Search

Background: We have utilized a noninvasive technique for measuring the partial pressure of oxygen (pO2) in alginate microcapsules implanted intraperitoneally in healthy nonhuman primates (NHPs). Average pO2 is important for determining if a transplant site and capsules with certain passive diffusion characteristics can support the islet viability, metabolic activity, and dose necessary to reverse diabetes., Methods: Perfluoro-15-crown-5-ether alginate capsules were infused intraperitoneally into 3 healthy NHPs. Peritoneal pO2 levels were measured on days 0 and 7 using fluorine-19 magnetic resonance relaxometry and a fiber-optic probe. Fluorine-19 MRI was used to determine the locations of capsules within the peritoneal space on days 0 and 7. Gross and histologic evaluations of the capsules were used to assess their biocompatibility postmortem., Results: At day 0 immediately after infusion of capsules equilibrated to room air, capsules were concentrated near the infusion site, and the pO2 measurement using magnetic resonance relaxometry was 147 ± 9 mm Hg. On day 7 after capsules were dispersed throughout the peritoneal cavity, the pO2 level was 61 ± 11 mm Hg. Measurements using the fiber-optic oxygen sensor were 132 ± 7.5 mm Hg (day 0) and 89 ± 6.1 mm Hg (day 7). Perfluoro-15-crown-5-ether capsules retrieved on day 7 were intact and free-floating without host cell attachment, although the numbers of peritoneal CD20 B cells, CD4 and CD8 T cells, and CD14 macrophages increased consistent with a mild foreign body reaction., Conclusions: The peritoneal pO2 of normal NHPs is relatively low and we predict would decrease further when encapsulated islets are transplanted intraperitoneally.

Background: All human islets used in research and for the clinical treatment of diabetes are subject to ischemic damage during pancreas procurement, preservation, and islet isolation. A major factor influencing islet function is exposure of pancreata to cold ischemia during unavoidable windows of preservation by static cold storage (SCS). Improved preservation methods may prevent this functional deterioration. In the present study, we investigated whether pancreas preservation by gaseous oxygen perfusion (persufflation) better preserved islet function versus SCS., Methods: Human pancreata were preserved by SCS or by persufflation in combination with SCS. Islets were subsequently isolated, and preparations in each group matched for SCS or total preservation time were compared using dynamic glucose-stimulated insulin secretion as a measure of β-cell function and RNA sequencing to elucidate transcriptomic changes., Results: Persufflated pancreata had reduced SCS time, which resulted in islets with higher glucose-stimulated insulin secretion compared to islets from SCS only pancreata. RNA sequencing of islets from persufflated pancreata identified reduced inflammatory and greater metabolic gene expression, consistent with expectations of reducing cold ischemic exposure. Portions of these transcriptional responses were not associated with time spent in SCS and were attributable to pancreatic reoxygenation. Furthermore, persufflation extended the total preservation time by 50% without any detectable decline in islet function or viability., Conclusions: These data demonstrate that pancreas preservation by persufflation rather than SCS before islet isolation reduces inflammatory responses and promotes metabolic pathways in human islets, which results in improved β cell function.

Purpose of Review: To summarize current literature and recent findings on the potential of humidified oxygenated gas perfusion (persufflation) as an alternative method for improved organ preservation., Recent Findings: Although there are some conflicting data, the majority of the evidence suggests that persufflation, by enhancing oxygenation, can improve preservation and even rescue organs, including organs with prior exposure to warm ischemia. In some cases, persufflation produced better results than hypothermic machine perfusion. The timing of persufflation is of importance; benefits of persufflation appear to increase as the timing of its administration postprocurement decreases. This may be particularly true for tissues that are more sensitive to ischemia, such as the pancreas prior to islet isolation. Combining oxygen persufflation with nitric oxide and addition of pulsatile flow may provide further benefits and amplify its effects on improving transplant outcomes., Summary: Persufflation is a promising, relatively simple, preservation technique that enables improved oxygenation, which provides protection and improvement in the graft condition during preservation and prior to transplantation. More detailed studies are needed to optimize persufflation and evaluate its short and long-term effects in vivo.

