Antibacterial activity of flavonoids and their structure-activity relationship: An update review

The Discovery of Potential SARS-CoV-2 Natural Inhibitors among 4924 African Metabolites Targeting the Papain-like Protease: A Multi-Phase In Silico Approach

Four compounds, hippacine, 4,2'-dihydroxy-4'-methoxychalcone, 2',5'-dihydroxy-4-methoxychalcone, and wighteone, were selected from 4924 African natural metabolites as potential inhibitors against SARS-CoV-2 papain-like protease (PLpro, PDB ID: 3E9S). A multi-phased in silico approach was employed to select the most similar metabolites to the co-crystallized ligand (TTT) of the PLpro through molecular fingerprints and structural similarity studies. Followingly, to examine the binding of the selected metabolites with the PLpro (molecular docking. Further, to confirm this binding through molecular dynamics simulations. Finally, in silico ADMET and toxicity studies were carried out to prefer the most convenient compounds and their drug-likeness. The obtained results could be a weapon in the battle against COVID-19 via more in vitro and in vivo studies.

Anti-Inflammatory, Antioxidative, and Nitric Oxide-Scavenging Activities of a Quercetin Nanosuspension with Polyethylene Glycol in LPS-Induced RAW 264.7 Macrophages

Quercetin (Qu) is a dietary antioxidant and a member of flavonoids in the plant polyphenol family. Qu has a high ability to scavenge reactive oxygen species (ROS) and reactive nitrogen species (RNS) molecules; hence, exhibiting beneficial effects in preventing obesity, diabetes, cancer, cardiovascular diseases, and inflammation. However, quercetin has low bioavailability due to poor water solubility, low absorption, and rapid excretion from the body. To address these issues, the usage of Qu nanosuspensions can improve physical stability, solubility, and pharmacokinetics. Therefore, we developed a Qu and polyethylene glycol nanosuspension (Qu-PEG NS) and confirmed its interaction by Fourier transform infrared analysis. Qu-PEG NS did not show cytotoxicity to HaCaT and RAW 264.7 cells. Furthermore, Qu-PEG NS effectively reduced the nitrogen oxide (NO) production in lipopolysaccharide (LPS)-induced inflammatory RAW 264.7 cells. Additionally, Qu-PEG NS effectively lowered the levels of COX-2, NF-κB p65, and IL-1β in the LPS-induced inflammatory RAW 264.7 cells. Specifically, Qu-PEG NS exhibited anti-inflammatory properties by scavenging the ROS and RNS and mediated the inhibition of NF-κB signaling pathways. In addition, Qu-PEG NS had a high antioxidant effect and antibacterial activity against Escherichia coli and Bacillus cereus. Therefore, the developed novel nanosuspension showed comparable antioxidant, anti-inflammatory, and antibacterial functions and may also improve solubility and physical stability compared to raw quercetin.

Antibacterial and Anti-Inflammatory Potential of Chinese Medicinal Herbs: Lonicerae flos, Lonicerae japonicae flos, Scutellaria baicalensis Georgi, and Forsythia suspensa

Chinese herbal medicine (CHM) represents a potent, safe, and efficacious reservoir of treatment options against an array of microbial infections and inflammatory diseases. It has a long history of positive clinical outcomes with minimal or no side effects while enhancing and bolstering the host's protection against infections. With its unique ability to prevent, treat, and manage a wide range of diseased conditions, CHM has been successfully practiced in China for thousands of years. In the modern medical era, where harsh therapeutic drugs and antimicrobial resistance (AMR) present a significant challenge, CHM warrants further exploration. The present review highlights and focuses on 4 major CHM-based herbs, that is, ( Lonicerae flos [ LF] , Lonicerae japonicae flos [ LJF] , Scutellaria baicalensis Georgi [ SBG] , and Forsythia suspensa [ FS]) in terms of their antibacterial and anti-inflammatory efficacies. A detailed literature survey was done by the team using a systematic electronic search from PubMed, Science Direct, Google Scholar, Research Gate, books, etc. This was followed by data collecting, pertinent data extraction, in-depth analysis, and composing the final review. Each herb has been discussed in detail describing its mechanism adopted and the bioactive components involved in alleviating bacterial infections and inflammatory damage. Further, proof of efficacy by detailing the major past studies and major findings has been discussed for each of the 4 herbs. This review will give the scientific community the opportunity to update their knowledge on the subject, which is crucial for heralding the process of bringing CHM-based medicines closer to clinical development given the area of alternative medicine's rapid advancements.

Preparation and Application of Molecularly Imprinted Polymers for Flavonoids: Review and Perspective

The separation and detection of flavonoids from various natural products have attracted increasing attention in the field of natural product research and development. Depending on the high specificity of molecularly imprinted polymers (MIPs), MIPs are proposed as efficient adsorbents for the selective extraction and separation of flavonoids from complex samples. At present, a comprehensive review article to summarize the separation and purification of flavonoids using molecular imprinting, and the employment of MIP-based sensors for the detection of flavonoids is still lacking. Here, we reviewed the general preparation methods of MIPs towards flavonoids, including bulk polymerization, precipitation polymerization, surface imprinting and emulsion polymerization. Additionally, a variety of applications of MIPs towards flavonoids are summarized, such as the different forms of MIP-based solid phase extraction (SPE) for the separation of flavonoids, and the MIP-based sensors for the detection of flavonoids. Finally, we discussed the advantages and disadvantages of the current synthetic methods for preparing MIPs of flavonoids and prospected the approaches for detecting flavonoids in the future. The purpose of this review is to provide helpful suggestions for the novel preparation methods of MIPs for the extraction of flavonoids and emerging applications of MIPs for the detection of flavonoids from natural products and biological samples.

Algerian date palm (Phoenix dactylifera L.) fruit cultivars: HPLC fingerprinting and antibacterial activity

The abusive use of antibiotics causes the destruction of intestinal flora and the proliferation of antibiotic-resistant pathogens. Date palm is used in traditional medicine in the Saharan regions due to its biological properties. The study aimed to identify the phytochemical composition and assess the antibacterial activity of the methanolic extracts of three date cultivars from Algeria. Their total phenolic, flavonoid, and flavonol contents were measured spectrophotometrically. The phytochemical screening was conducted by HPLC fingerprinting using twenty-three pure phenolic compounds as standards. The antibacterial activity against pathogenic bacterial species was assessed using the disk diffusion method. The colorimetric methods showed that the total phenolic, flavonoid, and flavonol contents ranged from 2.13 ± 0.09 to 2.67 ± 0.02 mg GAE/100 g DW, 1.33 ± 0.21 to 1.55 ± 0.13 mg CEQ/100 g DW, and 0.41 ± 0.23 to 0.47 ± 0.05 mg REQ/100 g DW, respectively. HPLC fingerprinting showed that the extracts of date cultivars served as an excellent source of bioactive compounds (gallic acid, tannic acid, ferulic acid, vanillin, caffeine, quercetin, luteolin, rutin, aspegenin, isorhamnetin, and hesperidin). They also exhibited an antibacterial potential with an inhibition zone diameter ranging from 8.40 to 12.50 mm. The results clearly demonstrate the antibacterial potency of date palm fruits, which could be attributed to their considerable content of phenolic compounds such as gallic acid, rutin, quercetin, and luteolin.

