Reynosin and santamarine: two sesquiterpene lactones from Ambrosia confertiflora with bactericidal activity against clinical strains of Mycobacterium tuberculosis

Abstract

Context: Tuberculosis is primarily caused by Mycobacterium tuberculosis (Mtb). Previous studies have shown that the dichloromethanic extract of Ambrosia confertiflora DC (Asteraceae) inhibited Mtb.

Objective: To isolate the compounds responsible for the mycobactericidal activity against clinical Mtb strains.

Materials and methods: The dichloromethanic extract of aerial parts of A. confertiflora was separated using chromatography columns. Mycobactericidal activity of the isolated compounds was evaluated using the Alamar Blue bioassay (128–16 μg/mL, 7 days). Cytotoxicity was tested against normal cell line L929 using the MTT ([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium]) assay (100–3.125 μg/mL, 48 h). Compound structures were elucidated by ¹H and ¹³C uni- and bidimensional NMR.

Results: Two sesquiterpene lactones (SQLs) with mycobactericidal activity were identified: santamarine and reynosin. Reynosin was the most active compound, with a minimal bactericidal concentration (MBC) of 128 μg/mL against the H37Rv, 366-2009 and 104-2010 Mtb strains and a minimal inhibitory concentration (MIC) of 64, 64, 128, 128 and 128 μg/mL against the H37Rv, 104-2010, 63-2009, 366-2009 and 430-2010 Mtb strains, respectively. Santamarine had MBCs of 128 μg/mL against the H3Rv and 104-2010 Mtb strains and MICs of 128 μg/mL against the H37Rv, 366-2009 and 104-2010 Mtb strains. We also isolated 1,10-epoxyparthenolide but only showed mycobacteriostatic activity (MIC 128 μg/mL) against the Mtb strain. Compounds were tested against the L929 cell line and the calculated selectivity index was <1.

Discussion and conclusions: This is the first report of the mycobactericidal activity of these compounds against clinical Mtb strains. It is also the first report of the isolation of 1,10-epoxyparthenolide from A. confertiflora. The anti-mycobacterial activity of A. confertiflora was attributed to the SQLs identified.

Keywords:

• 1,10-Epoxyparthenolide
• mycobactericidal
• sesquiterpenlactones

Acknowledgements

The authors wish to thank to: InDRE for providing the Mtb H37Rv reference strain and the LESP-SON for allowing us to work in their BSL-3 laboratory and for all the support and facilities provided; Chemist María del Rosario Aguayo Verdugo and her work team at LESP-SON for the Mtb clinical strains; Professor Jesús Sánchez-Escalante from the Herbarium of the UNISON for the authentication of A. confertiflora; MSc. Heriberto Torres-Moreno for his support in the cytotoxicity evaluation; and Chemist Eréndira García Ríos and MSc. Lucía del Carmen Márquez Alonso for HPLC analysis. This research was supported by the Mexican Council of Science and Technology (CONACyT) PDCPN 2013-17215469.

Disclosure statement

The authors report no declarations of interest.