Molecular aspects of paracetamol-induced hepatotoxicity and its mechanism-based prevention

Integrating cellular metabolism into a multiscale whole-body model

Cellular metabolism continuously processes an enormous range of external compounds into endogenous metabolites and is as such a key element in human physiology. The multifaceted physiological role of the metabolic network fulfilling the catalytic conversions can only be fully understood from a whole-body perspective where the causal interplay of the metabolic states of individual cells, the surrounding tissue and the whole organism are simultaneously considered. We here present an approach relying on dynamic flux balance analysis that allows the integration of metabolic networks at the cellular scale into standardized physiologically-based pharmacokinetic models at the whole-body level. To evaluate our approach we integrated a genome-scale network reconstruction of a human hepatocyte into the liver tissue of a physiologically-based pharmacokinetic model of a human adult. The resulting multiscale model was used to investigate hyperuricemia therapy, ammonia detoxification and paracetamol-induced toxication at a systems level. The specific models simultaneously integrate multiple layers of biological organization and offer mechanistic insights into pathology and medication. The approach presented may in future support a mechanistic understanding in diagnostics and drug development.

Cellular metabolism is a key element in human physiology. Ideally the metabolic network needs to be considered within the context of the surrounding tissue and organism since the various levels of biological organization are mutually influencing each other. To mechanistically describe the interplay between intracellular space and extracellular environment, we here integrate the genome-scale metabolic network model HepatoNet1 at the cellular scale into physiologically-based pharmacokinetic models at the whole-body level. The resulting multiscale model allows the quantitative description of metabolic behavior in the context of time-resolved metabolite concentration profiles in the body and the surrounding liver tissue. The model has been applied to three case studies covering fundamental aspects of medicine and pharmacology: drug administration, biomarker identification and drug-induced toxication. Most notably, our multiscale approach fosters an improved quantitative understanding of drug action and the impact of metabolic disorders at an organism level, based on a genome-scale representation of cellular metabolism. Computational models such as the one presented include various aspects of human physiology and may therefore significantly support rational approaches in medical diagnostics and pharmaceutical drug development in the future.

The blood-brain barrier: In vitro methods and toxicological applications

The blood-brain barrier (BBB) is reviewed with reference to in vitro cell culture models and their use and potential use in toxicological studies. The structure, function and in vitro study of brain microvessel endothelial cells (BMEC) is briefly described, as well as the effects of a number of xenobiotics, such as solvents, metals, polycations and herbicides, on the viability and barrier function of the BBB model. The biotransformation of xenobiotics is increasingly thought to be responsible for many toxic reactions seen in living systems. Few studies have addressed the effects of the products of biotransformation on the integrity of the barrier model. Many of the specific human bioactivating enzymes, such as cytochrome P-450s, can now be conveniently studied in eukaryotic in vitro gene expression systems. The combination of such systems with a well characterized porcine BMEC culture model might be useful in the study of reactive metabolites on the BBB, in terms of changes in indices of functional and structural BMEC viability. The potential applications and the value of such an experimental approach are discussed.

Taurine and liver diseases: a focus on the heterogeneous protective properties of taurine

Taurine (2-aminoethylsulfonic acid) has many physiological and pharmacological functions in most tissues. It is abundantly maintained in the liver by both endogenous biosynthesis and exogenous transport, but is decreased in liver diseases. In the hepatic lobule, there are heterogeneous differences in metabolism between the pericentral (PC) and periportal regions, and the distributions of the biosynthesis capacity and specific taurine transporter expression are predominantly in the PC region. In cases of depletion of hepatic taurine level, serious liver damages were observed in the PC region. Taurine has protective effects against xenobiotics-induced liver damages in the PC region, but not xenobiotics-induced PP region damages. The xenobiotics that injure the PC region are mainly catabolized by NADPH-dependent cytochrome P450 2E1 that is also predominantly expressed in the PC region. Taurine treatment seems to be a useful agent for CYP2E1-related liver diseases with predominant damages in the PC region.

Hepatoprotective effect of ethanolic extract of Trichosanthes lobata on paracetamol-induced liver toxicity in rats

BACKGROUND

Trichosanthes lobata (family cucurbitaceae) is used to treat malarial fever and liver disorders. This study aims to investigate possible hepatoprotective activities of ethanolic extract of Trichosanthes lobata against paracetamol-induced hepatotoxicity.

METHODS

Hepatotoxicity was induced in Wistar male rats by oral administration, 2 g/kg body weight on 7th day after the administration of ethanolic extract of Trichosanthes lobata and silymarin (100 mg/kg). Ethanolic extract of Trichosanthes lobata was administered orally at doses of 200 mg/kg and 400 mg/kg body weight daily for 7 days. Several serum markers, aspartate transaminase, alanine transaminase, alkaline phosphatase, bilirubin, total protein was measured to assess the effect of the extract on paracetamol (acetaminophen)-induced hepatic damage. The study included histopathological examination of liver sections.

RESULTS

Blood samples from rats treated with ethanolic extract of Trichosanthes lobata (200 mg/kg body weight and 400 mg/kg body weight) had significant reductions in serum markers in paracetamol administered animals, indicating the effect of the extract in restoring the normal functional ability of hepatocytes. Silymarin (100 mg/kg, p.o.) was used as a reference drug.

CONCLUSION

The ethanolic extract of Trichosanthes lobata exhibits protective effects against paracetamol‒induced hepatotoxicity.

Effects of kale ingestion on pharmacokinetics of acetaminophen in rats

Kale is a cruciferous vegetable (Brassicaceae) that contains a large amount of health-promoting phytochemicals. The chronic ingestion of cabbage of the same family is known to accelerate conjugating acetaminophen (AA) and decrease the plasma AA level. Therefore, we examined to clarify the effects of kale on the pharmacokinetics of AA, its glucuronide (AA-G) and sulfate (AA-S). AA was orally administered to rats pre-treated with kale or cabbage (2000 mg/kg/day) for one week. Blood samples were collected from the jugular vein, and the concentrations of AA, AA-G and AA-S were determined. In results, kale ingestion induced an increase in the area under the concentration-time curve (AUC) and a decrease in the clearance of AA, whereas cabbage had almost no influence. In addition, there were significant differences in the AUC of AA-G between the control and kale groups. mRNA expression levels of UDP-glucuronosyltransferases, the enzymes involved in glucuronidation, in the kale group were significantly higher than those in the control group. In conclusion, kale ingestion increased the plasma concentrations of both AA and AA-G. The results suggest that kale ingestion accelerates the glucuronidation of AA, but an increase of plasma AA levels has a different cause than the cause of glucuronidation.

