Aspidin BB, a phloroglucinol derivative, exerts its antibacterial activity against Staphylococcus aureus by inducing the generation of reactive oxygen species

Antimicrobial activity and mechanism of anti-MRSA of phloroglucinol derivatives

BACKGROUND

In previous studies, authors have completed the total synthesis of several phloroglucinol natural products and synthesized a series of their derivatives, which were tested with good biological activities.

OBJECTIVES

To discover anti-MRSA lead compound and study their mechanism of action.

METHODS

Phloroglucinol derivatives were tested to investigate their activities against several gram-positive strains including Methicillin-resistant Staphylococcus aureus (MRSA). The mechanism study was conducted by determining extracellular potassium ion concentration, intracellular NADPH oxidase content, SOD activity, ROS amount in MRSA and MRSA survival rate under A5 treatment. The in vitro cytotoxicity test of A5 was conducted.

RESULTS

The activity of monocyclic compounds was stronger than that of bicyclic compounds, and compound A5 showed the best MIC value of 0.98 μg/mL and MBC value of 1.95 μg/mL, which were 4-8 times lower than that of vancomycin. The mechanism study of A5 showed that it achieved anti-MRSA effect through membrane damage, which is proved by increased concentration of extracellular potassium ion after A5 treatment. Another possible mechanism is the over ROS production induced cell death, which is suggested by observed alternation of several reactive oxygen species (ROS) related indicators including NADPH concentration, superoxide dismutase (SOD) activity, ROS content and bacterial survival rate after A5 treatment. The cytotoxicity results in vitro showed that A5 was basically non-toxic to cells.

CONCLUSION

Acylphloroglucinol derivative A5 showed good anti-MRSA activity, possibly via membrane damage and ROS-mediated oxidative stress mechanism. It deserves further exploration to be a potential lead for the development of new anti-MRSA agent.

The traditional utilization, biological activity and chemical composition of edible fern species

ETHNOPHARMACOLOGICAL RELEVANCE

Ferns form an important part of the human diet. Young fern fiddleheads are mostly consumed as vegetables, while the rhizomes are often extracted for starch. These edible ferns are also often employed in traditional medicine, where all parts of the plant are used, mostly to prepare extracts. These extracts are applied either externally as lotions and baths or internally as potions, decoctions and teas. Ailments traditionally treated with ferns include coughs, colds, fevers, pain, burns and wounds, asthma, rheumatism, diarrhoea, or skin diseases (eczema, rashes, itching, leprosy).

AIM OF THE REVIEW

This review aims to compile the worldwide knowledge on the traditional medicinal uses of edible fern species correlating to reported biological activities and isolated bioactive compounds.

MATERIALS AND METHODS

The articles and books published on edible fern species were searched through the online databases Web of Science, Pubmed and Google Scholar, with critical evaluation of the hits. The time period up to the end of 2022 was included.

RESULTS

First, the edible fern species were identified based on the literature data. A total of 90 fern species were identified that are eaten around the world and are also used in traditional medicine. Ailments treated are often associated with inflammation or bacterial infection. However, only the most common and well-known fern species, were investigated for their biological activity. The most studied species are Blechnum orientale L., Cibotium barometz (L.) J. Sm., Diplazium esculentum (Retz.) Sw., Marsilea minuta L., Osmunda japonica Thunb., Polypodium vulgare L., and Stenochlaena palustris (Burm.) Bedd. Most of the fern extracts have been studied for their antioxidant, anti-inflammatory and antimicrobial activities. Not surprisingly, antioxidant capacity has been the most studied, with results reported for 28 edible fern species. Ferns have been found to be very rich sources of flavonoids, polyphenols, polyunsaturated fatty acids, carotenoids, terpenoids and steroids and most of these compounds are remarkable free radical scavengers responsible for the outstanding antioxidant capacity of fern extracts. As far as clinical trials are concerned, extracts from only three edible fern species have been evaluated.

