Characterization of alpha-terpineol as an anti-inflammatory component of orange juice by in vitro studies using oral buccal cells.

Epithelial buccal cells (KB) were exposed to orange juice or orange juice fractions containing either the dry matter (DM), the volatile compounds (aqueous distillate, AD), or individual nonvolatile or volatile components. Intracellular formation of the pro-inflammatory cytokine IL-6 was analyzed by flow cytometry. Exposure to whole orange juice resulted in an increase in IL-6 formation of 23% compared to nontreated control cells, whereas treatment of the cells with either DM or AD resulted in a 22 or 1% increase, respectively. Dose-response experiments revealed that exposure of the cells to a 2- or 4-fold concentrated AD resulted in an increased IL-6 formation, whereas an inhibiting effect was measured after treatment of the cells with an 8-fold concentrated AD. These results indicated the presence of pro- as well as anti-inflammatory compounds in the aqueous distillate. To identify the active principles, volatile compounds present in the AD-treated cells were analyzed by GC-MS. In particular, limonene, linalool, and alpha-terpineol were shown to be present in significant amounts. Subsequent studies on the IL-6 formation revealed that limonene had a stimulating effect and alpha-terpineol had an inhibiting effect, whereas linalool had no effect. This anti-inflammatory effect of alpha-terpineol on IL-6 formation was verified by quantitative real-time reverse transcription Polymerase Chain Reaction experiments in which alpha-terpineol inhibited the gene expression of the IL-6 receptor.