Pancreatic islet cell autotransplantation in the canine model

The impact of bacterial colonization on graft success after total pancreatectomy with autologous islet transplantation: considerations for early definitive surgical intervention

OBJECTIVE

The purpose of this study was to determine whether bacterial contamination of islets affects graft success after total pancreatectomy with islet autotransplantation (TPIAT).

BACKGROUND

Factors associated with insulin independence after TPIAT are inconclusive. Although bacterial contamination does not preclude transplantation, the impact of bacterial contamination on graft success is unknown.

METHODS

Patients who received TPIAT at the University of Virginia between January 2007 and January 2016 were reviewed. Patient charts were reviewed for bacterial contamination and patients were prospectively contacted to assess rates of insulin independence.

RESULTS

There was no significant difference in demographic or perioperative data between patients who achieved insulin independence and those who did not. However, six of 27 patients analyzed (22.2%) grew bacterial contaminants from culture of the final islet preparations. These patients had significantly lower islet yield and C-peptide at most recent follow-up (P<.05), and none of these patients achieved insulin independence.

CONCLUSIONS

Islet transplant solutions are often culture positive, likely secondary to preprocurement pancreatic manipulation and introduction of enteric flora. Although autotransplantation of culture-positive islets is safe, it is associated with higher rates of graft failure and poor islet yield. Consideration should be given to identify patients who may develop refractory chronic pancreatitis and offer early operative management to prevent bacterial colonization.

Pancreatic islet transplantation: from dogs to humans and back again

Pancreatic islet transplantation is a cell-based therapy that provides a potential cure for type 1 diabetes mellitus. After the introduction of an automated method for islet isolation and steroid-free immunosuppressive protocols, reversal of diabetes by islet transplantation is now performed at major human medical centers around the world. Despite extensive use of animal models in islet transplantation research, practical concerns have slowed the introduction of the technique into clinical veterinary practice and only a small number of studies have reported results of transplantation in dogs with spontaneously occurring diabetes mellitus; however, recent advances in islet isolation and encapsulation may make it possible to perform islet transplantation without immunosuppression in companion animals. This review summarizes experimental and clinical studies of pancreatic islet transplantation in dogs, including future directions for cell therapy in animals with naturally occurring disease.

Pancreatic islet allograft in spleen with immunosuppression with cyclosporine. Experimental model in dogs

PURPOSE

To study the functional behavior of the allograft with immunosuppression of pancreatic islets in the spleen.

METHODS

Five groups of 10 Mongrel dogs were used: Group A (control) underwent biochemical tests; Group B underwent total pancreatectomy; Group C underwent total pancreatectomy and pancreatic islet autotransplant in the spleen; Group D underwent pancreatic islet allograft in the spleen without immunosuppressive therapy; Group E underwent pancreatic islet allograft in the spleen and immunosuppression with cyclosporine. All of the animals with grafts received pancreatic islets prepared by the mechanical-enzymatic method - stationary collagenase digestion and purification with dextran discontinuous density gradient, implanted in the spleen.

RESULTS

The animals with autotransplant and those with allografts with immunosuppression that became normoglycemic showed altered results of intravenous tolerance glucose (p < 0.001) and peripheral and splenic vein plasmatic insulin levels were significantly lower (p < 0.001) in animals that had allografts with immunosuppression than in those with just autotransplants.

CONCLUSIONS

In the animals with immunosuppression with cyclosporine subjected to allograft of pancreatic islets prepared with the mechanical-enzymatic preparation method (stationary collagenase digestion and purification with dextran discontinuous density gradient), the production of insulin is decreased and the response to intravenous glucose is altered.

Effect of various immunosuppressive monotherapies on survival and histopathology of monkey islet xenografts in rats

BACKGROUND

The isolation and testing of monkey islets after transplantation in small animal models provides basic information about their functional capacity. We describe the effect of cyclosporine A (CsA), tacrolimus (FK506) or prednisolone monotherapy on preventing monkey islet graft rejection after xenoTx in a rat model. Histopathological aspects are reported.

METHODS

Indian bonnet monkey (Macaca radiata radiata) islets were isolated by a simple stationary digestion technique using collagenase. The islets were purified with dextran density gradients and were transplanted under the renal capsule of normal or diabetic rats. The rats received a daily dose of CsA, or FK506, or prednisolone, and the grafts were removed at different intervals to determine islet survival. The effect of discontinuation of CsA on islet graft survival was also monitored. Histological examination of islets transplanted into normal or streptozotocin-induced diabetic rats was carried out. In diabetic rats, islet survival was determined by the graft's ability to achieve euglycemia.

RESULTS

Reversal of diabetes was achieved in all transplanted diabetic rats, demonstrating the efficacy of the isolated monkey islets. Histological examination indicated that monkey islets survived in the presence of continuous high-dose immunosuppressive monotherapy in rats. Various types of infiltrating cells were observed in the grafted area at varying times after transplantation, depending on the immunosuppressive treatment. After discontinuation of CsA, the grafts were protected for a short period.

CONCLUSIONS

This study provided evidence for monkey islet survival after transplantation into rats receiving immunosuppressive monotherapy. Basic information on infiltrating cell types may be important in the study of xenograft rejection.

Islet auto-transplantation into an omental or splenic site results in a normal beta cell but abnormal alpha cell response to mild non-insulin-induced hypoglycemia

The present studies were designed to determine if totally pancreatectomized dogs that underwent islet auto-transplantation retained a functional pancreatic counterregulatory response to mild non-insulin-induced hypoglycemia. Six dogs underwent total pancreatectomy followed by islet auto-transplantation to spleen or omentum. The animals recovered and fasting plasma glucose and insulin levels were normal. Each study consisted of a 40-min control and 2-h test period. At the onset of the test period, a glycogen phosphorylase inhibitor was administered to create mild hypoglycemia. Plasma glucose in the transplanted dogs fell from 120 +/- 4 to 80 +/- 3 mg/dL, similar to the minimum in control dogs without islet auto-transplantation (108 +/- 2 to 84 +/- 5 mg/dL). The fall in plasma insulin was similar in both groups. Glucagon, however, rose in response to hypoglycemia in the control dogs (Delta24 +/- 7 pg/mL; p < 0.05), but failed to rise significantly in the transplanted dogs (Delta9 +/- 6 pg/mL). In fact, only 1 of 7 control dogs failed to increase plasma glucagon by at least 25%, whereas 4 of 6 transplanted dogs failed to do so. In conclusion, in conscious dogs with successfully auto-transplanted islets, the beta cell response to mild non-insulin-induced hypoglycemia was normal, whereas the alpha cell response was not.