MP6 Quantitative Structure Activity Relationships (QSARs)
Monday, 14 November 2005: 8:00 AM - 5:30 PM in Exhibit Hall

(KOL-1117-830442) Increased endocrine activity of xenobiotic chemicals as mediated by metabolic activation.

Kolanczyk, R¹, Tapper, M¹, Nelson, B², Wehinger, V², Denny, J¹, Kuehl, D¹, Sheedy, B¹, Mazur, C³, Jones, J³, Schmieder, P¹, ¹ US EPA, ORD/NHEERL, Mid-Continent Ecology Division, Duluth, Minnesota, USA² US EPA Student Services Contractors, Duluth, Minnesota, USA³ US EPA, ORD, NERL, Ecosystems Research Division, Athens, Georgia, USA

ABSTRACT- EPA is faced with long lists of chemicals that need to be assessed for hazard. This research is part of a larger effort to develop in vitro assays and QSARs applicable to untested chemicals on EPA inventories through study of estrogen receptor (ER) binding and estrogen mediated gene expression in fish. The current effort investigates metabolic activation of chemicals resulting in increased estrogenicity. Phenophthalin (PLIN) was shown not to bind trout ER in a competitive binding assay but vitellogenin expression was induced in trout liver slices exposed to 10^-4 and 10^-3.7 M PLIN. Phenolphthalein (PLEIN), a metabolite of PLIN, was subsequently determined to be formed when slices were exposed to PLIN. PLEIN binds rtER with a relative binding affinity (RBA) of 0.020%. Slices exposed to PLEIN expressed vitellogenin mRNA at 10^-4.3 10^-4 and 10^-3.7 M, with no detectable PLIN present. Thus, vitellogenin expression noted in PLIN slice exposures was explained by metabolism to PLEIN in trout liver slices. A second model chemical, 4,4′-diaminodiphenylmethane (MDA) was not shown to bind rtER, but did induce vitellogenin mRNA production in tissue slices at 10^-4.3 10^-4 and 10^-3.7 M in amounts nearly equal to reference estradiol induction, thus indicating metabolic activation of MDA. A series of experiments were performed to identify a potential metabolite responsible for the observed increase in activity. Hydroxylamine-MDA, nitroso-MDA, azo-MDA, or azoxy-MDA were not observed. Acetylated-MDA was observed and tested in both ER-binding and tissue slice vitellogenin induction assays. Comparisons of Phase I metabolic activation in trout and rat liver microsomes is also presented to elucidate cross species similarities and to enhance predictive models. This abstract does not necessarily reflect U.S. EPA policy.

Key words: rainbow trout, rat, metabolism, estrogenicity