Cátia Ramalhete

Isoflavones as Apoptosis Inducers in Human Hepatoma HuH‐7 Cells

Nine flavonoids isolated from the ethyl acetate extract of Pycnanthus angolensis were assayed for their potential apoptosis induction activities in human hepatoma HuH‐7 cells. These flavonoids include eight isoflavones, namely irilone (1), tectorigenine (2), formononetin (3), genistein (4), 2′‐hydroxybiochanin A (5), mixture of biochanin A (6) and prunetin (7), and 4′,7‐dihydroxy‐2′‐methoxyisoflavan (8), and the flavanone liguiritigentin (9). Their chemical structures were characterized by spectroscopic methods including 2D NMR experiments. Methodology for cell death detection included the LDH assay, Hoechst staining, TUNEL staining and general caspase‐3‐like activity assay. The compounds tested showed higher apoptosis induction profiles in HuH‐7 cells compared with the control. Caspase activity assays confirmed the apoptosis inducing activity of these flavonoids. Copyright

Inhibition of efflux pumps in meticillin-resistant Staphylococcus aureus and Enterococcus faecalis resistant strains by triterpenoids from Momordica balsamina

Six cucurbitane-type triterpenoids (1-6) isolated from the aerial parts of Momordica balsamina were evaluated for their ability to inhibit the activity of bacterial efflux pumps of methicillin-resistant Staphylococcus aureus (MRSA) COL(OXA), Enterococcus faecalis ATCC 29212, Salmonella enterica subsp. I serovar Typhimurium 5408 and S. Typhimurium 5408CIP strains. The latter strain overproduces the AcrB transporter of the AcrAB-TolC efflux pump six-fold compared with its parent. Compounds 4-6 were also tested for similar activity against Escherichia coli AG100 wild-type strain and E. coli AG100TET8 that overproduces the AcrAB-TolC efflux pump. Evaluation of efflux activity was performed using a semi-automated method that measures accumulation of the universal efflux pump substrate ethidium bromide (EtBr). Some of the compounds significantly inhibited efflux of EtBr by MRSA COL(OXA) and E. faecalis ATCC 29212. A correlation between activity and the topological polar surface area of the compounds was found for MRSA COL(OXA).

New antimalarials with a triterpenic scaffold from Momordica balsamina

Bioassay-guided fractionation of the methanol extract of Momordica balsamina led to the isolation of three new cucurbitane-type triterpenoids, balsaminols C-E (1-3). Their structures were elucidated on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC and NOESY). Balsaminols C-E, together with ten cucurbitacins isolated from the same plant (4-13), were evaluated for their antimalarial activity against the Plasmodium falciparum chloroquine-sensitive strain 3D7 and the chloroquine-resistant clone Dd2. Most of the compounds displayed antimalarial activity. Compounds 9 and 12 revealed the highest antiplasmodial effects against both strains (IC50 values: 4.6, and 7.4 microM, 3D7, respectively; 4.0, and 8.2 microM, Dd2, respectively). Structure-activity relationships are discussed. Furthermore, the preliminary toxicity toward human cells of compounds 1-5 and 9 was investigated in breast cancer cell line (MCF-7). Compounds were inactive or showed weak toxicity (IC50 values>19.0).

New potent P-glycoprotein modulators with the cucurbitane scaffold and their synergistic interaction with doxorubicin on resistant cancer cells.

The novel cucurbitacins, balsaminagenin A and B (1-2) and balsaminoside A (3) and the know cucurbitacin karavelagenin C (4), together with five new mono or diacylated derivatives (5-9) of karavelagenin C were evaluated for multidrug resistance reversing activity on human MDR1 gene transfected mouse lymphoma cells. Compounds 2-6 exhibited a strong activity compared with that of the positive control, verapamil. Structure-activity relationships are discussed. Moreover, in the checkerboard model of combination chemotherapy, the interaction between doxorubicin and compounds 2-5 synergistically enhanced the effect of the anticancer drug. Compounds 1-4 were isolated from the aerial parts of Momordica balsamina L. The structures of the compounds were established on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC and NOESY).

