Ping-Hui Gao

Potent In Vitro Synergism of Fluconazole and Berberine Chloride against Clinical Isolates of Candida albicans Resistant to Fluconazole

ABSTRACT In vitro interaction of fluconazole and berberine chloride was investigated against 40 fluconazole-resistant clinical isolates of Candida albicans. Synergism in fungistatic activity was found with the checkerboard microdilution assay. The findings of agar diffusion tests and time-kill curves confirmed the synergistic interaction, but no antagonistic action was observed.

Proteomic analysis reveals a synergistic mechanism of fluconazole and berberine against fluconazole-resistant Candida albicans: endogenous ROS augmentation.

Our previous study showed that concomitant use of berberine (BBR) and fluconazole (FLC) provided a synergistic action against FLC-resistant Candida albicans (C. albicans) clinical strains in vitro. To clarify the mechanism underlying this action, we performed a comparative proteomic study in untreated control cells and cells treated with FLC and/or BBR in 2 clinical strains of C. albicans resistant to FLC. Our analyses identified 16 differentially expressed proteins, most of which were related to energy metabolisms (e.g., Gap1, Adh1, and Aco1). Functional analyses revealed that FLC + BBR treatment increased mitochondrial membrane potential, decreased intracellular ATP level, inhibited ATP-synthase activity, and increased generation of endogenous reactive oxygen species (ROS) in FLC-resistant strains. In addition, checkerboard microdilution assay showed that addition of antioxidant ascorbic acid or reduced glutathione reduced the synergistic antifungal activity of FLC + BBR significantly. These results suggest that mitochondrial aerobic respiration shift and endogenous ROS augmentation contribute to the synergistic action of FLC + BBR against FLC-resistant C. albicans.

In vitro activity of baicalein against Candida albicans biofilms

Candidiasis can be associated with the formation of biofilms on bioprosthetic surfaces. The intrinsic resistance of Candida albicans biofilms to the most commonly used antifungal agents has been demonstrated. Here we examined the effect of baicalein (BE) on C. albicans biofilm formation. Confocal laser scanning microscopy showed that C. albicans biofilm was inhibited and growth was predominantly composed of yeast cells and pseudohyphae. The effect of inhibition was dose-dependent. Over 70% inhibition of biofilms was observed at BE concentrations between 4 microg/mL and 32 microg/mL. Moreover, BE was active against different growth stages of biofilms, with 89% and 52% inhibition when BE was added at 0 h and 24 h of the incubation period, respectively. The water-hydrocarbon two-phase assay showed a decrease in cell surface hydrophobicity in the BE-treated groups compared with the control group. Consistent with this, real-time reverse transcriptase polymerase chain reaction (RT-PCR) results showed that BE-treated cells expressed lower levels of CSH1 mRNA than cells grown in the absence of BE. Our data provide useful information for the development of new strategies to reduce the incidence of device-associated infections.

Candida albicans cells lacking CaMCA1-encoded metacaspase show resistance to oxidative stress-induced death and change in energy metabolism

Candida albicans, an opportunistic pathogen, can undergo programmed cell death upon various stimuli, including oxidative stress. In this study, we showed that deletion of CaMCA1, a homologue of Saccharomyces cerevisiae metacaspase YCA1, could both attenuated oxidative stress-induced cell death and caspase activation. Compared to wild-type strain, Camca1Delta mutant showed higher accumulation of trehalose and transcription of the genes related to trehalose biosynthesis (TPS2 and TPS3) under the condition of oxidative stress. Furthermore, lower intracellular ATP concentration and mitochondrial membrane potential, less endogenous reactive oxygen species (ROS) generation were observed in Camca1Delta mutant. Our results suggest that CaMCA1 might mediate the sensitiveness to oxidative stress by affecting energy metabolism in C. albicans.

