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Xinxin Ding - One of the best experts on this subject based on the ideXlab platform.
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2004a). Identification of critical amino acid residues of human CYP2A13 for the Metabolic Activation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a tobaccospecific carcinogen. Drug Metab. Dispos
2020Co-Authors: Jian Shen, Xinxin Ding, Junyan HongAbstract:ABSTRACT: Among all the known human cytochrome P450 enzymes, CYP2A13 has the highest efficiency in catalyzing the Metabolic Activation (keto aldehyde and keto alcohol formation) of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent lung carcinogen in animals and a suspected human lung carcinogen. As part of the structure-activity relationship (SAR) study, the present work was done to identify the key amino acid residues in CYP2A13 that are responsible for this high catalytic efficiency by using a series of mutants (Ala Arg mutants showed a 9-fold increase in the catalytic efficiency for coumarin 7-hydroxylation. Together with the computational substrate docking, our study provides new SAR information of human CYP2A13
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the tissue specific toxicity of methimazole in the mouse olfactory mucosa is partly mediated through target tissue Metabolic Activation by cyp2a5
Drug Metabolism and Disposition, 2011Co-Authors: Fang Xie, Melissa J Behr, Xin Zhou, Mary Beth Genter, Xinxin DingAbstract:The antithyroid drug methimazole (MMZ) can cause severe, tissue-specific toxicity in mouse olfactory mucosa (OM), presumably through a sequential Metabolic Activation of MMZ by cytochrome P450 (P450) and flavin monooxygenases (FMO). The aims of this study were to determine whether CYP2A5, one of the most abundant P450 enzymes in the mouse OM, is involved in MMZ Metabolic Activation, by comparing Cyp2a5-null with wild-type (WT) mice, and whether hepatic microsomal P450 enzymes, including CYP2A5, are essential for MMZ-induced OM toxicity, by comparing liver-Cpr-null (LCN) mice, which have little P450 activity in hepatocytes, with WT mice. We showed that the loss of CYP2A5 expression did not alter systemic clearance of MMZ (at 50 mg/kg, i.p.); but it did significantly decrease the rates of MMZ metabolism in the OM, whereas FMO expression in the OM was not reduced. MMZ induced depletion of nonprotein thiols, as well as pathological changes, in the OM of WT mice; the extent of these changes was much reduced in the Cyp2a5-null mice. Thus, CYP2A5 plays an important role in mediating MMZ toxicity in the OM. In contrast, the rate of systemic clearance of MMZ was significantly reduced in the LCN mice, compared to WT mice, whereas the MMZ-induced OM toxicity was not prevented. Therefore, hepatic P450 enzymes are essential for systemic MMZ clearance, but they are not required for MMZ-induced OM toxicity. We conclude that the tissue-specific toxicity of MMZ is mediated by target tissue Metabolic Activation, and the reaction is partly catalyzed by CYP2A5 in the OM.
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cyp2a13 variable expression and role in human lung microsomal Metabolic Activation of the tobacco specific carcinogen 4 methylnitrosamino 1 3 pyridyl 1 butanone
Journal of Pharmacology and Experimental Therapeutics, 2007Co-Authors: Xiuling Zhang, Xinxin Ding, Jaime Dagostino, Qingyu Zhang, Linda B Von Weymarn, Sharon E MurphyAbstract:CYP2A13 is the most efficient cytochrome P450 enzyme in the Metabolic Activation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific lung carcinogen. The aims of this study were to determine the levels of CYP2A13 protein in human lung microsomes and to ascertain whether CYP2A13 plays any role in lung microsomal NNK Metabolic Activation. The expression of CYP2A6 and CYP2A13 was examined using a high-resolution immunoblotting method, following immunopurification with an anti-CYP2A5 antibody. We found that, of 116 human lung microsomal samples analyzed, ∼90% had detectable CYP2A6, whereas only 12% had detectable CYP2A13 with a detection limit of ∼2 fmol of CYP2A/mg protein. For the majority of microsomal samples analyzed, the level of CYP2A13 was found to be lower than the level of CYP2A6; overall, the highest level of CYP2A13 found (∼20 fmol/mg protein) was ∼10-fold lower than the highest level of CYP2A6 detected. Quantitative RNA-polymerase chain reaction analysis confirmed that the highly variable expression of the CYP2A proteins was consistent with variations in the levels of the corresponding CYP2A mRNAs in the same tissue samples. It is noteworthy that the level of CYP2A13, but not CYP2A6, was correlated with lung microsomal NNK Metabolic Activation activity. Furthermore, the addition of 8-methoxypsoralen, a CYP2A inhibitor, led to greater inhibition of NNK Metabolic Activation in microsomes containing relatively high levels of CYP2A13 than in samples containing no detectable CYP2A13. Taken together, these data indicate that human lung microsomal CYP2A13 is active in NNK Metabolic Activation. Therefore, individuals having relatively high levels of CYP2A13 expression will likely have an increased risk of developing smoking-related lung cancer.
