Microplastic polyethylene induced inner ear dysfunction in murine model

Abstract

While the hazardous effects of microplastics (MPs) are increasingly reported, it remains uncertain if MPs induce inner ear dysfunction. Nonetheless, prevalence of inner ear dysfunction was observed across all age groups. In this study, we investigated whether MP polyethylene affect inner ear function in a murine model. To detect hearing loss and balance defect after polyethylene (PE) exposure, we evaluated hearing threshold levels, assessed cerebral glucose metabolism, conducted transcriptome analysis, and performed behavioral studies. C57BL/6 J mice (5-week-old) were grouped into control (n = 10) and PE-fed groups (n = 10). Mice were orally administered 100 ppm/100 μL (equivalent to 10 μg) of PE every day for 4 months. We identified the accumulation of PE in the cochlea and vestibular region. The fragmented PE in inner ear was 3.00 ± 0.38 µm in size; the administered PE concentration was 1.14 ± 1.06 mg/g. Fourier transform infrared spectrometry confirmed that the properties of the MP were identical with those of PE fed to the mice. Transcriptomic analysis showed up-regulation of PER1, NR4A3 and CEBPB at the PE exposed inner ear tissue and it was confirmed using qRT-PCR, western blotting, and immunofluorescence staining. We observed abnormalities in balance related behavior assessment in the PE group. Exposure to PE increased the hearing thresholds and decreased glucose metabolism in the bilateral lateral entorhinal cortex, right primary auditory cortex, and right secondary auditory cortex. We can conclude that PE exposure induced inner ear dysfunction such as hearing loss and balance disorder.

Keywords: Balance disorder; Hearing loss; Inner ear dysfunction; Microplastic; Polyethylene; Positron emission tomography.