Adjustment of the Ratio Between Collagenase Class II and I Improves Islet Isolation Outcome

A Practical Guide to Rodent Islet Isolation and Assessment Revisited

Insufficient insulin secretion is a key component of both type 1 and type 2 diabetes. Since insulin is released by the islets of Langerhans, obtaining viable and functional islets is critical for research and transplantation. The effective and efficient isolation of these small islands of endocrine cells from the sea of exocrine tissue that is the rest of the pancreas is not necessarily simple or quick. Choosing and administering the digestive enzyme, separation of the islets from acinar tissue, and culture of islets are all things that must be considered. The purpose of this review is to provide a history of the development of islet isolation procedures and to serve as a practical guide to rodent islet research for newcomers to islet biology. We discuss key elements of mouse islet isolation including choosing collagenase, the digestion process, purification of islets using a density gradient, and islet culture conditions. In addition, this paper reviews techniques for assessing islet viability and function such as visual assessment, glucose-stimulated insulin secretion and intracellular calcium measurements. A detailed protocol is provided that describes a common method our laboratory uses to obtain viable and functional mouse islets for in vitro study. This review thus provides a strong foundation for successful procurement and purification of high-quality mouse islets for research purposes.

Recombinant collagenase from Grimontia hollisae as a tissue dissociation enzyme for isolating primary cells

Collagenase products are crucial to isolate primary cells in basic research and clinical therapies, where their stability in collagenolytic activity is required. However, currently standard collagenase products from Clostridium histolyticum lack such stability. Previously, we produced a recombinant 74-kDa collagenase from Grimontia hollisae, which spontaneously became truncated to ~60 kDa and possessed no stability. In this study, to generate G. hollisae collagenase useful as a collagenase product, we designed recombinant 62-kDa collagenase consisting only of the catalytic domain, which exhibits high production efficiency. We demonstrated that this recombinant collagenase is stable and active under physiological conditions. Moreover, it possesses higher specific activity against collagen and cleaves a wider variety of collagens than a standard collagenase product from C. histolyticum. Furthermore, it dissociated murine pancreata by digesting the collagens within the pancreata in a dose-dependent manner, and this dissociation facilitated isolation of pancreatic islets with masses and numbers comparable to those isolated using the standard collagenase from C. histolyticum. Implantation of these isolated islets into five diabetic mice led to normalisation of the blood glucose concentrations of all the recipients. These findings suggest that recombinant 62-kDa collagenase from G. hollisae can be used as a collagenase product to isolate primary cells.

Collagenase H is crucial for isolation of rat pancreatic islets

The role(s) of collagenase G (ColG) and collagenase H (ColH) during pancreatic islet isolation remains controversial, possibly due to the enzyme blends used in the previous studies. We herein examined the role of ColG and ColH using highly pure enzyme blends of recombinant collagenase of each subtype. Rat pancreases were digested using thermolysin, together with ColG, ColH, or ColG/ColH (n = 9, respectively). No tryptic-like activity was detected in any components of the enzyme blends. The efficiency of the collagenase subtypes was evaluated by islet yield and function. Immunohistochemical analysis, in vitro collagen digestion assay, and mass spectrometry were also performed to examine the target matrix components of the crucial collagenase subtype. The islet yield was highest in the ColG/ColH group (4,101 ± 460 islet equivalents). A substantial number of functional islets (2,811 ± 581 islet equivalents) was obtained in the ColH group, whereas no islets were retrieved in the ColG group. Mass spectrometry demonstrated that ColH reacts with collagen I and III. In the immunohistochemical analysis, both collagen I and III were located in exocrine tissues, although collagen III expression was more pronounced. The collagen digestion assay showed that collagen III was more effectively digested by ColH than by ColG. The present study reveals that ColH is crucial, while ColG plays only a supporting role, in rat islet isolation. In addition, collagen III appears to be one of the key targets of ColH.

Exendin-4 protects hypoxic islets from oxidative stress and improves islet transplantation outcome

Oxidative stress produced during pancreatic islet isolation leads to significant β-cell damage. Homeostatic cytokines secreted subsequently to islet transplantation damage β-cells by generating oxygen free radicals. In this study, exendin-4, a glucagon-like peptide-1 analog improved islet transplantation outcome by increasing the survival of diabetic recipient mice from 58% to 100%. We hypothesized that this beneficial effect was due to the ability of exendin-4 to reduce oxidative stress. Further experiments showed that it significantly reduced the apoptotic rate of cultured β-cells subjected to hypoxia or to IL-1β. Reduction of apoptotic events was confirmed in pancreatic islet grafts of exendin-4-treated mice. Exendin-4 enhanced Akt phosphorylation of β-cells and insulin released from them. It even augmented insulin secretion from islets cultivated at hypoxic conditions. Exposure to hypoxia led to a decrease in the activation of Akt, which was reversed when β-cells were pretreated with exendin-4. Moreover, exendin-4 increased the activity of redox enzymes in a hypoxia-treated β-cell line and reduced reactive oxygen species production in isolated pancreatic islets. Recovery from diabetes in mice transplanted with hypoxic islets was more efficient when they received exendin-4. In conclusion, exendin-4 rescued islets from oxidative stress caused by hypoxia or due to cytokine exposure. It improved the outcome of syngenic and xenogenic islet transplantation.

