A model for determining an effective in vivo dose of transplanted islets based on in vitro insulin secretion

Abstract

Increasing dosages of islet macrobeads transplanted into diabetic rats, based on multiples of in vitro insulin secretion matched to the recipient's exogenous insulin requirements, correlated with improved blood glucose regulation and increased duration of graft function. These results demonstrate the usefulness of a standardized model for the evaluation of the functional effectiveness of islets intended for transplantation, in this case using intraperitoneally implanted agarose macrobeads, in diabetic rats. The results suggest that some features of this islet-dosing methodology may be applicable, and indeed necessary, to clinical allogeneic and xenogeneic islet transplantation.

Long‐term efficacy and safety of porcine islet macrobeads in nonimmunosuppressed diabetic cynomolgus macaques

“…56 Our islet dosing strategy was not based on IEQ per kg body weight, but instead was based on total 24 h insulin secretion per macrobead during in vitro culture. 57 Based on the non-optimal environment of the peritoneal cavity (e.g., oxygen and other nutritional limitations, inflammatory mediators) as compared to an incubator with precisely controlled parameters, we used a 2× dose of the estimated number of required macrobeads in an attempt to reduce the administration of exogenous insulin by half. Using this strategy, most animals in our study were able to decrease exogenous insulin by 30% or more during the first year of the study, suggesting that our dosing strategy still underestimated the required macrobead number to reliably achieve a 50% insulin reduction.…”

“…The culture medium was changed weekly and 24‐h post‐change medium samples were taken for porcine‐insulin ELISA assays (Mercodia, Uppsala, Sweden) to measure average daily insulin secretion per macrobead for each production lot prior to implantation in diabetic animals (Table 1). This in vitro methodology provides a continuous timeline of 24‐h insulin production in response to high glucose media and has proven to be a reliable indicator of in vivo function 57,58 . Graphs of islet macrobead insulin production for each lot of macrobeads used in the current study are included as Figure S1.…”

“…This in vitro methodology provides a continuous timeline of 24-h insulin production in response to high glucose media and has proven to be a reliable indicator of in vivo function. 57,58 Graphs of islet macrobead insulin production for each lot of macrobeads used in the current study are included as Figure S1. Uniformity of macrobead diameter (7-9 mm), agarose coating (0.5-1.0 mm), and an even distribution of islets within the macrobeads were also confirmed as quality assessments.…”

Xenotransplantation literature update, November/December 2018

“…The authors found that adult porcine islets, which were defined as over two years old, had the strongest membranes and 50 times more insulin than younger cells . Holdcraft et al were interested in finding an appropriate dosage of islets to include in each encapsulation. They performed islet transplants of varying doses in rats, continuously testing blood sugar levels in vivo and later the insulin secretion in culture .…”

“…Holdcraft et al were interested in finding an appropriate dosage of islets to include in each encapsulation. They performed islet transplants of varying doses in rats, continuously testing blood sugar levels in vivo and later the insulin secretion in culture . The data suggest that multiple doses were better than a single dose in maintaining good blood sugar control …”