Role of physicochemical characteristics in the uptake of TiO2 nanoparticles by fibroblasts

The relation between the physico-chemical properties of nanoparticles (NPs) and the degree of cellular uptake is incompletely elucidated. In this study, we investigated the influence on the cellular uptake of a wide range of fully characterized TiO₂ NPs. L929 fibroblasts were exposed for 24 h to clinically relevant concentrations of nano-TiO₂ and the degree of their association was assessed by ultrahigh resolution imaging microscopy (URI), scanning (SEM) and transmission (TEM) electron microscopy, as well as inductivity coupled plasma–mass spectroscopy (ICP–MS). The role of actin polymerization, a central feature of active internalization, was also studied and the results indicated that the internalization of TiO₂ NPs involves a combination of actin-dependent uptake of large agglomerates as well as non actin-dependent uptake of small agglomerates. SEM and TEM revealed that the agglomerates of all NPs types were attached to the cellular membrane as well as internalized and confined inside cytoplasmic vesicles. URI and ICP–MS demonstrated that the particle association with cells was dose-dependent. The highest association was observed for spherical particles having mixed anatase–rutile crystallographic phase and the lowest for spindle-shaped rutile particles. ICP–MS revealed that the association was size-dependent in the order 5 > 10 > 40 nm for anatase spherical nanoparticles.     

Influence of silver and titanium dioxide nanoparticles on in vitro blood-brain barrier permeability

An in vitro blood-brain barrier (BBB) model being composed of co-culture with endothelial (bEnd.3) and astrocyte-like (ALT) cells was established to evaluate the toxicity and permeability of Ag nanoparticles (AgNPs; 8 nm) and TiO₂ nanoparticles (TiO₂NPs; 6 nm and 35 nm) in normal and inflammatory central nervous system. Lipopolysaccharide (LPS) was pre-treated to simulate the inflammatory responses. Both AgNPs and Ag ions can decrease transendothelial electrical resistance (TEER) value, and cause discontinuous tight junction proteins (claudin-5 and zonula occludens-1) of BBB. However, only the Ag ions induced inflammatory cytokines to release, and had less cell-to-cell permeability than AgNPs, which indicated that the toxicity of AgNPs was distinct from Ag ions. LPS itself disrupted BBB, while co-treatment with AgNPs and LPS dramatically enhanced the disruption and permeability coefficient. On the other hand, TiO₂NPs exposure increased BBB penetration by size, and disrupted tight junction proteins without size dependence, and many of TiO₂NPs accumulated in the endothelial cells were observed. This study provided the new insight of toxic potency of AgNPs and TiO₂NPs in BBB.     

Activation of human neutrophils by titanium dioxide (TiO2) nanoparticles

This paper describes the in vitro effects of titanium dioxide (TiO₂) nanoparticles (NPs) upon human neutrophils. Kinetic experiments revealed no cell necrosis after 24 h of treatment with TiO₂ (0–100 μg/ml). In contrast, TiO₂-induced change in cellular morphology in a concentration-dependent manner in neutrophils over time, indicating its potential to activate these cells. To further support this, we demonstrated that TiO₂ markedly and rapidly induced tyrosine phosphorylation events, including phosphorylation of two key enzymes, p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinases-1/2 (Erk-1/2). We also determined the effects of TiO₂ on two neutrophil functions requiring a longer exposure period between NPs and cells: apoptosis and cytokine production. Interestingly, at concentrations ⩾20 μg/ml, TiO₂ inhibited neutrophil apoptosis in a concentration-dependent manner after 24 h of treatment. Supernatants from TiO₂-induced neutrophils were harvested after 24 h and tested for the presence of 36 different analytes (cytokines, chemokines) using an antibody array assay. TiO₂ treatment increased production of 13 (36%) analytes, including IL-8, which exhibited the greatest increase (∼16 × control cell levels). The increased production of IL-8 was confirmed by ELISA. We conclude that TiO₂ exerts important neutrophil agonistic properties in vitro.     

