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

Potential Anti-Candida albicans Mechanism of Trichoderma Acid from Trichoderma spirale

Candida albicans is the main causal pathogen of fungal infections in human beings. Although diverse anti-C. albicans drugs have been explored, the drug resistance and side effects of these drugs are intensifying. Thus, it is urgent to explore new anti-C. albicans compounds from natural products. In this study, we identified trichoderma acid (TA), a compound from Trichoderma spirale with a strong inhibitory effect on C. albicans. Transcriptomic and iTRAQ-based proteomic analyses of TA-treated C. albicans in combination with scanning electronic microscopy and reactive oxygen species (ROS) detection were performed to investigate the potential targets of TA. The most significant differentially expressed genes and proteins after TA treatment were verified through Western blot analysis. Our results revealed that mitochondrial membrane potential, endoplasmic reticulum, ribosomes in the mitochondria, and cell walls were disrupted in TA-treated C. albicans, leading to the accumulation of ROS. The impaired enzymatic activities of superoxide dismutase further contributed to the increase in ROS concentration. The high concentration of ROS led to DNA damage and cell skeleton destruction. The expression levels of Rho-related GTP-binding protein RhoE (RND3), asparagine synthetase (ASNS), glutathione S-transferase, and heat shock protein 70 were significantly up-regulated in response to apoptosis and toxin stimulation. These findings suggest that RND3, ASNS, and supereoxide dismutase 5 are the potential targets of TA, as further demonstrated through Western blot analysis. The combination of transcriptomic, proteomic, and cellular analyses would provide clues for the anti-C. albicans mechanism of TA and the defensive response mechanism of C. albicans. TA is thus recognized as a promising new anti-C. albicans leading compound that alleviates the hazard of C. albicans infection in human beings.

Antifungal mechanisms of volatile organic compounds produced by Pseudomonas fluorescens ZX as biological fumigants against Botrytis cinerea

To explore the antifungal mechanisms of volatile organic compounds (VOCs) produced by Pseudomonas fluorescens ZX against Botrytis cinerea, biochemical analyses and transcriptomic techniques were employed in this work. The results showed that P. fluorescens ZX-producing VOCs can increase the cell membrane permeability of B. cinerea and disrupt cell membrane integrity, resulting in leakage of the pathogen's cellular contents, inhibition of ergosterol biosynthesis (about 76%), and an increase in malondialdehyde (MDA) content. Additionally, for B. cinerea respiration, P. fluorescens ZX-producing VOCs (1 × 10⁹ CFU /mL) significantly inhibited the activities of ATPase (55.7%), malate dehydrogenase (MDH) (33.1%), and succinate dehydrogenase (SDH) (57.9%), seriously interfering with energy metabolism and causing accumulation of reactive oxygen species (ROS). Furthermore, transcriptome analysis of B. cinerea following exposure to VOCs revealed 4590 differentially expressed genes (DEGs) (1388 upregulated, 3202 downregulated). Through GO analysis, these DEGs were determined to be enriched in intrinsic components of membrane, integral components of membrane, and membrane parts, while KEGG analysis indicated that they were enriched in many amino acid metabolism pathways. Significantly, the DEGs related to ergosterol biosynthesis, ATPase, mitochondrial respiratory chain, malate dehydrogenase, and cell membrane showed down-regulation, corroborating the biochemical analyses. Taken together, these results suggest that the antifungal activity of P. fluorescens ZX-producing VOCs against B. cinerea occurs primary mechanisms: causing significant damage to the cell membrane, negatively affecting respiration, and interfering with amino acid metabolism.

