ABSTRACT
Inhaled fibres with certain physico-chemical properties are known to induce mesothelioma in humans. The induction of reactive oxygen (ROS) or nitrogen species (RNS) have been suggested as molecular mechanism of fibre induced carcinogenesis. In earlier studies we were able to demonstrate that crocidolite asbestos in vivo induces mutations in transgenic rats with a specific molecular spectrum that indicates the involvement of 8-hydroxydeoxyguanosine (8-OHdG) as pre-mutagenic adduct. 8-OHdG may be induced by primary (direct) and/or secondary (cellular mediated) mechanisms. Therefore, the induction of 8-OHdG as well as the inflammatory response of animals treated with fibre samples significantly differing in their physico-chemical characteristics was investigated. As appropriate system to study mesothelioma carcinogenesis, intraperitoneal injection in rats was used with samples of UICC crocidolite, crocidolite with reduced iron content, and a vitreous fibre (MMVF 11). Equal numbers of carcinogenic fibres from each sample revealed significant comparable increases in 8-OHdG induction. Parameters of inflammation (percentage of macrophages and TNF-alpha secretion) correlated significantly with the induction of 8-OHdG, 10 weeks after treatment.
Subject(s)
Asbestos, Crocidolite/toxicity , DNA/genetics , Guanine/analogs & derivatives , Guanine/metabolism , Mineral Fibers/toxicity , 8-Hydroxy-2'-Deoxyguanosine/analogs & derivatives , Animals , Asbestos, Crocidolite/administration & dosage , DNA/chemistry , DNA/drug effects , Female , Guanine/analysis , Humans , Injections, Intraperitoneal , Macrophages, Peritoneal/drug effects , Macrophages, Peritoneal/metabolism , Rats , Rats, Wistar , Therapeutic Irrigation , Tumor Necrosis Factor-alpha/metabolismABSTRACT
DNA damage due to reactive oxygen or nitrogen species is proposed to be involved in the molecular mechanism of asbestos-induced carcinogenicity. However, indications for this hypothesis came mainly from in vitro assays using cultured cells or cell-free systems. In the present study, the mutagenicity of crocidolite fibers and the underlying molecular mechanisms were investigated in vivo. Mutation frequencies were determined in DNA of omenta, a relevant target tissue for mesothelioma carcinogenesis, using lacI transgenic rats. The mutagenic effect of 2 and 5 mg of crocidolite asbestos was demonstrated, with a maximal relative increase in mutation frequency of 3.4 compared with the control group. The molecular analysis of the mutations revealed striking differences according to mutation types between asbestos-induced mutations and spontaneous mutations. Therefore, a specific molecular mechanism induced by crocidolite that differs from that induced by the generation of spontaneous mutations can be proposed. G to T transversions, which are known to be induced by the premutagenic DNA adduct 8-hydroxydeoxyguanosine (8-OHdG), were the most prominent mutation type (29%) within crocidolite-induced mutations. In additional experiments, 8-OHdG in DNA of omenta from rats treated with 1 or 2 mg of crocidolite asbestos was determined. Levels of 8-OHdG in animals treated with crocidolite were significantly increased compared with negative controls. These data give strong evidence for the involvement of reactive oxygen or nitrogen species in crocidolite-induced mutagenesis in vivo.