The alternative oxidase of Candida albicans causes reduced fluconazole susceptibility

OBJECTIVES To evaluate the effect of Candida albicans mitochondrial respiratory status on antifungal azole susceptibility. METHODS The inhibitors cyanide and salicylhydroxamic acid (SHAM) were each combined with azoles to examine the effect of the combinations on C. albicans. C. albicans strains deleted for the alternative oxidase (Aox) were also examined for susceptibility to azoles and for the generation of intracellular reactive oxygen species (ROS). A chequerboard microdilution assay was performed on several C. albicans clinical strains including azole-resistant isolates to explore the combined effect of fluconazole and inhibitors of Aox. RESULTS The induction of the alternative respiratory pathway by cyanide decreased susceptibility to azoles, while the inhibition of alternative respiration by SHAM increased azole susceptibility. It was found that ROS production was increased in the absence of Aox in C. albicans upon treatment by antifungals such as miconazole and benomyl. The combination of fluconazole with SHAM resulted in a synergistic effect on the killing of C. albicans clinical isolates. CONCLUSION These results demonstrate that the induction of the alternative respiratory pathway confers reduced susceptibility to antifungal azoles, potentially through a mechanism that involves decreased intracellular ROS production during exposure to antifungal agents.

RTA2 is involved in calcineurin-mediated azole resistance and sphingoid long-chain base release in Candida albicans

Abstract.The calcineurin pathway has been reported to be essential for the development of azole resistance in Candida albicans. The depletion or ectopic over-expression of RTA2 increased or decreased susceptibility of C. albicans to azoles, respectively. CaCl2- induced activation of the calcineurin pathway in wildtype C. albicans promoted resistance to azoles, while the Ca2+ chelator (EGTA), calcineurin inhibitors (FK506 and cyclosporin A) and the deletion of RTA2 blocked the resistance-promoting effects of CaCl2. Furthermore, we found that RTA2 was up-regulated in a calcineurin-dependent manner. The depletion of RTA2 also made the cell membrane of C. albicans liable to be destroyed by azoles and RTA2 over-expression attenuated the destroying effects. Finally, the disruption of RTA2 caused an increased accumulation of dihydrosphingosine (DHS), one of the two sphingolipid long-chain bases, by decreasing release of DHS. In conclusion, our findings suggest that RTA2 is involved in calcineurin-mediated azole resistance and sphingoid long-chain base release in C. albicans.

RTA2, a novel gene involved in azole resistance in Candida albicans

Widespread and repeated use of azoles, particularly fluconazole, has led to the rapid development of azole resistance in Candida albicans. Overexpression of CDR1, CDR2, and CaMDR1 has been reported contributing to azole resistance in C. albicans. In this study, hyper-resistant C. albicans mutant, with the above three genes deleted, was obtained by exposure to fluconazole and fluphenezine for 28 passages. Thirty-five differentially expressed genes were identified in the hyper-resistant mutant by microarray analysis; among the 13 up-regulated genes, we successfully constructed the rta2 and ipf14030 null mutants in C. albicans strain with deletions of CDR1, CDR2 and CaMDR1. Using spot dilution assay, we demonstrated that the disruption of RTA2 increased the susceptibility of C. albicans to azoles while the disruption of IPF14030 did not influence the sensitivity of C. albicans to azoles. Meanwhile, we found that ectopic overexpression of RTA2 in C. albicans strain with deletions of CDR1, CDR2 and CaMDR1 conferred resistance to azoles. RTA2 expression was found elevated in clinical azole-resistant isolates of C. albicans. In conclusion, our findings suggest that RTA2 is involved in the development of azole resistance in C. albicans.

2-Amino-nonyl-6-methoxyl-tetralin muriate inhibits sterol C-14 reductase in the ergosterol biosynthetic pathway