Cytotoxicity of TiO2 nanoparticles to mussel hemocytes and gill cells in vitro: Influence of synthesis method,crystalline structure,size and additive

Abstract

Increasing the production and applications of TiO₂ nanoparticles (NPs) has led to grow concerns about the consequences for the environment. In this study, we investigated the effects of a set of TiO₂ NPs on the viability of mussel hemocytes and gill cells using neutral red and thiazolyl tetrazolium bromide assays. For this, we compared the cytotoxicity of TiO₂ NPs (0.1–100?mg Ti/L) produced by different techniques: rutile NPs (60?nm) produced by milling and containing disodium laureth sulfosuccinate (DSLS), rutile NPs (10, 40 and 60?nm) produced by wet chemistry and anatase/rutile NPs (～100?nm) produced by plasma synthesis. The commercially available P25 anatase/rutile NPs (10–20?nm) were also tested. Exposures were performed in parallel with their respective bulk forms and the cytotoxicity of the additive DSLS was also tested. Z potential values in distilled water indicated different stabilities depending on the NP type and all NPs tested formed agglomerates/aggregates in cell culture media. In general, TiO₂ NPs showed a relatively low and dose-dependent toxicity for both cell models with the two assays tested. NPs produced by milling showed the highest effects, probably due to the toxicity of DSLS. Size-dependent toxicity was found for NPs produced by wet chemistry (10?nm?>?40?nm and 60?nm). All TiO₂ NPs tested were more toxic than bulk forms excepting for plasma produced ones, which were the least toxic TiO₂ tested. The mixture bulk anatase/rutile TiO₂ was more toxic than bulk rutile TiO₂. In conclusion, the toxicity of TiO₂ NPs varied with the mode of synthesis, crystalline structure and size of NPs and can also be influenced by the presence of additives in the suspensions.     

Effects of TiO2 nanoparticles at predicted environmental relevant concentration on the marine scallop Chlamys farreri: An integrated biomarker approach

Manufactured nanoparticles (NPs) have caused extensive concern about their toxic effects on the marine environment. However, the chronic toxicity of NPs at predicted environmental relevant concentration on the marine organisms is poorly understood. In this study, we investigated the oxidative stress, neurotoxicity and histopathological effects of TiO₂ NPs at predicted environmental relevant concentration (1 mg/L) to marine scallop Chlamys farreri. The results showed that TiO₂ NPs caused obviously oxidative damage on the scallops as evidenced by the significantly elevated superoxide dismutase (SOD), catalase (CAT) activities and malondialdehyde (MDA) contents. The increased acetylcholine esterase (AChE) activities reflected neurotoxicity of TiO₂ NPs. The histopathological analysis revealed alterations in the gill and digestive gland, such as dysplastic and necrosis. Additionally, integrated biomarker response (IBR) values indicated that TiO₂ NPs can cause strong toxic effects on the scallop. These results suggested that predicted environmental relevant TiO₂ NPs can cause adverse effects on scallops and IBR analysis can be used as an effective approach for risk assessment of NPs on the marine organisms.     

Anti-angiogenic effect of bare titanium dioxide nanoparticles on pathologic neovascularization without unbearable toxicity

Local application requires fewer nanoparticles than systemic delivery to achieve effective concentration. In this study, we investigated the potential toxicity and efficacy of bare titanium dioxide (TiO₂) nanoparticles by local administration into the eye. Mono-disperse, 20 nm-size TiO₂ nanoparticles did not affect the viability of retinal constituent cells within certain range of concentrations (~ 1.30 μg/mL). Furthermore, local delivery of TiO₂ nanoparticles did not induce any significant toxicity at the level of gene expression and histologic integrity in the retina of C57BL/6 mice. Interestingly, at the low concentration (130 ng/mL) without definite toxicity, these nanoparticles suppressed in vitro angiogenesis processes and in vivo retinal neovascularization in oxygen-induced retinopathy mice when they are administered intravitreally. Taken together, our results demonstrate that even TiO₂ nanoparticles can be safely utilized for the treatment of retinal diseases at the adequate concentration levels, especially through local administration.From the Clinical EditorIn this paper the local application of titanium dioxide is described as a local treatment for retinal diseases associated with neovascularization. While these nanoparticles have known systemic toxicity, this work demonstrates that when applied locally in a mouse model, they can be used without observable toxicity even in their native forms.     

