Influence of neutral protease activity on human islet isolation outcome

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.

Quantifying the Effects of Different Neutral Proteases on Human Islet Integrity

Efficient islet release from the pancreas requires the combination of collagenase, neutral protease (cNP), or thermolysin (TL). Recently, it has been shown that clostripain (CP) may also contribute to efficient islet release from the human pancreas. The aim of this study was to evaluate the impact of these proteases on human islet integrity in a prospective approach. Islets were isolated from the pancreas of 10 brain-dead human organ donors. Purified islets were precultured for 3 to 4 d at 37 °C to ensure that preparations were cleared of predamaged islets, and only integral islets were subjected to 90 min of incubation at 37 °C in Hank’s balanced salt solution supplemented with cNP, TL, or CP. The protease concentrations were calculated for a pancreas of 100 g trimmed weight utilizing 120 dimethyl-casein units of cNP, 70,000 caseinase units of TL, or 200 benzoyl-l-arginine-ethyl-ester units of CP (1×). These activities were then increased both 5× and 10×. After subsequent 24-h culture in enzyme-free culture medium, treated islets were assessed and normalized to sham-treated controls. Compared with controls and CP, islet yield was significantly reduced by using the 5× activity of cNP and TL, inducing also fragmentation and DNA release. Viability significantly decreased not until adding the 1× activity of cNP, 5× activity of TL, or 10× activity of CP. Although mitochondrial function was significantly lowered by 1× cNP and 5× TL, CP did not affect mitochondria at any concentration. cNP- and TL-incubated islets significantly lost intracellular insulin already at 1× activity, while the 10× activity of CP had to be added to observe a similar effect. cNP and TL have a similar toxic potency regarding islet integrity. CP also induces adverse effects on islets, but the toxic threshold is generally higher. We hypothesize that CP can serve as supplementary protease to minimize cNP or TL activity for efficient pancreas digestion.

Comparison of Clostripain and Neutral Protease as Supplementary Enzymes for Human Islet Isolation

Although human islet transplantation has been established as valid and safe treatment for patients with type 1 diabetes, the utilization rates of human pancreases for clinical islet transplantation are still limited and substantially determined by the quality and composition of collagenase blends. While function and integrity of collagenase has been extensively investigated, information is still lacking about the most suitable supplementary neutral proteases. The present study compared islet isolation outcome after pancreas digestion by means of collagenase used alone or supplemented with either neutral protease (NP), clostripain (CP), or both proteases. Decent amounts of islet equivalents (IEQ) were isolated using collagenase alone (3090 ± 550 IEQ/g), or in combination with NP (2340 ± 450 IEQ/g) or CP (2740 ± 280 IEQ/g). Nevertheless, the proportion of undigested tissue was higher after using collagenase alone (21.1 ± 1.1%, P < 0.05) compared with addition of NP (13.3 ± 2.2%) or CP plus NP (13.7 ± 2.6%). Likewise, the percentage of embedded islets was highest using collagenase only (13 ± 2%) and lowest adding NP plus CP (4 ± 1%, P < 0.01). The latter combination resulted in lowest post-culture overall survival (42.7 ± 3.9%), while highest survival was observed after supplementation with CP (74.5 ± 4.8%, P < 0.01). An insulin response toward glucose challenge was present in all experimental groups, but the stimulation index was significantly decreased using collagenase plus NP (2.0 ± 0.12) compared with supplementation with CP (3.16 ± 0.4, P < 0.001). This study demonstrates for the first time that it is possible to isolate significant numbers of human islets combining collagenase only with CP. The supplementation with CP is an effective means to substantially reduce NP activity, which significantly decreases survival and viability after culture. This will facilitate the manufacturing of enzyme blends with less harmful characteristics.

