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 bioac tive glasses is thought to be the principal reaction for bone-bioactive gla ss bonding. The contribution of biological molecules on cell-bioactive glas s interaction is largely unknown. To further analyze the mechanisms involve d 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 ma de of bioactive (BAG, 53% SiO2), biocompatible (BCG, 58% SiO2) and control (G0) glasses were extensively conditioned with phosphate buffer and DMEM me dium 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 i n Col-I mRNA levels in cells grown on the two bioactive glasses when compar ed 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 als o 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 b etween 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 stainin g were mostly seen on BAG plates under a light microscope. In confocal micr oscopy, a bright FITC-stained F-actin ring was present in the cytoplasm of cells grown on BAG dish, demonstrating an active Functional status. Stimula tion of the expression of BMP-2 and other bone mRNAs by bioactive glasses i n osteoblastic cells suggests biological involvement of bone related growth factors, peptides and cytokines in bone - bioactive glass bonding. (C) 200 1 Elsevier Science Ltd. All rights reserved.