Evaluation of different types of alginate microcapsules as bioreactors for producing endostatin

Comparison of Linear Poly Ethylene Imine (LPEI) and Poly L-Lysine (PLL) in Fabrication of CHOK1 Cell-Loaded Multilayer Alginate Microcapsules

Purpose: Poly l-lysine (PLL) has been introduced as a strengthening covering layer for alginate microcapsules which are the most convenient way for cell encapsulation. Some disadvantages of PLL such as high price and low biocompatibility have prompted scientists to find better alternatives. Linear poly ethylene imine (LPEI), thanks to its highly similar structure to PLL, could be considered as a proper cost-effective alternative. In this study LPEI and PLL were compared as covering layers of cell-loaded alginate-LPEI-alginate (cALA) and alginate-PLL-alginate (cAPA) microcapsules. Methods: In addition to the physico-mechanical properties, the encapsulation efficiency, cell survival post encapsulation, cell viability, and cellular metabolic activity within the microcapsules were evaluated using trypan blue, live/dead cell staining, and MTT test, respectively. Results: Physico-mechanical evaluation of the microcapsules revealed that the cell microencapsulation process did not affect their shape, size, and mechanical stability. Although the encapsulation efficiency for cALA and cAPA was not different (P >0.05), cell survival post encapsulation was higher in cALA than in cAPA (P<0.05) which could be the reason for the higher cell viability and also cellular metabolic activity within these microcapsules in comparison to cAPA. Conclusion: Here, based on these results, ALA could be introduced as a preferable alternative to APA for cell encapsulation.

The effect of molecular weights of microencapsulating polymers on viability of mouse-cloned pancreatic β-cells: biomaterials, osmotic forces and potential applications in diabetes treatment

INTRODUCTION

Ideal cell-containing microcapsules should be capable of maintaining cell viability and exhibit significant structural stability to support cellular functionality. To date, such microcapsules remain unavailable; thus, this study used our well-established microencapsulating methods to examine a total of 32 different microencapsulating formulations and correlate polymers' molecular weights (M_wt) and UDCA addition, with cell viability and microcapsules' stability, postmicroencapsulation.

METHODS

MIN6 mouse-cloned pancreatic β-cells were microencapsulated using control (n = 16; without UDCA) and test (n = 16; with UDCA) different polymers. Confocal microscopic imaging, cell viability, and microcapsules' stability were assessed.

RESULTS

Best cell viability (>50%) was obtained at average M_wt of 50,000 g/mol (poly-l-ornithine), followed by 110,000 g/mol (poly-l-lysine). There was no linear correlation between M_wt and viability. Confocal imagining showed similar microcapsules' shape and cell distribution among all different polymers' molecular weights, which suggests that the microencapsulating method was efficient and maintained microcapsules' uniformity. UDCA addition resulted in enhanced osmotic stability of the microcapsules and improved cell viability, when the formulation contained 1% polylornithine, 1% polyethylene glycol, 20% Eudragit^® NM30D, 1% polytetrafluoroethylene, or 5% pentamethylcyclopentasiloxane.

CONCLUSIONS

UDCA addition improved microenvironmental conditions within the microcapsules but this effect was largely dependent on the polymer systems used.

Culture of hESC-derived pancreatic progenitors in alginate-based scaffolds

The effect of alginate-based scaffolds with added basement membrane proteins on the in vitro development of hESC-derived pancreatic progenitors was investigated. Cell clusters were encapsulated in scaffolds containing the basement membrane proteins collagen IV, laminin, fibronectin, or extracellular matrix-derived peptides, and maintained in culture for up to 46 days. The cells remained viable throughout the experiment with no signs of central necrosis. Whereas nonencapsulated cells aggregated into larger clusters, some of which showed signs of morphological changes and tissue organization, the alginate matrix stabilized the cluster size and displayed more homogeneous cell morphologies, allowing culture for long periods of time. For all conditions tested, a stable or declining expression of insulin and PDX1 and an increase in glucagon and somatostatin over time indicated a progressive reduction in beta cell-related gene expression. Alginate scaffolds can provide a chemically defined, xeno-free and easily scalable alternative for culture of pancreatic progenitors. Although no increase in insulin and PDX1 gene expression after alginate-immobilized cell culture was seen in this study, further optimization of the matrix physicochemical and biological properties and of the medium composition may still be a relevant strategy to promote the stabilization or maturation of stem cell-derived beta cells.