Multicenter Assessment of Animal-free Collagenase AF-1 for Human Islet Isolation

Animal-free (AF) SERVA Collagenase AF-1 and Neutral Protease (NP) AF GMP Grade have recently become available for human islet isolation. This report describes the initial experiences of 3 different islet transplant centers. Thirty-four human pancreases were digested using 1 vial of the 6 different lots of Collagenase AF-1 (2,000–2,583 PZ-U/vial) supplemented with 4 different lots of NP AF in a range of 50 to 160 DMC-U per pancreas. Isolation, culture, and quality assessment were performed using standard techniques as previously described. All data are presented as mean ± standard error of the mean (SEM). Variability of pancreas weight was associated with a wide range of collagenase and NP activities, ranging from 12.7 to 46.6 PZ-U/g (26.0 ± 1.5 PZ-U/g) and 0.4 to 3.0 DMC-U/g (1.5 ± 0.1 DMC-U/g), respectively. Postpurification islet yield was 296,494 ± 33,620 islet equivalents (IEQ) equivalent to 3,274 ± 450 IEQ/g with a purity of 55.9% ± 3.2%. Quality assessment performed after 2 to 4 d of culture demonstrated a viability of 88.1% ± 1.5% and a stimulation index of 3.7 ± 0.7. Eighteen of the 34 preparations were transplanted into type 1 diabetic patients equivalent to a transplantation rate of 52.9%. Six preparations, which were infused into patients as first transplant, could be analyzed and increased the fasting C-peptide level from 0.11 ± 0.08 pretransplant to 1.23 ± 0.24 and 2.27 ± 0.31 ng/mL 3 and 6 mo posttransplant (P < 0.05), respectively. Insulin requirements were simultaneously reduced at the same time from 39.2 ± 3.8 IU/d before transplantation to 10.8 ± 4.1 and 4.0 ± 2.3 IU/d, after 3 and 6 mo posttransplant (P < 0.05), respectively. This study demonstrates the efficiency of AF SERVA Collagenase AF-1 and NP AF for clinical islet isolation and transplantation. The new plant-based production process makes these products a safe new option for the islet field.

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.

Synergistic Effect of Neutral Protease and Clostripain on Rat Pancreatic Islet Isolation

BACKGROUND

Islet isolation currently requires collagenase, neutral protease and other components. Thermolysin (TL) from Bacillus thermoproteolyticus is the gold standard neutral protease. However, we speculated that neutral protease derived from Clostridium histolyticum (Ch; ChNP) would be biologically superior for islet isolation. Tryptic-like activity has also been reported to be important. Therefore, we focused on clostripain (CP), since it is one of the main proteases in Clostridium histolyticum which possesses tryptic-like activity. We then examined the synergistic effects of highly purified ChNP and CP on rat islet isolation.

METHODS

The same amount of collagenase was used in all four groups (TL, ChNP, TL+CP and ChNP+CP; n = 12/group). The efficiency was evaluated by the islet yield and function. An immunohistochemical analysis, in vitro digestion assay for each enzyme component and evaluation of the activation of endogenous exocrine proteases during islet isolation were also performed.

RESULTS

The islet yield of the TL group was significantly higher than that of the ChNP group (P < 0.01). The islet yield was dose dependently increased in the ChNP+CP group, but was decreased in the TL + CP group. The islet yield in the ChNP + CP group was significantly higher than that in the TL group, but their islet function was similar. Different specificities for laminin, especially laminin-511, were observed in the TL, ChNP, and CP groups.

CONCLUSIONS

Clostripain had a strong synergistic effect with ChNP, but not with TL. Therefore, ChNP and CP, in combination with collagenase derived from the same bacteria, may effectively increase the isolation efficiency without affecting the quality of islets.

Pancreatic Islets: Methods for Isolation and Purification of Juvenile and Adult Pig Islets

The current situation of organ transplantation is mainly determined by the disbalance between the number of available organs and the number of patients on the waiting list. This obvious dilemma might be solved by the transplantation of porcine organs into human patients. The metabolic similarities which exist between both species made pancreatic islets of Langerhans to that donor tissue which will be most likely transplanted in human recipients. Nevertheless, the successful isolation of significant yields of viable porcine islets is extremely difficult and requires extensive experiences in the field. This review is focussing on the technical challenges, pitfalls and particularities that are associated with the isolation of islets from juvenile and adult pigs considering donor variables that can affect porcine islet isolation outcome.

