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.

Recently, we reported experimental evidence to support the notion that in Drosophila melanogaster, urate is involved in defense against toxic eŠects of environmental cigarette smoke (ECS). To obtain further information pertaining to the defense mechanisms involving urate and other antioxidants, the present study measured the levels of urate, its precursors and glutathione, and SOD activity in larval ‰ies of wild-type strains (Oregon-R and Canton-S) and two urate-null mutant strains (ma-l and ry 1 ) following exposure to ECS for various durations. In both wild type strains, unlike the case in either of the mutant strains, the urate level signiˆcantly increased above the basal level in a manner dependent on the duration of ECS exposure. Similar increases in the level of urate precursors were found in Canton-S and in both of the urate-null strains. There was a slight increase in glutathione level above the control level following ECS exposure for a short time, followed by an exposure-dependent decrease to less than 60% of the control level within the exposure range used in all of the four strains. On the other hand, no appreciable change was found in the SOD activity prior to or following ECS exposure, irrespective of the strain examined. In terms of the survival of treated larvae to adulthood under the conditions used for the measurements of urate and others, it was found that wild-type strain Canton-S was as sensitive as the urate-null mutant strains and clearly more sensitive than wild-type strains Oregon-R and Hikone-R. This was so despite the fact that, compared with Oregon-R, Canton-S contained urate at relatively higher levels prior to and following ECS exposure, and that the glutathione levels in Canton-S prior to and following treatment were comparable with those in other strains. These results are discussed with respect to the involvement of urate and glutathione in defense against the toxicity of ECS and the possible existence of another defense mechanism which is deˆcient in the Canton-S strain.

Background Apoptotic cell death is an important survival system for multicellular organisms because it removes damaged cells. Mutation is also a survival method for dealing with damaged cells in multicellular and also unicellular organisms, when DNA lesions are not removed. However, to the best of our knowledge, no reports have comprehensively explored the direct relationship between apoptosis and somatic cell mutations induced by various mutagenic factors. Results Mutation was examined by the wing-spot test, which is used to detect somatic cell mutations, including chromosomal recombination. Apoptosis was observed in the wing discs by acridine orange staining in situ. After treatment with chemical mutagens, ultraviolet light (UV), and X-ray, both the apoptotic frequency and mutagenic activity increased in a dose-dependent manner at non-toxic doses. When we used DNA repair-deficient Drosophila strains, the correlation coefficient of the relationship between apoptosis and mutagenicity, differed from that of the wild-type. To explore how apoptosis affects the behavior of mutated cells, we determined the spot size, i.e., the number of mutated cells in a spot. In parallel with an increase in apoptosis, the spot size increased with MNU or X-ray treatment dose-dependently; however, this increase was not seen with UV irradiation. In addition, BrdU incorporation, an indicator of cell proliferation, in the wing discs was suppressed at 6 h, with peak at 12 h post-treatment with X-ray, and that it started to increase again at 24 h; however, this was not seen with UV irradiation. Conclusion Damage-induced apoptosis and mutation might be coordinated with each other, and the frequency of apoptosis and mutagenicity are balanced depending on the type of DNA damage. From the data of the spot size and BrdU incorporation, it is possible that mutated cells replace apoptotic cells due to their high frequency of cell division, resulting in enlargement of the spot size after MNU or X-ray treatment. We consider that the induction of mutation, apoptosis, and/or cell growth varies in multi-cellular organisms depending on the type of the mutagens, and that their balance and coordination have an important function to counter DNA damage for the survival of the organism.