CONCLUSIONS

The extracts of edible fern species exert antioxidant anti-inflammatory and related biological activities, which is consistent with their traditional medicinal use in the treatment of wounds, burns, colds, coughs, skin diseases and intestinal diseases. However, studies to prove pharmacological activities are scarce, and require chemical-biological standardization. Furthermore, correct botanical classification needs to be included in publications to simplify data acquisition. Finally, more in-depth phytochemical studies, allowing the linking of traditional use to pharmacological relevance are needed to be done in a standardized way.

Antiviral and antibacterial properties of phloroglucinols: a review on naturally occurring and (semi)synthetic derivatives with potential therapeutic interest

Phloroglucinol and derived compounds comprise a huge class of secondary metabolites widely distributed in plants and brown algae. A vast array of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and anticancer has been associated to this class of compounds. In this review, the available data on the antiviral and antibacterial capacity of phloroglucinols have been analyzed. Some of these compounds and derivatives show important antimicrobial properties in vitro. Phloroglucinols have been shown to be effective against viruses, such as human immunodeficiency virus (HIV), herpes or enterovirus, and preliminary data through docking analysis suggest that they can be effective against SARS-CoV-19. Also, some phloroglucinols derivatives have shown antibacterial effects against diverse bacteria strains, including Bacillus subtilis and Staphylococcus aureus, and (semi)synthetic development of novel compounds have led to phloroglucinols with a significantly increased biological activity. However, therapeutic use of these compounds is hindered by the absence of in vivo studies and scarcity of information on their mechanisms of action, and hence further research efforts are required. On the basis of this consideration, our work aims to gather data regarding the efficacy of natural-occurring and synthetic phloroglucinol derivatives as antiviral and antibacterial agents against human pathogens, which have been published during the last three decades. The recollection of results reported in this review represents a valuable source of updated information that will potentially help researchers in the development of novel antimicrobial agents.

Treatment of Staphylococcus aureus and Candida albicans polymicrobial biofilms by phloroglucinol-gold nanoparticles

The co-isolation of Staphylococcus aureus and Candida albicans from host tissues and organs and their in vitro and in vivo interaction studies suggest a synergistic relationship in forming polymicrobial biofilms. In particular, during polymicrobial biofilm formation, S. aureus becomes coated in the extracellular matrix secreted by C. albicans, leading to enhanced resistance to antibiotics. Accordingly, understanding the interactions between S. aureus and C. albicans in polymicrobial biofilms is of utmost importance in establishing treatment strategies for polymicrobial infections. As an alternate technique, nanoparticles were used in this investigation to suppress polymicrobial biofilm. The current study aims to manufacture gold nanoparticles (AuNPs) using phloroglucinol (PG), a natural chemical, and test their inhibitory capabilities against S. aureus and C. albicans biofilms in standard and host-mimicking media (like saliva and sputum). PG-AuNPs have a spherical form with an average size of 46.71 ± 6.40 nm. The minimum inhibitory concentration (MIC) values differed when PG-AuNPs were evaluated in the standard and host-mimicking artificial media. The MIC of PG-AuNPs against S. aureus and C. albicans was 2048 μg/mL in both the standard and artificial sputum media. However, the MIC in saliva was only 128 μg/mL. The initial stage polymicrobial biofilm of S. aureus and C. albicans was dramatically decreased at the sub-MIC of PG-AuNPs in both standard and host-mimicking media. S. aureus and C. albicans mature polymicrobial biofilms were more effectively eliminated by MIC and sub-MIC of PG-AuNPs. This study indicates that PG-AuNPs have the ability to limit the formation of polymicrobial biofilms caused by bacterial and fungal diseases.

Antibacterial activity and antibacterial mechanism of flavaspidic acid BB against Staphylococcus haemelyticus

BACKGROUND

Staphylococcus haemolyticus (S. haemolyticus) is the main etiological factor in skin and soft tissue infections (SSTI). S. haemolyticus infections are an important concern worldwide, especially with the associated biofilms and drug resistance. Herein, we investigated the inhibitory effect of Flavaspidic acid BB obtained from plant extractions on clinical S. haemolyticus strains and their biofilms. Moreover, we predicted its ability to bind to the protein-binding site by molecular simulation. Since the combination of Hsp70 and RNase P synthase after molecular simulation with flavaspidic acid BB is relatively stable, enzyme-linked immunosorbent assay (ELISA) was used to investigate Hsp70 and RNase P synthase to verify the potential antimicrobial targets of flavaspidic acid BB.

