Mammalian cell toxicity and candidacidal mechanism of Arg- or Lys-containing Trp-rich model antimicrobial peptides and their d-enantiomeric peptides.

In this study, we investigated the mammalian cell toxicity and candidacidal mechanism of Arg- or Lys-containing Trp-rich model antimicrobial peptides (K(6)L(2)W(3) and R(6)L(2)W(3)) and their d-enantiomeric peptides (K(6)L(2)W(3)-d and R(6)L(2)W(3)-d). Arg-containing peptides were more toxic to human erythrocytes and mammalian cells as compared to Lys-containing peptides. Arg-containing peptides is slightly more hydrophobic than Lys-containing counterparts, as judged from their reverse phase-high performance liquid chromatography (RP-HPLC) retention time. These results suggested that a little difference in hydrophobicity of these peptides affect their hemolytic activity and mammalian cell toxicity. Interestingly, K(6)L(2)W(3) and K(6)L(2)W(3)-d almost similar mammalian cell cytotoxicity, whereas R(6)L(2)W(3)-d showed much higher cytotoxicity as compared to R(6)L(2)W(3). A low ability to facilitate fluorescent marker escape from Candida albicans membrane-mimicking vesicles suggested that the major target site of Lys-containing peptides may be not the cell membrane but the cytoplasm of C. albicans. Confocal laser-scanning microscopy revealed that FITC-labeled Lys-containing peptides penetrated the cell wall and cell membrane and accumulated inside the cells, whereas FITC-labeled Arg-containing peptides did not penetrate but associated with the membranes. Collectively, our results suggested that the ultimate target site of action of Arg-containing peptides and Lys-containing peptides may be the membrane and the cytoplasm of C. albicans, respectively.