Reaction of 1,2,3,4-Diepoxybutane with 2‘-Deoxyguanosine:  Initial Products and Their Stabilities and Decomposition Patterns under Physiological Conditions

Abstract

Abstract1,2,3,4-Diepoxybutane (DEB), an in vivo metabolite of 1,3-butadiene (BD), is a carcinogen and a potent mutagen. Previously, DEB was shown to react with 2′-deoxyguanosine (dG) under physiological conditions to produce seven major nucleoside adducts resulting from alkylation at the N1-(P8 and P9), N7-(P5 and P5′) and both the N1-and N 2 -positions of dG to form six-membered (P4-1 and P4-2) and seven-membered fused ring systems (P6), respectively (Zhang and Elfarra, Chem. Res. Toxicol. 2003, 16, 1606 ibid, 2004, 17, 521). In the present study the stabilities and decomposition products of the seven adducts under in vitro physiological conditions (phosphate buffer containing KCl, pH 7.4, 37 °C) were investigated. The results showed that P4-1, P4-2 and P6 were stable, whereas P5, P5′, P8 and P9 were labile with half-lives of 2.6, 2.7, 16 and 16 h, respectively. P5 and P5′ decomposed initially by the loss of the deoxyribose moiety to yield the corresponding guanine adduct P5D, which exhibited a half-life of 33 h and decomposed through opening of the remaining oxirane ring by dihydrogen phosphate ion, water or chloride ion. Decomposition of P8 yielded P4-1, P6 and nucleoside products resulting from opening of the oxirane ring by dihydrogen phosphate ion, water or chloride ion. Similarly, decomposition of P9 led to formation of P4-2, P6, and nucleoside products resulting from opening of the oxirane ring by dihydrogen phosphate ion, water or chloride ion. These results indicate that the initial products of the reaction of DEB with dG are P5, P5′, P8 and P9, whereas P4-1, P4-2 and P6 are secondary products. The results may also facilitate development of useful biomarkers of exposure to DEB.

Characterization of 1,2,3,4-Diepoxybutane−2‘-Deoxyguanosine Cross-Linking Products Formed at Physiological and Nonphysiological Conditions

“…These results could be explained by instability of P5 and P5′, the likely major initial products of the DEB-dG reaction in acetic acid. P5 and P5′ are short-lived; their half-lives at pH 7.4 and 37 °C are 2.6 and 2.7 h, respectively (40). They are even much more short-lived at weakly acidic conditions; their half-lives at pH 4.0 and 37 °C are only 44 min 7 .…”

“…Therefore the possibility that the P8-dG and P9-dG cross-linking products were formed through the reaction of P8 and P9 with guanine was excluded. The two cross-linking products were considered to be either N1-N7 or N1-N1 cross-linking products based upon the known reactivity of the N7 and N1 positions of dG towards DEB and EB (11,39,40). A cross-linking product of P8 or P9 with dG, which contains two deoxyribose moieties, would have a molecular weight of 619 or 620 for N1-N1 or N1-N7 cross-links, respectively.…”

“…In an effort to assess the relative rates of the cross-linking reactions in comparison with overall decomposition reactions, the half-lives of P5, P5′, P5D, P8, and P9 in the presence of dG were determined to be 2.6, 2.7, 33, 16, and 16 h, respectively, which are identical to the half-lives of these adducts in the absence of dG (40). These results, which indicate that the rates of the cross-linking reactions were low relative to the overall decomposition reactions, are consistent with the observation that the peak areas of N7G-N1dG-BD accounted for less than 1% of the total peak areas in the HPLC chromatograms of the P8-dG and P9-dG reaction mixtures (Figure 2A).…”

“…The four products were labile; their half-lives at pH 7.4 and 37 °C were 2.6, 2.7, 16, and 16 h, respectively (40). P5 and P5′ first decomposed to 2-amino-7-(2-hydroxy-2-oxiranylethyl)-1,7-dihydro-6H-purin-6-one (P5D) 3 after cleavage of the glycosidic bond (Scheme 1), and P5D further decomposed to final guanine products through opening of the oxirane ring by water, or chloride or dihydrogen phosphate ion present in the solution (40). In contrast, no cleavage of the glycosidic bond was observed during the decomposition of P8 and P9; all of the identified decomposition products of P8 and P9 contained the deoxyribose moiety (40).…”

“…P5 and P5′ first decomposed to 2-amino-7-(2-hydroxy-2-oxiranylethyl)-1,7-dihydro-6H-purin-6-one (P5D) 3 after cleavage of the glycosidic bond (Scheme 1), and P5D further decomposed to final guanine products through opening of the oxirane ring by water, or chloride or dihydrogen phosphate ion present in the solution (40). In contrast, no cleavage of the glycosidic bond was observed during the decomposition of P8 and P9; all of the identified decomposition products of P8 and P9 contained the deoxyribose moiety (40). Because each of P5, P5′, P5D, P8, and P9 contains an oxirane ring, these adducts were expected to be capable of further reacting with dG to form cross-linking products.…”