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

The challenge of correctly reporting hormones content and secretion in isolated human islets

Background

An increased access of research laboratories to isolated human islets has improved our understanding of the biology of the endocrine pancreas and hence the mechanisms causing diabetes. However, in vitro studies of human islets remain technically challenging, and optimal use of such precious material requires a minimum of rigor and coordination to optimize the reliability and share of the information. A detailed report of the demographics of pancreas donors and of the procedures of islet handling after isolation is important but insufficient. Correct characterization of islet basic functions (a token of quality) at the time of experimentation is also crucial.

Scope of review

I have analyzed the literature reporting measurements of insulin and glucagon in the human pancreas or isolated human islets. The published information is often fragmentary. Elementary features such as islet size, insulin content, or rate of hormone secretion are either unreported or incorrectly reported in many papers. Although internal comparisons between control and test groups may remain valid, comparisons with data from other laboratories are problematic. The drawbacks, pitfalls and errors of common ways of expressing hormone content or secretion rates are discussed and alternatives to harmonize data presentation are proposed.

Major Conclusions

Greater coherence and rigor in the report of in vitro studies using human islets are necessary to ensure optimal progress in our understanding of the pathogenesis of diabetes.

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.

Hypoxia-Induced Damage in Human Islets Is Reduced With the Use of Mesenchymal Stem Cell-Preconditioned Medium

BACKGROUND

Mesenchymal stem cells (MSCs) are protective for islets when cotransplanted in a hypoxic environment. However, the risk of neoplasia is increased when MSCs are transplanted into immunosuppressed patients. This initial study aimed to investigate whether the production of protective factors from MSC can be stimulated by different culture conditions to benefit human islets cultured in hypoxia.

METHODS

MSC were isolated from human adipose tissue and cultured for 2 days in supplemented Minimum Essential Media α (MEMα) and 21% (21%-MEMα) or 1% oxygen (1%-MEMα). Native MEMα served as control. After MSC harvesting, cell-depleted media were frozen at -20°C until use for human islet culture in 2% oxygen for 72-96 hours before islet characterization. Data were normalized to control islets cultured in native MEMα and 2% oxygen (mean ± SEM).

RESULTS

After culture in 21%- or 1%-MEMα, islet recovery increased to 117 ± 12% (NS) and 138 ± 12% (P < .05), respectively. Viability did not change after culture in native MEMα (59 ± 2%), 21%-MEMα (59 ± 3%), or 1%-MEMα (61 ± 3%). Compared with control samples, the glucose stimulation index was increased after culture in 21%-MEMα (P < .05) or 1%-MEMα (P < .05). Overall survival was higher in 1%-MEMα (143 ± 14%) than in 21%-MEMα (119 ± 14%; NS) or native MEMα (P < .05).

CONCLUSIONS

This study demonstrates that MSC-preconditioned MEMα increases survival and in vitro function of hypoxic human islets. These findings indicate that hypoxic MSCs seem to produce factors that improve survival of islets suffering from hypoxia.

Effect of Etanercept Concentration on Human Islet Integrity

BACKGROUND

Etanercept is widely used as an antiinflammatory drug to improve engraftment after intraportal islet transplantation. In contrast to other immunosuppressive agents, very little is known about detrimental effects of etanercept on islets. The aim of this pilot study was to define the toxic range of etanercept.

METHODS

Human islets isolated from 8 donors were cultured for 4-5 days at 37°C in culture medium supplemented with etanercept at concentrations from 2.5 to 40 μg/mL, corresponding to potential in vivo levels within the portal vein. After culture, islet equivalent (IEQ) yield, fragmentation index (islet number/IEQ), purity, viability, and stimulated insulin release (2 vs 20 mmol/L) were assessed and normalized to islets before culture.

RESULTS

Yield (73 ± 8%) and viability (91 ± 4%) were highest with 5 μg/mL etanercept. Islet loss was evident when etanercept was ≥10 μg/mL (55 ± 7%; P < .05 vs control). Fragmentation (154 ± 34%; P < .05) was markedly increased and viability (81 ± 4%, P < .05) markedly decreased with etanercept >10 μg/mL. The accumulation of cell debris at concentrations ≥20 μg/mL resulted in a significant reduction of islet purity (84 ± 3%; P < .05). Etanercept did not interfere with stimulated insulin secretion at concentrations ≤10 μg/mL. The maximum stimulation index was noted at 2.5 μg/mL (1.8 ± 0.1).

CONCLUSIONS

Etanercept is tolerated by isolated human islets at concentrations <10 μg/mL. Our data suggest that the tight range between benefit and toxicity should be considered for dosage and administration of etanercept.

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.

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.