Chemical Composition, Acetylcholinesterase-Inhibitory Potential and Antioxidant Activity of Essential Oils from Three Populations of Parthenium hysterophorus L. in Ecuador

In this study, we analyzed the essential oils (EOs) extracted by steam distillation from the leaves and flowers of <i>Parthenium hysterophorus</i> L., grown in three different locations in southern Ecuador: Espíndola (ESP), Loja (LOJ) and Quilanga (QUI). Approximately 97.45%, 98.27% and 95.99% of the oil constituents were identified using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID). Sesquiterpene hydrocarbons were predominant in the EOs. The most representative constituents of the sample from ESP were germacrene D (35.08%), myrcene (11.32%), (<i>E</i>)-β-ocimene (10.21%), (<i>E</i>)-caryophyllene (7.90%), germacra-4(15),5,10(14)-trien-1-α-ol (5.18%) and (<i>E</i>, <i>E</i>)-α-farnesene (4.99%), with an AChE IC₅₀ of 14.78 and with 16.38 and 93.16 µg/mL from ABTS and DPPH, respectively. The EOs from LOJ were characterized by the abundant presence of germacrene D (28.30%), myrcene (13.95%), (E)-β-ocimene (10.51%) and isolongifolan-7-α-ol (8.26%), with an AChE IC₅₀ of 16.65 and with 36.18 and 158.43 µg/mL from ABTS and DPPH, respectively. Finally, the EOs from QUI contained germacrene D (32.20%), myrcene (13.36%), (E)-β-ocimene (8.54%), (<i>E</i>, <i>E</i>)-α-farnesene (6.77%), germacra-4(15),5,10(14)-trien-1-α-ol (5.69%) and (E)-caryophyllene (5.37%), with an AChE IC₅₀ of 10.69 and with 14.50 and 92.98 µg/mL from ABTS and DPPH, respectively. This study identifies chemotypic variation in <i>P. hysterophorus</i> collected from different locations and, for the first time, the AChE inhibitor was evaluated. These findings provide a scientific basis for the clinical application of <i>P. hysterophorus</i> EOs in the future treatment of Alzheimer's disease.