Naturally occurring phenolic antibacterial compounds show effectiveness against oral bacteria by a quantitative structure-activity relationship study

Glycolysis and Automated Plaque Regrowth Method for Evaluation of Antimicrobial Performance

PURPOSE

This study explored the potential of a new in vitro method in evaluating antiplaque benefits from five sets of antimicrobial systems including cetylpyridinium chloride (CPC), stannous fluoride (SnF2), Listerine essential oil mouthwashes (+/- alcohol), zinc chloride (ZnCl2), and sodium fluoride. (NaF).

METHODS

Gingival dental plaque was collected and propagated using sterilized tryptic soy broth and sucrose, and then allocated into separate glycolysis and regrowth recipes for antiplaque evaluations. Glycolysis measurements (in duplicate) were recorded via pH microelectrode on plaque-treatment samples thermomixed (1200 rpm, 37 °C) for 4 h. For plaque regrowth, optical densities (in duplicate) were automatically collected on plaque-treatment samples using a microplate reader (linear shaking, 37 °C) from baseline to 4 h.

RESULTS

Calculations of percent change in pH and optical density were performed and analyzed for each set of antimicrobial treatment groups. Statistical analysis (one-way ANOVA, Student-Newman-Keuls stepwise comparison tests) revealed dose responses and significant differences (p < 0.05) among treatment groups, including between negative and clinically relevant positive controls.

CONCLUSIONS

This lab method produces results consistent with published clinical observations. This glycolysis and plaque growth method is sensitive to antimicrobial mechanisms of action, and may offer a convenient and clinically relevant screening tool in the evaluation of putative antimicrobial agents and formulations.

Recent advances in oxidative phenol coupling for the total synthesis of natural products

Covering: 2008 to 2023This review will describe oxidative phenol coupling as applied in the total synthesis of natural products. This review covers catalytic and electrochemical methods with a brief comparison to stoichiometric and enzymatic systems assessing their practicality, atom economy, and other measures. Natural products forged by C-C and C-O oxidative phenol couplings as well as from alkenyl phenol couplings will be addressed. Additionally, exploration into catalytic oxidative coupling of phenols and other related species (carbazoles, indoles, aryl ethers, etc.) will be surveyed. Future directions of this particular area of research will also be assessed.

Reticular framework materials for photocatalytic organic reactions

Photocatalytic organic reactions, harvesting solar energy to produce high value-added organic chemicals, have attracted increasing attention as a sustainable approach to address the global energy crisis and environmental issues. Reticular framework materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are widely considered as promising candidates for photocatalysis owing to their high crystallinity, tailorable pore environment and extensive structural diversity. Although the design and synthesis of MOFs and COFs have been intensively developed in the last 20 years, their applications in photocatalytic organic transformations are still in the preliminary stage, making their systematic summary necessary. Thus, this review aims to provide a comprehensive understanding and useful guidelines for the exploration of suitable MOF and COF photocatalysts towards appropriate photocatalytic organic reactions. The commonly used reactions are categorized to facilitate the identification of suitable reaction types. From a practical viewpoint, the fundamentals of experimental design, including active species, performance evaluation and external reaction conditions, are discussed in detail for easy experimentation. Furthermore, the latest advances in photocatalytic organic reactions of MOFs and COFs, including their composites, are comprehensively summarized according to the actual active sites, together with the discussion of their structure-property relationship. We believe that this study will be helpful for researchers to design novel reticular framework photocatalysts for various organic synthetic applications.

Magnolia officinalis L. bark extract and respiratory diseases: From traditional Chinese medicine to western medicine via network target

The understanding of the use of Magnolia officinalis L. (Magnoliaceae) as a possible dietary supplement for supporting the treatment of airway pathologies might be of clinical interest. Two commercially available bark extracts (M. officinalis extract [MOE]) were characterized by quantitation in honokiol and magnolol content by means of high-performance liquid chromatography with UV detection. MOE effects, as well as those of the reference compounds per se, on some targets connected to airway pathologies (antibacterial- and lung and trachea relaxing- activities) were investigated. Results showed that MOE possessed interesting antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pneumoniae. This was accompanied by a spasmolytic and antispasmodic activity, possibly owing to its ability to concurrently modulate different targets such as H₁ -, β₂ - and muscarinic receptors and l-type calcium channels involved in bronchodilation. All these effects were directly related to the MOE content in honokiol and magnolol. In conclusion, the properties of MOE highlighted here strongly encourage its application as dietary supplement in the treatment of airway diseases.