Inhibitors of Asexual Reproduction of the Plant Pathogen Phytophthora from Tomato Juice: Structure-Activity Relationships and Transcriptome Analysis

Phytophthora is a genus of fungus-like microorganisms that damages important crops, such as potatoes and tomatoes. Its asexual reproduction, which results in the production of numerous motile zoospores, is the cause of quick and severe outbreaks and crop damage. The search for substances that selectively inhibit the asexual reproduction of Phytophthora led to the isolation of the known natural products naringenin and flazin from tomato juice. They inhibit the sporangia formation of Phytophthora capsici at IC₅₀ values of 8.8 and 7.2 μM. The study of the structure-activity relationship of 11 flavonoids, including naringenin, demonstrated that genistein was the most active (IC₅₀ = 4.6 μM) and flavonols/flavanonols possessing the 3-hydroxy function showed little activity (IC₅₀ = from 100 to >1000 μM). To demonstrate the mechanism of asexual reproduction inhibition by genistein, transcriptome analysis was carried out, which revealed the downregulation of some genes related to cell differentiation. The results suggest that certain flavonoids are environmentally benign agents that could be used to protect agricultural products from Phytophthora pathogens.

New Insights into the Antimicrobial Potential of Polyalthia longifolia-Antibiofilm Activity and Synergistic Effect in Combination with Penicillin against Staphylococcus aureus

Widespread antibiotic resistance has led to the urgent need for the identification of new antimicrobials. Plants are considered a valuable potential resource for new effective antimicrobial compounds. Therefore, in the present study, we focused on the antimicrobial activity of Polyalthia longifolia plants harvested from Cameroon using the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assays. The mechanism of action was investigated by employing fluorescence and scanning electron microscopy. The anti-Staphylococcus aureus activity was studied using biofilm inhibition and checkerboard assays. Our results revealed that the tested extracts possess important antimicrobial activities, notably against Gram positive bacteria (MICs as low as 0.039 mg/mL). P. longifolia leaf extracts exhibited a significant bactericidal effect, with a total kill effect recorded after only 2 h of exposure at concentrations equivalent to MBC (0.078 and 0.156 mg/mL). The extracts showed a synergistic antibacterial activity in combination with penicillin against a MRSA clinical isolate and significantly inhibited S. aureus biofilm formation. The mechanism of action is related to the impairment of cell membrane integrity and cell lysis. All these findings suggest that P. longifolia could be an important source of reliable compounds used to develop new antimicrobials.

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.

Cocktail of isobavachalcone and curcumin enhance eradication of Staphylococcus aureus biofilm from orthopedic implants by gentamicin and alleviate inflammatory osteolysis

Orthopedic device-related infection (ODRI) caused by Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA) biofilm may lead to persist infection and severe inflammatory osteolysis. Previous studies have demonstrated that both isobavachalcone and curcumin possess antimicrobial activity, recent studies also reveal their antiosteoporosis, anti-inflammation, and immunoregulatory effect. Thus, this study aims to investigate whether the combination of isobavachalcone and curcumin can enhance the anti-S. aureus biofilm activity of gentamicin and alleviate inflammatory osteolysis in vivo. EUCAST and a standardized MBEC assay were used to verify the synergy between isobavachalcone and curcumin with gentamicin against planktonic S. aureus and its biofilm in vitro, then the antimicrobial and immunoregulatory effect of cocktail therapy was demonstrated in a femoral ODRI mouse model in vivo by μCT analysis, histopathology, quantification of bacteria in bone and myeloid-derived suppressor cell (MDSC) in bone marrow. We tested on standard MSSA ATCC25923 and MRSA USA300, 5 clinical isolated MSSA, and 2 clinical isolated MRSA strains and found that gentamicin with curcumin (62.5–250 μg/ml) and gentamicin with isobavachalcone (1.56 μg/ml) are synergistic against planktonic MSSA, while gentamicin (128 μg/ml) with curcumin (31.25–62.5, 250–500 μg/ml) and gentamicin (64–128 μg/ml) with isobavachalcone (1.56–12.5 μg/ml) exhibit synergistic effect against MSSA biofilm. Results of further study revealed that cocktail of 128 μg/ml gentamicin together with 125 μg/ml curcumin +6.25 μg/ml isobavachalcone showed promising biofilm eradication effect with synergy against USA300 biofilm in vitro. Daily intraperitoneal administration of 20 mg/kg/day isobavachalcone, 20 mg/kg/day curcumin, and 20 mg/kg/day gentamicin, can reduce inflammatory osteolysis and maintain microarchitecture of trabecular bone during orthopedic device-related MRSA infection in mice. Cocktail therapy also enhanced reduction of MDSC M1 polarization in peri-implant tissue, suppression of MDSC amplification in bone marrow, and Eradication of USA300 biofilm in vivo. Together, these results suggest that the combination of isobavachalcone and curcumin as adjuvants administrated together with gentamicin significantly enhances its antimicrobial effect against S. aureus biofilm, and can also modify topical inflammation in ODRI and protect bone microstructure in vivo, which may serve as a potential treatment strategy, especially for S. aureus induced ODRI.

Total Syntheses and Antibacterial Evaluations of Neocyclomorusin and Related Flavones

Neocyclomorusin (1), a natural bioactive pyranoflavone mainly isolated from plants of the Moraceae family, was synthesized for the first time using a Friedel-Crafts reaction, a Baker-Venkataraman (BK-VK) rearrangement, a selective epoxidation, and a novel SN2-type cyclization as the key steps. The present protocol was also successfully applied for the total synthesis of oxyisocyclointegrin (2). Structurally related natural products morusin (23) and cudraflavone B (24) were also prepared. We investigated the antibacterial activities of these natural compounds against both Gram-negative and Gram-positive strains. The prenylated flavones, morusin (23) and cudraflavone B (24), showed comparable activity to ampicillin and kanacycin A against Staphylococcus aureus. Both morusin (23) and cudraflavone B (24) showed better antibacterial activities than ampicillin against the Gram-positive bacteria Staphylococcus epidermidis and Bacillus subtilis. Both neocyclomorusin (1) and oxyisocyclointegrin (2) displayed disappointing antimicrobial activities against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Bacillus subtilis strains.

Activity of antibacterial phytochemicals and their potential use as natural food preservatives

The risk to human health from bacterial foodborne infection is presently controlled by the addition of antimicrobial preservatives to food. However, the use of chemical preservatives such as sodium nitrite poses a health risk in themselves with concerns around carcinogenic effects. This makes the development of improved preservatives a priority for the food industry. One promising source of novel antimicrobial compounds can be found in nature; phytochemicals, in particular polyphenols are secondary metabolites produced by plants for numerous purposes including antimicrobial defence. There has been significant study of phytochemicals; including quantifying their antimicrobial activity, potential to synergise with current antibiotics and the feasibility of their application as natural food preservatives. However, there remains significant uncertainty about the relative antimicrobial efficacy of different phytochemicals, their mechanisms of action (MOA) and the potential for emergence of bacterial resistance to their effects. This review summarizes recent work relevant to the potential development of phytochemicals as antimicrobial agents.

