Background
Pulmonary alveolar proteinosis (PAP) is a rare lung disease with primary (usually autoimmune) and secondary forms. Unlike the autoimmune type, which can be treated with cytokine therapy or whole-lung lavage, the secondary form associated with occupational particulate exposure, such as indium compounds, has no established therapy and remains challenging to treat.

Results
PAP was experimentally induced in rats through intratracheal exposure to indium oxide nanoparticles (In2O3 NPs). To assess potential therapeutic interventions, we administered four pharmacological agents: aspirin and naproxen, which are expected to attenuate inflammation, and pioglitazone and indomethacin, peroxisome proliferator-activated receptor (PPAR)-γ agonists anticipated to restore impaired surfactant homeostasis. The efficacy of their amelioration of In2O3 NP-induced PAP and the underlying mechanisms were evaluated by bronchoalveolar lavage fluid analysis, histopathology, and gene expression profiling. Treatment with pioglitazone and indomethacin markedly attenuated In2O3 NP–induced PAP by reducing foamy macrophage accumulation and restoring the expression of PPAR-γ and its downstream ATP-binding cassette (ABC) transporters, such as ABCG1 and ABCG4. In contrast, aspirin and naproxen only slightly decreased neutrophil infiltration. Among the tested agents, indomethacin showed relatively pronounced effects on several PAP-related endpoints, suggesting its potential to improve macrophage lipid handling and surfactant balance.

Conclusion
Targeting PPAR-γ–dependent macrophage lipid regulation may serve to attenuate In2O3 NP-induced secondary PAP-like pathology by reducing foamy macrophage accumulation and improving surfactant clearance. The effects were more pronounced when treatment was administered before disease establishment, whereas established pathology was only partially reversed, supporting the PPAR-γ–ABC transporter pathway as a potential target for future intervention.