Effect of cigarette smoke exposure on the modulation of 8-oxo-2'-deoxyguanosine in rat lungs as analyzed by 32P-postlabeling and HPLC-ECD

Cigarette smoke contains several oxidants and free radicals. In the present study, we examined the formation of 8-oxo-2'-deoxyguanosine (8-oxodG) in the lungs of female Sprague-Dawley rats exposed to side-stream cigarette smoke for 6 h a day, 7 days a week for 1, 2, 4 and 12 weeks in a whole body-exposure system. The samples were analyzed for 8-oxodG by 32P-postlabeling-TLC enrichment and HPLC-ECD techniques to confirm and compare results. Animals were sacrificed 15 h after the cessation of smoke exposure and lung DNA was isolated by phenol/Sevag extractions in the presence of the free radical traps, 8-hydroxyquinoline (6.8 mM) and N-t-butyl-α-phenyl nitrone (500 μM) to minimize artifactual formation of 8-oxodG during sample work up. Analysis of lung DNA by 32P-postlabeling-TLC showed 8-oxodG levels (mean ± SE) of 1.45±0.24, 2.68±0.65, 2.23±0.28 and 2.93±0.54 per 106 nucleotides after 1, 2, 4 and 12 weeks of smoke exposure. The respective values in sham-treated rats were 2.76±0.19, 3.69±0.20, 1.44±0.43 and 2.84±0.45 per 106 nucleotides, suggesting no significant effect of smoke exposure on tissue levels of 8-oxodG. HPLC-ECD procedure yielded slightly higher values for 8-oxodG in all groups, however, again significant differences between sham and smoke-exposed groups were not detected. It is concluded that the chronic exposure to side-stream cigarette smoke does not enhance the formation of 8-oxodG in rat lungs.