Complex Reactivity of Bisphenol A Diglycidyl Ether (BADGE) with DNA

Bisphenol A diglycidyl ether (BADGE) is a diepoxide product used in the synthesis of epoxy resins. Its genotoxic properties were strongly suggested by its ability to induce mutations and micronuclei, but the exact nature of the underlying DNA damage remains to be established. For this purpose, we first applied cellular tests (the Comet assay and 53BP1 immunostaining) to show that direct induction of strand breaks was not the favored genotoxic pathway for BADGE. Consequently, we investigated the formation of DNA adducts using UHPLC coupled with tandem mass spectrometry (UHPLC-MS/MS) analysis following enzymatic hydrolysis. Analyses using single-stage mass spectrometry, product ion scan, and neutral loss monitoring showed that BADGE readily formed monoadducts with DNA bases. The structural assignments were confirmed by the results of accurate thermal degradation studies, which showed that BADGE reacted with DNA like other aliphatic epoxides. We also obtained unambiguous evidence that the reaction of BADGE with DNA led to the formation of biadducts between nonadjacent bases. This was explained by the transient formation of monoadducts bearing a BADGE moiety with an unreacted epoxide group. A sensitive quantitative UHPLC-MS/MS assay was then developed for the detection of BADGE adducts in cellular DNA. All the adducts identified in isolated DNA were also detected in cellular DNA. The proportions between the monoadducts were similar, but the relative yield of biadducts was lower in cellular than in isolated DNA. A time-course study of the level of adducts in DNA also showed that BADGE adducts were substrates for the cellular repair machinery. The present results definitively show that BADGE is a DNA-damaging chemical. The detected adducts represent novel biomarkers of the genotoxicity of BADGE.