High value valorization of lignin as environmental benign antimicrobial

Lignin is a natural aromatic polymer of p-hydroxyphenylpropanoids with various biological activities. Noticeably, plants have made use of lignin as biocides to defend themselves from pathogen microbial invasions. Thus, the use of isolated lignin as environmentally benign antimicrobial is believed to be a promising high value approach for lignin valorization. On the other hand, as green and sustainable product of plant photosynthesis, lignin should be beneficial to reduce the carbon footprint of antimicrobial industry. There have been many reports that make use of lignin to prepare antimicrobials for different applications. However, lignin is highly heterogeneous polymers different in their monomers, linkages, molecular weight, and functional groups. The structure and property relationship, and the mechanism of action of lignin as antimicrobial remains ambiguous. To show light on these issues, we reviewed the publications on lignin chemistry, antimicrobial activity of lignin models and isolated lignin and associated mechanism of actions, approaches in synthesis of lignin with improved antimicrobial activity, and the applications of lignin as antimicrobial in different fields. Hopefully, this review will help and inspire researchers in the preparation of lignin antimicrobial for their applications.

Vanillin Derivatives Reverse Fusobacterium nucleatum-Induced Proliferation and Migration of Colorectal Cancer Through E-Cadherin/β-Catenin Pathway

Colorectal cancer (CRC) is a common clinical malignant tumor and closely related to intestinal microbiome disorders. Especially, Fusobacterium nucleatum (F. nucleatum) is one of the most prevalent pathogens in CRC. However, its change in CRC patients of Northwest China, an area with a high incidence of gastrointestinal tumors, is unclear, and therapeutic strategies targeting F. nucleatum remain unresolved. Here, fecal samples of healthy people and CRC patients were studied using 16S rRNA sequencing to explore microbial community alterations. Additionally, vanillin derivate (IPM711 and IPM712) intervention by coculture with CRC cells and potential mechanism were investigated. Results showed that intestinal microbial homeostasis was gradually dysregulated, and the abundance of Fusobacterium was higher in CRC patients. Moreover, IPM711 and IPM712 showed better anti-F. nucleatum activity than vanillin by increasing cell membrane permeability and destroying bacterial integrity. In addition, IPM711 and IPM712 could downregulate the expression of E-cadherin and β-catenin, thus, suppressing the migration of HCT116. Collectively, IPM711 and IPM712 have both anticolorectal cancer and anti-F. nucleatum activities, providing potential natural product drug candidates for microbe-targeted strategies for the treatment of CRC.

Inhibition of biofilm formation by alpha-mangostin loaded nanoparticles against Staphylococcus aureus

This study aimed to investigate the antibiofilm activity of alpha-mangostin (AMG) loaded nanoparticles (nanoAMG) against Staphylococcus aureus, including the methicillin-resistant strain MRSA252. The results indicated that treatment with 24 μmol/L nanoAMG inhibited the formation of biofilm biomass by 53-62%, compared to 40-44% for free AMG (p < 0.05). At 48 μmol/L, biofilms in all nanoAMG treated samples were nearly fully disrupted for the two tested strains, MRSA252 and the methicillin-sensitive strain NCTC6571. That concentration resulted in killing of biofilm cells. A lower concentration of 12 µmol/L nanoAMG inhibited initial adherence of the two bacterial strains by > 50%. In contrast, activity of nanoAMG was limited on preformed mature biofilms, which at a concentration of 48 µmol/L were reduced only by 27% and 22% for NCTC6571 and MRSA252, respectively. The effects of AMG or nanoAMG on the expression of biofilm-related genes showed some noticeable differences between the two strains. For instance, the expression level of ebpS was downregulated in MRSA252 and upregulated in NCTC6571 when those strains were treated with either AMG or nanoAMG. In contrast, the expression of fnbB was down regulated in NCTC6571, while it was up-regulated in the MRSA252. The expression of other biofilm-related genes (icaC, clfB and fnbA) was down regulated in both strains. In conclusion, our results suggest that AMG coated nanoparticles had enhanced biological activity as compared to free AMG, indicating that nanoAMG could be a new and promising inhibitor of biofilm formation to tackle S. aureus, including strains that are resistant to multiple antibiotics.

