Neurotoxic Effects of Metal and Metal Oxide Nanoparticles and the Protective Role of Natural Bioactive Compounds

Nanomaterials (NMs) are increasingly utilized in drug delivery, diagnostic imaging, and therapeutic applications. However, their widespread use raises concerns regarding potential neurotoxicity, particularly for metal and metal oxide nanoparticles. Accumulating evidence indicates that these nanoparticles induce neurotoxicity through interconnected mechanisms, including excessive reactive oxygen species generation, activation of neuroinflammatory pathways, mitochondrial dysfunction, and disruption of blood–brain barrier integrity. These molecular events collectively lead to synaptic impairment, neuronal apoptosis, and progressive cognitive and behavioral deficits, with toxicity severity influenced by dose, exposure duration, and age. Given that in vitro models often fail to capture complex systemic interactions such as nanoparticle biodistribution, blood–brain barrier dynamics, and neuroimmune responses, this review places particular emphasis on in vivo studies to provide a more physiologically relevant understanding of nanoparticle-induced neurotoxicity. Importantly, a growing body of in vivo evidence demonstrates that natural bioactive compounds can mitigate these effects by targeting key pathogenic pathways, including oxidative stress, inflammation, and mitochondrial dysfunction, while preserving neuronal integrity. These findings highlight the therapeutic potential of natural bioactives as protective agents against nanoparticle-induced neurotoxicity and as candidates for broader neuroprotective strategies. This review summarizes the mechanistic basis of metal and metal oxide nanoparticle neurotoxicity and critically evaluates the protective role of natural bioactive compounds, with a focus on evidence derived from animal models.