Effect of ethane-1-hydroxy-1,1-bisphosphonate (EHBP) on endochondral ossification lesions induced by a lethal oral dose of uranyl nitrate

The Cytotoxic Effects of Human Mesenchymal Stem Cells Induced by Uranium

Bone is a major tissue for uranium deposition in human body. Considering mesenchymal stem cells (MSCs) play a vital role in bone formation and injury recovery, studying the mechanism of MSCs responding to uranium poisoning can benefit the understanding of bone damage and repair after uranium exposure. Cellular structural alterations were analyzed via transmission electron microscopy (TEM). Changes in cellular behaviors were assessed through cellular viability, apoptosis, and the production of DNA double-strand breaks (DSBs). In addition, the influence of gap junctional intercellular communication (GJIC) on uranium toxicity was assessed. The disruption of MSCs was elevated with the increase in uranyl nitrate concentration, as shown by TEM micrograph. This was verified by the results of cellular viability and DSB production. Interestingly, the results of apoptosis assay indicated significant apoptosis occurred, which was accompanied with an obvious disruption of cellular membranes. Furthermore, closely contacted cell confluence groups exhibited resistant to uranium poisoning in contrast to sparse growth groups, which can be eliminated with the pretreatment of a GJIC inhibitor in the close connection group. To verify the association between GJIC and cytotoxic effects of uranyl nitrate, GJIC function was evaluated by wound healing and cellular migration. The results showed an inhibition of the healing ratio and migration ability induced by the exposure of uranyl nitrate. The low transfer efficiency of the dye coupling experiment and depressed expression of gap functional protein connexins confirmed the impairment of GJIC function. These results suggest that uranium toxicity is involved with GJIC dysfunction.

Europium(III) Meets Etidronic Acid (HEDP): A Coordination Study Combining Spectroscopic, Spectrometric, and Quantum Chemical Methods

Etidronic acid (1-Hydroxyethylidene-1,1-diphosphonic acid, HEDP, H₄L) is a proposed decorporation agent for U(VI). This paper studied its complex formation with Eu(III), an inactive analog of trivalent actinides, over a wide pH range, at varying metal-to-ligand ratios (M:L) and total concentrations. Combining spectroscopic, spectrometric, and quantum chemical methods, five distinct Eu(III)-HEDP complexes were found, four of which were characterized. The readily soluble EuH₂L⁺ and Eu(H₂L)₂^- species with log β values of 23.7 ± 0.1 and 45.1 ± 0.9 are formed at acidic pH. At near-neutral pH, EuHL⁰_s forms with a log β of ~23.6 and, additionally, a most probably polynuclear complex. The readily dissolved EuL^- species with a log β of ~11.2 is formed at alkaline pH. A six-membered chelate ring is the key motif in all solution structures. The equilibrium between the Eu(III)-HEDP species is influenced by several parameters, i.e., pH, M:L, total Eu(III) and HEDP concentrations, and time. Overall, the present work sheds light on the very complex speciation in the HEDP-Eu(III) system and indicates that, for risk assessment of potential decorporation scenarios, side reactions of HEDP with trivalent actinides and lanthanides should also be taken into account.

Low doses of uranium and osteoclastic bone resorption: key reciprocal effects evidenced using new in vitro biomimetic models of bone matrix

Uranium is widely spread in the environment due to its natural and anthropogenic occurrences, hence the importance of understanding its impact on human health. The skeleton is the main site of long-term accumulation of this actinide. However, interactions of this metal with biological processes involving the mineralized extracellular matrix and bone cells are still poorly understood. To get a better insight into these interactions, we developed new biomimetic bone matrices containing low doses of natural uranium (up to 0.85 µg of uranium per cm²). These models were characterized by spectroscopic and microscopic approaches before being used as a support for the culture and differentiation of pre-osteoclastic cells. In doing so, we demonstrate that uranium can exert opposite effects on osteoclast resorption depending on its concentration in the bone microenvironment. Our results also provide evidence for the first time that resorption contributes to the remobilization of bone matrix-bound uranium. In agreement with this, we identified, by HRTEM, uranium phosphate internalized in vesicles of resorbing osteoclasts. Thanks to the biomimetic matrices we developed, this study highlights the complex mutual effects between osteoclasts and uranium. This demonstrates the relevance of these 3D models to further study the cellular mechanisms at play in response to uranium storage in bone tissue, and thus better understand the impact of environmental exposure to uranium on human bone health.

Surveillance results and bone effects in the Gulf War depleted uranium-exposed cohort

A small group of Gulf War I veterans wounded in depleted uranium (DU) friendly-fire incidents have been monitored in a clinical surveillance program since 1993. During the spring of 2017, 42 members of the cohort were evaluated with a protocol which includes exposure monitoring for total and isotopic uranium concentrations in urine and a comprehensive assessment of health outcomes including measures of bone metabolism, and for participants >50 years, bone mineral density (BMD) determination. Elevated urine U concentrations were observed in cohort members with retained DU shrapnel fragments. Only the mean serum estradiol concentration, a marker of bone metabolism, was found to be significantly different for lower-vs- higher urine U (uU) cohort sub-groups. For the first time, a significant deficit in BMD was observed in the over age 50, high uU sub-group. After more than 25 years since first exposure to DU, an aging cohort of military veterans continues to exhibit few U-related adverse health effects in known target organs of U toxicity. The new finding of reduced BMD in older cohort members, while biologically plausible, was not suggested by other measures of bone metabolism in the full (all ages) cohort, as these were predominantly within normal limits over time. Only estradiol was recently found to display a difference as a function of uU grouping. As BMD is further impacted by aging and the U-burden from fragment absorption accrues in this cohort, a U effect may be clarified in future surveillance visits.

