Titanium dioxide nanoparticles oral exposure induce osteoblast apoptosis, inhibit osteogenic ability and increase lipogenesis in mouse

Titanium dioxide nanoparticles (TiO2-NPs) are widely used in food, paint, coating, cosmetic, and composite orthodontic material. As a common food additive, TiO2-NPs can accumulate in various organs of human body, but the effect and underlying mechanism of bone remain unclear. Here mice were exposed to TiO2-NPs by oral gavage, and histological staining of femoral sections showed that TiO2-NPs reduced bone formation and enhanced osteoclast activity and lipogenesis, contributing to decreased trabecula bone. Transmission electron microscope (TEM) as well as biochemical and flow cytometry analysis of osteoblast exhibited that TiO2-NPs accumulated in osteoblast cytoplasm and impaired mitochondria ultrastructure with increased reactive oxygen species (ROS) and lipid hyperoxide, resulting in osteoblast apoptosis. In terms of mechanism, TiO2-NPs treatment inhibited expression of AKT and then increased pro-apoptotic protein Bax expression which was failure to form heterodimers with decreased anti-apoptotic Bcl-2, activating downstream Caspase-9 and Caspase-3 and inducing apoptosis. Additionally, TiO2-NPs suppressed Wnt3a level and then activated anti-Glycogen synthesis kinase (GSK-3β) phosphorylation, and ultimately resulted in degradation of β-catenin which down-regulated Runt-related transcription factor 2 (Runx2) and Osterix, inhibiting expression of osteogenic related proteins. Together, these results revealed that exposure of TiO2-NPs induced apoptosis and inhibited osteoblast differentiation through suppressing PI3K/AKT and Wnt/β-catenin signaling pathways, resulting in reduction of trabecula bone.

Study on the hematological toxicity of Cyprinus carpio exposed to water-soluble fraction of crude oil and TiO2 nanoparticles in the dark and ultraviolet

This study is addressing the potential toxicity concerns of crude oil in common carp (Cyprinus carpio) with the novel use of TiO2-NP for enhancing photocatalytic degradation of WSF of crude oil prepared under UV light or darkness. Blood samples were taken, and the biochemical parameters were analyzed. The levels of ALT, AST and ALP were significantly higher in fish exposed to UV-treated WSF. However, they were significantly lower in the groups exposed to UV-treated TiO2-NPs and the combination of WSF and TiO2-NPs. The levels of total protein, triglycerides, albumin and cholesterol were significantly lower in treatments exposed to UV-treated and dark-conditioned WSF compared to the control group, but they were significantly higher in fish exposed to UV-treated TiO2-NPs and the combination of WSF and TiO2-NPs compared to fish exposed under dark conditions and were not significantly different from the control group. The toxicity of UV-treated WSF was significantly higher than that of dark-conditioned WSF. The toxicity of TiO2-NPs was lower in the presence of UV and was similar to the control treatment. The results of the study suggests that photocatalytic TiO2-NPs and UV radiation reduce toxicity of the water-soluble fraction of crude oil on common carp.

Titanium dioxide nanoparticles mitigate cadmium toxicity in Coriandrum sativum L. through modulating antioxidant system, stress markers and reducing cadmium uptake

Anthropogenic activities are the foremost reason of metal pollution in soils of the cultivated areas, resulting abnormal physiochemical processes in plants. Among metals contaminants, cadmium (Cd) is one of the most injurious contaminants that deleteriously affect physiological activities, growth and yield of the crop plants. Keeping in view the stress mitigation potential of titanium dioxide (TiO₂), the existing research work was premeditated to inspect the beneficial role of seed priming with titanium dioxide nanoparticles (TiO₂-NPs) on biochemical, morphological and physiological characteristics of Coriandrum sativum L. (coriander) plants under Cd stress. For this purpose, C. sativum seeds were primed with 0, 40, 80 and 160 mg L^-1 TiO₂-NPs. Cadmium stress triggered a significant decrease in chlorophyll a content (49%), chlorophyll b content (44%), photosynthetic rate (62%) and plant growth (51%) as compared with control. Tanium dioxide nanoparticles treated seedlings exhibited reduced Cd contents besides improved agronomic traits (seedlings biomass, number of seeds and yield). The TiO₂-NPs treatment declined the magnitude of EL and MDA by 1.5 fold and 1.71 fold, respectively. Furthermore, TiO₂-NPs diminished oxidative injuries in plants exposed to Cd stress. Additionally, TiO₂-NPs enhanced the biosynthesis of osmatic regulators (proline) by 47% which helped in the mitigation of Cd persuaded toxicity in plants. Briefly, treatment of 80 mg L^-1 TiO₂-NPs perhaps ameliorates the deleterious influence of Cd stress and enhance the yield of coriander.

