Effects of fluoride on human bone cells in vitro: differences in responsiveness between stromal osteoblast precursors and mature osteoblasts.

The cellular effects of sodium fluoride (NaF) on human bone cells in vitro have been variable and dependent on the culture system used. Variability could be attributed to differences in responsiveness to NaF among different populations of cells at various stages of differentiation in the osteoblastic lineage. In this study we compared the effects of NaF in serum-free medium on cultures of more differentiated human osteoblast-like (hOB) cells derived from trabecular bone explants and on osteoblast committed precursors derived from human bone marrow, i.e. human marrow stromal osteoblast-like (hMS(OB)) cells. Sodium fluoride (10(-5) mol/l) increased proliferation of hMS(OB) cells (p < 0.05, N = 10) but was not mitogenic to hOB cells (p > 0.05, N = 10). Alkaline phosphatase (AP) production increased in both hMS(OB) (p < 0.05, N = 9) and hOB cells (p < 0.05, N = 9). No significant effects on procollagen type I propeptide production were obtained in either culture. In the presence of 1,25-dihydroxycholecalciferol (10(-9) mol/l), NaF enhanced alkaline phosphatase (p < 0.05, N = 8), procollagen type I propeptide (p < 0.05, N = 7) and osteocalcin (p < 0.05, N = 7) production by hMS(OB) cells but not by hOB cells. Our results suggest that osteoblast precursors are more sensitive to NaF action than mature osteoblasts and that the in vivo effects of NaF on bone formation may be mediated by stimulating proliferation and differentiation of committed osteoblast precursors in bone marrow.