Cyp1a2 protects against reactive oxygen production in mouse liver microsomes

Dose-dependent exposure to indoxyl sulfate alters AHR signaling, sirtuins gene expression, oxidative DNA damage, and bone mineral status in rats

Indoxyl sulfate (IS), an agonist of aryl hydrocarbon receptors (AhR), can accumulate in patients with chronic kidney disease, but its direct effect on bone is not clear. The present study investigated the effect of chronic exposure to low (100 mg/kg b.w.; 100 IS) and high (200 mg/kg b.w.; 200 IS) dose of IS on bone AhR pathway, sirtuins (SIRTs) expression, oxidative DNA damage and bone mineral status in Wistar rats. The accumulation of IS was observed only in trabecular bone tissue in both doses. The differences were observed in the bone parameters, depending on the applied IS dose. The exposure to 100 IS increased AhR repressor (AhRR)-CYP1A2 gene expression, which was associated with SIRT-1, SIRT-3 and SIRT-7 expression. At the low dose group, the oxidative DNA damage marker was unchanged in the bone samples, and it was inversely related to the abovementioned SIRTs expression. In contrast, the exposure to 200 IS reduced the expression of AhRR, CYP1A, SIRT-3 and SIRT-7 genes compared to 100 IS. The level of oxidative DNA damage was higher in trabecular bone in 200 IS group. Femoral bone mineral density was decreased, and inverse relations were noticed between the level of trabecular oxidative DNA damage and parameters of bone mineral status. In conclusion, IS modulates AhR-depending signaling affecting SIRTs expression, oxidative DNA damage and bone mineral status in a dose dependent manner.

Exploring the Mechanism of Hepatotoxicity Induced by Dictamnus dasycarpus Based on Network Pharmacology, Molecular Docking and Experimental Pharmacology

The root bark of Dictamnus dasycarpus Turcz is a traditional Chinese medicine, Dictamni Cortex (DC), which is mainly used in the clinical treatment of skin inflammation, eczema, rubella, rheumatism, and gynecological inflammation. Unexpectedly, there are some cases of liver injury after the administration of DC. However, the mechanism of hepatotoxicity remains ambiguous. The aim of this study was to explore the mechanism and substance bases of DC hepatotoxicity based on network pharmacology and molecular docking, verified through pharmacological experiments. Partial prototype components and metabolites in vivo of quinoline alkaloids from DC were selected as candidate compounds, whose targets were collected from databases. Network pharmacology was applied to study the potential hepatotoxic mechanism after correlating the targets of candidate compounds with the targets of hepatotoxicity. Molecular docking was simulated to uncover the molecular mechanism. Furthermore, the hepatotoxicity of the extract and its constituents from DC was evaluated in vivo and in vitro. We constructed the "potential toxic components-toxic target-toxic pathway" network. Our results showed that the targets of DC included CYP1A2 and GSR, participating in heterologous steroid metabolism, REDOX metabolism, drug metabolism, heterocyclic metabolic processes, the synthesis of steroid hormone, cytochrome P450 metabolism, chemical carcinogens and bile secretion pathways. In vitro and in vivo experiments displayed that DC could result in a decrease in GSH-Px and oxidative stress, simultaneously inhibiting the expression of CYP1A2 and inducing hepatotoxicity. These results further indicated the mechanism of hepatotoxicity induced by Dictamnus dasycarpus, providing a basic theory to explore and prevent hepatotoxicity in the clinical usage of Dictamnus dasycarpus.

Metabolism and Mechanism of Human Cytochrome P450 Enzyme 1A2

Human cytochrome P450 enzyme 1A2 (CYP1A2) is one of the most important cytochrome P450 (CYP) enzymes in the liver, accounting for 13% to 15% of hepatic CYP enzymes. CYP1A2 metabolises many clinical drugs, such as phenacetin, caffeine, clozapine, tacrine, propranolol, and mexiletine. CYP1A2 also metabolises certain precarcinogens such as aflatoxins, mycotoxins, nitrosamines, and endogenous substances such as steroids. The regulation of CYP1A2 is influenced by many factors. The transcription of CYP1A2 involves not only the aromatic hydrocarbon receptor pathway but also many additional transcription factors, and CYP1A2 expression may be affected by transcription coactivators and compression factors. Degradation of CYP1A2 mRNA and protein, alternative splicing, RNA stability, regulatory microRNAs, and DNA methylation are also known to affect the regulation of CYP1A2. Many factors can lead to changes in the activity of CYP1A2. Smoking, polycyclic aromatic hydrocarbon ingestion, and certain drugs (e.g., omeprazole) increase its activity, while many clinical drugs such as theophylline, fluvoxamine, quinolone antibiotics, verapamil, cimetidine, and oral contraceptives can inhibit CYP1A2 activity. Here, we review the drugs metabolised by CYP1A2, the metabolic mechanism of CYP1A2, and various factors that influence CYP1A2 metabolism. The metabolic mechanism of CYP1A2 is of great significance in the development of personalised medicine and CYP1A2 target-based drugs.

Oxidative Stress Management in Chronic Liver Diseases and Hepatocellular Carcinoma

Chronic viral hepatitis B and C and non-alcoholic fatty liver disease (NAFLD) have been widely acknowledged to be the leading causes of liver cirrhosis and hepatocellular carcinoma. As anti-viral treatment progresses, the impact of NAFLD is increasing. NAFLD can coexist with chronic viral hepatitis and exacerbate its progression. Oxidative stress has been recognized as a chronic liver disease progression-related and cancer-initiating stress response. However, there are still many unresolved issues concerning oxidative stress, such as the correlation between the natural history of the disease and promising treatment protocols. Recent findings indicate that oxidative stress is also an anti-cancer response that is necessary to kill cancer cells. Oxidative stress might therefore be a cancer-initiating response that should be down regulated in the pre-cancerous stage in patients with risk factors for cancer, while it is an anti-cancer cell response that should not be down regulated in the post-cancerous stage, especially in patients using anti-cancer agents. Antioxidant nutrients should be administered carefully according to the patients’ disease status. In this review, we will highlight these paradoxical effects of oxidative stress in chronic liver diseases, pre- and post-carcinogenesis.

