Effect of lysozyme on the stability of polyester nanocapsules and nanoparticles: stabilization approaches

The efficacy of colloidal particles as drug carriers is closely related to their interaction with proteins and enzymes in different body fluids. In the present work, we analysed the interaction phenomenon between lysozyme (LZM), a positively charged enzyme that is highly concentrated in mucosas, and two different drug carriers: nanocapsules made of an oily core coated by the polymer poly-epsilon-caprolactone (PECL) and nanoparticles made solely of PECL. Results showed that the interaction of LZM with these colloidal drug carriers is highly affected by their surface charge. Nanocapsules, because of their important negative charge (-40 mV), adsorbed a great amount of LZM, which is positively charged. This adsorption process, which was also evidenced by the significant reduction of the nanocapsules' negative surface charge, led to the degradation of the polymer coating and the aggregation of the nanocapsules. In contrast, nanoparticles had a low negative surface charge (-8 mV) and adsorbed only a small amount of LZM, which did not cause the destabilization of the system. Furthermore, the molecular weight of the polymer forming the nanoparticles did not change. Finally, it was observed that the destabilizing effects caused by the adsorption of LZM onto the nanocapsules can be prevented by previous adsorption of the cationic poly(amino acid) poly-L-lysine. Using this approach the adsorption of LZM was hindered and its consequences avoided.