Print Email Facebook Twitter Characterization of human cytochrome P450s involved in the bioactivation of tri-Ortho-Cresyl phosphate (ToCP) Title Characterization of human cytochrome P450s involved in the bioactivation of tri-Ortho-Cresyl phosphate (ToCP) Author Reinen, J. Nematollahi, L. Fidder, A. Vermeulen, N.P.E. Noort, D. Commandeur, J.N.M. Publication year 2015 Abstract Tri-ortho-cresyl phosphate (ToCP) is a multipurpose organophosphorus compound that is neurotoxic and suspected to be involved in aerotoxic syndrome in humans. It has been reported that not ToCP itself but a metabolite of ToCP, namely, 2-(ortho-cresyl)-4H-1,2,3-benzodioxaphosphoran-2-one (CBDP), may be responsible for this effect as it can irreversibly bind to human butyrylcholinesterase (BuChE) and human acetylcholinesterase (AChE). The bioactivation of ToCP into CBDP involves Cytochrome P450s (P450s). However, the individual human P450s responsible for this bioactivation have not been identified yet. In the present study, we aimed to investigate the metabolism of ToCP by different P450s and to determine the inhibitory effect of the in vitro generated ToCP-metabolites on human BuChE and AChE. Human liver microsomes, rat liver microsomes, and recombinant human P450s were used for that purpose. The recombinant P450s 2B6, 2C18, 2D6, 3A4 and 3A5 showed highest activity of ToCP-bioactivation to BuChE-inhibitory metabolites. Inhibition experiments using pooled human liver microsomes indicated that P450 3A4 and 3A5 were mainly involved in human hepatic bioactivation of ToCP. In addition, these experiments indicated a minor role for P450 1A2. Formation of CBDP by in-house expressed recombinant human P450s 1A2 and 3A4 was proven by both LC-MS and GC-MS analysis. When ToCP was incubated with P450 1A2 and 3A4 in the presence of human BuChE, CBDP-BuChE-adducts were detected by LC-MS/MS which were not present in the corresponding control incubations. These results confirmed the role of human P450s 1A2 and 3A4 in ToCP metabolism and demonstrated that CBDP is the metabolite responsible for the BuChE inactivation. Interindividual differences at the level of P450 1A2 and 3A4 might play an important role in the susceptibility of humans in developing neurotoxic effects, such as aerotoxic syndrome, after exposure to ToCP. © 2015 American Chemical Society Subject Observation, Weapon & Protection SystemsCBRN - CBRN ProtectionTS - Technical SciencesToxicology2(ortho cresyl) 4h 1,2,3 benzodioxaphosphoran 2 oneCytochrome P450 1A2Cytochrome P450 2C18Cytochrome P450 2D6Cytochrome P450 3A4Cytochrome P450 3A5Organophosphorus compoundUnclassified drugAnimal cellBiotransformationCholinesterase inhibitionControlled studyEnzyme inactivationHumanshuman cellHydrolysisIC50In vitro studyLiver microsomeLiver microsome metabolismNeurotoxicityNonhumanRatsAcetylcholinesterase, 9000-81-1Cholinesterase, 9001-08-5cytochrome P450, 9035-51-2Cytochrome P450 3A4, 329736-03-0Cytochrome P450 3A5, 336874-97-6Tri ortho cresyl phosphate, 78-30-8 To reference this document use: http://resolver.tudelft.nl/uuid:0e4751a3-f3d8-4055-807f-eeefbb818fa6 DOI https://doi.org/10.1021/tx500490v TNO identifier 528077 ISSN 0893-228X Source Chemical Research in Toxicology, 28 (4 (20 April)), 711-721 Document type article Files To receive the publication files, please send an e-mail request to TNO Library.