National Institute of Respiratory Diseases, Mexico
Title: Nordihydroguaiaretic acid inhibits Mycobacterium tuberculosis survival in vitro and in infected human cell line
Martha Torres Rojas was from National Institute of Respiratory Diseases, Mexico
Background: Medicinal plants have been essential for the generation of drugs; even they are excellent source of compounds with wide biological activities. In Mexico, the plants are used to treat infection diseases, including tuberculosis (TB). This is a contagious illness that provokes a serious public health problem. Among the plants more used in the traditional medicine for treat TB, it has been Larrea tridentata (creosote). Numerous natural compounds like alkaloids, flavonoids have been isolated from L. tridentata, for example Nordihydroguaiaretic acid (NDGA) is a lignan with beneficial properties. The aim of this study was to evaluate the effect of NDGA on growth of Mycobacterium tuberculosis in vitro and survival in infected macrophages derived from the human cell line THP-1. Methods: The anti-mycobacterial activity of (0.01-1.0 mg/ml) NDGA in vitro was evaluated on the growth by counting viable cells per unit colony-forming (CFU). To investigate the toxicity of this compound, THP-1 cells were treated with 1.0-100 ug/ml of NDGA by five days. Finally, NDGA effect on survival of Mycobacterium in THP-1 was evaluated. For this purpose, THP-1 were infected at a multiplicity ratio 1:10 for 1 h, then the non-phagocytized bacteria were removed by washing. After, the infected THP-1 were incubated for 1, 3 and 5 days in the presence or absence of NDGA [0.07 mg / ml]. Rifampicin (RIF) was added at 0.002 mg/ml as bactericidal controls. Subsequently, the THP-1 were lysed for intracellular bacterial growth detection by counting CFU. Results: In this paper we showed that NDGA decreased significantly the growth of M. tuberculosis in vitro. Surprisingly, it was found that the addition of NDGA (0.07 mg/ml) inhibited intracellular bacterial growth 65%, while RIF reduced over 98% with compared to the control (P <0.05). The results suggested that NDGA has two mechanisms to inhibit M. tuberculosis survival. In one way, NDGA inhibits directly the growth in vitro; probably avoiding the bacterial duplication and the other way, this compound in low concentration (0.007 g/ml) was able to induce autophagy in THP-1. This mechanism could contributed to eliminate intracellular mycobacterium Conclusion: NDGA inhibited the growth of M. tuberculosis, so it could be candidate as a drug for the treatment of drug-resistant tuberculosis, where antibiotics such as INH and IRF could not be used.