Evaluation of an ethnopharmacologically selected Bhutanese medicinal plants for their major classes of phytochemicals and biological activities

Ethnopharmacological relevance

As many as 229 medicinal plants have been currently used in the Bhutanese Traditional Medicine (BTM) as a chief ingredient of polyherbal formulations and these plants have been individually indicated for treating various types of infections including malaria, tumor, and microbial. We have focused our study only on seven species of these plants.

Aim of the study

We aim to evaluate the antiplasmodial, antimicrobial, anti-Trypanosoma brucei rhodesiense and cytotoxicity activities of the seven medicinal plants of Bhutan selected using an ethno-directed bio-rational approach. This study creates a scientific basis for their use in the BTM and gives foundation for further phytochemical and biological evaluations which can result in the discovery of new drug lead compounds.

Materials and methods

A three stage process was conducted which consisted of: (1) an assessment of a pharmacopoeia and a formulary book of the BTM for their mode of plant uses; (2) selecting 25 anti-infective medicinal plants based on the five established criteria, collecting them, and screening for their major classes of phytochemicals using appropriate test protocols; and (3) finally analyzing the crude extracts of the seven medicinal plants, using the standard test protocols, for their antiplasmodial, antimicrobial, anti-Trypanosoma brucei rhodesiense and cytotoxicity activities as directed by the ethnopharmacological uses of each plant.

Results

Out of 25 medicinal plants screened for their major classes of phytochemicals, the majority contained tannins, alkaloids and flavonoids. Out of the seven plant species investigated for their biological activities, all seven of them exhibited mild antimicrobial properties, five plants gave significant in vitro antiplasmodial activities, two plants gave moderate anti-Trypanosoma brucei rhodesiense activity, and one plant showed mild cytotoxicity. Meconopsis simplicifolia showed the highest antiplasmodial activity with IC₅₀ values of 0.40 μg/ml against TM4/8.2 strain (a wild type chloroquine and antifolate sensitive strain) and 6.39 μg/ml against K1CB1 (multidrug resistant strain) strain. Significantly the extracts from this plant did not show any cytotoxicity.

Conclusions

These findings provide the scientific basis for the use of seven medicinal plants in the BTM for the treatment of malaria, microbial infections, infectious fevers, and the Trypanosoma brucei rhodesiense infection. The results also form a good preliminary basis for the prioritization of candidate plant species for further in-depth phytochemical and pharmacological investigations toward our quest to unearth lead antiparasitic, anticancer and antimicrobial compounds.