Expression and Roles of Antimicrobial Peptides in Innate Defense of Airway Mucosa: Potential Implication in Cystic Fibrosis

© Copyright © 2020 Geitani, Moubareck, Xu, Karam Sarkis and Touqui. The treatment of respiratory infections is associated with the dissemination of antibiotic resistance in the community and clinical settings. Development of new antibiotics is notoriously costly and slow; therefore, alternative strategies are needed. Antimicrobial peptides (AMPs), the central effector molecules of the immune system, are being considered as alternatives to conventional antibiotics. Most AMPs are epithelium-derived and play a key role in host defense at mucosal surfaces. They are classified on the basis of their structure and amino acid motifs. These peptides display a range of activities, including not only direct antimicrobial activity, but also immunomodulation and wound repair. In the lung, airway epithelial cells and neutrophils, in particular, contribute to AMP synthesis. The relevance of AMPs for host defense against infection has been demonstrated in animal models and is supported by observations in patient studies, showing altered expression and/or unfavorable circumstances for their action in a variety of lung diseases. Of note, AMPs are active against bacterial strains that are resistant to conventional antibiotics, including multidrug-resistant bacteria. Several strategies have been proposed to use these peptides in the treatment of infections, including direct administration of AMPs. In this review, we focus on studies related to direct bactericidal effects of AMPs and their potential clinical applications with a particular focus on cystic fibrosis

Cationic antimicrobial peptides: alternatives and/or adjuvants to antibiotics active against methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa

Abstract Background Methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa are becoming difficult to treat with antibiotics whereas Cationic Antimicrobial Peptides (CAMPs) represent promising alternatives. The effects of four CAMPs (LL-37: human cathelicidin, CAMA: cecropin(1–7)-melittin A(2–9) amide, magainin-II and nisin) were investigated against clinical and laboratory S. aureus (n = 10) and P. aeruginosa (n = 11) isolates either susceptible or resistant to antibiotics. Minimal Inhibitory Concentrations (MICs), Minimal Bactericidal Concentrations (MBCs), and bacterial survival rates (2 h post-treatment) were determined by microbroth dilution. The antipseudomonal effects of the antibiotics colistin or imipenem combined to LL-37 or CAMA were also studied. The toxicity of CAMPs used alone and in combination with antibiotics was evaluated on two human lung epithelial cell lines by determining the quantity of released cytoplasmic lactate dehydrogenase (LDH). Attempts to induce bacterial resistance to gentamicin, LL-37 or CAMA were also performed. Results The results revealed the rapid antibacterial effect of LL-37 and CAMA against both antibiotic susceptible and resistant strains with almost a total reduction in bacterial count 2 h post-treatment. Magainin-II and nisin were less active against tested strains. When antibiotics were combined with LL-37 or CAMA, MICs of colistin decreased up to eight-fold and MICs of imipenem decreased up to four-fold. Cytotoxicity assays revealed non-significant LDH-release suggesting no cell damage in all experiments. Induction of bacterial resistance to LL-37 was transient, tardive and much lower than that to gentamicin and induction of resistance to CAMA was not observed. Conclusion This study showed the potent and rapid antibacterial activity of CAMPs on both laboratory and clinical isolates of S. aureus and P. aeruginosa either susceptible or resistant to antibiotics. Most importantly, CAMPs synergized the efficacy of antibiotics, had non toxic effects on human cells and were associated with transient and low levels of induced resistance

Bactericidal effects and stability of LL-37 and CAMA in the presence of human lung epithelial cells

Cationic antimicrobial peptides (CAMPs) are important actors in host innate immunity and represent a promising alternative to combat antibiotic resistance. Here, the bactericidal activity of two CAMPs (LL-37, and CAMA) was evaluated against Pseudomonas aeruginosa (PA) in the presence of IB3-1 cells, a cell line derived from patients with cystic fibrosis. The two CAMPs exerted different effects on PA survival depending on the timing of their administration. We observed a greater bactericidal effect when IB3-1 cells were pretreated with sub-minimum bactericidal concentrations (Sub-MBCs) of the CAMPs prior to infection. These findings suggest that CAMPs induce the production of factors by IB3-1 cells that improve their bactericidal action. However, we observed no bactericidal effect when supra-minimum bactericidal concentrations (Supra-MBCs) of the CAMPs were added to IB3-1 cells at the same time or after infection. Western-blot analysis showed a large decrease in LL-37 levels in supernatants of infected IB3-1 cells and an increase in LL-37 binding to these cells after LL-37 administration. LL-37 induced a weak inflammatory response in the cells without being toxic. In conclusion, our findings suggest a potential prophylactic action of CAMPs. The bactericidal effects were low when the CAMPs were added after cell infection, likely due to degradation of CAMPs by bacterial or epithelial cell proteases and/or due to adherence of CAMPs to cells becoming less available for direct bacterial killing