With the expansion in
use of TiO2-np, a superior comprehension of their wellbeing is vital. In the
present study the impact of different crystal phases of TiO2-np (anatase,
rutile and anatase: rutile mixture; 20-26nm) were studied for cyto-genotoxicity and global DNA methylation and hydroxymethylation. Cytotoxic response was observed at a concentration of
25μg/ml for the particles tested. Results of comet and micronucleus (with and
without CytB) assays revealed significant genotoxic effect of these particles.
Flow cytometry revealed cell cycle arrest in the S-phase. Based on the results,
toxicity of the particles could be correlated with their physico-chemical
properties (i.e. smaller size and hydrodynamic diameter and larger surface
area), anatase form being the most toxic. From the results of the
cyto-genotoxicity assays, concentrations were determined for the epigenetic
study. Effect on global DNA methylation and hydroxymethylation levels were
studied at cyto-genotoxic (25μg/ml), genotoxic (12.5μg/ml) and sub
cyto-genotoxic (3.25μg/ml) concentrations using LC-MS/MS analysis. Though no
significant changes were observed for 3h treatment schedule; significant
hypomethylation were observed at 24h for anatase (significant at 3.25 and
25μg/ml), rutile (significant at 3.25 and 25μg/ml) and anatase: rutile mixture
(significant at 25μg/ml) forms. The results suggest that epigenetic changes
could occur at sub cyto-genotoxic concentrations. And hence for complete
characterization of nanoparticle toxicity, epigenetic studies should be
performed along with conventional toxicity testing methods.
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