The Mycobacterium tuberculosis iniA gene is essential for activity of an efflux pump that confers drug tolerance to both isoniazid and ethambutol

Little is known about the intracellular events that occur following the initial inhibition of Mycobacterium tuberculosis by the first-line antituberculosis drugs isoniazid (INH) and ethambutol (EMB). Understanding these pathways should provide significant insights into the adaptive strategies M. tuberculosis undertakes to survive antibiotics. We have discovered that the M. tuberculosis iniA gene (Rv 0342) participates in the development of tolerance to both INH and EMB. This gene is strongly induced along with iniB and iniC (Rv 0341 and Rv 0343) by treatment of Mycobacterium bovis BCG or M. tuberculosis with INH or EMB. BCG strains overexpressing M. tuberculosis iniA grew and survived longer than control strains upon exposure to inhibitory concentrations of either INH or EMB. An M. tuberculosis strain containing an iniA deletion showed increased susceptibility to INH. Additional studies showed that overexpression of M. tuberculosis iniA in BCG conferred resistance to ethidium bromide, and the deletion of iniA in M. tuberculosis resulted in increased accumulation of intracellular ethidium bromide. The pump inhibitor reserpine reversed both tolerance to INH and resistance to ethidium bromide in BCG. These results suggest that iniA functions through an MDR-pump like mechanism, although IniA does not appear to directly transport INH from the cell. Analysis of two-dimensional crystals of the IniA protein revealed that this predicted transmembrane protein forms multimeric structures containing a central pore, providing further evidence that iniA is a pump component. Our studies elucidate a potentially unique adaptive pathway in mycobacteria. Drugs designed to inhibit the iniA gene product may shorten the time required to treat tuberculosis and may help prevent the clinical emergence of drug resistance.     

Potential ofVinca rosea extracts in modulating trace element profile

Diethylnitrosamine (DEN) was used as cancer-inducing agent in the experimental animals.Vinca rosea extract was supplemented with the drinking water as a chemopreventive agent. After 4 wk of treatment, animals were sacrificed and livers were excised. Nuclei and mitochondria were separated by differential centrifugation. The proton-induced X-ray emission technique has been used as the analytical method. Elemental analysis were performed for whole liver, nuclei, and mitochondria.V. rosea plant parts were also analyzed for elemental contents. Treatment with DEN caused an increase of Ni, Zn, and Cr levels in the whole liver and nuclei. There is an increase in Fe concentration in the liver, although the level decreased in mitochondria. The concentrations of Br and Ca were unchanged in the liver as a whole, but there were substantial increases of Br in nuclei and mitochondria, whereas Ca levels depleted drastically in these two organelles.Vinca extracts were effective in reverting the changes in the elemental concentration in the hepatic tissue as a whole, but were not that effective at subcellular levels.