Antimicrobial peptide AMP-17 exerts anti-Candida albicans effects through ROS-mediated apoptosis and necrosis

There is a need for new anti-Candida albicans (C. albicans) drugs owing to the emergence of drug resistance in recent years. AMP-17, an antimicrobial peptide from Musca domestica (M. domestica), is known to be an effective inhibitor of many fungal pathogens, including C. albicans. In this study, we investigated the potential mechanism underlying the anti-C. albicans effects of AMP-17 using flow cytometry, transmission electron microscopy, fluorescent probes, fluorescence microplate reader, and confocal laser microscopy. Transmission electron microscopy showed that, following AMP-17 treatment, the shape of C. albicans cells became irregular, and vacuoles could be seen in the cytoplasm. Furthermore, AMP-17 treatment resulted in an increase in reactive oxygen species (ROS) levels, depolarization of the mitochondrial membrane potential (MMP), and changes in the cell cycle, leading to the apoptosis and necrosis, which ultimately contributed to the death of C. albicans cells.

Biocontrol of Candida albicans by Antagonistic Microorganisms and Bioactive Compounds

Candida albicans is an endogenous opportunistic pathogenic fungus that is harmless when the host system remains stable. However, C. albicans could seriously threaten human life and health when the body’s immune function declines or the normal flora is out of balance. Due to the increasing resistance of candidiasis to existing drugs, it is important to find new strategies to help treat this type of systemic fungal disease. Biological control is considered as a promising strategy which is more friendly and safer. In this review, we compare the bacteriostatic behavior of different antagonistic microorganisms (bacteria and fungi) against C. albicans. In addition, natural products with unique structures have attracted researchers’ attention. Therefore, the bioactive nature products produced by different microorganisms and their possible inhibitory mechanisms are also reviewed. The application of biological control strategies and the discovery of new compounds with antifungal activity will reduce the resistance of C. albicans, thereby promoting the development of novel diverse antifungal drugs.

Cadmium toxicity mediated by the inhibition of SLC2A4 expression in human proximal Tubule cells

Cadmium (Cd) is an environmental contaminant that causes renal toxicity. We have previously demonstrated that Cd induces renal toxicity by altering transcriptional activities. In this study, we show that Cd markedly inhibited the activity of transcription factor MEF2A in HK-2 human proximal tubule cells, which generated significant cytotoxicity in the cells. This reduction in the nuclear levels of MEF2A protein may be involved in the Cd-induced inhibition of MEF2A activity. We also demonstrate that one of the glucose transporters, GLUT4, was downregulated not only by Cd treatment but also by MEF2A knockdown. Knockdown of SLC2A4, encoding GLUT4, eliminated both cell viability and Cd toxicity. Cd treatment or SLC2A4 deficiency reduced the cellular concentration of glucose. Therefore, the suppression of SLC2A4 expression, which mediates the reduction in cellular glucose, is involved in Cd toxicity. The Cd toxicity induced by the reduction in GLUT4 may be associated with a reduction of cellular ATP levels in HK-2 cells. The levels of Slc2a4 mRNA in the kidney of mice exposed to Cd for 6 or 12 months were significantly lower than those in the control group. These results demonstrate that Cd exerts its cytotoxicity through the suppression in SLC2A4 expression and the subsequent inhibition of MEF2A transcriptional activity. Cd-induced suppression of SLC2A4 expression also reduces cellular ATP levels, partly by reducing glucose levels. This study suggests that the glucose transporter plays an important role in the renal toxicity of Cd, and provides a crucial breakthrough in our understanding of the mechanism of Cd toxicity.

Reactive oxygen mediated apoptosis as a therapeutic approach against opportunistic Candida albicans

Candida albicans are polymorphic fungal species commonly occurs in a symbiotic association with the host's usual microflora. Certain specific changes in its usual microenvironment can lead to diseases ranging from external mucosal to severally lethal systemic infections like invasive candidiasis hospital-acquired fatal infection caused by different species of Candida. The patient acquired with this infection has a high mortality and morbidity rate, ranging from 40% to 60%. This is an ill-posed problem by its very nature. Hence, early diagnosis and management is a crucial part. Antifungal drug resistance against the first and second generation of antifungal drugs has made it difficult to treat such fatal diseases. After a few dormant years, recently, there has been a rapid turnover of identifying novel drugs with low toxicity to limit the problem of drug resistance. After an initial overview of related work, we examine specific prior work on how a change in oxidative stress can facilitate apoptosis in C. albicans. Subsequently, it was investigated that Candida spp. suppresses the production of ROS mediated host defense system. Here, we have reviewed possibly all the small molecule inhibitors, natural products, antimicrobial peptide, and some naturally derived semi-synthetic compounds which are known to influence oxidative stress, to generate a proper apoptotic response in C. albicans and thus might be a novel therapeutic approach to augment the current treatment options.