Tabernines A−C, β-Carbolines from the Leaves of Tabernaemontana elegans

Three novel beta-carboline indole alkaloids (1-3) have been isolated from a MeOH extract of the leaves of Tabernaemontana elegans. The structures were established by means of spectroscopic techniques including 2D NMR experiments. Compounds 1 and 2 contain a two-carbon unit, attached to a structurally related beta-carboline skeleton, as part of an additional six-membered ring in 1 and a seven-membered ring in 2. To the best of our knowledge, this is the first report of beta-carboline indole alkaloids from the genus Tabernaemontana. Compounds 1-3 were evaluated for their ability to modulate multidrug resistance in mouse lymphoma cell lines. Compounds 1 and 3 exhibited a weak activity.

Antibacterial activity of some African medicinal plants used traditionally against infectious diseases.

Context: Plants are known to play a crucial role in African traditional medicine for the treatment of infection diseases. Objectives: To investigate the claimed antimicrobial properties of plants traditionally used in African countries, providing scientific validation for their use. Materials and methods: Eighty-three polar and non-polar extracts from 22 medicinal plants were screened for their antibacterial activity against Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and Mycobacterium smegmatis using the broth microdilution method. Results and Discussion: In vitro antibacterial activity against one or more tested bacteria was shown by 83% of the extracts. The highest activity was obtained with the methanol extracts of the aerial parts of Acacia karroo Hayne (Fabaceae) and Anacardium occidentale L. (Anacardiaceae) and the roots of Bridelia cathartica G. Bertol (Euphorbiaceae), against S. aureus (minimum inhibitory concentration (MIC) = 7.5 µg/mL). The same MIC values were exhibited against E. faecalis by the methanol extract of A. occidentale, the dichloromethane and methanol extracts of B. cathartica and the ethyl acetate extract of Momordica balsamina l. (Curcubitaceae) leaves. Gram-negative bacteria were less sensitive; the growth of P. aeruginosa was significantly inhibited (MIC = 31 µg/mL) by the n-hexane and methanol extracts of Gomphocarpus fruticosus (l.) Ait. (Asclepiadaceae) fruits and by the dichloromethane extract of Trichilia emetica Vahl (Meliaceae) seeds. Most of the active extracts were rich in fenols/flavonoids. Conclusion: This study supports the use of most of the studied plants in traditional medicine, for the treatment of infectious diseases. Some of them are worthy of further investigation.

Triterpenoids as inhibitors of erythrocytic and liver stages of Plasmodium infections

Bioassay-guided fractionation of the methanol extract of Momordica balsamina led to the isolation of two new cucurbitane-type triterpenoids, balsaminol F (1) and balsaminoside B (2), along with the known glycosylated cucurbitacins, cucurbita-5,24-diene-3β,23(R)-diol-7-O-β-D-glucopyranoside (3) and kuguaglycoside A (4). Compound 1 was acylated yielding two new triesters, triacetylbalsaminol F (5) and tribenzoylbalsaminol F (6). The structures were elucidated based on spectroscopic methods including 2D-NMR experiments (COSY, HMQC, HMBC and NOESY). Compounds 1-6, were evaluated for their antimalarial activity against the erythrocytic stages of the Plasmodium falciparum chloroquine-sensitive strain 3D7 and the chloroquine-resistant clone Dd2. Assessment of compounds (1-3 and 5, 6) activity against the liver stage of Plasmodium berghei was also performed, measuring the luminescence intensity in Huh-7 cells infected with a firefly luciferase-expressing P. berghei line, PbGFP-Luc(con). Active compounds were shown to inhibit the parasites intracellular development rather than its ability to invade hepatic cells. Toxicity of compounds (1-3 and 5, 6) was assessed on the same cell line and on mouse primary hepatocytes through the fluorescence measurement of cell confluency. Furthermore, toxicity of compounds 1-6 towards human cells was also investigated in the MCF-7 breast cancer cell line, showing that they were not toxic or exhibited weak toxicity. In blood stages of P. falciparum, compounds 1-5 displayed antimalarial activity, revealing triacetylbalsaminol F (5) the highest antiplasmodial effects (IC(50) values: 0.4μM, 3D7; 0.2μM, Dd2). The highest antiplasmodial activity against the liver stages of P.berghei was also displayed by compound 5, with high inhibitory activity and no toxicity.

