Enhanced survival and insulin secretion of insulinoma cell aggregates by incorporating gelatin hydrogel microspheres.

INTRODUCTION: The objective of this study is to evaluate the survival and glucose-induced insulin secretion of rat-derived insulinoma cells (INS-1) from their aggregates incorporating different size of gelatin hydrogel microspheres comparing with microspheres-free cell aggregates. METHODS: The gelatin hydrogel microspheres were prepared by the conventional w/o emulsion method. The INS-1 cells were cultured in a V-bottomed well, combining with or without the gelatin hydrogel microspheres to form their aggregates with or without microspheres. RESULTS: When the cell viability, the live cell number, the reductase activity, and the insulin secretion of cell aggregates were evaluated 7 or 14 days after incubation, the cell aggregates incorporating gelatin hydrogel microspheres showed higher cell viability, reductase activity and a larger number of live cells. The cell aggregates incorporating larger size and number of gelatin hydrogel microspheres secreted a larger amount of insulin, compared with those incorporating smaller size and number of microspheres or without microspheres. CONCLUSION: It is conceivable that the incorporation of gelatin hydrogel microspheres in cell aggregates is promising to improve their survival and insulin secretion function.

Insulin secretion of mixed insulinoma aggregates-gelatin hydrogel microspheres after subcutaneous transplantation.

INTRODUCTION: The objective of this study is to evaluate the insulin secretion of mixed aggregates of insulinoma cells (INS-1) and gelatin hydrogel microspheres after their subcutaneous transplantation. METHODS: Gelatin hydrogel microspheres were prepared by the conventional w/o emulsion method. Cell aggregates mixed with or without the hydrogel microspheres were encapsulated into a pouched-device of polytetrafluoroethylene membrane. An agarose hydrogel or MedGel™ incorporating basic fibroblast growth factor (bFGF) was subcutaneously implanted to induce vascularization. After the vascularization induction, cell aggregates encapsulated in the pouched-device was transplanted. RESULTS: The vascularization had the potential to enable transplanted cell aggregates to enhance the level of insulin secretion compared with those of no vascularization induction. In addition, the insulin secretion of cell aggregates was significantly promoted by the mixing of gelatin hydrogel microspheres even in the pouched-device encapsulated state. CONCLUSION: It is possible that the microspheres mixing gives cells in aggregates better survival condition, resulting in promoted insulin secretion.

Relationship between drug dissolution and leaching of plasticizer for pellets coated with an aqueous Eudragit S100:L100 dispersion.

In order to investigate the relationship between drug dissolution and leaching of plasticizer, theophylline pellets coated with 30% (w/w) Eudragit S100:L100 (1:1) plasticized with different levels of triethyl citrate (TEC) were prepared. The influence of storage conditions on the dissolution profile of theophylline and leaching of TEC was determined. Theophylline was found to dissolve completely from pellets coated with Eudragit S100:L100 (1:1) plasticized with 50% TEC at pH 6.0 after 2h. The shape of the pellets was maintained during dissolution testing. Cracks due to the leaching of TEC were observed in the scanning electron micrographs (SEMs) following dissolution testing at pH 6.0. Both the dissolution of theophylline and the leaching of TEC decreased during storage due to further coalescence of the acrylic polymers. The dissolution profiles of theophylline showed a biphasic pattern and the lag times were estimated as the time points at which a second, rapid release of theophylline was initiated. Subsequently, the percent of TEC leached at the lag time was calculated. While the lag time was increased by storage time and humidity, the percent of TEC leached at the lag time was unchanged as a function of storage condition and was dependent on the initial TEC levels in the films. In conclusion, the plasticizer content in the film coating influenced the dissolution profile of theophylline from pellets coated with Eudragit S100:L100 (1:1). A large amount of the TEC was leached from the enteric films before drug release was initiated and a TEC level of approximately 30% in the films, based on the polymer weight, was the critical amount of TEC for initiating drug release during dissolution testing at pH 6.0. While enteric films are more soluble and dissolve faster at higher pH values, the kinetics of plasticizer release was one of the important factors controlling the dissolution of drugs at pH 6.0, at which pH the enteric polymers were insoluble.

Physicochemical properties of enteric films prepared from aqueous dispersions and organic solutions.

Cast films composed of mixtures of Eudragit S100:L100 (1:1) and plasticized with triethyl citrate (TEC) were prepared from aqueous dispersions and organic solutions, and the physicochemical properties and the weight loss of cast films during dissolution testing were examined. The tensile strength of the organic cast films was significantly higher and the percent elongation was lower than that of the aqueous cast films. The weight loss of the organic films was also lower than that of the aqueous films. Furthermore, leaching of the TEC from the aqueous films was rapid and the TEC was found to diffuse from the films within one hour at pH 6.0, the pH at which the Eudragit S100:L100 (1:1) films were insoluble. In contrast to the aqueous films, minimal levels of the TEC diffused from the organic cast films, and the disintegration of acrylic polymers occurred simultaneously with the release of TEC from the film during dissolution testing at pH 7.0. For Eudragit L100-55, which could form films at lower TEC levels than Eudragit S100:L100, both the organic and aqueous films showed the same weight loss after four hours in pH 5.0 media. These results demonstrated that for Eudragit S100:L100 cast films, the high levels of TEC needed for film formation from aqueous dispersions resulted in rapid dissolution and disintegration at pH 6.0 and above. While aqueous dispersions are preferred for the coating of solid substrates, for Eudragit S100:L100 film coatings, a change from organic solutions to aqueous dispersions in the coating process will impact film properties and product performance.