Kalopanaxsaponin A induces reactive oxygen species mediated mitochondrial dysfunction and cell membrane destruction in Candida albicans

Candidiasis causes high morbidity and mortality among immunocompromised patients. Antifungal drug resistance and cytotoxicity highlight the need of effective antifungal therapeutics. In this study, we found that kalopanaxsaponin A (KPA), a triterpenoid saponin natural product, could inhibit the proliferation of various Candida species, and exerted a fungicidal effect against C. albicans. To further explore its antifungal action mode, spectrofluorophotometer, fluorescence microscopy and transmission electron microscopy were performed, showing that KPA treatment induced the accumulation of intracellular reactive oxygen species (ROS), resulting in mitochondrial dysfunction. Meanwhile, KPA treatment also broke down the membrane barrier of C. albicans causing the leakage of intracellular trehalose, the entrance of extracellular impermeable substance and the decrease of ergosterol content. Both ROS accumulation and membrane destruction contributed to the death of C. albicans cells. Our work preliminarily elucidated the potential mechanisms of KPA against C. albicans on a cellular level, and might provide a potential option for the treatment of clinical candidiasis.

A semisynthetic borrelidin analogue BN-3b exerts potent antifungal activity against Candida albicans through ROS-mediated oxidative damage

In the process of investigating the antifungal structure-activity relationships (SAR) of borrelidin and discovering antifungal leads, a semisynthetic borrelidin analogue, BN-3b with antifungal activity against Candida albicans, was achieved. In this study, we found that oxidative damage induced by endogenous reactive oxygen species (ROS) plays an important role in the antifungal activity of BN-3b. Further investigation indicated that BN-3b stimulated ROS accumulation, increased malondialdehyde (MDA) levels, and decreased reduced/oxidized glutathione (GSH/GSSG) ratio. Moreover, BN-3b decreased mitochondrial membrane potential (MMP) and ATP generation. Ultrastructure analysis revealed that BN-3b severely damaged the cell membrane of C. albicans. Quantitative PCR (RT-qPCR) analysis revealed that virulence factors of C. albicans SAPs, PLB1, PLB2, HWP1, ALSs, and LIPs were all down-regulated after BN-3b exposure. We also found that BN-3b markedly inhibited the hyphal formation of C. albicans. In addition, in vivo studies revealed that BN-3b significantly prolonged survival and decreased fungal burden in mouse model of disseminated candidiasis.

In Vitro Anti-Biofilm Activities of Citral and Thymol Against Candida Tropicalis

Candida tropicalis is an emerging non-albicans Candida species which is pathogenic to the immune-compromised humans, especially in tropical countries, including India. The acquired resistance of Candida species towards antifungal therapies is of major concern. Moreover, limited efficacy and dosage constraint of synthetic drugs have indicated the prerequisite of finding new and natural drugs for treatment. In the present study, we have compared the influence of citral and thymol on C. tropicalis and its biofilm along with expression levels of certain antifungal tolerance genes. The antifungal and anti-biofilm activities of the both were studied using 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide sodium salt (XTT) reduction assay, field emission scanning electron microscope (FE-SEM) and confocal laser scanning microscope (CLSM) and real-time reverse transcription polymerase chain reaction (RT-PCR) analysis. Citral and thymol have damaged the cells with distorted surface and less viability. Quantitative real-time PCR analysis showed augmented expression of the cell membrane biosynthesis genes including ERG11/CYT450 against citral and the cell wall related tolerance genes involving CNB1 against thymol thus, depicting their differential mode of actions.

