Multigenerational Exposure to Uranium Changes Sperm Metabolome in Rats.

Male infertility is a major public health issue that can be induced by a host of lifestyle risk factors such as environment, nutrition, smoking, stress, and endocrine disruptors. Regarding the human population exposed to uranium, it is necessary to explore these effects on male reproduction in multigenerational studies. The sensitivity of mass spectrometry (MS)-based methods has already proved to be extremely useful in metabolite identification in rats exposed to low doses of uranium, but also in human sperm. We applied this method to rat sperm over three generations (F0, F1 and F2) with multigenerational uranium exposure. Our results show a significant content of uranium in generation F0, and a reduction in the pregnancy rate only in generation F1. Based on principal component analysis (PCA), we observed discriminant profiles between generations. The partial least squares discriminant analysis (PLS-DA) of the 48 annotated variables confirmed that parental exposure of generation F0 (during both the preconceptional and prenatal periods) can have metabolic effects on spermatozoa for the next two generations. Metabolomics applied to epididymal spermatozoa is a novel approach to detecting the multigenerational effects of uranium in an experimental model, but could be also recommended to identify potential biomarkers evaluating the impact of uranium on sperm in exposed infertile men.

Concerted Uranium Research in Europe (CURE): toward a collaborative project integrating dosimetry, epidemiology and radiobiology to study the effects of occupational uranium exposure.

The potential health impacts of chronic exposures to uranium, as they occur in occupational settings, are not well characterized. Most epidemiological studies have been limited by small sample sizes, and a lack of harmonization of methods used to quantify radiation doses resulting from uranium exposure. Experimental studies have shown that uranium has biological effects, but their implications for human health are not clear. New studies that would combine the strengths of large, well-designed epidemiological datasets with those of state-of-the-art biological methods would help improve the characterization of the biological and health effects of occupational uranium exposure. The aim of the European Commission concerted action CURE (Concerted Uranium Research in Europe) was to develop protocols for such a future collaborative research project, in which dosimetry, epidemiology and biology would be integrated to better characterize the effects of occupational uranium exposure. These protocols were developed from existing European cohorts of workers exposed to uranium together with expertise in epidemiology, biology and dosimetry of CURE partner institutions. The preparatory work of CURE should allow a large scale collaborative project to be launched, in order to better characterize the effects of uranium exposure and more generally of alpha particles and low doses of ionizing radiation.

Molecular, cellular, and tissue impact of depleted uranium on xenobiotic-metabolizing enzymes.

Enzymes that metabolize xenobiotics (XME) are well recognized in experimental models as representative indicators of organ detoxification functions and of exposure to toxicants. As several in vivo studies have shown, uranium can alter XME in the rat liver or kidneys after either acute or chronic exposure. To determine how length or level of exposure affects these changes in XME, we continued our investigation of chronic rat exposure to depleted uranium (DU, uranyl nitrate). The first study examined the effect of duration (1-18 months) of chronic exposure to DU, the second evaluated dose dependence, from a level close to that found in the environment near mining sites (0.2 mg/L) to a supra-environmental dose (120 mg/L, 10 times the highest level naturally found in the environment), and the third was an in vitro assessment of whether DU exposure directly affects XME and, in particular, CYP3A. The experimental in vivo models used here demonstrated that CYP3A is the enzyme modified to the greatest extent: high gene expression changed after 6 and 9 months. The most substantial effects were observed in the liver of rats after 9 months of exposure to 120 mg/L of DU: CYP3A gene and protein expression and enzyme activity all decreased by more than 40 %. Nonetheless, no direct effect of DU by itself was observed after in vitro exposure of rat microsomal preparations, HepG2 cells, or human primary hepatocytes. Overall, these results probably indicate the occurrence of regulatory or adaptive mechanisms that could explain the indirect effect observed in vivo after chronic exposure.

In utero exposure to ionizing radiation and metabolic regulation: perspectives for future multi- and trans-generation effects studies.

