Persistence of N7-(2,3,4-trihydroxybutyl)guanine adducts in the livers of mice and rats exposed to 1,3-butadiene

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/10⁶ normal bases) was also present in an almost 2-fold excess over meso-THBG (2.2 adducts/10⁶ normal bases). However, 6-days after exposure to BD, (±)THBG (1.2 adducts/10⁶ normal bases) and meso-THBG (1.0 adduct/10⁶ 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.