Oral ingestion of polystyrene nanoplastics causes memory impairment and neuroinflammation by microglial uptake
Nanoplastics are produced by breakdown of plastics in environmental contamination or commercial use for cosmetics or daily expenses. Emerging evidence indicate that ingested nanoplastics with a size smaller than 100 nm have the potential to reach the brain and induces neurotoxicity. However, the potential toxicity of nanoplastics on brain are limited because of difficulties in synthesize of nanoplastics. In present study, we synthesized the fluorescent polystyrene nanoplastics (PSNPs) and examined the toxicity of PSNPs in brain in vivo and in vitro analyses by comparison to IR-813 fluorophore. Synthesized PSNPs were characterized by fluorescence imaging system, scanning electron microscopy, and Fourier-transform infrared spectroscopy. PSNPs were detected in adult mice brain by oral ingestion. In addition, a series of behavioral analyses showed that oral ingestion of PSNPs induced memory impairments. Among brain cells, PSNPs were predominantly internalized in microglia, and uptake of PSNPs induced microglial activation. In addition, the conditioned medium derived from microglia exposed to PSNPs repressed hippocampal neuronal activity. Furthermore, transcriptome analysis showed that PSNPs changed gene expressions in microglia, elevation of neuroinflammation in contrast to suppression of neurotrophic factors. These results indicated that predominant uptake of PSNPs in microglia induced elevation of neuroninflammatory responses whereas suppression of neurotrophic factors that may contribute to the cognitive impairment.  Our findings indicate the toxic mechanism and potential detrimental effect of nanoplastic in brain and suggest a potential risk of cognitive impairment by exposure to nanoplastics. Overall design: To delve into the underlying mechanism behind impaired behavior and neuronal activity by PSNPs exposure,  RNA-seq was performed in microglia exposed to IR-813 or PSNPs.