Phenolic constituents of licorice. VIII. Structures of glicophenone and glicoisoflavanone, and effects of licorice phenolics on methicillin-resistant Staphylococcus aureus

Genome Mining for New Enzyme Chemistry

A revolution in the field of biocatalysis has enabled scalable access to compounds of high societal values using enzymes. The construction of biocatalytic routes relies on the reservoir of available enzymatic transformations. A review of uncharacterized proteins predicted from genomic sequencing projects shows that a treasure trove of enzyme chemistry awaits to be uncovered. This Review highlights enzymatic transformations discovered through various genome mining methods and showcases their potential future applications in biocatalysis.

Pharmacological effects and mechanism of Maxing Shigan decoction in the treatment of Pseudomonas aeruginosa pneumonia

ETHNOPHARMACOLOGICAL RELEVANCE

Maxing Shigan Decoction (MXSG) is a traditional Chinese Medicine effectively used in respiratory infections and bacterial pneumonia. However, the mechanism of MXSG treating acute Pseudomonas aeruginosa (P. aeruginosa) pneumonia is still unclear.

AIM OF THE STUDY

This study aimed to investigate the therapeutic effects of MXSG on acute P. aeruginosa pneumonia and explore its potential mechanisms.

MATERIALS AND METHODS

HPLC-MS analysis was performed to analyze the chemical composition. Antibacterial effects in vitro were evaluated by minimum inhibitory concentration (MIC). Forty-five male BALB/c mice were divided into control group, model group, levofloxacin group, MXSG-L (7.7 g/kg/d), and MXSG-H group (15.4 g/kg/d). Mice were intranasal instillation with P. aeruginosa to induce acute P. aeruginosa pneumonia model. Levofloxacin and MXSG were administered by oral gavage once a day. After 3 days of treatment, the lung index measurement, micro-CT, arterial blood gas analysis, bacteria load determination, and HE staining were performed. Network pharmacological analysis and transcriptome sequencing were employed to predict the potential mechanisms of MXSG on bacterial pneumonia. The expressions of relating genes were detected by immunofluorescence, Western blot, and RT-PCR.

RESULTS

In vitro, MIC of P. aeruginosa is greater than 500 mg/mL. In the treatment of acute P. aeruginosa pneumonia model, MXSG significantly improved body weight loss, lung index, and pulmonary lesions. MXSG treatment also reduced the bacterial load and ameliorated oxygen saturation significantly. Transcriptomes, immunofluorescence, Western blot, and RT-PCR analysis showed MXSG treating acute P. aeruginosa pneumonia through the IL-17 signaling pathway and HIF-1α/IL-6/STAT3 signaling pathway.

CONCLUSIONS

We demonstrated the efficacy and mechanism of MXSG in the treatment of acute P. aeruginosa pneumonia, which provides a scientific basis for its clinical application.

Interactions of naturally occurring compounds with antimicrobials

Antibiotics are among the most often used medications in human healthcare and agriculture. Overusing these substances can lead to complications such as increasing antibiotic resistance in bacteria or a toxic effect when administering large amounts. To solve these problems, new solutions in antibacterial therapy are needed. The use of natural products in medicine has been known for centuries. Some of them have antibacterial activity, hence the idea to combine their activity with commercial antibiotics to reduce the latter's use. This review presents collected information on natural compounds (terpenes, alkaloids, flavonoids, tannins, sulfoxides, and mycotoxins), of which various drug interactions have been observed. Many of the indicated compounds show synergistic or additive interactions with antibiotics, which suggests their potential for use in antibacterial therapy, reducing the toxicity of the antibiotics used and the risk of further development of bacterial resistance. Unfortunately, there are also compounds which interact antagonistically, potentially hindering the therapy of bacterial infection. Depending on its mechanism of action, each compound can behave differently in combination with different antibiotics and when acting against various bacterial strains.

Isolation and biological activity of natural chalcones based on antibacterial mechanism classification

Bacterial infection, which is still one of the leading causes of death in humans, poses an enormous threat to the worldwide public health system. Antibiotics are the primary medications used to treat bacterial diseases. Currently, the discovery of antibiotics has reached an impasse, and due to the abuse of antibiotics resulting in bacterial antibiotic resistance, researchers have a critical desire to develop new antibacterial agents in order to combat the deteriorating antibacterial situation. Natural chalcones, the flavonoids consisting of two phenolic rings and a three-carbon α, β-unsaturated carbonyl system, possess a variety of biological and pharmacological properties, including anti-cancer, anti-inflammatory, antibacterial, and so on. Due to their potent antibacterial properties, natural chalcones possess the potential to become a new treatment for infectious diseases that circumvents existing antibiotic resistance. Currently, the majority of research on natural chalcones focuses on their synthesis, biological and pharmacological activities, etc. A few studies have been conducted on their antibacterial activity and mechanism. Therefore, this review focuses on the antibacterial activity and mechanisms of seventeen natural chalcones. Firstly, seventeen natural chalcones have been classified based on differences in antibacterial mechanisms. Secondly, a summary of the isolation and biological activity of seventeen natural chalcones was provided, with a focus on their antibacterial activity. Thirdly, the antibacterial mechanisms of natural chalcones were summarized, including those that act on bacterial cell membranes, biological macromolecules, biofilms, and quorum sensing systems. This review aims to lay the groundwork for the discovery of novel antibacterial agents based on chalcones.

Pharmacological Activities and Pharmacokinetics of Glycycoumarin

Glycycoumarin is a representative coumarin compound with significant pharmacological activities isolated from Glycyrrhiza uralensis Fisch., Fabaceae. Studies have shown that glycycoumarin has many biological activities, such as anti-tumor, liver protection, antispasmodic, antibacterial, and antivirus. However, the poor solubility of glycycoumarin in water and the accompanying reactions of the phase I (hydroxylation) and II (glucuronidation) metabolism limit its druggability, which manifests as low absorption in the body after oral administration and low free drug concentration, ultimately leading to low bioavailability. Therefore, a comprehensive review of the pharmacological effects and pharmacokinetics of glycycoumarin is presented to provide a reference for further research and application as a therapeutic agent.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s43450-022-00342-x.

