Collagenase and Human Islet Isolation

Primary Hepatocyte Isolation and Cultures: Technical Aspects, Challenges and Advancements

Hepatocytes are differentiated cells that account for 80% of the hepatic volume and perform all major functions of the liver. In vivo, after an acute insult, adult hepatocytes retain their ability to proliferate and participate in liver regeneration. However, in vitro, prolonged culture and proliferation of viable and functional primary hepatocytes have remained the major and the most challenging goal of hepatocyte-based cell therapies and liver tissue engineering. The first functional cultures of rat primary hepatocytes between two layers of collagen gel, also termed as the "sandwich cultures", were reported in 1989. Since this study, several technical developments including choice of hydrogels, type of microenvironment, growth factors and culture conditions, mono or co-cultures of hepatocytes along with other supporting cell types have evolved for both rat and human primary hepatocytes in recent years. All these improvements have led to a substantial improvement in the number, life-span and hepatic functions of these cells in vitro for several downstream applications. In the current review, we highlight the details, limitations and prospects of different technical strategies being used in primary hepatocyte cultures. We discuss the use of newer biomaterials as scaffolds for efficient culture of primary hepatocytes. We also describe the derivation of mature hepatocytes from other cellular sources such as induced pluripotent stem cells, bone marrow stem cells and 3D liver organoids. Finally, we also explain the use of perfusion-based bioreactor systems and bioengineering strategies to support the long-term function of hepatocytes in 3D conditions.

Secretion of collagenases by Saccharomyces cerevisiae for collagen degradation

Background

The production and processing of animal-based products generates many collagen-rich by-products, which have received attention both for exploitation to increase their added value and to reduce their negative environmental impact. The collagen-rich by-products can be hydrolyzed by collagenases for further utilization. Therefore, collagenases are of benefit for efficient collagen materials processing. An alternative and safe way to produce secreted collagenases is needed.

Results

Two collagenases from Hathewaya histolytica, ColG and ColH, were successfully secreted by the yeast Saccharomyces cerevisiae. Compared with the native signal peptide of collagenase, the α-factor leader is more efficient in guiding collagenase secretion. Collagenase secretion was significantly increased in YPD medium by supplementing with calcium and zinc ions. Recombinant collagenase titers reached 68 U/mL and 55 U/mL for ColG and ColH, respectively. Collagenase expression imposed metabolic perturbations on yeast cells; substrate consumption, metabolites production and intracellular cofactor levels changed in engineered strains. Both recombinant collagenases from yeast could hydrolyze soluble and insoluble collagen materials. Recombinant ColG and ColH showed a synergistic effect on efficient collagen digestion.

Conclusions

Sufficient calcium and zinc ions are essential for active collagenase production by yeast. Collagenase secretion was increased by optimization of expression cassettes. Collagenase expression imposed metabolic burden and cofactor perturbations on yeast cells, which could be improved through metabolic engineering. Our work provides a useful way to produce collagenases for collagen resource utilization.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02186-y.

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.

A Preliminary Characterization of a Novel Recombinant Clostridial Collagenase Blend

Clostridial collagenases are essential biotechnological tissue dissociation agents owing to their ability to cleave different types of collagen. Standardization of collagenase-based protocols has been hampered by impurities in products manufactured from Clostridium histolyticum. To enhance the purification process, we produced recombinant collagenase classes G and H, taking advantage of the Escherichia coli expression system. The respective gene sequences were derived from C. histolyticum and modified by addition of a C-terminal polyhistidine tag. Harvested bacteria were lysed and the collagenase protein was affinity purified using a His-tag column. The purity, identity, integrity of the eluted collagenases G and H were determined by SDS electrophoresis and Western blot. The proteolytic activity of the collagenase G and H blend (rColGH) was determined by the standard FALGPA assay. The tissue dissociation activity was verified using a standardized method for isolation of rat pancreatic islets. Biocompatibility of the blend was validated by a standardized viability assay on the isolated islets. Two batches of rColGH were produced and compared to a commercially available collagenase. Based on our results, we conclude that rColGH is a functional and non-toxic novel recombinant collagenase worth further characterization and blend optimization in order to make it a competitive commercial product.