Enhancement of the structural stability of full-length clostridial collagenase by calcium ions

The clostridial collagenases G and H are multidomain proteins. For collagen digestion, the domain arrangement is likely to play an important role in collagen binding and hydrolysis. In this study, the full-length collagenase H protein from Clostridium histolyticum was expressed in Escherichia coli and purified. The N-terminal amino acid of the purified protein was Ala31. The expressed protein showed enzymatic activity against azocoll as a substrate. To investigate the role of Ca(2+) in providing structural stability to the full-length collagenase H, biophysical measurements were conducted using the recombinant protein. Size exclusion chromatography revealed that the Ca(2+) chelation by EGTA induced interdomain conformational changes. Dynamic light scattering measurements showed an increase in the percent polydispersity as the Ca(2+) was chelated, suggesting an increase in protein flexibility. In addition to these conformational changes, differential scanning fluorimetry measurements revealed that the thermostability was decreased by Ca(2+) chelation, in comparison with the thermal melting point (T(m)). The melting point changed from 54 to 49°C by the Ca(2+) chelation, and it was restored to 54°C by the addition of excess Ca(2+). These results indicated that the interdomain flexibility and the domain arrangement of full-length collagenase H are reversibly regulated by Ca(2+).

Islet versus pancreas transplantation in Brazil: Defining criteria for pancreas allocation decision

BACKGROUND

Many studies have evaluated whether there are characteristics related to pancreas donors and the islet isolation process that can influence pancreatic islet yield. However, this analysis has not yet been performed in Brazil, one of the world leaders in whole pancreas organ transplantation (WOPT), where pancreas allocation for pancreatic islet transplantation (PIT) has no officially defined criteria. Definition of parameters that would predict the outcome of islet isolation from local pancreas donors would be useful for defining allocation priority in Brazil.

OBJECTIVE

To analyze the relationship between multiple donor-related and islet isolation variables with the total number of isolated pancreatic islet equivalents (IEQ) in a brazilian sample of pancreas donors.

METHODS

Several variables were analyzed in 74 pancreata relative to the outcome of total IEQs obtained at the end of the process.

RESULTS

In univariate analysis, body mass index (BMI) (p = 0.003), the presence of fatty infiltrates in the pancreas as observed during harvesting (p = 0.042) and pancreas digestion time (p = 0.046) were identified as variables related to a greater IEQ yield. In a multivariate analysis a statistically significant contribution to the variability of islet yield was found only for the BMI (p = 0.017). A ROC curve defined a BMI = 30 as a cut-off point, with pancreata from donors with BMI > 30 yielding more islets than donors with BMI < 30 (p< 0.001).

CONCLUSION

These data reinforce the importance of the donor BMI as a defining parameter for successful islet isolation and establishes this variable as a potential pancreas allocation criterion in Brazil, where there is unequal competition for good quality organs between WOPT and PIT.

Collagenase isoforms for pancreas digestion

The available information concerning the characteristics and composition of collagenase batches, which are effective in the digestion of human pancreas for islet transplants, is scarce and incomplete. A large inter- and intrabatched variability in activity and efficiency of blend enzymes available for isolation has been observed. The aim of this study was to characterize enzyme blend components. Liberase batches were characterized by SDS-PAGE analyses, microelectrophoresis, and then by MALDI-TOF MS analysis. Three main bands were detected by SDS-PAGE analysis and submitted to MALDI-TOF MS analysis. Two bands were found to correspond to class I (isoform beta and another of 106 kDa) and one to class II (isoform delta) collagenase. These results represent an important step towards a complete characterization of enzymes, with the final aim of identifying key components for a standardized product.

Modified method for isolation of langerhans islets from mice

Successful isolation of Langerhans islets is a crucial prerequisite for their experimental or possible clinical use such as transplantation. Centrifugation in a Ficoll gradient is a common step used for separation of Langerhans islets from exocrine tissue. However, islets have been reported to be negatively affected by employing Ficoll gradients. Therefore, the aim of this study was to modify the isolation procedure by excluding Ficoll gradient centrifugation to obtain a similar or better yield of viable, functional islets. In our modification of the isolation procedure, the separation of islets from exocrine tissue was based on their sedimentation rate combined with their differential ability to attach to the surface of culture dishes for suspension cells. The resulting purity of islets facilitated their handpicking from the suspension. The mean yield was 900 viable, insulin-producing islets per mouse, which was comparable to or even higher than the yield in commonly used protocols. Our modification of the isolation method may be useful when centrifugation in Ficoll gradient is undesirable due to potential toxicity.

Degraded collagenase deteriorates islet viability

OBJECTIVE

The utilization of purified enzyme blends consisting of collagenase class I (CI) and II (CII) and neutral protease is an essential step for clinical islet isolation. Previous studies suggested that the use of enzyme lots containing degraded CI reduced islet release from human pancreata. The present study sought to assess the effect of degraded collagenase on islet function in vitro and posttransplantation.

MATERIALS AND METHODS

Crude collagenase was chromatographically separated into CI, CII, and a mixture of degraded CI and CII isomers. Subsequently, classes were recombined to obtain a CII/CI ratio of 0.5. Rat islets were isolated utilizing neutral protease and 20 units of recombined collagenase containing either intact (Ci) or degraded isomers (Cd).

RESULTS

Digestion time was reduced utilizing Cd (P < .001). The highest islet yield and lowest islet fragmentation were obtained with Ci (P < .01). Utilization of Cd corresponded to a reduction in viability and in vitro function (NS). Islet transplantation reversed hyperglycemia in diabetic nude mice, but revealed an absence of weight gain in recipients receiving islets isolated using Cd (P < .01).

CONCLUSION

This study suggested that islet function posttransplantation is affected by degraded collagenase isomers. This finding has to be considered for the purification process of collagenase.

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.