Improved Islet Purity by the Hypertonic-Hypotonic Method

Introducing a New Experimental Islet Transplantation Model using Biomimetic Hydrogel and a Simple High Yield Islet Isolation Technique

BACKGROUND

Islet transplantation could be an ideal alternative treatment to insulin therapy for type 1 diabetes Mellitus (T1DM). This clinical and experimental field requires a model that covers problems such as requiring a large number of functional and viable islets, the optimal transplantation site, and the prevention of islet dispersion. Hence, the methods of choice for isolation of functional islets and transplantation are crucial.

METHODS

The present study has introduced an experimental model that overcomes some critical issues in islet transplantation, including in situ pancreas perfusion by digestive enzymes through common bile duct. In comparison with conventional methods, we inflated the pancreas in Petri dishes with only 1 ml collagenase type XI solution, which was followed by hand-picking isolation or Ficoll gradient separation to purify the islets. Then we used a hydrogel composite in which the islets were embedded and transplanted into the peritoneal cavity of the streptozotocin-induced diabetic C57BL/6 mice.

RESULTS

As compared to the yield of the classical methods, in our modified technique, the mean yield of isolation was about 130-200 viable islets/mouse pancreas. In vitro glucose-mediated insulin secretion assay indicated an appropriate response in isolated islets. In addition, data from in vivo experiments revealed that the allograft remarkably maintained blood glucose levels under 400 mg/dl and hydrogel composite prevents the passage of immune cells.

CONCLUSION

In the model presented here, the rapid islet isolation technique and the application of biomimetic hydrogel wrapping of islets could facilitate islet transplantation procedures.

Engineering islet for improved performance by optimized reaggregation in alginate gel beads

After islet isolation, diffusion has become the main mechanism to transport oxygen and nutrients into the core of islets. However, diffusion has limitations, by which nutrients cannot effectively reach the core of large islets and can eventually cause core cell death and islet loss. This problem can be resolved by dispersing islets into single islet cells, but single islet cells do not exhibit insulin release function in in vitro culture. In this study, we intended to establish a new islet engineering approach by forming islet cell clusters to improve islet survival and function. Therefore, alginate gels were used to encapsulate islet cells to form artificial islets after dispersion of islets into single cells. The shape of the islet cell clusters was similar to native islets, and the size of the islet cell clusters was limited to a maximum diameter of 100 μm. By limiting the diameter of this engineered islet cell cluster, cell viability was nearly 100%, a significant improvement over natural islets. Importantly, islet cell clusters express the genes of islets, including Isl-1, Gcg, and insulin-1, and insulin secretion ability was maintained in vitro.