The standardization of pancreatic donors for islet isolation

Donor Blood Tests do Not Predict Pancreas Graft Survival After Simultaneous Pancreas Kidney Transplantation; a National Cohort Study

Simultaneous pancreas-kidney (SPK) transplantation improves quality of life and limits progression of diabetic complications. There is reluctance to accept pancreata from donors with abnormal blood tests, due to concern of inferior outcomes. We investigated whether donor amylase and liver blood tests (markers of visceral ischaemic injury) predict pancreas graft outcome using the UK Transplant Registry (2016-2021). 857 SPK recipients were included (619 following brainstem death, 238 following circulatory death). Peak donor amylase ranged from 8 to 3300 U/L (median = 70), and this had no impact on pancreas graft survival when adjusting for multiple confounders (aHR = 0.944, 95% CI = 0.754-1.81). Peak alanine transaminases also did not influence pancreas graft survival in multivariable models (aHR = 0.967, 95% CI = 0.848-1.102). Restricted cubic splines were used to assess associations between donor blood tests and pancreas graft survival without assuming linear relationships; these confirmed neither amylase, nor transaminases, significantly impact pancreas transplant outcome. This is the largest, most statistically robust study evaluating donor blood tests and transplant outcome. Provided other factors are acceptable, pancreata from donors with mild or moderately raised amylase and transaminases can be accepted with confidence. The use of pancreas grafts from such donors is therefore a safe, immediate, and simple approach to expand the donor pool to reach increasing demands.

Isolation and Purification of Human Pancreatic Islets

Successful islet isolation is the key to islet transplantation in diabetic patients. However, islet isolation is a technically complex and time-consuming manual process. Optimizing the islet isolation process can improve islet yield and quality, reduce operators, and thus reduce costs.The isolation and purification of human islets include pancreas acquisition and preservation, pancreas digestion, islet purification, islet culture, and islet quality identification. Briefly, after the duodenum was removed, the pancreas was trimmed, the main pancreatic duct was intubated at the distal end of the pancreatic head, collagenase was injected into the pancreatic duct, and the perfused pancreatic tissue was cut and then digested in a Ricordi chamber. A digestion temperature of 37 °C was continuously used to assess the number of samples and the integrity of the lysed and released islets. At the end of the digestion process, collect the digested tissue in a 500 mL centrifuge tube prefilled with 25 mL of cold (4 °C) human serum albumin and centrifuge twice at 150 g for 3 min. After mixing with UW solution as islet storage solution, put it on ice (shake occasionally to prevent clumping) after 30 min. Digested pancreatic tissue was centrifuged at 2200 rpm for 5 min in a COBE 2991 cell processor to isolate islets from exocrine tissue using a continuous density gradient. The purified islet fractions were washed twice in HBSS supplemented with 10% human serum albumin and finally collected in CMRL1066 medium supplemented with the corresponding liquid. The purity of purified islets was calculated by DTZ staining, the survival rate of islets was calculated by FDA/PI staining, and islet function was determined by in vitro glucose-stimulated insulin secretion test.

Improved recovery of human islets from young donor pancreases utilizing increased protease dose to collagenase for digesting peri-islet extracellular matrix

Human islet isolation from young donor pancreases (YDP) utilizing the current purified standard dose of collagenase-protease enzyme mixtures often results in the release of a high percentage of mantled islets. Mantled islets are those surrounded by exocrine tissue and are difficult to purify by density gradient centrifugation, leading to poor islet recovery. Based on difference in extracellular matrix, and total collagen content between YDP and old donor pancreas (ODP, > 35 Y) led us to compare results from islet isolation using increased collagenase combination (ICC) or increased protease combination (IPC), to the standard enzyme combination (SEC) in a "trisected" pancreas model to overcome the donor-to-donor variability. These results showed a reduced percentage of mantled islets (17% ± 7.5%) and higher postpurification islet recovery (83.8% ± 5.6%) with IPC. Furthermore, these results were confirmed in 13 consecutive whole pancreas islet isolations utilizing IPC from VitaCyte, Roche, or SERVA collagenase-protease enzyme mixtures. Results obtained from in vitro and in vivo islet functional assessment indicated that islets isolated using IPC retained normal islet morphology, insulin secretion, and the ability to reverse diabetes after transplantation in diabetic nude mice. This is the first report utilizing trisected pancreas to assess the effectiveness of different enzyme combinations to improve islet recovery from young donor pancreases.

