In Vivo Selection of Biocompatible Alginates for Islet Encapsulation and Subcutaneous Transplantation

Abstract

Islet encapsulation requires several properties including (1) biocompatibility, (2) immunoprotection, and (3) oxygen diffusion for islet survival and diabetes correction. New chemical alginates were tested in vivo and compared with traditional high-mannuronate and -guluronate alginates. New alginates with coupled peptide sequence (sterile lyophilized high mannuronate [SLM]-RGD3% and sterile lyophilized high guluronate [SLG]-RGD3%), to improve encapsulated cell adherence in the matrix, and alginates with a very low viscosity (VLDM7% and VLDG7%), to reduce implant size by loading a higher number of islets per volume of polymer, were implanted subcutaneously in 70 Wistar rats for comparison with alginates of high viscosity and high content of mannuronic (SLM3%) or guluronic acids (SLG3%). Permeability of alginates to 36-, 75-, and 150-kDa lectins coupled to fluorescein isothiocynate was quantified before implantation and at 2, 4, and 12 weeks after implantation. Biocompatibility (fibrosis, graft stability, immunologic infiltration by CD3/CD68 cells, and neovascularization) was assessed at each explantation time. Permeability to small molecules was found for all alginates. Impermeability to 150-kDa molecules, such as IgG, was observed only for SLM3% before implantation and was maintained up to 12 weeks after implantation. SLM3% and SLG3% demonstrated better graft stability with lower CD3/CD68 recruitment and fibrosis than the other alginates. SLM3% induced a significantly higher angiogenesis and maintained oxygen pressure at approximately 40 mm Hg for up to 4 weeks after implantation as measured by in vivo electronic paramagnetic resonance oximetry. SLM-encapsulated pig islets implanted subcutaneously in rats demonstrated no inflammatory/immunologic reactions and islets functioned for up to 60 days without immunosuppression. A traditional alginate made of high mannuronic content (SLM3%) is an adapted material to immunoprotect islets in subcutaneous tissue. No improvement was found with lower viscosity and use of GRGDSP-peptide sequence.

Functional improvement of porcine neonatal pancreatic cell clustersviaconformal encapsulation using an air-driven encapsulator

“…Thus, there is a need to confirm that the capsule possesses permeability to molecules of low molecular weight such as glucose, nutrients, insulin and metabolites (＜75 kDa). The immunoglobulin molecular weight limits are 150, 500 and 800 kDa for IgG, activated complements and IgM, respectively (Vériter et al, 2010). To this end, 100 to 200 μm alginate capsules were used to confirm the penetration of variously sized dextrans.…”

Islet transplantation in rodents: do encapsulated islets really work?

“…Yun et al (63) have reported that PEG-based chemical immunomodulation can provide a semi-permanent effective therapy that protects transplanted islets at least for 1 year when accompanied by cyclosporine. Furthermore, Vériter et al (58) have tested originals alginates with respect to sterile lyophilized high mannuronated and they have had an optimum result with high mannuronated with high viscosity alginate.…”

Method measuring oxygen tension and transport within subcutaneous devices

“…17 However, direct measurement of oxygen levels within microencapsulated devices in vivo has not been previously reported, where such measurements are ultimately required to assay the efficacy of implant technologies that claim to promote oxygen delivery. In a study of relatively large alginate disc implants (1 to 1.5 cm 2 surface area at 3-to 6-mm thick) by Veriter et al, 18 oxygen within implanted devices was directly measured through the use of electronic paramagnetic resonance oximetry in rats. However, current research shows that such thick devices cannot retain islet function, likely due to diffusional limitations, thus promoting microencapsulation technologies such as thin sheets or microbeads of permeable materials.…”