Neurotoxicity of Environmental Metal Toxicants: Special Issue

TDCPP and TiO2 NPs aggregates synergistically induce SH-SY5Y cell neurotoxicity by excessive mitochondrial fission and mitophagy inhibition

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP), a halogen-containing phosphorus flame retardant, is widely used and has been shown to possess health risks to humans. The sustained release of artificial nanomaterials into the environment increases the toxicological risks of their coexisting pollutants. Nanomaterials may seriously change the environmental behavior and fate of pollutants. In this study, we investigated this combined toxicity and the potential mechanisms of toxicity of TDCPP and titanium dioxide nanoparticles (TiO2 NPs) aggregates on human neuroblastoma SH-SY5Y cells. TDCPP and TiO2 NPs aggregates were exposed in various concentration combinations, revealing that TDCPP (25 μg/mL) reduced cell viability, while synergistic exposure to TiO2 NPs aggregates exacerbated cytotoxicity. This combined exposure also disrupted mitochondrial function, leading to dysregulation in the expression of mitochondrial fission proteins (DRP1 and FIS1) and fusion proteins (OPA1 and MFN1). Consequently, excessive mitochondrial fission occurred, facilitating the translocation of cytochrome C from mitochondria to activate apoptotic signaling pathways. Furthermore, exposure of the combination of TDCPP and TiO2 NPs aggregates activated upstream mitochondrial autophagy but disrupted downstream Parkin recruitment to damaged mitochondria, preventing autophagosome-lysosome fusion and thereby disrupting mitochondrial autophagy. Altogether, our findings suggest that TDCPP and TiO2 NPs aggregates may stimulate apoptosis in neuronal SH-SY5Y cells by inducing mitochondrial hyperfission and inhibiting mitochondrial autophagy.

Unscrambling the Role of Redox-Active Biometals in Dopaminergic Neuronal Death and Promising Metal Chelation-Based Therapy for Parkinson's Disease

Biometals are all metal ions that are essential for all living organisms. About 40% of all enzymes with known structures require biometals to function correctly. The main target of damage by biometals is the central nervous system (CNS). Biometal dysregulation (metal deficiency or overload) is related to pathological processes. Chronic occupational and environmental exposure to biometals, including iron and copper, is related to an increased risk of developing Parkinson's disease (PD). Indeed, biometals have been shown to induce a dopaminergic neuronal loss in the substantia nigra. Although the etiology of PD is still unknown, oxidative stress dysregulation, mitochondrial dysfunction, and inhibition of both the ubiquitin-proteasome system (UPS) and autophagy are related to dopaminergic neuronal death. Herein, we addressed the involvement of redox-active biometals, iron, and copper, as oxidative stress and neuronal death inducers, as well as the current metal chelation-based therapy in PD.