Isolation and characterization of an antifungal compound 5-hydroxy-7,4'-dimethoxyflavone from Combretum zeyheri

Antibacterial stigmastane-type steroids and other constituents from the leaves of Vernonia glabra (Steetz) Vatke (Asteraceae)

Two new stigmastane steroids (1 and 2) were isolated from the methanol extract of the leaves of Vernonia glabra, together with seventeen known compounds (3-19) including one fatty acid, four triterpenoids, four steroids, one trinitropropanoyl glucoside, and seven flavonoids. The structures of compounds 1 and 2 were assigned based on their IR, NMR and MS data, and by comparison with literature values. The MeOH extract, its fractions and isolated compounds were subjected to in vitro antibacterial assay against two Gram-positive (Staphylococcus aureus ATCC25923 and Streptococcus pneumoniae ATCC49619) and two Gram-negative (Escherichia coli ATCC8739 and Klebsiella pneumoniae ATCC10031) bacteria, using broth microdilution method. The extract and fractions exhibited (16 ≤ MIC ≤ 512 μg/mL) antibacterial activities. The isolated and tested compounds were also active (16 ≤ MIC ≤ 128 μg/mL) against the four pathogenic bacteria, with compound 2 being the most active and E. coli, the most sensitive microorganism.

Antibacterial Activity and Proposed Mode of Action of Extracts from Selected Zimbabwean Medicinal Plants against Acinetobacter baumannii

Acinetobacter baumannii was identified by the WHO as a priority pathogen in which the research and development of new antibiotics is urgently needed. Plant phytochemicals have potential as sources of new antimicrobials. The objective of the study was to determine the antibacterial activity of extracts of selected Zimbabwean medicinal plants against A. baumannii and determine their possible mode of action. Extracts were prepared from the leaves of the eight plants including the bark of Erythrina abyssinica using solvents of different polarities. Antibacterial activity was evaluated using the microbroth dilution method coupled with the in vitro iodonitrotetrazolium colorimetric assay. The effect of the extracts on membrane integrity was determined by quantifying the amount of protein and nucleic acid leaked from the cells after exposure to the extracts. The effects of the extracts on biofilms were investigated. Toxicity studies were carried out using sheep erythrocytes and murine peritoneal cells. Seven out of eight evaluated plant extracts were found to have antibacterial activity. The Combretum apiculatum acetonie (CAA) extract showed the highest inhibitory activity against A. baumannii with a minimal inhibitory concentration of 125 µg/mL. The minimum inhibitory concentration (MIC) of the CAA extract caused a protein leakage of 32 µg/mL from A. baumannii. The Combretum apiculatum acetonie (CAA), C. apiculatum methanolic (CAM), Combretum zeyheri methanolic (CZM), and Erythrina abyssinica methanolic (EAM) extracts inhibited A. baumannii biofilm formation. The EAM extract was shown to disrupt mature biofilms. The potent extracts were nontoxic to sheep erythrocytes and mouse peritoneal cells. The activities shown by the extracts indicate that the plants have potential as sources of effective antibacterial and antibiofilm formation agents against A. baumannii.

Tackling multi-drug resistant fungi by efflux pump inhibitors

The emergence of multidrug-resistant fungi is of grave concern, and its infections are responsible for significant deaths among immunocompromised patients. The treatment of fungal infections primarily relies on a clinical class of antibiotics, including azoles, polyenes, echinocandins, polyketides, and a nucleotide analogue. However, the incidence of fungal infections is increasing as the treatment for human and plant fungal infections overlaps with antifungal drugs. The need for new antifungal agents acting on different targets than known targets is undeniable. Also, the pace at which loss of fungal susceptibility to antibiotics cannot be undermined. There are several modes by which fungi can develop resistance to antibiotics, including reduced drug uptake, drug target alteration, and a reduction in the cellular concentration of the drug due to active extrusions and biofilm formation. The efflux pump's overexpression in the fungi primarily reduced the antibiotic's concentration to a sub-lethal concentration, thus responsible for developing resistant fungus strains. Several strategies are used to check antibiotic resistance in multi-drug resistant fungi, including synthesizing antibiotic analogs and giving antibiotics in combination therapies. Among them, the efflux pump protein inhibitors are considered potential adjuvants to antibiotics and can block the efflux of antibiotics by inhibiting efflux pump protein transporters. Moreover, it can sensitize the antifungal drugs to multi-drug resistant fungi with overexpressed efflux pump proteins. This review discusses the natural lead molecules, repurposable drugs, and formulation strategies to overcome the efflux pump activity in the fungi.

