Antimicrobial and immunomodulatory activity of PMAP-23 derived peptides

The Porcine Myeloid Antibacterial Peptide (PMAP)-23 is a porcine host defence peptide with described strong antibacterial activity against Gram-positive and Gram-negative bacteria, and fungi. In this study, PMAP-23 and short and/or mutated derivatives were tested for antibacterial and immunomodulatory activities to determine core elements of the peptide required for functionality. Shortening of the peptide on either N- or C-terminus did not lead to a strong reduction in antibacterial activity, but interestingly, all C-terminal truncated forms were strongly inhibited by salt addition. However, the two N-terminally truncated forms were not sensitive to salt, similarly to the full-length peptide. In addition, none of the peptides were shown to be hemolytic or toxic in concentrations up to 40 μM. Full length PMAP-23 induced IL-8 production in porcine epithelial cells, however, this activity was lost in all truncated peptides. None of the peptides inhibited LPS-induced cytokine production of monocytes, contrary to the control peptide, chicken CATH-2. Using isothermal titration calorimetry, it was shown that PMAP-23, in contrast to CATH-2, was unable to directly bind LPS. Finally, all PMAP-23 derived peptides reduced the uptake of beads by freshly isolated monocytes. Therefore, it is concluded that the function of PMAP-23 is mainly antibacterial with only limited immunomodulating capacity, and that the full-length peptide is required for the full spectrum of activities.