Establishing a model of primary bovine hepatocytes with responsive growth hormone receptor expression

The liver becomes resistant to growth hormone before parturition in dairy cows (uncoupling of the somatotropic axis). However, the mechanism of growth hormone insensitivity has not been fully described. The aim of the present study was to improve a previous model of adult bovine hepatocytes in a sandwich culture system to ensure growth hormone receptor (GHR) expression. First, we modified the protocol for hepatocyte retrieval and tested the effect of short (18 min) and long (up to 30 min) warm ischemia on hepatocyte viability. Second, we used medium additives that affect GHR expression in vivo-insulin (INS), dexamethasone (DEX), both (INS+DEX), or no hormone additives (CTRL)-to ensure the functionality of hepatocytes, as measured by lactate dehydrogenase activity and urea concentration in the medium. We also used reverse transcriptase PCR of hepatocytes to evaluate expression of albumin (ALB), hepatocyte nuclear factor 4α (HNF4A), nuclear factor-κ-B-inhibitor α (NFKBIA), cytosolic phosphoenolpyruvate carboxykinase (PCK1), and vimentin (VIM) mRNA. Moreover, we analyzed the expression of GHRtot (GHR), GHR1A, insulin-like growth factor-1 (IGF1), and IGF binding protein-2 (IGFBP2) in response to exposure to media with the different compositions. Modification of the protocol (changes in rinsing and perfusion times, buffer composition, and the volume and standardization of collagenase) led to increased cell counts and cell viability. Short warm ischemia with the modified protocol significantly increased cell count (4.7 × 10⁷ ± 1.9 × 10⁷ vs. 3.5 × 10⁶ ± 1.5 × 10⁶ vital cells/g of liver) and viability (79.1 ± 8.4 vs. 37.1 ± 8.9%). Therefore, we gathered hepatocytes from the liver after short warm ischemia with the modified protocol. For these hepatocytes, lactate dehydrogenase activity was lower in media with INS and with DEX than in media with INS+DEX or CTRL; urea concentrations were highest at d 4 for INS+DEX. As well, HNF4A and ALB were more highly expressed in hepatocytes cultured with INS and INS+DEX than in those cultured with DEX or CTRL, and the substitution of DEX suppressed VIM and NFKBIA expression but increased PCK1 expression. The expression of GHR, GHR1A, and IGF1 was suppressed by dexamethasone (DEX and INS+DEX), whereas INS distinctly increased GHR, GHR1A, and IGF1 mRNA expression. Hepatocytes in a sandwich culture showed influenceable GHR expression; this study provides a model that can be used in studies examining factors that influence the expression and signal transduction of GHR in dairy cows.

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

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

Evaluation of a Purified Enzyme Blend for the Recovery and Function of Canine Pancreatic Islets

Recently developed technologies enabling the production of a reproducible, purified enzyme blend for optimal human pancreatic islet isolation has renewed interest in clinical islet transplantation. The canine model has been an ideal preclinical model for the development of islet transplantation protocols. As seen in other species, the application of crude collagenase for isolating canine islets resulted in highly variable islet yields, extensive islet fragmentation, and variable islet functionality. We compared the function of commercially available crude collagenases with that of Liberase™-CI purified enzyme blend for canine islet isolation. We also compared two manufacturing runs of Liberase-CI enzyme (lots 1 and 2) to demonstrate reproducibility of islet recovery and function. We report on the improved recovery and function of islets isolated using Liberase-CI enzyme. No difference in dog age, mean body weight, or pancreas weight were observed between the experimental groups. We observed a significantly higher postpurification recovery of islet equivalent number (IE) from pancreases processed using two lots of Liberase-CI enzyme (189 ± 20 × 103 IE, n = 4) and lot 2 (234 ± 39 × 103 IE, n = 7) than that obtained from pancreases processed with Sigma Type V (116.8 ± 27 × 103 IE, n = 5), Serva collagenase (49 ± 11.6 × 103 IE, n = 5, p < 0.05) or Boehringer–Mannheim (BM) Type P collagenase (85.4 ± 25 × 103 IE, n = 5, p < 0.05, ANOVA). No significant differences were observed in islet yield recovery from pancreases processed using the two production lots of Liberase-CI enzyme. Islet survival after 48 h in culture at 37°C was significantly higher from islets isolated using Liberase-CI enzyme (88 ± 3.7% survival) when compared to Sigma Type V (81.8 ± 3.3%), Serva (71.7 ± 2.8%), and BM Type P (77 ± 7.2%) (p < 0.05). Islet functional testing in vitro demonstrated islets isolated using crude collagenase had an increased insulin basal release and a reduced insulin stimulated response when compared with islets isolated using the two lots of Liberase-CI enzyme. The calculated stimulation index was 7.8 ± 1.7, 3.1 ± 0.6, and 4.8 ± 1.1 for Sigma Type V, Serva, and BM Type P isolated islets, respectively, compared to 15.7 ± 1.6 and 16.2 ± 1.9 for islets isolated with Liberase-CI enzyme production lots 1 and 2, respectively (p < 0.05). This evaluation demonstrates that a purified enzyme blend can significantly improve islet recovery and function. It also demonstrates the manufacturing reproducibility of Liberase-CI enzyme lots resulting in the isolation of canine islets with the same degree of efficacy. A blend of purified enzymes, specifically formulated for canine islet isolation, can consistently yield large numbers of islets that survive longer in culture and demonstrate an improved insulin response in vitro.

