Synergistic Antifungal Activity of Isoquercitrin: Apoptosis and Membrane Permeabilization Related to Reactive Oxygen Species inCandida albicans

Specifically Targeting Metacaspases of Candida: A New Therapeutic Opportunity

The World Health Organization (WHO) recently published a list of fungal priority pathogens, including Candida albicans and C. auris. The increased level of resistance of Candida is raising concern, considering the availability of only four classes of medicine. The WHO is seeking novel agent classes with different targets and mechanisms of action. Targeting Candida metacaspases to control intrinsic cell death could provide new therapeutic opportunities for invasive candidiasis. In this review, we provide the available evidence for Candida cell death, describe Candida metacaspases, and discuss the potential of Candida metacaspases to offer a new specific target. Targeting Candida cell death has good scientific rationale given that the fungicidal activity of many marketed antifungals is mediated, among others, by cell death triggering. But none of the available antifungals are specifically activating Candida metacaspases, making this target a new therapeutic opportunity for non-susceptible isolates. It is expected that antifungals based on the activation of fungi metacaspases will have a broad spectrum of action, as metacaspases have been described in many fungi, including filamentous fungi. Considering this original mechanism of action, it could be of great interest to combine these new antifungal candidates with existing antifungals. This approach would help to avoid the development of antifungal resistance, which is especially increasing in Candida.

Metal Nanoparticles to Combat Candida albicans Infections: An Update

Candidiasis is an opportunistic mycosis with high annual incidence worldwide. In these infections, Candida albicans is the chief pathogen owing to its multiple virulence factors. C. albicans infections are usually treated with azoles, polyenes and echinocandins. However, these antifungals may have limitations regarding toxicity, relapse of infections, high cost, and emergence of antifungal resistance. Thus, the development of nanocarrier systems, such as metal nanoparticles, has been widely investigated. Metal nanoparticles are particulate dispersions or solid particles 10-100 nm in size, with unique physical and chemical properties that make them useful in biomedical applications. In this review, we focus on the activity of silver, gold, and iron nanoparticles against C. albicans. We discuss the use of metal nanoparticles as delivery vehicles for antifungal drugs or natural compounds to increase their biocompatibility and effectiveness. Promisingly, most of these nanoparticles exhibit potential antifungal activity through multi-target mechanisms in C. albicans cells and biofilms, which can minimize the emergence of antifungal resistance. The cytotoxicity of metal nanoparticles is a concern, and adjustments in synthesis approaches or coating techniques have been addressed to overcome these limitations, with great emphasis on green synthesis.

Recent developments on the anti-Candida effect of amphotericin B combined with a second drug - a mini-review

Invasive Candida infections threaten human health due to the increasing incidence of resistance to the currently available antifungal agents. Amphotericin B (AMB) is the gold standard therapy to treat these infections. Nevertheless, the use of such substance in the clinic is aggravated by its toxicity. Since AMB binds to membrane sterols, it forms pores on human plasma membranes, mainly in kidney cells, leading to nephrotoxicity. The combination of this drug to a second substance could allow for the use of smaller concentrations of AMB, consequently lowering the probability of adverse effects. This mini-review summarizes information regarding an array of substances that enhance AMB antifungal activity. It may be noticed that several of these compounds target plasma membrane. Interestingly, substances approved for human use also presented combinatory anti-Candida activity with AMB. These data reinforce the potential of associating AMB to another drug as a promising therapeutical alternative to treat Candida infections. Further studies, regarding mechanism of action, pharmacokinetics and toxicity parameters must be conducted to confirm the role of these substances as adjuvant agents in candidiasis therapy.

