Volatile oils

Essential oils (EOs) are omnipresent in human life, both in medical and healthcare sectors as well as in food and wellness industries. EOs have a broad range of bioactivities, ranging from anti-inflammatory, restorative and detoxifying capacities to neurologic and anxiolytic actions. There may, however, be unintended health implications of exposure to volatile substances. EOs have complex chemical compositions, and the volatile character of the active compounds requires new technical and scientific approaches to assess their activities. This project involves the investigation of EO bioactivities using a novel exposure incubator system, which allows long-term treatment of cell cultures with volatile compounds over a broad range of concentrations. The system includes a humidified gas flow that carries volatile compounds at defined concentrations to airliquid interphase (ALI) cultures of cells. Concentrations of compounds in the gas stream can be measured online with a coupled gas chromatography system. This study proposes to investigate the potential adverse effects of EO on epithelial-immune cell models of lung and skin. Sensitisation of the respiratory tract to chemicals and skin exposures may be linked. Although several EO compounds have been characterized as antioxidants in vitro, these mainly lipophilic compounds can easily permeabilise membranes, leading to oxidative stress and cytotoxicity. At low (non-lethal) concentrations, however, antioxidant compounds may be more relevant. Several EO compounds have been characterized as potential antigens. Cellular responses to different concentrations of reference compounds and chemically analysed lavender, tea tree and thyme oils will be analysed with response profiles examined using pathway- focused assays. These treatments will include (i) topical and volatile application of EOs to cells to compare their response profiles, (ii) a detailed characteriziation of EO effects in regard to epithelial immune cell crosstalk and (iii) pre-treatment of cells with stressors such as reactive oxygen species (ROS), ozone or endotoxin. Several redox-regulated pathways have been reported to be dose- dependently regulated by a variety of natural products and drugs. The effects of EOs on antioxidant response element (ARE)/NF-E2-related factor 2 (Nrf-2)-mediated signalling, cytokine production, neopterin formation and activation of the enzyme indoleamine 2,3-dioxygenase (IDO) will be assayed, resulting in a comprehensive assessment of EO activities. Further, transcriptional profiles will be analysed for activated pathways and networks to identify new important signalling cascades in an unbiased manner. By using a innovative exposure incubator system to expose ALI epithelial-immune cell cultures to volatile compounds, we aim to contribute to the development of in vitro assays to assess the activities of volatile components in the gas phase, and to obtain deeper insights into EO bioactivities.

Regardless of being intended or not, exposures to essential oils (EOs) are omnipresent in human life, e.g. in the medical or health sector, or in nutrition or wellness applications. EO constituents are remarkably bioactive, effects range from anti-inflammatory, restorative, detoxifying to anxiolytic properties and many more. Several EO constituents show antioxidant properties in vitro, however these mainly lipophilic compounds can easily permeabilise membranes, leading to oxidative stress and cytotoxicity, in particular at high treatment concentrations. There is an utmost need for a detailed mode of action analysis of biological effects of volatile compounds. However, detailed investigations on their cellular effects are limited. The lipophilic and volatile properties of the chemicals hamper their analysis with the help of submerged cell cultures. Thus, the difficulty to model realistic exposure scenarios is a major challenge, in particular when focusing on low concentrations of compounds. To investigate potential target mechanisms in more detail, we optimized in vitro models of lung epithelial cell cultures maintained at air-liquid interface (ALI) and co- cultured with immune cells. A novel exposure platform, which was specifically developed for this purpose, first allowed a continuous treatment of ALI cell cultures for longer periods with volatile compounds at defined concentrations. We investigated effects of EOs and reference compounds at sublethal concentrations, addressing oxidative stress-related mechanisms and immunological cascades. By integrating pathway-focused and unbiased transcriptional analysis, we defined readout pathways that can be used to sensitively predict outcome. Importantly, our major findings showed that many compounds impact on cellular responses over the amino acid and lipid metabolome. In particular immunology-related pathways turned out to be most sensitive. Moreover, the degree and also the direction of perturbation was strongly dependent on the basal state of the cell cultures. To summarize, besides providing a better understanding of cellular responses activated by volatile compounds, the investigated in vitro approach turned out to be a valuable strategy for risk benefit assessment of a broad range of volatile chemicals.