Recent advances in the antioxidant activity and mechanisms of chalcone derivatives: a computational review

In this review, we have reported the antioxidant mechanisms and structure-antioxidant activity relationship of several chalcone derivatives, investigated in the recent past, based on the density functional theory (DFT) calculations, considering free radical scavenging and metal chelation ability. The antioxidant mechanisms include hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), single electron transfer followed by proton transfer (SET-PT), sequential proton loss hydrogen atom transfer (SPLHAT), sequential double proton loss electron transfer (SdPLET), sequential triple proton loss double electron transfer (StPLdET), sequential triple proton loss triple electron transfer (StPLtET), double HAT, double SPLET, double SET-PT, triple HAT, triple SET-PT, triple SPLET, proton-coupled electron transfer (PCET), single electron transfer (SET), radical adduct formation (RAF) and radical adduct formation followed by hydrogen atom abstraction (RAF-HAA). Furthermore, solvent effects have also been considered using different solvation models. The feasibility of scavenging different reactive oxygen and nitrogen species (ROS/RNS) has been discussed considering various factors such as the number and position of hydroxyl as well as methoxy groups present in the antioxidant molecule, stability of the species formed after scavenging reactive species, nature of substituent, steric effects, etc. This review opens new perspectives for designing new compounds with better antioxidant potential.

Flavonoids as Promising Neuroprotectants and Their Therapeutic Potential against Alzheimer’s Disease

Alzheimer's disease (AD) is one of the serious and progressive neurodegenerative disorders in the elderly worldwide. Various genetic, environmental, and lifestyle factors are associated with its pathogenesis that affect neuronal cells to degenerate over the period of time. AD is characterized by cognitive dysfunctions, behavioural disability, and psychological impairments due to the accumulation of amyloid beta (Aβ) peptides and neurofibrillary tangles (NFT). Several research reports have shown that flavonoids are the polyphenolic compounds that significantly improve cognitive functions and inhibit or delay the amyloid beta aggregation or NFT formation in AD. Current research has uncovered that dietary use of flavonoid-rich food sources essentially increases intellectual abilities and postpones or hinders the senescence cycle and related neurodegenerative problems including AD. During AD pathogenesis, multiple signalling pathways are involved and to target a single pathway may relieve the symptoms but not provides the permanent cure. Flavonoids communicate with different signalling pathways and adjust their activities, accordingly prompting valuable neuroprotective impacts. Flavonoids likewise hamper the movement of obsessive indications of neurodegenerative disorders by hindering neuronal apoptosis incited by neurotoxic substances. In this short review, we briefly discussed about the classification of flavonoids and their neuroprotective properties that could be used as a potential source for the treatment of AD. In this review, we also highlight the structural features of flavonoids, their beneficial roles in human health, and significance in plants as well as their microbial production.

Anticancer and antibacterial flavonoids from the callus of Ampelopsis grossedentata; a new weapon to mitigate the proliferation of cancer cells and bacteria

A new flavonoid angelioue (1) together with five known compounds cuminatanol (2), myricetin (3), epigallocatechin (4), taxifolin (5) and dihydromyricetin (6) was isolated from the callus extract of Ampelopsis grossedentata (Hand.-Mazz.) W. T. Wang and the structures were elucidated based on their detailed spectroscopic data. Among the compounds, the new compound angelioue (1) displayed significant antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) with the MIC value of 6.68 μg mL-1 and MBC value of 53.42 μg mL-1; in contrast the other compounds showed moderate to no antibacterial activity. In addition, known dihydromyricetin (6) exhibited potent cytotoxic activities against mouse breast cancer cells (4T1), human lung adenocarcinoma (A549) and human non-small cell lung cancer (NCI-H1975) tumor cell lines with GI50 values of 17.47, 18.91 and 20.50 μM mL-1, respectively. The compounds 1-5 exhibited low micro-molar inhibitory activities. Moreover, the structure-activity relationships of the most active compounds for antibacterial and cytotoxic activities are discussed. The present findings clearly suggest that the A. grossedentata callus is a good source of bioactive compounds.

Promising Antimycobacterial Activities of Flavonoids against Mycobacterium sp. Drug Targets: A Comprehensive Review

Tuberculosis (TB) caused by the bacterial pathogen Mycobacterium tuberculosis (Mtb) remains a threat to mankind, with over a billion of deaths in the last two centuries. Recent advancements in science have contributed to an understanding of Mtb pathogenesis and developed effective control tools, including effective drugs to control the global pandemic. However, the emergence of drug resistant Mtb strains has seriously affected the TB eradication program around the world. There is, therefore, an urgent need to develop new drugs for TB treatment, which has grown researchers’ interest in small molecule-based drug designing and development. The small molecules-based treatments hold significant potential to overcome drug resistance and even provide opportunities for multimodal therapy. In this context, various natural and synthetic flavonoids were reported for the effective treatment of TB. In this review, we have summarized the recent advancement in the understanding of Mtb pathogenesis and the importance of both natural and synthetic flavonoids against Mtb infection studied using in vitro and in silico methods. We have also included flavonoids that are able to inhibit the growth of non-tubercular mycobacterial organisms. Hence, understanding the therapeutic properties of flavonoids can be useful for the future treatment of TB.

Flavonoids affect the endophytic bacterial community in Ginkgo biloba leaves with increasing altitude

Altitude affects plant growth and metabolism, but the effect of altitude on plant endophytic microorganisms is still unclear. In this study, we selected 16 Ginkgo biloba trees to study the response of leaves' endophytes to flavonoids and altitude (from 530 m to 1,310 m). HPLC results showed that flavonoids in Ginkgo biloba leaves increased by more than 150% with attitude rising from 530 m to 1,310 m, which revealed a positive correlation with altitude. Ginkgo biloba might regulate the increased flavonoids in leaves to resist the increasing light intensity. 16S rDNA sequencing results showed that the endophytic bacterial communities of Ginkgo biloba at different altitudes significantly differed. Ginkgo leaf endophytes' alpha diversity decreased with increasing flavonoids content and altitude. The increased flavonoids might increase the environmental pressure on endophytes and affect the endophytic community in Ginkgo biloba leaves. The bacterial network in Ginkgo biloba leaves became more complex with increasing altitude, which might be one of the strategies of leaf endophytes to cope with increasing flavonoids. Metagenomes results predicted with PICRUSt showed that the abundance of flavonoid biosynthesis and photosynthesis genes were significantly decreased with the increase of flavonoid contents. High flavonoid content in leaves appeared to inhibit microbial flavonoid synthesis. Our findings indicate that altitude can modulate microbial community structure through regulating plant metabolites, which is important to uncovering the interaction of microbes, host and the environment.

Perspectives for Uses of Propolis in Therapy against Infectious Diseases

Propolis has gained wide popularity over the last decades in several parts of the world. In parallel, the literature about propolis composition and biological properties increased markedly. A great number of papers have demonstrated that propolis from different parts of the world is composed mainly of phenolic substances, frequently flavonoids, derived from plant resins. Propolis has a relevant role in increasing the social immunity of bee hives. Experimental evidence indicates that propolis and its components have activity against bacteria, fungi, and viruses. Mechanisms of action on bacteria, fungi, and viruses are known for several propolis components. Experiments have shown that propolis may act synergistically with antibiotics, antifungals, and antivirus drugs, permitting the administration of lower doses of drugs and higher antimicrobial effects. The current trend of growing resistance of microbial pathogens to the available drugs has encouraged the introduction of propolis in therapy against infectious diseases. Because propolis composition is widely variable, standardized propolis extracts have been produced. Successful clinical trials have included propolis extracts as medicine in dentistry and as an adjuvant in the treatment of patients against COVID-19. Present world health conditions encourage initiatives toward the spread of the niche of propolis, not only as traditional and alternative medicine but also as a relevant protagonist in anti-infectious therapy. Production of propolis and other apiary products is environmentally friendly and may contribute to alleviating the current crisis of the decline of bee populations. Propolis production has had social-economic relevance in Brazil, providing benefits to underprivileged people.

