Circadian rhythm of cytochrome P4502E1 and its effect on disposition kinetics of chlorzoxazone in rats

The aim of this report is to study the circadian rhythm of cytochrome P4502E1 (CYP2E1) and its effect on the disposition kinetics of chlorzoxazone in male Wistar rats. The rats were housed under a 12-h light/dark cycle (lights from 9:00 to 21:00) with food and water ad libitum for 3 months. It was found that the expression of microsomal CYP2E1 mRNA in the liver during the dark phase was significantly lower than during the light phase, whereas the content of CYP2E1 protein and its hydroxylation activity were significantly higher. Therefore, chlorzoxazone 20 mg/kg was intravenously administered at 12:00 (light phase group) or 24:00 (dark phase group) to determine the effect on the disposition kinetics. The value of the area under the plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) of chlorzoxazone showed no significant difference between the two groups. However, the value of chlorzoxazone half-life in plasma of the light phase group was significant longer than the dark phase group. The AUC(0-8 h) of 6-hydroxychlorzoxazone, a metabolite formed from chlorzoxazone mainly by CYP2E1, was significantly higher in the dark phase than in the light phase. In conclusion, microsomal CYP2E1 shows a substantial circadian variation in rats, and this was associated with a decrease of chlorzoxazone half life, and an increase of 6-hydroxychlorzoxazone production. Therefore, the temporal variations of therapeutic response and toxicological effects may have to be taken into consideration for other xenobiotics that are predominantly metabolized by CYP2E1, particularly those with a short half-life.     

Aquaporin-4 knockout enhances astrocyte toxicity induced by 1-methyl-4-phenylpyridinium ion and lipopolysaccharide via increasing the expression of cytochrome P4502E1

The role of aquaporin-4 (AQP4) in the regulation of astrocytes function has been widely investigated. However, there is little information about its contribution to the drug metabolism enzymes such as Cytochrome P4502E1. In the present study, we investigated whether AQP4 is involved in the process of the cell damage caused by MPP⁺ and LPS through regulating the expression of CYP2E1 in astrocytes. Compared to the wild-type, in primary astrocytes, AQP4 knockout increased the cell damage and the reactive oxygen species (ROS) production which were induced by MPP⁺, LPS and ethanol. Notably, AQP4 knockout enhanced the up-regulation of the expression of CYP2E1 in astrocytes exposed to MPP⁺, LPS and ethanol. Furthermore, Diallylsulphide (DAS), a CYP2E1 inhibitor, partially or almost abolished the cell injury and the ROS production of the astrocytes induced by MPP⁺ and LPS. These findings indicate AQP4 protects astrocytes from the damage caused by MPP⁺ and LPS through reducing the ROS production correlation to the diminished expression of CYP2E1.     

MPTP-induced model of Parkinson's disease in cytochrome P450 2E1knockout mice

Evidence for involvement of cytochrome P450 2E1 in the MPTP-induced mouse model of PD has been reported [Vaglini, F., Pardini, C., Viaggi, C., Bartoli, C., Dinucci, D., Corsini, G.U., 2004. Involvement of cytochrome P450 2E1 in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease. J. Neurochem. 91, 285–298]. We studied the sensitivity of Cyp2e1(−/−) mice to the acute administration of MPTP in comparison with their wild-type counterparts. In Cyp2e1(−/−) mice, the reduction of striatal DA content was less pronounced 7 days after MPTP treatment compared to treated wild-type mice. Similarly, TH immunoreactivity analysis of the substantia nigra of Cyp2e1(−/−) mice did not show any neuronal lesions after MPTP treatment. In contrast to this, wild-type animals showed a minimal but significant lesioning by the toxin as evaluated also by means of non-stereologic computerized assisted analysis of this brain area. Striatal levels of DA metabolites after 7 days were variably affected by the toxin, but consistent differences between the two animal strains were not observed.We evaluated short-term changes in the levels of striatal DA and its metabolites, and we monitored striatal MPP⁺ levels. Striatal MPP⁺ was cleared more rapidly in Cyp2e1(−/−) mice than in wild-type animals and, consistently, striatal DA content decreased faster in Cyp2e1(−/−) mice than in wild-type animals, and 3-methoxytyramine and HVA levels showed an early and sharp rise. Our findings suggest that Cyp2e1(−/−) mice are weakly sensitive to MPTP-induced brain lesions, markedly in contrast with a protective role of the enzyme as suggested previously. The differences observed between the knockout mice and their wild-type counterparts are modest and may be due to an efficient compensatory mechanism or genetic drift in the colonies.     