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.

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.

Novel drug delivery systems for actinides (uranium and plutonium) decontamination agents

The possibility of accidents in the nuclear industry or of nuclear terrorist attacks makes the development of new decontamination strategies crucial. Among radionuclides, actinides such as uranium and plutonium and their different isotopes are considered as the most dangerous contaminants, plutonium displaying mostly a radiological toxicity whereas uranium exhibits mainly a chemical toxicity. Contamination occurs through ingestion, skin or lung exposure with subsequent absorption and distribution of the radionuclides to different tissues where they induce damaging effects. Different chelating agents have been synthesized but their efficacy is limited by their low tissue specificity and high toxicity. For these reasons, several groups have developed smart delivery systems to increase the local concentration of the chelating agent or to improve its biodistribution. The aim of this review is to highlight these strategies.

Modes of action associated with uranium induced adverse effects in bone function and development

Uranium, a naturally occurring element used in military and industrial applications, accumulates in the skeletal system of animals and humans. Evidence from animal and in-vitro studies demonstrates that uranium exposure is associated with alterations in normal bone functions. The available studies suggest that upon absorption uranium directly affects bone development and maintenance by inhibiting osteoblast differentiation and normal functions, and indirectly by disrupting renal production of Vitamin D. Animal studies also provide evidence for increased susceptibility to uranium-induced bone toxicity during early life stages. The objective of this review is to provide a summary of uranium-induced bone toxicity and the potential mechanisms by which uranium can interfere with bone development and promote fragility. Since normal Vitamin D production and osteoblast functions are essential for bone growth and maintenance, young individuals and the elderly may represent potentially susceptible populations to uranium-induced bone damage.

Catch-up of delayed tooth eruption associated with uranium intoxication

The population at large is at risk of oral exposure to uranium. Previous studies performed at our laboratory showed delayed tooth eruption 7 d post-administration of a single oral dose of uranyl nitrate in newborn rats. Rat kidney exhibiting severe damage 2 d post-acute uranyl nitrate exposure showed signs of recovery after 7 d; however, tooth eruption and development were significantly lower as compared with their age-matched controls. The aim of the present work was to establish whether tooth eruption and development, delayed by uranium exposure, can catch up to normal values at longer experimental times. In addition, since it is well documented that uranium intoxication by other routes of entry causes alterations in bone growth, we also aimed to evaluate the effect of oral exposure to uranium on mandibular growth. An experimental group of 16 1-d-old Wistar rats received a single 90 mg kg-1 body weight oral dose of uranyl nitrate. Another group of 16 age-matched rats received an equal volume of saline solution and served as the control. Eight animals in each group were killed 7 d post-treatment, and the remaining animals were killed 27 d after the onset of the experiment. Morphometric measurements of mandibular growth were performed on radiographs. Tooth eruption and development were evaluated histomorphometrically on histologic sections obtained at the level of the mesial root of the first molar. Our results showed that the tooth eruption, dental development, and mandibular growth retardation observed 7 d post-acute uranyl nitrate exposure caught up completely after 27 d.

Ultrastructural and metabolic changes in osteoblasts exposed to uranyl nitrate

Exposure to uranium is an occupational hazard to workers who continually handle uranium and an environmental risk to the population at large. Since the cellular and molecular pathways of uranium toxicity in osteoblast cells are still unknown, the aim of the present work was to evaluate the adverse effects of uranyl nitrate (UN) on osteoblasts both in vivo and in vitro. Herein we studied the osteoblastic ultrastructural changes induced by UN in vivo and analyzed cell proliferation, generation of reactive oxygen species (ROS), apoptosis, and alkaline phosphatase (APh) activity in osteoblasts exposed to various UN concentrations (0.1, 1, 10, and 100 microM) in vitro. Cell proliferation was quantified by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, ROS was determined using the nitro blue tetrazolium test, apoptosis was morphologically determined using Hoechst 3332 and APh activity was assayed spectrophotometrically. Electron microscopy revealed that the ultrastructure of active and inactive osteoblasts exposed to uranium presented cytoplasmic and nuclear alterations. In vitro, 1-100 microM UN failed to modify cell proliferation ratio and to induce apoptosis. ROS generation increased in a dose-dependent manner in all tested doses. APh activity was found to decrease in 1-100 microM UN-treated cells vs. controls. Our results show that UN modifies osteoblast cell metabolism by increasing ROS generation and reducing APh activity, suggesting that ROS may play a more complex role in cell physiology than simply causing oxidative damage.