α-phellandrene, a celery component, protects intestinal epithelial cells against oxidative and inflammatory stress through modulation of Nrf2 and NF-κB signaling

α-Phellandrene (α-PA) is a naturally occurring monoterpene present in celery and dill and has attracted increasing interest as a food-derived bioactive compound. However, its biochemical effects on intestinal epithelial cells under oxidative and inflammatory stress remain insufficiently characterized. This study investigated the protective mechanisms of α-PA against oxidative and inflammatory stress using normal rat intestinal epithelial IEC-6 cells as an in vitro model. Cellular oxidative and inflammatory stress was induced using 5-fluorouracil (5-FU). The results demonstrated that α-PA significantly reduced intracellular reactive oxygen species and lipid peroxidation while enhancing antioxidant capacity by upregulating glutathione levels, heme oxygenase-1, and glutamate–cysteine ligase subunits. In parallel, α-PA attenuated inflammatory responses by suppressing nitric oxide and prostaglandin E2 production and by reducing the secretion of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α, which are important pro-inflammatory cytokines, while restoring anti-inflammatory IL-10 levels. These protective effects were associated with coordinated activation of Nrf2 signaling and suppression of NF-κB nuclear translocation and DNA-binding activity. From a food biochemistry perspective, this study provides mechanistic insight into how dietary monoterpenes may contribute to intestinal epithelial resilience under oxidative and inflammatory stress conditions.