TRANSPLANTATION OF PARATHYROID TISSUE IN EXPERIMENTAL HYPOPARATHYROIDISM - IN-VITRO AND IN-VIVO FUNCTION OF PARATHYROID TISSUE MICROENCAPSULATED WITH A NOVEL AMITOGENIC ALGINATE

Microencapsulation of tissues is an alternative to postoperative immun osuppression in transplantation. In 1994 iso-, allo- and xenotransplan tation of microencapsulated parathyroid tissue was achieved in vivo. H owever, continued analysis of the coating substance (an alginate) dete rmined mitogenic properties. Here, we report on the in vitro and in vi vo function of parathyroid tissue microencapsulated with a novel amito genic alginate suitable for use in humans. To assess in vitro function , parathyroid tissue encapsulated with mitogenic and amitogenic algina te was exposed to rising concentrations of calcium. For in vivo experi ments, it was isotransplanted into parathyroidectomized rats. PTH rele ase into medium and PTH serum levels as well as calcium levels of reci pient rats were analyzed and compared to native (non-microencapsulated ) tissue and empty capsules, respectively. In vivo, transplants were e xcised and subjected to histologic examination six months after trans- plantation. In vitro, parathyroid tissue encapsulated with amitogenic alginate releases approximately half of the PTH of native tissue, not different from tissue encapsulated with the mitogenic alginate. In viv o, the novel alginate preserved parathyroid function similar to that o f native tissue over the six month period resulting in complete revers al of hypoparathyroidism. Correspondingly, histologic examination reve aled vital parathyroid tissue in intact microcapsules. By establishing in vitro function and successful long-term transplantation, we have d ocumented the principle of microencapsulation of parathyroid tissue to be effective also with the novel amitogenic alginate, which is suitab le for clinical use.