Improved yield of canine islet isolation from deceased donors

The Future of Diabetes Therapies: New Insulins and Insulin Delivery Systems, Glucagon-Like Peptide 1 Analogs, and Sodium-Glucose Cotransporter Type 2 Inhibitors, and Beta Cell Replacement Therapy

As the prevalence of diabetes mellitus increases, so too does the number of available treatment modalities. Many diabetic therapies available in human medicine or on the horizon could hold promise in the management of small animal diabetes. However, it is important to consider how species differences in pathophysiology, management practices and goals, and lifestyle may affect the translation of such treatment modalities for veterinary use. This review article aimed to familiarize veterinarians with the more promising novel diabetic therapies and explore their possible applications in the treatment of canine and feline diabetes mellitus.

In vitro generation of transplantable insulin-producing cells from canine adipose-derived mesenchymal stem cells

Canine mesenchymal stem cells (cMSCs) have potential applications for regenerative therapy, including the generation of insulin-producing cells (IPCs) for studying and treating diabetes. In this study, we established a useful protocol for generating IPCs from canine adipose mesenchymal stem cells (cAD-MSCs). Subsequently, in vitro preservation of pluronic F127-coated alginate (ALGPA)-encapsulated cAD-MSC-derived IPCs was performed to verify ready-to-use IPCs. IPCs were induced from cAD-MSCs with the modulated three-stepwise protocol. The first step of definitive endoderm (DE) induction showed that the cooperation of Chir99021 and Activin A created the effective production of Sox17-expressed DE cells. The second step for pancreatic endocrine (PE) progenitor induction from DE indicated that the treatment with taurine, retinoic acid, FGF2, EGF, TGFβ inhibitor, dorsomorphin, nicotinamide, and DAPT showed the significant upregulation of the pancreatic endocrine precursor markers Pdx1 and Ngn3. The last step of IPC production, the combination of taurine, nicotinamide, Glp-1, forskolin, PI3K inhibitor, and TGFβ inhibitor, yielded efficiently functional IPCs from PE precursors. Afterward, the maintenance of ALGPA-encapsulated cAD-MSC-derived IPCs with VSCBIC-1, a specialized medium, enhanced IPC properties. Conclusion, the modulated three-stepwise protocol generates the functional IPCs. Together, the encapsulation of cAD-MSC-derived IPCs and the cultivation with VSCBIC-1 enrich the maturation of generated IPCs.

PEGDA microencapsulated allogeneic islets reverse canine diabetes without immunosuppression

Background

Protection of islets without systemic immunosuppression has been a long-sought goal in the islet transplant field. We conducted a pilot biocompatibility/safety study in healthy dogs followed by a dose-finding efficacy study in diabetic dogs using polyethylene glycol diacrylate (PEGDA) microencapsulated allogeneic canine islets.

Methods

Prior to the transplants, characterization of the canine islets included the calculations determining the average cell number/islet equivalent. Following measurements of purity, insulin secretion, and insulin, DNA and ATP content, the islets were encapsulated and transplanted interperitoneally into dogs via a catheter, which predominantly attached to the omentum. In the healthy dogs, half of the microspheres injected contained canine islets, the other half of the omentum received empty PEGDA microspheres.

Results

In the biocompatibility study, healthy dogs received increasing doses of cells up to 1.7 M cells/kg body weight, yet no hypoglycemic events were recorded and the dogs presented with no adverse events. At necropsy the microspheres were identified and described as clear with attachment to the omentum. Several of the blood chemistry values that were abnormal prior to the transplants normalized after the transplant. The same observation was made for the diabetic dogs that received higher doses of canine islets. In all diabetic dogs, the insulin required to attempt to control blood glucose was cut by 50–100% after the transplant, down to no required insulin for the course of the 60-day study. The dogs had no adverse events and behavioral monitoring suggested normal activity after recovery from the transplant.

