Comparison of the effects of enriched uranium and 137-cesium on the behaviour of rats after chronic exposure.

PURPOSE: A radionuclide that accumulates in the central nervous system is likely to exert both a chemical and a radiological effect. The present study aimed at assessing the behavioral effect of two radionuclides previously shown to accumulate in the central nervous system after chronic exposure--uranium and cesium. MATERIALS AND METHODS: Rats were exposed for 9 months to drinking water contaminated with either enriched uranium at a dosage of 40 mg U x l(-1) or 137-cesium at a dosage of 6500 Bq x l(-1), which correspond to the highest concentrations measured in some wells in the south of Finland (uranium) or in the milk in Belarus in the year following the Chernobyl accident (137-cesium). RESULTS: At this level of exposure, 137-cesium had no effect on the locomotor activity measured in an open-field, on immobility time in a forced swimming test, on spontaneous alternation in a Y-maze and on novel object exploration in an object recognition test. Enriched uranium exposure specifically reduced the spontaneous alternation measured in the Y-maze after 3 and 9 months exposure although it did not affect the other parameters. CONCLUSION: Enriched uranium exposure altered the spatial working memory capacities and this effect was correlated with previously described accumulation of uranium in the hippocampus which is one of the cerebral areas involved in this memory system.

Parental exposure to enriched uranium induced delayed hyperactivity in rat offspring.

Several recent reports suggest that chronic exposure to uranium could induce behavioural effects in adult rats. As the immature brains are known to be more susceptible to toxic effects, rats were observed in an open field, in a Y-maze and in an elevated plus-maze at 2, 5 and 9 months old after exposure to enriched uranium (40 mg l-1) during gestation and lactation. The rats exposed to enriched uranium showed a significant decrease in alternation in the Y-maze at 2 months old which reflects a slight decrease in the spatial working memory capacities as previously described in adult rats. However, the main result was a delayed hyperactivity in the rats exposed to enriched uranium, which appeared to a slight extent at 5 months old and was more evident at 9 months old. Although this effect could not be directly explained by some uranium accumulation in the target organs, this experiment showed that early exposure to enriched uranium can induce a very late effect on the rat behaviour and that such studies should not be restricted to the effects observed on young rats.

Role of the sodium-dependent phosphate co-transporters and of the phosphate complexes of uranyl in the cytotoxicity of uranium in LLC-PK1 cells.

Although uranium is a well-characterized nephrotoxic agent, very little is known at the cellular and molecular level about the mechanisms underlying the uptake and toxicity of this element in proximal tubule cells. The aim of this study was thus to characterize the species of uranium that are responsible for its cytotoxicity and define the mechanism which is involved in the uptake of the cytotoxic fraction of uranium using two cell lines derived from kidney proximal (LLC-PK(1)) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK(1) cells with colchicine, cytochalasin D, concanavalin A and PMA increased the sodium-dependent phosphate co-transport and the cytotoxicity of uranium. On the contrary, replacement of the extra-cellular sodium with N-methyl-D-glucamine highly reduced the transport of phosphate and the cytotoxic effect of uranium. Uranium cytotoxicity was also dependent upon the extra-cellular concentration of phosphate and decreased in a concentration-dependent manner by 0.1-10 mM phosphonoformic acid, a competitive inhibitor of phosphate uptake. Consistent with these observations, over-expression of the rat proximal tubule sodium-dependent phosphate co-transporter NaPi-IIa in stably transfected MDCK cells significantly increased the cytotoxicity of uranium, and computer modeling of uranium speciation showed that uranium cytotoxicity was directly dependent on the presence of the phosphate complexes of uranyl UO(2)(PO(4))(-) and UO(2)(HPO(4))(aq). Taken together, these data suggest that the cytotoxic fraction of uranium is a phosphate complex of uranyl whose uptake is mediated by a sodium-dependent phosphate co-transporter system.

Accumulation and distribution of uranium in rats after chronic exposure by ingestion.

