Antimicrobial activity and inhibition of the NorA efflux pump of Staphylococcus aureus by extract and isolated compounds from Arrabidaea brachypoda

Therapeutic potential of botanical drugs and their metabolites in the treatment of pelvic inflammatory disease

The application of botanical drugs and their metabolites in the treatment of pelvic inflammatory disease (PID) has garnered significant attention. Owing to their broad-spectrum activity, global accessibility, and structural diversity, botanical drugs have emerged as promising candidates for adjunctive or alternative therapies. This review systematically summarizes botanical drugs and their metabolites, focusing on their antimicrobial potential against endogenous and exogenous pathogens associated with PID. Specifically, it addresses various underlying antibacterial mechanisms, including interference with bacterial cell membranes and cell walls, inhibition of pathogen-specific efflux pumps, modulation of pathogen-related gene expression, and synergistic effects when combined with conventional antibiotics. This review highlights the therapeutic promise of botanical drugs and their metabolites, emphasizing critical findings regarding their inhibitory effects on PID-associated pathogens. Such insights provide valuable guidance for future therapeutic strategies and may support ongoing antibiotic discovery and development.

Copper induced augmentation of antibiotic resistance in Acinetobacter baumannii MCC 3114

Increasing antibiotic resistance among the common nosocomial pathogen i.e. Acinetobacter baumannii poses life threat to the health care workers as well as to the society. The dissemination of antibiotic resistance in this pathogen at an alarming rate could be not only due to the overuse of antibiotics but also due to the stress caused by exposure of bacterium to several environmental contaminants in their niches. In the present study, effect of copper stress on augmentation in the antibiotic resistance of A. baumannii MCC 3114 against three clinically used antibiotics was investigated along with the phenotypic and genotypic alterations in the cell. It induced 8, 44 and 22-fold increase in resistance against colistin, ciprofloxacin and levofloxacin, respectively. Moreover, the biofilm formation of adapted culture was significantly enhanced due to a dense EPS around the cell (as revealed by SEM images). The structural changes in EPS were demonstrated by FTIR spectroscopy. The adequate growth of adapted MCC 3114 despite increased level of ROS indicates its persistence in copper and ROS stress. The physiological alterations in cell viz., increased efflux pump activity and decreased membrane permeability was observed. Molecular analysis revealed increased expression of efflux pump related genes, oxidative stress genes, integron and antibiotic resistance genes. In sum, our study revealed that the exposure of the critical pathogen, A. baunmannii to copper in hospital settings and environmental reservoirs can impose adaptive pressure which may lead to genotypic as well phenotypic changes in cell resulting into the augmentation of antibiotic resistance.

Zein Nanoparticles-Loaded Flavonoids-Rich Fraction from Fridericia platyphylla: Potential Antileishmanial Applications

Background/Objectives: Leishmaniasis, caused by protozoa of the genus Leishmania, is a major global health issue due to the limitations of current treatments, which include low efficacy, high costs, and severe side effects. This study aimed to develop a more effective and less toxic therapy by utilizing zein nanoparticles (ZNPs) in combination with a nonpolar fraction (DCMF) from Fridericia platyphylla (Syn. Arrabidaea brachypoda), a plant rich in dimeric flavonoids called brachydins. Methods: Zein nanoparticles were used as carriers to encapsulate DCMF. The system was characterized by measuring particle diameter, polydispersity index, zeta potential, and encapsulation efficiency. Analytical techniques such as FTIR, DSC, and AFM were employed to confirm the encapsulation and stability of DCMF. Antileishmanial activity was assessed against Leishmania amazonensis promastigotes and amastigotes, while cytotoxicity was tested on RAW264.7 macrophages. Results: The ZNP-DCMF system exhibited favorable properties, including a particle diameter of 141 nm, a polydispersity index below 0.2, and a zeta potential of 11.3 mV. DCMF was encapsulated with an efficiency of 94.6% and remained stable for 49 days. In antileishmanial assays, ZNP-DCMF inhibited the viability of promastigotes with an IC50 of 36.33 μg/mL and amastigotes with an IC50 of 0.72 μg/mL, demonstrating higher selectivity (SI = 694.44) compared to DCMF alone (SI = 43.11). ZNP-DCMF was non-cytotoxic to RAW264.7 macrophages, with a CC50 > 500 μg/mL. Conclusions: Combining F. platyphylla DCMF with zein nanoparticles as a carrier presents a promising approach for leishmaniasis treatment, offering improved efficacy, reduced toxicity, and protection of bioactive compounds from degradation.