Phytol from Scoparia dulcis prevents NF-κB-mediated inflammatory responses during macrophage polarization

Macrophages are primary immune cells that mediate a wide range of inflammatory diseases through their polarization potential. In this study, phytol isolated from Scoparia dulcis has been explored against 7-ketocholesterol and bacterial lipopolysaccharide-induced macrophage polarization in IC-21 cells. Isolated phytol has been characterized using GC-MS, TLC, HPTLC, FTIR, 1H-NMR, and HPLC analyses. The immunomodulatory effects of viable concentrations of phytol were tested on oxidative stress, arginase activity, nuclear and mitochondrial membrane potentials in IC-21 cells in addition to the modulation of calcium and lipids. Further, gene and protein expression of atherogenic markers were studied. Results showed that the isolated phytol at a viable concentration of 400 µg/ml effectively reduced the production of nitric oxide, superoxide anion (ROS generation), calcium and lipid accumulation, stabilized nuclear and mitochondrial membranes, and increased arginase activity. The atherogenic markers including iNOS, COX-2, IL-6, IL-1β, MMP-9, CD36, and NF-κB were significantly downregulated at the levels of gene and protein expression, while macrophage surface and nuclear receptor markers (CD206, CD163, and PPAR-γ) were significantly upregulated by phytol pre-treatment in macrophages. Therefore, the present pharmacognostic study supports the role of phytol isolated from Scoparia dulcis in preventing M2-M1 macrophage polarization under inflammatory conditions, making it a promising compound.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03924-9.

Metabolomic profile, anti-trypanosomal potential and molecular docking studies of Thunbergia grandifolia

Trypanosomiasis is a protozoan disease transmitted via Trypanosoma brucei. This study aimed to examine the metabolic profile and anti-trypanosomal effect of methanol extract of Thunbergia grandifolia leaves. The liquid chromatography-high resolution electrospray ionisation mass spectrometry (LC-HRESIMS) revealed the identification of fifteen compounds of iridoid, flavonoid, lignan, phenolic acid, and alkaloid classes. The extract displayed a promising inhibitory activity against T. brucei TC 221 with MIC value of 1.90 μg/mL within 72 h. A subsequent in silico analysis of the dereplicated compounds (i.e. inverse docking, molecular dynamic simulation, and absolute binding free energy) suggested both rhodesain and farnesyl diphosphate synthase as probable targets for two compounds among those dereplicated ones in the plant extract (i.e. diphyllin and avacennone B). The absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiling of diphyllin and avacennone were calculated accordingly, where both compounds showed acceptable drug-like properties. This study highlighted the antiparasitic potential of T. grandifolia leaves.

Metabolite profiling of Borneo's Gonystylus bancanus through comprehensive extraction from various polarity of solvents

Gonystylus bancanus wood or ramin wood has been generally known as a source of agarwood (gaharu) bouya, a kind of agarwood inferior type, or under the exported trading name of aetoxylon oil. The massive exploitation of ramin wood is causing this plant's extinction and putting it on Appendix II CITES and IUCN Red List of Threatened Species. To date, no scientific publication concerns the chemical exploration of G. bancanus wood and preserving this germplasm through its metabolite profiling. Therefore, research focused on chemical components profiling of G. bancanus is promised. This research is aimed to explore metabolomics and analyze the influence of solvent polarities on the partitioning of metabolites in G. bancanus wood. A range of solvents in different polarities was applied to provide comprehensive extraction of metabolites in G. bancanus wood. Moreover, a hydrodistillation was also carried out to extract the volatile compounds despite the non-volatile ones. LCMS and GCMS analyses were performed to identify volatile and non-volatile components in the extracts and essential oil. Multivariate data analysis was processed using Principal Component Analysis (PCA) and agglomerative hierarchical clustering. 142 metabolites were identified by LCMS analysis, while 89 metabolites were identified by GCMS analysis. Terpenoids, flavonoids, phenyl propanoids, and saccharides are some major compound classes available from LCMS data. Oxygenated sesquiterpenes, especially 10-epi-γ-eudesmol, and β-eudesmol, are the major volatile components identified from GCMS analysis. PCA of LCMS analysis demonstrated that PC1 discriminated two clusters: essential oil, dichloromethane, and n-hexane extracts were in the positive quadrant, while methanol and ethyl acetate extracts were in the negative quadrant. Three-dimensional analysis of GCMS data revealed that n-hexane extract was in the superior quadrant, and its composition can be significantly distinguished from other extracts and essential oil. G. bancanus wood comprises valuable metabolites, i.e., terpenoids, which benefit the essential oil industry. Comprehensive extraction by performing solvents in different polarities on G. bancanus wood could allow exploration of fully extracted metabolites, supported by the exhibition of identified metabolites from LCMS and GCMS analysis.

