Quercetin as the active principle of Hypericum hircinum exerts a selective inhibitory activity against MAO-A: extraction, biological analysis, and computational study

The Antidepressant-like Effect of Ethanol Extract of Daylily Flowers ( Jīn Zhēn Huā) in Rats

According to the prediction of the 2008 World Health Organization (WHO) report, depression will be the highest burden disease by the year 2030. Daylily flower ( Jīn Zhēn Huā ; the flower of Hemerocallis fulva) is traditionally used for soothing in Chinese dietary therapy. The major flavonoid of daylily flowers, rutin, is also characterized to be an antidepressant. In this study, we investigated the antidepressant effects of ethanol extract of daylily flowers (DFEtoH) and rutin by forced swimming test (FST) and neurotransmitter metabolism of brain regions (frontal cortex, hippocampus, striatum, and amygdala). Results show that either short- or long-term tests, the extract and rutin significantly reduce the immobility time and increased swimming time of FST, which are compared with the vehicle (P < 0.05). The extract and rutin also increase the serotonin, norepinephrine, and dopamine concentration of these brain regions (P < 0.05). In long-term tests, the daylily flowers extract markedly increased serotonin concentration and reduced serotonin turnover rate in these brain regions but not frontal cortex. In conclusion, present data illustrated that DFEtoH does have antidepressant-like effects possibly via the regulation of serotonergic system. Moreover, rutin might be playing a very important role in the antidepressant-like effects of DFEtoH.

Inhibition of LOX by flavonoids: a structure-activity relationship study

The lipoxygenase (LOX) products have been identified as mediators of a series of inflammatory diseases, namely rheumatoid arthritis, inflammatory bowel disease, psoriasis, allergic rhinitis, atherosclerosis and certain types of cancer. Hence, LOX inhibitors are of interest for the modulation of these phenomena and resolution of the inflammatory processes. During LOX activity, peroxyl radical complexes are part of the reaction and may function as sources of free radicals. Thus antioxidants, such as flavonoids, capable of inhibiting lipid peroxidation and scavenging free radicals, may act as LOX inhibitors. The aim of this work was to assess the structure-activity relationship among a series of flavonoids concerning 5-LOX inhibition, through a systematic study of the inhibition of the formation of LTB4 in human neutrophils. The type of inhibition of the flavonoids was further studied using soybean LOX, type I, and Saturation Transfer Difference (1)H NMR (STD-(1)H NMR) was used to characterize the binding epitopes of the compounds to LOX-1. The obtained results reinforce flavonoids as effective inhibitors of LTB4 production in human neutrophils. It was also possible to establish a structure/activity relationship for the inhibitory activity and the type of inhibition.

An automated sequential injection spectrophotometric method for evaluation of tyramine oxidase inhibitory activity of some flavonoids

An automated sequential injection (SI) spectrophotometric system has been developed for evaluation of tyramine oxidase (TOD) inhibitory activity. The method is based on the inhibition of TOD that catalyzes the oxidation of tyramine substrate to produce aldehyde and hydrogen peroxide (H₂O₂). The produced H₂O₂ reacts with vanillic acid and 4-aminoantipyrine (4-AA) in the presence of peroxidase (POD) to form a quinoneimine dye, the absorbance of which is measured of absorbance at wavelength of 490 nm. The decrease of the quinoneimine dye is related to an increase of TOD inhibitory activity. Under the optimum conditions: 1.0 mM tyramine, 8 U mL(-1) TOD, 1.0 mM vanillic acid, 1.0 mM 4-AA and delay time of 10 s, some flavonoid compounds were examined for the TOD inhibitory activity expressed as IC₅₀ value. It was found that flavonols (quercetin and myricetin) and flavans (epicatechin gallate (ECG) and epigallocatechin (EGC)) showed higher TOD inhibitory activity than flavones and flavanones. The results of IC₅₀ values obtained from the proposed method and a batch-wise method were not significantly different from each other. Moreover, the SI system enabled automation of the analysis, leading to more convenient, more sensitive and faster analysis than the batch-wise method. A precise timing of the system also improves precision and accuracy of the assay, especially when the measurement of absorbance at non-steady state condition is involved.

