3-O-methylquercetin more selectively inhibits phosphodiesterase subtype 3

Phosphodiesterase 5 and Arginase Inhibitory Activities of the Extracts from Some Members of Nelumbonaceae and Nymphaeaceae Families

The objectives of this study were (1) to investigate the effect of extracts from some plants in the families Nelumbonaceae and Nymphaeaceae on phosphodiesterase 5 (PDE5) and arginase, which have been used in erectile dysfunction treatment, and (2) to isolate and identify the compounds responsible for such activities. The characterization and quantitative analysis of flavonoid constituents in the active extracts were performed by HPLC. Thirty-seven ethanolic extracts from different parts of plants in the genus Nymphaea and Victoria of Nymphaeaceae and genus Nelumbo of Nelumbonaceae were screened for PDE5 and arginase inhibitory activities. The ethanolic extracts of the receptacles and pollens of Nelumbo nucifera Gaertn., petals of Nymphaea cyanea Roxb. ex G.Don, Nymphaea stellata Willd., and Victoria amazonica (Poepp.) Sowerby and the petals and receptacles of Nymphaea pubescens Willd. showed IC50 values on PDE5 of less than 25 μg/mL while none of the extracts showed effects on arginase. The most active extract, N. pubescens petal extract, was fractionated to isolate and identify the PDE5 inhibitors. The results showed that six flavonoid constituents including quercetin 3'-O-β-xylopyranoside (1), quercetin 3-methyl ether 3'-O-β-xylopyranoside (2), quercetin (3), 3-O-methylquercetin (4), kaempferol (5) and 3-O-methylkaempferol (6) inhibited PDE5 with IC50 values at the micromolar level.

Network Pharmacology-Based Identification of Potential Targets of Lonicerae japonicae Flos Acting on Anti-Inflammatory Effects

Lonicerae japonicae flos (LJF) is widely used for the treatment of inflammation-related diseases in traditional Chinese medicine (TCM). To clarify the anti-inflammatory mechanism of LJF, 29 compounds with high content in LJF were selected for network pharmacology. Then, a comprehensive network pharmacology strategy was implemented, which involved compound-inflammation-target construction, protein-protein interaction (PPI) network analysis, and enrichment analysis. Finally, molecular docking and in vitro experiments were performed to verify the anti-inflammatory activity and targets of the key compound. As a result, 279 inflammation-associated proteins were identified, which are mainly involved in the AGE/RAGE signaling pathway in diabetic complications, the HIF-1 signaling pathway, the PI3K-AKT signaling pathway, and EGFR tyrosine kinase inhibitor resistance. A total of 12 compounds were linked to more than 35 targets, including apigenin, kaempferol, quercetin, luteolin, and ferulic acid. The results of molecular docking showed that AKT has the most binding activity, exhibiting certain binding activity with 10 compounds, including vanillic acid, protocatechuic acid, secologanic acid, quercetin, and luteolin; the results of qRT-PCR and WB confirmed that two key compounds, secologanic acid and luteolin, could significantly decrease the secretion of TNF-α and the AKT expression of RAW264.7 murine macrophages stimulated by LPS (lipopolysaccharide). These results demonstrate that the comprehensive strategy can serve as a universal method to illustrate the anti-inflammatory mechanisms of traditional Chinese medicine by identifying the pathways or targets.

Natural Molecules as Talented Inhibitors of Nucleotide Pyrophosphatases/Phosphodiesterases (PDEs)

BACKGROUND

Phosphodiesterases (PDEs) are a wide group of enzymes with multiple therapeutic actions, including vasorelaxation, cardiotonic, antidepressant, anti-inflammatory, antithrombotic, anti-spasmolytic, memory-enhancing, and anti-asthmatic. PDEs with eleven subtypes from PDE-1 to PDE-11 typically catalyze the cleavage of the phosphodiester bond and, hence, degrades either cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP).

OBJECTIVE

Several selective or non-selective inhibitors of the PDE subtypes are used clinically, i.e. sildenafil, rolipram, cysteine, etc. Recently, interest in plant-based pharmacologically bioactive compounds having potent PDEs inhibitory potential has increased. Purposely, extensive research has been carried out on natural products to explore new inhibitors of various PDEs. Therefore, this review summarizes the published data on natural PDEs inhibitors and their potential therapeutic applications.