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human cytochrome p450 cyp2a13 predominant expression in the respiratory tract and its high efficiency Metabolic Activation of a tobacco specific carcinogen 4 methylnitrosamino 1 3 pyridyl 1 butanone
Cancer Research, 2000Co-Authors: Ziping Bao, Qingyu Zhang, Theresa J Smith, Junyan Hong, Xinxin DingAbstract:The human CYP2A subfamily comprises three genes, CYP2A6, CYP2A7, and CYP2A13. CYP2A6 is active toward many carcinogens and is the major coumarin 7-hydroxylase and nicotine C-oxidase in the liver, whereas CYP2A7 is not functional. The function of CYP2A13 has not been characterized. In this study, a CYP2A13 cDNA was prepared by RNA-PCR from human nasal mucosa and was translated using a baculovirus expression system. In a reconstituted system, the expressed CYP2A13 was more active than CYP2A6 in the Metabolic Activation of hexamethylphosphoramide, N,N-dimethylaniline, 2'-methoxyacetophenone, and N-nitrosomethylphenylamine but was much less active than CYP2A6 in coumarin 7-hydroxylation. Of particular interest, CYP2A13 was highly active in the Metabolic Activation of a major tobacco-specific carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, with a catalytic efficiency much greater than that of other human cytochrome P450 isoforms examined previously. The tissue distribution of CYP2A13 was determined with isoform-specific RNA-PCR. CYP2A13 mRNA was detected in liver and a number of extrahepatic tissues, including nasal mucosa, lung, trachea, brain, mammary gland, prostate, testis, and uterus, but not in heart, kidney, bone marrow, colon, small intestine, spleen, stomach, thymus, or skeletal muscle. Quantitative PCR analysis further revealed that CYP2A13 mRNA is expressed at the highest level in the nasal mucosa, followed by the lung and the trachea. Together, these findings suggest that CYP2A13 plays important roles in xenobiotic toxicity and tobacco-related tumorigenesis in the human respiratory tract.
Jiang Zheng - One of the best experts on this subject based on the ideXlab platform.
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dioscorea bulbifera l induced hepatotoxicity and involvement of Metabolic Activation of furanoterpenoids
Drug Metabolism Reviews, 2020Co-Authors: Ying Peng, Jiang ZhengAbstract:The rhizome of Dioscorea bulbifera L. (DBL) is a popular traditional herb in the treatment of goiters, breast lumps, and tumors. Unfortunately, DBL can give rise to severe hepatotoxicity. More than 100 cases of liver injury, due to the usage of DBL in China, have been reported in the past half-century. The main toxic components of DBL are furanoditerpenoids diosbulbin B (DSB) as well as 8-epidiosbulbin E (EEA). This toxic effect requires Metabolic oxidation of the furan ring mediated by cytochrome P450 enzymes, and the P450 3A subfamily is the main enzyme responsible for the reported hepatotoxicity. cis-Enedial intermediates resulting from furan ring oxidation can react with nucleophilic sites of macromolecules, such as protein and DNA, which may trigger the toxicities. This review illustrates the liver injury induced by DBL including Metabolic Activation of DSB and EEA, the essential components responsible for DBL-induced hepatotoxicity, along with biochemical mechanisms of their toxic actions. It will facilitate the development of approaches to prevent and intervene in liver injury induced by DBL for its safe use in clinical practice.
