Etude expérimentale des effets combinés du mélange uranium – cadmium sur la croissance et la fécondité du nématode C. elegans

International audienc

Etude expérimentale des effets combinés du mélange uranium – cadmium sur la croissance et la fécondité du nématode C. elegans

International audienc

Nested interactions in the uranium and cadmium combined toxicity to the C. elegans.

International audienceUranium (U) is a natural ubiquitous radioelement whose occurrence may be magnified in the vicinity of some nuclear fuel cycle facilities orintensive farming areas. As mixtures are common in environment, U may be found associated with other contaminants such as cadmium (Cd).The exposure of organisms to these mixtures may result in unexpected synergism or antagonism that may be explained by interactions occurringat the exposure, toxicokinetics and/or toxicodynamic levels. The identification of these interactions and their underlying mechanisms may be ofinterest for a better risk characterization of multi-metallic polluted sites. In the present study, toxicity of binary mixture of U and Cd was assessedover time on physiological parameters, maximal length and brood size, in a partial lifespan experiment with the soil nematode Caenorhabditiselegans. A 49-condition fractional factorial design (extended design) was used with U and Cd concentrations, representative of some highlypolluted soils, ranging from 0.95 to 1.30 mM and 0.006 to 0.040 mM, respectively. Combined effects were analyzed using MixTox tool (Jonkeret al., 2005) to identify possible synergistic or antagonistic interactions.The best description of the toxic effects was met with the response addition concept and considering a dose-level dependent interaction model.An early significant antagonism was found at 1.2 d. Then, a continuous antagonism was identified for mixture levels upper than the EC36 or atlow U concentrations. As diet is suspected to be the main route of exposure of C. elegans to contaminants, an investigation of the diffusion of Uand Cd from agar to bacteria and their bioaccumulation by nematodes was achieved in a reduced design (8 conditions). A significant reductionof Cd internalization by C. elegans was observed in case of co-exposure with U and these results were correlated with the concentration of contaminants in bacteria. The observed antagonism of toxicity may thus be the resultant of an interaction at the exposure level where the diffusion oradsorption of Cd to bacteria is decreased by U. These findings underline the importance of studying chemical mixtures at various levels to fullyunderstand the underlying mechanisms and thus, avoid misinterpretations in the prediction of combined toxicity. Measurements of U and Cdconcentrations in bacteria are currently performed with the extended design in order to reinterpret the combined toxic effects on the basis ofthese concentrations

Assessment of growth, genotoxic responses and expression of stress related genes in the Pacific oyster Crassostrea gigas following chronic exposure to ionizing radiation

International audienceMarine organisms are exposed to low doses of anthropogenic contaminants during their entire life. Authorized amounts of radionuclides are discharged in the Channel by nuclear facilities. The Pacific oyster was used to investigate the potential impact of chronic exposure to ionizing radiation. Though we exposed larvae and spat for two weeks to much higher concentrations than those encountered near nuclear facilities, oyster growth and expression of 9 selected stress genes were not significantly changed. To determine potential DNA damage, 2. year old oysters were exposed for two weeks to tritiated water. The comet assay was used to evaluate the level of DNA strand breaks in haemocytes, whilst the 'clearance rate' was used as a measure of physiological effects. Whilst other parameters did not alter, DNA damage significantly increased. Our results highlight the significance of the observed DNA damage and their potential consequences at higher levels of biological organization. © 2015 Elsevier Ltd

Interplay between ionizing radiation effects and aging in C. elegans

International audienceLiving species are chronically exposed to environmental ionizing radiations from sources that can be overexpressed by nuclear accidents. In invertebrates, reproduction is the most radiosensitive studied endpoint, likely to be connected with aging. Surprisingly, aging is a sparsely investigated endpoint after chronic ionizing radiation, whereas understanding it is of fundamental interest in biology and medicine. Indeed, aging and aging-related diseases (e.g., cancer and degenerative diseases) cause about 90 % of deaths in developed countries. Therefore, glp-1 sterile Caenorhabditis elegans nematode was used to assess the impact of chronic gamma irradiation on the lifespan. Analyses were performed, at the individual level, on aging and, in order to delve deeper into the mechanisms, at the molecular level, on oxidative damage (carbonylation), biomolecules (lipids, proteins and nucleic acids) and their colocalization. We observed that ionizing radiation accelerates aging (whatever the duration (3 to 19 days)/dose (0.5 to 24 Gy)/dose rate (7 and 52 mGy.h 1) tested) leading to a longevity value equivalent to that of wt nematode (~25-30 days). Moreover, the level of protein oxidative damage (carbonylation) turned out to be good cellular biomarker of aging, since it increases with age. Conversely, chronic radiation treatments reduced carbonylation levels and induced neutral lipid catabolism whatever the dose rate and the final delivered dose. Finally, under some conditions a lipid-protein colocalization without any carbonyl was observed; this could be linked to yolk accumulation in glp-1 nematodes. To conclude, we noticed through this study a link between chronic gamma exposure, lifespan shortening and lipid level decrease associated with a decrease in the overall carbonylation

