Antibacterial activity of the plant-derived compounds 23-methyl-6-O-desmethylauricepyrone and (Z,Z)-5-(trideca-4,7-dienyl)resorcinol and their synergy with antibiotics against methicillin-susceptible and -resistant Staphylococcus aureus

Cytotoxic and antimicrobial mycophenolic acid derivatives from an endophytic fungus Penicillium sp. MNP-HS-2 associated with Macrozamia communis

Macrozamia communis and its associated endophytic fungi are untapped sources of bioactive metabolites with great potential for medicinal exploitation. Chemical investigation of the mycelial extract derived from an endophytic fungus Penicillium sp. MNP-HS-2 associated with M. communis fruit afforded four mycophenolic acid derivatives recognized as previously undescribed natural products (1-4), together with nine known metabolites (5-13). Chemical structures of isolated compounds were determined based on extensive spectroscopic analyses, including 1D/2D NMR and HRESIMS. The absolute stereochemistry of alternatain E (1) was unambiguously established by comparing its experimental and calculated time-dependent density functional theory electronic circular dichroism spectra (TDDFT-ECD). All isolated compounds were assessed for their antimicrobial and cytotoxic activities, where mycophenolic acid methyl ester (7), displayed significant cytotoxic activity against seven different cell lines with IC50 values in the low micromolar to nanomolar range. Mycophenolene A (3) exhibited significant antibacterial activity against Staphylococcus aureus (MIC = 2.1 μg/mL).

Extracts from Argentinian native plants reverse fluconazole resistance in Candida species by inhibiting the efflux transporters Mdr1 and Cdr1

BACKGROUND

The development of multidrug resistance (MDR) associated with the overexpression of the efflux transporters Mdr1 and Cdr1 in Candida species impedes antifungal therapies. The urgent need for novel agents able to inhibit the function of both pumps, led us to evaluate this property in 137 extracts obtained from Argentinian plants.

METHODS

The ability of the extracts to reverse efflux pump-mediated MDR was determined with an agar chemosensitization assay using fluconazole (FCZ) resistant Mdr1- and Cdr1-overexpressing clinical isolates of Candida albicans and Candida glabrata as well as Saccharomyces cerevisiae strains selectively expressing Mdr1 (AD/CaMDR1) or Cdr1 (AD/CaCDR1). The resistance-reversing activity of the most potent extracts was further confirmed using a Nile Red accumulation assay.

RESULTS

Fifteen plant extracts overcame the FCZ resistance of Candida albicans 1114, which overexpresses CaMdr1 and CaCdr1, and AD/CaMDR1, with those from Acalypha communis and Solanum atriplicifolium being the most effective showing 4- to 16-fold reversal of resistance at concentrations ≥ 25 µg/mL. Both extracts, and to a lesser extent that from Pterocaulon alopecuroides, also restored FCZ sensitivity in CgCdr1-overexpressing C. glabrata 109 and in AD/CaCDR1 with fold reversal values ranging from 4 to 32 and therefore demonstrating a dual effect against Mdr1 and Cdr1. Both, A. communis and S. atriplicifolium extracts at concentrations ≥ 12.5 and ≥ 25 µg/mL, respectively, increased the intracellular Nile Red accumulation in all yeast strains overexpressing efflux pumps.

CONCLUSIONS

The non-toxic and highly active extracts from A. communis and S. atripicifolium, provide promising sources of compounds for potentiating the antifungal effect of FCZ by blocking the efflux function of Mdr1 and Cdr1 transporters.

The thiophene α-terthienylmethanol isolated from Tagetes minuta inhibits angiogenesis by targeting protein kinase C isozymes α and β2

Background: Tumor angiogenesis is considered as a crucial pathologic feature of cancer with a key role in multidrug resistance (MDR). Adverse effects of the currently available drugs and the development of resistance to these remain as the hardest obstacles to defeat.

Objetive: This work explores flora from Argentina as a source of new chemical entities with antiangiogenic activity.

Methods: Tube formation assay using bovine aortic endothelial cells (BAECs) was the experiment of choice to assess antiangiogenic activity. The effect of the pure compound in cell invasiveness was investigated through the trans-well migration assay. The inhibitory effect of the pure compound on VEGFR-2 and PKC isozymes α and β2 activation was studied by molecular and massive dynamic simulations. Cytotoxicity on peripheral blood mononuclear cells and erythrocyte cells was evaluated by means of MTT and hemolysis assay, respectively. In silico prediction of pharmacological properties (ADME) and evaluation of drug-likeness features were performed using the SwissADME online tool.

