Thiolate chitosan nanoparticles capable to delivery nitric oxide: synthesis, characterization and antibacterial potential

Abstract

Nitric oxide (NO) is a small but powerful molecule. It is involved in several biological pathways such as vasodilation, wound healing and toxicity towards pathogens. At high concentrations, NO has a toxicity towards bacteria, virus and fungi which has a great biomedical potential. However, NO has a small half-life of just a few seconds and this hazards its clinical application. In this scenario, the combination of nanotechnology with NO donors can create new strategies to load and deliver NO. Polymeric nanomaterial intrinsically have advantages such as low toxicity, biodegradability and low-cost. In this study, we used chemically modified chitosan (CS) to prepare nanoparticles capable of loading and releasing NO with antibacterial activity. CS was chemically modified to add a thiol group (-SH) to its structure. This modification was performed by the reaction with thioglycolic acid (TGA) in the presence of a carbodiimide (EDC). The thiol groups in CS structure serve a double function: create an anchorage site for NO and increase polymer mucoadesivity. The synthesis of thiolated chitosan nanoparticles (TCS NP) occurred by ionotropic gelation method using sodium tripolyphosphate (TPP) as counter ion. The NO donor precursor molecule, mercaptosuccinic acid (MSA), was encapsulated into TCS NP to increase loading capacity of NO. To identify the best paraments of the synthesis we used the ratios 1:3, 1:4, 1:5, 1:6 and 1:7 for TCS:TPP. TCS NPs were characterized by dynamic light scattering (DLS), microscopy electron transmission (MET) and nanoparticle tracking analysis (NTA). The release of NO was characterized by a kinetic using Uv-vis spectroscopy. Finally, the antibacterial potential was evaluated by minimum inhibitory concentration (MIC) assay against Staphylococcus aureus, Streptococcus mutans and Escherichia coli strains. The ratio 1:5 showed the most adequate size parameters and the other analysis were performed using it. The hydrodynamic size was found to be 113.0 ± 1.6 nm, PDI of 0.292 ± 0.035 and zeta potential of 27.1 ± 0.9. The MET images indicated small and spherical nanoparticles. The kinetic profiles showed a linear release of NO reaching the 100% after 150 min. The antibacterial effect was tested for E. coli, S. aureus and S. mutans. The MIC values was 50 µg mL for NO-CS NP, this result was 50% lower compared to TCS NPs for S. mutans and E. coli. The TCS NP has suitable properties for the biomedical field with potential for antibacterial application.