Phenanthrene-enriched extract from Eulophia macrobulbon using subcritical dimethyl ether for phosphodiesterase-5A1 inhibition.

Eulophia macrobulbon (E.C.Parish & Rchb.f.) Hook.f. contains a natural PDE5A1 inhibitor, phenanthrene, 1-(4'-hydroxybenzyl)-4,8- dimethoxyphenanthrene-2,7-diol (HDP), a potential agent for the treatment of erectile dysfunction. The aim of this study was to improve the extraction efficiency of HDP from E. macrobulbon by using a more environmentally friendly extraction method, subcritical liquid dimethyl ether extraction (sDME), instead of classical solvent extraction (CSE) and ultrasound-assisted extraction (UAE). The efficiency and quality of the extracts obtained were evaluated using the following criteria: %process yield; solvent amount; extraction time; temperature; %HDP content by LC-MS, bioactivity as inhibition of phosphodiesterase-5A1 (PDE5A1) by radio-enzymatic assay; and chemical profiles by LC-QTOF-MS. sDME provided the highest content of HDP in the extract at 4.47%, much higher than the use of ethanol (0.4-0.5%), ethyl acetate (1.2-1.7%), or dichloromethane (0.7-1.4%). The process yield for sDME (1.5-2.7%) was similar to or lower than the other solvents (0.9-17%), but as long as the process yield is not prohibitively low, the concentration is a more important measure for clinical use. The optimal conditions for sDME extraction were: Extraction time, 40 min; 200% water as co-solvent; sample-to-solvent ratio of 1:8; temperature, 35 °C. Phenanthrene aglycone and glycoside derivatives were the major constituents of the sDME extracts and lesser amounts of phenolic compounds and sugars. The inhibition of PDE5A1 by sDME (IC50 0.67 ± 0.22 µg/ml) was tenfold more potent than ethanolic extract and other extraction methods, suggesting a high probability of clinical efficacy. Thus, sDME was a more efficient, faster, solvent-saving and environmentally friendly extraction method and more selective for phenanthrene when extracted from E. macrobulbon.

Discovery of Lipid Peroxidation Inhibitors from Bacopa Species Prioritized through Multivariate Data Analysis and Multi-Informative Molecular Networking.

A major goal in the discovery of bioactive natural products is to rapidly identify active compound(s) and dereplicate known molecules from complex biological extracts. The conventional bioassay-guided fractionation process can be time consuming and often requires multi-step procedures. Herein, we apply a metabolomic strategy merging multivariate data analysis and multi-informative molecular maps to rapidly prioritize bioactive molecules directly from crude plant extracts. The strategy was applied to 59 extracts of three Bacopa species (B. monnieri, B. caroliniana and B. floribunda), which were profiled by UHPLC-HRMS2 and screened for anti-lipid peroxidation activity. Using this approach, six lipid peroxidation inhibitors 1‒6 of three Bacopa spp. were discovered, three of them being new compounds: monnieraside IV (4), monnieraside V (5) and monnieraside VI (6). The results demonstrate that this combined approach could efficiently guide the discovery of new bioactive natural products. Furthermore, the approach allowed to evidence that main semi-quantitative changes in composition linked to the anti-lipid peroxidation activity were also correlated to seasonal effects notably for B. monnieri.

Elucidation of Vasodilation Response and Structure Activity Relationships of N²,N4-Disubstituted Quinazoline 2,4-Diamines in a Rat Pulmonary Artery Model.