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Identification of Quinone Methide Intermediate Resulting from Metabolic Activation of Icaritin in Vitro and in Vivo
2019Co-Authors: Yan Chen, Ying Peng, Xiucai Guo, Jiang ZhengAbstract:Many herbal medicines such as epimedium have been reported to cause adverse effects, and icaritin is the common aglycone of many glucosides in epimedium. Our present work aimed at the clarification of the Metabolic Activation of icaritin possibly responsible for the adverse effects of epimedium. A quinone methide metabolite (M1) was detected in icaritin-fortified microsomal incubations. A glutathione (GSH) conjugate (M2) and N-acetyl-l-cysteine (NAC) conjugate (M3) derived from icaritin were observed in GSH/NAC-supplemented rat/human liver microsomal incubations. CYP3A family was the predominant enzyme catalyzing the bioActivation of icaritin. In conclusion, sufficient evidence indicates the Metabolic Activation of icaritin to quinone methide metabolite
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Metabolic Activation and Cytotoxicity of Aloe-Emodin Mediated by Sulfotransferases
2019Co-Authors: Yutong You, Xiucai Guo, Ying Peng, Jiang ZhengAbstract:Aloe-emodin (AE) is a major anthraquinone ingredient of numerous traditional Chinese medicines with a variety of beneficial biological activities in vitro. Previous studies suggested that AE possessed cytotoxicity and genotoxicity. Nevertheless, the mechanisms of the toxic action of AE have not yet been fully clarified. The present study aimed at characterization of Metabolic pathways of AE to better understand the mechanisms of AE-induced cytotoxicity. An AE-derived glutathione conjugate (AE-GSH) was observed in rat liver cytosol incubations containing AE and GSH, along with 3′-phosphoadenosine-5′-phosphosulfate (PAPS). Similar incubation fortified with N-acetylcysteine (NAC) in place of GSH offered an AE-NAC conjugate corresponding to the GSH conjugate. The formation of the two conjugates was found to require PAPS. The two conjugates were respectively detected in bile and urine of rats given AE. Sulfotransferase (SULT) inhibitor pentachlorophenol (PCP) suppressed the production of the observed AE-GSH/NAC conjugates in vivo, which suggested that SULTs participated in the process of the Metabolic Activation of AE. The presence of PCP attenuated cell susceptibility to AE-induced cytotoxicity. The present study illustrated potential association of sulfation-mediated bioActivation of AE with its cytotoxicity
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cytochrome p450 mediated Metabolic Activation of chrysophanol
Chemico-Biological Interactions, 2018Co-Authors: Ying Sun, Ying Peng, Xin Xin, Kehan Zhang, Tiantian Cui, Jiang ZhengAbstract:Abstract Chrysophanol, a major anthraquinone component occurring in many traditional Chinese herbs, is accepted as important active component with various pharmacological actions such as antibacterial and anticancer activity. Previous studies demonstrated that exposure to chrysophanol induced cytotoxicity, but the mechanisms of the toxic effects remain unknown. In the present metabolism study, three oxidative metabolites (M1-M3, aloe-emodine, 7-hydroxychrysophanol, and 2-hydroxychrysophanol) and five GSH conjugates (M4-M8) were detected in rat and human liver microsomal incubations of chrysophanol supplemented with GSH, and the formation of the metabolites was NADPH dependent except M4 and M5. M4 and M5 were directly derived from parent compound chrysophanol, M6 arose from M2, and M7 and M8 resulted from the oxidation of M4 and M5. Metabolites M5 and M6 were also observed in bile of rats after exposure to chrysophanol, M1-M3 and one NAC conjugate (M9) were detected in urine of rats administrated chrysophanol, and urinary metabolite M9 originated from the degradation of biliary GSH conjugation M6. Recombinant P450 enzyme incubation and microsome inhibition studies demonstrated that P450 1A2 was the primary enzyme responsible for the Metabolic Activation of chrysophanol and that P450 2B6 and P450 3A4 also participated in the generation of the oxidative metabolites. These findings helped us to understand the mechanisms of chrysophanol-induced cytotoxicity.
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in vitro and in vivo Metabolic Activation of berbamine to quinone methide intermediate
Journal of Biochemical and Molecular Toxicology, 2017Co-Authors: Yao Sun, Tong Yao, Ying Peng, Jiang ZhengAbstract:Berbamine (BBM) is a bisbenzylisoquinoline alkaloid isolated from herbal medicine Berberis amurensis. BBM has been widely used for the treatment of leukemia. Recent studies demonstrated that exposure to BBM can give rise to cytotoxicity. The major objective of this study was to explore the Metabolic Activation of BBM in vitro and in vivo. Two oxidative metabolites (M1 and M2) and an N-acetylcysteine (NAC) conjugate (M3) were detected in human liver microsomal incubations of BBM supplemented with NAC, and the formation of all metabolites was NADPH dependent. Microsomal inhibition and recombinant P450 enzyme incubation studies demonstrated that P450 3A4 was the major enzyme responsible for the Metabolic Activation of BBM. In addition, a BBM-cysteine conjugate (M4) was detected in the urine of rats given BBM. The metabolism study will facilitate the understanding of the biochemical mechanisms of BBM-induced cytotoxicity.
Heinz H Schmeiser - One of the best experts on this subject based on the ideXlab platform.
