Determination of in vitro relative potency (REP) values for mono-ortho polychlorinated biphenyls after purification with active charcoal.
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 (H1G1.1c3 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 (10microM) being most effectively; inducing gene expression to approximately 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 H1G1.1c3 mouse cells, PCB-105, -118 and -156 (10microM) significantly reduced TCDD-induced AhR-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.
Peters
A K
AK
Institute for Risk Assessment Sciences (IRAS), Utrecht University, PO Box 80176, 3508 TD Utrecht, The Netherlands. L.Peters@iras.uu.nl
Leonards
P E
PE
Zhao
B
B
Bergman
A
A
Denison
M S
MS
Van den Berg
M
M
D000818:Animals; D045744:Cell Line, Tumor; D002606:Charcoal / Q000737:chemistry*; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D011078:Polychlorinated Biphenyls / Q000737:chemistry* / Q000494:pharmacology*; D051381:Rats; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism
D018336:Receptors, Aryl Hydrocarbon; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D002606:Charcoal; D011078:Polychlorinated Biphenyls; D019363:Cytochrome P-450 CYP1A1