New Insight into Intrachromosomal Deletions Induced by Chrysotile in the gpt delta Transgenic Mutation Assay

Abstract

BackgroundGenotoxicity is often a prerequisite to the development of malignancy. Considerable evidence has shown that exposure to asbestos fibers results in the generation of chromosomal aberrations and multilocus mutations using various in vitro approaches. However, there is less evidence to demonstrate the contribution of deletions to the mutagenicity of asbestos fibers in vivo.ObjectivesIn the present study, we investigated the mutant fractions and the patterns induced by chrysotile fibers in gpt delta transgenic mouse primary embryo fibroblasts (MEFs) and compared the results obtained with hydrogen peroxide (H2O2) in an attempt to illustrate the role of oxyradicals in fiber mutagenesis.ResultsChrysotile fibers induced a dose-dependent increase in mutation yield at the redBA/gam loci in transgenic MEF cells. The number of λ mutants losing both redBA and gam loci induced by chrysotiles at a dose of 1 μg/cm2 increased by > 5-fold relative to nontreated controls (p < 0.005). Mutation spectra analyses showed that the ratio of λ mutants losing the redBA/gam region induced by chrysotiles was similar to those induced by equitoxic doses of H2O2. Moreover, treatment with catalase abrogated the accumulation of γ-H2AX, a biomarker of DNA double-strand breaks, induced by chrysotile fibers.ConclusionsOur results provide novel information on the frequencies and types of mutations induced by asbestos fibers in the gpt delta transgenic mouse mutagenic assay, which shows great promise for evaluating fiber/particle mutagenicity in vivo.

Malignant mesothelioma as an oxidative stress-induced cancer: An update

“…These chromosomal aberrations induced by asbestos fibers were shown to be counteracted by iron chelators, free radical scavengers, or antioxidants [63,64], highlighting again the pivotal role of oxidative stress in asbestos-induced genotoxicity.…”

DNA Double-Strand Breaks by Asbestos, Silica, and Titanium Dioxide

“…Oxidation of DCFH by Fenton reaction-generated hydroxyl radicals (ÁOH), H 2 O 2 , horseradish peroxidase (HRP), Fe(II), or peroxynitrite results in a nonspecific, highly fluorescent DCF (31)(32)(33). DCFDA for H 2 O 2 is also oxidized to a fluorescent product in the presence of ÁO 2 2 and reactive species, and localizes mainly in the mitochondria (34). Dihydroethydium (DHE), on the other hand, is more specific for superoxide.…”

Novel DNA Polymerases and Novel Genotoxicity Assays

“…These results suggest that GDL1 cells are useful to characterize mutations induced by chemicals at the molecular levels. To characterize molecular events induced by exposure to asbestos, embryonicˆbroblasts of gpt delta mice were exposure to chrysotile asbestos (7). The exposure enhanced the Spi -mutation frequency in a dose-dependent manner.…”

“…Although the mechanisms by which asbestos induce tumors are still being debated, it is evident that asbestos is genotoxic. Asbestos induces oxidative DNA damage, deletions in DNA, chromosome aberrations, micronucleus formation, aneuploidy and polyploidy formation in mammalian cells (7)(8)(9). Hence, the genotoxicity could, at least in part, account for the causes of asbestos-induced tumors.…”