Conclusions and implications

The study provides evidence that PEGDA microencapsulated canine islets reversed the signs of diabetes without immunosuppression and led to states of insulin-independence or significantly lowered insulin requirements in the recipients.

Production and Characterization of a Conditionally Immortalized Dog Beta-Cell Line from Fetal Canine Pancreas

Since the 1970s, rodent and human insulin-secreting pancreatic beta-cell lines have been developed and found useful for studying beta-cell biology. Surprisingly, although the dog has been widely used as a translational model for diabetes, no canine insulin-secreting beta cells have ever been produced. Here, a targeted oncogenesis protocol previously described by some of us for generating human beta cells was adapted to produce canine beta cells. Canine fetal pancreata were obtained by cesarean section between 42 and 55 days of gestation, and fragments of fetal glands were transduced with a lentiviral vector expressing SV40LT under the control of the insulin promoter. Two Lox P sites flanking the sequence allowed subsequent transgene excision by Cre recombinase expression. When grafted into SCID mice, these transduced pancreata formed insulinomas. ACT-164 is the cell line described in this report. Insulin mRNA expression and protein content were lower than reported with adult cells, but the ACT-164 cells were functional, and their insulin production in vitro increased under glucose stimulation. Transgene excision upon Cre expression arrested proliferation and enhanced insulin expression and production. When grafted in SCID mice, intact and excised cells reversed chemically induced diabetes. We have thus produced an excisable canine beta-cell line. These cells may play an important role in the study of several aspects of the cell transplantation procedure including the encapsulation process, which is difficult to investigate in rodents. Although much more work is needed to improve the excision procedure and achieve 100% removal of large T antigen expression, we have shown that functional cells can be obtained and might in the future be used for replacement therapy in diabetic dogs.

Tailored generation of insulin producing cells from canine mesenchymal stem cells derived from bone marrow and adipose tissue

The trend of regenerative therapy for diabetes in human and veterinary practices has conceptually been proven according to the Edmonton protocol and animal models. Establishing an alternative insulin-producing cell (IPC) resource for further clinical application is a challenging task. This study investigated IPC generation from two practical canine mesenchymal stem cells (cMSCs), canine bone marrow-derived MSCs (cBM-MSCs) and canine adipose-derived MSCs (cAD-MSCs). The results illustrated that cBM-MSCs and cAD-MSCs contain distinct pancreatic differentiation potential and require the tailor-made induction protocols. The effective generation of cBM-MSC-derived IPCs needs the integration of genetic and microenvironment manipulation using a hanging-drop culture of PDX1-transfected cBM-MSCs under a three-step pancreatic induction protocol. However, this protocol is resource- and time-consuming. Another study on cAD-MSC-derived IPC generation found that IPC colonies could be obtained by a low attachment culture under the three-step induction protocol. Further, Notch signaling inhibition during pancreatic endoderm/progenitor induction yielded IPC colonies through the trend of glucose-responsive C-peptide secretion. Thus, this study showed that IPCs could be obtained from cBM-MSCs and cAD-MSCs through different induction techniques. Also, further signaling manipulation studies should be conducted to maximize the protocol’s efficiency.

A Versatile Microencapsulation Platform for Hyaluronic Acid and Polyethylene Glycol

