Influence of Uranium Speciation on Normal Rat Kidney (NRK-52E) Proximal Cell Cytotoxicity

Effect of Ba(II), Eu(III), and U(VI) on rat NRK-52E and human HEK-293 kidney cells in vitro

Heavy metals pose a potential health risk to humans when they enter the organism. Renal excretion is one of the elimination pathways and, therefore, investigations with kidney cells are of particular interest. In the present study, the effects of Ba(II), Eu(III), and U(VI) on rat and human renal cells were investigated in vitro. A combination of microscopic, biochemical, analytical, and spectroscopic methods was used to assess cell viability, cell death mechanisms, and intracellular metal uptake of exposed cells as well as metal speciation in cell culture medium and inside cells. For Eu(III) and U(VI), cytotoxicity and intracellular uptake are positively correlated and depend on concentration and exposure time. An enhanced apoptosis occurs upon Eu(III) exposure whereas U(VI) exposure leads to enhanced apoptosis and (secondary) necrosis. In contrast to that, Ba(II) exhibits no cytotoxic effect at all and its intracellular uptake is time-independently very low. In general, both cell lines give similar results with rat cells being more sensitive than human cells. The dominant binding motifs of Eu(III) in cell culture medium as well as cell suspensions are (organo-) phosphate groups. Additionally, a protein complex is formed in medium at low Eu(III) concentration. In contrast, U(VI) forms a carbonate complex in cell culture medium as well as each one phosphate and carbonate complex in cell suspensions. Using chemical microscopy, Eu(III) was localized in granular, vesicular compartments near the nucleus and the intracellular Eu(III) species equals the one in cell suspensions. Overall, this study contributes to a better understanding of the interactions of Ba(II), Eu(III), and U(VI) on a cellular and molecular level. Since Ba(II) and Eu(III) serve as inactive analogs of the radioactive Ra(II) and Am(III)/Cm(III), the results of this study are also of importance for the health risk assessment of these radionuclides.

Induction of lysosomal exocytosis and biogenesis via TRPML1 activation for the treatment of uranium-induced nephrotoxicity

Uranium (U) is a well-known nephrotoxicant which forms precipitates in the lysosomes of renal proximal tubular epithelial cells (PTECs) after U-exposure at a cytotoxic dose. However, the roles of lysosomes in U decorporation and detoxification remain to be elucidated. Mucolipin transient receptor potential channel 1 (TRPML1) is a major lysosomal Ca2+ channel regulating lysosomal exocytosis. We herein demonstrate that the delayed administration of the specific TRPML1 agonist ML-SA1 significantly decreases U accumulation in the kidney, mitigates renal proximal tubular injury, increases apical exocytosis of lysosomes and reduces lysosomal membrane permeabilization (LMP) in renal PTECs of male mice with single-dose U poisoning or multiple-dose U exposure. Mechanistic studies reveal that ML-SA1 stimulates intracellular U removal and reduces U-induced LMP and cell death through activating the positive TRPML1-TFEB feedback loop and consequent lysosomal exocytosis and biogenesis in U-loaded PTECs in vitro. Together, our studies demonstrate that TRPML1 activation is an attractive therapeutic strategy for the treatment of U-induced nephrotoxicity.

Review of Knowledge of Uranium-Induced Kidney Toxicity for the Development of an Adverse Outcome Pathway to Renal Impairment

An adverse outcome pathway (AOP) is a conceptual construct of causally and sequentially linked events, which occur during exposure to stressors, with an adverse outcome relevant to risk assessment. The development of an AOP is a means of identifying knowledge gaps in order to prioritize research assessing the health risks associated with exposure to physical or chemical stressors. In this paper, a review of knowledge was proposed, examining experimental and epidemiological data, in order to identify relevant key events and potential key event relationships in an AOP for renal impairment, relevant to stressors such as uranium (U). Other stressors may promote similar pathways, and this review is a necessary step to compare and combine knowledge reported for nephrotoxicants. U metal ions are filtered through the glomerular membrane of the kidneys, then concentrate in the cortical and juxtaglomerular areas, and bind to the brush border membrane of the proximal convoluted tubules. U uptake by epithelial cells occurs through endocytosis and the sodium-dependent phosphate co-transporter (NaPi-IIa). The identified key events start with the inhibition of the mitochondria electron transfer chain and the collapse of mitochondrial membrane potential, due to cytochrome b5/cytochrome c disruption. In the nucleus, U directly interacts with negatively charged DNA phosphate, thereby inducing an adduct formation, and possibly DNA strand breaks or cross-links. U also compromises DNA repair by inhibiting zing finger proteins. Thereafter, U triggers the Nrf2, NF-κB, or endoplasmic reticulum stress pathways. The resulting cellular key events include oxidative stress, DNA strand breaks and chromosomal aberrations, apoptosis, and pro-inflammatory effects. Finally, the main adverse outcome is tubular damage of the S2 and S3 segments of the kidneys, leading to tubular cell death, and then kidney failure. The attribution of renal carcinogenesis due to U is controversial, and specific experimental or epidemiological studies must be conducted. A tentative construction of an AOP for uranium-induced kidney toxicity and failure was proposed.

Uranium induces kidney cells apoptosis via reactive oxygen species generation, endoplasmic reticulum stress and inhibition of PI3K/AKT/mTOR signaling in culture

Uranium (U) induces generation of excessive intracellular reactive oxygen species (ROS), which is generally considered as a possible mediator of U-triggered kidney tubular cells injury and nephrotoxicity. Our goal is designed to elucidate that the precise molecular mechanism in ROS downstream is association with U-induced NRK-52^E cells apoptosis. The results show that U intoxication in NRK-52^E cells reduced cell activity and triggered apoptosis, as demonstrated by flow cytometry and apoptotic marker cleaved Caspase-3 expression. U exposure triggered endoplasmic reticulum (ER) stress, which is involvement of apoptosis determined by marker molecules including GRP78, PERK, IRE1, ATF6, CHOP, cleaved Caspase-12, and Caspase-3. Administration of antioxidant N-acetylcysteine (NAC) effectively blocked U-triggered ROS generation, ER stress, and apoptosis. U contamination evidently decreased the expression of phosphorylation PI3K, AKT, and mTOR and ratios of their respective phosphorylation to the corresponding total proteins. Application of a PI3K activator IGF-1 significantly abolished these adverse effects of U intoxication on PI3K/AKT/mTOR signaling and subsequently abrogated U-triggered apoptosis. NAC also effectively reversed down-regulation of phosphorylated PI3K induced by U exposure. Taken together, these data strongly suggest that U treatment induces NRK-52^E cells apoptosis through ROS production, ER stress, and down-regulation of PI3K/AKT/mTOR signaling. Targeting ROS formation-, ER stress-, and PI3K/AKT/mTOR pathway-mediated apoptosis could be a novel approach for attenuating U-triggered nephrotoxicity.