Encapsulated cell therapy for neurodegenerative diseases: from promise to product

Delivering therapeutic molecules, including trophic factor proteins, across the blood brain barrier to the brain parenchyma to treat chronic neurodegenerative diseases remains one of the great challenges in biology. To be effective, delivery needs to occur in a long-term and stable manner at sufficient quantities directly to the target region in a manner that is selective but yet covers enough of the target site to be efficacious. One promising approach uses cellular implants that produce and deliver therapeutic molecules directly to the brain region of interest. Implanted cells can be precisely positioned into the desired region and can be protected from host immunological attack by encapsulating them and by surrounding them within an immunoisolatory, semipermeable capsule. In this approach, cells are enclosed within a semiporous capsule with a perm selective membrane barrier that admits oxygen and required nutrients and releases bioactive cell secretions while restricting passage of larger cytotoxic agents from the host immune defense system. Recent advances in human cell line development have increased the levels of secreted therapeutic molecules from encapsulated cells, and membrane extrusion techniques have led to the first ever clinical demonstrations of long-term survival and function of encapsulated cells in the brain parenchyma. As such, cell encapsulation is capable of providing a targeted, continuous, de novo synthesized source of very high levels of therapeutic molecules that can be distributed over significant portions of the brain.

Advances in biocompatibility and physico-chemical characterization of microspheres for cell encapsulation

Cell encapsulation has already shown its high potential and holds the promise for future cell therapies to enter the clinics as a large scale treatment option for various types of diseases. The advancement in cell biology towards this goal has to be complemented with functional biomaterials suitable for cell encapsulation. This cannot be achieved without understanding the close correlation between cell performance and properties of microspheres. The ongoing challenges in the field of cell encapsulation require a critical view on techniques and approaches currently utilized to characterize microspheres. This review deals with both principal subjects of microspheres characterization in the cell encapsulation field: physico-chemical characterization and biocompatibility. The up-to-day knowledge is summarized and discussed with the focus to identify missing knowledge and uncertainties, and to propose the mandatory next steps in characterization of microspheres for cell encapsulation. The primary conclusion of this review is that further success in development of microspheres for cell therapies cannot be accomplished without careful selection of characterization techniques, which are employed in conjunction with biological tests.

Microencapsulation of small intestinal neuroendocrine neoplasm cells for tumor model studies

Basic cancer research is dependent on reliable in vitro and in vivo tumor models. The serotonin (5-HT) producing small intestinal neuroendocrine tumor cell line KRJ-1 has been used in in vitro proliferation and secretion studies, but its use in in vivo models has been hampered by problems related to the xeno-barrier and tumor formation. This may be overcome by the encapsulation of tumor cells into alginate microspheres, which can function as bioreactors and protect against the host immune system. We used alginate encapsulation of KRJ-1 cells to achieve long-term functionality, growth and survival. Different conditions, including capsule size, variations in M/G content, gelling ions (Ca(2+) /Ba(2+)) and microcapsule core properties, and variations in KRJ-1 cell condition (single cells/spheroids) were tested. Viability and cell growth was evaluated with MTT, and confocal laser scanner microscopy combined with LIVE/DEAD viability stains. 5-HT secretion was measured to determine functionality. Under all conditions, single cell encapsulation proved unfavorable due to gradual cell death, while encapsulation of aggregates/spheroids resulted in surviving, functional bioreactors. The most ideal spheroids for encapsulation were 200-350 μm. Long-term survival (>30 days) was seen with solid Ca(2+) /Ba(2+) microbeads and hollow microcapsules. Basal 5-HT secretion was increased (sixfold) after hollow microcapsule encapsulation, while Ca(2+) /Ba(2+) microbeads was associated with normal basal secretion and responsiveness to cAMP/PKA activation. In conclusion, encapsulation of KRJ-1 cells into hollow microcapsules produces a bioreactor with a high constitutively activate basal 5-HT secretion, while Ca(2+) /Ba(2+) microbeads provide a more stable bioreactor similar to non-encapsulated cells. Alginate microspheres technology can thus be used to tailor different functional bioreactors for both in vitro and in vivo studies.