Antimicrobial Quantitative Relationship and Mechanism of Plant Flavonoids to Gram-Positive Bacteria

Antimicrobial resistance (AMR) poses a serious threat to human health, and new antimicrobial agents are desperately needed. Plant flavonoids are increasingly being paid attention to for their antibacterial activities, for the enhancing of the antibacterial activity of antimicrobials, and for the reversing of AMR. To obtain more scientific and reliable equations, another two regression equations, between the minimum inhibitory concentration (MIC) (y) and the lipophilicity parameter ACD/LogP or LogD7.40 (x), were established once again, based on the reported data. Using statistical methods, the best one of the four regression equations, including the two previously reported, with regard to the antimicrobial quantitative relationship of plant flavonoids to Gram-positive bacteria, is y = −0.1285 x6 + 0.7944 x5 + 51.785 x4 − 947.64 x3 + 6638.7 x2 − 21,273 x + 26,087; here, x is the LogP value. From this equation, the MICs of most plant flavonoids to Gram-positive bacteria can be calculated, and the minimum MIC was predicted as approximately 0.9644 μM and was probably from 0.24 to 0.96 μM. This more reliable equation further proved that the lipophilicity is a key factor of plant flavonoids against Gram-positive bacteria; this was further confirmed by the more intuitive evidence subsequently provided. Based on the antibacterial mechanism proposed in our previous work, these also confirmed the antibacterial mechanism: the cell membrane is the major site of plant flavonoids acting on the Gram-positive bacteria, and this involves the damage of the phospholipid bilayers. The above will greatly accelerate the discovery and application of plant flavonoids with remarkable antibacterial activity and the thorough research on their antimicrobial mechanism.

Comprehensive insight into anti-staphylococcal and anti-enterococcal action of brominated and chlorinated pyrazine-based chalcones

The greatest threat and medicinal impact within gram-positive pathogens are posed by two bacterial genera, Staphylococcus and Enterococcus. Chalcones have a wide range of biological activities and are recognized as effective templates in medicinal chemistry. This study provides comprehensive insight into the anti-staphylococcal and anti-enterococcal activities of two recently published brominated and chlorinated pyrazine-based chalcones, CH-0y and CH-0w. Their effects against 4 reference and 12 staphylococcal and enterococcal clinical isolates were evaluated. Bactericidal action, the activity in combination with selected conventional antibiotics, the study of post-antimicrobial effect (PAE, PAE/SME), and in vitro and in vivo toxicity, were included. In CH-0y, anti-staphylococcal activity ranging from MIC = 15.625 to 62.5 μM, and activity against E. faecium from 31.25 to 62.5 μM was determined. In CH-0w, anti-staphylococcal activity ranging from 31.25 to 125 μM, and activity against E. faecium and E. faecalis (62.5 μM) was revealed. Both CH-0y and CH-0w showed bactericidal action, beneficial impact on bacterial growth delay within PAE and PAE/SME studies, and non/low toxicity in vivo. Compared to CH-0w, CH-0y seems to have higher anti-staphylococcal and less toxic potential. In conclusion, chalcones CH-0y and CH-0w could be considered as structural pattern for future adjuvants to selected antibiotic drugs.

Prenylated Flavonoids in Topical Infections and Wound Healing

The review presents prenylated flavonoids as potential therapeutic agents for the treatment of topical skin infections and wounds, as they can restore the balance in the wound microenvironment. A thorough two-stage search of scientific papers published between 2000 and 2022 was conducted, with independent assessment of results by two reviewers. The main criteria were an MIC (minimum inhibitory concentration) of up to 32 µg/mL, a microdilution/macrodilution broth method according to CLSI (Clinical and Laboratory Standards Institute) or EUCAST (European Committee on Antimicrobial Susceptibility Testing), pathogens responsible for skin infections, and additional antioxidant, anti-inflammatory, and low cytotoxic effects. A total of 127 structurally diverse flavonoids showed promising antimicrobial activity against pathogens affecting wound healing, predominantly Staphylococcus aureus strains, but only artocarpin, diplacone, isobavachalcone, licochalcone A, sophoraflavanone G, and xanthohumol showed multiple activity, including antimicrobial, antioxidant, and anti-inflammatory along with low cytotoxicity important for wound healing. Although prenylated flavonoids appear to be promising in wound therapy of humans, and also animals, their activity was measured only in vitro and in vivo. Future studies are, therefore, needed to establish rational dosing according to MIC and MBC (minimum bactericidal concentration) values, test potential toxicity to human cells, measure healing kinetics, and consider formulation in smart drug release systems and/or delivery technologies to increase their bioavailability.

Production and Secretion of Isowighteone in Hairy Root Cultures of Pigeon Pea (Cajanus cajan) Co-Treated with Multiple Elicitors

Isowighteone (3’-isoprenyl genistein) is a prenylated stilbenoid derivative that exhibits neuroprotective, antibacterial, and anti-inflammatory properties. To establish a bioproduction system for this bioactive compound, hairy root cultures of pigeon pea (Cajanus cajan (L.) Millsp.) were developed via Agrobacterium rhizogenes-mediated transformation. The cultures were co-treated with methyl jasmonate, cyclodextrin, hydrogen peroxide, and magnesium chloride to enhance the production of isowighteone. The amount of isowighteone that accumulated in the culture medium upon elicitation varied with the period of elicitation. Isowighteone was purified from extracts of the culture medium by semi-preparative HPLC, and its identity was confirmed by tandem mass spectrometry. After 144 h of elicitation in 12-day-old hairy root culture, the total yield of isowighteone was 8058.618 ± 445.78 μg/g DW, of which approximately 96% was found in the culture medium. The yield of isowighteone in the elicited hairy root culture was approximately 277-fold higher than in the non-elicited root culture. The difference between the phenotypes of the elicited and non-elicited pigeon pea hairy roots was studied using scanning electron microscopy. The non-elicited hairy roots had uniform surfaces whereas the elicited roots had non-uniform shapes. Pigeon pea hairy roots provide a sustainable platform for producing and studying the biosynthesis of isowighteone.

