Serine-protease inhibition during islet isolation increases islet yield from human pancreases with prolonged ischemia

Pancreas Preservation in Modified Histidine-lactobionate Solution Is Superior to That in University of Wisconsin Solution for Porcine Islet Isolation

BACKGROUND

We previously reported that modified extracellular-type trehalose-containing Kyoto (MK) solution, which contains a trypsin inhibitor (ulinastatin), significantly improved the islet yield compared with University of Wisconsin (UW) preservation, which is the gold standard for organ preservation for islet isolation. In this study, we evaluated the efficiency of a modified histidine-lactobionate (MHL) solution in addition to UW or MK solution. The MHL solution has a high sodium-low potassium composition with low viscosity compared with the UW solution. Moreover, similar to MK solution, MHL solution also contains ulinastatin.

METHODS

Porcine pancreata were preserved in UW, MK, or MHL solution, followed by islet isolation. An optimized number (1500 IE) of isolated islets from each group were then transplanted into streptozotocin-induced diabetic mice.

RESULTS

The islet yield before and after purification was significantly higher in the MHL group than in the UW group. On the contrary, the islet yield before and after purification was not significantly different between the MHL and MK groups. Preserving the porcine pancreata in MHL solution improved the outcome of islet transplantation in streptozotocin-induced diabetic mice compared with that in UW solution.

CONCLUSIONS

Pancreas preservation with MHL solution preserves islet function better than UW solution. The effect of MHL solution is similar to that of MK solution, suggesting that MHL solution can be used as an alternative to MK solution for pancreatic islet transplantation.

An islet maturation media to improve the development of young porcine islets during in vitro culture

BACKGROUND

The use of pancreata from pre-weaned piglets has the potential to serve as an unlimited alternative source of islets for clinical xenotransplantation. As pre-weaned porcine islets (PPIs) are immature and require prolonged culture, we developed an islet maturation media (IMM) and evaluated its effect on improving the quantity and quality of PPIs over 14 days of culture.

METHODS

PPIs were isolated from the pancreata of pre-weaned Yorkshire piglets (8-15 days old). Each independent islet isolation was divided for culture in either control Ham's F-10 media (n = 5) or IMM (n = 5) for 14 days. On day 3, 7 and 14 of culture, islets were assessed for islet yield, isolation index, viability, insulin content, endocrine cellular composition, differentiation of beta cells, and insulin secretion during glucose stimulation.

RESULTS

In comparison to control islets, culturing PPIs in IMM significantly increased islet yield. PPIs cultured in IMM also maintained a stable isolation index and viability throughout 14 days of culture. The insulin content, endocrine cellular composition, and differentiation of beta cells were significantly improved in PPIs cultured in IMM, which subsequently augmented their insulin secretory capacity in response to glucose challenge compared to control islets.

CONCLUSIONS

Culturing PPIs in IMM increases islet yield, isolation index, viability, insulin content, endocrine cellular composition, differentiation of endocrine progenitor cells toward beta cells, and insulin secretion. Due to the improved islet quantity and quality after in vitro culture, the use of IMM in the culture of PPIs will assist to advance the outcomes of clinical islet xenotransplantation.

Effectiveness of different molecular forms of C. histolyticum class I collagenase to recover islets

One factor that may contribute to variability between different lots of purified collagenase to recover islets is the molecular form of C. histolyticum class I (C1) collagenase used in the isolation procedure. Two different enzyme mixtures containing C1, class II (C2) collagenase and BP Protease were compared for their effectiveness to recover islets from split adult porcine pancreas. The same enzyme activities per g trimmed tissue were used for all isolations with the only difference being the mass of C1 required to achieve 25,000 collagen degradation activity U/g tissue. The results show no differences in performance of the two enzyme mixtures. The only significant difference is 19 fold more truncated C1 was required to achieve the same result as intact C1.

Evaluating the Effect of Serine Proteases on Collagenase Activity during Human Islet Isolation

Inconsistencies in human islet yields after collagenase digestion have been attributed to the activation of endogenous enzymes of the donor pancreas. It has been suggested that pancreatic serine proteases contribute to the proteolysis of collagenase. This study defined the effects of endogenous enzymes within the pancreas on pancreas dissociation during collagenase digestion. Levels of collagenase activity from samples taken throughout several steps in islet isolation procedures, both with and without the addition of the serine protease inhibitor Pefabloc, were determined by a spectrophotometric assay using N-[3-(2-furyl)acryloyl]-Leu-Gly-Pro-Ala as the substrate. Results clearly demonstrated that the level of collagenase activity remains stable throughout the isolation procedure despite differences in the donor factors from several cadaveric donor pancreases. This was further demonstrated by observing no difference in activity levels after incubating commercial collagenase preparations with serine proteases and analyzing by means of collagenase activity and SDS-PAGE. These data show that the presence of serine proteases does not affect the level of collagenase activity; however, they likely damage the islet cells upon prolonged digestion of the pancreatic tissue. Further efforts at examining exogenous and endogenous enzyme levels may result in the development of an enzyme cocktail that is both stable and effective for digesting the human pancreas while preserving islet function and viability.

Endogenous Pancreatic Enzyme Activity Levels Show no Significant Effect on Human Islet Isolation Yield

Despite advances in human islet isolation, islet yield remains inconsistent and unreliable. In recent studies, it has been suggested that serine proteases, in particular trypsin, have been shown to have a damaging effect on islet yield. This study evaluated enzyme activity levels throughout 42 human islet isolation procedures. Trypsin, chymotrypsin, and elastase activity was determined spectrophotometrically using suitable chromophoric substrates. The results of the islet isolations were rated as successful (n = 19) or unsuccessful (n = 23) based on the islet yield and functionality. The enzyme activity profiles of the isolations were compared. No significant differences in donor-related variables were found in this study. However, in the successful isolations, a significantly greater amount (85.6 ± 1.9%; p = 0.0017) of the pancreas was digested in a significantly shorter digestion time (19.7 ± 0.6 min; p = 0.0054) compared with 74.8 ± 2.5% of digested tissue in 22.6 ± 0.7 min in the poor isolations. This study showed no significant effect of serine protease levels on the outcome of islet isolations, regardless of enzyme inhibitor supplementation. These data suggest that serine protease activity does not sufficiently affect islet yield. However, the data show that the most successful human islet isolations are achieved when the maximum amount of tissue is digested in the shortest amount of time. This suggests that further understanding of the isolation process should focus on the role of the collagenase digestion solution in the dissociation of the endocrine–exocrine tissue connection.

Enzyme Development for Human Islet Isolation: Five Decades of Progress or Stagnation?

