The effect of D-amino acid-containing basic peptides with different hydrophobicity on the antimicrobial and cytotoxic activity

In order to investigate the structure-activity relationships between the hydrophobicity, differences in the number of positive charged amino acids and D-amino acids as well as their action mechanism with different bio-membranes, we designed and synthesized two sets of 12-mer model peptides originating from an amphiphilic antimicrobial model peptide and a D-amino acid-containing non-amphiphilic peptide. The introduction of D-amino acid in peptides led not only to decreases in the hydrophobicity, helical content, and hemolytic activity, but to an increase in the antimicrobial activity against Gram-positive and -negative bacteria. The relative peptide hydrophobicity was estimated in terms of the peptide elution time, expressed by linear trifluoroacetic acid (TFA)-water to TFA-acetonitrile gradients on C18 reverse-phase high-performance liquid chromatography (RP-HPLC). The retention behavior of model peptides on RP-HPLC is correlated with the activity and selectivity for mammalian cells, Gram-positive and -negative bacteria: The a-helical amphiphiIic structure is required for cytolytic ability against mammalian cells, but is not necessary for bacterial activity. Additionally, the peptides have different hydrophobicity regions in which they show their optimum activity against both bacteria and erythrocytes. In the highest hydrophobisity region the peptides display high levels of hemolytic activity. At medium hydrophobicity levels, the peptides are able to display to high levels of activity against Gram-positive bacteria. In the lowest hydrophobisity regions the peptides are able to display high levels of activity against Gram-negative bacteria. This may be useful in designing clinically effective antimicrobial peptides with highly potent activity and high bacterial selectivity.