Preparation of aminoglycoside-loaded chitosan nanoparticles using dextran sulphate as a counterion

Purpose. To prepare aminoglycoside (AG) (streptomycin, gentamicin and tobramycin) loaded chitosan nanoparticles with high drug incorporation efficiency and test the in vivo oral efficacy of streptomycin (SM) loaded chitosan nanoparticles in a Mycobacterium tuberculosis (TB) chronic infection mouse model. Method. Dextran sulphate (a polyanion) was used to shield the positive charge of AG and increase the drug incorporation in the chitosan nanoparticle. By varying the concentration of each component, the formulation of SM-loaded chitosan nanoparticle was optimized by monitoring the drug incorporation efficacy and particle size. The mechanism of the nanoparticle formation was suggested and the preparation method was applied to two other aminoglycosides (AG): gentamicin (GM) and tobramycin (TM). The resulting nanoparticles were characterized by particle diameter, drug incorporation efficacy, drug loading efficacy and zeta potential. The in vitro drug release from these nanoparticles was carried out in pH 1.2 and pH 7.4 buffer. Preliminary in vivo oral efficacy studies of SM-loaded chitosan nanoparticles was performed in a Mycobacterium tuberculosis (TB) chronic infection mouse model. Results. The optimal concentration of streptomycin (SM)/dextran sulphate/chitosan/tripolyphosphate (TPP) for SM nanoparticles preparation was 2/1.2/2/0.8 mg mL(-1). Through calculation, the optimal concentrations of dextran sulphate are 2.5 mg mL(-1)and 2.4 mg mL(-1) for 2mg mL(-1) gentamicin and tobramycin, respectively (Table 1). The resulting AG chitosan nanoparticles had a high drug incorporation efficacy with particle sizes in the nanometre range. The in vitro drug release studies showed that more than 60% drug is retained inside the nanoparticles in pH 1.2 buffer after 6 h. The preliminary in vivo results indicated that oral SM chitosan nanoparticles induced one log 10 reduction (p<0.01) in growth of the bacilli and were as effective as subcutaneously injected aqueous SM solution at the same concentration (100 mg kg(-1)). Conclusion. Dextran sulphate can significantly increase AG incorporation into the chitosan nanoparticles. The concentration of each component was critical in preparing AG-loaded chitosan nanoparticles. The chitosan nanoparticles designed in this study may provide a promising oral drug delivery formulation for AG which usually, in tuberculosis treatment, is administrated as an injectible preparation.