First insight on in vitro metabolism of three newly identified aryl organophosphate esters via a suspect coupled with nontarget screening approach

The ubiquity of organophosphate esters (OPEs) in the environment has triggered research into metabolic pathways of OPEs. Using liquid chromatography coupled with a hybrid quadrupole Orbitrap high-resolution mass spectrometer, a suspect and characteristic fragment ion-based nontarget screening strategy for the identification of unknown OPE metabolites was developed and evaluated. Then, this integrated approach was successfully used for investigation of three newly identified organophosphate esters (NOPEs), namely 2-biphenylol diphenyl phosphate (BPDPP), tris(2-biphenyl) phosphate (TBPHP), and naphthalen-2-yl diphenyl phosphate (NDPHP), in human liver microsomes (HLMs). The results demonstrated that BPDPP, TBPHP, and NDPHP were effectively metabolized by HLMs, with zero-order kinetics (R2 = 0.48−0.94) within the time frame of the assay. The suspected approach identified a considerable number of dearylated phosphate (DP), and hydroxylated metabolites for each of NOPEs after incubation with HLMs for 2 h. In addition, the nontarget approach further identified 9 novel metabolites including 2 epoxide intermediates and 7 oxidative ring-opening compounds, which were first reported in the Phase I metabolism of OPEs. Collectively, this study provided a novel suspect coupled with nontarget screening approach and was successfully used to screen metabolites of three NOPEs. For the first time, we observed direct evidence that oxidative ring-opening might serve as another primary metabolic pathway regarding the metabolism of aryl OPEs.