Base selectivity and effects of sequence and DNA secondary structure on the formation of covalent adducts derived from the equine estrogen metabolite 4-hydroxyequilenin
- Authors
- Kolbanovskiy, A; Kuzmin, V; Shastry, A; Kolbanovskaya, M; Chen, DD; 장민선; Bolton, JL; Geacintov, NE
- Issue Date
- Nov-2005
- Publisher
- American Chemical Society
- Citation
- Chemical Research in Toxicology, v.18, no.11, pp 1737 - 1747
- Pages
- 11
- Journal Title
- Chemical Research in Toxicology
- Volume
- 18
- Number
- 11
- Start Page
- 1737
- End Page
- 1747
- URI
- https://scholarworks.sookmyung.ac.kr/handle/2020.sw.sookmyung/148714
- DOI
- 10.1021/tx050190x
- ISSN
- 0893-228X
1520-5010
- Abstract
- Equilenin, an important component of a widely prescribed hormone replacement formualtion for postmenopausal women, is metabolized by mammalian P450 enzymes to the catechol 4-hydroxyequilenin (4-OHEN). The oxidized o-quinone derivative of 4-OHEN is known to form cyclic covalent adducts with DNA [Bolton, J. (1998) Chem. Res. Toxicol. 11, 1113] in vitro and in vivo. The characteristics of 4-OHEN-DNA adduct formation were investigated with the oligonucleotides 5'-d(CCATCGCTACC) (I), its complementary strand 5'-d(GGTAGCGATGG) (II), one rich in C and the other in G, and the duplexes I-II The identities of the modified bases were elucidated in terms of four stereoisomeric 4-OHEN-2'-deoxynucleoside standards described earlier (Shen et al. (2001) Chem. Res. Toxicol. 11, 94; Embrechts et al. J. Mass Spectrom. 36, 317). The reactions of 4-OHEN with C are favored overwhelmingly in both single-stranded I and II with no guanine adducts observed in either case, and only minor proportions of A adducts were detected in sequence II. However, guanine adducts are observed in oligonucleotides that contain only G and unreactive T residues. The relative levels of cyclic covalent adducts observed in single-stranded I, II, and duplex I-II are similar to 54:21:5, with only the end C groups in I modified in the I-II duplex. When 4-OHEN is reacted with calf thymus DNA, the reaction yield of cyclic adducts is more than similar to 10(3)-fold lower than in I. The cyclic 4-OHEN adducts lead to a pronounced thermal destabilization of duplexes I-II. Overall, cyclic adduct formation is markedly dependent on the sequence context and secondary structure of the DNA. The latter effect is attributed to the poor accessibilities of 4-OHEN to the reactive nucleotide Watson-Crick hydrogen-bonding interface in the interior of the duplex. In the single-stranded oligonucleotides I and II, the strikingly different selectivities of adduct formation are attributed to the formation of noncovalent preassociation complexes that favor reaction geometries with C, rather than with A or G. Finally, the levels of several typical biomarkers of oxidative DNA damage (including 8-oxo-2'-deoxyguanosine) are formed in I in aqueous solutions with a yield at least 10 times smaller than the yield of cyclic 4-OHEN-dC adducts under identical reaction conditions.
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