Polychlorinated diphenyl sulfides can induce ROS and genotoxicity via the AhR-CYP1A1 pathway

Polychlorinated diphenyl sulfides (PCDPSs) are a group of chemicals that can interact and activate the aryl hydrocarbon receptor (AhR). Previous studies have shown that PCDPSs can cause oxidative stress in livers. However, information on genotoxicity of PCDPSs is limited. In this study, it is hypothesized that PCDPSs can produce reactive oxygen species (ROS) by activating the AhR and inducing expression of CYP1A1, which subsequently causes genotoxicity. HepG2 cells (transfected with AhR and CYP1A1 siRNA or not) were exposed to six PCDPSs. ROS and expression of five genes were measured to confirm relationships between genotoxicity and signaling along AhR pathway. After 24 h, a significant concentration-dependent ROS was observed. Production of ROS varied with the number of Cl atoms. And the formation of ROS decreases with the increase of the number of Cl atoms, which was consistent with results observed for polychlorinated biphenyls (PCBs). Most of the tested PCDPSs up-regulated expression of CYP1A1 enzyme via signaling AhR pathways. The exposure to 2,3',4,5-tetra-CDPS at 10 μM up-regulated the CYP1A1 mRNA in HepG2 cells to 29-fold. Expression of CYP1A1 mRNA was related to the number of substituted Cl, probably due to the stronger ability of more chlorinated PCDPSs to bind to and activate the AhR. However, there was no significant quantitative relationship between expression of CYP1A1 and concentrations of ROS, probably due to other oxidases' influence. Furthermore, PCDPSs also caused induction of OGG1 and XRS2 more than 2 times, indicates oxidation of bases and breaks of strands. The transfection of cells with siRNA to silence expression of the CYP1A1 gene results in ROS at background levels, further supporting the proposed mechanism PCDPSs inducing ROS and DNA damage via the AhR-mediated pathway.

Schisantherin A alleviated alcohol-induced liver injury by the regulation of alcohol metabolism and NF-kB pathway

Schisantherin A (SinA), one of the most abundant active ingredients of Schisandra chinensis, was reported to protect and benefit the liver, however, its effect on alcohol-induced liver injury (ALI) was still not clear. In the present study, an ALI mice model was induced by feeding mice an alcohol-containing liquid diet for four weeks. Then, 100 mg/kg or 200 mg/kg SinA was administered to mice every day by gavage for the last two weeks. Histopathological analysis showed that alcohol-induced liver lipid vacuoles were reduced by SinA. The activities of aspartate aminotransferase (AST, 61.90 ± 14.65 vs. 93.65 ± 20.50, 50.46 ± 13.21 vs. 93.65 ± 20.50) and alanine transaminase (ALT, 41.29 ± 9.20 vs. 64.04 ± 18.13, 36.52 ± 7.71 vs. 64.04 ± 18.13) in the serum of ALI mice were significantly reduced by 100 mg/kg or 200 mg/kg SinA when compared with control mice. Alcohol-induced oxidative stress and the inflammatory response in the liver were suppressed by SinA in a dose-dependent manner. Meanwhile, treatment with SinA decreased alcohol dehydrogenase (ADH) activity and increased acetaldehyde dehydrogenase (ALDH) activity in ALI mice. Alcohol-induced upregulation of CYP2E1 and CYP1A2 in the liver was inhibited by SinA. Further, SinA suppressed activation of the NF-kB pathway in ALI mice. In conclusion, our findings demonstrate that SinA is able to protect against ALI, and this may be, at least in part, caused by regulation of alcohol metabolism and the NF-kB pathway. Our data suggest a therapeutic potential of SinA in the treatment of ALI.

The influence of CYP1A2 genotype in the blood pressure response to caffeine ingestion is affected by physical activity status and caffeine consumption level

This study aimed to investigate whether the influence of CYP1A2 genotype in the blood pressure (BP) response to caffeine ingestion was affected by physical activity status and habitual caffeine consumption. Thirty-seven participants (19-50 years old) took place in the study and were categorized according to i) genotype: CYP1A2 (AA) "fast metabolizer", and CYP1A2 (AC) "slow metabolizer"; ii) physical activity level: sedentary (S) and physically active (A); and iii) caffeine consumption level: non-habitual caffeine consumer (NC) and habitual heavy caffeine consumer (C). All groups had BP assessed before (basal) and 1 hourh after (post) caffeine ingestion (6 mg·kg^-1). It was observed that AC genotype individuals had increased basal-DBP and post-caffeine SBP when compared to AA individuals. Additionally, acute caffeine ingestion increased SBP only in the AC group. It was also found that physical activity only modulated the BP responses to acute caffeine ingestion in AC individuals. Furthermore, the results indicated that the habitual heavy caffeine consumers AC individuals had increased basal-DBP when compared to the AA ones. Our results suggest that the influence of CYP1A2 genotype in the basal and post-caffeine BP response to caffeine ingestion is modified by physical activity status and caffeine consumption level.

β-Naphthoflavone treatment attenuates neonatal hyperoxic lung injury in wild type and Cyp1a2-knockout mice

Exposure to supraphysiological concentrations of oxygen (hyperoxia) leads to bronchopulmonary dysplasia (BPD), one of the most common pulmonary morbidities in preterm neonates, which is more prevalent in males than females. Beta-naphthoflavone (BNF) is protective against hyperoxic lung injury in adult and neonatal wild type (WT) mice and in and mice lacking Cyp1a1gene. In this investigation, we tested the hypothesis that BNF treatment will attenuate neonatal hyperoxic lung injury in WT and Cyp1a2-/- mice, and elucidated the effect of sex-specific differences. Newborn WT or Cyp1a2-/- mice were treated with BNF (10mg/kg) or the vehicle corn oil (CO) i.p., from postnatal day (PND) 2 to 8 once every other day, while being maintained in room air or hyperoxia (85% O2) for 14days. Hyperoxia exposure lead to alveolar simplification and arrest in angiogenesis in WT as well as Cyp1a2-/- mice No significant differences were seen between WT and Cyp1a2-/- mice. Cyp1a2-/- female mice had better preservation of pulmonary angiogenesis at PND15 compared to similarly exposed males. BNF treatment attenuated lung injury and inflammation in both genotypes, and this was accompanied by a significant induction of hepatic and pulmonary CYP1A1 in WT but not in Cyp1a2-/- mice. BNF treatment increased NADPH quinone oxidoreductase (NQO1) mRNA levels in Cyp1a2-/- mouse livers compared to WT mice. These results suggest that BNF is protective in neonatal mice exposed to hyperoxia independent of CYP1A2 and this may entail the protective effect of phase II enzymes like NQO1.

Antioxidant Functions of the Aryl Hydrocarbon Receptor

The aryl hydrocarbon receptor (AhR) is a transcription factor belonging to the basic helix-loop-helix/PER-ARNT-SIM family. It is activated by a variety of ligands, such as environmental contaminants like polycyclic aromatic hydrocarbons or dioxins, but also by naturally occurring compounds and endogenous ligands. Binding of the ligand leads to dimerization of the AhR with aryl hydrocarbon receptor nuclear translocator (ARNT) and transcriptional activation of several xenobiotic phase I and phase II metabolizing enzymes. It is generally accepted that the toxic responses of polycyclic aromatic hydrocarbons, dioxins, and structurally related compounds are mediated by activation of the AhR. A multitude of studies indicate that the AhR operates beyond xenobiotic metabolism and exerts pleiotropic functions. Increasing evidence points to a protective role of the AhR against carcinogenesis and oxidative stress. Herein, I will highlight data demonstrating a causal role of the AhR in the antioxidant response and present novel findings on potential AhR-mediated antioxidative mechanisms.

Diminished Resistance to Hyperoxia in Brains of Reproductively Senescent Female CBA/H Mice

Background

We have explored sex differences in ability to maintain redox balance during acute oxidative stress in brains of mice. We aimed to determine if there were differences in oxidative/antioxidative status upon hyperoxia in brains of reproductively senescent CBA/H mice in order to elucidate some of the possible mechanisms of lifespan regulation.

