Bioaccessibility as a determining factor in the bioavailability and toxicokinetics of cadmium compounds.

Cadmium toxicity occurs where there is absorption and accumulation of cadmium ions (Cd2+) in tissues beyond tolerable levels. Significant differences in the release of Cd2+ from cadmium compounds in biological fluids, like gastric fluid, may indicate differences in bioavailability and absorption. This means that direct read-across from high solubility cadmium compounds to lower solubility compounds may not accurately reflect potential hazards. Here, the relative bioaccessibility in gastric fluid of cadmium telluride and cadmium chloride was evaluated using in vitro bioelution tests whilst the toxicokinetic behavior of these two compounds were compared after dietary administration for 90 days in male and female Wistar Han rats following OECD TG 408. Cadmium chloride was highly bioaccessible, whilst cadmium telluride showed low solubility in simulated gastric fluid (90 % and 1.5 % bioaccessibility, respectively). This difference in bioaccessibility was also reflected by a difference in bioavailability as shown by the difference in the liver and kidney concentrations of cadmium after repeat oral exposure. Feeding at doses of 750 and 1500 ppm of cadmium telluride did not result in tissue cadmium levels above the lower limit of quantification (LLOQ). In contrast, feeding with a lower test substance concentration yet higher concentration of bioaccessible cadmium (30 ppm cadmium chloride) resulted in tissue accumulation of cadmium. Only slight, non-adverse changes in hematology and clinical chemistry parameters were seen at these doses, indicating an absence of significant cadmium mediated toxicity towards target organs (kidney and liver), reflected in minimal cadmium accumulation in these organs. This study demonstrates that bioelution tests can help determine the bioaccessibility of cadmium, which can be used to estimate the potential for target tissue toxicity based on known toxicokinetic profiles and threshold levels for cadmium toxicity, while reducing and refining animal testing.

Strong accumulation capacity of hyperaccumulator Solanum nigrum L. for low or insoluble Cd compounds in soil and its implication for phytoremediation.

This experiment is to explore whether one hyperaccumulator shows the strongly accumulative capacities for low or insoluble Cd compounds in soil. Soil potting experiment was conducted to analyze the accumulation capacity of Solanum nigrum L. for 10 different Cd compounds under two levels. The results clearly indicated: The Cd concentrations of shoots and roots were very high for different Cd compounds in soils even with low or insoluble Cd compounds compared with easily soluble Cd in the treatments of soil contaminated with Cd at different concentrations. Furthermore, the EFs and TFs were all larger than 1 either. Based on the results, although the bioavailabilities of some Cd compounds in soil were lower, S. nigrum's ability to accumulate them was still very strong. Phytoremediation may be widely used to treat with soil contaminated by different cadmium compounds. In addition, the total Cd content is also very important in evaluating the risk of Cd contamination in soil. Thus, phytoextraction is promising.

A new method for evaluating the bioaccessibility of different foodborne forms of cadmium.

The bioabsorption and biotoxicity of cadmium are closely related to its binding form. Currently, total concentration is used as the indicator for evaluating cadmium toxicity in food, but it might not accurately reflect cadmium's toxic effects. This study attempted to evaluate the toxicity of the different forms of cadmium including cadmium-malate, cadmium-glutathione, and cadmium-metallothionein that are commonly found in food. The in vitro physiologically based extraction test (PBET) combined with Visual MINTEQ modeling was used to predict the toxicity of different forms of cadmium, and acute toxicity testing was performed in mice for validating their results. The in vivo experimental results showed that different forms of cadmium had diverse biotoxicities of which PBET was a good predictor. In particular, the simulation of cadmium ions in PBET using the MINTEQ software revealed that the free cadmium ion content in the simulated intestinal fluid had a superior linear relationship than the total cadmium concentration with the toxicology indexes. Verification using the other two forms of cadmium confirmed the accuracy of the prediction of their biotoxicity. These findings hopefully provide an important reference for a more accurate and rapid safety assessment of cadmium in food.

