Evaluation of antimycobacterial activity of some Piper species
Searching for new TB drugs from plant sources of India is a promising approach as India provides a rich tradition in medicinal plants combined with a high biodiversity . As a part of the project to identify antimycobacterial natural products from Indian medicinal plants, three Piper species viz., P. cubeba, P. longum and P. retrofractum are being studied with the aim to isolate and characterize antimycobacterial compounds. These species are reported to be used for treating TB or TB-related diseases in ethnomedicine in India .
The dried fruits of all the three Piper species were extracted successively with n-hexane and chloroform in a Soxhlet apparatus and separately with 70% ethanol in water by maceration at room temperature. The resulting 9 extracts were tested for antimycobacterial activity in vitro against M. smegmatis (ATCC 14468) and M. fortuitum (ATCC 6841) using a micro-dilution assay in cation-adjusted Mueller-Hinton broth as reported previously . The hexane and 70% ethanolic extracts of P. cubeba and P. longum exhibited significant antimycobacterial activity with MIC values of 64µg/ml (M. smegmatis) and 32–64µg/ml (M. fortuitum), resp. In case of P. retrofractum only the 70% ethanolic extract showed activity with an MIC value of 64µg/ml (M. fortuitum). The fractionation of the hexane extract of P. cubeba resulted in the isolation of (-)-cubebin which was inactive at 128µg/ml whereas the hexane extract of P. longum resulted in the isolation of piperine which exhibited an MIC value of 128µg/ml (M. smegmatis, M. fortuitum). Ethambutol and isoniazid were used as positive controls and exhibited MIC values of 1–8 and 2–8µg/ml respectively. The activity of the isolated compounds could not entirely explain the activity of the crude extracts and further active compounds or synergism with other constituents seem to occur.
References: 1. Gautam, R., Jachak, S.M. (2007)J. Ethnopharmacol. 110: 200–234.
2. Stavri, M. et al. (2004) Phytother Res 18: 774–776.