Inhibitory effects of 7-epiclusianone on glucan synthesis, acidogenicity and biofilm formation by Streptococcus mutans

Targeting glucosyltransferases to combat dental caries: Current perspectives and future prospects

The emergence of antimicrobial resistance within bacterial communities poses formidable challenges to existing therapeutic strategies aimed at mitigating biofilm-mediated infections. Recent advancements in this domain have spurred the development of targeted antimicrobial agents, designed to selectively eradicate the primary etiological agents while preserving the beneficial microbial diversity of the oral cavity. Targeting glucosyltransferases (GTFs), which play crucial roles in dental biofilm formation, offers a precise strategy to inhibit extracellular polysaccharide synthesis without compromising oral microbiota. This review article delves into the intricate mechanisms underlying dental caries, with a specific focus on the role of GTFs, enzymes produced by S. mutans. It further provides an overview of current research on GTF inhibitors, exploring their mechanisms of action, efficacy, and potential applications in clinical practice. Furthermore, it discusses the challenges and opportunities in the development of novel GTF inhibitors, emphasizing the need for innovative approaches to combat biofilm-mediated oral diseases effectively.

Synergistic inhibitory activity of Glycyrrhizae Radix and Rubi Fructus extracts on biofilm formation of Streptococcus mutans

BACKGROUND

Streptococcus mutans is a bacterium that causes oral diseases. Plaque, a biofilm produced by S. mutans and other bacteria, makes it difficult to remove cariogenic oral microorganisms, including biofilm producers. Glucan synthesis by glucosyltransferase is one of the mechanisms underlying plaque formation. This study demonstrates the effectiveness of inhibiting biofilm formation by interfering with the glucosyltransferase activity of S. mutans using edible herbal medicines.

METHODS

This study investigated the inhibitory activity of Glycyrrhizae Radix extract, Rubi Fructus extract, glycyrrhizin from Glycyrrhizae Radix, and ellagic acid from Rubi Fructus against glucosyltransferase activity of S. mutans. Enzyme kinetic analysis identified the mechanism by which glycyrrhizin and ellagic acid inhibit enzyme activity.

RESULTS

The conditions for synergistically inhibiting biofilm formation by combining Glycyrrhizae Radix and Rubi Fructus extracts were identified. Biofilm formation was also synergistically inhibited by mixing their respective active constituents, glycyrrhizin and ellagic acid. Glycyrrhizin and ellagic acid inhibited glucosyltransferase via noncompetitive and uncompetitive mechanisms, respectively, indicating that they inhibit it via distinct mechanisms.

CONCLUSIONS

This study presents an effective oral hygiene method using the synergistic activity of two natural plant extracts to inhibit biofilm formation through different inhibitory mechanisms against glucosyltransferase of S. mutans.

Semysinthetic biflavonoid Morelloflavone-7,4',7″,3‴,4‴-penta-O-butanoyl is a more potent inhibitor of Proprotein Convertases Subtilisin/Kexin PC1/3 than Kex2 and Furin

BACKGROUND

Garcinia brasiliensis is a species native to the Amazon forest. The white mucilaginous pulp is used in folk medicine as a wound healing agent and for peptic ulcer, urinary, and tumor disease treatments. The activity of the proprotein convertases (PCs) Subtilisin/Kex is associated with the development of viral, bacterial and fungal infections, osteoporosis, hyperglycemia, atherosclerosis, cardiovascular, neurodegenerative and neoplastic diseases.

METHODS

Morelloflavone (BF1) and semisynthetic biflavonoid (BF2, 3 and 4) from Garcinia brasiliensis were tested as inhibitor of PCs Kex2, PC1/3 and Furin, and determined IC50, Ki, human proinflammatory cytokines secretion in Caco-2 cells, mechanism of inhibition, and performed molecular docking studies.

RESULTS

Biflavonoids were more effective in the inhibition of neuroendocrine PC1/3 than mammalian Furin and fungal Kex2. BF1 presented a mixed inhibition mechanism for Kex2 and PC1, and competitive inhibition for Furin. BF4 has no good interaction with Kex2 and Furin since carboxypropyl groups results in steric hindrance to ligand-protein interactions. Carboxypropyl groups of BF4 promote steric hindrance with Kex2 and Furin, but effective in the affinity of PC1/3. BF4 was more efficient at inhibiting PCl/3 (IC50 = 1.13 μM and Ki = 0,59 μM, simple linear competitive mechanism of inhibition) than Kex2, Furin. Also, our results strongly suggested that BF4 also inhibits the endogenous cellular PC1/3 activity in Caco-2 cells, since PC1/3 inhibition by BF4 causes a large increase in IL-8 and IL-1β secretion in Caco-2 cells.

