High-resolution mass spectrometry provides novel insights into products of human metabolism of organophosphate and brominated flame retardants

Abstract

The high resolution, accurate mass, and fast scanning features of the Orbitrap(TM) mass spectrometer, combined with the separation power of ultrahigh-performance liquid chromatography were applied for the first time to study the metabolic profiles of several organic flame retardants (FRs) present in indoor dust. To mimic real-life exposure, in vitro cultured HepG2 human hepatocyte cell lines were exposed simultaneously to various FRs in an indoor dust extract for 24 h. Target parent FRs, hexabromocyclododecanes (α-, β-, and γ-HBCDs), tris-2-chloroethyl phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), were separated in a single run for the first time using alternating positive and negative heated ESI source. Further metabolite separation and identification was achieved using full scan (70,000 full width at half maximum (FWHM)), accurate mass (up to 1 ppm) spectrometry. Structural confirmation was performed via all ion fragmentation (AIF) spectra using the optional higher collisional dissociation (HCD) cell and MS/MS analysis. First insights into human metabolism of HBCDs revealed several hydroxylated and debrominated phase I metabolites, in addition to conjugated phase II glucuronides. Furthermore, various hydroxylated, oxidized, and conjugated metabolites of chlorinated phosphorous FRs were identified, leading to the suggestion of α-oxidation as a significant metabolic pathway for these compounds.

Kinetics of tris (1-chloro-2-propyl) phosphate (TCIPP) metabolism in human liver microsomes and serum

“…The qualitative profile of metabolites, namely BCIPHIPP as major metabolite, was comparable both to our previously published work (Van den Eede et al 2013b) and to the findings of Abdallah et al (2015). Although the latter did not report any presence of TCIPP-M3, this could have been due to the lower substrate concentrations used as TCIPP-M3 gave only a minor signal in our samples.…”

“…PON1 is expressed both in liver and in serum (Furlong et al 2000) and catalyzes the hydrolysis reaction with formation of a dialkyl phosphate (diethyl phosphate for paraoxon) and an alcohol (4-nitrophenol for paraoxon). For TCIPP only the hepatic metabolism has been studied so far, either focusing on oxidative processes or not distinguishing between oxidative and hydrolytic reactions (EU 2008, Van den Eede et al 2013b, Abdallah et al 2015. In order to provide a more complete dataset for integration in pharmacokinetic models, it is necessary to investigate the stability of TCIPP in presence of liver and serum enzymes, such as PON1, and to confirm the extent of contribution of oxidative and hydrolytic enzymes to TCIPP degradation in vitro.…”

Biotransformation of three phosphate flame retardants and plasticizers in primary human hepatocytes: untargeted metabolite screening and quantitative assessment

“…The absence of TCIPP‐M3 was in agreement with results from exposure of HepG2 cells to TCIPP (Abdallah et al , ). In liver subcellular fractions, TCIPP‐M3 was also only a minor contributor to the metabolite profile (Van den Eede et al , ).…”

“…In liver subcellular fractions, TCIPP‐M3 was also only a minor contributor to the metabolite profile (Van den Eede et al , ). In contrast to the reported metabolites in HepG2 cells (Abdallah et al , ), we could not detect any glutathione adduct. We also hoped to find a glucuronide conjugate of BCIPHIPP, as this metabolite was not present in its free form in human urine (Van den Eede et al , ).…”

Evaluation of 3D-human skin equivalents for assessment of human dermal absorption of some brominated flame retardants

“…The receptor fluid, skin tissue and cotton bud samples were extracted according to a previously reported QuEChERs-based method (Abdallah et al, 2015b) (more details in the supplementary data section).…”