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Aromatherapy and plant-based essential oils are widely used as complementary and alternative therapies for various symptoms, including anxiety, mild mood disorders, and cancer-related pain. In a previous study, we developed an in vitro assay using immortalized hypothalamic neuronal cells (GT1-7 cells). In this study, we used this assay to investigate the effects of Geranium oil on the cytotoxicity of the oestrogen receptor (ER) antagonist: tamoxifen (TMX). The results showed that Geranium oil augmented TMX-induced cell death in a dose-dependent manner without directly reducing the viability of GT1-7 cells. Cotreatment with Geranium oil and ER agonist β -estradiol (E2) attenuated the inhibition of GT1-7 cell growth. Moreover, Geranium oil and geraniol, a major constituent of Geranium oil, showed weak agonist activity on ER α and ER β with geraniol augmenting TMX-induced cell death similar to that observed in Geranium oil. Both compounds impair E2 activity. These data indicate that geraniol is an essential constituent of Geranium oil., Competing Interests: All authors declare that there are no conflicts of interest., (Copyright © 2022 Dai Mizuno et al.)

Aromatherapy and plant-based essential oils are widely used as complementary and alternative therapies for symptoms including anxiety. Furthermore, it was reportedly effective for the care of several diseases such as Alzheimer's disease and depressive illness. To investigate the pharmacological effects of essential oils, we developed an in vitro assay system using immortalized hypothalamic neuronal cells (GT1-7 cells). In this study, we evaluated the effects of essential oils on neuronal death induced by hydrogen peroxide (H2O2), aluminum, zinc, or the antagonist of estrogen receptor (tamoxifen). Among tests of various essential oils, we found that H2O2-induced neuronal death was attenuated by the essential oils of damask rose, eucalyptus, fennel, geranium, ginger, kabosu, mandarin, myrrh, and neroli. Damask rose oil had protective effects against aluminum-induced neurotoxicity, while geranium and rosemary oil showed protective activity against zinc-induced neurotoxicity. In contrast, geranium oil and ginger oil enhanced the neurotoxicity of tamoxifen. Our in vitro assay system could be useful for the neuropharmacological and endocrine pharmacological studies of essential oils.