CONCLUSIONS

BF4 is a potent and selective inhibitor of PC1/3.

GENERAL SIGNIFICANCE

BF4 is the best candidate for further clinical studies on inhibition of PC1/3.

Molecular mechanisms of inhibiting glucosyltransferases for biofilm formation in Streptococcus mutans

Glucosyltransferases (Gtfs) play critical roles in the etiology and pathogenesis of Streptococcus mutans (S. mutans)- mediated dental caries including early childhood caries. Gtfs enhance the biofilm formation and promotes colonization of cariogenic bacteria by generating biofilm extracellular polysaccharides (EPSs), the key virulence property in the cariogenic process. Therefore, Gtfs have become an appealing target for effective therapeutic interventions that inhibit cariogenic biofilms. Importantly, targeting Gtfs selectively impairs the S. mutans virulence without affecting S. mutans existence or the existence of other species in the oral cavity. Over the past decade, numerous Gtfs inhibitory molecules have been identified, mainly including natural and synthetic compounds and their derivatives, antibodies, and metal ions. These therapeutic agents exert their inhibitory role in inhibiting the expression gtf genes and the activities and secretion of Gtfs enzymes with a wide range of sensitivity and effectiveness. Understanding molecular mechanisms of inhibiting Gtfs will contribute to instructing drug combination strategies, which is more effective for inhibiting Gtfs than one drug or class of drugs. This review highlights our current understanding of Gtfs activities and their potential utility, and discusses challenges and opportunities for future exploration of Gtfs as a therapeutic target.

MapZ deficiency leads to defects in the envelope structure and changes stress tolerance of Streptococcus mutans

Cell division is a central process in bacteria and a prerequisite for pathogenicity. Several proteins are involved in this process to ensure the accurate localization and proper function of the division machinery. In Streptococcus mutans, MapZ marks the division sites and position of the Z-ring to regulate cell division; however, whether MapZ deficiency can impair the cariogenic virulence of S. mutans remains unclear. Here, using a phenotypic assay and RNA-seq, we investigated the role of MapZ in cell envelope maintenance, biofilm formation, and stress tolerance in S. mutans. The results show that MapZ is important for normal cell shape and envelope structure, and its deletion causes abnormal septum structure and a thin cell wall. Subsequently, we found that the absence of MapZ leads to a greater level of cell death within 12 h biofilms, but it does not seem to affect biofilm architecture and accumulation. mapZ deletion also results in a decreased acid and osmotic stress tolerance. Furthermore, RNA-seq data reveal that MapZ deficiency causes changes in the expression levels of genes involved in transport systems, sugar metabolism, nature competence, and bacteriocin synthesis. Interestingly, we found that mapZ mutation renders S. mutans more sensitive to chlorhexidine. Taken together, our study suggests that MapZ plays a role in maintaining cell envelope structure and stress tolerance in S. mutans, showing a potential application as a drug target for caries prevention.

Phytotoxic property of metabolites isolated from Garcinia gardneriana

Garcinia gardneriana is a medicinal tree species used in Brazil in the treatment of hepatitis and gastritis. This use is attributed to phenolic compounds, mainly 7-epiclusianone, guttiferone-A and fukugetin, which present several proven biological activities. However, to the best of our knowledge, no study on the phytotoxic activity of G. gardneriana extracts has been conducted until now. This research proposed to isolate and quantify by high-performance liquid chromatography (HPLC) the major compounds from G. gardneriana seed extracts in ethyl acetate and to evaluate their phytotoxic activities. The natural products 7-epiclusianone, guttiferone-A and fukugetin were quantified at concentrations varying from 0.46 to 1.13 mg mL^-1 and were isolated with yields ranging from 7% to 23% (w/w). The phytotoxic assay indicated that the crude extract showed no action on the dry matter of Sorghum bicolor plants, but the isolated compounds fukugetin and 7-epiclusianone had moderate activity. On the other hand, guttiferone-A displayed a greater herbicide activity than glyphosate, a positive control, even in almost three times lower concentrations, causing severe intoxication in the plants. This work is the first report on this activity by the extract of G. gardneriana and its isolated compounds. Besides that, guttiferone-A showed up as a scaffold for the development of new agrochemicals. Complementing these findings, computational studies suggested that this benzophenone can interact effectively with transferase enzymes type, in special caffeic acid O-methyltransferase from S. bicolor (PDB code: 4PGH), indicating a possible mechanism of action in this plant.

