The effect of isolation methods and the use of different enzymes on islet yield and in vivo function

Revisiting pancreatic islet isolation in murine models: A practical and effective technical protocol

The endocrine pancreas is composed of clusters of cell groups called pancreatic islets. These cells are responsible for the synthesis and secretion of hormones crucial for glycemic homeostasis, such as insulin and glucagon. Therefore, these cells were the targets of many studies. One method to study and/or understand endocrine pancreatic physiology is the isolation of these islets and stimulation of hormone production using different concentrations of glucose, agonists, and/or antagonists of specific secretagogues and mimicking the stimulation of hormonal synthesis and secretion. Many researchers studied pancreatic physiology in murine models due to their ease of maintenance and rapid development. However, the isolation of pancreatic islets involves meticulous processes that may vary between rodent species. The present study describes a simple and effective technical protocol for isolating intact islets from mice and rats for use as a practical guide for researchers. The method involves digestion of the acinar parenchyma by intraductal collagenase. Isolated islets are suitable for in vitro endocrine secretion analyses, microscopy techniques, and biochemical analyses.

Pretransplant HOMA-β Is Predictive of Insulin Independence in 7 Patients With Chronic Pancreatitis Undergoing Islet Autotransplantation

Islet and β-cell function is intrinsic to glucose homeostasis. Pancreatectomy and islet autotransplantation (PIAT) for chronic pancreatitis (CP) treatment is a useful model for assessing islet function in the absence of immune-suppression and to perform extensive presurgical metabolic evaluations not possible from deceased donors. We recently showed that in CP-PIAT patients, preoperative islet identity loss presented with postoperative glycemic loss. Here, we examine presurgical islet function using Homeostatic Model Assessment-Beta Cell Function (%) (HOMA-β) and glycemic variables and compared them with postsurgical insulin independence and their predicted alignment with Secretory Unit of Islet Transplant Objects (SUITO) and beta cell score after transplantation (BETA-2) scores.

Comparison of Islet Characterization from Use of Standard Crude Collagenase to GMP-Grade Collagenase Enzyme Blends in Preweaned Porcine Islet Isolations

For the advancement of porcine xenotransplantation for clinical use in type 1 diabetes mellitus, the concerns of a sustainable and safe digestion enzyme blend must be overcome. Incorporating good manufacturing practices (GMP) can facilitate this through utilizing GMP-grade enzymes. In conjunction, still taking into account the cost-effectiveness, a wide concern. We evaluated how GMP-grade enzyme blends impact our piglet islets and their long-term effects.  Preweaned porcine islets (PPIs) were isolated from 8- to 10-day-old pigs. Digestion enzyme blends, collagenase type V (Type V), collagenase AF-1 GMP-grade with collagenase NB 6 GMP-grade (AF-1 and NB 6), and collagenase AF-1 GMP-grade with collagenase neutral protease AF GMP-grade (AF-1 and NP AF) were compared. Islet quality control assessments, islet yield, viability, and function, were performed on days 3 and 7, and cell content was performed on day 7.  GMP-grade AF-1 and NB 6 (17,209 ± 2,730 islet equivalent per gram of pancreatic tissue [IE/g] on day 3, 9,001 ± 1,034 IE/g on day 7) and AF-1 and NP AF (17,214 ± 3,901 IE/g on day 3, 8,833 ± 2,398 IE/g on day 7) showed a significant increase in islet yield compared to Type V (4,618 ± 1,240 IE/g on day 3, 1,923 ± 704 IE/g on day 7). Islet size, viability, and function showed comparable results in all enzyme blends. There was no significant difference in islet cellular content between enzyme blends.  This study demonstrated a comparison of GMP-grade collagenase enzyme blends and a standard crude collagenase enzyme in preweaned-aged porcine, a novel topic in this age. GMP-grade enzyme blends of AF-1 and NB 6 and AF-1 and NP AF resulted in substantially higher yields and as effective PPIs compared to Type V. In the long run, considering costs, integrity, and sustainability, GMP-grade enzyme blends are more favorable for clinical application due to high reproducibility in comparison to undefined manufacturing processes of standard enzymes.

