Research Project 1
PCBs: Metabolism, Genotoxicity and Gene Expression in Vivo
Airborne PCBs are those that have higher vapor pressures, lower chlorination, and should be substrates for metabolic activation. Dr. Robertson's team hypothesizes that the lower halogenated biphenyls are activated by hepatic enzymes to oxygenated species that are electrophilic and bind to proteins and DMA.
Preliminary data indeed show that PCBs are metabolized to electrophiles and free radicals that bind to cellular targets and that the metabolism of PCBs produces reactive oxygen species, resulting in DMA strand breaks and 8-oxodeoxyguanosine formation in DMA and that a quinone/semiquinone may be a/the major metabolite involved in these effects. Employing the Solt-Farber initiation-selection protocol, the researchers also identified several lower chlorinated biphenyls as initiators of hepatocarcinogenesis in the rat. The goals of this study are to:
1) determine the initiating potential of airborne, semi-volatile PCBs and to analyze the structural and metabolic requirements needed for carcinogenic potency,
2) analyze for oncogene mutations and karyoptypic changes during PCB carcinogenesis in the Solt-Farber experiments,
3) investigate the types of genotypic damage induced by PCBs and their metabolites in vitro, in cells in culture, and in vivo,
4) examine the ease of formation and the reactivity of PCB-derived semiquinone radicals, and
5) determine the biologic effects and the influence of Route of Exposure (IP vs. inhalation) of airborne PCBs (a typical "air mixture" of PCBs, or single PCB congeners, or hydroxy-PCBs) on specific changes in expression of xenobiotic-metabolizing enzymes, antioxidant enzymes or redox indicators in the rat.
Jointly these studies may explain why some PCBs are activated to genotoxins, while others are not, which target genes are involved, the nature of the DNA lesions, and the mutations that ensue. These data may also provide clues about whether nutritional or other interventions are warranted to protect highly exposed humans. These mechanistic and susceptibility issues will form a basis for the quantitative human health risk assessment for these important Superfund chemicals, arising from multiple sources.
Project Leader: Larry Robertson, PhD, MPH
Dr. Robertson oversees and coordinates the entire project and designs, plans and supervises the proposed experiments listed in Aim #1 and Aim #5. He will be responsible for analyzing and publishing the results of the proposed experiments.
Co-Project Leader: Gabriele Ludewig, PhD
Dr. Ludewig is trained as a toxicologist (cyto-and genotoxicity, cell culture etc) and has spent three years as a postdoctoral scholar applying methods of molecular biology and yeast genetics to study the mechanisms of toxicity and resistance of the drug Pentamidine. She oversees all studies of Aim #2 and Aim #3.
Co-Project Leader: Garry Buettner, PhD
Dr. Buettner is Professor of Radiation Oncology/Free Radical and Radiation Biology and
Director of the ESR Facility at the University of Iowa College of Medicine. He oversees all studies of Aim # 4. He has over twenty years of research experience in free radical biology.
Co-Project Leader: Howard Glauert, PhD
Dr. Glauert is responsible for aspects of the initiation studies. He will collaborate on the design and supervision of these studies and will supervise the preparation of the frozen tissue sections, histochemical staining and the quantitation of altered hepatic foci.