Effect of adrenaline and noradrenaline on biofilm formation and virulence factors of Streptococcus mutans UA159

OBJECTIVES

To evaluate in vitro the effects of adrenaline and noradrenaline on the biofilm formation on orthodontic brackets, acid production and expression of virulence genes of Streptococcus mutans UA159 (S. mutans).

DESIGN

S. mutans UA159 biofilm was formed on orthodontic brackets under exposure to adrenaline (100 μM), noradrenaline (50 μM) or PBS solution (control group) in triptone-yeast extract with 1 % sucrose. After 24 h, biofilm formation was quantified through Colony Forming Units / mL (CFU/mL) and RNA was extracted to perform gene expression analysis through real-time reverse transcriptase-PCR (RT-qPCR). Evaluation of acid production was carried out on planktonic cultures for 6 h. One-way ANOVA followed by Tukey's test was carried to determine statistical difference. The level of significance was set at 5 %.

RESULTS

Catecholamines stimulated biofilm formation of S. mutans in orthodontic brackets (p < 0,05) but did not interfere with acid production (pH reduction) or the expression of the tested genes related to biofilm formation (gtfB, gtfC, gbpA, gbpB, gbpC, gbpD and brpA), aciduric (relA) and acidogenic properties (ldh).

CONCLUSIONS

The present study was the first to demonstrate that catecholamines can stimulate S. mutans UA159 biofilm formation. These findings can contribute to clarify the role of stress on bacterial metabolism and contribute to the understanding of a possible role on caries development, mainly in orthodontic patients.

Bioactive Dental Adhesive System With tt-Farnesol: Effects on Dental Biofilm and Bonding Properties

Background

Composite dental restorations are commonly used to restore cavitated carious lesions. Unfortunately, the main reason for failure is the development of secondary caries adjacent to the restoration. To improve the long-term survival of restorations, antibacterial agents have been added into dental materials. In this study, we assessed the antibacterial and bonding capacity of a commercial universal dental adhesive incorporated with the antibacterial agent tt-farnesol creating 3 experimental adhesives: 0.38% (v/v), 1.90% (v/v), and 3.80% (v/v), plus a control (no incorporation of tt-farnesol).

Methods

The antibacterial activity was evaluated by assessing colony-forming units (CFU), biofilm dry weight (DW) and production of extracellular insoluble polysaccharides (EIP) at day 2, 3, and 5 of biofilm growth post surface treatment on the surface of composite disks. The effect of tt-farnesol on the chemical and bonding capacity of the adhesive system was assessed via pH analysis, degree of conversion (DC), and microtensile bond strengths to human dentin in both self-etch and etch-and-rinse application modes. A qualitative analysis of the effects of tt-farnesol on biofilm formation was evaluated using scanning electron microscopy (SEM). The sealing capacity of all adhesive systems tested was evaluated using confocal laser scanning microscopy (CLSM).

Results

The 3.80% (v/v) experimental adhesive exhibited the lowest CFU count and lowest production of EIP at day 5. DW and pH values did no exhibit statistical differences among all tested groups. Bond strengths and DC decreased with the incorporation of the antibacterial agent into the adhesive system regardless of the concentration of tt-farnesol.

Conclusion

The incorporation of tt-farnesol into the adhesive system significantly reduced bacterial viability and production of EIP; however, the bonding properties of the experimental dental adhesives were altered.

Antiproliferative Activity and Antioxidant Potential of Extracts of Garcinia gardneriana

The aim of this study was to evaluate the antiproliferative activity, the antioxidant potential, and the chemical profile obtained from the whole fruit and from leaves of Garcinia gardneriana, a fruit tree from Brazilian Cerrado. To determine in vitro antiproliferative activity, the following neoplastic cell lines were considered, along with an immortalized nontumor cell line. The antioxidant potential was determined, and the evaluation of antiradical air activity was performed. The levels of vitamin C and carotenoids were determined. The chemical profile was analyzed by high-performance liquid chromatography coupled to a diode array detector and a mass spectrometer using electrospray ionization interface. The chloroform fraction of the leaf showed antioxidant activity. The vitamin C content had lower values in fruits and higher in leaves. The content of carotenoids for fruits and leaves was expressive. The ethanolic extract and the hexane and chloroform fractions of fruits were active in all neoplastic lines tested. The leaves showed cytotoxic activity in the hexane fraction in the breast carcinoma line. The analysis of data obtained verified the presence of dimers, monomers, and tetramers of hexoses, polycarboxylic acids, xanthones, flavonoids, biflavonoids, and benzophenones.

