Short communicationIn vitro activity of (-)-deoxypergularinine, on its own and in combination with anti-tubercular drugs, against resistant strains of Mycobacterium tuberculosis
Graphical abstract
Introduction
Tuberculosis (TB) is a widespread infectious disease usually caused by Mycobacterium tuberculosis. The disease causes an estimated 1.7 million deaths annually and the current annual number of new cases worldwide (over 9 million) is higher than at any other time in history (Lawn and Zumla 2011). The two antibiotics most commonly prescribed are rifampicin and isoniazid (INH), but treatment can be prolonged, often requiring several months. Active TB is best treated with a combination of several antibiotics to reduce the risk of development of antibiotic-resistance. However, such resistance is a growing problem when multiple drug-resistant tuberculosis (MDR-TB) infections are to be treated; the bacteria are not killed by first-line standard treatments (i.e. the strains are resistant to [at least] rifampicin and INH). Inappropriate treatment is the principal risk factor for development of MDR-TB. The association between TB and HIV, and the increasing emergence of MDR-TB and extensively drug-resistant TB (XDR-TB; such strains are resistant to second-line drugs, for example capreomycin, kanamycin, and/or amikacin), have worsened the situation; the threat to health is serious (Matteelli et al. 2014). Therefore, new anti-TB agents active against MDR/XDR-TB are urgently required.
The dried roots of Cynanchum atratum Bunge (Asclepiadaceae), commonly termed “Bai Wei” in Chinese, are rich in C-21 steroidal glycosides (Zhao et al. 2009), cynatratosides, pregnan glycosides (Bai et al., 2009), seco-pregnan steroidal glycosides (Yan et al., 2014), and 2,4-dihydroxyacetophenone (Yuan et al., 2007). C. atratum exerts anti-osteoporotic effects (Mukudai et al., 2014), anti-acetylcholinesterase, anti-amnesic, (Lee et al., 2005), anti-tobacco mosaic virus (TMV) (Yan et al., 2014), and anti-parasitic effects (Fu et al., 2014). In the present study, we isolated (-)-deoxypergularinine from the roots of C. atratum and tested it against M. tuberculosis H37Rv, MDR/XDR-TB, pyrazinamide-resistant-TB, INH-resistant-TB, rifampicin-resistant-TB, and streptomycin-resistant-TB strains. The alkaloid was evaluated both alone and in combination with existing drugs.
Section snippets
Preparation of crude plant extract
Air-dried roots of C. atratum were purchased from the medicinal herbs market of Jegi-dong, Dongdaemun-gu, South Korea. A voucher specimen was deposited in the Herbarium of the College of Life Science, Soonchunhyang University (SCH-2013-0017). The roots (1.0 kg) were extracted three times with EtOH (9 L × 7 days) at room temperature and the extract concentrated under reduced pressure. The dried extract (238.1 g) was suspended in water (1 L) and partitioned with n-hexane (fr. A, 33.2 g), dichloromethane
Results and discussion
The ethanol extract of C. atratum was fractionated successively with these solvents (n-hexane, dichloromethane, and EtOAc). The n-hexane and the dichloromethane sub-extracts exhibited moderate anti-TB activities (MICs 200 µg/ml) but the EtOAc extract had no such effect. The natural compound AB6163 was obtained as a colourless powder from the roots of C. atratum. HR-EIMS revealed a molecular ion at m/z 363.1841 (Calcd. for C23H25NO3). 13C NMR (CDCl3) revealed the resonances of 23 carbon atoms
Conflict of interest
All authors have no conflict of interest to disclose.
Acknowledgments
This work was supported by a grant from the Ministry of Health & Welfare R&D Project, Republic of Korea (HI13C0828), and in part by the Soonchunhyang University Research Fund.
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