Fabrication of Supramolecular Antibacterial Nanofibers with Membrane-Disruptive Mechanism

Novel β-Hairpin Antimicrobial Peptide Containing the β-Turn Sequence of -NG- and the Tryptophan Zippers Facilitate Self-Assembly into Nanofibers, Exhibiting Excellent Antimicrobial Performance

Antimicrobial peptides (AMPs) have emerged as promising agents to combat the antibiotic resistance crisis due to their rapid bactericidal activity and low propensity for drug resistance. However, AMPs face challenges in terms of balancing enhanced antimicrobial efficacy with increased toxicity during modification processes. In this study, de novo d-type β-hairpin AMPs are designed. The conformational transformation of self-assembling peptide W-4 in the environment of the bacterial membrane and the erythrocyte membrane affected its antibacterial activity and hemolytic activity and finally showed a high antibacterial effect and low toxicity. Furthermore, W-4 displays remarkable stability, minimal occurrence of drug resistance, and synergistic effects when combined with antibiotics. The in vivo studies confirm its high safety and potent wound-healing properties at the sites infected by bacteria. This study substantiates that nanostructured AMPs possess enhanced biocompatibility. These advances reveal the superiority of self-assembled AMPs and contribute to the development of nanoantibacterial materials.

Hierarchical assembly of tryptophan zipper peptides into stress-relaxing bioactive hydrogels

Soft materials in nature are formed through reversible supramolecular assembly of biological polymers into dynamic hierarchical networks. Rational design has led to self-assembling peptides with structural similarities to natural materials. However, recreating the dynamic functional properties inherent to natural systems remains challenging. Here we report the discovery of a short peptide based on the tryptophan zipper (trpzip) motif, that shows multiscale hierarchical ordering that leads to emergent dynamic properties. Trpzip hydrogels are antimicrobial and self-healing, with tunable viscoelasticity and unique yield-stress properties that allow immediate harvest of embedded cells through a flick of the wrist. This characteristic makes Trpzip hydrogels amenable to syringe extrusion, which we demonstrate with examples of cell delivery and bioprinting. Trpzip hydrogels display innate bioactivity, allowing propagation of human intestinal organoids with apical-basal polarization. Considering these extensive attributes, we anticipate the Trpzip motif will prove a versatile building block for supramolecular assembly of soft materials for biotechnology and medicine.

Broad-spectrum hybrid antimicrobial peptides derived from PMAP-23 with potential LPS binding ability

Antimicrobial peptides, as an integral part of the innate immune system, kill bacteria through a special mechanism of action, making them less susceptible to drug resistance. However, Lipopolysaccharide (LPS) as the permeation barrier on the bacterial membrane, inhibits the antibacterial activity of antimicrobial peptides and triggers the inflammatory response. GWKRKRFG is an LPS binding sequence with a β-boomerang motif that can be linked to antimicrobial peptides to enhance their LPS affinity and reduce the possibility of LPS-induced inflammatory responses. In this study, a series of hybrid peptides were designed by conjugating the reported LPS binding sequence to the C-/N-terminal sequences of the natural porcine antimicrobial peptide PMAP-23 to increase the LPS affinity of peptides. Among all the designed hybrid peptides, 4R-PP-G8 showed the best antibacterial activity, nonhemolytic activity, and excellent cell selectivity. The presence of LPS not only induced the secondary structure transformation of 4R-PP-G8 from a random structure to an α-helical structure but also reduced the antibacterial activity of 4R-PP-G8 in a dose-dependent manner, indicating the excellent binding ability of 4R-PP-G8 to LPS. The LPS/LTA binding assay further verified the interaction between the peptide and LPS. The membrane permeability test verified that 4R-PP-G8 possessed a strong capability to penetrate the bacterial membrane after interacting with LPS. More direct membrane disruption was observed under FE-SEM and TEM. In conclusion, we provided a simple and efficient method to improve the LPS binding ability of antimicrobial peptides and enhance their antimicrobial activity, resulting in the peptide 4R-PP-G8 with clinical application potential.

