Cyto-genotoxicity of amphibole asbestos fibers in cultured human lung epithelial cell line: role of surface iron.

The present investigations correlate the potentials of the reactive oxygen species (ROS) generation and the cyto-genotoxicity of amphibole asbestos fibers (amosite, crocidolite and tremolite) with their surface iron, under in vitro controlled conditions, using A549 cells (human lung epithelial cell line). The mobilizable surface iron was measured by Atomic Absorption Spectroscopy; the production of ROS was investigated using 2, 7 dichloro-dihydrofluorescein-diacetate (DCFH-DA) dye; for cytotoxicity assessment, the intracellular organelles specific damages were measured, using 3-(4, 5 dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide salt (MTT) assay; and, the genotoxic potential of amphibole fibers was determined by cytokinesis block micronucleus (CBMN) assay. In the study, highest amount of ROS was generated by crocidolite followed by tremolite and minimum with amosite. In MTT assay, the time- and concentration-dependent decrease in percent cell viability was recorded with all the three amphibole fibers, tremolite being most cytotoxic, followed by crocidolite, and then amosite. In genotoxicity assay, an increase in the frequency of micronuclei (MNi) in binucleated (BN) cells was observed, where crocidolite was most genotoxic, followed by tremolite, and amosite the least.The comparison of results depicts a clear trend of cyto-genotoxic potential paralleling the ROS generation, suggesting a definite role of oxidative stress in fiber-induced toxicity. However, amosite contains maximum surface iron (28%), followed by crocidolite (27%), and tremolite carrying least (as contaminant) or no iron, the mobilizable surface iron is maximum in crocidolite followed by amosite and is minimum in tremolite. The mobilizable iron somewhat corresponds with the ROS generation capacity of these fibers. This shows that the surface iron could be mainly responsible for amphibole asbestos-induced ROS toxicity; though it may not be the only factor responsible, other factors like shape and size etc., also play role in amphibole asbestos-induced toxicity.