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Understanding Air-Liquid Interface Cell Exposure Systems: A Comprehensive Assessment of Various Systems under Identical Conditions

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Presented at the 2018 Society of Toxicology Annual Meeting.

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Understanding Air-Liquid Interface Cell Exposure Systems: A Comprehensive Assessment of Various Systems under Identical Conditions

  1. 1. Understanding Air-Liquid Interface Cell Exposure Systems: A Comprehensive Assessment of Various Systems Under Identical Conditions José Zavala, PhD ORISE Postdoctoral Fellow NHEERL, EPHD, Inhalation Toxicology Facilities Branch Mentor: Mark Higuchi Email: zavala-mendez.jose@epa.gov SOT Annual Meeting March 15, 2018
  2. 2. Disclaimer: This presentation does not necessarily reflect EPA policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use
  3. 3. No ALI Exposure Standards • Inconsistency in published literature Exposure conditions Biological results Monitoring of test chemical/particle • Difficult to evaluate and compare biological results • Various ALI systems exists but cannot be compared based on existing studies.
  4. 4. Example C lean A ir O zone C lean A ir O zone 0 2 4 6 8 10 12 ** 9 hours 24 hours LDH (FoldChangeOverAirCt.) C lean A ir O zone C lean A ir O zone 0 250 500 750 1000 *9 hours 24 hours * IL-8(pg/mL) Exposure System: GIVES Membrane Inserts: 12-mm Snapwells (6-well format) Pollutant: Ozone Concentration: 0.4 ppm Exposure Length: 4 hours Cell Type: A549 Results: ↑ cytotoxicity, ↑ pro-inflammatory cytokine secretion Zavala et al. Inhal Toxicol., 2016, 28(6), 251-259 Exposure System: VITROCELL Membrane Inserts: 24-mm Transwells (6-well format) Pollutant: Ozone Concentration: 4.0 ppm Exposure Length: 4 hours Cell Type: A549 Results: NO cytotoxicity, NO changes in pro-inflammatory cytokines Anderson et al. Toxicol In Vitro., 2013 Mar; 27(2): 721-730
  5. 5. Comparison of ALI Exposure Systems Study Objective: How well does each system deliver gases and particles to the target area (i.e., cell inserts).
  6. 6. •Fluorescent polystyrene latex (PSL) spheres were used as a surrogate for PM. Evaluation of Particle Delivery to Culture Inserts •PSL spheres were nebulized and delivered to the in vitro systems. •Deposition was quantified by dissolving particles in ethyl acetate and using a spectrofluorometer. •This method involves NO CELLS. •Filters were placed on cell culture inserts filled with DPBS in the basolateral side to simulate the conductive culture medium.
  7. 7. Evaluation of Gas Delivery to Culture Inserts • We used a fluorescence- based method with 125 ppb O3 as a test gas and measured its reactivity on an indigo dye- impregnated filter inside each well. • The method involves NO CELLS; measuring chemical reaction • Normalized data to an impinger system operated at 250 mL/min as a positive control.
  8. 8. VITROCELL® Systems Model 6 CF Principle of Operation Gases: Diffusion Particles: Diffusion/Sedimentation Flow Rate: 2-10 mL/min • Air flow is perpendicular to the cells • Air flow is perpendicular to the cells • System relies on the particle’s natural electrical charge for ESP to work. • System uses an isokinetic sampler instead of manifold. Model 6 CF Principle of Operation Gases: Diffusion Particles: Electrostatic Precipitation (ESP) (Positive or Negative Polarity) Flow Rate: 2-10 mL/min
  9. 9. VITROCELL® Systems Performance • In 6 CF system, carbon-impregnated silicone tubing reduces tubing loses with 50-nm particles. • ESP on 6/3 CF relying on particle’s natural charge enhances deposition. • In 6 CF system, Teflon tubing, while impractical, improves gas delivery. • 6/3 CF system has very poor gas delivery. • Tubing and nozzles were investigated to determine their role.
  10. 10. • This chamber has 2 modes of operation EPA’s Cell Culture Exposure System (CCES) Principle of Operation Gases: Diffusion Particles: Thermophoresis (THP) (Thermal Gradient) Flow Rate: 25-50 mL/min • CCES with 6-well format uses both modes. • CCES with 24-well format uses Mode 1 only.
  11. 11. EPA’s CCES Performance 1 µm • In both formats format, flow rate of 25 mL/min/well is better than 5 mL/min/well. • Regardless of multi-well format, gas is delivered at similar relative efficiencies. • In 6-well format, thermophoresis enhances deposition for 50 nm particles, but not 1 µm. • In 6-well format, flow rate of 25 mL/min is better than 5 mL/min. 50 nm
  12. 12. Gas In Vitro Exposure System (GIVES) Principle of Operation Gases: Diffusion Particles: Diffusion/Sedimentation Flow Rate: > 1 L/min • Particles < 1 µm do not induce biological effects. • Virtually a “gas-only” system Ebersviller et al. Atmos. Chem. Phys., 2012, 12277-12292
  13. 13. GIVES Performance • Flow rates of 1 and 2 L/min were tested for gas delivery. • Small increase in delivery observed at 2 L/min. • A high relative efficiency was observed. • Only flow rate of 1 L/min tested. • As expected, particle loading is very poor regardless of particle size. • Residence time of particles inside GIVES too short for gravitational setting to have an effect.
  14. 14. Principle of Operation Gases: Diffusion Particles: Electrostatic Precipitation (ESP) (Positive Electric Field) Flow Rate: 2.2 L/min • Corona wire allows unipolar charging of particles to enhance the particle deposition. • Air flow is horizontal to the cells Gillings Sampler Zavala et al. Chemico-Biological Interactions., 220 (2014), 158-168
  15. 15. Gillings Sampler Performance • Only 1 operating condition was tested for gas delivery as flow rate and multi-well format were fixed. • A high relative efficiency was observed. • 50 nm, 500 nm, and 1 µm particles tested since ESP is good for wide range of particles. • Particle loading is consistent regardless of particle size. • Using 1 um particles, the effect of unipolar charging with ESP was investigated.
  16. 16. Ranking of Systems Under Normal Operating Conditions Gas Delivery
  17. 17. Particles • An external force, such as THP or ESP, is needed to enhance particle deposition. — Relying on sedimentation/diffusion will produce little/no effect on cells exposed unless very high concentrations are used (e.g. several mg/m3) • Unipolar charging of particles significantly increases deposition • Gillings Sampler is most effective at delivering particles. Gases • Selecting the appropriate flow rate and tubing is critical. • The Gillings Sampler is most effective for delivering gases. Characterization of systems is needed prior to their use to understand their advantages and limitations Overall Observations
  18. 18. Acknowledgements EPA • Mark Higuchi • Allen Ledbetter • Earl Puckett • Todd Krantz Funding • Oak Ridge Institute for Science and Education (ORISE) • Intramural research programs at the U.S. EPA UNC • Will Vizuete (Gillings Sampler) Health Canada • Paul White (Vitrocell 6 CF) VITROCELL • Tobias Krebs (Vitrocell 6/3 w ESP)
  19. 19. José Zavala, PhD ORISE Postdoctoral Fellow NHEERL, EPHD, Inhalation Toxicology Facilities Branch Mentor: Mark Higuchi Email: zavala-mendez.jose@epa.gov SOT Annual Meeting March 15, 2018 Questions?

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