Results: Among the plants screened, T. minuta, showed an outstanding effect with an IC₅₀ of 33.6 ± 3.4 μg/ml. Bio-guided isolation yielded the terthiophene α-terthienylmethanol as its active metabolite. This compound inhibited VEGF-induced tube formation with an IC₅₀ of 2.7 ± 0.4 μM and significantly impaired the invasiveness of bovine aortic endothelial cells (BAECs) as well as of the highly aggressive breast cancer cells, MDA-MB-231, when tested at 10 μM. Direct VEGFR-2 and PKC inhibition were both explored by means of massive molecular dynamics simulations. The results obtained validated the inhibitory effect on protein kinase C (PKC) isozymes α and β2 as the main mechanism underlying its antiangiogenic activity. α-terthienylmethanol showed no evidence of toxicity against peripheral blood mononuclear and erythrocyte cells.

Conclusion: These findings support this thiophene as a promising antiangiogenic phytochemical to fight against several types of cancer mainly those with MDR phenotype.

Interactions between Medical Plant-Derived Bioactive Compounds: Focus on Antimicrobial Combination Effects

It is accepted that the medicinal use of complex mixtures of plant-derived bioactive compounds is more effective than purified bioactive compounds due to beneficial combination interactions. However, synergy and antagonism are very difficult to study in a meticulous fashion since most established methods were designed to reduce the complexity of mixtures and identify single bioactive compounds. This study represents a critical review of the current scientific literature on the combined effects of plant-derived extracts/bioactive compounds. A particular emphasis is provided on the identification of antimicrobial synergistic or antagonistic combinations using recent metabolomics methods and elucidation of approaches identifying potential mechanisms that underlie their interactions. Proven examples of synergistic/antagonistic antimicrobial activity of bioactive compounds are also discussed. The focus is also put on the current challenges, difficulties, and problems that need to be overcome and future perspectives surrounding combination effects. The utilization of bioactive compounds from medicinal plant extracts as appropriate antimicrobials is important and needs to be facilitated by means of new metabolomics technologies to discover the most effective combinations among them. Understanding the nature of the interactions between medicinal plant-derived bioactive compounds will result in the development of new combination antimicrobial therapies.

Inhibition of MurA Enzyme from Escherichia coli and Staphylococcus aureus by Diterpenes from Lepechinia meyenii and Their Synthetic Analogs

Enzymes MurA and MurF, involved in bacterial cell wall synthesis, have been validated as targets for the discovery of novel antibiotics. A panel of plant-origin antibacterial diterpenes and synthetic analogs derived therefrom were investigated for their inhibitory properties on these enzymes from Escherichia coli and Staphylococcus aureus. Six compounds were proven to be effective for inhibiting MurA from both bacteria, with IC50 values ranging from 1.1 to 25.1 µM. To further mechanistically investigate the nature of binding and to explain the activity, these compounds were docked into the active site of MurA from E. coli. The aromatic ring of the active compounds showed a T-shaped π-π interaction with the phenyl ring of Phe328, and at least one hydrogen bond was formed between the hydroxy groups and Arg120 and/or Arg91. The results disclosed here establish new chemical scaffolds for the development of novel entities targeting MurA as potential antibiotics to combat the threat of pathogenic bacteria, particularly resistant strains.

Synthesis and structure-activity relationships of novel abietane diterpenoids with activity against Staphylococcus aureus

Aim: To find alternative compounds against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA), novel derivatives from dehydroabietic acid were synthesized. Methods & results: Compound 12 was the most effective against 15 MRSA and 11 MSSA with minimum inhibitory concentration values ranging from 3.9 to 15.6 μg/ml. Although less active than 12, compound 11, followed by 25 and 13, also exhibited anti-staphylococcal activity. Additional studies showed that compound 12 is devoid of toxic effect on non-target cells. A structure-activity relationship study revealed that an oxime at C-13 together with a hydroxyl at C-12 could play a key role in the activity. Conclusion: These structures, in particular compound 12, could arise as templates for the development of agents against MRSA and MSSA.