Histochemical Analysis of the Role of Class I and Class II Clostridium Histolyticum Collagenase in the Degradation of Rat Pancreatic Extracellular Matrix for Islet Isolation

To understand why class II Clostridium histolyticum collagenase is much more effective than class I in the isolation of rat pancreatic islets, we analyzed the role of these collagenases in pancreatic tissue dissociation. Crude collagenase was purified and then fractionated into class I and II with different enzyme activities and protein compositions. Pancreatic tissue was incubated with either class I, class II, or class I + II, with or without added protease, under conditions that eliminated endogenous proteolytic activity. The degradation of pancreatic extracellular matrix was monitored by selective histochemical staining of tissue samples. Class I and II showed similar capacities to degrade glycoproteins and degraded about one-third of the glycoproteins during 120 min of incubation. The degradation of collagens by class I and II was relatively more effective, 80 to 95% of the collagens being removed in 120 min, and also class dependent. Both in the presence and absence of protease, class II was more effective at degrading collagens than class I, but this difference in efficacy was less apparent than with islet isolation. Class I + II degraded collagens faster and more complete than did the individual classes, indicating a synergistic effect of class I and II. Evaluation of collagen degradation at various pancreatic locations did not show a selective degradation of collagens by any of the collagenase classes. The present data offer a partial explanation for the major role of class II in islet isolation.

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

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

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

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

Comparison of Size, Viability, and Function of Fetal Pig Islet-Like Cell Clusters after Digestion Using Collagenase or Liberase

Liberase is a highly purified blend of collagenases that has been specifically developed to eliminate the numerous problems associated with the conventional use of crude collagenase when isolating islet-like cell clusters (ICCs) from pancreases of different species. The influence of Liberase on yield, size, viability, and function of ICCs has been documented when this enzyme was used to digest adult but not fetal pancreases. In this study, we compared the effects of collagenase and Liberase on fetal pig ICCs. A total of eight fetal pig pancreas digestions were analyzed. Fetuses were obtained from Large White Landrace pigs of gestational age 80 ± 2.1 days. The pancreases were digested with either 3 mg/ml collagenase P or 1.2 mg/ml Liberase HI. The time taken to digest the pancreas was shorter for collagenase when compared with Liberase (22 ± 2 vs. 31 ± 2 min). The size of ICCs was similar for both collagenase (83 ± 0.5 μm) and Liberase (79 ± 0.4 μm) as was the number of ICCs produced per pancreas (7653 ± 1297 vs. 8101 ± 1177). Viability, as assessed using fluorescent markers, was slightly greater for Liberase (79 ± 1% vs. 76 ± 1%, p < 0.05). Responsiveness to β-cell stimulus (20 mM KCl) was similar for both methods of isolation, as was the insulin content of the ICCs, both in vitro and at 1 month after transplantation of 1500 ICCs beneath the renal capsule of immunoincompetent mice. Despite the high content of endotoxins in collagenase, the above results show that this enzyme was equally as efficient as Liberase in isolating functional ICCs from fetal pig pancreas.

The Morphology of Islets within the Porcine Donor Pancreas Determines the Isolation Result: Successful Isolation of Pancreatic Islets can Now be Achieved from Young Market Pigs

Clinical islet allotransplantation has become an increasingly efficient “routine ” therapy in recent years. Shortage of human donor organs leads to porcine pancreatic islets as a potential source for islet xenotransplantation. Yet it is still very difficult to isolate sufficient numbers of intact porcine islets, particularly from young market pigs. In the following study islets were successfully isolated from retired breeders [4806 ± 720 islet equivalents per gram organ (IEQ/g); n = 25; 2–3 years old; RB] and also from young hybrid pigs [2868 ± 260 IEQ/g; n = 65; 4–6 months old; HY] using LiberasePI and a modified version of Ricordi's digestion-filtration technique. As expected, isolations from RB showed significantly better results (p < 0.002). A retrospective histological analysis of almost all donor pancreases showed that the majority of organs from RB (80%) contained mainly large islets (diameter >200 μm), in contrast to only 35% of all pancreases from HY. Remarkably, the islet size in situ, regardless whether detected in RB or HY, strongly determined the isolation result. A donor organ with predominantly large islets resulted in significantly higher numbers of IEQs compared with a donor organ with predominantly small islets [RBLarge Islets: 5680 ± 3,318 IEQ/g n = 20); RBSmall Islets: 1353 ± 427 IEQ/g (n = 5); p < 0.02]. In addition, isolation results were strongly influenced by the quality of the LiberasePI batch, and therefore single batch testing is invariably required. Purification was performed using Ficoll or OptiPrep™ density gradient centrifugation manually or in the COBE cell processor. Although islet purity was highest when OptiPrep™ was used, final islet yields did not differ between the different purification methods. Our study demonstrates that islet size in situ is an extremely critical parameter for highly successful islet isolation; consequently, we are now performing a morphological screening of each donor organ prior to the isolation process. Under these conditions highly successful isolations can reliably be performed even from young market pigs.

