Porcine Neonatal Pancreatic Cell Clusters Maintain Their Multipotency in Culture and After Transplantation

Magnetic Resonance Imaging of Transplanted Porcine Neonatal Pancreatic Cell Clusters Labeled with Exendin-4-Conjugated Manganese Magnetism-Engineered Iron Oxide Nanoparticles

Recently, we have shown that manganese magnetism-engineered iron oxide nanoparticles (MnMEIO NPs) conjugated with exendin-4 (Ex4) act as a contrast agent that directly trace implanted mouse islet β-cells by magnetic resonance imaging (MRI). Here we further advanced this technology to track implanted porcine neonatal pancreatic cell clusters (NPCCs) containing ducts, endocrine, and exocrine cells. NPCCs from one-day-old neonatal pigs were isolated, cultured for three days, and then incubated overnight with MnMEIO-Ex4 NPs. Binding of NPCCs and MnMEIO-Ex4 NPs was confirmed with Prussian blue staining in vitro prior to the transplantation of 2000 MnMEIO-Ex4 NP-labeled NPCCs beneath the left renal capsule of six nondiabetic nude mice. The 7.0 T MRI on recipients revealed persistent hypointense areas at implantation sites for up to 54 days. The MR signal intensity of the graft on left kidney reduced 62–88% compared to the mirror areas on the contralateral kidney. Histological studies showed colocalization of insulin/iron and SOX9/iron staining in NPCC grafts, indicating that MnMEIO-Ex4 NPs were taken up by mature β-cells and pancreatic progenitors. We conclude that MnMEIO-Ex4 NPs are excellent contrast agents for detecting and long-term monitoring implanted NPCCs by MRI.

Optimization of an O2-balanced bioartificial pancreas for type 1 diabetes using statistical design of experiment

A bioartificial pancreas (BAP) encapsulating high pancreatic islets concentration is a promising alternative for type 1 diabetes therapy. However, the main limitation of this approach is O2 supply, especially until graft neovascularization. Here, we described a methodology to design an optimal O2-balanced BAP using statistical design of experiment (DoE). A full factorial DoE was first performed to screen two O2-technologies on their ability to preserve pseudo-islet viability and function under hypoxia and normoxia. Then, response surface methodology was used to define the optimal O2-carrier and islet seeding concentrations to maximize the number of viable pseudo-islets in the BAP containing an O2-generator under hypoxia. Monitoring of viability, function and maturation of neonatal pig islets for 15 days in vitro demonstrated the efficiency of the optimal O2-balanced BAP. The findings should allow the design of a more realistic BAP for humans with high islets concentration by maintaining the O2 balance in the device.

Butyrate and Class I Histone Deacetylase Inhibitors Promote Differentiation of Neonatal Porcine Islet Cells into Beta Cells

Neonatal porcine islets-like clusters (NPICCs) are a promising source for cell therapy of type 1 diabetes. Freshly isolated NPICCs are composed of progenitor cells and endocrine cells, which undergo a maturation process lasting several weeks until the normal beta cell function has developed. Here, we investigated the effects of short-chain fatty acids on the maturation of islet cells isolated from two to three day-old piglets. NPICCs were cultivated with acetate, butyrate and propionate (0–2000 µM) for one to eight days. Incubation with butyrate resulted in a significant upregulation of insulin gene expression and an increased beta cell number, whereas acetate or propionate had only marginal effects. Treatment with specific inhibitors of G-protein-coupled receptor GPR41 (β-hydroxybutyrate) and/or GPR43 (GPLG0974) did not abolish butyrate induced insulin expression. However, incubation of NPICCs with class I histone deacetylase inhibitors (HDACi) mocetinostat and MS275, but not selective class II HDACi (TMP269, MC1568) mimicked the butyrate effect on beta cell differentiation. Our study revealed that butyrate treatment has the capacity to increase the number of beta cells, which may be predominantly mediated through its HDAC inhibitory activity. Butyrate and specific class I HDAC inhibitors may represent beneficial supplements to promote differentiation of neonatal porcine islet cells towards beta cells for cell replacement therapies.

Magnetic Resonance Imaging of Transplanted Porcine Neonatal Pancreatic Cell Clusters Labeled with Chitosan-Coated Superparamagnetic Iron Oxide Nanoparticles in Mice

Neonatal pancreatic cell clusters (NPCCs) are potential tissues for the treatment of diabetes. Different from adult cells, they continuously proliferate and differentiate after transplantation. In this study, we utilized magnetic resonance imaging (MRI) to detect and monitor implanted NPCCs. NPCCs were isolated from one-day-old neonatal pigs, cultured for three days, and then incubated overnight with the contrast agent chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles. In vitro, Prussian blue staining and MR scans of CSPIO-labeled NPCCs were performed. In vivo, we transplanted 2000 CSPIO-labeled NPCCs under the kidney capsule of nondiabetic nude mice. Recipients were scanned with 7.0T MRI. Grafts were removed for histology with insulin and Prussian blue staining. After being incubated overnight with CSPIO, NPCCs showed positive iron staining and appeared as dark spots on MR scans. After transplantation of CSPIO-labeled NPCCs, persistent hypointense areas were observed at recipients’ implant sites for up to 54 days. Moreover, histology showed colocalization of the insulin and iron staining in 15-, 51- and 55-day NPCC grafts. Our results indicate that transplanted NPCCs survived and differentiated to β cells after transplantation, and that MRI is a useful tool for the detection and monitoring of CSPIO-labeled NPCC grafts.

