Volume 147, Issue 1, 2 May 2013, Pages 232–237
The Canadian medicinal plant Heracleum maximum contains antimycobacterial diynes and furanocoumarins
Abstract
Ethnopharmacological relevance
Heracleum maximum
is amongst the most commonly used plants by the indigenous peoples of
North America. The First Nations of the eastern Canada use infusions of Heracleum maximum
roots for the treatment of respiratory ailments including tuberculosis.
Previous investigations of extracts derived from the roots of Heracleum maximum have
shown it to possess antimycobacterial activity. Aim of the study: To
isolate and identify antimycobacterial constituents from the roots of Heracleum maximum.
Materials and methods
A methanolic extract of Heracleum maximum
roots was subjected to bioassay guided fractionation using the
microplate resazurin assay (MRA) to assess inhibitory activity against Mycobacterium tuberculosis strain H37Ra. The antimycobacterial constituents were identified by NMR, MS and polarimetry.
Results
The polyacetylene (3R,8S)-falcarindiol
and the furanocoumarins bergapten, isobergapten, angelicin, sphondin,
pimpinellin, isopimpinellin and 6-isopentenyloxyisobergapten were
isolated from the Heracleum maximum root extract. (3R,8S)-Falcarindiol and 6-isopentenyloxyisobergapten exhibited MICs of 24 μM and 167 μM and IC50s of 6 μM and 27 μM against Mycobacterium tuberculosis
H37Ra respectively. The remaining furanocoumarins bergapten,
isobergapten, angelicin, sphondin, pimpinellin, and isopimpinellin were
less active, with MICs of 925, 1850, 2149, 1859, 812 and 1625 μM and IC50s of 125, 344, 350, 351, 389 and 406 μM.
Conclusions
(3R,8S)-Falcarindiol,
bergapten, isobergapten, angelicin, sphondin, pimpinellin,
isopimpinellin and 6-isopentenyloxyisobergapten were identified as the
principal constituents responsible for the antimycobacterial activity of
the roots of Heracleum maximum. This work supports the ethnopharmacological use of Heracleum maximum by Canadian First Nations and Native American communities as a treatment for infectious diseases, specifically tuberculosis.
Graphical abstract
Abbreviations
- [α]D, specific rotation measured at 589 nm and the temperature indicated;
- 1D, one dimensional;
- 2D, two dimensional;
- ACS, American Chemical Society;
- bs, broad singlet;
- c, concentration in g/100 mL;
- CH2Cl2, dichloromethane;
- d, doublet;
- DMSO, dimethyl sulfoxide;
- EtOAc, ethyl acetate;
- HPLC, high performance liquid chromatography;
- HRESIMS, high resolution electrospray ionization mass spectrometry;
- IC50, median inhibitory concentration;
- IR, infrared;
- LC–MS, liquid chromatography–mass spectrometry;
- m, multiplet;
- MeOH, methanol;
- MIC, minimum inhibitory concentration;
- MRA, microplate resazurin assay;
- MS, mass spectroscopy;
- NaCl, sodium chloride;
- nBuOH, 1-butanol;
- NMR, nuclear magnetic resonance;
- q, quartet;
- s, singlet;
- SD, standard deviation;
- t, triplet;
- TLC, thin layer chromatography
Keywords
- Antimycobacterial activity;
- C-17 diynes;
- (3R8S)-falcarindiol;
- Furanocoumarins;
- Heracleum maximum;
- Mycobacterium tuberculosis
1. Introduction
The
global prevalence of tuberculosis infection is currently estimated to
be one-third of the population, causing close to one and a half million
deaths and infecting as many as nine million people every year (WHO, 2012).
Due to the highly infectious nature of tuberculosis, the limited number
of therapeutic agents currently available, and the growing number of
drug-resistant strains, there is an urgent need for the development of
new anti-tuberculosis therapies (Koul et al., 2011).
The medicinal ethnobotanical knowledge of the Canadian First Nations
peoples has been shown to be a valid resource for identifying bioactive
plants with studies demonstrating a high degree of correlation between
traditional medicinal uses and observed biological activity (Carpenter et al., 2012, Jones et al., 2000, Li et al., 2012, McCutcheon et al., 1992, McCutcheon et al., 1994, McCutcheon et al., 1997 and McCutcheon et al., 1995).
Canadian plants that have documented applications as treatments for
tuberculosis therefore represent an important resource in the search for
antimycobacterial natural products.
Heracleum maximum,
or cow parsnip, is a member of the plant family Apiaceae (previously
known as Umbelliferae) and is ranked as the sixth most commonly used
plant by the indigenous peoples of North America ( Moerman, 1998)
where it has been used for numerous purposes including medicine, food,
fiber, and the preparation of dyes. Eastern Canadian First Nations
communities use Heracleum maximum as a traditional medicine to treat various infectious diseases ( Mechling, 1959) and respiratory ailments ( Hinds, 2000 and Walker, 2008) that include tuberculosis ( Lacey, 1993). Most commonly, Heracleum maximum is prepared as a tea by steeping the roots in hot water ( Webster et al., 2006), and aqueous extracts of the root have previously been shown to possess significant antimycobacterial activity ( Webster et al., 2010), stimulate the immune system through the production of interleukin-6 ( Webster et al., 2006) and are not toxic to a variety of primary human cell lines ( Webster et al., 2010). Methanolic extracts of Heracleum maximum have also demonstrated antimycobacterial, antibacterial and antifungal activity ( McCutcheon et al., 1992, McCutcheon et al., 1994 and McCutcheon et al., 1997).
The previous reports of antimycobacterial activity being observed for both aqueous and methanolic extracts of Heracleum maximum roots ( McCutcheon et al., 1997 and Webster et al., 2010) prompted us to investigate the antimycobacterial constituents of this plant through bioassay guided fractionation.