Fluorogenic Peptide Substrate for Quantification of Bacterial Enzyme Activities

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

Beta-cell replacement therapy: current outcomes and future landscape

PURPOSE OF REVIEW

This article provides a summary of the current outcomes of β-cell replacement strategies, an algorithm for choosing a specific modality while highlighting associated advantages and disadvantages, and outlines remaining challenges and areas of active investigation in β-cell replacement therapy.

RECENT FINDINGS

The most recent reports of islet cell allotransplantation have shown improvements over previous eras and now rival some outcomes of pancreas alone transplantation. Active areas of investigation are focused on improving techniques for islet isolation, graft monitoring, and managing challenges posed by the innate and alloimmune systems.

SUMMARY

Patients with insulin-dependent diabetes who continue to experience life threatening hypoglycemia despite maximal medical management can benefit from β-cell replacement. Emerging nontransplant technologies have not provided a physiologic euglycemic state to the extent offered by transplantation. Islet transplantation eliminates hypoglycemic episodes/unawareness, facilitates normalization of hemoglobin A1c (HbA1c), decreases microvascular disease progression, and improves quality of life for patients with problematic diabetes. Mid- and long-term outcomes of islet transplantation performed at expert centers approximate those of registry reports of solitary pancreas transplant, whereas the complication profile is quite favorable.

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.

Successful human islet isolation and transplantation indicating the importance of class 1 collagenase and collagen degradation activity assay

BACKGROUND

Purified tissue dissociation enzymes (TDEs) are critical to successful human islet isolation required for clinical transplantation, but little is known about the characteristics of the key enzymes-class I (C1) and class II (C2) collagenase from Clostridium histolyticum-used in these procedures. Here, we show the differences between the C1 collagenase found in purified collagenase products manufactured by three suppliers and the impact of differences in C1 between two suppliers on human islet yield.

METHODS

Collagenase from Roche, Serva/Nordmark (Uetersen, Germany), and VitaCyte (Indianapolis, IN) were analyzed by analytical high-performance liquid chromatography and collagen degradation activity (CDA), an assay that preferentially detects intact C1 collagenase. Human islet isolations were performed using current standard practices.

RESULTS

These studies showed that the highest amount of intact C1 that correlated with a high specific CDA (CDA unit per milligram of protein). The highest specific CDA was found in VitaCyte product followed by the Roche and Serva/Nordmark products. The products of VitaCyte were used successfully for human islet isolation (n=14) with an average final islet yield obtained was 419,100+/-150,900 islet equivalent number (IEQ) (4147+/-1759 IEQ/g pancreas). Four of these preparations were used successfully in clinical transplantation procedures. These TDEs gave significantly better results when compared with earlier data where 27 isolations were performed using Serva NB1 collagenase and NB neutral protease where the final islet yield was 217,500+/-152,400 IEQ (2134+/-1524 IEQ/g pancreas).

CONCLUSIONS

These data indicate the importance of intact C1 and the use of the appropriate analytical assays to correlate biochemical characteristics of TDEs to islet quality and yield.

Nonsimultaneous administration of pancreas dissociation enzymes during islet isolation

BACKGROUND

Successful islet isolation relies heavily on enzyme products. Among them, Liberase was used in islet transplantation programs until the islet community was notified of the use of a bovine brain component during the manufacturing process. To minimize potential risk of prion disease transmission, many islet isolation facilities switched to Serva enzyme, which is considered to pose less risk. However, this conversion significantly affected the field in transplant activity. Here, we report our successful conversion from Liberase to Serva collagenase with the use of a modified digestion protocol.

METHODS

We compared the quality of Serva versus Liberase enzyme using chromatography and collagenase activity assay. On the basis of the findings, we developed a pancreas digestion protocol optimized for Serva enzyme, where only collagenase was injected into the pancreas through the duct, and then neutral protease was added to the circulating system during the digestion phase.

RESULTS

Class I collagenase activity of Serva was remarkably reduced compared with Liberase. Chromatography of Serva demonstrated suspected degradation of class I collagenase. When the modified protocol was applied to donor pancreata more than 35 years of age, we recovered 3119+/-147 islet equivalent/g pancreas with a success rate of 51% (35/68), whereas the standard method yielded only 1809+/-266 islet equivalent/g pancreas (P=0.02) with a success rate of 11% (1/9). This beneficial effect of the modified method was, however, diminished when applied to younger donor pancreata.

