Date of Award

5-2010

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry and Molecular Biology

Advisor

Gregory Mayer

Second Committee Member

Carol Kim

Third Committee Member

Jean MacRae

Abstract

Estrogens and estrogen mimics represent a wide range of aquatic contaminants that elicit deleterious effects on exposed organisms. Despite well-characterized reproductive effects of environmental estrogens, less is known about non-reproductive impacts of exogenous estrogen exposure. Additionally, estrogens are known carcinogens, implicated in multiple human cancers. Little or no research has examined the effects of xenoestrogens on DNA repair despite being known carcinogens. The goal of this research was to test the hypothesis that aquatic estrogens enhance the effects of environmental mutagens by altering DNA repair. Of particular interest is nucleotide excision repair (NER), the only repair pathway to remove structurally diverse DNA lesions that cause helical distortion, such as DNA adducts caused by ubiquitous environmental carcinogens. Research presented here shows that 17α-ethinylestradiol (EE2), a semi-synthetic hormone found in most oral contraceptives, alters hepatic mRNA levels of several key NER genes including XPC, XPA, XPD and XPF in adult male and female zebrafish exposed to environmentally relevant concentrations. Physiologically relevant concentrations of EE2 suppressed rate and magnitude of bulky adduct repair in zebrafish liver (ZFL) cells. This suppression of repair capacity in ZFL cells was not ameliorated in the presence of a complete estrogen receptor antagonist, which is known to antagonize the zebrafish estrogen receptor esr1. In adult zebrafish co-exposed to EE2 and benzo(a)pyrene (BaP), a prototypic polycyclic aromatic hydrocarbon and bulky adduct forming mutagen, hepatic mRNA levels of XPC and XPA were increased in comparison to fish exposed to EE2 alone. Regardless of hepatic NER transcript levels, fish co-exposed to EE2 and BaP exhibited increased BPDE-DNA adduct levels in comparison to both controls and fish exposed to BaP alone. In addition to single chemical exposures, adult zebrafish exposed to wastewater treatment effluent, a significant source of aquatic estrogens, exhibited altered NER transcript levels and decreased NER capacity. Collectively, this has significant implications for aquatic organisms living in contaminated environments, indicating the potential for higher mutation rates and increased neoplastic transformation with estrogen co-exposure than would be expected with mutagens alone. This research also presents an additional carcinogenic mode of action for estrogens, alteration of DNA repair.

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