Biodistribution and Systemic Effects in Mice Following Intravenous Administration of Cadmium Telluride Quantum Dot Nanoparticles.

Quantum dots (QDs) are engineered nanoparticles (NPs) of semiconductor structure that possess unique optical and electronic properties and are widely used in biomedical applications; however, their risks are not entirely understood. This study investigated the tissue distribution and toxic effects of cadmium telluride quantum dots (CdTe-QDs) in male BALB/c mice for up to 1 week after single-dose intravenous injections. CdTe-QDs were detected in the blood, lung, heart, liver, spleen, kidney, testis and brain. Most CdTe-QDs accumulated in the liver, followed by the spleen and kidney. At high doses, exposure to CdTe-QDs resulted in mild dehydration, lethargy, ruffled fur, hunched posture, and body weight loss. Histological analysis of the tissues, upon highest dose exposures, revealed hepatic hemorrhage and necrotic areas in the spleen. The sera of mice treated with high doses of CdTe-QDs showed significant increases in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin levels, as well as a reduction in albumin. CdTe-QD exposure also led to a reduced number of platelets and elevated total white blood cell counts, including monocytes and neutrophils, serum amyloid A, and several pro-inflammatory cytokines. These results demonstrated that the liver is the main target of CdTe-QDs and that exposure to CdTe-QDs leads to hepatic and splenic injury, as well as systemic effects, in mice. By contrast, cadmium chloride (CdCl2), at an equivalent concentration of cadmium, appeared to have a different pharmacokinetic pattern from that of CdTe-QDs, having minimal effects on the aforementioned parameters, suggesting that cadmium alone cannot fully explain the toxicity of CdTe-QDs.

Evaluation of Quantum Dot Skin Penetration in Porcine Skin: Effect of Age and Anatomical Site of Topical Application.

BACKGROUND: Pig skin is a widely acknowledged surrogate for human skin for in vitro/ex vivo skin penetration studies with application for small molecules and nanosystems. We have investigated the influence of biological factors such as age and anatomical site on the penetration and distribution of nanoparticles (2.1 nm hydrophilic CdTe/CdS quantum dots: QDs) in adult pig skin (APS), weanling pig skin (WPS) and newborn pig skin (NBPS) at two different anatomical sites (ear and abdomen). METHODS: QDs in saline were applied to 1 × 1 cm2 skin (62.5 pmol/cm2) with 2-min finger rubbing using a standardized protocol. After 6- or 24-h incubation on Franz diffusion cells, tape stripping (×10) followed by manual follicular casting was conducted. Cadmium in QDs was quantified using inductively coupled plasma mass spectrometry for all samples. The presence of QDs in similarly treated skin samples was also captured using multiphoton tomography. RESULTS: QDs were mainly localized in hair follicles after 6 and 24 h of exposure with no cadmium detected in the Franz cell receptor compartment regardless of pig age or anatomical site. The amount of QDs deposited in the follicles was similar at 6 h but higher on APS and WPS ears compared to NBPS ears at 24 h. This is associated with the high follicle density and small follicle diameter of the NBPS compared to the smaller density of much larger follicles on the APS. NBPS showed consistent QD distribution for ear and abdomen up to 24 h. CONCLUSIONS: There is minimal penetration of QDs through pig skin. Density and diameter of follicles in association with age of pigs and application site influenced the amount of QDs deposited in follicles. The structure of the stratum corneum, follicle density and diameter of NBPS are similar to human skin suggesting that NBPS is an appropriate model for human skin in the evaluation of topical applications of a range of chemicals including nanosystems.

The role of epicuticular waxes on foliar metal transfer and phytotoxicity in edible vegetables: case of Brassica oleracea species exposed to manufactured particles.