Selective MAO-B inhibitors: a lesson from natural products

Monoamine oxidases (MAOs) are mitochondrial bound enzymes, which catalyze the oxidative deamination of monoamine neurotransmitters. Inside the brain, MAOs are present in two isoforms: MAO-A and MAO-B. The activity of MAO-B is generally higher in patients affected by neurodegenerative diseases like Alzheimer's and Parkinson's. Therefore, the search for potent and selective MAO-B inhibitors is still a challenge for medicinal chemists. Nature has always been a source of inspiration for the discovery of new lead compounds. Moreover, natural medicine is a major component in all traditional medicine systems. In this review, we present the latest discoveries in the search for selective MAO-B inhibitors from natural sources. For clarity, compounds have been classified on the basis of structural analogy or source: flavonoids, xanthones, tannins, proanthocyanidins, iridoid glucosides, curcumin, alkaloids, cannabinoids, and natural sources extracts. MAO inhibition values reported in the text are not always consistent due to the high variability of MAO sources (bovine, pig, rat brain or liver, and human) and to the heterogeneity of the experimental protocols used.

Hypericum hircinum L. components as new single-molecule inhibitors of both HIV-1 reverse transcriptase-associated DNA polymerase and ribonuclease H activities

Among HIV-1 reverse transcriptase (RT)-associated functions, DNA polymerase and Ribonuclease H (RNase H) are both essential for HIV replication and excellent targets for drug development. While all RT inhibitors approved for therapy target the DNA polymerase activity, there is the pressing need for new RT inhibitors possibly targeting the RNase H function. In the last 20 years, many natural substances have shown antiviral activity against HIV-1, but only a few against the RNase H function. In this study, we have tested the ethanolic extracts obtained by the Hypericum hircinum L. (Hypericaceae) growing in Sardinia (Italy) on the HIV-1 RT-associated RNase H function and found that they have inhibitory effects. Active extracts were fractionated up to obtain the main components that have been isolated, tested, and identified to be betulinic acid, shikimic acid, chlorogenic acid, quercetin, 5,7,3',5'-tetrahydroxyflavanone, and 5,7,3',5'-tetrahydroxyflavanone 7-O-glucoside. Betulinic acid and 5,7,3',5'-tetrahydroxyflavanone 7-O-glucoside were active on both RT-associated activities, and betulinic acid was also active on HIV-1 mutant RTs resistant to efavirenz. Overall, our results suggest that some of these compounds inhibit the HIV-1 RT binding to an allosteric site previously described for other natural compounds and are potential leads for further drug development of a single molecules having dual inhibitory activity.

Screening of plants used in Danish folk medicine to treat depression and anxiety for affinity to the serotonin transporter and inhibition of MAO-A

ETHNOPHARMACOLOGICAL RELEVANCE

A number of plant species are used in Danish folk medicine for treatment of depression and anxiety.

MATERIALS AND METHODS

Aqueous and ethanolic extracts of 17 plant species were tested for affinity to the serotonin transporter and for inhibition of MAO-A-both targets for antidepressive treatment.

RESULTS

An ethanolic extract of aerial parts of Borago officinalis had affinity to the serotonin transporter. Ten extracts, from eight plants, had IC(50) values below 25μg/ml extract in the MAO-A assay. The most active extracts in the MAO-A assay were the ethanol extract of seeds of Trigonella foenum-graecum (IC(50) 4μg/ml); ethanol extract of leaves of Apium graveolens (IC(50) 5μg/ml) and the water extract of aerial parts of Calluna vulgaris (IC(50) 8μg/ml).

CONCLUSIONS

Besides Borago officinalis, which toxicity profile excludes it from further development as an herbal drug, none of the plants had potential as serotonin reuptake inhibitors. Several plants had MAO-A inhibitory activity.