Background: Encapsulation devices have the potential to enable cell-based insulin replacement therapies (such as human islet or stem cell-derived β cell transplantation) without immunosuppression. However, reasonably sized encapsulation devices promote ischemia due to high β cell densities creating prohibitively large diffusional distances for nutrients. It is hypothesized that even acute ischemic exposure will compromise the therapeutic potential of cell-based insulin replacement. In this study, the acute effects of high-density ischemia were investigated in human islets to develop a detailed profile of early ischemia induced changes and targets for intervention., Methods: Human islets were exposed in a pairwise model simulating high-density encapsulation to normoxic or ischemic culture for 12 hours, after which viability and function were measured. RNA sequencing was conducted to assess transcriptome-wide changes in gene expression., Results: Islet viability after acute ischemic exposure was reduced compared to normoxic culture conditions (P < 0.01). Insulin secretion was also diminished, with ischemic β cells losing their insulin secretory response to stimulatory glucose levels (P < 0.01). RNA sequencing revealed 657 differentially expressed genes following ischemia, with many that are associated with increased inflammatory and hypoxia-response signaling and decreased nutrient transport and metabolism., Conclusions: In order for cell-based insulin replacement to be applied as a treatment for type 1 diabetes, oxygen and nutrient delivery to β cells will need to be maintained. We demonstrate that even brief ischemic exposure such as would be experienced in encapsulation devices damages islet viability and β cell function and leads to increased inflammatory signaling.

Background: The islet size distribution in a preparation may contribute to islet transplant outcomes. At the same islet equivalent (IE) dose, larger islets may exhibit poorer therapeutic value and this may be because of oxygen diffusion limitations that worsen in proportion to islet size., Methods: To test this hypothesis, we studied the impact of islet size index (ISI) and other islet product characteristics on outcomes after islet autotransplant (IAT) in recipients receiving a marginal islet dose (2000-4999 IEs per kg body weight) from January 1, 2009 to June 11, 2012, at the University of Minnesota (n=58). ISI was defined as the number of IE divided by the number of islet particles (IPs) in a preparation; an ISI less than 1 indicates a mean islet diameter that is less than 150 μm. The primary post-IAT outcome was 6-month insulin use status., Results: Logistic regression analysis indicate that IPs/kg (P=0.001), IEs/kg (P=0.019), total IPs transplanted (P=0.040), and ISI (P=0.074) were most strongly correlated with the primary outcome. The ISI (mean±standard error) was lower for recipients achieving insulin independence at 6 months (0.71±0.05) versus those partially (0.83±0.05) or completely (1.00±0.07) insulin dependent. The combination of islet dose (expressed as units IPs/kg) and ISI exhibited a sensitivity of 75% and specificity of 74% in predicting insulin independence in this population of patients., Conclusion: Islet autotransplant recipients of a marginal islet doses were more likely to achieve insulin independence when transplanted with a greater number of smaller islets.

Background: In the absence of a reliable islet potency assay, nude mice (NM) transplantation is the criterion standard to assess islet quality for clinical transplantation. There are factors other than islet quality that affect the transplant outcome., Methods: Here, we analyzed the transplant outcomes in 335 NM receiving islets from human (n=103), porcine (n=205), and nonhuman primate (NHP; n=27) donors. The islets (750, 1000, and 2000 islet equivalents [IEQ]) were transplanted under the kidney capsule of streptozotocin-induced diabetic NM., Results: The proportion of mice that achieved normoglycemia was significantly higher in the group implanted with 2000 IEQ of human, porcine, or NHP islets (75% normoglycemic) versus groups that were implanted with 750 IEQ (7% normoglycemic) and 1000 IEQ (30% normoglycemic). In this study, we observed that the purity of porcine islet preparations (P≤0.001), islet pellet size in porcine preparations (P≤ 0.01), and mice recipient body weight for human islet preparations (P=0.013) were independently associated with successful transplant outcome. NHP islets of 1000 IEQ were sufficient to achieve normoglycemic condition (83%). An islet mass of 2000 IEQ, high islet purity, increased recipient body weight, and high islet pellet volume increased the likelihood of successful reversal of diabetes in transplanted mice. Also, higher insulin secretory status of islets at basal stimulus was associated with a reduced mouse cure rate. The cumulative incidence of graft failure was significantly greater in human islets (56.12%) compared with porcine islets (35.57%; P≤0.001)., Conclusion: Factors affecting NM bioassay were identified (islet mass, islet purity, pellet size, in vitro insulin secretory capability, and mouse recipient body weight) and should be considered when evaluating islet function.

