(479c) Development of a Delivery Strategy for Bioactive Albumin to Aid Bone Regeneration

Serum albumin is one of the most abundant plasma proteins and it is widely used in cell culture. Others have found that albumin production is upregulated during bone healing and the addition of albumin at bone injury sites aids in healing. Further, we have demonstrated that albumin enhances cell adhesion to hydroxyapatite coatings, suggesting its role in bone regeneration may be related to its ability to recruit cells to the injury site. However, the mechanisms behind this activity have not been thoroughly investigated. Based on this prior work, we hypothesized that calcium ions induce a bioactive conformation to albumin that promotes osteoblast adhesion and differentiation.

In this work the influence of calcium ions on the bioactivity of albumin will be discussed. First, molecular dynamics simulations demonstrate that increasing levels of calcium exposure induces an unfolding of the overall albumin structure, without impacting the native secondary structure. Two-dimensional cell adhesion and proliferation investigations demonstrate that increasing calcium exposure levels increases MC3T3-E1 cell adhesion and proliferation, but calcium becomes toxic when it remains in the system at higher levels. Further, the cell integrin mediated binding interactions show that cell adhesion occurs through at least two separate pathways, which have opposite correlation trends with calcium exposure concentration. Finally, results demonstrating the MC3T3-E1 cell adhesion and proliferation to calcium modified albumin delivered from a polyampholyte polymer scaffold confirm that bioactive albumin can be delivered from a polymeric biomaterial. As before, there appears to be a critical calcium concentration threshold, as high levels of calcium begin to impact both the cell attachment and viability, along with the underlying polyampholyte polymer scaffold.

The collective results of this work confirm the hypothesis that calcium impacts the conformation of albumin, leading to enhanced osteoblast adhesion and proliferation. Because the integrin mediated binding pathways demonstrate a calcium concentration dependency, the results also suggest that calcium modified albumin impacts osteoblast differentiation, and confirmatory studies are on-going. Overall, calcium modified albumin shows promise in aiding bone regeneration when delivered via a polyampholyte scaffold.