RESULTS

The minimum inhibitory concentrations (MIC) of flavaspidic acid BB on 16 clinical strains of S. haemolyticus was 5 ~ 480 µg/mL, and BB had a slightly higher inhibitory effect on the biofilm than MUP. The inhibitory effect of flavaspidic acid BB on biofilm formation was better with an increase in the concentration of BB. Molecular simulation verified its ability to bind to the protein-binding site. The combination of ELISA kits showed that flavaspidic acid BB promoted the activity of Hsp70 and inhibited the activity of RNase P, revealing that flavaspidic acid BB could effectively inhibit the utilization and re-synthesis of protein and tRNA synthesis, thus inhibiting bacterial growth and biofilm formation to a certain extent.

CONCLUSIONS

This study could potentially provide a new prospect for the development of flavaspidic acid BB as an antibacterial agent for resistant strains.

Phloroglucinol Derivative Carbomer Hydrogel Accelerates MRSA-Infected Wounds’ Healing

Globally, wound infection is considered to be one of the major healthcare problems, with bacterial infections being the most critical threat, leading to poor and delayed wound healing, and even death. As a superbug, methicillin-resistant Staphylococcus aureus (MRSA) causes a profound hazard to public health safety, prompting us to search for alternative treatment approaches. Herein, the MTT test and Hoechst/propidium iodide (PI) staining demonstrated that PD was slightly less toxic to human fibroblasts including Human keratinocytes (HaCaT) cell line than Silver sulfadiazine (SSD), and Vancomycin (Van). In the MRSA-infected wound model, PD hydrogel (1%, 2.5%) was applied with for 14 days. The wound healing of PD hydrogel groups was superior to the SSD, Van, and control groups. Remarkably, the experimental results showed that PD reduced the number of skin bacteria, reduced inflammation, and upregulated the expression of PCNA (keratinocyte proliferation marker) and CD31 (angiogenesis manufacturer) at the wound site by histology (including hematoxylin–eosin (HE) staining, Masson staining) and immunohistochemistry. Additionally, no toxicity, hemocompatibility or histopathological changes to organs were observed. Altogether, these results suggested the potential of PD hydrogel as a safe, effective, and low toxicity hydrogel for the future clinical treatment of MRSA-infected wounds.

Flavaspidic acid BB combined with mupirocin improves its anti-bacterial and anti-biofilm activities against Staphylococcus epidermidis

BACKGROUND

The increase in drug-resistant opportunistic pathogenic bacteria, especially of antibiotic-resistant Staphylococcus epidermidis (S. epidermidis), has led to difficulties in the treatment of skin and soft tissue infections (SSTI). The major reason for bacterial resistance is the formation of bacterial biofilm. Here, we report a promising combination therapy of flavaspidic acid BB (BB) and mupirocin, which can effectively eradicate the biofilm of S. epidermidis and eliminate its drug resistance.

RESULT

The susceptibility test showed that the combination of BB and mupirocin has good antibacterial and antibiofilm activities, and the fractional inhibitory concentration index (FICI) of BB combined with mupirocin was 0.51 ± 0.00 ~ 0.75 ± 0.05, showing synergistic effect. Moreover, the time-kill curve assay results indicated that the combination of drugs can effectively inhibit the planktonic S. epidermidis. After drugs treatment, the drug-combination showed significantly inhibitory effects on the metabolic activity and total biomass in each stage of biofilm formation. The synergistic effect is likely related to the adhesion between bacteria, which is confirmed by field emission scanning electron microscope. And the expression level of aap, sarA and agrA genes were detected by real-time quantitative PCR (qRT-PCR).

CONCLUSION

Our study provides the experimental data for the use of BB for the clinical treatment of skin infections and further demonstrate the potential of BB as a novel biofilm inhibitor.