Valorisation of liquorice (Glycyrrhiza) roots: antimicrobial activity and cytotoxicity of prenylated (iso)flavonoids and chalcones from liquorice spent (G. glabra, G. inflata, and G. uralensis)

Prenylated phenolics are antimicrobials found in liquorice (Glycyrrhiza spp.).

Quantitative Mapping of Flavor and Pharmacologically Active Compounds in European Licorice Roots (Glycyrrhiza glabra L.) in Response to Growth Conditions and Arbuscular Mycorrhiza Symbiosis

Application of a sensitive UHPLC-MS/MS_MRM method enabled the simultaneous quantitation of 23 sweet-, licorice-, and bitter-tasting saponins in Glycyrrhiza glabra L., Glycyrrhiza uralensis Fisch., different licorice plants and root compartments, processed licorice, as well as different Glycyrrhiza spp. The combination of quantitative data with sweet, licorice, and bitter taste thresholds led to the determination of dose-over-threshold factors to elucidate the sweet, licorice, and bitter impact of the individual saponins with and without mycorrhiza symbiosis to evaluate the licorice root quality. Aside from glycyrrhizin (1), which is the predominant sweet- and licorice-tasting saponin in all licorice samples, 20 out of 22 quantitated saponins contributed to the taste profile of licorice roots. Next to sweet-/licorice-tasting glycyrrhizin (1), 24-hydroxy-glycyrrhizin (9), 30-hydroxy-glycyrrhizin (11), and 11-deoxo-24-hydroxy-glycyrrhizin (14) as well as licorice tasting saponins 20α-galacturonic acid glycyrrhizin (17), 24-hydroxy-20α-glycyrrhizin (21), and 11-deoxo-glycyrrhizin (12) were determined as key contributors to licorice root's unique taste profile. A quantitative comparison of 23 saponins as well as 28 polyphenols between licorice roots inoculated with arbuscular mycorrhiza fungi and controls showed that important taste-mediating saponins were increased in mycorrhizal roots, and these alterations depended on the growth substrate and the level of phosphate fertilization.

Insights into the molecular properties underlying antibacterial activity of prenylated (iso)flavonoids against MRSA

High resistance towards traditional antibiotics has urged the development of new, natural therapeutics against methicillin-resistant Staphylococcus aureus (MRSA). Prenylated (iso)flavonoids, present mainly in the Fabaceae, can serve as promising candidates. Herein, the anti-MRSA properties of 23 prenylated (iso)flavonoids were assessed in-vitro. The di-prenylated (iso)flavonoids, glabrol (flavanone) and 6,8-diprenyl genistein (isoflavone), together with the mono-prenylated, 4'-O-methyl glabridin (isoflavan), were the most active anti-MRSA compounds (Minimum Inhibitory Concentrations (MIC) ≤ 10 µg/mL, 30 µM). The in-house activity data was complemented with literature data to yield an extended, curated dataset of 67 molecules for the development of robust in-silico prediction models. A QSAR model having a good fit (R²_adj 0.61), low average prediction errors and a good predictive power (Q²) for the training (4% and Q²_LOO 0.57, respectively) and the test set (5% and Q²_test 0.75, respectively) was obtained. Furthermore, the model predicted well the activity of an external validation set (on average 5% prediction errors), as well as the level of activity (low, moderate, high) of prenylated (iso)flavonoids against other Gram-positive bacteria. For the first time, the importance of formal charge, besides hydrophobic volume and hydrogen-bonding, in the anti-MRSA activity was highlighted, thereby suggesting potentially different modes of action of the different prenylated (iso)flavonoids.

Isoflavonoid-Antibiotic Thin Films Fabricated by MAPLE with Improved Resistance to Microbial Colonization

Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) bacteria represent major infectious threats in the hospital environment due to their wide distribution, opportunistic behavior, and increasing antibiotic resistance. This study reports on the deposition of polyvinylpyrrolidone/antibiotic/isoflavonoid thin films by the matrix-assisted pulsed laser evaporation (MAPLE) method as anti-adhesion barrier coatings, on biomedical surfaces for improved resistance to microbial colonization. The thin films were characterized by Fourier transform infrared spectroscopy, infrared microscopy, and scanning electron microscopy. In vitro biological assay tests were performed to evaluate the influence of the thin films on the development of biofilms formed by Gram-positive and Gram-negative bacterial strains. In vitro biocompatibility tests were assessed on human endothelial cells examined for up to five days of incubation, via qualitative and quantitative methods. The results of this study revealed that the laser-fabricated coatings are biocompatible and resistant to microbial colonization and biofilm formation, making them successful candidates for biomedical devices and contact surfaces that would otherwise be amenable to contact transmission.

Antibacterial activity and mechanism of plant flavonoids to gram-positive bacteria predicted from their lipophilicities

Antimicrobial resistance seriously threatened human health, and new antimicrobial agents are desperately needed. As one of the largest classes of plant secondary metabolite, flavonoids can be widely found in various parts of the plant, and their antibacterial activities have been increasingly paid attention to. Based on the physicochemical parameters and antibacterial activities of sixty-six flavonoids reported, two regression equations between their ACD/LogP or LogD_7.40 and their minimum inhibitory concentrations (MICs) to gram-positive bacteria were established with the correlation coefficients above 0.93, and then were verified by another sixty-eight flavonoids reported. From these two equations, the MICs of most flavonoids against gram-positive bacteria could be roughly calculated from their ACD/LogP or LogD_7.40, and the minimum MIC was predicted as approximately 10.2 or 4.8 μM, more likely falls into the range from 2.6 to 10.2 μM, or from 1.2 to 4.8 μM. Simultaneously, both tendentiously concave regression curves indicated that the lipophilicity is a key factor for flavonoids against gram-positive bacteria. Combined with the literature analyses, the results also suggested that the cell membrane is the main site of flavonoids acting on gram-positive bacteria, and which likely involves the damage of phospholipid bilayers, the inhibition of the respiratory chain or the ATP synthesis, or some others.

