Neurotoxicity of silver nanoparticles stabilized with different coating agents: In vitro response of neuronal precursor cells

Molecular mechanisms of silver nanoparticle-induced neurotoxic injury and new perspectives for its neurotoxicity studies: A critical review

Silver nanoparticles (AgNPs) garnered significant attention and applications in the field of nanotechnology due to their unique physicochemical properties. However, with the increasing exposure of AgNPs in the environment and biological systems, concerns about their potential neurotoxicity have also risen. Recent studies on the neurotoxic effects and mechanisms of AgNPs have often relied on traditional toxicological research methods and perspectives. This reliance has limited the extrapolation of these findings to the human brain environment and hindered a deep understanding of the neurotoxicity of AgNPs. This review first outlines the molecular mechanisms of AgNPs-induced neurotoxic injury from a traditional research perspective, identifying oxidative stress, inflammatory responses, and autophagy disorders as key areas of current research. Related molecular signaling pathways, including the nuclear transcription factor-κB (NF-κB) signaling pathway, the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, and the calcium signaling pathway, have been implicated in the neurotoxic injury process induced by AgNPs. Subsequently, we elucidated the unique advantages of the 3D brain organoids applied to the neurotoxicity study of AgNPs by drawing on relevant studies in the same field. We also emphasize that establishing a standardized 3D brain organoids construction platform is a crucial prerequisite for its widespread application. Furthermore, we suggest that future studies should explore the neurotoxicity mechanisms of AgNPs through the lenses of "adaptive homeostasis" and "structure-activity relationship analysis". In conclusion, the neurotoxicity of AgNPs should be comprehensively evaluated by integrating new research techniques and perspectives, ultimately allowing these nanoparticles to better serve human society.

Silver nanoparticles induce iron accumulation-associated cognitive impairment via modulating neuronal ferroptosis

Silver nanoparticles (AgNPs) are widely used in daily life and medical fields owing to their unique physicochemical properties. Daily exposure to AgNPs has become a great concern regarding their potential toxicity to human beings, especially to the central nervous system. Ferroptosis, a newly recognized programmed cell death, was recently reported to be associated with the neurodegenerative process. However, whether and how ferroptosis contributes to AgNPs-induced neurotoxicity remain unclear. In this study, we investigated the role of ferroptosis in neurotoxic effects induced by AgNPs using in vitro and in vivo models. Our results showed that AgNPs induced a notable dose-dependent cytotoxic effect on HT-22 cells and cognitive impairment in mice as indicated by a decline in learning and memory and brain tissue injuries. These findings were accompanied by iron overload caused by the disruption of the iron transport system and activation of NCOA4-mediated autophagic degradation of ferritin. The excessive free iron subsequently induced GSH depletion, loss of GPX and SOD activities, differential expression of Nrf2 signaling pathway elements, down-regulation of GPX4 protein and production of lipid peroxides, initiating ferroptosis cascades. The mitigating effects of ferrostatin-1 and deferoxamine on iron overload, redox imbalance, neuronal cell death, impairment of mice learning and memory, Aβ deposition and synaptic plasticity reduction suggested ferroptosis as a potential molecular mechanism in AgNPs-induced neurotoxicity. Taken together, these results demonstrated that AgNPs induced neuronal cell death and cognitive impairment with Aβ deposition and reduction of synaptic plasticity, which were mediated by ferroptosis caused by iron-mediated lipid peroxidation. Our study provides new insights into the underlying mechanisms of AgNPs-induced neurotoxicity and predicts potential preventive strategies.

Nanoparticles and neurodegeneration: Insights on multiple pathways of programmed cell death regulated by nanoparticles

Currently, nanoparticles (NPs) are extensively applied in the diagnosis and treatment of neurodegenerative diseases (NDs). With the rapid development and increasing exposure to the public, the potential neurotoxicity associated with NDs caused by NPs has attracted the researchers' attentions but their biosafety assessments are still far behind relevant application studies. Based on recent research, this review aims to conduct a comprehensive and systematic analysis of neurotoxicity induced by NPs. The 191 studies selected according to inclusion and exclusion criteria were imported into the software, and the co-citations and keywords of the included literatures were analyzed to find the breakthrough point of previous studies. According to the available studies, the routes of NPs entering into the normal and injured brain were various, and then to be distributed and accumulated in living bodies. When analyzing the adverse effects induced by NPs, we focused on multiple programmed cell deaths (PCDs), especially ferroptosis triggered by NPs and their tight connection and crosstalk that have been found playing critical roles in the pathogenesis of NDs and their underlying toxic mechanisms. The activation of multiple PCD pathways by NPs provides a scientific basis for the occurrence and development of NDs. Furthermore, the adoption of new methodologies for evaluating the biosafety of NPs would benefit the next generation risk assessment (NGRA) of NPs and their toxic interventions. This would help ensure their safe application and sustainable development in the field of medical neurobiology.