Pulmonary arterial hypertension (PAH) is a rare and progressive disease arising from various etiologies and pathogenesis. PAH decreases life expectancy due to pulmonary vascular remodeling, elevation of mean pulmonary arterial pressure, and ultimately progresses to heart failure. While clinical treatments are available to reduce the associated symptoms, a complete cure has yet to be found. Phosphodiesterase-5 (PDE-5) inhibition has been identified as a possible intervention point in PAH treatment. The functional vasodilation response to N²,N4-diamino quinazoline analogues with differing PDE-5 inhibitory activities and varying physicochemical properties were assessed in both endothelium-intact and denuded rat pulmonary arteries to gain greater insight into their mode of action. All analogues produced vasorelaxant effects with EC50s ranging from 0.58 ± 0.22 µM to ˃30 µM. It was observed that vasodilation response in intact vessels was highly correlated with that of denuded vessels. The ~10% drop in activity is consistent with a loss of the nitric oxide mediated cyclic guanosine monophosphate (NO/cGMP) pathway in the latter case. A moderate correlation between the vasodilation response and PDE-5 inhibitory activity in the intact vessels was observed. Experimental protocol using the alpha-adrenergic (α1) receptor agonist, phenylephrine (PE), was undertaken to assess whether quinazoline derivatives showed competitive behavior similar to the α1 receptor blocker, prazosin, itself a quinazoline derivative, or to the PDE-5 inhibitor, sildenafil. Competitive experiments with the α1-adrenergic receptor agonist point to quinazoline derivatives under investigation here act via PDE-5 inhibition and not the former. The pre-incubation of pulmonary arterial rings with quinazoline test compounds (10 µM) reduced the contractile response to PE around 40⁻60%. The most promising compound (9) possessed ~32 folds higher selectivity in terms of vasodilation to its mammalian A549 cell cytotoxicity. This study provides experi0 0mental basis for PDE-5 inhibition as the mode of action for vasodilation by N²,N4-diamino quinazoline analogues along with their safety studies that may be beneficial in the treatment of various cardiovascular pathologies.

Phosphodiesterase 5 Inhibitors from Derris scandens.

Phosphodiesterase 5 inhibitors have been used as a first-line medicine for the treatment of erectile dysfunction. In the search for new phosphodiesterase 5 inhibitors from natural sources, we found that the 95% ethanol extract of Derris scandens stem showed phosphodiesterase 5 inhibitory activity with an IC50 value of about 7 µg/mL. Seven isoflavones and a coumarin constituent isolated from this plant were investigated for phosphodiesterase 5 inhibitory activity. The results showed that osajin (8: ), 4',5,7-trihydroxybiprenylisoflavone (4: ), and derrisisoflavone A (2: ) had the ability to inhibit phosphodiesterase 5 with IC50 values of 4, 8, and 9 µM, respectively. These compounds exhibited selectivity on phosphodiesterase 5 over phosphodiesterase 1, however, the selectivity on phosphodiesterase 5 over phosphodiesterase 6 was low. In order to quantitatively determine these bioactive constituents in D. scandens extract, LC-QTOF-MS method has been developed and validated. The limit of quantitation values in the range of 0.1 - 5 µg/mL were obtained. The assay showed satisfactory precision and accuracy. The results from our method showed that the 95% ethanol extract of D. scandens stem was comprised of all eight compounds, with derrisisoflavone A (2: ) and lupalbigenin (3: ) presenting as the major constituents.

Sesquiterpene-Enriched Extract of Curcuma aeruginosa Roxb. Retards Axillary Hair Growth: A Randomised, Placebo-Controlled, Double-Blind Study.

BACKGROUND: Sesquiterpenes in Curcuma aeruginosa Roxb. inhibit steroid 5α-reductase and dihydrotestosterone production, and reverse androgenic alopecia. This study sought to show that a high sesquiterpene C. aeruginosa extract (CA-ext) retards axillary hair growth in women. METHODS: Thirty women (age 20-52 years) were recruited into a 12-week, double-blind, placebo-controlled intervention for CA-ext treatment, where they were randomly allocated to a left or right armpit group. At weekly intervals, axillary hair length was measured videometrically, the hair was shaved, and lotion was applied (to the contralateral axilla) twice daily via roll-on applicators containing either CA-ext or placebo. The primary endpoint of the study was hair growth. RESULTS: Participants showed 22% (range 8-56%, p < 0.0001) reduced axillary hair growth with CA-ext compared to placebo, albeit delayed by 6 weeks. Participants were satisfied with the treatment and no apparent adverse effects were reported. The quantities of lotion used for each axilla were identical between test and placebo throughout the trial for each participant. Participants reported having shorter and finer armpit hair with the test lotion but disliked its smell, even though it was perfumed. The "free of irritation" description gained the highest questionnaire ratings. CONCLUSION: CA-ext in lotion is an efficacious inhibitor of axillary hair growth, the preparation was well accepted and matched the effectiveness of finasteride. Thus, with some refinement, it should provide an alternative pharmacological treatment for unwanted androgenic hair.