METHODS

For this purpose, natural compounds with PDE inhibitory potential have been surveyed through several databases, including PubMed, Web of Sciences (WoS), Scopus, and Google Scholar.

RESULTS

According to a detailed literature survey, the most promising class of herbal compounds with PDE-inhibiting property has been found to belong to phenolics, including flavonoids (luteolin, kaempferol, icariin, etc.). Many other encouraging inhibitors from plants have also been identified, such as coumarins (23, 24) (licoarylcoumarin and glycocoumarin,), saponins ( agapanthussaponins), lignans (31, 33) [(±)-schizandrin and kobusin], terpenes (28, 29, 31) (perianradulcin A, quinovic acid, and ursolic acid), anthraquinones (18, 19) (emodin and chrysophanol), and alkaloids (Sanjoinine-D) (36).

CONCLUSION

In this review, studies have revealed the PDE-inhibitory potential of natural plant extracts and their bioactive constituents in treating various diseases; however, further clinical studies comprising synergistic use of different therapies (synthetic & natural) to acquire multi-targeted results might also be a promising option.

Hesperetin-5,7,3'-O-Trimethylether Dually Inhibits Phosphodiesterase 3/4 and Methacholine-Induced Airway Hyperresponsiveness in Sensitized and Challenged Mice

Introduction

Hesperetin-5,7,3ʹ-O-trimethylether (HTME), a synthetic liposoluble hesperetin, has been reported to be a dual phosphodiesterase (PDE)3/4 inhibitor. We investigated its inhibitory effects on methacholine (MCh)-induced airway hyperresponsiveness (AHR) and its potential for treating atypical asthma and COPD.

Methods

FlexiVent system was used to determine AHR in ovalbumin (OVA) sensitized and challenged mice. Determination of cytokines was performed by using mouse T helper (Th)1/Th2 cytokine CBA kits, and of total immunoglobulin (Ig)E and OVA-specific IgE using ELISA kits. The number of inflammatory cells was counted using a hemocytometer. Xylazine/ketamine-induced anesthesia was to assess nausea, vomiting, and gastric hypersecretion in these mice.

Results

HTME dually and competitively inhibited PDE3/4 activities in the Lineweaver–Burk analysis. HTME (30 and 100 μmol/kg) dose-dependently and significantly decreased the airway resistance (R_L) and increased lung dynamic compliance (C_dyn) values induced by MCh. It significantly suppressed numbers of total inflammatory cells and neutrophils, and levels of cytokines in bronchoalveolar lavage fluid (BALF). HTME dose-dependently and significantly inhibited total and OVA-specific IgE levels in the BALF and serum. However, HTME did not influence xylazine/ketamine-induced anesthesia.

Conclusion

HTME exerted anti-inflammatory and bronchodilator effects and may be useful in treating chronic obstructive pulmonary disease and allergic atypical asthma with no gastrointestinal side effects.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Herbs to curb cyclic nucleotide phosphodiesterase and their potential role in Alzheimer's disease

Cyclic nucleotides viz., cAMP/cGMP has been well known to play important role in cellular function and deficiency in their levels has been implicated in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease (AD). Phosphodiesterases (PDE) are the enzymes involved in the metabolism of cyclic nucleotides and the inhibition of phosphodiesterases is considered to be viable strategy to restore the level of cyclic nucleotides and their functions in the brain. Various synthetic PDE inhibitors had been used clinically for various disorders and also suggested to be useful candidates for treating neurological disorders. However, side effects of these synthetic PDE inhibitors have limited their use in clinical practice. Natural plant extracts or their bio-active compounds are considered to be safe and are widely acceptable. During the last decade, many plant extracts or their bio-active compounds were tested pre-clinically for PDE inhibitory activity and are reported to be equally potent in inhibiting PDE's, as that of synthetic compounds. The present review is aimed to discuss the potential plant extract/compounds with PDE inhibitory activity and critically discuss their potential role in Alzheimer's disease.

