Influence Of Norfloxacin On Single-walled Carbon Nanotube Toxicity To Human Epithelial Cells And Study The Toxicity Mechanism

Carbon nanotubes (CNTs) with their unique one-dimensional hollow nanostructureand unusual properties such as ultimate electrical, thermal conductivities andmechanical strength can be widely used in the field of composite materials, electricityand nanomedicine. With increasing use and production of CNTs, the professional andpublic exposure to CNTs is expected to increase significantly. In addition, the CNTscould also co-exist with some organic pollutants in the environment, which might be abigger threat to both environment and human beings. As the lungs are the primaryroute of entry for inhaled CNTs, lung toxicity is of particular concern. As the basicstructure and functional unit of the organisms, cells in vitro have some characteristicswhich use as organism test, such as short test cycle, high sensitivity, easy-controlledculture conditions and so on, and it can interpret toxicity mechanism from the Angleof molecular. Therefore, in this study, the human lung cells (A549) were selected astest cells, the aim was to explore the toxic effects and response mechanism ofsingle-walled carbon nanotubes (SWCNT) to cells under the action of Norfloxacin(NOR). The main results were present as follows:(1) Toxicity of SWCNT to A549cells at different concentrations and exposure timeswas investigated in this study. As the growth of the exposure time, the toxicity effectwas the most obvious at24h, and with concentration increasing, A549cell viabilitydecreased gradually after exposure to SWCNT for24h at different concentrations. the24h IC50was65mg/L. Therefore, A549cells exposed to65mg/L SWCNT for24hwas chosen for the following experiments.(2)NOR within the range from0to40mg/L had no toxic effect on A549cells.65mg/L SWCNT got adsorption equilibrium with40mg/L NOR in24h. Afterequilibration, toxicity effect of SWCNT to A549cell was reduced in NOR solution. （3）Compared with uptake content of SWCNT between the cells with and withoutsodium azide and2-deoxyglucose by Observing with laser confocal fluorescencemicroscope (LCFM), endocytosis was confirmed to be one of the important pathwaysof SWCNT uptake. Using transmission electron microscope (TEM) we found thatSWCNT entered cells alone, which mainly distributed in the lysosome and cytoplasm,while the combination of SWCNT and NOR entered cells, SWCNTs mainlydistributed in the cytoplasm.(4) Intracellular SWCNT generated ROS and made H2O2and OH accumulated,which could result in oxidative stress to cells. The activity of CAT and SOD wasincreased by feedback regulation. Hence it strengthened the capacity of scavengingexcessive free radical and enhanced the antioxidant capacity of the cell. However，astime increased, ROS could be accumulated again, which caused lipid peroxidation ofcell, destructed the stability of the cell membrane and resulted in leakage of lactatedehydrogenase.（5）When SWCNT in the NOR solution, comparing with the cell culture media,reduced the amount of ROS, leading to reduce the content of MDA and decrease therelease of lactate dehydrogenase. Hence, cell toxicity was lower.