Calcium Phosphate Cement Chamber as Immunoisolative Device for Bioartificial Pancreas
Date Issued
2009
Date
2009
Author(s)
Yang, Kai-Chiang
Abstract
Immune rejection and insufficient donor supply are the restrictions of islet transplantation for type 1 diabetes (T1D). A strategy so called as immunoisolation was purposed to facilitate the use of xenogeneic cell sources to resolve the issue of an insufficient donor supply in the absence of immunosuppression. Most studies utilized polymeric materials as an immunoisolative material to encapsulate islets as a bioartificial pancreas (BAP) and implanted in the peritoneal cavity. However, BAPs would be dysfunctional because of the fibrous tissue overgrowth and an insufficient oxygen supply. Accordingly, a calcium phosphate cement (CPC) chamber was utilized to replace the polymeric material as an immunoisolative device. BAPs were implanted in the intramedullary cavity instead of the peritoneal cavity. We hope the newborn bone tissues can grow on the CPC chamber to avoid the development of fibrous tissue. In the meantime, the sufficient partial oxygen pressure in the intramedullary cavity can overcome the issue of hypoxia. The purpose of this study was as to evaluate the feasibility of the use of a CPC chamber as an immunoisolative device, and to demonstrate the possibility of intramedullary cavity as an implanted site for BAPs.etracalcium phosphate was first prepared and mixed with dicalcium phosphate in equimolar to fabricate a CPC chamber. The CPC chamber was analyzed by X-ray diffraction, scanning electron microscope and mercury intrusion porosimetry. The molecular weight cut-off (MWCO) and material-mediated cytotoxicity of CPC chamber were also evaluated. Results showed that the CPC chamber was non-cytotoxicity to insulinoma cells. The microstructure of CPC chamber satisfied the requirements of an immunoisolative device with the MWCO of 12.4 kDa, which can totally cut-off the diffusion of immune stimulatory molecules.ext, an insulinoma cell line was applied as a cell source and encapsulated in agarose microspheres. Insulinoma/agarose microspheres were enclosed in a preformed CPC chamber to create a BAP. BAPs were evaluated in vitro by insulin secretion, cell viability, live/dead cell ratio, cytokine-mediated cytotoxicity assay, and implanted in the peritoneal cavity of diabetic rats as preliminary in vivo study. Non-fasting blood glucose level (NFBG) and serum insulin level were analyzed perioperatively; BAPs were also retrieved for histological examination. Results showed insulinoma cells enclosed in the CPC chamber had normal viability, survival and insulin secretion even when cultured in media with cytokines. The NFBG of rats was decreased from 460±50 to 132±43 mg/dl four day post-operation and maintained in euglycemia for 22 days; serum insulin level was increased from 0.34±0.11 to 1.43±0.30 μg/dl post-operation. Histological examination revealed the fibrous tissues overgrowth and immune related cells competed for oxygen resulting in hypoxia could be attributed to the dysfunction of BAPs. APs were then implanted in the femoral intramedullary cavity of diabetic canines. Pre- and postprandial blood glucose level was monitored perioperatively. Blood samples were collected for the analysis of C-peptide level and physiological conditions were observed at pre-determined intervals. BAPs were retrieved 12 weeks post-operation for histological examinations. A spontaneous diabetic feline was also received the BAPs implantation. Results showed the preprandial blood glucose level of diabetic canines was decreased from 424±23 to 243±33 mg/dl one day post-operation and maintained in the range of 219-349 mg/dl for 12 weeks. Serum C-peptide level was increased from 5.3±2.8 to 105.7±19.4 pmol/l. The decreasing rate of postprandial blood glucose was accelerated. Histological examinations revealed recipients’ bone tissues binding to the surfaces of BAPs directly; there was no fibrous tissue development. Immunohistochemical stain showed positive insulin staining for the enclosed insulinoma cells. For the diabetic feline, the peak point of two hours glucose curve was decreased from 398 to 165-290 mg/dl post-operation; the effectiveness of exogenous insulin was extended from 2 to 10-14 hrs and the physiological conditions were improved.his study proves the feasibility of using a CPC chamber as an immunoisolative device. The possibility of intramedullary cavity as an implanted site for BAPs had also been proved. BAPs implanted into the intramedullary cavity can avoid the problems of fibrous tissue outgrowth and hypoxia. The use of native islets to replace the insulinoma cells and to increase the number of implanted BAPs or the islet cells density within BAPs should be considered to achieve insulin independent, and may provide a new treatment for T1D in the future.
Subjects
Type 1 diabetes
Xenotransplantation
Immunoisolation
Bioartificial pancreas
Calcium phosphate cement.
SDGs
Type
thesis
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