Abstract:
BACKGROUND : 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 aim of this
study was to isolate and characterize antimycobacterial compounds by bioassay-guided fractionation of the
acetone leaf extract of Oxyanthus speciosus.
METHODS: A 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.
RESULTS : Two 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.
CONCLUSION : This 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.
