title: Biotransformation of three phosphate flame retardants and plasticizers in primary human hepatocytes: untargeted metabolite screening and quantitative assessment.
abstract: Tris(2-butoxyethyl) phosphate (TBOEP), triphenyl phosphate (TPHP) and tris(1-chloro-2-propyl) phosphate (TCIPP) are current high-volume organophosphate flame retardants/plasticizers (PFRs) and are abundant in the indoor environment. While recent in vitro research has indicated potential toxic effects in the endocrine system, biotransformation of these compounds is still underexplored. In this study, we aimed to characterize the metabolite formation for three PFRs in primary human hepatocytes, an in vitro system that mimics in vivo liver metabolism more closely than hepatic subcellular fractions or cell lines. Cryopreserved human hepatocytes were thawed and suspended in media with 50 μm TBOEP or TCIPP, or 20 μm TPHP up to 2 h. Extracts were analyzed by liquid chromatography-quadrupole-time-of-flight-mass spectrometry. Quantification of biotransformation products in hepatocytes exposed for 2 h revealed that bis(1-chloro-2-propyl) phosphate and diphenyl phosphate corresponded to less than half of the depletion of TCIPP and TPHP, respectively, while bis(2-butoxyethyl) 2-hydroxyethyl phosphate compared to 40-66% of the depletion of TBOEP. Other metabolite structures of these PFRs were produced at 4- to 10-fold lower rates. These findings help interpret biological levels of the major metabolites and relate it to levels of their parent PFR. Percentage of substrate depletion was largest for TBOEP followed by comparable values for TPHP and TCIPP, indicating that hepatic clearance of TPHP and TCIPP would be slower than that of TBOEP. The resulting higher levels and longer presence of TPHP in the circulation after exposure, would allow TPHP a larger time window to exert its suspected adverse effects compared to TBOEP. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Antwerp, Belgium. nelevandeneede@gmail.com.
authors.forename: Nele
authors.initials: N
authors.lastname: Van den Eede
authors.affiliation: Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Antwerp, Belgium.
authors.forename: Ingrid
authors.initials: I
authors.lastname: de Meester
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Antwerp, Belgium.
authors.forename: Walid
authors.initials: W
authors.lastname: Maho
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Antwerp, Belgium.
authors.forename: Hugo
authors.initials: H
authors.lastname: Neels
authors.affiliation: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610, Antwerp, Belgium. adrian.covaci@uantwerpen.be.
authors.forename: Adrian
authors.initials: A
authors.lastname: Covaci
mesh_terms: D001711:Biotransformation; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D005411:Flame Retardants / Q000032:analysis / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D013058:Mass Spectrometry; D015394:Molecular Structure; D010755:Organophosphates / Q000032:analysis / Q000378:metabolism*; D009943:Organophosphorus Compounds / Q000032:analysis / Q000378:metabolism*; D010968:Plasticizers / Q000032:analysis / Q000378:metabolism*; D061251:Primary Cell Culture
chemical_list: D005411:Flame Retardants; D010755:Organophosphates; D009943:Organophosphorus Compounds; D010968:Plasticizers; C072782:tri-(2-chloroisopropyl)phosphate; C013320:tris(2-butoxyethyl) phosphate; C005445:triphenyl phosphate
keywords: clearance; in vitro; liver; metabolite; organophosphate flame retardants