microRNA blood signature for localized radiation injury

A radiological accident, whether from industrial, medical, or malicious origin, may result in localized exposure to high doses of ionizing radiations, leading to the development of local radiation injury (LRI), that may evolve toward deep ulceration and necrosis of the skin and underlying tissues. Early diagnosis is therefore crucial to facilitate identification and management of LRI victims. Circulating microRNAs (miRNA) have been studied as potential diagnostic biomarkers of several diseases including hematological defects following whole-body irradiation (WBI). This study aims to identify a blood miRNA signature associated with LRI in a preclinical C57BL/6J mouse model of hindlimb irradiation using different 10-MV X-ray doses that lead to injuries of different severities. To this end, we first performed broad-spectrum plasma miRNA profiling, followed by a targeted validation step, on two independent animal cohorts. Using a multivariate sparse partial least square discriminant analysis, we identified a panel of eight circulating miRNAs able to segregate mice according to LRI severity. Interestingly, these miRNAs were previously associated with WBI (miR-150-5p, miR-342-3p, miR-146a-5p), inflammation (miR-18a-5p, miR-148b-3p, miR-532-5p) and skin diseases (miR-139-5p, miR-195-5p). Our results suggest the use of circulating miRNAs as suitable molecular biomarkers for LRI prognosis and diagnosis.

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.

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.

Deep models of integrated multiscale molecular data decipher the endothelial cell response to ionizing radiation

The vascular endothelium is a hot spot in the response to radiation therapy for both tumors and normal tissues. To improve patient outcomes, interpretable systemic hypotheses are needed to help radiobiologists and radiation oncologists propose endothelial targets that could protect normal tissues from the adverse effects of radiation therapy and/or enhance its antitumor potential. To this end, we captured the kinetics of multi-omics layers-i.e. miRNome, targeted transcriptome, proteome, and metabolome-in irradiated primary human endothelial cells cultured in vitro. We then designed a strategy of deep learning as in convolutional graph networks that facilitates unsupervised high-level feature extraction of important omics data to learn how ionizing radiation-induced endothelial dysfunction may evolve over time. Last, we present experimental data showing that some of the features identified using our approach are involved in the alteration of angiogenesis by ionizing radiation.

Protection and safety of a repeated dosage of KI for iodine thyroid blocking during pregnancy

In case of nuclear power plant accidents resulting in the release of radioactive iodine (¹³¹I) in large amounts, a single intake of stable iodine is recommended in order to prevent¹³¹I fixation to the thyroid gland. However, in situations of prolonged exposure to¹³¹I (e.g. Fukushima-Daiichi natural and nuclear disaster), repetitive administration of iodine may be necessary to ensure adequate protection, with acceptable safety in vulnerable populations including pregnant women. Here we conducted toxicological studies on adult rats progeny following prolonged exposure to potassium iodide (KI)in utero. Pregnant Wistar rats were treated with 1 mg kg d^-1KI or saline water for 2 or 4 d either between gestation days gestational day (GD) GD 9-12, or GD13-16. Plasma samples from the progeny were tested 30 d post-weaning for clinical biochemistry, thyroid hormones, and anti-thyroid antibody levels. Thyroid and brain were collected for gene expression analysis. The hormonal status was similar for the mothers in all experimental conditions. In the offspring, while thyroid-stimulating hormone and anti-thyroid peroxidase (anti-TPO) antibody levels were similar in all groups, a significant increase of FT3 and FT4 levels was observed in GD9-GD10 and in GD13-GD14 animals treated for 2 d, respectively. In addition, FT4 levels were mildly decreased in 4 d treated GD13-16 individuals. Moreover, a significant decrease in the expression level of thyroid genes involved in iodide metabolism, TPO and apical iodide transporter, was observed in GD13-GD14 animals treated for 2 d. We conclude that repeated KI administration for 2-4 d during gestation did not induce strong thyroid toxicity.

Effect of repetitive potassium iodide on thyroid and cardiovascular functions in elderly rats

Background

To date, paediatric thyroid cancer has been the most severe health consequence of the Chernobyl accident, caused by radioactive iodine (¹³¹I) aerosol's dispersion. WHO recommends a single dose of potassium iodide (KI) to reduce this risk. Following the Fukushima accident, it became obvious that repetitive doses of KI may be necessary due to multiple exposures to ¹³¹I. Knowledge about the effects of repeated ITB (Iodine Thyroid Blocking) is scarce and controversial. KI may affect the thyroid hormones synthesis; which is crucial for the cardiovascular function. Furthermore, myocardial and vascular endothelial tissues are sensitizes to subtle changes at the concentration of circulating pituitary and/or thyroid hormones.

Objective

In this preclinical study, we aimed to assess the effects of repeated ITB in elderly male rats.

Methods

Twelve months old male Wistar rats were subjected to either KI or saline solution for eight days. Analyses were performed 24 h and 30 days after the treatment discontinuation.

