Abstract: OBJECTIVE： To investigate protective effects of N-acetylcysteine (NAC) on genotocicity induced by titanium dioxide nanoparticles (TiO₂-NPs) in human normal hepatocytes L- 02 and human normal lung epithelial cells HBE. METHODS：L-02 and HBE cells grown in log phase were divided into 3 groups： control group (normal culture)，TiO₂-NPs exposed group (80 μg/mL)，and TiO₂-NPs (80 μg/mL) and NAC (20 μmol/L) co-exposed group. After the cells in each group were exposed for 72 h，H₂O₂ kit was used to detect the intracellular H₂O₂ level; telomere length (TL) of L-02 and HBE cells in each group was measured by realtime quantitative PCR; chromosomal instability (CIN) and cell death indexes were evaluated by cytokinesisblock micronucleus cytome assay (CBMN-Cyt). RESULTS： Compared with the control group， TiO₂-NPs exposed for 72 h significantly increased intracellular H₂O₂ levels in L-02 and HBE cells (P<0.05)，resulting in shortened TL，increased CIN and cell death (P<0.05). When co-exposed with TiO₂-NPs and NAC for 72 h， the H₂O₂ levels and CIN among the two types cells were significantly higher than those of the control group (P< 0.05)，while TL and cell death had no significant differences compared with the control group (P>0.05). When compared with the TiO₂-NPs group，increased TL (P<0.05)，decreased CIN，and decreased cell death rates were found in TiO₂-NPs and NAC co-exposed group (both P<0.05). CONCLUSION： The antioxidant NAC strongly reduced the telomere shortening and cell death induced by TiO₂-NPs in L- 02 and HBE cells， showing the effects of protecting cells under the stress of TiO₂-NPs.

Key words: N-acetylcysteine, titanium dioxide nanoparticles, telomere, genetic damage, protective effect