Evaluation of the toxicity of combustion smokes at the air-liquid interface: a comparison between two lung cell models and two exposure methods

In vitro tests at the air-liquid interface (ALI) represent valuable alternatives to animal experiments to assess the acute toxicity of inhalable compounds. However, these methods still need to be characterized for the toxicity evaluation of complex mixtures such as combustion smokes. In this study, Alveolar type I or Alveolar type 2 cells in co-culture with macrophages were investigated as models for evaluating the acute toxicity of complex mixtures at the air-liquid interface. In that purpose, smokes/obscurants were generated from pyrotechnic devices of known toxic potentials in a 1.3 m3 chamber and the co-cultures were exposed to smokes in static (directly in the chamber) or in dynamic using Vitrocell (R) modules. After exposure to smokes, static exposure induced higher cell mortality compared to dynamic, likely due to an increased dose. Nevertheless, we could still discriminate between a high-toxic (TA) and a low-toxic (RP) smoke using both exposure methods. Due to important cell mortality in static, oxidative and inflammatory potentials were only evaluated in dynamic mode. Reactive oxygen species were generated in response to smokes in hAELVI-THP-1 but not in A549-THP-1. After exposure to TA, increased levels of IL-1 beta, IL-6, and TNF-alpha were released by A549-THP-1 compared to the control while hAELVI-THP-1 released significant amount of IL-8. No inflammation was reported following exposure to RP, likely due to important cell mortality. Although discrepancies exist between the two cell models and exposure modes, these results suggest that both co-cultures and exposure methods remain promising for evaluating the toxicity of inhalable mixtures such as smokes.