Immune System Modifications Induced in a Mouse Model of Chronic Exposure to (90)Sr.

Strontium 90 ((90)Sr) remains in the environment long after a major nuclear disaster occurs. As a result, populations living on contaminated land are potentially exposed to daily ingesting of low quantities of (90)Sr. The potential long-term health effects of such chronic contamination are unknown. In this study, we used a mouse model to evaluate the effects of (90)Sr ingestion on the immune system, the animals were chronically exposed to (90)Sr in drinking water at a concentration of 20 kBq/l, for a daily ingestion of 80-100 Bq/day. This resulted in a reduced number of CD19(+) B lymphocytes in the bone marrow and spleen in steady-state conditions. In contrast, the results from a vaccine experiment performed as a functional test of the immune system showed that in response to T-dependent antigens, there was a reduction in IgG specific to tetanus toxin (TT), a balanced Th1/Th2 response inducer antigen, but not to keyhole limpet hemocyanin (KLH), a strong Th2 response inducer antigen. This was accompanied by a reduction in Th1 cells in the spleen, consistent with the observed reduction in specific IgG concentration. The precise mechanisms by which (90)Sr acts on the immune system remain to be elucidated. However, our results suggest that (90)Sr ingestion may be responsible for some of the reported effects of internal contamination on the immune system in civilian populations exposed to the Chernobyl fallout.

Chronic exposure to low concentrations of strontium 90 affects bone physiology but not the hematopoietic system in mice.

The aim of this work was to delineate the effects of chronic ingestion of strontium 90 ((90) Sr) at low concentrations on the hematopoiesis and the bone physiology. A mouse model was used for that purpose. Parent animals ingested water containing 20 kBq l(-1) of (90) Sr two weeks before mating. Offspring were then continuously contaminated with (90) Sr through placental transfer during fetal life, through lactation after birth and through drinking water after weaning. At various ages between birth and 20 weeks, animals were tested for hematopoietic parameters such as blood cell counts, colony forming cells in spleen and bone marrow and cytokine concentrations in the plasma. However, we did not find any modification in (90) Sr ingesting animals as compared with control animals. By contrast, the analysis of bone physiology showed a modification of gene expression towards bone resorption. This was confirmed by an increase in C-telopeptide of collagen in the plasma of (90) Sr ingesting animals as compared with control animals. This modification in bone metabolism was not linked to a modification of the phosphocalcic homeostasis, as measured by calcium, phosphorus, vitamin D and parathyroid hormone in the blood. Overall these results suggest that the chronic ingestion of (90) Sr at low concentration in the long term may induce modifications in bone metabolism but not in hematopoiesis.

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.

Biokinetics of 90Sr after chronic ingestion in a juvenile and adult mouse model.

The aim of our study was to define the biokinetics of (90)Sr after chronic contamination by ingestion using a juvenile and adult murine model. Animals ingested (90)Sr by drinking water containing 20 kBq l(-1) of (90)Sr. For the juvenile model, parents received (90)Sr before mating and their offspring were killed between birth and 20 weeks of ingestion. For the adult model, (90)Sr ingestion started at 9 weeks of age and they were killed after different ingestion periods up to 20 weeks. The body weight, food and water consumption of the animals were monitored on a weekly basis. Before killing and sampling of organs, animals were put in metabolic cages. (90)Sr in organs and excreta was determined by liquid scintillation ß counting. Highest (90)Sr contents were found in bones and were generally higher in females than in males, and (90)Sr retention varied according to the skeletal sites. An accumulation of (90)Sr in the bones was observed over time for both models, with a plateau level at adult age for the juvenile model. The highest rate of (90)Sr accumulation in bones was observed in early life of offspring, i.e. before the age of 6 weeks. With the exception of the digestive tract, (90)Sr was below the detection limit in all other organs sampled. Overall, our results confirm that (90)Sr mainly accumulates in bones. Furthermore, our results indicate that there are gender- and age-dependent differences in the distribution of (90)Sr after low-dose chronic ingestion in the mouse model. These results provide the basis for future studies on possible non-cancerous effects during chronic, long-term exposure to (90)Sr through ingestion in a mouse model, especially on the immune and hematopoietic systems.

Influence on the mouse immune system of chronic ingestion of 137Cs.

The aim of this work was to determine the possible occurrence of damage to the immune system during the course of chronic ingestion of (137)Cs. BALB/C mice were used, with (137)Cs intake via drinking water at a concentration of 20 kBq l(-1). Adults received (137)Cs before mating and offspring were sacrificed at various ages between birth and 20 weeks. Phenotypic analysis of circulating blood cells and thymocytes did not show any significant modification of immune cell populations in animals ingesting (137)Cs as compared with control animals, with the exception of a slight increase in Treg percentage at the age of 12 weeks. Functional tests, including proliferative response to mitogens such as phytohaemagglutinin, response to alloantigens in mixed lymphocyte reaction and immunoglobulin response to vaccine antigens such as tetanus toxin and keyhole limpet haemocyanin did not show any significant functional modification of the immune system in (137)Cs-ingesting animals as compared with control animals. Overall, our results suggest that chronic ingestion of a low concentration of (137)Cs in drinking water in the long term does not have any biologically relevant effect on the immune system.

Effect of nephrotoxic treatment with gentamicin on rats chronically exposed to uranium.