PURPOSE: The radiation protection community has been particularly attentive to the risks of delayed effects on offspring from low dose or low dose-rate exposures to ionizing radiation. Despite this, the current epidemiologic studies and scientific data are still insufficient to provide the necessary evidence for improving risk assessment guidelines. This literature review aims to inform future studies on multigenerational and transgenerational effects. It primarily focuses on animal studies involving in utero exposure and discusses crucial elements for interpreting the results. These elements include in utero exposure scenarios relative to the developmental stages of the embryo/fetus, and the primary biological mechanisms responsible for transmitting heritable or hereditary effects to future generations. The review addresses several issues within the contexts of both multigenerational and transgenerational effects, with a focus on hereditary perspectives. CONCLUSIONS: Knowledge consolidation in the field of Developmental Origins of Health and Disease (DOHaD) has led us to propose a new study strategy. This strategy aims to address the transgenerational effects of in utero exposure to low dose and low dose-rate radiation. Within this concept, there is a possibility that disruption of epigenetic programming in embryonic and fetal cells may occur. This disruption could lead to metabolic dysfunction, which in turn may cause abnormal responses to future environmental challenges, consequently increasing disease risk. Lastly, we discuss methodological limitations in our studies. These limitations are related to cohort size, follow-up time, model radiosensitivity, and analytical techniques. We propose scientific and analytical strategies for future research in this field.

Artificial intelligence in biology and medicine, and radioprotection research: perspectives from Jerusalem.

While AI is widely used in biomedical research and medical practice, its use is constrained to few specific practical areas, e.g., radiomics. Participants of the workshop on "Artificial Intelligence in Biology and Medicine" (Jerusalem, Feb 14-15, 2023), both researchers and practitioners, aimed to build a holistic picture by exploring AI advancements, challenges and perspectives, as well as to suggest new fields for AI applications. Presentations showcased the potential of large language models (LLMs) in generating molecular structures, predicting protein-ligand interactions, and promoting democratization of AI development. Ethical concerns in medical decision making were also addressed. In biological applications, AI integration of multi-omics and clinical data elucidated the health relevant effects of low doses of ionizing radiation. Bayesian latent modeling identified statistical associations between unobserved variables. Medical applications highlighted liquid biopsy methods for non-invasive diagnostics, routine laboratory tests to identify overlooked illnesses, and AI's role in oral and maxillofacial imaging. Explainable AI and diverse image processing tools improved diagnostics, while text classification detected anorexic behavior in blog posts. The workshop fostered knowledge sharing, discussions, and emphasized the need for further AI development in radioprotection research in support of emerging public health issues. The organizers plan to continue the initiative as an annual event, promoting collaboration and addressing issues and perspectives in AI applications with a focus on low-dose radioprotection research. Researchers involved in radioprotection research and experts in relevant public policy domains are invited to explore the utility of AI in low-dose radiation research at the next workshop.

Use of omics analysis for low-dose radiotoxicology and health risk assessment: the case of uranium.

Exposure to environmental pollution and the increase in the incidence of multifactorial diseases in the population have become health problems for industrialized countries. In this context, the question of the health impact of exposure to these pollutants is not clearly identified in the low-dose range. This article looks at this problem using the example of preclinical studies of the effects of chronic low-dose exposure to uranium in rats. These studies demonstrate the value of molecular screening analyses (omics) and multimodal integrative approaches, of which the extreme sensitivity and breadth of observation spectrum make it possible to observe all the biological processes affected and the mechanisms of action triggered at the molecular level by exposure to low doses. They also show the value of these analytical approaches for finding diagnostic biomarkers or indicators of prognosis, which can be necessary to evaluate a risk. Finally, the results of these studies raise the question of the health risk caused by epigenomic deregulations occurring during critical developmental phases and their potential contribution to the development of chronic diseases that are metabolic in origin or to the development of certain cancer liable in the long term to affect the exposed adult and possibly its progeny.

Early Metabolomic Markers of Acute Low-Dose Exposure to Uranium in Rats.

