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Islet transplantation is a promising therapy for T1DM. Key factors influencing islet yield have been identified with conflicting results. In this study, we analyzed 276 isolations to identify variables for islet yield and, additionally, islet size and size distribution. Pearson correlation analyses demonstrated that BMI had a positive correlation with pancreas size, actual islet count (AIC), and islet equivalent (IEQ)/g (all p ≤0.009), while CIT had a negative correlation with AIC and IEQ/g (all p ≤0.003). In mixed linear regression, BMI also had a positive correlation with islet size but only for shorter digestion times (≤15 min); there was no association between BMI and islet size for longer digestion times (>15 min). CIT was not associated with islet size. Donor age, sex, and preservation solutions were shown to have no correlation with islet yields or size distribution. Pancreas size had a positive correlation with AIC and a negative association with IEQ/g; it also had positive association with islet size but only for females, not males. Overdigestion was positively associated with islet counts; however, there was also a greater proportion of smaller islets when digestion rate was >74% ( p = 0.005). Of the three collagenases analyzed, Sigma V had the lowest digestion rate (mean = 65%), approximately 5% or 10% lower than Roche Liberase HI ( p = 0.04) and Serva NB1 ( p = 0.0003), respectively; however, the Sigma V group showed better islet size preservation. Yet, the enzymes resulted in similar IEQ/g digested tissue. Of the isolated islets, 70.2% were smaller than 150 μm and contributed only 20.4% to the total IEQ, while 7.4% of the islets were larger than 250 μm but contributed 42.4% to the total IEQ. In summary, BMI, pancreas size, and CIT are useful variables for predicting islet yield, but selection of enzyme and balancing digestion time and rate are also important.

Diazoxide (DZ) is a pharmacological opener of ATP-sensitive K(+) channels that has been used for mimicking ischemic preconditioning and shows protection against ischemic damage. Here we investigated whether diazoxide supplementation to University of Wisconsin (UW) solution has cellular protection during islet isolation and improves in vivo islet transplant outcomes in a rodent ischemia model. C57/B6 mice pancreata were flushed with UW or UW + DZ solution and cold preserved for 6 or 10 h prior to islet isolation. Islet yield, in vitro and in vivo function, mitochondrial morphology, and apoptosis were evaluated. Significantly higher islet yields were observed in the UW + DZ group than in the UW group (237.5 ± 25.6 vs. 108.7 ± 49.3, p < 0.01). The islets from the UW + DZ group displayed a significantly higher glucose-induced insulin secretion (0.97 ng/ml ± 0.15 vs. 0.758 ng/ml ± 0.21, p = 0.009) and insulin content (60.96 ng/islet ± 13.94 vs. 42.09 ng/islet ± 8.15, p = 0.002). The DZ-treated islets had well-preserved mitochondrial morphology with superior responses of mitochondrial potentials, and calcium influx responded to glucose. A higher number of living cells and less late apoptotic cells were observed in the UW + DZ group (p < 0.05). Additionally, the islets from the UW + DZ group had a significantly higher cure rate and improved glucose tolerance. This study is the first to report mitoprotective effects of DZ for pancreas preservation and islet isolation. In the future, it will be necessary to further understand the underlying mechanism for the mitoprotection and to test this promising approach for pancreas preservation and the islet isolation process in nonhuman primates and ultimately humans.

Islet transplantation is a promising therapy for T1DM. Key factors influencing islet yield have been identified with conflicting results. In this study, we analyzed 276 isolations to identify variables for islet yield and, additionally, islet size and size distribution. Pearson correlation analyses demonstrated that BMI had a positive correlation with pancreas size, actual islet count (AIC), and islet equivalent (IEQ)/g (all p ≤ 0.009), while CIT had a negative correlation with AIC and IEQ/g (all p ≤ 0.003). In mixed linear regression, BMI also had a positive correlation with islet size but only for shorter digestion times (≤15 min); there was no association between BMI and islet size for longer digestion times (>15 min). CIT was not associated with islet size. Donor age, sex, and preservation solutions were shown to have no correlation with islet yields or size distribution. Pancreas size had a positive correlation with AIC and a negative association with IEQ/g; it also had positive association with islet size but only for females, not males. Overdigestion was positively associated with islet counts; however, there was also a greater proportion of smaller islets when digestion rate was >74% (p = 0.005). Of the three collagenases analyzed, Sigma V had the lowest digestion rate (mean = 65%), approximately 5% or 10% lower than Roche Liberase HI (p = 0.04) and Serva NB1 (p = 0.0003), respectively; however, the Sigma V group showed better islet size preservation. Yet, the enzymes resulted in similar IEQ/g digested tissue. Of the isolated islets, 70.2% were smaller than 150 µm and contributed only 20.4% to the total IEQ, while 7.4% of the islets were larger than 250 µm but contributed 42.4% to the total IEQ. In summary, BMI, pancreas size, and CIT are useful variables for predicting islet yield, but selection of enzyme and balancing digestion time and rate are also important.