CONCLUSIONS

Our study brings new insight into the role of collagenase and noncollagenolytic protease on pancreas dissociation.

The importance of tryptic-like activity in purified enzyme blends for efficient islet isolation

BACKGROUND

The isolation of islets from the human pancreas critically depends on an efficient enzyme blend. Previous studies have solely focused on the presence of collagenase and neutral protease/thermolysin. Despite improved characterization of these components, the lot-related variability in efficacy still persists suggesting that additional so far disregarded enzymes are required for efficient islet cleavage.

METHODS

Varying activities of a tryptic-like enzyme were identified within collagenase NB1 lots, which were selected according to a matched ratio between tryptic-like and collagenase activity (TLA-ratio). Rat and human pancreata were processed with current standard procedures.

RESULTS

Increasing the TLA-ratio from 1.3% to 10% reduced pancreas dissociation time in rats by 50% without affecting islet yield, viability, or posttransplant function in diabetic nude mice. Enhancing the TLA-ratio from 1.3% to 12.6% for human pancreas processing resulted in a significant reduction of recirculation time and increased incrementally human islet yield without affecting purity, in vitro function or recovery after culture. Optimized pancreas digestion correlated with a higher percentage of islet preparations fulfilling quality criteria for clinical transplantation.

CONCLUSIONS

We conclude that TLA is an effective component that should be included in moderate amounts in enzyme blends for human islet isolation to optimize the efficiency and minimize the lot-related variability.

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.

Collagenase penetrates human pancreatic islets following standard intraductal administration

BACKGROUND

: To optimize human islet isolation, it is important to improve our understanding of the collagenase digestion phase. Previous studies of collagenase action were mostly concerned with optimizing its composition, but the delivery and distribution of collagenase at the islet-exocrine interface is likely to be important for liberation of intact islets. The aim of this study was to characterize collagenase distribution in relation to islets in infused human pancreases.

METHODS

: Human pancreases were retrieved from multiorgan donors with appropriate consent. Tissue samples were taken from the neck, body, and tail regions before and after collagenase infusion by manual syringe-loading (n=10) or recirculating perfusion (n=8), and snap frozen in liquid nitrogen. Frozen sections were immunolabeled for collagenase, insulin, CK19, collagen VI and CD31, then assessed by confocal microscopy.

RESULTS

: Collagenase labeling was widespread throughout the pancreas, associated with collagen VI, and adjacent to CK19-labeled ducts. Collagenase was found within 67%+/-2% of islets ("intraislet"), associated with capillaries (CD31-positive). Intraislet collagenase was observed in 70%+/-3% of islets in the pancreatic tail, compared with 58%+/-2% and 53%+/-2% of islets in the body and neck, respectively (P<0.05 tail vs. neck), and was more prevalent in islets with diameters more than 150 microm (98%+/-1% of islets >150 microm vs. 52%+/-2% of islets <150 microm, P<0.05). There was no difference in intraislet collagenase labeling between perfused and syringe-loaded pancreases.

CONCLUSIONS

: Using current infusion techniques, collagenase penetrates the islet interior. This could cause islet fragmentation, and consequently, low islet yields. This study underlies the need to optimize collagenase delivery to preserve intact islets.

Detrimental effect of excessive collagenase class II on human islet isolation outcome

Commercially available purified collagenases, derived from Clostridium histolyticum, contain two different classes of collagenase: class I collagenase (CI) and class II collagenase (CII) at a predetermined ratio. In this study, using purified CI and CII in separate vials, we had a unique opportunity to investigate the effect of the proportion between two collagenase classes on clinical human islet isolation. Pancreas organs derived from deceased donors were prospectively assigned to one of three different enzyme protocols: group A--CII:CI = 1:1 vial; group B--1:2; group C--1.5:1. As a result, their total collagenase activities were 2116, 2230, and 3117 Wunsch units/pancreas in groups A, B, and C, respectively but thermolysin dosage was adjusted to 624-988 Units/g pancreas. The pancreas was not efficiently digested in group C in spite of a relatively longer digestion time and significantly higher Wunsch activity, resulting in the poorest islet isolation outcome among the three groups. Additional retrospective analysis revealed that this suboptimal outcome in group C was not because of the absolute excessive amount of collagenase activity but as a result of the relatively high proportion of CII (i.e., unbalanced CII/CI ratio). Our study suggests that an excessive CII is ineffective in releasing islets from human pancreas, and rather a balanced CII/CI ratio is of paramount importance.

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.

