|Abstract:||Type-1 diabetes (T1D), also known as insulin-dependent diabetes, is characterized by the inability of pancreas to produce sufficient amount of insulin to regulate blood glucose level in the body. Long-term complications such as nephropathy, neuropathy, retinopathy and cardiovascular disease make T1D a major health problem throughout the world. For the past few decades, allotransplantation of insulin-producing islets from the pancreas of deceased human donors has shown promising results in the restoration and sustenance of normoglycemia. Islet transplantation is a suitable procedure, especially for adolescents since it has substantially lower risk in operating procedure than whole-pancreas transplantation. However, only small percentage of patients of T1D can be treated with islet allotransplantation because of the limited donor availability.
Xenotransplantation using porcine islet is a good alternative treatment of T1D. Porcine islet is an ideal substitute of beta cell function for human islet for several reasons: availability, compatibility and functional similarity to human islets. In recent years, treatment with porcine islets has shown significant progress of providing sustained normoglycemia in diabetes-induced nonhuman primates (NHPs), which has demonstrated the feasibility of clinical xenotransplantation. Yet, there are still a number of barriers to overcome in order to accomplish successful clinical application for xenotransplantation.
Harvesting and preserving viable islets with high yield is a first crucial step in porcine islet xenotransplantation. The major limiting factor, however, is the intrinsic fragility of the porcine pancreas that causes various complications in obtaining sufficient amount of healthy islets. Early inflammatory responses and rejection are also the major problems for clinical xenotransplantation. Immunosuppressive drug is used to regulate the inflammation yet the drug itself in long term induces toxicity in the body. Securing the islets with appropriate encapsulation technology is crucial as it ensures the prolonged viability and function of the islets while avoiding immune reaction from the host after the transplant.
In the first part of the thesis, we demonstrate the isolation and purification method composed of three key components: enzymatic digestion, mechanical disruption and density gradient purification. Porcine pancreata were procured from young commercial breed pigs from the university slaughterhouse. Average time consumption of single islet isolation with the modified procedure is 60 min. Islet yield, purity, viability, in vitro function, and morphology were assessed after the isolation. The resulting islet viability and purity were comparable with those achieved in published literature. Clinically relevant yield and quality can be obtained with the use of standard laboratory equipment, which makes this method time- and cost-effective.
The second part of the thesis presents single-step fabrication of core/shell alginate microcapsules using precision particle fabrication (PPF) system to demonstrate the feasibility of successful clinical xenotransplantation. PPF system has following capabilities: precise control of capsule size, ability to process material with high viscosity, high throughput and prevention of cell protrusion. These advantages allow only minimal intervention during the fabrication process, thus making the system suitable for various cell delivery applications including islet encapsulation. Islets with appropriate concentration (in IEQ) for clinical applications were encapsulated in the core of the microcapsules with PPF system. The average duration of microcapsule fabrication process was 10 min. Islet morphology and viability were assessed immediately after the encapsulation. The intracapsular environment of the alginate microcapsules induces cell-cell and cell-matrix interactions, thus providing hospitable environment for the encapsulated islets. The results showed islets with high survivability after the entire encapsulation process. Future study aimed for improved viability and function of the islets in vivo can further support the rationale of the present method as alternative therapeutic option for T1D patients.