A combinatorial action of GmMYB176 and GmbZIP5 controls isoflavonoid biosynthesis in soybean (Glycine max)

GmMYB176 is an R1 MYB transcription factor that regulates multiple genes in the isoflavonoid biosynthetic pathway, thereby affecting their levels in soybean roots. While GmMYB176 is important for isoflavonoid synthesis, it is not sufficient for the function and requires additional cofactor(s). The aim of this study was to identify the GmMYB176 interactome for the regulation of isoflavonoid biosynthesis in soybean. Here, we demonstrate that a bZIP transcription factor GmbZIP5 co-immunoprecipitates with GmMYB176 and shows protein-protein interaction in planta. RNAi silencing of GmbZIP5 reduced the isoflavonoid level in soybean hairy roots. Furthermore, co-overexpression of GmMYB176 and GmbZIP5 enhanced the level of multiple isoflavonoid phytoallexins including glyceollin, isowighteone and a unique O-methylhydroxy isoflavone in soybean hairy roots. These findings could be utilized to develop biotechnological strategies to manipulate the metabolite levels either to enhance plant defense mechanisms or for human health benefits in soybean or other economically important crops.

A combinatorial action of GmMYB176 and GmbZIP5 controls isoflavonoid biosynthesis in soybean (Glycine max)

GmMYB176 is an R1 MYB transcription factor that regulates multiple genes in the isoflavonoid biosynthetic pathway, thereby affecting their levels in soybean roots. While GmMYB176 is important for isoflavonoid synthesis, it is not sufficient for the function and requires additional cofactor(s). The aim of this study was to identify the GmMYB176 interactome for the regulation of isoflavonoid biosynthesis in soybean. Here, we demonstrate that a bZIP transcription factor GmbZIP5 co-immunoprecipitates with GmMYB176 and shows protein-protein interaction in planta. RNAi silencing of GmbZIP5 reduced the isoflavonoid level in soybean hairy roots. Furthermore, co-overexpression of GmMYB176 and GmbZIP5 enhanced the level of multiple isoflavonoid phytoallexins including glyceollin, isowighteone and a unique O-methylhydroxy isoflavone in soybean hairy roots. These findings could be utilized to develop biotechnological strategies to manipulate the metabolite levels either to enhance plant defense mechanisms or for human health benefits in soybean or other economically important crops.

Selection of Reference Genes for qRT-PCR Analysis in Medicinal Plant Glycyrrhiza under Abiotic Stresses and Hormonal Treatments

Best known as licorice, Glycyrrhiza Linn., a genus of herbaceous perennial legume, has been used as a traditional herbal medicine in Asia and a flavoring agent for tobacco and food industry in Europe and America. Abiotic stresses and hormonal treatments can significantly impact the development and metabolism of secondary metabolites in Glycyrrhiza. To better understand the biosynthesis of the trace-amount bioactive compounds, we first screened for the suitable reference genes for quantitative real-time reverse transcription PCR (qRT-PCR) analysis in Glycyrrhiza. The expression profiles of 14 candidate reference genes, including Actin1 (ACT), Clathrin complex AP1 (CAC), Cyclophilin (CYP), Heat-shock protein 40 (DNAJ), Dehydration responsive element binding gene (DREB), Translation elongation factor1 (EF1), Ras related protein (RAN), Translation initiation factor (TIF1), β-Tubulin (TUB), Ubiquitin-conjugating enzyme E2 (UBC2), ATP binding-box transpoter 2 (ABCC2), COP9 signal compex subunit 3 (COPS3), Citrate synthase (CS), and R3H domain protein 2 (R3HDM2) from two congeneric species, Glycyrrhiza uralensis F. and Glycyrrhiza inflata B., were examined under abiotic stresses (osmotic and salinity) and hormonal treatments (Abscisic acid (ABA) and methyl jasmonic acid (MeJA)) using a panel of software, including geNorm, NormFinder, BestKeeper, and Delta CT. The overall stability, however, was provided by RefFinder, a comprehensive ranking system integrating inputs from all four algorithms. In G. uralensis, the most stable reference genes under osmotic stress, salt stress, ABA treatment, and MeJA treatment were TIF1, DNAJ, CS, and ABCC2 for leaves and DNAJ, DREB, CAC, and CAC for roots, respectively. In comparison, the top ranked genes were TUB, CAC, UBC2, and RAN for leaves and TIF1, ABCC2, CAC, and UBC2 for roots, respectively, under stress and hormonal treatments in G. inflata. ACT and TIF1, on the other hand, were the least stable genes under the most experimental conditions in the two congeneric species. Finally, our survey of the reference genes in legume shows that EF, ACT, UBC2, and TUB were the top choices for the abiotic stresses while EF, UBC2, CAC, and ABCC2 were recommended for the hormonal treatments in Leguminosae. Our combined results provide reliable normalizers for accurate gene quantifications in Glycyrrhiza species, which will allow us to exploit its medicinal potential in general and antiviral activities in particular.

High-performance liquid chromatographic profile and 1H quantitative nuclear magnetic resonance analyses for quality control of a Xinjiang licorice extract

Various pharmacological properties of Xinjiang licorice flavonoids have been reported recently. We have investigated constituents corresponding to distinct peaks on the high-performance liquid chromatography (HPLC) profile of a flavonoid-rich extract from licorice, and identified 13 flavonoids, including licochalcone A (1), licochalcone B (3), glabrone (4), and echinatin (5), by isolating them and then performing high-resolution electrospray ionization mass spectrometry and 1H nuclear magnetic resonance (NMR) spectral analyses. We then applied the 1H quantitative NMR (qNMR) method for analysis of major flavonoids, 1 and 3–5 in the extract. The 1H qNMR results were supported by 13C NMR analysis. The results demonstrated the utility of the combination of HPLC profiling and qNMR analyses for quality control of Xinjiang licorice. Additionally, we observed a moderate inhibitory effect of the most abundant constituent, licochalcone A (1), on acetylcholine esterase activity, suggesting utility as a seed for drug development.

