Neurotoxicity of Silver Nanoparticles in Rat Brain After Intragastric Exposure.

It is known that the biological half-life of silver in the central nervous system is longer than in other organs. However, the potential toxicity of silver nanoparticles (NPs) on brain tissue and the underlying mechanism(s) of action are not well understood. In this study, neurotoxicity of silver NPs was examined in rat after intragastric administration. After a two-week exposure to low-dose (1 mg/kg, body weight) or high-dose (10 mg/kg) silver NPs, the pathological and ultrastructural changes in brain tissue were evaluated with H&E staining and transmission electron microscopy. The mRNA expression levels of key tight junction proteins of the blood-brain barrier (BBB) were analyzed by real-time RT-PCR, and several inflammatory factors were assessed in blood using ELISA assay. We observed neuron shrinkage, cytoplasmic or foot swelling of astrocytes, and extra-vascular lymphocytes in silver NP exposure groups. The cadherin 1 (2(-ΔΔCt): 1.45-fold/control) and Claudin-1 (2(-ΔΔCt): 2.77-fold/control) were slightly increase in mRNA expression levels, and IL-4 significantly increased after silver NP exposure. It was suggest that silver NP can induce neuronal degeneration and astrocyte swelling, even with a low-dose (1 mg/kg) oral exposure. One potential mechanism for the effects of silver NPs to the nervous cells is involved in inflammatory effects.

Toxic responses in rat embryonic cells to silver nanoparticles and released silver ions as analyzed via gene expression profiles and transmission electron microscopy.

After exposing rat embryonic cells to 20 µg/mL of silver nanoparticle (NP) suspension and their released ions for different time periods, silver nanoparticles were found in cellular nuclei, mitochondria, cytoplasm and lysosomes by transmission electron microscopy (TEM). We also observed mitochondrial destruction, distension of endoplasmic reticulum and apoptotic bodies. Global gene expression analysis showed a total of 279 genes that were up-regulated and 389 genes that were down-regulated in the silver-NP suspension exposure group, while 3 genes were up-regulated and 41 genes were down-regulated in the silver ion exposure group. Further, the GO pathway analysis suggested that these differentially expressed genes are involved in several biological processes, such as energy metabolism, oxygen transport, enzyme activities, molecular binding, etc. It is possible that inhibition of oxygen transport is mediated by the significant down-regulation of genes of the globin family, which might play an important role in silver ion-induced toxicity. KEGG pathway analysis showed that there were 23 signal pathways that were affected in the cells after exposure to silver-NP suspension, but not silver ion alone. The most significant change concerned inflammatory signal pathways, which were only found in silver-NP suspension exposed cells, indicating that inflammatory response might play an important role in the mechanism(s) of silver-NP-induced toxicity. The significant up-regulation of matrix metalloproteinases 3 and 9 suggests that silver NPs could induce extracellular matrix degradation via an inflammatory signaling pathway. The significant up-regulation of secretory leukocyte peptidase inhibitor and serine protease inhibitor 2c was considered to be an embryonic cellular defense mechanism in response to silver-NP-induced inflammation.

Genotoxicity and molecular response of silver nanoparticle (NP)-based hydrogel.