Exploration of Baicalein-Core Derivatives as Potent Antifungal Agents: SAR and Mechanism Insights

Baicalein (BE), the major component of Scutellaria Baicalensis, exhibited potently antifungal activity against drug-resistant Candida albicans, and strong inhibition on biofilm formation. Therefore, a series of baicalein-core derivatives were designed and synthesized to find more potent compounds and investigate structure-activity relationship (SAR) and mode of action (MoA). Results demonstrate that A4 and B5 exert a more potent antifungal effect (MIC80 = 0.125 μg/mL) than BE (MIC80 = 4 μg/mL) when used in combination with fluconazole (FLC), while the MIC80 of FLC dropped from 128 μg/mL to 1 μg/mL. SAR analysis indicates that the presence of 5-OH is crucial for synergistic antifungal activities, while o-dihydroxyls and vic-trihydroxyls are an essential pharmacophore, whether they are located on the A ring or the B ring of flavonoids. The MoA demonstrated that these compounds exhibited potent antifungal effects by inhibiting hypha formation of C. albicans. However, sterol composition assay and enzymatic assay conducted in vitro indicated minimal impact of these compounds on sterol biosynthesis and Eno1. These findings were further confirmed by the results of the in-silico assay, which assessed the stability of the complexes. Moreover, the inhibition of hypha of this kind of compound could be attributed to their effect on the catalytic subunit of 1,3-β-d-glucan synthase, 1,3-β-d-glucan-UDP glucosyltransferase and glycosyl-phosphatidylinositol protein, rather than inhibiting ergosterol biosynthesis and Eno1 activity by Induced-Fit Docking and Molecular Dynamics Simulations. This study presents potential antifungal agents with synergistic effects that can effectively inhibit hypha formation. It also provides new insights into the MoA.

Fractionation and Antibacterial Evaluation of the Surface Compounds from the Leaves of Combretum zeyheri on Selected Pathogenic Bacteria

Combretum zeyheri is traditionally used for the treatment of many infections, including bacterial infections. The aim of this study was to fractionate and evaluate antibacterial activity of the crude extract of C. zeyheri, as well as the surface compounds from the leaves of C. zeyheri, in two pathogenic bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. The antibacterial activities of fractions obtained from chromatographic separations were determined using broth microdilution assay on the laboratory and clinical strains of S. aureus and P. aeruginosa. The fractionation of the compounds on the leaf surface yielded 262 fractions. The fractionated compounds with similar TLC profiles were pooled together to yield 47 pools. The extract and pooled fractions CZSC151154, CZSC155160, and CZSC209213 showed significant antibacterial activity with MIC values ranging from 12.5 μg/ml to 100 μg/ml. The clinical strain of S. aureus had MIC greater than 100 μg/ml for CZSC151154 and CZSC155160. The minimum bactericidal concentration values for these fractions were also in the range of 12.5 μg/ml to 100 μg/ml. The extract and fractions CZSC151154, CZSC155160, and CZSC209213 showed a concentration-dependent inhibition of growth in S. aureus. Analyses of the CZSC209213 pool by LC-MS showed the presence of nine compounds which are (3R,7R)-1,3,7-octanetriol, (-)-tortuosamine, 11-aminoundecanoic acid, 1-piperidinecarboxaldehyde, 3-hydroxy-4-isopropylbenzyl alcohol 3-glucoside, hydroxy-isocaproic acid, oleamide, palmitic amide, phytospingosine, and sphinganine. In conclusion, C. zeyheri leaf surface compounds exhibited antibacterial activity. The crude extract and the pooled fractions showed concentration-dependent inhibition of growth on S. aureus. Results from this study indicate the potential of C. zeyheri as a source of lead compounds that may be further developed into antibacterial drugs.

Cytotoxicity and antimicrobial activity of isolated compounds from Monsonia angustifolia and Dodonaea angustifolia

ETHNOPHARMACOLOGICAL RELEVANCE

Monsonia angustifolia is traditionally used to treat anthrax, heartburn, diarrhea, eye infections and hemorrhoids. Dodonaea angustifolia is frequently used as a treatment for dental pain, microbial infections and jungle fever. The two plant species were selected due to the presence of secondary metabolites such as coumarins, flavonoids, terpenoids, saponins and polyphenolics from the crude extracts, which exhibit pharmacological significance. The pure isolated compounds from the crude extracts are known for their diverse structures and interesting pharmacophores.

AIM

To isolate and identify antibacterial and antifungal chemical constituents from Monsonia angustifolia and Dodonaea angustifolia plant extracts and evaluate the cytotoxicity of pure compounds from the crude extracts.

MATERIALS AND METHODS

Extractives from M. angustifolia and D. angustifolia plants were isolated using chromatographic techniques and structures were elucidated based on NMR, IR and MS spectroscopic techniques. A microplate serial dilution method was used to evaluate the antibacterial activity of extracts and pure compounds against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and antifungal activity against Candida albicans and Cryptococcus neoformans. The cytotoxicity was determined using the 3-(4, 5-dimethylthiazol)-2, 5-diphenyl tetrazolium bromide (MTT) assay.

RESULTS

The dichloromethane, ethyl acetate and methanol crude extracts from the plants exhibited significant inhibition of microbial growth. The phytochemical investigation of these active crude extracts led to the isolation of five pure active compounds, 5-methoxyjusticidin A (1), cis-phytyl diterpenoidal fatty acid ester (2), stigmasterol (3), β-sitosterol (4) and 5-hydroxy-7,4'-dimethoxyflavone (5). Stigmasterol (3) showed good antifungal activity against Cryptococcus neoformans with a minimum inhibition concentration (MIC) of 25 μg/mL and Candida albicans (MIC = 50 μg/mL).

