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Although asbestos is a well established human carcinogen, the underlying carcinogenic mechanisms are not known. We show previously that chrysotile asbestos is a potent gene and chromosomal mutagen that induces mostly large multilocus deletions in the human hamster hybrid (AL) cells and that oxyradicals play an important role in the mutagenic process. Since mitochondrial DNA might be more susceptible to permanent damage due to its close proximity to reactive radical species and it’s less efficient DNA repair capacity, we examined the status of mtDNA in chrysotile treated telomerase (hTERT) -immortalized human small airway epithelial cells (SAECs). Asbestos treatment (1 to 6 μg/cm2 dose for ten days) induced mtDNA depletions in a dose dependent manner as determined by quantitative real-time PCR and reported as the ratio of mtDNA to nuclear DNA (nDNA) levels. Compared to untreated cells (mtDNA/nDNA = 1.00), the ratios of mtDNA to nDNA in 1, 2, 4 and 6µg/cm2 chrysotile treated cells were 0.84 ± 0.12, 0.69 ± 0.05, 0.66 ± 0.18, and 0.22 ± 0.04, respectively. In these experiments, ditercalinium treated SAECs were used as a positive control (mtDNA/nDNA = 0.11 ± 0.01). Likewise, asbestos induces mtDNA deletions. Using common deletion PCR, the 493 bp PCR product was detected in both asbestos-treated SAECs and in the positive control (plasma DNA from a ‘common deletion’ patient who carries homoplasmic mtDNA 4977-bp common deletion). The PCR products were purified and sequenced to further confirm the results. Sequences from SAECs were the same as those of the positive control and sequence alignment indicated that there was a 4977-bp deletion junction. These results suggest that chrysotile asbestos induced mitochondrial DNA mutations in human cells, which might play a role in asbestos-mediated genotoxicity.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA