Extra amino group-containing gramicidin S analogs possessing outer membrane-permeabilizing activity

Antibacterial Activity of Membrane-Permeabilizing Bactericidal Cyclodextrin Derivatives

Antimicrobial peptides that act by disrupting bacterial membranes are attractive agents for treating drug-resistant bacteria. This study investigates a membrane-disrupting peptide mimic made of a cyclic oligosaccharide cyclodextrin scaffold that can be chemically polyfunctionalized. An antibacterial functional group on the peptide was simplified to an alkylamino group that combines cationic and hydrophobic moieties, the former to interact with the anionic bacterial membrane and the latter with the membrane interior. The cyclodextrins equipped with eight alkylamino groups on the molecules using a poly-click reaction exhibited antibacterial activity against Gram-positive and Gram-negative bacteria, including drug-resistant pathogens such as carbapenem-resistant Enterobacteriaceae. Several lines of evidence showed that these agents disrupt bacterial membranes, leading to rapid bacterial cell death. The resulting membrane perturbation was directly visualized using high-speed atomic force microscopy imaging. In Gram-negative bacteria, the membrane-permeabilizing action of these derivatives allowed the entry of co-treated traditional antibiotics, which were then active against these bacteria.

Polymyxin B-inspired non-hemolytic tyrocidine A analogues with significantly enhanced activity against gram-negative bacteria: How cationicity impacts cell specificity and antibacterial mechanism

Naturally occurring cyclic antimicrobial peptides (AMPs) such as tyrocidine A (Tyrc A) and gramicidin S (GS) are appealing targets for the development of novel antibiotics. However, their therapeutic potentials are limited by undesired hemolytic activity and relatively poor activity against Gram-negative bacteria. Inspired by polycationic lipopeptide polymyxin B (PMB), the so called 'last-resort' antibiotic for the treatment of infections caused by multidrug-resistant Gram-negative bacteria, we synthesized and biologically evaluated a series of polycationic analogues derived from Tyrc A. We were able to obtain peptide 8 that possesses 5 positive charges exhibiting potent activities against both Gram-negative and Gram-positive bacteria along with totally diminished hemolytic activity. Intriguingly, antibacterial mechanism studies revealed that, rather than the 'pore forming' model that possessed by Tyrc A, peptide 8 likely diffuses membrane in a 'detergent-like' manner. Furthermore, when treating mice with peritonitis-sepsis, peptide 8 showed excellent antibacterial and anti-inflammatory activities in vivo.

Gramicidin S-inspired antimicrobial cyclodextrin to disrupt gram-negative and gram-positive bacterial membranes

A membrane-active antimicrobial peptide gramicidin S-like amphiphilic structure was prepared from cyclodextrin. The mimic was a cyclic oligomer composed of 6-amino-modified glucose 2,3-di-O-propanoates and it exhibited antimicrobial activity against Gram-positive and Gram-negative bacteria, together with no resistance development and low haemolytic activity against red blood cells.

Graphene oxide as a nanocarrier for gramicidin (GOGD) for high antibacterial performance

As a powerful and novel nanocarrier, graphene oxide (GO) is employed to load a water insoluble antibacterial drug, gramicidin (GD), for effective antibacterial treatments.

Solvent-free thermocyclization of the unactivated linear gramicidin S precursor and analogues

A convenient thermocyclization of the linear gramicidin S precursor and its analogues is demonstrated. With the preorganized β-sheet conformation, the unactivated linear precursors can cyclize into the corresponding head-to-tail cyclic products in high yield after being heated under solvent-free conditions.

Proline residue-modified polycationic analogs of gramicidin S with high antibacterial activity against both Gram-positive and Gram-negative bacteria and low hemolytic activity*

Novel polycationic analogs of the cyclic decapeptide antibiotic, gramicidin S, possessing NH(2), D/L-Phe-NH or L-Lys-NH groups at the 4alpha- or 4beta-positions of the L-Pro residues, were synthesized. While L-Pro(4alpha/beta-NH(2))-containing analogs exhibited much weaker antibacterial activity, the D/L-Phe and L-Lys-substituted analogs exhibited higher antibacterial activity against Gram-negative bacteria than the parent gramicidin S. All of these additional amino group-containing analogs showed substantially reduced toxicity against human blood cells.

Bacterial cytoplasmic membrane permeability assay using ion-selective electrodes

We used K(+) and tetraphenylphosphonium (TPP(+)) electrodes simultaneously to evaluate the ability of antimicrobial peptides to form channels (or more generally to increase permeability) and to abolish membrane potential in bacterial cytoplasmic membranes in situ. Such evaluations are usually made independently by colorimetric monitoring of the hydrolysis of a chromogenic substrate by a cytoplasmic enzyme or by fluorimetric determination of membrane depolarization using a membrane potential-sensitive dye. In the present study, the K(+) electrode was used to evaluate channel-forming ability by monitoring the efflux of K(+) originally present in the cytoplasm of bacteria, while the TPP(+) electrode was used to examine membrane depolarization causing the efflux of TPP(+) accumulated in the cytoplasm of bacteria dependent on membrane potential. Thus, the combination of these two electrodes enabled us to clarify how the peptide-induced formation of ion channels is involved in disrupting the energy-generating system in situ.