Early and Delayed Impact of Nanosilver on the Glutamatergic NMDA Receptor Complex in Immature Rat Brain.

Silver nanoparticles (AgNPs) are the one of the most extensively used nanomaterials. The strong antimicrobial properties of AgNPs have led to their use in a wide range of medical and consumer products. Although the neurotoxicity of AgNPs has been confirmed, the molecular mechanisms have not been extensively studied, particularly in immature organisms. Based on information gained from previous in vitro studies, in the present work, we examine whether ionotropic NMDA glutamate receptors contribute to AgNP-induced neurotoxicity in an animal model of exposure. In brains of immature rats subjected to a low dose of AgNPs, we identified ultrastructural and molecular alterations in the postsynaptic region of synapses where NMDA receptors are localized as a multiprotein complex. We revealed decreased expression of several NMDA receptor complex-related proteins, such as GluN1 and GluN2B subunits, scaffolding proteins PSD95 and SynGAP, as well as neuronal nitric oxide synthase (nNOS). Elucidating the changes in NMDA receptor-mediated molecular mechanisms induced by AgNPs, we also identified downregulation of the GluN2B-PSD95-nNOS-cGMP signaling pathway which maintains LTP/LTD processes underlying learning and memory formation during development. This observation is accompanied by decreased density of NMDA receptors, as assessed by a radioligand binding assay. The observed effects are reversible over the post-exposure time. This investigation reveals that NMDA receptors in immature rats are a target of AgNPs, thereby indicating the potential health hazard for children and infants resulting from the extensive use of products containing AgNPs.

Early Postnatal Exposure to a Low Dose of Nanoparticulate Silver Induces Alterations in Glutamate Transporters in Brain of Immature Rats.

Due to strong antimicrobial properties, silver nanoparticles (AgNPs) are used in a wide range of medical and consumer products, including those dedicated for infants and children. While AgNPs are known to exert neurotoxic effects, current knowledge concerning their impact on the developing brain is scarce. During investigations of mechanisms of neurotoxicity in immature rats, we studied the influence of AgNPs on glutamate transporter systems which are involved in regulation of extracellular concentration of glutamate, an excitotoxic amino acid, and compared it with positive control-Ag citrate. We identified significant deposition of AgNPs in brain tissue of exposed rats over the post-exposure time. Ultrastructural alterations in endoplasmic reticulum (ER) and Golgi complexes were observed in neurons of AgNP-exposed rats, which are characteristics of ER stress. These changes presumably underlie substantial long-lasting downregulation of neuronal glutamate transporter EAAC1, which was noted in AgNP-exposed rats. Conversely, the expression of astroglial glutamate transporters GLT-1 and GLAST was not affected by exposure to AgNPs, but the activity of the transporters was diminished. These results indicate that even low doses of AgNPs administered during an early stage of life create a substantial risk for health of immature organisms. Hence, the safety of AgNP-containing products for infants and children should be carefully considered.

Ultrastructural and biochemical features of cerebral microvessels of adult rat subjected to a low dose of silver nanoparticles.

The widespread use of silver nanoparticles (AgNPs) in medicine and in multiple commercial products has motivated researchers to investigate their potentially hazardous effects in organisms. Since AgNPs may easily enter the brain through the blood-brain barrier (BBB), characterization of their interactions with cellular components of the neurovascular unit (NVU) is of particular importance. Therefore, in an animal model of prolonged low-dose exposure, we investigate the extent and mechanisms of influence of AgNPs on cerebral microvessels. Adult rats were treated orally with small (10 nm) AgNPs in a dose of 0.2 mg/kg b.w. over a 2-week period. A silver citrate-exposed group was established as a positive control of ionic silver effects. Alterations in the expression of tight junction proteins claudin-5, ZO-1, and occludin, were observed. These effects are accompanied by ultrastructural features indicating enhanced permeability of microvessels such as focal edema of perivascular astrocytic processes and surrounding neuropil. We did not identify changes in the expression of PDGFßR which is a marker of pericytes. Ultrastructural alterations in these cells were not identified. The results show that altered integrity of cerebral vessels under a low-dose of AgNP-exposure may be the consequence of dysfunction of endothelial cells caused by disruption of tight junction proteins.