Findings

We reported a significant increase (18%) in some urinary parameters related to renal function, a subtle decrease of plasma TSH level, a significant increase (379%) in renin and a significant decrease (50%) in aldosterone upon KI administration. At the molecular level, the expression of thyroid and cardiovascular genes was significantly affected by the treatment. However, in our experimental settlement, animal heart rate was not significantly affected thirty days after KI discontinuation. ECG patterns did not change after administration of KI, and arrhythmia was not observed in these conditions despite the PR-intervals decreased significantly. Cardiovascular physiology was preserved.

Conclusion

Our results indicate that repeated ITB in elderly rats is characterized by molecular modifications of cardiovascular key actors, particularly the Renin-angiotensin-aldosterone axis with a preserved physiological homeostasis. This new scientific evidence may be useful for the maturation of ITB guidelines especially for elderly sub-population.

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Repeated ITB impairs the expression of genes involved in thyroid and cardiovascular functioning in elderly rats.

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Repeated ITB impairs biochemical profile and the Renin-Angiotensin- Aldosterone axis.

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Repeated ITB do not impair cardiovascular function.

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ITB guidelines especially for elderly sub-population may take into account the risk benefit balance.

Metabolomics evaluation of repeated administration of potassium iodide on adult male rats

The long-lasting consequence of a new iodine thyroid blocking strategy (ITB) to be used in case of nuclear accident is evaluated in male Wistar rats using a metabolomics approach applied 30 days after ITB completion. The design used 1 mg/kg/day of KI over 8 days. Thyroid hormones remained unchanged, but there was a metabolic shift measured mainly in thyroid then in plasma and urine. In the thyroid, tyrosine metabolism associated to catecholamine metabolism was more clearly impacted than thyroid hormones pathway. It was accompanied by a peripheral metabolic shift including metabolic regulators, branched-chain amino acids, oxidant stress and inflammation-associated response. Our results suggested that iodide intake can impact gut microbiota metabolism, which was related to host metabolic regulations including in the thyroid. As there were no clear clinical signs of dysfunction or toxicity, we concluded that the measured metabolomics response to the new ITB strategy, especially in thyroid, is unlikely to reveal a pathological condition but a shift towards a new adaptive homeostatic state, called 'allostatic regulation'. The question now is whether or not the shift is permanent and if so at what cost for long-term health. We anticipate our data as a start point for further regulatory toxicity studies.

P2573Modelling the duchenne muscular dystrophy-induced dilated cardiomyopathy using patient-specific induced pluripotent stem cells-derived cardiomyocytes

Introduction

Duchenne Muscular Dystrophy (DMD) is a X-linked degenerative pathology with a prevalence of 1/3500 boys due to absence of functional dystrophin in muscles. In a late stage of DMD, patients developed a dilated cardiomyopathy (DCM) which can lead to heart failure and premature death.

In the past, we showed that DMD (mdx) mice exhibit a perturbation of the intracellular calcium homeostasis correlated to a pathological remodelling of the calcium ryanodine receptor channel (RyR2) leading to DCM with aging. However, mouse model does not represent a pertinent prototype to study DMD. Human pluripotent stem-cell derived-cardiomyocytes (hiPSC-CMs) are a pertinent tool to model patient-specific inherited cardiac diseases and screen pharmacological drugs in a Petri dish.

Objective

Based on the clinical history of DMD patients in the local Hospital, our main objective is to model DMD-induced DCM using hiPSC-CMs and compare the functional and molecular features with the clinical echocardiography. To that, we hypothesize that hiPSC-CMs are a powerful technology to model in vitro DCM and to better understand the pathophysiological mechanisms underlying DCM.

Methods

3 blood samples from DMD patients with different DCM degrees of severity and 3 from healthy control (HC) were collected, reprogrammed in hiPSC and differentiated into cardiomyocytes.

Results

Our preliminary data indicate that DMD hiPSC-CMs present an abnormal intracellular calcium homeostasis characterized by the presence of leaky diastolic calcium events compared to HC hiPSC-CMs suggesting a RyR2 dysfunction. In DMD hiPSC-CMs, we also observe alterations in the contractile properties and a perturbation of the mitochondrial respiration.

Conclusion

Our results support the fact that DMD-inducing DCM can be modelled in the dish using patient-specific hiPSC-CMs. Such modelling may provide a better understanding of the pathophysiological mechanisms and the pharmacological treatment of the DMD-induced DCM.

Assessment of the effects of repeated doses of potassium iodide intake during pregnancy on male and female rat offspring using metabolomics and lipidomics

