Nano-sized TiO (nTiO) induces metabolic perturbations in Physarum polycephalum macroplasmodium to counter oxidative stress under dark conditions.

Nano-sized TiO (nTiO) exerts an oxidative effect on cells upon exposure to solar or UV irradiation and ecotoxicity of the nTiO is an urgent concern. Little information is available regarding the effect of TiO on cells under dark conditions. Metabolomics is a unique approach to the discovery of biomarkers of nTiO cytotoxicity, and leads to the identification of perturbed metabolic pathways and the mechanism underlying nTiO toxicity. In the present study, gas chromatography mass spectrometry (GC/MS)-based metabolomics was performed to investigate the effect of nTiO on sensitive cells (P. polycephalum macroplasmodium) under dark conditions. According to the multivariate pattern recognition analysis, at least 60 potential metabolic biomarkers related to sugar metabolism, amino acid metabolism, nucleotide metabolism, polyamine biosynthesis, and secondary metabolites pathways were significantly perturbed by nTiO. Notably, many metabolic biomarkers and pathways were related to anti-oxidant mechanisms in the living organism, suggesting that nTiO may induce oxidative stress, even under dark conditions. This speculation was further validated by the biochemical levels of reactive oxygen species (ROS), 8-hydroxy-2-deoxyguanosine (8-OHdG), and total soluble phenols (TSP). We inferred that the oxidative stress might be related to nTiO-induced imbalance of cellular ROS. To the best of our knowledge, the present study is the first to investigate the nTiO-induced metabolic perturbations in slime mold, provide a new perspective of the mechanism underlying nTiO toxicity under dark conditions, and show that metabolomics can be employed as a rapid, reliable and powerful tool to investigate the interaction among organisms, the environment, and nanomaterials.