Nanotechnology in toothpaste: Fundamentals, trends, and safety

Several studies have revealed that healthcare nanomaterials are widely used in numerous areas of dentistry, including prevention, diagnosis, treatment, and repair. Nanomaterials in dental cosmetics are utilized to enhance the efficacy of toothpaste and other mouthwashes. Nanoparticles are added to toothpastes for a variety of reasons, including dental decay prevention, remineralization, hypersensitivity reduction, brightening, and antibacterial qualities. In this review, the benefits and uses of many common nanomaterials found in toothpaste are outlined. Additionally, the capacity and clinical applications of nanoparticles as anti-bacterial, whitening, hypersensitivity, and remineralizing agents in the treatment of dental problems and periodontitis are discussed.

Amelioration of neurobehavioral, biochemical, and morphological alterations associated with silver nanoparticles exposure by taurine in rats

The adverse effect of silver nanoparticles (AgNPs) on the nervous system is an emerging concern of public interest globally. Taurine, an essential amino acid required for neurogenesis in the nervous system, is well-documented to possess antioxidant, anti-inflammatory, and antiapoptotic activities. Yet, there is no report in the literature on the effect of taurine on neurotoxicity related to AgNPs exposure. Here, we investigated the neurobehavioral and biochemical responses associated with coexposure to AgNPs (200 µg/kg body weight) and taurine (50 and 100 mg/kg body weight) in rats. Locomotor incompetence, motor deficits, and anxiogenic-like behavior induced by AgNPs were significantly alleviated by both doses of taurine. Taurine administration enhanced exploratory behavior typified by increased track plot densities with diminished heat maps intensity in AgNPs-treated rats. Biochemical data indicated that the reduction in cerebral and cerebellar acetylcholinesterase activity, antioxidant enzyme activities, and glutathione level by AgNPs treatment were markedly upturned by both doses of taurine. The significant abatement in cerebral and cerebellar oxidative stress indices namely reactive oxygen and nitrogen species, hydrogen peroxide, and lipid peroxidation was evident in rats cotreated with AgNPs and taurine. Further, taurine administration abated nitric oxide and tumor necrosis factor-alpha levels cum myeloperoxidase and caspase-3 activities in AgNPs-treated rats. Amelioration of AgNPs-induced neurotoxicity by taurine was confirmed by histochemical staining and histomorphometry. In conclusion, taurine via attenuation of oxido-inflammatory stress and caspase-3 activation protected against neurotoxicity induced by AgNPs in rats.

Long-term application of silver nanoparticles in dental restoration materials: potential toxic injury to the CNS

Silver nanoparticles (AgNPs) have durable and remarkable antimicrobial effects on pathogenic microorganisms, such as bacteria and fungi, in dental plaques. As such, they are widely added to dental restoration materials, including composite resins, denture bases, adhesives, and implants, to solve the problems of denture stomatitis, peri-implant inflammation, and oral infection caused by the long-term use of these dental restoration materials. However, AgNPs can be absorbed into the blood circulatory system through the nasal/oral mucosa, lungs, gastrointestinal tract, skin, and other pathways and then distributed into the lungs, kidneys, liver, spleen, and testes, thereby causing toxic injury to these tissues and organs. It can even be transported across the blood-brain barrier (BBB) and continuously accumulate in brain tissues, causing injury and dysfunction of neurons and glial cells; consequently, neurotoxicity occurs. Other nanomaterials with antibacterial or remineralization properties are added to dental restoration materials with AgNPs. However, studies have yet to reveal the neurotoxicity caused by dental restoration materials containing AgNPs. In this review, we summarize the application of AgNPs in dental restoration materials, the mechanism of AgNPs in cytotoxicity and toxic injury to the BBB, and the related research on the accumulation of AgNPs to cause changes of neurotoxicity. We also discuss the mechanisms of neurotoxicity caused by AgNPs and the mode and rate of AgNPs released from dental restorative materials added with AgNPs to evaluate the probability of neurotoxic injury to the central nervous system (CNS), and then provide a theoretical basis for developing new composite dental restoration materials. Mechanism of neurotoxicity caused by AgNPs: AgNPs in the blood circulation enter the brain tissue after being transported across the BBB through transendothelial cell pathway and paracellular transport pathway, and continuously accumulate in brain tissue, causing damage and dysfunction of neurons and glial cells which ultimately leads to neurotoxicity. The uptake of AgNPs by neurons, astrocytes and microglia causes damage to these cells. AgNPs with non-neurotoxic level often increases the secretion of a variety of cytokines, up-regulates the expression of metallothionein in glial cells, even up-regulates autophagy and inflammation response to protect neurons from the toxic damage of AgNPs. However, the protective effect of glial cells induced by AgNPs exposure to neurotoxic levels is insufficient, which leads to neuronal damage and dysfunction and even neuronal programmed cell death, eventually cause neurotoxicity.

