Simplified Head-to-Tail Cyclic Polypeptides as Biomaterial-Associated Antimicrobials with Endotoxin Neutralizing and Anti-Inflammatory Capabilities

Abstract

The therapeutic application of antimicrobial peptides (AMPs), a potential type of peptide-based biomaterial, is impeded by their poor antimicrobial activity and potential cytotoxicity as a lack of understanding of their structure–activity relationships. In order to comprehensively enhance the antibacterial and clinical application potency of AMPs, a rational approach was applied to design amphiphilic peptides, including head-to-tail cyclic, linear and D-proline antimicrobial peptides using the template (IR)nP(IR)nP (n = 1, 2 and 3). Results showed that these amphiphilic peptides demonstrated antimicrobial activity in a size-dependent manner and that cyclic peptide OIR3, which contained three repeating units (IR)3, had greater antimicrobial potency and cell selectivity than liner peptide IR3, DIR3 with D-Pro and gramicidin S (GS). Surface plasmon resonance and endotoxin neutralization assays indicated that OIR3 had significant endotoxin neutralization capabilities, which suggested that the effects of OIR3 were mediated by binding to lipopolysaccharides (LPS). Using fluorescence spectrometry and electron microscopy, we found that OIR3 strongly promoted membrane disruption and thereby induced cell lysis. In addition, an LPS-induced inflammation assay showed that OIR3 inhibited the pro-inflammatory factor TNF-α in RAW264.7 cells. OIR3 was able to reduce oxazolone-induced skin inflammation in allergic dermatitis mouse model via the inhibition of TNF-α, IL-1β and IL-6 mRNA expression. Collectively, the engineered head-to-tail cyclic peptide OIR3 was considerable potential candidate for use as a clinical therapeutic for the treatment of bacterial infections and skin inflammation.

Current synthetic chemistry towards cyclic antimicrobial peptides

“…More importantly, the synthesized cyclic peptides showed very low hemolytic activity and cell toxicity up to 128 μM. OIR3 also exhibited anti‐inflammatory activity in an LPS‐induced inflammation assay in RAW264.7 cells and in an oxazolone‐induced skin inflammation in allergic dermatitis mouse model 14 …”

“…OIR3 also exhibited anti-inflammatory activity in an LPS-induced inflammation assay in RAW264.7 cells and in an oxazolone-induced skin inflammation in allergic dermatitis mouse model. 14 Tyrocidine A (Tyrc A) (Figure 2) is structurally similar to GS and also produced by Bacillus Brevis. 15 Compared with GS, Tyrc A has…”

Structure–activity relationships of antibacterial peptides

“…Furthermore, head-to-tail cyclic peptides are more resistant to endo and exopeptidases hydrolysis compared to linear peptides (Góngora-Benítez et al, 2014). Moreover, they have greater potential with enhanced activity in developing novel antibacterial agents (Dong et al, 2019).…”

Hybridization with Insect Cecropin A (1–8) Improve the Stability and Selectivity of Naturally Occurring Peptides

“…These drawbacks include potential toxicity, high production costs and instability in body fluid with high salt concentration [20,21]. To overcome these problems, some modifications have been proposed, including residue substitution [22], hybridization of naturally occurring peptides, cyclization of linear peptides [23]. Hybridization could take advantage of different functional sequences, which make it an attractive approach to obtain novel AMPs [24,25].…”