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RELATIVE BINDING AFFINITY OF ENDOCRINE DISRUPTING CHEMICALS TO ESTROGEN RECEPTOR IN TWO SPECIES OF FRESHWATER FISH
Citation:
Denny, J. S., T. R. Henry, AND P. K. Schmieder. RELATIVE BINDING AFFINITY OF ENDOCRINE DISRUPTING CHEMICALS TO ESTROGEN RECEPTOR IN TWO SPECIES OF FRESHWATER FISH. Presented at Society of Toxicology 42nd Annual Meeting, Salt Lake City, UT, March 9-13, 2003.
Description:
The US EPA has been mandated to screen industrial chemicals and pesticides for potential endocrine activity. To evaluate the potential for chemicals to cause endocrine disruption in fish we have previously measured the affinity of a number of chemicals for the rainbow trout estrogen receptor. In order to assess the plausibility of making inter-species extrapolations based on the rainbow trout data base, this study was designed to determine if relative binding affinity (RBA) of chemicals for the fathead minnow estrogen receptor (fhmER) is similar to binding affinities of the same chemicals to trout estrogen receptor (rtER). Ten chemicals previously tested in rainbow trout estrogen receptor binding assays were selected for testing in the fathead minnow. Liver tissue from 20 (male) to 50 (female) fathead minnows was used as the source of cytosolic estrogen receptor. Binding affinity of test chemicals was measured by incubating liver cytosol (255 l) with a saturating concentration (5 nM) of 3H-estradiol (3H-E2) and a range of test chemical concentrations for 20 hr at 4?C. Bound chemical was determined as the amount of 3H-E2 displaced from the estrogen receptor. The relative binding affinity of a test chemical was calculated as: (IC50 of E2/IC50 of chemical)*100. (E2 = 100%). Chemicals tested include estradiol (E2), estrone (E1), estriol (E3), ethinylestradiol (EE), diethystilbestrol (DES), methylestradiol (MeE2), genistein (GEN), tamoxifen (TAM), testosterone (T), methyltestosterone (MT), -trenbolone (ATren), -trenbolone (BTren), p-tert-octylphenol (PTOP), p-nonylphenol (PNP) and methoxychlor (MXC). DES, EE, MeE2 and E1 bound with high affinity to the fhmER, having RBAs of 590, 170, 70 and 30%, respectively. E3, TAM and GEN had moderate RBAs of 5, 4 and 1, respectively. The alkylphenols had weak binding affinity for the fhmER, with RBAs of 0.1 and 0.01, respectively. The androgens ATren (RBA = 0.002) and BTren (RBA = 0.02) were able to fully displace 3H-E2, whereas T and MT elicited only partial displacement such that RBAs could not be calculated. Similarly, MXC only partially displaced 3H-E2, such that RBA could not be determined. This weak affinity of T, MT and MXC for the fhmER was also seen with the rtER. Comparison of binding affinities of the chemicals tested for fhmER and rtER shows that the rank order of RBAs are identical across species. This abstract does not necessarily reflect EPA policy.