Comparative oxidative damages induced by silver nanoparticles with different sizes and coatings in Caenorhabditis elegans

Silver nanoparticles (AgNPs) are widely used in many commercial and medical products. Serious concerns are paid on their adverse potentials to the environment and human health. In this study, toxic effects and oxidative stress induced by AgNPs with different sizes and coatings (20 nm AgNPs, 20 nm polyvinylpyrrolidone (PVP) -AgNPs and 50 nm AgNPs) in Caenorhabditis elegans (C. elegans) were investigated. The toxic effects including the shortened lifespan and decreased frequency of head thrashes and body bends of C. elegans were induced in a dose-dependent manner by AgNPs. The reactive oxygen species (ROS) production and the oxidative stress-related indicators including malondialdehyde (MDA) and glutathione (GSH) in nematodes were changed after exposure to three kinds of AgNPs. These effects were the most obvious in a 20 nm PVP-AgNPs exposure group. AgNPs could also induce the expression of genes related to oxidative stress in nematodes. In addition, the up-regulation of mtl-1 and mtl-2 in nematodes might reduce the oxidative damage caused by AgNPs, by using transgenic strains CF2222 and CL2120 nematodes. Metallothionein (MT), an antioxidant, could relieve the oxidative damage caused by AgNPs. These results suggested that 20 nm PVP-AgNPs with a smaller particle size and better dispersion have stronger toxic effects and the oxidative damage to nematodes. Mtl-1 and mtl-2 might be involved in alleviating the oxidative damage caused by AgNPs. Our findings provide clues for the safety evaluation and mechanism information of metal nanoparticles.

Particle surface functionalization affects mechanism of endocytosis and adverse effects of silver nanoparticles in mammalian kidney cells

Silver nanoparticles (AgNPs) show a plethora of possible applications due to their antimicrobial properties. Different coatings of AgNPs are used in order to increase stability, availability, and activity. However, the question about the toxicity after prolonged exposure still remains. Here, we show that different surface coatings affect in vitro toxicity and internalization of AgNPs in porcine kidney (PK15) cells. AgNPs coated with cetyltrimethylammonium bromide (CTAB), poly(vinylpyrrolidone) (PVP), sodium bis(2-ethylhexyl)-sulfosuccinate (AOT), poly-L-lysine (PLL), and bovine serum albumin (BSA) were toxic at the concentration of 10 mg Ag/L and higher. The toxicity increased in the following manner: PVP-AgNPs < CTAB-AgNPs < PLL-AgNPs < AOT-AgNPs < BSA-AgNPs. All types of AgNPs were internalized by the PK15 cells in a dose-dependent manner with greater internalization of AgNPs bearing positive surface charge. Transmission electron microscopy (TEM) experiments showed that AgNPs were located in the lysosomal compartments, while the co-treatment with known inhibitors of endocytosis pathways suggested macropinocytosis as the preferred internalization pathway. When inside the cell, all types of AgNPs induced the formation of reactive oxygen species while decreasing the concentration of the cell's endogenous antioxidant glutathione. The comet assay indicated possible genotoxicity of tested AgNPs starting at the concentration of 2 mg Ag/L or higher, depending on the surface functionalization. This study demonstrates the toxicity of AgNPs pointing to the importance of biosafety evaluation when developing novel AgNPs-containing materials.

