UBC Theses and Dissertations
Genotoxicity of chewing tobacco samples Woolcock, Bruce Wayne
The intra-oral use of tobacco-containing mixtures plays an important aetiological role in the occurrence of oral cancers. In vitro genotoxicity assays may provide means for the rapid evaluation of factors contributing to or modulating this form of tobacco carcinogenesis. An essential requirement for an effective test system is the capability to detect the genotoxic effects of a variety of tobacco mixtures which are expected to differ in chemical composition. Freshly prepared aqueous extracts of four tobacco mixtures, locally available snuff and "chewing" tobacco, Khaini tobacco (India) and nass (Uzbekistan, USSR), were assayed for genotoxic activity in three different test systems: chromosome aberrations in Chinese hamster ovary cells, micronuclei in Chinese hamster ovary cells and unscheduled DNA synthesis in human fibroblasts. A DNA repair inhibition test was included as a complement to the unscheduled DNA synthesis assay. All four tobacco extracts were found to contain direct acting agents capable of inducing chromosome aberrations and micronuclei formation in Chinese hamster ovary cells. Catalase was found to suppress the clastogenic activity of the chewing and Khaini tobaccos, implicating H₂O₂-mediated production of chromosome damage. The genotoxic activities of snuff and nass did not appear to be dependent on the generation of H₂O₂. Only the chewing tobacco initiated unscheduled DNA synthesis in human fibroblasts. All tobacco extracts reduced the levels of UV initiated unscheduled DNA synthesis, indicating the extracts exerted an inhibitory effect on DNA repair. The failure of the snuff, Khaini tobacco and nass to induce a demonstrable unscheduled DNA synthesis was interpreted to be a consequence of this inhibition. On the basis of these results it was concluded that the chromosome aberration and micronucleus tests in Chinese hamster ovary cells, but not the unscheduled DNA synthesis, appear to be suitable as test systems for the study of factors influencing oral tobacco carcinogenicity.
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