TRAP assay in osteoclast differentiation. Assays were performed after 3, 5, 7 and 10 days of differentiation. The graph shows that only mononucleated cells exhibited a significant increase of TRAP activity after 7 and 10 days of osteoclast differentiation. TRAP activity in MC3T3-E1 remained constant, similar to control activity. Results are presented as mean ± SD (n = 3). The * indicate significant difference (p < 0.05) of mononucleated cells and MC3T3-E1 respectively as compared with day 0 activity for the same culture period.