In comparison to procedures used for the separation of individual cell types from other organs, the process of human pancreatic islet isolation aims to digest the pancreatic exocrine matrix completely without dispersing the individual cells within the endocrine cell cluster. This objective is unique within the field of tissue separation, and outlines the challenge of islet isolation to balance two opposing priorities. Although significant progress has been made in the characterization and production of enzyme blends for islet isolation, there are still numerous areas which require improvement. The ultimate goal of enzyme production, namely the routine production of a consistent and standardized enzyme blend, has still not been realized. This seems to be mainly the result of a lack of detailed knowledge regarding the structure of the pancreatic extracellular matrix and the synergistic interplay between collagenase and different supplementary proteases during the degradation of the extracellular matrix. Furthermore, the activation of intrinsic proteolytic enzymes produced by the pancreatic acinar cells, also impacts on the chance of a successful outcome of human islet isolation. This overview discusses the challenges of pancreatic enzymatic digestion during human islet isolation, and outlines the developments in this field over the past 5 decades.

Metabolomics Study of the Effects of Inflammation, Hypoxia, and High Glucose on Isolated Human Pancreatic Islets

The transplantation of human pancreatic islets is a therapeutic possibility for a subset of type 1 diabetic patients who experience severe hypoglycemia. Pre- and post-transplantation loss in islet viability and function, however, is a major efficacy-limiting impediment. To investigate the effects of inflammation and hypoxia, the main obstacles hampering the survival and function of isolated, cultured, and transplanted islets, we conducted a comprehensive metabolomics evaluation of human islets in parallel with dynamic glucose-stimulated insulin release (GSIR) perifusion studies for functional evaluation. Metabolomics profiling of media and cell samples identified a total of 241 and 361 biochemicals, respectively. Metabolites that were altered in highly significant manner in both included, for example, kynurenine, kynurenate, citrulline, and mannitol/sorbitol under inflammation (all elevated) plus lactate (elevated) and N-formylmethionine (depressed) for hypoxia. Dynamic GSIR experiments, which capture both first- and second-phase insulin release, found severely depressed insulin-secretion under hypoxia, whereas elevated baseline and stimulated insulin-secretion was measured for islet exposed to the inflammatory cytokine cocktail (IL-1β, IFN-γ, and TNF-α). Because of the uniquely large changes observed in kynurenine and kynurenate, they might serve as potential biomarkers of islet inflammation, and indoleamine-2,3-dioxygenase on the corresponding pathway could be a worthwhile therapeutic target to dampen inflammatory effects.

Fluorogenic Peptide Substrate for Quantification of Bacterial Enzyme Activities

A novel peptide substrate (A G G P L G P P G P G G) was developed for quantifying the activities of bacterial enzymes using a highly sensitive Fluorescence Resonance Energy Transfer (FRET) based assay. The peptide substrate was cleaved by collagenase class I, II, Liberase MTF C/T, collagenase NB1, and thermolysin/neutral protease, which was significantly enhanced in the presence of CaCl2. However, the activities of these enzymes were significantly decreased in the presence of ZnSO4 or ZnCl2. Collagenase I, II, Liberase MTF C/T, thermolysin/neutral protease share similar cleavage sites, L↓G and P↓G. However, collagenase NB1 cleaves the peptide substrate at G↓P and P↓L, in addition to P↓G. The enzyme activity is pH dependent, within a range of 6.8 to 7.5, but was significantly diminished at pH 8.0. Interestingly, the peptide substrate was not cleaved by endogenous pancreatic protease such as trypsin, chymotrypsin, and elastase. In conclusion, the novel peptide substrate is collagenase, thermolysin/neutral protease specific and can be applied to quantify enzyme activities from different microbes. Furthermore, the assay can be used for fine-tuning reaction mixtures of various agents to enhance the overall activity of a cocktail of multiple enzymes and achieve optimal organ/tissue digestion, while protecting the integrity of the target cells.

Impact of donor age and weaning status on pancreatic exocrine and endocrine tissue maturation in pigs

BACKGROUND

During the process of islet isolation, pancreatic enzymes are activated and released, adversely affecting islet survival and function. We hypothesize that the exocrine component of pancreases harvested from pre-weaned juvenile pigs is immature and hence pancreatic tissue from these donors is protected from injury during isolation and prolonged tissue culture.

METHODS

Biopsy specimens taken from pancreases harvested from neonatal (5-10 days), pre-weaned juvenile (18-22 days), weaned juvenile (45-60 days), and young adult pigs (>90 days) were fixed and stained with hematoxylin and eosin. Sections were examined under a fluorescent microscope to evaluate exocrine zymogen fluorescence intensity (ZFI) and under an electron microscope to evaluate exocrine zymogen granule density (ZGD).

RESULTS

Exocrine content estimation showed significantly lower ZFI and ZGD in juvenile pig pancreases (1.5 ± 0.04 U/μm(2) , ZFI; 1.03 ± 0.07 × 10(3) /100 μm(2) , ZGD) compared to young adult pigs (2.4 ± 0.05U/μm(2) , ZFI; 1.53 ± 0.08 × 10(3) /100 μm(2) ZGD). Islets in juvenile pig pancreases were on average smaller (105.2 ± 11.2 μm) than islets in young adult pigs (192 ± 7.7 μm), but their insulin content was comparable (80.9 ± 2.2% juvenile; 84.2 ± 0.3% young adult, P > 0.05). All data expressed as mean ± SEM.

CONCLUSION

Porcine islet xenotransplantation continues to make strides toward utilization in clinical trials of type 1 diabetes. Porcine donor age and weaning status influence the extent of exocrine maturation of the pancreas. Juvenile porcine pancreases may represent an alternative donor source for islet xenotransplantation as their exocrine component is relatively immature; this preserves islet viability during extended tissue culture following isolation.

Effects of Donor-, Pancreas-, and Isolation-Related Variables on Human Islet Isolation Outcome: A Systematic Review

Different factors have been reported to influence islet isolation outcome, but their importance varies between studies and are hampered by the small sample sizes in most studies. The purpose of this study was to perform a systematic review to assess the impact of donor-, pancreas-, and isolation-related variables on successful human islet isolation outcome. PubMed, Embase, and Web of Science were searched electronically in April 2009. All studies reporting on donor-, pancreas-, and isolation-related factors relating to prepurification and postpurification islet isolation yield and proportion of successful islet isolations were selected. Seventy-four retrospective studies had sufficient data and were included in the analyses. Higher pre- and postpurification islet yields and a higher proportion of successful islet isolations were obtained when pancreata were preserved with the two-layer method rather than University of Wisconsin solution in donors with shorter cold ischemia times (CITs) [1 h longer CIT resulted in an average decline of prepurification and postpurification yields and proportion of successful isolations of 59 islet equivalents (IEQs)/g, 54 IEQs/g, and 21%, respectively]. Higher prepurification yields and higher percentage of successful islet isolations were found in younger donors with higher body mass index. Lower yields were found in donation after brain death donors compared to donation after cardiac death donors. Higher postpurification yields were found for isolation with Serva collagenase. This review identified donor-, pancreas-, and isolation-related factors that influence islet isolation yield. Standardized reports of these factors in all future studies may improve the power and identify additional factors and thereby contribute to improving islet isolation yield.