Research Progress of Polycyclic Polyprenylated Acylphloroglucinols

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of hybrid natural products sharing the mevalonate/methylerythritol phosphate and polyketide biosynthetic pathways and showing considerable structure and bioactivity diversity. This review discusses the progress of research into the chemistry and biological activity of 421 natural PPAPs in the past 11 years as well as in-depth studies of biological activities and total synthesis of some PPAPs isolated before 2006. We created an online database of all PPAPs known to date at http://www.chem.uky.edu/research/grossman/PPAPs . Two subclasses of biosynthetically related metabolites, spirocyclic PPAPs with octahydrospiro[cyclohexan-1,5'-indene]-2,4,6-trione core and complicated PPAPs produced by intramolecular [4 + 2] cycloadditions of MPAPs, are brought into the PPAP family. Some PPAPs' relative or absolute configurations are reassigned or critically discussed, and the confusing trivial names in PPAPs investigations are clarified. Pharmacologic studies have revealed a new molecular mechanism whereby hyperforin and its derivatives regulate neurotransmitter levels by activating TRPC6 as well as the antitumor mechanism of garcinol and its analogues. The antineoplastic potential of some type B PPAPs such as oblongifolin C and guttiferone K has increased significantly. As a result of the recent appearances of innovative synthetic methods and strategies, the total syntheses of 22 natural PPAPs including hyperforin, garcinol, and plukenetione A have been accomplished.

Plant Natural Products Targeting Bacterial Virulence Factors

Decreased antimicrobial efficiency has become a global public health issue. The paucity of new antibacterial drugs is evident, and the arsenal against infectious diseases needs to be improved urgently. The selection of plants as a source of prototype compounds is appropriate, since plant species naturally produce a wide range of secondary metabolites that act as a chemical line of defense against microorganisms in the environment. Although traditional approaches to combat microbial infections remain effective, targeting microbial virulence rather than survival seems to be an exciting strategy, since the modulation of virulence factors might lead to a milder evolutionary pressure for the development of resistance. Additionally, anti-infective chemotherapies may be successfully achieved by combining antivirulence and conventional antimicrobials, extending the lifespan of these drugs. This review presents an updated discussion of natural compounds isolated from plants with chemically characterized structures and activity against the major bacterial virulence factors: quorum sensing, bacterial biofilms, bacterial motility, bacterial toxins, bacterial pigments, bacterial enzymes, and bacterial surfactants. Moreover, a critical analysis of the most promising virulence factors is presented, highlighting their potential as targets to attenuate bacterial virulence. The ongoing progress in the field of antivirulence therapy may therefore help to translate this promising concept into real intervention strategies in clinical areas.

Inhibition of Streptococcus mutans polysaccharide synthesis by molecules targeting glycosyltransferase activity

Glycosyltransferase (Gtf) is one of the crucial virulence factors of Streptococcus mutans, a major etiological pathogen of dental caries. All the available evidence indicates that extracellular polysaccharide, particularly glucans produced by S. mutans Gtfs, contribute to the cariogenicity of dental biofilms. Therefore, inhibition of Gtf activity and the consequential polysaccharide synthesis may impair the virulence of cariogenic biofilms, which could be an alternative strategy to prevent the biofilm-related disease. Up to now, many Gtf inhibitors have been recognized in natural products, which remain the major and largely unexplored source of Gtf inhibitors. These include catechin-based polyphenols, flavonoids, proanthocyanidin oligomers, polymeric polyphenols, and some other plant-derived compounds. Metal ions, oxidizing agents, and some other synthetic compounds represent another source of Gtf inhibitors, with some novel molecules either discovered by structure-based virtual screening or synthesized based on key structures of known inhibitors as templates. Antibodies that inhibit one or more Gtfs have also been developed as topical agents. Although many agents have been shown to possess potent inhibitory activity against glucan synthesis by Gtfs, bacterial cell adherence, and caries development in animal models, much research remains to be performed to find out their mechanism of action, biological safety, cariostatic efficacies, and overall influence on the entire oral community. As a strategy to inhibit the virulence of cariogenic microbes rather than eradicate them from the microbial community, Gtf inhibition represents an approach of great potential to prevent dental caries.