Preparedness for nuclear accident responsiveness includes interventions to protect pregnancies against prolonged exposure to radioactive iodine. The aim of this study was to investigate a new design consisting of repeated administration of potassium iodide (KI, 1 mg/kg) for 8 days in late pregnancy gestational day 9-16 (GD9-GD16) in rats. The later-life effects of this early-life iodine thyroid blocking (ITB) strategy were assessed in offspring two months afterbirth. Functional behavioral tests including forced swimming test (FST) and rotarod test (RRT) in rats of both genders showed lower FST performance in KI-treated females and lower RRT performance in KI-treated male pups. This performance decline was associated with metabolic disruptions in cortex involving amino acid metabolism, tyrosine metabolism, as well as docosahexaenoic acid (DHA) lipids and signaling lipids in males and females. Beyond these behavior-associated metabolic changes, a portion of the captured metabolome (17-25%) and lipidome (3.7-7.35%) remained sensitive to in utero KI prophylactic treatment in both cortex and plasma of post-weaning rats, with some gender-related variance. Only part of these disruptions was attributed to lower levels of TSH and T4 (males only). The KI-induced metabolic shifts involved a broad spectrum of functions encompassing metabolic and cell homeostasis and cell signaling functions. Irrespective Regardless of gender and tissues, the predominant effects of KI affected neurotransmitters, amino acid metabolism, and omega-3 DHA metabolism. Taken together, data demonstrated that repeated daily KI administration at 1 mg/kg/day for 8 days during late pregnancy failed to protect the mother-fetus against nuclear accident radiation. Abbreviations: CV-ANOVA: Cross-validation analysis of variance; DHA: Docosahexaenoic acid; FST: Forced swimming test; FT3: plasma free triiodothyronine; FT4: plasma free thyroxine; GD: Gestational day; ITB: Iodine thyroid blocking; KI: potassium iodide; LC/MS: Liquid chromatography coupled with mass spectrometry; MTBE: Methyl tert-butyl ether; m/z: mass-to-charge ratio; PLS-DA: Partial least squares-discriminant analysis; PRIODAC: Repeated stable iodide prophylaxis in accidental radioactive releases; RRT: Rotarod test; TSH: Thyroid-stimulating hormone; VIP: Variable importance in projection.

A systems biology approach to propose a new mechanism of regulation of repetitive prophylaxis of stable iodide on sodium/iodide symporter (NIS)

Our group showed that repetitive dose of potassium iodide (KI) for eight days offers an efficient protection for exposure to repeated radioactive emissions without adverse effects on adult rats. However, differential expression of genes implicated in Wolff-Chaikoff effect was observed. To understand the Wolff-Chaikoff regulation and its molecular constituents during repetitive administration of KI, a biochemical reaction network was constructed as a "geographical" map of the thyrocyte depicting iodide and thyroid hormone synthesis. Path analysis of the network has been performed to investigate the presence of a regulatory circuit of the node iodide to the node "nis transcription". NIS is responsible for the uptake of KI and plays an important role in the Wolff-Chaikoff effect. The map is a source for the most updated information about iodide and thyroid hormone metabolism. Based on this map, we propose a hypothesis that shows a putative mechanism behind NIS regulation and KI uptake.

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.

Impact of repeated dose of stable iodine in an in utero rat model using a metabolomic approach

The Fukushima nuclear power plant blast resulted in the release of 131Iodine for several weeks. This unexpected issue challenged the iodin doctrine [1], in which the counter-measure is to provide a unique iodine tablet to saturate thyroid during the radioactive contamination not expected to last more than several hours. A new doctrine must be implemented to take into account such case of extended exposure based on repeated iodine administration with adapted dosage. But repeated administration of iodine can block the thyroid [2] and few scientific evidences regarding repeated iodine administration (and its potential undesirable effect) are at our disposal [3]. Moreover, unborn and young children are at high risk during a nuclear incident: it is currently recognized that one of the risks of exposure to radioactive iodine is the development of thyroid cancer, especially when exposure occurred during childhood [4]. Their protection is a main priority. Our goal was to evaluate the potential undesirable effects of such repeated iodine administration in the offspring using an untargeted metabolomic approach on a rat reproductive model.

Effect of repetitive potassium iodide on elderly rat’s thyroid

Background: Nuclear power plant emergencies had often been accompanied by radioactivity release into the environment, thyroid cancer is one of the major health consequences due to the effect of radioactive iodine (131I) that emits ϒ ray and β particles resulting in thyroid DNA damage and late onset thyroid cancer. Intake of a single dose of potassium iodide (KI) is recommended to reduce this risk. However in case of prolonged radioiodine release as noticed during Chernobyl and Fukushima accidents, more than one dose of KI may be basic to ensure adequate protection [1]. Whereas a single dose of KI is admitted to be safe, knowledge about the effects of repeated KI administration are scarce, few studies demonstrated the potential efficiency of repetitive KI intake in humans [2] and non-human primates [3] without hormonal variations. These studies are relevant in the field of radiation protection and give a base evidence of the possible use of repetitive KI. On the other hand, we have studies on rodents that showed an impact of chronic iodine excess on pituitary thyroid axis function [4]. Our previous work on adult male rats demonstrated the safety of repeated administration of KI over 8 days [5]. Indeed in the elderly persons KI administration in case of nuclear emergency remains a topic of debate, because of the possible impact in cardiovascular diseases. Thyroid hormones are well-known for their profound effects on cardiovascular function and metabolism; myocardial and vascular endothelial tissues have receptors for thyroid hormones and are sensitive even to subtle changes in the concentrations of circulating pituitary and/or thyroid hormones i.e. subclinical hypothyroidism and hyperthyroidism. It is well established that hyperthyroidism induces a hyper-dynamic cardiovascular state, which is associated with a faster heart rate, enhanced left ventricular systolic and diastolic function whereas hypothyroidism is characterized by the opposite changes. Atrial fibrillation is the most common cardiac arrhythmia in the elderly, the prevalence and incidence increase with advancing age [6]. Several interventional trials showed that treatment of subclinical thyroid diseases improves cardiovascular risk factors, which implies potential benefits for reducing cardiovascular events. Objective: The aim of this study is to assess the effects of repeated KI intake on the thyroid function of aged male rats. Methods: A twelve months old male rats were subjected to either KI or saline solution over 8 days. Clinical biochemistry, pituitary and thyroid hormones level, and thyroid genes expression were analyzed 30 days after the treatment discontinuation. Findings: urinary assessment shows a subtle increase of some parameters (Creatinin, Uric Acid, Urea, Glucose, Potassium, Sodium and Chlorine), plasma biochemistry reveals a subtle variation of some parameters (an increase of Creatinin, Glucose and phosphorus; and a decrease of Chlorine level). Regarding pituitary-thyroid hormones we get a significant decrease of TSH level without thyroid hormones variation. At the molecular level, we observe a significant increase of TPO (+100%), AIT (+299%) and Tg (+38%) mRNA expression. On the other hand we get a significant decrease of TSHR (-51%) mRNA expression. Conclusion and perspectives: Our first results indicate that repeated KI intake affects the clinical biochemistry and the pituitary-thyroid axis function in elderly rats. To go further we are investigating the impact of these variations on the cardiovascular function and its parameters. Cardiac output data, cardiovascular gene expression, oxidative stress and inflammatory analysis are being processed. This study will contribute to the evolution of iodine policy and the harmonization of the current KI guidelines.

