Hepatic CYP2E1 Research Articles

Wnt/β-Catenin Signaling Drives Thioacetamide-Mediated Heteroprotection Against Acetaminophen-Induced Lethal Liver Injury.

Preplacement of compensatory tissue repair (CTR) by exposure to a nonlethal dose of a toxicant protects animals against a lethal dose of another toxicant. Although CTR is known to heteroprotect, the underlying molecular mechanisms are not completely known. Here, we investigated the mechanisms of heteroprotection using thioacetamide (TA): acetaminophen (APAP) heteroprotection model. Male Swiss Webster mice received a low dose of TA or distilled water (DW) vehicle 24 hours prior to a lethal dose of APAP. Liver injury, tissue repair, and promitogenic signaling were studied over a time course of 24 hours after APAP overdose to the TA- and DW-primed mice (TA + APAP and DW + APAP, respectively). Thioacetamide pretreatment afforded 100% protection against APAP overdose compared to 100% lethality in the DW + APAP-treated mice. Although hepatic Cyp2e1 was similar at the time of APAP administration, immediate activation of hepatic c-Jun N-terminal kinases (JNK) was observed in the TA + APAP-treated mice compared to its delayed activation in the DW + APAP group. In contrast to the DW + APAP group, the TA + APAP-treated mice exhibited extensive CTR, which was secondary to the timely activation of Wnt/β-catenin pathway. Our data indicate that rapid activation and appropriate termination of Wnt/β-catenin signaling and modulation of JNK activity underlie TA + APAP heteroprotection.

Metallothionein protects against isoniazid-induced liver injury through the inhibition of CYP2E1-dependent oxidative and nitrosative impairment in mice

Oxidative stress mediated by hepatic CYP2E1 during isoniazid (INH) metabolism is considered responsible for INH hepatotoxicity. This study attempts to determine whether metallothionein (MT), a cysteine-rich antioxidant can protect against INH-induced liver injury by using a MT-I/II deficient mouse model (MT−/− mice). MT−/− mice and the corresponding wild-type mice received intragastric administrations of 0, 75, 150 and 300 mg/kg of INH for 15 days. The results showed that 150 and 300 mg/kg of INH induced liver injury in both types of mice, as evidenced by increased liver index and histopathological change of liver vacuolar degeneration. Increased hepatic MDA level and 3-NT expression, and decreased GSH content and SOD activity were also observed in both types of mice, indicating the involvement of oxidative and nitrosative stress. INH treatment upregulated hepatic CYP2E1 expression in both types of mice, and the severity of liver injury was in concert with the elevation of CYP2E1 expression. Comparative analyses revealed liver vacuolar degeneration and oxidative and nitrosative stress were more severe in MT−/− mice than wild-type mice, suggesting the hepatoprotection of MT against INH hepatotoxicity. Taken together, these findings clearly demonstrate that MT protects against INH-induced liver toxicity by ameliorating CYP2E1-dependent oxidative and nitrosative impairment.

Association between effectiveness of tuberculosis treatment and cytochrome P-4502E1 polymorphism of the patients.

The risk of antituberculosis (TB) drug-induced liver injury could be determined by patients' genotype polymorphism of the xenobiotic-metabolizing enzymes. To find the meaning of cytochrome P-4502E1 (CYP2E1) polymorphism in TB patients. Corresponding of CYP2E1 polymorphism in TB patients with the level of isoniazid and rifampicin as well as for the outcome and toxicity development during inpatient TB treatment. CYP2E1 genotype was detected with the help of polymerase chain reaction and endonuclease analysis. The level of rifampicin, isoniazid, diene conjugates (DC), and catalase activity in the blood was determined spectrophotometrically. We have considered medical records at the beginning and at the end of inpatient treatment. Kruskal-Wallis, ANOVA, and Chi-square tests were used in this study. The concentration of rifampicin 6 h after its intake was 17.6% higher in carriers of slow metabolizer (SM) CYP2E1 genotype than in patients with rapid metabolizer (RM) genotype that proved a participation of hepatic enzyme CYP2E1 in metabolism of rifampicin. According to obtained results in TB patients with RM genotype, the indexes of cytolysis (alanine aminotransferase, aspartate aminotransferase) and bile stasis (gamma-glutathione transferase) were higher comparatively to SM genotype both before and after inpatient treatment. This correlated with a higher concentration of DC in the blood (+8.6%) and lower plasma catalase activity (-50.0%) in the patients with RM genotype comparatively with the patients with SM genotypes. Polymorphism of CYP2E1 genotype is an important criterion for the development of hepatotoxicity before and during TB treatment while increased rifampicin level has no influence on it.