Inflammatory response in islet transplantation

Islet cell transplantation is a promising beta cell replacement therapy for patients with brittle type 1 diabetes as well as refractory chronic pancreatitis. Despite the vast advancements made in this field, challenges still remain in achieving high frequency and long-term successful transplant outcomes. Here we review recent advances in understanding the role of inflammation in islet transplantation and development of strategies to prevent damage to islets from inflammation. The inflammatory response associated with islets has been recognized as the primary cause of early damage to islets and graft loss after transplantation. Details on cell signaling pathways in islets triggered by cytokines and harmful inflammatory events during pancreas procurement, pancreas preservation, islet isolation, and islet infusion are presented. Robust control of pre- and peritransplant islet inflammation could improve posttransplant islet survival and in turn enhance the benefits of islet cell transplantation for patients who are insulin dependent. We discuss several potent anti-inflammatory strategies that show promise for improving islet engraftment. Further understanding of molecular mechanisms involved in the inflammatory response will provide the basis for developing potent therapeutic strategies for enhancing the quality and success of islet transplantation.

Implementation of a simplified method of islet isolation for allogeneic islet transplantation in cynomolgus monkeys

OBJECTIVES

The present study describes a simple and cost-effective islet isolation procedure. Using this method, allogeneic islets reverse diabetes in cynomolgus monkeys.

METHODS

Pancreatic tissue from 11 cynomolgus monkeys were digested, collected, and purified using a simplified method. Islet quantification, purity, viability, and glucose static incubation were conducted immediately after isolation. Five streptozotocin-induced monkeys with diabetes were transplanted intrahepatically, and liver biopsies from 3 of these monkeys were taken at different time points for histologic study.

RESULTS

The mean (SD) of viability, purity, and static glucose incubation stimulation index were 94.4% (2.3%), 91.8% (3.4%), and 2.6 (1.7), respectively. Monkeys who received a mean (SD) dose of 19,968 (2273) islet equivalent per kilogram (n = 4) from 2 to 3 donors who achieved prolonged normoglycemia (57-232 days), whereas the single monkey who received an islet dose of 8000 islet equivalent per kilogram did not experience diabetes reversal. Immunohistochemical assessment of the liver biopsies taken from the monkeys with normoglycemia revealed an insulin- and glucagon-positive islet graft for up to 6 months with minimal peri-islet inflammatory infiltration.

CONCLUSIONS

This study demonstrates that cynomolgus monkey islets can be successfully and efficiently harvested using a simple isolation method, and these islets can restore normoglycemia in monkeys with diabetes.

Improvement of porcine islet isolation by inhibition of trypsin activity during pancreas preservation and digestion using α1-antitrypsin

Porcine islets are considered to be a promising resource for xenotransplantation. However, it is difficult to isolate porcine islets because of the marked fragility and rapid dissociation. Endogenous trypsin is one of the main factors to damage islets during the isolation procedure. Recent studies have suggested that trypsin inhibitors during the preservation of pancreas or the collagenase digestion can improve the result of islet isolation. In this study, we examined whether α1-antitrypsin (Aralast™), which inhibits several endogenous proteases and has immunomodulatory properties, can protect islets from the proteases and improve the results of porcine islet isolation. Twelve porcine pancreata were divided into three groups: without Aralast group (standard, n = 5), preserved with Aralast using the ductal injection (DI) method (DI, n = 3), and with Aralast using the DI method and in the collagenase solution (DI+C, n = 4). Efficacy of islet isolation was assessed by islet yields, purity, and viability. The trypsin activity of the preservation and the digestion solution during the isolation procedure was measured. During islet isolation, the trypsin activity in DI+C group was significantly inhibited compared to the standard group, whereas DI group showed less effect than DI+C group. The average of postpurification islet equivalents (IEQ) per pancreas weight in the DI+C group was significantly higher than the standard group (standard: 3516 ± 497 IEQ/g, DI: 4607 ± 1090 IEQ/g, DI+C: 7097 ± 995 IEQ/g; p = 0.017 between standard and DI+C). In the DI+C group, stimulation index was higher than in other groups, although there was no significant difference. The presence of Aralast in both DI solution and collagenase solution markedly inhibited trypsin activity during pancreas digestion procedure and improved the porcine islet isolation. Inhibition of trypsin activity by Aralast could improve porcine islet isolation.

A model to evaluate toxic factors influencing islets during collagenase digestion: the role of serine protease inhibitor in the protection of islets

The recovery of all of the islets contained in a pancreas is the goal of islet isolation for transplantation. This study reveals an environment that injures the isolated islets during digestion and proposes a new model for optimal islet isolation. Islets were isolated from Wistar rat pancreases by stationary collagenase digestion while the digestion time was varied at 15, 30, 60, and 120 min. The digested pancreas and islets were analyzed histologically and adenosine nucleotides were measured. Overnight cultured islets (40 islets) were cocultured for 30 min with the supernatants obtained from pancreatic collagenase digestion at different digestion periods in order to assess the toxic environment. The peak yields of islets were obtained at 30 min of digestion. The histological study of digested pancreas showed that the exocrine cells lost their cellular integrity at 120 min of digestion, but the islet cells were left intact. Accordingly, the ATP levels of the pancreatic tissue decreased during the digestion period. The coculture experiment demonstrated that the islets cultured with the supernatants from the collagenase digestion showed digestion time-dependent disruption of the cellular integrity of islets in accordance with a rapid decrease of ATP levels in the islets. The addition of serine protease inhibitors into this coculture clearly showed protection of islets, which maintained high ATP levels in association with intact membrane integrity as assessed by AO/PI staining. Morphological deterioration of islets as well as a marked ATP decrease was evident in the entire digested pancreas as well as in islets cocultured in the supernatants from the collagenase digestion. Various factors toxic to the islets can therefore be analyzed in future experiments using this coculture model for obtaining a good yield of viable islets.

