HDI treatment accelerates the appearance of alkaline phosphatase activity in differentiating MC3T3 cells. MC3T3 cells were cultured for the indicated times in osteogenic medium. The medium was changed three days with the HDIs or vehicle added only at day 0. Fold change in ALP activity is shown in relation to values obtained at the start of the culture (day 0). * denotes a statistically significant change of p < 0.01 by one-way ANOVA of the HDI-treated sample versus the DMSO-treated sample at that time point.