Inhibitory effects of hesperetin derivatives on guinea pig phosphodiesterases and their ratios between high- and low-affinity rolipram binding

The phosphodiesterase (PDE)4 molecule exists as two distinct conformers, PDE4H and PDE4L , which have high and low affinities, respectively, for the selective PDE4 inhibitor, rolipram. The inhibition of PDE4H and PDE4L is associated with adverse responses, such as nausea, vomiting, and gastric hypersecretion, and with anti-inflammatory and bronchodilator effects, respectively. We determined the therapeutic (PDE4H/PDE4L) ratios of hesperetin-7-O-methylether, hesperetin-5,7,3'-O-trimethylether (HTME), hesperetin-7-O-acetate, hesperetin-7,3'-O-diacetate, hesperetin-5,7,3'-O-triacetate (HTA), hesperetin-5,7,3'-O-tripropionate, hesperetin-5,7,3'-O-tributyrate, hesperetin-5,7,3'-O-triisobutyrate, and hesperetin-5,7,3'-O-tripivatate, and compared these ratios to those of hesperetin, hesperetin-7,3'-O-dimethylether, hesperidin, and hesperidin-3'-O-methylether to identify derivatives with therapeutic ratios and to characterize the structure-activity relationships among these compounds. The activities of PDE isozymes 1 through 5 were measured using a two-step procedure using [(3)H]adenosine 3',5'-cyclic monophosphate or [(3)H]guanosine 3',5'-cyclic monophosphate as substrates. The inhibitory concentration (IC50) for 50% of PDE4 inhibition and effective concentration (EC50) for replacing 50% of [(3)H]rolipram binding on high-affinity rolipram-binding sites was taken as the PDE4L and PDE4H value, respectively. The HTME and the HTA dually inhibited PDE3 and PDE4, and displayed PDE4H/PDE4L ratios of 18.3 and 20.8, respectively, suggesting that they may be candidate drugs for treating asthma and chronic obstructive pulmonary disease (COPD) because the combined inhibition of PDE3 and PDE4 has synergistically anti-inflammatory and bronchodilator effects in COPD patients.

Hesperidin-3'-o-methylether is more potent than hesperidin in phosphodiesterase inhibition and suppression of ovalbumin-induced airway hyperresponsiveness

Hesperidin is present in the traditional Chinese medicine, "Chen Pi," and recently was reported to have anti-inflammatory effects. Therefore, we were interested in comparing the effects of hesperidin and hesperidin-3'-O-methylether on phosphodiesterase inhibition and airway hyperresponsiveness (AHR) in a murine model of asthma. In the present results, hesperidin-3'-O-methylether, but not hesperidin, at 30 μmol/kg (p.o.) significantly attenuated the enhanced pause (P(enh)) value, suppressed the increases in numbers of total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils, suppressed total and OVA-specific immunoglobulin (Ig)E levels in the serum and BALF, and enhanced the level of total IgG(2a) in the serum of sensitized and challenged mice, suggesting that hesperidin-3'-O-methylether is more potent than hesperidin in suppression of AHR and immunoregulation. The different potency between them may be due to their aglycons, because these two flavanone glycosides should be hydrolyzed by β-glucosidase after oral administration. Neither influenced xylazine/ketamine-induced anesthesia, suggesting that they may have few or no adverse effects, such as nausea, vomiting, and gastric hypersecretion. In conclusion, hesperidin-3'-O-methylether is more potent in phosphodiesterase inhibition and suppression of AHR and has higher therapeutic (PDE4(H)/PDE4(L)) ratio than hesperidin. Thus, hesperidin-3'-O-methylether may have more potential for use in treating allergic asthma and chronic obstructive pulmonary disease.

