ROS-Responsive Poly(α-l-lysine)-Based Nanoparticles Loaded with Doxycycline Combat Oxidative Stress and Bacterial Infection

Bacterial pneumonia is one of the major threats in clinical practice, and the reactive oxygen species (ROS) generated at the infection site can exacerbate the damage. Currently, conventional antibiotic therapies have low utilization, and their excessive use can result in substantial toxicity. Nanocarrier systems provide an ideal approach for treating bacterial infection by facilitating more efficient utilization of antibiotics. In this study, the ROS-responsive amphiphilic nanoparticles (NPs) are developed and used to encapsulate the antibiotic doxycycline (DOXY) to achieve antibacterial and antioxidant functionalities. The NPs are prepared from poly(α-l-lysine) (α-PLL) and phenylboronic acid pinacol ester simultaneously conjugated carbonyldiimidazole (abbreviated as CDIPB). The phenylboronic acid ester groups on CDIPB could react with excessive ROS to suppress oxidative damage at the infection site. The ROS-responsive degradation of CDIPB also facilitates the rapid release of internal DOXY, effectively killing the accumulated bacteria. Additionally, in vitro cell experiments demonstrate the good biocompatibility of the NPs. These results suggest that the ROS-responsive amphiphilic nanoparticles can serve as a novel nanoplatform for the treatment of bacterial pneumonia.

Constructing antibacterial polymer nanocapsules based on pyridine quaternary ammonium salt

Excessive use of antibiotics accelerates the development and spread of drug-resistant strains, which is a huge challenge for the field of medical health worldwide. Quaternary ammonium salt polymers are considered to be membrane-active bactericidal groups with vast potential to control bacterial infections and inhibit drug resistance. Herein, we report on the creative synthesis and characterization of novel antimicrobial polymer nanocapsules based on pyridine quaternary ammonium salt. The antimicrobial polymer nanocapsules were formed by reaction of C₃ symmetrical rigid monomer 2,4,6‑tris(4‑pyridyl)‑1,3,5‑triazine (TPT) and a flexible linker 1,2‑dibromoethane. The polymer nanocapsule was constructed as a cationic hollow sphere composed of a two-dimensional sheet whose main chain was formed by the pyridine quaternary ammonium salt, and a part of the bromide ion was adsorbed on the sphere. This hollow nanocapsule was characterized in detail by DLS, SEM, TEM, AFM, EDS and EA. When the cationic polymer nanocapsules are close to the Gram-negative Escherichia coli, the negatively charged phospholipid molecules in the bacterial membrane are attracted to the cationic surface and lead to rupture of cells. SEM confirmed the breakage of Escherichia coli membranes. The minimum inhibitory concentration was found to be 0.04 mg/mL, and the minimum bactericidal concentration was 0.1 mg/mL. Our experiments demonstrated that the adsorption of negatively charged phospholipid molecules on the surface of the pyridine quaternary ammonium salt polymer can kill Gram-negative bacteria without inserting quaternary ammonium salt hydrophobic groups into the cell membrane.

Antimicrobial Titanium Surface via Click-Immobilization of Peptide and Its in Vitro/Vivo Activity

The use of antimicrobial peptides (AMPs)-functionalized titanium implants is an efficient method for preventing bacterial infection. However, the attachment of AMPs to the surface of titanium implants remains a challenge. In this study, a "clickable" titanium surface was developed by using a silane coupling agent with an alkynyl group. The antimicrobial titanium implant was then constructed through the reaction between the "clickable" surface and azido-AMPs (PEG-HHC36:N₃-PEG₁₂-KRWWKWWRR) via click chemistry of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Such an antimicrobial titanium implant, with an AMP density of 897.4 ± 67.3 ng/cm² (2.5 ± 0.2 molecules per nm²) on the surface, exhibited good and stable antimicrobial activity, inhibited 90.2% of Staphylococcus aureus and 88.1% of Escherichia coli after 2.5 h of incubation, and even inhibited 69.5% of Staphylococcus aureus after 4 days of degradation. The CCK-8 assay indicated that the antimicrobial titanium implant exhibited negligible cytotoxicity to mouse bone mesenchymal stem cells. In vivo assay illustrated that this implant could kill 78.8% of Staphylococcus aureus after 7 days. This method has great potential for the preparation of antimicrobial titanium implants and the prevention of infections in the clinic.

Aggregation-Induced Emission Probe for Study of the Bactericidal Mechanism of Antimicrobial Peptides

Multidrug resistant bacterial infection has become one of the most serious threats to human health. Antimicrobial peptides (AMPs) have been identified as potential alternatives to antibiotics owing to their excellent bactericidal activity. However, the complicated bactericidal mechanism of AMPs is still poorly understood. Fluorescence imaging has many advantages in terms of dynamic monitoring, easy operation, and high sensitivity. In this study, we developed an aggregation-induced emission (AIE)-active probe AMP-2HBT by decorating the antimicrobial peptide HHC36 (KRWWKWWRR) with an AIEgen of 2-(2-hydroxyphenyl)benzothiazole (HBT). This AIE-active probe exhibited an excellent light-up fluorescence after binding with bacteria, enabling a real-time monitoring of the binding process. Moreover, a similar time-dependent bactericidal kinetics was observed for the AIE-active probe and HHC36 peptide, which indicated that the bactericidal activity of the peptide was not compromised by decorating with the AIEgen. The bactericidal mechanism of HHC36 peptide was further investigated by super-resolution fluorescence microscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM), which suggested that the probe tended to accumulate on the bacterial membrane and efficiently disrupt the membrane structure to kill both Gram-positive and -negative bacteria. This AIE-active probe thus provided a convenient tool to investigate the bactericidal mechanism of AMPs.

Synthesis, Self-Assembly, and Biomedical Applications of Antimicrobial Peptide-Polymer Conjugates

Antimicrobial peptides (AMPs) have been attracting much attention due to their excellent antimicrobial efficiency and low rate in driving antimicrobial resistance (AMR), which has been increasing globally to alarming levels. Conjugation of AMPs into functional polymers not only preserves excellent antimicrobial activities but reduces the toxicity and offers more functionalities, which brings new insight toward developing multifunctional biomedical materials such as hydrogels, polymer vesicles, polymer micelles, and so forth. These nanomaterials have been exhibiting excellent antimicrobial activity against a broad spectrum of bacteria including multidrug-resistant (MDR) ones, high selectivity, and low cytotoxicity, suggesting promising potentials in wound dressing, implant coating, antibiofilm, tissue engineering, and so forth. This Perspective seeks to highlight the state-of-the-art strategy for the synthesis, self-assembly, and biomedical applications of AMP-polymer conjugates and explore the promising directions for future research ranging from synthetic strategies, multistage and stimuli-responsive antibacterial activities, antifungi applications, and potentials in elimination of inflammation during medical treatment. It also will provide perspectives on how to stem the remaining challenges and unresolved problems in combating bacteria, including MDR ones.

Preparation of an antimicrobial surface by direct assembly of antimicrobial peptide with its surface binding activity

The designed antimicrobial peptide has surface binding activity onto titanium, gold, polymethyl methacrylate and hydroxyapatite substrates.

Novel monobactams utilizing a siderophore uptake mechanism for the treatment of gram-negative infections

Novel siderophore-linked monobactams with in vitro and in vivo anti-microbial activity against MDR Gram-negative pathogens are described.