title: In vitro biotransformation of tris(2-butoxyethyl) phosphate (TBOEP) in human liver and serum.
abstract: Tris(2-butoxyethyl) phosphate (TBOEP) is a plasticizer present in indoor dust, reaching levels of several micrograms per gram. Such levels could lead to significant daily exposure of adults and children. Currently, no toxicokinetic data are available to estimate TBOEP clearance in humans after uptake and therefore, one objective of this study was to investigate intrinsic clearance of TBOEP by human liver microsome (HLM) and serum enzymes. Another objective was to generate information to identify and prioritize several metabolites of TBOEP for investigation of human exposure by biomonitoring. 1D and 2D-NMR methodologies were successfully applied on a mixture of the metabolites to confirm the structure of 3-HO-TBOEP (bis(2-butoxyethyl) 3-hydroxyl-2-butoxyethyl phosphate) and to tentatively assign structures to 1-HO-TBOEP and 2-HO-TBOEP. HO-TBOEP isomers and bis(2-butoxyethyl) phosphate (BBOEP), bis(2-butoxyethyl) hydroxyethyl phosphate (BBOEHEP) were further monitored by liquid chromatography-tandem mass spectrometry. Rates of formation of BBOEHEP and HO-TBOEP metabolites by liver enzymes were best described by the Michaelis-Menten model. Apparent Km values for BBOEHEP, 3-HO-TBOEP, and sum of 1- and 2-HO-TBOEP isomer formation were 152, 197 and 148μM, respectively. Apparent Vmax values for the formation of BBOEHEP, 3-HO-TBOEP, and the sum of 1- and 2-HO-TBOEP isomers were 2560, 643, and 254pmol/min/mg protein, respectively. No detectable formation of BBOEP occurred with liver or serum enzymes. Our findings indicate that intrinsic clearance of TBOEP is mainly catalyzed by oxidative enzymes in the liver and that its major in vitro metabolite is BBOEHEP. These findings can be applied in human biomonitoring studies and risk assessment.
authors: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium. Electronic address: nele.vandeneede@uantwerpen.be.
authors: Nele
authors: N
authors: Van den Eede
authors: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium.
authors: Claudio
authors: C
authors: Erratico
authors: Natural Products & Food Research and Analysis (NatuRA), Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium.
authors: Vassiliki
authors: V
authors: Exarchou
authors: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium.
authors: Walid
authors: W
authors: Maho
authors: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium.
authors: Hugo
authors: H
authors: Neels
authors: Toxicological Center, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Antwerp, Belgium. Electronic address: adrian.covaci@uantwerpen.be.
authors: Adrian
authors: A
authors: Covaci
mesh_terms: D001711:Biotransformation; D002853:Chromatography, Liquid / Q000379:methods; D004391:Dust / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000097:blood* / Q000493:pharmacokinetics*; D010968:Plasticizers / Q000493:pharmacokinetics*; D053719:Tandem Mass Spectrometry / Q000379:methods
chemical_list: D004391:Dust; D009943:Organophosphorus Compounds; D010968:Plasticizers; C013320:tris(2-butoxyethyl) phosphate
keywords: Human liver microsomes; In vitro clearance; Metabolism; Serum; TBOEP; Tris(2-butoxyethyl) phosphate