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

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 bioactivity 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% SiO2), biocompatible (BCG, 58% SiO2) 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 GO at 14 days. Striking differences in BMP-2 mRNA levels existed between BAG and CO 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. (C) 2001 Elsevier Science Ltd. All rights reserved.