A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

A novel approach for hepatocyte transplantation at the liver surface

Hepatocyte transplantation (HTx) is a promising alternative to liver transplantation; however, poor engraftment remains a major challenge. Although co-transplantation with adipose tissue-derived stromal cells (ADSCs) or islets improves engraftment, exposure of these cells to the portal vein enhances innate immune responses, resulting in a significant loss of hepatocytes. Therefore, we investigated HTx at the liver surface as a novel approach that does not involve the portal vein. Hepatocytes were transplanted onto the liver surface of syngeneic analbuminemic rats with or without ADSCs and/or islets. Serum albumin levels and immunohistochemical staining of the transplanted hepatocytes were evaluated. Hepatocyte engraftment was compared between the liver surface and intraportal groups. To examine the detailed mechanisms behind co-transplantation, co-cultured supernatants were analyzed using multiplex assays, and inhibition tests using neutralizing antibodies were performed. Results showed that islet and ADSC co-transplantation markedly enhanced hepatocyte engraftment at the liver surface (P < 0.01), and its efficiency was comparable to that of intraportal transplantation (P = 0.35). In the co-transplantation group, cells were not necessarily in proximity, suggesting that humoral factors are important. In an in vitro study, hepatocyte function was significantly improved by co-culturing with islets and ADSCs (P < 0.01). Multiplex assays and inhibition tests revealed several important humoral factors, most notably insulin, which promoted hepatocyte engraftment. These findings suggest that HTx at the liver surface, together with crucial factors, may be a novel alternative strategy for intraportal transplantation.

A novel method of pancreatic islet transplantation at the liver surface using a gelatin hydrogel nonwoven fabric

Considering the limitations of intraportal transplantation (Tx), we sought to establish an alternative approach for it-transplanting islets onto the liver surface (LS) by optimizing adipose tissue-derived stem cell (ADSC) co-Tx procedures with a gelatin hydrogel nonwoven fabric (GHNF). In the in vivo study, we examined the use of the GHNF, the effectiveness of islet covering materials, and preferred procedures for ADSC co-Tx using a syngeneic rat model. Immunohistochemical staining was performed to evaluate the extracellular matrix (ECM) expression and angiogenesis. In the in vitro study, we analyzed the culture supernatants to identify crucial factors secreted from ADSCs in different ADSC co-Tx procedures. It was shown that the GHNF should be used to cover the islets but not to embed internally (encapsulate) them. Utilization of the GHNF in LS Tx resulted in significantly better glucose changes (P = 0.0002) and cure rate of diabetic recipients (P = 0.0003) than the use of a common adhesion barrier. Although neovascularization was comparable among groups, ECM reconstitution tended to be higher when the GHNF was used. ADSC co-Tx further enhanced ECM reconstitution only when ADSCs were cultured in the GHNF before islet Tx. Leptin, vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), and several chemokines were identified as candidate factors for enhancing ECM reconstitution (P < 0.001). The inhibition assay using antagonist suggested that leptin might be at least in part responsible for the difference in transplant efficiency in distinct ADSC co-Tx methods. This study showed that the GHNF effectively improved the outcomes of LS islet Tx, mainly due to ECM reconstitution around the islets. Furthermore, we established a novel method of LS islet Tx by combining a GHNF with ADSCs, which is equally effective as intraportal Tx.

A Gelatin Hydrogel Nonwoven Fabric Combined With Adipose Tissue-Derived Stem Cells Enhances Subcutaneous Islet Engraftment

