In Vitro 5-Lipoxygenase Activity of Three Indigenous South African Aromatic Plants Used in Traditional Healing and the Stereospecific Activity of Limonene in the 5-Lipoxygenase Assay

An investigation was undertaken to determine the 5-lipoxygenase inhibitory activity of aromatic plants traditionally used to treat dermatological pathologies. Guided by ethnobotanical literature and availability from natural sources, the essential oils of Helichrysum odoratissimum (L.) Less., Heteropyxis natalensis Harv. and Lippia javanica (Burm. f.) Spreng, were collected. The hydrodistilled essential oils displayed promising 5-lipoxygenase inhibitory activity with IC50 values between 35 and 75 ppm. The oil compositions were determined by GC and GC/MS. Major compounds possibly contributing to the anti-inflammatory activity include β-caryophyllene, 1,8-cineole and limonene. Enantiomers and racemic mixtures of limonene displayed significantly different 5-lipoxygenase inhibitory activity suggesting stereoselectivity of the enzyme-catalyzed reaction. Furthermore, the monoterpene 1,8-cineole appeared to cause partial potentiation of the anti-inflammatory activity displayed by limonene.