Quantitative Assessment of Collagenase Blends for Human Islet Isolation

BACKGROUND

The variability in collagenase blends has been speculated as the single most important determinant of the success or failure in isolated islet yields in clinical islet transplantation. Examination of the formulation and potency of the widely used Liberase HI enzyme blend will uncover possible sources of imprecision.

METHODS

High performance liquid chromatography (HPLC) and kinetic measurements of collagenase and protease activity were used to assess potency. Between four and nine clinical lots were assessed for various parameters such as relative formulation of collagenase isoforms, and recovered collagenase and protease potencies postreconstitution.

RESULTS

Six vials from a single typical lot had a mean enzyme content of 489+/-62.5 mg (mean+/-SEM; range 398-610 mg). The mean recovered collagenase activity was 2235+/-310 Wünsch units (WU)/vial (range 1794-2968 WU/vial). The percent coefficients of variation for collagenase and protease activity in these vials were 17.4%, and 13.4%, respectively. The increase in the presence of the collagenase Ib (CIb) isoform detected by HPLC analysis was related to the chronological order of the date of manufacture. The CIb isoform was found to have a reduced specific activity compared to intact collagenase I (CI) (3.8+/-1.2 WU/mg vs. 2.1+/-0.7 WU/mg, P < 0.05). The presence of CIb was related to reduced islet yields in twelve human isolations studied.

CONCLUSIONS

Variation in potency was observed between, and within lots of Liberase HI in this study. Differences in relative collagenase isoform composition may also affect the stability and potency characteristics of these blends.

Improved enzymatic isolation of fibroblasts for the creation of autologous skin substitutes

The number of medical applications using autologous fibroblasts is increasing rapidly. We investigated thoroughly the procedure to isolate cells from skin using the enzymatic tissue dissociation procedure. Tissue digestion efficiency, cell viability, and yield were investigated in relation to size of tissue fragments, digestion volume to tissue ratio, digestion time, and importance of other protease activities present in Clostridium histolyticum collagenase (CHC) (neutral protease, clostripain, and trypsin). The results showed that digestion was optimal with small tissue fragments (2-3 mm3) and with volumes tissue ratios > or =2 ml/g tissue. For incubations < or =10 h, the digestion efficiency and cell isolation yields were significantly improved by increasing the collagenase, neutral protease, or clostripain activity, whereas trypsin activity had no effects. However, a too high proteolytic activity of one of the proteases present in CHC digestion solution or long exposure times interfered with cell viability and cell culture yields. The optimal range of CHC proteases activities per milliliter digestion solutions was determined for digestions < or =10 h (collagenase 2700-3900 Mandl U/ml, neutral protease 5100-10,000 caseinase U/ml, and clostripain 35-48 BAEE U/ml) and for longer digestions (>14 h) (collagenase 1350- 3000 U/ml, neutral protease 2550-7700 U/ml, and clostripain 18-36 U/ml). Using these conditions, a maximum fibroblast expansion was achieved when isolated cells were seeded at 1 x 10(4) cells/cm2. These results did not only allow selection of optimal CHC batches able to digest dermal tissue with an high cell viability but also significantly increased the fibroblast yields, enabling us to produce autologous dermal tissue in a clinically acceptable time frame of 3 wk.

Assessment of a novel two-component enzyme preparation for human islet isolation and transplantation

BACKGROUND

Biologic characteristics of enzyme products used for islet isolation are critical for the success of islet transplantation. In particular, lot-to-lot variability significantly affects the yields of the isolation procedure. In this study, we have evaluated a new enzyme preparation in which highly purified collagenase can be blended with separately supplied neutral protease in a predetermined ratio.

METHODS

We compared the results of human-islet isolations performed either with Collagenase NB1 supplemented with Neutral Protease NB (group I, n=9) or with Liberase (group II, n=9).

RESULTS

Endotoxin contents of the enzyme preparations were lower in group I. Total islet yields were similar in both groups, but islet equivalents per gram of pancreas was higher in group I (4,020+/-1,240 vs. 2,360+/-1,350; P<0.05). Islet morphology was improved in group I with significantly higher proportion of free and intact islets (71+/-9% vs. 52+/-14%; P<0.01). In vitro function was improved and apoptosis rate was lower in group I.

CONCLUSIONS

This new enzyme blend was as efficient as Liberase in terms of islet yields and showed improvements in islet morphology, viability, and in vitro function. The possibility to control lot-to-lot variability and the low endotoxin contents make Collagenase NB1 a promising product for human-islet isolation.

