Manipulating turn residues on de novo designed β-hairpin peptides for selectivity against drug-resistant bacteria

Important structural features of antimicrobial peptides towards specific activity: Trends in the development of efficient therapeutics

Proteins and peptides, as polypeptide chains, have usually got unique conformational structures for effective biological activity. Antimicrobial peptides (AMPs) are a group of bioactive peptides, which have been increasingly studied during recent years for their promising antibacterial, antifungal, antiviral and anti-inflammatory activity, as well as, other esteemed bioactivities. Numerous AMPs have been separated from a wide range of natural resources, or produced in vitro through chemical synthesis and recombinant protein expression. Natural AMPs have had limited clinical application due to several drawbacks, such as their short half-life due to protease degradation, lack of activity at physiological salt concentrations, toxicity to mammalian cells, and the absence of suitable methods of delivery for the AMPs that are targeted and sustained. The creation of synthetic analogs of AMPs would both avoid the drawbacks of the natural analogs and maintain or even increase the antimicrobial effectiveness. The structure-activity relationship of discovered AMPs or their derivatives facilitates the development of synthetic AMPs. This review discovered that the relationship between the activity of AMPs and their positive net charge, hydrophobicity, and amino acid sequence and the relationship between AMPs' function and other features like their topology, glycosylation, and halogenation.

Cathelicidin AS-12W Derived from the Alligator sinensis and Its Antimicrobial Activity Against Drug-Resistant Gram-Negative Bacteria In Vitro and In Vivo

Antimicrobial peptides (AMPs) have the potential to treat multidrug-resistant bacterial infections. Cathelicidins are a class of cationic antimicrobial peptides that are found in nearly all vertebrates. Herein, we determined the mature peptide region of Alligator sinensis cathelicidin by comparing its cathelicidin peptide sequence with those of other reptiles and designed nine peptide mutants based on the Alligator sinensis cathelicidin mature peptide. According to the antibacterial activity and cytotoxicity screening, the peptide AS-12W demonstrated broad-spectrum antibacterial activity and exhibited low erythrocyte hemolytic activity. In particular, AS-12W exhibited strong antibacterial activity and rapid bactericidal activity against carbapenem-resistant Pseudomonas aeruginosa in vitro. Additionally, AS-12W effectively removed carbapenem-resistant P. aeruginosa from blood and organs in vivo, leading to improved survival rates in septic mice. Furthermore, AS-12W exhibited good stability and tolerance to harsh conditions such as high heat, high salt, strong acid, and strong alkali, and it also displayed high stability toward trypsin and simulated gastric fluid (SGF). Moreover, AS-12W showed significant anti-inflammatory effects in vitro by inhibiting the production of proinflammatory factors induced by lipopolysaccharide (LPS). Due to its antibacterial mechanism against Escherichia coli, we found that this peptide could neutralize the negative charge on the surface of the bacteria and disrupt the integrity of the bacterial cell membrane. In addition, AS-12W has the ability to bind to the genomic DNA of bacteria and stimulate the production of reactive oxygen species (ROS) within bacteria, which is believed to be the reason for the good antibacterial activity of AS-12W. These results demonstrated that AS-12W exhibits remarkable antibacterial activity, particularly against carbapenem-resistant P. aeruginosa. Therefore, it is a potential candidate for antibacterial drug development.

Combating bacterial infections with host defense peptides: Shifting focus from bacteria to host immunity

The increasing prevalence of multidrug-resistant bacterial infections necessitates the exploration of novel paradigms for anti-infective therapy. Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), have garnered extensive recognition as immunomodulatory molecules that leverage natural host mechanisms to enhance therapeutic benefits. The unique immune mechanism exhibited by certain HDPs that involves self-assembly into supramolecular nanonets capable of inducing bacterial agglutination and entrapping is significantly important. This process effectively prevents microbial invasion and subsequent dissemination and significantly mitigates selective pressure for the evolution of microbial resistance, highlighting the potential of HDP-based antimicrobial therapy. Recent advancements in this field have focused on developing bio-responsive materials in the form of supramolecular nanonets. A comprehensive overview of the immunomodulatory and bacteria-agglutinating activities of HDPs, along with a discussion on optimization strategies for synthetic derivatives, is presented in this article. These optimized derivatives exhibit improved biological properties and therapeutic potential, making them suitable for future clinical applications as effective anti-infective therapeutics.

