However, the results obtained by quantifying bacterial membrane disruption using using diS-C3-(5) may indicate the more specific mode of action. The intensities of enhancement did not correlate with the susceptibilities of the bacteria for the tested AMPs. VS-4718 research buy The killing of E. coli JM109 was most efficiently enhanced for ASABF-α and polymyxin B, suggesting that the efficacy of NP4P enhancement depends on the species of bacteria rather than on that of AMPs. These results support our hypothesis that NP4P independently interacts with cytoplasmic membranes

and not with AMPs. For acidic liposomes, membrane disruption of ASABF-α was inhibited in the presence of 20 μg/mL NP4P. The dose-response curve was shifted to a higher concentration (IC50 = 0.23 μg/mL without NP4P, and Cytoskeletal Signaling inhibitor 0.53 μg/ml with NP4P), indicating that NP4P was a competitive inhibitor. This inhibition could be due to charge neutralization of the membrane surface by NP4P binding and prevention of ASABF-α binding in a similar manner to that observed between magainin 2 and an acyclic tachyplesin

I analogue [16], i.e., NP4P and ASABF-α also bind to the liposomal membrane independently. This observation does not contradict our hypothesis mentioned above. The exact mechanisms for NP4P enhancement at the molecular level remains to be elucidated. Tideglusib Conclusions NP4P selectively enhances the bactericidal activities of membrane-disrupting AMPs (ASABF-α, nisin, and polymyxin B). NP4P is not bactericidal and does not inhibit growth at ≤ 300 μg/mL against all tested bacteria, suggesting that the effect of NP4P is enhancement and is distinct from PIK3C2G the previously reported synergy among AMPs and/or low-molecular mass antimicrobials [6–20]. Enhancement intensities depend on microbial species. Relatively good enhancement was achieved for S. aureus and E. coli. Increasing the efficacy

of membrane disruption against the bacterial cytoplasmic membrane may contribute to enhancement by NP4P. AMPs are immune effectors against microbial infections in vertebrates, invertebrates, and plants. In humans, the deficiency in AMP functions often causes reduced resistance against infectious diseases [31, 32], indicating that resistance may increase by enhancing the effect of AMPs. AMP-enhancers without antimicrobial activities are promising as immunopotentiators since they do not disturb the autonomic control of immunity. Although salt-inhibition remains to be resolved for practical use in mammals, NP4P is believed to be the first peptide which exerts AMP-enhancer activity. Methods Microorganisms E. coli JM109 was purchased from Takara (Otsu, Japan). Other strains described below were transferred from the National Institute of Technology and Evaluation, Kazusa, Japan: S. aureus IFO12732, B. subtilis IFO3134, M. luteus IFO12708, P. aeruginosa IFO3899, S. typhimurium IFO13245 and S. marcescens IFO3736. Peptides and other AMPs NP4P, cecropin P4 and indolicidin were prepared at Biologica Co.