S-Petasin, the Main Sesquiterpene of Petasites formosanus, Inhibits Phosphodiesterase Activity and Suppresses Ovalbumin-Induced Airway Hyperresponsiveness

S-Petasin is the main sesquiterpene of Petasites formosanus, a traditional folk medicine used to treat hypertension, tumors and asthma in Taiwan. The aim of the present study was to investigate its inhibitory effects on phosphodiesterase (PDE) 1–5, and on ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) in a murine model of allergic asthma. S-Petasin concentration-dependently inhibited PDE3 and PDE4 activities with 50% inhibitory concentrations (IC₅₀) of 25.5, and 17.5 μM, respectively. According to the Lineweaver-Burk analysis, S-petasin competitively inhibited PDE3 and PDE4 activities with respective dissociation constants for inhibitor binding (K_i) of 25.3 and 18.1 μM, respectively. Both IC₅₀ and K_i values for PDE3 were significantly greater than those for PDE4. S-Petasin (10–30 μmol/kg, administered subcutaneously (s.c.)) dose-dependently and significantly attenuated the enhanced pause (P_enh) value induced by methacholine (MCh) in sensitized and challenged mice. It also significantly suppressed the increases in total inflammatory cells, lymphocytes, neutrophils, eosinophils and levels of cytokines, including interleukin (IL)-2, IL-4 and IL-5, tumor necrosis factor (TNF)-α and interferon (IFN)-γ in bronchoalveolar lavage fluid (BALF) of these mice. In addition, S-petasin (10–30 μmol/kg, s.c.) dose-dependently and significantly attenuated total and OVA-specific immunoglobulin E (IgE) levels in the serum and BALF, and enhanced the IgG_2a level in serum of these mice. The PDE4_H value of S-petasin was >300 μM; therefore, its PDE4_H/PDE4_L value was calculated to be >17. In conclusion, the present results for S-petasin at least partially explain why Petasites formosanus is used as a folk medicine to treat asthma in Taiwan.

Genistein, a competitive PDE1-4 inhibitor, may bind on high-affinity rolipram binding sites of brain cell membranes and then induce gastrointestinal adverse effects

The affinities of genistein on phosphodiesterase (PDE)1-4 and cause of gastrointestinal adverse effects of genistein remain unclear. Female BALB/c mice were actively sensitized by intraperitoneal injections of ovalbumin and challenged by aerosolized ovalbumin (1%). After secondary challenge, aerosolized methacholine (6.25-50mg/ml) induced increases of enhanced pause (P(enh)) values in conscious mice in a concentration-dependent manner. Genistein (30-100 micromol/kg, i.p.) markedly inhibited methacholine (12.5-50mg/ml)-induced increase of P(enh) value in the sensitized and challenged mice. In addition, genistein significantly reduced total inflammatory cells, macrophages, lymphocytes, neutrophils, and eosinophils in bronchoalveolar lavage fluid, with the exception that lymphocytes and neutrophils were not significantly inhibited by genistein at the lowest dose (10 micromol/kg). Genistein also markedly attenuated the release of cytokines, including interleukin (IL)-2, IL-4, IL-5, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. Genistein competitively inhibited PDE1-4, with a K(i) value ranging from 4.3 to 13.7 microM. Genistein (3-300 microM) concentration-dependently displaced 2nM [(3)H]-rolipram bound on high-affinity rolipram binding sites of brain cell membranes. The therapeutic ratio of genistein was calculated to be 7.9. Genistein (100 micromol/kg, s.c.) significantly shortened xylazine/ketamine-induced anesthesia, suggesting that genistein administered at a higher dose may have gastrointestinal adverse effects. In conclusion, owing to the low therapeutic ratio of genistein, the gastrointestinal adverse effects may be induced via the binding of genistein on high-affinity rolipram binding sites of brain cell membranes, when it is used for a long term or at higher doses for treating allergies, asthma or chronic obstructive pulmonary disease.

A review of the herbal phosphodiesterase inhibitors; future perspective of new drugs

Phosphodiesterase inhibitors (PDEIs) are a class of drugs that are widely used because of their various pharmacological properties including cardiotonic, vasodilator, smooth muscle relaxant, antidepressant, antithrombotic, bronchodilator, antiinflammatory and enhancer of cognitive function. In the recent years, interest in drugs of plant origin has been progressively increased. Some pharmacologically active substances that come from plants demonstrate PDEI activity. They mainly belong to alkaloids, flavonoids, and saponins. In this review, studies on herbal PDEI were reviewed and their possible therapeutic applications were discussed. Screening plants for PDE inhibitory activity may help to develop standardized phytotherapeutic products or find new sources for new lead structures with PDEI pharmacological activity. The studies discussed in this paper are mainly in vitro and for more reasonable and conclusive results, it is required to conduct in vivo and finally human and clinical tests.