Aldo-keto reductase-7A protects liver cells and tissues from acetaminophen-induced oxidative stress and hepatotoxicity

Aldo-keto reductase-7A (AKR7A) is an enzyme important for bioactivation and biodetoxification. Previous studies suggested that Akr7a might be transcriptionally regulated by oxidative stress-responsive transcription factor nuclear factor erythroid 2 p45-related factor 2 (Nrf2), a protein highly responsive to acetaminophen (APAP) or its intermediate metabolite, N-acetyl-p-benzoquinoneimine (NAPQI). This study was, therefore, carried out to investigate whether Akr7a is involved in the protection against APAP-induced oxidative stress and hepatotoxicity. We found that in response to APAP or NAPQI exposure, Akr7a3 mRNA and protein were significantly up-regulated in vitro in human HepG2 and LO2 cells. Similarly, strong induction was observed for Akr7a5 in mouse AML12 hepatocytes exposed to APAP. In vivo in wild-type rats, significant up-regulation of hepatic AKR7A1 protein was observed after administration of APAP. On the other hand, depletion of Nrf2 reduced the expression of Akr7a3, suggesting that Nrf2, indeed, contributes significantly to the induction of Akr7a. Moreover, loss of cell viability in Nrf2-depleted cells was significantly rescued by coexpression of AKR7A3. Furthermore, increased AKR7A3 in HepG2 cells was associated with the up-regulation of oxidative stress-related enzymes to enhance cellular antioxidant defense, which appeared to contribute significantly to protection against APAP-induced toxicity. In a line of transgenic rats overexpressing AKR7A1, increased AKR7A1 stimulated the expression of Nrf2 and other Nrf2-regulated genes, but did not better protect rats from APAP insults. In contrast, depletion of Akr7a5 in vitro in cultured AML12 cells or depletion of Akr7a1 in vivo in rat liver greatly increased APAP-induced hepatotoxicity.

CONCLUSION

AKR7A proteins are significantly up-regulated in response to APAP/NAPQI exposure to contribute significantly to protection against APAP-induced hepatotoxicity. AKR7A mediates this protection, in part, through enhancing hepatocellular antioxidant defense.

Protective effect of Woodfordia fruticosa flowers against acetaminophen-induced hepatic toxicity in rats

CONTEXT

The flowers of Woodfordia fruticosa Kurz. (Lythraceae) are commonly used for the treatment of several ailments which includes rheumatism, leucorrhea, menorrhagia, asthma, liver disorder, and inflammatory conditions.

OBJECTIVE

To evaluate the hepatoprotective property of Woodfordia fruticosa flowers against acetaminophen-induced hepatic injury in rats.

MATERIAL AND METHODS

Acetaminophen (3 g/kg bw)-induced hepatotoxicity study was carried out by observing the effect of methanol extract of Woodfordia fruticosa flowers (400 and 600 mg/kg, bw) on some serum marker enzymes, albumin, blood urea nitrogen levels as well as liver total protein, nonenzymetic glutathione reduced content, and enzymatic antioxidant glutathione peroxidase, with histopathological evidence.

RESULTS AND DISCUSSION

Pretreatment of rats with methanol extract of Woodfordia fruticosa flowers effectively prevented the acetaminophen-induced hepatic damage as indicated by the serum marker enzymes aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase and other biochemical parameters (albumin and blood urea nitrogen). Parallel to these changes, the methanol extract of Woodfordia fruticosa flowers also prevented acetaminophen-induced oxidative stress in the rat liver by inhibiting depletion of liver total protein and restoring the levels of nonenzymatic antioxidant glutathione reduced. The biochemical changes were consistent with histopathological observations suggesting marked hepatoprotective effect of the methanol extract of Woodfordia fruticosa flowers.

CONCLUSION

The results suggested that methanol extract of Woodfordia fruticosa flowers possesses protective effect against acetaminophen-induced hepatotoxicity.

Silymarin nanoparticle prevents paracetamol-induced hepatotoxicity

Silymarin (Sm) is a polyphenolic component extracted from Silybum marianum. It is an antioxidant, traditionally used as an immunostimulant, hepatoprotectant, and dietary supplement. Relatively recently, Sm has proved to be a valuable chemopreventive and a useful antineoplastic agent. Medical success for Sm is, however, constrained by very low aqueous solubility and associated biopharmaceutical limitations. Sm flavonolignans are also susceptible to ion-catalyzed degradation in the gut. Proven antihepatotoxic activity of Sm cannot therefore be fully exploited in acute chemical poisoning conditions like that in paracetamol overdose. Moreover, a synchronous delivery that is required for hepatic regeneration is difficult to achieve by itself. This work is meant to circumvent the inherent limitations of Sm through the use of nanotechnology. Sm nanoparticles (Smnps) were prepared by nanoprecipitation in polyvinyl alcohol stabilized Eudragit RS100^® polymer (Rohm Pharma GmbH, Darmstadt, Germany). Process parameter optimization provided 67.39% entrapment efficiency and a Gaussian particle distribution of average size 120.37 nm. Sm release from the nanoparticles was considerably sustained for all formulations. Smnps were strongly protective against hepatic damage when tested in a paracetamol overdose hepatotoxicity model. Nanoparticles recorded no animal death even when administered after an established paracetamol-induced hepatic necrosis. Preventing progress of paracetamol hepatic damage was traced for an efficient glutathione regeneration to a level of 11.3 μmol/g in hepatic tissue due to Smnps.

Rat Liver Cytochrome P450-mediated Metabolic Activation of Methoxsalen and Structurally Related Compounds and its Relation to Enzyme Inhibition

The metabolic activation and enzyme inhibition characteristics of methoxsalen were investigated in rat liver microsomes obtained from untreated animals and those treated with a number of prototypic inducers of cytochrome P450.

Glutathione depletion assays have been carried out which show reactive metabolite generation to be markedly increased following phenobarbitone and β-naphthoflavone induction. Moreover, isoniazid induction led to levels of glutathione depletion significantly higher than those seen with other forms of induction, suggesting an important role for the cytochrome P4502E1 isozyme in the metabolic activation process.