Adenine nucleotide levels in a closed enzymatic digestion system for porcine islet isolation

Obtaining viable islets is a crucial step for successful islet transplantation. Adenosine triphosphate (ATP) is a marker of cell viability. However, little is known about any changes in the energy status of the tissues that are being digested during the digestion phase. We herein examined whether the ATP content in serially digested pancreatic tissue samples could be specific objective parameters that signal the optimal point to stop the digestion process. We obtained partial pancreata (body to tail) from 4- to 5-year-old pigs from a slaughterhouse. The tissue samples were preserved in M-Kyoto solution for less than 3 h. They were digested using an automated enzymatic and mechanical dissociation system at 37°C for 90 min following intraductal injection of Liberase HI. Samples were collected from the digestive circuit every 5 or 10 min to determine the ATP level, total adenine nucleotide (TAN) level, islet count (count/g), and yield of islet equivalent (IEQ) in the serial digestive fluids. The ATP and TAN levels, IEQ and islet count were increased and then decreased during digestion process. The profile of these parameters differed from case to case. However, when ATP changing ratio (respective value/precedent value) was compared with IEQ changing ratio, a greater than threefold increase in the ATP changing ratio followed by an increase in the islet count changing ratio within 5 min was consistently observed, indicating the optimal time to stop the digestion. The ATP levels of the handpicked islets in the digested samples were lower in the overdigested phase in comparison to those in the earlier digested phase. These results indicate that the ATP level in digested fluid could be an effective indicator to estimate the viability of cells as well as determine the optimal time to terminate the digestion process in order to obtain viable islets.

Comparison of ulinastatin, gabexate mesilate, and nafamostat mesilate in preservation solution for islet isolation

For islet transplantation, maintaining organ viability after pancreas procurement is critically important for optimal graft function and survival. We recently reported that islet yield was significantly higher in the modified ET-Kyoto (MK) solution, which includes a trypsin inhibitor (ulinastatin), compared with the UW solution, and that the advantages of MK solution are trypsin inhibition and less collagenase inhibition. In this study, we compared ulinastatin with other trypsin inhibitors, gabexate mesilate, and nafamostat mesilate, in preservation solution for islet isolation. Ulinastatin was easily dissolved in ET-Kyoto solution, while ET-Kyoto with gabexate mesilate and nafamostat mesilate became cloudy immediately after addition. Although there were no significant differences in islet yield among the three groups, viability was significantly higher for the MK group than for the GK group or the NK group. The stimulation index was significantly higher for the MK group than for the GK group. In summary, there are no other trypsin inhibitors that are more effective than ulinastatin. Based on these data, we now use ET-Kyoto solution with ulinastatin for clinical islet transplantation.

Implication of mitochondrial cytoprotection in human islet isolation and transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes.

Significant improvement in islet yield and survival with modified ET-Kyoto solution: ET-Kyoto/Neutrophil elastase inhibitor

Although islet transplantation can achieve insulin independence in patients with type 1 diabetes, sufficient number of islets derived from two or more donors is usually required to achieve normoglycemia. Activated neutrophils and neutrophil elastase (NE), which is released from these neutrophils, can directly cause injury in islet grafts. We hypothesized that inhibition of NE improves islet isolation and islet allograft survival. We tested our hypothesis by examining the effects of modified ET-Kyoto solution supplemented with sivelestat, a NE inhibitor (S-Kyoto solution), on islet yield and viability in islet isolation and the effect of intraperitoneally injected sivelestat on islet graft survival in a mouse allotransplant model. NE and proinflammatory cytokines such as tumor necrosis factor (TNF)-α and interleukin (IL)-6 increased markedly at the end of warm digestion during islet isolation and exhibited direct cytotoxic activity against the islets causing their apoptosis. The use of S-Kyoto solution significantly improved islet yield and viability. Furthermore, treatment with sivelestat resulted in significant prolongation of islet allograft survival in recipient mice. Furthermore, serum levels of IL-6 and TNF-α at 1 and 2 weeks posttransplantation were significantly higher in islet recipients than before transplantation. Our results indicated that NE released from activated neutrophils negatively affects islet survival and that its suppression both in vitro and in vivo improved islet yield and prolonged islet graft survival. The results suggest that inhibition of NE activity could be potentially useful in islet transplantation for patients with type 1 diabetes mellitus.

Analysis of beta-cell gene expression reveals inflammatory signaling and evidence of dedifferentiation following human islet isolation and culture

The stresses encountered during islet isolation and culture may have deleterious effects on beta-cell physiology. However, the biological response of human islet cells to isolation remains poorly characterized. A better understanding of the network of signaling pathways induced by islet isolation and culturing may lead to strategies aimed at improving islet graft survival and function. Laser capture microdissection (LCM) was used to extract beta-cell RNA from 1) intact pancreatic islets, 2) freshly isolated islets, 3) islets cultured for 3 days, and changes in gene expression were examined by microarray analysis. We identified a strong inflammatory response induced by islet isolation that continues during in-vitro culture manifested by upregulation of several cytokines and cytokine-receptors. The most highly upregulated gene, interleukin-8 (IL-8), was induced by 3.6-fold following islet isolation and 56-fold after 3 days in culture. Immunofluorescence studies showed that the majority of IL-8 was produced by beta-cells themselves. We also observed that several pancreas-specific transcription factors were down-regulated in cultured islets. Concordantly, several pancreatic progenitor cell-specific transcription factors like SOX4, SOX9, and ID2 were upregulated in cultured islets, suggesting progressive transformation of mature beta-cell phenotype toward an immature endocrine cell phenotype. Our findings suggest islet isolation and culture induces an inflammatory response and loss of the mature endocrine cell phenotype. A better understanding of the signals required to maintain a mature beta-cell phenotype may help improve the efficacy of islet transplantation.

Insulin degradation by acinar cell proteases creates a dysfunctional environment for human islets before/after transplantation: benefits of α-1 antitrypsin treatment

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.

Improvement of pancreatic islet cell isolation for transplantation

Pancreatic islet transplantation is a promising treatment for diabetes but still faces several challenges. Poor islet isolation efficiency and poor long-term insulin independence are currently two major issues, although donor shortage and the need for immunosuppressants also need to be addressed. We established the Kyoto islet isolation method (KIIM), which has enabled us to isolate and transplant islets even from non-heart-beating donors. KIIM involves 1) cooling the donor pancreas in situ, 2) preserving the ducts with modified Kyoto solution, 3) using a modified two-layer pancreas preservation method, and 4) adjusting the density of the density gradient centrifugation and using an iodixanol-based solution for purification. KIIM has enabled us to transplant 17 islet preparations out of 21 isolations (an 81% success rate). All transplanted islets functioned, and all transplanted patients had improved glycemic control without hypoglycemic unawareness. Recently, we used KIIM for islet isolation from a brain-dead donor at Baylor, which resulted in a very high islet yield (789,984 IE) with high viability (100% by fluorescein diacetate/propidium iodide staining and a stimulation index of 4.7). This preliminary evidence suggests that KIIM may also be promising for islet isolation from brain-dead donors. In addition, to assess engrafted islet mass, we developed a secretory unit of islet transplant objects (SUITO) index: fasting C-peptide (ng/dL) / [fasting blood glucose (mg/dL) - 63] x 1500. This simple index has enabled us to monitor the engrafted islet mass. This index should be useful when deciding whether to perform additional islet transplantations to maintain insulin independence. Poor islet isolation efficacy and poor long-term results could be resolved with ongoing research.

