Transcriptome Analyses of Candida albicans Biofilms, Exposed to Arachidonic Acid and Fluconazole, Indicates Potential Drug Targets

Borneol serves as an adjuvant agent to promote the cellular uptake of curcumin for enhancing its photodynamic fungicidal efficacy against Candida albicans

Candida albicans (C. albicans), a major opportunistic pathogenic fungus, is known to cause superficial skin infections. Unfortunately, the misuse of antibiotics has led to the emergence of drug resistance in fungi. Antimicrobial photodynamic therapy (aPDT), a non-antibiotic alternative, has shown potential in treating drug-resistant fungal infections. Curcumin is a photodynamically active phytochemical whose photodynamic fungicidal efficacy is largely dependent on its intracellular accumulation. However, curcumin faces challenges in penetrating the cytoplasm due to its poor water solubility and the fungal cell wall. Borneol, another monoterpenoid phytochemical, is known for its ability to enhance drug absorption. In this study, we showed that borneol improved the cellular uptake of curcumin, thereby enhancing its photodynamic fungicidal efficacy against C. albicans. This effect was attributed to borneol's ability to increase cell permeability. Transcriptomic analysis further confirmed that borneol disrupted the normal structure and function of the C. albicans cell wall and membrane, resulting in dysregulated mRNA expression of related genes and ultimately increased cell permeability. As a result, the excessive accumulation of curcumin in C. albicans triggered the overproduction of intracellular ROS upon exposure to blue light. These excessive intracellular ROS disrupted various cellular structures, interfered with essential cellular processes, inhibited biofilm formation and reduced virulence. Remarkably, borneol was also found to enhance curcumin uptake by C. albicans within biofilms, further enhancing the anti-biofilm efficacy of curcumin-mediated aPDT (Cur-aPDT). In conclusion, the results of this study strongly support the potential of borneol as an adjuvant agent to Cur-aPDT in treating superficial cutaneous fungal infections.

Reprogramming in Candida albicans Gene Expression Network under Butanol Stress Abrogates Hyphal Development

Candida albicans is the causative agent of invasive fungal infections. Its hyphae-forming ability is regarded as one of the important virulence factors. To unravel the impact of butanol on Candida albicans, it was placed in O+ve complete human serum with butanol (1% v/v). The Candida transcriptome under butanol stress was then identified by mRNA sequencing. Studies including electron microscopy demonstrated the inhibition of hyphae formation in Candida under the influence of butanol, without any significant alteration in growth rate. The numbers of genes upregulated in the butanol in comparison to the serum alone were 1061 (20 min), 804 (45 min), and 537 (120 min). Candida cells exhibited the downregulation of six hypha-specific transcription factors and the induction of four repressor/regulator genes. Many of the hypha-specific genes exhibited repression in the medium with butanol. The genes related to adhesion also exhibited repression, whereas, among the heat-shock genes, three showed inductions in the presence of butanol. The fungal-specific genes exhibited induction as well as repression in the butanol-treated Candida cells. Furthermore, ten upregulated genes formed the core stress gene set in the presence of butanol. In the gene ontology analysis, enrichment of the processes related to non-coding RNA, ribosome biosynthesis, and metabolism was observed in the induced gene set. On the other side, a few GO biological process terms, including biofilm formation and filamentous growth, were enriched in the repressed gene set. Taken together, under butanol stress, Candida albicans is unable to extend hyphae and shows growth by budding. Many of the genes with perturbed expression may have fitness or virulence attributes and may provide prospective sites of antifungal targets against C. albicans.

Investigating the role of Candida albicans as a universal substrate for oral bacteria using a transcriptomic approach: implications for interkingdom biofilm control?

Candida albicans is frequently identified as a colonizer of the oral cavity in health and has recently been termed a "keystone" commensal due to its role on the bacterial communities. However, the role that C. albicans plays in such interactions is not fully understood. Therefore, this study aimed to identify the relationship between C. albicans and bacteria associated with oral symbiosis and dysbiosis. To do this, we evaluated the ability of C. albicans to support the growth of the aerobic commensal Streptococcus gordonii and the anaerobic pathogens Fusobacterium nucleatum and Porphyromonas gingivalis in the biofilm environment. RNA-Sequencing with the Illumina platform was then utilized to identify C. albicans gene expression and functional pathways involved during such interactions in dual-species and a 4-species biofilm model. Results indicated that C. albicans was capable of supporting growth of all three bacteria, with a significant increase in colony counts of each bacteria in the dual-species biofilm (p < 0.05). We identified specific functional enrichment of pathways in our 4-species community as well as transcriptional profiles unique to the F. nucleatum and S. gordonii dual-species biofilms, indicating a species-specific effect on C. albicans. Candida-related hemin acquisition and heat shock protein mediated processes were unique to the organism following co-culture with anaerobic and aerobic bacteria, respectively, suggestive that such pathways may be feasible options for therapeutic targeting to interfere with these fungal-bacterial interactions. Targeted antifungal therapy may be considered as an option for biofilm destabilization and treatment of complex communities. Moving forward, we propose that further studies must continue to investigate the role of this fungal organism in the context of the interkingdom nature of oral diseases.

