Storage and microencapsulation of islets for transplantation

Polyvinyl Pyrrolidone: A Novel Cryoprotectant in Islet Cell Cryopreservation

The present study was performed on the basis of the hypothesis that the low molecular weight (MW) compounds, DMSO and glycerol, permeate the cell and interact hydrophobically with intracellular proteins, thereby perturbing the cytoskeletal architecture of frozen cells and diminishing islet cell integrity and function. Isolated rat islets were cultured overnight (18–24 h) at 37°C in RPMI medium supplemented with 10% fetal calf serum and 1% mixture of penicillin/streptomycin. Using a programmable temperature controller, samples of precounted islets were then frozen under liquid nitrogen, in the presence of either 2 M DMSO (MW = 0.078 kDa), 3 M glycerol (MW = 0.092 kDa), 5% polyethylene glycol (PEG, MW = 20 kDa), or 10% polyvinylpyrrolidone (PVP, MW = 40 kDa), and stored at −80°C for 1 week. Following thawing and overnight (18–24 h) culture, intact islet recovery was determined by islet counting after dithizone staining. Islet function was assessed by determination of glucose-stimulated insulin secretion in perifusion experiments with Krebs-Ringer bicarbonate buffer, pH 7.4, containing either basal (3.3 mM) or high (16.7 mM) glucose concentrations. The assessment of islet recovery and function of all cryopreserved samples was performed only after thawing and overnight culture (18–24 h) of islets. The mean ± SEM percent intact islet recovery was higher with PVP compared with DMSO (82 ± 4.6 vs. 62.7 ± 3.1%, respectively, p < 0.005, n = 9). Furthermore, the glucose stimulation index of insulin secretion by islets taken from samples frozen with PEG and PVP, after thawing and overnight culture, was comparable to that of freshly isolated islets, in contrast to DMSO and glycerol. There was no significant difference in intact islet recovery and function between samples frozen with PVP and those frozen with PEG. Samples frozen with DMSO and glycerol had similar results in islet recovery and function. These data show that PVP is a new and potent cryoprotectant for islet cell freezing.

Fibroblast growth factor-1 (FGF-1) loaded microbeads enhance local capillary neovascularization

BACKGROUND

Growth of new blood vessels (neovascularization) occurs naturally in the body, but the slow rate of the process may not be sufficient for survival of engineered tissues and transplanted cells, such as pancreatic islets. For transplanted islets, it is crucial that the transplantation site has sufficient vasculature to support the needs of the islets. Therefore, the specific aim of this research was quantify the effect of FGF-1 incorporation into alginate microbeads on neovascularization of such capsules in an in vivo rat transplant model.

MATERIALS AND METHODS

Microbeads loaded with FGF-1 or control beads (beads without FGF-1) were implanted in the rat omental pouch model. Animals were sacrificed 7 d post-implantation.

RESULTS

Microbeads loaded with FGF-1 stimulated a significant increase in vascular density compared with control rats implanted with control beads.

CONCLUSIONS

These results indicate that alginate microbeads loaded with FGF-1 enhance local neovascularization around implanted microbeads. These data provide a compelling impetus for experimental pursuit of FGF-loaded alginate microcapsules for vascularization of transplanted islets.

Cryopreservation of Freshly Isolated Porcine Islet Cells

INTRODUCTION

The use of xenogenic islet cells may be a possibility to overcome the shortage of human donor organs to treat diabetes. Microencapsulation seems to be a promising method for immunoprotection. Since isolation, purification, encapsulation, and transplantation of islet cells are labor intensive, cryopreservation has emerged as an attractive system of islet banking. The aim of this study was to determine the influence of three different freezing media (FM) on viability of freshly isolated porcine islet cells (FIPIC).

METHODS

FIPIC were isolated using a modified Ricordi method and purification performed using a Lymphoprep density gradient. Viability of FIPIC prior to freezing and after thawing was determined using the MTT-based Cell Growth Determination Kit. Insulin production was detected using enzyme-linked immunosorbent assay. Three different FM containing dimethylsulfoxide (DMSO) or glycerol and sucrose were used for cryoprotection of FIPIC.

RESULTS

Isolation and purification of FIPIC resulted in 95% +/- 1.3% viability and 97% +/- 1.4% purity. Cryopreservation with FM I (containing DMEM, FCS, DMSO) yielded 98.4% and FM III (containing DMEM, FCS, glycerol) 93.1% viability, whereas only 85.6% were alive when cryoprotection is performed with FM II (containing DMSO, BM). Glucose stimulation revealed a loss of 2.8% and 1.9% of insulin secretion per microgram DNA when working with FM I and FM III, but a decrease in glucose-dependent insulin secretion of 7.8% (P < .05) when FIPIC were stored in FM II.

DISCUSSION

Low concentrations of DMSO or the use of glycerol and sucrose seem to be equivalent to cryopreserve FIPIC.

Cryopreservation of Insulin-Producing Cells Microencapsulated in Sodium Cellulose Sulfate

INTRODUCTION

Diabetes mellitus may be treated with pancreatic islet cell transplantation. The use of xenogenic islet cells may overcome the shortage of human donor organs. Microencapsulation seems to be a promising method for immunoprotection. Since isolation, purification, encapsulation, and transplantation of islet cells are labor-intensive, cryopreservation has emerged as an attractive system for islet banking. In this study sodium cellulose sulfate (NaCS), a novel method for microencapsulation of islet cells, was tested for its capability to protect cells during cryopreservation.