Pancreas procurement and preservation for islet transplantation: personal considerations

Pancreatic islet transplantation is a promising option for the treatment of type 1 diabetic patients. After the successful demonstration of the Edmonton protocol, islet transplantation has advanced significantly on several fronts, including improved pancreas procurement and preservation systems. Since we frequently use pancreata from donors after cardiac death in Japan,we have applied the in situ regional organ cooling system for pancreas procurement to reduce the warm ischemic time. To reduce the apoptosis of pancreatic tissue during cold preservation, we have applied the ductal injection of preservation solution. For pancreas preservation, we use modified Kyoto solution, which is advantageous at trypsin inhibition and less collagenase inhibition. In this paper, we show pancreas procurement and preservation in our group for islet transplantation.

Clinical allogeneic and autologous islet cell transplantation: update

Islet cell transplantation is categorized as a β-cell replacement therapy for diabetic patients who lack the ability to secrete insulin. Allogeneic islet cell transplantation is for the treatment of type 1 diabetes, and autologous islet cell transplantation is for the prevention of surgical diabetes after a total pancreatectomy. The issues of allogeneic islet cell transplantation include poor efficacy of islet isolation, the need for multiple donor pancreata, difficulty maintaining insulin independence and undesirable side effects of immunosuppressive drugs. Those issues have been solved step by step and allogeneic islet cell transplantation is almost ready to be the standard therapy. The donor shortage will be the next issue and marginal and/or living donor islet cell transplantation might alleviate the issue. Xeno-islet cell transplantation, β-cell regeneration from human stem cells and gene induction of the naïve pancreas represent the next generation of β-cell replacement therapy. Autologous islet cell transplantation after total pancreatectomy for the treatment of chronic pancreatitis with severe abdominal pain is the standard therapy, even though only limited centers are able to perform this treatment. Remote center autologous islet cell transplantation is an attractive option for hospitals performing total pancreatectomies without the proper islet isolation facilities.

Tissue dissociation enzymes for isolating human islets for transplantation: factors to consider in setting enzyme acceptance criteria

Tissue dissociation enzymes are critical reagents that affect the yield and quality of human pancreatic islets required for islet transplantation. The United States Food and Drug Administration's oversight of this procedure recommends laboratories to set acceptance criteria for enzymes used in the manufacture of islet products for transplantation. Currently, many laboratories base this selection on personal experience because biochemical analysis is not predictive of success of the islet isolation procedure. This review identifies the challenges of correlating results from enzyme biochemical analysis to their effectiveness in human islet isolation and suggests a path forward to address these challenges to improve control of the islet manufacturing process.

Experience of islet isolation without neutral protease supplementation

BACKGROUND

We have reported improved islet isolation outcomes using a new digestion protocol where the pancreas is perfused only with collagenase, and neutral protease (NP) is administered during the digestion phase. Since the inception of this protocol, we have had some cases where administration of NP was not required. Our new protocol was utilized in 94 islet isolations. The timing of adding NP was dependent on the progression of digestion but in 10 cases the progression was rapid and most islets in the assessment samples were free from the exocrine tissue. As a result NP was not added at all for these isolations (no-NP group). In the remaining 84 isolations, NP was added during digestion phase (control group).

RESULTS

Pancreata in the each group were digested with a similar collagenase dose. Digestion time was shorter in the no-NP (15.0±1.8 vs 19.5±0.6 min, P=0.004). At post-digestion, the no-NP had fewer trapped islets (10.9±2.8 vs 28.1±2.4%, P=0.009). Post-purification islet yield was similar (355±45 x10 ( 3) vs 318±17 x10 ( 3) IE, P=0.29). Five preparations in the no-NP were used for clinical transplantation, leading to a 64.3±15.2% reduction in insulin usage. Interestingly, cold ischemia time was longer in the no-NP (10.3±0.9 vs 7.9±0.4 h, P=0.04). One particular collagenase lot having the highest NP activity contamination was used in 7 isolations in the no-NP. Our experience indicates that supplementation of collagenase with NP is not always necessary for effective isolation. Cold ischemia time and NP contamination should be evaluated for optimal NP dosage.

Islet isolation for clinical transplantation

Islet transplantation is emerging as a viable treatment option for selected patients with type 1 diabetes. Following the initial report in 2000 from Edmonton of insulin independence in seven out of seven consecutive recipients, there has been a huge expansion in clinical islet transplantation. The challenge we now face is the apparent decline in graft function over time. Isolating high-quality human islets which survive and function for a longer period will no doubt contribute to further improvement in long-term clinical outcome. This chapter reviews the selection of appropriate donors for islet isolation and transplantation, describes each step during islet isolation, and discusses the scope for further improvements.

Comparison of modified Celsior solution and M-kyoto solution for pancreas preservation in human islet isolation

Since the successful demonstration of the Edmonton protocol, islet transplantation has advanced significantly on several fronts, including improved pancreas preservation systems. In this study, we evaluated two different types of organ preservation solutions for human islet isolation. Modified Celsior (Celsior solution with hydroxyethyl starch and nafamostat mesilate; HNC) solution and modified Kyoto (MK) solution were compared for pancreas preservation prior to islet isolation. Islet yield after purification was significantly higher in the MK group than in the HNC group (MK = 6186 ± 985 IE/g; HNC = 3091 ± 344 IE/g). The HNC group had a longer phase I period (digestion time), a higher volume of undigested tissue, and a higher percentage of embedded islets, suggesting that the solution may inhibit collagenase. However, there was no significant difference in ATP content in the pancreata or in the attainability of posttransplant normoglycemia in diabetic nude mice between the two groups, suggesting that the quality of islets was similar among the two groups. In conclusion, MK solution is better for pancreas preservation before islet isolation than HNC solution due to the higher percentage of islets that can be isolated from the donor pancreas. MK solution should be the solution of choice among the commercially available solutions for pancreatic islet isolation leading to transplantation.

