Human Nasal Epithelial Cells Exposed to Eucalyptus globulus Leaf Oil Reveal Novel Information About the Interactions Between Cells and Volatile Plant Oils

Objectives: The effects of Eucalyptus globulus leaf oil on human nasal epithelial cells were examined in this study. Methods: Nasal epithelial samples were obtained from physiologically sound tissue, as is customary in septorhinoplasty. After arrival in the lab, the tissue samples were washed several times in phosphate-buffered saline (PBS) containing a 2% (v/v) antibiotic-antimycotic solution to remove surface contaminants and blood residues. The samples were then placed in sterile conical tubes. The incubation temperature was set at 37 °C in a humidified environment containing 5% CO₂. Every day, we checked the morphology and proliferation of the cells and replenished the medium as needed. After cell attachment, cultures were incubated continuously for 24 hours with varying concentrations of Eucalyptus globulus leaf oil (1, 5, 15, 25, 50, 75, and 100 µL per well). To measure the metabolic activity of cells, the MTT colorimetric assay was used. Results: The measured half-maximal inhibitory concentration (IC₅₀) was 31.55 µL, and the corresponding logIC₅₀ value was 1.499, according to nonlinear regression analysis of the dose-response relationship. The regression model, with a good fit ( R ² = 0.8745), supports the idea of a repeatable relationship between the amount of oil exposure and reduced metabolic activity. Exposure to Eucalyptus globulus leaf oil in primary human nasal epithelial cells did not cause a sudden cytotoxic collapse but rather a gradual regulation of metabolic activity. Cell viability was significantly reduced compared with the negative control group when all tested concentrations of Eucalyptus globulus leaf oil were evaluated statistically. The reaction profile of Eucalyptus globulus leaf oil differed from that of more cytotoxic agents; specifically, the pattern of viability loss indicated a controlled, volume-dependent inhibitory effect rather than an immediate cytotoxic threshold. Conclusions: The current results indicate that the leaf oil of the Eucalyptus globulus tree inhibits the metabolic activity of primary human nasal epithelial cells in a dose-dependent manner, although it does not cause an immediate cytotoxic reaction. This progressive modulation trend suggests a physiologically active interaction with nasal epithelial cells rather than generic cellular harm. From an otorhinolaryngological perspective, these findings lend credence to the idea that, under controlled conditions, topical formulations, inhalational therapies, and nasal sprays containing Eucalyptus globulus leaf oil could be beneficial adjuncts. To determine the optimal dosing regimen, ensure it won’t harm the mucosa, and use these findings from the laboratory to inform clinical practice in ENT, more in vivo and clinical trials are needed.