Mechanisms of Enhanced Osteoblast Adhesion on Nanophase Alumina Involve Vitronectin

TLDR

The study examined how vitronectin’s concentration, conformation, and bioactivity on nanophase alumina influence osteoblast adhesion. The authors used surface‑enhanced Raman scattering to assess vitronectin conformation on nanophase alumina. Vitronectin adsorbed at higher concentrations on nanophase alumina, with increased calcium and reduced apolipoprotein A‑I promoting its unfolding and exposure of adhesive epitopes, leading to dose‑dependent osteoblast adhesion that can be inhibited by blocking cell‑surface receptors.

Abstract

The role, including concentration, conformation, and bioactivity, of adsorbed vitronectin in enhancing osteoblast adhesion on nanophase alumina was investigated in the present study. Vitronectin adsorbed in a competitive environment in the highest concentration on nanophase alumina compared to conventional alumina. Enhanced adsorption of vitronectin on nanophase alumina was possibly due to decreased adsorption of apolipoprotein A-I and/or increased adsorption of calcium on nanophase alumina. In a novel manner, the present study utilized surface-enhanced Raman scattering (SERS) to determine the conformation of vitronectin adsorbed on nanophase alumina. These results provided the first evidence of increased unfolding of vitronectin adsorbed on nanophase alumina. Increased adsorption of calcium on nanophase alumina may affect the conformation of adsorbed vitronectin specifically to promote unfolding of the macromolecule to expose cell-adhesive epitopes recognized by specific cell-membrane receptors. Results of the present study also provided evidence of dose-dependent inhibition of osteoblast adhesion on nanophase alumina pretreated with vitronectin following preincubation (and thus blocking respective cell-membrane receptors) with either Arginine-Glycine-Aspartic Acid-Serine (RGDS) or Lysine-Arginine-Serine-Arginine (KRSR). These events, namely, enhanced vitronectin adsorption, comformation, and bioactivity, may explain the increased osteoblast adhesion on nanophase alumina.