Germacrone and sesquiterpene-enriched extracts from Curcuma aeruginosa Roxb. increase skin penetration of minoxidil, a hair growth promoter.

Minoxidil is approved for topical treatment of androgenic alopecia but hampered by poor cutaneous absorption. Recently, the randomized control trial showed that hair loss treatment of minoxidil was improved by co-application of the anti-androgen, Curcuma aeruginosa Roxb. extract. Here, we aimed to show that the apparent synergism arises from improved cutaneous penetration of minoxidil by bioactive compound, germacrone or C. aeruginosa (as an n-hexane extract, or essential oil). The partition coefficient of germacrone was determined by HPLC. Skin penetration was measured ex vivo on Franz diffusion cells using full thickness human foreskin as membranes. The receiver solution was sampled hourly for 8 h after which the skin was removed, the stratum corneum separated, and minoxidil assayed in this and in the remaining viable skin layer by HPLC. Skin penetration of minoxidil with 0.2 and 2% extract was increased ~ 4-fold (accumulated amount in receiver + skin viable layer after 8 h). Furthermore, germacrone enhanced minoxidil flux by ~ 10-fold and C. aeruginosa essential oil by ~ 20-fold. This work suggests three clinical consequences: (i) minoxidil efficacy is promoted, (ii) lower doses of minoxidil suffice, and (iii) C. aeruginosa extract/essential oil or germacrone can supplement treatment outcomes by acting as anti-androgen, thereby introducing a more effective topical treatment strategy for androgenic alopecia.

Curcuma aeruginosa Roxb. essential oil slows hair-growth and lightens skin in axillae; a randomised, double blinded trial.

BACKGROUND: Androgenic hair-growth contributes to secondary gender characteristics but can be troublesome in women. Inhibiting axillary hair-growth via 5-α-reductases using the Thai medicinal plant, Curcuma aeruginosa Roxb. is an attractive treatment strategy. HYPOTHESIS/PURPOSE: C. aeruginosa essential oil (CA-oil) formulated as a lotion is an efficacious and safe inhibitor of axillary hair growth. STUDY DESIGN: This trial was a single center, randomized, double-blind, placebo controlled 10 weeks, intervention in 60 women (18-23 years) and 2 weeks washout with axillary hair length was the primary end-point. METHODS: Bioactive-enriched essential oil of C. aeruginosa was formulated with a base lotion. All participants were pre-challenged with lotions by 4-h patch irritation tests to exclude skin reactions. Participants were randomly allocated to use either 1 or 5%w/w CA-oil lotion on one axilla and base-lotion (placebo) to the other for 10 weeks followed by placebo in both axillae for 2 weeks. Every week, the axillae were photographed to measure hair lengths, shaved, and roll-on applicators containing appropriate lotion replaced. Also, skin melanin by spectrophotometry and hair density were measured. RESULTS: From weeks 5-11 of trial, 1 and 5%w/w CA-oil retarded growth by 13 ± 1.5% and 16 ± 0.9% respectively, while placebo was ineffective. CA-oil had no influence on hair density. Both concentrations of CA-oil rapidly and equally effectively brightened skin within 3 weeks which persisted 2 weeks after treatment ceased while placebo darkened the skin. Adherence appeared good as judged by consistency of lotion consumption and between axillae. Participants were satisfied with the treatment and reported reduced hairiness, freedom from any discomforts, but product odour attracted some negative comment. No adverse reactions ascribed to CA-oil were detected or reported. CONCLUSION: This study points to a safe and efficacious dual action on retarding hair-growth and skin lightening by CA-oil.

