Design improvements to in vitro gastrointestinal models to evaluate effectiveness of insulin encapsulation in nanoparticles
Reilly, Kaitlin Elizabeth
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The goal of this study was to develop a model of the gastrointestinal tract (GIT) to be used for in vitro testing of oral insulin delivery devices. The method and intensity of mixing and effects of gastrointestinal fluids with and without enzymes were evaluated. Comparisons were made between an actively mixed simulator and a passively mixed simulator, where the actively mixed simulator is a magnetically stirred flask while the passively mixed simulator is a flexible container on a rocking stage. Slower mixing times and larger time constants for mixing were seen for the passively mixed simulator during a pH tracer experiment. Release studies were performed with several oral insulin delivery device models to evaluate the effects of different mixing techniques on insulin release. In all cases, the more intense mixing of the actively mixed simulator resulted in more insulin release. When using a nanoparticle model in intestinal fluid for example, 100% insulin release was observed in the actively mixed simulator while only 53% was released in the passively mixed simulator after 1 hour. Trypsin and pepsin were used to determine the ability of a drug delivery device to protect insulin from enzymatic degradation in which trypsin was added to simulated intestinal fluid and pepsin was added to simulated gastric fluid. Premature insulin release and insulin denaturation at body temperature occurred in the intestinal fluid so the protective effects against trypsin were unable to be effectively evaluated. An increase in insulin loss from 70% to 95% was detected in the presence of pepsin compared to gastric fluid without enzymes in the actively mixed simulator, indicating that acid hydrolysis of insulin as well as protease attack by pepsin will impact the behavior of an insulin delivery device. An improvement in insulin retention was observed in the passively mixed simulator. After 1 hour, insulin retained was increased from 4% in the actively mixed simulator to 10% in the passively mixed simulator, and after 2 hours, this increase was 2% to 7%. Premature insulin release from the delivery device, acid hydrolysis, temperature denaturation, and enzymatic degradation are factors limiting the effectiveness of oral insulin.