Anti-Leishmania activity and molecular docking of unusual flavonoids-rich fraction from Arrabidaea brachypoda (Bignoniaceae)

Leishmaniases comprise a group of infectious parasitic diseases caused by various species of Leishmania and are considered a significant public health problem worldwide. Only a few medications, including miltefosine, amphotericin B, and meglumine antimonate, are used in current therapy. These medications are associated with severe side effects, low efficacy, high cost, and the need for hospital support. Additionally, there have been occurrences of drug resistance. Additionally, only a limited number of drugs, such as meglumine antimonate, amphotericin B, and miltefosine, are available, all of which are associated with severe side effects. In this context, the need for new effective drugs with fewer adverse effects is evident. Therefore, this study investigated the anti-Leishmania activity of a dichloromethane fraction (DCMF) extracted from Arrabidaea brachypoda roots. This fraction inhibited the viability of L. infantum, L. braziliensis, and L. Mexicana promastigotes, with IC50 values of 10.13, 11.44, and 11.16 µg/mL, respectively, and against L. infantum amastigotes (IC50 = 4.81 µg/mL). Moreover, the DCMF exhibited moderate cytotoxicity (CC50 = 25.15) towards RAW264.7 macrophages, with a selectivity index (SI) of 5.2. Notably, the DCMF caused damage to the macrophage genome only at 40 µg/mL, which is greater than the IC50 found for all Leishmania species. The results suggest that DCMF demonstrates similar antileishmanial effectiveness to isolated brachydin B, without causing genotoxic effects on mammalian cells. This finding is crucial because the isolation of the compounds relies on several steps and is very costly while obtaining the DCMF fraction is a simple and cost-effective process. Furthermore, In addition, the potential mechanisms of action of brachydins were also investigated. The computational analysis indicates that brachydin compounds bind to the Triosephosphate isomerase (TIM) enzyme via two main mechanisms: destabilizing the interface between the homodimers and interacting with catalytic residues situated at the site of binding. Based on all the results, DCMF exhibits promise as a therapeutic agent for leishmaniasis due to its significantly reduced toxicity in comparison to the adverse effects associated with current reference treatments.

Unlocking bacterial defense: Exploring the potent inhibition of NorA efflux pump by coumarin derivatives in Staphylococcus aureus

The occurrence of bacterial resistance has been increasing, compromising the treatment of various infections. The high virulence of Staphylococcus aureus allows for the maintenance of the infectious process, causing many deaths and hospitalizations. The MepA and NorA efflux pumps are transporter proteins responsible for expelling antimicrobial agents such as fluoroquinolones from the bacterial cell. Coumarins are phenolic compounds that have been studied for their diverse biological actions, including against bacteria. A pharmacokinetic in silico characterization of compounds C10, C11, C13, and C14 was carried out according to the principles of Lipinski's Rule of Five, in addition to searching for similarity in ChemBL and subsequent search for publications in CAS SciFinder. All compounds were evaluated for their in vitro antibacterial and modulatory activity against standard and multidrug-resistant Gram-positive and Gram-negative strains. The effect of coumarins C9, C10, C11, C13, and C14 as efflux pump inhibitors in Staphylococcus aureus strains was evaluated using the microdilution method (MepA or NorA) and fluorimetry (NorA). The behavior of coumarins regarding the efflux pump was determined from their interaction properties with the membrane and coumarin-protein using molecular docking and molecular dynamics simulations. Only the isolated coumarin compound C13 showed antibacterial activity against standard strains of Staphylococcus aureus and Escherichia coli. However, the other tested coumarins showed modulatory capacity for fluoroquinolone and aminoglycoside antibacterials. Compounds C10, C13, and C14 were effective in reducing the MIC of both antibiotics for both multidrug-resistant strains, while C11 potentiated the effect of norfloxacin and gentamicin for Gram-positive and Gram-negative bacteria and only norfloxacin for Gram-negative. Only coumarin C14 produced synergistic effects when associated with ciprofloxacin in MepA-carrying strains. All tested coumarins have the ability to inhibit the NorA efflux pump present in Staphylococcus aureus, both in reducing the MIC and inducing increased ethidium bromide fluorescence emission in fluorimetry. The findings of this study offer an atomistic perspective on the potential of coumarins as active inhibitors of the NorA pump, highlighting their specific mode of action mainly targeting protein inhibition. In molecular docking, it was observed that coumarins are capable of interacting with various amino acid residues of the NorA pump. The simulation showed that coumarin C10 can cross the bilayer; however, the other coumarins interacted with the membrane but were unable to cross it. Coumarins demonstrated their potentiating role in the effect of norfloxacin through a dual mechanism: efflux pump inhibition through direct interaction with the protein (C9, C10, C11, and C13) and increased interaction with the membrane (C10 and C13). In the context of pharmacokinetic prediction studies, the studied structures have a suitable chemical profile for possible oral use. We suggest that coumarin derivatives may be an interesting alternative in the future for the treatment of resistant bacterial infections, with the possibility of a synergistic effect with other antibacterials, although further studies are needed to characterize their therapeutic effects and toxicity.

Antimicrobial and antibiofilm activity of highly soluble polypyrrole against methicillin-resistant Staphylococcus aureus

AIMS

The purpose was to evaluate the antimicrobial activity of highly soluble polypyrrole (Hs-PPy), alone or combined with oxacillin, as well as its antibiofilm potential against methicillin-resistant Staphylococcus aureus strains. Furthermore, the in silico inhibitory mechanism in efflux pumps was also investigated.

