Determination of in vitro relative potency (REP) values for mono-ortho polychlorinated biphenyls after purification with active charcoal
Peters, A.K. ; Leonards, P.E.G. ; Zhao, B. ; Bergman, A. ; Denison, M.S. ; Berg, M. van den - \ 2006
Toxicology Letters 165 (2006)3. - ISSN 0378-4274 - p. 230 - 241.
dioxin-like compounds - aryl-hydrocarbon receptor - toxic equivalency factors - dibenzo-p-dioxins - monkeys macaca-fascicularis - o-deethylase induction - ah receptor - risk-assessment - h4iie cells - dependent induction
The TEF system for dioxin-like compounds has included assignment of TEF values for mono-ortho polychlorinated biphenyls (MO-PCBs). Small traces of aryl hydrocarbon receptor (AhR)-active impurities could result in artifactually higher relative potency (REP) values. MO-PCBs -105, -118, -156, and -167 were purified on an active charcoal column to remove AhR agonists that could be present as impurities. Activation or inhibition of AhR-dependent gene expression by purified MO-PCBs was studied in stably transfected cell lines (HlG1.1c3 mouse, H4G1.1c2 rat hepatoma), containing an AhR-responsive (AhR-EGFP) reporter gene. In addition, EROD activity was used as marker for CYP1A1 activity in these cell lines. MO-PCBs -105,-118,-156 induced AhR-EGFP expression in both rodent cell lines, with PCB-156 (10 mu M) being most effectively; inducing gene expression to similar to 27% of TCDD (mouse cells) and 62.5 +/- 3.4% (rat cells) of TCDD. This concurred with increased EROD activity in both cell lines to maxima of 20.5 +/- 1.5% and 68 +/- 3.2% of TCDD, respectively. No induction was observed for PCB-167. In the HIG1.1c3 mouse cells, PCB-105, -118 and -156 (10 mu M) significantly reduced TCDD-induced AbR-EGFP expression to 50.9 +/- 2.9%, 58.3 +/- 2.2% and 70.8 +/- 1.3% of TCDD. Reduced EROD activity was also observed, of 39.3 +/- 2.8%, 67 +/- 5% and 48.3 +/- 4% compared to TCDD. PCB-167 did not result in significant reduction. In rat cells, only PCB-156 resulted in significant decrease in TCDD-induced AhR-EGFP expression of 35%, suggesting species differences play a role. Our results suggest that purification of MO-PCBs is an essential step in determining accurate REP values, and could very likely lead to lower TEF values than those presently assigned by the WHO. (c) 2006 Elsevier Ireland Ltd. All rights reserved.