Proposed molecular model for electrostatic interactions between insulin and chitosan. Nano-complexation and activity in cultured cells

The objective of this contribution was to propose a model that would explain the nanocomplexes formation between Human Recombinant Insulin (I) and a polydisperse Chitosan (CS). Such an objective implied exploring I and CS concentration conditions that allowed the formation of complexes with defined and reproducible submicronic dimensions. I-CS complexes were obtained by mixing I and CS solutions at pH 2 and then increasing the pH up to 6 promoting electrostatic interactions between them. Colloidal stages of I and I-CS nano-complexes formation were characterized by dynamic light scattering (DLS), zeta-potential, solutions flow behavior and absorbance measurements. 1.10(-2)%, w/w, of CS allowed covering completely the surface protein aggregates constituting core-shell nano-structures of 200 nm, with a.-potential of 17,5 mV. Solution dynamic viscosity results kept relation with different stages of nano-complexation process. Biological activity of I-CS complexes was studied in 3T3-L1 cultured fibroblast showing a delayed and sustained activity as compared to free insulin. ICS nano-complexes could be an alternative for developing a new generation of drugs allowing I protection from the hostile conditions of the body and increasing its absorption. These findings have basic and practical impacts as they could be exploited to exert the controlled release of I in therapeutic formulations by using the I-CS nanocomplexes.