Development of human dermal epithelial cell-based bioassay for the dioxins

None of bioassays is complete for assessing biological impact in humans upon the xenobiotic exposure due to species and organ-specific responsiveness. Thus, it is speculated that the human cell-based bioassay may be more appropriate system because of its direct relevance to humans. Here, we have developed a human epidermal cell-based bioassay for the dioxins and related compounds. The AD12-SV40-immortalized human keratinocyte cell line was stably transfected with a recombinant expression vector which contains the luciferase gene under dioxin-inducible control of four DREs. The tansfectants showed a consistent dose–response of luciferase activity upon dioxin exposure even after 120 passages. The maximal half effective dose (EC50) was 200 pM with a maximum of 32-fold induction of luciferase activity at 5 nM. The minimum detection limit was 10 pM. Optimal exposure time for the assay was 24 h. When cells were treated with aryl hydrocarbon receptor agonists of different toxic equivalent factor (TEF) values, the shape of the dose–response curve for each compound was parallel to that of TCDD and the maximum response was similar, indicating that this bioassay system can be applied to generate the total toxic equivalency (TEQ) estimate from the samples. When relative induction potency of luciferase activities for each compound was calculated, it was similar to WHO-TEF values within an order of magnitude. This human cell system can be used as an efficient screening tool to quantify the TEQ values of dioxin-like chemicals in the samples and may help understand the interspecies difference between humans and animals.