title: Augmentation of the bactericidal activities of human cathelicidin CAP18/LL-37-derived antimicrobial peptides by amino acid substitutions.
abstract: OBJECTIVE
  Mammalian myeloid and epithelial cells express various peptide antibiotics (such as defensins and cathelicidins) that contribute to the innate host defense against invading micro-organisms. Among these, human cathelicidin CAP18/LL-37 (L1-S37) possesses potent antibacterial activities against Gram-positive and Gram-negative bacteria. In this study, to develop peptide derivatives with improved bactericidal actions, we utilized the amphipathic 18-mer peptide (K15-V32) of LL-37 as a template, and evaluated the activities of modified peptides.
  
  
  METHODS
  Antibacterial activities of the peptides (0.022 approximately 4.4 microM corresponding to 0.1 approximately 10 microg/ml) were assessed by alamarBlue assay using Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Escherichia coli and Pseudomonas aeruginosa as target organisms. Furthermore, the membrane-permeabilization activities of the peptides were examined by using E. coli ML-35p as a target.
  
  
  RESULTS
  By substituting E16 and K25 with two L residues, the hydrophobicity of the peptide (18-mer LL) was increased, and by further substituting Q22, D26 and N30 with three K residues, the cationicity of the peptide (18-mer LLKKK) was enhanced. Among peptide derivatives, 18-mer LLKKK exhibited the most potent antibacterial actions against S. aureus (methicillin-resistant and -sensitive), S. pneumoniae, S. pyogenes, E. coli and P. aeruginosa, and possessed the most powerful membrane-permeabilizing activities against E. coli ML-35p at the effective concentrations (p <0.05, 18-mer LLKKK vs. 18-mer LL, 18-mer K15-V32 and LL-37).
  
  
  CONCLUSIONS
  Bactericidal activities of the amphipathic human CAP18/LL-37-derived 18-mer peptide can be augmented by modifying its hydrophobicity and cationicity, and 18-mer LLKKK is the most potent among peptide derivatives with therapeutic potential for Gram-positive and Gram-negative bacterial infections.
authors.affiliation: Department of Host Defense and Biochemical Research, School of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo, 113-8421, Japan. nagaokai@med.juntendo.ac.jp
authors.forename: I
authors.initials: I
authors.lastname: Nagaoka
authors.forename: K
authors.initials: K
authors.lastname: Kuwahara-Arai
authors.forename: H
authors.initials: H
authors.lastname: Tamura
authors.forename: K
authors.initials: K
authors.lastname: Hiramatsu
authors.forename: M
authors.initials: M
authors.lastname: Hirata
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics* / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D054804:Cathelicidins; D002463:Cell Membrane Permeability / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004926:Escherichia coli / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects; D006801:Humans; D008264:Macrophages / Q000502:physiology; D051379:Mice; D009000:Monocytes / Q000502:physiology
chemical_list: D023181:Antimicrobial Cationic Peptides; D054804:Cathelicidins