Material/Methods

The brains of 12-month-old male and female CBA/H mice (n=9 per sex and treatment) subjected to 18-h hyperoxia were evaluated for lipid peroxidation (LPO), antioxidative enzyme expression and activity - superoxide dismutase 1 and 2 (Sod-1, Sod-2), catalase (Cat), glutathione peroxidase 1 (Gpx-1), heme-oxygenase 1 (Ho-1), nad NF-E2-related factor 2 (Nrf2), and for 2-deoxy-2-[¹⁸F] fluoro-D-glucose (¹⁸FDG) uptake.

Results

No increase in LPO was observed after hyperoxia, regardless of sex. Expression of Nrf-2 showed significant downregulation in hyperoxia-treated males (p=0.001), and upregulation in hyperoxia-treated females (p=0.023). Also, in females hyperoxia upregulated Sod-1 (p=0.046), and Ho-1 (p=0.014) genes. SOD1 protein was upregulated in both sexes after hyperoxia (p=0.009 for males and p=0.011 for females). SOD2 protein was upregulated only in females (p=0.008) while CAT (p=0.026) and HO-1 (p=0.042) proteins were increased after hyperoxia only in males. Uptake of ¹⁸FDG was decreased after hyperoxia in the back brain of females.

Conclusions

We found that females at their reproductive senescence are more susceptible to hyperoxia, compared to males. We propose this model of hyperoxia as a useful tool to assess sex differences in adaptive response to acute stress conditions, which may be partially responsible for observed sex differences in longevity of CBA/H mice.

Sex-specific differences in hyperoxic lung injury in mice: role of cytochrome P450 (CYP)1A

Sex-specific differences in pulmonary morbidity in adults and preterm infants are well documented. Hyperoxia contributes to lung injury in experimental animals and humans. Cytochrome P450 (CYP) 1A enzymes have been shown to play a mechanistic role in hyperoxic lung injury (HLI) in animal models. Whether CYP1A enzymes contribute to gender-specific differences in relation to HLI is unknown. In this investigation, we tested the hypothesis that mice will display gender-specific differences in HLI, and that this phenomenon will be altered in mice lacking the genes for Cyp1a1 or 1a2. Eight week-old male and female wild type (WT) (C57BL/6J) mice, Cyp1a1-/-, and Cyp1a2-/- mice were exposed to 72h of hyperoxia (FiO2>0.95). Lung injury and inflammation were assessed and pulmonary and hepatic CYP1A1 and CYP1A2 levels were quantified at the enzyme activity, protein and mRNA level. Upon exposure to hyperoxia, liver and lung microsomal proteins showed higher pulmonary CYP1A1 (apoprotein level and activity) in WT females compared to WT males and a greater induction in hepatic CYP1A2 mRNA levels and activity in WT females after hyperoxia exposure. The gender based female advantage was lost or reversed in Cyp1a1-/- and Cyp1a2-/- mice. These findings suggest an important role for CYP1A enzymes in the gender-specific modulation of hyperoxic lung injury.

In Vivo Exposures to Particulate Matter Collected from Saudi Arabia or Nickel Chloride Display Similar Dysregulation of Metabolic Syndrome Genes

Particulate matter (PM) exposures have been linked to mortality, low birth weights, hospital admissions, and diseases associated with metabolic syndrome, including diabetes mellitus, cardiovascular disease, and obesity. In a previous in vitro and in vivo study, data demonstrated that PM(10μm) collected from Jeddah, Saudi Arabia (PMSA), altered expression of genes involved in lipid and cholesterol metabolism, as well as many other genes associated with metabolic disorders. PMSA contains a relatively high concentration of nickel (Ni), known to be linked to several metabolic disorders. In order to evaluate whether Ni and PM exposures induce similar gene expression profiles, mice were exposed to 100 μg/50 μl PM(SA) (PM-100), 50 μg/50 μl nickel chloride (Ni-50), or 100 μg/50 μl nickel chloride (Ni-100) twice per week for 4 wk and hepatic gene expression changes were determined. Ultimately, 55 of the same genes were altered in all 3 exposures. However, where the two Ni groups differed markedly was in the regulation (up or down) of these genes. Ni-100 and PM-100 groups displayed similar regulations, whereby 104 of the 107 genes were similarly modulated. Many of the 107 genes are involved in metabolic syndrome and include ALDH4A1, BCO2, CYP1A, CYP2U, TOP2A. In addition, the top affected pathways, such as fatty acid α-oxidation, and lipid and carbohydrate metabolism, are involved in metabolic diseases. Most notably, the top diseased outcome affected by these changes in gene expression was cardiovascular disease. Given these data, it appears that Ni and PM(SA) exposures display similar gene expression profiles, modulating the expression of genes involved in metabolic disorders.

A feedback mechanism to control apoptosis occurs in the digestive gland of the oyster crassostrea gigas exposed to the paralytic shellfish toxins producer Alexandrium catenella

To better understand the effect of Paralytic Shellfish Toxins (PSTs) accumulation in the digestive gland of the Pacific oyster, Crassostrea gigas, we experimentally exposed individual oysters for 48 h to a PSTs producer, the dinoflagellate Alexandrium catenella. In comparison to the effect of the non-toxic Alexandrium tamarense, on the eight apoptotic related genes tested, Bax and BI.1 were significantly upregulated in oysters exposed 48 h to A. catenella. Among the five detoxification related genes tested, the expression of cytochrome P450 (CYP1A) was shown to be correlated with toxin concentration in the digestive gland of oysters exposed to the toxic dinoflagellate. Beside this, we observed a significant increase in ROS production, a decrease in caspase-3/7 activity and normal percentage of apoptotic cells in this tissue. Taken together, these results suggest a feedback mechanism, which may occur in the digestive gland where BI.1 could play a key role in preventing the induction of apoptosis by PSTs. Moreover, the expression of CYP1A, Bax and BI.1 were found to be significantly correlated to the occurrence of natural toxic events, suggesting that the expression of these genes together could be used as biomarker to assess the biological responses of oysters to stress caused by PSTs.

Oxidative stress pathways in noncancerous human liver tissue to predict hepatocellular carcinoma recurrence: a prospective, multicenter study

The prediction of cancer recurrence holds the key to improvement of the postoperative prognosis of patients. In this study, the recurrence of early-stage hepatocellular carcinoma (HCC) after curative hepatectomy was analyzed by the genome-wide gene-expression profiling on cancer tissue and the noncancerous liver tissue. Using the training set of 78 cases, the cytochrome P450 1A2 (CYP1A2) gene in noncancerous liver tissue was identified as the predictive candidate for postoperative recurrence (hazard ratio [HR], 0.447; 95% confidence interval [CI], 0.249-0.808; P = 0.010). Multivariate analysis revealed the statistically significant advantage of CYP1A2 down-regulation to predict recurrence (odds ratio, 0.534; 95% CI, 0.276-0.916; P = 0.036), and the expression of CYP1A2 protein was confirmed immunohistochemically. An independently multi-institutional cohort of 211 patients, using tissue microarrays, validated that loss of expression of CYP1A2 in noncancerous liver tissue as the only predictive factor of recurrence after curative hepatectomy for early-stage HCC (HR, 0.480; 95% CI, 0.256-0.902; P = 0.038). Gene set-enrichment analysis revealed close association of CYP1A2 down-regulation with oxidative stress pathways in liver tissue (P < 0.001, false discovery rate [FDR] = 0.042; P = 0.006, FDR = 0.035). Our results indicate these pathways as the molecular targets to prevent recurrence, as well as the potential prediction of the super high-risk population of HCC using liver tissue.