Tellimagrandin II, A Type of Plant Polyphenol Extracted from Trapa bispinosa Inhibits Antibiotic Resistance of Drug-Resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has become a critical global concern. Identifying new candidates of anti-S. aureus agents is urgently required because the therapeutic strategies for infected patients are limited currently. Therefore, the present study investigated whether Tellimagrandin II (TGII), a pure compound extracted from the shells of Trapa bispinosa, exhibits antibacterial effects against MRSA. We first showed that TGII exerted potent inhibitory activity against MRSA with a minimum inhibitory concentration of 128 μg/mL. The obtained fractional inhibitory concentration suggested that TGII could alone exert antistaphylococcal activity, and TGII combined with low doses of antibiotics displayed synergistic effects against MRSA. Moreover, we found that TGII exerted bactericidal activity by reducing the expression of mecA followed by the negative regulation of the penicillin-binding protein 2a (PBP2a) of MRSA. Transmission electron microscopy (TEM) images further confirmed that TGII destroyed the integrity of the cell wall of MRSA and caused the loss of cytoplasm content. In conclusion, we evidenced the antibacterial effects of TGII against MRSA, which enables the effective dose of current antibiotics to be reduced and the predicament of drug-resistant S. aureus isolates to be overcome.

Antibacterial effects of extracts obtained from plants of Argentina: Bioguided isolation of compounds from the anti-infectious medicinal plant Lepechinia meyenii

ETHNOPHARMACOLOGICAL RELEVANCE

The mostly native species from Argentina are used in traditional medicine generally for the treatment of pain and inflammation, respiratory, gastro-intestinal and urinary disorders and as antiseptics.

AIM OF THE STUDY

Since these ailments may be associated with bacterial infections and that it is necessary to discover alternative compounds with antibacterial activity, 69 extracts from these plants were screened for their activity against pathogenic bacteria. The most effective extract was then submitted to bioguided isolation to obtain the compounds responsible for this activity.

MATERIALS AND METHODS

Extracts and fractions were screened using agar dilution, and compounds using microbroth dilution methods. A large panel of pathogenic bacteria was used, especially methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). Bioguided fractionation was performed using successive chromatographic techniques, while the chemical structures of the isolated compounds were determined by nuclear magnetic resonance (NMR). Additionally, a series of derivatives of the most active compound were prepared in order to study the chemical features required for achieving the antibacterial effect.

RESULTS

Lepechinia meyenii (Walp.) Epling (Lamiaceae) extract showed itself the most effective, with minimum inhibitory concentration (MIC) against Gram positive and negative bacteria ranging from 62.5 to 500 μg/mL, and showing better activity on MRSA than on MSSA. Activity-guided fractionation yielded the abietanes carnosol (1), rosmanol (2) and carnosic acid (3) as active principles, with MICs ranging from 15.6-31.2, 15.6-62.5 and 7.8-15.6 μg/mL, respectively against 15 MRSA strains, and 15.6-31.2, 31.2-62.5 and 7.8-15.6 μg/mL, respectively against 11 MSSA strains, maintaining higher activity against the resistant bacteria, as does the extract. In addition, Enterococcus faecalis was sensitive to 1-3 with MICs of 15.6-62.5 μg/mL. The structure activity analysis showed that 12-OH is necessary for remarkable activity, but methylation in C-20 significantly increased this, as observed with 20-methyl carnosate (5) displaying the greatest effect, even more so than 3, with MICs of 3.9 μg/mL against all the tested MRSA and 3.9-7.8 μg/mL against the MSSA.

CONCLUSIONS

The results of this study contribute to validate the traditional antibacterial use of species native to Argentina, particularly of L. meyenii. The chemical structures of the compounds obtained may aid the design of antibacterial agents, especially those effective against MRSA.

Inhibitory effects of compounds isolated from Lepechinia meyenii on tyrosinase

To contribute enzymatic browning inhibitors to the food industry and also extend knowledge about the phytochemical profile of the anti-tyrosinase plant Lepechinia meyenii, its ethanol extract was subjected to bioguided fractionation. Three hydroxycinnamic acids, p-coumaric acid (1), caffeic acid (2) and rosmarinic acid (3), were isolated as mainly responsible for its activity. Compounds 1, 2 and 3 showed themselves highly effective for inhibiting tyrosinase with IC₅₀ values of 0.30, 1.50 and 4.14 μM, respectively, for monophenolase activity and 0.62, 2.30 and 8.59 μM, respectively for diphenolase activity. This is the first report describing the isolation of the compounds causing the tyrosinase inhibitory activity of L. meyenii extract. The inhibitory kinetics of 1-3 using both L-tyrosine and L-DOPA as substrates was investigated and the results obtained were discussed at molecular level by docking analysis. The resulting compounds 1-3 and a phenolic-enriched fraction of the extract, 2.9-fold more active than the starting material, may be suitable as non-toxic and inexpensive alternatives for the control of deleterious enzymatic darkening.

