Maâmar Souidi

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.

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.

Initial evaluation and follow-up of acute radiation syndrome in two patients from the Dakar accident

The aim of this work was to evaluate and follow up the evolution of radiation damage in two victims of a radiation accident. Blood samples were used for cytogenetic evaluation of radiation dose and heterogeneity. The radiation dose estimates were 1 Gy and 2.3 Gy in the two most exposed patients. Plasma was used for the measurement of the Flt3 ligand as a marker of haematopoietic aplasia, citrulline for damage to the jejunal mucosal epithelium and oxysterols for damage to the liver, the central nervous system and the vascular compartment. The use of these biological indicators demonstrated the presence of a haematopoietic syndrome and suggested the presence of subclinical radiation-induced damage to the liver in one of the two patients. These results support the interest in using these biological indicators in order to evaluate radiation damage, especially in complex accidental situations.

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.

Chronic exposure to natural uranium via drinking water affects bone in growing rats.

BACKGROUND Bone is the main site of uranium accumulation after long term contamination. Several studies describe that at high dose of exposure, uranium impairs bone growth. Nevertheless little is known about the effects of chronic exposure at low doses of this radionuclide on bone, especially when ingested via drinking water, which is considered as the main exposure pathway for the public. METHODS In this study, male rats were exposed to natural uranium in drinking water for a 9 month period, either at 40 mg l(-1) starting just after birth (post-natal model) or starting at 3 months of age (adult model). RESULTS In the post-natal model at 40 mg l(-1), three-dimensional microtomography analysis showed that NU decreased significantly the cortical bone diameter in NU-contaminated rats. Bone histomorphometry analysis also showed a significant increase of the osteoid thickness in trabecular bone of the femur of NU-contaminated rats. In addition, mRNA expression in trabecular bone of genes involved in osteoblast differentiation (OSX, BMP2, RUNX2), bone remodeling (TRAP, OCN), bone mineralization (BSP, OPN, DMP1), calcium transport (TRPV5) as well as vitamin D receptor (VDR) was significantly decreased in this model. In contrast, in the adult model, no morphometric, cellular and molecular changes were observed in bone. GENERAL SIGNIFICANCE This study showed for the first time that NU at this concentration has no detectable effect in adult bone while it significantly affects growing bone, which thus appears more sensitive to low dose contamination by this radionuclide.

Chronic Contamination with 137Cesium in Rat: Effect on Liver Cholesterol Metabolism

After the Chernobyl nuclear accident, epidemiological studies on human populations living in 137Cs-contaminated areas revealed the increase frequencies of thyroid cancer and evoked the apparition of cardiovascular diseases, hormonal effect, liver alteration, and lipid disorder. Actually, it raises a problem of public safety for the populations living on these territories that are exposed to low levels of 137Cs during a long period through food. Then it is necessary to study potential effect of this chronic contamination. To mimic this situation, the authors investigate the potential biological effects of chronic exposure to 137Cs at a postaccidental dose (150 Bq/rat/day) on hepatic metabolism of cholesterol in rat. Plasma lipid level, gene expression and activity were analyzed. It was observed that in 137Cs-exposed rats, gene expression of low-density lipoprotein receptor (LDLr), apolipoprotein B (apoB), and liver X receptor α (LXRα) are increased (95%, p < .05; 34%, p < .05; 20%, p < 0.05, respectively), whereas transporter adenosine triphosphate–binding cassette transporter G5 (ABCG5) is decreased (42%, p < .05). In addition, cytochrome P450 27A1 (CYP27A1) activity is increased (34%, p < .05) in contaminated rat liver. In conclusion, the results suggest that 137Cs contamination at low-level induces molecular modifications of the liver cholesterol metabolism without leading to a dysregulation of its homeostasis. These results suggest that chronic long term exposure at low-level of 137Cs may evolve to lipid disorder.

Contamination with Depleted or Enriched Uranium Differently Affects Steroidogenesis Metabolism in Rat

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

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.

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.

Molecular modifications of cholesterol metabolism in the liver and the brain after chronic contamination with cesium 137

Twenty years after Chernobyl accident, the daily ingestion of foodstuff grown on contaminated grounds remains the main source for internal exposure to ionizing radiations, and primarily to cesium 137 ((137)Cs). Though the effects of a long-term internal contamination with radionuclides are poorly documented, several non-cancerous pathologies have been described in this population. However, lipid metabolism was never investigated after chronic internal contamination although disturbances were observed in externally-exposed people. In this regard, we assessed the effects of a chronic ingestion of (137)Cs on hepatic and cerebral cholesterol metabolism. To mimic a chronically-exposed population, rats were given (137)Cs-supplemented water at a post-accidental dose (150 Bq/rat/day) during 9 months. The plasma profile, and brain and liver cholesterol concentrations were unchanged. A decrease of ACAT 2, Apo E, and LXRmRNA levels was recorded in the liver. In the brain, a decrease of CYP27A1 and ACAT 1 gene expression was observed. These results clearly show that cholesterol metabolism is not disrupted by a chronic ingestion of (137)Cs, although several molecular alterations are observed. This work would be interestingly completed by studying the influence of (137)Cs in models likely more sensitive to contaminants, such as the fetus or individuals susceptible to a lipidic disease.