Evaluation of energy state of islet independent of size using a newly developed ATP bioluminescence assay

Clinical Islet Isolation

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

Influence of the Two-Layer Preservation Method on Human Pancreatic Islet Isolation: A Meta-Analysis

Introduction

There has been continuous debate on whether the Two-Layer Method (TLM) is superior to the University of Wisconsin solution (UW) for preserving human pancreas prior to islet isolation. The objective of the current meta-analysis is to assess which method is superior.

Methods

We searched electronic databases (MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials) for relevant human trials published in the English language from January 2000 to October 2013. Data on donor characteristics and islet isolation outcomes were extracted.

Results

14 articles containing 18 human studies were included in this meta-analysis. In comparison to UW alone, TLM alone produced a significantly higher islet yield (weighted mean difference, 776.32; 95% confidence interval; 370.82-1181.82; P = .0002). TLM alone also yielded higher proportion of transplantable preparations (odds ratio, 1.60; 95% confidence interval; 1.15-2.23; P = .005). The following measures did not differ: islet viability (weighted mean difference, 2.10; −2.41-6.60; P = .360), purity (weighted mean difference, −0.92; −3.75-1.91; P = .520) and function assessed by measuring the stimulation index (weighted mean difference, 0.17; −0.21-0.55; P = .380). When comparing TLM following UW storage with UW alone, the results were similar to the previous ones.

Conclusions

This data indicates that the TLM can improve islet yield and increase the opportunities of human pancreatic islet transplantation. Therefore, the TLM should be recommended for preserving human pancreas prior to islet isolation.

A model to evaluate toxic factors influencing islets during collagenase digestion: the role of serine protease inhibitor in the protection of islets

The recovery of all of the islets contained in a pancreas is the goal of islet isolation for transplantation. This study reveals an environment that injures the isolated islets during digestion and proposes a new model for optimal islet isolation. Islets were isolated from Wistar rat pancreases by stationary collagenase digestion while the digestion time was varied at 15, 30, 60, and 120 min. The digested pancreas and islets were analyzed histologically and adenosine nucleotides were measured. Overnight cultured islets (40 islets) were cocultured for 30 min with the supernatants obtained from pancreatic collagenase digestion at different digestion periods in order to assess the toxic environment. The peak yields of islets were obtained at 30 min of digestion. The histological study of digested pancreas showed that the exocrine cells lost their cellular integrity at 120 min of digestion, but the islet cells were left intact. Accordingly, the ATP levels of the pancreatic tissue decreased during the digestion period. The coculture experiment demonstrated that the islets cultured with the supernatants from the collagenase digestion showed digestion time-dependent disruption of the cellular integrity of islets in accordance with a rapid decrease of ATP levels in the islets. The addition of serine protease inhibitors into this coculture clearly showed protection of islets, which maintained high ATP levels in association with intact membrane integrity as assessed by AO/PI staining. Morphological deterioration of islets as well as a marked ATP decrease was evident in the entire digested pancreas as well as in islets cocultured in the supernatants from the collagenase digestion. Various factors toxic to the islets can therefore be analyzed in future experiments using this coculture model for obtaining a good yield of viable islets.

Adenine nucleotide levels in a closed enzymatic digestion system for porcine islet isolation

Obtaining viable islets is a crucial step for successful islet transplantation. Adenosine triphosphate (ATP) is a marker of cell viability. However, little is known about any changes in the energy status of the tissues that are being digested during the digestion phase. We herein examined whether the ATP content in serially digested pancreatic tissue samples could be specific objective parameters that signal the optimal point to stop the digestion process. We obtained partial pancreata (body to tail) from 4- to 5-year-old pigs from a slaughterhouse. The tissue samples were preserved in M-Kyoto solution for less than 3 h. They were digested using an automated enzymatic and mechanical dissociation system at 37°C for 90 min following intraductal injection of Liberase HI. Samples were collected from the digestive circuit every 5 or 10 min to determine the ATP level, total adenine nucleotide (TAN) level, islet count (count/g), and yield of islet equivalent (IEQ) in the serial digestive fluids. The ATP and TAN levels, IEQ and islet count were increased and then decreased during digestion process. The profile of these parameters differed from case to case. However, when ATP changing ratio (respective value/precedent value) was compared with IEQ changing ratio, a greater than threefold increase in the ATP changing ratio followed by an increase in the islet count changing ratio within 5 min was consistently observed, indicating the optimal time to stop the digestion. The ATP levels of the handpicked islets in the digested samples were lower in the overdigested phase in comparison to those in the earlier digested phase. These results indicate that the ATP level in digested fluid could be an effective indicator to estimate the viability of cells as well as determine the optimal time to terminate the digestion process in order to obtain viable islets.

Tauroursodeoxycholate (TUDCA), chemical chaperone, enhances function of islets by reducing ER stress

The exposure to acute or chronic endoplasmic reticulum (ER) stress has been known to induce dysfunction of islets, leading to apoptosis. The reduction of ER stress in islet isolation for transplantation is critical for islet protection. In this study, we investigated whether tauroursodeoxycholate (TUDCA) could inhibit ER stress induced by thapsigargin, and restore the decreased glucose stimulation index of islets. In pig islets, thapsigargin decreased the insulin secretion by high glucose stimulation in a time-dependent manner (1h, 1.35+/-0.16; 2h, 1.21+/-0.13; 4h, 1.17+/-0.16 vs. 0h, 1.81+/-0.15, n=4, p<0.05, respectively). However, the treatment of TUDCA restored the decreased insulin secretion index induced by thapsigargin (thapsigargin, 1.25+/-0.12 vs. thapsigargin+TUDCA, 2.13+/-0.19, n=5, p<0.05). Furthermore, the culture of isolated islets for 24h with TUDCA significantly reduced the rate of islet regression (37.4+/-5.8% vs. 14.5+/-6.4%, n=12, p<0.05). The treatment of TUDCA enhanced ATP contents in islets (27.2+/-3.2pmol/20IEQs vs. 21.7+/-2.8pmol/20IEQs, n=9, p<0.05). The insulin secretion index by high glucose stimulation is also increased by treatment of TUDCA (2.42+/-0.15 vs. 1.92+/-0.12, n=12, p<0.05). Taken together, we suggest that TUDCA could be a useful agent for islet protection in islet isolation for transplantation.

ATP measurement predicts porcine islet transplantation outcome in nude mice

Current nude mice islet transplantation studies cannot be used prospectively. Therefore, to predict transplantation outcomes, reliable and rapid assays for islet quality assessment are warranted. This study evaluated the predictive power of the porcine islet ATP content on the outcomes of islet transplantation in nude mice. Here, we report that the ATP measurement using a small number of handpicked islets with a diameter of 100 to 150 mum is a good predictor of islet graft efficacy in nude mice. Using receiver-operator characteristic analysis, the area under the curve of the ATP content using a small number of handpicked islets was 0.867 (95% confidence interval 0.744-0.989, P<0.001). The sensitivity and the specificity measured were 83.3% and 73.3%, respectively. In conclusion, a simple and a rapid measurement of intraislet ATP content could be a promising substitute for current nude mice islet transplantation studies.