The influence of combined trophic factors on the success of fetal pancreas grafts

Background. Fetal pancreas (FP) has the capacity for abundant proliferation and beta cell differentiation. Insulin-like growth factor-1 (IGF-1) promotes FP engraftment in the i.m. site and reversal of diabetes in a rodent model. However, reversal of diabetes by an FP transplant in rats under the influence of IGF-1 is still an inefficient process requiring multiple FP grafts and a prolonged latent period. Numerous other growth and differentiation factors, which include platelet derived growth factor (PDGF), vascular endothelial growth factor, endothelial cell growth factor-alpha and pancreatic islet neogenesis-associated protein, have been implicated in beta cell neogenesis and proliferation. We have analyzed the in vivo role of these growth factors in FP engraftment and reversal of streptozotocin-induced diabetes in rats. Methods. IGF-1 alone or in combination with other trophic factors was locally administered to eight FP isografts in the thigh muscle of diabetic rats. Results. Diabetes was reversed in a mean of 60 ± 26 days in 11 of 11 animals treated with IGF-1. PDGF alone did not promote reversal of diabetes; however, PDGF + IGF-1 resulted in euglycemia in 6 of 6, with a mean of 36 ± 14 days (P < 0.05). Islet neogenesis-associated protein + IGF-1 resulted in reversal of diabetes in 6 of 6 rats with a mean interval of 50 ± 10 days. Vascular endothelial growth factor or endothelial cell growth factor-alpha + IGF-1 provided no advantage compared with IGF-1 alone. Conclusions. These results demonstrate that IGF-1 is a potent trophic factor for transplanted FP and that PDGF acts synergistically with IGF-1 to promote reversal of diabetes by transplanting FP.