Protective effects of Polygonatum kingianum polysaccharides and aqueous extract on uranium-induced toxicity in human kidney (HK-2) cells

The current detoxification options of uranium, a toxic radioactive heavy metal, have obvious side effects. Polygonatum kingianum (PK), a natural product with the function of antioxidant, may be effective in detoxification and prevention of uranium-induced nephrotoxicity. Here, we studied the protective effects of PK polysaccharides (PKP) and aqueous extract (PKAE) on uranium-induced toxicity in human kidney (HK-2) cells. First, the physicochemical properties of PKP and PKAE were characterized. Assays on cultured cells demonstrated that pretreatment with PKP and PKAE significantly increased metabolic activity, relieved morphological impairments, and alleviated apoptosis. The impairments caused by uranium exposure were ameliorated (mitochondrial membrane potential and ATP level increased while reactive oxygen species decreased). Molecular mechanistic studies revealed that PKP and PKAE alleviated uranium-induced cytotoxicity by regulating mitochondria-mediated apoptosis and the GSK-3β/Fyn/Nrf2 pathway. Collectively, our data support the preventive and therapeutic applications of PKP and PKAE for uranium poisoning.

The effect of four lanthanides onto a rat kidney cell line (NRK-52E) is dependent on the composition of the cell culture medium

Lanthanide (Ln) exposure poses a serious health risk to animals and humans. In this study, we investigated the effect of 10^-9-10^-3 M La, Ce, Eu, and Yb exposure onto the viability of rat renal NRK-52E cells in dependence on Ln concentration, exposure time, and composition of the cell culture medium. Especially, the influence of fetal bovine serum (FBS) and citrate onto Ln cytotoxicity, solubility, and speciation was investigated. For this, in vitro cell viability studies using the XTT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using TRLFS and ICP-MS, respectively. The theoretical Ln speciation was predicted using thermodynamic modeling. All Ln exhibit a concentration- and time-dependent effect on NRK-52E cells. FBS is the key parameter influencing both Ln solubility and cytotoxicity. We demonstrate that FBS is able to bind Ln³⁺ ions, thus, promoting solubility and reducing cytotoxicity after Ln exposure for 24 and 48 h. In contrast, citrate addition to the cell culture medium has no significant effect on Ln solubility and speciation nor cytotoxicity after Ln exposure for 24 and 48 h. However, a striking increase of cell viability is observable after Ln exposure for 8 h. Out of the four Ln elements under investigation, Ce is the most effective. Results from TRLFS and solubility measurements correlate well to those from in vitro cell culture experiments. In contrast, results from thermodynamic modeling do not correlate to TRLFS results, hence, demonstrating that big gaps in the database render this method, currently, inapplicable for the prediction of Ln speciation in cell culture media. Finally, this study demonstrates the importance and the synergistic effects of combining chemical and spectroscopic methods with cell culture techniques and biological methods.

The determination of the thermodynamic constants of MgUO2(CO3)32- complex in NaClO4 and NaCl media by time-resolved luminescence spectroscopy, and applications in different geochemical contexts

The formation constants and specific ion interaction coefficients of MgUO₂(CO₃)₃^2- complex were determined in 0.1 to 1.0 mol kg_w^-1 NaCl and 0.10 to 2.21 mol kg_w^-1 NaClO₄ media in the framework of the specific ion interaction theory (SIT), by time-resolved laser-induced luminescence spectroscopy. The upper limits of ionic strength were chosen in order to limit luminescence quenching effects generated by high concentrations of Cl^- and ClO₄^- already observed during our earlier studies on Ca_nUO₂(CO₃)₃^(4-2n)- complexes (Shang & Reiller, Dalton Trans., 49, 466; Shang et al., Dalton Trans., 49, 15443). The cumulative formation constant determined is , and the specific ion interaction coefficients are ε(MgUO₂(CO₃)₃^2-, Na⁺) = 0.19 ± 0.11 kg_w mol^-1 in NaClO₄ and ε(MgUO₂(CO₃)₃^2-, Na⁺) = 0.09 ± 0.16 kg_w mol^-1 in NaCl. Two gratings of 300 and 1800 lines per mm were used to acquire MgUO₂(CO₃)₃^2- luminescence spectra, where the high-resolution 1800 lines per mm grating detected slight spectral shifts for the principal luminescent bands relative to Ca_nUO₂(CO₃)₃^(4-2n)-. The applications of the consistent set of thermodynamic constants and ε values for M_nUO₂(CO₃)₃^(4-2n)- (M = Mg and Ca) were examined in different geochemical contexts, where Mg over Ca concentration ratio varies to help defining the relative importance of these species.

Uranium(VI) toxicity in tobacco BY-2 cell suspension culture - A physiological study

For the first time, the physiological and cellular responses of Nicotiana tabacum (BY-2) cells to uranium (U) as an abiotic stressor were studied using a multi-analytic approach that combined biochemical analysis, thermodynamic modeling and spectroscopic studies. The goal of this investigation was to determine the U threshold toxicity in tobacco BY-2 cells, the influence of U on the homeostasis of micro-macro essential nutrients, as well as the effect of Fe starvation on U bioassociation in cultured BY-2 cells. Our findings demonstrated that U interferes with the homeostasis of essential elements. The interaction of U with BY-2 cells confirmed both time- and concentration-dependent kinetics. Under Fe deficiency, a reduced level of U was detected in the cells compared to Fe-sufficient conditions. Interestingly, blocking the Ca channels with gadolinium chloride caused a decrease in U concentration in the BY-2 cells. Spectroscopic studies evidenced changes in the U speciation in the culture media with increasing exposure time under both Fe-sufficient and deficient conditions, leading us to conclude that different stress response reactions are related to Fe metabolism. Moreover, it is suggested that U toxicity in BY-2 cells is highly dependent on the existence of other micro-macro elements as shown by negative synergistic effects of U and Fe on cell viability.