METHODS AND RESULTS

Ten clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and two reference strains were used. Antimicrobial activity was determined by broth microdilution, and the combination effect with oxacillin was evaluated by the checkerboard assay. The biofilm formation capacity of MRSA and the interference of Hs-PPy were evaluated. The inhibitory action of Hs-PPy on the efflux pump was evaluated in silico through molecular docking. Hs-PPy showed activity against the isolates, with inhibitory action between 62.5 and 125 µg ml-1 and bactericidal action at 62.5 µg ml-1, as well as synergism in association with oxacillin. The isolates ranged from moderate to strong biofilm producers, and Hs-PPy interfered with the formation of this structure, but not with mature biofilm. There was no in silico interaction with the efflux protein EmrD, the closest homolog to NorA.

CONCLUSIONS

Hs-PPy interferes with biofilm formation by MRSA, has synergistic potential, and is an efflux pump inhibitor.

Multidrug Efflux System-mediated resistance in Staphylococcus aureus under a One Health approach

The aim of the study was to track the spread of antimicrobial resistance among the different sectors of One Health through the detection of Multidrug-Efflux-System in multidrug-resistant Staphylococcus aureus isolates. Multidrug-resistant (MDR) and methicillin-resistant (MRSA) S. aureus isolates were selected: 25 of human, one of animal and eight of food origin. The efflux system genes norA, norB, norC, LmrS, tet38 and msrA were screened by PCR. The activity of the efflux systems was determined by the minimum inhibitory concentration (MIC) of tetracycline and ciprofloxacin in the presence and absence of CCCP and in the quantification of ethidium bromide efflux. Furthermore, biofilm formation was determined in the presence and absence of the CCCP. The molecular epidemiology of the isolates was traced with the aid of PFGE. The gene norC was the most prevalent, detected in all isolates and msrA was the least prevalent, detected in only two isolates from humans. There was no difference in the MICs of tetracycline and ciprofloxacin in the presence of CCCP, but 55.9% of isolates showed ethidium bromide efflux. The presence of CCCP decreased the biofilm formation. Regarding the molecular epidemiology, in three clusters was a mixture of the isolates from different origins. Therefore, S. aureus MDR with active multidrug efflux systems are circulating between One Health domains and it is necessary to consider strategies to decrease this circulation in order to prevent the dissemination of resistance mediated by MES.

Innovative Microemulsion Loaded with Unusual Dimeric Flavonoids from Fridericia platyphylla (Cham.) L.G. Lohmann Roots

Fridericia platyphylla (Cham.) L.G. Lohmann is a species native to the Brazilian cerrado, with promising bioactivity. The organic fraction of the roots is rich in unusual dimeric flavonoids, reported as potential candidates for cancer treatment. The exploration of these flavonoids is very important, considering their diverse biological activities and the need for innovative therapeutic options. This work aimed to develop and characterize a microemulsion loaded with a non-polar fraction (DCM). The constituents were chosen, and the pseudo-ternary diagram was constructed to determine the region of microemulsion formation. The microemulsions blank (ME), with 3% (ME3) and 5% (ME5) of fraction DCM, were characterized in terms of droplet size, zeta potential, and polydispersity index. Both MEs showed particle sizes <100 nm; only ME3 exhibited better values for polydispersity index and zeta potential and was therefore selected for further study. The organoleptic and physicochemical characteristics were evaluated, revealing limpidity and transparency typical of these microstructures, physiologically acceptable pH, refractive index of 1.42±0.01, and density of 1.017 g/cm3±0.01. The stability tests showed good stability profiles even after exposure to extreme thermal conditions, with minimal changes in pH and the content of the incorporated fraction. The in vitro release study demonstrated that ME3 enabled the controlled release of the fraction, with a cumulative amount released over 60% within 6 h. Furthermore, fraction DCM and ME3 exhibited no toxicity in Tenebrio molitor larvae. The developed microemulsion exhibited excellent properties, so this study represents the first successful attempt to develop a formulation that incorporates the dimeric flavonoid fraction.

Counteracting antibiotic resistance enzymes and efflux pumps

Bacterial pathogens are constantly evolving new resistance mechanisms against antibiotics; hence, strategies to potentiate existing antibiotics or combat mechanisms of resistance using adjuvants are always in demand. Recently, inhibitors have been identified that counteract enzymatic modification of the drugs isoniazid and rifampin, which have implications in the study of multi-drug-resistant mycobacteria. A wealth of structural studies on efflux pumps from diverse bacteria has also fueled the design of new small-molecule and peptide-based agents to prevent the active transport of antibiotics. We envision that these findings will inspire microbiologists to apply existing adjuvants to clinically relevant resistant strains, or to use described platforms to discover novel antibiotic adjuvant scaffolds.

The Major Facilitator Superfamily and Antimicrobial Resistance Efflux Pumps of the ESKAPEE Pathogen Staphylococcus aureus

The ESKAPEE bacterial pathogen Staphylococcus aureus has posed a serious public health concern for centuries. Throughout its evolutionary course, S. aureus has developed strains with resistance to antimicrobial agents. The bacterial pathogen has acquired multidrug resistance, causing, in many cases, untreatable infectious diseases and raising serious public safety and healthcare concerns. Amongst the various mechanisms for antimicrobial resistance, integral membrane proteins that serve as secondary active transporters from the major facilitator superfamily constitute a chief system of multidrug resistance. These MFS transporters actively export structurally different antimicrobial agents from the cells of S. aureus. This review article discusses the S. aureus-specific MFS multidrug efflux pump systems from a molecular mechanistic perspective, paying particular attention to structure-function relationships, modulation of antimicrobial resistance mediated by MFS drug efflux pumps, and direction for future investigation.