CONCLUSION

Compounds (1-5) isolated from Monsonia angustifolia and Dodonaea angustifolia showed antibacterial and antifungal activities and were non-toxic against Madin-Darby canine kidney (MDCK) cells and VERO monkey kidney (VERO) cells.

Scutellaria petiolata Hemsl. ex Lace & Prain (Lamiaceae).: A New Insight in Biomedical Therapies

The recent investigation was designed to explore Scutellaria petiolata Hemsl. ex Lace & Prain (Lamiaceae) whole plant in various extracts (methanol (SPM), dichloromethane (SPDCM), n-Hexane (SPNH), and aqueous (SPAQ) for a phytochemicals assessment, ESI-LC-MS chemical analysis, in vitro antimicrobials, and antioxidants and in vivo anti-inflammatory and analgesic potential. The qualitative detection shows that all the representative groups were present in the analyzed samples. The examined samples display the greatest amount of total flavonoid content (TFC, 78.2 ± 0.22 mg QE/mg) and total phenolic contents (TPC, 66.2 ± 0.33 mg GAE/g) in the SPM extract. The SPM extract proceeded to the ESI-LC-MS to identify the chemical constituents that presented nineteen bioactive ingredients, depicted for the first time from S. petiolata mainly contributed by flavonoids. The analyzed samples produced considerable capability to defy the microbes. The SPM extract was observed effective and offered an appreciable zone of inhibition (ZOI), 17.8 ± 0.04 mm against the bacterial strain Salmonellatyphi and 18.8 ± 0.04 mm against Klebsiella pneumonia. Moreover, the SPM extract also exhibited 19.4 ± 0.01 mm against the bacterial strains Bacillus atrophaeus and 18.8 ± 0.04 mm against Bacillus subtilis in comparison to the standard levofloxacin (Gram-negative) and erythromycin (Gram-positive) bacterial strains that displayed 23.6 ± 0.02 mm and 23.2 ± 0.05 mm ZOI, correspondingly. In addition to that, the SPD fraction was noticed efficiently against the fungal strains used with ZOI 19.07 ± 0.02 mm against Aspergillus parasiticus and 18.87 ± 0.04 mm against the Aspergillus niger as equated to the standard with 21.5 ± 0.02 mm ZOI. In the DPPH (2,2-diphenyl-1-picrylhydrazyl) analysis, the SPM extract had the maximum scavenging capacity with IC₅₀ of 78.75 ± 0.19 µg/mL succeeded by the SPDCM fraction with an IC₅₀ of 140.50 ± 0.20 µg/mL free radicals scavenging potential. Through the ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) assay, the similar extract (SPM) presented an IC₅₀ = 85.91 ± 0.24 µg/mL followed by the SPDCM fractions with IC₅₀ = 182.50 ± 0.35 µg/mL, and n-Hexane fractions were reported to be the least active between the tested samples in comparison to ascorbic acid of IC₅₀ = 67.14 ± 0.25 µg/mL for DPPH and IC₅₀ of 69.96 ± 0.18 µg/mL for ABTS assay. In the in vivo activities, the SPM extract was the most effective with 55.14% inhibition as compared to diclofenac sodium with 70.58% inhibition against animals. The same SPM crude extract with 50.88% inhibition had the most analgesic efficacy as compared to aspirin having 62.19% inhibition. Hence, it was assumed from our results that all the tested samples, especially the SPM and SPDCM extracts, have significant capabilities for the investigated activities that could be due to the presence of the bioactive compounds. Further research is needed to isolate the responsible chemical constituents to produce innovative medications.

Synbiotic Musa acuminata skin extract and Streptococcus salivarius K12 inhibit candida species biofilm formation

This study aimed to determine the effect of synbiotic Musa acuminata skin extract (MASE) and Streptococcus salivarius K12 (K12) on Candida species biofilm formation. Liquid chromatography quadrupole time-of-flight (LC-Q-TOF-MS) was conducted to characterize MASE. To determine the effect of synbiotic on Candida biofilm, 200 µL of RPMI-1640 containing Candida, K12, and MASE were pipetted into the same well and incubated at 37 °C for 72 h. A similar protocol was repeated with K12 or MASE to determine the probiotic and prebiotic effects, respectively. Dimorphism, biofilm biomass, and Candida total cell count (TCC) were determined. A total of 60 compounds were detected in MASE. C. albicans (ALT5) and Candida lusitaniae exhibited the highest reduction in biofilm biomass when co-cultured with prebiotic (77.70 ± 7.67%) and synbiotic (97.73 ± 0.28%), respectively. All Candida spp. had decreased TCC and hyphae when co-cultured with synbiotic. In conclusion, MASE and K12 inhibit Candida biofilm formation.