Interactions of a prenylated flavonoid from Dalea elegans with fluconazole against azole- resistant Candida albicans

BACKGROUND

The prenylated flavonoid 2', 4'-dihydroxy-5'-(1'″, 1'″-dimethylallyl)-8-prenylpinocembrin (8PP, formerly 6PP) shows antifungal activity, inhibits rhodamine 6G efflux and reverses fluconazole (FCZ) resistance in azole-resistant Candida albicans overexpressing cdr1, cdr2 and mdr1 transporters.

PURPOSE AND DESIGN

In this paper, we tried to characterize 8PP in vitro interactions on the cell growth and lethality of C. albicans. We also initiated preliminary in vivo toxicological studies on mice.

METHODS

The effects of 8PP and FCZ on cell growth and viability of C. albicans were evaluated by CLSI guidelines. The checkerboard assay was used to search for interactions on cell growth. The time-kill assay was used to study fungicidal effects. Acute toxicity was evaluated at a single dose schedules.

RESULTS

From the checkerboard design, and using a starting inoculum of 10³CFU/ml, the fractional inhibitory concentration (FIC) of FCZ and 8PP could be determined as 0.11 and 0.50, respectively, with a FIC index value (FICI) of 0.61. This FICI and the isobologram showing a concave shape suggests an additive interaction between them. At a higher starting inoculum (10⁵CFU/ml), C. albicans growth and viability were decreased by FCZ, 8PP and their combination in a concentration-dependent way. For FCZ, minimum fungicidal concentration (MFC) and FC₅₀ (the concentration that kills 50% of the fungal cells) were 4-fold reduced (280-70µM) in combination with 125µM 8PP. A decrease of 3 log units in viable counts with respect to control was reached (3.65 ± 1.05 ‰, p< 0.0001). Thus, both fungistatic compounds when combined achieved an almost complete fungicidal effect at lower concentrations respecting of each of them alone. In preliminary toxicological assessment, lethal dose 50% (LD₅₀) for 8PP by the i.p. route was 357 and 245mg/kg, for female and male adult albino mice, respectively. FCZ LD₅₀ was 785 and 650mg/kg for female and male animals, respectively CONCLUSIONS: In vitro results suggest additive interactions between 8PP and FCZ with respect to C. albicans cell growth. Besides killing per se, 8PP helps FCZ to achieve an almost complete fungicidal effect, which would be crucial to eradicate fungal infections.

Antibacterial and Cytotoxic Activity of Compounds Isolated from Flourensia oolepis

The antibacterial and cytotoxic effects of metabolites isolated from an antibacterial extract of Flourensia oolepis were evaluated. Bioguided fractionation led to five flavonoids, identified as 2′,4′-dihydroxychalcone (1), isoliquiritigenin (2), pinocembrin (3), 7-hydroxyflavanone (4), and 7,4′-dihydroxy-3′-methoxyflavanone (5). Compound 1 showed the highest antibacterial effect, with minimum inhibitory concentration (MIC) values ranging from 31 to 62 and 62 to 250 μg/mL, against Gram-positive and Gram-negative bacteria, respectively. On further assays, the cytotoxic effect of compounds 1–5 was determined by MTT assay on acute lymphoblastic leukemia (ALL) and chronic myeloid leukemia (CML) cell lines including their multidrug resistant (MDR) phenotypes. Compound 1 induced a remarkable cytotoxic activity toward ALL cells (IC₅₀ = 6.6–9.9 μM) and a lower effect against CML cells (IC₅₀ = 27.5–30.0 μM). Flow cytometry was used to analyze cell cycle distribution and cell death by PI-labeled cells and by Annexin V/PI staining, respectively. Upon treatment, 1 induced cell cycle arrest in the G₂/M phase accompanied by a strong induction of apoptosis. These results describe for the first time the antibacterial metabolites of F. oolepis extract, with 1 being the most effective. This chalcone also emerges as a selective cytotoxic agent against sensitive and resistant leukemic cells, highlighting its potential as a lead compound.

