How Oxygen Availability Affects the Antimicrobial Efficacy of Host Defense Peptides: Lessons Learned from Studying the Copper-Binding Peptides Piscidins 1 and 3

Abstract

The development of new therapeutic options against Clostridioides difficile (C. difficile) infection is a critical public health concern, as the causative bacterium is highly resistant to multiple classes of antibiotics. Antimicrobial host-defense peptides (HDPs) are highly effective at simultaneously modulating the immune system function and directly killing bacteria through membrane disruption and oxidative damage. The copper-binding HDPs piscidin 1 and piscidin 3 have previously shown potent antimicrobial activity against a number of Gram-negative and Gram-positive bacterial species but have never been investigated in an anaerobic environment. Synergy between piscidins and metal ions increases bacterial killing aerobically. Here, we performed growth inhibition and time-kill assays against C. difficile showing that both piscidins suppress proliferation of C. difficile by killing bacterial cells. Microscopy experiments show that the peptides accumulate at sites of membrane curvature. We find that both piscidins are effective against epidemic C. difficile strains that are highly resistant to other stresses. Notably, copper does not enhance piscidin activity against C. difficile. Thus, while antimicrobial activity of piscidin peptides is conserved in aerobic and anaerobic settings, the peptide–copper interaction depends on environmental oxygen to achieve its maximum potency. The development of pharmaceuticals from HDPs such as piscidin will necessitate consideration of oxygen levels in the targeted tissue.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

“…Piscidins and ixosin are AMP that contain the copper- and nickel-binding ATCUN motif. Bactericidal activity under aerobic conditions is enhanced when these AMP bind copper, but under anaerobic conditions two piscidins (p1 and p3) and ixosin retain activity, but this does not depend on the presence of copper ions (Libardo et al, 2016 ; Oludiran et al, 2019 ). Thus, it would appear that antimicrobial activity of AMP under anaerobic conditions is dependent on the AMP used and for the purposes of AMP vs. anaerobes would need to be assessed on a case-by-case basis.…”

Metal–Peptide Complexes as Promising Antibiotics to Fight Emerging Drug Resistance: New Perspectives in Tuberculosis

“…More recently, in a study related to the Clostridioides difficile infection, a hospital-acquired disease highly resistant to multiple classes of antibiotics, it has been pointed out that P1, P3 activities strongly depend on the anaerobic conditions corroborating the hypothesis related to the formation of radical species during their MOA [79]. Ovispirin 3 (OV-3) is a synthetic AMP derived from the sheep myeloid antimicrobial peptide (SMAP-29) [80], a cathelicidin member, with antimicrobial activity against a variety of pathogens [81,82].…”

Metallated Anticancer Peptides: An Expanded Mechanism that Encompasses Physical and Chemical Bilayer Disruption

“…This is significant because it identifies metallation as a chemical modification that can improve the biological activity of this family of HDPs, several of which have already proven to be promising templates for the development of novel strategies to treat infections, inflammation, and cancer 7,8,[15][16][17][18][19][20][21][22] . Specific valuable features of P1 and P3 include their broad spectrum activity in the micromolar and sub-micromolar (for P1) range, antiinflammatory properties, and pH-resiliency in the physiological range 33,47,56,[99][100][101] . P1, which has been more tested in vivo than P3, has very good pharmacodynamics and pharmacokinetics characteristics 61,62,101 .…”