MG132 alleviates liver injury induced by intestinal ischemia/reperfusion in rats: involvement of the AhR and NFκB pathways

BACKGROUND

MG132 is a potent antioxidant and has been reported to play a protective role in ischemia/reperfusion (I/R) of many organs. Recent studies have shown that the Aryl hydrocarbon receptor (AhR) may play a beneficial role in I/R of many organs and an AhR agonist has been implicated in an anti-inflammatory role. MG132 might function as an AhR agonist through proteasome inhibition, possibly through the inhibition of NFκB. Herein, we hypothesized that MG132 may play a protective role in liver injury induced by intestinal I/R and we analyzed the expression behavior of AhR and NFκB to determine whether the two factors play a role in intestinal I/R.

MATERIALS AND METHODS

Thirty-two Sprague-Dawley rats were divided into four groups: control, I/R, MG132 control, and MG132 pretreatment. The I/R and MG132 pretreatment groups were subjected to mesenteric arterial ischemia for 1 h and reperfusion for 3 h. The control and MG132 control groups underwent surgical preparation including isolation of the superior mesenteric artery (SMA) without occlusion. The MG132 control and MG132 pretreatment groups were subjected to intraperitoneal administration of 0.5 mg/kg MG132 30 min before surgery. We collected serum specimens to measure TNF-α, IL-6, liver tissue levels of malondialdehyde (MDA), AhR, and cyp1a2; NFκB, IκBα, and ICAM-1 were also tested. Histologic changes of liver and intestine were subsequently evaluated.

RESULTS

Compared with the control group, significant increases in MDA, NFκB, and ICAM-1 levels were accompanied by decreases in AhR, cyp1a2, and IκBα expression in the liver in the I/R group, which is consistent with liver and intestinal tissue injury. MG132 blocked the alterations of the indicators above. There were no changes in the MG132 control group compared with the control group in the indicators above.

CONCLUSIONS

This study demonstrated that MG132 has a significant effect in protection against liver injury induced by intestinal I/R, which may be due to modulation of the AhR and NFκB pathways.

Omeprazole attenuates hyperoxic lung injury in mice via aryl hydrocarbon receptor activation and is associated with increased expression of cytochrome P4501A enzymes

Hyperoxia contributes to lung injury in experimental animals and bronchopulmonary dysplasia (BPD) in preterm infants. Cytochrome P4501A (CYP1A) enzymes, which are regulated by the aryl hydrocarbon receptor (AhR), have been shown to attenuate hyperoxic lung injury in rodents. Omeprazole, a proton pump inhibitor, used in humans to treat gastric acid-related disorders, induces hepatic CYP1A in vitro. However, the mechanism by which omeprazole induces CYP1A and its impact on CYP1A expression in vivo and hyperoxic lung injury are unknown. Therefore, we tested the hypothesis that omeprazole attenuates hyperoxic lung injury in adult wild-type (WT) C57BL/6J mice by an AhR-mediated induction of pulmonary and hepatic CYP1A enzymes. Accordingly, we determined the effects of omeprazole on pulmonary and hepatic CYP1A expression and hyperoxic lung injury in adult WT and AhR dysfunctional (AhRd) mice. We found that omeprazole attenuated lung injury in WT mice. Attenuation of lung injury by omeprazole paralleled enhanced pulmonary CYP1A1 and hepatic CYP1A2 expression in the omeprazole-treated mice. On the other hand, omeprazole failed to enhance pulmonary CYP1A1 and hepatic CYP1A2 expression and protect against hyperoxic lung injury in AhRd mice. In conclusion, our results suggest that omeprazole attenuates hyperoxic lung injury in mice by AhR-mediated mechanisms, and this phenomenon is associated with induction of CYP1A enzymes. These studies have important implications for the prevention and/or treatment of hyperoxia-induced disorders such as BPD in infants and acute respiratory distress syndrome in older children and adults.

Maneb and paraquat-induced modulation of toxicant responsive genes in the rat liver: comparison with polymorphonuclear leukocytes

Experimental studies have shown that toxicant responsive genes, cytochrome P450s (CYPs) and glutathione S-transferases (GSTs) play a critical role in pesticide-induced toxicity. CYPs play pro-oxidant role and GSTs offer protection in maneb (MB) and paraquat (PQ)-induced brain and lung toxicities. The present study aimed to investigate the effect of repeated exposures of MB and/or PQ on lipid peroxidation (LPO), glutathione content (GSH) and toxicant responsive genes, i.e., CYP1A1, 1A2, 2E1, GSTA4-4, GSTA1-1 and GSTA3-3 in the liver and to correlate the same with polymorphonuclear leukocytes (PMNs). A significant augmentation in LPO and reduction in GSH content was observed in a time of exposure dependent manner in the liver and PMNs of MB and/or PQ treated animals. The expression and catalytic activity of CYP2E1 and GSTA4-4 were significantly increased following MB and/or PQ exposure both in the liver and PMNs. Although the expression of GSTA3-3 was increased, the expression of GSTA1-1 was unaltered after MB and/or PQ treatment in both the liver and PMNs. MB augmented the expression and catalytic activity of CYP1A1 in the liver, however, CYP1A2 was unaffected. PQ, on the other hand, significantly increased hepatic CYP1A2 expression and catalytic activity. MB and/or PQ did not produce any significant changes in CYP1A1 and CYP1A2 in PMNs. The results of the study thus demonstrate that MB and PQ differentially regulate hepatic CYP1A1 and CYP1A2 while LPO, GSH, CYP2E1, GSTA4-4 and GSTA3-3 are modulated in the similar fashions both in the liver and PMNs.

Cyp4a14 overexpression induced by hyperoxia in female CBA mice as a possible contributor of increased resistance to oxidative stress

The beneficial effects of hyperoxia have been noted in treatment of several diseases and pathological states. However, the excessive production of ROS under hyperoxic conditions can directly damage cellular macromolecules if the imbalance in antioxidant status exists. Cytochrome P450 (Cyp) 4a14 has an important role in the metabolism of lipids and as a source of ROS in oxidative stress. This study investigated the oxidant/antioxidant status as a response to hyperoxia treatment in liver of young CBA/Hr mice of both sexes and whether the observed response is mediated by Cyp4a14 via PPAR isoforms in a sex-dependent manner. The overexpression of Cyp4a14, lack of both LPO and of 4-hydroxynonenal(HNE)-protein adducts revealed by immunohistochemical analysis in hyperoxia-treated females indicates their greater resistance to hyperoxia compared to males, which is parallelled to changes in PPARbeta/delta and PPARgamma expression. These results suggest the presence of sex-dependent changes in all investigated parameters, which points out sex-related susceptibility towards oxidative stress and hyperoxia treatment of various pathological conditions and diseases.