Evaluation of the inhibitory effects of quercetin-related flavonoids and tea catechins on the monoamine oxidase-A reaction in mouse brain mitochondria

Quercetin, a typical dietary flavonoid, is thought to exert antidepressant effects by inhibiting the monoamine oxidase-A (MAO-A) reaction, which is responsible for regulation of the metabolism of the neurotransmitter 5-hydroxytryptamine (5-HT) in the brain. This study compared the MAO-A inhibitory activity of quercetin with those of O-methylated quercetin (isorhamnetin, tamarixetin), luteolin, and green tea catechins ((-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epigallocatechin gallate) by measuring the formation of the oxidative deamination product of 5-HT, 5-hydroxyindole aldehyde (5-HIAL), in mouse brain mitochondria. Quercetin was inferior to luteolin in the inhibition of MAO-A activity, whereas isorhamnetin, tamarixetin, and tea catechins scarcely exerted inhibitory activity. Quercetin did not affect MAO-A activity in mouse intestinal mitochondria, indicating that it does not evoke side effects on the metabolism of dietary monoamines in the gut. These data suggest that quercetin is a weak (but safe) MAO-A inhibitor in the modulation of 5-HT levels in the brain.

Effects of ethanolic extract of pine needles (Pinus eldarica Medw.) on reserpine-induced depression-like behavior in male Wistar rats

Background:

In this study, the antidepressant activity of ethanolic extract of Pinus eldarica Medw needles was assessed using forced swimming test (FST) in rats.

Materials and Methods:

Male Wistar rats were randomly divided into six Groups and treated as follows: first group was received only reserpine (6 mg/kg, i.p.), second group was received reserpine (6 mg/kg, i.p.) and imipramine (10 mg/kg, i.p.), three experimental groups received reserpine (6 mg/kg, i.p.) and three doses of pine needle extract (100, 300, and 500 mg/kg, p.o.) respectively and the final group (control group) received only vehicle (5% DMSO, i.p.).

Results:

Acute oral administration of ethanolic extract of P. eldarica Medw needles at a dosage of 300 mg/kg reduced reserpine-induced increase in immobility time in the FST, demonstrating an antidepressant effect in the FST. Additionally, extract treatment did not modify the ambulation and rearing evaluated in open field test, indicating that antidepressant effect found in the forced swimming test was not based on the stimulation of locomotor activity.

Conclusion:

These results indicate that ethanolic extract of Pinus eldarica needles possesses an antidepressant activity.

Involvement of monoaminergic systems in the antidepressant-like effect of Eugenia brasiliensis Lam. (Myrtaceae) in the tail suspension test in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Several species of Eugenia L. are used in folk medicine for the treatment of various diseases. Eugenia brasiliensis is used for the treatment of inflammatory diseases, whereas Eugenia. uniflora is used for the treatment of symptoms related to depression and mood disorders, and is used in Brazil by the Guarani Indians as a tonic stimulant.

AIM OF THE STUDY

To investigate the antidepressant-like effect of hydroalcoholic extracts of different plant species of genus Eugenia and to characterize the participation of the monoaminergic systems in the mechanism of action of the specie that afforded the most prominent antidepressant-like efficacy.

MATERIALS AND METHODS

In the first set of experiments, the effects of hydroalcoholic extracts of Eugenia beaurepaireana, Eugenia brasiliensis, Eugenia catharinae, Eugenia umbelliflora and Eugenia uniflora and the antidepressant fluoxetine (positive control) administered acutely by p.o. route were evaluated in the tail suspension test (TST) and locomotor activity was assessed in the open-field test in mice. In the second set of experiments, the involvement of the monoaminergic systems in the antidepressant-like activity of Eugenia brasiliensis was evaluated by treating mice with several pharmacological agonists and antagonists. The effects of the combined administration of sub-effective doses of Eugenia brasiliensis and the antidepressants fluoxetine, imipramine and bupropion were also evaluated.

