ASSESSMENT OF THE REPRODUCIBILITY OF ALGINATE ENCAPSULATION OF PANCREATIC-ISLETS USING THE MTT COLORIMETRIC ASSAY

Radioisotope diffusion experiments demonstrate that alginate/polyamino acid encapsulation can prevent antibody and cytotoxic cell contact in vitro. The unpredictable outcome of xenotransplantation of encapsulate d islets may reflect incomplete encapsulation. We have assessed a cyto toxic/MTT (tetrazolium) assay to test antibody permeability of capsule s. Samples of free porcine islet tissue, and islet tissue encapsulated in alginate/poly-L-lysine/alginate microspheres were incubated with f resh autologous pig serum or normal human serum overnight. Cell metabo lism was assessed by the MTT assay. Data from eight experiments (10 re plicates/experiment) were analyzed using the Mann-Whitney U-test. Valu es were deemed significant when p < 0.05. Free islets cultured in huma n serum showed a significant reduction in metabolism when compared wit h islets cultured in pig serum: percentage reduction 52 +/- 23% (mean +/- SD). The differences in formazan production were significant in al l experiments (p < 0.05). Alginate encapsulation of islets or removal of xenoreactive antibodies in human serum by adsorption was shown to p revent the effects of complement-mediated lysis. However, in one of th e eight experiments, there was a significant reduction in islet metabo lism after exposure of encapsulated porcine islets to human serum. In conclusion, it has been shown that alginate encapsulation can prevent complement-mediated lysis. However, the encapsulation process employed was imperfect and did not prevent complement-mediated lysis of porcin e islets in all experiments. The cytotoxicity/MTT assay allows investi gation of the permeability of capsules to serum antibodies and could b e performed to determine the viability of the islets and the integrity of microcapsules prior to transplantation.