Oliveria decumbens Vent. (Apiaceae): Biological screening and chemical compositions

Oliveria decumbens Vent. (Apiaceae), a single aromatic species in Iran, is traditionally used for healing inflammation, gastrointestinal disorders, and infections.

Regarding the importance of O. decumbens in traditional medicine, we aimed to set out the plant's biological screening and analyze the chemical components of the active fractions.

Air-dried O. decumbens aerial parts were macerated by ethanol:water (70:30). Using a liquid-liquid extraction (LLE) technique, n-hexane, dichloromethane (DCM), ethyl acetate (EtOAc), n-butanol (n-BuOH), and water were successively used to fractionate the crude extract into different portions. Various biological activities were performed on the crude extract, fractions, and some experiments on pure compounds. The bioassays were as follows: antibacterial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhi (using microplate alamar blue assay; MABA), antifungal activity against Aspergillus niger, A. fumigatus, Candida albicans, C. glabarate, Fusarium lini, Microspurum canis, and Trichophyton rubrum (using agar tube dilution method), antileishmanial activity against Leishmania major and L. tropica using a 96-well serial dilution protocol, anti-inflammatory activity using the respiratory burst assay, cytotoxicity against HeLa (cervical cancer) and BJ (normal fibroblast) cells using MTT assay, insecticidal activity against Tribolium castaneum, Sitophilus oryzae, and Rhyzopertha dominica (using the contact toxicity method), larvicidal activity against Aedes aegypti, anti-DPPH^• activity, and cytotoxicity against brine shrimp (Artemia salina) in a lethality assay. Eventually, the phytochemicals from the active fractions were studied by gas chromatography coupled with mass spectrometry (GC-MS).

Interestingly, the DCM fraction was the most active, followed by the n-hexane fraction in the biological assays, including antibacterial (>80% inhibition), leishmanicidal (IC_{50 (L.major)} = 29.4 μg/mL, and IC_{50 (L.tropica)} = 30.0 μg/mL), anti-inflammatory (IC₅₀ = 15.8 μg/mL), insecticidal (>80% inhibition), and larvicidal (100% inhibition of A. aegypti) assays. Further GC-MS analysis of the DCM and n-hexane fractions resulted in the characterization of 12 and 14 phytoconstituents, respectively, compared with the NIST library. Thymol and carvacrol were abundant in both fractions. To lesser quantities, the presence of monoterpenoids (p-cymen-8-ol, thymoquinone, 3-hydroxy-β-damascone, and 3-hydroxy-7,8-dihydro-β-ionol), phenylpropanoids (methoxyeugenol, elemicin, and 4-[(1E)-3-hydroxy-1-propenyl]-2-methoxyphanol, simple phenolics (salicylic acid and 4-methoxy-2,3,6-trimethyl-phenol), and a coumarin (6,7-dimethoxy-coumarin) were detected in the DCM fraction. On the other hand, besides a coumarin and monoterpenoids, the fatty acids (tetradecanoid acid, n-hexadecanoic acid, and linolenic acid) and a sesquiterpene (spathulenol) were observed in the n-hexane fraction. The EtOAc fraction scavenged the DPPH^• radicals better than other fractions (IC₅₀ = 41.4 μg/mL), while in brine shrimp lethality assay, the crude extract was more active than n-hexane and DCM fractions with LD₅₀ = 385.20, 660.28, and 699.74 μg/mL, respectively. Surprisingly, the crude extract and fractions were ineffective against assayed fungal strains and tested cancer and non-cancer cell lines.

Our findings showed that O. decumbens deserves to be a multi-bioactive medicinal plant, besides its ability for cereal protection against pests. To understand the principal mechanism of action, in silico, in vitro, and in vivo experiments may clarify the ambiguities and even figure out the synergistic behavior of the minor secondary metabolites.