Isoquercitrin, isolated from Aster yomena triggers ROS-mediated apoptosis in Candida albicans

Ethanolic extract of Caesalpinia bonduc seeds triggers yeast metacaspase-dependent apoptotic pathway mediated by mitochondrial dysfunction through enhanced production of calcium and reactive oxygen species (ROS) in Candida albicans

Candida albicans is a widespread disease-causing yeast affecting humankind, which leads to urinary tract, cutaneous and various lethal systemic infections. As this infection rate steadily increases, it is becoming a significant public health problem. Recently, Caesalpinia bonduc has received much attention from researchers due to its diverse pharmacological properties, including antimicrobial effects. Accordingly, we first planned to explore the in-vitro anticandidal potential of three extracts obtained from C. bonduc seeds against four Candida species. Initially, the anticandidal activity of the seed extracts was checked by the microdilution technique. Out of three seed extracts tested, ethanolic extract of C. bonduc seed (EECS) recorded the best activity against C. albicans. Hence, we next aimed to find out the anticandidal mechanism of EECS in C. albicans. The liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis showed that the major compounds present in the EECS were tocopherols, fucosterol, linoleic acid, β-amyrin, β-sitosterol, campesterol, cassane furanoditerpene, Norcassane furanoditerpene and other diterpenes. To evaluate the cell death mechanism in C. albicans, a series of parameters related to apoptosis, viz., reactive oxygen species (ROS) production, membrane permeability, mitochondrial membrane potential, release of cytochrome c, DNA fragmentation, nuclear condensation, increased Ca²⁺ level in cytosolic and mitochondrial and activation of metacaspase, were analyzed. The results showed that EECS treatment resulted in the elevation of ROS, which leads to plasma membrane permeability in C. albicans. Annexin V staining further confirms the early stage of apoptosis through phosphatidylserine (PS) externalization. We further inspected the late apoptotic stage using DAPI and TUNEL staining assays. From the results, it can be concluded that EECS triggered mitochondrial dysfunction by releasing high levels of ROS, cytochrome c and Ca²⁺resulting in the activation of metacaspase mediated apoptosis, which is the central mechanism behind the cell death of C. albicans. Finally, a Galleria mellonella-C. albicans infection system was employed to assess the in-vivo potential of EECS. The outcomes displayed that the EECS considerably enhanced the recovery rate of G. mellonella larvae from infection after the treatment. Additionally, EECS also recorded low hemolytic activity. This study thus spotlights the anticandidal potential and mechanism of action of EECS against C. albicans and thus delivers a promising treatment approach to manage C. albicans infection in the future.

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.

Induction of Apoptosis in HeLa Cells by a Novel Peptide from Fruiting Bodies of Morchella importuna via the Mitochondrial Apoptotic Pathway

Morels (Morchella spp.) are a genus of edible fungi with important economic and medicinal value. In this study, a novel peptide (MIPP) was extracted from the fruiting bodies of Morchella importuna using gel filtration chromatography. Structural analysis showed that the molecular mass of MIPP is 831 Da, and it has a simple amino acid sequence: Ser-Leu-Ser-Leu-Ser-Val-Ala-Arg. To explore the antitumor activity of MIPP, the effect of MIPP on HeLa cell apoptosis and the underlying preventative mechanisms were investigated. Results showed that MIPP reduced the viability of HeLa cells in a concentration-dependent manner. TUNEL analysis and flow cytometric examination showed that MIPP decreased cell proliferation via a mitochondrial-dependent pathway, as manifested by downregulation of Bcl-2/Bax, promotion of the movement of cytochrome C from the mitochondria to the cytoplasm, and triggering of caspase-9 and caspase-3. Therefore, MIPP may be a promising tumor-preventive agent, especially in human cervical cancer.

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.

A New Antifungal Agent (4-phenyl-1, 3-thiazol-2-yl) Hydrazine Induces Oxidative Damage in Candida albicans

A gradual rise in immunocompromised patients over past years has led to the increasing incidence of invasive fungal infections. Development of effective fungicides can not only provide new means for clinical treatment, but also reduce the occurrence of fungal resistance. We identified a new antifungal agent (4-phenyl-1, 3-thiazol-2-yl), hydrazine (numbered as 31C) which showed high-efficiency, broad-spectrum and specific activities. The minimum inhibitory concentration of 31C against pathogenic fungi was between 0.0625-4 μg/ml in vitro, while 31C had no obvious cytotoxicity to human umbilical vein endothelial cells with the concentration of 4 μg/ml. In addition, 31C of 0.5 μg/ml could exhibit significant fungicidal activity and inhibit the biofilm formation of C. albicans. In vivo fungal infection model showed that 31C of 10 mg/kg significantly increased the survival rate of Galleria mellonella. Further study revealed that 31C-treatment increased the reactive oxygen species (ROS) in C. albicans and elevated the expression of some genes related to anti-oxidative stress response, including CAP1, CTA1, TRR1, and SODs. Consistently, 31C-induced high levels of intracellular ROS resulted in considerable DNA damage, which played a critical role in antifungal-induced cellular death. The addition of ROS scavengers, such as glutathione (GSH), N-Acetyl-L-cysteine (NAC) or oligomeric proanthocyanidins (OPC), dramatically reduced the antifungal activities of 31C and rescued the 31C-induced filamentation defect. Collectively, these results showed that 31C exhibited strong antifungal activity and induced obvious oxidative damage, which indicated that compounds with a structure similar to 31C may provide new sight for antifungal drug development.