A Review: The Anti-inflammatory, Anticancer and Antibacterial Properties of Four Kinds of Licorice Flavonoids Isolated from Licorice

Plants have always been an important source of medicines for humans, and licorice is a very significant herb in the development of humans. As a traditional herb, it is widely cultivated in China, Japan, Russia, Spain and India. With the development of organic chemistry and biochemistry, various chemical ingredients extracted from licorice have been studied and identified. Among them, many chemical components were considered to have strong pharmacological activities, such as anti-inflammatory, anti-ulcer, antibacterial, anticancer and so on. Based on those reports, licorice has attracted the attention of many researchers in recent years, and they are devoted to discovering the active ingredients and mechanism of action of active compounds. Licorice flavonoids are one of the main extracts of licorice root and stem and have many potential biological properties. This paper aims to summarize the four kinds of licorice flavonoids, including liquiritigenin, isoliquiritigenin, licochalcone (including licochalcone A and licochalcone B) and glabridin, about their biological activities of anti-inflammatory, anticancer, antibacterial.

Comprehensive multivariate correlations between climatic effect, metabolite-profile, antioxidant capacity and antibacterial activity of Brazilian red propolis metabolites during seasonal study

The standardization of apiceutical products like as propolis extracts has been widely debated worldwide and variations in the propolis chemical composition are still very relevant topics for use-standardized of different propolis-type as medication by much of the world’s population. The present manuscript discuss important issues related to the climate effect and variations in propolis metabolite-profiling changes, antioxidant capacity and variations of the antibacterial activity of the Brazilian red propolis metabolites using comprehensive multivariate correlations. It was observed the increasing of guttiferones concentrations during the intense drought period and drastic decreasing in rainy period. The climate variation induced the high concentration of flavonoids in rainy period with pronounced dropped in some rainy months. The Pearson´s analysis demonstrated correlation between IC₅₀ from DPPH and guttiferones and flavonoids concentrations. The PCA-X and Hotelling T2 test showed outliers during the months with lowest concentrations of formononetin and isoliquiritigenin was observed in antibacterial tests. The PLS-DA, OPLS-DA and VIP analysis demonstrate guttiferone E, guttiferone B, liquiritigenin, naringenin are considered important substances responsible by anti-staphylococcal activity in red propolis composition during the rainy season and drought period, but a synergistic effect with other flavonoids and isoflavonoids are not ruled out.

Chalcone derivatives and their antibacterial activities: Current development

The increase in antibiotic resistance due to various factors has encouraged the look for novel compounds which are active against multidrug-resistant pathogens. In this framework, chalcone-based compounds showed a diversity of pharmacological properties, and its derivatives possess a high degree of structural diversity, and it is helpful for the discovery of new therapeutic agents. The growing resistance to antibiotics worldwide has endangered their efficacy. This has led to a surging interest in the discovery of new antibacterial agents. Thus, there is an urgent need for new antibacterial drug candidates with increased strength, new targets, low cost, superior pharmacokinetic properties, and minimum side effects. The present review concluded and focuses on the recent developments in the area of medicinal chemistry to explore the diverse chemical structures of potent antibacterial agents and also describes its structure-activity relationships studies. The various synthetic structures leading to this class of neutral protective compound is common and additional structural optimization is promising for potential drug discovery and development.

Phytochemical Constituents and Pharmacological Effects of Licorice: A Review

Licorice (or “liquorice”) is one of most widely used in foods, herbal medicine, and extensively researched medicinal plants of the world. In traditional medicine licorice roots have been used against treating many ailments including lung diseases, arthritis, kidney diseases, eczema, heart diseases, gastric ulcer, low blood pressure, allergies, liver toxicity, and certain microbial infections. Licorice extract contains sugars, starch, bitters, resins, essential oils, tannins, inorganic salts, and low levels of nitrogenous constituents such as proteins, individual amino acids, and nucleic acids. A large number of biological active compounds have been isolated from Glycyrrhiza species, where triterpene saponins and flavonoids are the main constitutes which show broad biological activity. This review examines recent studies on the phytochemical and pharmacological data and describes some side effects and toxicity of licorice and its bioactive components.

QSAR-based molecular signatures of prenylated (iso)flavonoids underlying antimicrobial potency against and membrane-disruption in Gram positive and Gram negative bacteria

Prenylated flavonoids and isoflavonoids are phytochemicals with remarkable antibacterial activity. In this study, 30 prenylated (iso)flavonoids were tested against Listeria monocytogenes and Escherichia coli (the latter in combination with an efflux pump inhibitor). Minimum inhibitory concentrations of the most active compounds ranged between 6.3–15.0 µg/mL. Quantitative structure-activity relationships (QSAR) analysis was performed and linear regression models were proposed with R² between 0.77–0.80, average R²_m between 0.70–0.75, Q²_LOO between 0.66–0.69, and relatively low amount of descriptors. Shape descriptors (related to flexibility and globularity), together with hydrophilic/hydrophobic volume and surface area descriptors, were identified as important molecular characteristics related to activity. A 3D pharmacophore model explaining the effect of the prenyl position on the activity of compounds was developed for each bacterium. These models predicted active compounds with an accuracy of 71–88%. With regard to the mode of action, good antibacterial prenylated (iso)flavonoids with low relative hydrophobic surface area caused remarkable membrane permeabilization, whereas those with higher relative hydrophobic surface area did not. Based on the QSAR and membrane permeabilization studies, the mode of action of antibacterial prenylated (iso)flavonoids was putatively rationalized.

Protective effect and molecular mechanism of liquiritin on oxybuprocaine-induced apoptosis of human corneal endothelial cells

This study was designed to investigate the protective effect and possible molecular mechanism of liquiritin on oxybuprocaine-induced apoptosis of human corneal endothelial cells (HCECs). In this study, the effect of oxybuprocaine on the proliferation of HCEC-12 was detected using cell counting kit-8 (CCK-8). The inductive effect of oxybuprocaine on HCEC-12 apoptosis and protective effect of liquiritin against oxybuprocaine-induced HCEC-12 apoptosis were tested by Annexin V/propidium iodide (PI) staining and flow cytometry. The production of reactive oxygen species (ROS) was analyzed by 2,7-dichlorodi-hydrofluorescein diacetate (DCFH-DA) staining and fluorescent-activated cell sorting (FACS), and the expression of nuclear factor-κB (NF-κB) p65 and apoptosis-related proteins, caspase-3 and Bax, was determined by western blot analysis. Our results show that liquiritin resisted the inhibitory effect of oxybuprocaine on the proliferation of HCEC-12, and cell activity had the most significant increase in pretreatment with liquiritin group in the concentration of 8 mg/ml; compared with that in oxybuprocaine group. Apoptosis in pretreatment with liquiritin was distinctly decreased and liquiritin resisted the production of ROS in HCEC-12 induced by oxybuprocaine. Investigation of molecular mechanism revealed that the pretreatment with liquiritin and pyrrolidinedithiocarbamic acid (PDTC) obviously blocked the expression of NF-κB p65 in nuclear protein increased by oxybuprocaine and the expression levels of total proteins, caspase-3 and Bax.Moreover, tumor necrosis factor-α (TNF-α) blocked the inhibitory effect of liquiritin on the expression of NF-κB p65 in nuclear protein and total proteins, caspase-3 and Bax, thus obstructing the protective effect of liquiritin on corneal epithelial cells. The results of this study indicated that liquiritin reduces the expression of apoptosis protein and increases the expression of anti-apoptotic protein through inhibiting NF-κB signal pathway, thus resisting HCEC-12 apoptosis induced by oxybuprocaine.

