bis(1-3-dibutylbarbiturate)trimethine-oxonol and fluorexon

Bac8c (RIWVIWRR-NH2) is an analogue peptide derived through complete substitution analysis of the linear bovine host defense peptide variant Bac2A. In the present study, the antifungal mechanism of Bac8c against pathogenic fungi was investigated, with a particular focus on the effects of Bac8c on the cytoplasmic membrane. We used bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)] staining and 3,3'-dipropylthiacarbocyanine iodide [DiSC3(5)] assays to show that Bac8c induced disturbances in the membrane potential of Candida albicans. An increase in membrane permeability and suppression of cell wall regeneration were also observed in Bac8c-treated C. albicans. We studied the effects of Bac8c treatment on model membranes to elucidate its antifungal mechanism. Using calcein and FITC-labeled dextran leakage assays from Bac8c-treated large unilamellar vesicles (LUVs) and giant unilamellar vesicles (GUVs), we found that Bac8c has a pore-forming action on fungal membranes, with an estimated pore radius of between 2.3 and 3.3 nm. A membrane-targeted mechanism of action was also supported by the observation of potassium release from the cytosol of Bac8c-treated C. albicans. These results indicate that Bac8c is considered as a potential candidate to develop a novel antimicrobial agent because of its low-cost production characteristics and high antimicrobial activity via its ability to induce membrane perturbations in fungi.

Topics: Animals; Antifungal Agents; Antimicrobial Cationic Peptides; Barbiturates; Benzothiazoles; Biological Transport; Candida albicans; Carbocyanines; Cattle; Cell Membrane; Cell Membrane Permeability; Cell Wall; Dextrans; Fluorescein-5-isothiocyanate; Fluoresceins; Fluorescent Dyes; Isoxazoles; Membrane Potentials; Microbial Sensitivity Tests; Potassium; Spectrometry, Fluorescence; Unilamellar Liposomes

Scolopendin 2 is a 16-mer peptide (AGLQFPVGRIGRLLRK) derived from the centipede Scolopendra subspinipes mutilans. We observed that this peptide exhibited antimicrobial activity in a salt-dependent manner against various fungal and bacterial pathogens and showed no hemolytic effect in the range of 1.6 μM to 100 μM. Circular dichroism analysis showed that the peptide has an α-helical properties. Furthermore, we determined the mechanism(s) of action using flow cytometry and by investigating the release of intracellular potassium. The results showed that the peptide permeabilized the membranes of Escherichia coli O157 and Candida albicans, resulting in loss of intracellular potassium ions. Additionally, bis-(1,3-dibutylbarbituric acid) trimethine oxonol and 3,3'-dipropylthiacarbocyanine iodide assays showed that the peptide caused membrane depolarization. Using giant unilamellar vesicles encapsulating calcein and large unilamellar vesicles containing fluorescein isothiocyanate-dextran, which were similar in composition to typical E. coli O157 and C. albicans membranes, we demonstrated that scolopendin 2 disrupts membranes, resulting in a pore size between 4.8 nm and 5.0 nm. Thus, we have demonstrated that a cationic antimicrobial peptide, scolopendin 2, exerts its broad-spectrum antimicrobial effects by forming pores in the cell membrane.

Topics: Amino Acid Motifs; Animals; Anti-Infective Agents; Antimicrobial Cationic Peptides; Arthropod Proteins; Arthropods; Barbiturates; Benzothiazoles; Candida albicans; Carbocyanines; Cell Membrane; Dextrans; Erythrocytes; Escherichia coli O157; Fluorescein-5-isothiocyanate; Fluoresceins; Fluorescent Dyes; Humans; Isoxazoles; Microbial Sensitivity Tests; Molecular Sequence Data; Spectrometry, Fluorescence; Unilamellar Liposomes

The aim of this study is to investigate the antifungal mechanism of curcumin. This polyphenolic compound has been used traditionally in Asia for medicinal, culinary, and other purposes. Although antifungal effect of curcumin has been reported, this is the first study for its mode of action underlying disruption of plasma membrane in Candida albicans. The leakage of potassium ion from the fungal cytosol and dissipation in membrane potential was detected by bis-(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC4 ] staining. We also investigated an increase in membrane permeability in curcumin-treated C. albicans with influx of propidium iodide assay. Fluorescence analysis with 1,6-diphenyl-1,3,5-hexatriene supported the membrane-targeted mechanism of action indicating membrane disruption. On the basis of these results, we studied the effects of curcumin treatment on model membrane to elucidate its antifungal mechanism. Using calcein leakage assays from curcumin-treated large unilamellar vesicles and giant unilamellar vesicles, we found that curcumin has membrane-active mechanism inducing leakage of intracellular component through the flappy membrane. Therefore, this study suggests that curcumin exerts antifungal activity via inducing disruption of fungal plasma membrane.

Topics: Antifungal Agents; Barbiturates; Candida albicans; Cell Membrane; Curcumin; Diphenylhexatriene; Fluoresceins; Fluorescence; Isoxazoles; Potassium; Propidium