Césium 137 : propriétés et effets biologiques après contamination interne

Caesium-137 (Cs¹³⁷) is a radionuclide present in the environment mainly as the result of the atmospheric nuclear weapons testing and accidents arising in nuclear power plants like the Chernobyl accident in 1986. Nowadays, the health consequences resulting from a chronic exposure to this radionuclide remain unknown. After absorption, the caesium is distributed relatively homogeneously within the body, with a more important load in children than in adults. The toxicity of Cs¹³⁷ is mainly due to its radiological properties. A high dose of Cs¹³⁷ is responsible for a medullar dystrophy, disorders of the reproductive function, and effects on liver and renal functions. Disorders of bone mineralization and brain damages were also described in human beings. At lowest dose, Cs¹³⁷ induces disturbances of wakefulness-sleep cycle, but not accompanied with behavioural disorders. The cardiovascular system was also perturbed. Biological effects of Cs¹³⁷ on the metabolisms of the vitamin D, cholesterol and steroid hormones were described, but do not lead to clinical symptoms. In human beings, Cs¹³⁷ leads to an immune deficiency, congenital and foetal deformations, an increased of thyroid cancer, as well as neurological disorders. It seems that children are more sensitive to the toxic effects of caesium than the adults. At present, the only effective treatment for the decorporation of the ingested Cs¹³⁷ is the Prussian Blue (Radiogardase^®). The use of pectin to decorporate the ingested Cs¹³⁷, in children notably, is sometimes proposed, but its administration still remains an open question. To conclude, the available scientific data suggest that Cs¹³⁷ could affect a number of physiological and metabolic functions and consequently, could participate in the health risks associated to the presence of other contaminants in the environment.     

CD44 induced enhancement of phosphatase activity and calcium influx: Modifications of EGR-1 expression and cell proliferation

The purpose of this study was to investigate how CD44 impaired Akt phosphorylation, EGR-1 expression and cell proliferation. E6.1 Jurkat cells, which lack endogenous CD44 expression, were engineered to express CD44. Previously we showed that Akt is hypophosphorylated, EGR-1 expression is reduced and proliferation is impaired in CD44 expressing E6.1 Jurkat cells. The cell cycle was studied using flow cytometry and the role of calcium (Ca²⁺) in Akt phosphorylation and EGR-1 expression was investigated using Western blotting. Phosphatase activity was assessed using a commercially available kit. CD44 expressing cells showed disruption at the G₁ to S transition. Chelation of Ca²⁺ from the culture media impaired Akt phosphorylation and EGR-1 expression in both CD44 expressing cells and the open vector control. Moreover, Ni²⁺ disrupted cell proliferation in both cell types suggesting Ca²⁺ import through calcium release activated calcium channels (CRAC). Staining of cells with fura-2 AM showed significantly higher Ca²⁺ in CD44 expressing cells as compared with the vehicle control. Finally, non-calcium mediated phosphatase activity was significantly greater in CD44 expressing cells. We propose that the enhanced phosphatase activity in the CD44 cells increased the dephosphorylation rate of Akt; at the same time, the increased intracellular concentration of Ca²⁺ in the CD44 cells ensured that the phosphorylation of Akt remains intact albeit at lower concentrations as compared with the vector control. Reduced Akt phosphorylation resulted in lowered expression of EGR-1 and hence, reduced the cell proliferation rate.     

Calculation of the force field required for nucleus deformation during cell migration through constrictions

During cell migration in confinement, the nucleus has to deform for a cell to pass through small constrictions. Such nuclear deformations require significant forces. A direct experimental measure of the deformation force field is extremely challenging. However, experimental images of nuclear shape are relatively easy to obtain. Therefore, here we present a method to calculate predictions of the deformation force field based purely on analysis of experimental images of nuclei before and after deformation. Such an inverse calculation is technically non-trivial and relies on a mechanical model for the nucleus. Here we compare two simple continuum elastic models of a cell nucleus undergoing deformation. In the first, we treat the nucleus as a homogeneous elastic solid and, in the second, as an elastic shell. For each of these models we calculate the force field required to produce the deformation given by experimental images of nuclei in dendritic cells migrating in microchannels with constrictions of controlled dimensions. These microfabricated channels provide a simplified confined environment mimicking that experienced by cells in tissues. Our calculations predict the forces felt by a deforming nucleus as a migrating cell encounters a constriction. Since a direct experimental measure of the deformation force field is very challenging and has not yet been achieved, our numerical approaches can make important predictions motivating further experiments, even though all the parameters are not yet available. We demonstrate the power of our method by showing how it predicts lateral forces corresponding to actin polymerisation around the nucleus, providing evidence for actin generated forces squeezing the sides of the nucleus as it enters a constriction. In addition, the algorithm we have developed could be adapted to analyse experimental images of deformation in other situations.     

