Commercially available essential oils extracted from Artemisia dracunculus L., Inula graveolens L., Lavandula officinalis Chaix, and Ocimum sanctum L. and the components of these oils were screened by the microplate assay method for determining their acetylcholinesterase (AChE) inhibitory activity. The composition profiles of the oils were characterized by gas chromatography-mass spectrometry (GC-MS) analysis, and the relationships between the oil components and the AChE inhibitory activity of the oils were outlined. The results showed that all of the oils, except that of A. dracunculus from Hungary, exhibited AChE inhibitory activity, and the A. dracunculus oil from France showed the most potent inhibitory activity [50% inhibition concentration (IC(50)) = 0.058 mg/mL]. The AChE inhibitory activity of I. graveolens oil has not been reported to date, and this study is the first to reveal this activity in the oil. Among the essential oil components, five components, namely, 1,8-cineole, α-pinene, eugenol, α-terpineol, and terpinen-4-ol, showed AChE inhibitory activity, with IC(50) values of 0.015, 0.022, 0.48, 1.3, and 3.2 mg/mL, respectively. Eugenol, in particular, was found to be a potent AChE inhibitor along with determination of the IC(50) value, a finding that has been reported for the first time in this study. However, the ratio of the contribution of the active components, including a novel AChE inhibitor, to the observed AChE inhibitory activity of the essential oils was not very high. The results of this study raise concerns about the AChE inhibitory activity of widely produced and readily accessible commercial essential oils.

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) with 3-5 rings are ubiquitous environmental contaminants. However, toxicities of ClPAHs remain unclear. In this study, aryl hydrocarbon receptor (AhR)-mediated activities of ClPAHs were investigated by using a yeast assay system. All environmentally relevant 18 ClPAHs showed the AhR activities in the test; the activities were elevated with the number of chlorine atoms on the lower molecular weight PAH ( approximately three-ring and fluoranthene derivatives) but not for higher molecular weight ClPAHs (>four-ring). The similar trends were also observed in certain ClPAHs-induced cytochrome P450 1A1 expression in MCF-7 cells. The structure-activity relationship between the AhR activity and the corresponding solvent accessible surface area of ClPAHs revealed a parabolic relationship, with approximately 350 A (2)/molecule as the optimal dimensions as the ligand for binding to AhR. These findings indicate that the spatial dimensions of ClPAHs apparently influence their ability to activate the AhR. Finally, we discussed the toxicity of exposure to ClPAHs based on the AhR activities, estimated that it would be approximately 30-50 times higher than that of dioxins.

Superaromatic stabilization energy (SSE), previously proposed by us, can be used as a novel local aromaticity index for benzene rings in polycyclic aromatic hydrocarbons (PAHs). SSE can be interpreted as the first local aromaticity index explicitly related to all relevant circuits in a polycyclic π-system, an origin of local aromaticity, being free of local aromaticity arising from adjacent six-site circuits. Therefore, this quantity is best suited for characterizing the electronic structure of large pericondensed PAHs and graphene nanoflakes.