Data describing the biokinetics of radionuclides after contamination come mainly from experimental acute exposures of laboratory animals and follow-up of incidental exposures of humans. These data were compiled to form reference models that could be used for dose calculation in humans. In case of protracted exposure, the same models are applied, assuming that they are not modified by the duration of exposure. This work aims at testing this hypothesis. It presents new experimental data on retention of uranium after chronic intake, which are compared to values calculated from a biokinetic model that is based on experiments of acute exposure of rats to uranium. Experiments were performed with 56 male Sprague Dawley rats, from which 35 were exposed during their whole adult life to 40 mg L of uranyl nitrate dissolved in mineral water and 21 were kept as controls. Animals were euthanatized at 32, 95, 186, 312, 368, and 570 d after the beginning of contamination. Urine and all tissues were removed, weighted, mineralized, and then analyzed for uranium content by Kinetics Phosphorescence Analysis (KPA) or by ICP-MS. Experimental data showed that uranium accumulated in most organs, following a nonmonotonous pattern. Peaks of activities were observed at 1-3, 10, and 19 mo after the beginning of exposure. Additionally, accumulation was shown to occur in tissues such as teeth and brain that are not usually described as target organs. Comparison with model prediction showed that the accumulation of uranium in target organs after chronic exposure is overestimated by the use of a model designed for acute exposure. These differences indicate that protracted exposure to uranium may induce changes in biokinetic parameters when compared to acute contamination and that calculation of dose resulting from chronic intake of radionuclides may need specific models that are not currently available.

Chronic ingestion of uranyl nitrate perturbs acetylcholinesterase activity and monoamine metabolism in male rat brain.

Recent animal studies have shown that uranium can reach the brain after chronic exposure. However, little information is available on the neurological effects of chronic long-term exposure to uranium. In the present study, the effects during 1.5, 6 and 9-month periods of chronic ingestion of uranyl nitrate (UN) in drinking water (40 mg of uranium per litre) on cholinergic acetylcholinesterase (AChE) activity and on dopaminergic and serotoninergic metabolisms were investigated in several areas of male Srague Dawley rat brains. Uranium brain accumulation and distribution was also investigated after 1.5 and 9 months. Both after 1.5, 6 and 9 months of exposure, AChE activity was unaffected in the striatum, hippocampus and frontal cortex. Nevertheless, AChE activity was transitionally perturbed in the cerebellum after 6 months of exposure. After 1.5 months of exposure, DA level increased in hypothalamus. After 6 months of exposure, a tiny but significant modification of the DAergic turnover ratio was detected in the frontal cortex. And after 9 months, UN produced a significant decrease in the 5HIAA level and the 5HTergic turn-over ratio in the frontal cortex and also a decrease in the DOPAC level and DAergic turn-over ratio in the striatum. Uranium brain accumulation was statistically significant in striatum after 1.5 months and in striatum, hippocampus and frontal cortex after 9 months of exposure. Although neurochemical changes did not always correlated with increased accumulation of uranium in specific areas, these results suggest that chronic ingestion of UN can cause chronic and progressive perturbations of physiological level of neurotransmitter systems. Considering previous reports on behavioural uranium-induced effects and the involvement of neurotransmitters in various behavioural processes, it would be crucial to determine whether these neurochemical disorders were accompanied by neurobehavioral deficits even at 40 mg of uranium per litre exposure.

The chemical speciation of uranium in water does not influence its absorption from the gastrointestinal tract of rats.

Studies of the chemical speciation of uranium in water can enhance the knowledge of the mechanisms of its absorption from the gastrointestinal tract and its storage in the body. They can also help to improve the dosimetric models recommended by the International Commission on Radiological Protection (ICRP). The aim of this work was to assess the influence of uranium speciation on its absorption from the gastrointestinal tract by using both computer speciation modeling and direct measurement of the fractional absorption in vivo in rats after ingestion of five different samples of contaminated water. Preliminary ex vivo studies with human saliva and gastric juice showed that 90% of uranium was recovered with the natural components of the fluid studied. The computer studies of uranium speciation among the electrolytes of these fluids showed that under the set conditions, the chemical species changed in a broadly similar manner under the influence of fluid composition and pH. In vivo studies in rats validated these observations by indicating an average fractional absorption of about 0.4% for each of five different water samples. It is concluded that the chemical form of uranium in the water ingested did not influence its absorption into the body.