Pancreatic beta cell/islet mass and body mass index

Body mass index (BMI) is widely used to define obesity. In studies of pancreatic beta-cell/islet mass, BMI is also a common standard for matching control subjects in comparative studies along with age and sex, based on the existing dogma of their significant positive correlation reported in the literature. We aimed to test the feasibility of BMI and BSA to assess obesity and predict beta-cell/islet mass. We used National Health and Nutrition Examination Survey (NHANES) data that provided dual-energy Xray absorptiometry (DXA)-measured fat mass (percent body fat; %BF), BMI, and BSA for adult subjects (20-75y; 4,879 males and 4,953 females). We then analyzed 152 cases of islet isolation performed at our center for correlation between islet yields and various donor anthropometric indices. From NHANES, over 50% of male subjects and 60% of female subjects with BMI:20.1-28.1 were obese as defined by %BF, indicating a poor correlation between BMI and %BF. BSA was also a poor indicator of %BF, as broad overlap was observed in different BSA ranges. Additionally, BMI and BSA ranges markedly varied between sex and race/ethnicity groups. From islet isolation, BMI and BSA accounted for only a small proportion of variance in islet equivalent (IEQ; r² = 0.09 and 0.11, respectively). BMI and obesity were strongly correlated in cases of high BMI subjects. However, the critical populations were non-obese subjects with BMI ranging from 20.1-28.1, in which a substantial proportion of individuals may carry excess body fat. Correlations between BMI, BSA, pancreas weight and beta-cell/islet mass were low.

Development of a Simple In Vitro Assay to Assess Digestion of the Extracellular Matrix of the Human Pancreas by Collagenase Enzyme Blends

Despite huge advances in the field of islet transplantation over the last two decades, current islet isolation methods remain suboptimal, with transplantable yields obtained in less than half of all pancreases processed worldwide. Successful islet isolation is dependent on the ability of collagenase-based enzyme blends to digest extracellular matrix components at the islet–exocrine interface. The limited availability of donor pancreases hinders the use of full-scale islet isolations to characterize pancreas digestion by different enzyme components or blends, or allow the influence of inter-pancreatic variability between donors to be explored. We have developed a method that allows multiple enzyme components to be tested on any one pancreas. Biopsies of 0.5 cm³ were taken from seven standard (age ≥45) and eight young (age ≤35) pancreases. Serial cryosections were treated with Serva collagenase, neutral protease (NP), or the two enzymes together at clinically relevant concentrations. Following digestion, insulin and either collagen IV or laminin-α5 were detected by immunofluorescent labeling. Protein loss at the islet–exocrine interface was semi-quantified morphometrically, with reference to a control section. Differential digestion of the two proteins based on the enzyme components used was seen, with protein digestion significantly influenced by donor age. Treatment with collagenase and NP alone was significantly more effective at digesting collagen IV in the standard donor group, as was the NP mediated digestion of laminin-α5. Collagenase alone was not capable of significantly digesting laminin-α5 in either donor group. Combining the two enzymes ameliorated the age-related differences in the digestion of both proteins. No significant differences in protein loss were detected by the method when analyzed by two independent operators, demonstrating the reproducibility of the assay. The development of this simple yet reproducible assay has implications for both enzyme batch testing and identifying inter-donor digestion variability, while utilizing small amounts of both enzyme and human tissue.

