Pituitary hollow fiber units in the dwarf mouse

Hollow fiber membrane diffusive permeability regulates encapsulated cell line biomass, proliferation, and small molecule release

Using histological and HPLC methods, we examined the influence of hollow fiber membrane transport properties on encapsulated PC12 cell biomass, proliferation and the release of dopamine over 4 weeks in culture. Our data indicated that encapsulated cell biomass, the number of proliferating cells, and the quantity of dopamine released increased as a function of increasing hollow fiber encapsulation membrane diffusive permeability. Overall the percentage of viable cells and the biomass architecture, however, was not significantly affected by differences in membrane transport. When compared to membrane sieving properties, membrane diffusive transport and membrane hydraulic permeability were better indicators of biomass size, proliferating cell number, and dopamine release from encapsulated cells. Studies examining the sustained release of DA from membranes of differing permeability suggest that membrane diffusive permeability can be used to regulate the quantity of small molecules released per unit time at steady state, and should be considered when dosing is an important determinant of implant efficacy.

Materials for immunoisolated cell transplantation

Encapsulated cell therapy provides site-specific continuous delivery of cell-synthesized molecules. Cell encapsulation therapy is based on the concept of immunoisolation. Foreign cells are surrounded with a semi-permeable membrane prior to transplantation to shield them from the host's natural defense system. This membrane is selectively permeable to transport of nutrients and therapeutic agents but relatively impermeable to larger molecules and cells of the hosts' immune system. Most encapsulation devices also utilize an internal matrix to keep cells suspended within the capsule. Proper choice of materials and materials processing techniques to formulate membrane and matrix components is essential to the success of these devices. A successful encapsulation device recreates the natural three-dimensional tissue environment that supports cell function and maintains cell viability. This review summarizes recent developments in materials development for cell encapsulation devices and highlights some ongoing challenges faced by those in the field.

Cytomedical therapy for IgG1 plasmacytosis in human interleukin-6 transgenic mice using hybridoma cells microencapsulated in alginate-poly(L)lysine-alginate membrane

Cytomedical therapy for human interleukin-6 transgenic mice (hIL-6 Tgm) was implemented by the intraperitoneal injection of alginate-poly(L)lysine-alginate (APA) membranes microencapsulating SK2 hybridoma cells (APA-SK2 cells) which secrete anti-hIL-6 monoclonal antibodies (SK2 mAb). IgG1 plasmacytosis in the hIL-6 Tgm was suppressed by a single injection of APA-SK2 cells, and the survival time of these mice was remarkably prolonged. The viable cell number and the SK2 mAb-secretion of APA-SK2 cells increased for at least one month both under culture conditions and in allogeneic recipients (in vivo). Moreover, SK2 mAb which were secreted from APA-SK2 cells injected into allogeneic recipients was detected in serum at high concentrations; 3-5 mg/ml from day 14 to day 50 post-injection. In contrast, the injection of free SK2 cells had no therapeutic effect on hIL-6 Tgm. These results strongly suggest that APA membranes microencapsulating cells which were modified to secrete molecules useful for the treatment of a disorder were effective as an in vivo long-term delivery system of bioactive molecules, as 'cytomedicine'.

Hollow fibers for hepatocyte encapsulation and transplantation: studies of survival and function in rats

In this study, the feasibility of transplanting hepatocytes using hollow fibers (HF) was investigated. Experiments were carried out in vitro and in vivo to determine the viability and function of hepatocytes encapsulated in four different types of commercially available HF: regenerated cellulose HF (RCHF), polysulfone HF of two different sizes (PSHF-1 and PSHF-2), and polyvinylidine HF (PVDF). Hepatocytes remained viable in all types of HF for at least 1 wk in vitro as measured by light microscopy and their ability to synthesize protein and secrete albumin. However, the levels of protein synthesis and albumin secretion in these cells varied significantly between different HF (RCHF > PSHF-2 > PVDF approximately PSHF-1) and appeared to be inversely related to their internal diameters (215, 500, 1000, and 1100 microns for RCHF, PSHF-2, PVDF, and PSHF-1, respectively). While PSHF-2, PVDF, and PSHF-1 did not support long term viability in vivo, hepatocytes in RCHF survived after implantation in the mesentery. After 24 h in vivo, the hepatocytes appeared morphologically intact and exhibited a similar rate of protein synthesis when compared with cells cultured in parallel. The hepatocytes in RCHF also maintained the ability to synthesize protein after 7 days in vivo. These results suggest that HF of appropriate size may be useful for hepatocyte transplantation applications in which prevascularization is not possible.

Use of semipermeable polyurethane hollow fibers for pituitary organ culture

A new model for organ culture of endocrine tissue is described. Rat anterior pituitary fragments were cultured for 4 wk within semipermeable polyurethane isocyanate hollow fibers. Growth hormone and prolactin, two of the anterior pituitary hormones, were released into the medium during the entire culture period. Electron microscopy of the pituitary fragments after 2 wk in culture showed a rim of viable tissue in all specimens examined. Individual cells, from this outer rim, exhibited excellent organelle preservation and numerous secretory granules. Experiments involving potassium depolarization and 10(-6) M dopamine provided evidence for the normal responsiveness of the cultured pituitary tissue to both stimulatory and inhibitory factors. These studies illustrate the potential utility of the described organ culture system for further investigations of endocrine physiology.

Hollow fiber-encapsulated pituitary cells for the study of adenohypophyseal regulation of growth in poultry: 1. Preparation and use

A technique for transplantation of viable, functionally active pituitary cells was adapted for use in poultry. Enzymatically dispersed adenohypophyseal cells were prepared from broiler strain donor chicks and loaded into hollow fiber capsules; ultrafiltration membranes consisting of an open-celled, spongy outer layer of polymer material with an internal lumen which is surrounded by a thin skin of tightly controlled pore size. Cell-filled capsules were surgically implanted intracranially into pituitary-intact, recipient birds for extended time periods. Immunoreactive growth hormone (I-GH)-containing cells persisted in hollow fiber capsules for up to 30 days of implantation. Final capsule I-GH reflected starting cell densities. Capsules implanted intracranially became highly vascularized, with capillary endings imbedded in the spongy, open-celled outer surface of the capsule. This provides a means for hormones secreted by cells contained within the capsule to reach the peripheral circulation. Mean plasma I-GH concentration of birds implanted at 10 weeks of age with capsules containing donor cells from 2 to 3-week-old chicks was significantly higher than sham-implanted controls by 2 weeks postimplantation. Thus, hollow fiber-encapsulated pituitary cells remain viable for extended time periods when implanted intracranially in pituitary-intact chickens. These capsules provide a means by which naturally secreted pituitary hormones may be administered in vivo and provide a viable model system for studies of adenohypophyseal hormone action.