7-Epiclusianone, a Benzophenone Extracted from Garcinia brasiliensis (Clusiaceae), Induces Cell Cycle Arrest in G1/S Transition in A549 Cells

Lung cancer is the leading cause of cancer deaths in the world. Disease stage is the most relevant factor influencing mortality. Unfortunately, most patients are still diagnosed at an advanced stage and their five-year survival rate is only 4%. Thus, it is relevant to identify novel drugs that can improve the treatment options for lung cancer. Natural products have been an important source for the discovery of new compounds with pharmacological potential including antineoplastic agents. We have previously isolated a prenylated benzophenone (7-epiclusianone) from Garcinia brasiliensis (Clusiaceae) that has several biological properties including antiproliferative activity against cancer cell lines. In continuation with our studies, the present work aimed to investigate the mechanisms involved with antiproliferative activity of 7-epiclusianone in A549 cells. Our data showed that 7-epiclusianone reduced the viability of A549 cells in a concentration-dependent manner (IC50 of 16.13 ± 1.12 μM). Cells were arrested in G1/S transition and apoptosis was induced. In addition, we observed morphological changes with cytoskeleton disorganization in consequence of the treatment. Taken together, the results showed that cell cycle arrest in G1/S transition is the main mechanism involved with antiproliferative activity of 7-epiclusianone. Our results are promising and open up the prospect of using this compound in further anticancer in vivo studies.

A systematic review for anti-inflammatory property of clusiaceae family: a preclinical approach

Background. Clusiaceae family (sensu lato) is extensively used in ethnomedicine for treating a number of disease conditions which include cancer, inflammation, and infection. The aim of this review is to report the pharmacological potential of plants of Clusiaceae family with the anti-inflammatory activity in animal experiments. Methods. A systematic review about experiments investigating anti-inflammatory activity of Clusiaceae family was carried out by searching bibliographic databases such as Medline, Scopus and Embase. In this update, the search terms were "anti-inflammatory agents," "Clusiaceae," and "animals, laboratory." Results. A total of 255 publications with plants this family were identified. From the initial 255 studies, a total of 21 studies were selected for the final analysis. Studies with genera Allanblackia, Clusia, Garcinia or Rheedia, and Hypericum showed significant anti-inflammatory activity. The findings include a decrease of total leukocytes, a number of neutrophils, total protein concentration, granuloma formation, and paw or ear edema formation. Other interesting findings included decreased of the MPO activity, and inflammatory mediators such as NF- κ B and iNOS expression, PGE2 and Il-1 β levels and a decrease in chronic inflammation. Conclusion. The data reported suggests the anti-inflammatory effect potential of Clusiaceae family in animal experiments.

Enhancement of fluoride activity against Streptococcus mutans biofilms by a substance separated from Polygonum cuspidatum

Polygonum cuspidatum is a plant with spreading rhizomes and numerous reddish-brown stems that has been used in Korean folk medicine to improve oral hygiene. Nevertheless, there are no reports related to its possible effect on the virulence of dental biofilms. In this study, the ability of a fraction (F1) separated from P. cuspidatum, alone or in combination with fluoride, to disrupt virulence factors and the composition of Streptococcus mutans biofilms was examined. F1 was mainly composed of resveratrol, emodin and physcion (approximately 16.2%, 18.9% and 2.07% of the weight of F1, respectively). F1 showed inhibitory effects on acid production and F-ATPase activity of S. mutans in biofilms, and could enhance fluoride activity against acid production and acid tolerance of S. mutans in biofilms. When S. mutans biofilms were briefly treated with F1 (10 min, a total of five times), the biomass accumulation, water-insoluble polysaccharides and intracellular iodophilic polysaccharides were reduced. Furthermore, the fluoride activity against biomass accumulation was enhanced by F1. These results suggest that F1 may be useful in the control of dental biofilms and in improving the cariostatic properties of fluoride without increasing its exposure.

