Effect of titanium dioxide nanoparticles on glucose homeostasis after oral administration

As food additives, titanium dioxide nanoparticles (TiO₂ NPs) have been widely used in various products that are usually simultaneously consumed with a high content of sugar, thus necessitating research on the effect of TiO₂ NPs on glucose homeostasis. We conducted an animal study to explore the effect of orally administrated TiO₂ NPs on glucose absorption and metabolism in rats at 0, 2, 10 and 50 mg kg^–1 body weight day^–1 for 30 and 90 days. The results showed that oral exposure to TiO₂ NPs caused a slight and temporary hypoglycemic effect in rats at 30 days post‐exposure but recovered at 90 days post‐exposure. Decreased levels of intestinal glucose absorption and increased levels of hepatic glucose metabolism may be responsible for the hypoglycemic effect. Remodeling of the villi in the small intestine that decreased the surface area available for glucose absorption and increased levels of hepatic glucose uptake, utilization and storage related to hepatocellular injury are supposed to be the mechanisms. Our results demonstrated that dietary intake of TiO₂ NPs as food additives could affect the absorption and metabolism of glucose.     

Toxicity of titanium dioxide nanoparticles to rainbow trout (Oncorhynchus mykiss): gill injury, oxidative stress, and other physiological effects

Mammalian and in vitro studies have raised concerns about the toxicity of titanium dioxide nanoparticles (TiO2 NPs), but there are very limited data on ecotoxicity to aquatic life. This paper is an observational study where we aim to describe the toxicity of TiO2 NPs to the main body systems of rainbow trout. Stock solutions of dispersed TiO2 NPs were prepared by sonication without using solvents. A semi-static test system was used to expose rainbow trout to either a freshwater control, 0.1, 0.5, or 1.0 mg l(-1) TiO2 NPs for up to 14 days. Exposure to TiO2 NPs caused some gill pathologies including oedema and thickening of the lamellae. No major haematological or blood disturbances were observed in terms of red and white blood cell counts, haematocrit values, whole blood haemoglobin, and plasma Na+ or K+ concentrations. Tissue metal levels (Na+, K+, Ca2+ and Mn) were generally unaffected. However, some exposure concentration-dependent changes in tissue Cu and Zn levels were observed, especially in the brain. Exposure to TiO2 NPs caused statistically significant decreases in Na+K+-ATPase activity (ANOVA, P<0.05) in the gills and intestine, and a trend of decreasing enzyme activity in the brain (the latter was not statistically significant). Thiobarbituric acid reactive substances (TBARS) showed exposure concentration-dependent and statistically significant (ANOVA or Kruskal-Wallis test, P<0.05) increases (two-fold or more) in the gill, intestine and brain, but not the liver during exposure to TiO2 NPs compared to controls. TiO2 NP exposure caused statistically significant (ANOVA, P<0.05) increases in the total glutathione levels in the gills, but depletion of hepatic glutathione compared to controls. Total glutathione levels in the brain and intestine were unaffected. Liver cells exposed to TiO2 NPs showed minor fatty change and lipidosis, and some hepatocytes showed condensed nuclear bodies (apoptotic bodies). Fish probably ingested water containing TiO2 NPs during exposure (stress-induced drinking) which may have resulted in some areas of erosion on the intestinal epithelium. Overall we conclude that titanium dioxide nanoparticles are not a major ionoregulatory toxicant, or haemolytic, at the concentration and exposure times used. Respiratory distress is a concern and sub-lethal toxicity involves oxidative stress, organ pathologies, and the induction of anti-oxidant defences, such as glutathione.     