Comparison of Neutral Proteases and Collagenase Class I as Essential Enzymes for Human Islet Isolation

Efficient islet isolation requires synergistic interaction between collagenase class I (CI) and class II (CII). The CI degradation alters the ratio between CI and CII and is responsible for batch-to-batch variations. This study compares the role of neutral protease (NP) plus clostripain (CP) with CI as essential enzymes for human islet isolation.

METHODS

Human islets were isolated using 4 different enzyme mixtures composed of CII plus either intact (CI-115) or degraded CI (CI-100). Blends were administered either with or without NP/CP. Purified islets were cultured for 3 to 4 days before islet quality assessment.

RESULTS

Whereas using intact CI-115 without NP/CP did not significantly reduce islet yield (3429 ± 631 vs 3087 ± 970 islet equivalent/g, nonsignificant), administration of degraded CI-100 without NP/CP decreased islet yield from 3501 ± 580 to 1312 ± 244 islet equivalent/g (P < 0.01), doubled the amount of undigested tissue from 11.8 ± 1.6 to 24.4 ± 1.2% (P < 0.01) and triplicated the percentage of trapped islets from 7.7 ± 2.8 to 22.5 ± 3.6% (P < 0.05). Islet yield did not vary between supplemented CI-115 and CI-100, but was increased using CI-115 when NP/CP was omitted (P < 0.05). A trend toward higher viability and increased secretory insulin response was noted in both CI-100 and CI-115 when NP/CP was not added.

CONCLUSIONS

This study suggests that NP/CP can compensate reduced CI activity. Future attempts to optimize enzyme blends should consider the possibility to increase the proportion of collagenase CI to reduce the need for potentially harmful NPs.

Clostripain, the Missing Link in the Enzyme Blend for Efficient Human Islet Isolation

Effective digestive enzymes are crucial for successful islet isolation. Supplemental proteases are essential as they synergize with collagenase for effective pancreas digestion. The presence of tryptic-like activity has been implicated in efficient enzyme blends and the present study aimed to evaluate if addition of clostripain, an enzyme with tryptic-like activity, could improve efficacy of the islet isolation procedure.

METHODS

Clostripain was added to the enzyme blend just before pancreas perfusion. Islets were isolated per standard method and numerous isolation parameters, islet quality control, and the number of isolations fulfilling standard transplantation criteria were evaluated. Two control organs per clostripain organ were chosen by blindly matching against body mass index, cold ischemia time, hemoglobin A1c, donor sex, and donor age.

RESULTS

There were no differences in pancreas weight, dissection time, digestion time, harvest time, percent digested pancreas, or total pellet volume before islet purification between control or clostripain pancreases. Glucose-stimulated insulin release results were similar between groups. Total isolation islet equivalents, purified tissue volume and islet equivalents/g pancreas as well as fulfillment of transplantation criteria favored clostripain processed pancreases.

CONCLUSIONS

The addition of clostripain to the enzyme blend soundly improved islet yields and transplantation rates. It gently aided pancreas digestion and maintained proper islet functionality. The addition of clostripain to the enzyme blend has now been implemented into standard isolation protocols at the isolation centers in Uppsala and in Oslo.

Characterization and functional assessment of Clostridium histolyticum class I (C1) collagenases and the synergistic degradation of native collagen in enzyme mixtures containing class II (C2) collagenase

OBJECTIVES

Clostridium histolyticum expresses two classes of collagenases, C1 and C2. However, degradation of these enzymes by proteases during the fermentation or purification process may lead to numerous molecular forms that lead to inconsistent release of islets from human pancreata. This report defines the amino acid sequence of the truncated forms of C1 (C1b or C1c) that contain a single collagen-binding domain (CBD) and investigates the synergy between the different forms of C1 collagenase and C2 to degrade native collagen.

