Ozone Responsive Gene Expression as a Model for Describing Repeat Exposure Response Trajectories and Interindividual...

Area of Science:

• Environmental Health
• Toxicology
• In Vitro Models

Background:

• Inhaled chemical exposures are common globally, necessitating evaluation of adverse effects from single and repeated exposures.
• New Approach Methodologies (NAMs) are crucial for assessing thousands of chemicals and exposure scenarios.
• Key challenges for NAMs include understanding acute assay outcomes for long-term events and capturing interindividual variability.

Purpose of the Study:

• To investigate if single acute ozone (O3) exposure outcomes predict responses to repeated exposures.
• To characterize interindividual variability in gene induction in primary human bronchial epithelial cells.
• To inform sample size calculations for in vitro studies assessing human variability.

Main Methods:

• Utilized a primary human bronchial epithelial cell air-liquid interface model.
• Exposed cells to ozone (O3), a model oxidant and environmental chemical.
• Measured induction of proinflammatory genes, including interleukin (IL)-8, IL-6, heme oxygenase 1 (HMOX1), and cyclooxygenase 2 (COX2) transcripts.

Main Results:

• Ozone-induced proinflammatory gene induction was attenuated in repeated exposures compared to single exposures.
• Single acute exposure outcomes did not reliably represent responses after repeated or chronic exposures.
• Observed significant interindividual variability in transcript induction across 25 unique donors, with ranges up to 14.2-fold for HMOX1.

Conclusions:

• Single acute in vitro exposure outcomes do not accurately predict long-term or repeated exposure effects.
• Significant interindividual variability in gene responses necessitates careful consideration in human population risk assessment.
• Sample size calculations indicate a high number of donors are required to detect small fold-changes in certain gene transcripts, informing uncertainty factor determination.