Antifungal Saponins from the Maya Medicinal Plant Cestrum schlechtendahlii G. Don (Solanaceae).

Bioassay-guided fractionation of the crude extract (80% EtOH) of the leaves of Cestrum schlechtendahlii, a plant used by Q'eqchi' Maya healers for treatment of athlete's foot, resulted in the isolation and identification of two spirostanol saponins (1 and 2). Structure elucidation by MS, 1D-NMR, and 2D-NMR spectroscopic methods identified them to be the known saponin (25R)-1ß,2α-dihydroxy-5α-spirostan-3-ß-yl-O-α-L-rhamnopyranosyl-(1 → 2)-ß-D-galactopyranoside (1) and new saponin (25R)-1ß,2α-dihydroxy-5α-spirostan-3-ß-yl-O-ß-D-galactopyranoside (2). While 2 showed little or no antifungal activity at the highest concentration tested, 1 inhibited growth of Saccharomyces cerevisiae (minimum inhibitory concentration (MIC) of 15-25 µM), Candida albicans, Cryptococcus neoformans, and Fusarium graminearum (MIC of 132-198 µM).

Souroubea sympetala (Marcgraviaceae): a medicinal plant that exerts anxiolysis through interaction with the GABAA benzodiazepine receptor.

The mode of action of the anxiolytic medicinal plant Souroubea sympetala was investigated to test the hypothesis that extracts and the active principle act at the pharmacologically important GABAA-benzodiazepine (GABAA-BZD) receptor. Leaf extracts prepared by ethyl acetate extraction or supercritical extraction, previously determined to have 5.54 mg/g and 6.78 mg/g of the active principle, betulinic acid, respectively, reduced behavioural parameters associated with anxiety in a rat model. When animals were pretreated with the GABAA-BZD receptor antagonist flumazenil, followed by the plant extracts, or a more soluble derivative of the active principle, the methyl ester of betulinic acid (MeBA), flumazenil eliminated the anxiety-reducing effect of plant extracts and MeBA, demonstrating that S. sympetala acts via an agonist action on the GABAA-BZD receptor. An in vitro GABAA-BZD competitive receptor binding assay also demonstrated that S. sympetala extracts have an affinity for the GABAA-BZD receptor, with an EC50 value of 123 µg/mL (EtOAc leaf extract) and 154 µg/mL (supercritical CO2 extract). These experiments indicate that S. sympetala acts at the GABAA-BZD receptor to elicit anxiolysis.

Inhibition of bacterial quorum sensing and biofilm formation by extracts of neotropical rainforest plants.

Bacterial biofilms are responsible for many persistent infections by many clinically relevant pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. Biofilms are much more resistant to conventional antibiotics than their planktonic counterparts. Quorum sensing, an intercellular communication system, controls pathogenesis and biofilm formation in most bacterial species. Quorum sensing provides an important pharmacological target since its inhibition does not provide a selective pressure for resistance. In this study, we investigated the quorum sensing and biofilm inhibitory activities of 126 plant extracts from 71 species collected from neotropical rainforests in Costa Rica. Quorum sensing and biofilm interference were assessed using a modified disc diffusion bioassay with Chromobacterium violaceum ATCC 12,472 and a spectrophotometric bioassay with Pseudomonas aeruginosa PA14, respectively. Species with significant anti-quorum sensing and/or anti-biofilm activities belonged to the Meliaceae, Melastomataceae, Lepidobotryaceae, Sapindaceae, and Simaroubaceae families. IC50 values ranged from 45 to 266 µg/mL. Extracts of these active species could lead to future development of botanical treatments for biofilm-associated infections.