Cucurbitane-Type Triterpenoids from the African Plant Momordica balsamina

Phytochemical investigation of the aerial parts of Momordica balsamina led to the isolation of five new cucurbitane-type triterpenoids (1-5) and two known analogues (6, 7). Their structures were elucidated on the basis of spectroscopic methods including 2D NMR experiments (COSY, HMQC, HMBC, and NOESY). The new compounds feature unusual oxidation patterns in the cucurbitane skeleton, such as at C-29 (1-3) and C-12 (4, 5). Compounds 1-4, 6, and 7 were evaluated for in vitro cytotoxicity against human breast cancer cells (MCF-7), using the MTT assay.

Karavilagenin C derivatives as antimalarials

Karavilagenin C (1), a cucurbitane-type triterpenoid, previously isolated from the aerial parts of Momordica balsamina, was acylated with different alkanoyl, aroyl and cinnamoyl chlorides/anydrides, yielding ten new mono or diesters, karavoates F (7) and H-P (8-16). Furthermore, the new compound cucurbalsaminol C (17) was isolated from the same plant. Their structures were assigned by spectroscopic methods, including 2D NMR experiments. Compounds 1 and 17 and the acyl derivatives 8-16 along with other five esters (2-6, karavoates A-E), previously prepared from 1, were evaluated for their in vitro antimalarial activity against the chloroquine-sensitive (3D7) and the chloroquine-resistant (Dd2) strains of Plasmodium falciparum. Compound 1 exhibited a moderate activity and 17 was inactive. However, a remarkable antiplasmodial activity was observed for most of karavilagenin C alkanoyl and monoaroyl/cynamoyl derivatives. Karavoates B, D, E, I, and M were the most active, displaying IC(50) values similar to those found for chloroquine, particularly against the resistant strain (IC(50) <0.6μM). Structure-activity relationships (SAR) are discussed. Moreover, the preliminary toxicity toward human cells of compounds 1-17 was also evaluated in breast cancer cell line (MCF-7). Most of the esters showed no toxicity, displaying, in general, much higher selectivity index values than those obtained for the parent compound.

In vitro schistosomicidal activity of balsaminol F and karavilagenin C.

Five cucurbitane-type triterpenes (1-5), previously isolated from the African medicinal plant Momordica balsamina, along with five ester derivatives (6-10) of karavilagenin C (2), were evaluated for their potential schistosomicidal activity against Schistosoma mansoni adult worms. The natural compounds were isolated from the ethyl acetate-soluble fraction of the methanol extract of the aerial parts of M. balsamina. In a preliminary study, a significant schistosomicidal activity was observed for both the crude methanol extract and the ethyl acetate fraction. The compounds responsible for the activity were found to be balsaminol F (1) and karavilagenin C (2) with LC50 values of 14.7 ± 1.5 and 28.9 ± 1.8 µM, respectively, after 24 h of incubation (positive control praziquantel, LC₅₀ = 1.2 ± 0.1 µM). Both compounds (1, 2), at 10-50 µM, induced significant reductions in the motor activity of the worms and significantly decreased the egg production. Furthermore, they were able (at 10-100 µM) to separate the adult worm pairs into male and female after 24 h. Compounds 3-5, bearing a sugar moiety as a substituent, and the acylated derivatives of karavilagenin C (6-10) were inactive, suggesting that the presence of free hydroxyl groups in the tetracyclic skeleton might be important for the activity. A correlation between activity and the molecular volume/weight of compounds was also found.