A putative mechanism of the Sodium/Iodide Symporter regulation during repetitive administration of stable Iodide described by a Systems Biology approach

A single dose of potassium iodide (KI) against a prolonged exposure to repeated radioactivity might not be effective enough to protect the thyroid. Our group have shown that a repetitive dose of KI for eight days offers efficient protection without adverse effects in male rats [1].

DO MULTIPLE ADMINISTRATIONS OF STABLE IODINE PROTECT POPULATION CHRONICALLY EXPOSED TO RADIOACTIVE IODINE: WHAT IS PRIODAC RESEARCH PROGRAM (2014-22) TEACHING US?

Single dose of potassium iodide (KI) is recommended to prevent the risk of thyroid cancer during nuclear accidents. However in the case of repeated/protracted radioiodine release, a unique dose of KI may not protect efficiently the thyroid against the risk of further developing a radiation-induced cancer. The new WHO guidelines for the use in planning for and responding to radiological and nuclear emergencies identify the need of more data on this subject as one of the four research priorities. The aims of the PRIODAC project are (1) to assess the associated side effects of repeated intakes of KI, (2) to better understand the molecular mechanisms regulating the metabolism of iodine, (3) to revise the regulatory French marketing authorization of 65-mg KI tablets and (4) to develop new recommendations related to the administration of KI toward a better international harmonization. A review of the literature and the preliminary data are presented here.

Stress as an immunomodulator: liver X receptors maybe the answer

Stress is a reflex response, both psychological and physiological, of the body to a difficult situation that requires adaptation. Stress is at the intersection of the objective event and the subjective event. The physiological mechanisms involved in chronic stress are numerous and can contribute to a wide variety of disorders, in all systems including the immune system. Stress modifies the Th1/Th2 balance via the HPA axis and a set of immune mediators. This will make the body more vulnerable to external infections in a scientific way while others claim the opposite, stress could be considered immune stimulatory. The development of synthetic LXR ligands such as T0901317 and GW3965 as well as an understanding of the direct involvement of these receptors in the regulation of proopiomelanocortin (POMC) gene expression and indirectly by producing a variety of cytokines in a stressor response, will open in the near future new therapeutic methods against the undesirable effects of stress on the behavior of the immune system.

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.

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.

Optimal KI Prophylactic Dose Determination for Thyroid Radiation Protection After a Single Administration in Adult Rats

A dose–response study was performed in adult rats to select an optimal stable potassium iodide (KI) dose which could be implemented in repeated prophylaxis, in case of prolonged exposure to radioactive iodine. Increasing doses of KI were given orally to rats 1 hour before internal exposure simulated by I-125 injection. I-125 incorporation in the thyroid was measured by γ-spectrometry, and KI protection effect was modeled by pharmacological functions. The measurement method by inductively coupled plasma mass spectrometry previously developed for the quantification of stable iodine in urine was adapted to correlate KI effect with its distribution in the thyroid. More than 75% blockade of iodine I-125 incorporation in the thyroid was achieved for KI single doses above 0.5 to 0.7 mg/kg. Stable iodine content in the thyroid 24 hours after KI administration displayed a biphasic response, with a maximum level for a dose around 1 mg/kg. Besides, the urinary excretion of stable iodine is described by a sigmoid function. The change in the rate of iodine excretion for doses above 1 mg/kg KI suggests a body overload in iodine and corroborates a possible saturation of the thyroid. The results show that 1 mg/kg KI could be regarded as an optimal dose for thyroid protection.

