Antimicrobial and anti-inflammatory activities of designed antimicrobial peptide P18 analogues

To develop antimicrobial peptides having higher bacterial selectivity than a novel antimicrobial peptide P18, we synthesized several analogues. The P18 analogues are designed by movement of the N-terminal Trp2 residue in P18 (P18-W6, P18-W8 and P18-W15) and the substitution of the central Pro9 residue with D-Pro or Nala (P18-Nala9 and P18-D-Pro9). These analogues retained potent antibacterial activity but displayed less hemolytic activity than P18. From the viewpoint of their therapeutic index, P18 analogues had approximate 3- to 7-fold higher bacterial selectivity compared to P18. The analogues preferentially bind to bacterial membrane-mimicking negatively charged liposomes as well as does P18. Their high specificity to negatively charged phospholipids corresponds well with their high bacterial selectivity. Furthermore, P18-W6, P18-W8 and P18-Nala9 induced a significant inhibition in NO production from LPS-stimulated macrophage RAW264.7 cells, as well as P18. This result suggests that these peptides appear to have promising therapeutic potential for future development as a novel anti-inflammatory agent as well as antimicrobial agent.