Yo-Chan Jeong Doctoral Dissertation Final Oral Defense, 6/6
| July 12, 2005 | |
| Yo-Chan Jeong presented the final oral defense of his dissertation on June 6, 2005, at 2:00 P.M. in the Ibrahim Seminar Room (1301 McGavran-Greenberg). Full details are as follows:Formation, Repair, and Measurement of M1G, a Secondary DNA Lesion Produced by Reactive Oxygen Species
The objective of this study is to comprehensively evaluate the role of pyrimido[1,2-a]purin-10(3H)-one (M1G) in the toxicity and carcinogenicity of reactive oxygen species (ROS)-inducing chemicals. To accomplish this objective, two hypotheses were tested by examining the formation and repair of M1G. The first hypothesis was that ROS produced from either normal metabolism or chemical exposure results in the formation of M1G. The second hypothesis was that a deficiency in DNA nucleotide excision repair causes the accumulation of M1G. To test these hypotheses, a new method for measuring M1G was developed. Aldehyde reactive probe (ARP) was used to selectively label M1G-dR to produce stable ARP-M1G-dR conjugates followed by a subsequent measurement by LC-ESI-MS/MS. The accuracy of this assay was further improved by the use of analytical and internal standard DNA prepared from calf thymus DNA (CTD) and 15N-labeled bacterial DNA, respectively. The present study also carefully examined the artifactual formation or loss of M1G during DNA isolation. The result of this study demonstrated that M1G is less prone to oxidation compared to the primary ROS lesions during DNA isolation. The new M1G assay was then used to investigate the formation of M1G in in vitro or in vivo experiments using endogenous or exogenous ROS-inducing chemicals. Treatments of CTD with hydrogen peroxide, 1,4-tetrachlorobezoquinone, estrogen catechols, or polyunsaturated fatty acids resulted in dose-dependent M1G formation. In addition, genomic DNA was routinely isolated from rat tissues after chronic exposures to polychlorinated biphenyls (PCBs). Chronic exposures of PCBs resulted in dose-dependent accumulations of M1G in liver. These in vitro and in vivo data verify the first hypothesis. Finally, the effect of a nucleotide excision repair-deficiency on the accumulation of M1G was investigated by the treatment of mice with a single oral dose of carbon tetrachloride (CCl4). While CCl4 resulted in significant liver toxicity in both wild type and XPA null mice, CCl4 had only statistically significant effects on the number of M1G adducts in liver and kidney of XPA null mice. These results verify the second hypothesis. Overall, the present study provides fundamental information regarding the molecular pathways for the formation and repair of M1G. Committee: For further information please contact Rebecca Riggsbee Lloyd by email at Rebecca_Lloyd@unc.edu |