Self-Assembly of Antimicrobial Peptide-Based Micelles Breaks the Limitation of Trypsin

Targeting the limitation of antimicrobial peptides (AMPs) application in vivo, self-assembled AMPs library with specific nanostructures is expected to gradually overtake monomer AMPs libraries in the future. Peptide polymers are fascinating self-assembling nanoscale structures that have great advantage in biomedical applications because of their satisfactory biocompatibility and versatile properties. Herein, we describe a strategy for inducing the self-assembly of T9W into nanostructured antimicrobial micelles with evidently improved pharmacological properties, that is, PEGylation at the C-terminal of T9W (CT9W₁₀₀₀), an antibacterial biomaterial that self-assembles in aqueous media without exogenous excipients, has been developed. Compared with parental molecular, the CT9W₁₀₀₀ is more effective against Pseudomonas aeruginosa, and its antibacterial spectrum had also been broadened. Additionally, CT9W₁₀₀₀ micelles had higher stability under salt ion, serum, and acid-base environments. Importantly, the self-assembled structure is highly resistant to trypsin degradation, probably allowing T9W to be applied in clinical settings in the future. Mechanistically, by acting on membranes and through supplementary bactericidal mechanisms, CT9W₁₀₀₀ micelles contribute to the antibacterial process. Collectively, CT9W₁₀₀₀ micelles exhibited good biocompatibility in vitro and in vivo, resulting in highly effective treatment in a mouse acute lung injury model induced by P. aeruginosa PAO1 without drug resistance. These advances may profoundly accelerate the clinical transformation of T9W and promote the development of a combination of peptide-based antibiotics and PEGylated nanotechnology.

Peptide–Polymer Conjugates: A Promising Therapeutic Solution for Drug-Resistant Bacteria

By 2050, it is estimated that 10 million people will die of drug-resistant bacterial infection caused by antibiotic abuse. Antimicrobial peptide (AMP) is widely used to prevent such circumstances, for the positively charged AMPs can kill drug-resistant bacteria by destroying negatively charged bacterial cell membrane, and has excellent antibacterial efficiency and low drug resistance. However, due to the defects in low in vivo stability, easy degradation, and certain cytotoxicity, its practical clinical application is limited. The emergence of peptide–polymer conjugates (PPC) helps AMPs overcome these shortcomings. By combining with functional polymers, the positive charge of AMPs is partially shielded, and its stability and water solubility are improved, so as to prolong the in vivo circulation time of AMPs and reduce its cytotoxicity. At the same time, the self-assembly ability of PPC enables it to assemble into different nanostructures to undertake specific antibacterial tasks. At present, PPC is mainly used in wound dressing, bone tissue repair, antibacterial coating of medical devices, nerve repair, tumor treatment, and oral health maintenance. In this study, we summarize the structure, synthesis methods, and the clinical applications of PPC, so as to present the current challenges and discuss the future prospects of antibacterial therapeutic materials.

Optimized proteolytic resistance motif (DabW)-based U1-2WD: A membrane-induced self-aggregating peptide to trigger bacterial agglutination and death

The biggest application bottleneck of antimicrobial peptides (AMPs) is the low oral bioavailability caused by the poor stability of digestive enzymes in the gastrointestinal tract. However, the research methods and evaluation criteria of available studies about anti-proteolytic strategies are not uniform and far from the actual environment in vivo. Here, we developed a research system and evaluation criteria for proteolytic resistance and systematically evaluated the effectiveness of different strategies for improving the protease stability of AMPs on the same platform for the first time. After a comprehensive analysis, Dab modification is identified as the most effective strategy to improve the trypsin stability of AMPs. By further modulating the proteolytic resistance optimization motif (DabW)_n, U1-2WD is obtained with ideal stability and antimicrobial properties in vivo and in vitro. Notably, U1-2WD has a unique antibacterial mechanism, which forms amorphous aggregates in the bacteria environment to trigger the agglutination of bacterial cells to prevent bacterial escape. It then kills bacteria by disrupting bacterial membranes and inhibiting bacterial energy metabolism. Overall, our work has led to a new understanding of the effectiveness of proteolytic resistance strategies and accelerated the development of anti-proteolytic AMPs to combat multidrug-resistant bacterial infections. STATEMENT OF SIGNIFICANCE: We developed research system and evaluation criteria for proteolytic resistance and systematically evaluated the effectiveness of different strategies for improving protease stability of AMPs on the same platform for the first time. we found effective strategies to resist trypsin hydrolysis: modification with backbone (β-Arg), D-enantiomer (D-Arg) and L-2,4-diaminobutanoic acid (Dab). Further, the proteolytic resistance optimization motif (DabW)n was designed. When n=3, derivative U1-2WD was obtained with desirable stability and antimicrobial properties in vivo and in vitro. Notably, U1-2WD has a unique antibacterial mechanism, which can self-aggregate into amorphous aggregates in the bacteria environment to mediate the agglutination and sedimentation of bacterial cells to prevent bacterial escape, and then kill bacteria by destroying bacterial membranes and inhibiting bacterial energy metabolism.

