Xenotransplantation of parathyroids in rats using barium-alginate and polyacrylic acid multilayer microcapsules

The integrity and function of encapsulated parathyroid tissue following xen otransplantation is limited by oxygen and nutrition supply and capsule fibr osis. Since some of these factors depend on stability and biocompatibility of the coating material, multilayer microcapsules have been developed. Parathyroid tissue pieces and digested single cells from pigs were encapsul ated in barium-alginate and in polyacrylic acid (PAA) multilayer capsules. After 7 days of culture the function of the encapsulated cells were assesse d. Subsequently, in a part of the cultured microcapsules the viability was directly assessed whereas the other part was transplanted in dark animal [D A] rats for 30 days. After explantation viability and fibrotic reaction wer e examined. Single cells showed a significant increase in parathyroid hormo ne [PTH] secretion when exposed to medium low in calcium, whereas minced ti ssue pieces revealed necrosis without stimulatory responsiveness. Morphomet ry showed significantly better viability of single cells compared with minc ed tissue in vitro and in vivo. The fibrotic reaction against capsules with minced tissue was more pronounc ed than for capsules containing single cells. There was no difference betwe en barium alginate and PAA capsules when containing minced tissue. In singl e cells, however, the fibrous tissue reaction differed significantly betwee n barium alginate and PAA capsules. Encapsulated single cells of parathyroid tissue maintain detectable functio n and viability. In contrast minced tissue underwent necrosis and induced s ignificantly more connective tissue reaction than single cells indicating a n interrelationship between necrosis and fibrosis.