Floricolin C elicits intracellular reactive oxygen species accumulation and disrupts mitochondria to exert fungicidal action

Candida albicans, one of the most prevalent fungal pathogens, causes severe mucosal and invasive infections in predisposed individuals. The rise of fungal infection and drug resistance demands the development of novel antifungal agents. In this study, we observed that floricolin C (FC), a p-terphenyl pigment from an endolichenic fungus, killed C. albicans cells in the planktonic state or within biofilms through reactive oxygen species (ROS) accumulation. Further tests revealed that FC could directly damage the mitochondria to cause ROS accumulation. In addition, FC can quench thiol-based agents through a Michael reaction involving the α,β-unsaturated carbonyl group, whose effect may chelate intracellular thiol-based molecules or proteins in C. albicans, resulting in an imbalance in redox homeostasis. Increased ROS generation led to mitochondrial dysfunction, nuclear dispersion and consequently cell death. We further demonstrated that FC could prevent biofilm formation of other Candida species and eradicate their pre-formed biofilms. An in vivo study demonstrated that FC prolonged the survival of C. albicans-infected Caenorhabditis elegans. Taken together, our study provides the basis for the application of FC to combat Candida infections.

Efflux pump-mediated resistance to antifungal compounds can be prevented by conjugation with triphenylphosphonium cation

Antifungal resistance due to upregulation of efflux pumps is prevalent in clinical Candida isolates. Potential efflux pump substrates (PEPSs), which are active against strains deficient in efflux pumps but inactive against wild-type strains, are usually missed in routine antifungal screening. Here we present a method for identification of PEPSs, and show that conjugation with mitochondria-targeting triphenylphosphonium cation (TPP⁺) can enhance or restore the compounds’ antifungal activity. The screening method involves co-culturing a wild-type C. albicans strain and a Cdr efflux pump-deficient strain, labelled with different fluorescent proteins. We identify several PEPSs from a library of natural terpenes, and restore their antifungal activity against wild-type and azole-resistant C. albicans by conjugation with TPP⁺. The most active conjugate (IS-2-Pi-TPP) kills C. albicans cells, prevents biofilm formation and eliminates preformed biofilms, without inducing significant resistance. The antifungal activity is accompanied by mitochondrial dysfunction and increased levels of intracellular reactive oxygen species. In addition, IS-2-Pi-TPP is effective against C. albicans in a mouse model of skin infection.

Antifungal resistance due to upregulation of efflux pumps is common in Candida albicans. Here, the authors show that conjugation with mitochondria-targeting triphenylphosphonium cation can enhance or restore the antifungal activity of potential efflux pump substrates.

Bafilomycin C1 exert antifungal effect through disturbing sterol biosynthesis in Candida albicans

In a previous study on discovering new antimicrobial agents from microbial sources, nine bafilomycins were isolated from the fermentation broth of Streptomyces albolongus. Among them, bafilomycin C1 (Baf C1) showed strong antifungal activity against Candida albicans, with MIC value of 1.56 μg/mL. The aim of this study was to evaluate the action mechanism of Baf C1 against C. albicans. Quantitative PCR analysis revealed that ergosterol biosynthesis-related genes of C. albicans ACS1, HMG1, IDI1, ERG1, ERG2, ERG6, ERG7, ERG8, ERG9, ERG12, ERG13, ERG20, ERG24, ERG251, ERG252, ERG26, ERG27, and ERG28 were all down-regulated (Log₂fold change < -1) after Baf C1(4 μg/mL) exposure. Moreover, the expression of MET6 gene, encoded methionine synthase, was also down-regulated (2.7-fold). It is corresponding with the quantitative PCR result, the content of ergosterol has dropped about 41% compared with the control. Transmission electron microscope examination also revealed that the Baf C1 strongly destroyed the cell membrane of C. albicans. In addition, the content of farnesol was significantly increased, about 2.1-fold compared with the control. The results indicated Baf C1 caused aberrations in sterol biosynthesis, leaded to the lack of ergosterol of the fungal membrane.

