Fatma Tosun

Antitrypanosomal and Antileishmanial Activities of Flavonoids and Their Analogues: In Vitro, In Vivo, Structure-Activity Relationship, and Quantitative Structure-Activity Relationship Studies

ABSTRACT Trypanosomiasis and leishmaniasis are important parasitic diseases affecting millions of people in Africa, Asia, and South America. In a previous study, we identified several flavonoid glycosides as antiprotozoal principles from a Turkish plant. Here we surveyed a large set of flavonoid aglycones and glycosides, as well as a panel of other related compounds of phenolic and phenylpropanoid nature, for their in vitro activities against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, and Leishmania donovani. The cytotoxicities of more than 100 compounds for mammalian L6 cells were also assessed and compared to their antiparasitic activities. Several compounds were investigated in vivo for their antileishmanial and antitrypanosomal efficacies in mouse models. Overall, the best in vitro trypanocidal activity for T. brucei rhodesiense was exerted by 7,8-dihydroxyflavone (50% inhibitory concentration [IC50], 68 ng/ml), followed by 3-hydroxyflavone, rhamnetin, and 7,8,3′,4′-tetrahydroxyflavone (IC50s, 0.5 μg/ml) and catechol (IC50, 0.8 μg/ml). The activity against T. cruzi was moderate, and only chrysin dimethylether and 3-hydroxydaidzein had IC50s less than 5.0 μg/ml. The majority of the metabolites tested possessed remarkable leishmanicidal potential. Fisetin, 3-hydroxyflavone, luteolin, and quercetin were the most potent, giving IC50s of 0.6, 0.7, 0.8, and 1.0 μg/ml, respectively. 7,8-Dihydroxyflavone and quercetin appeared to ameliorate parasitic infections in mouse models. Generally, the test compounds lacked cytotoxicity in vitro and in vivo. By screening a large number of flavonoids and analogues, we were able to establish some general trends with respect to the structure-activity relationship, but it was not possible to draw clear and detailed quantitative structure-activity relationships for any of the bioactivities by two different approaches. However, our results can help in directing the rational design of 7,8-dihydroxyflavone and quercetin derivatives as potent and effective antiprotozoal agents.

Screening of Various Phenolic Acids and Flavonoid Derivatives for their Anticholinesterase Potential

Alzheimer’s disease (AD), the most common form of dementia, is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioural changes. The oldest, on which most currently available drug therapies are based, is known as the “cholinergic hypothesis” and suggests that AD begins as a deficiency in the production of the neurotransmitter acetylcholine. Therefore, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitors have gained a great popularity for the treatment of AD. In this study, we screened in vitro inhibitory activities of a number of phenolic acids (chlorogenic, caffeic, gallic, and quinic acids) as well as of various flavonoid derivatives (genistein, biochanin A, naringin, apigenin, quercetin, luteolin-7-O-rutinoside, kaempferol-3-O-galactoside, diosmin, silibinin, and silymarin) against AChE and BChE at 1 mg/ml concentration using a microplate-reader assay based on the Ellman method. Among them, only quercetin showed a substantial inhibition (76.2%) against AChE, while genistein (65.7%), luteolin-7-O-rutinoside (54.9%), and silibinin (51.4%) exerted a moderate inhibition on BChE.

Alkaloid profile and antimicrobial activity of Lupinus angustifolius L. alkaloid extract

Purpose of the present study was to evaluate alkaloid profile of the aerial parts of Lupinus angustifolius growing in Turkey by capillary gas chromatography-mass spectrometry (GC-MS). Fifteen alkaloids were identified by capillary GC-MS. 13α-Hydroxylupanine (50.78%) and lupanine (23.55%) were determined as the main alkaloids in the aerial parts of L. angustifolius. Ammodendrine, isoangustifoline, tetrahydrorhombifoline, angustifoline, α-isolupanine, 5,6-dehydrolupanine, 11,12-dehydrolupanine, 13α-acetoxylupanine, 13α-isovaleroyloxylupanine, 13α-valeroyloxylupanine, 13α-tigloyloxylupanine, 13α-cis-cinnamoyloxylupanine and 13α-cis-cinnamoyloxy-17-oxolupanine were identified as the minor alkaloids of the plant. Furthermore, antibacterial and antifungal activities of L. angustifolius alkaloid extract were tested against standard strains of the following bacteria; Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus as well as the fungi; Candida albicans and C. krusei. The alkaloid extract showed significant activity on B. subtilis, S. aureus and P. aeruginosa while it was weakly active on E. coli. On the other hand, the extract possessed moderate activity against C. albicans and C. krusei.

Coumarin, Anthroquinone and Stilbene Derivatives with Anticholinesterase Activity

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are the key enzymes in pathogenesis of Alzheimer’s disease (AD), which is characterized by a deficit in central cholinergic transmission. In the current study, AChE and BChE inhibitory activities of seven coumarin derivatives [umbelliferone (1), 4-methylumbelliferone (2), 4-hydroxycoumarin (3), scopoletin (4), 8-methoxypsoralen (5), bergapten (6), and iso-bergapten (7)], a furanocoumarin mixture obtained from Heracleum crenatifolium Boiss. (Umbelliferae), as well as of two anthroquinone derivatives [rhein (8) and aloe-emodine (9)] and one stilbene, rhapontin (10), were tested by the spectrophotometric method of Ellman using an ELISA microplate-reader at 1 mg mL-1. Among them, the furanocoumarin mixture [(68.8 ± 0.76)%], bergapten [(62.4 ± 0.74)%], aloe-emodine [(57.2 ± 1.32)%], scopoletin [(53.1 ± 0.83)%], and 4-methylumbelliferone [(62.3 ± 1.03)%] showed over 50% inhibition against AchE, while umbelliferone [(54.3 ± 0.23)%], 4-methylumbelliferone [(80.9 ± 1.17)%], scopoletin [(73.5 ± 1.01)%], 8-methoxypsoralen [(67.1 ± 0.98)%], as well as the furanocoumarin mixture [(76.7 ± 0.95)%] had a notable anti-BChE effect.

