Size and age dependent Neurotoxicity of Engineered nanoparticles from metals in Rats. Role of Nitric oxide in brain pathology

Previous studies from our laboratory show that chronic administration of engineered nanoparticles from metals, e.g., Cu, Ag, or Al (50-60 nm, 50 mg/kg, i.p. daily for 1 week) are able to induce profound blood-brain barrier (BBB) disruption, brain edema formation and brain pathology in adult rats (age 18 to 22 weeks). This effect was most pronounced by Ag followed by Cu and Al indicating that the constituents of nanoparticles play crucial roles in neurotoxicity. However, effects of size dependent neurotoxicity of nanoparticles in vivo situation are still unknown. In present investigation, we examined the effects of different size ranges of engineered nanoparticles from Cu, Ag and Al on brain pathology in rats. In view of the fact that age is also an important factor in brain pathology, we also evaluated age-related neurotoxicity of nanoparticles in our rat model. Three different sizes of Cu, Ag or Al nanoparticles (20 to 30 nm; 50 to 60 nm, or 130 to 150 nm) were administered intraperitoneally (50 mg /kg, i.p.) in separate set of rats (n = 5 to 7) in 3 different age groups (9 to 10 weeks; 18 to 20 weeks or 30 to 35 weeks old). Saline treated rats served as controls. Breakdown of the BBB to Evans blue albumin (EBA) and radioiodine, brain water content, neuronal injury, astrocytic activation, myelin damages and nitric oxide synthase (NOS) immunoreactivity was examined using standard procedures. Our results showed that brain pathology caused by different nanoparticles were inversely related to their sizes. Thus, smaller nanoparticles from Ag, Cu or Al induced most pronounced BBB breakdown (EBA +480 to 680%; radioiodine +850 to 1025%), brain edema formation (+4 to 6 %) as well as neuronal injuries (+30 to 40%), glial fibrillary acidic protein (GFAP) upregulation (+40 to 56% increase) and myelin vesiculation (+30 to 35 % damage) in youngest animals compared to controls. Interestingly, the oldest animals (30 to 35 weeks of age) also showed massive brain pathology as compared to young adults (18 to 20 weeks old). The Ag and Cu exhibited greater brain damage compared from Al nanoparticles in all age groups regardless of their sizes. This confirms that the composition of nanoparticles is important in neurotoxicity. The very young and elderly age groups exhibited greater neurotoxicity to nanoparticles suggests that children and elderly are more vulnerable to nanoparticles induced brain damage. The nanoparticles induced brain damage correlated well with the upregulation of neuronal and inducible NOS activity in the brain indicating that nanoparticles induced size and age dependent neurotoxicity could probably mediated via increased production of nitric oxide, not reported earlier.