The brain is a target organ after acute exposure to depleted uranium.

The health effects of depleted uranium (DU) are mainly caused by its chemical toxicity. Although the kidneys are the main target organs for uranium toxicity, uranium can also reach the brain. In this paper, the central effects of acute exposure to DU were studied in relation to health parameters and the sleep-wake cycle of adult rats. Animals were injected intraperitoneally with 144+/-10 microg DU kg-1 as nitrate. Three days after injection, the amounts of uranium in the kidneys represented 2.6 microg of DU g-1 of tissue, considered as a sub-nephrotoxic dosage. The central effect of uranium could be seen through a decrease in food intake as early as the first day after exposure and shorter paradoxical sleep 3 days after acute DU exposure (-18% of controls). With a lower dosage of DU (70+/-8 microg DU kg-1), no significant effect was observed on the sleep-wake cycle. The present study intends to illustrate the fact that the brain is a target organ, as are the kidneys, after acute exposure to a moderate dosage of DU. The mechanisms by which uranium causes these early neurophysiological perturbations shall be discussed.

A local approach to reduce industrial uranium wound contamination in rats.

The aim of this work is to develop a new approach to partially decontaminate wounds after industrial uranium contamination, during the interval of time between contamination and transfer of the patient to the infirmary. A wound dressing and a paste mixed or not with uranium-chelating ligands, ethane-1-hydroxy-1,1-bisphosphonate (EHBP) and carballylic amido bis phosphonic acid (CAPBP), were tested in vitro on muscles and in vivo on rats after deposit of uranium oxide compounds. The dressing and the paste, composed of carboxymethylcellulose-based hydrocolloids known to be highly absorbent, were applied on simulated wounds a few minutes after the contamination. The incorporation of chelating ligands did not improve the efficacy of the dressing or paste, and the best results were obtained with the dressing. In vivo, after 1 h of contact with the wound, the dressing absorbed about 30% and 60% of a UO4 compound deposited intra- and intermuscularly, respectively. After intramuscular deposit, the efficacy of the dressing was not reduced if the contact time decreased from 1 h to 15 min. Therefore, this wound dressing could be a practical option to treat uranium-contaminated wounds, but its efficacy depends on the localization of the uranium deposit.

Effect of U and 137Cs chronic contamination on dopamine and serotonin metabolism in the central nervous system of the rat.

Following the Chernobyl accident, the most significant problem for the population of the former Soviet Union for the next 50-70 years will be chronic internal contamination by radionuclides. One of the few experiments carried out in this field reported that neurotransmitter metabolism in the central nervous system of the rat was disturbed after feeding with oats contaminated by 137Cs for 1 month. The present study assessed the effect of chronic contamination by depleted U or 137Cs on the metabolism of two neurotransmitters in cerebral areas of rats. Dopamine and serotonin were chosen because their metabolism has been shown to be disturbed after external irradiation, even at moderate doses. Dopamine, serotonin, and some of their catabolites were measured by high-pressure liquid chromatography coupled with an electrochemical detector in five cerebral structures of rats contaminated over a 1-month period by drinking water (40 mg U.L -1 or 6500 Bq 137Cs.L -1). In the striatum, hippocampus, cerebral cortex, thalamus, and cerebellum, the dopamine, serotonin, and catabolite levels were not significantly different between the control rats and rats contaminated by U or 137Cs. These results are not in accordance with those previously described.

Efficacy of 3,4,3-LI(1,2-HOPO) for decorporation of Pu, Am and U from rats injected intramuscularly with high-fired particles of MOX.

This study aimed to assess the efficacy of 3,4,3-LI(1,2-HOPO) for reducing uranium, plutonium and americium in rats after intramuscular injection of (U-Pu)O2 particles (MOX). Sixteen rats were contaminated by intramuscular injection of a 1 mg MOX suspension and then treated daily for 7 d with LIHOPO (30 or 200 micromol kg(-1)) or DTPA (30 micromol kg(-1)). LIHOPO was inefficient for removing Pu, Am and U from the wound site. However, it reduced Pu retention in carcass and liver by factors of 2 and 6 respectively, and Am retention in carcass and liver by factors of 10 and 30. In contrast, the effect of LIHOPO on U was to decrease the retention in kidneys by a factor of 75. These results confirm that LIHOPO is a good candidate for use after contamination with MOX, in combination with localised wound lavage or surgical treatment aimed at removing most of the contaminant at the wound site.

