In vitro anti-cariogenic activity of dichloromethane fraction from Rheum undulatum L. root

Ethnobotanical Uses, Phytochemistry and Pharmacology of Different Rheum Species (Polygonaceae): A Review

Today, there is an increased tendency to use herbal remedies. Rhubarb refers to several species of the genus Rheum L. in the Polygonaceae family. This species-rich genus is mainly distributed in Asian countries. Several medicinal effects have been attributed to the Rheum spp. in the traditional and modern medicine such as healing lungs, liver, kidney, womb and bladder diseases, cancer, diabetes, insect bites, relapsing fevers, diarrhea and constipation. Various in vitro, in vivo and clinical studies have investigated the therapeutic effect of extracts, fractions and pure compounds isolated from different species of this genus. Considering the positive findings, several pharmaceutical formulations containing rhubarb extract like capsules, drops, mouthwashes and different topical formulations are now present in the market. However, there are other traditional therapeutic effects of rhubarb that have not been studied yet and it is of great importance to perform confirmatory experiments or clinical investigations. The current review summarizes general information regarding botany, phytochemistry, ethnobotany and pharmacological aspects of Rheum spp. It is hoped that the present review could motivate subsequent research on the other medicinal properties of these plants that have been neglected until today.

Stilbenes contribute to the anticancer effects of Rheum undulatum L. through activation of apoptosis

Rheum undulatum L. (R. undulatum) is a medicinal plant used for the treatment of inflammatory diseases in East Asian countries. Numerous stilbenes isolated from R. undulatum have been revealed to possess anticancer effects. The aim of the present study was to evaluate the effect of extracts and compounds isolated from R. undulatum on human gastric cancer cell viability and to elucidate their molecular mechanism of action on the apoptosis pathway. The results demonstrated that aloe-emodin and chrysophanol 1-O-β-D-glucopyranoside, isolated from the methanolic extract of dried rhizomes of R. undulatum, exhibited anti-proliferative effects on the human gastric carcinoma cell line AGS, with IC₅₀ values of 84.66±0.44 and 68.28±0.29 µM, respectively. The percentage of apoptotic cells increased significantly following treatment with each compound at a concentration of 100 µM, compared with that in the non-treated group in the image-based cytometry assay. Western blot analysis revealed that these compounds activated the caspase cascade and inhibited B-cell lymphoma-2, an anti-apoptotic protein.

Rhaponticin decreases the metastatic and angiogenic abilities of cancer cells via suppression of the HIF‑1α pathway

Rhaponticin (RA; 3′5-dihydroxy-4′-methoxystilbene 3-O-β-D-glucopyranoside) is a component isolated from various medicinal herbs including Rheum undulatum L. RA has been reported to be an effective treatment for allergy, diabetes, thrombosis, liver steatosis, lung fibrosis and colitis. In addition, RA effectively inhibits tumor growth and induces apoptosis; however, the effects of RA, at non-cytotoxic doses, on the metastasis and angiogenesis of malignant cancer cells have, to be the best of our knowledge, not been identified. In the present study, it was identified that RA suppressed the metastatic potential of MDA-MB231 breast cancer cells, including colony formation, migration and invasion. Human umbilical vein endothelial cells (HUVECs) treated with RA exhibited a decreased ability to form tube-like networks and to migrate across a Transwell membrane, when compared with RA-untreated HUVECs. Using the chick chorioallantoic membrane assay, RA treatment significantly suppressed spontaneous and vascular endothelial growth factor (VEGF)-induced angiogenesis. Furthermore, RA inhibited the production of pro-angiogenic factors, including matrix metalloproteinase (MMP)-9, pentraxin-3, interleukin-8, VEGF and placental growth factor under normoxic and hypoxic conditions, and suppressed the phorbol 12-myristate 13-acetate-induced increase in the gelatinolytic MMP-9 activity and MMP-9 expression in HT1080 cells. RA also significantly inhibited the hypoxia-inducible factor (HIF)-1α pathway, leading to decreased HIF-1α accumulation and HIF-1α nuclear expression under hypoxia. These results indicated that RA exhibits potent anti-metastatic and anti-angiogenic activities with no cytotoxicity via suppression of the HIF-1α signaling pathway. Thus, RA may control malignant cancer cells by inhibiting the spread from primary tumors and expansion to distant organs.