Chiloscyphenol A derived from Chinese liverworts exerts fungicidal action by eliciting both mitochondrial dysfunction and plasma membrane destruction

This study aimed to characterize the antifungal effects of chiloscyphenol A (CA), a natural small molecule isolated from Chinese liverworts, and investigate its mode of action. CA was effective against five tested Candida species with a minimal inhibitory concentration (MIC) of 8-32 μg/ml and exhibited fungicidal activity against Candida albicans in both the planktonic state and mature biofilms. The in vivo study using Caenorhabditis elegans showed that CA prolonged the survival of C. albicans infected worms. Further investigations revealed that CA resulted in mitochondrial dysfunction as indicated by mtΔψ hyperpolarization, increased ATP production and intracellular ROS accumulation, and aggregated distribution of Tom70. In addition, CA caused perturbation of the cell membrane and increased membrane permeability, as demonstrated by specific staining and confocal microscopic and transmission electron microscopy (TEM) observations and by calcein-leakage measurements. This conclusion was further confirmed by the decreased cell size of CA-treated cells via three-dimensional contour-plot analysis using flow cytometry. Taken together, these results suggest that CA exerts fungicidal activity by eliciting both mitochondrial dysfunction and plasma membrane destruction in C. albicans. The elucidated mechanism supports the potential application of CA against clinical fungal infections.

PARP-1 overexpression contributes to Cadmium-induced death in rat proximal tubular cells via parthanatos and the MAPK signalling pathway

Parthanatos is a newly discovered form of PARP-1-dependent programmed cell death. It has been reported to play an important role in several cancer or tumour cells; however, few studies have been performed in normal cells. Cadmium is a highly toxic pollutant and is reported to induce autophagy and apoptosis in multiple cell types. Although cadmium toxicity induces cell death, the underlying mechanism is not fully understood. Therefore, in this study we aimed to investigate the mechanism of Cadmium -induced cell damage using rat proximal tubular cell line NRK-52E and primary rat proximal tubular (rPT) cells. Our results indicated that parthanatos and the MAPK signalling pathway contribute to Cadmium-induced cell death, and that oxidative stress and mitochondrial damage play key roles in this process. In addition, parthanatos with oxidative stress has a synergistic effect on apoptosis, and JNK1/2 and p38 contribute to parthanatos.

Biatriosporin D displays anti-virulence activity through decreasing the intracellular cAMP levels

Candidiasis has long been a serious human health problem, and novel antifungal approaches are greatly needed. During both superficial and systemic infection, C. albicans relies on a battery of virulence factors, such as adherence, filamentation, and biofilm formation. In this study, we found that a small phenolic compound, Biatriosporin D (BD), isolated from an endolichenic fungus, Biatriospora sp., displayed anti-virulence activity by inhibiting adhesion, hyphal morphogenesis and biofilm formation of C. albicans. Of note is the high efficacy of BD in preventing filamentation with a much lower dose than its MIC value. Furthermore, BD prolonged the survival of worms infected by C. albicans in vivo. Quantitative real-time PCR analysis, exogenous cAMP rescue experiments and intracellular cAMP measurements revealed that BD regulates the Ras1-cAMP-Efg1 pathway by reducing cAMP levels to inhibit the hyphal formation. Further investigation showed that BD could upregulate Dpp3 to synthesize much more farnesol, which could inhibit the activity of Cdc35 and reduce the generation of cAMP. Taken together, these findings indicate that BD stimulates the expression of Dpp3 to synthesize more farnesol that directly inhibits the Cdc35 activity, reducing intracellular cAMP and thereby disrupting the morphologic transition and attenuating the virulence of C. albicans. Our study uncovers the underlying mechanism of BD as a prodrug in fighting against pathogenic C. albicans and provides a potential application of BD in fighting clinically relevant fungal infections by targeting fungal virulence.

Honokiol induces reactive oxygen species-mediated apoptosis in Candida albicans through mitochondrial dysfunction

Objective

To investigate the effects of honokiol on induction of reactive oxygen species (ROS), antioxidant defense systems, mitochondrial dysfunction, and apoptosis in Candida albicans.