Effect of DTPA on the nephrotoxicity induced by uranium in the rat.

The only treatment proposed after human contamination with MOX (mixed oxide of uranium and plutonium) is diethylenetriaminepentaacetic acid (DTPA), because plutonium is considered to be the major risk. However, both DTPA and uranium are nephrotoxic at high dosages and DTPA has been shown to increase in vitro the cytotoxicity induced by uranium on cultured epithelial tubular cells. This work aimed to test this effect in vivo. Rats were injected with subtoxic (57 microg kg(-1)) to toxic (639 microg kg(-1)) amounts of uranium as nitrate at 0 h, they received two DTPA injections (30 micromol kg(-1)) at 2 min and 24 h and were euthanased at 48 h. The nephrotoxic effects were evaluated by measurement of the body weight gain, food and water intake, measurement of biochemical parameters in urine and blood, and histological examination of one kidney. The main result was that DTPA did not increase the nephrotoxicity induced by uranium in the range of concentrations tested, which was inconsistent with the in vitro results.

Effect of absorption parameters on calculation of the dose coefficient: example of classification of industrial uranium compounds.

In the Human Respiratory Tract Model (HRTM) described in ICRP Publication 66, time-dependent dissolution is described by three parameters: the fraction dissolved rapidly, fr, and the rapid and slow dissolution rates sr and ss. The effect of these parameters on the dose coefficient has been studied. A theoretical analysis was carried out to determine the sensitivity of the dose coefficient to variations in the values of these absorption parameters. Experimental values of the absorption parameters and the doses per unit intake (DPUI) were obtained from in vitro dissolution tests, or from in vivo experiments with rats, for five industrial uranium compounds UO2, U3O8, UO4, UF4 and a mixture of uranium oxides. These compounds were classified in terms of absorption types (F, M or S) according to ICRP. The overall result was that the factor which has the greatest influence on the dose coefficient was the slow dissolution rate ss. This was verified experimentally, with a variation of 20% to 55% for the DPUI according to the absorption type of the compound. In contrast, the rapid dissolution rate sr had little effect on the dose coefficient, excepted for Type F compounds.

Reduction of uranium transfer by local chelation in simulated wounds in rats.

The aim of the paper is to develop a new approach to treat uranium-contaminated wounds. The efficacy of a local uranium chelator, carballylic amido bis phosphonic acid (CAPBP) was assessed using two different uranium compounds. Rats were contaminated by intramuscular injections of uranyl nitrate or an industrial U04 compound to simulate wound contamination. CAPBP was injected intramuscularly (i.m.) or intraperitoneally (i.p.) at a dosage of 30 micromol kg(-1). In one experiment, the local administration of CAPBP was combined with a systemic administration of ethane-1-hydroxy-1,1-biphosphonate (EHBP). The local CAPBP treatment resulted in increased retention of uranium at the wound site: about 30% for uranyl nitrate or U04 after the first day and about 15% of UO4 after the third day. Consequently, it reduced uranium translocation into the blood and deposition in the kidneys and bone. The combined treatment reduced the uranium deposits in the kidneys, bone and carcass to about one-half of those observed in controls 3 days after U04 contamination. The local CAPBP treatment increased the interval of time between contamination and uranium deposit in the target organs. Thus, it can increase the efficacy of nonspecific local treatments or specific systemic treatments. It could be given rapidly through spray or gel after an accident.

Effect of external irradiation on the gastrointestinal absorption of uranium and neptunium in rats.

