Effects of PM_2.5 sub-chronic exposure on liver metabolomics in mice

Background Atmospheric fine particulate matter (PM_2.5) can disrupt the metabolic homeostasis of the liver and accelerate the progression of liver diseases, but there are few studies on the effects of sub-chronic PM_2.5 exposure on the liver metabolome.

Objectives To investigate the effects of sub-chronic exposure to concentrated PM_2.5 on hepatic metabolomics in mice by liquid chromatography-mass spectrometry (LC-MS), and to identify potentially affected metabolites and metabolic pathways.

Methods Twelve male C57BL/6J (6 weeks old) mice were randomly divided into two groups: a concentrated PM_2.5 exposure group and a clean air exposure group. The mice were exposed to concentrated PM_2.5 using the "Shanghai Meteorological and Environmental Animal Exposure System" at Fudan University. The exposure duration was 8 h per day, 6 d per week, for a total of 8 weeks. The mice's liver tissues were collected 24 h after the completion of exposure. LC-MS was performed to assess changes in the hepatic metabolome. Orthogonal partial least squares discriminant analysis and t-test were employed to identify differentially regulated metabolites between the two groups under the conditions of variable important in projection (VIP)≥1.0 and P<0.05. Metabolic pathway enrichment analysis was performed using MetaboAnalyst 5.0 software and the Kyoto Encyclopedia of Genes and Genomes (KEGG).

Results A total of 297 differentially regulated metabolites were identified between the concentrated PM_2.5 exposure group and the clean air group. Among these metabolites, 142 were upregulated and 155 were downregulated. A total of 38 metabolic pathways were altered, with 7 pathways showing significant perturbation (P<0.05). These pathways involved amino acid metabolism, glucose metabolism, nucleotide metabolism, as well as cofactor and vitamin metabolism. The 7 significant metabolic pathways were pantothenic acid and coenzyme A biosynthesis; purine metabolism; amino sugar and nucleotide sugar metabolism; arginine biosynthesis; alanine, aspartate and glutamate metabolism; aminoacyl-tRNA biosynthesis; and fructose and mannose metabolism.

Conclusion The results from metabolomics analysis suggest that sub-chronic exposure to PM_2.5 may disrupt hepatic energy metabolism and induce oxidative stress damage. Aspartic acid, succinic acid, ornithine, fumaric acid, as well as purine and xanthine derivatives, were identified as potential early biomarkers of hepatic response to sub-chronic PM_2.5 exposure.