Semi-Automated Assessment of Human Islet Viability Predicts Transplantation Outcomes in a Diabetic Mouse Model

In clinical and experimental human pancreatic islet transplantations, establishing pretransplant assessments that accurately predict transplantation outcomes is crucial. Conventional in vitro viability assessment that relies on manual counting of viable islets is a routine pretransplant assessment. However, this method does not correlate with transplantation outcomes; to improve the method, we recently introduced a semi-automated method using imaging software to objectively determine area-based viability. The goal of the present study was to correlate semi-automated viability assessment with posttransplantation outcomes of human islet transplantations in diabetic immunodeficient mice, the gold standard for in vivo functional assessment of isolated human islets. We collected data from 61 human islet isolations and 188 subsequent in vivo mouse transplantations. We assessed islet viability by fluorescein diacetate and propidium iodide staining using both the conventional and semi-automated method. Transplantations of 1,200 islet equivalents under the kidney capsule were performed in streptozotocin-induced diabetic immunodeficient mice. Among the pretransplant variables, including donor factors and post-isolation assessments, viability measured using the semi-automated method demonstrated a strong influence on in vivo islet transplantation outcomes in multivariate analysis. We calculated an optimized cutoff value (96.1%) for viability measured using the semi-automated method and showed a significant difference in diabetes reversal rate for islets with viability above this cutoff (77% reversal) vs. below this cutoff (49% reversal). We performed a detailed analysis to show that both the objective measurement and the improved area-based scoring system, which distinguished between small and large islets, were key features of the semi-automated method that allowed for precise evaluation of viability. Taken together, our results suggest that semi-automated viability assessment offers a promising alternative pretransplant assessment over conventional manual assessment to predict human islet transplantation outcomes.

Variability in endocrine cell identity in patients with chronic pancreatitis undergoing islet autotransplantation

Beta-cell dedifferentiation as shown by cellular colocalization of insulin with glucagon and/or vimentin, and decreased expression of MAFA and/or urocortin3 has been suggested to contribute to metabolic decompensation in type 2 diabetes, and was recently described postimplantation in islet allotransplant patients. Dysglycaemia and diabetes mellitus are often encountered preoperatively in patients undergoing pancreatectomy and islet autotransplantation (PIAT). In this series of case reports, we document variation in islet phenotypic identity in three patients with chronic pancreatitis (CP) without diabetes or significant insulin resistance who subsequently underwent PIAT. Pancreas histology was examined using colocalization of endocrine hormones, mesenchymal and pan-endocrine markers in islets, and the relative expression of MAFA and urocortin3 in insulin-expressing cells as compared to that of nondiabetic and type 2 diabetic donors. We present results of pre- and posttransplant clinical metabolic testing. Varying degrees of islet-cell dedifferentiation are identified in nondiabetic patients with CP at the time of PIAT, and may need further investigation.

Evaluation of collagenase gold plus BP protease in isolating islets from human pancreata

Selection of enzymes for optimal pancreas digestion is essential for successful human islet isolations. The aim of this study was to evaluate the efficacy and outcome of using Collagenase Gold plus BP protease (VitaCyte) (n = 8) by comparing it to two commercially available enzymes, Liberase MTF C/T (Roche) (n = 48) and Collagenase NB1/NP (Serva) (n = 15). The isolation outcomes were assessed by islet counting, viability, glucose-stimulated oxygen consumption rate (OCR), and successful graft-rate following transplantation in diabetic NOD scid mice. The pancreas donor characteristics were not significantly different between the tested enzyme groups regarding their BMI, pancreas weight, cold ischemia time (CIT) and HbA1c. The results show that digested tissue volume was not statistically significant between the VitaCyte enzyme (34.25 ± 5.4 mL) and the Roche enzyme (55.25 ± 3.42 mL, p = 0.073), however, this was significant with Serva enzyme (64.07 ± 7.95 mL, p = 0.020). Interestingly, the islet yields were not statistically different between all enzyme groups. Moreover, when islets were transplanted into NOD scid mice, the reversal rate of diabetes for the VitaCyte enzyme group was similar to all enzyme groups. In conclusion, the effectiveness of Collagenase Gold plus BP protease is comparable to the MTF C/T and the Collagenase NB1/NP enzymes; the low cost could facilitate the use of more pancreata for islet isolations.