Effect of cadmium on the extracellular Na+, K+, and Ca2+ in the gill and small intestine of Goldfish Carassius auratus

In this study, the toxic effect of cadmium on extracellular Na⁺, K⁺, and Ca²⁺ in the gill and small intestine of goldfish Carassius auratus was determined with the technique of ion chromatograph. Two-way ANOVA indicated that the two factors (Cd²⁺ treatment and time) and the interaction factor had significant effect on the level of Na⁺, K⁺, and Ca²⁺ in the small intestine and gill. 1.0 mg/L Cd²⁺ significantly increased Ca²⁺ level in the small intestine, but Ca²⁺ level in the gill was significantly decreased by 1.0 and 5.0 mg/L Cd²⁺ at 24, 48, and 72 h. Na⁺ and K⁺ level in the small intestine and gill was increased by 1.0 mg/L Cd²⁺ at three time points, but increased by 5.0 mg/L Cd²⁺ at a certain different time. In addition, Na⁺ level was significantly decreased by 5.0 mg/L Cd²⁺ at 24 or 48 h in the small intestine and gill. The results indicated that Cd²⁺ played an important role in regulating the level of Na⁺, K⁺, and Ca²⁺ in the small intestine and gill of goldfish C. auratus. A method was constructed to investigate the extracellular Na⁺, K⁺ and Ca²⁺ in the tissues of gold fish with ion chromatography.     

Enzymatic alterations and RNA/DNA ratio in intestine of rainbow trout, <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>, induced by chronic exposure to carbamazepine

We investigated the effect of long-term exposure to carbamazepine (CBZ) on the enzymatic alterations and RNA/DNA ratio in intestine tissue of rainbow trout. Fish were exposed to sublethal concentrations of CBZ (1.0 μg/l, 0.2 or 2.0 mg/l) for 42 days. Digestive enzymes (proteolytic enzymes and amylase) and energy metabolic enzyme (Na⁺-K⁺-ATPase) and antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], and glutathione reductase [GR]) in fish intestine were measured. In addition, intestinal RNA/DNA ratio was determined after 42 days exposure. Carbamazepine exposure at 2.0 mg/l led to significantly inhibited (P < 0.05) activity of Na⁺-K⁺-ATPase. Activities of the antioxidant enzymes SOD, CAT, and GPx in CBZ-treated groups gradually increased at lower concentration of CBZ (1.0 μg/l and 0.2 mg/l), then significantly inhibited (P < 0.05) at 2.0 mg/l. After 42 days, the RNA/DNA ratio in fish intestine was significantly lower (P < 0.05) in groups exposed to CBZ at 2.0 mg/l than in other groups. However, there was no statistical significance (P > 0.05) in the activities of digestive enzymes (proteolytic enzyme and amylase) and GR in all groups. In short, prolonged exposure to CBZ resulted in different responses of various enzymes and significantly lower RNA/DNA ratio in fish intestine. Furthermore, molecular and genetic mechanisms of these physiological responses in fish are not clear, which need to be further studied.     

Effect of pH on uptake,tissue distribution and retention of hexavalent chromium in rainbow trout (Salmo gairdneri)

Uptake, distribution and retention of chromium in rainbow trout (Salmo guirdneri) was studied after short-term (2–4 days) exposure to ⁵¹CrO₄^2? -containing Na₂CrO₄ solutions of different concentrations (2–50 mg/l Cr) and pH (7.8 and 6.5). At pH 7.8, highest contents of chromium were found in gill, liver, kidney, and digestive tract of the trout. Chromium was not distributed evenly among the different subcellular fractions of the tissues, but was concentrated in the nuclear fraction of the gill tissue and in the soluble fraction of the kidney and liver tissue. Upon transfer of exposed fish to tap-water, chromium was rapidly eliminated from blood, gill and digestive tract. However, chromium contents tended to remain high in kidney and liver. When the pH was decreased from 7.8 to 6.5, the lethal action of hexavalent chromium increased and a different pattern of accumulation and elimination of chromium was observed. The major differences were found in the gills, which concentrated significantly more chromium at pH 6.5 than at pH 7.8, irrespective of the exposure time and concentration. As an electronspin-resonance signal characteristic for trivalent or pentavalent chromium was detected in the gills, the differences must have been at least partly due to the higher oxidizing action of hexavalent chromium at the lower pH.     