Uranium inhibits mammalian mitochondrial cytochrome c oxidase and ATP synthase

As an emerging pollutant, uranium poses serious concerns to ecological and human health. The kidney has been established as a major deposition site and the most sensitive target organ for uranium poisoning, and the underlying toxicological mechanisms have been associated with oxidative stress and mitochondrial respiration. However, the identities of key molecular targets in uranium-induced toxicity remain elusive. In this study, we comprehensively evaluated the in vitro effects of uranium on ten critical enzymes in the mitochondrial respiration pathway and discovered that respiratory chain complex IV (cytochrome c oxidase) and complex V (ATP synthase) were strongly inhibited. The inhibitory effects were validated with mitochondria from human renal proximal tubule cells-the most affected renal site in uranium poisoning. The IC₅₀ values (around 1 mg/L) are physiologically relevant, as they are comparable to known kidney accumulation levels in uranium poisoning. In addition, these inhibitory effects could explain the well-documented uranium-induced reactive oxygen species generation and mitochondrial alterations. In conclusion, cytochrome c oxidase and ATP synthase are possibly key molecular targets underlying the toxic effects of uranium.

Emerging health risks and underlying toxicological mechanisms of uranium contamination: Lessons from the past two decades

Uranium contamination is a global health concern. Regarding natural or anthropogenic uranium contamination, the major sources of concern are groundwater, mining, phosphate fertilizers, nuclear facilities, and military activities. Many epidemiological and laboratory studies have demonstrated that environmental and occupational uranium exposure can induce multifarious health problems. Uranium exposure may cause health risks because of its chemotoxicity and radiotoxicity in natural or anthropogenic scenarios: the former is generally thought to play a more significant role with regard to the natural uranium exposure, and the latter is more relevant to enriched uranium exposure. The understanding of the health risks and underlying toxicological mechanisms of uranium remains at a preliminary stage, and many controversial findings require further research. In order to present state-of-the-art status in this field, this review will primarily focus on the chemotoxicity of uranium, rather than its radiotoxicity, as well as the involved toxicological mechanisms. First, the natural or anthropogenic uranium contamination scenarios will be briefly summarized. Second, the health risks upon natural uranium exposure, for example, nephrotoxicity, bone toxicity, reproductive toxicity, hepatotoxicity, neurotoxicity, and pulmonary toxicity, will be discussed based on the reported epidemiological cases and laboratory studies. Third, the recent advances regarding the toxicological mechanisms of uranium-induced chemotoxicity will be highlighted, including oxidative stress, genetic damage, protein impairment, inflammation, and metabolic disorder. Finally, the gaps and challenges in the knowledge of uranium-induced chemotoxicity and underlying mechanisms will be discussed.

Passage of uranium through human cerebral microvascular endothelial cells: influence of time exposure in mono- and co-culture in vitro models

PURPOSE

Depleted uranium (DU) has several civilian and military applications. The effects of this emerging environmental pollutant on human health raise some concerns. Previous experimental studies have shown that uranium (U) exposure can disturb the central nervous system. A small quantity of U reaches the brain via the blood, but the effects on the blood-brain barrier (BBB) remain unclear.

MATERIALS AND METHODS

In the present work, two cell culture models were exposed to DU for different times to study its cytotoxicity, paracellular permeability and extracellular concentration of U. The well-known immortalized human cerebral microvascular endothelial cells, hCMEC/D3, were cultured on the filter in the first model. In the second model, human primary cells of pericytes were cultured under the filter to understand the influence of cell environment after U exposure.

RESULTS

The results show that U is not cytotoxic to hCMEC/D3 cells or pericytes until 500 µM (1.6 Bq.L^-1). In addition, acute or chronic low-dose exposure of U did not disturb permeability and was conserved in both cell culture models. However, U is able to reach the brain compartment. During the first hours of exposure, the passage of U to the abluminal compartment was significantly reduced in the presence of pericytes. Electronic microscopy studies evidenced the formation of needlelike structures, like urchin-shaped precipitates, from 1 h of exposure. Analytical microscopy confirmed the U composition of these precipitates. Interestingly, precipitated U was detected only in endothelial cells and not in pericytes. U was localized in multilamellar or multivesicular bodies along the endo-lysosomal pathway, suggesting the involvement of these traffic vesicles in U sequestration and/or elimination.

CONCLUSIONS

We show for the first time the in vitro passage of U across a human cerebral microvascular endothelial cells, and the intracellular localization of U precipitates without any cytotoxicity or modification of paracellular permeability. The difference between the results obtained with monolayers and co-culture models with pericytes illustrates the need to use complex in vitro models in order to mimic the neurovascular unit. Further in vivo studies should be performed to better understand the passage of U across the blood-brain barrier potentially involved in behavioral consequences.

Influence of Angiotensin II on cell viability and apoptosis in rat renal proximal tubular epithelial cells in in vitro studies

Introduction:

Angiotensin II (Ang II) is multifunctional peptide that plays an important role in blood pressure regulation and maintenance electrolyte homeostasis. It shows biological effects by activating two main receptors: AT₁ and AT₂. The aim of the present work was to investigate the effect of Ang II on NRK-52E cells in in vitro studies. Furthermore, an attempt was made to determine the effectiveness of the AT₁ and AT₂ receptor blocker activity (respectively, losartan and PD123319).

Methods:

The study was carried out using adherent NRK-52E cell line. Immunofluorescence and Western Blot method were used to confirm the presence of AT₁ and AT₂ receptors in the cells. The SRB and MTT tests showed decrease in the viability of NRK-52E cells incubated with Ang II in comparison to the control (without Ang II).

Results:

The blockade of the AT₁ receptor caused an increase in cell viability in comparison to cells incubated with Ang II only. The blockade of AT₂ receptor also triggered statistically significant increase in cell viability in comparison with cells only exposed to Ang II. Combined administration of blockers for both receptors (losartan and PD123319) decreased Ang II cytotoxicity against NRK-52E cell line. The apoptosis was only observed in cells incubated with Ang II in comparison with control cells. However, simultaneous use of both blockers caused statistically significant decrease in apoptosis.

Conclusions:

The result of our study indicates that Ang II causes damaging effect on NRK-52E cells by directing them to programmed cell death. It seems that not only does the AT₂ receptor itself play an important role in the induction of apoptosis, but also its interaction with AT₁ receptor does as well.

Advances on the toxicity of uranium to different organisms

The extensive application of radioactive element uranium (U) and its compounds in the nuclear industry has significantly increased the risk of exposure to the environment. Therefore, research on the safety risks and toxicity mechanisms of U exposure has received increasing attention. This paper reviews the toxic effects of U on different species under different conditions, and summarizes the potential toxicity mechanisms. Under the exposure of U, reactive oxygen species (ROS) produced in cells will damage membrane structure in cells, and inhibit respiratory chain reaction by reducing the production of NADH and ATP. It also induce the expression of apoptosis factors such as Bcl-2, Bid, Bax, and caspase family to cause apoptosis cascade reaction, leading to DNA degradation and cell death. We innovatively list some methods to reduce the toxicity of U because some microorganisms can precipitate uranyl ions through biomineralization or reduction processes. Our work provides a solid foundation for further risk assessment of U.