Involvement of a proapoptotic gene (BBC3) in islet injury mediated by cold preservation and rewarming

Long-term pancreatic cold ischemia contributes to decreased islet number and viability after isolation and culture, leading to poor islet transplantation outcome in patients with type 1 diabetes. In this study, we examined mechanisms of pancreatic cold preservation and rewarming-induced injury by interrogating the proapoptotic gene BBC3/Bbc3, also known as Puma (p53 upregulated modulator of apoptosis), using three experimental models: 1) bioluminescence imaging of isolated luciferase-transgenic ("Firefly") Lewis rat islets, 2) cold preservation of en bloc-harvested pancreata from Bbc3-knockout (KO) mice, and 3) cold preservation and rewarming of human pancreata and isolated islets. Cold preservation-mediated islet injury occurred during rewarming in "Firefly" islets. Silencing Bbc3 by transfecting Bbc3 siRNA into islets in vitro prior to cold preservation improved postpreservation mitochondrial viability. Cold preservation resulted in decreased postisolation islet yield in both wild-type and Bbc3 KO pancreata. However, after culture, the islet viability was significantly higher in Bbc3-KO islets, suggesting that different mechanisms are involved in islet damage/loss during isolation and culture. Furthermore, Bbc3-KO islets from cold-preserved pancreata showed reduced HMGB1 (high-mobility group box 1 protein) expression and decreased levels of 4-hydroxynonenal (4-HNE) protein adducts, which was indicative of reduced oxidative stress. During human islet isolation, BBC3 protein was upregulated in digested tissue from cold-preserved pancreata. Hypoxia in cold preservation increased BBC3 mRNA and protein in isolated human islets after rewarming in culture and reduced islet viability. These results demonstrated the involvement of BBC3/Bbc3 in cold preservation/rewarming-mediated islet injury, possibly through modulating HMGB1- and oxidative stress-mediated injury to islets.

Clinical Islet Isolation

The overarching success of islet transplantation relies on the success in the laboratory to isolate the islets. This chapter focuses on the processes of human islet cell isolation and the ways to optimally provide islet cells for transplantation. The major improvements in regards to the choice of enzyme type, way the digested pancreas tissue is handled to best separate islets from the acinar and surrounding tissues, the various methods of purification of the islets, their subsequent culture and quality assurance to improve outcomes to culminate in safe and effective islet transplantation will be discussed. After decades of improvements, islet cell isolation and transplantation now clearly offer a safe, effective and feasible therapeutic treatment option for an increasing number of patients suffering from type 1 diabetes specifically for those with severe hypoglycaemic unawareness.

The Choice of Enzyme for Human Pancreas Digestion is a Critical Factor for Increasing the Success of Islet Isolation

BACKGROUND

We evaluated three commercially available enzymes for pancreatic digestion by comparing key parameters during the islet isolation process, as well as islet quality post-isolation.

METHODS

Retrospectively compared and analyzed islet isolations from pancreata using three different enzyme groups: Liberase HI (n=63), Collagenase NB1/Neutral Protease (NP) (n=43), and Liberase Mammalian Tissue Free Collagenase/Thermolysin (MTF C/T) (n=115). A standardized islet isolation and purification method was used. Islet quality assessment was carried out using islet count, viability, in vitro glucose-stimulated insulin secretion (GSIS), glucose-stimulated oxygen consumption rate (ΔOCR), and in vivo transplantation model in mice.

