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Relative Potency Estimation of Dioxin-like Activity by Dioxins , Furans , and Coplanar PCBs Using Chemically Activated Luciferase Gene Expression Assay ( H 4 IIE-luc Assay )

Chemical analysis of dioxin-like compounds (DLCs) requires usually very high cost, trained expertise and extended time for the pretreatment and instrumental operation procedure. Alternatively, recently developed in vitro cell-based bioassays offer a rapid, sensitive, and relatively inexpensive solution to estimate the potency of most DLCs including dioxins, furans and co-PCBs. In the present study, we investigated the relative potency (REP) of the cytochrome P450 gene expression through aryl hydrocarbon receptor (AhR) of 21 dioxin-like compounds by using the recombinant cell line (H4IIE-luc), which is stably transfected with firefly luciferase reporter gene to rat hepatoma cell. We exposed the cell system to get a full doseresponse curves of 2,3,7,8-TCDD and other representative DLCs to estimate effect concentrations (e.g. EC50) and thereby to compare the REP of each DLC to 2,3,7,8-TCDD. The toxic equivalency factor (TEF) of 2,3,7,8-TCDD was the highest followed by 2,3,7,8TCDF, 1,2,3,7,8-PeCDD and PCB 126. The TEFs of dioxins and furans were relatively higher than those of coplanar PCBs. The TEFs quantified using H4IIEluc in this study were not the same with TEFs recommended by WHO, but they were largely comparable in spite of some outliers including PCB 81, 1,2,3,4,6,7,8HpCDD, 2,3, 7,8-TCDF, PCB 105 and PCB 118 which showed big difference. The difference may be due to the metabolic capacities between in vivo and in vitro system. TCDD toxic equivalent (TEQ) can be estimated as the sum of the concentration multiplied by TEF of each DLC. Therefore, TEQ values for environmental samples estimated by H4IIE-luc bioassay is affected both by TEF value and chemical concentration. Thus, 2,3, 7,8-TCDF, 1,2,3,4,6,7,8-HpCDD and PCB 81 among DLC, which showed big different TEF values may give a big difference in TEQ estimation in environmental sample. In order to improve TEQ predictability more by using H4IIE-luc cell line bioassay, the characterization of the difference between TEFH4IIE and TEFWHO and the distribution pattern of DLC in the samples should be focused more in future study.