What do we know about actinides-proteins interactions?

Since the early 40s when the first research related to the development of the atomic bomb began for the Manhattan Project, actinides (An) and their association with the use of nuclear energy for civil applications, such as in the generation of electricity, have been a constant source of interest and fear. In 1962, the first Society of Toxicology (SOT), led by H. Hodge, was established at the University of Rochester (USA). It was commissioned as part of the Manhattan Project to assess the impact of nuclear weapons production on workers’ health. As a result of this initiative, the retention and excretion rates of radioactive heavy metals, their physiological impact in the event of acute exposure and their main biological targets were assessed. In this context, the scientific community began to focus on the role of proteins in the transportation and in vivo accumulation of An. The first studies focused on the identification of these proteins. Thereafter, the continuous development of physico-chemical characterization techniques has made it possible to go further and specify the modes of interaction with proteins from both a thermodynamic and structural point of view, as well as from the point of view of their biological activity. This article reviews the work performed in this area since the Manhattan Project. It is divided into three parts: first, the identification of the most affine proteins; second, the study of the affinity and structure of protein-An complexes; and third, the impact of actinide ligation on protein conformation and function.

Effect of Calcium on the Bioavailability of Dissolved Uranium(VI) in Plant Roots under Circumneutral pH

We integrated field measurements, hydroponic experiments, microscopy, and spectroscopy to investigate the effect of Ca(II) on dissolved U(VI) uptake by plants in 1 mM HCO₃^- solutions at circumneutral pH. The accumulation of U in plants (3.1-21.3 mg kg^-1) from the stream bank of the Rio Paguate, Jackpile Mine, New Mexico served as a motivation for this study. Brassica juncea was the model plant used for the laboratory experiments conducted over a range of U (30-700 μg L^-1) and Ca (0-240 mg L^-1) concentrations. The initial U uptake followed pseudo-second-order kinetics. The initial U uptake rate ( V₀) ranged from 4.4 to 62 μg g^-1 h^-1 in experiments with no added Ca and from 0.73 to 2.07 μg g^-1 h^-1 in experiments with 12 mg L^-1 Ca. No measurable U uptake over time was detected for experiments with 240 mg L^-1 Ca. Ternary Ca-U-CO₃ complexes may affect the decrease in U bioavailability observed in this study. Elemental X-ray mapping using scanning transmission electron microscopy-energy-dispersive spectrometry detected U-P-bearing precipitates within root cell walls in water free of Ca. These results suggest that root interactions with Ca and carbonate in solution affect the bioavailability of U in plants. This study contributes relevant information to applications related to U transport and remediation of contaminated sites.

3,2-Hydroxypyridinone-Grafted Chitosan Oligosaccharide Nanoparticles as Efficient Decorporation Agents for Simultaneous Removal of Uranium and Radiation-Induced Reactive Oxygen Species in Vivo

Most of the key radionuclides in the nuclear fuel cycle, such as actinides, possess a combination of heavy metal chemotoxicity and radiotoxicity and therefore represent a severe threat to the ecological environment and public safety. The radiotoxicity originates from direct radiation-induced organ damage and indirect damage, mostly through radiation-induced reactive oxygen species (ROS). Although effective chelating agents that can accelerate the excretion of actinides, such as uranium, have been developed in the past several decades, very few of them can reduce radiation-induced damage from internal contamination. In fact, the strategy of simultaneous removal of actinides and their induced-ROS in vivo has scarcely been considered. Here, we report a 3,2-hydroxypyridinone-grafted chitosan oligosaccharide nanoparticle (COS-HOPO) as a new type of decorporation agent that is effective for the removal of both uranium and ROS in vivo. The cytotoxicity and decorporation assays indicate that the marriage of chitosan oligosaccharide (COS) and hydroxypyridinone (HOPO) gives rise to a remarkable decrease in toxicity and promotion of the uranium removal capability from both kidneys and femurs. The decorporation efficacy can reach up to 43% in rat proximal tubular epithelial cells (NRK-52E), 44% in kidneys, and 32% in femurs. Moreover, the ROS levels of the cells treated with COS-HOPO are significantly lower than those of the control group, implying a promising radiation protection effect. The detoxification mechanism of COS-HOPO is closely related to both chelating U(VI)- and scavenging U(VI)-induced intracellular ROS.

Uranium exposure of human dopaminergic cells results in low cytotoxicity, accumulation within sub-cytoplasmic regions, and down regulation of MAO-B

Natural uranium is an ubiquitous element present in the environment and human exposure to low levels of uranium is unavoidable. Although the main target of acute uranium toxicity is the kidney, some concerns have been recently raised about neurological effects of chronic exposure to low levels of uranium. Only very few studies have addressed the molecular mechanisms of uranium neurotoxicity, indicating that the cholinergic and dopaminergic systems could be altered. The main objective of this study was to investigate the mechanisms of natural uranium toxicity, after 7-day continuous exposure, on terminally differentiated human SH-SY5Y cells exhibiting a dopaminergic phenotype. Cell viability was first assessed showing that uranium cytotoxicity only occurred at high exposure concentrations (> 125 μM), far from the expected values for uranium in the blood even after occupational exposure. SH-SY5Y differentiated cells were then continuously exposed to 1, 10, 125 or 250 μM of natural uranium for 7 days and uranium quantitative subcellular distribution was investigated by means of micro-PIXE (Particle Induced X-ray Emission). The subcellular element imaging revealed that uranium was located in defined perinuclear regions of the cytoplasm, suggesting its accumulation in organelles. Uranium was not detected in the nucleus of the differentiated cells. Quantitative analysis evidenced a very low intracellular uranium content at non-cytotoxic levels of exposure (1 and 10 μM). At higher levels of exposure (125 and 250 μM), when cytotoxic effects begin, a larger and disproportional intracellular accumulation of uranium was observed. Finally the expression of dopamine-related genes was quantified using real time qRT-PCR. The expression of monoamine oxidase B (MAO-B) gene was statistically significantly decreased after exposure to uranium while other dopamine-related genes were not modified. The down regulation of MAO-B was confirmed at the protein level. This original result suggests that the inhibition of dopamine catabolism, but also of other MAO-B substrates, could constitute selective effects of uranium neurotoxicity.

