Figure 1.
Schematic model of nanoparticles binding to pegylated islet.
Avidin groups on the nanoparticle surface mediate nanoparticle attachment to biotinylated PEG that coats the islet.
Figure 2.
Nanoparticle coating of mouse islets.
(A) Islets incubated with PEG plus coumarin-6 (green)-labeled nanoparticles (Nano) observed under fluorescence (left) and confocal (right) microscopes. Scale bar, 50 µm. (B) Naked control islets (CTR), or pegylated islets coated with coumarin-6 labeled nanoparticles (Nano) imaged by SEM immediately after encapsulation. Scale bar, 100 µm. (C) Islets imaged at 21 days post culture: images e–g show naked islets (CTR), images h–j show islets draped with PEG plus coumarin-6-nano (Nano). The naked islets show degradation in marked contrast to the well-preserved nano-pegylated islets. Scale bar, 50 µm.
Figure 3.
Encapsulation does not affect islet function.
(A) Insulin secretion (ng/mL/h/islet) was measured in naked (light grey bars, CTR) and nano-PEG-encapsulated (dark grey bars, Nano) islet cultures cultured overnight after encapsulation stimulated with 2.8 mM, or 28 mM glucose for 24 h. (B) Insulin stimulation index of the naked and nanoparticle-coated islets shown in (A). At least 20 islets were included in each group, and the data represents 3 individual experiments.
Figure 4.
Prolonged viability of encapsulated islets in vitro.
(A) Staining of viable (green) versus dead (red) cells in cultures of naked islets (CTR), pegylated islets (PEG), or pegylated plus empty-nanoparticle islets (Nano) at 1 d, 7 d, 14 d, and 21 d. (B) Percentages of viable cells in the different groups during culture. (C) Insulin staining in naked (CTR) and PEG-Nano-coated islets at 2 d and 14 d culture: more insulin positive cells were observed in islets encapsulated with nanoparticles (lower panels) compared to naked islets (upper panels). At least 10 islets were included in each group. Red represents insulin staining, blue staining (DAPI) represents nuclear staining in all cells. * p<0.05 and ** p<0.01.
Figure 5.
Prolonged functionality of encapsulated islets in vivo.
Pancreatic islets from DBA/2 mice were grafted under the kidney capsule of C57BL/6 recipients: the islets were either untreated (Ctrl); or encapsulated in PEG alone (PEG alone); or with PEG decorated with empty nanoparticles (PEG+Empty Nano); or with PEG decorated with LIF-containing nanoparticles (PEG+LIF-Nano). The ability of these grafts to support normoglycemia over 100 d is shown as “% survival” in (A). Histology of grafts taken from recipients showing normoglycemia at 100 d revealed well-preserved β cells containing insulin, as illustrated in (B).
Table 1.
Long-term normoglycemia derived from pegylated DBA/2 islet grafts in C57BL/6 recipients.