In this study, the antifungal effects of silver nano-particles (nano-Ag) and their mode of action were investigated. Nano-Ag showed antifungal effects on fungi tested with low hemolytic effects against human erythrocytes. To elucidate the antifungal mode of action of nano-Ag, flow cytometry analysis, a glucose-release test, transmission electron microscopy (TEM) and the change in membrane dynamics using 1,6-diphenyl-1,3,5-hexatriene (DPH), as a plasma membrane probe, were performed with Candida albicans. The results suggest nano-Ag may exert an antifungal activity by disrupting the structure of the cell membrane and inhibiting the normal budding process due to the destruction of the membrane integrity. The present study indicates nano-Ag has considerable antifungal activity, deserving further investigation for clinical applications.
Chlorogenic acid is a polyphenol compound, derived from several fruit and plants. The aim of this study was to assess the in vitro antifungal activity of chlorogenic acid and its mode of action. The results indicate that chlorogenic acid exhibits antifungal activities against certain pathogenic fungi in an energy-independent manner, without any hemolytic effect on human erythrocytes. To elucidate the antifungal mode of action of chlorogenic acid, flow cytometry analysis by using DiBAC 4 (3) and changes in membrane dynamics using 1,6-diphenyl-1,3,5-hexatriene (DPH) were performed with Candida albicans. The results suggest that chlorogenic acid may exert antifungal activity by disrupting the structure of the cell membrane. It is demonstrated that chlorogenic acid is a valid lead compound for the development of bioactive alternatives for treatment of fungal infections. Fig. 5 Concentration of released trehalose and glucose from C. albicans by chlorogenic acid and amphotericin B. The error bars represent the SD for three independent experiments, performed in triplicate.
Resveratrol, a phenolic antioxidant found in grapes, has been known to mediate various biological activities on the human body. In the present study, we tested the antifungal activity of resveratrol against human pathogenic fungi before carrying out further studies to elucidate the antifungal mechanism(s) of resveratrol. Resveratrol displayed potent antifungal activity against human pathogenic fungi at concentration levels of 10-20 microg/mL. Furthermore, time-kill curve exhibited fungicidal effect of resveratrol on C. albicans, but the compound had no hemolytic activity against human erythrocytes. The destruction of C. albicans cells by resveratrol was confirmed by scanning electron microscopy. These results suggest that resveratrol could be employed as a therapeutic agent to treat fungal infections of humans.
Pleurocidin (Ple) is a 25-residue peptide which is derived from the skin mucous secretion of the winter flounder (Pleuronectes americanus). In this study, we investigated antifungal effects and its mode of action of Ple on human pathogenic fungi. Ple showed potent antifungal activity with low hemolytic activity. To investigate the antifungal mechanisms of Ple, the cellular localization and membrane interaction of Ple were examined. Protoplast regeneration and membrane-disrupting activity by DPH-labeled membrane support the idea, that Ple exerts fungicidal activity against the human pathogenic fungus Candida albicans with the disruption of a plasma membrane. To aim for which was the application of a therapeutic agent, we designed a synthetic enantiomeric peptide composed of all-d-amino acids to enhance proteolytic resistance. The synthetic all-d-Ple also displayed two-fold more potent antifungal activity than that of all-l-Ple, and its antifungal activity showed proteolytic resistance against various proteases. Therefore, these results suggest a therapeutic potential of all-d-Ple with regard to its proteolytic resistance against human fungal infections.
Piscidin, a 22-residue cationic peptide isolated from the mast cells of hybrid striped bass, has potent antimicrobial activities. In the present study, we investigated the fungicidal activity and mode of action of piscidins. Fungicidal and hemolytic assays were examined in order to assess their potency and toxicity, respectively. The results showed that fungicidal and hemolytic activities were higher for piscidin 1 (P1) than piscidin 3 (P3). Additionally, the abilities to permeabilize the model phospholipids membranes were also higher for P1 than P3, which were consistent with the biological activities of P1 and P3. These results suggest that the biological action of the peptides may be carried out through the lipid membrane. To understand the fungicidal properties of P1, we focused on a membrane-active mechanism of the peptide by in vivo testing against Candida albicans as the model organism. Flow cytometric analysis by using bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC 4 (3)] and protoplast regeneration experiments showed that P1 caused fungal membrane damage. Furthermore, fluorescence analysis, using 1,6-diphenyl-1,3,5-hexatriene, revealed that these peptides created pores in fungal membranes. Thus, the present study demonstrated that piscidins exert their fungicidal effects by disrupting fungal membrane through pore formation.
Indole-3-carbinol (I3C) is a naturally occurring constituent of cruciferous vegetables. The aim of this study was to assess the in vitro antimicrobial activity of I3C and its mode of action. By using an NCCLS broth microdilution assay, the activity of I3C was evaluated against human pathogenic microorganisms including clinically isolated antibiotic-resistant bacterial strains. The results indicated that I3C exhibited broad spectrum antimicrobial activities. To elucidate the physiological changes of the fungal cells induced by I3C, we performed a flow cytometric analysis for a cell cycle. The results showed that I3C arrested the cell cycle at the G 2 /M phase in Candida albicans. To understand the antifungal mode of action of I3C, the change in the membrane dynamics was monitored by using fluorescence changing experiments against C. albicans. The results suggest that I3C may exert antifungal activity by disrupting the structure of the cell membrane. The present study indicates that I3C has considerable antimicrobial activity, deserving further investigation for clinical applications.
Amentoflavone is a plant bif avonoid that was isolated from an ethyl acetate extract of the whole plant of Selaginella tamariscina (Beauv.) spring. 1D and 2D NMR spectroscopy including DEPT, HMQC, and HMBC were used to determine its structure. Amentoflavone exhibited potent antifungal activity against several pathogenic fungal strains but had a very low hemolytic effect on human erythrocytes. In particular, amentoflavone induced the accumulation of intracellular trehalose on C. albicans as a stress response to the drug, and disrupted the dimorphic transition that forms pseudo-hyphae during pathogenesis. In conclusion, amentoflavone has great potential to be a lead compound for the development of antifungal agents.
Korean red ginseng saponins (ginsenosides) have been reported as having various biological properties, but the combinational effects with commercial antibiotics and the mode of action of ginsenosides remain mostly unknown. In this study, saponins were isolated from Korean red ginseng, and the antibacterial effects of ginsenosides were investigated. Ginsenosides showed antibacterial activities toward pathogenic Gram-positive and Gram-negative bacteria. To elucidate the antibacterial mode of action of ginsenosides, we measured the release of the fluorescent marker calcein from negatively charged PC/PG (1 : 1, w/w) liposomes, which mimic bacterial membranes. The results suggest that ginsenosides may exert antibacterial activity by disrupting the cell membrane. To estimate the general combination effects of ginsenosides and commercial antibiotics, such as kanamycin and cefotaxime, on antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) strains that were clinically isolated from an infected patient, the fraction inhibitory concentration (FIC) indexes were determined by a checkerboard study. The FIC indexes showed synergistic or additive effects between the ginsenosides and antibiotics tested.
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