伊藤 泰平

The aims of this study were to produce mesobiliverdin IX alpha, an analog of anti-inflammatory biliverdin IX alpha, and to test its ability to enhance rat pancreatic islet yield for allograft transplantation into diabetic recipients. Mesobiliverdin IX alpha was synthesized from phycocyanobilin derived from cyanobacteria, and its identity and purity were analyzed by chromatographic and spectroscopic methods. Mesobiliverdin IX alpha was a substrate for human NADPH biliverdin reductase. Excised Lewis rat pancreata infused with mesobiliverdin IX alpha and biliverdin IX alpha-HCl (1-100 mu M) yielded islet equivalents as high as 86.7 and 36.5%, respectively, above those from non-treated controls, and the islets showed a high degree of viability based on dithizone staining. When transplanted into livers of streptozotocin-induced diabetic rats, islets from pancreata infused with mesobiliverdin IX alpha lowered non-fasting blood glucose (BG) levels in 55.6% of the recipients and in 22.2% of control recipients. In intravenous glucose tolerance tests, fasting BG levels of 56 post-operative day recipients with islets from mesobiliverdin IX alpha infused pancreata were lower than those for controls and showed responses that indicate recovery of insulin-dependent function. In conclusion, mesobiliverdin IX alpha infusion of pancreata enhanced yields of functional islets capable of reversing insulin dysfunction in diabetic recipients. Since its production is scalable, mesobiliverdin IX alpha has clinical potential as a protectant of pancreatic islets for allograft transplantation.

Background. Bone marrow-derived mesenchymal stem cells (MSCs) are known to produce vascular endothelial growth factor. We hypothesize that co-transplantation of MSCs and islets promotes revascularization and improves islet graft function. Methods. Lewis rat islets were infused into the liver of streptozotocin-diabetic syngeneic recipients or transplanted under the renal capsule of nonobese diabetic severe combined immunodeficiency (NOD SCID) mice with MSCs isolated from Lewis bone marrow and expanded in culture. Results. Co-transplantation of 500 islets and 10(7) MSCs (islet-MSCs) reversed diabetes in all eight recipients, whereas islet-alone transplantation achieved euglycemia in 3 of 10 recipients. With 300 islets, five of nine islet-MSCs and 1 of 10 islets-alone recipients reversed diabetes. Results of intravenous glucose tolerance tests performed on day 56 were significantly better in islet-MSCs than islet-alone recipients. One week after transplantation, well-preserved islet structure and higher number of capillaries were found in the liver of islet-MSCs recipients, whereas islet-alone grafts were fragmented with very few capillaries. Islets showed a similar morphology when transplanted with MSCs in nonobese diabetic severe combined immunodeficiency mice with a significantly higher capillary per beta-cell ratio than that in islet-alone grafts (0.135 +/- 0.046 vs. 0.052 +/- 0.028 capillary segments per beta-cell, P<0.01). One week after transplantation, islets were surrounded by MSCs labeled with carboxyfluorescein succinimidyl ester or Qdot nanocrystals, and some labeled MSCs positively stained for vascular endothelial growth factor or von Willebrand factor. Conclusion. Our results demonstrate the improvement of islet graft morphology and function by co-transplantation with MSCs. This improvement is attributable, at least in part, to the promotion of graft revascularization mediated by MSCs.