Comparison of trypsin inhibitors in preservation solution for islet isolation

Islet transplantation has recently emerged as an effective therapy and potential cure for type 1 diabetes mellitus. Recent reports show that the two-layer method (TLM), which employs oxygenated perfluorochemical (PFC) and University of Wisconsin (UW) solution, is superior to simple cold storage in UW for pancreas preservation in islet transplantation. Moreover, we recently reported that islet yield was significantly higher in the ET-Kyoto solution with ulinastatin (MK)/PFC preservation solution compared with the UW/PFC preservation solution in the porcine model and that the advantages of MK solution are trypsin inhibition and less collagenase inhibition. In this study, we compared ulinastatin with another trypsin inhibitor, Pefabloc, in preservation solution for islet isolation. Islet yield before purification was higher in the MK/PFC group compared with the ET-Kyoto with Pefabloc (PK)/PFC group. The stimulation index was higher for the MK/PFC group than for the PK/PFC group. These data suggest that ET-Kyoto with ulinastatin was the better combination for pancreas preservation than ET-Kyoto with Pefabloc. Based on these data, we now use ET-Kyoto solution with ulinastatin for clinical islet transplantation.

Ductal injection of preservation solution increases islet yields in islet isolation and improves islet graft function

For islet transplantation, it is important to obtain an available islet mass adequate for diabetes reversal from a single donor pancreas. A recent report demonstrated that the use of M-Kyoto solution instead of UW solution improved islet yields in the two-layer method for pancreas preservation. The present study investigated whether the ductal injection of a large volume of preservation solution (UW and M-Kyoto solution) before pancreas storage improves islet yields. Islet yield both before and after purification was significantly higher in the ductal injection (+) group compared with the ductal injection (-) group. TUNEL-positive cells in the ductal injection (+) group were significantly decreased in comparison to the ductal injection (-) group. The ductal injection of preservation solution increased the ATP level in the pancreas tissue and reduced trypsin activity during the digestion step. Annexin V and PI assays showed that the ductal injection prevents islet apoptosis. In a transplant model, the ductal injection improved islet graft function. These findings suggest that the ductal injection of preservation solution, especially the M-Kyoto solution, leads to improved outcomes for pancreatic islet transplantation. Based on these data, this technique is now used for clinical islet transplantation from non-heart-beating donor pancreata or living donor pancreas.

Endogenous pancreatic protease activity and methods for impeding their function

Pefabloc and Trasylol are serine protease inhibitors that have been used during islet isolation to inhibit endogenous proteases (trypsin, chymotrypsin, and elastase) and improve islet yields. Using in vitro studies, we evaluated the effects of Pefabloc and Trasylol on the activities of these proteases and the effect of Pefabloc on islet function. In addition, it has been reported that Protector Solution (PS) enhances the efficiency of Pefabloc. Thus, we evaluated the efficacy of Pefabloc in the presence or absence of PS. EnzCheck protease assay was used to measure the activities of trypsin, chymotrypsin, elastase, liberase, and thermolysin in the presence or absence of 0.4 mmol/L Pefabloc (with or without PS) or 0.43 micromol/L Trasylol. We also tested switch samples containing the highest concentration of enzymes. Pefabloc significantly inhibited trypsin, chymotrypsin, elastase, and switch, but not liberase or thermolysin. Trasylol significantly inhibited all enzymes except for elastase and switch sample. Unexpectedly, the potency of Pefabloc was abrogated when diluted first in PS. Insulin release was diminished when islets were incubated or perifused with Pefabloc. In conclusion, Pefabloc when added appropriately significantly blocked in vitro protease activity. Unfortunately, Pefabloc also decreased islet insulin secretion, making it unsuitable for islet isolation. Trasylol cannot be used with collagenase because it impaired both liberase and thermolysin.

Allogeneic islet transplantation

Significant progress has been made in the field of beta-cell replacement therapies by islet transplantation in patients with unstable Type 1 diabetes mellitus (T1DM). Recent clinical trials have shown that islet transplantation can reproducibly lead to insulin independence when adequate islet numbers are implanted. Benefits include improvement of glycemic control, prevention of severe hypoglycemia and amelioration of quality of life. Numerous challenges still limit this therapeutic option from becoming the treatment of choice for T1DM. The limitations are primarily associated with the low islet yield of human pancreas isolations and the need for chronic immunosuppressive therapies. Herein the authors present an overview of the historical progress of islet transplantation and outline the recent advances of the field. Cellular therapies offer the potential for a cure for patients with T1DM. The progress in beta-cell replacement treatment by islet transplantation as well as those of emerging immune interventions for the restoration of self tolerance justify great optimism for years to come.

Application of the two-layer method on pancreas digestion results in improved islet yield and maintained viability of isolated islets

BACKGROUND

Oxygenation of the pancreas during preservation by the two-layer method (TLM) has shown beneficial effects in islet transplantation. Here, we apply this concept (oxygenation) to the isolation process.

METHODS

Rat pancreases were digested using four different methods. Pancreases were digested with preoxygenated perfluorocarbon (PFC) in group 2 and without it in group 1. Additionally, adenosine was included in the collagenase solution in subgroups B but not in subgroups A. Islet yields and viability were compared between groups.

RESULTS

Tissue oxygen tension in group 1 was essentially zero during digestion, but rapidly reached around 300 mm Hg and was maintained in group 2. The tissue adenosine triphosphate (ATP) level in rat pancreas just after laparotomy (control) was 4.2+/-0.7 micromol/g dry weight; after digestion, it was 0.12+/-0.03 micromol/g, 0.70+/-0.10 micromol/g, 0.30+/-0.18 micromol/g, and 2.90+/-0.80 micromol/g in groups 1A, 1B, 2A, and 2B, respectively. No significant differences were observed between group 2B and control (P=0.19). Islet yields (IEQ/pancreas) were 1600+/-400, 1400+/-400, 1300+/-400, and 2400+/-100 in groups 1A, 1B, 2A, and 2B, respectively. The islet yield of group 2B was significantly higher than other groups (P<0.05). The cure rate after transplanting 200 islets into athymic nude mice did not differ (80% in all groups). The stimulation indices in the four groups were also the same.

CONCLUSIONS

Tissue ATP levels after digestion were well maintained using TLM with adenosine digestion method. Consequently, greater numbers of islets could be retrieved. The new method was at least equivalent to islet function isolated by conventional method. Clinical study is therefore warranted.

