DNA damage induced by Strontium-90 exposure at low concentrations in mesenchymal stromal cells: the functional consequences

Exploring the potential of Gloeomargarita lithophora for radionuclides bioremediation

Current physico-chemical techniques for remediating 90Sr traces from effluents are costly and can exhibit a low selectivity for Sr over Ca. Therefore, there is an incentive to develop an alternative method. In this study, we demonstrate that the cyanobacterium Gloeomargarita lithophora can rapidly remove more than 90 % of the 90Sr activity from a nuclear plant effluent within 24 h. This process occurs through two steps: a first rapid and passive phase of 90Sr sorbtion to the cell surface, followed by an active phase of 90Sr accumulation within the cells, partially driven by photosynthesis. We show that 90Sr sequestration within G. lithophora cells is stable with no release of 90Sr into the surrounding medium. Furthermore, we evidence that incorporation of 2.05 × 107 Bq g-1DCW of 90Sr and exposure to an estimated dose rate of 1.7 mGy h-1 for 5 days did not result in cell death. To go further in the development of a bioremediation method, we established the capacity to sequester 90Sr in a synthetic medium mimicking the radioactivity and mineral composition of a real industrial nuclear effluent. These results highlight G. lithophora as a promising solution for effective bioremediation of water contaminated with 90Sr, especially from nuclear plant effluents.

Strontium-90 in Baby Teeth as a Basis for Estimating U.S. Cancer Deaths From Nuclear Weapons Fallout

Nuclear weapons testing in the atmosphere during the 1950s and 1960s deposited fallout throughout the world, exposing all humans to food and water before the Limited Test Ban Treaty ended large-scale tests. The largest effort to measure in vivo fallout in humans, performed by Washington University (USA), collected over 300,000 deciduous teeth to document a sustained increase in Strontium-90 (Sr-90) during testing and a sharp decline after the test ban. Sr-90 patterns and trends in teeth were consistent with those of bones and milk. Sr-90 is still detectable in about 100,000 of the teeth, which were never tested. Tooth donors were born during atmospheric testing (1946-1965) and thus exposed to fallout in utero and during infancy/childhood, when exposures pose the greatest health risk. Preliminary analysis of global fallout's health risk in the United States indicates recent cancer mortality in several high-fallout areas exceeded that of states with the lowest fallout, peaking for the cohort born in the early 1960s, when fallout was highest. These findings support subsequent measurement of Sr-90 in deciduous teeth of persons who died of diseases such as cancer, along with controls, a novel approach to assessing fallout hazards.

Binding mechanism of strontium to biopolymer hydrogel composite materials

Strontium-90 is a radionuclide of concern that is mobile in soil and groundwater and is a threat to life. Activated hydrogel biopolymer composites were fabricated for strontium remediation from groundwater. Batch uptake demonstrated a maximal stontium uptake capacity of 109 mg g−1, much higher than unactivated hydrogel controls. Activation also more than doubled the decontamination factor at environmentally relevant concentrations. EXAFS was used to investigate the binding mechanism, revealing inner sphere complexation of strontium for the first time. Biopolymer composities synthesized for these studies are sustainable and cheap remediation materials that exhibit good strontium uptake and inner sphere binding.

Synergy of flow injection system and molecular recognition technology products for rapid determination of 89,90Sr and 210Pb

A rapid, automated separation procedure was developed for radioactive strontium and lead isotope determination. This system includes a portable automated system for the preconcentration and sequential elution of targeting isotopes with an Na₂H₂EDTA solution from solid phase extraction materials, AnaLig®Sr-01 and SuperLig®620, provided by IBC Technologies. Strontium and lead were separated from the majority of matrix constituents to obtain pure fractions of Pb and Sr prior to radiometric detection. In case of barium presence, it can also be fully isolated and completely separated from Sr. The automated procedure can be successfully used for preconcentration and separation from high as well as low radioactivity samples. With only a 1 mL column filled with SuperLig®620, it is possible to isolate Sr and Pb with 100% recovery from 1 L to 2 L of sample at a flow rate of up to 10 mL min^-1 within several hours. ^89,90Sr isotopes can be further determined by Cherenkov counting, while ²¹⁰Pb isotopes can be determined by either gamma spectrometry or liquid scintillation counter. The method was tested and validated using certified standard materials and proficiency test samples. The synergy of automated separation and detection procedures enables the determination of the low level activity of ⁹⁰Sr and ²¹⁰Pb in a short time with detection limits of 20 mBq L^-1 for both isotopes. The proposed method enables lower labour costs, minimal size of apparatuses and columns, low separation time, and reduced secondary waste production. The automated procedure may be easily implemented in laboratories worldwide and can also be used at sampling sites.

