We have previously shown that exposure to TiO2 nanoparticles (NPs) reduces the resistance of HeLa cells to bacterial infection. Here we demonstrate that the increased infectivity is associated with enhanced asymmetry in the cholesterol distribution. We applied a live cell imaging method which uses tunable orthogonal cholesterol sensors to visualize and quantify in-situ cholesterol distribution between the two leaflets of the plasma membrane (PM). In the control culture, we found marked transbilayer asymmetry of cholesterol, with the concentration in the outer plasma membrane (OPM) being 13 +/- 2-fold higher than that in the inner plasma membrane (IPM). Exposure of the culture to 0.1 mg/mL of rutile TiO2 NPs increased the asymmetry such that the concentration in the OPM was 51 +/- 10 times higher, while the total cholesterol content increased only 21 +/- 2%. This change in cholesterol gradient may explain the increase in bacterial infectivity in HeLa cells exposed to TiO2 NPs since many pathogens, including Staphylococcus aureus used in the present study, require cholesterol for proper membrane attachment and virulence. RT-PCR indicated that exposure to TiO2 was responsible for upregulation of the ABCA1 and ABCG1 mRNAs, which are responsible for the production of the cholesterol transporter proteins that facilitate cholesterol transport across cellular membranes. This was confirmed by the observation of an overall decrease in bacterial infection in ABCA1 knockout or methyl-beta-cyclodextrin-treated HeLa cells, as regardless of TiO2 NP exposure. Hence rather than preventing bacterial infection, TiO2 nanoparticles upregulate genes associated with membrane cholesterol production and distribution, hence increasing infectivity. Statement of significance A great deal of work has been done regarding the toxicology of the particles, especially focusing on detrimental outcomes associated with reactive oxygen species (ROS) production. In this paper we show unambiguously a very surprising result, namely the ability of these particles to enhance bacterial infection even at very small exposure levels, where none of the deleterious effects of ROS products can yet be detected. Using a new imaging technique, we are able to demonstrate, in operando, the effect of the particles on cholesterol generation and distribution in live HeLa cells. This paper also represents the first in a series where we explore other consequences of increased membrane cholesterol, due to particle exposure, which are known to have multiple other consequences on human tissue function and development. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We have previously shown that exposure to TiO2 nanoparticles (NPs) reduces the resistance of HeLa cells to bacterial infection. Here we demonstrate that the increased infectivity is associated with enhanced asymmetry in the cholesterol distribution. We applied a new live cell imaging method which uses tunable orthogonal cholesterol sensors to visualize and quantify in-situ cholesterol distribution between the two leaflets of the plasma membrane (PM). In the control culture, we found marked transbilayer asymmetry of cholesterol, with the concentration in the outer plasma membrane (OPM) being 12.5(2.2)-fold higher than that in the inner plasma membrane (IPM). Exposure of the culture to 0.1 mg/mL of rutile TiO2 NPs increased the asymmetry such that the concentration in the OPM was 50.8(9.5) times higher, while the total cholesterol content increased only 20.5(2.4)%. This change in cholesterol gradient may explain the increase in bacterial infectivity in HeLa cells exposed to TiO2 NPs since many pathogens, including Staphylococcus aureus used in the present study, require cholesterol for proper membrane attachment and virulence. RT-PCR indicated that exposure to TiO2 was responsible for upregulation of the ABCA1 and ABCG1 mRNAs, which are responsible for the production of the cholesterol transporter proteins that facilitate cholesterol transport across cellular membranes. This was confirmed by the observation of an overall decrease in bacterial infection in ABCA1 knockout or methyl-β-cyclodextrin-treated HeLa cells, as regardless of TiO2 NP exposure. Hence rather than preventing bacterial infection, TiO2 nanoparticles upregulate genes associated with membrane cholesterol production and distribution, hence increasing infectivity.

Background: Increasing production of nanomaterials requires fast and proper assessment of its potential toxicity. Therefore, there is a need to develop new assays that can be performed in vitro, be cost effective, and allow faster screening of engineered nanomaterials (ENMs).Results: Herein, we report that titanium dioxide (TiO2) nanoparticles (NPs) can induce damage to adipose derived stromal cells (ADSCs) at concentrations which are rated as safe by standard assays such as measuring proliferation, reactive oxygen species (ROS), and lactate dehydrogenase (LDH) levels. Specifically, we demonstrated that low concentrations of TiO2 NPs, at which cellular LDH, ROS, or proliferation profiles were not affected, induced changes in the ADSCs secretory function and differentiation capability. These two functions are essential for ADSCs in wound healing, energy expenditure, and metabolism with serious health implications in vivo.Conclusions: We demonstrated that cytotoxicity assays based on specialized cell functions exhibit greater sensitivity and reveal damage induced by ENMs that was not otherwise detected by traditional ROS, LDH, and proliferation assays. For proper toxicological assessment of ENMs standard ROS, LDH, and proliferation assays should be combined with assays that investigate cellular functions relevant to the specific cell type.

The effect of pretreatment atmosphere on 1,3-butadiene hydrogenation over biosynthesized Pd/γ-Al2O3 catalysts was reported.

Background: Titanium dioxide (TiO2) is one of the most common nanoparticles found in industry ranging from food additives to energy generation. Approximately four million tons of TiO2 particles are produced worldwide each year with approximately 3000 tons being produced in nanoparticulate form, hence exposure to these particles is almost certain.Results: Even though TiO2 is also used as an anti-bacterial agent in combination with UV, we have found that, in the absence of UV, exposure of HeLa cells to TiO2 nanoparticles significantly increased their risk of bacterial invasion. HeLa cells cultured with 0.1 mg/ml rutile and anatase TiO2 nanoparticles for 24 h prior to exposure to bacteria had 350 and 250 % respectively more bacteria per cell. The increase was attributed to bacterial polysaccharides absorption on TiO2 NPs, increased extracellular LDH, and changes in the mechanical response of the cell membrane. On the other hand, macrophages exposed to TiO2 particles ingested 40 % fewer bacteria, further increasing the risk of infection.Conclusions: In combination, these two factors raise serious concerns regarding the impact of exposure to TiO2 nanoparticles on the ability of organisms to resist bacterial infection.

The development of environmentally benign methods for the synthesis of nanomaterials has become increasingly relevant as chemists look to shape a more sustainable future. In this critical review, we present current work towards developing alternative methods for synthesizing a wide range of high-quality nanomaterials with predictable and controllable size, shape, composition, morphology and crystallinity. In particular, we focus on the inherent advantages of utilizing porous membrane templates, ultrasonic and microwave irradiation, alternative solvent systems, as well as biologically-inspired reagents as reasonably cost-effective, environmentally responsible methods to generate metal, metal oxide, fluoride, sulfide, selenide and phosphate nanomaterials.