PURPOSE: The gastrointestinal absorption and systemic distribution of uranium and neptunium were determined after external gamma irradiation. MATERIALS AND METHODS: Rats were exposed to a single whole-body dose of gamma radiation (6Gy; 0.75Gy.min(-1)). Three days after irradiation they were orally and/or intravenously contaminated with 100 microg.kg(-1) uranium or 3kBq.kg(-1) neptunium. The gastrointestinal absorption and organ distribution of both radionuclides were measured 6 days after irradiation. RESULTS: External irradiation increased the intestinal transit time of uranium and neptunium but had no effect on their gastrointestinal absorption. The average fractional absorption was determined to be 0.93 and 0.98% (uranium) and 4.7 and 4.8% (neptunium) for the irradiated and non-irradiated rats respectively. The excretion of uranium and neptunium was not affected by the irradiation. CONCLUSION: A 6 Gy whole-body irradiation (gamma; 0.75Gy.min(-1)) did not affect the absorption of uranium and neptunium after oral intake.

Efficacy of 3,4,3-LIHOPO for reducing neptunium retention in the rat after simulated wound contamination.

PURPOSE: The ligand 3,4,3-Li(1,2-HOPO) was tested for Np removal after intramuscular injection of 237Np nitrate in rats. MATERIALS AND METHODS: Two experiments were performed, one with simultaneous injection of neptunium and LIHOPO at dosages ranging from 3 to 200 micromol kg(-1) and the other with delayed administration of LIHOPO 30 micromol kg(-1) from 5 min to 30 min after Np injection. RESULTS: The data obtained after simultaneous injections showed that the ligand dosage effectiveness was not linear and depended on the tissues being considered. For bones, the best results were obtained with 200 micromol kg(-1) LIHOPO, where retention was reduced to 11% of controls. Maximum efficacies for removal in liver and kidney were obtained with 30 micromol kg(-1) LIHOPO, where retention was reduced to 39% and 1.6% of controls, respectively. At higher dosages, LIHOPO seemed to have a reverse effect on these tissues, demonstrated by a significant accumulation of the radionuclide. The delayed administration of LIHOPO dramatically decreased its efficacy. When administered 5 min after Np, LIHOPO was still efficient (60%, 37%, 7% of controls in bone, liver, kidneys, respectively) but not when treatment was delayed to 30 min. CONCLUSIONS: These results demonstrated that LIHOPO was able to complex Np at the wound site but not after translocation to blood.

Efficacy of ethane-1-hydroxy-1,1-bisphosphonate (EHBP) for the decorporation of uranium after intramuscular contamination in rats.

PURPOSE: To obtain compounds that will effectively reduce the fixation of uranium in its main target organs: bone and kidney. There is an urgent need for a chelating agent that is suitable and available for human use. MATERIALS AND METHODS: The efficacy of ethane-1-hydroxy-1,1-bisphosphonate (EHBP), already in use as a therapeutic agent, was investigated in animal experiments. The effect of different treatment regimens was investigated on rats (EHBP: 50-100 micromol kg(-1); ligand/uranium ratio 2500 to 5000). RESULTS: The present study shows that one prompt injection of EHBP reduced uranium deposition in kidneys by a factor of five after acute intramuscular contamination in rats. At the same time, the total body uranium in the treated animals was 70% of controls. When the treatment was delayed 30 min after contamination, the kidney content was still reduced by a factor of two. CONCLUSIONS: EHBP has the advantage of clinical acceptance as a therapeutic agent for other purposes and its toxicity has been well studied. It therefore has a role in the treatment of human contamination with uranium.

The effects of the initial lung deposit on uranium biokinetics after administration as UF4 and UO4.

This study was designed to assess the effect of the initial lung deposit (ILD) on uranium biokinetics in rats after intracheal instillation of biologically soluble uranium compounds. Rats received various doses of either UO4 or UF4 dust. The uranium content was determined in the kidneys, lungs, remaining carcass, urine and faeces at intervals of up to 30 days. The percentages of uranium absorbed into blood, transferred to tissues, and excreted in urine were independent of the uranium lung deposit for the two compounds. The K/K + U ratio 24 h after installation (K is the per cent of uranium retained in the kidneys and U the per cent excreted in urine) which can be used to evaluate kidney function, was essentially constant in the range from 0.02 to 12.5 microg U g(-1) kidneys.