Natural products in caries research: current (limited) knowledge, challenges and future perspective

Dental caries is the most prevalent and costly oral infectious disease worldwide. Virulent biofilms firmly attached to tooth surfaces are prime biological factors associated with this disease. The formation of an exopolysaccharide-rich biofilm matrix, acidification of the milieu and persistent low pH at the tooth-biofilm interface are major controlling virulence factors that modulate dental caries pathogenesis. Each one offers a selective therapeutic target for prevention. Although fluoride, delivered in various modalities, remains the mainstay for the prevention of caries, additional approaches are required to enhance its effectiveness. Available antiplaque approaches are based on the use of broad-spectrum microbicidal agents, e.g. chlorhexidine. Natural products offer a rich source of structurally diverse substances with a wide range of biological activities, which could be useful for the development of alternative or adjunctive anticaries therapies. However, it is a challenging approach owing to complex chemistry and isolation procedures to derive active compounds from natural products. Furthermore, most of the studies have been focused on the general inhibitory effects on glucan synthesis as well as on bacterial metabolism and growth, often employing methods that do not address the pathophysiological aspects of the disease (e.g. bacteria in biofilms) and the length of exposure/retention in the mouth. Thus, the true value of natural products in caries prevention and/or their exact mechanisms of action remain largely unknown. Nevertheless, natural substances potentially active against virulent properties of cariogenic organisms have been identified. This review focuses on gaps in the current knowledge and presents a model for investigating the use of natural products in anticaries chemotherapy.

MK615: a new therapeutic approach for the treatment of oral disease

The oral cavity is inhabited by over 500 different bacterial species. Dental caries and periodontitis are major bacterial infectious diseases in the oral cavity. Prunus mume Sieb. et Zucc., which is a variety of Japanese apricot known as Ume in Japanese, has been a traditional Japanese medicine for centuries, and is a familiar and commonly consumed food. The health benefits of Ume are now being widely recognized. Recent studies showed that MK615, an extract of compounds from Ume, has strong anticancer and anti-inflammatory effects. However, the potential role of MK615 in the antimicrobial field remains unknown. Therefore, we hypothesize that MK615 has antimicrobial activities against a range of oral bacterial pathogens. Here, we show that MK615 may be a potent inhibitor of the growth of some oral bacteria and an inhibitor of biofilm formation by Streptococcus mutans, the principal etiological agent of human dental caries. Our findings suggest that MK615 has potential as a therapeutic agent for treating and preventing oral diseases such as dental caries and periodontitis.

Antimicrobial actions of α-mangostin against oral streptococci

The increasing prevalence of dental caries is making it more of a major world health problem. Caries is the direct result of acid production by cariogenic oral bacteria, especially Streptococcus mutans. New and better antimicrobial agents active against cariogenic bacteria are badly needed, especially natural agents derived directly from plants. We have evaluated the inhibitory actions of α-mangostin, a xanthone purified from ethanolic extracts of the tropical plant Garcinia mangostana L., by repeated silica gel chromatography. α-Mangostin was found to be a potent inhibitor of acid production by S. mutans UA159, active against membrane enzymes, including the F(H+)-ATPase and the phosphoenolpyruvate - sugar phosphotransferase system. α-Mangostin also inhibited the glycolytic enzymes aldolase, glyceraldehyde-3-phosphate dehydrogenase, and lactic dehydrogenase. Glycolysis by intact cells in suspensions or biofilms was inhibited by α-mangostin at concentrations of 12 and 120 µmol·L⁻¹, respectively, in a pH-dependent manner, with greater potency at lower pH values. Other targets for inhibition by α-mangostin included (i) malolactic fermentation, involved in alkali production from malate, and (ii) NADH oxidase, the major respiratory enzyme for S. mutans. The overall conclusion is that α-mangostin is a multitarget inhibitor of mutans streptococci and may be useful as an anticaries agent.

A new small molecule specifically inhibits the cariogenic bacterium Streptococcus mutans in multispecies biofilms

Streptococcus mutans is a major cariogenic bacterium. It has adapted to the biofilm lifestyle, which is essential for pathogenesis of dental caries. We aimed to identify small molecules that can inhibit cariogenic S. mutans and to discover lead structures that could give rise to therapeutics for dental caries. In this study, we screened a focused small-molecule library of 506 compounds. Eight small molecules which inhibited S. mutans at a concentration of 4 μM or less but did not affect cell growth or biofilm formation of commensal bacteria, represented by Streptococcus sanguinis and Streptococcus gordonii, in monospecies biofilms were identified. The active compounds share similar structural properties, which are characterized by a 2-aminoimidazole (2-AI) or 2-aminobenzimidazole (2-ABI) subunit. In multispecies biofilm models, the most active compound also inhibited cell survival and biofilm formation of S. mutans but did not affect commensal streptococci. This inhibitor downregulated the expression of six biofilm-associated genes, ftf, pac, relA, comDE, gbpB, and gtfB, in planktonic S. mutans cells, while it downregulated the expression of only ftf, pac, and relA in the biofilm cells of S. mutans. The most potent compound also inhibited production of two key adhesins of S. mutans, antigen I/II and glucosyltransferase (GTF). However, the compound did not alter the expression of the corresponding genes in both S. sanguinis and S. gordonii, indicating that it possesses a selective inhibitory activity against S. mutans.

