In vivo exposure of mixed microplastic particles in mice and its impacts on the murine gut microbiome and metabolome

Microplastics (MPs) are emerging environmental contaminants due to increasing global plastic production and waste. MPs, defined as plastic particles less than 5 mm in diameter, are formed through the degradation of larger plastics via sunlight, weathering, and microbes. These plastic compounds are widely detected in water, soil, and food, as well as human stool and blood. The gut microbiome, often referred to as our second genome, is important in human health and is the primary point of contact for orally ingested MPs. To investigate the impact of ingested MPs on the gut microbiome and the metabolome, 8-week-old male and female C57BL/6 mice were orally gavaged with mixed plastic (5 µm) exposure consisting of polystyrene, polyethylene, and the biodegradable/biocompatible plastic, poly(lactic-co-glycolic acid), twice a week for 4 weeks at 0, 2, or 4 mg/week (n = 8/group). Fecal pellets were collected for bacterial DNA extraction and metagenomic shotgun sequencing, and serum was subjected to targeted and untargeted metabolomics. A total of 1,162 bacterial species and 1,437 metabolites were evaluated for downstream analysis. MPs' exposure resulted in significant sex-specific and dose-dependent changes to the gut microbiome composition, along with substantial regulation of predicted metabolic pathways. Untargeted metabolomics in serum showed that a low MPs dose displayed a more prominent effect on key metabolic pathways, such as amino acid metabolism, sugar metabolism, and inflammation. Additionally, short-chain fatty acid (SCFA)-targeted metabolomics showed significant changes in neuroprotective SCFA levels in both sexes. Our study demonstrates that MPs dysregulate the gut microbiome and serum metabolome, highlighting potential human disease risks.