Bioaccumulation of ionic titanium and titanium dioxide nanoparticles in zebrafish eleutheroembryos

Abstract

The production of titanium dioxide nanoparticles (TiO₂ NPs) for commercial applications has greatly increased over the last years and consequently the potential risk for human health. There is a growing awareness of the need to understand the behavior and influence these nanoparticles exert on the environment. Bioaccumulation serves as a good integrator to assess chemical exposure in aquatic systems and is dependent on factors, such as the exposure routes, diet and the aqueous medium. We analyzed the experimental bioaccumulation capability of ionic titanium and TiO₂ NPs by zebrafish (Danio rerio) eleutheroembryos through bioconcentration factors (BCFs), after 48 or 72?h of exposure. The stability of both chemical forms in an aquatic medium was fully characterized for further bioaccumulation studies. Several stabilizing agents (humic acids, soluble starch, polyethylene glycol, Na₄P₂O₇ and Na₂HPO₄) for anatase and rutile, the two allotrophs of TiO₂ NPs, were evaluated to check the evolution of the aggregation process. Around 60% of TiO₂ NPs remained disaggregated under simulated environmental conditions with the addition of 50?mg?L^?1 of humic acids. However, the presence of eleutheroembryos in the exposure medium increased TiO₂ NPs aggregation in the experimental tests. The BCFs values obtained in all cases were <100, which classifies ionic titanium and TiO₂ NPs as non-bioaccumulative substances, under the REACH regulations.     

Effects of cadmium alone and in combination with low molecular weight chitosan on metallothionein,glutathione‐S‐transferase,acid phosphatase,and ATPase of freshwater crab Sinopotamon yangtsekiense

Cadmium (Cd) is an environmental contaminant showing a variety of deleterious effects, including the potential threat for the ecological environment and human health via food chains. Low molecular weight chitosan (LMWC) has been demonstrated to be an effective antioxidant. Metallothionein (MT) mRNA levels and activities of glutathione‐S‐transferase (GST), superoxide dismutase (SOD), acid phosphatase (ACP), Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as malondialdehyde (MDA) contents in the gills of the freshwater crab Sinopotamon yangtsekiense were analyzed in vivo in order to determine the injury of Cd exposure on the gill tissues as well as the protective effect of LMWC against this injury. The results showed that there was an apparent accumulation of Cd in the gills, which was lessened by the presence of LMWC. Moreover, Cd²⁺ significantly increased the gill MT mRNA levels, ACP activity and MDA content while decreasing the activities of SOD, GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in the crabs relative to the control. Cotreatment with LMWC reduced the levels of MT mRNA and ACP but raised the activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase in gill tissues compared with the crabs exposed to Cd²⁺ alone. These results suggest that LMWC may exert its protective effect through chelating Cd²⁺ to form LMWC‐Cd²⁺ complex, elevating the antioxidative activities of GST, Na⁺,K⁺‐ATPase, and Ca²⁺‐ATPase as well as alleviating the stress pressure on MT and ACP, consequently protecting the cell from the adverse effects of Cd. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 298–309, 2014.     

The combined effect of copper and low pH on antioxidant defenses and biochemical parameters in neotropical fish pacu, <Emphasis Type="Italic">Piaractus mesopotamicus</Emphasis> (Holmberg, 1887)