Iron oxide nanoparticles mediated cytotoxicity via PI3K/AKT pathway: Role of quercetin

Recently Fe₂O₃ NPs (iron oxide nanoparticles) have been extensively used in medical imaging and in industry also. As a result, people are increasingly exposed day by day to those nanoparticles. The adverse effect of Fe₂O₃ NPs is not so significant at lower doses but at higher doses Fe₂O₃ NPs causes significant damage to cells. The present study investigates the cell signaling mechanism of Fe₂O₃ NPs induced oxidative stress and cytotoxicity in vitro using murine hepatocytes as the working model. In addition, the cytoprotective action of quercetin in this pathophysiology has also been investigated. Dose-dependent studies suggest that incubation of hepatocytes with 250 μg/ml Fe₂O₃ NPs for 4 h significantly decreased the cell viability and intra-cellular antioxidant ability. This study also showed that exposure to Fe₂O₃ NPs caused hepatocytes death via apoptotic pathway. Incubation of hepatocytes with quercetin (50 μmol/L) prior to 1 h of Fe₂O₃ NPs exposure protects the cells from the altering activities of antioxidant indices, cytotoxicity and apoptotic death. Results suggest that Fe₂O₃ NPs induced cellular damage and quercetin plays a protective role in Fe₂O₃ NPs induced cytotoxicity and apoptotic death.     

Folate-mediated poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) nanoparticles for targeting drug delivery

A novel targeting drug delivery system (TDDS) has been developed. Such a TDDS was prepared by W₁/O/W₂ solvent extraction/evaporation method, adopting poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) [P(HB-HO)] as the drug carrier, folic acid (FA) as the targeting ligand, and doxorubicin (DOX) as the model anticancer drug. The average size, drug loading capacity and encapsulation efficiency of the prepared DOX-loaded, folate-mediated P(HB-HO) nanoparticles (DOX/FA–PEG–P(HB-HO) NPs) were found to be around 240 nm, 29.6% and 83.5%. The in vitro release profile displayed that nearly 50% DOX was released in the first 5 days. The intracellular uptake tests of the nanoparticles (NPs) in vitro showed that the DOX/FA–PEG–P(HB-HO) NPs were more efficiently taken up by HeLa cells compared to non-folate-mediated P(HB-HO) NPs. In addition, DOX/FA–PEG–P(HB-HO) NPs (IC₅₀ = 0.87 μM) showed greater cytotoxicity to HeLa cells than other treated groups. In vivo anti-tumor activity of the DOX/FA–PEG–P(HB-HO) NPs showed a much better therapeutic efficacy in inhibiting tumor growth, and the final mean tumor volume was 178.91 ± 17.43 mm³, significantly smaller than normal saline control group (542.58 ± 45.19 mm³). All these results have illustrated that our techniques for the preparing of DOX/FA–PEG–P(HB-HO) NPs developed in present work are feasible and these NPs are effective in selective delivery of anticancer drug to the folate receptor-overexpressed cancer cells. The new TDDS may be a competent candidate in application in targeting treatment of cancers.     

