A Nitric Oxide Releasing Biomimetic Nanomatrix for the Revascularization of Pancreatic Islet Grafts
Chdinma P. Anakwenze; Ho-Wook Jun, Ph.D.; Dong Jin Lim; and Adinarayana Andukuri University of Alabama at Birmingham, Birmingham, AL
Scaffolds for successful pancreatic islet cell transplantation are limited by graft failure due to inadequate revascularization. Transplanted islets normally revascularize within 2 weeks of transplantation, but the low oxygen tension and vascular density found in transplanted islets suggest insufficient revascularization. The assembly of a functional islet microvasculature requires the coordinated interactions of islet cells and endothelial cells. As nitric oxide (NO) has previously been shown to promote endothelial cell migration and angiogenesis in ischemic tissues, the goal of this study is to develop a NO releasing peptide amphiphile (PA) nanomatrix that will promote endothelial cell adhesion, and spreading in an islet graft, which in turn will support islet graft revascularization. In light of this goal, PAs containing endothelial cell adhesive ligands (YIGSR) and polylysine (KKKKK) NO donor residues were synthesized using Fmoc chemistry and then combined in a 9:1 (PA-YIGSR:PA-KKKKK) ratio to form PA-YK. PA-YK was then reacted with pure NO to develop PA-YK-NO, an endothelium mimicking NO releasing PA, and then self assembled into nanofibers by solvent evaporation technique. Successful self-assembly was characterized by transmission electron microscopy (TEM) and NO release was profiled using Griess assay. Cell adhesion, and morphology of human umbilical vein endothelial cells (HUVECs) and the MIN-6 pancreatic beta cell line seeded on PA-YK-NO was studied using Live/Dead and Picogreen DNA assay. PA-YK and tissue culture plate were used as control surfaces. NO was successfully released from the nanomatrix in a biphasic manner with an initial burst release followed by a slow sustained release over a period of 30 days. This biomimetic nanomatrix was found to support the spreading and adhesion of HUVECs while simultaneously promoting supporting the growth of the MIN-6 cell line. The NO release profile is ideal for the recruitment of endothelial cells during the subsequent 2 weeks after transplantation when revascularization normally takes place. Our data also shows that this NO releasing PA nanomatrix supports the growth of MIN-6 cells and the recruitment of endothelial cells and therefore has great potential for improving the revascularization of islet cell transplants, thus leading to successful clinical outcomes. Future experiments will examine the potential for PA-YK-NO to increase pancreatic ß cell adhesion, proliferation and insulin secretion.