Effects of herbal products and their constituents on human cytochrome P4502E1 activity

Ethanolic extracts from fresh Echinacea purpurea and Spilanthes acmella and dried Hydrastis canadensis were examined with regard to their ability to inhibit cytochrome P450_2E1 mediated oxidation of p-nitrophenol in vitro. In addition, individual constituents of these extracts, including alkylamides from E. purpurea and S. acmella, caffeic acid derivatives from E. purpurea, and several of the major alkaloids from H. canadensis, were tested for inhibition using the same assay. H. canadensis (goldenseal) was a strong inhibitor of the P450_2E1, and the inhibition appeared to be related to the presence of the alkaloids berberine, hydrastine and canadine in the extract. These compounds inhibited 2E1 with K_I values ranging from 2.8 μM for hydrastine to 18 μM for berberine. The alkylamides present in E. purpurea and S. acmella also showed significant inhibition at concentrations as low as 25 μM, whereas the caffeic acid derivatives had no effect. Commercial green tea preparations, along with four of the individual tea catechins, were also examined and were found to have no effect on the activity of P450_2E1.     

Mechanism of chloroform-induced renal toxicity: non-involvement of hepatic cytochrome P450-dependent metabolism

Chloroform causes hepatic and renal toxicity in a number of species. In vitro studies have indicated that chloroform can be metabolized by P450 enzymes in the kidney to nephrotoxic intermediate, although direct in vivo evidence for the role of renal P450 in the nephrotoxicity has not been reported. This study was to determine whether chloroform renal toxicity persists in a mouse model with a liver-specific deletion of the P450 reductase (Cpr) gene (liver-Cpr-null). Chloroform-induced renal toxicity and chloroform tissue levels were compared between the liver-Cpr-null and wild-type mice at 24 h following differing doses of chloroform. At a chloroform dose of 150 mg/kg, the levels of blood urea nitrogen (BUN) were five times higher in the exposed group than in the vehicle-treated one for the liver-Cpr-null mice, but they were only slightly higher in the exposed group than in the vehicle-treated group for the wild-type mice. Severe lesions were found in the kidney of the liver-Cpr-null mice, while only mild lesions were found in the wild-type mice. At a chloroform dose of 300 mg/kg, severe kidney lesions were observed in both strains, yet the BUN levels were still higher in the liver-Cpr-null than in the wild-type mice. Higher chloroform levels were found in the tissues of the liver-Cpr-null mice. These findings indicated that loss of hepatic P450-dependent chloroform metabolism does not protect against chloroform-induced renal toxicity, suggesting that renal P450 enzymes play an essential role in chloroform renal toxicity.     

Mutagenicity of cytochrome P450 2E1 substrates in the Ames test with the metabolic competent S. typhimurium strain YG7108pin3ERb5