Effect of Antibiotic Amphotericin B Combinations with Selected 1,3,4-Thiadiazole Derivatives on RPTECs in an In Vitro Model

4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol (C1) and 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl] benzene1,3-diol (NTBD) are representative derivatives of the thiadiazole group, with a high antimycotic potential and minimal toxicity against normal human fibroblast cells. The present study has proved its ability to synergize with the antifungal activity of AmB. The aim of this work was to evaluate the cytotoxic effects of C1 or NTBD, alone or in combination with AmB, on human renal proximal tubule epithelial cells (RPTECs) in vitro. Cell viability was assessed with the MTT assay. Flow cytometry and spectrofluorimetric techniques were used to assess the type of cell death and production of reactive oxygen species (ROS), respectively. The ELISA assay was performed to measure the caspase-2, -3, and -9 activity. ATR-FTIR spectroscopy was used to evaluate biomolecular changes in RPTECs induced by the tested formulas. The combinations of C1/NTBD and AmB did not exert a strong inhibitory effect on the viability/growth of kidney cells, as evidenced by the negligible changes in the apoptotic/necrotic rate and caspase activity, compared to the control cells. Both NTBD and C1 displayed stronger anti-oxidant activity when combined with AmB. The relatively low nephrotoxicity of the thiadiazole derivative combinations and the protective activity against AmB-induced oxidative stress may indicate their potential use in the therapy of fungal infections.

Redox Impact on Bacterial Macromolecule: A Promising Avenue for Discovery and Development of Novel Antibacterials

Antibiotic resistance in bacteria has remained a serious public health concern, resulting in substantial deaths and morbidity each year. Factors such as mutation and abuse of currently available antibiotics have contributed to the bulk of the menace. Hence, the introduction and implementation of new therapeutic strategies are imperative. Of these strategies, data supporting the role of reactive oxygen species (ROS) in bacterial lethality are intriguing, with several antimicrobials, including antibiotics such as fluoroquinolones, β-lactams, and aminoglycosides, as well as natural plant compounds, being remarkably implicated. Following treatment with ROS-inducing antimicrobials, ROS such as O₂^•-, ^•OH, and H₂O₂ generated in bacteria, which the organism is unable to detoxify, damage cellular macromolecules such as proteins, lipids, and nucleic acids and results in cell death. Despite the unique mechanism of action of ROS-inducing antibacterials and significant studies on ROS-mediated means of bacterial killing, the field remains a topical one, with contradicting viewpoints that require frequent review. Here, we appraised the antibacterial agents (antibiotics, natural and synthetic compounds) implicated in ROS generation and the safety concerns associated with their usage. Further, background information on the sources and types of ROS in bacteria, the mechanism of bacterial lethality via oxidative stress, as well as viewpoints on the ROS hypothesis undermining and solidifying this concept are discussed.

Synergistic In Vitro Interaction of Isavuconazole and Isoquercitrin against Candida glabrata

In vitro interactions of broad-spectrum azole isavuconazole with flavonoid isoquercitrin were evaluated by a broth microdilution checkerboard technique based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) reference methodology for antifungal susceptibility testing against 60 Candida strains belonging to the species Candida albicans (n = 10), Candida glabrata (n = 30), Candida kefyr (n = 6), Candida krusei (n = 5), Candida parapsilosis (n = 4), and Candida tropicalis (n = 5). The results were analyzed with the fractional inhibitory concentration index and by response surface analysis based on the Bliss model. Synergy was found for all C. glabrata strains, when the results were interpreted by the fractional inhibitory concentration index, and for 60% of the strains when response surface analysis was used. Interaction for all other species was indifferent for all strains tested, whatever interpretation model used. Importantly, antagonistic interaction was never observed.

Augmenting Azoles with Drug Synergy to Expand the Antifungal Toolbox

Fungal infections impact the lives of at least 12 million people every year, killing over 1.5 million. Wide-spread use of fungicides and prophylactic antifungal therapy have driven resistance in many serious fungal pathogens, and there is an urgent need to expand the current antifungal arsenal. Recent research has focused on improving azoles, our most successful class of antifungals, by looking for synergistic interactions with secondary compounds. Synergists can co-operate with azoles by targeting steps in related pathways, or they may act on mechanisms related to resistance such as active efflux or on totally disparate pathways or processes. A variety of sources of potential synergists have been explored, including pre-existing antimicrobials, pharmaceuticals approved for other uses, bioactive natural compounds and phytochemicals, and novel synthetic compounds. Synergy can successfully widen the antifungal spectrum, decrease inhibitory dosages, reduce toxicity, and prevent the development of resistance. This review highlights the diversity of mechanisms that have been exploited for the purposes of azole synergy and demonstrates that synergy remains a promising approach for meeting the urgent need for novel antifungal strategies.

