Determination of in vitro relative potency (REP) values for mono-ortho polychlorinated biphenyls after purification with active charcoal.

Abstract

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.

• Authors: A K Peters, P E Leonards, B Zhao, A Bergman, M S Denison, M Van den Berg
• Journal: Toxicology letters (Toxicol Lett) Vol. 165 Issue 3 Pg. 230-41 (Sep 10 2006) ISSN: 0378-4274 [Print] Netherlands
• PMID: 16750337 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• Receptors, Aryl Hydrocarbon
• enhanced green fluorescent protein
• Green Fluorescent Proteins
• Charcoal
• Polychlorinated Biphenyls
• Cytochrome P-450 CYP1A1

Topics

• Animals
• Cell Line, Tumor
• Charcoal (chemistry)
• Cytochrome P-450 CYP1A1 (genetics, metabolism)
• Gene Expression Regulation (drug effects)
• Green Fluorescent Proteins (metabolism)
• Mice
• Polychlorinated Biphenyls (chemistry, pharmacology)
• Rats
• Receptors, Aryl Hydrocarbon (genetics, metabolism)