[The effect and mechanism of exposure to polystyrene nanoplastics on lipid metabolism in mice liver]

Objective: To investigate the effect and potential mechanism of exposure to 20 nm polystyrene nanoplastics (PS-NPs) on lipid metabolism in mice liver. Methods: An animal experimental model was designed, which was completed from September 2022 to July 2023 on the exposure omics platform of the School of Public Health at Capital Medical University and the Key Laboratory of Environment and Population Health at the Chinese Center for Disease Control and Prevention.1 mg/kg and 10 mg/kg PS-NPs tail vein mice exposure models were constructed. After exposure 7 d, serum was collected to measure the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) and air flow assisted desorption electrospray ionization-mass spectrometry imaging (AFADESI-MSI) analysis were used to analyze the mRNA levels of fatty acid esterification related genes (Dgat1 and Dgat2) and lipid transport related genes (ApoB, Cd36, ApoE and Mttp) and metabolites' spatial changes in liver tissue. In vivo imaging system (IVIS) and tissue shake sections were employed to observe the fluorescence biological distribution of PS-NPs. t-test or one-way ANOVA was used to explore the difference between groups. Results: The serum ALT levels were (83.97±4.58), (91.17±13.69) and (142.43±6.09) U/L in the control group, 1 mg/kg PS-NPs exposure group and 10 mg/kg PS-NPs exposure group respectively (F=37.281, P<0.05). The relative mRNA levels of Dgat1, Dgat2, ApoB, Cd36 and ApoE were (1.49±0.63, 2.53±0.32, 2.45±0.54), (1.07±0.38, 1.86±0.83, 2.23±0.73), (1.01±0.13, 1.58±0.43, 2.03±0.52), (1.01±0.14, 1.55±0.37, 1.52±0.51), (1.01±0.17, 2.11±0.27, 2.39±0.93) in these three groups respectively. The differences were statistically significant (F=11.54, 6.95, 14.90, 5.98 and 14.68, P<0.05). AFADESI-MSI analysis found that PS-NPs exposure led to a significant decrease in the levels of glutarylcarnitine and O-Linoleoylcarnitine (t=4.12 and 3.35, P<0.05), which were associated with lipid beta oxidation. The content of triglycerides (TG) (m/z 921.726 4, t=8.69, P<0.05; m/z 919.711 4, t=3.20, P<0.05), phosphatidylic acid (PA) (m/z 895.712 3, t=3.60, P<0.05; m/z 821.526 6, t=3.36, P<0.05), lysophosphatidylcholine (LysoPC) (m/z 560.310 6, t=3.35, P<0.05; m/z 582.295 3, t=6.28, P<0.05), phosphatidylcholine (PC) (m/z 778.533 9, t=3.53, P<0.05; m/z 804.549 6, t=3.60, P<0.05; m/z 820.523 1, t=3.37, P<0.05), phosphatidylethanolamine (PE) (m/z 772.523 3, t=3.08, P<0.05) showed a significant increase in the PS-NPs exposure group. In vivo and in vitro imaging and in situ cell localization revealed that PS-NPs were mainly enriched in hepatic stellate cells and hepatic Kupffer cells in liver tissue. Conclusion: Exposure to PS-NPs induces disorder of liver lipid metabolism, which may be related to the accumulation of PS-NPs in hepatic stellate cells and hepatic Kupffer cells, providing basis for searching early biomarkers of PS-NPs exposure and further mechanism research.