Phloroglucinol and Its Derivatives: Antimicrobial Properties toward Microbial Pathogens

Phloroglucinol (PG) is a natural product isolated from plants, algae, and microorganisms. Aside from that, the number of PG derivatives has expanded due to the discovery of their potential biological roles. Aside from its diverse biological activities, PG and its derivatives have been widely utilized to treat microbial infections caused by bacteria, fungus, and viruses. The rapid emergence of antimicrobial-resistant microbial infections necessitates the chemical synthesis of numerous PG derivatives in order to meet the growing demand for drugs. This review focuses on the use of PG and its derivatives to control microbial infection and the underlying mechanism of action. Furthermore, as future perspectives, some of the various alternative strategies, such as the use of PG and its derivatives in conjugation, nanoformulation, antibiotic combination, and encapsulation, have been thoroughly discussed. This review will enable the researcher to investigate the possible antibacterial properties of PG and its derivatives, either free or in the form of various formulations.

Glabridin synergy with norfloxacin induces ROS in multidrug resistant Staphylococcus aureus

Glabridin (Glb), a polyphenolic flavonoid inhibits the growth of MDRSA (Multidrug resistant S. aureus) 4627 by inducing ROS. Glb in combination with Norfloxacin (Nor) synergistically induced oxidative stress. Increased ROS/RNS levels, in particular, affected macromolecules' (DNA, lipid, protein) integrity and distorted cell morphology. We found correlation between drug-effects and up-/down-regulation of oxidative stress-related as well as MDR genes. These findings could considerably potentiate the dosing routine of Nor in combination with Glb, which holds a promising prospective as a antibacterial agent against S. aureus.

Endophytic Fungi from Dalbergia odorifera T. Chen Producing Naringenin Inhibit the Growth of Staphylococcus aureus by Interfering with Cell Membrane, DNA, and Protein

This study focused on the antibacterial effects of the endophytic fungi producing naringenin from Dalbergia odorifera T. Chen against Staphylococcus aureus. The antibacterial activity was measured by the inhibition diameters, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). The time-killing curve was also used to evaluate its antibacterial efficacy. The results of antibacterial activity determinations showed that endophytic fungi secondary metabolites can inhibit the growth of five pathogenic bacteria (S. aureus, Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa, and Bacillus subtilis) and the most sensitive strain was S. aureus that had the MIC and MBC values of 0.13 and 0.50 mg/mL, respectively. The membrane permeability study was measured by a DNA leakage assay and electrical conductivity assay. Furthermore, the whole-cell protein lysates and DNA fragmentation assay was evaluated. The morphology of S. aureus treated with the endophytic fungi products was observed by scanning electron microscopy (SEM). The probable antibacterial mechanism of endophytic fungi secondary metabolites was the increased membrane permeability that leads to leaks of nucleic acids and proteins. SEM results further confirmed that the extracts can interfere with the integrity of S. aureus cell membrane and further inhibit the growth of bacteria, resulting in the death of bacteria. This study provides a new perspective for the antibacterial functions of endophytic fungi secondary metabolites for biomedical applications.

Potent and Non-Cytotoxic Antibacterial Compounds Against Methicillin-Resistant Staphylococcus aureus Isolated from Psiloxylon mauritianum, A Medicinal Plant from Reunion Island

With the occurrence of antibiotic-resistant Staphylococcus aureus strains, identification of new anti-staphylococcal drugs has become a necessity. It has long been demonstrated that plants are a large and diverse source of antibacterial compounds. Psiloxylon mauritianum, an endemic medicinal plant from Reunion Island, was chemically investigated for its reported biological activity against S. aureus. Aspidin VB, a phloroglucinol derivative never before described, together with Aspidin BB, were first isolated from the ethyl acetate extract of P. mauritianum leaves. Their structures were elucidated from spectroscopic data. Aspidin VB exhibited strong antibacterial activity against standard and methicillin-resistant S. aureus strains, with a minimal inhibition concentration (MIC) of 0.25 μg/mL, and no cytotoxicity was observed at 10-5 M in MRC5 cells. Due to its biological activities, Aspidin VB appears to be a good natural lead in the fight against S. aureus.