Exploring the Physicochemical, Electroactive, and Biodelivery Properties of Metal Nanoparticles on Peripheral Nerve Regeneration

Despite the advances in the regeneration/rehabilitation field of damaged tissues, the functional recovery of peripheral nerves (PNs), especially in a long gap injury, is considered a great medical challenge. Recent progress in nanomedicine has provided great hope for PN regeneration through the strategy of controlling cell behavior by metal nanoparticles individually or loaded on scaffolds/conduits. Despite the confirmed toxicity of metal nanoparticles due to long-term accumulation in nontarget tissues, they play a role in the damaged PN regeneration based on the topography modification of scaffolds/conduits, enhancing neurotrophic factor secretion, the ion flow improvement, and the regulation of electrical signals. Determining the fate of neural progenitor cells would be a major achievement in PN regeneration, which seems to be achievable by metal nanoparticles through altering cell vital approaches and controlling their functions. Therefore, in this literature, an attempt was made to provide an overview of the effective activities of metal nanoparticles on the PN regeneration, until the vital clues of the PN regeneration and how they are changed by metal nanoparticles are revealed to the researcher.

Toxic implications of silver nanoparticles on the central nervous system: A systematic literature review

Silver nanoparticles have many medical and commercial applications, but their effects on human health are poorly understood. They are used extensively in products of daily use, but little is known about their potential neurotoxic effects. A xenobiotic metal, silver, has no known physiological significance in the human body as a trace metal. Biokinetics of silver nanoparticles indicates its elimination from the body via urine and feces route. However, a substantial amount of evidence from both in vitro and in vivo experimental research unequivocally establish the fact of easier penetration of smaller nanoparticles across the blood-brain barrier to enter in brain and thereby interaction with cellular components to induce neurotoxic effects. Toxicological effects of silver nanoparticles rely on the degree of exposure, particle size, surface coating, and agglomeration state as well as the type of cell or organism used to evaluate its toxicity. This review covers pertinent facts and the present state of knowledge about the neurotoxicity of silver nanoparticles reviewing the impacts on oxidative stress, neuroinflammation, mitochondrial function, neurodegeneration, apoptosis, and necrosis. The effect of silver nanoparticles on the central nervous system is a topic of growing interest and concern that requires immediate consideration.

The cytological and electrophysiological effects of silver nanoparticles on neuron-like PC12 cells

The aim of this study was to investigate the toxic effects and mechanism of silver nanoparticles (SNPs) on the cytological and electrophysiological properties of rat adrenal pheochromocytoma (PC12) cells. Different concentrations of SNPs (20 nm) were prepared, and the effects of different application durations on the cell viability and electrical excitability of PC12 quasi-neuronal networks were investigated. The effects of 200 μM SNPs on the neurite length, cell membrane potential (CMP) difference, intracellular Ca2+ content, mitochondrial membrane potential (MMP) difference, adenosine triphosphate (ATP) content, and reactive oxygen species (ROS) content of networks were then investigated. The results showed that 200 μM SNPs produced grade 1 cytotoxicity at 48 h of interaction, and the other concentrations of SNPs were noncytotoxic. Noncytotoxic 5 μM SNPs significantly increased electrical excitability, and noncytotoxic 100 μM SNPs led to an initial increase followed by a significant decrease in electrical excitability. Cytotoxic SNPs (200 μM) significantly decreased electrical excitability. SNPs (200 μM) led to decreases in neurite length, MMP difference and ATP content and increases in CMP difference and intracellular Ca2+ and ROS levels. The results revealed that not only cell viability but also electrophysiological properties should be considered when evaluating nanoparticle-induced neurotoxicity. The SNP-induced cytotoxicity mainly originated from its effects on ATP content, cytoskeletal structure and ROS content. The decrease in electrical excitability was mainly due to the decrease in ATP content. ATP content may thus be an important indicator of both cell viability and electrical excitability in PC12 quasi-neuronal networks.

