Biocompatibility and antibacterial activity of nitrogen-doped titanium dioxide nanoparticles for use in dental resin formulations.

The addition of antibacterial functionality to dental resins presents an opportunity to extend their useful lifetime by reducing secondary caries caused by bacterial recolonization. In this study, the potential efficacy of nitrogen-doped titanium dioxide nanoparticles for this purpose was determined. Nitrogen doping was carried out to extend the ultraviolet absorbance into longer wavelength blue light for increased biocompatibility. Titanium dioxide nanoparticles (approximately 20-30 nm) were synthesized with and without nitrogen doping using a sol-gel method. Ultraviolet-Visible spectroscopy indicated a band of trap states, with increasing blue light absorbance as the concentration of the nitrogen dopant increased. Electron paramagnetic resonance measurements indicated the formation of superoxide and hydroxyl radicals upon particle exposure to visible light and oxygen. The particles were significantly toxic to Escherichia coli in a dose-dependent manner after a 1-hour exposure to a blue light source (480 nm). Intracellular reactive oxygen species assay demonstrated that the particles caused a stress response in human gingival epithelial cells when exposed to 1 hour of blue light, though this did not result in detectable release of cytokines. No decrease in cell viability was observed by water-soluble tetrazolium dye assay. The results show that nitrogen-doped titanium dioxide nanoparticles have antibacterial activity when exposed to blue light, and are biocompatible at these concentrations.

Oxidative stress-mediated inhibition of intestinal epithelial cell proliferation by silver nanoparticles.

Given the increasing use of silver nanoparticles (Ag NP) by the food and food packaging industries, this study investigated potential consequences of Ag NP ingestion in intestinal epithelial C2BBe1 cells. Treatment of proliferating cells (<10,000 cells/cm(2)) with 0.25 µg/cm(2) (1.25 µg/mL) of 23 nm Ag NP for 24 h induced 15% necrotic cell death and an 80% reduction in metabolic activity and decreased the GSH/GSSG ratio, indicating oxidative stress. G2/M phase cell cycle arrest and complete inhibition of cell proliferation was also induced by Ag NP treatment. Simulated in vitro digestion of Ag NP prior to cell exposure required the use of slightly higher doses to induce the same toxicity, likely due to slower Ag dissolution. Treatment of cells with silica, titania, and ZnO NP partially inhibited cell proliferation, but inhibition at low doses was unique to Ag NP. These data suggest that Ag NP induces oxidative stress, cell cycle arrest, and the inhibition of cell proliferation. However, toxicity and induction of oxidative stress were not observed in confluent cells (>100,000 cells/cm(2)) treated with 10 µg/cm(2) (40-50 µg/mL) Ag NP, indicating that these cells are less sensitive to Ag NP.

Uptake of bright fluorophore core-silica shell nanoparticles by biological systems.

Nanoparticles are used in a variety of consumer applications. Silica nanoparticles in particular are common, including as a component of foods. There are concerns that ingested nano-silica particles can cross the intestinal epithelium, enter the circulation, and accumulate in tissues and organs. Thus, tracking these particles is of interest, and fluorescence spectroscopic methods are well-suited for this purpose. However, nanosilica is not fluorescent. In this article, we focus on core-silica shell nanoparticles, using fluorescent Rhodamine 6G, Rhodamine 800, or CdSe/CdS/ZnS quantum dots as the core. These stable fluorophore/silica nanoparticles had surface characteristics similar to those of commercial silica particles. Thus, they were used as model particles to examine internalization by cultured cells, including an epithelial cell line relevant to the gastrointestinal tract. Finally, these particles were administered to mice by gavage, and their presence in various organs, including stomach, small intestine, cecum, colon, kidney, lung, brain, and spleen, was examined. By combining confocal fluorescence microscopy with inductively coupled plasma mass spectrometry, the presence of nanoparticles, rather than their dissolved form, was established in liver tissues.

Minimal intestinal epithelial cell toxicity in response to short- and long-term food-relevant inorganic nanoparticle exposure.

Toxicity of commercial nanoparticles of titania, silica, and zinc oxides is being investigated in this in vitro study. Particles of these compositions are found in many food items, and thus this study is directed toward particle behavior in simulated digestion media and their interaction with intestinal epithelial cell line C2BBe1, a clone of Caco-2 cells, originally isolated from a human colon cancer. Even though the primary particle size of all three particles was below 50 nm, the particles appeared as aggregates in culture media with a negatively charged surface. In the presence of pepsin (pH 2), the charge on the titania became positive, and silica was almost neutral and aggregated extensively, whereas ZnO dissolved. For silica and titania, treatment with simulated intestinal digestive solution led to a strongly negatively charged surface and particle sizes approaching values similar to those in media. On the basis of infrared spectroscopy, we concluded that the surface of silica and titania was covered with bile salts/proteins after this treatment. Transmission electron microscopy indicated that the C2BBe1 cells internalized all three particles. Toxicity assays included investigation of necrosis, apoptosis, membrane damage, and mitochondrial activity. Titania and SiO2 particles suspended in media at loading levels of 10 µg/cm² exhibited no toxicity. With ZnO at the same loading level, mild toxicity was observed based only on the LDH assay and decrease of mitochondrial activity and not necrosis or apoptosis. Titania particles exposed to the simulated digestion media exhibited mild toxicity based on decrease of mitochondrial activity, likely due to transport of toxic bile salts via adsorption on the particle surface.

Contrast of the biological activity of negatively and positively charged microwave synthesized CdSe/ZnS quantum dots.

Quantum dots (QDs) are semiconductor nanocrystals that have found use in bioimaging, cell tracking, and drug delivery. This article compares the cytotoxicity and cellular interactions of positively and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method using a murine alveolar macrophage-like cell culture model. Keeping the core semiconductor the same, QD charge was varied by altering the surface capping molecule; negatively charged QDs were formed with mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine (THIO-QDs). The size and charge of these two QDs were investigated in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media) relevant for the biological studies. MPA-QDs were found to have negative zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62 nm in size, while large aggregates (greater than 1000 nm) formed when these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs retained positive zeta potential in RPMI and were found to have a negative zeta potential in RPMI + FBS and nearly neutral zeta potential in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs caused comparable levels of apoptosis and necrosis. Both QDs induced significant tumor necrosis factor-alpha (TNF-α) secretion only at high concentrations (>250 nM). Both types of QDs were internalized via clathrin-dependent endocytosis. Using real-time, live cell imaging, we found that MPA-QDs interact with the cell surface within minutes and progress through the endocytic pathway to the lysosomes upon internalization. With the THIO-QDs, the internalization process was slower, but the pathways could not be mapped because of spectroscopic interference caused by QD aggregates. Finally, MPA-QDs were found to associate with cell surface scavenger receptors, while the THIO-QDs did not. This study indicates that the surface charge and aggregation characteristics of QDs change drastically in biological culture conditions and, in turn, influence nanoparticle and cellular interactions.