Investigation of antifungal activity of surfactin against mycotoxigenic phytopathogenic fungus Fusarium moniliforme and its impact in seed germination and mycotoxicosis

The mycotoxigenic phytopathogenic fungus such as Fusarium moniliforme contamination in maize kernels may not only affect seed germination but also negatively cause mycotoxicosis in animals and humans. There is no effective fungicides to control the growth of F. moniliforme on maize kernels. Hence, effective bioactive compounds are needed to prevent plant and animal diseases associated with F. moniliforme contamination in cereals. Surfactin is an well-known antimicrobial lipopeptide has strong antifungal activities against several phytopathogenic fungi and may have potential uses in agriculture. So, in this present study the antifungal activity of surfactin extracted from Brevibacillus brevis KN8(2) was investigated against F. moniliforme, further its impact in seed germination and mycotoxicosis was also studied. Our results showed that surfactin inhibited and damaged the hyphae of F. moniliforme in in vitro. The agarose gel electrophoresis, SDS-PAGE analysis and biochemical assay presented that surfactin damaged the DNA, protein and reduced the GSH content in F. moniliforme. Furthermore, surfactin prevent maize seed germination problem and mycotoxicosis in animal model associated with F. moniliforme via prevention of F. moniliforme contamination on maize kernels. These findings revealed that surfactin could be an effective bio-fungicide in the plant disease management.

Antifungal Agents: Design, Synthesis, Antifungal Activity and Molecular Docking of Phloroglucinol Derivatives

Pseudoaspidinol is a phloroglucinol derivative with Antifungal activity and is a major active component of Dryopteris fragrans. In our previous work, we studied the total synthesis of pseudoaspidinol belonging to a phloroglucinol derivative and investigated its antifungal activity as well as its intermediates. However, the results showed these compounds have low antifungal activity. In this study, in order to increase antifungal activities of phloroglucinol derivatives, we introduced antifungal pharmacophore allylamine into the methylphloroglucinol. Meanwhile, we remained C1⁻C4 acyl group in C-6 position of methylphloroglucinol using pseudoaspidinol as the lead compound to obtain novel phloroglucinol derivatives, synthesized 17 compounds, and evaluated antifungal activities on Trichophyton rubrum and Trichophyton mentagrophytes in vitro. Molecular docking verified their ability to combine the protein binding site. The results indicated that most of the compounds had strong antifungal activity, in which compound 17 were found to be the most active on Trichophyton rubrum with Minimum Inhibitory Concentration (MIC) of 3.05 μg/mL and of Trichophyton mentagrophytes with MIC of 5.13 μg/mL. Docking results showed that compounds had a nice combination with the protein binding site. These researches could lay the foundation for developing antifungal agents of clinical value.

Preparation, Antidermatophyte Activity, and Mechanism of Methylphloroglucinol Derivatives

In this study a variety of phloroglucinols were isolated from the plant, and the activity experiment showed that the phloroglucinols had strong antifungal activity, especially methylphloroglucinol derivatives such as aspidin PB, dryofragin, aspidinol, aspidin BB, aspidin AB, and albicanol, in which the hydroxyl group of methylphloroglucinol is the active group of compounds, and C-2 or C-6 is the active site. The introduction of different groups in this position could change the properties and bioactivity of the compounds. In this study, different functional groups were introduced to the structure of methylphloroglucinol to obtain methylphloroglucinol derivatives that were synthesized, and antidermatophyte activities on Trichophyton rubrum, Trichophyton mentagrophytes, Microsporum canis, and Gypsum microspore bacteria were evaluated. Molecular docking verified its ability to combine the protein binding site. The antidermatophyte mechanism of compounds on cytochrome P450 sterol 14a-demethylase, squalene epoxidase, and β-1,3-glucan synthase was investigated by the enzyme-linked immunosorbent assay. The results showed that compounds had an inhibitory effect on four kinds of common dermatophytes in varying degrees, in which compound g had the strongest activities, the binding mode of methylphloroglucinol and its derivatives were similar to those of three enzymes, and compounds e and g had significant effects on the activity of the three enzymes, and compound g had a slightly stronger effect than the blank group. Compounds e and g also had a significant effect on the ergosterol synthesis of M. canis. This study could supply some antidermatophyte leading structure and possible mechanism for studying and developing new antifungal agents.

