Evaluation of the cytotoxic and genotoxic effects by melamine and cyanuric acid co-exposure in human embryonic kidney 293 cells.

The melamine and cyanuric acid (CA) complex has been suggested to cause the toxic effects observed in melamine-contaminated food or milk. However, the cytotoxic and genotoxic effects of co-exposure to melamine and CA are not fully clear. Therefore, the cytotoxic effects of melamine and CA were first examined by co-exposure in human kidney 293 cells using the MTT assay. During a 24-h period for the three concentrations tested (0.5, 1, and 5 mg/mL), neither melamine nor CA alone showed significant toxic effects on 293 cells at 0.5 mg/mL, while higher concentrations led to decreased in cell viability. However, co-exposure to several combinations of melamine and CA [100:1, 10:1, 1:10, and 1:100 (v:v), at a final concentration of 0.5 mg/mL] did cause cytotoxicity with higher levels of CA leading to higher cytotoxicity. By contrast, while neither melamine nor CA alone induced phosphorylated-H2AX (gammaH2AX) foci formation, melamine and CA at a 100:1 ratio induced gammaH2AX foci 24 h post-treatment. The alkaline comet assay also revealed the presence of DNA damage following melamine and CA co-exposure. In vivo assay also revealed the presence of melamine-CA complex in the kidney. These data indicated that the cytotoxic and genotoxic effects of melamine and CA co-exposure differ from those of melamine or CA alone.