In silico and in vitro evaluation of efflux pumps inhibition of α,β-amyrin

The use of the bacterial efflux pump mechanism to reduce the concentrations of antibiotics in the intracellular to the extracellular region is one of the main mechanisms by which bacteria acquire resistance to antibiotics. The present study aims to evaluate the antibacterial activity of the α,β-amyrin mixture isolated from Protium heptaphyllum against the multidrug-resistant strains of Escherichia coli 06 and Staphylococcus aureus 10, and to verify the inhibition of the efflux resistance mechanisms against the strains of S. aureus 1199B and K2068, carrying the NorA and MepA efflux pumps, respectively. The α,β-amyrin did not show clinically relevant direct bacterial activity. However, the α,β-amyrin when associated with the gentamicin antibiotic presented synergistic effect against the multidrug-resistant bacterial strain of S. aureus 10. In strains with efflux pumps, α,β-amyrin was able to inhibit the action of the efflux protein NorA against Ethidium Bromide. However, this inhibitory effect was not observed in the MepA efflux pump. In addition, when evaluating the effect of standard efflux pump inhibitors, clorptomazine and CCCP, α,β-amyrin showed a decrease in MIC, demonstrating the presence of the efflux mechanism through synergism. Docking studies indicate that α, β-amyrin have a higher affinity energy to MepA, and NorA than ciprofloxacin and norfloxacin. Also, α, β-amyrin bind to the same region of the binding site as these antibiotics. It was concluded that the α, β-amyrin has the potential to increase antibacterial activity with the association of antibiotics, together with the ability to be a strong candidate for an efflux pump inhibitor.Communicated by Ramaswamy H. Sarma.

The Current State of Knowledge in Biological Properties of Cirsimaritin

The search for natural plant-based products as new pharmacological alternatives to treat various human pathologies has taken on great importance for researchers and research laboratories. In this context, research has intensified to extract and identify natural molecules endowed with biological effects. The objective of this study is to review the source and pharmacological properties of cirsimaritin. The identification and isolation of this flavonoid from various natural sources, including medicinal plants such as Artemisia judaica, Cirsium japonicum, Lithocarpus dealbatus, Microtea debilis, and Ocimum sanctum, has been carried out and verified using different spectral techniques. Biological effect investigations are carried out with a wide variety of experimental models in vitro and in vivo and laboratory techniques. The results of these research works showed the biological properties of cirsimaritin including anticancer, antimicrobial, antidiabetic, antiparasitic, antioxidant, and anti-inflammatory effects. The mechanisms involved in the multiple activities of this molecule are diverse and include sub-cellular, cellular, and molecular levels. Indeed, this bioactive induces anti-inflammatory and antiproliferative effects by inhibiting cell membrane receptors, interference with signaling pathways, and inhibiting transcriptional factors such as Nf-κB involved in cell promotion and proliferation. In the light of these results, cirsimaritin appears as a promising and viable alternative natural bioactive drug to treat many pathological conditions.

Ethyl Acetate Fraction of Bixa orellana and Its Component Ellagic Acid Exert Antibacterial and Anti-Inflammatory Properties against Mycobacterium abscessus subsp. massiliense

Mycobacterium abscessus subsp. massiliense (Mabs) causes chronic infections, which has led to the need for new antimycobacterial agents. In this study, we investigated the antimycobacterial and anti-inflammatory activities of the ethyl acetate fraction of Bixa orellana leaves (BoEA) and ellagic acid (ElAc). In silico analysis predicted that ElAc had low toxicity, was not mutagenic or carcinogenic, and had antimicrobial and anti-inflammatory activities. Apparently, ElAc can interact with COX2 and Dihydrofolate reductase (DHFR) enzymes, which could explain both activities. In vitro analysis showed that BoEA and ElAc exerted antimicrobial activity against Mabs (minimum inhibitory concentration of 1.56, 1.56 mg/mL and bactericidal concentration of 6.25, 3.12 mg/mL, respectively. Clarithromycin showed MIC and MBC of 1 and 6 µg/mL). Treatment with BoEA or ElAc increased survival of Tenebrio molitor larvae after lethal infection with Mabs and reduced carrageenan-induced paw edema in mice, around 40% of edema volume after the fourth hour, similarly to diclofenac. In conclusion, BoEA and ElAc exert antimicrobial effects against Mabs and have anti-inflammatory effects, making them potential sources of antimycobacterial drugs. The biological activities of ElAc may be due to its high binding affinities predicted for COX2 and DHFR enzymes.