Poor metabolic competence of in vitro systems was proposed to be one of their major shortcomings accounting for false negative results in genotoxicity testing. For several "low molecular weight cancer suspects" this was specifically attributed to the lack of cytochrome P450 2E1 (CYP2E1) in conventional in vitro metabolising systems. One promising attempt to overcome this problem is the transfection of "methyltransferase-deficient"S. typhimurium strains with the plasmid pin3ERb5. This plasmid contains DNA encoding for a complete electron transport chain, comprising P450 reductase, cytochrome b5 and cytochrome P450 2E1. In order to answer the question if CYP2E1 substrates that yield negative or inconclusive results in the Ames test can be activated by metabolic competent bacterial strains, we used YG7108pin3ERb5 to investigate the following compounds: acetamide, acrylamide, acrylonitrile, allyl chloride, ethyl acrylate, ethyl carbamate, methyl-methacrylate, vinyl acetate, N-nitrosopyrrolidine, trichloroethylene and tetrachloroethylene. N-Nitrosodiethylamine served as a positive control. In addition to these known or proposed CYP2E1 substrates, we investigated the polycyclic aromatic hydrocarbon benzo[alpha]pyrene and the heterocyclic aromatic amines 2-aminofluorene and 2-aminoanthracene. RESULTS: The extensive metabolic competence of the transformed strain is underlined by results showing strong mutagenicity between 10 and 500 micro g N-nitrosopyrrolidine per plate. Unexpectedly, 2-aminoanthracene was mutagenic at a concentration range between 25 and 250 micro g per plate using YG7108pin3ERb5. Moreover, we demonstrate for the first time a clear response of sufficiently characterised allyl chloride in the Ames test at a reasonably low concentration range between 300 and 1500 micro g per plate. We achieved similar results in the parent strain YG7108 with conventional metabolic activation. Without metabolic activation less pronounced mutagenicity occurred, suggesting a contribution of a direct alkylating effect. Propylene oxide is usually contained in allyl chloride as stabilizer at amounts up to 0.09%. Though YG7108 revealed to be very sensitive towards propylene oxide, allyl chloride dissolved in water was not mutagenic, showing that no water soluble compounds contribute to its mutagenicity. None of the remaining compounds showed mutagenic effects using YG7108pin3ERb5. CONCLUSION: YG7108pin3ERb5 and its parent strain YG7108 are sensitive for compounds which are negative in conventional tester strains including N-nitrosodiethylamine, N-nitrosopyrrolidine, propylene oxide and allyl chloride.     

Hepatotoxicity and P-4502E1-dependent metabolic oxidation of N,N-dimethylformamide in rats and mice

 A comparative biochemical and histological study on the hepatotoxicity of a single dose of N,N-dimethylformamide (DMF) and N-methylformamide (NMF) in control and acetone-treated SD male rats and CD-1 male mice was performed. In control and acetone-pretreated rats, neither DMF nor NMF caused hepatic damage or elevation of plasma transaminases. In contrast, in acetonized but not in control mice, DMF administration yielded some evidence of liver necrosis and elevation of ALAT (alanine-amino transferase) activity. After a DMF dose of 1000 mg/kg, ALAT activity was found 1215± 832 mU/ml and 47±18 mU/ml in acetonized and control mice, respectively. NMF treatment was hepatotoxic in control mice and lethal in acetonized mice. In control mice, an NMF dose of 600 mg/kg increased ALAT activity from a basal value of 35±5 to 2210± 1898 mU/ml. When the oxidative metabolism of DMF was investigated, microsomes from both rats and mice preinduced by acetone increased the demethylation rate of DMF 7 to 10-fold compared to that (about 0.25 nmol/min per mg protein) of the corresponding control microsomes. The enzymatic affinities for DMF oxidation, however, were different: in mice the K_m (0.05 mM) was one order of magnitude lower than that (0.56 mM) found in rats. The experiments performed with purified rat and mouse P-450 2E1 in a reconstituted system confirmed that the P-450 2E1 isoforms are very active catalysts towards DMF oxidation (the turnover was about 10 nmol/min per nmol P-450 for both enzymes) but with a strikingly different affinity. Whereas the K_m for mouse P-450 2E1 was 0.08± 0.03 mM, that for rat P-450 2E1 was 1.1±0.2 mM. These findings indicate that the higher susceptibility of mice, compared with rats, to DMF hepatotoxicity, could be ascribed, at least in part, to the higher metabolic capacity of mouse P-450 2E1 with respect to that of rats. Received: 6 July 1994 / Accepted: 20 September 1994     

Effect of cytochrome P450 inhibitors and anticonvulsants on the acute toxicity of acrylonitrile