Resveratrol Ameliorates Experimental Alcoholic Liver Disease by Modulating Oxidative Stress

The aim of this study was to investigate the hepatoprotective effects of resveratrol in alcoholic liver disease (ALD). Alcohol was administered to healthy female rats starting from 6% (v/v) and gradually increased to 20% (v/v) by the fifth week. After 16 weeks of intervention, liver enzymes (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]) were analyzed using a chemistry analyzer, while hepatic antioxidant enzymes, oxidative stress markers, and caspase 3 activity were assessed using ELISA kits. Furthermore, hepatic CYP2E1 protein levels and mRNA levels of antioxidant and inflammation-related genes were determined using western blotting and RT-PCR, respectively. The results showed that resveratrol significantly attenuated alcohol-induced elevation of liver enzymes and improved hepatic antioxidant enzymes. Resveratrol also attenuated alcohol-induced CYP2E1 increase, oxidative stress, and apoptosis (caspase 3 activity). Moreover, genes associated with oxidative stress and inflammation were regulated by resveratrol supplementation. Taken together, the results suggested that resveratrol alleviated ALD through regulation of oxidative stress, apoptosis, and inflammation, which was mediated at the transcriptional level. The data suggests that resveratrol is a promising natural therapeutic agent against chronic ALD.

Effects of rosmarinic acid on acetaminophen-induced hepatotoxicity in male Wistar rats

Context: Drug-induced liver injury is a significant worldwide clinical problem. Rosmarinic acid (RA), a natural phenol, has antioxidant effects. Objective: The effects of RA against acetaminophen (N-acetyl-p-amino-phenol (APAP))-induced oxidative damage and hepatotoxicity in rats were investigated. Materials and methods: Male Wistar rats were pretreated with RA (10, 50 and 100 mg/kg, i.g.) for one week. On day 7, rats received APAP (500 mg/kg, i.p.). Then aspartate aminotransferase (AST), alanine aminotransferase (ALT), albumin, total protein, malondialdehyde (MDA), glutathione (GSH), total antioxidant capacity (TAC), glutathione S-transferase (GST), cytochrome CYP450 and histopathological changes were determined. Results: APAP-induced oxidative stress in liver by a significant increase in the level of MDA (7.6 ± 0.21 nmol/mg) as well as a decrease in the contents of TAC (1.75 ± 0.14 μmol/g), GSH (1.9 ± 0.22 μmol/g) and GST) 3.2 ± 0.28 U/mg). RA treatment decreased MDA (4.32 ± 0.35 nmol/mg) but increased the contents of TAC (3.51 ± 0.34 μmol/g), GSH (3.42 ± 0.16 μmol/g) and GST (5.71 ± 0.71 μmol/g) in APAP group. RA 100 mg/kg decreased ALT (91.5 ± 1.5 U/L), AST (169 ± 8.8 U/L) and CYP450 (3 ± 0.2 nmol/min/mg) in APAP group. Histologically RA attenuated hepatic damage by decreasing necrosis, inflammation, and haemorrhage in liver sections of APAP group. Discussion and conclusions: This is the first report that oral administration of RA dose-dependently elicited significant hepatoprotective effects in rats through inhibition of hepatic CYP2E1 activity and lipid peroxidation. RA-protected hepatic GSH and GST reserves and total tissue antioxidant capacity.