Methoxsalen was shown to be an extremely potent inhibitor of 7-ethoxycoumarin-O-de-ethylase activity, with inhibition constants of the order of μm with microsomes obtained from untreated, phenobarbitone- and β-aphthoflavone-induced animals. In contrast, constants obtained with microsomes obtained from isoniazid-induced animals were found to be markedly higher.

Comparisons of the inhibition of 7-ethoxy and 7-pentoxyresorufin-O-dealkylase activities by methoxsalen and a number of structurally-related compounds have shown that a complete tricyclic ring system and an unsaturated 4′,5′-bond are structural prerequisites in the formation of reactive metabolites which inhibit cytochrome P450. These data implicate the furan ring system as the source of these metabolites and rule out the involvement of the pyrone ring system in the inhibition process.

Acetaminophen-NAPQI hepatotoxicity: a cell line model system genome-wide association study

Acetaminophen is the leading cause of acute hepatic failure in many developed nations. Acetaminophen hepatotoxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinonimine (NAPQI). We performed a "discovery" genome-wide association study using a cell line-based model system to study the possible contribution of genomics to NAPQI-induced cytotoxicity. A total of 176 lymphoblastoid cell lines from healthy subjects were treated with increasing concentrations of NAPQI. Inhibiting concentration 50 values were determined and were associated with "glutathione pathway" gene single nucleotide polymorphisms (SNPs) and genome-wide basal messenger RNA expression, as well as with 1.3 million genome-wide SNPs. A group of SNPs in linkage disequilibrium on chromosome 3 was highly associated with NAPQI toxicity. The p value for rs2880961, the SNP with the lowest p value, was 1.88 × 10(-7). This group of SNPs mapped to a "gene desert," but chromatin immunoprecipitation assays demonstrated binding of several transcription factor proteins including heat shock factor 1 (HSF1) and HSF2, at or near rs2880961. These chromosome 3 SNPs were not significantly associated with variation in basal expression for any of the genome-wide genes represented on the Affymetrix U133 Plus 2.0 GeneChip. We have used a cell line-based model system to identify a SNP signal associated with NAPQI cytotoxicity. If these observations are validated in future clinical studies, this SNP signal might represent a potential biomarker for risk of acetaminophen hepatotoxicity. The mechanisms responsible for this association remain unclear.

Carotenoid lutein protects rats from paracetamol-, carbon tetrachloride- and ethanol-induced hepatic damage

OBJECTIVES

Carotenoids are a class of natural fat-soluble pigments that are found in many fruits and vegetables. Consumption of a diet rich in carotenoids has been epidemiologically correlated with a lower risk for several diseases. In the present study the carotenoid lutein (3,3'-dihydroxy-beta,epsilon-carotene) was evaluated for its hepatoprotective activity in rats.

METHODS

Paracetamol, 20% ethanol and carbon tetrachloride were used to induce liver toxicity.

KEY FINDINGS

Levels of serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase and alkaline phosphatases, which were increased in the serum, were found to be significantly reduced by the treatment of lutein in a dose-dependent manner, indicating that lutein may reduce the hepatotoxicity induced by these agents(. )Serum bilirubin was also significantly lower in lutein-treated groups compared with control. Increased lipid peroxidation, conjugated diene and hydroperoxides in the liver tissue produced by the administration of paracetamol were found to be reduced in the lutein-treated groups. Levels of antioxidant enzymes, like superoxide dismutase, catalase, glutathione peroxidase and glutathione, were found to be increased in lutein-treated groups compared with control group during alcohol- and CCl(4)-induced liver toxicity. Hydroxyproline, which is an indicator of fibrosis in liver tissue, was high in the ethanol-treated control group. Hydroxyproline levels were decreased by simultaneous lutein administration.

CONCLUSIONS

Histopathological evidence confirmed the protection offered by lutein from the tissue damage caused by hepatotoxins. The hepatoprotective action may be due to lutein's ability to scavenge reactive oxygen radicals.

Antioxidant properties of Baccharis trimera in the neutrophils of Fisher rats

ETHNOPHARMACOLOGICAL RELEVANCE

Baccharis trimera (Less.) (Asteraceae) is a native plant of Brazil. Also known as "carqueja", it has been popularly used to treat liver diseases, diabetes, as well as digestive disorders. Other studies have described the hepatoprotective, antioxidant and anti-inflammatory activities of the species.

AIM OF THE STUDY

The aim of the present study was to investigate the antioxidant properties of Baccharis trimera in the neutrophils of Fisher rats in both in vitro and in vivo experimental models.

MATERIAL AND METHODS

In the in vitro assay, the neutrophils of male rats were isolated and incubated with Baccharis trimera extract at concentrations of 0.5, 5.0 and 50.0 microg/mL. In the in vivo assay, male rats were first treated with crude extract 600 mg/kg body weight of Baccharis trimera or with 50 mg/kg body weight of quercetin (reference substance) and then treated with 835 mg/kg of acetaminophen (APAP) after 24 h.

RESULTS

The hydroethanolic extract of Baccharis trimera reduced the release of reactive oxygen species in the neutrophils in both the in vitro and in vivo experimental models. Therefore confirming its antioxidant effect.

CONCLUSION

The results of this study confirm the antioxidant effect of Baccharis trimera.

Development of acetaminophen proline prodrug

In this research work, proline ester prodrug of acetaminophen (Pro-APAP) was synthesized and evaluated for its stability in PBS buffer at various pH and Caco-2 cell homogenate. The Pro-APAP is more stable at lower pH than higher pH, with half-life of 120min in PBS buffer at pH 2.0, half-life of 65min at pH 5.0, and half life of 3.5min at pH 7.4, respectively. The half-life of Pro-APAP in Caco-2 cell homogenate is about 1min, much shorter than the half-life in PBS buffer at pH 7.4, indicating enzymes in the cell homogenate contribute to the hydrolysis of the ester bond. Carboxypeptidase A was incubated with Pro-APAP at pH 7.4 with half-life of 3.8min which is very close to the half life in buffer itself. This clearly indicates carboxypeptidase A is not one of the enzymes contributing to the hydrolysis of the prodrug. Physicochemical characteristics such as melting point and stability of newly synthesized prodrug were determined by MDSC technique.