Some of the more striking expressions of toxicity are the tremors and seizures observed approximately 100 min after exposure of rats to an acutely toxic dose of acrylonitrile (AN). These early events are followed by a second wave of severe clonic convulsions that occur just prior to death at about 3–4 h. For AN, at least two chemical entities could produce these toxic effects, namely the parent AN molecule, the metabolically-released cyanide, or both. Which of these two agents is responsible for each of the symptoms of acute intoxication is not known. To help dissect the toxicity, it was anticipated that an effective inhibitor of the oxidative metabolism of AN to cyanide could help us to understand which toxic symptoms might be associated with each agent. Three inhibitors of oxidative metabolism were tested, namely SKF-525A, 1-benzylimidazole and metyrapone and one alternative substrate, ethanol. As compared to SKF-525A and metyrapone, both 1-benzylimidazole and ethanol were highly effective in reducing blood cyanide levels to insignificant levels in rats treated with an LD90 dose of AN. In addition, both agents abolished the early seizure activity, suggesting that this first phase of seizures is due to cyanide and not the parent molecule. 1-Benzylimidazole did not prevent the severe clonic convulsive phase preceding death, suggesting that these terminal convulsions are due to the toxic effects of the parent AN molecule. The CNS depressant ethanol was only partially effective in attenuating the terminal convulsions. None of these agents affected the incidence of AN-induced mortality, clearly establishing that, even in the absence of cyanide, the parent AN molecule is acutely toxic. The partial effectiveness of ethanol suggested that anticonvulsants might be of benefit. Both phenobarbital and phenytoin protected rats from both the early and terminal convulsions, while valproic acid was ineffective. These effects were not related to a reduction in blood cyanide levels but rather due to their inherent anticonvulsant activity.     

淫羊藿苷对小鼠肝微粒体细胞色素P450酶及其亚型CYP2E1活性的影响

目的 研究淫羊藿苷对小鼠肝脏微粒体细胞色素P450(CYP)总酶含量及其亚型CYP2E1、CYP3A和CYP1A1活性的影响.方法 给予小鼠ig淫羊藿苷(50、100、200 mg·kg-1·d-1),3d后钙沉淀法制备肝细胞微粒体,UV法测定肝微粒体CYP的含量及其亚型CYP2E1与CYP3A的活性;荧光分光光度法测定肝微粒体CYP1A1的活性.结果 高剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的含量(约54%)、抑制CYP2E1的活性(抑制率为53.1%),对CYP3A和CYP1A1的活性无影响.结论 大剂量淫羊藿苷可降低小鼠肝脏微粒体CYP的总含量,并抑制其亚型CYP2E1的活性.     

Role of cytochrome P450 2E1 in the metabolism of acrylamide and acrylonitrile in mice

Acrylonitrile (AN) and acrylamide (AM) are commonly used in the synthesis of plastics and polymers. In rodents, AM and AN are metabolized to the epoxides glycidamide and cyanoethylene oxide, respectively. The aim of this study was to determine the role of cytochrome P450 in the metabolism of AM and AN in vivo. Wild-type (WT) mice, WT mice pretreated with aminobenzotriazole (ABT, 50 mg/kg ip, 2 h pre-exposure), and mice devoid of cytochrome P450 2E1 (P450 2E1-null) were treated with 50 mg/kg [(13)C]AM po. WT mice and P450 2E1-null mice were treated with 2.5 or 10 mg/kg [(13)C]AN po. Urine was collected for 24 h, and metabolites were characterized using (13)C NMR. WT mice excreted metabolites derived from the epoxides and from direct GSH conjugation with AM or AN. Only metabolites derived from direct GSH conjugation with AM or AN were observed in the urine from ABT-pretreated WT mice and P450 2E1-null mice. On the basis of evaluation of urinary metabolites at these doses, these data suggest that P450 2E1 is possibly the only cytochrome P450 enzyme involved in the metabolism of AM and AN in mice, that inhibiting total P450 activity does not result in new pathways of non-P450 metabolism of AM, and that mice devoid of P450 2E1 do not excrete metabolites of AM or AN that would be produced by oxidation by other cytochrome P450s. P450 2E1-null mice may be an appropriate model for the investigation of the role of oxidative metabolism in the toxicity or carcinogenicity of these compounds.     

