Preparation of insulin carrier systems for oral delivery, characterization and release study

According to the International Diabetes Federation's data in 2013, 382 million people around the world are suffering from Diabetes Mellitus and 548 million dollars of the world's health expenditure is spent on diabetes each year. Patients with insulin dependent Diabetes Mellitus are exposed to repeatedly injection administration each day. Developments in biotechnology has opened the opportunity for therapeutic use of many proteins. Insulin, which is used in the treatment of diabetes mellitus, is one of them. Oral bioavailability of an unprotected protein drug is less than 1-2% due to the gastric and intestinal protease activity and physical barriers like acidic gastric pH, mucus, and protease-containing microvilli. For this reason, versatile formulation strategies are needed in order to provide oral applicability to proteins. In our thesis, it was aimed to develop microemulsion system which is, applicable for oral insulin delivery. For this purpose, in the preformulation experiments a water-in-oil microemulsion system which is composed of Plurol Oleique as the oil, Tween80 and Lecithin as surfactants, etanol as co-surfactant, was developed. A solution of recombinant insulin (100 IU/mL) was added as the internal water phase. Different ratios of chitosan and sodium tripolyphosphate were examined for the inner phase of the microemulsion to obtain more stable system, with higher protective function against acidic and enzymatic degradation. The obtained formulations were characterized and their physicochemical properties were investigated. According to stability studies, formulations were stable at +4˚C for 6 months. Circular dichroism analyses revealed that conformational stability of insulin is not affected by the preparation conditions and the presence of chitosan and/or sodium tripolyphosphate. Furthermore, release properties of formulations were investigated under different pH levels, to simulate gastric and intestinal conditions. According to these studies, further experiments were carried out with the formulations which provided greater gastric protection and higher intestinal insulin release. Toxicity studies on L929 mouse fibroblast cells were performed with these formulations and toxic doses on these cells were determined. In vivo experiments were carried out with Wistar Albino rats. In these experiments standard insulin solution, microemulsion containing only insulin and optimal microemulsion which contains chitosan and sodium tripolyphosphate were administered intragastrically to the animals. The optimal formulation provided effective reduction on blood glucose level from the 1st to the 8th hour after administration. The reduction on blood glucose level was statistically significant at the 8th hour, as compared to the other groups. In conclusion, the developed water-in-oil microemulsion system containing insulin, chitosan and sodium tripolyphosphate in the inner phase may be suggested as an alternative dosage forms for oral insulin delivery.