Phytochemical analysis and biological activities of essential oil and extract of Phlomis rigida Labill.

The genus Phlomis is a member of Lamiaceae (Labiatae) family. About 10 species of this genus, among more than 100 species, are endemic to Iran. Phlomis rigida Labill. can be used as antimicrobial, anti-inflammatory, wound healing and antioxidant in drug investigations, based on literature.

The aim of this study is to evaluate the composition, antioxidant, antibacterial and cytotoxic activity of essential oils and extract from leaves and flowers of P. rigida from Iran. The present study is the first research on P. rigida from Iran.

Essential oils of leaves and flowers of P. rigida were studied by GC-MS and GC-FID to evaluate the chemical compositions. DPPH free radical scavenging method was used to evaluate the antioxidant effect of leaves and flowers extracts. Antimicrobial properties of the essential oils and extracts were investigated against various microorganisms in brain heart infusion agar to evaluate the minimum inhibitory concentration. A brine shrimp test (BST) was done to study the cytotoxicity of methanol extracts and essential oils from leaves and flowers in different concentrations. The growth inhibitory effects of the methanol extract from leaves and flowers were assessed against four cancer cell lines including MCF-7, MDBK, HT-29 and A-549.

Essential oils analysis showed 34 compounds and the main compounds were (Z)-β-ocimene (25.6 %), isobornyl acetate (16.6 %), trans-verbenol (12.6 %) and α-pinene (7.6 %). As a result of analysis of methanol extracts from leaves, luteolin, luteolin-7-O-glucoside and rosmarinic acid were isolated and identification for the first time from P. rigida growing in Iran. Investigation of antibacterial properties of the essential oil of flowers also showed 16 mm diameters of inhibition zone against Proteus vulgaris.

The results of this study showed that the antibacterial effect of P. rigida essential oil could be due to the presence of its monoterpenes.