Protective effect of rosiglitazone against acetaminophen-induced acute liver injury is associated with down-regulation of hepatic NADPH oxidases

The peroxisome proliferator-activated receptor gamma (PPAR-γ) is a ligand-activated nuclear receptor that regulates glucose and lipid metabolism. The aim of the present study was to investigate the effects of rosiglitazone (RSG), a synthetic PPAR-γ agonist, on acetaminophen (APAP)-induced acute liver injury. Male CD-1 mice were injected with APAP (300mg/kg). Some mice were pretreated with RSG (20mg/kg) 48, 24 and 1h before APAP injection. As expected, RSG pretreatment alleviated APAP-induced acute liver injury. Moreover, RSG pretreatment attenuated APAP-induced hepatic cell death and improved the survival. Although it did not affect hepatic cytochrome P450 (CYP)2E1 expression, RSG pretreatment attenuated reduction of hepatic glutathione peroxidase (GSH-Px), glutathione reductase (GSH-Rd) and glutathione S-transferase (GST) activities, inhibited upregulation of hepatic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)-2 and NOX-4, and alleviated hepatic GSH depletion during APAP-induced acute liver injury. In addition, RSG pretreatment suppressed activation of hepatic nuclear factor kappa B (NF-κB) and extracellular signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK) signaling during APAP-induced acute liver injury. These results provide a novel mechanistic explanation for RSG-mediated protection against APAP-induced acute liver injury. The present results suggest that synthetic PPAR-γ agonists might be effective agents for preventing the progression of APAP-induced acute liver injury.

Tlr4-mutant mice are resistant to acute alcohol-induced sterol-regulatory element binding protein activation and hepatic lipid accumulation.

Previous studies demonstrated that acute alcohol intoxication caused hepatic lipid accumulation. The present study showed that acute alcohol intoxication caused hepatic lipid accumulation in Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic sterol-regulatory element binding protein (SREBP)-1, a transcription factor regulating fatty acid and triglyceride (TG) synthesis, was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic Fas, Acc, Scd-1 and Dgat-2, the key genes for fatty acid and TG synthesis, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Additional experiment showed that hepatic MyD88 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic NF-κB was activated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Moreover, hepatic GSH content was reduced and hepatic MDA level was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic CYP2E1 was elevated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Hepatic p67phox and gp91phox, two NADPH oxidase subunits, were up-regulated in alcohol-treated Tlr4-wild-type mice but not in Tlr4-mutant mice. Alpha-phenyl-N-t-butylnitrone (PBN), a free radical spin-trapping agent, protected against alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation. In conclusion, Tlr4-mutant mice are resistant to acute alcohol-induced hepatic SREBP-1 activation and hepatic lipid accumulation.

Soy isoflavones reduce acetaminophen-induced liver injury by inhibiting cytochrome P-450-mediated bioactivation and glutathione depletion and increasing urinary drug excretion in rats

Soy isoflavones (SI) are phytochemicals with various biological activities. Acetaminophen can cause acute liver injury when overdosed. In this study, to investigate the effects of SI on the metabolism and toxicity of acetaminophen in liver, rats were fed a controlled diet with or without 120 mg/kg SI-rich product for 2 weeks and were then intraperitoneally injected with acetaminophen. Cytochrome P-450 (CYP), phase II enzymes, membrane transporters, and glutathione in liver were evaluated. Acetaminophen-induced elevations in plasma alanine aminotransferase activity and decreases in liver glutathione levels were ameliorated in rats treated with SI. SI reduced hepatic CYP2E1 and CYP3A activities and acetaminophen-protein adduct contents. Hepatic UDP-glucuronosyltransferase activity and urinary acetaminophen excretion were increased by SI after acetaminophen treatment. Protein expression of multidrug-resistance-associated protein 2/3 and connexin 32 in liver, however, was not changed by SI. Our results indicate that SI-rich product may act as functional food which can reduce acetaminophen-induced hepatotoxicity.