The effects of gender, age, ethnicity, and liver cirrhosis on cytochrome P450 enzyme activity in human liver microsomes and inducibility in cultured human hepatocytes

We have measured cytochrome P450 (CYP) activity in nearly 150 samples of human liver microsomes and 64 samples of cryopreserved human hepatocytes, and we have performed induction studies in over 90 preparations of cultured human hepatocytes. We have analyzed these data to examine whether the expression of CYP enzyme activity in liver microsomes and isolated hepatocytes or the inducibility of CYP enzymes in cultured hepatocytes is influenced by the gender, age, or ethnicity of the donor (the latter being limited to Caucasians, African Americans, and Hispanics due to a paucity of livers from Asian donors). In human liver microsomes, there were no statistically significant differences (P > 0.05) in CYP activity as a function of age, gender, or ethnicity with one exception. 7-Ethoxyresorufin O-dealkylase (CYP1A2) activity was greater in males than females, which is consistent with clinical observation. Liver microsomal testosterone 6beta-hydroxylase (CYP3A4) activity was slightly greater in females than males, but the difference was not significant. However, in cryopreserved human hepatocytes, the gender difference in CYP3A4 activity (females = twice males) did reach statistical significance, which supports the clinical observation that females metabolize certain CYP3A4 substrates faster than do males. Compared with those from Caucasians and African Americans, liver microsomes from Hispanics had about twice the average activity of CYP2A6, CYP2B6, and CYP2C8 and half the activity of CYP1A2, although this apparent ethnic difference may be a consequence of the relatively low number of Hispanic donors. Primary cultures of hepatocytes were treated with beta-naphthoflavone, an inducer of CYP1A2, phenobarbital or rifampin, both of which induce CYP2B6, CYP2C9, CYP2C19, and CYP3A4, albeit it to different extents. Induction of these CYP enzymes in freshly cultured hepatocytes did not appear to be influenced by the gender or age of the donor. Furthermore, CYP3A4 induction in hepatocytes isolated from cirrhotic liver was comparable to that in normal hepatocytes, which supports the "healthy hepatocyte, sick environment" hypothesis of liver cirrhosis. This review summarizes these findings and discusses their implications for the use of human liver microsomes and hepatocytes for in vitro studies of drug metabolism and enzyme induction, which play a key role in drug development.     

Species and sex-dependent toxicokinetics of 1-bromopropane: the role of hepatic cytochrome P450 oxidation and glutathione (GSH)

Abstract

1. The objectives of the current studies were to evaluate the factors influencing the toxicokinetics of 1-bromopropane (1-BP) in rodents after intravenous (IV) and inhalation exposure.

2. F-344 rats were administered 1-BP via IV bolus injection at 5 and 20?mg/kg and blood concentration determined versus time. F-344 rats and B6C3F1 mice were also exposed to starting inhalation concentrations 70, 240, 800 and 2700?ppm 1-BP in a closed gas uptake system and chamber 1-BP levels were monitored for 6?h. Plasma bromide concentrations were determined to estimate total metabolized dose. Rats were pretreated with chemical inhibitors of cytochrome P450 and glutathione (GSH) synthesis, prior to exposure to 1-BP at 800?ppm within inhalation chambers.

3. Systemic clearance of 1-BP in rat was rapid and decreased with increasing dose. As inhalation chamber concentration of 1-BP increased, the terminal elimination rates decreased. Half-life of 1-BP in rats following inhibition of P450 (9.6?h) or depletion of GSH (4.1?h) increased relative to controls (2.0?h) at 800?ppm. The percentage of 1-BP metabolized decreased with increasing inhalation exposure. Hepatic levels of GSH were significantly lowered regardless of the exposure level in both rats and mice. Chamber concentration–time curves were fit to a two compartment model which was used to estimate metabolic rate constants.

