Vascular endothelial growth factor as a survival factor for human islets: effect of immunosuppressive drugs

Abstract

Aims/hypothesis Rapamycin, part of the immunosuppressive regimen of the Edmonton protocol, has been shown to inhibit vascular endothelial growth factor (VEGF) production and VEGF-mediated survival signalling in tumour cell lines. This study investigates the survival-promoting activities of VEGF in human islets and the effects of rapamycin on islet viability.Materials and methods Levels of VEGF and its receptors in isolated human islets and whole pancreas was determined by western blotting and immunostaining. Islet viability following VEGF or immunosuppressive drug treatment was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Islet VEGF release was measured by ELISA. Mouse islets infected with an adenovirus expressing the gene for VEGF were transplanted syngeneically into streptozotocin-induced diabetic mice, with blood glucose levels measured three times per week. Results Isolated human islets produced multiple isoforms of VEGF and VEGF receptors 1, 2 and 3 and the coreceptor neuropilin 1. Exogenous VEGF (10 ng/ml) prevented human islet death induced by serum starvation, which suggests that VEGF can act as a survival factor for human islets. Transplantation of mouse islets infected with a VEGF-expressing adenovirus in a syngeneic model, improved glycaemic control at day 1 post-transplantation (p< 0.05). Rapamycin at 10 and 100 ng/ml significantly reduced islet VEGF release (by 37±4% and 43±6%, respectively; p<0.05) and at 100 ng/ml reduced islet viability (by 36±9%) and insulin release (by 47±7%, all vs vehicle-treated controls; p<0.05). Tacrolimus had no effect on islet VEGF release or viability. Conclusions/interpretation Our data suggest that rapamycin may have deleterious effects on islet survival posttransplantation, both through a direct effect on islet viability and indirectly through blockade of VEGF-mediated revascularisation.

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

“…These results indicate that incorporation of VEGF may be beneficial for islet metabolism and survival. VEGF has been previously shown to boost MTT metabolism and viability in isolated islets [67]. …”

Self-assembling glucagon-like peptide 1-mimetic peptide amphiphiles for enhanced activity and proliferation of insulin-secreting cells

“…To alleviate these sequelae of inadequate glycemic control and free patients from the burden of daily insulin injection, islet cell transplantation (ICT) has been proposed as a permanent treatment for T1DM[4]. The Edmonton protocol for intrahepatic ICT has achieved insulin independence in up to 80% of patients for a median of 3 years[5, 6] but is limited by the loss of transplanted β-cell mass and function due to immune-mediated and inflammation-induced apoptosis[7, 8], lack of vascularization[9], decreased proliferative potential[10], and impaired insulin secretion[11]. Current approaches to preventing the loss of β-cell mass and function resulting from these deleterious phenomena include the use of biomaterial scaffolds to control the islet microenvironment[12] and the addition of biological functionality to islets through genetic modification[13], substrate immobilization[14], or ligand presentation[15–17].…”

Rapamycin does not adversely affect intrahepatic islet engraftment in mice and improves early islet engraftment in humans

“…As time reveals the somewhat disappointing long-term results of islet transplantation with this protocol, 2 a number of publications have appeared, addressing a possible deleterious role of rapamycin on islet or β-cell engraftment, function, survival and regeneration. [4][5][6][7][8][9][10][11][12] During engraftment, due to its antiangiogenic activities, 13 RAPA could be detrimental for islet survival after transplantation. Islets are transplanted as single islets or islet clusters that are considered avascular after collagenase digestion and isolation.…”