Response of human ciliated respiratory cells to a mixture of menthol, eucalyptus oil and pine needle oil

Nasal respiratory cells were harvested from 45 healthy individuals using a microcurette technique. Following harvest, cells were placed on microporous polycarbonate membranes and exposed for 30 min using a gas/liquid interface technique to a mixture of menthol, eucalyptus oil and pine needle oil (MEP), eucalyptus oil alone (ECO), and pine needle oil alone (PNO) at concentrations ranging between 0.2 and 11 g/m³. Ambient air served as control. Ciliary beat frequency (CBF) was assessed before and after exposure using video-interference-contrast microscopy. Control exposure to air (n = 10) did not alter CBF (7.1 ± 0.9 Hz before and 7.0 ± 0.9 Hz after exposure, -1.3% decrease), whereas a dose dependent decrease of CBF following exposure to MEP (max. decrease -22.6% at a concentration of 10 g/m³, p < 0.01), ECO (max. decrease -32.5% at a concentration of 7.5 g/m³, p < 0.01) and PNO (max. decrease -56.1% at a concentration of 9.4 g/m³, p < 0.01) was observed. The data show that essential oils in high concentrations can reduce in-vitro ciliary activity of human respiratory cells not protected by a mucus layer. These effects have to be verified by in vivo investigations.