Nano-based antileishmanial agents: A toxicological study on nanoparticles for future treatment of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is endemic in the tropical and subtropical countries. Antileishmanial drugs that are traditionally used for treatment of CL are mainly toxic, ineffective for some parasite isolates, and mostly expensive. Previous studies showed that some metal and metal oxide nanoparticles have antimicrobial activity. Moreover, the use of nanoparticles together with ultra violet (UV) and infra red (IR) light increases toxic effects of nanoparticles by generation of reactive oxygen species (ROSs) and heat, respectively. There is little information on antileishmanial activity of nanoparticles, alone or together with UV/IR. Thus, the purpose of this research was to study antileishmanial effects of some nanoparticles including silver nanoparticles (Ag NPs), gold nanoparticles (Au NPs), titanium dioxide nanoparticles (TiO₂ NPs), zinc oxide nanoparticles (ZnO NPs), and magnesium oxide nanoparticles (MgO NPs) on Leishmania major parasites under UV, IR, and dark conditions. After 24 h exposure to nanoparticles, different biological parameters such as cell viability, proliferation, infectivity, and infection index were investigated under UV/IR/dark conditions. In this study, the highest antileishmanial activity was seen for Ag NPs, followed by Au NPs, TiO₂ NPs, ZnO NPs, and MgO NPs. Both UV and IR light increased antileishmanial properties of all nanoparticles. In spite of antileishmanial activity of nanoparticles under UV, IR, and dark conditions, these nanoparticles had high cytotoxicity on macrophages, which must be considered in future studies. The authors declare that the use of nanoparticles for treatment of CL may have both positive and negative consequences.     

Improving sublingual delivery of weak base compounds using pHmax concept: Application to propranolol

The purpose of the present work was to provide theoretical and experimental support in generating an optimal pH (pH_max) for a representative weak base compound (propranolol), that can lead to enhanced sublingual absorption. Initially equations for pH-solubility and pH-permeability profiles were derived and compared to the profiles obtained experimentally. Excellent correlation (R² = 0.999) of solubility profiles was obtained using non-linear regression, and the permeability profiles further predicted that at certain pH (pH_max), optimal mucosal permeation could be achieved. Subsequently, in a pharmacokinetics study, a buffered sublingual propranolol tablet, designed to achieve its pH_max (when dissolved in saliva), were compared to that from a marketed product (Inderal^® which could not achieve pH_max) in 8 healthy subjects. Each subject received the products sublingually for 15 min followed by swallowing the remaining drug–saliva. The plasma propranolol concentrations of AUC during first 30 min from the buffered tablet were significantly higher than that from the Inderal^® tablet (p < 0.05), and no significant differences in the remaining AUC were observed. These in vitro and in vivo results on propranolol provided experimental confirmation of the pH_max concept as well as its utility in sublingual drug delivery. Such an approach may be applicable to other similar compounds to improve sublingual drug delivery.     

Oral administration of nano-titanium dioxide particle disrupts hepatic metabolic functions in a mouse model

TiO₂ nano-particle (TiO₂ NP) is widely used in industrial, household necessities, as well as medicinal products. However, the effect of TiO₂ NP on liver metabolic function has not been reported. In this study, after mice were orally administered TiO₂ NP (21 nm) for 14 days, the serum and liver tissues were assayed by biochemical analysis, real time quantitative polymerase chain reaction, western blot and transmission electron microscopy. The serum bilirubin was increased in a dose dependent manner. Deposition of TiO₂ NP in hepatocytes and the abnormality of microstructures was observed. Expression of metabolic genes involved in the endogenous and exogenous metabolism was modified, supporting the toxic phenotype. Collectively, oral administration of TiO₂ NP (21 nm) led to deposition of particles in hepatocytes, mitochondrial edema, and the disturbance of liver metabolism function. These data suggested oral administration disrupts liver metabolic functions, which was more sensitive than regular approaches to detect material hepatotoxicity. This study provided useful information for risk analysis and regulation of TiO₂ NPs by administration agencies.     