METHODS

Highly purified collagenase isoforms were purified from C. histolyticum culture supernatants using established column chromatography techniques and analyzed using high-pressure liquid chromatograph (HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MS). The collagen-degrading activity (CDA) assay was used to investigate the synergy between different collagenase molecular forms.

RESULTS

MS was used to confirm the sequence of full-length C2 and C1 from the reported gene sequence. These results were correlated with the molecular weights observed on the SDS- PAGE and elution after analytical anion-exchange HPLC. HPLC peaks designated as C1b and C1c were both confirmed to be C1 lacking the terminal CBD. The only difference being the cleavage site leading to a 12 amino acid difference between the two forms. A non-additive synergy in CDA relative to activity of individual collagenases was observed for C2 with each of the three C1 molecular forms. The C1 molecular forms did not display this synergy in the absence of C2.

CONCLUSIONS

These observations support earlier reports that suggest the two collagenases bind to different portions of the collagen and have different specificities to cut native collagen. Although the implications of this are not yet understood, they are fundamental in advancing the understanding of how collagenases work together along with the neutral protease to breakdown the extracellular matrix for islet isolation.

Pre-transplant signal induction for vascularisation in human islets

Human islet transplant success is partially impaired by slow revascularisation. Our study investigated the potential for rotational cell culture (RC) of human islets combined with thiazolidinedione (TZD) stimulation of peroxisome proliferator-activated receptor gamma (PPARγ) to upregulate vascular endothelial growth factor (VEGF) expression in the islets. Four groups of human islets were studied: static culture (SC) with and without 25 mmol/L TZD and RC with and without 25 mmol/L TZD. These were assessed for insulin secretion and soluble VEGF-A release. Both proteins were quantified by enzyme-linked immunosorbent assay (ELISA), supported with qualitative immunofluorescence staining. RC + TZD increased insulin secretion by >20% (p < 0.05-0.001) in response to 16.7 mmol/L glucose and 16.7 mmol/L glucose + 10 mmol/L theophylline (G + T). This effect was seen at all time intervals compared with SC and without addition of TZD. Soluble VEGF-A release was significantly augmented by RC and TZD exposure with an increased effect of >30% (p < 0.001) at 72 h under both SC and RC conditions. RC supplemented with a TZD enhances and prolongs the release of insulin and soluble VEGF-A by isolated human islets.

Clinical islet isolation outcomes with a highly purified neutral protease for pancreas dissociation

BACKGROUND

Pancreas dissociation is a critical initial component of the islet isolation procedure and introduces high variability based on factors including the enzyme type, specificity and potency. Product refinement and alterations to the application strategies have improved isolation outcomes over time; however, islet utilization from donor organs remains low. In this study we evaluate a low endotoxin-high activity grade neutral protease in clinical islet isolation.

MATERIALS AND METHODS

The use of a non-collagenolytic enzyme, either thermolysin or high active neutral protease, was randomized in clinical islet isolations to evaluate efficacy. Additionally a retrospective comparison to neutral protease NB was conducted.

RESULTS

The thermolysin group had lower trapped islet population and increased purity and post-culture islet mass in comparison to high active grade neutral protease. Comparison of neutral protease NB GMP grade to high active neutral protease displayed no measurable difference in islet mass or viability and transplantation outcomes at 1 mo post-transplant were favorable for both groups.

CONCLUSIONS

High activity neutral protease can generate clinical grade islets and may prove beneficial to islet function and viability based on a reduced endotoxin load but dosing of neutral protease requires ongoing optimization.

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.

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.

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.