Preliminary characterization of a murine model for 1-bromopropane neurotoxicity: Role of cytochrome P450.

Neurotoxicity of 1-bromopropane (1-BP) has been reported in both human cases and animal studies. To date, neurotoxicity of 1-BP has been induced in rats but not in mice due to the lethal hepatotoxicity of 1-BP. Oxidization by cytochromes P450 and conjugation with glutathione (GSH) are two critical metabolism pathways of 1-BP and play important roles in toxicity of 1-BP. The aim of the present study was to establish a murine model of 1-BP neurotoxicity, by reducing the hepatotoxicity of 1-BP with 1-aminobenzotriazole (1-ABT); a commonly used nonspecific P450s inhibitor. The results showed that subcutaneous or intraperitoneal injection of 1-ABT at 50mg/kg body weight BID (100mg/kg BW/day) for 3days, inhibited about 92-96% of hepatic microsomal CYP2E1 activity, but only inhibited about 62-64% of CYP2E1 activity in brain microsomes. Mice treated with 1-ABT survived even after exposure to 1200ppm 1-BP for 4 weeks and histopathological studies showed that treatment with 1-ABT protected mice from 1-BP-induced hepatic necrosis, hepatocyte degeneration, and hemorrhage. After 4-week exposure to 1-BP, the brain weight of 1-ABT(+)/1200ppm 1-BP group was decreased significantly. In 1-ABT-treated groups, expression of hippocampal Ran protein and cerebral cortical GRP78 was dose-dependently increased by exposure to 1-BP. We conclude that the control of hepatic P450 activity allows the observation of effects of 1-BP on the murine brain at a higher concentration by reduction of hepatotoxicity. The study suggests that further experiments with liver-specific control of P450 activity using gene technology might provide better murine models for 1-bromopropane-induced neurotoxicity.

CHIP(-/-)-Mouse Liver: Adiponectin-AMPK-FOXO-Activation Overrides CYP2E1-Elicited JNK1-Activation, Delaying Onset of NASH: Therapeutic Implications.

Genetic ablation of C-terminus of Hsc70-interacting protein (CHIP) E3 ubiquitin-ligase impairs hepatic cytochrome P450 CYP2E1 degradation. Consequent CYP2E1 gain of function accelerates reactive O2 species (ROS) production, triggering oxidative/proteotoxic stress associated with sustained activation of c-Jun NH2-terminal kinase (JNK)-signaling cascades, pro-inflammatory effectors/cytokines, insulin resistance, progressive hepatocellular ballooning and microvesicular steatosis. Despite this, little evidence of nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) was found in CHIP−/−-mice over the first 8–9-months of life. We herein document that this lack of tissue injury is largely due to the concurrent up-regulation and/or activation of the adiponectin-5′-AMP-activated protein kinase (AMPK)-forkhead box O (FOXO)-signaling axis stemming from at the least three synergistic features: Up-regulated expression of adipose tissue adiponectin and its hepatic adipoR1/adipoR2 receptors, stabilization of hepatic AMPKα1-isoform, identified herein for the first time as a CHIP-ubiquitination substrate (unlike its AMPKα2-isoform), as well as nuclear stabilization of FOXOs, well-known CHIP-ubiquitination targets. Such beneficial predominance of the adiponectin-AMPK-FOXO-signaling axis over the sustained JNK-elevation and injurious insulin resistance in CHIP−/−-livers apparently counteracts/delays rapid progression of the hepatic microvesicular steatosis to the characteristic macrovesicular steatosis observed in clinical NASH and/or rodent NASH-models.