Licocoumarone isolated from Glycyrrhiza uralensis selectively alters LPS-induced inflammatory responses in RAW 264.7 macrophages

The effects of licocoumarone (LC) isolated from Glycyrrhiza uralensis were studied in LPS-stimulated RAW 264.7 macrophages. Our study demonstrated that LC dose-dependently attenuated LPS-induced NO production by down-regulating iNOS expression. Additionally, the treatment with LC inhibited LPS-induced expression of cytokines including IL-1β, IL-6 and IL-10, but not TNF-α, at both mRNA and protein levels. Similar suppressive effects of LC were observed on LPS-stimulated murine peritoneal macrophages as well. Furthermore, LC significantly reduced LPS-stimulated NF-κB activation by inhibition of IκBα degradation and p65 phosphorylation. The results from NF-κB-luc reporter gene assay further support the inhibitory effect of LC on NF-κB activation. Further studies showed that LC also interfered with the MAPKs and STAT3 signaling pathways, which are typical inflammatory signaling pathways triggered by LPS. Taken together, these results show that LC attenuates LPS-induced cytokine gene expression in RAW 264.7 macrophages through mechanisms that involve NF-κB, MAPKs and STAT3 signaling pathways, but the pattern of inhibition differs from that of a global immunosuppresant. Our study indicates that LC is a functional constituent of Glycyrrhiza uralensis with potential implications in infectious and immune-related diseases.

Economic Importance

The beneficial effects of liquorice in treating chills, colds, and coughs have been fully discussed in Ayurveda, as well as in the texts of ancient Egyptians, Greeks, and Romans. The plant has been prescribed for dropsy during the period of famous Hippocrates. The reason being that it was quite helpful as thirst-quenching drugs (Biondi et al. in J Nat Prod 68:1099–1102, 2005; Mamedov and Egamberdieva in Herbals and human health-phytochemistry. Springer Nature Publishers, 41 pp, 2017). No doubt, the clinical use of liquorice in modern medicine started around 1930; Pedanios Dioscorides of Anazarba (Adana), first century AD-Father of Pharmacists, mentions that it is highly effective in the treatment of stomach and intestinal ulcers. In Ayurveda, people in ancient Hindu culture have used it for improving sexual vigor.

Effect of Zuccagnia punctata Cav. (Fabaceae) extract on pro-inflammatory enzymes and on planktonic cells and biofilm from Staphylococcus aureus. Toxicity studies

Zuccagnia punctata Cav. (Fabaceae), a native plant from Argentina has been used traditionally as medicinal species. The aim of the study was to validate the antibiotic and anti-inflammatory potential of Z. punctata organic extract (ZpE) and the major compounds; 2',4'-dihydroxy-3'-methoxychalcone (DHMC), 2',4'-dihydroxychalcone (DHC), 7-hydroxyflavanone (7-HF) and 3,7-dihydroxyflavone (DHF); using an in vitro model. The antibiotic activity was determined using a broth microdilution method and the minimum inhibitory concentration (MIC) was determined. The extract and the isolation compounds affect the normal growth of all assayed Staphylococcus aureus strains. The MIC values for ZpE and isolated compounds were between 125 and 500 μg/mL and between 25 and 400 μg/mL, respectively, against all assayed strains. The inhibitory effect of extract and isolated compounds on biofilm formation and on pro-inflammatory enzymes (sPLA₂, COX-2, LOX) was analyzed. The compound DHC was the most active on sPLA₂ while DHF and DHMC showed the highest activity on LOX. Both the extract and pure compounds except DHMC were active against COX-2. It can be concluded that the phytocomplex and the pure compounds possessed antibiotic and anti-inflammatory activities under the conditions tested, and could be a good alternative therapy for infective and inflammatory processes.

Inhibitory effect of totarol on exotoxin proteins hemolysin and enterotoxins secreted by Staphylococcus aureus

Staphylococcus aureus (S. aureus) causes a wide variety of infections, which are of major concern worldwide. S. aureus produces multiple virulence factors, resulting in food infection and poisoning. These virulence factors include hyaluronidases, proteases, coagulases, lipases, deoxyribonucleases and enterotoxins. Among the extracellular proteins produced by S. aureus that contribute to pathogenicity, the exotoxins α-hemolysin, staphylococcal enterotoxin A (SEA) and staphylococcal enterotoxin B (SEB) are thought to be of major significance. Totarol, a plant extract, has been revealed to inhibit the proliferation of several pathogens effectively. However, there are no reports on the effects of totarol on the production of α-hemolysin, SEA or SEB secreted by S. aureus. The aim of this study was to evaluate the effects of totarol on these three exotoxins. Hemolysis assay, western blotting and real-time reverse transcriptase-PCR assay were performed to identify the influence of graded subinhibitory concentrations of totarol on the production of α-hemolysin and the two major enterotoxins, SEA and SEB, by S. aureus in a dose-dependent manner. Moreover, an enzyme linked immunosorbent assay showed that the TNF-α production of RAW264.7 cells stimulated by S. aureus supernatants was inhibited by subinhibitory concentrations of totarol. Form the data, we propose that totarol could potentially be used as a promising natural compound in the food and pharmaceutical industries.

