In vitro assessment of plutonium uptake and release using the human macrophage-like THP-1 cells

Take a Swipe at Actinide Bioavailability: Application of a New In Vitro Method

ABSTRACT

Filter swipe tests are used for routine analyses of actinides in nuclear industrial, research, and weapon facilities as well as following accidental release. Actinide physicochemical properties will determine in part bioavailability and internal contamination levels. The aim of this work was to develop and validate a new approach to predict actinide bioavailability recovered by filter swipe tests. As proof of concept and to simulate a routine or an accidental situation, filter swipes were obtained from a nuclear research facility glove box. A recently-developed biomimetic assay for prediction of actinide bioavailability was adapted for bioavailability measurements using material obtained from these filter swipes. In addition, the efficacy of the clinically-used chelator, diethylenetriamine pentaacetate (Ca-DTPA), to enhance transportability was determined. This report shows that it is possible to evaluate physicochemical properties and to predict bioavailability of filter swipe-associated actinides.

Determination of drug efficacy to dissolve cobalt oxide particles in cellular models: Towards a therapeutic approach to decrease pulmonary retention

Following accidental inhalation of radioactive cobalt particles, the poorly soluble and highly radioactive Co₃O₄ particles are retained for long periods in lungs. To decrease their retention time is of crucial importance to minimize radiation-induced damage. As dissolved cobalt is quickly transferred to blood and eliminated by urinary excretion, enhancing the dissolution of particles would favor ⁶⁰Co elimination. We evaluated the ability of ascorbic acid alone or associated with the chelating agents DTPA¹, DFOB² or EDTA³ to enhance dissolution of cobalt particles after macrophage engulfment, and the drug effects on the translocation of the soluble species CoCl₂ through an epithelial barrier. We exposed differentiated THP-1 macrophage-like cells and Calu-3 lung epithelial cells cultured in a bicameral system to cobalt and selected molecules up to 7 days. DTPA, the recommended treatment in man, used alone showed no effect, whereas ascorbic acid significantly increased dissolution of Co₃O₄ particles. An additional efficacy in intracellular particles dissolution was observed for combinations of ascorbic acid with DTPA and EDTA. Except for DFOB, treatments did not significantly modify translocation of dissolved cobalt across the epithelial lung barrier. Our study provides new insights for decorporating strategies following radioactive cobalt particle intake.

In vitro evidence of the influence of complexation of Pu and Am on uptake by human lung epithelial cells Calu-3

Understanding the mechanisms involved in retention and clearance of actinides from the lungs after accidental intake is essential for the evaluation of the associated radiological risks. Although the absorption of radioelements has been shown in vivo to depend on their nature and physico-chemical properties, their mechanisms of translocation remain unknown. In this study, we have evaluated in vitro the binding and uptake by bronchial epithelial cells Calu-3 of 2 transuranic actinides, plutonium (Pu) and americium (Am), as the first steps of translocation across the pulmonary barrier. For this purpose, Calu-3 cells grown to confluence in 24-well plates were exposed to the radioelements for 24 h under various culture conditions. Two compartments were identified for the association of actinides to cells, corresponding to the membrane bound and internalized fractions. Binding of Pu was slightly higher than of Am, and depended on its initial chemical form (nitrate, citrate, colloids). Uptake of Pu and Am nitrate was higher in serum-free conditions than in supplemented medium, with an active mechanism involved in Pu internalization. Overall, our results suggest that complexation of actinides to bioligands may have an influence on their uptake by pulmonary epithelial cells, and therefore possibly on their subsequent absorption into blood.

