Investigating the Mechanisms of Toxicity of Benzene and its Metabolite Benzoquinone and the Role of Sulforaphane as a Potential Protective Agent in CD-1 Mouse Development
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Benzene is an environmental pollutant and a known human leukemogen. It is also suspected to be associated with in utero-initiated leukemia. However, the mechanisms of benzene-mediated toxicity and carcinogenicity in both adults and fetuses are not well understood. Two main research hypotheses were tested in this thesis work. The first was that exposure to the benzene metabolite, benzoquinone, leads to increased levels of reactive oxygen species (ROS) and DNA damage in cultured mouse fetal liver cells, and that epigenetic changes in CD-1 mouse fetal livers would result from in vivo exposure to benzene. The second was that exposure to the phytochemical, sulforaphane (SFN), would induce detoxification enzymes in CD-1 mouse fetal livers in vitro and in vivo, and that this would confer protection against benzene-induced cellular damage. Our data demonstrated that exposure to benzoquinone increased ROS levels, increased DNA damage, and altered DNA repair gene expression in cultured CD-1 mouse fetal liver cells. Additionally, although we found that SFN induced various metabolizing enzymes involved in the detoxification of benzene metabolites, SFN did not protect against the deleterious effects of benzene found in this study. In a separate study, we examined whether SFN could induce fetal and/or maternal enzymes involved in benzene detoxification in vivo in CD-1 mice and how this compared to non-pregnant CD-1 mice. While we found that chronic SFN exposure induced both gene expression and activity of liver detoxification enzymes of both pregnant and non-pregnant mice, SFN had no effect on expression levels or activity of these genes in fetal livers exposed in utero. Lastly, we investigated the effect of benzene exposure on DNA methylation and histone modifications in vivo. Benzene exposure decreased global DNA methylation in maternal bone marrow only, having no effect on any other epigenetic modifications measured in these studies. Taken together, the data presented in this thesis only partially supported our hypotheses; nevertheless, they provide valuable information for future research directions pertaining to benzene-associated transplacental carcinogenesis.