Encapsulation of human islets in novel inhomogeneous alginate-ca2+/ba2+ microbeads: in vitro and in vivo function

Abstract

Microencapsulation may allow for immunosuppression-free islet transplantation. Herein we investigated whether human islets can be shipped safely to a remote encapsulation core facility and maintain in vitro and in vivo functionality. In non-encapsulated islets before and encapsulated islets after shipment, viability was 88.3+/-2.5 and 87.5+/-2.7% (n=6, p=0.30). Stimulation index after static glucose incubation was 5.4+/-0.5 and 6.3+/-0.4 (n=6, p=0.18), respectively. After intraperitoneal transplantation, long-term normoglycemia was consistently achieved with 3,000, 5,000, and 10,000 IEQ encapsulated human islets. When transplanting 1,000 IEQ, mice returned to hyperglycemia after 30-55 (n=4/7) and 160 days (n=3/7). Transplanted mice showed human oral glucose tolerance with lower glucose levels than non-diabetic control mice. Capsules retrieved after transplantation were intact, with only minimal overgrowth. This study shows that human islets maintained the viability and in vitro function after encapsulation and the inhomogeneous alginate-Ca(2+)/Ba(2+) microbeads allow for long-term in vivo human islet graft function, despite long-distance shipment.

Figure 1

DTZ-staining non-encapsulated (A) and encapsulated human islets (B) (light-microscope, 40x). Viability staining (Sytogreen, green for alive cells; Ethidium bromide, red for dead cells) non-encapsulated (C) and encapsulated islets (D).

Figure 2

In vitro dynamic insulin secretion (A) and intracellular Ca²⁺ measurement (B) with non-encapsulated control and encapsulated islets. Values were presented as mean ± SEM from three independent experiments.

Figure 3

Non-fasting blood glucose levels and body weights change in the STZ-induced diabetic nude mice transplanted with different amounts of encapsulated human islets (10,000, 5,000, 3,000, and 1,000 IEQ).

Figure 4

Oral glucose tolerance tests performed at 30 weeks after transplantation in the 3,000 IEQ encapsulated islets transplanted, diabetic non-transplanted, and normal control mice. Values were presented as mean ± SEM (A). In vitro dynamic insulin secretion test of the retrieved capsules at 130 days after transplantation. Values were presented as mean ± SEM from three different experiments (B).

Figure 5

Direct light microscopy photos with DTZ (A, 40×) and H&E (B, 400×) staining of the retrieved capsules at 130 days after transplantation. The arrow indicates the border of the capsule. DTZ (C, 40×) and insulin fluorescent stained (D, Confocal Microscopy) pictures of the retrieved capsules at day 329 after transplantation.