Biochemical effects of some CeO 2 , SiO 2 , and TiO 2 nanomaterials in HepG2 cells.

The potential mammalian hepatotoxicity of nanomaterials was explored in dose-response and structure-activity studies in human hepatic HepG2 cells exposed to between 10 and 1000 μg/ml of five different CeO ₂ , three SiO ₂ , and one TiO ₂ -based particles for 3 days. Various biochemical parameters were then evaluated to study cytotoxicity, cell growth, hepatic function, and oxidative stress. Few indications of cytotoxicity were observed between 10 and 30 μg/ml. In the 100 to 300 μg/ml exposure range, a moderate degree of cytotoxicity was often observed. At 1000 μg/ml exposures, all but TiO ₂ showed a high degree of cytotoxicity. Cytotoxicity per se did not seem to fully explain the observed patterns of biochemical parameters. Four nanomaterials (all three SiO ₂ ) decreased glucose 6-phosphate dehydrogenase activity with some significant decreases observed at 30 μg/ml. In the range of 100 to 1000 μg/ml, the activities of glutathione reductase (by all three SiO ₂ ) and glutathione peroxidase were decreased by some nanomaterials. Decreased glutathione concentration was also found after exposure to four nanomaterials (all three nano SiO ₂ particles). In this study, the more responsive and informative assays were glucose 6-phosphate dehydrogenase, glutathione reductase, superoxide dismutase, lactate dehydrogenase, and aspartate transaminase. In this study, there were six factors that contribute to oxidative stress observed in nanomaterials exposed to hepatocytes (decreased glutathione content, reduced glucose 6-phosphate dehydrogenase, glutathione reductase, glutathione peroxidase, superoxide dismutase, and increased catalase activities). With respect to structure-activity, nanomaterials of SiO ₂ were more effective than CeO ₂ in reducing glutathione content, glucose 6-phosphate dehydrogenase, glutathione reductase, and superoxide dismutase activities.