Copper sulfate is widely used in aquaculture. Exposure to this compound can be harmful to fish, resulting in oxidative metabolism alterations and gill tissue damage. Pacu, Piaractus mesopotamicus, (wt = 43.4 ± 3.35 g) were distributed in experimental tanks (n = 10; 180 l) and exposed for 48 h to control (without copper addition), 0.4Cu (0.4 mg l⁻¹), 0CupH (without copper addition, pH = 5.0) and 0.4CupH (0.4 mg l⁻¹, pH = 5.0). In liver and red muscle, the superoxide dismutase (SOD) was responsive to the increases in the aquatic copper. The plasmatic intermediary metabolites and hematological variables in the fish of group 0.4Cu were similar to those of the control group. Conversely, the exposure to 0.4CupH caused an increase in the plasmatic lactate, number of red blood cells (RBC) and hemoglobin (Hb). Plasmatic copper concentration [Cu_p] increased in group 0.4Cu and 0.4CupH, which is higher in group 0.4CupH, suggests an effect of water pH on the absorbed copper. Exposure to 0.4Cu and 0.4CupH resulted in a reduction in the Na⁺/K⁺-ATPase activity and an increase in metallothionein (MT) in the gills. Exposure to 0CupH caused a decrease in glucose and pyruvate concentrations and an increase in RBC, Hb, and the branchial Na⁺/K⁺-ATPase activity. These responses suggest that the fish triggered mechanisms to revert the blood acidosis, save energy and increase the oxygen uptake. MT was an effective biomarker, responding to copper in different pHs and dissolved oxygen. Combined-factors caused more significant disturbance in the biomarkers than single-factors.     

Essential metal (Cu,Zn) exposures alter the activity of ATPases in gill,kidney and muscle of tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

An acute (96 h—0.1, 0.5, 1.0, 1.5 μg/ml) and chronic (up to 30 days—0.05 μg/ml) protocols of Cu and Zn were applied to freshwater fish Oreochromis niloticus to investigate these essential metal effects on the activities of gill, kidney and muscle Na⁺/K⁺-ATPase, Mg²⁺-ATPase and Ca²⁺-ATPase. In vitro effects of both metals (20 min—0.1, 0.5, 1.0, 1.5 μg/ml) were also measured to be able to compare both exposure routes. Data showed that ATPase activities, in general, decreased following all the exposure conditions, though there were some increases especially in Mg²⁺-ATPase activity. Among the enzymes, Na⁺/K⁺-ATPase and Ca²⁺-ATPase appeared to be more sensitive than Mg²⁺-ATPase to the metals. The data also indicated that effects of Cu on ATPase activity in the tissues of O. niloticus were stronger than the effects of Zn, possibly due to higher toxic effects of Cu. In vivo and in vitro exposures of metals showed similar trends with a few exceptions, especially in the gill. Variability of ATPase activity is determined by tissue type, metal species, concentration and duration. This work showed that even essential metals can alter significantly activities of ATPases in fish and thus suggests using them as a sensitive biomarker in metal contaminated waters.     

No evidence of the genotoxic potential of gold,silver, zinc oxide and titanium dioxide nanoparticles in the SOS chromotest

Gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), zinc oxide nanoparticles (ZnO NPs) and titanium dioxide nanoparticles (TiO₂ NPs) are widely used in cosmetic products such as preservatives, colorants and sunscreens. This study investigated the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO₂ NPs using the SOS chromotest with Escherichia coli PQ37. The maximum exposure concentrations for each nanoparticle were 3.23 mg l^–1 for Au NPs, 32.3 mg l^–1 for Ag NPs and 100 mg l^–1 for ZnO NPs and TiO₂ NPs. Additionally, in order to compare the genotoxicity of nanoparticles and corresponding dissolved ions, the ions were assessed in the same way as nanoparticles. The genotoxicity of the titanium ion was not assessed because of the extremely low solubility of TiO₂ NPs. Au NPs, Ag NPs, ZnO NPs, TiO₂ NPs and ions of Au, Ag and Zn, in a range of tested concentrations, exerted no effects in the SOS chromotest, evidenced by maximum IF (IFmax) values of below 1.5 for all chemicals. Owing to the results, nanosized Au NPs, Ag NPs, ZnO NPs, TiO₂ NPs and ions of Au, Ag and Zn are classified as non‐genotoxic on the basis of the SOS chromotest used in this study. To the best of our knowledge, this is the first study to evaluate the genotoxicity of Au NPs, Ag NPs, ZnO NPs and TiO₂ NPs using the SOS chromotest. Copyright © 2012 John Wiley & Sons, Ltd.     

