Cathelicidin-trypsin inhibitor loop conjugate represents a promising antibiotic candidate with protease stability

Peptide-based strategies for overcoming biofilm-associated infections: a comprehensive review

Biofilms represent resilient microbial communities responsible for inducing chronic infections in human subjects. Given the escalating challenges associated with antibiotic therapy failures in clinical infections linked to biofilm formation, a peptide-based approach emerges as a promising alternative to effectively combat these notoriously resistant biofilms. Contrary to conventional antimicrobial peptides, which predominantly target cellular membranes, antibiofilm peptides necessitate a multifaceted approach, addressing various "biofilm-specific factors." These factors encompass Extracellular Polymeric Substance (EPS) degradation, membrane targeting, cell signaling, and regulatory mechanisms. Recent research endeavors have been directed toward assessing the potential of peptides as potent antibiofilm agents. However, to translate these peptides into viable clinical applications, several critical considerations must be meticulously evaluated during the peptide design process. This review serves to furnish an all-encompassing summary of the pivotal factors and parameters that necessitate contemplation for the successful development of an efficacious antibiofilm peptide.

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.

Cath-DM-NT, a peptide derived from the skin of Duttaphrynus melanostictus, shows dual lectin-like and antioxidant activity

Chansu, a mixture extracted from Duttaphrynus melanostictus or Bufo gargarizans Cantor, is a traditional Chinese medicine with a broad range of medical applications. However, the peptides/proteins in it have not received adequate attention. Herein, a Cathelicidin-DM-derived peptide named Cath-DM-NT was identified from the skin of D. melanostictus. Previous studies have shown that Cathelicidin-DM has significant antibacterial activity, while Cath-DM-NT has no antibacterial activity. In this study, Cath-DM-NT is found to have lectin-like activity which can agglutinate erythrocytes and bacteria, and bind to lipopolysaccharide (LPS). In addition, Cath-DM-NT has antioxidant activity, which can scavenge 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and nitric oxide (NO) radicals and reduce Fe3+. Consistently, Cath-DM-NT can protect PC12 cells from H2O2-induced oxidative damage and carrageenan-induced paw edema, reduce malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation, and restore superoxide dismutase (SOD) and glutathione (GSH) levels. Our study suggests that Cath-DM-NT can serve as a lead compound for the development of drugs with dual lectin and antioxidant effects.

Antibacterial action mechanisms and mode of trypsin inhibitors: a systematic review

This systematic review (SR) aimed to gather studies describing the antibacterial action mechanisms and mode of trypsin inhibitors. The review protocol was registered (PROSPERO: CRD42020189069). Original articles resulting from studies in animal models, in bacterial culture, and using cells that describe antibacterial action of trypsin inhibitor-type peptides or proteins were selected in PubMed, Science Direct, Scopus, Web of Science, BVS, and EMBASE. The methodological quality assessment was performed using the PRISMA and OHAT tool. 2382 articles were retrieved, 17 of which were eligible. Four studies demonstrated the action mechanism directly on the bacterial membrane, and the fifth study on endogenous proteases extracted from the bacteria themselves. The antibacterial action mode was presented in the other studies, which can generate bacteriostatic or bactericidal effects without describing the mechanisms. This study generated information to enable new preclinical or clinical studies with molecules contributing to public health.

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.

Antimicrobial property of Pichia pastoris-derived natto peptide against foodborne bacteria and its preservative potential to maintain pork quality during refrigerated storage

Pork spoilage caused by foodborne bacteria contamination always leads to substantial economic loss in the meat industry. The toxicity and drug resistance of chemical preservatives have raised public concerns about their safety and stability. In this study, natto peptide from Pichia pastoris was prepared using DNA recombinant technology. It showed an excellent antibacterial effect against Gram-positive and -negative bacteria, with minimum inhibitory concentrations (MICs) ranging from 6 to 30 μg/ml. Of note, natto peptide exhibited low cytotoxicity and hemolytic activity. The application of natto peptide on pork during refrigerated storage dramatically decreased the growth of Staphylococcus spp., Escherichia spp., and Pseudomonas spp. The bactericidal properties remained in force when natto peptide was used in pork models contaminated with artificial bacteria. Moreover, the application of natto peptide (90 μg/ml) inhibited the increase in pH variation and drip loss, decreased the generation of total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS), and maintained a high sensory quality score during pork storage. These results implied that P. pastoris-derived natto peptide could extend the storage time of pork, and it has the potential to be a promising antiseptic biopreservative to replace chemical preservatives.