Cytochrome P450 gender-related differences in response to hyperoxia in young CBA mice

Cytochrome P450 monooxygenases (CYPs) represent large class of heme-containing enzymes that catalyze the metabolism of various endogenous and exogenous substrates. Although they are found in many tissues, the function of the particular subset of their isoforms does not appear to be the same. Many CYP genes exhibit sexually dimorphic expression, while others are sex-independent. Moreover, as a source of reactive oxygen species (ROS), P450 system is believed to play the important role in various pathological conditions and diseases. The aim of this study was to observe the effect of hyperoxia on oxidant/antioxidant status in the liver of young male and female mice and to determine whether the observed effects are associated with the expression of Heme oxygenase-1 (HO-1) and CYP genes associated with stress (Cyp1a1, Cyp1a2, Cyp2a5, and Cyp2e1) or stress and gender-related responses (Cyp2b9). In this study, we demonstrated gender-related effect of hyperoxia on oxidant/antioxidant status and on expression of certain P450 enzymes. Our results suggest that females are less susceptible to hyperoxia induced oxidative stress by two major mechanisms: upregulated expression of HO-1 genes and different expression of certain P450 enzymes. Therefore, our study could provide additional data of gender-dependent responses in susceptibility to oxidative stress, chemical toxicity and drug efficiency in treatment of diseases.

2,3,7,8-tetrachlorodibenzo-p-dioxin increases reactive oxygen species production in human endothelial cells via induction of cytochrome P4501A1

Studies in our laboratory have demonstrated that subchronic 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD) exposure of adult mice results in hypertension, cardiac hypertrophy, and reduced nitric oxide (NO)-mediated vasodilation. Moreover, increased superoxide anion production was observed in cardiovascular organs of TCDD-exposed mice and this increase contributed to the reduced NO-mediated vasodilation. Since cytochrome P4501A1 (CYP1A1) can contribute to some TCDD-induced toxicity, we tested the hypothesis that TCDD increases reactive oxygen species (ROS) in endothelial cells by the induction of CYP1A1. A concentration-response to 24h TCDD exposure (10pM-10nM) was performed in confluent primary human aortic endothelial cells (HAECs). Oxidant-sensitive fluorescent probes dihydroethidium (DHE) and 2',7'-dichlorofluorescin diacetate (DCFH-DA), were used to measure superoxide anion, and hydrogen peroxide and hydroxyl radical, respectively. NO was also measured using the fluorescent probe diaminofluorescein-2 diacetate (DAF-2DA). These assessments were conducted in HAECs transfected with siRNA targeting the aryl hydrocarbon receptor (AhR), CYP1A1, or CYP1B1. TCDD concentration-dependently increased CYP1A1 and CYP1B1 mRNA, protein, and enzyme activity. Moreover, 1nM TCDD maximally increased DHE (Cont=1.0+/-0.3; TCDD=5.1+/-1.0; p=0.002) and DCFH-DA (Cont=1.0+/-0.2; TCDD=4.1+/-0.5; p=0.002) fluorescence and maximally decreased DAF-2DA fluorescence (Cont=1.0+/-0.4; TCDD=0.68+/-0.1). siRNA targeting AhR and CYP1A1 significantly decreased TCDD-induced DHE (siAhR: Cont=1.0+/-0.1; TCDD=1.3+/-0.2; p=0.093) (siCYP1A1: Cont=1.0+/-0.1; TCDD=1.1+/-0.1; p=0.454) and DCFH-DA (siAhR: Cont=1.0+/-0.2; TCDD=1.3+/-0.3; p=0.370) (siCYP1A1: Cont=1.0+/-0.1; TCDD=1.3+/-0.2; p=0.114) fluorescence and increased DAF-2DA fluorescence (siAhR: Cont=1.00+/-0.03; TCDD=0.97+/-0.03; p=0.481) (siCYP1A1: Cont=1.00+/-0.03; TCDD=0.92+/-0.03; p=0.034), while siRNA targeting CYP1B1 did not. These data suggest that TCDD-induced increase in ROS is AhR-dependent and may be mediated, in part, by CYP1A1 induction.

Protective Effects of the Antioxidant 4b,5,9b,10-Tetrahydroindeno[1,2-b]indole Against TCDD Toxicity in C57BL/6J Mice

The protection against 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD; 5 µg/kg body weight) toxicity by the antioxidant 4b,5,9b,10-tetrahydroindeno[1,2- b]indole (THII) was examined in female C57BL/6J mice. TCDD produced increases in the levels of hepatic lipid-derived aldehydes, rates of mitochondrial production of hydrogen peroxide and superoxide, and the oxidation state of cytosolic GSH. In contrast, mitochondrial GSH increased in reduction state, correlating with an increase in mitochondrial membrane potential. Systemically, TCDD lowered body weight gain, percentage body fat, and hepatic ATP levels, parameters prevented by concomitant administration of 100 µM THII in drinking water. However, TCDD-induced increases in mitochondrial respiration and decreased mitochondrial membrane fluidity were not prevented by THII. These results suggest that TCDD-mediated oxidative stress was not responsible for changes in mitochondrial respiration or membrane fluidity. Furthermore, although TCDD produced a large increase in mitochondrial oxygen consumption, this was not associated with the poor gain in weight produced by TCDD.

Molecular Mechanisms of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Cardiovascular Embryotoxicity

2,3,7,8 Tetrachlorodibenzo-p-dioxin (TCDD) and related planar halogenated aromatic hydrocarbons are widespread environmental contaminants and potent developmental toxicants. Hallmarks of embryonic exposure include edema, hemorrhage, and mortality. Recent studies in zebrafish and chicken have revealed direct impairment of cardiac muscle growth that may underlie these overt symptoms. TCDD toxicity is mediated by the aryl hydrocarbon receptor, but downstream targets remain unclear. Oxidative stress and growth factor modulation have been implicated in TCDD cardiovascular toxicity. Gene expression profiling is elucidating additional pathways by which TCDD might act. We review our understanding of the mechanism of TCDD embryotoxicity at morphological and molecular levels.

Antioxidant Protective Mechanisms against Reactive Oxygen Species (ROS) Generated by Mitochondrial P450 Systems in Steroidogenic Cells

Mitochondrial P450 type enzymes catalyze central steps in steroid biosynthesis, including cholesterol conversion to pregnenolone, 11beta and 18 hydroxylation in glucocorticoid and mineralocorticoid synthesis, C-27 hydroxylation of bile acids, and 1alpha and 24 hydroxylation of 25-OH-vitamin D. These monooxygenase reactions depend on electron transfer from NADPH via FAD adrenodoxin reductase and 2Fe-2S adrenodoxin. These systems can function as a futile NADPH oxidase, oxidizing NADPH in absence of substrate, and leak electrons via adrenodoxin and P450 to O(2), producing superoxide and other reactive oxygen species (ROS). The degree of uncoupling depends on the P450 and steroid substrate. Studies with purified proteins and overexpression in cultured cells show consistently that adrenodoxin, but not reductase, is responsible for ROS production that can lead to apoptosis. In the ovary and corpus luteum, antioxidant enzyme activities superoxide dismutase, catalase, and glutathione peroxidase parallel steroidogenesis. Antioxidant beta-carotene, alpha-tocopherol, and ascorbate can protect against oxidative damages of P450 systems. In testis Leydig cells, steroidogenesis is associated with aging of the steroidogenic capacity.

