Superfund Research Program
Developmental Toxicity of non-Dioxin-like PCBs and Chemical Mixtures
The long-term goal of this project is to understand the role of cytochrome P450 enzymes in developmental toxicity of environmental chemicals. Such effects are among the most significant concerns in environmental toxicology, and yet a mechanistic understanding is largely absent. This project studies the role of these enzymes in zebrafish and killifish.
In 2008, Dr. John Stegeman and his group of researchers completed the development of the zebrafish ‘defensome’ microarray and used this array to determine the embryonic expression of genes that are principally involved in dealing with toxic chemicals. In this study the research group examined the full complement of cytochrome P450 (CYP) genes (89 genes), at times from just after fertilization of zebrafish eggs to the time of hatching. For most of these genes, the two methods produced nearly identical results, and revealed intriguing patterns of expression of some genes. For example, a zebrafish gene that is homologue of human CYP2J2 was very highly expressed only at an intermediate stage of development. This gene is among those now selected for further analysis to assess roles in developmental effects of chemicals.
The second emphasis in 2008 was on the identification of new cytochrome P450 1 family genes in the estuarine killifish to determine whether these genes show a resistance to effects of aryl hydrocarbon receptor agonists in killifish from the New Bedford Harbor Superfund site, like that previously observed with CYP1A. The identification and characterization of new cytochrome P450 (CYP) genes, particularly in family 1, provides insight into the evolution of detoxification/bioactivation mechanisms of organic contaminants (e.g., PCBs and PAHs). Full-length sequences were obtained for heretofore undescribed killifish CYP1B1, 1C2 and 1D1. Killifishfrom New Bedford and from a reference site were injected with PCB126 or DMSO (control), and expression levels of CYP1A, 1B1, 1C1, 1C2 and 1D1 were analyzed by real-time testing in eight different organs (liver, gill, testis, gut, brain, eye, kidney, heart). PCB126 induced expression of CYP1A, 1B1, 1C1 and CYP1C2 in reference fish, but not in New Bedford fish. Interestingly, CYP1D1, which structurally is very similar to CYP1A, was not induced by PCB126 in any of the organs in either population. Differential responses of the CYP1s in response to PCB126 were observed, which could improve sensitivity in the use of CYP1s as biomarkers of aquatic contamination employing killifish.