The rapid industrialization and urbanization of intra- and peri-urban areas at the world scale are responsible for the degradation of the quality of edible crops, because of their contamination with airborne pollutants. Their consumption could lead to serious health risks. In this work, we aim to investigate the phytotoxicity induced by foliar transfer of atmospheric particles of industrial/urban origin. Leaves of cabbage plants (Brassica oleracea var. Prover) were contaminated with metal-rich particles (PbSO4 CuO and CdO) of micrometer size. A trichloroacetic acid (TCA) treatment was used to inhibit the synthesis of the epicuticular waxes in order to investigate their protective role against metallic particles toxicity. Besides the location of the particles on/in the leaves by microscopic techniques, photosynthetic activity measurements, genotoxicity assessment, and quantification of the gene expression have been studied for several durations of exposure (5, 10, and 15 days). The results show that the depletion of epicuticular waxes has a limited effect on the particle penetration in the leaf tissues. The stomatal openings appear to be the main pathway of particles entry inside the leaf tissues, as demonstrated by the overexpression of the BolC.CHLI1 gene. The effects of particles on the photosynthetic activity are limited, considering only the photosynthetic Fv/Fm parameter. The genotoxic effects were significant for the contaminated TCA-treated plants, especially after 10 days of exposure. Still, the cabbage plants are able to implement repair mechanisms quickly, and to thwart the physiological effects induced by the particles. Finally, the foliar contamination by metallic particles induces no serious damage to DNA, as observed by monitoring the BolC.OGG1 gene.

Matricidal hatching can induce multi-generational effects in nematode Caenorhabditis elegans after dietary exposure to nanoparticles.

In this study, we investigated multi-generational effects and generation particle transfer in Caenorhabditis elegans following maternal food exposure to core-shell quantum dots. We found that that the Bag of Worms (BOW) phenotype in aged worms induces changes in quantum dot distribution in the parental body, which is related to the inter-generation transfer of these nanoparticles and to their effects in the offspring. To confirm these results we examined a variety of endpoints, namely, survival, reproduction, aging phenotype, oxidative stress, and intestinal fat metabolism. We show that worms born to parents at different times after exposure show different phenotypic effects as a consequence of quantum dot transfer. This evidence of trans-generational transfer and the effects of nanoparticles highlights the complex multi-generational effects and potential safety hazards that can occur under real environmental conditions.

Effect of Nanoparticle Surface Coating on Cell Toxicity and Mitochondria Uptake.

We report on the effect of surface charge and the ligand coating composition of CdSe/ZnS core/shell quantum dot (QD) nanoparticles on human keratinocyte toxicity using fluorescent microscopy, flow cytometry, transmission electron microscopy. Two commonly reported positive charged (cysteamine, polyethylenimine) and two negative charged (glutathione, dihydrolipoic acid) ligands were studied. The QDs were fully characterized by UV-vis absorption spectroscopy, fluorescence emission spectroscopy, dynamic light scattering and zeta potential. Differences in surface coatings and charges were evaluated against cellular uptake, ROS generation, cytotoxicity, and mitochondrial targeting. Results show that the negative charged QDs coated with GSH exhibit excellent water solubility, high quantum yield and low cytotoxicity. Ligand composition is more important in ROS generation than surface charge whereas surface charge is an important driver of cytotoxicity. Most importantly we observe the selective accumulation of glutathione coated QDs in vesicles in the mitochondria matrix. This observation suggests a new strategy for developing mitochondria-targeted nanomaterials for drug/gene delivery.

Cadmium Telluride Quantum Dots as a Fluorescence Marker for Adipose Tissue Grafts.

Plastic and reconstructive surgeons increasingly apply adipose tissue grafting in a clinical setting, although the anticipation of graft survival is insecure. There are only few tools for tracking transplanted fat grafts in vivo.Murine adipose tissue clusters were incubated with negatively charged, mercaptoproprionic acid-coated cadmium telluride quantum dots (QDs) emitting in the dark red or near infrared. The intracellular localization of QDs was studied by confocal laser scanning microscopy.As a result, the adipose tissue clusters showed a proportional increase in fluorescence with increasing concentrations (1, 10, 16, 30, 50 nM) of cadmium telluride QDs. Laser scanning microscopy demonstrated a membrane bound localization of QDs. Vacuoles and cell nuclei of adipocytes were spared by QDs. We conclude that QDs were for the first time proven intracellular in adult adipocytes and demonstrate a strong fluorescence signal. Therefore, they may play an essential role for in vivo tracking of fat grafts.