Methods

To measure ROS accumulation, 2′,7′-dichlorofluorescein diacetate fluorescence was used. Lipid peroxidation was assessed using both fluorescence staining and a thiobarbituric acid reactive substances (TBARS) assay. Protein oxidation was determined using dinitrophenylhydrazine derivatization. Antioxidant enzymatic activities were measured using commercially available detection kits. Superoxide dismutase (SOD) genes expression was measured using real time RT-PCR. To assess its antifungal abilities and effectiveness on ROS accumulation, honokiol and the SOD inhibitor N,N′-diethyldithiocarbamate (DDC) were used simultaneously. Mitochondrial dysfunction was assessed by measuring the mitochondrial membrane potential (mtΔψ). Honokiol-induced apoptosis was assessed using an Annexin V-FITC apoptosis detection kit.

Results

ROS, lipid peroxidation, and protein oxidation occurred in a dose-dependent manner in C. albicans after honokiol treatment. Honokiol caused an increase in antioxidant enzymatic activity. In addition, honokiol treatment induced SOD genes expression in C. albicans cells. Moreover, addition of DDC resulted in increased endogenous ROS levels and potentiated the antifungal activity of honokiol. Mitochondrial dysfunction was confirmed by measured changes to mtΔψ. The level of apoptosis increased in a dose-dependent manner after honokiol treatment.

Conclusions

Collectively, these results indicate that honokiol acts as a pro-oxidant in C. albicans. Furthermore, the SOD inhibitor DDC can be used to potentiate the activity of honokiol against C. albicans.

Citronellal-induced disruption of membrane homeostasis in Candida albicans and attenuation of its virulence attributes

INTRODUCTION

There is an increasing burden of multidrug resistance. As a result, deciphering the mechanisms of action of natural compounds with antifungal activity has gained considerable prominence. We aimed to elucidate the probable mechanism of action of citronellal, a monoterpenoid found in the essential oil extracted from Cymbopogon plants, against Candida albicans.

METHODS

Drug susceptibility was measured by broth microdilution and spot assays. Ergosterol levels were estimated using the alcoholic potassium hydroxide method and H+ extrusion was assessed by monitoring the glucose-induced acidification of the external medium. Virulence traits were studied by hyphal morphogenesis and biofilm formation, along with fungal cell adherence to polystyrene surface and human oral epithelial cells.

RESULTS

Citronellal showed anticandidal activity against C. albicans and non-albicans species of Candida at a minimum inhibitory concentration of 1 mg/ml. Citronellal interfered with membrane homeostasis, which is the major target of known antifungal drugs, by increasing the hypersensitivity of the fungi to membrane-perturbing agents, reducing ergosterol levels, and diminishing glucose-induced H+ extrusion. In addition, oxidative and genotoxic stresses were induced via an increased production of reactive oxygen species. Furthermore, citronellal inhibited the virulent attributes of yeast-to-hypha transition and biofilm formation. It also reduced cell adherence to polystyrene surface and the human oral epithelial cells.

CONCLUSIONS

This is the first study to propose the cell membrane, morphogenetic switching, biofilm formation, and cell adherence of Candida albicans as potential targets for the anticandidal activity of citronellal. However, clinical investigations on the therapeutic applications of citronellal are required.

Retigeric acid B attenuates the virulence of Candida albicans via inhibiting adenylyl cyclase activity targeted by enhanced farnesol production

