Carbon nanotubes (CNTs) are one of the most representative nanomaterials that have newly appeared and drawn much attention for various applications. To examine the effect of CNTs on biological organisms, the reaction behavior of human hepatocytes, Hc cells, to CNTs was investigated in comparison with phagocytes. After hepatocytes were incubated in the culture medium with the addition of CNTs, CNTs were found in cytoplasms by OM (Optical Microscopy), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy). In the successive observation using the time-lapse OM system, hepatocytes showed the phagocytosis-like behavior to CNTs by changing their shapes and forming the long, straight pseudo-pods. The quantitative analysis showed that cell activities to scavenge CNT debris were constant during the observation for more than 22 hrs. Since these behaviors of hepatocytes apparently resemble those of phagocytes, the cell functional analysis was done and compared by measuring the expression of cytokines and superoxide dismutase (SOD) activity. When incubated with CNTs, THP-1 monocytes released TNF-α in a dose dependent manner to CNT content, while the amount released from hepatocytes were very low and there was almost no difference from control. These results indicate that hepatocytes have the phagocytosis-like ability to uptake foreign objects. However, their mechanism is completely different from that of phagocytotic cells in the point that they have no functions to lead to inflammation through cytokine cascade as monocytes exhibit. Throughout the study, hepatocytes could work without the acute toxicity such as cell death by CNTs. In situ observation could image the dynamic behavior of hepatocytes to perform the functions to treat the foreign objects. The results confirm that liver is an important organ to deal with them under non-inflammatory circumstances.
Key words: carbon nanotubes, hepatocyte, phagocytosis, in situ observation, inflammation