Eicosapentaenoic acid influences the pathogenesis of Candida albicans in Caenorhabditis elegans via inhibition of hyphal formation and stimulation of the host immune response

The intake of omega-3 polyunsaturated fatty acids, including eicosapentaenoic acid (EPA), is associated with health benefits due to its anti-inflammatory properties. This fatty acid also exhibits antifungal properties in vitro. In order to determine if this antifungal property is valid in vivo, we examined how EPA affects Candida albicans pathogenesis in the Caenorhabditis elegans infection model, an alternative to mammalian host models. The nematodes were supplemented with EPA prior to infection, and the influence of EPA on C. elegans lipid metabolism, survival and immune response was studied. In addition, the influence of EPA on hyphal formation in C. albicans was investigated. It was discovered that EPA supplementation changed the lipid composition, but not the unsaturation index of C. elegans by regulating genes involved in fatty acid and eicosanoid production. EPA supplementation also delayed killing of C. elegans by C. albicans due to the inhibition of hyphal formation in vivo, via the action of the eicosanoid metabolite of EPA, 17,18-epoxyeicosatetraenoic acid. Moreover, EPA supplementation also caused differential expression of biofilm-related gene expression in C. albicans and stimulated the immune response of C. elegans. This provides a link between EPA and host susceptibility to microbial infection in this model.

A first-in-class inhibitor of Hsp110 molecular chaperones of pathogenic fungi

Proteins of the Hsp110 family are molecular chaperones that play important roles in protein homeostasis in eukaryotes. The pathogenic fungus Candida albicans, which causes infections in humans, has a single Hsp110, termed Msi3. Here, we provide proof-of-principle evidence supporting fungal Hsp110s as targets for the development of new antifungal drugs. We identify a pyrazolo[3,4-b] pyridine derivative, termed HLQ2H (or 2H), that inhibits the biochemical and chaperone activities of Msi3, as well as the growth and viability of C. albicans. Moreover, the fungicidal activity of 2H correlates with its inhibition of in vivo protein folding. We propose 2H and related compounds as promising leads for development of new antifungals and as pharmacological tools for the study of the molecular mechanisms and functions of Hsp110s.

Antibiofilm Activity of Essential Fatty Acids Against Candida albicans from Vulvovaginal Candidiasis and Bloodstream Infections

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Natural Variation and the Role of Zn2Cys6 Transcription Factors SdrA, WarA and WarB in Sorbic Acid Resistance of Aspergillus niger

Weak acids, such as sorbic acid, are used as chemical food preservatives by the industry. Fungi overcome this weak-acid stress by inducing cellular responses mediated by transcription factors. In our research, a large-scale sorbic acid resistance screening was performed on 100 A. niger sensu stricto strains isolated from various sources to study strain variability in sorbic acid resistance. The minimal inhibitory concentration of undissociated (MIC_u) sorbic acid at pH = 4 in the MEB of the A. niger strains varies between 4.0 mM and 7.0 mM, with the average out of 100 strains being 4.8 ± 0.8 mM, when scored after 28 days. MIC_u values were roughly 1 mM lower when tested in commercial ice tea. Genome sequencing of the most sorbic-acid-sensitive strain among the isolates revealed a premature stop codon inside the sorbic acid response regulator encoding gene sdrA. Repairing this missense mutation increased the sorbic acid resistance, showing that the sorbic-acid-sensitive phenotype of this strain is caused by the loss of SdrA function. To identify additional transcription factors involved in weak-acid resistance, a transcription factor knock-out library consisting of 240 A. niger deletion strains was screened. The screen identified a novel transcription factor, WarB, which contributes to the resistance against a broad range of weak acids, including sorbic acid. The roles of SdrA, WarA and WarB in weak-acid resistance, including sorbic acid, were compared by creating single, double and the triple knock-out strains. All three transcription factors were found to have an additive effect on the sorbic acid stress response.