Background: The optimal enzyme blend that maximizes human islet yield for transplantation remains to be determined. In this study, we evaluated eight different enzyme combinations (ECs) in an attempt to improve islet yield. The ECs consisted of purified, intact or truncated class 1 (C1) and class 2 (C2) collagenases from Clostridium histolyticum (Ch), and neutral protease (NP) from Bacillus thermoproteolyticus rokko (thermolysin) or Ch (ChNP)., Methods: We report the results of 249 human islet isolations, including 99 deceased donors (research n=57, clinical n=42) and 150 chronic pancreatitis pancreases. We prepared a new enzyme mixture (NEM) composed of intact C1 and C2 collagenases and ChNP in place of thermolysin. The NEM was first tested in split pancreas (n=5) experiments and then used for islet autologous (n=21) and allogeneic transplantation (n=10). Islet isolation outcomes from eight different ECs were statistically compared using multivariate analysis., Results: The NEM consistently achieved higher islet yields from pancreatitis (P<0.003) and deceased donor pancreases (P<0.001) than other standard ECs. Using the NEM, islet products met release criteria for transplantation from 8 of 10 consecutive pancreases, averaging 6510 ± 2150 islet equivalent number/gram (IEQ/g) pancreas and 694,681 ± 147,356 total IEQ/transplantation. In autologous isolation, the NEM yielded more than 200,000 IEQ from 19 of 21 pancreases (averaging 422,893 ± 181,329 total IEQ and 5979 ± 1469 IEQ/kg recipient body weight) regardless of the severity of fibrosis., Conclusions: A NEM composed of ChNP with CIzyme high intact C1 collagenase recovers higher islet yield from deceased and pancreatitis pancreases while retaining islet quality and function.

Background: Pancreatic acinar cells are commonly cotransplanted along with islets during auto- and allotransplantations. The aims of this study were to identify how acinar cell proteases cause human islet cell loss before and after transplantation of impure islet preparations and to prevent islet loss and improve function with supplementation of α-1 antitrypsin (A1AT)., Methods: Acinar cell protease activity, insulin levels, and percent islet loss were measured after culture of pure and impure clinical islet preparations. The effect of proteases on ultrastructure of islets and β-cell insulin granules were examined by transmission electron microscopy. The number of insulin granules and insulin-labeled immunogold particles were counted. The in vivo effect of proteases on islet function was studied by transplanting acinar cells adjacent to islet grafts in diabetic mice. The effects of A1AT culture supplementation on protease activity, insulin levels, and islet function were assessed in pure and impure islets., Results: Islet loss after culture was significantly higher in impure relative to pure preparations (30% vs. 14%, P<0.04). Lower islet purity was associated with increased protease activity and decreased insulin levels in culture supernatants. Reduced β-cell insulin granules and insulin degradation by proteases were confirmed by transmission electron microscopy. Transplantations in mice showed delayed islet graft function when acinar cells were transplanted adjacent to the islets under the kidney capsule. Supplementation of A1AT to impure islet cultures maintained islet cell mass, restored insulin levels, and preserved islet functional integrity., Conclusion: Culture of impure human islet fractions in the presence of A1AT prevents insulin degradation and improves islet recovery.