Decreased expression of cytochromes P450 1A2, 2E1, and 3A4 and drug transporters Na+-taurocholate-cotransporting polypeptide, organic cation transporter 1, and organic anion-transporting peptide-C correlates with the progression of liver fibrosis in chronic hepatitis C patients

Patients with chronic hepatitis C viral infection underwent liver biopsies and laboratory studies for evaluation and to determine subsequent treatment. Changes in status of drug metabolism and disposition may vary with chronic hepatitis C stage and should be assessed. Total RNA was extracted from liver biopsy specimens (n = 63) and reverse transcribed to yield cDNA. Relative mRNA levels of drug-metabolizing enzymes, transporters, nuclear receptors, and proinflammatory cytokines were analyzed with normalization to glyceraldehyde 3-phosphate dehydrogenase expression. mRNAs encoding cytochromes P450 1A2, 2E1, and 3A4, and drug transporters, Na(+)-taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1 showed remarkable decreases, and tumor necrosis factor-alpha showed an increase according to fibrosis stage progression. HepG2 cells and primary hepatocytes of two human individuals were treated with interleukin 1beta, interleukin 6, or tumor necrosis factor-alpha. CYP1A2 and Na(+)-taurocholate-cotransporting polypeptide mRNA levels significantly decreased in HepG2 cells with interleukin 1beta and interleukin 6 treatments. CYP2E1 and organic cation transporter 1 mRNA levels significantly decreased with tumor necrosis factor-alpha treatment only in HepG2. These results suggested that down-regulation of CYP1A2, 2E1, and 3A4, and drug transporters, Na(+)-taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1, manifested in livers of patients with chronic hepatitis C viral infection, was associated, at least in part, with the elevated production of proinflammatory cytokines, including tumor necrosis factor-alpha.

Identification of novel toxicity-associated metabolites by metabolomics and mass isotopomer analysis of acetaminophen metabolism in wild-type and Cyp2e1-null mice

CYP2E1 is recognized as the most important enzyme for initiation of acetaminophen (APAP)-induced toxicity. In this study, the resistance of Cyp2e1-null mice to APAP treatment was confirmed by comparing serum aminotransferase activities and blood urea nitrogen levels in wild-type and Cyp2e1-null mice. However, unexpectedly, profiling of major known APAP metabolites in urine and serum revealed that the contribution of CYP2E1 to APAP metabolism decreased with increasing APAP doses administered. Measurement of hepatic glutathione and hydrogen peroxide levels exposed the importance of oxidative stress in determining the consequence of APAP overdose. Subsequent metabolomic analysis was capable of constructing a principal components analysis (PCA) model that delineated a relationship between urinary metabolomes and the responses to APAP treatment. Urinary ions high in wild-type mice treated with 400 mg/kg APAP were elucidated as 3-methoxy-APAP glucuronide (VII) and three novel APAP metabolites, including S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid (VI, formed by a Cys-APAP transamination reaction in kidney), 3,3'-biacetaminophen (VIII, an APAP dimer), and a benzothiazine compound (IX, originated from deacetylated APAP), through mass isotopomer analysis, accurate mass measurement, tandem mass spectrometry fragmentation, in vitro reactions, and chemical treatments. Dose-, time-, and genotype-dependent appearance of these minor APAP metabolites implied their association with the APAP-induced toxicity and potential biomarker application. Overall, the oxidative stress elicited by CYP2E1-mediated APAP metabolism might significantly contribute to APAP-induced toxicity. The combination of genetically modified animal models, mass isotopomer analysis, and metabolomics provides a powerful and efficient technical platform to characterize APAP-induced toxicity through identifying novel biomarkers and unraveling novel mechanisms.

670 nanometer light treatment attenuates dioxin toxicity in the developing chick embryo

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an acutely toxic anthropogenic chemical. Treatment with a red to near-infrared (630-1000 nm) light-emitting diode (LED) attenuates the toxicant-induced oxidative stress and energy deficit in neuronal cell culture. For this study, fertile chicken (Gallus gallus) eggs were injected once at the start of incubation with sunflower oil vehicle or 200 pg TCDD/g egg (200 parts per trillion), an environmentally relevant dose. Daily LED treatment after TCDD exposure reduced embryonic mortality by 47%. LED treatment of TCDD-exposed eggs also decreased the hepatic oxidized-to-reduced glutathione ratio by 88%. Activities of other hepatic indicators of oxidative stress, such as glutathione reductase and catalase, were increased after LED treatment of TCDD-exposed eggs. Our study demonstrates that 670 nm phototherapy can mitigate the oxidative stress and energy deficit resulting from developmental exposure to TCDD while reducing TCDD-induced embryo mortality. Moreover, LED treatment restores hepatic enzyme activities to control levels in TCDD-exposed embryos. The effective attenuation of TCDD-induced embryo toxicity by LED treatment could extend to mitigating the effects of other teratogens that induce oxidative and energy stress.

TCDD decreases ATP levels and increases reactive oxygen production through changes in mitochondrial F(0)F(1)-ATP synthase and ubiquinone

Mitochondria generate ATP and participate in signal transduction and cellular pathology and/or cell death. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) decreases hepatic ATP levels and generates mitochondrial oxidative DNA damage, which is exacerbated by increasing mitochondrial glutathione redox state and by inner membrane hyperpolarization. This study identifies mitochondrial targets of TCDD that initiate and sustain reactive oxygen production and decreased ATP levels. One week after treating mice with TCDD, liver ubiquinone (Q) levels were significantly decreased, while rates of succinoxidase and Q-cytochrome c oxidoreductase activities were increased. However, the expected increase in Q reduction state following TCDD treatment did not occur; instead, Q was more oxidized. These results could be explained by an ATP synthase defect, a premise supported by the unusual finding that TCDD lowers ATP/O ratios without concomitant changes in respiratory control ratios. Such results suggest either a futile cycle in ATP synthesis, or hydrolysis of newly synthesized ATP prior to release. The TCDD-mediated decrease in Q, concomitant with an increase in respiration, increases complex 3 redox cycling. This acts in concert with glutathione to increase membrane potential and reactive oxygen production. The proposed defect in ATP synthase explains both the greater respiratory rates and the lower tissue ATP levels.