Antimicrobial Properties Against Human Pathogens of Medicinal Plants from New Zealand

The emergence of resistant microorganisms towards standard antibiotics has stimulated an on-going exploration for new sources of antimicrobials. The microbial susceptibility of extracts produced from leaf, bark, or rhizome parts of nine different New Zealand bushes was investigated using liquid broth dilution and agar plating techniques. Minimum inhibitory (MIC) and lethal concentrations (MLC) were expressed in micrograms of dry extract per milliliters of solution. The lowest MIC of 62.5 μg/mL was determined for methanol extract of Kunzea ericoides against Bacillus cereus and Candida albicans, and ethyl acetate extract of Pseudowintera colorata against Staphylococcus aureus. Additionally, K. ericoides also presented the lowest MLC of 250 μg/mL against S. aureus and B. cereus (methanol extract), and against S. aureus (ethyl acetate extract). The methanol extract of Weinmannia racemosa was lethal to B. cereus (MLC = 250 µg/mL). Some of the extracts of Phormium tenax, Schefflera digitata, and Pomaderris kumeraho were antimicrobial against S. aureus and B. cereus (MIC = 500 µg/mL). The extracts of Geniostoma ligustrifolium and Melicytus ramiflorus plants did not exhibit antimicrobial activity.

Unusual dimeric flavonoids (brachydins) induce ultrastructural membrane alterations associated with antitumor activity in cancer cell lines

Notwithstanding the advances in molecular target-based drugs, chemotherapy remains the most common cancer treatment, despite its high toxicity. Consequently, effective anticancer therapies with fewer adverse effects are needed. Therefore, this study aimed to determine the anticancer activity of the dichloromethane fraction (DCMF) isolated from Arrabidae brachypoda roots, whose components are three unusual dimeric flavonoids. The toxicity of DCMF was investigated in breast (MCF-7), prostate (DU145), and cervical (HeLa) tumor cells, as well as non-tumor cells (PNT2), using sulforhodamine B (cell viability), Comet (genotoxicity), clonogenicity (reproductive capacity) and wound healing (cell migration) assays, and atomic force microscopy (AFM) for ultrastructural cell membrane alterations. Molecular docking revealed affinity between albumin and each rare flavonoid, supporting the impact of fetal bovine serum in DCMF antitumor activity. The IC₅₀ values for MCF7, HeLa, and DU145 were 2.77, 2.46, and 2.51 µg/mL, respectively, and 4.08 µg/mL for PNT2. DCFM was not genotoxic to tumor or normal cells when exposed to twice the IC₅₀ for up to 24 h, but it inhibited tumor cell migration and reproduction compared to normal cells. Additionally, AFM revealed alterations in the ultrastructure of tumor nuclear membrane surfaces, with a positive correlation between DCMF concentration and tumor cell roughness. Finally, we found a negative correlation between roughness and the ability of DCMF-treated tumor cells to migrate and form colonies with more than 50 cells. These findings suggest that DCFM acts by causing ultrastructural changes in tumor cell membranes while having fewer toxicological effects on normal cells.

The Antitumoral/Antimetastatic Action of the Flavonoid Brachydin A in Metastatic Prostate Tumor Spheroids In Vitro Is Mediated by (Parthanatos) PARP-Related Cell Death

Metastatic prostate cancer (mPCa) is resistant to several chemotherapeutic agents. Brachydin A (BrA), a glycosylated flavonoid extracted from Fridericia platyphylla, displays a remarkable antitumoral effect against in vitro mPCa cells cultured as bidimensional (2D) monolayers. Considering that three-dimensional (3D) cell cultures provide a more accurate response to chemotherapeutic agents, this study investigated the antiproliferative/antimetastatic effects of BrA and the molecular mechanisms underlying its action in mPCa spheroids (DU145) in vitro. BrA at 60–100 μM was cytotoxic, altered spheroid morphology/volume, and suppressed cell migration and tumor invasiveness. High-content analysis revealed that BrA (60–100 µM) reduced mitochondrial membrane potential and increased apoptosis and necrosis markers, indicating that it triggered cell death mechanisms. Molecular analysis showed that (i) 24-h treatment with BrA (80–100 µM) increased the protein levels of DNA disruption markers (cleaved-PARP and p-γ-H2AX) as well as decreased the protein levels of anti/pro-apoptotic (BCL-2, BAD, and RIP3K) and cell survival markers (p-AKT1 and p-44/42 MAPK); (ii) 72-h treatment with BrA increased the protein levels of effector caspases (CASP3, CASP7, and CASP8) and inflammation markers (NF-kB and TNF-α). Altogether, our results suggest that PARP-mediated cell death (parthanatos) is a potential mechanism of action. In conclusion, BrA confirms its potential as a candidate drug for preclinical studies against mPCa.

Bioactivity of Natural Polyphenols as Antiparasitic Agents and their Biochemical Targets

BACKGROUND

Leishmaniasis and trypanosomiasis are diseases that affect public health worldwide due to their high incidence, morbidity, and mortality. Available treatments are costly, prolonged, and toxic, not to mention the problem of parasite resistance. The development of alternative treatments is justified and polyphenols show promising activity.

OBJECTIVE

The main aim of this mini-review was to analyze the most promising phenolic compounds with reported antileishmanial and antitrypanosomal activity as well as their mechanisms of action.