Background: Using standard density gradient (SDG) ranges for human islet purification frequently results in islet loss and transplantation of lower islet mass. Measuring the densities of islet and acinar tissue beforehand to customize the gradient range for the actual COBE 2991 cell processor (COBE) purification is likely to maximize the recovery of islets. We developed an analytical test gradient system (ATGS) for predicting pancreatic tissue densities before COBE purification to minimize islet loss during purification., Methods: Human islets were isolated from deceased donor (n=30) and chronic pancreatitis pancreata (n=30). Pancreatic tissue densities were measured before purification by the ATGS, and the density gradient range for islet purification in a COBE was customized based on density profiles determined by the ATGS. The efficiency of custom density gradients (CDGs) to recover high islet yield was compared with predefined SDGs., Results: Pancreatic tissue densities from autografts were significantly higher than in allograft preparations. In allograft purifications, a higher proportion of islets were recovered using ATGS-guided CDGs (85.9%±18.0%) compared with the SDG method (69.2%±27.0%; P=0.048). Acinar contamination at 60%, 70%, and 80% cumulative islet yield for allografts was significantly lower in the CDG group. In autograft purifications, more islets were recovered with CDGs (81.9%±28.0%) than SDGs (55.8%±22.8%; P=0.03). CDGs effectively reduced islet loss by minimizing islet sedimentation in the COBE bag., Conclusions: Using ATGS-guided CDGs maximizes the islet recovery for successful transplantations by reducing acinar contamination in allograft preparations and by reducing sedimentation of islets in the COBE bag in autograft preparations.

Background: Purified tissue dissociation enzymes (TDEs) are critical to successful human islet isolation required for clinical transplantation, but little is known about the characteristics of the key enzymes-class I (C1) and class II (C2) collagenase from Clostridium histolyticum-used in these procedures. Here, we show the differences between the C1 collagenase found in purified collagenase products manufactured by three suppliers and the impact of differences in C1 between two suppliers on human islet yield., Methods: Collagenase from Roche, Serva/Nordmark (Uetersen, Germany), and VitaCyte (Indianapolis, IN) were analyzed by analytical high-performance liquid chromatography and collagen degradation activity (CDA), an assay that preferentially detects intact C1 collagenase. Human islet isolations were performed using current standard practices., Results: These studies showed that the highest amount of intact C1 that correlated with a high specific CDA (CDA unit per milligram of protein). The highest specific CDA was found in VitaCyte product followed by the Roche and Serva/Nordmark products. The products of VitaCyte were used successfully for human islet isolation (n=14) with an average final islet yield obtained was 419,100+/-150,900 islet equivalent number (IEQ) (4147+/-1759 IEQ/g pancreas). Four of these preparations were used successfully in clinical transplantation procedures. These TDEs gave significantly better results when compared with earlier data where 27 isolations were performed using Serva NB1 collagenase and NB neutral protease where the final islet yield was 217,500+/-152,400 IEQ (2134+/-1524 IEQ/g pancreas)., Conclusions: These data indicate the importance of intact C1 and the use of the appropriate analytical assays to correlate biochemical characteristics of TDEs to islet quality and yield.

Purpose of Review: There is a critical need for meaningful viability and potency assays that characterize islet preparations for release prior to clinical islet cell transplantation. Development, testing, and validation of such assays have been the subject of intense investigation for the last decade. These efforts are reviewed, highlighting the most recent results while focusing on the most promising assays., Recent Findings: Assays based on membrane integrity do not reflect true viability when applied to either intact islets or dispersed islet cells. Assays requiring disaggregation of intact islets into individual cells for assessment introduce additional problems of cell damage and loss. Assays evaluating mitochondrial function, specifically mitochondrial membrane potential, bioenergetic status, and cellular oxygen consumption rate, especially when conducted with intact islets, appear most promising in evaluating their quality prior to islet cell transplantation. Prospective, quantitative assays based on measurements of oxygen consumption rate with intact islets have been developed, validated, and their results correlated with transplant outcomes in the diabetic nude mouse bioassay., Conclusion: More sensitive and reliable islet viability and potency tests have been recently developed and tested. Those evaluating mitochondrial function are most promising, correlate with transplant outcomes in mice, and are currently being evaluated in the clinical setting.

