Amorphous silica nanoparticles size-dependently aggravate atopic dermatitis-like skin lesions following an intradermal injection.

BACKGROUND: Due to the rising use of nanomaterials (NMs), there is concern that NMs induce undesirable biological effects because of their unique physicochemical properties. Recently, we reported that amorphous silica nanoparticles (nSPs), which are one of the most widely used NMs, can penetrate the skin barrier and induce various biological effects, including an immune-modulating effect. Thus, it should be clarified whether nSPs can be a risk factor for the aggravation of skin immune diseases. Thus, in this study, we investigated the relationship between the size of SPs and adjuvant activity using a model for atopic dermatitis. RESULTS: We investigated the effects of nSPs on the AD induced by intradermaly injected-mite antigen Dermatophagoides pteronyssinus (Dp) in NC/Nga mice. Ear thickness measurements and histopathological analysis revealed that a combined injection of amorphous silica particles (SPs) and Dp induced aggravation of AD in an SP size-dependent manner compared to that of Dp alone. In particular, aggravation was observed remarkably in nSP-injected groups. Furthermore, these effects were correlated with the excessive induction of total IgE and a stronger systemic Th2 response. We demonstrated that these results are associated with the induction of IL-18 and thymic stromal lymphopoietin (TSLP) in the skin lesions. CONCLUSIONS: A particle size reduction in silica particles enhanced IL-18 and TSLP production, which leads to systemic Th2 response and aggravation of AD-like skin lesions as induced by Dp antigen treatment. We believe that appropriate regulation of nanoparticle physicochemical properties, including sizes, is a critical determinant for the design of safer forms of NMs.

Amorphous nanosilicas induce consumptive coagulopathy after systemic exposure.

We previously reported that well-dispersed amorphous nanosilicas with particle size 70 nm (nSP70) penetrate skin and produce systemic exposure after topical application. These findings underscore the need to examine biological effects after systemic exposure to nanosilicas. The present study was designed to examine the biological effects. BALB/c mice were intravenously injected with amorphous nanosilicas of sizes 70, 100, 300, 1000 nm and then assessed for survival, blood biochemistry, and coagulation. As a result, injection of nSP70 caused fatal toxicity, liver damage, and platelet depletion, suggesting that nSP70 caused consumptive coagulopathy. Additionally, nSP70 exerts procoagulant activity in vitro associated with an increase in specific surface area, which increases as diameter reduces. In contrast, nSP70-mediated procoagulant activity was absent in factor XII-deficient plasma. Collectively, we revealed that interaction between nSP70 and intrinsic coagulation factors such as factor XII, were deeply related to nSP70-induced harmful effects. In other words, it is suggested that if interaction between nSP70 and coagulation factors can be suppressed, nSP70-induced harmful effects may be avoided. These results would provide useful information for ensuring the safety of nanomaterials (NMs) and open new frontiers in biological fields by the use of NMs.

Effect of amorphous silica nanoparticles on in vitro RANKL-induced osteoclast differentiation in murine macrophages.

Amorphous silica nanoparticles (nSP) have been used as a polishing agent and/or as a remineralization promoter for teeth in the oral care field. The present study investigates the effects of nSP on osteoclast differentiation and the relationship between particle size and these effects. Our results revealed that nSP exerted higher cytotoxicity in macrophage cells compared with submicron-sized silica particles. However, tartrate-resistant acid phosphatase (TRAP) activity and the number of osteoclast cells (TRAP-positive multinucleated cells) were not changed by nSP treatment in the presence of receptor activator of nuclear factor κB ligand (RANKL) at doses that did not induce cytotoxicity by silica particles. These results indicated that nSP did not cause differentiation of osteoclasts. Collectively, the results suggested that nanosilica exerts no effect on RANKL-induced osteoclast differentiation of RAW264.7 cells, although a detailed mechanistic examination of the nSP70-mediated cytotoxic effect is needed.

Effect of surface properties of silica nanoparticles on their cytotoxicity and cellular distribution in murine macrophages.

Surface properties are often hypothesized to be important factors in the development of safer forms of nanomaterials (NMs). However, the results obtained from studying the cellular responses to NMs are often contradictory. Hence, the aim of this study was to investigate the relationship between the surface properties of silica nanoparticles and their cytotoxicity against a murine macrophage cell line (RAW264.7). The surface of the silica nanoparticles was either unmodified (nSP70) or modified with amine (nSP70-N) or carboxyl groups (nSP70-C). First, the properties of the silica nanoparticles were characterized. RAW264.7 cells were then exposed to nSP70, nSP70-N, or nSP70-C, and any cytotoxic effects were monitored by analyzing DNA synthesis. The results of this study show that nSP70-N and nSP70-C have a smaller effect on DNA synthesis activity by comparison to unmodified nSP70. Analysis of the intracellular localization of the silica nanoparticles revealed that nSP70 had penetrated into the nucleus, whereas nSP70-N and nSP70-C showed no nuclear localization. These results suggest that intracellular localization is a critical factor underlying the cytotoxicity of these silica nanoparticles. Thus, the surface properties of silica nanoparticles play an important role in determining their safety. Our results suggest that optimization of the surface characteristics of silica nanoparticles will contribute to the development of safer forms of NMs.

Tumor necrosis factor-alpha-nuclear factor-kappa B-signaling enhances St2b2 expression during 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperplasia.