Silver Nanoparticles Conjugated with Colistin Enhanced the Antimicrobial Activity against Gram-Negative Bacteria

Colistin is a potent peptide antibiotic that is effective against Gram-negative bacteria. However, nephrotoxicity limited its clinical use. Silver nanoparticles (AgNPs) have gained attention as a potential antimicrobial agent and nanodrug carrier. The conjugation of antibiotics and AgNPs has been found to increase the activity and decrease drug toxicity. In this study, colistin was conjugated with AgNPs (Col-AgNPs), which was confirmed by Fourier-transform infrared (FT-IR) and energy-dispersive X-ray (EDX) spectra. The optimized Col-AgNPs had the proper characteristics, including spherical shape, monodispersity, nanosized particle, high surface charge, and good stability. The powder X-ray diffraction (PXRD) pattern supported the crystallinity of Col-AgNPs and AgNPs. The drug loading of Col-AgNPs was 11.55 ± 0.93%. Col-AgNPs had higher activity against Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa) than AgNPs and colistin. The mechanism of actions of Col-AgNPs involved membrane disruption and genomic DNA damage. The Col-AgNPs and AgNPs were biocompatible with human red blood cells and renal cells at concentrations up to 16 µg/mL. Interestingly, Col-AgNPs exhibited higher cell survival than AgNPs and colistin at 32 µg/mL. Our results revealed that the Col-AgNPs could enhance the antimicrobial activity and cell biocompatibility more than colistin and AgNPs.

Silver Nanoparticles Induce a Size-dependent Neurotoxicity to SH-SY5Y Neuroblastoma Cells via Ferritinophagy-mediated Oxidative Stress

Silver nanoparticles (AgNPs) are widely used in a variety of consumer products because of their antibacterial and antifungal characteristics, but little is known about their toxicity to the brain. In this study, we investigated AgNP-induced neurotoxicity using the human neuroblastoma cancer (SH-SY5Y) cell line. After a 24 h treatment of AgNPs with two primary sizes (5 and 50 nm labeled as Ag-5 and Ag-50, respectively), a series of toxicological endpoints including cell viability, expression of proteins and genes in amyloid precursor protein (APP) amyloid hydrolysis process and ferritinophagy signaling pathways, oxidative stress, intracellular iron levels, and molecular regulators of iron metabolism were evaluated. Our results showed that both Ag-5 and Ag-50 induced notable neurotoxic effects on SH-SY5Y cells indicated by cell proliferation inhibition, increased BACE1 protein expression, and decreased APP and ADAM10 gene expression. Activation of nuclear receptor coactivator 4-mediated ferritinophagy and blockade of autophagic flux were induced by AgNPs, accompanied by intracellular iron accumulation and overexpression of divalent metal-ion transporter-1 and ferroportin1 in SH-SY5Y cells. In addition, AgNPs significantly decreased glutathione peroxidase 4 protein expression but increased malondialdehyde concentration, suggesting that AgNP-induced iron accumulation may trigger oxidative stress by disruption of the intracellular oxidant and antioxidant systems. In addition, compared with Ag-50, Ag-5 with higher cellular uptake efficiency caused more detrimental effects on SH-SY5Y cells. In conclusion, our findings demonstrated a size-dependent neurotoxicity in SH-SY5Y cells by AgNPs via ferritinophagy-mediated oxidative stress.

Overview of Neural Tube Defects: Gene–Environment Interactions, Preventative Approaches and Future Perspectives

Neural tube defects (NTDs) are the second most common congenital malformations of humans, characterized by impaired development of the central nervous system. Even though the etiology of most birth defects remains undetermined, genetic and environmental risk factors in the background of NTDs have been identified and extensively reported. On top of genetic and nutritional risks which include mutations in both coding and non-coding regions and maternal folate status, respectively, recent years have seen a rise in the identification of a variety of teratogens that could be implicated in NTD development. These include polycyclic aromatic hydrocarbons, arsenic, pesticides, maternal hyperthermia and antibiotics as well as pain and seizure medication. With an increase in understanding of teratogens leading to NTD formation, preventative and treatment approaches have witnessed great advances throughout the years. While the most common preventative approach includes folic acid food fortification as well as suggested inositol supplementation, treatment and management approaches differ greatly depending on the developmental stage and the site of the lesion and include prenatal surgery, stem cell transplantation and postnatal surgery. Because NTDs still represent a large health and financial burden for the patient and society as a whole, it is crucial to investigate potential risk factors and develop novel approaches in order to fully prevent this category of disorders.