Toothpaste Activity Test of Laban Leaf Methanol Extract (Vitex pinnata) Against the Growth of Streptococcus mutans Bacteria

BACKGROUND: One of the natural ingredients that can be used as a substitute for preventing dental caries is the methanol extract of Laban leaves. Laban contains various compounds that are known to have antibacterial properties. The traditional ability of Laban Leaf Methanol Extract has been proven to treat diseases caused by pathogenic microorganisms. AIM: The aim of the study was to analyzing the activity test of Laban leaf methanol extract toothpaste (Vitex pinnata) against the growth of Streptococcus mutans bacteria. METHODS: This type of laboratory experimental research (true experimental design) with post-test only control group design. This research was conducted at the Poltekkes Pharmacy Laboratory of the Ministry of Health in Aceh in July-August. The research sample consisted of Laban leaves collected randomly in the Ie Seu Um Geothermal area of Selawah Agam Aceh Besar. Data analysis was carried out descriptively. Antibacterial activity data were statistically processed with one-way ANOVA at a confidence level of α 0.05. RESULTS: The organoleptic test results observed for 3 weeks showed that there were differences in color and aroma; the higher the concentration of the resulting color, the darker it was, and resulting in a soft, sweet taste in the toothpaste of laban leaf methanol extract. The pH acidity test results showed an effect of storage time (the week I, week II, and week III) on toothpaste’s pH value. The viscosity test results showed that the toothpaste formula combined with the methanol extract of Laban leaves met the SNI 12-524-1995 standards regarding toothpaste. Toothpaste formula F3. 4.5% has the greatest viscosity, ranging from 241.0 (PDAs), and followed by F2. 240.4%, and F1. 237.6%. The higher the active ingredient concentration, the greater the viscosity value. The foam formation test results show that the foam’s stability is greatly influenced by particle size. The more the particle size, the lower the foam stability. ANOVA test results based on the concentration of significance value (0.000) <0.05, there is a difference in the number of bacterial colonies based on the concentration variable. ANOVA test results based on the repetition of significant values (0.423)> 0.05, which means that all repetitions have the same effect on the number of colonies, so there is no difference in the number of colonies based on the repetition variable. CONCLUSION: Minimum inhibitory concentration of toothpaste laban leaf methanol extract against S. mutans growth was aimed at a concentration of 4.5%, with an average number of bacterial colonies 108.5 × 10−7 CFU/mL).

Magnolia officinalis and Its Honokiol and Magnolol Constituents Inhibit Human Norovirus Surrogates

Norovirus is a major cause of foodborne disease and nonbacterial gastroenteritis globally. This study evaluated the antiviral effects of Magnolia officinalis extract and its honokiol and magnolol constituents against human norovirus surrogates, murine norovirus (MNV) and feline calicivirus (FCV) in vitro, and in model food systems. Pretreatment or cotreatment of M. officinalis extract at 1 mg/mL reduced MNV and FCV titers by 0.6-1.8 log. Honokiol and magnolol, which are the major polyphenols in the extract, showed significant antiviral effects against MNV and FCV. The virus-infected cells that were treated with M. officinalis extract exhibited significantly increased glutathione levels (p < 0.05). The extract, honokiol, and magnolol revealed ferric ion-reducing and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activities in a dose-dependent manner. Furthermore, MNV and FCV titers were reduced by >1.6 log or to undetectable levels in apple, orange, and plum juices and by 0.9 and 1.6 log in milk, respectively, when they were treated with the extract at 5 mg/mL. Therefore, the present study suggests that M. officinalis extract can be used as an antiviral food material to control norovirus foodborne diseases.

In Vitro Antibacterial Activities of Methanolic Extracts of Fruits, Seeds, and Bark of Zanthoxylum armatum DC

Crude methanol extracts of fruits, seeds, and bark of Zanthoxylum armatum were investigated in vitro for antimicrobial activities against 9 different bacterial strains: Bacillus subtilis, Enterococcus faecalis, Proteus vulgaris, Pseudomonas aeruginosa, Salmonella typhi, Shigella dysenteriae, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and Staphylococcus epidermidis using agar well diffusion method, and the MBC values were determined. Only 5 bacteria, i.e., Bacillus subtilis, Enterococcus faecalis, MRSA, Staphylococcus aureus, and Staphylococcus epidermidis exhibited antibacterial properties against the different extracts. The fruit and seed extracts showed activities against 5 bacteria, while the bark extract was active against 2 bacteria only (MRSA and Staphylococcus aureus). Staphylococcus aureus was found to be more susceptible for all the extracts compared to other strains. The maximum ZOI of 20.72 mm was produced by fruits (wild) and 18.10 mm (cultivated) against Staphylococcus aureus. Likewise, the least ZOI of 11.73 mm was produced by seeds (wild) and 11.29 mm (cultivated) against Escherichia faecalis. Similarly, the lowest MBC value of 0.78 mg/mL was obtained for fruit extracts against MRSA, 1.56 mg/mL for fruits, seeds, and bark extracts against Bacillus subtilis, MRSA, and Staphylococcus aureus, and highest value of 50 mg/mL for fruits and seeds extracts against S. epidermidis. The fruits, seeds, and bark extracts of Z. armatum exhibited remarkable antibacterial properties against different pathogenic bacteria causing several diseases, which suggests the potential use of this plant for treating different bacterial diseases such as skin infection, urinary tract infection, dental problems, diarrhea, and dysentery.

