Abstract
Cadaveric islet and stem cell-derived transplantations hold promise as treatments for type 1 diabetes. To tackle the issue of immunocompatibility, numerous cellular macroencapsulation techniques have been developed that utilize diffusion to transport insulin across an immunoisolating barrier. However, despite several devices progressing to human clinical trials, none have successfully managed to attain physiologic glucose control or insulin independence. Based on empirical evidence, macroencapsulation methods with multilayered, high islet surface density are incompatible with homeostatic, on-demand insulin delivery and physiologic glucose regulation, when reliant solely on diffusion. An additional driving force is essential to overcome the distance limit of diffusion. In this study, we present both theoretical proof and experimental validation that applying pressure at levels comparable to physiological diastolic blood pressure significantly enhances insulin flux across immunoisolation membranes—increasing it by nearly three orders of magnitude. This significant enhancement in transport rate allows for precise, sub-minute regulation of both bolus and basal insulin delivery. By incorporating this technique with a pump-based extravascular system, we demonstrate the ability to rapidly reduce glucose levels in diabetic rodent models, effectively replicating the timescale and therapeutic effect of subcutaneous insulin injection or infusion. This advance provides a potential path towards achieving insulin independence with islet macroencapsulation.
One Sentence Summary Towards improved glucose control, applying sub-minute pressure at physiological levels enhances therapeutic insulin transport from macroencapsulated islets.
Competing Interest Statement
EAT, RAL, JPA, and ASYP are co-inventors of a patent covering this study filed by Stanford University.
Footnotes
We revised the title of the paper to, Enhancing therapeutic insulin transport from macroencapsulated islets using sub-minute pressure at physiological levels, to more accurately reflect the findings we are presenting. In the introduction section, we discuss why current approaches and clinical trials have not achieved insulin independence, highlighting that most strategies prioritize enhancing cell viability to maximize islet surface density. This often involves improving oxygen and nutrient transport from outside to inside the encapsulation, while the transport of insulin from inside to outside has received less attention. To illustrate this point, we have incorporated a new figure (Figure 1), showing that despite these methods improving islet viability within subcutaneous macroencapsulation devices, insulin transport still predominantly depends on diffusion. This introduction provides a foundation for examining the limitations of insulin transport in existing subcutaneous methods. Our focus on insulin transport prompted the use of a simplified experimental setup that excluded oxygenation enhancements, a choice we clarify in the discussion section. There, we emphasize that incorporating oxygenation enhancements to maintain islet health will be crucial for the future success of long-term studies. We have clarified the reference to the pressure levels used in our study. In the introduction, we mention that macroencapsulation methods based on vascular perfusion directly utilize the physiological pressure difference between arteries and veins. This led us to investigate whether a brief application of similar pressure levels could significantly enhance insulin transport. Adopting a conservative approach, we utilized the normal human diastolic blood pressure of approximately 10.7 kPa. Our theoretical insights, grounded in an order-of-magnitude analysis, used 10 kPa as a reference, with experimental validations conducted at 11 kPa. This analysis suggests that a sub-minute application of this pressure level is sufficient and emphasizes the brief nature of the application, contrasting with the continuous pressure in vascular perfusion. In the discussion section, we propose an alternative approach: instead of maintaining constant pressure, we match the pressure application duration with the first phase of glucose-stimulated insulin secretion (5 minutes), resulting in a required pressure of about 1.1 kPa. This pressure is considerably lower than the 20 mmHg (2.7 kPa) used in low-pressure machine perfusion to preserve pancreas functionality, thus affirming 1.1 kPa as a very safe level for future research if needed.