Changes in metabolomics over time were studied in rats to identify early biomarkers and highlight the main metabolic pathways that are significantly altered in the period immediately following acute low-dose uranium exposure. A dose response relationship study was established from urine and plasma samples collected periodically over 9 months after the exposure of young adult male rats to uranyl nitrate. LC-MS and biostatistical analysis were used to identify early discriminant metabolites. As expected, low doses of uranium lead to time-based non-toxic biological effects, which can be used to identify early and delayed markers of exposure in both urine and plasma samples. A combination of surrogate markers for uranium exposure was validated from the most discriminant early markers for making effective predictions. N-methyl-nicotinamide, kynurenic acid, serotonin, tryptophan, tryptamine, and indole acetic acid associated with the nicotinate-nicotinamide and tryptophan pathway seem to be one of the main biological targets, as shown previously for chronic contaminations and completed, among others, by betaine metabolism. This study can be considered as a proof of concept for the relevance of metabolomics in the field of low-dose internal contamination by uranium, for the development of predictive diagnostic tests usable for radiotoxicological monitoring.

Multigenerational exposure to uranium changes morphometric parameters and global DNA methylation in rat sperm.

There is increasing evidence that environmental exposures early in fetal development influence phenotype and give rise to disease risk in the next generations. We previously found that lifelong exposure to uranium, an environmental contaminant, induced subtle testicular and hormonal defects; however, its impact on the reproductive system of multiple subsequent generations was unexplored. Herein, rats were exposed to a supra-environmental and non-nephrotoxic concentration of natural uranium (U, 40 mg·L-1 of drinking water) from postnatal life to adulthood (F0), during fetal life (F1), and only as the germ cells from the F1 generation (F2). General parameters (reproductive indices, epididymal weight) and sperm morphology were assessed in the three generations. In order to identify the epigenetic effects of U, we analyzed also the global DNA methylation profile and described for the first time the mRNA expression levels of markers involved in the (de)methylation system in rat epididymal spermatozoa. Our results showed that the F1 generation had a reduced pregnancy rate. Despite the sperm number being unmodified, sperm morphology was affected in the F0, F1 and F2 generations. Morphometric analysis for ten parameters was detailed for each generation. No common parameter was detected between the three generations, but the head and the middle-piece were always modified in the abnormal sperms. In the F1 U-exposed generation, the total number of abnormal sperm was significantly higher than in the F0 and F2 generations, suggesting that fetal exposure to uranium was more deleterious. This effect could be associated with the pregnancy rate to produce the F2 generation. Interestingly, global DNA methylation analysis showed also hypomethylation in the sperm DNA of the last F2 generation. In conclusion, our study demonstrates that uranium can induce morphological sperm defects and changes in the DNA methylation level after multigenerational exposure. The epigenetic transgenerational inheritance of U-induced reproductive defects should be assessed in further experiments.

Repeated potassium iodide exposure during pregnancy impairs progeny's brain development.

Protracted radioiodine release may require repeated intake of potassium iodide (KI) to protect thyroid gland. It is well established that iodine excess inhibits transiently the thyroid function. As developing fetus depends on maternal thyroid hormones (TH) supply, more knowledge is needed about the plausible effects that repeated KI intake can cause in this sensitive population, especially that even subtle variation of maternal thyroid function may have persistent consequences on progeny brain processing. The aim of this study is to assess the consequences of repeated intake of KI during pregnancy on the progeny's thyroid function and brain development. To do so pregnant Wistar rats received KI over eight days, and then thirty days after the weaning, male progeny was subjected to behavior test. Pituitary and thyroid hormones level, anti-thyroid antibodies level, organs morphology, gene expression and global DNA methylation were assessed. Thirty days after the weaning, KI-exposed male progeny showed an uncommon hormonal status, characterized by a decrease of both thyroid-stimulating hormone (-28%) and free thyroxine (-7%) levels. Motor coordination was altered in KI-exposed male progeny. At the cerebellar level, we observed a decrease of mRNA expression of DCX (-42%) and RC3 (-85%); on the other hand, at the cortical level, mRNA expression of MBP (+71%), MOBP (+90%) and Kcna1 (+42%) was increased. To conclude, repeated KI prophylaxis is not adequate during pregnancy since it led to long-term irreversible neurotoxicity in the male progeny.

