In vitro approaches to assess respiratory toxicity from volatile organic compounds: an in-depth review.

Abstract

Volatile organic compounds (VOCs) are ubiquitous inhaled pollutants. This review showcases current literature utilizing in vitro models of the human respiratory system to characterize the toxicity of VOCs. To map the existing evidence base, we conducted a scoping review following systematic search and screening procedures. Comprehensive searches of MEDLINE, Embase, Web of Science, CINAHL, PubMed, and CENTRAL identified 3,052 records. After screening, 144 original studies evaluating VOC exposures in human lung epithelial models met inclusion criteria. Overall, the current literature reflects substantial heterogeneity in cell models, exposure systems, and endpoints. Among 105 unique VOCs evaluated, acrolein, formaldehyde, toluene diisocyanate, and benzene were most frequently studied. Most investigations used submerged culture systems with liquid-phase VOC application, whereas fewer employed air-liquid interface (ALI) exposures that better mimic inhalation. Cytotoxicity, oxidative stress, proinflammatory signaling, and apoptosis were the most commonly measured endpoints, with oxidative stress frequently identified as an upstream driver of inflammatory and cytotoxic responses. However, mechanistic depth varied, and studies examining metabolism, barrier function, morphology, or transcriptomic regulation were relatively uncommon. Notably, chronic or repeated exposures were rarely conducted. Overall, this review highlights the variety of VOC exposure methods and commonly assessed biological endpoints, as well as the critical lack of more detailed mechanistic studies and somewhat limited VOC/mixture evaluation. The field is expansive but methodologically fragmented, underscoring the need for broader use of human respiratory cell models, more physiologically relevant exposure systems, improved dose characterization, and greater mechanistic resolution to advance understanding and throughput for VOC-induced pulmonary toxicity studies.