Acetaminophen induced acute liver failure via oxidative stress and JNK activation: protective role of taurine by the suppression of cytochrome P450 2E1

The present study was carried out to investigate whether taurine plays any beneficial role in acetaminophen (APAP)-induced acute hepatotoxicity. APAP exposure increased the plasma levels of ALT, ALP, LDH, TNF-alpha and NO production. Moreover, APAP treatment reduced the glutathione level and antioxidant enzyme activities, increased lipid peroxidation and caused hepatic DNA fragmentation which ultimately leads to cellular necrosis. Also, incubation of hepatocytes with APAP reduced cell viability, enhanced ROS generation and increased CYP2E1 activity. APAP overdose caused injury in the hepatic tissue and hepatocytes via the upregulation of CYP2E1 and JNK. Taurine treatment was effective in counteracting APAP-induced hepatic damages, oxidative stress and cellular necrosis. Results indicate that APAP overdose caused hepatic injury due to its metabolism to hepatotoxic NAPQI (N-acetyl-p-benzoquinone imine), usually catalysed by CYP2E1, and via the direct activation of JNK-dependent cell death pathway. Taurine possesses prophylactic as well as therapeutic potentials against APAP-induced hepatic injury.

Potential physiological effects of pharmaceutical compounds in Atlantic salmon (Salmo salar) implied by transcriptomic analysis

BACKGROUND, AIM, AND SCOPE

Pharmaceuticals are emerging pollutants widely used in everyday urban activities which can be detected in surface, ground, and drinking waters. Their presence is derived from consumption of medicines, disposal of expired medications, release of treated and untreated urban effluents, and from the pharmaceutical industry. Their growing use has become an alarming environmental problem which potentially will become dangerous in the future. However, there is still a lack of knowledge about long-term effects in non-target organisms as well as for human health. Toxicity testing has indicated a relatively low acute toxicity to fish species, but no information is available on possible sublethal effects. This study provides data on the physiological pathways involved in the exposure of Atlantic salmon as representative test species to three pharmaceutical compounds found in ground, surface, and drinking waters based on the evaluation of the xenobiotic-induced impairment resulting in the activation and silencing of specific genes.

MATERIALS AND METHODS

Individuals of Atlantic salmon (Salmo salar) parr were exposed during 5 days to environmentally relevant concentrations of three representative pharmaceutical compounds with high consumption rates: the analgesic acetaminophen (54.77+/-34.67 microg L(-1)), the anticonvulsant carbamazepine (7.85+/-0.13 microg L(-1)), and the beta-blocker atenolol (11.08+/-7.98 microg L(-1)). Five immature males were selected for transcriptome analysis in brain tissues by means of a 17k salmon cDNA microarray. For this purpose, mRNA was isolated and reverse-transcribed into cDNA which was labeled with fluorescent dyes and hybridized against a common pool to the arrays. Lists of significantly up- and down-regulated candidate genes were submitted to KEGG (Kyoto Encyclopedia of Genes and Genomes) in order to analyze for induced pathways and to evaluate the usefulness of this method in cases of not completely annotated test organisms.

RESULTS

Exposure during 5 days to environmentally relevant concentrations of the selected pharmaceutical compounds acetaminophen, carbamazepine, and atenolol produced differences in the expression of 659, 700, and 480 candidate genes, respectively. KEGG annotation numbers (KO annotations) were obtained for between 26.57% and 33.33% of these differently expressed genes per treatment in comparison to non-exposure conditions. Pathways that showed to be induced did not always follow previously reported targets or metabolic routes for the employed treatments; however, several other pathways have been found (four or more features) to be significantly induced.

DISCUSSION

Energy-related pathways have been altered under exposure in all the selected treatments, indicating a possible energy budget leakage due to additional processes resulting from the exposure to environmental contaminants. Observed induction of pathways may indicate additional processes involved in the mode of action of the selected pharmaceuticals which may not have been detected with conventional methods like quantitative PCR in which only suspected features are analyzed punctually for effects. The employment of novel high-throughput screening techniques in combination with global pathway analysis methods, even if the organism is not completely annotated, allows the examination of a much broader range of candidates for potential effects of exposure at the gene level.

CONCLUSIONS

The continuously growing number of annotations of representative species relevant for environmental quality testing is facilitating pathway analysis processes for not completely annotated organisms. KEGG has shown to be a useful tool for the analysis of induced pathways from data generated by microarray techniques with the selected pharmaceutical contaminants acetaminophen, carbamazepine, and atenolol, but further studies have to be carried out in order to determine if a similar expression pattern in terms of fold change quantity and pathways is observed after long-term exposure. Together with the information obtained in this study, it will then be possible to evaluate the potential risk that the continuous release of these compounds may have on the environment and ecosystem functioning.

Comparative impacts of knockouts of two antioxidant enzymes on acetaminophen-induced hepatotoxicity in mice

We have previously shown a more potent impact of knockout of Cu,Zn-superoxide dismutase (SOD1) than that of Se-dependent glutathione peroxidase-1 (GPX1) on murine hepatotoxicity induced by an intraperitoneal (ip) injection of a high dose of acetaminophen (APAP, 600 mg/kg). The objective of this experiment was to compare the temporal impacts of knockouts of GPX1 and SOD1 alone or together on mouse susceptibility to an injection of a low dose of APAP (300 mg/kg). The APAP-mediated rises in plasma alanine aminotransferase activity and nitrate/nitrite concentrations, hepatic GSH depletion, and hepatic protein nitration at 5 and (or) 24 h were nearly abolished (P < 0.05) in SOD1-/- or GPX1 and SOD1 double-knockout (DKO) mice, while GPX1-/- mice exerted only moderate or no change compared with the WT. Despite an increased (P < 0.05) APAP-N-acetylcysteine and decreased APAP-glucuronide (P < 0.05) relative to the total APAP metabolites in urine collected for 24 h after the APAP injection, the SOD1-/- mice displayed no shift in urinary APAP-cysteine compared with the WT mice. Knockout of SOD1 prevented the APAP-induced hepatic GPX inactivation (P < 0.05), whereas knockout of GPX1 aggravated the APAP-induced hepatic SOD activity loss (P < 0.05). However, the APAP-mediated activity changes of these enzymes in liver accompanied no protein alterations. In conclusion, knockout of GPX1 or SOD1 exerted differential impact on mouse susceptibility to this low dose of APAP, but neither shifted urinary APAP-cysteine formation.