Effects of TiO2-NPs pretreatment on UV-B stress tolerance in Arabidopsis thaliana

As the ozone hole in the North and South poles continues to increase, the entire ecosystem will face an environmental crisis caused by enhanced UV-B radiation. Considering the function of TiO₂ and the application of nanomaterials in agriculture, the effect of TiO₂-NPs on UV-B stress tolerance in Arabidopsis was investigated. The phenotype of plants was determined, and the expression patterns of antioxidant systems and related genes were analyzed. Modification of the antioxidant system and changes in the flavonoid content of plants were observed by histochemical staining. The effects of TiO₂-NPs and UV-B on mitosis were observed at the cellular level, and the degree of DNA damage was analyzed by the detection of CPDs content. The effects of TiO₂-NPs and UV-B on SOD isozymes were detected by SOD isozyme Native-PAGE electrophoresis. A laser confocal microscope was used to explore the protective mechanism of TiO₂-NPs against UV-B radiation. Results showed that pretreatment of TiO₂-NPs significantly alleviated the stress of UV-B radiation on plants. TiO₂-NPs activated the antioxidant system of plants, improved the activity of antioxidant enzymes, and promoted the synthesis of flavonoids. Moreover, TiO₂-NPs could effectively shield UV-B radiation to prevent the depolymerization of microtubules in plant cells. 10 mg/L of TiO₂-NPs is a safe and effective application dose, which has no biological toxicity to plants. Our research results reported for the first time that pretreatment of TiO₂-NPs could effectively alleviate UV-B stress to plants, providing new ideas for the application of nanomaterials in agriculture.

Physiological and biochemical response of wheat (Triticum aestivum) to TiO2 nanoparticles in phosphorous amended soil: A full life cycle study

Nanoparticles (NPs) application in soil as nano-fertilizers to increase crop yield is getting attention due to their higher efficiency and less environmental risks. This study investigated the interactive effects of variable titanium dioxide nanoparticles (TiO₂-NPs) levels (0, 30, 50 and 100 mg kg^-1) superimposed to phosphorus (P) fertilizer application in soil at the rates of 0, 25 and 50 mg kg^-1 on wheat crop. Physiological parameters of plants, their antioxidant enzymes activities (SOD, POD), and contents of crude protein, H₂O₂, MDA and metals/nutrients (Al, Ca, Mg, Fe, Zn and Cu) were measured. Data on physiological traits revealed that application of 50 mg kg^-1 of TiO₂-NPs without P fertilizer significantly enhanced the root and shoot length by 63 and 26%, respectively. Increased contents of nutrients in the shoots, viz., Ca (316%), Cu (296%), Al (171%) and Mg (187%) with 50 mg kg^-1 TiO₂-NPs treatment reflected improvement in crop growth and grain quality. Furthermore, P contents in plant tissues were raised up to 56% with 50 mg kg^-1 of TiO₂-NPs even in the absence of P fertilizer. In the soil, concentration of phytoavailable P was significantly increased up to 63.3% in the presence of 50 mg kg^-1 TiO₂-NPs as compared to control. Contents of crude protein in grain were also enhanced by 22.8% (at P₅₀) and 17.4% (at P₂₅) with 50 mg kg^-1 TiO₂-NPs application. Along with P application, TiO₂-NPs triggered the activities of SOD (2.06-33.97%) and POD (up to 13.19%), and H₂O₂ production (50.6-138.8%). However, MDA contents were not elevated significantly at any level of TiO₂-NPs, and remained at par with control. It was noteworthy that highest level of TiO₂-NPs, viz., 100 mg kg^-1 exhibited plant and nutrients response lower than that with 50 mg kg^-1. Further, TiO₂-NPs triggered the bioavailability of micronutrient heavy metals (Zn, Cu and Fe) and Al, which could have toxicity at higher concentrations. These results suggested that TiO₂-NPs might have some affinities with phosphate compounds and metal ions in the soil to bring them in soluble form, which enhanced their bioavailability. Although it improved the crop yield and quality, but toxic or negative impact of TiO₂-NPs was also apparent at higher dose. Therefore, investigations on the potential interactions of NPs with other nutrients and toxic metals are needed to enhance our understanding for the safer application of nano-fertilizer.

Functional sustainability of periphytic biofilms in organic matter and Cu2+ removal during prolonged exposure to TiO2 nanoparticles

Responses of microbial communities to nanotoxicity in aquatic ecosystems are largely unknown, particularly with respect to relationship between community dynamics and functions. Here, periphytic biofilms were selected as a model of species-rich microbial communities to elucidate their responses when exposed to titanium dioxide nanoparticles (TiO₂-NPs). Especially, the relationships between the functions (e.g. organic matter and Cu²⁺ removal) and community dynamics after long-term exposure to TiO₂-NPs were assessed systematically. After 5days exposure to TiO₂-NPs (5mgL^-1), periphytic biofilms showed sustainable functions in pollutant removal and strong plasticity in defensing the toxic disturbance of TiO₂-NPs, including photosynthesis and carbon metabolic diversity. The sustainable pollutant removal functions of periphytic biofilms were attributed to their functional redundancy. Specifically, periphytic biofilms altered their composition with cyanobacteria, Sphingobacteriia and Spirochaetes being the newly dominant taxa, and changed the carbon substrate utilization pattern to maintain high photosynthesis and metabolic rates. Moreover, extracellular polymeric substances (EPS) especially proteins were overproduced to bind the NPs and thereby reduce the nanotoxicity. The information obtained in this study may greatly help to understand the interactions between microbial community dynamics and function under NPs exposure conditions and functional redundancy is an important mechanism of periphytic biofilms to maintain sustainable functions.