[Research progress on the donor cell sources of pancreatic islet transplantation for treatment of diabetes mellitus]

Objective

To summarize the research progress on the source and selection of donor cells in the field of islet replacement therapy for diabetes mellitus.

Methods

Domestic and abroad literature concerning islet replacement therapy for diabetes mellitus, as well as donor source and donor selection was reviewed and analyzed thoroughly.

Results

The shortage of donor supply is still a major obstacle for the widely clinical application of pancreatic islet transplantation (PIT). Currently, in addition to the progress on the allogeneic/autologous donor islet supply, some remarkable achievements have been also attained in the application of xenogeneic islet (from pig donor), as well as islet like cells derived from stem cells and islet cell line, potentially enlarging the source of implantable cells.

Conclusion

Adequate and suitable donor cell supply is an essential prerequisite for widely clinical application of PIT therapy for type 1 diabetes mellitus (T1DM). Further perfection of organ donation system, together with development of immune-tolerance induction, gene and bioengineering technology etc. will possibly solve the problem of donor cell shortage and provide a basis for clinical application of cellular replacement therapy for T1DM.

Islet cell transplantation for the treatment of type 1 diabetes: recent advances and future challenges

Islet transplantation is a well-established therapeutic treatment for a subset of patients with complicated type I diabetes mellitus. Prior to the Edmonton Protocol, only 9% of the 267 islet transplant recipients since 1999 were insulin independent for >1 year. In 2000, the Edmonton group reported the achievement of insulin independence in seven consecutive patients, which in a collaborative team effort propagated expansion of clinical islet transplantation centers worldwide in an effort to ameliorate the consequences of this disease. To date, clinical islet transplantation has established improved success with insulin independence rates up to 5 years post-transplant with minimal complications. In spite of marked clinical success, donor availability and selection, engraftment, and side effects of immunosuppression remain as existing obstacles to be addressed to further improve this therapy. Clinical trials to improve engraftment, the availability of insulin-producing cell sources, as well as alternative transplant sites are currently under investigation to expand treatment. With ongoing experimental and clinical studies, islet transplantation continues to be an exciting and attractive therapy to treat type I diabetes mellitus with the prospect of shifting from a treatment for some to a cure for all.

A new enzyme mixture to increase the yield and transplant rate of autologous and allogeneic human islet products

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.

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.

Donor pancreata: evolving approaches to organ allocation for whole pancreas versus islet transplantation

As islet transplantation increasingly enters the clinical arena, its coexistence with vascularized pancreas transplantation makes it necessary to reassess the questions of donor selection and allocation. In answering these questions, one must put in the balance the short-term morbidity of pancreas transplantation with the long-term attrition of islet grafts. The preferential allocation of pancreases from obese and older donors for islet isolation has been based on their association with worse pancreas transplant outcomes and better islet isolation results in islet yields. In this overview, we show that transplanted islet mass does not necessarily correlate with graft function and make the case that donor selection criteria for islet transplantation, and hence allocation rules, may need to be redefined.

Current status of islet cell transplantation

Despite substantial advances in islet isolation methods and immunosuppressive protocol, pancreatic islet cell transplantation remains an experimental procedure currently limited to the most severe cases of type 1 diabetes mellitus. The objectives of this treatment are to prevent severe hypoglycemic episodes in patients with hypoglycemia unawareness and to achieve a more physiological metabolic control. Insulin independence and long term-graft function with improvement of quality of life have been obtained in several international islet transplant centers. However, experimental trials of islet transplantation clearly highlighted several obstacles that remain to be overcome before the procedure could be proposed to a much larger patient population. This review provides a brief historical perspective of islet transplantation, islet isolation techniques, the transplant procedure, immunosuppressive therapy, and outlines current challenges and future directions in clinical islet transplantation.

