Photoaged Tire Wear Particles Impair Neurotransmission in C. elegans

Gu Y, Jiang Y, Chen X, Li L, Chen H, Chen J, Wang C, Yu J, Chen C, Li H. Generation of environmentally persistent free radicals on photoaged tire wear particles and their neurotoxic effects on neurotransmission in Caenorhabditis elegans. Environ Int 2024;186:108640. doi: 10.1016/j.envint.2024.108640.

Background: Tire wear particles (TWP) are a major source of microplastics that accumulate in various environments. Under sunlight, these particles undergo photoaging, generating environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS), which can modify their chemical properties and toxicity. The nematode Caenorhabditis elegans is an established model for studying neurotoxic effects of environmental contaminants, yet the specific impact of EPFRs formed on photoaged TWP on neurotransmission remains unclear.

Hypothesis: This study hypothesized that EPFRs generated on photoaged TWP induce neurotoxicity in C. elegans by disrupting neurotransmission, leading to altered behavior and neurotransmitter balance.

Methods: The authors photoaged TWP under xenon-lamp irradiation for up to 50 days and assessed EPFR and ROS formation. Neurotoxicity assays in C. elegans evaluated locomotory behaviors, neurotransmitter levels and gene expression. Locomotory parameters such as head thrashes, body bends, wavelength and amplitude were quantified using the WormLab Imaging System and analyzed with WormLab. N-acetyl-L-cysteine was applied as a free-radical scavenger to verify EPFR involvement.

Results: Photoaging increased EPFRs and ROS on TWP, correlating positively with irradiation time. Exposure to 100 μg/L TWP-50 significantly reduced locomotory behaviors, dopamine, glutamate, serotonin and GABA contents, and downregulated neurotransmission-related genes (dat-1, dop-3, unc-30, unc-46, tph-1). Radical scavenging mitigated these effects, and EPFR levels negatively correlated with behavioral and biochemical endpoints.

Conclusions: EPFRs formed on photoaged TWP impair neurotransmission in C. elegans, causing neurobehavioral toxicity. These findings highlight EPFRs as key contributors to TWP toxicity and stress their consideration in environmental risk assessments of microplastic pollutants.