Co-Culture of Primary Human Bronchial Epithelial Cells at the Air–Liquid Interface and THP-1 Macrophages to Investigate the Toxicity of Polycyclic Aromatic Hydrocarbons

The development of new approach methodologies that include human cells differentiated into organotypic formats is of high interest due to their structural and functional similarities to tissues in vivo, enabling mechanistic understanding and translation to adverse health outcomes in humans. However, these systems often fail to capture complex intercellular signaling required for processes such as pulmonary inflammation induced by polycyclic aromatic hydrocarbons (PAHs). To investigate airway epithelial-macrophage interactions in response to benzo[a]pyrene and a PAH mixture (Tox Mix), co-culture models utilizing primary human bronchial epithelial cells (HBECs) differentiated at the air-liquid interface were cultured with THP-1 macrophages either directly or indirectly, alongside HBECs alone. After 24 h of exposure, cytokine expression (<i>IL1B</i>, <i>IL6</i>, <i>CXCL8</i>, <i>TNF</i>) as well as PAH biomarkers previously identified for chemical metabolism (<i>CYP1A1</i>, <i>CYP1B1</i>), oxidative stress (<i>ALDH3A1</i>, <i>HMOX1</i>, <i>NQO1</i>), and barrier integrity (<i>TJP2</i>) were evaluated. Cytotoxicity and barrier integrity were also assessed. HBECs alone and direct co-cultures exhibited similar responses after PAH treatment, while indirect co-cultures showed lower sensitivity to induction of inflammatory cytokines and <i>CYP1A1</i> and <i>CYP1B1</i> biomarker expression following exposure to PAHs. The expression of other biomarkers, including <i>ALDH3A1</i>, <i>HMOX1</i>, and <i>NQO1</i>, remained largely consistent across all models after treatment. Overall, these findings suggest that direct co-culture systems may provide a more physiologically relevant platform for studies of PAH-induced toxicity and demonstrate that the configuration of co-culture systems can influence cellular responses to chemical exposure.