DNA damaging potential of zinc oxide nanoparticles in human epidermal cells

At present, more than 20 countries worldwide are manufacturing and marketing different varieties of nanotech-based consumer products of which cosmetics form the largest category. Due to the extremely small size of the nanoparticles (NPs) being used, there is a concern that they may interact directly with macromolecules such as DNA. The present study was aimed to assess the genotoxicity of zinc oxide (ZnO) NPs, one of the widely used ingredients of cosmetics, and other dermatological preparations in human epidermal cell line (A431). A reduction in cell viability as a function of both NP concentration as well as exposure time was observed. ZnO NPs demonstrated a DNA damaging potential as evident from an increased Olive tail moment (OTM) of 2.13 ± 0.12 (0.8 μg/ml) compared to control 1.37 ± 0.12 in the Comet assay after an exposure of 6 h. ZnO NPs were also found to induce oxidative stress in cells indicated by depletion of glutathione (59% and 51%); catalase (64% and 55%) and superoxide dismutase (72% and 75%) at 0.8 and 0.08 μg/ml respectively. Our data demonstrates that ZnO NPs even at low concentrations possess a genotoxic potential in human epidermal cells which may be mediated through lipid peroxidation and oxidative stress. Hence, caution should be taken in their use in dermatological preparations as well as while handling.     

TiO2 nanoparticles and bulk material stimulate human peripheral blood mononuclear cells

Nanomaterials are increasingly produced and used throughout recent years. Consequently the probability of exposure to nanoparticles has risen. Because of their small 1–100 nm size, the physicochemical properties of nanomaterials may differ from standard bulk materials and may pose a threat to human health. Only little is known about the effects of nanoparticles on the human immune system. In this study, we investigated the effects of TiO₂ nanoparticles and bulk material in the in vitro model of human peripheral blood mononuclear cells (PBMC) and cytokine-induced neopterin formation and tryptophan breakdown was monitored. Both biochemical processes are closely related to the course of diseases like infections, atherogenesis and neurodegeneration. OCTi60 (25 nm diameter) TiO₂ nanoparticles and bulk material increased neopterin production in unstimulated PBMC and stimulated cells significantly, the effects were stronger for OCTi60 compared to bulk material, while P25 TiO₂ (25 nm diameter) nanoparticles had only little influence. No effect of TiO₂ nanoparticles on tryptophan breakdown was detected in unstimulated cells, whereas in stimulated cells, IDO activity and IFN-γ production were suppressed but only at the highest concentrations tested. Because neopterin was stimulated and tryptophan breakdown was suppressed in parallel, data suggests that the total effect of particles would be strongly pro-inflammatory.     

Intracellular trafficking of nuclear localization signal conjugated nanoparticles for cancer therapy

Doxorubicin (DOX) is an anticancer drug with an intracellular site of action in the nucleus. For high antitumour activity, it should be effectively internalized into the cancer cells and accumulate in the nucleus. In this study, we have prepared a nuclear localization signal conjugated doxorubicin loaded Poly (d,l-lactide-co-glycolide) nanoparticles (NPs), to deliver doxorubicin to the nucleus efficiently. Physico-chemical characterization of these NPs showed that the drug is molecularly dispersed in spherical and smooth surfaced nanoparticles. NPs (～226 nm in diameter, 46% encapsulation efficiency) under in vitro conditions exhibited sustained release of the encapsulated drug (63% release in 60 days). Cell cytotoxicity results showed that NLS conjugated NPs exhibited comparatively lower IC₅₀ value (2.3 μM/ml) than drug in solution (17.6 μM/ml) and unconjugated NPs (7.9 μM/ml) in breast cancer cell line MCF-7 as studied by MTT assay. Cellular uptake studies by confocal laser scanning microscopy (CLSM) and fluorescence spectrophotometer showed that greater amount of drug is targeted to the nucleus with NLS conjugated NPs as compared to drug in solution or unconjugated NPs. Flow cytometry experiments results showed that NLS conjugated NPs are showing greater cell cycle (G2/M phase) blocking and apoptosis than native DOX and unconjugated NPs. In conclusion, these results suggested that NLS conjugated doxorubicin loaded NPs could be potentially useful as novel drug delivery system for breast cancer therapy.     

