Formulation strategies to provide oxygen-release to contrast local hypoxia for transplanted islets

Oxygen dynamics and delivery strategies to enhance beta cell replacement therapy

Beta cell replacement therapy via pancreatic islet transplantation offers a promising treatment for type 1 diabetes as an alternative to insulin injections. However, posttransplantation oxygenation remains a critical challenge; isolated islets from donors lose vascularity and rely on slow oxygen diffusion for survival until revascularization occurs in the host tissue. This often results in significant hypoxia-induced acute graft loss. Overcoming the oxygenation barrier is crucial for advancing islet transplantation. This review is structured in three sections: the first examines oxygen dynamics in islet transplantation, focusing on factors affecting oxygen supply, including vascularity. It highlights oxygen dynamics specific to both transplant sites and islet grafts, with particular attention to extrahepatic sites such as subcutaneous tissue. The second section explores current oxygen delivery strategies, categorized into two main approaches: augmenting oxygen supply and enhancing effective oxygen solubility. The final section addresses key challenges, such as the lack of a clearly defined oxygen threshold for islet survival and the limited precision in measuring oxygen levels within small islet constructs. Recent advancements addressing these challenges are introduced. By deepening the understanding of oxygen dynamics and identifying current obstacles, this review aims to guide the development of innovative strategies for future research and clinical applications. These advancements are anticipated to enhance transplantation outcomes and bring us closer to a cure for type 1 diabetes.

Curcumin-loaded bioadhesive silk fibroin microsphere improves islet transplantation by mitigating oxidative stress and inhibiting apoptosis

Islet transplantation, a form of cell therapy involving the injection of healthy islet cells into the recipient's body for curative treatment of T1DM, often fails due to oxidative stress and inflammatory damage experienced by the transplanted islets. Curcumin, a naturally occurring polyphenol with potent anti-inflammatory and antioxidant properties, has been underutilized in islet protection due to challenges associated with its co-delivery and formulation. In this study, we developed bioadhesive curcumin microspheres (PDA/CUR@SF) by incorporating curcumin into a silk fibroin matrix and subsequently coating it with polydopamine to enhance islet adherence. Silk protein acts as a delivery carrier while polydopamine serves as an adhesive agent; both components synergistically provide anti-inflammatory effects. In vitro experiments demonstrated that PDA/CUR@SF enhances islet resistance against oxidative stress and inflammatory damage by improving cell viability and function. In vivo studies showed that PDA/CUR@SF prolongs stabilization of blood glucose levels in diabetic mice receiving islet transplantation while facilitating faster glucose clearance. Further analysis revealed that PDA/CUR@SF protects transplanted islets through co-grafting and promotes neovascularization. Overall, our findings suggest that PDA/CUR@SF offers a rational approach to improve outcomes in transplantation.

A novel intravascular bioartificial pancreas device shows safety and islet functionality over 30 days in nondiabetic swine

In this study using a discordant, xenogeneic, transplant model we demonstrate the functionality and safety of the first stent-based bioartificial pancreas (BAP) device implanted endovascularly into an artery, harnessing the high oxygen content in blood to support islet viability. The device is a self-expanding nitinol stent that is coated with a bilayer of polytetrafluoroethylene that forms channels to hold islets embedded in a hydrogel. We completed a 1-month study in the nondiabetic swine model (N = 3) to test the safety of the device and to assess islet functionality after device recovery. The luminal diameter of the devices from 3 animals on day 0 and day 30 was 10.01 ± 0.408 mm and 10.05 ± 0.25 mm, respectively. The stimulation index of the control and endovascular BAP devices explanted at day 30 were 3.35 ± 0.97 and 4.83 ±1.20, respectively, and the islets stained positively for insulin and glucagon after 30 days in vivo. This pilot study shows that BAP implantation into a peripheral artery is safe and supports islet functionality over 30 days, providing the groundwork for future work assessing the in vivo function of the device in diabetic swine.

Adaptive bilirubin nanoscavenger alleviates pulmonary oxidative stress and inflammation for acute lung injury therapy

INTRODUCTION

Acute lung injury (ALI) is a life-threatening condition characterized by rapidly progressing respiratory distress and hypoxemia. Oxidative stress-induced inflammation in lung tissue plays a crucial role in the progression of ALI. Excessive generation of reactive oxygen species (ROS) in the pulmonary microenvironment activates inflammatory signaling pathways, enhancing the transcription of pro-inflammatory factors and ultimately leading to tissue necrosis.

OBJECTIVES

Bilirubin (BR), an exceptional endogenous antioxidant, possesses the ability to counteract elevated levels of reactive oxygen species (ROS) through direct reactions or by inducing antioxidant systems such as Nrf2/HO-1 signaling. However, its limited solubility poses a hindrance to further applications. Hence, it is imperative to develop a suitable bilirubin-based system for biological utilization.