The potential of dandelion in the fight against gastrointestinal diseases: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Dandelion (Taraxacum officinale Weber ex F. H. Wigg.), as a garden weed grown globally, has long been consumed as a therapeutic herb. Its folkloric uses include treatments of digestive disorders (dyspepsia, anorexia, stomach disorders, gastritis and enteritis) and associate complex ailments involving uterine, liver and lung disorders.

AIM OF THE STUDY

The present study aims to critically assess the current state of research and summarize the potential roles of dandelion and its constituents in gastrointestinal (GI) -protective actions. A focus is placed on the reported bioactive components, pharmacological activities and modes of action (including molecular mechanisms and interactions among bioactive substances) of dandelion products/preparations and derived active constituents related to GI protection.

MATERIALS AND METHODS

The available information published prior to August 2021 was reviewed via SciFinder, Web of Science, Google Scholar, PubMed, Elsevier, Wiley On-line Library, and The Plant List. The search was based on the ethnomedical remedies, pharmacological activities, bioactive compounds of dandelion for GI protection, as well as the interactions of the components in dandelion with the gut microbiota or biological regulators, and with other ingested bioactive compounds. The key search words were "Taraxacum" and "dandelion".

RESULTS

T. coreanum Nakai, T. mongolicum and T. officinale are the most commonly used species for folkloric uses, with the whole plant, leaves and root of dandelion being used more frequently. GI-protective substances of dandelion include taraxasterol, taraxerol, caffeic acid, chicoric acid, chlorogenic acid, luteolin and its glucosides, polysaccharides, inulin, and β-sitosterol. Dandelion products and derived constituents exhibit pharmacological effects against GI disorders, mainly including dyspepsia, gastroesophageal reflux disease, gastritis, small intestinal ulcer, ulcerative colitis, liver diseases, gallstones, acute pancreatitis, and GI malignancy. The underlying molecular mechanisms may include immuno-inflammatory mechanisms, apoptosis mechanism, autophagy mechanism, and cholinergic mechanism, although interactions of dandelion's constituents with GI health-related biological entities (e.g., GI microbiota and associated biological modulators) or other ingested bioactive compounds shouldn't be ignored.

CONCLUSION

The review reveals some in vivo and in vitro studies on the potential of dandelion derived products as complementary and alternative medicines/therapeutics against GI disorders. The whole herb may alleviate some symptoms related GI immuno-inflammatory basing on the abundant anti-inflammatory and anti-oxide active substances. Dandelion root could be a nontoxic and effective anticancer alternative, owing to its abundant terpenoids and polysaccharides. However, research related to GI protective dandelion-derived products remains limited. Besides the need of identifying bioactive compounds/complexes in various dandelion species, more clinical studies are also required on the metabolism, bioavailability and safety of these substances to support their applications in food, medicine and pharmaceuticals.

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.

Kaempferia parviflora Rhizome Extract as Potential Anti-Acne Ingredient

Kaempferia parviflora (Black ginger) is used widely in medical fields as an anti-microorganism and anti-inflammation. In this study, the aim was to evaluate the in vitro and in vivo anti-acne efficacy of black ginger extract. The results indicate that the methanol and ethanol extracts showed the highest total phenolic contents, without a significant difference, whereas the n-hexane extract showed the highest total flavonoid content. Nine flavones were detected using UPLC−QTOF−MS, and the ethyl acetate extract showed the highest amount of 5,7-dimethoxyflavone (DMF) according to HPLC. Antibacterial activity against Staphylococcus aureus, S. epidermidis, and Cutibacterium acnes was observed. All the extracts showed antimicrobial activity against C. acnes, revealing MICs in the range of 0.015 to 0.030 mg/mL, whereas the ethyl acetate extract inhibited the growth of S. epidermidis with a MIC of 3.84 mg/mL. In addition, the ethyl acetate extract showed the highest activity regarding nitric oxide inhibition (IC50 = 12.59 ± 0.35 µg/mL). The ethyl acetate extract was shown to be safe regarding cell viability at 0.1 mg/mL. The anti-acne efficacy was evaluated on volunteers. The volunteers were treated in two groups: one administered a 0.02% ethyl acetate extract gel-cream (n = 9) and one administered a placebo (n = 9) for 6 weeks. The group treated with the gel-cream containing the extract showed 36.52 and 52.20% decreases in acne severity index (ASI) after 4 and 6 weeks, respectively, and 18.19 and 18.54% decreases in erythema, respectively. The results suggest that K. parviflora could be a potent active ingredient in anti-inflammatory and anti-acne products.

Flavonoid-Rich Fractions of Bauhinia holophylla Leaves Inhibit Candida albicans Biofilm Formation and Hyphae Growth

This study evaluated the effect of the extract and fractions of Bauhinia holophylla on Candida albicans planktonic growth, biofilm formation, mature biofilm, and hyphae growth. Three C. albicans strains (SC5314, ATCC 18804, and ATCC 10231) were tested. The crude extract and the fractions were obtained by exhaustive percolation and liquid–liquid partition, respectively. Phytochemical analyses of B. holophylla extract and fractions were performed using high-performance liquid chromatography coupled with a diode-array detector and mass spectrometry (HPLC-DAD-MS). A microdilution assay was used to evaluate the effect of the B. holophylla extract and fractions on C. albicans planktonic growth, and crystal violet staining was used to measure the total biomass of the biofilm. Hyphae growth was analyzed using light microscopy. Thirteen flavonoids were identified, with a predominance of the flavonol-3-O-glycoside type based on quercetin, myricetin, and kaempferol. Flavonoid-rich fractions of B. holophylla leaves displayed antifungal activity and inhibited both biofilm formation and hyphae growth in all the tested strains, but were not effective on C. albicans planktonic growth and mature biofilm. This study indicates that flavonoid-rich fractions from B. holophylla leaves interfere with the virulence of Candida species and support the use of Bauhinia spp. in folk medicine to treat infections.

A cellulose nanofibril-reinforced hydrogel with robust mechanical, self-healing, pH-responsive and antibacterial characteristics for wound dressing applications

Background

Bacterial infection in wounds has become a major threat to human life and health. With the growth use of synthetic antibiotics and the elevated evolution of drug resistant bacteria in human body cells requires the development of novel wound curing strategies. Herein, a novel pH-responsive hydrogel (RPC/PB) was fabricated using poly(vinyl alcohol)-borax (PB) and natural antibiotic resveratrol grafted cellulose nanofibrils (RPC) for bacterial-infected wound management.

Results

In this hydrogel matrix, RPC conjugate was interpenetrated in the PB network to form a semi-interpenetrating network that exhibited robust mechanical properties (fracture strength of 149.6 kPa), high self-healing efficiency (> 90%), and excellent adhesion performance (tissue shear stress of 54.2 kPa). Interestingly, the induced RPC/PB hydrogel showed pH-responsive drug release behavior, the cumulative release amount of resveratrol in pH 5.4 was 2.33 times than that of pH 7.4, which was adapted well to the acidic wound microenvironment. Additionally, this RPC/PB hydrogel exhibited excellent biocompatibility and antioxidant effect. Moreover, in vitro and in vivo results revealed that such RPC/PB hydrogel had excellent antibacterial, skin tissue regeneration and wound closure capabilities.