DNA methylation and potential multigenerational epigenetic effects linked to uranium chronic low-dose exposure in gonads of males and females rats

INTRODUCTION

An increased health problem in industrialised countries is the contemporary concern of public and scientific community as well. This has been attributed in part to accumulated environmental pollutants especially radioactive substances and the use of nuclear power plants worldwide. However, the outcome of chronic exposure to low doses of a radionuclide such as uranium remains unknown. Recently, a paradigm shift in the perception of risk of radiotoxicology has emerged through investigating the possibility of transmission of biological effects over generations, in particular by epigenetic pathways. These processes are known for their crucial roles associated with the development of several diseases.

OBJECTIVE

The current work investigates the epigenetic effect of chronic exposure to low doses of uranium and its inheritance across generations. Materials and Methods To test this proposition, a rodent multigenerational model, males and females, were exposed to a non-toxic concentration of uranium (40mgL^-1 drinking water) for nine months. The uranium effects on were evaluated over three generations (F0, F1 and F2) by analysing the DNA methylation profile and DNMT genes expression in ovaries and testes tissues.

RESULTS

Here we report a significant hypermethylation of testes DNA (p <0.005) whereas ovaries showed hypomethylated DNA (p <0.005). Interestingly, this DNA methylation profile was significantly maintained across generations F0, F1 and F2. Furthermore, qPCR results of both tissues imply a significant change in the expression of DNA methyltransferase genes (DNMT 1 and DNMT3a/b) as well.

CONCLUSION

Altogether, our work demonstrates for the first time a sex-dependance and inheritance of epigenetic marks, DNA methylation, as a biological response to the exposure to low doses of uranium. However, it is not clear which type of reproductive cell type is more responsive in this context.

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 17β-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.

Post-transcriptional regulation of cyclins D1, D3 and G1 and proliferation of human cancer cells depend on IMP-3 nuclear localization

RNA-binding proteins of the IMP family (insulin-like growth factor 2 (IGF2) mRNA-binding proteins 1-3) are important post-transcriptional regulators of gene expression. Multiple studies have linked high expression of IMP proteins, and especially of IMP-3, to an unfavorable prognosis in numerous types of cancer. The specific importance of IMP-3 for cancer transformation remains poorly understood. We here show that all three IMPs can directly bind the mRNAs of cyclins D1, D3 and G1 (CCND1, D3 and G1) in vivo and in vitro, and yet only IMP-3 regulates the expression of these cyclins in a significant manner in six human cancer cell lines of different origins. In the absence of IMP-3, the levels of CCND1, D3 and G1 proteins fall dramatically, and the cells accumulate in the G1 phase of the cell cycle, leading to almost complete proliferation arrest. Our results show that, compared with IMP-1 and IMP-2, IMP-3 is enriched in the nucleus, where it binds the transcripts of CCND1, D3 and G1. The nuclear localization of IMP-3 depends on its protein partner HNRNPM and is indispensable for the post-transcriptional regulation of expression of the cyclins. Cytoplasmic retention of IMP-3 and HNRNPM in human cancer cells leads to significant drop in proliferation. In conclusion, a nuclear IMP-3-HNRNPM complex is important for the efficient synthesis of CCND1, D3 and G1 and for the proliferation of human cancer cells.

Influence of environmental enrichment and depleted uranium on behaviour, cholesterol and acetylcholine in apolipoprotein E-deficient mice

Alzheimer's disease is associated with genetic risk factors, of which the apolipoprotein E (ApoE) is the most prevalent, and is affected by environmental factors that include education early in life and exposure to metals. The industrial and military use of depleted uranium (DU) resulted in an increase of its deposition in some areas and led to a possible environmental factor. The present study aims to ascertain the effects on the behaviour and the metabolism of cholesterol and acetylcholine of ApoE-/- mice exposed to enriched environment (EE) and exposed to DU (20 mg/L) for 14 weeks. Here we show that ApoE-/- mice were unaffected by the EE and their learning and memory were similar to those of the non-enriched ApoE-/- mice. ApoE-/- mice showed a significant decrease in total (-16 %) and free (-16 %) cholesterol in the entorhinal cortex in comparison to control wild-type mice. Whatever the housing conditions, the exposure to DU of ApoE-/- mice impaired working memory, but had no effect on anxiety-like behaviour, in comparison to control ApoE-/- mice. The exposure of ApoE-/- mice to DU also induced a trend toward higher total cholesterol content in the cerebral cortex (+15 %) compared to control ApoE-/- mice. In conclusion, these results demonstrate that enriched environment does not ameliorate neurobehaviour in ApoE-/- mice and that ApoE mutation induced specific effects on the brain cholesterol. These findings also suggested that DU exposure could modify the pathology in this ApoE model, with no influence of housing conditions.

