Encapsulated Cell Based Delivery of CNTF to the Vitreous Comparing a Polysulfone and a Polyethersulfone Membrane Formulated Device

Abstract

Abstract: : Purpose: The rate of CNTF delivery using encapsulated cell technology (ECT) was investigated using two encapsulation membranes formulated to create equivalent performance characteristics. Methods: Polyethersulfone (PES) and polysulfone (PS) membranes were fabricated by the wet–spinning method to produce hollow fibers with 870 µm inner diameter and 100 µm wall thickness. Both membranes were hydrophilized to minimize protein binding to their surfaces. Membrane fabrication was controlled to produce equivalent flux characteristics. Molecular weight cut–off and pore size distribution tests were conducted to predict membrane performance. Following membrane manufacture, CNTF producing NTC–201 cells were encapsulated in devices utilizing both membrane types. Devices were held in vitro and then implanted into the rabbit vitreous for 1 and 3 month periods. Explanted device CNTF release and vitreous levels of CNTF from enculeated eyes were quantified by ELISA. Encapsulated cell viability was evaluated using a metabolic activity assay and by histological examination of sectioned devices. Indirect ophthalmoscopic and fundus examination were conducted during this study to assess ocular irritation and wound healing. Results: Initial analytic characterization of both PS and PES membranes predicted that cell encapsulation using either membrane would achieve equivalent results. In vitro device performance, however, resulted in statistical (P < 0.05) differences of CNTF production comparing the PS and PES membrane device groups at 4, 6, 8 and 10 weeks. Furthermore, explant device CTNF and vitreous CTNF levels resulted in statistically greater CNTF production from the PS membrane device group compared to the PES membrane device group at both 1 and 3–months. Interestingly, in vitro and in vivo histomorphology revealed equivalent cell viability and distribution comparing both groups at each time point. Additional testing to determine the rate of recombinant CNTF diffusion across the membranes as well as detailed CNTF protein binding studies showed that CNTF preferentially binds to PES compared to PS. Conclusions: This study has demonstrated that fabrication of an ECT device using polysulfone rather than polyethersulfone to formulate the ECT encapsulation membrane will provide equivalent and perhaps increased levels of protein delivery to the vitreous. The use of this membrane material, therefore, could be considered as a potential improvement to Neurotech’s encapsulation cell technology.

Keywords: growth factors/growth factor receptors • retinitis • photoreceptors