Isolation and biological evaluation 7-hydroxy flavone from Avicennia officinalis L: insights from extensive in vitro, DFT, molecular docking and molecular dynamics simulation studies

The flavonoid based 7-hydroxy flavone (PubChem CID: 5281894; molecular formula: C₁₅H₁₀O₃) molecule has been isolated for the first time from the methanolic extract from the leaves of Avicennia officinalis L. in the tropical mangrove ecosystem of Andaman and Nicobar Islands (ANI), India. The molecular structure of bioactive compound was characterized by spectroscopic analysis, including FT-IR, ¹H, ¹³C NMR spectroscopy and ESI-HRMS and elucidated as 7-hydroxy flavone. An anticancer activity of isolated 7-hydroxy flavone was evaluated by in vitro study against two different human cancer cell lines namely, HeLa (cervical cells) and MDA-MB231 (breast cells) and they exhibited promising anticancer activity with IC₅₀ values are 22.5602 ± 0.21 µg/mL and 3.86474 ± 0.35 µg/mL, respectively. The antioxidant property of 7-hydroxy flavone at a standard concentration of 50 µg, was found to be (IC₅₀) 5.5486 ± 0.81 µg/mL. In summary, this investigation provides evidence that 7-hydroxy flavone exhibits both anticancer and antioxidant properties. Meanwhile, the antimicrobial activity ability of 7-hydroxy flavone were also evaluated using three Gram positive and two Gram negative strain exhibited no antimicrobial activities. Density-functional theory (DFT) studies confirm the structure is global minima in the PES, from the optimized geometry FMO and MESP map analyzed. Further, the molecular docking and molecular dynamics simulation studies result shows that 7-hydroxy flavone has the better binding ability with anti-apoptotic Bcl-2 protein with the estimated free energy of binding of -6.3 kcal/mol. This bioactive compound may be act as drug candidate for treating various kinds of cancers. HighlightsA 7-hydroxy flavone molecule has been isolated from Avicennia officinalis.The isolated pure compound was subjected to spectral analysis such as FT-IR, ¹H NMR, ¹³C NMR spectral data and HRMS analysis for skeleton of the molecule.The anticancer activity of 7-hydroxy flavone studied against Cervical (HeLa) cancer cell lines and breast (MDA-MB231) cancer cell lines with the IC₅₀ values of 22.5602 ± 0.21 µg/mL and 3.86474 ± 0.35 µg/mL), respectively.The antioxidant properties of 7-hydroxy flavone were found to be (IC₅₀) 5.5486 ± 0.81 µg/mL at a standard concentration of 50 µg.DFT, molecular docking and MD simulation results explained that 7-hydroxy flavone could be the most promising candidate to inhibit the function of anti-apoptotic Bcl-2 protein in cancerous cell.Communicated by Ramaswamy H. Sarma.

A new antimicrobial nor-friedelane-type triterpenoid and other constituents from Plectranthus glandulosus Hook. f. (Lamiaceae)

Chemical investigation of the ethanol extract from the whole plant of Plectranthus glandulosus led to the isolation of a new nor-triterpenoid (1) along with seventeen known compounds (2-18) including seven triterpenoids, nine flavonoids and one steroid. Their structures were established on the basis of 1D- and 2D-NMR, IR, and MS experiments, and by comparison of their spectroscopic data with those of similar compounds reported in the literature. The EtOH extract and some isolated triterpenoids (1-4 and 13) were subjected to in vitro antimicrobial assays against a panel of pathogenic microorganisms, including Gram-positive and Gram-negative bacteria, and fungi using broth microdilution method. The EtOH extract displayed moderate activity (MIC = 512 µg/mL) against Staphylococcus aureus MSSA1, Shigella flexneri SDINT and Cryptococcus neoformans H99. Compounds 1, 4 and 13 showed the most potent antimicrobial effect with MICs of 32-256 µg/mL.

Antifungal Activity of Extracts, Fractions, and Constituents from Coccoloba cowellii Leaves

Coccoloba cowellii Britton (Polygonaceae, order Caryophyllales) is an endemic and critically endangered plant species that only grows in the municipality of Camagüey, a province of Cuba. A preliminary investigation of its total methanolic extract led to the discovery of promising antifungal activity. In this study, a bioassay-guided fractionation allowed the isolation of quercetin and four methoxyflavonoids: 3-O-methylquercetin, myricetin 3,3′,4′-trimethyl ether, 6-methoxymyricetin 3,4′-dimethyl ether, and 6-methoxymyricetin 3,3′,4′-trimethyl ether. The leaf extract, fractions, and compounds were tested against various fungi and showed strong in vitro antifungal activity against Cryptococcus neoformans and various Candida spp. with no cytotoxicity (CC₅₀ > 64.0 µg/mL) on MRC-5 SV2 cells, determined by a resazurin assay. A Candida albicans SC5314 antibiofilm assay indicated that the antifungal activity of C. cowellii extracts and constituents is mainly targeted to planktonic cells. The total methanolic extract showed higher and broader activity compared with the fractions and mixture of compounds.