Phyllanthus urinaria extract attenuates acetaminophen induced hepatotoxicity: involvement of cytochrome P450 CYP2E1

Acetaminophen is a commonly used drug for the treatment of patients with common cold and influenza. However, an overdose of acetaminophen may be fatal. In this study we investigated whether mice, administered intraperitoneally with a lethal dose of acetaminophen, when followed by oral administration of Phyllanthus urinaria extract, may be prevented from death. Histopathological analysis of mouse liver sections showed that Phyllanthus urinaria extract may protect the hepatocytes from acetaminophen-induced necrosis. Therapeutic dose of Phyllanthus urinaria extract did not show any toxicological phenomenon on mice. Immunohistochemical staining with the cytochrome P450 CYP2E1 antibody revealed that Phyllanthus urinaria extract reduced the cytochrome P450 CYP2E1 protein level in mice pre-treated with a lethal dose of acetaminophen. Phyllanthus urinaria extract also inhibited the cytochrome P450 CYP2E1 enzymatic activity in vitro. Heavy metals, including arsenic, cadmium, mercury and lead, as well as herbicide residues were not found above their detection limits. High performance liquid chromatography identified corilagin and gallic acid as the major components of the Phyllanthus urinaria extract. We conclude that Phyllanthus urinaria extract is effective in attenuating the acetaminophen induced hepatotoxicity, and inhibition of cytochrome P450 CYP2E1 enzyme may be an important factor for its therapeutic mechanism.

Liver antioxidant capacity in the early phase of acute paracetamol-induced liver injury in mice

The aim of our study was to investigate the relationship between liver antioxidant capacity and hepatic injury in the early phase of acute paracetamol intoxication in mice. Male Swiss mice were divided into groups: (1) control, that received saline, (2) paracetamol-treated group (300 mg/kg intraperitoneally). Animals were sacrificed 6, 24 and 48 h after treatment. Oxidative stress parameters were determined in blood and liver samples spectrophotometrically. Liver malondialdehyde and nitrite + nitrate level were significantly increased 6 h after paracetamol administration in comparison with control group (p < 0.05). Paracetamol induced a significant reduction in total liver superoxide dismutase (SOD) and copper/zinc SOD activity at all time intervals (p < 0.01). However, manganese SOD activity was significantly increased within 6 h (p < 0.01), while its activity progressively declined 24 and 48 h after paracetamol administration in comparison with control group (p < 0.01). Content of sulfhydryl groups in the liver was increased 24 h after paracetamol administration (p < 0.05), while its level was decreased within next 24 h when compared to control animals (p < 0.01). Our data showed that liver antioxidant capacity increases in first 24 h of paracetamol-induced liver injury were in correlation with manganese SOD activity and increase in level of sulfhydryl groups.

Acetaminophen bioactivation by human cytochrome P450 enzymes and animal microsomes

Acetaminophen is a widely used analgesic antipyretic agent. When used at low doses, it is a safe drug, but at higher doses it can cause acute hepatic necrosis in humans and experimental animals. The key mechanism in the hepatotoxicity is cytochrome P450 (CYP)-catalysed formation of the reactive metabolite, N-acetyl-p-benzoquinone imine (NAPQI) that is capable of binding to cellular macromolecules and in that way an LC/MS liquid chromatography/mass spectrometry (LC/MS) method was developed to measure NAPQI formation by trapping it to reduced glutathione. This method was used to determine the bioactivation of acetaminophen at two concentrations: 50 microM therapeutic and 1 mM toxic by using nine human recombinant CYP enzymes: CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4; and with different microsomes from experimental animals. At the toxic concentration the formation of NAPQI-glutathione was highest with CYP3A4 followed by CYP2E1, CYP1A2, and CYP2D6. At the therapeutic concentration, CYP3A4 had also the highest bioactivation capacity. In a comparison of the enzyme kinetics, CYP3A4 was the most efficient CYP with the lowest K(m) value 130 microM (95% confidence interval = 63-210 microM). Dexamethasone-induced rat liver microsomes had the most effective bioactivation capacity at therapeutic and toxic acetaminophen concentrations. This study suggests that CYP3A4 is the major CYP enzyme form catalysing acetaminophen oxidation to NAPQI in human liver.

Rhus verniciflua Stokes prevents cisplatin-induced cytotoxicity and reactive oxygen species production in MDCK-I renal cells and intact mice

Cisplatin-induced oxidative stress can cause liver and kidney damage, thus limiting therapeutic efficacy. Thus, in the present study, since Rhus verniciflua Stokes (RVS) containing flavonoids has antioxidant effects, we investigated whether it can protect cisplatin-induced toxicity in vitro and in vivo, The in vitro effects of RVS on the cell viability and reactive oxygen species (ROS) production were investigated using cisplatin-treated Madin-Darby Canine kidney (MDCK)-I renal cells. Its in vivo effects were also studied in BALB/c mice inoculated with CT-26 colon adenocarcinoma cells and treated with cisplatin with or without RVS. Liver and renal functions were assessed together with indices of tissue oxidation. RVS prevented cisplatin-induced cytotoxicity and ROS release against MDCK-I cells. RVS alone exerted modest antitumor activity against CT-26 cells. When used concurrently with cisplatin, RVS prevented the increases in serum blood urea nitrogen (BUN), creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and NO, while reducing liver and kidney tissue MDA content, and increasing catalase, glutathione (GSH), and superoxide dismutase (SOD) activities. Moreover, the antitumor efficacy of cisplatin was not altered by concurrent administration of RVS. These findings demonstrate that RVS prevents cisplatin-induced toxicity in vitro and in vivo via an antioxidant activity without hurting its antitumor effectiveness, suggesting that RVS can be usefully applied to the neoplastic patients as a combined chemopreventive agent with cisplatin.

Effect of gamma irradiation on the efficacy of beta-glucan against acetaminophen induced toxicity in mice

The present study was conducted to compare the efficacy of unirradiated beta-glucan (UBG) and gamma irradiated beta-glucan (GIBG) against acetaminophen (APAP) induced hepatotoxicity in mice. Mice of BALB/c strain were pretreated with UBG and GIBG (50mg/kg, p.o.) for 7 days and on the 8th day they received an overdose of APAP (500 mg/kg, i.p.). Eight hours after the APAP injection, the levels of serum aminotransferase (AST) and alanine aminotransferase (ALT) were measured and liver, kidney and lung tissue were examined for morphological changes. A significant elevation (p<0.001) of the levels of AST and ALT was observed in mice toxicated with APAP. Histology data revealed severe liver centrilobular necrosis, portal vein damage with apparent toxicity in renal glomerulus and lung inflammation associated with edema. However, a significant inhibition (p<0.05) in the elevation of AST and ALT was observed in mice that received UBG and GIBG compared with APAP-treated mice. Histology examination revealed the non-statistical difference between the protective effects of GIBG and UBG against acetaminophen challenge. In conclusion, it was demonstrated that gamma irradiation induced no severe alteration in the protective activity of beta-glucan against APAP-induced hepatotoxicity.

