Low-concentration uranium enters the HepG2 cell nucleus rapidly and induces cell stress response

Intracellular uranium distribution: Comparison of cryogenic fixation versus chemical fixation methods for SIMS analysis

“…SIMS analyses show the presence of soluble uranium inside the cell nuclei no matter the sample preparation technique (Figure ) and confirms the previous data related to the uranium distribution within the nuclei (Guéguen et al, ; Rouas et al, ). Nevertheless uranium content in the cytoplasm seems to be lower when using the chemical preparation (Figures and ) compared with the cryopreparation (Figures and ).…”

“…These precipitated forms have been detected by TEM and more recently by our group using the SIMS technique (Rouas et al, ) at 100 µM after 24 hr of exposure. By contrast, with noncytotoxic uranium concentrations from 10 to 100 µM, we have shown for the first time the presence of the soluble form of uranium inside cells mainly in the nuclei (Guéguen et al, ; Rouas et al, ). These previous in vitro experiments have been achieved using samples chemically prepared for SIMS or MET.…”

“…Kidneys and more precisely the proximal tubular cells are one of the main accumulation sites and toxicity targets of soluble uranium compounds (Guéguen et al, 2017; Vicente‐Vicente et al, ). It has been previously shown by us and others that at level below 1 µg/g of kidney for in vivo experiments and below 100 µM for in vitro experiments, close to realistic exposure levels, uranium did not induced direct deleterious toxic effects but induced biological pathways related to cell and tissue defense (Guéguen et al, ; Leggett et al, 1989; Prat et al, ). Recent in vivo experimental studies have confirmed that uranium distribution is highly heterogeneous within the kidney and can reach concentration tenfold higher than the mean renal tissue level (Homma‐Takeda et al, ).…”

“…The uranium penetration into different cell types, as well as its cytotoxicity, have been first studied at precipitate form by TEM in vitro (Carrière et al, ; Ghadially, Lalonde, & Yang‐Steppuhn, ; Mirto et al, ). Recently we have shown, at lower noncytotoxic concentration, by SIMS that soluble or precipitate forms of depleted uranium inside the cells play a role in biological cell response (Guéguen et al, ; Rouas et al, ). Moreover, we have displayed for the first time the presence of soluble uranium within the nuclei using the SIMS technique in different cell cultures (kidney, hepatocyte and neuron) after 15 min to 24 hr of exposure to concentrations lower than 100 µM.…”

“…Two cell models were used, Human Hepatoma cells and Human Kidney cells (HepG2 and HK‐2), two target organs for uranium (Alexandra, Miller, Smith, & Page, ; Bao et al, ; Dedieu et al, ; Jalal Pourahmad, Tanbakosazan, Ghalandari, Ettehadi, & Dahaghin, ; Prat et al, ) after, respectively, 30 min and 2 hr exposure to a 50 µM uranium solution and SIMS analyses were performed. The concentration and duration of exposure were chosen according to our previous studies showing soluble uranium inside the cells without uranium precipitates (Guéguen et al, ).…”