pH-responsive chitosan nanoparticles from a novel twin-chain anionic amphiphile for controlled and targeted delivery of vancomycin.

The design and synthesis of novel pH-responsive nanoantibiotics is an emerging research area to address the antibiotic resistance crisis. The purpose of this study was therefore to synthesize a new anionic gemini surfactant (AGS) that could result in the formulation of pH-responsive chitosan nanoparticles (CSNPs) to treat methicillin-resistant Staphylococcus aureus (MRSA) infections. The coupling of oleic acid with 2,2-dimethyl-5,5-bis(hydroxymethyl)-1,3-dioxane and subsequent deprotection followed by a reaction with succinic anhydride and sodium bicarbonate yielded AGS. Critical micelle concentration (CMC) was determined using conductometry and in vitro cytotoxicity was performed using a MTT assay. Vancomycin loaded CSNPs containing AGS (DL_CSSNPs) were prepared by ionotropic gelation of chitosan with pentasodium tripolyphosphate. CSNPs were characterized for size, polydispersity index (PDI), zeta potential (ZP), entrapment efficiency, surface morphology, in vitro drug release and in vitro antibacterial activity (at pH 6.5 and 7.4). Results from the in vitro antibacterial activity were further supported by an in vivo study using a mice skin infection model. The CMC of AGS was found to be 1.3mM/L and it was non-toxic. The DL_CSSNPs were spherical with size, PDI and ZP of 220.57±5.9nm, 0.299±0.004 and 21.9±0.9mV respectively. An increase in the vancomycin release from the DL_CSSNPs was observed at pH 6.5 compared to pH 7.4. The minimum inhibitory concentration values at pH 6.5 and 7.4 against MRSA were 7.81 and 62.5μg/ml respectively. In vivo antibacterial activity showed that the MRSA burden in mice treated with DL_CSSNPs was reduced by almost 8-fold compared to those treated with pure vancomycin.