Identification and Characterization of 2鈥?Deoxyadenosine Adducts Formed by Isoprene Monoepoxides in Vitro

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• 作者：Petra Begemann ; Gunnar Boysen ; Nadia I. Georgieva ; Ramiah Sangaiah ; Karl M. Koshlap ; Hasan Koc ; Daping Zhang ; Bernard T. Golding ; Avram Gold ; James A. Swenberg
• 刊名：Chemical Research in Toxicology
• 出版年：2011
• 出版时间：July 18, 2011
• 年：2011
• 卷：24
• 期：7
• 页码：1048-1061
• 全文大小：1113K
• 年卷期：v.24,no.7(July 18, 2011)
• ISSN：1520-5010

文摘

Isoprene, the 2-methyl analogue of 1,3-butadiene, is ubiquitous in the environment, with major contributions to total isoprene emissions stemming from natural processes despite the compound being a bulk industrial chemical. Additionally, isoprene is a combustion product and a major component in cigarette smoke. Isoprene has been classified as possibly carcinogenic to humans (group 2B) by IARC and as reasonably anticipated to be a human carcinogen by the National Toxicology Program. Isoprene, like butadiene, requires metabolic activation to reactive epoxides to exhibit its carcinogenic properties. The mode of action has been postulated to be that of a genotoxic carcinogen, with the formation of promutagenic DNA adducts being essential for mutagenesis and carcinogenesis. In rodents, isoprene-induced tumors show unique point mutations (A鈫扵 transversions) in the K-ras protooncogene at codon 61. Therefore, we investigated adducts formed after the reaction of 2鈥?deoxyadenosine (dAdo) with the two monoepoxides of isoprene, 2-ethenyl-2-methyloxirane (IP-1,2-O) and propen-2-yloxirane (IP-3,4-O), under physiological conditions. The formation of N1-2鈥?deoxyinosine (N1-dIno) due to the deamination of N1-dAdo adducts was of particular interest, since N1-dIno adducts are suspected to have high mutagenic potential based on in vitro experiments. Major stable adducts were identified by HPLC, UV-spectroscopy, and LC-MS/MS and characterized by ¹H NMR and ¹H,¹³C HSQC and HMBC NMR experiments. Adducts of IP-1,2-O that were fully identified are R,S-C1-N⁶-dAdo, R-C2-N⁶-dAdo, and S-C2-N⁶-dAdo; adducts of IP-3,4-O are S-C3-N⁶-dAdo, R-C3-N⁶-dAdo, R,S-C4-N⁶-dAdo, S-C4-N1-dIno, R-C4-N1-dIno, R-C3-N1-dIno, S-C3-N1-dIno, and C3-N7-Ade. Both monoepoxides formed adducts on the terminal and internal oxirane carbons. This is the first study to describe adducts of isoprene monoepoxides with dAdo. Characterization of adducts formed by isoprene monoepoxides with deoxynucleosides and subsequently with DNA represent the first step toward evaluating their potential for being converted into a mutation or as biomarkers of isoprene metabolism and exposure.