Conclusion

Therefore, the generated RPC/PB hydrogel could be an excellent wound dressing for bacteria-infected wound healing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01523-5.

The Content of Phenolic Compounds and Mineral Elements in Edible Nuts

Edible nuts are an important component of a healthy diet, and their frequent consumption has beneficial impact on human health, including reducing the risk of cardiovascular and neurodegenerative diseases. Moreover, various factors, including cultivar, climate, soil characteristic, storage and treatment have influence on the chemical composition of nuts. Therefore, nine tree nut types and peanuts commonly available on Polish market were evaluated for phenolic profile and mineral elements content. The concentration of individual phenolic compounds, including flavonoids, aromatic acids and caffeic acid phenethyl ester (CAPE) was determined by ultra-high pressure liquid chromatography, while the content of macro-elements and trace minerals was analyzed by atomic absorption spectrometry. The phenolic profile of analyzed nuts substantially varied depending on the type of nut. The highest total content of all analyzed flavonoids was determined in walnuts (114.861 µg/g), while the lowest in almonds (1.717 µg/g). In turn, the highest total content of all tested aromatic acid was determined in pecans (33.743 µg/g), and the lowest in almonds (0.096 µg/g). Epicatechin and cinnamic acid were detected in the highest concentration in tested nuts. Moreover, in examined nuts (except walnuts and Brazil nuts), the presence of CAPE was confirmed. The tested nuts were also characterized by wide variation in element concentrations. Almonds contained high concentration of macro-elements (13,111.60 µg/g), while high content of trace elements was determined in pine nuts (192.79 µg/g). The obtained results indicate that the tested nuts are characterized by a significant diversity in the content of both phenolic compounds and minerals. However, all types of nuts, apart from the well-known source of fatty acids, are a rich source of various components with beneficial effect on human health.

Sustainable dyeing of wool yarns with renewable sources

Medical and healthcare fabrics are one of the most important fields in the textile industries worldwide. They are essential in all medical fields, especially where hygiene is required. Also, it is imperative to keep the ecosystem safe up to a great extent and also produce natural-based goods. Natural dyeing with plant sources can be claimed to be an excellent environmentally friendly procedure for providing healthcare fabrics. In this study, date seeds and Zenian were used as an eco-friendly mordant and dye, respectively, for dyeing wool yarns. Date seeds pre-treated wool yarns were dyed with the methanolic extract of Zenian by the exhaustion process at the optimum dyeing conditions of dye concentration 40 g/L, pH = 4, time = 45 min, and temperature 90 °C. The pre-treating of wool yarns with date seeds not only improved the dyeability of the samples but also enhanced the colorfastness to washing and light exposure. The results also show that the pre-treated and dyed samples have effective antibacterial activity against microorganism strains. Moreover, the data confirmed the dye bath obtained from the extract of Zenian does not represent a high environmentally polluting effect, and the elaborated dyeing process enables to reduce the biological oxygen demand (BOD) and chemical oxygen demand (COD) removal values significantly. The knowledge obtained from this work presents an appropriate promising foundation for the high-added-value application of agricultural waste products.

Tackling Multiple-Drug-Resistant Bacteria With Conventional and Complex Phytochemicals

Emerging antibiotic resistance in bacteria endorses the failure of existing drugs with chronic illness, complicated treatment, and ever-increasing expenditures. Bacteria acquire the nature to adapt to starving conditions, abiotic stress, antibiotics, and our immune defense mechanism due to its swift evolution. The intense and inappropriate use of antibiotics has led to the development of multidrug-resistant (MDR) strains of bacteria. Phytochemicals can be used as an alternative for complementing antibiotics due to their variation in metabolic, genetic, and physiological fronts as well as the rapid evolution of resistant microbes and lack of tactile management. Several phytochemicals from diverse groups, including alkaloids, phenols, coumarins, and terpenes, have effectively proved their inhibitory potential against MDR pathogens through their counter-action towards bacterial membrane proteins, efflux pumps, biofilms, and bacterial cell-to-cell communications, which are important factors in promoting the emergence of drug resistance. Plant extracts consist of a complex assortment of phytochemical elements, against which the development of bacterial resistance is quite deliberate. This review emphasizes the antibiotic resistance mechanisms of bacteria, the reversal mechanism of antibiotic resistance by phytochemicals, the bioactive potential of phytochemicals against MDR, and the scientific evidence on molecular, biochemical, and clinical aspects to treat bacterial pathogenesis in humans. Moreover, clinical efficacy, trial, safety, toxicity, and affordability investigations, current status and developments, related demands, and future prospects are also highlighted.

Antibacterial Modes of Herbal Flavonoids Combat Resistant Bacteria

The increasing dissemination of multidrug resistant (MDR) bacterial infections endangers global public health. How to develop effective antibacterial agents against resistant bacteria is becoming one of the most urgent demands to solve the drug resistance crisis. Traditional Chinese medicine (TCM) with multi-target antibacterial actions are emerging as an effective way to combat the antibacterial resistance. Based on the innovative concept of organic wholeness and syndrome differentiation, TCM use in antibacterial therapies is encouraging. Herein, advances on flavonoid compounds of heat-clearing Chinese medicine exhibit their potential for the therapy of resistant bacteria. In this review, we focus on the antibacterial modes of herbal flavonoids. Additionally, we overview the targets of flavonoid compounds and divide them into direct-acting antibacterial compounds (DACs) and host-acting antibacterial compounds (HACs) based on their modes of action. We also discuss the associated functional groups of flavonoid compounds and highlight recent pharmacological activities against diverse resistant bacteria to provide the candidate drugs for the clinical infection.

Analyses on Flavonoids and Transcriptome Reveals Key MYB Gene for Proanthocyanidins Regulation in Onobrychis Viciifolia

Onobrychis viciifolia (sainfoin) is one of the most high-quality legume forages, which is rich in proanthocyanidins that is beneficial for the health and production of animals. In this study, proanthocyanidins and total flavonoids in leaves of 46 different sainfoin germplasm resources were evaluated, and it showed that soluble proanthocyanidin contents varied greatly in these sainfoin germplasm resources, but total flavonoids did not show significant difference. Transcriptome sequencing with high and low proanthocyanidins sainfoin resulted in the identification of totally 52,926 unigenes in sainfoin, and they were classed into different GOC categories. Among them, 1,608 unigenes were differentially expressed in high and low proanthocyanidins sainfoin samples, including 1,160 genes that were upregulated and 448 genes that were downregulated. Analysis on gene enrichment via KEGG annotation revealed that the differentially expressed genes were mainly enriched in the phenylpropanoid biosynthetic pathway and the secondary metabolism pathway. We also analyzed the expression levels of structural genes of the proanthocyanidin/flavonoid pathway in roots, stems, and leaves in the high proanthocyanidin sainfoin via RT-qPCR and found that these genes were differentially expressed in these tissues. Among them, the expression levels of F3'5'H and ANR were higher in leaves than in roots or stems, which is consistent with proanthocyanidins content in these tissues. Among MYB genes that were differentially expressed, the expression of OvMYBPA2 was relatively high in high proanthocyanidin sainfoin. Over-expression level of OvMYBPA2 in alfalfa hairy roots resulted in decreased anthocyanin content but increased proanthocyanidin content. Our study provided transcriptome information for further functional characterization of proanthocyanidin biosynthesis-related genes in sainfoin and candidate key MYB genes for bioengineering of proanthocyanidins in plants.