Diallyl Disulfide (DADS) Ameliorates Intestinal Candida albicans Infection by Modulating the Gut microbiota and Metabolites and Providing Intestinal Protection in Mice

Diallyl disulfide (DADS), a garlic extract also known as allicin, has been reported to have numerous biological activities, including anticancer, antifungal, and inflammation-inhibiting activities, among others. Although many studies have assessed whether DADS can treat Candida albicans infection in vitro, its in vivo function and the underlying mechanism are still not clear. Accumulated evidence has implicated the gut microbiota as an important factor in the colonization and invasion of C. albicans. Thus, this study aimed to identify the mechanism by which DADS ameliorates dextran sulfate (DSS)-induced intestinal C. albicans infection based on the systematic analysis of the gut microbiota and metabolomics in mice. Here, we determined the body weight, survival, colon length, histological score, and inflammatory cytokine levels in the serum and intestines of experimental mice. Fecal samples were collected for gut microbiota and metabolite analysis by 16S rRNA gene sequencing and LC-MS metabolomics, respectively. DADS significantly alleviated DSS-induced intestinal C. albicans infection and altered the gut microbial community structure and metabolic profile in the mice. The abundances of some pathogenic bacteria, such as Proteobacteria, Escherichia-Shigella, and Streptococcus, were notably decreased after treatment with DADS. In contrast, SCFA-producing bacteria, namely, Ruminiclostridium, Oscillibacter, and Ruminococcaceae_UCG-013, greatly increased in number. The perturbance of metabolites in infectious mice was improved by DADS, with increases in secondary bile acids, arachidonic acid, indoles and their derivatives, which were highly related to the multiple differentially altered metabolic pathways, namely, bile secretion, arachidonic acid metabolism, and tryptophan metabolism. This study indicated that DADS could modulate gut microbiota and metabolites and protect the gut barrier to alleviate DSS-induced intestinal C. albicans infection in mice. Moreover, this work might also provide novel insight into the treatment of C. albicans infection using DADS.

What 'Omics Can Tell Us About Antifungal Adaptation

Invasive candidiasis, the most frequent healthcare-associated invasive fungal infection, is commonly caused by Candida albicans. However, in recent years other antifungal-resistant Candida species—namely Candida glabrata and Candidaauris—have emerged as a serious matter of concern. Much of our understanding of the mechanisms regulating antifungal resistance and tolerance relies on studies utilizing C. albicans, C. glabrataand the model yeast Saccharomyces cerevisiae. ‘Omics studies have been used to describe alterations in metabolic, genomic and transcriptomic expression profiles upon antifungal treatment of fungal cells. The physiological changes identified by these approaches could significantly affect fungal fitness in the host and survival during antifungal challenge, as well as provide further understanding of clinical resistance. Thus, this review aims to comparatively address ‘omics data for C. albicans, C. glabrata andS. cerevisiae published from 2000 to 2021 to identify what these technologies can tell us regarding cellular responses to antifungal therapy. We will also highlight possible effects on pathogen survival and identify future avenues for antifungal research.

Inhibitory effect of polyunsaturated fatty acids alone or in combination with fluconazole on Candida krusei biofilms in vitro and in Caenorhabditis elegans

The incidence of infections by non-albicans Candida species, including Candida krusei, is increasing. Candida krusei exhibits intrinsic resistance to fluconazole and rapidly develops acquired resistance to other antifungals. Moreover, this yeast can form biofilm with increased resistance. Hence, there is a need to develop novel therapeutic strategies to combat infections caused by this pathogen. One such approach is through combination therapy with natural compounds, such as polyunsaturated fatty acids (PUFAs). This study aims to investigate the effect of PUFAs on fluconazole susceptibility of C. krusei biofilms, as well as the conserved nature of these effects in the Caenorhabditis elegans infection model. C. krusei biofilms were exposed to various fatty acids as well as combinations of fluconazole and linoleic acid (LA) or gamma-linolenic acid (GLA). The effect of these treatments on biofilm formation, cell ultrastructure, membrane integrity, oxidative stress and efflux pump activity was evaluated. In addition, the ability of the PUFAs to prolong survival and reduce the fungal burden of infected C. elegans, in the absence and presence of fluconazole, was assessed. Two P|UFAs, LA and GLA had he displayed significant inhibition of C. krusei biofilms and both of them increased the susceptibility of C. krusei biofilm to fluconazole in vitro via induction of oxidative stress, cell membrane damage, and disruption of efflux pump activity. These PUFAs also extended the lifespan of infected nematodes and displayed a potentiating effect with fluconazole in this model. This may pave the way for future studies into novel antifungal drug targets and treatment options.

LAY ABSTRACT

The pathogenic yeast, Candida krusei, is naturally resistant to the antifungal drug, fluconazole. This study finds that polyunsaturated fatty acids, linoleic and gamma-linolenic acid, can inhibit C. krusei and overcome this resistance of in vitro biofilms, as well as in a nematode infection model.