Endothelium-dependent induction of vasorelaxation by Melissa officinalis L. ssp. officinalis in rat isolated thoracic aorta

In the current study, vasorelaxant effect produced by the aqueous extract of Melissa officinalis L. ssp. officinalis (MOO) (Lamiaceae) and its possible mechanism in isolated rat aortic rings precontracted with phenylephrine were examined. In the first series of experiments, effect of MOO on the baseline and phenylephrine (10(-5)M) precontracted arteries was investigated, while in the second group of experiments, endothelium intact or endothelium denuded effect was determined. The agents used were N(omega)-nitro-L-arginine (L-NAME), an irreversible inhibitor of nitric oxide (NO) synthase, indomethacin (10 microM), a cyclooxygenase (COX) inhibitor, and glibenclamide (10 microM), an ATP-sensitive potassium channel blocker. The extract was found to exert a vasorelaxant effect and rosmarinic acid quantity, the characteristic compound of the plant, was analyzed by reversed-phase high-performance liquid chromatography (18.75%), and was further confirmed by LC-MS analysis giving a prominent [M(+1)] molecular ion peak at m/z 365. Total phenol amount in the extract was determined using Folin-Ciocalteau reagent (0.284 mg/mg extract). Vasorelaxant effect of the extract was entirely dependent on the presence of endothelium and was abolished by pretreatment with L-NAME, whereas pretreatment with indomethacin and glibenclamide reduced the relaxation to a minor extent. Rosmarinic acid was also tested in the same manner as the extract and was found to exert vasorelaxant effect. These results suggest that the aqueous extract of MOO vasodilates via nitric oxide pathway with the possible involvement of prostacycline and endothelium-derived hyperpolarizing factor (EDHF) pathways as well.

The Evaluation of Plants from Turkey for in Vitro. Antimycobacterial Activity

Abstract In this research, extracts prepared from plant materials were tested against Mycobacterium tuberculosis. H37Rv (ATCC 27294). Of the 107 plants tested, five exhibited more than 90% inhibition of growth of Mycobacterium tuberculosis., at concentrations lower than 100 µg/ml. Jervin from Veratrum album. L., usnic acid from Usnea barbata. (L.) Mott, and alantolactone from Inula helenium. L. subsp. turcoracemosa. were isolated and their minimum inhibitory concentrations (MICs) were determined as 25, 12.5, and 3.125 µg/ml, respectively.

In vitro Anticholinesterase Activity of Various Alkaloids

In the current study, a number of alkaloids including retamine, cytisine, and sparteine (quinolizidine-type), yohimbine and vincamine (indole-type), scopolamine and atropine (tropane- type), colchicine (tropolone-type), allantoin (imidazolidine-type), trigonelline (pyridine- type) as well as octopamine, synephrine, and capsaicin (exocyclic amine-type) were tested in vitro for their inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at 1 mg/ml concentration by the Ellman method using an ELISA microplate reader. Among the alkaloids tested, only capsaicin exerted a remarkable inhibitory effect towards both AChE and BChE [(62.7 ± 0.79)% and (75.3 ± 0.98)%, respectively]. While the rest of the alkaloids did not show any significant inhibition against AChE, three of the alkaloids, namely retamine, sparteine, and yohimbine, exerted a noteworthy anti-BChE effect as compared to galanthamine, the reference drug.

LC-MS ANALYSIS OF DAIDZEIN IN THE TURKISH Genista SPECIES

In this research, total and free daidzein content in Genista species growing in Turkey were investigated using the LC-MS method. The highest amount of total and free daidzein in these species was found in Genista sessilifolia and G. lydia var. antiochia as 0.0056 and 0.0009%, respectively. Total and free daidzein content of the aerial parts of other Genista species varied from 0.0003 to 0.0044%, and from 0.0001 to 0.0008%, respectively.

GC-MS analysis and antimicrobial activity of alkaloid extract from Genista vuralii

In the present study, the alkaloid composition of the aerial parts of Genista vuralii A. Duran & H. Dural (Fabaceae) was investigated by capillary GC-MS. Ten quinolizidine alkaloids were identified by capillary GC-MS, namely, N-methylcytisine, cytisine, tetrahydrorhombifoline, 17-oxosparteine, 5,6-dehydrolupanine, lupanine, 17-oxolupanine, anagyrine, baptifoline, and 13α-tigloyloxylupanine. Among them, anagyrine (93.04%) was the most abundant alkaloid. Furthermore, antibacterial and antifungal activities of the alkaloid extract of G. vuralii were tested against standard strains of bacteria (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus) as well as fungi (Candida albicans, Candida krusei). The alkaloid extract of G. vuralii presented good activity against S. aureus, B. subtilis, and C. krusei, with minimum inhibitory concentrations (MIC) of 62.5 μg/mL. The remaining MIC values were found to range between 125 and 500 μg/mL. To the best of our knowledge, the current work is the first to report the alkaloid profile and antimicrobial activity of G. vuralii L. growing in Turkey.

10α-hydroxymethylsparteine, a new type of quinolizidine alkaloid from Genista sessilifolia

10α-Hydroxymethylsparteine (1), a novel type of quinolizidine alkaloid with a 16-carbon atom skeleton, was isolated from the aerial parts of Genista sessilifolia DC. The position of the hydroxymethyl substituent and the stereochemistry of compound 1 were established by analysis of its spectroscopic data.