Enhanced osteocalcin expression by osteoblast-like cells (MC3T3-E1) exposed to bioactive coating glass (SiO2–CaO–P2O5–MgO–K2O–Na2O system) ions

This study tested the hypothesis that bioactive coating glass (SiO2–CaO–P2O5–MgO–K2O–Na2O system), used for implant coatings, enhanced the induction of collagen type 1 synthesis and in turn enhanced the expression of downstream markers alkaline phosphatase, Runx2 and osteocalcin during osteoblast differentiation. The ions from experimental bioactive glass (6P53-b) and commercial BioglassTM (45S5) were added to osteoblast-like MC3T3-E1 subclone 4 cultures as a supplemented ion extract (glass conditioned medium (GCM)). Ion extracts contained significantly higher concentrations of Si and Ca (Si, 47.9 ± 10.4 ppm; Ca, 69.8 ± 14.0 for 45S5; Si, 33.4 ± 3.8 ppm; Ca, 57.1 ± 2.8 ppm for 6P53-b) compared with the control extract (Si < 0.1 ppm, Ca 49.0 ppm in α-MEM) (ANOVA, p < 0.05). Cell proliferation rate was enhanced (1.5× control) within the first 3 days after adding 45S5 and 6P53-b GCM. MC3T3-E1 subclone 4 cultures were then studied for their response to the addition of test media (GCM and control medium along with ascorbic acid (AA; 50 ppm)). Each GCM + AA treatment enhanced collagen type 1 synthesis as observed in both gene expression results (day 1, Col1α1, 45S5 GCM + AA: 3× control + AA; 6P53-b GCM + AA: 4× control + AA; day 5, Col1α2, 45S5 GCM + AA: 3.15× control + AA; 6P53-b GCM + AA: 2.35× control + AA) and in histological studies (Picrosirius stain) throughout the time course of early differentiation. Continued addition of each GCM and AA treatment led to enhanced expression of alkaline phosphatase (1.4× control + AA after 5 days, 2× control + AA after 10 days), Runx2 (2× control + AA after 7 days) and osteocalcin gene (day 3, 45S5 GCM + AA: 14× control + AA; day 5, 6P53-b GCM + AA: 19× control + AA) and protein expression (40×–70× control + AA after 6 days). These results indicated the enhanced effect of bioactive glass ions on key osteogenic markers important for the bone healing process.