title: Effects of exogenous phosphorus and silicon on osteoblast differentiation at the interface with bioactive ceramics.
abstract: In this study, we have investigated the effects of dissolved phosphorus and silicon on osteoblast differentiation in vitro. Neonatal rat calvarial osteoblasts were seeded on silica-calcium phosphate composites (SCPCS), hydroxyapatite (HA-200), and tissue culture polystyrene (TCPS) and incubated over 4 days in media containing 0 {minimal essential medium [MEM] (-)} or 3 mM β-glycerophosphate [MEM (+)]. Inductively coupled plasma analysis showed that P-content in original MEM (+) was 225% higher than that in MEM (-). Moreover, P-content in MEM (+) significantly increased to 3.4-4.4 mM and 3.6-4.7 mM after 2 and 4 days incubation with SCPC, respectively, owing to material dissolution and exogenous phosphate supplementation. In contrast, P-content in MEM (+) showed no change upon incubation with HA or TCPS. The P-content in MEM (-) incubated with SCPC was considerably lower than that in MEM (+). SCPC exhibited controlled Si-release in cell culture media [MEM (-) or MEM (+)], with Si-rich SCPC showing a significantly greater dissolution than Si-poor SCPC. Moreover, SCPC, unlike HA, demonstrated a cell- and solution-mediated dissolution over 4 days. Quantitative real-time PCR showed that in MEM (-), osteocalcin and osteopontin mRNA expression on Si-rich SCPC was significantly greater than that on HA, suggesting that Si plays an important role in enhancing bone-cell differentiation. However, osteoblast phenotypic expression on SCPC was significantly decreased after 4 days incubation in MEM (+), indicating that sustained exposure to elevated P-levels in the media can downregulate osteoblast function. Our results demonstrate that the controlled dissolution of SCPC provides a natural stimulus for bone-cell differentiation in vitro and could obviate the need of exogenous phosphate supplementation.
authors.affiliation: Biomet Inc, 56 E Bell Drive, Warsaw, Indiana 46582, USA.
authors.forename: Gautam
authors.initials: G
authors.lastname: Gupta
authors.forename: Sreenatha
authors.initials: S
authors.lastname: Kirakodu
authors.forename: Ahmed
authors.initials: A
authors.lastname: El-Ghannam
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D002516:Ceramics / Q000737:chemistry*; D015870:Gene Expression; D005994:Glycerophosphates / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D010758:Phosphorus / Q000494:pharmacology*; D051381:Rats; D012825:Silicon / Q000494:pharmacology*; D054457:Tissue Scaffolds
chemical_list: D005994:Glycerophosphates; D010758:Phosphorus; C031463:beta-glycerophosphoric acid; D012825:Silicon