An ethnopharmacological review on the therapeutical properties of flavonoids and their mechanisms of actions: A comprehensive review based on up to date knowledge

Flavonoids -a class of low molecular weight secondary metabolites- are ubiquitous and cornucopia throughout the plant kingdom. Structurally, the main structure consists of C6-C3-C6 rings with different substitution patterns so that many sub-classes are obtained, for example: flavonols, flavonolignans, flavonoid glycosides, flavans, anthocyanidins, aurones, anthocyanidins, flavones, neoflavonoids, chalcones, isoflavones, flavones and flavanones. Flavonoids are evaluated to have drug like nature since they possess different therapeutic activities, and can act as cardioprotective, antiviral, antidiabetic, anti-inflammatory, antibacterial, anticancer, and also work against Alzheimer's disease and others. However, information on the relationship between their structure and biological activity is scarce. Therefore, the present review tries to summarize all the therapeutic activities of flavonoids, their mechanisms of action and the structure activity relationship.

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Latest updated ethnopharmacological review of the therapeutic effects of flavonoids.

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Flavonoids are attracting attention because of their therapeutic properties.

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Flavonoids are valuable candidates for drug development against many dangerous diseases.

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This overview summarizes the most important therapeutic effect and mechanism of action of flavonoids.

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General knowledge about the structure activity relationship of flavonoids is summarized.

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Substitution of chemical groups in the structure of flavonoids can significantly change their biological and chemical properties.

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The chemical properties of the basic flavonoid structure should be considered in a drug-based structural program.

Potential, risks, and benefits of the extract recycled from Pteris vittata arsenic-rich biomass as a broiler growth promoter

The arsenic-rich biomass of Pteris vittata is a heavy burden to phytoremediation, but the compositions of extracts recycled from arsenic-rich biomass, such as rutin, may promote broiler growth. As such, this extract can be used to reduce the usage of antibiotics in the broiler industry and the cost of phytoremediation at the same time. Therefore, the critical issues for using extract from arsenic-rich biomass as a growth promoter have been studied, including its effective composition, health and environmental risks, and potential benefits and feasibility. Forty-five compounds were identified in the extract, and they were mainly flavonoids, chlorogenic acids, and proanthocyanidins, which can directly or indirectly influence the growth of broiler. The lifetime carcinogenic risks of broiler edible parts may be maximally increased by 4.75 × 10^-9 due to feeding the extract. The arsenic concentration of the farmland fertilized with the excrement from the broiler fed with the extract may increase by 0.00003-0.01857 mg/kg per year. Results revealed a feasible scenario that the sustainability of phytoremediation and broiler industry could be benefited through wastes from each other.

A novel use for an old drug: resistance reversal in Candida albicans by combining dihydroartemisinin with fluconazole

Aim: To investigate the effects of dihydroartemisinin combined with fluconazole against C. albicans in vitro and to explore the underlying mechanisms. Materials & methods: Checkerboard microdilution assay and time-kill curve method were employed to evaluate the static and dynamic antifungal effects against C. albicans. Reactive oxygen species (ROS) was measured by a fluorescent probe. Results: Combination of dihydroartemisinin and fluconazole exerted potent synergy against planktonic cells and biofilms of fluconazole-resistant C. albicans, with the fractional inhibitory concentration index values less than 0.07. A potent fungistatic activity of this drug combination could still be observed after 18 h. The accumulation of ROS induced by the drug combination might contribute to the synergy. Conclusion: Dihydroartemisinin reversed the resistance of C. albicans to fluconazole.