Inhibited biofilm formation and improved antibacterial activity of a novel nanoemulsion against cariogenic Streptococcus mutans in vitro and in vivo

The aim of this study was to prepare a novel nanoemulsion loaded with poorly water-soluble chlorhexidine acetate (CNE) to improve its solubility, and specifically enhance the antimicrobial activity against Streptococcus mutans in vitro and in vivo. In this study, a novel CNE nanoemulsion with an average size of 63.13 nm and zeta potential of −67.13 mV comprising 0.5% CNE, 19.2% Tween 80, 4.8% propylene glycol, and 6% isopropyl myristate was prepared by the phase inversion method. Important characteristics such as the content, size, zeta potential, and pH value of CNE did not change markedly, stored at room temperature for 1 year. Also, compared with chlorhexidine acetate water solution (CHX), the release profile results show that the CNE has visibly delayed releasing effect in both phosphate-buffered saline and artificial saliva solutions (P<0.005). The minimum inhibitory concentration and minimum bactericidal concentration of CHX for S. mutans (both 0.8 μg/mL) are both two times those of CNE (0.4 μg/mL). Besides, CNE of 0.8 μg/mL exhibited fast-acting bactericidal efficacy against S. mutans, causing 95.07% death within 5 minutes, compared to CHX (73.33%) (P<0.01). We observed that 5 mg/mL and 2 mg/mL CNE were both superior to CHX, significantly reducing oral S. mutans numbers and reducing the severity of carious lesions in Sprague Dawley rats (P<0.05), in an in vivo test. CNE treatment at a concentration of 0.2 μg/mL inhibited biofilm formation more effectively than CHX, as indicated by the crystal violet staining method, scanning electron microscopy, and atomic force microscopy. The cell membrane of S. mutans was also severely disrupted by 0.2 μg/mL CNE, as indicated by transmission electron microscopy. These results demonstrated that CNE greatly improved the solubility and antimicrobial activity of this agent against S. mutans both in vitro and in vivo. This novel nanoemulsion is a promising medicine for preventing and curing dental caries.

Desoxyrhapontigenin up-regulates Nrf2-mediated heme oxygenase-1 expression in macrophages and inflammatory lung injury

Heme oxygenase-1 (HO-1) is an important anti-inflammatory, antioxidative and cytoprotective enzyme that is regulated by the activation of the major transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In the present study, six stilbene derivatives isolated from Rheum undulatum L. were assessed for their antioxidative potential. In the tert-butylhydroperoxide (t-BHP)-induced RAW 264.7 macrophage cell line, desoxyrhapontigenin was the most potent component that reduced intracellular reactive oxygen species (ROS) and peroxynitrite. In response to desoxyrhapontigenin, the mRNA expression levels of antioxidant enzymes were up-regulated. An electrophoretic mobility shift assay (EMSA) confirmed that desoxyrhapontigenin promoted the DNA binding of Nrf2 and increased the expression of antioxidant proteins and enzymes regulated by Nrf2. Further investigation utilizing specific inhibitors of Akt, p38, JNK and ERK demonstrated that the phosphatidylinositol 3-kinase (PI3K)/Akt pathway mediates HO-1 expression. Moreover, the increase in Nrf2 expression mediated by treatment with desoxyrhapontigenin was reversed by Nrf2 or Akt gene knock-down. In the LPS-induced in vivo lung inflammation model, pretreatment with desoxyrhapontigenin markedly ameliorated LPS-induced lung inflammation and histological changes. Immunohistochemical analysis of Nrf2, HO-1 and p65 was conducted and confirmed that treatment with desoxyrhapontigenin induced Nrf2 and HO-1 expression but reduced p65 expression. These findings suggest that desoxyrhapontigenin may be a potential therapeutic candidate as an antioxidant or an anti-inflammatory agent.

