Sublethal injury and resuscitation of Candida albicans after amphotericin B treatment

Anticandidal Activity of Capsaicin and Its Effect on Ergosterol Biosynthesis and Membrane Integrity of Candida albicans

Oral candidiasis is an infection of the oral cavity commonly caused by Candida albicans. Endodontic treatment failure has also been found to be persistent from C. albicans in the root canal system. Despite the availability of antifungal drugs, the management of Candida oral infection is difficult as it exhibits resistance to a different class of antifungal drugs. Therefore, it is necessary to discover new antifungal compounds to cure fungal infections. This study aimed to examine the antifungal susceptibility of Capsaicin, an active compound of chili pepper. The susceptibility of Capsaicin and Fluconazole was tested against the Candida species by the CLSI (M27-A3) method. The effect of Capsaicin on the fungal cell wall was examined by the ergosterol inhibitory assay and observed by the scanning electron micrograph. The MIC range of Capsaicin against Candida isolates from oral (n = 30), endodontic (n = 8), and ATCC strains (n = 2) was 12.5−50 µg/mL. The MIC range of Fluconazole (128- 4 µg/mL) significantly decreased (2- to 4-fold) after the combination with Capsaicin (MIC/4) (p < 0.05). Capsaicin (at MIC) significantly reduced the mature biofilm of C. albicans by 70 to 89% (p < 0.01). The ergosterol content of the cell wall decreased significantly with the increase in the Capsaicin dose (p < 0.01). Capsaicin showed high sensitivity against the hyphae formation and demonstrated a more than 71% reduction in mature biofilm. A fluorescence microscopy revealed the membrane disruption of Capsaicin-treated C. albicans cells, whereas a micrograph of electron microscopy showed the distorted cells’ shape, ruptured cell walls, and shrinkage of cells after the release of intracellular content. The results conclude that Capsaicin had a potential antifungal activity that inhibits the ergosterol biosynthesis in the cell wall, and therefore, the cells’ structure and integrity were disrupted. More importantly, Capsaicin synergistically enhanced the Fluconazole antifungal activity, and the synergistic effect might be helpful in the prevention of Fluconazole resistance development and reduced drug-dosing.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Cuminal Inhibits Trichothecium roseum Growth by Triggering Cell Starvation: Transcriptome and Proteome Analysis

Trichothecium roseum is a harmful postharvest fungus causing serious damage, together with the secretion of insidious mycotoxins, on apples, melons, and other important fruits. Cuminal, a predominant component of Cuminum cyminum essential oil has proven to successfully inhibit the growth of T. roseum in vitro and in vivo. Electron microscopic observations revealed cuminal exposure impaired the fungal morphology and ultrastructure, particularly the plasmalemma. Transcriptome and proteome analysis was used to investigate the responses of T. roseum to exposure of cuminal. In total, 2825 differentially expressed transcripts (1516 up and 1309 down) and 225 differentially expressed proteins (90 up and 135 down) were determined. Overall, notable parts of these differentially expressed genes functionally belong to subcellular localities of the membrane system and cytosol, along with ribosomes, mitochondria and peroxisomes. According to the localization analysis and the biological annotation of these genes, carbohydrate and lipids metabolism, redox homeostasis, and asexual reproduction were among the most enriched gene ontology (GO) terms. Biological pathway enrichment analysis showed that lipids and amino acid degradation, ATP-binding cassette transporters, membrane reconstitution, mRNA surveillance pathway and peroxisome were elevated, whereas secondary metabolite biosynthesis, cell cycle, and glycolysis/gluconeogenesis were down regulated. Further integrated omics analysis showed that cuminal exposure first impaired the polarity of the cytoplasmic membrane and then triggered the reconstitution and dysfunction of fungal plasmalemma, resulting in handicapped nutrient procurement of the cells. Consequently, fungal cells showed starvation stress with limited carbohydrate metabolism, resulting a metabolic shift to catabolism of the cell's own components in response to the stress. Additionally, these predicaments brought about oxidative stress, which, in collaboration with the starvation, damaged certain critical organelles such as mitochondria. Such degeneration, accompanied by energy deficiency, suppressed the biosynthesis of essential proteins and inhibited fungal growth.

