyclin D(1) gene expression, was observed within 24 h, peaked at 48 h and then declined but remained elevated until 96 h. Liver injury in response to APAP was similar in PAI-KO as in WT animals during the first 12 h. However, plasma ALT values and the area of necrosis further increased during the following 12 h with development of massive intrahepatic hemorrhage. Approximately, 50% of the PAI-KO animals did not survive. Although liver injury of the surviving animals was repaired, the regeneration process was delayed until 48 h. A potential reason for this delay may have been due to the more severe injury and/or the increased expression of the cell cycle inhibitor p21. Our data indicate that PAI activation limits liver injury and mortality during APAP hepatotoxicity by preventing excessive hemorrhage and thereby facilitating tissue repair.

Role of the coagulation system in acetaminophen-induced hepatotoxicity in mice

Acetaminophen (N-acetyl-p-aminophenol [APAP]) is one of the leading causes of acute liver failure, and APAP hepatotoxicity is associated with coagulopathy in humans. We tested the hypothesis that activation of the coagulation system and downstream protease-activated receptor (PAR)-1 signaling contribute to APAP-induced liver injury. Fasted C57BL/J6 mice were treated with either saline or APAP (400 mg/kg intraperitoneally) and were euthanized 0.5-24 hours later. Hepatotoxicity and coagulation system activation occurred by 2 hours after administration of APAP. Treatment with APAP also caused a rapid and transient increase in liver procoagulant activity. In addition, significant deposition of fibrin was observed in the liver by 2 hours, and the concentration of plasminogen activator inhibitor-1 in plasma increased between 2 and 6 hours. Pretreatment with heparin attenuated the APAP-induced activation of the coagulation system and hepatocellular injury and diminished hepatic fibrin deposition at 6 hours. Loss of hepatocellular glutathione was similar in APAP-treated mice pretreated with saline or heparin, suggesting that heparin did not diminish bioactivation of APAP. In mice deficient in tissue factor, the principal cellular activator of coagulation, APAP-induced liver injury, activation of coagulation, and hepatic fibrin deposition were reduced at 6 hours. Formation of the tissue factor-factor VIIa complex leads to the generation of thrombin that can activate cells through cleavage of PAR-1. Mice lacking PAR-1 developed less injury and hepatic fibrin deposits at 6 hours in response to APAP than control mice.

CONCLUSION

Activation of the coagulation system and PAR-1 signaling contribute significantly to APAP-induced liver injury.

Toxicogenomics: a pivotal piece in the puzzle of toxicological research

Toxicogenomics, resulting from the merge of conventional toxicology with functional genomics, being the scientific field studying the complex interactions between the cellular genome, toxic agents in the environment, organ dysfunction and disease state. When an organism is exposed to a toxic agent the cells respond by altering the pattern of gene expression. Genes are transcribed into mRNA, which in turn is translated into proteins that serve in a variety of cellular functions. Toxicogenomics through microarray technology, offers large-scale detection and quantification of mRNA transcripts, related to alterations in mRNA stability or gene regulation. This may prove advantageous in toxicological research. In the present review, the applications of toxicogenomics, especially to mechanistic and predictive toxicology are reported. The limitations arising from the use of this technology are also discussed. Additionally, a brief report of other approaches, using other -omic technologies (proteomics and metabonomics) that overcome limitations and give global information related to toxicity, is included.

Toxicogenomics applied to predictive and exploratory toxicology for the safety assessment of new chemical entities: a long road with deep potholes

Toxicology is the perturbation of metabolism by external factors such as xenobiotics, environmental factors or drugs. As such, toxicology covers a broad range of fields from studies of the whole organism responses to minute biochemical events. Mechanistic toxicogenomics is an attempt to harness genomic tools to understand the physiological basis for a toxic event based on an analysis of transcriptional, translational or metabolomic profiles. These studies are complicated by non-toxic adaptive responses in transcript, protein or metabolite expression levels that have to be distinguished from those that are proximally related to the toxic event. Substantial progress has been made on the identification of biomarkers and the establishment of screens derived from such toxicogenomics studies. The ultimate goal, of course, is predictive toxicogenomics, which is an attempt to infer the likelihood of occurrence of a toxic event with exposure to a new agent based upon comparative responses with large databases of gene, protein or metabolite expression data. Gene expression databases are currently limited by the fact that measurable toxic phenotypes generally precede or at best coincide with the earliest observable changes in transcriptional profiles. Unfortunately, predictive protein databases have been limited by technical difficulties. Metabonomics-based databases, which would probably have the highest predictive value, are limited in turn by the inability to perform high dose studies in humans. This chapter will conclude by reviewing those elements of toxicogenomics that apply specifically to the development of anti-infectives and the potential for accurately modelling the toxicity of future drugs.