Anticancer Phenolics from Dryopteris fragrans (L.) Schott

Cancer is one of the most major diseases that threatens human health and life. The aim of this work was to obtain novel anticancer molecules from D. fragrans, a kind of medicinal plant. The structure of the new compound was identified using spectroscopic data (¹H-NMR, ¹³C-NMR and two dimensions NMR). Its anticancer properties were evaluated using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay against four human cells including lung cancer cells (A549), breast cancer cells (MCF-7), gastric cancer cells (SGC7901) and noncancerous human umbilical vein endothelial cells (HUVEC). A new phenylpropanoid-(E)-caffeic acid-9-O-β-d-xylpyranosyl-(1→2)-β-d-glucopyranosyl ester (1), with seven known compounds (2-8)-was isolated. The IC₅₀ value of compound 1 against MCF-7 cells was 2.65 ± 0.14 µM, and the IC₅₀ values of compound 8 against three cancer cells were below 20 µM.

The role of reactive oxygen species in the antimicrobial activity of pyochelin

The increase in prevalence of antimicrobial-resistant bacteria (ARB) is currently a serious threat, thus there is a need for new antimicrobial compounds to combat infections caused by these ARB. An antimicrobial-producing bacterium, Burkholderia paludis was recently isolated and was able to produce a type of siderophore with antimicrobial properties, later identified as pyochelin. The chelating ability of pyochelin has been well-characterized but not for its antimicrobial characteristics. It was found that pyochelin had MIC values (MBC values) of 3.13 µg/mL (6.26 µg/mL) and 6.26 µg/mL (25.00 µg/mL) against three Enterococcus strains and four Staphylococcus strains. Pyochelin was able to inhibit E. faecalis ATCC 700802 (a vancomycin-resistant strain) in a time and dose dependent manner via killing kinetics assay. It was demonstrated that pyochelin enhanced the production of intracellular reactive oxygen species (ROS) over time, which subsequently caused a significant increase in malondialdehyde (MDA) production (a marker for lipid peroxidation) and ultimately led to cell death by disrupting the integrity of the bacterial membrane (validated via BacLight assay). This study has revealed the mechanism of action of pyochelin as an antimicrobial agent for the first time and has shown that pyochelin might be able to combat infections caused by E. faecalis in the future.

A polyphenolic flavonoid glabridin: Oxidative stress response in multidrug-resistant Staphylococcus aureus

Glabridin a polyphenolic flavonoid from Glycyrrhiza glabra is known to possess several therapeutic properties. In the present study, we report for the first time the in vitro antibacterial activity (MIC values ranging from 3.12 to 25 μg/mL) of glabridin against multidrug-resistant clinical isolates of S. aureus by inducing oxidative stress. Increased levels of H2O2 and NO were observed in a dose-dependent manner after treatment of glabridin that further affected macromolecules such as DNA, lipids, and proteins. Surprisingly, glabridin was found to possess antioxidant properties when used at lower concentrations using three different methods including DPPH, FRAP, and SOD assays. These observations were further validated through the expression analysis of oxidative stress-responsive genes using qRT-PCR wherein glabridin was observed to up- and down-regulate these genes at lower and higher concentrations, respectively. In in vitro combination experiments, glabridin was found to reduce the MIC of different antibiotics such as norfloxacin, oxacillin, and vancomycin by up to 4-fold, while the MIC of glabridin itself was found to be reduced by up to 8-fold in the presence of antibiotics. A synergistic interaction was observed between norfloxacin and glabridin when used in combination against multidrug-resistant clinical isolate SA 4627 of Staphylococcus aureus at much lower concentrations, indicating the suitability of glabridin in combination therapy.