Conclusion

Attempts have been made to achieve oral insulin delivery using various systems. It has been proved that the insulin is subjected to acid catalyzed degradation in stomach, luminal degradation in intestine, and intracellular degradation. Scientists have been able to protect the insulin delivery systems from acidic environment of the stomach and target it to the intestine. The maximum bioavailability of the insulin has been reported to be very low because of the poor absorption of insulin from the intestine. The magnitude of apparent permeability of insulin has been reported to be more in the jejunem and ileum than in other parts of the intestine. Researchers have tried to increase the absorption of insulin from the intestine using absorption enhancers such as aprotinin (protease inhibitor), tween, oligoarginine, sodium glycochol-ate, deoxycholic acid, and taurodeoxycholate.

Researchers have prepared microspheres, liposomes, mi-croemulsions, niosomes, nanocubicles, and so forth for the oral delivery of insulin. Pharmacodynamic studies of the insulin from the delivery systems have been successfully carried out in streptozotocin- or alloxan-induced diabetic mice or rats or other animals. The loading of insulin in microparticulate delivery system was the highest. Chitosan-coated microparticles protected insulin from the gastric environment of the body and released it in intestinal pH. Chitosan-coated liposomes have also been reported to have excellent hypoglycemic effects. Limitations to the delivery of insulin have not resulted in fruitful results to date and there is still a need to prepare newer delivery systems, which can produce dose-dependent and reproducible effects in addition to increased bioavailability.

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