The Effect of Inorganic Polyphosphate on Osteoblasts

Objectives:Inorganic polyphosphate (PolyP) is a linear polymer of hundreds of orthophosphate (Pi) residues linked by high-energy, phosphoanhydride bonds. PolyP has a promoting effect on bone regeneration by enhancing osteoconductivity of the carrier and by increasing osteoinductivity of the damaged bone tissue. The purpose of the present study was to determine the effect of the inorganic polyphosphate on osteoblast-like cell MC3T3-E1 cell proliferation, maturation and mineralization. Methods: This study was designed to elucidate the effect of polyP on osteoblast-like cell, MC3T3-E1 cells. The cells were incubated with various concentrations of polyP (0, 0.001, 0.004 %) in combination of 10ng/ml of BMP-2, IGF-I, EGF, FGF, PDGF, or TGF-â1 and alkaline phosphatase activity were examined. The cells were incubated with polyP alone and we did alkaline phosphatase staining, calcium assay, alizarin red stainging of bone nodule formation, RT-PCR of osteocalcin mRNA and western blotting of IGF-I receptor, TGF-â1 receptor and collagen type I. Results:In this study, BMP and IGF increased alkaline phosphatase activity but EGF, FGF, PDGF TGF-â1 decreased ALP. PolyP showed inhibition ALP activity of increased activity by growth factor but stimulation ALP activity in combination with BMP at 5days. PolyP alone decreased ALP activity. After cell culture 5days, cell started to form inorganic crystal. 0.004% polyP showed more crystal formation but lower cell density than control. and polyP increased bone nodule formation and calcium accumulation. PolyP slightly decreased osteoclacin. Conclusions:These results suggest that polyP may modulate mineralization process in bone formation and may stimulate bone formation by increasing calcium accumulation. PolyP may be used as an agent as bone formation stimulator.