Systems toxicology: applications of toxicogenomics, transcriptomics, proteomics and metabolomics in toxicology

Toxicogenomics can facilitate the identification and characterization of toxicity, as illustrated in this review. Toxicogenomics, the application of the functional genomics technologies (transcriptomics, proteomics and metabolomics) in toxicology enables the study of adverse effects of xenobiotic substances in relation to structure and activity of the genome. The advantages and limitations of the different technologies are evaluated, and the prospects for integration of the technologies into a systems biology or systems toxicology approach are discussed. Applications of toxicogenomics in various laboratories around the world show that the crucial steps and sequence of events at the molecular level can be studied to provide detailed insights into mechanisms of toxic action. Toxicogenomics allowed for more sensitive and earlier detection of adverse effects in (animal) toxicity studies. Furthermore, the effects of exposure to mixtures could be studied in more detail. This review argues that in the (near) future, human health risk assessment will truly benefit from toxicogenomics (systems toxicology).

Gene expression profile in liver of differing ages of rats after single oral administration of acetaminophen

In order to verify the influence of the rat age on hepatotoxicity, male Sprague-Dawley rats of 6 (young) and 12 (adult) weeks of age were orally administered acetaminophen (APAP), isoniazid (INH), or carbon tetrachloride (CCl4). Liver samples were obtained in a time-course manner, and changes in gene expression examined by an Affymetrix GeneChip. APAP caused more prominent hepatic injury with respect to pathology and blood biochemistry in adults than in young rats, whereas no obvious age-related differences were observed in INH- or CCl4-treated rats. Comparing gene expression in control rats, CYP3A13 was higher and GSTY2c was lower in adults, suggesting that production of the active metabolite of APAP is higher and its detoxification is lower in adults. The total amount of glutathione and total SH in rat liver was found to be higher in adult rats whereas the extent of its reduction by APAP was larger in adults. A detailed analysis of genes showing age-related differences revealed that some of them were different not in their extent but in their time course, i.e., the stress responses occurred earlier in the young than in the adult, resulting in a difference at 24 hr after dosing. These results suggest that the age-related difference in toxicity would be attributed to a higher expression of CYP3A13, producing the active metabolite of APAP as well as the lower expression of the detoxification enzyme, GSTY2c, in adult rats. Furthermore, these differences affect the time course of APAP toxicity. The present study clearly depicts the advantage of the multi-time, multi-dose protocol employed in our project for analyzing the mechanism of toxicity by gene expression profiling.

Cross-species comparative toxicogenomics as an aid to safety assessment

Cross-species comparative toxicogenomics has the potential for improving the understanding of the different responses of animal models to toxicants at a molecular level. This understanding could then lead to a more accurate extrapolation of the risk posed by these toxicants to humans. Cross-species comparative studies have been carried out at the genomic sequence level and using microarrays to examine changes in global mRNA profiles. However, these studies face considerable bioinformatic challenges in terms of identifying which genes are truly orthologous across species. The resources to analyse such studies, in the context of such orthologues, beg improvement. Finally, the experimental design of such studies needs to be carefully considered to make their results fully interpretable. These issues are discussed, along with the current state-of-the-art cross-species comparative toxicogenomics in this review.

Gene interaction network analysis suggests differences between high and low doses of acetaminophen

Bayesian networks for quantifying linkages between genes were applied to detect differences in gene expression interaction networks between multiple doses of acetaminophen at multiple time points. Seventeen (17) genes were selected from the gene expression profiles from livers of rats orally exposed to 50, 150 and 1500 mg/kg acetaminophen (APAP) at 6, 24 and 48 h after exposure using a variety of statistical and bioinformatics approaches. The selected genes are related to three biological categories: apoptosis, oxidative stress and other. Gene interaction networks between all 17 genes were identified for the nine dose-time observation points by the TAO-Gen algorithm. Using k-means clustering analysis, the estimated nine networks could be clustered into two consensus networks, the first consisting of the low and middle dose groups, and the second consisting of the high dose. The analysis suggests that the networks could be segregated by doses and were consistent in structure over time of observation within grouped doses. The consensus networks were quantified to calculate the probability distribution for the strength of the linkage between genes connected in the networks. The quantifying analysis showed that, at lower doses, the genes related to the oxidative stress signaling pathway did not interact with the apoptosis-related genes. In contrast, the high-dose network demonstrated significant interactions between the oxidative stress genes and the apoptosis genes and also demonstrated a different network between genes in the oxidative stress pathway. The approaches shown here could provide predictive information to understand high- versus low-dose mechanisms of toxicity.

