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Journal Article 2015; 36(Suppl 1): 13-21 PubMed PMID: 26757129 Citation  Keywords:  Animals, Aristolochic Acids:metabolism, Arsenic:pharmacology, Balkan Nephropathy, Cadmium:pharmacology, Carcinogens:metabolism, Chromatography, High Pressure Liquid, Ions, Lead:pharmacology, Metals, Heavy:pharmacology, Microsomes, Liver:metabolism, Ochrat.   

OBJECTIVES: Balkan endemic nephropathy (BEN) is a chronic progressive fibrosis associated with upper urothelial carcinoma (UUC). Aetiology of BEN is still not fully explained. Although carcinogenic aristolochic acid I (AAI) was proven as the major cause of BEN/UUC, this nephropathy is considered to be multifactorial. Hence, we investigated whether other factors considered as potential causes of BEN [a mycotoxin ochratoxin A (OTA), Cd, Pb, Se and As ions and organic compounds (i.e. phthalates) released from lignite deposits in BEN areas] can influence detoxication of AAI, whose concentrations are crucial for BEN development.

METHODS: Oxidation of AAI to 8-hydroxyaristolochic acid I (AAIa) in the presence of Cd, Pb, Se, As ions, dibutylphthalate (DBP), butylbenzylphthalate (BBP), bis(2-ethylhexyl)phthalate (DEHP) and OTA by rat liver microsomes was determined by HPLC.

RESULTS: Only OTA, cadmium and selenium ions, and BBP inhibited AAI oxidation by rat liver microsomes. These compounds also inhibited activities of CYP1A1 and/or CYP2C6/11 catalysing AAI demethylation in rat livers. Therefore, these CYP inhibitions can be responsible for a decrease in AAIa formation. When the combined effects of these compounds were investigated, the most efficient inhibition was caused by OTA combined with BBP and selenium ions.

CONCLUSION: The results show low effects of BBP, cadmium and selenium ions, and/or their combinations on AAI detoxication. No effects were produced by the other metal ions (Pb, As) and phthalates DBP and DEHP. This finding suggests that they do not influence AAI-mediated BEN development. In contrast, OTA might influence this process, by inhibition of AAI detoxication....

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Journal Article 2015; 36(Suppl 1): 46-52 PubMed PMID: 26757127 Citation  Keywords:  Animals, Carcinogens:metabolism, Cytochrome P-450 Enzyme System:drug effects, Flavonols:pharmacology, Inhibitory Concentration 50, Intestine, Small:drug effects, Liver:drug effects, Male, RNA, Messenger:drug effects, Rats, Rats, Wistar, Real-Time Polymera.   

OBJECTIVES: Dihydromyricetin (DHM) is a flavonoid, which has been shown to antagonize effects of ethanol intoxication. As a potential pharmacological agent, its biological interactions with enzymes metabolizing foreign compounds should be tested. Thus, the aim of this study was to analyze the influence of DHM on the induction and metabolic activity of selected cytochromes P450 (CYPs).

METHODS: After flavonoid administration by oral gavage to stomach the CYP expression at protein and mRNA levels was determined in rat liver and small intestine. The effects of flavonoids on CYP1A1/2, CYP1A2 or CYP2B1/2 enzyme activities in microsomes were measured using marker activities of these enzymes. Flavonoid-mediated inhibition of recombinant CYP1A2 was also assayed with luciferin-ME substrate. The flavonoid interaction with aryl hydrocarbon receptor (AhR) was assayed by reporter luciferase activity in Hep2G cells.

RESULTS: The value of half maximal inhibitory concentration of DHM for CYP1A1/2, CYP1A2, and CYP2B1 were determined to be 4.1, 14.2, and 98.5 mmol.L(-1), respectively. With the exception of a weak induction of CYP2B1 and CYP1A2 in the middle part of small intestine and in the liver, respectively, DHM did not affect the CYP expression at protein levels. On the contrary, real-time PCR revealed elevated expression of CYP1A1 and CYP1A2 mRNA in proximal part of the small intestine while decreased in the middle part. In the study utilizing the HepG2 cells, DHM showed only an additive effect on the benzo[a]pyrene-mediated activation of Ah receptor.

CONCLUSIONS: Dihydromyricetin doesn't significantly interfere with metabolic activity of CYP1A1/2 and CYP2B1 enzymes....

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Comparative Study 2013; 34(Suppl 2): 55-63 PubMed PMID: 24362093 Citation  Keywords:  Animals, Benzo(a)pyrene:metabolism, Carcinogens:metabolism, Cytochrome P-450 CYP1A1:metabolism, Cytochromes b5:pharmacology, Humans, Inactivation, Metabolic, Male, Microsomes, Liver:drug effects, Oxidation-Reduction, Rats,.   