RESULTS

Donor characteristics were not significantly different among the three enzyme groups used in terms of age, sex, hospital stay duration, cause of death, body mass index (BMI), hemoglobin A1c (HbA1c), cold ischemia time (CIT), and pancreas weight. Digestion efficacy (percentage of digested tissue by weight) was significantly higher in the Liberase MTF C/T group (73.5 ± 1.5 %) when compared to the Liberase HI group (63.6 ± 2.3 %) (p<0.001) and the Collagenase NB1/NP group (61.7 ± 2.9%) (p<0.001). The stimulation index for GSIS was significantly higher in the Liberase MTF C/T group (5.3 ± 0.5) as compared to the Liberase HI (2.9 ± 0.2) (p<0.0001) and the Collagenase NB1/NP (3.6 ± 2.9) (p=0.012) groups. Furthermore, the Liberase MTF C/T enzymes showed the highest success rate of transplantation in diabetic NOD Scid mice (65%), which was significantly higher than the Liberase HI (42%, p=0.001) and the Collagenase NB1/NP enzymes (41%, p<0.001).

CONCLUSIONS

Liberase MTF C/T is superior to Liberase HI and Collagenase NB1/NP in terms of digestion efficacy and glucose-stimulated insulin secretion in vitro. Moreover, Liberase MTF C/T had a significantly higher success rate of transplantation in diabetic NOD Scid mice compared to Liberase HI and Collagenase NB1/NP enzymes.

Human pancreatic islet transplantation: an update and description of the establishment of a pancreatic islet isolation laboratory

Type 1 diabetes mellitus (T1DM) is associated with chronic complications that lead to high morbidity and mortality rates in young adults of productive age. Intensive insulin therapy has been able to reduce the likelihood of the development of chronic diabetes complications. However, this treatment is still associated with an increased incidence of hypoglycemia. In patients with "brittle T1DM", who have severe hypoglycemia without adrenergic symptoms (hypoglycemia unawareness), islet transplantation may be a therapeutic option to restore both insulin secretion and hypoglycemic perception. The Edmonton group demonstrated that most patients who received islet infusions from more than one donor and were treated with steroid-free immunosuppressive drugs displayed a considerable decline in the initial insulin independence rates at eight years following the transplantation, but showed permanent C-peptide secretion, which facilitated glycemic control and protected patients against hypoglycemic episodes. Recently, data published by the Collaborative Islet Transplant Registry (CITR) has revealed that approximately 50% of the patients who undergo islet transplantation are insulin independent after a 3-year follow-up. Therefore, islet transplantation is able to successfully decrease plasma glucose and HbA1c levels, the occurrence of severe hypoglycemia, and improve patient quality of life. The goal of this paper was to review the human islet isolation and transplantation processes, and to describe the establishment of a human islet isolation laboratory at the Endocrine Division of the Hospital de Clínicas de Porto Alegre - Rio Grande do Sul, Brazil.

Islet product characteristics and factors related to successful human islet transplantation from the Collaborative Islet Transplant Registry (CITR) 1999-2010

The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and transplants. This retrospective report analyzed 1017 islet isolation procedures performed for 537 recipients of allogeneic clinical islet transplantation in 1999-2010. This study describes changes in donor and islet isolation variables by era and factors associated with quantity and quality of final islet products. Donor body weight and BMI increased significantly over the period (p<0.001). Islet yield measures have improved with time including islet equivalent (IEQ)/particle ratio and IEQs infused. The average dose of islets infused significantly increased in the era of 2007-2010 when compared to 1999-2002 (445.4±156.8 vs. 421.3±155.4×0(3) IEQ; p<0.05). Islet purity and total number of β cells significantly improved over the study period (p<0.01 and <0.05, respectively). Otherwise, the quality of clinical islets has remained consistently very high through this period, and differs substantially from nonclinical islets. In multivariate analysis of all recipient, donor and islet factors, and medical management factors, the only islet product characteristic that correlated with clinical outcomes was total IEQs infused. This analysis shows improvements in both quantity and some quality criteria of clinical islets produced over 1999-2010, and these parallel improvements in clinical outcomes over the same period.