In vitro Assessment of the DNA Damage Response in Dental Mesenchymal Stromal Cells Following Low Dose X-ray Exposure

Stem cells contained within the dental mesenchymal stromal cell (MSC) population are crucial for tissue homeostasis. Assuring their genomic stability is therefore essential. Exposure of stem cells to ionizing radiation (IR) is potentially detrimental for normal tissue homeostasis. Although it has been established that exposure to high doses of ionizing radiation (IR) has severe adverse effects on MSCs, knowledge about the impact of low doses of IR is lacking. Here we investigated the effect of low doses of X-irradiation with medical imaging beam settings (<0.1 Gray; 900 mGray per hour), in vitro, on pediatric dental mesenchymal stromal cells containing dental pulp stem cells from deciduous teeth, dental follicle progenitor cells and stem cells from the apical papilla. DNA double strand break (DSB) formation and repair kinetics were monitored by immunocytochemistry of γH2AX and 53BP1 as well as cell cycle progression by flow cytometry and cellular senescence by senescence-associated β-galactosidase assay and ELISA. Increased DNA DSB repair foci, after exposure to low doses of X-rays, were measured as early as 30 min post-irradiation. The number of DSBs returned to baseline levels 24 h after irradiation. Cell cycle analysis revealed marginal effects of IR on cell cycle progression, although a slight G₂/M phase arrest was seen in dental pulp stromal cells from deciduous teeth 72 h after irradiation. Despite this cell cycle arrest, no radiation-induced senescence was observed. In conclusion, low X-ray IR doses (< 0.1 Gray; 900 mGray per hour), were able to induce significant increases in the number of DNA DSBs repair foci, but cell cycle progression seems to be minimally affected. This highlights the need for more detailed and extensive studies on the effects of exposure to low IR doses on different mesenchymal stromal cells.

Assessment of common housekeeping genes as reference for gene expression studies using RT-qPCR in mouse choroid plexus

Choroid plexus (ChP), a vascularized secretory epithelium located in all brain ventricles, plays critical roles in development, homeostasis and brain repair. Reverse transcription quantitative real-time PCR (RT-qPCR) is a popular and useful technique for measuring gene expression changes and also widely used in ChP studies. However, the reliability of RT-qPCR data is strongly dependent on the choice of reference genes, which are supposed to be stable across all samples. In this study, we validated the expression of 12 well established housekeeping genes in ChP in 2 independent experimental paradigms by using popular stability testing algorithms: BestKeeper, DeltaCq, geNorm and NormFinder. Rer1 and Rpl13a were identified as the most stable genes throughout mouse ChP development, while Hprt1 and Rpl27 were the most stable genes across conditions in a mouse sensory deprivation experiment. In addition, Rpl13a, Rpl27 and Tbp were mutually among the top five most stable genes in both experiments. Normalisation of Ttr and Otx2 expression levels using different housekeeping gene combinations demonstrated the profound effect of reference gene choice on target gene expression. Our study emphasized the importance of validating and selecting stable housekeeping genes under specific experimental conditions.