Titanium dioxide nanoparticles prime a specific activation state of macrophages

Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in foods, cosmetics, and medicine. Although the inhalation toxicity of TiO₂ NPs has been studied, the potential adverse effects of oral exposure of low-dose TiO₂ NPs are largely unclear. Herein, with macrophage cell lines, primary cells, and mouse models, we show that TiO₂ NPs prime macrophages into a specific activation state characterized by excessive inflammation and suppressed innate immune function. After a month of dietary exposure in mice or exposure in vitro to TiO₂ NPs (10 and 50?nm), the expressions of pro-inflammatory genes in macrophages were increased, and the expressions of anti-inflammatory genes were decreased. In addition, for macrophages exposed to TiO₂ NPs in vitro and in vivo, their chemotactic, phagocytic, and bactericidal activities were lower. This imbalance in the immune system could enhance the susceptibility to infections. In mice, after a month of dietary exposure to low doses of TiO₂ NPs, an aggravated septic shock occurred in response to lipopolysaccharide challenge, leading to elevated levels of inflammatory cytokines in serum and reduced overall survival. Moreover, TLR4-deficient mice and primary macrophages, or TLR4-independent stimuli, showed less response to TiO₂ NPs. These results demonstrate that TiO₂ NPs induce an abnormal state of macrophages characterized by excessive inflammation and suppressed innate immune function in a TLR4-dependent manner, which may suggest a potential health risk, particularly for those with additional complications, such as bacterial infections.     

Accumulation and toxicity of CuO and ZnO nanoparticles through waterborne and dietary exposure of goldfish (Carassius auratus)

Dietary and waterborne exposure to copper oxide (CuO) and zinc oxide (ZnO) nanoparticles (NPs) was conducted using a simplified model of an aquatic food chain consisting of zooplankton (Artemia salina) and goldfish (Carassius auratus) to determine bioaccumulation, toxic effects, and particle transport through trophic levels. Artemia contaminated with NPs were used as food in dietary exposure. Fish were exposed to suspensions of the NPs in waterborne exposure. ICP‐MS analysis showed that accumulation primarily occurred in the intestine, followed by the gills and liver. Dietary uptake was lower, but was found to be a potential pathway for transport of NPs to higher organisms. Waterborne exposure resulted in about a 10‐fold higher accumulation in the intestine. The heart, brain, and muscle tissue had no significant Cu or Zn. However, concentrations in muscle increased with NP concentration, which was ascribed to bioaccumulation of Cu and Zn released from NPs. Free Cu concentration in the medium was always higher than that of Zn, indicating CuO NPs dissolved more readily. ZnO NPs were relatively benign, even in waterborne exposure (p ≥ 0.05). In contrast, CuO NPs were toxic. Malondialdehyde levels in the liver and gills increased substantially (p < 0.05). Despite lower Cu accumulation, the liver exhibited significant oxidative stress, which could be from chronic exposure to Cu ions. © 2014 Wiley Periodicals, Inc. Environ Toxicol 30: 119–128, 2015.     

Chronic exposure to dichloroacetamide induces biochemical and histopathological changes in the gills of zebrafish

To evaluate the impact of DCAcAm on zebrafish gill, we measure the responses of antioxidant enzyme (superoxide dismutase, SOD), lipid peroxidation (malondialdehyde, MDA), ATPase (Na⁺/K⁺‐ATPase and Ca²⁺/Mg²⁺‐ATP) and histopathological changes of gill in adult zebrafish, after exposed to different concentrations of DCAcAm (0, 1, 10, 100, and 1000 μg L^?1) for 30 days. Results indicated that DCAcAm first increased and then decreased SOD activity, and DCAcAm also lowered the activities of Na⁺/K⁺‐ATPase and Ca²⁺/Mg²⁺‐ATPase. These results indicated that high affinity of DCAcAm probably be a main factor, which can damage the structures of enzymes, thereby inhibiting the SOD and ATPase activities. Besides, histopathological investigation results also manifested that chronic exposure to DCAcAm can damage the gill tissues, disrupting the normal function of gills. We conclude that chronic exposure to DCAcAm was harmful to organisms, not only influence gill function, but also further cause damage on the gill tissues.     