The mouse cholesterol sulfotransferase St2b2 contributes to epidermal differentiation by biosynthesizing cholesterol sulfate (CS) from cholesterol in the epidermis. 12-O-Tetradecanoylphorbol-13-acetate (TPA) causes epidermal hyperplasia, an abnormal increase in epidermal cell numbers resulting from aberrant cell differentiation and an increase in St2b2 protein levels. The mechanisms underlying enhanced St2b2 expression and the pathophysiologic significance of the increased expression are unclear, however. To verify whether increased St2b2 levels are necessary for TPA-induced epidermal hyperplasia, the effects of St2b2-specific small hairpin RNA (St2b2-shRNA) on hyperplasia were examined in mice. St2b2-shRNA clearly suppressed TPA-induced epidermal hyperplasia and the expression of a marker of epidermal differentiation, involucrin (INV). Interestingly, treating mouse epidermal cells with tumor necrosis factor-alpha (TNFα) increased St2b2 expression. Furthermore, treatment with TNFα-siRNA or anti-TNF receptor antibodies reduced the TPA-induced enhancement of St2b2 expression. Treatment with BAY 11-7082, a specific inhibitor of nuclear factor-kappa B (NF-κB), diminished TPA-induced St2b2 expression. These results suggested that enhancement of St2b2 expression by TPA treatment occurs mainly through the TNFα-NF-κB inflammatory signaling pathway, which in turn leads to increased CS concentrations in epidermal cells and hyperplasia.

Systemic distribution, nuclear entry and cytotoxicity of amorphous nanosilica following topical application.

Currently, nanomaterials (NMs) with particle sizes below 100 nm have been successfully employed in various industrial applications in medicine, cosmetics and foods. On the other hand, NMs can also be problematic in terms of eliciting a toxicological effect by their small size. However, biological and/or cellular responses to NMs are often inconsistent and even contradictory. In addition, relationships among NMs physicochemical properties, absorbency, localization and biological responses are not yet well understood. In order to open new frontiers in medical, cosmetics and foods fields by the safer NMs, it is necessary to collect the information of the detailed properties of NMs and then, build the prediction system of NMs safety. The present study was designed to examine the skin penetration, cellular localization, and cytotoxic effects of the well-dispersed amorphous silica particles of diameters ranging from 70 nm to 1000 nm. Our results suggested that the well-dispersed amorphous nanosilica of particle size 70 nm (nSP70) penetrated the skin barrier and caused systemic exposure in mouse, and induced mutagenic activity in vitro. Our information indicated that further studies of relation between physicochemical properties and biological responses are needed for the development and the safer form of NMs.

Amorphous nanosilica induce endocytosis-dependent ROS generation and DNA damage in human keratinocytes.

BACKGROUND: Clarifying the physicochemical properties of nanomaterials is crucial for hazard assessment and the safe application of these substances. With this in mind, we analyzed the relationship between particle size and the in vitro effect of amorphous nanosilica (nSP). Specifically, we evaluated the relationship between particle size of nSP and the in vitro biological effects using human keratinocyte cells (HaCaT). RESULTS: Our results indicate that exposure to nSP of 70 nm diameter (nSP70) induced an elevated level of reactive oxygen species (ROS), leading to DNA damage. A markedly reduced response was observed using submicron-sized silica particles of 300 and 1000 nm diameter. In addition, cytochalasin D-treatment reduced nSP70-mediated ROS generation and DNA damage, suggesting that endocytosis is involved in nSP70-mediated cellular effects. CONCLUSIONS: Thus, particle size affects amorphous silica-induced ROS generation and DNA damage of HaCaT cells. We believe clarification of the endocytosis pathway of nSP will provide useful information for hazard assessment as well as the design of safer forms of nSPs.

Chenodeoxycholic acid-mediated activation of the farnesoid X receptor negatively regulates hydroxysteroid sulfotransferase.

Hydroxysteroid sulfotransferase catalyzing bile acid sulfation plays an essential role in protection against lithocholic acid (LCA)-induced liver toxicity. Hepatic levels of Sult2a is up to 8-fold higher in farnesoid X receptor-null mice than in the wild-type mice. Thus, the influence of FXR ligand (chenodeoxycholic acid (CDCA) and LCA) feeding on hepatic Sult2a expression was examined in FXR-null and wild-type mice. Hepatic Sult2a protein content was elevated in FXR-null and wild-type mice fed a LCA (1% and 0.5%) diet. Treatment with 0.5% CDCA diet decreased hepatic Sult2a to 20% of the control in wild-type mice, but increased the content in FXR-null mice. Liver Sult2a1 (St2a4) mRNA levels were reduced to 26% in wild-type mice after feeding of a CDCA diet, while no decrease was observed on Sult2a1 mRNA levels in FXR-null mice after CDCA feeding. A significant inverse relationship (r(2)=0.523) was found between hepatic Sult2a protein content and small heterodimer partner (SHP) mRNA level. PCN-mediated increase in Sult2a protein levels were attenuated by CDCA feeding in wild-type mice, but not in FXR-null mice. Human SULT2A1 protein and mRNA levels were decreased in HepG2 cells treated with the FXR agonists, CDCA or GW4064 in dose-dependent manners, although SHP mRNA levels were increased. These results suggest that SULT2A is negatively regulated through CDCA-mediated FXR activation in mice and humans.