Pancreatic Islet Transplantation into the Submandibular Gland: Our Experimental Experience and a Review of the Relevant Literature

Could Transplantation into the Thyroid Gland Benefit Pancreatic Islet Grafting in Unstable Type 1 Diabetes (T1DM), Complicated Type 2 Diabetes (T2DM), and Patients with Total Pancreatectomy?

BACKGROUND

Insular allograft for unstable type 1 diabetes and autograft in pancreatectomy patients are nowadays considered established procedures with precise indications and predictable outcomes. The clinical outcome of islet transplantation is similar to that of pancreas transplantation, avoiding the complications associated with organ transplantation.

OBJECTIVE

We hypothesised that transplantation of islets of Langerhans within an endocrine organ could better promote their engraftment and function. This could help to resolve or ameliorate known pathological conditions such as unstable type 1 diabetes and complicated type 2 diabetes.

RATIONALE

Pancreatic islet transplantation is currently performed almost exclusively in the liver. The liver provides a sufficiently favourable environment, although not entirely. The hepatic parenchyma has a lower oxygen tension than the pancreatic parenchyma and the vascular structure of the liver is not typical of an exclusively endocrine organ. Moreover, islet transplantation into the liver is not without complications, including hematoma or portal vein thrombosis.

PROPOSED PROJECT

The thyroid gland is the endocrine gland proposed as a 'container'. In fact, it has all the characteristics of 'physio-compatibility' which can address the objectives assumed. It is indeed an ideal site because it is an easily accessible anatomical site that allows islets to be implanted using ultrasound-guided transcutaneous inoculation technique. Moreover, it has physiological and anatomical endocrine affinities with pancreatic islets and, if necessary, it can be removed, using hormone supplementation or replacement therapy.

CONCLUSIONS

The thyroid gland may be proposed as an ideal site for islet implantation due to its anatomical and physiocompatibility characteristics.

Reversal of Hyperglycemia by Subcutaneous Islet Engraftment Using an Atelocollagen Sponge as a Scaffold

Type 1 diabetes mellitus (T1DM) affects 8.4 million people worldwide, with patients primarily relying on exogenous insulin injections to maintain blood glucose levels. Islet transplantation via the portal vein has allowed for the direct internal release of insulin by glucose-sensitive islets. However, this method might not be desirable for future cell therapy transplanting pluripotent stem cell-derived β cells, facing challenges including difficulties in cell retrieval and graft loss due to the instant blood-mediated inflammatory reaction (IBMIR). Here, we established a subcutaneous transplantation protocol using an atelocollagen sponge as a scaffold. While the subcutaneous site has many advantages, the lack of a vascular bed limits its application. To address this issue, we performed angiogenesis stimulation at the transplantation site using bFGF absorbed in a gelatin sponge (Spongel), significantly improving the microvascular area. Our in vivo experiments also revealed angiogenesis stimulation is crucial for reversing hyperglycemia in streptozotocin (STZ)-induced diabetic mice. In addition to the angiogenic treatment, an atelocollagen sponge is used to carry the islets and helps avoid graft leakage. With 800 mouse islets delivered by the atelocollagen sponge, the STZ-induced diabetic mice showed a reversal of hyperglycemia and normalized glucose intolerance. Their normoglycemia was maintained until the graft was removed. Analysis of the harvested islet grafts exhibited a high vascularization and preserved morphologies, suggesting that using an atelocollagen sponge as a scaffold helps maintain the viability of the islet grafts.