RESULTS

We found that the mode of action of these natural compounds mainly lignans, neolignans, and flavonoids depends on the organism they act on and includes, macrophage activation, induction of morphological changes such as chromatin condensation, DNA fragmentation, accumulation of acidocalcisomes, and glycosomes, Golgi damage and mitochondrial dysfunction as well as negative regulation of mitochondrial enzymes and other essential enzymes for parasite survival such as arginase. This gives a wide scope for future research towards the rational development of anti-kinetoplastid drugs.

CONCLUSION

Although the specific molecular targets, bioavailability, route of administration, and dosages of some of these natural compounds need to be determined, polyphenols and their combinations represent a very promising and safe strategy to be considered for use against Leishmania spp and Trypanosoma spp. In addition, these compounds may provide a scaffold for developing new, more potent, and more selective antiprotozoal agents.

Structural basis for inhibition of the drug efflux pump NorA from Staphylococcus aureus

Membrane protein efflux pumps confer antibiotic resistance by extruding structurally distinct compounds and lowering their intracellular concentration. Yet, there are no clinically approved drugs to inhibit efflux pumps, which would potentiate the efficacy of existing antibiotics rendered ineffective by drug efflux. Here we identified synthetic antigen-binding fragments (Fabs) that inhibit the quinolone transporter NorA from methicillin-resistant Staphylococcus aureus (MRSA). Structures of two NorA-Fab complexes determined using cryo-electron microscopy reveal a Fab loop deeply inserted in the substrate-binding pocket of NorA. An arginine residue on this loop interacts with two neighboring aspartate and glutamate residues essential for NorA-mediated antibiotic resistance in MRSA. Peptide mimics of the Fab loop inhibit NorA with submicromolar potency and ablate MRSA growth in combination with the antibiotic norfloxacin. These findings establish a class of peptide inhibitors that block antibiotic efflux in MRSA by targeting indispensable residues in NorA without the need for membrane permeability.

Aglycone flavonoid brachydin A shows selective cytotoxicity and antitumoral activity in human metastatic prostate (DU145) cancer cells

In prostate cancer, flavonoids possess a wide variety of anticancer effects, focused on the antioxidant/pro-oxidant activity, inactivation of the androgen receptor, cell cycle arrest, apoptosis induction, metastasis inhibition, among others. This current research investigated the antitumoral in vitro activity of Brachydin A (BrA), a dimeric flavonoid isolated from Fridericia platyphylla, in human castration-resistant prostate cancer DU145. It was compared BrA selective effects in tumor prostate DU145 cells with non-tumor prostate epithelial PNT2 cells. Cell viability experiments (resazurin, neutral red, MTT, and LDH release assays) showed that BrA was sevenfold more cytotoxic to tumor cells than non-tumor prostate cells, with IC₅₀ values of 77.7 µM and 10.7 µM for PNT2 and DU145 cells, respectively. Furthermore, BrA induced necrosis and apoptosis (triple fluorescence staining assay) without interfering with oxidative stress (CM-H₂DCFDA) in DU145 cells. Also, BrA (15.36 µM) reduced cell proliferation on clonogenic assay (DU145 cells) but no change in cell number and protein content was observed when cell growth curve assay was used. Wound healing and transwell assays were used for checking the effects of BrA on cell migration and invasion, and BrA impaired these processes in PNT2 (wound healing) and DU145 cells (transwell). Our results inspire further studies to test BrA as a novel chemotherapeutic drug and to evaluate its effects on drug-resistant metastatic cancer cells.

Inhibition of Bacterial Efflux Pumps by Crude Extracts and Essential Oil from Myristica fragrans Houtt. (Nutmeg) Seeds against Methicillin-Resistant Staphylococcus aureus

Myristicafragrans Houtt. (Nutmeg) is a widely known folk medicine across several parts of Asia, particularly used in antimicrobial treatment. Bacterial resistance involves the expression of efflux pump systems (chromosomal norA and mepA) in methicillin-resistant Staphylococcus aureus (MRSA). Crude extract (CE) and essential oil (EO) obtained from nutmeg were applied as efflux pump inhibitors (EPIs), thereby enhancing the antimicrobial activity of the drugs they were used in. The major substances in CE and EO, which function as EPIs, in a descending order of % peak area include elemicin, myristicin, methoxyeugenol, myristicin, and asarone. Here, we investigated whether the low amount of CE and EO used as EPIs was sufficient to sensitize MRSA killing using the antibiotic ciprofloxacin, which acts as an efflux system. Interestingly, synergy between ciprofloxacin and CE or EO revealed the most significant viability of MRSA, depending on norA and mepA, the latter being responsible for EPI function of EO. Therefore, CE and EO obtained from nutmeg can act as EPIs in combination with substances that act as efflux systems, thereby ensuring that the MRSA strain is susceptible to antibiotic treatment.

An Update on Staphylococcus aureus NorA Efflux Pump Inhibitors

BACKGROUND

Methicillin-resistant and vancomycin-resistant Staphylococcus aureus are pathogens causing severe infectious diseases that pose real public health threats problems worldwide. In S. aureus, the most efficient multidrug-resistant system is the NorA efflux pump. For this reason, it is critical to identify efflux pump inhibitors.

