Designed Fabrication Of Silver Nanoparticle-based Acidity-sensitive Nanodrug Systems For Drug-resistant Bacterial Infection Therapy

Due to the abuse of traditional antibiotics and the lack of novel antibacterial drugs,drug-resistant bacterial strains have posed huge threat to the public health in the worldwide.Therefore,development of novel antibacterial agents for the treatment of drug-resistant pathogens induced infectious diseases and overcoming the bacterial drug resistance has emerged as an urgent issue.The formation of biofilm as well as the“planktonic bacteria to bacterial biofilm”life-circle are related to some sustained persistent bacterial infectious diseases.Biofilm formation is a lifestyle protecting the bacteria inside from the hazardous environment with diverse exopolymeric substrates,which can cause diffusion-reaction inhibition for antibiotics.Moreover,there is an inherent acidic microenvironment within the biofilm attributed to the metabolic activity of bacteria as well as the host immune response.Consequently,the drug resistance of the bacteria inside the biofilm is usually stronger than the planktonic bacteria.Moreover,biofilm formation is considered one of important mechanisms for the development of drug resistance of bacteria.Recent advances in pharmaceutics and nanotechnology provide promising alternatives to combat bacterial infectious diseases.Silver nanoparticles can inactive pathogens effectively via diverse approaches and have been widely used in daily life.Herein,according to the characteristics of the bacterial infection,especially the features of biofilm microenvironment,silver nanoparticle-based pH-sensitive nanodrug systems,whose antibacterial activity can be boosted in acidic condition through silver ions leaching or oxidase effect activation,are designed fabricated for drug-resistant bacterial infection therapy by affecting the“planktonic bacterial to bacterial biofilm”life-circle.We here firstly construct acidity-responsive silver nanoantibiotics(rAgNAs)by self-assembling of pH-sensitive polymer and ultrasmall silver nanoparticles(<5 nm)using the thin-film dispersion method via hydrophobic effect.Through the observation of the morphology,evaluation of the hydrodynamic radius and zeta potential,and analysis of the UV-vis absorption spectra,rAgNAs are demonstrated perform acidity-responsive structural transformation.In the neutral condition,rAgNAs are appeared as nanoassemblies of silver nanoparticles.When the environment turns to be acidic,rAgNAs go through disassembly process and release silver nanoparticles with rapid silver ions leaching.In vitro investigation confirmes the antibacterial and antibiofilm effect of rAgNAs,which can be further enhanced in the acidic microenvironment.Moreover,increased accumulation and penetration in the bacterial biofilm are also observed.Then the pyomyositis mice model is developed to evaluate the bactericidal effect of rAgNAs in vivo.During the therapeutic period,the appearance of the infected thighs,and the weights,mortality and clinical scores of the model mice are monitored.The results indicate that the rAgNAs treatment can suppress the progeression of the disease and increase the survival rate.At the end of the therapy,the assessment results of bacterial amount in the infected site and the serum TNF-αlevel imply the therapeutic effect of rAgNAs in vivo.In addition,the biocompatibility of rAgNAs is verified through the pathological assessment of the sections of the major organs collected from the mice after treatment.Apart from the strategy of ions leaching,some inorganic nanomaterials,including silver nanoparticles,are found to have enzymatic activity,such as oxidase and peroxidase,and can be utilized for antibacterial application through generation of reactive oxygen species.By controlled modulation of the ligands,the reactive activity can be tuned via changing the exposure condition of the active site in the surface of these organic nanoparticles.Hence,pH-sensitive polymers are replaced with pH-sensitive ligand with shorter chain length and pluoronic F127 to construct acidity-responsive silver nanozymes(Ag(R)).In the neutral condition,Ag(R)are appeared as nanoassemblies of silver nanoparticles with inhibited oxidase activity due to the shielding effect of the ligands.When the environment turns to be acidic,the pluoronic F127 is removed and Ag(R)go through disassembly process.The oxidase activity is switched on due to the decreased shielding effect.In vitro investigation confirmes that Ag(R)can significantly affect the“planktonic bacteria to bacterial biofilm”life-circle.Especially,the biofilm eradicating capacity of Ag(R)is much stronger than the Ag~+with same[Ag]equivalence.In addition,according to the results of the combined effect of Ag(R)with antibiotic(ampicillin,penicillin,and streptomycin)evaluated via chessboard method,Ag(R)can increase the drug sensitivity of methicillin-resistant Staphylococcus aureus to these three kinds of antibiotics.Interestingly,significant synergetic antibacterial effect of Ag(R)withβ-lactam antibiotics can be observed while silver ions don’t have such effect.Then the skin bacterial infection mice model is developed to evaluate the therapeutic effect of combined application of Ag(R)and ampicillin in vivo.The results reveal that the combined application of Ag(R)and ampicillin can significantly reduce the bacterial amount in the infected skin and accelerate the healing process.Subsequently,the mechanism study indicates that the acidity-responsive oxidase activity of Ag(R)can increase the bacterial membrane potential and thus influence the secretion of exopolymeric substances.Therefore,Ag(R)presents typical advantages in inhibiting biofilm formation as well as biofilm eradication.Besides,the change of physiological function of bacterial membrane affected by the membrane potential might be the reason of the significant synergetic antibacterial effect of Ag(R)withβ-lactam antibiotics which acting sites are on the bacterial membrane.In order to combat drug-resistant bacterial infection,according to the characteristics of the bacterial infection,especially the features of biofilm micronenvironment,this study utilizes the strategy of activity modulation by the pH responsive structural transformation,and constructs silver nanoparticle-based pH-sensitive nanodrug systems,whose antibacterial activity can be boosted in acidic condition through silver ions leaching or oxidase effect activation.Based on the proposed selective bactericidal effect avtivation in the acidic microenvironmt of bacterial infectious sites,this study provides a promising strategy as well as successful examples for the further development of antibacterial nanomedicines.