Inorganic polyphosphate: a possible stimulant of bone formation

Inorganic polyphosphates [ Poly( P)] are often distributed in osteoblasts. We undertook the present study to verify the hypothesis that Poly( P) stimulates osteoblasts and facilitates bone formation. The osteoblast-like cell line MC 3T3-E1 was cultured with Poly( P), and gene expression and potential mineralization were evaluated by reverse-transcription polymerase chain-reaction. Alkaline phosphatase activity, von Kossa staining, and resorption pit formation analyses were also determined. The potential role of Poly( P) in bone formation was assessed in a rat alveolar bone regeneration model. Poly( P) induced osteopontin, osteocalcin, collagen 1 alpha, and osteoprotegerin expression and increased alkaline phosphatase activity in MC 3T3- E1 cells. Dentin slice pit formation decreased with mouse osteoblast and bone marrow macrophage co-cultivation in the presence of Poly( P). Promotion of alveolar bone regeneration was observed locally in Poly( P)treated rats. These findings suggest that Poly( P) plays a role in osteoblastic differentiation, activation, and bone mineralization. Thus, local poly( P) delivery may have a therapeutic benefit in periodontal disease.