Estudo químico e avaliação das propriedades biológicas de Aspidosperma excelsum Benth

Abstract

Species of the genus Aspidosperma (Apocynaceae) are recognized for their quantity of indole alkaloids and their popular use in the treatment of diseases such as leishmaniasis, malaria, diabetes, among others. Among the 68 species of the genus cataloged in Brazil, the species Aspidosperma excelsum, known as Caparanauba, is constantly sold in popular fairs due to its medicinais properties. In this sense, the present study aimed to evaluate the chemical composition of the extracts of a commercial sample of the bark of A. excelsum and to determine the antioxidant, antimicrobial and antimalarial activity. The extracts were obtained from the suspension of the plant material in solvents with increasing order of polarity. The samples were subjected to a preliminary phytochemical analysis, as well as to classical chromatographic, spectrometric and spectroscopic methods (mass spectrometer and nuclear magnetic resonance). The extracts were evaluated for their antioxidant action against DPPH•, ABTS•+ radicals and iron ion reduction potential (FRAP), and antimicrobial action against strains of Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Burkholderia cepacia, Candida albicans and Candida parapsilosis, through the broth microdilution technique to determine the Minimum Inhibitory Concentration (MIC). The antimalarial activity was evaluated by in vitro microtest against Plasmodium falciparum, using the 3D7 strain (sensitive to chloroquine) and the cytotoxicity against the murine macrophage strain J774. In the preliminary phytochemical screening, the following classes of metabolites were identified: alkaloids, anthrones, triterpenes and steroids. The fractionation of the extracts resulted in the isolation and identification of the indole alkaloids carapanaubine and O-acetyliohimbine, and through the study of the fragmentation patterns of the crude extracts, three indole alkaloids were identified, spruceanumine B, 10-methoxydihydrocorinanteol and 11-methoxyiohimbine, in addition to 2-hydroxy-3-O-β-D-glucopyranosyloxy-benzoic, 9,12,13-trihydroxy-10,15-octadecadienoic and quinic acids. Regarding the biological study, the hexane extract showed moderate action, with a minimum inhibitory concentration (MIC) of 400 µg/mL, and the other extracts obtained weak activity, with MIC of 1600 µg/mL, against C. parapisilosis. All extracts showed weak antifungal activity against C. albicans and were inactive against all bacteria in the dilutions tested. All extracts analyzed showed low total phenolic content, with values ranging from 31.25 to 138.06 ± 0.9 mg GAE g-1. The antioxidant potential against the tested radicals was expressed in micromolar Trolox equivalents (μM TE). Regarding the evaluation against the ABTS•+ radical, the hexane extract was inactive, but the chloroform, ethyl acetate and methanol extracts showed relatively high mean values when compared to the Trolox standard, in the range between 500 and 1000 μM, with values between 801.88 ± 42.22 and 936.33 ± 61.28 μM TE. Regarding the DPPH• radical, the extracts demonstrated low antioxidant power. The EC-Aex and EA-Aex samples showed greater iron reduction power with values of 841.11 ± 0.016 and 816.67 ± 0.023 μM Fe2+/g, respectively. Regarding antimalarial activity, samples EC-Aex, EA-Aex and EM-Aex were active against the 3D7 strain of P. falciparum, presenting inhibition percentages of 98, 97.5 and 83%. The IC50 of the samples ranged from 10 ± 2.1 ng/mL to 25 ± 10 ng/mL. The EC-Aex and EA-Aex extracts showed significant antimalarial efficacy against P. falciparum, with a 50% cytotoxic concentration (CC50) of 25 ± 2.8 µg/mL and 78 ± 20 µg/mL. The hexane extract was inactive against P. falciparum. The results obtained demonstrate that subsequent studies with A. excelsum are promising in order to find compounds with pharmacological actions, since this species presented activities in the tests performed, in addition to contributing to traditional knowledge.