Medicinal plants from open-air markets in the State of Rio de Janeiro, Brazil as a potential source of new antimycobacterial agents

Abstract

Ethnopharmacological relevance: Several medicinal plants are traditionally traded in open-air markets in Rio de Janeiro State (Brazil) to treat tuberculosis (TB) and related symptoms. Aims of the study: Conduct a survey in the open-air markets of 20 cities of Rio de Janeiro State to find medicinal plants that are popularly used to treat tuberculosis and other related diseases and assess their in vitro antimycobacterial activity. Materials and methods: We used direct observation and semi-structured interviews and asked herbalists to list species (free listing) in order to gather data about the plant species most commonly used for lung problems. We calculated a Salience Index and acquired two species of “erva-de-passarinho” (mistletoe), Struthanthus marginatus and Struthanthus concinnus (Loranthaceae), commonly used to treat tuberculosis for a bioassay-guided isolation of the antimycobacterial active principles. Extracts, fractions and isolated compounds of both species were assayed in vitro against susceptible (H37Rv) and rifampicin-resistant (ATCC 35338) Mycobacterium tuberculosis strains. Results: From the interviews, we generated a list of 36 plant species belonging to 12 families. The mistletoes Struthanthus marginatus and Struthanthus concinnus showed high Salience Index values among plants used to treat tuberculosis. Bioassay-guided fractionation of hexane extracts from both species led to the isolation and/or identification of steroids and terpenoids. The Minimum Inhibitory Concentration (MIC) of the extracts and isolated compounds ranged from 25 to 200 μg/mL. Some of the isolated compounds have been previously assayed against Mycobacterium tuberculosis, others are reported here for the first time (obtusifoliol: MIC H37Rv 50 μg/mL, MIC ATCC 35338 12.5 μg/mL; 3-O-n-acil-lup-20(29)-en-3β,7β,15α-triol: MIC H37Rv 200 μg/mL, MIC ATCC 35338 100 μg/mL). Conclusions: This study demonstrated the importance of ethnobotanical surveys in markets as a source for new drugs and also for scientific validation of folk medicine.