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. We herein investigated whether the addition of adipose tissue-derived stem cells (ADSCs) to GHNF affected the outcome. A silicone spacer sandwiched between two GHNFs with (AG group) or without (GHNF group) ADSCs, or a silicone spacer alone (Silicone group) was implanted into the subcutaneous space of healthy mice at 6 weeks before transplantation, then diabetes was induced 7 days before transplantation. Syngeneic islets were transplanted into the pretreated space. Intraportal transplantation (IPO group) was also performed to compare the transplant efficiency. Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, and inflammatory mediators were evaluated. The results in the subcutaneous transplantation were compared using the Silicone group as a control. The results of the IPO group were also compared with those of the AG group. The AG group showed significantly better blood glucose changes than the Silicone and the IPO groups. The cure rate of AG group (72.7%) was the highest among the groups (GHNF; 40.0%, IPO; 40.0%, Silicone; 0%). The number of vWF-positive vessels in the subcutaneous space of the AG group was significantly higher than that in other groups before transplantation (P < 0.01). Lectin angiography also showed that the same results (P < 0.05). According to the results of the ADSCs tracing, ADSCs did not exist at the transplant site (6 weeks after implantation). The positive rates for laminin and collagen III constructed around the transplanted islets did not differ among groups. Inflammatory mediators were higher in the Silicone group, followed by the AG and GHNF groups. Pretreatment using bioabsorbable scaffolds combined with ADSCs enhanced neovascularization in subcutaneous space, and subcutaneous islet transplantation using GHNF with ADSCs was superior to intraportal islet transplantation.

Reversal of Hyperglycemia by Subcutaneous Islet Engraftment Using an Atelocollagen Sponge as a Scaffold

Type 1 diabetes mellitus (T1DM) affects 8.4 million people worldwide, with patients primarily relying on exogenous insulin injections to maintain blood glucose levels. Islet transplantation via the portal vein has allowed for the direct internal release of insulin by glucose-sensitive islets. However, this method might not be desirable for future cell therapy transplanting pluripotent stem cell-derived β cells, facing challenges including difficulties in cell retrieval and graft loss due to the instant blood-mediated inflammatory reaction (IBMIR). Here, we established a subcutaneous transplantation protocol using an atelocollagen sponge as a scaffold. While the subcutaneous site has many advantages, the lack of a vascular bed limits its application. To address this issue, we performed angiogenesis stimulation at the transplantation site using bFGF absorbed in a gelatin sponge (Spongel), significantly improving the microvascular area. Our in vivo experiments also revealed angiogenesis stimulation is crucial for reversing hyperglycemia in streptozotocin (STZ)-induced diabetic mice. In addition to the angiogenic treatment, an atelocollagen sponge is used to carry the islets and helps avoid graft leakage. With 800 mouse islets delivered by the atelocollagen sponge, the STZ-induced diabetic mice showed a reversal of hyperglycemia and normalized glucose intolerance. Their normoglycemia was maintained until the graft was removed. Analysis of the harvested islet grafts exhibited a high vascularization and preserved morphologies, suggesting that using an atelocollagen sponge as a scaffold helps maintain the viability of the islet grafts.

A Gelatin Hydrogel Nonwoven Fabric Enhances Subcutaneous Islet Engraftment in Rats

Although subcutaneous islet transplantation has many advantages, the subcutaneous space is poor in vessels and transplant efficiency is still low in animal models, except in mice. Subcutaneous islet transplantation using a two-step approach has been proposed, in which a favorable cavity is first prepared using various materials, followed by islet transplantation into the preformed cavity. We previously reported the efficacy of pretreatment using gelatin hydrogel nonwoven fabric (GHNF), and the length of the pretreatment period influenced the results in a mouse model. We investigated whether the preimplantation of GHNF could improve the subcutaneous islet transplantation outcomes in a rat model. GHNF sheets sandwiching a silicone spacer (GHNF group) and silicone spacers without GHNF sheets (control group) were implanted into the subcutaneous space of recipients three weeks before islet transplantation, and diabetes was induced seven days before islet transplantation. Syngeneic islets were transplanted into the space where the silicone spacer was removed. Blood glucose levels, glucose tolerance, immunohistochemistry, and neovascularization were evaluated. The GHNF group showed significantly better blood glucose changes than the control group (p < 0.01). The cure rate was significantly higher in the GHNF group (p < 0.05). The number of vWF-positive vessels was significantly higher in the GHNF group (p < 0.01), and lectin angiography showed the same tendency (p < 0.05). The expression of laminin and collagen III around the transplanted islets was also higher in the GHNF group (p < 0.01). GHNF pretreatment was effective in a rat model, and the main mechanisms might be neovascularization and compensation of the extracellular matrices.