Oxidative DNA damage corresponds to the long term survival of human cells treated with silver nanoparticles

We examined the relation between DNA damage and the clonogenic potential of 3 human cell lines, HepG2, HT29 and A549, treated with bare 20 nm or 200 nm silver nanoparticles (AgNPs). The endpoints examined were the DNA breakage estimated by the comet assay, the oxidative base damage recognized by formamido-pyrimidine glycosylase (FPG) and estimated with the FPG+comet assay, and the frequencies of histone γH2AX foci and micronuclei. Each cell line studied had a different pattern of DNA breakage and base damage versus the NPs concentration and time of treatment. The overall pattern of DNA breakage and base damage induction corresponded to the intracellular generation of reactive oxygen species. There was no increase in the frequencies of histone γH2AX foci and micronuclei as compared to those in the untreated cells. The reported experiments suggest that only the oxidative DNA damage corresponds to the loss of the clonogenic ability of cells treated with AgNPs.