Ability of the marine bacterium Pseudomonas fluorescens BA3SM1 to counteract the toxicity of CdSe nanoparticles.

UNLABELLED: In the marine environment, bacteria from estuarine and coastal sediments are among the first targets of nanoparticle pollution; it is therefore relevant to improve the knowledge of interactions between bacteria and nanoparticles. In this work, the response of the marine bacterium Pseudomonas fluorescens BA3SM1 to CdSe nanocrystals (CdSe NPs) of 3nm (NP3) and 8nm (NP8) in diameter was evaluated through microscopic, physiological, biochemical and proteomic approaches. Transmission electron microscopy images showed that NP3 were able to penetrate the bacteria, while NP8 were highly concentrated around the cells, embedded in large exopolysaccharides. In our experimental conditions, both CdSe NP sizes induced a decrease in respiration during the stationary growth phase, while only NP8 caused growth retardation and a decrease in pyoverdine production. Proteomic analyses highlighted that the strain responded to CdSe NP toxicity by inducing various defence mechanisms such as cell aggregation, extracellular CdSe NP sequestration, effective protection against oxidative stress, modifications of envelope organization and properties, and cadmium export. In addition, BA3SM1 presented a biosorption capacity of 1.6×10(16)NP3/g dry weight and 1.7×10(15)NP8/g dry weight. This strain therefore appears as a promising agent for NP bioremediation processes. Proteomic data are available via ProteomeXchange with identifier PXD004012. BIOLOGICAL SIGNIFICANCE: To the best of our knowledge, this is the first report focussing on the effects of CdSe colloidal nanocrystals (CdSe NPs) on a marine strain of Pseudomonas fluorescens. CdSe NPs are extensively used in the industry of renewable energies and it is regrettably expected that these pollutants will sometime soon appear in the marine environment through surface runoff, urban effluents and rivers. Bacteria living in estuarine and coastal sediments will be among the first targets of these new pollutants. The pseudomonads are frequently found in these ecosystems. They are involved in several biogeochemical cycles and are known for their high resistance to pollutants. Consequently, this study focussing on the effects of CdSe NPs on the marine strain P. fluorescens BA3SM1 is highly relevant for several reasons. First, it aims at improving knowledge about the interactions between bacteria and NPs. This is fundamental to effectively use NPs against pathogenic bacteria. Secondly, in spite of CdSe NP interactions with the bacterial cells, the strain BA3SM1 can develop various strategies to counteract CdSe NP toxicity and ensure its growth. It exhibits interesting properties to sequester CdSe NPs and it retains its ability to form biofilm. The strain therefore appears as a promising agent for NP bioremediation thanks to biofiltration processes. Finally, this study shows that CdSe NPs of 8nm in diameter cause a decrease in the secretion of siderophore pyoverdine, a secondary metabolite playing a key role in microbial ecology since it drives bacterial survival and competitiveness in ecosystems. Bacteria producing effective siderophores survive better in a Fe-deficient environment where they antagonize the growth of other microbes thought iron deprivation. Furthermore, siderophores are also employed as virulence factors in human pathogenic strains such as P. aeruginosa. Consequently, this study highlights that NPs can impact the secondary metabolism of bacteria with environmental and medical implications. In addition, in this work, Data-Dependant Acquisition (DDA) provided state of the art Mass Spectrometry data by Spectral Counting and MS1 Label-Free. The combination of these two well-known proteomic techniques including manual validations strengthened the identification and quantification of regulated proteins. Moreover, numerous correlations between proteomic analyses and other observations (physiological, biochemical, microscopic) consolidated our interpretations.