Combined effects of Uranium and Cadmium on Physiological Parameters of the Nematode Caenorhabditis elegans

International audienceUranium (U) is a natural ubiquitous radioelement whose occurrence may be magnified in the vicinity of some nuclear fuel cycle facilities orintensive farming areas. As mixtures are common in environment, U may be found associated with other contaminants such as cadmium (Cd).The exposure of organisms to these mixtures may result in unexpected synergism or antagonism that may be explained by interactions occurringat the exposure, toxicokinetics and/or toxicodynamic levels. The identification of these interactions and their underlying mechanisms may be ofinterest for a better risk characterization of multi-metallic polluted sites. In the present study, toxicity of binary mixture of U and Cd was assessedover time on physiological parameters, maximal length and brood size, in a partial lifespan experiment with the soil nematode Caenorhabditiselegans. A 49-condition fractional factorial design (extended design) was used with U and Cd concentrations, representative of some highlypolluted soils, ranging from 0.95 to 1.30 mM and 0.006 to 0.040 mM, respectively. Combined effects were analyzed using MixTox tool (Jonkeret al., 2005) to identify possible synergistic or antagonistic interactions.The best description of the toxic effects was met with the response addition concept and considering a dose-level dependent interaction model.An early significant antagonism was found at 1.2 d. Then, a continuous antagonism was identified for mixture levels upper than the EC36 or atlow U concentrations. As diet is suspected to be the main route of exposure of C. elegans to contaminants, an investigation of the diffusion of Uand Cd from agar to bacteria and their bioaccumulation by nematodes was achieved in a reduced design (8 conditions). A significant reductionof Cd internalization by C. elegans was observed in case of co-exposure with U and these results were correlated with the concentration of contaminants in bacteria. The observed antagonism of toxicity may thus be the resultant of an interaction at the exposure level where the diffusion oradsorption of Cd to bacteria is decreased by U. These findings underline the importance of studying chemical mixtures at various levels to fullyunderstand the underlying mechanisms and thus, avoid misinterpretations in the prediction of combined toxicity. Measurements of U and Cdconcentrations in bacteria are currently performed with the extended design in order to reinterpret the combined toxic effects on the basis ofthese concentrations

More than thirty years after the Chernobyl accident: what do we know about the effects of radiation on the environment?

Editorial

A dynamic energy-based model to analyze sublethal effects of chronic gamma irradiation in the nematode Caenorhabditis elegans

International audienceUnderstanding how toxic contaminants affect wildlife species at various levels of biological organization (subcellular, histological, physiological, organism, and population levels) is a major research goal in both ecotoxicology and radioecology. A mechanistic understanding of the links between different observed perturbations is necessary to predict the consequences for survival, growth, and reproduction, which are critical for population dynamics. In this context, experimental and modeling studies were conducted using the nematode Caenorhabditis elegans. A chronic exposure to external gamma radiation was conducted under controlled conditions. Results showed that somatic growth and reproduction were reduced with increasing dose rate. Modeling was used to investigate whether radiation effects might be assessed using a mechanistic model based upon the dynamic energy budget (DEB) theory. A DEB theory in toxicology (DEB-tox), specially adapted to the case of gamma radiation, was developed. Modelling results demonstrated the suitability of DEB-tox for the analysis of radiotoxicity and suggested that external gamma radiation predominantly induced a direct reduction in reproductive capacity in C. elegans and produced an increase in costs for growth and maturation, resulting in a delay in growth and spawning observed at the highest tested dose rate. © 2017 Taylor and Francis