OBJECTIVES: Cytochrome P450 (CYP) 1A1 is the most important enzyme in both activation and detoxification of carcinogenic benzo[a]pyrene (BaP), in combination with microsomal epoxide hydrolase (mEH). To evaluate metabolism of BaP in human, identification of a suitable animal model that mimics the metabolic fate of BaP in human is of great importance. The aim of this work was to compare BaP oxidation by human CYP1A1 and CYP1A1 of one animal model, rat. Investigation of the effect of cytochrome b5 on BaP oxidation by CYP1A1 was another target of this study.

METHODS: High performance liquid chromatography (HPLC) was employed for separation of BaP metabolites formed by enzymatic systems. Their structures were identified by mass- and NMR-spectrometry.

RESULTS: Human hepatic microsomes oxidized BaP to BaP-9,10-dihydrodiol, BaP-4,5-dihydrodiol, BaP-7,8-dihydrodiol, BaP-1,6-dione, BaP-3,6-dione and BaP-3-ol. The same metabolites were generated by rat liver microsomes, but BaP-9-ol and a metabolite Mx, the structure of which has not been identified as yet, were also formed in these microsomes. Human CYP1A1 expressed with NADPH:CYP reductase (POR) in Supersomes™ oxidized BaP to the same metabolites as microsomes, but BaP-4,5-dihydrodiol has not been detected. Rat recombinant CYP1A1 in this SupersomesTM system oxidized BaP to BaP-9,10-dihydrodiol, a metabolite Mx, BaP-4,5-dihydrodiol, BaP-7,8-dihydrodiol, BaP-1,6-dione, BaP-3,6-dione, BaP-9-ol and BaP-3-ol. Addition of cytochrome b5 to rat and human recombinant CYP1A1 systems led to a more than 2-fold increase in BaP oxidation.

CONCLUSION: The results show similarities between human and rat CYP1A1 in BaP oxidation and demonstrate rats as a suitable model mimicking BaP oxidation in human....

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Journal Article 2010; 31(Suppl 2): 36-45 PubMed PMID: 21187827 Citation  Keywords:  Aniline Compounds:metabolism, Animals, Anisoles:metabolism, Aryl Hydrocarbon Hydroxylases:physiology, Carcinogens:metabolism, Cytochrome P-450 CYP2E1:physiology, Cytochrome P-450 Enzyme System:physiology, Environmental Pollutants:metabolism, Hydroxylamine.   

OBJECTIVES: N-(2-methoxyphenyl)hydroxylamine is a human metabolite of two industrial and environmental pollutants and bladder carcinogens 2-methoxyaniline (o-anisidine) and 2-methoxynitrobenzene (o-nitroanisole). Metabolism of N-(2-methoxyphenyl)hydroxylamine by rat hepatic microsomes and identification of the major microsomal enzymes participating in this process are aims of this study.

METHODS: HPLC with UV detection was employed for the separation of N-(2-methoxyphenyl)hydroxylamine metabolites. Inducers and inhibitors of microsomal enzymes and rat recombinant CYPs were used to characterize the enzymes participating in N-(2-methoxyphenyl)hydroxylamine metabolism.

RESULTS: N-(2-methoxyphenyl)hydroxylamine is metabolized by rat hepatic microsomes predominantly to o-anisidine, the parent carcinogen from which N-(2-methoxyphenyl)hydroxylamine is formed, while o-aminophenol and two N-(2-methoxyphenyl)hydroxylamine metabolites, whose exact structures have not been identified as yet, are minor products. Selective inhibitors of microsomal CYPs, NADPH:CYP reductase and NADH:cytochrome b5 reductase and hepatic microsomes of rats pre-treated with specific inducers of CYPs and NADPH:CYP reductase were used to characterize rat liver microsomal enzymes reducing N-(2-methoxyphenyl)hydroxylamine to o-anisidine. Based on these studies, we attribute most of N-(2-methoxyphenyl)hydroxylamine metabolism to o-anisidine in rat liver to CYP2C, followed by CYP2E1, 2D and 2A. Among recombinant rat CYP enzymes tested in this study, rat CYP2C11 and 2E1, followed by CYP2A2, 2D1/2, 2C12, 3A1/2 and 1A1/2 were the most efficient enzymes metabolizing N-(2-methoxyphenyl)hydroxylamine to o-anisidine.

CONCLUSION: The results found in this study, the first report on the reduction of N-(2-methoxyphenyl)hydroxylamine by rat CYP enzymes, demonstrate that CYP2C, followed by CYP2E1, 2D and 2A are the major enzymes participating in this process in rat liver....

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