Potent antibacterial and antibiofilm activities of TICbf-14, a peptide with increased stability against trypsin

The poor stability of peptides against trypsin largely limits their development as potential antibacterial agents. Here, to obtain a peptide with increased trypsin stability and potent antibacterial activity, TICbf-14 derived from the cationic peptide Cbf-14 was designed by the addition of disulfide-bridged hendecapeptide (CWTKSIPPKPC) loop. Subsequently, the trypsin stability and antimicrobial and antibiofilm activities of this peptide were evaluated. The possible mechanisms underlying its mode of action were also clarified. The results showed that TICbf-14 exhibited elevated trypsin inhibitory activity and effectively mitigated lung histopathological damage in bacteria-infected mice by reducing the bacterial counts, further inhibiting the systemic dissemination of bacteria and host inflammation. Additionally, TICbf-14 significantly repressed bacterial swimming motility and notably inhibited biofilm formation. Considering the mode of action, we observed that TICbf-14 exhibited a potent membrane-disruptive mechanism, which was attributable to its destructive effect on ionic bridges between divalent cations and LPS of the bacterial membrane. Overall, TICbf-14, a bifunctional peptide with both antimicrobial and trypsin inhibitory activity, is highly likely to become an ideal candidate for drug development against bacteria.

The Impact of Lung Proteases on Snake-Derived Antimicrobial Peptides

Respiratory infections are a leading cause of global morbidity and mortality and are of significant concern for individuals with chronic inflammatory lung diseases. There is an urgent need for novel antimicrobials. Antimicrobial peptides (AMPs) are naturally occurring innate immune response peptides with therapeutic potential. However, therapeutic development has been hindered by issues with stability and cytotoxicity. Availing of direct drug delivery to the affected site, for example the lung, can reduce unwanted systemic side effects and lower the required dose. As cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) lungs typically exhibit elevated protease levels, the aim of this study was to assess their impact on snake-derived AMPs. Peptide cleavage was determined using SDS-PAGE and antimicrobial and anti-inflammatory activities of neutrophil elastase (NE)-incubated peptides were assessed using a radial diffusion assay (RDA) and an in vitro LPS-induced inflammation model, respectively. Although the snake-derived AMPs were found to be susceptible to cleavage by lung proteases including NE, several retained their function following NE-incubation. This facilitated the design of novel truncated derivatives that retained functionality following NE incubation. Snake-derived AMPs are tractable candidate treatments for use in environments that feature elevated NE levels, such as the CF airways.

Potent antibacterial activity of MSI-1 derived from the magainin 2 peptide against drug-resistant bacteria

The structural modification of existing AMPs is an effective strategy to develop antimicrobial agents with high-efficiency, low-cost and low-toxicity antimicrobial agents. Methods: Here, we truncated 14-amino-acids at the N-terminus of MSI-78 to obtain MSI and further modified MSI to obtain four peptide analogs: MSI-1, MSI-2, MSI-3 and MSI-4. These peptide mutants were evaluated regarding their antibacterial activity against various sensitive or resistant bacteria; toxicity against mammalian cells or mice; and stability against violent pH, temperature variations and high NaCl concentrations. Finally, we also elucidated the possible mechanisms underlying its mode of action. Results: The results showed that MSI-1 and MSI-3 displayed activity that was superior to that of MSI-78 with MICs of 4-16 μg/ml and MBCs of 8-64 μg/ml, respectively, especially against drug-resistant bacteria, due to the increase in percent helicity and amphiphilicity. However, MSI-3, with higher hydrophobicity and antibacterial activity, had a relatively higher hemolysis rate and toxicity than MSI-1. MSI-1 exerted rapid bactericidal activity and effectively improved the survival rate and wound closure in penicillin-resistant E. coli-infected mice by eliminating bacterial counts in mouse organs or subeschar, further inhibiting the systemic dissemination of bacteria. Additionally, MSI-1 displayed perfect stability against violent pH, temperature variations and high NaCl concentrations and has the ability to circumvent the development of drug resistance. In terms of the mode of action, we found that at the super-MIC level, MSI-1 exhibited direct antimicrobial activity by disrupting the integrity of the bacterial cell membrane, while at the sub-MIC level, it bound to bacterial DNA to inhibit DNA replication and protein expression and ultimately disrupted bacterial biological function. Conclusions: This novel peptide MSI-1 could be a potential candidate for drug development against infection induced by drug-resistant bacteria.