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.

Different digestion enzymes used for human pancreatic islet isolation: a mixed treatment comparison (MTC) meta-analysis

Collagenases are critical reagents determining yield and quality of isolated human pancreatic islets and may affect islet transplantation outcome. Some islet transplantation centers have compared 2 or more collagenase blends; however, the results regarding differences in quantity and quality of islets are conflicting. Thus, for the first time, a mixed treatment comparison (MTC) meta-analysis was carried out to compile data about the effect of different collagenases used for human pancreas digestion on islet yield, purity, viability and stimulation index (SI). Pubmed, Embase and Cochrane libraries were searched. Of 755 articles retrieved, a total of 15 articles fulfilled the eligibility criteria and were included in the MTC meta-analysis. Our results revealed that Vitacyte and Liberase MTF were associated with a small increase in islet yield (islet equivalent number/g pancreas) when compared with Sevac enzyme [standardized mean difference (95% credible interval - CrI) = -2.19 (-4.25 to -0.21) and -2.28 (-4.49 to -0.23), respectively]. However, all other enzyme comparisons did not show any significant difference regarding islet yield. Purity and viability percentages were not significantly different among any of the analyzed digestion enzymes. Interestingly, Vitacyte and Serva NB1 were associated with increased SI when compared with Liberase MTF enzyme [unstandardized weighted mean difference (95% CrI) = -1.69 (-2.87 to -0.51) and -1.07 (-1.79 to -0.39), respectively]. In conclusion, our MTC meta-analysis suggests that the digestion enzymes currently being used for islet isolation works with similar efficiency regarding islet yield, purity and viability; however, Vitacyte and Serva NB1 enzymes seem to be associated with an improved SI as compared with Liberase MTF.

The islet size to oxygen consumption ratio reliably predicts reversal of diabetes posttransplant

β-Cell replacement therapy by either whole-organ pancreas or islets of Langerhans transplantation can restore carbohydrate control to diabetic patients and reduces complications associated with the disease. One of the variables inherent in islet transplantation is the isolation of functional islets from donor pancreata. Islet isolations fail to consistently produce good-quality functional islets. A rapid pretransplant assay to determine posttransplant function of islets would be an invaluable tool. We have tested the novel hypothesis that modified oxygen consumption rates (OCR), standardized to DNA quantity (nmol/min-mg DNA), would serve as a pretransplant assessment of the metabolic potency of the islets postisolation. This study compares the ability of current in vitro assays to predict in vivo restoration of normoglycemia in a diabetic nude mouse posttransplantation of adult pig islets. There is known to be a diversity of islet sizes within each preparation. This parameter has not heretofore been effectively considered a critical factor in islet engraftment. Our results suggest a surprising finding that islet size influences the probability of restoring carbohydrate control. Based on this observation, we thus developed a novel predictor of islet graft function that combines the effects of both islet OCR and size. When OCR was divided by the islet index (size), a highly significant predictor of graft function was established (p = 0.0002, n = 75). Furthermore, when OCR/islet index values exceeded 70.0 nmol/min-mg DNA/islet index, an effective threshold of diabetes reversal was observed. This assay can be performed with as few as 1,000 islet equivalents (IEQ) and conducted in less than 60 min. Our data suggest that, using this novel method to assess islet cell function prior to transplantation, OCR/islet index thresholds provide a valuable tool in identifying which islet preparations are most likely to restore glycemic control posttransplant.

