Exposure to bleomycin nanoaerosol does not induce fibrosis in mice

Bleomycin (BLM), a cytostatic drug widely used in the treatment of cancer, often induces lung fibrosis as a side effect. This phenomenon has been exploited in biomedical studies to create a fibrosis model. Inhalation of BLM nanoaerosol particles (NAPs) was expected to induce severe fibrosis in mice. Instead, inhalation of BLM NAPs for 13 days with a total inhaled dose of ~1 mg/kg did not cause pneumofibrosis in CD-1 mice; only marked pneumonitis with infiltration of macrophages in all parts of the lungs was observed in all eight mice exposed. These changes were notably reversible within 2 weeks of cessation of exposure. Despite the limited number of animals it was confidently concluded that slow administration of BLM in the form of NAPs did not cause fibrosis as the bolus instillation of similar doses does.