β-amyrin-induced apoptosis in Candida albicans triggered by calcium

The emergence of drug-resistant pathogens has urged researchers to discover alternatives for traditional antibiotics. β-amyrin, which is included in the category of triterpenoids extracted from plants, is known for its antimicrobial activity, although the underlying mechanism has not yet been revealed. This study was conducted to elucidate the antifungal mode of action of β-amyrin against Candida albicans. Based on the relevance between triterpenoids and oxidative molecules, reactive oxygen species (ROS) concentrations were detected, which showed a noticeable increment. Disruption of Ca²⁺ homeostasis in the cytosol was additionally analyzed, which was supported by interactions between two. Subsequently, decrease in mitochondrial membrane potential, increment of mitochondrial Ca²⁺, and ROS concentration were monitored, which suggested mitochondrial dysfunction modulated by Ca²⁺. Further investigation confirmed oxidative damage through glutathione reduction and DNA fragmentation. Accumulation of lethal damages resulted in the activation of caspases and externalization of phosphatidylserine, indicating the induction of yeast apoptosis by β-amyrin in C. albicans.

Azole-triphenylphosphonium conjugates combat antifungal resistance and alleviate the development of drug-resistance

Azole antifungals are commonly used to treat fungal infections but have resulted in the occurrence of drug resistance. Therefore, developing azole derivatives (AZDs) that can both combat established drug-resistant fungal strains and evade drug resistance is of great importance. In this study, we synthesized a series of AZDs with a fluconazole (FLC) skeleton conjugated with a mitochondria-targeting triphenylphosphonium cation (TPP⁺). These AZDs displayed potent activity against both azole-sensitive and azole-resistant Candida strains without eliciting obvious resistance. Moreover, two representative AZDs, 20 and 25, exerted synergistic antifungal activity with Hsp90 inhibitors against C. albicans strains resistant to the combination treatment of FLC and Hsp90 inhibitors. AZD 25, which had minimal cytotoxicity, was effective in preventing C. albicans biofilm formation. Mechanistic investigation revealed that AZD 25 inhibited the biosynthesis of the fungal membrane component ergosterol and interfered with mitochondrial function. Our findings provide an alternative approach to address fungal resistance problems.

Synergistic antifungal effects of curcumin derivatives as fungal biofilm inhibitors with fluconazole

Lack of novel antifungal agents and severe drug resistance has led to high incidence and associated mortality of invasive fungal infections. To tackle the challenges, novel antifungal agents with anti-resistant potency are highly desirable. Thus, derivatives of curcumin were synthesized to restore the effectiveness of fluconazole (FLC) against FLC-resistant Candida spp. and structure-activity relationships were then discussed. Some novel derivatives showed promising features as novel antifungal lead compounds. Of them, compound 4 showed good alone or synergistic antifungal activity against FLC-resistant Candida spp. Moreover, compound 4 was proven as a potent inhibitor of Candida albicans biofilm formation and yeast-to-hypha morphological transition whether used alone or in combination with FLC, which was further confirmed by the inhibitory effect on cellular surface hydrophobicity of C. albicans. Compound 4 also inhibits intracellular ATP production of C. albicans and disrupts membrane permeability of C. albicans when used in combination with FLC. The results highlighted the potential of curcumin derivatives to overcome fluconazole-related and biofilm-related drug resistance.

Silver nanoparticles-induced H2O2 triggers apoptosis-like death and is associated with dinF in Escherichia coli

