Induction of apoptosis by melamine in differentiated PC12 cells.

Melamine (2, 4, 6-triamino-1, 3, 5-triazine) was found in milk powder as an additive to raise the measured protein content in 2008 and thereby resulted in the outbreak of renal failure in infants in China. Previous studies focused on the renal toxicity in dogs and in cats. However, the toxicity of melamine in the central nervous system (CNS) is of little concern. The purpose of this study was to assess the possibility of melamine toxicity in differentiated PC12 cells. MTT assay indicated that melamine (above 33 µg/ml and 12 h) inhibited the proliferation of differentiated PC12 cells in a concentration- and time-dependent manner. Hoechst 33258 staining and flow cytometry assay showed that melamine induced the apoptotic cell death rather than necrosis in a dose-dependent manner. Reduced superoxide dismutase activity indirectly indicated that melamine could cause oxidative damage in differentiated PC12 cells. These results suggest that melamine is able to cause cytotoxicity in differentiated PC12 cells with involvement of oxidative damage and will provide evidence for further research on the potential toxicity in CNS.

In vitro toxicity of multi-walled carbon nanotubes in C6 rat glioma cells.

The present study aimed to evaluate the potential toxicity and the general mechanism involved in multi-walled carbon nanotubes (MWCNT)-induced cytotoxicity in C6 rat glioma cell line. Two kinds of MWCNT, which were coded as MWCNT1 (measured 10-20 nm in diameter and 2 µm in average length) and MWCNT2 (measured 40-100 nm in diameter and 10 µm in average length), were used in this study. To elucidate the possible mechanisms of cytotoxicity induced by MWCNT, MTT assay and flow cytometry analysis for apoptosis and cell cycle, MDA and SOD assays for oxidative stress were quantitatively assessed. The exposure of C6 rat glioma cells to different sizes of two kinds of carbon nanotubes at concentrations between 25 and 400 µg/ml decreased the cell viability in a concentration- and time-dependent manner. The exposure of C6 rat glioma cells to MWCNT (200-400 µg/ml) resulted in a concentration dependent cell apoptosis and G1 cell cycle arrest, and increased the level of oxidative stress. Results demonstrate that smaller size of MWCNT seems to be more toxic than that of larger one. MWCNT-induced cytotoxicity in C6 cells is probably due to the increased oxidative stress.