Evaluation of gastric mucoadhesive properties of aminated gelatin microspheres

The gastric mucoadhesive properties of aminated gelatin microspheres were evaluated both in vitro and in vivo. The interactions of gelatin, aminated gelatin and microspheres with two kinds of commercial mucin were estimated in aqueous media. At a higher mucin concentration, aminated gelatin demonstrated a stronger interaction with mucin than either kind of the gelatin (isoelectric point (IEP): 5.0 and 9.0) under the same condition, although these interactions varied with varying media. At the same time, a larger amount of mucin was adsorbed to aminated gelatin microspheres than to either of the gelatin microspheres in the same condition. In the in vitro model of isolated and perfused rat stomach, the amount of aminated gelatin microspheres that remained in the stomach after perfusion was significantly larger than that of gelatin microspheres. However, no significant difference was observed whether the test was performed in simulated gastric fluid (SGF) or in phosphate-buffered saline (PBS, pH7.4). In the in vivo experiment, about 47% of the aminated gelatin microspheres remained in the stomach 2 h after oral administration in a capsule, whereas it was 29 and 34% for gelatin (IEP=5.0) and gelatin (IEP=9.0) microspheres, respectively. These results indicated that aminated gelatin microspheres demonstrated a higher gastric mucoadhesive ability than gelatin microspheres. The higher amino group content, improved chain flexibility and favorable polymer conformation were suggested to be the main factors that contributed to the stronger mucoadhesive properties of aminated gelatin microspheres than that of gelatin microspheres.