OBJECTIVE

In this paper, we present an update of the new natural and synthetic compounds that act as modulators of antibiotic resistance through the inhibition of the S. aureus NorA efflux pump.

RESULTS

Several classes of compounds capable of restoring the antibiotic activity have been identified against resistant-S. aureus strains, acting as NorA efflux pump inhibitors. The most promising classes of compounds were quinolines, indoles, pyridines, phenols, and sulfur-containing heterocycles. However, the substantial degree structural diversity of these compounds makes it difficult to establish good structure- activity correlations that allow the design of compounds with more promising activities and properties.

CONCLUSION

Despite substantial efforts put forth in the search for new antibiotic adjuvants that act as efflux pump inhibitors, and despite several promising results, there are currently no efflux pump inhibitors authorized for human or veterinary use, or in clinical trials. Unfortunately, it appears that infection control strategies have remained the same since the discovery of penicillin, and that most efforts remain focused on discovering new classes of antibiotics, rather than trying to prolong the life of available antibiotics, and simultaneously fighting mechanisms of bacterial resistance.

Novel DiOC3 96-well real-time efflux assay for discovery of NorA efflux pump inhibitors in Staphylococcus aureus

The NorA efflux pump is one of the most studied efflux systems in Staphylococcus aureus and confers multidrug resistance to a variety of dyes and antimicrobial compounds. Hence, inhibition of the NorA efflux pump might be a viable option for restoring susceptibility to antibiotics like fluoroquinolones. Fluorescent real-time efflux assays are important tools to identify putative efflux pump inhibitors. Nevertheless, the number of available compounds for usage in Staphylococcus aureus is limited. Previously, a 3-dipropyloxacarbocyanine iodide (DiOC₃) efflux assay was published that circumvented problems associated with the usage of ethidium bromide, namely slow efflux and suggested mutagenicity. However, the DiOC₃ assay protocol was cuvette - based and therefore needs to be adapted to the 96-well plate format. Hence, we optimized this assay for usage with 96-well plates. The new assay allows for rapid high-throughput efflux pump inhibitor screening.

In Vitro Anti-Inflammatory Activity in Arthritic Synoviocytes of A. brachypoda Root Extracts and Its Unusual Dimeric Flavonoids

Arrabidaea brachypoda is a plant commonly used for the treatment of kidney stones, arthritis and pain in traditional Brazilian medicine. Different in vitro and in vivo activities, ranging from antinociceptive to anti-Trypanosoma cruzi, have been reported for the dichloromethane root extract of Arrabidaea brachypoda (DCMAB) and isolated compounds. This work aimed to assess the in vitro anti-inflammatory activity in arthritic synoviocytes of the DCMAB, the hydroethanolic extract (HEAB) and three dimeric flavonoids isolated from the DCMAB. These compounds, brachydin A (1), B (2) and C (3), were isolated both by medium pressure liquid and high-speed counter current chromatography. Their quantification was performed by mass spectrometry on both DCMAB and HEAB. IL-1β activated human fibroblast-like synoviocytes were incubated with both extracts and isolated compounds to determine the levels of pro-inflammatory cytokine IL-6 by enzyme-linked immunosorbent assay (ELISA). DCMAB inhibited 30% of IL-6 release at 25 µg/mL, when compared with controls while HEAB was inactive. IC₅₀ values determined for 2 and 3 were 3-fold higher than 1. The DCMAB activity seems to be linked to higher proportions of compounds 2 and 3 in this extract. These observations could thus explain the traditional use of A. brachypoda roots in the treatment of osteoarthritis.

Characterization of the invitro cytotoxic effects of brachydins isolated from Fridericia platyphylla in a prostate cancer cell line

Brachydins (Br) A, B, and C are flavonoids extracted from Fridericia platyphylla (Cham.) L.G. Lohmann roots (synonym Arrabidaea brachypoda), whose extract previously exhibited cytotoxic and antitumor activity. In vitro cell culture of human prostate tumor cell line (PC-3) was used to determine cell viability as evidenced by MTT, neutral red, and LDH release using nine concentrations (0.24 to 30.72 µM) of each brachydin. A triple-fluorescent staining assay assessed the mechanism resulting in cell death. Genomic instability and protein expression were evaluated using comet assay and western blot analysis, respectively. The pro-oxidant status was analyzed using the5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H₂DCFDA) probe. The IC₅₀ values for brachydins BrA, BrB, and BrC were 23.41, 4.28, and 4.44 µM, respectively, and all compounds induced apoptosis and necrosis. BrB and BrC increased p21 levels indicating a possible G1 cell cycle arrest. BrA (6 µM) and BrB (3.84 µM) decreased phospho-AKT (AKT serine/threonine kinase) expression, which also influenced cell cycle and proliferation. BrA, BrB, and BrC elevated cleaved PARP (poly (ADP-ribose) polymerase), a protein related to DNA repair and induction of apoptotic processes. Therefore, this study determined the IC₅₀ values of brachydins in the PC-3 cell line as well as the influence on cell proliferation and cell death processes, such as apoptosis and necrosis, indicating the proteins involved in these processes.

