Non-targeted lipidomics reveals the distinct metabolic mechanisms of nZnO and Zn ions in fish liver

The toxicity of environmental pollutants is often manifested through metabolic disruptions and damage to detoxification organs. However, current understanding is insufficient to explain the physiological response mechanisms of metabolically abnormal fish exposed to secondary pollutants in complex natural environments. This study established a fish model with non-alcoholic fatty liver to evaluate the effects of Zn oxide nanoparticles (nZnO) and Zn²⁺ on physiological metabolism using untargeted lipidomics and bioimaging techniques. Nile red and hematoxylin and eosin (H&E) staining indicated that increased Zn levels reduced the number of lipid droplets (LDs) and hepatocyte vacuolization in the livers of groupers. Non-targeted lipidomics, employing an unsupervised K-means clustering algorithm, identified key lipid profiles that differentiated the effects of nZnO and Zn, including TG (16:0/16:1/18:1), PC (18:2/22:6), TG (18:2/18:2/22:6), SM (d18:1/24:1), and TG (16:1/18:1/18:2). The increased content of SM (d18:1/24:0) indicated that fish liver cells internalized nZnO via lipid raft structures on the cell membrane, a process distinct from Zn ion uptake. Moreover, nZnO/Zn treatments significantly activated lipolysis regulation in fish liver experiencing oxidative stress. This study contributed to the use of non-targeted lipidomics to identify differential biomarkers of nZnO and Zn, as well as their compensatory mechanisms in metabolically abnormal fish. These findings provide novel insights into the effects of nanometal exposure on aquatic animal health in complex environments.