Antimycobacterial terpenoids from Juniperus communis L. (Cuppressaceae)

Ethnopharmacological relevance

Juniperus communis is a plant which has been reported as a traditional cure for tuberculosis (TB) and other respiratory diseases.

Aim of the study

The aim of this study was to isolate and identify the constituents responsible for the activity of the n-hexane extract of Juniperus communis roots against Mycobacterium tuberculosis H₃₇Rv and Juniperus communis aerial parts against Mycobacterium aurum. Subsequently, it was to evaluate the activity of the pure isolated compounds against (i) drug-resistant Mycobacterium tuberculosis variants, (ii) non-replicating Mycobacterium tuberculosis and (iii) a range of non-tuberculous mycobacteria (NTM).

Materials and methods

The antimycobacterial activity of Juniperus communis extracts, fractions and constituents was determined against Mycobacterium tuberculosis H₃₇Rv, and against rifampicin-, isoniazid-, streptomycin- and moxifloxacin-resistant variants, using the microplate broth Alamar Blue assay (MABA) method. Isolated constituents were tested against non-replicating Mycobacterium tuberculosis H₃₇Rv, using the low oxygen recovery assay (LORA), and against NTM (Mycobacterium aurum, Mycobacterium phlei, Mycobacterium fortuitum and Mycobacterium smegmatis), using a broth microdilution method. Cytotoxicty studies were performed using mammalian Vero cells.

Results

The antimycobacterial activity of Juniperus communis was attributed to a sesquiterpene identified as longifolene (1) and two diterpenes, characterised as totarol (2) and trans-communic acid (3). All compounds were identified following analysis of their spectroscopic data (1D- and 2D-NMR, MS) and by comparison with the literature and commercial authentic standards when available. Revised assignments for 3 are reported. Totarol showed the best activity against Mycobacterium tuberculosis H₃₇Rv (MIC of 73.7 μM). It was also most active against the isoniazid-, streptomycin-, and moxifloxacin-resistant variants (MIC of 38.4, 83.4 and 60 μM, respectively). Longifolene and totarol were most active against the rifampicin-resistant variant (MICs of 24 and 20.2 μM, respectively). Totarol showed the best activity in the LORA assay (MIC of 81.3 μM) and against all NTM species (MICs in the range of 7–14 μM). Trans-communic acid showed good activity against Mycobacterium aurum (MIC of 13.2 μM). The low selectivity indices (SI) obtained following cytotoxicity studies indicated that the isolated terpenoids were relatively toxic towards mammalian cells. This is the first report of the isolation of (1) and (2) from Juniperus communis roots, and of (3) from the aerial parts. The antimycobacterial activity of (1) and (3), and the activity of (2) against Mycobacterium aurum, Mycobacterium fortuitum and Mycobacterium phlei, is reported for the first time. The effect of totarol on drug-resistant variants and non-replicating Mycobacterium tuberculosis has never been published.

Conclusions

The presence of antimycobacterial terpenoids in Juniperus communis aerial parts and roots justifies, to some extent, the ethnomedicinal use of this species as a traditional anti-TB remedy.