Specific binding of hydroxylated polychlorinated biphenyl metabolites and other substances to bovine calf uterine estrogen receptor: structure-binding relationships.

The objectives of this research were: (1) to survey a wide variety of structurally diverse (and mostly chlorinated) aromatic chemicals for specific binding to the calf uterine estrogen receptor; (2) to develop a quantitative structure-binding relationship (QSBR) for hydroxylated polychlorinated biphenyls (OH-PCBs). This report specifically includes data on substances that did not exhibit specific binding to ER thereby exploring the structural requirements for specific binding to the estrogen receptor. Although several other QSBRs for OH-PCBs have been reported, this study presents data on a larger, environmentally relevant set of OH-PCBs than previously reported. Fifty three chemicals were tested for the ability to bind specifically to calf uterine estrogen receptor. All but three OH-PCBs bound specifically to calf uterine ER. For DDT compounds, receptor binding affinity followed the pattern: o,p'-DDT > o,p'-DDE > o,p'-DDD (Not active). Also exhibiting measurable affinity were 17 beta-estradiol (a positive control and the native ligand of the estrogen receptor), 2,4,6-trichlorobiphenyl and 4-chloro-2-isopropyl-5-methylphenol. Substances that did not bind to calf uterine estrogen receptor comprised several individual PCB congeners, chlorinated naphthalenes and naphthalenols, chlorinated bibenzyls, chlorinated phenols, and 9-chloro-retene. For 25 hydroxylated PCBs, a five parameter QSBR was developed using multiple linear regression and selection of the most parsimonius model from a total of seven molecular modeling parameters examined. The QSBR model predicted the ER binding log (IC50) to within one log unit.

Effects of waterborne exposure to 4-nonylphenol and nonylphenol ethoxylate on secondary sex characteristics and gonads of fathead minnows (Pimephales promelas).

Fathead minnows were exposed to 4-nonylphenol (NP) or nonylphenol ethoxylate (NPEO) to determine the effects of these weak estrogen agonists on secondary sex characteristics and gonads of sexually mature males and females during 42-day continuous-flow exposures. Neither NP nor NPEO caused statistically significant effects on tubercles or fatpad size at the concentrations tested. Exposure to 1. 1 or 3.4 micrograms NP/L caused changes in the number and size of Sertoli cells and germ cell syncytia. Necrotic aggregates of various stages of germ cells in the spermatogenic sequence were observed in the testes of males exposed to NP. Electron microscopy of the testes of NP-exposed males revealed the presence of phagocytic cells in the lumina of seminiferous tubules. The cytoplasm of some Sertoli cells was distended with myelin figures and necrotic spermatozoa. No significant effects on the stages of follicular development were observed in females exposed to NP. There were no differences in the gonads or secondary sex characteristics of males or females exposed to 5.5 micrograms NPEO/L, the greatest concentration studied. The histologic responses observed are sensitive indicators of waterborne exposure to NP at environmentally relevant concentrations, but not as sensitive as induction of plasma vitellogenin. The secondary sex characteristics were not affected by concentrations of NP or NPEO as great as 3.4 or 5.5 micrograms/L, respectively. Histologic responses occurred at concentrations that were less than the final chronic value based on survival and approximately the same as those required to cause effects on egg production. The histologic effects caused by NP were similar to, but not exactly the same as those caused by exposure of fathead minnows to 17 beta-estradiol.

Hydroxylated polychlorinated biphenyl metabolites are anti-estrogenic in a stably transfected human breast adenocarcinoma (MCF7) cell line.

Hydroxylated metabolites of polychlorinated biphenyls (OHCBs) have been identified in blood of marine mammals, fish-eating birds, and humans at concentrations in some cases exceeding those of the unmetabolized polychlorinated biphenyls (PCBs). OHCBs have been associated with inhibition of vitamin A and thyroxin transport, estrogenicity in a mouse uterotrophic assay, and feminization of male turtle sexual development. OHCBs, representing both environmentally derived and laboratory exposure-derived metabolites, were tested in an in vitro bioassay utilizing an estrogen-responsive human breast adenocarcinoma cell line (MCF7-LUC) stably transfected with a luciferase reporter gene linked to estrogen responsive elements. OHCB activity was tested at three different media concentrations of 17beta-estradiol (E2), comparing the concentration-response curves using charcoal-stripped medium (0.0009 nM E2), and two physiologically relevant E2 concentrations (0.1 and 1.0 nM E2). Eleven of 13 OHCBs tested were anti-estrogenic. Evidence for an estrogen receptor mediated mechanism of action was apparent for only two OHCBs-4-OH-2',3,3',4',5,5'-Cl6-biphenyl and 4,4'-(OH)2-3,3',5,5'-Cl4-biphenyl. These two have not been identified in environmental samples. The remaining OHCBs exhibited "anti-estrogenicity" that was related to their effect on cell viability and, therefore, cannot be described as exhibiting "hormone disruption" solely by an estrogen receptor mediated mechanism. OHCB anti-estrogenic activity was eliminated in the presence of E2 concentrations normally found in humans, except for 4,4'(OH)2-3,3',5,5'-Cl4-biphenyl. 4-OH-2',3',4',5'-Cl4-biphenyl and 4-OH-2',4',6'-Cl3-biphenyl were partial estrogen agonists, exhibiting weak estrogenicity in the presence of 0.0009 nM E2 and weak anti-estrogenicity in the presence of 0.1 and 1 nM E2. Human metabolites of PCBs were not estrogenic in MCF7 cells.

A review of factors affecting productivity of bald eagles in the Great Lakes region: implications for recovery.

The bald eagle (Haliaeetus leucocephalus) population in North America declined greatly after World War II due primarily to the eggshell thinning effects of p,p'-DDE, a biodegradation product of DDT. After the banning of DDT in the United States and Canada during the early 1970s, the bald eagle population started to increase. However, this population recovery has not been uniform. Eagles nesting along the shorelines of the North American Great Lakes and rivers open to spawning runs of anadromous fishes from the Great Lakes still exhibit impaired reproduction. We have explored both ecological and toxicological factors that would limit reproduction of bald eagles in the Great Lakes region. Based on our studies, the most critical factors influencing eagle populations are concentrations of environmental toxicants. While there might be some continuing effects of DDE, total PCBs and most importantly 2,3,7,8-tetrachlordibenzo-p-dioxin equivalents (TCDD-EQ) in fishes from the Great Lakes and rivers open to spawning runs of anadromous fishes from the Great Lakes currently represent a significant hazard to bald eagles living along these shorelines or near these rivers and are most likely related to the impaired reproduction in bald eagles living there.