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-PK1) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK1 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 UO2(PO4)- and UO2(HPO4)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. © 2006 Elsevier Inc. All rights reserved

Development of an in vitro test for screening of chelators of uranium

This work deals with an in vitro spectrophotometric method to evaluate the chelating ability of various organic ligands for uranyl ion. In this way, an uranium complex formed with a peculiar ligand is chosen as a reference. Any modification of the UV-Visible absorbance of the U(VI) reference complex, owing to its dissociation upon the addition of a new ligand, permits to compare the affinity of the latter ligand for U(VI) with that of the reference ligand. This test allows to screen easily a lot of ligands before to evaluate their in vivo uranium chelating property

Apports de la spéciation biologique en dosimétrie interne

La spéciation est l',étude des caract,ristiques moléculaires des ,éléments radioactifs. Un des axes majeurs développé, dans ce domaine cherche à? décrire les mécanismes de complexation et de dépt des radionucléides dans les cellules. Ces ,études sont effectuées pour tenter d'élucider deux problèmes majeurs de la dosimétrie interne : l'estimation réaliste des doses reçues par les cellules cibles après contamination interne et amélioration des thérapeutiques proposées après incorporation accidentelle. Le présent rapport fait le point sur les derniers travaux réalisés, sur le Np et résume les principales avancées dans ce domaine

Interaction uranium-cellule cible : exemple de la transformation de particules d'UO

Interactions between uranium and target cells: Example of UO4 particle transformation within alveolar macrophages. Interactions between uranium and target cells: examples of UO4 particle transformation within alveolar macrophages. 
The understanding of the mechanisms involved in the in vivo dissolution of inhaled particles is necessary to improve the model for determining the parameters. With that perspective, the intracellular transformation of UO4 particles has been investigated. Indeed, very few is known about this compound encountered in the nuclear fuel cycle. After instillation of UO4 particles in rats, alveolar macrophages and lung tissues have been observed. The particles break up very quickly in ultrafine particles and in some cases, this mechanism is accompanied by the formation of uranyl phosphate needles. This phenomenon takes place at very early stage, i.e., within the first 24 hours after the instillation. Particles phagocytised by macrophages in vitro have been observed after inclusion of the cells directly on the culture dish. These observations have confirmed the corrosive action exerted by the macrophages on the UO4 particles