Applying a multiscale systems biology approach to study the effect of chronic low-dose exposure to uranium in rat kidneys.

Purpose: To examine the effects of low-dose exposure to uranium with a systems biology approach, a multiscale high-throughput multi-omics analysis was applied with a protocol for chronic exposure to the rat kidney. Methods: Male and female rats were contaminated for nine months through their drinking water with a nontoxic solution of uranyl nitrate. A multiscale approach enabled clinical monitoring associated with metabolomic and transcriptomic (mRNA and microRNA) analyses. Results: A sex-interaction effect was observed in the kidney, urine, and plasma metabolomes of contaminated rats. Moreover, urine and kidney metabolic profiles correlated and confirmed that the primary dysregulated metabolisms are those of nicotinate-nicotinamide and of unsaturated fatty acid biosynthesis. Upstream of the metabolic pathways, transcriptomic profiles of the kidney reveal gene activity focused on gene regulation mechanisms, cell signaling, cell structure, developmental processes, and cell proliferation. Examination of epigenetic post-transcriptional gene regulation processes showed significant dysregulation of 70 micro-RNAs. The multi-omics approach highlighted the activities of the cells' biological processes on multiple scales through analysis of gene expression, confirmed by changes observed in the metabolome. Conclusion: Our results showed changes in multi-omic profiles of rats exposed to low doses of uranium contamination, compared with controls. These changes involved gene expression as well as modifications in the transcriptome and the metabolome. The metabolomic profile confirmed that the main molecular targets of uranium in kidney cells are the metabolism of nicotinate-nicotinamide and the biosynthesis of unsaturated fatty acids. Additionally, gene expression analysis showed that the metabolism of fatty acids is targeted by processes associated with cell function. These results demonstrate that multiscale systems biology is useful in elucidating the most discriminative pathways from genomic to metabolomic levels for assessing the biological impact of this low-level environmental exposure, i.e. the exposome.

Contamination with depleted or enriched uranium differently affects steroidogenesis metabolism in rat.

Uranium is a naturally occurring heavy metal found in the Earth's crust. It is an alpha-emitter radioactive element from the actinide group that presents both radiotoxicant and chemotoxicant properties. Some studies revealed that uranium could affect the reproductive system. To distinguish chemical versus radiological effects of uranium on the metabolism of the steroids in the testis, rats were contaminated via their drinking water with depleted or enriched uranium. Animals were exposed to radionuclides for 9 months at a dose of 40 mg/L (560 Bq/L for depleted uranium, 1680 Bq/L for enriched uranium). Whereas depleted uranium did not seem to significantly affect the production of testicular steroid hormones in rats, enriched uranium significantly increased the level of circulating testosterone by 2.5-fold. Enriched uranium contamination led to significant increases in the mRNA levels of StAR (Steroidogenic Acute Regulatory protein; 3-fold, p = .001), cyp11a1 (cytochrome P45011a1; 2.2-fold, p < .001), cyp17a1 (cytochrome P45017a1; 2.5-fold, p = .014), cyp19a1 (cytochrome P45019a1; 2.3-fold, p = .021), and 5alpha -R1 (5alpha reductase type 1; 2.0-fold, p = .02), whereas depleted uranium contamination induces no changes in the expression of these genes. Moreover, expression levels of the nuclear receptors LXR (Liver X Receptor) and SF-1 (Steroidogenic Factor 1), as well as the transcription factor GATA-4, were modified following enriched uranium contamination. Altogether, these results show for the first time a differential effect among depleted or enriched uranium contamination on testicular steroidogenesis. It appears that the deleterious effects of uranium are mainly due to the radiological activity of the compound.

Low dose of uranium induces multigenerational epigenetic effects in rat kidney.