Constituents of Psoralea corylifolia Fruits and Their Effects on Methicillin-Resistant Staphylococcus aureus

Two new flavonoids, bakuisoflavone (1) and bakuflavanone (2), together with 15 known compounds, were isolated from the fruits of Psoralea corylifolia, and their structures were characterized by spectroscopic data. The effects of the isolated compounds on methicillin-resistant Staphylococcus aureus were also examined. We found that two compounds, isobavachalcone (10) and bakuchiol (12), showed noticeable antibacterial effects on the MRSA strains examined. Quantitation of the major constituents, including anti-MRSA constituents, was then performed. The results showed individual contents of 1.26%-16.49% (w/w) among the examined compounds in the ethyl acetate extract from P. corylifolia fruits.

Bioavailability of dietary polyphenols and gut microbiota metabolism: antimicrobial properties

Polyphenolic compounds are plant nutraceuticals showing a huge structural diversity, including chlorogenic acids, hydrolyzable tannins, and flavonoids (flavonols, flavanones, flavan-3-ols, anthocyanidins, isoflavones, and flavones). Most of them occur as glycosylated derivatives in plants and foods. In order to become bioactive at human body, these polyphenols must undergo diverse intestinal transformations, due to the action of digestive enzymes, but also by the action of microbiota metabolism. After elimination of sugar tailoring (generating the corresponding aglycons) and diverse hydroxyl moieties, as well as further backbone reorganizations, the final absorbed compounds enter the portal vein circulation towards liver (where other enzymatic transformations take place) and from there to other organs, including behind the digestive tract or via blood towards urine excretion. During this transit along diverse tissues and organs, they are able to carry out strong antiviral, antibacterial, and antiparasitic activities. This paper revises and discusses these antimicrobial activities of dietary polyphenols and their relevance for human health, shedding light on the importance of polyphenols structure recognition by specific enzymes produced by intestinal microbial taxa.

Chemopreventive Effects of Licorice and Its Components

Cancer is still a major health issue worldwide and identifying novel but safe compounds for prevention and treatment is a high priority. Licorice (Glycyrrhiza) is a perennial plant that is cultivated in many countries and has been reported to exert antioxidant, anti-inflammatory and anticancer effects. However, some components of licorice exert unwanted side effects and therefore identifying safer licorice components would be ideal. The anticancer activities of many of the licorice components appear to include cycle arrest, apoptosis induction, and general antioxidant effects. Commonly reported indirect protein targets important in tumorigenesis include many cell cycle-related proteins, apoptosis-associated proteins, MMP proteins, COX-2, GSK-β, Akt, NF-κB, and MAP kinases. Importantly, several licorice components were reported to directly bind to and inhibit the activities of PI3-K, MKK4, MKK7, JNK1, mTOR, and Cdk2, resulting in decreased carcinogenesis in several cell and mouse models with no obvious toxicity. This review focuses on specific components of licorice for which a direct protein target has been identified.

In vitro antimicrobial activities of 1-methoxyficifolinol, licorisoflavan A, and 6,8-diprenylgenistein against Streptococcus mutans

The objective of the study was to investigate the antimicrobial effects of purified single compounds from ethanol-extracted licorice root on Streptococcus mutans. The crude licorice root extract (CLE) was obtained from Glycyrrhiza uralensis, which was subjected to column chromatography to separate compounds. Purified compounds were identified by mass spectrometry and nuclear magnetic resonance. Antimicrobial activities of purified compounds from CLE were evaluated by determining the minimum inhibitory concentration and by performing time-kill kinetics. The inhibitory effects of the compounds on biofilm development were evaluated using crystal violet assay and confocal microscopy. Cell toxicity of substances to normal human gingival fibroblast (NHGF) cells was tested using a methyl thiazolyl tetrazolium assay. Chlorhexidine digluconate (CHX) was used in the control group. Three antimicrobial flavonoids, 1-methoxyficifolinol, licorisoflavan A, and 6,8-diprenylgenistein, were isolated from the CLE. We found that the three flavonoids and CHX had bactericidal effects on S. mutans UA159 at the concentration of ≥4 and ≥1 µg/ml, respectively. The purified compounds completely inhibited biofilm development of S. mutans UA159 at concentrations over 4 μg/ml, which was equivalent to 2 μg/ml of CHX. Confocal analysis showed that biofilms were sparsely scattered in the presence of over 4 μg/ml of the purified compounds. However, the three compounds purified from CLE showed less cytotoxic effects on NHGF cells than CHX at these biofilm-inhibitory concentrations. Our results suggest that purified flavonoids from CLE can be useful in developing oral hygiene products, such as gargling solutions and dentifrices for preventing dental caries.

Structures of new phenolics isolated from licorice, and the effectiveness of licorice phenolics on vancomycin-resistant Enterococci

Licorice, which is the underground part of Glycyrrhiza species, has been used widely in Asian and Western countries as a traditional medicine and as a food additive. Our continuous investigation on the constituents of roots and stolons of Glycyrrhiza uralensis led to the isolation of two new phenolics, in addition to 14 known compounds. Structural studies including spectroscopic and simple chemical derivatizations revealed that both of the new compounds had 2-aryl-3-methylbenzofuran structures. An examination of the effectiveness of licorice phenolics obtained in this study on vancomycin-resistant strains Enterococcus faecium FN-1 and Enterococcus faecalis NCTC12201 revealed that licoricidin showed the most potent antibacterial effects against both of E. faecalis and E. faecium with a minimum inhibitory concentration (MIC) of 1.9 × 10-5 M. 8-(γ,γ-Dimethylallyl)-wighteone, isoangustone A, 3'-(γ,γ-dimethylallyl)-kievitone, glyasperin C, and one of the new 3-methyl-2-phenylbenzofuran named neoglycybenzofuran also showed potent anti-vancomycin-resistant Enterococci effects (MIC 1.9 × 10-5-4.5 × 10-5 M for E. faecium and E. faecalis). The HPLC condition for simultaneous detection of the phenolics in the extract was investigated to assess the quality control of the natural antibacterial resource, and quantitative estimation of several major phenolics in the extract with the established HPLC condition was also performed. The results showed individual contents of 0.08%-0.57% w/w of EtOAc extract for the major phenolics in the materials examined.