Uranium is a radioactive heavy metal with a predominantly chemical toxicity, affecting especially the kidneys and more particularly the proximal tubular structure. Until now, few experimental studies have examined the effect of chronic low-dose exposure to uranium on kidney integrity: these mainly analyse standard markers such as creatinine and urea, and none has studied the effect of additional co-exposure to a nephrotoxic agent on rats chronically exposed to uranium. The aim of the present study is to examine the potential cumulative effect of treating uranium-exposed rats with a nephrotoxic drug. Neither physiological indicators (diuresis and creatinine clearance) nor standard plasma and urine markers (creatinine, urea and total protein) levels were deteriorated when uranium exposure was combined with gentamicin-induced nephrotoxicity. A histological study confirmed the preferential impact of gentamicin on the tubular structure and showed that uranium did not aggravate the histopathological renal lesions. Finally, the use of novel markers of kidney toxicity, such as KIM-1, osteopontin and kallikrein, provides new knowledge about the nephrotoxicity threshold of gentamicin, and allows us to conclude that under our experimental conditions, low dose uranium exposure did not induce signs of nephrotoxicity or enhance renal sensitivity to another nephrotoxicant.

Biodistribution of (137)Cs in a mouse model of chronic contamination by ingestion and effects on the hematopoietic system.

The aim of this work was to define the possible occurrence of hematological changes during the course of a chronic ingestion of (137)Cs. A mouse model was used, with ingestion through drinking water with a cesium concentration of 20 kBq l(-1). Ingestion started in parent animals before mating, and (137)Cs intake and its effect on the hematopoietic system was studied in offspring at various ages between birth and 20 weeks. (137)Cs content was measured in various organs, indicating that (137)Cs was distributed throughout the organism including lympho-hematopoietic organs, i.e., femurs, spleen and thymus. However, we did not observe any effect on the hematopoietic system, whatever the parameter used. In fact, blood cell counts, mononuclear cell counts and progenitor frequency in bone marrow and spleen, and Flt3-ligand, Erythropoietin, G-CSF and SDF-1 concentration in plasma remained unchanged when compared to control animals. Moreover, phenotypic analysis did not show any change in the proportions of bone marrow cell populations. These results indicate that, although (137)Cs was found in all organs implicated in the hematopoietic system, this did not induce any changes in bone marrow function.

Characterization and histological localization of multipotent mesenchymal stromal cells in the human postnatal thymus.

The aim of this work was to characterize multipotent mesenchymal stromal cells (MSCs) in the postnatal human thymus and to localize these MSCs in the organ. Adherent cells isolated from thymus samples were characterized by cell-surface antigen expression. This showed that adherent cells have a MSC profile as assessed by the expression of CD73 and CD105 markers and the lack of CD45 expression. These cells are able to differentiate in vitro into adipocytes, osteoblasts, and chondrocytes and to inhibit mixed lymphocyte reaction. This indicates that isolated cells have all of the characteristics of MSC. The fibroblast colony-forming unit (CFU-F) assay was used to determine their frequency in the postnatal thymus. This frequency was 60.9 +/- 14.8 CFU-F per 1 x 10(5) freshly isolated mononuclear cells. Moreover, taking advantage of CD34 and CD105 expression, immunohistological staining allowed us to localize MSC within interlobular trabeculae in close contact with the outer cortex. Polymerase chain reaction experiments indicated that thymic MSC expressed interleukin-7 and stromal cell-derived factor-1 messenger RNA. Overall, these results confirm previous findings of the presence in the adult human thymus of multipotent MSCs with a phenotype similar to adipose-derived adult stem cells. These results also show for the first time a histological localization of MSC in an organ. This suggests a possible role of thymic MSC in intrathymic differentiation.

Bone marrow stromal cells spontaneously produce Flt3-ligand: influence of ionizing radiations and cytokine stimulation.

PURPOSE: To define the ability of human bone marrow (BM) stromal cells to produce fms-like tyrosine kinase 3 (Flt3)-ligand (FL), and the effect of irradiation, tumour necrosis factor-alpha (TNFalpha) or tumour growth factor beta (TGFbeta) on FL production. MATERIAL AND METHODS: Primary BM stromal cell cultures were irradiated at 2-10 Gy or were stimulated with TNFalpha or TGFbeta1. The presence of FL was tested in culture supernatants and in cell lysate. The presence of a membrane-bound form of FL and the level of gene expression were also tested. RESULTS: Primary BM stromal cells spontaneously released FL. This production was increased by TNFalpha but not by TGFbeta1 or by irradiation. Chemical induction of osteoblastic differentiation from BM stromal cells also induced an increase in FL release. CONCLUSIONS: Our results suggest that the observed increase in FL concentration after in vivo irradiation is an indirect effect. The possible implication of BM stromal cells in these mechanisms is discussed.

Correlation between plasma Flt3-ligand concentration and hematopoiesis during G-CSF-induced CD34+ cell mobilization.

This study aimed to correlate blood Flt3-ligand (FL) concentration with CD34(+) cell number in blood and bone marrow (BM) during granulocyte colony-stimulating factor (G-CSF) mobilization. Nonhuman primates were injected with 10 microg/kg of G-CSF (Lenograstim) daily over a period of 5 days. Daily blood sampling and repeated BM sampling showed that FL concentration before mobilization was negatively correlated to the absolute number of BM CD34(+) cells, but also to the number of G-CSF-mobilized CD34(+) cells on days 3-5 of treatment. This showed that FL concentration in the blood reflected BM status before mobilization, and suggested that this parameter could be used as a predictive indicator of G-CSF-induced CD34(+) cell mobilization.