Inhibition of azole-resistant Candida albicans ATPase and oxidoreductase activity by a flavonoid from Dalea elegans.

BACKGROUND: The flavonoid 2', 4'-dihydroxy-5'-(1''', 1'''-dimethylallyl)-8-prenylpinocembrin (8PP) obtained from Dalea elegans roots inhibits cell growth and cdr pumps, in addition to reversing fluconazole (FCZ) resistance in Candida albicans. AIMS: To study the effects of 8PP and FCZ on cdr-associated ATPase and cell energy generation in azole-resistant C. albicans planktonic cultures. MATERIALS AND METHODS: ATPase activity was measured as oligomycin-sensitive release of inorganic phosphate in fractions containing plasmatic membranes. Cell oxidoreductase activity was evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) reduction in C. albicans cells. RESULTS: FCZ, 8PP and their combination at a concentration of 125 µM of each compound inhibit ATPase activity by 61; 58 and 70, respectively. Inhibitory concentration 50 % (IC50) of 8PP was 78.59 ± 1.45 and 104.70 ± 1.25 µM for FCZ. In combination with 125 µM 8PP, FCZ IC50 was reduced by 3 times. Km was 0.96 ± 0.35 mM and Vmax 43.58 ± 5.49 picomoles/mg protein.min. At 125 µM, 8PP shifts the ATP saturation plot to right. A Dixon study using 2 and 5 mM ATP suggests a competitive interaction of 8PP and ATP for the hydrolysis enzymatic site. FCZ, 8PP or their combination at 125 µM does not produce cytotoxicity dependent on oxidoreductase activity. At higher concentrations, toxic effects are observed with both drugs at the MTT assay. IC50 (µM) was 355 ± 6 and 789 ± 11, for 8PP and FCZ, respectively. CONCLUSIONS: The flavonoid 8PP inhibits competitively oligomycin-sensitive ATPase activity associated to cdr transporters and decreases oxidoreductase-dependent cell viability in azole-resistant Candida albicans.

Synthesis, Characterization, and Preliminary In Vitro Cytotoxic Evaluation of a Series of 2-Substituted Benzo [d] [1,3] Azoles.

A series of benzo [d] [1,3] azoles 2-substituted with benzyl- and allyl-sulfanyl groups were synthesized, and their cytotoxic activities were in vitro evaluated against a panel of six human cancer cell lines. The results showed that compounds BTA-1 and BMZ-2 have the best inhibitory effects, compound BMZ-2 being comparable in some cases with the reference drug tamoxifen and exhibiting a low cytotoxic effect against healthy cells. In silico molecular coupling studies at the tamoxifen binding site of ERα and GPER receptors revealed affinity and the possible mode of interaction of both compounds BTA-1 and BMZ-2.

In silico Studies on the Interaction between Mpro and PLpro From SARS-CoV-2 and Ebselen, its Metabolites and Derivatives.

The COVID-19 pandemic caused by the SARS-CoV-2 has mobilized scientific attention in search of a treatment. The cysteine-proteases, main protease (Mpro) and papain-like protease (PLpro) are important targets for antiviral drugs. In this work, we simulate the interactions between the Mpro and PLpro with Ebselen, its metabolites and derivatives with the aim of finding molecules that can potentially inhibit these enzymes. The docking data demonstrate that there are two main interactions between the thiol (-SH) group of Cys (from the protease active sites) and the electrophilic centers of the organoselenium molecules, i. e. the interaction with the carbonyl group (O=C… SH) and the interaction with the Se moiety (Se… SH). Both interactions may lead to an adduct formation and enzyme inhibition. Density Functional Theory (DFT) calculations with Ebselen indicate that the energetics of the thiol nucleophilic attack is more favorable on Se than on the carbonyl group, which is in accordance with experimental data (Jin et al. Nature, 2020, 582, 289-293). Therefore, organoselenium molecules should be further explored as inhibitors of the SARS-CoV-2 proteases. Furthermore, we suggest that some metabolites of Ebselen (e. g. Ebselen diselenide and methylebselenoxide) and derivatives ethaselen and ebsulfur should be tested in vitro as inhibitors of virus replication and its proteases.

Organization and dynamics of NBD-labeled lipids in lipid bilayer analyzed by FRET using the small membrane fluorescent probe AHBA as donor.

