Reversal of Diabetes in Mice with a Bioengineered Islet Implant Incorporating a Type I Collagen Hydrogel and Sustained Release of Vascular Endothelial Growth Factor

Abstract

We have developed a bioengineered implant (BI) to evaluate strategies to promote graft survival and function in models of islet transplantation in mice. The BI, sized for implantation within a fold of intestinal mesentery, consists of a disk-shaped, polyvinyl alcohol sponge infused with a type I collagen hydrogel that contains dispersed donor islets. To promote islet vascularization, the BI incorporates a spherical alginate hydrogel for sustained release of vascular endothelial growth factor (VEGF). BIs that contained 450–500 islets from syngeneic (C57Bl/6) donors and 20 ng of VEGF reversed streptozotocin (STZ)-induced diabetes in 100% of mice (8/8), whereas BIs that contained an equivalent number of islets, but which lacked VEGF, reversed STZ-induced diabetes in only 62.5% of mice (5/8). Between these “+VEGF” and “−VEGF” groups, the time to achieve normoglycemia (8–18 days after implantation) did not differ statistically; however, transitory, postoperative hypoglycemia was markedly reduced in the +VEGF group relative to the −VEGF group. Notably, none of the mice that achieved normoglycemia in these two groups required exogenous insulin therapy once the BIs began to fully regulate levels of blood glucose. Moreover, the transplanted mice responded to glucose challenge in a near-normal manner, as compared to the responses of healthy, nondiabetic (control) mice that had not received STZ. In future studies, the BIs described here will serve as platforms to evaluate the capability of immunomodulatory compounds, delivered locally within the BI, to prevent or reverse diabetes in the setting of autoimmune (type 1) diabetes.

Repurposed biological scaffolds: kidney to pancreas

“…35 While the kidney scaffold's vasculature is more robust and thus superior to nearly all other organs, a potential limitation to the repurposed-tissue strategy is that the collecting system extracellular milieu might not be optimal for pancreatic cells 36,37 without further chemical modification or use of appropriate growth factors. 25 Lack of native pancreatic matrix may be more important when using relatively undifferentiated precursors, 35 as indeed our findings do support the survival of insulinproducing cells.…”

“…Growth factors could be added to the scaffold or the media so as to further enhance vascularization, as has been successful when sustained release of VEGF was incorporated into synthetic collagen hydrogel or other proangiogenic polymer models. 24, 25 The geometry of the peritubular capillaries is also favorable due to its proximity to the tubular structures wherein trans-organ cells can be placed. This is relevant to recent evidence for the existence of crosstalk between cells in kidney capillary and tubule compartments.…”

Engineered VEGF-releasing PEG–MAL hydrogel for pancreatic islet vascularization

“…Addition of VEGF to the implant greatly enhanced the vascularization response in the immediate vicinity of grafted islets. Data from the literature suggests that augmenting islet vascularization with VEGF is beneficial in achieving better long-term islet survival and tighter control of blood glucose homeostasis [73]. …”

IL-10 Induction from Implants Delivering Pancreatic Islets and Hyaluronan

“…Islets were isolated as described previously [30]. Briefly, C57Bl/6 mice of 12–24 weeks age were anesthetized with 2,2,2-tribromoethanol in phosphate-buffered saline (PBS).…”

“…One volume of a stock solution of rat tail native type I collagen in dilute (0.02 N) acetic acid (BD Biosciences) was combined with 1/9 volume of 10-strength NaHCO 3 -saturated Medium 199 (Invitrogen) and sufficient DMEM and normal mouse serum (NMS) to yield a working solution containing 2.5 mg/mL collagen and 10% NMS [30]. The working solution was prepared just prior to assembly of the BIs and kept on ice until needed.…”