PURPOSE: A protocol of chronic exposure to low dose of uranium was established in order to distinguish the sexual differences and the developmental process that are critical windows for epigenetic effects over generations. METHODS: Both male and female rats were contaminated through their drinking water with a non-toxic solution of uranyl nitrate for 9 months. The exposed generation (F0) and the following two generations (F1 and F2) were examined. Clinical monitoring, global DNA methylation profile and DNA methyltransferases (DNMTs) gene expression were analyzed in kidneys. RESULTS: While the body weight of F1 males increased, a small decrease in kidney and body weight was observed in F2 males. In addition, global DNA hypermethylation profile in kidney cells was observed in F1 and F2 males. qPCR results reveal a significant increase of methyltransferase genes expression (DNMT1 and DNMT3a) for F2 females. CONCLUSIONS: In the field of public health policy and to raise attention to generational effects for the risk assessment of the environmental exposures, low doses of uranium do not imply clinical effects on adult exposed rats. However, our results confirm the importance of the developmental windows' sensitivity in addition to the sexual dimorphisms of the offspring.

Effects of repeated potassium iodide administration on genes involved in synthesis and secretion of thyroid hormone in adult male rat.

BACKGROUND: A single dose of potassium iodide (KI) is recommended to reduce the risk of thyroid cancer during nuclear accidents. However in case of prolonged radioiodine exposure, more than one dose of KI may be necessary. This work aims to evaluate the potential toxic effect of repeated administration of KI. METHODS: Adult Wistar rats received an optimal dose of KI 1 mg/kg over a period of 1, 4 or 8 days. RESULTS: hormonal status (TSH, FT4) of treated rats was unaffected. Contrariwise, a sequential Wolff-Chaikoff effect was observed, resulting in a prompt decrease of NIS and MCT8 mRNA expression (-58% and -26% respectively), followed by a delayed decrease of TPO mRNA expression (-33%) in conjunction with a stimulation of PDS mRNA expression (+62%). CONCLUSION: we show for the first time that repeated administration of KI at 1 mg/kg/24h doesn't cause modification of thyroid hormones level, but leads to a reversible modification of the expression of genes involved in the synthesis and secretion of thyroid hormones.

In vivo animal studies help achieve international consensus on standards and guidelines for health risk estimates for chronic exposure to low levels of tritium in drinking water.

Existing and future nuclear fusion technologies involve the production and use of large quantities of tritium, a highly volatile, but low toxicity beta-emitting isotope of hydrogen. Tritium has received international attention because of public and scientific concerns over its release to the environment and the potential health impact of its internalization. This article provides a brief summary of the current state of knowledge of both the biological and regulatory aspects of tritium exposure; it also explores the gaps in this knowledge and provides recommendations on the best ways forward for improving our understanding of the health effects of low-level exposure to it. Linking health effects specifically to tritium exposure is challenging in epidemiological studies due to high uncertainty in tritium dosimetry and often suboptimal cohort sizes. We therefore argued that limits for tritium in drinking water should be based on evidence derived from controlled in vivo animal tritium toxicity studies that use realistically low levels of tritium. This article presents one such mouse study, undertaken within an international collaboration, and discusses the implications of its main findings, such as the similarity of the biokinetics of tritiated water (HTO) and organically bound tritium (OBT) and the higher biological effectiveness of OBT. This discussion is consistent with the position expressed in this article that in vivo animal tritium toxicity studies carried out within large, multi-partner collaborations allow evaluation of a great variety of health-related endpoints and essential to the development of international consensus on the regulation of tritium levels in the environment. Environ. Mol. Mutagen. 59:586-594, 2018. © 2018 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Modifications of inflammatory pathways in rat intestine following chronic ingestion of depleted uranium.

