Silica-based bioactive glasses modulate expression of bone morphogenetic protein-2 mRNA in Saos-2 osteoblasts in vitro

Abstract

A chemical exchange of the silica gel layer forming on the surface of bioactive glasses is thought to be the principal reaction for bone–bioactive glass bonding. The contribution of biological molecules on cell–bioactive glass interaction is largely unknown. To further analyze the mechanisms involved in efficient bone bonding to bioactive glass, Saos-2 osteoblastic cells with proven osteogenic phenotype were cultured for 4, 7 and 14 days on two bioactive glasses with different Si contents. Culture plates and dishes made of bioactive (BAG, 53% SiO 2), biocompatible (BCG, 58% SiO 2) and control (G0) glasses were extensively conditioned with phosphate buffer and DMEM medium before seeding the cells. Northern hybridization was used for analysis of mRNA levels of collagen type I (Col-I), alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). A significant increase was observed in Col-I mRNA levels in cells grown on the two bioactive glasses when compared with those grown on controls at 4 and 7 days ( p<0.04). The mRNA level for ALP in the cultures of bioactive glasses-made plates and dishes was also increased over control at 7 days ( p<0.02) and remained this way between BAG and G0 at 14 days. Striking differences in BMP-2 mRNA levels existed between BAG and G0 plates and dishes at 7 days ( p<0.05). BMP-2 mRNA level in BAG group was higher than in BCG group at 4, 7 and 14 days, but without statistical significance. Saos-2 osteoblastic cells with strong ALP staining were mostly seen on BAG plates under a light microscope. In confocal microscopy, a bright FITC-stained F-actin ring was present in the cytoplasm of cells grown on BAG dish, demonstrating an active functional status. Stimulation of the expression of BMP-2 and other bone mRNAs by bioactive glasses in osteoblastic cells suggests biological involvement of bone related growth factors, peptides and cytokines in bone – bioactive glass bonding.