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Enhancement of the levels of antioxidant enzymes by desoxyrhapontigenin.

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Promotion of DNA binding affinity of Nrf2 in RAW 264.7 macrophages.

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Induction of HO-1 expression and inhibition of Keap1 by desoxyrhapontigenin via the Akt pathway.

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Amelioration of LPS-induced inflammatory lung injury in mice.

Effects of Japanese traditional herbal medicines (Kampo) on growth and virulence properties of Porphyromonas gingivalis and viability of oral epithelial cells

CONTEXT

Kampos, commonly used in Japanese traditional medicine, are standardized herbal mixtures that have been used for centuries to treat a variety of ailments. We hypothesized that Kampos may have unidentified properties that may be beneficial in periodontitis, an inflammatory disease affecting the tooth-supporting tissues.

OBJECTIVE

The aim of our study was to investigate various Kampos and their natural ingredients for their effects on Porphyromonas gingivalis growth, adherence to epithelial cells and proteinase activity. In addition, their effects on oral epithelial cell viability were evaluated.

MATERIALS AND METHODS

Growth inhibition of P. gingivalis by various Kampos and their natural ingredients was evaluated by a microdilution broth assay method. Their effects on P. gingivalis proteinase activity and adherence to oral epithelial cells were determined by fluorometric assays. The cytotoxicity of test compounds towards oral epithelial cells was evaluated by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] test.

RESULTS

Of the 27 Kampos tested, 7 were found to inhibit the growth of P. gingivalis. The lowest minimal inhibitory concentration (MIC) (250 µg/ml) was obtained with TJ-113. Analysis of the composition of the seven active Kampos showed that they contain Chinese rhubarb as a common ingredient. Therefore, additional growth inhibitory assays on P. gingivalis were carried out with purified anthraquinones known to be present in rhubarb. Aloe-emodin and rhein possessed the strongest antibacterial effects towards P. gingivalis with an MIC of 0.78 µg/ml. The seven Kampos containing rhubarb and purified anthraquinones also exhibited the capacity to decrease the adherence of P. gingivalis to oral epithelial cells and to reduce its proteinase activity. The most important anti-adherence effect of Kampo was obtained with TJ-126; at 250 µg/ml it reduced adherence of P. gingivalis to epithelial cells by 83%. Purified anthraquinones were found to be less active than Kampos. Kampo TJ-113 was found to be the most effective for inhibition of gelatin degradation (49% inhibition at 62.5 µg/ml). Again, purified anthraquinones inhibited gelatin degradation to a lesser extent. Lastly, none of the tested compounds showed cytotoxicity towards oral epithelial cells at the effective concentrations.

CONCLUSION

Kampos containing rhubarb and its anthraquinone derivatives may represent promising molecules for controlling periodontal diseases through their capacity to inhibit P. gingivalis growth and virulence properties.

Antimicrobial activity and total content of polyphenols of Rheum L. species growing in Poland

In the crude ethanol extracts obtained from the rhizome and roots of Rheum palmatum L., Rheum undulatum L. and Rheum rhaponticum L. growing in Poland concentration of polyphenols ranged from 46.11 to 76.45 mg/g. Concentration of tannins ranged from 7.07% to 8.67%, while anthracene derivatives and anthraquinones varied by species - R. palmatum measured 36.3 and 34 mg/g, while R. undulatum or R. rhaponticum did not exceed 20.4 and 18.1 or 19.8 mg/g and 16.6 mg/g, respectively. Using a broth microdilution method it was found that all of the Rheum spp. extracts were more active against reference strains of Gram-positive bacteria (Staphylococcus spp.) than against those of Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis). The strongest inhibitory effect against Staphylococcus spp. was exerted by R. undulatum extract with MIC = 125–250 μg/mL. The moderate in vitro antibacterial activity of R. undulatum suggests that this plant, often used in the European cuisine to improve flavour, may be also important and useful as an alternative or auxiliary medicine remedy in the treatment of uncomplicated superficial infections caused especially by clinically important staphylococci, potentially pathogenic S. aureus or opportunistic S. epidermidis.