Honokiol, magnolol and its monoacetyl derivative show strong anti-fungal effect on Fusarium isolates of clinical relevance

The antifungal activity of magnolol and honokiol, two naturally occurring hydroxylated biphenyls, and of their synthetic derivatives was evaluated on a collection of representative isolates of Fusarium oxysporum, F. solani and F. verticillioides of clinical and ecological concern. The tested compounds were proposed as a ‘natural’ alternative to conventional fungicides, even though a larger range of concentrations (5–400 μg/ml) was applied. The activity of magnolol and honokiol was compared with that of terbinafine (0.1–10 μg/ml), and fluconazole (1–50 μg/ml), two fungicides widely used in treating fungal infections on humans. Magnolol showed similar fungicidal activity compared to fluconazole, whereas honokiol was more effective in inhibiting mycelium growth compared to this fungicide on all tested clinical Fusarium spp. isolates. Compared to terbinafine, honokiol showed similar antifungal activity when tested on clinical F. solani isolates, whereas magnolol was less effective at all selected concentrations (5–400 μg/ml). The different position of the phenol-OH group, as well as its protection, explain different in vitro activities between magnolol, honokiol, and their derivatives. Furthermore, magnolol showed mycelium dry weight reduction at a concentration of 0.5 mM when tested on a set of agricultural isolates of Fusaria, leading to complete inhibition of some of them. Magnolol and honokiol are proposed as efficient and safe candidates for treating clinically relevant Fusaria.

Alpha mangostin loaded crosslinked silk fibroin-based nanoparticles for cancer chemotherapy

Silk fibroin has been utilized extensively for biomedical purposes, especially the drug delivery systems. This study introduced and characterized three novel α-mangostin loaded crosslinked fibroin nanoparticles (FNPs), using EDC or PEI as a crosslinker, for cancer treatment. All three formulas were spherical particles with a mean size of approximately 300 nm. By varying the type and/or amount of the crosslinkers, particle surface charge was controllable from -15 to +30 mV. Crosslinked FNPs exhibited higher drug entrapment efficiency (70%) and drug loading (7%) than non-crosslinked FNP. FT-IR, XRD, and DSC analytical methods confirmed that α-mangostin was entrapped in FNPs in molecular dispersion form. Compared to the free α-mangostin, the crosslinked FNPs increased the drug's solubility up to threefold. They also showed sustained release characteristics of more than 3 days, and reduced free α-mangostin hematotoxicity by 90%. The α-mangostin loaded FNPs were physicochemically stable for up to 24 h when dispersed in intravenous diluent and for at least 6 months when preserved as lyophilized powder at 4 °C. In terms of anticancer efficacy, on both Caco-2 colorectal and MCF-7 breast adenocarcinoma cell lines, all formulas maintain α-mangostin's apoptotic effect while exhibit greater cytotoxicity than the free drug. In conclusion, α-mangostin loaded crosslinked FNPs show high potential for cancer chemotherapy.

Double-shelled hollow rods assembled from nitrogen/sulfur-codoped carbon coated indium oxide nanoparticles as excellent photocatalysts

Excellent catalytic activity, high stability and easy recovery are three key elements for fabricating efficient photocatalysts, while developing a simple method to fabricate such photocatalysts with these three features at the same time is highly challenging. In this study, we successfully synthesized double-shelled hollow rods (DHR) assembled by nitrogen (N) and sulfur (S)-codoped carbon coated indium(III) oxide (In₂O₃) ultra-small nanoparticles (N,S-C/In₂O₃ DHR). N,S-C/In₂O₃ DHR exhibits remarkable photocatalytic activity, high stability and easy recovery for oxidative hydroxylation reaction of arylboronic acid substrates. The catalyst recovery and surface area were well balanced through improved light harvesting, contributed by concurrently enhancing the reflection on the outer porous shell and the diffraction in the inside double-shelled hollow structure, and increased separation rate of photogenerated carriers. Photocatalytic mechanism was investigated to identify the main reactive species in the catalytic reactions. The electron separation and transfer pathway via N,S-codoped graphite/In₂O₃ interface was revealed by theoretical calculations.

While photoredox catalysis presents exciting avenues for molecular transformations, balancing optimal photochemical and materials properties can be challenging. Here, the authors prepare carbon-coated In₂O₃ nanoparticles as recoverable photocatalysts for arylboronic acid oxidative hydroxylation.