The design of cell-selective tryptophan and arginine-rich antimicrobial peptides by introducing hydrophilic uncharged residues

Antimicrobial peptides (AMPs) are considered to be powerful weapons in the fight against traditional antibiotic resistance due to their unique membrane-disruptive mechanism. The combination of traditional and classical hydrophobic tryptophan (W) residues and hydrophilic charged arginine (R) residues is considered as the first choice for the minimalist design of AMPs due to its potent performance in antibacterial activity. However, some W- and R-rich AMPs that are not rationally designed and contain excessive repeats of W and R residues may cause severe cytotoxicity and hemolysis. To address this issue, we designed the (WRX)_n (where X = hydrophilic uncharged amino residues; n = number of repeat units) series engineered peptides with high cell selectivity by introducing hydrophilic uncharged threonine (T), serine (S), glutamine (Q) or asparagine (N) residues into the minimalist design of W- and R-rich AMPs. The results showed that the introduction of these hydrophilic uncharged amino residues, especially T residues, significantly improved the cell selectivity of the W- and R-rich engineered peptides. Among (WRX)_n series engineered peptides, T6 presents a mixture structure of β-turn and α-helix. It has broad spectrum and potent antibacterial activity (no activity against probiotics), good biocompatibility, high selectivity index, strong tolerance (physiological salts, serum acid, alkali, and heat conditions), rapid and efficient time-kill kinetics, and no tendency of resistance. Studies on antibacterial mechanism show that T6 exert antibacterial activity mainly by disrupting bacterial cell membrane and inducing the accumulation of reactive oxygen species in bacterial cells. Furthermore, T6 exhibited potent antibacterial and anti-inflammatory capabilities in vivo in a mouse peritonitis-sepsis model infected with Escherichia coli. In conclusion, our study confirms an effective strategy for the minimalist design of highly cell selective W- and R-rich AMPs by introducing hydrophilic uncharged T residues, which may trigger widespread attention to hydrophilic uncharged amino acid residues, including T residues, and provide new insights into the design of peptide-based antibacterial biomaterials. STATEMENT OF SIGNIFICANCE: We have introduced hydrophilic uncharged T, S, Q or N residues into the minimalist design of W- and R-rich engineered peptides and found that the introduction of these hydrophilic uncharged amino residues, especially the T residues, can significantly improve the cell selectivity of W- and R-rich engineered peptides. The target compound T6 showed potent antibacterial activity, high cell selectivity, strong tolerance, good in vivo efficacy and killed bacteria through multiple mechanisms mainly membrane-disruptive. These findings may spark widespread interest in hydrophilic uncharged amino acid residues, and provide new insights into the design of peptide-based antimicrobial biomaterials.

Designing Self-Assembling Chimeric Peptide Nanoparticles with High Stability for Combating Piglet Bacterial Infections

As a novel type of antibiotic alternative, peptide-based antibacterial drug shows potential application prospects attributable to their unique mechanism for lysing the membrane of pathogenic bacteria. However, peptide-based antibacterial drugs suffer from a series of problems, most notably their immature stability, which seriously hinders their application. In this study, self-assembling chimeric peptide nanoparticles (which offer excellent stability in the presence of proteases and salts) are constructed and applied to the treatment of bacterial infections. In vitro studies are used to demonstrate that peptide nanoparticles NPs1 and NPs2 offer broad-spectrum antibacterial activity and desirable biocompatibility, and they retain their antibacterial ability in physiological salt environments. Peptide nanoparticles NPs1 and NPs2 can resist degradation under high concentrations of proteases. In vivo studies illustrate that the toxicity caused by peptide nanoparticles NPs1 and NPs2 is negligible, and these nanoparticles can alleviate systemic bacterial infections in mice and piglets. The membrane permeation mechanism and interference with the cell cycle differ from that of antibiotics and mean that the nanoparticles are at a lower risk of inducing drug resistance. Collectively, these advances may accelerate the development of peptide-based antibacterial nanomaterials and can be applied to the construction of supramolecular nanomaterials.