Inhibitory effect of a bioactivity-guided fraction from Rheum undulatum on the acid production of Streptococcus mutans biofilms at sub-MIC levels

Rheum undulatum root has been used traditionally in Korea for the treatment of dental diseases. The purpose of this study was to separate a fraction from R. undulatum showing anti-acid production activity against Streptococcus mutans biofilms and identify the main components in that fraction. Methanol extract of R. undulatum root and its fractions were prepared. To select a fraction exhibiting anti-acid production activity, suspension glycolytic pH-drop assay was performed. Among the fractions tested, dichloromethane fraction exhibited the strongest activity in a dose-dependent manner. To examine the effect of the selected fraction on the anti-acid production of S. mutans biofilms, 74 h old S. mutans biofilms were used. The selected fraction reduced the initial rate of acid production of S. mutans biofilms at sub-minimum inhibitory concentration (MIC) levels. HPLC qualitative analysis of the selected fraction indicated that the presence of anthraquinone derivatives, such as aloe-emodin, emodin, chrysophanol and physcion, as main components.

Inhibition of human low density lipoprotein and high density lipoprotein oxidation by oligostilbenes from rhubarb

The objective of the present study was to elucidate the beneficial properties of ampelopsine B (1) and epsilon-Viniferin (2), two oligostilbenes isolated from rhubarb, toward cardiovascular disease by protecting human lipoproteins against lipid peroxidation. In low density lipoprotein (LDL) oxidation, both 1 and 2 exert an inhibitory activity against Cu(2+)-, 2,2'-azobis-(2-amidinopropane) hydrochloride (AAPH)-induced, as exhibited by prolongation of lag time from 52 to 118 and 136 min, respectively, and also increasing the lag time 38 to 105 and 128 min in high density lipoprotein (HDL) oxidation for 1 and 2, respectively, at the concentration of 3.0 microM. In generation of thiobarbituric acid reactive substances (TBARS), compounds 1 and 2 inhibited LDL oxidation mediated by either catalytic Cu(2+) or thermo-labile radical initiator (AAPH) in a dose-dependent manner with IC(50) values of 3.6 and 6.0 microM for 1, and 1.7 and 3.2 microM for 2, respectively. In addition, compounds 1-2 also showed strong ability to protect HDL oxidation induced by both Cu(2+) and AAPH with low IC(50) values. The results suggest that oligostilbenes 1-2 may have a role in preventing lipoprotein oxidation.

Lipoxygenase inhibitory constituents from rhubarb

Phytochemical study on the ethanol extract of rhubarb led to the isolation of fifteen compounds, including five anthraquinones: chrysophanol (1), physcion (2), emodin (7), chrysophanol-8-O-beta-D: -glucopyranoside (9) and emodin-8-O-beta-D: -glucopyranoside (15), and ten stilbenes: desoxyrhaponticin (3), rhaponticin (4), resveratrol (5), desoxyrhapotigenin (6), rhapontigenin (8), piceatannol-3'-O-beta-D: -glucopyranoside (10), piceid (11), epsilon-viniferin (12), ampelopsin B (13) and isorhaponticin (14). Their structures were identified by comparing the physicochemical data with those of published papers. Among the isolated compounds, stilbene derivatives (3-6, 8 and 10-14) showed remarkable inhibitory effect on lipoxygenase with IC(50) values ranging from 6.7 to 74.1 microM. The inhibition kinetics analyzed by Lineweaver-Burk plots found that they were competitive inhibitors with the linoleic acid at the active site of lipoxygenase. In addition, stilbenes exhibited significantly free radical scavenging activity against ABTS(.+) with trolox equivalent activity capacity (TEAC) values ranging from 1.16 to 4.64. Whereas, anthraquinone derivatives (1-2, 7, 9 and 15) neither inhibited lipoxygenase nor scavenged free radical ABTS(.+). These results indicated that stilbene derivatives were considerate to be mainly lipoxygenase inhibitor and free radical scavenger constituents of rhubarb.