Effects of Fe3+ and Fe2+ on Proliferation, Differentiation and Mineralization Function of Primary Osteoblasts in vitro

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromid(MTT), alkaline phosphatase(ALP) activity, oil red 0 assays and alizarin red-S(ARS) stain were used to evaluate the effects of Fe3+ and Fe2+, on proliferation, differentiation and mineralization function of primary osteoblasts(OBs) in vitro. The results indicate that both Fe3+ and Fe2+(1x10(-9)similar to 1x10(-4) mol.L-1) promote the proliferation of OBs, but turn to inhibit at a higher concentration of 1x10(-3) mol.L-1 Both Fe3+ and Fe2+(1x10(-8)similar to 1x10(-4) mol.L-1) inhibit differentiation of OBs, but have no effect on differentiation at a lower concentration of 1 x 10(-9) mol.L-1 for 48 h. Whereas, Fe3+ shows no effect on differentiation of OBs, Fe2+ begins to promote differentiation of OBs at concentration of 1 x 10(-6) mol.L-1, but Fe2+ inhibits differentiation of OBs at other concentrations by prolonging the incubation time. Fe3+ inhibits adipocytic trans-differentiation of OBs or has no effects on adipocytic trans-differentiation of OBs at tested concentrations. The promotion or inhibition effect of Fe2+ on adipocytic trans-differentiation of OBs depends on concentration and incubation time. Fe3+ and Fe2+(1 x 10(-8)similar to 1 x 10(-5) mol.L-1) inhibit and promote the formation of mineralized matrix nodules of OBs, respectively. Fe3+ and Fe2+ promote the formation of mineralized matrix nodules at a higher concentration of 10(-4) mol.L-1, but Fe3+ inhibits the formation of mineralized matrix nodules, Fe2+ shows no effect at a lower concentration of 1 x 10(-9) mol.L-1. The results suggest that concentration, culture time and valence state of iron ion are key factors for switching the biological effects of Fe3+ and Fe2+ from toxicity to activity, from damage to protection, or from down-regulation to up-regulation.