EVALUATING THE COMBINATION OF CHITOSAN AND NAVY BEAN LECTIN TOWARD BUILDING AN INSULIN-LOADED NANOCARRIER

Insulin is a peptide applied to treat diabetes. It is usually administrated via subcutaneous injection, which causes pain and discomfort to the patient. Therefore, it is necessary to develop new strategies for vehiculating insulin. In this sense, nanocarriers that are able to protect and modulate insulin release in the gastrointestinal tract can be used to allow its oral administration. Chitosan and lectin may be suitable for building these nanocarriers due to their particular properties (mucoadhesivity and cytoadhesivity, respectively), thus providing additional features to the carrier system. In this study, we aimed to develop nanocarriers based on chitosan/navy bean lectin complexes for vehiculating insulin. Firstly, rheology, microscopy, and zeta potential analyses were applied to obtain information on the mucoadhesive and cytoadhesive ability of the materials. Subsequently, we verified the capability of chitosan and lectin to conjugate with genipin (a natural crosslinking agent) and insulin in different experimental conditions (ratio and timing of addition of materials, chitosan hydrolysis) using spectrophotometric analysis. The presence of distinct interactions stabilizing the nanocarriers was observed with the native-PAGE electrophoresis approach. Also, the impact of the experimental conditions on the resulting nanocarriers was determined by experimental designs. Rheological analysis showed that both chitosan and hydrolyzed chitosan were able to interact with mucin, evidenced by a decrease in the viscosity. Lectin's ability to agglutinate red blood cells (and, by consequence, its cytoadhesivity) was confirmed by optical microscopy. Chitosan and lectin presented opposing charges in their natural pH, which allows the formation of electrostatic interactions between these materials. They could also conjugate with genipin, and lectin presented the highest crosslinking degree. Subsequently, nanoparticles were obtained by conjugating chitosan, lectin, genipin, and insulin under different experimental conditions. Native-PAGE electrophoresis showed these systems were stabilized through covalent, electrostatic, and hydrophobic interactions. Increasing chitosan concentration formed particles with higher zeta potential and smaller sizes, improving their stability, while adding insulin after the conjugation decreased the zeta potential and encapsulation efficiency. The latter suggests that insulin was anchored to the nanocarriers' surface, being more exposed to environmental conditions. Besides that, using hydrolyzed chitosan led to nanoparticles with lower zeta potential and greater sizes. Then, hydrolysis increased chitosan reactivity. Finally, when chitosan is the last ingredient added to the conjugation, lectin extensively crosslinks with insulin, which hampers its release. Our results provided valuable insights into designing nanocarriers for insulin oral delivery.