Active-MMP-13 and TIMP-1 concentrations in conditioned medium induced by mechanical strain in MC3T3-E1 cells. Conditioned media harvested from the cultured cells were used as samples. The concentrations of active form of MMP-13 and TIMP-1 in these supernatants were assayed using a comercially available enzyme-linked immunosorbent assay (ELISA) kits, as described in the Materials and methods. (A) The concentrations of active form of MMP-13. (B) The concentrations of TIMP-1. The results shown are means ± SD of five independent experiments. Significant differences from the 0% culture are shown by ANOVA and Student's t test (*P < 0.05, ** P < 0.01).