Protective effects of alpha1-acid glycoprotein and serum amyloid A on concanavalin A-induced liver failure via interleukin-6 induction by ME3738

We examined whether the 22beta-methoxyolean-12-ene-3beta,24(4beta)-diol (ME3738)-mediated selective induction of interleukin-6 increased alpha1-acid glycoprotein and serum amyloid A expression, and whether these proteins protected against liver injury in vitro and in vivo. ME3738 treatment in male mice increased gene expression of alpha1-acid glycoprotein subtypes and serum amyloid A 2 genes, and plasma concentration of serum amyloid A. Treatment with alpha1-acid glycoprotein at 5 mg/animal or serum amyloid A at 0.03 and 0.1 mg/animal prior to concanavalin A administration reduced multifocal necrosis in the liver. Treatment with alpha1-acid glycoprotein and serum amyloid A, but not alpha1-antitrypsin, protected Hep G2 cells against cell injury. These results suggest that alpha1-acid glycoprotein and serum amyloid A, increased by ME3738-induced interleukin-6, might protect against concanavalin A-induced liver injury.

Alterations in the rat serum proteome during liver injury from acetaminophen exposure

Changes in the serum proteome were identified during early, fulminant, and recovery phases of liver injury from acetaminophen in the rat. Male F344 rats received a single, noninjury dose or a high, injury-producing dose of acetaminophen for evaluation at 6 to 120 h. Two-dimensional gel electrophoresis of immunodepleted serum separated approximately 800 stained proteins per sample from which differentially expressed proteins were identified by mass spectrometry. Serum alanine aminotransferase/aspartate aminotransferase levels and histopathology revealed the greatest liver damage at 24 and 48 h after high-dose acetaminophen corresponding to the time of greatest serum protein alterations. After 24 h, 68 serum proteins were significantly altered of which 23 proteins were increased by >5-fold and 20 proteins were newly present compared with controls. Only minimal changes in serum proteins were noted at the low dose without any histopathology. Of the 54 total protein isoforms identified by mass spectrometry, gene ontology processes for 38 unique serum proteins revealed involvement of acute phase response, coagulation, protein degradation, intermediary metabolism, and various carrier proteins. Elevated serum tumor necrosis factor-alpha from 24 to 48 h suggested a mild inflammatory response accompanied by increased antioxidant capability demonstrated by increased serum catalase activity. Antibody array and enzyme-linked immunosorbent assay analyses also showed elevation in the chemokine monocyte chemoattractant protein-1 and the metalloprotease inhibitor tissue inhibitor of metalloproteinases-1 during this same period of liver injury. This study demonstrates that serum proteome alterations probably reflect both liver damage and a concerted, complex response of the body for organ repair and recovery during acute hepatic injury.

Differential metabolomics reveals ophthalmic acid as an oxidative stress biomarker indicating hepatic glutathione consumption

Metabolomics is an emerging tool that can be used to gain insights into cellular and physiological responses. Here we present a metabolome differential display method based on capillary electrophoresis time-of-flight mass spectrometry to profile liver metabolites following acetaminophen-induced hepatotoxicity. We globally detected 1,859 peaks in mouse liver extracts and highlighted multiple changes in metabolite levels, including an activation of the ophthalmate biosynthesis pathway. We confirmed that ophthalmate was synthesized from 2-aminobutyrate through consecutive reactions with gamma-glutamylcysteine and glutathione synthetase. Changes in ophthalmate level in mouse serum and liver extracts were closely correlated and ophthalmate levels increased significantly in conjunction with glutathione consumption. Overall, our results provide a broad picture of hepatic metabolite changes following acetaminophen treatment. In addition, we specifically found that serum ophthalmate is a sensitive indicator of hepatic GSH depletion, and may be a new biomarker for oxidative stress. Our method can thus pinpoint specific metabolite changes and provide insights into the perturbation of metabolic pathways on a large scale and serve as a powerful new tool for discovering low molecular weight biomarkers.

Identification of differentially expressed genes in hepatic HepG2 cells treated with acetaminophen using suppression subtractive hybridization

Acetaminophen (APAP) is widely used for the treatment of pain and fever. Although it is safe at therapeutic doses, APAP is toxic at higher doses and can cause severe damage to the liver. To clarify the mechanism of APAP-related liver damage, we attempted the identification of the differential gene expression in response to APAP treatment in hepatic HepG2 cells. In the present study, we used the technique of suppression subtractive hybridization (SSH) for the identification of the differentially expressed genes between untreated and treated cells and identified 14 candidate genes showing increased expression in response to APAP treatment. RT-PCR and real-time RT-PCR analysis confirmed that the expression of two genes was increased within 24 h following APAP treatment. Among them, only lysyl hydroxylase 2 expression was increased in a time- and dose-dependent manner. Furthermore, the expression of lysyl hydroxylase 2 was shown to be increased in the livers of APAP-treated mice compared to untreated controls. The increased expression of lysyl hydroxylase 2 was also observed when the cells were exposed to other hepatotoxins, ethanol and isoniazid. Since lysyl hydroxylase 2 is known to be a key enzyme of liver fibrosis, the increased expression of lysyl hydroxylase 2 may be involved in hepatotoxins-related liver fibrosis.