Phenanthrenes from Eulophia macrobulbon as Novel Phosphodiesterase-5 Inhibitors.

Phosphodiesterase 5 (PDE5) inhibitors can be used for the treatment of erectile dysfunction and pulmonary hypertension. In order to search for new leads of PDE5 inhibitors, we investigated the chemical constituents of the tubers of Eulophia macrobulbon (E.C. Parish & Rchb. f.) Hook. f. A new phenanthrene, 9,10-dihydro-4-(4'-hydroxybenzyl)-2,5-dimethoxyphenanthrene-1,7-dio (1) and three known phenanthrenes i.e., 1-(4'-hydroxybenzyl)-4,8- dimethoxyphenanthrene-2,7-diol (2), (9,10-dihydro-2,5-dimethoxyphenanthrene-1,7-diol (3) and 1,5,7-trimethoxyphenanthrene-2,6-diol). (4) were isolated Among these, 2 was the most potent PDE5 inhibitor (IC50 =1.67±0.54 µM) evaluated by the [3H]cGMP radioassay method, whereas 1 showed mild activity (IC50 = 62.3±3.3 µM). Their inhibitory selectivities against PDE5 over PDE6 were also studied. This study suggests phenanthrenes as a new class of PDE5 inhibitors.

Immunochromatographic determination of bacopaside I in biological samples.

We describe a novel immunochromatographic method for qualitative and quantitative analyses of bacopaside I, a bioactive constituent in Bacopa monnieri (L.) Wettst in biological samples. The assay was performed on polyethersulfone membrane using a polyclonal antibody raised against bacopaside I. The finalised method could quantitatively determine bacopaside I in the range of 31.3-1000.0ng and the detection and quantification limits were 1.0 and 31.3ng, respectively. The percentage recoveries of bacopaside I in blood and urine were nearly 100% indicating the accuracy of the extraction. The method was then applied for the determination of this compound in rat serum, urine and feces after an oral dose of 15mg/kg body weight. About 4% of the ingested dose of bacopaside I was detected in rat feces but none was detected in serum and urine which accorded with results from liquid chromatography tandem mass spectrometry. The accuracy, selectivity, sensitivity of the method are appropriate for in vivo pharmacokinetic studies.

A new label-free screen for steroid 5α-reductase inhibitors using LC-MS.

Steroid 5α-reductase (S5αR) plays an important role in metabolizing testosterone into active androgen dihydrotestosterone (DHT) which is involved in many androgen dependent disorders, such as androgenic alopecia, benign prostatic hyperplasia and acne. The method for screening for S5αR inhibition is key in finding new antagonists. In this study, the label-free S5αR inhibitory assay using LC-MS was developed. S5αR type 1 enzyme was obtained from LNCaP prostate cancer cells. The enzymatic assay was optimised for enzyme-substrate (testosterone) concentration, NADPH-cofactor concentration, solvent tolerance, enzyme activity stability and incubation time. The developed assay was validated by measuring the signal to background ratio (S/B), the signal to noise ratio (S/N), the signal window (SW) and the zeta factor Z' in accordance with published bioassay guidelines. The enzymatic reaction was performed in 96-well plates and DHT formation was determined by LC-MS. S/B, S/N, SW and Z' factor were well above acceptable criteria and the reproducibility was good using Z' factor other 3days and further validated by dutasteride and finasteride inhibition. The method was successfully applied to quantify S5αR inhibitory activity of some Thai herbal extracts. Two plant extracts, Impatiens balsamina L. and Curcuma longa L. showed IC50 at 5.4±0.2 and 9.0±1.2µgmL-1 and are therefore promising sources of new S5αR inhibitors. The assay has high selectability and reproducibility and suited to medium throughput screening required by phytochemistry.

