Effect of titanium dioxide nanoparticles on histone modifications and histone modifying enzymes expression in human...

Titanium dioxide (TiO₂) nanoparticles are widely manufactured, with a range of applications in consumer products. Significant toxicity of TiO₂ nanoparticles has, however, been recognized, suggesting considerable risk to human health. To evaluate fully their toxicity, assessment of the epigenetic action of these nanoparticles is critical. However, only few studies are available examining the capability of nanoparticles to alter epigenetic integrity. In the present study, the effect of TiO₂ nanoparticles exposure on histone modifications, a major epigenetic mechanism, was investigated in human colorectal (Caco-2) and lung (NL20) epithelial cell lines. Histone H3 and H4 modifications were assessed by array analysis using the EpiQuick^TM Histone H3 or H4 Modification Multiplex Assay. Seventeen histone modifications were identified with altered levels after exposure to TiO₂ nanoparticles. Changes in several selected histone modifications (Caco-2 cells: H3cit, H3K9me3, H3K27me3, H3K36me3, H3K9ac, and H4K8ac; NL20 cells: H3K4me3, H3K9me3, H3K27me3, H3K9ac, and H3K18ac) were verified by Western blot analysis. The results also revealed aberrant expression of histone modifying enzymes in TiO₂ exposed cells. Expression levels were determined by array analysis using the Human Epigenetic Chromatin Modification Enzymes RT² Profiler™ PCR Array, with 12 genes identified in both Caco-2 cells and NL20 cells. qRT-PCR analysis confirmed the array results for several selected histone modifying enzyme genes (ASH1L, CARM1, EHMT2, HAT1, HDAC9, KMT2E, NCOA1, SETDB2, and USP16). The findings from this study clearly demonstrate the impact of TiO₂ nanoparticles exposure on histone modification in two human cell lines, supporting potential involvement of this epigenetic mechanism in the toxicity of TiO₂ nanoparticles. Hence, for complete assessment of potential risk from nanoparticle exposure, epigenetic studies are critical.