Synergistic Effects in Semidilute Mixed Solutions of Alginate and Lactose-Modified Chitosan (Chitlac)

The present study specifically aimed at preparing and characterizing semidilute binary polymer mixtures of alginate and chitlac which might find an application in the field of cell encapsulation. A polyanion, alginate, and a polycation, a lactose-modified chitosan, were mixed under physiological conditions (pH 7.4 and NaCl 0.15) and at a semidilute concentration avoiding associative phase separation. The mutual solubility was found to be dependent on the charge screening effect of the added NaCl salt, being prevented below 0.05 M NaCl. A comparison with the behavior of the polyanion (alginate) under the same experimental conditions revealed that both the viscosity and the relaxation times of the binary polymer solutions are strongly affected by the presence of the polycation. In particular, the occurrence of electrostatic interactions between the two oppositely charged polysaccharides led to a synergistic effect on the zero-shear viscosity of the solution, which showed a 4.2-fold increase with respect to that of the main component of the solution, i.e., alginate. Moreover, the relaxation time, calculated as the reciprocal of the critical share rate, markedly increased upon reducing the alginate fraction in the binary polysaccharide solution. However, the formation of the soluble complexes and the synergistic effect are reduced upon increasing the concentration of the 1:1 electrolyte. By containing a gel-forming polyanion (alginate, e.g., with Ca(2+) ions) and a bioactive polycation (chitlac, bearing a beta-linked D-galactose), the present system can be regarded as a first step toward the development of biologically active scaffold from polysaccharide mixtures.

Optimization of microencapsulated recombinant CHO cell growth, endostatin production, and stability of microcapsulein vivo

Microencapsulation of recombinant cells secreting endostatin offers a promising approach to tumor gene therapy in which therapeutic protein is delivered in a sustainable and long-term fashion by encapsulated recombinant cells. However, the studies of cell growth and protein production in vivo are very limited. In this study, the effects of microencapsulation parameters on in vivo cell growth, endostatin production, and microcapsule stability after implantation in the peritoneal cavity of mice were for the first time investigated. Microcapsules with liquid core reached higher cell density and endostatin production at day 18 than microcapsules with solid core. There was no significant difference in stability whether the core of the microcapsule was solid or liquid. Decrease in microcapsule size increased the stability of microcapsule. The microcapsules kept intact in the peritoneal cavity of mice after 36 days of implantation when the microcapsules size was 240 microm in diameter, which gave rise to high endostatin production as well. The optimized microencapsulation conditions for in vivo implantation are liquid core and 240 microm in diameter. This study provides useful information for antiangiogenic gene therapy to tumors using microencapsulated recombinant cells.

Cell-compatible covalently reinforced beads obtained from a chemoenzymatically engineered alginate

A chemoenzymatic strategy has been exploited to make covalently linked alginate beads with high stability. This was achieved by grafting mannuronan (alginate with 100% mannuronic acid (M)) with methacrylate moieties and then performing two enzymatic steps converting M to guluronic acid (G) in alternating sequences (MG-blocks) and in G-blocks. In this way a methacrylate grafted alginate with better gel-forming ability was achieved. Covalent bindings were introduced into the beads by using a photoinitiating system that initiated polymerization of the methacrylate moieties. The covalent links were demonstrated by beads remaining intact after treatment with EDTA. The new chemoenzymatic photocrosslinked (CEPC) beads were compatible with cells with low post-encapsulation ability like C2C12 myoblasts and human pancreatic islets. The islets continued secreting insulin after encapsulation. On contrary, cells with a high post-encapsulation proliferative ability like 293-endo cells died within 2-week post-encapsulation. The exceptional stability and the cell compatibility of the new CEPC beads make them interesting as bioreactors for delivering therapeutic proteins in future applications.

Alginate-PLL microencapsulation: effect on the differentiation of embryonic stem cells into hepatocytes

The emergence of hepatocyte based clinical and pharmaceutical technologies, has been limited by the absence of a stable hepatocyte cell source. Embryonic stem cells may represent a potential solution to this cell source limitation problem since they are highly proliferative, renewable, and pluripotent. Although many investigators have described techniques to effectively differentiate stem cells into a variety of mature cell lineages, their practicality is limited by: (1) low yields of fully differentiated cells, (2) absence of large scale processing considerations, and (3) ineffective downstream enrichment protocols. Thus, a differentiation platform that may be modified to induce and sustain differentiated cell function and scaled to increase differentiated cell yield would improve current stem cell differentiation strategies. Microencapsulation provides a vehicle for the discrete control of key cell culture parameters such as the diffusion of growth factors, metabolites, and wastes. In addition, both cell seeding density and bead composition may be manipulated. In order to assess the feasibility of directing stem cell differentiation via microenvironment regulation, we have developed a murine embryonic stem cell (ES) alginate poly-l-lysine microencapsulation hepatocyte differentiation system. Our results indicate that the alginate microenvironment maintains cell viability, is conducive to ES cell differentiation, and maintains differentiated cellular function. This system may ultimately assist in developing scalable stem cell differentiation strategies.