Polyphenolic Constituent Structures ofZanthoxylum piperitumFruit and the Antibacterial Effects of Its Polymeric Procyanidin on Methicillin-ResistantStaphylococcus aureus

Zanthoxylum piperitum (Rutaceae) is used as a spice and a natural medicine in Japan. Our study found that ZP-CT-A, a polymeric proanthocyanidin purified from the fruit of this species, noticeably decreased the minimum inhibitory concentrations of beta-lactam antibiotics for methicillin-resistant Staphylococcus aureus (MRSA). The structure of ZP-CT-A was characterized on the basis of (13)C NMR and size exclusion chromatographic data and the results of thiolytic degradation. A mechanistic study of the effects of ZP-CT-A indicated that it suppressed the activity of beta-lactamase and largely decreased the stability of the bacterial cell membrane of MRSA, as shown by a reduction in the tolerance of MRSA to low osmotic pressure and high ionic strength solutions.

Newly-synthesized chalcones-inhibition of adherence and biofilm formation of methicillin-resistant Staphylococcus aureus

Biofilm formation and adherence of bacteria to host tissue are one of the most important virulence factors of methicillin-resistant strains of Staphylococcus aureus (MRSA). The number of resistant strains is seriously increasing during the past years and bacteria have become resistant, not only to methicillin, but also to other commonly used antistaphylococcal antibiotics. There is a great need for discovering a novel antimicrobial agent for the treatment of staphylococcal infections. One of the most promising groups of compounds appears to be chalcones. In present study we evaluated the in vitro effect of three newly synthesized chalcones: 1,3- Bis-(2-hydroxy-phenyl)-propenone, 3-(3-Hydroxy-phenyl)-1-(2-hydroxy-phenyl)-propenone and 3-(4-Hydroxy-phenyl)-1-(2-hydroxy-phenyl)-propenone on glycocalyx production, biofilm formation and adherence to human fibronectin of clinical isolates and laboratory control strain of MRSA (ATCC 43300). Subinhibitory concentrations of the tested compounds reduced the production of glycocalyx, biofilm formation and adherence to human fibronectin of all MRSA strains. Inhibition of biofilm formation was dose dependent and the most effective was 1,3- Bis-(2-hydroxy-phenyl)-propenone. In our study we demonstrated that three newly-synthesized chalcones exhibited significant effect on adherence and biofilm formation of MRSA strains. Chalcones may be considered as promising new antimicrobial agents that can be used for prevention of staphylococcal infections or as adjunct to antibiotics in conventional therapy.

A systematic review on biological activities of prenylated flavonoids

CONTEXT

Prenylated flavonoids are a unique class of naturally occurring flavonoids that exist especially for the plant's self-defensive strategy. This special class of flavonoids increases the bioactivities of their backbone flavonoids with non-prenylation; therefore, prenylated flavonoids have more potential to be developed and utilized.

OBJECTIVE

The number, position and type of the prenyl group on the flavonoids backbone structure may have close relationships with the bioactivities of flavonoids.

METHODS

PubMed and WEB OF KNOWLEDGE® were used to search articles published in English between 1 January 2002 and 31 December 2012, which discuss the structure-activity relationship between prenylated flavonoids and their bioactivities.

RESULTS

It is proposed that the prenyl-moiety makes the backbone compound more lipophilic, which leads to its high affinity with cell membranes. The prenylation brings the flavonoids with enhancement of antibacterial, anti-inflammatory, antioxidant, cytotoxicity, larvicidal as well as estrogenic activities. However, it is reported that the prenyl-moiety decreases the bioavailability and plasma absorption of prenylated flavonoids.

CONCLUSION

The prenyl group affects the bioactivities of flavonoids in certain ways, while the action mechanisms and the structure-activity relationship as well as more in vivo studies even clinical validation trials need to be further investigated.

Structures of two new flavonoids and effects of licorice phenolics on vancomycin-resistant Enterococcus species

Since our previous study revealed that several licorice phenolics have antibacterial effects on methicillin-resistant Staphylococcus aureus (MRSA), and suppressive effects on the oxacillin resistance of MRSA, we further investigated effectiveness of licorice constituents on vancomycin-resistant Enterococcus (VRE) bacteria, and purified 32 phenolic compounds. Two flavonoids among them were characterized structurally, and identified their structures as demethylglycyrol (31) and 5,7-di-O-methylluteone (32), respectively. Examination of antibacterial effects of licorice phenolics showed that 3-arylcoumarins such as licoarylcoumarin (9) and glycycoumarin (26), and 2-arylcoumarones such as gancaonin I (17), have moderate to potent antibacterial effects on the VRE strains used in this study.

Synergistic Effect between Cryptotanshinone and Antibiotics against Clinic Methicillin and Vancomycin-Resistant Staphylococcus aureus

Cryptotanshinone (CT), a major tanshinone of medicinal plant Salvia miltiorrhiza Bunge, demonstrated strong antibacterial activity against clinic isolated methicillin and vancomycin-resistant Staphylococcus aureus (MRSA and VRSA) in this experiment. The CT was determined against clinic isolated MRSA 1–16 with MIC and MBC values ranging from 4 to 32 and 8 to 128 μg/mL; for MSSA 1-2 from 16 to 32 μg/mL and 64 to 128 μg/mL; for VRSA 1-2 from 2 to 4 μg/mL and 4 to 16 μg/mL, respectively. The range of MIC₅₀ and MIC₉₀ of CT was 0.5–8 μg/mL and 4–64 μg/mL, respectively. The combination effects of CT with antibiotics were synergistic (FIC index <0.5) against most of tested clinic isolated MRSA, MSSA, and VRSA except additive, MRSA 4 and 16 in oxacillin, MRSA 6, 12, and 15 in ampicillin, and MRSA 6, 11, and 15 in vancomycin (FIC index < 0.75–1.0). Furthermore, a time-kill study showed that the growth of the tested bacteria was completely attenuated after 2–6 h of treatment with the 1/2 MIC of CT, regardless of whether it was administered alone or with ampicillin, oxacillin, or vancomycin. The results suggest that CT could be employed as a natural antibacterial agent against multidrug-resistant pathogens infection.