Effect of silicon on the osteogenesis of human osteoblasts

PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 1999 (Prosthodontics).Includes bibliographical references (leavaes 94-105).Bioactive glasses mainly composed of silicon (Si), calcium (Ca), and phosphorous (P) have been frequently used as synthetic bone graft material. The mechanism, however, underlying the osteogenic effect of bioactive glass still remains largely unknown. The objective of this in vitro study was to test the effect of conditioned medium with the major components of bioglass on medium pH change, cell attachment, proliferation, and osteogenetic activities. Normal human osteoblast cell cultures were established by harvesting alveolar bone obtained during tooth extraction of impacted third molar. Osteoblast cells were cultured in the medium supplemented with Si (100, 50, 10ppm) alone; and its combinations with Ca (33, 1.6.7, 3.3 ppm) and/or P (16.7, 8.3, 1.7 ppm) for three different time intervals at 16 hours, 12 and 20 days. The regular medium which already contains physiologic range of Ca and P was used as a control in this study. The culture medium was measured for pH changes. Cell attachment efficiency and proliferation rate were examined by measuring the optical density of crystal violet dye. Alkaline phosphatase (ALP) activity of the culture was measured using the p-nitrophenol reaction. [125]I radioisotope was used for labeling the expression of osteocalcin (OC). Alizarin red S staining was used to measure the amount of mineralization. Mean pH change decreased when the ce11s were cultured for a longer period. In addition, the various medium did not affect the cell attachment rate. However, silicon concentration did play a role in osteogenesis. In ce11 proliferation rate, SICP (100 ppm Si, 33 ppm Ca, 16.7 ppm P) showed significantly higher rate at 12 days of culture (p=0.03) and at 20 days of culture (p=0.0008). Alkaline phosphatase activities were significantly different at 12 days of culture (P=3.09x10[-12]) and 20 days of culture (P=1.07X10[-9]) in a dose-dependent manner. SICP showed highest ALP activity at both 12, 20 days of culture. Osteocalcin expressions were significantly different at 12 days of culture (P=l.07xl0[3]) and 20 days of culture (P=3.83x10[-5]) in a dose-dependent manner with highest value in SICP. Mineralization was significantly different at 12 days of culture (p=5.02xl0[-11]) and 20 days of culture (p=8.17xl0[-15]) in a dose-dependent manner. SICP had the highest value at both 12, 20 days of culture. This result demonstrated the important role of Si in osteogenesis, and how the combination of the three ions can multiply osteogenic activity. Future study of silicon, calcium, and phosphorous is recommended, to clarify the relationship between osteogenesis and these materials at the cellular level