CYP1A in TCDD toxicity and in physiology-with particular reference to CYP dependent arachidonic acid metabolism and other endogenous substrates

Toxicologic and physiologic roles of CYP1A enzyme induction, the major biochemical effect of aryl hydrocarbon receptor activation by TCDD and other receptor ligands, are unknown. Evidence is presented that CYP1A exerts biologic effects via metabolism of endogenous substrates (i.e., arachidonic acid, other eicosanoids, estrogens, bilirubin, and melatonin), production of reactive oxygen, and effects on K(+) and Ca(2+) channels. These interrelated pathways may connect CYP1A induction to TCDD toxicities, including cardiotoxicity, vascular dysfunction, and wasting. They may also underlie homeostatic roles for CYP1A, especially when transiently induced by common chemical exposures and environmental conditions (i.e., tryptophan photoproducts, dietary indoles, and changes in oxygen tension).

Induction of oxidative stress responses by dioxin and other ligands of the aryl hydrocarbon receptor

TCDD and other polyhalogenated aromatic hydrocarbon ligands of the aryl hydrocarbon receptor (AHR) have been classically considered as non-genotoxic compounds because they fail to be directly mutagenic in either bacteria or most in vitro assay systems. They do so in spite of having repeatedly been linked to oxidative stress and to mutagenic and carcinogenic outcomes. Oxidative stress, on the other hand, has been used as a marker for the toxicity of dioxin and its congeners. We have focused this review on the connection between oxidative stress induction and the toxic effects of fetal and adult dioxin exposure, with emphasis on the large species difference in sensitivity to this agent. We examine the roles that the dioxin-inducible cytochromes P450s play in the cellular and toxicological consequences of dioxin exposure with emphasis on oxidative stress involvement. Many components of the health consequences resulting from dioxin exposure may be attributable to epigenetic mechanisms arising from prolonged reactive oxygen generation.

For dioxin-induced birth defects, mouse or human CYP1A2 in maternal liver protects whereas mouse CYP1A1 and CYP1B1 are inconsequential

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces cleft palate and hydronephrosis in mice, when exposed in utero; these effects are mediated by the aryl hydrocarbon receptor. The Cyp1a1, Cyp1a2, and Cyp1b1 genes are up-regulated by the aryl hydrocarbon receptor. To elucidate their roles in dioxin-induced teratogenesis, we compared Cyp1a1(-/-), Cyp1a2(-/-), and Cyp1b1(-/-) knock-out mice with Cyp1(+/+) wild-type mice. Dioxin was administered (25 microg/kg, gavage) on gestational day 10, and embryos were examined on gestational day 18. The incidence of cleft palate and hydronephrosis was not significantly different in fetuses from Cyp1a1(-/-), Cyp1b1(-/-), and Cyp1(+/+) wild-type mice. To fetuses carried by Cyp1a2(-/-) dams, however, this dose of dioxin was lethal; this effect was absolutely dependent on the maternal Cyp1a2 genotype and independent of the embryonic Cyp1a2 genotype. Dioxin levels were highest in adipose tissue, mammary gland, and circulating blood of Cyp1a2(-/-) mothers, compared with that in the Cyp1(+/+) mothers, who showed highest dioxin levels in liver. More dioxin reached the embryos from Cyp1a2(-/-) dams, compared with that from Cyp1(+/+) dams. Fetuses from Cyp1a2(-/-) dams exhibited a approximately 6-fold increased sensitivity to cleft palate, hydronephrosis, and lethality. Using the humanized hCYP1A1_1A2 transgenic mouse (expressing the human CYP1A1 and CYP1A2 genes in the absence of mouse Cyp1a2 gene), the teratogenic effects of dioxin reverted to the wild-type phenotype. These data indicate that maternal mouse hepatic CYP1A2, by sequestering dioxin and thus altering the pharmacokinetics, protects the embryos from toxicity and birth defects; substitution of the human CYP1A2 trans-gene provides the same protection. In contrast, neither CYP1A1 nor CYP1B1 appears to play a role in dioxin-mediated teratogenesis.

Comparison of mouse hepatic mitochondrial versus microsomal cytochromes P450 following TCDD treatment

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces cytochromes P450 (CYPs) such as CYP1A1 and CYP1A2 via activation of the aromatic hydrocarbon receptor (AHR). Herein we describe the TCDD-dependent enrichment of CYPs in liver microsomes and mitoplasts from C57BL/6J mice. TCDD-induced accumulation of CYP1A1 and CYP1A2 was observed in microsomes and mitoplasts after treatment with 15 microg TCDD/kg/d for 3d. While microsomal CYP1 proteins peaked at 1 week and diminished thereafter, mitoplast CYP1 proteins persisted 8 weeks at high levels. TCDD also induced microsomal CYP2A5, but not microsomal proteins immunoreactive to CYP2C11, CYP3A2 or CYP4A1 antibodies. Nevertheless, each of these proteins increased in mitoplasts following TCDD exposure. These results suggest that TCDD increases mitochondrial CYP immunoreactive proteins under the transcriptional control of the AHR, as well as CYPs that are not under AHR control. We speculate that such mitochondrial CYPs may be involved in the generation, or mitigation, of the well-known TCDD-inducible oxidative stress response.

Gene Expression profile by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin in the Liver of Wild-Type (AhR+/+) and Aryl Hydrocarbon Receptor-Deficient (AhR-/-) Mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is one of the most toxic environmental pollutants that cause various biological effects on mammals. The purpose of our study was to identify the genes involved in hepatotoxicity and hepatocarcinogenesis caused by TCDD. C57BL/6 (AhR+/+, wild type) and B6.129-AhR<tm1Bra>/J (AhR-/-, knock out) mice were injected i.p. with a single treatment of TCDD at the dose of 100 microg/kg body weight. Relative liver weight was significantly increased at 72 hr after TCDD treatment without an apparent histopathological change in AhR+/+ mice (p<0.05). TCDD treatment also significantly increased activity of serum alanine aminotransferase in AhR-/- mice (p<0.05). The liver was analyzed for gene expression profiles 72 hr later. As compared with AhR-/- mice, the expression of 51 genes (>3-fold) was changed in AhR+/+ mice; 28 genes were induced, while 23 genes were repressed. Most of the genes were associated with chemotaxis, inflammation, carcinogenesis, acute-phase response, immune responses, cell metabolism, cell proliferation, signal transduction, and tumor suppression. This study suggests that the microarray analysis of genes in the liver of AhR+/+ and AhR-/- mice may help to clarify the mechanism of AhR-mediated hepatotoxicity and hepatocarcinogenesis by TCDD.

