Chemical Composition, Cytotoxicity, Antimicrobial and Antioxidant Activities of the Leaf and Stem Essential Oils of Agelaea Obliqua (P.Beauv) Baill (Connaraceae)

Agelaea obliqua is widely used in West African ethnomedicine for irritating throat, parasitic skin infections, bronchitis and as an aphrodisiac. Despite its extensive use, information on the chemical composition and biological activities of its essential oil (EO) remains limited. This study evaluated the chemical composition, cytotoxicity, antimicrobial and antioxidant activities of the leaf and stem EOs of A. obliqua. The plant (voucher FHI 113363) was collected from Agbegi-odofin secondary forest, Ikire, Osun State, Nigeria, and authenticated at the Forestry Research Institute of Nigeria (FRIN), Ibadan. EOs were obtained from air-dried leaves and stem by hydro-distillation using an all-glass Clevenger-type apparatus, and their constituents identified by Gas Chromatography-Mass Spectrometry (GC-MS). Cytotoxicity was assessed using the brine shrimp lethality test (BSLT); antimicrobial activity was evaluated against two Gram-positive and four Gram-negative bacteria and two fungi by the broth micro-dilution method, with Minimum Inhibitory Concentration (MIC) and Minimum Microbicidal Concentration (MMC) determined; and radical-scavenging activity was assessed by the DPPH assay against ascorbic acid and butylated hydroxyanisole (BHA) as standards. GC-MS identified 41 compounds (81.20%) in the leaf EO and 40 compounds (80.74%) in the stem EO, dominated by n-hexadecanoic acid (14.31% and 35.09%, respectively), phytol, oleic acid and 6,10,14-trimethyl-2-pentadecanone. Both EOs were cytotoxic to brine shrimp nauplii (LC50 15.69 and 109.51 µg/mL for leaf and stem, respectively). The stem EO showed strong antimicrobial activity against all tested bacteria and fungi, requiring as little as 0.78 µg/mL to eliminate Staphylococcus aureus and Klebsiella pneumoniae, while the leaf EO showed weak activity and no effect against Pseudomonas aeruginosa and S. aureus. Both oils showed moderate, concentration-dependent DPPH radical-scavenging activity relative to the reference standards. These findings support the ethnomedicinal use of A. obliqua and identify its essential oil, particularly from the stem, as a potential lead source for antimicrobial and antioxidant drug development.

Agelaea obliqua; essential oil; GC-MS; antimicrobial activity; antioxidant activity

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