Antagonism of Bacteria from Dog Dental Plaque against Human Cariogenic Bacteria

Dental caries are a process of demineralization and destruction of human teeth. They originate through many factors and are associated with biofilm formation, which consists of bacteria adhered to the teeth that form a structurally and functionally organized mass called dental plaque. Both the presence of Streptococcus mutans and the frequent consumption of sucrose correlate with a higher prevalence of caries in humans. In dogs, however, the incidence of this disease is low, due to factors such as differences in dental microbiota and/or their low consumption of sucrose. This work evaluated the antagonism of bacteria from dog's dental plaque against S. mutans, for the identification of producing strains of biotechnological products for use in preventing caries. This study used 95 bacterial isolates of canine dental plaque from the Veterinary Department at the Federal University of Viçosa, Minas Gerais, Brazil. A spot-on-the-lawn method was performed using Brain Heart Infusion agar with catalase for an initial identification of the antagonistic activity. Additional tests were conducted on the isolates classified as antagonists for confirmation of the activity, using modified Mann-Rogosa-Sharpe medium containing low dextrose concentration. These isolates were incubated at 37°C for 24 hours in anaerobiosis. The peptide nature of inhibition was evaluated using the following proteinases: proteinase K from Tritirachium album, bovine pancreatic trypsin, and type XII-A α-amylase from Bacillus licheniformis. In the initial identification of those strains exhibiting antimicrobial activity, 14 were classified as antagonists. One of the isolates (Bacillus sp.) indicated bacteriocinogenic activity, with a deformed inhibition halo on S. mutans by the addition of trypsin. These results suggest that this bacterial isolate may be applicable to biotechnological use to combat the main etiological agent of caries in humans. Further studies are needed to evaluate the bacteriocinogenic nature of the antimicrobial activities of the other 13 antagonistic bacterial isolates.

Solvent Extraction and Identification of Active Anticariogenic Metabolites in Piper cubeba L. through ¹H-NMR-Based Metabolomics Approach

The aim of this study was to determine the effects of different solvents for extraction, liquid⁻liquid partition, and concentrations of extracts and fractions of Piper cubeba L. on anticariogenic; antibacterial and anti-inflammatory activity against oral bacteria. Furthermore, ¹H-Nuclear Magnetic Resonance (NMR) coupled with multivariate data analysis (MVDA) was applied to discriminate between the extracts and fractions and examine the metabolites that correlate to the bioactivities. All tested bacteria were susceptible to Piper cubeba L. extracts and fractions. Different solvents extraction, liquid⁻liquid partition and concentrations of extracts and fractions have partially influenced the antibacterial activity. MTT assay showed that P. cubeba L. extracts and fractions were not toxic to RAW 264.7 cells at selected concentrations. Anti-inflammatory activity evaluated by nitric oxide (NO) production in lipopolysaccharide (LPS) stimulated cells showed a reduction in NO production in cells treated with P. cubeba L. extracts and fractions, compared to those without treatment. Twelve putative metabolites have been identified, which are (1) cubebin, (2) yatein, (3) hinokinin, (4) dihydrocubebin, (5) dihydroclusin, (6) cubebinin, (7) magnosalin, (8) p-cymene, (9) piperidine, (10) cubebol, (11) d-germacrene and (12) ledol. Different extraction and liquid⁻liquid partition solvents caused separation in principal component analysis (PCA) models. The partial least squares (PLS) models showed that higher anticariogenic activity was related more to the polar solvents, despite some of the active metabolites also present in the non-polar solvents. Hence, P. cubeba L. extracts and fractions exhibited antibacterial and anti-inflammatory activity and have potential to be developed as the anticariogenic agent.

Honokiol-Inspired Analogs as Inhibitors of Oral Bacteria

The oral microbiome is a complex ecological niche where both commensal and pathogenic bacteria coexist. Previous reports have cited that the plant isolate honokiol is a potent inhibitor of S. mutans biofilms. Herein we report a cross-coupling method that provides access to a concise library of honokiol-inspired analogs. Through this work we determined that the inhibitory activity of honokiol is highly dependent on the growth conditions. Further, we identify a series of analogs that display significant potency against oral bacteria leading to the discovery of a potent antimicrobial.

Antibiofilm activity of α-mangostin extracted from Garcinia mangostana L. against Staphylococcus aureus

OBJECTIVE

To isolate α-mangostin (AMG) from the peels of mangosteen (Garcinia mangostana L.), grown in Vietnam, and to investigate antibiofilm activity of this compound against three Staphylococcus aureus (S. aureus) strains, one of which was methicillin-resistant S. aureus (MRSA) and the other two strains were methicillin-sensitive S. aureus (MSSA).