Synergistic effects of tea polyphenol epigallocatechin 3-O-gallate and azole drugs against oral Candida isolates

BACKGROUND

The antifungal drug resistance has become an emerging problem in the management of candida infections worldwide. The objective of this study was to examine the efficacy of epigallocatechin 3-O-gallate (EGCG) alone and in combination with fluconazole/ketoconazole drugs against oral Candida isolates.

METHODS

Minimum inhibitory concentration (MIC) and minimum fungicidal concentrations (MFC) of EGCG against 60 oral Candida isolates and 4 ATCC strains were determined. Synergism of EGCG with azole drugs was evaluated by checkerboard micro-dilution method and calculated fractional inhibitory concentration index (FICI). Candida cells' ultrastructure was studied by electron microscopy.

RESULTS

MIC and MFC values of EGCG were in the range of 3.91-15.63 and 15.63-31.25μg/mL, respectively. Minimum biofilm inhibitory concentration (MBIC) range of EGCG (62.5-125μg/mL), was less than the ketoconazole (64-256μg/mL) and fluconazole (128-512μg/mL). The combination of EGCG with fluconazole/ketoconazole exhibited synergistic effects (ΣFICI≤0.50). EGCG with azole drugs showed high sensitivity against the tested isolates in growth curve assays. Against the biofilm, the susceptibility of fluconazole/ketoconazole significantly increased (3 to 5 fold), after combination with EGCG (MBIC/4) (P≤0.001). Electron microscopy of EGCG treated cells showed deformation of cell structure, ruptured cell wall and release of intracellular content. In molecular docking experiments, a strong interaction was observed between EGCG and fungal cell membrane molecule ergosterol.

CONCLUSION

We conclude that EGCG synergistically enhanced the antifungal potential of azole drugs. The synergistic potential of EGCG might be helpful in preventing the development of drug resistance, in lowering the drug dosage, and thus minimizing adverse effects.

Unveiling the Synergistic Interaction Between Liposomal Amphotericin B and Colistin

Patients with multiple comorbidities are often administered simultaneously or sequentially antifungals and antibacterial agents, without full knowledge of the consequences of drug interactions. Considering the clinical relevance of liposomal amphotericin B (L-AMB), the association between L-AMB and six antibacterial agents was evaluated against four clinical isolates and one type strain of Candida spp. and two clinical isolates and one type strain of Aspergillus fumigatus. In order to evaluate such combined effects, the minimal inhibitory concentration (MIC) of L-AMB was determined in the presence of 0.5-, 1-, 2-, and 4-fold peak plasma concentrations of each of the antibacterial drugs. Since the L-AMB/colistin (CST) association was the most synergic, viability assays were performed and the physiological status induced by this association was characterized. In addition, computational molecular dynamics studies were also performed in order to clarify the molecular interaction. The maximum synergistic effect with all antibacterial agents, except CST, was reached at fourfold the usual peak plasma concentrations, resulting in 2-to 8-fold L-AMB MIC reduction for Candida and 2-to 16-fold for Aspergillus. For CST, the greatest synergism was registered at peak plasma concentration (3 mg/L), with 4-to 8-fold L-AMB MIC reduction for Candida and 16-to 32-fold for Aspergillus. L-AMB at subinhibitory concentration (0.125 mg/L) combined with CST 3 mg/L resulted in: a decrease of fungal cell viability; an increase of cell membrane permeability; an increase of cellular metabolic activity soon after 1 h of exposure, which decreased until 24 h; and an increase of ROS production up to 24 h. From the molecular dynamics studies, AMB and CST molecules shown a propensity to form a stable molecular complex in solution, conferring a recognition and binding added value for membrane intercalation. Our results demonstrate that CST interacts synergistically with L-AMB, forming a stable complex, which promotes the fungicidal activity of L-AMB at low concentration.

