Mechanisms of Resistance of Aquatic Vertebrate Populations to Mixtures

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The Hudson River (HR) Estuary contains Superfund sites for PCBs, TCDD, and heavy metals. Atlantic tomcod from the HR bioaccumulate high tissue burdens of these contaminants, sometimes to record levels. We have used tomcod as a model to evaluate the ecological effects of these pollutants and to study the mechanistic bases of their toxicities. Tomcod from throughout the HR are highly resistant to environmentally relevant doses of coplanar PCBs and TCDD, but not PAHs, at a variety of molecular and organismic endpoints including early life stage toxicities and aryl hydrocarbon receptor (AHR) pathway-mediated gene expression. The overall objectives of this renewal application are to further describe the extent of resistance n the HR tomcod population and to characterize its mechanistic basis. Although, at one time, tomcod from the HR exhibited remarkably elevated prevalences of hepatic tumors, the role of PCBs in this process was never empirically addressed. In controlled laboratory studies, we will determine if tomcod offspring from the HR, compared to those from sensitive populations, are resistant to hepatic neoplasia and related preneoplastic endpoints such as preneoplastic lesions, K-ras activation, ROS modified bases, bulky DMA adducts after exposure to PCBs and PAHs. Fish from highly contaminated locales, such as Superfund sites, are usually co-exposed to aromatic hydrocarbon and metal contaminants. Chemical analyses indicate that this is the case for tomcod from the HR. Yet, little is known of their interactive effects in vivo. We will investigate the effects of co-exposure to Gr VI on B[a]P-induced mutations, DMA adducts, and nucleotide excision repair at the K-ras oncogene which is frequently mutated in environmentally-exposed and chemically-treated fishes. The mechanistic basis of resistance will be addressed. Genetic polymorphisms will be characterized and their frequencies enumerated at AHR2, AHRR, and ARNT1 in tomcod from the HR and non-resistant populations. Those which show significant allelic differences will be functionally evaluated in assays which will quantify ligand binding, nuclear transformation, and transactivation. Multiple AHRs shown to exist in other fishes will be isolated and their structure and expression compared between the HR and sensitive populations. Novel proteins associated with AHRs or DREs will be identified using a proteomics approach and their expression compared between tomcod from the HR and susceptible populations.