Hepatic cyp24a1 serves as a biomarker for diagnosing polystyrene microplastic exposure in Nile tilapia (Oreochromis niloticus).

Microplastics (MPs), particularly polystyrene (PS), pose a significant threat to aquatic ecosystems globally. Sensitive biomarkers for diagnosing PS exposure are critical for environmental monitoring, yet evolutionarily conserved diagnostic markers in fish remain poorly characterized. This study identified cytochrome P450 (CYP) superfamily members as potential biomarkers for PS exposure in Nile tilapia (Oreochromis niloticus), a globally farmed species and established toxicological model. We comprehensively characterized 88 CYP genes using whole-genome and multi-tissue transcriptomic analyses. Hepatic transcriptional responses to 100 nm PS exposure (100 μg/L) were profiled via RNA sequencing across acute (7 days), adaptive (14 days), and sub-chronic (21 days) exposure phases. Candidate biomarkers were validated by qPCR, Western blot, and immunofluorescence, with cross-species conservation assessed across fourteen teleosts. Histology revealed PS-induced hepatocyte nuclear pyknosis. Transcriptomic analysis identified dysregulation of CYP genes, and KEGG enrichment highlighted significant alteration in the cytochrome P450 pathway. Genomic analysis clustered the 88 CYP genes into 17 subfamilies, all harboring conserved P450 domains. Multi-tissue expression profiling (liver, testis, ovary, brain, heart, head kidney, kidney, skeletal muscle) indicated predominant hepatic expression for most CYP genes, aligning with the liver's metabolic role. Notably, Cyp24a1 exhibited sustained upregulation across all exposure phases, validated at the protein level. Immunofluorescence localized Cyp24a1 expression specifically to hepatic adipocytes. Phylogenetic analysis confirmed cyp24a1 conservation within teleosts. We propose hepatic cyp24a1 as a potential biomarker for diagnosing PS exposure in fish, with its early and persistent induction suggesting its potential utility for environmental monitoring.