Treatment of diabetic rats with encapsulated islets

Abstract

Immunoprotection of islets using bioisolator systems permits introduction of allogeneic cells to diabetic patients without the need for immunosuppression. Using TheraCyte immunoisolation devices, we investigated two rat models of type 1 diabetes mellitus (T1DM), BB rats and rats made diabetic by streptozotocin (STZ) treatment. We chose to implant islets after the onset of diabetes to mimic the probable treatment of children with T1DM as they are usually diagnosed after disease onset. We encapsulated 1000 rat islets and implanted them subcutaneously (SQ) into diabetic biobreeding (BB) rats and STZ-induced diabetic rats, defined as two or more consecutive days of blood glucose>350 mg/dl. Rats were monitored for weight and blood glucose. Untreated BB rats rapidly lost weight and were euthanized at >20% weight loss that occurred between 4 and 10 days from implantation. For period of 30-40 days following islet implantation weights of treated rats remained steady or increased. Rapid weight loss occurred after surgical removal of devices that contained insulin positive islets. STZ-treated rats that received encapsulated islets showed steady weight gain for up to 130 days, whereas untreated control rats showed steady weight loss that achieved >20% at around 55 days. Although islet implants did not normalize blood glucose, treated rats were apparently healthy and groomed normally. Autologous or allogeneic islets were equally effective in providing treatment. TheraCyte devices can sustain islets, protect allogeneic cells from immune attack and provide treatment for diabetic-mediated weight loss in both BB rats and STZ-induced diabetic rats.

Fig. 1

Weight profiles of lyp/lyp BB rats treated with encapsulated islets. Five control rats received mock or no surgery; black symbols (four females and one male). Seven BB diabetic rats (six females and one male) received 1000 islets. Five rats received autologous islets (open circles) and two rats received allogeneic islets (square symbols). Weight of rat at surgery is 100%. Arrow heads indicate when Theracyte-encapsulating devices were removed. Mock surgery (black arrow) indicates treated animal subjected to anaesthesia and blunt skin dissection without device removal. Control rats were killed when >20% weight loss reached.

Fig. 2

Cross-sections of Theracyte™ encapsulation devices removed from treated diabetic BB rat. The device shown was loaded with 1000 islets and removed from a treated rat 49 days after implantation (blue symbols in Fig. 1). (A, B) Insulin immunostaining shows islets in layers in a matrix of other cells. A control rat pancreas shows islets staining positive for insulin (C). Sections D–F were stained with haematoxylin and eosin and show cell distribution and blood vessels around the encapsulation device. Sections G–I were immunostained for smooth muscle cell actin and show smooth muscle cells around the islets. Lower magnification in G shows capillaries around the immunoisolation membrane that stain positive for smooth muscle cell actin. All magnifications 40× except section G that was 20×.

Fig. 3

Weight profiles of STZ induced diabetic rats treated with encapsulated allogeneic islets. Weight at STZ administration is 100%. Control rats receiving mock or no surgery (black closed symbols). Six diabetic rats receiving 1000 encapsulated islets (open symbols). Control rats were killed when >20% weight loss reached.