Genetic Differences in Lethality of Newborn Mice Treated In Utero with Coplanar versus Non-Coplanar Hexabromobiphenyl

Polybrominated biphenyl (PBB) exposure in humans is known to cause immunotoxicity and disorders related to the central nervous system. Coplanar PBBs bind to the aryl hydrocarbon receptor (AHR) in vertebrates. We compared the coplanar PBB, 3,3',4,4',5,5'-hexabromobiphenyl (cHBB), with its stereoisomer, the non-coplanar PBB, 2,2',4,4'6,6'-hexabromobiphenyl (ncHBB), using C57BL/6J (B6) inbred mice (having the high-affinity AHR) and congenic B6.D2-Ahr d mice (having the low-affinity AHR in a >99.8% C57BL/6J genetic background). Pregnant dams were treated i.p. with vehicle alone, cHBB, or ncHBB on gestational day 5 (GD 5). Unexpectedly, neonatal lethality within the first 72 h postpartum was significant in cHBB-treated B6 mice at doses as low as 2.5 mg/kg, whereas no deaths were seen in B6 pups whose mother had received ncHBB 100 mg/kg or in either B6.D2-Ahr d or Ahr(-/-) knockout mice whose mother had received cHBB 100 mg/kg. Histological and gross anatomical analyses of a battery of tissues in the mother or fetus at GD 18, as well as 24 h postpartum, revealed no significant differences, except for decreased thymus and spleen weights in cHBB-treated B6 GD 18 fetuses. Cross-fostering and genetics experiments confirmed the association of neonatal deaths principally with in utero (rather than lactational) exposure to cHBB, and also no paternal effect. For the end points of mouse neonatal lethality and immunotoxicity, cHBB appears to act through the high-affinity AHR receptor. Although dioxin in utero is well known to cause AHR-dependent cleft palate and hydronephrosis, cHBB did not; thus, chronic activation of the AHR appears to be necessary but not sufficient for AHR-mediated teratogenicity.

Genetic polymorphism of CYP1A2 increases the risk of myocardial infarction

BACKGROUND

There is growing evidence that DNA damage caused by mutagens found in tobacco smoke may contribute to the development of coronary heart disease (CHD). In order to bind to DNA many mutagens require metabolic activation by cytochrome P450 (CYP) 1A1 or CYP1A2. The objective of this study was to determine the effects of CYP1A1 and CYP1A2 genotypes on risk of myocardial infarction (MI) and whether smoking interacts with genotype to modify risk.

METHODS

Subjects (n = 873) with a first acute non-fatal MI and population based controls (n = 932) living in Costa Rica, matched for age, sex, and area of residence, were genotyped for CYP1A1*2A and CYP1A2*1F by restriction-fragment length polymorphism (RFLP)-PCR, and smoking status was determined by questionnaire.

RESULTS

After adjusting for matching variables and potential confounders, no association was observed between CYP1A1 genotype and risk of MI. Compared to individuals with the high inducibility CYP1A2*1A/*1A genotype, the adjusted odds ratio and 95% confidence intervals for risk of MI were 1.19 (0.97 to 1.47) for the *1A/*1F genotype and 1.55 (1.10 to 2.18) for the *1F/*1F genotype. No significant interactions were observed between smoking and either CYP1A1 or CYP1A2 genotype.

CONCLUSIONS

The low inducibility genotype for CYP1A2 was associated with an increased risk of MI. This effect was independent of smoking status and suggests that a substrate of CYP1A2 that is detoxified rather than activated may play a role in CHD.

Glutathione Redox State Regulates Mitochondrial Reactive OxygenProduction

Oxidative stress induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is poorly understood. Following one dose of TCDD (5 microg/kg body weight), mitochondrial succinate-dependent production of superoxide and H2O2 in mouse liver doubled at 7-28 days, then subsided by day 56; concomitantly, levels of GSH and GSSG increased in both cytosol and mitochondria. Cytosol displayed a typical oxidative stress response, consisting of diminished GSH relative to GSSG, decreased potential to reduce protein-SSG mixed disulfide bonds (type 1 thiol redox switch) or protein-SS-protein disulfide bonds (type 2 thiol redox switch), and a +10 mV change in GSSG/2GSH reduction potential. In contrast, mitochondria showed a rise in reduction state, consisting of increased GSH relative to GSSG, increases in type 1 and type 2 thiol redox switches, and a -25 mV change in GSSG/2GSH reduction potential. Comparing Ahr(-/-) knock-out and wild-type mice, we found that TCDD-induced thiol changes in both cytosol and mitochondria were dependent on the aromatic hydrocarbon receptor (AHR). GSH was rapidly taken up by mitochondria and stimulated succinate-dependent H2O2 production. A linear dependence of H2O2 production on the reduction potential for GSSG/2GSH exists between -150 and -300 mV. The TCDD-stimulated increase in succinate-dependent and thiol-stimulated production of reactive oxygen paralleled a four-fold increase in formamidopyrimidine DNA N-glycosylase (FPG)-sensitive cleavage sites in mitochondrial DNA, compared with a two-fold increase in nuclear DNA. These results suggest that TCDD produces an AHR-dependent oxidative stress in mitochondria, with concomitant mitochondrial DNA damage mediated, at least in part, by an increase in the mitochondrial thiol reduction state.

Altered expression of cytochrome P450 and possible correlation with preneoplastic changes in early stage of rat hepatocarcinogenesis

AIM

Correlation of cytochrome P450 (CYPs) with preneoplastic changes in the early stage of hepatocarcinogenesis is still unclear. To detect the expression of carcinogen-metabolizing related microsomal P450 enzymes, namely the CYP1A1, CYP1A2, CYP2B1/2, CYP2E1, and CYP3A, we performed the medium-term bioassay of Ito's model in Sprague-Dawley rats.

METHODS

The amount and activity of CYP were assessed by biochemical and immunohistochemical methods in week 8. The correlation between CYP expression and microsomal oxidative stress was investigated by comparing the generation of microsomal lipid peroxidation in the presence or absence of specific CYP inhibitor.

RESULTS

In the DEN-2-AAF and 2-AAF alone groups, the expression of CYP1A1 and CYP2E1 were up-regulated and the expression of CYP2B1/2 and CYP1A2 were quite the contrary. Strong staining of CYP2E1 and CYP2B1/2 was found around the centrolobular vein and weak staining in the altered hepatic foci revealed by immunohistochemical procedure. There was no significant change in the activity of CYP3A among the 4 groups. Altered hepatic tissue bore more microsomal NADPH (nicotinamide adenine dinucleotide phosphate,reduced form)-dependent lipid peroxidation than normal tissue. And the difference among the 4 groups disappeared when CYP2E1 was inhibited. More microsomal lipid peroxidation was generated when incubated with CYP1A inhibitor a-naphthoflavone.

CONCLUSION

CYP altered their expression levels and these alterations can play important roles in the alteration of cell redox status of preneoplastic tissue in the early stage of hepatocarcinogenesis.

Genetically altered mice to evaluate glutathione homeostasis in health and disease

The tripeptide glutathione (GSH) is part of an integrated antioxidant system that protects cells and tissues from oxidative damage. Oxidative stress can result from exposure to excessive amounts of endogenous and exogenous electrophiles. Until recently, animal and cell model systems used to investigate the role of GSH in disease processes had employed chemical agents that deplete cellular GSH by inhibiting GSH synthesis or by reacting chemically with GSH. Such models have proven useful, but questions concerning nonspecific effects of such chemicals remain. Recently, our laboratories and others have developed mouse models with genetic deficiencies in enzymes of the GSH biosynthetic pathway. This review focuses on the regulation of GSH homeostasis and, specifically, the new GSH-deficient mouse models that have been developed. These models will improve our understanding of the role of GSH in animal and human diseases.