Characterization of Islet Health and Function Prior to Transplantation

Transplantation of Islets of Langerhans offers a cell‐based insulin replacement therapy for Type 1 diabetes but requires lifelong immunosuppression. Devices that encapsulate transplanted islets or insulin‐producing cells can isolate and protect islets from the immune system eliminating need for immunosuppression. However, the required cell density may promote a hypoxic environment with subsequent beta cell dysfunction. We investigated the effects of a hypoxic environment on unencapsulated islet insulin secretion by incubating isolated human islets at low (1%) and normal (21%) oxygen tensions. After 24 hrs, the basal secretion rate (BSR) for islets maintained at 1% O2 (4.5 +/− 0.34 pg insulin/20min*ng DNA) was elevated compared to islets maintained in normoxic conditions (21%, 2.0 +/− 0.7 pg insulin/20min*ng DNA). For islets exposed to normoxia the stimulation index (SI) was 6.4 +/− 1.3. The SI in islets exposed to hypoxia was reduced by 50% (3.2 +/− 1.1). Thus, sufficient islet oxygenation is important for human islet function.To investigate the effect of hypoxic conditions on macroencapsulated islet function we placed a high density of rat islets, without supplemental oxygen, into a macroencapsulation device. By perifusion, we observed a delayed and decreased 1st phase insulin secretion when compared to free islets. After 4 days of high density culture within the macroencapsulation device, macroencapsulated rat islets assayed in static assays, showed increased basal secretion, reduced GSIS, and decreased insulin content when compared to free islets.To evaluate free and macroencapsulated cellular function we recently developed perifusion chambers capable of simultaneous measurement of oxygen consumption rate (OCR) and hormone secretion. We found that GSIS was correlated with increased OCR in substrate free media demonstrating the possible utility of dynamic OCR measurements as a real time assay for islet viability and potency. Islet function is sensitive to oxygen tension and metabolic exchange, and using new technologies we are developing strategies to characterize these effects to optimize cellular health and function.Support or Funding InformationJuvenile Diabetes Research Foundation Award #2‐SRA‐2018‐685‐S‐B. NIH Diabetes Impact Award #1DP3DK106933‐01