[Comparative analysis for the cytotoxicity and genotoxicity of multi-walled carbon nanotubes with different lengths and surface modifications in A549 cells].

OBJECTIVE: To compare the cytotoxicity and DNA strand breakage induced by multi-walled carbon nanotubes (MWCNTs) with different lengths and different surface modifications in human alveolar type II cells (A549 cells). METHODS: Two different lengths (5-15 μm, 350-700 nm) of MWCNTs and three different kinds of surface modified MWCNTs (COOH-MWCNTs, NH2-MWCNTs, and Tau-MWCNTs) were used in the experiments. The short MWCNTs were used as pristine MWCNTs to compare with the 3 surface modified MWCNTs. The cytotoxicity was determined by cell counting kit-8 (CCK-8) assay at the concentrations of 2, 8, and 32 mg/L at hours 12, 24, 36, and 48 respectively. Single cell gel electrophoresis (SCGE) assay was performed to evaluate DNA strand breakage in A549 cells after 24 h treatment of 8 mg/L of each tested material. RESULTS: Long multi-walled carbon nanotubes (Long-MWCNTs) and short multi-walled carbon nanotubes (Short-MWCNTs) showed a dose-dependent cytotoxicity within the exposure time 12-48 h. Especially, Long-MWCNTs showed greater cytotoxicity than Short-MWCNTs from 24 to 48 h at the same concentration. The relative cell viability of the 3 surface modified MWCNTs was higher than that of the pristine MWCNTs at h 12 at the concentration of 32 mg/L [COOH-MWCNTs (86.55±1.80)%, NH2-MWCNTs (84.67±1.32)%, Tau-MWCNTs (80.15±3.53)% and Pristine-MWCNTs (71.44±5.58)%], at h 24 at the concentration of 8 mg/L [COOH-MWCNTs (96.74±1.00)%, NH2-MWCNTs (96.74±3.35)%, Tau-MWCNTs (106.39±3.83)% and Pristine-MWCNTs (91.02±2.53)%], at h 24 at the concentration of 32 mg/L [COOH-MWCNTs (80.88±2.67)%, NH2-MWCNTs (82.90±3.25)%, Tau-MWCNTs (82.55±3.32)% and Pristine-MWCNTs (76.08±4.27)%] and at h 36 at the concentration of 8 mg/L [COOH-MWCNTs (96.87±1.05)%, NH2-MWCNTs (96.66±4.76)%, Tau-MWCNTs (100.23± 2.84)% and Pristine-MWCNTs (89.61±3.78)%], and the differences were statistically significant (P 0.05) at other observation time and exposure concentrations. The DNA strand breakage of the 3 surface modified MWCNTs: the Olive tail moment of COOH-MWCNTs was 1.56±0.22, the Olive tail moment of NH2-MWCNTs 2.25±1.62 and the Olive tail moment of Tau-MWCNTs 2.23±0.94; the tail DNA% of COOH-MWCNTs was (3.96± 0.60)%, the tail DNA% of NH2-MWCNTs (6.16±4.68)% and the tail DNA% of Tau-MWCNTs (6.05±2.31)%, which were lower than that of the pristine MWCNTs (P<0.05), whose Olive tail moment was 3.00±0.64 and tail DNA% (8.23±2.27)%. Moreover, the COOH-MWCNTs induced the lowest DNA damage among the three modified MWCNTs. CONCLUSION: Long-MWCNTs compared with Short-MWCNTs demonstrated a greater cytotoxicity and lower DNA strand breakage damage. The surface modifications of MWCNTs can reduce the cytotoxicity and DNA strand breakage in A549 cells.