A new amino acid for improving permeability and solubility in macrocyclic peptides through side chain-to-backbone hydrogen bonding.

Despite the notoriously poor membrane permeability of peptides in general, many cyclic peptide natural products show high passive membrane permeability and potently inhibit a variety of “undruggable” intracellular targets. A major impediment to designing cyclic peptides with good permeability is the high desolvation energy associated with the peptide backbone amide NH groups. Strategies for mitigating the deleterious effect of the backbone NH group on permeability include N-methylation, steric occlusion, and the formation of intramolecular hydrogen bonds with backbone carbonyl oxygens, while there have been relatively few studies on the use of polar side chains to sequester backbone NH groups. We investigated the ability of N,N-pyrrolidinyl glutamine (Pye), whose side chain contains a powerful hydrogen bond accepting C=O amide group but no hydrogen bond donors, to sequester exposed backbone NH groups in a series of cyclic hexapeptide diastereomers. Analyses of partition coefficients, lipophilic permeability efficiencies (LPE), artificial and cell-based permeability assays revealed that specific Leu-to-Pye substitutions conferred dramatic improvements in aqueous solubility and permeability in a scaffold- and position-dependent manner. Introduction of the Pye residue thus offers a complementary tool, alongside traditional approaches, for improving membrane permeability and solubility in cyclic peptides.

Effect of Polycation Nanostructures on Cell Membrane Permeability and Toxicity

The interaction of nanometric synthetic materials with cell membranes is one of the key factors determining their possible cytotoxicity. This work investigated the interaction of polycation nanostructures with lipid and...

Effects of Atmospheric Plasma Corona Discharge on Agrobacterium tumefaciens Survival

Soil-borne pathogenic microorganisms are known to cause extensive crop losses. Agrobacterium tumefaciens, a member of the Proteobacteria, causes the neoplastic crown gall disease in plants. Plant protection is mainly based on toxic chemicals that are harmful to the environment. The use of cold atmospheric-pressure plasma is an attractive method for microbial eradication. Its antimicrobial mechanism includes the formation of large quantities of reactive oxygen species (ROS). The advantages of eradicating bacteria using cold plasma are not needed for chemicals, short treatment, and environmental temperatures. This study examined the impact of plasma corona discharge exposure on A. tumefaciens viability, membrane permeability, relative cell size, and ROS formation. The results showed that 90 s of plasma exposure led to a reduction by four orders of magnitude when the initial concentration was 1 × 107 CFU/mL and in a dry environment. When the initial concentration was 1 × 106 CFU/mL, 45 s of exposure resulted in total bacterial eradication. In a liquid environment, in an initial concentration of 2.02 × 106 CFU/mL, there was no complete bacterial eradication even at the most prolonged examined exposure (90 s). The influence of plasma treatment on the membrane permeability of A. tumefaciens, and their possible recovery, were analyzed using flow cytometer analysis using propidium iodide (PI). When the plasma-treated bacteria were suspended in Luria–Bertani (LB) (rich medium), the PI-positive count of the plasma-treated bacteria after two hours was 12 ± 3.9%. At the 24th hour, this percentage was only 1.74 ± 0.6%, as the control (0.7 ± 0.1%). These results may indicate the repair of the plasma-treated bacteria that were suspended in LB. At the 24th hour, the relative cell size of the treated bacteria shifted to the right, to ~3 × 104 forward side scatter (FSC), about 0.5-fold higher than the untreated cells. Measurement of the ROS showed that the intracellular fluorescence of the 90-s plasma-treated cells led to significant fluorescence formation of 32 relative fluorescence units (RFU)/cell (9 × 104 fold, compared to the nontreated cells). This study showed that cold plasma is a useful method for A. tumefaciens eradication. The eradication mechanism involves ROS generation, membrane permeability, and changes in cell size.

Curcumin activation of a bacterial mechanosensitive channel underlies its membrane permeability and adjuvant properties

Curcumin, a natural compound isolated from the rhizome of turmeric, has been shown to have antibacterial properties. It has several physiological effects on bacteria including an apoptosis-like response involving RecA, membrane permeabilization, inhibiting septation, and it can also work synergistically with other antibiotics. The mechanism by which curcumin permeabilizes the bacterial membrane has been unclear. Most bacterial species contain a Mechanosensitive channel of large conductance, MscL, which serves the function of a biological emergency release valve; these large-pore channels open in response to membrane tension from osmotic shifts and, to avoid cell lysis, allow the release of solutes from the cytoplasm. Here we show that the MscL channel underlies the membrane permeabilization by curcumin as well as its synergistic properties with other antibiotics, by allowing access of antibiotics to the cytoplasm; MscL also appears to have an inhibitory role in septation, which is enhanced when activated by curcumin.

Autoinducer Analogs Can Provide Bactericidal Activity to Macrolides in Pseudomonas aeruginosa through Antibiotic Tolerance Reduction

Macrolide antibiotics are used in treating Pseudomonas aeruginosa chronic biofilm infections despite their unsatisfactory antibacterial activity, because they display several special activities, such as modulation of the bacterial quorum sensing and immunomodulatory effects on the host. In this study, we investigated the effects of the newly synthesized P. aeruginosa quorum-sensing autoinducer analogs (AIA-1, -2) on the activity of azithromycin and clarithromycin against P. aeruginosa. In the killing assay of planktonic cells, AIA-1 and -2 enhanced the bactericidal ability of macrolides against P. aeruginosa PAO1; however, they did not affect the minimum inhibitory concentrations of macrolides. In addition, AIA-1 and -2 considerably improved the killing activity of azithromycin and clarithromycin in biofilm cells. The results indicated that AIA-1 and -2 could affect antibiotic tolerance. Moreover, the results of hydrocarbon adherence and cell membrane permeability assays suggested that AIA-1 and -2 changed bacterial cell surface hydrophobicity and accelerated the outer membrane permeability of the hydrophobic antibiotics such as azithromycin and clarithromycin. Our study demonstrated that the new combination therapy of macrolides and AIA-1 and -2 may improve the therapeutic efficacy of macrolides in the treatment of chronic P. aeruginosa biofilm infections.