Pancreatic islet PEGylation as an immunological polymeric restraint

Dual-targeted nano-encapsulation of neonatal porcine islet-like cell clusters with triiodothyronine-loaded bifunctional polymersomes

There is growing evidence that neonatal porcine islet-like cell clusters (NPCCs) isolated from piglets can be used to treat type 1 diabetes in humans. However, graft rejection is a common complication in humans owing to the prevalence of xenoantigens in porcine. Therefore, researchers have investigated various islet encapsulation techniques that could protect against these antigens. To this end, this study presents a robust nano-encapsulation method based on bifunctional polymersomes (PSomes), in which N-hydroxysuccinimide (NHS) and maleimide (Mal) groups conjugated to the PSomes terminal interact with the amine and thiol groups on the surface of NPCCs to induce dual targeting via two covalent bonds. The findings indicate that the ratio of NHS to Mal on PSomes is optimal for dual targeting. Moreover, triiodothyronine (T3) is known to promotes pancreatic islet maturation and differentiation of endocrine cells into beta cells. T3 encapsulated in PSomes is shown to increase the glucose sensitivity of NPCCs and enhance insulin secretion from NPCCs. Furthermore, improvements in the nano-encapsulation efficiency and insulin-secreting capability of NPCCs through dual targeting via dual-Psomes are demonstrated. In conclusion, the proposed nano-encapsulation technique could pave the way for significant advances in islet nano-encapsulation and the imprevement of NPCC immaturity via T3 release.

Synthesis of PEG-dendron for surface modification of pancreatic islets and suppression of the immune response

Islet cell transplantation has been an effective method for the treatment of type 1 diabetes. The transplanted islets release insulin in response to changes in blood glucose levels. The clinical application of islet transplantation, however, has been hindered because of some critical problems including immune responses to grafted islets and side effects caused by overdosed immunosuppressive drugs. Herein, surface modification technology using poly(ethylene glycol) (PEG)-dendron was proposed to safeguard islets from the host immune system. PEG-dendron was synthesized by a divergent polymerization method and utilized to cover the islet antigen surface. Successful conjugation of PEG-dendron on the islet surface was achieved without affecting islet morphology, viability, and functionality at a concentration of 1.00%. Surface modification using PEG-dendron effectively prevented protein absorption and immune activation. Foremost, it improved the survival rate of islet grafts in vivo when combined with a low dose of immunosuppressive drugs. In conclusion, PEG-dendron is a potential candidate for the surface modification of pancreatic islets to mitigate immune responses after transplantation.

Advances in biocompatibility and physico-chemical characterization of microspheres for cell encapsulation

Cell encapsulation has already shown its high potential and holds the promise for future cell therapies to enter the clinics as a large scale treatment option for various types of diseases. The advancement in cell biology towards this goal has to be complemented with functional biomaterials suitable for cell encapsulation. This cannot be achieved without understanding the close correlation between cell performance and properties of microspheres. The ongoing challenges in the field of cell encapsulation require a critical view on techniques and approaches currently utilized to characterize microspheres. This review deals with both principal subjects of microspheres characterization in the cell encapsulation field: physico-chemical characterization and biocompatibility. The up-to-day knowledge is summarized and discussed with the focus to identify missing knowledge and uncertainties, and to propose the mandatory next steps in characterization of microspheres for cell encapsulation. The primary conclusion of this review is that further success in development of microspheres for cell therapies cannot be accomplished without careful selection of characterization techniques, which are employed in conjunction with biological tests.

Optimization of monomethoxy poly(ethylene glycol) grafting on Langerhans islets capsule using response surface method

Langerhans islet transplantation is a much less invasive approach compared with the pancreas transplantation to 'cure' diabetes. However, destruction of transplanted islets by the immune system is an impediment for a successful treatment. Chemical grafting of monomethoxy poly(ethylene glycol) onto pancreatic islet capsule is a novel approach in islet immunoisolation. The aim of this study was to determine an optimized condition for grafting of monomethoxy poly(ethylene glycol) succinimidyl propionate (mPEG-SPA) on islets capsule. Independent variables such as reaction time, the percentage of longer mPEG in the mixture, and polymer concentration were optimized using a three-factor, three-level Box-Behnken statistical design. The dependent variable was IL-2 (interleukin-2) secretion of lymphocytes co-cultured with PEGylated or uncoated control islets for 7 days co-culturing. A mathematical relationship is obtained which explained the main and quadratic effects and the interaction of factors which affected IL-2 secretion. Response surface methodology predicted the optimized values of reaction time, the percentage of longer mPEG in the mixture, and polymer concentration of 60 min to be 63.7% mPEG10 and 22 mg/mL, respectively, for the minimization of the secreted IL-2 as response. Islets which were PEGylated at this condition were transplanted to diabetic rats. The modified islets could survive for 24 days without the aid of any immunosuppressive drugs and it is the longest survival date reported so far. However, free islets (unmodified islets as control) are completely destroyed within 7 days. These results strongly suggest that this new protocol provides an effective clinical means of decreasing transplanted islet immunogenicity.