Guilherme Medeiros Antar

Antitrypanosomal activity and evaluation of the mechanism of action of diterpenes from aerial parts of Baccharis retusa (Asteraceae)

Baccharis retusa, a medicinal Brazilian plant from Asteraceae, has been used in Brazilian folk medicine to treatment of several illnesses, including parasitic diseases. Bioactivity-guided fractionation of the n-hexane extract from the aerial parts of B. retusa resulted in the isolation and characterization of three active related diterpenes: ent-15β-senecioyl-oxy-kaur-16-en-19-oic acid (1), ent-kaur-16-en-19-oic (2) and ent-16-oxo-17-nor-kauran-19-oic (3) acids. The structures of isolated compounds were defined by spectroscopic analysis, including NMR and HRESIMS. Antitrypanosomal activity of 1-3 was performed against cell-derived trypomastigotes using the colorimetric resazurin assay. The obtained results demonstrated that isolated compounds displayed a reduced toxicity against NCTC cells and were effective against the trypomastigote forms of T. cruzi with IC50 values of 3.8μM (1), 75.3μM (2) and 44.2μM (3). Additionally, compound 3 displayed activity against amastigote forms of T. cruzi with IC50 of 83.2μM. Compound 1 displayed the highest selectivity index (SI) when considered the trypomastigote forms, and its effect in the plasma membrane of parasite was evaluated using the fluorescent probe SYTOX Green. A considerable permeabilization (57%) in the membrane of the parasite was observed when compared to the untreated trypomastigotes. These data demonstrate, for the first time, the antitrypanosomal activity and mechanism of action of 1 and related compounds 2 and 3, obtained from aerial parts of B. retusa.

Novelties in Hyptidendron (Hyptidinae – Lamiaceae) from Brazil: A new species and a rediscovery

A new species, Hyptidendron roseum, from the Chapada dos Veadeiros region, Goiás state, is described and illustrated. It can be distinguished from its congeners by the combination of inflorescences composed of a unilateral cymose structures, sessile to subsessile leaves, a ring of trichomes in the throat of the calyx tube, and a dense indumentum of white uniseriate trichomes covering much of the plant. The new species is compared with similar species such as H. unilaterale and H. albidum. New specimens of another species, H. unilaterale, formerly known only from the type, were identified in herbaria and collected in the field. Photos in vivo of this species are provided for the first time, accompanying a full description and an illustration. We assess its conservation status and comment on its distribution, ecological aspects, and identification.

Terpenoids from Leaves of Guarea macrophylla Display In Vitro Cytotoxic Activity and Induce Apoptosis In Melanoma Cells

Guarea macrophylla is a Brazilian plant species that has been used in folk medicine to treat a range of diseases. Our ongoing work focuses on the discovery of new bioactive natural products derived from Brazilian flora. The current study describes the identification of cytotoxic compounds from the EtOH extract of leaves from G. macrophylla using bioactivity-guided fractionation. This approach resulted in the isolation and characterization of four compounds: cycloart-23E-ene-3β,25-diol (1), (23S*,24S*)-dihydroxycicloart-25-en-3-one (2), isopimara-7,15-diene-2α,3β-diol (3), and isopimara-7,15-dien-3β-ol (4), in which 2 and 3 are identified as new derivatives. In vitro assays were conducted to evaluate the cytotoxic activity of compounds 1-4 against a panel of cancer cell lines and to determine the possible mechanism(s) related to the activity of the compounds on B16F10Nex2 cells. The most active compound 1 induced cytotoxic effects on tumor cells, with IC50 values of 18.3, 52.1, and 58.9 µM against HL-60, HeLa, and B16F10-Nex2 tumor cells, respectively. Furthermore, it was observed in melanoma cells that compound 1 induced several specific apoptotic hallmarks, such as morphological changes in the cell shape structure, nuclear DNA condensation, specific chromatin fragmentation, and disruption in the mitochondrial membrane potential, which are related to the intrinsic apoptotic pathway.

Dioscorea compacta (Dioscoreaceae), a new endangered dwarf species from the Jalapão region, Tocantins, Brazil

SummaryThe Jalapão region located in the east of the state of Tocantins, central Brazil is the largest continuous area of protected cerrado, a hotspot of biodiversity. Here we present a new species of Dioscorea, found in dry soils in sandy open cerrado vegetation within the limits of two protected areas. This species differs from other similar species by its combination of dwarf habit, staminate flowers with three stamens plus three staminodes, compact pistillate inflorescences and spheroid unwinged seeds.