Role of the crystalline form of titanium dioxide nanoparticles: Rutile,and not anatase,induces toxic effects in Balb/3T3 mouse fibroblasts

The wide use of titanium dioxide nanoparticles (TiO₂ NPs) in industrial applications requires the investigation of their effects on human health. In this context, we investigated the effects of nanosized and bulk titania in two different crystalline forms (anatase and rutile) in vitro. By colony forming efficiency assay, a dose-dependent reduction of the clonogenic activity of Balb/3T3 mouse fibroblasts was detected in the presence of rutile, but not in the case of anatase NPs. Similarly, the cell transformation assay and the micronucleus test showed that rutile TiO₂ NPs were able to induce type-III foci formation in Balb/3T3 cells and appeared to be slightly genotoxic, whereas anatase TiO₂ NPs did not induce any significant neoplastic or genotoxic effect. Additionally, we investigated the interaction of TiO₂ NPs with Balb/3T3 cells and quantified the in vitro uptake of titania using mass spectrometry. Results showed that the internalization was independent of the crystalline form of TiO₂ NPs but size-dependent, as nano-titania were taken up more than their respective bulk materials.In conclusion, we demonstrated that the cytotoxic, neoplastic and genotoxic effects triggered in Balb/3T3 cells by TiO₂ NPs depend on the crystalline form of the nanomaterial, whereas the internalization is regulated by the particle size.     

TiO2 nanoparticles induce endothelial cell activation in a pneumocyte–endothelial co-culture model

The effects of particulate matter (PM) on endothelial cells have been evaluated in vitro by exposing isolated endothelial cells to different types of PM. Although some of the findings from these experiments have been corroborated by in vivo studies, an in vitro model that assesses the interaction among different cell types is necessary to achieve more realistic assays. We developed an in vitro model that mimics the alveolar–capillary interface, and we challenged the model using TiO₂ nanoparticles (TiO₂-NPs). Human umbilical endothelial cells (HUVECs) were cultured on the basolateral side of a membrane and pneumocytes (A549) on the apical side. Confluent co-cultures were exposed on the apical side to 10 μg/cm² of TiO₂-NPs or 10 ng/mL of TNFα for 24 h. Unexposed cultures were used as negative controls. We evaluated monocyte adhesion to HUVECs, adhesion molecule expression, nitric oxide concentration and proinflammatory cytokine release. The TiO₂-NPs added to the pneumocytes induced a 3- to 4-fold increase in monocyte adhesion to the HUVECs and significant increases in the expression of adhesion molecules (4-fold for P-selectin at 8 h, and about 8- and 10-fold for E-selectin, ICAM-1, VCAM-1 and PECAM-1 at 24 h). Nitric oxide production also increased significantly (2-fold). These results indicate that exposing pneumocytes to TiO₂-NPs causes endothelial cell activation.     

Maternal exposure to titanium dioxide nanoparticles during pregnancy; impaired memory and decreased hippocampal cell proliferation in rat offspring

Titanium dioxide nanoparticles (TiO₂-NPs) are massively produced in the environment, and because of their wide usage, they are a potential risk of damage to human health. TiO₂-NPs are often used as additives for paints, papers, and foods. The central nervous system (CNS), including hippocampal regions, is potentially susceptible targets for TiO₂-NPs. This study aimed to determine the effects of exposure to TiO₂-NPs during pregnancy on hippocampal cell proliferation and the learning and memory of offspring. Pregnant Wistar rats received intragastric TiO₂-NPs (100 mg/kg body weight) daily from gestational day (GD) 2 to (GD) 21. Animals in the control group received the same volume of distilled water via gavage. After delivery, the one-day-old neonates were deeply anesthetized and weighed. They were then killed and the brains of each group were collected. Sections of the brains from the rat offspring were stained using Ki-67 immunolabeling and the immunohistochemistry technique. Some of the male offspring (n = 12 for each group) were weaned at postnatal day (PND21), and housed until adulthood (PND60). Then the learning and memory in animals of each group were evaluated using passive avoidance and Morris water maze tests. The immunolabeling of Ki-67 protein as a proliferating cell marker showed that TiO₂-NPs significantly reduced cell proliferation in the hippocampus of the offspring (P < 0.05). Moreover, both the Morris water maze test and the passive avoidance test showed that exposure to TiO₂-NPs significantly impaired learning and memory in offspring (P < 0.05). These results may provide basic experimental evidence for a better understanding of the neurotoxic effects of TiO₂-NPs on neonatal and adult brains.     

