Cytotoxic and genotoxic characterization of aluminum and silicon oxide nanoparticles in macrophages.
OBJECTIVE
Although aluminum oxide and silicon oxide nanoparticles are currently available as dental materials, there is a lack of basic information concerning their biocompatibility. This study evaluates the biological responses of cultured macrophages (RAW264) to aluminum oxide (Al2O3NPs) and silicon oxide nanoparticles (SiO2NPs) by analyzing cytotoxicity and genotoxicity.


METHODS
The nanoparticles are amorphous and spherical, with diameters of 13 nm for the Al2O3NPs and 12 nm for the SiO2NPs. The cultured RAW264 are exposed to the nanoparticles (NPs) and examined for cytotoxicity using the WST-8 cell viability and Hoechst/PI apoptosis assay, for genotoxicity by micronucleus analysis, for changes in nuclear shape (deformed nuclei) and for comet assay using confocal microscopy, and micromorphological analysis is done using scanning and transmission electron microscopes.


RESULTS
Nuclei and DNA damage because of exposure to both types of NPs is observed by inmunostaining genotoxicity testing. The cytotoxicity and genotoxicity are well correlated in this study. Numerous NPs are observed as large aggregates in vesicles, but less or nonexistent NP internalization is seen in the nucleus or cytoplasm. These morphological results suggest that a primary cause of cell disruption is the chemical changes of the NPs in the low pH of vesicles (i.e., ionization of Al2O3 or SiO2) for both types of oxide NPs.


CONCLUSIONS
Although further research on the elution of NP concentrations on cell or tissue activity under simulated clinical conditions is required, NP concentrations over 200 μg/mL are large enough to induce cytotoxic and genotoxic effects to cells.
Department of Biomaterials Science, Osaka University, Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: masanori-h@mue.biglobe.ne.jp.
Masanori
M
Hashimoto
Department of Biomaterials Science, Osaka University, Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Satoshi
S
Imazato
D000535:Aluminum / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D001672:Biocompatible Materials / Q000633:toxicity; D002470:Cell Survival; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D008264:Macrophages / Q000187:drug effects*; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D053758:Nanoparticles; D012822:Silicon Dioxide / Q000633:toxicity*
D001672:Biocompatible Materials; D012822:Silicon Dioxide; D000535:Aluminum
Aluminum; Comet assay; Confocal microscopy; Cytotoxicity; Genotoxicity; Macrophage; Oxide-nanoparticle; SEM; Silica; TEM