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Metabolic Activation of carcinogenic aristolochic acid a risk factor for balkan endemic nephropathy
Mutation Research-reviews in Mutation Research, 2008Co-Authors: Marie Stiborova, Volker M Arlt, Eva Frei, Heinz H SchmeiserAbstract:Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is associated with tumor development in patients suffering from Chinese herbs nephropathy (now termed aristolochic acid nephropathy, AAN) and may also be a cause for the development of a similar type of nephropathy, the Balkan endemic nephropathy (BEN). Major DNA adducts [7-(deoxyadenosin-N6-yl)-aristolactam and 7-(deoxyguanosin-N2-yl)aristolactam] formed from AA after reductive Metabolic Activation were found in renal tissues of patients with both diseases. Understanding which human enzymes are involved in AA Activation and/or detoxication is important in the assessment of an individual's susceptibility to this plant carcinogen. This paper reviews major hepatic and renal enzymes responsible for AA-DNA adduct formation in humans. Phase I biotransformation enzymes play a crucial role in the Metabolic Activation of AA to species forming DNA adducts, while a role of phase II enzymes in this process is questionable. Most of the Activation of AA in human hepatic microsomes is mediated by cytochrome P450 (CYP) 1A2 and, to a lower extent, by CYP1A1; NADPH:CYP reductase plays a minor role. In human renal microsomes NADPH:CYP reductase is more effective in AA Activation. Prostaglandin H synthase (cyclooxygenase, COX) is another enzyme activating AA in human renal microsomes. Among the cytosolic reductases, NAD(P)H:quinone oxidoreductase (NQO1) is the most efficient in the Activation of AA in human liver and kidney. Studies with purified enzymes confirmed the importance of CYPs, NADPH:CYP reductase, COX and NQO1 in the AA Activation. The orientation of AA in the active sites of human CYP1A1, -1A2 and NQO1 was predicted from molecular modeling and explains the strong reductive potential of these enzymes for AA detected experimentally. We hypothesized that inter-individual variations in expressions and activities of enzymes activating AA may be one of the causes responsible for the different susceptibilities to this carcinogen reflected in the development of AA-induced nephropathies and associated urothelial cancer.
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human enzymes involved in the Metabolic Activation of the environmental contaminant 3 nitrobenzanthrone evidence for reductive Activation by human nadph cytochrome p450 reductase
Cancer Research, 2003Co-Authors: Volker M Arlt, Marie Stiborova, Alan Hewer, Heinz H SchmeiserAbstract:Determining the capability of humans to metabolize the suspected carcinogen 3-nitrobenzanthrone (3-NBA) and understanding which human enzymes are involved in its Activation are important in the assessment of individual susceptibility to this environmental contaminant found in diesel exhaust and ambient air pollution. We compared the ability of eight human hepatic microsomal samples to catalyze DNA adduct formation by 3-NBA. Using two enrichment procedures of the 32P-postlabeling method, nuclease P1 digestion and butanol extraction, we found that all hepatic microsomes were competent to activate 3-NBA. DNA adduct patterns with multiple adducts, qualitatively similar to those found recently in vivo in rats, were observed. Additionally one major DNA adduct generated by human microsomes was detected. The role of specific cytochromes P450 (P450) and NADPH:P450 reductase in the human hepatic microsomal samples in 3-NBA Activation was investigated by correlating the P450- and NADPH:P450 reductase-linked catalytic activities in each microsomal sample with the level of DNA adducts formed by the same microsomes. On the basis of this analysis, most of the hepatic microsomal Activation of 3-NBA was attributed to NADPH:P450 reductase. Inhibition of DNA adduct formation in human liver microsomes by α-lipoic acid, an inhibitor of NADPH:P450 reductase, supported this finding. Using the purified rabbit enzyme and recombinant human NADPH:P450 reductase expressed in Chinese hamster V79 cells, we confirmed the participation of this enzyme in the formation of 3-NBA-derived DNA adducts. Moreover, essentially the same DNA adduct pattern found in microsomes was detected in Metabolically competent human lymphoblastoid MCL-5 cells. The role of individual human recombinant P450s 1A1, 1A2, 1B1, 2A6, 2B6, 2D6, 2C9, 2E1, and 3A4 and of NADPH:P450 reductase in the Metabolic Activation of 3-NBA, catalyzing DNA adduct formation, was also examined using microsomes of baculovirus-transfected insect cells containing the recombinant enzymes (Supersomes). DNA adducts were observed in all Supersomes preparations, essentially similar to those found with human hepatic microsomes and in human cells. Of all of the recombinant human P450s, P450 2B6 and -2D6 were the most efficient to activate 3-NBA, followed by P450 1A1 and -1A2. These results demonstrate for the first time the potential of human NADPH:P450 reductase and recombinant P450s to contribute to the Metabolic Activation of 3-NBA by nitroreduction.