Candida albicans, the most prevalent fungal pathogen, undergoes yeast-to-hyphal switch which has long been identified as a key fungal virulence factor. We showed here that the lichen-derived small molecule retigeric acid B (RAB) acted as an inhibitor that significantly inhibited the filamentation of C. albicans, leading to the prolonged survival of nematodes infected by C. albicans. Quantitative real-time PCR analysis and intracellular cAMP measurement revealed RAB regulated the Ras1-cAMP-Efg1 pathway by reducing cAMP level to inhibit the hyphae formation. Confocal microscopic observation showed RAB induced the expression of Dpp3, synthesizing more farnesol, which was confirmed by gas chromatography-mass spectroscopy detection. An adenylyl cyclase activity assay demonstrated RAB could repress the activity of Cdc35 through stimulating farnesol synthesis, thus causing a decrease in cAMP synthesis, leading to retarded yeast-to-hyphal transition. Moreover, reduced levels of intracellular cAMP resulted in the inhibition of downstream adhesins. Together, these findings indicate that RAB stimulates farnesol production that directly inhibits the Cdc35 activity, reducing the synthesis of cAMP and thereby causing the disruption of the morphologic transition and attenuating the virulence of C. albicans. Our work illustrates the underlying mechanism of RAB-dependent inhibition of the yeast-to-hyphal switch and provides a potential application in treating the infection of C. albicans.

Chemosensitization as a means to augment commercial antifungal agents

Antimycotic chemosensitization and its mode of action are of growing interest. Currently, use of antifungal agents in agriculture and medicine has a number of obstacles. Foremost of these is development of resistance or cross-resistance to one or more antifungal agents. The generally high expense and negative impact, or side effects, associated with antifungal agents are two further issues of concern. Collectively, these problems are exacerbated by efforts to control resistant strains, which can evolve into a treadmill of higher dosages for longer periods. This cycle in turn, inflates cost of treatment, dramatically. A further problem is stagnation in development of new and effective antifungal agents, especially for treatment of human mycoses. Efforts to overcome some of these issues have involved using combinations of available antimycotics (e.g., combination therapy for invasive mycoses). However, this approach has had inconsistent success and is often associated with a marked increase in negative side effects. Chemosensitization by natural compounds to increase effectiveness of commercial antimycotics is a somewhat new approach to dealing with the aforementioned problems. The potential for safe natural products to improve antifungal activity has been observed for over three decades. Chemosensitizing agents possess antifungal activity, but at insufficient levels to serve as antimycotics, alone. Their main function is to disrupt fungal stress response, destabilize the structural integrity of cellular and vacuolar membranes or stimulate production of reactive oxygen species, augmenting oxidative stress and apoptosis. Use of safe chemosensitizing agents has potential benefit to both agriculture and medicine. When co-applied with a commercial antifungal agent, an additive or synergistic interaction may occur, augmenting antifungal efficacy. This augmentation, in turn, lowers effective dosages, costs, negative side effects and, in some cases, countermands resistance.

Bisbibenzyls, a new type of antifungal agent, inhibit morphogenesis switch and biofilm formation through upregulation of DPP3 in Candida albicans

The yeast-to-hypha transition plays a crucial role in the pathogenesis of C. albicans. Farnesol, a quorum sensing molecule (QSM) secreted by the fungal itself, could prevent the formation of hyphae and subsequently lead to the defect of biofilm formation. The DPP3, encoding phosphatase, is a key gene in regulating farnesol synthesis. In this study, we screened 24 bisbibenzyls and 2 bibenzyls that were isolated from bryophytes or chemically synthesized by using CLSI method for antifungal effect. Seven bisbibenzyls were found to have antifungal effects with IC₈₀ less than 32 µg/ml, and among them, plagiochin F, isoriccardin C and BS-34 were found to inhibit the hyphae and biofilm formation of C. albicans in a dose-dependent manner. To uncover the underlying relationship between morphogenesis switch and QSM formation, we measured the farnesol production by HPLC-MS and quantified Dpp3 expression by detecting the fluorescent intensity of green fluorescent protein tagged strain using Confocal Laser Scanning microscopy and Multifunction Microplate Reader. The DPP3 transcripts were determined by real-time PCR. The data indicated that the bisbibenzyls exerted antifungal effects through stimulating the synthesis of farnesol via upregulation of Dpp3, suggesting a potential antifungal application of bisbibenzyls. In addition, our assay provides a novel, visual and convenient method to measure active compounds against morphogenesis switch.