Fig. 3.

Dose- and time-dependent induction of MMP-2 and MMP-9 activities in HaCaT cells exposed to Nano-Ni. HaCaT cells were exposed to 10 or 20 μg/mL of Nano-Ni or Nano-TiO₂ for 24 h (a & b), or to 20 μg/mL of Nano-Ni for 12, 24, 48, or 72 h (c & d). Cells without treatment were used as control. MMP-2 and MMP-9 activities were determined in the conditioned media by gelatin zymography assay. A and C are the results of a single experiment, while B and D are normalized band densitometry readings averaged from three independent experiments ± SE. Supernatants collected from serum-free cultured HT1080 cells were used as a molecular weight marker for MMP-2 and MMP-9. * Significant difference as compared with the control group, p < 0.05; ^# Significant difference as compared with the same dose of Nano-TiO₂-treated group, p < 0.05