Phytochemical characterization of antimycobacterial crude extracts from medicinal plants traditionally used in Mozambique

Abstract

A number of medicinal plants have long been used by traditional healers to treat tuberculosis and related diseases in Mozambique [1,2]. The present study was aimed to evaluate selected medicinal plants for their in vitro antimycobacterial activity, and reveal the main classes of compounds which might account for the observed activity. Four organic solvents (n-hexane, dichloromethane, ethylacetate, and 70% ethanol) were used for the sequential extraction. Decoction of each plant material was prepared according to traditional use. Different species of mycobacteria, namely, M. smegmatis, M. bovis BCG, M. avium, and M. tuberculosis were employed to screen extracts by broth microdilution method. The cytotoxicity against human macrophages from the monocytic THP-1 cells was also evaluated. Overall, n-hexane extracts of Maerua edulis Gilg & Gilg-Ben. and Securidaca longepedunculata Fresen, ethyl acetate extract of Tabernaemontana elegans Stapf and dichloromethane extract of Zanthoxylum capense (Thunb.) Harv. were found to possess considerable activity against M. bovis BCG and M. tuberculosis H37Ra with MIC=15.6–62.5µg/mL. Tabernaemontana elegans ethyl acetate extract displayed strong activity against M. tuberculosis H37Rv (MIC 15.6µg/mL) as well as potent cytotoxic effects in THP-1 cells (IC50 <4µg/mL). Based on 1H NMR spectroscopic analysis, major components in both Maerua edulis and Securidaca longepedunculata n-hexane extracts were linear chain unsaturated fatty acids. Zanthoxylum capense dichloromethane extract contained more complex constituents (mostly phenolic compounds), and the prominent compounds in ethyl acetate extract of Tabernaemontana elegans were identified as indole alkaloids.