A novel method for real-time inhalation toxicity assessment in mice using respirometric system: A promising tool for respiratory toxicology

Inhalation toxicity assessment is a crucial tool for the identification and classification of hazardous materials like volatile organic carbons, aerosols, and particulate matter. Unlike traditional acute inhalation toxicity studies that use mortality as an endpoint, the Fixed Concentration Procedure (FCP) emphasizes "evident toxicity" by monitoring behavior, weight, and food intake. This reduces reliance on mortality but doesn't directly address respiratory system impact. The present study introduced a respirometer-based inhalation toxicity and respiratory status assessment method. The toxicity evaluation system integrated a respirometric system with an animal exposure chamber, enabling real-time monitoring of oxygen consumption. The ICR mice were exposed to various concentrations of benzene (10, 20, 40, and 80 mg/L of air), toluene (7.5, 15, 30, and 60 mg/L of air), and xylene (7.5, 15, 30, and 60 mg/L of air). The respiration rate decreased by 70 % and 69 % for benzene (80 mg/L of air) and toluene (60 mg/L of air), respectively, with EC₅₀ values of 32.5 mg/l and 21.2 mg/L based on oxygen consumption. Xylene did not exhibit EC₅₀ values at the tested concentrations. However, the oxygen consumption rate significantly decreased (46 %) at high concentrations (60 mg/L of air), indicating sub-lethal toxicological effects. Furthermore, the present study was also validated in the bleomycin-induced idiopathic pulmonary fibrosis (IPF) model, demonstrating its reliability as a respiratory impairment marker. The results exhibited a strong correlation between weight loss and less oxygen consumption in the BLM group (bleomycin-induced) as compared to the SHAM group (control), which was confirmed by histological examination and protein marker analysis. The results suggest the potential use of oxygen consumption as an endpoint measurement in inhalation toxicity assessment tests without animal sacrifice, and the present study could be useful for providing valuable insights into disease progression and pharmacological interventions.