Germacrene Analogs are Anti-androgenic on Androgen-dependent Cells.

Anti-androgenic drugs are treatments for androgen-related disorders such as benign prostatic hyperplasia, acne, hirsutism, and androgenic alopecia. Germacrone (1), a sesquiterpene isolated from hexane extracts of Curcuma aeruginosa Roxb. rhizome, is an androgen inhibitor of steroid 5-alpha reductase in- vitro. Here, we used the similarity of germacrone's ,t,B-unsaturated carbonyl to testosterone's α,ß-unsaturated carbonyl to find germacrene analogs obtained from this plant and by semi-synthesis that might be more potent steroid 5-alpha reductase inhibitors. 8-Hydroxy germacrene B (4) was -13-fold more potent than its parent, I and the most potent (ICso, 0.15 ± 0.022 mM) among 9 compounds tested. The conformation of its cyclodecadiene ring and the α,ß-unsaturated ketone/hydroxy in the germacrene molecule might be crucial role for its anti-androgen activity. Moreover, I and 4 showed mild cytotoxic effect on prostate cancer cells. Neither compound was cytotoxic towards human dermal papilla cells at 100 µg/mL. We show that this SAR strategy created promising anti-androgenics for androgen dependent disorders and may create further analogues with further improvements in selectivity and clinical efficacy.

Curcumin analogues inhibit phosphodiesterase-5 and dilate rat pulmonary arteries.

OBJECTIVES: Phosphodiesterase (PDE)-5 inhibitors are useful as vasodilators for the treatment of pulmonary arterial hypertension. We aimed to study curcumin analogues for PDE5 inhibitory activity and vasorelaxation of rat pulmonary arteries. METHODS: Three natural curcuminoids (1-3) and six synthetic analogues (4-9) were tested for PDE5 and PDE6 inhibitory activities using enzymatic radioassay. Their vasorelaxation was measured using freshly isolated segments of rat pulmonary artery and aorta. KEY FINDINGS: Curcuminoids (1-3) mildly inhibited PDE5 (half maximal inhibitory concentration (IC50 ) = 18 µm): the metamethoxyl of curcumin was important for PDE5 inhibition. But hydroxyl rearrangements, removing both methoxyls and one ketomethylene, yielded the potent 7 and 9 (IC50 = 4 µm) (compared with sildenafil, IC50 = 0.03 µm). Only 1, 3 and 4 were PDE5 selective over PDE6. Triazole-carboxylic addition provided water-solubility while preserving potency. All analogues possessed concentration-dependent vasorelaxant activity on pulmonary arteries (40% of maximal effective concentration (EC40 ) = 29-90 µm, maximum response = 60-90% at 300 µm), while compounds (1-8) were weakly acting in aorta (maximum response <40%). Only demethoxycurcumin (2) and analogues 5, 8, 9 had endothelium-dependent actions. Sildenafil was highly potent (EC40 = 0.04 µm) and highly endothelium dependent in pulmonary artery but weak on intact aorta (EC40 = 1.8 µm). Activity profiles suggest actions through additional cell pathways for promoting vasorelaxation. CONCLUSIONS: Curcumin analogues are potential leads for developing efficacious and selective PDE5 inhibitors and other pathologies of pulmonary hypertension.

Stability studies of antiandrogenic compounds in Curcuma aeruginosa†Roxb. extract.