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Metabolic Activation of the environmental contaminant 3 nitrobenzanthrone by human acetyltransferases and sulfotransferase
Carcinogenesis, 2002Co-Authors: Volker M Arlt, Hansruedi Glatt, Eva Muckel, Ulrike Pabel, Bernd L Sorg, Heinz H SchmeiserAbstract:3-Nitrobenzanthrone (3-NBA) an extremely potent mutagen and suspected human carcinogen identified in diesel exhaust and in airborne particulate matter was shown to form multiple DNA adducts in vitro and in vivo in rats. In order to investigate whether human N,Oacetyltransferases (NATs) and sulfotransferases (SULTs) contribute to the Metabolic Activation of 3-NBA we used a panel of newly constructed Chinese hamster lung fibroblast V79MZ derived cell lines expressing human NAT1, human NAT2 or human SULT1A1, as well as TA1538-derived Salmonella typhimurium strains expressing human NAT1 (DJ400) or human NAT2 (DJ460) and determined DNA binding and mutagenicity. The formation of 3-NBAderived DNA adducts was analysed by 32 P-postlabelling after exposing V79 cells to 0.01 µM 3-NBA or 0.1 µM N-acetyl-N-hydroxy-3-aminobenzanthrone (N-Ac-N-OHABA), a potential metabolite of 3-NBA. Similarly up to four major and two minor adducts were detectable for both compounds, the major ones being identical to those detected previously in DNA from rats treated with 3-NBA. Comparison of DNA binding between different V79MZ derived cells revealed that human NAT2 and, to a lesser extent, human NAT1 and human SULT1A1, contribute to the genotoxic potential of 3-NBA and N-Ac-N-OH-ABA to form DNA adducts. However, the extent of DNA binding by 3-NBA was higher in almost all V79 cells at a 10-fold lower concentration than by N-Ac-N-OH-ABA, suggesting that N-Ac-N-OH-ABA is not a major intermediate in the formation of 3-NBA-derived adducts. 3-NBA showed a 3.8fold and 16.8-fold higher mutagenic activity in Salmonella strains expressing human NAT1 and human NAT2, respectively, than in the acetyltransferase-deficient strain, whereas N-Ac-N-OH-ABA was only clearly (but weakly) mutagenic in Salmonella DJ460 expressing human NAT2. This finding Abbreviations: 3-ABA, 3-aminobenzanthrone; CYP, cytochrome P450; dA, 2-deoxyadenosine; dA-N-Ac-ABA, structurally unidentified 2-deoxyadenosine adduct; dG, 2-deoxyguanosine; dG-N-Ac-ABA, N-acetyl-3-amino-2-(2deoxyguanosin-8-yl)benzanthrone; dGp-N-Ac-ABA, N-acetyl-3-amino-2-(2deoxyguanosin-3-monophosphate-8-yl)benzanthrone; NAT, N,O-acetyltransferase; N-Ac-N-OH-ABA, N-acetyl-N-hydroxy-3-aminobenzanthrone; N-AcoN-Ac-ABA, N-acetoxy-N-acetyl-3-aminobenzanthrone; 3-NBA, 3-nitrobenzanthrone; N-OH-ABA, N-hydroxy-3-aminobenzanthrone; PAH, polycyclic aromatic hydrocarbon; RAL, relative adduct labelling; SULT, sulfotransferase; TLC, thin-layer chromatography. © Oxford University Press 1937 suggests that N-Ac-N-OH-ABA is not a major reactive metabolite responsible for the high mutagenic potency of 3-NBA in Salmonella. Collectively our results indicate that O-acetylation and O-sulfonation by human NATs and SULTs may contribute significantly to the high mutagenic and genotoxic potential of 3-NBA. Moreover, the yetunidentified four major 3-NBA-derived adducts may be DNA adducts without an N-acetyl group.
Ming W. Chou - One of the best experts on this subject based on the ideXlab platform.
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Metabolic Activation of the Tumorigenic Pyrrolizidine Alkaloid, Retrorsine, Leading to DNA Adduct Formation In Vivo
2013Co-Authors: Yu-ping Wang, Ming W. ChouAbstract:alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. The high toxicity of many pyrrolizidine alkaloids has caused considerable loss of free-ranging livestock due to liver and pulmonary lesions. Chronic exposure of toxic pyrrolizidine alkaloids to laboratory animals induces cancer. This investigation studies the Metabolic Activation of retrorsine, a representative naturally occurring tumorigenic pyrrolizidine alkaloid, and shows that a genotoxic mechanism is correlated to the tumorigenicity of retrorsine. Metabolism of retrorsine by liver microsomes of F344 female rats produced two metabolites, 6, 7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP), at a rate of 4.8 ± 0.1 nmol/mg/min, and retrorsine-N-oxide, at a rate of 17.6±0.5 nmol/mg/min. Metabolism was enhanced 1.7-fold by using liver microsomes prepared from dexamethasone-treated rats. DHP formation was inhibited 77 % and retrorsine N-oxide formation was inhibited 29 % by troleandomycin, a P450 3A enzyme inhibitor. Metabolism of retrorsine with lung, kidney, and spleen microsomes from dexamethasone-treated rats also generated DHP and the N-oxide derivative. When rat liver microsomal metabolism of retrorsine occurred in the presence of calf thymus DNA, a set of DHP-derived DNA adducts was formed; these adducts were detected and quantified by using a previously developed 32 P-postlabeling/HPLC method. These same DNA adducts were also found in liver DNA of rats gavaged with retrorsine. Since DHP-derived DNA adducts are suggested to be potential biomarkers of riddelliineinduce