Response of platelets to silver nanoparticles designed with different surface functionalization

Despite increasing use of silver nanoparticles (AgNPs) in different medicinal products, knowledge about their effects on hemostasis and platelets functionality is still scarce. Published scientific reports provide neither data on oxidative stress response of platelets to AgNPs nor information about the effects of AgNPs physicochemical properties on functionality and activation of platelets. This study aimed to explore the role of AgNPs surface functionalization on cell viability, particle uptake, oxidative stress response, and activation of platelets. Small sized, spherical AgNPs were surface functionalized by negatively charged sodium bis(2-ethylhexyl) sulphosuccinate (AOT), neutral polymer polyvinylpyrrolidone (PVP), positively charged polymer poly-l-lysine (PLL) and bovine serum albumin (BSA). Platelet viability, activation and particle uptake were evaluated by flow cytometry. Oxidative stress response was evaluated by measuring the levels of intracellular glutathione (GSH), peroxy and superoxide radicals using assays based on fluorescence dies. Cytotoxicity and uptake of AgNPs to platelets were found to be dose-dependent in a following order PLL-AgNP >> > BSA-AgNP > AOT-AgNP > PVP-AgNP. Particle internalization was further confirmed by transmission electron microscopy. Treatment of platelets with AgNPs induced superoxide radical formation, depletion of GSH and hyperpolarization of the mitochondrial membrane. Small, but statistically significant increase of P-selectin expression in cells treated with all AgNPs compared to non-treated controls evidenced AgNPs-induced activation of platelets. Increased PAC-1 expression was found only in platelets treated with PLL-AgNPs. Obtained results demonstrate that different surface decoration of AgNPs determines their biological effects on platelets highlighting the importance of careful design of AgNPs-based medicinal products regarding their biocompatibility and functionality.

Sex-related response in mice after sub-acute intraperitoneal exposure to silver nanoparticles

Silver nanoparticles (AgNPs) are among the most commercialized nanomaterials in biomedicine due to their antimicrobial and anti-inflammatory properties. Nevertheless, possible health hazards of exposure to AgNPs are yet to be understood and therefore raise public concern in regards of their safety. In this study, sex-related differences, role of steroidal hormones and influence of two different surface stabilizing agents (polymer vs. protein) on distribution and adverse effects of AgNPs were investigated in vivo. Intact and gonadectomised male and female mice were treated with seven AgNPs doses administered intraperitoneally during 21 days. After treatment, steroid hormone levels in serum, accumulation of Ag levels and oxidative stress biomarkers in liver, kidneys, brain and lungs were determined. Sex-related differences were observed in almost all tissues. Concentration of Ag was significantly higher in the liver of females compared to males. No significant difference was found for AgNP accumulation in lungs between females and males, while the lungs of intact males showed significantly higher Ag accumulation compared to gonadectomised group. Effect of surface coating was also observed, as Ag accumulation was significantly higher in kidneys and liver of intact females, as well as in kidneys and brain of intact males treated with protein-coated AgNPs compared to polymeric AgNPs. Oxidative stress response to AgNPs was the most pronounced in kidneys where protein-coated AgNPs induced stronger effects compared to polymeric AgNPs. Interestingly, protein-coated AgNPs reduced generation of reactive oxygen species in brains of females and gonadectomised males. Although there were no significant differences in levels of hormones in the AgNP-exposed animals compared to controls, sex-related differences in oxidative stress parameters were observed in all organs. Results of this study highlight the importance of including the sex-related differences and effects of protein corona in biosafety evaluation of AgNPs exposure.

The key role of autophagy in silver nanoparticle-induced BV2 cells inflammation and polarization

As the release of silver nanoparticles (AgNPs) in the environment continues to increase, great concerns have been raised about their potential toxicity to humans. It is urgent to assess the possible toxicity of AgNPs to the immune cells of the central nervous system due to the continuous accumulation of AgNPs in the brain. This study aimed to evaluate the neurotoxicity of AgNPs and the regulatory mechanism of autophagy in AgNPs-induced inflammation by using mouse microglia BV2 cell lines. AgNPs decreased the microglia cell activity in a concentration and time-dependent manner. The exposure of BV2 cells to AgNPs at a non-cytotoxic level of 5 μg/mL resulted in increase of pro-inflammatory cytokines and decrease of mRNA expression of anti-inflammatory cytokines. AgNPs exposure increased M1 markers of iNOS expression and decreased the expression of M2 markers of CD206 in a time-dependent manner. Meanwhile, the expression of inflammatory proteins IL-1β and NF-κB increased significantly. Additionally, AgNPs induced an increase in autophagosome and upregulation of LC3II, Beclin1, and p62 expression levels. Pretreatment by an autophagy inhibitor, 3-Methyladenine, caused more AgNPs-treated microglia to polarized into pro-inflammatory phenotypes. Inhibition of autophagy also increased the expression of inflammation-associated mRNA and proteins in BV2 cells. These results indicated that AgNPs could induce pro-inflammatory phenotypic polarization of microglia and the autophagy could play a key regulatory role in the pro-inflammatory phenotypic polarization of microglia induced by AgNPs.

