Functionalization of Alginate with Extracellular Matrix Peptides Enhances Viability and Function of Encapsulated Porcine Islets

Abstract

Translation of transplanted alginate-encapsulated pancreatic islets to treat type 1 diabetes has been hindered by inconsistent long-term efficacy. This loss of graft function can be partially attributed to islet dysfunction associated with the destruction of extracellular matrix (ECM) interactions during the islet isolation process as well as immunosuppression-associated side effects. This study aims at recapitulating islet-ECM interactions by the direct functionalization of alginate with the ECM-derived peptides RGD, LRE, YIGSR, PDGEA, and PDSGR. Peptide functionalization is controlled in a concentration-dependent manner and its presentation is found to be homogeneous across the microcapsule environment. Preweaned porcine islets are encapsulated in peptide-functionalized alginate microcapsules, and those encapsulated in RGD-functionalized alginate displays enhanced viability and glucose-stimulated insulin release. Effects are RGD-specific and not observed with its scrambled control RDG nor with LRE, YIGSR, PDGEA, and PDSGR. This study supports the sustained presentation of ECM-derived peptides in helping to maintain health of encapsulated pancreatic islets and may aid in prolonging longevity of encapsulated islet grafts.

Keywords: alginate; cell encapsulation; encapsulated pancreatic islets; type 1 diabetes.

Figure 1.

Fluorescence emission of (anthracenecarboxylic acid)-RGD-reacted alginates A) with varying oxidation degrees using a starting RGD concentration of 2.5 mm and B) varying initial peptide concentrations using alginate oxidized to a molar degree of 8%. C) Diminished fluorescence emission of (anthracenecarboxylic acid)-RGD in the presence of unmodified RGD (data presented as the average ± standard deviation (n=3)). ***P<0.001; one-way ANOVA with Tukey multiple comparisons correction.

Figure 2.

Fluorescence signal across a representative (anthracenecarboxylic-acid)-RGD-tagged alginate microcapsule (line across capsule indicates the spatial coordinates pertaining to the graph’s y-axis; scale bar = 200 μm).

Figure 3.

A) Quality assessments of pre-weaned porcine islets encapsulated in different peptide-modified alginates by live-dead confocal imaging (scale bar = 200 μm) B) Quantified cell viability (data presented as the mean ± SD, n≥3 biologically independent samples). ***P<0.001, nested one-way ANOVA with Dunnett’s multiple comparisons test.

Figure 4.

Functional assessment of islets by glucose-stimulated insulin response; ***P<0.001; nested t test for differences between insulin secretion at Low 1 vs High glucose challenge (data presented as the mean ± SEM (n≥4 biologically independent samples).