METHODS

AMG in n-hexane fraction was isolated on a silica gel column and chemically analyzed by HPLC and NMR. The antibiofilm activity of this compound was investigated by using a 96-well plate model for the formation of biofilms. Biofilm biomass was quantified using crystal violet. The viability of cells was observed under confocal microscopy using LIVE/DEAD BacLight stains. Biofilm composition was determined using specific chemical and enzyme tests for polysaccharide, protein and DNA. Membrane-damaging activity was assayed by measuring the hemolysis of human red blood cells in presence of AMG.

RESULTS

The results indicated that the isolated AMG, with a purity that exceeded 98%, had minimal inhibitory concentrations in the range of 4.6-9.2 μmol/L for the three strains tested. Interestingly, the MSSA strains were more sensitive to AMG than the MRSA strain. Minimal bactericidal concentrations were 2-fold higher than the minimal inhibitory concentration values for the three strains, indicating that AMG was a bactericidal compound. AMG also prevented biofilm formation effectively, albeit that again the MRSA strain was the most resistant. Interestingly, biofilms of the MRSA strain contained protein as a main component of the extracellular matrix, whereas this was polysaccharide in the MSSA strains. This might relate to the resistance of the MRSA 252 strain to AMG. Assays using human red blood cells indicated that AMG caused significant membrane damage with 50% of cell lysis occurred at concentration of about 36 μmol/L.

CONCLUSIONS

Our results provide evidence that the isolated AMG has inhibitory activity against biofilm formation by S. aureus, including MRSA. Thus, isolated AMG proposes a high potential to develop a novel phytopharmaceutical for the treatment of MRSA.

Nine phenylethanoid glycosides from Magnolia officinalis var. biloba fruits and their protective effects against free radical-induced oxidative damage

To systematically study the chemical constituents in Magnolia officinalis var. biloba fruits, nine phenylethanoid glycosides were isolated by solvent extraction, silica gel, and preparative high-performance liquid chromatography (HPLC). Their structures were elucidated by 1D and 2D NMR analyses, including COSY, HMQC and HMBC correlations, and HPLC analysis of sugar residue. Nine phenylethanoid glycosides, namely, magnoloside I_a (1), magnoloside I_c (2), crassifolioside (3), magnoloside I_b (4), magnoloside III_a (5), magnoloside IV_a (6), magnoloside II_a (7), magnoloside II_b (8) and magnoloside V_a (9), were first isolated from the n-butanol fraction of Magnolia officinalis var. biloba fruits alcohol extract. Free radical scavenging activities of the nine phenylethanoid glycosides were assessed using the DPPH, ABTS, and superoxide anion radical scavenging assays. Simultaneously, protective effects of all compounds against free radical-induced oxidative damage were evaluated by two different kinds of mitochondrial damage model. The protective effects were assessed by mitochondrial swelling, the formations of malondialdehyde (MDA) and lipid hydroperoxide (LOOH), the activities of catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD). All phenylethanoid glycosides showed significant protective effects.

In vitro synergism of magnolol and honokiol in combination with antibacterial agents against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA)

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is a problematic pathogen posing a serious therapeutic challenge in the clinic. It is often multidrug-resistant (MDR) to conventional classes of antibacterial agents and there is an urgent need to develop new agents or strategies for treatment. Magnolol (ML) and honokiol (HL) are two naturally occurring diallylbiphenols which have been reported to show inhibition of MRSA. In this study their synergistic effects with antibacterial agents were further evaluated via checkerboard and time-kill assays.

Methods

The susceptibility spectrum of clinical MRSA strains was tested by the disk diffusion method. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of ML and HL were assayed by broth microdilution. The synergy was evaluated through checkerboard microdilution and time-killing experiments.

Results

ML and HL showed similar activity against both MSSA and MRSA with MIC/MBC at 16 ~ 64 mg/L, with potency similar to amikacin (AMK) and gentamicin (GEN). When they were used in combination with conventional antibacterial agents, they showed bacteriostatic synergy with FICIs between 0.25 ~ 0.5, leading to the combined MICs decreasing to as low as 1 ~ 2 and 1 ~ 16 mg/L for ML (HL) and the agents, respectively. MIC₅₀ of the combinations decreased from 16 mg/L to 1 ~ 4 mg/L for ML (HL) and 8 ~ 128 mg/L to 2 ~ 64 mg/L for the antibacterial agents, which exhibited a broad spectrum of synergistic action with aminoglycosides (AMK, etilmicin (ETM) and GEN), floroquinolones (levofloxacin (LEV), ciprofloxacin and norfloxacin), fosfomycin (FOS) and piperacillin. The times of dilution (TOD, the extent of decreasing in MIC value) were determined up to 16 for the combined MIC. A more significant synergy after combining was determined as ML (HL) with AMK, ETM, GEN and FOS. ML (HL) combined with antibacterial agents did not show antagonistic effects on any of the ten MRSA strains. Reversal effects of MRSA resistance to AMK and GEN by ML and HL were also observed, respectively. All the combinations also showed better dynamic bactericidal activity against MRSA than any of single ML (HL) or the agents at 24 h incubation. The more significant synergy of combinations were determined as HL (ML) + ETM, HL + LEV and HL + AMK (GEN or FOS), with △LC₂₄ of 2.02 ~ 2.25.