The environmental contamination by dispersion of depleted uranium (DU) might result in its chronic ingestion of DU by local populations. The aim of this study was to determine if chronic ingestion of DU at low doses induces inflammatory reactions in intestine, first biological system exposed to uranium after ingestion. Experiments were performed with rats receiving uranium in drinking water (40 mg/l) during 3, 6, or 9 months. Several parameters referring to prostaglandin, histamine, cytokine, and nitric oxide (NO) pathways were assessed in ileum. Concerning the prostaglandin pathway, a twofold increase in gene expression of cyclooxygenase of type 2 was noted after 6 months, with no changes in prostaglandins levels. At the same time, a decrease in mast cell number was observed without any changes in histamine levels. Experiments on cytokines showed increased gene expression of interleukin (IL)-1beta and IL-10 at 6 months, and decreased messenger RNA level of CCL-2. This change was associated with decreased macrophage density. An opposite effect of DU was induced on neutrophils, since increased number was observed at 3 (x1.7) and 9 months (x3). The results obtained on NO pathway seemed to indicate that DU exposure inhibited this pathway (decreased endothelial NO synthase messenger RNA, inductive NO synthase activity and NO(2)(-)/NO(3)(-) levels) at 6 months. In conclusion, this study demonstrated that chronic ingestion of DU-induced time-dependent modifications of inflammatory pathways, notably in terms of immune cell content. The ultimate effects of DU contamination might be pathogenic by suppressing defense mechanisms or inducing hypersensitivity. Further experiments should be thus performed to determine real consequences on intestinal response to oral antigens.

Effects of ionizing radiation on the activity of the major hepatic enzymes implicated in bile acid biosynthesis in the rat.

In the days following high-dose radiation exposure, damage to small intestinal mucosa is aggravated by changes in the bile acid pool reaching the gut. Intestinal bile acid malabsorption, as described classically, may be associated with altered hepatic bile acid biosynthesis, which was the objective of this work. The activity of the main rate-limiting enzymes implicated in the bile acid biosynthesis were evaluated in the days following an 8-Gy gamma(60)Co total body irradiation of rats, with concomitant determination of biliary bile acid profiles and intestinal bile acid content. Modifications of biliary bile acid profiles, observed as early as the first post-irradiation day, were most marked at the third and fourth day, and resulted in an increased hydrophobicity index. In parallel, the intestinal bile acids' content was enhanced and hepatic enzymatic activities leading to bile acids were changed. A marked increase of sterol 12 alpha-hydroxylase and decrease of oxysterol 7 alpha-hydroxylase activity was observed at day 3, whereas both cholesterol 7 alpha-hydroxylase and oxysterol 7 alpha-hydroxylase activities were decreased at day 4 after irradiation. These results show, for the first time, radiation-induced modifications of hepatic enzymatic activities implicated in bile acid biosynthesis and suggest that they are mainly a consequence of radiation-altered intestinal absorption, which induces a physiological response of the enterohepatic bile acid recirculation.

Biomarkers for Uranium Risk Assessment for the Development of the CURE (Concerted Uranium Research in Europe) Molecular Epidemiological Protocol.

Despite substantial experimental and epidemiological research, there is limited knowledge of the uranium-induce health effects after chronic low-dose exposures in humans. Biological markers can objectively characterize pathological processes or environmental responses to uranium and confounding agents. The integration of such biological markers into a molecular epidemiological study would be a useful approach to improve and refine estimations of uranium-induced health risks. To initiate such a study, Concerted Uranium Research in Europe (CURE) was established, and involves biologists, epidemiologists and dosimetrists. The aims of the biological work package of CURE were: 1. To identify biomarkers and biological specimens relevant to uranium exposure; 2. To define standard operating procedures (SOPs); and 3. To set up a common protocol (logistic, questionnaire, ethical aspects) to perform a large-scale molecular epidemiologic study in uranium-exposed cohorts. An intensive literature review was performed and led to the identification of biomarkers related to: 1. retention organs (lungs, kidneys and bone); 2. other systems/organs with suspected effects (cardiovascular system, central nervous system and lympho-hematopoietic system); 3. target molecules (DNA damage, genomic instability); and 4. high-throughput methods for the identification of new biomarkers. To obtain high-quality biological materials, SOPs were established for the sampling and storage of different biospecimens. A questionnaire was developed to assess potential confounding factors. The proposed strategy can be adapted to other internal exposures and should improve the characterization of the biological and health effects that are relevant for risk assessment.

Chronic exposure of adult, postnatal and in utero rat models to low-dose 137Cesium: impact on circulating biomarkers.

