Effect of essential oils on the activity of human neutrophil myeloperoxidase in vitro

Myeloperoxidase (MPO) is a key component of innate immune defence, linked to inflammatory diseases. In the present work, the effect on MPO activity has been studied for 15 essential oils (EO) (bay laurel, cajeput, clove, coriander, ginger, juniper, lemon, lemon grass, niaouli, nutmeg, rosemary, red thyme, Spanish oregano, tarragon and tea tree) and 4 pure EO constituents (bornyl acetate, carvacrol, eugenol and thymol). MPO activity was assessed by oxidation of O-dianisidine dihydrochloride by H₂O₂ in A) absence of cells (MPO inhibition) and B) a human neutrophil preparation (extracellular release and inhibition of MPO) [1–3]. Quercetin was used as positive control. Inhibitory activity was mainly detected in the phenol rich EO (clove, red thyme and Spanish oregano) and the corresponding main constituents (eugenol, thymol and carvacrol). Clove EO, with IC₅₀ of 37.2±1.0µg/mL (test A) and 16.3±1.3µg/mL (test B), and eugenol, with IC₅₀ of 35.9±2.4µg/mL (test A) and 19.2±2.0µg/mL (test B), showed the highest activity. Results suggest that the inhibition mechanism of clove oil and eugenol involves direct enzyme inhibition and that it could also be linked to a modification in the extracellular release of MPO.

Acknowledgenments: Authors are grateful to Lidervet S.L. (Tarragona, Spain) for financial support. R. Pérez-Rosés was supported by the Generalitat de Catalunya and the European Social Fund.

References: 1. Bradley PP, et al. Blood 60(3): 618–622, 1982. 2. The Local Food-Nutraceuticals Consortium Pharmacol Res 52: 353–366, 2005. 3. Speyer CL, et al. Am J Physiol Cell Physiol 288: 881–890, 2005.