The chromogranin A-derived antifungal peptide CGA-N9 induces apoptosis in Candida tropicalis

CGA-N9, a peptide derived from human chromogranin A (CGA), was found to have antimicrobial activity in our previous investigation, but its mechanism of action remains unclear. Herein, the mechanism of action of CGA-N9 was investigated. We found that CGA-N9 induced the depolarization of the cell membrane and uptake of calcium ions into the cytosol and mitochondria. With the disruption of the mitochondrial membrane potential, the generation of intracellular reactive oxygen species (ROS) increased. Accordingly, we assessed apoptotic processes in Candida tropicalis cells post-treatment with CGA-N9 and found cytochrome c leakage, chromatin condensation and DNA degradation. The interaction of CGA-N9 with DNA in vitro showed that CGA-N9 did not degrade DNA but bound to DNA via an electrostatic interaction. In conclusion, CGA-N9 exhibits antifungal activity by inducing apoptosis in C. tropicalis.

Could Flavonoids Compete with Synthetic Azoles in Diminishing Candida albicans Infections? A Comparative Review Based on In Vitro Studies

Flavonoids are polyphenolic compounds with already confirmed various health benefits. This review will shed light on flavonoids as potential antifungals in Candida albicans infections. C. albicans is an opportunistic pathogen able to cause serious health issues due to numerous virulence factors amplifying its pathogenicity. One of the most important virulence factors is Candida ability to form biofilms which are highly resistant to the treatment of antifungal drugs; making diminishing of this pathogen even more challenging. This review will focus on current knowledge on individual flavonoid compounds having the potential to deal with C. albicans in vitro, with special turn on antibiofilm potential and insight into the mode of action, where available. Majority of the commercial drugs for the treatment of candidiasis belong to azole class, so the activity of flavonoids will be compared with the activity of newly synthetized azole compounds, as well as with azole drugs that are already on the market as official therapeutics. This literature review will provide pros and cons for pushing future research towards exploring novel synthetic azoles or further examination of a wide pallet of natural flavonoids.

In vitro response of human ovarian cancer cells to dietary bioflavonoid isoquercitrin

Isoquercitrin is a dietary bioflavonoid used as a food supplement. We studied the mechanism underlying its effect in human ovarian cancer cells using OVCAR-3 cell line. Viability, survival, apoptosis, release of human transforming growth factor-β1 (TGF-β1) and TGF-β1 receptor, and intracellular reactive oxygen species (ROS) generation by OVCAR-3 cells were examined after isoquercitrin treatment at concentrations 5, 10, 25, 50, and 100 μg mL^-1. AlamarBlue assay revealed that isoquercitrin did not cause any significant change (P > 0.05) in cell viability as compared to control. Apoptotic assay using flow cytometry did not find any significant change (P > 0.05) in the proportion of live, dead and apoptotic cells as compared to control. ELISA also showed that the release of human TGF-β1 and TGF-β1 receptor were not significantly (P > 0.05) affected by isoquercitrin as compared to control. Chemiluminescence assay demonstrated that lower concentrations (5, 10, and 25 μg mL^-1) were able to exhibit beneficial effects by inhibiting the generation of intracellular ROS. In contrast, elevated concentrations of 50 and 100 μg mL^-1 led to oxidative stress (P < 0.05). We concluded that the beneficial effect of isoquercitrin on ovarian cancer cells may be mediated by an antioxidative pathway that involves inhibition of intracellular ROS generation, thereby limiting oxidative stress.

DBA-induced caspase-3-dependent apoptosis occurs through mitochondrial translocation of cyt-c in the rat hippocampus

Dibromoacetic acid (DBA), a by-product of disinfection, develops in drinking water during chlorination or ozonation processes. Water intake is the main source of DBA exposure in humans, which is potentially neurotoxic. The present study investigated the neurotoxic effects of DBA by assessing the behavioral and biochemical characteristics of Sprague Dawley rats intragastrically treated with DBA at concentrations of 20, 50 and 125 mg kg^-1 body weight for 28 consecutive days. The results indicated that animal weight gain and food consumption were not significantly affected by DBA. However, shuttle box tests showed increases in mistake frequency and reaction latency between the control and high-dose group. We found significant changes in hippocampal neurons by histomorphological observation. Additionally, biochemical analysis indicated enhanced production of reactive oxygen species (ROS) resulting in disruption of cellular antioxidant defense systems including decreased mitochondrial superoxide dismutase (SOD) activity and release of cytochrome c (cyt-c) from mitochondria into the cytosol, which can induce neuronal apoptosis. Furthermore, the increase of cyt-c in the cytosol enhanced caspase-3 and caspase-9 activity, which was confirmed by poly ADP-ribose polymerase-1 (PARP-1) cleavage to its signature fragment of 85 kDa and decreased levels of protein kinase C-δ (PKC-δ) in the hippocampus. Meanwhile, DBA treatment caused differential modulation of apoptosis-associated proteins and mRNAs for phosphorylated apoptosis signal regulating kinase 1 (p-ASK-1), phosphorylated c-jun N-terminal kinase (p-JNK), cyt-c, Bax, Bcl-2, caspase-9 and cleaved caspase-3 accompanied by DNA damage. Taken together, these data indicate that DBA may induce neurotoxicity via caspase-3-dependent apoptosis involving mitochondrial translocation of cyt-c in the rat hippocampus.