Silver nanoparticles (AgNPs) are the most widely used nanomaterials as antimicrobial agents. AgNPs have been shown to inhibit the growth of and induce apoptosis-like death in Escherichia coli. However, the precise mechanism of AgNPs-induced apoptosis-like death and association with DNA damage-inducible protein F (dinF), a gene of SOS response, is unknown. Here, AgNPs-contributing depletion of intracellular glutathione levels and deactivation of glutathione peroxidase were shown. This step, indicating disruption of the antioxidant system, resulted in overall oxidative stress. Furthermore, DNA oxidation was accompanied, leading to DNA fragmentation. In addition, AgNPs appeared to induce apoptosis-like death via the SOS response. We used sodium pyruvate - an H₂O₂ quencher - to study the contribution of H₂O₂, which showed attenuation of AgNPs-induced DNA damage, SOS response, and apoptosis-like death. In dinF mutant, the strain showed a higher degree of DNA damage and apoptotic features. In conclusion, AgNPs mediate apoptosis-like cell death by H₂O₂-induced oxidative DNA damage. Furthermore, our result demonstrates that dinF participates in this process, which further supports that AgNPs induces SOS response. Our findings may contribute to expanding the new applications of AgNP-based nanomaterials in biomedical fields.

Antifungal Activity and Potential Mechanism of Panobinostat in Combination With Fluconazole Against Candida albicans

Invasive fungal infections are an emerging problem worldwide, which bring huge health challenges. Candida albicans, the most common opportunistic fungal pathogen, can cause bloodstream infections with high mortality in susceptible hosts. At present, available antifungal agents used in clinical practice are limited, and most of them also have some serious adverse effects. The emergence of drug resistance because of the wide use of antifungal agents is a new limitation to successful patient therapy. Drug combination therapy is increasingly becoming a way to enhance antifungal efficacy, and reduce drug resistance and potential toxicity. Panobinostat, as a pan-histone deacetylase inhibitor, has been approved by the United States Food and Drug Administration as novel antitumor agents. In this study, the antifungal effects and mechanisms of panobinostat combined with fluconazole (FLC) against C. albicans were explored for the first time. The results indicated that panobinostat could work synergistically with FLC against resistant C. albicans, the minimal inhibitory concentration (MIC) of panobinostat could decrease from 128 to 0.5–2 μg/ml and the MIC of FLC could decrease from >512 to 0.25–0.5 μg/ml, and the fractional inhibitory concentration index (FICI) value ranged from 0.0024 to 0.0166. It was not only synergized against planktonic cells but also against C. albicans biofilms performed ≤8 h when panobinostat is combined with fluconazole; the sessile MIC (sMIC) of panobinostat could decrease from >128 to 0.5–8 μg/ml and the sMIC of FLC from >1024 to 0.5–2 μg/ml, and the FICI value was <0.5. The Galleria mellonella infection model was used to evaluate the in vivo effect of the drug combination, and the result showed that the survival rate could be improved obviously. Finally, we explored the synergistic mechanisms of the drug combination. The hyphal growth, which plays roles in drug resistance, was found to be inhibited, and metacaspase which is related to cell apoptosis was activated (p < 0.01), whereas the synergistic effects were proven not to be related to the efflux pumps (p > 0.05). These findings might provide novel insights into the antifungal drug discovery and the treatment of candidiasis caused by C. albicans.

Photodynamic Therapy by Diaryl-Porphyrins to Control the Growth of Candida albicans

Candida albicans is an opportunistic pathogen that often causes skin infections such as oral thrush, nail fungus, athlete’s foot, and diaper rash. Under particular conditions, C. albicans alters the natural balance of the host microbiota, and as a result, the skin or its accessory structures lose their function and appearance. Conventional antimycotic drugs are highly toxic to host tissues, and long-lasting drug administration induces the arising of resistant strains that make the antimycotic therapy ineffective. Among new antimicrobial approaches to combine with traditional drugs, light-based techniques are very promising. In this study, a panel of dyes was considered for photodynamic therapy (PDT) applications to control the growth of the model strain C. albicans ATCC 14053. The chosen photosensitizers (PSs) belong to the family of synthetic porphyrins, and in particular, they are diaryl-porphyrins. Among these, two monocationic PSs were shown to be particularly efficient in killing C. albicans upon irradiation with light at 410 nm, in a light-dose-dependent manner. The elicited photo-oxidative stress induced the loss of the internal cellular architecture and death. The photodynamic treatment was also successful in inhibiting the biofilm formation of clinical C. albicans strains. In conclusion, this study supports the great potential of diaryl-porphyrins in antimicrobial PDT to control the growth of yeasts on body tissues easily reachable by light sources, such as skin and oral cavity.