Strontium stress disrupts miRNA biogenesis by reducing HYL1 protein levels in Arabidopsis

Strontium (Sr) is an emerging environmental pollutant that has become a major global concern after the nuclear accident at the Fukushima Daiichi Nuclear Power Plant in 2011. Although many studies have demonstrated the harmful effects of Sr on plant growth and development at the physiological level, knowledge regarding how plants sense and respond to Sr stress at the molecular level is limited. Recent studies have suggested that microRNAs (miRNAs) function as key regulators of plant growth and development as well as in the responses of plants to environmental stresses, including salinity, drought, cold, nutrient starvation, and heavy metals. In this study, we examined the global expression profile of miRNAs under Sr stress using small RNA sequencing analysis in Arabidopsis to better understand the molecular basis of plant responses to Sr stress. To identify specific Sr-responsive miRNAs, we performed comparative miRNA expression profiling analysis using control, CaCl₂-, and SrCl₂-treated seedlings. Compared to the control treatment, the expressions of most miRNAs were considerably decreased in the Sr-treated seedlings. However, under Sr stress, the expressions of primary miRNAs (pri-miRNAs) and their target genes were significantly increased; the protein levels of HYPONASTIC LEAVES 1 (HYL1), one of the core components of the microprocessor complex, were strongly reduced despite the increased HYL1 mRNA expression. In addition, hyl1-2 mutant plants were shown to be more sensitive to Sr stress than wild-type plants. Collectively, our results strongly suggested that Sr stress may be associated with the disruption of miRNA biogenesis by reducing the protein level of HYL1, which is required to maintain proper growth and development for plants. Our findings further indicated that some miRNAs may play important roles in plant responses to Sr stress.

Removal of Sr2+ using high-surface-area hydroxyapatite synthesized by non-additive in-situ precipitation

Owing to their high-risk factor, many attempts have been made to remove radionuclides from water. Sr²⁺ ions are the target of removal by synthesized hydroxyapatite in this research. A facile method for synthesizing high-surface-area hydroxyapatite by in-situ precipitation using excess diammonium phosphate solution and without any additive was developed. The highest surface area achieved using this method was 177.00 m²/g, and the synthesized hydroxyapatite was also mesoporous. The effects of different pH, temperatures, and ion concentrations during synthesis on the properties of the hydroxyapatite were assessed, and it was found that a low temperature and high pH were optimal for synthesizing high-surface-area hydroxyapatite. The maximum strontium removal capacity of 28.51 mg/g was achieved when the pH-7.5 solution was used. This performance is competitive in comparison with previously developed synthesized materials. Synthesized hydroxyapatite could effectively remove radioactive strontium from an aqueous solution for nuclear waste management.

Therapeutic Irradiation: Consequences for Bone and Bone Marrow Adipose Tissue

Radiotherapy continues to be one of the most accepted medical treatments for cancer. Localized irradiation is the most common treatment for prostate, pancreatic, rectal, cervical and endometrial malignancies. Conventional localized fractions are total doses of 30-62Gy at 1.8-2Gy per fraction, with administration of ~60Gy often used for tumor ablation. However, even the lowest dose of localized irradiation exposure can result in adverse complications to adjacent organs, tissues, and vessels, which absorb a portion of the treatment. Skeletal complications are common amongst cancer patients undergoing these localized treatments. Irradiation exposure causes deterioration to the overall quantity and quality of bone by interfering with the trabecular architecture through increased osteoclast activity and decreased osteoblast activity. Irradiation-induced bone damage parallels adipocyte infiltration of the bone marrow (BM) resulting in compositional alterations of the microenvironment that may further affect bone quality and disease state. There may also be direct effects of irradiation on the BM adipocyte/pre-adipocyte, although in vitro findings do not always agree and cellular response is dependent on irradiation dosage. Hematopoietic cells also become apoptotic upon irradiation, which causes a range of skeletal effects. Bone loss leaves patients at a greater risk for osteopenia, osteoporosis, osteonecrosis, and skeletal fractures that drastically reduce quality of life. Osteoanabolic agents stimulate bone formation and reduce fracture risk in patients with low bone density; thus, osteoanabolic or anti-resorptive agents may be useful co-treatments with irradiation. This review discusses these topics and proposes further research directions using novel or combination therapies to enhance bone health during irradiation.