Conclusion

ML and HL showed synergistic potentiation of antibacterial agents against clinical isolates of MRSA and warrant further pharmacological investigation.

Antimicrobial activity of the essential oil of Tetradenia riparia (Hochst.) Codd. (Lamiaceae) against cariogenic bacteria

In Brazilian folk medicine, Tetradenia riparia (Hochst.) Codd. (Lamiaceae) is used to treat toothaches and dental abscesses and diseases induced by worms, bacteria, or fungi. This paper aims to investigate the chemical composition and the antibacterial effects of the essential oil obtained from Tetradenia riparia leaves (TR-EO) grown in Southeastern Brazil against a representative panel of oral pathogens. We evaluated the antibacterial activity of TR-EO in terms of the minimal inhibitory concentration (MIC). We identified aromadendrene oxide (14.0%), (E,E)-farnesol (13.6%), dronabinol (12.5%), and fenchone (6.2%) as the major constituents of TR-EO. TR-EO displayed MIC values between 31.2 and 500 μg/mL, with the lowest MIC value being obtained against Streptococcus mitis (31.2 μg/mL), S. mutans (62.5 μg/mL), S. sobrinus (31.2 μg/mL), and Lactobacillus casei (62.5 μg/mL). In time-kill experiments, TR-EO demonstrated bactericidal activity against S. mutans within the first 12 h, resulting in a curve profile similar to that of chlorhexidine. These results revealed that the essential oil of Tetradenia riparia displays promising activity against most of the selected cariogenic bacteria, including Streptococcus mutans.

Natural products and caries prevention

Dental caries is considered as the most common polymicrobial oral disease in the world. With the aim of developing alternative approaches to reduce or prevent the decay, numerous papers showed the potential anticaries activity of a number of natural products. The natural products with anticaries effects are selected from e.g. food, beverages, flowers or traditional herbs. Most of the effective components are proven to be polyphenol compounds. Many of the natural products are studied as antibacterial agents, while some of them are found to be effective in shifting the de-/remineralization balance. However, the mechanisms of the anticaries effects are still unclear for most of the natural products. In the future, more efforts need to be made to seek novel effective natural products via in vitro experiment, animal study and in situ investigations, as well as to enhance their anticaries effects with the help of novel technology like nanotechnology.

Mucoadhesive electrospun chitosan-based nanofibre mats for dental caries prevention

The mucoadhesive electrospun nanofibre mats were developed using chitosan (CS) and thiolated chitosan (CS-SH) as mucoadhesive polymers. Garcinia mangostana (GM) extract was incorporated into nanofibre mats. The antibacterial activity in the single and combined agents was evaluated against dental caries pathogens. The morphology of mats was observed using SEM. The mats were evaluated for GM extract amount, mucoadhesion, in vitro release, antibacterial activity and cytotoxicity. The mucoadhesion and antibacterial activity were determined in healthy human volunteers. The prepared mats were in nanoscale with good physical and mucoadhesive properties. The CS-SH caused the higher mucoadhesion. All mats rapidly released active substances, which had the synergistic antibacterial activity. In addition, the reduction of bacteria and good mucoadhesion in the oral cavity occurred without cytotoxicity. The results suggest that mats have the potential to be mucoadhesive dosage forms to maintain oral hygiene by reducing the bacterial growth that causes the dental caries.

Combination effects of baicalein with antibiotics against oral pathogens

BACKGROUND

Baicalein is one of the major flavonoids in Scutellaria baicalensis Georgi, which has long been used in Asia as herbal medicine. Several biological effects of baicalein, such as antiviral, anti-inflammatiom, anti-hepatotoxicity, and anti-tumour properties, have been reported.

OBJECTIVE AND DESIGN

In this study, the antibacterial activities of baicalein were investigated in combination with ampicillin and/or gentamicin against oral bacteria.

RESULTS

Baicalein was determined with MIC and MBC values ranging from 80 to 320 and 160 to 640 μg/mL against oral bacteria. The range of MIC₅₀ and MIC₉₀ were 20-160 μg/mL and 80-320 μg/mL, respectively. The combination effects of baicalein with antibiotics were synergistic (FIC index <0.375-0.5 and FBCI <0.5) against oral bacteria. Furthermore, a time-kill study showed that the growth of the tested bacteria was completely attenuated after 1-6 h of treatment with the MIC₅₀ of baicalein, regardless of whether it was administered alone or with ampicillin or gentamicin.

