Effect of human islet rescue gradient purification on islet yield and fractional Beta cell viability

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.

Pre-transplant signal induction for vascularisation in human islets

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

Iodixanol-controlled density gradient during islet purification improves recovery rate in human islet isolation

BACKGROUND

For pancreatic islet transplantation, islet purification minimizes the risks associated with islet infusion through the portal vein by reducing the amount of transplanted tissue. However, the purification step may result in decreased numbers of islets recovered from digested tissue and be traumatic to the islets. In this study, we evaluated the effectiveness of iodixanol-controlled density gradients on the islet purification step.

METHODS

For 14.3% of the isolations, the density was 1.085 g/cm3, 32.1% were 1.090 g/cm3, 46.4% were 1.095 g/cm3, 3.6% were 1.100 g/cm3, and 3.6% were 1.105 g/cm3, indicating that the density varies with each isolation. This has profound implications for the difficulty of islet purification. According to the density of digested tissue before purification, the density of the purification solutions was controlled by changing the volumetric ratio of iodixanol and the purification solutions (iodixanol-Kyoto [IK] solutions).

RESULTS

Islet yield after purification and rate of postpurification recovery were significantly higher in the IK group than with standard continuous gradient purification by Ficoll solutions (islet yield=Ficoll group: 377,230+/-50,207 islet equivalents, IK group: 594,136+/-50,570 islet equivalents, P less than 0.01; percentage of recovery=Ficoll group: 55.6%+/-5.8%, IK group: 84.9%+/-4.2%, P less than 0.01). In vitro and in vivo assays suggest that the quality of islets was similar between the two groups.

CONCLUSION

Our data suggest that using an iodixanol-controlled density gradient improves the islet recovery rate in human islet isolation. On the basis of these data, we now use this purification method for clinical islet transplantation.