Airborne PCBs: Sources, Exposures, Toxicities, Remediation: K.C. Donnelly Externship - Promotion of Translational/Transdisciplinary Efforts in Graduate and Post-Doctoral Research

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PROJECT DESCRIPTION Due to inadvertent production and exposure to polychlorinated biphenyls (PCBs) from environmental sources, adverse health effects remain a critical public health issue long after the ban of commercial production. Through the proposed research, our goal is to gain knowledge related to P450-mediated metabolism through the KC Donnelly externship in partnership with the National Center for Toxicology Research (NCTR). Xenobiotic processing genes (XPGs), such as cytochrome P450s, are known to be expressed and active in the brain [1-8]. This can then lead to the metabolism of central nervous system (CNS)-active chemicals, leading to alterations in toxicokinetics and toxicodynamics of target cells through systemic circulation [9, 10]. Currently, I am working on examining metabolism of PCBs in rat primary astrocytes. However, it is still uncertain where metabolism of PCBs begins. Specifically, following ISRP Project 1, Aim 2, I will be examining region-specific biotransformation of PCBs and PCB metabolites in the adolescent rat brain in vitro (primary cells in culture) to characterize the following local metabolic conversions: oxidation of parent PCBs to OH-PCBs; conjugation of OH- and diOH-PCBs; deconjugation of OH-PCB sulfates (and glucuronides); and oxidation of diOH-PCBs to reactive quinones and subsequently, glutathione adducts (reviewed in [11-13]). To expand upon this work, the precise human metabolism of lower chlorinated PCBs is still uncertain and needs to be explored.Therefore, my overall objective is to examine the P450 isoform-specific metabolism of lower-chlorinated PCBs in state-of-the- art P450-overexpressing human hepatocytes developed by Dr. Lei Guo's laboratory at the National Center for Toxicology Research (NCTR) [14]. This model will be used to test the hypothesis that lower-chlorinated PCBs discovered by the ISRP in indoor and outdoor air, such as 2,2'5,5'-tetrachlorobiphenyl (PCB52) and 3,3’- dichlorobiphenyl (PCB11), are oxidized with different stereoselectivity by several human P450 isoforms, such as CYP2A6, CYP2B6, and CYP3A4 I will test this hypothesis by (1) determining which human P450 isoform is involved in the metabolism of PCB11 and PCB52 and (2) characterizing the PCB metabolites formed by different P450 isoforms using nontarget-high resolution mass spectrometry (Nt-HRMS). These results will inform future translational studies that assess the role of these P450 isoforms in the brain specific metabolism in human-relevant cell culture models. After treating the P450-overexpressing hepatocytes, both cell pellets and supernatant fractions will be collected to assess levels of metabolites present. Supernatant and cells will be flash frozen. These samples would then be transported back to the University of Iowa, where subsequent quantification of key metabolites would be accomplished with standards provided by the ISRP Synthesis Core [15-19]. The proposed studies will investigate the P450 specific metabolism of PCBs in hepatocytes and are a logical extension of the current ISRP goals to determine enzyme-specific metabolism.