Biology of Streptococcus mutans-derived glucosyltransferases: role in extracellular matrix formation of cariogenic biofilms

The importance of Streptococcus mutans in the etiology and pathogenesis of dental caries is certainly controversial, in part because excessive attention is paid to the numbers of S. mutans and acid production while the matrix within dental plaque has been neglected. S. mutans does not always dominate within plaque; many organisms are equally acidogenic and aciduric. It is also recognized that glucosyltransferases from S. mutans (Gtfs) play critical roles in the development of virulent dental plaque. Gtfs adsorb to enamel synthesizing glucans in situ, providing sites for avid colonization by microorganisms and an insoluble matrix for plaque. Gtfs also adsorb to surfaces of other oral microorganisms converting them to glucan producers. S. mutans expresses 3 genetically distinct Gtfs; each appears to play a different but overlapping role in the formation of virulent plaque. GtfC is adsorbed to enamel within pellicle whereas GtfB binds avidly to bacteria promoting tight cell clustering, and enhancing cohesion of plaque. GtfD forms a soluble, readily metabolizable polysaccharide and acts as a primer for GtfB. The behavior of soluble Gtfs does not mirror that observed with surface-adsorbed enzymes. Furthermore, the structure of polysaccharide matrix changes over time as a result of the action of mutanases and dextranases within plaque. Gtfs at distinct loci offer chemotherapeutic targets to prevent caries. Nevertheless, agents that inhibit Gtfs in solution frequently have a reduced or no effect on adsorbed enzymes. Clearly, conformational changes and reactions of Gtfs on surfaces are complex and modulate the pathogenesis of dental caries in situ, deserving further investigation.

Effects of 7-epiclusianone on Streptococcus mutans and caries development in rats

The aim of this study was to evaluate the effects of 7-epiclusianone (7-epi) on specific virulence attributes of Streptococcus mutans in vitro and on development of dental caries in vivo. 7-Epi was obtained and purified from fruits of Rheedia brasiliensis. We investigated its influence on surface-adsorbed glucosyltransferase (Gtf) B activity, acid production, and viability of S. MUTANS in biofilms, as well as on caries development using a rodent model. 7-Epi (100 µg/mL) significantly reduced the activity of surface-adsorbed GtfB (up to 48.0 ± 1.8 of inhibition at 100 µg/mL) and glycolytic pH-drop by S. mutans in biofilms (125 and 250 µg/mL) (vs. vehicle control, p < 0.05). In contrast, the test compound did not significantly affect the bacterial viability when compared to vehicle control (15 % ethanol, p > 0.05). Wistar rats treated topically with 7-epi (twice daily, 60-s exposure) showed significantly smaller number of and less severe smooth- and sulcal-surface carious lesions (p < 0.05), without reducing the S. mutans viable population from the animals' dental biofilms. In conclusion, the natural compound 7-epiclusianone may be a potentially novel pharmacological agent to prevent and control dental caries disease.

Separation of an effective fraction from turmeric against Streptococcus mutans biofilms by the comparison of curcuminoid content and anti-acidogenic activity

Turmeric has long been used as a colouring and flavouring agent for foods. Curcuminoids are the main component of turmeric and have a range of pharmacological activities. In this study, a fraction that could show anti-biofilm activity was separated from turmeric, based on a comparison of curcuminoid content and anti-acidogenic activity against Streptococcus mutans, and the effects of the separated fraction and curcuminoids on the adherence ability of S. mutans and the physiological ability of S. mutans biofilms were examined at sub-minimum inhibitory concentration (MIC) levels. The separated fraction and curcuminoids had inhibitory effects on the sucrose-dependant adherence of S. mutans to saliva-coated hydroxyapatite (sHA) discs and the acidogenicity and aciduricity of S. mutans biofilms. These results suggest that the separated turmeric fraction and its components, curcuminoids, may be useful for controlling dental biofilms and subsequent dental caries formation.