Luteolin, a non-selective competitive inhibitor of phosphodiesterases 1-5, displaced [3H]-rolipram from high-affinity rolipram binding sites and reversed xylazine/ketamine-induced anesthesia

The aim of the present study was to investigate the mode of action of luteolin on phisphodiesterase (PDE) 1-5, and the possible adverse effects, such as nausea, vomiting, and gastric hypersecretion, determined by replacing [(3)H]-rolipram binding and reversing xylazine/ketamine-induced anesthesia. The reversing effect was reported to occur through a presynaptic alpha(2)-adrenoceptor inhibition and trigger vomiting in ferrets. In contrast, clonidine, an alpha(2)-adrenoceptor agonist, prevented emesis induced by PDE4 inhibitors in ferrets. According to the Lineweaver-Burk analysis, luteolin (3-30 microM) competitively inhibited PDE1-5 activities, with K(i) values of 15.0, 6.4, 13.9, 11.1, and 9.5 microM, respectively, which did not significantly differ from each other. The equilibrium dissociation constant (K(d)) and maximal density (B(max)) for [(3)H]-rolipram binding at high-affinity rolipram binding sites of guinea pig brain cell membranes were 10.1 nM and 3.7 p mol/g of tissue, respectively. The EC(50) (PDE4(H)) values of luteolin and Ro 20-1724, a selective PDE4 inhibitor, for displacing 2 nM [(3)H]-rolipram binding were 11.2 microM and 45.6 nM, respectively. The therapeutic (PDE4(H)/PDE4(L)) ratios of luteolin and Ro 20-1724 were calculated to be 0.6, and 0.004, respectively. Both luteolin (10-30 micromol/kg, s.c.) and Ro 20-1724 (0.1-1 micromol/kg, s.c.) significantly reversed the xylazine/ketamine-induced anesthesia in mice. Although luteolin non-selectively and competitively inhibited PDE1-5, only PDE4 inhibition contributed to a reversing effect. In conclusion, because of the low therapeutic (PDE4(H)/PDE4(L)) ratio of luteolin, the gastrointestinal adverse effects such as nausea, vomiting and gastric hypersecretion should be carefully monitored, whenever luteolin is used for treating allergies, asthma or chronic obstructive pulmonary disease.

Inhibition of human cAMP-phosphodiesterase as a mechanism of the spasmolytic effect of Matricaria recutita L

Mechanisms underlying the spasmolytic activity of chamomile still remain unclear. Inhibition of cAMP- and cGMP-phosphodiesterases (PDE) is one of the mechanisms operated by spasmolytic drugs. In this study, the effect of chamomile on PDE was investigated. Human platelet cAMP-PDE and recombinant PDE5A1 were assayed in the presence of infusions prepared from sifted flowers and capitula. LC-ESI-MS/MS analysis showed different compositions in infusions made with sifted flowers and capitula. Chamomile inhibited cAMP-PDE activity (IC50 = 17.9-40.5 microg/mL), while cGMP-PDE5 was less affected (-15% at 50 microg/mL). Among the individual compounds tested, only flavonoids showed an inhibitory effect (IC50 = 1.3-14.9 microM), contributing to around 39% of the infusion inhibition; other compounds responsible for cAMP-PDE inhibition still remain unknown. Although experimental evidence supporting the use of chamomile for gastrointestinal minor spasms dates back to the fifties, cAMP-PDE inhibition as a likely mechanism underlying the spasmolytic activity is reported for the first time.

