Hepatic Mitochondrial Dysfunction and Gut Dysbiosis Induced by Polyethylene Microplastics in FVB/n Mice: A Comparative Study of Fluorescent and Non-Fluorescent Particles

The emerging problem that microplastics pose to our society is reflected in the exponential growth in investigations devoted to uncovering their toxicological potential in humans. However, these studies present several limitations, one of the most significant being the use of microplastics that do not represent their environmental counterparts. In this study, we evaluated the impact of two types of polyethylene microplastics (27–32 µm)—non-fluorescent and fluorescent—on the liver and intestine, targeting mitochondria. FVB/n mice were subjected to a subacute exposure to two concentrations representative of human exposure (0.002% (w/w) and 0.006% (w/w)). Both types of microplastics impaired mitochondrial respiration through disruption of NADH-linked pathways, with more pronounced effects at the highest concentration of fluorescent MPs. Electron transport chain complexes, particularly CIII and CIV, were affected, partially explaining the observed alterations in mitochondrial respiratory capacity. An increased SOD and GPx activity supported the link between mitochondrial dysfunction and increased reactive oxygen species overproduction under MPs exposure. Hepatic mitochondrial lipid remodelling was detected following exposure to fluorescent microplastics, while intestinal epithelial cells displayed impaired mitochondrial activity together with compromised cellular integrity, indicative of stress response. In parallel, shifts in gut composition suggest that PE MPs may contribute to intestinal barrier dysfunction. Overall, fluorescent MPs induced more severe mitochondrial and biochemical disturbances in both the liver and the intestine than their non-fluorescent counterparts. Our findings highlight mitochondria as central targets for microplastic-induced toxicity and underscore the need for improved MPs models in toxicological research.