Discovery of Quercetin and Its Analogs as Potent OXA-48 Beta-Lactamase Inhibitors

Carbapenem resistance in Enterobacteriaceae caused by OXA-48 β-lactamase is a growing global health threat and has rapidly spread in many regions of the world. Developing inhibitors is a promising way to overcome antibiotic resistance. However, there are few options for problematic OXA-48. Here we identified quercetin, fisetin, luteolin, 3′,4′,7-trihydroxyflavone, apigenin, kaempferol, and taxifolin as potent inhibitors of OXA-48 with IC₅₀ values ranging from 0.47 to 4.54 μM. Notably, the structure-activity relationship revealed that the substitute hydroxyl groups in the A and B rings of quercetin and its structural analogs improved the inhibitory effect against OXA-48. Mechanism studies including enzymatic kinetic assay, isothermal titration calorimetry (ITC), and surface plasmon resonance (SPR) analysis demonstrated that quercetin reversibly inhibited OXA-48 through a noncompetitive mode. Molecular docking suggested that hydroxyl groups at the 3′, 4′ and 7 positions in flavonoids formed hydrogen-bonding interactions with the side chains of Thr209, Ala194, and Gln193 in OXA-48. Quercetin, fisetin, luteolin, and 3′,4′,7-trihydroxyflavone effectively restored the antibacterial efficacy of piperacillin or imipenem against E. coli producing OXA-48, resulting in 2–8-fold reduction in MIC. Moreover, quercetin combined with piperacillin showed antimicrobial efficacy in mice infection model. These studies provide potential lead compounds for the development of β-lactamase inhibitors and in combination with β-lactams to combat OXA-48 producing pathogen.

Flavonoids as biopesticides - Systematic assessment of sources, structures, activities and environmental fate

Biopesticides obtained from renewable resources and associated with biodegradability have the potential to address resource limitations and environmental pollution, often caused by many conventional pesticides, due to the facility of natural products to run in natural nutrient cycles. Flavonoids are considered benign substitutes for pesticides, however, little comprehensive information of their pesticidal activities and critical evaluation of their associated advantages is available. Therefore, this systematic review assessed sources, structures, activities and the environmental fate of flavonoids on a basis of 201 selected publications. We identified 281 different flavonoids that were investigated for their pesticidal activity as either a pure compound or a flavonoid-containing extract, with quercetin, kaempferol, apigenin, luteolin and their glycosides as the most studied compounds. Agricultural or food waste, a potential sustainable source for flavonoids, represent 10.6% of the plant sources of flavonoids within these studies, showing the currently underutilization of these preferable feedstocks. Analysis of pesticidal activities and target organisms revealed a broad target spectrum for the class of flavonoids, including fungi, insects, plants, bacteria, algae, nematodes, molluscs and barnacles. Little information is available on the environmental fate and biodegradation of flavonoids, and a connection to studies investigating pesticidal activities is largely missing. Emerging from these findings is the need for comprehensive understanding of flavonoids pesticidal activities with emphasis on structural features that influence activity and target specificity to avoid risks for non-target organisms. Only if the target spectrum and environmental fate of a potential biopesticide are known it can serve as a benign substitute. Then, flavonoids can be integrated in a valorization process of agricultural and food waste shifting the extract-produce-consume linear chain to a more circular economy.

Hesperidin: A Review on Extraction Methods, Stability and Biological Activities

Hesperidin is a bioflavonoid occurring in high concentrations in citrus fruits. Its use has been associated with a great number of health benefits, including antioxidant, antibacterial, antimicrobial, anti-inflammatory and anticarcinogenic properties. The food industry uses large quantities of citrus fruit, especially for the production of juice. It results in the accumulation of huge amounts of by-products such as peels, seeds, cell and membrane residues, which are also a good source of hesperidin. Thus, its extraction from these by-products has attracted considerable scientific interest with aim to use as natural antioxidants. In this review, the extraction and determination methods for quantification of hesperidin in fruits and by-products are presented and discussed as well as its stability and biological activities.

Synthesis of Coumarin and Homoisoflavonoid Derivatives and Analogs: The Search for New Antifungal Agents

A set of twenty-four synthetic derivatives, with coumarin and homoisoflavonoid cores and structural analogs, were submitted for evaluation of antifungal activity against various species of Candida. The broth microdilution test was used to determine the Minimum Inhibitory Concentration (MIC) of the compounds and to verify the possible antifungal action mechanisms. The synthetic derivatives were obtained using various reaction methods, and six new compounds were obtained. The structures of the synthesized products were characterized by FTIR spectroscopy: ¹H-NMR, ¹³C-NMR, and HRMS. The coumarin derivative 8 presented the best antifungal profile, suggesting that the pentyloxy substituent at the C-7 position of coumarin ring could potentiate the bioactivity. Compound 8 was then evaluated against the biofilm of C. tropicalis ATCC 13803, which showed a statistically significant reduction in biofilm at concentrations of 0.268 µmol/mL and 0.067 µmol/mL, when compared to the growth control group. For a better understanding of their antifungal activity, compounds 8 and 21 were submitted to a study of the mode of action on the fungal cell wall and plasma membrane. It was observed that neither compound interacted directly with ergosterol present in the fungal plasma membrane or with the fungal cell wall. This suggests that their bioactivity was due to interaction involving other pharmacological targets. Compound 8 was also subjected to a molecular modeling study, which showed that its antifungal action mechanism occurred mainly through interference in the redox balance of the fungal cell, and by compromising the plasma membrane; not by direct interaction, but by interference in ergosterol synthesis. Another important finding was the antifungal capacity of homoisoflavonoids 23 and 24. Derivative 23 presented slightly higher antifungal activity, possibly due to the presence of the methoxyl substituent in the meta position in ring B.

Experimental and computational studies on the mechanism of the β-lactoglobulin-derived peptide inhibiting the antigenicity of β-lactoglobulin

In this study, through a combined simulated enzymolysis-molecular docking-molecular simulation-activity determination-action mechanism strategy, we screened a β-LG-derived peptide (VAGTWYSL) to inhibit the antigenicity of β-LG and explored its mechanism of action. Our results indicate that the inhibitory effect of the peptide on the antigenicity of β-LG is affected by different experimental conditions, including pH, reaction time and concentration. Three factors may contribute to the reduced allergenicity of β-LG. First, there must be sufficient forces between the peptide and β-LG, as a result, hydrophobic forces and hydrogen bonds are the main forces to maintain the structural stability of the complex. Second, the binding of the peptide changes the secondary structure of β-LG, especially with an increase in α-helices and a decrease in β-turns. Third, the peptide binds to the hydrophobic region of β-LG, involving the antigenic epitope region Val41-Lys60, which may reduce the antigenicity.

Bioinformatics analysis of amino acid decarboxylases related to four major biogenic amines in pickles

Microbial amino acid decarboxylases (AADs) produce biogenic amines (BAs) in fermented food. However, a systematic comparison of the AADs' properties from different microorganisms in pickle fermentation remains unexplored. Here, we bioinformatically analyzed the amino acid sequences of AADs corresponding to four major BAs for common microorganisms in pickle fermentation. We showed that their sequences, besides tyrosine decarboxylase, differed among microorganisms. Overall, the AAD sequences varied lesser among bacterial species than between bacteria and fungi, with those in Lactobacillus sharing occasionally high similarity with other bacteria. Most AADs were predicted as stable cytosolic endoenzymes. Molecular docking showed that most commonly used spice components in pickle production, especially pepper, chili, and ginger, strongly bind to the AAD active sites, thus may inhibit the enzymes and reduce the BA accumulation. This study provides insights for deeply understanding the different microbial AAD properties in pickle fermentation and reducing BAs by appropriately using spices.