Anti-asthmatic action of quercetin and rutin in conscious guinea-pigs challenged with aerosolized ovalbumin

The effects of quercetin and rutin on the asthmatic responses were studied in ovalbumin (OA)-sensitized conscious guinea pigs challenged with aerosolized-OA. We measured the specific airway resistance (sRaw) in the double-chambered plethysmograph during the immediate-phase response (IAR) and late-phase response (LAR) at 3 approximately 10 min and 24 hr after OA challenge, respectively. We counted leukocytes in bronchoalveolar lavage fluid (BALF) using Wright's stain, as well as in lung tissue fixed with 10% formalin and stained with H & E stain. Quercetin and rutin (7.5 mg/kg, p.o.) significantly and dose-dependently inhibited both sRaw on IAR (31.60 and 26.44%) and LAR (29.87 and 28.69%) but with less efficacy than dexamethasone (3 mg/kg) and salbutamol (0.3 mg/kg), which inhibited IAR by 36.71 and 69.45%, and LAR by 67.23 and 0%, respectively, Quercetin and rutin (15 mg/kg) also inhibited production of histamine, PLA2, and EPO, and recruitment of leukocytes, particularly neutrophils and eosinophils, during LAR. respectively. Dexamethasone (3 mg/kg) also significantly reduced the recruitment of neutrophils, eosinophils, and lymphocytes in BALF, and salbutamol (0.3 mg/kg) reduced neutrophils and eosinophils with lower activity than dexamethasone. These results indicate that quercetin and rutin may be useful in the treatment of IAR and LAR in asthma via inhibition of histamine release, PLA2, and EPO, and reduced recruitment of neutrophils and eosinophils into the lung.

Inhibitory effects of quercetin derivatives on phosphodiesterase isozymes and high-affinity [(3) H]-rolipram binding in guinea pig tissues

Rolipram has high (PDE4(H)) and low (PDE4(L)) affinities for phosphodiesterase (PDE)-4, respectively. In general, it is believed that inhibitions by PDE4(H) and PDE4(L) are respectively associated with an adverse response and with anti-inflammatory and bronchodilating effects. This has provided a rational basis for designing new compounds with high PDE4(H)/PDE4(L) ratios. In the present study, we attempted to determine the PDE4(H)/PDE4(L) ratios of quercetin (1), qercetin-3-O-methylether (3-MQ, 2), quercetin-3,7,4'-O-trimethylether (ayanin, 3), quercetin-3,7,3',4'-O- tetramethylether (QTME, 4), quercetin-3,5,7,3',4'-O-petamethylether (QPME, 5), quercetin-3,5,7,3',4'-O-pentaacetate (QPA, 6), and quercetin-3-O-methyl-5,7,3',4'-O-tetraacetate (QMTA, 7). The activities of PDE1 approximately 5, which were partially separated from homogenates of guinea pig lungs and hearts, were measured by a two-step procedure using adenosine 3',5'-cyclic monophosphate (cAMP) with [(3) H]-cAMP or guanosine 3',5'-cyclic monophosphate (cGMP) with [(3) H]-cGMP as substrates. The IC(50) values of all of these compounds except quercetin (1), 3-MQ (2), and QMTA (7) on PDE1 approximately 5 inhibition were determined. The anti-inflammatory effects of PDE4 inhibitors were reported to be associated with inhibition of PDE4 catalytic activity. Therefore, these IC(50) values for PDE4 inhibition were taken as the PDE4(L) values. The effective concentration (EC(50)), at which one half of the [(3) H]-rolipram bound to high-affinity rolipram binding sites (HARBSs) of brain cell membranes was replaced, was defined as the PDE4(H) value. In the present results, the PDE4(H)/PDE4(L) ratios of quercetin (1), ayanin (3), and QPME (5) were >30, >19, and 11, respectively (Table 1), which are higher than or equal to that of AWD12-281, the selective PDE4 inhibitor with the greatest potential currently undergoing clinical trials for treating asthma and chronic obstructive pulmonary disease.

Anti-proliferative effect of Euphorbia stenoclada in human airway smooth muscle cells in culture

The ethanolic extract of a Malagasy species Euphorbia stenoclada (ES) (Euphorbiaceae), traditionally used as a herbal remedy against asthma and acute bronchitis, was tested to evaluate possible anti-proliferative activity on human airway smooth muscle cells (HASMC). The ES ethanolic extract totally abolished the interleukin-1beta (IL-1beta) induced proliferation of HASMC (IC(50)=0.73+/-0.08 microg/mL). No cytotoxic effect was observed up to 20 microg/mL. A bioassay-guided fractionation of the ethanolic extract was performed by reversed-phase (RP) flash chromatography, giving five fractions (FA to FE) where fraction FE was the only active one (IC(50)=0.38+/-0.02 microg/mL). The purification of this bioactive fraction FE was carried out by RP-HPLC affording six sub-fractions 1-6, and only sub-fraction 5 kept the anti-proliferative activity. Its major constituent was identified as quercetin (IC(50)=0.49+/-0.12 microg/mL) by means of HPLC/UV/MS and co-elution with the authentic standard. Quercitrin was also identified in the fraction FE but was inactive. A structure-activity relationship with flavonols determined that methylation reduced the anti-proliferative activity whereas glycosylation abolished it. The present study shows that the anti-proliferative properties of Euphorbia stenoclada are mediated through the presence of quercetin that may explain the traditional use of this plant as a remedy against asthma.

