Nano- and Microplastics in the Brain: An Emerging Threat to Neural Health

Nano- and microplastics (NMPs), with nanoplastics posing higher risks due to their smaller size and greater capacity for cellular and subcellular penetration, are being referred to as ubiquitous environmental neurotoxicants, due to their ability to pass through biological barriers, including the blood-brain barrier (BBB) and nasal olfactory epithelium, and to remain lodged in neural tissue. Upon uptake, such particles disturb neuronal homeostasis by multiple converging pathways, including oxidative stress, mitochondrial dysfunction, pathological protein aggregation, and chronic neuroinflammation, all closely involved with the molecular signatures of neurodegenerative disorders (Alzheimer's, Parkinson's, Amyotrophic Lateral Sclerosis-ALS). In addition to their neurotoxicity, recent findings suggest that NMPs could disturb synaptic communication and neuroplasticity, thereby compromising the brain's capacity to recover from an injury, a trauma, or neurodegeneration, thus impacting the progression of the disease, our ability to treat it and eventually the efficacy of rehabilitation approaches. Despite these findings, our understanding remains hampered by analytical issues, the scarcity of standard detection methods, and a total lack of longitudinal studies in humans. This review combines multidisciplinary evidence on brain-plastic interactions and calls for accelerated advances in our ability to monitor bioaccumulation in humans, and to integrate neurotoxicology paradigms in the assessment of this underappreciated but growing threat to brain health.