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Metabolic Activation of the tumorigenic pyrrolizidine alkaloid monocrotaline leading to dna adduct formation in vivo
Cancer Letters, 2005Co-Authors: Yu-ping Wang, Jian Yan, Richard D Beger, Ming W. ChouAbstract:Pyrrolizidine alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. The high toxicity of many pyrrolizidine alkaloids has caused considerable loss of free-ranging livestock due to liver and pulmonary lesions. Chronic exposure of toxic pyrrolizidine alkaloids to laboratory animals induces cancer. This investigation studies the Metabolic Activation of retrorsine, a representative naturally occurring tumorigenic pyrrolizidine alkaloid, and shows that a genotoxic mechanism is correlated to the tumorigenicity of retrorsine. Metabolism of retrorsine by liver microsomes of F344 female rats produced two metabolites, 6, 7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP), at a rate of 4.8 ± 0.1 nmol/mg/min, and retrorsine-N-oxide, at a rate of 17.6±0.5 nmol/mg/min. Metabolism was enhanced 1.7-fold by using liver microsomes prepared from dexamethasone-treated rats. DHP formation was inhibited 77% and retrorsine N-oxide formation was inhibited 29% by troleandomycin, a P450 3A enzyme inhibitor. Metabolism of retrorsine with lung, kidney, and spleen microsomes from dexamethasone-treated rats also generated DHP and the N-oxide derivative. When rat liver microsomal metabolism of retrorsine occurred in the presence of calf thymus DNA, a set of DHP-derived DNA adducts was formed; these adducts were detected and quantified by using a previously developed 32 P-postlabeling/HPLC method. These same DNA adducts were also found in liver DNA of rats gavaged with retrorsine. Since DHP-derived DNA adducts are suggested to be potential biomarkers of riddelliine- induced tumorigenicity, our results indicate that (i) similar to the Metabolic Activation of riddelliine, the mechanism of retrorsine-induced carcinogenicity in rats is also through a genotoxic mechanism involving DHP; and (ii) the set of DHP-derived DNA adducts found in liver DNA of rats gavaged with retrorsine or riddelliine can serve as biomarkers for the tumorigenicity induced by retronecine-type pyrrolizidine alkaloids.
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Metabolic Activation of the tumorigenic pyrrolizidine alkaloid retrorsine leading to dna adduct formation in vivo
International Journal of Environmental Research and Public Health, 2005Co-Authors: Yu-ping Wang, Ming W. ChouAbstract:Pyrrolizidine alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. The high toxicity of many pyrrolizidine alkaloids has caused considerable loss of free-ranging livestock due to liver and pulmonary lesions. Chronic exposure of toxic pyrrolizidine alkaloids to laboratory animals induces cancer. This investigation studies the Metabolic Activation of retrorsine, a representative naturally occurring tumorigenic pyrrolizidine alkaloid, and shows that a genotoxic mechanism is correlated to the tumorigenicity of retrorsine. Metabolism of retrorsine by liver microsomes of F344 female rats produced two metabolites, 6, 7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP), at a rate of 4.8 ± 0.1 nmol/mg/min, and retrorsine-N-oxide, at a rate of 17.6±0.5 nmol/mg/min. Metabolism was enhanced 1.7-fold by using liver microsomes prepared from dexamethasone-treated rats. DHP formation was inhibited 77% and retrorsine N-oxide formation was inhibited 29% by troleandomycin, a P450 3A enzyme inhibitor. Metabolism of retrorsine with lung, kidney, and spleen microsomes from dexamethasone-treated rats also generated DHP and the N-oxide derivative. When rat liver microsomal metabolism of retrorsine occurred in the presence of calf thymus DNA, a set of DHP-derived DNA adducts was formed; these adducts were detected and quantified by using a previously developed 32P-postlabeling/HPLC method. These same DNA adducts were also found in liver DNA of rats gavaged with retrorsine. Since DHP-derived DNA adducts are suggested to be potential biomarkers of riddelliine-induced tumorigenicity, our results indicate that (i) similar to the Metabolic Activation of riddelliine, the mechanism of retrorsine-induced carcinogenicity in rats is also through a genotoxic mechanism involving DHP; and (ii) the set of DHP-derived DNA adducts found in liver DNA of rats gavaged with retrorsine or riddelliine can serve as biomarkers for the tumorigenicity induced by retronecine-type pyrrolizidine alkaloids.