Cell microencapsulation is a rapidly expanding field with broad potential for stem cell therapies and tissue engineering research. Traditional alginate microspheres suffer from poor biocompatibility, and microencapsulation of more advanced hydrogels is challenging due to their slower gelation rates. We have developed a novel, noncytotoxic, nonemulsion-based method to produce hydrogel microspheres compatible with a wide variety of materials, called core-shell spherification (CSS). Fabrication of microspheres by CSS derived from two slow-hardening hydrogels, hyaluronic acid (HA) and polyethylene glycol diacrylate (PEGDA), was characterized. HA microspheres were manufactured with two different crosslinking methods: thiolation and methacrylation. Microspheres of methacrylated HA (MeHA) had the greatest swelling ratio, the largest average diameter, and the lowest diffusion barrier. In contrast, PEGDA microspheres had the smallest diameters, the lowest swelling ratio, and the highest diffusion barrier, while microspheres of thiolated HA had characteristics that were in between the other two groups. To test the ability of the hydrogels to protect cells, while promoting function, diabetic NOD mice received intraperitoneal injections of PEGDA or MeHA microencapsulated canine islets. PEGDA microspheres reversed diabetes for the length of the study (up to 16 weeks). In contrast, islets encapsulated in MeHA microspheres at the same dose restored normoglycemia, but only transiently (3-4 weeks). Nonencapsulated canine islet transplanted at the same dose did not restore normoglycemia for any length of time. In conclusion, CSS provides a nontoxic microencapsulation procedure compatible with various hydrogel types.

Production, Characterization, and Function of Pseudoislets from Perinatal Canine Pancreas

We evaluated the cell composition and function of canine pancreatic pseudoislets (PIs) produced from 42- to 55-day-old fetuses, 1- to 21-day-old pups, and an adult dog pancreas. After mild collagenase treatment, partially digested tissues were cultured for 2–3 weeks. PI production started on culture day 3, was marked for 6 to 9 days, and then stopped. PI production was greatest with the neonatal specimens, reaching about 12 million aggregates per litter (55-day-old fetus) or per pancreas (1-day-old pup). Cell composition at all stages was similar to that in adult pancreatic islets, with predominant β cells, scant α cells and, most importantly, presence of δ cells. Among pancreatic markers assessed by quantitative real-time PCR (qRT-PCR) mRNA assay, insulin showed the highest expression levels in PIs from newborn and adult pancreas, although these were more than 1000 times lower than in adult islets. Pdx1 mRNA expression was high in PIs from 55-day-old pancreases and was lower at later stages. Consistent with the qRT-PCR results, the insulin content was far lower than reported in adult dog pancreatic islets. However, insulin release by PIs from 1-day-old pups was demonstrated and was stimulated by a high-glucose medium. PIs were transplanted into euglycemic and diabetic SCID mice. In euglycemic animals, the transplant cell composition underwent maturation and transplants were still viable after 6 months. In diabetic mice, the PI transplants produced insulin and partially controlled the hyperglycemia. These data indicate that PIs can be produced ex vivo from canine fetal or postnatal pancreases. Although functional PIs can be obtained, the production yield is most likely insufficient to meet the requirements for diabetic dog transplantation without further innovation in cell culture amplification.

Concise Review: Canine Diabetes Mellitus as a Translational Model for Innovative Regenerative Medicine Approaches

Diabetes mellitus (DM) is a common spontaneous endocrine disorder in dogs, which is defined by persistent hyperglycemia and insulin deficiency. Like type 1 diabetes (T1D) in people, canine DM is a complex and multifactorial disease in which genomic and epigenomic factors interact with environmental cues to induce pancreatic β‐cell loss and insulin deficiency, although the pathogenesis of canine DM is poorly defined and the role of autoimmunity is further controversial. Both diseases are incurable and require life‐long exogenous insulin therapy to maintain glucose homeostasis. Human pancreatic islet physiology, size, and cellular composition is further mirrored by canine islets. Although pancreatic or isolated islets transplantation are the only clinically validated methods to achieve long‐term normoglycemia and insulin independence, their availability does not meet the clinical need; they target a small portion of patients and have significant potential adverse effects. Therefore, providing a new source for β‐cell replacement is an unmet need. Naturally occurring DM in pet dogs, as a translational platform, is an untapped resource for various regenerative medicine applications that may offer some unique advantages given dogs' large size, longevity, heterogenic genetic background, similarity to human physiology and pathology, and long‐term clinical management. In this review, we outline different strategies for curative approaches, animal models used, and consider the value of canine DM as a translational animal/disease model for T1D in people. stem cells translational medicine2019;8:450–455