Subchronic exposure to diflubenzuron causes health disorders in neotropical freshwater fish,Prochilodus lineatus

The action of diflubenzuron (DFB) was evaluated in a freshwater fish, Prochilodus lineatus, after exposure to 0.06, 0.12, 0.25, or 0.50 mg L^?1 DFB for 14 days. Erythrocyte nuclear abnormalities (ENA), the gill activity of Na⁺/K⁺‐ATPase, H⁺‐ATPase and carbonic anhydrase (CA), and lipid peroxidation (LPO) and histopathological changes in the gills and liver were determined. The number of micronuclei increased in fish exposed to 0.25 and 0.50 mg L^?1 DFB. Plasma Cl^? and the CA activity decreased, while the activity of Na⁺/K⁺‐ATPase and of H⁺‐ATPase increased in fish exposed to 0.25 and 0.50 mg L^?1 DFB. LPO did not change in the gills but increased in the liver of fish exposed to 0.25 and 0.50 mg L^?1 DFB. In the gills, histopathological changes indicated disperse lesions and slight to moderate damage in fish exposed to 0.50 mg L^?1 DFB, whereas in the liver, these changes were significantly greater in fish exposed to 0.25 and 0.50 mg L^?1 DFB, indicating moderate to severe damage. Continuous exposure to DFB is potentially toxic to P. lineatus, causing heath disorders when the fish is exposed to the two highest DFB concentrations, which are applied to control parasites in aquaculture and to control mosquito populations in the environment. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 533–542, 2016.     

Effects of subchronic exposure to zinc nanoparticles on tissue accumulation,serum biochemistry,and histopathological changes in tilapia (Oreochromis niloticus)

Zinc nanoparticles (ZnNPs) are among the least investigated NPs and thus their toxicological effects are not known. In this study, tilapia (Oreochromis niloticus) were exposed to 1 and 10 mg/L suspensions of small size (SS, 40–60 nm) and large size (LS, 80–100 nm) ZnNPs for 14 days under semi‐static conditions. Total Zn levels in the intestine, liver, kidney, gill, muscle tissue, and brain were measured. Blood serum glucose (GLU), glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and lactate dehydrogenase (LDH) were examined to elucidate the physiological disturbances induced by ZnNPs. Organ pathologies were examined for the gills, liver, and kidney to identify injuries associated with exposure. Significant accumulation was observed in the order of intestine, liver, kidney, and gills. Zn levels exhibited time‐ and concentration‐dependent increase in the organs. Accumulation in kidney was also dependent on particle size; NPs SS‐ZnNPs were trapped more effectively than LS‐ZnNPs. No significant accumulation occurred in the brain (p > 0.05) while Zn levels in muscle tissue increased only marginally (p ≥ 0.05). Significant disturbances were noted in serum GOT and LDH (p < 0.05). The GPT levels fluctuated and were not statistically different from those of controls (p > 0.05). Histopathological tubular deformations and mononuclear cell infiltrations were observed in kidney sections. In addition, an increase in melano‐macrophage aggregation intensity was identified on the 7th day in treatments exposed to LS‐ZnNPs. Mononuclear cell infiltrations were identified in liver sections for all treatments. Both ZnNPs caused basal hyperplasia in gill sections. Fusions appeared in the gills after the 7th day in fish treated with 10 mg/L suspensions of SS‐ZnNPs. In addition, separations in the secondary lamella epithelia were observed. The results indicated that exposure to ZnNPs could lead to disturbances in blood biochemistry and cause histopathological injuries in the tissues of O. niloticus. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1213–1225, 2017.     

