GC-MS-Identified Alkamides and Evaluation of the Anti-Inflammatory, Antibacterial, and Antioxidant Activities of Wild Acmella radicans

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Abstract
Acmella radicans, commonly known as the “toothache plant,” is traditionally attributed with medicinal properties, although few studies have validated its biological effects. In the present study, a chemical analysis of the wild plant was performed using gas chromatography–mass spectrometry (GC-MS). In addition, the antioxidant, anti-inflammatory, and antibacterial potential of ethanolic extracts from the roots (RE) and aerial parts (AE), as well as their respective fractions, was evaluated. The dichloromethane fractions of the aerial parts (DFAE) and root extracts (DFRE) at a concentration of 25 μg/mL demonstrated the highest inhibition of nitric oxide (NO) production, reducing levels to 22.2 ± 1.9 and 22.2 ± 2.9 μM, respectively. Moreover, these fractions exhibited a notable inhibition of TNF-α production, lowering its concentration to 22.6 ± 3.3 pg/mL (DFAE) and 24.8 ± 5.3 pg/mL (DFRE) at 25 µg/mL. GC-MS chemical profiling revealed the presence of alkamides such as N-isobutyl-2E,6Z,8E-decatrienamide, N-(2-methylbutyl)-2E,6Z,8E-decatrienamide, and N-(2-phenylethyl)-2E,4Z-octadienamide in both root and aerial part extracts. The dichloromethane fractions showed a higher abundance of alkamides compared to the hexane fractions, suggesting that these compounds may be at least partially responsible for the observed anti-inflammatory activity. Additionally, AE showed moderate activity against S. typhimurium and low activity against other bacteria, while RE was especially effective against a resistant strain of S. aureus, indicating an MIC of 31.25 μg/mL, likely due to its high content of alkamides, particularly spilanthol. Several fractions also inhibited bacteria such as P. aeruginosa, S. aureus, and E. coli, possibly because of the presence of alkamides and compounds like β-amyrin.

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