Optimization, Characterization and Pharmacological Validation of the Endotoxin-Induced Acute Pneumonitis Mouse Model

Background/Objectives: In preclinical research of airway inflammation, the endotoxin (lipopolysaccharide: LPS)-induced acute interstitial pneumonitis is the most commonly used mechanism model. However, studies apply different LPS serotypes, doses, administration routes, and reference compounds, making result interpretation challenging and drawing conclusions difficult. Therefore, here we aimed to optimize, characterize, and validate this model with dexamethasone in mice. Methods: Pneumonitis was induced by intratracheal LPS (0.25, 1, 2.5, 5 mg/kg; E. coli O111:B4) in C57BL/6J and NMRI mice; controls received phosphate-buffered saline (PBS). Dexamethasone (5 mg/kg i.p.) was used as a positive control. Respiratory functions were measured by restrained plethysmography 24 h after induction, and core body temperature was monitored. Lungs were excised and weighed, and then myeloperoxidase (MPO) activity and histopathological analysis were performed to assess pulmonary inflammation. Results: LPS-induced significant body weight loss, perivascular pulmonary edema, MPO activity increase, neutrophil infiltration, and respiratory function impairment in a dose-independent manner. However, LPS-induced hypothermia dynamics and duration were dose-dependent. The inhibitory effects of the reference compound dexamethasone were only detectable in the case of the 0.25 mg/kg LPS dose on most inflammatory parameters. These results did not differ substantially between C57BL/6J and NMRI mouse strains. Conclusions: Very low doses of LPS induce characteristic functional and morphological inflammatory alterations in the lung, which do not worsen in response to even 20 times higher doses. Since the effect of pharmacological interventions is likely to be detectable in the case of the 0.25 mg/kg LPS dose, we suggest this protocol for testing novel anti-inflammatory agents.