Discovery and Rational Design of a Novel Bowman-Birk Related Protease Inhibitor

Anuran amphibian skin secretions are a rich source of peptides, many of which represent novel protease inhibitors and can potentially act as a source for protease inhibitor drug discovery. In this study, a novel bioactive Bowman-Birk type inhibitory hexadecapeptide of the Ranacyclin family from the defensive skin secretion of the Fukien gold-striped pond frog, Pelophlax plancyi fukienesis, was successfully isolated and identified, named PPF-BBI. The primary structure of the biosynthetic precursor was deduced from a cDNA sequence cloned from a skin-derived cDNA library, which contains a consensus motif representative of the Bowman-Birk type inhibitor. The peptide was chemically synthesized and displayed a potent inhibitory activity against trypsin (Ki of 0.17 µM), as well as an inhibitory activity against tryptase (Ki of 30.73 µM). A number of analogues of this peptide were produced by rational design. An analogue, which substituted the lysine (K) at the predicted P₁ position with phenylalanine (F), exhibited a potent chymotrypsin inhibitory activity (Ki of 0.851 µM). Alternatively, a more potent protease inhibitory activity, as well as antimicrobial activity, was observed when P¹⁶ was replaced by lysine, forming K¹⁶-PPF-BBI. The addition of the cell-penetrating peptide Tat with a trypsin inhibitory loop resulted in a peptide with a selective inhibitory activity toward trypsin, as well as a strong antifungal activity. This peptide also inhibited the growth of two lung cancer cells, H460 and H157, demonstrating that the targeted modifications of this peptide could effectively and efficiently alter its bioactivity.

Design and Assessment of Anti-Biofilm Peptides: Steps Toward Clinical Application

Highly antibiotic resistant, microbial communities, referred to as biofilms, cause various life-threatening infections in humans. At least two-thirds of all clinical infections are biofilm associated, and antibiotic therapy regularly fails to cure patients. Anti-biofilm peptides represent a promising approach to treat these infections by targeting biofilm-specific characteristics such as highly conserved regulatory mechanisms. They are being considered for clinical application and we discuss here key factors in discovery, design, and application, particularly the implementation of host-mimicking conditions, that are required to enable the successful advancement of potent anti-biofilm peptides from the bench to the clinic.

Python Cathelicidin CATHPb1 Protects against Multidrug-Resistant Staphylococcal Infections by Antimicrobial-Immunomodulatory Duality

Multidrug-resistant Staphylococcus aureus, including MRSA (methicillin-resistant) and VRSA (vancomycin-resistant), causes serious healthcare-associated infections, even sepsis and death. Here, we identified six novel cathelicidins (CATHPb1-6) from Python bivittatu, and CATHPb1 displayed the best in vitro pharmacological and toxicological profile. We further show that CATHPb1 exhibited evident protection in mice MRSA/VRSA infection models, given either 24 h before or 4 h after infection. The protection was all effective through different administration routes, but was blocked by in vivo depletion of monocyte/macrophages or neutrophils. CATHPb1 can rapidly and massively modulate macrophages/monocytes and neutrophils trafficking to the infection site, and potentiate their bactericidal functions. Meanwhile, CATHPb1 remarkably augmented neutrophil-mediated bacteria killing by facilitating neutrophil extracellular traps (NETs) formation and preventing its degradation. Acting through MAPKs and NF-κB pathways, CATHPb1 selectively enhanced the levels of chemokines while reducing the production of pro-inflammatory cytokines without undesirable toxicities. The much improved serum half-life and stabilities confer CATHPb1 an excellent prospect to become a novel therapeutic agent against multidrug-resistant staphylococcal infections.

As-CATH4 and 5, two vertebrate-derived natural host defense peptides, enhance the immuno-resistance efficiency against bacterial infections in Chinese mitten crab, Eriocheir sinensis

Host defense peptides (HDPs), a class of conserved components of animal innate immune system, possess direct antimicrobial activities against invading pathogens and broadly participate in boosting and modulating host immune responses. Cathelicidins is an important family of HDPs that has been identified exclusively in vertebrates. Considering the relatively conserved innate immune system between invertebrates and vertebrates, it is speculated that HDPs from vertebrates may also possess modulating functions on invertebrate innate immune system. In the present study, two novel cathelicidins (As-CATH4 and 5), which had been identified from the Chinese alligator in our previous study, were employed to investigate their functions as novel peptide immunostimulants in Chinese mitten crab. As-CATH4 and 5 exhibited potent, broad-spectrum, and rapid antimicrobial activities against all the tested aquatic pathogenic bacteria. Unlike traditional antibiotics, they target on bacterial cell membrane, induce membrane permeabilization and cell disruption, and ultimately result in cell death. The antimicrobial effect is far more rapid than traditional antibiotics. Therefore they are unlikely to induce bacteria resistance. After the crabs were administered with As-CATH4 and 5, the activities of lysozyme, acid phosphatase and alkaline phosphatase were significantly enhanced, which indicated that the immune system of crabs could be activated by As-CATH4 and 5. In bacteria challenge test, As-CATH4 and 5 could significantly decrease the bacterial numbers in crabs, and increase the survival rates of crabs in both pre-stimulation and co-stimulation groups. All of the results above indicated the great potential of As-CATH4 and 5 as novel peptide immunostimulants in the crab aquaculture.