Antioxidative Effects of 6-Methoxysorigenin and Its Derivatives from Rhamnus nakaharai

In the search for potential antioxidants, the naphthalenic compounds, 6-methoxysorigenin (2) and its glycosides [i.e. 6-methoxysorigenin-8-O-glucoside (3), alpha-sorinin (4), and 6-methoxysorigenin-8-rutinoside (5)] isolated from Rhamnus nakaharai together with two acylates (peracetate and perpropionate) of 2 were evaluated for antioxidant activities using 2,2-diphenyl-1-picrylhydrazyl (DPPH), metal chelating, and electron spin resonance (ESR) assays as well as anti-lipid peroxidation assay. The results showed that 2 possesses the most potent DPPH radical scavenging, metal chelating, and anti-lipid peroxidation activities with IC50 values of 3.48, 615.90, and 5.95 microg/ml, respectively. The glycosides 3, 4, and 5 showed decreasing antioxidant activity that was related to an increased substitution at 1,8-dihydroxyl with sugar molecules. This suggests the importance of 1,8-dihydroxyl of 2 in the antioxidative effect. The iron chelation result could further explain the main cause of increasing antioxidant activity in 2. The acylates of 2 (2a peracetate and 2b perpropionate), although lacking a free hydroxyl, also exhibited significant anti-lipid peroxidation effect. ESR results further demonstrated that 2 possesses strong antioxidant activities. Taken together, this study shows that 2 is a potent antioxidant and may also be used for designing new iron chelators for clinical applications.

FRS 1000, an extract of red onion peel, strongly inhibits phosphodiesterase 5A (PDE 5A)

As part of our ongoing search for flavonoids that are bioactive in humans, it was determined that FRS 1000, a beverage containing flavonoids extracted from onion peel, showed unexpected improvement of male sexual function. An in vitro enzyme assay clearly showed that FRS 1000 has a strong phosphodiesterase 5A (PDE 5A) inhibitory activity, which is considered to be important for treatment of erectile dysfunction. Detailed assays of each major ingredient indicated that the antioxidative flavonoid quercetin was responsible for the activity. Results also suggested that PDE 5A inhibition is not directly related to the free radical scavenging activity of flavonoids.

Mechanisms of suppression of nitric oxide production by 3-O-methylquercetin in RAW 264.7 cells

Rhamnus nakaharai Hayata (Rhamnaceae) is used as a folk medicine in Taiwan for treating constipation, inflammation, tumors, and asthma. 3-O-Methylquercetin (3-MQ), a main constituent of the plant, has been reported to have potential for use in the treatment of asthma. The mechanisms of anti-inflammation of 3-MQ are still unclear. Nitric oxide (NO) production induced by lipopolysaccharide (LPS) through iNOS expression in RAW 264.7 cells, a mouse macrophage cell line, may reflect the degree of inflammation and may provide a measure for assessing the effect of drugs on the inflammatory process. Therefore, we were interested in investigating the mechanisms of suppression of NO production by 3-MQ in RAW 264.7 cells. 3-MQ (1-10 microM) concentration-dependently inhibited LPS (100 ng/mL)-induced NO production in RAW 264.7 cells. The IC(50) value was calculated to be 4.23 microM. 3-MQ (1-10 microM) significantly and concentration-dependently inhibited LPS (100 ng/mL)-induced iNOS protein and mRNA expressions in cells. The IC(50) values were calculated to be 4.36 and 6.53 microM, respectively. There was no significant difference among these three IC(50) values of 3-MQ. In conclusion, 3-MQ may exert its anti-inflammatory effect through the inhibition of iNOS DNA transcription.