OBJECTIVES: Curcuma aeruginosa Roxb. extract is a 5α-reductase antagonist that can be used to treat hair loss. We aimed to study the stability of antiandrogenic constituents, germacrone and other sesquiterpene components in the extract. METHODS: Germacrone and the extract were analyzed as solid forms or solublized with polyethylene glycol-40 (PEG-40) or methanol using high-performance liquid chromatography and gas chromatography with flame ionization detector. The effects of pH, temperature and light on their stability were studied. KEY FINDINGS: Degradation of antiandrogenic compounds in C. aeruginosa was highly sensitive to temperature especially pure anhydrous germacrone, which was completely lost within 3 days at 45°C. Curiously, degradation was slower than as a dried extract. Paradoxically, when solubilized with PEG-40, it was largely intact even after 90 days at 45°C. The MS spectrum of a major degradation product suggested that it was elemenone probably produced by Cope rearrangement. Two other putative degradation products were germacrone-1,10-epoxide and germacrone-4,5-epoxide suggesting that oxidation of double bonds was an important mechanism. Germacrone stability was unaffected by pH (2.0-9.0) but only as dried extract it was slightly degraded by light. CONCLUSION: Antiandrogenic constituents of C. aeruginosa were instable at high temperature and in solid form. Thus, the extract would be optimately stored as a solution or otherwise as solid form at low temperature.

Conformational analysis of an anti-androgenic, (E,E)-8-hydroxygermacrene B, using NOESY and dynamic NMR spectroscopy.

(E,E)-8-Hydroxygermacrene B was prepared by ketone reduction of germacrone, a naturally occurring compound from Curcuma aeruginosa Roxb. with NaBH4 at low temperature (4 °C). This compound showed remarkable in vitro anti-androgenic activity (IC50 0.15±0.022 mM) applicable to male baldness treatments. NMR analysis at -50 °C indicated that there were four conformational isomers of (E,E)-8-hydroxygermacrene B in a ratio of 48:40:8:4. The major conformers were assigned by (1)H NMR and 2D-NOESY NMR spectroscopy as having methyl groups at C-10 and C-4 in up-down (UD) orientations (48% predominance) and UU (40%). (1)H NMR spectra implied another two minor conformers with these methyls having DU (8%) and DD (4%) orientations.

Anti-androgenic effect of sesquiterpenes isolated from the rhizomes of Curcuma aeruginosa Roxb.

Six sesquiterpenes: germacrone (1), zederone (2), dehydrocurdione (3), curcumenol (4), zedoarondiol (5) and isocurcumenol (6) were isolated from rhizomes of Curcuma aeruginosa Roxb. (Zingiberaceae). They inhibited 5α-reductase which converts testosterone to dihydrotestosterone (DHT). Germacrone (1) was the most potent (IC(50)=0.42±0.05 mg/mL). Compound 1 was anti-androgenic in LNCaP cells when proliferation was testosterone-induced. The growth of flank gland of male Syrian hamsters is dependent on circulating androgen and when maintained with testosterone, 1 (3, 30, 100µg) inhibited growth but was ineffective against DHT. The similar activity profile was observed on the 5α-reductase inhibitor, finasteride (100 µg) treatment group. The androgen receptor binding assay showed that 1 did not bind to the androgen receptor. In conclusion, 1 showed anti-androgenic effect on in vitro and in vivo assays. One of the possible mechanisms was inhibition 5α-reductase activity. Thus, 1 is a potential lead compound for treatment of androgen-dependent disorders.

Prospective acetylcholinesterase inhibitory activity of indole and its analogs.

Acetylcholinesterase (AChE) inhibitory activity is one of the proposed targets for indole analogs. Simple indoles with substitution of methoxy, carboxy or hydroxy at the benzene ring showed a low percent of inhibitory activity in eel-AChE. Adding a side chain at the pyrrole ring, such as serotonin, ß-carbolines and quinolines (the bioisostere of indole), improved the inhibitory activity significantly. However, proper substitution and conformation of the ring were required for good binding. The result of inhibition in human-AChE of serotonin, ß-carbolines and quinolines showed similar profile as eel-AChE with lower magnitude. The data from molecular docking showed that they shared the same binding site as galantamine.

Bisindole alkaloids and secoiridoids from Alstonia macrophylla Wall. ex G. Don.