RESULTS

The administration of the extracts from Eugenia brasiliensis, Eugenia catharinae and Eugenia umbelliflora, but not Eugenia beaurepaireana and Eugenia uniflora, exerted a significant antidepressant-like effect, without altering locomotor activity. The behavioral profile was similar to fluoxetine. Pre-treatment of mice with ketanserin, haloperidol, SCH23390, sulpiride, prazosin and yohimbine prevented the reduction of immobility time induced by Eugenia brasiliensis. Treatment with sub-effective doses of WAY100635, SKF38393, apomorphine, phenylephrine, but not clonidine, combined with a sub-effective dose of Eugenia brasiliensis decreased the immobility time in the TST. Furthermore, the combined administration of sub-effectives doses of Eugenia brasiliensis with fluoxetine, imipramine and bupropion produced an antidepressant-like effect.

CONCLUSIONS

This study show, for the first time, the antidepressant-like effect of species of the genus Eugenia, especially Eugenia brasiliensis, whose effects in the TST seem to be mediated by serotoninergic (5-HT(1A) and 5-HT(2) receptors), noradrenergic (α(1)-adrenoceptor) and dopaminergic (dopamine D(1) and D(2) receptors) systems.

Antidepressant effect and pharmacological evaluation of standardized extract of flavonoids from Byrsonima crassifolia

Byrsonima crassifolia (Malpighiaceae) has been used in traditional medicine for the treatment of some mental-related diseases; however, its specific neuropharmacological activities remain to be defined. The present study evaluates the anxiolytic, anticonvulsant, antidepressant, sedative effects produced by the extracts of Byrsonima crassifolia, and their influence on motor activity in ICR mice. Additionally, we determine the acute toxicity profiles of the Byrsonima crassifolia extracts and the presence of neuroactive constituents. Our results show that the methanolic extract of Byrsonima crassifolia produces a significant (P<0.05) antidepressant effect in the forced swimming test in mice at 500 mg/kg dose. However, it does not possess anxiolytic, sedative, or anticonvulsant properties, and does not cause a reduction of mice locomotion (P>0.05). Although the main compound of the methanolic extract was identified as quercetin 3-O-xyloside (12 mg/kg), our findings suggest that flavonoids, such as rutin (4.4 mg/kg), quercetin (1.4 mg/kg) and hesperidin (0.7 mg/kg), may be involved in the antidepressant effects. To the best of our knowledge, the present study constitutes the first report on the presence of the flavonoids with neuropharmacological activity rutin and hesperidin in Byrsonima crassifolia. In conclusion, the present results showed that the methanolic extract standardized on flavonoids content of Byrsonima crassifolia possesses potential antidepressant-like effects in the FST in mice, and could be considered as relatively safe toxicologically with no deaths of mice when orally administered at 2000 mg/kg.

Route of administration determines the anxiolytic activity of the flavonols kaempferol, quercetin and myricetin--are they prodrugs?

Several in vivo and in vitro studies have confirmed that flavonols are metabolized by the intestinal microflora to their corresponding hydroxyphenylacetic acids. In this article, a comparison of the anxiolytic activity of the flavonols kaempferol, quercetin and myricetin in the elevated plus maze after oral (po) and intraperitoneal (ip) administration to mice in a dose range of 0.1 to 2.0 mg/kg is presented. In addition, their corresponding metabolites p-hydroxyphenylacetic acid (p-HPAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were tested after intraperitoneal administration. Anxiolytic activity was detected for kaempferol and quercetin only after oral administration. No anxiolytic effects were observed when kaempferol and quercetin were given via the intraperitoneal administration route. The corresponding hydroxyphenylacetic metabolites p-HPAA and DOPAC showed anxiolytic effects after intraperitoneal application. In order to further test the hypothesis that flavonoids are possible prodrugs which require activation by intestinal bacteria, gut sterilization was performed using pretreatment with the antibiotic enrofloxacin (7.5 mg/day, po, for 4 days). After antibiotic treatment, the anxiolytic effect of kaempferol and quercetin disappeared, whereas it was still present for the positive control diazepam. Our results support the hypothesis that flavonoids act as prodrugs which are transformed into their active hydroxyphenylacetic acid metabolites by intestinal microflora.