The Toxic Effect of Silver Nanoparticles on Nerve Cells: A Systematic Review and Meta-Analysis

Despite the increasing use of silver nanoparticles in medical sciences, published studies on their interaction with nerve cells and evaluation of risks are dispersed. This systematic review and meta-analysis could be used to devise safety guidelines for the use of silver nanoparticles in industry and medicine to reduce adverse effects on the CNS.After extensive searches, the full text of 30 related studies was reviewed and data mining completed. Data were analyzed by calculating the mean of different ratios between treated and untreated groups. Linear regression between variables was evaluated by meta-regression. Subgroup analysis was also performed due to heterogeneity.Treatment with silver nanoparticles significantly reduced cell viability (SMD = -1.79%; 95% CI: -2.17 to -1.40; p < 0.0001). Concentration > 0.1 μg/mL could kill neurons, while lower concentration would not (SMD -0.258; 95% CI: -0.821 to 0.305; p = 369). In addition to the concentration, the coating, size of the nanoparticles, and cell type are also factors that influence SNP nerve cell toxicity. Measurement of apoptosis (SMD = 2.21; 95% CI: 1.62 to 2.80; p=0.001) and lactate dehydrogenase release rate (SMD = 0.9; 95% CI: 0.33 to 1.47; p < 0.0001) also confirmed the destructive effect of silver nanoparticles on nerve cells.

An Updated Review on Silver Nanoparticles in Biomedicine

Silver nanoparticles (AgNPs) represent one of the most explored categories of nanomaterials for new and improved biomaterials and biotechnologies, with impressive use in the pharmaceutical and cosmetic industry, anti-infective therapy and wound care, food and the textile industry. Their extensive and versatile applicability relies on the genuine and easy-tunable properties of nanosilver, including remarkable physicochemical behavior, exceptional antimicrobial efficiency, anti-inflammatory action and antitumor activity. Besides commercially available and clinically safe AgNPs-based products, a substantial number of recent studies assessed the applicability of nanosilver as therapeutic agents in augmented and alternative strategies for cancer therapy, sensing and diagnosis platforms, restorative and regenerative biomaterials. Given the beneficial interactions of AgNPs with living structures and their nontoxic effects on healthy human cells, they represent an accurate candidate for various biomedical products. In the present review, the most important and recent applications of AgNPs in biomedical products and biomedicine are considered.

Impact of surface functionalization on the toxicity and antimicrobial effects of selenium nanoparticles considering different routes of entry

Selenium nanoparticles (SeNPs) were first designed as nutritional supplements, but they are attractive also for use in diagnostic and therapeutic systems owing to their biocompatibility and protective effects. This study aimed to examine if different SeNPs stabilization strategies affect their (i) antimicrobial activity against bacteria Escherichia coli and Staphylococcus aureus and yeast Saccharomyces cerevisiae and (ii) toxicity to human cells of different biological barriers i.e., skin, oral and intestinal mucosa. For surface stabilization, polyvinylpyrrolidone (PVP), poly-L-lysine (PLL) and polyacrylic acid (PAA) were used rendering neutral, positively and negatively charged SeNPs, respectively. The SeNPs (primary size ~80 nm) showed toxic effects in human cells in vitro and in bacteria S. aureus, but not in E. coli and yeast S. cerevisiae. Toxicity of SeNPs (24 h IC₅₀) ranged from 1.4 to >100 mg Se/L, depending on surface functionalization (PLL > PAA > PVP) and was not caused by ionic Se. At subtoxic concentrations, all SeNPs were taken up by all human cell types, induced oxidative stress response and demonstrated genotoxicity. As the safety profile of SeNPs was dependent not only on target cells (mammalian cells, bacteria, yeast), but also on surface functionalization, these aspects should be considered during development of novel SeNPs-based biomedical products.