Assessment of physico-chemical and biokinetic properties of uranium peroxide hydrate UO4.

Comprehensive studies on the radiotoxicological risk of an intermediate compound UO4, which is not specified in ICRP Recommendations, were motivated by its increased use in the nuclear fuel cycle and the lack of information such as physico-chemical and biokinetic properties. The aim of this work was to give an experimental basis for assessing the appropriate limits on intake for workers exposed to UO4 and to provide guidance for the interpretation of personal monitoring data. Particle size measurement of the UO4 dust indicated a geometric diameter D of 0.5 microm, which corresponds to an activity median aerodynamic diameter (AMAD) of 1.1 microm. In vitro experiments conducted in culture medium showed that UO4 is a soluble compound with 66.2% dissolved in 1.9 d and 33.8% in 78 d. Results of dissolution obtained with macrophages showed a significant decrease of 50% at 1 d in terms of solubility. Biokinetic data in the rat obtained from two in vivo studies involving intratracheal instillation in rats indicated half-times in the lung of 0.5 d (96.6%) and 27 d (3.4%) for an initial lung deposit (ILD) of 195 microg, and 1.2 d (90.3%) and 38 d (9.7%) for an ILD of 7.6 microg. Absorption parameters to blood as defined in the ICRP Publication 66 human respiratory tract model were calculated with the specific software GIGAFIT and led to the rapid fraction fr (0.800 to 0.873), the rapid rate sr (0.525 to 0.928 d(-1)), and the slow rate ss (1.57 x 10(-2) to 2.42 x 10(-3) d(-1)). Effective dose coefficients by inhalation for this UO4 compound using the in vivo experimental results were calculated to be between 0.52 and 0.70 x 10(-6) Sv Bq(-1). Comparison of these values with effective dose coefficients defined in ICRP Publication 68 for workers showed that UO4 could be considered as a fast soluble compound of Type F.

Toxicokinetics of cadmium in lactating and nonlactating ewes after oral and intravenous administration.

We studied the toxicokinetics of cadmium on two groups of ewes, a lactating group and a nonlactating group, after single intravenous and oral administrations of cadmium chloride using a semisimultaneous method and a three-compartment model. The nonlactating ewes showed a low cadmium bioavailability (0.12-0.22%), a large steady-state volume of distribution (23.8 +/- 5.4 liter/kg), and a low blood clearance (0.20 +/- 0.03 liter/kg/day). Their mean residence time was 113 +/- 28 days. The lactating ewes had a higher bioavailability (0.33-1.7%). Their mean residence time was close to that in nonlactating ewes despite a greater blood clearance (0.46 +/- 0.013 liter/kg/day) because the volume of distribution of cadmium in the body was larger (Vss = 48.8 +/- 10.3 liter/kg). Their cadmium clearance in milk, changing with time, remained low and could not explain their higher blood clearance. In one nonlactating ewe, a greater cadmium bioavailability (5%) increased cadmium in the body. Increased cadmium amounts could induce renal damage and shorten the mean residence time (78 days).

In vivo non-invasive quantification of muscle damage following a single intramuscular injection of phenylbutazone in sheep.

Intramuscular drug administration can lead to more or less extensive muscle damage. The aim of the present study was to show the possibility of quantitating, in vivo and non-invasively, the equivalence of muscle destroyed by the administration of a test drug (phenylbutazone) known for its injurious properties. Creatine kinase (CK) kinetic parameters (clearance, volume of distribution) were measured in 6 sheep after an iv administration of muscle CK homogenate. In the same 6 sheep, CK release after iv and im 8 mg phenylbutazone/kg was measured. The calculated total CK released, based on the CK plasma clearance (0.28 mL/kg/min) and area under the curve of CK activity after im phenylbutazone administration was 191 +/- 140 U/kg. By relating this quantity to that of CK gluteal muscle (5114 +/- 891 U/g), it was calculated that im phenylbutazone administration was able to destroy an equivalence of 2.4 +/- 2.1 g of muscle. For the 2 main sites of im administration (neck and gluteal muscle), general equations are proposed to calculate the equivalence of muscle destroyed in sheep when only plasma CK activity following a test drug administration is available.