Intracellular uranium distribution: Comparison of cryogenic fixation versus chemical fixation methods for SIMS analysis

Localization of uranium within cells is mandatory for the comprehension of its cellular mechanism of toxicity. Secondary Ion Mass Spectrometry (SIMS) has recently shown its interest to detect and localize uranium at very low levels within the cells. This technique requires a specific sample preparation similar to the one used for Transmission Electronic Microscopy, achieved by implementing different chemical treatments to preserve as much as possible the living configuration uranium distribution into the observed sample. This study aims to compare the bioaccumulation sites of uranium within liver or kidney cells after chemical fixation and cryomethods preparations of the samples: SIMS analysis of theses samples show the localization of uranium soluble forms in the cell cytoplasm and nucleus with a more homogenous distribution when using cryopreparation probably due to the diffusible portion of uranium inside the cytoplasm.

Uranyl acetate induced DNA single strand breaks and AP sites in Chinese hamster ovary cells

The aim of this study is to characterize the genotoxicity of depleted uranium (DU) in Chinese Hamster Ovary cells (CHO) with mutations in various DNA repair pathways. CHO cells were exposed to 0-300 μM of soluble DU as uranyl acetate (UA) for 0-48 h. Intracellular UA concentrations were measured via inductively coupled mass spectrometry (ICP-MS) and visualized by transmission electron microscopy (TEM). Cytotoxicity was assessed in vitro by clonogenic survival assay. DNA damage response was assessed via Fast Micromethod® to determine UA-induced DNA single strand breaks. Results indicate that UA is entering the CHO cells, with the highest concentration localizing in the nucleus. Clonogenic assays show that UA is cytotoxic in each cell line with the greatest cytotoxicity in the base excision repair deficient EM9 cells and the nuclear excision repair deficient UV5 cells compared to the non-homologous end joining deficient V3.3 cells and the parental AA8 cells after 48 h. This indicates that UA is producing single strand breaks and forming UA-DNA adducts rather than double strand breaks in CHO cells. Fast Micromethod® results indicate an increased amount of single strand breaks in the EM9 cells after 48 h UA exposure compared to the V3.3 and AA8 cells. These results indicate that DU induces DNA damage via strand breaks and uranium-DNA adducts in treated cells. These results suggest that: (1) DU is genotoxic in CHO cells, and (2) DU is inducing single strand breaks rather than double strand breaks in vitro.

Methods for Analyzing the Impacts of Natural Uranium on In Vitro Osteoclastogenesis

Uranium has been shown to interfere with bone physiology and it is well established that this metal accumulates in bone. However, little is known about the effect of natural uranium on the behavior of bone cells. In particular, the impact of uranium on osteoclasts, the cells responsible for the resorption of the bone matrix, is not documented. To investigate this issue, we have established a new protocol using uranyl acetate as a source of natural uranium and the murine RAW 264.7 cell line as a model of osteoclast precursors. Herein, we detailed all the assays required to test uranium cytotoxicity on osteoclast precursors and to evaluate its impact on the osteoclastogenesis and on the resorbing function of mature osteoclasts. The conditions we have developed, in particular for the preparation of uranyl-containing culture media and for the seeding of RAW 264.7 cells allow to obtain reliable and highly reproductive results. Moreover, we have optimized the use of software tools to facilitate the analysis of various parameters such as the size of osteoclasts or the percentage of resorbed matrix.

Drinking Water Uranium and Potential Health Effects in the German Federal State of Bavaria

Mainly due to its nephrotoxic and osteotoxic potential, uranium (U) increasingly finds itself in the spotlight of environmental and health-related research. Germany decided on a binding U guideline value in drinking water of 10 µg/L, valid since 2011. It is yet widely unknown if and how public health was affected by elevated U concentrations before that. In this ecological study we summarized available drinking water U data for the German federal state of Bavaria (703 analyses in total for 553 different municipalities) at county level (for 76 out of 96 Bavarian counties, representing about 83% of Bavaria's and about 13% of Germany's total population) in terms of mean and maximum U concentration. Bavaria is known to regionally exhibit mainly geogenically elevated groundwater U with a maximum value of 40 µg/L in the database used here. Public health data were obtained from federal statistical authorities at county resolution. These included incidence rates of diagnosed diseases suspected to be potentially associated with chronic U uptake, e.g., diseases of the skeleton, the liver or the thyroid as well as tumor and genito-urinary diseases. The datasets were analyzed for interrelations and mutual spatial occurrence using statistical approaches and GIS as well as odds ratios and relative risks calculations. Weak but significant positive associations between maximum U concentrations and aggregated ICD-10 diagnose groups for growths/tumors as well as liver diseases were observed, elevated incidence rates of thyroid diseases seem to occur where mean drinking water U concentrations exceed 2 µg/L. Here, we discuss obtained results and their implications for potential impacts of hydrochemistry on public health in southeast Germany.

Uranium and Associated Heavy Metals in Ovis aries in a Mining Impacted Area in Northwestern New Mexico

The objective of this study was to determine uranium (U) and other heavy metal (HM) concentrations (As, Cd, Pb, Mo, and Se) in tissue samples collected from sheep (Ovis aries), the primary meat staple on the Navajo reservation in northwestern New Mexico. The study setting was a prime target of U mining, where more than 1100 unreclaimed abandoned U mines and structures remain. The forage and water sources for the sheep in this study were located within 3.2 km of abandoned U mines and structures. Tissue samples from sheep (n = 3), their local forage grasses (n = 24), soil (n = 24), and drinking water (n = 14) sources were collected. The samples were analyzed using Inductively Coupled Plasma-Mass Spectrometry. Results: In general, HMs concentrated more in the roots of forage compared to the above ground parts. The sheep forage samples fell below the National Research Council maximum tolerable concentration (5 mg/kg). The bioaccumulation factor ratio was >1 in several forage samples, ranging from 1.12 to 16.86 for Mo, Cd, and Se. The study findings showed that the concentrations of HMs were greatest in the liver and kidneys. Of the calculated human intake, Se Reference Dietary Intake and Mo Recommended Dietary Allowance were exceeded, but the tolerable upper limits for both were not exceeded. Food intake recommendations informed by research are needed for individuals especially those that may be more sensitive to HMs. Further study with larger sample sizes is needed to explore other impacted communities across the reservation.

Natural uranium impairs the differentiation and the resorbing function of osteoclasts

BACKGROUND

Uranium is a naturally occurring radionuclide ubiquitously present in the environment. The skeleton is the main site of uranium long-term accumulation. While it has been shown that natural uranium is able to perturb bone metabolism through its chemical toxicity, its impact on bone resorption by osteoclasts has been poorly explored. Here, we examined for the first time in vitro effects of natural uranium on osteoclasts.

METHODS

The effects of uranium on the RAW 264.7 monocyte/macrophage mouse cell line and primary murine osteoclastic cells were characterized by biochemical, molecular and functional analyses.