The ethanolic extract from stems of a Thai medicinal plant, Alstonia macrophylla Wall. ex G. Don (Apocynaceae) showed a significant inhibitory effect on acetylcholinesterase (AChE) determined by using Ellman assay. Four compounds i.e., a bisindole alkaloid, macralstonine (1), a new bisindole alkaloid, thungfaine (2), a secoiridoid glycoside, sweroside (3) and a new secoiridoid glycoside, naresuanoside (4) were isolated. Compound 4 showed moderate AChE and butyrylcholinesterase (BChE) inhibitory effects. Interestingly, compound 4 inhibited cell growth on human androgen-sensitive prostate cancer cell line (LNCaP) but no effect on viability of human foreskin fibroblast cells (HF).

Effect of 8-hydroxy-2-(N,N-di-n-propylamino)tetralin and MDMA on the discriminative stimulus effects of the classical hallucinogen DOM in rats.

Co-administration of the 5-HT1A serotonin receptor agonist (+/-)8-hydroxy-2-(N,N-di-n-propylamino)tetralin [(+/-)8-OH DPAT] enhances the discriminative stimulus effects of the classical hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) in rats. In the present investigation, using Sprague-Dawley rats trained to discriminate DOM (1.0 mg/kg) from saline vehicle under a VI-15 s schedule of reinforcement, it was shown that the stimulus-enhancing actions of 8-OH DPAT are related more to its R(+)-isomer than to its S(-)-enantiomer, and that the (+/-)- and R(+)8-OH DPAT-induced effects are antagonized by the 5-HT1A receptor antagonist NAN-190. (+/-)8-OH DPAT and its isomers substitute in rats trained to discriminate the designer drug N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA; methylenedioxymethamphetamine) from vehicle indicating some similarity of effect. On this basis, it was hypothesized that MDMA might be capable of enhancing the DOM stimulus. Co-administration of MDMA with low (i.e., 0.1 and 0.3 mg/kg) doses of DOM resulted in greater DOM-appropriate responding than engendered by administration of DOM alone. As such, the present findings are the first to demonstrate an MDMA-induced enhancing effect on the discriminative stimulus actions of a classical hallucinogen. The results also suggest that a 5-HT1A serotonin receptor mechanism might contribute to this phenomenon.

Acetylcholinesterase inhibitors from Stephania venosa tuber.

Acetylcholinesterase (AChE) inhibitors have lately gained interest as potential drugs in the treatment of Alzheimer's disease. Three AChE inhibitors were isolated from tubers of a Thai medicinal plant, Stephania venosa (Bl) Spreng. They were identified as quaternary protoberberine alkaloids, stepharanine, cyclanoline and N-methyl stepholidine. They expressed inhibitory activity on AChE with IC50 values (concentration that caused 50% inhibition of activity) of 14.10 +/- 0.81, 9.23 +/- 3.47 and 31.30 +/- 3.67 microM, respectively. The AChE inhibitory activity of these compounds was compared with those of the related compounds, palmatine, jatrorrhizine and berberine, as well as tertiary protoberberine alkaloids isolated from the same plant, stepholidine and corydalmine. The results suggest that the positive charge at the nitrogen of the tetrahydroisoquinoline portion, steric substitution at the nitrogen, planarity of the molecule or substitutions at C-2, -3, -9, and -10 affect the AChE inhibitory activity of protoberberine alkaloids.

Isoquinoline derivatives as potential acetylcholinesterase inhibitors.

Several bisbenzylisoquinoline alkaloid derivatives showed the inhibitory activity at acetylcholinesterase enzyme (AChE) in micromolar range. It is possible that monomeric moiety of bisbenzylisoquinoline alkaloid might be required for acetylcholinesterase enzyme inhibition. AChE inhibitory activity of related monomeric 1-benzylisoquinolines was examined by using Ellman colorimetric assay with galanthamine as a reference standard.