Protective effects of garlic oil against 1,3-dichloro-2-propanol-induced hepatotoxicity: role of CYP2E1 and MAPKs

1,3-Dichloro-2-propanol (1,3-DCP) is a well-known food contaminant that can be detected during the production of a wide range of foods. We investigated whether garlic oil (GO) has protective effects against 1,3-DCP-induced hepatotixicy and oxidative damage in rats. GO significantly attenuated the 1,3-DCP-induced increase in serum aminotransferase activities. This effect was accompanied by attenuation of the histopahological alterations in liver caused by 1,3-DCP. In 1,3-DCP-treated rats, GO prevented formation of hepatic malondialdehyde and depletion of reduced glutathione content, and promoted hepatic antioxidant enzymes activities. 1,3-DCP caused apoptosis in the liver with increases phosphorylation of mitogen-activated protein kinases (MAPKs); GO significantly attenuated these alterations and suppressed the expression of hepatic cytochrome P450 2E1 (CYP2E1). These results suggest that the protective effects of GO against 1,3-DCP-induced hepatotoxicity involve the ability to induce antioxidant enzymes, block metabolic activation of 1,3-DCP by suppressing CYP2E1 expression, and induce antiapoptotic activity by inhibiting phosphorylation of MAPKs.

Alleviative effects from boswellic acid on acetaminophen-induced hepatic injury.

Protective effects of boswellic acid (BA) against acetaminophen (APAP)-induced hepatotoxicity in Balb/ cA mice were examined. BA, at 0.05 or 0.1%, was supplied for 4 weeks. Acute liver injury was induced by APAP treatment. Results showed that BA intake increased hepatic BA bioavailability. APAP treatment decreased glutathione (GSH) level, increased reactive oxygen species (ROS) and oxidized glutathione (GSSG) production; and lowered activity and protein expression of glutathione reductase (GR) and heme oxygenase (HO)-1 in liver. BA intake at both doses alleviated subsequent APAP-induced oxidative stress by retaining GSH content, decreasing ROS and GSSG formations, reserving activity and expression of GR and HO-1 in liver, and lowering hepatic cytochrome P450 2E1 activity and expression. APAP treatment enhanced hepatic levels of interleukin-6, tumor necrosis factor-alpha and monocyte chemoattractant protein-1. BA pre-intake diminished APAP-induced release of those inflammatory cytokines and chemokines. APAP upregulated hepatic protein expression of toll-like receptor (TLR)-3, TLR-4, MyD88, nuclear factor kappa B (NF-κB) p50, NF-κB p65 and JNK. BA pre-intake at both doses suppressed the expression of NF-κB p65 and p-JNK, and only at 0.1% down-regulated hepatic TLR-3, TLR-4 and MyD88 expression. APAP led to obvious foci of inflammatory cell infiltration in liver, determined by H&E stain. BA intake at both doses attenuated hepatic inflammatory infiltration. These findings support that boswellic acid is a potent hepatoprotective agent.

Chronic administration of caderofloxacin, a new fluoroquinolone, increases hepatic CYP2E1 expression and activity in rats.

Caderofloxacin is a new fluoroquinolone that is under phase III clinical trials in China. Here we examined the effects of caderofloxacin on rat hepatic cytochrome P450 (CYP450) isoforms as well as the potential of caderofloxacin interacting with co-administered drugs. Male rats were treated with caderofloxacin (9 mg/kg, ig) once or twice daily for 14 consecutive days. The effects of caderofloxacin on CYP3A, 2D6, 2C19, 1A2, 2E1 and 2C9 were evaluated using a "cocktail" of 6 probes (midazolam, dextromethorphan, omeprazole, theophylline, chlorzoxazone and diclofenac) injected on d 0 (prior to caderofloxacin exposure) and d 15 (after caderofloxacin exposure). Hepatic microsomes from the caderofloxacin-treated rats were used to assess CYP2E1 activity and chlorzoxazone metabolism. The expression of CYP2E1 mRNA and protein in hepatic microsomes was analyzed with RT-PCR and Western blotting, respectively. Fourteen-day administration of caderofloxacin significantly increased the activity of hepatic CYP2E1, leading to enhanced metabolism of chlorzoxazone. In vitro microsomal study confirmed that CYP2E1 was a major metabolic enzyme involved in chlorzoxazone metabolism, and the 14-d administration of caderofloxacin significantly increased the activity of CYP2E1 in hepatic microsomes, resulting in increased formation of 6-hydroxychlorzoxazone. Furthermore, the 14-d administration of caderofloxacin significantly increased the expression of CYP2E1 mRNA and protein in liver microsomes, which was consistent with the pharmacokinetic results. Fourteen-day administration of caderofloxacin can induce the expression and activity of hepatic CYP2E1 in rats. When caderofloxacin is administered, a potential drug-drug interaction mediated by CYP2E1 induction should be considered.