Background: Islet transplantation is emerging as a treatment option for selected patients with type 1 diabetes. The limited human islet supply from cadavers and poor islet yield and quality remain substantial impediments to progress in the field. Use of porcine islets holds great promise for large-scale application of islet transplantation. Consistent isolation of porcine islets is dependent on advances in pancreas procurement, pancreas preservation, and islet isolation, requiring detailed knowledge of the porcine pancreatic anatomy. The primary aim of this study was to describe the vascular and ductal anatomy of the porcine pancreas to guide and improve organ preservation and enzyme perfusion., Methods: Pancreata were removed by en bloc viscerectomy from 65 female Landrace pigs., Results: Fifteen percentage of organs exhibited inconsistent vascular branching from the celiac trunk. All organs showed uniform patterns of branching at the superior mesenteric artery. The superior and inferior mesenteric veins merged to become the portal vein in all but one case in which the inferior mesenteric vein drained into the splenic vein. Ninety-seven percent of pancreata had three lobes: duodenal lobe (DL), connecting lobe (CL), and splenic lobe (SL); 39% demonstrated ductal communication between the CL and the other two lobes; 50% had ductal communication only between the CL and duodenal lobe; and 11% presented other types of ductal delineation., Conclusions: Accounting for the variations in vascular and ductal anatomy, as detailed in this study, will facilitate development of protocols for preservation, optimal enzyme administration, and pancreas distention and digestion, and will ultimately lead to substantial improvements in isolation outcomes.

Purpose of Review: To summarize advances and limitations in pancreas procurement and preservation for pancreas and islet transplantation, and review advances in islet protection and preservation., Recent Findings: Pancreases procured after cardiac death, with in-situ regional organ cooling, have been successfully used for islet transplantation. Colloid-free Celsior and histidine-tryptophan-ketoglutarate preservation solutions are comparable to University of Wisconsin solution when used for cold storage before pancreas transplantation. Colloid-free preservation solutions are inferior to University of Wisconsin solution for pancreas preservation prior to islet isolation and transplantation. Clinical reports on pancreas and islet transplants suggest that the two-layer method may not offer significant benefits over cold storage with the University of Wisconsin solution: improved oxygenation may depend on the graft size; benefits in experimental models may not translate to human organs. Improvements in islet yield and quality occurred from pancreases treated with inhibitors of stress-induced apoptosis during procurement, storage, isolation or culture. Pancreas perfusion may be desirable before islet isolation and transplantation and may improve islet yields and quality. Methods for real-time, noninvasive assessment of pancreas quality during preservation have been implemented and objective islet potency assays have been developed and validated. These innovations should contribute to objective evaluation and establishment of improved pancreas preservation and islet isolation strategies., Summary: Cold storage may be adequate for preservation before pancreas transplants, but insufficient when pancreases are processed for islets or when expanded donors are used. Supplementation of cold storage solutions with cytoprotective agents and perfusion may improve pancreas and islet transplant outcomes.

Purpose of Review: To summarize advances and limitations in pancreas procurement and preservation for pancreas and islet transplantation, and review advances in islet protection and preservation., Recent Findings: Pancreases procured after cardiac death, with in-situ regional organ cooling, have been successfully used for islet transplantation. Colloid-free Celsior and histidine-tryptophan-ketoglutarate preservation solutions are comparable to University of Wisconsin solution when used for cold storage before pancreas transplantation. Colloid-free preservation solutions are inferior to University of Wisconsin solution for pancreas preservation prior to islet isolation and transplantation. Clinical reports on pancreas transplants suggest that the two-layer method may not offer significant benefits over cold storage with the University of Wisconsin solution: improved oxygenation may depend on the graft size; benefits in experimental models may not translate to human organs. Improvements in islet yield and quality occurred from pancreases treated with inhibitors of stress-induced apoptosis during procurement, storage, isolation or culture desirable before islet isolation and transplantation and may improve islet yield and quality. Methods for real-time, noninvasive assessment of pancreas quality during preservation have been implemented and objective islet-potency assays have been developed and validated. These innovations should contribute to objective evaluation and establishment of improved pancreas-preservation and islet-isolation strategies., Summary: Cold storage may be adequate for preservation before pancreas transplants, but insufficient when pancreases are processed for islets or when expanded donors are used. Supplementation of cold-storage solutions with cytoprotective agents and perfusion may improve pancreas and islet transplant outcomes.