New Insights Regarding Yeast Survival following Exposure to Liposomal Amphotericin B

In vitro resistance to amphotericin B is an extremely rare event among pathogenic yeasts. However, in vivo response is sometimes reduced, resulting in an unfavorable outcome. Such adverse outcomes might be related to subfungicidal plasma concentrations. We aimed to clarify the mechanisms of liposomal amphotericin B (AMB-L; AmBisome)-induced lesions and the mechanisms responsible for yeast cell recovery following exposure at plasma concentrations. The physiological statuses developing following exposure to AMB-L at simulated plasma concentrations (20 to 0.1 mg/liter) and at a constant concentration (3 mg/liter) were assessed in a 24-h time course assay. Time-kill experiments also were carried out under the same AMB-L treatment conditions. Our results suggest that yeast cells develop compensatory responses related to membrane polarization, metabolic activity, and reactive oxygen species (ROS) production after exposure to high plasma concentrations (20 to 5 mg/liter) during the first 6 h; in the remaining 18 h, when exposed to lower concentrations, cells reveal almost full recovery with no evidence of fungicidal activity. In contrast, whenever cells are exposed to a constant concentration above the MIC, despite initially exhibiting compensatory stress responses, soon afterwards they exhibit membrane depolarization, a decrease of metabolic activity, increasing ROS production, and lastly, programmed cell death and necrosis, resulting in succumbing to AMB-L fungicidal effects. This study may represent a step forward in the support of AMB-L use for clinical treatment of invasive fungal infections, since it demonstrates the importance of maintaining levels of AMB-L above the MIC in plasma and tissues to ensure it produces its fungicidal effects.

A new look at the antibiotic amphotericin B effect on Candida albicans plasma membrane permeability and cell viability functions

Amphotericin B (AmB) is an antifungal polyene for which the most accepted mode of action is formation of protein-like ion channels in the cell membrane. Patch-clamp research on Candida albicans protoplasts carried out in the outside-out configuration showed that application of 0.05 and 0.1 μM AmB caused a decrease in seal resistance. Such a phenomenon can be correlated with a decrease in membrane tightness. AmB applied at a 0.05 μM concentration also caused a decrease in the number of active TOK1 (two-pore outward rectifiers) potassium channels, but did not significantly change their open probability. The results indicate that in C. albicans protoplast AmB causes a decrease in cell membrane integrity by interaction with its lipid phase but not with ion channels. Fluorescence microscopy techniques showed that AmB treatment, in clinical concentrations, had no effect on the percentage of PI-positive protoplasts. AmB treatment in the concentrations tested did not cause a rapid reduction of the number of C. albicans protoplasts. However, there was a significant loss of replication competency and numerous morphological and physiological disorders, including cytoplasm shrinking, abnormal morphology of the nucleus and mitochondria, a sudden decrease in the MTT reduction level and oxidative stress. Our results show that the induction of yeast cell death by AmB, at therapeutic doses, is a multistage and long-term process involving multiple intracellular pathways.

Canadian clinical practice guidelines for invasive candidiasis in adults

Candidemia and invasive candidiasis (C/IC) are life-threatening opportunistic infections that add excess morbidity, mortality and cost to the management of patients with a range of potentially curable underlying conditions. The Association of Medical Microbiology and Infectious Disease Canada developed evidence-based guidelines for the approach to the diagnosis and management of these infections in the ever-increasing population of at-risk adult patients in the health care system. Over the past few years, a new and broader understanding of the epidemiology and pathogenesis of C/IC has emerged and has been coupled with the availability of new antifungal agents and defined strategies for targeting groups at risk including, but not limited to, acute leukemia patients, hematopoietic stem cell transplants and solid organ transplants, and critical care unit patients. Accordingly, these guidelines have focused on patients at risk for C/IC, and on approaches of prevention, early therapy for suspected but unproven infection, and targeted therapy for probable and proven infection.

Amphotericin B mediates killing in Cryptococcus neoformans through the induction of a strong oxidative burst

We studied the effects of Amphotericin B (AmB) on Cryptococcus neoformans using different viability methods (CFUs enumeration, XTT assay and propidium iodide permeability). After 1h of incubation, there were no viable colonies when the cells were exposed to AmB concentrations ≥ 1 mg/L. In the same conditions, the cells did not become permeable to propidium iodide, a phenomenon that was not observed until 3h of incubation. When viability was measured in parallel using XTT assay, a result consistent with the CFUs was obtained, although we also observed a paradoxical effect in which at high AmB concentrations, a higher XTT reduction was measured than at intermediate AmB concentrations. This paradoxical effect was not observed after 3h of incubation with AmB, and lack of XTT reduction was observed at AmB concentrations higher than 1mg/L. When stained with dihydrofluorescein, AmB induced a strong intracellular oxidative burst. Consistent with oxidative damage, AmB induced protein carbonylation. Our results indicate that in C. neoformans, Amphotericin B causes intracellular damage mediated through the production of free radicals before damage on the cell membrane, measured by propidium iodide uptake.

