Abstract
BackgroundTuberculosis is a deadly disease caused by Mycobacterium species. The use of medicinal plants is an ancient global practice for the treatment and prevention of diverse ailments including tuberculosis. The aim of this study was to isolate and characterize antimycobacterial compounds by bioassay-guided fractionation of the acetone leaf extract of Oxyanthus speciosus.MethodsA two-fold serial microdilution method was used to determine the minimum inhibitory concentration (MIC) against mycobacteria. Cytotoxicity and nitric oxide inhibitory activity of the isolated compounds was determined to evaluate in vitro safety and potential anti-inflammatory activity. Intracellular efficacy of the crude extract against Mycobacterium-infected macrophages was also determined.ResultsTwo compounds were isolated and identified as lutein (1) and rotundic acid (2). These had good antimycobacterial activity against the four mycobacteria tested with MIC values ranging from 0.013 to 0.1 mg/mL. Rotundic acid had some cytotoxicity against C3A human liver cells. Lutein was not cytotoxic at the highest tested concentration (200 μg/mL) and inhibited nitric oxide production in RAW 264.7 macrophages by 94% at a concentration of 25 μg/mL. The acetone crude extract (120 μg/mL) of O. speciosus had intracellular antimycobacterial activity, reducing colony forming units by more than 90%, displaying bactericidal efficacy in a dose and time-dependent manner.ConclusionThis study provides good proof of the presence of synergism between different compounds in extracts and fractions. It is also the first report of the antimycobacterial activity of lutein and rotundic acid isolated from Oxyanthus speciosus. The promising activity of the crude extract of O. speciosus both in vitro and intracellularly in an in vitro macrophage model suggests its potential for development as an anti- tuberculosis (TB) herbal medicine.
Highlights
Tuberculosis is a deadly disease caused by Mycobacterium species
Structure elucidation and gas chromatography (GC)-mass spectrometry (MS) The acetone leaf crude extract of O. speciosus was subjected to bioassay-guided fractionation using open column chromatography and bioautography to determine the number of antimycobacterial compounds present [30] (Fig. 1)
The eluting solvent was removed from the chromatogram in a flow of air at room temperature, chromatograms were sprayed with a dense M. smegmatis culture, incubated overnight and sprayed with 0.2 mg/ml p-iodonitrotetrazolium violet to indicate Rf values of compounds that inhibited mycobacterial growth
Summary
Tuberculosis is a deadly disease caused by Mycobacterium species. The use of medicinal plants is an ancient global practice for the treatment and prevention of diverse ailments including tuberculosis. The innovation of tuberculin in 1890, Bacillus-Calmette Guerin (BCG) vaccine in 1908 and discoveries of antimycobacterial drugs in 1943 brought great hope for the eradication of this deadly disease until the pandemic of HIV/AIDS and upsurge of resistant strains (multi-drug, extensive-drug and total-drug resistant) ravaged humankind [2]. To effectively combat these drug resistant cases, new TB drugs with novel modes of action are desperately needed. An interdisciplinary approach is needed for the discovery of new chemical molecules against both active and latent forms of TB [4]
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