Reactive oxygen species modulate itraconazole-induced apoptosis via mitochondrial disruption in Candida albicans

Itraconazole (ITC), a well-known fungistatic agent, has potent fungicidal activity against Candida albicans. However, its mechanism of fungicidal activity has not been elucidated yet, and we aimed to identify the mechanism of ITC against C. albicans. ITC caused cell shrinkage via potassium leakage through the ion channel. Since shrunken cells could indicate apoptosis, we investigated apoptotic features. Annexin V-FITC and TUNEL assays indicated that fungicidal activity of ITC was involved in apoptosis. Subsequently, we confirmed an intracellular factor that could cause apoptosis. ITC treatment caused reactive oxygen species (ROS) accumulation. To confirm whether ROS is related with ITC-triggered cell death, cell viability was examined using the ROS scavenger N-acetylcysteine (NAC). NAC pretreatment recovered ITC-induced cell death, indicating that antifungal activity of ITC is associated with ROS, which is also confirmed by impaired glutathione-related antioxidant system and oxidized intracellular lipids. Moreover, ITC-induced mitochondrial dysfunction, in turn, triggered cytochrome c release and metacaspase activation, leading to apoptosis. Unlike the only ITC-treatment group, cells with NAC pretreatment did not show significant damage to mitochondria, and attenuated apoptotic features. Therefore, our results suggest that ITC induces apoptosis as fungicidal mechanism, and intracellular ROS is major factor to trigger the apoptosis by ITC in C. albicans.

Effect of isoquercitrin on membrane dynamics and apoptosis-like death in Escherichia coli

Minimum inhibitory concentration (MIC) is defined as the lowest concentration of a compound that completely inhibits microbial growth. Antibacterial mechanisms of compounds have been investigated at their sub-MICs as well as at their MIC. In this study, the effects of sub-MIC and MIC of isoquercitrin on Escherichia coli were investigated. The antibacterial effect of isoquercitrin was tested using the microdilution method. Sub-MICs of isoquercitrin induced the production of reactive oxygen species and depletion of glutathione. The oxidative effects induced by sub-MICs of isoquercitrin could be prolonged, finally resulting in apoptosis-like death. DNA fragmentation and phosphatidylserine externalization, which are regarded as the hallmarks of apoptosis, were evaluated using the TUNEL assay and Annexin V staining, respectively. Furthermore, isoquercitrin induced the peroxidation of membrane lipids and inner membrane permeabilization at both its sub-MIC and MIC. This suggested membrane damage in response to lipid oxidation. The uptake of membrane impermeable dyes, propidium iodide and calcein, demonstrated that isoquercitrin damaged the cell membrane at concentrations higher than its MIC. Thus, isoquercitrin induced apoptosis-like death and dysregulation of cell membrane dynamics.

Hydrogen sulfide may attenuate methylmercury-induced neurotoxicity via mitochondrial preservation

Hydrogen sulfide (H₂S) is a protective molecule and a novel gaseous mediator. Here we explored whether H₂S donor (NaHS) could attenuate methylmercury (MeHg)-induced neurotoxicity in rats. The adult rats were randomly divided into four groups, i.e., control, NaHS, MeHg, and NaHS + MeHg groups. Rats of the NaHS + MeHg group were intraperitoneally (i.p) injected with 5.6 mg/kg/d of NaHS together with 5 μg/kg/d of MeHg. Rats of the MeHg group and NaHS group were injected with 5 μg/kg/d of MeHg and 5.6 mg/kg/d of NaHS, respectively. All treatments were continued for 20 d, and the cerebral cortex of the rats was evaluated. The results showed that NaHS significantly reduced MeHg-induced oxidative stress, as indicated by reduced lipid peroxide content, and increased glutathione levels and glutathione peroxidase and thioredoxin reductase activities. NaHS attenuated MeHg-induced mitochondrial damage, as indicated by increased mitochondrial activity, reduced mitochondrial swelling, and the release of cytochrome C and apoptosis-inducing factors. NaHS also decreased the number of apoptotic cells compared to that observed in MeHg only-treated rats, as indicated in a TUNEL assay. Finally, NaHS increased DNA and RNA content, and the activities of acetylcholinesterase and Na⁺/K⁺-ATPase. These indices were all lower in the MeHg group than in the control group, and NaHS alone did not observably influence any of these indices compared to the control. Our results demonstrate that H₂S may protect against MeHg-induced neurotoxicity, and the mechanisms appear to involve the inhibition of oxidative stress and the protection of mitochondria.