Alterations in Epiphytic Bacterial Communities during the Occurrence of Green Rot Disease in Saccharina japonica Seedlings

Bacteria are one of the causes of green rot disease (GRD) in Saccharina japonica mariculture, which may lead to complete failure of seedling production. However, the association between bacterial community and host disease severity remains largely unknown. Therefore, in this study, the bacterial communities associated with GRD-infected seedlings with naturally varying disease severity from two seedling hatcheries in Northern China were analyzed to investigate the interactions between bacterial communities and GRD. The results indicated incorrect nutrient supply in both sites. Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes were prevalent in all samples. Significant structural alterations were detected for epibacterial communities, which were further evidenced by differently abundant bacterial taxa associated with seedlings with varying disease severity. The predicted pathways of bacterial adhesion and antimicrobial compounds biosynthesis were significantly enriched in less severely diseased seedlings, whereas glutathione metabolism and lipopolysaccharide biosynthesis were significantly increased in more severely diseased seedlings. The predicted categories of a two-component system, flagellar assembly, bacterial chemotaxis, and biofilm formation were significantly enriched in the bacterioplankton in more severely infected seawater. The differential bacterial community compositions and predicted functions provide new clues to elucidate the mechanism underlying the interaction between GRD occurrence and bacterial communities.

Study on the formation and stability of polyol-in-oil emulsion

In this study, the influence of polyols, emulsifiers and oils on the formation and stability of polyol-in-oil (P/O) emulsions was investigated. The interfacial tension in P/O systems is much lower than that of water-oil systems, so polyols and oils showed a greater affinity, which was not conducive to the stability of the emulsion system. High compatibility of the emulsifier and the inner and outer phases was the key to the formation of stable emulsions. Using polyethylene glycol 400 (PEG) as polyol phase, mineral oil or squalane as oil phase and cetyl PEG/PPG-10/1 dimethicone (EM 90) as emulsifier, long-term stable P/O emulsions with homogeneous droplets were successfully prepared.

Inhibition of Escherichia coli ATP synthase and cell growth by dietary pomegranate phenolics

Historically, people have been using pomegranate to alleviate many disease conditions. Pomegranate is known for its antiinflammatory, antioxidant, neuroprotective, anticancer, and antibacterial properties. In the current study, we examined effects of 8 dietary phenolics present in pomegranate (DPPs)-cyanidin-3-glucoside, cyanin chloride, delphinidin-3-glucoside, delphinidin-3,5-diglucoside, pelargonidin-3-glucoside, pelargonin chloride, punicalagin, and punicalin-on Escherichia coli ATP synthase and cell growth. DPPs caused complete or near complete (89%-100%) inhibition of wild-type E. coli ATP synthase and partial (5%-64%) inhibition of mutant enzymes αR283D, αE284R, βV265Q, and γT273A. Growth inhibition of wild-type, null, and mutant strains in the presence of DPPs were lower than that of isolated wild-type and mutant ATP synthase. On a molar scale, cyanin chloride was the most potent, and pelargonidin-3-glucoside was the least effective inhibitor of wild-type ATP synthase. Partial inhibition of mutant enzymes confirmed that αR283D, αE284R, βV265Q, and γT273A are essential in the formation of the phytochemical binding site. Our results establish that DPPs are potent inhibitors of wild-type E. coli ATP synthase and that the antimicrobial nature of DPPs can be associated with the binding and inhibition of microbial ATP synthase. Additionally, selective inhibition of microbial ATP synthase by DPPs is a useful method to combat antimicrobial resistance.

Bee Pollen Extracts: Chemical Composition, Antioxidant Properties, and Effect on the Growth of Selected Probiotic and Pathogenic Bacteria

This paper evaluated the chemical and biological properties of bee pollen samples from Romania. Firstly, the bee pollen alcoholic extracts (BPEs) were obtained from raw bee pollen harvested by Apis mellifera carpatica bees. The chemical composition of BPE was obtained by determination of total phenol content and total flavonoid content, UHPLC-DAD-ESI/MS analysis of phenolic compounds, and GC-MS analysis of fatty acids, esters, and terpenes. Additionally, the antioxidant activity was evaluated by the Trolox Equivalent Antioxidant Capacity method. Furthermore, the biological properties of BPE were evaluated (antimicrobial and cytotoxic activity). The raw BP samples studied in this paper had significant phenolic acid and flavonoid content, and moderate fatty acid, ester, and terpene content. P1, P2, and P4 have the highest TPC and TFC levels, and the best antioxidant activity. All BPEs studied had antimicrobial activity on pathogenic strains isolated from the clinic or standard strains. A synergistic antimicrobial effect of the BPEs was observed along with the soluble compounds of L. rhamnosus MF9 and E. faecalis 2M17 against some pathogenic (clinical) strains and, considering the tumour proliferation inhibitory activity, makes BP a potential prebiotic and antitumour agent for the gut environment.

New red-fleshed apple cultivars: a comprehensive review of processing effects, (poly)phenol bioavailability and biological effects

Red-fleshed apple cultivars with an enhanced content of anthocyanins have recently attracted the interest of apple producers and consumers due to their attractive color and promising added health benefits. In this paper, we provide the first comprehensive overview of new hybrid red-fleshed apples, mainly focusing on their (poly)phenolic composition, the effect of processing, the (poly)phenolic bioavailability and the biological effects. Evidence so far from in vitro and in vivo studies supports their added beneficial effects compared to common apples on health outcomes such as cancer, cardiovascular disease, inflammation and immune function, which are mainly related to their specific (poly)phenol composition.

Recent Advancements in Enhancing Antimicrobial Activity of Plant-Derived Polyphenols by Biochemical Means

Plants are a reservoir of phytochemicals, which are known to possess several beneficial health properties. Along with all the secondary metabolites, polyphenols have emerged as potential replacements for synthetic additives due to their lower toxicity and fewer side effects. However, controlling microbial growth using these preservatives requires very high doses of plant-derived compounds, which limits their use to only specific conditions. Their use at high concentrations leads to unavoidable changes in the organoleptic properties of foods. Therefore, the biochemical modification of natural preservatives can be a promising alternative to enhance the antimicrobial efficacy of plant-derived compounds/polyphenols. Amongst these modifications, low concentration of ascorbic acid (AA)–Cu (II), degradation products of ascorbic acid (DPAA), Maillard reaction products (MRPs), laccase–mediator (Lac–Med) and horse radish peroxidase (HRP)–H2O2 systems standout. This review reveals the importance of plant polyphenols, their role as antimicrobial agents, the mechanism of the biochemical methods and the ways these methods may be used in enhancing the antimicrobial potency of the plant polyphenols. Ultimately, this study may act as a base for the development of potent antimicrobial agents that may find their use in food applications.

