Identification of di-2-ethylhexyl terephthalate (DEHTP) metabolites using human liver microsomes for biomonitoring applications

Di-2-ethylhexyl terephthalate (DEHTP), a structural isomer of the plasticizer di-2-ethylhexyl phthalate (DEHP), is used in food packaging and medical devices, among other applications, and is a potential replacement for DEHP and other ortho-phthalate plasticizers. Identifying sensitive and specific biomarkers of DEHTP is necessary to assess humans' background exposure to DEHTP. Using mass spectrometry, we investigated the metabolism of DEHTP by human liver microsomes to identify in vitro DEHTP metabolites. We unequivocally identified terephthalic acid (TPA) and mono-2-ethylhydroxyhexyl terephthalate (MEHHTP), using authentic standards, and tentatively identified mono-2-ethylhexyl terephthalate (MEHTP) and two other oxidative metabolites of DEHTP: mono-2-ethyloxohexyl terephthalate (MEOHTP), and mono-2-ethyl-5-carboxypentyl terephthalate (MECPTP) from their mass spectrometry fragmentation patterns. We also evaluated the formation of in vitro metabolites of DEHP. DEHTP and DEHP produced similar metabolites, but their metabolite profiles differed considerably. DEHTP metabolized to form TPA, a metabolite of several terephthalates, as the major in vitro metabolite, followed by MEHTP, MEHHTP, MEOHTP and MECPTP. MEHTP, MEHHTP, MEOHTP and MECPTP, which are specific metabolites of DEHTP, may be suitable biomarkers for assessing exposure to DEHTP. Nonetheless, data on the urinary excretion fraction and temporal stability of these metabolites, among other considerations, are needed to demonstrate their utility as exposure biomarkers.