RESULTS

We observed a cytotoxicity effect of uranium on osteoclast precursors. Uranium concentrations in the μM range are able to inhibit osteoclast formation, mature osteoclast survival and mineral resorption but don't affect the expression of the osteoclast gene markers Nfatc1, Dc-stamp, Ctsk, Acp5, Atp6v0a3 or Atp6v0d2 in RAW 274.7 cells. Instead, we observed that uranium induces a dose-dependent accumulation of SQSTM1/p62 during osteoclastogenesis.

CONCLUSIONS

We show here that uranium impairs osteoclast formation and function in vitro. The decrease in available precursor cells, as well as the reduced viability of mature osteoclasts appears to account for these effects of uranium. The SQSTM1/p62 level increase observed in response to uranium exposure is of particular interest since this protein is a known regulator of osteoclast formation. A tempting hypothesis discussed herein is that SQSTM1/p62 dysregulation contributes to uranium effects on osteoclastogenesis.

GENERAL SIGNIFICANCE

We describe cellular and molecular effects of uranium that potentially affect bone homeostasis.

Uranium-induced rat kidney cell cytotoxicity is mediated by decreased endogenous hydrogen sulfide (H2S) generation involved in reduced Nrf2 levels

The mechanism of uranium-induced kidney cell cytotoxicity is not fully understood. Nrf2 is a transcription factor which can regulate gene expression of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) which are responsible for endogenous H2S formation. H2S is recognized as the gaseous mediator that exerts antioxidative and cytoprotective effects. Here, we assessed the in vitro effects of uranyl acetate on Nrf2 gene expression and endogenous H2S production in a stable rat kidney cell line (NRK-52E). The results imply that uranium treatment decreased cell viability and increased LDH release, indicating uranium-induced cytotoxicity. Uranium intoxication increased intracellular ROS and MDA contents, depleted GSH levels, and impaired SOD and CAT activities, which resulted in oxidative stress injuries. Uranium intoxication reduced CBS and CSE gene expression and endogenous H2S production. Uranium contamination decreased Nrf2 protein expression and nuclear translocation. RNA silencing of Nrf2 gene expression in kidney cells which had not been treated by uranium decreased CBS and CSE gene expression and endogenous H2S generation, which mirrored the effects of uranium exposure. In contrast, treating uranium-exposed kidney cells with Nrf2 activator (sulforaphane) preserved the protein levels of Nrf2, CBS and CSE, and endogenous H2S formation. Administration of NaHS (an H2S donor) to uranium-intoxicated kidney cells reduced cell damage and alleviated oxidative stress. These data imply that uranium-induced kidney cell cytotoxicity is mediated by decreased endogenous H2S production due to the down-regulation of CBS and CSE gene expression and reduced Nrf2 levels. Supplementary H2S generation and/or Nrf2 activation can mitigate the adverse effects of uranium on kidney cells.

Translocation of uranium from water to foodstuff while cooking

The present work report the unusual uranium uptake by foodstuff, especially those rich in carbohydrates like rice when they are cooked in water, contaminated with uranium. The major staple diet in South Asia, rice, was chosen to study its interaction with UO2(2+), the active uranium species in water, using inductively coupled plasma mass spectrometry. Highest uptake limit was checked by cooking rice at very high uranium concentration and it was found to be good scavenger of uranium. To gain insight into the mechanism of uptake, direct interaction of UO2(2+) with monosaccharides was also studied, using electrospray ionization mass spectrometry taking mannose as a model. The studies have been done with dissolved uranium salt, uranyl nitrate hexahydrate (UO2(NO3)2·6H2O), as well as the leachate of a stable oxide of uranium, UO2(s), both of which exist as UO2(2+) in water. Among the eight different rice varieties investigated, Karnataka Ponni showed the maximum uranium uptake whereas unpolished Basmati rice showed the minimum. Interaction with other foodstuffs (potato, carrot, peas, kidney beans and lentils) with and without NaCl affected the extent of chemical interaction but was not consistent with the carbohydrate content. Uranium interaction with D-mannose monitored through ESI-MS, under optimized instrumental parameters, identified the peaks corresponding to uranyl adduct with mannose monomer, dimer and trimer and the species were confirmed by MS/MS studies. The product ion mass spectra showed peaks illustrating water loss from the parent ion as the collision energy was increased, an evidence for the strong interaction of uranium with mannose. This study would constitute the essential background for understanding interaction of uranium with various foods. Extension of this work would involve identification of foodstuff as green heavy metal scavengers.

Low-concentration uranium enters the HepG2 cell nucleus rapidly and induces cell stress response

This study aimed to compare the cell stress effects of low and high uranium concentrations and relate them to its localization, precipitate formation, and exposure time. The time-course analysis shows that uranium appears in cell nuclei as a soluble form within 5 min of exposure, and quickly induces expression of antioxidant and DNA repair genes. On the other hand, precipitate formations began at the very beginning of exposure at the 300-μM concentration, but took longer to appear at lower concentrations. Adaptive response might occur at low concentrations but are overwhelmed at high concentrations, especially when uranium precipitates are abundant.

Chemical and biological insights into uranium-induced apoptosis of rat hepatic cell line

Uranium release into the environment is a threat to human health, and the mechanisms of cytotoxicity caused by uranium are not well-understood. To improve our understanding in this respect, we herein evaluated the effects of uranium exposure on normal rat hepatic BRL cells. As revealed by scanning electron microscopy and transmission electron microscope analysis, uranyl nitrate was found to be transformed into uranyl phosphate particles in the medium and taken up by BRL cells in an endocytotic uptake manner, which presumably initiates apoptosis of the cell, although soluble uranyl ion may also be toxic. The apoptosis of BRL cells upon uranium exposure was also confirmed by both the acridine orange and ethidium bromide double staining assay and the Annexin V/propidium iodide double staining assay. Further studies revealed that uranium induced the loss of mitochondrial membrane potential in a dose-dependent manner. Moreover, the uranium-induced apoptosis was found to be associated with the activation of caspase-3, caspase-8 and caspase-9, indicating both a mitochondria-dependent signaling pathway and a death receptor pathway by a crosstalk. This study provides new chemical and biological insights into the mechanism of uranium toxicity toward hepatic cells, which will help seek approaches for biological remediation of uranium.