Flavonoids and the CNS

Flavonoids are present in almost all terrestrial plants, where they provide UV-protection and colour. Flavonoids have a fused ring system consisting of an aromatic ring and a benzopyran ring with a phenyl substituent. The flavonoids can be divided into several classes depending on their structure. Flavonoids are present in food and medicinal plants and are thus consumed by humans. They are found in plants as glycosides. Before oral absorption, flavonoids undergo deglycosylation either by lactase phloridzin hydrolase or cytosolic β-glucocidase. The absorbed aglycone is then conjugated by methylation, sulphatation or glucuronidation. Both the aglycones and the conjugates can pass the blood-brain barrier. In the CNS several flavones bind to the benzodiazepine site on the GABA_A-receptor resulting in sedation, anxiolytic or anti-convulsive effects. Flavonoids of several classes are inhibitors of monoamine oxidase A or B, thereby working as anti-depressants or to improve the conditions of Parkinson’s patients. Flavanols, flavanones and anthocyanidins have protective effects preventing inflammatory processes leading to nerve injury. Flavonoids seem capable of influencing health and mood.

Improving the oral bioavailability of beneficial polyphenols through designed synergies

A substantial and growing consumer demand exists for plant-based functional foods that improve general health and wellbeing. Amongst consumed phytochemicals, the polyphenolic compounds tend to be the most bioactive. Many commonly consumed polyphenols have been shown to have specific and potent health-promoting activities when assessed by high-throughput in vitro assays and when administered to experimental animals by injection. However, very few have been shown to have any beneficial effects in animals or man when orally consumed, because of the poor bioavailability exhibited by most polyphenols following the ingestion. Consumed polyphenols, like most pharmaceuticals, are regarded as xenobiotics by the body and must overcome many barriers, including extensive enzymatic and chemical modification during digestion and absorption, to reach their site(s) of action. This is especially true for polyphenols targeting the brain, which is protected by the tightly regulated blood-brain barrier. Interestingly, many polyphenols are also known to specifically modify some of the metabolic and transport processes that govern bioavailability. Therefore, the opportunity exists to increase the bioactivity of beneficial polyphenols by designing specific synergistic interactions with polyphenols that improve their oral bioavailability. This hypothesis and review paper will discuss some of the endogenous systems that limit the bioavailability of ingested polyphenols to the body and the brain, and the means by which bioavailability may be improved by specifically designing synergies between orally consumed polyphenols.

Ecstasy-induced oxidative stress to adolescent rat brain mitochondria in vivo: influence of monoamine oxidase type A

The administration of a neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy') to the rat results in mitochondrial oxidative damage in the central nervous system, namely lipid and protein oxidation and mitochondrial DNA deletions with subsequent impairment of the correspondent protein expression. Although these toxic effects were shown to be prevented by monoamine oxidase B inhibition, the role of monoamine oxidase A (MAO-A) in MDMA-mediated mitochondrial damage remains to be evaluated. Thus, the aim of the present study was to clarify the potential interference of a specific inhibition of MAO-A by clorgyline, on the deleterious effects produced by a binge administration of a neurotoxic dose of MDMA (10 mg MDMA/kg of body weight, intraperitoneally, every 2 hours in a total of four administrations) to an adolescent rat model. The parameters evaluated were mitochondrial lipid peroxidation, protein carbonylation and expression of the respiratory chain protein subunits II of reduced nicotinamide adenine dinucleotide dehydrogenase (NDII) and I of cytochrome oxidase (COXI). Considering that hyperthermia has been shown to contribute to the neurotoxic effects of MDMA, another objective of the present study was to evaluate the body temperature changes mediated by MDMA with a MAO-A selective inhibition by clorgyline. The obtained results demonstrated that the administration of a neurotoxic binge dose of MDMA to an adolescent rat model previously treated with the specific MAO-A inhibitor, clorgyline, resulted in synergistic effects on serotonin- (5-HT) mediated behaviour and body temperature, provoking high mortality. Inhibition of MAO-A by clorgyline administration had no protective effect on MDMA-induced alterations on brain mitochondria (increased lipid peroxidation, protein carbonylation and decrease in the expression of the respiratory chain subunits NDII and COXI), although it aggravated MDMA-induced decrease in the expression of COXI. These results reinforce the notion that the concomitant use of MAO-A inhibitors and MDMA is counter indicated because of the resulting severe synergic toxicity.

