Molecular Simulation Of Interaction Mechanism Of Novel Flame Retardants With Cytochrome P450 Enzymes

With the phasing out of traditional flame retardants represented by polybrominated diphenyl ethers(PBDEs),tetrabromobisphenol A(TBBPA)derivatives and organophosphorus flame retardants(OPFRs)have been largely produced as the substitutes.However,these two types of chemicals have been widely detected in a variety of environmental media and organisms in recent years.Toxicological studies have shown that these chemicals have endocrine disrupting effects and neurodevelopmental toxicity for humans and animals,threatening ecological environment safety and human health.Cytochrome P450 enzymes(CYPs)are involved in the metabolism of various xenobiotics,and the previous studies have found that CYPs are the key catalysts of biotransformation of TBBPA and OPFRs.However,the current researches on the interactions of CYPs with TBBPA derivatives and OPFRs are relatively limited.The relevant metabolic activity and sites are still unclear,which calls for further investigation.In recent years,in addition to the experimental methods,in silico methods have become important tools to study the biotransformation and toxicity mechanism of various chemicals,and thus their applications have become more and more extensive.In this work,molecular docking and molecular dynamics(MD)simulations with binding free energy calculations were performed to systematically investigate the binding patterns and affinities of CYPs with TBBPA derivatives and OPFRs,and further clarify the binding mechanism and metabolic potential of these chemicals at the molecular level.The research content and main conclusions of this work are as follows:(1)9 TBBPA derivatives,including tetrabromobisphenol A bisacrylate(TBBPA-BA),tetrabromobisphenol A bis(allyl ether)(TBBPA-BAE),tetrabromobisphenol A bis(2,3-dibromopropyl ether)(TBBPA-BDBPE),tetrabromobisphenol A bis(glycidyl ether)(TBBPA-BGE),tetrabromobisphenol A bis(2-hydroxyethyl ether)bisacrylate(TBBPABHEEBA),tetrabromobisphenol A bis(2-hydroxyethyl ether)(TBBPA-BHEE),tetrabromobisphenol A bis(methyl ether)(TBBPA-BME),tetrabromobisphenol A bisacetate(TBBPA-BOAc),and tetrabromobisphenol A bispropanoate(TBBPA-BP),were employed to estimate their binding patterns and affinities in CYP3A4 through molecular docking and MD simulations with binding free energy calculations.The results show that the binding affinities of 9 chemicals in CYP3A4 follow the order of TBBPA-BDBPE >TBBPA-BHEEBA > TBBPA-BA > TBBPA-BGE > TBBPA-BP > TBBPA-BHEE >TBBPA-BOAc > TBBPA-BAE > TBBPA-BME,and van der Waals interaction serves as the main driving force for ligands binding.Residues Phe108,Leu482,Phe304,Leu211,Ile301,Arg105 and Phe213 contribute significantly to the binding of ligands.Further analyses of the binding modes indicate that CYP3A4 may be involved in the metabolism of these TBBPA derivatives except for TBBPA-BOAc and TBBPA-BP,among which TBBPA-BAE,TBBPA-BHEE and TBBPA-BME have one potential site of metabolism while TBBPA-BA,TBBPA-BDBPE,TBBPA-BGE and TBBPA-BHEEBA may have 2 or more preferred sites.This study clarifies the binding interactions of CYP3A4 with different TBBPA derivatives at the molecular level,which can provide meaningful guidance for evaluating the metabolic activity and mechanism of these chemicals mediated by CYP3A4.(2)The binding mechanism of 6 CYP isoforms(CYP1A1,1A2,2C9,2C19,2D6 and3A4)with 5 OPFRs including 2-ethylhexyl diphenyl phosphate(EHDPHP),tri(2-chloroethyl)phosphate(TCEP),tris(1-chloro-2-propyl)phosphate(TCIPP),tris(1,3-dichloro-2-propyl)phosphate(TDCIPP),and triethyl phosphate(TEP)were investigated through molecular docking and MD simulations.The results show that 6 CYP isoforms have strong binding affinities for EHDPHP and TDCIPP,but give weak binding potential to TEP.In addition to TEP,the binding affinities of OPFRs in CYP1A1 and CYP1A2 are stronger than those of other 4 CYPs,suggesting that OPFRs are more accessible to these two isoforms.Further analyses of the binding modes reveal that CYP1A1 may metabolize TCEP,TCIPP and TDCIPP;CYP1A2 may be involved in the metabolism of EHDPHP,TCEP and TEP;CYP2D6 may be involved in the metabolism of EHDPHP and TCEP;CYP2C9 can only metabolize TCEP;CYP3A4 can metabolize these 5 OPFRs,while CYP2C19 may have no metabolic activity to these chemicals.Moreover,the preferred site of EHDPHP metabolism is the carbon atom of benzene ring,generating the hydroxylated EHDPHP metabolite.In contrast,the α-carbon atoms of other 4 OPFRs are preferred metabolic sites,producing diesters as the major metabolites.This study systematically expounds the molecular mechanism of OPFRs binding in CYPs,which can provide a solid theoretical basis for further study of CYPs-mediated metabolism of OPFRs.