Biological effect of food additive titanium dioxide nanoparticles on intestine: an in vitro study

Titanium dioxide nanoparticles (TiO₂ NPs) are widely found in food‐related consumer products. Understanding the effect of TiO₂ NPs on the intestinal barrier and absorption is essential and vital for the safety assessment of orally administrated TiO₂ NPs. In this study, the cytotoxicity and translocation of two native TiO₂ NPs, and these two TiO₂ NPs pretreated with the digestion simulation fluid or bovine serum albumin were investigated in undifferentiated Caco‐2 cells, differentiated Caco‐2 cells and Caco‐2 monolayer. TiO₂ NPs with a concentration less than 200 µg ml^–1 did not induce any toxicity in differentiated cells and Caco‐2 monolayer after 24 h exposure. However, TiO₂ NPs pretreated with digestion simulation fluids at 200 µg ml^–1 inhibited the growth of undifferentiated Caco‐2 cells. Undifferentiated Caco‐2 cells swallowed native TiO₂ NPs easily, but not pretreated NPs, implying the protein coating on NPs impeded the cellular uptake. Compared with undifferentiated cells, differentiated ones possessed much lower uptake ability of these TiO₂ NPs. Similarly, the traverse of TiO₂ NPs through the Caco‐2 monolayer was also negligible. Therefore, we infer the possibility of TiO₂ NPs traversing through the intestine of animal or human after oral intake is quite low. This study provides valuable information for the risk assessment of TiO₂ NPs in food. Copyright © 2015 John Wiley & Sons, Ltd.     

Renal responses to acute lead waterborne exposure in the freshwater rainbow trout (Oncorhynchus mykiss)

The possible nephrotoxic effects of waterborne lead exposure (as Pb(NO₃)₂) were investigated in the freshwater rainbow trout (Oncorhynchus mykiss). Kidney lead accumulation was time-dependent, increasing upon exposure to 0.57 ± 0.01 mg dissolved Pb L⁻¹ for up to 96 h with a significantly higher burden occurring in the posterior kidney compared to the anterior segment. Urine analyses in trout exposed to 1.20 ± 0.09 mg dissolved Pb L⁻¹ revealed a significant increase in urinary lead excretion rate throughout 96 h of exposure. Urine flow rate and glomerular filtration rate (GFR) were not impacted with the exception of a significant decrease in GFR from 84 to 96 h in lead-exposed trout. Urine pH decreased significantly over time in lead-exposed fish. Correspondingly, urine ammonia excretion rate showed a marked increase from 48 h onwards. In experimental fish, urine glucose excretion was significantly greater by 96 h while urine lactate, urea and protein excretion were not significantly altered by lead exposure. The urine excretion rate of Ca²⁺ increased significantly by approximately 43% after only 24 h of lead exposure, and was maintained at a higher rate than controls for up to 96 h. Magnesium excretion increased in a time-dependent fashion, reaching a two- to three-fold rise by 96 h. In contrast, rates of Na⁺ and Cl⁻ excretion were decreased in experimental fish by approximately 30% by 48 h, this trend continuing for the duration of lead-exposure. There were no changes in any of these parameters in similarly treated control fish. Clearance ratio analyses indicated progressive decreases in the net reabsorption efficiencies of the renal system for Ca²⁺, Mg²⁺, Pb, and glucose, suggesting that the active tubular transport mechanisms for these substances were inhibited by lead exposure, while Na⁺, K⁺, Cl⁻, lactate, and protein reabsorptions were unaffected. Net ammonia secretion increased. We conclude that changes in renal function both reflect and help to minimize some of the associated disturbances in systemic physiology. Lead-induced ionoregulatory toxicity in rainbow trout, particularly the disturbance of Ca²⁺ homeostasis, is not exclusively a branchial phenomenon, but is in part a result of disruption of ionoregulatory mechanisms at the kidney. This action of lead outside the gills is critical to consider when developing guidelines for water quality.     