Toxicity and accumulation of Copper oxide (CuO) nanoparticles in different life stages of Artemia salina

Metal nanoparticles production rate and its applications have raised concerns about their release and toxicity to the aquatic and terrestrial organisms. The primary size of Copper Oxide nanoparticles (CuO NP’s) was found to be 114 ± 36 nm using Scanning Electron Microscopy (SEM) and a significant increase in the hydrodynamic diameter of CuO NP was seen within 1 h of interaction. The median lethal concentration (LC₅₀) values obtained from the acute toxicity studies on different life stages of Artemia salina was found to be 61.4, 35, 12.2 and 175.2 mg/L for 1d, 2d, 7d old and adult, respectively. The toxicity associated changes in biochemical markers such as Catalase, Reduced glutathione and Glutathione-S-Transferase were evident. The accumulation of Cu nanoparticles into the gut of Artemia salina was the major reason for toxicity. This study demonstrate the toxicity of CuO NPs to Artemia salina, and the obtained results necessitate the detailed investigation on the possible eco-toxicological implication of these nanomaterials.     

The noncellular reduction of MTT tetrazolium salt by TiO2 nanoparticles and its implications for cytotoxicity assays

We report results of noncellular tests, revealing the occurrence of photocatalytic interactions between titanium dioxide (TiO₂, titania) nanoparticles and the MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide] cytotoxicity indicator. These interactions induce the reduction of MTT and formation of purple formazan under biologically relevant conditions. Classical MTT assays have been performed to evaluate the production of formazan in DMEM-F12 and RPMI-1640 cell culture media (containing 10% fetal bovine serum-FBS) treated with Degussa-P25 TiO₂ nanoparticles, in the absence of cells. The colorimetric determinations revealed the noncellular MTT to formazan transformation induced by TiO₂ nanoparticles, under conditions commonly used for in vitro cytotoxicity testing of nanomaterials. The formazan precipitation was found to be proportional to the TiO₂ concentration, being enhanced under laboratory daylight exposure. The photocatalytic nature of the studied effect was assessed under UV irradiation at 365 nm. The biological significance of the reported reaction was established with respect to cellular reference experiments performed on V79-4, HeLa and B16 cell lines. The results show false viability increases with up to 14% (for TiO₂ concentrations generally higher than 50 μg/ml), induced by the TiO₂–MTT reaction. This type of artifacts may lead to underestimated toxicity or false proliferation results.     

The oxidative damage and inflammatory response induced by lead sulfide nanoparticles in rat lung

Lead sulfide nanoparticles (PbS NPs) are one important nanoparticle materials which is widely used in photoelectric production, but its potential health hazard to respiratory system is not clear. This study aimed to explore the possible mechanism of lung injury induced by PbS NPs. Male SD rats were treated with nanoparticles of 60 nm and 30 nm lead sulfide. The main methods were detecting the vigor of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) and the content of malondialdehyde (MDA) in both blood and lung tissues and observing the pathological changes in lung tissue. PbS NPs suppressed the activity of SOD and T-AOC, and increased serum MDA content (P < 0.05); both effects were observed together in lung tissues of 30-nm group (P < 0.05) accompanied by an obviously inflammatory response. PbS NPs induced oxidative damage and inflammatory response in lung tissue, which may be an underlying mechanism for its pulmonary toxicity. Additionally, the toxicity of PbS NPs was closely related with the size of nanoparticles.