Antifungal Activity of Isolated Compounds from the Leaves of Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal against Fusarium Pathogens

Crop diseases caused by Fusarium pathogens, among other microorganisms, threaten crop production in both commercial and smallholder farming. There are increasing concerns about the use of conventional synthetic fungicides due to fungal resistance and the associated negative effects of these chemicals on human health, livestock and the environment. This leads to the search for alternative fungicides from nature, especially from plants. The objectives of this study were to characterize isolated compounds from Combretum erythrophyllum (Burch.) Sond. and Withania somnifera (L.) Dunal leaf extracts, evaluate their antifungal activity against Fusarium pathogens, their phytotoxicity on maize seed germination and their cytotoxicity effect on Raw 264.7 macrophage cells. The investigation led to the isolation of antifungal compounds characterized as 5-hydroxy-7,4'-dimethoxyflavone, maslinic acid (21-hydroxy-3-oxo-olean-12-en-28-oic acid) and withaferin A (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide). The structural elucidation of the isolated compounds was established using nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy (MS) and, in comparison, with the available published data. These compounds showed good antifungal activity with minimum inhibitory concentrations (MIC) less than 1.0 mg/mL against one or more of the tested Fusarium pathogens (F. oxysporum, F. verticilloides, F. subglutinans, F. proliferatum, F. solani, F. graminearum, F. chlamydosporum and F. semitectum). The findings from this study indicate that medicinal plants are a good source of natural antifungals. Furthermore, the isolated antifungal compounds did not show any phytotoxic effects on maize seed germination. The toxicity of the compounds A (5-hydroxy-7,4'-dimethoxyflavone) and AI (4β,27-dihydroxy-1-oxo-5β,6β-epoxywitha-2-24-dienolide) was dose-dependent, while compound B (21-hydroxy-3-oxo-olean-12-en-28-oic acid) showed no toxicity effect against Raw 264.7 macrophage cells.

An Efflux Pumps Inhibitor Significantly Improved the Antibacterial Activity of Botanicals from Plectranthus glandulosus towards MDR Phenotypes

Bacterial multidrug resistance causes many therapeutic failures, making it more difficult to fight against bacterial diseases. This study aimed to investigate the antibacterial activity of extract, fractions, and phytochemicals from Plectranthus glandulosus (Lamiaceae) against multidrug-resistant (MDR) Gram-negative phenotypes expressing efflux pumps. The crude extract after extraction was subjected to column chromatography, and the structures of the isolated compounds were determined using spectrometric and spectroscopic techniques. Antibacterial assays of samples alone and in the presence of an efflux pump inhibitor (phenylalanine-arginine β-naphthylamide, PAβN) were carried out using the broth microdilution method. The phytochemical study of P. glandulosus plant extract afforded seven major fractions (A-G) which lead to the isolation of seventeen known compounds. The ethanol extract of P. glandulosus was not active at up to 1024 μg/mL, whereas its fractions showed MICs varying from 32 to 512 μg/mL on the studied bacteria. Fraction C of P. glandulosus showed the lowest MIC (32 μg/mL) on E. coli ATCC8739 strain. Fraction D presented the highest activity spectrum by inhibiting the growth of 90% (9/10) of the studied bacteria. The presence of PAβN has improved the activity of extract and all fractions. Overall, the tested phytochemicals showed low activity against the studied bacteria. The overall results obtained in this study show that some fractions from P. glandulosus, mainly fractions C and D, should be investigated more for their possible use to fight against MDR bacteria.

Antibacterial activity of Hibiscus rosa-sinensis L. red flower against antibiotic-resistant strains of Helicobacter pylori and identification of the flower constituents

Utilization of plant resources for treatment of Helicobacter pylori infections is one of the appealing approaches as rapid emergence of antibiotic-resistant strains is occurring throughout the world. Ethanol extract and its fractions from Hibiscus rosa-sinensis red flower were assessed for antibacterial and urease inhibitory activities towards forty-three clinical strains and two reference strains of H. pylori. The ethyl acetate fraction exhibited the most potent bacteriostatic activity with minimum inhibitory concentrations (MICs) of 0.2-0.25 mg/mL and minimum bactericidal concentrations (MBCs) of 1.25-1.5 mg/mL against all test strains, including forty-three strains resistant to one to four antibiotics, azithromycin (MICs, 8-256 µg/mL), erythromycin (MICs, 8-128 µg/mL), levofloxacin (MICs, 8-256 µg/mL), and/or metronidazole (MICs, 8-256 µg/mL). The fraction had similar antibacterial activities toward these test strains suggesting the preparation and the antibiotics do not have a common mechanism of anti-H. pylori activity. The fraction also had stronger effects on biofilm formation, morphological conversion, and urease activity of H. pylori than the other fractions and the ethanol extract. These flower preparations were non-toxic to three human cell lines, and nine compounds were also isolated and identified from the ethyl acetate fraction. In vivo research needs to be conducted to confirm the potential usefulness of H. rosa-sinensis flower and its constituents for effective prevention and treatment of H. pylori disease.