Combined effect of titanium dioxide nanoparticles and glucose on the cardiovascular system in young rats after oral administration

Titanium dioxide nanoparticles (TiO₂ NPs) have already been used as food additive in various products and are usually consumed with a considerable amount of sugar. Oral consumption of TiO₂ NPs poses concerning health risks; however, research on the combined effect of ingested TiO₂ NPs and glucose is limited. We examined young Sprague‐Dawley rats administrated TiO₂ NPs orally at doses of 0, 2, 10 and 50 mg/kg body weight per day with and without 1.8 g/kg body weight glucose for 30 and 90 days. Heart rate, systolic and diastolic blood pressure, blood biochemical parameters and histopathology of cardiac tissues was assessed to quantify cardiovascular damage. The results showed that oral exposure to TiO₂ NPs and high doses of glucose both could induce cardiovascular injuries. The toxic effects were dose‐, time‐ and gender‐dependent. The interaction effects between oral‐exposed TiO₂ NPs and glucose existed and revealed to be antagonism in most of the biological parameters. However, toxic effects of the high‐dose glucose seemed to be more severe than TiO₂ NPs and the interaction of TiO₂ NPs with glucose. These results suggest that it may be more important to control the sugar intake than TiO₂ NPs for protecting the health of TiO₂ NP consumers.     

TiO2 nanoparticle‐induced neurotoxicity may be involved in dysfunction of glutamate metabolism and its receptor expression in mice

Titanium dioxide nanoparticles (TiO₂ NPs) have been used in environmental management, food, medicine, and industry. But TiO₂ NPs have been demonstrated to cross the blood–brain barrier and store up in the brain organization, leading to glutamate‐mediated neurotoxicity. However, the neurotoxicity in the brain is not well understood. In this study, mice were exposed to 1.25, 2.5, or 5 mg/kg body weight TiO₂ NPs for 9 months, and the glutamate–glutamine cyclic pathway and expressions of glutamate receptors associated with the hippocampal neurotoxicity were investigated. Our findings showed elevations of glutamate release and phosphate‐activated glutaminase activity, and reductions in glutamine and glutamine synthetase in the hippocampus following exposure to TiO₂ NPs. Furthermore, TiO₂ NPs significantly inhibited the expression of N‐methyl‐d ‐aspartate receptor subunits (including NR1, NR2A, and NR2B) and metabotropic glutamate receptor 2 in mouse hippocampus. These findings suggest that the imbalance of glutamate metabolism triggered inhibitions of glutamate receptor expression in the TiO₂ NP‐exposed hippocampus. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 655–662, 2016.     

Mechanism of TiO2 nanoparticle‐induced neurotoxicity in zebrafish (Danio rerio)

Zebrafish (Danio rerio) has been used historically for evaluating the toxicity of environmental and aqueous toxicants, and there is an emerging literature reporting toxic effects of manufactured nanoparticles (NPs) in zebrafish embryos. Few researches, however, are focused on the neurotoxicity on adult zebrafish after subchronic exposure to TiO₂ NPs. This study was designed to evaluate the morphological changes, alterations of neurochemical contents, and expressions of memory behavior‐related genes in zebrafish brains caused by exposures to 5, 10, 20, and 40 μg/L TiO₂ NPs for 45 consecutive days. Our data indicated that spatial recognition memory and levels of norepinephrine, dopamine, and 5‐hydroxytryptamine were significantly decreased and NO levels were markedly elevated, and over proliferation of glial cells, neuron apoptosis, and TiO₂ NP aggregation were observed after low dose exposures of TiO₂ NPs. Furthermore, the low dose exposures of TiO₂ NPs significantly activated expressions of C‐fos, C‐jun, and BDNF genes, and suppressed expressions of p38, NGF, CREB, NR1, NR2ab, and GluR2 genes. These findings imply that low dose exposures of TiO₂ NPs may result in the brain damages in zebrafish, provide a developmental basis for evaluating the neurotoxicity of subchronic exposure, and raise the caution of aquatic application of TiO₂ NPs. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 163–175, 2016.