Fluorescent probes are employed to investigate natural and model membranes. It is important to know probe location and extent of perturbations they cause into the lipid bilayer. Förster Resonance Energy Transfer (FRET) is a useful tool to investigate phenomena involving plasma membranes, and reports in literature used relatively large fluorophores like 1,6-diphenylhexatriene, located at the center of the hydrophobic region, 4-aminophthalimide-based molecules located at lipid/water interfaces and BODIPY-labeled phosphatidylcholine. In this work we explored FRET process in 1,2-dimyristoyl-L-α-GPC large unilamellar vesicles, in gel and fluid phase, using as donor the very small group o-Abz bound to hexadecyl chain (2-amino-N-hexadecyl-benzamide - AHBA) and 7-nitro-2-1,3-benzoxadiazol-4-yl (NBD) labeled lipids as acceptor. From the intensity decay of donor in presence of acceptors, the FRET efficiency was calculated, and used to fit the model proposed by Fung and Stryer to that efficiency. Using lipid bilayer structural data, the procedure allowed the determination of Förster distance for each donor-acceptor pair in vesicles, without imposing any value for the orientational factor κ2. From distance distributions between o-Abz in AHBA and NBD in lipid bilayer obtained using the program CONTIN, we obtained donor-acceptor populations having different separation distances. The populations reflect the occurrence of FRET involving probes in the same or in opposite leaflet. A dynamic picture emerged showing how relative position of the probes is dependent on the structural thermal phase of the DMPC bilayer. The results emphasize the need of careful analysis in order to understand processes involving fluorescent probes in model membranes.

Fundamental Concepts of Azole Compounds and Triazole Antifungals: A Beginner's Review.

Azoles are the most widely used drugs in antifungal therapy. They have a wide spectrum of activity against pathogenic fungi that are clinically relevant. However, they have been associated with adverse reactions and toxicity, both of which can be significant in patients. Compared to diazoles, triazoles discriminate better between their intended molecular target, the fungal CYP51 enzyme, and several enzymes of the human CYP450 system. Over the years, this superior discrimination has led to the favoring of triazoles over diazoles in the treatment of systemic mycoses. Nevertheless, despite their being better able to discriminate between the fungal CYP51 and host CYP450 enzymes, they are still capable of inducing significant toxicity and adverse reactions in the host, especially when taken concomitantly with other therapeutic drugs by patients with compromised immune systems. In this writing, we review some of the fundamental concepts regarding the chemistry and mechanisms of action of azole compounds, as well as the spectrum of activity, pharmacokinetics, and adverse effects of triazole antifungals. In addition, we discuss some of the mechanisms that pathogenic fungi have developed to overcome the cytotoxic effects of therapeutic drugs, with an emphasis on triazoles.

Insights into the interaction and binding mode of a set of antifungal azoles as inhibitors of potential fungal enzyme-based targets.

Azole-containing compounds are a kind of chemical entities of natural and synthetic origin having a wide-range of activities. They are therefore considered as important moieties for fungicide development, mostly due to the possible action on several enzyme-based targets. As part of our research on fungicidal agents, the relationship between the ligand-enzyme affinities of several synthetic azole-containing compounds against a set of fungal enzyme-based targets was in silico evaluated through molecular docking. The affinity values of the test compounds were mostly higher than those of the respective test controls. Binding modes between enzymes and test compounds were firstly investigated through Vina scores and ligand-residue interactions. Furthermore, statistically relationships among docking scores were successfully found by multivariate analysis. They were mostly correlated with reported MIC80 values, so it denoted an evident discrimination of the test compounds. Strong electron withdrawing groups on phenylacrylamide moiety were responsible for establishing stronger complexes with the enzyme targets, being trichodiene synthase and α-L-fucosidase the most important ones. Moreover, stability of a set of representative protein/ligand complexes was also analyzed by 10 ns molecular dynamics simulations (MD). Significant differences into the MD runs were detected and directly correlated to docking performances. Finally, docking affinity scores and HOMO-LUMO energy gaps resulted well predicted by comparative molecular field analysis (CoMFA) models, demonstrating the structure type is particularly associated with those calculated properties and these results were thus consistent with the respective validation parameters.

Azole resistance in Candida spp. isolated from Catú Lake, Ceará, Brazil: an efflux-pump-mediated mechanism

Abstract Since, there is no study reporting the mechanism of azole resistance among yeasts isolated from aquatic environments; the present study aims to investigate the occurrence of antifungal resistance among yeasts isolated from an aquatic environment, and assess the efflux-pump activity of the azole-resistant strains to better understand the mechanism of resistance for this group of drugs. For this purpose, monthly water and sediment samples were collected from Catú Lake, Ceará, Brazil, from March 2011 to February 2012. The obtained yeasts were identified based on morphological and biochemical characteristics. Of the 46 isolates, 37 were Candida spp., 4 were Trichosporon asahii, 3 were Cryptococcus laurentii, 1 Rhodotorula mucilaginosa, and 1 was Kodamaea ohmeri. These isolates were subjected to broth microdilution assay with amphotericin B, itraconazole, and fluconazole, according to the methodology standardized by the Clinical and Laboratory Standards Institute (CLSI). The minimum inhibitory concentrations (MICs) of amphotericin B, itraconazole, and fluconazole were 0.03125–2 µg/mL, 0.0625 to ≥16 µg/mL, and 0.5 to ≥64 µg/mL, respectively, and 13 resistant azole-resistant Candida isolates were detected. A reduction in the azole MICs leading to the phenotypical reversal of the azole resistance was observed upon addition of efflux-pump inhibitors. These findings suggest that the azole resistance among environmental Candida spp. is most likely associated with the overexpression of efflux-pumps.

