C. Baudelin

Pravastatin Limits Radiation-Induced Vascular Dysfunction in the Skin

About half of people with cancer are treated with radiation therapy; however, normal tissue toxicity still remains a dose-limiting factor for this treatment. The skin response to ionizing radiation may involve multiple inflammatory outbreaks. The endothelium is known to play a critical role in radiation-induced vascular injury. Furthermore, endothelial dysfunction reflects a decreased availability of nitric oxide. Statins have been reported to preserve endothelial function through their antioxidant and anti-inflammatory activities. In this study, wild type and endothelial nitric oxide synthase (eNOS)(-/-) mice were subjected to dorsal skin irradiation and treated with pravastatin for 28 days. We demonstrated that pravastatin has a therapeutic effect on skin lesions and abolishes radiation-induced vascular functional activation by decreasing interactions between leukocytes and endothelium. Pravastatin limits the radiation-induced increase of blood CCL2 and CXCL1 production expression of inflammatory adhesion molecules such as E-selectin and intercellular adhesion molecule-1, and inflammatory cell migration in tissues. Pravastatin limits the in vivo and in vitro radiation-induced downregulation of eNOS. Moreover, pravastatin has no effect in eNOS(-/-) mice, demonstrating that eNOS plays a key role in the beneficial effect of pravastatin in radiation-induced skin lesions. In conclusion, pravastatin may be a good therapeutic approach to prevent or reduce radiation-induced skin damage.

Renal Anemia Induced by Chronic Ingestion of Depleted Uranium in Rats

Kidney disease is a frequent consequence of heavy metal exposure and renal anemia occurs secondarily to the progression of kidney deterioration into chronic disease. In contrast, little is known about effects on kidney of chronic exposure to low levels of depleted uranium (DU). Study was performed with rats exposed to DU at 40 mg/l by chronic ingestion during 9 months. In the present work, a approximately 20% reduction in red blood cell (RBC) count was observed after DU exposure. Hence, three hypotheses were tested to determinate origin of RBC loss: (1) reduced erythropoiesis, (2) increased RBC degradation, and/or (3) kidney dysfunction. Erythropoiesis was not reduced after exposure to DU as revealed by erythroid progenitors, blood Flt3 ligand and erythropoietin (EPO) blood and kidney levels. Concerning messenger RNA (mRNA) and protein levels of spleen iron recycling markers from RBC degradation (DMT1 [divalent metal transporter 1], iron regulated protein 1, HO1, HO2 [heme oxygenase 1 and 2], cluster of differentiation 36), increase in HO2 and DMT1 mRNA level was induced after chronic exposure to DU. Kidneys of DU-contaminated rats had more frequently high grade tubulo-interstitial and glomerular lesions, accumulated iron more frequently and presented more apoptotic cells. In addition, chronic exposure to DU induced increased gene expression of ceruloplasmin (x12), of DMT1 (x2.5), and decreased mRNA levels of erythropoietin receptor (x0.2). Increased mRNA level of DMT1 was associated to decreased protein level (x0.25). To conclude, a chronic ingestion of DU leads mainly to kidney deterioration that is probably responsible for RBC count decrease in rats. Spleen erythropoiesis and molecules involved in erythrocyte degradation were also modified by chronic DU exposure.

Absorption of uranium through the entire gastrointestinal tract of the rat.

The aim was to determine the gastrointestinal segments preferentially implicated in the absorption of uranium. The apparent permeability to uranium (233U) was measured ex vivo in Ussing chambers to assess uranium passage in the various parts of the small and large intestines. The transepithelial electrical parameters (potential difference, short-circuit current, transepithelial resistance and tissue conductance) were also recorded for each segment. Determination of in vivo uranium absorption after in-situ deposition of 233U in digestive segments (buccal cavity, ileum and proximal colon) and measurements of uranium in peripheral blood were then made to validate the ex vivo results. In addition, autoradiography was performed to localize the presence of uranium in the digestive segments. The in vivo experiments indicated that uranium absorption from the digestive tract was restricted to the small intestine (with no absorption from the buccal cavity, stomach or large intestine). The apparent permeability to uranium measured with ex vivo techniques was similar in the various parts of small intestine. In addition, the experiments demonstrated the existence of a transcellular pathway for uranium in the small intestine. The study indicates that uranium absorption from the gastrointestinal tract takes place exclusively in the small intestine, probably via a transcellular pathway.

