Antibacterial Activities And Applications Of Gold Nanoparticles Modified With Phenylboronic Acid Derivatives

Bacterial infections pose serious threats to human health and life.The discovery of antibiotics effectively controlled the development of bacterial infections and drastically reduced the mortality of infectious diseases.With the intensification of the irregular use and abuse of antibiotics,the problem of clinical bacterial resistance has become increasingly serious.Although researchers have screened many small molecule libraries and conventional natural medicines,discovering antibiotics with new modes of action is still a daunting scientific challenge.Therefore,it is urgent to develop new antibiotics or explore new antibacterial strategies which are not prone to bacterial resistance.Among the existing antibacterial nanomaterials,gold nanom aterials have the advantages of high preparation efficiency,controllable size,low cytotoxicity and good biosafety.The main component of the bacterial wall is polysaccharides.Inspired by the easy combination of boronic acid groups and polysaccharides,w e design gold nanoparticles modified based on phenylboronic acid and its derivatives to improve the targeted adhesion and evaluate its antibacterial properties and safety in vivo and in vitro.The details of the project are listed as follows:Gold nanoparticles modified with phenylboronic acid and its derivatives are prepared by the method of reducing chloroauric acid with sodium borohydride and the gold nanoparticles have uniform size and can be stored stably.Adjusting the molar ratio of chloroauric acid to ligand and controlling the reaction time,reaction temperature and stirring speed to optimize the synthesis conditions.The microdilution method is used to investigate the antibacterial properties of the gold nanoparticles.The minimum inhibitory concentration of the mercaptophenylboronic acid modified gold nanoparticles against Staphylococcus aureus(S.a,Gram-positive bacteria)is 6μg/m L and the minimum inhibitory concentration of the aminophenylboronic acid modified gold nanoparticles against Escherichia coli(E.coli,Gram-negative bacteria)is 2μg/m L.The electron microscope results show that the gold nanoparticles adhere to the bacterial wall and locate at the cytosol area of the bacteria,indicating that gold nanoparticles can induce the disruption of the bacterial cell wall and cause bacteriolysis,due to the exposed boronic acid groups of the gold nanoparticles for the polysaccharides combination.To accelerate the clinical translation of antibacterial gold nanoparticles mentioned above,the safety of the system is evaluated in vitro and in vivo.The antibacterial gold nanoparticles(60μg/m L)have no effect on the growth state and proliferation number of cells evaluated by cell counting kit-8.The red blood cell contact test verified that 80μg/m L of antibacterial gold nanoparticles will not cause hemolysis.The acute toxicity and metabolism of gold nanoparticles are further evaluated.After injecting the gold nanoparticles in different volumes(200,600 or800μL)and different concentrations into mice for 72 hours,liver and kidney function and immune function of the mice are good,and al l organs of the mice have no obvious damage.These investigations provide important references for future in vivo infectious trials.The antibacterial wound dressing loaded with gold nanoparticles is prepared by electrospinning.The structural properties and therapeutic effects are evaluated.Mechanical properties tests show that the Young’s modulus and elongation at break of the dressing are 49.8MPa and 6.332%,respectively.The similar microstructure(500-600nm)to the extracellular matrix is conducive to cell adhesion and migration.The therapeutic effect of the antibacterial wound dressings is evaluated on the dermal infection model.The experimental results show that the incorporation of nanoparticles has an excellent antibacterial effect against multi-drug resistant bacteria and can effectively promote wound healing.The wound healing area ratio reach more than 98% in 14 days.Furthermore,the remodeled hair follicles and sebaceous glands are observed by tissue staining,indicating that the gold nanoparticle-loaded dressing can effectively combat bacterial infections and promote tissue remodeling.Aiming at the intra-abdominal infection disease with a wide variety of pathogenic bacteria,the effects of oral administration and in situ intraperitoneal administration on the disease are explored in the abdominal infection model.Taking advantage of the large absorption area of the peritoneal membrane and omentum,the broad-spectrum antibacterial gold nanoparticles co-modified by mercaptophenylboronic acid and aminophenylboronic acid can be directly absorbed into the blood.The plasma concentration reaches the maximum at 6 hours after intraperitoneal administration.After treated with antibacterial gold nanoparticles,the survival rate of sensitive S.a or E.coli and their multi-drug resistant strains infected mice after 72 hours is 100%.The reason why aminophenylboronic acid can reduce chloroauric acid in vivo to synthesize antibacterial gold nanoparticles is analyzed.Aminophenylboronic acid can synthesize gold nanoparticles stably in a strong acid environment(p H2)without adding reducing agents has been verified.After 5 minutes of oral administration,antibacterial particles are formed in the stomach and pass through the gastrointestinal barrier through th e blood circulation to reach the whole body,which are separated from the stomach and intestinal cavity at different time points.In the treatment of infections caused by Gram-negative bacteria,the survival rate is 100% after 72 hours,which verified the feasibility of treating abdominal infections.In summary,the gold nanoparticles modified by phenylboronic acid derivatives in this thesis have antibacterial effects and clear antibacterial mechanisms.The biosafety and metabolism in vitro and in vivo of the gold nanoparticles are better than common antibiotics.The treatment effect is excellent in the skin infections and abdominal infections models by oral administration and intraperitoneal administration.Therefore,it has potential application to become a new type of antibacterial nanomaterials.