Azole resistance in Candida spp. isolated from Catú Lake, Ceará, Brazil: an efflux-pump-mediated mechanism.

Since, there is no study reporting the mechanism of azole resistance among yeasts isolated from aquatic environments; the present study aims to investigate the occurrence of antifungal resistance among yeasts isolated from an aquatic environment, and assess the efflux-pump activity of the azole-resistant strains to better understand the mechanism of resistance for this group of drugs. For this purpose, monthly water and sediment samples were collected from Catú Lake, Ceará, Brazil, from March 2011 to February 2012. The obtained yeasts were identified based on morphological and biochemical characteristics. Of the 46 isolates, 37 were Candida spp., 4 were Trichosporon asahii, 3 were Cryptococcus laurentii, 1 Rhodotorula mucilaginosa, and 1 was Kodamaea ohmeri. These isolates were subjected to broth microdilution assay with amphotericin B, itraconazole, and fluconazole, according to the methodology standardized by the Clinical and Laboratory Standards Institute (CLSI). The minimum inhibitory concentrations (MICs) of amphotericin B, itraconazole, and fluconazole were 0.03125-2µg/mL, 0.0625 to ≥16µg/mL, and 0.5 to ≥64µg/mL, respectively, and 13 resistant azole-resistant Candida isolates were detected. A reduction in the azole MICs leading to the phenotypical reversal of the azole resistance was observed upon addition of efflux-pump inhibitors. These findings suggest that the azole resistance among environmental Candida spp. is most likely associated with the overexpression of efflux-pumps.

Identification and properties of plasma membrane azole efflux pumps from the pathogenic fungi Cryptococcus gattii and Cryptococcus neoformans.

OBJECTIVES: Cryptococcus gattii from the North American Northwest (NW) have higher azole MICs than do non-NW C. gattii or Cryptococcus neoformans. Since mechanisms of azole resistance in C. gattii are not known, we identified C. gattii and C. neoformans plasma membrane azole efflux pumps and characterized their properties. METHODS: The C. gattii R265 genome was searched for orthologues of known fungal azole efflux genes, expression of candidate genes was assessed by RT-PCR and the expressed genes' cDNAs were cloned and expressed in Saccharomyces cerevisiae. Azole MICs and intracellular [(3)H]fluconazole were measured in C. gattii and C. neoformans and in S. cerevisiae expressing each cDNA of interest, as was [(3)H]fluconazole uptake by post-Golgi vesicles (PGVs) isolated from S. cerevisiae sec6-4 mutants expressing each cDNA of interest. RESULTS: Intracellular [(3)H]fluconazole concentrations were inversely correlated with fluconazole MICs only in 25 NW C. gattii strains. S. cerevisiae expressing three C. gattii cDNAs (encoded by orthologues of C. neoformans AFR1 and MDR1 and the previously unstudied gene AFR2) and their C. neoformans counterparts had higher azole MICs and lower intracellular [(3)H]fluconazole concentrations than did empty-vector controls. PGVs from S. cerevisiae expressing all six Cryptococcus cDNAs also accumulated more [(3)H]fluconazole than did controls, and [(3)H]fluconazole transport by all six transporters of interest was ATP dependent and was inhibited by excess unlabelled fluconazole, voriconazole, itraconazole and posaconazole. CONCLUSIONS: We conclude that C. gattii and C. neoformans AFR1, MDR1 and AFR2 encode ABC transporters that pump multiple azoles out of S. cerevisiae cells, thereby causing azole resistance.

Diphenyl diselenide and analogs are substrates of cerebral rat thioredoxin reductase: a pathway for their neuroprotective effects.

Thioredoxin reductase (TrxR) isoforms play important roles in cell physiology, protecting cells against oxidative processes. In addition to its endogenous substrates (Trx isoforms), hepatic TrxR can reduce organic selenium compounds such as ebselen and diphenyl diselenide to their selenol intermediates, which can be involved in their hepatoprotective properties. Taking this into account, the aim of the present study was to evaluate the hypothesis that ebselen, diphenyl diselenide and its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxydiphenyl diselenide, 4.4'-biscarboxy-diphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could be substrates of rat brain TrxR. In the presence of partially purified rat brain TrxR, diphenyl diselenide, bismethoxydiphenyl diselenide and bischlorodiphenyl diselenide (at 10, 15 and 20µM) stimulated NADPH oxidation, indicating that they are substrates of brain TrxR. In contrast, ebselen and bistrifluoromethyldiphenyl diselenide, that have been previously demonstrated to be substrate of hepatic TrxR, were not reduced by rat brain TrxR. The results presented here suggest that diphenyl diselenide can exert neuroprotective effects by mimicking glutathione peroxidase activity and also via its reduction by TrxR. However, ebselen was not reduced by brain TrxR, indicating that the neuroprotective properties of this compound is possibly mediate by its glutathione peroxidase-like activity.