Dodonaea viscosa var angustifolia derived 5,6,8-trihydroxy-7,4' dimethoxy flavone inhibits ergosterol synthesis and the production of hyphae and biofilm in Candida albicans

ETHNOPHARMACOLOGICAL RELEVANCE

Candida albicans is developing resistance to existing drugs increasing morbidity and mortality, which elevates an immediate need to explore new antifungal agents. Phytochemicals are an excellent source of therapeutic agents. We previously reported the antifungal activity of the crude extract of Dodonaea viscosa var. angustifolia Jacq. (DVA) from which a beneficial compound flavone: 5,6,8-trihydroxy-7,4' dimethoxy flavone (5,6,8-trihydroxy-7-methoxy-2-(4-methoxyphenyl)-4H-chromen-4-one) abbreviated as TMMC, was extracted.

AIM OF THE STUDY

The present study evaluated the effect of a TMMC subfraction on biofilms, membrane stability, ergosterol biosynthesis and germ tube (GT) formation in Candida albicans.

MATERIALS AND METHODS

Extracts were prepared and fractionated to obtain purified TMMC. Minimum inhibitory concentrations of TMMC were obtained and subinhibitory concentrations were selected for further studies. Confocal laser scanning microscopy (CLSM) was performed to assess the effect of TMMC on membrane permeability and sterol deposition using propidium iodide (PI) and filipin stains, respectively.

RESULTS

Minimum inhibitory concentrations (MIC) and Minimum Fungicidal concentrations (MFC) of TMMC were 0.39 mg/mL and 1.56 mg/mL, respectively. TMMC inhibited biofilm formation and damaged mature biofilms at 0.39 mg/mL and 1.56 mg/mL, respectively. CLSM further confirmed the disruption and architectural changes in biofilms following treatment with TMMC. TMMC also inhibited GT formation and ergosterol biosynthesis in a concentration dependent manner, which was further confirmed by varying sterol distribution and membrane disruption in treated and untreated cells.

CONCLUSIONS

With the multiple targets at different concentrations, TMMC warrants its potential use as antifungal drug against C. albicans. However further studies using animal models and more mechanistic approaches will be required.

Effective Inhibition of Candidiasis Using an Eco-Friendly Leaf Extract of Calotropis-gigantean-Mediated Silver Nanoparticles

The approaches used for the green biosynthesis of nanoparticles with clinical applications have been widely used in nanotechnology due to their potential to provide safe, eco-friendly, cost effective, high-stability, and high-loading-capacity nanoparticles. This study aimed to evaluate the anti-candidal activity of silver nanoparticles (AgNPs) biosynthesized using the aqueous leaf extract of Calotropis gigantea (CG) alone or in a combination with the plant extract of CG (AgNPs/CG). AgNPs were characterized using UV-Vis spectrophotometry, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results of the standard disk diffusion method revealed that AgNPs alone displayed anti-candidal activity (11.33-mm inhibition zone), while AgNPs/CG displayed a strong synergistic anti-candidal activity (17.76-mm inhibition zone). Similarly, AgNPs/CG completely inhibited the growth of C. albicans after 4 h of incubation, as measured using the time-kill assay. In addition, AgNPs/CG inhibited the dimorphic transition of C. albicans and suppressed both the adhesion and the biofilm formation of C. albicans by 41% and 38%, respectively. The treatment of Candida. albicans with AgNPs/CG showed a significant inhibition of the production of several antioxidant enzymes. Interestingly, AgNPs/CG did not show any cytotoxicity in animal cells, including the MCF-7 cell line and primary mouse bone marrow-derived mesenchymal stem cells (mBMSCs), at the concentration used to completely inhibit the dimorphic transition of C. albicans. In conclusion, we identified AgNPs/CG as a promising natural-product-based nanoparticle that can potentially be used as an anti-candidal drug.

Anti-Fungal Efficacy and Mechanisms of Flavonoids

The prevalence of fungal infections is growing at an alarming pace and the pathogenesis is still not clearly understood. Recurrence of these fungal diseases is often due to their evolutionary avoidance of antifungal resistance. The development of suitable novel antimicrobial agents for fungal diseases continues to be a major problem in the current clinical field. Hence, it is urgently necessary to develop surrogate agents that are more effective than conventional available drugs. Among the remarkable innovations from earlier investigations on natural-drugs, flavonoids are a group of plant-derived substances capable of promoting many valuable effects on humans. The identification of flavonoids with possible antifungal effects at small concentrations or in synergistic combinations could help to overcome this problem. A combination of flavonoids with available drugs is an excellent approach to reduce the side effects and toxicity. This review focuses on various naturally occurring flavonoids and their antifungal activities, modes of action, and synergetic use in combination with conventional drugs.

