Atividade antimicrobiana e estudo químico bioguiado de espécies de Aspidosperma

Abstract

Aspidosperma species belonging to the Apocynaceae family are restricted to the Americas. Ethnopharmacological studies have shown the use of these species as a potential agent against malaria and trypanosomatids, also used as antibiotics, anti-inflammatory and antitumor. The search for new chemical entities with antimicrobial activity has significant importance due to the versatility of microorganisms to acquire resistance to the therapeutic arsenal, and due to the prevalence of neglected diseases, such as leishmaniasis. These are endemic in developing countries have few therapeutic options, which are toxic and have limited effectiveness. The aim of this study was to evaluate the crude extracts and fractions from different parts of the species A. macrocarpon, A. tomentosum and A. pyrifolium, as the antimicrobial action and realize bioguided chemical study of the species with high activity against the microorganisms tested, and less toxic to mammalian cells. About antibacterial activity alkaloidal fraction from A. pyrifolium stem presented moderate minimal inhibitory concentration (MIC): 125 and 250 g/mL for Staphylococcus aureus and Bacillus subtilis, respectively. The ethyl acetate fraction of A. macrocarpon stem had a weak MIC of 250 g/mL on Candida parapsilosis. The activity of the extract of the stem bark of A. macrocapon against Leishmania amazonensis promastigotes showed inhibitory concentration (IC50) of 151.5 g/mL and selectivity index (SI) of 6.52 on LLCMK2 cells, this species were considered the most promising for the bioguided chemical study. The chloroform and ethyl acetate fractions of the A. macrocarpon stem bark showed IC50 29.00  1.65 and 29.50  0.95 g/mL, respectively on promastigotes forms of L. amazonensis. The bioguided study with chloroform fraction led to subfraction of monoacylglycerols, wich were the most active on L. amazonensis, with IC50 2.31  0.08 and 2.29  0.14 g/mL on promastigotes and intracellular amastigotes, respectively. SI showed that this fraction were 42 fold more toxic to L. amazonensis than to macrophages. Studies related to the mechanism of action of monoacylglycerols evaluated by optical microscopy, scanning electron (SEM) and transmission electron microscopy (TEM) showed abnormalities such as mitochondrial swelling, concentric membranes inside the mitochondria, presence of perforations on the cell surface of the parasite and autophagic vacuoles. These data together with results of flow cytometry showed necrosis and autophagy as a possible mechanism of cell death. Quercetin was identified as the active substance of the ethyl acetate fraction against evolutionary forms of L. amazonensis. This substance had, IC50 of 61.93  1.36 and 63.86  3.25 M/mL on promastigotes and intracellular amastigotes, respectively. Quercetin was evaluated in combination with amphotericin B (Q + A) and miltefosine (Q + M), the combinatorial effect of both was considered synergistic against all forms of L. amazonensis. The combinations Q+A and Q+M showed antagonistic action on macrophages and human erythrocytes. Evaluation of the combination using SEM and TEM associated with literature data indicate apoptotic cell death after treatment with both combinations. These findings are relevant as a first step in the search for new therapies for the treatment of cutaneous leishmaniasis.