4. These data suggest that in rat, 1-BP clearance is saturable and that elimination is highly dependent on both P450 and GSH-dependent metabolism. This investigation in rodents may provide an understanding of interspecies differences in toxicokinetics and eventually aid translation of animal studies to human risk assessment.     

The role of calcium in paracetamol (acetaminophen) cytotoxicity in PC12 cells transfected with CYP4502E1

Paracetamol-induced toxicity is mainly due to the accumulation of its CYP450-mediated N-hydroxylation product - N-acetylimidoquinone. We examined cell viability, proliferation rates and intracellular calcium in PC12 cells and in a PC12 cell line transfected with cytochrome P4502E1 exposed to paracetamol. This drug had a concentration-related effect on cell survival and a LD₅₀ which was significantly different between both cell types. A 48% decrease of PC12 cells was found following application of 5 mmol/L paracetamol for 48 h. A total 73% decrease in cell numbers was found in cells metabolizing the drug. Culture protein levels were diminished in a similar manner. Paracetamol increased intracellular calcium (by 662%) only in CYP4502E1-transfected cells. The protective role of EGTA and verapamil modulating calcium homeostasis was more evident in CYP4502E1-transfected cells. These results suggest that biotransformation of paracetamol by CYP2E1 increases its cytotoxicity and that a calcium imbalance may have a key role in the initiation of cell injury.     

Cytochrome P450 2E1 (CYP2E1) is essential for acrylonitrile metabolism to cyanide: comparative studies using CYP2E1-null and wild-type mice.

Acrylonitrile (AN) is a rodent carcinogen and suspected human carcinogen. Metabolism of AN proceeds via conjugation with glutathione or epoxidation via cytochrome P4502E1 (CYP2E1) to cyanoethylene oxide (CEO). It was hypothesized that CEO metabolism via epoxide hydrolase (EH) is the primary pathway for cyanide formation. The objective of this work is to assess the enzymatic basis of metabolism to cyanide. Male wild-type and CYP2E1-null mice received 0, 2.5, 10, 20, or 40 mg of AN/kg by gavage, and cyanide was measured in blood and tissues. CYP2E1 and EH expression were assessed using Western blot analyses. Present results demonstrated that cyanide concentrations in blood and tissues of AN-treated wild-type mice were higher at 1 versus 3 h, increased in a dose-dependent manner, and were significantly higher in AN-treated versus vehicle-treated mice. In contrast, cyanide concentrations in the blood and tissues of AN-treated CYP2E1-null mice were not statistically different from those of vehicle-treated mice. Furthermore, this work showed that EH is expressed in CYP2E1-null and wild-type mice. In conclusion, under the current experimental conditions using CYP2E1-null mice, current work demonstrated for the first time that CYP2E1-mediated oxidation is a prerequisite for AN metabolism to cyanide. Since earlier studies showed that CYP2E1 is the only enzyme responsible for AN epoxidation, it is concluded that AN metabolism to CEO is a prerequisite for cyanide formation, and this pathway is exclusively catalyzed by CYP2E1. Finally, this work confirmed that cyanide plays an essential role in the causation of the acute toxicity/mortality of AN.     

