P-255

Coating alginate microcapsules with heparin conjugate reduces pericapsular fibrotic overgrowth in allografted, isografted but not xenografted rats

B. Tuch¹, V. Vaithilingam¹, G. Kollarikova², M. Qi³, R. Larsson⁴, I. Lacik², J. Oberholzer³, G. Guillemin^5
1 Australian Foundation for Diabetes Research, Sydney, Australia; ² Slovak Institute of Polymer Sciences, Bratislava, Slovak Republic; ³ University of Illinois at Chicago, Chicago, USA; ⁴ Corline System AB, Uppsala, Sweden; ⁵ University of New South Wales, Sydney, Australia

Objective: Pericapsular fibrotic overgrowth is associated with poor survival of encapsulated pancreatic islets.The fibrotic overgrowth interferes with the passive transport of nutrient andoxygen across the membrane, leading to islet cell starvation and apoptosis. Modification of the microcapsule membrane aimed at preventing the fibroticovergrowth should improve graft survival. Here, we investigated whether heparin could be immobilized efficiently on alginate microcapsules, and tested their antifibrotic potential both in vitro and in vivo. We also assessed the effect of heparin immobilization on encapsulated human islet function both in vitro and in vivo.

Methods: Heparin conjugate was immobilized onto the microcapsules using a two-step procedure incorporating avidin and heparin, and its presence confirmed with both confocal microscopy and a coagulation test, the activated partial thromboplastin time. The effect of heparinisation on encapsulated human islets was assessed using viability, static stimulation and transplantation studies. Results: Confocal images demonstrated a smooth and coherent coating of heparin onto the surface of microcapsules. The bound heparin molecules were stable and retained their anti-clotting activity even after three weeks in culture. Heparin immobilization affected neither the viability nor the function of encapsulated human islets both in vitro and when transplanted into diabetic immunodeficient mice. Heparin immobilization was beneficial and significantly reduced the moderate pericapsular fibrotic overgrowth in allografted rats (cell adhesion score reduced by 45% from 12.3 to 6.8) and the minor fibrosis in isografted rats (score reduced by 49% from 0.6 to 0.3). No benefit was observed in xenograftedrats (score > 14.4).

Conclusion: Our results showed a simple method to successfully immobilize heparin on alginate microcapsules and demonstrated its beneficial effect in reducing fibroticovergrowth in allograft and isograft models. This should improve thebiocompatibility of various alginate microcapsules employed in designing abioartificial pancreas.

Disclosure: One of the authors, RL, has interests in Corline, which produced the heparin.

P-255

Coating alginate microcapsules with heparin conjugate reduces pericapsular fibrotic overgrowth in allografted, isografted but not xenografted rats

B. Tuch¹, V. Vaithilingam¹, G. Kollarikova², M. Qi³, R. Larsson⁴, I. Lacik², J. Oberholzer³, G. Guillemin^5
1 Australian Foundation for Diabetes Research, Sydney, Australia; ² Slovak Institute of Polymer Sciences, Bratislava, Slovak Republic; ³ University of Illinois at Chicago, Chicago, USA; ⁴ Corline System AB, Uppsala, Sweden; ⁵ University of New South Wales, Sydney, Australia

Objective: Pericapsular fibrotic overgrowth is associated with poor survival of encapsulated pancreatic islets.The fibrotic overgrowth interferes with the passive transport of nutrient andoxygen across the membrane, leading to islet cell starvation and apoptosis. Modification of the microcapsule membrane aimed at preventing the fibroticovergrowth should improve graft survival. Here, we investigated whether heparin could be immobilized efficiently on alginate microcapsules, and tested their antifibrotic potential both in vitro and in vivo. We also assessed the effect of heparin immobilization on encapsulated human islet function both in vitro and in vivo.

Methods: Heparin conjugate was immobilized onto the microcapsules using a two-step procedure incorporating avidin and heparin, and its presence confirmed with both confocal microscopy and a coagulation test, the activated partial thromboplastin time. The effect of heparinisation on encapsulated human islets was assessed using viability, static stimulation and transplantation studies. Results: Confocal images demonstrated a smooth and coherent coating of heparin onto the surface of microcapsules. The bound heparin molecules were stable and retained their anti-clotting activity even after three weeks in culture. Heparin immobilization affected neither the viability nor the function of encapsulated human islets both in vitro and when transplanted into diabetic immunodeficient mice. Heparin immobilization was beneficial and significantly reduced the moderate pericapsular fibrotic overgrowth in allografted rats (cell adhesion score reduced by 45% from 12.3 to 6.8) and the minor fibrosis in isografted rats (score reduced by 49% from 0.6 to 0.3). No benefit was observed in xenograftedrats (score > 14.4).

Conclusion: Our results showed a simple method to successfully immobilize heparin on alginate microcapsules and demonstrated its beneficial effect in reducing fibroticovergrowth in allograft and isograft models. This should improve thebiocompatibility of various alginate microcapsules employed in designing abioartificial pancreas.

Disclosure: One of the authors, RL, has interests in Corline, which produced the heparin.