Somatic-cell mutation induced by short exposures to cigarette smoke in urate-null, oxidative stress-sensitive Drosophila

Abstract

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.

Increase of somatic cell mutations in oxidative damage-sensitive drosophila

“…The roles of uric acid as an antioxidant and radical scavenger have been widely recognized in vitro and in several organisms, including primates [ 1 – 6 ]. Previously, we reported that ECS and paraquat induced mutations in a urate-null mutant Drosophila strain, but not in wild-type Drosophila [ 11 ]. We showed that ROS were produced in the larval bodies exposed to ECS, which suggested that ROS are implicated in the mutagenicity of ECS.…”

“…The Oregon-R and y v ma-l strains were kindly provided by Dr. H. Ryo (Osaka University, Suita, Japan). The y v ma-l; mwh strain was developed in our laboratory [ 11 ]. Both the ry 506 and mwh, ry 506 strains were obtained from the Drosophila Genomics and Genetic Resources Center at Kyoto Institute of Technology (Kyoto, Japan).…”

“…The Drosophila wing-spot test was performed to detect somatic cell mutations, including chromosomal recombination, according to the methods established by Graf et al [ 14 ] with slight modifications [ 11 ]. To obtain third-instar larvae, virgin females of the genotype y v ma-l; mwh were crossed with males that were either wild type (Oregon-R) or y v ma-l .…”

“…Previously, we reported that urate-null Drosophila mutants were sensitive to the toxicity of environmental cigarette smoke (ECS) [ 9 , 10 ], and that the effects of the ECS were apparent even in the next generation [ 10 ]. We also reported that somatic cell mutations were induced by ECS and the herbicide paraquat in urate-null Drosophila , but not in wild-type Drosophila [ 11 ]. Many mutagenic carcinogens need to be activated to ultimate mutagens by metabolic enzymes, such as cytochrome 450 (CYP), and ROS are likely produced during this activation process.…”

Systematic Mapping and Review of Landscape Fire Smoke (LFS) Exposure Impacts on Insects

“…Furthermore, the responses of insects to different sources of smoke pollution can be studied and summarized. For example, when Drosophila melanogaster are exposed to cigarette smoke for over six hours, there is an increasing possibility of gene mutagenesis ( Uchiyama et al 2016 ). Some butterfly species can display mortality when exposed to high-level air pollution induced by coal power plants, like Thecla betulae (Lepidoptera: Lycaenidae) ( Corke 1999 ).…”