Antifungal and Antibiofilm Activities and the Mechanism of Action of Repeating Lysine-Tryptophan Peptides against Candida albicans

Abstract

The rapid increase in the emergence of antifungal-resistant Candida albicans strains is becoming a serious health concern. Because antimicrobial peptides (AMPs) may provide a potential alternative to conventional antifungal agents, we have synthesized a series of peptides with a varying number of lysine and tryptophan repeats (KWn-NH2). The antifungal activity of these peptides increased with peptide length, but only the longest KW5 peptide displayed cytotoxicity towards a human keratinocyte cell line. The KW4 and KW5 peptides exhibited strong antifungal activity against C. albicans, even under conditions of high-salt and acidic pH, or the addition of fungal cell wall components. Moreover, KW4 inhibited biofilm formation by a fluconazole-resistant C. albicans strain. Circular dichroism and fluorescence spectroscopy indicated that fungal liposomes could interact with the longer peptides but that they did not release the fluorescent dye calcein. Subsequently, fluorescence assays with different dyes revealed that KW4 did not disrupt the membrane integrity of intact fungal cells. Scanning electron microscopy showed no changes in fungal morphology, while laser-scanning confocal microscopy indicated that KW4 can localize into the cytosol of C. albicans. Gel retardation assays revealed that KW4 can bind to fungal RNA as a potential intracellular target. Taken together, our data indicate that KW4 can inhibit cellular functions by binding to RNA and DNA after it has been translocated into the cell, resulting in the eradication of C. albicans.

Rondonin: antimicrobial properties and mechanism of action

“…The concentration of the peptide used in our experiment was lower than that used with indolicidin; however, the amount necessary for the delay to occur can be smaller since the plasmid used is smaller than the genomic DNA [111]. The same was observed to the synthetics peptides KWKW‐NH2 (KW2), KWKWKW‐NH2 (KW3), KWKWKWKW‐NH2 (KW4), and KWKWKWKWKW‐NH2 (KW5) [71].…”

“…This yeast had homogeneous growth at all pH levels, thus making it possible to test the activity of the synthetic peptide according to the same methodology for the tests of growth inhibition in liquid medium. As shown in Table 1, the anticandidal activity of the rondonin was preserved at low pH, suggesting that these peptides could potentially be used to inhibit C. albicans infections in different compartments of the human body (e.g., the skin, the vagina, chronic dental foci) that have acidic pH environment [72].…”

Mechanism of Antimicrobial Peptides: Antimicrobial, Anti-Inflammatory and Antibiofilm Activities

“…After the AMPs enter the cell membrane and accumulate, they can target intracellular macromolecules and biological processes for further activity [ 25 , 39 , 92 , 93 ]. Nonmembrane-targeting AMPs can bind to nucleic acids and proteins; inhibit the process of replication, transcription, and translation; destroy organelles; or affect the enzyme system to disturb the cell cycle and energy metabolism ( Table 2 and Figure 1 ) [ 37 , 39 , 40 , 42 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ].…”

“…Another possible reason is the research on intracellular effects is basically based on independent in vitro studies, and the biggest shortcoming of in vitro studies is that they cannot fully explain the precise mechanism in vivo [ 25 , 94 , 104 , 112 ]. In vitro experiments cannot timely simulate changes in the real pH value, salt concentration difference, and other components of the immune system in vivo [ 15 , 113 ].…”

Antimicrobial peptides as novel alternatives to antibiotics

“…Antimicrobial peptide are a kind of small molecule polypeptide, which are the first lines of defense against the invasion of pathogenic microorganisms, and an important component of host innate immunity. They have many biological functions such as antibacterial, antifungal, antiviral and anti-cancer and so on (Forkus et al, 2017;Ramamourthy et al, 2020). Antimicrobial peptide are ubiquitous in nature, they are mainly from plants, mammals, fish, amphibians, birds and humans.…”