Dose-dependent effects of necrostatin-1 supplementation to tissue culture media of young porcine islets

Previous studies have shown that necrostatin-1 (Nec-1) supplementation improved the viability of murine islets following exposure to nitric oxide, increased the survival of human islets during hypoxic culture, and augmented the maturation of pre-weaned porcine islets (PPIs) after 7 days of tissue culture. A limitation of these studies is that only one concentration of Nec-1 was used, and no studies have determined the optimal dose of Nec-1 for PPIs. Thus, the present study examined the effects of Nec-1 on PPIs at four different doses—0, 25, 50, 100, and 200 μM—after 7 days of tissue culture when supplemented on day 3. PPIs were isolated from pancreata of pre-weaned Yorkshire piglets (8–15 days old) and cultured in a specific islet maturation media added with Nec-1 on day 3 of tissue culture at 4 different doses—0, 25, 50, 100, and 200 μM (n = 6 for each dose). After 7 days of tissue culture, islets were assessed for recovery, viability, endocrine cellular content, GLUT2 expression in beta cells, and insulin secretion after glucose challenge. Nec-1 did not affect the viability of both intact islets and dissociated islets cells during tissue culture regardless of doses. Islets cultured in media supplemented with Nec-1 at 100 μM, but not 25, 50, or 200 μM, had a significantly higher recovery, composition of endocrine cells, GLUT2 expression in beta cells, and insulin secretion capacity than control islets cultured in media without Nec-1 supplementation. Moreover, culturing islets in 200 μM Nec-1 supplemented media not only failed to improve the insulin release but resulted in a lower glucose-induced insulin stimulation index compared to islets cultured in media added with 100 μM Nec-1. Xenotransplantation using porcine islets continues to demonstrate scientific advances to justify this area of research. Our findings indicate that Nec-1 supplementation at 100 μM was most effective to enhance the in vitro maturation of PPIs during tissue culture.

Recent progress in porcine islet isolation, culture and engraftment strategies for xenotransplantation

PURPOSE OF REVIEW

Xenotransplantation of porcine islets is a realistic option to restore β-cell function in type 1 diabetic patients. Among other factors, such as islet donor age (fetal, neonatal and adult) and genotype (wild type and genetically modified), choice of the transplantation site, and immune protection of the islets, efficient strategies for islet isolation, culture and engraftment are critical for the success of islet xenotransplantation.

RECENT FINDINGS

Neonatal porcine islets (NPIs) are immature at isolation and need to be matured in vitro or in vivo before they become fully functional. Recent developments include a scalable protocol for isolation of clinically relevant batches of NPIs and a stepwise differentiation protocol for directed maturation of NPIs. In addition, different sources of mesenchymal stem cells were shown to support survival and functional maturation of NPIs in vitro and in various transplantation models in vivo.

SUMMARY

A plethora of different culture media and supplements have been tested; however, a unique best culture system for NPIs is still missing. New insights, for example from single-cell analyses of islets or from stem cell differentiation toward β cells may help to optimize culture of porcine islets for xenotransplantation in an evidence-based manner.

Will Genetic Engineering Carry Xenotransplantation of Pig Islets to the Clinic?

PURPOSE OF REVIEW

Porcine islets represent a potentially attractive beta-cell source for xenotransplantation into patients with type 1 diabetes, who are not eligible to islet allo-transplantation due to a lack of suitable human donor organs. Recent progress in genetic engineering/gene editing of donor pigs provides new opportunities to overcome rejection of xeno-islets, to improve their engraftment and insulin secretion capacity, and to reduce the risk for transmission of porcine endogenous retroviruses. This review summarizes the current issues and progress in islet xenotransplantation with special emphasis on genetically modified/gene edited donor pigs.

RECENT FINDINGS

Attempts to overcome acute rejection of xeno-islets, especially after intraportal transplantation into the liver, include the genetic elimination of specific carbohydrate antigens such as αGal, Neu5Gc, and Sd(a) for which humans and-in part-non-human primates have natural antibodies that bind to these targets leading to activation of complement and coagulation. A complementary approach is the expression of one or more human complement regulatory proteins (hCD46, hCD55, hCD59). Transgenic attempts to overcome cellular rejection of islet xenotransplants include the expression of proteins that inhibit co-stimulation of T cells. Expression of glucagon-like peptide-1 and M3 muscarinic receptors has been shown to increase the insulin secretion of virally transduced porcine islets in vitro and it will be interesting to see the effects of these modifications in transgenic pigs and islet products derived from them. Genome-wide inactivation of porcine endogenous retrovirus (PERV) integrants by mutating their pol genes using CRISPR/Cas9 is a recent approach to reduce the risk for PERV transmission by xeno-islets. Genetic engineering/gene editing of xeno-islet donor pigs facilitated major progress towards clinical islet xenotransplantation. The required set of genetic modifications will depend on the source of islets (fetal/neonatal vs. adult), the mode of delivery (encapsulated vs. free), and the transplantation site.