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Aim: Natural or artificial substances have become an inseparable part of our lives. It is questionable whether adequate testing has been performed in order to ensure these substances do not pose a serious health risk. The principal aim of our research was to clarify the potential risk of adding essential oils to food, beverages and cosmetic products.Methods: The toxicity of substances frequently employed in cosmetics, aromatherapy and food industry (bergamot oil, Litsea cubeba oil, orange oil, citral) were investigated using cell line NIH3T3 (mouse fibroblasts) with/without UV irradiation. The MTT assay was used to estimate the cell viability. Reactive oxygen species (ROS) which are products of a number of natural cellular processes such as oxygen metabolism and inflammation were measured to determine the extent of cellular stress. DNA damage caused by strand breaks was examined by comet assay.Results: MTT test determined EC50 values for all tested substances, varying from 0.0023% v/v for bergamot oil to 0.018% v/v for citral. ROS production measurement showed that UV radiation induces oxidative stress to the cell resulting in higher ROS production compared to the control and non-irradiated samples. Comet assay revealed that both groups (UV, without UV) exert irreversible DNA damage resulting in a cell death.Conclusions: Our findings suggest that even low concentrations (lower than 0.0464% v/v) of orange oil can be considered as phototoxic (PIF value 8.2) and probably phototoxic for bergamot oil (PIF value 4.6). We also found significant changes in the cell viability, the ROS production and the DNA after the cells were exposed to the tested chemicals. Even though these substances are widely used as antioxidants it should be noted that they present a risk factor and their use in cosmetic and food products should be minimized. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of N -aryl-2,6-diphenyl-2 H -pyrazolo[4,3- c ]pyridin-7-amines. • Photodynamic effect and no dark toxicity in melanoma G361 cells. • Cell death through production of ROS and DNA damage. A small series of N -aryl-2,6-diphenyl-2 H -pyrazolo[4,3- c ]pyridin-7-amines was synthesized from easily accessible 1-phenyl-1 H -pyrazol-3-ol via 7-iodo-2,6-diphenyl-2 H -pyrazolo[4,3- c ]pyridine and 7-iodo-4-methyl-2,6-diphenyl-2 H -pyrazolo[4,3- c ]pyridine intermediates and their subsequent use in palladium catalyzed Buchwald-Hartwig cross-coupling reaction with various anilines. Majority of the compounds were not significantly cytotoxic to melanoma G361 cells in the dark up to 10 µM concentration, but their activity could be increased by irradiation with visible blue light (414 nm). The most active compound 10 possessed EC 50 values of 3.5, 1.6 and 0.9 µM in cells irradiated with 1, 5 and 10 J/cm2, respectively. The treatment caused generation of reactive oxygen species in cells and extensive DNA damage, documented by the comet assay and by detection of phosphorylated histone H2A.X, followed by apoptotic cell death. Our results suggest that N -aryl-2,6-diphenyl-2 H -pyrazolo[4,3- c ]pyridin-7-amines could serve as a potential source of photosensitizing compounds with anticancer activities. [ABSTRACT FROM AUTHOR]