Chemical Characterization, Sensory Evaluation, and Biological Activity in Neuronal Cells of Essential Oils (Rose, Eucalyptus, Lemon, and Clove) Used for Olfactory Training

Essential oils (EOs) are natural mixtures of volatile compounds characterized by beneficial pharmacological effects. The repeated inhalation of EOs in olfactory training (OT) has been demonstrated to improve the sense of smell in patients with olfactory deficits. We conducted a conjunct evaluation of the chemical composition, sensory profile, and bioactivity in cell models of commercial EOs of rose (EO1), eucalyptus (EO2), lemon (EO3), and clove (EO4) used for OT (StimuScent^®, Dos Medical, Sense Trading BV, Groningen, The Netherlands). Citronellol, 1,8-cineole, limonene, and eugenol emerged as the most abundant volatile compounds in EO1, EO2, EO3, and EO4, respectively, by GC-MS analysis. Some differences emerged (using a Likert-type scale) in the perception of EO's odor dimensions (pleasantness, intensity, and familiarity in subjects with hyposmia (n = 8) compared to controls (n = 22). Cytotoxicity assays (24 h of incubation) demonstrated the anticancer effects of EOs (5-100 μg/mL) on SH-SY5Y neuroblastoma cells (the order of potency was EO3 > EO4 > EO2 > EO1), while all EOs showed lower effects on the viability/morphology of human skin HaCaT keratinocytes. SH-SY5Y cancer cells grown for six days with different EOs (at 50 μg/mL) showed evident signs of toxicity and apoptosis. Marked changes in cell morphology (structure/number of processes) were evidenced in clove EO-treated cells. EO's sensory properties/bioactivity were also related to the in silico physicochemical/pharmacokinetic properties of the main EO components. Our results provide new insights into a more targeted EO application for OT.