ABBREVIATIONS

ANOVA: Analysis of Variance; BrA: Brachydin A; BrB: Brachydin B; BrC: Brachydin C; CGEN: Genetic Heritage Management Council; CID: Compound identification number; CM-H₂DCFDA, 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester; CO₂: Carbon dioxide; DMSO: Dimethyl sulfoxide; DNA: Deoxyribonucleic acid; DTT: Dithiothreitol; DXR: Doxorubicin; ECL: Chemiluminescence; EDTA: Ethylenediaminetetraacetic acid; FBS: Fetal bovine serum; H₂O₂: Hydrogen peroxide; HRMS: High-Resolution Mass Spectrometry; IC50: Half maximal inhibitory concentration; LDH: Lactate dehydrogenase; MTT, 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide; Na3VO4: Sodium Orthovanadate; NaOH: Sodium hydroxide; NCBI: National Center for Biotechnology Information; NMR: Nuclear Magnetic Resonance; PBS: Phosphate buffer saline; PCR: Polymerase chain reaction; PSMF: Phenylmethylsulfonyl fluoride; RPMI: Roswell Park Memorial Institute Medium; SDS-PAGE: Sodium Dodecyl Sulfate-Polyacrylamide gel electrophoresis; STR: Short tandem repeat; TBS-T: Tris-buffered saline and Polysorbate 20; UPHLC: Ultra-Performance Liquid Chromatography.

Chalcones Isolated from Arrabidaea brachypoda Flowers as Inhibitors of NorA and MepA Multidrug Efflux Pumps of Staphylococcus aureus

Bacterial resistance to antibiotics has become a public health issue around the world. The present study aimed to evaluate the antibacterial activity of chalcones isolated from flowers of Arrabidaea brachypoda, and their potential as efflux pump inhibitors of Staphylococcus aureus efflux pumps. Microdilution assays were performed with natural products from A. brachypoda. Chalcones 1, 3, 4, and 5 did not show intrinsic antimicrobial activity against all S. aureus strains tested, but they were able to potentiate the Norfloxacin action against the SA1199-B (norA) strain, with a better modulating action for the 4 trimethoxylated chalcone. All chalcones were also able to potentiate the action of EtBr against SA1199-B strain, suggesting a potential NorA inhibition. Moreover, chalcone 4 was able to interfere in the activity of MepA, and interfered weakly in the QacA/B activity. Molecular docking analyzes showed that tested chalcones are capable of binding in the hydrophobic cavity of NorA and MepA, in the same Norfloxacin binding site, indicating that chalcone 4 compete with the antibiotic for the same NorA and MepA binding sites. Association of chalcone 4 with Norfloxacin could be an alternative against multidrug resistant S. aureus over-productive of NorA or MepA.

Evaluation of the Antibacterial Activity and Efflux Pump Reversal of Thymol and Carvacrol against Staphylococcus aureus and Their Toxicity in Drosophila melanogaster

The antibacterial activity and efflux pump reversal of thymol and carvacrol were investigated against the Staphylococcus aureus IS-58 strain in this study, as well as their toxicity against Drosophila melanogaster. The minimum inhibitory concentration (MIC) was determined using the broth microdilution method, while efflux pump inhibition was assessed by reduction of the antibiotic and ethidium bromide (EtBr) MICs. D. melanogaster toxicity was tested using the fumigation method. Both thymol and carvacrol presented antibacterial activities with MICs of 72 and 256 µg/mL, respectively. The association between thymol and tetracycline demonstrated synergism, while the association between carvacrol and tetracycline presented antagonism. The compound and EtBr combinations did not differ from controls. Thymol and carvacrol toxicity against D. melanogaster were evidenced with EC50 values of 17.96 and 16.97 µg/mL, respectively, with 48 h of exposure. In conclusion, the compounds presented promising antibacterial activity against the tested strain, although no efficacy was observed in terms of efflux pump inhibition.

Functional and Structural Roles of the Major Facilitator Superfamily Bacterial Multidrug Efflux Pumps

Pathogenic microorganisms that are multidrug-resistant can pose severe clinical and public health concerns. In particular, bacterial multidrug efflux transporters of the major facilitator superfamily constitute a notable group of drug resistance mechanisms primarily because multidrug-resistant pathogens can become refractory to antimicrobial agents, thus resulting in potentially untreatable bacterial infections. The major facilitator superfamily is composed of thousands of solute transporters that are related in terms of their phylogenetic relationships, primary amino acid sequences, two- and three-dimensional structures, modes of energization (passive and secondary active), and in their mechanisms of solute and ion translocation across the membrane. The major facilitator superfamily is also composed of numerous families and sub-families of homologous transporters that are conserved across all living taxa, from bacteria to humans. Members of this superfamily share several classes of highly conserved amino acid sequence motifs that play essential mechanistic roles during transport. The structural and functional importance of multidrug efflux pumps that belong to the major facilitator family and that are harbored by Gram-negative and -positive bacterial pathogens are considered here.