Inhibition of Streptococcus mutans biofilm accumulation and development of dental caries in vivo by 7-epiclusianone and fluoride

7-Epiclusianone (7-epi), a novel naturally occurring compound isolated from Rheedia brasiliensis, effectively inhibits the synthesis of exopolymers and biofilm formation by Streptococcus mutans. In the present study, the ability of 7-epi, alone or in combination with fluoride (F), to disrupt biofilm development and pathogenicity of S. mutans in vivo was examined using a rodent model of dental caries. Treatment (twice-daily, 60s exposure) with 7-epi, alone or in combination with 125 ppm F, resulted in biofilms with less biomass and fewer insoluble glucans than did those treated with vehicle-control, and they also displayed significant cariostatic effects in vivo (p < 0.05). The combination 7-epi + 125 ppm F was as effective as 250 ppm F (positive-control) in reducing the development of both smooth- and sulcal-caries. No histopathological alterations were observed in the animals after the experimental period. The data show that 7-epiclusianone is a novel and effective antibiofilm/anticaries agent, which may enhance the cariostatic properties of fluoride.

Antiproliferative effect of benzophenones and their influence on cathepsin activity

The antiproliferative activity of two prenylated benzophenones isolated from Rheedia brasiliensis, the triprenylated garciniaphenone and the tetraprenylated benzophenone 7-epiclusianone, was investigated against human cancer cell lines. The antiproliferative activity on melanoma (UACC-62), breast (MCF-7), drug-resistant breast (NCI-ADR), lung/non-small cells (NCI460), ovarian (OVCAR 03), prostate (PC03), kidney (786-0), lung (NCI-460) and tongue (CRL-1624 and CRL-1623) cancer cells was determined using spectrophotometric quantification of the cellular protein content. The effect of these benzophenones on the activity of cathepsins B and G was also investigated. Garciniaphenone displayed cytostatic activity in all cell lines, whereas 7-epiclusianone showed a dose-dependent cytotoxic effect. The IC(50) values for cell proliferation revealed that 7-epiclusianone is more active than garciniaphenone against most of the cell lines. Furthermore, the antiproliferative effects demonstrated by garciniaphenone and 7-epiclusianone were related to their cathepsin inhibiting properties. In conclusion, 7-epiclusianone is a promising naturally occurring agent which displays multiple inhibitory effects which may be working in concert to inhibit cancer cell proliferation in vitro. The putative pathway by which 7-epiclusianone affects cancer cell development may involve cathepsin inhibition.

Influence of cranberry proanthocyanidins on formation of biofilms by Streptococcus mutans on saliva-coated apatitic surface and on dental caries development in vivo

Cranberry crude extracts, in various vehicles, have shown inhibitory effects on the formation of oral biofilms in vitro. The presence of proanthocyanidins (PAC) in cranberry extracts has been linked to biological activities against specific virulence attributes of Streptococcus mutans, e.g. the inhibition of glucosyltransferase (Gtf) activity. The aim of the present study was to determine the influence of a highly purified and chemically defined cranberry PAC fraction on S. mutans biofilm formation on saliva-coated hydroxyapatite surface, and on dental caries development in Sprague-Dawley rats. In addition, we examined the ability of specific PAC (ranging from low-molecular-weight monomers and dimers to high-molecular-weight oligomers/polymers) to inhibit GtfB activity and glycolytic pH drop by S. mutans cells, in an attempt to identify specific bioactive compounds. Topical applications (60-second exposure, twice daily) with PAC (1.5 mg/ml) during biofilm formation resulted in less biomass and fewer insoluble polysaccharides than the biofilms treated with vehicle control had (10% ethanol, v/v; p < 0.05). The incidence of smooth-surface caries in rats was significantly reduced by PAC treatment (twice daily), and resulted in less severe carious lesions compared to the vehicle control group (p < 0.05); the animals treated with PAC also showed significantly less caries severity on sulcal surfaces (p < 0.05). Furthermore, specific A-type PAC oligomers (dimers to dodecamers; 0.1 mg/ml) effectively diminished the synthesis of insoluble glucans by GtfB adsorbed on a saliva-coated hydroxyapatite surface, and also affected bacterial glycolysis. Our data show that cranberry PAC reduced the formation of biofilms by S. mutans in vitro and dental caries development in vivo, which may be attributed to the presence of specific bioactive A-type dimers and oligomers.