AbstractAim:To investigate the action mechanism of a novel chemical structural aminotetralin derivate, 2-Amino-Nonyl-6-Methoxyl-Tetralin Muriate (10b), against Candida albicans (C albicans) in the ergosterol biosynthetic pathway.Methods:Antifungal susceptibility test of 10b was carried out using broth microdilution method, the action mechanism of 10b against C albicans was investigated by GC-MS spectrometry and real-time RT-PCR assay, and cytotoxicity of 10b in vitro was assessed by MTS/PMS reduction assay.Results:10b reduced the ergosterol content markedly, and the 50% ergosterol content inhibitory concentration (ECIC50 value) was 0.08 μg/mL. Although the sterol composition of 10b-grown cells was completely identical with that of erg24 strain, the content of ergosta-8,14,22-trienol in 10b-grown cells was much higher than that in erg24 strain. Real-time RT-PCR assay revealed a global upregulation of sterol metabolism genes. In addition, the 50% inhibitory concentration (IC50 value) of 10b was 11.30 μg/mL for murine embryonic fibroblasts and 35.70 μg/mL for human normal liver cells.Conclusion:10b possessed a mode of action different from that of azoles and morpholines, whose targets were sterol C-14 reductase (encoded by ERG24 gene) and sterol C-5 desaturase (encoded by ERG3) related enzyme. Although 10b seemed to reduce MTS/PMS reduction in a dose dependent manner, IC50 value for mammalian cells was much higher than 50% minimum inhibitory concentration (MIC50) value for C albicans. This indicates that the formulation is preliminarily safe and warrants further study for possible human applications.

Ascorbic acid decreases the antifungal effect of fluconazole in the treatment of candidiasis.

1 The aim of the present study was to investigate the effects of ascorbic acid (AA) on the antifungal activity of fluconazole (FCZ) in a systemic murine candidiasis model as well as in vitro. 2 The murine model was established by infusion of Candida albicans via the tail vein. Control mice received no further treatment. Other groups of mice were injected with FCZ (0.5 mg/kg, i.p.) and then treated or not with 50 or 500 mg/kg AA intragastrically (i.g.) or i.p. In all groups, FCZ was administered i.p. 2 h after fungal inoculation, whereas AA was administered 6 h after fungal inoculation. Survival rate, kidney fungal burden and renal pathological changes were evaluated. 3 The in vitro effects of AA (5, 1 and 0.2 mmol/L) on the growth of various Candida strains in the presence of FCZ (0.125–64 µg/mL) were also investigated. The in vitro effects of two anti‐oxidants, namely N‐acetylcysteine (NAC; 5, 1 and 0.2 mmol/L) and reduced glutathione (GSH; 5, 1 and 0.2 mmol/L), on FCZ activity were evaluated to determine the mechanism of action of AA. 4 Intragastric administration of AA (50 or 500 mg/kg) significantly decreased the antifungal effect of 0.5 mg/kg FCZ. Although i.p. administration of AA (50 or 500 mg/kg) had no significant effect on the survival of mice, it dose‐dependently inhibited the activity of FCZ, with significant inhibition observed with 500 mg/kg AA. 5 In vitro, AA decreased the activity of FCZ against various Candida strains. Both NAC and GSH dose‐dependently decreased the activity of FCZ. 6 The results of the present study indicate that AA inhibits the antifungal activity of FCZ, suggesting that the two should not be used together clinically for the treatment of candidiasis.

Altered protein profile of lymphocytes in an antigen-specific model of colitis: a comparative proteomic study.

Abstract.Objective:Lymphocytes are deeply involved in the initiation and perpetuation of inflammatory response in inflammatory bowel disease (IBD) and lymphocyte-derived proteins are associated with the pathogenesis of the disease. The aim of this study was to identify the altered protein profiles of lymphocytes from rats with colitis.Methods:Colitis models were induced by colonic administration of trinitrobenzene sulfonic acid (TNBS) in 50% ethanol in male SD rats. Seven days after administration of TNBS/ethanol, lymphocytes were harvested from mesenteric lymph nodes (MLNs) and proteins were extracted. Two-dimensional polyacrylamide gel electrophoresis and PDQuest 2D-image-analysis software were used to display and analyze the protein spots. The differentially-expressed proteins were identified by tryptic in-gel digestion and mass spectrometry. Real-time RT-PCR was used for selected transcripts to validate the findings of the proteomics analysis.Results:A total of 1,100 protein spots including 26 proteins with at least a two-fold difference in abundance between colitis and control groups were identified. Among all the detected spots, 17 were up-regulated and 9 were down-regulated. It was found that the altered proteins included the regulators of the cell cycle and cell proliferation, signal transduction factors, inflammatory factors, apoptosis-related proteins and metabolic enzymes.Conclusions:In lymphocytes of rats with TNBS-induced colitis, 26 altered proteins were identified. They involve inflammation, apoptosis, metabolism, and regulation of the cell cycle, cell proliferation, and signal transduction.