Rat electropharmacograms of the flavonoids rutin and quercetin in comparison to those of moclobemide and clinically used reference drugs suggest antidepressive and/or neuroprotective action

In order to be able to test single constituents of herbal plant extracts with respect to possible clinical usefulness, the model of local field potential analysis leading to the so-called electropharmacogram has been successfully used in rats to classify the effects of theanine and theogallin in the past. The present investigation aims at the prediction of efficacy and possible mechanisms of action of rutin and quercetin. Adult rats (day-night converted) were instrumented with four bipolar concentric electrodes into the frontal cortex, hippocampus, striatum and reticular formation. Field potentials were recorded during a pre-drug reference period of 45 min followed by oral administration of the particular test compound and 4h recording thereafter. Data were transmitted wirelessly to the computer for spectral frequency analysis. Rutin (5-80 mg/kg) as well as quercetin (5-40 mg/kg orally) produced similar electropharmacograms with dose dependent decreases of spectral alpha2 and beta1 frequencies within all brain areas. Peak effects were reached 4h after administration. The pattern of changes approached that obtained after 2.5mg/kg of moclobemide during the first hour as revealed by discriminant analysis in comparison to a large matrix of other drugs with known clinical indications. Data suggest antidepressant capabilities for rutin and quercetin with inhibition of monoamino oxidase at least as part of the mechanism of action. Both compounds should be tested clinically in patients with symptoms of depression.

MAO-A inhibitory activity of quercetin from Calluna vulgaris (L.) Hull

AIM OF THE STUDY

This study investigated MAO-A inhibitory activity of methanol extract of Calluna vulgaris (L.) Hull., which traditionally has been used as a nerve calming remedy.

MATERIALS AND METHODS

A methanolic extract of Calluna vulgaris was partitioned against heptane, ethyl acetate and water. The three fractions were tested in a photometric peroxidase linked MAO-A bioassay. The ethyl acetate phase showed the highest MAO-A inhibitory activity. Quercetin was isolated by VLC through bioassay-guided fractionation and purified by re-crystallisation. The structure was elucidated by LC-MS and (1)H NMR.

RESULTS

The IC(50)-value for MAO-A inhibition by quercetin was 18+/-0.2 microM in an assay where the IC(50)-value for MAO-A inhibition by clorgylin was 0.2+/-0.02 microM.

CONCLUSION

The content of quercetin in Calluna vulgaris might explain the reported nerve calming effect of the plant.

Isolation of the MAO-inhibitor naringenin from Mentha aquatica L

AIMS OF THE STUDY

To isolate the compound(s) responsible for the MAO-inhibitory activity.

MATERIALS AND METHODS

Six extracts of varying polarity of Mentha aquatica L. were tested in a photometric peroxidase linked MAO bioassay. The 70% ethanol extract had highest inhibitory activity. (S)-Naringenin was isolated from the extract by bioassay guided fractionation on VLC and preparative TLC. The structure of the compound was determined by (1)H, (13)C and (13)C-DEPT NMR and optical rotation.

RESULTS

The IC(50) values for MAO inhibition by naringenin were 342+/-33 microM for the rat liver mitochondrial fraction, 955+/-129 microM for MAO-A and 288+/-18 microM for MAO-B.

CONCLUSIONS

The content of naringenin in Mentha aquatica might explain its use in traditional medicine for depression-like conditions.

