Investigating the effects of positive charge and hydrophobicity on the cell selectivity, mechanism of action and anti-inflammatory activity of a Trp-rich antimicrobial peptide indolicidin

Abstract

To investigate the effects of positive charge and hydrophobicity on the cell selectivity, mechanism of action and anti-inflammatory activity of a Trp-rich antimicrobial peptide indolicidin (IN), a series of IN analogs with Trp-->Lys substitution were synthesized. All IN analogs displayed an approximately 7- to 18-fold higher cell selectivity, compared with IN. IN, IN-1 and IN-2 depolarized (50-90%) the cytoplasmic membrane potential of Staphylococcus aureus close to minimal inhibitory concentration (5-10 microg mL(-1)). However, other IN analogs (IN-3 and IN-4) displayed very low ability in membrane depolarization even at 40 microg mL(-1). Confocal laser-scanning microscopy revealed that IN-3 and IN-4 penetrated the Escherichia coli cell membrane, whereas IN, IN-1 and IN-2 did not enter the cell membrane. In the gel retardation assay, IN-3 and IN-4 bound more strongly to DNA compared with IN, IN-1 and IN-2. These findings suggest that the mechanism of antimicrobial action of IN-3 and IN-4 may be involved in the inhibition of intracellular functions via interference with DNA/RNA synthesis. Unlike IN, all IN analogs did not inhibit nitric oxide production or inducible nitric oxide synthase mRNA expression in lipopolysaccharide-stimulated mouse macrophage RAW264.7 cells, indicating that the hydrophobicity of IN is more important for anti-inflammatory activity in lipopolysaccharide-treated macrophage cells than the positive charge.

Chicken cathelicidin-2-derived peptides with enhanced immunomodulatory and antibacterial activities against biological warfare agents

“…PheTrp substitutions in C1-15, resulting in peptide F2,5,12W, significantly increased the LPS-neutralising capacity. Recently, we [11] and others [12] reported the importance of hydrophobicity in neutralising LPS cytokine responses. In line with our observations, Nan et al [12] showed that substitution of Trp by Lys residues in the Trp-rich peptide indolicidin resulted in decreased hydrophobicity and loss of LPS-neutralising activity.…”

“…Recently, we [11] and others [12] reported the importance of hydrophobicity in neutralising LPS cytokine responses. In line with our observations, Nan et al [12] showed that substitution of Trp by Lys residues in the Trp-rich peptide indolicidin resulted in decreased hydrophobicity and loss of LPS-neutralising activity. Previously it was shown that inhibition of the pro-inflammatory response is mainly established by direct binding of cationic HDPs to LPS [11,13].…”

Structure-Activity Relationship of Synthetic Variants of the Milk-Derived Antimicrobial Peptide α s2 -Casein f(183–207)

“…The hydrophobicity and isoelectric point of the peptide variants were analyzed (Table 1), as a number of studies have reported a correlation between both parameters and antimicrobial activity (23)(24)(25)(26). However, no significant link between either parameter and activity could be observed for our collection of variants.…”

Extensive Manipulation of Caseicins A and B Highlights the Tolerance of These Antimicrobial Peptides to Change

“…The hydrophobicity of the caseicin variants was also analyzed, as a number of studies have discovered a correlation between hydrophobicity and antimicrobial activity (2,16,21). Unfortunately, we could not link antimicrobial activity with the percent hydrophobicity of the variant caseicins.…”