Attempts to quantitate immunocytochemistry at the electron microscope level

Summary The ability to localize intracellular macromoleculesin situ by high resolution techniques has been made possible by the development of antibody labelling of thin sections obtained either from tissues embedded in an hydrophilic matrix, or by ultracryotomy or from conventional plastic embedded tissue. When particle-tagged immunological reagents are used to visualize intracellular antigens, quantitative information can be obtained by combining particle counts with morphometric estimations of compartment volume. Various detection systems have been used successfully for quantitation, which include ferritin-conjugated antibodies, biotin-avidin-ferritin complexes and, more recently, gold-protein A conjugates. Examples of the use of these techniques the localization of secretory proteins in pancreatic exocrine cells, opsin and a large membrane protein in photoreceptor cells of frog retina, and contractile proteins in skeletal muscle are given. Quantitative data obtained by morphometric analysis, both in bovine and rat pancreatic exocrine cells, are compared with values assessed by biochemical methods.     

Enriching the concept of vulnerability in research ethics: An integrative and functional account

The concept of vulnerability is widely used in research ethics to signal attention to participants who require special protections in research. However, this concept is vague and under‐theorized. There is also growing concern that the dominant categorical approach to vulnerability (as exemplified by research ethics regulations and guidelines delineating vulnerable groups) is ethically problematic because of its assumptions about groups of people and is, in fact, not very guiding. An agreed‐upon strategy is to move from categorical towards analytical approaches (focused on analyzing types and sources of vulnerability) to vulnerability. Beyond this agreement, however, scholars have been advancing competing accounts of vulnerability without consensus about its appropriate operationalization in research ethics. Based on previous debates, we propose that a comprehensive account of vulnerability for research ethics must include four components: definition, normative justifications, application, and implications. Concluding that no existing accounts integrate these components in a functional (i.e., practically applicable) manner, we propose an integrative and functional account of vulnerability inspired by pragmatist theory and enriched by bioethics literature. Using an example of research on deep brain stimulation for treatment‐resistant depression, we illustrate how the integrative‐functional account can guide the analysis of vulnerability in research within a pragmatist, evidence‐based approach to research ethics. While ultimately there are concerns to be addressed in existing research ethics guidelines on vulnerability, the integrative‐functional account can serve as an analytic tool to help researchers, research ethics boards, and other relevant actors fill in the gaps in the current landscape of research ethics governance.     

Defects of two temperature-sensitive lysyl-transfer ribonucleic acid synthetase mutants of Bacillus subtilis

Two temperature-sensitive mutants (lysS1 and lysS2) of the lysyl-transfer ribonucleic acid synthetase (l-lysine:tRNA ligase [adenosine 5'-monophosphate], EC 6.1.1.6) of Bacillus subtilis have been isolated. Although protein synthesis is inhibited in both mutants at the restrictive temperature (42 to 45 C), the mutants remain viable in a minimal medium. In comparison with the wild-type lysyl-tRNA synthetase, the l-lysine-dependent exchange of [(32)P]pyrophosphate with adenosine 5'-triphosphate (ATP) for both mutant enzymes is decreased. The lysS1 enzyme is completely defective in the ATP-dependent attachment of l-lysine to tRNA, whereas the lysS2 enzyme has 3- to 10-fold reduced levels of this activity. Temperature-resistant transformants have wild-type enzyme levels, whereas partial revertants to temperature resistance have varied levels of enzyme activity. The attachment and exchange activities of the lysS2 enzyme are more heat labile in vitro than the wild-type enzyme, as is the attachment activity of a partial revertant of the lysS1 mutant. The lysS1 and the lysS2 lysyl-tRNA synthetases have higher apparent K(m) values for lysine and ATP, in both the activation and the attachment reactions. The lysS2 enzyme has a V(max) for tRNA(lys) one-third that of the wild-type enzyme. Molecular weights of approximately 150,000 for the wild-type and lysS2 enzymes and approximately 76,000 for the lysS1 enzyme were estimated from sedimentation positions in sucrose density gradients assayed by the ATP-pyrophosphate exchange activity. We propose that the two mutations (lysS1 and lysS2) directly affect the sites for exchange activity, but indirectly alter attachment activity as a consequence of defective subunit association.