Phytochemical Profile of Antibacterial Agents from Red Betel Leaf (Piper crocatum Ruiz and Pav) against Bacteria in Dental Caries

Based on data from The Global Burden of Disease Study in 2016, dental and oral health problems, especially dental caries, are a disease experienced by almost half of the world’s population (3.58 billion people). One of the main causes of dental caries is the pathogenesis of Streptococcus mutans. Prevention can be achieved by controlling S. mutans using an antibacterial agent. The most commonly used antibacterial for the treatment of dental caries is chlorhexidine. However, long-term use of chlorhexidine has been reported to cause resistance and some side effects. Therefore, the discovery of a natural antibacterial agent is an urgent need. A natural antibacterial agent that can be used are herbal medicines derived from medicinal plants. Piper crocatum Ruiz and Pav has the potential to be used as a natural antibacterial agent for treating dental and oral health problems. Several studies reported that the leaves of P. crocatum Ruiz and Pav contain secondary metabolites such as essential oils, flavonoids, alkaloids, terpenoids, tannins, and phenolic compounds that are active against S. mutans. This review summarizes some information about P. crocatum Ruiz and Pav, various isolation methods, bioactivity, S. mutans bacteria that cause dental caries, biofilm formation mechanism, antibacterial properties, and the antibacterial mechanism of secondary metabolites in P. crocatum Ruiz and Pav.

Antioxidants of Fruit Extracts as Antimicrobial Agents against Pathogenic Bacteria

Fruit is an essential part of the human diet and is of great interest because of its richness in phytochemicals. Various fruit extracts from citrus, berries and pomegranates have been shown to possess a broad spectrum of medicinal properties. Fruit phytochemicals are of considerable interest because of their antioxidant properties involving different mechanisms of action, which can act against different pathogenic bacteria. The antioxidant capacity of fruit phytochemicals involves different kinds of reactions, such as radical scavenging and chelation or complexation of metal ions. The interaction between fruit phytochemicals and bacteria has different repercussions: it disrupts the cell envelope, disturbs cell-cell communication and gene regulation, and suppresses metabolic and enzymatic activities. Consequently, fruit phytochemicals can directly inhibit bacterial growth or act indirectly by modulating the expression of virulence factors, both of which reduce microbial pathogenicity. The aim of this review was to report our current knowledge on various fruit extracts and their major bioactive compounds, and determine the effectiveness of organic acids, terpenes, polyphenols, and other types of phenolic compounds with antioxidant properties as a source of antimicrobial agents.

Phenolics as GABAA Receptor Ligands: An Updated Review

Natural products can act as potential GABA modulators, avoiding the undesirable effects of traditional pharmacology used for the inhibition of the central nervous system such as benzodiazepines (BZD). Phenolics, especially flavonoids and phlorotannins, have been considered as modulators of the BZD-site of GABA_A receptors (GABA_ARs), with sedative, anxiolytic or anticonvulsant effects. However, the wide chemical structural variability of flavonoids shows their potential action at more than one additional binding site on GABA_ARs, which may act either negatively, positively, by neutralizing GABA_ARs, or directly as allosteric agonists. Therefore, the aim of the present review is to compile and discuss an update of the role of phenolics, namely as pharmacological targets involving dysfunctions of the GABA system, analyzing both their different compounds and their mechanism as GABAergic modulators. We focus this review on articles written in English since the year 2010 until the present. Of course, although more research would be necessary to fully establish the type specificity of phenolics and their pharmacological activity, the evidence supports their potential as GABA_AR modulators, thereby favoring their inclusion in the development of new therapeutic targets based on natural products. Specifically, the data compiled in this review allows for the directing of future research towards ortho-dihydroxy diterpene galdosol, the flavonoids isoliquiritigenin (chalcone), rhusflavone and agathisflavone (biflavonoids), as well as the phlorotannins, dieckol and triphlorethol A. Clinically, flavonoids are the most interesting phenolics due to their potential as anticonvulsant and anxiolytic drugs, and phlorotannins are also of interest as sedative agents.

Identification of a candidate gene responsible for the G locus determining chartreuse bulb color in onion (Allium cepa L.) using bulked segregant RNA-Seq

A gene encoding a laccase responsible for chartreuse onion bulb color was identified. Markers tagging this gene showed perfect linkage with bulb colors among diverse germplasm. To identify a casual gene for the G locus determining chartreuse bulb color in onion (Allium cepa L.), bulked segregant RNA-Seq (BSR-Seq) was performed using yellow and chartreuse individuals of a segregating population. Through single nucleotide polymorphism (SNP) and differentially expressed gene (DEG) screening processes, 163 and 143 transcripts were selected, respectively. One transcript encoding a laccase-like protein was commonly identified from SNP and DEG screening. This transcript contained four highly conserved copper-binding domains known to be signature sequences of laccases. This gene was designated AcLAC12 since it showed high homology with Arabidopsis AtLAC12. A 4-bp deletion creating a premature stop codon was identified in exon 5 of the chartreuse allele. Another mutant allele in which an intact LTR-retrotransposon was transposed in exon 5 was identified from other chartreuse breeding lines. Genotypes of molecular markers tagging AcLAC12 were perfectly matched with bulb color phenotypes in segregating populations and diverse breeding lines. All chartreuse breeding lines contained inactive alleles of DFR-A gene determining red bulb color, indicating that chartreuse color appeared when both DFR-A and AcLAC12 genes were inactivated. Linkage maps showed that AcLAC12 was positioned at the end of chromosome 7. Transcription levels of structural genes encoding enzymes in anthocyanin biosynthesis pathway were generally reduced in chartreuse bulk compared with yellow bulk. Concentrations of total quercetins were also reduced in chartreuse onion. However, significant amounts of quercetins were detected in chartreuse onion, implying that AcLAC12 might be involved in modification of quercetin derivatives in onion.

The antibacterial activity of natural-derived flavonoids

Flavonoids, a wide variety of phenolic secondary metabolites, are found in almost all plant families in the leaves, stems, roots, flowers, and seeds. Flavonoids could exert antibacterial activity via damaging the cytoplasmic membrane, inhibiting energy metabolism, and inhibiting the synthesis of nucleic acids, so flavonoids are considered constitutive antibacterial substances. This review aims to outline the recent advances of natural-derived flavonoids, including flavonoid glycosides with antibacterial potential to provide novel antibacterial lead hits/candidates, covering articles published between January 2016 and July 2021.

Comparative Assessment of the Antibacterial Efficacies and Mechanisms of Different Tea Extracts

Tea is a popular beverage known for its unique taste and vast health benefits. The main components in tea change greatly during different processing methods, which makes teas capable of having different biological activities. We compared the antibacterial activity of four varieties of tea, including green, oolong, black, and Fuzhuan tea. All tea extracts showed antibacterial activity and Gram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus) were more susceptible to tea extracts than Gram-negative bacteria (Escherichia coli and Salmonella typhimurium). Green tea extracts inhibited bacterial pathogens much more effectively in all four varieties of tea with the minimum inhibitory concentration (MIC) values at 20 mg/mL, 10 mg/mL, 35 mg/mL, and 16 mg/mL for E. faecalis, S. aureus, E. coli, and S. typhimurium, respectively. Catechins should be considered as the main antibiotic components of the four tea extracts. Total catechins were extracted from green tea and evaluated their antibacterial activity. Additional studies showed that the catechins damaged the cell membrane and increased cell membrane permeability, leading to changes in the relative electrical conductivity and the release of certain components into the cytoplasm. Tea extracts, especially green tea extracts, should be considered as safe antibacterial food additives.