CONCLUSION

These results suggest that baicalein combined with other antibiotics may be microbiologically beneficial and not antagonistic.

Harvestman phenols and benzoquinones: characterisation and biosynthetic pathway

Benzoquinones are usually present in arthropod defence exudates. Here, we describe the chemical profiles of 12 harvestman species belonging to the neotropical family Gonyleptidae. Nine of the studied species produced benzoquinones, while three produced alkyl phenols. Two benzoquinones and one phenol exhibited biological activity against bacteria and fungi. We also studied the biosynthesis of 2-ethyl-1,4-benzoquinone by feeding Magnispina neptunus individuals with ¹³C-labelled precursors; the benzoquinones were biosynthesised through a polyketide pathway using acetate and propionate building blocks.

The effect of a dentifrice containing Magnolia extract on established plaque and gingivitis in man: a six-month clinical study

AIM

The aim was to evaluate the clinical effect of a dentifrice containing 0.3% Magnolia extract on dental plaque and gingivitis.

MATERIAL AND METHODS

The trial was a 6-month double-blind, stratified, randomized and 2-armed parallel group study. Forty-six subjects in the test group brushed their teeth with a dentifrice containing 0.3% Magnolia extract and 48 subjects in the control group brushed with a placebo dentifrice. Plaque and gingivitis were assessed at baseline, 3 and 6 months.

RESULTS

There was a significantly larger gingivitis reduction in the Magnolia group than in the control group (0.26 ± 0.11 versus 0.11 ± 0.12) (P < 0.001). There was a greater increase in the total number of healthy gingival units Gingival Index (GI score 0) in the Magnolia group than in the control group (149% versus 31%) and a larger reduction in inflamed gingival units (GI score 2/3) (60% versus 30%). Furthermore, at sites with similar amounts of plaque, less clinical signs of gingival inflammation were observed in the Magnolia group than in the control group.

CONCLUSION

Six months' unsupervised use of a dentifrice containing 0.3% Magnolia extract resulted in significantly greater gingivitis reduction than a corresponding control dentifrice.

Pimarane-type diterpenes obtained by biotransformation: antimicrobial properties against clinically isolated Gram-positive multidrug-resistant bacteria

The present study describes the antimicrobial activity of five pimarane-type diterpenes obtained by fungal biotransformation against several nosocomial multidrug-resistant bacteria. Among the investigated metabolites, ent-8(14),15-pimaradien-3β-ol was the most active compound, with very promising minimal inhibitory concentration values (between 8.0 and 25.0 µg mL(-1)). Time-kill assays using this metabolite against Staphylococcus aureus (HCRP180) revealed that this compound exerted its bactericidal effect within 24 h at all the evaluated concentrations (8.0, 16.0, and 24.0 µg mL(-1)). When this metabolite was associated with vancomycin at their minimal bactericidal concentration values, the resulting combination was able to drastically reduce the number of viable strains of S. aureus within the first 6 h, compared with these chemicals alone. The checkerboard assays conducted against this microorganism did not evidence any synergistic effects when this same combination was employed. In conclusion, our results point out that ent-8(14),15-pimaradien-3β-ol is an important metabolite in the search for new effective antimicrobial agents.

Antimicrobial evaluation of diterpenes from Copaifera langsdorffii oleoresin against periodontal anaerobic bacteria

The antimicrobial activity of four labdane-type diterpenes isolated from the oleoresin of Copaifera langsdorffii as well as of two commercially available diterpenes (sclareol and manool) was investigated against a representative panel of microorganisms responsible for periodontitis. Among all the evaluated compounds, (−)-copalic acid (CA) was the most active, displaying a very promising MIC value (3.1 µg mL⁻¹; 10.2 µM) against the key pathogen (Porphyromonas gingivalis) involved in this infectious disease. Moreover, CA did not exhibit cytotoxicity when tested in human fibroblasts. Time-kill curve assays performed with CA against P. gingivalis revealed that this compound only inhibited the growth of the inoculums in the first 12 h (bacteriostatic effect). However, its bactericidal effect was clearly noted thereafter (between 12 and 24 h). It was also possible to verify an additive effect when CA and chlorhexidine dihydrochloride (CHD, positive control) were associated at their MBC values. The time curve profile resulting from this combination showed that this association needed only six hours for the bactericidal effect to be noted. In summary, CA has shown to be an important metabolite for the control of periodontal diseases. Moreover, the use of standardized extracts based on copaiba oleoresin with high CA contents can be an important strategy in the development of novel oral care products.