Haloactamides versus halomethanes formation and toxicity in chloraminated drinking water

In this study we quantified the concentrations of nine haloacetamides (HAcAms) and nine halomethanes (HMs) in the final waters of five drinking water treatment plants (DWTPs) that use either chlorination or chloramination for disinfection and evaluated the toxicity of dichloroacetamide (DCAcAm) and dichloromethane (DCM) in normal rat kidney (NRK) cells using four in vitro toxicity assays. All the DWTPs final waters contained primarily di-HAcAms, followed by tri- and mono-HAcAms, and DCAcAm was the most abundant species of the 9 HAcAms, regardless of chlorination or chloramination being applied. In the final waters of DWTPs using chlorination, tri-HMs (trihalomethanes, THMs) accounted for the majority of HMs, whereas chloramination resulted in more di-HMs (especially DCM) than THMs. All four in vitro toxicity assays indicated that the NRK cell chronic cytotoxicity and acute genotoxicity of DCAcAm were substantially higher than that of DCM. In view of observed occurrence concentrations and quantified toxicity levels, the findings of this study suggest that DCAcAm represents a higher toxicity risk than DCM in chloraminated drinking waters.

Zinc protects human kidney cells from depleted uranium-induced apoptosis

Depleted uranium (DU) is a weak radioactive heavy metal, and zinc (Zn) is an effective antidote to heavy metal poisoning. However, the effect of Zn on DU-induced cytotoxicity and apoptosis is not completely understood. The purpose of this study was to evaluate the effect of Zn on DU-induced cell apoptosis in human kidney cells (HK-2) and explore its molecular mechanism. Pre-treatment with Zn significantly inhibited DU-induced apoptosis. It reduced the formation of reactive oxygen species in the cells, increased the catalase (CAT) and glutathione (GSH) concentrations, suppressed the DU-induced soluble Fas receptor (sFasR) and soluble Fas ligand (sFasL) overexpression, suppressed the release of cytochrome c and apoptosis inhibitor factor (AIF) from mitochondria to cytoplasm, inhibited the activation of caspase-9, caspase-8 and caspase-3, and induced metallothionein (MT) expression. Furthermore, exogenous MT effectively inhibited DU-induced cell apoptosis. In conclusion, mitochondrial and FasR-mediated apoptosis pathways contribute to DU-induced apoptosis in HK-2 cells. Through independent mechanisms, such as indirect antioxidant effects, inhibition of the activation of caspase-9, caspase-8 and caspase-3, and induction of MT expression, Zn inhibits DU-induced apoptosis.

Investigation of uranium binding forms in selected German mineral waters

Cryogenic time-resolved laser-induced fluorescence spectroscopy was successfully used to identify uranium binding forms in selected German mineral waters of extremely low uranium concentrations (<2.0 μg/L). The measurements were performed at a low temperature of 153 K. The spectroscopic data showed a prevalence of aquatic species Ca2UO2(CO3)3 in all investigated waters, while other uranyl-carbonate complexes, viz, UO2CO3(aq) and UO2(CO3)2 (2-), only existed as minor species. The pH value, alkalinity (CO3 (2-)), and the main water inorganic constituents, specifically the Ca(2+) concentration, showed a clear influence on uranium speciation. Speciation modeling was performed using the most recent thermodynamic data for aqueous complexes of uranium. The modeling results for the main uranium binding form in the investigated waters indicated a good agreement with the spectroscopy measurements.

Cobalt chloride speciation, mechanisms of cytotoxicity on human pulmonary cells, and synergistic toxicity with zinc

Cobalt is used in numerous industrial sectors, leading to occupational diseases, particularly by inhalation. Cobalt-associated mechanisms of toxicity are far from being understood and information that could improve knowledge in this area is required. We investigated the impact of a soluble cobalt compound, CoCl(2)·6H(2)O, on the BEAS-2B lung epithelial cell line, as well as its impact on metal homeostasis. Cobalt speciation in different culture media, in particular soluble and precipitated cobalt species, was investigated via theoretical and analytical approaches. The cytotoxic effects of cobalt on the cells were assessed. Upon exposure of BEAS-2B cells to cobalt, intracellular accumulation of cobalt and zinc was demonstrated using direct in situ microchemical analysis based on ion micro-beam techniques and analysis after cell lysis by inductively coupled plasma mass spectrometry (ICP-MS). Microchemical imaging revealed that cobalt was rather homogeneously distributed in the nucleus and in the cytoplasm whereas zinc was more abundant in the nucleus. The modulation of zinc homeostasis led to the evaluation of the effect of combined cobalt and zinc exposure. In this case, a clear synergistic increase in toxicity was observed as well as a substantial increase in zinc content within cells. Western blots performed under the same coexposure conditions revealed a decrease in ZnT1 expression, suggesting that cobalt could inhibit zinc release through the modulation of ZnT1. Overall, this study highlights the potential hazard to lung function, of combined exposure to cobalt and zinc.

Efficacy of Chelator CBMIDA-CaNa2 for the Removal of Uranium and Protection against Uranium-induced Cell Damage in Human Renal Proximal Tubular Cells

In animal experiments, catechol-3,6-bis(methyleiminodiacetic acid) (CBMIDA) was proven to be an effective chelator for the decorporation of uranium (U)(VI). In the present study, the authors investigated the molecular processes of CBMIDA-CaNa2 on the removal of U(VI) at the cellular level and explored its protective effects and mechanism against U(VI)-induced cell damage in HK-2 human renal proximal tubular cells. The results indicated that the chelating U(VI) effect of CBMIDA-CaNa2 was superior compared to that of DTPA-CaNa3; more specifically, at concentrations of 50 and 250 μM, CBMIDA-CaNa2 can significantly reduce U(VI) uptake and increase U(VI) release in U(VI)-exposed HK-2 cells after immediate or 24-h and 48-h delayed chelator administration better than those of DTPA-CaNa3. Furthermore, CBMIDA-CaNa2 significantly decreased the lactate dehydrogenase release and the formation of micronuclei and inhibited the production of intracellular reactive oxygen species (ROS) in HK-2 cells exposed to U(VI), whereas DTPA-CaNa3 was demonstrated to be ineffective. By reviewing the results of animal experiments conducted by several other investigators, including this lab, the authors found that removal efficacy and protective effects of these two chelators for U(VI) at the cellular level agreed well with those of animal studies. In addition, although U(VI) induced the increase of metallothionein protein expression in HK-2 cells, CBMIDA-CaNa2 can mobilize and remove the U(VI) from metallothionen (MT) after 48-h delayed chelator treatment. These results suggested that CBMIDA-CaNa2 protected against U(VI)-induced HK-2 cells damaged by reducing U(VI) uptake, increasing U(VI) release and scavenging the U(VI)-induced intracellular ROS.

