Anti-mycobacterial triterpenes from the Canadian medicinal plant Alnus incana.
BACKGROUND
Alnus incana, commonly known as the gray or speckled alder, is a medicinal plant used by some Canadian First Nations to treat symptoms associated with tuberculosis. The aim of this study was to assess the anti-mycobacterial activity of an Alnus incana bark extract and to identify the active constituents of the extract.


METHODS
Methanolic extracts of the bark of A. incana were subjected to bioassay guided fractionation using Mycobacterium tuberculosis (H37Ra). The active constituents were identified by NMR and MS.


RESULTS
Four pentacyclic lupane triterpenes were isolated and were identified as betulin, betulinic acid, betulone and lupenone. Betulin displayed a MIC of 12.5 μg/mL and an IC50 of 2.4 μg/mL against M. tuberculosis (H37Ra). Betulinic acid and betulone showed lower anti-mycobacterial activities with IC50 values of 84 and 57 μg/mL respectively. Lupenone was inactive against M. tuberculosis (H37Ra).


CONCLUSIONS
Betulin, betulinic acid and betulone were identified as the major anti-mycobacterial constituents in the bark of A. incana and the functionality at carbons 3 and 28 of the lupane skeleton would seem to be important in determining the anti-mycobacterial activity of the triterpenes. This work supports the ethnopharmacological use of A. incana by Canadian First Nations communities as a treatment for tuberculosis.
Department of Biology, University of New Brunswick, Saint John, New Brunswick, Canada E2L 4L5.
Haoxin
H
Li
Department of Medicine, Division of Infectious Diseases, Saint John Regional Hospital, Saint John, New Brunswick, Canada E2L 4L2.
Duncan
D
Webster
Department of Biology, University of New Brunswick, Saint John, New Brunswick, Canada E2L 4L5.
John A
JA
Johnson
Department of Biology, University of New Brunswick, Saint John, New Brunswick, Canada E2L 4L5; Department of Chemistry, University of New Brunswick, Saint John, New Brunswick, Canada E2L 4L5. Electronic address: cgray@unb.ca.
Christopher A
CA
Gray
D029661:Alnus / Q000737:chemistry*; D000900:Anti-Bacterial Agents / Q000302:isolation & purification* / Q000494:pharmacology; D057809:HEK293 Cells / Q000187:drug effects; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D053978:Pentacyclic Triterpenes; D008517:Phytotherapy / Q000379:methods; D024301:Plant Bark / Q000737:chemistry*; D010936:Plant Extracts / Q000302:isolation & purification* / Q000494:pharmacology; D014315:Triterpenes / Q000302:isolation & purification / Q000494:pharmacology; D000094062:Betulinic Acid
D000900:Anti-Bacterial Agents; D053978:Pentacyclic Triterpenes; D010936:Plant Extracts; D014315:Triterpenes; C002503:betulin; D000094062:Betulinic Acid
Alnus incana; Antimycobacterial activity; Betulin; Betulinic acid; Betulone; Mycobacterium tuberculosis