Abstract
BackgroundEssential oils and their constituents are commonly known for their antibacterial, antifungal and antiparasitic activity, and there are also reports on the antimycobacterial properties, but more experimental data are needed for the description of the mechanism of action or structural (and molecular) properties related to the antimicrobial activity.MethodsTwenty-five constituents of essential oils were evaluated against Mycobacterium tuberculosis H37Rv and Mycobacterium bovis AN5 by the Alamar Blue technique. Twenty compounds were modeled using in silico techniques descriptor generation and subsequent QSAR model building using genetic algorithms. The p-cymene, menthol, carvacrol and thymol were studied at the quantum mechanical level through the mapping of HOMO and LUMO orbitals. The cytotoxic activity against macrophages (J774A) was also evaluated for these four compounds using the Alamar Blue technique.ResultsAll compounds tested showed to be active antimicrobials against M. tuberculosis. Carvacrol and thymol were the most active terpenes, with MIC values of 2.02 and 0.78 μg/mL respectively. Cinnamaldehyde and cinnamic acid were the most active phenylpropanes with MIC values of 3.12 and 8.16 μg/mL respectively. The QSAR models included the octanol-water partition (LogP) ratio as the molecular property that contributes the most to the antimycobacterial activity and the phenolic group (nArOH) as the major structural element.ConclusionsThe description of the molecular properties and the structural characteristics responsible for antimycobacterial activity of the compounds tested, were used for the development of mathematical models that describe structure-activity relationship. The identification of molecular and structural descriptors provide insight into the mechanisms of action of the active molecules, and all this information can be used for the design of new structures that could be synthetized as potential new antimycobacterial agents.
Highlights
Essential oils and their constituents are commonly known for their antibacterial, antifungal and antiparasitic activity, and there are reports on the antimycobacterial properties, but more experimental data are needed for the description of the mechanism of action or structural properties related to the antimicrobial activity
In vitro potency of terpenes and phenylpropanes against M. tuberculosis and M. bovis The major components of the essential oils were initially solubilized in pure ethanol, and the higher amount of the solvent was used as control to test for inhibitory effects, but no inhibitory effects were observed with the amount of solvent used
When considering Minimum Inhibitory Concentration (MIC) values of all compounds tested, a higher antimycobacterial activity was observed for M. tuberculosis strain as compared to M. bovis, and statistical analysis showed differences between the two strains
Summary
Essential oils and their constituents are commonly known for their antibacterial, antifungal and antiparasitic activity, and there are reports on the antimycobacterial properties, but more experimental data are needed for the description of the mechanism of action or structural (and molecular) properties related to the antimicrobial activity. In Mexico there are more than 4000 species of medicinal plants [5] and many of them produce essential oils, which are water-insoluble highly volatile extracts obtained by hydrodistillation Their composition is complex and variable, but they are usually terpenes and/or phenylpropanes [6, 7]. Regarding antimycobacterial activity of terpenes and phenylpropanes, several reports have shown that chain free monoterpenes have antimycobacterial activities of pharmaceutical importance [10,11,12] These results have motivated the research on the molecular and reactivity properties of them, as the base for the design of new pharmacologically active compounds, that could use the molecules present in essential oils as building blocks
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