Effect of Laminin on the Interaction Between Islets and an Implantable Immunoisolation Polyurethane Membrane

The development of bio-artificial organs (sequestered cell cultures, implanted within an isolating membrane) is complicated by dynamic and interrelated variables. The primary objective of an implanted membrane for sequestration of insulin producing cells is to provide a barrier to the host's immune system. Implicit in this structural relationship in systems designed for the treatment of diabetes is the ability to create an environment that is favorable to the sequestered cells' viability and at the same time facilitate the availability of the released insulin in a kinetic relationship consistent with the normal physiology. This investigation conducted under a Phase I SBIR grant explored methods to promote a favorable interaction between islets harvested from neonate rats with a polyurethane membrane during in-vitro culture experiments. Laminin (LAM) extracellular matrix was used to stabilize islets within polyurethane membranes or within cell culture well inserts. Results indicated that insulin produced by islets enclosed within the polyurethane membranes with and without LAM was present for up to six weeks. However, when evaluating the Glucose Stimulated Insulin Secretion (GSIS) there was no evidence of Insulin Response in any of the treatment groups. Further study using LAM and islets in the presence of a cell culture insert (8.0 micron polycarbonate membrane) demonstarted that LAM impeded flow of media through the membrane. When media sampled from the well was compared to inside the insert at the 11.2 mM glucose phase of the GSIS, the average insulin concentration from the well was $<45.8$% of that found inside the cup. In addition, there was evidence of a positive effect on $β$-cell rate of cell division in the presence of LAM. The average number of brdU labeled cells per islet was significantly greater following prolactin (PRL; positive control @ 500 ng/ml), laminin–1 (50 $μ$g/ml) or the combination of PRL and LAM. The increases relative to the control islets averaged across the replications were: Laminin $+1.5$ times, Prolactin $+5.9$ times, PRL and LAM $+6.8$ times. In summary, there was no evidence of GSIS in experiments where laminin–1 was used to stabilize neonate rat islets within a polyurethane membrane. These results suggest that the presence of ECM on the inside of the polyurethane membrane impeded the insulin of the polyurethane membrane impeded the insulin diffusion kinetics through the membrane. The only potentially positive results from this study are that there is evidence of insulin diffusion over time indicating that the islets are functional, but a an unknown level of physiologic utility. Support for this study was provided by NIH SBIR Grant #1 R43 DK75220-01. Dr. Robert Sorenson, University of MN, and his lab graciously provided the neonate rat islets and advice.