Maternal protein restriction during lactation modulated the expression and activity of rat offspring hepatic CYP1A1, CYP1A2, CYP2B1, CYP2B2, and CYP2E1 during development.

Early nutrition plays a long-term role in the predisposition to chronic diseases and influences the metabolism of several drugs. This may happen through cytochromes P450 (CYPs) regulation, which are the main enzymes responsible for the metabolism of xenobiotics. Here, we analyzed the effects of maternal protein restriction (MPR) on the expression and activity of hepatic offspring’s CYPs during 90 days after birth, using Wistar rats as a mammal model. Hepatic CYP1A1, CYP1A2, CYP2B1, CYP2B2 and CYP2E1 mRNA and protein expression, and associated catalytic activities (ECOD, EROD, MROD, BROD, PROD and PNPH) were evaluated in 15-, 30-, 60-, and 90-day-old offspring from dams fed with either a 0% protein (MPR groups) or a standard diet (C groups) during the 10 first days of lactation. Results showed that most CYP genes were induced in 60- and 90-day-old MPR offspring. The inductions detected in MPR60 and MPR90 were of 5.0- and 2.0-fold (CYP1A2), 3.7- and 2.0-fold (CYP2B2) and 9.8- and 5.8– fold (CYP2E1), respectively, and a 3.8-fold increase of CYP2B1 in MPR90. No major alterations were detected in CYP protein expression. The most relevant CYP catalytic activities’ alterations were observed in EROD, BROD and PNPH. Nevertheless, they did not follow the same pattern observed for mRNA expression, except for an induction of EROD in MPR90 (3.5-fold) and of PNPH in MPR60 (2.2-fold). Together, these results suggest that MPR during lactation was capable of altering the expression and activity of the hepatic CYP enzymes evaluated in the offspring along development.

A cellular model to study drug-induced liver injury in nonalcoholic fatty liver disease: Application to acetaminophen

Obesity and nonalcoholic fatty liver disease (NAFLD) can increase susceptibility to hepatotoxicity induced by some xenobiotics including drugs, but the involved mechanisms are poorly understood. For acetaminophen (APAP), a role of hepatic cytochrome P450 2E1 (CYP2E1) is suspected since the activity of this enzyme is consistently enhanced during NAFLD. The first aim of our study was to set up a cellular model of NAFLD characterized not only by triglyceride accumulation but also by higher CYP2E1 activity. To this end, human HepaRG cells were incubated for one week with stearic acid or oleic acid, in the presence of different concentrations of insulin. Although cellular triglycerides and the expression of lipid-responsive genes were similar with both fatty acids, CYP2E1 activity was significantly increased only by stearic acid. CYP2E1 activity was reduced by insulin and this effect was reproduced in cultured primary human hepatocytes. Next, APAP cytotoxicity was assessed in HepaRG cells with or without lipid accretion and CYP2E1 induction. Experiments with a large range of APAP concentrations showed that the loss of ATP and glutathione was almost always greater in the presence of stearic acid. In cells pretreated with the CYP2E1 inhibitor chlormethiazole, recovery of ATP was significantly higher in the presence of stearate with low (2.5mM) or high (20mM) concentrations of APAP. Levels of APAP-glucuronide were significantly enhanced by insulin. Hence, HepaRG cells can be used as a valuable model of NAFLD to unveil important metabolic and hormonal factors which can increase susceptibility to drug-induced hepatotoxicity.

