Protective Effects of Shallot (Allium ascalonicum) Extracts Against PAH-Induced Oxidative Stress in Human Nasal Epithelial Cells

Polycyclic aromatic hydrocarbons (PAHs) are major toxic organic constituents attached to ambient fine particulate matter (PM2.5) and contribute substantially to PM2.5-associated oxidative stress and respiratory toxicity. This study investigated the protective effects of shallot (Allium ascalonicum) extracts against PAH-induced oxidative stress in human nasal epithelial cells (RPMI 2650). Shallot extracts were prepared using various extraction techniques and assessed for their phytochemical composition and antioxidant capacity. Among the extracts evaluated, the supercritical fluid extract exhibited the highest total flavonoid content and anti-inflammatory property, whereas the ethanolic extract (EtOH) exhibited the highest total phenolic content and antioxidant activity and was therefore selected for subsequent investigations. HPLC analysis of the EtOH extract identified quercetin and gallic acid as major phenolic constituents. Exposure of RPMI-2650 cells to PAHs (0.25 μg/mL) significantly induced intracellular reactive oxygen species (ROS) generation and lipid peroxidation while reducing superoxide dismutase (SOD) activity, indicating oxidative stress induction. Cotreatment with the ethanolic extract (1.25–5 μg/mL) effectively mitigated these effects by reducing ROS generation, suppressing lipid peroxidation, and restoring SOD activity in a dose-dependent manner. These protective effects are attributed to the antioxidant phytochemicals present in shallot, particularly quercetin. Collectively, these findings indicate that shallot extracts attenuate PAH-induced oxidative stress in human nasal epithelial cells.