Genotoxicity testing of PLGA–PEO nanoparticles in TK6 cells by the comet assay and the cytokinesis-block micronucleus assay

The in vitro genotoxicity of PLGA–PEO (poly-lactic-co-glycolic acid–polyethylene oxide copolymer) nanoparticles was assessed in TK6 cells using the comet assay as well as cytokinesis-block micronucleus (CBMN) assay. The cells were exposed to 0.12–75 μg/cm2 of PLGA–PEO nanoparticles during 2 and 24 h for analysis in the comet assay, and to 3–75 μg/cm2 of these nanoparticles during 4, 24, 48 and 72 h, respectively, for analysis in the CBMN assay. Two different protocols for treatment with cytochalasin B were used. We found that PLGA–PEO was neither cytotoxic (measured by relative cell growth activity and cytokinesis-block proliferation index (CBPI)), nor did it induce DNA strand-breaks (detected by the comet assay) or oxidative DNA lesions (measured by the comet assay modified with lesion-specific enzyme formamidopyrimidine-DNA-glycosylase). There were no statistically significant differences in the frequencies of micronucleated binucleated cells (MNBNCs) between untreated and treated cells in either of the conditions used. This suggests that PLGA–PEO did not have potential genotoxicity. However, using two experimental protocols of the micronucleus assay, PLGA–PEO nanoparticles showed a weak but significant increase in the level of MN in mononucleated cells, in cells treated for 48 h with PLGA–PEO nanoparticles when cytochalasin B was added for the last 24 h (1st protocol), and in cells treated for 24 h with PLGA–PEO nanoparticles followed by washing of NPs and addition of cytochalasin B for another 24 h (2nd protocol). It remains unclear whether the increase of MNMNC after treatment with PLGA–PEO nanoparticles is the effect of a possible, weak aneugenic potential or early effect of these particles, or due to another reason. These results suggest that aneugenicity in addition to clastogenicity may be considered as an important biomarker when assessing the genotoxic potential of polymeric nanoparticles.