The role of reactive oxygen species in the biological activity of antimicrobial agents: An updated mini review

Antimicrobial resistance remains a serious problem that results in high mortality and increased healthcare costs globally. One of the major issues is that resistant pathogens decrease the efficacy of conventional antimicrobials. Accordingly, development of novel antimicrobial agents and therapeutic strategies is urgently needed to overcome the challenge of antimicrobial resistance. A potential strategy is to kill pathogenic microorganisms via the formation of reactive oxygen species (ROS). ROS are defined as a number of highly reactive molecules that comprise molecular oxygen (O₂), superoxide anion (O₂^•-), hydrogen peroxide (H₂O₂) and hydroxyl radicals (^•OH). ROS exhibit antimicrobial actions against a broad range of pathogens through the induction of oxidative stress, which is an imbalance between ROS and the ability of the antioxidant defence system to detoxify ROS. ROS-dependent oxidative stress can damage cellular macromolecules, including DNA, lipids and proteins. This article reviews the antimicrobial action of ROS, challenges to ROS hypothesis, work to solidify ROS-mediated antimicrobial lethality hypothesis, recent developments in antimicrobial agents using ROS as an antimicrobial strategy, safety concerns related to ROS, and future directions in ROS research.

A Paradigm Shift in the Development of Anti-Candida Drugs

BACKGROUND

The considerable increase in the incidence of Candida infection in recent times has prompted the use of numerous antifungal agents, which has resulted in the development of resistance towards various antifungal agents. With rising Candida infections, the need for design and development of novel antifungal agents is in great demand. However, new therapeutic approaches are very essential in preventing the mortality rate and improving the patient outcome in those suffering from Candida infections.

OBJECTIVE

The present review objective is to describe the burden, types of Candidiasis, mechanism of action of antifungal agents and its resistance and the current novel approaches used to combat candidiasis.

METHODS

We have collected and analyzed 135 different peer-reviewed literature studies pertinent to candidiasis. In this review, we have compiled the major findings from these studies.

RESULTS AND CONCLUSION

The review describes the concerns related to candidiasis, its current treatment strategy, resistance mechanisms and imminent ways to tackle the problem. The review explored that natural plant extracts and essential oils could act as sources of newer therapeutic agents, however, the focus was on novel strategies, such as combinational therapy, new antibodies, utilization of photodynamic therapy and adaptive transfer primed immune cells with emphasis on the development of effective vaccination.

Synergistic antibacterial activity of gold nanoparticles caused by apoptosis-like death

AIMS

Metal nanoparticles are promising materials for the management of infectious diseases as known to have various antimicrobial activities in pathogenic micro-organisms. Among them, gold nanoparticles (AuNPs) are used in a wide range of fields such as photodynamic therapy, molecular diagnostics and drug delivery because of their unique physicochemical properties. However, little is known about the synergistic antibacterial activity and mechanism of AuNPs on pathogenic bacteria.

METHODS AND RESULTS

Combinations of AuNPs and cefotaxime and ciprofloxacin showed synergistic interaction against all Salmonella species, however the combination with kanamycin exhibited no interaction. We determined that AuNPs and in combinations with antibiotics exert its antibacterial effect through bacterial apoptosis-like death. AuNPs caused collapse of intracellular divalent cation homeostasis, and conventional antibiotics caused accumulation of reactive oxygen species, which induced apoptotic hallmarks such as membrane depolarization, caspase-like protein activation, cell filamentation and phosphatidylserine externalization.

CONCLUSIONS

The cation homeostasis disruption by AuNPs and the accumulation of reactive oxygen species by conventional antibiotics synergistically affected bacterial cell death and induced apoptosis-like death in Salmonella cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

The synergistic activity between AuNPs and antibiotics propose that the AuNPs are a potential antibacterial agent and adjuvant for antimicrobial chemotherapy.