Persistence of N7-(2,3,4-Trihydroxybutyl)guanine Adducts in the Livers of Mice and Rats Exposed to 1,3-Butadiene

Abstract

Liquid chromatography (LC) in combination with tandem mass spectrometry (MS/MS) and stable isotope methodology was employed for the analysis of the N7-guanine (Gua) adducts derived from 1,2:3, 4-diepoxybutane (BDO2) a reactive metabolite of 1,3-butadiene (BD). Two diastereomeric forms of N7-(2,3,4-trihydroxybutyl)guanine (THBG) were identified in the livers of both mice and rats. One of the diastereomers [(+/-)-THBG] was formed by reaction of DNA with (+/-)-BDO2, and the other diastereomer (meso-THBG) was formed by reaction of DNA with meso-BDO2. There was significantly more (+/-)-THBG and meso-THBG in the liver DNA of the mice when compared with those of the rats during the 10 days of exposure to BD and the 6 days of postexposure that were monitored. There was a 2-fold excess of (+/-)-THBG over meso-THBG in the rat liver at all the time points. In the mouse liver after 10 days of exposure to BD, the (+/-)-THBG (3.9 adducts/10(6) normal bases) was also present in an almost 2-fold excess over meso-THBG (2.2 adducts/10(6) normal bases). However, 6-days after exposure to BD, (+/-)-THBG (1.2 adducts/10(6) normal bases) and meso-THBG (1.0 adduct/10(6) normal bases) were present in almost equal amounts in the mouse liver. Furthermore, there was an almost 5-fold excess of the two THBG diastereomers in the mouse liver DNA 6 days after exposure to BD when compared with rat liver DNA. The half-lives of (+/-)-THBG and meso-THBG appeared to be slightly longer in mouse liver (4.1 and 5.5 days, respectively) than in rat liver (3.6 and 4.0 days, respectively). The apparent persistence of these adducts in the mouse may contribute to the increased susceptibility of this species to BD-induced carcinogenesis. It is possible that (+/-)-THBG and meso-THBG could have also been derived from the reaction of DNA with the hydrolysis product of BDO2, 1,2-dihydroxy-3,4-epoxybutane (DHEB). Surprisingly, a vast majority of the studies in which the mutagenic and carcinogenic potential of BDO2 have been examined have only employed the commercially available (+/-)-BDO2. In light of the present findings, additional studies will be required to determine the potency of meso-BDO2 and the DHEB that is the precursor to meso-THBG as mutagens and carcinogens.

Structural Characterization of the Major DNA−DNA Cross-Link of 1,2,3,4-Diepoxybutane

“…The assigned 13 C chemical shifts for the dihydroxybutane portion of the molecule ( Figure 5) are similar to the corresponding signals previously reported for N7-THBG (34). In the HMQC spectrum ( Figure 5A), only one 1 H cross-peak is observed for the C-OH carbon (69.2 ppm), while the C-N< carbon (51.5 ppm) has two bound protons ( Figure 5A).…”

Molecular Dosimetry of N-7 Guanine Adduct Formation in Mice and Rats Exposed to 1,3-Butadiene

“…These modifications in the chromatographic separation allowed baseline separation and simultaneous quantitation of all four adducts, including racemic and meso (47) forms of the THB-Gua. [ 13 C 4 ]THB-Gua (racemic) was used as the internal standard for both the racemic and meso THBGua (47). The response was linear for both THB-Gua and EB-Gua adducts over the working range with R 2 values of g0.9998.…”

“…Adducts induced by BD were assessed in skin DNA of mice treated with 1.9-153 µmol of DEB per mouse (43). The amounts of EB-Gua and THB-Gua adducts have been quantitated in livers of female B6C3F1 mice and female F344 rats exposed to 1250 ppm BD by inhalation for 10 days (41,46,47) and in lungs of female B6C3F1 mice (41).…”

Study for Catecholamine-2'-Deoxyguanosine Adduct Formation under Biomimetic Conditions Using Liquid Chromatography-Electrospray Ionization-Ion Trap Mass Spectrometry.

“…Mass spectrometry (MS) coupled with high-performance liquid chromatography (HPLC) techniques would seem to be a preferred method for these purposes, because much structural information can be obtained after the chromatographic separation using only trace amounts of precious samples. 20) In this paper, as our first model experiment, Ladrenaline, which is more widely distributed than dopamine, was reacted with 2′-deoxyguanosine (dG) with or without oxidant under biomimetic conditions (pH 7.5, 37°C). At least two DNA adducts were observed in the reaction mixture and were characterized using liquid chromatography-electrospray ionization-ion trap mass spectrometry (LC-ESI-ion trap MS) and photodiode array detection (PAD) as chemical evidences of the DNA modification by catecholamines.…”