Superfund Research Program
Developmental Toxicity of non-Dioxin-like PCBs and Chemical Mixtures
Cytochrome P450 enzymes are the enzymes most responsible for metabolism and clearance of foreign chemicals from the body. The overall goal of this continuing research is to determine how enzymes that metabolize pollutant chemicals, especially the cytochrome P450 enzymes, may be involved in toxicity of those chemicals during development. The studies focus on the zebrafish (Danio rerio) as a model for determining the developmental patterns of expression of the complete complement of cytochrome P450 genes in this species, and secondly, to determine the involvement of specific genes in the toxicity of selected chemicals to the developing embryo. Some findings will be confirmed in another fish, Fundulus heteroclitus, a marine species increasingly used as a model in marine toxicology.
There is three-fold significance of these studies: First, the information generated will be useful in understanding how chemicals may produce birth defects in animals generally, including in humans. Secondly, it will provide understanding of how pollutant chemicals could affect developing fish, environmental sentinels and a critical source of protein in the world. Third, the research will provide essential information and tools for other researchers who may study mechanisms of chemical effect in this model species for biomedical research.
In 2005, progress was made in identifying the full complement of zebrafish P450 genes. Gene predictions have been performed for all of the predicted zebrafish CYPs in the current release of the zebrafish genome (Zv5). These predictions were done using both the FGENESH+ and Genewise programs. Dr. Stegeman’s group estimates that there are approximately 70 CYPs in the zebrafish genome. The gene models are currently being checked by hand. Additional sequences of relevant receptors are also being gathered or predicted. Computer scripts are at present being written to design appropriate primers for cDNA for a focused microarray for analysis of CYP and nuclear receptor expression profiles.
The Stegeman group continued to test ideas regarding CYP1A roles in oxidative stress, including in zebrafish and in other species. They also have made further progress in collaboration with the Bioinformatics Core in the analysis of docking of planar PCB congeners and benzo[a]pyrene, and have done docking studies with dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) to human CYP1A1, rat CYP1A1 and fish CYP1A. The results are similar to the results with 3,3’,4,4’-tetrachlorobiphenyl, showing that the compounds dock deeper in the active site of the rat enzyme than in the human, and deeper in human than in the fish enzyme. This is consistent with the known rates of metabolism or in vivo clearance rates of TCDD by these species.