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effect of caloric restriction on the metabolism of 7 bromobenz a anthracene and 7 fluorobenz a anthracene by male b6c3f1 mouse liver microsomes reduction of Metabolic Activation pathway
Age, 1993Co-Authors: Ying Xiao, Ming W. Chou, Linda S Von Tungeln, Ronald W HartAbstract:The effect of caloric restriction (CR) on the in vitro metabolism of 7-bromobenz[a]anthracene (7-Br-BA) and 7-fluorobenz[a]anthracene (7-F-BA) by liver microsomes isolated from 5-and 12-month-old male B6C3F1 mice was studied. Mice were fed ad libitum (AL), or starting at 14 weeks of age, received 60% of the calories consumed by control mice. After microsomal incubation, metabolites were separated by HPLC and their structures identified by comparison of their spectra with known standards. The metabolites formed were: trans-3,4-dihydrodiol, trans-5,6-dihydrodiol, trans-8,9-dihydrodiol and trans-10,11-dihydrodiol, 5,6-epoxide, and 4-, 5-, 6-, 8-, and 9-phenolic derivatives. The formation of the 7-Br-BA trans-3,4-dihydrodiol and 7-F-BA trans-3,4-dihydrodiol, the proximate mutagens of 7-Br-BA and 7-F-BA, respectively, was lower in microsomal incubation mixtures derived from the 5-month-old CR mice as compared to those from the AL. These results suggest that CR can diminish the genotoxicity of polycyclic aromatic hydrocarbons by directly altering Metabolic Activation.
Volker M Arlt - One of the best experts on this subject based on the ideXlab platform.
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Metabolic Activation of carcinogenic aristolochic acid a risk factor for balkan endemic nephropathy
Mutation Research-reviews in Mutation Research, 2008Co-Authors: Marie Stiborova, Volker M Arlt, Eva Frei, Heinz H SchmeiserAbstract:Aristolochic acid (AA), a naturally occurring nephrotoxin and carcinogen, is associated with tumor development in patients suffering from Chinese herbs nephropathy (now termed aristolochic acid nephropathy, AAN) and may also be a cause for the development of a similar type of nephropathy, the Balkan endemic nephropathy (BEN). Major DNA adducts [7-(deoxyadenosin-N6-yl)-aristolactam and 7-(deoxyguanosin-N2-yl)aristolactam] formed from AA after reductive Metabolic Activation were found in renal tissues of patients with both diseases. Understanding which human enzymes are involved in AA Activation and/or detoxication is important in the assessment of an individual's susceptibility to this plant carcinogen. This paper reviews major hepatic and renal enzymes responsible for AA-DNA adduct formation in humans. Phase I biotransformation enzymes play a crucial role in the Metabolic Activation of AA to species forming DNA adducts, while a role of phase II enzymes in this process is questionable. Most of the Activation of AA in human hepatic microsomes is mediated by cytochrome P450 (CYP) 1A2 and, to a lower extent, by CYP1A1; NADPH:CYP reductase plays a minor role. In human renal microsomes NADPH:CYP reductase is more effective in AA Activation. Prostaglandin H synthase (cyclooxygenase, COX) is another enzyme activating AA in human renal microsomes. Among the cytosolic reductases, NAD(P)H:quinone oxidoreductase (NQO1) is the most efficient in the Activation of AA in human liver and kidney. Studies with purified enzymes confirmed the importance of CYPs, NADPH:CYP reductase, COX and NQO1 in the AA Activation. The orientation of AA in the active sites of human CYP1A1, -1A2 and NQO1 was predicted from molecular modeling and explains the strong reductive potential of these enzymes for AA detected experimentally. We hypothesized that inter-individual variations in expressions and activities of enzymes activating AA may be one of the causes responsible for the different susceptibilities to this carcinogen reflected in the development of AA-induced nephropathies and associated urothelial cancer.
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human enzymes involved in the Metabolic Activation of the environmental contaminant 3 nitrobenzanthrone evidence for reductive Activation by human nadph cytochrome p450 reductase
Cancer Research, 2003Co-Authors: Volker M Arlt, Marie Stiborova, Alan Hewer, Heinz H SchmeiserAbstract:Determining the capability of humans to metabolize the suspected carcinogen 3-nitrobenzanthrone (3-NBA) and understanding which human enzymes are involved in its Activation are important in the assessment of individual susceptibility to this environmental contaminant found in diesel exhaust and ambient air pollution. We compared the ability of eight human hepatic microsomal samples to catalyze DNA adduct formation by 3-NBA. Using two enrichment procedures of the 32P-postlabeling method, nuclease P1 digestion and butanol extraction, we found that all hepatic microsomes were competent to activate 3-NBA. DNA adduct patterns with multiple adducts, qualitatively similar to those found recently in vivo in rats, were observed. Additionally one major DNA adduct generated by human microsomes was detected. The role of specific cytochromes P450 (P450) and NADPH:P450 reductase in the human hepatic microsomal samples in 3-NBA Activation was investigated by correlating the P450- and NADPH:P450 reductase-linked catalytic activities in each microsomal sample with the level of DNA adducts formed by the same microsomes. On the basis of this analysis, most of the hepatic microsomal Activation of 3-NBA was attributed to NADPH:P450 reductase. Inhibition of DNA adduct formation in human liver microsomes by α-lipoic acid, an inhibitor of NADPH:P450 reductase, supported this finding. Using the purified rabbit enzyme and recombinant human NADPH:P450 reductase expressed in Chinese hamster V79 cells, we confirmed the participation of this enzyme in the formation of 3-NBA-derived DNA adducts. Moreover, essentially the same DNA adduct pattern found in microsomes was detected in Metabolically competent human lymphoblastoid MCL-5 cells. The role of individual human recombinant P450s 1A1, 1A2, 1B1, 2A6, 2B6, 2D6, 2C9, 2E1, and 3A4 and of NADPH:P450 reductase in the Metabolic Activation of 3-NBA, catalyzing DNA adduct formation, was also examined using microsomes of baculovirus-transfected insect cells containing the recombinant enzymes (Supersomes). DNA adducts were observed in all Supersomes preparations, essentially similar to those found with human hepatic microsomes and in human cells. Of all of the recombinant human P450s, P450 2B6 and -2D6 were the most efficient to activate 3-NBA, followed by P450 1A1 and -1A2. These results demonstrate for the first time the potential of human NADPH:P450 reductase and recombinant P450s to contribute to the Metabolic Activation of 3-NBA by nitroreduction.