Analytical tools for speciation in the field of toxicology

The knowledge of the speciation of elements at trace and ultra-trace level, in biological and environmental media is essential to acquire a better understanding of the mechanisms of toxicity, transport and accumulation in which they are involved. Determining the speciation of an element in a given medium is challenging and requires the knowledge of different methodological approaches: the calculation approach and the experimental approach through the use of dedicated analytical and spectroscopic tools. In this framework, this mini-review reports the approaches to investigate the speciation of elements in biological and environmental media as well as the experimental techniques of speciation analysis, illustrated by recent examples. The main analytical and spectroscopic techniques to obtain structural, molecular, elemental and isotopic information are described. A brief overview of separation techniques coupled with spectrometric techniques is given. Imaging and micro-localisation techniques, which aim at determining the in situ spatial distribution of elements and molecules in various solid samples, are also presented. The last part deals with the development of micro-analytical systems, since they open crucial perspectives to speciation analysis for low sample amounts and analysis on field.

Uranyl nitrate-exposed rat alveolar macrophages cell death: influence of superoxide anion and TNF α mediators

Uranium compounds are widely used in the nuclear fuel cycle, military and many other diverse industrial processes. Health risks associated with uranium exposure include nephrotoxicity, cancer, respiratory, and immune disorders. Macrophages present in body tissues are the main cell type involved in the internalization of uranium particles. To better understand the pathological effects associated with depleted uranium (DU) inhalation, we examined the metabolic activity, phagocytosis, genotoxicity and inflammation on DU-exposed rat alveolar macrophages (12.5-200 μM). Stability and dissolution of DU could differ depending on the dissolvent and in turn alter its biological action. We dissolved DU in sodium bicarbonate (NaHCO₃ 100 mM) and in what we consider a more physiological vehicle resembling human internal media: sodium chloride (NaCl 0.9%). We demonstrate that uranyl nitrate in NaCl solubilizes, enters the cell, and elicits its cytotoxic effect similarly to when it is diluted in NaHCO₃. We show that irrespective of the dissolvent employed, uranyl nitrate impairs cell metabolism, and at low doses induces both phagocytosis and generation of superoxide anion (O₂⁻). At high doses it provokes the secretion of TNFα and through all the range of doses tested, apoptosis. We herein suggest that at DU low doses O₂⁻ may act as the principal mediator of DNA damage while at higher doses the signaling pathway mediated by O₂⁻ may be blocked, prevailing damage to DNA by the TNFα route. The study of macrophage functions after uranyl nitrate treatment could provide insights into the pathophysiology of uranium-related diseases.

Distribution of soluble uranium in the nuclear cell compartment at subtoxic concentrations

Uranium is naturally found in the environment, and its extensive use results in an increased risk of human exposure. Kidney cells have mainly been used as in vitro models to study effects of uranium exposure, and very little about the effects on other cell types is known. The aim of this study was to assess the impact of depleted uranium exposure at the cellular level in human kidney (HEK-293), liver (HepG2), and neuronal (IMR-32) cell lines. Cytotoxicity studies showed that these cell lines reacted in a roughly similar manner to depleted uranium exposure, responding at a cytotoxicity threshold of 300-500 μM. Uranium was localized in cells with secondary ion mass spectrometry technology. Results showed that uranium precipitates at subtoxic concentrations (>100 μM). With this approach, we were able for the first time to observe the soluble form of uranium in the cell at low concentrations (10-100 μM). Moreover, this technique allows us to localize it mainly in the nucleus. These innovative results raise the question of how uranium penetrates into cells and open new perspectives for studying the mechanisms of uranium chemical toxicity.

HEAVY METALS TOXICITY AFTER ACUTE EXPOSURE OF CULTURED RENAL CELLS: INTRACELLULAR ACCUMULATION AND REPARTITION

Lead ( Pb ), cadmium ( Cd ) and uranium ( U ) present no known biological function but are toxic in various concentration ranges. Pb and Cd lead generally to nephrotoxicity consisting in proximal renal tubular dysfunction and accumulation while U has been reported to induce chemical kidney toxicity, functional and histological damages being as well mainly observed in proximal tubule cells. This work address the question of Cd , Pb , and U cytotoxicity, intracellular accumulation and repartition after acute intoxication of renal proximal tubule epithelial cells. After cells exposure to different concentrations of metals for various times, morphological changes were observed and intracellular concentrations and distributions of toxic metals were specified by PIXE coupled to RBS. Cell viability, measured by biochemical tests, was used as toxicity indicator. A direct correlation between cytotoxicity and intracellular accumulation in renal epithelial cells have been established. Finally, intracellular Pb and U localizations were detected while Cd was found to be uniformly distributed in renal cells.

Protective effects of ion-imprinted chitooligosaccharides as uranium-specific chelating agents against the cytotoxicity of depleted uranium in human kidney cells

Occupational internal contamination with depleted uranium (DU) compounds can induce radiological and chemical toxicity, and an effective and specific uranium-chelating agent for clinical use is urgently needed. The purpose of this study was to investigate whether a series of synthesized water-soluble metal-ion-imprinted chitooligosaccharides can be used as uranium-specific chelating agents, because the chitooligosaccharides have excellent heavy metal ion chelation property and the ion-imprinting technology can improve the selective recognition of template ions. DU-poisoned human renal proximal tubule epithelium cells (human kidney 2 cells, HK-2) were used to assess the detoxification of these chitooligosaccharides. The DU-chelating capacity and selectivity of the chitooligosaccharides were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Cell viability, cellular accumulation of DU, membrane damage, DNA damage, and morphological changes in the cellular ultrastructure were examined to assess the detoxification of these chitooligosaccharides. The results showed that the Cu²⁺-imprinted chitooligosaccharides, especially the Cu²⁺-imprinted glutaraldehyde-crosslinked carboxymethyl chitooligosaccharide (Cu-Glu-CMC), chelated DU effectively and specifically, and significantly reduced the loss of cell viability induced by DU and reduced cellular accumulation of DU in a dose-dependent manner, owing to their chelation of DU outside cells and their prevention of DU internalization. The ultrastructure observation clearly showed that Cu-Glu-CMC-chelated-DU precipitates, mostly outside cells, were grouped in significantly larger clusters, and they barely entered the cells by endocytosis or in any other way. Treatment with Cu-Glu-CMC also increased the activity of antioxidant enzymes, and reduced membrane damage and DNA damage induced by DU oxidant injury. Cu-Glu-CMC was more effective than the positive control drug, diethylenetriaminepentaacetic acid (DTPA), in protection of HK-2 cells against DU cytotoxicity, as a result of its chelation of UO₂²⁺ to prevent the DU internalization and its antioxidant activity.