Mass Spectrometric Determination of N7-HPTE-dG and N7-HPTE-Gua in Mammalian Cells and Mice Exposed to Methoxychlor, an Emergent Persistent Organic Pollutant

Methoxychlor (MXC) is an organopesticide classified as a “Proposed Persistent Organic Pollutant” in the Stockholm Convention, and recent studies revealed that MXC could induce DNA strand breaks, whereas its underlying mechanisms were underinvestigated. Here, we first reported that hydroxymethoxychlor (HPTE), one of MXC’s active metabolites, could be oxidized in vivo to form quinone intermediate, which attacked N7 position of 2′-deoxyguanosine to form N 7-HPTE-deoxyguanosine ( N 7-HPTE-dG), followed by depurination to produce N 7-HPTE-guanine ( N 7-HPTE-Gua) in MXC-treated mammalian cells and tissues from mice fed with MXC, employing an ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) method. We observed a positive correlation between the doses of MXC exposure and the levels of N 7-HPTE-Gua and N 7-HPTE-dG in cytoplasm and genomic DNA, respectively. Furthermore, after removal of exogenous MXC, the amount of genomic N 7-HPTE-dG was significantly decreased during 24 h, while the level of cytoplasmic N 7-HPTE-Gua was elevated during first 12 h, indicating the accumulation of the N 7-HPTE-Gua in cells. Additionally, for animal experiment, genomic N 7-HPTE-dG was observed in livers and cortexes from female C57BL/6 mice fed with MXC, suggesting a potential mechanism of its hepatoxicity and neurotoxicity. Overall, our study provides new understanding about the formation of MXC-induced DNA adducts in mammalian cells and animal models. ● MXC was activated to react with 2′-deoxyguanosine to form DNA adducts. ● Formation and removal of the MXC-DNA adduct was modulated by estrogen receptors. ● MXC-DNA adduct was observed in livers and cortexes from mice fed with MXC.