Ideal Duration of Pretreatment Using a Gelatin Hydrogel Nonwoven Fabric Prior to Subcutaneous Islet Transplantation

Abstract

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously revealed that a gelatin hydrogel nonwoven fabric (GHNF) markedly improved subcutaneous islet engraftment in comparison with intraportal islet transplantation. We herein investigated whether the duration of pretreatment using GHNF affected the outcome of subcutaneous islet transplantation. A silicone spacer with GHNF was implanted into the subcutaneous space of healthy mice at 2, 4, 6, or 8 weeks before transplantation, and then diabetes was induced 7 days before transplantation. Syngeneic islets were transplanted into the pretreated space. Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, inflammatory mediators, and gene expression were evaluated. The 6-week group showed significantly better blood glucose changes than the other groups ( P < 0.05). The cure rate of the 6-week group (60.0%) was the highest among the groups (2-week = 0%, 4-week = 50.0%, 8-week = 15.4%). The number of von Willebrand factor (vWF)–positive vessels in the 6-week group was significantly higher than in the other groups at pre-islet and post-islet transplantation ( P < 0.01 [vs 2-and 4-week groups] and P < 0.05 [vs all other groups], respectively). Notably, this beneficial effect was also observed when GHNF was implanted into diabetic mice injected with streptozotocin 7 days before GHNF implantation. The positive rates for laminin, collagen III, and collagen IV increased as the duration of pretreatment became longer and were significantly higher in the 8-week group ( P < 0.01). Inflammatory mediators, including interleukin (IL)-1b, granulocyte colony-stimulating factor (G-CSF), and interferon (IFN)-γ, were gradually downregulated according to the duration of GHNF pretreatment and re-elevated in the 8-week group. Taken together, the duration of GHNF pretreatment apparently had an impact on the outcomes of subcutaneous islet transplantation, and 6 weeks appeared to be the ideal duration. Islet graft revascularization, extracellular matrix compensation of the islet capsule, and the inflammatory status at the subcutaneous space would be crucial factors for successful subcutaneous islet transplantation.

A Gelatin Hydrogel Nonwoven Fabric Enhances Subcutaneous Islet Engraftment in Rats

“…Patikova et al reported that the ideal timing of islet transplantation, when the capillary network and collagen synthesis are maximized, is important for islet engraftment [ 27 ]. We also reported that the length of the GHNF-pretreatment period had a strong impact on the results of subcutaneous islet transplantation and that six weeks was the best duration when neovascularization was maximized and inflammatory reactions were minimized in a mouse model [ 12 ]. However, the extent of absorption of GHNF varies among animal species.…”

“…GHNF has been reported to be absorbed in vivo and replaced by recipient cells and ECM [ 17 ]. We previously reported that M2 macrophages, which have anti-inflammatory properties [ 32 ], accumulated between the gaps of GHNF [ 12 ]. The concentration of insulin-like growth factor-2, which maintains islet viability and has anti-apoptotic effects on islets [ 33 , 34 ], in the subcutaneous space, is high in the GHNF group in a mouse model [ 14 ].…”

“…Two GHNF sheets sandwiching a silicone spacer (26 mm diameter, 0.5 mm thickness) were placed into the left dorsal subcutaneous space 3 weeks before islet implantation (GHNF group), and a silicone spacer alone was also arranged in the same way (control group). The duration of pretreatment was determined according to a previous report in mice by comparison with hematoxylin–eosin staining [ 12 ]. GHNF and silicone spacers were implanted into healthy rats and STZ was injected 7 days before islet transplantation.…”

“…These approaches have several advantages: namely, new vessels for supporting islet grafts are induced in advance and foreign body responses to materials are reduced when the islets are transplanted. We recently reported that new vessels in the subcutaneous tissues continuously enriched until six weeks after the placement of materials [ 12 ]. We also demonstrated that inflammation in the subcutaneous space was extremely severe until two weeks after the implantation of the materials and that islet engraftment tended to be poor if the islets were transplanted during this period.…”

“…It is known to degrade gradually and thereafter is absorbed in vivo and finally replaced by the host tissues; therefore, it can be an ideal pretreatment material for our purpose since there is no need for removal. In fact, we could effectively restore diabetic mice with a marginal dose of subcutaneously transplanted islets [ 12 ]. Moreover, the results of subcutaneous islet transplantation using GHNF combined with adipose tissue-derived stem cells were surprisingly superior to those of intraportal transplantation, which is the current standard procedure (manuscript submitted).…”