Sustained delivery of the angiogenic QK peptide through the use of polyglutamate domains to control peptide release from bone graft materials

Angiogenesis plays a pivotal role in tissue regeneration following bone-grafting procedures; however, nonautogenous graft materials typically lack critical angiogenic growth factors. While much research has focused on modifying grafts with angiogenic factors, controlled delivery of these molecules remains a challenge. The current study describes a method for sustained delivery of an angiogenic peptide from hydroxyapatite (HA), a common alloplast material. Specifically, VEGF-derived QK peptides were synthesized with polyglutamate domains containing varying numbers of glutamates. The rate of peptide release from HA inversely correlated with glutamate number, with diglutamate-QK (E2-QK) released first, followed by tetraglutamate-QK (E4-QK), and finally, heptaglutamate-QK (E7-QK). By coating HA with a mixture of these peptides, termed, PGM-QK (polyglutamate-modified mixture), sequential peptide release was achieved, enabling gradient QK delivery. To evaluate bioactivity, HA disks were coated with PGM-QK and then placed in fresh media for 6 days. Media containing the released peptides was collected at varying time intervals and placed on human umbilical vein endothelial cells (HUVECs). Cells were evaluated for activation of angiogenic signaling pathways (ERK and Akt) and cell migration. Results showed that QK peptides were continuously released over the 6-day interval, and maintained their capacity to activate HUVECs. These findings point to a new approach for gradient delivery of an angiogenic stimulus.