Oral Exposure to Polystyrene Nanoplastics Disrupts Gut–Testis Metabolic Homeostasis and EGR1-Associated Steroidogenic Regulation in Male Mice

Abstract Polystyrene nanoplastics (PS-NPs) may impair male reproduction through gut–testis metabolic disruption. ICR mice received 100 nm PS-NPs (1 mg/mouse/day) orally for 28 days; fecal microbiota transplantation, metabolomics, sodium butyrate (NaB) supplementation, and TM3-cell assays were used. PS-NPs impaired intestinal barrier integrity and testicular steroidogenesis. Following antibiotic pretreatment, these abnormalities were partially reproduced in exposed-donor recipients relative to control-donor recipients. Untargeted metabolomics showed an FDR-significant decrease in relative testicular butanoic acid levels, while serum butyrate decreased in PS-NP-exposed mice and exposed-donor recipients. In vivo NaB supplementation partially improved reproductive and steroidogenesis-related outcomes in PS-NP-exposed mice. Exploratory analyses and validation experiments implicated a NaB-responsive EGR1–Cyp11a1 regulatory relationship in Leydig cells. These findings suggest that gut-associated butyrate disturbance contributes to PS-NP-induced steroidogenic dysfunction.