Quantitative assessment of islet cell products: estimating the accuracy of the existing protocol and accounting for islet size distribution

Remote processing of pancreas can restore normal glucose homeostasis in autologous islet transplantation after traumatic whipple pancreatectomy: technical considerations

An emergency autologous islet transplant after a traumatic Whipple operation and subsequent total pancreatectomy was performed for a 21-year-old patient who was wounded with multiple abdominal gunshot wounds. After Whipple pancreatectomy, the remnant pancreas (63.5 g), along with other damaged organs, was removed by the surgeons at Walter Reed Army Medical Center (WRAMC) and shipped to Diabetes Research Institute (DRI) for islet isolation. The pancreas was preserved in UW solution for 9.25 h prior to islet isolation. Upon arrival, the organ was visually inspected; the pancreatic head was missing, the rest of the pancreas was damaged and full of blood; the tail looked normal. A 16-gauge catheter was inserted into the main duct and directed towards tail of the pancreas after the dissection of main duct in the midbody of the pancreas. The pancreas was distended with collagenase solution (Roche MTF) through the catheter. During 10 min of intraductal delivery of enzyme, the gland was distended uniformly. No leakage of the solution was observed. The pancreas was transferred to a Ricordi chamber for automated mechanical and enzymatic digestion. Islets were purified using a COBE 2991 cell processor. Islet equivalents (IEQ; 221,250) of 40% purity and 90% viability were recovered during the isolation, which were shipped back to WRAMC and infused by intraportal injection into the patient. Immediate islet function was demonstrated by the rapid elevation of serum C peptide followed by insulin independence with near normal oral glucose tolerance test (OGTT) 1 and 2 months later. It is possible to restore near normal glucose tolerance with autologous islet transplantation after total pancreatectomy even with suboptimal number of islets while confirming that islets processed at a remote site are suitable for transplantation.

A local glucose-and oxygen concentration-based insulin secretion model for pancreatic islets

BACKGROUND

Because insulin is the main regulator of glucose homeostasis, quantitative models describing the dynamics of glucose-induced insulin secretion are of obvious interest. Here, a computational model is introduced that focuses not on organism-level concentrations, but on the quantitative modeling of local, cellular-level glucose-insulin dynamics by incorporating the detailed spatial distribution of the concentrations of interest within isolated avascular pancreatic islets.

METHODS

All nutrient consumption and hormone release rates were assumed to follow Hill-type sigmoid dependences on local concentrations. Insulin secretion rates depend on both the glucose concentration and its time-gradient, resulting in second-and first-phase responses, respectively. Since hypoxia may also be an important limiting factor in avascular islets, oxygen and cell viability considerations were also built in by incorporating and extending our previous islet cell oxygen consumption model. A finite element method (FEM) framework is used to combine reactive rates with mass transport by convection and diffusion as well as fluid-mechanics.

RESULTS

The model was calibrated using experimental results from dynamic glucose-stimulated insulin release (GSIR) perifusion studies with isolated islets. Further optimization is still needed, but calculated insulin responses to stepwise increments in the incoming glucose concentration are in good agreement with existing experimental insulin release data characterizing glucose and oxygen dependence. The model makes possible the detailed description of the intraislet spatial distributions of insulin, glucose, and oxygen levels. In agreement with recent observations, modeling also suggests that smaller islets perform better when transplanted and/or encapsulated.

CONCLUSIONS

An insulin secretion model was implemented by coupling local consumption and release rates to calculations of the spatial distributions of all species of interest. The resulting glucose-insulin control system fits in the general framework of a sigmoid proportional-integral-derivative controller, a generalized PID controller, more suitable for biological systems, which are always nonlinear due to the maximum response being limited. Because of the general framework of the implementation, simulations can be carried out for arbitrary geometries including cultured, perifused, transplanted, and encapsulated islets.

Quantification of the islet product: presentation of a standardized current good manufacturing practices compliant system with minimal variability

BACKGROUND

Accurate islet quantification has proven difficult to standardize in a good manufacturing practices (GMP) approved manner.

METHODS

The influence of assessment variables from both manual and computer-assisted digital image analysis (DIA) methods were compared using calibrated, standardized microspheres or islets alone. Additionally, a mixture of microspheres and exocrine tissue was used to evaluate the variability of both the current, internationally recognized, manual method and a novel GMP-friendly purity- and volume-based method (PV) evaluated by DIA in a semiclosed, culture bag system.

RESULTS

Computer-assisted DIA recorded known microsphere size distribution and quantities accurately. By using DIA to evaluate islets, the interindividual manually evaluated percent coefficients of variation (CV%; n=14) were reduced by almost half for both islet equivalents (IEs; 31% vs. 17%, P=0.002) and purity (20% vs. 13%, P=0.033). The microsphere pool mixed with exocrine tissue did not differ from expected IE with either method. However, manual IE resulted in a total CV% of 44.3% and a range spanning 258 k IE, whereas PV resulted in CV% of 10.7% and range of 60 k IE. Purity CV% for each method were similar approximating 10.5% and differed from expected by +7% for the manual method and +3% for PV.

CONCLUSION

The variability of standard counting methods for islet samples and clinical quantities of microspheres mixed with exocrine tissue were reduced with DIA. They were reduced even further by use of a semiclosed bag system compared with standard manual counting, thereby facilitating the standardization of islet evaluation according to GMP standards.