Metabolomics identifies a biological response to chronic low-dose natural uranium contamination in urine samples

Because uranium is a natural element present in the earth's crust, the population may be chronically exposed to low doses of it through drinking water. Additionally, the military and civil uses of uranium can also lead to environmental dispersion that can result in high or low doses of acute or chronic exposure. Recent experimental data suggest this might lead to relatively innocuous biological reactions. The aim of this study was to assess the biological changes in rats caused by ingestion of natural uranium in drinking water with a mean daily intake of 2.7 mg/kg for 9 months and to identify potential biomarkers related to such a contamination. Subsequently, we observed no pathology and standard clinical tests were unable to distinguish between treated and untreated animals. Conversely, LC-MS metabolomics identified urine as an appropriate biofluid for discriminating the experimental groups. Of the 1,376 features detected in urine, the most discriminant were metabolites involved in tryptophan, nicotinate, and nicotinamide metabolic pathways. In particular, N-methylnicotinamide, which was found at a level seven times higher in untreated than in contaminated rats, had the greatest discriminating power. These novel results establish a proof of principle for using metabolomics to address chronic low-dose uranium contamination. They open interesting perspectives for understanding the underlying biological mechanisms and designing a diagnostic test of exposure.

Intravenous human mesenchymal stem cells transplantation in NOD/SCID mice preserve liver integrity of irradiation damage

This work was initiated in an effort to evaluate the potential therapeutic contribution of the infusion of mesenchymal stem cells (MSC) for the correction of liver injuries. We subjected NOD-SCID mice to a 10.5-Gy abdominal irradiation and we tested the biological and histological markers of liver injury in the absence and after infusion of expanded human MSC. Irradiation alone induced a significant elevation of the ALT and AST. Apoptosis in the endothelial layer of vessels was observed. When MSC were infused in mice, a significant decrease of transaminases was measured, and a total disappearance of apoptotic cells. MSC were not found in liver. To explain the protection of liver without MSC engraftment, we hypothesize an indirect action of MSC on the liver via the intestinal tract. Pelvic or total body irradiation induces intestinal absorption defects leading to an alteration of the enterohepatic recirculation of bile acids. This alteration induces an increase in Deoxy Cholic Acid (DCA) which is hepatoxic. In this study, we confirm these results. DCA concentration increased approximately twofold after irradiation but stayed to the baseline level after MSC injection. We propose from our observations that, following irradiation, MSC infusion indirectly corrected liver dysfunction by preventing gut damage. This explanation would be consistent with the absence of MSC engraftment in liver. These results evidenced that MSC treatment of a target organ may have an effect on distant tissues. This observation comes in support to the interest for the use of MSC for cellular therapy in multiple pathologies proposed in the recent years.

Influence of depleted uranium on hepatic cholesterol metabolism in apolipoprotein E-deficient mice

Depleted uranium (DU) is uranium with a lower content of the fissile isotope U-235 than natural uranium. It is a radioelement and a waste product from the enrichment process of natural uranium. Because of its very high density, it is used in the civil industry and for military purposes. DU exposure can affect many vital systems in the human body, because in addition to being weakly radioactive, uranium is a toxic metal. It should be emphasized that, to be exposed to radiation from DU, you have to eat, drink, or breathe it, or get it on your skin. This particular study is focusing on the health effects of DU for the cholesterol metabolism. Previous studies on the same issue have shown that the cholesterol metabolism was modulated at molecular level in the liver of laboratory rodents contaminated for nine months with DU. However, this modulation was not correlated with some effects at organs or body levels. It was therefore decided to use a "pathological model" such as hypercholesterolemic apolipoprotein E-deficient laboratory mice in order to try to clarify the situation. The purpose of the present study is to assess the effects of a chronic ingestion (during 3 months) of a low level DU-supplemented water (20 mg L(-1)) on the above mentioned mice in order to determine a possible contamination effect. Afterwards the cholesterol metabolism was studied in the liver especially focused on the gene expressions of cholesterol-catabolising enzymes (CYP7A1, CYP27A1 and CYP7B1), as well as those of associated nuclear receptors (LXRα, FXR, PPARα, and SREBP 2). In addition, mRNA levels of other enzymes of interest were measured (ACAT 2, as well as HMGCoA Reductase and HMGCoA Synthase). The gene expression study was completed with SRB1 and LDLr, apolipoproteins A1 and B and membrane transporters ABC A1, ABC G5. The major effect induced by a low level of DU contamination in apo-E deficient mice was a decrease in hepatic gene expression of the enzyme CYP7B1 (-23%) and nuclear receptors LXRα (-24%), RXR (-32%), HNF4α (-21%) when compared to unexposed ones. These modifications on cholesterol metabolism did not lead to increased disturbances that are specific for apolipoprotein E-deficient mice, suggesting that chronic DU exposure did not worsen the pathology in this experimental model. In conclusion, the results of this study indicate that even for a sensitive pathologic model the exposure to a low dose of DU has no relevant impact. The results confirm the results of our first study carried out on healthy laboratory rodents where a sub-chronic contamination with low dose DU did not affect in vivo the metabolism of cholesterol.

Uranium microdistribution in renal cortex of rats after chronic exposure: a study by secondary ion mass spectrometry microscopy

For a few years, the biological effects on ecosystems and the public of the bioaccumulation of radionuclides in situations of chronic exposures have been studied. This work, in keeping with the ENVIRHOM French research program, presents the uranium microdistribution by secondary ion mass spectrometry (SIMS) technique in the renal cortex of rats following chronic exposure to this low level element in the drinking water (40 mg/L) as a function to exposure duration (6, 9, 12, and 18 months). The SIMS mass spectra and 238U+ ion images produced with a SIMS CAMECA 4F-E7 show the kinetic of uranium accumulation in the different structures of the kidney. For the rats contaminated up to 12 months, the radioelement is mainly fixed in the proximal tubules; then after 18 exposure months, uranium is detected in all the segments of the nephron. This work has also shown that ion microscopy is an analytical method to detect trace elements and give elemental cartography at the micrometer scale.