Retigeric acid B exerts antifungal effect through enhanced reactive oxygen species and decreased cAMP

BACKGROUND

Retigeric acid B (RAB), a triterpene acid isolated from Lobaria kurokawae exerts antifungal effect. The present study was designed to elucidate the underlying mechanisms by which RAB regulates the proliferation and cell death of Candida albicans.

METHODS

We measured the metabolic activity of C. albicans with WST1 Cell Proliferation and Cytotoxicity Assay Kit, analyzed the cell cycle by flow cytometry, visualized the ultrastructure by transmission electron microscopy (TEM) and investigated the apoptosis and necrosis induced by RAB using confocal microscopy. The reactive oxygen species (ROS) accumulation was determined by spectrophotometry, flow cytometry and fluorescent microscopy. The mtΔψ was detected using flow cytometry. And the levels of intracellular cAMP and ATP were measured with cAMP ELISA and ATP Assay Kits, respectively.

RESULTS

The proliferation of the yeasts was blocked in G(2)/M phase by a low dose of RAB treatment and in G(1) phase at high concentration. When cultured in phosphate buffered saline (PBS) deprived of energy source, yeasts displayed the phenotype of death caused by accumulated ROS, mtΔψ hyperpolarization and dramatic decrease in ATP level in the presence of high dose of RAB.

GENERAL SIGNIFICANCE

RAB inhibits the growth of C. albicans by stimulating ROS production and reducing intracellular cAMP. The ROS accumulation, mtΔψ hyperpolarization, ATP depletion and damaged plasma membrane integrity together mediate cell death of C. albicans induced by RAB. Our findings provide a novel molecular mechanism for exploring possible applications of lichen derived metabolites in fighting fungal infection in humans.

Plasma membrane damage to Candida albicans caused by chlorine dioxide (ClO2)

AIM

To investigate the plasma membrane damage of chlorine dioxide (ClO(2)) to Candida albicans ATCC10231 at or below the minimal fungicidal concentration (MFC).

METHODS AND RESULTS

ClO(2) at MFC or below was adopted to treat the cell suspensions of C. albicans ATCC10231. Using transmission electron microscopy, no visible physiological alteration of cell shape and plasma membrane occurred. Potassium (K(+)) leakages were significant; likewise, it showed time- and dose-dependent increases. However, adenosine triphosphate (ATP) leakages were very slight. Research shows that when 99% of the cells were inactivated, the leakage was measured at 0.04% of total ATP. Compared with the mortality-specific fluorescent dye of DiBAC(4)(3), majority of the inactivated cells were poorly stained by propidium iodide, another mortality-specific fluorescent dye which can be traced by flow cytometry.

CONCLUSION

At or below MFC, ClO(2) damages the plasma membranes of C. albicans mainly by permeabilization, rather than by the disruption of their integrity. K(+) leakage and the concomitant depolarization of the cell membrane are some of the critical events.

SIGNIFICANCE AND IMPACT OF THE STUDY

These insights into membrane damages are helpful in understanding the action mode of ClO(2).

Dormancy of Candida albicans cells in the presence of the polyene antibiotic amphotericin B: simple demonstration by flow cytometry

Flow cytometry light scattering was used to monitor size increase of Candida albicans (isolate ATCC 10231) cells in the presence or absence of the antifungal drug amphotericin B (AmB). This non-invasive and descriptive method allowed for the differentiation of dead and dormant sub-populations of cells. When inoculated into a growth medium without AmB, a progressive increase in light scattering was observed over a period of approximately 4 h, but without proliferation of the yeast. After this period, the light scattering distribution regressed to baseline level, whereas cell proliferation started. In the presence of AmB, all the cells shrank in size within approximately 4 h and proliferation was temporarily halted. However, in the presence of 0.4 microM AmB, a progressive increase of light scattering occurred after 21 h which was similar to that observed within the first 4 h in the absence of the antifungal. After approximately 24 h of incubation at this concentration of AmB, proliferation resumed. These observations indicate that this renewed cell proliferation was due to the reawakening of dormant cells in the presence of AmB (45% in the presence of 0.4 microM AmB) rather than the result of the development of viable cells that had escaped detection. This simple descriptive approach could be extended to other fungal strains or species, to other antifungal drugs and possibly to bacteria.