Iron Oxide Nanoparticles Induce Dopaminergic Damage: In vitro Pathways and In Vivo Imaging Reveals Mechanism of Neuronal Damage.

Various iron-oxide nanoparticles have been in use for a long time as therapeutic and imaging agents and for supplemental delivery in cases of iron-deficiency. While all of these products have a specified size range of ∼ 40 nm and above, efforts are underway to produce smaller particles, down to ∼ 1 nm. Here, we show that after a 24-h exposure of SHSY-5Y human neuroblastoma cells to 10 µg/ml of 10 and 30 nm ferric oxide nanoparticles (Fe-NPs), cellular dopamine content was depleted by 68 and 52 %, respectively. Increases in activated tyrosine kinase c-Abl, a molecular switch induced by oxidative stress, and neuronal α-synuclein expression, a protein marker associated with neuronal injury, were also observed (55 and 38 % percent increases, respectively). Inhibition of cell-proliferation, significant reductions in the number of active mitochondria, and a dose-dependent increase in reactive oxygen species (ROS) were observed in neuronal cells. Additionally, using a rat in vitro blood-brain barrier (BBB) model, a dose-dependent increase in ROS accompanied by increased fluorescein efflux demonstrated compromised BBB integrity. To assess translational implications, in vivo Fe-NP-induced neurotoxicity was determined using in vivo MRI and post-mortem neurochemical and neuropathological correlates in adult male rats after exposure to 50 mg/kg of 10 nm Fe-NPs. Significant decrease in T 2 values was observed. Dynamic observations suggested transfer and retention of Fe-NPs from brain vasculature into brain ventricles. A significant decrease in striatal dopamine and its metabolites was also observed, and neuropathological correlates provided additional evidence of significant nerve cell body and dopaminergic terminal damage as well as damage to neuronal vasculature after exposure to 10 nm Fe-NPs. These data demonstrate a neurotoxic potential of very small size iron nanoparticles and suggest that use of these ferric oxide nanoparticles may result in neurotoxicity, thereby limiting their clinical application.

Effects of adolescent treatment with nicotine, harmane, or norharmane in male Sprague-Dawley rats.

The initiation of tobacco use occurs most often in adolescence and may be especially detrimental as the adolescent brain is undergoing substantial development. In addition to nicotine, there are over 9000 other compounds present in tobacco products, including the ß-carbolines harmane and norharmane. The present study aimed to determine the long-term effects of adolescent exposure to nicotine (NIC), harmane (HAR), or norharmane (NOR) on locomotor activity, learning and memory, anxiety-like behavior, motor coordination, and monoamine/metabolite concentrations in the striatum and nucleus accumbens of male Sprague-Dawley rats. Beginning on postnatal day (PND) 27 and continuing through PND 55, subjects received twice daily intraperitoneal injections of 1ml/kg saline (CON), 0.5mg NIC/kg, 0.5mg HAR/kg, or 0.5mg NOR/kg. Body weight, food, and water intake were measured daily (PNDs 27-96). Locomotor activity was assessed on PND 40 or 41, PND 55, and PNDs 81 and 82. Other behaviors (anxiety-like behavior, motor coordination, and spatial learning and memory) were assessed at least 25 days after drug exposure ended (PNDs 80-91). On PND 97, subjects were decapitated and the striatum and nucleus accumbens were dissected and frozen for analysis. NIC treatment significantly decreased food intake, but did not alter locomotor activity during or after treatment. HAR and NOR treatment, however, caused significant open field hypoactivity. Motor coordination, water maze performance, and concentrations of monoamines and metabolites in the striatum and nucleus accumbens were unaltered by any drug treatment. These results indicate a long-lasting effect on activity levels from adolescent HAR or NOR treatment; however, there were few long-lasting NIC effects. Given the paucity of data describing effects of HAR or NOR exposure, these data should encourage additional studies of these tobacco constituents as well as constituent combination studies.

Effects of ultrafine diesel exhaust particles on oxidative stress generation and dopamine metabolism in PC-12 cells.

A major constituent of urban air pollution is diesel exhaust, a complex mixture of gases, chemicals, and particles. Recent evidence suggests that exposure to air pollution can increase the risk of a fatal stroke, cause cerebrovascular damage, and induce neuroinflammation and oxidative stress that may trigger neurodegenerative diseases, such as Parkinson's disease. The specific aim of this study was to determine whether ultrafine diesel exhaust particles (DEPs), the particle component of exhaust from diesel engines, can induce oxidative stress and effect dopamine metabolism in PC-12 cells. After 24 h exposure to DEPs of 200 nm or smaller, cell viability, ROS and nitric oxide (NO(2)) generation, and levels of dopamine (DA) and its metabolites, (dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)), were evaluated. Results indicated cell viability was not significantly changed by DEP exposure. However, ROS showed dramatic dose-dependent changes after DEP exposure (2.4 fold increase compared to control at 200 µg/mL). NO(2) levels were also dose-dependently increased after DEP exposure. Although not in a dose-dependent manner, upon DEP exposure, intracellular DA levels were increased while DOPAC and HVA levels decreased when compared to control. Results suggest that ultrafine DEPs lead to dopamine accumulation in the cytoplasm of PC-12 cells, possibly contributing to ROS formation. Further studies are warranted to elucidate this mechanism.

Porcine brain microvessel endothelial cells show pro-inflammatory response to the size and composition of metallic nanoparticles.

The purpose of the current studies was to determine if systemic exposure of various metallic nanoparticles differing in size and composition [silver (Ag-NPs, 25, 40 and 80 nm), copper-oxide (Cu-NPs, 40 and 60 nm) or gold (Au-NPs, 3 and 5 nm)] can induce the release of pro-inflammatory mediators that influence the restrictive nature of the blood-brain barrier (BBB) in vitro. Confluent porcine brain microvessel endothelial cells (pBMECs) (8-12 days) were treated with various metallic nanoparticles (15 µg/ml). Extracellular concentrations of pro-inflammatory mediators (IL-1ß, TNFα and PGE2) were evaluated using ELISA. pBMECs were cultured in standard 12-well Transwell® inserts, and permeability was evaluated by measuring the transport of fluorescein across the pBMEC monolayers. PGE2 release following Cu-NP exposure was significantly increased when compared to the control. Similar results were observed for Ag-NPs but not Au-NPs. The secretion of TNFα and IL-1ß was observed for both Cu-NPs and Ag-NPs but not in response to Au-NPs. The post-treatment time profiles of TNFα and IL-1ß revealed that the IL-1ß response was more persistent. The permeability ratios (exposure/control) were significantly greater following exposure to Cu-NPs or Ag-NPs, compared to Au-NPs. Together, these data suggest that the composition and size of NPs can cause significant pro-inflammatory response that can influence the integrity of the BBB.