Mitochondrial Targeting with Antioxidant Peptide SS-31 Prevents Mitochondrial Depolarization, Reduces Islet Cell Apoptosis, Increases Islet Cell Yield, and Improves Posttransplantation Function

Apoptotic cell death is a defined pathway for islet cell demise, and mitochondrial dysfunction contributes to islet cell apoptosis. The hypothesis that the novel peptide D-Arg-2', 6'-dimethyltyrosine-Lys-Phe-NH2 (SS-31), previously shown to target inner mitochondrial membrane and prevent oxidative damage of neuronal cells and other cell types, optimizes pancreatic islet isolation and improves posttransplantation function in recipients with diabetes was investigated. Herein is demonstrated that SS-31 readily penetrates intact mouse islets, preserves mitochondrial polarization, reduces islet cell apoptosis, and increases islet cell yield. Optimization of islet isolation is demonstrable after SS-31 pretreatment of islet (pancreas) donor mice and with the addition of SS-31 to reagents that are used in the isolation of mouse islets. The supplementation of in vitro culture medium with SS-31 reduced islet cell apoptosis and increased the viability of human islets, as ascertained by dual-parameter flow cytometry analysis. In a stringent marginal islet cell mass transplantation model (200 mouse islets transplanted under the renal capsule of syngeneic diabetic mice) and using islets that were derived from old mice (>24 wk), SS-31 treatment was associated with prompt and sustained normoglycemia, whereas the untreated islet graft recipients remained diabetic. Our data suggest a novel strategy to optimize islet isolation and reduce the need for multiple pancreata to achieve insulin independence in the recipient with type 1 diabetes. Because SS-31 was effective with "extended" islet donors, it is hypothesized that the antioxidant SS-31 may serve to increase the pool of eligible organ donors.

Adjustment of digestion enzyme composition improves islet isolation outcome from marginal grade human donor pancreata

Despite improvements and recent attempts to standardize techniques to isolate islets from human donor pancreata, there still exists the problem of consistently recovering sufficient quantities of high quality islets. Moreover, achieving consistent recoveries of high numbers of good quality islets becomes even more challenging from marginal grade human donor pancreata with prolonged cold ischemic times. In this study, we investigate whether addition of Pefabloc SC, a serine protease inhibitor, in combination with Pulmozyme, a recombinant human DNase I, to Liberase HI improves islet isolation outcome from marginal grade human donor pancreata (cold ischemic time > 12 h). Twenty-three marginal grade human donor pancreata were randomly digested using four different enzyme preparations: (1) Liberase alone (n = 6), (2) +Pefabloc (n = 7), (3) +Pefabloc/Pulmozyme (n = 5), and (4) +Pulmozyme (n = 5). Overall, there were no significant differences in donor age, body mass index (BMI), pancreas weight, and cold ischemic time. After purification, significantly higher islet yields (3,281 +/- 590 IE/g) were obtained with the Pefabloc/Pulmozyme group as compared to the Liberase alone (1,615 +/- 305 IE/g) or the Pefabloc group (1,255 +/- 261 IE/g) (P < 0.05). Significant improvements in islet viability were also noted from the Pefabloc/Pulmozyme group (87.3 +/- 4.4%) as opposed to islets isolated from the Pefabloc group (75.2 +/- 3.9%) (P < 0.05). No significant differences in insulin secretory response to glucose stimulation among the four groups were observed, which indicates that the addition of Pefabloc and/or Pulmozyme does not have a detrimental effect on the functionality of islets. It is concluded that the addition of Pefabloc in combination with Pulmozyme to the Liberse HI significantly improves islet isolation outcome and potentially impacts the viability and morphology of the islets obtained from marginal grade human donor pancreata with prolonged cold ischemic times.

The ADP/ATP ratio: A novel predictive assay for quality assessment of isolated pancreatic islets

The current standard assays for islet product release criteria are unable to predict the outcome after clinical islet transplantation. Therefore, establishment of reliable and rapid assays enabling pre-transplantation prediction of islet potency is warranted. In the present study, we have evaluated the adenosine diphosphate (ADP)/adenosine triphosphate (ATP) test, the glucose-stimulated insulin release, the loss of islets during the first 24 h in culture, and the insulin/deoxyribonucleic acid as predictive assays for the ability of isolated porcine islets to cure athymic mice with streptozotocin-induced diabetes. From the results presented, it is concluded that the measurement of the ADP/ATP ratio was the only test that correlated with transplantation outcome. In summary, we propose that the ADP/ATP assay is worthwhile as applied to human islet transplantation and seek to validate it as a rapid and potent predictor of transplant outcome.

Overcoming the Challenges Now Limiting Islet Transplantation: A Sequential, Integrated Approach

Steady improvements in islet cell processing technology and immunosuppressive protocols have made pancreatic islet transplantation a clinical reality for the treatment of patients with Type 1 diabetes mellitus (T1DM). Recent trials are showing that improved glycemic metabolic control, prevention of severe hypoglycemia, and better quality of life can be reproducibly achieved after transplantation of allogeneic islets in patients with unstable T1DM. Despite these encouraging results, challenges ahead comprise obtaining adequate islet cells for transplant, enhancing islets engraftment, sustaining beta cell mass and function over time, and defining effective immune interventions, among others. In order to overcome the current hurdles to the widespread application of islet transplantation there is a need for implementation of integrated, sequential therapeutic approaches.

Pancreatic islet transplantation for treating diabetes

Pancreatic islet transplantation is one of the options for treating diabetes and has been shown to improve the quality of life of severe diabetic patients. Since the Edmonton protocol was announced, islet transplantation have advanced considerably, including islet after kidney transplantation, utilisation of non-heart-beating donors, single-donor islet transplantation and living-donor islet transplantation. These advances were based on revised immunosuppression protocols, improved pancreas procurement and islet isolation methods, and enhanced islet engraftment. Further improvements are necessary to make islet transplantation a routine clinical treatment. To synergise efforts towards a cure for type 1 diabetes, a Diabetes Research Institute (DRI) Federation is currently being established to include leading diabetes research centres worldwide, including DRIs in Miami, Edmonton and Kyoto among others.

Prospective and challenges of islet transplantation for the therapy of autoimmune diabetes

Pancreatic islet cell transplantation is an attractive treatment of type 1 diabetes (T1D). The success enhanced by the Edmonton protocol has fostered phenomenal progress in the field of clinical islet transplantation in the past 5 years, with 1-year rates of insulin independence after transplantation near 80%. Long-term function of the transplanted islets, however, even under the Edmonton protocol, seems difficult to accomplish, with only 10% of patients maintaining insulin independence 5 years after transplantation. These results differ from the higher metabolic performance achieved by whole pancreas allotransplantation, and autologous islet cell transplantation, and form the basis for a limited applicability of islet allografts to selected adult patients. Candidate problems in islet allotransplantation deal with alloimmunity, autoimmunity, and the need for larger islet cell masses. Employment of animal islets and stem cells, as alternative sources of insulin production, will be considered to face the problem of human tissue shortage. Emerging evidence of the ability to reestablish endogenous insulin production in the pancreas even after the diabetic damage occurs envisions the exogenous supplementation of islets to patients also as a temporary therapeutic aid, useful to buy time toward a possible self-healing process of the pancreatic islets. All together, islet cell transplantation is moving forward.

