Toxicity Of Nano Titanium Dioxide To Physarum Polycephalum Based On Metabolomics And Transcriptome

Nano titanium dioxide?nTiO₂?is widely used in many fields due to its good properties.However,many wastes containing nTiO₂ are directly discharged into the environment,which has a serious impact on the environment.At present,there is no standard method to detect the toxicity of nTiO₂,which is adverse for the production of nTiO₂ and monitoring of environmental emissions.Other studies have shown that nTiO₂ has strong cytotoxicity,but due to some limiting factors in cells,such as difficulty in achieving synchronized culture,detecting single cells and limited ability to withstand high concentrations of nTiO₂,because of these factors the research on the cytotoxicity of nTiO₂ have progressed slowly.Physarum polycephalum is a slime mold,a single-cell eukaryotic organism,easy to culture and maintain,and which has the resistance of multicellular organisms.At the same time,it has been found to be highly resistant to nTiO₂.Therefore,in this study,we used that Physarum polycephalum as a model organism for cytotoxicity studies of nTiO₂.The metabolomics analysis is an important method to discover metabolic differences,identify disturbed metabolic pathways,understand the mechanism of toxicity and assess cytotoxicity.Transcriptome analysis has been applied to the early diagnosis of diseases and various toxic effects studies.This study used metabolomics and transcriptomes techniques to analyze the effects of nTiO₂ on the growth of Physarum polycephalum from physiological and biochemical levels,transcription levels and metabolite levels.In the results of physiological and biochemical levels,it was found that a high concentration of nTiO₂??15 mg/mL?lead to increase ROS levels,8-OhdG levels,CAT activity and transcription levels of CAT gene in the cell.This indicates that nTiO₂ may cause oxidative damage of DNA by inducing an imbalance of intracellular ROS.In the metabolic levels analysis,it was found that the metabolites of multiple biological pathways including TCA cycle,nucleotide synthesis and glucose metabolism in Physarum polycephalum took place varying degrees of changes after the stress of 9mg/mL nTiO₂ and 15 mg/mL nTiO₂.Meanwhile,12 metabolites with significant changes were screened.Further comparison of metabolites that significantly changed between the two treatment groups,they are D-arabitol,tartaric acid,glutathione,xanthine,cytidine and formononetin.These six metabolites are considered to be the most likely cytotoxic metabolic markers for nTiO₂.Formononetin is also considered to be an antidote to nTiO₂.In the analysis of the transcriptional levels,3503up-regulated and 4340 down-regulated differentially expressed mRNA were screened in the 15 mg/mL nTiO₂ treated group compared to the 9 mg/mL nTiO₂ treated group.These mRNA are enhanced in sugar metabolism,reactive oxygen metabolism,glutathione metabolism,TCA cycle and niacin and nicotinamide metabolism.This is mutually verifiable with the results of the metabolic levels.Among them,the glutathione transferase gene is considered to be an indicator gene for nTiO₂ toxicity.Simultaneously,891 up-regulated and 405 down-regulated lncRNA,as well as 269up-regulated and 261 down-regulated miRNA were also screened in the 15 mg/mL nTiO₂ treatment group.The results of Gene Ontology?GO?enrichment analysis of differentially expressed mRNA and differentially expressed miRNA target genes are highly consistent,allowing the results at the transcription levels to be self-validated.This study has a guiding significance for the establishment of the nTiO₂ toxicity detection method and it gives an effective means of monitoring the production and environmental emission of nTiO₂ to a certain range.In addition,it is clear that genes,metabolites,metabolic pathways and cellular pathways that are significantly altered by nTiO₂ stress in Physarum polycephalum and it also provide a useful complement to understand the mechanism of toxic effects of nTiO₂ on cells.Thus,the present study elucidates that the tolerance mechanism is one of the phenomena that helps the organism to survive in extreme stress conditions?nTiO₂ stress?.Furthermore,the study also reveals a novelty for the development of antidote or inhibitor of nTiO₂.