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Title: Intracellular accumulation dynamics and fate of zinc ions in alveolar epithelial cells exposed to airborne ZnO nanoparticles at the air–liquid interface

Airborne nanoparticles (NPs) that enter the respiratory tract are likely to reach the alveolar region. Accumulating observations support a role for zinc oxide (ZnO) NP dissolution in toxicity, but the majority of in vitro studies were conducted in cells exposed to NPs in growth media, where large doses of dissolved ions are shed into the exposure solution. To determine the precise intracellular accumulation dynamics and fate of zinc ions (Zn2+) shed by airborne NPs in the cellular environment, we exposed alveolar epithelial cells to aerosolized NPs at the air-liquid interface (ALI). Using a fluorescent indicator for Zn2+, together with organelle-specific fluorescent proteins, we quantified Zn2+ in single cells and organelles over time. We found that at the ALI, intracellular Zn2+ values peaked 3 h post exposure and decayed to normal values by 12 h, while in submersed cultures, intracellular Zn2+ values continued to increase over time. The lowest toxic NP dose at the ALI generated peak intracellular Zn2+ values that were nearly 3 folds lower than the peak values generated by the lowest toxic dose of NPs in submersed cultures, and 8 folds lower than the peak values generated by the lowest toxic dose of ZnSO4 or Zn2+. At themore » ALI, the majority of intracellular Zn2+ was found in endosomes and lysosomes as early as 1 h post exposure. In contrast, the majority of intracellular Zn2+ following exposures to ZnSO4 was found in other larger vesicles, with less than 10% in endosomes and lysosomes. In conclusion, together, our observations indicate that low but critical levels of intracellular Zn2+ have to be reached, concentrated specifically in endosomes and lysosomes, for toxicity to occur, and point to the focal dissolution of the NPs in the cellular environment and the accumulation of the ions specifically in endosomes and lysosomes as the processes underlying the potent toxicity of airborne ZnO NPs.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [1]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab.
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Fundamental & Computational Sciences Directorate
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Energy & Environment Directorate
Publication Date:
OSTI Identifier:
1177706
Report Number(s):
PNNL-SA--99125
Journal ID: ISSN 1743-5390; 44627; 600306000
Grant/Contract Number:
AC05-76RL01830; 1RC2ES018786-01
Type:
Accepted Manuscript
Journal Name:
Nanotoxicology
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 1743-5390
Publisher:
Informa Healthcare
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 59 BASIC BIOLOGICAL SCIENCES Intracellular; alveolar; epithelial; cells; nanoparticles; Environmental Molecular Sciences Laboratory; Airborne nanoparticles; air–liquid interface; endosomes; FluoZin-3; intracellular Zn2+; lysosomes