BACKGROUND: Since silver-nanoparticles (NPs) possess an antibacterial activity, they were commonly used in medical products and devices, food storage materials, cosmetics, various health care products, and industrial products. Various silver-NP based medical devices are available for clinical uses, such as silver-NP based dressing and silver-NP based hydrogel (silver-NP-hydrogel) for medical applications. Although the previous data have suggested silver-NPs induced toxicity in vivo and in vitro, there is lack information about the mechanisms of biological response and potential toxicity of silver-NP-hydrogel. METHODS: In this study, the genotoxicity of silver-NP-hydrogel was assayed using cytokinesis-block micronucleus (CBMN). The molecular response was studied using DNA microarray and GO pathway analysis. RESULTS AND DISCUSSION: The results of global gene expression analysis in HeLa cells showed that thousands of genes were up- or down-regulated at 48 h of silver-NP-hydrogel exposure. Further GO pathway analysis suggested that fourteen theoretical activating signaling pathways were attributed to up-regulated genes; and three signal pathways were attributed to down-regulated genes. It was discussed that the cells protect themselves against silver NP-mediated toxicity through up-regulating metallothionein genes and anti-oxidative stress genes. The changes in DNA damage, apoptosis and mitosis pathway were closely related to silver-NP-induced cytotoxicity and chromosome damage. The down-regulation of CDC14A via mitosis pathway might play a role in potential genotoxicity induced by silver-NPs. CONCLUSIONS: The silver-NP-hydrogel induced micronuclei formation in cellular level and broad spectrum molecular responses in gene expression level. The results of signal pathway analysis suggested that the balances between anti-ROS response and DNA damage, chromosome instability, mitosis inhibition might play important roles in silver-NP induced toxicity. The inflammatory factors were likely involved in silver-NP-hydrogel complex-induced toxic effects via JAK-STAT signal transduction pathway and immune response pathway. These biological responses eventually decide the future of the cells, survival or apoptosis.

Calcium upregulated survivin expression and associated osteogenesis of normal human osteoblasts.

Survivin is an antiapoptotic protein expressed in all phases of the normal cell cycle but is at its highest level during the G2/M interphase. This protein has been recently identified in normal human osteoblasts and has raised questions about the regulation of its expression. This study intends to verify if survivin expression could be manipulated by external factors such as calcium ions. Normal human alveolar bone explants recovered from six healthy donors were cultured to 2nd passage. Cells were cultured with essential medium as a control and with medium containing supplemental calcium ions at a concentration of 30 parts per million as a study group. Vitamin D(3) was added to all culture groups at the 5th and 18th days to promote differentiation. Differentiation markers were confirmed by performing mineralization, alkaline phosphatase (ALP), and osteocalcin assays at 7 and 21 days. Cell attachment was measured at 16 h and used as a reference for cell proliferation at 7 days and 21 days. Survivin levels were measured at 16 h, 7 and 21 days. Compared with the control group, the study group presented a significant increase of survivin expression at 16 h (p < 0.01), at 7 days (p < 0.01), and at 21 days (p < 0.05), a significant increase of cell proliferation, ALP activity and mineralization at 7 days (p < 0.05) and 21 days (p < 0.05), and a significant increase in osteocalcin expression only at 21 days (p < 0.01). This study demonstrated that survivin expression could be significantly upregulated by calcium-enhanced normal human osteoblast cultures, which might correlate to subsequent upregulation of cell proliferation and differentiation.

Microbial profile on metallic and ceramic bracket materials.

The placement of orthodontic appliances creates a favorable environment for the accumulation of a microbiota and food residues, which, in time, may cause caries or exacerbate any pre-existing periodontal disease. The purpose of the present study was to compare the total bacterial counts present on metallic and ceramic orthodontic brackets in order to clarify which bracket type has a higher plaque retaining capacity and to determine the levels of Streptococcus mutans and Lactobacillus spp on both types of brackets. Thirty-two metallic brackets and 24 ceramic brackets were collected from orthodontic patients at the day of debonding. Two brackets were collected from each patient; one from a maxillary central incisor and another from a maxillary second premolar. Sixteen patients who used metallic brackets and 12 patients who used ceramic brackets were sampled. Bacterial populations were studied using "checkerboard" DNA-DNA hybridization, which uses DNA probes to identify species in complex microbial samples. The significance of differences between groups was determined using the Mann-Whitney U-test. Results showed no significant differences between metallic and ceramic brackets with respect to the caries-inducing S mutans and L acidophilus spp counts. Mean counts of 8 of 35 additional species differed significantly between metallic and ceramic brackets with no obvious pattern favoring one bracket type over the other. This study showed higher mean counts of Treponema denticola, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum ss vincentii, Streptococcus anginosus, and Eubacterium nodatum on metallic brackets while higher counts of Eikenella corrodens, Campylobacter showae, and Selenomonas noxia were found on ceramic brackets.