The presence of 137Cesium (137Cs) in the environment after nuclear accidents at Chernobyl and more recently Fukushima Daiichi raises many health issues for the surrounding populations chronically exposed through the food chain. To mimic different exposure situations, we set up a male rat model of exposure by chronic ingestion of a 137Cs concentration likely to be ingested daily by residents of contaminated areas (6500 Bq.l-1) and tested contaminations lasting 9 months for adult, neonatal and fetal rats. We tested plasma and serum biochemistry to identify disturbances in general indicators (lipids, proteins, carbohydrates and electrolytes) and in biomarkers of thyroid, heart, brain, bone, kidney, liver and testis functions. Analysis of the general indicators showed increased levels of cholesterol (+26%), HDL cholesterol (+31%), phospholipids B (+15%) and phosphorus (+100%) in the postnatal group only. Thyroid, heart, brain, bone and kidney functions showed no blood changes in any model. The liver function evaluation showed changes in total bilirubin (+67%) and alkaline phosphatase (-11%) levels, but only for the rats exposed to 137Cs intake in adulthood. Large changes in 17ß-estradiol (-69%) and corticosterone (+36%) levels affected steroidogenesis, but only in the adult model. This study showed that response profiles differed according to age at exposure: lipid metabolism was most radiosensitive in the postnatal model, and steroid hormone metabolism was most radiosensitive in rats exposed in adulthood. There was no evidence of deleterious effects suggesting a potential impact on fertility or procreation.

Metabolomics reveals dose effects of low-dose chronic exposure to uranium in rats: identification of candidate biomarkers in urine samples.

INTRODUCTION: Data are sparse about the potential health risks of chronic low-dose contamination of humans by uranium (natural or anthropogenic) in drinking water. Previous studies report some molecular imbalances but no clinical signs due to uranium intake. OBJECTIVES: In a proof-of-principle study, we reported that metabolomics is an appropriate method for addressing this chronic low-dose exposure in a rat model (uranium dose: 40 mg L-1; duration: 9 months, n = 10). In the present study, our aim was to investigate the dose-effect pattern and identify additional potential biomarkers in urine samples. METHODS: Compared to our previous protocol, we doubled the number of rats per group (n = 20), added additional sampling time points (3 and 6 months) and included several lower doses of natural uranium (doses used: 40, 1.5, 0.15 and 0.015 mg L-1). LC-MS metabolomics was performed on urine samples and statistical analyses were made with SIMCA-P+ and R packages. RESULTS: The data confirmed our previous results and showed that discrimination was both dose and time related. Uranium exposure was revealed in rats contaminated for 9 months at a dose as low as 0.15 mg L-1. Eleven features, including the confidently identified N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide and 4-hydroxyphenylacetylglycine, discriminated control from contaminated rats with a specificity and a sensitivity ranging from 83 to 96 %, when combined into a composite score. CONCLUSION: These findings show promise for the elucidation of underlying radiotoxicologic mechanisms and the design of a diagnostic test to assess exposure in urine, in a dose range experimentally estimated to be above a threshold between 0.015 and 0.15 mg L-1.

Unexpected lack of deleterious effects of uranium on physiological systems following a chronic oral intake in adult rat.

Uranium level in drinking water is usually in the range of microgram-per-liter, but this value may be as much as 100 to 1000 times higher in some areas, which may raise question about the health consequences for human populations living in these areas. Our purpose was to improve knowledge of chemical effects of uranium following chronic ingestion. Experiments were performed on rats contaminated for 9 months via drinking water containing depleted uranium (0.2, 2, 5, 10, 20, 40, or 120 mg/L). Blood biochemical and hematological indicators were measured and several different types of investigations (molecular, functional, and structural) were conducted in organs (intestine, liver, kidneys, hematopoietic cells, and brain). The specific sensitivity of the organs to uranium was deduced from nondeleterious biological effects, with the following thresholds (in mg/L): 0.2 for brain, >2 for liver, >10 for kidneys, and >20 for intestine, indicating a NOAEL (No-Observed-Adverse-Effect Level) threshold for uranium superior to 120 m g/L. Based on the chemical uranium toxicity, the tolerable daily intake calculation yields a guideline value for humans of 1350 µg/L. This value was higher than the WHO value of 30 µg/L, indicating that this WHO guideline for uranium content in drinking water is very protective and might be reconsidered.