Successful human islet isolation utilizing recombinant collagenase

The enzymatic dissociation of acinar tissue by collagenase is a substantial step in the isolation of pancreatic islets. Although essential collagenase components have been purified, the variability in the activity of different batches limits long-term reproducibility of isolation success. The utilization of purified recombinant proteases would solve this problem. In the present study, pancreases from multiorgan donors were dissociated by means of digestion-filtration using either Liberase HI (n = 51) or a recombinant collagenase blend (n = 25). No significant differences were found regarding islet yield before and after purification, the percent of exocrine-attached islets, and final purity. However, the ratio between islet equivalents and islet numbers indicated a lesser fragmentation in islets isolated with recombinant collagenase (P < 0.01). In contrast, viability was slightly higher in islets isolated with Liberase (92.3 +/- 0.8 vs. 85.6 +/- 2.9%; P < 0.05). Insulin release during static glucose incubation was not different between experimental groups. Islet transplantation into diabetic nude mice resulted in sustained normoglycemia in either group until the graft was removed. These results demonstrated that viable human islets can be isolated using recombinant collagenase. Final optimization of this enzyme blend would offer continuous reproducibility of isolation success.

Pancreatic Islet Cell Transplantation

Pancreatic islet cell transplantation as a treatment for diabetes has hitherto been confined to small patient cohorts with limited success. This article summarizes the results of islet cell transplantation before and after the advent of the new 'Edmonton protocol' of immunosuppression and management of the donor pancreas. Adopting this regimen has achieved unprecedented success and renewed interest in this potential cure for diabetes. Central to recent improvements in the technique has been the transplantation of an adequate islet mass. Improved methods to procure, isolate, and purify islets for clinical use are now being adopted as a new 'gold standard'. The use of new immunosuppressive drugs has further improved clinical results. Corticosteroid sparing-based regimens, and agents such as humanized monoclonal antibodies, are likely to form the mainstay of immunosuppressive protocols with the aim of achieving donor-specific tolerance. Alternative sources of islet cells are also required to expand the technique in an era of reduced numbers of donor pancreata. Manipulation of stem cells and xenotransplantation may yet yield sufficient islets to overcome the problem of donor shortage. Islet cell transplantation now forms the basis of a prospective multicenter trial under the aegis of the Immune Tolerance Network. The results of this are awaited, but it appears that islet cell transplantation may yet emerge as an effective treatment option for some members of the diabetic population.

Beta cell replacement for the treatment of diabetes

The replacement of insulin-producing beta cells by islet transplantation can efficiently reverse diabetes. The recent improvements in clinical results were made possible by transplanting higher islet masses and through the introduction of new immunosuppressive protocols that avoid diabetogenicity. The need for alternatives to continuous immunosuppression, and an unlimited source of glucose-sensitive, insulin-secreting tissue, is emerging. In this review we discuss the various key steps in islet transplantation and offer perspectives for future developments in the replacement of insulin-producing beta cells for the treatment of type I diabetes.

Human islet cell transplantation--future prospects

BACKGROUND

Islet transplantation has the potential to cure diabetes mellitus. Nevertheless despite successful reversal of diabetes in many small animal models, the clinical situation has been far more challenging. The aim of this review is to discuss why insulin-independence after islet allotransplantation has been so difficult to achieve.

METHODS

A literature review was undertaken using Medline from 1975 to July 2000. Results reported to the International Islet Transplant Registry (ITR) up to December 1998 were also analysed.

RESULTS

Up to December 1998, 405 islet allotransplants have been reported the ITR. Of those accurately documented between 1990 and 1998 (n = 267) only 12% have achieved insulin-independence (greater than 7 days). However with refined peri-transplant protocols insulin independence at 1 year can reach 20%.

CONCLUSIONS

There are many factors which can explain the failure of achieving insulin-independence after islet allotransplantation. These include the use of diabetogenic immunosuppressive agents to abrogate both islet allo-immunity and auto-immunity, the critical islet mass to achieve insulin-independence and the detrimental effects of transplanting islets in an ectopic site. However recent evidence most notably from the Edmonton group demonstrates that islet allotransplantation still has great potential to become an established treatment option for diabetic patients.

Significant progress in porcine islet mass isolation utilizing liberase HI for enzymatic low-temperature pancreas digestion

BACKGROUND

Frequent success in human islet isolation is prevented by the large variability of scarce organ donors; this favors the future utilization of pigs as donors for clinical islet xenotransplantation. Porcine-specific difficulties of islet isolation are attributed to the intrinsic fragility of islets during pancreas digestion.

METHODS

To preserve islet integrity during efficient pancreas dissociation, porcine pancreata (n=48) were distended after cold storage with cold University of Wisconsin solution containing Liberase HI and digested at 24-28 degrees C using digestion-filtration. Pancreata distended with University of Wisconsin solution containing well-proven crude collagenase and digested at 32-34 degrees C served as controls (n=46). Monolayer Ficolldiatrizoate gradient purification was performed in a Cobe 2991.