The effect of ageing on isoniazid pharmacokinetics and hepatotoxicity in Fischer 344 rats.

Isoniazid is the first-line treatment for tuberculosis; however, its use is limited by hepatotoxicity. Age-related differences in isoniazid pharmacokinetics and hepatotoxicity are uncertain. We aimed to investigate these in young (3 ± 0 months, n = 26) and old (23.0 ± 0.2 months, n = 27) male Fischer 344 rats following a low- or high-dose toxic regimen of isoniazid or vehicle (4 doses/day over 2 days; low: 100, 75, 75, 75 mg/kg; high: 150, 105, 105, 105 mg/kg i.p. every 3 h). Fifteen hours after the last dose, animals were euthanized and sera and livers were prepared for analysis. Isoniazid treatment increased serum hepatotoxicity markers (alanine and aspartate transaminase) in young animals but not in old animals, and only reached significance with the high dose in young animals. Isoniazid treatment caused a trend towards an increase in necrosis in young animals with both doses. In contrast, microvesicular steatosis was increased in old isoniazid-treated animals, reaching significance only with the low dose (steatosis prevalence in old: vehicle 1/9, isoniazid 4/5; P < 0.05). Among isoniazid-treated animals, concentrations of toxic intermediates acetylhydrazine and hydrazine were higher in old than young animals (P < 0.05). With both doses, hepatic cytochrome P450 2E1 activity was higher in young animals compared with old (P < 0.05). There were no other age effects seen on any of the other measured enzymes involved in isoniazid metabolism (N-acetyl transferase, amidase, glutathione-S-transferase). These results show age-related changes in isoniazid pharmacokinetics may contribute towards differential patterns of toxicity and confirm that standard hepatotoxicity markers do not detect isoniazid-induced microvesicular steatosis.

Gene copy number variation analysis reveals dosage-insensitive expression of CYP2E1.

Gene copy number variants (CNVs) of CYP2E1 have been described but not functionally characterized. Here we investigated effects of CNVs on hepatic and lymphoblastoid CYP2E1 expression. Using available single-nuleotide polymorphism microarray data and quantitative PCR, CYP2E1 gene duplication and deletion carriers were identified. CYP2E1 mRNA, protein and enzyme activity (chlorzoxazone-6-hydroxylation) phenotypes of CYP2E1 were not associated with gene copy number. Analysis of gene expression in lymphoblastoid cell lines in relation to CNV confirmed this finding in an extrahepatic tissue and for other ethnicities. Further analyses identified a linked haplotype cluster with possible influence on gene expression. In summary, our data suggest a homeostatic, gene dosage-insensitive regulation of CYP2E1 expression by unknown gene dosage compensation mechanisms. This is in striking contrast to well-known structural variations of CYP2A6 and CYP2D6 that have a strong impact on expression and activity. These findings are important in the context of pharmacogenetic prediction.

Saponins isolated from the leaves of Panax notoginseng protect against alcoholic liver injury via inhibiting ethanol-induced oxidative stress and gut-derived endotoxin-mediated inflammation