Titanium dioxide nanoparticles induce mouse hippocampal neuron apoptosis via oxidative stress- and calcium imbalance-mediated endoplasmic reticulum stress

The purpose of this study was to explore the potential neurotoxicity and the underlying mechanism of titanium dioxide nanoparticles (TiO₂-NPs) to mouse hippocampal neuron HT22 cells. We found that TiO₂-NPs had concentration-dependent and time-dependent cytotoxicities to HT22 cells by the MTT assay. Propidium iodide (PI) staining with FACScan flow cytometry proved that TiO₂-NPs dose-dependently increased the apoptosis rate in HT22 cells, and the apoptotic features were observed by Hochest 33258 and AO/EB staining. The levels of calcium (Ca²⁺) and reactive oxygen species (ROS) were significantly increased in TiO₂-NPs-treated cells. Further studies by western blot and real-time QPCR proved that the protein and mRNA levels of GRP78, IRE-1α, ATF6, CHOP and caspase-12 were up-regulated after TiO₂-NPs treatment, which indicates that TiO₂-NPs-induced cytotoxicity is related to endoplasmic reticulum stress (ERS). Apoptosis-related protein cleaved caspase-3 and pro-apoptotic protein Bax expression levels were up-regulated, and the anti-apoptotic protein Bcl-2 expression level was down-regulated in TiO₂-NPs-treated cells. The antioxidant N-acetyl-L-cysteine (NAC) can significantly reduce TiO₂-NPs-induced ERS characterized by the down-regulation of GRP78 and cleaved caspase-12 levels, which indicates that oxidative stress is participated in TiO₂-NPs-induced ERS. Our study suggests that TiO₂-NPs-induced apoptosis in HT22 cells is through oxidative stress- and calcium imbalance-mediated ERS.

Biosafety assessment of titanium dioxide nanoparticles in acutely exposed nematode Caenorhabditis elegans with mutations of genes required for oxidative stress or stress response

We used Caenorhabditis elegans to investigate whether acute exposure to TiO2-NPs at the concentration of 20 μg L(-1) reflecting predicted environmental relevant concentration and 25 mg L(-1) reflecting concentration in food can cause toxicity on nematodes with mutations of susceptible genes. Among examined mutants associated with oxidative stress and stress response, we found that genes of sod-2, sod-3, mtl-2, and hsp-16.48 might be susceptible for TiO2-NPs toxicity. Mutations of these genes altered functions of both possible primary and secondary targeted organs in nematodes exposed to 25 mg L(-1) of TiO2-NPs for 24-h. Mutations of these genes caused similar expression patterns of genes required for oxidative stress in TiO2-NPs exposed mutant nematodes, implying their similar mechanisms to form the susceptible property. Nevertheless, acute exposure to 20 μg L(-1) of TiO2-NPs for 24-h and 25 mg L(-1) of TiO2-NPs for 0.48-h or 5.71-h did not influence functions of both possible primary and secondary targeted organs in sod-2, sod-3, mtl-2, and hsp-16.48 mutants. Therefore, our results suggest the relatively safe property of acute exposure to TiO2-NPs with certain durations at predicted environmental relevant concentrations or concentrations comparable to those in food in nematodes with mutations of some susceptible genes.

The in vivo underlying mechanism for recovery response formation in nano-titanium dioxide exposed Caenorhabditis elegans after transfer to the normal condition

So far, we still know little about mechanism for recovery response of engineered nanomaterials (ENMs). Here we used Caenorhabditis elegans to investigate recovery responses of titanium dioxide nanoparticles (TiO2-NPs) exposed animals and the underlying mechanism. After acute exposure to TiO2-NPs (100mg/L), endpoints including defecation and permeable state of intestinal barrier of exposed nematodes returned to control levels; however, after prolonged exposure to TiO2-NPs (100μg/L), endpoints of exposed nematodes could not be recovered to control levels under the normal condition. After prolonged exposure to TiO2-NPs, nematodes exhibited severe deficits in development of intestinal barrier and AVL and DVB neurons controlling defecation; however, after acute exposure to TiO2-NPs, nematodes had normal developmental state of intestinal barrier and AVL and DVB neurons. Our results imply that developmental states of intestinal barrier and AVL and DVB neurons may serve as a pivotal determinant for recovery response in TiO2-NPs exposed nematodes.

FROM THE CLINICAL EDITOR

This basic science study investigates the recovery response to TiO2 nanoparticles in a nematode model, and concludes that developmental states of the intestinal barrier and AVL and DVB neurons likely serve as determinants for recovery following TiO2-NP exposure.