Short-term effects of depleted uranium on immune status in rat intestine.

In the event of ingestion, the digestive tract is the first biological system exposed to depleted uranium (DU) intake via the intestinal lumen. However, little research has addressed the biological consequences of a contamination with depleted uranium on intestinal properties such as the barrier function and/or the immune status of this tissue. The aim of this study was to determine if the ingestion of depleted uranium led to changes in the gut immune system of the intestine. The experiments were performed at 1 and 3 d following a per os administration of DU to rats at sublethal dose (204 mg/kg). Several parameters refering to the immune status, such as gene and protein expressions of cytokines and chemokines, and localization and density of immune cell populations, were assessed in the intestine. In addition, the overall toxicity of DU on the small intestine was estimated in this study, with histological appearance, proliferation rate, differentiation pattern, and apoptosis process. Firstly, the results of this study indicated that DU was not toxic for the intestine, as measured by the proliferation, differentiation, and apoptosis processes. Concerning the immune properties of the intestine, the ingestion of depleted uranium induced some changes in the production of chemokines and in the expression of cytokines. A diminished production of monocyte chemoattractant protein-1 (MCP-1) was noted at 1 day post exposure. At 3 d, the increased gene expression of interferon γ (IFNγ) was associated with an enhanced mRNA level of Fas ligand, suggesting an activation of the apoptosis pathway. However, no increased apoptotic cells were observed at 3 d in the contaminated animals. There were no changes in the localization and density of neutrophils, helper T lymphocytes, and cytotoxic T lymphocytes after DU administration. In conclusion, these results suggest that depleted uranium is not toxic for the intestine after acute exposure. Nevertheless, DU seems to modulate the expression and/or production of cytokines (IFNγ) and chemokines (MCP-1) in the intestine. Further experiments need to be performed to determine if a chronic contamination at low dose leads in the long term to modifications of cytokines/chemokines patterns, and to subsequent changes in immune response of the intestine.

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.

Effects of chronic 137Cs ingestion on barrier properties of jejunal epithelium in rats.

Environmental contamination by 137Cs is of particular public health interest because of the various sources of fallout originating from nuclear weapons, radiological source disruptions, and the Chernobyl disaster. This dispersion may lead to a chronic ecosystem contamination and subsequent ingestion of contaminated foodstuffs. The aim of this study was to thus determine the impact of a chronic ingestion of low-dose 137Cs on small intestine functions in rats. The animals received 150 Bq per day in drinking water over 3 mo. At these environmental doses, 137Cs contamination did not modify the crypt and villus architecture. In addition, epithelial integrity was maintained following the chronic ingestion of 137Cs, as demonstrated by histological analyses (no breakdown of the surface mucosa) and electrical transepithelial parameters (no change in potential difference and tissue conductance). Furthermore, cesium contamination seemed to induce contradictory effects on the apoptosis pathway, with an increase in the gene expression of Fas/FasL and a decrease in the apoptotic cell number present in intestinal mucosa. No marked inflammation was observed following chronic ingestion of 137Cs, as indicated by neutrophil infiltration and gene expression of cytokines and chemokines. Results indicated no imbalance in the Th1/Th2 response induced by cesium at low doses. Finally, evaluation of the functionality of the jejunal epithelium in rats contaminated chronically with 137Cs did not demonstrate changes in the maximal response to carbachol, nor in the cholinergic sensitivity of rat jejunal epithelium. In conclusion, this study shows that chronic ingestion of 137Cs over 3 mo at postaccidental doses exerts few biological effects on the epithelium of rat jejunum with regard to morphology, inflammation status, apoptosis/proliferation processes, and secretory functions.

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.