The effects of digestion enzymes on islet viability and cellular composition

The choice of enzyme blend is critical for successful islet isolation. Islet yield, viability, integrity, and function are important factors that influence the outcome of islet transplantation. Liberase HI has been used as a standard enzyme for pancreas digestion and has successfully produced islets that reversed diabetes. However, the replacement of Liberase HI with collagenase NB1 has significantly influenced the process outcome, both in quality and quantity of the isolated islets. The assessment of islet cells by Flow Cytometry (FC) has been reported to be useful for evaluating islet quality. The aim of this study was to assess the isolation outcomes and islet quality when comparing human islet cell processed with Liberase HI and NB1. A total of 66 islet isolations, 46 processed using Liberase HI and 20 using Serva NB1, were retrospectively analyzed. Islet yield, function in vitro, islet cell viability by FC, as well as isolation-related factors were compared. There was no significant difference in donor characteristics such as age and height; however, body mass index (BMI) in the Liberase HI group was significantly higher. There was also no significant difference in prepurification, postisolation, or postculture IEQ or percent recovery between the two groups. Flow data showed Liberase HI preparations had a significantly higher percent of live cells (DAPI(-)) and NG(+)/TMRE(+) when compared to NB1. Stimulation Indices (SI) for Liberase HI (n = 45) showed 3.17 and NB1 (n = 18) 2.71 (p = NS). The results of Annexin V/DAPI staining for live, apoptotic, and necrotic cells were 50.7 ± 2.24%, 14.4 ± 1.02%, and 27.8 ± 1.92% for Liberase HI versus 48.1 ± 1.93%, 12.3 ± 0.92%, and 33.9 ± 2.28% for NB1. Islets isolated using Liberase HI showed higher viable β cells by NG/TMRE staining and decreased necrosis by Annexin V/DAPI staining. FC assessment may be useful for determining the choice of digestion enzyme to maximize viable islets.

Evaluation of viable β-cell mass is useful for selecting collagenase for human islet isolation: comparison of collagenase NB1 and liberase HI

The selection of enzyme blend is critical for the success of human islet isolations. Liberase HI collagenase (Roche) was introduced in the 1990s and had been widely used for clinical islet transplantation. More recently, a blend collagenase NB1 has been rendered available. The aim of this study was to evaluate the isolation outcomes and islet quality comparing human islet cells processed using NB1 and Liberase HI. A total of 90 isolations processed using NB1 (n = 40) or Liberase HI (n = 50) was retrospectively analyzed. Islet yield, function in vitro and in vivo, cellular (including β-cell-specific) viability and content, as well as isolation-related factors were compared. No significant differences in donor-related factors were found between the groups. There were also no significant differences in islet yields (NB1 vs. Liberase: 263,389 ± 21,550 vs. 324,256 ± 27,192 IEQ; p = n.s., respectively). The pancreata processed with NB1 showed a significantly longer digestion time (18.6 ± 0.7 vs. 14.5 ± 0.5 min, p < 0.01), lower β-cell viability (54.3 ± 3.4% vs. 72.0 ± 2.1%, p < 0.01), β-cell mass (93,671 ± 11,150 vs. 148,961 ± 12,812 IEQ, p < 0.01), and viable β-cell mass (47,317 ± 6,486 vs. 106,631 ± 10,228 VβIEQ, p < 0.01) than Liberase HI. In addition, islets obtained with Liberase showed significantly better graft function in in vivo assessment of islet potency. The utilization of collagenase NB1 in human islet isolation was associated with significantly lower β-cell viability, mass, and islet potency in vivo in our series when compared to Liberase HI, even though there was no significant difference in islet yields between the groups. Evaluation of viable β-cell mass contained in human islet preparations will be useful for selecting enzyme blends.

Highly purified versus filtered crude collagenase: comparable human islet isolation outcomes

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

Assessment of human islet isolation with four different collagenases

BACKGROUND

The isolation of islets from the human pancreas critically depends on the efficiency of the digestive enzymes. Liberase HI had been used as a standard preparation until the issues concerning bovine spongiform encephalopathy. Thus, we must now use other collagenases for clinical islet transplantation, four of which we have evaluated herein.

METHODS

The digestion of each of 17 pancreata from brain-dead donors was performed using the following collagenases: Liberase HI (HI; Roche, n = 9); Liberase MTF C/T (MTF; Roche, n = 4); Collagenase NB1 Premium Grade (NB1; Serva, n = 7); or Clzyme Collagenase HA (CI, VitaCyte, n = 4). Islet isolations were based on the Edmonton protocol for HI, whereas our modified islet isolation method was used for the three new enzymes (MTF, NB1, and CI).

