Intestinal uptake of insulin nanoparticles: facts or myths?

The oral route is the most suitable and physiological delivery route. Oral insulin delivery would minimize the health hazard implied in repeated injection, surpass complications arising from the need for sterile techniques associated with parenteral formulations and provide better glucose homeostasis. However, it is limited by various physiological barriers and still remains a scientific challenge. The desire to deliver insulin by the oral route in a conveniently and effectively way has led to the intense investigation of new delivery systems. Nanodelivery systems have been proposed to enhance the bioavailability of insulin after oral administration. This review article describes the gastrointestinal barriers to oral insulin delivery, including chemical, enzymatic and absorption barriers. The potential transport mechanisms of insulin delivered by nanoparticles across the intestinal epithelium are also addressed. Finally, how nanoparticles characteristics affect insulin pharmacological activity and bioavailability is discussed.