Noninvasive evaluation of the vascular response to transplantation of alginate encapsulated islets using the dorsal skin-fold model.

Alginate encapsulation reduces the risk of transplant rejection by evading immune-mediated cell injury and rejection; however, poor vascular perfusion results in graft failure. Since existing imaging models are incapable of quantifying the vascular response to biomaterial implants after transplantation, in this study, we demonstrate the use of in vivo laser speckle imaging (LSI) and wide-field functional imaging (WiFI) to monitor the microvascular environment surrounding biomaterial implants. The vascular response to two islet-containing biomaterial encapsulation devices, alginate microcapsules and a high-guluronate alginate sheet, was studied and compared after implantation into the mouse dorsal window chamber (N = 4 per implant group). Images obtained over a 14-day period using LSI and WiFI were analyzed using algorithms to quantify blood flow, hemoglobin oxygen saturation and vascular density. Using our method, we were able to monitor the changes in the peri-implant microvasculature noninvasively without the use of fluorescent dyes. Significant changes in blood flow, hemoglobin oxygen saturation and vascular density were noted as early as the first week post-transplant. The dorsal window chamber model enables comparison of host responses to transplanted biomaterials. Future experiments will study the effect of changes in alginate composition on the vascular and immune responses.

Young porcine endocrine pancreatic islets cultured in fibrin show improved resistance toward hydrogen peroxide.

AIM: To study the protective effect of a fibrin scaffold toward embedded young porcine endocrine pancreatic islets from hydrogen peroxide within the context of islet encapsulation in transplantation. METHODS: After isolation and in vitro maturation, groups of 200 young porcine islet equivalents (IEQ) were embedded in a 200 µL fibrin gel and exposed to 2 concentrations (10 and 100 µM) of hydrogen peroxide (H2O2) to investigate the ability of fibrin to protect islets against apoptotic stimuli. As a control, young porcine islets were seeded in tissue culture polystyrene (TCPS) well plates and exposed to the same H2O2 concentrations. Islet integrity, viability and function were then investigated. RESULTS: Morphologically, the integrity of islets embedded in fibrin gels was better preserved compared with that of islets cultured in TCPS plates, when exposed to H2O2. Immunofluorescence staining showed that insulin and glucagon expression was higher in islets cultured in fibrin. Overall, H2O2 incubation led to decreased insulin and glucagon expression. A TUNEL assay revealed elevated numbers of apoptotic cells for islets cultured in TCPS plates when compared with those embedded in fibrin. Islets cultured in TCPS plates and exposed to H2O2 had diminished ability to secrete insulin in response to glucose stimulation, whereas islets embedded in fibrin maintained their glucose responsiveness. Insulin trapped in fibrin was extracted and quantified, revealing insulin in the extract. CONCLUSIONS/INTERPRETATION: Fibrin has a protective effect on young porcine endocrine pancreatic islets exposed to hydrogen peroxide.

GPR54 peptide agonists stimulate insulin secretion from murine, porcine and human islets.

This study was designed to determine the effects of 10 and 13 amino acid forms of kisspeptin on dynamic insulin secretion from mammalian islets since it is not clear from published data whether the shorter peptide is stimulatory while the longer peptide inhibits insulin release. Insulin secretion was measured by radioimmunoassay following perifusion of human, pig, rat and mouse isolated islets with kisspeptin-10 or kisspeptin-13 in the presence of 20 mM glucose. Both peptides stimulated rapid, reversible potentiation of glucose-stimulated insulin secretion from islets of all species tested. These data indicate that both kisspeptin-10 and kisspeptin-13, which is an extension of kisspeptin-10 by three amino acids, act directly at islet ß-cells of various species to potentiate insulin secretion, and suggest that inhibitory effects reported in earlier studies may reflect differences in experimental protocols.