This study was designed to retrospectively compare the impact of crude Sigma V collagenase (Sigma V, n = 52) with high-purified Serva NB1 collagenase (Serva NB1, n = 42) on human islet isolation outcomes. A three-step filtration was applied to the crude Sigma V to remove endotoxin contamination and impurities; in addition, this process was used as a lot prescreening tool. Isolation outcomes were determined by digestion efficacy, islet yields, purity, viability, glucose-stimulated insulin release, and endotoxin content. The digestion efficacy between Sigma V and Serva NB1 was statistically significant (Sigma V: 64.71% vs. Serva NB1: 69.71%, p = 0.0014). However, the islet yields were similar (Sigma V: 23422.58 vs. Serva NB1: 271097 IEq, p = 0.23) between groups. There was no significant purity difference observed in fractions with purities greater than 75%. Viability (Sigma V: 93.3% vs. Serva NB1: 94.8%, p = 0.061) and stimulation indexes (Sigma V: 3.41 vs. Serva NB1: 2.74, p = 0.187) were also similar between the two groups. The impact of cold ischemia and age on the isolation outcome in the Sigma V group was comparable to the Serva NB1 group. The endotoxin content of the final products in the filtered Sigma V group was significantly less than that in the high-purified Serva NB1 group (0.022 vs. 0.052 EU/ml, p = 0.003). Additionally, in the Sigma V group there was minimal lot to lot variation and no significant loss of enzymatic activity after filtration. These findings indicate that the use of Sigma V or other crude enzyme blends for research pancreata is warranted to reduce isolation costs and increase the amount of islets available for critical islet research. These findings also validate the need for a systematic enzyme analysis to resolve these inconsistencies in overall enzyme quality once and for all.

Islet size has recently been demonstrated to be an important factor in determining human islet transplantation outcomes. In this study, a multi-layered microfluidic device was developed and quantified for size-based separation of a heterogeneous population of mouse islets. The device was fabricated using standard soft lithography and polydimethylsiloxane (PDMS). Size-based separation was first demonstrated via injection of a heterogeneous population of glass beads between 50-300 microm in diameter which were separated into five sub-populations based on their diameter. Next, a heterogeneous population of mouse pancreatic islets, between 50-250 microm in diameter was separated into four sub-populations. Throughout this process the islets remained intact without any signs of damage, as indicated by cell viability staining. Islet glucose-stimulated insulin secretion of each sub-population of islets was also evaluated demonstrating that islets smaller than 150 microm have superior stimulation indexes (SI) compared to islets larger than 150 microm. In this study, we found that islets between 100 microm and 150 microm in diameter had the greatest SI value in a heterogeneous population of islets.

Background: Islet transplantation is an emerging therapy for type 1 diabetes mellitus with variable success. Molecular therapeutics is a promising approach to improve islet graft function and transplant outcomes. Traditional delivery vectors, however, have poor cell penetration and generally lead to compromised islet function. Modified gold nanoparticles represent a potential alternative in that they are taken up into cells efficiently and have unique binding properties. The objective of this study was to investigate whether gold nanoparticles can transfect islets uniformly without compromising cellular function., Methods: Cy5-oligonucleotide-conjugated gold nanoparticle islet transfection was evaluated using confocal microscopy and flow cytometry. Isolated mice and human islets were transfected and evaluated for mitochondrial potential changes, calcium influx, and insulin secretion in response to glucose challenge and in vivo graft function., Results: Highly efficient gold nanoparticle uptake was observed. Transfected islets demonstrated normal mitochondrial function, calcium influx, and insulin release when stimulated by glucose. These islets produced a 100% diabetes cure rate after transplantation. Intraperitoneal glucose tolerance test demonstrated similar graft function as controls., Conclusion: We describe the development of a modified gold nanoparticle approach that allows for the efficient and nontoxic transfection of not only single cells but also more complex tissue architectures, such as pancreatic islets, both in vitro and in vivo., (Published by Mosby, Inc.)

Two different approaches of controlled cooling of the COBE 2991 cell-separator for islet purification were evaluated. The first method is the new Geneva COBE cooling system (GCCS), which consists of an electronically controlled liquid nitrogen injection system. The second is the University of Illinois at Chicago cooling system (UICCS), which consists of a specially designed "Cold Room" maintained at 1-8 C. For the GCCS, the mean temperatures of the gradient solutions were measured at the beginning and end of centrifugation were found to be 7 +/-0.7 C and 6.8 +/-0.6 C respectively. For the UICCS, the mean temperature of the gradients at the beginning and end of centrifugation were 4.7 +/-0.53 C and 7.03 C+/-0.91 C respectively. The presented COBE cooling systems can easily be adapted to a COBE 2991 cell-separator and are efficient in maintaining gradient solutions at a defined low temperature during centrifugation.

A microfluidic islet perifusion device was developed for the assessment of dynamic insulin secretion of multiple pancreatic islets and simultaneous fluorescence imaging of calcium influx and mitochondrial potential changes. The fanned out design of the second generation device optimized the efficient mixing and uniform distribution of rapid alternating solutions in the perifusion chamber and allowed for the generation of reproducible glucose gradients. Simultaneous imaging of calcium influx and mitochondrial potential changes in response to glucose stimulation showed high signal-noise ratio and spatial-temporal resolution. These results suggest that this system can be used for detailed study of the endocrine function of pancreatic islets with simultaneous imaging of intracellular ion fluxes and mitochondrial membrane potential changes. This tool can be used for quality assessment of islets preparation before transplantation and for in vitro studies of islet function.

A microfluidic islet perifusion device was developed for the assessment of dynamic insulin secretion of multiple islets and simultaneous fluorescence imaging of calcium influx and mitochondrial potential changes. The device consists of three layers: first layer contains an array of microscale wells (500 mum diameter and 150 mum depth) that help to immobilize the islets while exposed to flow and maximize the exposed surface area of the islets; the second layer contains a circular perifusion chamber (3 mm deep, 7 mm diameter); and the third layer contains an inlet-mixing channel that fans out before injection into the perifusion chamber (2 mm in width, 19 mm in length, and 500 mum in height) for optimizing the mixing efficiency prior to entering the perifusion chamber. The creation of various glucose gradients including a linear, bell shape, and square shapes also can be created in the microfluidic perifusion network and is demonstrated.