# Does Nanosilver Have a Pronounced Toxic Effect on Humans?
## 2 Results of Investigations Performed by Other Researchers  
### General Toxicity of AgNPsPs for Cells, Tissues, and Organs  
According to numerous publications, the main mechanism of the cellular and molecular toxicity of AgNPs is oxidative stress [10,11]. Thus, 20 nm spherical AgNPs reduced mRNA levels of sodium dismutase 1 and glutathione reductase in male Wistar rats [9]. In the presence of AgNPs, the formation of reactive oxygen species [10], the level of gene expression and the content of antioxidant proteins decrease, and DNA damage [11] increases. The prolonged exposure of adult rats to citrate-stabilized silver NPs at a low dose of 0.2 mg/kg resulted in a decrease in the level of expression of structural proteins, in particular, myelin in myelin sheath cells. AgNPs were also found to increase the body weight and body temperature of animals [12]. The level of developmental regulators (for example, neuronal) also decreases; however, the levels of expression of apoptosis regulators increase; therefore, ultimately, the cell often undergoes apoptosis. At the tissue level, inflammation, swelling, and, as an extreme outcome, necrosis, can develop [13]. In zebrafish, AgNPs caused a decrease in brain and muscle acetylcholinesteraseactive activity, as well as in liver and gill catalase activity. Contact with AgNPs also led to morphological changes such as the fusion of secondary lamellae, curvature, dilated marginal channel, and epithelial lifting [14]. The administration of male CD-1 mice with AgNPs of 10 nm size, compared with NPs with a size of 40 and 100 nm, resulted in overt hepatobiliary toxicity [15]. Some reports indicate that AgNPs are genotoxic and mutagenic, and the degree of their impact directly depends on the dose of NPs and inversely depends on their size [16, 17, 18]. After exposure of BEAS-2B cells to AgNPs of different primary particle sizes (10, 40, and 75 nm), a cytotoxic effect was observed only at a particle size of 10 nm [19]. The same finding was reported in [20]. Coating agents used to stabilize NPs in a solution can also affect general toxicity, including genotoxicity. For example, AgNPs coated with citrate had more noticeable toxic effects on L5718Y cells than those coated with polyvinylpyrrolidone [21]. The study by [PERSON] et al. [15] showed that the coating of NPs had no relevant impact on animals. Citrate-coated silver nanopowder was toxic to human skin HaCaT keratinocyte cells, whereas polyvinylpyrrolidone-coated silver nanoprism or nanoparticle powder did not exhibit any toxic effect [22]. In a study by [PERSON] et al. [19], the coating-dependent difference in the cytotoxicity of AgNPs was not detected. [PERSON] and al. [23] demonstrated a direct correlation between the toxicity of AgNPs and their surface charge. Thus, negatively charged citrate-coated AgNPs were less toxic to microorganisms than positively charged branched polyethyleneenimine-coated AgNPs. The low toxicity of citrate-coated AgNPs was observed in comparison with polyvinylpyrrolidone- and gum arabic-coated AgNPs [24]. It should be noted that the results of evaluating the mutagenicity of AgNPs may also depend on the chosen object of study; for example, [PERSON] et al. [25] did not find chromosomal abnormalities in plant cells after exposure to AgNPs. Studying the effect of AgNPs on freshwater invertebrates with different life strategies--namely, _Hydra vulgaris, Daphnia carinata_, and _Paratya austriensis_--the authors described _Daphnia carinata_ as the most sensitive species, followed by _Paratya austriensis_ and _Hydra vulgaris_[26]. Toxic effects of AgNPs on different organisms in the study by [PERSON] et al. [20] varied by about two orders of magnitude, with the lowest observed for crustaceans and algae and the highest for mammalian cells. The results of studies of the effects of NPs on the reproductive function and development of animal organisms are also ambiguous and often contradictory.