ALTERATIONS IN ESTROGEN METABOLISM CAUSED BY EXPOSURE TO PCBS

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The broad, long-term objective of this research is to determine the effects of exposure to polychlorinated biphenyls (PCBs) on the phase I and phase II metabolism of 17beta-estradiol (E2) in liver and extrahepatic tissues. Human exposure to PCBs may result in diverse endpoints such as impairment of intellectual development and reduced fertility. The alteration of estrogen metabolism by exposure to PCBs is a mechanism by which these xenobiotics may alter fertility, fecundity, and neuroendocrine development through disruption of normal estrogenic signal transduction. We hypothesize that, in a congener-specific manner, PCBs will increase the rates of E2 hydroxylation and conjugation in liver and in estrogen target tissues, and under some conditions aberrant estrogen metabolism will cause oxidative stress. Our Specific Aims are: (1) To determine the effects of exposure to PCBs (Aroclor 1248 and several individual congeners) on the rates cytochrome P450-catalyzed hydroxylation of E2. Microsomes prepared from liver, kidney,uterus, and brain of PCB- exposed female rates and from human-derived breast, liver, kidney, and uterine cells exposed to PCBs in vitro will be used for the E2 metabolism studies. (2) To determine the effects of exposure to PCBs on the phase II metabolism of E2 in liver and extrahepatic tissues. Estrogen glucuronsyltransferase, T3 and T4 glucuronosyltransferase, and estrogen sulfotransferase activities will be determined with microsomes prepared from tissues of PCB-exposed female rats and with human-derived cells in vitro. It will be determined whether estrogens and the thyroid hormones, T3 and T4, are substrates for the same conjugating enzymes. (3) To determine the effects of exposure to PCGs on the expression of cytochrome P450s of the CYP1A and the recently discovered CYP1B gene subfamilies. Immunochemical techniques, RNA blots, and the reverse transcriptase-polymerase chain reaction will be used to characterize gene expression in tissues of the female rat in vivo and in human breast, kidney, and endometrial cells in vitro. (4) To determine the effects of PCB exposure and PCB-induced estrogen metabolism on oxidative stress in tissues of the female rat and in human breast cells in vitro. Lipid peroxides, DNA strand breaks, and the presence of 8-hydroxyguanine in DNA will be measured as evidence of oxidative stress.