Dexamethasone enhances differentiation of human osteoblastic cells in vitro

We examined the effects of dexamethasone (Dex) on the differentiation of osteoblastic cells isolated from human bone in vitro. The morphology of the cells exposed to Dex was transformed into a polygonal shape, while the cells exhibited a fibroblastic spindle shape in the absence of Dex. Staining for alkaline phosphatase (ALP) was more intense in Dex-treated cultures. In monolayer cultures, mineralization by the human osteoblastic cells was also stimulated by Dex treatment. The ALP activity of the cells cultured for 6 days in 10−8–10−6 M Dex increased in a dose-dependent manner. Furthermore, the ALP activity of the cells treated with 10−7M Dex for 9 days was 1.4-fold higher than that of the cells treated with 10−7M Dex for the first 3 days, followed by withdrawal for 6 days. Biochemical indicators of osteoblastic differentiation, which include ALP activity and secretion of procollagen type I carboxy-terminal peptide (PICP) and osteocalcin, were significantly enhanced in the cells exposed to Dex at 10−7M for 5 days. On the other hand, the time-dependent increase of ALP activity and osteocalcin levels in the control cells suggested that the cells gradually differentiate in continuous culture after they reached confluency. These findings suggest that Dex at the indicated concentration in this study enhances differentiation of human osteoblastic cells in vitro.