RESULTS

Purified yield of islet equivalents per pancreas (mean+/-SEM) was almost doubled by Liberase HI compared with crude collagenase (526,480+/-46,560 vs. 270,270+/-19,420; P < 0.0001) and also significantly increased comparing islet equivalents per gram of pancreas (4,210+/-320 vs. 2,640+/-245; P=0.0004). Islet integrity was better preserved during Liberase HI digestion compared with crude collagenase digestion as indicated by isolation index (2.1+/-0.1 vs. 1.4+/-0.1; P<0.0001). Purity, viability, and in vitro function of islets did not differ between experimental groups. Preserved in vivo function of islets isolated by Liberase HI was demonstrated after subcapsular transplantation into 16 diabetic nude rats.

CONCLUSIONS

If the problems related to xenograft rejection and xenosis could be solved, low-temperature digestion of porcine pancreata using Liberase HI could serve as an essential prerequisite for successful 1:1 xenotransplantation of pig islets into type 1 diabetic human recipients.

Long-term survival, morphology and in vitro function of isolated pig islets under different culture conditions

BACKGROUND

Islet culture aims to optimize islet survival and to reduce islet immunogenicity. To achieve these objectives, culture periods at 37 degrees C and 22-24 degrees C are mainly used.

METHODS

This study compares the influence of donor age (juvenile vs. adult), temperature (22 degrees C vs. 37 degrees C), and serum supplementation (10% newborn calf serum [NCS] with 10% pig serum) on morphological integrity and in vitro function of porcine islets during long-term culture (LTC).

RESULTS

After 21 days at 22 degrees C, the survival rate of cultured islets isolated from juvenile donors was lower than of adult islets (23+/-0.9% vs. 88+/-2.8%, P<0.001). Compared with 37 degrees C, LTC at 22 degrees C increased survival of adult islets and DNA recovery (92+/-2.5% vs. 45+/-4.8%, P<0.001; 72+/-4.1% vs. 30+/-5.1%, P<0.001) and reduced viability (62+/-8% vs. 89+/-5%, P<0.05). LTC at 22 degrees C was associated with a reduction of insulin content (85+/-9 vs. 152+/-10 microU/islet equivalents [IEQ], P<0.01), 24 hr-insulin secretion (82+/-7 vs. 552+/-91 microU/ day/IEQ, P<0.001), and integrated dynamic insulin response to glucose (1093+/-124 vs. 3074+/-708 microU/60 min/100 IEQ, P<0.05), compared with 37 degrees C LTC. Histologic analysis revealed disintegration of islet periphery after 22 degrees C, whereas smoothly shaped islets were present after 37 degrees C LTC. Integrity after 14 days at 37 degrees C was significantly better preserved when medium CMRL 1066 was supplemented with 10% porcine serum, compared with 10% NCS (40+/-2.3% vs. 21+/-6.7%, P<0.05), contrasting with 22 degrees C (52+/-4.0% vs. 59+/-3.7%, not significant).

CONCLUSIONS

This study demonstrates that survival of cultured porcine islets is increased at 22 degrees C, whereas in vitro function and viability are better preserved at 37 degrees C. Survival at 37 degrees C can be improved by adding homologous serum to the medium.

A preliminary study of the activation of endogenous pancreatic exocrine enzymes during automated porcine islet isolation

The activation of endogenous pancreatic enzymes during automated pancreas digestion may be detrimental to islet isolation. In this report we assessed the activation of trypsin, chymotrypsin, elastase, carboxypeptidases A and B, phospholipase A2, and lipase using a porcine model. Four islet isolations were examined. Duplicate aliquots were taken from the automated circuit at 5-min time intervals up to the completion of pancreas digestion (approx 60 min). One aliquot was activated in vitro with exogenous trypsin in order to convert the enzymes into their active non-"proform," with the exception of trypsinogen, which was activated with exogenous enterokinase. This was done to assess the percentage activation of each individual enzyme (total potentially activatable enzyme release). The extent of activation between isolations was extremely variable. During the closed (recirculating) circuit phase of pancreas digestion there were both gradual and rapid increases in the levels of enzymes released. Peak activity of enzyme activation varied from 13 to 30 min; similarly, total potentially activatable peaks occurred between 13 and 38 min. Lipase and carboxypeptidase B showed greater than 70% activation, chymotrypsin, carboxypeptidase A, and phospholipase A2 between 50% and 70% activation, and trypsin and elastase less than 20%. There were up to 30-fold differences between the four islet preparations. In summary, it is unlikely that poor islet yields are soley explained by variations between collagenases; the variable activation of endogenous pancreatic exocrine enzymes is also likely to be influential to porcine islet yields.