Inhibitory effects of flavonoids on phosphodiesterase isozymes from guinea pig and their structure-activity relationships

The structure-activity relationships of flavonoids with regard to their inhibitory effects on phosphodiesterase (PDE) isozymes are little known. The activities of PDE1-5 were measured by a two-step procedure using cAMP with [(3)H]-cAMP or cGMP with [(3)H]-cGMP as substrates. In the present results, PDE1, 5, 2, and 4 isozymes were partially purified from guinea pig lungs in that order, and PDE3 was from the heart. The IC(50) values of PDE1-5 were greater than those reported previously for the reference drugs, vinpocetin, EHNA, milrinone, Ro 20-1724, and zaprinast, by 5-, 5-, 7-, 5-, and 3-fold, respectively. As shown in Table 2, luteolin revealed non-selective inhibition of PDE1-5 with IC(50) values in a range of 10-20 microM, as did genistein except with a low potency on PDE5. Daidzein, an inactive analogue of genistein in tyrosine kinase inhibition, showed selective inhibition of PDE3 with an IC(50) value of around 30 microM, as did eriodictyol with an IC(50) value of around 50 microM. Hesperetin and prunetin exhibited more-selective inhibition of PDE4 with IC(50) values of around 30 and 60 microM, respectively. Luteolin-7-glucoside exhibited dual inhibition of PDE2/PDE4 with an IC(50) value of around 40 microM. Diosmetin more-selectively inhibited PDE2 (IC(50) of 4.8 microM) than PDE1, PDE4, or PDE5. However, biochanin A more-selectively inhibited PDE4 (IC(50) of 8.5 microM) than PDE1 or PDE2. Apigenin inhibited PDE1-3 with IC(50) values of around 10-25 microM. Myricetin inhibited PDE1-4 with IC(50) values of around 10-40 microM. The same was true for quercetin, but we rather consider that it more-selectively inhibited PDE3 and PDE4 (IC(50) of < 10 microM). In conclusion, it is possible to synthesize useful drugs through elucidating the structure-activity relationships of flavonoids with respect to inhibition of PDE isozymes at concentrations used in this in vitro study.

Partial purification, kinetic analysis, and amino acid sequence information of a flavonol 3-O-methyltransferase from Serratula tinctoria

Serratula tinctoria (Asteraceae) accumulates mainly 3,3'-dimethylquercetin and small amounts of 3-methylquercetin as an intermediate. The fact that 3-methylquercetin rarely accumulates in plants in significant amounts, and given its important role as an antiviral and antiinflammatory agent that accumulates in response to stress conditions, prompted us to purify and characterize the enzyme involved in its methylation. The flavonol 3-O-methyltransferase (3-OMT) was partially purified by ammonium sulfate precipitation and successive chromatography on Superose-12, Mono-Q, and adenosine-agarose affinity columns, resulting in a 194-fold increase of its specific activity. The enzyme protein exhibited an expressed specificity for the methylation of position 3 of the flavonol, quercetin, although it also utilized kaempferol, myricetin, and some monomethyl flavonols as substrates. It exhibited a pH optimum of 7.6, a pI of 6.0, and an apparent molecular mass of 31 kD. Its K(m) values for quercetin as the substrate and S-adenosyl-l-Met (AdoMet) as the cosubstrate were 12 and 45 microm, respectively. The 3-OMT had no requirement for Mg(2+), but was severely inhibited by p-chloromercuribenzoate, suggesting the requirement for SH groups for catalytic activity. Quercetin methylation was competitively inhibited by S-adenosyl-l-homo-Cys with respect to the cosubstrate AdoMet, and followed a sequential bi-bi reaction mechanism, where AdoMet was the first to bind and S-adenosyl-l-homo-Cys was released last. In-gel trypsin digestion of the purified protein yielded several peptides, two of which exhibited strong amino acid sequence homology, upon protein identification, to a number of previously identified Group II plant OMTs. The availability of peptide sequences will allow the design of specific nucleotide probes for future cloning of the gene encoding this novel enzyme for its use in metabolic engineering.