Evidence for a differential translocation of actinides across human lung epithelial cell monolayer in vitro according to their physicochemical properties and the presence of a chelating agent

The epithelial cell plays a key role in the transfer of radionuclides from lungs to blood following pulmonary exposure. The present study was designed to evaluate the transfer across human lung epithelial cells of various actinides (plutonium, americium and uranium), the influence of the physicochemical properties of plutonium compounds and of the chelating agent diethylene triamine pentaacetic acid (DTPA). To address this question, Calu-3 cells grown in a bicameral culture system were used. The integrity of the epithelial barrier was evaluated by measuring transepithelial electrical resistance (TEER) and the passage of a fluorescent marker, lucifer yellow. Activity measurement in basal compartment following periodic collection of culture medium was made from 2 h to seven days. To facilitate data handling and analysis, the statistical tool STATBIODIS was used. The results indicate differences in transfer for the different elements, and according to Pu physicochemical properties. Though to various extents, the chelating agent DTPA always increased the transfer of Pu and Am across the epithelial cells, without altering the integrity of the epithelial barrier. This in vitro cell culture model, by mimicking translocation of actinides from lungs to blood, can represent a valuable tool to further understand the underlying mechanisms and properties controlling this process.

Research on the Radiotoxicology of Plutonium Using Animals: Consideration of the 3Rs-Replace, Reduce, Refine

To characterize the health effects of incorporated plutonium, many experiments have been conducted using different animal models. These range from (1) applied (tissue uptake/retention determination, decorporation therapy efficacy), (2) fundamental (gene expression, cancer induction), and (3) dosimetry models. In recent years, the use of animals for scientific purposes has become a public concern. The application of the 3Rs - Replace (use of alternative methods or animals not considered capable of experiencing pain, suffering, and distress), Reduce (reduction in animal numbers), and Refine (better animal welfare and minimization of suffering, pain and distress) - has increased to address ethical concerns and legislative requirements. The introduction of novel non-animal technologies is also an important factor as complementary options to animal experimentation. In radiotoxicology research, it seems there is a natural tendency to Replace given the possibility of data reuse obtained from contamination cases in man and animal studies. The creation of "registries" and "repositories" for nuclear industry workers (civil and military) is now a rich legacy for radiotoxicological measurements. Similarly, Reduction in animal numbers can be achieved by good experimental planning with prior statistical analyses of animal numbers required to obtain robust data. Multiple measurements in the same animal over time (external body counting, excreta collection) with appropriate detection instruments also allow Reduction. In terms of Refinement, this has become "de rigueur" and a necessity given the societal and legal concerns for animal welfare. For research in radiotoxicology, particularly long-term studies, better housing conditions within the constraints of radiation protection issues for research workers are an important concern. These are all pertinent considerations for the 3Rs remit and future research in radiotoxicology.

Comparative cytotoxicity of respirable surface-treated/untreated calcium carbonate rock dust particles in vitro

Calcium carbonate rock dust (RD) is used in mining to reduce the explosivity of aerosolized coal. During the dusting procedures, potential for human exposure occurs, raising health concerns. To improve RD aerosolization, several types of anti-caking surface treatments exist. The aim of the study was to evaluate cytotoxicity of four respirable RD samples: untreated/treated limestone (UL/TL), untreated/treated marble (UM/TM), and crystalline silica (SiO₂) as a positive control in A549 and THP-1 transformed human cell lines. Respirable fractions were generated and collected using FSP10 high flow-rate cyclone samplers. THP-1 cells were differentiated with phorbol-12-myristate-13-acetate (20 ng/ml, 48 h). Cells were exposed to seven different concentrations of RD and SiO₂ (0-0.2 mg/ml). RD caused a slight decrease in viability at 24 or 72 h post-exposure and were able to induce inflammatory cytokine production in A549 cells, however, with considerably less potency than SiO₂. In THP-1 cells at 24 h, there was significant dose-dependent lactate dehydrogenase, inflammatory cytokine and chemokine release. Caspase-1 activity was increased in SiO₂- and, on a lesser scale, in TM- exposed cells. To test if the increased toxicity of TM was uptake-related, THP-1 cells were pretreated with Cytochalasin D (CytD) or Bafilomycin A (BafA), followed by exposure to RD or SiO₂ for 6 h. CytD blocked the uptake and significantly decreased cytotoxicity of all particles, while BafA prevented caspase-1 activation but not cytotoxic effects of TM. Only TM was able to induce an inflammatory response in THP-1 cells, however it was much less pronounced compared to silica.