Protective Effects of macelignan on cisplatin-induced hepatotoxicity is associated with JNK activation

Cisplatin is one of the most effective antineoplastic drugs, but it has undesirable side effects such as hepatotoxicity at high doses. This study investigated the protective effect of macelignan, isolated from Myristica fragrans HOUTT. (nutmeg), against cisplatin-induced hepatotoxicity and the possible mechanisms involved in these effects in mice. Pretreatment with macelignan for 4 d significantly prevented the increased serum enzymatic activities of alanine and aspartate aminotransferase in a dose-dependent manner. The results also showed that the protective effects of macelignan on cisplatin-induced hepatotoxicity may be associated with the mitogen activated protein kinase (MAPK) signaling pathway. Cisplatin-induced phosphorylation of c-Jun N-terminal kinase1/2 (JNK1/2) and extracellular signal-regulated kinase1/2 (ERK1/2) was abrogated by pretreatment with macelignan, however, that of p38 was not significantly affected. It was also found that macelignan attenuated the expression of phosphorylated c-Jun in cisplatin-treated mice. Accordingly, it is suggested that the hepatoprotective effects of macelignan could be related to activation of the MAPK signaling pathway, especially JNK and c-Jun, its substrate. The present findings suggest that co-treatment of cisplatin with macelignan may provide more advantage than cisplatin treatment alone in cancer therapy.

Hepatoprotective effect of L-carnitine against acute acetaminophen toxicity in mice

L-carnitine is a cofactor in the transfer of long-chain fatty acid allowing the beta-oxidation of fatty acid in the mitochondria. It is also a known antioxidant with protective effects against lipid peroxidation. In this study, hepatoprotective effect of L-carnitine was investigated against acetaminophen (AA)-induced liver toxicity where mitochondrial dysfunction and oxidative stress are thought to be involved in AA hepatotoxicity. Sixty-four Balb/C mice were divided into eight groups. Mice were dosed with single-AA injection (500 mg/kg via the intra peritoneal route) with or without L-carnitine (500 mg/kg for 5 days starting 5 days before AA injection via intra peritoneal route) and sampled at 4, 8 and 24 h following AA injection. AA increased serum AST, ALT, total sialic acid (TSA) and MDA as well as tissue TSA and MDA levels significantly with the highest increase observed at 4 h, but there was a decrease in blood and tissue GSH level. Administration of L-carnitine significantly reduced AA-induced elevations in AST, ALT, TSA and MDA concentrations and increased GSH levels at all sampling points. AA also induced necrosis, hyperemia, sinusoidal congestion and hemorrhage with time-dependent increase in severity, but the degree of necrosis and histopathologic alterations were most severe at 24 h following AA administration. However, the degree of pathologic alterations was less severe with simultaneous L-carnitine application. These results suggest that AA results in oxidative damage in the liver with an acute effect. L-carnitine also has a prominent protective effect against AA toxicity and may be of therapeutic value in the treatment of AA-induced hepatotoxicity.

The biochemistry of drug metabolism--an introduction: Part 2. Redox reactions and their enzymes

This review continues a general presentation of the metabolism of drugs and other xenobiotics started in a recent issue of Chemistry & Biodiversity. This Part 2 presents the numerous oxidoreductases involved, their nomenclature, relevant biochemical properties, catalytic mechanisms, and the very diverse reactions they catalyze. Many medicinally, environmentally, and toxicologically relevant examples are presented and discussed. Cytochromes P450 occupy a majority of the pages of Part 2, but a large number of relevant oxidoreductases are also considered, e.g., flavin-containing monooxygenases, amine oxidases, molybdenum hydroxylases, peroxidases, and the innumerable dehydrogenases/reductases.

Effect of acetaminophen administration to rats chronically exposed to depleted uranium

The extensive use of depleted uranium (DU) in both civilian and military applications results in the increase of the number of human beings exposed to this compound. We previously found that DU chronic exposure induces the expression of CYP enzymes involved in the metabolism of xenobiotics (drugs). In order to evaluate the consequences of these changes on the metabolism of a drug, rats chronically exposed to DU (40mg/l) were treated by acetaminophen (APAP, 400mg/kg) at the end of the 9-month contamination. Acetaminophen is considered as a safe drug within the therapeutic range but in the case of overdose or in sensitive animals, hepatotoxicity and nephrotoxicity could occur. In the present work, plasma concentration of APAP was higher in the DU group compared to the non-contaminated group. In addition, administration of APAP to the DU-exposed rats increased plasma ALT (p<0.01) and AST (p<0.05) more rapidly than in the control group. Nevertheless, no histological alteration of the liver was observed but renal injury characterized by incomplete proximal tubular cell necrosis was higher for the DU-exposed rats. Moreover, in the kidney, CYP2E1 gene expression, an important CYP responsible for APAP bioactivation and toxicity, is increased (p<0.01) in the DU-exposed group compared to the control group. In the liver, CYP's activities were decreased between control and DU-exposed rats. These results could explain the worse elimination of APAP in the plasma and confirm our hypothesis of a modification of the drug metabolism following a DU chronic contamination.

Hepatoprotective and Antioxidant Activities ofVernonia amygdalinaon Acetaminophen-Induced Hepatic Damage in Mice

Vernonia amygdalina Del. (Family Compositae) is used in Nigerian folk medicine as a tonic and remedy against constipation, fever, high blood pressure, and many infectious diseases. We have evaluated the hepatoprotective and antioxidant effects of an aqueous extract of V. amygdalina leaves against acetaminophen-induced hepatotoxicity and oxidative stress in mice in vivo. Activities of liver marker enzymes in serum (glutamate-oxaloacetate transaminase, glutamate-pyruvate transaminase, lactate dehydrogenase, and alkaline phosphatase) and bilirubin levels were determined colorimetrically, while catalase activity, lipid peroxidation products, thiobarbituric acid-reactive substances (TBARS), iron, and total protein concentrations were measured in liver homogenate. Acetaminophen challenge (300 mg/kg, i.p) for 7 days caused significant (P < .01) increases in the levels of bilirubin, liver enzymes, TBARS, and iron, while catalase activity and total protein level were reduced significantly (P < .01). Preadministration of V. amygdalina resulted in a dose-dependent (50-100 mg/kg) reversal of acetaminophen-induced alterations of all the liver function parameters by 51.9-84.9%. Suppression of acetaminophen-induced lipid peroxidation and oxidative stress by the extract was also dose-dependent (50-100 mg/kg). The results of this study suggest that V. amygdalina elicits hepatoprotectivity through antioxidant activity on acetaminophen-induced hepatic damage in mice.