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Metabolic Activation of the environmental contaminant 3 nitrobenzanthrone by human acetyltransferases and sulfotransferase
Carcinogenesis, 2002Co-Authors: Volker M Arlt, Hansruedi Glatt, Eva Muckel, Ulrike Pabel, Bernd L Sorg, Heinz H SchmeiserAbstract:3-Nitrobenzanthrone (3-NBA) an extremely potent mutagen and suspected human carcinogen identified in diesel exhaust and in airborne particulate matter was shown to form multiple DNA adducts in vitro and in vivo in rats. In order to investigate whether human N,Oacetyltransferases (NATs) and sulfotransferases (SULTs) contribute to the Metabolic Activation of 3-NBA we used a panel of newly constructed Chinese hamster lung fibroblast V79MZ derived cell lines expressing human NAT1, human NAT2 or human SULT1A1, as well as TA1538-derived Salmonella typhimurium strains expressing human NAT1 (DJ400) or human NAT2 (DJ460) and determined DNA binding and mutagenicity. The formation of 3-NBAderived DNA adducts was analysed by 32 P-postlabelling after exposing V79 cells to 0.01 µM 3-NBA or 0.1 µM N-acetyl-N-hydroxy-3-aminobenzanthrone (N-Ac-N-OHABA), a potential metabolite of 3-NBA. Similarly up to four major and two minor adducts were detectable for both compounds, the major ones being identical to those detected previously in DNA from rats treated with 3-NBA. Comparison of DNA binding between different V79MZ derived cells revealed that human NAT2 and, to a lesser extent, human NAT1 and human SULT1A1, contribute to the genotoxic potential of 3-NBA and N-Ac-N-OH-ABA to form DNA adducts. However, the extent of DNA binding by 3-NBA was higher in almost all V79 cells at a 10-fold lower concentration than by N-Ac-N-OH-ABA, suggesting that N-Ac-N-OH-ABA is not a major intermediate in the formation of 3-NBA-derived adducts. 3-NBA showed a 3.8fold and 16.8-fold higher mutagenic activity in Salmonella strains expressing human NAT1 and human NAT2, respectively, than in the acetyltransferase-deficient strain, whereas N-Ac-N-OH-ABA was only clearly (but weakly) mutagenic in Salmonella DJ460 expressing human NAT2. This finding Abbreviations: 3-ABA, 3-aminobenzanthrone; CYP, cytochrome P450; dA, 2-deoxyadenosine; dA-N-Ac-ABA, structurally unidentified 2-deoxyadenosine adduct; dG, 2-deoxyguanosine; dG-N-Ac-ABA, N-acetyl-3-amino-2-(2deoxyguanosin-8-yl)benzanthrone; dGp-N-Ac-ABA, N-acetyl-3-amino-2-(2deoxyguanosin-3-monophosphate-8-yl)benzanthrone; NAT, N,O-acetyltransferase; N-Ac-N-OH-ABA, N-acetyl-N-hydroxy-3-aminobenzanthrone; N-AcoN-Ac-ABA, N-acetoxy-N-acetyl-3-aminobenzanthrone; 3-NBA, 3-nitrobenzanthrone; N-OH-ABA, N-hydroxy-3-aminobenzanthrone; PAH, polycyclic aromatic hydrocarbon; RAL, relative adduct labelling; SULT, sulfotransferase; TLC, thin-layer chromatography. © Oxford University Press 1937 suggests that N-Ac-N-OH-ABA is not a major reactive metabolite responsible for the high mutagenic potency of 3-NBA in Salmonella. Collectively our results indicate that O-acetylation and O-sulfonation by human NATs and SULTs may contribute significantly to the high mutagenic and genotoxic potential of 3-NBA. Moreover, the yetunidentified four major 3-NBA-derived adducts may be DNA adducts without an N-acetyl group.