TiO₂ nanoparticles induce oxidative DNA damage and apoptosis in human liver cells

Abstract

Titanium dioxide nanoparticles (TiO₂ NPs), widely used in consumer products, paints, pharmaceutical preparations and so on, have been shown to induce cytotoxicity, genotoxicity and carcinogenic responses in vitro and in vivo. The present study revealed that TiO₂ NPs induce significant (p < 0.05) oxidative DNA damage by the Fpg-Comet assay even at 1 µg/ml concentration. A corresponding increase in the micronucleus frequency was also observed. This could be attributed to the reduced glutathione levels with concomitant increase in lipid peroxidation and reactive oxygen species generation. Furthermore, immunoblot analysis revealed an increased expression of p53, BAX, Cyto-c, Apaf-1, caspase-9 and caspase-3 and decreased the level of Bcl-2 thereby indicating that apoptosis induced by TiO₂ NPs occurs via the caspase-dependent pathway. This study systematically shows that TiO₂ NPs induce DNA damage and cause apoptosis in HepG2 cells even at very low concentrations. Hence the use of such nanoparticles should be carefully monitored.

Keywords::

• Cellular uptake of TiO₂ NPs
• oxidative stress; genotoxicity
• HepG2
• apoptosis

Acknowledgment

The authors gratefully acknowledge the funding from CSIR, New Delhi, under its network project (NWP35), Supra institutional Project (SIP-008), OLP 009. The funding from the Department of Science and Technology, Government of India, under the nano mission project – DST-NSTI grant (SR/S5/NM-01/2007) and UK India Education and Research Initiative (UKIERI) standard award to Indian Institute of Toxicology Research, Lucknow, India (DST/INT/UKIERI/SA/P-10/2008), and the Department of Biotechnology, under the New INDIGO programme (NanoLINEN project) is gratefully acknowledged. RKS thanks University Grant Commission (UGC), New Delhi, for the award of Senior Research Fellowship. AK gratefully acknowledges ICMR-SRF fellowship.