The metabolomic approach identifies a biological signature of low-dose chronic exposure to cesium 137

Reports have described apparent biological effects of (137)Cs (the most persistent dispersed radionuclide) irradiation in people living in Chernobyl-contaminated territory. The sensitive analytical technology described here should now help assess the relation of this contamination to the observed effects. A rat model chronically exposed to (137)Cs through drinking water was developed to identify biomarkers of radiation-induced metabolic disorders, and the biological impact was evaluated by a metabolomic approach that allowed us to detect several hundred metabolites in biofluids and assess their association with disease states. After collection of plasma and urine from contaminated and non-contaminated rats at the end of the 9-months contamination period, analysis with a LC-MS system detected 742 features in urine and 1309 in plasma. Biostatistical discriminant analysis extracted a subset of 26 metabolite signals (2 urinary, 4 plasma non-polar, and 19 plasma polar metabolites) that in combination were able to predict from 68 up to 94% of the contaminated rats, depending on the prediction method used, with a misclassification rate as low as 5.3%. The difference in this metabolic score between the contaminated and non-contaminated rats was highly significant (P = 0.019 after ANOVA cross-validation). In conclusion, our proof-of-principle study demonstrated for the first time the usefulness of a metabolomic approach for addressing biological effects of chronic low-dose contamination. We can conclude that a metabolomic signature discriminated (137)Cs-contaminated from control animals in our model. Further validation is nevertheless required together with full annotation of the metabolic indicators.

Transcriptomic effects of depleted uranium on acetylcholine and cholesterol metabolisms in Alzheimer's disease model

Some heavy metals, or aluminium, could participate in the development of Alzheimer disease (AD). Depleted uranium (DU), another heavy metal, modulates the cholinergic system and the cholesterol metabolism in the brain of rats, but without neurological disorders. The aim of this study was to determine what happens in organisms exposed to DU that will/are developing the AD. This study was thus performed on a transgenic mouse model for human amyloid precursor protein (APP), the Tg2576 strain. The possible effects of DU through drinking water (20 mg/L) over an 8-month period were analyzed on acetylcholine and cholesterol metabolisms at gene level in the cerebral cortex. The mRNA levels of choline acetyl transferase (ChAT) vesicular acetylcholine transporter (VAChT) and ATP-binding cassette transporter A1 (ABC A1) decreased in control Tg2576 mice in comparison with wild-type mice (respectively -89%, -86% and -44%, p < 0.05). Chronic exposure of Tg2576 mice to DU increased mRNA levels of ChAT (+189%, p < 0.05), VAChT (+120%, p < 0.05) and ABC A1 (+52%, p < 0.05) compared to control Tg2576 mice. Overall, these modifications of acetylcholine and cholesterol metabolisms did not lead to increased disturbances that are specific of AD, suggesting that chronic DU exposure did not worsen the pathology in this experimental model.

Cholesterol 7alpha-hydroxylase (CYP7A1) activity is modified after chronic ingestion of depleted uranium in the rat

Depleted uranium (DU) is a radioactive heavy metal derived from the nuclear energy production. Its wide use in civilian and military items increases the risk of its environmental dissemination, and thus the risk of internal contamination of populations living in such contaminated territories. Previous studies have shown that vitamin D and cerebral cholesterol metabolisms were affected following chronic ingestion of DU. Even more than the brain, the liver is a crucial organ in cholesterol homeostasis since it regulates cholesterol distribution and elimination at body level. The aim of this work was to assess the impact of a low-level chronic ingestion of DU on hepatic cholesterol metabolism. Rats were contaminated with DU in their drinking water at a concentration of 40mg/l for 9 months. The major effect induced by DU was a decrease of CYP7A1 specific activity (-60%) correlated with a matching decrease of its product 7alpha-hydroxycholesterol in the plasma. Hepatic gene expression of transporters ABC A1, ABC G5, ABC G8 and of nuclear receptor RXR was increased, whereas that of catabolism enzyme CYP7B1 was decreased. Thus, after a chronic ingestion of DU, rats experience a modulation of cholesterol catabolism but overcome it, since their cholesterolemia is preserved and no pathology is declared.

Testicular steroidogenesis is not altered by 137 cesium Chernobyl fallout, following in utero or post-natal chronic exposure

The testis is especially sensitive to pollutants, including radionuclides. Following the Chernobyl nuclear power plant accident, several of these radionuclides were emitted and spread in the environment. Subsequently, children presented some disruptions of the endocrine system. To determine whether these disruptions were due to 137 cesium ((137)Cs) exposure, the effects of chronic contamination with low doses of (137)Cs in utero or from birth on testicular steroidogenesis in rats were studied. Contamination was continued for 9 months. No modification was observed in circulating level of hormones (17beta-estradiol, testosterone, follicle-stimulating hormone, luteinizing hormone) following in utero or post-natal contamination. Expression of several genes involved in testicular steroidogenesis was affected (cyp19a1, fxr, sf-1), without modification of protein expression or activity. Our results suggest that growing organisms may be affected at the molecular level by (137)Cs contamination at this post-accidental dose.

