Screening of potential uranium protein targets in fish ovaries after chronic waterborne exposure: Differences and similarities between roach and zebrafish

Translocation and transformation of uranium along the aquatic food chain: New insights into uranium risks to the environment

Uranium pollution in aquatic ecosystems poses a threat to organisms. However, the metabolism and toxicity of uranium along aquatic food chains remain unknown. Here, we established an artificial aquatic ecosystem to investigate the fate of uranium along the food chain and reveal its potential toxicity. The results displayed a dose- and time-dependent toxicity of uranium on algae, leading to cell deformation and impeding cell proliferation. When uranium-exposed algae are ingested by fish, uranium tends to concentrate in the intestinal system and bones of fish. Comparatively, direct water uranium exposure resulted in a remarkable uranium accumulation in the head, skin, and muscles of fish, suggesting different toxicity depending on distinct exposure pathways. High-level uranium pollution (20 mg L-1) intensifies the toxicity to fish through food intake compared to direct water exposure. It has also revealed that approximately 25 % and 20 % of U(VI) were reduced to lower valence forms during its accumulation in algae and fish, respectively, and over 10 % of U(IV, VI) converted to U(0) ultimately, through which uranium toxicity was mitigated due to the lower solubility and bioavailability. Overall, this study provides new insights into the fate of uranium during its delivery along the aquatic food chain and highlights the risks associated with consuming uranium-contaminated aquatic products.

Determination of the affinity of biomimetic peptides for uranium through the simultaneous coupling of HILIC to ESI-MS and ICP-MS

Several proteins have been identified in the past decades as targets of uranyl (UO₂²⁺) in vivo. However, the molecular interactions responsible for this affinity are still poorly known which requires the identification of the UO₂²⁺ coordination sites in these proteins. Biomimetic peptides are efficient chemical tools to characterize these sites. In this work, we developed a dedicated analytical method to determine the affinity of biomimetic, synthetic, multi-phosphorylated peptides for UO₂²⁺ and evaluate the effect of several structural parameters of these peptides on this affinity at physiological pH. The analytical strategy was based on the implementation of the simultaneous coupling of hydrophilic interaction chromatography (HILIC) with electrospray ionization mass spectrometry (ESI-MS) and inductively coupled plasma mass spectrometry (ICP-MS). An essential step had been devoted to the definition of the best separation conditions of UO₂²⁺ complexes formed with di-phosphorylated peptide isomers and also with peptides of different structure and degrees of phosphorylation. We performed the first separations of several sets of UO₂²⁺ complexes by HILIC ever reported in the literature. A dedicated method had then been developed for identifying the separated peptide complexes online by ESI-MS and simultaneously quantifying them by ICP-MS, based on uranium quantification using external calibration. Thus, the affinity of the peptides for UO₂²⁺ was determined and made it possible to demonstrate that (i) the increasing number of phosphorylated residues (pSer) promotes the affinity of the peptides for UO₂²⁺, (ii) the position of the pSer in the peptide backbone has very low impact on this affinity (iii) and finally the cyclic structure of the peptide favors the UO₂²⁺ complexation in comparison with the linear structure. These results are in agreement with those previously obtained by spectroscopic techniques, which allowed to validate the method. Through this approach, we obtained essential information to better understand the mechanisms of toxicity of UO₂²⁺ at the molecular level and to further develop selective decorporating agents by chelation.

Metal-binding biomolecules in the liver of northern pike (Esox lucius Linnaeus, 1758): The first data for the family Esocidae

Metal-handling strategies of various fish species are known to vary significantly in association with their intracellular metal behaviour. Thus, to better understand the possible consequences of increased metal exposure in fish it is important to perform comparative studies on metal-binding biomolecules in organs of different species. This study was the first of this kind on a liver of an esocid fish (northern pike, Esox lucius), and the gathered information were compared to fish belonging to three other families, Leuciscidae, Cyprinidae and Salmonidae. Distributions of ten elements among cytosolic biomolecules of different molecular masses were studied by size exclusion HPLC combined offline with high resolution ICP-MS. The results indicated predominant association of Co, Fe and Mo to high molecular mass biomolecules (>100 kDa), of Zn and Bi to both high and medium molecular mass biomolecules (>30 kDa), of Mn and Se to medium molecular mass biomolecules (30-100 kDa), and Ag, Cd and Cu to low molecular mass biomolecules (10-30 kDa), presumably metallothioneins. Evident binding to metallothioneins was also detected for Zn and Bi. For several metals, distinct differences were observed when cytosolic metal distributions of northern pike were compared to leuciscids, salmonids and cyprinids. More pronounced Zn binding to metallothioneins was recorded in leuciscids and cyprinids than both esocids and salmonids, whereas cytosolic Mn and Se distributions clearly differed between all studied fish families. Accordingly, in assessment of metal pollution it is vital to consider the exposed species, which requires prior comprehensive comparative research on numerous aquatic organisms.