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  • Title: Cellular responses by stable and uniform ultrafine titanium dioxide particles in culture-medium dispersions when secondary particle size was 100 nm or less.
    Author: Horie M, Nishio K, Fujita K, Kato H, Endoh S, Suzuki M, Nakamura A, Miyauchi A, Kinugasa S, Yamamoto K, Iwahashi H, Murayama H, Niki E, Yoshida Y.
    Journal: Toxicol In Vitro; 2010 Sep; 24(6):1629-38. PubMed ID: 20541599.
    Abstract:
    Even though there have been some investigations into cellular responses induced by ultrafine titanium dioxide (TiO(2)) in vitro, the relationship between cellular responses and secondary particle size is still not clear. In this study, a stable and uniform TiO(2)-cell culture-medium dispersion was prepared, and cellular responses prompted by "ultrafine secondary particles" were examined. The TiO(2)-DMEM-FBS dispersion included secondary particles in which the secondary particle size was 100 nm or less. In the present study, a "secondary particle" was defined as a complex aggregate of TiO(2) primary particles, proteins from FBS and other medium components. Secondary particle size did not influence the cell viability. The TiO(2)-DMEM-FBS dispersion introduced to the human keratinocyte HaCaT cells caused weak intracellular oxidative stress and apoptosis. The cellular influence of ultrafine TiO(2)in vitro is caused by the following mechanisms: (1) Secondary particles are formed. Ultrafine TiO(2) particles dispersed in medium immediately form secondary particles with proteins and salts. (2) "Ultrafine" secondary particles are taken up by the cells. The secondary particles reach the cells by diffusion and/or sedimentation and are taken up by the cells, through endocytosis. (3) Intracellular reactive oxygen species (ROS) level increases. Internalized secondary particles induce an increase in intracellular reactive oxygen species levels, although the secondary particles do not break up in the cell. In the case of ultrafine TiO(2), the increase of the intracellular ROS level was minimal. Moreover, the antioxidation system of cells such as glutathione was working. (4) Apoptotic cell death is induced. An accumulation of oxidative stress activates the apoptotic pathway (such as the caspase-3) and subsequently induces apoptotic cell death. After 24h of exposure to TiO(2), the percentage of apoptotic cells was only 6-7%. As a result, although the ultrafine TiO(2) particles induce some cellular responses, these cellular responses to ultrafine TiO(2) are weaker than those of other cytotoxic ultrafine metal oxide particles, such as nickel oxide.
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