Attenuation of LPS-Induced Pro-Inflammatory Gene Expression by Achillea santolina Essential Oil in RAW264.7 Macrophages

Achillea santolina is traditionally used for its anti-inflammatory properties. This study analysed the chemical composition of A. santolina essential oil (AS-EO) and evaluated its effects on LPS-induced pro-inflammatory gene expression in RAW264.7 macrophages. GC-MS analysis identified 13 compounds (93.2% of the oil), while 3 peaks (6.8%) remained unidentified. The oil was predominantly composed of monoterpenes (86.2%), with oxygenated monoterpenes representing 76.7%, featuring 1,8-cineole (20.2%), camphor (18.1%), and 4-terpineol (18.0%) as major components. AS-EO showed low cytotoxicity at concentrations up to 50 μg/mL. Pre-treatment with AS-EO (5–50 μg/mL) dose-dependently suppressed LPS-induced mRNA expression of TNF-α, IL-6, IL-1β, and COX-2, achieving maximum inhibition of 60.3%, 65.1%, 59.8%, and 54.7%, respectively, at 50 μg/mL (p < 0.0001). Assay validity was confirmed using dexamethasone (10 μM), which strongly inhibited gene expression (up to 95.2%, p < 0.0001). These findings indicate that AS-EO attenuates LPS-induced inflammatory gene expression in vitro, although the effects should be interpreted cautiously given the reduced viability at the highest concentration tested.