Fig. 2.

Dose- and time-dependent induction of MMP-2 and MMP-9 mRNAs in HaCaT cells exposed to Nano-Ni. Expression of MMP-2 and MMP-9 mRNA in HaCaT cells were determined by real-time PCR after cells were exposed to 10 or 20 μg/mL of Nano-Ni or Nano-TiO₂ for 24 h (a & c), or to 20 μg/mL of Nano-Ni for 12, 24, 48, or 72 h (b & d). Cells without treatment were used as control. Data represent mean ± SE (n = 3). * 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