The promiscuous and synergic molecular interaction of polyphenols in bactericidal activity: an opportunity to improve the performance of antibiotics?

Plant polyphenols are a potential source of new antimicrobial molecules against bacteria because most newly developed antimicrobial agents do not improve the clinical management of infectious diseases. The potential synergism between the major polyphenolic compounds present in a Cistus salviifolius extract, which was characterized by HPLC-ESI-MS/MS, was investigated by the isobole method and the fractional inhibitory concentration index determination. Pairwise combinations of selected flavonoids and ellagitannins present in C. salviifolius extract were assayed against the in vitro growth of Staphylococcus aureus. Some combinations revealed synergic effects, resulting in a reduction of the minimum inhibitory concentration required to inhibit 50% growth (MIC50 ) up to 20 times lower as compared with the individual compounds. Some of the combinations exhibited MIC50 values close to drug potency level (0.5-1 µg/mL). Punicalagin and myricetin were the major contributors in the combinations. The proportion between the compounds in the synergic mixtures is crucial and may explain the superior antimicrobial activity displayed by this extract when compared with other botanical extracts. The rational optimization of these combinations could lead to the design of potent antimicrobial phytopharmaceuticals, which may improve the performance of current antibiotics, taking advantage of the multi-targeted and synergic molecular interactions of selected polyphenols.

Synthesis, structure, self-assembly and genotoxicity evaluation of a series of Mn-Anderson cluster based polyoxometalate–organic hybrids

A new series of POM–organic hybrids have been developed which show less genotoxicity compared to the parent polyoxometalate cluster.

Complexes of silver(I) ions and silver phosphate nanoparticles with hyaluronic acid and/or chitosan as promising antimicrobial agents for vascular grafts

Polymers are currently widely used to replace a variety of natural materials with respect to their favourable physical and chemical properties, and due to their economic advantage. One of the most important branches of application of polymers is the production of different products for medical use. In this case, it is necessary to face a significant disadvantage of polymer products due to possible and very common colonization of the surface by various microorganisms that can pose a potential danger to the patient. One of the possible solutions is to prepare polymer with antibacterial/antimicrobial properties that is resistant to bacterial colonization. The aim of this study was to contribute to the development of antimicrobial polymeric material ideal for covering vascular implants with subsequent use in transplant surgery. Therefore, the complexes of polymeric substances (hyaluronic acid and chitosan) with silver nitrate or silver phosphate nanoparticles were created, and their effects on gram-positive bacterial culture of Staphylococcus aureus were monitored. Stages of formation of complexes of silver nitrate and silver phosphate nanoparticles with polymeric compounds were characterized using electrochemical and spectrophotometric methods. Furthermore, the antimicrobial activity of complexes was determined using the methods of determination of growth curves and zones of inhibition. The results of this study revealed that the complex of chitosan, with silver phosphate nanoparticles, was the most suitable in order to have an antibacterial effect on bacterial culture of Staphylococcus aureus. Formation of this complex was under way at low concentrations of chitosan. The results of electrochemical determination corresponded with the results of spectrophotometric methods and verified good interaction and formation of the complex. The complex has an outstanding antibacterial effect and this effect was of several orders higher compared to other investigated complexes.

Antibacterial activity evaluation of quaternary chitin against Escherichia coli and Staphylococcus aureus

Water-soluble quaternary chitin/chitosan derivatives, O-[(2-hydroxy-3-trimethylammonium)propyl chitin (OHT-chitin), N-[(2-hydroxy-3-trimethylammonium)propyl chitosan (NHT-chitosan), and N,N,N-trimethylchitosan (TMC), having identical molecular weight and same anion, were prepared, and their antibacterial activities against Escherichia coli and Staphylococcus aureus were evaluated. Their minimum inhibitory concentration (MIC) values varied from 0.04 mg/mL to 20.48 mg/mL, and the minimum bactericidal concentration (MBC) values varied from 0.16 mg/mL to 40.96 mg/mL against E. coli and S. aureus, respectively. Transmission electron microscopy (TEM) clearly showed that there was serious damage on the bacterial walls, whereas there was some dissimilarity between TMC-treated E. coli and S. aureus.