Large-scale comparison of Liberase HI and collagenase NB1 utilized for human islet isolation

For more than a decade Liberase HI was commonly used as the standard enzyme blend for clinical human islet isolation until enforced replacement by collagenase NB1 (NB1). This change resulted initially in a reduction in islet isolation outcome and transplant activities worldwide. This retrospective study was initiated to compare the efficiency of NB1 premium grade with Liberase in 197 human islet isolations. All pancreata were processed between January 2006 and June 2008 utilizing the same procedures for isolation and quality assessment except the administration of preselected lots of either Liberase (n = 101) or NB1 (n = 96). Utilizing Liberase, significantly more digested tissue and purified islet yield was produced compared to NB1. In contrast, the use of NB1 was associated with significantly higher purity and glucose stimulation index during dynamic perifusion. The expression of proinflammatory markers was almost identical except tissue factor expression, which was higher after utilization of Liberase. No difference was found in the percentage of pancreata fulfilling the criteria for clinical islet transplantation. The results suggest that Liberase is more efficient for pancreas dissociation than collagenase NB1 but seems to be more harmful to exocrine cells and islet tissue.

Human islet isolation for autologous transplantation: comparison of yield and function using SERVA/Nordmark versus Roche enzymes

Islet autotransplantation (IAT) is used to preserve as much insulin-secretory capacity as possible in patients undergoing total pancreatectomy for painful chronic pancreatitis. The enzyme used to dissociate the pancreas is a critical determinant of islet yield, which is correlated with posttransplant function. Here, we present our experience with IAT procedures to compare islet product data using the new enzyme SERVA/Nordmark (SN group; n = 46) with the standard enzyme Liberase-HI (LH group; n = 40). Total islet yields (mean +/- standard deviation; 216,417 +/- 79,278 islet equivalent [IEQ] in the LH group; 227,958 +/- 58,544 IEQ in the SN group; p = 0.67) were similar. However, the percentage of embedded islets is higher in the SN group compared to the LH group. Significant differences were found in pancreas digestion time, dilution time, and digested pancreas weight between the two groups. Multivariate linear regression analysis showed the two groups differed in portal venous pressure changes. The incidence of graft function and insulin independence was not different between the two groups. The SN and LH enzymes are associated with similar outcomes for IAT. Further optimization of the collagenase/neutral protease ratio is necessary to reduce the number of embedded islets obtained when using the SN enzyme.

Characterization of collagenase blend enzymes for human islet transplantation

BACKGROUND

Efficient islet isolation represents a necessary requirement for successful islet transplantation as a treatment for type 1 diabetes. The choice of collagenase for pancreas digestion is critical for the isolation outcome, and Liberase is the most widely used enzyme, although large intra-batched variability in activity and efficiency has been observed.

METHODS

The aim of this study was to characterize Liberase components and their relative role in pancreas digestion. Liberase batches were characterized by microelectrophoresis.

RESULTS

By means of microelectrophoresis, we identified three main proteins each with different prevalences between batches. Two proteins were found to correspond to class I (CI) and one to class II (CII) collagenase. In a series of 163 islet isolations, we observed that the CII correlated with islet yield (P<0.001) and digestion time (P<0.001); additionally, CI directly correlated with purity (P=0.028). Finally, when CII and one of the CI isoforms were >50 percentile, 15 of 36 preparations were transplanted, with 27 of 127 transplanted in the other cases (P=0.013).

CONCLUSION

These results represent an important step toward the characterization of enzymes, with the final aim of identifying key components for a standardized product.

Enhancing the success of human islet isolation through optimization and characterization of pancreas dissociation enzyme

A major obstacle to successful human islet isolation has been the variability of the enzymatic digestion phase. The aim of this study was to define optimal enzyme activity ranges normalized by the pancreas weight and to identify valid parameters for the optimal selection of successful lots of collagenase enzyme blends. Our results from 251 islet isolations showed that optimization of thermolysin dosage based on Caseinase unit/g pancreas contributed considerably to islet isolation outcome but that collagenase dosage measured by the manufacturer (Wünsch unit/g pancreas) was not a major determinant of islet isolation outcome. We also found that lot-to-lot inconsistency of enzyme performance was not explained by the activity values provided by the manufacturer, but rather by an in-house assay of class I collagenase (CI) and class II collagenase (CII); using a lot with a lower CII/CI resulted in a higher success rate. The odds of successful isolation was 8.67 times higher when a vial with CII/CI ratio <0.204 was used than when a vial with CII/CI >or=0.204 was used, suggesting that CII/CI ratio may be a strong predictor to distinguish potential lot success. This study provides a framework for improved enzymatic digestion in human islet isolation.