Vitamin E decreases endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells

Intestine is the gateway for newly absorbed tocopherols. This organ also plays a crucial role in cholesterol metabolism. Because tocopherols are known to impact cholesterol metabolism in the liver, we hypothesized that tocopherols could also modulate cholesterol metabolism in the intestine. This study aimed to verify this hypothesis and to unveil the mechanisms involved, using Caco-2 cells as a model of the human intestinal cell. Both α- and γ-tocopherol significantly (P<.05) decreased endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells. Tocopherols down-regulated (P<.05) up to half of the genes involved in the cholesterol synthesis pathway, together with CYP27A1, which is involved in oxysterol production. The activity of this enzyme, as well as the levels of intracellular oxysterols, was significantly diminished by tocopherols. Finally, tocopherols significantly reduced ABCA1 mRNA levels in Caco-2 cells. We conclude that tocopherols impair the endogenous synthesis and apo-AI-mediated secretion of cholesterol in Caco-2 cells. This effect involves a down-regulation of genes involved in the cholesterol synthesis pathway, resulting in down-regulation of CYP27A1 which, in turn, diminishes oxysterol concentrations. The outcome is a decrease of LXR activity, resulting in down-regulation of ABCA1. These data reinforce the effect of α- and γ-tocopherol on cholesterol metabolism via gene expression regulation.

Acetaminophen induces xenobiotic-metabolizing enzymes in rat: Impact of a uranium chronic exposure

The extensive use of uranium in civilian and military applications increases the risk of human chronic exposure. Uranium is a slightly radioactive heavy metal with a predominantly chemical toxicity, especially in kidney but also in liver. Few studies have previously shown some effects of uranium on xenobiotic-metabolizing enzymes (XME) that might disturb drug pharmacokinetic. The aim of this study was to determine whether a chronic (9 months) non-nephrotoxic low dose exposure to depleted uranium (DU, 1mg/rat/day) could modify the liver XME, using a single non-hepatotoxic acetaminophen (APAP) treatment (50mg/kg). Most of XME analysed were induced by APAP treatment at the gene expression level but at the protein level only CYP3A2 was significantly increased 3h after APAP treatment in DU-exposed rats whereas it remained at a basal level in unexposed rats. In conclusion, these results showed that a chronic non-nephrotoxic DU exposure specially modify CYP3A2 after a single therapeutic APAP treatment.

Enriched uranium affects the expression of vitamin D receptor and retinoid X receptor in rat kidney

An increasing awareness of the radiological impact of the nuclear power industry and other nuclear technologies is observed nowadays on general population. This led to renew interest to assess the health impact of the use of enriched uranium (EU). The aim of this work was to investigate in vivo the effects of a chronic exposure to EU on vitamin D(3) metabolism, a hormone essential in mineral and bone homeostasis. Rats were exposed to EU in their drinking water for 9 months at a concentration of 40 mg l(-1) (1mg/rat day). The contamination did not change vitamin D plasma level. Vitamin D receptor (vdr) and retinoid X receptor alpha (rxralpha), encoding nuclear receptors involved in the biological activities of vitamin D, showed a lower expression in kidney, while their protein levels were paradoxically increased. Gene expression of vitamin D target genes, epithelial Ca(2+) channel 1 (ecac1) and Calbindin-D28k (cabp-d28k), involved in renal calcium transport were decreased. Among the vitamin D target organs examined, these molecular modifications occurred exclusively in the kidney, which confirms that this organ is highly sensitive to uranium exposure. In conclusion, this study showed that a chronic exposure to EU affects both mRNA and protein expressions of renal nuclear receptors involved in vitamin D metabolism, without any modification of the circulating vitamin D.

In vivo effects of chronic contamination with 137 cesium on testicular and adrenal steroidogenesis

More than 20 years after Chernobyl nuclear power plant explosion, radionuclides are still mainly bound to the organic soil layers. The radiation exposure is dominated by the external exposure to gamma-radiation following the decay of (137)Cs and by soil-to-plant-to-human transfer of (137)Cs into the food chain. Because of this persistence of contamination with (137)Cs, questions regarding public health for people living in contaminated areas were raised. We investigated the biological effects of chronic exposure to (137)Cs on testicular and adrenal steroidogenesis metabolisms in rat. Animals were exposed to radionuclide in their drinking water for 9 months at a dose of 6,500 Bq/l (610 Bq/kg/day). Cesium contamination decreases the level of circulating 17beta-estradiol, and increases corticosterone level. In testis, several nuclear receptors messenger expression is disrupted; levels of mRNA encoding Liver X receptor alpha (LXRalpha) and LXRbeta are increased, whereas farnesoid X receptor mRNA presents a lower level. Adrenal metabolism presents a paradoxical decrease in cyp11a1 gene expression. In conclusion, our results show for the first time molecular and hormonal modifications in testicular and adrenal steroidogenic metabolism, induced by chronic contamination with low doses of (137)Cs.