Multipotent natural agents to combat Alzheimer's disease. Functional spectrum and structural features

With the accelerated aging of human society, Alzheimeros disease (AD) is becoming one of the biggest threats to human health. Since multiple pathogenetic factors are implicated in the disease, the current hitting-one-target therapeutic strategy has proved inefficient to AD. As a result, finding multipotent agents that aim at multiple targets is attracting more and more attention. Although multifunctional anti-AD agents can be created by incorporating two or more pharmacophores in one scaffold, naturally occurring multipotent agents also attracted much attention. In this review, we first describe the functions of some typical naturally originated multipotent anti-AD compounds, then summarize their structural features and reveal that phenolics with certain flexibility predominate in these agents, which are of significance to find novel multipotent drugs to combat AD and other neurodegenerative diseases as well.

Virtual screening for the discovery of bioactive natural products

In this survey the impact of the virtual screening concept is discussed in the field of drug discovery from nature. Confronted by a steadily increasing number of secondary metabolites and a growing number of molecular targets relevant in the therapy of human disorders, the huge amount of information needs to be handled. Virtual screening filtering experiments already showed great promise for dealing with large libraries of potential bioactive molecules. It can be utilized for browsing databases for molecules fitting either an established pharmacophore model or a three dimensional (3D) structure of a macromolecular target. However, for the discovery of natural lead candidates the application of this in silico tool has so far almost been neglected. There are several reasons for that. One concerns the scarce availability of natural product (NP) 3D databases in contrast to synthetic libraries; another reason is the problematic compatibility of NPs with modern robotized high throughput screening (HTS) technologies. Further arguments deal with the incalculable availability of pure natural compounds and their often too complex chemistry. Thus research in this field is time-consuming, highly complex, expensive and ineffective. Nevertheless, naturally derived compounds are among the most favorable source of drug candidates. A more rational and economic search for new lead structures from nature must therefore be a priority in order to overcome these problems. Here we demonstrate some basic principles, requirements and limitations of virtual screening strategies and support their applicability in NP research with already performed studies. A sensible exploitation of the molecular diversity of secondary metabolites however asks for virtual screening concepts that are interfaced with well-established strategies from classical pharmacognosy that are used in an effort to maximize their efficacy in drug discovery. Such integrated virtual screening workflows are outlined here and shall help to motivate NP researchers to dare a step towards this powerful in silico tool.

Monoamine oxidase inhibitory components fromCayratia japonica

Seven flavonoids were isolated from the whole plants and fruits of Cayratia japonica through the activity-guided isolation of a methanol extract using a monoamine oxidase (MAO) inhibition assay as a monitor. The chemical structures of the isolates were assigned as apigenin-7-O-beta-D-glucuronopyranoside (1), apigenin (2), luteolin (3), luteolin-7-O-beta-D-glucopyranoside (4), (+)-dihydroquercetin (taxifolin) (5), (+)-dihydrokaempferol (aromadendrin) (6) and quercetin (7). Among the isolated compounds, flavones such as apigenin (2) and luteolin (3), as well as the flavonol, quercetin (7) showed potent inhibitory effects against the MAO activity with IC50 values of 6.5, 22.6, and 31.6 microM, respectively. However, the flavone glycosides, apigenin-7-O-beta-D-glucuronopyranoside (1) and luteolin-7-O-beta-D-glucopyranoside (4), showed mild MAO inhibition (IC50 values: 81.7 and 118.6 microM, respectively). The flavanonol derivatives, taxifolin (5) and aromadendrin (6), also showed weak inhibition (IC50 values: 154.7 and 153.1 microM, respectively). Furthermore, quercetin (7) had a more potent inhibitory effect on MAO-A (IC50 value: 2.8 microM) than MAO-B (IC50 value: 90.0 microM). Apigenin (2) and luteolin (3) also preferentially inhibited MAO-A (IC50 values: 1.7 and 4.9 microM, respectively) compared with MAO-B (IC50 values: 12.8 and 59.7 microM, respectively).