Alveolar epithelial cells have been functionally implicated in Mycobacterium tuberculosis infection. This study investigated the role of ursolic acid (UA)-a triterpenoid carboxylic acid with potent antioxidant, anti-tumor, anti-inflammatory, and anti-tuberculosis properties in mycobacterial infection of alveolar epithelial A549 cells. We observed that M. tuberculosis successfully entered A549 cells. Cytotoxi-city was mediated by nitric oxide (NO). A549 toxicity peaked along with NO generation 72 h after infection. The NO generated by mycobacterial infection in A549 cells was insufficient to kill mycobacteria, as made evident by the mycobacteria growth indicator tube time to detect (MGIT TTD) and viable cell count assays. Treatment of mycobacteria-infected cells with UA reduced the expression of inducible nitric oxide synthase, NO generation, and eventually improved cell viability. Moreover, UA was found to quench the translocation of the transcription factor, nuclear factor kappa B (NF-κB), from the cytosol to the nucleus in mycobacteria-infected cells. This study is the first to demonstrate the cytotoxic role of NO in the eradication of mycobacteria and the role of UA in reducing this cytotoxicity in A549 cells.
Keywords: Mycobacterium tuberculosis; anti-tuberculosis; inducible nitric oxide synthase (iNOS); nuclear factor kappa B (NF-κB); ursolic acid.