RESULTS

There were no significant differences in donor age, body mass index, pancreas size, and cold ischemic time among the four groups. The phase I time in the NB1 group was significantly shorter than in the CI group (P = .0014). The prepurification IEQ/g in the HI group was significantly lower than the others (P = .0003 vs MTF, .0007 vs NB1, and .0009 vs CI, respectively). The postpurification IEQ/g in the MTF group was significantly higher than in the HI group (P = .006). The viability in the NB1 group was significantly greater than the HI group (P = .003).

CONCLUSION

Three new enzymes (MTF, NB1, and CI) may enable us to obtain higher islet yields than with HI.

A new method to value efficiency of enzyme blends for pancreatic tissue digestion

Islet transplantation, since the 1990s, has been an example of human cell therapy. Nevertheless, the islet isolation procedure is not completely standardized; in fact, >50% of islet procedures do not eventuate in transplantation due both to the variability of a donor's pancreas and to the unpredictable efficiency of an enzymatic blend. The enzymes used in pancreas isolation to digest several substrates are extracted from Clostridium histolyticum. In particular, they have strong collagenolytic activity compared with vertebrate collagenases. However, several impediments persist in human islet isolation success, probably owing to the variable composition and concentration of collagenases employed during the digestion phase. For islet isolation processes, neutral proteases play important roles. However, they should be considered to be double-edged swords, contributing to tissue dissociation but, sometimes, decreasing islet yield through fragmentation, breakdown, and inactivation. Protease activities cannot be preciously adjusted in a narrow range, there is no approach to determine the optimal dosage and composition of enzymes for extraction of human islets from the pancreas. At this time, available data on commercial enzymatic activity are not sufficient to predict their efficiency for pancreas digestion; consequently, it is difficult to select enzyme batches. For these reasons, we sought to generate an innovative evaluation assay to select enzymes useful for isolation procedures of pancreatic islets.

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.

Antiproinflammatory effects of iodixanol (OptiPrep)-based density gradient purification on human islet preparations

Islet isolation and purification using a continuous density gradient may reduce the volume of tissue necessary for implantation into patients, therefore minimizing the risks associated with intraportal infusion in islet transplantation. On the other hand, the purification procedure might result in a decreased number of islets recovered due to various stresses such as exposure to cytokine/chemokine. While a Ficoll-based density gradient has been widely used in purification for clinical trials, purification with iodixanol (OptiPrep) has been recently reported in islet transplant series with successful clinical outcomes. The aim of the current study was to compare the effects of the purification method using OptiPrep-based and Ficoll-based density gradients. Human islet isolations were performed using a modified automated method. After the digestion phase, pre-purification digests were divided into two groups and purified using a semiautomated cell processor with either a continuous Ficoll- or OptiPrep-based density gradient. The quantity, purity, viability, and cellular composition of islet preparations from each group were assessed. Cytokine/chemokine and tissue factor production from islet preparations after 48-h culture were also measured. Although islet purity, post-purification IEQ, islet recovery rate, FDA/PI, and fractional β-cell viability were comparable, β-cell mass after 48-h culture significantly improved in the OptiPrep group when compared to the Ficoll group. The production of cytokine/chemokine including IL-1β, TNF-α, IFN-γ, IL-6, IL-8, MIP-1β, MCP-1, and RANTES but not tissue factor from the OptiPrep group was significantly lower during 48-h culture after isolation. Each preparation contained the similar number of ductal cells and macrophages. Endotoxin level in both gradient medium was also comparable. The purification method using OptiPrep gradient media significantly reduced cytokine/chemokine production but not tissue factor from human islet preparations and improved β-cell survival during pretransplant culture. Our results suggest that the purification method using OptiPrep gradient media may be of assistance in increasing successful islet transplantation.

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.