Factors influencing the collagenase digestion phase of human islet isolation

Substantial advances in human islet isolation technology have occurred during the past decade. However, it is still difficult to recover the entire quantity of islets contained in a pancreas. A major obstacle to successful human islet isolation has been the variability of the collagenase digestion phase of islet isolation. Future advances in enzyme technology will make it possible to optimally liberate islets with enzyme blends "tailor-made" for each individual donor pancreas. Such innovative strategies will be advantageous in improving islet isolation efficiency, recovery, viability, and ultimately posttransplant function.

Characterisation of Collagen VI within the Islet-Exocrine Interface of the Human Pancreas: Implications for Clinical Islet Isolation?

BACKGROUND

To optimize the methods used for human islet isolation for transplantation, it is important to improve our understanding of the structure of the islet-exocrine interface. In this study, the composition of collagen subtypes in the interface have been characterized and quantified in human pancreas.

METHODS

Human adult pancreases were retrieved from older (mean age 55.7+/-3.0 yrs) and young donors (mean age 21.8+/-3.2 yrs). Tissue from the body of each pancreas was examined by quantitative immunohistochemistry. Collagen within the islet-exocrine interface was identified by immunolabeling for collagen I, IV, V or VI and islets identified either morphologically or by immunolabeling for insulin. Collagen subtypes were quantified and data expressed as collagen area at the interface relative to the islet area. Statistical analysis was by ANOVA or Mann Whitney U test.

RESULTS

In older pancreases, collagen IV, V and VI were present throughout the islet-exocrine interface, whereas collagen I was more variable. The mean peri-islet collagen VI proportion was significantly greater than that of collagen I or IV. Mean islet area and the proportional collagen VI content in specimens from younger subjects were not significantly different to those in older subjects.

CONCLUSIONS

Collagen VI is a major component of the islet-exocrine interface of the adult pancreas, the content being more than double that of collagen I or IV. However, the proportional collagen VI content was not dependent on the age of the donor. These data may facilitate the design of new collagenases, targeting major substrates such as collagen VI in order to improve clinical islet isolation.

Multi-lot analysis of custom collagenase enzyme blend in human islet isolations

INTRODUCTION

Variability currently in Liberase HI from lot to lot limits the ability to effectively isolate islets with consistency. Roche Diagnostics Inc (Indianapolis, Ind, USA) has developed a Custom Collagenase enzyme blend in hopes that producing collagenase II and I and thermolysin separately will eliminate variability. In this study we examined the variability in Custom Collagenase lots in respect to isolation results and isolation success rates and compared those to Liberase HI.

METHODS

We retrospectively analyzed records from 68 islet isolations where either Liberase HI (lot A: n = 23, Lot B: n = 20) or Custom Collagenase blend (Lot C: n = 10, Lot D: n = 15) was employed. Human islets were isolated from cadaveric pancreata using standardized methods performed in a controlled islet isolation facility.

RESULTS

Analysis of Liberase HI and Custom Collagenase using Student t test showed no difference between the two groups. Comparison of the two Custom Collagenase lots using the t test showed a statistical difference between undigested pancreas weight and pancreas digestion times. Using chi-square test, no statistical significance was found in isolation success rates from lot to lot.

CONCLUSION

Although the Custom Collagenase blend is comparable to Liberase HI in its ability to isolate human islets, variability still exists from lot to lot when used conventionally as Liberase HI is. The ability to predetermine doses is beneficial, and as techniques to manipulate the activity levels prior to isolations improve so to will the enzymes' ability to isolate islets on a consistent basis.