Mice deficient in Cu,Zn-superoxide dismutase are resistant to acetaminophen toxicity

Although antioxidants are used to treat an overdose of the analgaesic/antipyretic drug APAP (acetaminophen), roles of antioxidant enzymes in APAP-induced hepatotoxicity remain controversial. Our objective was to determine impacts of knockout of SOD1 (superoxide dismutase; Cu,Zn-SOD) alone or in combination with selenium-dependent GPX1 (glutathione peroxidase-1) on APAP-induced hepatotoxicity. All SOD1-null (SOD1-/-) and SOD1- and GPX1-double-knockout mice survived an intraperitoneal injection of 600 mg of APAP per kg of body mass, whereas 75% of WT (wild-type) and GPX1-null mice died within 20 h. Survival time of SOD1-/- mice injected with 1200 mg of APAP per kg of body mass was longer than that of the WT mice (934 compared with 315 min, P<0.05). The APAP-treated SOD1-/- mice had less (P<0.05) plasma ALT (alanine aminotransferase) activity increase and attenuated (P<0.05) hepatic glutathione depletion than the WT mice. The protection conferred by SOD1 deletion was associated with a block of the APAP-mediated hepatic protein nitration and a 50% reduction (P<0.05) in activity of a key APAP metabolism enzyme CYP2E1 (cytochrome P450 2E1) in liver. The SOD1 deletion also caused moderate shifts in the APAP metabolism profiles. In conclusion, deletion of SOD1 alone or in combination with GPX1 greatly enhanced mouse resistance to APAP overdose. Our results suggest a possible pro-oxidant role for the physiological level of SOD1 activity in APAP-mediated hepatotoxicity.

Mitochondrial oxidative stress and permeability transition in isoniazid and rifampicin induced liver injury in mice

BACKGROUND/AIMS

To evaluate the role of mitochondrial oxidative stress and permeability transition (MPT) in isoniazid (INH) and rifampicin (RMP) induced hepatotoxicity in mice.

METHODS

Liver damage was induced by co-treatment of INH (50 mg/kg) and RMP (100 mg/kg). Pre-treatment with either methionine or phorone was done to modulate hepatic GSH level. Liver cell injury was assessed biochemically and histologically. Evidence of apoptosis was sought by TUNEL test, caspase assay and histology.

RESULTS

INH and RMP co-treatment caused steatosis and increased apoptosis of the hepatocytes, hepatic oxidative stress, particularly in the mitochondrial fraction with increased mitochondrial permeability transition (MPT). Mitochondrial oxidative stress as well as liver cell injury was increased by prior treatment with phorone. This was attenuated by pretreatment with methionine suggesting a glutathione (GSH) dependent phenomenon.

CONCLUSIONS

Oxidative stress in the mitochondria and inappropriate MPT are important in the pathogenesis of apoptotic liver cell injury in INH-RMP hepatotoxicity. The phenomenon is GSH dependent and methionine supplementation might have a protective role.

Defensive nature of Sargassum polycystum (Brown alga) against acetaminophen-induced toxic hepatitis in rats: role of drug metabolizing microsomal enzyme system, tumor necrosis factor-alpha and fate of liver cell structural integrity

AIM

To assess the defensive nature of Sargassum polycystum (S. polycystum) (Brown alga) against acetaminophen (AAP)-induced changes in drug metabolizing microsomal enzyme system, tumor necrosis factor (TNF-alpha) and fine structural features of the liver during toxic hepatitis in rats.

METHODS

Male albino Wistar strain rats used for the study were randomly categorized into 4 groups. Group I consisted of normal control rats fed with standard diet. Group II rats were administered with acetaminophen (800 mg/kg body weight, intraperitoneally). Group III rats were pre-treated with S. polycystum extract alone. Group IV rats were orally pre-treated with S. polycystum extract (200 mg/kg body weight for 21 d) prior to acetaminophen induction (800 mg/kg body weight, intraperitoneally). Serum separated and liver was excised and microsomal fraction was isolated for assaying cytochrome P450, NADPH Cyt P450 reductase and b(5). Serum TNF-alpha was detected using ELISA. Fine structural features of liver were examined by transmission electron microscopy.

RESULTS

Rats intoxicated with acetaminophen showed considerable impairment in the activities of drug metabolizing microsomal enzymes, such as cytochrome P450, NADPH Cyt P450 reductase and b(5) when compared with the control rats. The rats intoxicated with acetaminophen also significantly triggered serum TNF-alpha when compared with the control rats. These severe alterations in the drug metabolizing enzymes were appreciably prevented in the rats pretreated with S. polycystum. The rats pretreated with S. polycystum showed considerable inhibition in the elevation of TNF-alpha compared to the rats intoxicated with acetaminophen. The electron microscopic observation showed considerable loss of structural integrity of the endoplasmic reticulum, lipid infiltration and ballooning of mitochondria in the acetaminophen-intoxicated rats, whereas the rats treated with S. polycystum showed considerable protection against acetaminophen-induced alterations in structural integrity.

CONCLUSION

These observations suggest that the animals treated with S. polycystum extract may have the ability to protect the drug metabolizing enzyme system and mitochondrial functional status from free radical attack, thereby showing its defense mechanism in protecting hepatic cells from acetaminophen toxic metabolite N-acetyl-para-benzoquinone-imine (NAPQI).

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.