Isolation and Purification of Potent Growth Inhibitors from Piper methysticum Root

Piper methysticum (kava) root is known to possess promising weed suppressing activity. The present study was conducted to search for potent plant growth inhibitors from the root of this medicinal pepper plant. The ethyl acetate (EtOAc) extract exhibited the strongest reduction on growth of Raphanus sativus (radish) (IC₅₀ shoot and root growth = 172.00 and 51.31 µg/mL respectively) among solvent extracts. From this active extract, nine potent growth inhibitors involved in the inhibitory activities of P. methysticum root were isolated, purified and characterized by column chromatography (CC), gas chromatography-mass spectrometry (GC-MS), electrospray ionization-mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR). The six fractions purified by CC included two flavanones: 5-hydroxy-4′,7-dimethoxyflavanone (C1) and 5,7-dihydroxy-4′-methoxy-6,8-dimethylflavanone (matteucinol, C2) and six kavalactones: 5,6-dehydro-kavain (C3), a mixture of kavain and yagonin (C4), yagonin (C5) and dihydro-5,6-dehydrokavain, 7,8-dihydrokavain, dihydromethysticin and methysticin (C6). The amounts of 5-hydroxy-4′,7-dimethoxyflavanone, matteucinol, 5,6-dehydrokavain and yangonin were 0.76, 2.50, 2.75 and 2.09 mg/g dry weight (DW), respectively. The two flavanones C1 and C2 exhibited the strongest inhibition on shoot elongation (IC₅₀ = 120.22 and 248.03 µg/mL, respectively), whilst the two kavalactone mixtures C4 and C6 showed the highest suppression on root growth of R. sativus (IC₅₀ = 7.70 and 15.67 µg/mL, respectively). This study was the first to report the purification and inhibitory activities of the two flavanones 5-hydroxy-4′,7-dimethoxyflavanone and matteucinol in P. methysticum root. The isolated constituents from P. methysticum root including the flavanones C1 and C2 and the mixtures C4 and C6 may possess distinct modes of action on plant growth. Findings of this study highlighted that the combinations of hexane-ethyl acetate by 9:1 and 8:2 ratios successfully purified flavanones and kavalactones in P. methysticum root.

A complex game of hide and seek: the search for new antifungals

Fungal infections directly affect millions of people each year. In addition to the invasive fungal infections of humans, the plants and animals that comprise our primary food source are also susceptible to diseases caused by these eukaryotic microbes. The need for antifungals, not only for our medical needs, but also for use in agriculture and livestock causes a high demand for novel antimycotics. Herein, we provide an overview of the most commonly used antifungals in medicine and agriculture. We also present a summary of the recent progress (from 2010-2016) in the discovery/development of new agents against fungal strains of medical/agricultural relevance, as well as information related to their biological activity, their mode(s) of action, and their mechanism(s) of resistance.

In vitro toxicity determination of antifungal constituents from Combretum zeyheri

BACKGROUND

Candida albicans is one of the organisms living on the human body symbiotically, but, in hosts with low immunity it becomes one of the most pathogenic fungal organisms. Combretum zeyheri has been reported to have antifungal, antibacterial and antioxidant activities. Medicinal plants are believed to be non-toxic by the general public. Toxicity studies, however, have indicated that they are capable of causing numerous side effects, therefore, evaluation of safety is required. The objective of this study was to determine the toxicity of the antifungal constituents of Combretum zeyheri on mammalian cells.

METHODS

Alkaloids, saponins, flavonoids-enriched extracts and crude ethanol extracts were prepared from the leaves of Combretum zeyheri. The broth microdilution method was used to investigate for antifungal activity, with miconazole used as the positive control. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to determine cell viability of the Candida albicans cells. The most potent extracts; the ethanol extract, alkaloids and saponins respectively, were further tested for their toxicity on sheep erythrocytes, mouse peritoneal macrophages and Jurkat T cells.

RESULTS

All Combretum zeyheri extracts displayed a dose-dependent antifungal activity and had IC50 values ranging from 16 μg/ml to 159 μg/ml for Candida albicans. The alkaloids, saponins and ethanol extracts were found to be non-toxic towards mouse peritoneal cells and Jurkat T cells. In the haemolysis assay, all extracts were haemolytic at varying degrees and showed their greatest haemolytic activity at the highest concentration of 5 mg/ml. The saponins were the least haemolytic, followed by the ethanol extracts and the alkaloids respectively. Although these extracts were haemolytic to some extent, they may considered safe at therapeutic concentrations since there was a large difference between the antifungal IC50 and haemolysis EC50 values, hence a large therapeutic window.

CONCLUSIONS

Combretum zeyheri antifungal constituents are, therefore, a potential source of lead compounds which can be developed into antifungal drugs of natural origin owing to Combretum zeyheri's effective antifungal activity and low toxicity to mammalian cells.