Estudo fitoquímico e farmacológico de Solanum subumbellatum Vell. (Solanaceae)

Abstract

The species Solanum subumbellatum (Solanaceae), also known as “jurubeba-de-cupim”, is native from Cerrado and is used in folk medicine against the flu, cold, bronchitis, asthma and as a diuretic. The plants of the genus Solanum are described in the literature as having antifungal and antioxidant activities. Thus, the objectives of this study were to unveil the biological activities of hexane (HE) and ethanolic (EE) extracts of root bark (RB), root core (RC), twigs (T), leaves (L) and fractions of S. subumbellatum by carrying out the chemical study of the most active extracts and fractions. In the antioxidant activity test by DPPH method (2,2-diphenyl-1-picrylhydrazyl) it was observed that the ethyl acetate fraction of the root bark (EAF-RB) showed the highest antioxidant activity (EC50 = 32.5 µg mL-1) compared to the ascorbic acid positive control (EC50 = 4.1 µg mL-1). By the ORAC method (oxygen radical absorption capacity), the values of FAE-CR (3862.5 µmol trolox eq g-1) and the dichloromethane fraction of root bark (DF-RB) (3920.3 µmol trolox eq g-1) have shown better results than the ascorbic acid positive control (2576.0 µmol trolox eq g-1). The EE-RB, EE-L and HE-L showed higher levels of total phenols, flavonoids and proanthocyanidins, respectively. Among the fractions, the FAE-CR followed by the FD-CR showed the highest levels of total phenols (137.6 mg EAG g-1 and 103.4 mg EAG g-1, respectively) and the FD-CR presented highest concentration of flavonoids (5.6 mg EQ g-1). The antifungal activity was performed by the broth microdilution method and the FD-CR was the most active against Candida albicans (MIC = 19.5 μg mL-1) and the hydromethanolic fraction of root bark (HMF-RB) was the most active against Cryptococcus neoformans (MIC = 78.0 μg mL-1), when compared to the positive control amphotericin (MIC = 0.5 μg mL-1). The most active fractions, DF-RB, EAF-RB and HMF-RB, were then subjected to high performance liquid chromatography coupled with mass spectrometry (HPLC-MS) in negative and positive mode, and the following chlorogenic acids were recorded: caffeic acid, ferulic acid, 5-O-caffeoylquinic acid, 4-O-feruloylquinic acid, in addition to ethyl caffeate, and steroidal alkaloids: 3-amino-hydroxy-dehydro-furostan-22-ol-O-(26)-β-D-Gly, fatimagraine, bhattacharyyaine, isojuripidine and jurubidine. These compounds have already been described in the literature and are related to biological activities. Ethyl caffeine was isolated from DF-RB and elucidated by MS and nuclear magnetic resonance (NMR). This compound has many biological activities already reported, such as antioxidant. Furthermore, ethyl caffeate showed strong bioactivity against C. krusei, C. albicans, C. guilliermondii, C. orthopsilosis and Cryptococcus neoformans (MIC's 4.7–18.7 µg mL−1). This is the first study to describe in the literature the chemical composition of S. subumbellatum, that let us conclude that this plant can be considered a good source of compounds with antioxidant and antifungal properties.