Toward maximizing the success rates of human islet isolation: influence of donor and isolation factors

In order to make islet transplantation a therapeutic option for patients with diabetes there is an urgent need for more efficient islet cell processing to maximize islet recovery. Improved donor management, organ recovery techniques, implementation of more stringent donor criteria, and improved islet cell processing techniques may contribute to enhance organ utilization for transplantation. We have analyzed the effects of donor and islet processing factors on the success rate of human islet cell processing for transplantation performed at a single islet cell processing center. Islet isolation outcomes improved when vasopressors, and in particular pitressin, and steroids were used for the management of multiorgan donors. Higher islet yields were obtained from adult male donors, BMI >25 kg/m2, adequate glycemic control during hospital stay, and when the pancreas was retrieved by a local surgical team. Successful isolations were obtained in 58% of the cases when > or = 4 donor criteria were met, and even higher success rates (69%) were observed when considering > or = 5 criteria. Our data suggest that a sequential, integrated approach is highly desirable to improve the success rate of islet cell processing.

Oscillatory membrane potential response to glucose in islet beta-cells: a comparison of islet-cell electrical activity in mouse and rat

In contrast to mouse, rat islet beta-cell membrane potential is reported not to oscillate in response to elevated glucose despite demonstrated oscillations in calcium and insulin secretion. We aim to clarify the electrical activity of rat islet beta-cells and characterize and compare the electrical activity of both alpha- and beta-cells in rat and mouse islets. We recorded electrical activity from alpha- and beta-cells within intact islets from both mouse and rat using the perforated whole-cell patch clamp technique. Fifty-six percent of both mouse and rat beta-cells exhibited an oscillatory response to 11.1 mm glucose. Responses to both 11.1 mm and 2.8 mm glucose were identical in the two species. Rat beta-cells exhibited incremental depolarization in a glucose concentration-dependent manner. We also demonstrated electrical activity in human islets recorded under the same conditions. In both mouse and rat alpha-cells 11 mm glucose caused hyperpolarization of the membrane potential, whereas 2.8 mm glucose produced action potential firing. No species differences were observed in the response of alpha-cells to glucose. This paper is the first to demonstrate and characterize oscillatory membrane potential fluctuations in the presence of elevated glucose in rat islet beta-cells in comparison with mouse. The findings promote the use of rat islets in future electrophysiological studies, enabling consistency between electrophysiological and insulin secretion studies. An inverse response of alpha-cell membrane potential to glucose furthers our understanding of the mechanisms underlying glucose sensitive glucagon secretion.

Current status of pancreatic islet transplantation

DM (diabetes mellitus) is a metabolic disorder of either absolute or relative insulin deficiency. Optimized insulin injections remain the mainstay life-sustaining therapy for patients with T1DM (Type I DM) in 2006; however, a small subset of patients with T1DM (approx. 10%) are exquisitely sensitive to insulin and lack counter-regulatory measures, putting them at higher risk of neuroglycopenia. One alternative strategy to injected insulin therapy is pancreatic islet transplantation. Islet transplantation came of age when Paul E. Lacy successfully reversed chemical diabetes in rodent models in 1972. In a landmark study published in 2000, Shapiro et al. [A. M. Shapiro, J. R. Lakey, E. A. Ryan, G. S. Korbutt, E. Toth, G. L. Warnock, N. M. Kneteman and R. V. Rajotte (2000) N. Engl. J. Med. 343, 230-238] reported seven consecutive patients treated with islet transplants under the Edmonton protocol, all of whom maintained insulin independence out to 1 year. Substantial progress has occurred in aspects of pancreas procurement, transportation (using the oxygenated two-layer method) and in islet isolation (with controlled enzymatic perfusion and subsequent digestion in the Ricordi chamber). Clinical protocols to optimize islet survival and function post-transplantation improved dramatically with the introduction of the Edmonton protocol, but it is clear that this approach still has potential limitations. Newer pharmacotherapies and interventions designed to promote islet survival, prevent apoptosis, to promote islet growth and to protect islets in the long run from immunological injury are rapidly approaching clinical trials, and it seems likely that clinical outcomes of islet transplantation will continue to improve at the current exponential pace.