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Elevation of vascular endothelial growth factor production and its effect on revascularization and function of graft islets in diabetic rats.

AIM
To determine whether the elevated vascular endothelial growth factor (VEGF) expression produced by the transfected vascular endothelial cells (VECs) could stimulate angiogenesis of the graft islets and exert its effect on the graft function.


METHODS
Thirty diabetic recipient rats were divided into three groups (n=10 per group). In the control group, 300 IEQ islets were transplanted in each rat under the capsule of the right kidney, which were considered as marginal grafts. In the VEC group, VEC together with the islets were transplanted in each rat. In the VEGF group, VEC transfected by pIRES2-EGFP/VEGF165 plasmid and the islets were transplanted in each rat. Blood glucose and insulin levels were evaluated every other day after operation. Intravenous glucose tolerance test (IVGTT) was performed 10 d after the transplantation. Hematoxylin and eosin (HE) staining was used to evaluate the histological features of the graft islets. Immunohistochemical staining was used to detect insulin-6, VEGF and CD34 (MVD) expression in the graft islets.


RESULTS
Blood glucose and insulin levels in the VEGF group restored to normal 3 d after transplantation. In contrast, diabetic rats receiving the same islets with or without normal VECs displayed moderate hyperglycemia and insulin, without a significant difference between these two groups. IVGTT showed that both the amplitude of blood glucose induction and the kinetics of blood glucose in the VEGF group restored to normal after transplantation. H&E and immunohistochemical staining showed the presence of a large amount of graft islets under the capsule of the kidney, which were positively stained with insulin-6 and VEGF antibodies in the VEGF group. In the cell masses, CD34-stained VECs were observed. The similar masses were also seen in the other two groups, but with a fewer positive cells stained with insulin-6 and CD34 antibodies. No VEGF-positive cells appeared in these groups. Microvessel density (MVD) was significantly higher in the VEGF group compared to the other two groups.


CONCLUSION
Elevated VEGF production by transfected vascular endothelial cells in the site of islet transplantation stimulates angiogenesis of the islet grafts. The accelerated islet revascularization in early stage could improve the outcome of islet transplantation, and enhance the graft survival.