Multifunctional Antibacterial Nanonets Attenuate Inflammatory Responses through Selective Trapping of Endotoxins and Pro-Inflammatory Cytokines

Extracellular lipopolysaccharide (LPS) released from bacteria cells can enter the bloodstream and cause septic complications with excessive host inflammatory responses. Target-specific strategies to inactivate inflammation mediators have largely failed to improve the prognosis of septic patients in clinical trials. By utilizing their high density of positive charges, de novo designed peptide nanonets are shown to selectively entrap the negatively charged LPS and pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). This in turn enables the nanonets to suppress LPS-induced cytokine production by murine macrophage cell line and rescue the antimicrobial activity of the last-resort antibiotic, colistin, from LPS binding. Using an acute lung injury model in mice, it is demonstrated that intratracheal administration of the fibrillating peptides is effective at lowering local release of TNF-α and IL-6. Together with previously shown ability to simultaneously trap and kill pathogenic bacteria, the peptide nanonets display remarkable potential as a holistic, multifunctional anti-infective, and anti-septic biomaterial.

An optimized antimicrobial peptide analog acts as an antibiotic adjuvant to reverse methicillin-resistant Staphylococcus aureus

The misuse of antibiotics in animal protein production has driven the emergence of a range of drug-resistant pathogens, which threaten existing public health security. Consequently, there is an urgent need to develop novel antimicrobials and new infection treatment options to address the challenges posed by the dramatic spread of antibiotic resistance. Piscidins, a class of fish-specific antimicrobial peptides (AMPs), are regarded as promising therapies for biomedical applications. Progress towards potential analogs from the piscidin family has been hampered by unenforceable structural optimization strategies. Here, we leverage a strategy of bioinformatics analysis combined with molecular dynamics (MD) simulation to identify specific functional hotspots in piscidins and rationally design related analogues. As expected, this approach yields a potent and non-toxic PIS-A-1 that can be used as an antibiotic adjuvant to reverse methicillin-resistant Staphylococcus aureus (MRSA) pathogens. Remarkably, the structural optimization scheme and application strategy proposed here will contribute richer therapeutic options for the safe production of animal protein.

Membrane-active amino acid-coupled polyetheramine derivatives with high selectivity and broad-spectrum antibacterial activity

Membrane active antimicrobial peptide mimics have been considered as promising alternatives to antibiotics, which interact with bacterial cell membranes to combat bacteria and avoid the emergence of multidrug-resistant bacteria. Herein, a series of star-shaped and membrane-active cationic polyetheramides derived from amino acids, were synthesized via condensation of amino acids and polyetheamine (T403). The antibacterial and anti-biofilm activitives as well as the biocompatibility of these amino acids derived polyetheramides (AAPEAs) were investigated in detail. The star-shaped AAPEAs showed high-efficient and broad-spectrum antibacterial activity against the Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) pathogens. In addition, the antibacterial activity was significantly affected by the type of amino acid. L-Trp-T403, which was obtained from L-tryptophan and polyetheramine, exhibited the best antibacterial activity with the minimum inhibitory concentration (MIC) of 1 µg/mL against methicillin-resistant S. aureus (MRSA). Time-kill kinetics and multi-passage resistance tests experiments indicated that L-Trp-T403 could rapidly kill bacteria within 1 h. This compound also showed potent antibacterial activity against bacteria over many passages. Moreover, the AAPEAs exhibited outstanding stability and long-term antibacterial activity in complex mammalian body fluids, as well as good biocompatibility, low hemolytic activity, slight toxicity for mammalian cell (L929) and low in vivo toxicity. The antibacterial activity of L-Trp-T403 was found to be based on the disruption of bacterial membranes, which leads to the leakage of the internal cytoplasm. The AAPEAs possessed high antibacterial and anti-biofilm activity, thus, they are promising to be used as long-term and biofilm-disrupting antimicrobial agents. STATEMENT OF SIGNIFICANCE: The growing epidemic of MDR-bacteria is becoming a severe public health threat. Here, a series of amino acids derived polyetheramides (AAPEAs) with a star-shaped polyether amide scaffold was synthesized. The star-shaped AAPEAs displayed broad-spectrum antibacterial activity against Gram-positive, Gram-negative bacteria and drug-resistant bacteria MRSA. Notably, the star-shaped AAPEAs were stable under plasma conditions and showed outstanding stability and long-term antibacterial activity in various complex mammalian fluids. Moreover, these star-shaped AAPEAs not only inhibited the formation of biofilms but also disrupted the established biofilms. Furthermore, the membrane-active AAPEAs eradicated bacteria via the fast membrane lytic mechanism, thus plausibly overcoming the MDR effect. These results demonstrate that membrane-active AAPEAs can serve as emerging long-term and biofilm-disrupting antimicrobial agents to treat biofilm-related infections.