The Effect of Terpinen-4-ol on Human Corneal Epithelium

To investigate the toxicity of terpinen-4-ol (T4O) on primary cultured human corneal epithelial cells (HCECs).

HCECs were exposed to various concentrations (0%-0.1%) of T4O for 15 minutes to 72 hours. Cell viability was assessed using the CCK8 kit and cell counting. Intracellular reactive oxygen species (ROS) were measured after 15 to 60 minutes of T4O exposure. Changes in cell morphology and cytoplasmic actin filaments were observed using phase contrast microscopy and immunocytochemistry. The expression levels of proteins involved in cell survival pathways (mTOR, Akt, Bcl-xL, and BAX) were evaluated by Western blot analysis.

T4O induced dose-dependent toxicity in HCECs. Exposure to 0.05% T4O for 15 minutes significantly decreased cell viability. Lower concentrations (0.025% and 0.0125%) also caused significant toxicity with longer exposure times. Prolonged exposure enhanced cytotoxicity, with 0.05% T4O reducing viability by half after 24 hours and 0.1% T4O causing complete cell death. Increased intracellular ROS and decreased levels of phosphorylated mTOR, phosphorylated Akt, and Bcl-xL, along with increased BAX expression, accompanied this toxicity. F-actin staining revealed significant changes in cell adhesion.

Our study demonstrates that T4O exposure causes significant toxicity in HCECs, depending on concentration and incubation time. This toxic response is associated with increased ROS and decreased cell survival pathway activity.

The corneal epithelial toxicity data of T4O revealed in this study may be useful in the future use of tea tree oil or the development of tee tree oil-containing eyelid scrub products for treating eyelid demodex infestation.