A comprehensive review of cytochrome P450 2E1 for xenobiotic metabolism

Abstract

Cytochrome P450 2E1 (CYP2E1) plays a vital role in drug-induced hepatotoxicity and cancers (e.g. lung and bladder cancer), since it is responsible for metabolizing a number of medications and environmental toxins to reactive intermediate metabolites. CYP2E1 was recently found to be the highest expressed CYP enzyme in human livers using a proteomics approach, and CYP2E1-related toxicity is strongly associated with its protein level that shows significant inter-individual variability related to ethnicity, age, and sex. Furthermore, the expression of CYP2E1 demonstrates regulation by extensive genetic polymorphism, endogenous hormones, cytokines, xenobiotics, and varying pathological states. Over the past decade, the knowledge of pharmacology, toxicology, and biology about CYP2E1 has grown remarkably, but the research progress has yet to be summarized. This study presents a timely systematic review on CYP2E1’s xenobiotic metabolism, genetic polymorphism, and inhibitors, with the focus on their clinical relevance for the efficacy and toxicity of various CYP2E1 substrates. Moreover, several knowledge gaps have been identified towards fully understanding the potential interactions among different CYP2E1 substrates in clinical settings. Through in-depth analyses of these knowns and unknowns, we expect this review will aid in future drug development and improve management of CYP2E1 related clinical toxicity.     

淫羊藿苷对不同月龄大鼠肝微粒体细胞色素P450的影响

目的 揭示淫羊藿苷(Ica)对大鼠肝微粒体细胞色素P450的含量及部分亚型的影响,并比较月龄的差异.方法 ig给予6月龄和18月龄的♂SD大鼠Ica( 60 mg· kg -1),4周后取肝脏,用钙沉淀法提取肝微粒体,BCA法测定微粒体蛋白浓度;用一氧化碳还原差示光谱法测定CYP450的含量;用ELISA法测定CYP1 A1、CYPb5的含量;用比色法测定苯胺羟化酶(反映CYP2E1活性)和红霉素-N-脱甲基酶(反映CYP3A活性)的活性;用real - time RT - PCR检测CYP1 A1、CYP2A3、CYP2E1、CYP3A1、CYP3A2和CYP4B1 mRNA的表达.结果 60 mg· kg-1 Ica明显增加了CYP450的总酶和CYP1 A1的含量、CYP3A的活性及CYP1 A1、CYP3A1、CYP3A2 mRNA的表达,降低了CYP2E1的活性及其mRNA的表达;但Ica对上述各指标的诱导或抑制作用在大鼠月龄方面差异不明显;Ica对CYPb5的含量及CYP2A3、CYP4B1 mRNA的表达未见明显影响.结论 Ica对大鼠肝微粒体CYP450总酶、CYPI A1和CYP3A具有诱导作用,对CYP2E1具有抑制作用,该作用未见明显月龄差异.     

Differential metabolism of acrylonitrile to cyanide is responsible for the greater sensitivity of male vs female mice: role of CYP2E1 and epoxide hydrolases

Acrylonitrile (AN) is a potent toxicant and a known rodent carcinogen. AN epoxidation to cyanoethylene oxide (CEO) via CYP2E1 and its subsequent metabolism via epoxide hydrolases (EH) to yield cyanide is thought to be responsible for the acute toxicity and mortality of AN. Recent reports showed that male mice are more sensitive than females to the acute toxicity/mortality of AN. The present work was undertaken to assess the metabolic and enzymatic basis for the greater sensitivity of male vs female mice to AN toxicity. Male and female wild-type and CYP2E1-null mice received AN at 0, 2.5, 10, 20, or 40 mg/kg by gavage. Cyanide concentrations were measured at 1 or 3 h after dosing. Current data demonstrated that cyanide levels in blood and tissues of AN-treated wild-type mice of both sexes were significantly greater than in vehicle-treated controls and increased in a dose-dependent manner. In contrast, cyanide levels in AN-treated CYP2E1-null mice were not statistically different from those measured in vehicle-treated controls. Furthermore, higher levels of cyanide were detected in male wild-type mice vs females in association with greater sensitivity of males to the acute toxicity/mortality of this chemical. Using Western blot analysis, negligible difference in CYP2E1 expression with higher levels of soluble and microsomal EH (sEH and mEH) was detected in the liver of male vs female mice. In kidneys, male mice exhibited higher expression of both renal CYP2E1 and sEH than did female mice. In conclusion, higher blood and tissue cyanide levels are responsible for the greater sensitivity of male vs female mice to AN. Further, higher expression of CYP2E1 and EH in male mice may contribute to greater formation of CEO and its subsequent metabolism to yield cyanide, respectively.