Epidemiological evidence indicates that cigarette smoke is harmful to human health. Mainstream cigarette smoke has already been demonstrated to induce tissue and cellular damage in animal models. In the present study, we examined the toxicity of environmental cigarette smoke (ECS) by exposing Drosophila melanogaster larvae from urate-null and wild-type strains to ECS for 3 or 6 h at the third instar stage. We then determined survival to adulthood and the fecundity of adult females that survived larval ECS exposure. The survival of the urate-null strain, but not the wild-type strain, decreased signiˆcantly in an exposure-dependent manner. Moreover, the fecundity of treated urate-null, but not wild-type, females decreased signiˆcantly relative to the control level, irrespective of mating partner exposure to ECS at the larvae stage. These results demonstrate the killing eŠect and reproductive toxicity of ECS on urate-null larvae of Drosophila. Since the urate-null strain is known to be sensitive to oxidative agents, we propose that the main cause of the observed toxic eŠects of ECS is oxidative stress.
We previously reported that a urate-null strain of Drosophila is hypersensitive to cigarette smoke (CS), and we suggested that CS induces oxidative stress in Drosophila because uric acid is a potent antioxidant. Although the carcinogenic risk of CS exposure is widely recognized; documentation of in vivo genotoxic activity of environmental CS, especially gaseous-phase CS, remains inconclusive. To date, somatic-cell mutations in Drosophila resulting from exposure to CS have not been detected via the somatic mutation and recombination test (wing spot test) with wild-type flies, a widely used Drosophila assay for the detection of somatic-cell mutation; moreover, genotoxicity has not been documented via a DNA repair test that involves DNA repair-deficient Drosophila. In this study, we used a new Drosophila strain (y v ma-l; mwh) to examine the mutagenicity induced by gaseous-phase CS; these flies are urate-null due to a mutation in ma-l, and they are heterozygous for multiple wing hair (mwh), a mutation that functions as a marker for somatic-cell mutation. In an assay with this newly developed strain, a superoxide anion-producing weed-killer, paraquat, exhibited significant mutagenicity; in contrast, paraquat was hardly mutagenic with a wild-type strain. Drosophila larvae were exposed to CS for 2, 4 or 6h, and then kept at 25°C on instant medium until adulthood. After eclosion, mutant spots, which consisted of mutant hairs on wings, were scored. The number of mutant spots increased significantly in an exposure time-dependent manner in the urate-null females (ma-l (-/-)), but not in the urate-positive females (ma-l (+/-)). In this study, we showed that short-term exposure to CS was mutagenic in this in vivo system. In addition, we obtained suggestive data regarding reactive oxygen species production in larva after CS exposure using the fluorescence probe H2DCFDA. These results suggest that oxidative damage, which might be countered by uric acid, was partly responsible for induction of somatic cell mutations in Drosophila larvae exposed to CS.
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