Hepatocyte-specific deletion of the keap1 gene activates Nrf2 and confers potent resistance against acute drug toxicity

Nrf2 is a key regulator of many detoxifying enzyme genes, and cytoplasmic protein Keap1 represses the Nrf2 activity under quiescent conditions. Germ line deletion of the keap1 gene results in constitutive activation of Nrf2, but the pups unexpectedly died before weaning. To investigate how constitutive activation of Nrf2 influences the detoxification system in adult mice, we generated mice bearing a hepatocyte-specific disruption of the keap1 gene. Homozygous mice were viable and their livers displayed no apparent abnormalities, but nuclear accumulation of Nrf2 is elevated. Microarray analysis revealed that, while many detoxifying enzyme genes are highly expressed, some of the typical Nrf2-dependent genes are only marginally increased in the Keap1-deficient liver. The mutant mice were significantly more resistant to toxic doses of acetaminophen than control animals. These results demonstrate that chronic activation of Nrf2 confers animals with resistance to xenobiotics without affecting the morphological and physiological integrity of hepatocytes.

Differential effects of acetaminophen on enzymatic and non-enzymatic antioxidant factors and plasma total antioxidant capacity in developing and adult rats

Recently we reported that ferric reducing ability of plasma (FRAP) assay, as an index of total antioxidant activity, increases in growing rats in response to high dose of vitamin K. In this study, it was found that acetaminophen (APAP) can cause elevation in FRAP in suckling and adult rats. This study was initiated to assess the contribution of individual antioxidant factors on elevation in FRAP. A surge in FRAP, 1 h after high dose APAP (250 or 450 mg/kg BW) administration was recorded in both young as well as adults. Whereas, low dose drug (25 mg/kg) failed to alter FRAP in both the age groups. Time-course studies show that drug-dependent elevation in FRAP begin rapidly, reaching a maximum at 1 h (> 500%). Increased FRAP was associated with a marked increase (approximately 14-fold) in plasma bilirubin, 6 h after drug administration at 450 mg/kg only in suckling rats. Similarly, APAP-related increase in superoxide dismutase activity in erythrocytes was limited to young rats of both the age groups. Other factors measured during this period viz., plasma uric acid, bilirubin and total protein together with catalase activity of erythrocytes remained unchanged in treated rats. Under these circumstances, APAP-related depletion in liver glutathione was almost similar in both the age groups. During a 12 h study, the concentration of lipid peroxidation products, in liver of treated groups remained within the levels of respective controls. The endpoint hepatotoxic effects of APAP was almost similar in both the age groups, suggesting that like adults, immature rats can cope with toxic effects of APAP owing to their drug-dependent induction in certain antioxidant factors.

Lack of protective effect of D-003, a mixture of high-molecular-weight primary acids from sugar cane wax, on liver damage induced by galactosamine in rats

D-003 is a mixture of very-high-molecular-weight aliphatic primary acids purified from sugar cane wax, wherein octacosanoic acid is the most abundant. Experimental and clinical studies have shown that D-003 lowers cholesterol and prevents plasma lipoprotein peroxidation (LP). D-003 has protected against the histological changes characteristic of CCl4- and paracetamol-induced hepatic injury in rats, in which LP plays a pivotal role for explaining the resulting hepatotoxicity. Galactosamine induces hepatotoxicity associated with depressed RNA and protein synthesis, not with LP. The aim of this study was to evaluate whether D-003 could prevent hepatoxicity induced by mechanisms others than increased LP. We investigated the effects on galactosamine hepatotoxicity in rats distributed into five groups: a negative control group, a positive control group, and three groups treated with galactosamine and D-003 (5, 25, and 100 mg/kg). To induce liver damage, galactosamine (800 mg/kg) was injected intraperitoneally 30 minutes after dosing with vehicle or D-003. Twenty-four hours later, rats were sacrificed, and livers were immediately removed for histopathological studies. Livers from positive controls showed the characteristic pattern of galactosamine-induced damage. Galactosamine significantly reduced the percentage of normal hepatocytes, increasing both necrotic or lipid-rich hepatocytes compared with negative controls. D-003, however, did not increase the percentage of normal hepatocytes compared with positive controls, indicating that treatment was not effective for preventing the hepatic injury induced with galactosamine. Likewise, D-003 failed to change the content of necrotic and lipid-rich hepatocytes relative to positive controls. It is concluded that D-003 did not protect against the histological changes of galactosamine-induced hepatotoxicity.

Cyclization-activated prodrugs. Synthesis, reactivity and toxicity of dipeptide esters of paracetamol

Dipeptide esters of paracetamol were prepared in high yields. These compounds are quantitatively hydrolyzed to paracetamol and corresponding 2,5-diketopiperazines at pH 7.4 and 37 degrees C. The reactivity is increased in sarcosine and proline peptides and decreased by bulky side chains at both the N- and C-terminal residues of the dipeptide carrier. Moreover, dipeptide esters of paracetamol did not affect the levels of hepatic glutathione. Thus, dipeptides seem promising candidates as carriers for cyclization-activated prodrugs.

Time course toxicogenomic profiles in CD-1 mice after nontoxic and nonlethal hepatotoxic paracetamol administration

Adverse drug reactions are a major clinical problem. Drug-induced hepatotoxicity constitutes a large percentage of these reactions. A thorough understanding of the genetic events, specifically, the early "decision-making" processes underlying biological changes caused by drugs and metabolites, is required. To assist in the understanding of these events, we have employed the model hepatotoxin, paracetamol (APAP), and GeneChip technology to investigate global genetic events seen after nontoxic and toxic doses in the mouse. Mice were dosed [vehicle, nontoxic APAP (1 mmol/kg), and toxic APAP (3.5 mmol/kg)], and individual hepatic RNA samples were hybridized to separate chips to determine interanimal variation. Statistical analysis detected 175 CD-1 mouse genes that were significantly regulated (P < 4.1 x 10(-6)), and nonsignificant genes were discarded. For clarity, the significantly regulated genes were then binned into categories according to their major function-antioxidant, glutathione, metabolism, transcription, immune, and apoptosis. There was no hepatic stress observed after dosing 1 mmol/kg APAP, when measured by serum alanine aminotransferase levels. Hepatic toxicity was observed at both 4 and 24 h after a 3.5 mmol/kg dose of APAP. Time course expression profiles for selected genes have been created. These results demonstrate that most active gene expression occurs around 4 h after a toxic dose of APAP. Down-regulation of these genes is observed over 24 h, coinciding with the development of overt toxicity. These data provide a deeper understanding of the in vivo time course of physiological responses of the liver to chemical stress and provide a logical step forward for the investigation of new chemical entities demonstrated positive in chemically reactive metabolite screens. The complete data set can be viewed at http://www.ebi.ac.uk/arrayexpress/. The accession number is E-MEXP-82.