Alginate purification has been shown to decrease the host
immune response to implanted alginate-based
microcapsules, but the direct effect of contaminants on
islet cell survival remains unknown.
Wistar rat islets were immobilized in
calcium alginate beads made with crude vs. purified
alginate and then incubated in CMRL
culture medium. Islet survival was evaluated at 1, 4, 7, 14 and 27days post-encapsulation. Islet viability was investigated using a dual
staining assay (
propidium iodide and orange
acridine). The
islet cell necrosis and the proportion of
apoptotic cells were quantified under
optical microscopy and with a
TUNEL assay, respectively. Islets immobilized in purified
alginate were more viable, and had fewer
necrotic centers, a smaller area of central
necrosis and a lower number of
apoptotic cells. At day 14 and 27 post-encapsulation, respectively, 48% and 23% of islets were viable with purified
alginate vs. 18% and 8% with crude
alginate (p<0.05). At day 14, the surface area of central
necrosis and the number of
necrotic islets were more important with the impure
alginate (65% vs. 45% and 73% vs. 53%, respectively; p<0.05). We conclude that
alginate purification improves the survival of islets that are immobilized in alginate-based
microcapsules. These findings indicate that caution should be taken in the interpretation of in vivo experiments, as the results could be explained by either a direct effect on islet survival or a modification of the host reaction, or both. Moreover, it suggests that the effect on islet viability should be assessed during the development of biomaterials for cell encapsulation.