METHODS

In this study, we developed a bilirubin-based ROS-sensitive adaptive nanoscavenger (GP@BR) by co-assembling bilirubin-conjugated glycol chitosan (GC-BR) and bilirubin-conjugated polyethylene glycol (PEG-BR), aiming to alleviate oxidative stress for ALI treatment.

RESULTS

The different conjugations endowed the bilirubin derivatives with varying sensitivity towards reacting with ROS, enabling GP@BR to exert antioxidative properties specifically in oxidative environments on demand. Besides its excellent antioxidant properties, GP@BR also demonstrated the ability to absorb excess inflammatory cytokines. Moreover, our optimized nanoscavenger facilitated bilirubin transport across the mucosal layer on pulmonary epithelial cells. In vivo studies confirmed that GP@BR significantly improved ALI symptoms and suppressed pulmonary fibrosis.

CONCLUSION

This study highlighted the potential of ROS-sensitive adaptive properties and multiple actions of this nanoscavenger in the treatment of ALI.

3D printed VEGF-CPO biomaterial scaffold to promote subcutaneous vascularization and survival of transplanted islets for the treatment of diabetes

Diabetes is a complex metabolic disease and islet transplantation is a promising approach for the treatment of diabetes. Unfortunately, the transplanted islets at the subcutaneous site are also affected by various adverse factors such as poor vascularization and hypoxia. In this study, we utilize biocompatible copolymers l-lactide and D,l-lactide to manufacture a biomaterial scaffold with a mesh-like structure via 3D printing technology, providing a material foundation for encapsulating pancreatic islet cells. The scaffold maintains the sustained release of vascular endothelial growth factor (VEGF) and a slow release of oxygen from calcium peroxide (CPO), thereby regulating the microenvironment for islet survival. This helps to improve insufficient subcutaneous vascularization and reduce islet death due to hypoxia post-transplantation. By pre-implanting VEGF-CPO scaffolds subcutaneously into diabetic rats, a sufficiently vascularized site is formed, thereby ensuring early survival of transplanted islets. In a word, the VEGF-CPO scaffold shows good biocompatibility both in vitro and in vivo, avoids the adverse effects on the implanted islets, and displays promising clinical transformation prospects.

Biomaterial-assisted strategies to improve islet graft revascularization and transplant outcomes

Islet transplantation holds significant promise as a curative approach for type 1 diabetes (T1D). However, the transition of islet transplantation from the experimental phase to widespread clinical implementation has not occurred yet. One major hurdle in this field is the challenge of insufficient vascularization and subsequent early loss of transplanted islets, especially in non-intraportal transplantation sites. The establishment of a fully functional vascular system following transplantation is crucial for the survival and secretion function of islet grafts. This vascular network not only ensures the delivery of oxygen and nutrients, but also plays a critical role in insulin release and the timely removal of metabolic waste from the grafts. This review summarizes recent advances in effective strategies to improve graft revascularization and enhance islet survival. These advancements include the local release and regulation of angiogenic factors (e.g., vascular endothelial growth factor, VEGF), co-transplantation of vascular fragments, and pre-vascularization of the graft site. These innovative approaches pave the way for the development of effective islet transplantation therapies for individuals with T1D.

A Bioartificial Pancreas with "Immune Stealth" and Continuous Oxygen Supply for Islet Transplantation

Transplantation of microencapsulated islet cells remains a promising strategy for the normalization of glucose metabolism control in type 1 diabetes mellitus. However, vigorous host immunologic rejection, fibrotic overgrowth around the microcapsules, and poor oxygen supply often lead to graft failure. Herein, a bioartificial pancreas is constructed, which incorporates the "stealth effect" based on polyethylene glycol copolymers and the high oxygen-carrying performance of fluorinated nanoparticles. Polycationic poly(l-lysine)-grafted-poly(ethylene glycol) is successfully coated on the surface of alginate microcapsules through electrostatic interaction, which can not only resist fibrinogen adhesion and avoid excessive fibrosis around the microcapsules but also isolate the host immune system from attacking, achieving a "stealth effect" of microencapsulated islet cells. Furthermore, the coloading of fluoride-based O2 nanocarriers gives them enhanced oxygen-carrying and continuous oxygen supply capabilities, thereby effectively prolonging the survival of islet cells. The intracapsular islet cells still display similar cell viability and almost normal insulin secretion function even in long-term culture under hypoxic conditions. Collectively, here a new approach is opened for microencapsulated islets to efficiently evade host immune attack and improve oxygen supply and a promising strategy is provided for islet transplantation in type 1 diabetes mellitus.