METHODS

HIT-T15 cells were microencapsulated in NaCS. Cells were frozen and thawed using three different media containing varying amounts of dimethylsulfoxide (DMSO) and glycerol. Cell viability and cell growth were monitored using 3-(-4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide before freezing and 1 week after thawing.

RESULTS

NaCS did not show any negative impact on the growth rates of encapsulated HIT-T15 cells compared with nonencapsulated controls. Nonencapsulated cells were adequately cryopreserved by both DMSO- and glycerol-containing freezing media. DMSO was not suitable for cryopreservation of encapsulated HIT-T15 cells, whereas glycerol seemed to produce no considerable cell loss during freezing and thawing.

DISCUSSION

Islet banking of cells encapsulated in NaCS was feasible. Microencapsulation did not harm islet cell recovery. As NaCS is less immunogenic and more biocompatible than other materials used for microencapsulation, it may be a promising method for immunoisolation of islet cells to replace the endocrine pancreas in a physiological way.

Cryopreservation of alginate-encapsulated recombinant cells for antiangiogenic therapy

The potential benefit of continuous local administration of antiangiogenic proteins to CNS tumors in vivo has recently been demonstrated using endostatin-producing recombinant cells encapsulated in alginate beads. Due to the treatment potential of transplanted alginate-encapsulated cells producing therapeutic proteins, we describe a successful method of cryopreservation (CP) of such beads, in which cellular viability, alginate structure, and protein secretion were maintained. Alginate beads containing human embryonic kidney cells (HEK 293 cells) stably transfected with the gene encoding for endostatin were cryopreserved in dimethyl sulfoxide (DMSO) using a slow freezing procedure. Briefly, the DMSO concentration was gradually increased prior to the freezing procedure. The cryotubes were further supercooled to -7.5 degrees C and nucleated. Thereafter, the samples were cooled at a rate of 0.25 degrees C/min and stored in liquid nitrogen. The viability of the encapsulated cells was assessed using confocal microscopy quantification (CLSM) technique and a MTS assay. The cell cycle distribution inside the beads was assessed by DNA flow cytometry and endostatin production was determined by an endostatin-specific ELISA assay, both prior to and after CP. CLSM measurements showed sustained esterase activity in the beads after thawing, with only a slight transient decrease 24 h after CP. The MTS assay verified these findings by displaying similar variations of intracellular dehydrogenase activity. Flow cytometric analyses revealed no cryorelated disturbances in cellular ploidy. Furthermore, ELISA measurements showed a well-preserved endostatin production after CP. In conclusion, this work describes the successful CP of alginate-encapsulated recombinant cells secreting a therapeutic protein. Together with previous published reports, these results further substantiate the feasibility and potential of cell encapsulation therapy in the treatment of malignant tumors.

Islet immunoisolation: experience with biopolymers

Incidence of Type I diabetes is increasing globally and has become a major health concern. There is enough evidence suggesting involvement of autoimmunity in destruction of insulin-producing islets of langerhans which leads to impaired glucose homeostasis. Islet transplantation is one of the approaches that received wide attention. Due to the autoimmune nature of the disease. strategies to protect transplanted islet graft from rejection are sought. Immunoisolation of islets inside semipermeable biocompatible materials is amongst them. Natural biopolymers have been used extensively as immunoisolation materials due to their satisfactory biocompatiblity and tissue tolerance. Here we attempt to address the need for islet immunoisolation and our experience in using natural biopolymers such as chitosan, cellulose and alginate for this application.

Bioartificial pancreas: materials, devices, function, and limitations

The term "bioartificial endocrine pancreas" (BEP) was introduced by Anthony Sun in 1980. It was in 1968, however, that Thomas Chang proposed the use of microencapsulated islets as artificial beta-cells. By applying a semipermeable membrane on the top of microcapsules, a system can be produced that is impermeable to viable islet cells and large effector molecules of the immune system, thus providing a protection for transplanted islets against rejection. Since then, the term BEP has not often appeared in papers. Instead, the term "bioartificial pancreas" (BAP) has gained widespread use. In a broader sense, BAP would include an application of suitable endocrine cells and protective polymeric vehicles, but not necessarily providing a filtration barrier of precisely defined properties (e.g., cells injected into a gel of hyaluronate).

Islet cell transplantation for the treatment of diabetes mellitus

Diabetes mellitus is estimated to affect at least 16 million individuals in the United States and 135 million persons worldwide. It is a significant cause of morbidity and early mortality. The related expenses are astronomical with at least 15% of healthcare expenditures in the United States being used for the treatment of diabetes and its complications, a figure that approaches US$100 billion annually. The Diabetes Control and Complications Trial (DCCT) convincingly showed that intensive glucose management delays the onset and slows the progression of diabetic complications. Numerous studies have shown that pancreas transplantation not only delays the onset and progression of diabetic complications, but in some cases reverses some of the effects of diabetes. Human islet cell transplantation provides an alternative, less invasive alternative to whole organ transplantation. Human islet allotransplantation would only exacerbate the organ shortage, as recipients usually require islets from more than one pancreas. Xenotransplantation of porcine islets is a more attractive option; however, the recipient's immune response to xenografted tissue would be a formidable obstacle. Microencapsulation of the islets is a method of immunoisolation that would prevent the need for immunosuppressive drugs and the risks associated with their long-term use and have the potential to make xenoislet transplantation a clinical reality.