Modified two-layer preservation method (M-Kyoto/PFC) improves islet yields in islet isolation

Islet allotransplantation can achieve insulin independence in patients with type I diabetes. Recent reports show that the two-layer method (TLM), which employs oxygenated perfluorochemical (PFC) and UW solution, is superior to simple cold storage in UW for pancreas preservation in islet transplantation. However, UW solution has several disadvantages, including the inhibition of Liberase activity. In this study, we investigated the features of a new solution, designated M-Kyoto solution. M-Kyoto solution contains trehalose and ulinastatin as distinct components. Trehalose has a cytoprotective effect against stress, and ulinastatin inhibits trypsin. In porcine islet isolation, islet yield was significantly higher in the M-Kyoto/PFC group compared with the UW/PFC group. There was no significant difference in ATP content in the pancreas between the two groups, suggesting that different islet yields are not due to their differences as energy sources. Compared with UW solution, M-Kyoto solution significantly inhibited trypsin activity in the digestion step; moreover, M-Kyoto solution inhibited collagenase digestion less than UW solution. In conclusion, the advantages of M-Kyoto solution are trypsin inhibition and less collagenase inhibition. Based on these data, we now use M-Kyoto solution for clinical islet transplantation from nonheart-beating donor pancreata.

Ameliorating injury during preservation and isolation of human islets using the two-layer method with perfluorocarbon and UW solution

This study assessed the effects of a two-layer method (TLM), using perfluorocarbon and UW solution, on the quality of human pancreata following storage and islet yield/function after isolation. In part A, TLM was applied immediately after procurement and the energetic profile was compared to a group treated with UW solution only (control) throughout 24-h storage. In part B, cadaveric human pancreata were procured and subjected to a TLM after cold storage in UW solution (TLM group) or UW solution (control group). Energetics, lipid peroxidation, and islet recovery/function were assessed after preservation at 4 degrees C. In part A, after 9-h storage, the energetic profile (ATP, ATP/ADP, energy charge) for the TLM group was superior to controls. In part B, TLM treatment resulted in consistently greater ATP, ATP/ADP, and energy charge values than with storage in UW solution alone (p < 0.05). UW treatment resulted in 40% greater peroxidative damage than in the TLM group (p < 0.05). Islet recovery and functional viability were 30-40% higher following TLM treatment (p < 0.05). These data support the hypothesis that islet viability and yields can be significantly improved using a brief period of TLM treatment following conventional UW storage; reduced energetic and oxidative stress are implicated as potential mechanisms.

Pancreatic islet cell transplantation using non-heart-beating donors (NHBDs)

Recent dramatic improvements in clinical islet cell transplantation demonstrated by the Edmonton group have increased the demand for this treatment, and donor shortage could become a major problem. Utilization of marginal donors could alleviate the donor shortage, and non-heart-beating donors (NHBDs) might be good resources. The University of Pennsylvania group demonstrated that it was possible to isolate islets from NHBDs, and the group actually transplanted islets from NHBDs, for the first time. The patient became insulin-independent; however, there had been no more cases using NHBDs until our group initiated islet transplantations from NHBDs in Japan. In order to utilize NHBDs effectively, we modified the standard islet isolation method. These modifications included minimizing the warm ischemic time, the use of trypsin inhibition during isolation, carrying out density measurement before purification and the use of a less toxic islet purification solution. With these modifications we were able to transplant nine of ten islet preparations from ten NHBDs (90%), into five type-1 diabetic patients. The first transplantation was performed on April 7, 2004 (the first time in Japan), and this patient became insulin-independent after the second islet transplantation (first time in Japan). All patients showed improved glycemic control and reduced insulin requirements, without hypoglycemic events. We also performed living-donor islet transplantation, with our modified islet isolation protocol, on January 19, 2005. The improved islet isolation protocol enabled us to perform effective islet transplantations from NHBDs, and it also enabled us to perform the living-donor islet transplantation.

Harmful delayed effects of exogenous isolation enzymes on isolated human islets: relevance to clinical transplantation

The isolation process exposes human pancreatic islets to exogenous isolation enzymes. Exposure to these enzymes, as a result of intraductal injection in the pancreas or simple contact of islets with enzyme components, causes internalization into the islet cells of enzymes and their by-products. Human islets exposed to Liberase-HI exhibit a decreased insulin secretory ability that correlates with the time of exposure. This phenomenon is paralleled by increased expression of adhesion molecules (CD106 and CD62p) and activation of apoptotic pathways (Bax and Bcl-2) in islet cells. Increased functional impairment is also observed after islet transplantation in diabetic immunodeficient mice. Experimental exposure of islet grafts to exogenous isolation enzymes causes intense inflammation (CD11b positive cells) at the transplant site and it was associated with sickness behavior and eventually death of mouse recipients. The extent of these adverse effects likely deceives the standard qualitative protocols currently in use to assess islet quality in vitro. Reducing the secondary effects of exogenous isolation enzymes on isolated human islets may be crucial to enhance the quality of islets as tissue grafts.

A simple method using a polymethylpenten chamber for isolation of human pancreatic islets

OBJECTIVES

Isolation of large numbers of intact and functional human islets remains difficult and expensive. We describe a novel method using a polymethylpenten chamber (PMPC) and compare its efficacy to the classic method using a stainless steel chamber (SSC).

METHODS

Five pancreases obtained from cadaveric donors were processed with the SSC method, and the islets were purified with a Cobe cell separator. The next 15 pancreases (similar donor characteristics) were distended with Liberase HI, minced, and digested in a PMPC whose thermic properties did not require continuous heating to maintain temperature of the prewarmed medium at 37 degrees C. The digestion was done in 2 phases to avoid damaging the first freed islets. Digested tissue was filtered on a column of 6-mm glass beads and 500-microm mesh screen, so that tissue volume was small enough to permit purification on discontinuous Ficoll gradients in tubes.

RESULTS

With the PMPC method, the extent of digestion (+/-70%), yield (approximately 5000 IEQ/g), and final purity (73%) and viability (84%) of the islets was similar to those with the SSC, but the proportion of large islets (>150 microm in diameter) was higher. Cell composition (beta vs. non-beta cells) of isolated islets was not different from that of islets in situ in the same pancreas. Islet function, assessed by perifusion, showed an excellent average stimulation index of approximately 13-fold (15 vs. 1 mmol/L glucose, without cAMP-raising agent).

CONCLUSIONS

This new method for isolation of human islets uses simple, low-cost, and potentially disposable material and requires a team of only 2 persons. The technique is as efficient as the classic SSC method and provides islets with excellent integrity and insulin-secreting capacity.