Effects of saponins from leaves of Panax notoginseng (LPNS) against alcoholic liver injury were evaluated, and their probable molecular mechanisms were further elucidated in a mouse model of chronic-plus-single-binge ethanol feeding. Alcohol exposure dramatically increased plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), triacylglycerol (TG) and endotoxin; these elevations were attenuated by treatment with LPNS at a dose of 100 or 300 mg/kg. LPNS was also found to suppress thiobarbituric acid reactive substances (TBARS) production, enhance glutathione (GSH) level and superoxide dismutase (SOD) activity in liver. The protective of LPNS against oxidative stress was associated with down-regulation of hepatic cytochrome P450 2E1 (CYP2E1), and upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) and haem oxygenase-1 (HO-1). Additionally, LPNS ameliorated gut leakiness via upregulating the expressions of tight junction proteins, and suppressed endotoxin-mediated inflammation via down-regulating toll-like receptor-4 (TLR-4), CD14 and p-NF-κB p65. These results demonstrate that treatment with LPNS effectively protects against alcoholic liver injury through reducing ethanol-induced oxidative stress and ameliorating gut-derived endotoxin-mediated inflammation.

Galangin Prevents Acute Hepatorenal Toxicity in Novel Propacetamol-Induced Acetaminophen-Overdosed Mice.

Acetaminophen (APAP) overdose causes severe liver and kidney damage. APAP-induced liver injury (AILI) represents the most frequent cause of drug-induced liver failure. APAP is relatively insoluble and can only be taken orally; however, its prodrug, propacetamol, is water soluble and usually injected directly. In this study, we examined the time-dependent effects of AILI after propacetamol injection in mice. After analyses of alanine aminotransferase and aspartate aminotransferase activities and liver histopathology, we demonstrated that a novel AILI mouse model can be established by single propacetamol injection. Furthermore, we compared the protective and therapeutic effects of galangin with a known liver protective extract, silymarin, and the only clinical agent for treating APAP toxicity, N-acetylcysteine (NAC), at the same dose in the model mice. We observed that galangin and silymarin were more effective than NAC for protecting against AILI. However, only NAC greatly improved both the survival time and rate consequent to a lethal dose of propacetamol. To decipher the hepatic protective mechanism(s) of galangin, galangin pretreatment significantly decreased the hepatic oxidative stress, increased hepatic glutathione level, and decreased hepatic microsomal CYP2E1 levels induced by propacetamol injection. In addition, propacetamol injection also reproduced the probability of APAP-induced kidney injury (AIKI), appearing similar to a clinical APAP overdose. Only galangin pretreatment showed the protective effect of AIKI. Thus, we have established a novel mouse model for AILI and AIKI using a single propacetamol injection. We also demonstrated that galangin provides significant protection against AILI and AIKI in this mouse model.

Altered cytochrome P450 activities and expression levels in the liver and intestines of the monosodium glutamate-induced mouse model of human obesity

Cytochromes P450 (CYPs) are enzymes present from bacteria to man involved in metabolism of endogenous and exogenous compounds incl. drugs. Our objective was to assess whether obesity leads to changes in activities and expression of CYPs in the mouse liver, small intestine and colon. An obese mouse model with repeated injection of monosodium glutamate (MSG) to newborns was used. Controls were treated with saline. All mice were sacrificed at 8 months. In the liver and intestines, levels of CYP mRNA and proteins were analyzed using RT-PCR and Western blotting. Activities of CYP enzymes were measured with specific substrates of human orthologous forms. At the end of the experiment, body weight, plasma insulin and leptin levels as well as the specific content of hepatic CYP enzymes were increased in obese mice. Among CYP enzymes, hepatic CYP2A5 activity, protein and mRNA expression increased most significantly in obese animals. Higher activities and protein levels of hepatic CYP2E1 and 3A in the obese mice were also found. No or a weak effect on CYPs 2C and 2D was observed. In the small intestine and colon, no changes of CYP enzymes were detected except for increased expression of CYP2E1 and decreased expression of CYP3A mRNAs in the colon of the obese mice. Results of our study suggest that the specific content and activities of some liver CYP enzymes (especially CYP2A5) can be increased in obese mice. Higher activity of CYP2A5 (CYP2A6 human ortholog) could lead to altered metabolism of drug substrates of this enzyme (valproic acid, nicotine, methoxyflurane).