Antitubercular activity of compounds isolated from Pelargonium sidoides

The recent increase in the incidence of tuberculosis with the emergence of multidrug-resistant (MDR) cases has lead to the search for new drugs that are effective against MDR strains of Mycobacterium tuberculosis and can augment the potential of existing drugs against tuberculosis. Pelargonium sidoides DC (Geraniaceae) is highly valued by traditional healers for its curative properties and is well-known to treat coughs, diarrhea, and tuberculosis. The butanol root extract was found have bioactive inhibitory activity against M. tuberculosis at a concentration of 2.5 x 10(3) mu g/mL. Phytochemical analysis of the active fraction from the root of P. sidoides led to the isolation and identification of six compounds: coumarins (umckalin, scopoletin, 6,8-dihydroxy-5.7dimethoxy- 2H-benzopyran-2-one, and 6,8-dihydroxy-7-methoxy-2H-benzopyran-2-one) and flavonoids (catechin and epigallocatechin, which is reported for the first time from P. sidoides). The isolated compounds were evaluated for antitubercular activity with M. smegmatis and M. tuberculosis. Intracellular activity of these compounds was also investigated using THP-1 human macrophages infected with M. tuberculosis. The isolated compounds did not show activity inhibitory against M. tuberculosis, intracellularly and extracellularly, at the highest concentration tested in the current study. Epigallocatechin and scopoletin showed good inhibitory activity against M. smegmatis, exhibiting a minimum inhibitory concentration (MIC) of 7.8 mu g/mL. Catechin and umckalin exhibited MIC values of 31.25 and 62.5 mu g/mL, respectively.